Exercise as a Molecular Therapeutic Tool in MASLD: From Signaling Pathways to Clinical Translation-A Narrative Review.

Akt Stimulates Hepatic SREBP1c and Lipogenesis through Parallel mTORC1-Dependent and Independent Pathways

Coffea arabica pulp aqueous extract attenuates oxidative stress and hepatic lipid accumulation in HepG2 cells

Non-alcoholic fatty liver disease (NAFLD) is a major health problem and occurs frequently in the context of obesity and type 2 diabetes mellitus (T2D). Insulin resistance of the liver and/or peripheral tissues is considered to drive ectopic lipid accumulation in hepatocytes, but individual contributions are not fully understood. Hepatocyte-specific Pten-deficiency in mice was shown previously to result in hepatic steatosis due to hyperactivated PKBb in the liver. However, the role of peripheral insulin sensitive tissues on PTEN/PKBb-dependent development of NAFLD has not been addressed. The aim of this thesis is to characterize the effects of systemically perturbed PTEN/PKBb signaling on hepatic lipid content using Pten-haplodeficient (Pten+/-/Pkbb+/+) mice and Pten-haplodeficient mice lacking Pkbb (Pten+/-/Pkbb-/-). We found that Pten+/-/Pkbb+/+ mice have a more than 2-fold reduction in hepatic lipid content compared to control mice, similar to the low level observed in Pten+/-/Pkbb-/- mice. Pten+/-/Pkbb+/+ mice showed enhanced insulin signaling in the liver indicating that extra-hepatic factors prevent hepatic lipid accumulation. Further results suggested that augmented PKBb activity in the skeletal muscle of Pten+/-/Pkbb+/+ mice might reduce hepatic lipid content. Indeed, skeletal muscle-specific expression of constitutively active PKBb reduced hepatic lipids in Pten+/+Pkbb+/+ mice and dominant negative PKBb increased hepatic lipid content in both Pten+/+Pkbb+/+ and Pten+/-/Pkbb+/+ mice. The results obtained during this study show that PKBb activity in skeletal muscle regulates lipid accumulation in the livers of Pten+/+Pkbb+/+ and Pten+/-/Pkbb+/+ mice, and emphasizes the role of skeletal muscle in the pathophysiology of NAFLD.

Endoplasmic reticulum stress is involved in hepatic SREBP-1c activation and lipid accumulation in fructose-fed mice

Empagliflozin (EMPA)-a sodium-glucose cotransporter type 2 inhibitor-reduces endoplasmic reticulum (ER) stress, oxidative stress, and inflammation during metabolic dysfunction-associated steatotic liver disease (MASLD) progression. However, the direct effects of EMPA on hepatic lipid metabolism and oxidative stress are unclear. Through the current study, we seek to explore the effects of EMPA on oxidative stress and related mechanisms in MASLD. To this end, MASLD was induced in C57BL/6J mice using a high-fat diet (HFD); nuclear respiratory factor 1 (NRF1) was downregulated via viral transduction (AAV8-shNrf1). Glucose homeostasis and liver histology were assessed, and oxidative stress and inflammation were measured. HFD-fed mice-derived liver tissue samples exhibited more lipid droplets, higher triglyceride levels, and elevated oxidative and ER stress than chow diet (CD)-fed mice. EMPA attenuated HFD-induced liver oxidative and ER stress. Additionally, the HFD significantly decreased NRF1 and Sirtuin (SIRT)7 expression compared with CD, which was rescued by EMPA treatment. However, these results did not affect insulin resistance or lipid synthesis-related changes upon EMPA treatment in the Nrf1-knockdown mice. Furthermore, EMPA alleviated HFD-induced hepatic steatosis and oxidative stress; however, these effects were lost in Nrf1-knockdown mice. Collectively, the results of this study suggest that EMPA ameliorates MASLD by reducing steatosis and attenuating oxidative stress via NRF1.

Hepatic lipid metabolism is modulated by the circadian rhythm; therefore, circadian disruption may promote obesity and hepatic lipid accumulation. This study aims to investigate dietary pterostilbene (PSB) 's protective effect against high-fat-diet (HFD)-induced lipid accumulation exacerbated by chronic jet lag and the potential role of gut microbiota therein. Mice were treated with a HFD and chronic jet lag for 14 weeks. The experimental group was supplemented with 0.25% (w/w) PSB in its diet to evaluate whether PSB had a beneficial effect. Our study found that chronic jet lag exacerbates HFD-induced obesity and hepatic lipid accumulation, but these adverse effects were significantly mitigated by PSB supplementation. Specifically, PSB promoted hepatic lipolysis and β-oxidation by upregulating SIRT1 expression, which indirectly reduced oxidative stress caused by lipid accumulation. Additionally, the PSB-induced elevation of SIRT1 and SIRT3 expression helped prevent excessive autophagy and mitochondrial fission by activating Nrf2-mediated antioxidant enzymes. The result was evidenced by the use of SIRT1 and SIRT3 inhibitors in in vitro studies, which demonstrated that activation of SIRT1 and SIRT3 by PSB is crucial for the translocation of PGC-1α and Nrf2, respectively. Moreover, the analysis of gut microbiota suggested that PSB's beneficial effects were partly due to its positive modulation of gut microbial composition and functionality. The findings of this study suggest the potential of dietary PSB as a candidate to improve hepatic lipid metabolism via several mechanisms. It may be developed as a treatment adjuvant in the future.

BackgroundNonalcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide, and is related to disturbed lipid metabolism and redox homeostasis. However, a definitive drug treatment has not been approved for this disease. Studies have found that electromagnetic fields (EMF) can ameliorate hepatic steatosis and oxidative stress. Nevertheless, the mechanism remains unclear.MethodsNAFLD models were established by feeding mice a high-fat diet. Simultaneously, EMF exposure is performed. The effects of the EMF on hepatic lipid deposition and oxidative stress were investigated. Additionally, the AMPK and Nrf2 pathways were analysed to confirm whether they were activated by the EMF.ResultsExposure to EMF decreased the body weight, liver weight and serum triglyceride (TG) levels and restrained the excessive hepatic lipid accumulation caused by feeding the HFD. The EMF boosted CaMKKβ protein expression, activated AMPK phosphorylation and suppressed mature SREBP-1c protein expression. Meanwhile, the activity of GSH-Px was enhanced following an increase in nuclear Nrf2 protein expression by PEMF. However, no change was observed in the activities of SOD and CAT. Consequently, EMF reduced hepatic reactive oxygen species (ROS) and MDA levels, which means that EMF relieved liver damage caused by oxidative stress in HFD-fed mice.ConclusionsEMF may activate the CaMKKβ/AMPK/SREBP-1c and Nrf2 pathways to control hepatic lipid deposition and oxidative stress. This investigation indicates that EMF may be a novel therapeutic method for NAFLD.

Objective Nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes (T2DM) commonly coexist and act synergistically to drive adverse clinical outcomes. This study is aimed at investigating the effects of exercise intervention and oral hypoglycaemic drug of metformin (MET) alone or combined on hepatic lipid accumulation. To investigate if oxidative stress and endoplasmic reticulum stress (ERS) are involved in lipotoxicity-induced hepatocyte apoptosis in diabetic mice and whether exercise and/or MET alleviated oxidative stress or ERS-apoptosis by AMPK-Nrf2-HO-1 signaling pathway. Methods Forty db/db mice with diabetes (random blood glucose ≥ 250 mg/dL) were randomly allocated into four groups: control (CON), exercise training alone (EX), metformin treatment alone (MET), and exercise combined with metformin (EM) groups. Hematoxylin-eosin and oil red O staining were carried out to observe hepatic lipid accumulation. Immunohistochemical and TUNEL methods were used to detect the protein expression of the binding immunoglobulin protein (BiP) and superoxide dismutase-1 (SOD1) and the apoptosis level of hepatocytes. ERS-related gene expression and the AMPK-Nrf2-HO-1 signaling pathway were tested by western blotting. Results Our data showed that db/db mice exhibited increased liver lipid accumulation, which induced oxidative and ER stress of the PERK-eIF2α-ATF4 pathway, and hepatocyte apoptosis. MET combined with exercise training significantly alleviated hepatic lipid accumulation by suppressing BiP expression, the central regulator of ER homeostasis, and its downstream PERK-eIF2α-ATF4 pathway, as well as upregulated the AMPK-Nrf2-HO-1 signaling pathway. Moreover, the combination of exercise and MET displayed protective effects on hepatocyte apoptosis by downregulating Bax expression and TUNEL-positive staining, restoring the balance of cleaved-caspase-3 and caspase-3, and improving the antioxidant defense system to prevent oxidative damage in db/db mice. Conclusion Compared to MET or exercise intervention alone, the combined exercise and metformin exhibited significant effect on ameliorating hepatic steatosis, inhibiting oxidative and ER stress-induced hepatocyte apoptosis via improving the capacity of the antioxidant defense system and suppression of the PERK-eIF2α-ATF4 pathway. Furthermore, upregulation of AMPK-Nrf2-HO-1 signaling pathway might be a key crosstalk between MET and exercise, which may have additive effects on alleviating hepatic lipid accumulation.

Long-term adjustment of hepatic lipid metabolism after chronic stress and the role of FGF21

Akkermansia muciniphila (AKK), classified as "lean bacteria," has emerged as a promising candidate for ameliorating metabolic disorders, including obesity, diabetes, and liver disease. In this study, we investigated the therapeutic potential of AKK to counteract metabolic dysfunctions induced by Olanzapine (OLZ), a first-class antipsychotic known for its high therapeutic efficacy but also its association with metabolic disturbances, particularly Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD). Previous studies have implicated progesterone receptor membrane component 1 (PGRMC1) as a key player in antipsychotic-induced metabolic side effects. Using male C57BL/6J mice fed a high-fat diet, we assessed the effects of AKK supplementation on OLZ-induced metabolic disturbances. Key parameters such as body weight, hepatic injury markers, glucose tolerance, insulin resistance, and lipid metabolism were analyzed. The study revealed that AKK supplementation reduced hepatic lipid accumulation, oxidative stress, and insulin resistance, while normalizing lipid and glucose metabolism. These effects are likely mediated through the restoration of PGRMC1/SIRT1/FOXO1 signaling pathway by AKK. Additionally, changes in gut microbiota composition, including a reduction in pathogenic bacteria such as Lactococcus and enrichment of beneficial bacteria, were observed. Overall, the study suggests that AKK has therapeutic potential to counteract OLZ-induced MASLD by modulating gut microbiota and key metabolic pathways, making it a promising strategy for managing metabolic side effects in patients receiving antipsychotic treatment.

Physical exercise is a potent non-pharmacological strategy for the prevention and management of chronic non-communicable diseases (NCDs), including type 2 diabetes, cardiovascular diseases, obesity, and certain cancers. Growing evidence demonstrates that the benefits of exercise extend beyond its physiological effects and are largely mediated by coordinated molecular and cellular adaptations. This review synthesizes current knowledge on the key mechanisms through which exercise modulates metabolic health, emphasizing intracellular signaling pathways, epigenetic regulation, and myokine-driven inter-organ communication. Exercise induces acute and chronic activation of pathways such as AMPK, PGC-1α, mTOR, MAPKs, and NF-κB, leading to enhanced mitochondrial biogenesis, improved oxidative capacity, refined energy sensing, and reduced inflammation. Additionally, repeated muscle contraction stimulates the release of myokines—including IL-6, irisin, BDNF, FGF21, apelin, and others—that act through endocrine and paracrine routes to regulate glucose and lipid metabolism, insulin secretion, adipose tissue remodeling, neuroplasticity, and systemic inflammatory tone. Epigenetic modifications and exercise-responsive microRNAs further contribute to long-term metabolic reprogramming. Collectively, these molecular adaptations establish exercise as a systemic biological stimulus capable of restoring metabolic homeostasis and counteracting the pathophysiological processes underlying NCDs. Understanding these mechanisms provides a foundation for developing targeted, personalized exercise-based interventions in preventive and therapeutic medicine.

In humans, low levels of growth hormone (GH) and its mediator, IGF-1, associate with hepatic lipid accumulation. In mice, congenital liver-specific ablation of the GH receptor (GHR) results in reductions in circulating IGF-1 and hepatic steatosis, associated with systemic insulin resistance. Due to the intricate relationship between GH and IGF-1, the relative contribution of each hormone to the development of hepatic steatosis is unclear. Our goal was to dissect the mechanisms by which hepatic GH resistance leads to steatosis and overall insulin resistance, independent of IGF-1. We have generated a combined mouse model with liver-specific ablation of GHR in which we restored liver IGF-1 expression via the hepatic IGF-1 transgene. We found that liver GHR ablation leads to increases in lipid uptake, de novo lipogenesis, hyperinsulinemia, and hyperglycemia accompanied with severe insulin resistance and increased body adiposity and serum lipids. Restoration of IGF-1 improved overall insulin sensitivity and lipid profile in serum and reduced body adiposity, but was insufficient to protect against steatosis-induced hepatic inflammation or oxidative stress. We conclude that the impaired metabolism in states of GH resistance results from direct actions of GH on lipid uptake and de novo lipogenesis, whereas its actions on extrahepatic tissues are mediated by IGF-1.

Alleviating effects of guar gum on high-fat diet-induced liver injury in common carp (Cyprinus carpio)

Angiopoietin-like protein 3 (Angptl3), a factor secreted by the liver, inhibits lipoprotein lipase and other lipases by forming a complex with Angptl4 and 8. However, whether inhibition of Angptl3 can alleviate hepatic lipid accumulation and atherosclerosis remains unclear. Therefore, this study explored the effect of small interfering RNA (siRNA)-based inactivation of Angptl3 on metabolic dysfunction-associated fatty liver disease (MAFLD) and atherosclerosis in male LDLR-deficient hamsters. Recombinant adeno-associated virus serotype 9 (AAV9) encoding Angptl3-siRNA or empty AAV (AAV9-null) were injected into male 4-month-old LDLR−/− hamsters via the jugular vein. Subsequently, all hamsters were administered with a 16-week high-fat diet (HFD) feeding to induce atherosclerosis. RT-PCR and pathological analysis were used to investigate the mechanism of hepatic lipid accumulation and detect atherosclerotic plaque formation in the heart and aorta. On HFD, Angptl3-siRNA-treated hamsters displayed significantly decreased plasma triglyceride (TG), total cholesterol, high-density lipoprotein-cholesterol, and glucose levels, compared with the AAV9-null hamsters. FPLC analysis further revealed a marked reduction of TG and cholesterol contents in VLDL/LDL fractions. Plasma apolipoprotein analysis showed relatively lower ApoB/ApoE levels and higher ApoA1 levels. Moreover, Angptl3-siRNA markedly accelerated the clearance of triglyceride-rich lipoproteins in LDLR−/− hamsters. Consistently, results from hepatic lipid extraction, Oil Red O and Sirius Red staining demonstrated that Angptl3-siRNA reduced hepatic lipid accumulation and ameliorated HFD-induced MAFLD. RT-PCR revealed a dramatic decrease in the expression of Acc1, Fasn, Srebp1c, Cd36, Fatp1, Tgfβ, Cd68, Tnfa, and Col1a1 as well as a marked increase in Abcg5, Abcg8, Ppara, and Cpt1 expression, which participated in fatty acid synthesis and oxidation, cholesterol synthesis and efflux, inflammation and fibrosis. Pathological analysis indicated that Angptl3-siRNA attenuated the formation of atherosclerotic plaques in the aortic root and aorta when compared with the control group. These findings demonstrated that siRNA-based inactivation of Angptl3 alleviated MAFLD and atherosclerosis induced by HFD in LDLR−/− hamsters, which further confirmed that inhibition of Angptl3 may provide a novel therapeutic approach for atherosclerosis by reducing hyperlipidemia and hepatic lipid accumulation.

Dysregulated autophagy contributes to liver steatosis, yet its regulation under distinct metabolic contexts remains poorly defined. Here, we identify bile acids (BAs) as critical modulators of hepatic autophagy. Circulating BA levels are elevated in human subjects with liver steatosis and independently associated with increased hepatic steatosis risk. High-fat diet (HFD) feeding increases circulating BA levels, while simultaneously reducing hepatic autophagic flux in mice, whereas pharmacological inhibition of farnesoid X receptor (FXR) enhances autophagy and alleviates steatosis in the livers of HFD-fed mice. Mechanistically, circulating BAs promote hepatic acetyl-CoA production through FXR-induced acyl-CoA oxidase 1 (ACOX1), which in turn suppresses autophagy by increasing the mechanistic target of rapamycin complex 1 (mTORC1) signaling. Similar to HFD feeding, prolonged fasting elevates BA levels and hepatic lipid accumulation, while concurrently upregulating hepatic miR-378, a positive regulator of BA synthesis. Although miR-378 exerts a cell-autonomous pro-autophagic effect during short-term fasting, it paradoxically drives lipid accumulation by suppressing hepatic autophagy via BA/FXR/ACOX1/acetyl-CoA axis in a non-cell-autonomous manner during either HFD feeding or prolonged fasting when BA action becomes considerable. Together, our study uncovers BAs as a previously unrecognized class of inhibitors of hepatic autophagy during prolonged fasting and in metabolic dysfunction-associated steatotic liver disease (MASLD), providing novel insights into context-dependent autophagic regulation of hepatic lipid metabolism and potential therapeutic strategies for MASLD.