Emerging role for branched-chain amino acids metabolism in fibrosis

JPH203 alleviates peritoneal fibrosis via inhibition of amino acid-mediated mTORC1 signaling

BACKGROUND AND AIMS

The mesothelial-mesenchymal transition (MMT) of mesothelial cells has been recognized as a critical process during progression of peritoneal fibrosis (PF). Despite its crucial role in amino acid transport and metabolism, the involvement of L-type amino acid transporter 1 (LAT1) and the potential therapeutic role of its inhibitor, JPH203, in fibrotic diseases remain unexplored. Considering the paucity of research on amino acid-mediated mTORC1 activation in PF, our study endeavors to elucidate the protective effects of JPH203 against PF and explore the involvement of amino acid-mediated mTORC1 signaling in this context.

METHODS

We established the transforming growth factor beta 1 (TGF-β1) induced MMT model in primary human mesothelial cells and the peritoneal dialysis fluid (PDF) induced PF model in mice. The therapeutic effects of JPH203 on PF were then examined on these two models by real-time quantitative polymerase chain reaction, western blotting, immunofluorescence staining, Masson's trichrome staining, H&E staining, picro-sirius red staining, and immunohistochemistry. The involvement of amino acid-mediated mTORC1 signaling was screened by RNA sequencing and further verified by western blotting in vitro.

RESULTS

LAT1 was significantly upregulated and JPH203 markedly attenuated fibrotic phenotype both in vitro and in vivo. RNA-seq unveiled a significant enrichment of mTOR signaling pathway in response to JPH203 treatment. Western blotting results indicated that JPH203 alleviates PF by inhibiting amino acid-mediated mTORC1 signaling, which differs from the direct inhibition observed with rapamycin.

CONCLUSION

JPH203 alleviates PF by inhibiting amino acid-mediated mTORC1 signaling.

Branched-chain amino acids and their metabolites decrease human and rat hepatic stellate cell activation

BACKGROUND

End-stage liver diseases (ESLDs) are a significant global health challenge due to their high prevalence and severe health impacts. Despite the severe outcomes associated with ESLDs, therapeutic options remain limited. Targeting the activation of hepatic stellate cells (HSCs), key drivers of extracellular matrix accumulation during liver injury presents a novel therapeutic approach. In ESLDs patients, branched-chain amino acids (BCAAs, leucine, isoleucine and valine) levels are decreased, and supplementation has been proposed to attenuate liver fibrosis and improve regeneration. However, their effects on HSCs require further investigation.

OBJECTIVE

To evaluate the efficacy of BCAAs and their metabolites, branched-chain α-keto acids (BCKAs), in modulating HSCs activation in human and rat models.

METHODS

Primary HSCs from rats and cirrhotic and non-cirrhotic human livers, were cultured and treated with BCAAs or BCKAs to assess their effects on both preventing (from day 1 of isolation) and reversing (from day 7 of isolation) HSCs activation.

RESULTS

In rat HSCs, leucine and BCKAs significantly reduced fibrotic markers and cell proliferation. In human HSCs, the metabolite of isoleucine decreased cell proliferation around 85% and increased the expression of branched-chain ketoacid dehydrogenase. The other metabolites also showed antifibrotic effects in HSCs from non-cirrhotic human livers.

CONCLUSION

BCAAs and their respective metabolites inhibit HSC activation with species-specific responses. Further research is needed to understand how BCAAs influence liver fibrogenesis. BCKAs supplementation could be a strategic approach for managing ESLDs, considering the nutritional status and amino acid profiles of patients.

Amplifying hepatic L-aspartate levels suppresses CCl4-induced liver fibrosis by reversing glucocorticoid receptor β-mediated mitochondrial malfunction

Liver fibrosis is a determinant-stage process of many chronic liver diseases and affected over 7.9 billion populations worldwide with increasing demands of ideal therapeutic agents. Discovery of active molecules with anti-hepatic fibrosis efficacies presents the most attacking filed. Here, we revealed that hepatic L-aspartate levels were decreased in CCl4-induced fibrotic mice. Instead, supplementation of L-aspartate orally alleviated typical manifestations of liver injury and fibrosis. These therapeutic efficacies were alongside improvements of mitochondrial adaptive oxidation. Notably, treatment with L-aspartate rebalanced hepatic cholesterol-steroid metabolism and reduced the levels of liver-impairing metabolites, including corticosterone (CORT). Mechanistically, L-aspartate treatment efficiently reversed CORT-mediated glucocorticoid receptor β (GRβ) signaling activation and subsequent transcriptional suppression of the mitochondrial genome by directly binding to the mitochondrial genome. Knockout of GRβ ameliorated corticosterone-mediated mitochondrial dysfunction and hepatocyte damage which also weakened the improvements of L-aspartate in suppressing GRβ signaling. These data suggest that L-aspartate ameliorates hepatic fibrosis by suppressing GRβ signaling via rebalancing cholesterol-steroid metabolism, would be an ideal candidate for clinical liver fibrosis treatment.

Multiomics Analysis Reveals Leucine Deprivation Promotes Bile Acid Synthesis by Upregulating Hepatic CYP7A1 and Intestinal Turicibacter sanguinis in Mice

BACKGROUND

Leucine, a branched-chain amino acid, participates in the regulation of lipid metabolism and the composition of the intestinal microbiota. However, the related mechanism remains unclear.

OBJECTIVES

Here, we aimed to reveal the potential mechanisms by which hepatic CYP7A1 (a rate-limiting enzyme for bile acid [BA] synthesis) and gut microbiota coregulate BA synthesis under leucine deprivation.

METHODS

To this end, 8-wk-old C57BL/6J mice were fed with either regular diets or leucine-free diets for 1 wk. Then, we investigated whether secondary BAs were synthesized by Turicibacter sanguinis in 7-wk-old C57BL/6J germ-free mice gavaged with T. sanguinis for 2 wk by determining BA concentrations in the plasma, liver, and cecum contents using liquid chromatography-tandem mass spectrometry.

RESULTS

The results showed that leucine deprivation resulted in a significant increase in total BA concentration in the plasma and an increase in the liver, but no difference in total BA was observed in the cecum contents before and after leucine deprivation. Furthermore, leucine deprivation significantly altered BA profiles such as taurocholic acid and ω-muricholic acid in the plasma, liver, and cecum contents. CYP7A1 expression was significantly upregulated in the liver under leucine deprivation. Leucine deprivation also regulated the composition of the gut microbiota; specifically, it significantly upregulated the relative abundance of T. sanguinis, thus enhancing the conversion of primary BAs into secondary BAs by intestinal T. sanguinis in mice.

CONCLUSIONS

Overall, leucine deprivation regulated BA profiles in enterohepatic circulation by upregulating hepatic CYP7A1 expression and increasing intestinal T. sanguinis abundance. Our findings reveal the contribution of gut microbiota to BA metabolism under dietary leucine deprivation.

Duality of Branched-Chain Amino Acids in Chronic Cardiovascular Disease: Potential Biomarkers versus Active Pathophysiological Promoters

Branched-chain amino acids (BCAAs), comprising leucine (Leu), isoleucine (Ile), and valine (Val), are essential nutrients vital for protein synthesis and metabolic regulation via specialized signaling networks. Their association with cardiovascular diseases (CVDs) has become a focal point of scientific debate, with emerging evidence suggesting both beneficial and detrimental roles. This review aims to dissect the multifaceted relationship between BCAAs and cardiovascular health, exploring the molecular mechanisms and clinical implications. Elevated BCAA levels have also been linked to insulin resistance (IR), type 2 diabetes mellitus (T2DM), inflammation, and dyslipidemia, which are well-established risk factors for CVD. Central to these processes are key pathways such as mammalian target of rapamycin (mTOR) signaling, nuclear factor kappa-light-chain-enhancer of activate B cells (NF-κB)-mediated inflammation, and oxidative stress. Additionally, the interplay between BCAA metabolism and gut microbiota, particularly the production of metabolites like trimethylamine-N-oxide (TMAO), adds another layer of complexity. Contrarily, some studies propose that BCAAs may have cardioprotective effects under certain conditions, contributing to muscle maintenance and metabolic health. This review critically evaluates the evidence, addressing the biological basis and signal transduction mechanism, and also discusses the potential for BCAAs to act as biomarkers versus active mediators of cardiovascular pathology. By presenting a balanced analysis, this review seeks to clarify the contentious roles of BCAAs in CVD, providing a foundation for future research and therapeutic strategies required because of the rising prevalence, incidence, and total burden of CVDs.

Urea cycle promotion via ammonia-upregulated CPS1 is involved in arsenite-induced pulmonary fibrosis through enhancing collagen synthesis

Arsenic exposure is connected with lung toxicity and is related to lung fibrotic changes. Idiopathic pulmonary fibrosis (IPF) is characterized by extracellular matrix (ECM) deposition. Various genetic mechanisms and environmental factors induce or exacerbate pulmonary fibrosis. Collagen synthesis induced by sodium arsenite (NaAsO2) is closely associated with IPF. Fibroblasts tend to fine-tune their metabolic networks to support their synthetic requirements in response to environmental stimuli. Alterations in metabolism have an influential role in the pathogenesis of IPF. However, it is unclear how arsenic affects the metabolism in IPF. The urea cycle (UC) is needed for collagen formation, which provides adequate levels of proline (Pro) for biosynthesis of collagen. Carbamoyl phosphate synthetase 1 (CPS1) converts the ammonia to carbamoyl phosphate, which controls the first reaction of the UC. We show that, in arsenite-exposed mice, high amounts of ammonia in the lung microenvironment promotes the expression levels of CPS1 and the Pro metabolism. Reduction of ammonia and CPS1 ablation inhibit collagen synthesis and ameliorate IPF phenotypes induced by arsenite. This work takes advantage of multi-omics data to enhance understanding of the underlying pathogenic mechanisms, the key molecules and the complicated cellular responses to this pollutant, which provide a target for the prevention of pulmonary fibrosis caused by arsenic.

Short-Chain Acyl-CoA Dehydrogenase as a Therapeutic Target for Cardiac Fibrosis

ABSTRACT

Cardiac fibrosis is considered as unbalanced extracellular matrix production and degradation, contributing to heart failure. Short-chain acyl-CoA dehydrogenase (SCAD) negatively regulates pathological cardiac hypertrophy. The purpose of this study was to investigate the possible role of SCAD in cardiac fibrosis. In vivo experiments were performed on spontaneously hypertensive rats (SHR) and SCAD-knockout mice. The cardiac tissues of hypertensive patients with cardiac fibrosis were used for the measurement of SCAD expression. In vitro experiments, with angiotensin II (Ang II), SCAD siRNA and adenovirus-SCAD were performed using cardiac fibroblasts (CFs). SCAD expression was significantly decreased in the left ventricles of SHR. Notably, swim training ameliorated cardiac fibrosis in SHR in association with the elevation of SCAD. The decrease in SCAD protein and mRNA expression levels in SHR CFs were in accordance with those in the left ventricular myocardium of SHR. In addition, SCAD expression was downregulated in CFs treated with Ang II in vitro, and SCAD siRNA interference induced the same changes in cardiac fibrosis as Ang II-treated CFs, while adenovirus-SCAD treatment significantly reduced the Ang II-induced CFs proliferation, alpha smooth muscle actin (α-SMA), and collagen expression. In SHR infected with adenovirus-SCAD, the cardiac fibrosis of the left ventricle was significantly decreased. However, cardiac fibrosis occurred in conventional SCAD-knockout mice. SCAD immunofluorescence intensity of cardiac tissue in hypertensive patients with cardiac fibrosis was lower than that of healthy subjects. Altogether, the current experimental outcomes indicate that SCAD has a negative regulatory effect on cardiac fibrosis and support its potential therapeutic target for suppressing cardiac fibrosis.

The disordered extracellular matrix landscape induced endometrial fibrosis of sheep: A multi-omics integrative analysis

Endometrial fibrosis leads to the destruction of endometrial function and affects reproductive performance. However, mechanisms underlying the development of endometrial fibrosis in sheep remain unclear. We use transcriptomic, proteomic, and metabolomic studies to reveal the formation mechanisms of endometrial fibrosis. The results showed that the fibrotic endometrial tissue phenotype presented fewer glands, accompanied by collagen deposition. Transcriptomic results indicated alterations in genes associated with the synthesis and degradation of extracellular matrix components, which alter metabolite homeostasis, especially in glycerophospholipid metabolism. Moreover, differentially expressed metabolites may play regulatory roles in key metabolic processes during fibrogenesis, including protein digestion and absorption, and amino acid synthesis. Affected by the aberrant genes, protein levels related to the extracellular matrix components were altered. In addition, based on Kyoto Encyclopedia of Genes and Genomes analysis of differentially expressed genes, metabolites and proteins, amino acid biosynthesis, glutathione, glycerophospholipid, arginine and proline metabolism, and cell adhesion are closely associated with fibrogenesis. Finally, we analyzed the dynamic changes in serum differential metabolites at different time points during fibrosis. Taken together, fibrosis development is related to metabolic obstacles in extracellular matrix synthesis and degradation triggered by disturbed gene and protein levels.

Metabolism Serves as a Bridge Between Cardiomyocytes and Immune Cells in Cardiovascular Diseases

Metabolic disorders of cardiomyocytes play an important role in the progression of various cardiovascular diseases. Metabolic reprogramming can provide ATP to cardiomyocytes and protect them during diseases, but this transformation also leads to adverse consequences such as oxidative stress, mitochondrial dysfunction, and eventually aggravates myocardial injury. Moreover, abnormal accumulation of metabolites induced by metabolic reprogramming of cardiomyocytes alters the cardiac microenvironment and affects the metabolism of immune cells. Immunometabolism, as a research hotspot, is involved in regulating the phenotype and function of immune cells. After myocardial injury, both cardiac resident immune cells and heart-infiltrating immune cells significantly contribute to the inflammation, repair and remodeling of the heart. In addition, metabolites generated by the metabolic reprogramming of immune cells can further affect the microenvironment, thereby affecting the function of cardiomyocytes and other immune cells. Therefore, metabolic reprogramming and abnormal metabolite levels may serve as a bridge between cardiomyocytes and immune cells, leading to the development of cardiovascular diseases. Herein, we summarize the metabolic relationship between cardiomyocytes and immune cells in cardiovascular diseases, and the effect on cardiac injury, which could be therapeutic strategy for cardiovascular diseases, especially in drug research.

Longitudinal assessment of bleomycin-induced pulmonary fibrosis by evaluating TGF-β1/Smad2, Nrf2 signaling and metabolomic analysis in mice

INTRODUCTION

Pulmonary fibrosis (PF) is characterized by an increase in collagen synthesis and deposition of extracellular matrix. Several factors, including transforming growth factor-β1 (TGF-β1), mothers against decapentaplegic homolog family proteins (Smad), and alpha-smooth muscle actin (α-SMA) trigger extracellular matrix (ECM) accumulation, fibroblast to myofibroblasts conversion, and epithelial-to-mesenchymal-transition (EMT) leading to PF. However, the role of cellular defense mechanisms such as the role of nuclear factor erythroid 2-related factor 2 (Nrf2) signaling during the onset and progression of PF is not understood completely.

AIM

The present study aims to analyze the involvement of TGF-β1/Smad signaling, and Nrf2 in the EMT and metabolic alterations that promote fibrosis in a time-dependent manner using bleomycin (BLM)-induced PF model in C57BL/6 mice.

KEY FINDINGS

Histopathological studies revealed loss of lung architecture and increased collagen deposition in BLM-exposed mice. BLM upregulated TGF-β1/Smad signaling and α-SMA at all time-points. The gradual increase in the accumulation of α-SMA and collagen implied the progression of PF. BLM exposure raises Nrf2 throughout each specified time-point, which suggests that Nrf2 activation might be responsible for TGF-β1-induced EMT and the development of PF. Further, metabolomic studies linked the development of PF to alterations in metabolic pathways. The pentose phosphate pathway (PPP) was consistently enriched across all the time-points. Additionally, alterations in 22 commonly enriched pathways, associated with fatty acid (FA) and amino acid metabolism were observed in 30- and 60-days.

SIGNIFICANCE

This study elucidates the association of TGF-β1/Smad and Nrf2 signaling in the EMT and metabolic alterations associated with the etiology and progression of PF.