Vitamin D and Sphingolipids: Role in Bone and Neural System.

1-alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3), is known to play an important physiological role on growth and differentiation in a variety of non-malignant and malignant cell types through classical actions, mediated by its specific receptor (VDR), and non-genomic actions resulting in the activation of specific signalling pathways. Due to the broad distribution of VDR in many tissues and the ability of 1,25(OH)2D3 to regulate fundamental processes, such as cell proliferation and differentiation, this steroid hormone has been suggested in the treatment of different diseases, from cancer to neurodegenerative diseases. In fact, structural 1,25(OH)2D3 analogues, with weaker collateral effects have recently entered in clinical trials. Other interesting molecules due to their pleiotropic actions are the bioactive sphingolipids (SLs), in particular ceramide (cer) and sphingosine 1-phosphate (S1P). Cells maintain a dynamic balance of these metabolites since cer and sphingoid bases mediate cell death while S1P exerts mitogenic effects and promote differentiation of several cell types including osteogenic and neural cells. The biological actions of 1,25(OH)2D3 and SLs, in particular S1P, share many common effectors, including calcium regulation, growth factor expression, inflammatory cytokines, etc. but whether they could act synergistically is still unknown and deserves further investigation.