Klotho protein activates the PKC pathway in the kidney and testis and suppresses 25-hydroxyvitamin D3 1α-hydroxylase gene expression

Homozygous Klotho mutant (kI(-/-)) mice exhibit a variety of phenotypes resembling human aging, including arteriosclerosis, infertility, skin atrophy, osteoporosis, and short life span. Calcium abnormality, one of the phenotypes in kI(-/-) mice, is thought to be due to the elevated gene expression of 25-hydroxyvitamin D, 1 a-hydroxylase in the kidney. We studied 25-hydroxyvitamin D-3 la-hydroxylase gene expression using a Klotho plasmid that we had previously constructed for Klotho protein production. It was found that Klotho protein medium upregulated cAMP and the PKC pathway, and suppressed 25-hydroxyvitamin D-3 1 alpha-hydroxylase in kidney cells. However, both cAMP and PKC are known to elevate 25-hydroxyvitamin D3 1 alpha-hydroxylase gene expression, therefore, another unknown calcium regulation pathway using Klotho protein medium might exist. Furthermore, we found that activation of the PKC pathway by Klotho was observed only in the kidney and testis, where the Klotho gene is expressed, although activation of the cAMP pathway was observed in any kind of cell. These data suggest that calcium regulation through 25-hydroxyvitamin D-3 1 alpha-hydroxylase by Klotho depends on non-cAMP and a non-PKC pathway and that the Klotho protein may have different signaling pathways, depending on the Klotho gene expression in different cells and organs.