Therapeutic effects of isosteviol sodium on non-alcoholic fatty liver disease by regulating autophagy via Sirt1/AMPK pathway

Autophagy and the unfolded protein response shape the non-alcoholic fatty liver landscape: decoding the labyrinth

The incidence of nonalcoholic fatty liver disease (NAFLD) is on the rise, mirroring a global surge in diabetes and metabolic syndrome, as its major leading causes. NAFLD represents a spectrum of liver disorders, ranging from nonalcoholic fatty liver (NAFL) to nonalcoholic steatohepatitis (NASH), which can potentially progress to cirrhosis and hepatocellular carcinoma (HCC). Mechanistically, we know the unfolded protein response (UPR) as a protective cellular mechanism, being triggered under circumstances of endoplasmic reticulum (ER) stress. The hepatic UPR is turned on in a broad spectrum of liver diseases, including NAFLD. Recent data also defines molecular mechanisms that may underlie the existing correlation between UPR activation and NAFLD. More interestingly, subsequent studies have demonstrated an additional mechanism, i.e. autophagy, to be involved in hepatic steatosis, and thus NAFLD pathogenesis, principally by regulating the insulin sensitivity, hepatocellular injury, innate immunity, fibrosis, and carcinogenesis. All these findings suggest possible mechanistic roles for autophagy in the progression of NAFLD and its complications. Both UPR and autophagy are dynamic and interconnected fluxes that act as protective responses to minimize the harmful effects of hepatic lipid accumulation, as well as the ER stress during NAFLD. The functions of UPR and autophagy in the liver, together with findings of decreased hepatic autophagy in correlation with conditions that predispose to NAFLD, such as obesity and aging, suggest that autophagy and UPR, alone or combined, may be novel therapeutic targets against the disease. In this review, we discuss the current evidence on the interplay between autophagy and the UPR in connection to the NAFLD pathogenesis.

Inspiring Tactics with the Improvement of Mitophagy and Redox Balance for the Development of Innovative Treatment against Polycystic Kidney Disease

Polycystic kidney disease (PKD) is the most common genetic form of chronic kidney disease (CKD), and it involves the development of multiple kidney cysts. Not enough medical breakthroughs have been made against PKD, a condition which features regional hypoxia and activation of the hypoxia-inducible factor (HIF) pathway. The following pathology of CKD can severely instigate kidney damage and/or renal failure. Significant evidence verifies an imperative role for mitophagy in normal kidney physiology and the pathology of CKD and/or PKD. Mitophagy serves as important component of mitochondrial quality control by removing impaired/dysfunctional mitochondria from the cell to warrant redox homeostasis and sustain cell viability. Interestingly, treatment with the peroxisome proliferator-activated receptor-α (PPAR-α) agonist could reduce the pathology of PDK and might improve the renal function of the disease via the modulation of mitophagy, as well as the condition of gut microbiome. Suitable modulation of mitophagy might be a favorable tactic for the prevention and/or treatment of kidney diseases such as PKD and CKD.

High-fat diet induces cognitive impairment through repression of SIRT1/AMPK-mediated autophagy

AIMS

Recent evidence suggests an association between a high-fat diet (HFD) and cognitive decline. HFD may reduce synaptic plasticity and cause tau hyperphosphorylation, but the mechanisms involved remain unclear. The purpose of this study was to explore whether Sirtuin1 (SIRT1)/AMP-activated protein kinase (AMPK) pathway was involved in this pathogenic effect in the HFD exposed mice.

METHODS

C57BL/6 mice at 12 months of age were fed a standard (9% kcal fat) or high-fat (60% kcal fat) diet for 22 weeks, and Neuro-2a (N2a) cells were treated with normal culture medium or a palmitic acid (PA) medium (100uM) for 40 h. After that, cognitive function was tested by Morris water maze (MWM). The levels of proteins involved in SIRT1/AMPK pathway and autophagy were measured using western blotting and immunofluorescence. We also assessed the phosphorylation of tau protein and synapse.

RESULTS

The mice presented impaired learning and memory abilities. We further found decreased levels of synaptophysin (Syn) and brain-derived neurotrophic factor (BDNF), increased tau46 and phosphorylated tau protein, and damaged neurons in mice after HFD or in N2a cells treated with PA medium. Moreover, HFD can also reduce the expression of SIRT1, inhibit AMPK phosphorylation, and block autophagic flow in both mice and cells. After treating the cells with the SIRT1 agonist SRT1720, SIRT1/AMPK pathway and autophagy-related proteins were partially reversed and the number of PA-induced positive cells was alleviated in senescence-associated β-galactosidase (SA-β-gal) staining.

CONCLUSIONS

HFD may inhibit the expression of SIRT1/AMPK pathway and disrupt autophagy flux, and result in tau hyperphosphorylation and synaptic dysfunction during aging, which ultimately lead to cognitive decline.

Current Advances in the Regulatory Effects of Bioactive Compounds from Dietary Resources on Nonalcoholic Fatty Liver Disease: Role of Autophagy

Nonalcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease characterized by lipid metabolic disorder primarily due to sedentary lifestyles and excessive food consumption. However, there are currently no approved and effective drugs available to treat NAFLD. In recent years, research has shown that dietary bioactive compounds, such as polysaccharides, polyphenols, flavones, and alkaloids, have the potential to improve NAFLD by regulating autophagy. However, there is no up-to-date review of research progress in this field. This review aims to systematically summarize and discuss the regulatory effects and molecular mechanisms of dietary bioactive compounds on NAFLD through the modulation of autophagy. The existing research has demonstrated that some dietary bioactive compounds can effectively improve various aspects of NAFLD progression, such as lipid metabolism, insulin resistance (IR), endoplasmic reticulum (ER) stress, oxidative stress, mitochondrial homeostasis, and inflammation. Molecular mechanism studies have revealed that they exert their beneficial effects on NAFLD through autophagy-mediated signaling pathways, predominantly involving transcription factor EB (TFEB), mammalian target of rapamycin (mTOR), adenosine monophosphate-activated protein kinase (AMPK), peroxisome proliferator-activated receptors (PPARs), SIRT, and PTEN-induced kinase 1 (PINK1)/parkin. Furthermore, the challenges and prospects of current research in this field are highlighted. Overall, this review provides valuable insights into the potential treatment of NAFLD using dietary bioactive compounds that can modulate autophagy.

Circ_0004535/miR-1827/CASP8 network involved in type 2 diabetes mellitus with nonalcoholic fatty liver disease

Diagnostic delay in type 2 diabetes mellitus (T2DM) with nonalcoholic fatty liver disease (NAFLD) patients often leads to a serious public health problem. Understanding the pathophysiological mechanisms of disease will help develop more effective treatments. High-throughput sequencing was used to determine the expression levels of circRNAs, and mRNAs in health controls, T2DM patients, and T2DM with NAFLD patients. Differentially expressed genes (DEcircRs, DEmRs) in T2DM with NAFLD were identified by differential analysis. The miRNAs with targeted relationship with the DEcircRs and DEmRs were respectively predicted to construct a ceRNA regulatory network. In addition, enrichment analysis of DEmRs in the ceRNA network was performed. The expression of important DEcircRs was further validated by quantitative real-time PCR (qRT-PCR). The steatosis was detected in glucose treated LO2 cells by overexpressing circ_0004535, and CASP8. There were 586 DEmRs, and 10 DEcircRs in both T2DM and T2DM with NAFLD patients. Combined with predicted results and differential analysis, the ceRNA networks were constructed. The DEmRs in the ceRNA networks were mainly enriched in Toll-like receptor signaling pathway, and apoptosis. Importantly, dual luciferase experiments validated the targeted binding of hsa_circ_0004535 and hsa-miR-1827 or hsa-miR-1827 and CASP8. qRT-PCR experiments validated that hsa_circ_0004535, and CASP8 was downregulated and hsa-miR-1827 was upregulated expression in peripheral blood of T2DM with NAFLD patients. Abnormal cell morphology, and increased lipid droplet fusion were observed in the glucose treated LO2 cells, overexpression of circ_0004535 and CASP8 ameliorated these changes. Our work provides a deeper understanding of ceRNA mediated pathogenesis of T2DM with NAFLD and provides a novel strategy for treatment.

Molecular mechanisms of metabolic disease-associated hepatic inflammation in non-alcoholic fatty liver disease and non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is the leading chronic liver disease worldwide, with a progressive form of non-alcoholic steatohepatitis (NASH). It may progress to advanced liver diseases, including liver fibrosis, cirrhosis, and hepatocellular carcinoma. NAFLD/NASH is a comorbidity of many metabolic disorders such as obesity, insulin resistance, type 2 diabetes, cardiovascular disease, and chronic kidney disease. These metabolic diseases are often accompanied by systemic or extrahepatic inflammation, which plays an important role in the pathogenesis and treatment of NAFLD or NASH. Metabolites, such as short-chain fatty acids, impact the function, inflammation, and death of hepatocytes, the primary parenchymal cells in the liver tissue. Cholangiocytes, the epithelial cells that line the bile ducts, can differentiate into proliferative hepatocytes in chronic liver injury. In addition, hepatic non-parenchymal cells, including liver sinusoidal endothelial cells, hepatic stellate cells, and innate and adaptive immune cells, are involved in liver inflammation. Proteins such as fibroblast growth factors, acetyl-coenzyme A carboxylases, and nuclear factor erythroid 2-related factor 2 are involved in liver metabolism and inflammation, which are potential targets for NASH treatment. This review focuses on the effects of metabolic disease-induced extrahepatic inflammation, liver inflammation, and the cellular and molecular mechanisms of liver metabolism on the development and progression of NAFLD and NASH, as well as the associated treatments.

Transforming growth factor-β signaling: From tissue fibrosis to therapeutic opportunities

Fibrosis refers to the excessive deposition of extracellular matrix components in the processes of wound repair or tissue regeneration after tissue damage. Fibrosis occurs in various organs such as lung, heart, liver, and kidney tissues, resulting in the failure of organ structural integrity and its functional impairment. It has long been thought to be relentlessly progressive and irreversible process, but both preclinical models and clinical trials in multiorgans have shown that fibrosis is a highly dynamic process. Transforming growth factor-beta (TGF-β) is a superfamily of related growth factors. Many studies have described that activation of profibrotic TGF-β signaling promotes infiltration and/or proliferation of preexisting fibroblasts, generation of myofibroblasts, extracellular matrix deposition, and inhibition of collagenolysis, which leads to fibrosis in the pathological milieu. This review describes the effect of TGF-β signaling in fibrotic-associate lung, heart, liver, and kidney tissues, followed by a detailed discussion of canonical and non-canonical TGF-β signaling pathway. In addition, this review also discusses therapeutic options by using natural products and chemical agents, for targeting tissue fibrosis via modulating TGF-β signaling to provide a more specific concept-driven therapy strategy for multiorgan fibrosis.

Isosteviol attenuates DSS-induced colitis by maintaining intestinal barrier function through PDK1/AKT/NF-κB signaling pathway

Inflammatory bowel diseases (IBD) are chronic debilitating inflammatory disorders of the gastrointestinal tract that is characterized by intestinal epithelial barrier dysfunction and excessive activation of the mucosal immune system. Isosteviol (IS) has been reported to possess anti-inflammatory properties. In this study, we aimed to investigate effects and mechanisms of IS against intestinal inflammation. C57BL/6 mice were randomly divided into Sham, IS, dextran sodium sulfate (DSS), and DSS + IS groups. In vivo colitis model was established using 3.0 % DSS. In vitro, tumor necrosis factor-α (TNF-α)-treated Caco-2 cells were used as an inflammatory model. Clinical characteristics, histological performance, proinflammatory cytokine expression, and intestinal barrier function were measured. In addition, activation of the pyruvate dehydrogenase kinase 1/protein kinase B/nuclear factor-κB (PDK1/AKT/NF-κB) signaling pathway was determined by western blotting and quantitative polymerase chain reaction. The results showed that IS mitigated DSS-induced colitis by reducing body weight loss, colonic shortening, and disease activity index score, and by inhibiting expressions of proinflammatory cytokines IL-1β, IL-6, and TNF-α. IS restored impaired barrier function by regulating tight junctions and intestinal epithelial permeability. Furthermore, we found that IS ameliorated intestinal barrier injury by regulating PDK1/AKT/NF-κB signaling pathway. In conclusion, our results demonstrate that IS attenuates experimental colitis by preserving intestinal barrier function, probably mediated by PDK1/AKT/NF-κB signaling pathway. These findings highlight the potential of IS as a therapeutic agent for IBD.

Red Pepper Seeds Inhibit Hepatic Lipid Accumulation by Inducing Autophagy via AMPK Activation

Although the red pepper and its seeds have been studied for metabolic diseases, the effects and potential mechanisms of red pepper seed extract (RPS) on hepatic lipid accumulation are not yet completely understood. This study aimed to evaluate the inhibitory effect of RPS on hepatic lipid accumulation via autophagy. C57BL/6 mice were fed a high-fat diet (HFD) or a HFD supplemented with RPS. RPS treatment inhibited hepatic lipid accumulation by suppressing lipogenesis, inducing hepatic autophagic flux, and activating AMPK in HFD-fed mice. To investigate the effect of RPS on an oleic acid (OA)-induced hepatic steatosis cell model, HepG2 cells were incubated in a high-glucose medium and OA, followed by RPS treatment. RPS treatment decreased OA-induced lipid accumulation and reduced the expression of lipogenesis-associated proteins. Autophagic flux dramatically increased in the RPS-treated group. RPS phosphorylated AMPK in a dose-dependent manner, thereby dephosphorylated mTOR. Autophagy inhibition with 3-methyladenine (3-MA) antagonized RPS-induced suppression of lipogenesis-related protein expressions. Moreover, the knockdown of endogenous AMPK also antagonized the RPS-induced regulation of lipid accumulation and autophagy. Our findings provide new insights into the beneficial effects of RPS on hepatic lipid accumulation through the AMPK-dependent autophagy-mediated downregulation of lipogenesis.