Increased Protein Arginine Methylation in Chronic Hypoxia

Hypoxia-inducible PRMT2 addiction in glioblastomas

Hypoxia-inducible transcription factors (HIFs) are key transcription factors for cellular response to low oxygen levels. However, the specific mediators responsible for activating downstream transcription are not well characterized. We previously identified Protein Arginine methyltransferase 2 (PRMT2), a highly expressed methyltransferase in glioblastoma multiforme, as a transcription co-activator. And we established a connection between PRMT2-mediated histone H3R8 asymmetric methylation (H3R8me2a) and transcription activation. Here we find that PRMT2 is activated by HIF1α under hypoxic conditions. And we demonstrate that PRMT2 and its H3R8me2a activity are required for the transcription activation of a significant subset of hypoxia-induced genes. Consequently, the inactivation of PRMT2 suppresses hypoxia-induced glioblastoma cell migration, attenuates tumor progression, and enhances chemotherapeutic sensitivity in mouse xenograft models. In addition, our analysis of clinical glioma specimens reveals a correlation between PRMT2 protein levels, HIF1α abundance, and an unfavorable prognosis. Our study establishes HIF1α-induced PRMT2 as a critical modulator in the activation of hypoxia-related transcriptional programs, ultimately driving malignant progression.

Effect of Obstructive Sleep Apnea and CPAP Treatment on the Bioavailability of Erythrocyte and Plasma Nitric Oxide

INTRODUCTION

Endothelial dysfunction resulting from decreased nitric oxide (NO) bioavailability is an important mechanism that increases cardiovascular risk in subjects with obstructive sleep apnea (OSA). NO is produced by nitric oxide synthase (NOS) in a reaction that converts L-arginine to L-citrulline. Asymmetric-dimethylarginine (ADMA) is created by L-arginine and is a naturally occurring competitive inhibitor of nitric oxide synthase (NOS). The aim of our study was to verify if erythrocytes could play a role in the storage and accumulation of ADMA in OSA patients. The crosstalk between erythrocyte-ADMA, SDMA, L-arginine, and L-citrulline levels and endothelial function was investigated in OSA subjects both at baseline and prospectively following 1-year CPAP (continuous positive airway pressure) treatment.

MATERIAL AND METHODS

A total of 46 subjects with OSA were enrolled in this study and divided into two groups: those with moderate-to-severe OSA and those with mild or no OSA. A physical examination was followed by blood collection for the assessment of biochemical cardiovascular risk factors and the nitric oxide bioavailability parameters both in plasma and erythrocytes. Vasodilative endothelial function was assessed using Laser Doppler Flowmetry (LDF).

RESULTS

No significant changes regarding the NO pathway metabolites were noted apart from the plasma L-citrulline concentration, which was decreased in patients with OSA (26.9 ± 7.4 vs. 33.1 ± 9.4 μM, p < 0.05). The erythrocyte ADMA concentration was lower than in plasma irrespective of the presence of OSA (0.33 ± 0.12 vs. 0.45 ± 0.08 μM in OSA, p < 0.05 and 0.33 ± 0.1 vs. 0.45 ± 0.07 μM in the control, p < 0.05). No significant changes regarding the LDF were found. CPAP treatment did not change the levels of NO metabolites in the erythrocytes.

CONCLUSIONS

The erythrocyte pool of the NO metabolic pathway intermediates does not depend on OSA and its treatment, whereas the erythrocytes could constitute a high-volume buffer in their storage Hence, the results from this prospective study are a step forward in understanding the role of the erythrocyte compartment and the intra-erythrocyte pathways regulating NO bioavailability and paracrine endothelial function in the hypoxia-reoxygenation setting, such as obstructive sleep apnea.

Involvement of inflammatory cytokines and epigenetic modification of the mtTFA complex in T-helper cells of patients' suffering from non-small cell lung cancer and chronic obstructive pulmonary disease

Dysregulated inflammatory response plays a crucial role in the pathogenesis of chronic obstructive pulmonary disease (COPD) and Non-Small cell lung cancer (NSCLC). Hence, the purpose of this research is to uncover the link between alterations in inflammatory cytokine levels and disease progression in CD4⁺T cells of patients suffering from COPD and lung cancer. We also investigated the epigenetic regulation of mtTFA to delineate the role of oxidative stress-mediated inflammation in Lung cancer and COPD. The RT² Profiler PCR array was used to examine the differential expression pattern of inflammatory genes in CD4⁺ T helper (Th) cells from COPD, NSCLC, and control subjects. Candidate inflammatory gene loci were selected and the enrichment of transcriptional factor and histone modifiers was analysed using ChIP-qPCR. In comparison to control subjects, a set of genes (e.g., BMP2, CCL2, IL5, VEGFA, etc.) are over-expressed whereas another set of genes (e.g., AIMP1, IFNG, LTA, LTB, TNF, etc.) are under-expressed in both COPD and NSCLC patients. The increased percent enrichment of inflammation-associated transcription factors including NF-kB, CREB, HIF1, and MYC at the loci of inflammatory genes was revealed by our chromatin immunoprecipitation (ChIP) data. H3K4me3, H3K9me3, H3K14Ac, HDAC1, 2, 3, 6 all showed dysregulated enrichment at the VEGFA gene locus. One of the epigenetic modifications, histone methylation, was found to be abnormal in the mtTFA complex in COPD and NSCLC patients in comparison to controls. Although there is mounting evidence of several links between these disorders, therapeutic options remain inadequate. Our findings contribute to the body of knowledge about therapeutic techniques that use inflammatory cytokines as a prognostic marker and highlight the need for epigenetic therapy for these debilitating lung diseases.

Endothelial PRMT5 plays a crucial role in angiogenesis after acute ischemic injury

Arginine methylation mediated by protein arginine methyltransferases (PRMTs) has been shown to be an important posttranslational mechanism involved in various biological processes. Herein, we sought to investigate whether PRMT5, a major type II enzyme, is involved in pathological angiogenesis and, if so, to elucidate the molecular mechanism involved. Our results show that PRMT5 expression is significantly upregulated in ischemic tissues and hypoxic endothelial cells (ECs). Endothelial-specific Prmt5-KO mice were generated to define the role of PRMT5 in hindlimb ischemia-induced angiogenesis. We found that these mice exhibited impaired recovery of blood perfusion and motor function of the lower limbs, an impairment that was accompanied by decreased vascular density and increased necrosis as compared with their WT littermates. Furthermore, both pharmacological and genetic inhibition of PRMT5 significantly attenuated EC proliferation, migration, tube formation, and aortic ring sprouting. Mechanistically, we showed that inhibition of PRMT5 markedly attenuated hypoxia-induced factor 1-α (HIF-1α) protein stability and vascular endothelial growth factor-induced (VEGF-induced) signaling pathways in ECs. Our results provide compelling evidence demonstrating a crucial role of PRMT5 in hypoxia-induced angiogenesis and suggest that inhibition of PRMT5 may provide novel therapeutic strategies for the treatment of abnormal angiogenesis-related diseases, such as cancer and diabetic retinopathy.

Dysregulation of the Nitric Oxide/Dimethylarginine Pathway in Hypoxic Pulmonary Vasoconstriction—Molecular Mechanisms and Clinical Significance

The pulmonary circulation responds to hypoxia with vasoconstriction, a mechanism that helps to adapt to short-lived hypoxic episodes. When sustained, hypoxic pulmonary vasoconstriction (HPV) may become deleterious, causing right ventricular hypertrophy and failure, and contributing to morbidity and mortality in the late stages of several chronic pulmonary diseases. Nitric oxide (NO) is an important endothelial vasodilator. Its release is regulated, amongst other mechanisms, by the presence of endogenous inhibitors like asymmetric dimethylarginine (ADMA). Evidence has accumulated in recent years that elevated ADMA may be implicated in the pathogenesis of HPV and in its clinical sequelae, like pulmonary arterial hypertension (PAH). PAH is one phenotypic trait in experimental models with disrupted ADMA metabolism. In high altitude, elevation of ADMA occurs during long-term exposure to chronic or chronic intermittent hypobaric hypoxia; ADMA is significantly associated with high altitude pulmonary hypertension. High ADMA concentration was also reported in patients with chronic obstructive lung disease, obstructive sleep apnoea syndrome, and overlap syndrome, suggesting a pathophysiological role for ADMA-mediated impairment of endothelium-dependent, NO-mediated pulmonary vasodilation in these clinically relevant conditions. Improved understanding of the molecular (dys-)regulation of pathways controlling ADMA concentration may help to dissect the pathophysiology and find novel therapeutic options for these diseases.

Epigenetic Mechanisms in Parenchymal Lung Diseases: Bystanders or Therapeutic Targets?

Epigenetic responses due to environmental changes alter chromatin structure, which in turn modifies the phenotype, gene expression profile, and activity of each cell type that has a role in the pathophysiology of a disease. Pulmonary diseases are one of the major causes of death in the world, including lung cancer, idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD), pulmonary hypertension (PH), lung tuberculosis, pulmonary embolism, and asthma. Several lines of evidence indicate that epigenetic modifications may be one of the main factors to explain the increasing incidence and prevalence of lung diseases including IPF and COPD. Interestingly, isolated fibroblasts and smooth muscle cells from patients with pulmonary diseases such as IPF and PH that were cultured ex vivo maintained the disease phenotype. The cells often show a hyper-proliferative, apoptosis-resistant phenotype with increased expression of extracellular matrix (ECM) and activated focal adhesions suggesting the presence of an epigenetically imprinted phenotype. Moreover, many abnormalities observed in molecular processes in IPF patients are shown to be epigenetically regulated, such as innate immunity, cellular senescence, and apoptotic cell death. DNA methylation, histone modification, and microRNA regulation constitute the most common epigenetic modification mechanisms.

Structure, Activity and Function of the PRMT2 Protein Arginine Methyltransferase

PRMT2 belongs to the protein arginine methyltransferase (PRMT) family, which catalyzes the arginine methylation of target proteins. As a type I enzyme, PRMT2 produces asymmetric dimethyl arginine and has been shown to have weak methyltransferase activity on histone substrates in vitro, suggesting that its authentic substrates have not yet been found. PRMT2 contains the canonical PRMT methylation core and a unique Src homology 3 domain. Studies have demonstrated its clear implication in many different cellular processes. PRMT2 acts as a coactivator of several nuclear hormone receptors and is known to interact with a multitude of splicing-related proteins. Furthermore, PRMT2 is aberrantly expressed in several cancer types, including breast cancer and glioblastoma. These reports highlight the crucial role played by PRMT2 and the need for a better characterization of its activity and cellular functions.

Protein arginine methyltransferase 8 modulates mitochondrial bioenergetics and neuroinflammation after hypoxic stress

Protein arginine methyltransferases (PRMTs) are a family of enzymes involved in gene regulation and protein/histone modifications. PRMT8 is primarily expressed in the central nervous system, specifically within the cellular membrane and synaptic vesicles. Recently, PRMT8 has been described to play key roles in neuronal signaling such as a regulator of dendritic arborization, synaptic function and maturation, and neuronal differentiation and plasticity. Here, we examined the role of PRMT8 in response to hypoxia-induced stress in brain metabolism. Our results from liquid chromatography mass spectrometry, mitochondrial oxygen consumption rate (OCR), and protein analyses indicate that PRMT8(-/-) knockout mice presented with altered membrane phospholipid composition, decreased mitochondrial stress capacity, and increased neuroinflammatory markers, such as TNF-α and ionized calcium binding adaptor molecule 1 (Iba1, a specific marker for microglia/macrophage activation) after hypoxic stress. Furthermore, adenovirus-based overexpression of PRMT8 reversed the changes in membrane phospholipid composition, mitochondrial stress capacity, and neuroinflammatory markers. Together, our findings establish PRMT8 as an important regulatory component of membrane phospholipid composition, short-term memory function, mitochondrial function, and neuroinflammation in response to hypoxic stress.

Endothelial Dysfunction Driven by Hypoxia-The Influence of Oxygen Deficiency on NO Bioavailability

Cardiovascular diseases (CVDs) are the leading cause of death worldwide. The initial stage of CVDs is characterized by endothelial dysfunction, defined as the limited bioavailability of nitric oxide (NO). Thus, any factors that interfere with the synthesis or metabolism of NO in endothelial cells are involved in CVD pathogenesis. It is well established that hypoxia is both the triggering factor as well as the accompanying factor in cardiovascular disease, and diminished tissue oxygen levels have been reported to influence endothelial NO bioavailability. In endothelial cells, NO is produced by endothelial nitric oxide synthase (eNOS) from L-Arg, with tetrahydrobiopterin (BH₄) as an essential cofactor. Here, we discuss the mechanisms by which hypoxia affects NO bioavailability, including regulation of eNOS expression and activity. What is particularly important is the fact that hypoxia contributes to the depletion of cofactor BH₄ and deficiency of substrate L-Arg, and thus elicits eNOS uncoupling-a state in which the enzyme produces superoxide instead of NO. eNOS uncoupling and the resulting oxidative stress is the major driver of endothelial dysfunction and atherogenesis. Moreover, hypoxia induces impairment in mitochondrial respiration and endothelial cell activation; thus, oxidative stress and inflammation, along with the hypoxic response, contribute to the development of endothelial dysfunction.

Upregulation of DDAH2 Limits Pulmonary Hypertension and Right Ventricular Hypertrophy During Chronic Hypoxia in Ddah1 Knockout Mice

Objective: Chronic hypoxia causes pulmonary vasoconstriction leading to pulmonary hypertension and right ventricular hypertrophy. Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) synthesis; its level increases in hypoxia (HX) concomitantly with reduced activity of dimethylarginine dimethylaminohydrolases (DDAH-1 and DDAH-2), enzymes metabolizing ADMA. Ddah1 knockout (KO) mice may therefore help to understand the pathophysiological roles of this enzyme and its substrate, ADMA, in the development of hypoxia-associated pulmonary hypertension.

Methods: Ddah1 KO mice and their wild-type (WT) littermates were subjected to normoxia (NX) or for 21 days. We measured ADMA concentration in plasma and lungs, DDAH1 and DDAH2 mRNA and protein expression in the lungs, right ventricular systolic pressure (RVSP), right ventricular hypertrophy by the Fulton index, and cardiomyocyte hypertrophy by dystrophin staining of the heart.

Results: Ddah1 KO mice had higher ADMA concentrations in plasma and in lung tissue than WT in NX (p < 0.05). ADMA significantly increased in WT-HX in plasma and lungs, while there were no significant differences in WT-HX vs. KO-HX. This finding was paralleled by a 38 ± 13% reduction in Ddah1 but not Ddah2 mRNA expression, and reduced DDAH1 protein expression but stable DDAH2 protein levels in WT mice. Ddah1 KO mice showed significant elevation of DDAH2 protein but not mRNA levels, which further increased in HX. HX led to increased RVSP and right ventricular hypertrophy in both, WT and KO mice, with no significant differences between both genotypes.

Conclusions: Chronic hypoxia causes an elevation of ADMA, which may impair NO production and lead to endothelial dysfunction and vasoconstriction. Downregulation of DDAH1 expression and activity may be involved in this; however, knockout of the Ddah1 gene does not modify the hypoxia-induced pathophysiological changes of pulmonary blood pressure and right ventricular hypertrophy, possibly due to compensatory upregulation of DDAH2 protein.

Effect of a Supervised Peridialytic Exercise Program on Serum Asymmetric Dimethylarginine in Maintenance Hemodialysis Patients

End-stage renal disease (ESRD) patients treated with maintenance haemodialysis (MHD) have alarmingly high atherosclerotic cardiovascular disease morbidity and mortality. Nitric oxide (NO) is the principal endogenous antiatherosclerotic molecule. Increased asymmetric dimethylarginine (ADMA), an endogenous NO synthase inhibitor, was strongly implicated in endothelial dysfunction, premature atherosclerosis, vascular events, and mortality. Regular physical exercise effectively decreased serum ADMA in several patient cohorts, but this potential benefit has not been specifically explored among MHD patients. Forty-four middle-aged ESRD patients treated with thrice-weekly MHD for ≥6 months completed a 6-months regimen of peridialytic lower limb exercise comprising predialytic 10–12 stretching cycles and 20–30 minutes of intradialytic pedaling cycles. Before and after the study, predialytic haemoglobin, serum ADMA, urea, creatinine, calcium, phosphorus, and C-reactive protein (CRP) were measured. Dialysis adequacy was assessed by single-pool Kt/V. The average total physical activity (PA) level was assessed by the International Physical Activity Questionnaire (IPAQ). P values <0.05 denoted a statistical significance. The overall level of PA, on both categorical and continuous scales, has significantly increased after application of the exercise program. However, S. ADMA increased from a median of 2375 to 3000 ng/mL (P=0.016). Thirty-one patients sustained an increase in S. ADMA (ADMA_Inc), whereas 13 patients had a declining or stable S. ADMA (ADMA_Dec). Compared with ADMA_Inc, ADMA_Dec patients had significantly higher Kt/V (P=0.02), higher grade of the basal general PA level (P=0.017), and significantly fewer intradialytic hypotension episodes (IDHs) (P=0.019). The increase in the S. ADMA and the poststudy S. ADMA level had statistically significant positive correlations with the number of IDHs (r = 0.401, P=0.007 and r = 0.305, P=0.044, respectively). A 6-month program of combined aerobic and resistance peridialytic exercise failed to reduce S. ADMA in most MHD patients studied. A modest S. ADMA decline, however, occurred in patients with higher basal PA levels, higher Kt/V, and less IDHs. A potential exercise benefit may be promoted by a multidisciplinary approach targeting increased PA, improved dialysis efficiency, and prevention of IDHs.

Targeting chromatin dysregulation in organ fibrosis

Fibrosis leads to destruction of organ architecture accompanied by chronic inflammation and loss of function. Fibrosis affects nearly every organ in the body and accounts for ∼45% of total deaths worldwide. Over the past decade, tremendous progress has been made in understanding the basic mechanisms leading to organ fibrosis. However, we are limited with therapeutic options and there is a significant need to develop highly effective anti-fibrotic therapies. Recent advances in sequencing technologies have advanced the burgeoning field of epigenetics towards molecular understanding at a higher resolution. Here we provide a comprehensive review of the recent advances in chromatin regulatory processes, specifically DNA methylation, post-translational modification of histones, and chromatin remodeling complexes in kidney, liver and lung fibrosis. Although this research field is young, we discuss new strategies for potential therapeutic interventions for treating organ fibrosis.

The U-shaped association of altitudes with prevalence of hypertension among residents in Tibet, China

We aimed to evaluate the association of altitudes with the prevalence of hypertension among residents aged 15 years and above in Tibet, China. Data for 11,407 Tibetan residents from the National Health Services Survey in 2013 were analyzed. Association between altitudes and prevalence of physician-diagnosed hypertension was assessed by two logistic regression models as follows: (i) a base model adjusted for age and gender, and (ii) a full model additionally adjusted for body mass index, education, marital status, area of residence, distance to the nearest medical institute, smoking, drinking, and exercise. Nonlinear relationship between altitudes and prevalence of hypertension was explored by restricted cubic spline analyses. Sensitivity analyses were conducted by restricting to residents of rural and/or nomadic areas. The prevalence of hypertension was estimated to be 37.6%. We found a U-shaped association between altitudes and prevalence of physician-diagnosed hypertension with a turning point at around 3800 m (12,467 ft). For residents living above 3800 m, a 1000 m increase in altitudes was associated with 2.05 (95% confidence interval [CI]: 1.62-2.61) times higher odds of having physician-diagnosed hypertension, after adjusting for age and gender. When further controlling for all covariates, the odds ratio (OR) dropped to 1.87 (95% CI: 1.46-2.41). For residents living below 3800 m, a 1000 m increase was associated with 0.29 (95% CI: 0.19-0.44) times less likelihood of having physician-diagnosed hypertension in the full model. Sensitivity analyses among residents in rural and/or nomadic areas showed similar associations. To conclude, altitudes were in a U-shaped association with prevalence of hypertension.

Metabolism of asymmetric dimethylarginine in hypoxia: from bench to bedside

Acute hypoxia and chronic hypoxia induce pulmonary vasoconstriction. While hypoxic pulmonary vasoconstriction is a physiological response if parts of the lung are affected, global exposure to hypoxic conditions may lead to clinical conditions like high-altitude pulmonary hypertension. Nitric oxide is the major vasodilator released from the vascular endothelium. Nitric oxide-dependent vasodilation is impaired in hypoxic conditions. Inhibition of nitric oxide synthesis is the most rapid and easily reversible molecular mechanism to regulate nitric oxide-dependent vascular function in response to physiological and pathophysiological stimuli. Asymmetric dimethylarginine is an endogenous, competitive inhibitor of nitric oxide synthase and a risk marker for major cardiovascular events and mortality. Elevated asymmetric dimethylarginine has been observed in animal models of hypoxia as well as in human cohorts under chronic and chronic intermittent hypoxia at high altitude. In lowlanders, asymmetric dimethylarginine is high in patients with pulmonary hypertension. We have recently shown that high asymmetric dimethylarginine at sea level is a predictor for high-altitude pulmonary hypertension. Asymmetric dimethylarginine is a highly regulated molecule, both by its biosynthesis and metabolism. Methylation of L-arginine by protein arginine methyltransferases was shown to be increased in hypoxia. Furthermore, the metabolism of asymmetric dimethylarginine by dimethylarginine dimethylaminohydrolases (DDAH1 and DDAH2) is decreased in animal models of hypoxia. Whether these changes are caused by transcriptional or posttranslational modifications remains to be elucidated. Current data suggest a major role of asymmetric dimethylarginine in regulating pulmonary arterial nitric oxide production in hypoxia. Further studies are needed to decipher the molecular mechanisms regulating asymmetric dimethylarginine in hypoxia and to understand their clinical significance.

Protein Arginine Methyltransferases in Cardiovascular and Neuronal Function

The methylation of arginine residues by protein arginine methyltransferases (PRMTs) is a type of post-translational modification which is important for numerous cellular processes, including mRNA splicing, DNA repair, signal transduction, protein interaction, and transport. PRMTs have been extensively associated with various pathologies, including cancer, inflammation, and immunity response. However, the role of PRMTs has not been well described in vascular and neurological function. Aberrant expression of PRMTs can alter its metabolic products, asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA). Increased ADMA levels are recognized as an independent risk factor for cardiovascular disease and mortality. Recent studies have provided considerable advances in the development of small-molecule inhibitors of PRMTs to study their function under normal and pathological states. In this review, we aim to elucidate the particular roles of PRMTs in vascular and neuronal function as a potential target for cardiovascular and neurological diseases.

Asymmetric Dimethylarginine at Sea Level Is a Predictive Marker of Hypoxic Pulmonary Arterial Hypertension at High Altitude

Background: Prolonged exposure to altitude-associated chronic hypoxia (CH) may cause high-altitude pulmonary hypertension (HAPH). Chronic intermittent hypobaric hypoxia (CIH) occurs in individuals who commute between sea level and high altitude. CIH is associated with repetitive acute hypoxic acclimatization and conveys the long-term risk of HAPH. As nitric oxide (NO) regulates pulmonary vascular tone and asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of NO synthesis, we investigated whether ADMA concentration at sea level predicts HAPH among Chilean frontiers personnel exposed to 6 months of CIH.

Methods: In this prospective study, 123 healthy army draftees were subjected to CIH (5 days at 3,550 m, 2 days at sea level) for 6 months. In 100 study participants with complete data, ADMA, symmetric dimethylarginine (SDMA), L-arginine, arterial oxygen saturation (SaO₂), systemic blood pressure, and hematocrit were assessed at months 0 (sea level), 1, 4, and 6. Acclimatization to altitude was determined using the Lake Louise Score (LLS) and the presence of acute mountain sickness (AMS). Echocardiography was performed after 6 months of CIH in 43 individuals with either good (n = 23) or poor (n = 20) acclimatization.

Results: SaO₂ acutely decreased at altitude and plateaued at 90% thereafter. ADMA increased and SDMA decreased during the study course. The incidence of AMS and the LLS was high after the first ascent (53 and 3.1 ± 2.4) and at 1 month of CIH (47 and 3.0 ± 2.6), but decreased to 20 and 1.4 ± 2.0 at month 6 (both p < 0.001). Eighteen participants (42%) showed a mean pulmonary arterial pressure (mPAP) >25 mm Hg, out of which 9 (21%) were classified as HAPH (mPAP ≥ 30 mm Hg). ADMA at sea level was significantly associated with mPAP at high altitude in month 6 (R = 0.413; p = 0.007). In ROC analysis, a cutoff for baseline ADMA of 0.665 μmol/L was determined to predict HAPH (mPAP > 30 mm Hg) with a sensitivity of 100% and a specificity of 63.6%.

Conclusions: ADMA concentration increases during CIH. ADMA at sea level is an independent predictive biomarker of HAPH. SDMA concentration decreases during CIH and shows no association with HAPH. Our data support a role of impaired NO-mediated pulmonary vasodilation in the pathogenesis of HAPH.

The methylation induced by protein arginine methyltransferase 5 promotes tumorigenesis and progression of lung cancer

Arginine methylation as a common pattern of post-translational modification is involved in many cellular biological processes. Protein arginine methyltransferase 5 (PRMT5) is a primary enzyme in charge of symmetric dimethylation (me2s) of arginine residues. Increasing literatures lead to the belief that PRMT5, as a potential oncogene, plays crucial roles in the tumorigenesis and progression of cancers. First of all, PRMT5 is overexpressed in several cancer cells, with various sub-cellular localization in different type of cells and different phases. Besides, PRMT5 participates in controlling cellular proliferation, differentiation, invasion, migration as well apoptosis through histone and other protein methylation. Moreover, PRMT5 is essential for growth and metastasis of lung cancer cells, and its overexpression indicates a poor clinical outcome of lung cancer. Therefore, in this review, we reviewed the substantial new literatures on PRMT5 and its functions, in order to highlight the significance of understanding this essential enzyme in lung cancer tumorigenesis and progression.

Oxymatrine prevents the development of monocrotaline-induced pulmonary hypertension via regulation of the NG, NG-dimethyl-L-arginine metabolism pathways in rats

The purpose of this study was to investigate the potential effect of oxymatrine in monocrotaline-induced pulmonary hypertension and its possible influence on the N^G,N^G-dimethyl-L-arginine (ADMA) metabolism pathway. Pulmonary hypertension was induced in rats by a single-dose injection of monocrotaline (60 mg/kg). Daily oral administration of oxymatrine (25, 50 and 100 mg/kg) was started on the day following the monocrotaline injection for 28 days. Oxymatrine (50 and 100 mg/kg) significantly attenuated monocrotaline-induced lung and right ventricular hypertrophy, right ventricular systolic pressure elevation, and right ventricular dysfunction. Oxymatrine also reduced the thickening of monocrotaline-induced pulmonary arterial medial wall. Meanwhile, oxymatrine normalized the level of pulmonary asymmetric ADMA and attenuated the upregulated expression of protein arginine methyltransferase 1 (PRMT1). Oxymatrine had no effect on the expression of protein arginine methyltransferase 2 (PRMT2) and N^G,N^G-Dimethylarginine dimethylaminohydrolase 1 (DDAH1), which were upregulated in monocrotaline-induced pulmonary arterial hypertensive rats. However, the expression of the protein N^G,N^G-Dimethylarginine dimethylaminohydrolase 2 (DDAH2) did not differ among all groups (all P﹥0.05). These results suggest that oxymatrine may offer protective effects on the development of pulmonary hypertension by ameliorating pulmonary remodeling and modulating the ADMA metabolism pathway.

Protein arginine N-methyltransferase 2 reverses tamoxifen resistance in breast cancer cells through suppression of ER-α36

Breast cancer is one of the most common malignancies in females, and 17β-estradiol (E2)/estrogen receptor α (ERα) signaling plays an important role in the initiation and progression of breast cancer. The role of the ER-α subtype and its co-regulator in the initiation of breast cancer and the occurrence of tamoxifen resistance remains to be further elucidated. In our previous studies, protein arginine N-methyltransferase 2 (PRMT2), a co-regulator of estrogen receptor-α (ER-α), was confirmed to interact with ER-α66 and has the ability to inhibit cell proliferation in breast cancer cells. In the present study, we found that tamoxifen treatment induced a decrease in PRMT2 and an increase in ER-α36 as well as ER-α36-mediated non-genomic effect in MDA-MB-231 cells, which were relatively resistant to tamoxifen by contrast to MCF-7 cells. Moreover, PRMT2 was able to interact with ER-α36 directly, suppress ER-α36 and downstream PI3K/Akt and MAPK/ERK signaling, reversing the tamoxifen resistance of breast cancer cells. The present study may be meaningful for understanding the role of PRMT2 in breast cancer progression and for developing a new endocrine therapeutic strategy for breast cancer patients with tamoxifen resistance.

The potential for targeted rewriting of epigenetic marks in COPD as a new therapeutic approach

Chronic obstructive pulmonary disease (COPD) is an age and smoking related progressive, pulmonary disorder presenting with poorly reversible airflow limitation as a result of chronic bronchitis and emphysema. The prevalence, disease burden for the individual, and mortality of COPD continues to increase, whereas no effective treatment strategies are available. For many years now, a combination of bronchodilators and anti-inflammatory corticosteroids has been most widely used for therapeutic management of patients with persistent COPD. However, this approach has had disappointing results as a large number of COPD patients are corticosteroid resistant. In patients with COPD, there is emerging evidence showing aberrant expression of epigenetic marks such as DNA methylation, histone modifications and microRNAs in blood, sputum and lung tissue. Therefore, novel therapeutic approaches may exist using epigenetic therapy. This review aims to describe and summarize current knowledge of aberrant expression of epigenetic marks in COPD. In addition, tools available for restoration of epigenetic marks are described, as well as delivery mechanisms of epigenetic editors to cells. Targeting epigenetic marks might be a very promising tool for treatment and lung regeneration in COPD in the future.

Arginine Methylation: The Coming of Age

Arginine methylation is a common post-translational modification functioning as an epigenetic regulator of transcription and playing key roles in pre-mRNA splicing, DNA damage signaling, mRNA translation, cell signaling, and cell fate decision. Recently, a wealth of studies using transgenic mouse models and selective PRMT inhibitors helped define physiological roles for protein arginine methyltransferases (PRMTs) linking them to diseases such as cancer and metabolic, neurodegenerative, and muscular disorders. This review describes the recent molecular advances that have been uncovered in normal and diseased mammalian cells.

Effect of iloprost on biomarkers in patients with congenital heart disease-pulmonary arterial hypertension

Some biomarkers play important roles in the endothelial dysfunction of patients with pulmonary arterial hypertension (PAH), including nitric oxide (NO), endothelin‐1 (ET‐1), asymmetric dimethylarginine (ADMA), galectin‐3 (Gal‐3), B‐type natriuretic peptide (BNP), and uric acid (UA). However, studies on these biomarkers in pulmonary artery blood in congenital heart disease‐PAH (CHD‐PAH) and the effect of iloprost on the regulation of biomarkers are lacking. This study investigated potential CHD‐PAH biomarkers and their association with the severity of disease. The effect of iloprost on the regulation of these biomarkers was also studied. A total of 31 patients with CHD‐PAH were enrolled. Seven with positive effects of iloprost (the average reduction in mPAP 11.13±1.73 mm Hg) and 19 with negative effects of iloprost (the average reduction in mPAP 4.21±4.87 mm Hg; iloprost positive group [IPG] vs iloprost negative group [ING], P<.01) and five age‐matched controls were studied. The pulmonary artery blood sample was collected before and after inhaling iloprost, and the plasma concentrations of Gal‐3, ADMA, ET‐1, and NO were measured. A significant positive linear relationship was observed between mPAP and plasma ET‐1, BNP, ADMA, and UA levels in all patients with CHD‐PAH. ET‐1, ADMA, BNP, and UA levels had a significant linear relationship with mean pulmonary arterial pressure, which could be used to predict the severity of CHD‐PAH. ET‐1 might be a potential biomarker to pre‐evaluate the effect of iloprost on CHD‐PAH. Iloprost could affect the expression of Gal‐3 and, therefore, the process of fibrosis could be influenced by iloprost.

PRMT2β, a C-terminal splice variant of PRMT2, inhibits the growth of breast cancer cells

Our previous study reported several alternative splicing variants of arginine N-methyltransferase 2 (PRMT2), which lose different exons in the C-terminals of the wild-type PRMT2 gene. Particularly, due to frame-shifting, PRMT2β encodes a novel amino acid sequence at the C-terminus of the protein, the function of which is not understood. In the present study, we determined the role of PRMT2β in breast cancer cell proliferation, apoptosis and its effect on the Akt signaling pathway. Stable breast cancer MCF7 cell line with lentivirus-mediated PRMT2β overexpression was obtained after selection by puromycin for 2 weeks. The effect of lentivirus-mediated PRMT2β overexpression on breast cancer cellular oncogenic properties was evaluated by MTT, colony formation, cell cycle analysis and apoptosis assays in MCF7 cells. Luciferase activity assay and western blot analysis were performed to characterize the effects of PRMT2β on cyclin D1 promoter activities and the Akt signaling pathway. Tissue microarray was performed to investigate the association of PRMT2β with breast cancer progression. Lentivirus-mediated PRMT2β overexpression suppressed the cell proliferation and colony formation of breast cancer MCF7 cells. PRMT2β overexpression induced cell cycle arrest and apoptosis of MCF7 cells. Furthermore, PRMT2β was revealed to suppress the transcription activity of the cyclin D1 promoter, and PRMT2β was also found to inhibit cyclin D1 expression via the suppression of Akt/GSK-3β signaling in breast cancer cells. Clinically, it was revealed that PRMT2β expression was negatively correlated with human epidermal growth factor receptor 2 (HER2) (p=0.033) in breast tumors. Our results revealed that PRMT2β, a novel splice variant of PRMT2, plays potential antitumor effect by suppressing cyclin D1 expression and inhibiting Akt signaling activity. This also opens a new avenue for treating breast cancer.

Serum asymmetric dimethylarginine and arginine levels predict microvascular and macrovascular complications in type 2 diabetes mellitus

BACKGROUND

Increased oxidative stress in diabetes increases nitric oxide (NO) oxidation and low l-arginine (Arg) could further reduce NO and impair vascular function, thereby accelerating, in the long run, vascular complications. We therefore measured Arg and asymmetric dimethylarginine (ADMA) levels in patients with type 2 diabetes mellitus (T2DM) and healthy controls. Additionally, we observed the diabetic individuals over time to see if Arg and asymmetric dimethylarginine predicted T2DM complications.

METHODS

We examined baseline serum Arg and ADMA levels in a cohort of 105 participants with type 2 diabetes and compared them with an age- and weight-matched nondiabetic group of 137 individuals who served as a reference population. Additionally, we assessed whether Arg and/or ADMA predicted macrovascular and microvascular complications over 6 years of follow-up.

RESULTS

Serum Arg was lower in individuals with T2DM than in controls (64 ± 28 vs 75 ± 31 μmol/L; P = .009) and inversely related to hemoglobin A1c (r = -0.2; P = .002). Over follow-up, we observed that participants with T2DM in the lowest quartile of Arg had increased risk for the subsequent evolution of nephropathy, peripheral neuropathy, and composite microvascular complications (odds ratio [OR] = 5.5; 95% confidence interval [CI] -1.9 to 16; P = .002). The highest ADMA quartile was associated with increased risk for both microvascular (OR = 4.5; 95% CI -1.4 to 14.1; P = .009) and 6.5-year incident macrovascular complications (OR = 8.3; 95% CI 1.9-35.5; P = .004).

CONCLUSION

l-Arginine levels are lower in individuals with T2DM than in matched controls. Both low Arg and high ADMA, independent of each other and adjusted for classical risk factors, predict the incidence of microvascular complications.

Effect of nitric oxide deficiency on the pulmonary PTHrP system

Nitric oxide (NO) deficiency is common in pulmonary diseases, but its effect on pulmonary remodelling is still controversial. As pulmonary parathyroid hormone-related protein (PTHrP) expression is a key regulator of pulmonary fibrosis and development, the effect of chronic NO deficiency on the pulmonary PTHrP system and its relationship with oxidative stress was addressed. NO bioavailability in adult rats was reduced by systemic administration of L-NAME via tap water. To clarify the role of NO synthase (NOS)-3-derived NO on pulmonary expression of PTHrP, NOS-3-deficient mice were used. Captopril and hydralazine were used to reduce the hypertensive effect of L-NAME treatment and to interfere with the pulmonary renin-angiotensin system (RAS). Quantitative RT-PCR and immunoblot techniques were used to characterize the expression of key proteins involved in pulmonary remodelling. L-NAME administration significantly reduced pulmonary NO concentration and caused oxidative stress as characterized by increased pulmonary nitrite concentration and increased expression of NOX2, p47phox and p67phox. Furthermore, L-NAME induced the pulmonary expression of PTHrP and of its corresponding receptor, PTH-1R. Expression of PTHrP and PTH-1R correlated with the expression of two well-established PTHrP downstream targets, ADRP and PPARγ, suggesting an activation of the pulmonary PTHrP system by NO deficiency. Captopril reduced the expression of PTHrP, profibrotic markers and ornithine decarboxylase, but neither that of PTH-1R nor that of ADRP and PPARγ. All transcriptional changes were confirmed in NOS-3-deficient mice. In conclusion, NOS-3-derived NO suppresses pulmonary PTHrP and PTH-1R expression, thereby modifying pulmonary remodelling.

Novel Protein Arginine Methyltransferase 8 Isoform Is Essential for Cell Proliferation

Identification of molecular mechanisms that regulate cellular replicative lifespan is needed to better understand the transition between a normal and a neoplastic cell phenotype. We have previously reported that low oxygen-mediated activity of FGF2 leads to an increase in cellular lifespan and acquisition of regeneration competence in human dermal fibroblasts (iRC cells). Though cells display a more plastic developmental phenotype, they remain non-tumorigenic when injected into SCID mice (Page et al. [2009] Cloning Stem Cells 11:417-426; Page et al. [2011] Eng Part A 17:2629-2640) allowing for investigation of mechanisms that regulate increased cellular lifespan in a non-tumorigenic system. Analysis of chromatin modification enzymes by qRT-PCR revealed a 13.3-fold upregulation of the arginine methyltransferase PRMT8 in iRC cells. Increased protein expression was confirmed in both iRC and human embryonic stem cells-the first demonstration of endogenous human PRMT8 expression outside the brain. Furthermore, iRC cells express a novel PRMT8 mRNA variant. Using siRNA-mediated knockdown we demonstrated that this novel variant was required for proliferation of human dermal fibroblasts (hDFs) and grade IV glioblastomas. PRMT8 upregulation in a non-tumorigenic system may offer a potential diagnostic biomarker and a therapeutic target for cells in pre-cancerous and cancerous states. J. Cell. Biochem. 117: 2056-2066, 2016. © 2016 Wiley Periodicals, Inc.

Coactivator-Associated Arginine Methyltransferase-1 Function in Alveolar Epithelial Senescence and Elastase-Induced Emphysema Susceptibility

Chronic obstructive pulmonary disease (COPD) is characterized by an irreversible loss of lung function and is one of the most prevalent and severe diseases worldwide. A major feature of COPD is emphysema, which is the progressive loss of alveolar tissue. Coactivator-associated arginine methyltransferase-1 (CARM1) regulates histone methylation and the transcription of genes involved in senescence, proliferation, and differentiation. Complete loss of CARM1 leads to disrupted differentiation and maturation of alveolar epithelial type II (ATII) cells. We thus hypothesized that CARM1 regulates the development and progression of emphysema. To address this, we investigated the contribution of CARM1 to alveolar rarefication using the mouse model of elastase-induced emphysema in vivo and small interfering (si)RNA-mediated knockdown in ATII-like LA4 cells in vitro. We demonstrate that emphysema progression in vivo is associated with a time-dependent down-regulation of CARM1. Importantly, elastase-treated CARM1 haploinsufficient mice show significantly increased airspace enlargement (52.5 ± 9.6 μm versus 38.8 ± 5.5 μm; P < 0.01) and lung compliance (2.8 ± 0.32 μl/cm H2O versus 2.4 ± 0.4 μl/cm H2O; P < 0.04) compared with controls. The knockdown of CARM1 in LA4 cells led to decreased sirtuin 1 expression (0.034 ± 0.003 versus 0.022 ± 0.001; P < 0.05) but increased expression of p16 (0.27 ± 0.013 versus 0.31 ± 0.010; P < 0.5) and p21 (0.81 ± 0.088 versus 1.28 ± 0.063; P < 0.01) and higher β-galactosidase-positive senescent cells (50.57 ± 7.36% versus 2.21 ± 0.34%; P < 0.001) compared with scrambled siRNA. We further demonstrated that CARM1 haploinsufficiency impairs transdifferentiation and wound healing (32.18 ± 0.9512% versus 8.769 ± 1.967%; P < 0.001) of alveolar epithelial cells. Overall, these results reveal a novel function of CARM1 in regulating emphysema development and premature lung aging via alveolar senescence as well as impaired regeneration, repair, and differentiation of ATII cells.

Small Molecule Inhibitors of Protein Arginine Methyltransferases

INTRODUCTION

Arginine methylation is an abundant posttranslational modification occurring in mammalian cells and catalyzed by protein arginine methyltransferases (PRMTs). Misregulation and aberrant expression of PRMTs are associated with various disease states, notably cancer. PRMTs are prominent therapeutic targets in drug discovery.

AREAS COVERED

The authors provide an updated review of the research on the development of chemical modulators for PRMTs. Great efforts are seen in screening and designing potent and selective PRMT inhibitors, and a number of micromolar and submicromolar inhibitors have been obtained for key PRMT enzymes such as PRMT1, CARM1, and PRMT5. The authors provide a focus on their chemical structures, mechanism of action, and pharmacological activities. Pros and cons of each type of inhibitors are also discussed.

EXPERT OPINION

Several key challenging issues exist in PRMT inhibitor discovery. Structural mechanisms of many PRMT inhibitors remain unclear. There lacks consistency in potency data due to divergence of assay methods and conditions. Physiologically relevant cellular assays are warranted. Substantial engagements are needed to investigate pharmacodynamics and pharmacokinetics of the new PRMT inhibitors in pertinent disease models. Discovery and evaluation of potent, isoform-selective, cell-permeable and in vivo-active PRMT modulators will continue to be an active arena of research in years ahead.

Effect of protein arginine methyltransferase-1 inhibition on hypoxia-induced vasoconstriction

Hypoxia is defined as a decrease in the oxygen supply to a level below physiological levels which is insufficient to maintain cellular function, in the presence of unrestricted coronary inflow. It is one of the leading causes of global mortality and morbidity, due to its association with the pathology of cancer, cardiovascular disease and stroke. The common feature in these pathologies is the limitation of oxygen availability that participates in the development of these conditions. The pulmonary response to hypoxia, when hypoxia is localized, is hypoxic pulmonary vasoconstriction (HPV). HPV is a physiological and self-regulatory mechanism by which pulmonary capillary blood flow is automatically adjusted to alveolar ventilation for maintaining the optimal balance of ventilation and perfusion. In pathological conditions, HPV occurs as an acute episode during progressive critical illness or as a sustained response with vascular remodeling and pulmonary hypertension. Inspite of the hypoxia-induced shift in the redox status to a more oxidized state, the endothelium-dependent mediators of HPV that cause vasoconstrictor response to hypoxia include nitric oxide (NO), endothelin-1 and angiotensin-II. Indeed, in chronic hypoxia, due to the enhanced reactive oxygen species (ROS) generation, inhibition of endothelial nitric oxide synthase (eNOS) activity and reduced nitric oxide (NO) production there is an imbalance in the vasoconstriction-vasodilation status toward constriction. It is our hypothesis that, in hypoxic stress, a key player in initiating this imbalance is the enzyme, protein arginine methyltransferase-1 (PRMT1) which indirectly affects eNOS activity by increased production of asymmetric dimethylarginine (ADMA), a NOS-inhibitor. Thus, pharmacological inhibition of PRMT1 should restore the cellular and vascular homeostasis in hypoxic conditions.

PRMT1 Upregulated by Epithelial Proinflammatory Cytokines Participates in COX2 Expression in Fibroblasts and Chronic Antigen-Induced Pulmonary Inflammation

Protein arginine methyltransferase (PRMT)1, methylating both histones and key cellular proteins, has emerged as a key regulator of various cellular processes. This study aimed to identify the mechanism that regulates PRMT1 in chronic Ag-induced pulmonary inflammation (AIPI) in the E3 rat asthma model. E3 rats were challenged with OVA for 1 or 8 wk to induce acute or chronic AIPI. Expression of mRNAs was detected by real-time quantitative PCR. PRMT1, TGF-β, COX2, and vascular endothelial growth factor protein expression in lung tissues was determined by immunohistochemistry staining and Western blotting. In the in vitro study, IL-4-stimulated lung epithelial cell (A549) medium (ISEM) with or without anti-TGF-β Ab was applied to human fibroblasts from lung (HFL1). The proliferation of HFL1 was determined by MTT. AMI-1 (pan-PRMT inhibitor) was administered intranasally to chronic AIPI rats to determine PRMT effects on asthmatic parameters. In lung tissue sections, PRMT1 expression was significantly upregulated, mainly in epithelial cells, in acute AIPI lungs, whereas it was significantly upregulated mainly in fibroblasts in chronic AIPI lungs. The in vitro study revealed that ISEM elevates PRMT1, COX2, and vascular endothelial growth factor expressions, and it promoted fibroblast proliferation. The application of anti-TGF-β Ab suppressed COX2 upregulation by ISEM. AMI-1 inhibited the expression of COX2 in TGF-β-stimulated cells. In the in vivo experiment, AMI-1 administered to AIPI rats reduced COX2 production and humoral immune response, and it abrogated mucus secretion and collagen generation. These findings suggested that TGF-β-induced PRMT1 expression participates in fibroblast proliferation and chronic airway inflammation in AIPI.

Antidiabetic drug metformin is effective on the metabolism of asymmetric dimethylarginine in experimental liver injury

AIMS

We aimed to investigate the pharmacological efficiency of metformin on asymmetric dimethylarginine (ADMA) metabolism in inflammation caused by the lipopolysaccharide (LPS)/D-galactosamine (D-GalN) treatment.

METHODS

Adult Sprague-Dawley rats were injected LPS/D-GalN intraperitoneally. One half of the animals was injected metformin (250 mg kg(-1) body mass for one week) prior to LPS/D-GalN treatment. Six hours after the LPS/D-GalN injection, livers were removed, and used for the measurements of dimethylarginine dimethylaminohydrolase (DDAH) and myeloperoxidase (MPO) activities, glutathione (GSH), ADMA and arginine levels. Liver tissues were examined histopathologically. The Kruskal-Wallis (posthoc Mann-Whitney U) test was used for the statistics. LPS/D-GalN injections caused liver injury as evidenced by the activities of aminotransferases and arginase. GSH level and DDAH activity were decreased in the liver. Metformin pretreatment alleviated the activity of serum enzymes, and attenuated histopathological lesions caused by LPS/D-GalN injections. LPS/D-GalN-induced inflammation, as confirmed by the increased MPO activity, created an asymmetrical distribution of arginine and ADMA between the tissue and plasma. Metformin decreased tissue ADMA level while it restored the DDAH activity and GSH.

CONCLUSION

Our findings showed that metformin administration for one week has a potency to protect liver through regulating ADMA metabolism in LPS/D-GalN-induced injury.

miR-21/DDAH1 pathway regulates pulmonary vascular responses to hypoxia

The NOS (nitric oxide synthase) inhibitor ADMA (asymmetric dimethylarginine) contributes to the pathogenesis of pulmonary hypertension. Reduced levels of the enzymes metabolizing ADMA, dimethylarginine dimethylaminohydrolases (DDAH1 and DDAH2) and increased levels of miR-21 are linked to disease pathology, but the mechanisms are not understood. In the present study we assessed the potential role of miR-21 in the regulation of hypoxia-induced changes in ADMA metabolism in vitro and in vivo. Hypoxia inhibited DDAH1 and DDAH2 expression and increased ADMA levels in cultured human pulmonary endothelial cells. In contrast, in human pulmonary smooth muscle cells, only DDAH2 was reduced whereas ADMA levels remained unchanged. Endothelium-specific down-regulation of DDAH1 by miR-21 in hypoxia induced endothelial dysfunction and was prevented by overexpression of DDAH1 and miR-21 blockade. DDAH1, but not DDAH2, mRNA levels were reduced, whereas miR-21 levels were elevated in lung tissues from patients with pulmonary arterial hypertension and mice with pulmonary hypertension exposed to 2 weeks of hypoxia. Hypoxic mice treated with miR-21 inhibitors and DDAH1 transgenic mice showed elevated lung DDAH1, increased cGMP levels and attenuated pulmonary hypertension. Regulation of DDAH1 by miR-21 plays a role in the development of hypoxia-induced pulmonary hypertension and may be of broader significance in pulmonary hypertension.

Role of the oligopeptide permease ABC Transporter of Moraxella catarrhalis in nutrient acquisition and persistence in the respiratory tract

Moraxella catarrhalis is a strict human pathogen that causes otitis media in children and exacerbations of chronic obstructive pulmonary disease in adults, resulting in significant worldwide morbidity and mortality. M. catarrhalis has a growth requirement for arginine; thus, acquiring arginine is important for fitness and survival. M. catarrhalis has a putative oligopeptide permease ABC transport operon (opp) consisting of five genes (oppB, oppC, oppD, oppF, and oppA), encoding two permeases, two ATPases, and a substrate binding protein. Thermal shift assays showed that the purified recombinant substrate binding protein OppA binds to peptides 3 to 16 amino acid residues in length regardless of the amino acid composition. A mutant in which the oppBCDFA gene cluster is knocked out showed impaired growth in minimal medium where the only source of arginine came from a peptide 5 to 10 amino acid residues in length. Whether methylated arginine supports growth of M. catarrhalis is important in understanding fitness in the respiratory tract because methylated arginine is abundant in host tissues. No growth of wild-type M. catarrhalis was observed in minimal medium in which arginine was present only in methylated form, indicating that the bacterium requires l-arginine. An oppA knockout mutant showed marked impairment in its capacity to persist in the respiratory tract compared to the wild type in a mouse pulmonary clearance model. We conclude that the Opp system mediates both uptake of peptides and fitness in the respiratory tract.

Arginine metabolism in asthma

Nitric oxide (NO) is important in the regulation of airway tone and airway responsiveness. Alterations in the L-arginine metabolism resulting in reduced availability of the substrate L-arginine for NO synthases, as well as the presence of NO synthase inhibitors such as asymmetric dimethylarginine, contribute to the reduced NO formation and airway dysfunction in asthma. Therapeutic interventions aiming to modulate the impaired L-arginine metabolism may help correct the enhanced airway tone and responsiveness in asthma.

Transcriptional repression of hypoxia-inducible factor-1 (HIF-1) by the protein arginine methyltransferase PRMT1

Hypoxia-inducible factors (HIF) are essential for the adaptive response of cells to low-oxygen conditions. Transcription of HIF-α subunits and HIF activity are repressed by the arginine methyltransferase PRMT1. Therefore PRMT1 is a novel regulator of hypoxic cell responses.

Hypoxia-inducible factors (HIF-1 and HIF-2) are essential mediators for the adaptive transcriptional response of cells and tissues to low-oxygen conditions. Under hypoxia or when cells are treated with various nonhypoxic stimuli, the active HIF-α subunits are mainly regulated through increased protein stabilization. For HIF-1α, it is clear that further transcriptional, translational, and posttranslational regulations are important for complete HIF-1 activity. Novel evidence links hypoxia and HIF-1 to arginine methylation, an important protein modification. These studies suggest that arginine methyltransferases may be important for hypoxic responses. Protein arginine methyltransferase 1 (PRMT1), the predominant arginine methyltransferase, can act as a transcriptional activator or repressor by modifying a diverse set of substrates. In this work, we show that PRMT1 is a repressor of both HIF-1 and HIF-2. The cellular depletion of PRMT1 by small interference RNA targeting leads to increased HIF transcriptional activity. This activation is the result of enhanced HIF-α subunit transcription, which allows increased HIF-α subunit availability. We provide evidence that PRMT1-dependent HIF-1α regulation is mediated through the activities of both specificity protein 1 (Sp1) and Sp3, two transcription factors known to control HIF-1α expression. This study therefore identifies PRMT1 as a novel regulator of HIF-1– and HIF-2–mediated responses.

Asymmetric dimethylarginine blocks nitric oxide-mediated alcohol-stimulated cilia beating

The airway epithelium is exposed to alcohol during drinking through direct exhalation of volatized ethanol from the bronchial circulation. Alcohol exposure leads to a rapid increase in the cilia beat frequency (CBF) of bronchial epithelial cells followed by a chronic desensitization of cilia stimulatory responses. This effect is governed in part by the nitric oxide regulation of cyclic guanosine and adenosine monophosphate-dependent protein kinases (PKG and PKA) and is not fully understood. Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is implicated in the pathogenesis of several pulmonary disorders. We hypothesized that the inhibition of nitric oxide synthase by ADMA blocks alcohol-stimulated increases in CBF. To test this hypothesis, ciliated primary bovine bronchial epithelial cells (BBEC) were preincubated with ADMA (100 µM) and stimulated with 100 mM ethanol. CBF was measured and PKA assayed. By 1 hr, ethanol activated PKA, resulting in elevated CBF. Both alcohol-induced PKA activation and CBF were inhibited in the presence of ADMA. ADMA alone had no effect on PKA activity or CBF. Using a mouse model overexpressing the ADMA-degrading enzyme, dimethylarginine dimethylaminohydrolase (DDAH), we examined PKA and CBF in precision-cut mouse lung slices. Alcohol-stimulated increases in lung slice PKA and CBF were temporally enhanced in the DDAH mice versus control mice.

Effects of dimethylarginine dimethylaminohydrolase-1 overexpression on the response of the pulmonary vasculature to hypoxia

Acute and sustained hypoxic pulmonary vasoconstriction (HPV), as well as chronic pulmonary hypertension (PH), is modulated by nitric oxide (NO). NO synthesis can be decreased by asymmetric dimethylarginine (ADMA), which is degraded by dimethylarginine dimethylaminohydrolase-1 (DDAH1). We investigated the effects of DDAH1 overexpression (DDAH1(tg)) on HPV and chronic hypoxia-induced PH. HPV was measured during acute (10 min) and sustained (3 h) hypoxia in isolated mouse lungs. Chronic PH was induced by the exposure of mice to 4 weeks of hypoxia. ADMA and cyclic 3',5'-guanosine monophosphate (cGMP) were determined by ELISA, and NO generation was determined by chemiluminescence. DDAH1 overexpression exerted no effects on acute HPV. However, DDAH1(tg) mice showed decreased sustained HPV compared with wild-type (WT) mice. Concomitantly, ADMA was decreased, and concentrations of NO and cGMP were significantly increased in DDAH1(tg). The administration of either Nω-nitro-l-arginine or 1H-[1,2,4]oxadiazolo [4,3-a]quinoxalin-1-one potentiated sustained HPV and partly abolished the differences in sustained HPV between WT and DDAH1(tg) mice. The overexpression of DDAH1 exerted no effect on the development of chronic hypoxia-induced PH. DDAH1 overexpression selectively decreased the sustained phase of HPV, partly via activation of the NO-cGMP pathway. Thus, increased ADMA concentrations modulate sustained HPV, but not acute HPV or chronic hypoxia-induced PH.

Epigenetic regulation of hypoxia-responsive gene expression: focusing on chromatin and DNA modifications

Mammalian cells constantly encounter hypoxia, which is a stress condition occurring during development and physiological processes. To adapt to this inevitable condition, cells develop various mechanisms to cope with this stress and survive. In addition to the activation/stabilization of transcriptional regulators (hypoxia-inducible factors), other epigenetic mechanisms of gene regulation are used. These mechanisms are mediated by various players including transcriptional coregulators, chromatin-modifying complexes, histone modification enzymes and changes in DNA methylation status. Recent progress in all the fields mentioned above has greatly improved the knowledge of how gene regulation contributes to the hypoxic response. This review should shed light on the molecular epigenetic mechanisms of hypoxia-induced gene regulation and help understand the processes adapted by cells to cope with hypoxia.

Identification of small-molecule enhancers of arginine methylation catalyzed by coactivator-associated arginine methyltransferase 1

Arginine methylation is a common post-translational modification that is crucial in modulating gene expression at multiple critical levels. The arginine methyltransferases (PRMTs) are envisaged as promising druggable targets, but their role in physiological and pathological pathways is far from being clear due to the limited number of modulators reported to date. In this effort, enzyme activators can be invaluable tools useful as gain-of-function reagents to interrogate the biological roles in cells and in vivo of PRMTs. Yet the identification of such molecules is rarely pursued. Herein we describe a series of aryl ureido acetamido indole carboxylates (dubbed "uracandolates"), able to increase the methylation of histone (H3) or nonhistone (polyadenylate-binding protein 1, PABP1) substrates induced by coactivator-associated arginine methyltransferase 1 (CARM1), both in in vitro and cellular settings. To the best of our knowledge, this is the first report of compounds acting as CARM1 activators.

Protein Arginine Methyltransferases (PRMTs): promising targets for the treatment of pulmonary disorders

Protein arginine methylation is a novel posttranslational modification that plays a pivotal role in a variety of intracellular events, such as signal transduction, protein-protein interaction and transcriptional regulation, either by the direct regulation of protein function or by metabolic products originating from protein arginine methylation that influence nitric oxide (NO)-dependent processes. A growing body of evidence suggests that both mechanisms are implicated in cardiovascular and pulmonary diseases. This review will present and discuss recent research on PRMTs and the methylation of non-histone proteins and its consequences for the pathogenesis of various lung disorders, including lung cancer, pulmonary fibrosis, pulmonary hypertension, chronic obstructive pulmonary disease and asthma. This article will also highlight novel directions for possible future investigations to evaluate the functional contribution of arginine methylation in lung homeostasis and disease.

Chromatin as an oxygen sensor and active player in the hypoxia response

Changes in the availability or demand for oxygen induce dramatic changes at the cellular level. Primarily, activation of a family of oxygen labile transcription factors, Hypoxia Inducible Factor (HIF), initiates a variety of cellular processes required to re-instate oxygen homeostasis. Oxygen is sensed by molecular dioxygenases in cells, such as the prolyl-hydroxylases (PHDs), enzymes which are responsible for the oxygen-dependent regulation of HIF. As HIF is a transcription factor it must bind DNA sequences of its target genes possibly in the context of a complex chromatin structure. How chromatin structure changes in response to hypoxia is currently unknown. However, the identification of a novel class of histone demethylases as true dioxygenases suggests that chromatin can act as an oxygen sensor and plays an active role in the coordination of the cellular response to hypoxia. This review will discuss the current knowledge on how hypoxia engages with different proteins involved in chromatin organisation and dynamics.