Significance Of Adipose Tissue Research Articles

Roles of Transmembrane Protein 97 (TMEM97) in Adipose Tissue and Skeletal Muscle.

The combination of sarcopenia and obesity (sarcopenic obesity) is associated with the development of metabolic syndrome and cardiovascular events. The molecular pathways that develop sarcopenic obesity have studied intensively. Transmembrane protein 97 (TMEM97) is 176 amino acids conserved integral membrane protein with four transmembrane domains that is expressed in several types of cancer. Its physiological significance in adipose tissue and skeletal muscle has been unclear. We studied TMEM97-transgenic mice and mice lacking TMEM97, and our findings indicate that TMEM97 expression is regulated in adipose tissue and skeletal muscle from obesity. TMEM97 represses adipogenesis and promotes myogenesis in vitro. Fat-specific TMEM97 transgenic mice showed systemic insulin resistance. Mice overexpressing TMEM97 in skeletal muscle exhibited systemic insulin resistance. Mice lacking TMEM97 were protected against diet-induced obesity and insulin resistance. These phenotypes are associated with the effects of TMEM97 on inflammation genes in adipose tissue and skeletal muscle. Our findings indicates that there is a link between TMEM97 and chronic inflammation in obesity.

Adipose Tissue as Pain Generator in the Lower Back and Lower Extremity: Application in Musculoskeletal Medicine.

Description Adipose tissue (AT) has diverse and important functions in body insulation, mechanical protection, energy metabolism and the endocrine system. Despite its relative abundance in the human body, the clinical significance of AT in musculoskeletal (MSK) medicine, particularly its role in painful MSK conditions, is under-recognized. Pain associated with AT can be divided into intrinsic (AT as a primary pain generator), extrinsic (AT as a secondary pain generator) or mixed origin. Understanding AT as an MSK pain generator, both by mechanism and its specific role in pain generation by body region, enhances the clinical decision-making process and guides therapeutic strategies in patients with AT-related MSK disorders. This article reviews the existing literature of AT in the context of pain generation in the lower back and lower extremity to increase clinician awareness and stimulate further investigation into AT in MSK medicine.

RhoA induces expression of inflammatory cytokine in adipocytes

Rho GTPase regulates actin cytoskeleton organization and assembly in many cell types, however, its significance in adipose tissue is not well characterized. Here, we demonstrate high RhoA activity in adipose tissues of C57BL/6J mice. To determine the effect of RhoA activation on 3T3-L1 cells, stable cell lines overexpressing G14VRhoA fused to destabilizing domain of FKBP12 (DD-G14VRhoA-L1) were generated. Treatment of DD-G14VRhoA-L1 cells with Shield1 following their differentiation into adipocytes, resulted in the appearance of thick cortical actin filaments, and increased the mRNA expression levels of plasminogen activator inhibitor type-1 (PAI-1) and monocyte chemoattractant protein-1 (MCP-1). The induction of PAI-1 and MCP-1 was inhibited by treatment with a Rho-associated kinase (ROCK) inhibitor, Y-27632. In 3T3-L1 adipocytes, tumor necrosis factor-α activated RhoA and increased mRNA expression of PAI-1 and MCP-1, and their treatment with Y-27632 partially inhibited these changes. The results indicate that RhoA-ROCK pathway induces inflammatory cytokine expression in adipocytes.

Profiling adipocytokine secretion from creeping fat in Crohnʼs disease

Adipose tissue is recognized as a compartment secreting highly active molecules. Creeping fat represents a characteristic feature of Crohn's disease (CD). Proinflammatory or anti-inflammatory adipose-derived secretory products, now generally called adipocytokines, may play a role in the pathogenesis of CD. Adipose tissue specimens were obtained from creeping fat contiguous to the involved intestine of 10 patients with CD. Mesenteric adipose tissue specimens resected from 13 patients with colon cancer (CC) and from 7 patients with diverticulitis served as controls. Three fat tissue specimen per well and 6 to 8 wells per patient were incubated ex vivo for 24 h. The release of adiponectin, resistin, leptin, interleukin-6, macrophage colony-stimulating factor, monocyte chemotactic protein-1, and migration inhibitory factor was measured by ELISA. The expression of AdipoR1 and AdipoR2 receptors was investigated by real-time quantitative polymerase chain reaction in a subset of adipose tissues. The secretion of adiponectin and macrophage colony-stimulating factor, as well as leptin and migration inhibitory factor, was significantly upregulated in CD compared with CC and diverticulitis or CC only, respectively. Resistin, interleukin-6, and monocyte chemotactic protein-1 were not specifically induced in CD but were associated with unspecific inflammation. Adiponectin receptor expression was not different in CC, CD, or diverticulitis. Steroid treatment in CD patients had differential effects on the ex vivo secretion of adipocytokines. A specific secretion pattern of proinflammatory and anti-inflammatory adipocytokines indicates the significance of adipose tissue in intestinal inflammation in CD. Future investigations of this intestinal compartment may provide novel insights into the pathophysiological role of creeping fat and CD.

PYY3-36 reinforces insulin action on glucose disposal in mice fed a high-fat diet.

Peptide YY(3-36) (PYY(3-36)) is released by the gut in response to nutrient ingestion. It modulates the activities of orexigenic neuropeptide Y (NPY) neurons and anorexigenic proopiomelanocortin (POMC) neurons in the hypothalamus to inhibit food intake. Because both NPY and POMC have also been shown to impact insulin action, we wondered whether PYY(3-36) could improve insulin sensitivity. To address this question, we examined the acute effect of intravenous PYY(3-36) on glucose and free fatty acid (FFA) flux during a hyperinsulinemic-euglycemic clamp in mice maintained on a high-fat diet for 2 weeks before the experiment. We also evaluated the effects of PYY(3-36) infusion on glucose uptake in muscle and adipose tissue in this experimental context. Under basal conditions, none of the metabolic parameters were affected by PYY(3-36). Under hyperinsulinemic conditions, glucose disposal was significantly increased in PYY(3-36)-infused compared with vehicle-infused mice (103.8 +/- 10.9 vs. 76.1 +/- 11.4 micromol.min(-1).kg(-1), respectively; P = 0.001). Accordingly, glucose uptake in muscle and adipose tissue was greater in PYY(3-36)-treated animals, although the difference with controls did not reach statistical significance in adipose tissue (muscle: 2.1 +/- 0.5 vs. 1.5 +/- 0.5 micromol/g tissue, P = 0.049; adipose tissue: 0.8 +/- 0.4 vs. 0.4 +/- 0.3 micromol/g tissue, P = 0.08). In contrast, PYY(3-36) did not impact insulin action on endogenous glucose production or FFA metabolism. These data indicate that PYY(3-36) reinforces insulin action on glucose disposal in mice fed a high-fat diet, through a mechanism that is independent of food intake and body weight. In contrast, it leaves glucose production and lipid flux largely unaffected in this experimental context.

Significance of Adipose Tissue and Liver as Sites of Fatty Acid Synthesis in the Pig and the Efficiency of Utilization of Various Substrates for Lipogenesis

A combination of in vivo and in vitro techniques as well as the assay of the activity of several enzymes presumably involved in lipogenesis have been employed to study the relative importance of liver and adipose tissue in overall fatty acid synthesis in the pig. Both the in vivo and in vitro results indicate that when glucose-U-14C is used as substrate, virtually all the newly synthesized fatty acids are formed in the adipose tissue. The incorporation of acetate-1-14C into liver fatty acids was, however, much greater than that of glucose-U-14C, suggesting that, if acetate was freely available in vivo, the contribution of liver to overall lipogenesis may be appreciable. Data on the activity of citrate cleavage enzyme and of three NADPH-generating dehydrogenase enzymes in liver and adipose tissue complement the results obtained in the lipogenic studies. The hepatic capacity for the production of cytoplasmic acetyl CoA from mitochondrially derived citrate is insignificant, as is its ability to generate NADPH required in the reductive synthesis of fatty acids. Collectively the results indicate that the adipose tissue plays a major, if not a nearly exclusive role in fatty acid synthesis in the pig. Nonsaponifiable lipid synthesis in the liver requires acetate rather than glucose as a starting substrate.