The N-degron pathway mediates lipophagy: The chemical modulation of lipophagy in obesity and NAFLD

Selenium corrects dysregulated mitophagy and lipophagy in obesity-related acute pancreatitis through the GPX1-Mfn2-PLIN2 axis

The incidence of acute pancreatitis (AP) has been on the rise in recent years. Obesity, a significant contributor to AP, increases the risk of AP and promotes disease progression, leading to adverse outcomes. Mitophagy and lipophagy are two main types of selective autophagy in AP and obesity, but their contribution to comorbidity in obesity-related AP (OB-AP) remains unknown. This study demonstrated that OB-AP exhibited more severe pancreatic injury than AP in vivo and in vitro. We found that the balance between mitophagy and lipophagy was disrupted, with a significant increase in mitophagy and a corresponding significant decrease in lipophagy. Mechanistically, overexpression of selenoprotein glutathione peroxidase 1 (GPX1) stabilized mitofusin 2 (Mfn2) protein, promoting the interaction between Mfn2 and perilipin 2 (PLIN2), and thereby attenuating excessive mitophagy and increasing lipophagy. Selenium supplementation improved pancreatic autophagy homeostasis in OB-AP through increasing GPX1 expression, thereby reducing disease severity. Notably, OB-AP patients exhibited lower selenium levels than healthy individuals. In conclusion, selenium supplementation enhanced GPX1 expression, corrected the imbalance between mitophagy and lipophagy, and mitigated disease severity in OB-AP through the GPX1-Mfn2-PLIN2 axis, and therefore has therapeutic potential in OB-AP.

The N-degron pathway mediates the autophagic degradation of cytosolic mitochondrial DNA during sterile innate immune responses

The human body reacts to tissue damage by generating damage-associated molecular patterns (DAMPs) that activate sterile immune responses. To date, little is known about how DAMPs are removed to avoid excessive immune responses. Here, we show that proteasomal dysfunction induces the release of mitochondrial DNA (mtDNA) as a DAMP that activates the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon gene (STING) pathway and is subsequently degraded through the N-degron pathway. In the resolution phase of sterile immune responses, DNA-dependent protein kinase (DNA-PK) senses cytosolic mtDNA and activates N-terminal (Nt-) arginylation by ATE1 R-transferases. The substrates of Nt-arginylation include the molecular chaperone BiP/GRP78 retrotranslocated from the endoplasmic reticulum (ER). R-BiP, the Nt-arginylated species of BiP, is associated with cytosolic mtDNA to accelerate its targeting to autophagic membranes for lysosomal degradation. Thus, cytosolic mtDNA activates the N-degron pathway to facilitate its own degradation and form a negative feedback loop, by which the cell can turn off sterile immune responses at the right time.

Mechanisms and therapeutic implications of selective autophagy in nonalcoholic fatty liver disease

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) has become the most common chronic liver disease worldwide, whereas there is no approved drug therapy due to its complexity. Studies are emerging to discuss the role of selective autophagy in the pathogenesis of NAFLD, because the specificity among the features of selective autophagy makes it a crucial process in mitigating hepatocyte damage caused by aberrant accumulation of dysfunctional organelles, for which no other pathway can compensate.

AIM OF REVIEW

This review aims to summarize the types, functions, and dynamics of selective autophagy that are of particular importance in the initiation and progression of NAFLD. And on this basis, the review outlines the therapeutic strategies against NAFLD, in particular the medications and potential natural products that can modulate selective autophagy in the pathogenesis of this disease.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The critical roles of lipophagy and mitophagy in the pathogenesis of NAFLD are well established, while reticulophagy and pexophagy are still being identified in this disease due to the insufficient understanding of their molecular details. As gradual blockage of autophagic flux reveals the complexity of NAFLD, studies unraveling the underlying mechanisms have made it possible to successfully treat NAFLD with multiple pharmacological compounds that target associated pathways. Overall, it is convinced that the continued research into selective autophagy occurring in NAFLD will further enhance the understanding of the pathogenesis and uncover novel therapeutic targets.

Polysaccharides targeting autophagy to alleviate metabolic syndrome

Metabolic syndrome is a prevalent non-communicable disease characterized by central obesity, insulin resistance, hypertension, hyperglycemia, and hyperlipidemia. Epidemiological statistics indicate that one-third of the world's population is affected by metabolic syndrome. Unfortunately, owing to complicated pathogenesis and limited pharmacological options, the growing prevalence of metabolic syndrome threatens human health worldwide. Autophagy is an intracellular degradation mechanism that involves the degradation of unfolded or aggregated proteins and damaged cellular organelles, thereby maintaining metabolic homeostasis. Increasing evidence indicates that dysfunctional autophagy is closely associated with the development of metabolic syndrome, making it an attractive therapeutic target. Furthermore, a growing number of plant-derived polysaccharides have been shown to regulate autophagy, thereby alleviating metabolic syndrome, such as Astragalus polysaccharides, Laminaria japonica polysaccharides, Ganoderma lucidum polysaccharides and Lycium barbarum polysaccharides. In this review, we summarize recent advances in the discovery of autophagy modulators of plant polysaccharides for the treatment of metabolic syndrome, with the aim of providing precursor compounds for the development of new therapeutic agents. Additionally, we look forward to seeing more diseases being treated with plant polysaccharides by regulating autophagy, as well as the discovery of more intricate mechanisms that govern autophagy.

Autophagy and lysosomal dysfunction in diabetes and its complications

Autophagy is critical for energy homeostasis and the function of organelles such as endoplasmic reticulum (ER) and mitochondria. Dysregulated autophagy due to aging, environmental factors, or genetic predisposition can be an underlying cause of not only diabetes through β-cell dysfunction and metabolic inflammation, but also diabetic complications such as diabetic kidney diseases (DKDs). Dysfunction of lysosomes, effector organelles of autophagic degradation, due to metabolic stress or nutrients/metabolites accumulating in metabolic diseases is also emerging as a cause or aggravating element in diabetes and its complications. Here, we discuss the etiological role of dysregulated autophagy and lysosomal dysfunction in diabetes and a potential role of autophagy or lysosomal modulation as a new avenue for treatment of diabetes and its complications.

Heat shock proteins (HSPs) in non-alcoholic fatty liver disease (NAFLD): from molecular mechanisms to therapeutic avenues

Non-alcoholic fatty liver disease (NAFLD), a spectrum of liver conditions characterized by fat accumulation without excessive alcohol consumption, represents a significant global health burden. The intricate molecular landscape underlying NAFLD pathogenesis involves lipid handling, inflammation, oxidative stress, and mitochondrial dysfunction, with endoplasmic reticulum (ER) stress emerging as a key contributor. ER stress triggers the unfolded protein response (UPR), impacting hepatic steatosis in NAFLD and contributing to inflammation, fibrosis, and progression to NASH and eventually hepatocellular carcinoma (HCC). Heat shock proteins (HSPs), including small HSPs such as HSP20 and HSP27, HSP60, HSP70, GRP78, and HSP90, are integral to cellular stress responses. They aid in protein folding, prevent aggregation, and facilitate degradation, thus mitigating cellular damage under stress conditions. In NAFLD, aberrant HSP expression and function contribute to disease pathogenesis. Understanding the specific roles of HSP subtypes in NAFLD offers insights into potential therapeutic interventions. This review discusses the involvement of HSPs in NAFLD pathophysiology and highlights their therapeutic potential. By elucidating the molecular mechanisms underlying HSP-mediated protection in NAFLD, this article aims to pave the way for the development of targeted therapies for this prevalent liver disorder.

Chondrocyte autophagy mediated by T-2 toxin via AKT/TSC/Rheb/mTOR signaling pathway and protective effect of CSA-SeNP

OBJECTIVE

Kashin-Beck disease (KBD) is an endemic, degenerative, and cartilage-damaging disease for which low selenium and T-2 toxins are considered environmental pathogenic factors. This study aimed to investigate the molecular mechanisms of autophagy in cartilage damage caused by T-2 toxin and the protective effect of chondroitin sulfate A nano-elemental selenium (CSA-SeNP) on the cartilage.

METHODS

KBD chondrocytes and C28/I2 human chondrocyte cell lines were used. T-2 toxin, AKT inhibitor, and CSA-SeNP treatment experiments were conducted separately, with a treatment time of 24 h. Autophagy was monitored using MDC staining, and mRFP-GFP-LC3 adenovirus, respectively. RT-qPCR and western blotting were used to detect the expression of the relevant genes and proteins.

RESULTS

The suppression of autophagy observed in KBD chondrocytes was replicated by applying 10 ng/mL T-2 toxin to C28/I2 chondrocytes for 24 h. The AKT/TSCR/Rheb/mTOR signaling pathway was activated by T-2 toxin, which inhibits autophagy. The supplementation with CSA-SeNP alleviated the inhibition of autophagy by T-2 toxin through the AKT/TSCR/Rheb/mTOR signaling pathway.

CONCLUSIONS

Loss of autophagy regulated by the AKT/TSCR/Rheb/mTOR signaling pathway plays an important role in cartilage damage caused by T-2 toxin. CSA-SeNP supplementation attenuated inhibition of autophagy in chondrocytes by T-2 toxin by modulating this signaling pathway. These findings provide promising new targets for the prevention and treatment of cartilage disease.

Lipid Regulatory Element Interact with CD44 on Mitochondrial Bioenergetics in Bovine Adipocyte Differentiation and Lipometabolism

The CD44 gene is a critical factor in animal physiological processes and has been shown to affect insulin resistance and fat accumulation in mammals. Nevertheless, little research has been conducted on its precise functions in lipid metabolism and adipogenic differentiation in beef cattle. This study analyzed the expression of CD44 and miR-199a-3p during bovine preadipocyte differentiation. The luciferase reporter assay demonstrated that CD44 was a direct target of miR-199a-3p. Increased accumulation of lipid droplets and triglyceride levels, altered fatty acid metabolism, and accelerated preadipocyte differentiation were all caused by the upregulation of miR-199a-3p or a reduction in CD44 expression. CD44 knockdown upregulated the expression of adipocyte-specific genes (LPL and FABP4) and altered the levels of lipid metabolites (SOPC, l-arginine, and heptadecanoic acid). Multiomics highlights enriched pathways involved in energy metabolism (MAPK, cAMP, and calcium signaling) and shifts in mitochondrial respiration and glycolysis, indicating that CD44 plays a regulatory role in lipid metabolism. The findings show that intracellular lipolysis, glycolysis, mitochondrial respiration, fat deposition, and lipid droplet composition are all impacted by miR-199a-3p, which modulates CD44 in bovine adipocytes.

Autophagy and hepatic lipid metabolism: mechanistic insight and therapeutic potential for MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) originates from a homeostatic imbalance in hepatic lipid metabolism. Increased fat deposition in the liver of people suffering from MASLD predisposes them to develop further metabolic derangements, including diabetes mellitus, metabolic dysfunction-associated steatohepatitis (MASH), and other end-stage liver diseases. Unfortunately, only limited pharmacological therapies exist for MASLD to date. Autophagy, a cellular catabolic process, has emerged as a primary mechanism of lipid metabolism in mammalian hepatocytes. Furthermore, preclinical studies with autophagy modulators have shown promising results in resolving MASLD and mitigating its progress into deleterious liver pathologies. In this review, we discuss our current understanding of autophagy-mediated hepatic lipid metabolism, its therapeutic modulation for MASLD treatment, and current limitations and scope for clinical translation.

Ubiquitination of cytoplasmic HMGB1 by RNF186 regulates hepatic lipophagy in non-alcoholic fatty liver disease

BACKGROUND

Lipophagy is a vital biological process that maintains the balance of intracellular lipid metabolism in nonalcoholic fatty liver disease (NAFLD). However, the precise regulatory mechanism of RNF186 in hepatic lipophagy is still unclear. This study investigates the roles and mechanisms of RNF186 in the regulation of lipophagy during the development of NAFLD.

METHODS

In this study, we employed RNF186 knockout mice as well as human liver cells and mouse primary hepatocytes (MPHs) to investigate the role and mechanisms of RNF186 in lipophagy during the progression of NAFLD. Additionally, liver specimens from individuals with NAFLD were examined to assess the expression of RNF186 and its associated factors.

RESULTS

Here, we provide evidence that depletion of RNF186 enhances lipophagy in hepatocytes of a NAFLD model. Mechanistically, RNF186 acts as an E3 ubiquitin ligase that targets cytoplasmic HMGB1 for lysine 48 (K48)- and K63-linked ubiquitination, leading to its subsequent proteasomal degradation. Importantly, the translocation of HMGB1 from the nucleus to the cytoplasm is responsible for inducing lipophagy in NAFLD samples. Knockdown of HMGB1 significantly reduces the activation of lipophagy and mediates the decrease in lipid accumulation caused by RNF186 depletion in hepatocytes. Furthermore, we find that maintaining the nuclear HMGB1 level and inhibiting its nuclear-cytoplasmic shuttling are critical for the proper function of RNF186 in NAFLD. Additionally, the expression of RNF186 and HMGB1 in human NAFLD samples, along with factors related to lipophagy, suggest that RNF186 may play a similar role in the pathogenesis of human fatty liver.

CONCLUSION

RNF186 deficiency accelerates hepatic lipophagy in NAFLD through the inhibition of ubiquitination and degradation of cytoplasmic HMGB1. Consequently, targeting the RNF186-HMGB1 axis may offer a promising strategy for the prevention and treatment of NAFLD.