Effect of 1,25-dihydroxyvitamin D₃on regulatory T cells in ovariectomized mice

To investigate the correlation between regulatory T (Treg) cells and postmenopausal osteoporosis and the antiosteoporotic effect of 1,25-dihydroxyvitamin D3 [1,25(OH)₂D₃] in relation to Treg cells.

Fifty female BALB/c mice were randomly divided into five groups: the basal control (BAS), Sham, ovariectomy (OVX), OVX+diethylstilbestrol (OVX+DES), and OVX+1,25(OH)₂D₃. Tibias were harvested and processed with decalcification for quantitative bone histomorphometry. Femurs were stained by immunohistochemistry to detect Foxp3 protein expression. Spleens were used to detect Treg and Foxp3 gene expression by flow cytometry and quantitative RT-PCR, respectively.

In comparison with the Sham group, a significant decrease was found in the OVX group in such indices as trabecular bone volume/total tissue area (BV/TV), trabecular number (Tb.N) and trabecular thickness (Tb.Th). 1,25(OH)₂D₃and DES partly prevented the decrease in BV/TV, Tb.N, Tb.Th in OVX mice. Treg cell number, Foxp3 mRNA expression in spleen and Foxp3 protein expression in femur significantly decreased in the OVX-treated group compared with those in the sham group. 1,25(OH)2D₃and DES significantly increased Treg cell number and Foxp3 expression. Treg cells and Foxp3 gene expression were related to bone histomorphometric parameters.

The decrease in Treg cell numbers is relevant to the postmenopausal osteoporosis. The antiosteoporosis of 1,25(OH)₂D₃is related to regulatory T cells.