Wnts comprise a family of secreted signaling proteins that regulate diverse developmental processes. Activation of Wnt signaling by Wnt10b inhibits differentiation of preadipocytes and blocks adipose tissue development; however, the effect of Wnt10b on other mesenchymal lineages has not been defined. To explore the physiological role of Wnt signaling in bone development, we analyzed FABP4-Wnt10b mice, which express the Wnt10b transgene in marrow. Femurs from FABP4-Wnt10b mice have almost four times as much bone in the distal metaphyses and are mechanically stronger. These mice maintain elevated bone mass at least through 23 months of age. In addition, FABP4-Wnt10b mice are protected from the bone loss characteristic of estrogen deficiency. We used pharmacological and genetic approaches to demonstrate that canonical Wnt signaling stimulates osteoblastogenesis and inhibits adipogenesis of bipotential mesenchymal precursors. Wnt10b shifts cell fate toward the osteoblast lineage by induction of the osteoblastogenic transcription factors Runx2, Dlx5, and osterix and suppression of the adipogenic transcription factors C͞EBP␣ and PPAR␥. One mechanism whereby Wnt10b promotes osteoblastogenesis is suppression of PPAR␥ expression. Finally, Wnt10b؊͞؊ mice have decreased trabecular bone and serum osteocalcin, confirming that Wnt10b is an endogenous regulator of bone formation.adipogenesis ͉ development ͉ stem cells M esenchymal progenitors can differentiate into a number of cell types, including adipocytes and osteoblasts (1). One factor that regulates the reciprocal relationship between these lineages is Wnt signaling, which inhibits adipogenesis and stimulates osteoblastogenesis. Activation of Wnt signaling blocks preadipocyte differentiation by inhibiting expression of the adipogenic transcription factors C͞EBP␣ and PPAR␥ (2-5). The endogenous inhibitory Wnt signal may be initiated by Wnt10b, which is expressed in preadipocytes and stromal vascular cells but not in adipocytes (2, 3). Expression of Wnt10b from the FABP4 promoter decreases accumulation of white adipose tissue by Ϸ50% and completely blocks the development of brown fat (6, 7). Furthermore, FABP4-Wnt10b mice resist diet-induced obesity and the associated glucose intolerance.The first indication that Wnt signaling plays a critical role in bone formation came from human studies where inactivating mutations in the Wnt coreceptor LRP5 were shown to cause osteoporosis (8). These findings were supported by the observation that LRP5Ϫ͞Ϫ mice also have low bone mass (9). Furthermore, gain-of-function mutations in LRP5 that increase Wnt signaling result in higher bone density in humans and mice (10,11). Consistent with the effects of LRP5 on bone mass being mediated through canonical Wnt signaling, activation of this pathway in vitro results in the expression of alkaline phosphatase, an early osteoblast marker (12)(13)(14). Although these and other studies suggest that endogenous Wnt signaling regulates osteoblastogenesis and bone formation (15), a specific Wnt or Wnts...

Wnt is a family of secreted signaling proteins that regulate diverse developmental processes. Activation of canonical Wnt signaling by Wnt10b inhibits differentiation of preadipocytes in vitro. To determine whether Wnt signaling blocks adipogenesis in vivo, we created transgenic mice in which Wnt10b is expressed from the FABP4 promoter. Expression of Wnt10b in adipose impairs development of this tissue throughout the body, with a decline of ϳ50% in total body fat and a reduction of ϳ60% in weight of epididymal and perirenal depots. FABP4-Wnt10b mice resist accumulation of adipose tissue when fed a high fat diet. Furthermore, transgenic mice are more glucose-tolerant and insulin-sensitive than wild type mice. Expression of Wnt10b from the FABP4 promoter also blocks development of brown adipose tissue. Interscapular tissue of FABP4-Wnt10b mice has the visual appearance of white adipose tissue but expresses neither brown (e.g. uncoupling protein 1) nor white adipocyte markers. Transgenic mice are unable to maintain a core body temperature when placed in a cold environment, providing further evidence that Wnt10b inhibits development of brown adipose tissue. Although food intake is not altered in FABP4-Wnt10b mice, oxygen consumption is decreased. Thus, FABP4-Wnt10b mice on a chow diet gain more weight than controls, largely because of an increase in weight of skin. In summary, inhibition by Wnt10b of white and brown adipose tissue development results in lean mice without lipodystrophic diabetes.The program followed by preadipocytes as they differentiate into adipocytes has been well characterized (1-3). Activation of a cascade of transcription factors, including PPAR␥ 1 and members of the C/EBP family, results in global changes in gene expression that cause the loss of preadipocyte characteristics and the acquisition of the adipocyte phenotype. Whether preadipocytes remain quiescent, divide, or differentiate is influenced by both inhibitory and stimulatory factors (4). One of the endogenous factors proposed to repress adipogenesis is Wnt10b, which belongs to a large family of secreted, cysteine-rich proteins that regulate diverse cellular processes, including development. Although Wnt regulates cell fate through several signaling pathways (5, 6), activation of the canonical Wnt/␤-catenin pathway is sufficient to inhibit differentiation and apoptosis of preadipocytes (7-11). A model for the canonical signaling pathway has arisen from extensive genetic and biochemical studies. In the absence of Wnt, glycogen synthase kinase-3 phosphorylates ␤-catenin, which targets this protein for ubiquitin-mediated degradation by the proteasome. In the presence of Wnt, activation of Frizzled receptors and low density lipoprotein receptor-related protein coreceptors disrupts the complex of proteins that contain glycogen synthase kinase-3 and ␤-catenin. Hypophosphorylated ␤-catenin then accumulates in the cytosol, translocates to the nucleus, and binds to T-cell factor/lymphoid-enhancing factor transcription factors to mediate the eff...

OBJECTIVEPeripheral insulin resistance is linked to an increase in reactive oxygen species (ROS), leading in part to the production of reactive lipid aldehydes that modify the side chains of protein amino acids in a reaction termed protein carbonylation. The primary enzymatic method for lipid aldehyde detoxification is via glutathione S-transferase A4 (GSTA4) dependent glutathionylation. The objective of this study was to evaluate the expression of GSTA4 and the role(s) of protein carbonylation in adipocyte function.RESEARCH DESIGN AND METHODSGSTA4-silenced 3T3-L1 adipocytes and GSTA4-null mice were evaluated for metabolic processes, mitochondrial function, and reactive oxygen species production. GSTA4 expression in human obesity was evaluated using microarray analysis.RESULTSGSTA4 expression is selectively downregulated in adipose tissue of obese insulin-resistant C57BL/6J mice and in human obesity-linked insulin resistance. Tumor necrosis factor-α treatment of 3T3-L1 adipocytes decreased GSTA4 expression, and silencing GSTA4 mRNA in cultured adipocytes resulted in increased protein carbonylation, increased mitochondrial ROS, dysfunctional state 3 respiration, and altered glucose transport and lipolysis. Mitochondrial function in adipocytes of lean or obese GSTA4-null mice was significantly compromised compared with wild-type controls and was accompanied by an increase in superoxide anion.CONCLUSIONSThese results indicate that downregulation of GSTA4 in adipose tissue leads to increased protein carbonylation, ROS production, and mitochondrial dysfunction and may contribute to the development of insulin resistance and type 2 diabetes.