Contrary Effects of BMP-2 and ATRA on Adipogenesis in Mouse Mesenchymal Fibroblasts

Synergistic effects of fibroblast growth factor-2 and bone morphogenetic protein-2 on bone induction

The present study investigated the synergistic effect of co-administering fibroblast growth factor-2 (FGF-2) and bone morphogenetic protein-2 (BMP-2) on osteoblastic differentiation in C2C12 cells and in rats. C2C12 murine myoblast cells represent a well-accepted in vitro model system to study the ability of BMP-2 to alter cell lineage from the myogenic to the osteogenic phenotype. The osteoblastic differentiation potency was determined by alkaline phosphatase (ALP) and Alizarin red S staining. ALP activity and calcium concentrations were colorimetrically measured. Simultaneous administration of 4 µg/ml recombinant human BMP-2 with 2 ng/ml FGF-2 markedly enhanced ALP activity (an early marker of osteogenesis) of C2C12 cells. This combination also increased extracellular signal-regulated kinase1/2 mitogen activated protein kinase signaling that is involved in the promoting effect of FGF-2 on BMP-2-induced osteoblastic differentiation in C2C12 cells. Calcium deposition (a late marker of osteogenesis) and the expression of CD34 (a marker of new vessels) were promoted optimally by simultaneous local sustained administration of FGF-2 and BMP-2 using collagen and chitosan-coated antigen-extracted porcine cancellous implants in a rat ectopic implantation model. The synergistic effects of a combination of BMP-2 and FGF-2 may have potential for bone regenerative therapeutics.

TGFβ-mediated suppression of CD248 in non-cancer cells via canonical Smad-dependent signaling pathways is uncoupled in cancer cells

Background

CD248 is a cell surface glycoprotein, highly expressed by stromal cells and fibroblasts of tumors and inflammatory lesions, but virtually undetectable in healthy adult tissues. CD248 promotes tumorigenesis, while lack of CD248 in mice confers resistance to tumor growth. Mechanisms by which CD248 is downregulated are poorly understood, hindering the development of anti-cancer therapies.

Methods

We sought to characterize the molecular mechanisms by which CD248 is downregulated by surveying its expression in different cells in response to cytokines and growth factors.

Results

Only transforming growth factor (TGFβ) suppressed CD248 protein and mRNA levels in cultured fibroblasts and vascular smooth muscle cells in a concentration- and time-dependent manner. TGFβ transcriptionally downregulated CD248 by signaling through canonical Smad2/3-dependent pathways, but not via mitogen activated protein kinases p38 or ERK1/2. Notably, cancer associated fibroblasts (CAF) and cancer cells were resistant to TGFβ mediated suppression of CD248.

Conclusions

The findings indicate that decoupling of CD248 regulation by TGFβ may contribute to its tumor-promoting properties, and underline the importance of exploring the TGFβ-CD248 signaling pathway as a potential therapeutic target for early prevention of cancer and proliferative disorders.

All-trans retinoic acid modulates bone morphogenic protein 9-induced osteogenesis and adipogenesis of preadipocytes through BMP/Smad and Wnt/β-catenin signaling pathways

It is known that excessive adipogenesis contributes to osteoporosis, suggesting that trans-differentiation of adipogenic committed preadipocytes into osteoblasts may be a potential therapeutical approach for osteoporosis. We explored whether bone morphogenic protein 9 (BMP9) could induce 3T3-L1 preadipocytes to trans-differentiate into osteoblasts. BMP9 effectively increased expression of osteogenic markers and promoted mineralization in preadipocytes. However, BMP9 also led to adipogenic differentiation of preadipocytes, as evidenced by increased lipid accumulation and up-regulation of adipogenic transcription factors. In order to regulate the switch between osetogenesis and adipogenesis, we evaluated the effect of all-trans retinoic acid (ATRA) on BMP9-induced differentiation of preadipocytes. We found that ATRA enhanced BMP9-induced osteogenic differentiation and blocked BMP9-induced adipogenic differentiation both in vitro and in vivo. Mechanistically, ATRA was shown to elevate BMP9 expression and activate BMP/Smad signaling. Additionally, BMP9 and ATRA exerted a synergistic effect on activation of Wnt/β-catenin signaling. Knockdown of β-catenin abolished the stimulatory effect of ATRA on BMP9-induced alkaline phosphatase activity and reversed the inhibitory effect of ATRA on BMP9-induced adipogenesis in preadipocytes. Furthermore, ATRA and BMP9 synergistically repressed glycogen synthase kinase 3β (GSK3β) activity and promoted Akt phosphorylation, and inhibited expression of phosphatase and tensin homologue deleted on chromosome 10 (PTEN) that antagonizes phosphatidylinositol-3-kinase (PI3K) function, suggesting that Wnt/β-catenin signaling was activated at least partly through PI3K/Akt/GSK3β pathway. Collectively, ATRA mediated BMP9-induced osteogenic or adipogenic differentiation of 3T3-L1 preadipocytes by BMP/Smad and Wnt/β-catenin signaling. The combination of BMP9 and ATRA may be explored as an effective therapeutic strategy for osteoporosis.

TGF-b superfamily cytokine MIC-1/GDF15 is a physiological appetite and body weight regulator

The TGF-b superfamily cytokine MIC-1/GDF15 circulates in all humans and when overproduced in cancer leads to anorexia/cachexia, by direct action on brain feeding centres. In these studies we have examined the role of physiologically relevant levels of MIC-1/GDF15 in the regulation of appetite, body weight and basal metabolic rate. MIC-1/GDF15 gene knockout mice (MIC-1^−/−) weighed more and had increased adiposity, which was associated with increased spontaneous food intake. Female MIC-1^−/− mice exhibited some additional alterations in reduced basal energy expenditure and physical activity, possibly owing to the associated decrease in total lean mass. Further, infusion of human recombinant MIC-1/GDF15 sufficient to raise serum levels in MIC-1^−/− mice to within the normal human range reduced body weight and food intake. Taken together, our findings suggest that MIC-1/GDF15 is involved in the physiological regulation of appetite and energy storage.

Retinoids and nuclear retinoid receptors in white and brown adipose tissues: physiopathologic aspects

Vitamin A, ingested either as retinol or β-carotene from animal- or plant-derived foods respectively, is a nutrient essential for many biological functions such as embryonic development, vision, immune response, tissue remodeling, and metabolism. Its main active metabolite is all

Tob2 inhibits peroxisome proliferator-activated receptor γ2 expression by sequestering Smads and C/EBPα during adipocyte differentiation

Adipogenesis is an important component of adipose tissue development and is critically related to obesity. A cascade of transcription factors is involved in adipogenesis, in which peroxisome proliferator-activated receptor gamma (PPARγ) and CCAAT/enhancer-binding proteins (C/EBPs) play pivotal roles. Bone morphogenetic proteins (BMPs) and Smad proteins are implicated in this cascade, although the precise regulatory mechanisms have yet to be elucidated. Here, we show that Tob2, a member of the Tob/BTG antiproliferative protein family, inhibits adipogenesis by interfering with Smad signaling. tob2 expression is downregulated in the white adipose tissue of high-fat diet-induced or genetically mutated obese mice. Consistent with this, tob2(-/-) mice exhibit increased adiposity with augmented expression of the genes encoding the type 1A BMP receptor (BMPR1A) and PPARγ2 as well as their target genes. We further show accelerated adipogenesis in primary tob2(-/-) preadipocytes. Furthermore, exogenously expressed Tob2 inhibits adipogenic differentiation of 3T3-L1 preadipocytes: the Tob2 protein suppresses PPARγ2 transcription by inhibiting BMP2-induced Smad1/5 phosphorylation through its interaction with Smad6 and by sequestering C/EBPα from the PPARγ2 promoter. Thus, Tob2 negatively regulates adipogenesis by inhibiting PPARγ2 expression.

Emerging roles for the transforming growth factor-{beta} superfamily in regulating adiposity and energy expenditure

Members of the TGF-β superfamily regulate many aspects of development, including adipogenesis. Studies in cells and animal models have characterized the effects of superfamily signaling on adipocyte development, adiposity, and energy expenditure. Although bone morphogenetic protein (BMP) 4 is generally considered a protein that promotes the differentiation of white adipocytes, BMP7 has emerged as a selective regulator of brown adipogenesis. Conversely, TGF-β and activin A inhibit adipocyte development, a process augmented in TGF-β-treated cells by Smads 6 and 7, negative regulators of canonical TGF-β signaling. Other superfamily members have mixed effects on adipogenesis depending on cell culture conditions, the timing of expression, and the cell type, and many of these effects occur by altering the expression or activities of proteins that control the adipogenic cascade, including members of the CCAAT/enhancer binding protein family and peroxisome proliferator-activated receptor-γ. BMP7, growth differentiation factor (GDF) 8, and GDF3 are versatile in their mechanisms of action, and altering their normal expression characteristics has significant effects on adiposity in vivo. In addition to their roles in adipogenesis, activins and BMP7 regulate energy expenditure by affecting the expression of genes that contribute to mitochondrial biogenesis and function. GDF8 signals through its own receptors during adipogenesis while antagonizing BMP7, an example of a ligand from one major branch of the superfamily regulating the other. With such intricate relationships that ultimately affect adiposity, TGF-β superfamily signaling holds considerable promise as a target for treating human obesity and its comorbidities.

Pre-activation of retinoid signaling facilitates neuronal differentiation of mesenchymal stem cells

Mesenchymal stem cells (MSCs) can differentiate into neurons in an appropriate cellular environment. Retinoid signaling pathway is required in neural development. However, the effect and mechanism through retinoid signaling regulates neuronal differentiation of MSCs are still poorly understood. Here, we report that all-trans-retinoic acid (ATRA) pre-induction improved neuronal differentiation of rat MSCs. We found that, when MSCs were exposed to different concentrations of ATRA (0.01-100 micromol/L) for 24 h and then cultured with modified neuronal induction medium (MNM), 1 micromol/L ATRA pre-induction significantly improved neuronal differentiation efficiency and neural-cell survival. Compared with MNM alone induced neural-like cells, ATRA/MNM induced cells expressed higher levels of Nestin, neuron specific enolase (NSE), microtubule-associated protein-2 (MAP-2), but lower levels of CD68, glial fibrillary acidic protein (GFAP), and glial cell line-derived neurotrophic factor(GDNF), also exhibited higher resting membrane potential and intracellular calcium concentration, supporting that ATRA pre-induction promotes maturation and function of derived neurons but not neuroglia cells from MSCs. Endogenous retinoid X receptors (RXR) RXRalpha and RXRgamma (and to a lesser extent, RXRbeta) were weakly expressed in MSCs. But the expression of RARalpha and RARgamma was readily detectable, whereas RARbeta was undetectable. However, at 24 h after ATRA treatment, the expression of RARbeta, not RARalpha or RARgamma, increased significantly. We further found the subnuclear redistribution of RARbeta in differentiated neurons, suggesting that RARbeta may function as a major mediator of retinoid signaling during neuronal differentiation from MSCs. ATRA treatment upregulated the expression of Vimentin and Stra13, while it downregulated the expression of Brachyury in MSCs. Thus, our results demonstrate that pre-activation of retinoid signaling by ATRA facilitates neuronal differentiation of MSCs.