Mitochondrial oxidative stress mediates angiotensin II-induced cardiac hypertrophy and Galphaq overexpression-induced heart failure

Mitochondrial dysfunction and oxidative stress in heart disease

Beyond their role as a cellular powerhouse, mitochondria are emerging as integral players in molecular signaling and cell fate determination through reactive oxygen species (ROS). While ROS production has historically been portrayed as an unregulated process driving oxidative stress and disease pathology, contemporary studies reveal that ROS also facilitate normal physiology. Mitochondria are especially abundant in cardiac tissue; hence, mitochondrial dysregulation and ROS production are thought to contribute significantly to cardiac pathology. Moreover, there is growing appreciation that medical therapies designed to mediate mitochondrial ROS production can be important strategies to ameliorate cardiac disease. In this review, we highlight evidence from animal models that illustrates the strong connections between mitochondrial ROS and cardiac disease, discuss advancements in the development of mitochondria-targeted antioxidant therapies, and identify challenges faced in bringing such therapies into the clinic.

Heart disease progression could be tackled by targeting signaling molecules that cause oxidative stress. Jennifer Kwong at Emory University School of Medicine in Atlanta, USA, and co-workers reviewed research into the role of mitochondria and their associated signaling molecules in the development of heart disease. Mitochondria are a major source of reactive oxygen species (ROS), signaling molecules involved in muscle contraction and calcium transfer in the heart, but they also destroy ROS to maintain a balance. Disruption to this balance can lead to elevated ROS, causing DNA and cellular damage, triggering disease. Animal trials using drugs to target mitochondrial ROS show promise in limiting heart disease progression. Further research is needed to determine whether this approach will work in humans and which specific heart problems might benefit from such therapies.

Redox Regulation of the Microcirculation

The microcirculation maintains tissue homeostasis through local regulation of blood flow and oxygen delivery. Perturbations in microvascular function are characteristic of several diseases and may be early indicators of pathological changes in the cardiovascular system and in parenchymal tissue function. These changes are often mediated by various reactive oxygen species and linked to disruptions in pathways such as vasodilation or angiogenesis. This overview compiles recent advances relating to redox regulation of the microcirculation by adopting both cellular and functional perspectives. Findings from a variety of vascular beds and models are integrated to describe common effects of different reactive species on microvascular function. Gaps in understanding and areas for further research are outlined. © 2020 American Physiological Society. Compr Physiol 10:229-260, 2020.

Angiotensin II Type I Receptor Antagonism Attenuates Nicotine-Induced Cardiac Remodeling, Dysfunction, and Aggravation of Myocardial Ischemia-Reperfusion Injury in Rats

Increased exposure to nicotine contributes to the development of cardiac dysfunction by promoting oxidative stress, fibrosis, and inflammation. These deleterious events altogether render cardiac myocytes more susceptible to acute cardiac insults such as ischemia-reperfusion (I/R) injury. This study sought to elucidate the role of angiotensin II type I (AT1) receptors in cardiac injury resulting from prolonged nicotine administration in a rat model. Male Sprague-Dawley rats were given nicotine (0.6 mg/kg ip) for 28 days to induce cardiac dysfunction, alone or in combination with the AT1 receptor antagonist, irbesartan (10 mg/kg, po). Vehicle-treated rats were used as controls. Rat hearts isolated from each experimental group at study endpoint were examined for changes in function, histology, gene expression, and susceptibility against acute I/R injury determined ex vivo. Rats administered nicotine alone exhibited significantly increased cardiac expression of angiotensin II and angiotensin-converting enzyme (ACE) in addition to elevated systolic blood pressure (SBP) and heart rate. Furthermore, nicotine administration markedly reduced left ventricular (LV) performance with concomitant increases in myocardial oxidative stress, fibrosis, and inflammation. Concomitant treatment with irbesartan attenuated these effects, lowering blood pressure, heart rate, oxidative stress, and expression of fibrotic and inflammatory genes. Importantly, the irbesartan-treated group also manifested reduced susceptibility to I/R injury ex vivo. These findings suggest that AT1 receptors play an important role in nicotine-induced cardiac dysfunction, and pharmacological approaches targeting cardiac AT1 receptors may thus benefit patients with sustained exposure to nicotine.

Curcumin Management of Myocardial Fibrosis and its Mechanisms of Action: A Review

Myocardial fibrosis is implicated as a leading risk factor for heart failure, arrhythmia, and sudden death after cardiac injury, as the excessive interstitial extracellular matrix impedes heart contraction and electrical conduction. Complicated mechanisms involving oxidative stress, pro-inflammatory cytokines, chemokine families, NLRP3 inflammasomes, growth factors, and non-coding RNAs participate in cardiac fibrogenesis and make it difficult to designate specific and effective therapies. Oriental herbs have been popular for thousands of years in the health care of Asian residents, due to their multi-targeted, multi-faceted approaches and their multi-functional effects in fighting difficult and complicated diseases, including cardiovascular disorders such as myocardial fibrosis. Curcumin, a natural polyphenol and yellow pigment obtained from the spice turmeric, was found to have strong anti-oxidant and anti-inflammatory properties. Increasing evidence has shown that curcumin can be used to prevent and treat myocardial fibrosis, when the myocardium suffers pathological pro-fibrotic changes in vivo and in vitro. The present review focuses on recent studies elucidating the mechanisms of curcumin in treating different pathologic conditions, including ischemia, hypoxia/reoxygenation, pressure or volume overload, and hyperglycemia or high-fat-induced cardiac fibrosis. Novel analogs such as C66, B2BrBC, Y20, and J17 have been designed to maximize the therapeutic potentials of curcumin. These optimized curcumin analogs with improved bioavailability and pharmacokinetic profiles need to be clinically verified before curcumin could be recommended for the treatment of myocardial fibrosis.

Hyperactive ryanodine receptors in human heart failure and ischaemic cardiomyopathy reside outside of couplons

Aims

In ventricular myocytes from humans and large mammals, the transverse and axial tubular system (TATS) network is less extensive than in rodents with consequently a greater proportion of ryanodine receptors (RyRs) not coupled to this membrane system. TATS remodelling in heart failure (HF) and after myocardial infarction (MI) increases the fraction of non-coupled RyRs. Here we investigate whether this remodelling alters the activity of coupled and non-coupled RyR sub-populations through changes in local signalling. We study myocytes from patients with end-stage HF, compared with non-failing (non-HF), and myocytes from pigs with MI and reduced left ventricular (LV) function, compared with sham intervention (SHAM).

Methods and results

Single LV myocytes for functional studies were isolated according to standard protocols. Immunofluorescent staining visualized organization of TATS and RyRs. Ca²⁺ was measured by confocal imaging (fluo-4 as indicator) and using whole-cell patch-clamp (37°C). Spontaneous Ca²⁺ release events, Ca²⁺ sparks, as a readout for RyR activity were recorded during a 15 s period following conditioning stimulation at 2 Hz. Sparks were assigned to cell regions categorized as coupled or non-coupled sites according to a previously developed method. Human HF myocytes had more non-coupled sites and these had more spontaneous activity than in non-HF. Hyperactivity of these non-coupled RyRs was reduced by Ca²⁺/calmodulin-dependent kinase II (CaMKII) inhibition. Myocytes from MI pigs had similar changes compared with SHAM controls as seen in human HF myocytes. As well as by CaMKII inhibition, in MI, the increased activity of non-coupled sites was inhibited by mitochondrial reactive oxygen species (mito-ROS) scavenging. Under adrenergic stimulation, Ca²⁺ waves were more frequent and originated at non-coupled sites, generating larger Na⁺/Ca²⁺ exchange currents in MI than in SHAM. Inhibition of CaMKII or mito-ROS scavenging reduced spontaneous Ca²⁺ waves, and improved excitation–contraction coupling.

Conclusions

In HF and after MI, RyR microdomain re-organization enhances spontaneous Ca²⁺ release at non-coupled sites in a manner dependent on CaMKII activation and mito-ROS production. This specific modulation generates a substrate for arrhythmia that appears to be responsive to selective pharmacologic modulation.

Mitochondrial function in the heart: the insight into mechanisms and therapeutic potentials

Mitochondrial dysfunction is considered as a crucial contributory factor in cardiac pathology. This has highlighted the therapeutic potential of targeting mitochondria to prevent or treat cardiac disease. Mitochondrial dysfunction is associated with aberrant electron transport chain activity, reduced ATP production, an abnormal shift in metabolic substrates, ROS overproduction and impaired mitochondrial dynamics. This review will cover the mitochondrial functions and how they are altered in various disease conditions. Furthermore, the mechanisms that lead to mitochondrial defects and the protective mechanisms that prevent mitochondrial damage will be discussed. Finally, potential mitochondrial targets for novel therapeutic intervention will be explored. We will highlight the development of small molecules that target mitochondria from different perspectives and their current progress in clinical trials. LINKED ARTICLES: This article is part of a themed section on Mitochondrial Pharmacology: Featured Mechanisms and Approaches for Therapy Translation. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.22/issuetoc.

Differential effects of various genetic mouse models of the mechanistic target of rapamycin complex I inhibition on heart failure

Inhibition of mammalian target of rapamycin complex I (mTORC1) by rapamycin improves cardiac function in both aging and heart failure. While the protective mechanisms are not fully understood in mammals, they are presumably mediated through metabolic regulation and suppression of protein translation by reduced phosphorylation of 4EBP1, a target of mTORC1. Using transverse aortic constriction (TAC) and Gαq overexpression-induced heart failure models, we examined the effect of cardiac-specific heterozygous deletion (het) of Raptor, a component of mTORC1, and cardiac-specific transgenic overexpression of wild type or phosphorylation site mutant 4EBP1. In wild-type mice with TAC-induced heart failure, quantitative shotgun proteomics revealed decreased abundance of proteins of mitochondrial metabolism and increased abundance of proteins in oxidative stress response, ubiquitin, and other pathways. The Raptor het ameliorated both TAC- and Gαq overexpression-induced heart failure and the associated proteomic remodeling, especially those pathways involved in mitochondrial function, citric acid cycle, and ubiquitination. In contrast, transgenic overexpression of either wild type or mutant 4EBP1 aggravated TAC and Gαq, consistent with reduced adaptive hypertrophy by suppression of protein translation, in parallel with adverse remodeling of left ventricular proteomes. Partial mTORC1 inhibition by Raptor heterozygous deletion ameliorates heart failure and is associated with better preservation of the mitochondrial proteome; however, this effect does not appear to be mediated through suppression of protein translation by increased 4EBP1. Increased activity of 4EBP1 reduced adaptive hypertrophy and aggravated heart failure, suggesting that protein translation is essential for adaptive hypertrophy in pressure overload.

Angiotensin II Influences Pre-mRNA Splicing Regulation by Enhancing RBM20 Transcription Through Activation of the MAPK/ELK1 Signaling Pathway

RNA binding motif 20 (RBM20) is a key regulator of pre-mRNA splicing of titin and other genes that are associated with cardiac diseases. Hormones, like insulin, triiodothyronine (T3), and angiotensin II (Ang II), can regulate gene-splicing through RBM20, but the detailed mechanism remains unclear. This study was aimed at investigating the signaling mechanism by which hormones regulate pre-mRNA splicing through RBM20. We first examined the role of RBM20 in Z-, I-, and M-band titin splicing at different ages in wild type (WT) and RBM20 knockout (KO) rats using RT-PCR; we found that RBM20 is the predominant regulator of I-band titin splicing at all ages. Then we treated rats with propylthiouracil (PTU), T3, streptozotocin (STZ), and Ang II and evaluated the impact of these hormones on the splicing of titin, LIM domain binding 3 (Ldb3), calcium/calmodulin-dependent protein kinase II gamma (Camk2g), and triadin (Trdn). We determined the activation of mitogen-activated protein kinase (MAPK) signaling in primary cardiomyocytes treated with insulin, T3, and Ang II using western blotting; MAPK signaling was activated and RBM20 expression increased after treatment. Two downstream transcriptional factors c-jun and ETS Transcription Factor (ELK1) can bind the promoter of RBM20. A dual-luciferase activity assay revealed that Ang II, but not insulin and T3, can trigger ELK1 and thus promote transcription of RBM20. This study revealed that Ang II can trigger ELK1 through activation of MAPK signaling by enhancing RBM20 expression which regulates pre-mRNA splicing. Our study provides a potential therapeutic target for the treatment of cardiac diseases in RBM20-mediated pre-mRNA splicing.

NADPH oxidases and oxidase crosstalk in cardiovascular diseases: novel therapeutic targets

Reactive oxygen species (ROS)-dependent production of ROS underlies sustained oxidative stress, which has been implicated in the pathogenesis of cardiovascular diseases such as hypertension, aortic aneurysm, hypercholesterolaemia, atherosclerosis, diabetic vascular complications, cardiac ischaemia-reperfusion injury, myocardial infarction, heart failure and cardiac arrhythmias. Interactions between different oxidases or oxidase systems have been intensively investigated for their roles in inducing sustained oxidative stress. In this Review, we discuss the latest data on the pathobiology of each oxidase component, the complex crosstalk between different oxidase components and the consequences of this crosstalk in mediating cardiovascular disease processes, focusing on the central role of particular NADPH oxidase (NOX) isoforms that are activated in specific cardiovascular diseases. An improved understanding of these mechanisms might facilitate the development of novel therapeutic agents targeting these oxidase systems and their interactions, which could be effective in the prevention and treatment of cardiovascular disorders.

Mitochondrial protection by simvastatin against angiotensin II-mediated heart failure

BACKGROUND AND PURPOSE

Mitochondrial dysfunction plays a role in the progression of cardiovascular diseases including heart failure. 3-Hydroxy-3-methylglutaryl-CoA reductase inhibitors (statins), which inhibit ROS synthesis, show cardioprotective effects in chronic heart failure. However, the beneficial role of statins in mitochondrial protection in heart failure remains unclear.

EXPERIMENTAL APPROACH

Rats were treated with angiotensin II (1.5 mg·kg-1 ·day-1 ) or co-administered simvastatin (oral, 10 mg·kg-1 ) for 14 days; and then administration was stopped for the following 14 days. Cardiac structure/function was examined by wheat germ agglutinin staining and echocardiography. Mitochondrial morphology and the numbers of lipid droplets, lysosomes, autophagosomes, and mitophagosomes were determined by transmission electron microscopy. Human cardiomyocytes were stimulated, and intracellular ROS and mitochondrial membrane potential (ΔΨm ) changes were measured by flow cytometry and JC-1 staining, respectively. Autophagy and mitophagy-related and mitochondria-regulated apoptotic proteins were identified by immunohistochemistry and western blotting.

KEY RESULTS

Simvastatin significantly reduced ROS production and attenuated the disruption of ΔΨm . Simvastatin induced the accumulation of lipid droplets to provide energy for maintaining mitochondrial function, promoted autophagy and mitophagy, and inhibited mitochondria-mediated apoptosis. These findings suggest that mitochondrial protection mediated by simvastatin plays a therapeutic role in heart failure prevention by modulating antioxidant status and promoting energy supplies for autophagy and mitophagy to inhibit mitochondrial damage and cardiomyocyte apoptosis.

CONCLUSION AND IMPLICATIONS

Mitochondria play a key role in mediating heart failure progression. Simvastatin attenuated heart failure, induced by angiotensin II, via mitochondrial protection and might provide a new therapy to prevent heart failure.

TRPC3 deficiency attenuates high salt-induced cardiac hypertrophy by alleviating cardiac mitochondrial dysfunction

Long-term high salt intake leads to cardiac hypertrophy, but the mechanism remains elusive. Transient receptor potential channel, canonical 3(TRPC3), located in mitochondria, regulates mitochondrial calcium and reactive oxygen species(ROS) production. Herein, we investigated whether TRPC3 participates in high salt-induced cardiac hypertrophy by impairing cardiac mitochondrial function. High salt treatment increased the expression of mitochondrial TRPC3 in cardiomyocytes, accompanied by enhanced mitochondrial calcium uptake and elevated ROS production. Inhibition of TRPC3 significantly reduced high salt-induced ROS generation, promoted ATP production by stimulating oxidative phosphorylation, and increased enzyme activity in mitochondria in cardiomyocytes. Additionally, TRPC3 deficiency inhibited high salt-induced cardiac hypertrophy in vivo. A long-term high salt diet increased cardiac mitochondrial TRPC3 expression, elevated expression of cardiac hypertrophic markers atrial natriuretic peptide (ANP),brain natriuretic peptide (BNP) and β-myosin heavy chain (β-MHC) and decreased ATP production and mitochondrial complex I and II enzyme activity in a TRPC3-dependent manner. TRPC3 deficiency antagonises high salt diet-mediated cardiac hypertrophy by ameliorating TRPC3-mediated cardiac mitochondrial dysfunction. TRPC3 may therefore represent a novel target for preventing high salt-induced cardiac damage.

Calcium Signaling and Reactive Oxygen Species in Mitochondria

In heart failure, alterations of Na⁺ and Ca²⁺ handling, energetic deficit, and oxidative stress in cardiac myocytes are important pathophysiological hallmarks. Mitochondria are central to these processes because they are the main source for ATP, but also reactive oxygen species (ROS), and their function is critically controlled by Ca²⁺ During physiological variations of workload, mitochondrial Ca²⁺ uptake is required to match energy supply to demand but also to keep the antioxidative capacity in a reduced state to prevent excessive emission of ROS. Mitochondria take up Ca²⁺ via the mitochondrial Ca²⁺ uniporter, which exists in a multiprotein complex whose molecular components were identified only recently. In heart failure, deterioration of cytosolic Ca²⁺ and Na⁺ handling hampers mitochondrial Ca²⁺ uptake and the ensuing Krebs cycle-induced regeneration of the reduced forms of NADH (nicotinamide adenine dinucleotide) and NADPH (nicotinamide adenine dinucleotide phosphate), giving rise to energetic deficit and oxidative stress. ROS emission from mitochondria can trigger further ROS release from neighboring mitochondria termed ROS-induced ROS release, and cross talk between different ROS sources provides a spatially confined cellular network of redox signaling. Although low levels of ROS may serve physiological roles, higher levels interfere with excitation-contraction coupling, induce maladaptive cardiac remodeling through redox-sensitive kinases, and cell death through mitochondrial permeability transition. Targeting the dysregulated interplay between excitation-contraction coupling and mitochondrial energetics may ameliorate the progression of heart failure.

Anatomically specific reactive oxygen species production participates in Marfan syndrome aneurysm formation

Marfan syndrome (MFS) is a connective tissue disorder that results in aortic root aneurysm formation. Reactive oxygen species (ROS) seem to play a role in aortic wall remodelling in MFS, although the mechanism remains unknown. MFS Fbn1^C1039G/+ mouse root/ascending (AS) and descending (DES) aortic samples were examined using DHE staining, lucigenin‐enhanced chemiluminescence (LGCL), Verhoeff's elastin‐Van Gieson staining (elastin breakdown) and in situ zymography for protease activity. Fbn1^C1039G/+ AS‐ or DES‐derived smooth muscle cells (SMC) were treated with anti‐TGF‐β antibody, angiotensin II (AngII), anti‐TGF‐β antibody + AngII, or isotype control. ROS were detected during early aneurysm formation in the Fbn1^C1039G/+ AS aorta, but absent in normal‐sized DES aorta. Fbn1^C1039G/+ mice treated with the unspecific NADPH oxidase inhibitor, apocynin reduced AS aneurysm formation, with attenuated elastin fragmentation. In situ zymography revealed apocynin treatment decreased protease activity. In vitro SMC studies showed Fbn1^C1039G/+‐derived AS SMC had increased NADPH activity compared to DES‐derived SMC. AS SMC NADPH activity increased with AngII treatment and appeared TGF‐β dependent. In conclusion, ROS play a role in MFS aneurysm development and correspond anatomically with aneurysmal aortic segments. ROS inhibition via apocynin treatment attenuates MFS aneurysm progression. AngII enhances ROS production in MFS AS SMCs and is likely TGF‐β dependent.

Oxidative Stress in the Pathogenesis and Evolution of Chronic Kidney Disease: Untangling Ariadne's Thread

Amplification of oxidative stress is present since the early stages of chronic kidney disease (CKD), holding a key position in the pathogenesis of renal failure. Induction of renal pro-oxidant enzymes with excess generation of reactive oxygen species (ROS) and accumulation of dityrosine-containing protein products produced during oxidative stress (advanced oxidation protein products—AOPPs) have been directly linked to podocyte damage, proteinuria, and the development of focal segmental glomerulosclerosis (FSGS) as well as tubulointerstitial fibrosis. Vascular oxidative stress is considered to play a critical role in CKD progression, and ROS are potential mediators of the impaired myogenic responses of afferent renal arterioles in CKD and impaired renal autoregulation. Both oxidative stress and inflammation are CKD hallmarks. Oxidative stress promotes inflammation via formation of proinflammatory oxidized lipids or AOPPs, whereas activation of nuclear factor κB transcription factor in the pro-oxidant milieu promotes the expression of proinflammatory cytokines and recruitment of proinflammatory cells. Accumulating evidence implicates oxidative stress in various clinical models of CKD, including diabetic nephropathy, IgA nephropathy, polycystic kidney disease as well as the cardiorenal syndrome. The scope of this review is to tackle the issue of oxidative stress in CKD in a holistic manner so as to provide a future framework for potential interventions.

The Burden of Iron Deficiency in Heart Failure: Therapeutic Approach

Heart failure (HF) is highlighted by its burdening symptom-limited exercise capacity and recurrent hospitalizations. Despite substantial advances regarding disease-modifying drugs in HF with reduced ejection fraction, additional therapeutic strategies to improve quality of life are invaluable. Currently, iron deficiency (ID) is overwhelmingly recognized in over 30% to 50% of patients with stable chronic HF, which worsens prognosis. The established pathophysiological mechanisms of progressive HF may be intertwined with increasing myocardial iron scarcity, wherein one begets the other. Most importantly, ID constitutes a novel target for symptom relief in carefully selected patients. In this regard, intravenous iron may be a safe and efficacious intervention, potentially reducing HF hospitalizations. We discuss the evidence and gaps in knowledge concerning iron therapy in HF and propose a practical, comprehensive, clinically oriented algorithm for timely adequate iron replenishment in different clinical scenarios. Finally, we further debate imperative decision-making before intervention and the drawbacks of such a strategy.

Allosteric, transcriptional and post-translational control of mitochondrial energy metabolism

The heart is the organ with highest energy turnover rate (per unit weight) in our body. The heart relies on its flexible and powerful catabolic capacity to continuously generate large amounts of ATP utilizing many energy substrates including fatty acids, carbohydrates (glucose and lactate), ketones and amino acids. The normal health mainly utilizes fatty acids (40-60%) and glucose (20-40%) for ATP production while ketones and amino acids have a minor contribution (10-15% and 1-2%, respectively). Mitochondrial oxidative phosphorylation is the major contributor to cardiac energy production (95%) while cytosolic glycolysis has a marginal contribution (5%). The heart can dramatically and swiftly switch between energy-producing pathways and/or alter the share from each of the energy substrates based on cardiac workload, availability of each energy substrate and neuronal and hormonal activity. The heart is equipped with a highly sophisticated and powerful mitochondrial machinery which synchronizes cardiac energy production from different substrates and orchestrates the rate of ATP production to accommodate its contractility demands. This review discusses mitochondrial cardiac energy metabolism and how it is regulated. This includes a discussion on the allosteric control of cardiac energy metabolism by short-chain coenzyme A esters, including malonyl CoA and its effect on cardiac metabolic preference. We also discuss the transcriptional level of energy regulation and its role in the maturation of cardiac metabolism after birth and cardiac adaptability for different metabolic conditions and energy demands. The role post-translational modifications, namely phosphorylation, acetylation, malonylation, succinylation and glutarylation, play in regulating mitochondrial energy metabolism is also discussed.

Neurocognitive Disorders in Heart Failure: Novel Pathophysiological Mechanisms Underpinning Memory Loss and Learning Impairment

Heart failure (HF) is a major public health issue affecting more than 26 million people worldwide. HF is the most common cardiovascular disease in elder population; and it is associated with neurocognitive function decline, which represent underlying brain pathology diminishing learning and memory faculties. Both HF and neurocognitive impairment are associated with recurrent hospitalization episodes and increased mortality rate in older people, but particularly when they occur simultaneously. Overall, the published studies seem to confirm that HF patients display functional impairments relating to attention, memory, concentration, learning, and executive functioning compared with age-matched controls. However, little is known about the molecular mechanisms underpinning neurocognitive decline in HF. The present review round step recent evidence related to the possible molecular mechanism involved in the establishment of neurocognitive disorders during HF. We will make a special focus on cerebral ischemia, neuroinflammation and oxidative stress, Wnt signaling, and mitochondrial DNA alterations as possible mechanisms associated with cognitive decline in HF. Also, we provide an integrative mechanism linking pathophysiological hallmarks of altered cardiorespiratory control and the development of cognitive dysfunction in HF patients. Graphical Abstract Main molecular mechanisms involved in the establishment of cognitive impairment during heart failure. Heart failure is characterized by chronic activation of brain areas responsible for increasing cardiac sympathetic load. In addition, HF patients also show neurocognitive impairment, suggesting that the overall mechanisms that underpin cardiac sympathoexcitation may be related to the development of cognitive disorders in HF. In low cardiac output, HF cerebral infarction due to cardiac mural emboli and cerebral ischemia due to chronic or intermittent cerebral hypoperfusion has been described as a major mechanism related to the development of CI. In addition, while acute norepinephrine (NE) release may be relevant to induce neural plasticity in the hippocampus, chronic or tonic release of NE may exert the opposite effects due to desensitization of the adrenergic signaling pathway due to receptor internalization. Enhanced chemoreflex drive is a major source of sympathoexcitation in HF, and this phenomenon elevates brain ROS levels and induces neuroinflammation through breathing instability. Importantly, both oxidative stress and neuroinflammation can induce mitochondrial dysfunction and vice versa. Then, this ROS inflammatory pathway may propagate within the brain and potentially contribute to the development of cognitive impairment in HF through the activation/inhibition of key molecular pathways involved in neurocognitive decline such as the Wnt signaling pathway.

Mitochondrial Regulation of Stem Cells in Bone Homeostasis

Mitochondria have emerged as key contributors to the organismal homeostasis, in which mitochondrial regulation of stem cells is becoming increasingly important. Originated from mesenchymal stem cell (MSC) and hematopoietic stem cell (HSC) lineage commitments and interactions, bone is a representative organ where the mitochondrial essentiality to stem cell function has most recently been discovered, underlying skeletal health, aging, and diseases. Furthermore, mitochondrial medications based on modulating stem cell specification are emerging to provide promising therapies to counteract bone aging and pathologies. Here we review the cutting-edge knowledge regarding mitochondrial regulation of stem cells in bone homeostasis, highlighting mechanistic insights as well as mitochondrial strategies for augmented bone healing and tissue regeneration.

Propofol Protects Lung Endothelial Barrier Function by Suppression of High-Mobility Group Box 1 (HMGB1) Release and Mitochondrial Oxidative Damage Catalyzed by HMGB1

Background

The processes of mechanical ventilation-induced lung injury (VILI) triggers the release of high-mobility group box 1 (HMGB1), a prominent damage-associated molecular pattern (DAMP) family member, which can cause damage to pulmonary vascular endothelial cells. We aimed to determine whether propofol protected against endothelial cell injury induced by HMGB1 in vitro and in vivo.

Material/Methods

ICR mice (male) were mechanically ventilated for 4 h after anesthetization at both low tidal volume (LVT, 6 ml/kg) and high tidal volume (HVT, 30 ml/kg). A propofol bolus (10 mg/kg) was administered to the animals prior to the onset of ventilation, followed by infusion at 5 mg/(kg·h). We obtained confluent cultures of mouse lung vascular endothelial cells (MLVECs) and then performed cyclic stretching at 20% stretch for 4 h with or without propofol.

Results

HMGB1 reduced the expression of tight junctions between endothelial cells, including VE-cadherin and ZO-1, and increased endothelial permeability, and both were blocked by propofol. We found that MLVECs exhibited mitochondrial oxidative damage by HMGB1, which was successfully suppressed through administration of MnTBAP as well as propofol. Propofol ameliorated HVT-associated lung vascular hyperpermeability and HMGB1 production in vivo. Propofol also inhibited HMBG1 release caused by cyclic stretching in MLVECs in vitro.

Conclusions

Our results prove that the cyto-protective function of propofol protects against lung ventilation-induced dysfunction of the lung endothelial barrier. This function of propofol is mediated through inhibition of HMGB1 release caused by mechanical stretching and mitochondrial oxidative damage triggered by HMGB1.

WIPI1 is a conserved mediator of right ventricular failure

Right ventricular dysfunction is highly prevalent across cardiopulmonary diseases and independently predicts death in both heart failure (HF) and pulmonary hypertension (PH). Progression towards right ventricular failure (RVF) can occur in spite of optimal medical treatment of HF or PH, highlighting current insufficient understanding of RVF molecular pathophysiology. To identify molecular mechanisms that may distinctly underlie RVF, we investigated the cardiac ventricular transcriptome of advanced HF patients, with and without RVF. Using an integrated systems genomic and functional biology approach, we identified an RVF-specific gene module, for which WIPI1 served as a hub and HSPB6 and MAP4 as drivers, and confirmed the ventricular specificity of Wipi1, Hspb6, and Map4 transcriptional changes in adult murine models of pressure overload induced RV- versus LV- failure. We uncovered a shift towards non-canonical autophagy in the failing RV that correlated with RV-specific Wipi1 upregulation. In vitro siRNA silencing of Wipi1 in neonatal rat ventricular myocytes limited non-canonical autophagy and blunted aldosterone-induced mitochondrial superoxide levels. Our findings suggest that Wipi1 regulates mitochondrial oxidative signaling and non-canonical autophagy in cardiac myocytes. Together with our human transcriptomic analysis and corroborating studies in an RVF mouse model, these data render Wipi1 a potential target for RV-directed HF therapy.

Inflammation and fibrosis in murine models of heart failure

Heart failure is a consequence of various cardiovascular diseases and associated with poor prognosis. Despite progress in the treatment of heart failure in the past decades, prevalence and hospitalisation rates are still increasing. Heart failure is typically associated with cardiac remodelling. Here, inflammation and fibrosis are thought to play crucial roles. During cardiac inflammation, immune cells invade the cardiac tissue and modulate tissue-damaging responses. Cardiac fibrosis, however, is characterised by an increased amount and a disrupted composition of extracellular matrix proteins. As evidence exists that cardiac inflammation and fibrosis are potentially reversible in experimental and clinical set ups, they are interesting targets for innovative heart failure treatments. In this context, animal models are important as they mimic clinical conditions of heart failure patients. The advantages of mice in this respect are short generation times and genetic modifications. As numerous murine models of heart failure exist, the selection of a proper disease model for a distinct research question is demanding. To facilitate this selection, this review aims to provide an overview about the current understanding of the pathogenesis of cardiac inflammation and fibrosis in six frequently used murine models of heart failure. Hence, it compares the models of myocardial infarction with or without reperfusion, transverse aortic constriction, chronic subjection to angiotensin II or deoxycorticosterone acetate, and coxsackievirus B3-induced viral myocarditis in this context. It furthermore provides information about the clinical relevance and the limitations of each model, and, if applicable, about the recent advancements in their methodological proceedings.

Increased calpain-1 in mitochondria induces dilated heart failure in mice: role of mitochondrial superoxide anion

We and others have reported that calpain-1 was increased in myocardial mitochondria from various animal models of heart disease. This study investigated whether constitutive up-regulation of calpain-1 restricted to mitochondria induced myocardial injury and heart failure and, if so, whether these phenotypes could be rescued by selective inhibition of mitochondrial superoxide production. Transgenic mice with human CAPN1 up-regulation restricted to mitochondria in cardiomyocytes (Tg-mtCapn1/tTA) were generated and characterized with low and high over-expression of transgenic human CAPN1 restricted to mitochondria, respectively. Transgenic up-regulation of mitochondria-targeted CAPN1 dose-dependently induced cardiac cell death, adverse myocardial remodeling, heart failure, and early death in mice, the changes of which were associated with mitochondrial dysfunction and mitochondrial superoxide generation. Importantly, a daily injection of mitochondria-targeted superoxide dismutase mimetics mito-TEMPO for 1 month starting from age 2 months attenuated cardiac cell death, adverse myocardial remodeling and heart failure, and reduced mortality in Tg-mtCapn1/tTA mice. In contrast, administration of TEMPO did not achieve similar cardiac protection in transgenic mice. Furthermore, transgenic up-regulation of mitochondria-targeted CAPN1 induced a reduction of ATP5A1 protein and ATP synthase activity in hearts. In cultured cardiomyocytes, increased calpain-1 in mitochondria promoted mitochondrial permeability transition pore (mPTP) opening and induced cell death, which were prevented by over-expression of ATP5A1, mito-TEMPO or cyclosporin A, an inhibitor of mPTP opening. In conclusion, this study has provided direct evidence demonstrating that increased mitochondrial calpain-1 is an important mechanism contributing to myocardial injury and heart failure by disrupting ATP synthase, and promoting mitochondrial superoxide generation and mPTP opening.

c‑Jun/Ap‑1 is upregulated in an Ang II‑induced abdominal aortic aneurysm formation model and mediates Chop expression in mouse aortic smooth muscle cells

Abdominal aortic aneurysm (AAA) is an asymptomatic, potentially lethal disease whose ruptures have a high mortality rate. An effective pharmacological approach to decrease expansion or prevent the rupture of AAAs in humans remains lacking. Previous studies have suggested that activator protein 1 (c-Jun/AP-1) and C/EBP homologous protein (Chop) are involved in the development of AAA. The purpose of the present study was to investigate whether c-Jun/AP-1 mediates Chop overexpression in AAA. c-Jun/AP-1 and Chop protein levels were determined in an angiotensin II (Ang II)-induced AAA model using apolipoprotein E-deficient mice. Additionally, mouse aortic smooth muscle cells (MOVAS cell line) were treated with Ang II. Apoptosis was evaluated via TUNEL assay, MOVAS cell migration ability was assessed by monolayer wound healing assay and the levels of c-Jun/AP-1 and Chop were determined by western blotting, immunofluorescence and immunocytochemical assays. Following c-Jun silencing using c-Jun-specific small interfering (si)RNA, Chop expression was evaluated. Furthermore, chromatin immunoprecipitation (ChIP) was used to investigate whether c-Jun/Ap-1 binds directly to the DNA damage-inducible transcript 3 protein (Ddit3) promoter. It was observed that c-Jun/AP-1 and Chop were synchronously overexpressed in Ang II-induced AAA and Ang II-treated cells, and that apoptosis and migration were induced by Ang II. In addition, Chop was suppressed when c-Jun was silenced by targeted siRNA. Notably, the ChIP assay demonstrated that the DNA fragments pulled down by primary antibodies against c-Jun/Ap-1 were able to be amplified by (Ddit3) promoter-specific primers. c-Jun/AP-1 may therefore mediate Chop expression in MOVAS cells via Ddit3. These results suggested that c-Jun/AP-1 may be a novel target for AAA therapy.

Epigenetically dysregulated genes and pathways implicated in the pathogenesis of non-syndromic high myopia

Myopia, commonly referred to as nearsightedness, is one of the most common causes of visual disability throughout the world. It affects more people worldwide than any other chronic visual impairment condition. Although the prevalence varies among various ethnic groups, the incidence of myopia is increasing in all populations across globe. Thus, it is considered a pressing public health problem. Both genetics and environment play a role in development of myopia. To elucidate the epigenetic mechanism(s) underlying the pathophysiology of high-myopia, we conducted methylation profiling in 18 cases and 18 matched controls (aged 4–12 years), using Illumina MethylationEPIC BeadChips array. The degree of myopia was variable among subjects, ranging from −6 to −15D. We identified 1541 hypermethylated CpGs, representing 1745 genes (2.0-fold or higher) (false discovery rate (FDR) p ≤ 0.05), multiple CpGs were p < 5 × 10⁻⁸ with a receiver operating characteristic area under the curve (ROC-AUC) ≥ 0.75 in high-myopia subjects compared to controls. Among these, 48 CpGs had excellent correlation (AUC ≥ 0.90). Herein, we present the first genome-wide DNA methylation analysis in a unique high-myopia cohort, showing extensive and discrete methylation changes relative to controls. The genes we identified hold significant potential as targets for novel therapeutic intervention either alone, or in combination.

Nanotized PPARα Overexpression Targeted to Hypertrophied Myocardium Improves Cardiac Function by Attenuating the p53-GSK3β-Mediated Mitochondrial Death Pathway

AIMS

Metabolic remodeling of cardiac muscles during pathological hypertrophy is characterized by downregulation of fatty acid oxidation (FAO) regulator, peroxisome proliferator-activated receptor alpha (PPARα). Thereby, we hypothesized that a cardiac-specific induction of PPARα might restore the FAO-related protein expression and resultant energy deficit. In the present study, consequences of PPARα augmentation were evaluated for amelioration of chronic oxidative stress, myocyte apoptosis, and cardiac function during pathological cardiac hypertrophy.

RESULTS

Nanotized PPARα overexpression targeted to myocardium was done by a stearic acid-modified carboxymethyl-chitosan (CMC) conjugated to a 20-mer myocyte-targeted peptide (CMCP). Overexpression of PPARα ameliorated pathological hypertrophy and improved cardiac function. Augmented PPARα in hypertrophied myocytes revealed downregulated p53 acetylation (lys 382), leading to reduced apoptosis. Such cells showed increased binding of PPARα with p53 that in turn reduced interaction of p53 with glycogen synthase kinase-3β (GSK3β), which upregulated inactive phospho-GSK3β (serine [Ser]9) expression within mitochondrial protein fraction. Altogether, the altered molecular milieu in PPARα-overexpressed hypertrophy groups restored mitochondrial structure and function both in vitro and in vivo.

INNOVATION

Cardiomyocyte-targeted overexpression of a protein of interest (PPARα) by nanotized plasmid has been described for the first time in this study. Our data provide a novel insight towards regression of pathological hypertrophy by ameliorating mitochondrial oxidative stress in targeted PPARα-overexpressed myocardium.

CONCLUSION

PPARα-overexpression during pathological hypertrophy showed substantial betterment of mitochondrial structure and function, along with downregulated apoptosis. Myocardium-targeted overexpression of PPARα during pathological cardiac hypertrophy led to an overall improvement of cardiac energy deficit and subsequent cardiac function, thereby, opening up a potential avenue for cardiac tissue engineering during hypertrophic cardiac pathophysiology.

Novel role of mitochondrial GTPases 1 in pathological cardiac hypertrophy

While most mitochondrial proteins are encoded in the nucleus and translated on cytosolic/endoplasmic reticulum ribosomes, proteins encoded by mitochondrial DNA are translated on mitochondrial ribosomes. Mitochondrial GTPases 1 (MTG1) regulates mitochondrial ribosome assembly and translation, but its impact on cardiac adaptation to stress is unknown. Here, we found that MTG1 is dramatically elevated in hearts of dilated cardiomyopathy patients and in mice exposed to left ventricular pressure overload (AB). To examine the role of MTG1 in cardiac hypertrophy and heart failure, MTG1 loss/gain of function studies were performed in cultured cardiomyocytes and mice exposed to hypertrophic stress. MTG1 shRNA and adenoviral overexpression studies indicated that MTG1 expression attenuates angiotensin II-induced hypertrophy in cultured cardiomyocytes, while MTG1 KO mice exhibited no observable cardiac phenotype under basal conditions. MTG1 deficiency significantly exacerbated AB-induced cardiac hypertrophy, expression of hypertrophic stress markers, fibrosis, and LV dysfunction in comparison to WT mice. Conversely, transgenic cardiac MTG1 expression attenuated AB-induced hypertrophy and LV dysfunction. Mechanistically, MTG1 preserved mitochondrial respiratory chain complex activity during pressure overload, which further attenuated ROS generation. Moreover, we demonstrated that TAK1, P38 and JNK1/2 activity is downregulated in the MTG1 overexpression group. Importantly, dampening oxidative stress with N-acetylcysteine (NAC) lowered hypertrophy in MTG1 KO to WT levels. Collectively, our data indicate that MTG1 protects against pressure overload-induced cardiac hypertrophy and dysfunction by preserving mitochondrial function and reducing oxidative stress and downstream TAK1 stress signaling.

Mitoquinone ameliorates pressure overload-induced cardiac fibrosis and left ventricular dysfunction in mice

Increasing evidence indicates that mitochondrial-associated redox signaling contributes to the pathophysiology of heart failure (HF). The mitochondrial-targeted antioxidant, mitoquinone (MitoQ), is capable of modifying mitochondrial signaling and has shown beneficial effects on HF-dependent mitochondrial dysfunction. However, the potential therapeutic impact of MitoQ-based mitochondrial therapies for HF in response to pressure overload is reliant upon demonstration of improved cardiac contractile function and suppression of deleterious cardiac remodeling. Using a new (patho)physiologically relevant model of pressure overload-induced HF we tested the hypothesis that MitoQ is capable of ameliorating cardiac contractile dysfunction and suppressing fibrosis. To test this C57BL/6J mice were subjected to left ventricular (LV) pressure overload by ascending aortic constriction (AAC) followed by MitoQ treatment (2 µmol) for 7 consecutive days. Doppler echocardiography showed that AAC caused severe LV dysfunction and hypertrophic remodeling. MitoQ attenuated pressure overload-induced apoptosis, hypertrophic remodeling, fibrosis and LV dysfunction. Profibrogenic transforming growth factor-β1 (TGF-β1) and NADPH oxidase 4 (NOX4, a major modulator of fibrosis related redox signaling) expression increased markedly after AAC. MitoQ blunted TGF-β1 and NOX4 upregulation and the downstream ACC-dependent fibrotic gene expressions. In addition, MitoQ prevented Nrf2 downregulation and activation of TGF-β1-mediated profibrogenic signaling in cardiac fibroblasts (CF). Finally, MitoQ ameliorated the dysregulation of cardiac remodeling-associated long noncoding RNAs (lncRNAs) in AAC myocardium, phenylephrine-treated cardiomyocytes, and TGF-β1-treated CF. The present study demonstrates for the first time that MitoQ improves cardiac hypertrophic remodeling, fibrosis, LV dysfunction and dysregulation of lncRNAs in pressure overload hearts, by inhibiting the interplay between TGF-β1 and mitochondrial associated redox signaling.

Lycopene protects against pressure overload-induced cardiac hypertrophy by attenuating oxidative stress

Oxidative stress is considered an important pathogenic process of cardiac hypertrophy. Lycopene is a kind of carotenoid antioxidant that protects the cardiovascular system, so we hypothesized that lycopene might inhibit cardiac hypertrophy by attenuating oxidative stress. Phenylephrine and pressure overload were used to set up the hypertrophic models in vitro and in vivo respectively. Our data revealed that treatment with lycopene can significantly block pressure overload-induced cardiac hypertrophy in in vitro and in vivo studies. Further studies demonstrated that lycopene can reverse the increase in reactive oxygen species (ROS) generation during the process of hypertrophy and can retard the activation of ROS-dependent pro-hypertrophic MAPK and Akt signaling pathways. In addition, protective effects of lycopene on the permeability transition pore opening in neonatal cardiomyocytes were observed. Moreover, we demonstrated that lycopene restored impaired antioxidant response element (ARE) activity and activated ARE-driven expression of antioxidant genes. Consequently, our findings indicated that lycopene inhibited cardiac hypertrophy by suppressing ROS-dependent mechanisms.

Zidovudine-Mediated Autophagy Inhibition Enhances Mitochondrial Toxicity in Muscle Cells

Nucleoside reverse transcriptase inhibitors (NRTI), such as zidovudine (AZT), are constituents of HIV-1 therapy and are used for the prevention of mother-to-child transmission. Prolonged thymidine analogue exposure has been associated with mitochondrial toxicities to heart, liver, and skeletal muscle. We hypothesized that the thymidine analogue AZT might interfere with autophagy in myocytes, a lysosomal degradation pathway implicated in the regulation of mitochondrial recycling, cell survival, and the pathogenesis of myodegenerative diseases. The impact of AZT and lamivudine (3TC) on C2C12 myocyte autophagy was studied using various methods based on LC3-green fluorescent protein overexpression or LC3 staining in combination with Western blotting, flow cytometry, and confocal and electron microscopy. Lysosomal and mitochondrial functions were studied using appropriate staining for lysosomal mass, acidity, cathepsin activity, as well as mitochondrial mass and membrane potential in combination with flow cytometry and confocal microscopy. AZT, but not 3TC, exerted a significant dose- and time-dependent inhibitory effect on late stages of autophagosome maturation, which was reversible upon mTOR inhibition. Inhibition of late autophagy at therapeutic drug concentrations led to dysfunctional mitochondrial accumulation with membrane hyperpolarization and increased reactive oxygen species (ROS) generation and, ultimately, compromised cell viability. These AZT effects could be readily replicated by pharmacological and genetic inhibition of myocyte autophagy and, most importantly, could be rescued by pharmacological stimulation of autophagolysosomal biogenesis. Our data suggest that the thymidine analogue AZT inhibits autophagy in myocytes, which in turn leads to the accumulation of dysfunctional mitochondria with increased ROS generation and compromised cell viability. This novel mechanism could contribute to our understanding of the long-term side effects of antiviral agents.

Adrenergic Regulation of Drp1-Driven Mitochondrial Fission in Cardiac Physio-Pathology

Abnormal mitochondrial morphology, especially fragmented mitochondria, and mitochondrial dysfunction are hallmarks of a variety of human diseases including heart failure (HF). Although emerging evidence suggests a link between mitochondrial fragmentation and cardiac dysfunction, it is still not well described which cardiac signaling pathway regulates mitochondrial morphology and function under pathophysiological conditions such as HF. Mitochondria change their shape and location via the activity of mitochondrial fission and fusion proteins. This mechanism is suggested as an important modulator for mitochondrial and cellular functions including bioenergetics, reactive oxygen species (ROS) generation, spatiotemporal dynamics of Ca²⁺ signaling, cell growth, and death in the mammalian cell- and tissue-specific manners. Recent reports show that a mitochondrial fission protein, dynamin-like/related protein 1 (DLP1/Drp1), is post-translationally modified via cell signaling pathways, which control its subcellular localization, stability, and activity in cardiomyocytes/heart. In this review, we summarize the possible molecular mechanisms for causing post-translational modifications (PTMs) of DLP1/Drp1 in cardiomyocytes, and further discuss how these PTMs of DLP1/Drp1 mediate abnormal mitochondrial morphology and mitochondrial dysfunction under adrenergic signaling activation that contributes to the development and progression of HF.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Mitochondrial Dysfunction-Associated Arrhythmogenic Substrates in Diabetes Mellitus

There is increasing evidence that diabetic cardiomyopathy increases the risk of cardiac arrhythmia and sudden cardiac death. While the detailed mechanisms remain incompletely understood, the loss of mitochondrial function, which is often observed in the heart of patients with diabetes, has emerged as a key contributor to the arrhythmogenic substrates. In this mini review, the pathophysiology of mitochondrial dysfunction in diabetes mellitus is explored in detail, followed by descriptions of several mechanisms potentially linking mitochondria to arrhythmogenesis in the context of diabetic cardiomyopathy.

Nanoparticles for postinfarct ventricular remodeling

In recent years, tremendous progress has been made in the treatment of acute myocardial infarction, but pathological ventricular remodeling often causes survivors to suffer from fatal heart failure. Currently, there is no effective therapy to attenuate ventricular remodeling. Recently, nanoparticle-based drug delivery systems are widely applied in biomedicine especially in cancer and liver fibrosis, owing to its excellent physical, chemical and biological properties. Therefore, the use of nanoparticles as delivery vehicles of small molecules, polypeptides, etc. to improve postinfarct ventricular remodeling is expected. In this review, we summarize the updated researches in this fast-growing area and suggest further works needed.

Cardiomyocyte gene programs encoding morphological and functional signatures in cardiac hypertrophy and failure

Pressure overload induces a transition from cardiac hypertrophy to heart failure, but its underlying mechanisms remain elusive. Here we reconstruct a trajectory of cardiomyocyte remodeling and clarify distinct cardiomyocyte gene programs encoding morphological and functional signatures in cardiac hypertrophy and failure, by integrating single-cardiomyocyte transcriptome with cell morphology, epigenomic state and heart function. During early hypertrophy, cardiomyocytes activate mitochondrial translation/metabolism genes, whose expression is correlated with cell size and linked to ERK1/2 and NRF1/2 transcriptional networks. Persistent overload leads to a bifurcation into adaptive and failing cardiomyocytes, and p53 signaling is specifically activated in late hypertrophy. Cardiomyocyte-specific p53 deletion shows that cardiomyocyte remodeling is initiated by p53-independent mitochondrial activation and morphological hypertrophy, followed by p53-dependent mitochondrial inhibition, morphological elongation, and heart failure gene program activation. Human single-cardiomyocyte analysis validates the conservation of the pathogenic transcriptional signatures. Collectively, cardiomyocyte identity is encoded in transcriptional programs that orchestrate morphological and functional phenotypes.

Single-Stranded DNA-Binding Protein 1 Abrogates Cardiac Fibroblast Proliferation and Collagen Expression Induced by Angiotensin II

Angiotensin II (Ang II), an effective component of renin-angiotensin system, plays a pivotal role in cardiac fibrosis, which may further contribute to heart failure. Single-stranded DNA-binding protein 1 (SSBP1), a DNA damage response protein, regulates both mitochondrial function and extracellular matrix remodeling. In this study, we aim to investigate the role of SSBP1 in cardiac fibrosis that is induced by Ang II. We infused C57BL/6J mice with vehicle or Ang II and valsartan using implanted osmotic mini-pumps. Moreover, heart function was examined by echocardiography and cardiac fibrosis was analyzed via picrosirus red staining. The expression of COL1A1, COL3A1, SSBP1, p53, Nox1, and Nox4 was analyzed via qRT-PCR and/or immunoblots. The SSBP1 expression was manipulated via SSBP1 shRNA and pcDNA3.1/SSBP1 plasmids, while the p53 expression was enhanced via AdCMV-p53 infection. The exposure to Ang II increased the mouse heart weight, systolic blood pressure, interventricular septal thickness diastolic (IVSTD) and left ventricular end posterior wall dimension diastolic (LVPWD), which were counteracted by valsartan. While cardiac fibrosis was induced with Ang II treatment, it was relieved using valsartan. Furthermore, Ang II treatment caused mitochondrial dysfunction, oxidative stress, and down-regulated SSBP1 expression. The knockdown of SSBP1 increased cardiac fibroblast proliferation, collagen expression, and decreased p53 expression, which was impeded via SSBP1 overexpression. Moreover, the forced expression of p53 abated the fibroblast proliferation and collagen expression that was induced by Ang II. To summarize, SSBP1 was down-regulated by Ang II and implicated in cardiac fibroblast proliferation and collagen expression partly via the p53 protein.

Effects of low dose of aliskiren on isoproterenol-induced acute myocardial infarction in rats

This study examined the effects of aliskiren (Ali) (direct renin inhibitor) on serum cardiac enzymes (LDH and CK-MB), electrocardiography (ECG) changes, myocardial oxidative stress markers (MDA, CAT, and GSH) and the expression of Bcl2, HO-1, and Nrf2 genes in isoproterenol (ISO)-induced myocardial infarction (MI). A total of 40 male albino rats were allocated into four groups, (1) normal control (NC) group, (2) Ali group (rats received Ali at 10 mg/kg/day p.o. for 5 days), (3) ISO group (rats received ISO 150 mg/kg i.p. for two consecutive days at 24 h intervals), and (4) Ali + ISO group (rats received ISO + Ali at 10 mg/kg/day p.o. for 5 days from the 2^nd dose of ISO). ISO group showed significant rise in serum cardiac enzymes (CK-MB and LDH), myocardial damage scores, myocardial MDA, HO-1, myocardial Nrf2 expression with significant reduction in myocardial antioxidants (CAT and GSH), and Bcl2 expression compared to the normal group (p < 0.05). ECG showed ST segment elevation, prolonged QT interval and QRS complex, and increased heart rate in ISO group. Co-administration of Ali and ISO caused significant increase in cardiac enzymes and morphology with increase in MDA, serum K, and creatinine with significant decrease in Bcl2, HO-1, and Nrf2 without significant changes in ECG parameters compared to ISO group. We concluded that low dose of Ali seems to exacerbate the myocardial injury in ISO-MI, which might be due to the enhanced oxidative stress and apoptosis.

Lysophosphatidic Acid Is Associated With Cardiac Dysfunction and Hypertrophy by Suppressing Autophagy via the LPA3/AKT/mTOR Pathway

Background: Lysophosphatidic acid (LPA), as a phospholipid signal molecule, participates in the regulation of various biological functions. Our previous study demonstrated that LPA induces cardiomyocyte hypertrophy in vitro; however, the functional role of LPA in the post-infarct heart remains unknown. Growing evidence has demonstrated that autophagy is involved in regulation of cardiac hypertrophy. The aim of the current work was to investigate the effects of LPA on cardiac function and hypertrophy during myocardial infarction (MI) and determine the regulatory role of autophagy in LPA-induced cardiomyocyte hypertrophy.

Methods:In vivo experiments were conducted in Sprague-Dawley rats subjected to MI surgery or a sham operation, and rats with MI were assigned to receive an intraperitoneal injection of LPA (1 mg/kg) or vehicle for 5 weeks. The in vitro experiments were conducted in H9C2 cardiomyoblasts.

Results: LPA treatment aggravated cardiac dysfunction, increased cardiac hypertrophy, and reduced autophagy after MI in vivo. LPA suppressed autophagy activation, as indicated by a decreased LC3II-to-LC3I ratio, increased p62 expression, and reduced autophagosome formation in vitro. Rapamycin, an autophagy enhancer, attenuated LPA-induced autophagy inhibition and H9C2 cardiomyoblast hypertrophy, while autophagy inhibition with Beclin1 siRNA did not further enhance the hypertrophic response in LPA-treated cardiomyocytes. Moreover, we demonstrated that LPA suppressed autophagy through the AKT/mTOR signaling pathway because mTOR and PI3K inhibitors significantly prevented LPA-induced mTOR phosphorylation and autophagy inhibition. In addition, we found that knockdown of LPA3 alleviated LPA-mediated autophagy suppression in H9C2 cardiomyoblasts, suggesting that LPA suppresses autophagy through activation of the LPA3 and AKT/mTOR pathways.

Conclusion: These findings suggest that LPA plays an important role in mediating cardiac dysfunction and hypertrophy after a MI, and that LPA suppresses autophagy through activation of the LPA3 and AKT/mTOR pathways to induce cardiomyocyte hypertrophy.

Working Toward an Improved Understanding of Chronic Cardiorenal Syndrome Type 4

Chronic diseases of the heart and of the kidneys commonly coexist in individuals. Certainly combined and persistent heart and kidney failure can arise from a common pathologic insult, for example, as a consequence of poorly controlled hypertension or of severe diffuse arterial disease. However, strong evidence is emerging to suggest that cross talk exists between the heart and the kidney. Independent processes are set in motion when kidney function is chronically diminished, and these processes can have distinct adverse effects on the heart. The complex chronic heart condition that results from chronic kidney disease (CKD) has been termed cardiorenal syndrome type 4. This review will include an updated description of the cardiac morphology in patients who have CKD, an overview of the most likely CKD-sourced culprits for these cardiac changes, and the potential therapeutic strategies to limit cardiac complications in patients who have CKD.

Mitochondrial dysfunction in pathophysiology of heart failure

Mitochondrial dysfunction has been implicated in the development of heart failure. Oxidative metabolism in mitochondria is the main energy source of the heart, and the inability to generate and transfer energy has long been considered the primary mechanism linking mitochondrial dysfunction and contractile failure. However, the role of mitochondria in heart failure is now increasingly recognized to be beyond that of a failed power plant. In this Review, we summarize recent evidence demonstrating vicious cycles of pathophysiological mechanisms during the pathological remodeling of the heart that drive mitochondrial contributions from being compensatory to being a suicide mission. These mechanisms include bottlenecks of metabolic flux, redox imbalance, protein modification, ROS-induced ROS generation, impaired mitochondrial Ca2+ homeostasis, and inflammation. The interpretation of these findings will lead us to novel avenues for disease mechanisms and therapy.

Enhancing Mitochondrial Health to Treat Hypertension

PURPOSE OF REVIEW

This review summarizes literature pertaining to the dawning field of therapeutic targeting of mitochondria in hypertension and discusses the potential of these interventions to ameliorate hypertension-induced organ damage.

RECENT FINDINGS

In recent years, mitochondrial dysfunction has been reported as an important contributor to the pathogenesis of hypertension-related renal, cardiac, and vascular disease. This in turn prompted development of novel mitochondria-targeted compounds, some of which have shown promising efficacy in experimental studies and safety in clinical trials. In addition, drugs that do not directly target mitochondria have shown remarkable benefits in preserving these organelles in experimental hypertension. Enhancing mitochondrial health is emerging as a novel feasible approach to treat hypertension. Future perspectives include mechanistic experimental studies to establish a cause-effect relationship between mitochondrial dysfunction and hypertension and further clinical trials to confirm the reno-, cardio-, and vasculo-protective properties of these compounds in hypertension.

Cardiac fibrosis: Cell biological mechanisms, molecular pathways and therapeutic opportunities

Cardiac fibrosis is a common pathophysiologic companion of most myocardial diseases, and is associated with systolic and diastolic dysfunction, arrhythmogenesis, and adverse outcome. Because the adult mammalian heart has negligible regenerative capacity, death of a large number of cardiomyocytes results in reparative fibrosis, a process that is critical for preservation of the structural integrity of the infarcted ventricle. On the other hand, pathophysiologic stimuli, such as pressure overload, volume overload, metabolic dysfunction, and aging may cause interstitial and perivascular fibrosis in the absence of infarction. Activated myofibroblasts are the main effector cells in cardiac fibrosis; their expansion following myocardial injury is primarily driven through activation of resident interstitial cell populations. Several other cell types, including cardiomyocytes, endothelial cells, pericytes, macrophages, lymphocytes and mast cells may contribute to the fibrotic process, by producing proteases that participate in matrix metabolism, by secreting fibrogenic mediators and matricellular proteins, or by exerting contact-dependent actions on fibroblast phenotype. The mechanisms of induction of fibrogenic signals are dependent on the type of primary myocardial injury. Activation of neurohumoral pathways stimulates fibroblasts both directly, and through effects on immune cell populations. Cytokines and growth factors, such as Tumor Necrosis Factor-α, Interleukin (IL)-1, IL-10, chemokines, members of the Transforming Growth Factor-β family, IL-11, and Platelet-Derived Growth Factors are secreted in the cardiac interstitium and play distinct roles in activating specific aspects of the fibrotic response. Secreted fibrogenic mediators and matricellular proteins bind to cell surface receptors in fibroblasts, such as cytokine receptors, integrins, syndecans and CD44, and transduce intracellular signaling cascades that regulate genes involved in synthesis, processing and metabolism of the extracellular matrix. Endogenous pathways involved in negative regulation of fibrosis are critical for cardiac repair and may protect the myocardium from excessive fibrogenic responses. Due to the reparative nature of many forms of cardiac fibrosis, targeting fibrotic remodeling following myocardial injury poses major challenges. Development of effective therapies will require careful dissection of the cell biological mechanisms, study of the functional consequences of fibrotic changes on the myocardium, and identification of heart failure patient subsets with overactive fibrotic responses.

Mitochondrial ROS Drive Sudden Cardiac Death and Chronic Proteome Remodeling in Heart Failure

RATIONALE

Despite increasing prevalence and incidence of heart failure (HF), therapeutic options remain limited. In early stages of HF, sudden cardiac death (SCD) from ventricular arrhythmias claims many lives. Reactive oxygen species (ROS) have been implicated in both arrhythmias and contractile dysfunction. However, little is known about how ROS in specific subcellular compartments contribute to HF or SCD pathophysiology. The role of ROS in chronic proteome remodeling has not been explored.

OBJECTIVE

We will test the hypothesis that elevated mitochondrial ROS (mROS) is a principal source of oxidative stress in HF and in vivo reduction of mROS mitigates SCD.

METHODS AND RESULTS

Using a unique guinea pig model of nonischemic HF that recapitulates important features of human HF, including prolonged QT interval and high incidence of spontaneous arrhythmic SCD, compartment-specific ROS sensors revealed increased mROS in resting and contracting left ventricular myocytes in failing hearts. Importantly, the mitochondrially targeted antioxidant (MitoTEMPO) normalized global cellular ROS. Further, in vivo MitoTEMPO treatment of HF animals prevented and reversed HF, eliminated SCD by decreasing dispersion of repolarization and ventricular arrhythmias, suppressed chronic HF-induced remodeling of the expression proteome, and prevented specific phosphoproteome alterations. Pathway analysis of mROS-sensitive networks indicated that increased mROS in HF disrupts the normal coupling between cytosolic signals and nuclear gene programs driving mitochondrial function, antioxidant enzymes, Ca²⁺ handling, and action potential repolarization, suggesting new targets for therapeutic intervention.

CONCLUSIONS

mROS drive both acute emergent events, such as electrical instability responsible for SCD, and those that mediate chronic HF remodeling, characterized by suppression or altered phosphorylation of metabolic, antioxidant, and ion transport protein networks. In vivo reduction of mROS prevents and reverses electrical instability, SCD, and HF. Our findings support the feasibility of targeting the mitochondria as a potential new therapy for HF and SCD while identifying new mROS-sensitive protein modifications.

Pathological presentation of cardiac mitochondria in a rat model for chronic kidney disease

BACKGROUND

Mitochondria hold crucial importance in organs with high energy demand especially the heart. We investigated whether chronic kidney disease (CKD), which eventually culminates in cardiorenal syndrome, could affect cardiac mitochondria and assessed the potential involvement of angiotensin II (AngII) in the process.

METHODS

Male Lewis rats underwent 5/6 nephrectomy allowing CKD development for eight months or for eleven weeks. Short-term CKD rats were administered with AngII receptor blocker (ARB). Cardiac function was assessed by echocardiography and cardiac sections were evaluated for interstitial fibrosis and cardiomyocytes' hypertrophy. Electron microscopy was used to explore the spatial organization of the cardiomyocytes. Expression levels of mitochondrial content and activity markers were tested in order to delineate the underlying mechanisms for mitochondrial pathology in the CKD setting with or without ARB administration.

RESULTS

CKD per-se resulted in induced cardiac interstitial fibrosis and cardiomyocytes' hypertrophy combined with a marked disruption of the mitochondrial structure. Moreover, CKD led to enhanced cytochrome C leakage to the cytosol and to enhanced PARP-1 cleavage which are associated with cellular apoptosis. ARB treatment did not improve kidney function but markedly reduced left ventricular mass, cardiomyocytes' hypertrophy and interstitial fibrosis. Interestingly, ARB administration improved the spatial organization of cardiac mitochondria and reduced their increased volume compared to untreated CKD animals. Nevertheless, ARB did not improve mitochondrial content, mitochondrial biogenesis or the respiratory enzyme activity. ARB mildly upregulated protein levels of mitochondrial fusion-related proteins.

CONCLUSIONS

CKD results in cardiac pathological changes combined with mitochondrial damage and elevated apoptotic markers. We anticipate that the increased mitochondrial volume mainly represents mitochondrial swelling that occurs during the pathological process of cardiac hypertrophy. Chronic administration of ARB may improve the pathological appearance of the heart. Further recognition of the molecular pathways leading to mitochondrial insult and appropriate intervention is of crucial importance.

Mitochondria and cardiovascular diseases-from pathophysiology to treatment

Mitochondria are the source of cellular energy production and are present in different types of cells. However, their function is especially important for the heart due to the high demands in energy which is achieved through oxidative phosphorylation. Mitochondria form large networks which regulate metabolism and the optimal function is achieved through the balance between mitochondrial fusion and mitochondrial fission. Moreover, mitochondrial function is upon quality control via the process of mitophagy which removes the damaged organelles. Mitochondrial dysfunction is associated with the development of numerous cardiac diseases such as atherosclerosis, ischemia-reperfusion (I/R) injury, hypertension, diabetes, cardiac hypertrophy and heart failure (HF), due to the uncontrolled production of reactive oxygen species (ROS). Therefore, early control of mitochondrial dysfunction is a crucial step in the therapy of cardiac diseases. A number of anti-oxidant molecules and medications have been used but the results are inconsistent among the studies. Eventually, the aim of future research is to design molecules which selectively target mitochondrial dysfunction and restore the capacity of cellular anti-oxidant enzymes.