High-altitude chronic hypoxia ameliorates obesity-induced non-alcoholic fatty liver disease in mice by regulating mitochondrial and AMPK signaling

Hypoxia ameliorates high-fat-diet-induced hepatic lipid accumulation by modulating the HIF2α/PP4C signaling

Hepatic lipid accumulation is a hallmark of metabolically associated fatty liver disease (MAFLD), which contributes to the progression of cirrhosis and even hepatoma. However, the underlying mechanisms remain poorly understood. Protein phosphatase 4C (PP4C) is an important enzyme that exists widely in the body and participates in cell metabolism. Hypoxia can affect the development of metabolic diseases. In this study, we investigated the role of PP4C in hepatic lipid metabolism under hypoxia in vivo and in vitro. Hypoxia-inducible factor 2α (HIF2α), PP4C, phosphorylated AU-rich element RNA-binding factor 1(pAUF1), acetyl-CoA carboxylase 1 (ACC1), and carnitine palmitoyl transferase-1 (CPT1) were analyzed via western blotting and immunofluorescence. The mechanism by which PP4C affects hepatic lipid accumulation under hypoxia was evaluated in stable transfected cell lines. Compared with those in the 2200 m HFD group, body weight, triglyceride (TG), total cholesterol (TC), amino alanine transferase (ALT), aspartate transaminase (AST), and lipid accumulation were lower in the 4500 m HFD group (P < 0.05). Compared with those in the 4500 m ND group, ACC1 and PP4C levels were lower than in the 4500 m HFD group, but HIF2α, pAUF1, and CPT1 levels were greater (P < 0.05). Knockdown of HIF2α prevented the hypoxia-induced reduction of PP4C, confirming the regulatory role of the HIF2α-PP4C axis in hepatic lipid metabolism. PP4C could affect the phosphorylation and expression localization of AU-rich element RNA-binding factor 1 (AUF1). PP4C enhanced lipid accumulation by reducing pAUF1, while the knockdown of PP4C had the opposite effect; pAUF1 had no change. Compared with those in the control group, ACC1 levels were decreased and CPT1 levels were increased in the AUF1 overexpression group, whereas ACC1 and CPT1 levels were not altered in the AUF1 knockdown group (P < 0.05). In conclusion, hypoxia might improve lipid accumulation by downregulating PP4C via HIF2a. PP4C is involved in hepatic lipid metabolism by regulating AUF1 phosphorylation under different oxygen concentrations. PP4C might be a promising target for treating hepatic lipid accumulation.

Altitude and Metabolic Dysfunction-Associated Fatty Liver Disease (MAFLD) in China: A Population-Based Study

Yufei Wang, Qiong Meng, Jin Zhang, Bing Guo, Nanyan Li, Qian Deng, Julinling Hu, Quzong Deji, Han Guan, Wangjiu Danzhen, Hui Yu, Zhifeng Li, and Junmin Zhou. Altitude and metabolic dysfunction-associated fatty liver disease (MAFLD) in China: a population-based study. High Alt Med Biol. 26:148-155, 2025. Objectives: The epidemiological evidence for the relationship between altitude and metabolic dysfunction-associated fatty liver disease (MAFLD) is scarce. This study aims to examine the altitude-MAFLD relationship and explore the potential mediators explaining the relationship. Methods: Data were derived from the China Multi-Ethnic Cohort. The participants' altitude information was extracted from their residential addresses. MAFLD was diagnosed based on radiographically confirmed hepatic steatosis and any one of the following three items: overweight/obese status, diabetes mellitus, or metabolic dysregulation. We performed multivariable logistic regression and mediation analyses to assess the altitude-MAFLD associations and potential mediators, respectively. In the mediation analysis, mediation proportion is an estimate of the extent to which the total effect (altitude-MAFLD association) is accounted for by the pathway through the mediators. Results: In total, 87,679 participants (female: 60.7%, mean age: 51.36 years) were included. The odds ratio of MAFLD was 1.61 (95% confidence interval [CI]: 1.52-1.71) between high and low altitudes, 1.52 (95% CI: 1.43-1.62) between high and middle altitudes, and 1.06 (95% CI: 1.01-1.10) between middle and low altitudes. Of the total estimated effect between high and low altitude, physical activity and vegetable intake accounted for 15.7% (95% CI: 12.8-19.1) and 3.8% (95% CI: 1.2-6.6), respectively. Of the total estimated effect between high and middle altitude, physical activity and vegetable intake accounted for 31.4% (95% CI: 26.2-34.8) and 2.3% (95% CI: 0.6-3.8), respectively. Of the total estimated effect between middle and low altitude, vegetable intake accounted for 11.8% (95% CI: 3.2-61.5). Conclusion: Higher altitude was associated with increased odds of MAFLD, and physical activity and vegetable intake mediated such association. Multifaceted efforts should be taken in public health to promote healthy lifestyles among higher altitude residents.

Correlation of organelle interactions in the development of non-alcoholic fatty liver disease

Organelles, despite having distinct functions, interact with each other. Interactions between organelles typically occur at membrane contact sites (MCSs) to maintain cellular homeostasis, allowing the exchange of metabolites and other pieces of information required for normal cellular physiology. Imbalances in organelle interactions may lead to various pathological processes. Increasing evidence suggests that abnormalorganelle interactions contribute to the pathogenesis of non-alcoholic fatty liver disease (NAFLD). However, the key role of organelle interactions in NAFLD has not been fully evaluated and researched. In this review, we summarize the role of organelle interactions in NAFLD and emphasize their correlation with cellular calcium homeostasis, lipid transport, and mitochondrial dynamics.

Effect of high-altitude hypoxia on function and cytoarchitecture of rats' liver

The liver is central to metabolic, detoxification, and homeostatic functions. Exposure to hypobaric hypoxia at high altitudes causes detrimental effects on the liver, leading to injury. This study evaluated the effect of hypoxia-induced at high altitudes on liver function, oxidative stress, and histopathological changes in rats. This study used 24 male Wistar rats (aged 8-10 weeks). The hypoxia (hypobaric hypoxia) was inducted at a high altitude of 2,100 m above sea level. Normoxia is defined as 40 m above the sea level. The rats were randomly divided into two groups: a control group maintained at low altitudes and an experimental group exposed to high altitudes for eight weeks. Blood samples were collected from all rats through a cardiac puncture, and liver samples were taken through an abdominal approach. All samples were processed through standard methods and evaluated for liver function tests and histopathological assessment. Serum aspartate aminotransferase and alanine transaminase levels significantly increased by 25% and 30%, respectively, in the high-altitude group compared to controls (p < 0.01), indicating mild hepatocellular damage. Oxidative stress assessment indicated a significant elevation in malondialdehyde by 42% in the liver homogenates of high-altitude rats compared to controls (p < 0.001). Moreover, Superoxide dismutase activity and glutathione content decreased by 18% and 22% in the high-altitude group (p < 0.01), confirming the increased oxidative stress. Histologically, minimal inflammatory infiltration was observed in the rat livers at high altitudes, with no signs of necrosis or severe structural changes. Subclinical liver dysfunction, as evidenced by altered serum enzyme levels and increased oxidative stress with mild histological changes, is induced by high-altitude hypoxia in rats. This study's results support that a hypobaric hypoxic environment physiologically stresses the liver. Further research into the long-term implications of hypobaric hypoxia and the adaptive responses of the liver is warranted.

Regular exercise alleviates metabolic dysfunction-associated steatohepatitis through rescuing mitochondrial oxidative stress and dysfunction in liver

Metabolic dysfunction-associated steatohepatitis (MASH) is characterized by severe mitochondrial dysfunction, associated with the production of mitochondrial reactive oxygen species (mROS). The substantial generation of mROS in the MASH liver, resulting from lipid surplus and electron transport chain (ETC) overload, impairs mitochondrial structure and functionality, thereby contributing to the development of severe hepatic steatosis and inflammation. Regular exercise represents an effective strategy for the treatment of MASH. Understanding the effects of exercise on oxidative stress and mitochondrial function is essential for effective treatment of MASH. This article reviews the pathological alterations in mitochondrial β-oxidation, ETC efficiency and mROS production within MASH liver. Additionally, it discusses how exercise influences the redox state and mitochondrial quality control mechanisms-such as biogenesis, mitophagy, fusion, and fission-within the MASH liver. The article emphasizes the importance of in-depth studies on exercise-induced MASH mitigation through the enhancement of mitochondrial redox balance, quality control, and function. Exploring the relationship between exercise and hepatic mitochondria could provide valuable insights into identifying potential therapeutic targets for MASH.

The role of tissue oxygenation in obesity-related cardiometabolic complications

Obesity is a complex, multifactorial, chronic disease that acts as a gateway to a range of other diseases. Evidence from recent studies suggests that changes in oxygen availability in the microenvironment of metabolic organs may exert an important role in the development of obesity-related cardiometabolic complications. In this review, we will first discuss results from observational and controlled laboratory studies that examined the relationship between reduced oxygen availability and obesity-related metabolic derangements. Next, the effects of alterations in oxygen partial pressure (pO2) in the adipose tissue, skeletal muscle and the liver microenvironment on physiological processes in these key metabolic organs will be addressed, and how this might relate to cardiometabolic complications. Since many obesity-related chronic diseases, including type 2 diabetes mellitus, cardiovascular diseases, chronic kidney disease, chronic obstructive pulmonary disease and obstructive sleep apnea, are characterized by changes in pO2 in the tissue microenvironment, a better understanding of the metabolic impact of altered tissue oxygenation can provide valuable insights into the complex interplay between environmental and biological factors involved in the pathophysiology of metabolic impairments. This may ultimately contribute to the development of novel strategies to prevent and treat obesity-related cardiometabolic diseases.

Predictive Value of TyG and TyG-BMI Indices for Non-Alcoholic Fatty Liver Disease in High-Altitude Regions of China: A Cross-Sectional Study

Background: The associations between triglyceride glucose (TyG), triglyceride glucose-body mass index (TyG-BMI), and non-alcoholic fatty liver disease (NAFLD) in high-altitude regions remain unclear. Methods: This is a cross-sectional, population-based study comprising 1384 adults living in Jianchuan county, China, which has an average altitude of over 2200 m. Logistic regressions were used to examine the associations between TyG, TyG-BMI, and NAFLD. Receiver operating characteristic (ROC) curves were utilized to compare the predictive ability of TyG, TyG-BMI, hepatic steatosis index (HSI), and triglyceride glucose-alanine aminotransferase (TyG-ALT). Results: In total, 307 (35.7%) male and 81 (15.4%) female participants were diagnosed with NAFLD. Individuals with NAFLD had higher BMI, blood pressure, and TyG indices. The adjusted odds ratios (95% confidence intervals) for the highest quartile of TyG and TyG-BMI were 16.04 (8.51-30.25) and 48.55 (25.12-93.81), respectively. The areas under the ROC curve were 0.811 (95% CI: 0.787-0.836) for TyG, 0.883 (95% CI: 0.864-0.902) for TyG-BMI, 0.839 (95% CI: 0.817-0.863) for HSI, and 0.831 (95% CI: 0.801-0.855) for TyG-ALT. Tyg-BMI had the highest sensitivity (0.832) and specificity (0.780) compared to the other indices. Conclusions: Both TyG and TyG-BMI were associated with higher NAFLD risk in people living in high-altitude regions, while TyG-BMI had greater predictive capabilities.

A global view on quantitative proteomic and metabolic analysis of rat livers under different hypoxia protocols

Hypobaric hypoxia causes altitude sickness and significantly affects human health. As of now, focusing on rats different proteomic and metabolic changes exposed to different hypoxic times at extreme altitude is blank. Our study integrated in vivo experiments with tandem mass tag (TMT)- and gas chromatography time-of-flight (GC-TOF)-based proteomic and metabolomic assessments, respectively. Male Sprague-Dawley rats were exposed to long-term constant hypoxia for 40 days or short-term constant hypoxia for three days, and their responses were compared with those of a normal control group. Post-hypoxia, serum marker assays related to lipid metabolism revealed significant increases in the levels of low-density lipoprotein (LDL), triglycerides (TG), and total cholesterol (TC) in the liver. In contrast, high-density lipoprotein (HDL) levels were upregulated in the long-term constant hypoxia cohorts and were significantly reduced in the short-term constant hypoxia cohorts. Furthermore, metabolic pathway analysis indicated that glycerolipid and glycerophospholipid metabolisms were the most significantly affected pathways in long-term hypoxia group. Subsequently, RT-qPCR analyses were performed to corroborate the key regulatory elements, including macrophage galactose-type lectin (MGL) and Fatty Acid Desaturase 2 (FADS2). The results of this study provide new information for understanding the effects of different hypobaric hypoxia exposure protocols on protein expression and metabolism in low-altitude animals.

HIF-1α Pathway Orchestration by LCN2: A Key Player in Hypoxia-Mediated Colitis Exacerbation

In this study, we investigated the role of hypoxia in the development of chronic inflammatory bowel disease (IBD), focusing on its impact on the HIF-1α signaling pathway through the upregulation of lipocalin 2 (LCN2). Using a murine model of colitis induced by sodium dextran sulfate (DSS) under hypoxic conditions, transcriptome sequencing revealed LCN2 as a key gene involved in hypoxia-mediated exacerbation of colitis. Bioinformatics analysis highlighted the involvement of crucial pathways, including HIF-1α and glycolysis, in the inflammatory process. Immune infiltration analysis demonstrated the polarization of M1 macrophages in response to hypoxic stimulation. In vitro studies using RAW264.7 cells further elucidated the exacerbation of inflammation and its impact on M1 macrophage polarization under hypoxic conditions. LCN2 knockout cells reversed hypoxia-induced inflammatory responses, and the HIF-1α pathway activator dimethyloxaloylglycine (DMOG) confirmed LCN2's role in mediating inflammation via the HIF-1α-induced glycolysis pathway. In a DSS-induced colitis mouse model, oral administration of LCN2-silencing lentivirus and DMOG under hypoxic conditions validated the exacerbation of colitis. Evaluation of colonic tissues revealed altered macrophage polarization, increased levels of inflammatory factors, and activation of the HIF-1α and glycolysis pathways. In conclusion, our findings suggest that hypoxia exacerbates colitis by modulating the HIF-1α pathway through LCN2, influencing M1 macrophage polarization in glycolysis. This study contributes to a better understanding of the mechanisms underlying IBD, providing potential therapeutic targets for intervention.

BNIP3 in hypoxia-induced mitophagy: Novel insights and promising target for non-alcoholic fatty liver disease

BNIP3 localizes to the outer mitochondrial membrane, has been demonstrated to be extensively involved in abnormalities to mitochondrial metabolic function and dynamicsand in non-alcoholic fatty liver disease (NAFLD). However, its role in NAFLD under hypoxia remains unclear. This study aimed to investigate the expression and the role of BNIP3 in NAFLD under hypoxia, and explore its involvement in regulating NAFLD mitophagy, fatty acid β-oxidation both in vivo and in vitro. BNIP3-mediated mitophagy level was analyzed using real-time quantitative polymerase chain reaction, Western blotting, immunofluorescence and electron microscopy. The role of BNIP3 in fatty acid β-oxidation was evaluated using lipid droplet staining, triglyceride content determination, and cellular energy metabolism. The results showed that compared with the HFD-2200 m, the body weight, inflammatory liver injury, and lipid deposition were significantly reduced in the HFD-4500 m group (P < 0.05), but autophagy and mitophagy were increased, and the expression of the mitophagy receptor BNIP3 was increased (P < 0.05). Compared to the control group, BNIP3 knockdown in the hypoxia group resulted in decreased levels of CPT1, ATGL, and p-HSL in lipid-accumulating hepatocytes, lipid droplet accumulation and triglyceride content increased (P < 0.05). Moreover, the ability of lipid-accumulating hepatocytes to oxidize fatty acids was reduced by BNIP3 knockdown in the hypoxia group (P < 0.05). Therefore, it can be concluded that, in NAFLD mice under hypoxia, BNIP3-mediated mitophagy promotes fatty acid β-oxidation. This study elucidated the role of BNIP3 in promoting fatty acid β-oxidation in NAFLD under hypoxia, and suggests BNIP3 may serve as a novel potential therapeutic target for NAFLD.

Kaempferol ameliorates pulmonary vascular remodeling in chronic hypoxia-induced pulmonary hypertension rats via regulating Akt-GSK3β-cyclin axis

Excessive proliferation of pulmonary artery smooth muscle cells (PASMCs) is considered a major contributor to elevated pulmonary vascular resistance and a key mechanism of vascular remodeling in hypoxia-induced pulmonary hypertension (HPH). Kaempferol is a natural flavonoid compound and can be derived from numerous common medicinal herbs and vegetables, which exhibit antiproliferative and proapoptotic properties, however, the effects of kaempferol on vascular remodeling in HPH remain unexplored. In this study, SD rats were placed in a hypobaric hypoxia chamber for four weeks to establish a pulmonary hypertension model and given either kaempferol or sildenafil (an inhibitor of PDE-5) during days 1-28, after which the hemodynamic parameter and pulmonary vascular morphometry were assessed. Furthermore, primary rat PASMCs were exposed to hypoxic conditions to generate a cell proliferation model, then incubated with either kaempferol or LY294002 (an inhibitor of PI3K). Immunoblotting and real-time quantitative PCR assessed the protein and mRNA expression levels in HPH rat lungs and PASMCs. We found that kaempferol reduced pulmonary artery pressure and pulmonary vascular remodeling, and alleviated right ventricular hypertrophy in HPH rats. The mechanistic analysis demonstrated that kaempferol reduced the protein levels of phosphorylation of Akt and GSK3β, leading to decreased expression of pro-proliferation (CDK2, CDK4, Cyclin D1, and PCNA) and anti-apoptotic related proteins (Bcl-2) and increased expression of pro-apoptosis proteins (Bax and cleaved caspase 3). These results collectively demonstrate that kaempferol ameliorates HPH in rats by inhibiting PASMC proliferation and pro-apoptosis via modulation of the Akt/GSK3β/CyclinD axis.

Protective effect and mechanism of lactoferrin combined with hypoxia against high-fat diet induced obesity and non-alcoholic fatty liver disease in mice

Obesity is a global epidemic, it can induce glucose and lipid metabolism disorder and non-alcoholic fatty liver disease (NAFLD). This study explored a new way to control weight and improve fatty liver, namely, living in hypoxia environment and supplement with lactoferrin (Lf). Sixty male C57BL/6J mice were divided into six groups, namely, control, hypoxia, high-fat diet, hypoxia + high-fat diet, hypoxia + high-fat diet + low dose Lf intervention, and hypoxia + high-fat diet + high-dose Lf intervention. Mice in the hypoxia treatment groups were treated with approximately 11.5 % oxygen for 6 h every day for 8 weeks. Results showed that interventions combining Lf and hypoxia treatments showed better effect against obesity and NAFLD than hypoxia treatment alone. The interventions controlled weight gain in mice, improved glucolipid metabolism in mice. The combination intervention reduced cholesterol absorption by reducing the level of hydrophobic bile acids, and elevating the level of hydrophilic bile acids. Gut microbiota analysis revealed that the combination intervention considerably elevated short chain fatty acids (SCFAs)-producing bacteria level, and reduced the Desulfovibrionaceae_unclassified level. Thus, Lf combined with hypoxia intervention effectively prevents obesity and NAFLD by restoring gut microbiota composition and bile acid profile.

Lipid metabolism in non-alcoholic fatty liver disease in patients with different body weights in mid-mountain conditions

Aim. To study the peculiarities of lipid metabolism disorders in non-alcoholic fatty liver disease in lean and obese patients in medium altitude conditions. Materials and methods. The study was carried out within the framework of the project Etiopathogenetic features and rates of development of non-alcoholic fatty liver disease (NAFLD) in the conditions of Kyrgyzstan (№ of state registration MHN/TZ-2020-3). An open comparative study of patients with two forms of NAFLD: fatty liver and non-alcoholic steatohepatitis (n=236) living in low mountains (Bishkek, altitude above sea level 750800 m; n=111) and middle mountains (At-Bashy district , Naryn region, height above sea level 20462300 m; n=125) Kyrgyzstan. The average age of the patients was 55.70.95 years. Given that genetic factors may play a role in the development of NAFLD, we analyzed a population represented only by ethnic Kyrgyz. Patients in each group were divided into lean (BMI23) and obese (BMI23) groups. To determine physical activity, a physical activity questionnaire was used, which was compiled on the basis of the materials of the International Physical Activity Prevalence Study www.ipaq.ki.se. Physical examination included measurement of anthropometric parameters (height, body weight, waist circumference), calculation of body mass index (BMI), skeletal muscle mass index (SMM), percentage of body fat. According to the grades of the WHO, the degree of obesity was assessed by BMI for Asians. Blood samples were taken for research in the morning on an empty stomach after at least 12 hours of fasting. The following indicators were determined: glucose, lipid spectrum (total cholesterol, HDL cholesterol, LDL cholesterol, triglycerides), alanine aminotransferase (ALT), aspartate aminotransferase (AST) levels. The BARD scale was used as a predictor for assessing the development of liver fibrosis in patients with NAFLD. The scoring system included three variables: BMI, AST/ALT, and the presence of DM 2. The diagnosis of NAFLD made on the basis of history, laboratory tests, ultrasound examination of the liver, and exclusion of other liver diseases. The results were analyzed using the SPSS 16.0 statistical software package for Windows. A p-value0.05 was considered statistically significant at the 95% confidence level. Results. It was found that the inhabitants of the middle mountains with NAFLD are represented by a lower BMI relative to the inhabitants of the low mountains. In women, the levels of SMM and the percentage of fat are significantly and statistically significantly correlated (r=-0.971; p0.001), while in men these two indicators are not related. Men showed a trend towards higher percentages of fat, regardless of body weight and region of residence. For women, this indicator was within acceptable limits and did not exceed 31%. There was found a statistically significant difference in total cholesterol levels between low and middle mountain people in the group of obese patients (p0.001) suffering from NAFLD. Statistically significant low ALT indices were revealed in the group of obese patients living in mid-mountain conditions. Conclusion. Taken together, our results suggest that chronic mid-mountain hypoxia may slow down the course of overweight-induced NAFLD.

Hypoxia as a Double-Edged Sword to Combat Obesity and Comorbidities

The global epidemic of obesity is tightly associated with numerous comorbidities, such as type II diabetes, cardiovascular diseases and the metabolic syndrome. Among the key features of obesity, some studies have suggested the abnormal expansion of adipose-tissue-induced local endogenous hypoxic, while other studies indicated endogenous hyperoxia as the opposite trend. Endogenous hypoxic aggravates dysfunction in adipose tissue and stimulates secretion of inflammatory molecules, which contribute to obesity. In contrast, hypoxic exposure combined with training effectively generate exogenous hypoxic to reduce body weight and downregulate metabolic risks. The (patho)physiological effects in adipose tissue are distinct from those of endogenous hypoxic. We critically assess the latest advances on the molecular mediators of endogenous hypoxic that regulate the dysfunction in adipose tissue. Subsequently we propose potential therapeutic targets in adipose tissues and the small molecules that may reverse the detrimental effect of local endogenous hypoxic. More importantly, we discuss alterations of metabolic pathways in adipose tissue and the metabolic benefits brought by hypoxic exercise. In terms of therapeutic intervention, numerous approaches have been developed to treat obesity, nevertheless durability and safety remain the major concern. Thus, a combination of the therapies that suppress endogenous hypoxic with exercise plans that augment exogenous hypoxic may accelerate the development of more effective and durable medications to treat obesity and comorbidities.

Effects of Six Weeks of Hypoxia Exposure on Hepatic Fatty Acid Metabolism in ApoE Knockout Mice Fed a High-Fat Diet

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease with a characteristic of abnormal lipid metabolism. In the present study, we employed apolipoprotein E knockout (ApoE KO) mice to investigate the effects of hypoxia exposure on hepatic fatty acid metabolism and to test whether a high-fat diet (HFD) would suppress the beneficial effect caused by hypoxia treatment. ApoE KO mice were fed a HFD for 12 weeks, and then were forwarded into a six-week experiment with four groups: HFD + normoxia, normal diet (ND) + normoxia, HFD + hypoxia exposure (HE), and ND + HE. The C57BL/6J wild type (WT) mice were fed a ND for 18 weeks as the baseline control. The hypoxia exposure was performed in daytime with normobaric hypoxia (11.2% oxygen, 1 h per time, three times per week). Body weight, food and energy intake, plasma lipid profiles, hepatic lipid contents, plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST), and molecular/biochemical makers and regulators of the fatty acid synthesis and oxidation in the liver were measured at the end of interventions. Six weeks of hypoxia exposure decreased plasma triglycerides (TG), total cholesterol (TC), and low-density lipoprotein cholesterol (LDL-C) contents but did not change hepatic TG and non-esterified fatty acid (NEFA) levels in ApoE KO mice fed a HFD or ND. Furthermore, hypoxia exposure decreased the mRNA expression of Fasn, Scd1, and Srebp-1c significantly in the HFD + HE group compared with those in the HFD + normoxia group; after replacing a HFD with a ND, hypoxia treatment achieved more significant changes in the measured variables. In addition, the protein expression of HIF-1α was increased only in the ND + HE group but not in the HFD + HE group. Even though hypoxia exposure did not affect hepatic TG and NEFA levels, at the genetic level, the intervention had significant effects on hepatic metabolic indices of fatty acid synthesis, especially in the ND + HE group, while HFD suppressed the beneficial effect of hypoxia on hepatic lipid metabolism in male ApoE KO mice. The dietary intervention of shifting HFD to ND could be more effective in reducing hepatic lipid accumulation than hypoxia intervention.

Hepatocyte Mitochondrial Dynamics and Bioenergetics in Obesity-Related Non-Alcoholic Fatty Liver Disease

PURPOSE OF THE REVIEW

Mitochondrial dysfunction has long been proposed to play a crucial role in the pathogenesis of a considerable number of disorders, such as neurodegeneration, cancer, cardiovascular, and metabolic disorders, including obesity-related insulin resistance and non-alcoholic fatty liver disease (NAFLD). Mitochondria are highly dynamic organelles that undergo functional and structural adaptations to meet the metabolic requirements of the cell. Alterations in nutrient availability or cellular energy needs can modify their formation through biogenesis and the opposite processes of fission and fusion, the fragmentation, and connection of mitochondrial network areas respectively. Herein, we review and discuss the current literature on the significance of mitochondrial adaptations in obesity and metabolic dysregulation, emphasizing on the role of hepatocyte mitochondrial flexibility in obesity and NAFLD.

RECENT FINDINGS

Accumulating evidence suggests the involvement of mitochondrial morphology and bioenergetics dysregulations to the emergence of NAFLD and its progress to non-alcoholic steatohepatitis (NASH). Most relevant data suggests that changes in liver mitochondrial dynamics and bioenergetics hold a key role in the pathogenesis of NAFLD. During obesity and NAFLD, oxidative stress occurs due to the excessive production of ROS, leading to mitochondrial dysfunction. As a result, mitochondria become incompetent and uncoupled from respiratory chain activities, further promoting hepatic fat accumulation, while leading to liver inflammation, insulin resistance, and disease's deterioration. Elucidation of the mechanisms leading to dysfunctional mitochondrial activity of the hepatocytes during NAFLD is of predominant importance for the development of novel therapeutic approaches towards the treatment of this metabolic disorder.

Mitochondrial Dysfunction and Chronic Liver Disease

Mitochondria are generally considered the powerhouse of the cell, a small subcellular organelle that produces most of the cellular energy in the form of adenosine triphosphate (ATP). In addition, mitochondria are involved in various biological functions, such as biosynthesis, lipid metabolism, oxidative phosphorylation, cell signal transduction, and apoptosis. Mitochondrial dysfunction is manifested in different aspects, like increased mitochondrial reactive oxygen species (ROS), mitochondrial DNA (mtDNA) damage, adenosine triphosphate (ATP) synthesis disorder, abnormal mitophagy, as well as changes in mitochondrial morphology and structure. Mitochondrial dysfunction is related to the occurrence and development of various chronic liver diseases, including hepatocellular carcinoma (HCC), viral hepatitis, drug-induced liver injury (DILI), alcoholic fatty liver (AFL), and non-alcoholic fatty liver (NAFL). In this review, we summarize and discuss the role and mechanisms of mitochondrial dysfunction in chronic liver disease, focusing on and discussing some of the latest studies on mitochondria and chronic liver disease.

BAIBA Involves in Hypoxic Training Induced Browning of White Adipose Tissue in Obese Rats

In recent years, obesity has become an important risk factor for human health; how to effectively prevent and reduce the occurrence of obesity is a hot research topic in recent years. Hypoxic training effectively improves abnormalities of lipid metabolism caused by obesity. The current study explored the effects of hypoxic training on BAIBA secretion and white fat browning in inguinal fat in obese rats. Analyses were performed by HPLC/MS/MS—MS/MS, RT-q PCR and western blot methods. The findings showed that 4 weeks of hypoxic training reduced body weight, Lee’s index, and regulated blood lipid profile in obese rats. Hypoxic training up-regulated BAIBA concentration in gastrocnemius muscle and circulation in obese rats. Hypoxic training significantly upregulated expression of PPARα and UCP-1 in inguinal fat of obese rats and increased white fat browning. The findings showed that BAIBA may involve in improveing blood lipid profile and white fat browning by modulating PPARα and UCP-1 expression.

Role of mitochondrial genetic interactions in determining adaptation to high altitude human population

Physiological and haplogroup studies performed to understand high-altitude adaptation in humans are limited to individual genes and polymorphic sites. Due to stochastic evolutionary forces, the frequency of a polymorphism is affected by changes in the frequency of a near-by polymorphism on the same DNA sample making them connected in terms of evolution. Here, first, we provide a method to model these mitochondrial polymorphisms as "co-mutation networks" for three high-altitude populations, Tibetan, Ethiopian and Andean. Then, by transforming these co-mutation networks into weighted and undirected gene-gene interaction (GGI) networks, we were able to identify functionally enriched genetic interactions of CYB and CO3 genes in Tibetan and Andean populations, while NADH dehydrogenase genes in the Ethiopian population playing a significant role in high altitude adaptation. These co-mutation based genetic networks provide insights into the role of different set of genes in high-altitude adaptation in human sub-populations.

Curcumin alleviates hepatic steatosis by improving mitochondrial function in postnatal overfed rats and fatty L02 cells through the SIRT3 pathway

Postnatal overfeeding could increase the risk of non-alcoholic fatty liver disease (NAFLD) in adulthood. This study investigated the effects of curcumin (CUR) on hepatic steatosis in postnatal overfed rats and elucidated potential mechanisms in mitochondrial functions. Male rats were adjusted to ten (normal litter, NL) or three (small litter, SL) at postnatal day 3. After weaning, NL rats were fed with normal diet (NL) or a high-fat diet (NH) for 10 weeks. SL rats were fed with normal diet (SL), a high-fat diet (SH), a normal diet supplemented with 2% CUR (SL-CUR) or a high-fat diet supplemented with 2% CUR (SH-CUR). At week 13, compared with NL rats, SL and NH rats showed increased body weight, glucose intolerance, dyslipidemia and hepatic lipid accumulation, and these changes were more obvious in SH rats. The opposite trends were observed in SL-CUR and SH-CUR rats. Moreover, CUR could preserve mitochondrial biogenesis and antioxidant response in postnatal overfed rats, and upregulated the mRNA and protein levels of SIRT3. In vitro, L02 cells were exposed to free fatty acids and/or CUR. CUR decreased the levels of cellular lipids and mitochondrial reactive oxygen species, and increased the mitochondrial DNA copy number and superoxide dismutase activity in fatty L02 cells. However, these effects were blocked after SIRT3 silencing. It was concluded that postnatal overfeeding damaged mitochondrial biogenesis and antioxidant response, and increased hepatic lipids and the severity of high-fat-induced NAFLD, while CUR alleviated hepatic steatosis, at least partially, by enhancing mitochondrial function through SIRT3.

Metabolomic Analysis of Carbohydrate and Amino Acid Changes Induced by Hypoxia in Naked Mole-Rat Brain and Liver

Hypoxia poses a major physiological challenge for mammals and has significant impacts on cellular and systemic metabolism. As with many other small rodents, naked mole-rats (NMRs; Heterocephalus glaber), who are among the most hypoxia-tolerant mammals, respond to hypoxia by supressing energy demand (i.e., through a reduction in metabolic rate mediated by a variety of cell- and tissue-level strategies), and altering metabolic fuel use to rely primarily on carbohydrates. However, little is known regarding specific metabolite changes that underlie these responses. We hypothesized that NMR tissues utilize multiple strategies in responding to acute hypoxia, including the modulation of signalling pathways to reduce anabolism and reprogram carbohydrate metabolism. To address this question, we evaluated changes of 64 metabolites in NMR brain and liver following in vivo hypoxia exposure (7% O₂, 4 h). We also examined changes in matched tissues from similarly treated hypoxia-intolerant mice. We report that, following exposure to in vivo hypoxia: (1) phenylalanine, tyrosine and tryptophan anabolism are supressed both in NMR brain and liver; (2) carbohydrate metabolism is reprogramed in NMR brain and liver, but in a divergent manner; (3) redox state is significantly altered in NMR brain; and (4) the AMP/ATP ratio is elevated in liver. Overall, our results suggest that hypoxia induces significant metabolic remodelling in NMR brain and liver via alterations of multiple metabolic pathways.

Salidroside attenuates CoCl2-simulated hypoxia injury in PC12 cells partly by mitochondrial protection

Salidroside has been shown to exert neuroprotective effects against hypoxia. However, its mitochondrial protective mechanisms still remain elusive. The present study aimed to explore the mitochondrial protection of salidroside on PC12 cells and the involved mechanisms. The hypoxic injury of PC12 cells was triggered by CoCl₂ stimulus. The contents of LDH release, SOD, GSH-PX, Na⁺-K⁺-ATPase, ATP, NAD⁺ and NADH were determined by using commercial biochemical kits. Clark-type oxygen electrode and Seahorse XFe24 analyzer were employed to evaluate cell respiration and measure oxygen consumption rate (OCR), respectively. Mitochondrial swelling and mitochondrial membrane potential (MMP) were measured by using isolated mitochondria from the brain tissue of mice. The proteins expression of cleaved Caspase-3, HIF-1α, ISCU1/2, COX10 and PFKP were tested by immunofluorescence and Western blot. While the genes expression of Caspase-3, HIF-1α, ISCU1/2, COX10 and miR-210 were tested by quantitative real-time PCR (qRT-PCR) analysis. Salidroside alleviated CoCl₂-induced oxidative stress in PC12 cells as evidenced by increased cell viability, decreased LDH release and elevated GSH-PX and SOD activities. Salidroside could inhibit apoptosis by suppressing the level of cleaved Caspase-3 and Caspase-3. The enhanced mitochondrial energy synthesis by salidroside treatment was evidenced by the increases of Na⁺-K⁺-ATPase activity, ATP content, NAD⁺/NADH ratio, cellular respiration and OCR. In addition, salidroside could reduce mitochondrial swelling and MMP dissipation in isolated mitochondria. The results of immunofluorescence, Western blot and qRT-PCR analyses further revealed that salidroside raised the level of HIF-1α, ISCU1/2, COX10, and miR-210. Collectively, salidroside can reverse CoCl₂-simulated hypoxia injury in PC12 cells partly by mitochondrial protection via inhibiting oxidative stress event, anti-apoptosis and enhancing mitochondrial energy synthesis.

Features of the Course of Non-alcoholic Fatty Liver Disease in Experimental Animals at High Altitudes

Background: Nearly 25% of adults worldwide are affected by non-alcoholic fatty liver disease (NAFLD). taged changes in the liver from steatosis progress to non-alcoholic steatohepatitis (NASH) and its complicated forms such as fibrosis, cirrhosis, and hepatocellular carcinoma. There are very few data in the literature on the development of NAFLD in conditions of high altitude. There are no data on the state of pro- and anti-inflammatory cytokines in NAFLD in high altitude conditions. Thus, simulating NAFLD on animals in artificial highlands will help find answers to these questions. Aim: to study the features of the course of non-alcoholic fatty liver disease (NAFLD) in experimental animals in artificial high-mountain conditions. Material and methods: The study was carried out on 180 male Wistar rats. 7 groups of experimental animals were formed, which were divided into control and experimental groups. The rats of the control group were on a standard diet. Non-alcoholic fatty liver disease was modeled by keeping animals on a diet (Ackermann et al., 2005) rich in fructose and fat in low and high mountain conditions (in a pressure chamber 6000 m above sea level) for 35 and 70 days. In all groups of animals, the following was determined: the concentration of total bilirubin (TB), the activity of the enzymes aspartate aminotransferase (AST), alanine aminotransferase (ALT), the level of total cholesterol (TC), low-density lipoprotein cholesterol (LDL), the total protein content in plasma (TP), pro- and anti-inflammatory cytokines. Results: In animals on a diet enriched with fructose and fat, it equally led to the inhibition of the synthetic function of the liver, both in high altitude and in low altitudes. Liver enzyme levels were uncertain. AST levels were high in all major groups, with a similar upward trend at 5 and 10 weeks on the fructose-fortified diet. The greatest shift was observed on the part of ALT in animals under conditions of hypobaric hypoxia, the growth of which was statistically significantly lower than in the low- altitude groups. The opposite picture was observed in pigment metabolism. Indicators of total cholesterol and LDL increased almost twofold in the main high- altitude groups, and were significantly higher than the indicators of low- altitude animals with p <0.001. The activity of pro- and anti-inflammatory cytokines in the main group, when the animals were raised in the pressure chamber, statistically significantly increased after 5 weeks compared to the low-altitude group by more than 2 times and statistically significantly correlated with cytolysis syndromes, hypercholesterolemia and impaired synthetic function against the background of liver hypoergosis. Conclusion: Non-alcoholic fatty liver disease in animals on a special diet enriched with fructose under conditions of hypobaric hypoxia is characterized by deeper violations of pigment metabolism, pro- and anti-inflammatory cytokines and lipid spectrum with simultaneously statistically significant low alanine aminotransferase indices compared to low-altitude groups on an identical diet.

Mechanism of Paeoniae Radix Alba in the Treatment of Non-alcoholic Fatty Liver Disease Based on Sequential Metabolites Identification Approach, Network Pharmacology, and Binding Affinity Measurement

Screening functional food ingredients (FFI) from medicinal and edible plants (MEP) has still remained a great challenge due to the complexity of MEP and its obscure function mechanisms. Herein, an integrated strategy based on sequential metabolites identification approach, network pharmacology, molecular docking, and surface plasmon resonance (SPR) analysis was proposed for quickly identifying the active constituents in MEP. First, the sequential biotransformation process of MEP, including intestinal absorption and metabolism, and hepatic metabolism, was investigated by oral gavage, and intestinal perfusion with venous sampling method. Then the blood samples were analyzed by UPLC-Q Exactive Orbitrap HRMS. Second, the network pharmacology approach was used to explore the potential targets and possible mechanisms of the in vivo metabolites of MEP. Third, molecular docking and SPR approaches were used to verify the specific interactions between protein targets and representative ingredients. The proposed integrated strategy was successfully used to explore the heptoprotective components and the underlying molecular mechanism of Paeoniae Radix Alba (PRA). A total of 44 compounds were identified in blood samples, including 17 porotypes and 27 metabolites. The associated metabolic pathways were oxidation, methylation, sulfation, and glucuronidation. After further screening, 31 bioactive candidates and 377 related targets were obtained. In addition, the bioactive components contained in PRA may have therapeutic potentials for non-alcoholic fatty liver disease (NAFLD). The above results demonstrated the proposed strategy may provide a feasible tool for screening FFI and elaborating the complex function mechanisms of MEP.

Dynamics of Pro- and Anti-inflammatory Cytokines in Experimental Animals with Non-alcoholic Fatty Liver Disease Under Conditions of Hypobaric Hypoxia

AIM: The aim of the study was to study the level of pro- and anti-inflammatory cytokines, tumor necrosis factor-alpha (TNF-α), and interleukin 4 (IL-4), on a model of non-alcoholic fatty liver disease (NAFLD) in experimental animals under conditions of low mountains and hypobaric hypoxia. METHODS: The study was carried out on 180 male Wistar rats, which were divided into control and experimental groups. The rats of the control group were on a standard diet. NAFLD was modeled by keeping animals on a diet (Ackermann et al., 2005) rich in fructose and fat in conditions of low mountains and hypobaric hypoxia (in a pressure chamber 6000 m above sea level) for 35 and 70 days. Total cholesterol (TC) and lipid spectrum, pro- and anti-inflammatory cytokines were determined in all groups of animals. RESULTS: The activity of pro- and anti-inflammatory cytokines in the main group during the rise of animals in the pressure chamber increased statistically significantly on the 35th day in comparison with the low-altitude group by more than 2 times, and on the 70th day of staying at the high-altitude did not have convincing differences from the low-altitude group. The cytokine index (TNF-α/IL-4) of animals in conditions of hypobaric hypoxia on a fructose enriched diet increased by more than 1.5 times after 5 weeks, staying at an altitude for 10 weeks led to a decrease of TNF-α/IL-4 in relation to the low-mountain group, in which the opposite picture was observed - a tendency towards an increase in TNF-α/IL-4. IL-4 and TNF-α _levels were statistically significantly correlated with lipid metabolism disorders. CONCLUSION: NAFLD in animals on a special diet enriched with fructose under conditions of hypobaric hypoxia leads to deeper disturbances in the system of pro- and anti-inflammatory cytokines and the lipid spectrum.

Long-Term High-Fat Diet Inhibits the Recovery of Myocardial Mitochondrial Function After Chronic Hypoxia Reoxygenation in Rats

Yan, Jun, Kang Song, Sisi Zhou, and Ri-Li Ge. Long-term high-fat diet inhibits the recovery of myocardial mitochondrial function after chronic hypoxia reoxygenation in rats. High Alt Med Biol. 16:000-000, 2021. Aims: A high-fat diet (HFD) is associated with cardiovascular diseases and mitochondrial dysfunction. Obesity incidence is low at high altitudes, but the impact of HFD, which is closely associated with obesity at high altitudes, and the effects of reoxygenation on the heart are unclear. In this study, we investigated the effects of long-term HFD consumption on mitochondrial function in the myocardium after chronic hypoxia reoxygenation. Main Methods: Sprague-Dawley rats were randomized into the following six groups: normoxia groups, including a control group and HFD group; chronic hypoxia groups, including a normal chow diet (CH-CD) group and an HFD (CH-HFD) group; and hypoxic-reoxygenated (HR) groups, including a hypoxia-reoxygenation normal chow diet (HR-CD) group and a hypoxia-reoxygenation HFD (HR-HFD) group. All rats were euthanized in this study. Results: We found that chronic hypoxia aggravated myocardial mitochondrial dysfunction. The Flameng score (in which the higher the score, the more severe the mitochondrial damage) was used to assess the extent of mitochondrial structural damage. Compared with the control group and HFD group, the Flameng scores of the CH-CD and CH-HFD groups were significantly increased, respectively [1.260 ± 0.063 vs. 0.68 ± 0.05 (p < 0.05); 2.03 ± 0.07 vs. 1.48 ± 0.05 (p < 0.05)]. Moreover, progressive reoxygenation facilitated the recovery of myocardial mitochondrial function; this process was inhibited by long-term HFD. After reoxygenation, the Flameng scores in the HR-CD group became comparable to those in the CH-CD group [0.86 ± 0.05 vs. 1.26 ± 0.06 (p < 0.05)]. However, no significant changes were observed in the Flameng score between the HR-HFD and CH-HFD groups. Significance: Long-term HFD consumption inhibits myocardial mitochondrial function after reoxygenation. This finding may be helpful for the prevention and control of risk factors related to cardiovascular diseases in plateau residents.

A rapid juvenile murine model of nonalcoholic steatohepatitis (NASH): Chronic intermittent hypoxia exacerbates Western diet-induced NASH

AIMS

Many dietary NASH models require a long duration to establish (4-6 months). Chronic intermittent hypoxia (CIH), a cardinal hallmark of obstructive sleep apnea (OSA), may accelerate the progression of pediatric nonalcoholic fatty liver disease (NAFLD). However, diet-induced obese (DIO) mice exposed to CIH have not been perceived as a fast or reliable tool in NASH research. This study was designed to establish a rapid juvenile murine NASH model, and determine whether the combination of CIH and a western-style diet (hypercaloric fatty diet plus high fructose) can fully display key pathologic features of NASH.

METHODS

C57BL/6 N mice (3 weeks old) fed a control diet or western diet (WD) were exposed to CIH (9% nadir of inspired oxygen levels) or room air for 6 and 12 weeks.

KEY FINDINGS

The Control/CIH group mainly exhibited hyperinsulinemia and insulin resistance (IR). In contrast, mice fed a WD developed weight gain after 3 weeks, microvesicular steatosis in 6 weeks, and indices of metabolic disorders at 12 weeks. Furthermore, CIH exposure accelerated WD- induced macromicrovesicular steatosis (liver triglycerides and de novo lipogenesis), liver injury (ballooned hepatocytes and liver enzymes), lobular/portal inflammation (inflammatory cytokines and macrophage recruitment), and fibrogenesis (hydroxyproline content and TGF-β protein). Notably, only the WD/CIH group exhibited elevated hepatic MDA content, protein levels of NOX4, α-SMA and collagen I, as well as reduced Nrf2 and HO-1 protein expression.

SIGNIFICANCE

WD/CIH treatment rapidly mimics the histological characteristics of pediatric NASH with metabolic dysfunction and fibrosis, representing an appropriate experimental model for NASH research.

Modeling Diet-Induced Metabolic Syndrome in Rodents

Standardized animal models represent one of the most valuable tools available to understand the mechanism underlying the metabolic syndrome (MetS) and to seek for new therapeutic strategies. However, there is considerable variability in the studies conducted with this essential purpose. This review presents an updated discussion of the most recent studies using diverse experimental conditions to induce MetS in rodents with unbalanced diets, discusses the key findings in metabolic outcomes, and critically evaluates what we have been learned from them and how to advance in the field. The study includes scientific reports sourced from the Web of Science and PubMed databases, published between January 2013 and June 2020, which used hypercaloric diets to induce metabolic disorders, and address the impact of the diet on metabolic parameters. The collected data are used as support to discuss variables such as sex, species, and age of the animals, the most favorable type of diet, and the ideal diet length to generate metabolic changes. The experimental characteristics propose herein improve the performance of a preclinical model that resembles the human MetS and will guide researchers to investigate new therapeutic alternatives with confidence and higher translational validity.