| We have hypothesized that vitamin D3 and the steroid hormone derived from it, 1,25-dihydroxyvitamin D3 (1,25-(OH)2D 3), may implement the protective biological effects of sunlight in multiple sclerosis (MS)-susceptible individuals because low sunlight exposure correlated with increased MS risk and sunlight catalyzes vitamin D3 synthesis. 1,25-(OH)2D3 supplementation inhibited experimental autoimmune encephalomyelitis (EAE), a MS model. Further, 1,25-(OH)2D 3 treatment reversed EAE disease. To understand the disease resolution process initiation, mice with severe EAE were treated with 1,25-(OH) 2D3 or placebo for 6 hr and spinal cord gene transcription patterns analyzed by microarray. When 1,25-(OH)2D3 was administered, several genes whose expression increased or decreased with EAE, returned to homeostatic levels while others with pro-apoptotic functions increased significantly. These results suggest that sensitization of inflammatory cells to apoptotic signals may be one mechanism by which 1,25-(OH)2D 3 resolved EAE. Next, the precursor, vitamin D3, was tested for the ability to protect mice from EAE. Vitamin D3 protected female, but not male, mice from EAE. Correlating with protection, the vitamin D3-fed, females had higher spinal cord 1,25-(OH)2D 3 and fewer spinal cord transcripts for the catabolic enzyme CYP24A1 compared to males. Ovariectomy abolished protection from EAE and reduced spinal cord 1,25-(OH)2D3 levels indicating female sex hormones influenced spinal cord vitamin D3 metabolism. If sufficient spinal cord 1,25-(OH)2D3 levels are achieved by 1,25-(OH)2D3 supplementation, both sexes are protected from EAE and we hypothesized regulatory T cells and interleukin (IL)-10, the anti-inflammatory cytokine they produce, are intrinsic to 1,25-(OH)2 D3-mediated protection from EAE. To test this hypothesis, we attempted to protect mice with a disrupted IL-10 or IL-10 receptor (IL-10R) gene from EAE with 1,25-(OH) 2D3 treatment and found neither IL-10-/- nor IL-10R-/- mice were protected. Further, 1,25-(OH)2D3 failed to inhibit EAE in irradiated B6.CD45.1 mice transplanted with B6.IL-10-/- bone marrow (BM), or B6.IL-10-/- recipients transplanted with B6.CD45.1 BM. Thus, 1,25-(OH)2D3-mediated inhibition of EAE required the IL-10-IL-10R pathway and IL-10 gene expression in both radiosensitive hematopoietic cells and radioresistant spinal cord cells. In summary, 1,25-(OH)2D3 may sensitize inflammatory cells to apoptotic signals and 1,25-(OH)2D3-mediated protection from EAE requires IL-10, while female sex hormones influence vitamin D3 metabolism in the inflamed spinal cord. |
