Study Of Proteasome Inhibitor MG-132 On Post-Infarction Myocardial Remodeling In Rats

ObjectiveThe uibiqitin-proteasome pathway has emerged as a important player in the degradation of cellular protein, it is concerned with the control of inflammatory processes, regulation of cell cycle, gene expression and cell apoptosis. The ubiquitin-proteasome system (UPS) is rich in the myocardial tissue, dysfunction of UPS play a role in myocardial ischemia, congestive heart failure and hypertrophy. Evidences have shown that cell apoptosis and inflammatory processes are important mechanism of myocardial remodeling after myocardial infarction. Nucleus factor kappa B (NF-κB) plays an important role in the development of inflammation and heat shock protein 70 (Hsp70) is concerned with cell apoptosis, whereas NF-κB and Hsp70 are controlled by UPS. Because the activation of NF-κB is increased and Hsp70 is decreased after myocardial infarction, proteasome inhibitor may attenuate myocardial remodeling through inhibiting activation of NF-κB and inducing expression of Hsp70. The aim of this study is to determine weather proteasome inhibitor MG-132, which had never been used in myocardial infarction model before, can improve myocardial remodeling after myocardial infarction.MethodsThe myocardial infarction model in Adult Sprague-Dawley rats was induced by ligation of left anterior descending coronary artery. Rats that survived over 24 hours after acute myocardial infarction were randomly divided into MG-132 intervention group (MG group),Pyrrolidine Dithiocarbamate intervention group (PDTC group),MG-132 intervention group(MG group) and MG-132 combined with Quercetin intervention group (MG + Q group), myocardial infarction group (MI group). In addtion, rats who did not ligated left anterior descending coronary artery were designated as sham-operated group(SH group). The intervention measures of the groups were as follows:MG group: MG-132 0.1mg/kg/d, intraperitoneal injection for 28 days. PDTC group: PDTC 80mg/kg, daily intraperitoneal injection for 28 days.MG+Q group: MG-132 0.1mg/kg, daily intraperitoneal injection and Quercetin 100mg/kg, daily intraperitoneal injection.. MI group: given normal saline for 28 days. SH group: given normal saline for 28 days.On 28th day, the changes of left ventricle structure were measured by echocardiography. Then, rats were killed, the weight of left ventricular was obtained and the left ventricular weight index (LVWI) was calculated, and infarct size was evaluated. The surface area, circumference, diameter of myocardial cells in non-infarct zone were measured by image analysis software after HE staining. By Sirius red staining, the total collagen, typeⅠandⅢcollagen volume fraction in non-infarcted zone were analyzed by image analysis software.The mRNA levels of NF-kappa B p65, IL-1β,MMP2 and HSP70 were determined by reverse transcription–polymerase chain reaction(RT-PCR), the protein levels of above-mentioned indicators and caspase-3 were determined by immunohistochemistry and western blot method. In addtion, myocardium cell apoptosis of non-infarct size was detected by TUNEL assay.ResultsCompared with SH group, the values of left ventricle posterior wall thickness (LVPWT) and left ventricle end diastolic diameter(LVEDD) were significantly increased in MI group and MG group (P<0.01), however, the value of left ventricle anterior wall thickness (LVAWT) was significantly decreased (P<0.01). The LVPWT, LVEDD and LVWI in MG group were significantly lower than those in MI group(P<0.01), whereas LVAWT in MG group significantly higher than that in MI group (P<0.01). NO rat was developed heart failure and dead in SH group. The morbidity and mortality of heart failure in MI group and MG group had no significant difference (P>0.05),The surface area, circumference, diameter of myocardial cell zone and the collagen volume fraction of total collagen, typeⅠ, typeⅢcollagen in non-infarct zone in MI group, MG group and PDTC group were significantly increased than those in SH group (P<0.01). Compared with MI group, the parameters above-mentioned in MG group and PDTC group were significantly decreased (P<0.01), especially in MG group, the difference between MG group and PDTC group had statistical significance (P<0.01).The mRNA levels and the protein levels of NF-kappa B p65, IL-1βand MMP2 in MI group, MG group and PDTC group were significantly increased compared with SH group (P<0.01).however, these parameters in MG group and PDTC group were significantly lower than those in MI group (P<0.01). The mRNA level and the protein expression level of NF-kappaB p65 and IL-1βin PDTC group were lower than those in MG group (P<0.01) , while the mRNA level and the protein expression level of MMP2 in PDTC group were higher than those in MG group(P<0.01).The apoptosis index in SH group, MI group, MG group and MG+Q group were respectively 0.89±0.12, 21.31±0.82, 5.27±0.51 and 7.15±0.41. Compared with the SH group, apoptosis index of myocardial cells in non-infarct zone in MI group, MG group and MG+Q group was increased significantly (P<0.01), however, this index in MG group and MG+Q group was lower than that in MI group (P<0.01),especially in MG group. Compared with the MG+Q group, this index in MG group was lower than that in MG+Q group (P<0.01).The mRNA levels and protein expression levels of HSP70 between MI group and SH group had no difference statistically, however, those in MG group and MG+Q group were increased significantly (P<0.01), especially in MG group(P<0.01). Compared with the MG+Q group, those in MG group was higher than that in MG+Q group (P<0.01).Compared with SH group, the protein expression levels of Caspase-3 in MI group, MG group and MG+Q group were increased significantly. however, the levels in MG group and MG+Q group were lower significantly than those in MI group(P<0.01), especially in MG group(P<0.01).Conclusion(1)proteasome inhibitor MG-132 can improved left ventricular structure remodeling and historic remodeling following acute myocardial infarction in rats.(2)MG-132 is able to inhibit the activation of NF-K B and the expression of inflammatory factor (such as IL-1β), as well as to increase the expression of HSP 70, to reduce the expression of Caspase-3, lead to apparent reduction of myocardial cell apoptosis. These maybe are the main mechanisms of MG-132 in improving remodeling following myocardial infact.(3)this experimental study is failed to demonstrate that MG-132 can reduce the morbidity and mortality of heart failure after myocardial infarct in rats.