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摘要
Vitamin D receptor (VDR)-mediated 1,25-dihydroxyvitamin D-3 (1,25(OH)(2)D-3)-dependent gene expression is compromised in the VDR null mouse. The biological consequences include: hypocalcemia, hypophosphatemia, elevated parathyroid hormone (PTH) and 1,25(OH)(2)D-3, and consequential skeletal abnormalities. CYP24A1 is a cytochrome P450 enzyme that is involved in the side chain oxidation and destruction of both 1,25(OH)(2)D-3 and 25-hydroxyvitamin D-3 (25-OH-D-3). In the current studies, we used liquid chromatography-tandem mass spectrometry technology to compare the metabolic profiles of VDR null mice fed either a normal or a calcium and phosphate-enriched rescue diet and to assess the consequence of transgenic expression of either mouse or human VDR genes in the same background. Serum 1,25(OH)(2)D-3 levels in VDR null mice on normal chow were highly elevated (> 3000 pg/mL) coincident with undetectable levels of catabolites such as 24,25-(OH)(2)D-3 and 25-OH-D-3-26,23-lactone normally observed in wild-type mice. The rescue diet corrected serum Ca-vertical bar vertical bar, PTH, and 1,25(OH)(2)D-3 values and restored basal expression of Cyp24a1 as evidenced by both renal expression of Cyp24a1 and detection of 24,25-(OH)(2)D-3 and the 25-OH-D-3-26,23-lactone. Unexpectedly, this diet also resulted in supranormal levels of 3-epi-24,25-(OH)(2)D-3 and 3-epi-25-OH-D-3-26,23-lactone. The reappearance of serum 24,25-(OH)(2)D-3 and renal Cyp24a1 expression after rescue suggests that basal levels of Cyp24a1 may be repressed by high PTH. Introduction of transgenes for either mouse or human VDR also normalized vitamin D metabolism in VDR null mice, whereas this metabolic pattern was unaffected by a transgene encoding a ligand binding-deficient mutant (L233S) human VDR. We conclude that liquid chromatography-tandem mass spectrometry-based metabolic profiling is an ideal analytical method to study mouse models with alterations in calcium/phosphate homeostasis.
- 出版日期2015-12
