Gα12 overexpression induced by miR-16 dysregulation contributes to liver fibrosis by promoting autophagy in hepatic stellate cells

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.

Paeoniflorin modulates oxidative stress, inflammation and hepatic stellate cells activation to alleviate CCl4-induced hepatic fibrosis by upregulation of heme oxygenase-1 in mice

OBJECTIVES

The role of Paeoniflorin on hepatic fibrosis and the specific mechanisms has not yet been elucidated. Therefore, we explored whether Paeoniflorin exerted protective effects on carbon tetrachloride (CCl4)-induced hepatic fibrosis and the underlying mechanisms.

METHODS

A model of hepatic fibrosis was induced by intraperitoneally injecting with CCl4 (10% 5 μl/g) twice a week for 7 weeks. To explore the effects of Paeoniflorin, mice were treated with Paeoniflorin (100 mg/kg) by gavage once a day at 1 week after modeling until they were sacrificed.

KEY FINDINGS

Paeoniflorin remarkably improved liver function and histopathological changes of hepatic tissues in CCl4-induced liver injury. Besides, the serum MAO enzyme activity and hydroxyproline contents were notably decreased following the intervention of Paeoniflorin. The decreased expression of Vimentin, α-SMA, Col1a and Desmin manifested the inhibition of the hepatic stellate cells (HSCs) activation. Interestingly, Paeoniflorin intervention significantly upregulated the expression of heme oxygenase-1, and attenuated the inflammatory cytokines production as well as the CCl4-induced oxidative stress imbalance.

CONCLUSIONS

Paeoniflorin could effectively alleviate CCl4-induced hepatic fibrosis by upregulation of heme oxygenase-1, and it might be a new effective option for the comprehensive treatment of hepatic fibrosis.

CRISPR-mediated BMP9 ablation promotes liver steatosis via the down-regulation of PPARα expression

Obesity drives the development of nonalcoholic fatty liver disease (NAFLD) characterized by hepatic steatosis. Several bone morphogenetic proteins (BMPs) except BMP9 were reported related to metabolic syndrome. This study demonstrates that liver cytokine BMP9 is decreased in the liver and serum of NAFLD model mice and patients. BMP9 knockdown induces lipid accumulation in Hepa 1-6 cells. BMP9-knockout mice exhibit hepatosteatosis due to down-regulated peroxisome proliferator-activated receptor α (PPARα) expression and reduced fatty acid oxidation. In vitro, recombinant BMP9 treatment attenuates triglyceride accumulation by enhancing PPARα promoter activity via the activation of p-smad. PPARα-specific antagonist GW6471 abolishes the effect of BMP9 knockdown. Furthermore, adeno-associated virus-mediated BMP9 overexpression in mouse liver markedly relieves liver steatosis and obesity-related metabolic syndrome. These findings indicate that BMP9 plays a critical role in regulating hepatic lipid metabolism in a PPARα-dependent manner and may provide a previously unknown insight into NAFLD therapeutic approaches.

Endoplasmic reticulum stress and autophagy dysregulation in alcoholic and non-alcoholic liver diseases

Alcoholic and non-alcoholic liver diseases begin from an imbalance in lipid metabolism in hepatocytes as the earliest response. Both liver diseases share common disease features and stages (i.e., steatosis, hepatitis, cirrhosis, and hepatocellular carcinoma). However, the two diseases have differential pathogenesis and clinical symptoms. Studies have elucidated the molecular basis underlying similarities and differences in the pathogenesis of the diseases; the factors contributing to the progression of liver diseases include depletion of sulfhydryl pools, enhanced levels of reactive oxygen and nitrogen intermediates, increased sensitivity of hepatocytes to toxic cytokines, mitochondrial dysfunction, and insulin resistance. Endoplasmic reticulum (ER) stress, which is caused by the accumulation of misfolded proteins and calcium depletion, contributes to the pathogenesis, often causing catastrophic cell death. Several studies have demonstrated a mechanism by which ER stress triggers liver disease progression. Autophagy is an evolutionarily conserved process that regulates organelle turnover and cellular energy balance through decomposing damaged organelles including mitochondria, misfolded proteins, and lipid droplets. Autophagy dysregulation also exacerbates liver diseases. Thus, autophagy-related molecules can be potential therapeutic targets for liver diseases. Since ER stress and autophagy are closely linked to each other, an understanding of the molecules, gene clusters, and networks engaged in these processes would be of help to find new remedies for alcoholic and non-alcoholic liver diseases. In this review, we summarize the recent findings and perspectives in the context of the molecular pathogenesis of the liver diseases.

Predicting Nonalcoholic Fatty Liver Disease through a Panel of Plasma Biomarkers and MicroRNAs in Female West Virginia Population

(1) Background: Nonalcoholic fatty liver disease (NAFLD) is primarily characterized by the presence of fatty liver, hepatic inflammation and fibrogenesis eventually leading to nonalcoholic steatohepatitis (NASH) or cirrhosis. Obesity and diabetes are common risk factors associated with the development and progression of NAFLD, with one of the highest prevalence of these diseased conditions in the West Virginia population. Currently, the diagnosis of NAFLD is limited to radiologic studies and biopsies, which are not cost-effective and highly invasive. Hence, this study aimed to develop a panel and assess the progressive levels of circulatory biomarkers and miRNA expression in patients at risk for progression to NASH to allow early intervention strategies. (2) Methods: In total, 62 female patients were enrolled and blood samples were collected after 8–10 h of fasting. Computed tomography was performed on abdomen/pelvis following IV contrast administration. The patients were divided into the following groups: Healthy subjects with normal BMI and normal fasting blood glucose (Control, n = 20), Obese with high BMI and normal fasting blood glucose (Obese, n = 20) and Obese with high fasting blood glucose (Obese + DM, n = 22). Based on findings from CT, another subset was created from Obese + DM group with patients who showed signs of fatty liver infiltration (Obese + DM(FI), n = 10). ELISA was performed for measurement of plasma biomarkers and RT-PCR was performed for circulating miRNA expression. (3) Results: Our results show significantly increased levels of plasma IL-6, Leptin and FABP-1, while significantly decreased level of adiponectin in Obese, Obese + DM and Obese + DM(FI) group, as compared to healthy controls. The level of CK-18 was significantly increased in Obese + DM(FI) group as compared to control. Subsequently, the expression of miR-122, miR-34a, miR-375, miR-16 and miR-21 was significantly increased in Obese + DM and Obese + DM(FI) group as compared to healthy control. Our results also show distinct correlation of IL-6, FABP-1 and adiponectin levels with the expression of miRNAs in relation to the extent of NAFLD progression. (4) Conclusion: Our results support the clinical application of these biomarkers and miRNAs in monitoring the progression of NAFLD, suggesting a more advanced diagnostic potential of this panel than conventional methods. This panel may provide an appropriate method for early prognosis and management of NAFLD and subsequent adverse hepatic pathophysiology, potentially reducing the disease burden on the West Virginia population.

HIF-1α-upregulated lncRNA-H19 regulates lipid droplet metabolism through the AMPKα pathway in hepatic stellate cells

Activation of hepatic stellate cells (HSCs) is a central event in the pathogenesis of liver fibrosis and is characterized by the disappearance of lipid droplets. Although the exogenous supplementation of lipid droplet content can effectively reverse the activation of HSCs, the underlying molecular mechanisms are largely unknown. In our current study, we sought to investigate the role of lncRNA-H19 in the process of lipid droplets disappearance and to further examine the underlying molecular mechanisms. We found that the lncRNA-H19 level was increased in CCl4-induced fibrotic liver, which activated HSCs. Further research showed that hypoxia inducible factor-1α (HIF-1α) significantly increased lncRNA-H19 expression by binding to the lncRNA-H19 promoter at two hypoxia response element (HRE) sites located at 492-499 and 515-522 bp. Importantly, lncRNA-H19 knockdown markedly inhibited HSC activation and alleviated liver fibrosis, indicating that lncRNA-H19 may be a potential target for anti-fibrosis therapeutic approaches. Moreover, lncRNA-H19 knockdown could reverse the lipid droplet phenotype of activated HSCs, inhibiting the phosphorylated AMPKα-mediated lipid oxidation signaling pathway. The AMPK agonist AICAR promoted AMPKα phosphorylation and abrogated lipid droplets restoration in HSCs transfected with the lncRNA-H19 knockdown plasmid. Experimental molecular analysis showed that lncRNA-H19 triggered AMPKα to interact with LKB1 and resulted in AMPKα phosphorylation, which accelerating lipid droplets degradation and lipid oxidation. Taken together, our results highlighted the role of lncRNA-H19 in the metabolism of lipid droplets in HSCs, and revealed a new molecular target for alleviating liver fibrosis.

miR-16 integrates signal pathways in myofibroblasts: determinant of cell fate necessary for fibrosis resolution

Liver fibrosis is characterized by the transdifferentiation of hepatic stellate cells (HSCs) to myofibroblasts and poor response to treatment. This can be attributed to the myofibroblast-specific resistance to phenotype reversal. In this study, we complemented miR-16 into miR-16-deficient myofibroblasts and analyzed the global role of miR-16 using transcriptome profiling and generating a pathway-based action model underlying transcriptomic regulation. Phenotypic analysis of myofibroblasts and fibrogenic characterization were used to understand the effect of miR-16 on phenotypic remodeling of myofibroblasts. miR-16 expression altered the transcriptome of myofibroblasts to resemble that of HSCs. Simultaneous targeting of Smad2 and Wnt3a, etc. by miR-16 integrated signaling pathways of TGF-β and Wnt, etc., which underlay the comprehensive regulation of transcriptome. The synergistic effect of miR-16 on the signaling pathways abolished the phenotypic characteristics of myofibroblasts, including collagen production and inhibition of adipogenesis. In vivo, myofibroblast-specific expression of miR-16 not only eliminated mesenchymal cells with myofibroblast characteristics but also restored the phenotype of HSCs in perisinusoidal space. This phenotypic remodeling resolved liver fibrosis induced by chronic wound healing. Therefore, miR-16 may integrate signaling pathways crucial for the fate determination of myofibroblasts. Its global effect induces the reversal of HSC-to-myofibroblast transdifferentiation and, subsequently, the resolution of fibrogenesis. Taken together, these findings highlight the potential of miR-16 as a promising therapeutic target for liver fibrosis.

Self-eating: friend or foe? The emerging role of autophagy in fibrotic diseases

Fibrosis occurs in most human organs including the liver, lung, heart and kidney, and is crucial for the progression of most chronic diseases. As an indispensable catabolic process for intracellular quality control and homeostasis, autophagy occurs in most mammalian cells and is implicated in many biological processes including fibrogenesis. Although advances have been made in understanding autophagy process, the potential role of autophagy in fibrotic diseases remains controversial and has recently attracted a great deal of attention. In the current review, we summarize the commonalities of autophagy affecting different types of fibrosis in different organs, including the liver, lung, heart, and kidney as well as in cystic fibrosis, systematically outline the contradictory results and highlight the distinct role of autophagy during the various stages of fibrosis. In summary, the exact role autophagy plays in fibrogenesis depends on specific cell types and different stimuli, and identifying and evaluating the pathogenic contribution of autophagy in fibrogenesis will promote the discovery of novel therapeutic strategies for the clinical management of these fibrotic diseases.

Gα12/13 signaling in metabolic diseases

As the key governors of diverse physiological processes, G protein-coupled receptors (GPCRs) have drawn attention as primary targets for several diseases, including diabetes and cardiovascular disease. Heterotrimeric G proteins converge signals from ~800 members of the GPCR family. Among the members of the G protein α family, the Gα₁₂ family members comprising Gα₁₂ and Gα₁₃ have been referred to as gep oncogenes. Gα_12/13 levels are altered in metabolic organs, including the liver and muscles, in metabolic diseases. The roles of Gα_12/13 in metabolic diseases have been investigated. In this review, we highlight findings demonstrating Gα_12/13 amplifying or dampening regulators of phenotype changes. We discuss the molecular basis of G protein biology in the context of posttranslational modifications to heterotrimeric G proteins and the cell signaling axis. We also highlight findings providing insights into the organ-specific, metabolic and pathological roles of G proteins in changes associated with specific cells, energy homeostasis, glucose metabolism, liver fibrosis and the immune and cardiovascular systems. This review summarizes the currently available knowledge on the importance of Gα_12/13 in the physiology and pathogenesis of metabolic diseases, which is presented according to the basic understanding of their metabolic actions and underlying cellular and molecular bases.

Understanding the activities of two members of a vital category of proteins called G proteins, which initiate metabolic changes when signaling molecules bind to cells, could lead to new therapies for many diseases. Researchers in South Korea and Japan, led by Sang Geon Kim at Seoul National University, review the significance of the Gα12 and Gα13 proteins in diseases characterised by significant changes in metabolism, including liver conditions and disorders of the cardiovascular and immune systems. Specific roles for the proteins have been identified by a variety of methods, including studying the effect of disabling the genes that code for them in mice. Recent insights suggest that drugs interfering with the activity of these Gα proteins might help treat many conditions in which the molecular signalling networks involving the proteins are disrupted.

MicroRNA-98 Inhibits Hepatic Stellate Cell Activation and Attenuates Liver Fibrosis by Regulating HLF Expression

Liver fibrosis is a major endpoint of patients with chronic liver diseases. The molecular mechanisms behind liver fibrosis remain largely unknown. Many studies have indicated the role of microRNA (miRNA) in hepatic tumorigenesis. But the role of miRNA in liver fibrosis is little known. Activated hepatic stellate cells (HSCs) can secret extracellular matrix proteins (ECM) and are the major contributors to liver fibrosis/cirrhosis. Here, a microarray assay of quiescent and transforming growth factor β1 (TGF-β1) activated HSCs indicated that miR-98 might play a crucial role in liver fibrosis. We found that miR-98 was significantly downregulated in activated HSCs. miR-98 overexpression inhibited HSCs activation. Furthermore, we hypothesized that miR-98 regulated hepatic leukemia factor (HLF) expression by binding to the 3′ UTR of its mRNA directly, as evidenced by luciferase reporter assay. HLF overexpression increased HSCs activation by inducing hypoxia inducible factor-1 alpha (HIF-1α) expression, resulting in the activation of TGF-β/Smad2/3 signaling pathway. Besides, low expression of miR-98 was also found in liver tissues from various fibrotic murine models, including carbon tetrachloride (CCl₄), bile duct ligation (BDL), and high-fat diet (HFD)-induced liver fibrosis. miR-98 overexpression in vivo by ago-miR-98 injection could attenuate CCl₄-, BDL-, and HFD-induced murine hepatic fibrosis. Meanwhile, miR-98 overexpression suppressed HLF expression and reduced fibrosis marker expression. Collectively, our study demonstrates that miR-98 suppress HSCs activation by targeting HLF directly and interacting with HIF-1α/TGF-β/Smad2/3 signaling pathway, which may be an effective therapeutic target for liver fibrosis.

Platycodin D alleviates liver fibrosis and activation of hepatic stellate cells by regulating JNK/c-JUN signal pathway

Liver fibrosis is involved in the progression of most chronic liver diseases. Even though we have made a huge progress in order to understand the pathogenesis of liver fibrosis, however, there is still a lack of productive treatments. Being a traditional Chinese medicine, Platycodin D (PD), an oleanane kind of triterpenoid saponin has been put to extensive use for treating different kinds of illnesses that include not just anti-nociceptive, but also antiviral, anti-inflammatory, and anti-cancer for thousands of years. Nonetheless, there has been no clarification made for its effects on the progression of liver fibrosis. In this manner, we carried out in vitro studies for the purpose of investigating the anti-fibrosis impact of PD. Activation of hepatic stellate cells was evaluated by means of the detection of the proliferation of HSCs and the expression of specific proteins. We discovered the fact that PD had the potential of activating HSCs. Thereafter, we detected the apoptosis and autophagy of the HSCs; as the results suggested, PD induced apoptosis and autophagy of the HSCs. It augmented the expression level of apoptotic proteins that included Bax, Cytochrome C (cyto-c), cleaved caspase3 and cleaved caspase9, in addition to the autophagy relevant proteins, for instance, LC3II, beclin1, Atg5 and Atg9. Further research was carried out for the investigation of the underlying molecular mechanism, and discovered that PD promoted the phosphorylation of JNK and c-Jun. Treating the JNK inhibitor P600125 inhibited the effect of PD, confirming the impact of PD on the regulation of JNK/c-Jun pathway. Thus, we speculated that PD alleviates liver fibrosis and activation of hepatic stellate via promoting phosphorylation of JNK and c-Jun and further altering the autophagy along with apoptosis of HSCs.

TGF-β/Smad and JAK/STAT pathways are involved in the anti-fibrotic effects of propylene glycol alginate sodium sulphate on hepatic fibrosis

Liver fibrosis, a consequence of unhealthy modern lifestyles, has a growing impact on human health, particularly in developed countries. Here, we have explored the anti-fibrotic effects of propylene glycol alginate sodium sulphate (PSS), a natural extract from brown algae, in fibrotic mice and cell models. Thus, we established bile duct ligature and carbon tetrachloride mouse models and LX-2 cell models with or without PSS treatment. Liver pathological sections and the relevant indicators in serum and liver tissues were examined. PSS prevented hepatic injury and fibrosis to a significant extent, and induced up-regulation of matrix metalloproteinase-2 and down-regulation of tissue inhibitor of metalloproteinase-1 through suppressing the transforming growth factor β1 (TGF-β1)/Smad pathway. PSS additionally exerted an anti-autophagy effect through suppressing the Janus kinase (JAK) 2/transducer and activator of transcription 3 (STAT3) pathway. In conclusion, PSS prevents hepatic fibrosis by suppressing inflammation, promoting extracellular matrix (ECM) decomposition and inactivating hepatic stellate cells through mechanisms involving the TGF-β1/Smad2/3 and JAK2/STAT3 pathways in vivo and in vitro.

Pharmacological Inhibition of Transient Receptor Potential Vanilloid 4 (TRPV4) Channel Alleviates Carbon Tetrachloride-Induced Liver Fibrosis in Mice

BACKGROUND

Transient receptor potential vanilloid 4 (TRPV4) is a member of the TRP channel family and is involved in diverse physiological and pathological processes. Accumulating evidence from in vitro studies indicates that TRPV4 has a potential role in liver fibrosis, but its precise role in the pathophysiological development of this condition is unclear. Exogenous interventions and endogenous reactions should be considered.

METHODS

This study used a mouse model of carbon tetrachloride (CCl4)-induced liver fibrosis to investigate the effects of intraperitoneal injection of the novel TRPV4 channel selective agonist GSK1016790A (GSK) and antagonist HC-067047 (HC).

RESULTS

As compared with the CCl4 group, collagen fiber deposition and alpha-smooth muscle actin (α-SMA) levels were markedly higher and hepatic lobule disorganization was worse in the CCl4+GSK group, while collagen fiber deposition was significantly lower and hepatic lobule disorganization was less severe in the CCl4+HC group.

CONCLUSIONS

The present findings suggest that activation of TRPV4 channels worsens liver fibrosis and that inhibition of TRPV4 channels may alleviate liver fibrosis in vivo.

COX-2 in liver fibrosis

As a vital inducible sensor, cyclooxygenase-2 (COX-2) plays an important role in the progress of hepatic fibrogenesis. Activation of hepatic stellate cells (HSCs) in the liver can significantly accelerate the onset and development of liver fibrosis. COX-2 overexpression triggers inflammation that is an important inducer in hepatic fibrosis. Increasing evidence indicates that COX-2 is involved in the main pathogenesis of liver fibrosis, such as inflammation, apoptosis, and cell senescence. Moreover, COX-2 expression is altered in patients and animal models with non-alcoholic fatty liver disease or cirrhosis. These findings suggest that COX-2 has a broad and critical role in the development of liver fibrosis. In this review, we summarize the latest advances in the regulation and signal transduction of COX-2 and its impact on liver fibrosis.

Induction of E6AP by microRNA-302c dysregulation inhibits TGF-β-dependent fibrogenesis in hepatic stellate cells

Hepatic stellate cells (HSCs) are essential for liver fibrosis. E6 associated protein (E6AP) is one of the E3-ubiquitin-protein ligase and has been studied in proliferation and cellular stress. Currently, no information is available on the role of E6AP on transforming growth factor-β (TGF-β) signaling and hepatic fibrogenesis. This study examined whether E6AP is overexpressed in activated HSCs, and if so, its effect on hepatic fibrogenesis and the molecular mechanism. E6AP was expressed higher in HSCs than hepatocytes, and was up-regulated in activated HSCs, HSCs from the livers of carbon tetrachloride-injected mice, or TGF-β-treated LX-2 cells. The TGF-β-mediated E6AP up-regulation was not due to altered mRNA level nor protein stability. Thus, we performed microRNA (miRNA, miR) analysis and found that miR-302c was dysregulated in TGF-β-treated LX-2 cells or activated primary HSCs. We revealed that miR-302c was a modulator of E6AP. E6AP overexpression inhibited TGF-β-induced expression of plasminogen activator inhibitor-1 in LX-2 cells, albeit it was independent of Smad pathway. Additionally, E6AP inhibited TGF-β-mediated phosphorylation of mitogen-activated protein kinases. To conclude, E6AP overexpression due to decreased miR-302c in HSCs attenuated hepatic fibrogenesis through inhibition of the TGF-β-induced mitogen-activated protein kinase signaling pathway, implying that E6AP and other molecules may contribute to protection against liver fibrosis.

Induction of E6AP by microRNA-302c dysregulation inhibits TGF-β-dependent fibrogenesis in hepatic stellate cells

Hepatic stellate cells (HSCs) are essential for liver fibrosis. E6 associated protein (E6AP) is one of the E3-ubiquitin-protein ligase and has been studied in proliferation and cellular stress. Currently, no information is available on the role of E6AP on transforming growth factor-β (TGF-β) signaling and hepatic fibrogenesis. This study examined whether E6AP is overexpressed in activated HSCs, and if so, its effect on hepatic fibrogenesis and the molecular mechanism. E6AP was expressed higher in HSCs than hepatocytes, and was up-regulated in activated HSCs, HSCs from the livers of carbon tetrachloride-injected mice, or TGF-β-treated LX-2 cells. The TGF-β-mediated E6AP up-regulation was not due to altered mRNA level nor protein stability. Thus, we performed microRNA (miRNA, miR) analysis and found that miR-302c was dysregulated in TGF-β-treated LX-2 cells or activated primary HSCs. We revealed that miR-302c was a modulator of E6AP. E6AP overexpression inhibited TGF-β-induced expression of plasminogen activator inhibitor-1 in LX-2 cells, albeit it was independent of Smad pathway. Additionally, E6AP inhibited TGF-β-mediated phosphorylation of mitogen-activated protein kinases. To conclude, E6AP overexpression due to decreased miR-302c in HSCs attenuated hepatic fibrogenesis through inhibition of the TGF-β-induced mitogen-activated protein kinase signaling pathway, implying that E6AP and other molecules may contribute to protection against liver fibrosis.

Heterotrimeric G Proteins as Therapeutic Targets in Drug Discovery

Heterotrimeric G proteins are molecular switches in GPCR signaling pathways and regulate a plethora of physiological and pathological processes. GPCRs are efficient drug targets, and more than 30% of the drugs in use target them. However, selectively targeting an individual GPCR may be undesirable in various multifactorial diseases in which multiple receptors are involved. In addition, abnormal activation or expression of G proteins is frequently associated with diseases. Furthermore, G proteins harboring mutations often result in malignant diseases. Thus, targeting G proteins instead of GPCRs might provide alternative approaches for combating these diseases. In this review, we discuss the biochemistry of heterotrimeric G proteins, describe the G protein-associated diseases, and summarize the currently known modulators that can regulate the activities of G proteins. The outlook for targeting G proteins to treat diverse diseases is also included in this manuscript.

Hypoxia induces the activation of hepatic stellate cells through the PVT1-miR-152-ATG14 signaling pathway

Increasing studies have indicated that hypoxia serves as a pivotal microenvironmental factor that facilitates activation of hepatic stellate cells (HSCs). However, the mechanism by which hypoxia activates HSCs is not clear. Here, we demonstrated that plasmacytoma variant translocation 1 (PVT1) and autophagy were overexpressed in liver fibrotic specimens. In primary mouse HSCs, both PVT1 and autophagy were induced by hypoxia. Further study showed that hypoxia-induced autophagy depended on expression of PVT1 and miR-152 in HSCs. Luciferase reporter assay indicated that autophagy-related gene 14 (ATG14) was a direct target of miR-152. In addition, inhibition of autophagy by 3-methyladenine and Beclin-1 siRNA impeded activation of HSCs cultured in 1% O₂. Taken together, autophagy induction via the PVT1-miR-152-ATG14 signaling pathway contributes to activation of HSCs under hypoxia condition.

Ubiquitin-Like Post-Translational Modifications (Ubl-PTMs): Small Peptides with Huge Impact in Liver Fibrosis

Liver fibrosis is characterized by the excessive deposition of extracellular matrix proteins including collagen that occurs in most types of chronic liver disease. Even though our knowledge of the cellular and molecular mechanisms of liver fibrosis has deeply improved in the last years, therapeutic approaches for liver fibrosis remain limited. Profiling and characterization of the post-translational modifications (PTMs) of proteins, and more specifically NEDDylation and SUMOylation ubiquitin-like (Ubls) modifications, can provide a better understanding of the liver fibrosis pathology as well as novel and more effective therapeutic approaches. On this basis, in the last years, several studies have described how changes in the intermediates of the Ubl cascades are altered during liver fibrosis and how specific targeting of particular enzymes mediating these ubiquitin-like modifications can improve liver fibrosis, mainly in in vitro models of hepatic stellate cells, the main fibrogenic cell type, and in pre-clinical mouse models of liver fibrosis. The development of novel inhibitors of the Ubl modifications as well as novel strategies to assess the modified proteome can provide new insights into the overall role of Ubl modifications in liver fibrosis.

Emerging Roles of Lipophagy in Health and Disease

The term lipophagy is used to describe the autophagic degradation of lipid droplets, the main lipid storage organelles of eukaryotic cells. Ever since its discovery in 2009, lipophagy has emerged as a significant component of lipid metabolism with important implications for organismal health. This review aims to provide a brief summary of our current knowledge on the mechanisms that are responsible for regulating lipophagy and the impact the process has under physiological and pathological conditions.

RAB18 modulates autophagy in human stellate cells

BACKGROUND

Macroautophagy (or autophagy) is a conserved degradative pathway that breaks down sequestered cytoplasmic proteins and organelles in specialized double-membrane compartments called autophagosomes that fuse with lysosomes. Several proteins orchestrate this process, specifically Rab GTPases that are master regulators of molecular trafficking. RAB18 GTPase, a known mediator of stellate cell activation, is known to modulate autophagic flux in fibroblasts. However, its role in autophagy is unexplored in hepatic stellate cells.

OBJECTIVE

The aim of this study was to investigate the role of RAB18 in modulating autophagy in hepatic stellate cells.

METHODS

Role of RAB18 was determined by genetic depletion, pharmacologic inhibition, and overexpression studies to monitor autophagy flux and proteostasis in human LX2 stellate cell line.

RESULTS

RAB18 knockdown increases autophagy flux and regulates proteostasis. LX2 cells stimulated with transforming growth factor-beta robustly increases expression of profibrotic genes such as COL1A1 and ACTA2 along with RAB18 and its guanine nucleotide exchange factor, RAB3GAP1.

CONCLUSION

The study elucidates a role for RAB18 in autophagy and regulation of proteostasis in human stellate cells. Molecular insights into this process can provide therapeutic opportunities for intervention in liver fibrosis.

Inhibitory Effect of Sestrin 2 on Hepatic Stellate Cell Activation and Liver Fibrosis

Aims: Hepatic fibrosis results from chronic liver injury and inflammatory responses. Sestrin 2 (Sesn2), an evolutionarily conserved antioxidant enzyme, reduces the severities of acute hepatitis and metabolic liver diseases. However, the role of Sesn2 in the pathogenesis of liver fibrosis remains obscure. Here, we used cultured hepatic stellate cells (HSCs) and chronic carbon tetrachloride (CCl₄) and bile duct ligation (BDL) murine models to investigate the effects of Sesn2 on fibrogenesis. Results: Sesn2 protein and mRNA levels were upregulated in activated primary HSCs, and by increasing transcription, transforming growth factor-β (TGF-β) also increased Sesn2 expression in HSCs. Furthermore, Smad activation was primarily initiated by TGF-β signaling, and Smad3 activation increased Sesn2 luciferase activity. In silico analysis of the 5' upstream region of the Sesn2 gene revealed a putative Smad-binding element (SBE), and its deletion demonstrated that the SBE between -964 and -956 bp within human Sesn2 promoter was critically required for TGF-β-mediated response. Moreover, ectopic expression of Sesn2 reduced gene expressions associated with HSC activation, and this was accompanied by marked decreases in SBE luciferase activity and Smad phosphorylation. Infection of recombinant adenovirus Sesn2 reduced hepatic injury severity, as evidenced by reductions in CCl₄- or BDL-induced alanine aminotransferase and aspartate aminotransferase, and inhibited collagen accumulation. Furthermore, HSC-specific lentiviral delivery of Sesn2 prevented CCl₄-induced liver fibrosis. Finally, Sesn2 expression was downregulated in the livers of patients with liver cirrhosis and in mouse models of hepatic fibrosis. Innovation and Conclusion: Our findings suggest that Sesn2 has the potential to inhibit HSC activation and hepatic fibrosis.

Overexpression of miR-224-3p alleviates apoptosis from cerebral ischemia reperfusion injury by targeting FIP200

AIMS

In previous studies, numerous differential microRNAs (miRNAs) in cerebral ischemic/reperfusion (I/R) injury were identified using the miRNA microarray analysis. However, the relationship between miRNA and cerebral I/R injury remains largely unknown. In this study, we investigated the function and explored the possible mechanism of miR-224-3p in cerebral I/R injury.

METHODS

Oxygen glucose deprivation model in N2a cells were used to perform the cerebral I/R injury in vitro. Trypan blue staining, reactive oxygen species (ROS) production, and caspase-3 were measured to evaluate the function of miR-224-3p.

RESULTS

Overexpression of miR-224-3p alleviated the apoptosis induced by oxygen glucose deprivation (OGD) and cleaved caspase-3 was significantly reduced. We further provided the possible mechanism that miR-224-3p may protect cells from cerebral I/R injury by targeting FAK family-interacting protein (FIP200). Further rescue experiment proved that overexpression of FIP200 partially blocked the effect of miR-224-3p.

CONCLUSIONS

We evaluated the function and mechanism of miR-224-3p in ischemic brain injury. miR-224-3p may serve as a potential target for new therapeutic intervention.

Modulated Autophagy by MicroRNAs in Osteoarthritis Chondrocytes

Osteoarthritis (OA) is a chronic joint disease characterized by articular cartilage regression. The etiology of OA is diverse, the exact pathogenesis of which remains unclear. Autophagy is a conserved maintenance mechanism in eukaryotic cells. Dysfunction of chondrocyte autophagy is regarded as a crucial pathogenesis of cartilage degradation in OA. MircoRNAs (miRNAs) are a category of small noncoding RNAs, acting as posttranscriptional modulators that regulate biological processes and cell signaling pathways via target genes. A series of miRNAs are involved in the progression of chondrocyte autophagy and are connected with numerous factors and pathways. This article focuses on the mechanisms of chondrocyte autophagy in OA and reviews the role of miRNA in their modulation. Potentially relevant miRNAs are also discussed in order to provide new directions for future research and improve our understanding of the autophagic network of miRNAs.

Autophagy in liver diseases: Time for translation?

Autophagy is a self-eating catabolic pathway that contributes to liver homeostasis through its role in energy balance and in the quality control of the cytoplasm, by removing misfolded proteins, damaged organelles and lipid droplets. Autophagy not only regulates hepatocyte functions but also impacts on non-parenchymal cells, such as endothelial cells, macrophages and hepatic stellate cells. Deregulation of autophagy has been linked to many liver diseases and its modulation is now recognized as a potential new therapeutic strategy. Indeed, enhancing autophagy may prevent the progression of a number of liver diseases, including storage disorders (alpha-1 antitrypsin deficiency, Wilson's disease), acute liver injury, non-alcoholic steatohepatitis and chronic alcohol-related liver disease. Nevertheless, in some situations such as fibrosis, targeting specific liver cells must be considered, as autophagy displays opposing functions depending on the cell type. In addition, an optimal therapeutic time-window should be identified, since autophagy might be beneficial in the initial stages of disease, but detrimental at more advanced stages, as in the case of hepatocellular carcinoma. Finally, identifying biomarkers of autophagy and methods to monitor autophagic flux in vivo are important steps for the future development of personalized autophagy-targeting strategies. In this review, we provide an update on the regulatory role of autophagy in various aspects of liver pathophysiology, describing the different strategies to manipulate autophagy and discussing the potential to modulate autophagy as a therapeutic strategy in the context of liver diseases.

SVIP alleviates CCl4-induced liver fibrosis via activating autophagy and protecting hepatocytes

Prolonged parenchymal cell death leads to activation of fibrogenic cells and extracellular matrix accumulation and eventually liver fibrosis. Autophagy, a major catabolic process of intracellular degradation and recycling, participates in hepatic fibrosis. However, the precise role of autophagy in the pathogenesis of hepatic fibrosis is controversial. The present study aims to investigate the key role of small VCP/p97 interacting protein (SVIP) against CCl₄-induced hepatic fibrosis via activating autophagy. Autophagy could be activated by SVIP in HepG2 cells, but starvation cannot increase SVIP expression in vitro and in vivo. Moreover, SVIP expression, in agreement with autophagic activity and the volume of lipid droplets, first increases and then decreases during the progression of liver fibrosis with CCl₄ treatment in vivo and in vivo. Further, overexpression of SVIP can protect HepG2 cells from the toxicity of CCl₄, which could be enhanced by starvation. Finally, starvation keeps SVIP and autophagy at such high levels in the rat livers that markedly delays the progress of hepatic fibrosis. Probably, the protective effect of SVIP is associated with stabilizing nuclear factor (erythroid-derived 2)-related factor 2 (Nrf2) and transcription factor EB (TFEB). The current study provides insight into the biological role of SVIP and autophagy in regulating hepatic fibrosis, targeting SVIP might be a novel therapeutic strategy in the future.

Relevance of Autophagy in Parenchymal and Non-Parenchymal Liver Cells for Health and Disease

Autophagy is a highly conserved intracellular process for the ordered degradation and recycling of cellular components in lysosomes. In the liver, parenchymal cells (i.e., mainly hepatocytes) utilize autophagy to provide amino acids, glucose, and free fatty acids as sources of energy and biosynthesis functions, but also for recycling and controlling organelles such as mitochondria. Non-parenchymal cells of the liver, including endothelial cells, macrophages (Kupffer cells), and hepatic stellate cells (HSC), also employ autophagy, either for maintaining cellular homeostasis (macrophages, endothelium) or for providing energy for their activation (stellate cells). In hepatocytes, autophagy contributes to essential homeostatic functions (e.g., gluconeogenesis, glycogenolysis, fatty acid oxidation), but is also implicated in diseases. For instance, storage disorders (alpha 1 antitrypsin deficiency, Wilson's disease), metabolic (non-alcoholic steatohepatitis, NASH), and toxic (alcohol) liver diseases may benefit from augmenting autophagy in hepatocytes. In hepatic fibrosis, autophagy has been implicated in the fibrogenic activation of HSC to collagen-producing myofibroblasts. In hepatocellular carcinoma (HCC), autophagy may contribute to tumor surveillance as well as invasiveness, indicating a dual and stage-dependent function in cancer. As many drugs directly or indirectly modulate autophagy, it is intriguing to investigate autophagy-targeting, possibly even cell type-directed strategies for the treatment of hereditary liver diseases, NASH, fibrosis, and HCC.

miRNA Signature in NAFLD: A Turning Point for a Non-Invasive Diagnosis

Nonalcoholic fatty liver disease (NAFLD) defines a wide pathological spectrum ranging from simple steatosis to nonalcoholic steatohepatitis (NASH) which may predispose to liver cirrhosis and hepatocellular carcinoma. It represents the leading cause of hepatic damage worldwide. Diagnosis of NASH still requires liver biopsy but due to the high prevalence of NAFLD, this procedure, which is invasive, is not practicable for mass screening. Thus, it is crucial to non-invasively identify NAFLD patients at higher risk of progression to NASH and fibrosis. It has been demonstrated that hepatic fat content and progressive liver damage have a strong heritable component. Therefore, genetic variants associated with NAFLD have been proposed as non-invasive markers to be used in clinical practice. However, genetic variability is not completely explained by these common variants and it is possible that many of the phenotypic differences result from gene-environment interactions. Indeed, NAFLD development and progression is also modulated by epigenetic factors, in particular microRNAs (miRNAs), which control at post-transcriptional level many complementary target mRNAs and whose dysregulation has been shown to have high prognostic and predictive value in NAFLD. The premise of the current review is to discuss the role of miRNAs as pathogenic factors, risk predictors and therapeutic targets in NAFLD.

Gα12 ablation exacerbates liver steatosis and obesity by suppressing USP22/SIRT1-regulated mitochondrial respiration

Nonalcoholic fatty liver disease (NAFLD) arises from mitochondrial dysfunction under sustained imbalance between energy intake and expenditure, but the underlying mechanisms controlling mitochondrial respiration have not been entirely understood. Heterotrimeric G proteins converge with activated GPCRs to modulate cell-signaling pathways to maintain metabolic homeostasis. Here, we investigated the regulatory role of G protein α12 (Gα12) on hepatic lipid metabolism and whole-body energy expenditure in mice. Fasting increased Gα12 levels in mouse liver. Gα12 ablation markedly augmented fasting-induced hepatic fat accumulation. cDNA microarray analysis from Gna12-KO liver revealed that the Gα12-signaling pathway regulated sirtuin 1 (SIRT1) and PPARα, which are responsible for mitochondrial respiration. Defective induction of SIRT1 upon fasting was observed in the liver of Gna12-KO mice, which was reversed by lentivirus-mediated Gα12 overexpression in hepatocytes. Mechanistically, Gα12 stabilized SIRT1 protein through transcriptional induction of ubiquitin-specific peptidase 22 (USP22) via HIF-1α increase. Gα12 levels were markedly diminished in liver biopsies from NAFLD patients. Consistently, Gna12-KO mice fed a high-fat diet displayed greater susceptibility to diet-induced liver steatosis and obesity due to decrease in energy expenditure. Our results demonstrate that Gα12 regulates SIRT1-dependent mitochondrial respiration through HIF-1α-dependent USP22 induction, identifying Gα12 as an upstream molecule that contributes to the regulation of mitochondrial energy expenditure.

Inter-Individual Variability in Acute Toxicity of R-Pulegone and R-Menthofuran in Human Liver Slices and Their Influence on miRNA Expression Changes in Comparison to Acetaminophen

Monoterpenes R-pulegone (PUL) and R-menthofuran (MF), abundant in the Lamiaceae family, are frequently used in herb and food products. Although their hepatotoxicity was shown in rodent species, information about their effects in human liver has been limited. The aim of our study was to test the effects of PUL, MF and acetaminophen (APAP, as a reference compound) on cell viability and microRNA (miRNA) expression in human precision-cut liver slices. Slices from five patients were used to follow up on the inter-individual variability. PUL was toxic in all liver samples (the half-maximal effective concentration was 4.0 µg/mg of tissue), while MF and surprisingly APAP only in two and three liver samples, respectively. PUL also changed miRNA expression more significantly than MF and APAP. The most pronounced effect was a marked decrease of miR-155-5p expression caused by PUL even in non-toxic concentrations in all five liver samples. Our results showed that PUL is much more toxic than MF and APAP in human liver and that miR-155-5p could be a good marker of PUL early hepatotoxicity. Marked inter-individual variabilities in all our results demonstrate the high probability of significant differences in the hepatotoxicity of tested compounds among people.