Lipophagy and epigenetic alterations are related to metabolic dysfunction-associated steatotic liver disease progression in an experimental model

BACKGROUND Genetic and epigenetic alterations are related to metabolic dysfunction-associated steatotic liver disease(MASLD)pathogenesis.AIM To evaluate micro(mi)RNAs and lipophagy markers in an experimental model of metabolic dysfunction-associated steatohepatitis(MASH).METHODS Adult male Sprague Dawley rats were randomized into two groups:Control group(n=10)fed a standard diet;and intervention group(n=10)fed a high-fat-choline-deficient diet for 16 weeks.Molecular evaluation of li-pophagy markers in liver tissue[sirtuin-1,p62/sequestosome-1,transcription factor-EB,perilipin-2(Plin2),Plin3,Plin5,lysosome-associated membrane proteins-2,rubicon,and Cd36],and serum miRNAs were performed.RESULTS Animals in the intervention group developed MASH and showed a significant decrease in sirtuin-1(P=0.020)and p62/sequestosome-1(P<0.001);the opposite was reported for transcription factor-EB(P=0.020),Plin2(P=0.003),Plin3(P=0.031),and Plin5(P=0.005)compared to the control group.There was no significant difference between groups for lysosome-associated membrane proteins-2(P=0.715),rubicon(P=0.166),and Cd36(P=0.312).The intervention group showed a significant increase in miR-34a(P=0.005)and miR-21(P=0.043)compared to the control.There was no significant difference between groups for miR-375(P=0.905),miR-26b(P=0.698),and miR-155(P=0.688).CONCLUSION Animals with MASH presented expression changes in markers related to lysosomal stress and autophagy as well as in miRNAs related to inflammation and fibrogenesis,processes that promote MASLD progression.

Fibroblast growth factor 21(FGF21) attenuates tacrolimus-induced hepatic lipid accumulation through transcription factor EB(TFEB)-regulated lipophagy

Tacrolimus(TAC),also called FK506,is one of the classical immunosuppressants to prevent allograft rejection after liver transplantation.However,it has been proved to be associated with post-transplant hyperlipemia.The mechanism behind this is unknown,and it is urgent to explore preventive strategies for hyperlipemia after transplantation.Therefore,we established a hyperlipemia mouse model to investigate the mechanism,by injecting TAC intraperitoneally for eight weeks.After TAC treatment,the mice developed hyperlipemia(manifested as elevated triglyceride(TG)and low-density lipoprotein cholesterol(LDL-c),as well as decreased high-density lipoprotein cholesterol(HDL-c)).Accumulation of lipid droplets was observed in the liver.In addition to lipid accumulation,TAC induced inhibition of the autophagy-lysosome pathway(microtubule-associated protein 1light chain 3β(LC3B)II/I and LC3B II/actin ratios,transcription factor EB(TFEB),protein 62(P62),and lysosomal-associated membrane protein 1(LAMP1))and downregulation of fibroblast growth factor 21(FGF21)in vivo.Overexpression of FGF21may reverse TAC-induced TG accumulation.In this mouse model,the recombinant FGF21 protein ameliorated hepatic lipid accumulation and hyperlipemia through repair of the autophagy-lysosome pathway.We conclude that TAC downregulates FGF21and thus exacerbates lipid accumulation by impairing the autophagy-lysosome pathway.Recombinant FGF21 protein treatment could therefore reverse TAC-caused lipid accumulation and hypertriglyceridemia by enhancing autophagy.

ORP8 acts as a lipophagy receptor to mediate lipid droplet turnover

Lipophagy,the selective engulfment of lipid droplets(LDs)by autophagosomes for lysosomal degradation,is critical to lipid and energy homeostasis.Here we show that the lipid transfer protein ORP8 is located on LDs and mediates the encapsulation of LDs by autophagosomal membranes.This function of oRP8 is independent of its lipid transporter activity and is achieved through direct interaction with phagophore-anchored LC3/GABARAPs.Upon lipophagy induction,ORP8 has increased localization on LDs and is phosphorylated by AMPK,thereby enhancing its affinity for LC3/GABARAPs.Deletion of ORP8 or interruption of ORP8-LC3/GABARAP interaction results in accumulation of LDs and increased intracellular triglyceride.Overexpression of ORP8 alleviates LD and triglyceride deposition in the liver of ob/ob mice,and Osbpl8 mice exhibit liver lipid clearance defects.Our results suggest that ORP8 is a lipophagy receptor that plays a key role in cellular lipid metabolism.

Selenium reduces hepatopancreas lipid accumulation of grass carp(Ctenopharyngodon idella)fed high-fat diet via lipophagy activation

It has been reported that selenium(Se)can reduce hepatopancreas lipid accumulation induced by highfat diet.However,its mechanism is still unknown.This study aims to investigate the specific mechanisms by which Se alleviates high-fat diet-induced lipid accumulation.Grass carp were fed control diet(4.8%lipid,Con),high-fat diet(8.8%lipid,HFD)or HFD supplemented with 0.3 mg/kg nano-Se(HSe0.3)for 10weeks.Growth performance,Se deposition,lipid accumulation,hepatic ultrastructure,and gene and protein expression levels associated with autophagy were examined.Furthermore,oleic acid(OA)was used to incubate the grass carp hepatocytes(L8824)for 24 h,and then the L8824 were incubated with sodium selenite in presence or absence of an autophagy inhibitor for 24 h.L8824 was analyzed for triglyceride concentration,immunofluorescence,and gene and protein expression levels associated with autophagy.We found that dietary nano-Se improved the growth of fish fed HFD and also decreased hepatosomatic index and intraperitoneal fat ratio of fish fed HFD(P<0.05).HFD significantly increased hepatopancreas lipid accumulation and decreased autophagic activity(P<0.05).Treatment of grass carp fed HFD with nano-Se decreased lipid accumulation and restored hepatic autophagy(P<0.05).In vitro,Se(100μM sodium selenite)obviously activated autophagy in L8824 incubated with OA,and consequently reduced the lipid accumulation induced by OA(P<0.05).Furthermore,using pharmacological inhibition(chloroquine)of the autophagy greatly diminished the beneficial effects of Se on alleviating OA-induced lipid accumulation and increased the co-localization of lipid droplets with autophagosome(P<0.05),which indicated that Se increased autophagic flux.In conclusion,these results suggest that Se alleviates HFD-induced hepatopancreas lipid accumulation by activating lipophagy.

Light-up lipid droplets for the visualization of lipophagy and atherosclerosis by coumarin-derived bioprobe

Lipid droplets(LDs) are intracellular lipid-metabolism organelles that involved in many physiological processes,metabolic disorders as well as diseases such as atherosclerosis.However,the specific probes that can visually locate abnormal LDs-rich tissues and track LDs-associated behavior to the naked eye with adequate biosafety still are rare.Herein,we develop a new design strategy of LDs-targeted probe based on the solvatochromism of coumarin derivatives.The results revealed that the emission wavelength of coumarin fluorophores gradually red shift in different solvents with increasing polarity,while absorption wavelength almost unchanged.As a result,the enlarged stokes shift of coumarin was emerged from oil to water.Furthermore,properly reducing water solubility and adding electronic donor at the structure of coumarins can enlarge this type of solvatochromism.This discovery was utilized to develop suitable probe for the image of LDs and LDs-rich tissues with high resolution and biosafety.Therefore,LDs-associated behavior was visible to the naked eye during the process of lipophagy and atherosclerosis.We deem that the developed probe here offers a new possibility to accurately diagnosis and analyse LDs-related diseases in clinic and preclinical study.

Suppression of hepatic steatosis in non-alcoholic steatohepatitis model by modified Xiaoyao San formula:Evidence,mechanisms and perspective

In this letter,we comment on a recent publication by Mei et al,in the World Journal of Hepatology,investigating the hepatoprotective effects of the modified Xiaoyao San(MXS)formula in a male rat model of non-alcoholic steatohepatitis(NASH).The authors found that MXS treatment mitigated hepatic steatosis and inflam-mation in the NASH model,as evidenced by the reduction in lipid droplets(LDs),fibrosis markers and lipogenic factors.Interestingly,these hepatoprotective effects were associated with androgen upregulation(based on metabolomics analysis of male steroid hormone metabolites),adenosine 5’-monophosphate-activated protein kinase(AMPK)activation,and restoration of phosphatase and tensin homolog(PTEN)expression.However,the authors did not clearly discuss the relationships between MXS-induced hepatic steatosis reduction in the NASH model,and androgen upregulation,AMPK activation,and restoration of PTEN expression.This editorial emphasizes the reported mechanisms and explains how they act or interact with each other to reduce hepatic steatosis and inflammation in the NASH model.As a perspective,we propose additional mechanisms(such as autophagy/lipophagy activation in hepatocytes)for the clearance of LDs and suppression of hepatic steatosis by MXS in the NASH model.A proper understanding of the mechanisms of MXS-induced reduction of hepatic steatosis might help in the treatment of NASH and related diseases.

Role of autophagy in the pathophysiology of nonalcoholic fatty liver disease:A controversial issue

Autophagy is a mechanism involved in cellular homeostasis under basal and stressed conditions delivering cytoplasmic content to the lysosomes for degradation to macronutrients.The potential role of autophagy in disease is increasingly recognised and investigated in the last decade.Nowadays it is commonly accepted that autophagy plays a role in the hepatic lipid metabolism.Hence,dysfunction of autophagy may be an underlying cause of non-alcoholic fatty liver disease.However,controversy of the exact role of autophagy in the lipid metabolism exists:some publications report a lipolytic function of autophagy,whereas others claim a lipogenic function.This review aims to give an update of the present knowledge on autophagy in the hepatic lipid metabolism,hepatic insulin resistance,steatohepatitis and hepatic fibrogenesis.

Autophagy in liver diseases

Autophagy is the liver cell energy recycling system regulating a variety of homeostatic mechanisms.Damaged organelles,lipids and proteins are degraded in the lysosomes and their elements are re-used by the cell.Investigations on autophagy have led to the award of two Nobel Prizes and a health of important reports.In this review we describe the fundamental functions of autophagy in the liver including new data on the regulation of autophagy.Moreover we emphasize the fact that autophagy acts like a two edge sword in many occasions with the most prominent paradigm being its involvement in the initiation and progress of hepatocellular carcinoma.We also focused to the implication of autophagy and its specialized forms of lipophagy and mitophagy in the pathogenesis of various liver diseases.We analyzed autophagy not only in well studied diseases,like alcoholic and nonalcoholic fatty liver and liver fibrosis but also in viral hepatitis,biliary diseases,autoimmune hepatitis and rare diseases including inherited metabolic diseases and also acetaminophene hepatotoxicity.We also stressed the different consequences that activation or impairment of autophagy may have in hepatocytes as opposed to Kupffer cells,sinusoidal endothelial cells or hepatic stellate cells.Finally,we analyzed the limited clinical data compared to the extensive experimental evidence and the possible future therapeutic interventions based on autophagy manipulation.

Role of autophagy in liver physiology and pathophysiology

Autophagy is a highly conserved intracellular degradation pathway by which bulk cytoplasm and superfluous or damaged organelles are enveloped by double membrane structures termed autophagosomes. The autophago-somes then fuse with lysosomes for degradation of their contents, and the resulting amino acids can then recycle back to the cytosol. Autophagy is normally activated in response to nutrient deprivation and other stressors and occurs in all eukaryotes. In addition to maintaining energy and nutrient balance in the liver, it is now clear that autophagy plays a role in liver protein aggregates related diseases, hepatocyte cell death, steatohepatitis, hepatitis virus infection and hepatocellular carcinoma. In this review, I discuss the recent findings of autophagy with a focus on its role in liver pathophysiology.

Ethanol-induced hepatic autophagy: Friend or foe?

Excessive alcohol intake may induce hepatic apoptosis, steatosis, fibrosis, cirrhosis and even cancer. Ethanolinduced activation of general or selective autophagy as mitophagy or lipophagy in hepatocytes is generally considered a prosurvival mechanism. On the other side of the coin, upregulation of autophagy in nonhepatocytes as stellate cells may stimulate fibrogenesis and subsequently induce detrimental effects on the liver. The autophagic response of other non-hepatocytes as macrophages and endothelial cells is unknown yet and needs to be investigated as these cells play important roles in ethanol-induced hepatic steatosis and damage. Selective pharmacological stimulation of autophagy in hepatocytes may be of therapeutic importance in alcoholic liver disease.

Complex role of autophagy in regulation of hepatic lipid andlipoprotein metabolism

Discovering new therapeutic interventions to treat lipid and lipoprotein disorders is of great interest and the discovery of autophagy as a regulator of lipid metabolism has opened up new avenues for targeting modulators of this pathway. Autophagy is a degradative process that targets cellular components to the lysosome and recent studies have indicated a role for autophagy in regulating hepatic lipid metabolism(known as lipophagy) as well as lipoprotein assembly. Autophagy directly targets apolipoprotein B-100(apoB100), the structural protein component of very lowdensity lipoproteins(VLDLs), and further targets lipid droplets(LDs), the cellular storage for neutral lipids.Autophagy thus plays a complex and dual role in VLDL particle assembly by regulating apoB 100 degradation as well as aiding the maturation of VLDL particles by hydrolyzing lipid from LDs. The purpose of this article is to review our current understanding of molecular and cellular mechanisms mediating authophagic control of hepatic lipid biogenesis and VLDL production as well as dysregulation in insulin resistance and dyslipidemia.

mTORC1 signaling in hepatic lipid metabolism

The mechanistic target of rapamycin （mTOR） signaling pathway regulates many metabolic and physiological processes in different organs or tissues. DysregulaUon of mTOR signaling has been implicated in many human diseases including obesity, diabetes, cancer, fatty liver diseases, and neuronal disorders. Here we review recent progress in understanding how mTORC1 （mTOR complex 1） signaling regulates lipid metabolism in the liver.

Roles of organelle-specific autophagy in hepatocytes in the development and treatment of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease(NAFLD)is a disorder of lipid metabolism.The lipotoxic intermediates of lipid metabolism cause mitochondrial dysfunction and endoplasmic reticulum stress.Organelle-specific autophagy is responsible for the removal of dysfunctional organelles to maintain intracellular homeostasis.Lipophagy contributes to lipid turnover by degrading lipid droplets.The level of autophagy changes during the course of NAFLD,and the activation of hepatocyte autophagy might represent a method of treating NAFLD.