Mitochondrial Adaptation in Nonalcoholic Fatty Liver Disease: Novel Mechanisms and Treatment Strategies

Potential of Chlorogenic Acid in the Management of Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD): Animal Studies and Clinical Trials-A Narrative Review

Chlorogenic acid (CGA) is a natural polyphenol found in coffee, tea, vegetables, and fruits. It exhibits strong antioxidant activity and possesses several other biological properties, including anti-inflammatory effects, antimicrobial activity, and insulin-sensitizing properties. Moreover, it may improve lipid and glucose metabolism. This review summarizes the available information on the therapeutic effect of CGA in metabolic dysfunction-associated steatotic liver disease (MASLD). As the literature search engine, the browsers in the PubMed, Scopus, Web of Science databases, and ClinicalTrials.gov register were used. Animal trials and clinical studies suggest that CGA has promising therapeutic potential in treating MASLD and hepatic steatosis. Its mechanisms of action include antioxidant, anti-inflammatory, and anti-apoptotic effects via the activation of the Nrf2 signaling pathway and the inhibition of the TLR4/NF-κB signaling cascade. Furthermore, the alleviation of liver disease by CGA also involves other important molecules such as AMPK and important physiological processes such as the intestinal barrier and gut microbiota. Nevertheless, the specific target cell and key molecule to which CGA is directed remain unidentified and require further study.

The mitochondrial multi-omic response to exercise training across rat tissues

Mitochondria have diverse functions critical to whole-body metabolic homeostasis. Endurance training alters mitochondrial activity, but systematic characterization of these adaptations is lacking. Here, the Molecular Transducers of Physical Activity Consortium mapped the temporal, multi-omic changes in mitochondrial analytes across 19 tissues in male and female rats trained for 1, 2, 4, or 8 weeks. Training elicited substantial changes in the adrenal gland, brown adipose, colon, heart, and skeletal muscle. The colon showed non-linear response dynamics, whereas mitochondrial pathways were downregulated in brown adipose and adrenal tissues. Protein acetylation increased in the liver, with a shift in lipid metabolism, whereas oxidative proteins increased in striated muscles. Exercise-upregulated networks were downregulated in human diabetes and cirrhosis. Knockdown of the central network protein 17-beta-hydroxysteroid dehydrogenase 10 (HSD17B10) elevated oxygen consumption, indicative of metabolic stress. We provide a multi-omic, multi-tissue, temporal atlas of the mitochondrial response to exercise training and identify candidates linked to mitochondrial dysfunction.

Pharmacological SERCA activation limits diet-induced steatohepatitis and restores liver metabolic function in mice

Metabolic dysfunction-associated steatotic liver disease is the most common form of liver disease and poses significant health risks to patients who progress to metabolic dysfunction-associated steatohepatitis. Fatty acid overload alters endoplasmic reticulum (ER) calcium stores and induces mitochondrial oxidative stress in hepatocytes, leading to hepatocellular inflammation and apoptosis. Obese mice have impaired liver sarco/ER Ca2+-ATPase (SERCA) function, which normally maintains intracellular calcium homeostasis by transporting Ca2+ ions from the cytoplasm to the ER. We hypothesized that restoration of SERCA activity would improve diet-induced steatohepatitis in mice by limiting ER stress and mitochondrial dysfunction. WT and melanocortin-4 receptor KO (Mc4r-/-) mice were placed on either chow or Western diet (WD) for 8 weeks. Half of the WD-fed mice were administered CDN1163 to activate SERCA, which reduced liver fibrosis and inflammation. SERCA activation also restored glucose tolerance and insulin sensitivity, improved histological markers of metabolic dysfunction-associated steatohepatitis, increased expression of antioxidant enzymes, and decreased expression of oxidative stress and ER stress genes. CDN1163 decreased hepatic citric acid cycle flux and liver pyruvate cycling, enhanced expression of mitochondrial respiratory genes, and shifted hepatocellular [NADH]/[NAD+] and [NADPH]/[NADP+] ratios to a less oxidized state, which was associated with elevated PUFA content of liver lipids. In sum, the data demonstrate that pharmacological SERCA activation limits metabolic dysfunction-associated steatotic liver disease progression and prevents metabolic dysfunction induced by WD feeding in mice.

MASLD/MASH and type 2 diabetes: Two sides of the same coin? From single PPAR to pan-PPAR agonists

Type 2 diabetes (T2D) and metabolic dysfunction-associated steatotic liver disease (MASLD), mainly related to nutrition and lack of physical activity, are both very common conditions, share several disease pathways and clinical manifestations, and increasingly co-occur with disease progression. Insulin resistance is an upstream node in the biology of both conditions and triggers liver parenchymal injury, inflammation and fibrosis. Peroxisome proliferator-activated receptor (PPAR) nuclear transcription factors are master regulators of energy homeostasis - insulin signaling in liver, adipose and skeletal muscle tissue - and affect immune and fibrogenesis pathways. Among distinct yet overlapping effects, PPARα regulates lipid metabolism and energy expenditure, PPARβ/δ has anti-inflammatory effects and increases glucose uptake by skeletal muscle, while PPARγ improves insulin sensitivity and exerts direct antifibrotic effects on hepatic stellate cells. Together PPARs thus represent pharmacological targets across the entire biology of MASH. Single PPAR agonists are approved for hypertriglyceridemia (PPARα) and T2D (PPARγ), but these, as well as dual PPAR agonists, have shown mixed results as anti-MASH treatments in clinical trials. Agonists of all three PPAR isoforms have the potential to improve the full disease spectrum from insulin resistance to fibrosis, and correspondingly to improve cardiometabolic and hepatic health, as has been shown (phase II data) with the pan-PPAR agonist lanifibranor.

Deciphering the molecular pathways of saroglitazar: A dual PPAR α/γ agonist for managing metabolic NAFLD

Saroglitazar (SARO), a dual peroxisome proliferator activated receptor (PPAR)-α/γ agonist, has been used to treat metabolic diseases such as insulin resistance and diabetic dyslipidemia in patients with non-alcoholic fatty liver disease (NAFLD). SARO, administered at a dose of 4 mg/day, has been consistently studied in clinical trials with different time points ranging from 4 to 24 weeks with NAFLD patients. Due to its PPAR-γ agonistic action, SARO prevents adipose tissue-mediated fatty acid delivery to the liver by increasing insulin sensitivity and regulating adiponectin and leptin levels in adipose tissue. In hepatocytes, SARO induces fatty acid β-oxidation in mitochondria and transcriptionally activates lipid metabolizing genes in peroxisomes. SARO inhibits insulin resistance, thereby preventing the activation of sterol regulatory element-binding proteins -1c and carbohydrate response element binding protein in hepatocytes through its PPAR-α agonistic action. SARO treatment reduces lipotoxicity-mediated oxidative stress by activating the nuclear factor erythroid 2-related factor 2 and transcriptionally expressing the antioxidants from the antioxidant response element in the nucleus through its PPAR-γ agonistic action. SARO provides a PPAR-α/γ-mediated anti-inflammatory effect by preventing the phosphorylation of mitogen-activated protein kinases (JNK and ERK) and nuclear factor kappa B in hepatocytes. Additionally, SARO interferes with transforming growth factor-β/Smad downstream signaling, thereby reducing liver fibrosis progression through its PPAR-α/γ agonistic actions. Thus, SARO improves insulin resistance and dyslipidemia in NAFLD, reduces lipid accumulation in the liver, and thereby prevents mitochondrial toxicity, oxidative stress, inflammation, and fibrosis progression. This review summarizes the possible molecular mechanism of SARO in the NAFLD.

Membrane Lipid Replacement for reconstituting mitochondrial function and moderating cancer-related fatigue, pain and other symptoms while counteracting the adverse effects of cancer cytotoxic therapy

Cancer-related fatigue, pain, gastrointestinal and other symptoms are among the most familiar complaints in practically every type and stage of cancer, especially metastatic cancers. Such symptoms are also related to cancer oxidative stress and the damage instigated by cancer cytotoxic therapies to cellular membranes, especially mitochondrial membranes. Cancer cytotoxic therapies (chemotherapy and radiotherapy) often cause adverse symptoms and induce patients to terminate their anti-neoplastic regimens. Cancer-related fatigue, pain and other symptoms and the adverse effects of cancer cytotoxic therapies can be safely moderated with oral Membrane Lipid Replacement (MLR) glycerolphospholipids and mitochondrial cofactors, such as coenzyme Q10. MLR provides essential membrane lipids and precursors to maintain mitochondrial and other cellular membrane functions and reduces fatigue, pain, gastrointestinal, inflammation and other symptoms. In addition, patients with a variety of chronic symptoms benefit from MLR supplements, and MLR also has the ability to enhance the bioavailability of nutrients and slowly remove toxic, hydrophobic molecules from cells and tissues.

Machine learning-based algorithm identifies key mitochondria-related genes in non-alcoholic steatohepatitis

BACKGROUND

Evidence suggests that hepatocyte mitochondrial dysfunction leads to abnormal lipid metabolism, redox imbalance, and programmed cell death, driving the onset and progression of non-alcoholic steatohepatitis (NASH). Identifying hub mitochondrial genes linked to NASH may unveil potential therapeutic targets.

METHODS

Mitochondrial hub genes implicated in NASH were identified via analysis using 134 algorithms.

RESULTS

The Random Forest algorithm (RF), the most effective among the 134 algorithms, identified three genes: Aldo-keto reductase family 1 member B10 (AKR1B10), thymidylate synthase (TYMS), and triggering receptor expressed in myeloid cell 2 (TREM2). They were upregulated and positively associated with genes promoting inflammation, genes involved in lipid synthesis, fibrosis, and nonalcoholic steatohepatitis activity scores in patients with NASH. Moreover, using these three genes, patients with NASH were accurately categorized into cluster 1, exhibiting heightened disease severity, and cluster 2, distinguished by milder disease activity.

CONCLUSION

These three genes are pivotal mitochondrial genes implicated in NASH progression.

Hepatic glucose metabolism in the steatotic liver

The liver is central in regulating glucose homeostasis, being the major contributor to endogenous glucose production and the greatest reserve of glucose as glycogen. It is both a target and regulator of the action of glucoregulatory hormones. Hepatic metabolic functions are altered in and contribute to the highly prevalent steatotic liver disease (SLD), including metabolic dysfunction-associated SLD (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH). In this Review, we describe the dysregulation of hepatic glucose metabolism in MASLD and MASH and associated metabolic comorbidities, and how advances in techniques and models for the assessment of hepatic glucose fluxes in vivo have led to the identification of the mechanisms related to the alterations in glucose metabolism in MASLD and comorbidities. These fluxes can ultimately increase hepatic glucose production concomitantly with fat accumulation and alterations in the secretion and action of glucoregulatory hormones. No pharmacological treatment has yet been approved for MASLD or MASH, but some antihyperglycaemic drugs approved for treating type 2 diabetes have shown positive effects on hepatic glucose metabolism and hepatosteatosis. A deep understanding of how MASLD affects glucose metabolic fluxes and glucoregulatory hormones might assist in the early identification of at-risk individuals and the use or development of targeted therapies.

Lactate transporter MCT1 in hepatic stellate cells promotes fibrotic collagen expression in nonalcoholic steatohepatitis

Circulating lactate is a fuel source for liver metabolism but may exacerbate metabolic diseases such as nonalcoholic steatohepatitis (NASH). Indeed, haploinsufficiency of lactate transporter monocarboxylate transporter 1 (MCT1) in mice reportedly promotes resistance to hepatic steatosis and inflammation. Here, we used adeno-associated virus (AAV) vectors to deliver thyroxin binding globulin (TBG)-Cre or lecithin-retinol acyltransferase (Lrat)-Cre to MCT1fl/fl mice on a choline-deficient, high-fat NASH diet to deplete hepatocyte or stellate cell MCT1, respectively. Stellate cell MCT1KO (AAV-Lrat-Cre) attenuated liver type 1 collagen protein expression and caused a downward trend in trichrome staining. MCT1 depletion in cultured human LX2 stellate cells also diminished collagen 1 protein expression. Tetra-ethylenglycol-cholesterol (Chol)-conjugated siRNAs, which enter all hepatic cell types, and hepatocyte-selective tri-N-acetyl galactosamine (GN)-conjugated siRNAs were then used to evaluate MCT1 function in a genetically obese NASH mouse model. MCT1 silencing by Chol-siRNA decreased liver collagen 1 levels, while hepatocyte-selective MCT1 depletion by AAV-TBG-Cre or by GN-siRNA unexpectedly increased collagen 1 and total fibrosis without effect on triglyceride accumulation. These findings demonstrate that stellate cell lactate transporter MCT1 significantly contributes to liver fibrosis through increased collagen 1 protein expression in vitro and in vivo, while hepatocyte MCT1 appears not to be an attractive therapeutic target for NASH.

Does Resveratrol Improve Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD)?

Metabolic dysfunction-associated steatotic liver disease (MASLD) is influenced by a variety of factors, including environmental and genetic factors. The most significant outcome is the alteration of free fatty acid and triglyceride metabolism. Lipotoxicity, impaired autophagy, chronic inflammation, and oxidative stress, as well as coexisting insulin resistance, obesity, and changes in the composition of gut microbiota, are also considered crucial factors in the pathogenesis of MASLD. Resveratrol is a polyphenolic compound that belongs to the stilbene subgroup. This review summarises the available information on the therapeutic effects of resveratrol against MASLD. Resveratrol has demonstrated promising antisteatotic, antioxidant, and anti-inflammatory activities in liver cells in in vitro and animal studies. Resveratrol has been associated with inhibiting the NF-κB pathway, activating the SIRT-1 and AMPK pathways, normalizing the intestinal microbiome, and alleviating intestinal inflammation. However, clinical studies have yielded inconclusive results regarding the efficacy of resveratrol in alleviating hepatic steatosis or reducing any of the parameters found in MASLD in human patients. The lack of homogeneity between studies, low bioavailability of resveratrol, and population variability when compared to animal models could be the reasons for this.

Single-cell transcriptome reveals a novel mechanism of C-Kit+-liver sinusoidal endothelial cells in NASH

AIM

To understand how liver sinusoidal endothelial cells (LSECs) respond to nonalcoholic steatohepatitis (NASH).

METHODS

We profiled single-LSEC from livers of control and MCD-fed mice. The functions of C-Kit+-LSECs were determined using coculture and bone marrow transplantation (BMT) methods.

RESULTS

Three special clusters of single-LSEC were differentiated. C-Kit+-LSECs of cluster 0, Msr1+-LSECs of cluster 1 and Bmp4+Selp+-VECs of cluster 2 were revealed, and these cells with diverse ectopic expressions of genes participated in regulation of endothelial, fibrosis and lipid metabolism in NASH. The number of C-Kit+-primary LSECs isolated from MCD mice was lower than control mice. Immunofluorescence co-staining of CD31 and C-KIT showed C-Kit+-LSECs located in hepatic sinusoid were also reduced in NASH patients and MCD mice, compared to AIH patients and control mice respectively. Interestingly, lipotoxic hepatocytes/HSCs cocultured with C-Kit+-LSECs or the livers of MCD mice receipting of C-Kit+-BMCs (bone marrow cells) showed less steatosis, inflammation and fibrosis, higher expression of prolipolytic FXR and PPAR-α, lower expression of TNF-α and α-SMA. Furthermore, coculturing or BMT of C-Kit+-endothelial derived cells could increase the levels of hepatic mitochondrial LC3B, decrease the degree of mitochondrial damage and ROS production through activating Pink1-mediated mitophagy pathway in NASH.

CONCLUSIONS

Hence, a novel transcriptomic view of LSECs was revealed to have heterogeneity and complexity in NASH. Importantly, a cluster of C-Kit+-LSECs was confirmed to recovery Pink1-related mitophagy and NASH progression.

Pyridostigmine attenuated high-fat-diet induced liver injury by the reduction of mitochondrial damage and oxidative stress via α7nAChR and M3AChR

Obesity is a major cause of nonalcohol fatty liver disease (NAFLD), which is characterized by hepatic fibrosis, lipotoxicity, inflammation, and apoptosis. Previous studies have shown that an imbalance in the autonomic nervous system is closely related to the pathogenesis of NAFLD. In this study, we investigated the effects of pyridostigmine (PYR), a cholinesterase (AChE) inhibitor, on HFD-induced liver injury and explored the potential mechanisms involving mitochondrial damage and oxidative stress. A murine model of HFD-induced obesity was established using the C57BL/6 mice, and PYR (3 mg/kg/d) or placebo was administered for 20 weeks. PYR reduced the body weight and liver weight of the HFD-fed mice. Additionally, the serum levels of IL-6, TNF-α, cholesterol, and triglyceride were significantly lower in the PYR-treated versus the untreated mice, corresponding to a decrease in hepatic fibrosis, lipid accumulation, and apoptosis in the former. Furthermore, the mitochondrial morphology improved significantly in the PYR-treated group. Consistently, PYR upregulated ATP production and the mRNA level of the mitochondrial dynamic factors OPA1, Drp1 and Fis1, and the mitochondrial unfolded protein response (UPRmt) factors LONP1 and HSP60. Moreover, PYR treatment activated the Keap1/Nrf2 pathway and upregulated HO-1 and NQO-1, which mitigated oxidative injury as indicated by decreased 8-OHDG, MDA and H2 O2 levels, and increased SOD activity. Finally, PYR elevated acetylcholine (ACh) levels by inhibiting AChE, and upregulated the α7nAChR and M3AChR proteins in the HFD-fed mice. PYR alleviated obesity-induced hepatic injury in mice by mitigating mitochondrial damage and oxidative stress via α7nAChR and M3AChR.

GBA3 promotes fatty acid oxidation and alleviates non-alcoholic fatty liver by increasing CPT2 transcription

BACKGROUND

Excessive lipids accumulation and hepatocytes death are prominent characteristics of non-alcoholic fatty liver disease (NAFLD). Nonetheless, the precise pathophysiological mechanisms are not fully elucidated.

METHODS

HepG2 cells stimulated with palmitic acids and rats fed with high-fat diet were used as models for NAFLD. The impact of Glucosylceramidase Beta 3 (GBA3) on fatty acid oxidation (FAO) was assessed using Seahorse metabolic analyzer. Lipid content was measured both in vitro and in vivo. To evaluate NAFLD progression, histological analysis was performed along with measurements of inflammatory factors and liver enzyme levels. Western blot and immunohistochemistry were employed to examine the activity levels of necroptosis. Flow cytometry and reactive oxygen species (ROS) staining were utilized to assess levels of oxidative stress.

RESULTS

GBA3 promoted FAO and enhanced the mitochondrial membrane potential without affecting glycolysis. These reduced the lipid accumulation. Rats supplemented with GBA3 exhibited lower levels of inflammatory factors and liver enzymes, resulting in a slower progression of NAFLD. GBA3 overexpression reduced ROS and the ratio of cell apoptosis. Phosphorylation level was reduced in the essential mediator, MLKL, implicated in necroptosis. Mechanistically, as a transcriptional coactivator, GBA3 promoted the expression of Carnitine Palmitoyltransferase 2 (CPT2), which resulted in enhanced FAO.

CONCLUSIONS

Increased FAO resulting from GBA3 reduced oxidative stress and the production of ROS, thereby inhibiting necroptosis and delaying the progression of NAFLD. Our research offers novel insights into the potential therapeutic applications of GBA3 and FAO in the management and treatment of NAFLD.

ACACA reduces lipid accumulation through dual regulation of lipid metabolism and mitochondrial function via AMPK- PPARα- CPT1A axis

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a multifaceted metabolic disorder, whose global prevalence is rapidly increasing. Acetyl CoA carboxylases 1 (ACACA) is the key enzyme that controls the rate of fatty acid synthesis. Hence, it is crucial to investigate the function of ACACA in regulating lipid metabolism during the progress of NAFLD.

METHODS

Firstly, a fatty liver mouse model was established by high-fat diet at 2nd, 12th, and 20th week, respectively. Then, transcriptome analysis was performed on liver samples to investigate the underlying mechanisms and identify the target gene of the occurrence and development of NAFLD. Afterwards, lipid accumulation cell model was induced by palmitic acid and oleic acid (PA ∶ OA molar ratio = 1∶2). Next, we silenced the target gene ACACA using small interfering RNAs (siRNAs) or the CMS-121 inhibitor. Subsequently, experiments were performed comprehensively the effects of inhibiting ACACA on mitochondrial function and lipid metabolism, as well as on AMPK- PPARα- CPT1A pathway.

RESULTS

This data indicated that the pathways significantly affected by high-fat diet include lipid metabolism and mitochondrial function. Then, we focus on the target gene ACACA. In addition, the in vitro results suggested that inhibiting of ACACA in vitro reduces intracellular lipid accumulation, specifically the content of TG and TC. Furthermore, ACACA ameliorated mitochondrial dysfunction and alleviate oxidative stress, including MMP complete, ATP and ROS production, as well as the expression of mitochondria respiratory chain complex (MRC) and AMPK proteins. Meanwhile, ACACA inhibition enhances lipid metabolism through activation of PPARα/CPT1A, leading to a decrease in intracellular lipid accumulation.

CONCLUSION

Targeting ACACA can reduce lipid accumulation by mediating the AMPK- PPARα- CPT1A pathway, which regulates lipid metabolism and alleviates mitochondrial dysfunction.

The Emerging Role of Glucagon-Like Peptide-1 Receptor Agonists for the Treatment of Metabolic Dysfunction-Associated Steatohepatitis

Metabolic dysfunction-associated steatotic liver disease (MASLD) affects 1 in 3-4 adult individuals and can progress to metabolic dysfunction-associated steatohepatitis (MASH) and cirrhosis. Insulin resistance plays a central role in MASLD/MASH pathophysiology with higher rates of MASLD (2 in 3) and MASH with fibrosis (1 in 5) in adults with obesity and diabetes. This review summarizes the role of glucagon-like peptide-1 receptor agonists in treating MASLD/MASH. Although not approved by the Food and Drug Administration for the treatment of MASLD, this class of medication is available to treat obesity and type 2 diabetes and has been shown to reverse steatohepatitis, reduce cardiovascular risk, and is safe to use across the spectrum of MASLD with or without fibrosis.

Comparison of HepaRG and HepG2 cell lines to model mitochondrial respiratory adaptations in non‑alcoholic fatty liver disease

Although some clinical studies have reported increased mitochondrial respiration in patients with fatty liver and early non‑alcoholic steatohepatitis (NASH), there is a lack of in vitro models of non‑alcoholic fatty liver disease (NAFLD) with similar findings. Despite being the most commonly used immortalized cell line for in vitro models of NAFLD, HepG2 cells exposed to free fatty acids (FFAs) exhibit a decreased mitochondrial respiration. On the other hand, the use of HepaRG cells to study mitochondrial respiratory changes following exposure to FFAs has not yet been fully explored. Therefore, the present study aimed to assess cellular energy metabolism, particularly mitochondrial respiration, and lipotoxicity in FFA‑treated HepaRG and HepG2 cells. HepaRG and HepG2 cells were exposed to FFAs, followed by comparative analyses that examained cellular metabolism, mitochondrial respiratory enzyme activities, mitochondrial morphology, lipotoxicity, the mRNA expression of selected genes and triacylglycerol (TAG) accumulation. FFAs stimulated mitochondrial respiration and glycolysis in HepaRG cells, but not in HepG2 cells. Stimulated complex I, II‑driven respiration and β‑oxidation were linked to increased complex I and II activities in FFA‑treated HepaRG cells, but not in FFA‑treated HepG2 cells. Exposure to FFAs disrupted mitochondrial morphology in both HepaRG and HepG2 cells. Lipotoxicity was induced to a greater extent in FFA‑treated HepaRG cells than in FFA‑treated HepG2 cells. TAG accumulation was less prominent in HepaRG cells than in HepG2 cells. On the whole, the present study demonstrates that stimulated mitochondrial respiration is associated with lipotoxicity in FFA‑treated HepaRG cells, but not in FFA‑treated HepG2 cells. These findings suggest that HepaRG cells are more suitable for assessing mitochondrial respiratory adaptations in the developed in vitro model of early‑stage NASH.

Hepatoprotective Activity and Mechanisms of Prenylated Stilbenoids

Dietary prenylated stilbenoids, found in various food sources, offer multiple health benefits, including liver protection. However, the underlying mechanisms of hepatoprotection remain unclear. In this study, we synthesized 13 natural prenylated stilbenoids and examined their hepatoprotective activities, with silent mating type information regulation 2 homologue-1 (SIRT1) as the primary target for screening. Among all of the prenylated stilbenoids tested, 4-C-geranyl oxyresveratrol demonstrated superior performance. It activated SIRT1 activity more effectively than resveratrol, a well-known SIRT1 activator. To further investigate the mechanism of liver protection, two in vitro models were used: the palmitic acid-induced lipid accumulation model and the H2O2-induced apoptosis model. Our findings suggested that 4-C-geranyl oxyresveratrol mitigated lipid accumulation through the SIRT1-PGC1α pathway, reduced apoptosis via the SIRT1-p53-p21 pathway, and exerted antioxidant effects through the SIRT1-Nrf2 pathway. These findings provide new insights into the chemical basis of the health benefits of prenylated stilbenoids and their potential use as functional food additives.

Thyroid Hormone and Mitochondrial Dysfunction: Therapeutic Implications for Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD)

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly termed nonalcoholic fatty liver disease (NAFLD), is a widespread global health concern that affects around 25% of the global population. Its influence is expanding, and it is anticipated to overtake alcohol as the leading cause of liver failure and liver-related death worldwide. Unfortunately, there are no approved therapies for MASLD; as such, national and international regulatory health agencies undertook strategies and action plans designed to expedite the development of drugs for treatment of MASLD. A sedentary lifestyle and an unhealthy diet intake are important risk factors. Western countries have a greater estimated prevalence of MASLD partly due to lifestyle habits. Mitochondrial dysfunction is strongly linked to the development of MASLD. Further, it has been speculated that mitophagy, a type of mitochondrial quality control, may be impaired in MASLD. Thyroid hormone (TH) coordinates signals from the nuclear and mitochondrial genomes to control mitochondrial biogenesis and function in hepatocytes. Mitochondria are known TH targets, and preclinical and clinical studies suggest that TH, thyroid receptor β (TR-β) analogs, and synthetic analogs specific to the liver could be of therapeutic benefit in treating MASLD. In this review, we highlight how mitochondrial dysfunction contributes to development of MASLD, and how understanding the role of TH in improving mitochondrial function paved the way for innovative drug development programs of TH-based therapies targeting MASLD.

Arbutin alleviates fatty liver by inhibiting ferroptosis via FTO/SLC7A11 pathway

Non-alcoholic fatty liver disease (NAFLD) is a potentially serious disease that affects 30 % of the global population and poses a significant risk to human health. However, to date, no safe, effective and appropriate treatment modalities are available. In recent years, ferroptosis has emerged as a significant mode of cell death and has been found to play a key regulatory role in the development of NAFLD. In this study, we found that arbutin (ARB), a natural antioxidant derived from Arctostaphylos uva-ursi (L.), inhibits the onset of ferroptosis and ameliorates high-fat diet-induced NAFLD in vivo and in vitro. Using reverse docking, we identified the demethylase fat mass and obesity-related protein (FTO) as a potential target of ARB. Subsequent mechanistic studies revealed that ARB plays a role in controlling methylation of the SLC7A11 gene through inhibition of FTO. In addition, we demonstrated that SLC7A11 could alleviate the development of NAFLD in vivo and in vitro. Our findings identify the FTO/SLC7A11 axis as a potential therapeutic target for the treatment of NAFLD. Specifically, we show that ARB alleviates NAFLD by acting on the FTO/SLC7A11 pathway to inhibit ferroptosis.

Mitochondrial pyruvate carrier 1 regulates fatty acid synthase lactylation and mediates treatment of nonalcoholic fatty liver disease

BACKGROUND AND AIMS

NAFLD has become a major metabolic disease worldwide. A few studies have reported the potential relationship between mitochondrial pyruvate carrier 1 (MPC1) and inflammation, fibrosis, and insulin sensitivity in obese or NASH mouse models. However, the impact of MPC1 on NAFLD-related liver lipid metabolism and its role in the NAFLD progression require further investigation.

APPROACH AND RESULTS

MPC1 expression was measured in liver tissues from normal controls and patients with NAFLD. We characterized the metabolic phenotypes and expression of genes involved in hepatic lipid accumulation in MPC1 systemic heterozygous knockout (MPC1 +/- ) mice. Hepatic protein lactylation was detected using Tandem Mass Tags proteomics and verified by the overexpression of lactylation mutants in cells. Finally, the effect of MPC1 inhibition on liver inflammation was examined in mice and AML-12 cells. Here, we found that MPC1 expression was positively correlated to liver lipid deposition in patients with NAFLD. MPC1 +/- mice fed with high-fat diet had reduced hepatic lipid accumulation but no change in the expression of lipid synthesis-related genes. MPC1 knockout affected the lactylation of several proteins, especially fatty acid synthase, through the regulation of lactate levels in hepatocytes. Lactylation at the K673 site of fatty acid synthase inhibited fatty acid synthase activity, which mediated the downregulation of liver lipid accumulation by MPC1. Moreover, although MPC1 knockout caused lactate accumulation, inflammation level was controlled because of mitochondrial protection and macrophage polarization.

CONCLUSIONS

In NAFLD, MPC1 levels are positively correlated with hepatic lipid deposition; the enhanced lactylation at fatty acid synthase K673 site may be a downstream mechanism.

Lactate transporter MCT1 in hepatic stellate cells promotes fibrotic collagen expression in nonalcoholic steatohepatitis

Circulating lactate is a fuel source for liver metabolism but may exacerbate metabolic diseases such as nonalcoholic steatohepatitis (NASH). Indeed, haploinsufficiency of lactate transporter monocarboxylate transporter 1 (MCT1) in mice reportedly promotes resistance to hepatic steatosis and inflammation. Here, we used adeno-associated virus (AAV) vectors to deliver thyroxin binding globulin (TBG)-Cre or lecithin-retinol acyltransferase (Lrat)-Cre to MCT1fl/fl mice on a choline deficient, high fat NASH diet to deplete hepatocyte or stellate cell MCT1, respectively. Stellate cell MCT1KO (AAV-Lrat-Cre) attenuated liver type 1 collagen protein expression and caused a downward trend in trichrome staining. MCT1 depletion in cultured human LX2 stellate cells also diminished collagen 1 protein expression. Tetra-ethylenglycol-cholesterol (Chol)-conjugated siRNAs, which enter all hepatic cell types, and hepatocyte-selective tri-N-acetyl galactosamine (GN)-conjugated siRNAs were then used to evaluate MCT1 function in a genetically obese NASH mouse model. MCT1 silencing by Chol-siRNA decreased liver collagen 1 levels, while hepatocyte-selective MCT1 depletion by AAV-TBG-Cre or by GN-siRNA unexpectedly increased collagen 1 and total fibrosis without effect on triglyceride accumulation. These findings demonstrate that stellate cell lactate transporter MCT1 significantly contributes to liver fibrosis through increased collagen 1 protein expression in vitro and in vivo, while hepatocyte MCT1 appears not to be an attractive therapeutic target for NASH.

Lipid Disorders and Metabolic-Associated Fatty Liver Disease

Dyslipidemia has been linked metabolic-associated fatty liver disease (MAFLD). Several genes and transcription factors involved in lipid metabolism can increase susceptibility to MAFLD. Multiple parallel 'hits' have been proposed for developing hepatic steatosis, NASH, and MAFLD, including insulin resistance and subsequent free fatty acid excess, de novo lipogenesis, and excessive hepatic triglyceride and cholesterol deposition in the liver. This lead to defective beta-oxidation in the mitochondria and VLDL export and increased inflammation. Given the significant cardiovascular risk, dyslipidemia associated with MAFLD should be managed by lifestyle changes and lipid-lowering agents such as statins, fenofibrate, and omega-3 fatty acids, with judicious use of insulin-sensitizing agents, and adequate control of dysglycemia.

CD38 Inhibition Protects Fructose-Induced Toxicity in Primary Hepatocytes

A fructose-enriched diet is thought to contribute to hepatic injury in developing non-alcoholic steatohepatitis (NASH). However, the cellular mechanism of fructose-induced hepatic damage remains poorly understood. This study aimed to determine whether fructose induces cell death in primary hepatocytes, and if so, to establish the underlying cellular mechanisms. Our results revealed that treatment with high fructose concentrations for 48 h induced mitochondria-mediated apoptotic death in mouse primary hepatocytes (MPHs). Endoplasmic reticulum stress responses were involved in fructose-induced death as the levels of phosho-eIF2α, phospho-C-Jun-N-terminal kinase (JNK), and C/EBP homologous protein (CHOP) increased, and a chemical chaperone tauroursodeoxycholic acid (TUDCA) prevented cell death. The impaired oxidation metabolism of fatty acids was also possibly involved in the fructose-induced toxicity as treatment with an AMP-activated kinase (AMPK) activator and a PPAR-α agonist significantly protected against fructose-induced death, while carnitine palmitoyl transferase I inhibitor exacerbated the toxicity. However, uric acid-mediated toxicity was not involved in fructose-induced death as uric acid was not toxic to MPHs, and the inhibition of xanthine oxidase (a key enzyme in uric acid synthesis) did not affect cell death. On the other hand, treatment with inhibitors of the nicotinamide adenine dinucleotide (NAD)+-consuming enzyme CD38 or CD38 gene knockdown significantly protected against fructose-induced toxicity in MPHs, and fructose treatment increased CD38 levels. These data suggest that CD38 upregulation plays a role in hepatic injury in the fructose-enriched diet-mediated NASH. Thus, CD38 inhibition may be a promising therapeutic strategy to prevent fructose-enriched diet-mediated NASH.

Mitochondrial heterogeneity in diseases

As key organelles involved in cellular metabolism, mitochondria frequently undergo adaptive changes in morphology, components and functions in response to various environmental stresses and cellular demands. Previous studies of mitochondria research have gradually evolved, from focusing on morphological change analysis to systematic multiomics, thereby revealing the mitochondrial variation between cells or within the mitochondrial population within a single cell. The phenomenon of mitochondrial variation features is defined as mitochondrial heterogeneity. Moreover, mitochondrial heterogeneity has been reported to influence a variety of physiological processes, including tissue homeostasis, tissue repair, immunoregulation, and tumor progression. Here, we comprehensively review the mitochondrial heterogeneity in different tissues under pathological states, involving variant features of mitochondrial DNA, RNA, protein and lipid components. Then, the mechanisms that contribute to mitochondrial heterogeneity are also summarized, such as the mutation of the mitochondrial genome and the import of mitochondrial proteins that result in the heterogeneity of mitochondrial DNA and protein components. Additionally, multiple perspectives are investigated to better comprehend the mysteries of mitochondrial heterogeneity between cells. Finally, we summarize the prospective mitochondrial heterogeneity-targeting therapies in terms of alleviating mitochondrial oxidative damage, reducing mitochondrial carbon stress and enhancing mitochondrial biogenesis to relieve various pathological conditions. The possibility of recent technological advances in targeted mitochondrial gene editing is also discussed.

Nonalcoholic Fatty Liver Disease and Omega-3 Fatty Acids: Mechanisms and Clinical Use

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic fatty liver disease worldwide, particularly in obese and type 2 diabetic individuals. Currently, there are no therapies for NAFLD that have been approved by the US Food and Drug Administration. Herein, we examine the rationale for using ω3 polyunsaturated fatty acids (PUFAs) in NAFLD therapy. This focus is based on the finding that NAFLD severity is associated with a reduction of hepatic C20-22 ω3 PUFAs. Because C20-22 ω3 PUFAs are pleiotropic regulators of cell function, loss of C20-22 ω3 PUFAs has the potential to significantly impact hepatic function. We describe NAFLD prevalence and pathophysiology as well as current NAFLD therapies. We also present evidence from clinical and preclinical studies that evaluated the capacity of C20-22 ω3 PUFAs to treat NAFLD. Given the clinical and preclinical evidence, dietary C20-22 ω3 PUFA supplementation has the potential to decrease human NAFLD severity by reducing hepatosteatosis and liver injury.

Thrap3 promotes nonalcoholic fatty liver disease by suppressing AMPK-mediated autophagy

Autophagy functions in cellular quality control and metabolic regulation. Dysregulation of autophagy is one of the major pathogenic factors contributing to the progression of nonalcoholic fatty liver disease (NAFLD). Autophagy is involved in the breakdown of intracellular lipids and the maintenance of healthy mitochondria in NAFLD. However, the mechanisms underlying autophagy dysregulation in NAFLD remain unclear. Here, we demonstrate that the hepatic expression level of Thrap3 was significantly increased in NAFLD conditions. Liver-specific Thrap3 knockout improved lipid accumulation and metabolic properties in a high-fat diet (HFD)-induced NAFLD model. Furthermore, Thrap3 deficiency enhanced autophagy and mitochondrial function. Interestingly, Thrap3 knockout increased the cytosolic translocation of AMPK from the nucleus and enhanced its activation through physical interaction. The translocation of AMPK was regulated by direct binding with AMPK and the C-terminal domain of Thrap3. Our results indicate a role for Thrap3 in NAFLD progression and suggest that Thrap3 is a potential target for NAFLD treatment.

Mitochondrial metabolic dysfunction and non-alcoholic fatty liver disease: new insights from pathogenic mechanisms to clinically targeted therapy

Metabolic dysfunction-associated fatty liver disease (MAFLD) is among the most widespread metabolic disease globally, and its associated complications including insulin resistance and diabetes have become threatening conditions for human health. Previous studies on non-alcoholic fatty liver disease (NAFLD) were focused on the liver's lipid metabolism. However, growing evidence suggests that mitochondrial metabolism is involved in the pathogenesis of NAFLD to varying degrees in several ways, for instance in cellular division, oxidative stress, autophagy, and mitochondrial quality control. Ultimately, liver function gradually declines as a result of mitochondrial dysfunction. The liver is unable to transfer the excess lipid droplets outside the liver. Therefore, how to regulate hepatic mitochondrial function to treat NAFLD has become the focus of current research. This review provides details about the intrinsic link of NAFLD with mitochondrial metabolism and the mechanisms by which mitochondrial dysfunctions contribute to NAFLD progression. Given the crucial role of mitochondrial metabolism in NAFLD progression, the application potential of multiple mitochondrial function improvement modalities (including physical exercise, diabetic medications, small molecule agonists targeting Sirt3, and mitochondria-specific antioxidants) in the treatment of NAFLD was evaluated hoping to provide new insights into NAFLD treatment.

Circular RNAs in hepatocellular carcinoma: biogenesis, function, and pathology

Hepatocellular carcinoma (HCC) is one of the most common causes of cancer-related death worldwide. Both genetic and environmental factors through a multitude of underlying molecular mechanisms participate in the pathogenesis of HCC. Recently, numerous studies have shown that circular RNAs (circRNAs), an emerging class of non-coding RNAs characterized by the presence of covalent bonds linking 3' and 5' ends, play an important role in the initiation and progression of cancers, including HCC. In this review, we outline the current status of the field of circRNAs, with an emphasis on the functions and mechanisms of circRNAs in HCC and its microenvironment. We also summarize and discuss recent advances of circRNAs as biomarkers and therapeutic targets. These efforts are anticipated to throw new insights into future perspectives about circRNAs in basic, translational and clinical research, eventually advancing the diagnosis, prevention and treatment of HCC.

Diabetes and cirrhosis: Current concepts on diagnosis and management

Type 2 diabetes mellitus is often associated with cirrhosis as comorbidities, acute illness, medications, and other conditions profoundly alter glucose metabolism. Both conditions are closely related in NAFLD, the leading cause of chronic liver disease, and given its rising burden worldwide, management of type 2 diabetes mellitus in cirrhosis will be an increasingly common dilemma. Having diabetes increases cirrhosis-related complications, including HCC as well as overall mortality. In the absence of effective treatments for cirrhosis, patients with type 2 diabetes mellitus should be systematically screened as early as possible for NAFLD-related fibrosis/cirrhosis using noninvasive tools, starting with a FIB-4 index followed by transient elastography, if available. In people with cirrhosis, an early diagnosis of diabetes is critical for an optimal management strategy (ie, nutritional goals, and glycemic targets). Diagnosis of diabetes may be missed if based on A1C in patients with cirrhosis and impaired liver function (Child-Pugh B-C) as anemia may turn the test unreliable. Clinicians must also become aware of their high risk of hypoglycemia, especially in decompensated cirrhosis where insulin is the only therapy. Care should be within multidisciplinary teams (nutritionists, obesity management teams, endocrinologists, hepatologists, and others) and take advantage of novel glucose-monitoring devices. Clinicians should become familiar with the safety and efficacy of diabetes medications for patients with advanced fibrosis and compensated cirrhosis. Management is conditioned by whether the patient has either compensated or decompensated cirrhosis. This review gives an update on the complex relationship between cirrhosis and type 2 diabetes mellitus, with a focus on its diagnosis and treatment, and highlights knowledge gaps and future directions.

Compatibility of Polygonati Rhizoma and Angelicae Sinensis Radix enhance the alleviation of metabolic dysfunction-associated fatty liver disease by promoting fatty acid β-oxidation

Jiuzhuan Huangjing Pills (JHP) composed of Polygonati Rhizoma (PR) and Angelicae Sinensis Radix (ASR) remedied mitochondria to cure metabolic dysfunction-associated fatty liver disease (MAFLD). However, a comparison of the anti-MAFLD ability between JHP prescription and PR and ASR single-medicines in MAFLD has not been performed, and the action mechanisms and substances remain unknown. Our results show that JHP, PR and ASR decreased serum and liver lipid levels. The effects of JHP were stronger than those of PR and ASR. JHP, PR and ASR afforded protection to mitochondrial ultrastructure, and regulated oxidative stress and energy metabolism in mitochondria. JHP also regulated the expression of β-oxidation genes, which were not regulated by PR and ASR. JHP-, PR- and ASR-derived components in mitochondrial extracts regulated oxidative stress, energy metabolism, and β-oxidation gene expression and alleviated cellular steatosis. Four, six and eleven compounds were identified in mitochondrial extracts from PR-, ASR- and JHP-treated rats, respectively. The data suggest that JHP, PR and ASR alleviated MAFLD by remedying mitochondria, while the ability of JHP was stronger than that of PR and ASR, which was involved with the β-oxidation promotion. The compounds identified may be the main ingredients in the three extracts active in MAFLD improvement.

Metabolic Syndrome and Its Association with Nonalcoholic Steatohepatitis

The relationship between insulin resistance, metabolic syndrome (MetS), and nonalcoholic fatty liver disease (NAFLD) is complicated. Although insulin resistance is almost universal in people with NAFLD and MetS, NAFLD may be present without features of MetS and vice versa. While NAFLD has a strong correlation with cardiometabolic risk factors, these are not intrinsic components of this condition. Taken together, our knowledge gaps call for caution regarding the common assertion that NAFLD is the hepatic manifestation of the MetS, and for defining NAFLD in broad terms as a "metabolic dysfunction" based on a diverse and poorly understood constellation of cardiometabolic features.

Branched-chain amino acids alter cellular redox to induce lipid oxidation and reduce de novo lipogenesis in the liver

Metabolic and molecular interactions between branched-chain amino acid (BCAA) and lipid metabolism are evident in insulin-resistant tissues. However, it remains unclear whether insulin resistance is a prerequisite for these relationships and whether BCAAs or their metabolic intermediates can modulate hepatic lipid oxidation and synthesis. We hypothesized that BCAAs can alter hepatic oxidative function and de novo lipogenesis, independent of them being anaplerotic substrates for the mitochondria. Mice (C57BL/6NJ) were reared on a low-fat (LF), LF diet plus 1.5X BCAAs (LB), high-fat (HF) or HF diet plus 1.5X BCAAs (HB) for 12 wk. Hepatic metabolism was profiled utilizing stable isotopes coupled to mass spectrometry and nuclear magnetic resonance, together with fed-to-fasted changes in gene and protein expression. A greater induction of lipid oxidation and ketogenesis on fasting was evident in the BCAA-supplemented, insulin-sensitive livers from LB mice, whereas their rates of hepatic de novo lipogenesis remained lower than their LF counterparts. Onset of insulin resistance in HF and HB mice livers blunted these responses. Whole body turnover of BCAAs and their ketoacids, their serum concentrations, and the ketogenic flux from BCAA catabolism, all remained similar between fasted LF and LB mice. This suggested that the impact of BCAAs on lipid metabolism can occur independent of them or their degradation products fueling anaplerosis through the liver mitochondria. Furthermore, the greater induction of lipid oxidation in the LB livers accompanied higher mitochondrial NADH/NAD+ ratio and higher fed-to-fasting phosphorylation of AMPKα and ACC. Taken together, our results provide evidence that BCAA supplementation, under conditions of insulin sensitivity, improved the feeding-to-fasting induction of hepatic lipid oxidation through changes in cellular redox, thus providing a favorable biochemical environment for flux through β-oxidation and lower de novo lipogenesis.NEW & NOTEWORTHY Branched-chain amino acids (BCAAs) have been shown to modulate lipid metabolic networks in various tissues, especially during insulin resistance. In this study we show that the dietary supplementation of BCAAs to normal, insulin-sensitive mice resulted in higher mitochondrial NADH:NAD+ ratios and AMPK activation in the liver. This change in the cellular redox status provided an optimal metabolic milieu to increase fatty acid oxidation while keeping the rates of de novo lipogenesis lower in the BCAA-supplemented mice livers.

Acetaminophen-Induced Hepatotoxicity in Obesity and Nonalcoholic Fatty Liver Disease: A Critical Review

The epidemic of obesity, type 2 diabetes and nonalcoholic liver disease (NAFLD) favors drug consumption, which augments the risk of adverse events including liver injury. For more than 30 years, a series of experimental and clinical investigations reported or suggested that the common pain reliever acetaminophen (APAP) could be more hepatotoxic in obesity and related metabolic diseases, at least after an overdose. Nonetheless, several investigations did not reproduce these data. This discrepancy might come from the extent of obesity and steatosis, accumulation of specific lipid species, mitochondrial dysfunction and diabetes-related parameters such as ketonemia and hyperglycemia. Among these factors, some of them seem pivotal for the induction of cytochrome P450 2E1 (CYP2E1), which favors the conversion of APAP to the toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI). In contrast, other factors might explain why obesity and NAFLD are not always associated with more frequent or more severe APAP-induced acute hepatotoxicity, such as increased volume of distribution in the body, higher hepatic glucuronidation and reduced CYP3A4 activity. Accordingly, the occurrence and outcome of APAP-induced liver injury in an obese individual with NAFLD would depend on a delicate balance between metabolic factors that augment the generation of NAPQI and others that can mitigate hepatotoxicity.

Heme oxygenase-1 prevents non-alcoholic steatohepatitis through modulating mitochondrial quality control

AIM

Nonalcoholic steatohepatitis (NASH) is a severe form of nonalcoholic fatty liver disease (NAFLD) and lacks effective treatment options. Heme oxygenase-1 (HO-1) is a critical defense against oxidative stress and inflammation in the liver injury. This study aims to investigate the protective role and underlying mechanisms of HO-1 in NASH pathogenesis.

METHODS

The hepatocyte-specific HO-1 knockout (HO-1^HEPKO ) mice on a C57BL/6J background (HO-1^fl/fl /Alb-Cre) were generated and fed a high-fat/western-style diet (HFD) or methionine-choline-deficient diet (MCD). Changes in mitochondrial ultrastructure were observed by transmission electron microscopy and confocal microscopy. A mitochondrial PCR array was used to identify the crucial genes associated with mitochondrial dysfunction.

RESULTS

Hepatocyte-specific HO-1^HEPKO mice developed steatohepatitis with severe steatosis, ballooning, and necroinflammation. Dysregulated hepatic expression of mitochondria-related proteins, including DRP1, Tomm20, MFN1 and MFN2 were detected in NASH animals. Ultrastructural mitochondrial damage was observed in HO-1^HEPKO mice. Mitochondrial dysfunction was recapitulated in HO-1-knockdown cells in vitro, as evidenced by decreased membrane potential, reduced ATP content, and mtDNA damage. Conversely, HO-1 overexpression restored these changes in vitro. Mechanistically, HO-1 deficiency reduced the inhibitory effect on Tomm20, leading to mitochondrial dysfunction, and thereby causing steatohepatitis.

CONCLUSIONS

HO-1 attenuates diet-induced steatohepatitis by preventing mitochondrial dysfunction, indicating that HO-1 may constitute a potential therapeutic target for NASH.

Non-alcoholic Fatty Liver Disease (NAFLD), Type 2 Diabetes, and Non-viral Hepatocarcinoma: Pathophysiological Mechanisms and New Therapeutic Strategies

In recent years, the incidence of non-viral hepatocellular carcinoma (HCC) has increased dramatically, which is probably related to the increased prevalence of metabolic syndrome, together with obesity and type 2 diabetes mellitus (T2DM). Several epidemiological studies have established the association between T2DM and the incidence of HCC and have demonstrated the role of diabetes mellitus as an independent risk factor for the development of HCC. The pathophysiological mechanisms underlying the development of Non-alcoholic fatty liver disease (NAFLD) and its progression to Non-alcoholic steatohepatitis (NASH) and cirrhosis are various and involve pro-inflammatory agents, oxidative stress, apoptosis, adipokines, JNK-1 activation, increased IGF-1 activity, immunomodulation, and alteration of the gut microbiota. Moreover, these mechanisms are thought to play a significant role in the development of NAFLD-related hepatocellular carcinoma. Early diagnosis and the timely correction of risk factors are essential to prevent the onset of liver fibrosis and HCC. The purpose of this review is to summarize the current evidence on the association among obesity, NASH/NAFLD, T2DM, and HCC, with an emphasis on clinical impact. In addition, we will examine the main mechanisms underlying this complex relationship, and the promising strategies that have recently emerged for these diseases' treatments.

Hepatocyte-specific miR-33 deletion attenuates NAFLD-NASH-HCC progression

The complexity of the multiple mechanisms underlying non-alcoholic fatty liver disease (NAFLD) progression remains a significant challenge for the development of effective therapeutics. miRNAs have shown great promise as regulators of biological processes and as therapeutic targets for complex diseases. Here, we study the role of hepatic miR-33, an important regulator of lipid metabolism, during the progression of NAFLD. We report that miR-33 is overexpressed in hepatocytes isolated from mice with NAFLD and demonstrate that its specific suppression in hepatocytes (miR-33 HKO ) improves multiple aspects of the disease, including insulin resistance, steatosis, and inflammation and limits the progression to non-alcoholic steatohepatitis (NASH), fibrosis and hepatocellular carcinoma (HCC). Mechanistically, we find that hepatic miR-33 deficiency reduces lipid biosynthesis and promotes mitochondrial fatty acid oxidation to reduce lipid burden in hepatocytes. Additionally, miR-33 deficiency improves mitochondrial function, reducing oxidative stress. In miR-33 deficient hepatocytes, we found an increase in AMPKα activation, which regulates several pathways resulting in the attenuation of liver disease. The reduction in lipid accumulation and liver injury resulted in decreased transcriptional activity of the YAP/TAZ pathway, which may be involved in the reduced progression to HCC in the HKO livers. Together, these results suggest suppressing hepatic miR-33 may be an effective therapeutic approach at different stages of NAFLD/NASH/HCC disease progression.

The mitochondrial multi-omic response to exercise training across tissues

Mitochondria are adaptable organelles with diverse cellular functions critical to whole-body metabolic homeostasis. While chronic endurance exercise training is known to alter mitochondrial activity, these adaptations have not yet been systematically characterized. Here, the Molecular Transducers of Physical Activity Consortium (MoTrPAC) mapped the longitudinal, multi-omic changes in mitochondrial analytes across 19 tissues in male and female rats endurance trained for 1, 2, 4 or 8 weeks. Training elicited substantial changes in the adrenal gland, brown adipose, colon, heart and skeletal muscle, while we detected mild responses in the brain, lung, small intestine and testes. The colon response was characterized by non-linear dynamics that resulted in upregulation of mitochondrial function that was more prominent in females. Brown adipose and adrenal tissues were characterized by substantial downregulation of mitochondrial pathways. Training induced a previously unrecognized robust upregulation of mitochondrial protein abundance and acetylation in the liver, and a concomitant shift in lipid metabolism. The striated muscles demonstrated a highly coordinated response to increase oxidative capacity, with the majority of changes occurring in protein abundance and post-translational modifications. We identified exercise upregulated networks that are downregulated in human type 2 diabetes and liver cirrhosis. In both cases HSD17B10, a central dehydrogenase in multiple metabolic pathways and mitochondrial tRNA maturation, was the main hub. In summary, we provide a multi-omic, cross-tissue atlas of the mitochondrial response to training and identify candidates for prevention of disease-associated mitochondrial dysfunction.

The Role of Oxidative Inactivation of Phosphatase PTEN and TCPTP in Fatty Liver Disease

Alcoholic liver disease (ALD) and nonalcoholic fatty liver disease (NAFLD) are becoming increasingly prevalent worldwide. Despite the different etiologies, their spectra and histological feature are similar, from simple steatosis to more advanced stages such as steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Studies including peroxiredoxin knockout models revealed that oxidative stress is crucial in these diseases, which present as consequences of redox imbalance. Protein tyrosine phosphatases (PTPs) are a superfamily of enzymes that are major targets of reactive oxygen species (ROS) because of an oxidation-susceptible nucleophilic cysteine in their active site. Herein, we review the oxidative inactivation of two tumor suppressor PTPs, phosphatase and tensin homolog deleted on chromosome 10 (PTEN) and T-cell protein tyrosine phosphatase (TCPTP), and their contribution to the pathogenicity of ALD and NAFLD, respectively. This review might provide a better understanding of the pathogenic mechanisms of these diseases and help develop new therapeutic strategies to treat fatty liver disease.

Zuogui-Jiangtang-Qinggan-Fang alleviates high-fat diet-induced type 2 diabetes mellitus with non-alcoholic fatty liver disease by modulating gut microbiome-metabolites-short chain fatty acid composition

Non-alcoholic fatty liver disease (NAFLD) pathogenesis is affected by dysbiosis of the gut microbiome and the metabolites it generates. Therefore, restoring the equilibrium between the gut microbiome and the generated metabolites may have therapeutic potential for the syndrome. Zuogui Jiangtang Qinggan Fang (ZGJTQGF) is a Chinese herbal formulation used clinically to treat type 2 diabetic mellitus (T2DM) and fatty liver disease. However, its pharmacological mechanisms have not been well characterized. This work aimed to evaluate the hepatoprotective mechanism of ZGJTQGF in T2DM with NAFLD mice by incorporating gut microbiota, short-chain fatty acids（SCFAs）, and metabolomic analysis, and then to provide strong support for clinical treatment of T2DM with NAFLD. The sequencing of 16 S rRNA revealed that ZGJTQGF therapy modified the composition and abundance of the gut microbiome, raised the level of SCFAs, and restored the intestinal mucosal barrier. The non-targeted metabolomic analysis of liver tissues identified 212 compounds, of which108 were differentially expressed between the HFD and ZGJTQGF groups. Moreover, L-glutamic acid, L-Phenylalanine, Glycine, Taurine, Deoxycholic acid, and citric acid levels were also considerably altered by ZGJTQGF. Our findings suggest that ZGJTQGF ameliorates HFD-induced hepatic steatosis by modulating the gut microbiota composition and its metabolites and boosting the levels of SCFAs. More notably, ZGJTQGF may be a promising medication for preventing and treating NAFLD.

Epidemiologic, Genetic, Pathogenic, Metabolic, Epigenetic Aspects Involved in NASH-HCC: Current Therapeutic Strategies

Hepatocellular carcinoma (HCC) is the most common primary liver cancer and is the sixth most frequent cancer in the world, being the third cause of cancer-related deaths. Nonalcoholic steatohepatitis (NASH) is characterized by fatty infiltration, oxidative stress and necroinflammation of the liver, with or without fibrosis, which can progress to advanced liver fibrosis, cirrhosis and HCC. Obesity, metabolic syndrome, insulin resistance, and diabetes exacerbates the course of NASH, which elevate the risk of HCC. The growing prevalence of obesity are related with increasing incidence of NASH, which may play a growing role in HCC epidemiology worldwide. In addition, HCC initiation and progression is driven by reprogramming of metabolism, which indicates growing appreciation of metabolism in the pathogenesis of this disease. Although no specific preventive pharmacological treatments have recommended for NASH, dietary restriction and exercise are recommended. This review focuses on the molecular connections between HCC and NASH, including genetic and risk factors, highlighting the metabolic reprogramming and aberrant epigenetic alterations in the development of HCC in NASH. Current therapeutic aspects of NASH/HCC are also reviewed.

Hepatic PLIN5 Deficiency Impairs Lipogenesis through Mitochondrial Dysfunction

Regulation of lipid droplets (LDs) metabolism is the core of controlling intracellular fatty acids (FAs) fluxes, and perilipin 5 (PLIN5) plays a key role in this process. Our previous studies have found that hepatic PLIN5 deficiency reduces LDs accumulation, but the trafficking of FAs produced from this pathway and the interaction between mitochondria and LDs in this process are largely unknown. Here, we found that the deficiency of PLIN5 decreases LDs accumulation by increasing FAs efflux. In addition, the decreased lipogenesis of PLIN5-deficient hepatocytes is accompanied by mitochondrial dysfunction, suggesting that PLIN5 plays an important role in mediating the interaction between LDs and mitochondria. Importantly, PLIN5 ablation negates oxidative capacity differences of peri-droplet and cytosolic mitochondria. In summary, these data indicate that PLIN5 plays a vital role in maintaining mitochondrial-mediated lipogenesis, which provides an important new perspective on the regulation of liver lipid storage and the relationship between PLIN5 and mitochondria.

Environmental Chemical Exposures and Mitochondrial Dysfunction: a Review of Recent Literature

PURPOSE OF REVIEW

Mitochondria play various roles that are important for cell function and survival; therefore, significant mitochondrial dysfunction may have chronic consequences that extend beyond the cell. Mitochondria are already susceptible to damage, which may be exacerbated by environmental exposures. Therefore, the aim of this review is to summarize the recent literature (2012-2022) looking at the effects of six ubiquitous classes of compounds on mitochondrial dysfunction in human populations.

RECENT FINDINGS

The literature suggests that there are a number of biomarkers that are commonly used to identify mitochondrial dysfunction, each with certain advantages and limitations. Classes of environmental toxicants such as polycyclic aromatic hydrocarbons, air pollutants, heavy metals, endocrine-disrupting compounds, pesticides, and nanomaterials can damage the mitochondria in varied ways, with changes in mtDNA copy number and measures of oxidative damage the most commonly measured in human populations. Other significant biomarkers include changes in mitochondrial membrane potential, calcium levels, and ATP levels. This review identifies the biomarkers that are commonly used to characterize mitochondrial dysfunction but suggests that emerging mitochondrial biomarkers, such as cell-free mitochondria and blood cardiolipin levels, may provide greater insight into the impacts of exposures on mitochondrial function. This review identifies that the mtDNA copy number and measures of oxidative damage are commonly used to characterize mitochondrial dysfunction, but suggests using novel approaches in addition to well-characterized ones to create standardized protocols. We identified a dearth of studies on mitochondrial dysfunction in human populations exposed to metals, endocrine-disrupting chemicals, pesticides, and nanoparticles as a gap in knowledge that needs attention.

Modulatory effect of camel milk on intestinal microbiota of mice with non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a common metabolic disease of life, usually caused by unhealthy diet and lifestyle. Compared to normal individuals, the structure of the intestinal flora of NAFLD patients is altered accordingly. This study investigates the effect of camel milk on the regulation of intestinal flora structure in mice with high-fat diet-induced NAFLD. NAFLD model was established by feeding C57BL/6J mice a high-fat diet for 12 weeks, meanwhile camel milk (3.0 g/kg/d), cow milk (3.0 g/kg/d), and silymarin (200 mg/kg/d) were administered by gavage, respectively. Food intake and changes of physiological indexes in mice were observed and recorded. The 16S rRNA gene V3-V4 region was sequenced and the intestinal flora diversity and gene function were predicted in the colon contents of mice from different group. The results showed that camel milk enhanced glucolipid metabolism by downregulate the levels of blood glucose and triglyceride (TG) in serum, reduced lipid accumulation by downregulate the level of TG in the liver and improved liver tissue structure in NAFLD mice (p < 0.05). Meanwhile, camel milk had a positive modulatory effect on the intestinal flora of NAFLD mice, increasing the relative abundance of beneficial bacteria and decreasing the relative abundance of harmful bacteria in the intestinal flora of NAFLD mice, and silymarin had a similar modulatory effect. At the genus level, camel milk increased the relative abundance of Bacteroides, norank_f_Muribaculaceae and Alloprevotella and decreased the relative abundance of Dubosiella and Coriobacteriaceae_UCG-002 (p < 0.05). Camel milk also enhanced Carbohydrate metabolism, Amino acid metabolism, Energy metabolism, Metabolism of cofactors and vitamins and Lipid metabolism in NAFLD mice, thus reducing the degree of hepatic lipid accumulation in NAFLD mice and maintaining the normal structure of the liver. In conclusion, camel milk can improve the structure and diversity of intestinal flora and enhance the levels of substance and energy metabolism in NAFLD mice, which has a positive effect on alleviating NAFLD and improving the structure of intestinal flora.

PPARα in the Epigenetic Driver Seat of NAFLD: New Therapeutic Opportunities for Epigenetic Drugs?

Nonalcoholic fatty liver disease (NAFLD) is a growing epidemic and the most common cause of chronic liver disease worldwide. It consists of a spectrum of liver disorders ranging from simple steatosis to NASH which predisposes patients to further fibrosis, cirrhosis and even hepatocarcinoma. Despite much research, an approved treatment is still lacking. Finding new therapeutic targets has therefore been a main priority. Known as a main regulator of the lipid metabolism and highly expressed in the liver, the nuclear receptor peroxisome proliferator-activated receptor-α (PPARα) has been identified as an attractive therapeutic target. Since its expression is silenced by DNA hypermethylation in NAFLD patients, many research strategies have aimed to restore the expression of PPARα and its target genes involved in lipid metabolism. Although previously tested PPARα agonists did not ameliorate the disease, current research has shown that PPARα also interacts and regulates epigenetic DNMT1, JMJD3, TET and SIRT1 enzymes. Moreover, there is a growing body of evidence suggesting the orchestrating role of epigenetics in the development and progression of NAFLD. Therefore, current therapeutic strategies are shifting more towards epigenetic drugs. This review provides a concise overview of the epigenetic regulation of NAFLD with a focus on PPARα regulation and highlights recently identified epigenetic interaction partners of PPARα.

Non-alcoholic fatty liver disease (NAFLD) and mental illness: Mechanisms linking mood, metabolism and medicines

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease in the world and one of the leading indications for liver transplantation. It is one of the many manifestations of insulin resistance and metabolic syndrome as well as an independent risk factor for cardiovascular disease. There is growing evidence linking the incidence of NAFLD with psychiatric illnesses such as schizophrenia, bipolar disorder and depression mechanistically via genetic, metabolic, inflammatory and environmental factors including smoking and psychiatric medications. Indeed, patients prescribed antipsychotic medications, regardless of diagnosis, have higher incidence of NAFLD than population norms. The mechanistic pharmacology of antipsychotic-associated NAFLD is beginning to emerge. In this review, we aim to discuss the pathophysiology of NAFLD including its risk factors, insulin resistance and systemic inflammation as well as its intersection with psychiatric illnesses.

Mouse promyelocytic leukemia zinc finger protein (PLZF) regulates hepatic lipid and glucose homeostasis dependent on SIRT1

Previous studies have demonstrated that promyelocytic leukemia zinc finger protein (PLZF) promotes the expression of gluconeogenic genes and hepatic glucose output, which leads to hyperglycemia. However, the role played by PLZF in regulating lipid metabolism is not known. In this study, we aimed to examine the function of PLZF in regulating hepatic lipid and glucose homeostasis and the underlying mechanisms. The expression of PLZF was determined in different mouse models with regard to non-alcoholic fatty liver disease (NAFLD). In the next step, adenoviruses that express PLZF (Ad-PLZF) or PLZF-specific shRNA (Ad-shPLZF) were utilized to alter PLZF expression in mouse livers and in primary hepatocytes. For the phenotype of the fatty liver, histologic and biochemical analyses of hepatic triglyceride (TG), serum TG and cholesterol levels were carried out. The underlying molecular mechanism for the regulation of lipid metabolism by PLZF was further explored using luciferase reporter gene assay and ChIP analysis. The results demonstrated that PLZF expression was upregulated in livers derived from ob/ob, db/db and diet-induced obesity (DIO) mice. Liver PLZF-overexpressing C57BL/6J mice showed fatty liver phenotype, liver inflammation, impaired glucose tolerance and insulin sensitivity. On the other hand, hepatic PLZF knockdown in db/db and DIO mice alleviated hepatic steatosis. Of note, we found that PLZF activates SREBP-1c gene transcription through binding directly to the promoter fragment of this gene, which would induce a repressor-to-activator conversion depending on its interaction with SIRT1 in the role played by PLZF in the transcription process through deacetylation. Thus, PLZF is identified as an essential regulator of hepatic lipid and glucose metabolism, where the modulation of its liver expression could open up a therapeutic path for treating NAFLD.

Dietary supplementation with Tolypocladium sinense mycelium prevents dyslipidemia inflammation in high fat diet mice by modulation of gut microbiota in mice

Obesity is a risk factor for many serious health problems, associated with inflammation, hyperlipidemia, and gut dysbiosis. Prevention of obesity is especially important for human health. Tolypocladium sinense is one of the fungi isolated from Chinese caterpillar fungus, which is a traditional Chinese medicine with putative gut microbiota modulation effects. Here, we established a high-fat diet (HFD)-induced hyperlipidemia mice model, which was supplemented with lyophilized T. sinense mycelium (TSP) daily to evaluate its anti-obesity effects. The results indicated that TSP supplementation can effectively alleviate the inflammatory response and oxidative stress levels caused by obesity. TSP significantly prevented obesity and suppressed dyslipidemia by regulating the expression of lipid metabolism genes in the liver. TSP is also effective in preventing the HFD-induced decline in short-chain fatty acid (SCFA) content. Gut microbiota profiling showed that TSP supplementation reversed HFD diet-induced bacterial abundance and also altered the metabolic pathways of functional microorganisms, as revealed by KEGG analysis. It is noteworthy that, correlation analysis reveals the up-regulated gut microbiota (Lactobacillus and Prevotella_9) are closely correlated with lipid metabolism parameters, gene expression of liver lipid metabolism and inflammatory. Additionally, the role of TSP in the regulation of lipid metabolism was reconfirmed by fecal microbiota transplantation. To sum up, our results provide the evidence that TSP may be used as prebiotic agents to prevent obesity by altering the gut microbiota, alleviating the inflammatory response and regulating gene expression of liver lipid metabolism.