Regulation of Wnt Signaling during Adipogenesis

Abstract

We have identified Wnt10b as a potent inhibitor of adipogenesis that must be suppressed for preadipocytes to differentiate in vitro. Here, we demonstrate that a specific inhibitor of glycogen synthase kinase 3, CHIR 99021, mimics Wnt signaling in preadipocytes. CHIR 99021 stabilizes free cytosolic ␤-catenin and inhibits adipogenesis by blocking induction of CCAAT/enhancer-binding protein ␣ and peroxisome proliferatoractivated receptor ␥. Preadipocyte differentiation is inhibited when 3T3-L1 cells are exposed to CHIR 99021 for any 24 h period during the first 3 days of adipogenesis. Consistent with this time frame of inhibition, expression of Wnt10b mRNA is suppressed upon induction of differentiation, with a 50% decline by 6 h and complete inhibition by 36 h. Of the agents used to induce differentiation, exposure of 3T3-L1 cells to methyl-isobutylxanthine or cAMP is sufficient to suppress expression of Wnt10b mRNA. Inhibition of adipogenesis by Wnt10b is likely mediated by Wnt receptors, Frizzled 1, 2, and/or 5, and co-receptors low density lipoprotein receptor-related proteins 5 and 6. These receptors, like Wnt10b, are highly expressed in preadipocytes and stromal vascular cells. Finally, we demonstrate that disruption of extracellular Wnt signaling by expression of secreted Frizzled related proteins causes spontaneous adipocyte conversion.White adipose tissue is an important depot for short and long term energy storage. In addition, adipose tissue is an endocrine organ that regulates energy homeostasis through secretion of leptin, Acrp30/adiponectin, resistin, and other factors (1). The study of adipocyte biology has been greatly facilitated by development of immortalized preadipocyte lines (e.g. 3T3-L1) (2) that differentiate into adipocytes and recapitulate many of the metabolic and endocrine functions of adipocytes in vivo. Analysis of differentiation in preadipocyte lines and in animals has led to a paradigmatic model of the genetic program of adipogenesis (3-5). In response to stimulators of adipogenesis, two transcription factors, CCAAT/enhancer-binding protein ␤ (C/ EBP␤) 1 and C/EBP␦ are rapidly and transiently induced. These proteins then stimulate expression of the key adipogenic transcription factors, C/EBP␣ and peroxisome proliferator-activated receptor ␥ (PPAR␥), which together induce expression of the complement of genes necessary to create the adipocyte phenotype. Investigations of factors that regulate progression through this adipogenic program are important for our understanding of adipocyte differentiation. Differentiation of preadipocytes into adipocytes is regulated by a balance of local and endocrine factors that either stimulate or inhibit differentiation (6). Well known factors that stimulate differentiation of preadipocyte lines include glucocorticoid agonists, high concentrations of insulin to stimulate the insulinlike growth factor 1 receptor, PPAR␥ agonists, and agents that elevate cAMP (3). Factors that counter these positive stimuli include Wnt10b, tumor necrosis factor ␣ (TNF␣), ...

Biological aging alters circadian mechanisms in murine adipose tissue depots

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Small molecule-based disruption of the Axin/β-catenin protein complex regulates mesenchymal stem cell differentiation

“…Other evidence for a role of the Wnt/ β-catenin pathway in regulating mesenchymal stem cell differentiation is illustrated by the genetic deletion of the Wnt antagonist Sfrp1, which leads to a 20% reduction in body fat concomitant with increased bone mass [41]. Furthermore, treatments with pharmacological inhibitors of GSK-3β stabilize intracellular β-catenin, thereby stimulating osteoblastogenesis and blocking adipocyte differentiation [42,43]. In the present study, disruption of the interaction of Axin and β-catenin by a small molecule, rather than inhibition of GSK-3β activity, promoted mesenchymal precursors to differentiate into osteoblasts and restrained adipocyte differentiation, mimicking the activation of the Wnt/β-catenin pathway.…”

Expression of genes involved in adipogenesis and lipid metabolism in subcutaneous adipose tissue and longissimus muscle in low-marbled Pirenaica beef cattle

“…This factor has been shown to repress adipogenesis by blocking PPARG and CEPBA induction by stabilizing β-catenin, which interacts transcriptionally to activate Wnt target gene expression (Bennet et al, 2002), although the molecular mechanism by which Wnt/β-catenin signalling suppresses the expression of these two genes is poorly understood. The overexpression of WNT10B observed in the LM seems to agree with the low level of development of the IM AT as represented by the small amount of IM chemical fat and small adipocyte size.…”