Serum MEPE-ASARM-peptides are elevated in X-linked rickets ( HYP): implications for phosphaturia and rickets.
MEPE (Matrix Extracellular PhosphoglycoprotEin) expression is markedly elevated in X-linked-hypophosphatemic-rickets ( HYP) and tumor-induced osteomalacia (TIO). In normal individuals, circulating serum-levels of MEPE are tightly correlated with serum-phosphorus, parathyroid hormone ( PTH) and bone mineral density (BMD). Also, MEPE derived, C-terminal ASARM-peptides are candidate minhibins and/or phosphatonins. Our aims were to determine: 1. whether MEPE-ASARM-peptide(s) are abnormally elevated in HYP/hyp serum, and, 2. whether the ASARM-peptide(s) accumulate in hyp mice kidney renal-tubules. Using a specific competitive ELISA we measured a five fold increase (P=0.007) of serum ASARM-peptide(s) in human HYP patients (normal subjects 3.25 microM n=9; S.E.M.=0.51 and HYP-patients 15.74 microM, n=9; S.E.M.=3.32). A 6.23 fold increase (P=0.008) was measured in hyp male mice compared with their normal male siblings (normal-siblings, 3.73 muM, S.E.M.=0.57, n=3; and hyp-mice 23.4 microM, n=3, S.E.M.=4.01). Renal immuno-histological screening also revealed a dramatic increase of ASARM-peptides in regions anatomically consistent with the proximal convoluted tubules. This study demonstrates for the first time that markedly elevated serum levels of protease-resistant ASARM-peptide(s) occur in HYP/hyp and they accumulate in murine hyp kidneys. These peptides are thus likely responsible for the phosphaturia and defective mineralization in HYP/hyp and TIO.[1]References
- Serum MEPE-ASARM-peptides are elevated in X-linked rickets (HYP): implications for phosphaturia and rickets. Bresler, D., Bruder, J., Mohnike, K., Fraser, W.D., Rowe, P.S. J. Endocrinol. (2004) [Pubmed]
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