SREBP-1c impairs ULK1 sulfhydration-mediated autophagic flux to promote hepatic steatosis in high-fat-diet-fed mice.

A metabolic imbalance between lipid synthesis and degradation can lead to hepatic lipid accumulation, a characteristic of patients with non-alcoholic fatty liver disease (NAFLD). Here, we report that high-fat-diet-induced sterol regulatory element-binding protein (SREBP)-1c, a key transcription factor that regulates lipid biosynthesis, impairs autophagic lipid catabolism via altered H2S signaling. SREBP-1c reduced cystathionine gamma-lyase (CSE) via miR-216a, which in turn decreased hepatic H2S levels and sulfhydration-dependent activation of Unc-51-like autophagy-activating kinase 1 (ULK1). Furthermore, Cys951Ser mutation of ULK1 decreased autolysosome formation and promoted hepatic lipid accumulation in mice, suggesting that the loss of ULK1 sulfhydration was directly associated with the pathogenesis of NAFLD. Moreover, silencing of CSE in SREBP-1c knockout mice increased liver triglycerides, confirming the connection between CSE, autophagy, and SREBP-1c. Overall, our results uncover a 2-fold mechanism for SREBP-1c-driven hepatic lipid accumulation through reciprocal activation and inhibition of hepatic lipid biosynthesis and degradation, respectively.

SMILE Downregulation during Melanogenesis Induces MITF Transcription in B16F10 Cells.

SMILE (small heterodimer partner-interacting leucine zipper protein) is a transcriptional corepressor that potently regulates various cellular processes such as metabolism and growth in numerous tissues. However, its regulatory role in skin tissue remains uncharacterized. Here, we demonstrated that SMILE expression markedly decreased in human melanoma biopsy specimens and was inversely correlated with that of microphthalmia-associated transcription factor (MITF). During melanogenesis, α-melanocyte-stimulating hormone (α-MSH) induction of MITF was mediated by a decrease in SMILE expression in B16F10 mouse melanoma cells. Mechanistically, SMILE was regulated by α-MSH/cAMP/protein kinase A signaling and suppressed MITF promoter activity via corepressing transcriptional activity of the cAMP response element-binding protein. Moreover, SMILE overexpression significantly reduced α-MSH-induced MITF and melanogenic genes, thereby inhibiting melanin production in melanocytes. Conversely, SMILE inhibition increased the transcription of melanogenic genes and melanin contents. These results indicate that SMILE is a downstream effector of cAMP-mediated signaling and is a critical factor in the regulation of melanogenic transcription; in addition, they suggest a potential role of SMILE as a corepressor in skin pigmentation.

SREBP-1c Deficiency Affects Hippocampal Micromorphometry and Hippocampus-Dependent Memory Ability in Mice.

Changes in structural and functional neuroplasticity have been implicated in various neurological disorders. Sterol regulatory element-binding protein (SREBP)-1c is a critical regulatory molecule of lipid homeostasis in the brain. Recently, our findings have shown the potential involvement of SREBP-1c deficiency in the alteration of novel modulatory molecules in the hippocampus and occurrence of schizophrenia-like behaviors in mice. However, the possible underlying mechanisms, related to neuronal plasticity in the hippocampus, are yet to be elucidated. In this study, we investigated the hippocampus-dependent memory function and neuronal architecture of hippocampal neurons in SREBP-1c knockout (KO) mice. During the passive avoidance test, SREBP-1c KO mice showed memory impairment. Based on Golgi staining, the dendritic complexity, length, and branch points were significantly decreased in the apical cornu ammonis (CA) 1, CA3, and dentate gyrus (DG) subregions of the hippocampi of SREBP-1c KO mice, compared with those of wild-type (WT) mice. Additionally, significant decreases in the dendritic diameters were detected in the CA3 and DG subregions, and spine density was also significantly decreased in the apical CA3 subregion of the hippocampi of KO mice, compared with that of WT mice. Alterations in the proportions of stubby and thin-shaped dendritic spines were observed in the apical subcompartments of CA1 and CA3 in the hippocampi of KO mice. Furthermore, the corresponding differential decreases in the levels of SREBP-1 expression in the hippocampal subregions (particularly, a significant decrease in the level in the CA3) were detected by immunofluorescence. This study suggests that the contributions of SREBP-1c to the structural plasticity of the mouse hippocampus may have underlain the behavioral alterations. These findings offer insights into the critical role of SREBP-1c in hippocampal functioning in mice.

Transcriptome Profiling Reveals Novel Candidate Genes Related to Hippocampal Dysfunction in SREBP-1c Knockout Mice.

Lipid homeostasis is an important component of brain function, and its disturbance causes several neurological disorders, such as Huntington's, Alzheimer's, and Parkinson's diseases as well as mood disorders. Sterol regulatory element-binding protein-1c (SREBP-1c) is a key modulatory molecule involved in lipid homeostasis in the central nervous system. However, little is known about the biological effects of SREBP-1c in the brain. Our previous study uncovered that mice deficient in SREBP-1c exhibit schizophrenia-like behaviors. To investigate whether there are novel molecular mechanisms involved in the neurological aberrations caused by SREBP-1c deficiency, we analyzed the transcriptomes of the hippocampus of SREBP-1c knockout (KO) mice and wild-type mice. We found seven differentially expressed genes (three up-regulated and four down-regulated genes) in the hippocampus of SREBP-1c KO mice. For further verification, we selected the three most significantly changed genes: glucagon-like peptide 2 receptors (GLP2R) involved in hippocampal neurogenesis and neuroplasticity as well as in cognitive impairments; necdin (NDN) which is related to neuronal death and neurodevelopmental disorders; and Erb-B2 receptor tyrosine kinase 4 (ERBB4) which is a receptor for schizophrenia-linked protein, neuregulin-1. The protein levels of GLP2R and NDN were considerably decreased, but the level of ERBB4 was significantly increased in the hippocampus of SREBP-1c KO mice. However, further confirmation is warranted to establish the translatability of these findings from this rodent model into human patients. We suggest that these data provide novel molecular evidence for the modulatory role of SREBP-1c in the mouse hippocampus.

Modulation of the Autophagy-lysosomal Pathway in Hepatocellular Carcinoma Using Small Molecules.

Hepatocellular carcinoma (HCC) accounts for approximately 90% of all cases of primary liver cancer; it is the third most frequent cause of cancer-related death worldwide. In early-stage disease, surgical resection and liver transplantation are considered curative treatments. However, the majority of HCC patients present with advanced-stage disease that is treated using palliative systemic therapy. Since HCC is heterogeneous owing to its multiple etiologies, various risk factors, and inherent resistance to chemotherapy, the development of an effective systemic treatment strategy for HCC remains a considerable challenge. Autophagy is a lysosome-dependent catabolic degradation pathway that is essential for maintaining cellular energy homeostasis. Autophagy dysfunction is closely linked with the pathogenesis of various cancers; therefore, the discovery of small molecules that can modulate autophagy has attracted considerable interest in the development of a systemic treatment strategy for advanced HCC. Here, we reviewed the roles of autophagy in HCC and the recent advances regarding small molecules that target autophagy regulatory mechanisms.

miRNA and cholesterol homeostasis.

MicroRNAs (miRNAs) have recently emerged as a novel class of epigenetic regulators of gene expression. They are systemically involved in the control of lipid metabolism through a complex interactive mechanism that involves gene regulatory networks. Hence, they can contribute to defective lipid metabolism and metabolic diseases. Here, we review recent advances in the roles of lipid-sensing transcription factors in regulating miRNA gene networks, as well as miRNA expression and function in the regulation of cholesterol metabolism. This article is part of a Special Issue entitled: MicroRNAs and lipid/energy metabolism and related diseases edited by Carlos Fernández-Hernando and Yajaira Suárez.

Glu-Phe from onion (Allium Cepa L.) attenuates lipogenesis in hepatocytes.

A Glu-Phe (EF) was isolated from onion (Allium cepa L. cv. Sunpower). The chemical structure of EF was determined by nuclear magnetic resonance and electrospray ionization-mass (ESI-MS) spectroscopy. We showed that EF reduced lipid accumulation in mouse hepatocytes by inhibiting the expression of sterol regulatory element-binding protein-1c (SREBP-1c) and its lipogenic target genes. We also found that AMP-activated protein kinase (AMPK) was required for the inhibitory effect of EF on lipid accumulation in mouse hepatocytes. Furthermore, EF was qualified in nine onion cultivars by selective multiple reaction-monitoring detection of liquid chromatography-ESI-MS. These results suggest that EF could contribute to the beneficial effect of onion supplement in maintaining hepatic lipid homeostasis.

Protocatechuic Acid from Pear Inhibits Melanogenesis in Melanoma Cells.

Despite the critical role of melanin in the protection of skin against UV radiation, excess production of melanin can lead to hyperpigmentation and skin cancer. Pear fruits are often used in traditional medicine for the treatment of melasma; therefore, we investigated the effects of pear extract (PE) and its component, protocatechuic acid (PCA), on melanogenesis in mouse melanoma cells. We found that PE and PCA significantly suppressed melanin content and cellular tyrosinase activity through a decrease in the expression of melanogenic enzymes and microphthalmia-associated transcription factor (Mitf) in α-melanocyte stimulating hormone-stimulated mouse melanoma cells. Moreover, PCA decreased cyclic adenosine monophosphate (cAMP) levels and cAMP-responsive element-binding protein phosphorylation, which downregulated Mitf promoter activation and subsequently mediated the inhibition of melanogenesis. These results suggested that pear may be an effective skin lightening agent that targets either a tyrosinase activity or a melanogenic pathway.

Anti-inflammatory activity of the ethanol extract of Dictamnus dasycarpus leaf in lipopolysaccharide-activated macrophages.

BACKGROUND: Dictamnus dasycarpus is widely used as a traditional remedy for the treatment of eczema, rheumatism, and other inflammatory diseases in Asia. The current study investigates the molecular mechanism of anti-inflammatory action of the ethanol extract of Dictamnus dasycarpus leaf (DE) in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells. METHODS: Nitric oxide (NO) production was assessed by Griess reaction and the mRNA and protein expressions of pro inflammatory cytokines, transcription factor, and enzymes were determined by real-time RT-PCR and immunoblotting analysis. RESULTS: DE (0.5 and 1 mg/mL) suppressed the NO production by 10 and 33%, respectively, compared to the untreated group in LPS-stimulated RAW 264.7 cells. DE (0.5 and 1 mg/mL) reduced the mRNA expression of key transcription factor nuclear factor-κB by 7 and 24%, respectively compared to the untreated group in LPS activated macrophage. The pro inflammatory cytokines such as tumor necrosis factor α and interleukin 1ß were also decreased by DE treatment. Moreover, the protein expression of pro inflammatory enzymes, inducible nitric oxide synthase and cyclooxygenase 2 were also dramatically attenuated by DE in a dose dependent manner. CONCLUSIONS: These results suggest that Dictamnus dasycarpus leaf has a potent anti-inflammatory activity and can be used for the development of new anti-inflammatory agents.

Hydrogen Sulfide and Liver Health: Insights into Liver Diseases.

Significance: Hydrogen sulfide (H2S) is a recently recognized gasotransmitter involved in physiological and pathological conditions in mammals. It protects organs from oxidative stress, inflammation, hypertension, and cell death. With abundant expression of H2S-production enzymes, the liver is closely linked to H2S signaling. Recent Advances: Hepatic H2S comes from various sources, including gut microbiota, exogenous sulfur salts, and endogenous production. Recent studies highlight the importance of hepatic H2S in liver diseases such as nonalcoholic fatty liver disease (NAFLD), liver injury, and cancer, particularly at advanced stages. Endogenous H2S production deficiency is associated with severe liver disease, while exogenous H2S donors protect against liver dysfunction. Critical Issues: However, the roles of H2S in NAFLD, liver injury, and liver cancer are still debated, and its effects depend on donor type, dosage, treatment duration, and cell type, suggesting a multifaceted role. This review aimed to critically evaluate H2S production, metabolism, mode of action, and roles in liver function and disease. Future Direction: Understanding H2S's precise roles and mechanisms in liver health will advance potential therapeutic applications in preclinical and clinical research. Targeting H2S-producing enzymes and exogenous H2S sources, alone or in combination with other drugs, could be explored. Quantifying endogenous H2S levels may aid in diagnosing and managing liver diseases. Antioxid. Redox Signal. 40, 122-144.

Loss of SREBP-1c ameliorates iron-induced liver fibrosis by decreasing lipocalin-2.

Sterol regulatory element-binding protein (SREBP)-1c is involved in cellular lipid homeostasis and cholesterol biosynthesis and is highly increased in nonalcoholic steatohepatitis (NASH). However, the molecular mechanism by which SREBP-1c regulates hepatic stellate cells (HSCs) activation in NASH animal models and patients have not been fully elucidated. In this study, we examined the role of SREBP-1c in NASH and the regulation of LCN2 gene expression. Wild-type and SREBP-1c knockout (1cKO) mice were fed a high-fat/high-sucrose diet, treated with carbon tetrachloride (CCl4), and subjected to lipocalin-2 (LCN2) overexpression. The role of LCN2 in NASH progression was assessed using mouse primary hepatocytes, Kupffer cells, and HSCs. LCN2 expression was examined in samples from normal patients and those with NASH. LCN2 gene expression and secretion increased in CCl4-induced liver fibrosis mice model, and SREBP-1c regulated LCN2 gene transcription. Moreover, treatment with holo-LCN2 stimulated intracellular iron accumulation and fibrosis-related gene expression in mouse primary HSCs, but these effects were not observed in 1cKO HSCs, indicating that SREBP-1c-induced LCN2 expression and secretion could stimulate HSCs activation through iron accumulation. Furthermore, LCN2 expression was strongly correlated with inflammation and fibrosis in patients with NASH. Our findings indicate that SREBP-1c regulates Lcn2 gene expression, contributing to diet-induced NASH. Reduced Lcn2 expression in 1cKO mice protects against NASH development. Therefore, the activation of Lcn2 by SREBP-1c establishes a new connection between iron and lipid metabolism, affecting inflammation and HSCs activation. These findings may lead to new therapeutic strategies for NASH.

Quercetin reduces high-fat diet-induced fat accumulation in the liver by regulating lipid metabolism genes.

To understand the molecular mechanisms underlying the influence of quercetin on the physiological effects of hyperlipidemia, we investigated its role in the prevention of high-fat diet (HFD)-induced obesity and found that it regulated hepatic gene expression related to lipid metabolism. Quercetin supplementation in mice significantly reduced the HFD-induced gains in body weight, liver weight, and white adipose tissue weight compared with the mice fed only with HFD. It also significantly reduced HFD-induced increases in serum lipids, including cholesterol, triglyceride, and thiobarbituric acid-reactive substance (TBARS). Consistent with the reduced liver weight and white adipose tissue weight, hepatic lipid accumulation and the size of lipid droplets in the epididymal fat pads were also reduced by quercetin supplementation. To further investigate how quercetin may reduce obesity, we analyzed lipid metabolism-related genes in the liver. Quercetin supplementation altered expression profiles of several lipid metabolism-related genes, including Fnta, Pon1, Pparg, Aldh1b1, Apoa4, Abcg5, Gpam, Acaca, Cd36, Fdft1, and Fasn, relative to those in HFD control mice. The expression patterns of these genes observed by quantitative reverse transcriptase-polymerase chain reaction were confirmed by immunoblot assays. Collectively, our results indicate that quercetin prevents HFD-induced obesity in C57B1/6 mice, and its anti-obesity effects may be related to the regulation of lipogenesis at the level of transcription.

Zinc-chelated Vitamin C Stimulates Adipogenesis of 3T3-L1 Cells.

Adipose tissue development and function play a critical role in the regulation of energy balance, lipid metabolism, and the pathophysiology of metabolic syndromes. Although the effect of zinc ascorbate supplementation in diabetes or glycemic control is known in humans, the underlying mechanism is not well described. Here, we investigated the effect of a zinc-chelated vitamin C (ZnC) compound on the adipogenic differentiation of 3T3-L1 preadipocytes. Treatment with ZnC for 8 d significantly promoted adipogenesis, which was characterized by increased glycerol-3-phosphate dehydrogenase activity and intracellular lipid accumulation in 3T3-L1 cells. Meanwhile, ZnC induced a pronounced up-regulation of the expression of glucose transporter type 4 (GLUT4) and the adipocyte-specific gene adipocyte protein 2 (aP2). Analysis of mRNA and protein levels further showed that ZnC increased the sequential expression of peroxisome proliferator-activated receptor gamma (PPARγ) and CCAAT/enhancer-binding protein alpha (C/EBPα), the key transcription factors of adipogenesis. These results indicate that ZnC could promote adipogenesis through PPARγ and C/EBPα, which act synergistically for the expression of aP2 and GLUT4, leading to the generation of insulin-responsive adipocytes and can thereby be useful as a novel therapeutic agent for the management of diabetes and related metabolic disorders.

SCAP deficiency facilitates obesity and insulin resistance through shifting adipose tissue macrophage polarization.

INTRODUCTION: Sterol regulatory element binding protein (SREBP) cleavage-associating protein (SCAP) is a sterol-regulated escort protein that translocates SREBPs from the endoplasmic reticulum to the Golgi apparatus, thereby activating lipid metabolism and cholesterol synthesis. Although SCAP regulates lipid metabolism in metabolic tissues, such as the liver and muscle, the effect of macrophage-specific SCAP deficiency in adipose tissue macrophages (ATMs) of patients with metabolic diseases is not completely understood. OBJECTIVES: Here, we examined the function of SCAP in high-fat/high-sucrose diet (HFHS)-fed mice and investigated its role in the polarization of classical activated macrophages in adipose tissue. METHODS: Macrophage-specific SCAP knockout (mKO) mice were generated through crossbreeding lysozyme 2-cre mice with SCAP floxed mice which were then fed HFHS for 12 weeks. Primary macrophages were derived from bone marrow cells and analyzed further. RESULTS: We found that fat accumulation and the appearance of proinflammatory M1 macrophages were both higher in HFHS-fed SCAP mKO mice relative to floxed control mice. We traced the effect to a defect in the lipopolysaccharide-mediated increase in SREBP-1a that occurs in control but not SCAP mKO mice. Mechanistically, SREBP-1a increased expression of cholesterol 25-hydroxylase transcription, resulting in an increase in the production of 25-hydroxycholesterol (25-HC), an endogenous agonist of liver X receptor alpha (LXRα) which increased expression of cholesterol efflux to limit cholesterol accumulation and M1 polarization. In the absence of SCAP mediated activation of SREBP-1a, increased M1 macrophage polarization resulted in reduced cholesterol efflux downstream from 25-HC-dependent LXRα activation. CONCLUSION: Overall, the activation of the SCAP-SREBP-1a pathway in macrophages may provide a novel therapeutic strategy that ameliorates obesity by controlling cholesterol homeostasis in ATMs.

Gut bitter taste receptor signalling induces ABCB1 through a mechanism involving CCK.

T2Rs (bitter taste-sensing type 2 receptors) are expressed in the oral cavity to prevent ingestion of dietary toxins through taste avoidance. They are also expressed in other cell types, including gut enteroendocrine cells, where their physiological role is enigmatic. Previously, we proposed that T2R-dependent CCK (cholecystokinin) secretion from enteroendocrine cells limits absorption of dietary toxins, but an active mechanism was lacking. In the present study we show that T2R signalling activates ABCB1 (ATP-binding cassette B1) in intestinal cells through a CCK signalling mechanism. PTC (phenylthiocarbamide), an agonist for the T2R38 bitter receptor, increased ABCB1 expression in both intestinal cells and mouse intestine. PTC induction of ABCB1 was decreased by either T2R38 siRNA (small interfering RNA) or treatment with YM022, a gastrin receptor antagonist. Thus gut ABCB1 is regulated through signalling by CCK/gastrin released in response to PTC stimulation of T2R38 on enteroendocrine cells. We also show that PTC increases the efflux activity of ABCB1, suggesting that T2R signalling limits the absorption of bitter tasting/toxic substances through modulation of gut efflux membrane transporters.

Genome-wide interrogation of hepatic FXR reveals an asymmetric IR-1 motif and synergy with LRH-1.

We used mouse hepatic chromatin enriched with an FXR antibody and chromatin immunoprecipitation-sequencing (ChIP-seq) to evaluate FXR binding on a genome-wide scale. This identified 1656 FXR-binding sites and 10% were located within 2 kb of a transcription start site which is much higher than predicted by random occurrence. A motif search uncovered a canonical nuclear receptor IR-1 site, consistent with in vitro DNA-binding studies reported previously. A separate nuclear receptor half-site for monomeric receptors such as LRH-1 was co-enriched and FXR activation of four newly identified promoters was significantly augmented by an LRH-1 expression vector in a co-transfection assay. There were 1038 genes located within 20 kb of a peak and a gene set enrichment analysis showed that genes identified by our ChIP-seq analysis are highly correlated with genes activated by an FXR-VP16 adenovirus in primary mouse hepatocytes providing functional relevance to the genome-wide binding study. Gene Ontology analysis showed FXR-binding sites close to many genes in lipid, fatty acid and steroid metabolism. Other broad gene clusters related to metabolism, transport, signaling and glycolysis were also significantly enriched. Thus, FXR may have a much wider role in cellular metabolism than previously appreciated.

Therapeutic strategy targeting host lipolysis limits infection by SARS-CoV-2 and influenza A virus.

The biosynthesis of host lipids and/or lipid droplets (LDs) has been studied extensively as a putative therapeutic target in diverse viral infections. However, directly targeting the LD lipolytic catabolism in virus-infected cells has not been widely investigated. Here, we show the linkage of the LD-associated lipase activation to the breakdown of LDs for the generation of free fatty acids (FFAs) at the late stage of diverse RNA viral infections, which represents a broad-spectrum antiviral target. Dysfunction of membrane transporter systems due to virus-induced cell injury results in intracellular malnutrition at the late stage of infection, thereby making the virus more dependent on the FFAs generated from LD storage for viral morphogenesis and as a source of energy. The replication of SARS-CoV-2 and influenza A virus (IAV), which is suppressed by the treatment with LD-associated lipases inhibitors, is rescued by supplementation with FFAs. The administration of lipase inhibitors, either individually or in a combination with virus-targeting drugs, protects mice from lethal IAV infection and mitigates severe lung lesions in SARS-CoV-2-infected hamsters. Moreover, the lipase inhibitors significantly reduce proinflammatory cytokine levels in the lungs of SARS-CoV-2- and IAV-challenged animals, a cause of a cytokine storm important for the critical infection or mortality of COVID-19 and IAV patients. In conclusion, the results reveal that lipase-mediated intracellular LD lipolysis is commonly exploited to facilitate RNA virus replication and furthermore suggest that pharmacological inhibitors of LD-associated lipases could be used to curb current COVID-19- and future pandemic outbreaks of potentially troublesome RNA virus infection in humans.

SREBP-2 regulates gut peptide secretion through intestinal bitter taste receptor signaling in mice.

Bitter taste-sensing G protein-coupled receptors (type 2 taste receptors [T2Rs]) are expressed in taste receptor cells of the tongue, where they play an important role in limiting ingestion of bitter-tasting, potentially toxic compounds. T2Rs are also expressed in gut-derived enteroendocrine cells, where they have also been hypothesized to play a role in limiting toxin absorption. In this study, we have shown that T2R gene expression in both cultured mouse enteroendocrine cells and mouse intestine is regulated by the cholesterol-sensitive SREBP-2. In addition, T2R stimulation of cholecystokinin (CCK) secretion was enhanced directly by SREBP-2 in cultured cells and in mice fed chow supplemented with lovastatin and ezetimibe (L/E) to decrease dietary sterol absorption and increase nuclear activity of SREBP-2. Low-cholesterol diets are naturally composed of high amounts of plant matter that is likely to contain dietary toxins, and CCK is known to improve dietary absorption of fats, slow gastric emptying, and decrease food intake. Thus, these studies suggest that SREBP-2 activation of bitter signaling receptors in the intestine may sensitize the gut to a low-fat diet and to potential accompanying food-borne toxins that make it past the initial aversive response in the mouth.

The interplay of microRNAs and transcription factors in autophagy regulation in nonalcoholic fatty liver disease.

The autophagy-lysosomal degradation system has an important role in maintaining liver homeostasis by removing unnecessary intracellular components. Impaired autophagy has been linked to nonalcoholic fatty liver disease (NAFLD), which includes hepatitis, steatosis, fibrosis, and cirrhosis. Thus, gaining an understanding of the mechanisms that regulate autophagy and how autophagy contributes to the development and progression of NAFLD has become the focus of recent studies. Autophagy regulation has been thought to be primarily regulated by cytoplasmic processes; however, recent studies have shown that microRNAs (miRNAs) and transcription factors (TFs) also act as key regulators of autophagy by targeting autophagy-related genes. In this review, we summarize the miRNAs and TFs that regulate the autophagy pathway in NAFLD. We further focus on the transcriptional and posttranscriptional regulation of autophagy and discuss the complex regulatory networks involving these regulators in autophagy. Finally, we highlight the potential of targeting miRNAs and TFs involved in the regulation of autophagy for the treatment of NAFLD.

Impairment of ULK1 sulfhydration-mediated lipophagy by SREBF1/SREBP-1c in hepatic steatosis.

Nonalcoholic fatty liver disease (NAFLD) affects a quarter of the global population. However, its pathogenesis is not completely understood. In our recent study, we have demonstrated that in a high-fat diet-induced liver steatosis model, the activation of SREBF1/SREBP-1c (sterol regulatory element binding transcription factor 1) directly upregulates Mir216a transcription, which inhibits CTH/CSE (cystathionase (cystathionine gamma-lyase)) expression and its function in hydrogen sulfide (H2S) production. Reduced H2S production suppresses the sulfhydration of ULK1 (unc-51 like autophagy activating kinase 1), consequently inhibiting autophagic flux and lipid droplet turnover. A single substitution mutation (C951S) in ULK1 or the silencing of CTH impairs ULK1 sulfhydration-mediated lipophagy, thereby promoting hepatic steatosis in mice. Interestingly, the sulfhydration of ULK1 increases its intrinsic kinase activity to modulate autophagy at both initiation and progression stages of autophagic catabolic flux. This study reveals that SREBF1/SREBP-1c contributes to hepatic lipid accumulation through its combined effect of increased lipid synthesis coupled with decreased lipid degradation mediated by autophagic dysregulation.