Ablation of Myeloid ADK (Adenosine Kinase) Epigenetically Suppresses Atherosclerosis in ApoE-/- (Apolipoprotein E Deficient) Mice

Adenosine Kinase: An Epigenetic Modulator and Drug Target

Adenosine kinase (ADK, EC: 2.7.1.20) is an evolutionarily ancient ribokinase, which acts as a metabolic regulator by transferring a phosphoryl group to adenosine to form AMP. The enzyme is of interest as a therapeutic target because its inhibition is one of the most effective means to raise the levels of adenosine and hence adenosine receptor activation. For these reasons, ADK has received significant attention in drug discovery efforts in the early 2000s for indications such as epilepsy, chronic pain, and inflammation; however, the report of adverse events regarding cardiovascular and hepatic function as well as instances of microhemorrhage in the brain of preclinical models prevented further development efforts. Recent findings emphasize the importance of compartmentalization of the adenosine system reflected by two distinct isoforms of the enzyme, ADK-S and ADK-L, expressed in the cytoplasm and the cell nucleus, respectively. Newly identified adenosine receptor independent functions of adenosine as a regulator of biochemical transmethylation reactions, which include DNA and histone methylation, identify ADK-L as a distinct therapeutic target for the regulation of the nuclear methylome. This newly recognized role of ADK-L as an epigenetic regulator points toward the potential disease-modifying properties of the next generation of ADK inhibitors. Continued efforts to develop therapeutic strategies to separate nuclear from extracellular functions of adenosine would enable the development of targeted therapeutics with reduced adverse event potential. This review will summarize recent advances in the discovery of novel ADK inhibitors and discuss their potential therapeutic use in conditions ranging from epilepsy to cancer.

Adenosine Monophosphate Improves Lipolysis in Obese Mice by Reducing DNA Methylation via ADORA2A Activation by Ecto-5'-Nucleotidase (CD73)

The previous work discovers the potential of adenosine monophosphate (AMP) to alleviate obesity-related metabolic diseases, but the underlying molecular mechanisms remain incompletely understood. Here, AMP is confirmed to enhance white fat decomposition and improve abnormal glucose and lipid metabolism in mice fed with a high-fat (HF) diet. Mechanically, AMP is converted to adenosine (ADO) through ecto-5'-nucleotidase (CD73), and adenosine A2A receptor (ADORA2A) signaling activation is involved in the down-regulation of methylation in white adipose tissue, thereby reducing the hormone-sensitive lipase (HSL) methylation level and promoting HSL transcription and white fat decomposition. Moreover, the metabolic benefits of AMP are found to be partially eliminated in ADORA2A knockout mice, but re-expression of ADORA2A can reproduce the AMP-induced metabolic regulation in white fat. These findings reveal the mechanism that AMP, as the upstream of ADO, stimulates ADORA2A signaling and white fat DNA methylation to participate in the anti-obesity effect.

Adenosine kinase inhibits β-cell proliferation by upregulating DNA methyltransferase 3A expression

AIM

To investigate the effects of adenosine kinase (ADK), a key enzyme in determining intracellular adenosine levels, on β cells, and their underlying mechanism.

METHODS

Genetic animal models and transgenic immortalized cells were applied to study the effect of ADK on islet beta-cell proliferation and function. The beta-cell mass and response to glucose were measured in vivo using mice with beta-cell-specific ADK overexpression, and in vitro using ADK-overexpressed immortalized beta-cell.

RESULTS

The expression of ADK in human islets at high abundance, especially in β cells, was decreased during the process of β-cell proliferation. Additionally, a transgenic mouse model (ADKtg/tg /Mip-Cre) was generated wherein the mouse Insulin1 gene promoter specifically overexpressed ADK in pancreatic β cells. The ADKtg/tg /Mip-Cre model exhibited impaired glucose tolerance, decreased fasting plasma insulin, loss of β-cell mass, and inhibited β-cell proliferation. Proteomic analysis revealed that ADK overexpression inhibited the expression of several proteins that promote cell proliferation and insulin secretion. Upregulating ADK in the β-cell line inhibited the expression of β-cell related regulatory molecules, including FoxO1, Appl1, Pxn, Pdx-1, Creb and Slc16a3. Subsequent in vitro experiments indicated that the inhibition of β-cell proliferation and the decreased expression of Pdx-1, Creb and Slc16a3 were rescued by DNA methyltransferase 3A (DNMT3A) knockdown in β cells.

CONCLUSION

In this study, we found that the overexpression of ADK decreased the expression of several genes that regulate β cells, resulting in the inhibition of β-cell proliferation and dysfunction by upregulating the expression of DNMT3A.

Accumulation of endogenous adenosine improves cardiomyocyte metabolism via epigenetic reprogramming in an ischemia-reperfusion model

Adenosine kinase (ADK) plays the major role in cardiac adenosine metabolism, so that inhibition of ADK increases myocardial adenosine levels. While the cardioprotective actions of extracellular adenosine against ischemia/reperfusion (I/R) are well-established, the role of cellular adenosine in protection against I/R remains unknown. Here we investigated the role of cellular adenosine in epigenetic regulation on cardiomyocyte gene expression, glucose metabolism and tolerance to I/R. Evans blue/TTC staining and echocardiography were used to assess the extent of I/R injury in mice. Glucose metabolism was evaluated by positron emission tomography and computed tomography (PET/CT). Methylated DNA immunoprecipitation (MeDIP) and bisulfite sequencing PCR (BSP) were used to evaluate DNA methylation. Lentiviral/adenovirus transduction was used to overexpress DNMT1, and the OSI-906 was administered to inhibit IGF-1. Cardiomyocyte-specific ADK/IGF-1-knockout mice were used for mechanistic experiments.Cardiomyocyte-specific ADK knockout enhanced glucose metabolism and ameliorated myocardial I/R injury in vivo. Mechanistically, ADK deletion caused cellular adenosine accumulation, decreased DNA methyltransferase 1 (DNMT1) expression and caused hypomethylation of multiple metabolic genes, including insulin growth factor 1 (IGF-1). DNMT1 overexpression abrogated these beneficial effects by enhancing apoptosis and decreasing IGF-1 expression. Inhibition of IGF-1 signaling with OSI-906 or genetic knocking down of IGF-1 also abrogated the cardioprotective effects of ADK knockout, revealing the therapeutic potential of increasing IGF-1 expression in attenuating myocardial I/R injury. In conclusion, the present study demonstrated that cardiomyocyte ADK deletion ameliorates myocardial I/R injury via epigenetic upregulation of IGF-1 expression via the cardiomyocyte adenosine/DNMT1/IGF-1 axis.

Myeloid BAF60a deficiency alters metabolic homeostasis and exacerbates atherosclerosis

Atherosclerosis, a leading health concern, stems from the dynamic involvement of immune cells in vascular plaques. Despite its significance, the interplay between chromatin remodeling and transcriptional regulation in plaque macrophages is understudied. We discovered the reduced expression of Baf60a, a component of the switch/sucrose non-fermentable (SWI/SNF) chromatin remodeling complex, in macrophages from advanced plaques. Myeloid-specific Baf60a deletion compromised mitochondrial integrity and heightened adhesion, apoptosis, and plaque development. BAF60a preserves mitochondrial energy homeostasis under pro-atherogenic stimuli by retaining nuclear respiratory factor 1 (NRF1) accessibility at critical genes. Overexpression of BAF60a rescued mitochondrial dysfunction in an NRF1-dependent manner. This study illuminates the BAF60a-NRF1 axis as a mitochondrial function modulator in atherosclerosis, proposing the rejuvenation of perturbed chromatin remodeling machinery as a potential therapeutic target.

Multi-ancestry genome-wide study identifies effector genes and druggable pathways for coronary artery calcification

Coronary artery calcification (CAC), a measure of subclinical atherosclerosis, predicts future symptomatic coronary artery disease (CAD). Identifying genetic risk factors for CAC may point to new therapeutic avenues for prevention. Currently, there are only four known risk loci for CAC identified from genome-wide association studies (GWAS) in the general population. Here we conducted the largest multi-ancestry GWAS meta-analysis of CAC to date, which comprised 26,909 individuals of European ancestry and 8,867 individuals of African ancestry. We identified 11 independent risk loci, of which eight were new for CAC and five had not been reported for CAD. These new CAC loci are related to bone mineralization, phosphate catabolism and hormone metabolic pathways. Several new loci harbor candidate causal genes supported by multiple lines of functional evidence and are regulators of smooth muscle cell-mediated calcification ex vivo and in vitro. Together, these findings help refine the genetic architecture of CAC and extend our understanding of the biological and potential druggable pathways underlying CAC.

Adenosine kinase promotes post-infarction cardiac repair by epigenetically maintaining reparative macrophage phenotype

Pro-inflammatory and reparative macrophages are crucial in clearing necrotic myocardium and promoting cardiac repair after myocardial infarction (MI), respectively. Extracellular adenosine has been demonstrated to modulate macrophage polarization through adenosine receptors. However, the role of intracellular adenosine in macrophage polarization has not been explored and adenosine kinase (ADK) is a major enzyme regulating intracellular adenosine levels. Here, we aimed to elucidate the role of ADK in macrophage polarization and its subsequent impact on MI. We demonstrated that ADK was upregulated in bone marrow-derived macrophages (BMDMs) after IL-4 treatment and was highly expressed in the infarct area at day 7 post-MI, especially in macrophages. Compared with wild-type mice, myeloid-specific Adk knockout mice showed increased infarct size, limited myofibroblast differentiation, reduced collagen deposition and more severe cardiac dysfunction after MI, which was related to impaired reparative macrophage phenotype in MI tissue. We found that ADK deletion or inhibition significantly decreased the expression of reparative genes, such as Arg1, Ym1, Fizz1, and Cd206 in BMDMs after IL-4 treatment. The increased intracellular adenosine due to Adk deletion inhibited transmethylation reactions and decreased the trimethylation of H3K4 in BMDMs after IL-4 treatment. Mechanistically, we demonstrated that Adk deletion suppressed reparative macrophage phenotype through decreased IRF4 expression, which resulted from reduced levels of H3K4me3 on the Irf4 promotor. Together, our study reveals that ADK exerts a protective effect against MI by promoting reparative macrophage polarization through epigenetic mechanisms.

Hepatocyte Adenosine Kinase Promotes Excessive Fat Deposition and Liver Inflammation

BACKGROUND & AIMS

Nonalcoholic fatty liver disease is highly associated with obesity and progresses to nonalcoholic steatohepatitis when the liver develops overt inflammatory damage. While removing adenosine in the purine salvage pathway, adenosine kinase (ADK) regulates methylation reactions. We aimed to study whether hepatocyte ADK functions as an obesogenic gene/enzyme to promote excessive fat deposition and liver inflammation.

METHODS

Liver sections of human subjects were examined for ADK expression using immunohistochemistry. Mice with hepatocyte-specific ADK disruption or overexpression were examined for hepatic fat deposition and inflammation. Liver lipidomics, hepatocyte RNA sequencing (RNA-seq), and single-cell RNA-seq for liver nonparenchymal cells were performed to analyze ADK regulation of hepatocyte metabolic responses and hepatocyte-nonparenchymal cells crosstalk.

RESULTS

Whereas patients with nonalcoholic fatty liver disease had increased hepatic ADK levels, mice with hepatocyte-specific ADK disruption displayed decreased hepatic fat deposition on a chow diet and were protected from diet-induced excessive hepatic fat deposition and inflammation. In contrast, mice with hepatocyte-specific ADK overexpression displayed increased body weight and adiposity and elevated degrees of hepatic steatosis and inflammation compared with control mice. RNA-seq and epigenetic analyses indicated that ADK increased hepatic DNA methylation and decreased hepatic Ppara expression and fatty acid oxidation. Lipidomic and single-cell RNA-seq analyses indicated that ADK-driven hepatocyte factors, due to mitochondrial dysfunction, enhanced macrophage proinflammatory activation in manners involving increased expression of stimulator of interferon genes.

CONCLUSIONS

Hepatocyte ADK functions to promote excessive fat deposition and liver inflammation through suppressing hepatocyte fatty acid oxidation and producing hepatocyte-derived proinflammatory mediators. Therefore, hepatocyte ADK is a therapeutic target for managing obesity and nonalcoholic fatty liver disease.

Construction and validation of a metabolic-related genes prognostic model for oral squamous cell carcinoma based on bioinformatics

BACKGROUND

Oral squamous cell carcinoma (OSCC) accounts for a frequently-occurring head and neck cancer, which is characterized by high rates of morbidity and mortality. Metabolism-related genes (MRGs) show close association with OSCC development, metastasis and progression, so we constructed an MRGs-based OSCC prognosis model for evaluating OSCC prognostic outcome.

METHODS

This work obtained gene expression profile as well as the relevant clinical information from the The Cancer Genome Atlas (TCGA) database, determined the MRGs related to OSCC by difference analysis, screened the prognosis-related MRGs by performing univariate Cox analysis, and used such identified MRGs for constructing the OSCC prognosis prediction model through Lasso-Cox regression. Besides, we validated the model with the GSE41613 dataset based on Gene Expression Omnibus (GEO) database.

RESULTS

The present work screened 317 differentially expressed MRGs from the database, identified 12 OSCC prognostic MRGs through univariate Cox regression, and then established a clinical prognostic model composed of 11 MRGs by Lasso-Cox analysis. Based on the optimal risk score threshold, cases were classified as low- or high-risk group. As suggested by Kaplan-Meier (KM) analysis, survival rate was obviously different between the two groups in the TCGA training set (P < 0.001). According to subsequent univariate and multivariate Cox regression, risk score served as the factor to predict prognosis relative to additional clinical features (P < 0.001). Besides, area under ROC curve (AUC) values for patient survival at 1, 3 and 5 years were determined as 0.63, 0.70, and 0.76, separately, indicating that the prognostic model has good predictive accuracy. Then, we validated this clinical prognostic model using GSE41613. To enhance our model prediction accuracy, age, gender, risk score together with TNM stage were incorporated in a nomogram. As indicated by results of ROC curve and calibration curve analyses, the as-constructed nomogram had enhanced prediction accuracy compared with clinicopathological features alone, besides, combining clinicopathological characteristics with risk score contributed to predicting patient prognosis and guiding clinical decision-making.

CONCLUSION

In this study, 11 MRGs prognostic models based on TCGA database showed superior predictive performance and had a certain clinical application prospect in guiding individualized.

Epigenetic Control of Vascular Smooth Muscle Cell Function in Atherosclerosis: A Role for DNA Methylation

Atherosclerosis is a complex vascular inflammatory disease in which multiple cell types are involved, including vascular smooth muscle cells (VSMCs). In response to vascular injury and inflammatory stimuli, VSMCs undergo a "phenotypic switching" characterized by extracellular matrix secretion, loss of contractility, and abnormal proliferation and migration, which play a key role in the progression of atherosclerosis. DNA methylation modification is an important epigenetic mechanism that plays an important role in atherosclerosis. Studies investigating abnormal DNA methylation in patients with atherosclerosis have determined a specific DNA methylation profile, and proposed multiple pathways and genes involved in the etiopathogenesis of atherosclerosis. Recent studies have also revealed that DNA methylation modification controls VSMC function by regulating gene expression involved in atherosclerosis. In this review, we summarize the recent advances regarding the epigenetic control of VSMC function by DNA methylation in atherosclerosis and provide insights into the development of VSMC-centered therapeutic strategies.

Adenosine-Metabolizing Enzymes, Adenosine Kinase and Adenosine Deaminase, in Cancer

The immunosuppressive effect of adenosine in the microenvironment of a tumor is well established. Presently, researchers are developing approaches in immune therapy that target inhibition of adenosine or its signaling such as CD39 or CD73 inhibiting antibodies or adenosine A2A receptor antagonists. However, numerous enzymatic pathways that control ATP-adenosine balance, as well as understudied intracellular adenosine regulation, can prevent successful immunotherapy. This review contains the latest data on two adenosine-lowering enzymes: adenosine kinase (ADK) and adenosine deaminase (ADA). ADK deletes adenosine by its phosphorylation into 5′-adenosine monophosphate. Recent studies have revealed an association between a long nuclear ADK isoform and an increase in global DNA methylation, which explains epigenetic receptor-independent role of adenosine. ADA regulates the level of adenosine by converting it to inosine. The changes in the activity of ADA are detected in patients with various cancer types. The article focuses on the biological significance of these enzymes and their roles in the development of cancer. Perspectives of future studies on these enzymes in therapy for cancer are discussed.

Glycolysis links reciprocal activation of myeloid cells and endothelial cells in the retinal angiogenic niche

The coordination of metabolic signals among different cellular components in pathological retinal angiogenesis is poorly understood. Here, we showed that in the pathological angiogenic vascular niche, retinal myeloid cells, particularly macrophages/microglia that are spatially adjacent to endothelial cells (ECs), are highly glycolytic. We refer to these macrophages/microglia that exhibit a unique angiogenic phenotype with increased expression of both M1 and M2 markers and enhanced production of both proinflammatory and proangiogenic cytokines as pathological retinal angiogenesis-associated glycolytic macrophages/microglia (PRAGMs). The phenotype of PRAGMs was recapitulated in bone marrow-derived macrophages or retinal microglia stimulated by lactate that was produced by hypoxic retinal ECs. Knockout of 6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase (PFKFB3; Pfkfb3 for rodents), a glycolytic activator in myeloid cells, impaired the ability of macrophages/microglia to acquire an angiogenic phenotype, rendering them unable to promote EC proliferation and sprouting and pathological neovascularization in a mouse model of oxygen-induced proliferative retinopathy. Mechanistically, hyperglycolytic macrophages/microglia produced large amount of acetyl-coenzyme A, leading to histone acetylation and PRAGM-related gene induction, thus reprogramming macrophages/microglia into an angiogenic phenotype. These findings reveal a critical role of glycolytic metabolites as initiators of reciprocal activation of macrophages/microglia and ECs in the retinal angiogenic niche and suggest that strategies targeting the metabolic communication between these cell types may be efficacious in the treatment of pathological retinal angiogenesis.

Adenosine kinase: An epigenetic modulator in development and disease

Adenosine kinase (ADK) is the key regulator of adenosine and catalyzes the metabolism of adenosine to 5'-adenosine monophosphate. The enzyme exists in two isoforms: a long isoform (ADK-long, ADK-L) and a short isoform (ADK-short, ADK-S). The two isoforms are developmentally regulated and are differentially expressed in distinct subcellular compartments with ADK-L localized in the nucleus and ADK-S localized in the cytoplasm. The nuclear localization of ADK-L and its biochemical link to the transmethylation pathway suggest a specific role for gene regulation via epigenetic mechanisms. Recent evidence reveals an adenosine receptor-independent role of ADK in determining the global methylation status of DNA and thereby contributing to epigenomic regulation. Here we summarize recent progress in understanding the biochemical interactions between adenosine metabolism by ADK-L and epigenetic modifications linked to transmethylation reactions. This review will provide a comprehensive overview of ADK-associated changes in DNA methylation in developmental, as well as in pathological conditions including brain injury, epilepsy, vascular diseases, cancer, and diabetes. Challenges in investigating the epigenetic role of ADK for therapeutic gains are briefly discussed.

Adenosine kinase is critical for neointima formation after vascular injury by inducing aberrant DNA hypermethylation

AIMS

Adenosine receptors and extracellular adenosine have been demonstrated to modulate vascular smooth muscle cell (VSMC) proliferation and neointima formation. Adenosine kinase (ADK) is a major enzyme regulating intracellular adenosine levels but is function in VSMC remains unclear. Here, we investigated the role of ADK in vascular injury-induced smooth muscle proliferation and delineated the mechanisms underlying its action.

METHODS AND RESULTS

We found that ADK expression was higher in the neointima of injured vessels and in platelet-derived growth factor-treated VSMCs. Genetic and pharmacological inhibition of ADK was enough to attenuate arterial injury-induced neointima formation due to inhibition of VSMC proliferation. Mechanistically, using infinium methylation assays and bisulfite sequencing, we showed that ADK metabolized the intracellular adenosine and potentiated the transmethylation pathway, then induced the aberrant DNA hypermethylation. Pharmacological inhibition of aberrant DNA hypermethylation increased KLF4 expression and suppressed VSMC proliferation as well as the neointima formation. Importantly, in human femoral arteries, we observed increased ADK expression and DNA hypermethylation as well as decreased KLF4 expression in neointimal VSMCs of stenotic vessels suggesting that our findings in mice are relevant for human disease and may hold translational significance.

CONCLUSION

Our study unravels a novel mechanism by which ADK promotes VSMC proliferation via inducing aberrant DNA hypermethylation, thereby down-regulating KLF4 expression and promoting neointima formation. These findings advance the possibility of targeting ADK as an epigenetic modulator to combat vascular injury.

Epigenetic factors in atherosclerosis: DNA methylation, folic acid metabolism, and intestinal microbiota

Atherosclerosis is a complex disease, influenced by both genetic and non-genetic factors. The most important epigenetic mechanism in the pathogenesis of atherosclerosis is DNA methylation, which involves modification of the gene without changes in the gene sequence. Nutrients involved in one-carbon metabolism interact to regulate DNA methylation, especially folic acid and B vitamins. Deficiencies in folic acid and other nutrients, such as vitamins B6 and B12, can increase homocysteine levels, induce endothelial dysfunction, and accelerate atherosclerotic pathological processes. Supplemented nutrients can improve DNA methylation status, reduce levels of inflammatory factors, and delay the process of atherosclerosis. In this review, the influence of intestinal flora on folate metabolism and epigenetics is also considered.

Dysregulation of adenosine kinase isoforms in breast cancer

Dysregulated adenosine signaling pathway has been evidenced in the pathogenesis of breast cancer. However, the role of adenosine kinase (ADK) in tumorigenesis remains unclear while it crucially regulates the removal and availability of adenosine. ADK has two isoforms that localize to discrete subcellular spaces: i.e., nuclear, long-isoform (ADK-L) and cytosolic, short-isoform (ADK-S). We hypothesized that these two ADK isoforms would be differentially expressed in breast cancer and may contribute to divergent cellular actions in cancer. In this study, we examined the expression profiles of ADK isoforms in breast cancer tissues from 46 patient and followed up with an in vitro investigation by knocking down the expression of ADK-L or ADK-S using CRISPR gene editing to evaluate the role of ADK isoform in cancer progression and metastasis of cultured triple-negative breast cancer cell line MDA-MB-231. We demonstrated that (i) ADK-L expression level was significantly increased in breast cancer tissues versus paired normal tissues adjacent to tumor, whereas the ADK-S expression levels were not significantly different between cancerous and normal tissues; (ii) CRISPR/Cas9-mediated downregulation of ADK isoforms, led to suppressed cellular proliferation, division, and migration of cultured breast cancer cells; (iii) ADK-L knockdown significantly upregulated gene expression of matrix metalloproteinase (ADAM23, 9.93-fold; MMP9, 24.58-fold) and downregulated expression of cyclin D2 (CCND2, -30.76-fold), adhesive glycoprotein THBS1 (-8.28-fold), and cystatin E/M (CST6, -16.32-fold). Our findings suggest a potential role of ADK-L in mitogenesis, tumorigenesis, and tumor-associated tissue remodeling and invasion; and the manipulation of ADK-L holds promise as a therapeutic strategy for aggressive breast cancer.