Decreased Mitochondrial Pyruvate Transport Activity in the Diabetic Heart: ROLE OF MITOCHONDRIAL PYRUVATE CARRIER 2 (MPC2) ACETYLATION

MARCH5 promotes aerobic glycolysis to facilitate ovarian cancer progression via ubiquitinating MPC1

MARCH5 is a ring-finger E3 ubiquitin ligase located in the outer membrane of mitochondria. A previous study has reported that MARCH5 was up-regulated and contributed to the migration and invasion of OC cells by serving as a competing endogenous RNA. However, as a mitochondrial localized E3 ubiquitin ligase, the function of MARCH5 in mitochondrial-associated metabolism reprogramming in human cancers remains largely unexplored, including OC. We first assessed the glycolysis effect of MARCH5 in OC both in vitro and in vivo. Then we analyzed the effect of MARCH5 knockdown or overexpression on respiratory activity by evaluating oxygen consumption rate, activities of OXPHOS complexes and production of ATP in OC cells with MARCH5. Co-immunoprecipitation, western-blot, and in vitro and vivo experiments were performed to investigate the molecular mechanisms underlying MARCH5-enhanced aerobic glycolysis s in OC. In this study, we demonstrate that the abnormal upregulation of MARCH5 is accompanied by significantly increased aerobic glycolysis in OC. Mechanistically, MARCH5 promotes aerobic glycolysis via ubiquitinating and degrading mitochondrial pyruvate carrier 1 (MPC1), which mediates the transport of cytosolic pyruvate into mitochondria by localizing on mitochondria outer membrane. In line with this, MPC1 expression is significantly decreased and its downregulation is closely correlated with unfavorable survival. Furthermore, in vitro and in vivo assays revealed that MARCH5 upregulation-enhanced aerobic glycolysis played a critical role in the proliferation and metastasis of OC cells. Taken together, we identify a MARCH5-regulated aerobic glycolysis mechanism by degradation of MPC1, and provide a rationale for therapeutic targeting of aerobic glycolysis via MARCH5-MPC1 axis inhibition.

Lactylation Modification in Cardiometabolic Disorders: Function and Mechanism

Cardiovascular disease (CVD) is recognized as the primary cause of mortality and morbidity on a global scale, and developing a clear treatment is an important tool for improving it. Cardiometabolic disorder (CMD) is a syndrome resulting from the combination of cardiovascular, endocrine, pro-thrombotic, and inflammatory health hazards. Due to their complex pathological mechanisms, there is a lack of effective diagnostic and treatment methods for cardiac metabolic disorders. Lactylation is a type of post-translational modification (PTM) that plays a regulatory role in various cellular physiological processes by inducing changes in the spatial conformation of proteins. Numerous studies have reported that lactylation modification plays a crucial role in post-translational modifications and is closely related to cardiac metabolic diseases. This article discusses the molecular biology of lactylation modifications and outlines the roles and mechanisms of lactylation modifications in cardiometabolic disorders, offering valuable insights for the diagnosis and treatment of such conditions.

Loss of Cardiac PFKFB2 Drives Metabolic, Functional, and Electrophysiological Remodeling in the Heart

BACKGROUND

Phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2) is a critical glycolytic regulator responsible for upregulation of glycolysis in response to insulin and adrenergic signaling. PFKFB2, the cardiac isoform of PFK-2, is degraded in the heart in the absence of insulin signaling, contributing to diabetes-induced cardiac metabolic inflexibility. However, previous studies have not examined how the loss of PFKFB2 affects global cardiac metabolism and function.

METHODS AND RESULTS

To address this, we have generated a mouse model with a cardiomyocyte-specific knockout of PFKFB2 (cKO). Using 9-month-old cKO and control mice, we characterized the impacts of PFKFB2 on cardiac metabolism, function, and electrophysiology. cKO mice have a shortened life span of 9 months. Metabolically, cKO mice are characterized by increased glycolytic enzyme abundance and pyruvate dehydrogenase activity, as well as decreased mitochondrial abundance and beta oxidation, suggesting a shift toward glucose metabolism. This was supported by a decrease in the ratio of palmitoyl carnitine to pyruvate-dependent mitochondrial respiration in cKO relative to control animals. Metabolomic, proteomic, and Western blot data support the activation of ancillary glucose metabolism, including pentose phosphate and hexosamine biosynthesis pathways. Physiologically, cKO animals exhibited impaired systolic function and left ventricular dilation, represented by reduced fractional shortening and increased left ventricular internal diameter, respectively. This was accompanied by electrophysiological alterations including increased QT interval and other metrics of delayed ventricular conduction.

CONCLUSIONS

Loss of PFKFB2 results in metabolic remodeling marked by cardiac ancillary pathway activation. This could delineate an underpinning of pathologic changes to mechanical and electrical function in the heart.

Mitochondrial pyruvate transport regulates presynaptic metabolism and neurotransmission

Glucose has long been considered the primary fuel source for the brain. However, glucose levels fluctuate in the brain during sleep, intense circuit activity, or dietary restrictions, posing significant metabolic stress. Here, we demonstrate that the mammalian brain utilizes pyruvate as a fuel source, and pyruvate can support neuronal viability in the absence of glucose. Nerve terminals are sites of metabolic vulnerability within a neuron and we show that mitochondrial pyruvate uptake is a critical step in oxidative ATP production in hippocampal terminals. We find that the mitochondrial pyruvate carrier is post-translationally modified by lysine acetylation which in turn modulates mitochondrial pyruvate uptake. Importantly, our data reveal that the mitochondrial pyruvate carrier regulates distinct steps in synaptic transmission, namely, the spatiotemporal pattern of synaptic vesicle release and the efficiency of vesicle retrieval, functions that have profound implications for synaptic plasticity. In summary, we identify pyruvate as a potent neuronal fuel and mitochondrial pyruvate uptake as a critical node for the metabolic control of synaptic transmission in hippocampal terminals.

Reduced mitochondrial pyruvate carrier expression in hearts with heart failure and reduced ejection fraction patients: ischemic vs. non-ischemic origin

Introduction and objectives

Mitochondrial pyruvate carrier (MPC) mediates the entry of pyruvate into mitochondria, determining whether pyruvate is incorporated into the Krebs cycle or metabolized in the cytosol. In heart failure (HF), a large amount of pyruvate is metabolized to lactate in the cytosol rather than being oxidized inside the mitochondria. Thus, MPC activity or expression might play a key role in the fate of pyruvate during HF. The purpose of this work was to study the levels of the two subunits of this carrier, named MPC1 and MPC2, in human hearts with HF of different etiologies.

Methods

Protein and mRNA expression analyses were conducted in cardiac tissues from three donor groups: patients with HF with reduced ejection fraction (HFrEF) with ischemic cardiomyopathy (ICM) or idiopathic dilated cardiomyopathy (IDC), and donors without cardiac pathology (Control). MPC2 plasma levels were determined by ELISA.

Results

Significant reductions in the levels of MPC1, MPC2, and Sirtuin 3 (SIRT3) were observed in ICM patients compared with the levels in the Control group. However, no statistically significant differences were revealed in the analysis of MPC1 and MPC2 gene expression among the groups. Interestingly, Pyruvate dehydrogenase complex (PDH) subunits expression were increased in the ICM patients. In the case of IDC patients, a significant decrease in MPC1 was observed only when compared with the Control group. Notably, plasma MPC2 levels were found to be elevated in both disease groups compared with that in the Control group.

Conclusion

Decreases in MPC1 and/or MPC2 levels were detected in the cardiac tissues of HFrEF patients, with ischemic or idiopatic origen, indicating a potential reduction in mitochondrial pyruvate uptake in the heart, which could be linked to unfavorable clinical features.

Light-phase prednisone promotes glucose oxidation in heart through novel transactivation targets of cardiomyocyte-specific GR and KLF15

Circadian time of intake determines the cardioprotective outcome of glucocorticoids in normal and infarcted hearts. The cardiomyocyte-specific glucocorticoid receptor (GR) is genetically required to preserve normal heart function in the long-term. The GR co-factor KLF15 is a pleiotropic regulator of cardiac metabolism. However, the cardiomyocyte-autonomous metabolic targets of the GR-KLF15 concerted epigenetic action remain undefined. Here we report that circadian time of intake determines the activation of a transcriptional and functional glucose oxidation program in heart by the glucocorticoid prednisone with comparable magnitude between sexes. We overlayed transcriptomics, epigenomics and cardiomyocyte-specific inducible ablation of either GR or KLF15. Downstream of a light-phase prednisone stimulation in mice, we found that both factors are non-redundantly required in heart to transactivate the adiponectin receptor expression (Adipor1) and promote insulin-stimulated glucose uptake, as well as transactivate the mitochondrial pyruvate complex expression (Mpc1/2) and promote pyruvate oxidation. We then challenged this time-specific drug effect in obese diabetic db/db mice, where the heart shows insulin resistance and defective glucose oxidation. Opposite to dark-phase dosing, light-phase prednisone rescued glucose oxidation in db/db cardiomyocytes and diastolic function in db/db hearts towards control-like levels with sex-independent magnitude of effect. In summary, our study identifies novel cardiomyocyte-autonomous metabolic targets of the GR-KLF15 concerted program mediating the time-specific cardioprotective effects of glucocorticoids on cardiomyocyte glucose utilization.

Mitochondrial pyruvate carrier 1 regulates fatty acid synthase lactylation and mediates treatment of nonalcoholic fatty liver disease

BACKGROUND AND AIMS

NAFLD has become a major metabolic disease worldwide. A few studies have reported the potential relationship between mitochondrial pyruvate carrier 1 (MPC1) and inflammation, fibrosis, and insulin sensitivity in obese or NASH mouse models. However, the impact of MPC1 on NAFLD-related liver lipid metabolism and its role in the NAFLD progression require further investigation.

APPROACH AND RESULTS

MPC1 expression was measured in liver tissues from normal controls and patients with NAFLD. We characterized the metabolic phenotypes and expression of genes involved in hepatic lipid accumulation in MPC1 systemic heterozygous knockout (MPC1 +/- ) mice. Hepatic protein lactylation was detected using Tandem Mass Tags proteomics and verified by the overexpression of lactylation mutants in cells. Finally, the effect of MPC1 inhibition on liver inflammation was examined in mice and AML-12 cells. Here, we found that MPC1 expression was positively correlated to liver lipid deposition in patients with NAFLD. MPC1 +/- mice fed with high-fat diet had reduced hepatic lipid accumulation but no change in the expression of lipid synthesis-related genes. MPC1 knockout affected the lactylation of several proteins, especially fatty acid synthase, through the regulation of lactate levels in hepatocytes. Lactylation at the K673 site of fatty acid synthase inhibited fatty acid synthase activity, which mediated the downregulation of liver lipid accumulation by MPC1. Moreover, although MPC1 knockout caused lactate accumulation, inflammation level was controlled because of mitochondrial protection and macrophage polarization.

CONCLUSIONS

In NAFLD, MPC1 levels are positively correlated with hepatic lipid deposition; the enhanced lactylation at fatty acid synthase K673 site may be a downstream mechanism.

Loss of cardiac PFKFB2 drives Metabolic, Functional, and Electrophysiological Remodeling in the Heart

Background

Phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2) is a critical glycolytic regulator responsible for upregulation of glycolysis in response to insulin and adrenergic signaling. PFKFB2, the cardiac isoform of PFK-2, is degraded in the heart in the absence of insulin signaling, contributing to diabetes-induced cardiac metabolic inflexibility. However, previous studies have not examined how the loss of PFKFB2 affects global cardiac metabolism and function.

Methods

To address this, we have generated a mouse model with a cardiomyocyte-specific knockout of PFKFB2 (cKO). Using 9-month-old cKO and control (CON) mice, we characterized impacts of PFKFB2 on cardiac metabolism, function, and electrophysiology.

Results

cKO mice have a shortened lifespan of 9 months. Metabolically, cKO mice are characterized by increased glycolytic enzyme abundance and pyruvate dehydrogenase (PDH) activity, as well as decreased mitochondrial abundance and beta oxidation, suggesting a shift toward glucose metabolism. This was supported by a decrease in the ratio of palmitoyl carnitine to pyruvate-dependent mitochondrial respiration in cKO relative to CON animals. Metabolomic, proteomic, and western blot data support the activation of ancillary glucose metabolism, including pentose phosphate and hexosamine biosynthesis pathways. Physiologically, cKO animals exhibited impaired systolic function and left ventricular (LV) dilation, represented by reduced fractional shortening and increased LV internal diameter, respectively. This was accompanied by electrophysiological alterations including increased QT interval and other metrics of delayed ventricular conduction.

Conclusions

Loss of PFKFB2 results in metabolic remodeling marked by cardiac ancillary pathway activation. This could delineate an underpinning of pathologic changes to mechanical and electrical function in the heart.

Clinical Perspective

What is New?: We have generated a novel cardiomyocyte-specific knockout model of PFKFB2, the cardiac isoform of the primary glycolytic regulator Phosphofructokinase-2 (cKO).The cKO model demonstrates that loss of cardiac PFKFB2 drives metabolic reprogramming and shunting of glucose metabolites to ancillary metabolic pathways.The loss of cardiac PFKFB2 promotes electrophysiological and functional remodeling in the cKO heart.What are the Clinical Implications?: PFKFB2 is degraded in the absence of insulin signaling, making its loss particularly relevant to diabetes and the pathophysiology of diabetic cardiomyopathy.Changes which we observe in the cKO model are consistent with those often observed in diabetes and heart failure of other etiologies.Defining PFKFB2 loss as a driver of cardiac pathogenesis identifies it as a target for future investigation and potential therapeutic intervention.

Fibroblast-to-cardiomyocyte lactate shuttle modulates hypertensive cardiac remodelling

BACKGROUND

Cardiac fibroblasts (CFs) and cardiomyocytes are the major cell populations in the heart. CFs not only support cardiomyocytes by producing extracellular matrix (ECM) but also assimilate myocardial nutrient metabolism. Recent studies suggest that the classical intercellular lactate shuttle may function in the heart, with lactate transported from CFs to cardiomyocytes. However, the underlying mechanisms regarding the generation and delivery of lactate from CFs to cardiomyocytes have yet to be explored.

RESULTS

In this study, we found that angiotensin II (Ang II) induced CFs differentiation into myofibroblasts that, driven by cell metabolism, then underwent a shift from oxidative phosphorylation to aerobic glycolysis. During this metabolic conversion, the expression of amino acid synthesis 5-like 1 (GCN5L1) was upregulated and bound to and acetylated mitochondrial pyruvate carrier 2 (MPC2) at lysine residue 19. Hyperacetylation of MPC2k19 disrupted mitochondrial pyruvate uptake and mitochondrial respiration. GCN5L1 ablation downregulated MPC2K19 acetylation, stimulated mitochondrial pyruvate metabolism, and inhibited glycolysis and lactate accumulation. In addition, myofibroblast-specific GCN5L1-knockout mice (GCN5L1fl/fl: Periostin-Cre) showed reduced myocardial hypertrophy and collagen content in the myocardium. Moreover, cardiomyocyte-specific monocarboxylate transporter 1 (MCT1)-knockout mice (MCT1fl/fl: Myh6-Cre) exhibited blocked shuttling of lactate from CFs to cardiomyocytes and attenuated Ang II-induced cardiac hypertrophy.

CONCLUSIONS

Our findings suggest that GCN5L1-MPC2 signalling pathway alters metabolic patterns, and blocking MCT1 interrupts the fibroblast-to-cardiomyocyte lactate shuttle, which may attenuate cardiac remodelling in hypertension.

Increased cardiac PFK-2 protects against high-fat diet-induced cardiomyopathy and mediates beneficial systemic metabolic effects

A healthy heart adapts to changes in nutrient availability and energy demands. In metabolic diseases like type 2 diabetes (T2D), increased reliance on fatty acids for energy production contributes to mitochondrial dysfunction and cardiomyopathy. A principal regulator of cardiac metabolism is 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2), which is a central driver of glycolysis. We hypothesized that increasing PFK-2 activity could mitigate cardiac dysfunction induced by high-fat diet (HFD). Wild type (WT) and cardiac-specific transgenic mice expressing PFK-2 (GlycoHi) were fed a low fat or HFD for 16 weeks to induce metabolic dysfunction. Metabolic phenotypes were determined by measuring mitochondrial bioenergetics and performing targeted quantitative proteomic and metabolomic analysis. Increasing cardiac PFK-2 had beneficial effects on cardiac and mitochondrial function. Unexpectedly, GlycoHi mice also exhibited sex-dependent systemic protection from HFD, including increased glucose homeostasis. These findings support improving glycolysis via PFK-2 activity can mitigate mitochondrial and functional changes that occur with metabolic syndrome.

Protein posttranslational modifications in health and diseases: Functions, regulatory mechanisms, and therapeutic implications

Protein posttranslational modifications (PTMs) refer to the breaking or generation of covalent bonds on the backbones or amino acid side chains of proteins and expand the diversity of proteins, which provides the basis for the emergence of organismal complexity. To date, more than 650 types of protein modifications, such as the most well-known phosphorylation, ubiquitination, glycosylation, methylation, SUMOylation, short-chain and long-chain acylation modifications, redox modifications, and irreversible modifications, have been described, and the inventory is still increasing. By changing the protein conformation, localization, activity, stability, charges, and interactions with other biomolecules, PTMs ultimately alter the phenotypes and biological processes of cells. The homeostasis of protein modifications is important to human health. Abnormal PTMs may cause changes in protein properties and loss of protein functions, which are closely related to the occurrence and development of various diseases. In this review, we systematically introduce the characteristics, regulatory mechanisms, and functions of various PTMs in health and diseases. In addition, the therapeutic prospects in various diseases by targeting PTMs and associated regulatory enzymes are also summarized. This work will deepen the understanding of protein modifications in health and diseases and promote the discovery of diagnostic and prognostic markers and drug targets for diseases.

The loss of cardiac SIRT3 decreases metabolic flexibility and proteostasis in an age-dependent manner

SIRT3 is a longevity factor that acts as the primary deacetylase in mitochondria. Although ubiquitously expressed, previous global SIRT3 knockout studies have shown primarily a cardiac-specific phenotype. Here, we sought to determine how specifically knocking out SIRT3 in cardiomyocytes (SIRTcKO mice) temporally affects cardiac function and metabolism. Mice displayed an age-dependent increase in cardiac pathology, with 10-month-old mice exhibiting significant loss of systolic function, hypertrophy, and fibrosis. While mitochondrial function was maintained at 10 months, proteomics and metabolic phenotyping indicated SIRT3 hearts had increased reliance on glucose as an energy substrate. Additionally, there was a significant increase in branched-chain amino acids in SIRT3cKO hearts without concurrent increases in mTOR activity. Heavy water labeling experiments demonstrated that, by 3 months of age, there was an increase in protein synthesis that promoted hypertrophic growth with a potential loss of proteostasis in SIRT3cKO hearts. Cumulatively, these data show that the cardiomyocyte-specific loss of SIRT3 results in severe pathology with an accelerated aging phenotype.

Metformin acts in the gut and induces gut-liver crosstalk

Metformin is the most prescribed drug for DM2, but its site and mechanism of action are still not well established. Here, we investigated the effects of metformin on basolateral intestinal glucose uptake (BIGU), and its consequences on hepatic glucose production (HGP). In diabetic patients and mice, the primary site of metformin action was the gut, increasing BIGU, evaluated through PET-CT. In mice and CaCo2 cells, this increase in BIGU resulted from an increase in GLUT1 and GLUT2, secondary to ATF4 and AMPK. In hyperglycemia, metformin increased the lactate (reducing pH and bicarbonate in portal vein) and acetate production in the gut, modulating liver pyruvate carboxylase, MPC1/2, and FBP1, establishing a gut-liver crosstalk that reduces HGP. In normoglycemia, metformin-induced increases in BIGU is accompanied by hypoglycemia in the portal vein, generating a counter-regulatory mechanism that avoids reductions or even increases HGP. In summary, metformin increases BIGU and through gut-liver crosstalk influences HGP.

Diabetic cardiomyopathy: a brief summary on lipid toxicity

Diabetes mellitus (DM) is a serious epidemic around the globe, and cardiovascular diseases account for the majority of deaths in patients with DM. Diabetic cardiomyopathy (DCM) is defined as a cardiac dysfunction derived from DM without the presence of coronary artery diseases and hypertension. Patients with either type 1 or type 2 DM are at high risk of developing DCM and even heart failure. Metabolic disorders of obesity and insulin resistance in type 2 diabetic environments result in dyslipidaemia and subsequent lipid-induced toxicity (lipotoxicity) in organs including the heart. Although various mechanisms have been proposed underlying DCM, it remains incompletely understood how lipotoxicity alters cardiac function and how DM induces clinical heart syndrome. With recent progress, we here summarize the latest discoveries on lipid-induced cardiac toxicity in diabetic hearts and discuss the underlying therapies and controversies in clinical DCM.

The mitochondrial pyruvate carrier at the crossroads of intermediary metabolism

Pyruvate metabolism, a central nexus of carbon homeostasis, is an evolutionarily conserved process and aberrant pyruvate metabolism is associated with and contributes to numerous human metabolic disorders including diabetes, cancer, and heart disease. As a product of glycolysis, pyruvate is primarily generated in the cytosol before being transported into the mitochondrion for further metabolism. Pyruvate entry into the mitochondrial matrix is a critical step for efficient generation of reducing equivalents and ATP and for the biosynthesis of glucose, fatty acids, and amino acids from pyruvate. However, for many years, the identity of the carrier protein(s) that transported pyruvate into the mitochondrial matrix remained a mystery. In 2012, the molecular-genetic identification of the mitochondrial pyruvate carrier (MPC), a heterodimeric complex composed of protein subunits MPC1 and MPC2, enabled studies that shed light on the many metabolic and physiological processes regulated by pyruvate metabolism. A better understanding of the mechanisms regulating pyruvate transport and the processes affected by pyruvate metabolism may enable novel therapeutics to modulate mitochondrial pyruvate flux to treat a variety of disorders. Herein, we review our current knowledge of the MPC, discuss recent advances in the understanding of mitochondrial pyruvate metabolism in various tissue and cell types, and address some of the outstanding questions relevant to this field.

Guidelines on Models of Diabetic Heart Disease

Diabetes is a major risk factor for cardiovascular diseases, including diabetic cardiomyopathy, atherosclerosis, myocardial infarction, and heart failure. As cardiovascular disease represents the number one cause of death in people with diabetes, there has been a major emphasis on understanding the mechanisms by which diabetes promotes cardiovascular disease, and how antidiabetic therapies impact diabetic heart disease. With a wide array of models to study diabetes (both type 1 and type 2), the field has made major progress in answering these questions. However, each model has its own inherent limitations. Therefore, the purpose of this guidelines document is to provide the field with information on which aspects of cardiovascular disease in the human diabetic population are most accurately reproduced by the available models. This review aims to emphasize the advantages and disadvantages of each model, and to highlight the practical challenges and technical considerations involved. We will review the preclinical animal models of diabetes (based on their method of induction), appraise models of diabetes-related atherosclerosis and heart failure, and discuss in vitro models of diabetic heart disease. These guidelines will allow researchers to select the appropriate model of diabetic heart disease, depending on the specific research question being addressed.

A new recognition moiety diphenylborinate in the detection of pyruvate via Lewis acid/base sensing pathway and its bioimaging applications

Developing new reaction based recognizing units can enhance the specificity of target analyte molecules in practical applications of real samples and biosystems. Therefore, introducing a recognizing moiety diphenylborinate was encountered for the detection of pyruvate biomolecule through Lewis acid-base reaction based sensing strategy. The construction of the Schiff-base back bone between quinoline and N-(diethylamino)salicylaldehyde-diphenylborinate (QSB) were expressed the red shift from blue emission of quinoline in to green as that of dative bond developed between Schiff base nitrogen and boron atoms. The new sensing approach was involved such a way that fluorophore QSB is a Lewis acid while pyruvate acts as Lewis base, where the elimination of Lewis pair produced a weak green fluorescence including the formation of quinoline, N-(diethylamino)salicylaldehyde (QS). The switching products were witnessed through ¹H NMR titration, HR-MS and FT-IR studies. The good selectivity and interference ability were achieved in presence of 1000-fold excess of possible interferences with LOD of 16 nM. Moreover, the tracking ability of the probe was employed towards pyruvate in live HeLa cell imaging for evaluating an exogenous and endogenous signals producing ability and its mitochondria targeting property was investigated successfully. Further, the practical utility of the probe was tested with milk samples and obtained good recovery results.

Neuraminidase 1 deficiency attenuates cardiac dysfunction, oxidative stress, fibrosis, inflammatory via AMPK-SIRT3 pathway in diabetic cardiomyopathy mice

Diabetic cardiomyopathy (DCM) is associated with oxidative stress and augmented inflammation in the heart. Neuraminidases (NEU) 1 has initially been described as a lysosomal protein which plays a role in the catabolism of glycosylated proteins. We investigated the role of NEU1 in the myocardium in diabetic heart. Streptozotocin (STZ) was injected intraperitoneally to induce diabetes in mice. Neonatal rat ventricular myocytes (NRVMs) were used to verify the effect of shNEU1 in vitro. NEU1 is up-regulated in cardiomyocytes under diabetic conditions. NEU1 inhibition alleviated oxidative stress, inflammation and apoptosis, and improved cardiac function in STZ-induced diabetic mice. Furthermore, NEU1 inhibition also attenuated the high glucose-induced increased reactive oxygen species generation, inflammation and, cell death in vitro. ShNEU1 activated Sirtuin 3 (SIRT3) signaling pathway, and SIRT3 deficiency blocked shNEU1-mediated cardioprotective effects in vitro. More importantly, we found AMPKα was responsible for the elevation of SIRT3 expression via AMPKα-deficiency studies in vitro and in vivo. Knockdown of LKB1 reversed the effect elicited by shNEU1 in vitro. In conclusion, NEU1 inhibition activates AMPKα via LKB1, and subsequently activates sirt3, thereby regulating fibrosis, inflammation, apoptosis and oxidative stress in diabetic myocardial tissue.

Insulin signaling alters antioxidant capacity in the diabetic heart

Diabetic cardiomyopathy is associated with an increase in oxidative stress. However, antioxidant therapy has shown a limited capacity to mitigate disease pathology. The molecular mechanisms responsible for the modulation of reactive oxygen species (ROS) production and clearance must be better defined. The objective of this study was to determine how insulin affects superoxide radical (O₂^•–) levels. O₂^•– production was evaluated in adult cardiomyocytes isolated from control and Akita (type 1 diabetic) mice by spin-trapping electron paramagnetic resonance spectroscopy. We found that the basal rates of O₂^•– production were comparable in control and Akita cardiomyocytes. However, culturing cardiomyocytes without insulin resulted in a significant increase in O₂^•– production only in the Akita group. In contrast, O₂^•– production was unaffected by high glucose and/or fatty acid supplementation. The increase in O₂^•– was due in part to a decrease in superoxide dismutase (SOD) activity. The PI3K inhibitor, LY294002, decreased Akita SOD activity when insulin was present, indicating that the modulation of antioxidant activity is through insulin signaling. The effect of insulin on mitochondrial O₂^•– production was evaluated in Akita mice that underwent a 1-week treatment of insulin. Mitochondria isolated from insulin-treated Akita mice produced less O₂^•– than vehicle-treated diabetic mice. Quantitative proteomics was performed on whole heart homogenates to determine how insulin affects antioxidant protein expression. Of 29 antioxidant enzymes quantified, thioredoxin 1 was the only one that was significantly enhanced by insulin treatment. In vitro analysis of thioredoxin 1 revealed a previously undescribed capacity of the enzyme to directly scavenge O₂^•–. These findings demonstrate that insulin has a role in mitigating cardiac oxidative stress in diabetes via regulation of endogenous antioxidant activity.

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Insulin decreases ROS production in T1D Akita cardiomyocytes.

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Insulin signaling downstream of PI3K is required for this effect.

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Insulin increases the antioxidant capacity in the Akita heart.

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Trx1 is upregulated by insulin in the Akita heart in vivo.

Post-translational Acetylation Control of Cardiac Energy Metabolism

Perturbations in myocardial energy substrate metabolism are key contributors to the pathogenesis of heart diseases. However, the underlying causes of these metabolic alterations remain poorly understood. Recently, post-translational acetylation-mediated modification of metabolic enzymes has emerged as one of the important regulatory mechanisms for these metabolic changes. Nevertheless, despite the growing reports of a large number of acetylated cardiac mitochondrial proteins involved in energy metabolism, the functional consequences of these acetylation changes and how they correlate to metabolic alterations and myocardial dysfunction are not clearly defined. This review summarizes the evidence for a role of cardiac mitochondrial protein acetylation in altering the function of major metabolic enzymes and myocardial energy metabolism in various cardiovascular disease conditions.

Heart failure-emerging roles for the mitochondrial pyruvate carrier

The mitochondrial pyruvate carrier (MPC) is the entry point for the glycolytic end-product pyruvate to the mitochondria. MPC activity, which is controlled by its abundance and post-translational regulation, determines whether pyruvate is oxidised in the mitochondria or metabolised in the cytosol. MPC serves as a crucial metabolic branch point that determines the fate of pyruvate in the cell, enabling metabolic adaptations during health, such as exercise, or as a result of disease. Decreased MPC expression in several cancers limits the mitochondrial oxidation of pyruvate and contributes to lactate accumulation in the cytosol, highlighting its role as a contributing, causal mediator of the Warburg effect. Pyruvate is handled similarly in the failing heart where a large proportion of it is reduced to lactate in the cytosol instead of being fully oxidised in the mitochondria. Several recent studies have found that the MPC abundance was also reduced in failing human and mouse hearts that were characterised by maladaptive hypertrophic growth, emulating the anabolic scenario observed in some cancer cells. In this review we discuss the evidence implicating the MPC as an important, perhaps causal, mediator of heart failure progression.

The Importance of Mitochondrial Pyruvate Carrier in Cancer Cell Metabolism and Tumorigenesis

Simple Summary

The characteristic metabolic hallmark of cancer cells is the massive catabolism of glucose by glycolysis, even under aerobic conditions—the so-called Warburg effect. Although energetically unfavorable, glycolysis provides “building blocks” to sustain the unlimited growth of malignant cells. Aberrant glycolysis is also responsible for lactate accumulation and acidosis in the tumor milieu, which fosters hypoxia and immunosuppression. One of the mechanisms used by cancer cells to increase glycolytic flow is the negative regulation of the proteins that conform the mitochondrial pyruvate carrier (MPC) complex, which transports pyruvate into the mitochondrial matrix to be metabolized in the tricarboxylic acid (TCA) cycle. Evidence suggests that MPC downregulation in tumor cells impacts many aspects of tumorigenesis, including cancer cell-intrinsic (proliferation, invasiveness, stemness, resistance to therapy) and -extrinsic (angiogenesis, anti-tumor immune activity) properties. In many cancers, but not in all, MPC downregulation is associated with poor survival. MPC regulation is therefore central to tackling glycolysis in tumors.

Abstract

Pyruvate is a key molecule in the metabolic fate of mammalian cells; it is the crossroads from where metabolism proceeds either oxidatively or ends with the production of lactic acid. Pyruvate metabolism is regulated by many enzymes that together control carbon flux. Mitochondrial pyruvate carrier (MPC) is responsible for importing pyruvate from the cytosol to the mitochondrial matrix, where it is oxidatively phosphorylated to produce adenosine triphosphate (ATP) and to generate intermediates used in multiple biosynthetic pathways. MPC activity has an important role in glucose homeostasis, and its alteration is associated with diabetes, heart failure, and neurodegeneration. In cancer, however, controversy surrounds MPC function. In some cancers, MPC upregulation appears to be associated with a poor prognosis. However, most transformed cells undergo a switch from oxidative to glycolytic metabolism, the so-called Warburg effect, which, amongst other possibilities, is induced by MPC malfunction or downregulation. Consequently, impaired MPC function might induce tumors with strong proliferative, migratory, and invasive capabilities. Moreover, glycolytic cancer cells secrete lactate, acidifying the microenvironment, which in turn induces angiogenesis, immunosuppression, and the expansion of stromal cell populations supporting tumor growth. This review examines the latest findings regarding the tumorigenic processes affected by MPC.

Blocking mitochondrial pyruvate import in brown adipocytes induces energy wasting via lipid cycling

Combined fatty acid esterification and lipolysis, termed lipid cycling, is an ATP‐consuming process that contributes to energy expenditure. Therefore, interventions that stimulate energy expenditure through lipid cycling are of great interest. Here we find that pharmacological and genetic inhibition of the mitochondrial pyruvate carrier (MPC) in brown adipocytes activates lipid cycling and energy expenditure, even in the absence of adrenergic stimulation. We show that the resulting increase in ATP demand elevates mitochondrial respiration coupled to ATP synthesis and fueled by lipid oxidation. We identify that glutamine consumption and the Malate‐Aspartate Shuttle are required for the increase in Energy Expenditure induced by MPC inhibition in Brown Adipocytes (MAShEEBA). We thus demonstrate that energy expenditure through enhanced lipid cycling can be activated in brown adipocytes by decreasing mitochondrial pyruvate availability. We present a new mechanism to increase energy expenditure and fat oxidation in brown adipocytes, which does not require adrenergic stimulation of mitochondrial uncoupling.

Protein acetylation and deacetylation: An important regulatory modification in gene transcription (Review)

Cells primarily rely on proteins to perform the majority of their physiological functions, and the function of proteins is regulated by post-translational modifications (PTMs). The acetylation of proteins is a dynamic and highly specific PTM, which has an important influence on the functions of proteins, such as gene transcription and signal transduction. The acetylation of proteins is primarily dependent on lysine acetyltransferases and lysine deacetylases. In recent years, due to the widespread use of mass spectrometry and the emergence of new technologies, such as protein chips, studies on protein acetylation have been further developed. Compared with histone acetylation, acetylation of non-histone proteins has gradually become the focus of research due to its important regulatory mechanisms and wide range of applications. The discovery of specific protein acetylation sites using bioinformatic tools can greatly aid the understanding of the underlying mechanisms of protein acetylation involved in related physiological and pathological processes.

Rescue of myocardial energetic dysfunction in diabetes through the correction of mitochondrial hyperacetylation by honokiol

Cardiac energetic dysfunction has been reported in patients with type 2 diabetes (T2D) and is an independent predictor of mortality. Identification of the mechanisms driving mitochondrial dysfunction, and therapeutic strategies to rescue these modifications, will improve myocardial energetics in T2D. We demonstrate using ³¹P-magnetic resonance spectroscopy (³¹P-MRS) that decreased cardiac ATP and phosphocreatine (PCr) concentrations occurred before contractile dysfunction or a reduction in PCr/ATP ratio in T2D. Real-time mitochondrial ATP synthesis rates and state 3 respiration rates were similarly depressed in T2D, implicating dysfunctional mitochondrial energy production. Driving this energetic dysfunction in T2D was an increase in mitochondrial protein acetylation, and increased ex vivo acetylation was shown to proportionally decrease mitochondrial respiration rates. Treating T2D rats in vivo with the mitochondrial deacetylase SIRT3 activator honokiol reversed the hyperacetylation of mitochondrial proteins and restored mitochondrial respiration rates to control levels. Using ¹³C-hyperpolarized MRS, respiration with different substrates, and enzyme assays, we localized this improvement to increased glutamate dehydrogenase activity. Finally, honokiol treatment increased ATP and PCr concentrations and increased total ATP synthesis flux in the T2D heart. In conclusion, hyperacetylation drives energetic dysfunction in T2D, and reversing acetylation with the SIRT3 activator honokiol rescued myocardial and mitochondrial energetics in T2D.

Pharmacologically targeting mitochondrial acetylation provides a mechanism to rescue impaired myocardial energy generation in type 2 diabetes.

Mitochondrial Pyruvate Carrier Function in Health and Disease across the Lifespan

As a nodal mediator of pyruvate metabolism, the mitochondrial pyruvate carrier (MPC) plays a pivotal role in many physiological and pathological processes across the human lifespan, from embryonic development to aging-associated neurodegeneration. Emerging research highlights the importance of the MPC in diverse conditions, such as immune cell activation, cancer cell stemness, and dopamine production in Parkinson’s disease models. Whether MPC function ameliorates or contributes to disease is highly specific to tissue and cell type. Cell- and tissue-specific differences in MPC content and activity suggest that MPC function is tightly regulated as a mechanism of metabolic, cellular, and organismal control. Accordingly, recent studies on cancer and diabetes have identified protein–protein interactions, post-translational processes, and transcriptional factors that modulate MPC function. This growing body of literature demonstrates that the MPC and other mitochondrial carriers comprise a versatile and dynamic network undergirding the metabolism of health and disease.

The Multifaceted Pyruvate Metabolism: Role of the Mitochondrial Pyruvate Carrier

Pyruvate, the end product of glycolysis, plays a major role in cell metabolism. Produced in the cytosol, it is oxidized in the mitochondria where it fuels the citric acid cycle and boosts oxidative phosphorylation. Its sole entry point into mitochondria is through the recently identified mitochondrial pyruvate carrier (MPC). In this review, we report the latest findings on the physiology of the MPC and we discuss how a dysfunctional MPC can lead to diverse pathologies, including neurodegenerative diseases, metabolic disorders, and cancer.

A Mitochondrial Approach to Cardiovascular Risk and Disease

BACKGROUND

Cardiovascular diseases (CVDs) are a leading risk factor for mortality worldwide and the number of CVDs victims is predicted to rise through 2030. While several external parameters (genetic, behavioral, environmental and physiological) contribute to cardiovascular morbidity and mortality; intrinsic metabolic and functional determinants such as insulin resistance, hyperglycemia, inflammation, high blood pressure and dyslipidemia are considered to be dominant factors.

METHODS

Pubmed searches were performed using different keywords related with mitochondria and cardiovascular disease and risk. In vitro, animal and human results were extracted from the hits obtained.

RESULTS

High cardiac energy demand is sustained by mitochondrial ATP production, and abnormal mitochondrial function has been associated with several lifestyle- and aging-related pathologies in the developed world such as diabetes, non-alcoholic fatty liver disease (NAFLD) and kidney diseases, that in turn can lead to cardiac injury. In order to delay cardiac mitochondrial dysfunction in the context of cardiovascular risk, regular physical activity has been shown to improve mitochondrial parameters and myocardial tolerance to ischemia-reperfusion (IR). Furthermore, pharmacological interventions can prevent the risk of CVDs. Therapeutic agents that can target mitochondria, decreasing ROS production and improve its function have been intensively researched. One example is the mitochondria-targeted antioxidant MitoQ10, which already showed beneficial effects in hypertensive rat models. Carvedilol or antidiabetic drugs also showed protective effects by preventing cardiac mitochondrial oxidative damage.

CONCLUSION

This review highlights the role of mitochondrial dysfunction in CVDs, also show-casing several approaches that act by improving mitochondrial function in the heart, contributing to decrease some of the risk factors associated with CVDs.

Acetylation in cardiovascular diseases: Molecular mechanisms and clinical implications

Acetylation belongs to a class of post-translational modification (PTM) processes that epigenetically regulate gene expression and gene transcriptional activity. Reversible histone acetylation on lysine residues governs the interactions between DNA and histones to mediate chromatin remodeling and gene transcription. Non-histone protein acetylation complicates cellular function whereas acetylation of key mitochondrial enzymes regulates bioenergetic metabolism. Acetylation and deacetylation of functional proteins are essential to the delicated homeostatic regulation of embryonic development, postnatal maturation, cardiomyocyte differentiation, cardiac remodeling and onset of various cardiovascular diseases including obesity, diabetes mellitus, cardiometabolic diseases, ischemia-reperfusion injury, cardiac remodeling, hypertension, and arrhythmias. Histone acetyltransferase (HATs) and histone deacetylases (HDACs) are essential enzymes mainly responsible for the regulation of lysine acetylation levels, thus providing possible drugable targets for therapeutic interventions in the management of cardiovascular diseases.

20,000 picometers under the OMM: diving into the vastness of mitochondrial metabolite transport

The metabolic compartmentalization enabled by mitochondria is key feature of many cellular processes such as energy conversion to ATP production, redox balance, and the biosynthesis of heme, urea, nucleotides, lipids, and others. For a majority of these functions, metabolites need to be transported across the impermeable inner mitochondrial membrane by dedicated carrier proteins. Here, we examine the substrates, structural features, and human health implications of four mitochondrial metabolite carrier families: the SLC25A family, the mitochondrial ABCB transporters, the mitochondrial pyruvate carrier (MPC), and the sideroflexin proteins.

Can We Prevent Mitochondrial Dysfunction and Diabetic Cardiomyopathy in Type 1 Diabetes Mellitus? Pathophysiology and Treatment Options

Type 1 diabetes mellitus is a disease involving changes to energy metabolism. Chronic hyperglycemia is a major cause of diabetes complications. Hyperglycemia induces mechanisms that generate the excessive production of reactive oxygen species, leading to the development of oxidative stress. Studies with animal models have indicated the involvement of mitochondrial dysfunction in the pathogenesis of diabetic cardiomyopathy. In the current review, we aimed to collect scientific reports linking disorders in mitochondrial functioning with the development of diabetic cardiomyopathy in type 1 diabetes mellitus. We also aimed to present therapeutic approaches counteracting the development of mitochondrial dysfunction and diabetic cardiomyopathy in type 1 diabetes mellitus.

Enhancing cardiac glycolysis causes an increase in PDK4 content in response to short-term high-fat diet

The healthy heart has a dynamic capacity to respond and adapt to changes in nutrient availability. Metabolic inflexibility, such as occurs with diabetes, increases cardiac reliance on fatty acids to meet energetic demands, and this results in deleterious effects, including mitochondrial dysfunction, that contribute to pathophysiology. Enhancing glucose usage may mitigate metabolic inflexibility and be advantageous under such conditions. Here, we sought to identify how mitochondrial function and cardiac metabolism are affected in a transgenic mouse model of enhanced cardiac glycolysis (Glyco^Hi) basally and following a short-term (7-day) high-fat diet (HFD). Glyco^Hi mice constitutively express an active form of phosphofructokinase-2, resulting in elevated levels of the PFK-1 allosteric activator fructose 2,6-bisphosphate. We report that basally Glyco^Hi mitochondria exhibit augmented pyruvate-supported respiration relative to fatty acids. Nevertheless, both WT and Glyco^Hi mitochondria had a similar shift toward increased rates of fatty acid-supported respiration following HFD. Metabolic profiling by GC-MS revealed distinct features based on both genotype and diet, with a unique increase in branched-chain amino acids in the Glyco^Hi HFD group. Targeted quantitative proteomics analysis also supported both genotype- and diet-dependent changes in protein expression and uncovered an enhanced expression of pyruvate dehydrogenase kinase 4 (PDK4) in the Glyco^Hi HFD group. These results support a newly identified mechanism whereby the levels of fructose 2,6-bisphosphate promote mitochondrial PDK4 levels and identify a secondary adaptive response that prevents excessive mitochondrial pyruvate oxidation when glycolysis is sustained after a high-fat dietary challenge.

Glucagon up-regulates hepatic mitochondrial pyruvate carrier 1 through cAMP-responsive element-binding protein; inhibition of hepatic gluconeogenesis by ginsenoside Rb1

BACKGROUND AND PURPOSE

Hepatic mitochondrial pyruvate carrier (MPC) transports pyruvate into mitochondria. This study investigated the involvement of MPC1 in hepatic glucagon response, in order to identify a possible pharmacological intervention.

EXPERIMENTAL APPROACH

The correlation between hepatic glucagon response and MPC1 induction was investigated in fasted mice and primary hepatocytes. The effects of ginsenoside Rb1 on MPC1 function were observed.

KEY RESULTS

Glucagon challenge raised blood glucose with hepatic MPC1 induction, and inhibition of MPC induction coincided with a reduced rise in blood glucose. cAMP-responsive element-binding protein (CREB) knockdown blocked glucagon-induced MPC1 expression, while CREB overexpression increased MPC1 expression. Luciferase reporter, chromatin immunoprecipitation assay, and promoter mutation confirmed that CREB increased MPC1 transcription through gene promoter induction. CREB regulated transcription co-activator 2 nuclear translocation was also required for CREB to promote MPC1 induction. Glucagon shifted mitochondrial pyruvate towards carboxylation for gluconeogenesis via the opposite regulation of pyruvate dehydrogenase and carboxylase with respect to MPC1 induction. MPC1 induction was necessary for glucagon to promote pyruvate-driven hepatic glucose production (HGP), but glucagon failed to influence HGP from other gluconeogenic substrates routed into the tricarboxylic acid cycle, independent of MPC. Rb1 blocked cAMP signalling by inhibiting AC activity and deactivated CREB by dephosphorylation, possibly contributing to inhibiting MPC1 induction to reduce HGP.

CONCLUSIONS AND IMPLICATIONS

CREB transcriptionally up-regulates MPC1 to provide pyruvate for gluconeogenesis. Rb1 reduced cAMP formation which consequently reduced CREB-mediated MPC1 induction and thereby might contribute to limiting pyruvate-dependent HGP. These results suggest a therapeutic strategy to reduce hyperglycaemia in diabetes.

The yeast mitochondrial pyruvate carrier is a hetero-dimer in its functional state

The mitochondrial pyruvate carrier (MPC) is critical for cellular homeostasis, as it is required in central metabolism for transporting pyruvate from the cytosol into the mitochondrial matrix. MPC has been implicated in many diseases and is being investigated as a drug target. A few years ago, small membrane proteins, called MPC1 and MPC2 in mammals and Mpc1, Mpc2 and Mpc3 in yeast, were proposed to form large protein complexes responsible for this function. However, the MPC complexes have never been isolated and their composition, oligomeric state and functional properties have not been defined. Here, we identify the functional unit of MPC from Saccharomyces cerevisiae In contrast to earlier hypotheses, we demonstrate that MPC is a hetero-dimer, not a multimeric complex. When not engaged in hetero-dimers, the yeast Mpc proteins can also form homo-dimers that are, however, inactive. We show that the earlier described substrate transport properties and inhibitor profiles are embodied by the hetero-dimer. This work provides a foundation for elucidating the structure of the functional complex and the mechanism of substrate transport and inhibition.

Loss of GCN5L1 in cardiac cells limits mitochondrial respiratory capacity under hyperglycemic conditions

The mitochondrial acetyltransferase-related protein GCN5L1 controls the activity of fuel substrate metabolism enzymes in several tissues. While previous studies have demonstrated that GCN5L1 regulates fatty acid oxidation in the prediabetic heart, our understanding of its role in overt diabetes is not fully developed. In this study, we examined how hyperglycemic conditions regulate GCN5L1 expression in cardiac tissues, and modeled the subsequent effect in cardiac cells in vitro. We show that GCN5L1 abundance is significantly reduced under diabetic conditions in vivo, which correlated with reduced acetylation of known GCN5L1 fuel metabolism substrate enzymes. Treatment of cardiac cells with high glucose reduced Gcn5l1 expression in vitro, while expression of the counteracting deacetylase enzyme, Sirt3, was unchanged. Finally, we show that genetic depletion of GCN5L1 in H9c2 cells leads to reduced mitochondrial oxidative capacity under high glucose conditions. These data suggest that GCN5L1 expression is highly responsive to changes in cellular glucose levels, and that loss of GCN5L1 activity under hyperglycemic conditions impairs cardiac energy metabolism.

miR-21-5p regulates mitochondrial respiration and lipid content in H9C2 cells

Cardiovascular-related pathologies are the single leading cause of death in patients with chronic kidney disease (CKD). Previously, we found that a 5/6th nephrectomy model of CKD leads to an upregulation of miR-21-5p in the left ventricle, targeting peroxisome proliferator-activated receptor-α and altering the expression of numerous transcripts involved with fatty acid oxidation and glycolysis. In the present study, we evaluated the potential for knockdown or overexpression of miR-21-5p to regulate lipid content, lipid peroxidation, and mitochondrial respiration in H9C2 cells. Cells were transfected with anti-miR-21-5p (40 nM), pre-miR-21-5p (20 nM), or the appropriate scrambled oligonucleotide controls before lipid treatment in culture or as part of the Agilent Seahorse XF fatty acid oxidation assay. Overexpression of miR-21-5p attenuated the lipid-induced increase in cellular lipid content, whereas suppression of miR-21-5p augmented it. The abundance of malondialdehyde, a product of lipid peroxidation, was significantly increased with lipid treatment in control cells but attenuated in pre-miR-21-5p-transfected cells. This suggests that miR-21-5p reduces oxidative stress. The cellular oxygen consumption rate (OCR) was increased in both pre-miR-21-5p- and anti-miR-21-5p-transfected cells. Levels of intracellular ATP were significantly higher in anti-mR-21-5p-transfected cells. Pre-miR-21-5p blocked additional increases in OCR in response to etomoxir and palmitic acid. Conversely, anti-miR-21-5p-transfected cells exhibited reduced OCR with both etomoxir and palmitic acid, and the glycolytic capacity was concomitantly reduced. Together, these results indicate that overexpression of miR-21-5p attenuates both lipid content and lipid peroxidation in H9C2 cells. This likely occurs by reducing cellular lipid uptake and utilization, shifting cellular metabolism toward reliance on the glycolytic pathway. NEW & NOTEWORTHY Both overexpression and suppression of miR-21-5p augment basal and maximal mitochondrial respiration. Our data suggest that reliance on glycolytic and fatty acid oxidation pathways can be modulated by the abundance of miR-21-5p within the cell. miR-21-5p regulation of mitochondrial respiration can be modulated by extracellular lipids.

Berberine Reduces Pyruvate-driven Hepatic Glucose Production by Limiting Mitochondrial Import of Pyruvate through Mitochondrial Pyruvate Carrier 1

BACKGROUND

Mitochondrial pyruvate import via mitochondrial pyruvate carrier (MPC) is a central step in hepatic gluconeogenesis. Berberine inhibits hepatic gluconeogenesis, but the mechanism is incompletely understood. This study aims to investigate whether berberine could reduce excessive hepatic glucose production (HGP) by limiting mitochondrial import of pyruvate through MPC1.

METHODS

High-fat diet (HFD) feeding augmented HGP. The effects of berberine on hepatic fatty acid oxidation, sirtuin3 (SIRT3) induction and mitochondrial pyruvate carrier 1 (MPC1) function were examined.

FINDINGS

HFD feeding increased hepatic acetyl coenzyme A (acetyl CoA) accumulation with impaired pyruvate dehydrogenase (PDH) activity and increased pyruvate carboxylase (PC) induction. Berberine reduced acetyl CoA accumulation by limiting fatty acid oxidation and prevented mitochondrial pyruvate shift from oxidation to gluconeogenesis through carboxylation. Upon pyruvate response, SIRT3 binded to MPC1 and stabilized MPC1 protein via deacetylation modification, facilitating mitochondrial import of pyruvate. Berberine preserved the acetylation of MPC1 by suppression of SIRT3 induction and impaired MPC1 protein stabilization via protein degradation, resultantly limiting mitochondrial pyruvate supply for gluconeogenesis.

INTERPRETATION

Berberine reduced acetyl CoA contents by limiting fatty acid oxidation and increased MPC1 degradation via preserving acetylation, thereby restraining HGP by blocking mitochondrial import of pyruvate. These findings suggest that limitation of mitochondrial pyruvate import might be a therapeutic strategy to prevent excessive hepatic glucose production.

Human mitochondrial pyruvate carrier 2 as an autonomous membrane transporter

The active transport of glycolytic pyruvate across the inner mitochondrial membrane is thought to involve two mitochondrial pyruvate carrier subunits, MPC1 and MPC2, assembled as a 150 kDa heterotypic oligomer. Here, the recombinant production of human MPC through a co-expression strategy is first described; however, substantial complex formation was not observed, and predominantly individual subunits were purified. In contrast to MPC1, which co-purifies with a host chaperone, we demonstrated that MPC2 homo-oligomers promote efficient pyruvate transport into proteoliposomes. The derived functional requirements and kinetic features of MPC2 resemble those previously demonstrated for MPC in the literature. Distinctly, chemical inhibition of transport is observed only for a thiazolidinedione derivative. The autonomous transport role for MPC2 is validated in cells when the ectopic expression of human MPC2 in yeast lacking endogenous MPC stimulated growth and increased oxygen consumption. Multiple oligomeric species of MPC2 across mitochondrial isolates, purified protein and artificial lipid bilayers suggest functional high-order complexes. Significant changes in the secondary structure content of MPC2, as probed by synchrotron radiation circular dichroism, further supports the interaction between the protein and ligands. Our results provide the initial framework for the independent role of MPC2 in homeostasis and diseases related to dysregulated pyruvate metabolism.

SIRT3: A New Regulator of Cardiovascular Diseases

Cardiovascular diseases (CVDs) are the leading causes of death worldwide, and defects in mitochondrial function contribute largely to the occurrence of CVDs. Recent studies suggest that sirtuin 3 (SIRT3), the mitochondrial NAD⁺-dependent deacetylase, may regulate mitochondrial function and biosynthetic pathways such as glucose and fatty acid metabolism and the tricarboxylic acid (TCA) cycle, oxidative stress, and apoptosis by reversible protein lysine deacetylation. SIRT3 regulates glucose and lipid metabolism and maintains myocardial ATP levels, which protects the heart from metabolic disturbances. SIRT3 can also protect cardiomyocytes from oxidative stress-mediated cell damage and block the development of cardiac hypertrophy. Recent reports show that SIRT3 is involved in the protection of several heart diseases. This review discusses the progress in SIRT3-related research and the role of SIRT3 in the prevention and treatment of CVDs.

Cardiac Insulin Signaling Regulates Glycolysis Through Phosphofructokinase 2 Content and Activity

BACKGROUND

The healthy heart has a dynamic capacity to respond and adapt to changes in nutrient availability. Diabetes mellitus disrupts this metabolic flexibility and promotes cardiomyopathy through mechanisms that are not completely understood. Phosphofructokinase 2 (PFK-2) is a primary regulator of cardiac glycolysis and substrate selection, yet its regulation under normal and pathological conditions is unknown. This study was undertaken to determine how changes in insulin signaling affect PFK-2 content, activity, and cardiac metabolism.

METHODS AND RESULTS

Streptozotocin-induced diabetes mellitus, high-fat diet feeding, and fasted mice were used to identify how decreased insulin signaling affects PFK-2 and cardiac metabolism. Primary adult cardiomyocytes were used to define the mechanisms that regulate PFK-2 degradation. Both type 1 diabetes mellitus and a high-fat diet induced a significant decrease in cardiac PFK-2 protein content without affecting its transcript levels. Overnight fasting also induced a decrease in PFK-2, suggesting it is rapidly degraded in the absence of insulin signaling. An unbiased metabolomic study demonstrated that decreased PFK-2 in fasted animals is accompanied by an increase in glycolytic intermediates upstream of phosphofructokianse-1, whereas those downstream are diminished. Mechanistic studies using cardiomyocytes showed that, in the absence of insulin signaling, PFK-2 is rapidly degraded via both proteasomal- and chaperone-mediated autophagy.

CONCLUSIONS

The loss of PFK-2 content as a result of reduced insulin signaling impairs the capacity to dynamically regulate glycolysis and elevates the levels of early glycolytic intermediates. Although this may be beneficial in the fasted state to conserve systemic glucose, it represents a pathological impairment in diabetes mellitus.

Lipid (per) oxidation in mitochondria: an emerging target in the ageing process?

Lipids are essential for physiological processes such as maintaining membrane integrity, providing a source of energy and acting as signalling molecules to control processes including cell proliferation, metabolism, inflammation and apoptosis. Disruption of lipid homeostasis can promote pathological changes that contribute towards biological ageing and age-related diseases. Several age-related diseases have been associated with altered lipid metabolism and an elevation in highly damaging lipid peroxidation products; the latter has been ascribed, at least in part, to mitochondrial dysfunction and elevated ROS formation. In addition, senescent cells, which are known to contribute significantly to age-related pathologies, are also associated with impaired mitochondrial function and changes in lipid metabolism. Therapeutic targeting of dysfunctional mitochondrial and pathological lipid metabolism is an emerging strategy for alleviating their negative impact during ageing and the progression to age-related diseases. Such therapies could include the use of drugs that prevent mitochondrial uncoupling, inhibit inflammatory lipid synthesis, modulate lipid transport or storage, reduce mitochondrial oxidative stress and eliminate senescent cells from tissues. In this review, we provide an overview of lipid structure and function, with emphasis on mitochondrial lipids and their potential for therapeutic targeting during ageing and age-related disease.

Overexpression of MPC1 inhibits the proliferation, migration, invasion, and stem cell-like properties of gastric cancer cells

Invasion and metastasis are major malignant characteristics of human gastric cancer (GC), but the molecular mechanisms underlying the invasion and metastasis of GC cells remain elusive. MPC1, a key factor that controls pyruvate transportation through the inner mitochondrial membrane, was reported to be downregulated and correlated with poor prognosis in several cancers. However, the effects of MPC1 on human GC have not been illustrated. In this study, we investigated the potential role of MPC1 in the proliferation, migration, invasion, and stem cell-like properties of human GC cells and evaluated its prognostic significance for patients with GC. We found that MPC1 protein and mRNA levels were significantly decreased in GC tissues and cell lines. Low MPC1 expression was associated with tumor T stage, N stage, and advanced tumor node metastasis stage. Decreased MPC1 expression was an independent prognostic marker and correlated with poor overall survival of patients with GC. Furthermore, overexpression of MPC1 inhibited the proliferation, migration, invasion, and stem cell-like properties of GC cells. These findings suggest that MPC1 may be a novel prognostic marker and a potential therapeutic target in human GC.