Hepatocyte HIF-1 and Intermittent Hypoxia Independently Impact Liver Fibrosis in Murine NAFLD

SMPD3 Inhibition Contributes to Nicotinamide-Ameliorated Hepatic Steatosis in Chronic Alcohol-Fed Mice

Alcohol-associated liver disease (ALD) is characterized by the reduction of hepatic nicotinamide adenine dinucleotide (NAD+), which exacerbates hepatic steatosis. The present study was conducted to investigate the protective role of nicotinamide (NAM), a foodborne precursor of NAD+ biosynthesis, in ALD. C57BL/6N mice were employed to establish the ALD model and were administered NAM by gavage. Our results showed that NAM supplementation significantly ameliorated alcohol-induced NAD+ reduction and lipid accumulation in both mice liver and cultured AML-12 hepatocytes and improved lipid metabolism-associated gene disorders. Alcohol-induced liver injury and oxidative stress were also blocked by NAM administration. Further transcriptomics analysis and validation revealed that alcohol-stimulated sphingomyelin phosphodiesterase 3 (SMPD3) was significantly reversed by NAM, along with the reduction of hepatic ceramide levels. Importantly, SMPD3 was upregulated in the livers of ALD patients. Genetically silencing SMPD3 alleviated alcohol-induced lipid accumulation in hepatocytes. ChIP assay identified SMPD3 as a direct downstream target of hypoxia-inducible factor 1 alpha (HIF-1α). Liver-specific Hif1α knockdown reduced the level of hepatic SMPD3 expression in mice. Activation of HIF-1α abolished the prevention of intrahepatic liver lipid deposition by NAM, while SMPD3 knockdown reversed HIF-1α activation-stimulated lipid accumulation, indicating that a HIF-1α-regulated SMPD3 pathway was involved in the beneficial role of NAM. NAM improved liver oxidative stress, while antioxidant MitoQ administration rescued HIF-1α/SMPD3 activation in ALD mice, implying that the antioxidant effect of NAM contributed to its inhibitory role on the HIF-1α/SMPD3 pathway. In conclusion, NAM ameliorates chronic alcohol intake-induced hepatic steatosis by inhibiting SMPD3. This study provides new insights into the mechanistic understanding of ALD and highlights NAM as a therapeutic choice for ALD treatment.

Mechanism of liver x receptor alpha in intestine, liver and adipose tissues in metabolic associated fatty liver disease

Metabolism associated fatty liver disease (MAFLD) has emerged as a growing global health challenge with limited effective treatments. Research on nuclear receptors offers promising new therapeutic avenues for MAFLD. The liver X receptor (LXR) has gained attention for its roles in tumors and metabolic and inflammatory diseases; However, its effects on MAFLD treatment remain a subject of debate. This review explores the therapeutic role of LXRα in MAFLD, focusing on its functions in the intestine, hepatic and adipose tissue, and summarizes recent advancements in LXRα ligands over the past five years. In the intestine, LXRα activation enhances the efflux of non-biliary cholesterol and reduces inflammation in the gut-liver axis by regulating intestinal high-density lipoprotein synthesis and its interaction with lipopolysaccharide. In the liver, LXRα activation facilitates cholesterol transport, influences hepatic lipid synthesis, and exerts anti-inflammatory effects. In adipose tissue, LXRα helps delay MAFLD progression by managing lipid autophagy and insulin resistance. Ligands that modulate LXRα transcriptional activity show considerable promise for MAFLD treatment.

Low-frequency, mild-gradient chronic intermittent hypoxia still induces liver fibrogenesis in mice on a high-fat diet

The fibrogenesis of metabolic dysfunction-associated steatotic liver disease (MASLD) may progress when complicated by obstructive sleep apnea (OSA). Studies using animal models have shown that high-frequency intermittent hypoxia (IH) exposure, which resembles human OSA, accelerates liver fibrosis in fatty liver. This study highlights that low-frequency, mild-gradient intermittent hypoxia (IH) can exacerbate fibrogenesis in fatty liver disease, even without significantly raising markers of liver injury or insulin resistance. Using a mice model on a high-fat diet (HFD), we found that while routine liver tests (e.g., ALT, AST) and cholesterol levels remained comparable between HFD mice exposed to room air (RA) versus those exposed to chronic intermittent hypoxia (CIH), indicators of liver fibrosis and oxidative stress were elevated in the latter group. This suggests that even low-frequency, mild-gradient IH can increase oxidative stress and fibrotic activity within the liver, primarily through the upregulation of specific markers like ICAM-1 and osteopontin (OPN), which may play a role CIH-induced liver inflammation and fibrosis in fatty liver. In conclusion. Our study further notes that these hypoxia-related changes occurred without significantly worsening systemic insulin resistance, focusing attention on localized liver impacts rather than global metabolic disruptions. The findings underscore the potential role of oxidative stress and specific cytokines in the progression of liver fibrosis in MASLD, especially when complicated by conditions that introduce IH.

The traditional Chinese medicine formula Zhihan Anshen Tang (ZHAST) against obstructive sleep apnea hypopnea syndrome: network pharmacology and molecular docking approach

Introduction

The current treaments for Obstructive Sleep Apnea Hypopnea (OSAHS) are Continuous Positive Airway Pressure (CPAP) and lifestyle modifications, which is not suitable for all patients. Traditional Chinese medicine (TCM) has increasingly demonstrated its efficacy and benefits in treating OSAHS. Zhihan Anshen Tang (ZHAST), has been demonstrated its efficacy and clinical metrics for treating OSAHS patients. However, its key ingredients and mechanisms of action are still unknown.

Methods

Using network pharmacology, we investigated the potential mechanisms of ZHAST through which OSAHS.

Results

In addition, the key targets, including TNF, IL6, GAPDH, STAT3, HIF1A, and JUN, are revealed by the topological analysis. According to the findings of the GO enrichment analysis, genes were enriched in inflammatory responses, hypoxia responses, positive regulation of angiogenesis, protein phosphorylation, and regulation of cell proliferation. KEGG pathway enrichment analysis suggests that the signaling pathway of ZHAST in OSAHS are MAPK and AGE-RAGE signaling pathway, especially in diabetic complications. In addition, it is demonstrated that the enoxolone in ZHASTs have high affinity with the relevant targets by molecular docking and molecular dynamics simulations.

Disscussion

To my knowledge, this is the first network pharmacological molecular docking study about a Chinese medicine effective against OSA. This investigation integrates molecular docking and network pharmacology to identify the effective compounds, related targets, and potential mechanism of ZHASTs in the treatment of OSAHS, providing the prospect of traditional Chinese medicines with modern medical research.

Mechanosensitive Ion Channel PIEZO1 as a Key Regulator of Intestinal Fibrosis in Crohn's Disease

BACKGROUND

We aimed to elucidate the function of the mechanosensitive ion channel PIEZO1 in intestinal fibrosis, which is invariably associated with Crohn's disease (CD) and often results in strictures and obstructions, requiring surgical intervention. Notably, PIEZO1 is strongly expressed in fibrotic tissues and linked with fibrotic progression.

METHODS

Intestinal tissues were procured from 28 patients diagnosed with CD and 8 healthy control subjects. Histological and immunofluorescence assays verified that PIEZO1 is substantially overexpressed in fibrotic intestinal tissues and is involved in epithelial‒mesenchymal transition (EMT). Further gene knockout experiments and transcriptome sequencing elucidated the specific role of PIEZO1 in the pathogenesis of intestinal fibrosis in CD. We generated mice with Piezo1 deletion specifically in intestinal epithelial cells (Piezo1f/f  Vilcre) to validate in vivo that inhibiting Piezo1 function attenuates or reverses intestinal fibrosis associated with CD.

RESULTS

PIEZO1 expression was strongly increased in the fibrotic small intestine of CD patients, thereby promoting EMT and exacerbating intestinal fibrosis. In vivo investigations revealed that the conditional suppression of Piezo1 in intestinal epithelial cells significantly mitigated intestinal fibrosis in dextran sulphate sodium (DSS)- and 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced chronic colitis model mice. In vitro examinations revealed that Piezo1 expression in intestinal epithelial cells preserved the stability of HIF-1α, induced EMT to stimulate the expression of fibrosis-associated molecules, and promoted fibrosis.

CONCLUSION

PIEZO1 plays a pivotal role in the regulation of intestinal fibrosis by maintaining the levels of HIF-1α, thereby promoting EMT. Therapeutic strategies targeting PIEZO1 could be used to prevent intestinal fibrosis in CD patients.

Genetic Loss of HIF-Prolyl-Hydroxylase 1, but Not Pharmacological Inhibition, Mitigates Hepatic Fibrosis

Liver fibrosis is characterized by excessive deposition of extracellular matrix due to chronic inflammation of the liver. Hepatic stellate cells (HSCs) become activated and produce increased amounts of extracellular matrix. Loss of HIF-prolyl-hydroxylase 1 (PHD1) attenuates HSC activation and fibrotic tissue remodeling in a murine model of biliary liver fibrosis. Herein, the protective effect of PHD1 deficiency (PHD1-/-) in an additional (toxic) model of liver fibrosis was validated and the effect of dimethyloxalylglycine (DMOG), a pan-HIF-prolyl-hydroxylase inhibitor, on the development of liver fibrosis, was evaluated. Liver fibrosis was induced utilizing carbon tetrachloride in wild-type (WT) and PHD1-/- mice treated with either vehicle or DMOG. To assess fibrosis development, expression of profibrotic genes in the livers was analyzed by Sirius red staining. When compared with WT mice, PHD1-/- mice developed less-severe liver fibrosis. DMOG treatment did not prevent this liver fibrosis. PHD1-/- mice had fewer α-SMA+ cells and less macrophage infiltration compared with WT mice. Expression of profibrogenic and proinflammatory genes was reduced in livers from carbon tetrachloride-exposed PHD1-/- mice. In vitro analyses of PHD1-deficient human HSCs revealed attenuated mRNA levels of profibrotic genes, as well as impaired migration and invasion. Although PHD1 deficiency attenuated activation of HSCs, pharmacologic PHD inhibition did not ameliorate fibrosis development. These data indicate that selective PHD1 inhibitors could prove effective in preventing and treating liver fibrosis.

Hypoxia-inducible factor-1α inhibitor promotes non-alcoholic steatohepatitis development and increases hepatocellular lipid accumulation via TSKU upregulation

Non-alcoholic steatohepatitis (NASH) is the progressive form of non-alcoholic fatty liver disease (NAFLD) which is the most common chronic liver disease worldwide. Hypoxia-inducible factor-1α (HIF1α) inhibitor is emerging as a promising therapeutic strategy for diseases. However, the role of HIF1α inhibitor in NASH is still unclear. A choline-deficient, l-amino acid-defined, high-fat diet (CDAHFD) -induced NASH mouse model was established to identify the impacts of HIF1α inhibitor KC7F2 on the development of NASH. We found that KC7F2 treatment substantially aggravated lipid accumulation, inflammation, and fibrosis in the liver of NASH mice presumably via increasing Tsukushi (TSKU) expression in the liver. Mechanistically, KC7F2 up-regulated expression of TSKU in hepatocyte in vitro, which led to increased hepatocellular lipid accumulation and was reversed when TSKU was knockdown in hepatocyte. Our findings indicated that HIF1α inhibitor promotes the development of NASH presumably via increasing TSKU expression in the liver, suggesting that HIF1α attenuates NASH, and that we should assess the potential liver toxicity when use HIF1α inhibitor or medicines that can decrease the expression of HIF1α to therapy other diseases.

Regulation of pathologic fibroblast functions in digestive diseases: a role for hypoxia?

The recent uncovering of fibroblast heterogeneity has given great insight into the versatility of the stroma. Among other cellular processes, fibroblasts are now thought to contribute to the coordination of immune responses in a range of chronic inflammatory diseases and cancer. Although the pathologic roles of myofibroblasts, inflammatory fibroblasts, and cancer-associated fibroblasts in disease are reasonably well understood, the mechanisms behind their activation remain to be uncovered. In the gastrointestinal (GI) tract, several interleukins and tumor necrosis factor superfamily members have been identified as possible mediators driving the acquisition of inflammatory and fibrotic properties in fibroblasts. In addition to cytokines, other microenvironmental factors such as nutrient and oxygen availability are likely contributors to this process. In this respect, the phenomenon of low cellular oxygen levels known as hypoxia is common in a plethora of GI diseases. Indeed, the cross talk between hypoxia and inflammation is well-documented, with an abundance of studies suggesting that oxygen-sensing enzymes may have regulatory effects on inflammatory signaling pathways such as NF-κB. However, the impact that this has in GI fibroblasts in the context of chronic diseases has not been fully uncovered. Here we discuss the role of fibroblasts in GI diseases, the mediators that have emerged as regulators of their functions and the potential impact of hypoxia in this process, highlighting areas that require further investigation.

Assessment of hypoxia status in a rat chronic liver disease model using IVIM and T1 mapping

Objectives

This study was aimed to assess the diagnostic performance of intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI) and T1 mapping in detecting hypoxia status of chronic liver disease using a carbon tetrachloride (CCl4)-induced rat model.

Materials and methods

The hypoxia group of chronic liver disease consisted of eight rats induced by injection of CCl4 and the control group consisted of nine rats injected with pure olive oil. All 17 rats underwent MRI examination at week 13 after injection, using T1 mapping and IVIM. Liver specimens were subjected to immunohistochemical staining for the exogenous hypoxia marker pimonidazole and the endogenous hypoxia marker HIF-1α and scored semi-quantitatively. Differences in MRI multiparameters, pimonidazole H-scores, and HIF-1α were analyzed between the control and hypoxia groups. Correlations between MRI multiparameters and H-score, and MRI multiparameters and HIF-1α, were analyzed, and the diagnostic performance of multiparameter MRI was evaluated by receiver operating characteristic (ROC) curve analysis.

Results

There were significant differences between the control group and the hypoxia group in D* values (p = 0.01) and f values (p = 0.025) of IVIM parameters, T1 mapping (p = 0.003), HIF-1α (p < 0.001) and pimonidazole scores (p = 0.004). D* (r = 0.508, p = 0.037) and T1 mapping (r = 0.489, p = 0.046) values positively correlated with pimonidazole scores. D* (r = 0.556, p = 0.020) and T1 mapping (r = 0.505, p = 0.039) showed a positive correlation with HIF-1α. The optimal cut-off value of T1 mapping was 941.527, and the sensitivity, specificity, and AUC were 87.5, 77.8, and 0.889 (95% confidence interval [CI]: 0.734-1), respectively.

Conclusion

IVIM and T1 Mapping are promising methods for non-invasive detection of hypoxia status in chronic liver diseases.

Exposure of Primary Human Skin Fibroblasts to Carbon Dioxide-Containing Solution Significantly Reduces TGF-β-Induced Myofibroblast Differentiation In Vitro

Wound healing as a result of a skin injury involves a series of dynamic physiological processes, leading to wound closure, re-epithelialization, and the remodeling of the extracellular matrix (ECM). The primary scar formed by the new ECM never fully regains the original tissue's strength or flexibility. Moreover, in some cases, due to dysregulated fibroblast activity, proliferation, and differentiation, the normal scarring can be replaced by pathological fibrotic tissue, leading to hypertrophic scars or keloids. These disorders can cause significant physical impairment and psychological stress and represent significant challenges in medical management in the wound-healing process. The present study aimed to investigate the therapeutic effects of exogenously applied carbon dioxide (CO2) on fibroblast behavior, focusing on viability, proliferation, migration, and differentiation to myofibroblasts. We found that CO2 exposure for up to 60 min did not significantly affect fibroblast viability, apoptosis rate, or proliferation and migration capacities. However, a notable finding was the significant reduction in α-smooth muscle actin (α-SMA) protein expression, indicative of myofibroblast differentiation inhibition, following CO2 exposure. This effect was specific to CO2 and concentration as well as time-dependent, with longer exposure durations leading to greater reductions in α-SMA expression. Furthermore, the inhibition of myofibroblast differentiation correlated with a statistically significantly reduced glycolytic and mitochondrial energy metabolism, and as a result, with a reduced ATP synthesis rate. This very noticeable decrease in cellular energy levels seemed to be specific to CO2 exposure and could not be observed in the control cultures using nitrogen (N2)-saturated solutions, indicating a unique and hypoxia-independent effect of CO2 on fibroblast metabolism. These findings suggest that exogenously applied CO2 may possess fibroblast differentiation-reducing properties by modulating fibroblast's energy metabolism and could offer new therapeutic options in the prevention of scar and keloid development.

The impact of aerobic and anaerobic exercise interventions on the management and outcomes of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a metabolic disorder that includes non-alcoholic hepatic steatosis without or with moderate inflammation and non-alcoholic steatohepatitis (NASH), characterized by necroinflammation and a more rapid progression of fibrosis. It is the primary pathological basis for hepatocellular carcinoma. With its prevalence escalating annually, NAFLD has emerged as a global health epidemic, presenting a significant hazard to public health worldwide. Existing studies have shown that physical activity and exercise training have a positive effect on NAFLD. However, the extent to which exercise improves NAFLD depends on the type, intensity, and duration. Therefore, the type of exercise that has the best effect on improving NAFLD remains to be explored. To date, the most valuable discussions involve aerobic and anaerobic exercise. Exercise intervenes in the pathological process of NAFLD by regulating physiological changes in cells through multiple signaling pathways. The review aims to summarize the signaling pathways affected by two different exercise types associated with the onset and progression of NAFLD. It provides a new basis for improving and managing NAFLD in clinical practice.

Lipid nanoparticle-mediated hepatocyte delivery of siRNA and silibinin in metabolic dysfunction-associated steatotic liver disease

Lipid nanoparticle-mediated co-delivery of siRNA and small molecule holds a great potential to treat metabolic dysfunction-associated steatotic liver disease (MASLD). However, targeted delivery of therapeutics to hepatocytes remains challenging. Taking the advantage of rising low density lipoprotein receptor/very-low density lipoprotein receptor (LDLR/VLDR) levels in MASLD, the biological fate of dinonylamine-ethylene glycol chlorophosphate-1-nonanol (DNNA-COP-NA) based lipid nanoparticles (LNPs) was oriented to liver tissues via apolipoprotein E (ApoE)-LDLR/VLDLR pathway. We then adopted a three-round screening strategy to optimize the formulation with both high potency and selectivity to deliver siRNA-HIF-1α (siHIF1α) and silibinin (SLB) payloads to hepatocytes. The optimized SLB/siHIF1α-LNPs mediates great siRNA delivery and transfection of hepatocytes. In high fat diet (HFD)- and carbon tetrachloride (CCl4)-induced mouse models of MASLD, SLB/siHIF1α-LNPs enabled the silencing of hypoxia inducible factor-1α (HIF-1α), a therapeutic target primarily expressed by hepatocytes, leading to significantly reduced inflammation and liver fibrosis synergized with SLB. Moreover, it is demonstrated the hepatocyte-targeting delivery of SLB/siHIF1α-LNPs has the potential to restore the immune homeostasis by modulating the population of Tregs and cytotoxic T cells in spleen. This proof-of-concept study enable siRNA and small molecule co-delivery to hepatocytes through intrinsic variation of targeting receptors for MASLD therapy.

Beneficial effects of intermittent fasting on nonalcoholic fatty liver disease: a narrative review

Nonalcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases, and it is characterized by a series of fatty liver diseases that can lead to severe liver disease. Although no therapeutic drug has been approved as an effective therapy for NAFLD to date, dietary changes and physical activity are thought to be the cornerstone of NAFLD management. For this reason, some articles are available to analyze the studies done so far using various modifications of intermittent fasting (IF) among animals and patients with NAFLD. Data from preclinical and clinical trials suggested that IF positively impacts inflammatory and metabolic markers in both animals and humans. Inflammation and oxidative stress are the major risk factors involved in the pathogenesis of NAFLD. IF has been shown to have positive benefits in alleviating metabolic disorders, promoting the browning of white tissue, resetting circadian rhythm, and activating autophagy of cells. This review is intended to provide a detailed synopsis of the protocols, potential mechanisms of action, and supporting evidence for IF in NAFLD. We will highlight what is currently known about IF approaches in NAFLD treatments in clinical populations with mechanism insight from animal studies, and the safety concerns in certain patient groups.

Graphical Abstract

The protocols of intermittent fasting (IF) are various. Data from trials suggested that IF positively impacts both humans and animals. IF has been shown to have potential treatments for nonalcoholic fatty liver disease.

Sleep patterns, genetic susceptibility, and risk of cirrhosis among individuals with nonalcoholic fatty liver disease

BACKGROUND

The associations between sleep patterns or behaviors and the risk of cirrhosis and the influence of genetic susceptibility on these associations among NAFLD participants remain inadequately elucidated.

METHODS

This study conducted a prospective follow-up of 112,196 NAFLD participants diagnosed at baseline from the UK Biobank cohort study. Five sleep behaviors were collected to measure a healthy sleep score. Five genetic variants were used to construct a polygenic risk score. We used Cox proportional hazard model to assess hazard ratios (HR) and 95% confidence intervals (CIs) for incidence of cirrhosis.

RESULTS

During the follow-up, 592 incident cirrhosis cases were documented. Healthy sleep pattern was associated with reduced risk of cirrhosis in a dose-response manner (ptrend < 0.001). Participants with favourable sleep score (versus unfavourable sleep score) had an HR of 0.55 for cirrhosis risk (95% CI 0.39-0.78). Multivariable-adjusted HRs (95% CIs) of cirrhosis incidence for NAFLDs with no frequent insomnia, sleeping for 7-8 h per day, and no excessive daytime dozing behaviors were 0.73 (0.61-0.87), 0.79 (0.66-0.93), and 0.69 (0.50-0.95), respectively. Compared with participants with favourable sleep pattern and low genetic risk, those with unfavourable sleep pattern and high genetic risk had higher risks of cirrhosis incidence (HR 3.16, 95% CI 1.88-5.33). In addition, a significant interaction between chronotype and genetic risk was detected for the incidence of cirrhosis (p for multiplicative interaction = 0.004).

CONCLUSION

An association was observed between healthy sleep pattern and decreased risk of cirrhosis among NAFLD participants, regardless of low or high genetic risk.

Causal association of circulating cytokines with sarcopenia-related traits: A Mendelian randomization study

BACKGROUND

Observational studies have reported that circulating cytokines are associated with sarcopenia. However, the causal relationship between circulating cytokines and sarcopenia has not been elucidated.

OBJECTIVES

This study aimed to investigate the causal relationship between circulating cytokines and sarcopenia with genetic data using Mendelian randomization (MR).

METHODS

Two-sample bidirectional MR analysis was performed to investigate the causal relationship in individuals of European ancestry. The publicly available genome-wide association study statistics were used to select the key eligible single nucleotide polymorphisms significantly associated with circulating cytokines. Multiple MR analysis approaches, including inverse variance weighted (IVW), MR-Egger, weighted median method (WMM), and MR-Pleiotropy residual Sum and Outlier (MR-PRESSO) methods, were used for the analysis. Sarcopenia-related traits were appendicular lean mass (ALM) and grip strength.

RESULTS

This study demonstrated the causal effect of genetically predicted circulating interleukin interleukin-16 (IL16) levels on both ALM [odds ratio (OR) = 0.990, 95% confidence interval (CI): 0.980-1.000, P = 0.049] and grip strength (OR = 0.971, 95% CI: 0.948-0.995, P = 0.020]. Additionally, C-X-C motif chemokine ligand 10 (CXCL10), interleukin-1beta (IL1B), and hepatocyte growth factor (HGF) were correlated with ALM, while vascular endothelial growth factor (VEGF), interleukin-12 (IL12), and interleukin-15 (IL15) were correlated with grip strength. The results of MR-Egger, weighted median, weighted mode, and simple mode methods were consistent with the IVW estimates. Sensitivity analysis revealed that horizontal pleiotropy did not bias the causal estimates.

CONCLUSION

These findings indicate that inflammatory cytokines exert a significant causal effect on sarcopenia and provide promising leads for the development of novel therapeutic targets for the disease. By evaluating the role of circulating cytokines in the pathologic condition via a genetic epidemiological approach, our study made contributions to a further investigation of underlying mechanisms of sarcopenia.

Association of Obstructive Sleep Apnea with Nonalcoholic Fatty Liver Disease: Evidence, Mechanism, and Treatment

Obstructive sleep apnea (OSA), a common sleep-disordered breathing condition, is characterized by intermittent hypoxia (IH) and sleep fragmentation and has been implicated in the pathogenesis and severity of nonalcoholic fatty liver disease (NAFLD). Abnormal molecular changes mediated by IH, such as high expression of hypoxia-inducible factors, are reportedly involved in abnormal pathophysiological states, including insulin resistance, abnormal lipid metabolism, cell death, and inflammation, which mediate the development of NAFLD. However, the relationship between IH and NAFLD remains to be fully elucidated. In this review, we discuss the clinical correlation between OSA and NAFLD, focusing on the molecular mechanisms of IH in NAFLD progression. We meticulously summarize clinical studies evaluating the therapeutic efficacy of continuous positive airway pressure treatment for NAFLD in OSA. Additionally, we compile potential molecular biomarkers for the co-occurrence of OSA and NAFLD. Finally, we discuss the current research progress and challenges in the field of OSA and NAFLD and propose future directions and prospects.

Exploration of the Key Genes Involved in Non-alcoholic Fatty Liver Disease and Possible MicroRNA Therapeutic Targets

Background

MicroRNAs (miRNAs) are promising therapeutic agents for non-alcoholic fatty liver disease (NAFLD). This study aimed to identify key genes/proteins involved in NAFLD pathogenesis and progression and to evaluate miRNAs influencing their expression.

Methods

Gene expression profiles from datasets GSE151158, GSE163211, GSE135251, GSE167523, GSE46300, and online databases were analyzed to identify significant NAFLD-related genes. Then, protein-protein interaction networks and module analysis identified hub genes/proteins, which were validated using real-time PCR in oleic acid-treated HepG2 cells. Functional enrichment analysis evaluated signaling pathways and biological processes. Gene-miRNA interaction networks identified miRNAs targeting critical NAFLD genes.

Results

The most critical overexpressed hub genes/proteins included: TNF, VEGFA, TLR4, CYP2E1, ACE, SCD, FASN, SREBF2, and TGFB1 based on PPI network analysis, of which TNF, TLR4, SCD, FASN, SREBF2, and TGFB1 were up-regulated in oleic acid-treated HepG2 cells. Functional enrichment analysis for biological processes highlighted programmed necrotic cell death, lipid metabolic process response to reactive oxygen species, and inflammation. In the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, the highest adjusted P-value signaling pathways encompassed AGE-RAGE in diabetic complications, TNF, and HIF-1 signaling pathways. In gene-miRNA network analysis, miR-16 and miR-124 were highlighted as the miRNAs exerting the most influence on important NAFLD-related genes.

Conclusion

In silico analyses identified NAFLD therapeutic targets and miRNA candidates to guide further experimental investigation.

Effects of Environmental Hypoxia on Serum Hematological and Biochemical Parameters, Hypoxia-Inducible Factor (hif) Gene Expression and HIF Pathway in Hybrid Sturgeon (Acipenser schrenckii ♂ × Acipenser baerii ♀)

Hypoxia is a globally pressing environmental problem in aquatic ecosystems. In the present study, a comprehensive analysis was performed to evaluate the effects of hypoxia on physiological responses (hematology, cortisol, biochemistry, hif gene expression and the HIF pathway) of hybrid sturgeons (Acipenser schrenckii ♂ × Acipenser baerii ♀). A total of 180 hybrid sturgeon adults were exposed to dissolved oxygen (DO) levels of 7.00 ± 0.2 mg/L (control, N), 3.5 ± 0.2 mg/L (moderate hypoxia, MH) or 1.00 ± 0.1 mg/L (severe hypoxia, SH) and were sampled at 1 h, 6 h and 24 h after hypoxia. The results showed that the red blood cell (RBC) counts and the hemoglobin (HGB) concentration were significantly increased 6 h and 24 h after hypoxia in the SH group. The serum cortisol concentrations gradually increased with the decrease in the DO levels. Moreover, several serum biochemical parameters (AST, AKP, HBDB, LDH, GLU, TP and T-Bil) were significantly altered at 24 h in the SH group. The HIFs are transcription activators that function as master regulators in hypoxia. In this study, a complete set of six hif genes were identified and characterized in hybrid sturgeon for the first time. After hypoxia, five out of six sturgeon hif genes were significantly differentially expressed in gills, especially hif-1α and hif-3α, with more than 20-fold changes, suggesting their important roles in adaptation to hypoxia in hybrid sturgeon. A meta-analysis indicated that the HIF pathway, a major pathway for adaptation to hypoxic environments, was activated in the liver of the hybrid sturgeon 24 h after the hypoxia challenge. Our study demonstrated that hypoxia, particularly severe hypoxia (1.00 ± 0.1 mg/L), could cause considerable stress for the hybrid sturgeon. These results shed light on their adaptive mechanisms and potential biomarkers for hypoxia tolerance, aiding in aquaculture and conservation efforts.

Network pharmacological analysis on the mechanism of Linggui Zhugan decoction for nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD), represents a chronic progressive disease that imposes a significant burden on patients and the healthcare system. Linggui Zhugan decoction (LGZGD) plays a substantial role in treating NAFLD, but its exact molecular mechanism is unknown. Using network pharmacology, this study aimed to investigate the mechanism of action of LGZGD in treating NAFLD. Active ingredients and targets were identified through the integration of data from the TCMSP, GEO, GeneCards, and OMIM databases. Cytoscape 3.9.1 software, in conjunction with the STRING platform, was employed to construct network diagrams and screen core targets. The enrichment analysis of gene ontology and the Kyoto Encyclopedia of Genes and Genomes pathways were conducted by using the R. Molecular docking of the active ingredients and core targets was performed with AutoDock Vina software. We obtained 93 and 112 active ingredients and potential targets using the bioinformatic analysis of LGZGD in treating NAFLD. The primary ingredients of LGZGD included quercetin, kaempferol, and naringenin. The core targets were identified AKT1, MYC, HSP90AA1, HIF1A, ESR1, TP53, and STAT3. Gene ontology function enrichment analysis revealed associations with responses to nutrient and oxygen levels, nuclear receptor activity, and ligand-activated transcription factor activity. Kyoto Encyclopedia of Genes and Genomes signaling pathway analysis implicated the involvement of the PI3K-Akt, IL-17, TNF, Th17 cell differentiation, HIF-1, and TLR signaling pathways. Molecular docking studies indicated strong binding affinities between active ingredients and targets. LGZGD intervenes in NAFLD through a multi-ingredient, multi-target, and multi-pathway approach. Treatment with LGZGD can improve insulin resistance, oxidative stress, inflammation, and lipid metabolism associated with NAFLD.

Intermittent hypoxia induces hepatic senescence through promoting oxidative stress in a mouse model

PURPOSE

Metabolic-associated fatty liver disease (MAFLD) is an aging-related disease. Obstructive sleep apnea (OSA) may cause MAFLD. This study aimed to explore whether or not intermittent hypoxia (IH), the hallmark of OSA, induces liver aging through oxidative stress.

METHODS

C57BL/6J male mice were administered normal air (control), IH, or antioxidant tempol + IH daily for 6 weeks before the collection of serum and liver tissue samples. A histological examination was conducted to assess liver aging. ELISA was performed to measure liver function indicator levels in the serum and oxidative stress indicator activities in the liver. Western blot analysis was carried out to determine the protein expression of the markers related to oxidative stress, inflammation, and senescence.

RESULTS

Compared with control, IH resulted in significant increases in serum ALT, AST, and TG levels in mice (all P < 0.001), along with lobular inflammation and accumulation of collagen and fat in the liver. The protein levels of inflammatory factors and senescent markers were significantly increased in the IH mouse liver compared with those in the control mouse liver. Meanwhile, IH significantly reduced SOD and CAT activities while enhancing p22phox and Nrf2 protein expression in mouse liver compared with control. Importantly, antioxidant therapy with tempol effectively abrogated the effects of IH on oxidative stress response and aging-related liver injury.

CONCLUSIONS

Our findings suggest that IH induces liver inflammation and aging through oxidative stress. OSA may exacerbate target organ aging and participate in target organ damage. Strategies targeting oxidative stress may prevent and treat OSA-related MAFLD.

Causal relationship between sleep apnea and non-alcoholic fatty liver disease: A Mendelian randomization study

BACKGROUND

Observational studies indicate that sleep apnea is associated with non-alcoholic fatty liver disease (NAFLD) and its related metabolic features, independent of confounding factors including obesity. However, the causal relationships remain to be determined.

METHODS

Univariable and multivariable Mendelian randomization (MR) analyses were performed to investigate the causal relationship between sleep apnea and NAFLD, along with its typical features including liver function, glycemic traits and lipid profiles. Summary-level data for sleep apnea were obtained from the Finngen consortium (33,423 cases and 307,648 controls). Summary-level data for NAFLD were available from a GWAS meta-analysis (8434 cases and 770,180 controls), and data for 12 NAFLD-related features from corresponding published GWASs. The inverse variance weighted (IVW) analysis was employed as the primary statistical method. Bidirectional MR and CAUSE analysis were conducted to avoid reverse causality and false positive findings.

RESULTS

In univariable MR analyses, we found evidence to support a causal effect of genetically predicted sleep apnea on NAFLD (OR = 1.50, 95% CI = 1.18-1.91) and HDL-C (β = -0.045, 95% CI = -0.090 to -0.001). In reverse MR, genetically predicted serum TG was associated with an increased risk of sleep apnea (OR = 1.07, 95% CI = 1.02-1.12), while genetically predicted HDL-C was associated with a decreased risk of sleep apnea (OR = 0.93, 95% CI = 0.89-0.98). After adjusting body mass index or educational attainment, none of these causal associations were retained. However, CAUSE method and MR analyses focusing on lipoprotein subfractions supported a causal effect of sleep apnea on HDL-C and HDL subfractions.

CONCLUSION

This MR study indicated that sleep apnea has no direct causal association with NAFLD, elevated liver enzymes and insulin resistance. Our results showed suggestive inverse associations of genetically predicted sleep apnea on HDL-C and HDL subfractions, indicating that both HDL-C levels and HDL function may be causally implicated in sleep apnea.

Hypoxia-inducible factor-2α promotes fibrosis in non-alcoholic fatty liver disease by enhancing glutamine catabolism and inhibiting yes-associated protein phosphorylation in hepatic stellate cells

Non-alcoholic fatty liver disease (NAFLD) has a high global prevalence and affects approximately one-third of adults, owing to high-fat dietary habits and a sedentary lifestyle. The role of hypoxia-inducible factor 2α (HIF-2α) in NAFLD progression remains unknown. This study aimed to investigate the effects of chronic hypoxia on NAFLD progression by examining the role of hypoxia-inducible factor 2α (HIF-2α) activation and that of hepatic stellate cell (HSC)-derived myofibroblasts through glutaminolysis. We hypothesised that hypoxia exacerbates NAFLD by promoting HIF-2α upregulation and inhibiting phosphorylated yes-associated protein (YAP), and that increasing YAP expression enhances HSC-derived myofibroblasts. We studied patients with NAFLD living at high altitudes, as well as animal models and cultured cells. The results revealed significant increases in HSC-derived myofibroblasts and collagen accumulation caused by HIF-2α and YAP upregulation, both in patients and in a mouse model for hypoxia and NAFLD. HIF-2α and HIF-2α-dependent YAP downregulation reduced HSC activation and myofibroblast levels in persistent chronic hypoxia. Furthermore, hypoxia-induced HIF-2α upregulation promoted YAP and inhibited YAP phosphorylation, leading to glutaminase 1 (GLS1), SLC38A1, α-SMA, and Collagen-1 overexpression. Additionally, hypoxia restored mitochondrial adenosine triphosphate production and reactive oxygen species (ROS) overproduction. Thus, chronic hypoxia-induced HIF-2α activation enhances fibrosis and NAFLD progression by restoring mitochondrial ROS production and glutaminase-1-induced glutaminolysis, which is mediated through the inhibition of YAP phosphorylation and increased YAP nuclear translocation. In summary, HIF-2α plays a pivotal role in NAFLD progression during chronic hypoxia.

Advances in RNA therapeutics for modulation of 'undruggable' targets

Over the past decades, drug discovery utilizing small pharmacological compounds, fragment-based therapeutics, and antibody therapy have significantly advanced treatment options for many human diseases. However, a major bottleneck has been that>70% of human proteins/genomic regions are 'undruggable' by the above-mentioned approaches. Many of these proteins constitute essential drug targets against complex multifactorial diseases like cancer, immunological disorders, and neurological diseases. Therefore, alternative approaches are required to target these proteins or genomic regions in human cells. RNA therapeutics is a promising approach for many of the traditionally 'undruggable' targets by utilizing methods such as antisense oligonucleotides, RNA interference, CRISPR/Cas-based genome editing, aptamers, and the development of mRNA therapeutics. In the following chapter, we will put emphasis on recent advancements utilizing these approaches against challenging drug targets, such as intranuclear proteins, intrinsically disordered proteins, untranslated genomic regions, and targets expressed in inaccessible tissues.

A novel clinical prediction scoring system of high-altitude pulmonary hypertension

Background

High-altitude pulmonary hypertension (HAPH) is a common disease in regions of high altitude where performing right heart catheterization (RHC) is challenging. The development of a diagnostic scoring system is crucial for effective disease screening.

Methods

A total of 148 individuals were included in a retrospective analysis, and an additional 42 residents were prospectively enrolled. We conducted a multivariable analysis to identify independent predictors of HAPH. Subsequently, we devised a prediction score based on the retrospective training set to anticipate the occurrence and severity of HAPH. This scoring system was further subjected to validation in the prospective cohort, in which all participants underwent RHC.

Results

This scoring system, referred to as the GENTH score model (Glycated hemoglobin [OR = 4.5], Echocardiography sign [OR = 9.1], New York Heart Association-functional class [OR = 12.5], Total bilirubin [OR = 3.3], and Hematocrit [OR = 3.6]), incorporated five independent risk factors and demonstrated strong predictive accuracy. In the training set, the area under the curve (AUC) values for predicting the occurrence and severity of HAPH were 0.851 and 0.832, respectively, while in the validation set, they were 0.841 and 0.893. In the validation set, GENTH score model cutoff values of ≤18 or >18 points were established for excluding or confirming HAPH, and a threshold of >30 points indicated severe HAPH.

Conclusions

The GENTH score model, combining laboratory and echocardiography indicators, represents an effective tool for distinguishing potential HAPH patients and identifying those with severe HAPH. This scoring system improves the clinical screening of HAPH diseases and offers valuable insights into disease diagnosis and management.

Molecular mechanisms of metabolic disease-associated hepatic inflammation in non-alcoholic fatty liver disease and non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is the leading chronic liver disease worldwide, with a progressive form of non-alcoholic steatohepatitis (NASH). It may progress to advanced liver diseases, including liver fibrosis, cirrhosis, and hepatocellular carcinoma. NAFLD/NASH is a comorbidity of many metabolic disorders such as obesity, insulin resistance, type 2 diabetes, cardiovascular disease, and chronic kidney disease. These metabolic diseases are often accompanied by systemic or extrahepatic inflammation, which plays an important role in the pathogenesis and treatment of NAFLD or NASH. Metabolites, such as short-chain fatty acids, impact the function, inflammation, and death of hepatocytes, the primary parenchymal cells in the liver tissue. Cholangiocytes, the epithelial cells that line the bile ducts, can differentiate into proliferative hepatocytes in chronic liver injury. In addition, hepatic non-parenchymal cells, including liver sinusoidal endothelial cells, hepatic stellate cells, and innate and adaptive immune cells, are involved in liver inflammation. Proteins such as fibroblast growth factors, acetyl-coenzyme A carboxylases, and nuclear factor erythroid 2-related factor 2 are involved in liver metabolism and inflammation, which are potential targets for NASH treatment. This review focuses on the effects of metabolic disease-induced extrahepatic inflammation, liver inflammation, and the cellular and molecular mechanisms of liver metabolism on the development and progression of NAFLD and NASH, as well as the associated treatments.

The impact of obstructive sleep apnea on nonalcoholic fatty liver disease

Obstructive sleep apnea (OSA) is characterized by episodic sleep state-dependent collapse of the upper airway, with consequent hypoxia, hypercapnia, and arousal from sleep. OSA contributes to multisystem damage; in severe cases, sudden cardiac death might occur. In addition to causing respiratory, cardiovascular and endocrine metabolic diseases, OSA is also closely associated with nonalcoholic fatty liver disease (NAFLD). As the prevalence of OSA and NAFLD increases rapidly, they significantly exert adverse effects on the health of human beings. The authors retrieved relevant documents on OSA and NAFLD from PubMed and Medline. This narrative review elaborates on the current knowledge of OSA and NAFLD, demonstrates the impact of OSA on NAFLD, and clarifies the underlying mechanisms of OSA in the progression of NAFLD. Although there is a lack of sufficient high-quality clinical studies to prove the causal or concomitant relationship between OSA and NAFLD, existing evidence has confirmed the effect of OSA on NAFLD. Elucidating the underlying mechanisms through which OSA impacts NAFLD would hold considerable importance in terms of both prevention and the identification of potential therapeutic targets for NAFLD.

The effects of intermittent hypoxia on hepatic expression of fatty acid translocase CD36 in lean and diet-induced obese mice

BACKGROUND

Both obstructive sleep apnea (OSA) and non-alcoholic fatty liver disease (NAFLD) are prevalent within obese individuals. We aimed to investigate the effects of intermittent hypoxia (IH), a clinical feature of OSA, on hepatic expression of fatty acid translocase (CD36) in relation to liver injury in lean and diet-induced obese mice.

METHODS

Four-week-old male C57BL/6J mice were randomized to standard diet (SD) or high fat (HF) diet groups. At 13-week-old, all mice were exposed to either air or IH (IH30; thirty hypoxic episodes per hour) for four weeks. We assessed liver injury through lipid profile, oxidative and inflammatory stress, histological scoring and hepatic CD36 expression.

RESULTS

In lean mice, IH elevated serum and hepatic triglyceride and free fatty acid (FFA) levels, in line with upregulation of hepatic CD36 expression and myeloperoxidase (MPO)-positive cells in support of inflammatory infiltrates along with increase in serum malondialdehyde (MDA), C-X-C motif chemokine ligand 1(CXCL-1) and monocyte chemoattractant protein-1 (MCP-1). In diet-induced obese mice, an increase in hepatic alanine transaminase (ALT) activity, serum and hepatic levels of lipid parameters and inflammatory markers, serum MDA level, hepatic expressions of CD36 and α-smooth muscle actin (α-SMA), and MPO-positive cells was observed. IH potentiated hepatic ALT activity, serum CXCL-1 and hepatic interleukin-6 (IL-6), in line with inflammatory infiltrates, but paradoxically, reduced hepatic FFA level and hepatic CD36 expression, compared to obese mice without IH exposure. However, IH further augmented diet-induced liver steatosis and fibrosis as shown by histological scores.

CONCLUSION

This study contributes to support that IH featuring OSA may lead to liver injury via differential regulation of hepatic CD36 expression in lean and diet-induced obese mice.

VEGFA Promotes Skeletal Muscle Regeneration in Aging

Aging is associated with loss of skeletal muscle regeneration. Differentially regulated vascular endothelial growth factor (VEGF)A with aging may partially underlies this loss of regenerative capacity. To assess the role of VEGFA in muscle regeneration, young (12-14 weeks old) and old C57BL/6 mice (24,25 months old) are subjected to cryoinjury in the tibialis anterior (TA) muscle to induce muscle regeneration. The average cross-sectional area (CSA) of regenerating myofibers is 33% smaller in old as compared to young (p < 0.01) mice, which correlates with a two-fold loss of muscle VEGFA protein levels (p = 0.02). The capillary density in the TA is similar between the two groups. Young VEGFlo mice, with a 50% decrease in systemic VEGFA activity, exhibit a two-fold reduction in the average regenerating fiber CSA following cryoinjury (p < 0.01) in comparison to littermate controls. ML228, a hypoxia signaling activator known to increase VEGFA levels, augments muscle VEGFA levels and increases average CSA of regenerating fibers in both old mice (25% increase, p < 0.01) and VEGFlo (20% increase, p < 0.01) mice, but not in young or littermate controls. These results suggest that VEGFA may be a therapeutic target in age-related muscle loss.

Duration of intermittent hypoxia impacts metabolic outcomes and severity of murine NAFLD

Rationale

Obstructive sleep apnea (OSA) is associated with metabolic dysfunction, including progression of nonalcoholic fatty liver disease (NAFLD). Chronic intermittent hypoxia (IH) as a model of OSA worsens hepatic steatosis and fibrosis in rodents with diet induced obesity. However, IH also causes weight loss, thus complicating attempts to co-model OSA and NAFLD. We sought to determine the effect of various durations of IH exposure on metabolic and liver-related outcomes in a murine NAFLD model. We hypothesized that longer IH duration would worsen the NAFLD phenotype.

Methods

Male C57BL/6J mice (n = 32) were fed a high trans-fat diet for 24 weeks, to induce NAFLD with severe steatohepatitis. Mice were exposed to an IH profile modeling severe OSA, for variable durations (0, 6, 12, or 18 weeks). Intraperitoneal glucose tolerance test was measured at baseline and at six-week intervals. Liver triglycerides, collagen and other markers of NAFLD were measured at sacrifice.

Results

Mice exposed to IH for 12 weeks gained less weight (p = 0.023), and had lower liver weight (p = 0.008) relative to room air controls. These effects were not observed in the other IH groups. IH of longer duration transiently worsened glucose tolerance, but this effect was not seen in the groups exposed to shorter durations of IH. IH exposure for 12 or 18 weeks exacerbated liver fibrosis, with the largest increase in hepatic collagen observed in mice exposed to IH for 12 weeks.

Discussion

Duration of IH significantly impacts clinically relevant outcomes in a NAFLD model, including body weight, fasting glucose, glucose tolerance, and liver fibrosis.

Targeted MicroRNA Profiling Reveals That Exendin-4 Modulates the Expression of Several MicroRNAs to Reduce Steatosis in HepG2 Cells

Excess hepatic lipid accumulation is the hallmark of non-alcoholic fatty liver disease (NAFLD), for which no medication is currently approved. However, glucagon-like peptide-1 receptor agonists (GLP-1RAs), already approved for treating type 2 diabetes, have lately emerged as possible treatments. Herein we aim to investigate how the GLP-1RA exendin-4 (Ex-4) affects the microRNA (miRNAs) expression profile using an in vitro model of steatosis. Total RNA, including miRNAs, was isolated from control, steatotic, and Ex-4-treated steatotic cells and used for probing a panel of 799 highly curated miRNAs using NanoString technology. Enrichment pathway analysis was used to find the signaling pathways and cellular functions associated with the differentially expressed miRNAs. Our data shows that Ex-4 reversed the expression of a set of miRNAs. Functional enrichment analysis highlighted many relevant signaling pathways and cellular functions enriched in the differentially expressed miRNAs, including hepatic fibrosis, insulin receptor, PPAR, Wnt/β-Catenin, VEGF, and mTOR receptor signaling pathways, fibrosis of the liver, cirrhosis of the liver, proliferation of hepatic stellate cells, diabetes mellitus, glucose metabolism disorder and proliferation of liver cells. Our findings suggest that miRNAs may play essential roles in the processes driving steatosis reduction in response to GLP-1R agonists, which warrants further functional investigation.

Identifying a distinct fibrosis subset of NAFLD via molecular profiling and the involvement of profibrotic macrophages

BACKGROUND

There are emerging studies suggesting that non-alcoholic fatty liver disease (NAFLD) is a heterogeneous disease with multiple etiologies and molecular phenotypes. Fibrosis is the key process in NAFLD progression. In this study, we aimed to explore molecular phenotypes of NAFLD with a particular focus on the fibrosis phenotype and also aimed to explore the changes of macrophage subsets in the fibrosis subset of NAFLD.

METHODS

To assess the transcriptomic alterations of key factors in NAFLD and fibrosis progression, we included 14 different transcriptomic datasets of liver tissues. In addition, two single-cell RNA sequencing (scRNA-seq) datasets were included to construct transcriptomic signatures that could represent specific cells. To explore the molecular subsets of fibrosis in NAFLD based on the transcriptomic features, we used a high-quality RNA-sequencing (RNA-seq) dataset of liver tissues from patients with NAFLD. Non-negative matrix factorization (NMF) was used to analyze the molecular subsets of NAFLD based on the gene set variation analysis (GSVA) enrichment scores of key molecule features in liver tissues.

RESULTS

The key transcriptomic signatures on NAFLD including non-alcoholic steatohepatitis (NASH) signature, fibrosis signature, non-alcoholic fatty liver (NAFL) signature, liver aging signature and TGF-β signature were constructed by liver transcriptome datasets. We analyzed two liver scRNA-seq datasets and constructed cell type-specific transcriptomic signatures based on the genes that were highly expressed in each cell subset. We analyzed the molecular subsets of NAFLD by NMF and categorized four main subsets of NAFLD. Cluster 4 subset is mainly characterized by liver fibrosis. Patients with Cluster 4 subset have more advanced liver fibrosis than patients with other subsets, or may have a high risk of liver fibrosis progression. Furthermore, we identified two key monocyte-macrophage subsets which were both significantly correlated with the progression of liver fibrosis in NAFLD patients.

CONCLUSION

Our study revealed the molecular subtypes of NAFLD by integrating key information from transcriptomic expression profiling and liver microenvironment, and identified a novel and distinct fibrosis subset of NAFLD. The fibrosis subset is significantly correlated with the profibrotic macrophages and M2 macrophage subset. These two liver macrophage subsets may be important players in the progression of liver fibrosis of NAFLD patients.

The Influence of Sex Hormones in Liver Function and Disease

The liver performs a multitude of bodily functions, whilst retaining the ability to regenerate damaged tissue. In this review, we discuss sex steroid biology, regulation of mammalian liver physiology and the development of new model systems to improve our understanding of liver biology in health and disease. A major risk factor for the development of liver disease is hepatic fibrosis. Key drivers of this process are metabolic dysfunction and pathologic activation of the immune system. Although non-alcoholic fatty liver disease (NAFLD) is largely regarded as benign, it does progress to non-alcoholic steatohepatitis in a subset of patients, increasing their risk of developing cirrhosis and hepatocellular carcinoma. NAFLD susceptibility varies across the population, with obesity and insulin resistance playing a strong role in the disease development. Additionally, sex and age have been identified as important risk factors. In addition to the regulation of liver biochemistry, sex hormones also regulate the immune system, with sexual dimorphism described for both innate and adaptive immune responses. Therefore, sex differences in liver metabolism, immunity and their interplay are important factors to consider when designing, studying and developing therapeutic strategies to treat human liver disease. The purpose of this review is to provide the reader with a general overview of sex steroid biology and their regulation of mammalian liver physiology.

Sleep Apnea, Obesity, and Diabetes - an Intertwined Trio

PURPOSE OF REVIEW

To synthesize the existing literature regarding the complex interplay between sleep disturbance, obesity, and diabetes. The review emphasizes the three pillars of health being diet, exercise, and sleep, with the notion that if one is ignored, then the other two could suffer.

RECENT FINDINGS

Sleep deprivation is associated with incident obesity, perhaps mediated by dysregulation in leptin and ghrelin - hormones important in regulation of appetite. Sleep apnea is very common particularly among obese people with type 2 diabetes mellitus. Treatment of sleep apnea has clear symptomatic benefits although its impact on long-term cardiometabolic health is less clear. Sleep disturbance may be an important modifiable risk for patients at risk of cardiometabolic disease. An assessment of sleep health may be an important component of the comprehensive care of patients with obesity and diabetes mellitus.

Hepatocyte-specific knockout of HIF-2α cannot alleviate carbon tetrachloride-induced liver fibrosis in mice

Background

The effects of hypoxia inducible factor-2α (HIF-2α) deficiency on liver fibrosis have not been demonstrated in a fibrosis model induced by carbon tetrachloride (CCl4). We aimed to examine whether hepatocyte-specific HIF-2α deletion could ameliorate CCl4-induced liver fibrosis in mice.

Methods

Hepatocyte-specific HIF-2α knockout mice were created using an albumin promoter-driven Cre recombinase. HIF-2α knockout (KO) mice and floxed control wild-type (WT) mice were fed a normal diet (ND) and received either twice weekly intraperitoneal injections of CCl4 solution (CCl4 dissolved in olive oil) or the corresponding amount of olive oil for 8 weeks. The indicators of liver function, glucose and lipid metabolism, and liver histology were compared among the different groups.

Results

Hepatocyte-specific HIF-2α knockout had no effect on the growth, liver function, glucose or lipid metabolism in mice. CCl4-treated KO and WT mice had a similar pattern of injury and inflammatory cell infiltration in the liver. Quantification of Masson staining, α-smooth muscle actin (α-SMA) immunohistochemistry, and the hydroxyproline (HYP) content revealed similar liver fibrosis levels between KO and WT mice injected intraperitoneally with CCl4. Immunohistochemistry analysis suggested that HIF-2α was mainly expressed in the portal area and hepatic sinusoids but not in hepatocytes. Bioinformatics analyses further indicated that HIF-2α expression was neither liver specific nor hepatocyte specific, and the effect of HIF-2α in hepatocytes on liver fibrosis may not be as important as that in liver sinuses.

Conclusions

Hepatocyte HIF-2α expression may not be a key factor in the initiation of liver fibrogenesis, and hepatocyte-specific deletion of HIF-2α may not be the ideal therapeutic strategy for liver fibrosis.

Resveratrol Regulates Glucose and Lipid Metabolism in Diabetic Rats by Inhibition of PDK1/AKT Phosphorylation and HIF-1α Expression

Purpose

To explore the underlying mechanism of the anti-diabetic effect of resveratrol (RSV) on regulating glycolipid metabolism in diabetic rats induced by streptozotocin (STZ) and a high-fat diet (HFD).

Methods

Male Wistar rats were randomized into three groups. Two groups were fed a high-fat diet and intraperitoneally injected with STZ (35 mg/kg), with one group also treated with RSV (30 mg/kg/d), and the third, control group was fed a normal diet. After 12 weeks, blood lipid levels and fasting blood glucose (FBG) were assessed. Histopathological changes were evaluated by hematoxylin-eosin (HE) staining and periodic acid-Schiff (PAS) staining. The protein expression of hypoxia-inducible factor 1α (HIF-1α) was assessed by Western blotting and immunofluorescence, and the proteins level of 3-phosphoinositide-dependent protein kinase 1 (PDK1), phosphorylated-PDK1 (p-PDK1), phosphorylated-protein kinase B (p-AKT), glucose transporter 1 (GLUT1) and low-density lipoprotein receptor (LDLR) in the liver were analyzed by Western blotting. The mRNA levels of Hif-1α, Glut1 and Ldlr in the liver were determined by RT-qPCR.

Results

RSV treatment significantly reduced liver/body weight ratio (L/W, P < 0.05), FBG (P < 0.01) and serum concentrations of total cholesterol (TC, P < 0.05), triglycerides (TG, P < 0.01) and low-density lipoprotein-cholesterol (LDL-C, P < 0.05) in diabetic rats. RSV also improved diabetic symptoms, attenuated liver steatosis and increased liver glycogen accumulation. RSV treatment significantly downregulated the proteins expression of p-PDK1 and p-AKT (P < 0.01) and the levels of HIF-1α (P < 0.05) and GLUT1 (P < 0.01), while significantly upregulating the level of LDLR (P < 0.05).

Conclusion

RSV was effective in improving glycolipid metabolism in diabetic rats, probably by inhibiting the PDK1/AKT/HIF-1α pathway and regulation of its downstream target levels. These findings may provide new insight into the mechanism of action of RSV in the treatment of diabetes.

Shuangyu Tiaozhi decoction alleviates non-alcoholic fatty liver disease by improving lipid deposition, insulin resistance, and inflammation in vitro and in vivo

Non-alcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases worldwide. Our previous studies have found that Shuangyu Tiaozhi Decoction (SYTZD) could produce an improvement in NAFLD-related indicators, but the underlying mechanism associated with this improvement remains unclear. The study aimed to investigate the potential mechanism of SYTZD against NAFLD through network pharmacology and experimental verification. The components of SYTZD and SYTZD drug containing serum were analyzed using ultra-performance liquid chromatography to quadrupole/time-of-flight mass spectrometry (UPLC-Q/TOF-MS). Active components and targets of SYTZD were screened by the traditional Chinese medical systems pharmacology (TCMSP) and encyclopedia of traditional Chinese medicine (ETCM) databases. NAFLD-related targets were collected from the GeneCards and DisGeNET databases. The component-disease targets were mapped to identify the common targets of SYTZD against NAFLD. Protein-protein interaction (PPI) network of the common targets was constructed for selecting the core targets. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of the core targets was performed using the database for annotation, visualization, and integrated discovery (DAVID) database. Furthermore, animal and cell models were constructed for validating the predictions of network pharmacology. Lipid accumulation, liver histopathology, insulin resistance, and core gene expression were measured by oil red O staining, hematoxylin and eosin staining, insulin tolerance test, real-time quantitative polymerase chain reaction, and Western blotting, respectively. Two components and 22 targets of SYTZD against NAFLD were identified by UPLC-Q/TOF-MS and relevant databases. PPI analysis found that ESR1, FASN, mTOR, HIF-1α, VEGFA, and GSK-3β might be the core targets of SYTZD against NAFLD, which were mainly enriched in the thyroid hormone pathway, insulin resistance pathway, HIF-1 pathway, mTOR pathway, and AMPK pathway. Experimental results revealed that SYTZD might exert multiple anti-NAFLD mechanisms, including improvements in lipid deposition, inflammation, and insulin resistance. SYTZD treatment led to decreases in the lipid profiles, hepatic enzyme levels, inflammatory cytokines, and homeostatic model assessment for insulin resistance (HOMA-IR). SYTZD treatment affected relative mRNA and protein levels associated with various pathways. Our findings reveal that SYTZD could alleviate NAFLD through a multi-component, multi-target, and multi-pathway mechanism of action.

Dysregulated autophagic activity induced in response to chronic intermittent hypoxia contributes to the pathogenesis of NAFLD

Chronic intermittent hypoxia (CIH) is a pathological characteristic of obstructive sleep apnea (OSA) that has been linked to the pathogenesis of nonalcoholic fatty liver disease (NAFLD). The specific link between CIH, autophagic activity, and NAFLD, however, has not previously been characterized. The goal of this study was to assess the relationship between CIH-induced autophagy and the pathogenesis of OSA-associated NAFLD. Western blotting was used to assess the expression of proteins associated with lipid synthesis, endoplasmic reticulum (ER) stress, and autophagic activity. To establish an in vivo model system, C57BL/6 mice were subjected to CIH conditions for 8 h per day over a 12-week period, and were administered chloroquine (CQ) for 1 week prior to euthanization. Levels of serum and liver triglycerides in these animals were assessed, as were proteins related to hepatic autophagy, ER stress, and lipogenesis. qPCR was additionally used to assess hepatic inflammation-related gene expression, while transmission electron microscopy was used to monitor lipid droplet (LD) accumulation and ER morphology. OSA patients and CIH model mice exhibited increases in the expression of proteins associated with hepatic autophagy, ER stress, and lipogenesis. CIH was also associated with more pronounced LD accumulation, hepatic inflammation, and hepatic steatosis in these mice. While serum and hepatic TG and TC levels and serum ALT/AST were increased in response to CIH treatment, the administration of CQ to these mice led to reductions in ER stress-related proteins (XBP1, IRE1α, EIF2α) and lipogenesis-related proteins (ACC, SCD1, FASn), in addition to significantly reducing hepatic inflammation, steatosis, and LD accumulation in these animals. These results suggest that persistent CIH can drive dysregulated hepatic autophagic activity, hepatic steatosis, and ER stress, highlighting potential targets for therapeutic intervention aimed at preventing or treating OSA-associated NAFLD.

Combined intermittent and sustained hypoxia is a novel and deleterious cardio-metabolic phenotype

STUDY OBJECTIVES

Chronic obstructive pulmonary disease and obstructive sleep apnea overlap syndrome is associated with excess mortality, and outcomes are related to the degree of hypoxemia. People at high altitudes are susceptible to periodic breathing, and hypoxia at altitude is associated with cardio-metabolic dysfunction. Hypoxemia in these scenarios may be described as superimposed sustained hypoxia (SH) plus intermittent hypoxia (IH), or overlap hypoxia (OH), the effects of which have not been investigated. We aimed to characterize the cardio-metabolic consequences of OH in mice.

METHODS

C57BL/6J mice were subjected to either SH (FiO2 = 0.10), IH (FiO2 = 0.21 for 12 h, and FiO2 oscillating between 0.21 and 0.06, 60 times/hour, for 12 h), OH (FiO2 = 0.13 for 12 h, and FiO2 oscillating between 0.13 and 0.06, 60 times/hour, for 12 h), or room air (RA), n = 8/group. Blood pressure and intraperitoneal glucose tolerance test were measured serially, and right ventricular systolic pressure (RVSP) was assessed.

RESULTS

Systolic blood pressure transiently increased in IH and OH relative to SH and RA. RVSP did not increase in IH, but increased in SH and OH by 52% (p < .001) and 20% (p = .001). Glucose disposal worsened in IH and improved in SH, with no change in OH. Serum low- and very-low-density lipoproteins increased in OH and SH, but not in IH. Hepatic oxidative stress increased in all hypoxic groups, with the highest increase in OH.

CONCLUSIONS

OH may represent a unique and deleterious cardio-metabolic stimulus, causing systemic and pulmonary hypertension, and without protective metabolic effects characteristic of SH.

HIF-1α mediates renal fibrosis by regulating metabolic remodeling of renal tubule epithelial cells

Hypoxia-inducible factor 1-α (HIF-1α) mediates the occurrence and development of renal diseases and fibrosis. In the process, dysregulated cellular metabolism was suggested to be involved in several pathological processes. Here, we found that HIF-1α expression was increased in the early stage of renal fibrosis, and significant metabolic remodeling was triggered. Epigenetic events that drive diseases were characterized previously. Our study showed that ten-eleven translocation-2 (TET2) was upregulated in both renal fibrosis models and metabolite-treated samples. Furthermore, we found that the promoter of α-SMA was hypomethylated at CpG sites, which promoted the expression of α-SMA and the occurrence of renal fibrosis. HIF-1α inhibition alleviated renal fibrosis development by improving metabolic remodeling and TET2 activation. Our studies provide novel insight into HIF-1α-mediated metabolic remodeling in the pathogenesis of renal fibrosis and propose a concept that targets this pathway to treat fibrotic disorders.

Chronic Intermittent Hypoxia Exposure Alternative to Exercise Alleviates High-Fat-Diet-Induced Obesity and Fatty Liver

Obesity often concurs with nonalcoholic fatty liver disease (NAFLD), both of which are detrimental to human health. Thus far, exercise appears to be an effective treatment approach. However, its effects cannot last long and, moreover, it is difficult to achieve for many obese people. Thus, it is necessary to look into alternative remedies. The present study explored a noninvasive, easy, tolerable physical alternative. In our experiment, C57BL/6 mice were fed with a high-fat diet (HFD) to induce overweight/obesity and were exposed to 10% oxygen for one hour every day. We found that hypoxia exerted protective effects. First, it offset HFD-induced bodyweight gain and insulin resistance. Secondly, hypoxia reversed the HFD-induced enlargement of white and brown adipocytes and fatty liver, and protected liver function. Thirdly, HFD downregulated the expression of genes required for lipolysis and thermogenesis, such as UCP1, ADR3(beta3-adrenergic receptor), CPT1A, ATGL, PPARα, and PGC1α, M2 macrophage markers arginase and CD206 in the liver, and UCP1 and PPARγ in brown fat, while these molecules were upregulated by hypoxia. Furthermore, hypoxia induced the activation of AMPK, an energy sensing enzyme. Fourthly, our results showed that hypoxia increased serum levels of epinephrine. Indeed, the effects of hypoxia on bodyweight, fatty liver, and associated changes in gene expression ever tested were reproduced by injection of epinephrine and prevented by propranolol at varying degrees. Altogether, our data suggest that hypoxia triggers stress responses where epinephrine plays important roles. Therefore, our study sheds light on the hope to use hypoxia to treat the daunting disorders, obesity and NAFLD.

The Cardiovascular and Metabolic Effects of Chronic Hypoxia in Animal Models: A Mini-Review

Animal models are useful to understand the myriad physiological effects of hypoxia. Such models attempt to recapitulate the hypoxemia of human disease in various ways. In this mini-review, we consider the various animal models which have been deployed to understand the effects of chronic hypoxia on pulmonary and systemic blood pressure, glucose and lipid metabolism, atherosclerosis, and stroke. Chronic sustained hypoxia (CSH)-a model of chronic lung or heart diseases in which hypoxemia may be longstanding and persistent, or of high altitude, in which effective atmospheric oxygen concentration is low-reliably induces pulmonary hypertension in rodents, and appears to have protective effects on glucose metabolism. Chronic intermittent hypoxia (CIH) has long been used as a model of obstructive sleep apnea (OSA), in which recurrent airway occlusion results in intermittent reductions in oxyhemoglobin saturations throughout the night. CIH was first shown to increase systemic blood pressure, but has also been associated with other maladaptive physiological changes, including glucose dysregulation, atherosclerosis, progression of nonalcoholic fatty liver disease, and endothelial dysfunction. However, models of CIH have generally been implemented so as to mimic severe human OSA, with comparatively less focus on milder hypoxic regimens. Here we discuss CSH and CIH conceptually, the effects of these stimuli, and limitations of the available data.

Intermittent Hypoxia Rewires the Liver Transcriptome and Fires up Fatty Acids Usage for Mitochondrial Respiration

Sleep Apnea Syndrome (SAS) is one of the most common chronic diseases, affecting nearly one billion people worldwide. The repetitive occurrence of abnormal respiratory events generates cyclical desaturation-reoxygenation sequences known as intermittent hypoxia (IH). Among SAS metabolic sequelae, it has been established by experimental and clinical studies that SAS is an independent risk factor for the development and progression of non-alcoholic fatty liver disease (NAFLD). The principal goal of this study was to decrypt the molecular mechanisms at the onset of IH-mediated liver injury. To address this question, we used a unique mouse model of SAS exposed to IH, employed unbiased high-throughput transcriptomics and computed network analysis. This led us to examine hepatic mitochondrial ultrastructure and function using electron microscopy, high-resolution respirometry and flux analysis in isolated mitochondria. Transcriptomics and network analysis revealed that IH reprograms Nuclear Respiratory Factor- (NRF-) dependent gene expression and showed that mitochondria play a central role. We thus demonstrated that IH boosts the oxidative capacity from fatty acids of liver mitochondria. Lastly, the unbalance between oxidative stress and antioxidant defense is tied to an increase in hepatic ROS production and DNA damage during IH. We provide a comprehensive analysis of liver metabolism during IH and reveal the key role of the mitochondria at the origin of development of liver disease. These findings contribute to the understanding of the mechanisms underlying NAFLD development and progression during SAS and provide a rationale for novel therapeutic targets and biomarker discovery.

Effects of Intermittent Hypoxia on Cytokine Expression Involved in Insulin Resistance

Sleep apnea syndrome (SAS) is a prevalent disorder characterized by recurrent apnea or hypoxia episodes leading to intermittent hypoxia (IH) and arousals during sleep. Currently, the relationship between SAS and metabolic diseases is being actively analyzed, and SAS is considered to be an independent risk factor for the development and progression of insulin resistance/type 2 diabetes (T2DM). Accumulating evidence suggests that the short cycles of decreased oxygen saturation and rapid reoxygenation, a typical feature of SAS, contribute to the development of glucose intolerance and insulin resistance. In addition to IH, several pathological conditions may also contribute to insulin resistance, including sympathetic nervous system hyperactivity, oxidative stress, vascular endothelial dysfunction, and the activation of inflammatory cytokines. However, the detailed mechanism by which IH induces insulin resistance in SAS patients has not been fully revealed. We have previously reported that IH stress may exacerbate insulin resistance/T2DM, especially in hepatocytes, adipocytes, and skeletal muscle cells, by causing abnormal cytokine expression/secretion from each cell. Adipose tissues, skeletal muscle, and the liver are the main endocrine organs producing hepatokines, adipokines, and myokines, respectively. In this review, we focus on the effect of IH on hepatokine, adipokine, and myokine expression.

Intermittent hypoxia increases ROS/HIF-1α 'related oxidative stress and inflammation and worsens bleomycin-induced pulmonary fibrosis in adult male C57BL/6J mice

Obstructive sleep apnea (OSA) has been increasingly recognized as a risk factor for idiopathic pulmonary fibrosis (IPF). The intermittent hypoxia (IH) and re-oxygenation of OSA contribute to poor outcomes of IPF, however, the potential mechanism remains unknown. Here, C57BL/6J mice were administered intratracheal injection of Bleomycin (BLM) or saline and then exposed to IH (alternating cycles of FiO2 21% for 60S and FiO2 10% for 30 s, 40 cycles/hour, 8 h/day) to mimic OSA or intermittent air (IA) for 4 days, 8 days or 21 days. This study found that pulmonary fibrosis in BLM + IH treated mice was more severe than that in BLM + IA group at day 8 and 21, but not observed at day 4. Besides, the expression of reactive oxygen species (ROS) and hypoxia inducible factor-1α (HIF-1α),which are related to hypoxia reduced oxidative stress and inflammation, were higher in BLM + IH treated mice than BLM + IA mice, and IH increased these indexes in BLM treated mice from day 4 to day 21. Interestingly, a positive linear correlation between the HIF-1α expression and hydroxyproline (HYP) content was observed. We further found some inflammatory cells in bronchoalveolar lavage fluid were increased significantly from day 4 to 21, and there was a positive correlation between inflammation and ROS expression. Our results demonstrated that IH aggravated BLM-induced pulmonary fibrosis, and ROS/HIF-1α related oxidative stress and inflammation involved. The increase of ROS/HIF-1α related oxidative stress and inflammation may be a potential mechanism of moderate-to-severe OSA in potentiating pulmonary fibrosis of IPF, which warrants further study.

Hypoxia-Inducible Factors as Key Players in the Pathogenesis of Non-alcoholic Fatty Liver Disease and Non-alcoholic Steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) and its more severe form non-alcoholic steatohepatitis (NASH) are a major public health concern with high and increasing global prevalence, and a significant disease burden owing to its progression to more severe forms of liver disease and the associated risk of cardiovascular disease. Treatment options, however, remain scarce, and a better understanding of the pathological and physiological processes involved could enable the development of new therapeutic strategies. One process implicated in the pathology of NAFLD and NASH is cellular oxygen sensing, coordinated largely by the hypoxia-inducible factor (HIF) family of transcription factors. Activation of HIFs has been demonstrated in patients and mouse models of NAFLD and NASH and studies of activation and inhibition of HIFs using pharmacological and genetic tools point toward important roles for these transcription factors in modulating central aspects of the disease. HIFs appear to act in several cell types in the liver to worsen steatosis, inflammation, and fibrosis, but may nevertheless improve insulin sensitivity. Moreover, in liver and other tissues, HIF activation alters mitochondrial respiratory function and metabolism, having an impact on energetic and redox homeostasis. This article aims to provide an overview of current understanding of the roles of HIFs in NAFLD, highlighting areas where further research is needed.