Toll like receptor 4- a potential transmembrane receptor contributes to the cardiac remodeling of hypertension

AIM: To observe the expression of Toll like receptor 4 (TLR4) in the left ventricle of Goldblatt rats and to explore the role and mechanism of TLR4 in left ventricular remodeling of hypertension.METHODS: Goldblatt model of Two-kidney,one-clip(2K1C) renovascular hypertension was induced in twenty-five rats(H group),and twenty rats served the sham-operated group(sham group).The tail cuff blood pressure was detected every week and echocardiogram was observed every other week.After eight weeks of operation,the rats were killed and the samples of the left ventricle were collected.The concentration of AngⅡ in left ventricle was assessed by radioimmunoassay.Western blotting and RT-PCR were used to exam the mRNA and protein expression of TLR4 in the left ventricle.Immunohistochemistry was adopted to exam the location of TLR4 in the myocardium.RESULTS: TLR4 mRNA and protein expression were consistently upregulated in the left ventricle of H group compared with sham group.In H group,predominantly sarcolemmal staining was observed,especially focal areas of intense TLR4 staining were found in juxtaposed regions of two or more adjacent myocytes;However,in sham group,TLR4 expression was diffuse and presumably cytoplasmic.Considerable correlation was found between blood pressure,MESS,LVMI,RWT,the concentration of AngⅡ in left ventricle and the protein expression of TLR4 in myocytes.CONCLUSION: During the development of left ventricular remodeling of Goldblatt rats,expression of TLR4 increases significantly.Enhanced expression of TLR4 locates in the sarcolemma,especially in juxtaposed regions of two or more adjacent myocytes.These indicate that TLR4 transmembrane receptor which is closely relative with inflammation and immunity probably contributes to the development of ventricular remodeling.     

Effects and mechanism of fenofibrate and pioglitazone on ventricular remodelingin in pressure overload rats

AIM: To study the effects and mechanism of peroxisome proliferator-activated receptors (PPARs) ligands,fenofibrate and pioglitazone,on ventricular remodeling in pressure overload rats.METHODS: A pressure overload model was established by the constriction of abdominal aorta in Wistar rats.The hemodynamics and ventricular remodeling parameters,plasma and myocardial renin activity,angiotensin Ⅱ and aldosteron,the mRNA expression of angiotensin Ⅱ type 1 receptor (AT1) were investigated in the constriction of abdominal aorta group (CAA group,n=7) at 12-week after operation and treated experimental groups in which rats were treated with fenofibrate (F group,n=8),pioglitazone (P group,n=7),concomitant fenofibrate and pioglitazone (F+P group,n=6) for 12 weeks since 2 days after operation.The sham-operated rats served as controls (n=8).RESULTS: The ratio of left ventricular weight to body weight,mean arterial pressure,left ventricular systolic pressure,left ventricular end diastolic pressure,left ventricular systolic pressure and heart rate were significantly lower,the maximum left ventricular pressure rising and declining rates(±dp/dtmax) were significantly higher in all treated experimental groups than those in CAA group.Fenofibrate or pioglitazone had no effect on plasma and myocardial levels of renin,angiotensin Ⅱand aldosteron.The mRNA expression of AT1 was downregulated in treated groups except F group.CONCLUSION: PPAR ligands have no effect on plasma and myocardial levels of renin,angiotensin Ⅱand aldosteron,but fenofibrate and pioglitazone inhibit ventricular remodeling,decrease preload and afterload,increase ±dp/dtmax in pressure overload rats.The expression of mRNA of AT1 is downregulated in myocardium of pressure overload rats by the PPARγ signaling pathway.     

Zacopride attenuates pressure overload-induced ventricular remodeling in rats

AIM:To investigate the protective effect of zacopride (ZAC) on the pressure-overload left ventricular remodeling in the rats induced by coarctation of abdominal aorta. METHODS:Male Sprague-Dawley (SD) rats with pressure overload were induced by the coarctation of abdominal aorta. The model rats were intraperitoneally administered with ZAC, chloroquine (Chlor), and zacopride+chlorquine (ZAC+Chlor). The study duration was 8 weeks. The cardiac structure and function were assessed by echocardiography. The heart weight/body weight (HW/BW) ratio and the left ventricular weight/body weight (LVW/BW) ratio were calculated. The changes of structure and shape in myocardial tissue were observed with HE staining. The ultrastructure of the myocytes was observed under transmission electron microscope. The inward rectifier potassium channel (I_K1) protein expression was determined by Western blot. The mRNA expression of Kir2.1 was detected by RT-PCR. RESULTS:Compared with vehicle group, ZAC improved cardiac function, as indicated by the decreased left ventricular end-diastolic dimension (LVEDD) and left ventricular end systolic dimension (LVESD) (P<0.05), and the increased left ventricular ejection fraction (LVEF) and left ventricular fractional shortening (LVFS) (P<0.01). The HW/BW and LVW/BW ratios were significantly decreased, and the cross-sectional area of the cardiomyocytes was significantly less in ZAC group than that in vehicle group (P<0.01). The ultrastructure of the myocytes was significantly improved. Chlor blocked the protective effect of zacopride on the pressure-overload left ventricular remodeling. The protein level of I_K1 and mRNA expression of Kir2.1 in the cardiac tissues in ZAC group were significantly increased compared with vehicle group (P<0.01). CONCLUSION:I_K1 agonist ZAC significantly attenuates pressure overload-induced ventricular remodeling in rats.     

Inhibitory effects of right cervical sympathetic trunk transection on inflammatory response after acute myocardial infarction in rats and its influence on HMGB1/TLR4/NF-κB signaling pathway

AIM: To observe the effects of transection of right cervical sympathetic trunk (TCST) on inflammatory response and expression of high mobility group box 1 (HMGB1) and TLR4/NF-κB signaling pathway in the rats after acute myocardial infarction (AMI). METHODS: AMI model was established by ligation of left anterior descending coronary artery in SD rats, then the model rats were randomly divided into MI group and MI+TCST group. MI+TCST model was performed by transection of right cervical sympathetic trunk after left anterior descending coronary artery ligation. The rats in MI group and MI+TCST group were divided into 1, 3, 7, 14 and 28 d subgroups, and another sham operation group threading without ligation, with 8 rats in above each group. After modeling for 4 weeks, the cardiac function was measured by echocardiography. All rats were killed to harvest the hearts for mesuring cardiac hypertrophy index. The myocardial tissue close to infarction was observed with HE staining. The relative mRNA expression levels of HMGB1, tumor necrosis factor α(TNF-α) and interleukin (IL)-6 at different time points were detected by real-time PCR. The protein expression of HMGB1 and TLR4 at different time points after AMI was determined by Western blot. The effect of transection of right cervical sympathetic trunk on the expressions of HMGB1 and TLR4/NF-κB signaling pathway was also analyzed.RESULTS: Compared with the MI group, left ventricular ejection fraction (LVEF) and left ventricular shorterning fraction (LVFS) were significantly higher (P<0.05), left ventricular end-diastole dimension (LVEDd), left ventricular end-systole dimension (LVESd) and cardiac hypertrophy index were significantly lower (P<0.05), and the mRNA levels of HMGB1, TNF-α and IL-6 decreased significantly in MI+TCST group (P<0.05). Western blot results revealed that the protein expression level of HMGB1 increased in the infarct border zone at 3 d, and reached its peak at 7 d, then gradually decreased, and at 28 d after MI in MI group was still significantly higher than that in sham group (P<0.05). The protein expression of TLR4 was consistent with that of HMGB1. Transection of right cervical sympathetic trunk reduced protein expression of HMGB1 and TLR4/NF-κB signaling pathway-related proteins (P<0.05).CONCLUSION: Transection of right cervical sympathetic trunk improves ventricular remodeling and maintaining cardiac function. The mechanism may be related to inhibiting HMGB1/TLR4/NF-κB signaling pathway to reduce inflammatory response.     

Effects of metformin on pressure overload-induced cardiac hypertrophy in rats

AIM: To study the effects of metformin on the pressure overload-induced cardiac hypertrophy in rats. METHODS: Transverse aortic constriction (TAC) model of rat was made through laparotomy. One week after TAC surgery, the rats were randomly divided into 5 groups (n=8 in each group) and were administered with the corresponding drugs orally every day for 8 weeks: sham group (sham surgery, administered with 2 mL distilled water); TAC group (TAC rats, administered with 2 mL distilled water); metformin (MET) group (TAC rats, administered with MET at dose of 300 mg·kg^-1·d^-1); MN group [TAC rats, administered with MET at dose of 300 mg·kg^-1·d^-1 plus NOS inhibitor, N^G-nitro-L-arginine methyl ester (L-NAME) 50 mg·kg^-1·d^-1] and L-NAME group (TAC rats, administered with L-NAME at dose of 50 mg·kg^-1·d^-1). After treated for 8 weeks, the echocardiography, hemodynamics, the ratio of heart weight to body weight (HW/BW) and histological examination of the heart were performed. The levels of myocardial AMP-activated protein kinase subunit α (AMPKα), p-AMPKα Thr172, endothelial nitric oxide synthase (eNOS) and p-eNOS Ser1177 were detected by Western blotting. Plasma and myocardial nitric oxide (NO) were detected biochemically. RESULTS: After 8 weeks treatment, the wall thickness of left ventricle, the heart weight/body weight ratio (HW/BW), and the left ventricular myocardial perivascular fibrosis and myocardial interstitial fibrosis of the animals in TAC group were significantly increased as compared to those in sham rats. Treatment with MET for 8 weeks significantly attenuated left ventricular hypertrophy and improved cardiac function in TAC rats. These effects of MET were mostly abolished by L-NAME. Molecular biology and biochemical testing revealed that the levels of left ventricular myocardial p-AMPKα Thr172 and p-eNOS Ser1177, as well as the levels of myocardial and serum NO were significantly increased in MET group. CONCLUSION: Long-term MET treatment significantly inhibits the cardiac hypertrophy and the myocardial fibrosis and improves the cardiac functions in pressure-overload rats. The anti-hypertrophic effects of MET may be mediated via activation of AMPK-eNOS signaling pathway.     

Therapeutic effect of neuregulin-1β on pressure overload-induced myocardial hypertrophy in rats

AIM：To investigate the therapeutic effect and the mechanism of neuregulin-1β (NRG-1β) on the rat model of myocardial hypertrophy induced by pressure overload．METHODS：Eight weeks after coarctation of abdominal aorta, the Wistar rats were randomly divided into 4 groups: myocardial hypertrophy (model) group, sham operation (sham) group, NRG-1β treatment group (intravenous injection of NRG-1β at dose of 10 μg/kg daily for 7 d) and NRG-1β+Herceptin (HERCE) treatment group ［intravenous injection of NRG-1β (10 μg/kg) plus HERCE (10 μg/kg) daily for 7 d］. The characteristics of heart functions were evaluated by the methods of hemodynamics and echocardiography. Masson staining was employed to observe the pathological changes of myocardial tissues. The concentration of angiotensin II (Ang II) in myocardial tissues was measured by radioimmunoassay. The level of tumor necrosis factor α (TNF-α) in myocardial tissues was detected by ELISA. The mRNA expression of B-cell lymphoma/leukemia-2 (bcl-2) and bcl-2-associated X protein (bax) in the myocardium was determined by RT-PCR. RESULTS：The left ventricular ejection fraction (LVEF) and left ventricular fraction shortening (LVFS) were higher, while the left ventricular end-systolic diameter (LVESD) and left ventricular end-diastolic diameter (LVEDD) were smaller in NRG-1β group than those in model group. The left ventricular end-systolic pressure (LVESP) and maximal rate of increase/decrease in left ventricular pressure (±dp/dtmax) were higher, and left ventricular end-diastolic pressure (LVEDP) was significantly lower in NRG-1β group than those in model group. Compared with model group, treatment with NRG-1β decreased collagen volume fraction (CVF), reduced the Ang II and TNF-α, increased bcl-2 mRNA expression, and decreased bax mRNA expression in myocardial tissues. No difference of the above parameters between model group and NRG-1β+HERCE treatment group was observed. CONCLUSION：NRG-1 reduces the expression of Ang II and TNF-α in myocardial tissues in pressure-overload rats, thus reducing Ang II and TNF-α mediated myocardial interstitial remodeling. Increase in the mRNA expression of bcl-2 and decrease in the mRNA expression of bax by NRG-1 inhibit myocardial cell apoptosis, which is responsible for its role of improving cardiac function of myocardial hypertrophy induced by pressure overload.     

Effect of fluvastatin on left ventricular remodeling and caspase-3 expression after myocardial infarction in rats

AIM: To observe the effect of fluvastatin (FV) on left ventricular remodeling and expression of caspase-3 after myocardial infarction (MI) in rats. METHODS: Rats were divided into 4 groups: group Ⅰ (sham), group Ⅱ (sham+FV), group Ⅲ (MI) and group Ⅳ (MI+FV). group Ⅱ and Ⅳ were treated with FV (10 mg·kg^-1·d^-1) for 4 weeks. The left ventricular structure, echocardiography and hydroxyproline were observed. The expression of caspase-3 was measured by immunohistochemistry and RT-PCR. RESULTS: Compared with MI group, there was a improvement of ultrastructure and index of left ventricular remodeling, and decrease in hydroxyproline in MI+FV group (all P<0.05). The number of caspase-3 positive cells also decreased in MI+FV group, and RT-PCR showed the level of caspase-3 mRNA expression was lower than that in MI group (P<0.05). CONCLUSION: Fluvastatin improves left ventricular remodeling after myocardial infarction, decreases the expression of caspase-3 and inhibits apoptosis.     

Effects of irbesartan and perindopril on the myocardial expression of connexin 43, desmin and cardiac troponin T in rat cardiac hypertrophy induced by pressure overload

AIM: To investigate the effects of angiotensinⅡ receptor type Ⅰ antagonist irbesartan and angiotensin-converting enzyme inhibitor perindopril on the myocardial expression of connexin 43 (CX43), desmin and cardiac troponin T (cTnT) in the pressure overload-induced rat cardiac hypertrophy. METHODS: 40 male adult Sprague-Dawley rats were divided into 5 groups (8 animals for each): sham operation group and other four groups with ventricular hypertrophy caused by banding aortic artery. Drugs were given one week after operation as follows: sham operation group, normal saline (2 mL·kg-1·d-1 ig) was given; Operative groups: animals with ventricular hypertrophy were treated with normal saline 2 mL·kg-1·d-1 ig; Treatment groups: animals with ventricular hypertrophy were treated with perindopril 2 mg·kg-1·d-1 ig, irbesartan 20 mg·kg-1·d-1 ig or irbesartan 20 mg·kg-1·d-1 ig plus perindopril 2 mg·kg-1·d-1 ig, respectively. Left ventricular mass index (LVMI), transverse diameter of myocardial cell (TDM), and myocardial expression of CX43, desmin and cTnT by immunohistochemistry were performed at the end of 8 weeks of drug intervention. RESULTS: LVMI, TDM were remarkably decreased after drug intervention, compared to animals of operative group (P<0.05). Left ventricular hypertrophy induced by aortic banding in rats were associated with marked disorganization of gap junction distribution. In hypertrophied myocytes, CX43 immunolabeling was dispersed over the entire cell surface rather than confined to the intercalated disks. The CX43 were mainly distributed in the intercalated disks in irbesartan group, perindopril group and their combined group. The myocardial expression of CX43, desmin and cTnT in the operative group was lower than that in irbesartan group, perindopril group and their combined group (P<0.05). CONCLUSION: These data indicate that irbesartan and perindopril play beneficial roles in the myocardial CX43, desmin and cTnT expression and their distribution, and the restoration of myocardial cell structure and gap junction in pressure-overload myocardium hypertrophy.     

Changes of calcium handling protein after acute myocardial infarction in rats and effect of carvedilol

AIM: To observe the changes of sarcoplasmic reticulum Ca2+-ATPase (SERCA)， phospholamban (PLB) during heart failure after acute myocardial infarction (AMI) in rats and the effect of carvedilol. METHODS: Rats were randomly assigned to normal control group, sham-operation group, AMI group and carvedilol (CAR) group. 6 weeks later, in vivo hemodynamic, morphometry and SERCA, PLB mRNA and protein expression of myocytes were measured in all animals. RESULTS: In comparison with sham-operation group, LV end diastolic pressure (LVEDP) and weight of ventricles were increased, while maximal rate of rise and fall (±dp/dt) of LV pressure were decreased in AMI group. After treatment with carvedilol, these parameters were all improved. The mRNA and protein expression of SERCA were downregulated (P<0.01). PLB mRNA and protein expression were upregulated (P<0.01) in AMI group relative to sham-operation group. Carvedilol restored the low expression of SERCA mRNA and protein (P<0.05), but was no effect on PLB mRNA and protein expression (P>0.05). CONCLUSIONS: The changes of SERCA and PLB may be the important mechanism of contractile dysfunction in heart failure after AMI. Carvedilol is effective in preventing LV dysfunction after AMI. The molecular mechanism may be related with normalization of SERCA expression.     

Effects of Tongxinluo on connexin 43 remodeling and ventricular arrhythmia after myocardial infarction in rats

AIM: To determine the effects of Tongxinluo(TXL) on connexin 43(Cx43) remodeling and ventricular arrhythmia(VA) after myocardial infarction(MI) in rats. METHODS: Male SD rats were randomly divided into sham-operated(sham) group(n=25) and operation group(n=75). The left anterior descending(LAD) was ligated in operated group, while the rats in sham group only underwent pericardiotomy. The rats in operation group which survived for 3 d after operation were randomly assigned to TXL group and MI group. The rats in TXL group was administrated with TXL(2 g·kg^-1·d^-1, intragastric administration) for 4 weeks, while normal saline was applied to the rats in sham group and MI group. The levels of interleukin-1β(IL-1β) and endothelin-1(ET-1) in the tissue from the border zone were measured by ELISA after treatment. The distribution and the mRNA and protein expression of Cx43 were detected by immunohistochemical staining, RT-PCR and Western blotting, respectively. The burst pacing was used to induce ventricular arrhythmia(VA). RESULTS: Compared with sham group, the levels of IL-1β and ET-1 and the incidence of VA were significantly increased, while the mRNA and protein expression of Cx43 was markedly reduced with irregular distribution in MI group(P<0.05). Compared with MI group, the levels of IL-1β and ET-1 and the incidence of VA were significantly reduced, while the expression of Cx43 at mRNA and protein levels was markedly increased with augmented linear distribution in the myocardial cell intercalated disc in TXL group(P<0.05). CONCLUSION: TXL reduces the incidence of VA after MI via inhibiting the Cx43 remodeling.     

Effects of carvedilol,cilazapril and their combination on left ventricular remodeling after acute myocardial infarction in rats

AIM:To compare the effects of carvedilol, cilazapril and their combination on left ventricular remodeling(LVRM) after acute myocardial infarction(AMI) in rats. METHODS: Twenty-four hours after AMI operation, 100 surviving rats were randomly assigned to: ①AMI control(n= 25), ②AMI+carvedilol(1 mg·kg^-1 ·d^-1, n= 25)(C1), ③AMI+cilazapril(1 mg·kg^-1 ·d^-1, n= 25)(Z1), and ④ AMI+combination(n= 25) groups. Sham-operated group(n= 17) were selected randomly. After 4 weeks of therapy with the drugs gastric gavage, hemodynamic and pathological studies were performed. RESULTS: There were no significant differences in MI size among the four AMI groups(all P> 0.05) Left ventricular(LV) end diastolic pressure(LVEDP), volume(LVV), weight(LVW) and septal thickness(STh) were all higher and left ventricular pressure maximal rate of rise and fall(±d p /d t) were lower(all P< 0.01) in AMI group than sham-operated group. The LVEDP, LVV, LVW and STh were all lower and ±dp /dt were higher in Z1, C1, and combination groups than those in AMI group(P< 0.05, P< 0.01), with LVEDP and STh were more lower in the combination group than in the two monotherapy group(P< 0.05, P< 0.01), but there were no significant differences in other variables among the three therapy groups. CONCLUSION: Carvedilol, cilazapril and their combination all can prevent from LVRM after AMI in rats, improve hemodynamics and LV function, with the combination superior.     

Over-expression of endophilin A2 attenuates myocardial hypertrophy induced by isoprenaline

AIM:To examine the effect of endophilin A2 (EndoA2) over-expression on myocardial hypertrophy induced by isoprenaline (ISO). METHODS:Healthy male SD rats were divided into 4 groups, including sham group, Ad-EndoA2 group, ISO group and ISO+Ad-EndoA2 group. The rats in Ad-EndoA2 group and ISO+Ad-EndoA2 group were injected with Ad-EndoA2 adenovirus into the wall of the left ventricle 1 d before the administration of normal saline or ISO, while the rats in sham group and ISO group were injected with PBS. Subsequently, normal saline or ISO were subcutaneously injected into the rats for 7 consecutive days. After 7 d, small-animal echocardiography was used to detect the cardiac function. The hearts were harvested. The heart weight index, hematoxylin and eosin (HE) staining, and the expression of fetal genes were observed to identify myocardial hypertrophy. The protein expression of LC3 and P62 was detected by Western blot. RESULTS:The results of small-animal echocardiography showed that the rats in ISO group were in the compensatory period of myocardial hypertrophy compared with sham group, evidenced by increased LVAWs, LVPWs, EF and FS, and decreased LVIDs and CO (P<0.05). In addition, the results of heart weight index, HE staining and RT-qPCR showed that myocardial hypertrophy was induced by ISO successfully (P<0.05). Over-expression of EndoA2 inhibited myocardial hypertrophy induced by ISO and improved cardiac function (P<0.05). The results of Western blot showed that EndoA2 over-expression obviously reversed the decreased level of autophagy induced by ISO (P<0.05).CONCLUSION:Over-expression of EndoA2 may attenuate myocardial hypertrophy induced by ISO due to strengthening autophagy.     

Effects of irbesartan and perindopril on pressure overload-induced cardiac hypertrophy in rats

AIM: To observe the effects of irbesartan and perindopril on pressure-overload cardiac hypertrophy in rats. METHODS: 40 male adult Sprague Dawley rats were divided into 5 groups. One was sham operation group, other four were aortic banding groups. One week after operation, all rats were gavaged with normal saline, perindopril, irbesartan or combination of perindopril and irbesartan. Morphometric determination, calcineurin (CaN) expression, CaN and sarcoplasmic reticulum (SR) Ca²⁺-ATPase activity were performed at the end of 6 weeks of drug intervention. RESULTS: Left ventricular mass index (LVMI), transverse diameter of myocardical cell (TDM), CaN activity were remarkably decreased after drug intervention and this decrease was most remarkable in the combination group. SR Ca²⁺-ATPase activity increased after drug intervention, especially in the combination group. CaN expression in myocardium were remarkably decreased after drug intervention. LVMI was positively correlated with TDM and CaN, negatively correlated with SR Ca²⁺-ATPase. CONCLUSION: Both irbesartan and perindopril decrease CaN activity, increase SR Ca²⁺-ATPase activity and combination of them has synergic effects on regressing of ventricular hypertrophy.     

Effect of erythropoietin on expression of myocardial NADPH oxidase in pressure overload rats

AIM:To explore the effect of erythropoietin （EPO） on the expression of myocardial NADPH oxidase （Nox） in the pressure overload rats. METHODS:Male SD rats (n=36) were used to establish a pressure overload myocardial hypertrophy model by abdominal aorta ligation. The animals were divided into model group, control group (sham, without narrowing abdominal aorta, the rest of the operation was the same as the model) and recombinant human erythropoietin (rhEPO) treatment group (intraperitoneal injection of rhEPO postoperatively, 4 000 U/kg, twice a week). After 8 weeks, the cardiac ultrasound imaging and hemodynamic evaluation were conducted to determine the cardiac functions. Masson staining was used to observe the degree of myocardial fibrosis. The expression of Nox2 and Nox4 at mRNA and protein levels was detected by real-time quantitative PCR and Western blotting. The protein levels of myocardial inflammatory factors CD45, F4/80 and TGF-β were determined by Western blotting. RESULTS:Compared with model group, the left ventricular ejection fraction (LVEF), left ventricular fractional shortening (LVFS), left ventricular end-systolic pressure (LVESP) and left ventricular pressure maximum rising and falling rates (±dp/dtmax) increased significantly in EPO treatment group (P<0.01). At the same time, left ventricular end-systolic diameter (LVESD), left ventricular end-diastolic diameter (LVEDD) and left ventricular end-diastolic pressure (LVEDP) were decreased in EPO treatment group (P<0.01). EPO reduced the degree of myocardial fibrosis caused by pressure overload (P<0.01) and decreased the expression of Nox2 and Nox4 at mRNA and protein levels in the myocardium (P<0.05 or P<0.01), and reduced the protein expression of myocardial inflammatory factors CD45, F4/80 and TGF-β. CONCLUSION: EPO inhibits rat myocar-dial fibrosis induced by pressure overload, improves heart functions by decreasing NADPH oxidase activity and inhibiting myocardial oxidative stress levels and myocardial inflammatory reaction.     

Effect of PPARδ activation on expression of MMP-9 and fibronectin in infarcted myocardium

AIM:To investigate the effect of peroxisome proliferator-activated receptor δ (PPARδ) activation with dietary GW610742X on the expression of matrix metalloproteinase-9 (MMP-9) and fibronectin (FN) in infarcted and remodeling myocardium. METHODS: Wistar rats were divided into 4 groups: control group, sham group, myocardial infarction (MI) group and MI+GW610742X (GW) group. The left coronary artery was ligated to establish the MI model. PPARδ activator GW610742X (100 mg·kg^-1·d^-1) was given to the rats in GW group. At the 3rd month of the procedure, the expression of PPARδ, MMP-9 and FN at mRNA and protein levels in the left ventricular free wall(LVFW) of the heart from each group was identified and the distribution of FN was detected by immunofluorescence. RESULTS: After 3 months following the procedure, obvious necrosis and fibrosis in LVFW were observed in MI group. The expression of PPARδ in MI group was higher than that in control, sham and GW groups (P<0.01), and PPARδ expression in GW group was lower than that in control and sham group (P<0.05). In MI and GW groups, the expression of MMP-9 was higher while the expression of FN was lower than those in control and sham group (P<0.05 or P<0.01). In GW group, the expression of MMP-9 was lower (P<0.05) while the expression of FN was higher (P<0.01) than those in MI group. Meanwhile, the expression of MMP-9 and FN in sham group was similar to those in control group (P>0.05). CONCLUSION: MMP-9 is upregulated and FN is downregulated in infarcted myocardium during the remodeling process. Activation of PPARδ inhibits the upregulation of MMP-9 and degradation of FN, thus ameliorating the myocardial remodeling.     

Inhibitory effect of aerobic exercise on left ventricular remodeling and sympathetic neural remodeling in rats with heart failure after myocardial infarction

AIM: To investigate the effects of long-term aerobic exercise on the heart and sympathetic neural remodeling (structure and function remodeling) in heart failure rats induced by myocardial infarction. METHODS: Heart failure model after myocardial infarction was performed by ligating anterior descending coronary artery in the Wistar rats. Four weeks after operation, the rats were randomly divided into sham operation sedentary (S) group, heart failure sedentary (H) group and heart failure exercise (HE) group. The animals in HE group underwent 10-week treadmill running, while those in S group and H group were sustained in a resting state. The cardiac structure and function including left ventricular internal diameter at diastole (LVIDd), left ventricular internal diameter at systole (LVIDs), left ventricular anterior wall diameter at diastole (LVAWDd), left ventricular anterior wall diameter at systole (LVAWDs), left ventricular posterior wall diameter at diastole (LVPWDd) and left ventricular posterior wall diameter at systole (LVPWDs), and cardiac function parameters including fractional shortening (FS) and left ventricular ejection fraction (LVEF) were measured by echocardiography. The myocardium was collected for histopathological observation with Masson staining, and the collagen volume fraction (CVF) was determined. The concentrations of norepinephrine (NE) in the myocardium and plasma were measured by high-pressure liquid chromatography. The frequency domain analysis was applied for determining the heart rate variability (HRV) via subcutaneous recording electrode involving total power (TP), normalized low power (LFn), normalized high power (HFn) and LF/HF ratio. The mRNA expression of collagen type I (Col-I), collagen type III (Col-III), atrial natriuretic factor (ANF), α-myosin heavy chain (α-MHC), β-myosin heavy chain (β-MHC), sarcoplasmic endoplasmic reticulum Ca²⁺-ATPase (SERCA2a) was detected by real-time PCR. The protein levels of nerve growth factor (NGF) and its receptor (TrkA), and tyrosine hydroxylase (TH) were measured by Western blotting. RESULTS: (1) Compared with S group, body weight (BW), LVIDd, FS, LVEF, TP, HFn, the mRNA expression of α-MHC and SERCA2a, and the protein levels of NGF, TrkA and TH decreased (P<0.05). Left ventricular weight (LVW), left ventricular mass index (LVMI), LVAWDd, LVAWDs, LVPWDd, LVPWDs, CVF, plasma and myocardial NE content, LFn, LF/HF, and the mRNA expression of ANF, β-MHC, Col-I and Col-III increased (P<0.05) in H group. (2) Compared with H group, LVW, LVMI, LVIDd, FS, LVEF, TP, HFn, the mRNA expression of α-MHC and SERCA2a, and the protein levels of NGF, TrkA and TH were raised (P<0.05), while CVF, plasma and myocardial NE content, LFn, LF/HF, and the mRNA expression of ANF, β-MHC, Col-I and Col-III decreased (P<0.05) in HE group. CONCLUSION: Long-term aerobic exercise training leads to inhibition of heart and sympathetic neural remodeling and improvement of cardiac function and autonomic modulation in the rats after myocardial infarction.     

Role of PARP-2 in cardiac hypertrophy in rats

AIM: To investigate the expression of poly(ADP-ribose) polymerase-2 (PARP-2) during rat cardiac hypertrophy in vitro and in vivo, and to explore the effects of PARP-2 on the cardiac hypertrophy. METHODS: Abdominal aortic coarctation (AAC) was performed to establish a model of pressure overload-induced cardiac hypertrophy in SD rats. The expression of PARP-2 at mRNA and protein levels in the myocardium was determined by real-time PCR and Western blot. The hypertrophy model of the cardiomyocytes was induced by treating the cells with angiotensin Ⅱ (AngⅡ). PARP-2 was knocked down by siRNAs in neonatal rat cardiomyocytes and the cardiomyocyte hypertrophy was evaluated by measuring the mRNA levels of ANF, BNP, and β-MHC and the cellular surface area. RESULTS: The expression of PARP-2 at mRNA and protein levels was both increased in the AAC rats as compared with those in the sham animals. The expression of PARP-2 at mRNA and protein levels was also increased in a time- and concentration-dependent manner in AngⅡ-induced hypertrophy model of the cardiomyocytes. In the neonatal rat cardiomyocytes, knockdown of PARP-2 expression by siRNA attenuated AngⅡ-induced cardiac hypertrophy of the cardiomyocytes, indicating that endogenous PARP-2 played a positive regulatory role in cardiac hypertrophy. CONCLUSION: The mRNA and protein levels of PARP-2 increase in the in vitro and in vivo models of cardiac hypertrophy. Knockdown of PARP-2 protects cardiomyocytes from hypertrophy.