FASEB J. Pierce now sold as Thermo Scientific
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Published as doi: 10.1096/fj.06-5895fje.
This Article
Right arrow Abstract Freely available
Right arrow Summary
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
fj.06-5895fjev1
20/13/2411    most recent
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Samardzija, M.
Right arrow Articles by Grimm, C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Samardzija, M.
Right arrow Articles by Grimm, C.
(The FASEB Journal. 2006;20:2411-2413.)
© 2006 FASEB

Differential role of Jak-STAT signaling in retinal degenerations

Marijana Samardzija, Andreas Wenzel, Svenja Aufenberg, Markus Thiersch, Charlotte Remé and Christian Grimm1

Laboratory for Retinal Cell Biology, Department Ophthalmology, Center for Integrative Human Physiology (CIHP) and Neuroscience Center Zurich (ZNZ), University Hospital, Zürich, Switzerland

1Correspondence: Laboratory for Retinal Cell Biology, Department Ophthalmology, University Hospital, Frauenklinikstrasse 24, 8091 Zürich, Switzerland. E-mail: cgrimm{at}opht.unizh.ch

ABSTRACT

Retinal degeneration is a major cause of severe visual impairment or blindness. Understanding the underlying molecular mechanisms is a prerequisite to develop therapeutic approaches for human patients. We show in three mouse models that induced and inherited retinal degeneration induces LIF and CLC as members of the interleukin (IL)-6 family of proteins, activates proteins of the Jak-STAT signaling pathway, and up-regulates suppressors of cytokine signaling as a negative feedback loop. Inhibition of Jak2 leads to protection of photoreceptors in a model of induced but not in a model of inherited retinal degeneration. Differential activation of Akt suggests alternative pathways for cell death and/or survival in different models. Proteins induced during photoreceptor degeneration are not mainly expressed in photoreceptors but in cells of other retinal layers. This suggests a model in which photoreceptor injury is signaled to cells of the inner retina, which in turn initiate a response either to support viability or accelerate death of injured cells.—Samardzija, M., Wenzel, A., Aufenberg, S., Thiersch, M., Remé, C., Grimm, C. Differential role of Jak-STAT signaling in retinal degenerations.


Key Words: apoptosis • neuroprotection • photoreceptor

THE NEURONAL RETINA IS DESIGNED to absorb photons and convert the information into electrical signals that are transmitted to the brain. Due to their high specialization, photoreceptors are highly vulnerable to any endogenous or exogenous disturbances. So far more than 150 genes are known to cause some form of retinal disorder when mutated (http://www.sph.uth.tmc.edu/Retnet/). Retinitis pigmentosa (RP) and age-related macular degeneration (AMD), two frequent causes of severe visual impairment or blindness in patients, are characterized by the progressive loss of visual cells by apoptosis. Various animal models have been generated and used to investigate the molecular mechanisms of disease induction and progression. Besides genetically modified animals, the model of light-induced photoreceptor apoptosis is widely used to analyze signaling pathways during retinal cell death and to test the efficacy of neuroprotective substances (1 2 3 4 5 6 7 8) .

Inhibition of photoreceptor apoptosis is one possible strategy to protect morphology and function of the retina and to prolong the period of useful vision in patients. Several compounds, including cytokines like fibroblast growth factor-2 (FGF-2), pigment epithelium-derived factor (PEDF), and ciliary neurotrophic factor (CNTF), have been shown to be protective in light damage and in models of inherited retinal degeneration; other factors protect photoreceptors only in induced but not inherited models (2 , 5 , 9 10 11 12 13) . The mechanisms of protection are still largely unknown but may involve differential intracellular signaling cascades. CNTF, for example, is suggested to activate the Janus kinase signal transducer and activator of transcription (Jak-STAT) signaling pathway in ganglion cells and Muller cells. Such activated Muller cells may initiate a secondary, neuroprotective activity to preserve photoreceptor viability (14) . FGF-2 and glial-derived neurotrophic factor (GDNF) might be such factors produced and released by Muller cells upon proper stimulation (15) . In addition to Jak-STAT signaling, CNTF may also stimulate cell survival through phosphatidylinositol-3 phosphate kinase (PI3K)-mediated Akt signaling (16 , 17) .

Upon binding to the heterodimeric receptor complex containing gp130, members of the IL-6 family of cytokines induce autophosphorylation of cytoplasmic Jak kinases, which then phosphorylate downstream molecules such as transcription factors of the signal transducer and activator of transcription (STAT) family of proteins. In addition to the IL-6 family of cytokines that consists of seven members (leukemia inhibitory factor, LIF; cardiotrophin-1, CT-1; CNTF; cardiotrophin-like cytokine, CLC; oncostatin M, OSM; neuropoetin, NP; interleukin-6 (IL-6), IFN alpha and gamma are similarly strong activators of the Jak-STAT pathway (18) . Of particular interest is the fact that Jak-STAT signaling has been implicated in both pro- and antiapoptotic mechanisms. STAT1 is frequently described as being proapoptotic whereas STAT3 is often found in proliferating tumor cells and is suspected to be antiapoptotic (19 20 21) . This signaling cascade is controlled by a negative feedback loop involving members of the suppressor of cytokine signaling (SOCS) family of proteins (22) .

Here we show that retinal degeneration in three different mouse models of induced and inherited photoreceptor apoptosis activates expression of several proteins of the IL-6 family of cytokines. This leads to the phosphorylation of members of the Jak-STAT signaling pathway and to the activation of a negative feedback loop by the increased expression of several members of the SOCS family. Interference with this pathway protects the retinal tissue against an acute toxic insult but not against photoreceptor degeneration in an inherited model. Our results suggest that Jak-STAT-mediated regulation of an intracellular response to photoreceptor degeneration is of differential importance for the retina depending on the nature of the insult.

RESULTS

Induction of LIF and CLC by acute light exposure
Injury or stress to the retina or to the optic nerve induces the expression of several neurotrophic factors, including CNTF and FGF-2. These molecules may act as survival factors protecting photoreceptors and other retinal cells from further damage (23 24 25 26 27 28) . In the search for additional factors relevant for retinal injury, we tested expression of cytokines of the IL-6 family in BALB/c mice after exposure to high levels of white light, a treatment that represents a strong retinal insult leading to rapid photoreceptor apoptosis. Whereas CLC and LIF where highly up-regulated, peaking 12 h after light exposure, expression CNTF showed a slow response with a slight increase after 36 h (Fig. 1 A, B; Supplemental Table 1). CT-1 remained unchanged throughout the period investigated. TGF-ß, another cytokine involved in many regulatory and inflammatory processes in the retina, increased slightly 48 h after light exposure. Increased expression of LIF and CLC well preceded the light-induced release of free nucleosomes, which peaks ~ 36 h after exposure and indicates a late stage of apoptosis (Fig. 1B ) (2) . Increased CNTF expression largely coincided with the apoptotic wave as detected by the biochemical detection of free nucleosomes.


Figure 1
View larger version (17K):
[in this window]
[in a new window]
  		Figure 1. Members of the IL-6 family of cytokines are induced upon exposure to damaging light. BALB/c mice were not (dark control, d) or were exposed to 5000 lux of white light for 1 h and retinal RNA was prepared immediately (i) or 6 to 72 h after light exposure, as indicated. After isolation, identical amounts of RNA were reverse transcribed. Equal amounts of cDNAs from three different animals of a particular condition were pooled and used for exponential PCR. PCR amplifications were done in triplicate. Thus, each signal represents the average RNA level of three mice. A) Radiolabeled products after exponential RT-PCR were separated by nondenaturing PAGE. B) Signal intensities were determined on a PhosphorImager. Gene expression is shown semiquantitatively and relative to ß-Act RNA levels. Dark control levels were set to 1. The dotted line represents the time course of apoptosis (release of nucleosomes) after light treatment. These data were published before (2) and are shown here for informative purposes.

Induction of the janus-activated kinase (JAK)-STAT pathway by acute light exposure
Upon binding to their respective receptors, members of the IL-6 family of cytokines activate the Jak/STAT signaling pathway. Functional receptors are heterodimeric complexes consisting of a common gp130 protein and of specific proteins like CNTF receptor or LIF receptor, all of which are expressed in the mammalian retina (Fig. 2 ; see Fig. 6 ) (29) . In extracts of untreated retinas, activated (phosphorylated) Jak2, STAT1, and STAT3 were not or were only barely (p-STAT3) detectable, in contrast to p-Akt473 and p-Erk1,2 (Fig. 2) . After light exposure, phosphorylation of Jak2, STAT1, STAT3, and Erk1,2 strongly increased, peaking ~ 6 to 12 h postillumination. The level of p-Akt473 remained largely unchanged, as did expression of gp130. GFAP expression, a marker for activated Muller glia cells, increased slightly over time as it was observed earlier (30) . Total levels of individual proteins remained largely constant, although STAT1 and STAT3 showed a slight increase with time.


Figure 2
View larger version (66K):
[in this window]
[in a new window]
  		Figure 2. Induction of the Jak-STAT pathway in the retina after acute light exposure. A) BALB/c mice were not (dark control, d) or were exposed to 5000 lux of white light for 1 h. After light exposure, mice were sacrificed immediately (i) or after 2 to 96 h in darkness, as indicated. Proteins were extracted from isolated retinas and detected by Western blot.


Figure 3
View larger version (19K):
[in this window]
[in a new window]
  		Figure 3. Members of the suppressor of cytokine signaling family are induced upon exposure to damaging light. BALB/c mice were not (dark control, d) or were exposed to 5000 lux of white light for 1 h and retinal RNA was prepared immediately (i) or after 6 to 72 h, as indicated. After isolation, identical amounts of RNA were reverse transcribed. Equal amounts of cDNAs from three different animals of a particular condition were pooled and used for exponential PCR. PCR amplifications were done in triplicate. Thus, each signal represents the average RNA level of three mice. A) Radiolabeled products after exponential RT-PCR were separated by nondenaturing PAGE. B) Signal intensities were determined on a PhosphorImager. Gene expression is shown semiquantitatively and relative to ß-Act RNA levels. Dark control levels were set to 1. See also Supplemental Table 1.


Figure 4
View larger version (64K):
[in this window]
[in a new window]
  		Figure 4. Induction of the Jak-STAT signaling pathway is associated with retinal damage. Three strains of mice were or were not (dark control, d) exposed to 13,000 lux of white fluorescent light for 2 h. Retinal proteins were isolated at 6 h after illumination and analyzed by Western blot, as indicated. Retinas of c-fos–/– mice on the Rpe65450M background (strain 1) are resistant to light exposure whereas retinas of c-fos–/– mice on the Rpe65450L genetic background (strain 2) are susceptible. WT mice (SV129BL/6) on the Rpe65450M background (strain 3) are susceptible. Phosphorylation of Jak-STAT was only induced in mice susceptible to light damage. ERK1,2 was induced in all strains of mice on light exposure. The phosphorylation pattern of one dark control and of one (strain 3) or of two different animals exposed to light (strains 1 and 2) is shown.


Figure 5
View larger version (103K):
[in this window]
[in a new window]
  		Figure 5. Members of the Jak-STAT signaling pathway are differentially induced in inherited retinal degeneration. A) Retinal proteins of rd1 and corresponding WT (wt) mice were extracted at indicated postnatal days and analyzed by Western blot. B) Same analysis as in panel A, but using VPP mice as an autosomal dominant model for retinal degeneration. Time points for analysis were chosen according to the different time frame of degeneration in the two models.


Figure 6
View larger version (46K):
[in this window]
[in a new window]
  		Figure 6. Expression of members of the IL-6 family of cytokines and of the SOCS family is induced in models of inherited retinal degeneration. A) Retinal RNA of rd1 and corresponding WT (wt) mice was isolated at indicated postnatal days. After isolation, identical amounts of RNA from three different animals were pooled, reverse transcribed and the resulting cDNA was used for exponential PCR. Thus, each signal represents the average RNA level of three mice. B) Same as in panel A, but using VPP mice as an autosomal dominant model for retinal degeneration.

Not only activation of proteins by a specific stimulus but also a timely controlled attenuation of the response is essential for an appropriate cellular reaction. The SOCS family of inhibitory proteins consists of eight members (CIS and SOCS1–7). CIS, SOCS1, and SOCS3 showed a distinct induction at the gene expression level, peaking ~6 (SOCS1) or 12 h after illumination, respectively. Expression of SOCS4, SOCS5, SOCS6, and SOCS7 was slightly (2-fold) and transiently reduced. Levels of SOCS2 RNA remained constant throughout the experiment (Fig. 3 A, B; Supplemental Table 1).

Correlation with photoreceptor injury
Light-induced phosphorylation of the Jak-STAT proteins in the retina might be a physiological response to the light pulse after dark adaptation or it might be associated with retinal injury. We tested these possibilities by analyzing three mouse strains that are differentially susceptible to light damage. The mice exposed to high levels of light were 1) mice deficient for c-Fos expressing the RPE65450Met variant (resistant to light damage, ref. 31 ), 2) mice deficient for c-Fos expressing the RPE65450Leu variant (susceptible to light damage, ref. 32 ), and 3) control mice expressing the RPE65450Met variant (susceptible to light damage, ref. 33 ). A comparison of the phosphorylation pattern in these three mouse strains should reveal whether Jak-STAT activation is a general response to light (if so, activation should be detected in all three lines) or whether activation is associated with damage (up-regulation in strains 2 and 3 only). The influence of c-Fos can be assessed by comparing strains 1 and 3, and a potential role for the leucine-methionine variant in RPE65 can be analyzed by a comparison of strains 1 and 2 (Fig. 4 ). Exposure to excessive light-induced phosphorylation of Jak2, STAT1, STAT3 in strains susceptible to light damage (strains 2 and 3) but not in the resistant strain 1, as shown by the phosphorylation pattern at 6 h after light exposure. This demonstrates that activation of Jak/STAT correlates with light damage and not with light absorption per se. Furthermore, activation is not directly influenced by the presence or absence of c-Fos and/or the Leu450Met variant in RPE65. In contrast, increased phosphorylation of Erk1,2 was detected in all mouse strains after light exposure. Thus, activation of Jak2, STAT1, and STAT3 may be part of the degenerative pathway induced by excessive light whereas phosphorylation of Erk1,2 is not, and may represent a physiological response of the retina to light or perhaps be part of a protective pathway.

The Jak-STAT pathway in inherited retinal degenerations
We used a model for autosomal recessive RP (rd1; ref. 34 ) and a model for autosomal dominant RP (VPP; ref. 35 ) to test whether the signaling pathway activated in the light-induced model of photoreceptor apoptosis might also play a role in inherited retinal degeneration. Since the degeneration in VPP mice proceeds slower than in rd1 mice (12) , the time frame of analysis was adjusted accordingly. As in the light damage model, p-STAT3 levels were up-regulated during the phase of photoreceptor degeneration in both inherited models (Fig. 5 ), as were levels of total STAT3 protein. Similarly, total levels of STAT1 protein were elevated although p-STAT1 was not (rd1, Fig. 5A ) or barely (VPP, Fig. 5B ) detectable. In contrast to the induced model, levels of phosphorylated Jak2 were not or were only marginally elevated, and levels of p-Erk1,2 remained constant. Instead, levels of p-Akt473 remained high in the inherited models and declined at the end of postnatal retinal development in wild-type (WT) mice. The strong induction of GFAP may reflect activation of Muller glia cells and the process of retinal remodeling (36 , 37) . At PND 37, when there are hardly any photoreceptors left in the rd1 retina (12 , 38) , all analyzed proteins were expressed at higher or at similar levels as in WT mice. This argues that these proteins are not predominantly expressed in photoreceptors, an interpretation that is in line with the results of the immunofluorescent stainings for Jak2, STAT1, and STAT3 (Fig. 7 A).


Figure 7
View larger version (94K):
[in this window]
[in a new window]
  		Figure 7. Immunofluorescent stainings detecting Jak-STAT proteins (A) or apoptotic cells (B). A) Cryosections of WT (left column), light-exposed WT mice at 12 h after exposure (middle column) and VPP mice at 28 days of age (right column) were stained with antibodies, as indicated. The panels in the left column are merged pictures of fluorescent (antibody staining, red) and Nomarski images (for a better visualization of retinal structures). The middle and right columns show fluorescent images only. B) Staining for apoptotic cells (TUNEL staining). No TUNEL-positive cells are detected in WT control retinas. Light exposure of WT cells induced apoptosis and TUNEL-positive stainings in a large number of cells in the ONL but not in other cell layers. Arrowheads point to TUNEL-positive cells in the ONL of VPP mice. RPE: retinal pigment epithelium; ONL: outer nuclear layer; INL: inner nuclear layer; IPL: inner plexiform layer; GCL: ganglion cell layer.

As in the light damage model, expression of LIF, CLC, and SOCS3 was robustly induced in the two inherited models of retinal degeneration. SOCS1 was up-regulated slightly in both models and CIS was induced in VPP mice only during the initial phase of degeneration (Fig. 6 A, B). CNTF was up-regulated late in the light damage model (Fig. 1) and was moderately induced in the rd1 mouse retina. FGF-2 was strongly up-regulated in the VPP mouse but not or only marginally in the rd1 retina. Again, expression of these genes did not decline with loss of photoreceptors, whereas expression of the rod-specific gene rhodopsin did (Fig. 6A ). These results suggest that different models of retinal degeneration differentially activate members of the Jak-STAT signaling pathway.

Retinal localization of Jak/STAT proteins and photoreceptor degeneration
We used immunofluorescence to investigate the retinal localization of Jak/STAT proteins in the models of induced (light damage) and inherited (VPP) retinal degeneration (Fig. 7A ). In untreated mice, Jak2 and STAT3 localized to some but not all cells of the inner nuclear layer and of the ganglion cell layer. Some STAT3 staining could also be detected in inner segments of photoreceptor cells and in the outer plexiform layer (OPL). STAT1 localized mainly to the inner plexiform layer (IPL) and OPL as well as to the ganglion cells. The pattern of the STAT1 staining in the IPL may reflect stratification within the layer and therefore the synaptic complexes between bipolar, amacrine, and ganglion cells. Light treatment of the retinas did not alter the distribution of STAT1 and STAT3 but seemed to have caused a shift of Jak2 localization mainly to the IPL and OPL (between ONL and INL). Note that a similar shift of Jak2 localization to the IPL was detected in degenerating VPP retinas. Most important, however, no increased localization to the ONL was found in light-damaged retinas even though light exposure induced cell death exclusively in this cell layer (Fig. 7B ).

An increased immunofluorescence for STAT3 was detected in the ONL of 28-day-old VPP mice whereas STAT1 staining remained largely unaffected. STAT3 was also the main protein that was differentially expressed in the VPP mice when analyzed by Western blot (Fig. 5) . However, increased immunofluorescence did not seem to correlate with the few apoptotic photoreceptors present in the ONL at the time point analyzed (Fig. 7B ).

Inhibition of Jak-STAT signaling pathway protects against induced but not inherited retinal degeneration
The differential activation of members of the Jak-STAT pathway in the induced and inherited models of retinal degeneration may suggest that interference with this signaling may lead to different effects. We used AG-490, a tyrosine kinase inhibitor specific for the Jak family kinases (39 40 41) , in an attempt to dissect the role of the Jak/STAT signaling pathway in the different models of retinal degeneration. AG-490 was injected intraperitoneally (i.p.) immediately before onset of light exposure. The phosphorylation pattern of Jak2, STAT1, and STAT3 was analyzed 18 h thereafter (Fig. 8 A). In contrast to mice injected with carrier or to uninjected mice, AG-490-treated mice did not show increased protein phosphorylation. Furthermore, AG-490 treatment, and thus interference with the Jak-STAT pathway, significantly reduced light damage susceptibility of photoreceptors as indicated by reduced internucleosomal DNA cleavage (Fig. 8B ). AG-490-treated mice had only few scattered photoreceptor nuclei showing condensed chromatin (pyknotic nuclei) as a classical sign of apoptosis (Fig. 8C , middle panel), whereas mice treated with carrier showed a highly increased number of pyknotic nuclei (Fig. 8C , bottom panel).


Figure 8
View larger version (111K):
[in this window]
[in a new window]
  		Figure 8. Inhibition of Jak signaling prevents retinal degeneration after bright light exposure. A) BALB/c mice received immediately before light exposure no (not injected) or a single injection of 800 µg AG-490 (ag) or of carrier DMSO (dm), as indicated. Mice were not (dark) or were subsequently exposed for 1 h to 5000 lux and phosphorylation of proteins was tested 18 h after exposure. Retinal proteins from separate animals were loaded in each lane. B) Retinas of animals not exposed to light (dark) or of animals pretreated either with AG-490 (ag) or DMSO (dm) and exposed for 1 h to 5000 lux were used to quantify apoptosis by ELISA. *P = 0.003, two-tailed t test; n = 10 mice for each condition. C) Light microscopy 18 h after light exposure. Retinas of dark control mice showed regular photoreceptors (upper panel). Retinas of AG-490 (ag) -treated mice exhibited few apoptotic photoreceptor nuclei (arrowheads, middle panel) and retinas of carrier (DMSO, dm) -treated mice had significantly more dying photoreceptors (arrowheads, lower panel). ROS: rod outer segments; RIS: rod inner segments. Other abbreviations as in Fig. 7 .

To assess a potential role for Jak2 in STAT3 activation and retinal degeneration in the VPP mouse as a model for inherited retinal degeneration, we treated VPP mice with daily injections of AG-490, starting at PND 15 and ending at PND 27. Analysis was at PND 28. The retina of 15-day-old VPP mice had 7 to 9 rows of photoreceptor nuclei and distinct (but shortened) inner and outer segments (not shown). AG-490 treatment slightly reduced phosphorylation levels of Jak2. Levels of p-STAT3, however, were still elevated and comparable to untreated VPP mice (Fig. 9 A). The amount of rhodopsin per retina was measured to quantify photoreceptor degeneration. Four-wk-old WT mice had 0.43 ± 0.083 (n=3) nmol rhodopsin whereas untreated VPP mice of the same age had only 0.071 ± 0.015 (n=3) nmol and AG-490-treated mice had 0.065 ± 0.014 (n=4) rhodopsin left. Thus, despite AG-490 treatment, >80% of the photoreceptors were lost (Fig. 9B ). Morphological evaluation of retinas from 4-wk-old animals showed that control VPP and AG-490-treated VPP mice had retained about three rows of photoreceptor nuclei compared with 12 rows in a WT retina (Fig. 9C ).


Figure 9
View larger version (48K):
[in this window]
[in a new window]
  		Figure 9. AG-490 treatment does not prevent photoreceptor degeneration in the VPP mouse. VPP mice received 12 i.p. injections on 12 consecutive days (A–C) or one single (D) injections of 800 µg AG-490. Daily injected mice were treated starting at PND15 and ending at PND 27. Mice were sacrificed for analysis at PND 28. A) Western blot analysis of total retinal protein of VPP or WT (wt) mice that were (ag) or were not (n) repetitively treated with AG-490. AG-490 treatment reduced Jak2 phosphorylation in VPP mice to similar levels as in wt mice. Phosphorylation of STAT3 was still prominent. Shown are two different mice treated with AG-490. B) Photoreceptor loss at PND 28 was quantified by measurement of retinal rhodopsin in wt (n=3), VPP (n=3) and AG-490-treated VPP mice (n=4). C) Morphological evaluation of retinal degeneration in WT (left panel), VPP (middle panel) and AG-490-treated VPP mice (right panel) at PND 28. Abbreviations as in Fig. 7 . D) Western blot analysis of total retinal protein of 28-day-old VPP or WT (wt) mice that were not treated (n) or were treated with either DMSO (dm) or a single injection of 800 µg AG-490 (ag). Analysis was 19 h after injection. Shown are four different mice treated with AG-490 and a single mouse for each control.

To test whether the lack of an effect of AG-490 treatment on STAT3 phosphorylation was due to an adaptational response of the retina to the long-term treatment, we analyzed phosphorylation pattern 19 h after the injection of a single dose of AG-490. The timing and treatment are comparable to the experimental protocol of AG-490 application and analysis in the light damage experiments (Fig. 8) . However, STAT3 phosphorylation was not reduced after this treatment (Fig 9D ). In addition, there was no obvious reduction in Jak2 phosphorylation. Thus, the continuously present stimulus in the VPP mouse (the mutant protein) may require several repetitive applications of AG-490 to establish an effect on Jak2 phosphorylation.

MATERIALS AND METHODS

Mice and light exposure
Animals were treated in accordance with the regulations of the Veterinary Authority of Zurich and with the statement of ‘The Association for Research in Vision and Ophthalmology’ for the use of animals in research. c-fos WT and c-fos knockout (c-fos–/–) mice were on mixed SV129BL/6 background. Genotyping for c-fos and for the Rpe65 variant at position 450 was done as described (12 , 32) . VPP mice were kept on a mixed SV129BL/6 background and genotyped using upstream primer 5'-AGA CTG ACA TGG GGA GGA ATT CCC AGA-3' and downstream primer 5'-CAG CTG CTC GAA GTG ACT CCG ACC-3. Rd1 (C3H) and BALB/c mice were from Harlan (Netherlands). Six to 8-wk-old male BALB/c mice were dark-adapted overnight (16 h) and exposed to 5000 lux of white fluorescent light for 1 h. After exposure, mice were returned to darkness for 24 h before they were returned to cyclic (12 h:12 h) light. Pigmented c-fos–/– or c-fos+/+ mice were dark adapted as above, their pupils dilated (1% Cyclogyl, Alcon, Cham, Switzerland; and 5% phenylephrine, Ciba Vision, Niederwangen, Switzerland) 1 h prior to light exposure, and exposed to 13,000 lux of white light for 2 h.

Microscopy, immunofluorescence, and TUNEL staining
For light microscopy, eyes were fixed in 2.5% glutaraldehyde in 0.1 M cacodylate buffer, pH 7.3, at 4°C overnight. For each eye, the superior and inferior retina were prepared, washed in cacodylate buffer, incubated in osmium tetroxide for 1 h, dehydrated, and embedded in Epon 812. Sections (0.5 µm) were prepared from the lower central retina (most affected in our light damage model) and counterstained with methylene blue.

For immunofluorescence and TUNEL staining, eyes of adult WT control or light exposed (2 h at 13,000 lux, analysis was at+12 h) mice, respectively, or of 28-day-old VPP mice of the Rpe65450M background (64) were enucleated, embedded in Tissue Tec OCT compound (Mioles Inc., Elkhart, IN, USA), and frozen in liquid nitrogen. Sections (10 µ) were dried and fixed in acetone for 10 min at 4°C. Sections were washed in PBST (PBS+0.05% Triton X-100) for 2 x 5 min at room temperature. After blocking in PBST + 10% normal goat serum (NGS) for 1 h at room temperature, sections were incubated with the respective primary antibodies (anti-Jak2, Biosource; Camarillo, CA, USA; anti-STAT1 and anti-STAT3, Cell Signaling; Beverly, MA, USA). Sections were washed 3 x 10 min in PBST and Cy3-conjugated secondary anti-rabbit antibodies (Jackson ImmunoResesarch, Soham, UK) were added in PBST + 3% NGS (dilution 1/500) for 1–2 h at room temperature. Sections were washed 2 x 10 min in PBST and 1 x in PBS. TUNEL staining was done according to the manufacturer’s recommendation (Roche diagnostics, Basel, Switzerland).

Western blot
Retinas were homogenized in 100 mM Tris/HCl, pH 8.0, and analyzed for protein content using Bradford reagent. Standard SDS-PAGE and Western blot were performed. For immunodetection, the following antibodies were used: anti-Jak2 (#44–406, Biosource), anti-STAT1 (#9172, Cell Signaling), anti-STAT3 (#9132, Cell Signaling), anti-ERK1,2 (#9102, NEB), anti-Akt (#9272, Cell Signaling), anti-gp130 (sc-656, Santa Cruz), anti-GFAP (G-3893, Sigma), anti-ß-actin (sc-1616, Santa Cruz), anti-phospho-Jak2pYpY1007/1008 (#44–426, Biosource), anti-phospho-STAT1Tyr701 (#9171, Cell Signaling), anti-phospho-STAT3Tyr705 (#9131, Cell Signaling), anti-phospho-ERK1,2Thr202/Tyr204 (#9101, NEB), anti-phospho-AktTyr473 (#9271, Cell Signaling). Blots were incubated overnight at 4°C with primary antibodies followed by a 1 h incubation at room temperature with HRP-conjugated secondary antibodies. Immunoreactivity was visualized using the Renaissance-Western blot detection kit (Perkin Elmer Life Sciences, Emeryville, CA, USA).

RNA preparation and RT-polymerase chain reaction (RT-PCR)
Retinas were removed through a slit in the cornea and immediately frozen in liquid nitrogen. Total retinal RNA was prepared using the RNeasy RNA isolation kit (Qiagen, Hilden, Germany), including DNase treatment to digest residual genomic DNA. Identical amounts of RNA were used for reverse transcription using oligo(dT) and M-MLV reverse transcriptase (Promega, Madison, WI, USA). cDNAs from three different animals were pooled and amplified with specific primers (Table 1 ). Amplification was stopped at cycle numbers ensuring analysis of products in the linear amplification phase of the polymerase chain reaction (PCR) (numbers of cycles were determined in pre-experiments). Downstream primers were 32P-end-labeled. Amplification products were resolved on a 6% native polyacrylamide gel, quantified on a PhosphorImager, and normalized to ß-actin expression. In experiments without quantification, PCR products were resolved on a 1.5% agarose gel.


View this table:
[in this window]
[in a new window]
  		Table 1. PCR primers used for amplifications

AG-490 injections, ELISA cell death assay, rhodopsin measurements
AG-490 (LC Laboratories, Woburn, MA, USA) was dissolved in 56% DMSO. AG-490 (40 µg/g) (65 , 66) was injected i.p. immediately before light exposure or daily ~ 10 AM, respectively. Control animals were injected with 56% DMSO. Cell death was quantified 18 h after light exposure using the ELISA-based Cell Death Detection Kit (Roche Diagnostics, Basel, Switzerland) according to the manufacturer’s recommendation. The rhodopsin content was determined as described (67) .

DISCUSSION

Retinal degeneration is a leading cause of blindness in human patients. Here we investigated signaling pathways in an induced, an autosomal recessive, and an autosomal dominant model for the disease in humans. We show that proteins of the Jak-STAT pathway were induced in all models but that the individual activation patterns were death stimulus-specific. Differentially activated proteins include cytokine ligands, STAT transcription factors, and molecules of a negative feedback loop. The neuroprotective effect of the inhibition of Jak2 in induced but not in inherited cell death suggests that this signaling cascade is of differential importance depending on the death stimulus.

The Jak-STAT signaling pathway, and especially STAT1 and STAT3 proteins have been implicated in neurodegenerative as well as neuroprotective mechanisms (42) . In the light-treated retina, STAT1 and STAT3 proteins were both activated, suggesting that cell death as well as cell survival pathways were induced. We speculate that the retina generates death factors promoting apoptosis of photoreceptors that are damaged beyond rescue and survival factors that help to rescue damaged photoreceptors that are still viable. The nature of such factors remains to be determined, but their production may be differentially controlled by STAT1 and STAT3, respectively.

Jak2, STAT1, and STAT3 proteins were found mainly in the INL, GCL, IPL, and OPL but rarely in photoreceptors (Fig. 7) , which agrees with previous reports (14 , 43 , 44) . However, photoreceptors are the cells primarily affected in all models of retinal degeneration used here. Thus, the fate of photoreceptors might be determined by other cell types through STAT1/STAT3-regulated production and release of growth factors and/or cytokines. Recently, injection of CT-1 (a member of the IL-6 family of cytokines) into the eyes of a rat model for inherited retinal disease increased phosphorylation of STAT3 and STAT1 and protected photoreceptors. Increased phosphorylation colocalized with Muller cells, implicating these cells in the regulation of photoreceptor apoptosis in a paracrine fashion (45) . Evidence suggests that the neuroprotective effect of CNTF on photoreceptors and ganglion cells may be mediated through induction of STAT3 (14 , 46) . Our results here are in line with such a conclusion.

Peak activation of the Jak-STAT pathway was at 12 h postillumination whereas the peak of apoptotic release of nucleosomes was found ~ 36 h after exposure (2) , supporting the notion that Jak-STAT signaling is an early event that may regulate the fate of photoreceptor cells. Thus, it is conceivable that interference with such an early event can influence the progression of the degeneration. The tyrosine kinase inhibitor AG-490 interferes with Jak kinases, including Jak2 (39 40 41) . Thus, reduced activation of STAT1 and STAT3 may have been through inhibition of Jak2, although we cannot completely rule out an involvement of other AG-490-responsive kinases. Since the presumable proapoptotic pathway (STAT1) was blocked, the simultaneous reduction of the presumable antiapoptotic STAT3 pathway was not disastrous for the retina, and the net result of the treatment was protection of photoreceptors.

In the case of the analyzed models for inherited photoreceptor degeneration, mainly STAT3 but not STAT1 was activated throughout the degenerative period. Although STAT1 may be an important death mediator in the light damage model, it may not be involved in the inherited models. Also, phosphorylation of Jak2 was at best slightly increased in the VPP mouse and remained at basal levels in the rd1 retina. Since cell death in the inherited models stretches over an extended period, activation of the proteins may only occur in a small number of cells simultaneously and may therefore go undetected in Western blot experiments. However, the immunofluorescent stainings did not give evidence that the proteins colocalize with dying (TUNEL-positive) cells. This suggests that photoreceptor degeneration in the inherited models may be independent of Jak2, a conclusion corroborated by the ineffectiveness of AG-490 treatment of VPP mice. The strong activation of STAT3 in these mice therefore may be by an alternative pathway, which may include, for example, an oxidative stress response (47 , 48) . Nevertheless, activation of the (presumably) protective STAT3 signaling obviously is not sufficient for rescuing photoreceptors in the inherited model. Although STAT3 is activated in induced and inherited models, the signaling system through which STAT3 is activated may be different. The differential effectiveness of many factors on induction and progression of induced or inherited retinal degeneration (2) also argues for the existence of multiple signaling systems that lead to photoreceptor cell death. To develop therapeutic strategies for a large variety of diseases, it will be important to identify and understand these signaling events.

The sustained phosphorylation of Akt in both models of inherited retinal degeneration argues for molecular mechanisms in addition to STAT3 signaling. The PI3K-Akt pathway has been shown to be important for the survival of several neuronal cell types (49 50 51) , and Akt has been suggested to be part of a retinal defense mechanism in response to toxic insults (52) , perhaps through the activation of CNTF expression (17) . At least in the rd1 retina, steady-state levels of CNTF mRNA were moderately elevated in the late phase of degeneration, as has been reported by others (53) . In the rd1 retina, Akt and pAkt expression did not decline at P37, a time point when the rd1 mouse has lost almost all photoreceptors. This indicates that the majority of Akt is not expressed in photoreceptors. The same holds true for the other genes tested (Figs. 5 , 6) as judged by their expression pattern during aging. The immunofluorescent studies (Fig. 7) support this conclusion. Therefore, induction of the genes and proteins shown here might be a response of cells in the INL and/or GCL to photoreceptor injury. The protection of photoreceptors against light damage by inhibition of Jak2 may thus suggest a model in which photoreceptors signal injury to cells in the INL, which then initiate the appropriate response to either support survival or promote death of the injured photoreceptors. In addition, induction of a general defense mechanism may ensure survival of cells not directly damaged by the applied toxic stimulus. Such a defense mechanism may involve CNTF in the rd1 mouse and FGF-2 in the VPP mouse. Chronic up-regulation of FGF-2 may slow down the progression of photoreceptor degeneration in the VPP mouse as has been suggested for other models (54) .

It is tempting to speculate that the cells that "rule" over the fate of other cells might be the Muller glia cells. These cells have been shown to react strongly to retinal injury and they seem to release neurotrophic factors, including the protective cytokines FGF-2 and CNTF, in protocols of preconditioning and neuroprotection (14 , 15 , 26 , 55 56 57 58) .

The role of LIF
The role of CLC and LIF, the two members of the IL-6 family of cytokines that were induced in all models of retinal degeneration, is unclear. They may act in an autocrine or paracrine fashion. In the rd1 mouse, expression of CLC and LIF was still up-regulated even after most photoreceptors had died and were cleared from the subretinal space. The same long-lasting stimulation was observed for p-STAT3, p-Akt473, and GFAP. This may suggest that these factors play a role in the retina even after photoreceptor degeneration—for example, in the remodeling of second order neurons, which begins as early as PND10 in the rd1 retina (36 , 37) . LIF may be of particular interest in this respect since this factor was shown to keep cells in an undifferentiated state to modulate stem cell renewal (59 , 60) . In the postnatal retina, LIF blocks expression of Nrl and Crx transcription factors (61) , disrupts synaptic organization (62) , and arrests developing photoreceptors in a pre-rod stage (63) . Increased expression of LIF in a degenerating retina may therefore be required for the adjustment of the remaining cells of the INL and GCL to the new retinal architecture.

In summary, we show the differential regulation of the IL-6 family of cytokines and of the Jak-STAT signaling pathway in different models of retinal degeneration. Interference with this signaling protects a model of induced but not a model of inherited photoreceptor apoptosis, suggesting that regulation/execution of cell death of visual cells strongly depends on the particular apoptotic stimulus. The expression pattern of the various factors supports a pivotal regulatory role of the INL and/or GCL in photoreceptor apoptosis. Treatment strategies to prevent photoreceptor degeneration in human blinding diseases may thus need to target the regulatory molecular response of cells apart from photoreceptors.

ACKNOWLEDGMENTS

The authors wish to thank Coni Imsand, Gaby Hoegger, and Hedwig Wariwoda for excellent technical assistance and Muna Naash for providing the VPP transgenic mouse line. This work was supported by the Swiss National Science Foundation (3100A0–105793), the Novartis Foundation, the German Research Council (SP1088), and by a grant from the European Community (EVI-GenoRet; LSHG-computed tomography-512036). The authors are especially thankful for the generous support by the H. Messerli Fonds. The Laboratory of Retinal Cell Biology is a member of the Center of Integrative Human Physiology (CIHP) and of the Neuroscience Center Zurich (ZNZ) of the University of Zurich.

Received for publication February 16, 2006. Accepted for publication June 12, 2006.

REFERENCES

  1. Reme, C. E., Grimm, C., Hafezi, F., Marti, A., Wenzel, A. (1998) Apoptotic cell death in retinal degenerations. Prog. Retin. Eye Res. 17,443-464[CrossRef][Medline]
  2. Wenzel, A., Grimm, C., Samardzija, M., Reme, C. E. (2005) Molecular mechanisms of light-induced photoreceptor apoptosis and neuroprotection for retinal degeneration. Prog. Retin. Eye Res. 24,275-306[CrossRef][Medline]
  3. Grimm, C., Wenzel, A., Groszer, M., Mayser, H., Seeliger, M., Samardzija, M., Bauer, C., Gassmann, M., Reme, C. E. (2002) HIF-1-induced erythropoietin in the hypoxic retina protects against light-induced retinal degeneration. Nat. Med. 8,718-724[CrossRef][Medline]
  4. Wenzel, A., Grimm, C., Seeliger, M. W., Jaissle, G., Hafezi, F., Kretschmer, R., Zrenner, E., Reme, C. E. (2001) Prevention of photoreceptor apoptosis by activation of the glucocorticoid receptor. Invest Ophthalmol. Vis. Sci. 42,1653-1659[Abstract/Free Full Text]
  5. Imai, D., Yoneya, S., Gehlbach, P. L., Wei, L. L., Mori, K. (2005) Intraocular gene transfer of pigment epithelium-derived factor rescues photoreceptors from light-induced cell death. J. Cell. Physiol. 202,570-578[CrossRef][Medline]
  6. Organisciak, D. T., Darrow, R. A., Barsalou, L., Darrow, R. M., Lininger, L. A. (1999) Light-induced damage in the retina: differential effects of dimethylthiourea on photoreceptor survival, apoptosis and DNA oxidation. Photochem. Photobiol. 70,261-268[CrossRef][Medline]
  7. Ranchon, I., Chen, S., Alvarez, K., Anderson, R. E. (2001) Systemic administration of phenyl-N-tert-butylnitrone protects the retina from light damage. Invest. Ophthalmol. Vis. Sci. 42,1375-1379[Abstract/Free Full Text]
  8. Zhang, C., Lei, B., Lam, T. T., Yang, F., Sinha, D., Tso, M. O. (2004) Neuroprotection of photoreceptors by minocycline in light-induced retinal degeneration. Invest. Ophthalmol. Vis. Sci. 45,2753-2759[Abstract/Free Full Text]
  9. LaVail, M. M., Unoki, K., Yasumura, D., Matthes, M. T., Yancopoulos, G. D., Steinberg, R. H. (1992) Multiple growth factors, cytokines, and neurotrophins rescue photoreceptors from the damaging effects of constant light. Proc. Natl. Acad. Sci. U. S. A. 89,11249-11253[Abstract/Free Full Text]
  10. Tao, W., Wen, R., Goddard, M. B., Sherman, S. D., O’Rourke, P. J., Stabila, P. F., Bell, W. J., Dean, B. J., Kauper, K. A., Budz, V. A., et al (2002) Encapsulated cell-based delivery of CNTF reduces photoreceptor degeneration in animal models of retinitis pigmentosa. Invest Ophthalmol. Vis. Sci. 43,3292-3298[Abstract/Free Full Text]
  11. Cao, W., Tombran-Tink, J., Elias, R., Sezate, S., Mrazek, D., McGinnis, J. F. (2001) In vivo protection of photoreceptors from light damage by pigment epithelium-derived factor. Invest. Ophthalmol. Vis. Sci. 42,1646-1652[Abstract/Free Full Text]
  12. Grimm, C., Wenzel, A., Stanescu, D., Samardzija, M., Hotop, S., Groszer, M., Naash, M., Gassmann, M., Reme, C. (2004) Constitutive overexpression of human erythropoietin protects the mouse retina against induced but not inherited retinal degeneration. J. Neurosci. 24,5651-5658[Abstract/Free Full Text]
  13. Kaldi, I., Dittmar, M., Pierce, P., Anderson, R. E. (2003) L-NAME protects against acute light damage in albino rats, but not against retinal degeneration in P23H and S334ter transgenic rats. Exp. Eye Res. 76,453-461[CrossRef][Medline]
  14. Peterson, W. M., Wang, Q., Tzekova, R., Wiegand, S. J. (2000) Ciliary neurotrophic factor and stress stimuli activate the Jak-STAT pathway in retinal neurons and glia. J. Neurosci. 20,4081-4090[Abstract/Free Full Text]
  15. Harada, T., Harada, C., Kohsaka, S., Wada, E., Yoshida, K., Ohno, S., Mamada, H., Tanaka, K., Parada, L. F., Wada, K. (2002) Microglia-Muller glia cell interactions control neurotrophic factor production during light-induced retinal degeneration. J. Neurosci. 22,9228-9236[Abstract/Free Full Text]
  16. Alonzi, T., Middleton, G., Wyatt, S., Buchman, V., Betz, U. A., Muller, W., Musiani, P., Poli, V., Davies, A. M. (2001) Role of STAT3 and PI 3-kinase/Akt in mediating the survival actions of cytokines on sensory neurons. Mol. Cell. Neurosci. 18,270-282[CrossRef][Medline]
  17. Ikeda, K., Tatsuno, T., Noguchi, H., Nakayama, C. (2004) Ciliary neurotrophic factor protects rat retina cells in vitro and in vivo via PI3 kinase. Curr. Eye Res. 29,349-355[CrossRef][Medline]
  18. Platanias, L. C. (2005) Mechanisms of type-I- and type-II-interferon-mediated signalling. Nat. Rev. Immunol. 5,375-386[CrossRef][Medline]
  19. Stephanou, A. (2004) Role of STAT-1 and STAT-3 in ischaemia/reperfusion injury. J. Cell. Mol. Med. 8,519-525[Medline]
  20. Calo, V., Migliavacca, M., Bazan, V., Macaluso, M., Buscemi, M., Gebbia, N., Russo, A. (2003) STAT proteins: from normal control of cellular events to tumorigenesis. J. Cell. Physiol. 197,157-168[CrossRef][Medline]
  21. Aaronson, D. S., Horvath, C. M. (2002) A road map for those who don’t know JAK-STAT. Science 296,1653-1655[Abstract/Free Full Text]
  22. Krebs, D. L., Hilton, D. J. (2000) SOCS: physiological suppressors of cytokine signaling. J. Cell Sci. 113,2813-2819[Abstract]
  23. Cao, W., Wen, R., Li, F., Lavail, M. M., Steinberg, R. H. (1997) Mechanical injury increases bFGF and CNTF mRNA expression in the mouse retina. Exp. Eye Res. 65,241-248[CrossRef][Medline]
  24. Casson, R. J., Chidlow, G., Wood, J. P., Vidal-Sanz, M., Osborne, N. N. (2004) The effect of retinal ganglion cell injury on light-induced photoreceptor degeneration. Invest. Ophthalmol. Vis. Sci. 45,685-693[Abstract/Free Full Text]
  25. Nir, I., Liu, C., Wen, R. (1999) Light treatment enhances photoreceptor survival in dystrophic retinas of Royal College of Surgeons rats. Invest. Ophthalmol. Vis. Sci. 40,2383-2390[Abstract/Free Full Text]
  26. Walsh, N., Valter, K., Stone, J. (2001) Cellular and subcellular patterns of expression of bFGF and CNTF in the normal and light stressed adult rat retina. Exp. Eye Res. 72,495-501[CrossRef][Medline]
  27. Wen, R., Song, Y., Cheng, T., Matthes, M. T., Yasumura, D., LaVail, M. M., Steinberg, R. H. (1995) Injury-induced upregulation of bFGF and CNTF mRNAS in the rat retina. J. Neurosci. 15,7377-7385[Abstract]
  28. Valter, K., Bisti, S., Gargini, C., Di Loreto, S., Maccarone, R., Cervetto, L., Stone, J. (2005) Time course of neurotrophic factor upregulation and retinal protection against light-induced damage after optic nerve section. Invest. Ophthalmol. Vis. Sci. 46,1748-1754[Abstract/Free Full Text]
  29. Beltran, W. A., Rohrer, H., Aguirre, G. D. (2005) Immunolocalization of ciliary neurotrophic factor receptor alpha (CNTFRalpha) in mammalian photoreceptor cells. Mol. Vis. 11,232-244[Medline]
  30. De Raad, S., Szczesny, P. J., Munz, K., Reme, C. E. (1996) Light damage in the rat retina: glial fibrillary acidic protein accumulates in Muller cells in correlation with photoreceptor damage. Ophthal. Res. 28,99-107
  31. Hafezi, F., Steinbach, J. P., Marti, A., Munz, K., Wang, Z. Q., Wagner, E. F., Aguzzi, A., Reme, C. E. (1997) The absence of c-fos prevents light-induced apoptotic cell death of photoreceptors in retinal degeneration in vivo. Nat. Med. 3,346-349[CrossRef][Medline]
  32. Wenzel, A., Grimm, C., Samardzija, M., Reme, C. E. (2003) The genetic modifier Rpe65Leu(450): effect on light damage susceptibility in c-Fos-deficient mice. Invest. Ophthalmol. Vis. Sci. 44,2798-2802[Abstract/Free Full Text]
  33. Wenzel, A., Reme, C. E., Williams, T. P., Hafezi, F., Grimm, C. (2001) The Rpe65 Leu450Met variation increases retinal resistance against light-induced degeneration by slowing rhodopsin regeneration. J. Neurosci. 21,53-58[Abstract/Free Full Text]
  34. Bowes, C., Li, T., Danciger, M., Baxter, L. C., Applebury, M. L., Farber, D. B. (1990) Retinal degeneration in the rd mouse is caused by a defect in the beta subunit of rod cGMP-phosphodiesterase. Nature 347,677-680[CrossRef][Medline]
  35. Naash, M. I., Ripps, H., Li, S., Goto, Y., Peachey, N. S. (1996) Polygenic disease and retinitis pigmentosa: albinism exacerbates photoreceptor degeneration induced by the expression of a mutant opsin in transgenic mice. J. Neurosci. 16,7853-7858[Abstract/Free Full Text]
  36. Strettoi, E., Pignatelli, V., Rossi, C., Porciatti, V., Falsini, B. (2003) Remodeling of second-order neurons in the retina of rd/rd mutant mice. Vision Res. 43,867-877[CrossRef][Medline]
  37. Marc, R. E., Jones, B. W., Watt, C. B., Strettoi, E. (2003) Neural remodeling in retinal degeneration. Prog. Retin. Eye Res. 22,607-655[CrossRef][Medline]
  38. Bowes, C., Li, T., Frankel, W. N., Danciger, M., Coffin, J. M., Applebury, M. L., Farber, D. B. (1993) Localization of a retroviral element within the rd gene coding for the ß subunit of cGMP phosphodiesterase. Proc. Natl. Acad. Sci. U. S. A. 90,2955-2959[Abstract/Free Full Text]
  39. Burdelya, L., Catlett-Falcone, R., Levitzki, A., Cheng, F., Mora, L. B., Sotomayor, E., Coppola, D., Sun, J., Sebti, S., Dalton, W. S., et al (2002) Combination therapy with AG-490 and interleukin 12 achieves greater antitumor effects than either agent alone. Mol. Cancer Ther. 1,893-899[Abstract/Free Full Text]
  40. Meydan, N., Grunberger, T., Dadi, H., Shahar, M., Arpaia, E., Lapidot, Z., Leeder, J. S., Freedman, M., Cohen, A., Gazit, A., et al (1996) Inhibition of acute lymphoblastic leukaemia by a Jak-2 inhibitor. Nature 379,645-648[CrossRef][Medline]
  41. Wang, L. H., Kirken, R. A., Erwin, R. A., Yu, C. R., Farrar, W. L. (1999) JAK3, STAT, and MAPK signaling pathways as novel molecular targets for the tyrphostin AG-490 regulation of IL-2-mediated T cell response. J. Immunol. 162,3897-3904[Abstract/Free Full Text]
  42. Battle, T. E., Frank, D. A. (2002) The role of STATs in apoptosis. Curr. Mol. Med. 2,381-392[CrossRef][Medline]
  43. Zhang, S. S., Wei, J. Y., Li, C., Barnstable, C. J., Fu, X. Y. (2003) Expression and activation of STAT proteins during mouse retina development. Exp. Eye Res. 76,421-431[CrossRef][Medline]
  44. Rhee, K. D., Yang, X. J. (2003) Expression of cytokine signal transduction components in the postnatal mouse retina. Mol. Vis. 9,715-722[Medline]
  45. Song, Y., Zhao, L., Tao, W., Laties, A. M., Luo, Z., Wen, R. (2003) Photoreceptor protection by cardiotrophin-1 in transgenic rats with the rhodopsin mutation s334ter. Invest. Ophthalmol. Vis. Sci. 44,4069-4075[Abstract/Free Full Text]
  46. Ji, J. Z., Elyaman, W., Yip, H. K., Lee, V. W., Yick, L. W., Hugon, J., So, K. F. (2004) CNTF promotes survival of retinal ganglion cells after induction of ocular hypertension in rats: the possible involvement of STAT3 pathway. Eur. J. Neurosci. 19,265-272[CrossRef][Medline]
  47. Dikdan, G. S., Saba, S. C., Dela Torre, A. N., Roth, J., Wang, S., Koneru, B. (2004) Role of oxidative stress in the increased activation of signal transducers and activators of transcription-3 in the fatty livers of obese Zucker rats. Surgery 136,677-685[CrossRef][Medline]
  48. Carballo, M., Conde, M., El Bekay, R., Martin-Nieto, J., Camacho, M. J., Monteseirin, J., Conde, J., Bedoya, F. J., Sobrino, F. (1999) Oxidative stress triggers STAT3 tyrosine phosphorylation and nuclear translocation in human lymphocytes. J. Biol. Chem. 274,17580-17586[Abstract/Free Full Text]
  49. Brunet, A., Datta, S. R., Greenberg, M. E. (2001) Transcription-dependent and -independent control of neuronal survival by the PI3K-Akt signaling pathway. Curr. Opin. Neurobiol. 11,297-305[CrossRef][Medline]
  50. Barber, A. J., Nakamura, M., Wolpert, E. B., Reiter, C. E., Seigel, G. M., Antonetti, D. A., Gardner, T. W. (2001) Insulin rescues retinal neurons from apoptosis by a phosphatidylinositol 3-kinase/Akt-mediated mechanism that reduces the activation of caspase-3. J. Biol. Chem. 276,32814-32821[Abstract/Free Full Text]
  51. Datta, S. R., Brunet, A., Greenberg, M. E. (1999) Cellular survival: a play in three Akts. Genes Dev. 13,2905-2927[Free Full Text]
  52. Johnson, L. E., van Veen, T., Ekstrom, P. A. (2005) Differential Akt activation in the photoreceptors of normal and rd1 mice. Cell Tissue Res. 320,213-222[CrossRef][Medline]
  53. Jomary, C., Cullen, J., Jones, S. E. (2006) Inactivation of the Akt survival pathway during photoreceptor apoptosis in the retinal degeneration mouse. Invest. Ophthalmol. Vis. Sci. 47,1620-1629[Abstract/Free Full Text]
  54. Yu, D. Y., Cringle, S., Valter, K., Walsh, N., Lee, D., Stone, J. (2004) Photoreceptor death, trophic factor expression, retinal oxygen status, and photoreceptor function in the P23H rat. Invest. Ophthalmol. Vis. Sci. 45,2013-2019[Abstract/Free Full Text]
  55. Wang, Y., Smith, S. B., Ogilvie, J. M., McCool, D. J., Sarthy, V. (2002) Ciliary neurotrophic factor induces glial fibrillary acidic protein in retinal Muller cells through the JAK/STAT signal transduction pathway. Curr. Eye Res. 24,305-312[CrossRef][Medline]
  56. Chun, M. H., Ju, W. K., Kim, K. Y., Lee, M. Y., Hofmann, H. D., Kirsch, M., Oh, S. J. (2000) Upregulation of ciliary neurotrophic factor in reactive Muller cells in the rat retina following optic nerve transection. Brain Res. 868,358-362[CrossRef][Medline]
  57. Harada, T., Harada, C., Nakayama, N., Okuyama, S., Yoshida, K., Kohsaka, S., Matsuda, H., Wada, K. (2000) Modification of glial-neuronal cell interactions prevents photoreceptor apoptosis during light-induced retinal degeneration. Neuron 26,533-541[CrossRef][Medline]
  58. Harada, C., Harada, T., Quah, H. M., Maekawa, F., Yoshida, K., Ohno, S., Wada, K., Parada, L. F., Tanaka, K. (2003) Potential role of glial cell line-derived neurotrophic factor receptors in Muller glial cells during light-induced retinal degeneration. Neuroscience 122,229-235[CrossRef][Medline]
  59. Murray, P., Edgar, D. (2001) The regulation of embryonic stem cell differentiation by leukaemia inhibitory factor (LIF). Differentiation 68,227-234[CrossRef][Medline]
  60. Cartwright, P., McLean, C., Sheppard, A., Rivett, D., Jones, K., Dalton, S. (2005) LIF/STAT3 controls ES cell self-renewal and pluripotency by a Myc-dependent mechanism. Development 132,885-896[Abstract/Free Full Text]
  61. Graham, D. R., Overbeek, P. A., Ash, J. D. (2005) Leukemia inhibitory factor blocks expression of Crx and Nrl transcription factors to inhibit photoreceptor differentiation. Invest. Ophthalmol. Vis. Sci. 46,2601-2610[Abstract/Free Full Text]
  62. Sherry, D. M., Mitchell, R., Li, H., Graham, D. R., Ash, J. D. (2005) Leukemia inhibitory factor inhibits neuronal development and disrupts synaptic organization in the mouse retina. J. Neurosci. Res. 82,316-332[CrossRef][Medline]
  63. Neophytou, C., Vernallis, A. B., Smith, A., Raff, M. C. (1997) Muller-cell-derived leukaemia inhibitory factor arrests rod photoreceptor differentiation at a postmitotic pre-rod stage of development. Development 124,2345-2354[Abstract]
  64. Samardzija, M., Wenzel, A., Naash, M., Reme, C. E., Grimm, C. (2006) Rpe65 as a modifier gene for inherited retinal degeneration. Eur. J. Neurosci. 23,1028-1034[CrossRef][Medline]
  65. Xuan, Y. T., Guo, Y., Han, H., Zhu, Y., Bolli, R. (2001) An essential role of the JAK-STAT pathway in ischemic preconditioning. Proc. Natl. Acad. Sci. U. S. A. 98,9050-9055[Abstract/Free Full Text]
  66. Yamauchi, K., Osuka, K., Takayasu, M., Usuda, N., Nakazawa, A., Nakahara, N., Yoshida, M., Aoshima, C., Hara, M., Yoshida, J. (2006) Activation of JAK/STAT signalling in neurons following spinal cord injury in mice. J. Neurochem. 96,1060-1070[CrossRef][Medline]
  67. Kueng-Hitz, N., Grimm, C., Lansel, N., Hafezi, F., He, L., Fox, D. A., Reme, C. E., Niemeyer, G., Wenzel, A. (2000) The retina of c-fos-/- mice: electrophysiologic, morphologic and biochemical aspects. Invest. Ophthalmol. Vis. Sci. 41,909-916[Abstract/Free Full Text]



This article has been cited by other articles:


Home page
 J. Biol. Chem.Home page
Y. Ozawa, K. Nakao, T. Kurihara, T. Shimazaki, S. Shimmura, S. Ishida, A. Yoshimura, K. Tsubota, and H. Okano
Roles of STAT3/SOCS3 Pathway in Regulating the Visual Function and Ubiquitin-Proteasome-dependent Degradation of Rhodopsin during Retinal Inflammation
J. Biol. Chem., September 5, 2008; 283(36): 24561 - 24570.
[Abstract] [Full Text] [PDF]

Home page
 IOVSHome page
D. Y. Chong, C. S. Boehlke, Q.-D. Zheng, L. Zhang, Y. Han, and D. N. Zacks
Interleukin-6 as a Photoreceptor Neuroprotectant in an Experimental Model of Retinal Detachment
Invest. Ophthalmol. Vis. Sci., July 1, 2008; 49(7): 3193 - 3200.
[Abstract] [Full Text] [PDF]

Home page
 DiabetesHome page
X. Liu, M. G. Mameza, Y. S. Lee, C. I. Eseonu, C.-R. Yu, J. J. Kang Derwent, and C. E. Egwuagu
Suppressors of Cytokine-Signaling Proteins Induce Insulin Resistance in the Retina and Promote Survival of Retinal Cells
Diabetes, June 1, 2008; 57(6): 1651 - 1658.
[Abstract] [Full Text] [PDF]

Home page
 Hum Mol GenetHome page
M. Samardzija, J. von Lintig, N. Tanimoto, V. Oberhauser, M. Thiersch, C. E. Reme, M. Seeliger, C. Grimm, and A. Wenzel
R91W mutation in Rpe65 leads to milder early-onset retinal dystrophy due to the generation of low levels of 11-cis-retinal
Hum. Mol. Genet., January 15, 2008; 17(2): 281 - 292.
[Abstract] [Full Text] [PDF]

Home page
 IOVSHome page
D. Gu, W. A. Beltran, Z. Li, G. M. Acland, and G. D. Aguirre
Clinical Light Exposure, Photoreceptor Degeneration, and AP-1 Activation: A Cell Death or Cell Survival Signal in the Rhodopsin Mutant Retina?
Invest. Ophthalmol. Vis. Sci., November 1, 2007; 48(11): 4907 - 4918.
[Abstract] [Full Text] [PDF]