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Role of monoamine oxidase A in cardiac hypertrophy and transition to heart failure
Full text linkOxidative stress has been implicated in numerous pathologies and a number of intracellular sources of ROS have already been identified. Mitochondria and especially mitochondrial respiratory chain, are considered as major intracellular sources of ROS. However, other potential sites responsible for ROS generation are present in the mitochondria and could be equally important, but have not been investigated up to date. In the present thesis, we investigated the role of monoamine oxidases, flavoenzymes located at the level of outer mitochondrial membrane, in the oxidative stress in cardiac myocytes, in relation to cardiac remodeling and transition from hypertrophy to heart failure.
Initially, the expression level of each MAO isoform was determined at the cardiac level. These studies showed that MAO-A is the major isoform present at the cardiac level and that low concentrations of clorgyline (0.05-1 ?M) are able to completely prevent H2O2 production in the presence of MAO substrates such as tyramine and serotonin. At this concentration clorgyline did not affect mitochondrial function or ROS production by mitochondrial respiratory chain.
To investigate the role of MAO in the oxidative stress, HL-1 cardiomyocytes were treated with H2O2 or arachidonic acid to induce an increase in ROS production measured by fluorescent probe Mitotracker Red. Treatment with these agents induced a 1.6- and 1.4-fold increase in oxidative stress, respectively. When cells were pretreated with 1 ?M clorgyline, specific inhibitor of MAO-A isoform, this increase in ROS production was reduced or completely prevented. On the contrary, when cells were pretreated with specific MAO-B inhibitor selegiline, no protective effect was observed. This suggests that MAO-A is the major isoform expressed at the cardiomyocyte level and involved in the oxidative stress. To further confirm the specificity of MAO-A inhibition, we genetically silenced the expression of MAO-A by 90% by means of siRNA. Results identical to those obtained using the pharmacological inhibitor clorgyline were observed in siRNA treated cells. These results unequivocally demonstrate that MAO inhibitors are specific and that MAO-A plays an important role in the onset and amplification of oxidative stress.
Given the relevant role of MAO-A in the oxidative stress, we investigated its involvement in hypertrophy and heart failure, a condition strongly favored by increased oxidative burden. In vitro studies revealed that MAO-A expression was increased by 2-fold when neonatal rat cardiomyocytes were stimulated with prohypertrophic agent norepinephrine (NE) and incubation of the cells with clorgyline reduced the extent of NE-induced hypertrophy. Furthermore, stimulation of MAO-A activity by its substrate tyramine induced the expression of NFAT3 and NFAT4, well known mediators of maladaptive hypertrophy, and this increase was significantly reduced in cells pretreated with clorgyline. These changes were paralleled by an increase in mitochondrial ROS production, which was completely prevented with clorgyline.
To further confirm whether these in vitro findings could be of any significance in a more complex, in vivo setting, C57Bl6 mice were subjected to transverse aortic constriction (TAC) to induce pressure-overload. This procedure initially results in concentric hypertrophy as a compensatory mechanism for the
increase in pressure, leading to eccentric hypertrophy, chamber dilation and heart failure in a long term. MAO-A expression was 3.6-fold higher in mice after 6 weeks of TAC, a time-point associated with chamber dilation and decreased left ventricular (LV) function. Inhibition of MAO-A (CLO) in these mice resulted in reduced hypertrophy and LV dimensions compared to control mice, as calculated LV mass was significantly reduced in CLO group. LV end-diastolic and endsystolic dimensions were 3.5- and 1.3-fold increased in saline treated mice, reflecting chamber remodeling and dilation. This increase in chamber dimensions was absent in CLO group. Cardiac function was also markedly improved in CLO group. Both fractional shortening and ejection fraction were comparable to the values measured in sham operated mice, while they were reduced by 50% in saline treated mice. Differences in morphological and functional data were accompanied also by changes at the molecular level. Fetal gene reprogramming, measured as increase in ANP expression was 4-fold reduced in CLO mice. Reduction in hypertrophy and improvement in cardiac function were also associated with decreased levels of oxidative stress in CLO mice, as determined by DHE staining, and reduced activation of pro-hypertrophic and pro-apoptotic pathways, determined by measuring the levels of activated Akt and cleaved caspase 3. This suggests that clorgyline exerts its protective effects by reducing the levels of oxidative stress and promoting cell viability.
Taken together, these data demonstrate for the first time that MAO-A plays a major role in the onset and amplification of oxidative stress, contributing to the transition from compensated hypertrophy to dilated cardiomyopathy in vivo
The Dual Function of Reactive Oxygen/Nitrogen Species in Bioenergetics and Cell Death: The Role of ATP Synthase
Full text link: Reactive oxygen species (ROS) and reactive nitrogen species (RNS) targeting mitochondria are major causative factors in disease pathogenesis. The mitochondrial permeability transition pore (PTP) is a mega-channel modulated by calcium and ROS/RNS modifications and it has been described to play a crucial role in many pathophysiological events since prolonged channel opening causes cell death. The recent identification that dimers of ATP synthase form the PTP and the fact that posttranslational modifications caused by ROS/RNS also affect cellular bioenergetics through the modulation of ATP synthase catalysis reveal a dual function of these modifications in the cells. Here, we describe mitochondria as a major site of production and as a target of ROS/RNS and discuss the pathophysiological conditions in which oxidative and nitrosative modifications modulate the catalytic and pore-forming activities of ATP synthase
Cyclophilin D and p66Shc contribute to KCl-induced Ca2+ increase in pulmonary artery smooth muscle cells: a potentially relevant phenomenon awaiting a definite mechanism
No full textMitochondrial ROS Formation in the Pathogenesis of Diabetic Cardiomyopathy
Full text linkDiabetic cardiomyopathy is a result of diabetes-induced changes in the structure and function of the heart. Hyperglycemia affects multiple pathways in the diabetic heart, but excessive reactive oxygen species (ROS) generation and oxidative stress represent common denominators associated with adverse tissue remodeling. Indeed, key processes underlying cardiac remodeling in diabetes are redox sensitive, including inflammation, organelle dysfunction, alteration in ion homeostasis, cardiomyocyte hypertrophy, apoptosis, fibrosis, and contractile dysfunction. Extensive experimental evidence supports the involvement of mitochondrial ROS formation in the alterations characterizing the diabetic heart. In this review we will outline the central role of mitochondrial ROS and alterations in the redox status contributing to the development of diabetic cardiomyopathy. We will discuss the role of different sources of ROS involved in this process, with a specific emphasis on mitochondrial ROS producing enzymes within cardiomyocytes. Finally, the therapeutic potential of pharmacological inhibitors of ROS sources within the mitochondria will be discussed
Reactive oxygen species and redox compartmentalization.
Full text linkReactive oxygen species (ROS) formation and signaling are of major importance and regulate a number of processes in physiological conditions. A disruption in redox status regulation, however, has been associated with numerous pathological conditions. In recent years it has become increasingly clear that oxidative and reductive modifications are confined in a spatio-temporal manner. This makes ROS signaling similar to that of Ca(2+) or other second messengers. Some subcellular compartments are more oxidizing (such as lysosomes or peroxisomes) whereas others are more reducing (mitochondria, nuclei). Moreover, although more reducing, mitochondria are especially susceptible to oxidation, most likely due to the high number of exposed thiols present in that compartment. Recent advances in the development of redox probes allow specific measurement of defined ROS in different cellular compartments in intact living cells or organisms. The availability of these tools now allows simultaneous spatio-temporal measurements and correlation between ROS generation and organelle and/or cellular function. The study of ROS compartmentalization and microdomains will help elucidate their role in physiology and disease. Here we will examine redox probes currently available and how ROS generation may vary between subcellular compartments. Furthermore, we will discuss ROS compartmentalization in physiological and pathological conditions focusing our attention on mitochondria, since their vulnerability to oxidative stress is likely at the basis of several diseases
IP3 receptor trafficking at the ER-mitochondria contacts impacts on mitochondrial Ca2+ homeostasis and metabolism
No full text: The close contacts between endoplasmic reticulum and mitochondria (ERMCs) play a key role in metabolic regulation, Ca2+ homeostasis, reactive oxygen species production, and many other cell functions. Nevertheless, it is not fully clear how these contacts dynamically rearrange to support cell functions. In a recent Nature Communications article [1], Katona et al. elegantly showed that motile IP3Rs can be captured at ERMCs to promptly mediate Ca2+ transfer and stimulate mitochondrial oxidative metabolism
Mitochondrial reactive oxygen species in physiology and disease
No full text: Mitochondrial reactive oxygen species (mROS) are routinely produced at several sites within the organelle. The balance in their formation and elimination is maintained by a complex and robust antioxidant system. mROS may act as second messengers and regulate a number of physiological processes, such as insulin signaling, cell differentiation and proliferation, wound healing, etc. Nevertheless, when a sudden or sustained increase in ROS formation is not efficiently neutralized by the endogenous antioxidant defense system, the detrimental impact of high mROS levels on cell function and viability eventually results in disease development. In this review, we will focus on the dual role of mROS in pathophysiology, emphasizing the physiological role exerted by a regulated mROS production/elimination, and discussing the detrimental effects evoked by an imbalance in mitochondrial redox state. Furthermore, we will touch upon the interplay between mROS and Ca2+ homeostasis
Genes, Geography and Geometry The "Critical Mass" in Hypertrophic Cardiomyopathy
No full textHCM is caused by mutations in one of a number of genes. Approximately 450 different mutations have been discovered in genes for functional/structural proteins in the sarcomere (13 related genes) and myofilaments. Most of the alterations are missense, with a single amino acid residue substituted for another. The majority of HCM molecular defects lie in genes encoding functional and regulatory sarcomeric proteins such as beta-myosin heavy chain , actin, cardiac troponin T and I, and tropomyosin, as well as structural proteins, ie, myosin binding protein C (MYBPC) and titin.2 Identifying the specific gene mutation underlying the disease in individuals has more than an etiological relevance, as specific gene mutations may contribute to the different phenotypic and functional outcomes in patients suffering from HCM
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