Oncostatin M promotes lipolysis in white adipocytes

Oncostatin M (OSM) is a member of the glycoprotein 130 cytokine family that is involved in chronic inflammation and increased in adipose tissue under obesity and insulin resistance. OSM was shown to inhibit adipogenesis, suppress browning, and contribute to insulin resistance in cultured white adipocytes. In contrast, OSM may have a metabolically favourable role on adipocytes in mouse models of obesity and insulin resistance. However, a putative role of OSM in modulating lipolysis has not been investigated in detail to date. To address this, cultured white adipocytes of mouse or human origin were exposed to 10 or 100 ng/ml of OSM for various time periods. In murine 3T3-L1 cells, OSM stimulation directly activated hormone-sensitive lipase (HSL) and other players of the lipolytic machinery, and dose-dependently increased free fatty acid and glycerol release. In parallel, OSM attenuated insulin-mediated suppression of lipolysis and induced phosphorylation of serine-residues on the insulin receptor substrate-1 (IRS1) protein. Key experiments were verified in a second murine and a human adipocyte cell line. Inhibiton of extracellular signal-regulated kinase (ERK)-1/2 activation, abolished OSM-mediated HSL phosphorylation and lipolysis. In conclusion, OSM signalling directly promotes lipolysis in white adipocytes in an ERK1/2-dependent manner

MiR-107 inhibits CDK6 expression, differentiation, and lipid storage in human adipocytes

MicroRNA-107 (miR-107) plays a regulatory role in obesity and insulin resistance, but the mechanisms of its function in adipocytes have not been elucidated in detail. Here we show that overexpression of miR-107 in pre- and mature human Simpson-Golabi-Behmel syndrome (SGBS) adipocytes attenuates differentiation and lipid accumulation. Our results suggest that miR-107 controls adipocyte differentiation via CDK6 and Notch signaling. CDK6 is a validated target of miR-107 and was downregulated upon miR-107 overexpression. Notch3, a signaling receptor involved in adipocyte differentiation, has been shown to decrease upon CDK6 depletion; Here Notch3 and its target Hes1 were downregulated by miR-107 overexpression. In mature adipocytes, miR-107 induces a triglyceride storage defect by impairing glucose uptake and triglyceride synthesis. To conclude, our data suggests that miR-107 has distinct functional roles in preadipocytes and mature adipocytes; Its elevated expression at these different stages of adipocytes may on one hand dampen adipogenesis, and on the other, promote ectopic fatty acid accumulation and reduced glucose tolerance.Peer reviewe

MicroRNA-192*impairs adipocyte triglyceride storage

We investigated the expression of miR-192* (miR-192-3p) in the visceral adipose tissue (VAT) of obese subjects and its function in cultured human adipocytes. This miRNA is a 3' arm derived from the same pre-miRNA as miR-192 (miR-192-5p) implicated in type 2 diabetes, liver disease and cancers, and is predicted to target key genes in lipid metabolism. In morbidly obese subjects undergoing bariatric surgery preceded by a very low calorie diet, miR-192* in VAT correlated negatively (r = -0.387; p = 0.046) with serum triglyceride (TG) and positively with high-density lipoprotein (HDL) concentration (r = 0.396; p = 0.041). In a less obese patient cohort, the miRNA correlated negatively with the body mass index (r = -0.537; p = 0.026). To characterize the function of miR-192*, we overexpressed it in cultured adipocytes and analyzed the expression of adipogenic differentiation markers as well as cellular TG content. Reduced TG and expression of the adipocyte marker proteins aP2 (adipocyte protein 2) and perilipin 1 were observed. The function of miR-192* was further investigated by transcriptomic profiling of adipocytes expressing this miRNA, revealing impacts on key lipogenic genes. A number of the mRNA alterations were validated by qPCR. Western analysis confirmed a marked reduction of the lipogenic enzyme SCD (stearoyl coenzyme A desaturase-1), the fatty aldehyde dehydrogenase ALDH3A2 (aldehyde dehydrogenase 3 family member A2) and the high-density lipoprotein receptor SCARB1 (scavenger receptor B, type I). SCD and ALDH3A2 were demonstrated to be direct targets of miR-192*. To conclude, the present data identify miR-192* as a novel controller of adipocyte differentiation and lipid homeostasis. (C) 2016 Elsevier B.V. All rights reserved.Peer reviewe

Insulin-inducible THRSP maintains mitochondrial function and regulates sphingolipid metabolism in human adipocytes

Background Thyroid hormone responsive protein (THRSP) is a lipogenic nuclear protein that is highly expressed in murine adipose tissue, but its role in humans remains unknown. Methods We characterized the insulin regulation of THRSP in vivo in human adipose tissue biopsies and in vitro in Simpson-Golabi-Behmel syndrome (SGBS) adipocytes. To this end, we measured whole-body insulin sensitivity using the euglycemic insulin clamp technique in 36 subjects [age 40 +/- 9 years, body mass index (BMI) 27.3 +/- 5.0 kg/m(2)]. Adipose tissue biopsies were obtained at baseline and after 180 and 360 min of euglycemic hyperinsulinemia for measurement of THRSP mRNA concentrations. To identify functions affected by THRSP, we performed a transcriptomic analysis of THRSP-silenced SGBS adipocytes. Mitochondrial function was assessed by measuring mitochondrial respiration as well as oxidation and uptake of radiolabeled oleate and glucose. Lipid composition in THRSP silencing was studied by lipidomic analysis. Results We found insulin to increase THRSP mRNA expression 5- and 8-fold after 180 and 360 min of in vivo euglycemic hyperinsulinemia. This induction was impaired in insulin-resistant subjects, and THRSP expression was closely correlated with whole-body insulin sensitivity. In vitro, insulin increased both THRSP mRNA and protein concentrations in SGBS adipocytes in a phosphoinositide 3-kinase (PI3K)-dependent manner. A transcriptomic analysis of THRSP-silenced adipocytes showed alterations in mitochondrial functions and pathways of lipid metabolism, which were corroborated by significantly impaired mitochondrial respiration and fatty acid oxidation. A lipidomic analysis revealed decreased hexosylceramide concentrations, supported by the transcript concentrations of enzymes regulating sphingolipid metabolism. Conclusions THRSP is regulated by insulin both in vivo in human adipose tissue and in vitro in adipocytes, and its expression is downregulated by insulin resistance. As THRSP silencing decreases mitochondrial respiration and fatty acid oxidation, its downregulation in human adipose tissue could contribute to mitochondrial dysfunction. Furthermore, disturbed sphingolipid metabolism could add to metabolic dysfunction in obese adipose tissue.Peer reviewe

Regulation of Angiopoietin-Like Proteins (ANGPTLs) 3 and 8 by Insulin

Objective: Circulating ANGPTL8 has recently been used as a marker of insulin action. We studied expression and insulin regulation of ANGPTL8 and ANGPTL3 in vivo and in vitro. Design and Methods: Expression of ANGPTL8 and ANGPTL3 was studied in 34 paired samples of human liver and adipose tissue. Effects of insulin on 1) plasma concentrations and adipose tissue expression of ANGPTL8 and ANGPTL3 (in vivo 6-h euglycemic hyperinsulinemia; n = 18), and 2) ANGPTL8 and ANGPTL3 gene and protein expression in immortalized human hepatocytes (IHH) and adipocytes were measured. Effect of ANGPTL3 on secretion of ANGPTL8 in cells stably over-expressing ANGPTL3, -8, or both was determined. Results: ANGPTL3 was only expressed in the liver, whereas ANGPTL8 was expressed in both tissues. In vivo hyperinsulinemia significantly decreased both plasma ANGPTL8 and ANGPTL3 at 3 and 6 hours. Insulin increased ANGPTL8 expression in human adipose tissue 14- and 18-fold at 3 and 6 hours and ANGPTL8 was the most insulin-responsive transcript on microarray. Insulin also increased ANPGTL8 in cultured adipocytes and IHH but the protein mainly remained intracellular. In vitro in IHH, insulin decreased ANGPTL3 gene expression and secretion of ANGPTL3 into growth medium. Overexpression of ANGPTL8 in CHO cells did not result in its release into culture medium while abundant secretion occurred in cells co-expressing ANGPTL3 and -8. Conclusions: Insulin decreases plasma ANGPTL3 by decreasing ANGPTL3 expression in the liver. Insulin markedly increases ANGPTL8 in adipose tissue and the liver but not in plasma. These data show that measurement of plasma ANGPTL3 but not -8 reflects insulin action in target tissues.Peer reviewe

Genome-wide association identifies nine common variants associated with fasting proinsulin levels and provides new insights into the pathophysiology of type 2 diabetes.

OBJECTIVE: Proinsulin is a precursor of mature insulin and C-peptide. Higher circulating proinsulin levels are associated with impaired β-cell function, raised glucose levels, insulin resistance, and type 2 diabetes (T2D). Studies of the insulin processing pathway could provide new insights about T2D pathophysiology. RESEARCH DESIGN AND METHODS: We have conducted a meta-analysis of genome-wide association tests of ∼2.5 million genotyped or imputed single nucleotide polymorphisms (SNPs) and fasting proinsulin levels in 10,701 nondiabetic adults of European ancestry, with follow-up of 23 loci in up to 16,378 individuals, using additive genetic models adjusted for age, sex, fasting insulin, and study-specific covariates. RESULTS: Nine SNPs at eight loci were associated with proinsulin levels (P < 5 × 10(-8)). Two loci (LARP6 and SGSM2) have not been previously related to metabolic traits, one (MADD) has been associated with fasting glucose, one (PCSK1) has been implicated in obesity, and four (TCF7L2, SLC30A8, VPS13C/C2CD4A/B, and ARAP1, formerly CENTD2) increase T2D risk. The proinsulin-raising allele of ARAP1 was associated with a lower fasting glucose (P = 1.7 × 10(-4)), improved β-cell function (P = 1.1 × 10(-5)), and lower risk of T2D (odds ratio 0.88; P = 7.8 × 10(-6)). Notably, PCSK1 encodes the protein prohormone convertase 1/3, the first enzyme in the insulin processing pathway. A genotype score composed of the nine proinsulin-raising alleles was not associated with coronary disease in two large case-control datasets. CONCLUSIONS: We have identified nine genetic variants associated with fasting proinsulin. Our findings illuminate the biology underlying glucose homeostasis and T2D development in humans and argue against a direct role of proinsulin in coronary artery disease pathogenesis

Resveratrol suppresses PAI-1 gene expression in a human in vitro model of inflamed adipose tissue

Abstract Increased plasminogen activator inhibitor-1 (PAI-1) levels are associated with a number of pathophysiological complications; among them is obesity. Resveratrol was proposed to improve obesity-related health problems, but the effect of resveratrol on PAI-1 gene expression in obesity is not completely understood. In this study, we used SGBS adipocytes and a model of human adipose tissue inflammation to examine the effects of resveratrol on the production of PAI-1. Treatment of SGBS adipocytes with resveratrol reduced PAI-1 mRNA and protein in a time- and concentration-dependent manner. Further experiments showed that obesity-associated inflammatory conditions lead to the upregulation of PAI-1 gene expression which was antagonized by resveratrol. Although signaling via PI3K, Sirt1, AMPK, ROS, and Nrf2 appeared to play a significant role in the modulation of PAI-1 gene expression under noninflammatory conditions, those signaling components were not involved in mediating the resveratrol effects on PAI-1 production under inflammatory conditions. Instead, we demonstrate that the resveratrol effects on PAI-1 induction under inflammatory conditions were mediated via inhibition of the NFκB pathway. Together, resveratrol can act as NFκB inhibitor in adipocytes and thus the subsequently reduced PAI-1 expression in inflamed adipose tissue might provide a new insight towards novel treatment options of obesity

Obesity and inflammation:reduced cytokine expression due to resveratrol in a human in vitro model of inflamed adipose tissue

Abstract Obesity is associated with an inflammatory status and linked with a number of pathophysiological complications among them cardiovascular disease, type 2 diabetes mellitus, or the metabolic syndrome. Resveratrol was proposed to improve obesity-related inflammatory problems, but the effect of resveratrol on cytokine expression in obesity is not completely understood. In this study, we used an in vitro model of human adipose tissue inflammation to examine the effects of resveratrol on the production of the inflammatory cytokines interleukin 6 (IL-6), IL-8, and monocyte chemoattractant protein 1 (MCP-1). We found that resveratrol reduced IL-6, IL-8, and MCP-1 levels in a concentration-dependent manner in adipocytes under inflammatory conditions. Further experiments showed that the action of resveratrol was mainly due to its NFκB inhibitory potential. Thus, our data support the concept that resveratrol can alleviate obesity-induced up-regulation of inflammatory cytokines providing a new insight toward novel treatment options in obesity

Human adipocyte differentiation and composition of disease-relevant lipids are regulated by miR-221-3p

MicroRNA-221-3p (miR-221-3p) is associated with both metabolic diseases and cancers. However, its role in terminal adipocyte differentiation and lipid metabolism are uncharacterized. miR-221-3p or its inhibitor was transfected into differentiating or mature human adipocytes. Triglyceride (TG) content and adipogenic gene expression were monitored, global lipidome analysis was carried out, and mechanisms underlying the effects of miR-221-3p were investigated. Finally, cross-talk between miR-221-3p expressing adipocytes and MCF-7 breast carcinoma (BC) cells was studied, and miR-221-3p expression in tumor-proximal adipose biopsies from BC patients analyzed. miR-221-3p overexpression inhibited terminal differentiation of adipocytes, as judged from reduced TG storage and gene expression of the adipogenic markers SCDI , GLUT4, FAS, DGATI /2, AP2, ATGL and AdipoQ, whereas the miR-221-3p inhibitor increased TG storage. Knockdown of the predicted miR-221-3p target, 14-3-3 gamma, had similar antiadipogenic effects as miR-221-3p overexpression, indicating it as a potential mediator of mir-221-3p function. Importantly, miR-221-3p overexpression inhibited de novo lipogenesis but increased the concentrations of ceramides and sphingomyelins, while reducing diacylglycerols, concomitant with suppression of sphingomyelin phosphodiesterase, ATP citrate lyase, and acid ceramidase. miR-221-3p expression was elevated in tumor proximal adipose tissue from patients with invasive BC. Conditioned medium of miR-221-3p overexpressing adipocytes stimulated the invasion and proliferation of BC cells, while medium of the BC cells enhanced miR-221-3p expression in adipocytes. Elevated miR-221-3p impairs adipocyte lipid storage and differentiation, and modifies their ceramide, sphingomyelin, and diacylglycerol content. These alterations are relevant for metabolic diseases but may also affect cancer progression.Peer reviewe