Hypoxia enhances IPF mesenchymal progenitor cell fibrogenicity via the lactate/GPR81/HIF1α pathway

Mechanisms for Regulatory Effects of Exercise on Metabolic Diseases from the Lactate-Lactylation Perspective

Metabolic diseases, including cardiovascular diseases, type 2 diabetes mellitus (T2DM), osteoporosis, and non-alcoholic fatty liver disease (NAFLD), constitute a major global health burden associated with chronic morbidity and mortality. Lactate, once considered as a metabolic byproduct, has emerged as a key regulator of cellular reprogramming through lactylation, a novel post-translational modification (PTM) that dynamically couples metabolic flux to chromatin remodeling. Lactylation exerts dual regulatory roles as a signaling molecule via GPR81/GPR4-mediated pathways and as a substrate for the covalent modification of histones and metabolic enzymes. Pathologically, chronic hyperlactatemia suppresses mitochondrial biogenesis, driving metabolic cardiomyopathy through the epigenetic silencing of oxidative metabolism genes. Conversely, exercise-induced lactate surges transiently enhance insulin sensitivity via AMPK/PGC-1α/GLUT4 signaling, resolve inflammation through GPR81-mediated M2 macrophage polarization, and restore mitochondrial function via lactylation-dependent pathways. This review delineates lactylation as a spatiotemporal rheostat: chronic dysregulation perpetuates metabolic disorders, whereas acute exercise-mediated lactylation remodels transcriptional networks to restore metabolic homeostasis. Future research should integrate multiomics to clarify lactylation's spatiotemporal dynamics, tissue-specific thresholds, metabolism-immunity interactions, and metabolic-epigenetic crosstalk for the precision management of metabolic diseases.

Targeting Lactic Acid Modification in Ischemic Heart Diseases: Novel Therapeutics and Mechanism

Ischemic heart disease (IHD), especially acute myocardial infarction (AMI), has a high mortality rate and poses a great threat to human health. When myocardial infarction occurs, the structure and function of the myocardium are significantly damaged, and its metabolisms switch from oxidative phosphorylation to glycolysis, producing lactate. Lactylation, as a newly discovered post-translational modification (PMT) in recent years, is involved in the regulation of gene expression, and cell proliferation. Emerging studies have revealed that lactate and lactylation modifications participate in inflammation and cardiac repair, and play an important role in cardiovascular diseases, such as myocardial infarction, myocardial fibrosis, and heart failure. Therefore, in this review, we discuss how glucose metabolism, glycolytic end-product lactate, and lactylation potentially interact with pathological processes, including inflammation, cardiac fibrosis, and heart failure. And targeting glycolysis and lactylation modification could provide a promising future for cardiovascular diseases.

Developing an IPF Prognostic Model and Screening for Key Genes Based on Cold Exposure-Related Genes Using Bioinformatics Approaches

Background: Cold exposure has an impact on various respiratory diseases. However, its relationship with idiopathic pulmonary fibrosis (IPF) remains to be elucidated. In this study, bioinformatics methods were utilized to explore the potential link between cold exposure and IPF. Methods: Cold exposure-related genes (CERGs) were identified using RNA-Seq data from mice exposed to cold versus room temperature conditions, along with cross-species orthologous gene conversion. Consensus clustering analysis was performed based on the CERGs. A prognostic model was established using univariate and multivariate risk analyses, as well as Lasso-Cox analysis. Differential analysis, WGCNA, and Lasso-Cox methods were employed to screen for signature genes. Results: This study identified 151 CERGs. Clustering analysis based on these CERGs revealed that IPF patients could be divided into two subgroups with differing severity levels. Significant differences were observed between these two subgroups in terms of hypoxia score, EMT score, GAP score, immune infiltration patterns, and mortality rates. A nine-gene prognostic model for IPF was established based on the CERG (AUC: 1 year: 0.81, 3 years: 0.79, 5 years: 0.91), which outperformed the GAP score (AUC: 1 year: 0.66, 3 years: 0.75, 5 years: 0.72) in prognostic accuracy. IPF patients were classified into high-risk and low-risk groups based on the RiskScore from the prognostic model, with significant differences observed between these groups in hypoxia score, EMT score, GAP score, immune infiltration patterns, and mortality rates. Ultimately, six high-risk signature genes associated with cold exposure in IPF were identified: GASK1B, HRK1, HTRA1, KCNN4, MMP9, and SPP1. Conclusions: This study suggests that cold exposure may be a potential environmental factor contributing to the progression of IPF. The prognostic model built upon cold exposure-related genes provides an effective tool for assessing the severity of IPF patients. Meanwhile, GASK1B, HRK1, HTRA1, KCNN4, MMP9, and SPP1 hold promise as potential biomarkers and therapeutic targets for IPF.

Identification of lactylation-associated fibroblast subclusters predicting prognosis and cancer immunotherapy response in colon cancer

BACKGROUND

Lactylation plays an important role in tumor progression. This study aimed to clarify the impact of lactylation on cancer-associated fibroblasts(CAFs).

METHODS

Single-cell and bulk RNA sequence data, along with survival information, were obtained from TCGA and GEO datasets. Significant lactylation-associated genes were acquired by differential analysis and used to construct a prognostic model via Cox and LASSO regression analyses. Next, single-cell analysis, enrichment and pathway analysis, pseudotemporal trajectory and survival analysis were used to identify significant lactylation-associated fibroblast subclusters in colon cancer. IMvigor210 and PRJEB23709 cohorts were applied to assess the response to immunotherapy. In vitro experiments were conducted to explore how lactylation affect fibroblasts.

RESULTS

We established a lactylation-associated prognostic model with 17 risk genes in TCGA and further validated it in GEO datasets. Single-cell analysis revealed the lactylation level of fibroblasts in colon cancer was greater than that in normal tissues. Moreover, five lactylation-associated fibroblast subclusters were identified via the NMF algorithm. Patients with lower scores of FB_2_CALD1, FB_3_TPM4 and FB_4_AHNAK subclusters had better clinical prognosis in colon cancer and were more likely to benefit from immunotherapy. Further experiments demonstrated that lactylation could enhance the proliferation, migration and invasion ability of fibroblasts and up-regulate the expression of COL1A1, which was similar to the effect of colon cancer cells.

CONCLUSION

This study identified key fibroblast subclusters with prognostic value and implied that lactylation might help transform fibroblasts into CAFs in colon cancer for the first time, which provides new paths for understanding the evolution of CAFs and cancer therapeutic strategies.

How oxygenation shapes immune responses: emerging roles for physioxia and pathological hypoxia

Most eukaryotes require oxygen for their survival and, with increasing multicellular complexity, oxygen availability and delivery rates vary across the tissues of complex organisms. In humans, healthy tissues have markedly different oxygen gradients, ranging from the hypoxic environment of the bone marrow (where our haematopoietic stem cells reside) to the lungs and their alveoli, which are among the most oxygenated areas of the body. Immune cells are therefore required to adapt to varying oxygen availability as they move from the bone marrow to peripheral organs to mediate their effector functions. These changing oxygen gradients are exaggerated during inflammation, where oxygenation is often depleted owing to alterations in tissue perfusion and increased cellular activity. As such, it is important to consider the effects of oxygenation on shaping the immune response during tissue homeostasis and disease conditions. In this Review, we address the relevance of both physiological oxygenation (physioxia) and disease-associated hypoxia (where cellular oxygen demand outstrips supply) for immune cell functions, discussing the relevance of hypoxia for immune responses in the settings of tissue homeostasis, inflammation, infection, cancer and disease immunotherapy.

Unveiling lactylation modification: A new hope for cancer treatment

This review article delves into the multifaceted role of lactylation modification in antitumor therapy, revealing the complex interplay between lactylation modification and the tumor microenvironment (TME), metabolic reprogramming, gene expression, and immunotherapy. As an emerging epigenetic modification, lactylation has a significant impact on the metabolic pathways of tumor cells, immune evasion, gene expression regulation, and sensitivity to chemotherapy drugs. Studies have shown that lactylation modification significantly alters the development and therapeutic response of tumors by affecting metabolites in the TME, immune cell functions, and signaling pathways. In the field of immunotherapy, the regulatory role of lactylation modification provides a new perspective and potential targets for tumor treatment, including modulating the sensitivity of tumors to immunotherapy by affecting the expression of immune checkpoint molecules and the infiltration of immune cells. Moreover, research progress on lactylation modification in various types of tumors indicates that it may serve as a biomarker to predict patients' responses to chemotherapy and immunotherapy. Overall, research on lactylation modification provides a theoretical foundation for the development of new tumor treatment strategies and holds promise for improving patient prognosis and quality of life. Future research will further explore the application potential of lactylation modification in tumor therapy and how to improve treatment efficacy by targeting lactylation modification.

The role of lactate and lactylation in ischemic cardiomyopathy: Mechanisms and gene expression

Ischemic cardiomyopathy (ICM) is a significant global public health issue, with its pathophysiology encompassing atherosclerotic plaque formation, thrombosis, hypoperfusion, ischemic cell death, and left ventricular remodeling. Lactate is not only regarded as an energy metabolite but also acts as a signaling molecule that influences various physiological processes, regulating metabolism and muscle contraction. Lactylation, an emerging epigenetic modification, affects protein functionality and gene expression through the P300 enzyme. In ICM, lactate accumulation leads to pH imbalance and myocardial cell dysfunction, impacting cellular signaling. This paper will analyze the role of lactylation in ICM, focusing on coronary artery disease (ASCVD) and myocardial infarction (MI). It will also explore the differential expression and immunological characteristics of lactylation-related genes in normal and ICM tissues, providing potential targets for future research.

Lactate in skin homeostasis: metabolism, skin barrier, and immunomodulation

Lactate, once considered merely a byproduct of glycolysis, is now increasingly recognized as a multifunctional signaling molecule with roles beyond energy metabolism. It functions as an enzyme cofactor and binds to specific receptors to modulate cellular functions. In the skin, lactate is produced by various cell types. It is then transferred between cells or to the extracellular space, helping to balance cellular pH and to provide signals that regulate skin barrier and skin immunity. Additionally, lactate/lactate-related genes hold promising therapeutic potential for the treatment of skin tumors, inflammatory skin diseases, hair loss, and in cosmetic dermatology. This article highlights the latest advances in our understanding of lactate's biological effects on the skin and explores its therapeutic potential, offering insights into future research directions.

Regulation of lactate accumulation in bovine mammary epithelial cells by LPS-induced HIF-1α/MCT1 pathway

Lactate has been increasingly recognized for its role in diseases progression, necessitating a deeper understanding of its metabolic processes and regulatory mechanisms. This study aimed to evaluate the impact of lipopolysaccharide (LPS) on lactate accumulation in bovine mammary epithelial cells (BMECs) and to elucidate the underlying regulatory mechanisms. Further optimization of LPS treatment points was achieved by assessing the content of key glycolytic enzymes-hexokinases (HK), pyruvate kinase (PK) and pyruvate dehydrogenase (PDH)-as well as the expression levels of HK2, pyruvate dehydrogenase kinase4 (PDK4) and lactate dehydrogenase (LDHA). Our results indicate that LPS can promote intracellular glycolysis and inhibits pyruvate synthesis, thereby increasing lactate content. BMECs were cultured and divided into a control group (CON) and an LPS-stimulated group (10 μg/mL for 6 h, LPS group). LPS was found to upregulate expression levels of HIF-1α and MCT1, suggesting a role for HIF-1α and MCT1 in cellular glucose metabolism. To explore the effect of HIF-1α on lactate accumulation, BMECs were stimulated with a HIF-1α inducer (COCL2) and HIF-1α inhibitor (DMBPA). COCL2 was observed to promote lactate accumulation, while DMBPA inhibited it. Additionally, modulation of HIF-1α expression influenced the expression of MCT1, which is a crucial transporter for extracellular lactate influx. To investigate the specific impact of MCT1 on intracellular lactate, we utilized overexpression plasmids and small interfering RNA to modulate MCT1 expression. The findings indicate that while MCT1 expression alone does not affect intracellular lactate levels, it does modulate the changes induced by LPS. In conclusion, our study suggests that LPS regulates lactate accumulation in BMECs through the HIF-1α/MCT1 pathway, providing insights into the metabolic dysregulation associated with LPS-induced stress in dairy cattle.

Identification and verification of the optimal feature genes of ferroptosis in thyroid-associated orbitopathy

Background

Thyroid-associated orbitopathy (TAO) is an autoimmune inflammatory disorder of the orbital adipose tissue, primarily causing oxidative stress injury and tissue remodeling in the orbital connective tissue. Ferroptosis is a form of programmed cell death driven by the accumulation of reactive oxygen species (ROS), iron metabolism disorder, and lipid peroxidation. This study aims to identify and validate the optimal feature genes (OFGs) of ferroptosis with diagnostic and therapeutic potential in TAO orbital adipose tissue through bioinformatics analysis and to assess their correlation with disease-related immune cell infiltration.

Methods

Search of the Gene Expression Omnibus database for TAO-related gene datasets led to the selection of GSE58331 for differential gene expression analysis. WGCNA was employed to identify key disease modules and hub genes. The intersection of DEGs, hub genes and ferroptosis-related gene yielded key genes of ferroptosis. Machine learning algorithms identified OFGs of ferroptosis. Meanwhile, by comparing the expression of FRGs in the orbital adipose tissue and the orbital fibroblasts (OFs) of healthy controls and TAO patients, as well as co-culturing macrophages and OFs in vitro, the influence of macrophages on FRGs in OFs was explored. CIBERSORT analyzed immune cell infiltration to determine proportions of immune cell types in each sample, and Spearman correlation analysis explored relationships between OFGs and infiltrating immune cells. Finally, GSEA determined the function of each key biomarker based on the median expression of OFGs.

Results

Three TAO FRGs (ACO1, MMD, and HCAR1) were screened in the dataset. The ROC results of ACO1 showed that the AUC value was greater than 0.8 in all the datasets, which was the strongest for disease specificity and diagnostic ability. Validation results showed that, in addition to MMD, the expression of ACO1 and HCAR1 in orbital adipose tissue of TAO patients was significantly down-regulated, while M2-type macrophages might be involved in regulating the expression of ACO1 in orbital adipose-derived OFs. CIBERSORT immune cell infiltration analysis showed that in orbital adipose tissue of TAO patients, memory B-lymphocytes, T regulatory cells, NK-cells, M0-type macrophages, M1-type macrophages, resting dendritic cells, activated mast cells, and neutrophils infiltration levels were significantly elevated.

Conclusion

Through bioinformatics analysis, this study identified and validated two OFGs of ferroptosis with diagnostic and therapeutic potential in TAO orbital adipose tissue, suggesting that the downregulation of ACO1 and HCAR1 may be potential molecular targets in the pathogenesis of TAO.

Lipocalin-2 induced LDHA expression promotes vascular remodelling in pulmonary hypertension

Aerobic glycolysis is involved in the pathogenesis of pulmonary hypertension (PH). The mechanisms by which glycolysis is increased and how it contributes to pulmonary vascular remodelling are not yet fully understood. In this study, we demonstrated that elevated lipocalin-2 (LCN2) in PH significantly enhances aerobic glycolysis in human pulmonary artery smooth muscle cells (PASMCs) by up-regulating LDHA expression. Knockout of Lcn2 or having heterozygous LDHA deficiency in mice significantly inhibits the progression of hypoxic PH. Our study reveals that LCN2 stimulates LDHA expression by activating Akt-HIF-1α signalling pathway. Inhibition of Akt or HIF-1α reduces LDHA expression and proliferation of PASMCs. Both Akt and HIF-1α play critical roles in the development of PH and are suppressed in the pulmonary vessels of hypoxic PH mice lacking LCN2. These findings shed light on the LCN2-Akt-HIF1α-LDHA axis in aerobic glycolysis in PH.

Lactate activates ER stress to promote alveolar epithelial cells apoptosis in pulmonary fibrosis

Pulmonary fibrosis (PF) is a chronic, progressive lung disease characterized by fibroblast proliferation, extensive extracellular matrix and collagen deposition, accompanied by inflammatory damage, ultimately leading to death due to respiratory failure. Endoplasmic reticulum (ER) stress in pulmonary fibrotic tissue is indeed recognized as a significant factor exacerbating PF development. Emerging evidences indicated a potential association between ER stress induced by lactate and cellular apoptosis in PF. However, the mechanisms in this process need further elucidation. In this paper, pulmonary fibrosis model was induced by bleomycin (BLM) intratracheally in mice. In the cellular model, type II epithelial cells were treated by lactate and TGF-β to detect ER stress and apoptosis markers. Lactate could promote ER stress response and apoptosis. Mechanically, lactate activated Caspase-12 via ATF4-Chop axis to induce cell apoptosis and promote fibrosis. ER stress inhibitor could effectively suppress alveolar epithelial cells apoptosis and pulmonary fibrosis. We concluded that pro-fibrotic properties of lactate are associated with alveolar epithelial cells apoptosis by causing ER stress and thus provide new potential therapeutic targets for pulmonary fibrosis.

The role of nonhistone lactylation in disease

In 2019, a novel post-translational modification termed lactylation was identified, which established a connection among lactate, transcriptional regulation and epigenetics. Lactate, which is traditionally viewed as a metabolic byproduct, is now recognized for its significant functional role, including modulating the tumor microenvironment, engaging in signaling and interfering in immune regulation. While research on lactylation (KLA) is advancing, the focus has primarily been on histone lactylation. This paper aims to explore the less-studied area of nonhistone lactylation, highlighting its involvement in certain diseases and physiological processes. Additionally, the clinical relevance and potential implications of nonhistone lactylation will be discussed.

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.

The role and molecular mechanism of CTHRC1 in fibrosis

Fibrosis, a pathological state characterized by the excessive accumulation of extracellular matrix components, is primarily driven by the overactivation of fibroblasts. This condition becomes particularly pronounced under chronic inflammatory conditions. Fibrosis can occur in several tissues throughout the body. Among the notable discoveries in the study of fibrosis is the role of Collagen Triple Helix Repeat Containing-1 (CTHRC1), a protein that has emerged as a critical regulator in the fibrotic process. CTHRC1 is rapidly expressed on the outer membrane of fibroblasts and intimal smooth muscle cells following vascular injury, such as that induced by balloon angioplasty. This expression denotes the organism efforts to repair and restructure compromised tissue, signifying a critical component of the tissue repair mechanism in reaction to fibrosis. It plays a pivotal role in promoting cell migration and aiding tissue repair post-injury, contributing significantly to various pathophysiological processes including revascularization, bone formation, developmental morphological changes, inflammatory arthritis, and the progression of cancer. Significantly, researchers have observed marked expression of CTHRC1 across a variety of fibrotic conditions, closely associating it with the progression of the disease. Intervention with CTHRC1 can affect the occurrence and progression of fibrosis. This review aims to comprehensively explore the role and underlying mechanisms of CTHRC1 in fibrotic diseases, highlighting its potential as a key target for therapeutic interventions.

Deletion of GPR81 activates CREB/Smad7 pathway and alleviates liver fibrosis in mice

BACKGROUND

Enhanced glycolysis is a crucial metabolic event that drives the development of liver fibrosis, but the molecular mechanisms have not been fully understood. Lactate is the endproduct of glycolysis, which has recently been identified as a bioactive metabolite binding to G-protein-coupled receptor 81 (GPR81). We then questioned whether GPR81 is implicated in the development of liver fibrosis.

METHODS

The level of GPR81 was determined in mice with carbon tetrachloride (CCl4)-induced liver fibrosis and in transforming growth factor beta 1 (TGF-β1)-activated hepatic stellate cells (HSCs) LX-2. To investigate the significance of GPR81 in liver fibrosis, wild-type (WT) and GPR81 knockout (KO) mice were exposed to CCl4, and then the degree of liver fibrosis was determined. In addition, the GPR81 agonist 3,5-dihydroxybenzoic acid (DHBA) was supplemented in CCl4-challenged mice and TGF-β1-activated LX-2 cells to further investigate the pathological roles of GPR81 on HSCs activation.

RESULTS

CCl4 exposure or TGF-β1 stimulation significantly upregulated the expression of GPR81, while deletion of GPR81 alleviated CCl4-induced elevation of aminotransferase, production of pro-inflammatory cytokines, and deposition of collagen. Consistently, the production of TGF-β1, the expression of alpha-smooth muscle actin (α-SMA) and collagen I (COL1A1), as well as the elevation of hydroxyproline were suppressed in GPR81 deficient mice. Supplementation with DHBA enhanced CCl4-induced liver fibrogenesis in WT mice but not in GPR81 KO mice. DHBA also promoted TGF-β1-induced LX-2 activation. Mechanistically, GPR81 suppressed cAMP/CREB and then inhibited the expression of Smad7, a negative regulator of Smad3, which resulted in increased phosphorylation of Smad3 and enhanced activation of HSCs.

CONCLUSION

GPR81 might be a detrimental factor that promotes the development of liver fibrosis by regulating CREB/Smad7 pathway.

Untreated Obstructive Sleep Apnea in Interstitial Lung Disease and Impact on Interstitial Lung Disease Outcomes

Subjects with interstitial lung disease (ILD) often suffer from nocturnal cough, insomnia, and poor sleep quality. Subjects with ILD and obstructive sleep apnea (OSA) seem to have relatively mild symptoms from sleep fragmentation compared to subjects with only ILD. The overlap of ILD, OSA, and sleeping hypoxemia may be associated with poor outcome, even though there is no agreement on which sleep parameter is mostly associated with worsening ILD prognosis. Randomized controlled trials are needed to understand when positive airway pressure (PAP) treatment is required in subjects with ILD and OSA and the impact of PAP treatment on ILD progression.

Lactate facilitated mitochondrial fission-derived ROS to promote pulmonary fibrosis via ERK/DRP-1 signaling

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, fibrotic interstitial lung diseases, which mainly existed in middle-aged and elderly people. The accumulation of reactive oxygen species (ROS) is a common characteristic of IPF. Previous research also shown that lactate levels can be abnormally elevated in IPF patients. Emerging evidence suggested a relationship between lactate and ROS in IPF which needs further elucidation. In this article, we utilized a mouse model of BLM-induced pulmonary fibrosis to detect alterations in ROS levels and other indicators associated with fibrosis. Lactate could induce mitochondrial fragmentation by modulating expression and activity of DRP1 and ERK. Moreover, Increased ROS promoted P65 translocation into nucleus, leading to expression of lung fibrotic markers. Finally, Ulixertinib, Mdivi-1 and Mito-TEMPO, which were inhibitor activity of ERK, DRP1 and mtROS, respectively, could effectively prevented mitochondrial damage and production of ROS and eventually alleviate pulmonary fibrosis. Taken together, these findings suggested that lactate could promote lung fibrosis by increasing mitochondrial fission-derived ROS via ERK/DRP1 signaling, which may provide novel therapeutic solutions for IPF.

The HIF-1α/PLOD2 axis integrates extracellular matrix organization and cell metabolism leading to aberrant musculoskeletal repair

While hypoxic signaling has been shown to play a role in many cellular processes, its role in metabolism-linked extracellular matrix (ECM) organization and downstream processes of cell fate after musculoskeletal injury remains to be determined. Heterotopic ossification (HO) is a debilitating condition where abnormal bone formation occurs within extra-skeletal tissues. Hypoxia and hypoxia-inducible factor 1α (HIF-1α) activation have been shown to promote HO. However, the underlying molecular mechanisms by which the HIF-1α pathway in mesenchymal progenitor cells (MPCs) contributes to pathologic bone formation remain to be elucidated. Here, we used a proven mouse injury-induced HO model to investigate the role of HIF-1α on aberrant cell fate. Using single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics analyses of the HO site, we found that collagen ECM organization is the most highly up-regulated biological process in MPCs. Zeugopod mesenchymal cell-specific deletion of Hif1α (Hoxa11-CreERT2; Hif1afl/fl) significantly mitigated HO in vivo. ScRNA-seq analysis of these Hoxa11-CreERT2; Hif1afl/fl mice identified the PLOD2/LOX pathway for collagen cross-linking as downstream of the HIF-1α regulation of HO. Importantly, our scRNA-seq data and mechanistic studies further uncovered that glucose metabolism in MPCs is most highly impacted by HIF-1α deletion. From a translational aspect, a pan-LOX inhibitor significantly decreased HO. A newly screened compound revealed that the inhibition of PLOD2 activity in MPCs significantly decreased osteogenic differentiation and glycolytic metabolism. This suggests that the HIF-1α/PLOD2/LOX axis linked to metabolism regulates HO-forming MPC fate. These results suggest that the HIF-1α/PLOD2/LOX pathway represents a promising strategy to mitigate HO formation.

Metabolite-sensing GPCRs in rheumatoid arthritis

Persistent inflammation in damaged joints results in metabolic dysregulation of the synovial microenvironment, causing pathogenic alteration of cell activity in rheumatoid arthritis (RA). Recently, the role of metabolite and metabolite-sensing G protein-coupled receptors (GPCRs) in the RA-related inflammatory immune response (IIR) has become a focus of research attention. These GPCRs participate in the progression of RA by modulating immune cell activation, migration, and inflammatory responses. Here, we discuss recent evidence implicating metabolic dysregulation in RA pathogenesis, focusing on the connection between RA-related IIR and GPCR signals originating from the synovial joint and gut. Furthermore, we discuss future directions for targeting metabolite-sensing GPCRs for therapeutic benefit, emphasizing the importance of identifying endogenous ligands and investigating the various transduction mechanisms involved.

Glycolysis Reprogramming in Idiopathic Pulmonary Fibrosis: Unveiling the Mystery of Lactate in the Lung

Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive lung disease characterized by excessive deposition of fibrotic connective tissue in the lungs. Emerging evidence suggests that metabolic alterations, particularly glycolysis reprogramming, play a crucial role in the pathogenesis of IPF. Lactate, once considered a metabolic waste product, is now recognized as a signaling molecule involved in various cellular processes. In the context of IPF, lactate has been shown to promote fibroblast activation, myofibroblast differentiation, and extracellular matrix remodeling. Furthermore, lactate can modulate immune responses and contribute to the pro-inflammatory microenvironment observed in IPF. In addition, lactate has been implicated in the crosstalk between different cell types involved in IPF; it can influence cell-cell communication, cytokine production, and the activation of profibrotic signaling pathways. This review aims to summarize the current research progress on the role of glycolytic reprogramming and lactate in IPF and its potential implications to clarify the role of lactate in IPF and to provide a reference and direction for future research. In conclusion, elucidating the intricate interplay between lactate metabolism and fibrotic processes may lead to the development of innovative therapeutic strategies for IPF.

Lactate Mediates High-Intensity Interval Training-Induced Promotion of Hippocampal Mitochondrial Function through the GPR81-ERK1/2 Pathway

Mitochondrial biogenesis and fusion are essential for maintaining healthy mitochondria and ATP production. High-intensity interval training (HIIT) can enhance mitochondrial function in mouse hippocampi, but its underlying mechanism is not completely understood. Lactate generated during HIIT may mediate the beneficial effects of HIIT on neuroplasticity by activating the lactate receptor GPR81. Furthermore, growing evidence shows that lactate contributes to mitochondrial function. Given that mitochondrial function is crucial for cerebral physiological processes, the current study aimed to determine the mechanism of HIIT in hippocampal mitochondrial function. In vivo, GPR81 was knocked down in the hippocampi of mice via the injection of adeno-associated virus (AAV) vectors. The GPR81-knockdown mice were subjected to HIIT. The results demonstrated that HIIT increased mitochondria numbers, ATP production, and oxidative phosphorylation (OXPHOS) in the hippocampi of mice. In addition, HIIT induced mitochondrial biogenesis, fusion, synaptic plasticity, and ERK1/2 phosphorylation but not in GPR81-knockdown mice. In vitro, Neuro-2A cells were treated with L-lactate, a GPR81 agonist, and an ERK1/2 inhibitor. The results showed that both L-lactate and the GPR81 agonist increased mitochondrial biogenesis, fusion, ATP levels, OXPHOS, mitochondrial membrane potential, and synaptic plasticity. However, the inhibition of ERK1/2 phosphorylation blunted L-lactate or the GPR81 agonist-induced promotion of mitochondrial function and synaptic plasticity. In conclusion, our findings suggest that lactate mediates HIIT-induced promotion of mitochondrial function through the GPR81-ERK1/2 pathway.

Versatile lactate signaling via HCAR1: a multifaceted GPCR involved in many biological processes

G-coupled protein receptors (GPCRs) are the ultimate refuge of pharmacology and medicine as more than 40% of all marketed drugs are directly targeting these receptors. Through cell surface expression, they are at the forefront of cellular communication with the outside world. Metabolites among the conveyors of this communication are becoming more prominent with the recognition of them as ligands for GPCRs. HCAR1 is a GPCR conveyor of lactate. It is a class A GPCR coupled to Gαi which reduces cellular cAMP along with the downstream Gβγ signaling. It was first found to inhibit lipolysis, and lately has been implicated in diverse cellular processes, including neural activities, angiogenesis, inflammation, vision, cardiovascular function, stem cell proliferation, and involved in promoting pathogenesis for different conditions, such as cancer. Other than signaling from the plasma membrane, HCAR1 shows nuclear localization with different location-biased activities therein. Although different functions for HCAR1 are being discovered, its cell and molecular mechanisms are yet ill understood. Here, we provide a comprehensive review on HCAR1, which covers the literature on the subject, and discusses its importance and relevance in various biological phenomena.

Lactate modulates iron metabolism by binding soluble adenylyl cyclase

Overproduction of lactate (LA) can occur during exercise and in many diseases such as cancers. Individuals with hyperlactatemia often display anemia, decreased serum iron, and elevated hepcidin, a key regulator of iron metabolism. However, it is unknown whether and how LA regulates hepcidin expression. Here, we show LA binds to soluble adenylyl cyclase (sAC) in normal hepatocytes and affects systemic iron homeostasis in mice by increasing hepcidin expression. Comprehensive in vitro, in vivo, and in silico experiments show that the LA-sAC interaction raises cyclic adenosine monophosphate (cAMP) levels, which activates the PKA-Smad1/5/8 signaling pathway to increase hepcidin transcription. We verified this regulatory axis in wild-type mice and in mice with disordered iron homeostasis. LA also regulates hepcidin in humans at rest and subjected to extensive exercise that produce elevated LA. Our study links hyperlactatemia to iron deficiency, offering a mechanistic explanation for anemias seen in athletes and patients with lactic acidosis.

Immunometabolism changes in fibrosis: from mechanisms to therapeutic strategies

Immune cells are essential for initiating and developing the fibrotic process by releasing cytokines and growth factors that activate fibroblasts and promote extracellular matrix deposition. Immunometabolism describes how metabolic alterations affect the function of immune cells and how inflammation and immune responses regulate systemic metabolism. The disturbed immune cell function and their interactions with other cells in the tissue microenvironment lead to the origin and advancement of fibrosis. Understanding the dysregulated metabolic alterations and interactions between fibroblasts and the immune cells is critical for providing new therapeutic targets for fibrosis. This review provides an overview of recent advances in the pathophysiology of fibrosis from the immunometabolism aspect, highlighting the altered metabolic pathways in critical immune cell populations and the impact of inflammation on fibroblast metabolism during the development of fibrosis. We also discuss how this knowledge could be leveraged to develop novel therapeutic strategies for treating fibrotic diseases.