Angiotensin‐(1‐7), the product of ACE2 ameliorates NAFLD by acting through its receptor Mas to regulate hepatic mitochondrial function and glycolipid metabolism

Mechanisms underpinning the effect of exercise on the non-alcoholic fatty liver disease: review

Non-alcoholic Fatty Liver Disease (NAFLD) - whose terminology was recently replaced by metabolic liver disease (MAFLD) - is an accumulation of triglycerides in the liver of >5 % of its weight. Epidemiological studies indicated an association between NAFLD and reduced physical activity. In addition, exercise has been shown to improve NAFLD independently of weight loss. In this paper, we aim to systematically review molecular changes in sedentary experimental NAFLD models vs. those subjected to exercise. We utilized the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist and standard review techniques. Studies were considered for inclusion if they addressed the primary question: the mechanisms by which exercise influenced NAFLD. This review summarized experimental evidence of improvements in NAFLD with exercise in the absence of weight loss. The pathways involved appeared to have AMPK as a common denominator. See also the graphical abstract(Fig. 1).

The Pathophysiological Associations Between Obesity, NAFLD, and Atherosclerotic Cardiovascular Diseases

Obesity, non-alcoholic fatty liver disease (NAFLD), and atherosclerotic cardiovascular diseases are common and growing public health concerns. Previous epidemiological studies unfolded the robust correlation between obesity, NAFLD, and atherosclerotic cardiovascular diseases. Obesity is a well-known risk factor for NAFLD, and both of them can markedly increase the odds of atherosclerotic cardiovascular diseases. On the other hand, significant weight loss achieved by lifestyle modification, bariatric surgery, or medications, such as semaglutide, can concomitantly improve NAFLD and atherosclerotic cardiovascular diseases. Therefore, certain pathophysiological links are involved in the development of NAFLD in obesity, and atherosclerotic cardiovascular diseases in obesity and NAFLD. Moreover, recent studies indicated that simultaneously targeting several mechanisms by tirzepatide and retatrutide leads to greater weight loss and markedly improves the complications of metabolic syndrome. These findings remind the importance of a mechanistic viewpoint for breaking the association between obesity, NAFLD, and atherosclerotic cardiovascular diseases. In this review article, we mainly focus on shared pathophysiological mechanisms, including insulin resistance, dyslipidemia, GLP1 signaling, inflammation, oxidative stress, mitochondrial dysfunction, gut dysbiosis, renin-angiotensin-aldosterone system (RAAS) overactivity, and endothelial dysfunction. Most of these pathophysiological alterations are primarily initiated by obesity. The development of NAFLD further exacerbates these molecular and cellular alterations, leading to atherosclerotic cardiovascular disease development or progression as the final manifestation of molecular perturbation. A better insight into these mechanisms makes it feasible to develop new multi-target approaches to simultaneously unhinge the deleterious chain of events linking obesity and NAFLD to atherosclerotic cardiovascular diseases.

Indole alleviates nonalcoholic fatty liver disease in an ACE2-dependent manner

Indole is a microbial metabolite produced by the gut microbiota through the degradation of dietary tryptophan, known for its well-established anti-inflammatory and antioxidant properties. In this study, we collected fecal samples from mice fed a high-fat diet (HFD) and those on a standard diet (SD), then conducted 16S rRNA sequencing to analyze their gut microbiota. The analysis revealed distinct differences in the dominant bacterial species between the two groups, with a significant decrease in indole-producing probiotics in the HFD mice compared to the SD group. Then we administered oral indole treatment to male C57BL/6J mice with HFD-induced NAFLD and observed a significant improvement in hepatic steatosis and inflammation. Notably, indole alleviated the HFD-induced decline in serum Angiotensin-(1-7) [Ang-(1-7)] levels and Angiotensin-Converting Enzyme 2 (ACE2) expression. To further investigate the role of indole and ACE2 in NAFLD, we conducted experiments using ACE2 knockout (ACE2KO) mice that were also induced with HFD-induced NAFLD and treated with indole. Interestingly, the protective effects of indole were compromised in the absence of ACE2. In HepG2 cells, indole similarly stimulated ACE2 expression and, in an ACE2-dependent manner, reduced ROS generation, maintained mitochondrial membrane potential stability, and increased SIRT3 expression. In summary, our results highlight the formation of a biologically active gut-liver axis between the gut microbiota and the liver through the tryptophan metabolite indole, which mitigates NAFLD in an ACE2-dependent manner. Elevating dietary tryptophan and increasing indole levels may represent an effective approach for preventing and treating NAFLD.

Exploring the Th2 Response in Obesity and Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD): A Potential Modulator of the Renin-Angiotensin System (RAS) Pathway in Hypertension Development

Non-alcoholic fatty liver disease (NAFLD), now referred to as metabolic dysfunction-associated steatotic liver disease (MASLD), is alarmingly increasing alongside the cases of obesity worldwide. MASLD is an underestimated metabolic abnormality closely linked with a higher risk of developing systemic arterial hypertension (SAH). However, the underlying mechanism of association between MASLD and SAH remains unknown. Inflammation may link these two entities by regulating the renin-angiotensin system (RAS). For this reason, in this study, we evaluated the hepatic expression of a cytokine profile and critical molecules in the RAS pathway in patients with morbid obesity and MASLD, both with SAH. We found a statistically significant correlation between ACE levels and the cytokines IL-4, IL-10, and IL-13 of Th2 response. Furthermore, according to a multiple linear regression analysis, the cytokines IL-4 and IL-13 were the best predictors of ACE levels. Moreover, we observed increased hepatic IL-13 expression in patients with morbid obesity, MASLD, and SAH compared to those without SAH. These results allow us to propose, for the first time, that the Th2 response, through regulating the RAS, could play a critical role in developing SAH in individuals with MASLD and obesity.

Hepatic angiotensin-converting enzyme 2 expression in metabolic dysfunction-associated steatotic liver disease and in patients with fatal COVID-19

BACKGROUND

Metabolic dysfunction-associated steatotic liver disease (MASLD), characterised by hepatic lipid accumulation, causes inflammation and oxidative stress accompanied by cell damage and fibrosis. Liver injury (LI) is also frequently reported in patients hospitalised with coronavirus disease 2019 (COVID-19), while pre-existing MASLD increases the risk of LI and the development of COVID-19-associated cholangiopathy. Mechanisms of injury at the cellular level remain unclear, but it may be significant that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which causes COVID-19, uses angiotensin-converting expression enzyme 2 (ACE2), a key regulator of the 'anti-inflammatory' arm of the renin-angiotensin system, for viral attachment and host cell invasion.

AIM

To determine if hepatic ACE2 levels are altered during progression of MASLD and in patients who died with severe COVID-19.

METHODS

ACE2 protein levels and localisation, and histological fibrosis and lipid droplet accumulation as markers of MASLD were determined in formalin-fixed liver tissue sections across the MASLD pathological spectrum (isolated hepatocellular steatosis, metabolic dysfunction-associated steatohepatitis (MASH) +/- fibrosis, end-stage cirrhosis) and in post-mortem tissues from patients who had died with severe COVID-19, using ACE2 immunohistochemistry and haematoxylin and eosin and picrosirius red staining of total collagen and lipid droplet areas, followed by quantification using machine learning-based image pixel classifiers.

RESULTS

ACE2 staining is primarily intracellular and concentrated in the cytoplasm of centrilobular hepatocytes and apical membranes of bile duct cholangiocytes. Strikingly, ACE2 protein levels are elevated in non-fibrotic MASH compared to healthy controls but not in the progression to MASH with fibrosis and in cirrhosis. ACE2 protein levels and histological fibrosis are not associated, but ACE2 and liver lipid droplet content are significantly correlated across the MASLD spectrum. Hepatic ACE2 levels are also increased in COVID-19 patients, especially those showing evidence of LI, but are not correlated with the presence of SARS-CoV-2 virus in the liver. However, there is a clear association between the hepatic lipid droplet content and the presence of the virus, suggesting a possible functional link.

CONCLUSION

Hepatic ACE2 levels were elevated in nonfibrotic MASH and COVID-19 patients with LI, while lipid accumulation may promote intra-hepatic SARS-CoV-2 replication, accelerating MASLD progression and COVID-19-mediated liver damage.

Terf2ip deficiency accelerates non-alcoholic steatohepatitis through regulating lipophagy and fatty acid oxidation via Sirt1/AMPK pathway

BACKGROUND & AIMS

Our previous study has demonstrated that Telomeric repeat-binding factor 2-interacting protein 1(Terf2ip), played an important role in hepatic ischemia reperfusion injury. This study is aimed to explore the function and mechanism of Terf2ip in non-alcoholic steatohepatitis (NASH).

METHODS

The expression of Terf2ip was detected in liver tissue samples obtained from patients diagnosed with NASH. Mice NASH models were constructed by fed with high-fat diet (HFD) or methionine/choline deficient diet (MCD) in Terf2ip knockout and wild type (WT) mice. To further investigate the role of Terf2ip in NASH, adeno-associated viruses (AAV)-Terf2ip was administrated to mice.

RESULTS

We observed a significant down-regulation of Terf2ip levels in the livers of NASH patients and mice NASH models. Terf2ip deficiency was associated with an exacerbation of hepatic steatosis in mice under HFD or MCD. Additionally, Terf2ip deficiency impaired lipophagy and fatty acid oxidation (FAO) in NASH models. Mechanically, we discovered that Terf2ip bound to the promoter region of Sirt1 to regulate Sirt1/AMPK pathway activation. As a result, Terf2ip deficiency was shown to inhibit lipophagy through the AMPK pathway, while the activation of Sirt1 alleviated steatohepatitis in the livers of mice. Finally, re-expression of Terf2ip in hepatocyes alleviated liver steatosis, inflammation, and restored lipophagy.

CONCLUSIONS

These results revealed that Terf2ip played a protective role in the progression of NASH through regulating lipophagy and FAO by binding to Sirt1 promoter. Our findings provided a potential therapeutic target for the treatment of NASH.

Myeloid-Mas Signaling Modulates Pathogenic Crosstalk among MYC+CD63+ Endothelial Cells, MMP12+ Macrophages, and Monocytes in Acetaminophen-Induced Liver Injury

Acetaminophen overdose is a leading cause of acute liver failure (ALF). Despite the pivotal role of the inflammatory microenvironment in the progression of advanced acetaminophen-induced liver injury (AILI), a comprehensive understanding of the underlying cellular interactions and molecular mechanisms remains elusive. Mas is a G protein-coupled receptor highly expressed by myeloid cells; however, its role in the AILI microenvironment remains to be elucidated. A multidimensional approach, including single-cell RNA sequencing, spatial transcriptomics, and hour-long intravital imaging, is employed to characterize the microenvironment in Mas1 deficient mice at the systemic and cell-specific levels. The characteristic landscape of mouse AILI models involves reciprocal cellular communication among MYC+CD63+ endothelial cells, MMP12+ macrophages, and monocytes, which is maintained by enhanced glycolysis and the NF-κB/TNF-α signaling pathway due to myeloid-Mas deficiency. Importantly, the pathogenic microenvironment is delineated in samples obtained from patients with ALF, demonstrating its clinical relevance. In summary, these findings greatly enhance the understanding of the microenvironment in advanced AILI and offer potential avenues for patient stratification and identification of novel therapeutic targets.

Untargeted metabolomics uncovers metabolic dysregulation and tissue sensitivity in ACE2 knockout mice

Angiotensin-converting enzyme 2 (ACE2) polymorphisms are associated with increased risk of type 2 diabetes mellitus (T2DM), obesity and dyslipidemia, which have been determined in various populations. Consistently, ACE2 knockout (ACE2 KO) mice display damaged energy metabolism in multiple tissues, especially the key metabolic tissues such as liver, skeletal muscle and epididymal white adipose tissue (eWAT) and show even more severe phenotype under high-fat diet (HFD) induced metabolic stress. However, the effects of ACE2 on global metabolomics profiling and the tissue sensitivity remain unclear. To understand how tissues independently and collectively respond to ACE2, we performed untargeted metabolomics in serum in ACE2 KO and control wild type (WT) mice both on normal diet (ND) and HFD, and in three key metabolic tissues (liver, skeletal muscle and eWAT) after HFD treatment. The results showed significant alterations in metabolic profiling in ACE2 KO mice. We identified 275 and 168 serum metabolites differing significantly between WT and ACE2 KO mice fed on ND and HFD, respectively. And the altered metabolites in the ACE2 KO group varied from 90 to 196 in liver, muscle and eWAT. The alterations in ND and HFD serum were most similar. Compared with WT mice, ACE2 KO mice showed an increase in N-phenylacetylglutamine (PAGln), methyl indole-3-acetate, 5-hydroxytryptophol, cholic acid, deoxycholic acid and 12(S)-HETE, while LPC (19:0) and LPE (16:1) decreased. Moreover, LPC (20:0), LPC (20:1) and PC (14:0e/6:0) were reduced in both ND and HFD serum, paralleling the decreases identified in HFD skeletal muscle. Interestingly, DL-tryptophan, indole and Gly-Phe decreased in both ND and HFD serum but were elevated in HFD liver of ACE2 KO mice. A low level of l-ergothioneine was observed among liver, muscle, and epididymal fat tissue of ACE2 KO mice. Pathway analysis demonstrated that different tissues exhibited different dysregulated metabolic pathways. In conclusion, these results revealed that ACE2 deficiency leads to an overall state of metabolic distress, which may provide a new insight into the underlying pathogenesis in metabolic disorders in both ACE2 KO mice and in patients with certain genetic variant of ACE2 gene.

Benzoylaconitine: A promising ACE2-targeted agonist for enhancing cardiac function in heart failure

Benzoylaconitine is a natural product in the treatment of cardiovascular disease. However, its pharmacological effect, direct target protein, and molecular mechanisms for the treatment of heart failure are unclear. In this study, benzoylaconitine inhibited Ang II-induced cell hypertrophy and fibrosis in rat primary cardiomyocytes and rat fibroblasts, while attenuating cardiac function and cardiac remodeling in TAC mice. Using the limited proteolysis-mass spectrometry (LiP-MS) method, the angiotensin-converting enzyme 2 (ACE2) was confirmed as a direct binding target of benzoylaconitine for the treatment of heart failure. In ACE2-knockdown cells and ACE2-/- mice, benzoylaconitine failed to ameliorate cardiomyocyte hypertrophy, fibrosis, and heart failure. Online RNA-sequence analysis indicated p38/ERK-mediated mitochondrial reactive oxygen species (ROS) and nuclear factor kappa B (NF-κB) activation are the possible downstream molecular mechanisms for the effect of BAC-ACE2 interaction. Further studies in ACE2-knockdown cells and ACE2-/- mice suggested that benzoylaconitine targeted ACE2 to suppress p38/ERK-mediated mitochondrial ROS and NF-κB pathway activation. Our findings suggest that benzoylaconitine is a promising ACE2 agonist in regulating mitochondrial ROS release and inflammation activation to improve cardiac function in the treatment of heart failure.

The Counteracting Effects of Ang II and Ang-(1-7) on the Function andGrowth of Insulin-secreting NIT-1 Cells

INTRODUCTION

China now has the highest number of diabetes in the world. Angiotensin II (Ang II) causes insulin resistance by acting on the insulin signaling pathway of peripheral target tissues. However, its effect on islet β-cells remains unclear. The possible role of Angiotensin-( 1-7) [Ang-(1-7)] as an antagonist to the effects of Ang II and in treating diabetes needs to be elucidated.

OBJECTIVES

To assess the effects of Ang II and Ang-(1-7) on the function and growth of islet β cell line NIT-1, which is derived from the islets of non-obese diabetic/large T-antigen (NOD/LT) mice with insulinoma.

METHODS

NIT-1 cells were treated with Ang II, Ang-(1-7) and their respective receptor antagonists. The impact on cell function and growth was then evaluated.

RESULTS

Ang II significantly reduced insulin-stimulated IR-β-Tyr and Akt-Ser; while Ang-(1-7), saralasin (an Ang II receptor antagonist), and diphenyleneiodonium [DPI, a nicotinamide adenine dinucleotide phosphate oxidase (NOX) antagonist] reversed the inhibiting effect. Conversely, Ang II significantly increased insulin-stimulated intracellular H2O2 and P47 phox, while saralasin and DPI reverted the effect. Furthermore, Ang-(1-7) reduced the elevated concentrations of ROS and MDA while increasing the proliferation rate that was reduced by high glucose, all of which were reversed by A-779, an antagonist of the Mas receptor (MasR).

CONCLUSION

Angiotensin II poses a negative regulatory effect on insulin signal transduction, increases oxidative stress, and may inhibit the transcription of insulin genes stimulated by insulin in NIT-1 cells. Meanwhile, angiotensin-(1-7) blocked these effects via MasR. These results corroborate the rising potential of the renin-angiotensin system (RAS) in treating diabetes.

New Insights into the Pathogenesis of Metabolic-Associated Fatty Liver Disease (MAFLD): Gut-Liver-Heart Crosstalk

Metabolism-associated fatty liver disease (MAFLD) is a multifaceted disease that involves complex interactions between various organs, including the gut and heart. It is defined by hepatic lipid accumulation and is related to metabolic dysfunction, obesity, and diabetes. Understanding the intricate interplay of the gut-liver-heart crosstalk is crucial for unraveling the complexities of MAFLD and developing effective treatment and prevention strategies. The gut-liver crosstalk participates in the regulation of the metabolic and inflammatory processes through host-microbiome interactions. Gut microbiota have been associated with the development and progression of MAFLD, and its dysbiosis contributes to insulin resistance, inflammation, and oxidative stress. Metabolites derived from the gut microbiota enter the systemic circulation and influence both the liver and heart, resulting in the gut-liver-heart axis playing an important role in MAFLD. Furthermore, growing evidence suggests that insulin resistance, endothelial dysfunction, and systemic inflammation in MAFLD may contribute to an increased risk of cardiovascular disease (CVD). Additionally, the dysregulation of lipid metabolism in MAFLD may also lead to cardiac dysfunction and heart failure. Overall, the crosstalk between the liver and heart involves a complex interplay of molecular pathways that contribute to the development of CVD in patients with MAFLD. This review emphasizes the current understanding of the gut-liver-heart crosstalk as a foundation for optimizing patient outcomes with MAFLD.

COVID-19 associated liver injury: An updated review on the mechanisms and management of risk groups

Coronavirus disease 2019 (COVID-19) has been associated with various liver injury cases worldwide. To date, the prevalence, mechanism, clinical manifestations, diagnosis, and outcomes of COVID-19-induced liver injury in various at-risk groups are not well defined. Liver injury may arise in the prevention and treatment of COVID-19 from direct causes such as viral infection and indirect causes such as systemic inflammation, hypoxic changes, and drugs that exacerbate any pre-existing liver disease. Studies have found that patients with underlying liver disease are at higher risk of COVID-19-induced liver injury. Certain condition of cardiopulmonary and metabolic diseases and vulnerable stages in lifespan may also involve in the development of COVID-19-induced liver injury. This review summarized studies of COVID-19-induced liver injury in different at-risk groups regarding their clinical characteristics, parameters, and correlations of the severity with these indicators and signs as well as potential treatment suggestions, to increase attention to physiological and pathological conditions and continue liver function monitoring as they can help in strengthening early supportive treatment and reducing the incidence of adverse outcomes.

Hepatocyte-specific Mas activation enhances lipophagy and fatty acid oxidation to protect against acetaminophen-induced hepatotoxicity in mice

BACKGROUND & AIMS

Acetaminophen (APAP) is the most common cause of drug-induced liver injury (DILI); however, treatment options are limited. Mas is a G protein-coupled receptor whose role in APAP-induced hepatotoxicity has not yet been examined.

METHODS

Intrahepatic Mas expression was determined in both human and mouse DILI models. Mas1^-/-, Alb^creMas1^f/f, Ppara^-/-, Mas1^-/-Ppara^-/- and wild-type mice were challenged with APAP for the in vivo analyses of Mas-AKT-FOXO1 axis-dependent lipophagy and fatty acid oxidation (FAO), using pharmacological compounds and genetic tools. Liver samples were collected for RNA-sequencing, proteomics, metabolomics, lipidomics, and metabolic flux analysis. Live-imaging of liver and histological, biochemical, and molecular studies were performed to evaluate APAP-induced hepatotoxicity in mice. Primary hepatocytes and hepatic cell lines were exposed to APAP for in vitro analysis.

RESULTS

Intrahepatic Mas expression was significantly upregulated in human and mouse DILI models. Mice with systemic, liver-specific, or hepatocyte-specific Mas1 deficiency were vulnerable to APAP-induced hepatotoxicity. They exhibited substantially impaired lipophagy and downstream FAO, which was accompanied by the activation of AKT and suppression of FOXO1. In addition, the prophylactic activation of Mas conferred strong protection against APAP challenge in mice, with remarkably enhanced lipophagy and FAO dependent on the AKT-FOXO1 axis. Moreover, the protective effects of AVE0991 were substantially diminished by the inhibition of either lipophagy or FAO.

CONCLUSIONS

The activation of Mas on hepatocytes enhanced AKT-FOXO1-dependent lipophagy and downstream FAO, protecting mice from APAP-induced hepatotoxicity and indicating that hepatocyte-specific Mas might be a novel therapeutic target for DILI.

IMPACT AND IMPLICATIONS

Mas signalling arises as a novel therapeutic target for patients with APAP-induced liver injury. The Mas-AKT/FOXO1-fatty acid degradation pathway could be critical for the development of treatment strategies for APAP overdose. When Mas signalling is targeted, the extent of liver injury should be considered at the time of administration. These findings obtained from APAP-challenged mice still need to be confirmed in a clinical context.

Alamandine/MrgD axis prevents TGF-β1-mediated fibroblast activation via regulation of aerobic glycolysis and mitophagy

BACKGROUND

Idiopathic pulmonary fibrosis is a chronic progressive, lethal disease in which ectopic lung fibroblast (LF) activation plays a vital part. We have previously shown that alamandine (ALA) exerts anti-fibrosis effects via the MAS-related G-protein coupled receptor D (MrgD). Here, we further investigate how it moderates transforming growth factor β1 (TGF-β1)-induced LF activation by regulating glucose metabolism and mitochondria autophagy (mitophagy).

METHODS

In vitro, we examined glycolysis-related protein hexokinase 2 (HK2), 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3), and lactic acid in cells treated with TGF-β1. The oxygen consumption rate and the extracellular acidification rate were detected using Seahorse assays. Then, mitophagy was evaluated using transmission electron microscopy, mt-Keima, and the co-localization of Parkin and COX IV with LC3 and LAMP1, respectively. The autophagic degradation of HK2 and PFKFB3 was detected by 3MA and bafilomycin A1 and assessed by their co-localization with LC3 and LAMP1, respectively. The effects of ALA on LF activation markers collagen I and α-SMA were detected. The effects of ALA on glucose metabolism, mitophagy, and the activation of LF were also investigated in vivo.

RESULTS

We found that the ALA/MrgD axis improved TGF-β1-mediated LF activation by repressing glycolysis by downregulating HK2 and PFKFB3 expression. Lactic acid sustained positive feedback between glycolysis and LF activation by maintaining the expression of HK2 and PFKFB3. We also showed that glycolysis enhancement resulted from blocking the autophagic degradation of HK2 and PFKFB3 while upregulated mRNA levels by TGF-β1, while all of those improved by ALA adding. Importantly, we determined that moderation of Parkin/LC3-mediated mitophagy by TGF-β1 also promotes glycolysis but is reversed by ALA. Furthermore, we proved that ALA counteracts the effects of bleomycin on HK2, PFKFB3, LC3, Parkin, and LF activation in vivo.

CONCLUSION

In this study, we show that the ALA/MrgD axis prevents TGF-β1-mediated fibroblast activation via regulation of aerobic glycolysis and mitophagy.

Angiotensin(1-7) attenuates visceral adipose tissue expansion and lipogenesis by suppression of endoplasmic reticulum stress via Mas receptor

BACKGROUND

White adipose tissue can be classified based on its location as subcutaneous and visceral fat, and the latter accumulation is reported to be more detrimental to metabolism. Endoplasmic reticulum (ER) stress has been demonstrated to regulate lipogenesis. The peptide angiotensin(1-7) [Ang(1-7)], which can be produced from angiotensin II (AngII) by angiotensin-converting enzyme 2 (ACE2), plays its role through Mas receptor, also participates in the regulation of lipid metabolism in adipose tissue, however, whether ER stress is involved in the mechanism remains unclear. Therefore, we aimed to explore the role of Ang(1-7) pathway in regulating visceral adipose tissue expansion and ER stress.

METHODS

ACE2 knockout (KO), Mas KO and C57BL/6 J mice were fed with high fat diet. Db/db mice were treated with either normal saline, Ang(1-7) or Ang(1-7) combined with Mas receptor inhibitor A779 using mini osmotic pumps. Fat mass was weighted, fat distribution was evaluated by MRI, and lipid profile and adipokines in epididymal adipose tissue were measured by ELISA kits, and histology of epididymal adipose tissue was also analyzed in multiple animal models. Additionally, differentiated 3T3-L1 cells were pre-loaded with palmitic acid to induce ER stress, then treated with drugs as those administrated to db/db mice. ER stress and lipogenesis related proteins in mice adipose and differentiated 3T3L-1 cells were analyzed by Western blot.

RESULTS

ACE2 or Mas KO mice exhibited increased visceral adipose tissue, adipocyte size and protein expression of lipogenesis and ER stress related markers in epididymal adipose tissue compared to wild-type mice. Db/db mice treated with Ang(1-7) displayed decreased visceral fat mass, adipocyte size and protein expression of lipogenesis and ER stress markers in epididymal adipose tissue compared to those treated with normal saline, while A779 partly attenuated these effects. Additionally, Ang(1-7) improved ER stress and lipogenesis markers in differentiated 3T3-L1 cells pre-loaded with palmitic acid.

CONCLUSIONS

Our findings indicated that Ang(1-7) attenuated visceral adipose tissue expansion and lipogenesis by suppression of ER stress via Mas receptor. The present study provides a potential perspective for Ang(1-7) for the therapeutics of obesity and related disorders.

System analysis based on the cuproptosis-related genes identifies LIPT1 as a novel therapy target for liver hepatocellular carcinoma

BACKGROUND

Liver hepatocellular carcinoma (LIHC) ranks sixth among the most common types of cancer with a high mortality rate. Cuproptosis is a newly discovered type of cell death in tumor, which is characterized by accumulation of intracellular copper leading to the aggregation of mitochondrial lipoproteins and destabilization of proteins. Thus, understanding the exact effects of cuproptosis-related genes in LIHC and determining their prognosticvalue is critical. However, the prognostic model of LIHC based on cuproptosis-related genes has not been reported.

METHODS

Firstly, we downloaded transcriptome data and clinical information of LIHC patients from TCGA and GEO (GSE76427), respectively. We then extracted the expression of cuproptosis-related genes and established a prognostic model by lasso cox regression analysis. Afterwards, the prediction performance of the model was evaluated by Kaplan-Meier survival analysis and receiver operating characteristic curve (ROC). Then, the prognostic model and the expression levels of the three genes were validated using the dataset from GEO. Subsequently, we divided LIHC patients into two subtypes by non-negative matrix factorization (NMF) classification and performed survival analysis. We constructed a Sankey plot linking different subtypes and prognostic models. Next, we calculate the drug sensitivity of each sample from patients in the high-risk group and low-risk group by the R package pRRophetic. Finally, we verified the function of LIPT1 in LIHC.

RESULTS

Using lasso cox regression analysis, we developed a prognostic risk model based on three cuproptosis-related genes (GCSH, LIPT1 and CDKN2A). Both in the training and in the test sets, the overall survival (OS) of LIHC patients in the low-risk group was significantly longer than that in the high-risk group. By performing NMF cluster, we identified two molecular subtypes of LIHC (C1 and C2), with C1 subtype having significantly longer OS and PFS than C2 subtype. The ROC analysis indicated that our model had a precisely predictive capacity for patients with LIHC. The multivariate Cox regression analysis indicated that the risk score is an independent predictor. Subsequently, we identified 71 compounds with IC50 values that differed between the high-risk and low-risk groups. Finally, we determined that knockdown of LIPT1 gene expression inhibited proliferation and invasion of hepatoma cells.

CONCLUSION

In this study, we developed a novel prognostic model for hepatocellular carcinoma based on cuproptosis-related genes that can effectively predict the prognosis of LIHC patients. The model may be helpful for clinicians to make clinical decisions for patients with LIHC and provide valuable insights for individualized treatment. Two distinct subtypes of LIHC were identified based on cuproptosis-related genes, with different prognosis and immune characteristics. In addition, we verified that LIPT1 may promote proliferation, invasion and migration of LIHC cells. LIPT1 might be a new potential target for therapy of LIHC.

Corilagin prevents non-alcoholic fatty liver disease via improving lipid metabolism and glucose homeostasis in high fat diet-fed mice

Non-alcoholic fatty liver disease (NAFLD) has been considered to be one of the most common chronic liver diseases. However, no validated pharmacological therapies have been officially proved in clinic due to its complex pathogenesis. The purpose of this study was to examine the protective effects of Corilagin (referred to Cori) against NAFLD in mice under a high fat diet (HFD) condition. Mice were fed either a normal control diet (NCD) or HFD with or without Cori (5 or 10 mg/kg body weight) for 15 weeks. In our results, Cori treatment significantly attenuated HFD-induced hepatic steatosis, high NAFLD activity score (NAD) and liver injury. Consistently, Cori treatment remarkably alleviated HFD-induced hepatic lipid accumulation (e.g., triglycerides (TG) and total cholesterol (TC) contents in liver), and improved plasma lipid concentrations (e.g., plasma TG, TC, low-density lipoprotein cholesterol (LDL-c), high-density lipoprotein cholesterol (HDL-c)). Moreover, Cori treatment ameliorated NAFLD associated metabolic disorders such as glucose intolerance and insulin resistance in HFD-fed mice. Additionally, Cori treatment dramatically changed HFD-induced liver gene expression profiles, and identified overlapped differentially expressed genes (DEGs) between NCD vs. HFD group and HFD vs. HCR (high fat diet plus treatment with Cori) group. With these DEGs, we observed a marked enrichment of Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, which were closely associated with the metabolic balance in liver. Particularly, we found several potential hub proteins against NAFLD development with analyses of protein-protein interaction (PPI) network and qPCR assays. Collectively, our results revealed the important protective effects of Cori against the progress of NAFLD, which was probably mediated through improving dysregulated lipid metabolism and insulin resistance in HFD-fed mice. Additionally, Cori-dependent overlapped DEGs might serve as a featured NAFLD-associated gene expression signature for the diagnosis, treatment, as well as drug discovery and development of NAFLD in the near future.

The spike of SARS-CoV-2 promotes metabolic rewiring in hepatocytes

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes a multi-organ damage that includes hepatic dysfunction, which has been observed in over 50% of COVID-19 patients. Liver injury in COVID-19 could be attributed to the cytopathic effects, exacerbated immune responses or treatment-associated drug toxicity. Herein we demonstrate that hepatocytes are susceptible to infection in different models: primary hepatocytes derived from humanized angiotensin-converting enzyme-2 mice (hACE2) and primary human hepatocytes. Pseudotyped viral particles expressing the full-length spike of SARS-CoV-2 and recombinant receptor binding domain (RBD) bind to ACE2 expressed by hepatocytes, promoting metabolic reprogramming towards glycolysis but also impaired mitochondrial activity. Human and hACE2 primary hepatocytes, where steatosis and inflammation were induced by methionine and choline deprivation, are more vulnerable to infection. Inhibition of the renin-angiotensin system increases the susceptibility of primary hepatocytes to infection with pseudotyped viral particles. Metformin, a common therapeutic option for hyperglycemia in type 2 diabetes patients known to partially attenuate fatty liver, reduces the infection of human and hACE2 hepatocytes. In summary, we provide evidence that hepatocytes are amenable to infection with SARS-CoV-2 pseudovirus, and we propose that metformin could be a therapeutic option to attenuate infection by SARS-CoV-2 in patients with fatty liver.

ACE2 pathway regulates thermogenesis and energy metabolism

Identification of key regulators of energy homeostasis holds important therapeutic promise for metabolic disorders, such as obesity and diabetes. ACE2 cleaves angiotensin II (Ang II) to generate Ang-(1-7) which acts mainly through the Mas1 receptor. Here, we identify ACE2 pathway as a critical regulator in the maintenance of thermogenesis and energy expenditure. We found that ACE2 is highly expressed in brown adipose tissue (BAT) and that cold stimulation increases ACE2 and Ang-(1-7) levels in BAT and serum. Ace2 knockout mice (Ace2^-/y) and Mas1 knockout mice (Mas1^-/-) displayed impaired thermogenesis. Mice transplanted with brown adipose tissue from Mas1^-/- display metabolic abnormalities consistent with those seen in the Ace2 and Mas1 knockout mice. In contrast, impaired thermogenesis of Lepr^db/db obese diabetic mice and high-fat diet-induced obese mice were ameliorated by overexpression of Ace2 or continuous infusion of Ang-(1-7). Activation of ACE2 pathway was associated with improvement of metabolic parameters, including blood glucose, lipids, and energy expenditure in multiple animal models. Consistently, ACE2 pathway remarkably enhanced the browning of white adipose tissue. Mechanistically, we showed that ACE2 pathway activated Akt/FoxO1 and PKA pathway, leading to induction of UCP1 and activation of mitochondrial function. Our data propose that adaptive thermogenesis requires regulation of ACE2 pathway and highlight novel potential therapeutic targets for the treatment of metabolic disorders.

Functional analysis of co-expression networks of zebrafish ace2 reveals enrichment of pathways associated with development and disease

Human Angiotensin I Converting Enzyme 2 (ACE2) plays an essential role in blood pressure regulation and SARS-CoV-2 entry. ACE2 has a highly conserved, one-to-one ortholog (ace2) in zebrafish, which is an important model for human diseases. However, the zebrafish ace2 expression profile has not yet been studied during early development, between genders, across different genotypes, or in disease. Moreover, a network-based meta-analysis for the extraction of functionally enriched pathways associated with differential ace2 expression is lacking in the literature. Herein, we first identified significant development-, tissue-, genotype-, and gender-specific modulations in ace2 expression via meta-analysis of zebrafish Affymetrix transcriptomics datasets (n_datasets = 107); and the correlation analysis of ace2 meta-differential expression profile revealed distinct positively and negatively correlated local functionally enriched gene networks. Moreover, we demonstrated that ace2 expression was significantly modulated under different physiological and pathological conditions related to development, tissue, gender, diet, infection, and inflammation using additional RNA-seq datasets. Our findings implicate a novel translational role for zebrafish ace2 in organ differentiation and pathologies observed in the intestines and liver.

The mechanisms of renin-angiotensin system in hepatocellular carcinoma: From the perspective of liver fibrosis, HCC cell proliferation, metastasis and angiogenesis, and corresponding protection measures

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide, of which the occurrence and development involve a variety of pathophysiological processes, such as liver fibrosis, hepatocellular malignant proliferation, metastasis, and tumor angiogenesis. Some important cytokines, such as TGF-β, PI3K, protein kinase B (Akt), VEGF and NF-κB, can regulate the growth, proliferation, diffusion, metastasis, and apoptosis of HCC cells by acting on the corresponding signaling pathways. Besides, many studies have shown that the formation of HCC is closely related to the main components of renin-angiotensin system (RAS), such as Ang II, ACE, ACE2, MasR, AT1R, and AT2R. Therefore, this review focused on liver fibrosis, HCC cell proliferation, metastasis, tumor angiogenesis, and corresponding protective measures. ACE-Ang II-AT1 axis and ACE2-Ang-(1-7)-MasR axis were taken as the main lines to introduce the mechanism of RAS in the occurrence and development of HCC, so as to provide references for future clinical work and scientific research.

ACE2 and energy metabolism: the connection between COVID-19 and chronic metabolic disorders

The renin-angiotensin system (RAS) has currently attracted increasing attention due to its potential function in regulating energy homeostasis, other than the actions on cellular growth, blood pressure, fluid, and electrolyte balance. The existence of RAS is well established in metabolic organs, including pancreas, liver, skeletal muscle, and adipose tissue, where activation of angiotensin-converting enzyme (ACE) - angiotensin II pathway contributes to the impairment of insulin secretion, glucose transport, fat distribution, and adipokines production. However, the activation of angiotensin-converting enzyme 2 (ACE2) - angiotensin (1-7) pathway, a novel branch of the RAS, plays an opposite role in the ACE pathway, which could reverse these consequences by improving local microcirculation, inflammation, stress state, structure remolding, and insulin signaling pathway. In addition, new studies indicate the protective RAS arm possesses extraordinary ability to enhance brown adipose tissue (BAT) activity and induces browning of white adipose tissue, and consequently, it leads to increased energy expenditure in the form of heat instead of ATP synthesis. Interestingly, ACE2 is the receptor of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is threating public health worldwide. The main complications of SARS-CoV-2 infected death patients include many energy metabolism-related chronic diseases, such as diabetes. The specific mechanism leading to this phenomenon is largely unknown. Here, we summarize the latest pharmacological and genetic tools on regulating ACE/ACE2 balance and highlight the beneficial effects of the ACE2 pathway axis hyperactivity on glycolipid metabolism, as well as the thermogenic modulation.