Altered TNSALP expression and phosphate regulation contribute to reduced mineralization in mice lacking androgen receptor

While androgen receptor (AR)-deficient mice developed osteopenia in endochondral bones due to the high bone turnover with increased bone resorption by osteoclasts, little is known about the mechanism of intramembranous bone loss contributed by AR in osteoblasts. Here, we discovered a dramatic decrease in the area of calcification, new bone, and the number of osteocytes in calvaria from AR-deficient mice related to a reduction in mineralization caused, in part, by the diminished activity of AR-deficient osteoblasts. Enforced AR expression in differentiated osteoblasts boosts mineralization while knockdown of AR expression prevents androgeninduced mineralization. We identified the tissue-nonspecific alkaline phosphatase (TNSALP) and several members of small integrin binding ligand N-linked glycoprotein (SIBLING) gene family as androgen target genes required for AR-mediated bone formation. We show that inorganic phosphate (P_i) levels and TNSALP activity increased in response to androgen/AR and P_i signals increase the expression and translocation of AR. The ectopic expression of TNSALP or P_i partially rescued the bone loss due to AR deficiency. Thus, androgen/AR signaling plays an essential role in bone formation by coordinating the expression of genes associated with phosphate regulation.