WISP1 (Wnt1-inducible signaling pathway protein-1, also known as CCN4) is a member of the secreted extracellular matrix–associated proteins of the CCN family and a target gene of the Wingless-type (WNT) signaling pathway. Growing evidence links the WNT signaling pathway to the regulation of adipogenesis and low-grade inflammation in obesity. We aimed to validate WISP1 as a novel adipokine. Human adipocyte differentiation was associated with increased WISP1 expression and secretion. Stimulation of human macrophages with WISP1 led to a proinflammatory response. Circulating WISP1 and WISP1 subcutaneous adipose tissue expression were regulated by weight changes in humans and mice. WISP1 expression in visceral and subcutaneous fat tissue was associated with markers of insulin resistance and inflammation in glucose-tolerant subjects. In patients with nonalcoholic fatty liver disease, we found no correlation among disease activity score, liver fat content, and WISP1 expression. Insulin regulated WISP1 expression in adipocytes in vitro but had no acute effect on WISP1 gene expression in subcutaneous fat tissue in overweight subjects who had undergone hyperinsulinemic clamp experiments. The data suggest that WISP1 may play a role in linking obesity to inflammation and insulin resistance and could be a novel therapeutic target for obesity.

Objective: Adipose tissue-derived factors link non-alcoholic fatty liver disease (NAFLD) with obesity, which has also been reported for circulating chemerin. On the other hand, hepatic chemerin and chemokine-like receptor 1 (CMKLR1) mRNA expression has not yet been studied in an extensively characterized patient collective. Design: This study was cross-sectional and experimental in design. Methods: Liver tissue samples were harvested from 47 subjects and histologically examined according to the NAFLD activity score (NAS). The concentrations of chemerin and CMKLR1 were measured using semi-quantitative real-time PCR, and the concentration of serum chemerin was measured using ELISA. To evaluate potential effects of chemerin and CMKLR1, cultured primary human hepatocytes (PHHs) were exposed to selected metabolites known to play a role in NAFLD (insulin, glucagon, palmitoic acid, and interleukin-6 (IL6)). Results: Chemerin and CMKLR1 mRNA levels were elevated in the human liver. Their expression was correlated with the NAS (R 2 Z0.543; P!0.001 and R 2 Z0.355; PZ0.014 respectively) and was significantly elevated in patients with definite non-alcoholic steatohepatitis (NASH) (P!0.05 respectively). Linear regression analysis confirmed an independent association of liver fibrosis, steatosis, inflammation, and hepatocyte ballooning with hepatic chemerin mRNA expression (P!0.05 respectively). The expression of hepatic chemerin and CMKLR1 was correlated with the measures of obesity (P!0.05). The incubation of PHHs with IL6 significantly increased the expression of CMKLR1 mRNA (PZ0.027), while that of chemerin remained unaffected (PO0.05). None of the other metabolites showed an influence (PO0.05). Conclusion: This is the first study to show that chemerin mRNA expression is significantly elevated in the liver of NASH patients and that CMKLR1 expression is upregulated in liver inflammation, whereby IL6 could play a causal role.

Angiopoietin-like protein 8 (ANGPTL8)/betatrophin expression in visceral adipose tissue and associations with circulating fatty acid profile have not yet been investigated.Forty subjects were included in a cross-sectional study, 57 in a dietary weight reduction intervention. Circulating Angiopoietin-like protein 8/betatrophin was measured in all subjects. Liver and adipose tissue were sampled and plasma fatty acids and tissue Angiopoietin-like protein 8/betatrophin expression were evaluated in the cross-sectional study. In the intervention study oral glucose testing and liver magnetic resonance scanning at baseline and after 6 months were performed. Angiopoietin-like protein 8/betatrophin mRNA was increased in visceral compared to subcutaneous adipose tissue (p<0.001). Circulating ANGPTL8/betatrophin correlated with liver steatosis (r=0.42, p=0.047), triacylglycerols (r=0.34, p=0.046), saturated (r=0.43, p=0.022), monounsaturated (r=0.51, p=0.007), and polyunsaturated fatty acids (r=-0.53, p=0.004). In the intervention study, baseline Angiopoietin-like protein 8/betatrophin correlated with age (r=0.32, p=0.010) and triacylglycerols (r=0.30, p=0.02) and was increased with hepatic steatosis (p=0.033). Weight loss reduced liver fat by 45% and circulating Angiopoietin-like protein 8/betatrophin by 11% (288±17 vs. 258±17 pg/ml; p=0.015). Angiopoietin-like protein 8/betatrophin is related to liver steatosis, while visceral adipose tissue represents an additional site of expression in humans.

Diabetes mellitus type 2 (T2DM), insulin therapy, and hyperinsulinemia are independent risk factors of liver cancer. Recently, the use of a novel inhibitor of insulin degrading enzyme (IDE) was proposed as a new therapeutic strategy in T2DM. However, IDE inhibition might stimulate liver cell proliferation via increased intracellular insulin concentration. The aim of this study was to characterize effects of inhibition of IDE activity in HepG2 hepatoma cells and to analyze liver specific expression of IDE in subjects with T2DM. HepG2 cells were treated with 10 nM insulin for 24 h with or without inhibition of IDE activity using IDE RNAi, and cell transcriptome and proliferation rate were analyzed. Human liver samples (n = 22) were used for the gene expression profiling by microarrays. In HepG2 cells, IDE knockdown changed expression of genes involved in cell cycle and apoptosis pathways. Proliferation rate was lower in IDE knockdown cells than in controls. Microarray analysis revealed the decrease of hepatic IDE expression in subjects with T2DM accompanied by the downregulation of the p53-dependent genes FAS and CCNG2, but not by the upregulation of proliferation markers MKI67, MCM2 and PCNA. Similar results were found in the liver microarray dataset from GEO Profiles database. In conclusion, IDE expression is decreased in liver of subjects with T2DM which is accompanied by the dysregulation of p53 pathway. Prolonged use of IDE inhibitors for T2DM treatment should be carefully tested in animal studies regarding its potential effect on hepatic tumorigenesis.

The liver integrates multiple metabolic pathways to warrant systemic energy homeostasis. An excessive lipogenic flux due to chronic dietary stimulation contributes to the development of hepatic steatosis, dyslipidemia and hyperglycemia. Here we show that the oxidoreductase retinol saturase (RetSat) is involved in the development of fatty liver. Hepatic RetSat expression correlates with steatosis and serum triglycerides (TGs) in humans. Liver-specific depletion of RetSat in dietary obese mice lowers hepatic and circulating TGs and normalizes hyperglycemia. Mechanistically, RetSat depletion reduces the activity of carbohydrate response element binding protein (ChREBP), a cellular hexose-phosphate sensor and inducer of lipogenesis. Defects upon RetSat depletion are rescued by ectopic expression of ChREBP but not by its putative enzymatic product 13,14-dihydroretinol, suggesting that RetSat affects hepatic glucose sensing independent of retinol conversion. Thus, RetSat is a critical regulator of liver metabolism functioning upstream of ChREBP. Pharmacological inhibition of liver RetSat may represent a therapeutic approach for steatosis.