Characterization of the kinetics of cardiac cytosolic malate dehydrogenase and comparative analysis of cytosolic and mitochondrial isoforms

Molecular Characteristics of the Malate Dehydrogenase (MDH) Gene Family in Spirometra mansoni (Cestoda: Diphyllobothriidea)

The plerocercoid larva of Spirometra mansoni can cause a parasitic zoonosis-sparganosis. Malate dehydrogenase (MDH) plays a very important role in the life activities of parasites. However, little is known about the MDH family in S. mansoni. We identified eight new MDH members in S. mansoni in this study. Clustering analysis divided SmMDHs into two groups and revealed patterns similar to the conserved motif organization. RT-qPCR suggested that five MDHs were highly expressed in the mature proglottid and that three MDHs were highly expressed in the gravid proglottid. Phylogenetic analysis revealed that SmMDHs contain both conserved family members and members in the process of further diversification. rSmMDH has an NAD binding domain, a dimer interface and a substrate binding domain. Natural SmMDH was immunolocalized in the tissues and follicles around the uterus in the mature or gravid proglottid and eggshells. The maximum forward and reverse reaction activities of rSmMDH were observed at pH 8.5 and 9.0, respectively. The optimum temperature for enzyme activity was 37 °C in the forward reaction and 40 °C in the reverse reaction. These results lay the foundation for studying the molecular functions and mechanisms of MDHs in S. mansoni and related taxa.

Roles of the oncometabolite enantiomers of 2-hydroxyglutarate and their metabolism by diverse dehydrogenases

2-Hydroxyglutarate (2HG) is an oncometabolite that can contribute to tumor progression. Two enantiomer forms, L-2HG and D-2HG, arise from independent pathways starting from the precursor α-ketoglutarate (αKG). L-2HG production occurs through the promiscuous activities of malate dehydrogenase (MDH) and lactate dehydrogenase (LDH) under acidic and/or hypoxic conditions. D-2HG frequently accumulates by gain-of-function mutations in the genes encoding two isoforms of isocitrate dehydrogenase (IDH1 and IDH2). Cognate metabolite repair enzymes, L- and D-2-hydroxyglutarate dehydrogenases, oxidize the enantiomers and cause abnormally high 2HG accumulation and disease when mutated. Elevated levels of either oncometabolite affect redox homeostasis, metabolism, and immune system functioning. Moreover, the oncometabolites inhibit several α-ketoglutarate-dependent dioxygenases resulting in epigenetic changes such as DNA and histone hypermethylation as well as deficiencies in DNA repair. L-2HG, and D-2HG in some cases, inhibit degradation of hypoxia-inducible factor (HIF1α), a transcription factor that alters gene expression to adapt to hypoxic conditions, favoring tumorigenesis. Patients with the rare disease 2-hydroxyglutaric aciduria (2HGA) have exceedingly high levels of 2HG, which is neurotoxic, causing developmental delays and brain abnormalities. D-2HG also has specific effects on collagen production and NADPH pools. Recently, D-2HG has been targeted in new chemotherapies aimed at disrupting the gain-of-function IDH1 and IDH2 mutants, resulting in successful clinical trials for several cancers.

Dietary Ferulic Acid Increases Endurance Capacity by Promoting Skeletal Muscle Oxidative Phenotype, Mitochondrial Function, and Antioxidant Capacity

SCOPE

Endurance capacity is essential for endurance athletes' achievement and individuals' health. Nutritional supplements are a proven way to enhance endurance capacity. Previous studies have shown that ferulic acid (FA) enhances endurance capacity, but the underlying mechanism is unclear. The study is aimed to investigate the mechanism by which FA increases endurance capacity.

METHODS AND RESULTS

Forty mice are divided into control and 0.5% FA-supplemented groups, and an exhaustive swimming test demonstrates increased endurance capacity with FA supplementation. This study investigates the underlying mechanism for this effect of FA. Firstly, RT-PCR and western blot analysis find that FA increases the transformation from fast to slow muscle fiber. Additionally, adenosine triphosphate concentration, metabolic enzyme activity, and mitochondrial DNA analysis find that FA increases mitochondrial biogenesis and activates nuclear factor erythroid 2-related factor (NRF)1 signaling pathway in muscle. Besides, through antioxidant capacity analysis, this study finds that FA activates NRF2 signaling pathway and improves the antioxidant capacity in muscle. Moreover, inhibiting NRF2 eliminates FA's effect on muscle fiber transformation in C2C12 cells.

CONCLUSION

Our results suggest that FA increases endurance capacity by promoting skeletal muscle oxidative phenotype, mitochondrial function, and antioxidant capacity, which may be related to the NRF1 and NRF2 signaling pathways.

Clozapine-induced Myocarditis: Pathophysiologic Mechanisms and Implications for Therapeutic Approaches

Clozapine, a superior treatment for treatment-resistant schizophrenia can cause potentially life-threatening myocarditis and dilated cardiomyopathy. While the occurrence of this condition is well known, its molecular mechanisms are unclear and may be multifactorial. Putative mechanisms warrant an in-depth review not only from the perspective of toxicity but also for understanding the molecular mechanisms of the adverse cardiac effects of clozapine and the development of novel therapeutic approaches. Clozapine-induced cardiac toxicity encompasses a diverse set of pathways, including (i) immune modulation and proinflammatory processes encompassing an IgEmediated (type I hypersensitivity) response and perhaps a cytokine release syndrome (ii) catecholaminergic activation (iii) induction of free radicals and oxidative stress (iv) activation of cardiomyocyte cell death pathways, including apoptosis, ischemia through impairment in coronary blood flow via changes in endothelial production of NO and vasoconstriction induced by norepinephrine as well as other factors released from cardiac mast cells. (v) In addition, an extensive examination of the effects of clozapine on non-cardiac cellular proteins demonstrates that clozapine can impair enzymes involved in cellular metabolism, such as pyruvate kinase, mitochondrial malate dehydrogenase, and other proteins, including α-enolase, triosephosphate isomerase and cofilin, which might explain clozapine-induced reductions in myocardial energy generation for cell viability as well as contractile function. Pharmacologic antagonism of these cellular protein effects may lead to the development of strategies to antagonize the cardiac damage induced by clozapine.

Ellagic acid enhances muscle endurance by affecting the muscle fiber type, mitochondrial biogenesis and function

Ellagic acid (EA) is a natural polyphenolic compound, which shows various effects, such as anti-inflammatory and antioxidant effects and inhibition of platelet aggregation. In this study, we investigated the effect of EA on muscle endurance and explored its possible underlying mechanism. Our data showed that EA significantly improved muscle endurance in mice. EA increased the protein level of slow myosin heavy chain (MyHC) I and decreased the protein level of fast MyHC. We also found that the AMP-activated protein kinase (AMPK) signaling pathway was activated by EA. Finally, our data indicated that EA could increase mitochondrial biogenesis and function by increasing the content of mitochondrial DNA (mtDNA), the concentration of ATP, the activities of succinodehydrogenase (SDH) and malate dehydrogenase (MDH), and the mRNA levels of ATP synthase (ATP5G), mtDNA transcription factor A (TFAM), mitochondrial transcription factor b1 (Tfb1m) and citrate synthase (Cs) in mice and C2C12 myotubes. These results proved that EA could enhance muscle endurance via transforming the muscle fiber type and improving mitochondrial biogenesis and function.

Kinetic characterization and thermostability of C. elegans cytoplasmic and mitochondrial malate dehydrogenases

Malate dehydrogenase (MDH) catalyzes the conversion of NAD⁺ and malate to NADH and oxaloacetate in the citric acid cycle. Eukaryotes have one MDH isozyme that is imported into the mitochondria and one in the cytoplasm. We overexpressed and purified Caenorhabditis elegans cytoplasmic MDH-1 and mitochondrial MDH-2 in E. coli. Our goal was to compare the kinetic and structural properties of these enzymes because C. elegans can survive adverse environmental conditions, such as lack of food and elevated temperatures. In steady-state enzyme kinetics assays, we measured K_M values for oxaloacetate of 54 and 52 μM and K_M values for NADH of 61 and 107 μM for MDH-1 and MDH-2, respectively. We partially purified endogenous MDH-1 and MDH-2 from a mixed population of worms and separated them using anion exchange chromatography. Both endogenous enzymes had a K_M for oxaloacetate similar to that of the corresponding recombinant enzyme. Recombinant MDH-1 and MDH-2 had maximum activity at 40 °C and 35 °C, respectively. In a thermotolerance assay, MDH-1 was much more thermostable than MDH-2. Protein homology modeling predicted that MDH-1 had more intersubunit salt-bridges than mammalian MDH1 enzymes, and these ionic interactions may contribute to its thermostability. In contrast, the MDH-2 homology model predicted fewer intersubunit ionic interactions compared to mammalian MDH2 enzymes. These results suggest that the increased stability of MDH-1 may facilitate its ability to remain active in adverse environmental conditions. In contrast, MDH-2 may use other strategies, such as protein binding partners, to function under similar conditions.

Urinary malate dehydrogenase 2 is a new biomarker for early detection of non-small-cell lung cancer

Reliable and noninvasive biomarkers for the early diagnosis of non‐small‐cell lung cancer (NSCLC) are an unmet need. This study aimed to screen and validate potential urinary biomarkers for the early diagnosis of NSCLC. Using protein mass spectrometry, urinary MDH2 was found to be abundant both in patients with lung cancer and lung cancer model mice compared with controls. Urine samples obtained as retrospective and prospective cohorts including 1091 NSCLC patients and 736 healthy controls were measured using ELISA. Patients with stage I NSCLC had higher urinary MDH2 compared with healthy controls. The area under the receiver‐operating characteristic curve (AUC) for the urinary MDH2 was 0.7679 and 0.7234 in retrospective and prospective cohorts to distinguish stage I cases from controls. Urinary MDH2 levels correlated with gender and smoking history. MDH2 expression levels were elevated in lung cancer tissues. MDH2 knockdown using shRNA inhibited the proliferation of lung cancer cells. Our study demonstrated that urinary MDH2 concentration was higher in early‐stage NSCLC patients compared with that in controls and that MDH2 could serve as a potential biomarker for early detection of NSCLC.

Quantitative proteomics analysis of young and elderly skin with DIA mass spectrometry reveals new skin aging-related proteins

Skin aging is a specific manifestation of the physiological aging process that occurs in virtually all organisms. In this study, we used data independent acquisition mass spectrometry to perform a comparative analysis of protein expression in volar forearm skin samples from of 20 healthy young and elderly Chinese individuals. Our quantitative proteomic analysis identified a total of 95 differentially expressed proteins (DEPs) in aged skin compared to young skin. Enrichment analyses of these DEPs (57 upregulated and 38 downregulated proteins) based on the GO, KEGG, and KOG databases revealed functional clusters associated with immunity and inflammation, oxidative stress, biosynthesis and metabolism, proteases, cell proliferation, cell differentiation, and apoptosis. We also found that GAPDH, which was downregulated in aged skin samples, was the top hub gene in a protein-protein interaction network analysis. Some of the DEPs identified herein had been previously correlated with aging of the skin and other organs, while others may represent novel age-related entities. Our non-invasive proteomics analysis of human epidermal proteins may guide future research on skin aging to help develop treatments for age-related skin conditions and rejuvenation.

Creation of a formate: malate oxidoreductase by fusion of dehydrogenase enzymes with PEGylated cofactor swing arms

Enzymatic biocatalysis can be limited by the necessity of soluble cofactors. Here, we introduced PEGylated nicotinamide adenine dinucleotide (NAD(H)) swing arms to two covalently fused dehydrogenase enzymes to eliminate their nicotinamide cofactor requirements. A formate dehydrogenase and cytosolic malate dehydrogenase were connected via SpyCatcher-SpyTag fusions. Bifunctionalized polyethylene glycol chains tethered NAD(H) to the fusion protein. This produced a formate:malate oxidoreductase that exhibited cofactor-independent ping-pong kinetics with predictable Michaelis constants. Kinetic modeling was used to explore the effective cofactor concentrations available for electron transfer in the complexes. This approach could be used to create additional cofactor-independent transhydrogenase biocatalysts by swapping fused dehydrogenases.

miR-126-5p targets Malate Dehydrogenase 1 in non-small cell lung carcinomas

Malate Dehydrogenase (MDH) 1 has recently been shown to be highly expressed and display prognostic value in non-small cell lung carcinomas (NSCLCs). However, it is not known how MDH1 expression is regulated and there is no current molecular or chemical strategy that specifically targets MDH1. This may be due to structural and enzymatic similarities with its isoenzyme, malate dehydrogenase 2 (MDH2). However, MDH1 and MDH2 are encoded by distinct genes and this opens up the possibility for modulation at the expression level. Here, we screened in silico for microRNAs (miRs) that selectively targets the 3'UTR region of MDH1. These analyses revealed that mir-126-5p has three binding sites in the 3'UTR region of MDH1. Additionally, we show that expression of miR-126-5p suppresses the enzymatic activity of MDH1, mitochondrial respiration and caused cell death in NSCLC cell lines.

Characterization of the Role of the Malate Dehydrogenases to Lung Tumor Cell Survival

Cellular compartmentalization of biochemical processes in eukaryotic cells is critical for many functions including shuttling of reducing equivalents across membranes. Although coordination of metabolic flux between different organelles is vital for cell physiology, its impact on tumor cell survival is not well understood. By using an integrative approach, we have dissected the role of the key metabolic enzymes Malate dehydrogenases (MDH1 and MDH2) to the survival of Non-small Cell Lung Carcinomas. Here, we report that while both the MDH1 (cytosolic) and the MDH2 (mitochondrial) enzymes display elevated levels in patients compared to normal counterparts, only high expression of MDH1 is associated with poor prognosis. We further show that the MDH1 enzymatic activity is significantly higher in NSCLC cells than that of MDH2. Accordingly, genetic depletion of MDH1 leads to significantly higher toxicity than depletion of MDH2. These findings provide molecular insights into the metabolic characteristics of the malate isoenzymes and mark MDH1 as a potential therapeutic target in these tumors.

Determination of the catalytic mechanism for mitochondrial malate dehydrogenase

The kinetics of malate dehydrogenase (MDH) catalyzed oxidation/reduction of L-malate/oxaloacetate is pH-dependent due to the proton generated/taken up during the reaction. Previous kinetic studies on the mitochondrial MDH did not yield a consensus kinetic model that explains both substrate and pH dependency of the initial velocity. In this study, we propose, to our knowledge, a new kinetic mechanism to explain kinetic data acquired over a range of pH and substrate concentrations. Progress curves in the forward and reverse reaction directions were obtained under a variety of reactant concentrations to identify associated kinetic parameters. Experiments were conducted at physiologically relevant ionic strength of 0.17 M, pH ranging between 6.5 and 9.0, and at 25 °C. The developed model was built on the prior observation of proton uptake upon binding of NADH to MDH, and that the MDH-catalyzed oxidation of NADH may follow an ordered bi-bi mechanism with NADH/NAD binding to the enzyme first, followed by the binding of oxaloacetate/L-malate. This basic mechanism was expanded to account for additional ionic states to explain the pH dependency of the kinetic behavior, resulting in what we believe to be the first kinetic model explaining both substrate and pH dependency of the reaction velocity.