Coordinated maturational regulation of PHEX and renal phosphate transport inhibitory activity

Evidence for the pathophysiological role of PHEX in X-linked hypophosphatemia

Teresa Nesbitt, Ikuma Fujiwara, Ronald Thomas, Zhousheng Xiao, Leigh Quarles, Marc K. Drezner

Research output: Contribution to journalArticle

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Abstract

The mechanism by which inactivating mutations of PHEX (phosphate- regulating gene with homologies to endopeptidases on the X chromosome) cause X-linked hypophosphatemia remains unknown. However; recent reports suggest errant PHEX activity in osteoblasts may fail to inactivate a phosphaturic factor produced by these cells. To test this possibility, we examined coordinated maturational expression of PHEX and production of phosphate transport inhibitory activity in osteoblasts from normal and hyp-mice. We assessed the inhibitory activity in conditioned medium by examining the effects on opossum kidney cell phosphate transport and osteoblast PHEX expression by reverse transcriptase-polymerase chain reaction during a 17-day maturational period. Inhibitory activity increased as a function of osteoblast maturational stage, with no activity after 3 days and persistent activity by 6 days of culture. More significantly, equal phosphate transport inhibitory activity in conditioned medium from normal and hyp-mouse osteoblasts (control 1.90 ± 0.12, normal 1.48 ± 0.10, hyp 1.45 ± 0.04 nmol/mg of protein/minute) was observed at 6 days. However, by 10 days hyp- mouse osteoblasts exhibited greater inhibitory activity than controls, and by 17 days the difference in phosphate transport inhibition maximized (control 2.08 ± 0.09, normal 1.88 ± 0.06, hyp 1.58 ± 0.06 nmol/mg of protein/minute). Concurrently, we observed absent PHEX expression in normal osteoblasts after 3 days, limited production at 6 days, and significant production by day 10 of culture, while hyp-mouse osteoblasts exhibited limited PHEX activity secondary to an inactivating mutation. The data suggest that the presence of inactivating PHEX mutations results in the enhanced renal phosphate transport inhibitory activity exhibited by hyp-mouse osteoblasts.

Original languageEnglish (US)
Pages (from-to)2027-2035
Number of pages9
JournalJournal of Bone and Mineral Research
Volume14
Issue number12
DOIs
StatePublished - Jan 1 1999

Fingerprint

Familial Hypophosphatemic Rickets
Osteoblasts
Phosphates
Kidney
Conditioned Culture Medium
Mutation
Opossums
Endopeptidases
X Chromosome
Reverse Transcriptase Polymerase Chain Reaction
Proteins

All Science Journal Classification (ASJC) codes

  • Endocrinology, Diabetes and Metabolism
  • Orthopedics and Sports Medicine

Cite this

Coordinated maturational regulation of PHEX and renal phosphate transport inhibitory activity : Evidence for the pathophysiological role of PHEX in X-linked hypophosphatemia. / Nesbitt, Teresa; Fujiwara, Ikuma; Thomas, Ronald; Xiao, Zhousheng; Quarles, Leigh; Drezner, Marc K.

In: Journal of Bone and Mineral Research, Vol. 14, No. 12, 01.01.1999, p. 2027-2035.

Research output: Contribution to journalArticle

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