Activation of inflammation is an important mechanism in the development of nonalcoholic steatohepatitis (NASH). This study aims to delineate how mitophagy affects NLRP3 inflammasome activation in hepatic lipotoxicity. Mice were fed a high fat/calorie diet (HFCD) for 24 weeks. Primary rat hepatocytes were treated with palmitic acid (PA) for various periods of time. Mitophagy was measured by protein levels of LC3II and P62. NLRP3, caspase-1, interleukin (IL)-18, and IL-1β at mRNA and protein levels were used as indicators of inflammasome activation. Along with steatotic progression in HFCDfed mice, ratio of LC3II/β-actin was decreased concurrently with increased levels of liver P62, NLRP3, caspase-1, IL-1β, IL-18, and serum IL-1β levels in late-stage NASH. PA treatment resulted in mitochondrial oxidative stress and initiated mitophagy in primary hepatocytes. The addition of cyclosporine A did not change LC3II/Τοmm20 ratios; but P62 levels were increased after an extended duration of PA exposure, indicating a defect in autophagic activity. Along with impaired mitophagy, mRNA and protein levels of NLRP3, caspase-1, IL-18 and IL-1β were upregulated by PA treatment. Pretreatment with MCC950, N-acetyl cysteine or acetyl-L-carnitine reversed inflammasome activation and a pyroptotic cascade. Additionally, mitophagic flux was partially recovered as indicated by increases in LC3II/Tomm20 ratio, parkin, and PINK1 expression, and decreased P62 expression. The findings suggest that impaired mitophagy triggers hepatic NLRP3 inflammasome activation in a murine NASH model and primary hepatocytes. The new insights into inflammasome activation through mitophagy advance our understanding of how fatty acids elicit lipotoxicity through oxidant stress and autophagy in mitochondria.

There are varieties of murine models of nonalcoholic steatohepatitis (NASH) with different pathophysiologic characteristics. For preclinical assessment, a standardized model would allow comparisons of various pharmacotherapeutic candidates in efficacy, pharmacokinetics, pharmaco-metabolism, and adverse effects under a same system. The present study aims to characterize murine NASH models by comparing end-points of major abnormalities. NASH was induced by feeding high fructose/glucose in drinking water (HF/G), high-fat/calorie diet (HFCD), and in combination (HFCD-HF/G) in mice for 8 or 16 weeks. HF/G feeding caused a minimal fat accumulation and increase in free fatty acids (FFA). In contrast, HFCD-HF/G feeding resulted in a remarkable increase in body weight, subcutaneous and visceral adipose tissue, macrosteatosis with a nearly seven-fold increase in triglyceride and FFA content, accompanied with marked hepatocellular injury, inflammatory responses, fibrosis, and insulin resistance, and represented as typical NASH in histopathology, metabolic, and adipokine profiles in a progressive manner. Meanwhile, mice fed HFCD displayed significant steatosis, necroptosis, fibrosis, insulin resistance, metabolic, and adipokine profiles, and the extent is less than those fed HFCD-HF/G. Significant MCP-1, CCR-2, and NLRP-1/3 activation were found in mice fed HFCD and HFCD-HF/G for 16 weeks, whereas gene expression of CPT-1 and ACOX-1 was down-regulated in these two groups in comparison to the controls. Nuclear receptors, such as SREBP-1c, FXR, LXR-α, PPAR-α, and PPAR-γ, were strikingly elevated in the HFCD-HF/G group. In conclusion, feeding HFCD-HF/G resulted in a reliable NASH model in mice with remarkable necroptosis, steatosis, fibrosis, and insulin resistance as well as a disordered profile of lipid metabolism and adipokine, and HFCD caused significant NASH features in histopathology and metabolic profiles only at a late stage. Whereas HF/G feeding barely led to minimal fat accumulation, some changes at molecular levels and metabolic disturbance in mice.

Seipin deficiency is responsible for type 2 congenital generalized lipodystrophy with severe loss of adipose tissue (AT) and could lead to renal failure in humans. However, the effect of Seipin on renal function is poorly understood. Here we report that Seipin knockout (SKO) mice exhibited impaired renal function, enlarged glomerular and mesangial surface areas, renal depositions of lipid, and advanced glycation end products. Elevated glycosuria and increased electrolyte excretion were also detected. Relative renal gene expression in fatty acid oxidation and reabsorption pathways were impaired in SKO mice. Elevated glycosuria might be associated with reduced renal glucose transporter 2 levels. To improve renal function, AT transplantation or leptin administration alone was performed. Both treatments effectively ameliorated renal injury by improving all of the parameters that were measured in the kidney. The treatments also rescued insulin resistance and low plasma leptin levels in SKO mice. Our findings demonstrate for the first time that Seipin deficiency induces renal injury, which is closely related to glucolipotoxicity and impaired renal reabsorption in SKO mice, and is primarily caused by the loss of AT and especially the lack of leptin. AT transplantation and leptin administration are two effective treatments for renal injury in Seipin-deficient mice.-Liu, X.-J., Wu, X.-Y., Wang, H., Wang, S.-X., Kong, W., Zhang, L., Liu, G., Huang, W. Renal injury in Seipin-deficient lipodystrophic mice and its reversal by adipose tissue transplantation or leptin administration alone: adipose tissue-kidney crosstalk.

Seipin deficiency is responsible for type 2 congenital generalized lipodystrophy with severe loss of adipose tissue and can lead to hepatic steatosis, insulin resistance (IR), and dyslipidemia in humans. Adipose tissue secretes many adipokines that are central to the regulation of metabolism. In this study, we investigated whether transplantation of normal adipose tissue could ameliorate severe hepatic steatosis, IR, and dyslipidemia in lipoatrophic seipin knockout (SKO) mice. Normal adipose tissue from wild-type mice was transplanted into 6-wk-old SKO mice. At 4 mo after adipose tissue transplantation (AT), the transplanted fat survived with detectable blood vessels, and the reduced levels of plasma leptin, a major adipokine, were dramatically increased. Severe hepatic steatosis, IR, and dyslipidemia in SKO mice were ameliorated after AT. In addition, abnormal hepatic lipogenesis and β-oxidation gene expression in SKO mice were improved after AT. Our results suggest that AT may be an effective treatment to improve lipodystrophy-associated metabolic disorders.

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