Lipophagy is a cellular pathway targeting the lysosomal degradation of lipid droplets, playing a role in promoting lipid turnover and renewal. Abnormal lipophagy processes can lead to the occurrence and development of non-alcoholic fatty liver disease (NAFLD), characterized by the deposition of lipid droplets (LDs) in the liver. The importance of exercise training in preventing and improving NAFLD has been well-established, but the exact mechanisms remain unclear. Recent research findings suggest that lipophagy may serve as a crucial hub for liver lipid turnover under exercise conditions. Exercise may alleviate hepatic lipid accumulation and mitigate inflammatory responses and fibrosis through lipophagy, thereby improving the onset and progression of NAFLD.

The communication between mitochondria and the endoplasmic reticulum (ER) is facilitated by a dynamic membrane structure formed by protein complexes known as mitochondria-associated membranes (MAMs). The structural and functional integrity of MAMs is crucial for insulin signal transduction, relying heavily on their regulation of intracellular calcium homeostasis, lipid homeostasis, mitochondrial quality control, and endoplasmic reticulum stress (ERS). This article reviews recent research findings, suggesting that exercise may promote the remodeling of MAMs structure and function by modulating the expression of molecules associated with their structure and function. This, in turn, restores cellular homeostasis and ultimately contributes to the amelioration of insulin resistance (IR). These insights provide additional possibilities for the study and treatment of insulin resistance-related metabolic disorders such as obesity, diabetes, fatty liver, and atherosclerosis.

Objective: Mitochondria‐associated membranes (MAMs) serve pivotal functions in hepatic insulin resistance (IR). Our aim was to explore the potential role of MAMs in mitigating hepatic IR through exercise and to compare the effects of different intensities of exercise on hepatic MAMs formation in high‐fat diet (HFD) mice.Methods: Male C57BL/6J mice were fed an HFD and randomly assigned to undergo supervised high‐intensity interval training (HIIT) or moderate‐intensity continuous training (MICT). IR was evaluated using the serum triglyceride/high‐density lipoprotein cholesterol ratio (TG/HDL‐C), glucose tolerance test (GTT), and insulin tolerance test (ITT). Hepatic steatosis was observed using hematoxylin–eosin (H&E) and oil red O staining. The phosphatidylinositol 3‐kinase/protein kinase B/glycogen synthase kinase 3 beta (PI3K‐AKT‐GSK3β) signaling pathway was assessed to determine hepatic IR. MAMs were evaluated through immunofluorescence (colocalization of voltage‐dependent anion‐selective channel 1 [VDAC1] and inositol 1,4,5‐triphosphate receptor [IP3R]).Results: After 8 weeks on an HFD, there was notable inhibition of the hepatic PI3K/Akt/GSK3β signaling pathway, accompanied by a marked reduction in hepatic IP3R‐VDAC1 colocalization levels. Both 8‐week HIIT and MICT significantly enhanced the hepatic PI3K/Akt/GSK3β signaling and colocalization levels of IP3R‐VDAC1 in HFD mice, with MICT exhibiting a stronger effect on hepatic MAMs formation. Furthermore, the colocalization of hepatic IP3R‐VDAC1 positively correlated with the expression levels of phosphorylation of protein kinase B (p‐AKT) and phosphorylation of glycogen synthase kinase 3 beta (p‐GSK3β), while displaying a negative correlation with serum triglyceride/high‐density lipoprotein cholesterol levels.Conclusion: The reduction in hepatic MAMs formation induced by HFD correlates with the development of hepatic IR. Both HIIT and MICT effectively bolster hepatic MAMs formation in HFD mice, with MICT demonstrating superior efficacy. Thus, MAMs might wield a pivotal role in exercise‐induced alleviation of hepatic IR. image

FAM132b, also known as myonectin, has been identified as a myokine produced by exercise. It is a secreted protein precursor that belongs to the adipolin/erythroferrone family, and has hormone activity in circulation to regulate cellular iron homeostasis and lipid metabolism via unknown receptors. Here, adeno-associated viral vectors (AAV9) were engineered to induce overexpression of FAM132b with 2 codon mutations (A136T and P159A). Treatment of mice under high-fat diet feeding with FAM132b gene transfer resulted in marked reductions in body weight, fat depot, adipocytes size, glucose intolerance and insulin resistance. Moreover, FAM132b overproduction reduced glycemic response to epinephrine (EPI) in whole body and increased lipolytic response to EPI in adipose tissues. This adrenergic response of adipose tissue led to the result that gene transfer reduced glycogen utilization and increased fat consumption in skeletal muscle during exercise. FAM132b knockdown by shRNA significantly increased glycemic response to EPI in vivo and reduced adipocytes response to EPI and adipose tissue browning. Structural analysis suggested that FAM132b mutants delivered by AAV9 may form a weak bond with ADRB2, and potentially bind to insulin against insulin receptor by blocking the receptor binding sites on insulin B-chain. Our study underscores the potential of FAM132b gene therapy with codon optimization to treat obesity by modulating adrenergic response and interfering insulin action. Significance: We show here that AAV9-mediated expression of FAM132b with A136T and P159A is a safe and effective therapeutic strategy for improving glucose homeostasis. This is the first demonstration of a therapeutic effect on metabolic disorders in mice with FAM132b codon optimization. These therapeutic effects indicate that FAM132b gene transfer with selective codon mutants in vivo might be a valid therapy for diabetes that can be extended to other metabolic disorders.