Sirtuin 3 deficiency is associated with inhibited mitochondrial function and pulmonary arterial hypertension in rodents and humans

Melatonin protects against thoracic aortic aneurysm and dissection through SIRT1-dependent regulation of oxidative stress and vascular smooth muscle cell loss

Melatonin functions as an endogenous protective molecule in multiple vascular diseases, whereas its effects on thoracic aortic aneurysm and dissection (TAAD) and underlying mechanisms have not been reported. In this study, TAAD mouse model was successfully induced by β-aminopropionitrile fumarate (BAPN). We found that melatonin treatment remarkably prevented the deterioration of TAAD, evidenced by decreased incidence, ameliorated aneurysmal dilation and vascular stiffness, improved aortic morphology, and inhibited elastin degradation, macrophage infiltration, and matrix metalloproteinase expression. Moreover, melatonin blunted oxidative stress damage and vascular smooth muscle cell (VSMC) loss. Notably, BAPN induced a decrease in SIRT1 expression and activity of mouse aorta, whereas melatonin treatment reversed it. Further mechanistic study demonstrated that blocking SIRT1 signaling partially inhibited these beneficial effects of melatonin on TAAD. Additionally, the melatonin receptor was involved in this phenomenon. Our study is the first to report that melatonin exerts therapeutic effects against TAAD by reducing oxidative stress and VSMC loss via activation of SIRT1 signaling in a receptor-dependent manner, thus suggesting a novel therapeutic strategy for TAAD.

Beyond the genome: challenges and potential for epigenetics-driven therapeutic approaches in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a devastating disease of the cardiopulmonary system caused by the narrowing of the pulmonary arteries, leading to increased vascular resistance and pressure. This leads to right ventricle remodeling, dysfunction, and eventually, death. While conventional therapies have largely focused on targeting vasodilation, other pathological features of PAH including aberrant inflammation, mitochondrial dynamics, cell proliferation, and migration have not been well explored. Thus, despite some recent improvements in PAH treatment, the life expectancy and quality of life for patients with PAH remains poor. Showing many similarities to cancers, PAH is characterized by increased pulmonary arterial smooth muscle cell proliferation, decreased apoptotic signaling pathways, and changes in metabolism. The recent successes of therapies targeting epigenetic modifiers for the treatment of cancer has prompted epigenetic research in PAH, revealing many new potential therapeutic targets. In this minireview we discuss the emergence of epigenetic dysregulation in PAH and highlight epigenetic-targeting compounds that may be effective for the treatment of PAH.

The dominant model analysis of Sirt3 genetic variants is associated with susceptibility to tuberculosis in a Chinese Han population

Tuberculosis (TB) is a complex infectious disease caused by the pathogen Mycobacterium tuberculosis (Mtb) which has coexisted with humanity since the Neolithic. Recent research indicated that SIRT3 plays a pivotal role in promoting the antimycobacterial response of mitochondria and autophagy during Mtb infection. A case-control study comprised 900 TB patients and 1534 healthy controls who were retrospectively enrolled to assess the association between Sirt3 gene polymorphisms and TB susceptibility. In total, five single-nucleotide polymorphisms (SNPs) (rs511744, rs3782118, rs7104764, rs536715 and rs28365927) were selected through database 1000 Genomes Project and offline software Haploview V4.2 and genotyped by a customized 2 × 48-Plex SNPscan™ Kit. Our results suggested that the minor allele genotypes (A carriers) of rs3782118 confers the decreased risk of TB susceptibility (p_Bonferroni = 0.032), and a similar but more significant effect was observed under the dominant model analysis (OR 0.787, 95% CI 0.666-0.931, p_Bonferroni = 0.026). Haplotype analysis showed that haplotype AGAAG (rs511744/rs3782118/rs7104764/rs536715/rs28365927) was associated with an increased risk of TB (p = 0.023, OR 1.159, 95% CI 1.019-1.317). In stratification analysis, we found that rs3782118 was associated with decreased risk of TB in female subgroup under the dominant model analysis (p_Bonferroni = 0.016, OR 0.678, 95% CI 0.523-0.878). Moreover, functional annotations for three loci (rs7930823, rs3782116 and rs3782115) which are strongly linked to rs3782118 indicated that they may be responsible for the changes in some motifs. In conclusion, our study suggested that the SNP rs3782118 was associated with a lower susceptibility to TB, especially under the dominant model analysis and that the haplotype AGAAG (containing the major allele G of rs3782118) was associated with an increased risk of TB. Further independent cohort studies are necessary to validate the protective effect of Sirt3 genetic variants on the risk of TB.

Rats with a Human Mutation of NFU1 Develop Pulmonary Hypertension

NFU1 is a mitochondrial protein that is involved in the biosynthesis of iron-sulfur clusters, and its genetic modification is associated with disorders of mitochondrial energy metabolism. Patients with autosomal-recessive inheritance of the NFU1 mutation G208C have reduced activity of the respiratory chain Complex II and decreased levels of lipoic-acid-dependent enzymes, and develop pulmonary arterial hypertension (PAH) in ∼70% of cases. We investigated whether rats with a human mutation in NFU1 are also predisposed to PAH development. A point mutation in rat NFU1^G206C (human G208C) was introduced through CRISPR/Cas9 genome editing. Hemodynamic data, tissue samples, and fresh mitochondria were collected and analyzed. NFU1^G206C rats showed increased right ventricular pressure, right ventricular hypertrophy, and high levels of pulmonary artery remodeling. Computed tomography and angiography of the pulmonary vasculature indicated severe angioobliterative changes in NFU1^G206C rats. Importantly, the penetrance of the PAH phenotype was found to be more prevalent in females than in males, replicating the established sex difference among patients with PAH. Male and female homozygote rats exhibited decreased expression and activity of mitochondrial Complex II, and markedly decreased pyruvate dehydrogenase activity and lipoate binding. The limited development of PAH in males correlated with the preserved levels of oligomeric NFU1, increased expression of ISCU (an alternative branch of the iron-sulfur assembly system), and increased complex IV activity. Thus, the male sex has additional plasticity to overcome the iron-sulfur cluster deficiency. Our work describes a novel, humanized rat model of NFU1 deficiency that showed mitochondrial dysfunction similar to that observed in patients and developed PAH with the same sex dimorphism.

Pulmonary arterial hypertension: Cellular and molecular changes in the lung

The range of cell types identified in the pathogenesis of pulmonary arterial hypertension (PAH) has expanded substantially since the first pathological descriptions of this disease. This, in turn, has provided needed clarity on the gamut of molecular mechanisms that regulate vascular remodeling and promote characteristic cardiopulmonary hemodynamic changes that define PAH clinically. Insight derived from these scientific advances suggest that the PAH arteriopathy is due to the convergence of numerous molecular mechanisms driving cornerstone endophenotypes, such as plexigenic, hypertrophic, and fibrotic histopathological changes. Interestingly, while some endophenotypes are observed commonly in multiple cell types, such as dysregulated metabolism, other events such as endothelial-mesenchymal transition are cell type-specific. Integrating data from classical PAH vascular cell types with fresh information in pericytes, adventitial fibroblasts, and other PAH contributors recognized more recently has enriched the field with deeper understanding on the molecular basis of this disease. This added complexity, however, also serves as the basis for utilizing novel analytical strategies that emphasize functional signaling pathways when extracting information from big datasets. With these concepts as the backdrop, the current work offers a concise summary of cellular and molecular changes in the lung that drive PAH and may, thus, be important for discovering novel therapeutic targets or applications to clarify PAH onset and disease trajectory.

New Insights into the Implication of Mitochondrial Dysfunction in Tissue, Peripheral Blood Mononuclear Cells, and Platelets during Lung Diseases

Lung diseases such as chronic obstructive pulmonary disease, asthma, pulmonary arterial hypertension, or idiopathic pulmonary fibrosis are major causes of morbidity and mortality. Complex, their physiopathology is multifactorial and includes lung mitochondrial dysfunction and enhanced reactive oxygen species (ROS) release, which deserves increased attention. Further, and importantly, circulating blood cells (peripheral blood mononuclear cells-(PBMCs) and platelets) likely participate in these systemic diseases. This review presents the data published so far and shows that circulating blood cells mitochondrial oxidative capacity are likely to be reduced in chronic obstructive pulmonary disease (COPD), but enhanced in asthma and pulmonary arterial hypertension in a context of increased oxidative stress. Besides such PBMCs or platelets bioenergetics modifications, mitochondrial DNA (mtDNA) changes have also been observed in patients. These new insights open exciting challenges to determine their role as biomarkers or potential guide to a new therapeutic approach in lung diseases.

Modulation of mitochondria and NADPH oxidase function by the nitrate-nitrite-NO pathway in metabolic disease with focus on type 2 diabetes

Mitochondria play fundamental role in maintaining cellular metabolic homeostasis, and metabolic disorders including type 2 diabetes (T2D) have been associated with mitochondrial dysfunction. Pathophysiological mechanisms are coupled to increased production of reactive oxygen species and oxidative stress, together with reduced bioactivity/signaling of nitric oxide (NO). Novel strategies restoring these abnormalities may have therapeutic potential in order to prevent or even treat T2D and associated cardiovascular and renal co-morbidities. A diet rich in green leafy vegetables, which contains high concentrations of inorganic nitrate, has been shown to reduce the risk of T2D. To this regard research has shown that in addition to the classical NO synthase (NOS) dependent pathway, nitrate from our diet can work as an alternative precursor for NO and other bioactive nitrogen oxide species via serial reductions of nitrate (i.e. nitrate-nitrite-NO pathway). This non-conventional pathway may act as an efficient back-up system during various pathological conditions when the endogenous NOS system is compromised (e.g. acidemia, hypoxia, ischemia, aging, oxidative stress). A number of experimental studies have demonstrated protective effects of nitrate supplementation in models of obesity, metabolic syndrome and T2D. Recently, attention has been directed towards the effects of nitrate/nitrite on mitochondrial functions including beiging/browning of white adipose tissue, PGC-1α and SIRT3 dependent AMPK activation, GLUT4 translocation and mitochondrial fusion-dependent improvements in glucose homeostasis, as well as dampening of NADPH oxidase activity. In this review, we examine recent research related to the effects of bioactive nitrogen oxide species on mitochondrial function with emphasis on T2D.

Current and future treatments of pulmonary arterial hypertension

Therapeutic options for pulmonary arterial hypertension (PAH) have increased over the last decades. The advent of pharmacological therapies targeting the prostacyclin, endothelin, and NO pathways has significantly improved outcomes. However, for the vast majority of patients, PAH remains a life-limiting illness with no prospect of cure. PAH is characterised by pulmonary vascular remodelling. Current research focusses on targeting the underlying pathways of aberrant proliferation, migration, and apoptosis. Despite success in preclinical models, using a plethora of novel approaches targeting cellular GPCRs, ion channels, metabolism, epigenetics, growth factor receptors, transcription factors, and inflammation, successful transfer to human disease with positive outcomes in clinical trials is limited. This review provides an overview of novel targets addressed by clinical trials and gives an outlook on novel preclinical perspectives in PAH. LINKED ARTICLES: This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.1/issuetoc.

Mitochondria in the Pulmonary Vasculature in Health and Disease: Oxygen-Sensing, Metabolism, and Dynamics

In lung vascular cells, mitochondria serve a canonical metabolic role, governing energy homeostasis. In addition, mitochondria exist in dynamic networks, which serve noncanonical functions, including regulation of redox signaling, cell cycle, apoptosis, and mitochondrial quality control. Mitochondria in pulmonary artery smooth muscle cells (PASMC) are oxygen sensors and initiate hypoxic pulmonary vasoconstriction. Acquired dysfunction of mitochondrial metabolism and dynamics contribute to a cancer-like phenotype in pulmonary arterial hypertension (PAH). Acquired mitochondrial abnormalities, such as increased pyruvate dehydrogenase kinase (PDK) and pyruvate kinase muscle isoform 2 (PKM2) expression, which increase uncoupled glycolysis (the Warburg phenomenon), are implicated in PAH. Warburg metabolism sustains energy homeostasis by the inhibition of oxidative metabolism that reduces mitochondrial apoptosis, allowing unchecked cell accumulation. Warburg metabolism is initiated by the induction of a pseudohypoxic state, in which DNA methyltransferase (DNMT)-mediated changes in redox signaling cause normoxic activation of HIF-1α and increase PDK expression. Furthermore, mitochondrial division is coordinated with nuclear division through a process called mitotic fission. Increased mitotic fission in PAH, driven by increased fission and reduced fusion favors rapid cell cycle progression and apoptosis resistance. Downregulation of the mitochondrial calcium uniporter complex (MCUC) occurs in PAH and is one potential unifying mechanism linking Warburg metabolism and mitochondrial fission. Mitochondrial metabolic and dynamic disorders combine to promote the hyperproliferative, apoptosis-resistant, phenotype in PAH PASMC, endothelial cells, and fibroblasts. Understanding the molecular mechanism regulating mitochondrial metabolism and dynamics has permitted identification of new biomarkers, nuclear and CT imaging modalities, and new therapeutic targets for PAH. © 2020 American Physiological Society. Compr Physiol 10:713-765, 2020.

Metabolic syndrome, neurohumoral modulation, and pulmonary arterial hypertension

Pulmonary vascular disease, including pulmonary arterial hypertension (PAH), is increasingly recognized to be affected by systemic alterations including up-regulation of the renin-angiotensin-aldosterone system and perturbations to metabolic pathways, particularly glucose and fat metabolism. There is increasing preclinical and clinical data that each of these pathways can promote pulmonary vascular disease and right heart failure and are not simply disease markers. More recently, trials of therapeutics aimed at neurohormonal activation or metabolic dysfunction are beginning to shed light on how interventions in these pathways may affect patients with PAH. This review will focus on underlying mechanistic data that supports neurohormonal activation and metabolic dysfunction in the pathogenesis of PAH and right heart failure as well as discussing early translational data in patients with PAH.

Targeting histone acetylation in pulmonary hypertension and right ventricular hypertrophy

Epigenetic mechanisms, including DNA methylation and histone post-translational modifications (PTMs), have been known to regulate chromatin structure and lineage-specific gene expression during cardiovascular development and disease. However, alterations in the landscape of histone PTMs and their contribution to the pathogenesis of incurable cardiovascular diseases such as pulmonary hypertension (PH) and associated right heart failure (RHF) remain largely unexplored. This review focusses on the studies in PH and RHF that investigated the gene families that write (histone acetyltransferases), read (bromodomain-containing proteins) or erase (histone deacetylases [HDACs] and sirtuins [SIRT]) acetyl moieties from the ε-amino group of lysine residues of histones and non-histone proteins. Analysis of cells and tissues isolated from the in vivo preclinical models of PH and human pulmonary arterial hypertension not only confirmed significant alterations in the expression levels of multiple HDACs, SIRT1, SIRT3 and BRD4 proteins but also demonstrated their strong association to proliferative, inflammatory and fibrotic phenotypes linked to the pathological vascular remodelling process. Due to the reversible nature of post-translational protein acetylation, the therapeutic efficacy of numerous small-molecule inhibitors (vorinostat, valproic acid, sodium butyrate, mocetinostat, entinostat, tubastatin A, apabetalone, JQ1 and resveratrol) have been evaluated in different preclinical models of cardiovascular disease, which revealed the promising therapeutic benefits of targeting histone acetylation pathways in the attenuation of cardiac hypertrophy, fibrosis, left heart dysfunction, PH and RHF. This review also emphasizes the need for deeper molecular insights into the contribution of epigenetic changes to PH pathogenesis and therapeutic evaluation of isoform-specific modulation in ex vivo and in vivo models of PH and RHF. LINKED ARTICLES: This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.1/issuetoc.

The yin and yang faces of the mitochondrial deacetylase sirtuin 3 in age-related disorders

Aging, the most important risk factor for many of the chronic diseases affecting Western society, is associated with a decline in mitochondrial function and dynamics. Sirtuin 3 (SIRT3) is a mitochondrial deacetylase that has emerged as a key regulator of fundamental processes which are frequently dysregulated in aging and related disorders. This review highlights recent advances and controversies regarding the yin and yang functions of SIRT3 in metabolic, cardiovascular and neurodegenerative diseases, as well as the use of SIRT3 modulators as a therapeutic strategy against those disorders. Although most studies point to a protective role upon SIRT3 activation, there are conflicting findings that need a better elucidation. The discovery of novel SIRT3 modulators with higher selectivity together with the assessment of the relative importance of different SIRT3 enzymatic activities and the relevance of crosstalk between distinct sirtuin isoforms will be pivotal to validate SIRT3 as a useful drug target for the prevention and treatment of age-related diseases.

The Biological Bases of Group 2 Pulmonary Hypertension

Pulmonary hypertension (PH) is a potentially fatal condition with a prevalence of around 1% in the world population and most commonly caused by left heart disease (PH-LHD). Usually, in PH-LHD, the increase of pulmonary pressure is only conditioned by the retrograde transmission of the left atrial pressure. However, in some cases, the long-term retrograde pressure overload may trigger complex and irreversible biomechanical and biological changes in the pulmonary vasculature. This latter clinical entity, designated as combined pre- and post-capillary PH, is associated with very poor outcomes. The underlying mechanisms of this progression are poorly understood, and most of the current knowledge comes from the field of Group 1-PAH. Treatment is also an unsolved issue in patients with PH-LHD. Targeting the molecular pathways that regulate pulmonary hemodynamics and vascular remodeling has provided excellent results in other forms of PH but has a neutral or detrimental result in patients with PH-LHD. Therefore, a deep and comprehensive biological characterization of PH-LHD is essential to improve the diagnostic and prognostic evaluation of patients and, eventually, identify new therapeutic targets. Ongoing research is aimed at identify candidate genes, variants, non-coding RNAs, and other biomarkers with potential diagnostic and therapeutic implications. In this review, we discuss the state-of-the-art cellular, molecular, genetic, and epigenetic mechanisms potentially involved in PH-LHD. Signaling and effective pathways are particularly emphasized, as well as the current knowledge on -omic biomarkers. Our final aim is to provide readers with the biological foundations on which to ground both clinical and pre-clinical research in the field of PH-LHD.

Dichotomous Sirtuins: Implications for Drug Discovery in Neurodegenerative and Cardiometabolic Diseases

Sirtuins (SIRT1-7), a class of NAD⁺-dependent deacylases, are central regulators of metabolic homeostasis and stress responses. While numerous salutary effects associated with sirtuin activation, especially SIRT1, are well documented, other reports show health benefits resulting from sirtuin inhibition. Furthermore, conflicting findings have been obtained regarding the pathophysiological role of specific sirtuin isoforms, suggesting that sirtuins act as 'double-edged swords'. Here, we provide an integrated overview of the different findings on the role of mammalian sirtuins in neurodegenerative and cardiometabolic disorders and attempt to dissect the reasons behind these different effects. Finally, we discuss how addressing these obstacles may provide a better understanding of the complex sirtuin biology and improve the likelihood of identifying effective and selective drug targets for a variety of human disorders.

Redox Biology of Peroxisome Proliferator-Activated Receptor-γ in Pulmonary Hypertension

Significance: Peroxisome proliferator-activated receptor-gamma (PPARγ) maintains pulmonary vascular health through coordination of antioxidant defense systems, inflammation, and cellular metabolism. Insufficient PPARγ contributes to pulmonary hypertension (PH) pathogenesis, whereas therapeutic restoration of PPARγ activity attenuates PH in preclinical models. Recent Advances: Numerous studies in the past decade have elucidated the complex mechanisms by which PPARγ in the pulmonary vasculature and right ventricle (RV) protects against PH. The scope of PPARγ-interconnected pathways continues to expand and includes induction of antioxidant genes, transrepression of inflammatory signaling, regulation of mitochondrial biogenesis and bioenergetic integrity, control of cell cycle and proliferation, and regulation of vascular tone through interactions with nitric oxide and endogenous vasoactive molecules. Furthermore, PPARγ interacts with an extensive regulatory network of transcription factors and microRNAs leading to broad impact on cell signaling. Critical Issues: Abundant evidence suggests that targeting PPARγ exerts diverse salutary effects in PH and represents a novel and potentially translatable therapeutic strategy. However, progress has been slowed by an incomplete understanding of how specific PPARγ pathways are critically disrupted across PH disease subtypes and lack of optimal pharmacological ligands. Future Directions: Recent studies indicate that ligand-induced post-translational modifications of the PPARγ receptor differentially induce therapeutic benefits versus adverse side effects of PPARγ receptor activation. Strategies to selectively target PPARγ activity in diseased cells of pulmonary circulation and RV, coupled with development of ligands designed to specifically regulate post-translational PPARγ modifications, may unlock the full therapeutic potential of this versatile master transcriptional and metabolic regulator in PH.

Epigenetic Modulation in the Initiation and Progression of Pulmonary Hypertension

Pulmonary hypertension (PH) is a severe disease with multiple etiologies. In addition to genetics, recent studies have revealed the epigenetic modulation in the initiation and progression of PH. In this review, we summarize the epigenetic mechanisms in the pathogenesis of PH, specifically, DNA methylation, histone modifications, and microRNAs. We further emphasize the diagnostic and therapeutic potential of these epigenetic hallmarks in PH. Finally, we highlight the developmental reprogramming in adult-onset PH because of adverse perinatal exposures such as intrauterine growth restriction and extrauterine growth restriction. Therefore, epigenetic modifications provide promise for the therapy and prevention of PH.

Metabolism and Redox in Pulmonary Vascular Physiology and Pathophysiology

Significance: This review considers how some systems controlling pulmonary vascular function are potentially regulated by redox processes to examine how and why conditions such as prolonged hypoxia, pathological mediators, and other factors promoting vascular remodeling contribute to the development of pulmonary hypertension (PH). Recent Advances and Critical Issues: Aspects of vascular remodeling induction mechanisms described are associated with shifts in glucose metabolism through the pentose phosphate pathway and increased cytosolic NADPH generation by glucose-6-phosphate dehydrogenase, increased glycolysis generation of cytosolic NADH and lactate, mitochondrial dysfunction associated with superoxide dismutase-2 depletion, changes in reactive oxygen species and iron metabolism, and redox signaling. Future Directions: The regulation and impact of hypoxia-inducible factor and the function of cGMP-dependent and redox regulation of protein kinase G are considered for their potential roles as key sensors and coordinators of redox and metabolic processes controlling the progression of vascular pathophysiology in PH, and how modulating aspects of metabolic and redox regulatory systems potentially function in beneficial therapeutic approaches.

Sirtuins and NAD+ in the Development and Treatment of Metabolic and Cardiovascular Diseases

The sirtuin family of nicotinamide adenine dinucleotide-dependent deacylases (SIRT1-7) are thought to be responsible, in large part, for the cardiometabolic benefits of lean diets and exercise and when upregulated can delay key aspects of aging. SIRT1, for example, protects against a decline in vascular endothelial function, metabolic syndrome, ischemia-reperfusion injury, obesity, and cardiomyopathy, and SIRT3 is protective against dyslipidemia and ischemia-reperfusion injury. With increasing age, however, nicotinamide adenine dinucleotide levels and sirtuin activity steadily decrease, and the decline is further exacerbated by obesity and sedentary lifestyles. Activation of sirtuins or nicotinamide adenine dinucleotide repletion induces angiogenesis, insulin sensitivity, and other health benefits in a wide range of age-related cardiovascular and metabolic disease models. Human clinical trials testing agents that activate SIRT1 or boost nicotinamide adenine dinucleotide levels are in progress and show promise in their ability to improve the health of cardiovascular and metabolic disease patients.

Selenoprotein P Promotes the Development of Pulmonary Arterial Hypertension: Possible Novel Therapeutic Target

BACKGROUND

Excessive proliferation and apoptosis resistance of pulmonary artery smooth muscle cells (PASMCs) are key mechanisms of pulmonary arterial hypertension (PAH). Despite the multiple combination therapy, a considerable number of patients develop severe pulmonary hypertension (PH) because of the lack of diagnostic biomarker and antiproliferative therapies for PASMCs.

METHODS

Microarray analyses were used to identify a novel therapeutic target for PAH. In vitro experiments, including lung and serum samples from patients with PAH, cultured PAH-PASMCs, and high-throughput screening of 3336 low-molecular-weight compounds, were used for mechanistic study and exploring a novel therapeutic agent. Five genetically modified mouse strains, including PASMC-specific selenoprotein P (SeP) knockout mice and PH model rats, were used to study the role of SeP and therapeutic capacity of the compounds for the development of PH in vivo.

RESULTS

Microarray analysis revealed a 32-fold increase in SeP in PAH-PASMCs compared with control PASMCs. SeP is a widely expressed extracellular protein maintaining cellular metabolism. Immunoreactivity of SeP was enhanced in the thickened media of pulmonary arteries in PAH. Serum SeP levels were also elevated in patients with PH compared with controls, and high serum SeP predicted poor outcome. SeP-knockout mice ( SeP^-/-) exposed to chronic hypoxia showed significantly reduced right ventricular systolic pressure, right ventricular hypertrophy, and pulmonary artery remodeling compared with controls. In contrast, systemic SeP-overexpressing mice showed exacerbation of hypoxia-induced PH. Furthermore, PASMC-specific SeP^-/- mice showed reduced hypoxia-induced PH compared with controls, whereas neither liver-specific SeP knockout nor liver-specific SeP-overexpressing mice showed significant differences with controls. Altogether, protein levels of SeP in the lungs were associated with the development of PH. Mechanistic experiments demonstrated that SeP promotes PASMC proliferation and resistance to apoptosis through increased oxidative stress and mitochondrial dysfunction, which were associated with activated hypoxia-inducible factor-1α and dysregulated glutathione metabolism. It is important to note that the high-throughput screening of 3336 compounds identified that sanguinarine, a plant alkaloid with antiproliferative effects, reduced SeP expression and proliferation in PASMCs and ameliorated PH in mice and rats.

CONCLUSIONS

These results indicate that SeP promotes the development of PH, suggesting that it is a novel biomarker and therapeutic target of the disorder.

Sirtuin 3 Therapy Attenuates Aging Expression, Oxidative Stress Parameters, and Neointimal Hyperplasia Formation in Vein Grafts

BACKGROUND

Vein graft (VG) failure due to neointimal hyperplasia remains an important and unresolved problem in cardiovascular surgery. Sirtuin3 (SIRT3) is associated with oxidative stress and lifespan. We aimed to measure SIRT3 expression in the veins of humans and rats during aging, explore the inhibitory effects of SIRT3 on vascular smooth muscle cell (VSMC) proliferation and neointimal hyperplasia in VGs, and investigate the underlying mechanisms.

METHODS

SIRT3 mRNA and protein levels in saphenous veins of young and older humans and in veins of young and old rats were measured by quantitative real-time polymerized chain reaction (PCR) and Western blot analysis. Young and old male rats were randomized to the control (control), graft (graft), adenovirus-encoding green fluorescent protein (Ad-GFP), and adenovirus encoding SIRT3 (Ad-SIRT3) groups. At 7 days after operation, the mRNA and protein levels of SIRT3 and endothelial nitric oxide synthase (eNOS) were measured by quantitative real-time PCR and Western blot analysis. The mRNA levels and enzyme activity of manganese superoxide dismutase (MnSOD) and catalase (CAT) were measured by quantitative real-time PCR and enzymatic activity assay kits, and total nitric oxide (NO) levels were measured by biochemical assay kits. Histomorphometric analysis of VGs and immunohistochemical staining for proliferative activity were performed at 4 weeks after operation. The hemodynamic parameters of the VGs were also measured by ultrasonic examination.

RESULTS

SIRT3 mRNA and protein levels were lower in older human and rat veins than in younger human and rat veins. Ad-SIRT3 treatment significantly increased the expression and concentration of SIRT3, MnSOD, CAT, eNOS, and NO in VGs at 7 days after operation. Ad-SIRT3 gene transfer reduced the neointimal thickness and neointimal area/media area ratio in the VGs of the Ad-SIRT3 groups compared with the graft and Ad-GFP groups, especially in old rats. Proliferative activity was lower in the Ad-SIRT3 groups than in the other groups. The hemodynamic parameters of VGs were obviously improved in the Ad-SIRT3 groups.

CONCLUSIONS

SIRT3 expression decreases in the veins of humans and rats during aging. Furthermore, SIRT3 overexpression can significantly reduce VSMC proliferation and neointimal hyperplasia in VGs. Local intravenous delivery of adenovirus encoding SIRT3 may be a promising gene therapy for preventing VG failure.

Peroxisome Proliferator-Activated Receptor-γ Coactivator-1α Inhibits Vascular Calcification Through Sirtuin 3-Mediated Reduction of Mitochondrial Oxidative Stress

Aims: Vascular calcification is associated with cardiovascular death in patients with chronic kidney disease (CKD). Peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) plays an important role in various cardiovascular diseases. However, its role in vascular calcification remains unknown. Results: Adenine-induced rat CKD model was used to induce arterial medial calcification. The level of PGC-1α decreased in abdominal aorta of CKD rats. Overexpression of PGC-1α significantly ameliorated calcium deposition in rat abdominal aorta, isolated carotid rings, and cultured vascular smooth muscle cells (VSMCs). Mitochondrial reactive oxygen species (mtROS) increased in calcifying aorta and VSMCs. Upregulation of PGC-1α inhibited, whereas PGC-1α depletion promoted β-glycerophosphate-induced mtROS production and calcium deposition. Moreover, PGC-1α increased superoxide dismutase 1 (SOD1) and SOD2 contents in vivo and in vitro, whereas SOD2 deletion eliminated PGC-1α-mediated mtROS change and promoted calcium deposition. Mechanistically, sirtuin 3 (SIRT3) expression declined in calcifying aorta and VSMCs, while PGC-1α overexpression restored SIRT3 expression. Inhibition of SIRT3 by 3-TYP or siRNA (small interfering RNA) reduced PGC-1α-induced upregulation of SOD1 and SOD2, and abolished the protective effect of PGC-1α on calcification of VSMCs. Importantly, PGC-1α was reduced in calcified femoral arteries in CKD patients. In phosphate-induced human umbilical arterial calcification, upregulation of PGC-1α attenuated calcium nodule formation, while this protective effect was abolished by SIRT3 inhibitor. Innovation: We showed for the first time that PGC-1α is an important endogenous regulator against vascular calcification. Induction of PGC-1α could be a potential strategy to treat vascular calcification in CKD patients. Conclusions: PGC-1α protected against vascular calcification by SIRT3-mediated mtROS reduction.

The Search for Disease-Modifying Therapies in Pulmonary Hypertension

Pulmonary hypertension (PH) and its severe subtype pulmonary arterial hypertension (PAH) encompass a set of multifactorial diseases defined by sustained elevation of pulmonary arterial pressure and pulmonary vascular resistance leading to right ventricular failure and subsequent death. Pulmonary hypertension is characterized by vascular remodeling in association with smooth muscle cell proliferation of the arterioles, medial thickening, and plexiform lesion formation. Despite our recent advances in understanding its pathogenesis and related therapeutic discoveries, PH still remains a progressive disease without a cure. Nevertheless, development of drugs that specifically target molecular pathways involved in disease pathogenesis has led to improvement in life quality and clinical outcomes in patients with PAH. There are presently more than 12 Food and Drug Administration-approved vasodilator drugs in the United States for the treatment of PAH; however, mortality with contemporary therapies remains high. More recently, there have been exuberant efforts to develop new pharmacologic therapies that target the fundamental origins of PH and thus could represent disease-modifying opportunities. This review aims to summarize recent developments on key signaling pathways and molecular targets that drive PH disease progression, with emphasis on new therapeutic options under development.

Sirtuin 1 regulates pulmonary artery smooth muscle cell proliferation: role in pulmonary arterial hypertension

OBJECTIVE

Energy metabolism shift from oxidative phosphorylation toward glycolysis in pulmonary artery smooth muscle cells (PASMCs) is suggested to be involved in their hyperproliferation in pulmonary arterial hypertension (PAH). Here, we studied the role of the deacetylase sirtuin1 (SIRT1) in energy metabolism regulation in PASMCs via various pathways including activation of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), master regulator of mitochondrial biogenesis.

APPROACH AND RESULTS

Contents of PGC-1α and its downstream targets as well as markers of mitochondrial mass (voltage-dependent anion channel and citrate synthase) were diminished in human PAH PASMCs. These cells and platelet-derived growth factor-stimulated rat PASMCs demonstrated a shift in cellular acetylated/deacetylated state, as evidenced by the increase of the acetylated forms of SIRT1 targets: histone H1 and Forkhead box protein O1. Rat and human PASMC proliferation was potentiated by SIRT1 pharmacological inhibition or specific downregulation via short-interfering RNA. Moreover, after chronic hypoxia exposure, SIRT1 inducible knock out mice displayed a more intense vascular remodeling compared with their control littermates, which was associated with an increase in right ventricle pressure and hypertrophy. SIRT1 activator Stac-3 decreased the acetylation of histone H1 and Forkhead box protein O1 and strongly inhibited rat and human PASMC proliferation without affecting cell mortality. This effect was associated with the activation of mitochondrial biogenesis evidenced by higher expression of mitochondrial markers and downstream targets of PGC-1α.

CONCLUSION

Altered acetylation/deacetylation balance as the result of SIRT1 inactivation is involved in the pathogenesis of PAH, and this enzyme could be a promising therapeutic target for PAH treatment.

Identification of Celastramycin as a Novel Therapeutic Agent for Pulmonary Arterial Hypertension

RATIONALE

Pulmonary arterial hypertension (PAH) is characterized by enhanced proliferation of pulmonary artery smooth muscle cells (PASMCs) accompanying increased production of inflammatory factors and adaptation of the mitochondrial metabolism to a hyperproliferative state. However, all the drugs in clinical use target pulmonary vascular dilatation, which may not be effective for patients with advanced PAH.

OBJECTIVE

We aimed to discover a novel drug for PAH that inhibits PASMC proliferation.

METHODS AND RESULTS

We screened 5562 compounds from original library using high-throughput screening system to discover compounds which inhibit proliferation of PASMCs from patients with PAH (PAH-PASMCs). We found that celastramycin, a benzoyl pyrrole-type compound originally found in a bacteria extract, inhibited the proliferation of PAH-PASMCs in a dose-dependent manner with relatively small effects on PASMCs from healthy donors. Then, we made 25 analogs of celastramycin and selected the lead compound, which significantly inhibited cell proliferation of PAH-PASMCs and reduced cytosolic reactive oxygen species levels. Mechanistic analysis demonstrated that celastramycin reduced the protein levels of HIF-1α (hypoxia-inducible factor 1α), which impairs aerobic metabolism, and κB (nuclear factor-κB), which induces proinflammatory signals, in PAH-PASMCs, leading to reduced secretion of inflammatory cytokine. Importantly, celastramycin treatment reduced reactive oxygen species levels in PAH-PASMCs with increased protein levels of Nrf2 (nuclear factor erythroid 2-related factor 2), a master regulator of cellular response against oxidative stress. Furthermore, celastramycin treatment improved mitochondrial energy metabolism with recovered mitochondrial network formation in PAH-PASMCs. Moreover, these celastramycin-mediated effects were regulated by ZFC3H1 (zinc finger C3H1 domain-containing protein), a binding partner of celastramycin. Finally, celastramycin treatment ameliorated pulmonary hypertension in 3 experimental animal models, accompanied by reduced inflammatory changes in the lungs.

CONCLUSIONS

These results indicate that celastramycin ameliorates pulmonary hypertension, reducing excessive proliferation of PAH-PASMCs with less inflammation and reactive oxygen species levels, and recovered mitochondrial energy metabolism. Thus, celastramycin is a novel drug for PAH that targets antiproliferative effects on PAH-PASMCs.

Novel Insights on Systemic and Brain Aging, Stroke, Amyotrophic Lateral Sclerosis, and Alzheimer's Disease

The mechanisms that underlie the pathophysiology of aging, amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD) and stroke are not fully understood and have been the focus of intense and constant investigation worldwide. Studies that provide insights on aging and age-related disease mechanisms are critical for advancing novel therapies that promote successful aging and prevent or cure multiple age-related diseases. The April 2019 issue of the journal, "Aging & Disease" published a series of articles that confer fresh insights on numerous age-related conditions and diseases. The age-related topics include the detrimental effect of overweight on energy metabolism and muscle integrity, senoinflammation as the cause of neuroinflammation, the link between systemic C-reactive protein and brain white matter loss, the role of miR-34a in promoting healthy heart and brain, the potential of sirtuin 3 for reducing cardiac and pulmonary fibrosis, and the promise of statin therapy for ameliorating asymptomatic intracranial atherosclerotic stenosis. Additional aging-related articles highlighted the involvement of miR-181b-5p and high mobility group box-1 in hypertension, Yes-associated protein in cataract formation, multiple miRs and long noncoding RNAs in coronary artery disease development, the role of higher meat consumption on sleep problems, and the link between glycated hemoglobin and depression. The topics related to ALS suggested that individuals with higher education and living in a rural environment have a higher risk for developing ALS, and collagen XIX alpha 1 is a prognostic biomarker of ALS. The topics discussed on AD implied that extracellular amyloid β42 is likely the cause of intraneuronal neurofibrillary tangle accumulation in familial AD and traditional oriental concoctions may be useful for slowing down the progression of AD. The article on stroke suggested that inhibition of the complement system is likely helpful in promoting brain repair after ischemic stroke. The significance of the above findings for understanding the pathogenesis in aging, ALS, AD, and stroke, slowing down the progression of aging, ALS and AD, and promoting brain repair after stroke are discussed.

SUMOylation of Vps34 by SUMO1 promotes phenotypic switching of vascular smooth muscle cells by activating autophagy in pulmonary arterial hypertension

INTRODUCTION

Pulmonary arterial hypertension (PAH) is a life-threatening disease without effective therapies. PAH is associated with a progressive increase in pulmonary vascular resistance and irreversible pulmonary vascular remodeling. SUMO1 (small ubiquitin-related modifier 1) can bind to target proteins and lead to protein SUMOylation, an important post-translational modification with a key role in many diseases. However, the contribution of SUMO1 to PAH remains to be fully characterized.

METHODS

In this study, we explored the role of SUMO1 in the dedifferentiation of vascular smooth muscle cells (VSMCs) involved in hypoxia-induced pulmonary vascular remodeling and PAH in vivo and in vitro.

RESULTS

In a mouse model of hypoxic PAH, SUMO1 expression was significantly increased, which was associated with activation of autophagy (increased LC3b and decreased p62), dedifferentiation of pulmonary arterial VSMCs (reduced α-SMA, SM22 and SM-MHC), and pulmonary vascular remodeling. Similar results were obtained in a MCT-induced PAH model. Overexpression of SUMO1 significantly increased VSMCs proliferation, migration, hypoxia-induced VSMCs dedifferentiation, and autophagy, but these effects were abolished by inhibition of autophagy by 3-MA in aortic VSMCs. Furthermore, SUMO1 knockdown reversed hypoxia-induced proliferation and migration of PASMCs. Mechanistically, SUMO1 promotes Vps34 SUMOylation and the assembly of the Beclin-1-Vps34-Atg14 complex, thereby inducing autophagy, whereas Vps34 mutation K840R reduces Vps34 SUMOylation and inhibits VSMCs dedifferentiation.

DISCUSSION

Our data uncovers an important role of SUMO1 in VSMCs proliferation, migration, autophagy, and phenotypic switching (dedifferentiation) involved in pulmonary vascular remodeling and PAH. Targeting of the SUMO1-Vps34-autophagy signaling axis may be exploited to develop therapeutic strategies to treat PAH.

The Role of Pathological Aging in Cardiac and Pulmonary Fibrosis

Aging promotes a range of degenerative pathologies characterized by progressive losses of tissue and/or cellular function. Fibrosis is the hardening, overgrowth and scarring of various tissues characterized by the accumulation of extracellular matrix components. Aging is an important predisposing factor common for fibrotic heart and respiratory disease. Age-related processes such as senescence, inflammaging, autophagy and mitochondrial dysfunction are interconnected biological processes that diminish the regenerative capacity of the aged heart and lung and have been shown to play a crucial role in cardiac fibrosis and idiopathic pulmonary fibrosis. This review focuses on these four processes of aging in relation to their role in fibrosis. It has long been established that the heart and lung are linked both functionally and anatomically when it comes to health and disease, with an ever-expanding aging population, the incidence of fibrotic disease and therefore the number of fibrosis-related deaths will continue to rise. There are currently no feasible therapies to treat the effects of chronic fibrosis therefore highlighting the importance of exploring the processes of aging and its role in inducing and exacerbating fibrosis of each organ. The focus of this review may help to highlight potential avenues of therapeutic exploration

Drug repositioning in pulmonary arterial hypertension: challenges and opportunities

Despite many advances in medical therapy for pulmonary arterial hypertension (PAH) over the past 20 years, long-term survival is still poor. Novel therapies which target the underlying pathology of PAH and which could be added to current vasodilatory therapies to halt disease progression and potentially reverse pulmonary vascular remodeling are highly sought after. Given the high attrition rates, substantial costs, and slow pace of new drug development, repositioning of “old” drugs is increasingly becoming an attractive path to identify novel treatment options, especially for a rare disease such as PAH.

We here summarize the limitations of current PAH therapy, the general concept of repurposing and repositioning, success stories of approved repositioned drugs in PAH as well as novel repositioned drugs that show promise in preclinical models of pulmonary hypertension (PH) and are currently tested in clinical trials. We furthermore discuss various data-driven as well as experimental approaches currently used to identify repurposed drug candidates and review challenges for the “repositioning community” with regards to funding and patent and regulatory considerations, and to illustrate opportunities for collaborative solutions for drug repositioning relevant to PAH.

SIRT3 promotes antimycobacterial defenses by coordinating mitochondrial and autophagic functions

SIRT3 (sirtuin 3), a mitochondrial protein deacetylase, maintains respiratory function, but its role in the regulation of innate immune defense is largely unknown. Herein, we show that SIRT3 coordinates mitochondrial function and macroautophagy/autophagy activation to promote anti-mycobacterial responses through PPARA (peroxisome proliferator activated receptor alpha). SIRT3 deficiency enhanced inflammatory responses and mitochondrial dysfunction, leading to defective host defense and pathological inflammation during mycobacterial infection. Antibody-mediated depletion of polymorphonuclear neutrophils significantly increased protection against mycobacterial infection in sirt3^-/- mice. In addition, mitochondrial oxidative stress promoted excessive inflammation induced by Mycobacterium tuberculosis infection in sirt3^-/- macrophages. Notably, SIRT3 was essential for the enhancement of PPARA, a key regulator of mitochondrial homeostasis and autophagy activation in the context of infection. Importantly, overexpression of either PPARA or TFEB (transcription factor EB) in sirt3^-/- macrophages recovered antimicrobial activity through autophagy activation. Furthermore, pharmacological activation of SIRT3 enhanced antibacterial autophagy and functional mitochondrial pools during mycobacterial infection. Finally, the levels of SIRT3 and PPARA were downregulated and inversely correlated with TNF (tumor necrosis factor) levels in peripheral blood mononuclear cells from tuberculosis patients. Collectively, these data demonstrate a previously unappreciated function of SIRT3 in orchestrating mitochondrial and autophagic functions to promote antimycobacterial responses. Abbreviations: Ab: antibody; BCG: M. bovis Bacillus Calmette-Guérin; Baf-A₁: bafilomycin A₁; BMDMs: bone marrow-derived macrophages; CFU: colony forming unit; CXCL5: C-X-C motif chemokine ligand 5; EGFP: enhanced green fluorescent protein; ERFP: enhanced red fluorescent protein; FOXO3: forkhead box O3; HC: healthy controls; H&E: haematoxylin and eosin; HKL: honokiol; IHC: immunohistochemistry; IL1B: interleukin 1 beta; IL6: interleukin 6; IL12B: interleukin 12B; MDMs: monocyte-derived macrophages; MMP: mitochondrial membrane potential; Mtb: Mycobacterium tuberculosis; PBMC: peripheral blood mononuclear cells; PBS: phosphate buffered saline; PMN: polymorphonuclear neutrophil; PPARA: peroxisome proliferator activated receptor alpha; ROS: reactive oxygen species; SIRT3: sirtuin 3; TB: tuberculosis; TEM: transmission electron microscopy; TFEB: transcription factor EB; TNF: tumor necrosis factor.

Pathology and pathobiology of pulmonary hypertension: state of the art and research perspectives

Clinical and translational research has played a major role in advancing our understanding of pulmonary hypertension (PH), including pulmonary arterial hypertension and other forms of PH with severe vascular remodelling (e.g. chronic thromboembolic PH and pulmonary veno-occlusive disease). However, PH remains an incurable condition with a high mortality rate, underscoring the need for a better transfer of novel scientific knowledge into healthcare interventions. Herein, we review recent findings in pathology (with the questioning of the strict morphological categorisation of various forms of PH into pre- or post-capillary involvement of pulmonary vessels) and cellular mechanisms contributing to the onset and progression of pulmonary vascular remodelling associated with various forms of PH. We also discuss ways to improve management and to support and optimise drug development in this research field.

Nicotinamide riboside regulates inflammation and mitochondrial markers in AML12 hepatocytes

BACKGROUND/OBJECTIVES

The NAD⁺ precursor nicotinamide riboside (NR) is a type of vitamin B₃ found in cow's milk and yeast-containing food products such as beer. Recent studies suggested that NR prevents hearing loss, high-fat diet-induced obesity, Alzheimer's disease, and mitochondrial myopathy. The objective of this study was to investigate the effects of NR on inflammation and mitochondrial biogenesis in AML12 mouse hepatocytes.

MATERIALS/METHODS

A subset of hepatocytes was treated with palmitic acid (PA; 250 µM) for 48 h to induce hepatocyte steatosis. The hepatocytes were treated with NR (10 µM and 10 mM) for 24 h with and without PA. The cell viability and the levels of sirtuins, inflammatory markers, and mitochondrial markers were analyzed.

RESULTS

Cytotoxicity of NR was examined by PrestoBlue assay. Exposure to NR had no effect on cell viability or morphology. Gene expression of sirtuin 1 (Sirt1) and Sirt3 was significantly upregulated by NR in PA-treated hepatocytes. However, Sirt1 activities were increased in hepatocytes treated with low-dose NR. Hepatic pro-inflammatory markers including tumor necrosis factor-alpha and interleukin-6 were decreased in NR-treated cells. NR upregulated anti-inflammatory molecule adiponectin, and, tended to down-regulate hepatokine fetuin-A in PA-treated hepatocytes, suggesting its inverse regulation on these cytokines. NR increased levels of mitochondrial markers including peroxisome proliferator-activated receptor γ coactivator-1α, carnitine palmitoyltransferase 1, uncoupling protein 2, transcription factor A, mitochondrial and mitochondrial DNA in PA-treated hepatocytes.

CONCLUSIONS

These data demonstrated that NR attenuated hepatic inflammation and increased levels of mitochondrial markers in hepatocytes.

Cellular Metabolism in Lung Health and Disease

The lung is often overlooked as a metabolically active organ, yet biochemical studies have long demonstrated that glucose utilization surpasses that of many other organs, including the heart, kidney, and brain. For most cells in the lung, energy consumption is relegated to performing common cellular tasks, like mRNA transcription and protein translation. However, certain lung cell populations engage in more specialized types of energy-consuming behaviors, such as the beating of cilia or the production of surfactant. While many extrapulmonary diseases are now linked to abnormalities in cellular metabolism, the pulmonary community has only recently embraced the concept of metabolic dysfunction as a driver of respiratory pathology. Herein, we provide an overview of the major metabolic pathways in the lung and discuss how cells sense and adapt to low-energy states. Moreover, we review some of the emerging evidence that links alterations in cellular metabolism to the pathobiology of several common respiratory diseases.

Recent advances in mouse models for systemic sclerosis

SSc is a complex rheumatoid disease characterized by autoimmunity, fibrosis and vasculopathy. Mouse models provide powerful research tools for exploring the pathogenesis of the human diseases. Each mouse model can represent a specific way leading to the development of disease. Moreover, mouse models can be used to investigate the role of candidate molecule in the pathogenesis of disease. So far, more than twenty mouse models for SSc have been established and provide new insights in the understanding of the pathogenesis of SSc. In this review, we provide an overview on recent advances in the field of experimental SSc. We introduce novel mouse models generated in the recent years and discuss their relevance to the SSc pathogenesis. Moreover, we summarize and discuss recent findings in the pathogenesis of classical SSc mouse models.

New cases of Glucose-6-Phosphate Dehydrogenase deficiency in Pulmonary Arterial Hypertension

Pulmonary Arterial Hypertension (PAH) is a fatal disorder with limited treatment options and reduced life expectancy after diagnosis. Complex genetic backgrounds in PAH complicates identification of causative mutations that is essential for an understanding of the disease diagnostics and etiology especially for idiopathic PAH (iPAH). Hemolysis has been implicated as contributing to the pathobiology of PAH. Glucose-6-Phosphate Dehydrogenase (G6PD) expression and activity define erythrocyte's antioxidant capacity, and its decrease contributes to erythrocyte fragility. As G6PD deficiency was previously reported in a limited number of PAH cases, we tested whether iPAH patients exhibit underlying G6PD alterations in erythrocytes. A cohort of 22 PAH patients and 8 non-PAH patients were recruited for this study. DNA isolated from Peripheral Blood Mononuclear Cells (PBMC) was used for detection of mutations in the coding region of the G6PD gene. RNA isolated from PBMC was used for determination of G6PD mRNA expression level. G6PD activity was measured in Red Blood Cell (RBC) pellets. Three patients had missense mutations in G6PD (Val291Met, Asn126Asp, Asp194Glu), however, only one mutation (Val291Met) results in a severe G6PD deficiency. A single patient with mutation (Asn126Asp) showed a 21% decrease in G6PD activity, two subjects showed G6PD deficiency without mutations, and one patient had a decreased level of G6PD mRNA and reduced enzyme levels. This study demonstrates that a moderate decrease in G6PD activity is associated with PAH. Screening for G6PD activity and mutations in the G6PD gene may provide early detection of individuals predisposed to PAH.

Emerging role of SIRT3 in endothelial metabolism, angiogenesis, and cardiovascular disease

Sirtuin 3 (SIRT3) a mitochondrial enzyme that plays an important role in energy homeostasis, cardiac remodeling, and heart failure (HF). The expression of SIRT3 declines with advanced age, cardiovascular, and metabolic diseases. Accumulating evidence suggests that SIRT3 plays a critical role in protecting the heart from cardiac hypertrophy, cardiac dysfunction associated with HF, and in the protection of cardiac cells from stress-mediated cell death. Clinical studies have demonstrated that HF with preserved ejection fraction (HFpEF) in patients present with abnormalities in coronary microcirculation related to endothelial dysfunction and coronary microvascular rarefaction. Although SIRT3-mediated regulation of mitochondrial homeostasis and heart function has been intensively investigated, the effect of SIRT3 on endothelial cell (EC) glycolytic metabolism and microvascular function has not been well studied. ECs utilize glycolysis for generating ATP rather than oxidative phosphorylation to maintain their normal functions and promote angiogenesis and EC-cardiomyocyte interactions. Emerging evidence indicates that SIRT3 is involved in the regulation of endothelial metabolism and angiogenesis and thus affects the development of cardiovascular diseases associated with aging. This review will discuss the current knowledge of SIRT3 and its functional role on endothelial metabolism, cardiac function, and cardiovascular diseases.

Mitochondrial metabolism in pulmonary hypertension: beyond mountains there are mountains

Pulmonary hypertension (PH) is a heterogeneous and fatal disease of the lung vasculature, where metabolic and mitochondrial dysfunction may drive pathogenesis. Similar to the Warburg effect in cancer, a shift from mitochondrial oxidation to glycolysis occurs in diseased pulmonary vessels and the right ventricle. However, appreciation of metabolic events in PH beyond the Warburg effect is only just emerging. This Review discusses molecular, translational, and clinical concepts centered on the mitochondria and highlights promising, controversial, and challenging areas of investigation. If we can move beyond the "mountains" of obstacles in this field and elucidate these fundamental tenets of pulmonary vascular metabolism, such work has the potential to usher in much-needed diagnostic and therapeutic approaches for the mitochondrial and metabolic management of PH.

Altered mitochondrial acetylation profiles in a kainic acid model of temporal lobe epilepsy

Impaired bioenergetics and oxidative damage in the mitochondria are implicated in the etiology of temporal lobe epilepsy, and hyperacetylation of mitochondrial proteins has recently emerged as a critical negative regulator of mitochondrial functions. However, the roles of mitochondrial acetylation and activity of the primary mitochondrial deacetylase, SIRT3, have not been explored in acquired epilepsy. We investigated changes in mitochondrial acetylation and SIRT3 activity in the development of chronic epilepsy in the kainic acid rat model of TLE. Hippocampal measurements were made at 48 h, 1 week and 12 weeks corresponding to the acute, latent and chronic stages of epileptogenesis. Assessment of hippocampal bioenergetics demonstrated a ≥ 27% decrease in the ATP/ADP ratio at all phases of epileptogenesis (p < 0.05), whereas cellular NAD+ levels were decreased by ≥ 41% in the acute and latent time points (p < 0.05), but not in chronically epileptic rats. In spontaneously epileptic rats, we found decreased protein expression of SIRT3 and a 60% increase in global mitochondrial acetylation, as well as enhanced acetylation of the known SIRT3 substrates MnSOD, Ndufa9 of Complex I and IDH2 (all p < 0.05), suggesting SIRT3 dysfunction in chronic epilepsy. Mass spectrometry-based acetylomics investigation of hippocampal mitochondria demonstrated a 79% increase in unique acetylated proteins from rats in the chronic phase vs. controls. Pathway analysis identified numerous mitochondrial bioenergetic pathways affected by mitochondrial acetylation. These results suggest SIRT3 dysfunction and aberrant protein acetylation may contribute to mitochondrial dysfunction in chronic epilepsy.

Recent advances in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare disorder with a high mortality rate. Treatment options have improved in the last 20 years, but patients still die prematurely of right heart failure. Though rare, it is heterogeneous at the genetic and molecular level, and understanding and exploiting this is key to the development of more effective treatments. BMPR2, encoding bone morphogenetic receptor type 2, is the most commonly affected gene in both familial and non-familial PAH, but rare mutations have been identified in other genes. Transcriptomic, proteomic, and metabolomic studies looking for endophenotypes are under way. There is no shortage of candidate new drug targets for PAH, but the selection and prioritisation of these are challenges for the research community.

Inhibition of pyruvate dehydrogenase kinase improves pulmonary arterial hypertension in genetically susceptible patients

Pulmonary arterial hypertension (PAH) is a progressive vascular disease with a high mortality rate. It is characterized by an occlusive vascular remodeling due to a pro-proliferative and antiapoptotic environment in the wall of resistance pulmonary arteries (PAs). Proliferating cells exhibit a cancer-like metabolic switch where mitochondrial glucose oxidation is suppressed, whereas glycolysis is up-regulated as the major source of adenosine triphosphate production. This multifactorial mitochondrial suppression leads to inhibition of apoptosis and downstream signaling promoting proliferation. We report an increase in pyruvate dehydrogenase kinase (PDK), an inhibitor of the mitochondrial enzyme pyruvate dehydrogenase (PDH, the gatekeeping enzyme of glucose oxidation) in the PAs of human PAH compared to healthy lungs. Treatment of explanted human PAH lungs with the PDK inhibitor dichloroacetate (DCA) ex vivo activated PDH and increased mitochondrial respiration. In a 4-month, open-label study, DCA (3 to 6.25 mg/kg b.i.d.) administered to patients with idiopathic PAH (iPAH) already on approved iPAH therapies led to reduction in mean PA pressure and pulmonary vascular resistance and improvement in functional capacity, but with a range of individual responses. Lack of ex vivo and clinical response was associated with the presence of functional variants of SIRT3 and UCP2 that predict reduced protein function. Impaired function of these proteins causes PDK-independent mitochondrial suppression and pulmonary hypertension in mice. This first-in-human trial of a mitochondria-targeting drug in iPAH demonstrates that PDK is a druggable target and offers hemodynamic improvement in genetically susceptible patients, paving the way for novel precision medicine approaches in this disease.

Suppression of Endothelial-to-Mesenchymal Transition by SIRT (Sirtuin) 3 Alleviated the Development of Hypertensive Renal Injury

Endothelial-to-mesenchymal transition (EndoMT) has recently emerged as a potentially important contributor in promoting fibrosis in chronic kidney disease. However, little is known about the role and molecular basis of its involvement in hypertensive renal injury. Here, we aim to determine the role of SIRT (sirtuin) 3 on EndoMT in hypertensive renal injury and to explore its underlying mechanisms. We found that SIRT3 expression was significantly reduced in Ang II (angiotensin II)-induced hypertensive model, accompanied with induction of EndoMT and increased reactive oxygen species and renal fibrosis. In SIRT3^-/- (SIRT3 knockout) mice subjected to Ang II infusion, renal dysfunction was aggravated with an increased EndoMT and reactive oxygen species level, whereas in SIRT3-Tg^EC (SIRT3 endothelial cell-specific transgenic) mice, the Ang II-induced renal fibrosis and EndoMT and oxidative stress were ameliorated. With primary mouse glomerular endothelial cells, we confirmed that Ang II treatment initiated EndoMT and decreased catalase expression, which were suppressed by SIRT3 overexpression. Using immunoprecipitation, luciferase, and chromatin immunoprecipitation assay, we demonstrated that SIRT3-mediated deacetylation and nuclear localization of Foxo3a (forkhead box O3a) resulted in activated Foxo3a-dependent catalase expression. Moreover, Foxo3a knockdown abolished SIRT3-mediated suppression of EndoMT. In conclusion, these results established the SIRT3-Foxo3a-catalase pathway as a critical factor in the maintenance of endothelial homeostasis and point to an important role of EndoMT in the vascular pathology of renal fibrosis, which may provide a new therapeutic target to impede the progression of hypertensive renal injury.

An Official American Thoracic Society Workshop Report: Obesity and Metabolism. An Emerging Frontier in Lung Health and Disease

The world is in the midst of an unprecedented epidemic of obesity. This epidemic has changed the presentation and etiology of common diseases. For example, steatohepatitis, directly attributable to obesity, is now the most common cause of cirrhosis in the United States. Type 2 diabetes is increasingly being diagnosed in children. Pulmonary researchers and clinicians are just beginning to appreciate the impact of obesity and altered metabolism on common pulmonary diseases. Obesity has recently been identified as a major risk factor for the development of asthma and for acute respiratory distress syndrome. Obesity is associated with profound changes in pulmonary physiology, the development of pulmonary hypertension, sleep-disordered breathing, and altered susceptibility to pulmonary infection. In short, obesity is leading to dramatic changes in lung health and disease. Simultaneously, the rapidly developing field of metabolism, including mitochondrial function, is shifting the paradigms by which the pathophysiology of many pulmonary diseases is understood. Altered metabolism can lead to profound changes in both innate and adaptive immunity, as well as the function of structural cells. To address this emerging field, a 3-day meeting on obesity, metabolism, and lung disease was convened in October 2015 to discuss recent findings, foster research initiatives, and ultimately guide clinical care. The major findings arising from this meeting are reported in this document.

Metabolic Reprogramming and Redox Signaling in Pulmonary Hypertension

Pulmonary hypertension is a complex disease of the pulmonary vasculature, which in severe cases terminates in right heart failure. Complex remodeling of pulmonary arteries comprises the central issue of its pathology. This includes extensive proliferation, apoptotic resistance and inflammation. As such, the molecular and cellular features of pulmonary hypertension resemble hallmark characteristics of cancer cell behavior. The vascular remodeling derives from significant metabolic changes in resident cells, which we describe in detail. It affects not only cells of pulmonary artery wall, but also its immediate microenvironment involving cells of immune system (i.e., macrophages). Thus aberrant metabolism constitutes principle component of the cancer-like theory of pulmonary hypertension. The metabolic changes in pulmonary artery cells resemble the cancer associated Warburg effect, involving incomplete glucose oxidation through aerobic glycolysis with depressed mitochondrial catabolism enabling the fueling of anabolic reactions with amino acids, nucleotides and lipids to sustain proliferation. Macrophages also undergo overlapping but distinct metabolic reprogramming inducing specific activation or polarization states that enable their participation in the vascular remodeling process. Such metabolic synergy drives chronic inflammation further contributing to remodeling. Enhanced glycolytic flux together with suppressed mitochondrial bioenergetics promotes the accumulation of reducing equivalents, NAD(P)H. We discuss the enzymes and reactions involved. The reducing equivalents modulate the regulation of proteins using NAD(P)H as the transcriptional co-repressor C-terminal binding protein 1 cofactor and significantly impact redox status (through GSH, NAD(P)H oxidases, etc.), which together act to control the phenotype of the cells of pulmonary arteries. The altered mitochondrial metabolism changes its redox poise, which together with enhanced NAD(P)H oxidase activity and reduced enzymatic antioxidant activity promotes a pro-oxidative cellular status. Herein we discuss all described metabolic changes along with resultant alterations in redox status, which result in excessive proliferation, apoptotic resistance, and inflammation, further leading to pulmonary arterial wall remodeling and thus establishing pulmonary artery hypertension pathology.

Epigenetic Regulation and Its Therapeutic Potential in Pulmonary Hypertension

Recent advances in epigenetics have made a tremendous impact on our knowledge of biological phenomena and the environmental stressors on complex diseases. Understanding the mechanism of epigenetic reprogramming during the occurrence of pulmonary hypertension (PH) is important for advanced studies and clinical therapy. In this article, we review the discovery of novel epigenetic mechanisms associated with PH including DNA methylation, histone modification, and noncoding RNA interference. In addition, we highlight the role of epigenetic mechanisms in adult PAH resulting from undesirable perinatal environments-Extrauterine growth restriction (EUGR) and Intrauterine growth retardation (IUGR). Lastly, we give a comprehensive summary for the remaining challenges and discuss future methods of epigenetic targeted therapy for pulmonary hypertension.