Inhibition of Jak2 phosphorylation attenuates pressure overload cardiac hypertrophy

RationaleWe examined the role of Jak2 kinase phosphorylation in the development of pressure overload hypertrophy in mice subjected to transverse aortic constriction (TAC) and treated with tyrphostin AG490, a pharmacological inhibitor of Jak2.MethodsControl mice (sham), subjected to TAC for 15 days (TAC) or to TAC and treated with 48 μg/kg/day i.p. of tyrphostin AG490 (TAC + AG490) were evaluated for morphological, physiological, and molecular changes associated with pressure overload hypertrophy.ResultsMice subjected to TAC alone developed concentric hypertrophy that accompanied activation of the components of the Jak/STAT signaling pathway manifested by an increase in phosphorylation of Jak2 and STAT3. We also observed increased phosphorylation of MAPK p44/p42, p38 MAPK and JNK in the TAC group, as well as, an increase in expression of MKP-1 phosphatase which negatively regulates MAPK kinases. Treatment of aortic constricted mice with tyrphostin AG490 failed to develop hypertrophy and showed a marked reduction in phosphorylation of Jak2 and STAT3. There was, however, in TAC and AG490 treated mice, a notable increase in the phosphorylation state of the MAPK p44/42, whereas MKP-1 phosphatase was downregulated.ConclusionThese findings suggest that Jak2 kinase plays an important role in left ventricular remodeling during pressure overload hypertrophy. Pharmacological inhibition of Jak2 kinase during pressure overload blocks the development of concentric hypertrophy.     

卡托普利对实验大鼠左室肥厚的干预作用

目的观察卡托普利逆转压力负荷增加大鼠左室肥厚的作用。方法采用腹主动脉狭窄所致压力负荷增加大鼠左室肥厚模型,将雄性SD大鼠36只随机分为假手术组、模型组、卡托普利组,观察用药4周后左室重量指数（LVMI）、左室心肌病理形态HE染色、左室心肌细胞超微结构等指标的改变。结果模型组LVMI明显高于假手术组（P〈0．01）,卡托普利组（2．32±0．35）明显低于模型组（2．98±0．36）,P〈0．01;左室心肌病理形态HE染色、左室心肌细胞超微结构的改变与LVMI的改变基本一致。结论卡托普利具有逆转心肌肥厚的作用。     

An antidiabetic thiazolidinedione induces eccentric cardiac hypertrophy by cardiac volume overload in rats

1. To assess the involvement of volume overload in the development of cardiac hypertrophy during treatment with an antidiabetic thiazolidinedione, changes in cardiac anatomy and parameters of cardiac volume overload were evaluated in female Sprague-Dawley rats treated with the thiazolidinedione derivative T-174. 2. Two week administration of T-174 (13 and 114 mg/kg per day) increased absolute and relative heart weights by 11-24%, demonstrating the development of cardiac hypertrophy. There was no evidence of oedema in hearts from treated rats. 3. Both plasma and blood volumes were increased in T-174-treated rats without any changes in systolic blood pressure and heart rate, whereas haematocrit was decreased. In accordance with the existence of volume overload, both left ventricular end-diastolic pressure and right atrial pressure were increased. Morphometric analysis of hearts revealed that T-174 induced eccentric heart hypertrophy, as characterized by a small increase in wall thickness and a large increase in the chamber volume, which is characteristic of volume overload. Volume overload is suggested as the possible trigger mechanism because blood volume expansion preceded cardiac hypertrophy and there was a high correlation between heart weight and blood volume. 4. T-174-treated streptozotocin-induced diabetic rats also exhibited blood volume expansion and cardiac hypertrophy. 5. These findings suggest that cardiac volume overload is induced by plasma volume expansion and contributes to the development of eccentric cardiac hypertrophy during treatment with antidiabetic thiazolidinediones. Although thiazolidinediones are insulin-sensitizing agents, these cardiac effects are likely to be mediated independently of insulin.     

Metformin attenuates pressure overload-induced cardiac hypertrophy via AMPK activation

Aim:

To identify the role of metformin in cardiac hypertrophy and investigate the possible mechanism underlying this effect.

Methods:

Wild type and AMPKα2 knockout (AMPKα2^−/−) littermates were subjected to left ventricular pressure overload caused by transverse aortic constriction. After administration of metformin (200 mg·kg⁻¹·d⁻¹) for 6 weeks, the degree of cardiac hypertrophy was evaluated using echocardiography and anatomic and histological methods. The antihypertrophic mechanism of metformin was analyzed using Western blotting.

Results:

Metformin significantly attenuated cardiac hypertrophy induced by pressure overload in wild type mice, but the antihypertrophic actions of metformin were ablated in AMPKα2^−/− mice. Furthermore, metformin suppressed the phosphorylation of Akt/protein kinase B (AKT) and mammalian target of rapamycin (mTOR) in response to pressure overload in wild type mice, but not in AMPKα2^−/− mice.

Conclusion:

Long-term administration of metformin may attenuate cardiac hypertrophy induced by pressure overload in nondiabetic mice, and this attenuation is highly dependent on AMPK activation. These findings may provide a potential therapy for patients at risk of developing pathological cardiac hypertrophy.     

葛根素预防压力过载性心脏肥大的保护作用及机制

目的研究葛根素对心脏肥大大鼠的保护作用,并探讨其相关机制。方法将主动脉缩窄术(降主动脉结扎,aortic banding,AB)所致心脏肥大的40只雄性Spraguee Dawley大鼠(体质量80~100g),分为阳性对照组(control组)、假手术组(shamoperated,SO组)、葛根素组(Pue组)和雷帕霉素组(RAPa组)。检测各组经相应药物治疗后,腺苷酸活化蛋白激酶(5′-adenosine monophosphate kinase,AMPK)的活性及自噬功能。同时,体外检测异丙肾上腺素和3-甲基腺嘌呤所致的心肌影响。结果葛根素组治疗3周后,大鼠明显恢复自噬;葛根素治疗6周后,有效地限制大鼠心脏细胞肥大和细胞凋亡。雷帕霉素组具有相似作用。体外研究,葛根素对异丙肾上腺素所致的H9c2细胞也具有类似的抗肥大和抗细胞凋亡作用。用3-甲基腺嘌呤预处理H9c2细胞,抑制自噬功能后,葛根素的保护作用被阻断。结论葛根素通过AMPK/mTOR信号途径,部分恢复细胞自噬功能,发挥抗心脏细胞肥大和抗细胞凋亡作用。     

Distinct role of adrenoceptor subtypes in cardiac adaptation to chronic pressure overload

1. With the generation of gene knockout (KO) or transgenic overexpression (TG) mouse models targeting adrenoceptors (AR), recent studies in vivo have investigated the role of AR subtypes in pressure overload-induced left ventricular (LV) hypertrophy and remodelling. 2. Although subjecting alpha(1B)-KO mice to transverse aortic constriction (TAC) did not reveal significant phenotype differences compared with controls, mice deficient in both alpha(1A)- and alpha(1B)-AR responded to TAC with poor survival, increased cardiomyocyte apoptosis, more severe fibrosis and dysfunction, but a similar degree of LV hypertrophy, compared with wild-type littermates. Following TAC, alpha(1B)-TG mice developed more severe hypertrophy, interstitial fibrosis and LV dysfunction. In contrast, overexpression of alpha(1A)-AR preserved cardiac function and reduced death from heart failure without affecting the degree of LV hypertrophy. Thus, alpha(1A)- and alpha(1B)-adrenoceptor signalling impacts differently on myocardial adaptation to pressure overload. 3. The absence of both beta(1)- and beta(2)-AR significantly suppressed pressure overload-evoked hypertrophy, fibrosis and expression of inflammatory or fibrogenic genes. Conversely, studies on beta(2)-TG mice with TAC revealed adverse consequences, including accelerated development of heart failure, poor survival and more severe interstitial fibrosis, but a comparable degree of hypertrophy compared with wild-type littermates. 4. Collectively, these findings suggest that the effect of ARs on pressure overload-induced myocardial adaptation is subtype specific. Whereas activation of alpha(1B)-AR or beta(2)-AR contributes to maladaptation and the onset of heart failure, activation of alpha(1A)-AR or inactivation of beta(2)-AR is beneficial in the setting of chronic pressure overload.     

压力负荷联合超容量负荷致家兔心力衰竭模型的建立

目的 探讨压力负荷联合超容量负荷建立家兔心衰模型的可行性.方法 16只家兔随机分心衰组(8只)和假手术组(8只);先制备腹主动脉缩窄、1周后制备主动脉瓣关闭不全致压力负荷及超容量负荷,利用心导管术和心脏多谱勒观察手术前后家兔血流动力学及心脏结构和功能的变化.结果 (1)心衰组术后主动脉收缩压、脉压、左室舒张末压较术前明显增加(P<0.05);(2)心衰组术后左房内径、室间隔厚度、左室后壁厚度、左室收缩和舒张末内径均明显增加(P<0.05),射血分数及左室缩短率明显降低(P<0.05);(3)心衰组心脏及左室/体重比、肺脏/体重比明显高于假手术组(P<0.05).结论 压力负荷联合超容量负荷建立心衰模型方法可行,心衰形成时间短,成功率高,符合人类心衰病理生理过程.     

Knockout of beta(1)- and beta(2)-adrenoceptors attenuates pressure overload-induced cardiac hypertrophy and fibrosis

BACKGROUND AND PURPOSE: The role of beta-adrenoceptors in heart disease remains controversial. Although beta-blockers ameliorate the progression of heart disease, the mechanism remains undefined. We investigated the effect of beta-adrenoceptors on cardiac hypertrophic growth using beta(1)- and beta(2)-adrenoreceptor knockout and wild-type (WT) mice.EXPERIMENTAL APPROACH :Mice were subjected to aortic banding or sham surgery, and their cardiac function was determined by echocardiography and micromanometry.KEY RESULTS: At 4 and 12 weeks after aortic banding, the left ventricle:body mass ratio was increased by 80-87% in wild-type mice, but only by 15% in knockouts, relative to sham-operated groups. Despite the blunted hypertrophic growth, ventricular function in knockouts was maintained. WT mice responded to pressure overload with up-regulation of gene expression of inflammatory cytokines and fibrogenic growth factors, and with severe cardiac fibrosis. All these effects were absent in the knockout animals.CONCLUSION AND IMPLICATIONS:Our findings of a markedly attenuated cardiac hypertrophy and fibrosis following pressure overload in this knockout model emphasize that beta-adrenoceptor signalling plays a central role in cardiac hypertrophy and maladaptation following pressure overload.     

肉苁蓉苯乙醇总苷对压力超负荷大鼠心肌肥厚及PI3K/PKB信号通路的影响

目的探讨肉苁蓉苯乙醇总苷(CPhGs)对压力超负荷大鼠心肌肥厚的抑制作用及其可能的作用机制。方法♂SPF级SD大鼠70只,随机分为空白组(Con)、假手术组(Sham)、模型组(Mod)、阳性药对照组(Vst)、CPhGs 125、250、500 mg·kg^-1组。检测心脏超声指标、心脏体质量指数(HWI)、心肌组织病理学变化、心肌细胞面积(AMC),Elisa法检测血浆ET-1、BNP水平,Western blot法检测p-PI3K、PI3K、p-PKB、PKB蛋白表达变化。结果与Mod组相比,CPhGs不同剂量给药后,LVPWT、HWI、血浆ET-1和BNP、AMC均有不同程度下降,LVEDD、LVEF、LVFS以及心肌组织p-PI3K、p-PKB蛋白表达有不同程度的增加,其中CPhGs 250、500 mg·kg^-1组相比于Mod组各指标有明显差异(P<0.05或0.01);与Vst组相比,CPhGs 500 mg·kg^-1组各指标,没有明显差异。结论CPhGs对压力超负荷引起的大鼠心肌肥厚具有抑制作用,其作用可能与PI3K/PKB信号通路的激活有关。     

西红花酸对压力超负荷所致大鼠心肌肥厚的影响

目的研究西红花酸对压力超负荷所致大鼠心肌肥厚的影响。方法腹主动脉部分狭窄术致心肌肥厚,采用试剂盒测定Na⁺-K⁺ ATPase和Ca²⁺-Mg²⁺ ATPase的活力及羟脯氨酸的含量,SDS-PAGE检测MMPs的活力。结果 模型组ATPase活性降低更加明显,羟脯氨酸的含量明显增加,MMPs活力明显增强。西红花酸能显著提高心肌组织的ATPase活力,降低胶原的含量,抑制MMPs的活力。结论西红花酸对压力超负荷所致大鼠心肌肥厚具有一定的改善作用,抑制MMPs的活性可能是其作用机制之一。     

Interaction between renin–angiotensin and sympathetic nervous systems in a rat model of pressure overload cardiac hypertrophy

1 A raised cardiac workload activates neurohormones which will increase muscle mass and shift contractility to the right along the Frank‐Starling curve. 2 This study examined the interaction between the SNS and RAS in contributing to vascular responsiveness following the development of cardiac hypertrophy due to aortic banding. 3 Sprague Dawley rats (180–200 g) were assigned to one of six groups; Normal, Sham‐operated, Aortic Banded (AB), Aortic Banded treated with losartan (ABLOS), Aortic Banded treated with 6‐hydroxydopamine (ABSYMP) and Aortic banded treated with both losartan and 6‐hydroxydopamine (ABSYMPLOS). A constricting band was placed around the supra renal aorta on day zero with drug treatment from day 37 to day 44. Vasopressor responses to noradrenaline, phenylephrine, methoxamine and angiotensin II were measured on day 45. 4 The magnitudes of the MAP responses to all vasoactive agents, expressed as percentage changes, were similar in Normal and Sham groups, but reduced in the AB group. ABLOS group showed attenuated response to ANGII whereas all responses were enhanced in the ABSYM group. 5 A positive interaction between the two systems was observed with α_1A‐adrenoceptors identified as a major component of SNS and AT₁ receptors of RAS to induce vasopressor effects.     

奥美沙坦酯在大鼠超负荷心肌肥大作用中的定量分析

目的 探讨新型血管紧张素Ⅱ1型受体拮抗剂奥美沙坦酯（OLM）在压力超负荷心肌肥大反应过程中的作用.方法 选用SD大鼠21只,随机分为腹主动脉缩窄组（COA）、COA＋OLM组及对照组各7只,建立腹主动脉缩窄性高血压大鼠模型,测定大鼠平均动脉压（MAP）,测量大鼠心肌纤维的各项体视学指标,即平均自由程（入）、比表面（S/Y）、表面积密度（SV）及体积密度（VV）等参数并计算其结果.结果 COA组大鼠的MAP明显增高,心肌横断面积（a）及平均直径（d）明显增大,入、SV及VV与对照组比较差异有统计学意义（P＜0.01）;COA＋OLM组的MAP值大致恢复至正常水平,a、d、SV及VV等明显小于COA组（P＜0.05）,反映心肌细胞恢复状态的S/V及入则增大至正常水平.结论 OLM可明显改变体视学各项参数,有效逆转由压力超负荷引起的高血压和心肌肥大.     

Chronic inhibition of farnesyl pyrophosphate synthase attenuates cardiac hypertrophy and fibrosis in spontaneously hypertensive rats

Farnesyl pyrophosphate synthase (FPPS), an essential enzyme in the mevalonate pathway, was reported to be upregulated in young spontaneously hypertensive rats (SHR) when compared with Wistar-Kyoto (WKY) rats, and this was accompanied by development of left ventricular hypertrophy. Five-week-old rats were daily gavaged with vehicle or an FPPS inhibitor (alendronate, 1 or 10 mg/kg) and blood pressures was monitored by the tail-cuff method every other week. Twelve weeks of alendronate treatment attenuated the left ventricular weight to body weight ratio (LVW/BW), hydroxyproline content, collagen deposition in the interstitia, and gene expression of atrial natriuretic peptide, B-type natriuretic peptide, and procollagen type I/III in the SHR left ventricle, all of which were significantly higher in SHRs than in WKY rats. Furthermore, long-term treatment with an FPPS inhibitor significantly reduced RhoA activation, ERK phosphorylation, and TGF-β1 expression in the SHR left ventricle, all of which were upregulated more in SHRs than in WKY rats. In conclusion, chronic treatment with an FPPS inhibitor attenuates the development of cardiac hypertrophy and fibrosis, and the suppression of ERK1/2 phosphorylation and TGF-β1 expression with inhibition of RhoA activation may be an important mechanism.     

Effects of losartan on pressure overload-induced cardiac gene expression profiling in rats

1. In the present study, the effects of losartan on myocardial gene expression changes following cardiac hypertrophy were investigated. 2. Male Wistar rats were randomized to receive 5 or 30 mg/kg per day losartan (i.p.) 1 day after suprarenal abdominal aortic constriction. Two weeks later, cardiac morphology and function were recorded with echocardiography and mean arterial central pressure was measured using carotid catheters. Myocardial gene expression was assessed with cDNA microarrays. 3. The ratios of left ventricular weights to bodyweights, the posterior thickness of the left ventricle and mean arterial central pressure were significantly increased by aortic constriction and attenuated by losartan in a dose-related manner. Genes in different functional categories were regulated in pressure overload-induced cardiac hypertrophy and the majority of changes in gene expression were inhibited by losartan in a dose-dependent manner. 4. However, there were still some genes that were unaffected by losartan, even at a higher dose. In contrast, losartan, especially at a lower dose, was able to induce changes in the expression of several additional genes that were unregulated in simple aortic constriction. 5. In conclusion, losartan is able to inhibit pressure overload-induced cardiac hypertrophy, as well as the majority of pressure overload-related changes in gene expression. The genes that remained unaffected or those that were additionally induced by losartan are likely to be new targets for investigation or therapy.