Abstract Mesenchymal stem cells (MSCs) and heterogeneous bone marrow stromal cells (BMSCs) are multipotent progenitors that can differentiate into osteoblasts and bone marrow adipocytes (BMAd). The role of BMAd in skeletal homeostasis is not yet fully understood, in part due to a lack of reproducible in vitro models that faithfully mimic the biology and molecular signatures of BMAds to study their behavior. Here, we report the in vitro generation of murine BMSC- and MSC-derived Osterix-expressing BMAd-like cells via a trans-differentiation model (TD-BMAd), the development of a semi-automated analysis platform for quantification of lipid-laden cells, and the use of these models to interrogate the role of the glucocorticoid receptor (GR) in bone marrow adipose tissue (BMAT) as a regulator of osteoclastic bone resorption. The TD-BMAd cells stored intracellular lipids and robustly expressed BMAd-associated genes such as Sp7/Osx, Pparg, and Adipoq. The pro-osteoclastogenic gene Tnfsf11/Rankl was comparably expressed between TD-BMAd and osteoblasts. We previously reported that female mice with adult-onset conditional knockout (CKO) of the GR in Osx-expressing cells exhibited a low cortical bone mass and high BMAT phenotype. Here we demonstrate that this phenotype was associated with an increase in the abundance of cortical bone osteoclasts in female but not male GR CKO mice, but that surprisingly, GR-deficient osteoblasts from these mice did not express higher levels of pro-osteoclastogenic Rankl. Instead, TD-BMAd from female (but not male) GR-CKO mice expressed significantly higher levels of Rankl as compared to cells from GR-WT mice, suggesting that GR-deficient BMAT may be the source of the sexually dimorphic osteoclastogenic phenotype seen in vivo. Although this methodology is not intricate in nature, this simple culture technique and subsequent quantification platform may have broader utility for further studies of BMAd biology and lipid-laden cells.
Lindsay et al. (Wed,) studied this question.