Isorhapontigenin, a new resveratrol analog, attenuates cardiac hypertrophy via blocking signaling transduction pathways

Cardiac hypertrophy is a major cause of morbidity and mortality worldwide. The hypertrophic process is mediated, in part, by oxidative stress-mediated signaling pathways. We hypothesized that isorhapontigenin (ISO), a new resveratrol analog, inhibits cardiac hypertrophy by blocking oxidative stress and oxidative stress-mediated signaling pathways. We treated cardiomyocytes with angiotensin II (Ang II) with or without ISO and found that ISO inhibited Ang II-induced cardiac hypertrophy. These effects were associated with a decrease in the levels of reactive oxygen species and H2O2 and the content of intracellular malonaldehyde and an increase in the activities of superoxide dismutase and glutathione peroxidase. Ang II induced the phosphorylation of PKC, Erk1/2, JNK, and p38 in cardiomyocytes and such phosphorylation was inhibited by ISO. ISO also blocked the PKC-dependent PI3K-Akt-GSK3beta/p70S6K pathway. These effects lead to direct or indirect inhibition of NF-kappaB and AP-1 activation. Our results revealed that pretreatment with ISO significantly inhibited Ang II-mediated NF-kappaB through affecting the degradation and phosphorylation of IkappaBalpha and the activity of IKKbeta and AP-1 activation by influencing the expression of c-Fos and c-Jun proteins. In addition, we also established the molecular link between activation of PKC and MAPKs and activation of NF-kappaB and AP-1 in cardiomyocytes. We also found that ISO treatment significantly attenuated heart weight/body weight ratio by approximately 25%, decreased posterior wall thickness and left ventricle diastolic and systolic diameters, and increased 10% fractional shortening in an aortic-banded rat model. Furthermore, treatment with ISO significantly decreased cardiac myocyte size and systolic blood pressure. These findings suggest that ISO prevents the development of cardiac hypertrophy through an antioxidant mechanism involving inhibition of different intracellular signaling transduction pathways.     

Angiotensin II activates Akt/protein kinase B by an arachidonic acid/redox-dependent pathway and independent of phosphoinositide 3-kinase.

Angiotensin II (Ang II) exerts contractile and trophic effects in glomerular mesangial cells (MCs). One potential downstream target of Ang II is the protein kinase Akt/protein kinase B (PKB). We investigated the effect of Ang II on Akt/PKB activity in MCs. Ang II causes rapid activation of Akt/PKB (5-10 min) but delayed activation of phosphoinositide 3-kinase (PI3-K) (30 min). Activation of Akt/PKB by Ang II was not abrogated by the PI3-K inhibitors or by the introduction of a dominant negative PI3-K, indicating that in MCs, PI3-K is not an upstream mediator of Akt/PKB activation by Ang II. Incubation of MCs with phospholipase A2 inhibitors also blocked Akt/PKB activation by Ang II. AA mimicked the effect of Ang II. Inhibitors of cyclooxygenase-, lipoxyogenase-, and cytochrome P450-dependent metabolism did not influence AA-induced Akt/PKB activation. However, the antioxidants N-acetylcysteine and diphenylene iodonium inhibited both AA- and Ang II-induced Akt/PKB activation. Dominant negative mutant of Akt/PKB or antioxidants, but not the dominant negative form of PI3-K, inhibited Ang II-induced protein synthesis and cell hypertrophy. These data provide the first evidence that Ang II induces protein synthesis and hypertrophy in MCs through AA/redox-dependent pathway and Akt/PKB activation independent of PI3-K.     

血管紧张素Ⅱ对模拟缺血心室肌细胞L-型钙通道的影响

实验研究了血管紧张素II（AngⅡ)对模拟缺血心室肌细胞L－型钙离子通道的作用,用胶原酶酶解法急性分离豚鼠心室肌细胞,以全细胞膜片钳方法记录心室肌细胞的L－型钙电流（ICa L.)。采用低氧,无糖,高乳酸和酸中毒综合方式模拟缺血液灌流,造成心室肌细胞的模拟缺血,并在缺血的基础上继续用含100mmol/A AngⅡ灌流细胞,观察AngⅡ对模拟缺血心室肌细胞钙离子通道的影响,实验结果显示,模拟缺血时ICa.L峰值电流明显减小,最大激活电压为0mV,AngⅡ能抵抗模拟缺血对ICa,L的抑制效应,使ICa,L峰值电流增大,并使最大激活电压左移至－10mV。     

蛋白激酶Cδ可能参与肥大心肌细胞转向凋亡

为了探讨肥大心肌细胞对凋亡刺激的易感性及蛋白激酶Cδ(protein kinase Cδ,PKCδ)在其中的作用,以内皮素-1 (endothelin-1,ET-1)处理原代培养的新生大鼠心肌细胞,诱导心肌细胞肥大;再用血管紧张素Ⅱ(angiotensin II,Ang II)作为细胞凋亡诱导因子,采用鬼笔环肽(phalloidin)荧光染色与细胞面积测量两种方法检测心肌肥大,Hoechst 33258荧光染色检测细胞凋亡。结果显示：(1)1与10 nmol/L ET-1作用48h,心肌细胞肌原纤维排列整齐、染色增浓,随ET-1浓度增加而愈加明显,心肌细胞表面积分别增加42．5%和67．3%,以此作为轻度和中度心肌细胞肥大模型。(2)正常、轻度肥大与中度肥大心肌细胞受1nmol/L AngⅡ处理24h后,凋亡率分别为(15．54±1．32)%、(20．65±1．40)%与(29．33±3．52)%,三组之间有显著差异(P＜0．05)。(3)受AngⅡ刺激后,PKCδ特异性抑制剂rottlerin不影响正常心肌细胞的凋亡率,却有效抑制了轻度和中度肥大心肌细胞的凋亡。肥大心肌细胞凋亡易感性明显高于正常心肌细胞,抑制PKCδ可以抑制肥大心肌细胞凋亡,提示PKCδ参与肥大心肌细胞凋亡过程。     

Heme oxygenase-1 gene transfer inhibits angiotensin II-mediated rat cardiac myocyte apoptosis but not hypertrophy

Cardiac myocyte apoptosis underlies the pathophysiology of cardiomyopathy, and plays a critical role in the transition from myocardial hypertrophy to heart failure. Angiotensin II (Ang II) induces cardiac myocyte apoptosis and hypertrophy which contribute to heart failure possibly through enhanced oxidative stress; however, the mechanisms underlying the activation of both pathways and their interactions remain unclear. In the present study, we have investigated whether overexpression of the antioxidant protein heme oxygenase-1 (HO-1) protects against apoptosis and hypertrophy in cultured rat cardiac myocytes treated with Ang II. Our findings demonstrate that Ang II (100 nM, 24 h) alone upregulates HO-1 expression and induces both myocyte hypertrophy and apoptosis, assessed by measuring terminal deoxynucleotidyltransferase dUTP nick-end labelling (TUNEL) staining, caspase-3 activity and mitochondrial membrane potential. Ang II elicited apoptosis was augmented in the presence of tin protoporphyrin, an inhibitor of HO activity, while HO-1 gene transfer to myocytes attenuated Ang II-mediated apoptosis but not hypertrophy. Adenoviral overexpression of HO-1 was accompanied by a significant increase in Ang II induced phosphorylation of Akt, however, Ang II-mediated p38 mitogen activated protein kinase (MAPK) phosphorylation was attenuated. Inhibition of phosphotidylinositol-3-kinase enhanced myocyte apoptosis elicited by Ang II, however, p38MAPK inhibition had no effect, suggesting that overexpression of HO-1 protects myocytes via augmented Akt activation and not through modulation of p38MAPK activation. Our findings identify the signalling pathways by which HO-1 gene transfer protects against apoptosis and suggest that overexpression of HO-1 in cardiomyopathies may delay the transition from myocyte hypertrophy to heart failure.     

Rutaecarpine prevents hypertensive cardiac hypertrophy involving the inhibition of Nox4‐ROS‐ADAM17 pathway

Rutaecarpine attenuates hypertensive cardiac hypertrophy in the rats with abdominal artery constriction (AAC); however, its mechanism of action remains largely unknown. Our previous study indicated that NADPH oxidase 4 (Nox4) promotes angiotensin II (Ang II)‐induced cardiac hypertrophy through the pathway between reactive oxygen species (ROS) and a disintegrin and metalloproteinase‐17 (ADAM17) in primary cardiomyocytes. This research aimed to determine whether the Nox4‐ROS‐ADAM17 pathway is involved in the protective action of rutaecarpine against hypertensive cardiac hypertrophy. AAC‐induced hypertensive rats were adopted to evaluate the role of rutaecarpine in hypertensive cardiac hypertrophy. Western blotting and real‐time PCR were used to detect gene expression. Rutaecarpine inhibited hypertensive cardiac hypertrophy in AAC‐induced hypertensive rats. These findings were confirmed by the results of in vitro experiments that rutaecarpine significantly inhibited Ang II‐induced cardiac hypertrophy in primary cardiomyocytes. Likewise, rutaecarpine significantly suppressed the Nox4‐ROS‐ADAM17 pathway and over‐activation of extracellular signal‐regulated kinase (ERK) 1/2 pathway in the left ventricle of AAC‐induced hypertensive rats and primary cardiomyocytes stimulated with Ang II. The inhibition of Nox4‐ROS‐ADAM17 pathway and over‐activation of ERK1/2 might be associated with the beneficial role of rutaecarpine in hypertensive cardiac hypertrophy, thus providing additional evidence for preventing hypertensive cardiac hypertrophy with rutaecarpine.     

Pik3ip1 Modulates Cardiac Hypertrophy by Inhibiting PI3K Pathway

Cardiac hypertrophy is an adaptive response to various physiological and pathological stimuli. Phosphoinositide-3 kinase (PI3K) is a highly conserved lipid kinase involved in physiological cardiac hypertrophy (PHH). PI3K interacting protein1 (Pik3ip1) shares homology with the p85 regulatory subunit of PI3K and is known to interact with the p110 catalytic subunit of PI3K, leading to attenuation of PI3K activity in liver and immune cells. However, the role of Pik3ip1 in the heart remains unknown. In the present study, the effects of Pik3ip1 on cardiac hypertrophy were examined. We found that the expression level of Pik3ip1 was markedly higher in cardiomyocytes than in fibroblasts. The interaction of Pik3ip1 with the p110a subunit of PI3K in the heart was identified by immunoprecipitation using neonatal rat cardiomyocytes (NRCM). Approximately 35% knockdown of Pik3ip1 was sufficient to induce myocardial hypertrophy. Pik3ip1 deficiency was shown to lead to activation of PI3K/protein kinase B (AKT)/ mammalian target of rapamycin (mTOR) signaling pathway, increasing protein synthesis and cell size. However, adenovirus-mediated overexpression of Pik3ip1 attenuated PI3K-mediated cardiac hypertrophy. Pik3ip1 was upregulated by PHH due to swimming training, but not by pathological cardiac hypertrophy (PAH) due to pressure-overload, suggesting that Pik3ip1 plays a compensatory negative role for PHH. Collectively, our results elucidate the mechanisms for the roles of Pik3ip1 in PI3K/AKT signaling pathway.     

Regulation of insulin-like growth factor-1 by the renin-angiotensin system during regression of cardiac eccentric hypertrophy through angiotensin-converting enzyme inhibitor and AT1 antagonist

Angiotensin II (Ang II) mediates its effects through its non-tyrosine-kinase G protein coupled Ang-II type 1 receptor (AT1). Growing evidence indicates that a functional insulin-like growth factor-1 (IGF-1) tyrosine kinase receptor is required for Ang-II-induced mitogenesis. Along with Ang II, we have previously shown that changes in IGF-1 receptor binding at myofibers are causative agents for cardiac eccentric hypertrophy. This study investigated the interaction of the renin-angiotensin system with the IGF-1 receptor during the development and regression of cardiac hypertrophy. Alterations in IGF-1 binding were evaluated in the CHAPS-pretreated perfused heart. Four weeks of aortocaval shunt increased relative heart mass by 76% without a major change in body mass or systolic blood pressure. Binding studies showed that IGF-1 has a higher affinity for the cardiac myofibers of shunt than sham rats. Two weeks of treatment with the angiotensin-converting enzyme (ACE) inhibitor captopril (0.5 g/L in drinking water) or the AT1-antagonist losartan (10 mg/(kg x day)) reduced cardiac hypertrophy by 54 and 42%, respectively. However, while both ACE inhibition and AT1-antagonist treatments produced equivalent regression in ventricular hypertrophy, captopril was more efficacious than losartan in the regression of atrial hypertrophy. Regression of cardiac hypertrophy in the shunt by either captopril or losartan was accompanied with a reduction or normalization of the elevated IGF-1 affinity. Thus, the induction and regression of cardiac eccentric hypertrophy seems to be largely dependent on cross talk between the renin-angiotensin system and the IGF-1 axis at the receptor level.     

MicroRNA-375-3p inhibitor suppresses angiotensin II-induced cardiomyocyte hypertrophy by promoting lactate dehydrogenase B expression

Cardiac hypertrophy is a myocardial enlargement due to overload pressure, and the primary cause of heart failure. We investigated the function of miR-375-3p in cardiac hypertrophy and its regulating mechanisms. miR-375-3p was upregulated in hearts of the transverse aortic constriction rat model and angiotensin II (Ang II)-induced primary cardiomyocyte hypertrophy model; the opposite was observed for lactate dehydrogenase B (LDHB) protein expression. miR-375-3p knockdown reduced the surface area of primary cardiomyocytes increased by Ang II treatment and decreased the B-natriuretic peptide (BNP) and β-myosin heavy chain (β-MHC) messenger RNA (mRNA) and protein levels. miR-375-3p was also observed to directly target LDHB. LDHB knockdown increased the surface area of Ang II-treated primary cardiomyocytes and increased the BNP and β-MHC mRNA and protein levels. LDHB knockdown attenuated the effects of miR-375-3p on the surface area of primary cardiomyocytes and BNP and β-MHC levels. Therefore, miR-375-3p inhibitor suppresses Ang II-induced cardiomyocyte hypertrophy by promoting LDHB expression.     

Propofol depresses angiotensin II-induced cardiomyocyte hypertrophy in vitro

Cardiomyocyte hypertrophy is formed in response to pressure or volume overload, injury, or neurohormonal activation. The most important vascular hormone that contributes to the development of hypertrophy is angiotensin II (Ang II). Accumulating studies have suggested that reactive oxygen species (ROS) may play an important role in cardiac hypertrophy. Propofol is a general anesthetic that possesses antioxidant action. We therefore examined whether propofol inhibited Ang II-induced cardiomyocyte hypertrophy. Our results showed that both ROS formation and hypertrophic responses induced by Ang II in cardiomyocytes were partially blocked by propofol. Further studies showed that propofol inhibited the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) and mitogen-activated protein kinase/ERK kinase 1/2 (MEK1/2) induced by Ang II via a decrease in ROS production. In addition, propofol also markedly attenuated Ang II-stimulated nuclear factor-kappaB (NF-kappaB) activation via a decrease in ROS production. In conclusion, propofol prevents cardiomyocyte hypertrophy by interfering with the generation of ROS and involves the inhibition of the MEK/ERK signaling transduction pathway and NF-kappaB activation.     

Epigallocathechin-3 gallate inhibits cardiac hypertrophy through blocking reactive oxidative species-dependent and -independent signal pathways

Cardiac hypertrophy is a major cause of morbidity and mortality worldwide. Recent in vitro and in vivo studies have suggested that reactive oxygen species (ROS) may play an important role in cardiac hypertrophy. It was therefore thought to be of particular value to examine the effects of antioxidants on cardiac hypertrophy. Epigallocatechin-3-gallate (EGCG) is a major bioactive polyphenol present in green tea and a potent antioxidant. The current study was designed to test the hypothesis that EGCG inhibits cardiac hypertrophy in vitro and in vivo. In this study, we investigated the effects of EGCG on angiotensin II- (Ang II) and pressure-overload-induced cardiac hypertrophy. Our results showed that EGCG attenuated Ang II- and pressure-overload-mediated cardiac hypertrophy. Both reactive oxygen species generation and NADPH oxidase expressions induced by Ang II and pressure overload were suppressed by EGCG. The increased hypertension by pressure overload was almost completely blocked after EGCG treatment. Further studies showed that EGCG inhibited Ang II-induced NF-kappaB and AP-1 activation. Inhibition of the activity of NF-kappaB was through blocking ROS-dependent p38 and JNK signaling pathways, whereas inhibition of AP-1 activation was via blocking EGFR transactivation and its downstream events ERKs/PI3K/Akt/mTOR/p70(S6K). The combination of these actions resulted in repressing the reactivation of ANP and BNP, and ultimately preventing the progress of cardiac hypertrophy. These findings indicated that EGCG prevents the development of cardiac hypertrophy through ROS-dependent and -independent mechanisms involving inhibition of different intracellular signaling transductional pathways.     

Novel EGFR inhibitors attenuate cardiac hypertrophy induced by angiotensin II

Cardiac hypertrophy is an important risk factor for heart failure. Epidermal growth factor receptor (EGFR) has been found to play a role in the pathogenesis of various cardiovascular diseases. The aim of this current study was to examine the role of EGFR in angiotensin II (Ang II)‐induced cardiac hypertrophy and identify the underlying molecular mechanisms. In this study, we observed that both Ang II and EGF could increase the phospohorylation of EGFR and protein kinase B (AKT)/extracellular signal‐regulated kinase (ERK), and then induce cell hypertrophy in H9c2 cells. Both pharmacological inhibitors and genetic silencing significantly reduced Ang II‐induced EGFR signalling pathway activation, hypertrophic marker overexpression, and cell hypertrophy. In addition, our results showed that Ang II‐induced EGFR activation is mediated by c‐Src phosphorylation. In vivo, Ang II treatment significantly led to cardiac remodelling including cardiac hypertrophy, disorganization and fibrosis, accompanied by the activation of EGFR signalling pathway in the heart tissues, while all these molecular and pathological alterations were attenuated by the oral administration with EGFR inhibitors. In conclusion, the c‐Src‐dependent EGFR activation may play an important role in Ang II‐induced cardiac hypertrophy, and inhibition of EGFR by specific molecules may be an effective strategy for the treatment of Ang II‐associated cardiac diseases.     

Phosphatidylinositide 3-kinase regulates angiotensin II-induced cytosolic phospholipase A2 activity and growth in vascular smooth muscle cells

Angiotensin (Ang) II via the AT(1) receptor acts as a mitogen in vascular smooth muscle cells (VSMC) through stimulation of multiple signaling mechanisms, including tyrosine kinases and mitogen-activated protein kinase (MAPK). In addition, cytosolic phospholipase A(2)(cPLA(2))-dependent release of arachidonic acid (AA) is linked to VSMC growth and we have reported that Ang II stimulates cPLA(2) activity via the AT(1) receptor. The coupling of Ang II to the activation of cPLA(2) appears to involve mechanisms both upstream and downstream of MAPK such that AA stimulates MAPK activity which phosphorylates cPLA(2) to further enhance AA release. However, the upstream mechanisms responsible for activation of cPLA(2) are not well-defined. One possibility includes phosphatidylinositide 3-kinase (PI3K), since PI3K has been reported to participate in the upstream signaling events linked to activation of MAPK. However, it is not known whether PI3K is involved in the Ang II-induced activation of cPLA(2) or if this mechanism is associated with the Ang II-mediated growth of VSMC. Therefore, we used cultured rat VSMC to examine the role of PI3K in the Ang II-dependent phosphorylation of cPLA(2), release of AA, and growth induced by Ang II. Exposure of VSMC to Ang II (100 nM) increased [(3)H]thymidine incorporation, cell number, and the release of [(3)H]AA. Also, using Western analysis, Ang II increased the phosphorylation of MAPK and cPLA(2) which were blocked by the MAPK kinase inhibitor PD98059 (10 microM/L). Similarly, the PI3K inhibitor LY294002 (10 microM/L) abolished the Ang II-mediated increase in MAPK phosphorylation, as well as phosphoserine-PLA(2). Further, inhibition of PI3K blocked the Ang II-induced release of AA and VSMC mitogenesis. However, exogenous AA was able to restore VSMC growth in the presence of LY294002, as well as reverse the inhibition of MAPK and cPLA(2) phosphorylation by LY294002. Thus, it appears from these data that Ang II stimulates the PI3K-sensitive release of AA which stimulates MAPK to phosphorylate cPLA(2) and enhance AA release. This mechanism may play an important role in the Ang II-induced growth of VSMC.     

Basal and IGF-I-dependent regulation of potassium channels by MAP kinases and PI3-kinase during eccentric cardiac hypertrophy

The potassium channels I(K) and I(K1), responsible for the action potential repolarization and resting potential respectively, are altered during cardiac hypertrophy. The activation of insulin-like growth factor-I (IGF-I) during hypertrophy may affect channel activity. The aim was to examine the modulatory effects of IGF-I on I(K) and I(K1) through mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) pathways during hypertrophy. With the use of specific inhibitors for ERK1/2 (PD98059), p38 MAPK (SB203580) and PI3K/Akt (LY294002), Western blot and whole cell patch-clamp were conducted on sham and aorto-caval shunt-induced hypertrophy adult rat myocytes. Basal activation levels of MAPKs and Akt were increased during hypertrophy. Acute IGF-I (10(-8) M) enhanced basal activation levels of these kinases in normal hearts but only those of Akt in hypertrophied ones. I(K) and I(K1) activities were lowered by IGF-I. Inhibition of ERK1/2, p38 MAPK, or Akt reduced basal I(K) activity by 70, 32, or 50%, respectively, in normal cardiomyocytes vs. 53, 34, or 52% in hypertrophied ones. However, basal activity of I(K1) was reduced by 45, 48, or 45% in the former vs. 63, 43, or 24% in the latter. The inhibition of either MAPKs or Akt alleviated IGF-I effects on I(K) and I(K1). We conclude that basal I(K) and I(K1) are positively maintained by steady-state Akt and ERK activities. K+ channels seem to be regulated in a dichotomic manner by acutely stimulated MAPKs and Akt. Eccentric cardiac hypertrophy may be associated with a change in the regulation of the steady-state basal activities of K+ channels towards MAPKs, while that of the acute IGF-I-stimulated ones toward Akt.     

Intracellular signaling of angiotensin II-induced p70 S6 kinase phosphorylation at Ser(411) in vascular smooth muscle cells. Possible requirement of epidermal growth factor receptor, Ras, extracellular signal-regulated kinase, and Akt

Activation of p70 S6 kinase (p70(S6K)) by growth factors requires multiple signal inputs involving phosphoinositide 3-kinase (PI3K), its effector Akt, and an unidentified kinase that phosphorylates Ser/Thr residues (Ser(411), Ser(418), Ser(424), and Thr(421)) clustered at its autoinhibitory domain. However, the mechanism by which G protein-coupled receptors activate p70(S6K) remains largely uncertain. By using vascular smooth muscle cells in which we have demonstrated Ras/extracellular signal-regulated kinase (ERK) activation through Ca(2+)-dependent, epidermal growth factor (EGF) receptor transactivation by G(q)-coupled angiotensin II (Ang II) receptor, we present a unique cross-talk required for Ser(411) phosphorylation of p70(S6K) by Ang II. Both p70(S6K) Ser(411) and Akt Ser(473) phosphorylation by Ang II appear to involve EGF receptor transactivation and were inhibited by dominant-negative Ras, whereas the phosphorylation of p70(S6K) and ERK but not Akt was sensitive to the MEK inhibitor. By contrast, the phosphorylation of p70(S6K) and Akt but not ERK was sensitive to PI3K inhibitors. Similar inhibitory pattern on these phosphorylation sites by EGF but not insulin was observed. Taken together with the inhibition of Ang II-induced p70(S6K) activation by dominant-negative Ras and the MEK inhibitor, we conclude that Ang II-initiated activation of p70(S6K) requires both ERK cascade and PI3K/Akt cascade that bifurcate at the point of EGF receptor-dependent Ras activation.     

Scoparone alleviates Ang II-induced pathological myocardial hypertrophy in mice by inhibiting oxidative stress

Long-term poorly controlled myocardial hypertrophy often leads to heart failure and sudden death. Activation of ras-related C3 botulinum toxin substrate 1 (RAC1) by angiotensin II (Ang II) plays a pivotal role in myocardial hypertrophy. Previous studies have demonstrated that scoparone (SCO) has beneficial effects on hypertension and extracellular matrix remodelling. However, the function of SCO on Ang II-mediated myocardial hypertrophy remains unknown. In our study, a mouse model of myocardial hypertrophy was established by Ang II infusion (2 mg/kg/day) for 4 weeks, and SCO (60 mg/kg bodyweight) was administered by gavage daily. In vitro experiments were also performed. Our results showed that SCO could alleviate Ang II infusion-induced cardiac hypertrophy and fibrosis in mice. In vitro, SCO treatment blocks Ang II-induced cardiomyocyte hypertrophy, cardiac fibroblast collagen synthesis and differentiation to myofibroblasts. Meanwhile, we found that SCO treatment blocked Ang II-induced oxidative stress in cardiomyocytes and cardiac fibroblasts by inhibiting RAC1-GTP and total RAC1 in vivo and in vitro. Furthermore, reactive oxygen species (ROS) burst by overexpression of RAC1 completely abolished SCO-mediated protection in cardiomyocytes and cardiac fibroblasts in vitro. In conclusion, SCO, an antioxidant, may attenuate Ang II-induced myocardial hypertrophy by suppressing of RAC1 mediated oxidative stress.     

EPC-Derived Microvesicles Protect Cardiomyocytes from Ang II-Induced Hypertrophy and Apoptosis

Cell-released microvesicles (MVs) represent a novel way of cell-to-cell communication. Previous evidence indicates that endothelial progenitor cells (EPCs)-derived MVs can modulate endothelial cell survival and proliferation. In this study, we evaluated whether EPC-MVs protect cardiomyocytes (CMs) against angiotensin II (Ang II)-induced hypertrophy and apoptosis. The H9c2 CMs were exposed to Ang II in the presence or absence of EPC-MVs. Cell viability, apoptosis, surface area and β-myosin heavy chain (β-MHC) expression were analyzed. Meanwhile, reactive oxygen species (ROS), serine/threonine kinase (Akt), endothelial nitric oxide synthase (eNOS), and their phosphorylated proteins (p-Akt, p-eNOS) were measured. Phosphatidylinositol-3-kinase (PI3K) and NOS inhibitors were used for pathway verification. The role of MV-carried RNAs in mediating these effects was also explored. Results showed 1) EPC-MVs were able to protect CMs against Ang II-induced changes in cell viability, apoptosis, surface area, β-MHC expression and ROS over-production; 2) The effects were accompanied with the up-regulation of Akt/p-Akt and its downstream eNOS/p-eNOS, and were abolished by PI3K inhibition or partially blocked by NOS inhibition; 3) Depletion of RNAs from EPC-MVs partially or totally eliminated the effects of EPC-MVs. Our data indicate that EPC-MVs protect CMs from hypertrophy and apoptosis through activating the PI3K/Akt/eNOS pathway via the RNAs carried by EPC-MVs.