Osteoclastic estrogen receptor alpha mediates the osteoprotective estrogen action through Fas ligand signaling

Estrogen clearly prevents osteoporotic bone loss by attenuating bone resorption. The molecular basis of how this is accomplished, however, remains elusive. Here we report a critical role of osteoclastic ERa in mediating estrogen action on bone in females. We selectively ablated ERa in differentiated osteoclasts (ERa dOc/dOc). ERa dOc/dOc females, but not males, exhibited clear trabecular bone loss, similar to the osteoporotic bone phenotype in post-menopausal women. Recovery of bone loss by estrogen treatment of the ovariectomized ERa dOc/dOc females was ineffective in the trabecular areas of the long bones and lumbar vertebral bodies. Osteoclastic apoptosis, induced by estrogen, occurred simultaneously with up-regulation of Fas ligand (FasL) expression in intact trabecular bones of ERa +/+mice, but not in ERa dOc/dOc mice. ERa was also required for similar effects of estrogen and tamoxifen in cultured osteoclasts. These findings suggest that the osteoprotective actions of estrogen and SERMS are mediated at least in part through osteoclastic ERa in trabecular bone; and the life span of mature osteoclasts is regulated through activation of the Fas/FasL system. Keywords: Study about estrogen response of osteoclast-specific estrogen receptor alpha mice