In humans aging and glucocorticoid treatment are associated with reduced bone

In humans aging and glucocorticoid treatment are associated with reduced bone mass and increased marrow adiposity suggesting Ezatiostat that this differentiation of osteoblasts and adipocytes may be coordinately regulated. receptor and plays a crucial role in regulating bone mass. Here we show that targeted ablation of Gs�� in early osteoblast precursors but not in differentiated osteocytes results in a dramatic increase in bone marrow adipocytes. Mutant mice have reduced numbers of mesenchymal progenitors overall with an increase in the proportion of progenitors committed to the adipocyte lineage. Furthermore cells committed to the osteoblast lineage retain adipogenic potential both in vitro and in vivo. These findings have clinical implications for developing therapeutic Ezatiostat approaches to direct the commitment of mesenchymal progenitors into the osteoblast lineage. and test. All values are expressed as mean �� standard error of the mean. Results Ablation of Gs�� early in the osteoblast lineage (Gs��OsxKO mice) in osterix (Osx)-expressing progenitors leads to profound osteoporosis with early postnatal fractures.(53) Histological analysis of Osx1-GFP::Cre;Gs��fl/fl (Gs��OsxKO) mice at 2 weeks of age revealed abundant adipocytes within the secondary ossification center; in contrast no E.coli polyclonal to Flag Tag.Posi Tag is a 45 kDa recombinant protein expressed in E.coli. It contains five different Tags as shown in the figure. It is bacterial lysate supplied in reducing SDS-PAGE loading buffer. It is intended for use as a positive control in western blot experiments. adipocytes were found in the secondary ossification center of control littermates at this age (Fig. 1and but not mRNAs. mRNA levels of and found reduced mRNA levels in BMSCs isolated from mutant mice (Fig. 2all increased with adipogenic differentiation. However with the exception of confirmed differentiation of calvarial cells into cells of the adipocyte lineage (Fig. 3mRNA levels (Fig. 3is increased (Fig. 3and (Supplemental Fig. S2and Fig. 4<0.05 ... Discussion Ezatiostat Although increased marrow adiposity is frequently found in association with reduced bone mass the clinical significance of this finding is usually unknown. In patients with anorexia nervosa recovery of healthy weight is accompanied by increased bone mass and a reduction of marrow excess fat.(78) Even less is known about the effect of osteoporosis treatments on marrow fat. In one model Ezatiostat of increased marrow excess fat in rodents induced by hypophysectomy administration of growth hormone but not PTH reversed the accumulation of adipocytes.(79) We have extended our understanding of signaling pathways regulating the commitment of mesenchymal progenitors into osteoblast and adipocyte line-ages. Ablation of Gs�� in early osteoblast progenitors leads to a dramatic increase in bone marrow adipogenesis attributable at least in part to a shift in favor of adipocyte progenitors within the bone marrow. Canonical Wnt signaling has been shown to favor osteoblast over adipocyte lineage commitment and Gs��OsxKO mice have increased expression of the canonical Wnt pathway inhibitors sclerostin and Dkk1 in the osteoblast lineage with reduced Wnt signaling.(53) Interestingly ablation of Gs�� in osteocytes Ezatiostat also increases sclerostin expression yet does not result in increased marrow fat. Therefore it is unlikely that elevated sclerostin levels alone can explain the shift in the distribution of mesenchymal progenitors found in Gs��OsxKO mice despite the inhibitory effects of sclerostin on Wnt signaling. Inhibition of Wnt signaling by sclerostin may have different effects from loss of ��-catenin the transcriptional mediator of canonical Wnt signaling. In support of a cell-autonomous role for Wnt signaling in the regulation of osteoblast versus adipocyte commitment Song and colleagues have found that ablation of ��-catenin in Osx-expressing cells also leads to increased marrow adipogenesis.(34) Although PTH potently suppresses both sclerostin and Dkk1 (71 80 81 PTH can activate ��-catenin even in the absence of Dkk1 suppression (71 82 so PTH (and Gs��) may also have actions around the Wnt pathway independent of sclerostin suppression. In addition signaling downstream of the PPR has been shown to intersect Wnt signaling at other points.(67-69) In particular PKA has been demonstrated to have direct effects on Wnt signaling for instance via phosphorylation of ��-catenin.(70 71 However we Ezatiostat found that loss of Gs�� does not affect the ability of Wnt signaling to inhibit adipogenic differentiation of osteoprogenitors. The knockdown of elevated sclerostin expression will therefore be useful.