| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Department of Oral Medicine, Infection, and Immunity, Harvard School of Dental Medicine, Boston, Massachusetts, USA
1 Correspondence: Department of Oral Medicine, Infection, and Immunity, Harvard School of Dental Medicine, Room 304, 188 Longwood Ave., Boston, MA 02115, USA. E-mail: mrazzaque{at}hms.harvard.edu; razzaquems{at}yahoo.com
Hyp mice possess a mutation that inactivates the phosphate-regulating gene, which is homologous to the endopeptidases of the X-chromosome (PHEX). The mutation is associated with severe hypophosphatemia due to excessive urinary phosphate wasting. Such urinary phosphate wasting in Hyp mice is associated with an increased serum accumulation of fibroblast growth factor (FGF) 23. We wanted to determine the biological significance of increased serum FGF23 levels and concomitant hypophosphatemia in Hyp mice and to evaluate whether FGF23 activity could be modified by manipulating klotho (a cofactor of FGF23 signaling). We generated Hyp and klotho double-mutant mice (Hyp/klotho–/–). Severe hypophosphatemia of Hyp mice was reversed to hyperphosphatemia in Hyp/klotho–/– double mutants, despite the fact that the double mutants showed significantly increased serum levels of FGF23. Hyperphosphatemia in Hyp/klotho–/– mice was associated with increased renal expression of sodium/phosphate cotransporter 2a (NaPi2a) protein. Exogenous injection of bioactive parathyroid hormone 1-34 down-regulated renal expression of NaPi2a and consequently reduced serum levels of phosphate in Hyp/klotho–/– mice. Moreover, in contrast to the Hyp mice, the Hyp/klotho–/– mice showed significantly higher serum levels of 1,25-dihydroxyvitamin D and developed extensive calcification in soft tissues and vascular walls. Furthermore, compared with the Hyp mice, Hyp/klotho–/– mice were smaller in size, showed features of generalized tissue atrophy, and generally died by 15–20 wk of age. Our in vivo studies provide genetic evidence for a pathological role of increased FGF23 activities in regulating abnormal phosphate homeostasis in Hyp mice. Moreover, these results suggest that even when serum levels of FGF23 are significantly high, in the absence of klotho, FGF23 is unable to regulate systemic phosphate homeostasis. Our in vivo observations have significant clinical implications in diseases associated with increased FGF23 activity and suggest that the functions of FGF23 can be therapeutically modulated by manipulating the effects of klotho.—Nakatani, Y., Ohnishi, M., Razzaque, M. S. Inactivation of klotho function induces hyperphosphatemia even in presence of high serum fibroblast growth factor 23 levels in a genetically engineered hypophosphatemic (Hyp) mouse model.
Key Words: parathyroid hormone • vitamin D • calcification • survival • kidney • NaPi2a
This article has been cited by other articles:
|
|
 |
|
  M. Ohnishi and M. S. Razzaque Dietary and genetic evidence for phosphate toxicity accelerating mammalian aging FASEB J, September 1, 2010; 24(9): 3562 - 3571. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. Marks, E. S. Debnam, and R. J. Unwin Phosphate homeostasis and the renal-gastrointestinal axis Am J Physiol Renal Physiol, August 1, 2010; 299(2): F285 - F296. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. Bacchetta, L. Dubourg, J. Harambat, B. Ranchin, P. Abou-Jaoude, S. Arnaud, M. C. Carlier, M. Richard, and P. Cochat The Influence of Glomerular Filtration Rate and Age on Fibroblast Growth Factor 23 Serum Levels in Pediatric Chronic Kidney Disease J. Clin. Endocrinol. Metab., April 1, 2010; 95(4): 1741 - 1748. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. Goetz, Y. Nakada, M. C. Hu, H. Kurosu, L. Wang, T. Nakatani, M. Shi, A. V. Eliseenkova, M. S. Razzaque, O. W. Moe, et al. Isolated C-terminal tail of FGF23 alleviates hypophosphatemia by inhibiting FGF23-FGFR-Klotho complex formation PNAS, January 5, 2010; 107(1): 407 - 412. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
