Activation of proteinase 3 contributes to Non-alcoholic Fatty Liver Disease (NAFLD) and insulin resistance

Contains fulltext : 169891.pdf (publisher's version ) (Open Access)Activation of inflammatory pathways is known to accompany development of obesity-induced non-alcoholic fatty liver disease (NAFLD), insulin resistance and type 2 diabetes. In addition to caspase-1, the neutrophil serine proteases proteinase 3, neutrophil elastase and cathepsin G are able to process the inactive pro-inflammatory mediators IL-1beta and IL-18 to their bioactive forms, thereby regulating inflammatory responses. In the present study, we investigated whether proteinase 3 is involved in obesity-induced development of insulin resistance and NAFLD. We investigated the development of NAFLD and insulin resistance in mice deficient for neutrophil elastase/proteinase 3 and neutrophil elastase/cathepsin G and in wild-type mice treated with the neutrophil serine proteinase inhibitor human alpha-1 antitrypsin. Expression profiling of metabolically relevant tissues obtained from insulin resistant mice showed that expression of proteinase 3 was specifically upregulated in the liver, whereas neutrophil elastase, cathepsin G and caspase-1 were not. Neutrophil elastase/proteinase 3 deficient mice showed strongly reduced levels of lipids in the liver after fed a high fat diet. Moreover, these mice were resistant to high fat diet-induced weight gain, inflammation and insulin resistance. Injection of proteinase 3 exacerbated insulin resistance in caspase-1(-/-) mice, indicating that proteinase 3 acts independently of caspase-1. Treatment with alpha-1 antitrypsin during the last 10 days of a 16 week high fat diet reduced hepatic lipid content and decreased fasting glucose levels. We conclude that proteinase 3 is involved in NAFLD and insulin resistance and that inhibition of proteinase 3 may have therapeutic potential

Abnormal epigenetic changes during differentiation of human skeletal muscle stem cells from obese subjects

Contains fulltext : 169731.pdf (publisher's version ) (Open Access)BACKGROUND: Human skeletal muscle stem cells are important for muscle regeneration. However, the combined genome-wide DNA methylation and expression changes taking place during adult myogenesis have not been described in detail and novel myogenic factors may be discovered. Additionally, obesity is associated with low relative muscle mass and diminished metabolism. Epigenetic alterations taking place during myogenesis might contribute to these defects. METHODS: We used Infinium HumanMethylation450 BeadChip Kit (Illumina) and HumanHT-12 Expression BeadChip (Illumina) to analyze genome-wide DNA methylation and transcription before versus after differentiation of primary human myoblasts from 14 non-obese and 14 obese individuals. Functional follow-up experiments were performed using siRNA mediated gene silencing in primary human myoblasts and a transgenic mouse model. RESULTS: We observed genome-wide changes in DNA methylation and expression patterns during differentiation of primary human muscle stem cells (myoblasts). We identified epigenetic and transcriptional changes of myogenic transcription factors (MYOD1, MYOG, MYF5, MYF6, PAX7, MEF2A, MEF2C, and MEF2D), cell cycle regulators, metabolic enzymes and genes previously not linked to myogenesis, including IL32, metallothioneins, and pregnancy-specific beta-1-glycoproteins. Functional studies demonstrated IL-32 as a novel target that regulates human myogenesis, insulin sensitivity and ATP levels in muscle cells. Furthermore, IL32 transgenic mice had reduced insulin response and muscle weight. Remarkably, approximately 3.7 times more methylation changes (147,161 versus 39,572) were observed during differentiation of myoblasts from obese versus non-obese subjects. In accordance, DNMT1 expression increased during myogenesis only in obese subjects. Interestingly, numerous genes implicated in metabolic diseases and epigenetic regulation showed differential methylation and expression during differentiation only in obese subjects. CONCLUSIONS: Our study identifies IL-32 as a novel myogenic regulator, provides a comprehensive map of the dynamic epigenome during differentiation of human muscle stem cells and reveals abnormal epigenetic changes in obesity

IL-37 protects against obesity-induced inflammation and insulin resistance

Cytokines of the IL-1 family are important modulators of obesity-induced inflammation and the development of systemic insulin resistance. Here, we report that IL-37, a newly-described antiinflammatory member of the IL-1 family, affects obesity-induced inflammation and insulin resistance. IL-37 transgenic mice (IL-37tg) did not develop an obese phenotype in response to a high-fat diet (HFD). Unlike WT mice, IL-37tg mice exhibited reduced numbers of adipose tissue macrophages and preserved glucose tolerance and insulin sensitivity after 16 weeks of HFD. A short-term HFD intervention revealed that the IL-37-mediated improvement in glucose tolerance is independent of bodyweight. IL-37tg mice manifested a beneficial metabolic profile with higher circulating levels of the anti-inflammatory adipokine adiponectin. In vitro treatment of differentiating adipocytes with recombinant IL-37 reduced adipogenesis. The beneficial effects of recombinant IL-37 involved activation of AMPK signaling. In humans, steady-state IL-37 adipose tissue mRNA levels were positively correlated with insulin sensitivity, lower adipose tissue levels of leptin and a lower inflammatory status of the adipose tissue. These findings reveal IL-37 as an important anti-inflammatory modulator during obesity-induced inflammation and insulin resistance in both mice and humans and suggest that IL-37 is a potential target for the treatment of obesity-induced insulin resistance and type 2 diabetes

IL-37 protects against obesity-induced inflammation and insulin resistance

Cytokines of the IL-1 family are important modulators of obesity-induced inflammation and the development of systemic insulin resistance. Here, we report that IL-37, a newly-described antiinflammatory member of the IL-1 family, affects obesity-induced inflammation and insulin resistance. IL-37 transgenic mice (IL-37tg) did not develop an obese phenotype in response to a high-fat diet (HFD). Unlike WT mice, IL-37tg mice exhibited reduced numbers of adipose tissue macrophages and preserved glucose tolerance and insulin sensitivity after 16 weeks of HFD. A short-term HFD intervention revealed that the IL-37-mediated improvement in glucose tolerance is independent of bodyweight. IL-37tg mice manifested a beneficial metabolic profile with higher circulating levels of the anti-inflammatory adipokine adiponectin. In vitro treatment of differentiating adipocytes with recombinant IL-37 reduced adipogenesis. The beneficial effects of recombinant IL-37 involved activation of AMPK signaling. In humans, steady-state IL-37 adipose tissue mRNA levels were positively correlated with insulin sensitivity, lower adipose tissue levels of leptin and a lower inflammatory status of the adipose tissue. These findings reveal IL-37 as an important anti-inflammatory modulator during obesity-induced inflammation and insulin resistance in both mice and humans and suggest that IL-37 is a potential target for the treatment of obesity-induced insulin resistance and type 2 diabetes

Genetic and pharmacological inhibition of vanin-1 activity in animal models of type 2 diabetes

Vanins are enzymes that convert pantetheine to pantothenic acid (vitamin B5). Insights into the function of vanins have evolved lately, indicating vanin-1 to play a role in inflammation, oxidative stress and cell migration. Moreover, vanin-1 has recently gained attention as a novel modulator of hepatic glucose and lipid metabolism. In the present study, we investigated the role of vanin-1 in the development of hepatic steatosis and insulin resistance in animal models of obesity and diabetes. In addition, we evaluated the potency of RR6, a novel pharmacological vanin-1 inhibitor, as an anti-diabetic drug. Increased vanin activity was observed in plasma and liver of high fat diet (HFD)-induced obese mice, as well as ZDF-diabetic rats. Ablation of vanin-1 (Vnn1-/- mice) mildly improved glucose tolerance and insulin sensitivity in HFD-fed mice, but had no effects on body weight, hepatic steatosis or circulating lipid levels. Oral administration of RR6 for 8 days completely inhibited plasma vanin activity, but did not affect hepatic glucose production, insulin sensitivity or hepatic steatosis in ZDF-diabetes rats. In conclusion, absence of vanin-1 activity improves insulin sensitivity in HFD-fed animals, yet short-term inhibition of vanin activity may have limited value as an anti-diabetic strategy

TLR-3 is present in human adipocytes, but its signalling is not required for obesity- Induced inflammation in adipose tissue in vivo

Innate immunity plays a pivotal role in obesity-induced low-grade inflammation originating from adipose tissue. Key receptors of the innate immune system including Toll-like receptors- 2 and -4 (TLRs) are triggered by nutrient excess to promote inflammation. The role of other TLRs in this process is largely unknown. In addition to double-stranded viral mRNA, TLR-3 can also recognize mRNA from dying endogenous cells, a process that is frequently observed within obese adipose tissue. Here, we identified profound expression of TLR-3 in adipocytes and investigated its role during diet-induced obesity. Human adipose tissue biopsies (n=80) and an adipocyte cell-line were used to study TLR-3 expression and function. TLR-3-/- and WT animals were exposed to a high-fat diet (HFD) for 16 weeks to induce obesity. Expression of TLR-3 was significantly higher in human adipocytes compared to the non-adipocyte cells part of the adipose tissue. In vitro, TLR-3 expression was induced during differentiation of adipocytes and stimulation of the receptor led to elevated expression of pro-inflammatory cytokines. In vivo, TLR-3 deficiency did not significantly influence HFDinduced obesity, insulin sensitivity or inflammation. In humans, TLR-3 expression in adipose tissue did not correlate with BMI or insulin sensitivity (HOMA-IR). Together, our results demonstrate that TLR-3 is highly expressed in adipocytes and functionally active. However, TLR-3 appears to play a redundant role in obesity-induced inflammation and insulin resistance.</p

IL-37 expression reduces lean body mass in mice by reducing food intake

The human cytokine interleukin (IL)-37 is an anti-inflammatory member of the IL-1 family of cytokines. Transgenic expression of IL-37 in mice protects them from diet-induced obesity and associated metabolic complications including dyslipidemia, inflammation and insulin resistance. The precise mechanism of action leading to these beneficial metabolic effects is not entirely known. Therefore, we aimed to assess in detail the effect of transgenic IL-37 expression on energy balance, including food intake and energy expenditure. Feeding homozygous IL-37 transgenic mice and wild-type (WT) control mice a high-fat diet (HFD; 45% kcal palm fat) for 6 weeks showed that IL-37 reduced body weight related to a marked decrease in food intake. Subsequent mechanistic studies in mice with heterozygous IL-37 expression versus WT littermates, fed the HFD for 18 weeks, confirmed that IL-37 reduces food intake, which led to a decrease in lean body mass, but did not reduce fat mass and plasma lipid levels or alterations in energy expenditure independent of lean body mass. Taken together, this suggests that IL-37 reduces lean body mass by reducing food intake.</p

TLR-3 is present in human adipocytes, but its signalling is not required for obesity- Induced inflammation in adipose tissue in vivo

<p>Innate immunity plays a pivotal role in obesity-induced low-grade inflammation originating from adipose tissue. Key receptors of the innate immune system including Toll-like receptors- 2 and -4 (TLRs) are triggered by nutrient excess to promote inflammation. The role of other TLRs in this process is largely unknown. In addition to double-stranded viral mRNA, TLR-3 can also recognize mRNA from dying endogenous cells, a process that is frequently observed within obese adipose tissue. Here, we identified profound expression of TLR-3 in adipocytes and investigated its role during diet-induced obesity. Human adipose tissue biopsies (n=80) and an adipocyte cell-line were used to study TLR-3 expression and function. TLR-3-/- and WT animals were exposed to a high-fat diet (HFD) for 16 weeks to induce obesity. Expression of TLR-3 was significantly higher in human adipocytes compared to the non-adipocyte cells part of the adipose tissue. In vitro, TLR-3 expression was induced during differentiation of adipocytes and stimulation of the receptor led to elevated expression of pro-inflammatory cytokines. In vivo, TLR-3 deficiency did not significantly influence HFDinduced obesity, insulin sensitivity or inflammation. In humans, TLR-3 expression in adipose tissue did not correlate with BMI or insulin sensitivity (HOMA-IR). Together, our results demonstrate that TLR-3 is highly expressed in adipocytes and functionally active. However, TLR-3 appears to play a redundant role in obesity-induced inflammation and insulin resistance.</p

IL-37 expression reduces lean body mass in mice by reducing food intake

The human cytokine interleukin (IL)-37 is an anti-inflammatory member of the IL-1 family of cytokines. Transgenic expression of IL-37 in mice protects them from diet-induced obesity and associated metabolic complications including dyslipidemia, inflammation and insulin resistance. The precise mechanism of action leading to these beneficial metabolic effects is not entirely known. Therefore, we aimed to assess in detail the effect of transgenic IL-37 expression on energy balance, including food intake and energy expenditure. Feeding homozygous IL-37 transgenic mice and wild-type (WT) control mice a high-fat diet (HFD; 45% kcal palm fat) for 6 weeks showed that IL-37 reduced body weight related to a marked decrease in food intake. Subsequent mechanistic studies in mice with heterozygous IL-37 expression versus WT littermates, fed the HFD for 18 weeks, confirmed that IL-37 reduces food intake, which led to a decrease in lean body mass, but did not reduce fat mass and plasma lipid levels or alterations in energy expenditure independent of lean body mass. Taken together, this suggests that IL-37 reduces lean body mass by reducing food intake.</p

TLR-3 is functionally active in adipocytes.

<p>(a) Differentiated SGBS adipocytes were stimulated with either a TLR-3 (poly:IC 12.5μg/ml) or TLR-4 (LPS 50ng/ml) agonist. mRNA levels were measured for IL-8, MCP-1, IL-1 β, adiponectin and PPAR-γ. (b-f) SGBS adipocytes were treated with SiRNA against TLR-3 or scr SiRNA and stimulated with poly:IC. mRNA levels of (b) IL-8, (c) MCP-1, (d) IL-1β, (e) adiponectin, (f) PPAR- γ were subsequently measured. * p<0.05, ** p<0.01, *** p<0.001. Data are shown as means ± SEM.</p