Autophagy, Metabolism, and Alcohol-Related Liver Disease: Novel Modulators and Functions

Dendrobium nobile Lindl. alkaloids protect CCl4-induced acute liver injury via upregulating LAMP1 expression and activating autophagy flux

Dendrobium nobile Lindl. alkaloids (DNLA) are considered important active ingredients of Dendrobium, which have a variety of pharmacological functions. Recent studies indicate that DNLA has beneficial activity in acute liver injury. However, the specific mechanism by which DNLA produces liver protective effects is stills unclear. This study was designed to determine whether regulation of autophagy is involved in the mode of action of DNLA in liver protection. Using CCl4-induced acute liver injury (ALI) and cell culture models, the molecular mechanism of DNLA-mediated autophagy regulation was studied. The results showed that DNLA significantly improved CCl4-induced liver damage and oxidative stress, which was confirmed in AML-12 cells. DNLA promoted autophagy in cells treated with CCl4, manifested by reduced protein expressions of p62 and LC3-II. Fluorescence imaging showed a decrease in the number of autophagosomes in AML-12 cells transfected with mCherry-GFP-LC3B. In addition, DNLA inhibited lysosomal membrane permeabilization by upregulating lysosomal associated membrane protein-1 (LAMP1), thereby promoting autophagy, preventing CCl4-induced mitochondrial dysfunction, and reducing the production of mitochondrial reactive oxygen species (ROS). While pretreatment of cells with lysosomal inhibitor chloroquine weakened mitochondrial protection elicited by DNLA, overexpression of mitochondrial-targeted SOD2 in AML-12 cells significantly blocked CCl4 induced downregulation of LAMP1, thereby improving lysosome integrity and promoting lysosome dependent autophagy, suggesting that there may exist a bidirectional regulation between mitochondrial ROS and lysosome-autophagy activation. Collectively, these results demonstrated that DNLA can protect the liver injury mediated by dysregulation of lysosome-autophagy process through promoting ROS-lysosome-autophagy axis and improving mitochondrial damage.

The role of macroautophagy in substance use disorders

Macroautophagy, a universal cellular process, sends cellular material to lysosomes for breakdown and is often activated by stressors like hypoxia or drug exposure. It is vital for protein balance, neurotransmitter release, synaptic function, and neuron survival. The role of macroautophagy in substance use disorders is dual. On one hand, substances like cocaine, methamphetamine, opiates, and alcohol can activate macroautophagy pathways to degrade various neuroinflammatory factors in neuronal cells, providing a protective function. On the other hand, long-term and excessive use of addictive substances can inhibit macroautophagy pathways, obstructing the fusion of autophagosomes with lysosomes and losing the original protective function. This review first summarizes the key proteins and signaling pathways involved in macroautophagy, including mTORC1, AMPK, and endoplasmic reticulum stress, and suggests that the regulation of macroautophagy plays a central role in drug-rewarding behavior and addiction. Second, we focus on the interactions between macroautophagy and neuroinflammation induced by drugs, evaluating the potential of macroautophagy modulators as therapeutic strategies for substance use disorder (SUD), and identifying autophagy-related biomarkers that can be used for early diagnosis and monitoring of treatment response. Our review summarizes the important scientific basis involved in macroautophagy pathways for the development of new therapies for SUD.

LILAR, a novel long noncoding RNA regulating autophagy in the liver tissues of endotoxemic mice through a competing endogenous RNA mechanism

Sepsis is an often-deadly complication of infection that can lead to multiple organ failure. Previous studies have demonstrated that autophagy has a protective effect on liver injury in sepsis. Here, we report a novel long noncoding RNA (lncRNA), named lipopolysaccharide (LPS)-induced liver autophagy regulator (LILAR), which was highly induced in the liver tissues of endotoxemic mice. LILAR deficiency significantly increased the susceptibility of mice to LPS. In contrast, LILAR overexpression rescued the liver injury mediated by LILAR deficiency and increased the survival of LILAR knockout mice with endotoxemia. Autophagy-related protein 13 (Atg13) is a potential downstream target gene of LILAR. LILAR deficiency notably decreased Atg13 expression and suppressed autophagy in the livers of mice challenged with LPS. A reporter gene assay showed that LILAR competitively adsorbed miR-705 to increase the expression of Atg13 in cultured cells, indicating that LILAR participates in the regulation of the autophagy in the liver tissues of endotoxemic mice through a competitive endogenous RNA mechanism. In summary, we identified a novel lncRNA, LILAR, as a hepatic autophagy regulator, which not only promotes our understanding of liver pathophysiology but also provides a potential therapeutic target and/or diagnostic biomarker for liver injury in endotoxemia.

SQSTM1/p62 and Hepatic Mallory-Denk Body Formation in Alcohol-Associated Liver Disease

Sequestosome 1 (SQSTM1/p62; hereafter p62) is an autophagy receptor protein for selective autophagy primarily due to its direct interaction with the microtubule light chain 3 protein that specifically localizes on autophagosome membranes. As a result, impaired autophagy leads to the accumulation of p62. p62 is also a common component of many human liver disease-related cellular inclusion bodies, such as Mallory-Denk bodies, intracytoplasmic hyaline bodies, α1-antitrypsin aggregates, as well as p62 bodies and condensates. p62 also acts as an intracellular signaling hub, and it involves multiple signaling pathways, including nuclear factor erythroid 2-related factor 2, NF-κB, and the mechanistic target of rapamycin, which are critical for oxidative stress, inflammation, cell survival, metabolism, and liver tumorigenesis. This review discusses the recent insights of p62 in protein quality control, including the role of p62 in the formation and degradation of p62 stress granules and protein aggregates as well as regulation of multiple signaling pathways in the pathogenesis of alcohol-associated liver disease.

Autophagy and exosomes coordinately mediate quercetin's protective effects on alcoholic liver disease

Alcoholic liver disease (ALD), a spectrum of liver abnormalities induced by chronic alcohol abuse, continues to be the major cause of life-threatening liver disease in developed countries. Autophagy and exosomes were individually confirmed to be involved in the pathogenesis of ALD. Here, we sought to identify the role of autophagy and exosomes in the liver protective effects of quercetin. We observed decreased hepatic LC3II/LC3I and increased p62 level in ethanol-fed mice, and these changes were alleviated by quercetin. Meanwhile, nanoparticle tracking analysis (NTA) showed elevated serum exosomes numbers in ethanol-fed mice, which was combated by quercetin. Ethanol induced elevated LDH, ALT, and AST in HepG2 supernatant, which was alleviated by cytochalasin D (exosomes uptake inhibitor). Moreover, quercetin reduced ethanol-induced LDH and ALT elevation in vitro, and the effects of quercetin were reversed by Rab27a overexpression (induce exosomes release) or wortmannin treatment (autophagy inhibitor). Transcriptomic analysis supported that quercetin reversed the change of lysosome related genes disturbed by ethanol. Meanwhile, western blot analysis exhibited decreased hepatic expression of LAMP2 and ATPA6V1B2, and active Cathepsin B/Cathepsin B by quercetin treatment, indicating quercetin alleviated lysosome dysfunction in ethanol-fed mice. Baf A treatment or transfection of siTFEB offset quercetin's effects in ethanol-induced LDH and ALT elevation, exosomes release, and autophagy inhibition (LC3II/I and p62 accumulation). Taken together, quercetin coordinately activates autophagy and combats exosomes release by restoring lysosome function, and further mitigates ethanol-induced liver damage.

Deficiency of NLR family member NLRC5 alleviates alcohol induced hepatic injury and steatosis by enhancing autophagy of hepatocytes

Steatosis is regarded as an early response of the liver to excessive alcohol consumption, which ultimately results in alcoholic liver disease (ALD). Hepatocytes are the primary drivers of the pathological process known as hepatic damage and steatosis, which is characterized by significant fat accumulation and an abundance of fat vacuoles. NLRs, a family member of pattern recognition receptors, have recently been found to be crucial in liver disorders. In this study, we examined the possible impact of NLRC5, the largest NLR family member, on alcohol-induced fatty liver development using a gene knock-out mouse model. The mouse liver was severely damaged and developed steatosis as a result of chronic and excessive ethanol use, and this damage was prevented by the lack of NLRC5. Additionally, NLRC5 deletion reversed ethanol's ability to increase the serum concentrations of TG, T-CHO, ALT, and AST. Absence of NLRC5 reduced ethanol-stimulated aberrant expression of the vital regulators of lipid synthesis and metabolism, SREBP-1c, FAS and PPAR-α. Furthermore, loss- and gain-of-function research indicated that NLRC5 might affect the autophagy pathway in alcohol-induced hepatic steatosis progression. The functional role of NLRC5 in ALD is obviously impacted by the autophagy inducer rapamycin as well as the autophagy inhibitor 3-MA. Our research showed that NLRC5 was involved in ethanol-induced injury and steatosis of the liver, and may be considered a suitable therapeutic target for treating ALD.

Galacto-Oligosaccharide Alleviates Alcohol-Induced Liver Injury by Inhibiting Oxidative Stress and Inflammation

Alcoholic liver disease (ALD) is a primary cause of mortality and morbidity worldwide. Oxidative stress and inflammation are important pathogenic factors contributing to ALD. We investigated the protective mechanism of galacto-oligosaccharide (GOS) against ALD through their antioxidant and anti-inflammatory activities by performing in vivo and in vitro experiments. Western blot and RT‒PCR results indicated that the expression of cytochrome P450 protein 2E1 (CYP2E1) in liver tissues and L02 cells was reduced in the GOS-treated mice compared with the model group. In addition, GOS prominently reduced the expression of Kelch-like ECH-associated protein 1 (Keap1), increased the expression of the nuclear factor erythroid-2-related factor 2 (Nrf2) and haem oxygenase-1 (HO-1) proteins, and enhanced the antioxidant capacity. In addition, GOS decreased inflammation by reducing inflammatory factor levels and inhibiting the mitogen-activated protein kinase (MAPK)/nuclear factor kappa B (NF-κB) pathway. Based on these results, GOS may be a prospective functional food for the prevention and treatment of ALD.

Role of TFEB in Autophagy and the Pathogenesis of Liver Diseases

The transcription factor EB (TFEB) is a master regulator of lysosomal function and autophagy. Mechanistic target of rapamycin (mTOR)-mediated phosphorylation on TFEB is known to regulate TFEB subcellular localization and activity at the lysosomal surface. Recent studies have shown that TFEB also plays a critical role in physiological processes such as lipid metabolism, and dysfunction of TFEB has been observed in the pathogenesis of several diseases. Owing to its ability to improve disease status in murine models, TFEB has attracted attention as a therapeutic target for diseases. In this review, we will present the regulation of TFEB and its role in the pathogenesis of liver diseases, particularly non-alcoholic fatty liver disease (NAFLD).

Xenobiotic-Induced Aggravation of Metabolic-Associated Fatty Liver Disease

Metabolic-associated fatty liver disease (MAFLD), which is often linked to obesity, encompasses a large spectrum of hepatic lesions, including simple fatty liver, steatohepatitis, cirrhosis and hepatocellular carcinoma. Besides nutritional and genetic factors, different xenobiotics such as pharmaceuticals and environmental toxicants are suspected to aggravate MAFLD in obese individuals. More specifically, pre-existing fatty liver or steatohepatitis may worsen, or fatty liver may progress faster to steatohepatitis in treated patients, or exposed individuals. The mechanisms whereby xenobiotics can aggravate MAFLD are still poorly understood and are currently under deep investigations. Nevertheless, previous studies pointed to the role of different metabolic pathways and cellular events such as activation of de novo lipogenesis and mitochondrial dysfunction, mostly associated with reactive oxygen species overproduction. This review presents the available data gathered with some prototypic compounds with a focus on corticosteroids and rosiglitazone for pharmaceuticals as well as bisphenol A and perfluorooctanoic acid for endocrine disruptors. Although not typically considered as a xenobiotic, ethanol is also discussed because its abuse has dire consequences on obese liver.

Ceramide-1-phosphate and its transfer proteins in eukaryotes

Ceramide-1-phosphate (C1P) is a bioactive phosphorylated sphingolipid (SL), produced through the direct phosphorylation of ceramide by ceramide kinase. It plays important roles in regulating cell survival, migration, apoptosis and autophagy and is involved in inflammasome assembly/activation, which can stimulate group IVA cytosolic phospholipase A₂α and subsequently increase the levels of arachidonic acid and pro-inflammatory cytokines. Human C1P transfer protein (CPTP) can selectively transport C1P from the Golgi apparatus to specific cellular sites through a non-vesicular mechanism. Human CPTP also affects specific SL levels, thus regulating cell SL homeostasis. In addition, human CPTP plays a crucial role in the regulation of autophagy, inflammation and cell death; thus, human CPTP is closely associated with autophagy and inflammation-related diseases such as cardiovascular and neurodegenerative diseases, and cancers. Therefore, illustrating the functions and mechanisms of human CPTP is important for providing the research foundations for targeted therapy. The key human CPTP residues for C1P recognition and binding are highly conserved in eukaryotic orthologs, while the human CPTP homolog in Arabidopsis (accelerated cell death 11) also exhibits selective inter-membrane transfer of phyto-C1P. These results demonstrate that C1P transporters play fundamental roles in SL metabolism in cells. The present review summarized novel findings of C1P and its TPs in eukaryotes.

miR-151 Affects Low-Temperature Tolerance of Penaeus vannamei by Modulating Autophagy Under Low-Temperature Stress

MicroRNAs (miRNAs) play key roles in many physiologic and pathologic processes, including autophagy. Autophagy is cellular in an emergency response mechanism of environment stress, but their complex molecular regulatory mechanism under low-temperature stress is largely unknown in shrimp, especially miRNA-mediated regulation of autophagy in low-temperature tolerance. In this article, a shrimp PvTOR and miRNA pva-miR-151 cooperation in response to low-temperature stress has been reported. Pva-miR-151 showed expression patterns opposite to target PvTOR under low-temperature stress. The pva-miR-151 targets the 3'-UTR region of PvTOR, regulate the formation of autophagosome, which contribute to the degradation and recycling of damaged organelles. In addition, the low-temperature tolerance was correlated positively with autophagy in shrimp. Silenced pva-miR-151 increased sensitivity to low-temperature stress, whereas overexpression pva-miR-151 decreased the expression of PvTOR and p-TOR and increased tolerance to low-temperature stress by improving the formation of autophagosome and total hemocyte count. In addition, the TOR activator 3BDO can partially rescue autophagy induced by overexpression of pva-miR-151; these results indicate that miR-151 was necessary for the low-temperature tolerance in shrimp. Taken together, we provide a novel strategy and mechanism for shrimp breeding to improve shrimp low-temperature tolerance.

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.

Tea polyphenols alleviate tri-ortho-cresyl phosphate-induced autophagy of mouse ovarian granulosa cells

Tri-ortho-cresyl phosphate (TOCP), a widely used plasticizer in industry, can cause female reproductive damage. Tea polyphenols (TPs) have multiple health effects via inhibiting oxidative stress. However, the reproductive protection of TPs in TOCP-induced female reproductive system damage is yet to be elucidated. In the study, TOCP inhibited cell viability and induced autophagy of mouse ovarian granulosa cells; while TPs could rescue the inhibition of viability and induction of autophagy. 3-MA, an autophagy inhibitor, could also rescue the inhibition of cell viability. These results indicated that TPs played a protective role in TOCP-induced autophagy. Furthermore, TPs could inhibit the induction of oxidative stress of the cells by TOCP, which implying that TPs might alleviate TOCP-induced autophagy via inhibiting oxidative stress. Furthermore, TPs could rescue TOCP-induced autophagy and oxidative stress in the mouse ovarian tissues. Taken together, these results indicated that TPs could protect TOCP-induced ovarian damage via inhibiting oxidative stress.

The Impacts of Herbal Medicines and Natural Products on Regulating the Hepatic Lipid Metabolism

The dysregulation of hepatic lipid metabolism is one of the hallmarks in many liver diseases including alcoholic liver diseases (ALD) and non-alcoholic fatty liver diseases (NAFLD). Hepatic inflammation, lipoperoxidative stress as well as the imbalance between lipid availability and lipid disposal, are direct causes of liver steatosis. The application of herbal medicines with anti-oxidative stress and lipid-balancing properties has been extensively attempted as pharmaceutical intervention for liver disorders in experimental and clinical studies. Although the molecular mechanisms underlying their hepatoprotective effects warrant further exploration, increasing evidence demonstrated that many herbal medicines are involved in regulating lipid accumulation processes including hepatic lipolytic and lipogenic pathways, such as mitochondrial and peroxisomal β-oxidation, the secretion of very low density lipoprotein (VLDL), the non-esterified fatty acid (NEFA) uptake, and some vital hepatic lipogenic enzymes. Therefore, in this review, the pathways or crucial mediators participated in the dysregulation of hepatic lipid metabolism are systematically summarized, followed by the current evidences and advances in the positive impacts of herbal medicines and natural products on the lipid metabolism pathways are detailed. Furthermore, several herbal formulas, herbs or herbal derivatives, such as Erchen Dection, Danshen, resveratrol, and berberine, which have been extensively studied for their promising potential in mediating lipid metabolism, are particularly highlighted in this review.

The Effects of Ethanol on the Heart: Alcoholic Cardiomyopathy

Alcoholic-dilated Cardiomyopathy (ACM) is the most prevalent form of ethanol-induced heart damage. Ethanol induces ACM in a dose-dependent manner, independently of nutrition, vitamin, or electrolyte disturbances. It has synergistic effects with other heart risk factors. ACM produces a progressive reduction in myocardial contractility and heart chamber dilatation, leading to heart failure episodes and arrhythmias. Pathologically, ethanol induces myocytolysis, apoptosis, and necrosis of myocytes, with repair mechanisms causing hypertrophy and interstitial fibrosis. Myocyte ethanol targets include changes in membrane composition, receptors, ion channels, intracellular [Ca2+] transients, and structural proteins, and disrupt sarcomere contractility. Cardiac remodeling tries to compensate for this damage, establishing a balance between aggression and defense mechanisms. The final process of ACM is the result of dosage and individual predisposition. The ACM prognosis depends on the degree of persistent ethanol intake. Abstinence is the preferred goal, although controlled drinking may still improve cardiac function. New strategies are addressed to decrease myocyte hypertrophy and interstitial fibrosis and try to improve myocyte regeneration, minimizing ethanol-related cardiac damage. Growth factors and cardiomyokines are relevant molecules that may modify this process. Cardiac transplantation is the final measure in end-stage ACM but is limited to those subjects able to achieve abstinence.