Molecular Biology of the Cell 2015-03-01

Up-regulation of BMP2/4 signaling increases both osteoblast-specific marker expression and bone marrow adipogenesis in Gja1Jrt/+ stromal cell cultures.

Tanya Zappitelli, Frieda Chen, Jane E Aubin

Index: Mol. Biol. Cell 26(5) , 832-42, (2015)

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Abstract

Gja1(Jrt)/+ mice carry a mutation in one allele of the gap junction protein α1 gene (Gja1), resulting in a G60S connexin 43 (Cx43) mutant protein that is dominant negative for Cx43 protein production of <50% of wild-type (WT) levels and significantly reduced gap junction formation and function in osteoblasts and other Cx43-expressing cells. Previously we reported that Gja1(Jrt)/+ mice exhibited early-onset osteopenia caused by activation of osteoclasts secondary to activation of osteoblast lineage cells, which expressed increased RANKL and produced an abnormal resorption-stimulating bone matrix high in BSP content. Gja1(Jrt)/+ mice also displayed early and progressive bone marrow atrophy, with a significant increase in bone marrow adiposity versus WT littermates but no increase in adipose tissues elsewhere in the body. BMP2/4 production and signaling were increased in Gja1(Jrt)/+ trabecular bone and osteogenic stromal cell cultures, which contributed to the up-regulated expression of osteoblast-specific markers (e.g., Bsp and Ocn) in Gja1(Jrt)/+ osteoblasts and increased Pparg2 expression in bone marrow-derived adipoprogenitors in vitro. The elevated levels of BMP2/4 signaling in G60S Cx43-containing cells resulted at least in part from elevated levels of cAMP. We conclude that up-regulation of BMP2/4 signaling in trabecular bone and/or stromal cells increases osteoblast-specific marker expression in hyperactive Gja1(Jrt)/+ osteoblasts and may also increase bone marrow adipogenesis by up-regulation of Pparg2 in the Cx43-deficient Gja1(Jrt)/+ mouse model. © 2015 Zappitelli et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).