Regulation of gene expression by dietary Ca2+ in kidneys of 25-hydroxyvitamin D3-1α-hydroxylase knockout mice

Background. Pseudovitamin D deficiency rickets (PDDR) is an autosomal disease, characterized by undetectable levels of 1,25-dihydroxyvitamin D-3 (1,25(OH)(2)D-3), rickets and secondary hyperparathyroidism. Mice in which the 25-hydroxyvitamin D-3-1alpha-hydroxylase (1alpha-OHase) gene was inactivated, presented the same clinical phenotype as patients with PDDR. Methods. cDNA Microarray technology was used on kidneys of 1alpha-OHase knockout mice to study the expression profile of renal genes in this Ca2+-related disorder. Genome wide molecular events that occur during the rescue of these mice by high dietary Ca2+ intake were studied by the use of 15K cDNA microarray chips. Results. 1alpha-OHase knockout mice fed a normal Ca2+ diet developed severe hypocalcemia, rickets and died with an average life span of 12 +/- 2 weeks. Intriguingly, 1alpha-OHase(-/-) mice supplemented with an enriched Ca2+ diet were normocalcemic and not significantly different from wild-type mice. Inactivation of the 1alpha-OHase gene resulted in a significant regulation of +/- 1000 genes, whereas dietary Ca2+ supplementation of the 1alpha-OHase / mice revealed +/- 2000 controlled genes. Interestingly, 557 transcripts were regulated in both situations implicating the involvement in the dietary Ca2+-mediated rescue mechanism of the 1alpha-OHase(-/-) mice. Conspicuous regulated genes encoded for signaling molecules like the PDZ-domain containing protein channel interacting protein, FK binding protein type 4, kinases, and importantly Ca2+ transporting proteins including the Na+-Ca2+ exchanger, calbindin-D-28K and the Ca2+ sensor calmodulin. Conclusion. Dietary Ca2+ intake normalized disturbances in the Ca2+ homeostasis due to vitamin D deficiency that were accompanied by the regulation of a subset of renal genes, including well-known renal Ca2+ transport protein genes, but also genes not previously identified as playing a role in renal Ca2+ handling.