Distinct roles for intrinsic osteocyte abnormalities and systemic factors in regulation of FGF23 and bone mineralization in Hyp mice

Shiguang Liu, Wen Tang, Jianping Zhou, Luke Vierthaler, Leigh Quarles

Research output: Contribution to journalArticle

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Abstract

X-linked hypophosphatemia (XLH) is characterized by hypophosphatemia and impaired mineralization caused by mutations of the PHEX endopeptidase (phosphate-regulating gene with homologies to endopeptidases on the X chromosome), which leads to the overproduction of the phosphaturic fibroblast growth factor 23 (FGF23) in osteocytes. The mechanism whereby PHEX mutations increase FGF23 expression and impair mineralization is uncertain. Either an intrinsic osteocyte abnormality or unidentified PHEX substrates could stimulate FGF23 in XLH. Similarly, impaired mineralization in XLH could result solely from hypophosphatemia or from a concomitant PHEX-dependent intrinsic osteocyte abnormality. To distinguish between these possibilities, we assessed FGF23 expression and mineralization after reciprocal bone cross-transplantations between wild-type (WT) mice and the Hyp mouse model of XLH. We found that increased FGF23 expression in Hyp bone results from a local effect of PHEX deficiency, since FGF23 was increased in Hyp osteocytes before and after explantation into WT mice but was not increased in WT osteocytes after explantation into Hyp mice. WT bone explanted into Hyp mice developed rickets and osteomalacia, but Hyp bone explanted into WT mice displayed persistent osteomalacia and abnormalities in the primary spongiosa, indicating that both phosphate and PHEX independently regulate extracellular matrix mineralization. Unexpectedly, we observed a paradoxical suppression of FGF23 in juvenile Hyp bone explanted into adult Hyp mice, indicating the presence of an age-dependent systemic inhibitor of FGF23. Thus PHEX functions in bone to coordinate bone mineralization and systemic phosphate homeostasis by directly regulating the mineralization process and producing FGF23. In addition, systemic counter-regulatory factors that attenuate the upregulation of FGF23 expression in Hyp mouse osteocytes are present in older mice.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Volume293
Issue number6
DOIs
StatePublished - Dec 1 2007

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Osteocytes
Physiologic Calcification
Familial Hypophosphatemic Rickets
Bone and Bones
Hypophosphatemia
Osteomalacia
Endopeptidases
Phosphates
fibroblast growth factor 23
Rickets
Mutation
Bone Transplantation
X Chromosome
Extracellular Matrix
Homeostasis
Up-Regulation

All Science Journal Classification (ASJC) codes

  • Endocrinology, Diabetes and Metabolism
  • Physiology
  • Physiology (medical)

Cite this

Distinct roles for intrinsic osteocyte abnormalities and systemic factors in regulation of FGF23 and bone mineralization in Hyp mice. / Liu, Shiguang; Tang, Wen; Zhou, Jianping; Vierthaler, Luke; Quarles, Leigh.

In: American Journal of Physiology - Endocrinology and Metabolism, Vol. 293, No. 6, 01.12.2007.

Research output: Contribution to journalArticle

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