Integrated Action of Autophagy and Adipose Tissue Triglyceride Lipase Ameliorates Diet-Induced Hepatic Steatosis in Liver-Specific PLIN2 Knockout Mice

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.

Effect of Rab18 on liver injury and lipid accumulation by regulating perilipin 2 and peroxisome proliferator-activated receptor gamma in non-alcoholic fatty liver disease

BACKGROUND AND AIM

Nonalcoholic fatty liver disease (NAFLD) is currently one of the most common chronic liver diseases worldwide, characterized by the presence of lipid droplets. Rab18 is an important lipid droplet protein; however, its effects and mechanisms of action on NAFLD remain unclear.

METHODS

Free fatty acid-stimulated AML-12 cells and high-fat diet (HFD)-fed mice were used as NAFLD models. Lentiviruses overexpressing Rab18 (Rab18-OE) or knockdown (Rab18-KD) were used to generate stable cell lines for genetic analysis. Blood serum levels of alanine aminotransferase, aspartate aminotransferase, total cholesterol, triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, glucose, and leptin were measured using a biochemical autoanalyzer. Hematoxylin and eosin staining was performed to detect pathological damage to the liver. Lipid accumulation in the cells was assessed by Oil Red O staining. Target expression was measured using qPCR, western blotting, and immunocytochemistry.

RESULTS

Rab18 mRNA and protein expression levels increased in free fatty acid-stimulated AML-12 cells and the livers of HFD-fed mice. Rab18-OE increased lipid accumulation in vitro, which was attenuated by Rab18-KD. In vivo, Rab18-OE augmented liver pathological damage, serum alanine aminotransferase/aspartate aminotransferase activity, and triglyceride, total cholesterol, and low-density lipoprotein levels, whereas Rab18-KD decreased these indicators. Rab18-KD also downregulated blood glucose levels in HFD-fed mice. Mechanistically, Rab18-OE and Rab18-KD regulated the mRNA and protein expression levels of perilipin 2 (PLIN2) and peroxisome proliferator-activated receptor gamma (PPARγ) in vitro and in vivo, respectively. Immunocytochemistry revealed that Rab18 colocalized with PLIN2 and PPARγ in AML-12 cells.

CONCLUSION

Rab18 expression was elevated in vitro and in vivo in the NAFLD mouse model. Rab18 regulates PLIN2 and PPARγ expression to exaggerate liver injury and lipid accumulation in patients with NAFLD. Thus, Rab18 may be a crucial protein in this disease and a potential therapeutic target.

Intestinal Acyl-CoA synthetase 5 (ACSL5) deficiency potentiates postprandial GLP-1 & PYY secretion, reduces food intake, and protects against diet-induced obesity

OBJECTIVE

In the small intestine, the products of digestion of dietary triacylglycerol (TAG), fatty acids (FA) and monoacylglycerol, are taken up by absorptive cells, enterocytes, for systemic energy delivery. These digestion products can also bind receptors on endocrine cells to stimulate the release of hormones capable of influencing systemic energy metabolism. The initial phase of intestinal FA absorption involves the acylation of FAs to acyl-CoA by the acyl-CoA long chain synthetase (ACSL) enzymes. ACSL5 is abundantly expressed in the small intestinal epithelium where it is the major ACSL isoform, contributing approximately 80% of total ACSL activity. In mice with whole body deficiency of ACSL5, the rate of dietary fat absorption is reduced and energy expenditure is increased. However, the mechanisms by which intestinal ACSL5 contributes to intestinal FA metabolism, enteroendocrine signaling, and regulation of energy expenditure remain undefined. Here, we test the hypothesis that intestinal ACSL5 regulates energy metabolism by influencing dietary fat absorption and enteroendocrine signaling.

METHODS

To explore the role of intestinal ACSL5 in energy balance and intestinal dietary fat absorption, a novel mouse model of intestine specific ACSL5 deficiency (ACSL5IKO) was generated by breeding ACSL5 floxed (ACSL5loxP/loxP) to mice harboring the tamoxifen inducible, villin-Cre recombinase. ACSL5IKO and control, ACSL5loxP/loxP mice were fed chow (low in fat) or a 60% high fat diet (HFD), and metabolic phenotyping was performed including, body weight, body composition, insulin and glucose tolerance tests, energy expenditure, physical activity, and food intake studies. Pair-feeding studies were performed to determine the role of food intake in regulating development of obesity. Studies of dietary fat absorption, fecal lipid excretion, intestinal mucosal FA content, and circulating levels of glucagon like peptide 1 (GLP-1) and peptide YY (PYY) in response to a TAG challenge were performed. Treatment with a GLP-1 receptor antagonist was performed to determine the contribution of GLP-1 to acute regulation of food intake.

RESULTS

We found that ACSL5IKO mice experienced rapid and sustained protection from body weight and fat mass accumulation during HFD feeding. While intestine specific deficiency of ACSL5 delayed gastric emptying and reduced dietary fat secretion, it did not result in increased excretion of dietary lipid in feces. Energy expenditure and physical activity were not increased in ACSL5IKO mice. Mice deficient in intestinal ACSL5 display significantly reduced energy intake during HFD, but not chow feeding. When HFD intake of control mice was matched to ACSL5IKO during pair-feeding studies, no differences in body weight or fat mass gain were observed between groups. Postprandial GLP-1 and PYY were significantly elevated in ACSL5IKO mice secondary to increased FA content in the distal small intestine. Blockade of GLP-1 signaling by administration of a long-acting GLP-1 receptor antagonist partially restored HFD intake of ACSL5IKO.

CONCLUSIONS

These data indicate that intestinal ACSL5 serves as a critical regulator of energy balance, protecting mice from diet-induced obesity exclusively by increasing satiety and reducing food intake during HFD feeding. The reduction in food intake observed in ACSL5IKO mice is driven, in part, by increased postprandial GLP-1 and PYY secretion. These effects are only observed during HFD feeding, suggesting that altered processing of dietary fat following intestinal ACSL5 ablation contributes to GLP-1 and PYY mediated increases in satiety.

Exploring the role of genetic variations in NAFLD: implications for disease pathogenesis and precision medicine approaches

Non-alcoholic fatty liver disease (NAFLD) is one of the leading causes of chronic liver diseases, affecting more than one-quarter of people worldwide. Hepatic steatosis can progress to more severe forms of NAFLD, including NASH and cirrhosis. It also may develop secondary diseases such as diabetes and cardiovascular disease. Genetic and environmental factors regulate NAFLD incidence and progression, making it a complex disease. The contribution of various environmental risk factors, such as type 2 diabetes, obesity, hyperlipidemia, diet, and sedentary lifestyle, to the exacerbation of liver injury is highly understood. Nevertheless, the underlying mechanisms of genetic variations in the NAFLD occurrence or its deterioration still need to be clarified. Hence, understanding the genetic susceptibility to NAFLD is essential for controlling the course of the disease. The current review discusses genetics' role in the pathological pathways of NAFLD, including lipid and glucose metabolism, insulin resistance, cellular stresses, and immune responses. Additionally, it explains the role of the genetic components in the induction and progression of NAFLD in lean individuals. Finally, it highlights the utility of genetic knowledge in precision medicine for the early diagnosis and treatment of NAFLD patients.

Dysfunction of autophagy in high-fat diet-induced non-alcoholic fatty liver disease

ABBREVIATIONS

ACOX1: acyl-CoA oxidase 1; ADH5: alcohol dehydrogenase 5 (class III), chi polypeptide; ADIPOQ: adiponectin, C1Q and collagen domain containing; ATG: autophagy related; BECN1: beclin 1; CRTC2: CREB regulated transcription coactivator 2; ER: endoplasmic reticulum; F2RL1: F2R like trypsin receptor 1; FA: fatty acid; FOXO1: forkhead box O1; GLP1R: glucagon like peptide 1 receptor; GRK2: G protein-coupled receptor kinase 2; GTPase: guanosine triphosphatase; HFD: high-fat diet; HSCs: hepatic stellate cells; HTRA2: HtrA serine peptidase 2; IRGM: immunity related GTPase M; KD: knockdown; KDM6B: lysine demethylase 6B; KO: knockout; LAMP2: lysosomal associated membrane protein 2; LAP: LC3-associated phagocytosis; LDs: lipid droplets; Li KO: liver-specific knockout; LSECs: liver sinusoidal endothelial cells; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MAP3K5: mitogen-activated protein kinase kinase kinase 5; MED1: mediator complex subunit 1; MTOR: mechanistic target of rapamycin kinase; MTORC1: mechanistic target of rapamycin complex 1; NAFLD: non-alcoholic fatty liver disease; NASH: non-alcoholic steatohepatitis; NFE2L2: NFE2 like bZIP transcription factor 2; NOS3: nitric oxide synthase 3; NR1H3: nuclear receptor subfamily 1 group H member 3; OA: oleic acid; OE: overexpression; OSBPL8: oxysterol binding protein like 8; PA: palmitic acid; RUBCNL: rubicon like autophagy enhancer; PLIN2: perilipin 2; PLIN3: perilipin 3; PPARA: peroxisome proliferator activated receptor alpha; PRKAA2/AMPK: protein kinase AMP-activated catalytic subunit alpha 2; RAB: member RAS oncogene family; RPTOR: regulatory associated protein of MTOR complex 1; SCD: stearoyl-CoA desaturase; SIRT1: sirtuin 1; SIRT3: sirtuin 3; SNARE: soluble N-ethylmaleimide-sensitive factor attachment protein receptor; SQSTM1/p62: sequestosome 1; SREBF1: sterol regulatory element binding transcription factor 1;SREBF2: sterol regulatory element binding transcription factor 2; STING1: stimulator of interferon response cGAMP interactor 1; STX17: syntaxin 17; TAGs: triacylglycerols; TFEB: transcription factor EB; TP53/p53: tumor protein p53; ULK1: unc-51 like autophagy activating kinase 1; VMP1: vacuole membrane protein 1.

Analysis of gene expression changes during lipid droplet formation in HepG2 human liver cancer cells

Fatty liver is a condition of excessive triglyceride accumulation in hepatocytes. Additionally, hepatocytes exhibit a high degree of fat droplet accumulation during excessive alcohol consumption and metabolic syndrome. However, the molecular mechanisms involved in fat droplet formation remain unknown. The present study used an in vitro fatty liver formation model of the human liver cancer cell line, HepG2, to comprehensively search for fat droplet formation-related genes, and which exhibit changes in expression during fat droplet formation. Microarray analysis with extracted total RNA determined the genes that are involved in fat droplet formation and their expression was confirmed using quantitative polymerase chain reaction following the culture of the HepG2 cells in culture medium containing 0, 50, 200 and 500 µM of oleic acid for 24 h. The results revealed 142 genes demonstrating increased expression levels by >2.0-fold with oleic acid treatment and 426 genes demonstrating decreased expression levels. Perilipin 2 (PLIN2) was estimated as the gene most closely associated with fatty liver. Lipid droplet formation in the HepG2 cells induced by oleic acid led to the upregulation of PLIN2 in a concentration-dependent manner. On the whole, the findings of the present study indicate the involvement of genes in oleic acid-induced lipid droplet formation in HepG2 cells; PLIN2 in particular may play a crucial role in this process.

ATG14 plays a critical role in hepatic lipid droplet homeostasis

BACKGROUND & AIMS

Autophagy-related 14 (ATG14) is a key regulator of autophagy. ATG14 is also localized to lipid droplet; however, the function of ATG14 on lipid droplet remains unclear. In this study, we aimed to elucidate the role of ATG14 in lipid droplet homeostasis.

METHODS

ATG14 loss-of-function and gain-of-function in lipid droplet metabolism were analyzed by fluorescence imaging in ATG14 knockdown or overexpression hepatocytes. Specific domains involved in the ATG14 targeting to lipid droplets were analyzed by deletion or site-specific mutagenesis. ATG14-interacting proteins were analyzed by co-immunoprecipitation. The effect of ATG14 on lipolysis was analyzed in human hepatocytes and mouse livers that were deficient in ATG14, comparative gene identification-58 (CGI-58), or both.

RESULTS

Our data show that ATG14 is enriched on lipid droplets in hepatocytes. Mutagenesis analysis reveals that the Barkor/ATG14 autophagosome targeting sequence (BATS) domain of ATG14 is responsible for the ATG14 localization to lipid droplets. Co-immunoprecipitation analysis illustrates that ATG14 interacts with adipose triglyceride lipase (ATGL) and CGI-58. Moreover, ATG14 also enhances the interaction between ATGL and CGI-58. In vitro lipolysis analysis demonstrates that ATG14 deficiency remarkably decreases triglyceride hydrolysis.

CONCLUSIONS

Our data suggest that ATG14 can directly enhance lipid droplet breakdown through interactions with ATGL and CGI-58.

Lipid droplet deposition in the regenerating liver: A promoter, inhibitor, or bystander?

Liver regeneration (LR) is a complex process involving intricate networks of cellular connections, cytokines, and growth factors. During the early stages of LR, hepatocytes accumulate lipids, primarily triacylglycerol, and cholesterol esters, in the lipid droplets. Although it is widely accepted that this phenomenon contributes to LR, the impact of lipid droplet deposition on LR remains a matter of debate. Some studies have suggested that lipid droplet deposition has no effect or may even be detrimental to LR. This review article focuses on transient regeneration-associated steatosis and its relationship with the liver regenerative response.

Parallel CRISPR-Cas9 screens identify mechanisms of PLIN2 and lipid droplet regulation

Despite the key roles of perilipin-2 (PLIN2) in governing lipid droplet (LD) metabolism, the mechanisms that regulate PLIN2 levels remain incompletely understood. Here, we leverage a set of genome-edited human PLIN2 reporter cell lines in a series of CRISPR-Cas9 loss-of-function screens, identifying genetic modifiers that influence PLIN2 expression and post-translational stability under different metabolic conditions and in different cell types. These regulators include canonical genes that control lipid metabolism as well as genes involved in ubiquitination, transcription, and mitochondrial function. We further demonstrate a role for the E3 ligase MARCH6 in regulating triacylglycerol biosynthesis, thereby influencing LD abundance and PLIN2 stability. Finally, our CRISPR screens and several published screens provide the foundation for CRISPRlipid (http://crisprlipid.org), an online data commons for lipid-related functional genomics data. Our study identifies mechanisms of PLIN2 and LD regulation and provides an extensive resource for the exploration of LD biology and lipid metabolism.

Cardiac lipid metabolism, mitochondrial function, and heart failure

A fine balance between uptake, storage, and the use of high energy fuels, like lipids, is crucial in the homeostasis of different metabolic tissues. Nowhere is this balance more important and more precarious than in the heart. This highly energy-demanding muscle normally oxidizes almost all the available substrates to generate energy, with fatty acids being the preferred source under physiological conditions. In patients with cardiomyopathies and heart failure, changes in the main energetic substrate are observed; these hearts often prefer to utilize glucose rather than oxidizing fatty acids. An imbalance between uptake and oxidation of fatty acid can result in cellular lipid accumulation and cytotoxicity. In this review, we will focus on the sources and uptake pathways used to direct fatty acids to cardiomyocytes. We will then discuss the intracellular machinery used to either store or oxidize these lipids and explain how disruptions in homeostasis can lead to mitochondrial dysfunction and heart failure. Moreover, we will also discuss the role of cholesterol accumulation in cardiomyocytes. Our discussion will attempt to weave in vitro experiments and in vivo data from mice and humans and use several human diseases to illustrate metabolism gone haywire as a cause of or accomplice to cardiac dysfunction.

A novel HIF2A mutation causes dyslipidemia and promotes hepatic lipid accumulation

Hypoxia-inducible factor-2α (HIF-2α) is a transcription factor responsible for regulating genes related to angiogenesis and metabolism. This study aims to explore the effect of a previously unreported mutation c.C2473T (p.R825S) in the C-terminal transactivation domain (CTAD) of HIF-2α that we detected in tissue of patients with liver disease. We sequenced available liver and matched blood samples obtained during partial liver resection or liver transplantation performed for clinical indications including hepatocellular carcinoma and liver failure. In tandem, we constructed cell lines and a transgenic mouse model bearing the corresponding identified mutation in HIF-2α from which we extracted primary hepatocytes. Lipid accumulation was evaluated in these cells and liver tissue from the mouse model using Oil Red O staining and biochemical measurements. We identified a mutation in the CTAD of HIF-2α (c.C2473T; p.R825S) in 5 of 356 liver samples obtained from patients with hepatopathy and dyslipidemia. We found that introduction of this mutation into the mouse model led to an elevated triglyceride level, lipid droplet accumulation in liver of the mutant mice and in their extracted primary hepatocytes, and increased transcription of genes related to hepatic fatty acid transport and synthesis in the mutant compared to the control groups. In mutant mice and cells, the protein levels of nuclear HIF-2α and its target perilipin-2 (PLIN2), a lipid droplet-related gene, were also elevated. Decreased lipophagy was observed in mutant groups. Our study defines a subpopulation of dyslipidemia that is caused by this HIF-2α mutation. This may have implications for personalized treatment.

Aflatoxin B1 exposure triggers hepatic lipotoxicity via p53 and perilipin 2 interaction-mediated mitochondria-lipid droplet contacts: An in vitro and in vivo assessment

Aflatoxin B1 (AFB1) is one of the most toxic mycotoxins widely found in food contaminants, and its target organ is the liver. It poses a major food security and public health threat worldwide. However, the lipotoxicity mechanism of AFB1 exposure-induced liver injury remains unclear and requires further elucidation. Herein, we investigated the potential hepatic lipotoxicity of AFB1 exposure using in vitro and in vivo models to assess the public health hazards of high dietary AFB1 exposure. We demonstrated that low-dose of AFB1 (1.25 μM for 48 h, about one-fifth of the IC50 in HepG2 and HepaRG cells, IC50 are 5.995 μM and 5.266 μM, respectively) exposure significantly induced hepatic lipotoxicity, including abnormal lipid droplets (LDs) growth, mitochondria-LDs contacts increase, lipophagy disruption, and lipid accumulation. Mechanistically, we showed that AFB1 exposure promoted the mitochondrial p53 (mito-p53) and LDs-associated protein perilipin 2 (PLIN2) interaction-mediated mitochondria-LDs contacts, resulting in lipid accumulation in hepatocytes. Mito-p53-targeted inhibition, knockdown of PLIN2, and rapamycin application efficiently promoted the lysosome-dependent lipophagy and alleviated the hepatic lipotoxicity and liver injury induced by AFB1 exposure. Overall, our study found that mito-p53 and PLIN2 interaction mediates three organelles-mitochondria, LDs, and lysosomal networks to regulate lipid homeostasis in AFB1 exposure-induced hepatotoxicity, revealing how this unique trio of organelles works together and provides a novel insight into the targeted intervention in inter-organelle lipid sensing and trafficking for alleviating hazardous materials-induced hepatic lipotoxicity.

Hepatic Nampt Deficiency Aggravates Dyslipidemia and Fatty Liver in High Fat Diet Fed Mice

Nicotinamide phosphoribosyltransferase (Nampt) is the rate-limiting enzyme in the salvage pathway of nicotinamide adenine dinucleotide (NAD) biosynthesis. Thus far, hepatic Nampt has not been extensively explored in terms of its effects on serum lipid stability and liver lipids metabolism. In this study, hepatocyte-specific Nampt knockout (HC-Nampt^-/-) mice were generated by Cre/loxP system. Nampt mRNA expression was reduced in the liver, but not in other tissues, in HC-Nampt^-/- mice compared with wild-type (WT) mice. Hepatic Nampt deficiency had no effect on body weight and fasting blood glucose, and it did not induce atherosclerosis in mice under both normal chow diet (NCD) and high fat diet (HFD). At baseline state under NCD, hepatic Nampt deficiency also did not affect liver weight, liver function index, including alanine aminotransferase, aspartate aminotransferase, albumin and alkaline phosphatase, and serum levels of lipids, including triglycerides (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and non-esterified fatty acids (NEFA). However, under HFD, deficiency of hepatic Nampt resulted in increased liver weight, liver function index, and serum levels of TG, TC, HDL-C, and NEFA. Meanwhile, histopathological examination showed increased fat accumulation and fibrosis in the liver of HC-Nampt^-/- mice compared with WT mice. Taken together, our results show that hepatic Nampt deficiency aggravates dyslipidemia and liver damage in HFD fed mice. Hepatocyte Nampt can be a protective target against dyslipidemia and fatty liver.

Association analysis of PLIN2 gene polymorphisms and lambing performance in Qianbei Ma goats

Qianbei Ma goats are one of the three most valued local goat breeds in Guizhou, China; furthermore, it has lower litter size performance. The purpose of this study was to explore the correlation between SNP (single-nucleotide polymorphisms) of PLIN2 gene and lambing performance. The bioinformatics analysis, DNA sequencing, RT-qPCR and correlation analysis methods were used to analyse the evolutionary relationship of PLIN2 protein in 13 species, to detect the expression pattern of PLIN2 gene in the gonad axis of Qianbei sheep, to explore the dominant genotype of PLIN2 related to lambing traits and to screen molecular markers related to lambing performance to guide the breeding of Qianbei Ma goats. Results showed that the Qianbei Ma goat PLIN2 protein had the closest genetic relationship with sheep and the furthest from mice, there were significant or extremely significant differences in the expression levels of the PLIN2 gene in the gonadal axis of the mothers of single- and multi-lamb groups. Compared with the reference sequence, four SNPs were found, which were g.1006 C → A and g.1171 A → G in the first and second intron regions of the PLIN2 gene, g.8514 C → T in the exon 8 region and g.9122 A → T in the 3'UTR. The correlation analysis showed that g.1006 C → A, g.8514 C → T and g.9122 A → T had significant indigenous effects on the lambing performance of Qianbei Ma goats (p < .05). The number of third births for diploid H2H5 was significantly higher than that of diploid H1H2, and the number of first to third births for diploid H2H5 was large and stable. The results showed that PLIN2 gene could be used as a candidate gene related to lambing traits of Qianbei Ma goat.

Editorial: Highlights in Autophagy-From Basic Mechanisms to Human Disorder Treatments

Autophagy is an evolutionarily conserved catabolic process and represents a field of research that is constantly growing [...].

Biochanin A ameliorated oleate-induced steatosis in HepG2 cells by activating the SIRT3/AMPK/ULK-1 signaling pathway

Biochanin A (Bio-A), an isoflavone abundant in chickpeas, possesses hypoglycemic, hypolipidemic, and anti-inflammatory effects. However, whether Bio-A has antihepatosteatosis effect remains unclear. This study aimed to evaluate the antihepatosteatosis effect of Bio-A on oleate (OA)-treated hepatocytes, and explore the underlying mechanism. When incubated with OA for 24 h, HepG2 cells were treated with various concentrations of Bio-A for 24 h to obtain an optimal antihepatosteatosis dose. HepG2 cells were treated with the AMP-activated protein kinase (AMPK) inhibitor Compound C, or the sirtuin-3 (SIRT3) inhibitor 3-TYP, and incubated with 50 μM Bio-A. The results indicated that 12.6% of lipid content, particularly 11.0% of triglyceride content, and the expression of adipocyte differentiation-related protein were significantly decreased in Bio-A-treated hepatosteatosis cells, followed by an increase in the expression of Beclin 1, phosphorylation of Unc-51-like kinase 1 (ULK-1), the microtubule-associated protein 1 light chain 3 (LC3)-II/LC3-I ratio, and a decrease in expression of p62. The results indicated that Bio-A upregulated autophagosome formation and autophagy flux. In addition, Bio-A increased SIRT3 expression and AMPK phosphorylation in OA-treated HepG2 cells. Blockade of AMPK and SIRT3 blocked the antihepatosteatosis effect and ULK-1 activation by Bio-A. AMPK inhibition did not eliminate the activation of SIRT3 by Bio-A. AutoDock analysis demonstrated that interaction might exist between Bio-A and SIRT3. In conclusion, Bio-A reduced fat accumulation in OA-treated HepG2 cells by activating SIRT3/AMPK/ULK-1-mediated autophagy. The findings provide a theoretical basis for the effect of Bio-A on hepatic steatosis-related diseases. PRACTICAL APPLICATIONS: This study highlights the antihepatosteatosis effects of biochanin A (Bio-A) on oleate (OA)-treated hepatocytes. Bio-A, one of the isoflavones in Cicer arietinum Linn., possesses multiple bioactivities such as antiobesity, anti-inflammation, and hypoglycemic and hypolipidemic effects. This study provides a new application of Bio-A to treat hepatic steatosis, and revealed the underlying mechanism of Bio-A involved in the activation of the SIRT3/AMPK/ULK-1-mediated autophagy. The findings provide a theoretical basis for the application of Bio-A to hepatic steatosis-related diseases.

The effect of aerobic exercise on the lipophagy of adipose tissue in obese male mice

This article explores the obesity state and the changes in the level of lipophagy in adipose tissue after exercise to lose weight, so as to provide direction and basis for theoretical research on obesity prevention and control. We established a high-fat diet model of obese mice, and applied exercise intervention and intraperitoneal injection of chloroquine to inhibit autophagy. Long-term high-fat diet can cause obesity in mice, and the process of lipophagy is inhibited, which may be one of the reasons for fat accumulation. Eight weeks of aerobic exercise can effectively reduce the weight of obese mice and promote lipolysis; this process is mainly completed by lipase decomposition, in addition to require the participation of the lipophagy process.

Perilipins at a glance

Lipid droplets (LDs) are ubiquitous organelles that store and supply lipids for energy metabolism, membrane synthesis and production of lipid-derived signaling molecules. While compositional differences in the phospholipid monolayer or neutral lipid core of LDs impact their metabolism and function, the proteome of LDs has emerged as a major influencer in all aspects of LD biology. The perilipins (PLINs) are the most studied and abundant proteins residing on the LD surface. This Cell Science at a Glance and the accompanying poster summarize our current knowledge of the common and unique features of the mammalian PLIN family of proteins, the mechanisms through which they affect cell metabolism and signaling, and their links to disease.

ITCH E3 Ubiquitin Ligase downregulation compromises hepatic degradation of branched-chain amino acids

Objective

Metabolic syndrome, obesity, and steatosis are characterized by a range of dysregulations including defects in ubiquitin ligase tagging proteins for degradation. The identification of novel hepatic genes associated with fatty liver disease and metabolic dysregulation may be relevant to unravelling new mechanisms involved in liver disease progression

Methods

Through integrative analysis of liver transcriptomic and metabolomic obtained from obese subjects with steatosis, we identified itchy E ubiquitin protein ligase (ITCH) as a gene downregulated in human hepatic tissue in relation to steatosis grade. Wild-type or ITCH knockout mouse models of non-alcoholic fatty liver disease (NAFLD) and obesity-related hepatocellular carcinoma were analyzed to dissect the causal role of ITCH in steatosis

Results

We show that ITCH regulation of branched-chain amino acids (BCAAs) degradation enzymes is impaired in obese women with grade 3 compared with grade 0 steatosis, and that ITCH acts as a gatekeeper whose loss results in elevation of circulating BCAAs associated with hepatic steatosis. When ITCH expression was specifically restored in the liver of ITCH knockout mice, ACADSB mRNA and protein are restored, and BCAA levels are normalized both in liver and plasma

Conclusions

Our data support a novel functional role for ITCH in the hepatic regulation of BCAA metabolism and suggest that targeting ITCH in a liver-specific manner might help delay the progression of metabolic hepatic diseases and insulin resistance.

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ITCH expression is reduced in liver during NAFLD.

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Transcriptomics analysis of liver in obese women highlighted the interplay between ITCH and genes involved in BCAA degradation.

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Modulation of ITCH in models of metabolic hepatic diseases supported the association between ITCH and BCAA metabolism.

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Targeting ITCH in a liver specific manner might help to delay the progression of metabolic hepatic diseases and insulin resistance.

Macroautophagy and aging: The impact of cellular recycling on health and longevity

Aging is associated with many deleterious changes at the cellular level, including the accumulation of potentially toxic components that can have devastating effects on health. A key protective mechanism to this end is the cellular recycling process called autophagy. During autophagy, damaged or surplus cellular components are delivered to acidic vesicles called lysosomes, that secure degradation and recycling of the components. Numerous links between autophagy and aging exist. Autophagy declines with age, and increasing evidence suggests that this reduction plays important roles in both physiological aging and the development of age-associated disorders. Studies in pharmacologically and genetically manipulated model organisms indicate that defects in autophagy promote age-related diseases, and conversely, that enhancement of autophagy has beneficial effects on both healthspan and lifespan. Here, we review our current understanding of the role of autophagy in different physiological processes and their molecular links with aging and age-related diseases. We also highlight some recent advances in the field that could accelerate the development of autophagy-based therapeutic interventions.