IFNγ-IL12 axis regulates intercellular crosstalk in metabolic dysfunction-associated steatotic liver disease.

Obesity is a major cause of metabolic dysfunction-associated steatohepatitis (MASH) and is characterized by inflammation and insulin resistance. Interferon-γ (IFNγ) is a pro-inflammatory cytokine elevated in obesity and modulating macrophage functions. Here, we show that male mice with loss of IFNγ signaling in myeloid cells (Lyz-IFNγR2-/-) are protected from diet-induced insulin resistance despite fatty liver. Obesity-mediated liver inflammation is also attenuated with reduced interleukin (IL)-12, a cytokine primarily released by macrophages, and IL-12 treatment in vivo causes insulin resistance by impairing hepatic insulin signaling. Following MASH diets, Lyz-IFNγR2-/- mice are rescued from developing liver fibrosis, which is associated with reduced fibroblast growth factor (FGF) 21 levels. These results indicate critical roles for IFNγ signaling in macrophages and their release of IL-12 in modulating obesity-mediated insulin resistance and fatty liver progression to MASH. In this work, we identify the IFNγ-IL12 axis in regulating intercellular crosstalk in the liver and as potential therapeutic targets to treat MASH.

GABA-stimulated adipose-derived stem cells suppress subcutaneous adipose inflammation in obesity.

Accumulating evidence suggests that subcutaneous and visceral adipose tissues are differentially associated with metabolic disorders. In obesity, subcutaneous adipose tissue is beneficial for metabolic homeostasis because of repressed inflammation. However, the underlying mechanism remains unclear. Here, we demonstrate that γ-aminobutyric acid (GABA) sensitivity is crucial in determining fat depot-selective adipose tissue macrophage (ATM) infiltration in obesity. In diet-induced obesity, GABA reduced monocyte migration in subcutaneous inguinal adipose tissue (IAT), but not in visceral epididymal adipose tissue (EAT). Pharmacological modulation of the GABAB receptor affected the levels of ATM infiltration and adipose tissue inflammation in IAT, but not in EAT, and GABA administration ameliorated systemic insulin resistance and enhanced insulin-dependent glucose uptake in IAT, accompanied by lower inflammatory responses. Intriguingly, compared with adipose-derived stem cells (ADSCs) from EAT, IAT-ADSCs played key roles in mediating GABA responses that repressed ATM infiltration in high-fat diet-fed mice. These data suggest that selective GABA responses in IAT contribute to fat depot-selective suppression of inflammatory responses and protection from insulin resistance in obesity.

Hyperinsulinemia drives hepatic insulin resistance in male mice with liver-specific Ceacam1 deletion independently of lipolysis.

BACKGROUND: CEACAM1 regulates insulin sensitivity by promoting insulin clearance. Accordingly, global C57BL/6J.Cc1-/- null mice display hyperinsulinemia due to impaired insulin clearance at 2 months of age, followed by insulin resistance, steatohepatitis, visceral obesity and leptin resistance at 6 months. The study aimed at investigating the primary role of hepatic CEACAM1 in insulin and lipid homeostasis independently of its metabolic effect in extra-hepatic tissues. METHODS: Liver-specific C57BL/6J.AlbCre+Cc1fl/fl mice were generated and their metabolic phenotype was characterized by comparison to that of their littermate controls at 2-9 months of age, using hyperinsulinemic-euglycemic clamp analysis and indirect calorimetry. The effect of hyperphagia on insulin resistance was assessed by pair-feeding experiments. RESULTS: Liver-specific AlbCre+Cc1fl/fl mutants exhibited impaired insulin clearance and hyperinsulinemia at 2 months, followed by hepatic insulin resistance (assessed by hyperinsulinemic-euglycemic clamp analysis) and steatohepatitis at ~ 7 months of age, at which point visceral obesity and hyperphagia developed, in parallel to hyperleptinemia and blunted hypothalamic STAT3 phosphorylation in response to an intraperitoneal injection of leptin. Hyperinsulinemia caused hypothalamic insulin resistance, followed by increased fatty acid synthase activity, which together with defective hypothalamic leptin signaling contributed to hyperphagia and reduced physical activity. Pair-feeding experiment showed that hyperphagia caused systemic insulin resistance, including blunted insulin signaling in white adipose tissue and lipolysis, at 8-9 months of age. CONCLUSION: AlbCre+Cc1fl/fl mutants provide an in vivo demonstration of the key role of impaired hepatic insulin clearance and hyperinsulinemia in the pathogenesis of secondary hepatic insulin resistance independently of lipolysis. They also reveal an important role for the liver-hypothalamic axis in the regulation of energy balance and subsequently, systemic insulin sensitivity.

Endoplasmic reticulum chaperone GRP78 regulates macrophage function and insulin resistance in diet-induced obesity.

Obesity-mediated inflammation is a major cause of insulin resistance, and macrophages play an important role in this process. The 78-kDa glucose-regulated protein (GRP78) is a major endoplasmic reticulum chaperone that modulates unfolded protein response (UPR), and mice with GRP78 heterozygosity were resistant to diet-induced obesity. Here, we show that mice with macrophage-selective ablation of GRP78 (Lyz- GRP78-/-) are protected from skeletal muscle insulin resistance without changes in obesity compared with wild-type mice after 9 wk of high-fat diet. GRP78-deficient macrophages demonstrated adapted UPR with up-regulation of activating transcription factor (ATF)-4 and M2-polarization markers. Diet-induced adipose tissue inflammation was reduced, and bone marrow-derived macrophages from Lyz- GRP78-/- mice demonstrated a selective increase in IL-6 expression. Serum IL-13 levels were elevated by >4-fold in Lyz- GRP78-/- mice, and IL-6 stimulated the myocyte expression of IL-13 and IL-13 receptor. Lastly, recombinant IL-13 acutely increased glucose metabolism in Lyz- GRP78-/- mice. Taken together, our data indicate that GRP78 deficiency activates UPR by increasing ATF-4, and promotes M2-polarization of macrophages with a selective increase in IL-6 secretion. Macrophage-derived IL-6 stimulates the myocyte expression of IL-13 and regulates muscle glucose metabolism in a paracrine manner. Thus, our findings identify a novel crosstalk between macrophages and skeletal muscle in the modulation of obesity-mediated insulin resistance.-Kim, J. H., Lee, E., Friedline, R. H., Suk, S., Jung, D. Y., Dagdeviren, S., Hu, X., Inashima, K., Noh, H. L., Kwon, J. Y., Nambu, A., Huh, J. R., Han, M. S., Davis, R. J., Lee, A. S., Lee, K. W., Kim, J. K. Endoplasmic reticulum chaperone GRP78 regulates macrophage function and insulin resistance in diet-induced obesity.

Salicornia Extract Ameliorates Salt-Induced Aggravation of Nonalcoholic Fatty Liver Disease in Obese Mice Fed a High-Fat Diet.

High-fat and high-salt intakes are among the major risks of chronic diseases including obesity, nonalcoholic fatty liver disease (NAFLD), and nonalcoholic steatohepatitis (NASH). Salicornia is a halophytic plant known to exert antioxidant, antidiabetic, and hypolipidemic effects, and Salicornia-extracted salt (SS) has been used as a salt substitute. In this study, the effects of SS and purified salt (PS) on the aggravation of NAFLD/NASH were compared. C57BL/6J male mice (8-wk-old) were fed a high-fat diet (HFD) for 6 mo and divided into 3 dietary groups, which were additionally fed HFD, HFD + SS, and HFD + PS for 13 wk. PS induced aggravation of NAFLD/NASH in HFD-fed mice. Although the actual salt intake was same between the PS and SS groups as 1% of the diet (extrapolated from the World Health Organization [WHO] guideline), SS induced less liver injury and hepatic steatosis compared to PS. The hepatic mRNA expressions of inflammatory cytokines and fibrosis marker were significantly lower in the SS group than the PS group. Oxidative stress is one of the major causes of inflammation in NAFLD/NASH. Results of the component analysis showed that the major polyphenols that exhibited antioxidant activity in the Salicornia water extract were ferulic acid, caffeic acid, and isorhamnetin. These results suggest that even the level of salt intake recommended by WHO can accelerate the progression of liver disease in obese individuals consuming HFD. It is proposed that SS can be a salt substitute for obese individuals who consume HFD.

Gingerenone A, a polyphenol present in ginger, suppresses obesity and adipose tissue inflammation in high-fat diet-fed mice.

SCOPE: Ginger exerts protective effects on obesity and its complications. Our objectives here are to identify bioactive compounds that inhibit adipogenesis and lipid accumulation in vitro, elucidate the anti-obesity effect of gingerenone A (GA) in diet-induced obesity (DIO), and investigate whether GA affects adipose tissue inflammation (ATI). METHODS AND RESULTS: Oil red O staining showed that GA had the most potent inhibitory effect on adipogenesis and lipid accumulation in 3T3-L1 cells among ginger components tested at a single concentration (40 µM). Consistent with in vitro data, GA attenuates DIO by reducing fat mass in mice. This was accompanied by a modulation of fatty acid metabolism via activation of AMP-activated protein kinase (AMPK) in vitro and in vivo. Additionally, GA suppressed ATI by inhibiting macrophage recruitment and downregulating pro-inflammatory cytokines. CONCLUSION: These results suggest that GA may be used as a potential therapeutic candidate for the treatment of obesity and its complications by suppressing adipose expansion and inflammation.