Bone marrow stromal cell lines having high potential for osteoclast-supporting activity express PPARgamma1 and show high potential for differentiation into adipocytes.

Bone marrow stromal cells support osteoclast differentiation by expressing receptor activator of NF-kB ligand (RANKL). Although several bone marrow stromal cell lines have been established and characterized, the differentiation stage of the supporting cells for osteoclast differentiation remains unclear. We have established several bone marrow stromal cell lines from transgenic mice harboring the temperature-sensitive SV40 large T antigen. Some of these temperature-sensitive bone marrow stromal cell lines (TSB cell lines) support osteoclast differentiation and differentiate into osteoblasts, suggesting that osteoblast precursor cells support osteoclast differentiation. Here we show that the TSB cell lines that support osteoclast differentiation also expressed peroxisome proliferator-activated receptor gamma1 (PPARgamma1) and were able to differentiate into adipocytes. PPARgamma1 is an alternatively spliced form of PPARgamma that is responsible for the adipocyte differentiation and expressed in the adipocyte precursor cells. Immunofluorescence analysis of TSB cell lines and primary bone marrow stromal cells by use of anti-PPARgamma and anti-RANKL antibodies showed that fluorescent signals for RANKL were observed in the cells that expressed PPARgamma. Furthermore, activation of adipocyte differentiation by a PPARgamma agonist led to decreased RANKL expression. These results demonstrate that PPARgamma1-positive precursor cells for osteoblasts and adipocytes expressed RANKL and supported osteoclastogenesis.