MCT1 confirmed in rat striated muscle mitochondria

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.

Lactate metabolism in neurodegenerative diseases

Lactate, a byproduct of glycolysis, was thought to be a metabolic waste until the discovery of the Warburg effect. Lactate not only functions as a metabolic substrate to provide energy but can also function as a signaling molecule to modulate cellular functions under pathophysiological conditions. The Astrocyte-Neuron Lactate Shuttle has clarified that lactate plays a pivotal role in the central nervous system. Moreover, protein lactylation highlights the novel role of lactate in regulating transcription, cellular functions, and disease development. This review summarizes the recent advances in lactate metabolism and its role in neurodegenerative diseases, thus providing optimal perspectives for future research.

Lactate as a myokine and exerkine: drivers and signals of physiology and metabolism

No longer viewed as a metabolic waste product and cause of muscle fatigue, a contemporary view incorporates the roles of lactate in metabolism, sensing and signaling in normal as well as pathophysiological conditions. Lactate exists in millimolar concentrations in muscle, blood, and other tissues and can rise more than an order of magnitude as the result of increased production and clearance limitations. Lactate exerts its powerful driver-like influence by mass action, redox change, allosteric binding, and other mechanisms described in this article. Depending on the condition, such as during rest and exercise, following carbohydrate nutrition, injury, or pathology, lactate can serve as a myokine or exerkine with autocrine-, paracrine-, and endocrine-like functions that have important basic and translational implications. For instance, lactate signaling is: involved in reproductive biology, fueling the heart, muscle adaptation, and brain executive function, growth and development, and a treatment for inflammatory conditions. Lactate also works with many other mechanisms and factors in controlling cardiac output and pulmonary ventilation during exercise. Ironically, lactate can be disruptive of normal processes such as insulin secretion when insertion of lactate transporters into pancreatic β-cell membranes is not suppressed, and in carcinogenesis when factors that suppress carcinogenesis are inhibited, whereas factors that promote carcinogenesis are upregulated. Lactate signaling is important in areas of intermediary metabolism, redox biology, mitochondrial biogenesis, neurobiology, gut physiology, appetite regulation, nutrition, and overall health and vigor. The various roles of lactate as a myokine and exerkine are reviewed.NEW & NOTEWORTHY Lactate sensing and signaling is a relatively new and rapidly changing field. As a physiological signal lactate works both independently and in concert with other signals. Lactate operates via covalent binding and canonical signaling, redox change, and lactylation of DNA. Lactate can also serve as an element of feedback loops in cardiopulmonary regulation. From conception through aging lactate is not the only a myokine or exerkine, but it certainly deserves consideration as a physiological signal.

The Hepatic Mitochondrial Pyruvate Carrier as a Regulator of Systemic Metabolism and a Therapeutic Target for Treating Metabolic Disease

Pyruvate sits at an important metabolic crossroads of intermediary metabolism. As a product of glycolysis in the cytosol, it must be transported into the mitochondrial matrix for the energy stored in this nutrient to be fully harnessed to generate ATP or to become the building block of new biomolecules. Given the requirement for mitochondrial import, it is not surprising that the mitochondrial pyruvate carrier (MPC) has emerged as a target for therapeutic intervention in a variety of diseases characterized by altered mitochondrial and intermediary metabolism. In this review, we focus on the role of the MPC and related metabolic pathways in the liver in regulating hepatic and systemic energy metabolism and summarize the current state of targeting this pathway to treat diseases of the liver. Available evidence suggests that inhibiting the MPC in hepatocytes and other cells of the liver produces a variety of beneficial effects for treating type 2 diabetes and nonalcoholic steatohepatitis. We also highlight areas where our understanding is incomplete regarding the pleiotropic effects of MPC inhibition.

Revisiting the Warburg Effect with Focus on Lactate

Rewired metabolism is acknowledged as one of the drivers of tumor growth. As a result, aerobic glycolysis, or the Warburg effect, is a feature of many cancers. Increased glucose uptake and glycolysis provide intermediates for anabolic reactions necessary for cancer cell proliferation while contributing sufficient energy. However, the accompanying increased lactate production, seemingly wasting glucose carbon, was originally explained only by the need to regenerate NAD⁺ for successive rounds of glycolysis by the lactate dehydrogenase (LDH) reaction in the cytosol. After the discovery of a mitochondrial LDH isoform, lactate oxidation entered the picture, and lactate was recognized as an important oxidative fuel. It has also been revealed that lactate serves a variety of signaling functions and helps cells adapt to the new environment. Here, we discuss recent findings on lactate metabolism and signaling in cancer while attempting to explain why the Warburg effect is adopted by cancer cells.

Inhibition of monocarboxylate transporters (MCT) 1 and 4 reduces exercise capacity in mice

The concept of lactate shuttle is widely accepted in exercise physiology. Lactate transport is mediated by monocarboxylate transporters (MCT), which enable cells to take up and release lactate. However, the role of lactate during exercise has not yet been fully elucidated. In this study, we investigated the effects of lactate transport inhibition on exercise capacity and metabolism in mice. Here, we demonstrated that MCT1 inhibition by α-cyano-4-hydroxycinnamate administration (4-CIN, 200 mg/g of body weight) reduced the treadmill running duration at 20 m/min. The administration of 4-CIN increased the blood lactate concentration immediately after exercise. With matched exercise duration, the muscle lactate concentration was higher while muscle glycogen content was lower in 4-CIN-administered mice. Further, we showed that MCT4 inhibition by bindarit administration (50 mg/kg of body weight) reduced the treadmill running duration at 40 m/min. Bindarit administration increased the muscle lactate but did not alter the blood lactate and glucose concentrations, as well as muscle glycogen content, immediately after exercise. A negative correlation was observed between exercise duration at 40 m/min and muscle lactate concentration immediately after exercise. Our results suggest that lactate transport via MCT1 and MCT4 plays a pivotal role in sustaining exercise.

Tracing the lactate shuttle to the mitochondrial reticulum

Isotope tracer infusion studies employing lactate, glucose, glycerol, and fatty acid isotope tracers were central to the deduction and demonstration of the Lactate Shuttle at the whole-body level. In concert with the ability to perform tissue metabolite concentration measurements, as well as determinations of unidirectional and net metabolite exchanges by means of arterial-venous difference (a-v) and blood flow measurements across tissue beds including skeletal muscle, the heart and the brain, lactate shuttling within organs and tissues was made evident. From an extensive body of work on men and women, resting or exercising, before or after endurance training, at sea level or high altitude, we now know that Organ-Organ, Cell-Cell, and Intracellular Lactate Shuttles operate continuously. By means of lactate shuttling, fuel-energy substrates can be exchanged between producer (driver) cells, such as those in skeletal muscle, and consumer (recipient) cells, such as those in the brain, heart, muscle, liver and kidneys. Within tissues, lactate can be exchanged between white and red fibers within a muscle bed and between astrocytes and neurons in the brain. Within cells, lactate can be exchanged between the cytosol and mitochondria and between the cytosol and peroxisomes. Lactate shuttling between driver and recipient cells depends on concentration gradients created by the mitochondrial respiratory apparatus in recipient cells for oxidative disposal of lactate.

Lactate Is Answerable for Brain Function and Treating Brain Diseases: Energy Substrates and Signal Molecule

Research to date has provided novel insights into lactate's positive role in multiple brain functions and several brain diseases. Although notable controversies and discrepancies remain, the neurobiological role and the metabolic mechanisms of brain lactate have now been described. A theoretical framework on the relevance between lactate and brain function and brain diseases is presented. This review begins with the source and route of lactate formation in the brain and food; goes on to uncover the regulatory effect of lactate on brain function; and progresses to gathering the application and concentration variation of lactate in several brain diseases (diabetic encephalopathy, Alzheimer's disease, stroke, traumatic brain injury, and epilepsy) treatment. Finally, the dual role of lactate in the brain is discussed. This review highlights the biological effect of lactate, especially L-lactate, in brain function and disease studies and amplifies our understanding of past research.

Role of monocarboxylate transporters in head and neck squamous cell carcinoma

Head and Neck tumors are metabolically highly altered solid tumors. Head and Neck cancer cells may utilise different metabolic pathways for energy production. Whereas, glycolysis is the major source coupled with oxidative phosphorylation in a metabolic symbiosis manner that results in the proliferation and metastasis in Head and Neck Cancer. The monocarboxylate transporters (MCTs) constitute a family of 14 members among which MCT1-4 are responsible for transporting monocarboxylates such as l-lactate and pyruvate, and ketone bodies across the plasma membrane. Additionally, MCTs mediate absorption and distribution of monocarboxylates across the cell membrane. Head and Neck cancer cells are highly glycolytic in nature and generate significant amount of lactic acid in the extracellular environment. In such condition, MCTs play a critical role in the regulation of pH, and lactate shuttle maintenance. The intracellular lactate accumulation is harmful for the cells since it drastically lowers the intracellular pH. MCTs facilitate the export of lactate out of the cell. The lactate export mediated by MCTs is crucial for the cancer cells survival. Therefore, targeting MCTs is important and could be a potential therapeutic approach to control growth of the tumor.

Quantitative Assessment of Blood Lactate in Shock: Measure of Hypoxia or Beneficial Energy Source

Blood lactate concentration predicts mortality in critically ill patients and is clinically used in the diagnosis, grading of severity, and monitoring response to therapy of septic shock. This paper summarizes available quantitative data to provide the first comprehensive description and critique of the accepted concepts of the physiology of lactate in health and shock, with particular emphasis on the controversy of whether lactate release is simply a manifestation of tissue hypoxia versus a purposeful transfer ("shuttle") of lactate between tissues. Basic issues discussed include (1) effect of nonproductive lactate-pyruvate exchange that artifactually enhances flux measurements obtained with labeled lactate, (2) heterogeneous tissue oxygen partial pressure (Krogh model) and potential for unrecognized hypoxia that exists in all tissues, and (3) pathophysiology that distinguishes septic from other forms of shock. Our analysis suggests that due to exchange artifacts, the turnover rate of lactate and the lactate clearance are only about 60% of the values of 1.05 mmol/min/70 kg and 1.5 L/min/70 kg, respectively, determined from the standard tracer kinetics. Lactate turnover reflects lactate release primarily from muscle, gut, adipose, and erythrocytes and uptake by the liver and kidney, primarily for the purpose of energy production (TCA cycle) while the remainder is used for gluconeogenesis (Cori cycle). The well-studied physiology of exercise-induced hyperlactatemia demonstrates massive release from the contracting muscle accompanied by an increased lactate clearance that may occur in recovering nonexercising muscle as well as the liver. The very limited data on lactate kinetics in shock patients suggests that hyperlactatemia reflects both decreased clearance and increased production, possibly primarily in the gut. Our analysis of available data in health and shock suggests that the conventional concept of tissue hypoxia can account for most blood lactate findings and there is no need to implicate a purposeful production of lactate for export to other organs.

The tortuous path of lactate shuttle discovery: From cinders and boards to the lab and ICU

Once thought to be a waste product of oxygen limited (anaerobic) metabolism, lactate is now known to form continuously under fully oxygenated (aerobic) conditions. Lactate shuttling between producer (driver) and consumer cells fulfills at least 3 purposes; lactate is: (1) a major energy source, (2) the major gluconeogenic precursor, and (3) a signaling molecule. The Lactate Shuttle theory is applicable to diverse fields such as sports nutrition and hydration, resuscitation from acidosis and Dengue, treatment of traumatic brain injury, maintenance of glycemia, reduction of inflammation, cardiac support in heart failure and following a myocardial infarction, and to improve cognition. Yet, dysregulated lactate shuttling disrupts metabolic flexibility, and worse, supports oncogenesis. Lactate production in cancer (the Warburg effect) is involved in all main sequela for carcinogenesis: angiogenesis, immune escape, cell migration, metastasis, and self-sufficient metabolism. The history of the tortuous path of discovery in lactate metabolism and shuttling was discussed in the 2019 American College of Sports Medicine Joseph B. Wolffe Lecture in Orlando, FL.

Lactate as a fulcrum of metabolism

Mistakenly thought to be the consequence of oxygen lack in contracting skeletal muscle we now know that the L-enantiomer of the lactate anion is formed under fully aerobic conditions and is utilized continuously in diverse cells, tissues, organs and at the whole-body level. By shuttling between producer (driver) and consumer (recipient) cells lactate fulfills at least three purposes: 1] a major energy source for mitochondrial respiration; 2] the major gluconeogenic precursor; and 3] a signaling molecule. Working by mass action, cell redox regulation, allosteric binding, and reprogramming of chromatin by lactylation of lysine residues on histones, lactate has major influences in energy substrate partitioning. The physiological range of tissue [lactate] is 0.5–20 mM and the cellular Lactate/Pyruvate ratio (L/P) can range from 10 to >500; these changes during exercise and other stress-strain responses dwarf other metabolic signals in magnitude and span. Hence, lactate dynamics have rapid and major short- and long-term effects on cell redox and other control systems. By inhibiting lipolysis in adipose via HCAR-1, and muscle mitochondrial fatty acid uptake via malonyl-CoA and CPT1, lactate controls energy substrate partitioning. Repeated lactate exposure from regular exercise results in major effects on the expression of regulatory enzymes of glycolysis and mitochondrial respiration. Lactate is the fulcrum of metabolic regulation in vivo.

Monocarboxylate transporters in cancer

Background

Tumors are highly plastic metabolic entities composed of cancer and host cells that can adopt different metabolic phenotypes. For energy production, cancer cells may use 4 main fuels that are shuttled in 5 different metabolic pathways. Glucose fuels glycolysis that can be coupled to the tricarboxylic acid (TCA) cycle and oxidative phosphorylation (OXPHOS) in oxidative cancer cells or to lactic fermentation in proliferating and in hypoxic cancer cells. Lipids fuel lipolysis, glutamine fuels glutaminolysis, and lactate fuels the oxidative pathway of lactate, all of which are coupled to the TCA cycle and OXPHOS for energy production. This review focuses on the latter metabolic pathway.

Scope of review

Lactate, which is prominently produced by glycolytic cells in tumors, was only recently recognized as a major fuel for oxidative cancer cells and as a signaling agent. Its exchanges across membranes are gated by monocarboxylate transporters MCT1-4. This review summarizes the current knowledge about MCT structure, regulation and functions in cancer, with a specific focus on lactate metabolism, lactate-induced angiogenesis and MCT-dependent cancer metastasis. It also describes lactate signaling via cell surface lactate receptor GPR81.

Major conclusions

Lactate and MCTs, especially MCT1 and MCT4, are important contributors to tumor aggressiveness. Analyses of MCT-deficient (MCT^+/- and MCT^−/-) animals and (MCT-mutated) humans indicate that they are druggable, with MCT1 inhibitors being in advanced development phase and MCT4 inhibitors still in the discovery phase. Imaging lactate fluxes non-invasively using a lactate tracer for positron emission tomography would further help to identify responders to the treatments.

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In cancer, hypoxia and cell proliferation are associated to lactic acid production.

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Lactate exchanges are at the core of tumor metabolism.

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Transmembrane lactate trafficking depends on monocarboxylate transporters (MCTs).

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MCTs are implicated in tumor development and aggressiveness.

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Targeting MCTs is a therapeutic option for cancer treatment.

Differential effects of vitamin C or protandim on skeletal muscle adaptation to exercise

Maintaining proteostasis is a key mechanism for preserving cell function. Exercise-stimulated proteostasis is regulated, in part, by redox-sensitive signaling. Several studies suggest that supplementation with exogenous antioxidants blunts exercise-induced cellular adaptations, although this conclusion lacks consensus. Our group uses a fundamentally different approach to maintain redox balance by treatment with bioactive phytochemicals to activate the transcription factor nuclear factor (erythroid-derived 2)-like 2 and downstream endogenous antioxidant pathways. We hypothesized that vitamin C (VitC) would interfere with redox-sensitive proteostatic mechanisms in skeletal muscle, whereas phytochemical treatment would permit proteostatic maintenance. We measured protein and DNA synthesis in skeletal muscle from high-volume voluntary wheel-running rats. Whereas phytochemical treatment permitted mitochondrial and other proteostatic adaptations to exercise, VitC treatment did not. During an in vitro oxidative challenge, phytochemical treatment helped maintain proteostasis, including the mitochondrial fraction while VitC did not. Our findings support the conclusion that VitC can blunt some of the beneficial adaptations to exercise. We propose that regulation of endogenous antioxidants represents a novel approach to maintain redox balance while still permitting redox-sensitive proteostatic adaptations. NEW & NOTEWORTHY Whether vitamin C blocks aerobic exercise adaptions lacks consensus, perhaps because of approaches that only assess markers of mitochondrial biogenesis. By directly measuring mitochondrial biogenesis, we demonstrate that vitamin C blunts exercise-induced adaptations. Furthermore, we show that treatment with Protandim, a purported nuclear factor (erythroid-derived 2)-like 2 activator that upregulates endogenous antioxidants, permits mitochondrial biogenesis. We confirm that vitamin C blunts aerobic exercise adaptions, whereas Protandim does not, suggesting targeting the endogenous antioxidant network facilitates adaptations to exercise.

The Science and Translation of Lactate Shuttle Theory

Once thought to be a waste product of anaerobic metabolism, lactate is now known to form continuously under aerobic conditions. Shuttling between producer and consumer cells fulfills at least three purposes for lactate: (1) a major energy source, (2) the major gluconeogenic precursor, and (3) a signaling molecule. "Lactate shuttle" (LS) concepts describe the roles of lactate in delivery of oxidative and gluconeogenic substrates as well as in cell signaling. In medicine, it has long been recognized that the elevation of blood lactate correlates with illness or injury severity. However, with lactate shuttle theory in mind, some clinicians are now appreciating lactatemia as a "strain" and not a "stress" biomarker. In fact, clinical studies are utilizing lactate to treat pro-inflammatory conditions and to deliver optimal fuel for working muscles in sports medicine. The above, as well as historic and recent studies of lactate metabolism and shuttling, are discussed in the following review.

Chronic activation of AMP-activated protein kinase increases monocarboxylate transporter 2 and 4 expression in skeletal muscle

Acute activation of AMP-activated protein kinase (AMPK) increases monocarboxylate transporter (MCT) expression in skeletal muscle. However, the impact of chronic activation of AMPK on MCT expression in skeletal muscle is unknown. To investigate, MCT1, MCT2, and MCT4 mRNA expression and protein abundance were measured in the longissimus lumborum (glycolytic), masseter (oxidative), and heart from wild-type (control) and AMPK γ3 pigs. The AMPK γ3 gain in function mutation results in AMPK being constitutively active in glycolytic skeletal muscle and increases energy producing pathways. The MCT1 and MCT2 mRNA expression in muscle was lower ( < 0.05) from both wild-type and AMPK γ3 animals compared to other tissues. However, in both genotypes, MCT1 and MCT2 mRNA expression was greater ( < 0.05) in the masseter than the longissimus lumborum. The MCT1 protein was not detected in skeletal muscle, but MCT2 was greater ( < 0.05) in muscles with an oxidative muscle phenotype. Monocarboxylate transporter 2 was also detected in muscle mitochondria and may explain the differences between muscles. The MCT4 mRNA expression was intermediate among all tissues tested and greater ( < 0.05) in the longissimus lumborum than the masseter. Furthermore, MCT4 protein expression in the longissimus lumborum from AMPK γ3 animals was greater ( < 0.05) than in the longissimus lumborum from wild-type animals. In totality, these data indicate that chronic AMPK activation simultaneously increases MCT2 and MCT4 expression in skeletal muscle.

Chronic endurance exercise antagonizes the cardiac UCP2 and UCP3 protein up-regulation induced by nandrolone decanoate

BACKGROUND

Several lines of evidence revealed that chronic treatment of anabolic androgenic steroids (AASs) is accompanied with some cardiovascular side effects and in addition they also negatively mask the beneficial effects of exercise training on cardiac performance.

METHODS

The present study examined whether the nandrolone decanoate (ND)-induced cardiac effects were mediated by changing the cardiac uncoupling protein 2 (UCP2) and 3 (UCP3) expression. Five groups of male wistar-albino rats including sedentary control (SC), sedentary vehicle (SV), sedentary nandrolone decanoate (SND), exercise control (EC), and exercise nandrolone decanoate (END) were used. ND was injected (10 mg/kg/week, intramuscular) to the animals in the SND and END groups and endurance exercise training was performed on a treadmill five times per week.

RESULTS

The protein expressions of cardiac UCP2 and UCP3 have significantly increased in both the SND and EC groups compared to the SC ones. In contrast to UCP3, no significant differences were found between UCP2 protein expressions of the END and SC groups. Compared with the SND group, the exercise training significantly decreased the UCP2 and UCP3 protein expressions in the END group.

CONCLUSIONS

The study has indicated that endurance exercise in combination with ND can result in that the exercise effectively antagonizes the effects of ND treatment on UCP2 and UCP3 up-regulation.

Monocarboxylate transporters in the brain and in cancer

Monocarboxylate transporters (MCTs) constitute a family of 14 members among which MCT1-4 facilitate the passive transport of monocarboxylates such as lactate, pyruvate and ketone bodies together with protons across cell membranes. Their anchorage and activity at the plasma membrane requires interaction with chaperon protein such as basigin/CD147 and embigin/gp70. MCT1-4 are expressed in different tissues where they play important roles in physiological and pathological processes. This review focuses on the brain and on cancer. In the brain, MCTs control the delivery of lactate, produced by astrocytes, to neurons, where it is used as an oxidative fuel. Consequently, MCT dysfunctions are associated with pathologies of the central nervous system encompassing neurodegeneration and cognitive defects, epilepsy and metabolic disorders. In tumors, MCTs control the exchange of lactate and other monocarboxylates between glycolytic and oxidative cancer cells, between stromal and cancer cells and between glycolytic cells and endothelial cells. Lactate is not only a metabolic waste for glycolytic cells and a metabolic fuel for oxidative cells, but it also behaves as a signaling agent that promotes angiogenesis and as an immunosuppressive metabolite. Because MCTs gate the activities of lactate, drugs targeting these transporters have been developed that could constitute new anticancer treatments. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou.

Mitochondrial pyruvate carrier in Trypanosoma brucei

Pyruvate is a key product of glycolysis that regulates the energy metabolism of cells. In Trypanosoma brucei, the causative agent of sleeping sickness, the fate of pyruvate varies dramatically during the parasite life cycle. In bloodstream forms, pyruvate is mainly excreted, whereas in tsetse fly forms, pyruvate is metabolized in mitochondria yielding additional ATP molecules. The character of the molecular machinery that mediates pyruvate transport across mitochondrial membrane was elusive until the recent discovery of mitochondrial pyruvate carrier (MPC) in yeast and mammals. Here, we characterized pyruvate import into mitochondrion of T. brucei. We identified mpc1 and mpc2 homologs in the T. brucei genome with attributes of MPC protein family and we demonstrated that both proteins are present in the mitochondrial membrane of the parasite. Investigations of mpc1 or mpc2 gene knock-out cells proved that T. brucei MPC1/2 proteins facilitate mitochondrial pyruvate transport. Interestingly, MPC is expressed not only in procyclic trypanosomes with fully activated mitochondria but also in bloodstream trypanosomes in which most of pyruvate is excreted. Moreover, MPC appears to be essential for bloodstream forms, supporting the recently emerging picture that the functions of mitochondria in bloodstream forms are more diverse than it was originally thought.

Expression of Monocarboxylate Transporter Isoforms in Rat Skeletal Muscle Under Hypoxic Preconditioning and Endurance Training

Previously, we have reported the regulation of monocarboxylate transporters (MCT)1 and MCT4 by physiological stimuli such as hypoxia and exercise. In the present study, we have evaluated the effect of hypoxic preconditioning and training on expression of different MCT isoforms in muscles. We found the increased mRNA expression of MCT1, MCT11, and MCT12 after hypoxic preconditioning with cobalt chloride and training. However, the expression of other MCT isoforms increased marginally or even reduced after hypoxic preconditioning. Only the protein expression of MCT1 increased after hypoxia preconditioning. MCT2 protein expression increased after training only and MCT4 protein expression decreased both in preconditioning and hypoxic training. Furthermore, we found decreased plasma lactate level during hypoxia preconditioning (0.74-fold), exercise (0.78-fold), and hypoxia preconditioning along with exercise (0.67-fold), which indicates increased lactate uptake by skeletal muscle. The protein-protein interactions with hypoxia inducible factor-1 and MCT isoforms were also evaluated, but no interaction was found. In conclusion, we say that almost all MCTs are expressed in red gastrocnemius muscle at the mRNA level and their expression is regulated differently under hypoxia preconditioning and exercise condition.

Nandrolone decanoate negatively reverses the beneficial effects of exercise on cardiac muscle via sarcolemmal, but not mitochondrial K(ATP) channel

ATP-sensitive potassium channels are supposed to have a substantial role in improvement of cardiac performance. This study was performed to evaluate whether nandrolone decanoate (ND) and (or) exercise training could affect the expression of cardiac K(ATP) channel subunits. Thirty-five male albino Wistar rats were randomly divided into 5 groups, including sedentary control (SC), sedentary vehicle (SV), sedentary ND (SND), exercise control (EC), and exercise and ND (E+ND). Exercise training was performed on a treadmill 5 times per week. ND was injected (10 mg/kg/week, i.m.) to the rats in the SND and E+ND groups. Following cardiac isolation, the expression of both sarcolemmal and mitochondrial subunits of K(ATP) channel was measured using Western blot method. The expression of sarcolemmal, but not mitochondrial, subunits of K(ATP) channel (Kir6.2 and SUR2) of EC group was significantly higher compared with SC group while ND administration (SND group) did not show any change in their expression. In the E+ND group, ND administration led to decrease of the over-expression of sarcolemmal Kir6.2 and SUR2 which was previously induced by exercise. There was no significant association between the mitochondrial expression of either Kir6.2 or SUR2 proteins and administration of ND or exercise. Supra-physiological dosage of ND negatively reverses the effects of exercise on the cardiac muscle expression of sarcolemmal, but not mitochondrial, K(ATP) channel subunits.

Endogenous Nutritive Support after Traumatic Brain Injury: Peripheral Lactate Production for Glucose Supply via Gluconeogenesis

We evaluated the hypothesis that nutritive needs of injured brains are supported by large and coordinated increases in lactate shuttling throughout the body. To that end, we used dual isotope tracer ([6,6-(2)H2]glucose, i.e., D2-glucose, and [3-(13)C]lactate) techniques involving central venous tracer infusion along with cerebral (arterial [art] and jugular bulb [JB]) blood sampling. Patients with traumatic brain injury (TBI) who had nonpenetrating head injuries (n=12, all male) were entered into the study after consent of patients' legal representatives. Written and informed consent was obtained from healthy controls (n=6, including one female). As in previous investigations, the cerebral metabolic rate (CMR) for glucose was suppressed after TBI. Near normal arterial glucose and lactate levels in patients studied 5.7±2.2 days (range of days 2-10) post-injury, however, belied a 71% increase in systemic lactate production, compared with control, that was largely cleared by greater (hepatic+renal) glucose production. After TBI, gluconeogenesis from lactate clearance accounted for 67.1% of glucose rate of appearance (Ra), which was compared with 15.2% in healthy controls. We conclude that elevations in blood glucose concentration after TBI result from a massive mobilization of lactate from corporeal glycogen reserves. This previously unrecognized mobilization of lactate subserves hepatic and renal gluconeogenesis. As such, a lactate shuttle mechanism indirectly makes substrate available for the body and its essential organs, including the brain, after trauma. In addition, when elevations in arterial lactate concentration occur after TBI, lactate shuttling may provide substrate directly to vital organs of the body, including the injured brain.

Mitochondrial pyruvate transport: a historical perspective and future research directions

Pyruvate is the end-product of glycolysis, a major substrate for oxidative metabolism, and a branching point for glucose, lactate, fatty acid and amino acid synthesis. The mitochondrial enzymes that metabolize pyruvate are physically separated from cytosolic pyruvate pools and rely on a membrane transport system to shuttle pyruvate across the impermeable inner mitochondrial membrane (IMM). Despite long-standing acceptance that transport of pyruvate into the mitochondrial matrix by a carrier-mediated process is required for the bulk of its metabolism, it has taken almost 40 years to determine the molecular identity of an IMM pyruvate carrier. Our current understanding is that two proteins, mitochondrial pyruvate carriers MPC1 and MPC2, form a hetero-oligomeric complex in the IMM to facilitate pyruvate transport. This step is required for mitochondrial pyruvate oxidation and carboxylation-critical reactions in intermediary metabolism that are dysregulated in several common diseases. The identification of these transporter constituents opens the door to the identification of novel compounds that modulate MPC activity, with potential utility for treating diabetes, cardiovascular disease, cancer, neurodegenerative diseases, and other common causes of morbidity and mortality. The purpose of the present review is to detail the historical, current and future research investigations concerning mitochondrial pyruvate transport, and discuss the possible consequences of altered pyruvate transport in various metabolic tissues.

Monocarboxylate transporter expression at the onset of skeletal muscle regeneration

The onset of skeletal muscle regeneration is characterized by proliferating myoblasts. Proliferating myoblasts have an increased energy demand and lactate exchange across the sarcolemma can be used to address this increased demand. Monocarboxylate transporters (MCTs) are involved in lactate transport across the sarcolemma and are known to be affected by various physiological stimuli. However, MCT expression at the onset of skeletal muscle regeneration has not been determined. The purpose of this study was to determine if skeletal muscle regeneration altered MCT expression in regenerating tibialis anterior (TA) muscle. Male C57/BL6 mice were randomly assigned to either a control (uninjured) or bupivacaine (injured) group. Three days post injection, the TA was extracted for determination of protein and gene expression. A 21% decrease in muscle mass to tibia length (2.4 ± 0.1 mg/mm vs. 1.9 ± 0.2 mg/mm, P < 0.02) was observed. IGF-1 and MyoD gene expression increased 5.0-fold (P < 0.05) and 3.5-fold (P < 0.05), respectively, 3 days post bupivacaine injection. MCT-1 protein was decreased 32% (P < 0.03); however, MCT-1 gene expression was not altered. There was no difference in MCT4 protein or gene expression. Lactate dehydrogenase (LDH)-A protein expression increased 71% (P < 0.0004). Protein levels of LDH-B and mitochondrial enzyme cytochrome C oxidase subunit decreased 3 days post bupivacaine injection. CD147 and PKC-θ protein increased 64% (P < 0.03) and 79% (P < 0.02), respectively. MCT1 but not MCT4 expression is altered at the onset of skeletal muscle regeneration possibly in an attempt to regulate lactate uptake and use by skeletal muscle cells.

Possible pathway of Na(+) flux into mitochondria in ischemic heart

Previous studies showed that myocardial Na(+) overload during ischemia directly induced mitochondrial damage. The pathway for Na(+) flux into mitochondria remains unclear. We examined possible routes for Na(+) flux into mitochondria in the ischemic heart. Isolated perfused rat hearts were subjected to 15- to 35-min ischemia followed by 60-min reperfusion and then Na(+) content and respiratory function in mitochondria of the ischemic heart were determined. The mitochondrial Na(+) content of the ischemic heart was ischemic duration-dependently increased, associated with a reduction in mitochondrial respiratory function. To mimic induction of mitochondrial Na(+) overload in vitro, isolated mitochondria were incubated with 6.25 to 50 mM NaCl or sodium lactate, a metabolite of anaerobic glycolysis, in the presence and absence of a mitochondrial Na(+)/Ca(2+) exchanger inhibitor CGP37157 and a monocarboxylate transporter (MCT) inhibitor α-cyano-4-hydroxy cinnamic acid (CHCA). Incubation of mitochondria with NaCl or sodium lactate increased the mitochondrial Na(+) concentration. This increase in mitochondrial Na(+) was partially attenuated by the presence of either inhibitor. Combined treatment of mitochondria with both inhibitors attenuated sodium lactate-induced increase in Na(+) content to a greater degree than that treated with either agent. These results suggest that mitochondrial Na(+)/Ca(2+) exchanger and MCT inhibitor-sensitive Na(+) transporter are possible pathways for the mitochondrial Na(+) overload in the ischemic myocardium.

Expressional profile of cardiac uncoupling protein-2 following myocardial ischemia reperfusion in losartan- and ramiprilat-treated rats

BACKGROUND AND AIMS

The aim of this study was to investigate the early changes of cardiac uncoupling protein-2 (UCP2) expression following myocardial ischemia reperfusion in rats chronically treated with ramiprilat and losartan.

METHODS

Male Wistar rats were assigned into seven groups (six in each): intact (control); sham-operated; nontreated rats subjected to ischemia and reperfusion (IR); ramiprilat-treated rats with (Ram+IR) and without ischemia (Ram); losartan treated with (Los+IR) and without ischemia (Los). Quantitative evaluation of UCP2 mRNA was carried out using real-time reverse transcription-polymerase chain reaction (RT-PCR). Mitochondria were isolated, and protein expression was quantified by Western blotting.

RESULTS

In IR group: UCP2 protein but not mRNA level was increased in the ischemic area of the left ventricle (LV) (172% ± 26.7, p < 0.001 vs. LV of control). Following acute myocardial IR, UCP2 protein levels was increased in the ischemic area of the LV but not in RV, suggesting the local effect of ischemia on UCP2 expression. IR-induced overexpression of UCP2 was suppressed by ramiprilat and losartan.

CONCLUSION

These findings suggest that losartan and ramiprilat can suppress UCP2 expression following myocardial IR, and by this mechanism may protect the myocardium against IR injury.

Calorie restriction does not increase short-term or long-term protein synthesis

Increased protein synthesis is proposed as a mechanism of life-span extension during caloric restriction (CR). We hypothesized that CR does not increase protein synthesis in all tissues and protein fractions and that any increased protein synthesis with CR would be due to an increased anabolic effect of feeding. We used short- (4 hours) and long-term (6 weeks) methods to measure in vivo protein synthesis in lifelong ad libitum (AL) and CR mice. We did not detect an acute effect of feeding on protein synthesis while liver mitochondrial protein synthesis was lower in CR mice versus AL mice. Mammalian target of rapamycin (mTOR) signaling was repressed in liver and heart from CR mice indicative of energetic stress and suppression of growth. Our main findings were that CR did not increase rates of mixed protein synthesis over the long term or in response to acute feeding, and protein synthesis was maintained despite decreased mTOR signaling.

Exercise tames the wild side of the Myc network: a hypothesis

We propose that the well-documented therapeutic actions of repeated physical activities over human lifespan are mediated by the rapidly turning over proto-oncogenic Myc (myelocytomatosis) network of transcription factors. This transcription factor network is unique in utilizing promoter and epigenomic (acetylation/deacetylation, methylation/demethylation) mechanisms for controlling genes that include those encoding intermediary metabolism (the primary source of acetyl groups), mitochondrial functions and biogenesis, and coupling their expression with regulation of cell growth and proliferation. We further propose that remote functioning of the network occurs because there are two arms of this network, which consists of driver cells (e.g., working myocytes) that metabolize carbohydrates, fats, proteins, and oxygen and produce redox-modulating metabolites such as H₂O₂, NAD⁺, and lactate. The exercise-induced products represent autocrine, paracrine, or endocrine signals for target recipient cells (e.g., aortic endothelium, hepatocytes, and pancreatic β-cells) in which the metabolic signals are coupled with genomic networks and interorgan signaling is activated. And finally, we propose that lactate, the major metabolite released from working muscles and transported into recipient cells, links the two arms of the signaling pathway. Recently discovered contributions of the Myc network in stem cell development and maintenance further suggest that regular physical activity may prevent age-related diseases such as cardiovascular pathologies, cancers, diabetes, and neurological functions through prevention of stem cell dysfunctions and depletion with aging. Hence, regular physical activities may attenuate the various deleterious effects of the Myc network on health, the wild side of the Myc-network, through modulating transcription of genes associated with glucose and energy metabolism and maintain a healthy human status.

Do mice bred selectively for high locomotor activity have a greater reliance on lipids to power submaximal aerobic exercise?

Patterns of fuel use during locomotion are determined by exercise intensity and duration, and are remarkably similar across many mammalian taxa. However, as lipids have a high yield of ATP per mole and are stored in large quantities, their use should be favored in endurance-adapted animals. To examine the capacity for alteration or differential regulation of fuel-use patterns, we studied two lines of mice that had been selectively bred for high voluntary wheel running (HR), including one characterized by small hindlimb muscles (HR(mini)) and one without this phenotype (HR(normal)), as well as a nonselected control line. We evaluated: 1) maximal aerobic capacity (Vo(2 max)); 2) whole body fuel use during exercise by indirect calorimetry; 3) cardiac properties; and 4) many factors involved in regulating lipid use. HR mice achieved an increased Vo(2 max) compared with control mice, potentially in part due to HR cardiac capacities for metabolic fuel oxidation and the larger relative heart size of HR(mini) mice. HR mice also exhibited enhanced whole body lipid oxidation rates at 66% Vo(2 max), but HR(mini), HR(normal), and control mice did not differ in the proportional mix of fuels sustaining exercise (% total Vo(2)). However, HR(mini) gastrocnemius muscle had elevated fatty acid translocase (FAT/CD36) sarcolemmal protein and cellular mRNA, fatty acid binding protein (H-FABP) cytosolic protein, peroxisome proliferator-activated receptor (PPAR) α mRNA, and mass-specific activities of citrate synthase, β-hydroxyacyl-CoA dehydrogenase, and hexokinase. Therefore, high-running mouse lines had whole body fuel oxidation rates commensurate with maximal aerobic capacity, despite notable differences in skeletal muscle metabolic phenotypes.

Intracellular shuttle: the lactate aerobic metabolism

Lactate is a highly dynamic metabolite that can be used as a fuel by several cells of the human body, particularly during physical exercise. Traditionally, it has been believed that the first step of lactate oxidation occurs in cytosol; however, this idea was recently challenged. A new hypothesis has been presented based on the fact that lactate-to-pyruvate conversion cannot occur in cytosol, because the LDH enzyme characteristics and cytosolic environment do not allow the reaction in this way. Instead, the Intracellular Lactate Shuttle hypothesis states that lactate first enters in mitochondria and only then is metabolized. In several tissues of the human body this idea is well accepted but is quite resistant in skeletal muscle. In this paper, we will present not only the studies which are protagonists in this discussion, but the potential mechanism by which this oxidation occurs and also a link between lactate and mitochondrial proliferation. This new perspective brings some implications and comes to change our understanding of the interaction between the energy systems, because the product of one serves as a substrate for the other.

Lactate produced by glycogenolysis in astrocytes regulates memory processing

When administered either systemically or centrally, glucose is a potent enhancer of memory processes. Measures of glucose levels in extracellular fluid in the rat hippocampus during memory tests reveal that these levels are dynamic, decreasing in response to memory tasks and loads; exogenous glucose blocks these decreases and enhances memory. The present experiments test the hypothesis that glucose enhancement of memory is mediated by glycogen storage and then metabolism to lactate in astrocytes, which provide lactate to neurons as an energy substrate. Sensitive bioprobes were used to measure brain glucose and lactate levels in 1-sec samples. Extracellular glucose decreased and lactate increased while rats performed a spatial working memory task. Intrahippocampal infusions of lactate enhanced memory in this task. In addition, pharmacological inhibition of astrocytic glycogenolysis impaired memory and this impairment was reversed by administration of lactate or glucose, both of which can provide lactate to neurons in the absence of glycogenolysis. Pharmacological block of the monocarboxylate transporter responsible for lactate uptake into neurons also impaired memory and this impairment was not reversed by either glucose or lactate. These findings support the view that astrocytes regulate memory formation by controlling the provision of lactate to support neuronal functions.

Transpulmonary pyruvate kinetics

Shuttling of intermediary metabolites, such as pyruvate, contributes to the dynamic energy and biosynthetic needs of tissues. Tracer kinetic studies offer a powerful tool to measure the metabolism of substrates like pyruvate that are simultaneously taken up from and released into the circulation by organs. However, we understood that during each circulatory passage, the entire cardiac output transits the pulmonary circulation. Therefore, we examined the transpulmonary pyruvate kinetics in an anesthetized rat model during an unstimulated (Con), lactate clamp (LC), and epinephrine infusion (Epi) conditions using a primed-continuous infusion of [U-¹³C]pyruvate. Compared with Con and Epi stimulation, LC significantly increased mixed central venous ([v]) and arterial ([a]) pyruvate concentrations (P < 0.05). We hypothesized that the lungs, specifically the pulmonary capillary beds are sites of simultaneous production and removal of pyruvate and contributes significantly to whole body carbohydrate intermediary metabolism. Transpulmonary net pyruvate balances were positive during all three conditions, indicating net pyruvate uptake. Net balance was significantly greater during epinephrine stimulation compared with the unstimulated control (P < 0.05). Tracer-measured pyruvate fractional extraction averaged 42.8 ± 5.8% for all three conditions and was significantly higher during epinephrine stimulation (P < 0.05) than during either Con or LC conditions, that did not differ from each other. Pyruvate total release (tracer measured uptake - net balance) was significantly higher during epinephrine stimulation (400 ± 100 μg/min) vs. Con (30 ± 20 μg/min) (P < 0.05). These data are interpreted to mean that significant pyruvate extraction occurs during circulatory transport across lung parenchyma. The extent of pulmonary parenchymal pyruvate extraction predicts high expression of monocarboxylate (lactate/pyruvate) transporters (MCTs) in the tissue. Western blot analysis of whole lung homogenates detected three isoforms, MCT1, MCT2, and MCT4. We conclude that a major site of circulating pyruvate extraction resides with the lungs and that during times of elevated circulating lactate, pyruvate, or epinephrine stimulation, pyruvate extraction is increased.

Regulation of oligodendrocyte development and myelination by glucose and lactate

In the gray matter of the brain, astrocytes have been suggested to export lactate (derived from glucose or glycogen) to neurons to power their mitochondria. In the white matter, lactate can support axon function in conditions of energy deprivation, but it is not known whether lactate acts by preserving energy levels in axons or in oligodendrocytes, the myelinating processes of which are damaged rapidly in low energy conditions. Studies of cultured cells suggest that oligodendrocytes are the cell type in the brain that consumes lactate at the highest rate, in part to produce membrane lipids presumably for myelin. Here, we use pH imaging to show that oligodendrocytes in the white matter of the rat cerebellum and corpus callosum take up lactate via monocarboxylate transporters (MCTs), which we identify as MCT1 by confocal immunofluorescence and electron microscopy. Using cultured slices of developing cerebral cortex from mice in which oligodendrocyte lineage cells express GFP (green fluorescent protein) under the control of the Sox10 promoter, we show that a low glucose concentration reduces the number of oligodendrocyte lineage cells and myelination. Myelination is rescued when exogenous l-lactate is supplied. Thus, lactate can support oligodendrocyte development and myelination. In CNS diseases involving energy deprivation at times of myelination or remyelination, such as periventricular leukomalacia leading to cerebral palsy, stroke, and secondary ischemia after spinal cord injury, lactate transporters in oligodendrocytes may play an important role in minimizing the inhibition of myelination that occurs.

Monocarboxylate transporters (MCT) as lactate carriers in equine muscle and red blood cells

REASONS FOR PERFORMING STUDY

Monocarboxylate transporters (MCT) facilitate the transport of lactate across membranes. In red blood cells (RBC) the transport activity varies interindividually due to differences in the amount of an ancillary protein CD147. Similar variations in muscles could have a great influence on lactate accumulation during exercise.

OBJECTIVES

To study the expression of MCT isoforms and CD147 in the middle gluteal muscle.

METHODS

Venous blood and muscle biopsy samples were taken from 14 Standardbred horses. Lactate transport activity in RBC and the amounts of MCT1, 2, 4 and CD147 were measured.

RESULTS

In muscle MCT1, MCT4 and CD147 were found. Amount of MCT1 was variable and not dependent on age or training. Expression of MCT4 increased with age and correlated positively with CD147. CD147 in muscle correlated with that in RBC. MCT4 in muscle and CD147/MCT1 in RBC were higher in race fit than in moderately trained horses.

CONCLUSIONS

MCT isoform profile in equine muscle is similar to that in man. The correlation between CD147 in muscle and RBC supports the view that lactate transport activity in muscles may vary interindividually as with RBC.

POTENTIAL RELEVANCE

A larger number of horses need to be analysed to confirm the relationship of CD147 in muscle and RBC; and to allow the use the lactate transport activity in RBC as an indicator of the respective activity in muscles.

Acute β-adrenergic stimulation does not alter mitochondrial protein synthesis or markers of mitochondrial biogenesis in adult men

Exercise-induced expression of peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) is dramatically inhibited in mice pretreated with a β-adrenergic receptor (β-AR) antagonist, suggesting that β-ARs play an important role in the regulation of skeletal muscle PGC-1α expression, and potentially, mitochondrial biogenesis. Accordingly, we hypothesized that acute β-AR stimulation would induce transcriptional pathways involved in skeletal muscle mitochondrial biogenesis in humans. Whole body protein turnover (WBPT), myofibrillar protein synthesis (MyPS), skeletal muscle mitochondrial protein synthesis (MiPS), and mitochondrial biogenic signaling were determined in samples of vastus lateralis obtained on two separate occasions in 10 young adult males following 1 h of continuous intravenous administration of saline (CON) or a nonspecific β-AR agonist [isoproterenol (ISO): 12 ng·kg fat free mass−1·min−1], combined with coinfusion of [1,2]13C-leucine. β-AR stimulation induced appreciable increases in heart rate and systolic blood pressure (both P < 0.001) but did not affect mitochondrial biogenic signaling (no change in PGC-1α, TFAM, NRF-1, NRF-2, COX, or NADHox expression via RT-PCR; P > 0.05). Additionally, MiPS [CON: 0.099 ± 0.028, ISO: 0.074 ± 0.046 (mean ± SD); P > 0.05] and MyPS (CON: 0.059 ± 0.008, ISO: 0.055 ± 0.009; P > 0.05), as well as measures of WBPT were unaffected. On the basis of this investigation, we conclude that acute intravenous β-AR stimulation does not increase mitochondrial protein synthesis or biogenesis signals in skeletal muscle.

Metabolic, enzymatic, and transporter responses in human muscle during three consecutive days of exercise and recovery

This study investigated the responses in substrate- and energy-based properties to repetitive days of prolonged submaximal exercise and recovery. Twelve untrained volunteers (Vo(2)(peak) = 44.8 +/- 2.0 ml.kg(-1).min(-1), mean +/- SE) cycled ( approximately 60 Vo(2)(peak)) on three consecutive days followed by 3 days of recovery. Tissue samples were extracted from the vastus lateralis both pre- and postexercise on day 1 (E1), day 3 (E3), and during recovery (R1, R2, R3) and were analyzed for changes in metabolism, substrate, and enzymatic and transporter responses. For the metabolic properties (mmol/kg(-1) dry wt), exercise on E1 resulted in reductions (P < 0.05) in phosphocreatine (PCr; 80 +/- 1.9 vs. 41.2 +/- 3.0) and increases (P < 0.05) in inosine monophosphate (IMP; 0.13 +/- 0.01 vs. 0.61 +/- 0.2) and lactate (3.1 +/- 0.4 vs. 19.2 +/- 4.3). At E3, both IMP and lactate were lower (P < 0.05) during exercise. For the transporters, the experimental protocol resulted in a decrease (P < 0.05) in glucose transporter-1 (GLUT1; 29% by R1), an increase in GLUT4 (29% by E3), and increases (P < 0.05) for both monocarboxylate transporters (MCT) (for MCT1, 23% by R2 and for MCT4, 18% by R1). Of the mitochondrial and cytosolic enzyme activities examined, cytochrome c oxidase (COX), and hexokinase were both reduced (P < 0.05) by exercise at E1 and in the case of hexokinase and phosphorylase by exercise on E3. With the exception at COX, which was lower (P < 0.05) at R1, no differences in enzyme activities existed at rest between E, E3, and recovery days. Results suggest that the glucose and lactate transporters are among the earliest adaptive responses of substrate and metabolic properties studied to the sudden onset of regular low-intensity exercise.

Effects of high-intensity training on MCT1, MCT4, and NBC expressions in rat skeletal muscles: influence of chronic metabolic alkalosis

This study investigated the effects of high-intensity training, with or without induced metabolic alkalosis, on lactate transporter (MCT1 and MCT4) and sodium bicarbonate cotransporter (NBC) content in rat skeletal muscles. Male Wistar rats performed high-intensity training on a treadmill 5 times/wk for 5 wk, receiving either sodium bicarbonate (ALK-T) or a placebo (PLA-T) prior to each training session, and were compared with a group of control rats (CON). MCT1, MCT4, and NBC content was measured by Western blotting in soleus and extensor digitorum longus (EDL) skeletal muscles. Citrate synthase (CS) and phosphofructokinase (PFK) activities and muscle buffer capacity (betam) were also evaluated. Following training, CS and PFK activities were significantly higher in the soleus only (P < 0.05), whereas betam was significantly higher in both soleus and EDL (P < 0.05). MCT1 (PLA-T: 30%; ALK-T: 23%) and NBC contents (PLA-T: 85%; ALK-T: 60%) increased significantly only in the soleus following training (P < 0.01). MCT4 content in the soleus was significantly greater in ALK-T (115%) but not PLA-T compared with CON. There was no significant change in protein content in the EDL. Finally, NBC content was related only to MCT1 content in soleus (r = 0.50, P < 0.01). In conclusion, these results suggest that MCT1, MCT4, and NBC undergo fiber-specific adaptive changes in response to high-intensity training and that induced alkalosis has a positive effect on training-induced changes in MCT4 content. The correlation between MCT1 and NBC expression suggests that lactate transport may be facilitated by NBC in oxidative skeletal muscle, which may in turn favor better muscle pH regulation.

PPARdelta enhances keratinocyte proliferation in psoriasis and induces heparin-binding EGF-like growth factor

Psoriasis is a common skin disease involving keratinocyte proliferation and altered differentiation, as well as T-cell activation. Here, we show that altered gene transcription in psoriatic skin lesions is highly reproducible between independent data sets. Analysis of gene expression confirmed dysregulation in all expected functional categories, such as IFN signaling and keratinocyte differentiation, and allowed molecular fingerprinting of a previously characterized dendritic cell subset associated with psoriasis tumor necrosis factor alpha (TNF-alpha)- and inducible nitric oxide synthase (iNOS)-producing CD11b(INT) DC (Tip-DC). Unexpectedly, a large group of dysregulated transcripts was related to fatty acid signaling and adipocyte differentiation, exhibiting a pattern consistent with the activation of peroxisome proliferator-activated receptor delta (PPARdelta). PPARdelta itself was strongly induced in psoriasis in vivo. In primary keratinocytes, PPARdelta was induced by the transcription factor activator protein 1, in particular by junB, but not by canonical WNT signaling, in contrast to its regulation in colon carcinoma cells. Activation of PPARdelta enhanced proliferation of keratinocytes, while this was inhibited by knockdown of PPARdelta. Finally, heparin-binding EGF-like growth factor (HB-EGF), known to induce epidermal hyperplasia and itself overexpressed in psoriasis, was identified as a direct target gene of PPARdelta. The present data suggest that activation of PPARdelta is a major event in psoriasis, contributing to the hyperproliferative phenotype by induction of HB-EGF.