Differential expression of alpha-enolase in the normal and pathological cardiac growth

The role of glycolytic metabolic pathways in cardiovascular disease and potential therapeutic approaches

Cardiovascular disease (CVD) is a major threat to human health, accounting for 46% of non-communicable disease deaths. Glycolysis is a conserved and rigorous biological process that breaks down glucose into pyruvate, and its primary function is to provide the body with the energy and intermediate products needed for life activities. The non-glycolytic actions of enzymes associated with the glycolytic pathway have long been found to be associated with the development of CVD, typically exemplified by metabolic remodeling in heart failure, which is a condition in which the heart exhibits a rapid adaptive response to hypoxic and hypoxic conditions, occurring early in the course of heart failure. It is mainly characterized by a decrease in oxidative phosphorylation and a rise in the glycolytic pathway, and the rise in glycolysis is considered a hallmark of metabolic remodeling. In addition to this, the glycolytic metabolic pathway is the main source of energy for cardiomyocytes during ischemia-reperfusion. Not only that, the auxiliary pathways of glycolysis, such as the polyol pathway, hexosamine pathway, and pentose phosphate pathway, are also closely related to CVD. Therefore, targeting glycolysis is very attractive for therapeutic intervention in CVD. However, the relationship between glycolytic pathway and CVD is very complex, and some preclinical studies have confirmed that targeting glycolysis does have a certain degree of efficacy, but its specific role in the development of CVD has yet to be explored. This article aims to summarize the current knowledge regarding the glycolytic pathway and its key enzymes (including hexokinase (HK), phosphoglucose isomerase (PGI), phosphofructokinase-1 (PFK1), aldolase (Aldolase), phosphoglycerate metatase (PGAM), enolase (ENO) pyruvate kinase (PKM) lactate dehydrogenase (LDH)) for their role in cardiovascular diseases (e.g., heart failure, myocardial infarction, atherosclerosis) and possible emerging therapeutic targets.

Oncometabolism: A Paradigm for the Metabolic Remodeling of the Failing Heart

Heart failure is associated with profound alterations in cardiac intermediary metabolism. One of the prevailing hypotheses is that metabolic remodeling leads to a mismatch between cardiac energy (ATP) production and demand, thereby impairing cardiac function. However, even after decades of research, the relevance of metabolic remodeling in the pathogenesis of heart failure has remained elusive. Here we propose that cardiac metabolic remodeling should be looked upon from more perspectives than the mere production of ATP needed for cardiac contraction and relaxation. Recently, advances in cancer research have revealed that the metabolic rewiring of cancer cells, often coined as oncometabolism, directly impacts cellular phenotype and function. Accordingly, it is well feasible that the rewiring of cardiac cellular metabolism during the development of heart failure serves similar functions. In this review, we reflect on the influence of principal metabolic pathways on cellular phenotype as originally described in cancer cells and discuss their potential relevance for cardiac pathogenesis. We discuss current knowledge of metabolism-driven phenotypical alterations in the different cell types of the heart and evaluate their impact on cardiac pathogenesis and therapy.

Cardiac troponin I autoantibody induces myocardial dysfunction by PTEN signaling activation

Background

The objective of the current study was to study the molecular mechanism(s) underlying cardiac troponin I autoantibody (cTnIAAb) binding to cardiomyocyte and resultant myocardial damage/dysfunction.

Methods

cTnIAAb was purified from serum of 10 acute myocardial infarction (AMI) patients with left ventricular remodeling. Recombinant human cTnI was used to generate three mouse-derived monoclonal anti-cTnI antibodies (cTnImAb1, cTnImAb2, and cTnImAb3). The target proteins in cardiac myocyte membrane bound to cTnImAb and effect of cTnIAAb and cTnImAb on apoptosis and myocardial function were determined.

Findings

We found that cTnIAAb/cTnImAb1 directly bound to the cardiomyocyte membraneα-Enolase (ENO1) and triggered cell apoptosis via increased expression of ENO1 and Bax, decreased expression of Bcl2, subsequently activating Caspase8, Caspase 3, phosphatase and tensin homolog (PTEN) while inhibiting Akt activity. This cTnIAAb-ENO1-PTEN-Akt signaling axis contributed to increased myocardial apoptosis, myocardial collagen deposition, and impaired systolic dysfunction.

Interpretation

Results obtained in this study indicate that cTnIAAb is involved in the process of ventricular remodeling after myocardial injury.

Fund

The National Natural Science Foundation of China (Grant#: 81260026).

Proteomic analysis of rat serum revealed the effects of chronic sleep deprivation on metabolic, cardiovascular and nervous system

Sleep is an essential and fundamental physiological process that plays crucial roles in the balance of psychological and physical health. Sleep disorder may lead to adverse health outcomes. The effects of sleep deprivation were extensively studied, but its mechanism is still not fully understood. The present study aimed to identify the alterations of serum proteins associated with chronic sleep deprivation, and to seek for potential biomarkers of sleep disorder mediated diseases. A label-free quantitative proteomics technology was used to survey the global changes of serum proteins between normal rats and chronic sleep deprivation rats. A total of 309 proteins were detected in the serum samples and among them, 117 proteins showed more than 1.8-folds abundance alterations between the two groups. Functional enrichment and network analyses of the differential proteins revealed a close relationship between chronic sleep deprivation and several biological processes including energy metabolism, cardiovascular function and nervous function. And four proteins including pyruvate kinase M1, clusterin, kininogen1 and profilin-1were identified as potential biomarkers for chronic sleep deprivation. The four candidates were validated via parallel reaction monitoring (PRM) based targeted proteomics. In addition, protein expression alteration of the four proteins was confirmed in myocardium and brain of rat model. In summary, the comprehensive proteomic study revealed the biological impacts of chronic sleep deprivation and discovered several potential biomarkers. This study provides further insight into the pathological and molecular mechanisms underlying sleep disorders at protein level.

Opening of mitoKATP improves cardiac function and inhibits apoptosis via the AKT-Foxo1 signaling pathway in diabetic cardiomyopathy

Decreasing phosphorylation of AKT-Foxo1 is closely associated with the onset of insulin resistance and apoptosis during diabetic cardiomyopathy (DCM). Opening of mitochondrial ATP-sensitive potassium channels (mitoK_ATP) increases the expression of p-AKT in the process of reperfusion injury. It was therefore hypothesized that opening of mitoK_ATP may regulate the AKT-Foxo1 signaling pathway and improve cardiac function in DCM. In the present study, opening of mitoK_ATP by diazoxide (DZX) was found to improve cardiac function and attenuate cardiomyocyte apoptosis in db/db mice. DZX also significantly increased the expression of p-AKT and p-Foxo1. Similarly, DZX decreased the expression of the heart failure marker NT-proBNP, increased mitochondrial membrane potential, inhibited apoptosis, and increased the expression of p-AKT and p-Foxo1 when mimicking insulin resistance in cultured cardiomyocytes. Moreover, the protective effects of DZX were completely blocked by the specific AKT inhibitor MK-2206. These data suggest that the regulation of the AKT-Foxo1 signaling pathway by mitoK_ATP plays an important role in improving cardiac function and inhibiting apoptosis in DCM, and may therefore be a new potential therapeutic target for DCM.

Upregulation of α-enolase protects cardiomyocytes from phenylephrine-induced hypertrophy

Cardiac hypertrophy often refers to the abnormal growth of heart muscle through a variety of factors. The mechanisms of cardiomyocyte hypertrophy have been extensively investigated using neonatal rat cardiomyocytes treated with phenylephrine. α-Enolase is a glycolytic enzyme with "multifunctional jobs" beyond its catalytic activity. Its possible contribution to cardiac dysfunction remains to be determined. The present study aimed to investigate the change of α-enolase during cardiac hypertrophy and explore its role in this pathological process. We revealed that mRNA and protein levels of α-enolase were significantly upregulated in hypertrophic rat heart induced by abdominal aortic constriction and in phenylephrine-treated neonatal rat cardiomyocytes. Furthermore, knockdown of α-enolase by RNA interference in cardiomyocytes mimicked the hypertrophic responses and aggravated phenylephrine-induced hypertrophy without reducing the total glycolytic activity of enolase. In addition, knockdown of α-enolase led to an increase of GATA4 expression in the normal and phenylephrine-treated cardiomyocytes. Our results suggest that the elevation of α-enolase during cardiac hypertrophy is compensatory. It exerts a catalytic independent role in protecting cardiomyocytes against pathological hypertrophy.

The sarcomeric M-region: a molecular command center for diverse cellular processes

The sarcomeric M-region anchors thick filaments and withstands the mechanical stress of contractions by deformation, thus enabling distribution of physiological forces along the length of thick filaments. While the role of the M-region in supporting myofibrillar structure and contractility is well established, its role in mediating additional cellular processes has only recently started to emerge. As such, M-region is the hub of key protein players contributing to cytoskeletal remodeling, signal transduction, mechanosensing, metabolism, and proteasomal degradation. Mutations in genes encoding M-region related proteins lead to development of severe and lethal cardiac and skeletal myopathies affecting mankind. Herein, we describe the main cellular processes taking place at the M-region, other than thick filament assembly, and discuss human myopathies associated with mutant or truncated M-region proteins.

Upregulation of α-enolase in acute rejection of cardiac transplant in rat model: implications for the secretion of interleukin-17

Acute allograft rejection remains a major problem in solid organ transplantation. The enzyme α-enolase has been shown to induce an immune response in cardiac transplantation. In this study, we investigated the role of α-enolase in acute allograft rejection in a rat model of heart transplantation. Hearts from either (WF: RT1(u) ) or (Lew: RT1(1) ) rats were transplanted into (Lew: RT1(1) ) rats. No rejection occurred in the isograft group, for which the median survival time was >168 days, whereas the median survival time of the allograft group was significantly less at 10 ± 2.1 days (n = 8 per group, p < 0.001). Increased inflammation was observed in allografts, including increased α-enolase expression and increased numbers of infiltrating CD4(+) T cells (p < 0.05). By immunohistochemical staining, we confirmed that α-enolase was expressed not only in myocardial cells but also in the infiltrating lymphocytes. However, on the fifth day after transplantation, α-enolase expression was no longer observed in the lymphocytes (n = 3, p < 0.001). In contrast, no lymphocytes were found in isografts after transplantation (n = 3, p < 0.001). α-enolase expression was increased in lymphocytes, which are implicated in the acute rejection of cardiac transplants. Intragraft α-enolase inhibition may be useful as an adjuvant therapy to systemic immunosuppression in heart transplantation.

α-Enolase, a multifunctional protein: its role on pathophysiological situations

α-Enolase is a key glycolytic enzyme in the cytoplasm of prokaryotic and eukaryotic cells and is considered a multifunctional protein. α-enolase is expressed on the surface of several cell types, where it acts as a plasminogen receptor, concentrating proteolytic plasmin activity on the cell surface. In addition to glycolytic enzyme and plasminogen receptor functions, α-Enolase appears to have other cellular functions and subcellular localizations that are distinct from its well-established function in glycolysis. Furthermore, differential expression of α-enolase has been related to several pathologies, such as cancer, Alzheimer's disease, and rheumatoid arthritis, among others. We have identified α-enolase as a plasminogen receptor in several cell types. In particular, we have analyzed its role in myogenesis, as an example of extracellular remodelling process. We have shown that α-enolase is expressed on the cell surface of differentiating myocytes, and that inhibitors of α-enolase/plasminogen binding block myogenic fusion in vitro and skeletal muscle regeneration in mice. α-Enolase could be considered as a marker of pathological stress in a high number of diseases, performing several of its multiple functions, mainly as plasminogen receptor. This paper is focused on the multiple roles of the α-enolase/plasminogen axis, related to several pathologies.

Glycogen debranching enzyme 6 (AGL), enolase 1 (ENOSF1), ectonucleotide pyrophosphatase 2 (ENPP2_1), glutathione S-transferase 3 (GSTM3_3) and mannosidase (MAN2B2) metabolism computational network analysis between chimpanzee and human left cerebrum

We identified significantly higher expression of the genes glycogen debranching enzyme 6 (AGL), enolase 1 (ENOSF1), ectonucleotide pyrophosphatase 2 (ENPP2_1), glutathione S-transferase 3 (GSTM3_3) and mannosidase (MAN2B2) from human left cerebrums versus chimpanzees. Yet the distinct low- and high-expression AGL, ENOSF1, ENPP2_1, GSTM3_3 and MAN2B2 metabolism networks between chimpanzee and human left cerebrum remain to be elucidated. Here, we constructed low- and high-expression activated and inhibited upstream and downstream AGL, ENOSF1, ENPP2_1, GSTM3_3 and MAN2B2 metabolism network between chimpanzee and human left cerebrum in GEO data set by gene regulatory network inference method based on linear programming and decomposition procedure, under covering AGL, ENOSF1, ENPP2_1, GSTM3_3 and MAN2B2 pathway and matching metabolism enrichment analysis by CapitalBio MAS 3.0 integration of public databases, including Gene Ontology, KEGG, BioCarta, GenMapp, Intact, UniGene, OMIM, etc. Our results show that the AGL, ENOSF1, ENPP2_1, GSTM3_3 and MAN2B2 metabolism network has more activated and less inhibited molecules in chimpanzee, but less activated and more inhibited in the human left cerebrum. We inferred stronger carbohydrate, glutathione and proteoglycan metabolism, ATPase activity, but weaker base excision repair, arachidonic acid and drug metabolism as a result of inducing cell growth in low-expression AGL, ENOSF1, ENPP2_1, GSTM3_3 and MAN2B2 metabolism network of chimpanzee left cerebrum; whereas stronger lipid metabolism, amino acid catabolism, DNA repair but weaker inflammatory response, cell proliferation, glutathione and carbohydrate metabolism as a result of inducing cell differentiation in high-expression AGL, ENOSF1, ENPP2_1, GSTM3_3 and MAN2B2 metabolism network of human left cerebrum. Our inferences are consistent with recent reports and computational activation and inhibition gene number patterns, respectively.

Baseline Serum Cardiac Troponin I Concentrations in Sprague-Dawley, Spontaneous Hypertensive, Wistar, Wistar-Kyoto, and Fisher Rats as Determined with an Ultrasensitive Immunoassay

Cardiac troponins have proved to be reliable blood biomarkers for identifying a variety of myocardial alterations in humans and animals. Recently, an ultrasensitive cTnI assay (Erenna IA) has been used to demonstrate increases in baseline cTnI resulting from drug-induced myocardial injury in rats, dogs, and monkeys, as well as to document baseline cTnI ranges in Sprague-Dawley (SD) rats. The present study was initiated to use the Erenna cTnI assay to further document baseline cTnI concentrations in normal control animals from multiple strains, including SD, Spontaneous Hypertensive (SHR), Wistar, Wistar-Kyoto (WKY), and Fisher strains. Baseline cTnI concentrations were quantified in all rats tested, and males had higher mean cTnI concentrations than females of the same strain. SHR males had the highest mean cTnI concentrations and the largest cTnI variability. Interestingly, cTnI concentrations increased in castrated SHR compared with unaltered male SHR, whereas cTnI concentrations decreased in ovariectomized SHR compared with unaltered female SHR. These results show significant differences in cTnI concentrations between strains, sexes, and noncardiac surgical alterations in control animals, and identify these as potential contributing factors to cTnI baseline variability that should be taken into account when using ultrasensitive cTnI as a biomarker to assess preclinical cardiotoxicity.