Effects of PHEX antisense in human osteoblast cells.

X-linked hypophosphatemia (XLH) is an X-linked dominant disorder that is characterized by rachitic bone disease and hypophosphatemia due to renal phosphate transport defect. The candidate gene for XLH, PHEX, has recently been identified and found to share high homology with endopeptidases. PHEX is expressed in various tissues, including bones, and the available evidence today indicates that bones can release abnormal humoral factors that affect bone mineralization and proximal tubule phosphate transport in XLH. It was, therefore, hypothesized that the inactivating mutations of PHEX in bone may lead to the release of humoral factors and contribute to the phenotypic expression of the disease. To test this possibility, clones of MG-63 cells, a human osteoblast cell line, were produced and stably transfected with PHEX-antisense vectors, resulting in a decrease in PHEX expression at mRNA and protein levels. It was found that these antisense-transfected cells had impaired mineralization, with a decrease in 45Ca incorporation and calcification nodule formation. It was also found that the conditioned culture media collected from these antisense-transfected cells exhibited inhibitory activities on 45Ca incorporation by the nontransfected MG-63 cells and 32P uptake by the opossum kidney proximal tubular cells. The results of the study, therefore, provide strong evidence that supports the link between PHEX mutations and the pathogenesis of XLH.