Fifty years of the mitochondrial pyruvate carrier: New insights into its structure, function, and inhibition

Progress in Lactate Metabolism and Its Regulation via Small Molecule Drugs

Lactate, once viewed as a byproduct of glycolysis and a metabolic "waste", is now recognized as an energy-providing substrate and a signaling molecule that modulates cellular functions under pathological conditions. The discovery of histone lactylation in 2019 marked a paradigm shift, with subsequent studies revealing that lactate can undergo lactylation with both histone and non-histone proteins, implicating it in the pathogenesis of various diseases, including cancer, liver fibrosis, sepsis, ischemic stroke, and acute kidney injury. Aberrant lactate metabolism is associated with disease onset, and its levels can predict disease outcomes. Targeting lactate production, transport, and lactylation may offer therapeutic potential for multiple diseases, yet a systematic summary of the small molecules modulating lactate and its metabolism in various diseases is lacking. This review outlines the sources and clearance of lactate, as well as its roles in cancer, liver fibrosis, sepsis, ischemic stroke, myocardial infarction, and acute kidney injury, and summarizes the effects of small molecules on lactate regulation. It aims to provide a reference and direction for future research.

Lactate-mediated lactylation in human health and diseases: Progress and remaining challenges

BACKGROUND

Lactate was once considered as metabolic waste for a long time. In 2019, Professor Zhao Yingming's team from the University of Chicago found that lactate could also be used as a substrate to induce histone lactylation and regulate gene expression. Since then, researchers have discovered that lactate-mediated lactylation play important regulatory roles in various physiological and pathological processes.

AIM OF REVIEW

In this review, we aim to discuss the roles and mechanisms of lactylation in human health and diseases, as well as the effects of lactylation on proteins and metabolic modulators targeting lactylation.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In this work, we emphasize the crucial regulatory roles of lactylation in the development of numerous physiological and pathological processes. Of relevance, we discuss the current issues and challenges pertaining to lactylation. This review provides directions and a theoretical basis for future research and clinical translation of lactylation.

Design, synthesis and biological evaluation of novel cyano-cinnamate derivatives as mitochondrial pyruvate carrier inhibitors

Mitochondrial pyruvate carrier (MPC) inhibitors promote the development of hair follicle stem cells without affecting normal cells, which is promising for the treatment of hair loss. Herein, a series of cyano-cinnamate derivatives of UK-5099 were designed and synthesized. All these new compounds have been tested for their ability to promote cellular lactate production in vitro. Compound 4i (LA content:0.322 μmol/106cell) showed better cellular lactate production activity than UK-5099 (LA content:0.185 μmol/106cell). Further compound 4i was also tested on shaved mice by topical treatment and promoted obvious hair growth on mice.

Direct mitochondrial import of lactate supports resilient carbohydrate oxidation

Lactate is the highest turnover circulating metabolite in mammals. While traditionally viewed as a waste product, lactate is an important energy source for many organs, but first must be oxidized to pyruvate for entry into the tricarboxylic acid cycle (TCA cycle). This reaction is thought to occur in the cytosol, with pyruvate subsequently transported into mitochondria via the mitochondrial pyruvate carrier (MPC). Using 13C stable isotope tracing, we demonstrated that lactate is oxidized in the myocardial tissue of mice even when the MPC is genetically deleted. This MPC-independent lactate import and mitochondrial oxidation is dependent upon the monocarboxylate transporter 1 (MCT1/Slc16a1). Mitochondria isolated from the myocardium without MCT1 exhibit a specific defect in mitochondrial lactate, but not pyruvate, metabolism. The import and subsequent mitochondrial oxidation of lactate by mitochondrial lactate dehydrogenase (LDH) acts as an electron shuttle, generating sufficient NADH to support respiration even when the TCA cycle is disrupted. In response to diverse cardiac insults, animals with hearts lacking MCT1 undergo rapid progression to heart failure with reduced ejection fraction. Thus, the mitochondrial import and oxidation of lactate enables carbohydrate entry into the TCA cycle to sustain cardiac energetics and maintain myocardial structure and function under stress conditions.

Targeting Lactate: An Emerging Strategy for Macrophage Regulation in Chronic Inflammation and Cancer

Lactate accumulation and macrophage infiltration are pivotal features of both chronic inflammation and cancer. Lactate, once regarded merely as an aftereffect of glucose metabolism, is now gaining recognition for its burgeoning spectrum of biological roles and immunomodulatory significance. Recent studies have evidenced that macrophages display divergent immunophenotypes in different diseases, which play a pivotal role in disease management by modulating macrophage polarization within the disease microenvironment. The specific polarization patterns of macrophages in a high-lactate environment and their contribution to the progression of chronic inflammation and cancer remain contentious. This review presents current evidence on the crosstalk of lactate and macrophage in chronic inflammation and cancer. Additionally, we provide an in-depth exploration of the pivotal yet enigmatic mechanisms through which lactate orchestrates disease pathogenesis, thereby offering novel perspectives to the development of targeted therapeutic interventions for chronic inflammation and cancer.

Targeting mitochondrial homeostasis in the treatment of non-alcoholic fatty liver disease: a review

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide, and its prevalence is rapidly increasing. Antioxidants, lipid-lowering medications, and lifestyle interventions are the most commonly used treatment options for NAFLD, but their efficacy in inhibiting steatosis progression is limited and their long-term ineffectiveness and adverse effects have been widely reported. Therefore, it is important to gain a deeper understanding of the pathogenesis of NAFLD and to identify more effective therapeutic approaches. Mitochondrial homeostasis governs cellular redox biology, lipid metabolism, and cell death, all of which are crucial to control hepatic function. Recent findings have indicated that disruption of mitochondrial homeostasis occurs in the early stage of NAFLD and mitochondrial dysfunction reinforces disease progression. In this review, we summarize the physical roles of the mitochondria and describe their response and dysfunction in the context of NAFLD. We also discuss the drug targets associated with the mitochondria that are currently in the clinical trial phase of exploration. From our findings, we hope that the mitochondria may be a promising therapeutic target for the treatment of NAFLD.

UK5099 Inhibits the NLRP3 Inflammasome Independently of its Long-Established Target Mitochondrial Pyruvate Carrier

Targeting NLRP3 inflammasome has been recognized as a promising therapeutic strategy for the treatment of numerous common diseases. UK5099, a long-established inhibitor of mitochondrial pyruvate carrier (MPC), is previously found to inhibit macrophage inflammatory responses independent of MPC expression. However, the mechanisms by which UK5099 inhibit inflammatory responses remain unclear. Here, it is shown that UK5099 is a potent inhibitor of the NLRP3 inflammasome in both mouse and human primary macrophages. UK5099 selectively suppresses the activation of the NLRP3 but not the NLRC4 or AIM2 inflammasomes. Of note, UK5099 retains activities on NLRP3 in macrophages devoid of MPC expression, indicating this inhibitory effect is MPC-independent. Mechanistically, UK5099 abrogates mitochondria-NLRP3 interaction and in turn inhibits the assembly of the NLRP3 inflammasome. Further, a single dose of UK5099 persistently reduces IL-1β production in an endotoxemia mouse model. Importantly, structure modification reveals that the inhibitory activities of UK5099 on NLRP3 are unrelated to the existence of the activated double bond within the UK5099 molecule. Thus, this study uncovers a previously unknown molecular target for UK5099, which not only offers a new candidate for the treatment of NLRP3-driven diseases but also confounds its use as an MPC inhibitor in immunometabolism studies.

A Systematic Review of Proteomics in Obesity: Unpacking the Molecular Puzzle

PURPOSE OF REVIEW

The present study aims to review the existing literature to identify pathophysiological proteins in obesity by conducting a systematic review of proteomics studies. Proteomics may reveal the mechanisms of obesity development and clarify the links between obesity and related diseases, improving our comprehension of obesity and its clinical implications.

RECENT FINDINGS

Most of the molecular events implicated in obesity development remain incomplete. Proteomics stands as a powerful tool for elucidating the intricate interactions among proteins in the context of obesity. This methodology has the potential to identify proteins involved in pathological processes and to evaluate changes in protein abundance during obesity development, contributing to the identification of early disease predisposition, monitoring the effectiveness of interventions and improving disease management overall. Despite many non-targeted proteomic studies exploring obesity, a comprehensive and up-to-date systematic review of the molecular events implicated in obesity development is lacking. The lack of such a review presents a significant challenge for researchers trying to interpret the existing literature. This systematic review was conducted following the PRISMA guidelines and included sixteen human proteomic studies, each of which delineated proteins exhibiting significant alterations in obesity. A total of 41 proteins were reported to be altered in obesity by at least two or more studies. These proteins were involved in metabolic pathways, oxidative stress responses, inflammatory processes, protein folding, coagulation, as well as structure/cytoskeleton. Many of the identified proteomic biomarkers of obesity have also been reported to be dysregulated in obesity-related disease. Among them, seven proteins, which belong to metabolic pathways (aldehyde dehydrogenase and apolipoprotein A1), the chaperone family (albumin, heat shock protein beta 1, protein disulfide-isomerase A3) and oxidative stress and inflammation proteins (catalase and complement C3), could potentially serve as biomarkers for the progression of obesity and the development of comorbidities, contributing to personalized medicine in the field of obesity. Our systematic review in proteomics represents a substantial step forward in unravelling the complexities of protein alterations associated with obesity. It provides valuable insights into the pathophysiological mechanisms underlying obesity, thereby opening avenues for the discovery of potential biomarkers and the development of personalized medicine in obesity.

The Role of Mitochondrial Pyruvate Carrier in Neurological Disorders

The mitochondrial pyruvate carrier (MPC) is a specific protein complex located in the inner mitochondrial membrane. Comprising a heterodimer of two homodimeric membrane proteins, mitochondrial pyruvate carrier 1 and mitochondrial pyruvate carrier 2, MPC connects cytoplasmic metabolism to mitochondrial metabolism by transferring pyruvate from the cytoplasm to the mitochondria. The nervous system requires substantial energy to maintain its function, and the mitochondrial energy supply is closely linked to neurological function. Mitochondrial dysfunction can induce or exacerbate intracerebral pathologies. MPC influences mitochondrial function due to its specific role as a pyruvate transporter. However, recent studies on MPC and mitochondrial dysfunction in neurological disorders have yielded controversial results, and the underlying mechanisms remain unclear. In this brief review, we provide an overview of the structure and function of MPC. We further discuss the potential mechanisms and feasibility of targeting MPC in treating Parkinson's disease, Alzheimer's disease, and cerebral ischemia/hypoxia injury. This review aims to offer insights into MPC as a target for clinical treatment.

Computational structural prediction and chemical inhibition of the human mitochondrial pyruvate carrier protein heterodimer complex

The mitochondrial pyruvate carrier (MPC) plays a role in numerous diseases including neurodegeneration, metabolically dependent cancers, and the development of insulin resistance. Several previous studies in genetic mouse models or with existing inhibitors suggest that inhibition of the MPC could be used as a viable therapeutic strategy in these diseases. However, the MPC's structure is unknown, making it difficult to screen for and develop therapeutically viable inhibitors. Currently known MPC inhibitors would make for poor drugs due to their poor pharmacokinetic properties, or in the case of the thiazolidinediones (TZDs), off-target specificity for peroxisome-proliferator activated receptor gamma (PPARγ) leads to unwanted side effects. In this study, we develop several structural models for the MPC heterodimer complex and investigate the chemical interactions required for the binding of these known inhibitors to MPC and PPARγ. Based on these models, the MPC most likely takes on outward-facing (OF) and inward-facing (IF) conformations during pyruvate transport, and inhibitors likely plug the carrier to inhibit pyruvate transport. Although some chemical interactions are similar between MPC and PPARγ binding, there is likely enough difference to reduce PPARγ specificity for future development of novel, more specific MPC inhibitors.

Unlocking mitochondrial drug targets: The importance of mitochondrial transport proteins

A disturbed mitochondrial function contributes to the pathology of many common diseases. These organelles are therefore important therapeutic targets. On the contrary, many adverse effects of drugs can be explained by a mitochondrial off-target effect, in particular, due to an interaction with carrier proteins in the inner membrane. Yet this class of transport proteins remains underappreciated and understudied. The aim of this review is to provide a deeper understanding of the role of mitochondrial carriers in health and disease and their significance as drug targets. We present literature-based evidence that mitochondrial carrier proteins are associated with prevalent diseases and emphasize their potential as drug (off-)target sites by summarizing known mitochondrial drug-transporter interactions. Studying these carriers will enhance our knowledge of mitochondrial drug on- and off-targets and provide opportunities to further improve the efficacy and safety of drugs.

Membrane transporters in cell physiology, cancer metabolism and drug response

By controlling the passage of small molecules across lipid bilayers, membrane transporters influence not only the uptake and efflux of nutrients, but also the metabolic state of the cell. With more than 450 members, the Solute Carriers (SLCs) are the largest transporter super-family, clustering into families with different substrate specificities and regulatory properties. Cells of different types are, therefore, able to tailor their transporter expression signatures depending on their metabolic requirements, and the physiological importance of these proteins is illustrated by their mis-regulation in a number of disease states. In cancer, transporter expression is heterogeneous, and the SLC family has been shown to facilitate the accumulation of biomass, influence redox homeostasis, and also mediate metabolic crosstalk with other cell types within the tumour microenvironment. This Review explores the roles of membrane transporters in physiological and malignant settings, and how these roles can affect drug response, through either indirect modulation of sensitivity or the direct transport of small-molecule therapeutic compounds into cells.