Nitric oxide inhibits endothelin-1-induced neonatal cardiomyocyte hypertrophy via a RhoA-ROCK-dependent pathway

Although nitric oxide (NO) has received extensive attention as an anti-hypertrophic agent the mechanisms underlying its regulation of endothelin-1 (ET-1) have not been fully elucidated. Since RhoA has been identified as an important mediator of cardiac hypertrophy and is inhibited by NO in vascular tissue, we sought to determine whether the anti-ET-1 effects of NO in cardiomyocytes were mediated via inhibition of the RhoA-ROCK cascade in the context of cardiac hypertrophy. Neonatal rat ventricular myocytes were cultured in the presence of ET-1 (10 nM) with or without pre-treatment with the NO donor S-nitroso-n-acetylpenicillamine (SNAP; 100 μM), 8-Br-cGMP (cGMP; 100 μM), the RhoA inhibitor C3 exoenzyme (C3; 30 ng/ml), or the ROCK inhibitor Y-27632 (10 μM). ET-1-induced cardiomyocyte hypertrophy was prevented by pre-treatment with SNAP, cGMP, C3, or Y-27632. The hypertrophic response to ET-1 was associated with significantly increased gene and protein expression of both NOS2 and NOS1 although NOS3 was unaffected. ET-1 treatment for 15 min increased membrane-bound RhoA 2.6-fold (p < 0.05), which was prevented by both SNAP and cGMP (p < 0.05). These effects were associated with a complete abrogation of ET-1-induced phosphorylation of the downstream target of RhoA, cofilin-2, that was mimicked by direct inhibition of RhoA and ROCK. In addition, confocal microscopy and Western blotting revealed that 24 h ET-1 treatment reduced the G- to F-actin ratio 67% (p < 0.05) which was prevented by SNAP, cGMP, C3 and Y (p < 0.05). Taken together, these results suggest that the anti-hypertrophic effects of NO are due, in part, to cGMP-dependent inhibition of the RhoA-ROCK-cofilin signalling pathway. These findings may be important in understanding the mechanisms of anti-ET-1 and anti-hypertrophic effects of NO as well as in the development of novel RhoA-targeted therapeutic interventions for treating cardiac hypertrophy.     

Ischaemic Preconditioning Inhibits Opening of Mitochondrial Permeability Transition Pores in the Reperfused Rat Heart

Opening of the mitochondrial permeability transition pore (MPTP) is thought to be a critical event in mediating the damage to hearts that accompanies their reperfusion following prolonged ischaemia. Protection from reperfusion injury occurs if the prolonged ischaemic period is preceded by short ischaemic periods followed by recovery. Here we investigate whether such ischaemic preconditioning (IPC) is accompanied by inhibition of MPTP opening. MPTP opening in Langendorff-perfused rat hearts was determined by perfusion with 2-deoxy[³H]glucose ([³H]DOG) and measurement of mitochondrial [³H]DOG entrapment. We demonstrate that IPC inhibits initial MPTP opening in hearts reperfused after 30 min global ischaemia, and subsequently enhances pore closure as hearts recover. However, MPTP opening in mitochondria isolated from IPC hearts occurred more readily than control mitochondria, implying that MPTP inhibition by IPC in situ was secondary to other factors such as decreased calcium overload and oxidative stress. Hearts perfused with cyclosporin A or sanglifehrin A, powerful inhibitors of the MPTP, also recovered better from ischaemia than controls (improved haemodynamic function and less lactate dehydrogenase release). However, the mitochondrial DOG entrapment technique showed these agents to be less effective than IPC at preventing MPTP opening. Our data suggest that protection from reperfusion injury is better achieved by reducing factors that induce MPTP opening than by inhibiting the MPTP directly.     

Mitochondrial permeability transition pore opening during myocardial reperfusion--a target for cardioprotection

Reperfusion of the heart after a period of ischaemia leads to the opening of a nonspecific pore in the inner mitochondrial membrane, known as the mitochondrial permeability transition pore (MPTP). This transition causes mitochondria to become uncoupled and capable of hydrolysing rather than synthesising ATP. Unrestrained, this will lead to the loss of ionic homeostasis and ultimately necrotic cell death. The functional recovery of the Langendorff-perfused heart from ischaemia inversely correlates with the extent of pore opening, and inhibition of the MPTP provides protection against reperfusion injury. This may be mediated either by a direct interaction with the MPTP [e.g., by Cyclosporin A (CsA) and Sanglifehrin A (SfA)], or indirectly by decreasing calcium loading and reactive oxygen species (ROS; key inducers of pore opening) or lowering intracellular pH. Agents working in this way may include pyruvate, propofol, Na+/H+ antiporter inhibitors, and ischaemic preconditioning (IPC). Mitochondrial KATP channels have been implicated in preconditioning, but our own data suggest that the channel openers and blockers used in these studies work through alternative mechanisms. In addition to its role in necrosis, transient opening of the MPTP may occur and lead to the release of cytochrome c and other proapoptotic molecules that initiate the apoptotic cascade. However, only if subsequent MPTP closure occurs will ATP levels be maintained, ensuring that cell death continues down an apoptotic, rather than a necrotic, pathway.     

Distinct KATP channels mediate the antihypertrophic effects of adenosine receptor activation in neonatal rat ventricular myocytes

Recent evidence suggests that both adenosine receptor (AR) and K ATP channel activation exert antihypertrophic effects in cardiac myocytes. We studied the relative contributions of mitochondrial K ATP (mitoK ATP) and sarcolemmal K ATP (sarcK ATP) to the antihypertrophic effects of ARs in primary cultures of neonatal rat ventricular myocytes exposed for 24 h with the alpha1 adrenoceptor agonist phenylephrine (PE). The A1R agonist N6-cyclopentyladenosine (CPA), the A(2A)R agonist CGS21680 [2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine], and the A3R agonist N6-(3-iodobenzyl)adenosine-5'-methyluronamide (IB-MECA) all prevented PE-induced hypertrophy. Glibenclamide, a nonselective K(ATP) channel blocker reversed the antihypertrophic effect of all three AR agonists as determined by cell size and atrial natriuretic peptide expression and early c-fos up-regulation. In contrast, the mitoK(ATP) blocker 5-hydroxydecanoic acid selectively attenuated the effect of CGS21680 and IB-MECA, whereas HMR1098 [1-[[5-[2-(5-chloro-o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl]-3-methylthiourea, sodium salt], a specific blocker of sarcK(ATP), only abolished the antihypertrophic effect of CPA. Moreover, both CGS21680 and IB-MECA but not CPA decreased the mitochondrial membrane potential when PE was present, similarly to that seen with diazoxide, and both agents inhibited PE-stimulated elevation in mitochondrial Ca2+. All AR agonists diminished PE-induced phosphoserine/threonine kinase and protein kinase B up-regulation, which was unaffected by any K(ATP) blocker. Our data suggest that AR-mediated antihypertrophic effects are mediated by distinct K(ATP) channels, with sarcK(ATP) mediating the antihypertrophic effects of A1R activation, whereas mitoK(ATP) activation mediates the antihypertrophic effects of both A(2A)R and A3R agonists.     

Actin cytoskeleton dynamics promotes leptin-induced vascular smooth muscle hypertrophy via RhoA/ROCK- and phosphatidylinositol 3-kinase/protein kinase B-dependent pathways

Obesity is associated with increased leptin production that may contribute to cardiovascular pathology through a multiplicity of effects. Leptin has been shown to contribute to vascular remodeling through various mechanisms, including production of vascular smooth muscle (VSMC) hypertrophy; however, the mechanisms underlying the vascular hypertrophic effect of leptin remain unknown. In the present study, we investigated the contributions of the RhoA/Rho kinase (ROCK) and phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathways, actin dynamics, and the expression of serum-response factor (SRF) in the hypertrophic effects of leptin on vascular tissue. Strips of rat portal vein (RPV) were cultured with or without leptin at 3.1 nM for 1 to 3 days. Leptin significantly increased RhoA activity by 163 +/- 20%, whereas phosphorylation of downstream factors, including LIM kinase 1 and cofilin-2, was increased by 160 +/- 25 and 290 +/- 25%, respectively. Leptin also significantly phosphorylated Akt by 130 +/- 30%, which was inhibited by the PI3K inhibitor 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002). RhoA/ROCK and PI3K/Akt activation was associated with a significant increase in RPV wet weight (11 +/- 1%), protein synthesis (45 +/- 7%), SRF expression (136 +/- 11%), and polymerization of actin, as reflected by an increase in the F-/G-actin ratio, effects that were significantly attenuated by a leptin receptor (leptin obese receptor) antibody, the ROCK inhibitor (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) (Y-27632) as well as the PI3K inhibitor LY294002. Our results indicate that the activation of RhoA/ROCK and PI3K/Akt plays a pivotal role in leptin signaling, leading to the development of VSMC hypertrophy through a mechanism involving altered actin dynamics.     

Crosstalk between mitogen-activated protein kinases and mitochondria in cardiac diseases: Therapeutic perspectives

Cardiovascular diseases cause more mortality and morbidity worldwide than any other diseases. Although many intracellular signaling pathways influence cardiac physiology and pathology, the mitogen-activated protein kinase (MAPK) family has garnered significant attention because of its vast implications in signaling and crosstalk with other signaling networks. The extensively studied MAPKs ERK1/2, p38, JNK, and ERK5, demonstrate unique intracellular signaling mechanisms, responding to a myriad of mitogens and stressors and influencing the signaling of cardiac development, metabolism, performance, and pathogenesis. Definitive relationships between MAPK signaling and cardiac dysfunction remain elusive, despite 30 years of extensive clinical studies and basic research of various animal/cell models, severities of stress, and types of stimuli. Still, several studies have proven the importance of MAPK crosstalk with mitochondria, powerhouses of the cell that provide over 80% of ATP for normal cardiomyocyte function and play a crucial role in cell death. Although many questions remain unanswered, there exists enough evidence to consider the possibility of targeting MAPK–mitochondria interactions in the prevention and treatment of heart disease. The goal of this review is to integrate previous studies into a discussion of MAPKs and MAPK–mitochondria signaling in cardiac diseases, such as myocardial infarction (ischemia), hypertrophy and heart failure. A comprehensive understanding of relevant molecular mechanisms, as well as challenges for studies in this area, will facilitate the development of new pharmacological agents and genetic manipulations for therapy of cardiovascular diseases.     

NHE-1 inhibition-induced cardioprotection against ischaemia/reperfusion is associated with attenuation of the mitochondrial permeability transition

AIMS: The possible contribution of the cardiac mitochondrial permeability transition pore (PTP) towards the cardioprotective effects of Na(+)-H(+) exchanger-1 (NHE-1) inhibition was studied in hearts subjected to ischaemia/reperfusion (IR). METHODS AND RESULTS: Langendorff-perfused rat hearts were subjected to 40 min of global ischaemia and 60 min of reperfusion in the presence or absence of the NHE-1 specific inhibitor AVE-4890 (AVE, 5 microM). Mitochondrial PTP opening was determined in the intact heart using 2-deoxy-[(3)H]-glucose entrapment and in isolated mitochondria by monitoring the decrease of the calcium-induced light scattering. Mitochondrial respiration was measured with a Clark-type oxygen electrode whereas release of apoptosis-inducing factor (AIF) and endonuclease G (EndoG) and levels of cleaved poly-(ADP-ribose) polymerase (PARP) were analysed by western blotting. IR induced mitochondrial PTP opening, which was inhibited by 28% (P < 0.05) with AVE treatment. Mitochondria isolated from AVE-treated hearts demonstrated significantly less calcium-induced swelling and higher substrate oxidation at complex I and II as well as cytochrome c oxidase and citrate synthase activity. AVE treatment also suppressed IR-induced release of AIF and EndoG from mitochondria, prevented the IR-induced rise in cleaved PARP levels, and was associated with significantly enhanced postischaemic recovery of left ventricular developed pressure and a significant decrease in lactate dehydrogenase release. AVE did not affect PTP opening directly in isolated mitochondria. CONCLUSION: The beneficial effect of NHE-1 inhibition in hearts subjected to IR is associated with attenuation of mitochondrial PTP opening and apoptosis and the resultant mitochondrial dysfunction. The effect of AVE on PTP opening most likely is indirect, as pore opening was not affected by direct administration of AVE to mitochondrial suspensions.     

Angiotensin II‐preconditioning is associated with increased PKCε/PKCδ ratio and prosurvival kinases in mitochondria

Angiotensin II‐preconditioning (APC) has been shown to reproduce the cardioprotective effects of ischaemic preconditioning (IPC), however, the molecular mechanisms mediating the effects of APC remain unknown. In this study, Langendorff‐perfused rat hearts were subjected to IPC, APC or both (IPC/APC) followed by ischaemia‐reperfusion (IR), to determine translocation of PKCε, PKCδ, Akt, Erk1/2, JNK, p38 MAPK and GSK‐3β to mitochondria as an indicator of activation of the protein kinases. In agreement with previous observations, IPC, APC and IPC/APC increased the recovery of left ventricular developed pressure (LVDP), reduced infarct size (IS) and lactate dehydrogenase (LDH) release, compared to controls. These effects were associated with increased mitochondrial PKCε/PKCδ ratio, Akt, Erk1/2, JNK, and inhibition of permeability transition pore (mPTP) opening. Chelerythrine, a pan‐PKC inhibitor, abolished the enhancements of PKCε but increased PKCδ expression, and inhibited Akt, Erk1/2, and JNK protein levels. The drug had no effect on the APC‐ and IPC/APC‐induced cardioprotection as previously reported, but enhanced the post‐ischaemic LVDP in controls. Losartan, an angiotensin II type 1 receptor (AT1‐R) blocker, abolished the APC‐stimulated increase of LVDP and reduced PKCε, Akt, Erk1/2, JNK, and p38. Both drugs reduced ischaemic contracture and LDH release, and abolished the inhibition of mPTP by the preconditioning. Chelerythrine also prevented the reduction of IS by APC and IPC/APC. These results suggest that the cardioprotection induced by APC and IPC/APC involves an AT1‐R‐dependent translocation of PKCε and survival kinases to the mitochondria leading to mPTP inhibition. In chelerythrine‐treated hearts, however, alternate mechanisms appear to maintain cardiac function.     

Leptin-induced cardiomyocyte hypertrophy involves selective caveolae and RhoA/ROCK-dependent p38 MAPK translocation to nuclei

AIMS: Leptin-induced cardiomyocyte hypertrophy is dependent on both RhoA and p38 mitogen-activated protein kinase (p38 MAPK) activation. The present study investigated the role of lipid raft/caveolae in these responses and assessed the nature of p38 MAPK activation in mediating leptin-induced hypertrophy. METHODS AND RESULTS: Studies were carried out using cultured neonatal rat ventricular myocytes. Pharmacological, molecular, microscopy, and confocal imaging techniques were used to assess the role of caveolae in leptin-induced hypertrophy and to study the underlying cellular mechanisms. Leptin (3.1 nmol/L) treatment for 24 h significantly increased caveolae number two-fold and increased expression of caveolin-3 to 278 +/- 14% of control values. These effects were associated with increased cell surface area by 29 +/- 5% and leucine incorporation by 40 +/- 6%. The hypertrophic effect of leptin was associated with significant activation of RhoA (422 +/- 26%) and a decrease in the G-actin-to-F-actin ratio from 3.1 +/- 0.2 to 0.9 +/- 0.1. Caveolae disruption with methyl-beta-cyclodextrin (MbetaCD) potently attenuated leptin-induced cell hypertrophy and the associated signalling. RhoA was detected in caveolae fraction of a sucrose gradient after treatment with leptin for 5 min, indicating subcellular translocation of RhoA: this effect was inhibited by MbetaCD, the RhoA inhibitor C3 exoenzyme, and by disruption of actin filaments with latrunculin B. Furthermore, leptin-induced hypertrophy was associated with p38 MAPK but not with extracellular signal-regulated kinase (ERK1/2) translocation to nuclei, which was inhibited by MbetaCD, C3 exoenzyme, and the Rho kinase inhibitor Y-27632. CONCLUSION: Our results indicate that p38 import into nuclei represents a key mechanism for leptin-induced hypertrophy acting through lipid raft/caveolae and a RhoA-dependent pathway.