Sex differences in mitochondrial Ca2+ during ischemia/reperfusion injury: A role for S-Nitrosylation.

Sex differences in SR Ca2 + release in murine ventricular myocytes are regulated by the cAMP/PKA pathway

Although the recent identification of the mitochondrial Ca2+ uniporter (MCU) has resolved a long-standing mystery as to how Ca2+ freely enters the mitochondria, it has also evoked additional questions such as its mode of regulation and the identity of other associated factors. In an article recently published in Nature , Joiner et al1 provide data demonstrating that in the heart, matrix-localized Ca2+/calmodulin-dependent protein kinase II (CaMKII) can upregulate MCU activity in a manner requiring phosphorylation of the channel N terminus. They showed that inhibition of CaMKII-dependent MCU activity protected the heart from ischemic injury by presumably reducing Ca2+ influx and desensitizing the mitochondrial permeability transition pore (MPTP) to opening. Although these results demonstrate convincingly that CaMKII plays an important role in MCU regulation and subsequent response to cardiac injury, several questions remain unanswered. The ability of mitochondria to take up and sequester Ca2+ plays an important role in the buffering of cytosolic Ca2+, regulation of ATP production via the citric acid cycle, and regulation of apoptotic and necrotic cell death pathways.2 Although mitochondrial Ca2+ uptake was first described in the 1960s3 and the electrophysiological properties of the MCU were reported in 2004,4 it was not until 2011 that 2 articles were published revealing the genetic identity of the MCU.5,6 This pioneering work has initiated a search for additional members of the MCU complex (such as MICU17 and the recently discovered MCUR1),8 as well as an attempt to understand how MCU-mediated Ca2+ influx participates in the regulation of whole-cell Ca2+ signaling and whether well-described pathways that regulate other Ca2+ handling processes can similarly modulate MCU-dependent Ca2+ uptake. In the featured article, Joiner et al1 show that CaMKII serves …

Calcium signaling in vascular endothelial cells (ECs) and smooth muscle cells (VSMCs) is essential for the regulation of vascular tone. However, the changes to intracellular Ca2+ concentrations are often influenced by sex differences. Furthermore, a large body of evidence shows that sex hormone imbalance leads to dysregulation of Ca2+ signaling and this is a key factor in the pathogenesis of cardiovascular diseases. In this review, the effects of estrogens and androgens on vascular calcium-handling proteins are discussed, with emphasis on the associated genomic or nongenomic molecular mechanisms. The experimental models from which data were collected were also considered. The review highlights 1) in female ECs, transient receptor potential vanilloid 4 (TRPV4) and mitochondrial Ca2+ uniporter (MCU) enhance Ca2+-dependent nitric oxide (NO) generation. In males, only transient receptor potential canonical 3 (TRPC3) plays a fundamental role in this effect. 2) Female VSMCs have lower cytosolic Ca2+ levels than males due to differences in the activity and expression of stromal interaction molecule 1 (STIM1), calcium release-activated calcium modulator 1 (Orai1), calcium voltage-gated channel subunit-α1C (CaV1.2), Na+-K+-2Cl- symporter (NKCC1), and the Na+/K+-ATPase. 3) When compared with androgens, the influence of estrogens on Ca2+ homeostasis, vascular tone, and incidence of vascular disease is better documented. 4) Many studies use supraphysiological concentrations of sex hormones, which may limit the physiological relevance of outcomes. 5) Sex-dependent differences in Ca2+ signaling mean both sexes ought to be included in experimental design.

Metabolic adaptation to the chronic loss of Ca2+ signaling induced by KO of IP3 receptors or the mitochondrial Ca2+ uniporter

Neuronal death in response to excitotoxic levels of glutamate is dependent upon mitochondrial Ca2+ accumulation and is associated with a drop in ATP levels and a loss in ionic homeostasis. Yet the mapping of temporal events in mitochondria subsequent to Ca2+ sequestration is incomplete. By isolating mitochondria from primary cultures, we discovered that glutamate treatment of cortical neurons for 10 min caused 44% inhibition of ADP-stimulated respiration, whereas the maximal rate of electron transport (uncoupler-stimulated respiration) was inhibited by approximately 10%. The Ca2+ load in mitochondria from glutamate-treated neurons was estimated to be 167 +/- 19 nmol/mg protein. The glutamate-induced Ca2+ load was less than the maximal Ca2+ uptake capacity of the mitochondria determined in vitro (363 +/- 35 nmol/mg protein). Comparatively, mitochondria isolated from cerebellar granule cells demonstrated a higher Ca2+ uptake capacity (686 +/- 71 nmol/mg protein) than the cortical mitochondria, and the glutamate-induced load of Ca2+ was a smaller percentage of the maximal Ca2+ uptake capacity. Thus, this study indicated that Ca(2+)-induced impairment of mitochondrial ATP production is an early event in the excitotoxic cascade that may contribute to decreased cellular ATP and loss of ionic homeostasis that precede commitment to neuronal death.

Adrenergic Stimulation Accelerates Mitochondrial Ca2+ uptake by PYK2-Dependent Phosphorylation of Mitochondrial Ca2+ Uniporter in Cardiac H9C2 Cells

Increased mitochondrial free Ca2+ during ischemia is suppressed, but not eliminated by, germline deletion of the mitochondrial Ca2+ uniporter

Males and females show distinct differences in action potential waveform, ion channel expression patterns, and ECG characteristics. However, it is not known how sex-based differences in Ca2+ cycling might contribute to these differences in electrophysiological activity. The goal of this study was to investigate the differences in cellular Ca2+ transients in males and females and to examine how these might contribute to electrophysiological function. Ca2+ transients were measured in individual myocytes within microscopic regions of the fluo-4 AM-loaded left ventricular epicardium of intact rat heart of both sexes (3 to 5 mo old). Pacing protocols were used to measure transient characteristics at a basic cycle length of 500 ms and during 10-s trains of rapid pacing delivered to the left ventricular apex. Ca2+ transients were smaller in magnitude and longer in duration in females than in males. More importantly, the variability in Ca2+ transient characteristics between myocytes in a microscopic recording site (heterogeneity index) was greater for females than males for characteristics related to transient duration. The rate sensitivity of Ca2+ alternans development in individual myocytes was greater in females than in males, but there was also a greater heterogeneity in cellular responses to the rate dependence of alternans development in females. The longer Ca2+ transients in females were also associated with slower restitution, which was likely to be responsible for the development of Ca2+ and repolarization alternans at slower heart rates. These results demonstrate that there are distinct differences in cellular Ca2+ cycling in male and female rat hearts. Not only is there slower reuptake of Ca2+ in female rats, but there is greater local variability in Ca2+ cycling at the microscopic level. These sex-based differences in Ca2+ cycling could contribute to differences in ECG morphology and in arrhythmia sensitivity in males and females.

Nitric oxide (NO) is a gaseous signal mediator showing numerous important biological effects. NO has been shown in many instances to exhibit its action via the protein S-nitrosylation mechanism, in which binding of NO to Cys residues regulate protein function independently of activation of soluble guanylate cyclase. The direct link between protein S-nitrosylation and functional modulation, however, has been demonstrated only in limited examples. Furthermore, although most proteins have more than one Cys residue, the mechanism by which a certain Cys becomes a specific target residue of S-nitrosylation is poorly understood. We have previously reported that NO regulates currents through the cardiac slowly activating delayed rectifier potassium channel (I(Ks)) irrespective of soluble guanylate cyclase activation. Here we demonstrate using a biotin-switch assay that NO induced S-nitrosylation of the alpha-subunit of the I(Ks) channel, KCNQ1, at Cys(445) in the C terminus. A redox motif flanking Cys(445) and the interaction of KCNQ1 with calmodulin are required for preferential S-nitrosylation of Cys(445). A patch clamp experiment shows that S-nitrosylation of Cys(445) modulates the KCNQ1/KCNE1 channel function. Our data provide a molecular basis of NO-mediated regulation of the I(Ks) channel. This novel regulatory mechanism of the I(Ks) channel may play a role in previously demonstrated NO-mediated phenomenon in cardiac electrophysiology, including shortening in action potential duration in response to intracellular Ca(2+) or sex hormones.

Despite the popular concept that heart disease preferentially affects the male population, in every year for the past 16 years, cardiovascular disease has killed more women than men.1 Unfortunately, a disparity still exists between men and women in the diagnosis and aggressive treatment of heart disease. The perception that women are relatively protected is reflected by the fact that women are much more fearful of dying from some form of cancer than from cardiovascular disease.1 Understanding any risk factors that predispose or protect the female population from cardiovascular and coronary disease is therefore a compelling goal for the research community. See p 1419 Left ventricular hypertrophy is a compensatory response of the heart to a variety of stresses, and it is a strong predictor of morbidity and mortality in individuals whether or not they have been diagnosed with cardiovascular disease. Sex differences in the development of this disease over time have been suggested by clinical studies dealing with patients who suffer from aortic stenosis or hypertension.2,3 For example, older female patients with aortic stenosis tend to have increased hypertrophy accompanied by greater concentric remodeling and preserved left ventricular function when compared with male patients. Premenopausal women, in fact, exhibit a thinner posterior wall, smaller left ventricular mass, and better load-dependent and load-independent cardiac function than age-matched men under conditions of mild essential hypertension.4 Population studies have shown an age-dependent increase in left ventricular mass in healthy normotensive women that is not seen in men, as determined by echocardiography.5 These and many other studies in both humans and animals suggest that estrogens can affect the remodeling of the heart. Estrogens are potent vasodilators; they act in this capacity by increasing nitric oxide production. However, recent findings indicate that estrogens have direct actions on the myocardium as …

S-nitrosylation is a post-translational modification on cysteine(s) that can regulate protein function, and pannexin 1 (Panx1) channels are present in the vasculature, a tissue rich in nitric oxide (NO) species. Therefore, we investigated whether Panx1 can be S-nitrosylated and whether this modification can affect channel activity. Using the biotin switch assay, we found that application of the NO donor S-nitrosoglutathione (GSNO) or diethylammonium (Z)-1-1(N,N-diethylamino)diazen-1-ium-1,2-diolate (DEA NONOate) to human embryonic kidney (HEK) 293T cells expressing wild type (WT) Panx1 and mouse aortic endothelial cells induced Panx1 S-nitrosylation. Functionally, GSNO and DEA NONOate attenuated Panx1 currents; consistent with a role for S-nitrosylation, current inhibition was reversed by the reducing agent dithiothreitol and unaffected by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, a blocker of guanylate cyclase activity. In addition, ATP release was significantly inhibited by treatment with both NO donors. To identify which cysteine residue(s) was S-nitrosylated, we made single cysteine-to-alanine substitutions in Panx1 (Panx1(C40A), Panx1(C346A), and Panx1(C426A)). Mutation of these single cysteines did not prevent Panx1 S-nitrosylation; however, mutation of either Cys-40 or Cys-346 prevented Panx1 current inhibition and ATP release by GSNO. This observation suggested that multiple cysteines may be S-nitrosylated to regulate Panx1 channel function. Indeed, we found that mutation of both Cys-40 and Cys-346 (Panx1(C40A/C346A)) prevented Panx1 S-nitrosylation by GSNO as well as the GSNO-mediated inhibition of Panx1 current and ATP release. Taken together, these results indicate that S-nitrosylation of Panx1 at Cys-40 and Cys-346 inhibits Panx1 channel currents and ATP release.

Nitric oxide (NO) signaling is inextricably linked to both its physical and chemical properties. Due to its preferentially hydrophobic solubility, NO molecules tend to partition from the aqueous milieu into biological membranes. We hypothesized that plasma membrane ordering provided by cholesterol further couples the physics of NO diffusion with cellular signaling. Fluorescence lifetime quenching studies with pyrene liposome preparations showed that the presence of cholesterol decreased apparent diffusion coefficients of NO approximately 20-40%, depending on the phospholipid composition. Electrochemical measurements indicated that the diffusion rate of NO across artificial bilayer membranes were inversely related to cholesterol content. Sterol transport-defective Niemann-Pick type C1 (NPC1) fibroblasts exhibited increased plasma membrane cholesterol content but decreased activation of both intracellular soluble guanylyl cyclase and vasodilator-stimulated phosphoprotein (VASP) phosphorylation at Ser(239) induced by exogenous NO exposure relative to their normal human fibroblast (NHF) counterparts. Augmentation of plasma membrane cholesterol in NHF diminished production of both cGMP and VASP phosphorylation elicited by NO to NPC1-comparable levels. Conversely, decreasing membrane cholesterol in NPC1 resulted in the augmentation in both cGMP and VASP phosphorylation to a level similar to those observed in NHF. Increasing plasma membrane cholesterol contents in NHF, platelets, erythrocytes and tumor cells also resulted in an increased level of extracellular diaminofluorescein nitrosation following NO exposure. These findings suggest that the impact of cholesterol on membrane fluidity and microdomain structure contributes to the spatial heterogeneity of NO diffusion and signaling.

Introduction: Proline-rich tyrosine kinase 2 (Pyk2) and focal adhesion kinase (FAK) are abundantly expressed in cancer cells. In addition, these kinases are the potent therapeutic targets for cancer treatment and currently several selective FAK/Pyk2 inhibitors are in clinical trials. Recent study revealed that Pyk2 is also highly expressed in heart tissue and significantly activated during human heart failure. We have recently reported that α 1 -adrenoceptor (α 1 -AR) stimulation accelerates mitochondrial Ca 2+ uptake through Pyk2-dependent phospholylation of mitochondrial Ca 2+ uniporter (MCU). However, the roles of Pyk2 in cardiac mitochondrial physiology and pathophysiology have not been well established. Hypothesis: Persistent adrenergic signaling activates cell death signaling via Pyk2-dependent MCU activation and mitochondrial Ca 2+ overload. Methods: Using H9C2 cardiac myoblasts, mitochondrial Ca 2+ and reactive oxygen species (ROS) were measured using mitochondrial matrix-targeted Ca 2+ -sensitive inverse pericam and MitoSOX, respectively. Mitochondrial permeability transition pore (mPTP) activity was observed by measuring the amount of cytochrome c in cytosol by Western blotting or by monitoring the release of GFP-tagged mitochondrial protein, Smac-GFP using confocal microscopy. Results: Pyk2 was not only expressed in cytosol, but also in cardiac mitochondria. α 1 -AR agonist phenylephrine activated mitochondrial Pyk2 and enhanced mitochondrial Ca 2+ uptake via Pyk2-dependent MCU phosphorylation. In addition, persistent α 1 -AR stimulation increases ROS, activity of mPTP. These effects were abolished by co-expression of dominant-negative MCU or kinase-dead Pyk2, suggesting that Pyk2-dependent MCU activation followed by mitochondrial Ca 2+ overload are critical for this mechanism. Moreover, pretreatment of a potent FAK/Pyk2 inhibitor PF-431396 also effectively inhibited α 1 -AR-mediated ROS generation and mPTP activation. Conclusion: FAK/Pyk2 inhibitor prevents mitochondrial Ca 2+ overload, oxidative stress and mitochondrial injury under persistent adrenergic stimulation. Thus, Pyk2 may become a novel potent therapeutic target for preventing cardiac cell injury and death during heart failure.

Nitric oxide (NO) plays an important role in cardioprotection, and recent work from our group and others has implicated protein S-nitrosylation (SNO) as a critical component of NO-mediated protection in different models, including ischemic pre- and post-conditioning and sex-dependent cardioprotection. However, studies have yet to examine whether protein SNO levels are similarly increased with pharmacologic preconditioning in male and female hearts, and whether an increase in protein SNO levels, which is protective in male hearts, is sufficient to increase baseline protection in female hearts. Therefore, we pharmacologically preconditioned male and female hearts with the adenosine A1 receptor agonist N6-cyclohexyl adenosine (CHA). CHA administration prior to ischemia significantly improved functional recovery in both male and female hearts compared to baseline in a Langendorff-perfused heart model of ischemia-reperfusion injury (% of preischemic function ± SE: male baseline: 37.5±3.4% vs. male CHA: 55.3±3.2%; female baseline: 61.4±5.7% vs. female CHA: 76.0±6.2%). In a separate set of hearts, we found that CHA increased p-Akt and p-eNOS levels. We also used SNO-resin-assisted capture with LC-MS/MS to identify SNO proteins in male and female hearts, and determined that CHA perfusion induced a modest increase in protein SNO levels in both male (11.4%) and female (12.3%) hearts compared to baseline. These findings support a potential role for protein SNO in a model of pharmacologic preconditioning, and provide evidence to suggest that a modest increase in protein SNO levels is sufficient to protect both male and female hearts from ischemic injury. In addition, a number of the SNO proteins identified with CHA treatment were also observed with other forms of cardioprotective stimuli in prior studies, further supporting a role for protein SNO in cardioprotection.

Cold modulated nuclear S-nitrosoproteome analysis indicates redox modulation of novel Brassicaceae specific, myrosinase and napin in Brassica juncea