Abstract: Objective: To investigate the effect of miR-125b on the ventricular remodeling after myocardial infarction in the rats via phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway,and to elucidate itsmechanism. Methods: A total of 75 rats were divided into sham operation group, myocardial infarction group and miR-125b inhibitor group, with 25 rats in each group.The acute myocardial infarction models were established in the rats in myocardial infarction group and miR-125b inhibitor group.The rats in miR-125b inhibitor group was injected with miR-125b inhibitor via the tail vein.The rats were sacrificed 4 weeks later,the body weights were recorded;the hearts were obtained,and the big vessel and left and right auricular appendix were cut out;the heart weights were weighed.The heart weight/body weight (HW/BW), (left ventricle + ventricular septum) weight/body weight (LV+S)/BW, (left ventricular+ventricular septum) weight/heart weight (LV+S)/HW were calculated. HE staining was used to observe the morphological changes of myocardium tissue. Masson staining was used to observe the myocardial fibrosis,and the collagen volume integral of myocardium was calculated.Immunofluorescence staining was used to observe the expression levels of type Ⅰ collagen and type Ⅲ collagen proteins in the myocardium tissue of the rats. Western blotting method was used to detect the expression levels of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), PI3K, Akt and phosphorylated Akt (p-Akt) in the peripheral region of myocardial infarction of the rats. Results: The HE staining results showed that the myocarclial cells in sham operation group were arranged neatly;the myocardial cells in myocardial infaction group had hypertrophy and disordered arrangement; the myocardial cells in miR-125b inhibitor group were arranged neatly.Compared with sham operation group,the HW/BW, (LV+S)/BW and (LV+S)/HW of the rats in myocardial infarction group were elevated (P<0.05),the collagen volume integral was increased (P<0.05),the protein expression levels of type Ⅰ collagen and type Ⅲ collagen were increased (P<0.05),the expression levels ANP and BNP proteins were increased (P<0.05), and the expression levels of PI3K and p-Akt proteins were decreased (P<0.05).Compared with myocardial infarction group,the HW/BW, (LV+S)/BW and (LV+S)/HW of the rats in miR-125 b inhibitor group were decreased (P<0.05), the collagen volume integral was decreased (P<0.05),the expression levels of type Ⅰ collagen and type Ⅲ collagen proteins were decreased (P<0.05),the expression levels of ANP and BNP proteins were decreased (P<0.05), and the expression levels of PI3K and p-Akt proteins were increased(P<0.05). Conclusion: Inhibition of miR-125b can inhibit ventricular remodeling after myocardial infarction in the rats by inhibiting the PI3K/Akt signaling pathway,and plays an important role in reversing ventricular remodeling after myocardial infarction

Key words: micro RNA-125b, phosphatidylinositol 3 kinase, protein kinase B, myocardial infarction, ventricular remodeling