Simon N Dankel1, Therese H Røst2, Agné Kulyté3, Zina Fandalyuk4, Thomas Skurk5, Hans Hauner6, Jørn V Sagen2, Mikael Rydén3, Peter Arner3, Gunnar Mellgren7. 1. Mohn Nutrition Research Laboratory, Department of Clinical Science, University of Bergen, N-5020 Bergen, Norway; Hormone Laboratory, Haukeland University Hospital, N-5021 Bergen, Norway. Electronic address: simon.dankel@uib.no. 2. Mohn Nutrition Research Laboratory, Department of Clinical Science, University of Bergen, N-5020 Bergen, Norway; Hormone Laboratory, Haukeland University Hospital, N-5021 Bergen, Norway. 3. Department of Medicine (H7), Karolinska Institutet, C2-94 Karolinska University Hospital, Huddinge, 141 86 Stockholm, Sweden. 4. Mohn Nutrition Research Laboratory, Department of Clinical Science, University of Bergen, N-5020 Bergen, Norway. 5. ZIEL Institute for Food and Health, Technical University of Munich, 85354 Freising, Germany; Else Kroener-Fresenius Centre for Nutritional Medicine, School of Medicine, Technical University of Munich, 80992 Munich, Germany. 6. Else Kroener-Fresenius Centre for Nutritional Medicine, School of Medicine, Technical University of Munich, 80992 Munich, Germany; German Center of Diabetes Research, Helmholtz Center, Munich, Germany. 7. Mohn Nutrition Research Laboratory, Department of Clinical Science, University of Bergen, N-5020 Bergen, Norway; Hormone Laboratory, Haukeland University Hospital, N-5021 Bergen, Norway. Electronic address: gunnar.mellgren@uib.no.
Abstract
BACKGROUND: Adipose tissue plays a crucial role in diet- and obesity-related insulin resistance, with implications for several metabolic diseases. Identification of novel target genes and mechanisms that regulate adipocyte function could lead to improved treatment strategies. RND3 (RhoE/Rho8), a Rho-related GTP-binding protein that inhibits Rho kinase (ROCK) signaling, has been linked to diverse diseases such as apoptotic cardiomyopathy, heart failure, cancer and type 2 diabetes, in part by regulating cytoskeleton dynamics and insulin-mediated glucose uptake. RESULTS: We here investigated the expression of RND3 in adipose tissue in human obesity, and discovered a role for RND3 in regulating adipocyte metabolism. In cross-sectional and prospective studies, we observed 5-fold increased adipocyte levels of RND3 mRNA in obesity, reduced levels after surgery-induced weight loss, and positive correlations of RND3 mRNA with adipocyte size and surrogate measures of insulin resistance (HOMA2-IR and circulating triglyceride/high-density lipoprotein cholesterol (TAG/HDL-C) ratio). By screening for RND3-dependent gene expression following siRNA-mediated RND3 knockdown in differentiating human adipocytes, we found downregulation of inflammatory genes and upregulation of genes related to adipocyte ipolysis and insulin signaling. Treatment of adipocytes with tumor necrosis factor alpha (TNFα), lipopolysaccharide (LPS), hypoxia or cAMP analogs increased RND3 mRNA levels 1.5-2-fold. Functional assays in primary human adipocytes confirmed that RND3 knockdown reduces cAMP- and isoproterenol-induced lipolysis, which were mimicked by treating cells with ROCK inhibitor. This effect could partly be explained by reduced protein expression of adipose triglyceride lipase (ATGL) and phosphorylated hormone-sensitive lipase (HSL). CONCLUSION: We here uncovered a novel differential expression of adipose RND3 in obesity and insulin resistance, which may at least partly depend on a causal effect of RND3 on adipocyte lipolysis.
BACKGROUND: Adipose tissue plays a crucial role in diet- and obesity-related insulin resistance, with implications for several metabolic diseases. Identification of novel target genes and mechanisms that regulate adipocyte function could lead to improved treatment strategies. RND3 (RhoE/Rho8), a Rho-related GTP-binding protein that inhibits Rho kinase (ROCK) signaling, has been linked to diverse diseases such as apoptotic cardiomyopathy, heart failure, cancer and type 2 diabetes, in part by regulating cytoskeleton dynamics and insulin-mediated glucose uptake. RESULTS: We here investigated the expression of RND3 in adipose tissue in humanobesity, and discovered a role for RND3 in regulating adipocyte metabolism. In cross-sectional and prospective studies, we observed 5-fold increased adipocyte levels of RND3 mRNA in obesity, reduced levels after surgery-induced weight loss, and positive correlations of RND3 mRNA with adipocyte size and surrogate measures of insulin resistance (HOMA2-IR and circulating triglyceride/high-density lipoprotein cholesterol (TAG/HDL-C) ratio). By screening for RND3-dependent gene expression following siRNA-mediated RND3 knockdown in differentiating human adipocytes, we found downregulation of inflammatory genes and upregulation of genes related to adipocyte ipolysis and insulin signaling. Treatment of adipocytes with tumor necrosis factor alpha (TNFα), lipopolysaccharide (LPS), hypoxia or cAMP analogs increased RND3 mRNA levels 1.5-2-fold. Functional assays in primary human adipocytes confirmed that RND3 knockdown reduces cAMP- and isoproterenol-induced lipolysis, which were mimicked by treating cells with ROCK inhibitor. This effect could partly be explained by reduced protein expression of adipose triglyceride lipase (ATGL) and phosphorylated hormone-sensitive lipase (HSL). CONCLUSION: We here uncovered a novel differential expression of adipose RND3 in obesity and insulin resistance, which may at least partly depend on a causal effect of RND3 on adipocyte lipolysis.