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      Differential Roles of Insulin and IGF-1 Receptors in Adipose Tissue Development and Function

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          Abstract

          To determine the roles of insulin and insulin-like growth factor 1 (IGF-1) action in adipose tissue, we created mice lacking the insulin receptor (IR), IGF-1 receptor (IGF1R), or both using Cre-recombinase driven by the adiponectin promoter. Mice lacking IGF1R only (F-IGFRKO) had a ∼25% reduction in white adipose tissue (WAT) and brown adipose tissue (BAT), whereas mice lacking both IR and IGF1R (F-IR/IGFRKO) showed an almost complete absence of WAT and BAT. Interestingly, mice lacking only the IR (F-IRKO) had a 95% reduction in WAT, but a paradoxical 50% increase in BAT with accumulation of large unilocular lipid droplets. Both F-IRKO and F-IR/IGFRKO mice were unable to maintain body temperature in the cold and developed severe diabetes, ectopic lipid accumulation in liver and muscle, and pancreatic islet hyperplasia. Leptin treatment normalized blood glucose levels in both groups. Glucose levels also improved spontaneously by 1 year of age, despite sustained lipodystrophy and insulin resistance. Thus, loss of IR is sufficient to disrupt white fat formation, but not brown fat formation and/or maintenance, although it is required for normal BAT function and temperature homeostasis. IGF1R has only a modest contribution to both WAT and BAT formation and function.

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          Most cited references26

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          A novel serum protein similar to C1q, produced exclusively in adipocytes.

          We describe a novel 30-kDa secretory protein, Acrp30 (adipocyte complement-related protein of 30 kDa), that is made exclusively in adipocytes and whose mRNA is induced over 100-fold during adipocyte differentiation. Acrp30 is structurally similar to complement factor C1q and to a hibernation-specific protein isolated from the plasma of Siberian chipmunks; it forms large homo-oligomers that undergo a series of post-translational modifications. Like adipsin, secretion of Acrp30 is enhanced by insulin, and Acrp30 is an abundant serum protein. Acrp30 may be a factor that participates in the delicately balanced system of energy homeostasis involving food intake and carbohydrate and lipid catabolism. Our experiments also further corroborate the existence of an insulin-regulated secretory pathway in adipocytes.
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            Targeted disruption of the glucose transporter 4 selectively in muscle causes insulin resistance and glucose intolerance.

            The prevalence of type 2 diabetes mellitus is growing worldwide. By the year 2020, 250 million people will be afflicted. Most forms of type 2 diabetes are polygenic with complex inheritance patterns, and penetrance is strongly influenced by environmental factors. The specific genes involved are not yet known, but impaired glucose uptake in skeletal muscle is an early, genetically determined defect that is present in non-diabetic relatives of diabetic subjects. The rate-limiting step in muscle glucose use is the transmembrane transport of glucose mediated by glucose transporter (GLUT) 4 (ref. 4), which is expressed mainly in skeletal muscle, heart and adipose tissue. GLUT4 mediates glucose transport stimulated by insulin and contraction/exercise. The importance of GLUT4 and glucose uptake in muscle, however, was challenged by two recent observations. Whereas heterozygous GLUT4 knockout mice show moderate glucose intolerance, homozygous whole-body GLUT4 knockout (GLUT4-null) mice have only mild perturbations in glucose homeostasis and have growth retardation, depletion of fat stores, cardiac hypertrophy and failure, and a shortened life span. Moreover, muscle-specific inactivation of the insulin receptor results in minimal, if any, change in glucose tolerance. To determine the importance of glucose uptake into muscle for glucose homeostasis, we disrupted GLUT4 selectively in mouse muscles. A profound reduction in basal glucose transport and near-absence of stimulation by insulin or contraction resulted. These mice showed severe insulin resistance and glucose intolerance from an early age. Thus, GLUT4-mediated glucose transport in muscle is essential to the maintenance of normal glucose homeostasis.
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              Deletion of PPARgamma in adipose tissues of mice protects against high fat diet-induced obesity and insulin resistance.

              Peroxisome proliferator-activated receptor gamma (PPARgamma) plays a crucial role in adipocyte differentiation, glucose metabolism, and other physiological processes. To further explore the role of PPARgamma in adipose tissues, we used a Cre/loxP strategy to generate adipose-specific PPARgamma knockout mice. These animals exhibited marked abnormalities in the formation and function of both brown and white adipose tissues. When fed a high-fat diet, adipose-specific PPARgamma knockout mice displayed diminished weight gain despite hyperphagia, had diminished serum concentrations of both leptin and adiponectin, and did not develop glucose intolerance or insulin resistance. Characterization of in vivo glucose dynamics pointed to improved hepatic glucose metabolism as the basis for preventing high-fat diet-induced insulin resistance. Our findings further illustrate the essential role for PPARgamma in the development of adipose tissues and suggest that a compensatory induction of hepatic PPARgamma may stimulate an increase in glucose disposal by the liver.
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                Author and article information

                Journal
                Diabetes
                Diabetes
                diabetes
                diabetes
                Diabetes
                Diabetes
                American Diabetes Association
                0012-1797
                1939-327X
                August 2016
                13 May 2016
                : 65
                : 8
                : 2201-2213
                Affiliations
                [1] 1Section on Integrative Physiology and Metabolism, Joslin Diabetes Center and Department of Medicine, Harvard Medical School, Boston, MA
                [2] 2Division of Gastroenterology, Hepatology and Nutrition, Boston Children’s Hospital, Boston, MA
                [3] 3Islet Cell and Regenerative Medicine, Joslin Diabetes Center and Department of Medicine, Harvard Medical School, Boston, MA
                Author notes
                Corresponding author: C. Ronald Kahn, c.ronald.kahn@ 123456joslin.harvard.edu .

                J.B. and S.S. contributed equally to this work.

                Article
                0212
                10.2337/db16-0212
                4955980
                27207537
                11671914-3fdd-43fd-99f2-5ff21a40e0b2
                © 2016 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.
                History
                : 11 February 2016
                : 06 May 2016
                Page count
                Figures: 6, Tables: 0, Equations: 0, References: 38, Pages: 13
                Funding
                Funded by: National Institute of Diabetes and Digestive and Kidney Diseases http://dx.doi.org/10.13039/100000062
                Award ID: K08-DK-100543
                Categories
                Metabolism

                Endocrinology & Diabetes
                Endocrinology & Diabetes

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