A role for 1,25-dihydroxyvitamin D3 in control of bone-marrow collagen deposition?

It is suggested that 1,25-dihydroxyvitamin D3 (1,25-[OH]2D3), the active hormonal metabolite of vitamin D3, inhibits the formation of fibrous tissue (mainly collagen) in bone-marrow and also increases its degradation. 1,25-(OH)2D3 inhibits the proliferation of megakaryocytes which normally promote collagen synthesis. The hormone also directly antagonises collagen synthesis. Degradation of fibrous tissue is mediated by monocytes and macrophages, which contain collagenase, and the number and activity of these cells is increased by 1,25-(OH)2D3. Thus the various actions of this hormone contribute collectively to a reduction in collagen content; conversely a deficiency of 1,25-(OH)2D3 may allow abnormal accumulation of collagen in the marrow.