Regulatory effects of PI3K/AKT2/mTOR signaling pathway on autophagy activation in cardiac tissues of mice with vial myocarditis

Abstract

Objective To study the phosphorylation of AKT2 protein and autophagy activation in cardiac tissues of mice infected with coxsackievirus B3 (CVB3) for further analyzing the regulatory mechanism of PI3K/AKT2/mTOR signaling pathway on autophagy activation in viral myocarditis. Methods Thirty BALB/c mice were randomly divided into three groups (n=10): control group, myocarditis group and AKT activator-treated group. Those in the latter two groups were intraperitoneally injected with CVB3 to establish the mouse model of acute viral myocarditis. Daily intraperitoneal injection of 0.04 mg/g of Akt activator (SC79) was given to each mouse in the AKT activator-treated group 24 hours after CVB3 infection for 7 consecutive days, while the mice in the other two groups were given the same dose of normal saline. HE staining was used to observe the infiltration of inflammatory cells and tissue necrosis. Expression of CVB3 and inflammatory cytokines such as IL-1β and IL-6 in cardiac tissues at mRNA level was detected by q-PCR. Brain natriuretic peptide (BNP) and cardiac troponin I (cTnI) were measured by ELISA to evaluate myocardial injury. Changes in the expression of autophagy-related protein LC3 and Beclin1 at protein level as well as PI3K/AKT2/mTOR pathway were analyzed by Western blot assay. Results Compared with the control group, massive inflammatory cell infiltration was observed in cardiac specimens of mice with myocarditis, but no obvious tissue necrosis was detected. Moreover, expression of CVB3 and inflammatory factors in cardiac tissues at mRNA level, levels of BNP and cTnI in blood, LC3Ⅱ to LC3Ⅰratio as well as Beclin1 protein level in cardiac tissues were significantly increased after CVB3 infection (P<0.05), whereas the activity of PI3K/AKT2/mTOR signaling pathway was decreased. AKT activator not only down-regulated the LC3Ⅱ to LC3Ⅰratio and the expression of Beclin1 protein, but also enhanced the activation of PI3K/AKT2/mTOR signaling pathway in cardiac tissues of mice with myocarditis (P<0.05). Conclusion Enhanced autophagy and suppressed PI3K/AKT2/mTOR signaling pathway are observed in cardiac tissues of mice with myocarditis, indicating that the activation of autophagy may be regulated by PI3K/AKT2/mTOR signaling pathway. Key words: Autophagy; Myocarditis; PI3K/AKT2/mTOR signaling pathway