Partial rescue of the Hyp phenotype by osteoblast-targeted PHEX (phosphate-regulating gene with homologies to endopeptidases on the X chromosome) expression.
Inactivating mutations and/or deletions of PHEX/Phex (phosphate-regulating gene with homologies to endopeptidases on the X chromosome) are responsible for X-linked hypophosphatemic rickets in humans and in the murine homolog Hyp. The predominant osteoblastic expression of Phex has implicated a primary metabolic osteoblast defect in the pathophysiology of this disorder. By targeting PHEX expression to osteoblasts in the Hyp genetic background, we aimed to correct the corresponding biochemical and morphological abnormalities and obtain information on their pathogenetic mechanism. When transgene Phex expression, driven by a mouse pro-alpha1(I) collagen gene promoter, was crossed into the Hyp background, it improved the defective mineralization of bone and teeth but failed to correct the hypophosphatemia and altered vitamin D metabolism associated with the disorder. Ex vivo bone marrow cultures confirmed the amelioration in the Hyp-associated matrix mineralization defect after Phex expression. These findings suggest that while the Hyp bone and teeth abnormalities partially correct after PHEX gene transfer, additional factors and/or sites of PHEX expression are likely critical for the elaboration of the appropriate molecular signals that alter renal phosphate handling and vitamin D metabolism in this disorder.
Bai
Xiuying
X
Division of Endocrinology, Department of Medicine, Lady Davis Institute for Medical Research, McGill University, 3755 Cote Sainte Catherine Road, Montréal, Quebec, Canada H3T 1E2.
Miao
Dengshun
D
Panda
Dibiyendu
D
Grady
Scott
S
McKee
Marc D
MD
Goltzman
David
D
Karaplis
Andrew C
AC
D000469:Alkaline Phosphatase / Q000032:analysis; D000818:Animals; D001854:Bone Marrow Cells / Q000378:metabolism; D002113:Calcification, Physiologic; D002118:Calcium / Q000032:analysis; D002454:Cell Differentiation; D002478:Cells, Cultured; D015870:Gene Expression; D018390:Gene Targeting; D007015:Hypophosphatemia, Familial / Q000628:therapy*; D058574:Integrin-Binding Sialoprotein; D007668:Kidney / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D010006:Osteoblasts / Q000378:metabolism*; D010012:Osteogenesis; D053402:PHEX Phosphate Regulating Neutral Endopeptidase; D010641:Phenotype; D010710:Phosphates / Q000097:blood / Q000378:metabolism; D011506:Proteins / Q000235:genetics*; D012795:Sialoglycoproteins / Q000032:analysis; D014070:Tooth / Q000737:chemistry / Q000378:metabolism; D014074:Tooth Calcification; D014162:Transfection; D014807:Vitamin D / Q000378:metabolism; D019096:Vitronectin / Q000032:analysis
C546871:IBSP protein, human; C546872:Ibsp protein, mouse; D058574:Integrin-Binding Sialoprotein; D010710:Phosphates; D011506:Proteins; D012795:Sialoglycoproteins; D019096:Vitronectin; D014807:Vitamin D; D000469:Alkaline Phosphatase; D053402:PHEX Phosphate Regulating Neutral Endopeptidase; C506232:Phex protein, mouse; D002118:Calcium