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Irisin is an exercise-induced myokine, suggested to exert beneficial effects on metabolism. However, the studies on the regulation of irisin secretion and the expression of its precursor FNDC5 have shown conflicting data. The discrepancies among previous correlation studies in humans are related to the heterogeneity of the study population. The fact that irisin is not only a myokine but also an adipokine leads to the further complexity of the role of irisin in metabolic regulation. In this study, we examined the regulation of FNDC5 expression and irisin in circulation in both type 1 and type 2 diabetic mice, and their potential relationships with metabolic parameters. In streptozotocin (STZ)-induced type 1 diabetic mice, high-fat diet (HFD)-induced obese mice and db/db mice, the circulating irisin as well as FNDC5 gene expression in subcutaneous fat was downregulated. Muscle FNDC5 expression was only significantly lower in STZ mice, and epididymal fat FNDC5 expression was unaltered. It is interesting to note that plasma irisin levels correlated positively with subcutaneous fat FNDC5 expression, but not epididymal fat or muscle. Moreover, both irisin levels and subcutaneous fat FNDC5 correlated negatively with markers of insulin resistance. These results suggest a regulatory role for subcutaneous fat-derived FNDC5/irisin in metabolic disease.

Mechanical insults, such as stent implantation, can induce endothelial injury, vascular inflammation, and ultimately lead to vascular neointimal hyperplasia. Resolvin E1 (RvE1), derived from the ω3 fatty acid eicosapentaenoic acid, can facilitate the resolution of inflammation in many settings. We therefore aimed to determine if there was a role for RvE1 in preventing neointimal formation after arterial injury and to understand the underlying mechanisms. Vascular inflammation and neointimal hyperplasia were induced by wire injury in the femoral arteries of mice. Administration of exogenous RvE1 and endogenously generated RvE1 via dietary supplementation with eicosapentaenoic acid and aspirin markedly reduced vascular neointima formation in this model. Mechanistically, RvE1 was found to inhibit vascular neutrophil infiltration, promote macrophage polarization toward an M2-like phenotype, suppress T-cell trafficking by reducing RANTES secretion from vascular smooth muscle cells, and inhibit vascular smooth muscle cell migration. In summary, RvE1 demonstrated a protective role against vascular inflammation and remodeling in response to mechanical injury, suggesting that it may serve as an adjuvant therapeutic agent for percutaneous coronary interventions, such as stent implantation.-Liu, G., Gong, Y., Zhang, R., Piao, L., Li, X., Liu, Q., Yan, S., Shen, Y., Guo, S., Zhu, M., Yin, H., Funk, C. D., Zhang, J., Yu, Y. Resolvin E1 attenuates injury-induced vascular neointimal formation by inhibition of inflammatory responses and vascular smooth muscle cell migration.

8-Hydroxy-2-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage, has been recently shown to exert anti-inflammatory effects through inhibition of Rac1. Inflammation in adipose tissue is a hallmark of obesity-induced insulin resistance, but the therapeutic potential of 8-OHdG in treatment of metabolic diseases has not been fully elucidated. The aim of this study was to examine the effect of exogenously administered 8-OHdG on adipose tissue and whole body metabolism. In cultured adipocytes, 8-OHdG inhibited adipogenesis and reversed TNFα-induced insulin resistance. In high-fat diet (HFD)-induced obese mice, 8-OHdG administration blunted the rise in body weight and fat mass. The decrease in adipose tissue mass by 8-OHdG was due to reduced adipocyte hypertrophy through induction of adipose triglyceride lipase and inhibition of fatty acid synthase expression. 8-OHdG also inhibited the infiltration of macrophages, resulting in amelioration of adipose tissue inflammation and adipokine dysregulation. Moreover, 8-OHdG administration ameliorated adipocyte as well as systemic insulin sensitivity. Both in vivo and in vitro results showed that 8-OHdG induces AMPK activation and reduces JNK activation in adipocytes. In conclusion, our results show that orally administered 8-OHdG protects against HFD-induced metabolic disorders by regulating adipocyte metabolism.

Non-alcoholic fatty liver disease (NAFLD) has become the most prevalent liver disease in parallel with worldwide epidemic of obesity. Reactive oxygen species (ROS) contributes to the development and progression of NAFLD. Peroxisomes play an important role in fatty acid oxidation and ROS homeostasis, and catalase is an antioxidant exclusively expressed in peroxisome. The present study examined the role of endogenous catalase in early stage of NAFLD. 8-week-old male catalase knock-out (CKO) and age-matched C57BL/6J wild type (WT) mice were fed either a normal diet (ND: 18% of total calories from fat) or a high fat diet (HFD: 60% of total calories from fat) for 2 weeks. CKO mice gained body weight faster than WT mice at early period of HFD feeding. Plasma triglyceride and ALT, fasting plasma insulin, as well as liver lipid accumulation, inflammation (F4/80 staining), and oxidative stress (8-oxo-dG staining and nitrotyrosine level) were significantly increased in CKO but not in WT mice at 2 weeks of HFD feeding. While phosphorylation of Akt (Ser473) and PGC1α mRNA expression were decreased in both CKO and WT mice at HFD feeding, GSK3β phosphorylation and Cox4-il mRNA expression in the liver were decreased only in CKO-HF mice. Taken together, the present data demonstrated that endogenous catalase exerted beneficial effects in protecting liver injury including lipid accumulation and inflammation through maintaining liver redox balance from the early stage of HFD-induced metabolic stress.

Aims: Peroxisome is a critical organelle for fatty acid oxidation (FAO) and metabolism of reactive oxygen species (ROS). Increased oxidative stress in adipose tissue contributes to the development of insulin resistance and metabolic syndrome in obesity. This study aimed to investigate the role of peroxisomal fitness in maintaining adipocyte function, which has been under-rated in the obesity research area. Results: Reduced peroxisomal gene expressions in white adipose tissue (WAT) of obese mice suggested a close correlation between peroxisomes and obesity. Peroxisomal biogenesis factor 5 siRNA increased cellular ROS and inflammatory mediators in 3T3-L1 adipocytes. On the contrary, hydrogen peroxide or tumor necrosis factor-α treatment significantly decreased biogenesis- and function-related peroxisomal proteins, suggesting a positive feedback loop of ROS/inflammation and peroxisomal dysfunction. Correspondingly, catalase (a major peroxisomal antioxidant)-knockout mice fed with high-fat diet (HFD) exhibited suppressed peroxisomal proteins along with increased oxidative stress and accelerated obesity. In response to fenofibrate (a peroxisomal proliferator) treatment, WAT of HFD-fed wild-type mice showed not only increases in peroxisomal biogenesis and FAO but also attenuated features of adipocyte dysfunction and obesity. However, these results were not observed in peroxisome proliferator-activated receptor-alpha null obese mice. Innovation: Impaired peroxisomal fitness enhanced oxidative stress and inflammation in adipocytes, which exacerbates obesity. Conclusion: Adipose tissue peroxisomal homeostasis plays an important role in attenuating the features of obesity, and it can be a potential therapeutic target of obesity.

Background and Purpose Obesity is one of the most prevalent chronic diseases worldwide, and dysregulated adipocyte function plays an important role in obesity-associated metabolic disorder. The level of plasma plasminogen activator inhibitor-1 (PAI-1) is increased in obese subjects, and PAI-1 null mice show improved insulin sensitivity when subjected to high-fat and high-sucrose diet-induced metabolic stress, suggesting that a best-in-class PAI-1 inhibitor may become a novel therapeutic agent for obesity-associated metabolic syndrome. TM5441 is a novel orally active PAI-1 inhibitor that does not cause bleeding episodes. Hence, in the present study we examined the preventive effect of TM5441 on high-fat diet (HFD)-induced adipocyte dysfunction. Experimental Approach Ten-week-old C57BL/6J mice were fed a normal diet (18% of total calories from fat) or HFD (60% of total calories from fat) for 10 weeks, and TM5441 (20 mg·kg−1 oral gavage) was administered daily with the initiation of HFD. Key Results TM5441 prevented HFD-induced body weight gain and systemic insulin resistance. TM5441 normalized HFD-induced dysregulated JNK and Akt phosphorylation, suggesting that it prevents the insulin resistance of adipocytes. TM5441 also attenuated the macrophage infiltration and increased expression of pro-inflammatory cytokines, such as inducible nitric oxide synthase, induced by the HFD. In addition, TM5441 prevented the HFD-induced down-regulation of genes involved in mitochondrial biogenesis and function, suggesting that it may prevent adipocyte inflammation and dysregulation by maintaining mitochondrial fitness. Conclusion and Implications Our data suggest that TM5441 may become a novel therapeutic agent for obesity and obesity-related metabolic disorders.

Macrophages are important components of adipose tissue inflammation, which results in metabolic diseases such as insulin resistance. Notably, obesity induces a proinflammatory phenotypic switch in adipose tissue macrophages, and oxidative stress facilitates this switch. Thus, we examined the role of endogenous catalase, a key regulator of oxidative stress, in the activity of adipose tissue macrophages in obese mice. Catalase knockout (CKO) exacerbated insulin resistance, amplified oxidative stress, and accelerated macrophage infiltration into epididymal white adipose tissue in mice on normal or high-fat diet. Interestingly, catalase deficiency also enhanced classical macrophage activation (M1) and inflammation but suppressed alternative activation (M2) regardless of diet. Similarly, pharmacological inhibition of catalase activity using 3-aminotriazole induced the same phenotypic switch and inflammatory response in RAW264.7 macrophages. Finally, the same phenotypic switch and inflammatory responses were observed in primary bone marrow-derived macrophages from CKO mice. Taken together, the data indicate that endogenous catalase regulates the polarization of adipose tissue macrophages and thereby inhibits inflammation and insulin resistance.