Effect Of CGRP On Infracted Myocardium And Cardiac Stem Cell Recruitment After Acute Myocardial Infarction In Rats

Objective: The therapeutic effects of stem cells transplantation after acute myocardialinfarction (MI) have been widely recognized. However, its application may be limited byamplification cycle, immune rejection, survival rate, homing process, and communicationwith host cells. Stemness of cardiac stem cell (CSC) has been confirmed in multiplestudies. An agent recruiting inherent CSCs to participate in myocardial repair in situ afterMI may be more advantageous. Calcitonin gene related peptide (CGRP) is widelydistributed in the cardiovascular system and possesses strong cardioprotective effects.Multiple studies have confirmed that CGRP could promote proliferation and migration ofmesenchymal stem cells, endothelial cells, etc., and upregulate growth factors (bFGF,IGF-1,HGF) which can modulate the CSC biological effects. But in order to find outwhether the cardiovascular protective effect of CGRP is related to the CSC,rats weredirectly treated with CGRP in this study, to observe whether CGRP recruits CSC and toinvestigate the mechanism and its role in MI therapy.Methods:Rat acute MI model was induced by left anterior descending coronary arteryligation.104healthy SD rats were randomly divided into sham-operated group, controlgroup, and CGRP group. PBS (control group) or CGRP in PBS (CGRP group)(10μg/㎏)was injected into cardiac tissue after MI, while the rats in sham-operated group were onlygiven chest-open operation. The animals were sacrificed at3d,7d,14d and28d, with6rats ensured in each group at each point. Cardiac morphological changes were observed byHE, Masson and TTC staining; Cardiac function was assessed with echocardiography;Myocardial angiogenesis by immunological histological chemistry; VEGF with ELISA inmyocardial tissue; while CSC recruitment by immunofluorescence staining.Results:1.4weeks after operation, HE staining showed that in sham-operated group themyocardial cells were arranged orderly, without scar tissue; in control group, a large amount of myocardial cells were disappeared, with many disorderedly-arranged fibroticscar tissues; while compared with the control group, scar tissues were obviously fewer inCGRP group, with relatively more normal myocardial cells reserved. Masson stainingshowed that red myocardial cells were observed in sham-operated group, without any bluedyed collagen fiber; while a large number of blue collagen fibers could be seen in thecontrol group, where nucleus was dissolved and disappeared in the collagen, with lesssurvival myocardial cells; but collagen fibers was significantly reduced in CGRP group.2.4weeks after operation, LVDd, LVDs, FS and EF were assessed with echocardiography.The results showed that compared with the sham-operated group, both LVDd and LVDswere increased while FS and EF were decreased in the control group and CGRP group;compared with the control group, the above indexes were significantly improved in CGRPgroup (P<0.05).3. TTC staining showed that no infarct area was observed insham-operated group, while that was larger in the control group (31.72±4.00)%; comparedwith the control group, infarct size was obviously reduced in CGRP group (22.54±1.73)%(P<0.05).4. Immunohistochemical staining showed that capillary density in the peri-infactarea were increased in control group after MI compared with the sham-operated group(P<0.01); while that in CGRP group was increased even more significant than the controlgroup (P<0.01).5. ELISA was used to measure VEGF level of myocardial tissue on3,7,14and28days. VEGF levels in control group and CGRP group were obviously raised on3d, reached the peak on7d, fell on14day and decreased to the level of sham-operatedgroup on28d. On3,7, and14days, VEGF level of CGRP group was significantlyincreased than the control group (P<0.05).6. CSC recruitment was detected byimmunofluorescence staining on3,7, and14days. The results showed that numbers ofCSCs were increased on3d, reached the peak on7d and decreased significantly on14din the control group and CGRP group. Among them, CSCs were significantly increased inthe control group at each time point compared with the sham-operated group (P<0.05).CSCs in CGRP group were more obviously increased compared with the control group(P<0.05). Conclusion:1. CGRP could induce higher VEGF expression and promote angiogenesisin cardiac tissue, reduce the infarct size and left ventricular remodeling,improve the cardiacfunction, which has therapeutic effect on acute MI.2. CGRP could promote the CSCrecruitment in the infracted zone after acute MI, which reached the peak on the7thday.The mechanism could be related to VEGF.