Molecular insights into the role of mitochondria in non-alcoholic fatty liver disease

Mitochondria Matter: Systemic Aspects of Nonalcoholic Fatty Liver Disease (NAFLD) and Diagnostic Assessment of Liver Function by Stable Isotope Dynamic Breath Tests

The liver plays a key role in systemic metabolic processes, which include detoxification, synthesis, storage, and export of carbohydrates, lipids, and proteins. The raising trends of obesity and metabolic disorders worldwide is often associated with the nonalcoholic fatty liver disease (NAFLD), which has become the most frequent type of chronic liver disorder with risk of progression to cirrhosis and hepatocellular carcinoma. Liver mitochondria play a key role in degrading the pathways of carbohydrates, proteins, lipids, and xenobiotics, and to provide energy for the body cells. The morphological and functional integrity of mitochondria guarantee the proper functioning of β-oxidation of free fatty acids and of the tricarboxylic acid cycle. Evaluation of the liver in clinical medicine needs to be accurate in NAFLD patients and includes history, physical exam, imaging, and laboratory assays. Evaluation of mitochondrial function in chronic liver disease and NAFLD is now possible by novel diagnostic tools. "Dynamic" liver function tests include the breath test (BT) based on the use of substrates marked with the non-radioactive, naturally occurring stable isotope 13C. Hepatocellular metabolization of the substrate will generate 13CO2, which is excreted in breath and measured by mass spectrometry or infrared spectroscopy. Breath levels of 13CO2 are biomarkers of specific metabolic processes occurring in the hepatocyte cytosol, microsomes, and mitochondria. 13C-BTs explore distinct chronic liver diseases including simple liver steatosis, non-alcoholic steatohepatitis, liver fibrosis, cirrhosis, hepatocellular carcinoma, drug, and alcohol effects. In NAFLD, 13C-BT use substrates such as α-ketoisocaproic acid, methionine, and octanoic acid to assess mitochondrial oxidation capacity which can be impaired at an early stage of disease. 13C-BTs represent an indirect, cost-effective, and easy method to evaluate dynamic liver function. Further applications are expected in clinical medicine. In this review, we discuss the involvement of liver mitochondria in the progression of NAFLD, together with the role of 13C-BT in assessing mitochondrial function and its potential use in the prevention and management of NAFLD.

Exosomal microRNAs as diagnostic and therapeutic biomarkers in non-malignant liver diseases

The liver is a vital organ responsible for various physiological functions, such as metabolism, immune response, digestion, and detoxification. Crosstalk between hepatocytes, hepatic macrophages, and hepatic stellate cells is critical for liver pathology. Exosomes are small extracellular vesicles (50-150 nm) that play an important role in cell-cell or organ-organ communication as they transfer their cargo, such as protein, DNA, and RNA to recipient cells or distant organs. In various liver diseases, the number of liver cell-derived exosomes is increased and the exosomal microRNA (miRNA) profile is altered. Early studies investigated the value of circulating exosomal miRNAs as biomarkers. Several exosomal miRNAs showed excellent diagnostic values, suggesting their potential as diagnostic biomarkers in liver diseases. Exosomal miRNAs have emerged as critical regulators of liver pathology because they control the expression of multiple genes in recipient cells. In this review, we discuss the biology of exosomes and summarize the recent findings of exosome-mediated intercellular and organ-to-organ communication during liver pathology. As there are many review articles dealing with exosomal miRNAs in liver cancer, we focused on non-malignant liver diseases. The therapeutic potential of exosomal miRNAs in liver pathology is also highlighted.

Hesperetin ameliorates hepatic oxidative stress and inflammation via the PI3K/AKT-Nrf2-ARE pathway in oleic acid-induced HepG2 cells and a rat model of high-fat diet-induced NAFLD

Non-alcoholic fatty liver disease (NAFLD) is considered the most common liver disease. Dietary supplementation has become a promising strategy for managing NAFLD. Hesperetin, a citrus flavonoid, is mainly found in citrus fruits (oranges, grapefruit, and lemons) and possesses multiple pharmacological properties, including anti-cancer, anti-Alzheimer and anti-diabetic effects. However, the anti-NAFLD effect and mechanisms of hesperetin remain unclear. In this study, we investigated the therapeutic effect of hesperetin against NAFLD and the underlying mechanism in vitro and in vivo. In oleic acid (OA)-induced HepG2 cells, hesperetin upregulated antioxidant levels (SOD/GPx/GR/GCLC/HO-1) by triggering the PI3 K/AKT-Nrf2 pathway, alleviating OA-induced reactive oxygen species (ROS) overproduction and hepatotoxicity. Furthermore, hesperetin suppressed NF-κB activation and reduced inflammatory cytokine secretion (TNF-α and IL-6). More importantly, we revealed that this anti-inflammatory effect is attributed to reduced ROS overproduction by the Nrf2 pathway, as pre-treatment with Nrf2 siRNA or an inhibitor of superoxide dismutase (SOD) or/and glutathione peroxidase (GPx) abolished hesperetin-induced NF-κB inactivation and reductions in inflammatory cytokine secretion. In a rat model of high-fat diet (HFD)-induced NAFLD, we confirmed that hesperetin relieved hepatic steatosis, oxidative stress, inflammatory cell infiltration and fibrosis. Moreover, hesperetin activated the PI3 K/AKT-Nrf2 pathway in the liver, increasing antioxidant expression and inhibiting NF-κB activation and inflammatory cytokine secretion. In summary, our results demonstrate that hesperetin ameliorates hepatic oxidative stress through the PI3 K/AKT-Nrf2 pathway and that this antioxidative effect further suppresses NF-κB-mediated inflammation during NAFLD progression. Thus, our study suggests that hesperetin may be an effective dietary supplement for improving NAFLD by suppressing hepatic oxidative stress and inflammation.

Mitochondrial Mutations and Genetic Factors Determining NAFLD Risk

NAFLD (non-alcoholic fatty liver disease) is a widespread liver disease that is often linked with other life-threatening ailments (metabolic syndrome, insulin resistance, diabetes, cardiovascular disease, atherosclerosis, obesity, and others) and canprogress to more severe forms, such as NASH (non-alcoholic steatohepatitis), cirrhosis, and HCC (hepatocellular carcinoma). In this review, we summarized and analyzed data about single nucleotide polymorphism sites, identified in genes related to NAFLD development and progression. Additionally, the causative role of mitochondrial mutations and mitophagy malfunctions in NAFLD is discussed. The role of mitochondria-related metabolites of the urea cycle as a new non-invasive NAFLD biomarker is discussed. While mitochondria DNA mutations and SNPs (single nucleotide polymorphisms) canbe used as effective diagnostic markers and target for treatments, age and ethnic specificity should be taken into account.

Developmental programming: Metabolic tissue-specific changes in endoplasmic reticulum stress, mitochondrial oxidative and telomere length status induced by prenatal testosterone excess in the female sheep

Prenatal testosterone (T) excess-induced metabolic dysfunctions involve tissue specific changes in insulin sensitivity with insulin resistant, oxidative and lipotoxic state in liver/muscle and insulin sensitive but inflammatory and oxidative state in visceral adipose tissues (VAT). We hypothesized that mitochondrial dysfunction, endoplasmic reticulum (ER) stress and premature cellular senescence are contributors to the tissue-specific changes in insulin sensitivity. Markers of mitochondrial number, function, and oxidative phosphorylation (OxPhos), ER stress and cellular senescence (telomere length) were assessed in liver, muscle and 4 adipose (VAT, subcutaneous [SAT], epicardiac [ECAT] and perirenal [PRAT]) depots collected from control and prenatal T-treated female sheep at 21 months of age. Prenatal T treatment led to: (a) reduction in mitochondrial number and OxPhos complexes and increase in ER stress markers in muscle; (b) increase in fibrosis with trend towards increase in short telomere fragments in liver (c) depot-specific mitochondrial changes with OxPhos complexes namely increase in SAT and reduction in PRAT and increase in mitochondrial number in ECAT; (d) depot-specific ER stress marker changes with increase in VAT, reduction in SAT, contrasting changes in ECAT and no changes in PRAT; and (d) reduced shorter telomere fragments in SAT, ECAT and PRAT. These changes indicate insulin resistance may be driven by mitochondrial and ER dysfunction in muscle, fibrosis and premature senescence in liver, and depot-specific changes in mitochondrial function and ER stress without involving cellular senescence in adipose tissue. These findings provide mechanistic insights into pathophysiology of metabolic dysfunction among female offspring from hyperandrogenic pregnancies.

Mitochondrial dysfunction attenuates rapid regeneration in livers with toxin-induced fibrosis

BACKGROUND

The mechanism of associating liver partition and portal vein ligation for staged hepatectomy (ALPPS)-induced rapid liver regeneration remains poorly documented, especially in patients with fibrosis. Therefore, this study aims to investigate the underlying mechanism of ALPPS-induced accelerated regeneration in toxin-induced fibrosis models.

METHODS

The ALPPS-induced regeneration model was established in livers with thioacetamide (TAA)-induced fibrosis to determine the regenerative pathways involved in rapid regeneration. Confirmatory experiments were performed in transforming growth factor beta 1 (TGFβ1)-treated AML12 cells and mice with carbon tetrachloride (CCl4)-induced fibrosis. Finally, mitochondrial dysfunction was validated in fibrotic/non-fibrotic patients.

RESULTS

In TAA-induced fibrotic mice, ALPPS-induced regeneration was significantly inferior to that of the control group (P=0.027 at day 2 and P<0.001 at day 7). Furthermore, mitochondria-associated genes were significantly downregulated in TAA-challenged mice. Accordingly, the reduced production of ATP and elevated levels of malondialdehyde indicated disturbances in intracellular energy metabolism during the ALPPS-induced regenerative process after TAA treatment. Further investigations were performed in TGF-β1-treated AML12 cells and CCl4-treated mice, which indicated that mitochondrial dysfunction attenuated the capacity for rapid regeneration after ALPPS.

CONCLUSIONS

In summary, this study revealed that mitochondrial dysfunction led to inferior regeneration in livers with toxin-induced fibrosis and identified new therapeutic targets to improve the feasibility and safety of the ALPPS procedure. Further studies in human patients are required in the future.

Src homolog and collagen homolog1 isoforms in acute and chronic liver injuries

Src homolog and collagen homolog (SHC) proteins are adaptor proteins bound to cell surface receptors that play an important role in signal transduction and related diseases. As an important member of the SHC protein family, SHC1 regulates cell proliferation and apoptosis, reactive oxygen species (ROS) production, and oxidative stress. Three isomeric proteins namely, p46shc, p52shc, and p66shc, are produced from the same SHC1 gene locus. All the three proteins are found in the liver, and are widely expressed in various hepatic cells. SHC1 has been proven to be associated with acute and chronic liver injuries of different etiologies, and plays important roles in liver fibrosis and hepatocellular carcinoma (HCC). Therefore, this review summarizes recent studies that discuss and explore the role of SHC1 in the occurrence and progression of liver diseases. We also provide a theoretical basis for future studies.

Influence of Genistein on Hepatic Lipid Metabolism in an In Vitro Model of Hepatic Steatosis

Nonalcoholic fatty liver disease (NAFLD) is among the leading causes of end-stage liver disease. The impaired hepatic lipid metabolism in NAFLD is exhibited by dysregulated PPARα and SREBP-1c signaling pathways, which are central transcription factors associated with lipid degradation and de novo lipogenesis. Despite the growing prevalence of this disease, current pharmacological treatment options are unsatisfactory. Genistein, a soy isoflavone, has beneficial effects on lipid metabolism and may be a candidate for NAFLD treatment. In an in vitro model of hepatic steatosis, primary human hepatocytes (PHHs) were incubated with free fatty acids (FFAs) and different doses of genistein. Lipid accumulation and the cytotoxic effects of FFAs and genistein treatment were evaluated by colorimetric and enzymatic assays. Changes in lipid homeostasis were examined by RT-qPCR and Western blot analyses. PPARα protein expression was induced in steatotic PHHs, accompanied by an increase in CPT1L and ACSL1 mRNA. Genistein treatment increased PPARα protein expression only in control PHHs, while CPTL1 and ACSL1 were unchanged and PPARα mRNA was reduced. In steatotic PHHs, genistein reversed the increase in activated SREBP-1c protein. The model realistically reflected the molecular changes in hepatic steatosis. Genistein suppressed the activation of SREBP-1c in steatotic hepatocytes, but the genistein-mediated effects on PPARα were abolished by high hepatic lipid levels.

IL-6 Reduces Mitochondrial Replication, and IL-6 Receptors Reduce Chronic Inflammation in NAFLD and Type 2 Diabetes

Interleukin (IL)-6 family cytokines act through a receptor complex with gp130 subunits. IL-6 is a pleiotropic cytokine that regulates inflammation and liver regeneration. Mitochondria are the first to respond to stress and adapt their dynamics in conditions of damage. In this regard, the study aimed to investigate the role of the IL-6 cytokine family (sIL-6Ra, gp130/sIL-6Rb, and IL-11) in the regulation of mitochondrial dynamics in the liver in obese patients and to assess the contribution of these cytokines to the pathogenesis of type 2 diabetes mellitus (T2DM). We studied 134 obese patients with and without T2DM and 41 healthy donors. We found that increasing the concentration of sIL-6Ra and gp130/sIL-6Rb protected against carbohydrate disorders in obese patients and prevented non-alcoholic fatty liver disease (NAFLD) progression in obese patients. An increase in plasma IL-6 levels is associated with decreased, mitochondrial transcription factor A (TFAM) protein production in liver biopsies in obese patients with and without T2DM. Replication, transcription, and division processes in liver biopsy were reduced in patients with T2DM. Inflammatory processes stimulate liver cell apoptosis in obese patients with T2DM. The increase in IL-11 levels is associated with decreased pro-apoptotic Bcl-2-associated X protein (BAX) protein production in obese patients with and without T2DM.

Protective effects of ginsenoside-Rg2 and -Rh1 on liver function through inhibiting TAK1 and STAT3-mediated inflammatory activity and Nrf2/ARE-mediated antioxidant signaling pathway

Systemic or hepatic inflammation is caused by intraperitoneal application of lipopolysaccharide (LPS). In this study, we investigated anti-inflammatory and antioxidant properties of combination of ginsenoside-Rg2 (G-Rg2) and -Rh1 (G-Rh1) on liver function under LPS challenging. We first confirmed that G-Rg2 and -Rh1 at 100 μg/ml did not show cytotoxicity in HepG2 cells. G-Rg2 and -Rh1 treatment significantly inhibited activation of STAT3 and TAK1, and inflammatory factors including iNOS, TNF-α, and IL-1β in peritoneal macrophages. In HepG2 cells, G-Rg2 and -Rh1 treatment inhibited activation of STAT3 and TAK1/c-Jun N-terminal kinase, and down-regulated nuclear translocation of NF-κB transcription factor. In addition, LPS-induced mitochondrial dysfunction was restored by treatment with G-Rg2 and -Rh1. Interestingly, pretreatment with G-Rg2 and -Rh1 effectively inhibited mitochondrial damage-mediated ROS production induced by LPS stimulation, and alterations of Nrf2 nuclear translocation and ARE promotor activity were involved in G-Rg2 and -Rh1 effects on balancing ROS levels. In liver tissues of LPS-treated mice, G-Rg2 and -Rh1 treatment protected liver damages and increased Nrf2 expression while reducing CD45 expression. Taken together, G-Rg2 and -Rh1 exerts a protective effect on liver function by increasing antioxidant through Nrf2 and anti-inflammatory activities through STAT3/TAK1 and NF-κB signaling pathways in liver cells and macrophages.

Effects of Pyrroloquinoline Quinone on Lipid Metabolism and Anti-Oxidative Capacity in a High-Fat-Diet Metabolic Dysfunction-Associated Fatty Liver Disease Chick Model

Metabolic dysfunction-associated fatty liver disease (MAFLD) and its interaction with many metabolic pathways raises global public health concerns. This study aimed to determine the therapeutic effects of Pyrroloquinoline quinone (PQQ, provided by PQQ.Na₂) on MAFLD in a chick model and primary chicken hepatocytes with a focus on lipid metabolism, anti-oxidative capacity, and mitochondrial biogenesis. The MAFLD chick model was established on laying hens by feeding them a high-energy low-protein (HELP) diet. Primary hepatocytes isolated from the liver of laying hens were induced for steatosis by free fatty acids (FFA) and for oxidative stress by hydrogen peroxide (H₂O₂). In the MAFLD chick model, the dietary supplementation of PQQ conspicuously ameliorated the negative effects of the HELP diet on liver biological functions, suppressed the progression of MAFLD mainly through enhanced lipid metabolism and protection of liver from oxidative injury. In the steatosis and oxidative stress cell models, PQQ functions in the improvement of the lipid metabolism and hepatocytes tolerance to fatty degradation and oxidative damage by enhancing mitochondrial biogenesis and then increasing the anti-oxidative activity and anti-apoptosis capacity. At both the cellular and individual levels, PQQ was demonstrated to exert protective effects of hepatocyte and liver from fat accumulation through the improvement of mitochondrial biogenesis and maintenance of redox homeostasis. The key findings of the present study provide an in-depth knowledge on the ameliorative effects of PQQ on the progression of fatty liver and its mechanism of action, thus providing a theoretical basis for the application of PQQ, as an effective nutrient, into the prevention of MAFLD.

Inhibition of hyaluronan synthesis by 4-methylumbelliferone ameliorates non-alcoholic steatohepatitis in choline-deficient L-amino acid-defined diet-induced murine model

Hyaluronan (HA) as a glycosaminoglycan can bind to cell-surface receptors, such as TLR4, to regulate inflammation, tissue injury, repair, and fibrosis. 4-methylumbelliferone (4-MU), an inhibitor of HA synthesis, is a drug used for the treatment of biliary spasms. Currently, therapeutic interventions are not available for non-alcoholic steatohepatitis (NASH). In this study, we investigated the effects of 4-MU on NASH using a choline-deficient amino acid (CDAA) diet model. CDAA diet-fed mice showed NASH characteristics, including hepatocyte injury, hepatic steatosis, inflammation, and fibrogenesis. 4-MU treatment significantly reduced hepatic lipid contents in CDAA diet-fed mice. 4-MU reversed CDAA diet-mediated inhibition of Ppara and induction of Srebf1 and Slc27a2. Analysis of serum ALT and AST levels revealed that 4-MU treatment protected against hepatocellular damage induced by CDAA diet feeding. TLR4 regulates low molecular weight-HA-induced chemokine expression in hepatocytes. In CDAA diet-fed, 4-MU-treated mice, the upregulated chemokine/cytokine expression, such as Cxcl1, Cxcl2, and Tnf was attenuated with the decrease of macrophage infiltration into the liver. Moreover, HA inhibition repressed CDAA diet-induced mRNA expression of fibrogenic genes, Notch1, and Hes1 in the liver. In conclusion, 4-MU treatment inhibited liver steatosis and steatohepatitis in a mouse model of NASH, implicating that 4-MU may have therapeutic potential for NASH.

Astragaloside IV Alleviates Liver Inflammation, Oxidative Stress and Apoptosis to Protect Against Experimental Non-Alcoholic Fatty Liver Disease

PURPOSE

Non-alcoholic fatty liver disease (NAFLD) is the main form of chronic liver disease in the world. Astragaloside IV (ASIV) has been tested in experimental models of different diseases. The purpose of this study was to evaluate the effect and protective mechanism of ASIV on NAFLD.

METHODS

Lipopolysaccharide (LPS)- and palmitate acid (PA)-induced RAW264.7 cells and LO2 cells were used as a NAFLD model. The mice NAFLD model was evaluated by hematoxylin-eosin staining (HE staining), and aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels. Liver lipid metabolism was evaluated by triglyceride (TG) and total cholesterol (TC) kits and oil red O staining. Oxidative stress indicators were examined through biochemical methods. Inflammatory factors were explored through enzyme-linked immuno sorbent assay (ELISA), real-time quantitative PCR and oxidative stress indicator kits. The expression levels of 5-LO (5-lipoxygenase) and leukotriene A4 hydrolase (LTA4H) were checked by real-time quantitative PCR and Western blotting. Apoptosis was detected by Annexin V-FITC/PI cell apoptosis detection kit.

RESULTS

Our results showed that in vivo ASIV significantly reduced liver tissue damage, and serum AST, ALT and serum TG levels in NAFLD mice. In vitro, ASIV reduced cell supernatant TG and TC content increased by PA treatment, and significantly decreased the accumulation of intracellular lipid droplets induced by PA treatment. Additionally, ASIV reduced reactive oxygen species (ROS) and malondialdehyde (MDA) levels, and restored glutathione peroxidase (GSH-Px) levels in PA-treated LO2 cell supernatant. Furthermore, ASIV inhibited the production of proinflammatory cytokines (IL-6 and TNF-α) in RAW264.7 cells induced by LPS. We also found that ASIV downregulated the expression of 5-LO and LTB4 (leukotriene B4) in NAFLD mice. Moreover, ASIV restored apoptotic protein (Bax and Bcl-2) expression in PA-treated LO2 cells.

CONCLUSION

ASIV may reduce liver steatosis, hepatocyte oxidative stress and apoptosis, and decrease liver inflammation, thereby attenuating the progression of NAFLD and thus might be of therapeutic interest.

The Effect of Switching from Tenofovir Disoproxil Fumarate (TDF) to Tenofovir Alafenamide (TAF) on Liver Enzymes, Glucose, and Lipid Profile

Objective

We aimed to investigate the effect of switching from tenofovir disoproxil fumarate (TDF) to tenofovir alafenamide (TAF) on the hepatic safety and metabolic profile.

Methods

Consecutive HIV patients, enrolled in the Surveillance Cohort Long-term Toxicity Antiretrovirals/Antivirals (SCOLTA) project, switching from TDF to TAF were included. Changes from baseline (T0) to 6-month follow-up (T1) were evaluated using paired t-test and signed rank test.

Results

A total of 190 patients switched from TDF to TAF and had one 6-month follow-up visit. They were 80% male, 74.2% at CDC stage A–B, 93.7% with undetectable HIV-viral load. Mean age was 46.7±10.7 years, body mass index was 25.0±3.9 kg/m², median CD4 cell count was 634 cell/µL (interquartile range [IQR]=439–900), aspartate aminotransferase (AST) was 23 (IQR=19–30) IU/L, and alanine aminotransferase (ALT) was 24 (IQR=17–34) IU/L. At T1, both AST (median=−1, IQR=−5–2 IU/L, P=0.004) and ALT (median=−2, IQR=−7–3 IU/L, P=0.0004) showed a significant decrease. Among 28 patients with ALT >40 at baseline, reduction was significant both clinically (−17, IQR=−32–−1) and statistically (P=0.0003). Total cholesterol levels (TC) increased (+13.4±3.8 mg/dL, P=0.0006), as well as HDL-cholesterol (HDL-C) (+3.8±1.2 mg/dL, P=0.02), LDL Cholesterol (LDL-C) (+7.6±3.4, P=0.03) and glucose (+4.0±1.8 mg/dL, P=0.02). D:A:D: and Framingham risk score did not change at 6 months after switch.

Conclusion

A significant reduction of liver enzymes was observed after switching from TDF to TAF, especially in subjects with initial level of ALT >40 IU/L. Glucose, TC, HDL-C, and LDL-C increased, with no effect on cardiovascular risk scores.

The water extract of Sophorae tonkinensis Radix et Rhizoma alleviates non-alcoholic fatty liver disease and its mechanism

BACKGROUND

Sophorae tonkinensis Radix et Rhizoma is traditionally used for clearing away heat and toxic materials in China.

PURPOSE

This study aims to observe the amelioration of Sophorae tonkinensis water extract (STR) against non-alcoholic fatty liver disease (NAFLD) and the engaged mechanism.

METHODS

NAFLD was induced in mice fed by methionine and choline deficient (MCD) diet. Liver histological observation, Oil Red O, Masson's trichrome and F4/80 immunohistochemical staining were performed. Serum and liver biochemical parameters, hepatic gene and protein expression were detected. Cellular lipids accumulation in human normal liver l-02 and hepatoma HepRG cells were induced by 0.5 mM nonestesterified fatty acid (NEFA). The contents of matrine (MT) and oxymatrine (OMT) in STR were detected by using high-performance liquid chromatography (HPLC). Carnitine palmitoyltransferase 1A (CPT1A) expression and enzymatic activity were detected both in vivo and in vitro.

RESULTS

Serum alanine/aspartate aminotransferase (ALT/AST) activity, hepatic malondialdehyde (MDA) content and liver histological observation showed that STR alleviated hepatocellular damage in mice fed with MCD diet. Hepatic triglyceride (TG), total cholesterol (TC) and NEFA amounts, and Oil Red O staining showed that STR reduced hepatic lipids accumulation in mice fed with MCD diet. STR and its main compounds including MT and OMT decreased NEFA-induced cellular lipids accumulation in hepatocytes. STR enhanced CPT1A activity both in vivo and in vitro. MT and OMT also enhanced cellular CPT1A activity in l-02 hepatocytes treated with NEFA. Moreover, the CTP1A inhibitor etomoxir (ETO) reduced the lipid-lowering activity provided by STR, MT or OMT in vitro. Liver myeloperoxidase (MPO) activity and hydroxyproline content, Masson's trichrome and F4/80 immunohistochemical staining, and hepatic mRNA expression of some molecules involved in regulating inflammation or fibrosis demonstrated that STR alleviated hepatic inflammation and liver fibrosis in mice fed with MCD diet.

CONCLUSION

STR alleviated NAFLD by inhibiting hepatic inflammation and liver fibrosis, and reducing hepatic lipids accumulation through promoting fatty acids β-oxidation by enhancing liver CPT1A activity. MT and OMT may be the main active compounds contributing to the lipid-lowering activity provided by STR.

Understanding lipotoxicity in NAFLD pathogenesis: is CD36 a key driver?

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease worldwide. NAFLD stages range from simple steatosis (NAFL) to non-alcoholic steatohepatitis (NASH) which can progress to cirrhosis and hepatocellular carcinoma. One of the crucial events clearly involved in NAFLD progression is the lipotoxicity resulting from an excessive fatty acid (FFA) influx to hepatocytes. Hepatic lipotoxicity occurs when the capacity of the hepatocyte to manage and export FFAs as triglycerides (TGs) is overwhelmed. This review provides succinct insights into the molecular mechanisms responsible for lipotoxicity in NAFLD, including ER and oxidative stress, autophagy, lipoapotosis and inflammation. In addition, we highlight the role of CD36/FAT fatty acid translocase in NAFLD pathogenesis. Up-to-date, it is well known that CD36 increases FFA uptake and, in the liver, it drives hepatosteatosis onset and might contribute to its progression to NASH. Clinical studies have reinforced the significance of CD36 by showing increased content in the liver of NAFLD patients. Interestingly, circulating levels of a soluble form of CD36 (sCD36) are abnormally elevated in NAFLD patients and positively correlate with the histological grade of hepatic steatosis. In fact, the induction of CD36 translocation to the plasma membrane of the hepatocytes may be a determining factor in the physiopathology of hepatic steatosis in NAFLD patients. Given all these data, targeting the fatty acid translocase CD36 or some of its functional regulators may be a promising therapeutic approach for the prevention and treatment of NAFLD.

Role of Mitofusins and Mitophagy in Life or Death Decisions

Mitochondria entail an incredible dynamism in their morphology, impacting death signaling and selective elimination of the damaged organelles. In turn, by recycling the superfluous or malfunctioning mitochondria, mostly prevalent during aging, mitophagy contributes to maintain a healthy mitochondrial network. Mitofusins locate at the outer mitochondrial membrane and control the plastic behavior of mitochondria, by mediating fusion events. Besides deciding on mitochondrial interconnectivity, mitofusin 2 regulates physical contacts between mitochondria and the endoplasmic reticulum, but also serves as a decisive docking platform for mitophagy and apoptosis effectors. Thus, mitofusins integrate multiple bidirectional inputs from and into mitochondria and ensure proper energetic and metabolic cellular performance. Here, we review the role of mitofusins and mitophagy at the cross-road between life and apoptotic death decisions. Furthermore, we highlight the impact of this interplay on disease, focusing on how mitofusin 2 and mitophagy affect non-alcoholic fatty liver disease.

miR-29a Modulates GSK3β/SIRT1-Linked Mitochondrial Proteostatic Stress to Ameliorate Mouse Non-Alcoholic Steatohepatitis

MicroRNA-29a (miR-29a) has been shown to ameliorate hepatocellular damage, such as in the context of non-alcoholic fatty liver disease (NAFLD), steatohepatitis (NASH), and cholestatic injury. However, the mechanism mediating the hepatoprotective effect of miR-29a in diet-induced NASH remains elusive. In the present study, C57BL/6 mice of wild-type (WT) or miR-29a overexpression were fed with methionine–choline sufficient (MCS) or methionine–choline-deficient (MCD) diet for four weeks. The C57BL/6 mice harboring miR-29a overexpression presented reduced plasma AST, hepatic CD36, steatosis, and fibrosis induced by MCD. The TargetScan Release7.2-based bioinformatic analysis, KEGG pathway analysis, and luciferase reporter assay confirmed that miR-29a targets 3′UTR of glycogen synthase kinase 3 beta (Gsk3b) mRNA in the HepG2 hepatocyte cell line. Furthermore, miR-29a overexpression in the MCD-fed group resulted in inhibition of Gsk3b mRNA and GSK3β protein levels in the liver. GSK3β was notably expressed jointly with the extent of aggregated protein, which was then identified to be associated with mitochondrial unfolded protein response (UPR^mt), but not with endoplasmic reticulum UPR (UPR^ER). Additionally, in silico analysis of protein–protein interaction, in vivo, and in vitro correlation analyses of protein expression demonstrated that GSK3β closely associated with sirtuin 1(SIRT1). Finally, the implication of SIRT1-mediated mitochondrial biogenesis in the perturbation of proteostasis was observed. We herein provide novel insight into a hepatoprotective pathway, whereby miR-29a inhibits GSK3β to repress SIRT1-mediated mitochondrial biogenesis, leading to alleviation of mitochondrial proteostatic stress and UPR^mt in the context of NASH. miR-29a, GSK3β, and SIRT1 could thus serve as possible therapeutic targets to improve the treatment of NAFLD/NASH.

Mitochondrial Transfer by Human Mesenchymal Stromal Cells Ameliorates Hepatocyte Lipid Load in a Mouse Model of NASH

Mesenchymal stromal cell (MSC) transplantation ameliorated hepatic lipid load; tissue inflammation; and fibrosis in rodent animal models of non-alcoholic steatohepatitis (NASH) by as yet largely unknown mechanism(s). In a mouse model of NASH; we transplanted bone marrow-derived MSCs into the livers; which were analyzed one week thereafter. Combined metabolomic and proteomic data were applied to weighted gene correlation network analysis (WGCNA) and subsequent identification of key drivers. Livers were analyzed histologically and biochemically. The mechanisms of MSC action on hepatocyte lipid accumulation were studied in co-cultures of hepatocytes and MSCs by quantitative image analysis and immunocytochemistry. WGCNA and key driver analysis revealed that NASH caused the impairment of central carbon; amino acid; and lipid metabolism associated with mitochondrial and peroxisomal dysfunction; which was reversed by MSC treatment. MSC improved hepatic lipid metabolism and tissue homeostasis. In co-cultures of hepatocytes and MSCs; the decrease of lipid load was associated with the transfer of mitochondria from the MSCs to the hepatocytes via tunneling nanotubes (TNTs). Hence; MSCs may ameliorate lipid load and tissue perturbance by the donation of mitochondria to the hepatocytes. Thereby; they may provide oxidative capacity for lipid breakdown and thus promote recovery from NASH-induced metabolic impairment and tissue injury.

Protective Effects of Evogliptin on Steatohepatitis in High-Fat-Fed Mice

There are few studies on the effects of dipeptidyl peptidase-4 inhibitors on steatohepatitis. We explored whether evogliptin (Evo), a dipeptidyl peptidase-4 inhibitor, protects against steatohepatitis in a high-fat diet (HFD)-fed mice and whether these effects involve modulation of mitophagy. Adult male C57BL/J mice were divided into the normal diet (ND), HFD (45% of energy from fat) with Evo (250 mg/kg) (HFD + Evo), and HFD groups at 4 weeks of age and were sacrificed at 20 weeks of age. The HFD group showed hepatic lipid accumulation; this was decreased in the Evo + HFD group. There was an increased 8-hydroxydeoxyguanosine (8-OHDG) expression in the HFD group compared to ND mice. However, 8-OHDG expression levels were significantly decreased in the HFD + Evo group. Expressions of the mitophagy markers PTEN-induced kinase 1 (PINK1), Parkin, and BNIP-3 (BCL2 Interacting Protein 3) were significantly increased in the HFD group. However, the expressions of these markers were lower in the HFD + Evo group than that in the HFD group. Phospho-Akt was upregulated and p53 was downregulated in the HFD + Evo group compared to the HFD group. Evogliptin may alleviate steatohepatitis in HFD-fed mice by ameliorating steatosis and oxidative stress and by modulating mitophagy in the liver.

LRRK2 Regulates CPT1A to Promote β-Oxidation in HepG2 Cells

Leucine-rich repeat kinase 2 (LRRK2) is involved in lipid metabolism; however, the role of LRRK2 in lipid metabolism to affect non-alcoholic fatty liver disease (NAFLD) is still unclear. In the mouse model of NAFLD induced by a high-fat diet, we observed that LRRK2 was decreased in livers. In HepG2 cells, exposure to palmitic acid (PA) down-regulated LRRK2. Overexpression and knockdown of LRRK2 in HepG2 cells were performed to further investigate the roles of LRRK2 in lipid metabolism. Our results showed that β-oxidation in HepG2 cells was promoted by LRRK2 overexpression, whereas LRRK2 knockdown inhibited β-oxidation. The critical enzyme of β-oxidation, carnitine palmitoyltransferase 1A (CPT1A), was positively regulated by LRRK2. Our data suggested that the regulation of CPT1A by LRRK2 may be via the activation of AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor α (PPARα). The overexpression of LRRK2 reduced the concentration of a pro-inflammatory cytokine, tumor necrosis factor α (TNFα), induced by PA. The increase in β-oxidation may promote lipid catabolism to suppress inflammation induced by PA. These results indicated that LRRK2 participated in the regulation of β-oxidation and suggested that the decreased LRRK2 may promote inflammation by suppressing β-oxidation in the liver.

Omaveloxolone and TX63682 are hepatoprotective in the STAM mouse model of nonalcoholic steatohepatitis

Omaveloxolone is a potent activator of Nrf2, a master transcriptional regulator of a multitude of cytoprotective functions, including antioxidative, anti-inflammatory, and mitochondrial bioenergetic effects. Some of the most potent known effects of Nrf2 involve hepatoprotective functions. The purpose of this study was to evaluate the effects of omaveloxolone and TX63682, a closely related structural analog with similar oral bioavailability, in the STAM mouse model of nonalcoholic steatohepatitis (NASH). C57Bl/6 mice received a single subcutaneous injection of streptozotocin two days after birth and were fed a high-fat diet from 4 to 9 weeks of age. Omaveloxolone and TX63682 were orally administered at doses of 1, 3, and 10 mg/kg/d from 6 to 9 weeks of age. Consistent with the beneficial effects of Nrf2 on hepatoprotection and improved lipid handling, both omaveloxolone and TX63682 decreased hepatic fat deposition, hepatocellular ballooning, inflammatory cell infiltration, and collagen deposition. Omaveloxolone and TX63682 also improved blood glucose control, as evidenced by reductions in nonfasting blood glucose and glycated hemoglobin A1C concentrations. Reductions in liver and serum triglycerides with omaveloxolone and TX63682 treatment were also observed. Both omaveloxolone and TX63682 decreased leptin and increased adiponectin in serum, which is consistent with the anti-inflammatory and antifibrotic effects observed in the liver. These results were associated with significant induction of Nrf2 target gene expression in the liver, including NAD(P)H:quinone oxidoreductase 1, sulfiredoxin 1, and ferritin heavy chain 1. Overall, these data suggest that omaveloxolone and related Nrf2 activators may be useful for the treatment of NASH.

A Translational Mouse Model for NASH with Advanced Fibrosis and Atherosclerosis Expressing Key Pathways of Human Pathology

Non-alcoholic steatohepatitis (NASH) is a fast-growing liver disorder that is associated with an increased incidence of cardiovascular disease and type 2 diabetes. Animal models adequately mimicking this condition are scarce. We herein investigate whether Ldlr−/−. Leiden mice on different high-fat diets represent a suitable NASH model. Ldlr−/−. Leiden mice were fed a healthy chow diet or fed a high-fat diet (HFD) containing lard or a fast food diet (FFD) containing milk fat. Additionally, the response to treatment with obeticholic acid (OCA) was evaluated. Both high-fat diets induced obesity, hyperlipidemia, hyperinsulinemia, and increased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. Mice on both diets developed progressive macro- and microvesicular steatosis, hepatic inflammation, and fibrosis, along with atherosclerosis. HFD induced more severe hyperinsulinemia, while FFD induced more severe hepatic inflammation with advanced (F3) bridging fibrosis, as well as more severe atherosclerosis. OCA treatment significantly reduced hepatic inflammation and fibrosis, and it did not affect atherosclerosis. Hepatic transcriptome analysis was compared with human NASH and illustrated similarity. The present study defines a translational model of NASH with progressive liver fibrosis and simultaneous atherosclerosis development. By adaptation of the fat content of the diet, either insulin resistance (HFD) or hepatic inflammation and fibrosis (FFD) can be aggravated.

Expression of Notch family is altered in non‑alcoholic fatty liver disease

The aim of the present study was to explore the dynamic relationship between Notch and non‑alcoholic fatty liver disease (NAFLD), both in vitro and in vivo. The LX2, Huh7 and MIHA hepatic cell lines were used to establish a cell steatosis model induced by palmitic acid (PA) at different concentrations (0.1, 0.25 and 0.5 mM). Cell proliferation and migration were assessed using a 5‑bromo‑2'‑deoxyuridine kit and a wound healing assay. The dosage of 0.25 mM PA for 36‑48 h treatment was chosen for subsequent experiments. Steatotic cells were identified by Oil Red O staining. Feeding mice a methionine‑choline‑deficient (MCD) diet is known induce a model of NAFLD, compared with a methionine‑choline‑sufficient (MCS) diet. Therefore, Notch family mRNA expression was evaluated in the liver of MCD‑fed mice at varying time points (days 5, 10, 21 and 70) using reverse transcription‑quantitative PCR. Notch expression levels were also assessed in cell lines at 12, 24, 36 and 48 h after PA treatment. Notch signaling molecules changed in the PA or MCD model over time. In vitro, the mRNA levels of Notch1, ‑2 and ‑4 increased in all cell lines after 12‑h PA treatment. At 24 h, these genes were upregulated only in LX2 cells, while showing a 'down‑up' pattern in MIHA cells (i.e. these genes were downregulated at 24 h but upregulated at 36 h). However, expression of Notch1, ‑2, ‑3 and ‑4 mRNA rose significantly in the early stage (day 10) of NAFLD. At week 3, the levels of Notch1 and ‑2 were higher in the MCD group than in the MCS group, while the reverse was observed for Notch3 and ‑4. Expression of these four genes increased again in the late stage (day 70) of NAFLD. Therefore, these results indicated that Notch family members Notch1‑4 were involved in the development of NAFLD and played an important role in steatosis in this model.

Mitochondrial superoxide/hydrogen peroxide: An emerging therapeutic target for metabolic diseases

Mitochondria are well known for their roles as energy and metabolic factory. Mitochondrial reactive oxygen species (mtROS) refer to superoxide anion radical (^•O₂^-) and hydrogen peroxide (H₂O₂). They are byproducts of electron transport in mitochondrial respiratory chain and are implicated in the regulation of physiological and pathological signal transduction. Especially when mitochondrial ^•O₂^-/H₂O₂ production is disturbed, this disturbance is closely related to the occurrence and development of metabolic diseases. In this review, the sources of mitochondrial ^•O₂^-/H₂O₂ as well as mitochondrial antioxidant mechanisms are summarized. Furthermore, we particularly emphasize the essential role of mitochondrial ^•O₂^-/H₂O₂ in metabolic diseases. Specifically, perturbed mitochondrial ^•O₂^-/H₂O₂ regulation aggravates the progression of metabolic diseases, including diabetes, gout and nonalcoholic fatty liver disease (NAFLD). Given the deleterious effect of mitochondrial ^•O₂^-/H₂O₂ in the development of metabolic diseases, antioxidants targeting mitochondrial ^•O₂^-/H₂O₂ might be an attractive therapeutic approach for the prevention and treatment of metabolic diseases.

The Emerging Role of MicroRNAs in NAFLD: Highlight of MicroRNA-29a in Modulating Oxidative Stress, Inflammation, and Beyond

Non-alcoholic fatty liver disease (NAFLD) is a common cause of chronic liver disease and ranges from steatosis to steatohepatitis and to liver fibrosis. Lipotoxicity in hepatocytes, elevated oxidative stress and the activation of proinflammatory mediators of Kupffer cells, and fibrogenic pathways of activated hepatic stellate cells can contribute to the development of NAFLD. MicroRNAs (miRs) play a crucial role in the dysregulated metabolism and inflammatory signaling connected with NAFLD and its progression towards more severe stages. Of note, the protective effect of non-coding miR-29a on liver damage and its versatile action on epigenetic activity, mitochondrial homeostasis and immunomodulation may improve our perception of the pathogenesis of NAFLD. Herein, we review the biological functions of critical miRs in NAFLD, as well as highlight the emerging role of miR-29a in therapeutic application and the recent advances in molecular mechanisms underlying its liver protective effect.

Role and Mechanisms of Mitophagy in Liver Diseases

The mitochondrion is an organelle that plays a vital role in the regulation of hepatic cellular redox, lipid metabolism, and cell death. Mitochondrial dysfunction is associated with both acute and chronic liver diseases with emerging evidence indicating that mitophagy, a selective form of autophagy for damaged/excessive mitochondria, plays a key role in the liver’s physiology and pathophysiology. This review will focus on mitochondrial dynamics, mitophagy regulation, and their roles in various liver diseases (alcoholic liver disease, non-alcoholic fatty liver disease, drug-induced liver injury, hepatic ischemia-reperfusion injury, viral hepatitis, and cancer) with the hope that a better understanding of the molecular events and signaling pathways in mitophagy regulation will help identify promising targets for the future treatment of liver diseases.

Role of mitochondrial quality control in the pathogenesis of nonalcoholic fatty liver disease

Nutrient oversupply and mitochondrial dysfunction play central roles in nonalcoholic fatty liver disease (NAFLD). The mitochondria are the major sites of β-oxidation, a catabolic process by which fatty acids are broken down. The mitochondrial quality control (MQC) system includes mitochondrial fission, fusion, mitophagy and mitochondrial redox regulation, and is essential for the maintenance of the functionality and structural integrity of the mitochondria. Excessive and uncontrolled production of reactive oxygen species (ROS) in the mitochondria damages mitochondrial components, including membranes, proteins and mitochondrial DNA (mtDNA), and triggers the mitochondrial pathway of apoptosis. The functionality of some damaged mitochondria can be restored by fusion with normally functioning mitochondria, but when severely damaged, mitochondria are segregated from the remaining functional mitochondrial network through fission and are eventually degraded via mitochondrial autophagy, also called as mitophagy. In this review, we describe the functions and mechanisms of mitochondrial fission, fusion, oxidative stress and mitophagy in the development and progression of NAFLD.

Hepatocyte Injury and Hepatic Stem Cell Niche in the Progression of Non-Alcoholic Steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is a chronic liver disease characterized by lipid accumulation in hepatocytes in the absence of excessive alcohol consumption. The global prevalence of NAFLD is constantly increasing. NAFLD is a disease spectrum comprising distinct stages with different prognoses. Non-alcoholic steatohepatitis (NASH) is a progressive condition, characterized by liver inflammation and hepatocyte ballooning, with or without fibrosis. The natural history of NAFLD is negatively influenced by NASH onset and by the progression towards advanced fibrosis. Pathogenetic mechanisms and cellular interactions leading to NASH and fibrosis involve hepatocytes, liver macrophages, myofibroblast cell subpopulations, and the resident progenitor cell niche. These cells are implied in the regenerative trajectories following liver injury, and impairment or perturbation of these mechanisms could lead to NASH and fibrosis. Recent evidence underlines the contribution of extra-hepatic organs/tissues (e.g., gut, adipose tissue) in influencing NASH development by interacting with hepatic cells through various molecular pathways. The present review aims to summarize the role of hepatic parenchymal and non-parenchymal cells, their mutual influence, and the possible interactions with extra-hepatic tissues and organs in the pathogenesis of NAFLD.