Estrogen controls vitamin D3-mediated resistance to experimental autoimmune encephalomyelitis by controlling vitamin D3 metabolism and receptor expression.

Multiple sclerosis (MS) is an autoimmune, neurodegenerative disease with a rapidly increasing female gender bias. MS prevalence decreases with increasing sunlight exposure, supporting our hypothesis that the sunlight-dependent hormone 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) is a natural inhibitor of autoimmune T cell responses in MS. We found that vitamin D(3) inhibited experimental autoimmune encephalomyelitis (EAE) in intact female mice, but not in ovariectomized females or males. To learn whether 17beta-estradiol (E(2)) is essential for vitamin D(3)-mediated protection, ovariectomized female mice were given E(2) or placebo and evaluated for vitamin D(3)-mediated EAE resistance. Diestrus-level E(2) implants alone provided no benefit, but they restored vitamin D(3)-mediated EAE resistance in the ovariectomized females. Synergy between E(2) and vitamin D(3) occurred through vitamin D(3)-mediated enhancement of E(2) synthesis, as well as E(2)-mediated enhancement of vitamin D receptor expression in the inflamed CNS. In males, E(2) implants did not enable vitamin D(3) to inhibit EAE. The finding that vitamin D(3)-mediated protection in EAE is female-specific and E(2)-dependent suggests that declining vitamin D(3) supplies due to sun avoidance might be contributing to the rapidly increasing female gender bias in MS. Moreover, declining E(2) synthesis and vitamin D(3)-mediated protection with increasing age might be contributing to MS disease progression in older women.