Cell-to-cell lactate shuttle operates in heart and is important in age-related heart failure

Lactate and lactylation in cardiovascular diseases: current progress and future perspectives

Cardiovascular diseases (CVDs) are often linked to structural and functional impairments, such as heart defects and circulatory dysfunction, leading to compromised peripheral perfusion and heightened morbidity risks. Metabolic remodeling, particularly in the context of cardiac fibrosis and inflammation, is increasingly recognized as a pivotal factor in the pathogenesis of CVDs. Metabolic syndromes further predispose individuals to these conditions, underscoring the need to elucidate the metabolic underpinnings of CVDs. Lactate, a byproduct of glycolysis, is now recognized as a key molecule that connects cellular metabolism with the regulation of cellular activity. The transport of lactate between different cells is essential for metabolic homeostasis and signal transduction. Disruptions to lactate dynamics are implicated in various CVDs. Furthermore, lactylation, a novel post-translational modification, has been identified in cardiac cells, where it influences protein function and gene expression, thereby playing a significant role in CVD pathogenesis. In this review, we summarized recent advancements in understanding the role of lactate and lactylation in CVDs, offering fresh insights that could guide future research directions and therapeutic interventions. The potential of lactate metabolism and lactylation as innovative therapeutic targets for CVD is a promising avenue for exploration.

Lactate: an alternative pathway for the immunosuppressive properties of mesenchymal stem/stromal cells

BACKGROUND

The metabolic reprogramming of mesenchymal stem/stromal cells (MSC) favoring glycolysis has recently emerged as a new approach to improve their immunotherapeutic abilities. This strategy is associated with greater lactate release, and interestingly, recent studies have proposed lactate as a functional suppressive molecule, changing the old paradigm of lactate as a waste product. Therefore, we evaluated the role of lactate as an alternative mediator of MSC immunosuppressive properties and its contribution to the enhanced immunoregulatory activity of glycolytic MSCs.

MATERIALS AND METHODS

Murine CD4+ T cells from C57BL/6 male mice were differentiated into proinflammatory Th1 or Th17 cells and cultured with either L-lactate, MSCs pretreated or not with the glycolytic inductor, oligomycin, and MSCs pretreated or not with a chemical inhibitor of lactate dehydrogenase A (LDHA), galloflavin or LDH siRNA to prevent lactate production. Additionally, we validated our results using human umbilical cord-derived MSCs (UC-MSCs) in a murine model of delayed type 1 hypersensitivity (DTH).

RESULTS

Our results showed that 50 mM of exogenous L-lactate inhibited the proliferation rate and phenotype of CD4+ T cell-derived Th1 or Th17 by 40% and 60%, respectively. Moreover, the suppressive activity of both glycolytic and basal MSCs was impaired when LDH activity was reduced. Likewise, in the DTH inflammation model, lactate production was required for MSC anti-inflammatory activity. This lactate dependent-immunosuppressive mechanism was confirmed in UC-MSCs through the inhibition of LDH, which significantly decreased their capacity to control proliferation of activated CD4+ and CD8+ human T cells by 30%.

CONCLUSION

These findings identify a new MSC immunosuppressive pathway that is independent of the classical suppressive mechanism and demonstrated that the enhanced suppressive and therapeutic abilities of glycolytic MSCs depend at least in part on lactate production.

The role of lactate in cardiovascular diseases

Cardiovascular diseases pose a major threat worldwide. Common cardiovascular diseases include acute myocardial infarction (AMI), heart failure, atrial fibrillation (AF) and atherosclerosis. Glycolysis process often has changed during these cardiovascular diseases. Lactate, the end-product of glycolysis, has been overlooked in the past but has gradually been identified to play major biological functions in recent years. Similarly, the role of lactate in cardiovascular disease is gradually being recognized. Targeting lactate production, regulating lactate transport, and modulating circulating lactate levels may serve as potential strategies for the treatment of cardiovascular diseases in the future. The purpose of this review is to integrate relevant clinical and basic research on the role of lactate in the pathophysiological process of cardiovascular disease in recent years to clarify the important role of lactate in cardiovascular disease and to guide further studies exploring the role of lactate in cardiovascular and other diseases. Video Abstract.

Extracellular flux analysis in intact cardiac tissue slices-A novel tool to investigate cardiac substrate metabolism in mouse myocardium

AIM

Cardiac pathologies are accompanied by alterations in substrate metabolism, and extracellular flux analysis is a standard tool to investigate metabolic disturbances, especially in immortalized cell lines. However, preparations of primary cells, such as adult cardiomyocytes require enzymatic dissociation and cultivation affecting metabolism. Therefore, we developed a flux analyzer-based method for the assessment of substrate metabolism in intact vibratome-sliced mouse heart tissue.

METHODS

Oxygen consumption rates were determined using a Seahorse XFe24-analyzer and "islet capture plates." We demonstrate that tissue slices are suitable for extracellular flux analysis and metabolize both free fatty acids (FFA) and glucose/glutamine. Functional integrity of tissue slices was proven by optical mapping-based assessment of action potentials. In a proof-of-principle approach, the sensitivity of the method was tested by analyzing substrate metabolism in the remote myocardium after myocardial infarction (I/R).

RESULTS

Here, I/R increased uncoupled OCR compared with sham animals indicating a stimulated metabolic capacity. This increase was caused by a higher glucose/glutamine metabolism, whereas FFA oxidation was unchanged.

CONCLUSION

In conclusion, we describe a novel method to analyze cardiac substrate metabolism in intact cardiac tissue slices by extracellular flux analysis. The proof-of-principle experiment demonstrated that this approach has a sensitivity allowing the investigation of pathophysiologically relevant disturbances in cardiac substrate metabolism.

Enzymatic Degradation of Polylactic Acid Fibers Supported on a Hydrogel for Sustained Release of Lactate

The incorporation of exogenous lactate into cardiac tissues is a regenerative strategy that is rapidly gaining attention. In this work, two polymeric platforms were designed to achieve a sustained release of lactate, combining immediate and prolonged release profiles. Both platforms contained electrospun poly(lactic acid) (PLA) fibers and an alginate (Alg) hydrogel. In the first platform, named L/K(x)/Alg-PLA, lactate and proteinase K (x mg of enzyme per 1 g of PLA) were directly loaded into the Alg hydrogel, into which PLA fibers were assembled. In the second platform, L/Alg-K(x)/PLA, fibers were produced by electrospinning a proteinase K:PLA solution and, subsequently, assembled within the lactate-loaded hydrogel. After characterizing the chemical, morphological, and mechanical properties of the systems, as well as their cytotoxicity, the release profiles of the two platforms were determined considering different amounts of proteinase K (x = 5.2, 26, and 52 mg of proteinase K per 1 g of PLA), which is known to exhibit a broad cleavage activity. The profiles obtained using L/Alg-K(x)/PLA platforms with x = 26 and 52 were the closest to the criteria that must be met for cardiac tissue regeneration. Finally, the amount of lactate directly loaded in the Alg hydrogel for immediate release and the amount of protein in the electrospinning solution were adapted to achieve a constant lactate release of around 6 mM per day over 1 or 2 weeks. In the optimized bioplatform, in which 6 mM lactate was loaded in the hydrogel, the amount of fibers was increased by a factor of ×3, the amount of enzyme was adjusted to 40 mg per 1 g of PLA, and a daily lactate release of 5.9 ± 2.7 mM over a period of 11 days was achieved. Accordingly, the engineered device fully satisfied the characteristics and requirements for heart tissue regeneration.

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.

Metabolic landscape in cardiac aging: insights into molecular biology and therapeutic implications

Cardiac aging is evident by a reduction in function which subsequently contributes to heart failure. The metabolic microenvironment has been identified as a hallmark of malignancy, but recent studies have shed light on its role in cardiovascular diseases (CVDs). Various metabolic pathways in cardiomyocytes and noncardiomyocytes determine cellular senescence in the aging heart. Metabolic alteration is a common process throughout cardiac degeneration. Importantly, the involvement of cellular senescence in cardiac injuries, including heart failure and myocardial ischemia and infarction, has been reported. However, metabolic complexity among human aging hearts hinders the development of strategies that targets metabolic susceptibility. Advances over the past decade have linked cellular senescence and function with their metabolic reprogramming pathway in cardiac aging, including autophagy, oxidative stress, epigenetic modifications, chronic inflammation, and myocyte systolic phenotype regulation. In addition, metabolic status is involved in crucial aspects of myocardial biology, from fibrosis to hypertrophy and chronic inflammation. However, further elucidation of the metabolism involvement in cardiac degeneration is still needed. Thus, deciphering the mechanisms underlying how metabolic reprogramming impacts cardiac aging is thought to contribute to the novel interventions to protect or even restore cardiac function in aging hearts. Here, we summarize emerging concepts about metabolic landscapes of cardiac aging, with specific focuses on why metabolic profile alters during cardiac degeneration and how we could utilize the current knowledge to improve the management of cardiac aging.

NMR-Based Metabolomic Analysis of Cardiac Tissues Clarifies Molecular Mechanisms of CVB3-Induced Viral Myocarditis and Dilated Cardiomyopathy

Viral myocarditis (VMC), which is defined as inflammation of the myocardium with consequent myocardial injury, may develop chronic disease eventually leading to dilated cardiomyopathy (DCM). Molecular mechanisms underlying the progression from acute VMC (aVMC), to chronic VMC (cVMC) and finally to DCM, are still unclear. Here, we established mouse models of VMC and DCM with Coxsackievirus B3 infection and conducted NMR-based metabolomic analysis of aqueous metabolites extracted from cardiac tissues of three histologically classified groups including aVMC, cVMC and DCM. We showed that these three pathological groups were metabolically distinct from their normal counterparts and identified three impaired metabolic pathways shared by these pathological groups relative to normal controls, including nicotinate and nicotinamide metabolism; alanine, aspartate and glutamate metabolism; and D-glutamine and D-glutamate metabolism. We also identified two extra impaired metabolic pathways in the aVMC group, including glycine, serine and threonine metabolism; and taurine and hypotaurine metabolism Furthermore, we identified potential cardiac biomarkers for metabolically distinguishing these three pathological stages from normal controls. Our results indicate that the metabolomic analysis of cardiac tissues can provide valuable insights into the molecular mechanisms underlying the progression from acute VMC to DCM.

Lactate metabolism in human health and disease

The current understanding of lactate extends from its origins as a byproduct of glycolysis to its role in tumor metabolism, as identified by studies on the Warburg effect. The lactate shuttle hypothesis suggests that lactate plays an important role as a bridging signaling molecule that coordinates signaling among different cells, organs and tissues. Lactylation is a posttranslational modification initially reported by Professor Yingming Zhao’s research group in 2019. Subsequent studies confirmed that lactylation is a vital component of lactate function and is involved in tumor proliferation, neural excitation, inflammation and other biological processes. An indispensable substance for various physiological cellular functions, lactate plays a regulatory role in different aspects of energy metabolism and signal transduction. Therefore, a comprehensive review and summary of lactate is presented to clarify the role of lactate in disease and to provide a reference and direction for future research. This review offers a systematic overview of lactate homeostasis and its roles in physiological and pathological processes, as well as a comprehensive overview of the effects of lactylation in various diseases, particularly inflammation and cancer.

FBP2–A New Player in Regulation of Motility of Mitochondria and Stability of Microtubules in Cardiomyocytes

Recently, we have shown that the physiological roles of a multifunctional protein fructose 1,6-bisphosphatase 2 (FBP2, also called muscle FBP) depend on the oligomeric state of the protein. Here, we present several lines of evidence that in HL-1 cardiomyocytes, a forced, chemically induced reduction in the FBP2 dimer-tetramer ratio that imitates AMP and NAD⁺ action and restricts FBP2-mitochondria interaction, results in an increase in Tau phosphorylation, augmentation of FBP2-Tau and FBP2-MAP1B interactions, disturbance of tubulin network, marked reduction in the speed of mitochondrial trafficking and increase in mitophagy. These results not only highlight the significance of oligomerization for the regulation of FBP2 physiological role in the cell, but they also demonstrate a novel, important cellular function of this multitasking protein—a function that might be crucial for processes that take place during physiological and pathological cardiac remodeling, and during the onset of diseases which are rooted in the destabilization of MT and/or mitochondrial network dynamics.

Chemical Exchange Saturation Transfer for Lactate-Weighted Imaging at 3 T MRI: Comprehensive In Silico, In Vitro, In Situ, and In Vivo Evaluations

Based on in silico, in vitro, in situ, and in vivo evaluations, this study aims to establish and optimize the chemical exchange saturation transfer (CEST) imaging of lactate (Lactate-CEST—LATEST). To this end, we optimized LATEST sequences using Bloch−McConnell simulations for optimal detection of lactate with a clinical 3 T MRI scanner. The optimized sequences were used to image variable lactate concentrations in vitro (using phantom measurements), in situ (using nine human cadaveric lower leg specimens), and in vivo (using four healthy volunteers after exertional exercise) that were then statistically analyzed using the non-parametric Friedman test and Kendall Tau-b rank correlation. Within the simulated Bloch−McConnell equations framework, the magnetization transfer ratio asymmetry (MTRasym) value was quantified as 0.4% in the lactate-specific range of 0.5−1 ppm, both in vitro and in situ, and served as the imaging surrogate of the lactate level. In situ, significant differences (p < 0.001) and strong correlations (τ = 0.67) were observed between the MTRasym values and standardized intra-muscular lactate concentrations. In vivo, a temporary increase in the MTRasym values was detected after exertional exercise. In this bench-to-bedside comprehensive feasibility study, different lactate concentrations were detected using an optimized LATEST imaging protocol in vitro, in situ, and in vivo at 3 T, which prospectively paves the way towards non-invasive quantification and monitoring of lactate levels across a broad spectrum of diseases.

Lactate and Myocadiac Energy Metabolism

The myocardium is capable of utilizing different energy substrates, which is referred to as “metabolic flexibility.” This process assures ATP production from fatty acids, glucose, lactate, amino acids, and ketones, in the face of varying metabolic contexts. In the normal physiological state, the oxidation of fatty acids contributes to approximately 60% of energy required, and the oxidation of other substrates provides the rest. The accumulation of lactate in ischemic and hypoxic tissues has traditionally be considered as a by-product, and of little utility. However, recent evidence suggests that lactate may represent an important fuel for the myocardium during exercise or myocadiac stress. This new paradigm drives increasing interest in understanding its role in cardiac metabolism under both physiological and pathological conditions. In recent years, blood lactate has been regarded as a signal of stress in cardiac disease, linking to prognosis in patients with myocardial ischemia or heart failure. In this review, we discuss the importance of lactate as an energy source and its relevance to the progression and management of heart diseases.

Label-free imaging for quality control of cardiomyocyte differentiation

Human pluripotent stem cell (hPSC)-derived cardiomyocytes provide a promising regenerative cell therapy for cardiovascular patients and an important model system to accelerate drug discovery. However, cost-effective and time-efficient platforms must be developed to evaluate the quality of hPSC-derived cardiomyocytes during biomanufacturing. Here, we develop a non-invasive label-free live cell imaging platform to predict the efficiency of hPSC differentiation into cardiomyocytes. Autofluorescence imaging of metabolic co-enzymes is performed under varying differentiation conditions (cell density, concentration of Wnt signaling activator) across five hPSC lines. Live cell autofluorescence imaging and multivariate classification models provide high accuracy to separate low (< 50%) and high (≥ 50%) differentiation efficiency groups (quantified by cTnT expression on day 12) within 1 day after initiating differentiation (area under the receiver operating characteristic curve, 0.91). This non-invasive and label-free method could be used to avoid batch-to-batch and line-to-line variability in cell manufacturing from hPSCs.

Differentiation of hPSCs to cardiomyocytes suffers from high variability. Here the authors report a label-free live cell imaging platform based on autofluorescence imaging to enable the prediction of cardiomyocyte differentiation efficiency from hPSCs.

A novel remitting leukodystrophy associated with a variant in FBP2

Leukodystrophies are genetic disorders of cerebral white matter that almost exclusively have a progressive disease course. We became aware of three members of a family with a disorder characterized by a sudden loss of all previously acquired abilities around 1 year of age followed by almost complete recovery within 2 years. Cerebral MRI and myelin sensitive imaging showed a pronounced demyelination that progressed for several months despite signs of clinical improvement and was followed by remyelination. Exome sequencing did not-identify any mutations in known leukodystrophy genes but revealed a heterozygous variant in the FBP2 gene, c.343G>A, p. Val115Met, shared by the affected family members. Cerebral MRI of other family members demonstrated similar white matter abnormalities in all carriers of the variant in FBP2. The FBP2 gene codes for muscle fructose 1,6-bisphosphatase, an enzyme involved in gluconeogenesis that is highly expressed in brain tissue. Biochemical analysis showed that the variant has a dominant negative effect on enzymatic activity, substrate affinity, cooperativity and thermal stability. Moreover, it also affects the non-canonical functions of muscle fructose 1,6-bisphosphatase involved in mitochondrial protection and regulation of several nuclear processes. In patients’ fibroblasts, muscle fructose 1,6-bisphosphatase shows no colocalization with mitochondria and nuclei leading to increased reactive oxygen species production and a disturbed mitochondrial network. In conclusion, the results of this study indicate that the variant in FBP2 disturbs cerebral energy metabolism and is associated with a novel remitting leukodystrophy.

Metformin Benefits: Another Example for Alternative Energy Substrate Mechanism?

Since the UK Prospective Diabetes Study (UKPDS), metformin has been considered the first-line medication for patients with newly diagnosed type 2 diabetes. Though direct evidence from specific trials is still lacking, several studies have suggested that metformin may protect from diabetes- and nondiabetes-related comorbidities, including cardiovascular, renal, neurological, and neoplastic diseases. In the past few decades, several mechanisms of action have been proposed to explain metformin's protective effects, none being final. It is certain, however, that metformin increases lactate production, concentration, and, possibly, oxidation. Once considered a mere waste product of exercising skeletal muscle or anaerobiosis, lactate is now known to act as a major energy shuttle, redistributed from production sites to where it is needed. Through the direct uptake and oxidation of lactate produced elsewhere, all end organs can be rapidly supplied with fundamental energy, skipping glycolysis and its possible byproducts. Increased lactate production (and consequent oxidation) could therefore be considered a positive mechanism of action of metformin, except when, under specific circumstances, metformin and lactate become excessive, increasing the risk of lactic acidosis. We are proposing that, rather than considering metformin-induced lactate production as dangerous, it could be considered a mechanism through which metformin exerts its possible protective effect on the heart, kidneys, and brain and, to some extent, its antineoplastic action.

Expression of Fbp2, a Newly Discovered Constituent of Memory Formation Mechanisms, Is Regulated by Astrocyte-Neuron Crosstalk

Fbp2 (muscle isozyme of fructose 1,6-bisphosphatase) is a glyconeogenesis-regulating enzyme and a multifunctional protein indispensable for long-term potentiation (LTP) formation in the hippocampus. Here, we present evidence that expression of Fbp2 in murine hippocampal cell cultures is regulated by crosstalk between neurons and astrocytes. Co-culturing of the two cell types results in a decrease in Fbp2 expression in astrocytes, and its simultaneous increase in neurons, as compared to monocultures. These changes are regulated by paracrine signaling using extracellular vesicle (EV)-packed factors released to the culture medium. It is well accepted that astrocyte-neuron metabolic crosstalk plays a crucial role in shaping neuronal function, and recently we have suggested that Fbp2 is a hub linking neuronal signaling with redox and/or energetic state of brain during the formation of memory traces. Thus, our present results emphasize the importance of astrocyte-neuron crosstalk in the regulation of the cells' metabolism and synaptic plasticity, and bring us one step closer to a mechanistic understanding of the role of Fbp2 in these processes.