However, there are small numbers of MPCs in bone marrow (BM) of normal mice, and bone resorption decreases in mice and humans during aging23, resulting in less TGFβ1 being released from bone in aged mice, suggesting that there is another more common source(s) of TGFβ1 in BM causing osteoporosis. This evidence concerns the gene TGFB1 and osteoporosis.