Compromised hepatic mitochondrial fatty acid oxidation and reduced markers of mitochondrial turnover in human NAFLD

New insights into the role of mitochondrial dynamics in oxidative stress-induced diseases

The accumulation of excess reactive oxygen species (ROS) can lead to oxidative stress (OS), which can induce gene mutations, protein denaturation, and lipid peroxidation directly or indirectly. The expression is reduced ATP level in cells, increased cytoplasmic Ca2+, inflammation, and so on. Consequently, ROS are recognized as significant risk factors for human aging and various diseases, including diabetes, cardiovascular diseases, and neurodegenerative diseases. Mitochondria are involved in the production of ROS through the respiratory chain. Abnormal mitochondrial characteristics, including mitochondrial OS, mitochondrial fission, mitochondrial fusion, and mitophagy, play an important role in various tissues. However, previous excellent reviews focused on OS-induced diseases. In this review, we focus on the latest progress of OS-induced mitochondrial dynamics, discuss OS-induced mitochondrial damage-related diseases, and summarize the OS-induced mitochondrial dynamics-related signaling pathways. Additionally, it elaborates on potential therapeutic methods aimed at preventing oxidative stress from further exacerbating mitochondrial disorders.

Autophagy and hepatic lipid metabolism: mechanistic insight and therapeutic potential for MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) originates from a homeostatic imbalance in hepatic lipid metabolism. Increased fat deposition in the liver of people suffering from MASLD predisposes them to develop further metabolic derangements, including diabetes mellitus, metabolic dysfunction-associated steatohepatitis (MASH), and other end-stage liver diseases. Unfortunately, only limited pharmacological therapies exist for MASLD to date. Autophagy, a cellular catabolic process, has emerged as a primary mechanism of lipid metabolism in mammalian hepatocytes. Furthermore, preclinical studies with autophagy modulators have shown promising results in resolving MASLD and mitigating its progress into deleterious liver pathologies. In this review, we discuss our current understanding of autophagy-mediated hepatic lipid metabolism, its therapeutic modulation for MASLD treatment, and current limitations and scope for clinical translation.

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.

GSDME promotes MASLD by regulating pyroptosis, Drp1 citrullination-dependent mitochondrial dynamic, and energy balance in intestine and liver

Dysregulated metabolism, cell death, and inflammation contribute to the development of metabolic dysfunction-associated steatohepatitis (MASH). Pyroptosis, a recently identified form of programmed cell death, is closely linked to inflammation. However, the precise role of pyroptosis, particularly gasdermin-E (GSDME), in MASH development remains unknown. In this study, we observed GSDME cleavage and GSDME-associated interleukin-1β (IL-1β)/IL-18 induction in liver tissues of MASH patients and MASH mouse models induced by a choline-deficient high-fat diet (CDHFD) or a high-fat/high-cholesterol diet (HFHC). Compared with wild-type mice, global GSDME knockout mice exhibited reduced liver steatosis, steatohepatitis, fibrosis, endoplasmic reticulum stress, lipotoxicity and mitochondrial dysfunction in CDHFD- or HFHC-induced MASH models. Moreover, GSDME knockout resulted in increased energy expenditure, inhibited intestinal nutrient absorption, and reduced body weight. In the mice with GSDME deficiency, reintroduction of GSDME in myeloid cells-rather than hepatocytes-mimicked the MASH pathologies and metabolic dysfunctions, as well as the changes in the formation of neutrophil extracellular traps and hepatic macrophage/monocyte subclusters. These subclusters included shifts in Tim4+ or CD163+ resident Kupffer cells, Ly6Chi pro-inflammatory monocytes, and Ly6CloCCR2loCX3CR1hi patrolling monocytes. Integrated analyses of RNA sequencing and quantitative proteomics revealed a significant GSDME-dependent reduction in citrullination at the arginine-114 (R114) site of dynamin-related protein 1 (Drp1) during MASH. Mutation of Drp1 at R114 reduced its stability, impaired its ability to redistribute to mitochondria and regulate mitophagy, and ultimately promoted its degradation under MASH stress. GSDME deficiency reversed the de-citrullination of Drp1R114, preserved Drp1 stability, and enhanced mitochondrial function. Our study highlights the role of GSDME in promoting MASH through regulating pyroptosis, Drp1 citrullination-dependent mitochondrial function, and energy balance in the intestine and liver, and suggests that GSDME may be a potential therapeutic target for managing MASH.

Chlordecone-induced hepatotoxicity and fibrosis are mediated by the proteasomal degradation of septins

Chlordecone (CLD) is a pesticide persisting in soils and contaminating food webs. CLD is sequestered in the liver and poorly metabolized into chlordecol (CLDOH). In vitro liver cell models were used to investigate the fate and mechanistic effects of CLD and CLDOH using multiomics. A 3D-cell model was used to investigate whether CLD and CLDOH can affect susceptibility to the metabolic dysfunction-associated steatotic liver disease (MASLD). Hepatocytes were more sensitive to CLD than CLDOH. CLDOH was intensively metabolized into a glucuronide conjugate, whereas CLD was sequestered. CLD but not CLDOH induced a depletion of Septin-2,- 7,- 9,- 10,- 11 due to proteasomal degradation. Septin binding with CLD and CLDOH was confirmed by surface plasmon resonance. CLD disrupted lipid droplet size and increased saturated long-chain dicarboxylic acid production by inhibiting stearoyl-CoA desaturase (SCD) abundance. Neither CLD nor CLDOH induced steatosis, but CLD induced fibrosis in the 3D model of MASLD. To conclude, CLD hepatoxicity is specifically driven by the degradation of septins. CLDOH, was too rapidly metabolized to induce septin degradation. We show that the conversion of CLD to CLDOH reduced hepatotoxicity and fibrosis in liver organoids. This suggests that protective strategies could be explored to reduce the hepatotoxicity of CLD.

Ketogenesis supports hepatic polyunsaturated fatty acid homeostasis via fatty acid elongation

Therapeutic interventions targeting hepatic lipid metabolism in metabolic dysfunction-associated steatotic liver disease (MASLD) and steatohepatitis (MASH) remain elusive. Using mass spectrometry-based stable isotope tracing and shotgun lipidomics, we established a novel link between ketogenesis and MASLD pathophysiology. Our findings show that mouse liver and primary hepatocytes consume ketone bodies to support fatty acid (FA) biosynthesis via both de novo lipogenesis (DNL) and FA elongation. Analysis of 13 C-labeled FAs in hepatocytes lacking mitochondrial D-β-hydroxybutyrate dehydrogenase (BDH1) revealed a partial reliance on mitochondrial conversion of D-βOHB to acetoacetate (AcAc) for cytoplasmic DNL contribution, whereas FA elongation from ketone bodies was fully dependent on cytosolic acetoacetyl-CoA synthetase (AACS). Ketone bodies were essential for polyunsaturated FA (PUFA) homeostasis in hepatocytes, as loss of AACS diminished both free and esterified PUFAs. Ketogenic insufficiency depleted liver PUFAs and increased triacylglycerols, mimicking human MASLD, suggesting that ketogenesis supports PUFA homeostasis, and may mitigate MASLD-MASH progression in humans.

Autophagy alterations in obesity, type 2 diabetes, and metabolic dysfunction-associated steatotic liver disease: the evidence from human studies

Autophagy is an evolutionarily conserved process that plays a pivotal role in the maintenance of cellular homeostasis and its impairment has been implicated in the pathogenesis of various metabolic diseases including obesity, type 2 diabetes (T2D), and metabolic dysfunction-associated steatotic liver disease (MASLD). This review synthesizes the current evidence from human studies on autophagy alterations under these metabolic conditions. In obesity, most data point to autophagy upregulation during the initiation phase of autophagosome formation, potentially in response to proinflammatory conditions in the adipose tissue. Autophagosome formation appears to be enhanced under hyperglycemic or insulin-resistant conditions in patients with T2D, possibly acting as a compensatory mechanism to eliminate damaged organelles and proteins. Other studies have proposed that prolonged hyperglycemia and disrupted insulin signaling hinder autophagic flux, resulting in the accumulation of dysfunctional cellular components that can contribute to β-cell dysfunction. Evidence from patients with MASLD supports autophagy inhibition in disease progression. Nevertheless, given the available data, it is difficult to ascertain whether autophagy is enhanced or suppressed in these conditions because the levels of autophagy markers depend on the overall metabolism of specific organs, tissues, experimental conditions, or disease duration. Owing to these constraints, determining whether the observed shifts in autophagic activity precede or result from metabolic diseases remains challenging. Additionally, autophagy-modulating strategies are shortly discussed. To conclude, more studies investigating autophagy impairment are required to gain a more comprehensive understanding of its role in the pathogenesis of obesity, T2D, and MASLD and to unveil novel therapeutic strategies for these conditions.

Does curcumin improve liver enzymes levels in nonalcoholic fatty liver disease? A systematic review, meta-analysis, and meta-regression

The aim of this meta-analysis is to investigate the sources of heterogeneity in randomized clinical trials examining the effects of curcumin supplementation on liver aminotransferases in subjects with nonalcoholic fatty liver disease (NAFLD). We conducted a systematic search of the PubMed, SCOPUS, and Web of Science databases for randomized clinical trials and identified 15 studies (n = 835 subjects). We used random-effects models with DerSimonian-Laird methods to analyze the serum levels of alanine aminotransferase and aspartate aminotransferase enzymes. Our results indicate that curcumin did not affect serum alanine aminotransferase, but it did reduce aspartate aminotransferase levels. Notably, both outcomes showed high heterogeneity (p < 0.01). Subgroup analysis revealed that adding piperine to curcumin did not benefit aminotransferase levels in NAFLD patients. Additionally, we found a negative correlation between the duration of the intervention and the relative (mg/kg/day) curcumin dose with the reduction in liver aminotransferases. In summary, the sources of heterogeneity identified in our study are likely attributed to the duration of the intervention and the relative dose of curcumin. Consequently, longer trials utilizing high doses of curcumin could diminish the positive impact of curcumin in reducing serum levels of aminotransferases in patients with NAFLD.

Suppression of hepatic ChREBP⍺-CYP2C50 axis-driven fatty acid oxidation sensitizes mice to diet-induced MASLD/MASH

OBJECTIVES

Compromised hepatic fatty acid oxidation (FAO) has been observed in human MASH patients and animal models of MASLD/MASH. It remains poorly understood how and when the hepatic FAO pathway is suppressed during the progression of MASLD towards MASH. Hepatic ChREBP⍺ is a classical lipogenic transcription factor that responds to the intake of dietary sugars.

METHODS

We examined its role in regulating hepatocyte fatty acid oxidation (FAO) and the impact of hepatic Chrebpa deficiency on sensitivity to diet-induced MASLD/MASH in mice.

RESULTS

We discovered that hepatocyte ChREBP⍺ is both necessary and sufficient to maintain FAO in a cell-autonomous manner independently of its DNA-binding activity. Supplementation of synthetic PPAR⍺/δ agonist is sufficient to restore FAO in Chrebp-/- primary mouse hepatocytes. Hepatic ChREBP⍺ was decreased in mouse models of diet-induced MAFSLD/MASH and in patients with MASH. Hepatocyte-specific Chrebp⍺ knockout impaired FAO, aggravated liver steatosis and inflammation, leading to early-onset fibrosis in response to diet-induced MASH. Conversely, liver overexpression of ChREBP⍺-WT or its non-lipogenic mutant enhanced FAO, reduced lipid deposition, and alleviated liver injury, inflammation, and fibrosis. RNA-seq analysis identified the CYP450 epoxygenase (CYP2C50) pathway of arachidonic acid metabolism as a novel target of ChREBP⍺. Over-expression of CYP2C50 partially restores hepatic FAO in primary hepatocytes with Chrebp⍺ deficiency and attenuates preexisting MASH in the livers of hepatocyte-specific Chrebp⍺-deleted mice.

CONCLUSIONS

Our findings support the protective role of hepatocyte ChREBPa against diet-induced MASLD/MASH in mouse models in part via promoting CYP2C50-driven FAO.

Gut microbial metabolites in MASLD: Implications of mitochondrial dysfunction in the pathogenesis and treatment

With an increasing prevalence, metabolic dysfunction-associated steatotic liver disease (MASLD) has become a major global health problem. MASLD is well-known as a multifactorial disease. Mitochondrial dysfunction and alterations in the gut bacteria are 2 vital events in MASLD. Recent studies have highlighted the cross-talk between microbiota and mitochondria, and mitochondria are recognized as pivotal targets of the gut microbiota to modulate the host's physiological state. Mitochondrial dysfunction plays a vital role in MASLD and is associated with multiple pathological changes, including hepatocyte steatosis, oxidative stress, inflammation, and fibrosis. Metabolites are crucial mediators of the gut microbiota that influence extraintestinal organs. Additionally, regulation of the composition of gut bacteria may serve as a promising therapeutic strategy for MASLD. This study reviewed the potential roles of several common metabolites in MASLD, emphasizing their impact on mitochondrial function. Finally, we discuss the current treatments for MASLD, including probiotics, prebiotics, antibiotics, and fecal microbiota transplantation. These methods concentrate on restoring the gut microbiota to promote host health.

FOXO1 induced fatty acid oxidation in hepatic cells by targeting ALDH1L2

BACKGROUND AND AIM

Lipid metabolism disorder is the primary feature of numerous refractory chronic diseases. Fatty acid oxidation, an essential aerobic biological process, is closely related to the progression of NAFLD. The forkhead transcription factor FOXO1 has been reported to play an important role in lipid metabolism. However, the molecular mechanism through which FOXO1 regulates fatty acid oxidation remains unclear.

METHODS

Transcriptomic analysis was performed to examine the cellular expression profile to determine the functional role of FOXO1 in HepG2 cells with palmitic acid (PA)-induced lipid accumulation. FOXO1-binding motifs at the promoter region of aldehyde dehydrogenase 1 family member L2 (ALDH1L2) were predicted via bioinformatic analysis and confirmed via luciferase reporter assay. Overexpression of ALDH1L2 was induced to recover the impaired fatty acid oxidation in FOXO1-knockout cells.

RESULTS

Knockout of FOXO1 aggravated lipid deposition in hepatic cells. Transcriptomic profiling revealed that knockout of FOXO1 increased the expression of genes associated with fatty acid synthesis but decreased the expression of carnitine palmitoyltransferase1a (CPT1α) and adipose triglyceride lipase (ATGL), which contribute to fatty acid oxidation. Mechanistically, FOXO1 was identified as a transcription factor of ALDH1L2. Knockout of FOXO1 significantly decreased the protein expression of ALDH1L2 and CPT1α in vitro and in vivo. Furthermore, overexpression of ALDH1L2 restored fatty acid oxidation in FOXO1-knockout cells.

CONCLUSION

The findings of this study indicate that FOXO1 modulates fatty acid oxidation by targeting ALDH1L2.

Histological improvements following energy restriction and exercise: The role of insulin resistance in resolution of MASH

BACKGROUND & AIMS

Metabolic-dysfunction associated steatohepatitis (MASH) is one of the most common liver diseases worldwide and is characterized by multi-tissue insulin resistance. The effects of a 10-month energy restriction and exercise intervention on liver histology, anthropometrics, plasma biochemistries, and insulin sensitivity were compared to standard of care (control) to understand mechanisms that support liver health improvements.

METHODS

Following medical diagnosis of MASH, subjects were randomized to treatment (n=16) or control (n=8). Liver fat (MRS), 18-hour plasma biochemical measurements, and isotopically-labeled hyperinsulinemic-euglycemic clamps were completed pre- and post-intervention. Body composition and cardiorespiratory fitness (VO2peak) were also measured mid-intervention. Treatment subjects were counseled to reduce energy intake and completed supervised, high-intensity interval training (3x/week) for 10 months. Control subjects continued physician-directed care.

RESULTS

Treatment induced significant (P<0.05) reductions in body weight, fat mass, and liver injury, while VO2peak (P<0.05) and fatty acid (NEFA) suppression (P=0.06) were improved. Both groups exhibited reductions in total energy intake, HbA1c, hepatic insulin resistance, and liver fat (P<0.05). Compared to control, treatment induced a two-fold increase in peripheral insulin sensitivity which was significantly related to higher VO2peak and resolution of liver disease, despite no group differences in peripheral insulin sensitivity.

CONCLUSIONS

Exercise and energy-restriction elicited significant and clinically-meaningful treatment effects on liver health, potentially driven by a redistribution of excess nutrients to skeletal muscle, thereby reducing hepatic nutrient toxicity. Clinical guidelines should emphasize the addition of aerobic exercise in lifestyle treatments for the greatest histologic benefit in individuals with advanced MASH.

CLINICAL TRIAL NUMBER

NCT03151798.

Elevated PINK1/Parkin-Dependent Mitophagy and Boosted Mitochondrial Function Mediate Protection of HepG2 Cells from Excess Palmitic Acid by Hesperetin

Deregulation of mitochondrial functions in hepatocytes contributes to many liver diseases, such as nonalcoholic fatty liver disease (NAFLD). Lately, it was referred to as MAFLD (metabolism-associated fatty liver disease). Hesperetin (Hst), a bioactive flavonoid constituent of citrus fruit, has been proven to attenuate NAFLD. However, a potential connection between its preventive activities and the modulation of mitochondrial functions remains unclear. Here, our results showed that Hst alleviates palmitic acid (PA)-triggered NLRP3 inflammasome activation and cell death by inhibition of mitochondrial impairment in HepG2 cells. Hst reinstates fatty acid oxidation (FAO) rates measured by seahorse extracellular flux analyzer and intracellular acetyl-CoA levels as well as intracellular tricarboxylic acid cycle metabolites levels including NADH and FADH2 reduced by PA exposure. In addition, Hst protects HepG2 cells against PA-induced abnormal energetic profile, ATP generation reduction, overproduction of mitochondrial reactive oxygen species, and collapsed mitochondrial membrane potential. Furthermore, Hst improves the protein expression involved in PINK1/Parkin-mediated mitophagy. Our results demonstrate that it restores PA-impaired mitochondrial function and sustains cellular homeostasis due to the elevation of PINK1/Parkin-mediated mitophagy and the subsequent disposal of dysfunctional mitochondria. These results provide therapeutic potential for Hst utilization as an effective intervention against fatty liver disease.

Oligonucleotide therapies for nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) represents a severe disease subtype of nonalcoholic fatty liver disease (NAFLD) that is thought to be highly associated with systemic metabolic abnormalities. It is characterized by a series of substantial liver damage, including hepatocellular steatosis, inflammation, and fibrosis. The end stage of NASH, in some cases, may result in cirrhosis and hepatocellular carcinoma (HCC). Nowadays a large number of investigations are actively under way to test various therapeutic strategies, including emerging oligonucleotide drugs (e.g., antisense oligonucleotide, small interfering RNA, microRNA, mimic/inhibitor RNA, and small activating RNA) that have shown high potential in treating this fatal liver disease. This article systematically reviews the pathogenesis of NASH/NAFLD, the promising druggable targets proven by current studies in chemical compounds or biological drug development, and the feasibility and limitations of oligonucleotide-based therapeutic approaches under clinical or pre-clinical studies.

Global perspective on nonalcoholic fatty liver disease and nonalcoholic steatohepatitis - prevalence, clinical impact, economic implications and management strategies

BACKGROUND

The metabolically-based liver disease, nonalcoholic fatty liver disease (NAFLD), is the most common cause of chronic liver disease currently affecting 38% of the world's adult population. NAFLD can be progressive leading to nonalcoholic steatohepatitis (NASH), liver transplantation, liver cancer, liver-related mortality and is associated with decreased quality of life from impaired physical functioning and increased healthcare resource utilisation. However, screening for NAFLD is cost-prohibitive but screening for high risk NAFLD (NAFLD with F2 fibrosis or greater) is imperative.

AIM

To review the global perspective on NAFLD and NASH METHODS: We retrieved articles from PubMed using search terms NAFLD, prevalence, clinical burden, economic burden and management strategies.

RESULTS

NAFLD/NASH shows geographical variation across the globe. Highest prevalence rates are in South America and the Middle East and North Africa; lowest prevalence is in Africa. NAFLD's economic impact is from direct and indirect medical costs and loss in worker productivity. It is projected that, over the next two decades, the total cost of NAFLD and diabetes will exceed $1.5 trillion (USD). Risk stratification algorithms identifying "high risk NAFLD" were made following non-invasive tests for NAFLD identification and fibrosis development. These algorithms should be used in primary care and endocrinology settings so timely and appropriate interventions (lifestyle and cardiometabolic risk factor management) can be initiated.

CONCLUSIONS

To reduce the burgeoning burden of NAFLD/NASH, management should include risk stratification algorithms for accurate identification of patients, linkage to appropriate settings, and initiation of effective treatment regimens.

Transcriptomic insights into the lipotoxicity of high-fat high-fructose diet in rat and mouse

Along with the increasing prevalence of obesity worldwide, the deleterious effects of high-calorie diet are gradually recognized through more and more epidemiological studies. However, the concealed and chronic causality whitewashes its unhealthy character. Given an ingenious mechanism orchestrates the metabolic adaptation to high-fat high-fructose (HFF) diet and connive its lipotoxicity, in this study, an experimental rat/mouse model of obesity was induced and a comparative transcriptomic analysis was performed to probe the mystery. Our results demonstrated that HFF diet consumption altered the transcriptomic pattern as well as different high-calorie diet fed rat/mouse manifested distinct hepatic transcriptome. Validation with RT-qPCR and Western blotting confirmed that SREBP1-FASN involved in de novo lipogenesis partly mediated metabolic self-adaption. Moreover, hepatic ACSL1-CPT1A-CPT2 pathway involved in fatty acids β-oxidation, played a key role in the metabolic adaption to HFF. Collectively, our findings enrich the knowledge of the chronic adaptation mechanisms and also shed light on future investigations. Meanwhile, our results also suggest that efforts to restore the fatty acids metabolic fate could be a promising avenue to fight against obesity and associated steatosis and insulin resistance challenged by HFF diet.

Mitochondrial quality control in human health and disease

Mitochondria, the most crucial energy-generating organelles in eukaryotic cells, play a pivotal role in regulating energy metabolism. However, their significance extends beyond this, as they are also indispensable in vital life processes such as cell proliferation, differentiation, immune responses, and redox balance. In response to various physiological signals or external stimuli, a sophisticated mitochondrial quality control (MQC) mechanism has evolved, encompassing key processes like mitochondrial biogenesis, mitochondrial dynamics, and mitophagy, which have garnered increasing attention from researchers to unveil their specific molecular mechanisms. In this review, we present a comprehensive summary of the primary mechanisms and functions of key regulators involved in major components of MQC. Furthermore, the critical physiological functions regulated by MQC and its diverse roles in the progression of various systemic diseases have been described in detail. We also discuss agonists or antagonists targeting MQC, aiming to explore potential therapeutic and research prospects by enhancing MQC to stabilize mitochondrial function.

Hepatocellular RECK as a Critical Regulator of Metabolic Dysfunction-associated Steatohepatitis Development

BACKGROUND & AIMS

Reversion-inducing cysteine-rich protein with Kazal motifs (RECK) is an extracellular matrix regulator with anti-fibrotic effects. However, its expression and role in metabolic dysfunction-associated steatohepatitis (MASH) and hepatic fibrosis are poorly understood.

METHODS

We generated a novel transgenic mouse model with RECK overexpression specifically in hepatocytes to investigate its role in Western diet (WD)-induced liver disease. Proteomic analysis and in vitro studies were performed to mechanistically link RECK to hepatic inflammation and fibrosis.

RESULTS

Our results show that RECK expression is significantly decreased in liver biopsies from human patients diagnosed with MASH and correlated negatively with severity of metabolic dysfunction-associated steatotic liver disease (MASLD) and fibrosis. Similarly, RECK expression is downregulated in WD-induced MASH in wild-type mice. Hepatocyte-specific RECK overexpression significantly reduced hepatic pathology in WD-induced liver injury. Proteomic analysis highlighted changes in extracellular matrix and cell-signaling proteins. In vitro mechanistic studies linked RECK induction to reduced ADAM10 (a disintegrin and metalloproteinase domain-containing protein 10) and ADAM17 activity, amphiregulin release, epidermal growth factor receptor activation, and stellate cell activation.

CONCLUSION

Our in vivo and mechanistic in vitro studies reveal that RECK is a novel upstream regulator of inflammation and fibrosis in the diseased liver, its induction is hepatoprotective, and thus highlights its potential as a novel therapeutic in MASH.

Inhibition of Drp1-Filamin Protein Complex Prevents Hepatic Lipid Droplet Accumulation by Increasing Mitochondria-Lipid Droplet Contact

Lipid droplet (LD) accumulation in hepatocytes is one of the major symptoms associated with fatty liver disease. Mitochondria play a key role in catabolizing fatty acids for energy production through β-oxidation. The interplay between mitochondria and LD assumes a crucial role in lipid metabolism, while it is obscure how mitochondrial morphology affects systemic lipid metabolism in the liver. We previously reported that cilnidipine, an already existing anti-hypertensive drug, can prevent pathological mitochondrial fission by inhibiting protein-protein interaction between dynamin-related protein 1 (Drp1) and filamin, an actin-binding protein. Here, we found that cilnidipine and its new dihydropyridine (DHP) derivative, 1,4-DHP, which lacks Ca2+ channel-blocking action of cilnidipine, prevent the palmitic acid-induced Drp1-filamin interaction, LD accumulation and cytotoxicity of human hepatic HepG2 cells. Cilnidipine and 1,4-DHP also suppressed the LD accumulation accompanied by reducing mitochondrial contact with LD in obese model and high-fat diet-fed mouse livers. These results propose that targeting the Drp1-filamin interaction become a new strategy for the prevention or treatment of fatty liver disease.

Hepatic selective insulin resistance at the intersection of insulin signaling and metabolic dysfunction-associated steatotic liver disease

Insulin resistance (IR) is a major pathogenic factor in the progression of MASLD. In the liver, insulin suppresses gluconeogenesis and enhances de novo lipogenesis (DNL). During IR, there is a defect in insulin-mediated suppression of gluconeogenesis, but an unrestrained increase in hepatic lipogenesis persists. The mechanism of increased hepatic steatosis in IR is unclear and remains controversial. The key discrepancy is whether insulin retains its ability to directly regulate hepatic lipogenesis. Blocking insulin/IRS/AKT signaling reduces liver lipid deposition in IR, suggesting insulin can still regulate lipid metabolism; hepatic glucose metabolism that bypasses insulin's action may contribute to lipogenesis; and due to peripheral IR, other tissues are likely to impact liver lipid deposition. We here review the current understanding of insulin's action in governing different aspects of hepatic lipid metabolism under normal and IR states, with the purpose of highlighting the essential issues that remain unsettled.

Mitochondrial dysfunction: A promising therapeutic target for liver diseases

The liver is an important metabolic and detoxification organ and hence demands a large amount of energy, which is mainly produced by the mitochondria. Liver tissues of patients with alcohol-related or non-alcohol-related liver diseases contain ultrastructural mitochondrial lesions, mitochondrial DNA damage, disturbed mitochondrial dynamics, and compromised ATP production. Overproduction of mitochondrial reactive oxygen species induces oxidative damage to mitochondrial proteins and mitochondrial DNA, decreases mitochondrial membrane potential, triggers hepatocyte inflammation, and promotes programmed cell death, all of which impair liver function. Mitochondrial DNA may be a potential novel non-invasive biomarker of the risk of progression to liver cirrhosis and hepatocellular carcinoma in patients infected with the hepatitis B virus. We herein present a review of the mechanisms of mitochondrial dysfunction in the development of acute liver injury and chronic liver diseases, such as hepatocellular carcinoma, viral hepatitis, drug-induced liver injury, alcoholic liver disease, and non-alcoholic fatty liver disease. This review also discusses mitochondrion-centric therapies for treating liver diseases.

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.

Autophagy and the unfolded protein response shape the non-alcoholic fatty liver landscape: decoding the labyrinth

The incidence of nonalcoholic fatty liver disease (NAFLD) is on the rise, mirroring a global surge in diabetes and metabolic syndrome, as its major leading causes. NAFLD represents a spectrum of liver disorders, ranging from nonalcoholic fatty liver (NAFL) to nonalcoholic steatohepatitis (NASH), which can potentially progress to cirrhosis and hepatocellular carcinoma (HCC). Mechanistically, we know the unfolded protein response (UPR) as a protective cellular mechanism, being triggered under circumstances of endoplasmic reticulum (ER) stress. The hepatic UPR is turned on in a broad spectrum of liver diseases, including NAFLD. Recent data also defines molecular mechanisms that may underlie the existing correlation between UPR activation and NAFLD. More interestingly, subsequent studies have demonstrated an additional mechanism, i.e. autophagy, to be involved in hepatic steatosis, and thus NAFLD pathogenesis, principally by regulating the insulin sensitivity, hepatocellular injury, innate immunity, fibrosis, and carcinogenesis. All these findings suggest possible mechanistic roles for autophagy in the progression of NAFLD and its complications. Both UPR and autophagy are dynamic and interconnected fluxes that act as protective responses to minimize the harmful effects of hepatic lipid accumulation, as well as the ER stress during NAFLD. The functions of UPR and autophagy in the liver, together with findings of decreased hepatic autophagy in correlation with conditions that predispose to NAFLD, such as obesity and aging, suggest that autophagy and UPR, alone or combined, may be novel therapeutic targets against the disease. In this review, we discuss the current evidence on the interplay between autophagy and the UPR in connection to the NAFLD pathogenesis.

Mitochondria-Derived Vesicles, Sterile Inflammation, and Pyroptosis in Liver Cancer: Partners in Crime or Innocent Bystanders?

Alterations in cellular signaling, chronic inflammation, and tissue remodeling contribute to hepatocellular carcinoma (HCC) development. The release of damage-associated molecular patterns (DAMPs) upon tissue injury and the ensuing sterile inflammation have also been attributed a role in HCC pathogenesis. Cargoes of extracellular vesicles (EVs) and/or EVs themselves have been listed among circulating DAMPs but only partially investigated in HCC. Mitochondria-derived vesicles (MDVs), a subpopulation of EVs, are another missing link in the comprehension of the molecular mechanisms underlying the onset and progression of HCC biology. EVs have been involved in HCC growth, dissemination, angiogenesis, and immunosurveillance escape. The contribution of MDVs to these processes is presently unclear. Pyroptosis triggers systemic inflammation through caspase-dependent apoptotic cell death and is implicated in tumor immunity. The analysis of this process, together with MDV characterization, may help capture the relationship among HCC development, mitochondrial quality control, and inflammation. The combination of immune checkpoint inhibitors (i.e., atezolizumab and bevacizumab) has been approved as a synergistic first-line systemic treatment for unresectable or advanced HCC. The lack of biomarkers that may allow prediction of treatment response and, therefore, patient selection, is a major unmet need. Herein, we overview the molecular mechanisms linking mitochondrial dysfunction, inflammation, and pyroptosis, and discuss how immunotherapy targets, at least partly, these routes.

Examining the Pathogenesis of MAFLD and the Medicinal Properties of Natural Products from a Metabolic Perspective

Metabolic-associated fatty liver disease (MAFLD), characterized primarily by hepatic steatosis, has become the most prevalent liver disease worldwide, affecting approximately two-fifths of the global population. The pathogenesis of MAFLD is extremely complex, and to date, there are no approved therapeutic drugs for clinical use. Considerable evidence indicates that various metabolic disorders play a pivotal role in the progression of MAFLD, including lipids, carbohydrates, amino acids, and micronutrients. In recent years, the medicinal properties of natural products have attracted widespread attention, and numerous studies have reported their efficacy in ameliorating metabolic disorders and subsequently alleviating MAFLD. This review aims to summarize the metabolic-associated pathological mechanisms of MAFLD, as well as the natural products that regulate metabolic pathways to alleviate MAFLD.

Berberine Effects in Pre-Fibrotic Stages of Non-Alcoholic Fatty Liver Disease-Clinical and Pre-Clinical Overview and Systematic Review of the Literature

Non-alcoholic fatty liver disease (NAFLD) is the predominant cause of chronic liver conditions, and its progression is marked by evolution to non-alcoholic steatosis, steatohepatitis, cirrhosis related to non-alcoholic steatohepatitis, and the potential occurrence of hepatocellular carcinoma. In our systematic review, we searched two databases, Medline (via Pubmed Central) and Scopus, from inception to 5 February 2024, and included 73 types of research (nine clinical studies and 64 pre-clinical studies) from 2854 published papers. Our extensive research highlights the impact of Berberine on NAFLD pathophysiology mechanisms, such as Adenosine Monophosphate-Activated Protein Kinase (AMPK), gut dysbiosis, peroxisome proliferator-activated receptor (PPAR), Sirtuins, and inflammasome. Studies involving human subjects showed a measurable reduction of liver fat in addition to improved profiles of serum lipids and hepatic enzymes. While current drugs for NAFLD treatment are either scarce or still in development or launch phases, Berberine presents a promising profile. However, improvements in its formulation are necessary to enhance the bioavailability of this natural substance.

Innovative Molecular Targets and Therapeutic Approaches in Nonalcoholic Fatty Liver Disease/Nonalcoholic Steatohepatitis (NAFLD/NASH) 3.0

The aim of this Special Issue is to provide an update on the diagnosis and treatment of nonalcoholic fatty liver disease (NAFLD), which is the most prevalent liver disease worldwide; however, there are still no specific treatment agents [...].

Advances in management of metabolic dysfunction-associated steatotic liver disease: from mechanisms to therapeutics

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the leading cause of chronic liver disease that affects over 30% of the world's population. For decades, the heterogeneity of non-alcoholic fatty liver disease (NAFLD) has impeded our understanding of the disease mechanism and the development of effective medications. However, a recent change in the nomenclature from NAFLD to MASLD emphasizes the critical role of systemic metabolic dysfunction in the pathophysiology of this disease and therefore promotes the progress in the pharmaceutical treatment of MASLD. In this review, we focus on the mechanism underlying the abnormality of hepatic lipid metabolism in patients with MASLD, and summarize the latest progress in the therapeutic medications of MASLD that target metabolic disorders.

The Role Played by Mitochondria in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) refers to an endocrine disorder syndrome that are correlated with multiple organs and systems. PCOS has an effect on women at all stages of their lives, and it has an incidence nearly ranging from 6% to 20% worldwide. Mitochondrial dysfunctions (e.g., oxidative stress, dynamic imbalance, and abnormal quality control system) have been identified in patients and animal models of PCOS, and the above processes may play a certain role in the development of PCOS and its associated complications. However, their specific pathogenic roles should be investigated in depth. In this review, recent studies on the mechanisms of action of mitochondrial dysfunction in PCOS and its associated clinical manifestations are summarized from the perspective of tissues and organs, and some studies on the treatment of the disease by improving mitochondrial function are reviewed to highlight key role of mitochondrial dysfunction in this syndrome.

VCD-induced menopause mouse model reveals reprogramming of hepatic metabolism

OBJECTIVE

Menopause adversely impacts systemic energy metabolism and increases the risk of metabolic disease(s) including hepatic steatosis, but the mechanisms are largely unknown. Dosing female mice with vinyl cyclohexene dioxide (VCD) selectively causes follicular atresia in ovaries, leading to a murine menopause-like phenotype.

METHODS

In this study, we treated female C57BL6/J mice with VCD (160 mg/kg i.p. for 20 consecutive days followed by verification of the lack of estrous cycling) to investigate changes in body composition, energy expenditure (EE), hepatic mitochondrial function, and hepatic steatosis across different dietary conditions.

RESULTS

VCD treatment induced ovarian follicular loss and increased follicle-stimulating hormone (FSH) levels in female mice, mimicking a menopause-like phenotype. VCD treatment did not affect body composition, or EE in mice on a low-fat diet (LFD) or in response to a short-term (1-week) high-fat, high sucrose diet (HFHS). However, the transition to a HFHS lowered cage activity in VCD mice. A chronic HFHS diet (16 weeks) significantly increased weight gain, fat mass, and hepatic steatosis in VCD-treated mice compared to HFHS-fed controls. In the liver, VCD mice showed suppressed hepatic mitochondrial respiration on LFD, while chronic HFHS resulted in compensatory increases in hepatic mitochondrial respiration. Also, liver RNA sequencing revealed that VCD promoted global upregulation of hepatic lipid/cholesterol synthesis pathways.

CONCLUSION

Our findings suggest that the VCD-induced menopause model compromises hepatic mitochondrial function and lipid/cholesterol homeostasis that sets the stage for HFHS diet-induced steatosis while also increasing susceptibility to obesity.

Weight regain, but not weight loss exacerbates hepatic fibrosis during multiple weight cycling events in male mice

PURPOSE

Weight cycling is a phenomenon characterized by fluctuating body weight that is commonly observed in individuals employing intentional weight loss methods. Despite its prevalence, the impact of weight cycling on health remains equivocal. The current investigation aimed to examine the effects of weight cycling on liver health.

METHODS

The weight cycling model was established by switching the feeding method of mice between ad libitum (AL) and restricted intake (DR or 60% of AL) of the breeding diet to cause weight gain and weight loss, respectively. The weight cycling model comprised two and a half cycles, with one group terminating the experience during the weight-gain period (S-AL) and the other during the weight-loss period (S-DR). Liver tissue was collected to investigate morphology alterations, apoptosis, lipid metabolism, and mitochondrial homeostasis.

RESULTS

The results demonstrated that the termination point of weight cycling affected body weight and hepatic steatosis. All parameters examined in the S-DR mice exhibited a comparable trend to those observed in the DR mice. Notably, S-AL mice showed a significant increase in lipid metabolism-related proteins in the liver compared to AL-fed mice, along with reduced lipid droplets. Moreover, hepatic apoptosis and fibrosis were exacerbated in the S-AL mice compared to AL mice, whereas mitochondrial fusion, biogenesis, and mitophagy were decreased in the S-AL mice.

CONCLUSION

Weight cycling ending in weight gain exacerbated hepatic fibrosis, potentially by inducing apoptosis or disrupting mitochondrial homeostasis. Conversely, weight cycling ending in weight loss demonstrated beneficial effects on hepatic health.

Relationship between serum β-hydroxybutyrate and hepatic fatty acid oxidation in individuals with obesity and NAFLD

Nonalcoholic fatty liver disease (NAFLD) is characterized by excess lipid accumulation that can progress to inflammation (nonalcoholic steatohepatitis, NASH), and fibrosis. Serum β-hydroxybutyrate (β-HB), a product of the ketogenic pathway, is commonly used as a surrogate marker for hepatic fatty acid oxidation (FAO). However, it remains uncertain whether this relationship holds true in the context of NAFLD in humans. We compared fasting serum β-HB levels with direct measurement of liver mitochondrial palmitate oxidation in humans stratified based on NAFLD severity (n = 142). Patients were stratified based on NAFLD activity score (NAS): NAS = 0 (no disease), NAS = 1-2 (mild), NAS = 3-4 (moderate), and NAS ≥ 5 (advanced). Moderate and advanced NAFLD is associated with reductions in liver 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2), serum β-HB, but not 3-hydroxy-3-methylglutaryl-CoA lyase (HMGCL) mRNA, relative to no disease. Worsening liver mitochondrial complete palmitate oxidation corresponded with lower HMGCS2 mRNA but not total (complete + incomplete) palmitate oxidation. Interestingly, we found that liver HMGCS2 mRNA and serum β-HB correlated with liver mitochondrial β-hydroxyacyl-CoA dehydrogenase (β-HAD) activity and CPT1A mRNA. Also, lower mitochondrial mass and markers of mitochondrial turnover positively correlated with lower HMGCS2 in the liver. These data suggest that liver ketogenesis and FAO occur at comparable rates in individuals with NAFLD. Our findings support the utility of serum β-HB to serve as a marker of liver injury and hepatic FAO in the context of NAFLD.NEW & NOTEWORTHY Serum β-hydroxybutyrate (β-HB) is frequently utilized as a surrogate marker for hepatic fatty acid oxidation; however, few studies have investigated this relationship during states of liver disease. We found that the progression of nonalcoholic fatty liver disease (NAFLD) is associated with reductions in circulating β-HB and liver 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2). As well, decreased rates of hepatic fatty acid oxidation correlated with liver HMGCS2 mRNA and serum β-HB. Our work supports serum β-HB as a potential marker for hepatic fatty acid oxidation and liver injury during NAFLD.

Imbalance of mitochondrial fusion in peripheral blood mononuclear cells is associated with liver fibrosis in patients with metabolic dysfunction-associated steatohepatitis

Mitochondrial dysfunction and inflammation contribute to the pathophysiology of metabolic dysfunction-associated steatohepatitis (MASH). This study aims to evaluate the potential association between mitochondrial dynamics and cell death markers from peripheral blood mononuclear cells (PBMCs) and the presence of MASH with significant liver fibrosis among metabolic dysfunction-associated steatotic liver disease (MASLD) patients. Consecutive patients undergoing bariatric surgery from January to December 2022 were included. Patients with histologic steatosis were classified into MASH with significant fibrosis (F2-4) group or MASLD/MASH without significant fibrosis group (F0-1). Mitochondrial dynamic proteins and cell death markers were extracted from PBMCs. A total of 23 MASLD/MASH patients were included (significant fibrosis group, n = 7; without significant fibrosis group, n = 16). Of the mitochondrial dynamics and cell death markers evaluated, OPA1 protein, a marker of mitochondrial fusion is higher in MASH patients with significant fibrosis compared to those without (0.861 ± 0.100 vs. 0.560 ± 0.260 proportional to total protein, p = 0.001). Mitochondrial fusion/fission (OPA1/DRP1) ratio is significantly higher in MASH patients with significant fibrosis (1.072 ± 0.307 vs. 0.634 ± 0.313, p = 0.009). OPA1 (per 0.01 proportional to total protein) was associated with the presence of significant liver fibrosis with an OR of 1.08 (95%CI, 1.01-1.15, p = 0.035), and adjusted OR of 1.10 (95%CI, 1.00-1.21, p = 0.042). OPA1 from PBMCs is associated with MASH and substantial fibrosis. Future studies should explore if OPA1 could serve as a novel non-invasive liver fibrosis marker.

Glucagon-like Peptide 1, Glucose-Dependent Insulinotropic Polypeptide, and Glucagon Receptor Agonists in Metabolic Dysfunction-Associated Steatotic Liver Disease: Novel Medication in New Liver Disease Nomenclature

Glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are incretins that regulate postprandial glucose regulation, stimulating insulin secretion from pancreatic β-cells in response to food ingestion. Modified GLP-1 receptor agonists (GLP-1RAs) are being administered for the treatment of obesity and type 2 diabetes mellitus (T2DM). Strongly related to those disorders, metabolic dysfunction-associated steatotic liver disease (MASLD), especially its aggressive form, defined as metabolic dysfunction-associated steatohepatitis (MASH), is a major healthcare burden associated with high morbidity and extrahepatic complications. GLP-1RAs have been explored in MASH patients with evident improvement in liver dysfunction enzymes, glycemic control, and weight loss. Importantly, the combination of GLP-1RAs with GIP and/or glucagon RAs may be even more effective via synergistic mechanisms in amelioration of metabolic, biochemical, and histological parameters of MASLD but also has a beneficial impact on MASLD-related complications. In this current review, we aim to provide an overview of incretins' physiology, action, and signaling. Furthermore, we provide insight into the key pathophysiological mechanisms through which they impact MASLD aspects, as well as we analyze clinical data from human interventional studies. Finally, we discuss the current challenges and future perspectives pertinent to this growing area of research and clinical medicine.

A CDAHFD-induced mouse model mimicking human NASH in the metabolism of hepatic phosphatidylcholines and acyl carnitines

Non-alcoholic steatohepatitis (NASH) is the hepatic manifestation of a cluster of conditions associated with lipid metabolism disorders. Ideal animal models mimicking the human NASH need to be explored to better understand the pathogenesis. A choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD) has recently been used to induce the NASH model, but the advantages are not established. NASH models were induced using the well-known traditional methionine- and choline-deficient (MCD) diet for 5 weeks and the recently used CDAHFD for 3 weeks. Liver phenotypes were analyzed to evaluate the differences in markers related to NASH. Lipidomics and metabolism analyses were used to investigate the effects of dietary regimens on the lipidome of the liver. The CDAHFD induced stronger NASH responses than the MCD, including lipid deposition, liver injury, inflammation, bile acid overload and hepatocyte proliferation. A significant difference in the hepatic lipidome was revealed between the CDAHFD and MCD-induced NASH models. In particular, the CDAHFD reduced the hepatic levels of phosphatidylcholines (PCs) and acylcarnitines (ACs), which was supported by the metabolism analysis and in line with the tendency of human NASH. Pathologically, the CDAHFD could effectively induce a more human-like NASH model over the traditional MCD. The hepatic PCs, ACs and their metabolism in CDAHFD-treated mice were down-regulated, similar to those in human NASH.

Medium-Chain Fatty Acid Feeding Reduces Oxidation and Causes Panacinar Steatosis in Livers of Neonatal Pigs

BACKGROUND

Medium-chain fatty acids (MCFAs) are commonly used to enhance the caloric content of infant formulas. We previously reported that pigs fed MCFA developed hepatic steatosis when compared to those fed isocaloric long-chain fatty acid (LCFA) rich formula.

OBJECTIVES

The objectives of this study were to investigate: 1) whether MCFA and LCFA feeding affect hepatic fatty acid oxidation, and 2) how fat type alters the expression of hepatic fatty acid metabolic genes.

METHODS

Twenty-six, 7-d-old pigs were fed a low-energy control (CONT) formula, or 2 isocaloric high-energy formulas rich in LCFA or MCFA for 22 days. Livers were collected for examining ex vivo fatty acid oxidation, fatty acid content, and mRNA expression of fatty acid metabolic genes.

RESULTS

Liver fat was 20% for pigs in the MCFA compared with 2.9% and 4.6% for those in the CONT and LCFA groups (P < 0.05). MCFA-fed pigs had greater amounts of hepatic laurate, myristate, palmitate, and palmitoleate (14, 34, 49, and 9.3 mg · g-1) than those fed LCFA and CONT (1.8, 1.9, 19, 1.5 mg · g-1) formulas (P ≤ 0.05). Hepatic laurate and palmitate oxidation was reduced for pigs fed MCFA (29 mmol · mg-1 · h-1) compared with those fed CONT (54 mmol · mg-1 · h-1) and LCFA (51 mmol · mg-1 · h-1) formulas (P < 0.05). Expression of fatty acid synthase 3 (FASN-3), fatty acid binding protein 1 (FABP-1), and acetyl-CoA carboxylase 1 (ACACA-1) were 8-, 6-, and 2-fold greater for pigs in the MCFA than those in the LCFA and CONT groups (P < 0.05).

CONCLUSIONS

Feeding MCFA resulted in hepatic steatosis compared with an isocaloric formula rich in LCFA. Steatosis occurred concomitantly with reduced fatty acid oxidation but greater mRNA expression of fatty acid synthetic and catabolic genes.

Role of Insulin Resistance in the Development of Nonalcoholic Fatty Liver Disease in People With Type 2 Diabetes: From Bench to Patient Care

Insulin resistance is implicated in both the pathogenesis of nonalcoholic fatty liver disease (NAFLD) and its progression from steatosis to steatohepatitis, cirrhosis, and even hepatocellular carcinoma, which is known to be more common in people with type 2 diabetes. This article reviews the role of insulin resistance in the metabolic dysfunction observed in obesity, type 2 diabetes, atherogenic dyslipidemia, and hypertension and how it is a driver of the natural history of NAFLD by promoting glucotoxicity and lipotoxicity. The authors also review the genetic and environmental factors that stimulate steatohepatitis and fibrosis progression and their relationship with cardiovascular disease and summarize guidelines supporting the treatment of NAFLD with diabetes medications that reduce insulin resistance, such as pioglitazone or glucagon-like peptide 1 receptor agonists.

Human umbilical cord-derived mesenchymal stem cells ameliorate liver fibrosis by improving mitochondrial function via Slc25a47-Sirt3 signaling pathway

Chronic Liver fibrosis may progress to liver cirrhosis and hepatocellular carcinoma (HCC), hence cause a substantial global burden. However, effective therapies for blocking fibrosis are still lacking. Although mesenchymal stem cells (MSCs) have been proven beneficial to liver regeneration after damage, the underlying mechanism of their therapeutic effects are not fully understood. Oxidative stress and mitochondrial functionality alteration directly contributes to the hepatocyte apoptosis and development of liver fibrosis. This study aims to elucidate the mechanism by which hUC-MSC alleviates liver fibrosis and mitochondrial dysfunction. RNA-sequencing was performed to characterize the transcriptomic changes after implantation of hUC-MSCs in mice with liver fibrosis. Next, western blot, RT-PCR, immunohistochemical and immunofluorescence staining were used to evaluate the expression of different genes in vitro and in vivo. Additionally, mitochondrial morphological and dynamic changes, ROS content, and ATP production were examined. Slc25a47, a newly identified liver-specific mitochondrial NAD+ transporter, was notably reduced in CCl4-treated mice and H2O2-stimulated hepatocytes. Conversely, hUC-MSCs increased the Slc25a47 expression and NAD+ level within mitochondria, thereby enhanced Sirt3 protein activity and alleviated mitochondrial dysfunction in the liver. Furthermore, Slc25a47 knockdown could partially abrogate the protective effects of hUC-MSCs on H2O2-induced mitochondrial fission and oxidative stress in hepatocytes. Our study illustrates that Slc25a47 is a key molecular for hUC-MSCs to improve liver fibrosis and regulates mitochondrial function through Sirt3 for the first time, and providing a theoretical basis for the clinical translation of hUC-MSCs transplantation in the treatment of patients with liver fibrosis/cirrhosis.

Altered lipid metabolism as a predisposing factor for liver metastasis in MASLD

Recently, the incidence of metabolic dysfunction-associated steatotic liver disease (MASLD) is increasing due to the high prevalence of metabolic conditions, such as obesity and type 2 diabetes mellitus. Steatotic liver is a hotspot for cancer metastasis in MASLD. Altered lipid metabolism, a hallmark of MASLD, remodels the tissue microenvironment, making it conducive to the growth of metastatic liver cancer. Tumors exacerbate the dysregulation of hepatic metabolism by releasing extracellular vesicles and particles into the liver. Altered lipid metabolism influences the proliferation, differentiation, and functions of immune cells, contributing to the formation of an immunosuppressive and metastasis-prone liver microenvironment in MASLD. This review discusses the mechanisms by which the steatotic liver promotes liver metastasis progression, focusing on its role in fostering an immunosuppressive microenvironment in MASLD. Furthermore, this review highlights lipid metabolism manipulation strategies for the therapeutic management of metastatic liver cancer.

Loss of mitochondrial adaptation associates with deterioration of mitochondrial turnover and structure in metabolic dysfunction-associated steatotic liver disease

BACKGROUND

Obesity and type 2 diabetes frequently have metabolic dysfunction-associated steatotic liver disease (MASLD) including steatohepatitis (MASH). In obesity, the liver may adapt its oxidative capacity, but the role of mitochondrial turnover in MASLD remains uncertain.

METHODS

This cross-sectional study compared individuals with class III obesity (n = 8/group) without (control, OBE CON; NAFLD activity score: 0.4 ± 0.1) or with steatosis (OBE MASL, 2.3 ± 0.4), or MASH (OBE MASH, 5.3 ± 0.3, p < 0.05 vs. other groups). Hepatic mitochondrial ultrastructure was assessed by transmission electron microscopy, mitochondrial respiration by high-resolution respirometry, biomarkers of mitochondrial quality control and endoplasmic reticulum (ER) stress by Western Blot.

RESULTS

Mitochondrial oxidative capacity was 31 % higher in OBE MASL, but 25 % lower in OBE MASH (p < 0.05 vs. OBE CON). OBE MASH showed ~1.5fold lower mitochondrial number, but ~1.2-1.5fold higher diameter and area (p < 0.001 vs. other groups). Biomarkers of autophagy (p62), mitophagy (PINK1, PARKIN), fission (DRP-1, FIS1) and fusion (MFN1/2, OPA1) were reduced in OBE MASH (p < 0.05 vs. OBE CON). OBE MASL showed lower p62, p-PARKIN/PARKIN, and p-DRP-1 (p < 0.05 vs. OBE CON). OBE MASL and MASH showed higher ER stress markers (PERK, ATF4, p-eIF2α-S51/eIF2α; p < 0.05 vs. OBE CON). Mitochondrial diameter associated inversely with fusion/fission biomarkers and with oxidative capacity, but positively with H2O2.

CONCLUSION

Humans with hepatic steatosis already exhibit impaired mitochondrial turnover, despite upregulated oxidative capacity, and evidence for ER stress. In MASH, oxidative stress likely mediates progressive decline of mitochondrial turnover, ultrastructure and respiration indicating that mitochondrial quality control is key for energy metabolism and may have potential for targeting MASH. ClinGovTrial:NCT01477957.

Generation of inducible mitophagy mice

Mitophagy is programmed selective autophagy of mitochondria and is important for mitochondrial quality control and cellular homeostasis. Mitochondrial dysfunction and impaired mitophagy are closely associated with various diseases, including heart failure and diabetes. To better understand the pathophysiological role of mitophagy, we generated doxycycline-inducible mitophagy mice using a synthetic mitophagy adaptor protein consisting of an outer mitochondrial membrane targeting sequence and an engineered LIR. To evaluate the activation of mitophagy upon doxycycline treatment, we also generated mitophagy reporter mito-QC mice in which mitochondria tandemly express mCherry and GFP, and only GFP signals are lost in acidic lysosomes subjected to mitophagy. With the ROSA26 promoter-driven rtTA, mitophagy was observed at least in heart, liver, and skeletal muscle. We investigated the relationship between mitophagy activation and pressure overload heart failure or high fat diet-induced obesity. Unexpectedly, we were unable to confirm the protective effect of mitophagy in these two pathological models. Further titration of the level of mitophagy induction is required to demonstrate the potency of the protective effects of mitophagy in disease models.

Mechanisms and therapeutic implications of selective autophagy in nonalcoholic fatty liver disease

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) has become the most common chronic liver disease worldwide, whereas there is no approved drug therapy due to its complexity. Studies are emerging to discuss the role of selective autophagy in the pathogenesis of NAFLD, because the specificity among the features of selective autophagy makes it a crucial process in mitigating hepatocyte damage caused by aberrant accumulation of dysfunctional organelles, for which no other pathway can compensate.

AIM OF REVIEW

This review aims to summarize the types, functions, and dynamics of selective autophagy that are of particular importance in the initiation and progression of NAFLD. And on this basis, the review outlines the therapeutic strategies against NAFLD, in particular the medications and potential natural products that can modulate selective autophagy in the pathogenesis of this disease.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The critical roles of lipophagy and mitophagy in the pathogenesis of NAFLD are well established, while reticulophagy and pexophagy are still being identified in this disease due to the insufficient understanding of their molecular details. As gradual blockage of autophagic flux reveals the complexity of NAFLD, studies unraveling the underlying mechanisms have made it possible to successfully treat NAFLD with multiple pharmacological compounds that target associated pathways. Overall, it is convinced that the continued research into selective autophagy occurring in NAFLD will further enhance the understanding of the pathogenesis and uncover novel therapeutic targets.

Jianpi Shengqing Huazhuo Formula improves abnormal glucose and lipid metabolism in obesity by regulating mitochondrial biogenesis

ETHNOPHARMACOLOGICAL RELEVANCE

Jianpi Shengqing Huazhuo Formula (JSH) is a modified prescription based on traditional Chinese medicine theory and classic prescriptions (Buzhong Yiqi Decoction and Yuye Decoction). It has been found that JSH has a good effect on obese patients with early abnormal glucose and lipid metabolism. Therefore, this experiment was conducted to study its clinical efficacy and pharmacological effect.

AIM OF THE STUDY

To observe the clinical efficacy of JSH and explore the mechanism of the formula to improve glucose and lipid metabolism in obese rats.

MATERIALS AND METHODS

1.

CLINICAL OBSERVATION

10 overweight/obese patients with abnormal glucose and lipid metabolism were selected to observe the indicators of serum glucose, serum lipids and liver damage of the patients before and after treatment with JSH. 2. Animal experiments: Fifty Sprague-Dawley (SD) rats were randomly divided into control group, model group, Metformin group (120 mg/kg/day), JSH-L group (5 g/kg/day) and JSH-H group (20 g/kg/day), with 10 rats in each group. The obese SD rat model was produced by feeding 60% high-fat diet for 8 weeks, and the drug group was given prophylactic administration for 8 weeks. At the end of the experiment, body weight, abdominal fat, plasma glucose, plasma lipids, plasma alanine aminotransferase (ALT), and aspartate aminotransferase (AST) were measured. The levels of interleukin-6 (IL-6), interleukin 1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α) in plasma were detected by Elisa, and the changes of malondialdehyde (MDA), glutathione (GSH) and catalase (CAT) in plasma and liver tissue were detected by kits. The pathological changes and lipid deposition in liver were observed by HE staining and oil red O staining, and the changes in the number of mitochondria in liver cells were observed by transmission electron microscopy. RT-qPCR and Western Blot (WB) were used to detect the mitochondrial regulation-related indicators PGC-1α, NRF1, TFAM, MFN2, DRP1 and apoptosis-related indicators Bcl-2, Bax, caspase 8 in liver tissue.

RESULTS

1.

CLINICAL OBSERVATION

After one month administration, the patient's body weight, BMI, 2 h oral glucose tolerance test (2hOGTT), glycated hemoglobin (HbA1c), triglyceride (TG), total cholesterol (TC), low density lipoprotein cholesterol (LDL-C) decreased significantly, and the indicators of liver damage AST and ALT also decreased significantly. 2. Animal experiments: JSH can significantly reduce body weight and abdominal fat area, improve glucose and lipid metabolism, and also reduce plasma IL-6, IL-1β and TNF-α content in obese rats, and improve oxidative stress; HE staining and oil red O staining also showed that JSH can alleviate liver damage and lipid deposition in the liver. Further observations of liver cell ultrastructure showed that JSH can ameliorate the reduction of liver mitochondria caused by a high-fat diet and promote the expression of indicators of mitochondrial biogenesis related to PGC-1α, NRF1, and TFAM. Moreover, JSH could promote the expression of MFN2 and DRP1, decrease Bcl-2 and increase Bax in the liver.

CONCLUSIONS

1.

CLINICAL OBSERVATION

JSH can reduce body weight, serum glucose, serum lipid, and liver injury in overweight/obese patients. 2. Animal experiments: JSH regulates PGC-1α/NRF1/TFAM signaling pathway promotes liver mitochondrial biogenesis, improves glucose and lipid metabolism in obese rats, and regulates mitochondrial dependent apoptosis indicators Bcl-2/Bax to reduce liver injury.

Hepatic Zbtb18 (Zinc Finger and BTB Domain Containing 18) alleviates hepatic steatohepatitis via FXR (Farnesoid X Receptor)

A lasting imbalance between fatty acid synthesis and consumption leads to non-alcoholic fatty liver disease (NAFLD), coupled with hepatitis and insulin resistance. Yet the details of the underlying mechanisms are not fully understood. Here, we unraveled that the expression of the transcription factor Zbtb18 is markedly decreased in the livers of both patients and murine models of NAFLD. Hepatic Zbtb18 knockout promoted NAFLD features like impaired energy expenditure and fatty acid oxidation (FAO), and induced insulin resistance. Conversely, hepatic Zbtb18 overexpression alleviated hepato-steatosis, insulin resistance, and hyperglycemia in mice fed on a high-fat diet (HFD) or in diabetic mice. Notably, in vitro and in vivo mechanistic studies revealed that Zbtb18 transcriptional activation of Farnesoid X receptor (FXR) mediated FAO and Clathrin Heavy Chain (CLTC) protein hinders NLRP3 inflammasome activity. This key mechanism by which hepatocyte's Zbtb18 expression alleviates NAFLD and consequent liver fibrosis was further verified by FXR's deletion and forced expression in mice and cultured mouse primary hepatocytes (MPHs). Moreover, CLTC deletion significantly abrogated the hepatic Zbtb18 overexpression-driven inhibition of NLRP3 inflammasome activity in macrophages. Altogether, Zbtb18 transcriptionally activates the FXR-mediated FAO and CLTC expression, which inhibits NLRP3 inflammasome's activity alleviating inflammatory stress and insulin resistance, representing an attractive remedy for hepatic steatosis and fibrosis.

Cellular and molecular alterations in a human hepatocellular in vitro model of nonalcoholic fatty liver disease development and stratification

The rapidly increasing incidence of nonalcoholic fatty liver disease (NAFLD) is a growing health crisis worldwide. If not detected early, NAFLD progression can lead to irreversible pathological states, including liver fibrosis and cirrhosis. Using in vitro models to understand the molecular pathogenesis has been extremely beneficial; however, most studies have utilized only short-term exposures, highlighting a limitation in current research to model extended fat-induced liver injury. We treated Hep3B cells continuously with a low dose of oleic and palmitic free fatty acids (FFAs) for 7 or 28 days. Transcriptomic analysis identified dysregulated molecular pathways and differential expression of 984 and 917 genes after FFA treatment for 7 and 28 days respectively. DNA methylation analysis of altered DNA methylated regions (DMRs) found 7 DMRs in common. Pathway analysis of differentially expressed genes (DEGs) revealed transcriptomic changes primarily involved in lipid metabolism, small molecule biochemistry, and molecular transport. Western blot analysis revealed changes in PDK4 and CPT1A protein levels, indicative of mitochondrial stress. In line with this, there was mitochondrial morphological change demonstrating breakdown of the mitochondrial network. This in vitro model of human NAFL mimics results observed in human patients and may be used as a pre-clinical model for drug intervention.

Early-life exposure to gestational diabetes mellitus predisposes offspring to pediatric nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has emerged as the prevailing chronic liver disease in the pediatric population due to the global obesity pandemic. Evidence shows that prenatal and postnatal exposure to maternal abnormalities leads to a higher risk of pediatric NAFLD through persistent alterations in developmental programming. Gestational diabetes mellitus (GDM) is a hyperglycemic syndrome which has become the most prevalent complication in pregnant women. An increasing number of both epidemiologic investigations and animal model studies have validated adverse and long-term outcomes in offspring following GDM exposure in utero. Similarly, GDM is considered a crucial risk factor for pediatric NAFLD. This review aimed to summarize currently published studies concerning the inductive roles of GDM in offspring NAFLD development during childhood and adolescence. Dysregulations in hepatic lipid metabolism and gut microbiota in offspring, as well as dysfunctions in the placenta are potential factors in the pathogenesis of GDM-associated pediatric NAFLD. In addition, potentially effective interventions for GDM-associated offspring NAFLD are also discussed in this review. However, most of these therapeutic approaches still require further clinical research for validation.

Cell-type specific role of autophagy in the liver and its implications in non-alcoholic fatty liver disease

Autophagy, a cellular degradative process, has emerged as a key regulator of cellular energy production and stress mitigation. Dysregulated autophagy is a common phenomenon observed in several human diseases, and its restoration offers curative advantage. Non-alcoholic fatty liver disease (NAFLD), more recently renamed metabolic dysfunction-associated steatotic liver disease, is a major metabolic liver disease affecting almost 30% of the world population. Unfortunately, NAFLD has no pharmacological therapies available to date. Autophagy regulates several hepatic processes including lipid metabolism, inflammation, cellular integrity and cellular plasticity in both parenchymal (hepatocytes) and non-parenchymal cells (Kupffer cells, hepatic stellate cells and sinusoidal endothelial cells) with a profound impact on NAFLD progression. Understanding cell type-specific autophagy in the liver is essential in order to develop targeted treatments for liver diseases such as NAFLD. Modulating autophagy in specific cell types can have varying effects on liver function and pathology, making it a promising area of research for liver-related disorders. This review aims to summarize our present understanding of cell-type specific effects of autophagy and their implications in developing autophagy centric therapies for NAFLD.

Lipid Metabolism in Metabolic-Associated Steatotic Liver Disease (MASLD)

Metabolic-associated steatotic liver disease (MASLD) is a cluster of pathological conditions primarily developed due to the accumulation of ectopic fat in the hepatocytes. During the severe form of the disease, i.e., metabolic-associated steatohepatitis (MASH), accumulated lipids promote lipotoxicity, resulting in cellular inflammation, oxidative stress, and hepatocellular ballooning. If left untreated, the advanced form of the disease progresses to fibrosis of the tissue, resulting in irreversible hepatic cirrhosis or the development of hepatocellular carcinoma. Although numerous mechanisms have been identified as significant contributors to the development and advancement of MASLD, altered lipid metabolism continues to stand out as a major factor contributing to the disease. This paper briefly discusses the dysregulation in lipid metabolism during various stages of MASLD.

Cdo1-Camkk2-AMPK axis confers the protective effects of exercise against NAFLD in mice

Exercise is an effective non-pharmacological strategy for ameliorating nonalcoholic fatty liver disease (NAFLD), but the underlying mechanism needs further investigation. Cysteine dioxygenase type 1 (Cdo1) is a key enzyme for cysteine catabolism that is enriched in liver, whose role in NAFLD remains poorly understood. Here, we show that exercise induces the expression of hepatic Cdo1 via the cAMP/PKA/CREB signaling pathway. Hepatocyte-specific knockout of Cdo1 (Cdo1LKO) decreases basal metabolic rate of the mice and impairs the effect of exercise against NAFLD, whereas hepatocyte-specific overexpression of Cdo1 (Cdo1LTG) increases basal metabolic rate of the mice and synergizes with exercise to ameliorate NAFLD. Mechanistically, Cdo1 tethers Camkk2 to AMPK by interacting with both of them, thereby activating AMPK signaling. This promotes fatty acid oxidation and mitochondrial biogenesis in hepatocytes to attenuate hepatosteatosis. Therefore, by promoting hepatic Camkk2-AMPK signaling pathway, Cdo1 acts as an important downstream effector of exercise to combat against NAFLD.

Mitochondrial Dysfunction in Metabolic Dysfunction Fatty Liver Disease (MAFLD)

Nonalcoholic fatty liver disease (NAFLD) has become an increasingly common disease in Western countries and has become the major cause of liver cirrhosis or hepatocellular carcinoma (HCC) in addition to viral hepatitis in recent decades. Furthermore, studies have shown that NAFLD is inextricably linked to the development of extrahepatic diseases. However, there is currently no effective treatment to cure NAFLD. In addition, in 2020, NAFLD was renamed metabolic dysfunction fatty liver disease (MAFLD) to show that its pathogenesis is closely related to metabolic disorders. Recent studies have reported that the development of MAFLD is inextricably associated with mitochondrial dysfunction in hepatocytes and hepatic stellate cells (HSCs). Simultaneously, mitochondrial stress caused by structural and functional disorders stimulates the occurrence and accumulation of fat and lipo-toxicity in hepatocytes and HSCs. In addition, the interaction between mitochondrial dysfunction and the liver-gut axis has also become a new point during the development of MAFLD. In this review, we summarize the effects of several potential treatment strategies for MAFLD, including antioxidants, reagents, and intestinal microorganisms and metabolites.