(The FASEB Journal. 1999;13:S129-S134.)
© 1999 FASEB
The effect of microgravity on morphology and gene expression of osteoblasts in vitro
GEERT CARMELIET1 and
ROGER BOUILLON
Laboratory for Experimental Medicine and Endocrinology, Katholieke Universiteit Leuven, Belgium
1Correspondence: LEGENDO, Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium. E-mail: Geert.Carmeliet{at}med.kuleuven.ac.be
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ABSTRACT
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The mass and architecture of the skeletal system adapt, to some extent,
to their mechanical environment. A site-specific bone loss of 1–2% is
observed in astronauts and in-flight animals after 1 month of
spaceflight. Biochemical data of astronauts and histomorphometric
analysis of rat bones show that the change in bone mass is a result of
decreased bone formation in association with normal (or increased) bone
resorption. The changes in bone formation appear to be due in part to
decreased osteoblast differentiation, matrix maturation, and
mineralization. Recent data show that spaceflight alters the mRNA level
for several bone-specific proteins in rat bone, suggesting that the
characteristics of osteoblasts are altered during spaceflight. A
possible underlying mechanism is that osteoblasts themselves are
sensitive to altered gravity levels as suggested by several studies
investigating the effect of microgravity on osteoblasts in
vitro. Changes in cell and nuclear morphology were observed as
well as alterations in the expression of growth factors (interleukin-6
and insulin-like growth factor binding proteins) and matrix proteins
(collagen type I and osteocalcin). Taken together, this altered
cellular function in combination with differences in local or systemic
factors may mediate the effects of spaceflight on bone
physiology.—Carmeliet, G., Bouillon, R. The effect of microgravity on
morphology and gene expression of osteoblasts in vitro.
Key Words: bone formation • spaceflight • growth factors • matrix proteins
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INTRODUCTION
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BONE IS A MULTIFUNCTIONAL ORGAN and has to fulfill two
main functions: the provision of mechanical integrity for both
locomotion and protection, and the involvement in the metabolic
pathways associated with mineral homeostasis. Mechanical factors are
essential for the maintenance of skeletal integrity. The architecture
of bone is correlated to the mechanical stresses exerted on it,
resulting in a material with an optimal functional design. Certain
metabolic bone diseases such as osteoporosis are characterized by a
reduction in bone mass but also by a change in microarchitecture that
increases the susceptibility to fractures. On the other hand, absence
of gravity or mechanical load results in a very rapid and severe
uncoupling between bone formation and resorption, with fast bone loss.
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SPACEFLIGHT-INDUCED ALTERATIONS IN BONE METABOLISM OF HUMANS AND
RATS
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Skeletal unloading in humans and rats, as seen during spaceflight,
induces a series of events in bone, resulting in bone loss
(1-4)
and compromised bone mechanical properties
(5-9)
. It has been estimated that, in a microgravity
environment, on average about 1–2% of the skeleton is mobilized and
lost each month (10)
. Bone mass changes are, however,
site-specific rather than evenly distributed throughout the skeleton
with the tendency that weight-bearing bones are more affected by
microgravity than non-weight-bearing bones (11
,
12
). In addition, the duration of spaceflight and the
level of bone remodeling before unloading also appeared to be factors
able to modulate bone response to microgravity. Although no
pathological fractures have yet occurred, spaceflight-related bone loss
may have potentially serious consequences in long-term spaceflight,
especially because the recovery is a long-lasting process, if at all
possible (12
, 13
).
In normal bone there is an equilibrium between bone formation and bone
resorption. Recent biochemical data from astronauts confirmed the
previous findings in rats that microgravity induces an uncoupling of
bone remodeling between formation and resorption that could account for
bone loss. All bone formation parameters (bone alkaline phosphatase,
osteocalcin, and type 1 procollagen propeptide) were decreased, whereas
bone resorption markers (procollagen C-telopeptide, deoxypyridinolines)
were increased when measured during flight (14)
.
Histomorphometric analysis of bones from rats flown aboard space
missions showed a slowing or an arrest in cortical periosteal growth
(1
, 5
, 15-18
). Osteopenia was
found to develop in the metabolically active cancellous bone with a
reduction in the primary spongiosa width and trabecular thinning and
disappearance in the secondary spongiosa. The result was a substantial
metaphyseal bone loss. The magnitude of this response may, however, be
influenced by age, strain, and especially housing conditions
(18)
. In addition, bone mineralization rate and the
proportion of trabecular bone surface involved in mineralization
processes were markedly reduced in monkeys after an 11.5-day
spaceflight (19)
. Taken together these data demonstrate a
decrease in bone formation and defects in bone maturation, suggesting
an inappropriate functioning of osteoblasts in microgravity.
It is interesting to note that these histological findings are preceded
by detectable reductions in gene expression of two bone-related
proteins, prepro-
2(I) chain of type I procollagen and osteocalcin
(20)
. In addition, spaceflight alters the message level
for local growth factors: transforming growth factor ß1
(TGF-ß1)2gene expression is reduced in the hindlimb periosteum (21)
and insulin-like growth factor I (IGF-I) gene expression is increased
in the tibia (22
, 23
).
In conclusion, decreased osteoblast function likely plays an important
role in the process of spaceflight-induced bone loss. One possible
underlying mechanism is that the levels of systemic hormones or local
growth factors are altered. On the other hand, osteoblasts themselves
may be sensitive to altered gravity levels as has been shown for other
cell types.
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EFFECT OF MECHANICAL STIMULATION ON THE BIOLOGY OF BONE-DERIVED
CELLS
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During spaceflight mechanical loading of bone is minimal. The bone
cells appropriately placed to assess functional strains are the
osteoblasts, osteocytes, and bone lining cells. Osteoblasts and
osteocytes in vitro are responsive to mechanical stimuli, as
has been shown by using several methods to apply mechanical stress
in vitro. Stretching or bending of the cell substratum has
been widely used but recent evidence indicates that fluid flow over the
cell surface may also simulate the cellular effect of mechanical
loading of bone in vivo (24)
. The response of
bone-derived cells to mechanical stimulation in vitro
appears to be dependent on both the source of bone-derived cells used
and on the type of mechanical stimulation and may explain the apparent
conflicting observations.
Mechanical stimulation increases the proliferation of both primary
osteoblastic cultures and cell lines, although in some studies a
decreased proliferation was observed that was probably related to the
strain magnitude used. Recent experiments show that the early
proliferative response to mechanical strain is mediated through a
mechanism that involves the estrogen receptor because the estrogen
antagonist tamoxifen eliminates the strain-related proliferation of rat
long bone-derived osteoblasts (25)
.
The early effects in osteoblasts related to strain include an increased
activity of glucose-6-phosphate dehydrogenase and an increased
production of inositol triphosphate, cyclic AMP (26)
,
nitric oxide (27)
, and prostaglandin I2
(28)
, whereas an increased release of prostaglandin
E2 (PGE2) is detected only in bone cells
derived from non-weight-bearing calvaria (29)
. The
expression of inducible prostaglandin G/H synthase and of early genes
such as c-fos is also consistently increased (30
,
31
).
Within hours of being exposed to mechanical strain, bone cells produce
growth factors including IGFs (28)
, which are mitogenic
for bone cells. Mechanical strain also increases the level of
TGF-ß1 mRNA in MC3T3-E1 cells (32)
and
enhances the activation of released TGF-ß in mouse calvariae-derived
cells (33)
or its release in human osteoblasts (34)
.
An important aspect of osteoblast activity is the production of bone
matrix during the process of osteoblast differentiation. Based on
in vitro studies, osteoblast differentiation has been
characterized as a process of sequential expression of the genes for
collagen type I and alkaline phosphatase during the phase of matrix
formation and maturation followed by gene expression for osteocalcin
and osteopontin concurrent with the stage of mineralization
(35)
. Mechanical stimulation promotes alkaline
phosphatase, procollagen type I, osteopontin, and osteocalcin gene
expression in bone cells (36-38)
, although opposite
effects are also reported (39)
.
The mechanisms by which mechanical stimulation of osteoblasts is
transduced into intracellular signals and physiological effects are not
well understood. Mechanical strain increases the sensitivity and the
number of open cation-selective channels in UMR 106-01 cells
(40)
. The microfilament component of the cytoskeleton is
suggested to be involved in cellular mechanotransduction because
disruption of the actin cytoskeleton abolishes the prostaglandin and
osteopontin response to mechanical stimulation (41
,
42
). In addition, increased message levels of
ß1-integrin are detected in human osteosarcoma cells
after mechanical stimulation (43)
. Cyclic stretch also
increases gap junctional intercellular communication between
osteoblasts by increasing the level of the phosphorylated form of
connexin 43 and enhancing connexin 43 abundance on the cell surface of
adjoining cells (44)
. Taken together, these in
vitro data showing an altered proliferation and synthesis of
growth factors and matrix proteins are consistent with in
vivo data.
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SPACEFLIGHT-RELATED ALTERATIONS IN OSTEOBLAST CHARACTERISTICS
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A decreased osteoblast function is claimed to play a role in the
process of spaceflight-induced bone loss. As already mentioned, the
underlying mechanism may involve an altered cellular behavior as has
been observed in other cell types exposed to microgravity. Recent
experiments using several osteoblastic cell types show that cell
morphology as well as gene expression of growth factors and matrix
proteins are altered under microgravity conditions (Table 1
). Most of the studies refer to ground samples as control. Ideally,
an in-flight unit-gravity (1 g) centrifuge should be used as
an internal control as described in certain experiments.
Cell morphology
Changes in cell morphology have been observed after 4 days of
microgravity in rat osteosarcoma cells (ROS17/2.8), resulting in a
morphological mixed cell population (45
, 46
)
and in mouse osteoblastic cells (MC3T3-E1), which became rounded
(47)
. No major changes in cell focal adhesion parameters
were detected in ROS17/2.8 cells after a short period of simulated
microgravity (clinostat), whereas variations of gravity (parabolic
flight) induced a significant decrease in cell area that was associated
with reorganization of the focal contact plaques. However, after longer
exposures to microgravity, focal adhesions of ROS17/2.8 cells were
modified. The cytoskeleton of the flight MC3T3-E1 cells had a reduced
number of stress fibers and the nuclei of these cells were smaller,
oblong in shape, and with fewer punctate areas.
Gene expression
Altered gene expression related to microgravity has been detected
in several osteoblastic models. PGE2 production is
increased due, at least in part, to an increased level of inducible
prostaglandin G/H synthase-2 in rat bone stromal cells
(48)
. The message level of interleukin-6 (48)
and insulin-like growth factor binding protein (IGF-BP)-3 is increased,
whereas IGF BP-5 and IGF-BP-4 mRNA levels are decreased in
1,25(OH)2D3-treated rat stromal cells under
microgravity conditions. In addition, message levels for the
glucocorticoid receptor are increased in flight cultures
(49)
.
In our spaceflight experiment aboard the unmanned satellite Foton 10
(1995) the effect of microgravity on osteoblast
differentiation in vitro using the human osteosarcoma cell
line MG-63 was investigated. This cell line is considered to be
representative of a particular subpopulation of osteoblasts, i.e.
osteoblast precursors or early undifferentiated osteoblast-like cells.
Time course experiments showed that treatment of MG-63 cells with the
combination of 1,25(OH)2D3 and
TGF-ß2 induces a temporal sequence of protein expression
in that collagen type I production precedes alkaline phosphatase
activity, which is followed by osteocalcin (Fig. 1
). However, osteocalcin secretion is only moderately increased,
suggesting that MG-63 differentiation is stopped at the transition of
matrix maturation to matrix mineralization. Alterations in gene
expression of alkaline phosphatase and osteocalcin preceded at every
time point the concomitant changes at the protein level. Yet,
apparently conflicting results are observed when time profiles of
message levels for collagen I1 and of collagen type I content are
compared; these are probably due to a change in the translational
efficiency as well as abundance of procollagen mRNAs (50)
.
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Figure 1. Time course of differentiation-related gene and protein expression by
MG-63 cells after treatment with 1,25(OH)2D3
and TGF-ß2. A) Time-related gene expression.
Semi-quantification by competitive reverse transcriptase-polymerase
chain reaction of collagen I1, alkaline phosphatase, and osteocalcin
mRNA, corrected for ß-actin mRNA, was performed in untreated MG-63
cells and cells treated with 1,25(OH)2D3
(10-7 M) and TGF-ß2 (10 ng/ml) for 5, 10, 24,
48, and 72 h. The mRNA level of cells treated for 72 h was
taken as 100%. Data represent the mean of triplicate measurements of
one representative experiment out of two independent experiments.
B) Time-related protein expression. The production of
collagen type I, osteocalcin, and the expression of alkaline
phosphatase activity by MG-63 cells was quantified after treatment for
0, 5, 10, 24, 48, and 72 h. Data represent mean ±
SD of triplicate measurements of one representative
experiment out of three independent experiments.
|
|
These genes were quantified both at the protein and mRNA level in
untreated and hormone-treated [1,25(OH)2D3 and
TGF-ß2] cells cultured for 9 days under microgravity
conditions and compared with ground and in-flight unit-gravity cultures
(Table 2
). The expression of alkaline phosphatase activity after treatment
at microgravity was significantly lower compared to ground control,
whereas no alteration was detected in the production of collagen type I
between unit- and microgravity. In addition, gene expression for
collagen I1, alkaline phosphatase, and osteocalcin after treatment
at microgravity was significantly reduced (51
,
52
). A plausible explanation for the finding that collagen
mRNA level is decreased, whereas no effect is seen on the protein
level, is related to the observed difference in kinetics between gene
and protein expression under unit-gravity conditions. In addition to
their essential role in matrix formation, osteoblasts are also
considered to be local regulators of bone metabolism and remodeling via
the production of growth factors. Preliminary results show that message
levels for TGF-ß1 and latent TGF-ß binding protein 1
and 2 are altered in the flight samples compared to ground control
cultures. These data show that microgravity decreases the activity of
osteoblasts in vitro; in particular the differentiation of
MG-63 cells in response to systemic hormones and growth factors is
reduced by microgravity.
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CONCLUSIONS
|
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Alterations in the morphology, cytoskeleton, and gene expression
for growth factors and matrix proteins are observed in osteoblastic
cells in vitro under microgravity conditions. The underlying
mechanisms are not identified yet, but recent data support the concept
that molecular mechanisms link cell shape to gene expression. A
reciprocal relationship is postulated between gene expression and
tissue matrix comprising extracellular matrix, cytoskeleton, and
nuclear matrix (53)
. The response of the osteoblast to
mechanical loading may involve alterations in this cytoskeletal-nuclear
communication pathway. Whether a similar mechanism is involved in
microgravity-related gene expression remains to be elucidated.
Together, these in vitro data in combination with in
vivo results suggest that a combined action of an altered cellular
function and differences in local or systemic factors mediate the
dramatic effects of spaceflight on bone physiology.
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FOOTNOTES
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2 Abbreviations: TGF-ß1,
transforming growth factor ß1; IGF-1, insulin-like growth
factor 1; PGE2, prostaglandin E2.
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REFERENCES
|
|---|
-
Morey, E. R., Baylink, D. J. (1978) Inhibition of bone formation during space flight. Science 201,1138-1141[Abstract/Free Full Text]
-
Jee, W. S. S., Wronski, T. J., Morey, E. R., Kimmel, D. B. (1983) Effects of spaceflight on trabecular bone in rats. Am. J. Physiol. 244,R310-R314[Abstract/Free Full Text]
-
Vico, L., Alexandre, C. (1992) Microgravity and bone adaptation at the tissue level. J. Bone Miner. Res. 7,S445-S447
-
Zerath, E., Holy, X., Malouvier, A., Caissard, J. C., Nogues, C. (1991) Rat and monkey bone study in the Biocosmos 2044 space experiment. Physiologist 34,S194-S195[Medline]
-
Spengler, D. M., Morey, E. R., Carter, D. R., Turner, R. T., Baylink, D. J. (1983) Effects of spaceflight on structural and material strength of growing bone. Proc. Soc. Exp. Biol. Med. 174,224-228[Abstract]
-
Turner, R. T., Bell, N. H., Duvall, P., Bobyn, J. D., Spector, M., Morey-Holton, E., Baylink, D. J. (1985) Spaceflight results in formation of defective bone. Proc. Soc. Exp. Biol. Med. 180,544-549[Abstract]
-
Simmons, D. J., Russell, J. E., Grynpas, M. D. (1986) Bone maturation and quality of bone material in rats flown on the space shuttle "Spacelab-3 Mission.". Bone Miner 1,485-493[Medline]
-
Shaw, S. R., Vailas, A. C., Grindeland, R. E., Zernicke, R. F. (1988) Effects of a 1-wk spaceflight on morphological and mechanical properties of growing bone. Am. J. Physiol. 254,R78-R83[Abstract/Free Full Text]
-
Vailas, A. C., Zernicke, R. F., Grindeland, R. E., Kaplansky, A., Durnova, G. N., Li, K. C., Martinez, D. A. (1990) Effects of spaceflight on rat humerus geometry, biomechanics, and biochemistry. FASEB J 4,47-54[Abstract]
-
Tilton, F. E., Degioanni, J. J. C., Schneider, V. S. (1980) Long-term follow-up of Skylab bone demineralization. Aviat. Space Environ. Med. 51,1209-1213[Medline]
-
Collet, P., Uebelhart, D., Vico, L., Moro, L., Hartmann, D., Roth, M., Alexandre, C. (1997) Effects of 1- and 6-month spaceflight on bone mass and biochemistry in two humans. Bone 20,547-551[Medline]
-
Zerath, E., Godet, D., Holy, X., Andre, C., Renault, S., Hott, M., Marie, P. J. (1996) Effects of spaceflight and recovery on rat humeri and vertebrae: histological and cell culture studies. J. Appl. Physiol. 81,164-171[Abstract/Free Full Text]
-
Lafage-Proust, M. H., Collet, P., Dubost, J. M., Laroche, N., Alexandre, C., Vico, L. (1998) Space-related bone mineral redistribution and lack of bone mass recovery after reambulation in young rats. Am. J. Physiol. 274,R324-R334[Abstract/Free Full Text]
-
Caillot-Augusseau, A., Lafage-Proust, M. H., Soler, C., Pernod, J., Dubois, F., Alexandre, C. (1998) Bone formation and resorption biological markers in cosmonauts during and after a 180-day space flight (Euromir 95). Clin. Chem. 44,578-585[Abstract/Free Full Text]
-
Wronski, T. J., Morey, E. R. (1983) Effect of spaceflight on periosteal bone formation in rats. Am. J. Physiol 244,R305-R309[Abstract/Free Full Text]
-
Wronski, T. J., Morey-Holton, E. R., Doty, S. B., Maese, A. C., Walsh, C. C. (1987) Histomorphometric analysis of rat skeleton following spaceflight. Am. J. Physiol. 252,R252-R255[Abstract/Free Full Text]
-
Vico, L., Chappard, D., Palle, S., Bakulin, A. V., Novikov, V. E., Alexandre, C. (1988) Trabecular bone remodeling after seven days of weightlessness exposure (BIOCOSMOS 1667). Am. J. Physiol. 255,R243-R247[Abstract/Free Full Text]
-
Wronski, T. J., Li, M., Shen, Y., Miller, S. C., Bowman, B. M., Kostenuik, P., Halloran, B. P. (1998) Lack of effect of spaceflight on bone mass and bone formation in group-housed rats. J. Appl. Physiol. 85,279-285[Abstract/Free Full Text]
-
Zerath, E., Novikov, V., Leblanc, A., Bakulin, A., Oganov, V., Grynpas, M. (1996) Effects of spaceflight on bone mineralization in the rhesus monkey. J. Appl. Physiol. 81,194-200[Abstract/Free Full Text]
-
Backup, P., Westerlind, K., Harris, S., Spelsberg, T., Kline, B., Turner, R. (1994) Spaceflight results in reduced mRNA levels for tissue-specific proteins in the musculoskeletal system. Am. J. Physiol. 266,E567-E573[Abstract/Free Full Text]
-
Westerlind, K. C., Turner, R. T. (1995) The skeletal effects of spaceflight in growing rats: Tissue-specific alterations in mRNA levels for TGF-ß. J. Bone Miner. Res. 10,843-848[Medline]
-
Bikle, D. D., Harris, J., Halloran, B. P., Morey-Holton, E. (1994) Altered skeletal pattern of gene expression in response to spaceflight and hindlimb elevation. Am. J. Physiol. 267,E822-E827[Abstract/Free Full Text]
-
Cavolina, J. M., Evans, G. L., Harris, S. A., Zhang, M., Westerlind, K. C., Turner, R. T. (1997) The effects of orbital spaceflight on bone histomorphometry and messenger ribonucleic acid levels for bone matrix proteins and skeletal signaling peptides in ovariectomized growing rats. Endocrinology 138,1567-1576[Abstract/Free Full Text]
-
Duncan, R. L., Turner, C. H. (1995) Mechanotransduction and the functional response of bone to mechanical strain. Calcif. Tissue Int. 57,344-358[Medline]
-
Damien, E., Price, J. S., Lanyon, L. E. (1998) The estrogen receptor's involvement in osteoblasts' adaptive response to mechanical strain. J. Bone Miner. Res. 13,1275-1282[Medline]
-
Reich, K. M., Gay, C. V., Frangos, J. A. (1990) Fluid shear stress as a mediator of osteoblast cyclic adenosine monophosphate production. J. Cell. Physiol. 143,100-104[Medline]
-
Pitsillides, A. A., Rawlinson, S. C. F., Suswillo, R. F. L., Bourrin, S., Zaman, G., Lanyon, L. E. (1995) Mechanical strain-induced NO production by bone cells: a possible role in adaptive bone (re)modeling?. FASEB J 9,1614-1622[Abstract]
-
Zaman, G., Suswillo, R. F. L., Cheng, M. Z., Tavares, I. A., Lanyon, L. E. (1997) Early responses to dynamic strain change and prostaglandins in bone-derived cells in culture. J. Bone Miner. Res. 12,769-777[Medline]
-
Brighton, C. T., Strafford, B., Gross, S. B., Leatherwood, D. F., Williams, J. L., Pollack, S. R. (1991) The proliferative and synthetic response of isolated calvarial bone cells to cyclic biaxial mechanical strain. J. Bone Joint Surg. 73,320-331[Abstract/Free Full Text]
-
Klein-Nulend, J., Burger, E. H., Semeins, C. M., Raisz, L. G., Pilbeam, C. C. (1997) Pulsating fluid flow stimulates prostaglandin release and inducible prostaglandin G/H synthase mRNA expression in primary mouse bone cells. J. Bone Miner. Res. 12,45-51[Medline]
-
Kawata, A., Mikuni-Takagaki, Y. (1998) Mechanotransduction in stretched osteocytes—temporal expression of immediate early and other genes. Biochem. Biophys. Res. Commun. 246,404-408[Medline]
-
Zhuang, H., Wang, W., Tahernia, A. D., Levitz, C. L., Luchetti, W. T., Brighton, C. T. (1996) Mechanical strain-induced proliferation of osteoblastic cells parallels increased TGF-ß1 mRNA. Biochem. Biophys. Res. Commun. 229,449-453[Medline]
-
Klein-Nulend, J., Roelofsen, J., Sterck, J. G., Semeins, C. M., Burger, E. H. (1995) Mechanical loading stimulates the release of transforming growth factor-beta activity by cultured mouse calvariae and periosteal cells. J. Cell. Physiol. 163,115-119[Medline]
-
Neidlinger-Wilke, C., Stalla, I., Claes, L., Brand, R., Hoellen, I., Rübenacker, S., Arand, M., Kinzl, L. (1995) Human osteoblasts from younger normal and osteoporotic donors show differences in proliferation and TGFß-release in response to cyclic strain. J. Biomech. 28,1411-1418[Medline]
-
Stein, G. S., Lian, J. B., Stein, J. L., Van Wijnen, A. J., Montecino, M. (1996) Transcriptional control of osteoblast growth and differentiation. Physiol. Rev. 76,593-629[Abstract/Free Full Text]
-
Klein-Nulend, J., van der Plas, A., Semeins, C. M., Ajubi, N. E., Frangos, J. A., Nijweide, P. J., Burger, E. H. (1995) Sensitivity of osteocytes to biomechanical stress in vitro. FASEB J 9,441-445[Abstract/Free Full Text]
-
Mikuni-Takagaki, Y., Suzuki, Y., Kawase, T., Saito, S. (1996) Distinct responses of different populations of bone cells to mechanical stress. Endocrinology 137,2028-2035[Abstract]
-
Harter, L. V., Hruska, K. A., Duncan, R. L. (1995) Human osteoblast-like cells respond to mechanical strain with increased bone matrix protein production independent of hormonal regulation. Endocrinology 136,528-535[Abstract]
-
Ozawa, H., Imamura, K., Abe, E., Takahashi, N., Hiraide, T., Shibasaki, T., Fukuhara, Y., Suda, T. (1990) Effect of continuously applied compressive pressure on mouse osteoblast-like cells (MC3T3–E1) in vitro. J. Cell Physiol. 142,177-185[Medline]
-
Duncan, R. L., Hruska, K. A. (1994) Chronic, intermittent loading alters mechanosensitive channel characteristics in osteoblast-like cells. Am. J. Physiol. 267,F909-F916[Abstract/Free Full Text]
-
Ajubi, N. E., Klein-Nulend, J., Nijweide, P. J., Vrijheid-Lammers, T., Alblas, M. J., Burger, E. H. (1996) Pulsating fluid flow increases prostaglandin production by cultured chicken osteocytes—a cytoskeleton-dependent process. Biochem. Biophys. Res. Commun. 255,62-68
-
Toma, C. D., Ashkar, S., Gray, M. L., Schaffer, J. L., Gerstenfeld, L. C. (1997) Signal transduction of mechanical stimuli is dependent on microfilament integrity: identification of osteopontin as a mechanically induced gene in osteoblasts. J. Bone Miner. Res. 12,1626-1636[Medline]
-
Carvalho, R. S., Scott, J. E., Yen, E. H. K. (1995) The effects of mechanical stimulation on the distribution of ß1 integrin and expression of ß1-integrin mRNA in TE-85 human osteosarcoma cells. Arch. Oral. Biol. 40,257-266[Medline]
-
Ziambaras, K., Lecanda, F., Steinberg, T. H., Civitelli, R. (1998) Cyclic stretch enhances gap junctional communication between osteoblastic cells. J. Bone Miner. Res. 13,218-228[Medline]
-
Guignandon, A., Genty, C., Vico, L., Lafage-Proust, M. H., Palle, S., Alexandre, C. (1997) Demonstration of feasibility of automated osteoblastic line culture in space flight. Bone 20,109-116[Medline]
-
Guignandon, A., Usson, Y., Laroche, N., Lafage-Proust, M. H., Sabido, O., Alexandre, C., Vico, L. (1997) Effects of intermittent or continuous gravitational stresses on cell-matrix adhesion: quantitative analysis of focal contacts in osteoblastic ROS17/2.8 cells. Exp. Cell Res. 236,66-75[Medline]
-
Hughes-Fulford, M., Lewis, M. L. (1996) Effects of microgravity on osteoblast growth activation. Exp. Cell Res. 224,103-109[Medline]
-
Kumei, Y., Shimokawa, H., Katano, H., Hara, E., Akiyama, H., Hirano, M., Mukai, C., Nagaoka, S., Whitson, P. A., Sams, C. F. (1996) Microgravity induces prostaglandin E2 and interleukin-6 production in normal rat osteoblasts: role in bone demineralization. J. Biotechnol. 47,313-324[Medline]
-
Kumei, Y., Shimokawa, H., Katano, H., Akiyama, H., Hirano, M., Mukai, C., Nagaoka, S., Whitson, P. A., Sams, C. F. (1998) Spaceflight modulates insulin-like growth factor binding proteins and glucocorticoid receptor in osteoblasts. J. Appl. Physiol. 85,139-147[Abstract/Free Full Text]
-
Franceshi, R. T., Romano, P. R., Park, P. Y. (1988) Regulation of type I collagen synthesis by 1,25-dihydroxyvitamin D3 in human osteosarcoma cells. J. Biol. Chem. 35,18938-18945
-
Carmeliet, G., Nys, G., Bouillon, R. (1997) Microgravity reduces the differentiation of human osteoblastic MG-63 cells. J. Bone Miner. Res. 12,786-794[Medline]
-
Carmeliet, G., Nys, G., Stockmans, I., Bouillon, R. (1998) Gene expression related to the differentiation of osteoblastic cells is altered by microgravity. Bone 22,139S-143S[Medline]
-
Bidwell, J. P., Alvarez, M., Feister, H., Onyia, J., Hock, J. (1998) Nuclear matrix proteins and osteoblast gene expression. J. Bone Miner. Res. 13,155-167[Medline]
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ABSTRACT
INTRODUCTION
