LAUSR

ABSTRACT Prolonged and intense stress can exceed the body's normal self-regulation and limited compensatory and repair capacity, resulting in pathological damage to the body. In this study, we established a rat stress myocardial injury model to explore the protective effect of melatonin (MLT) on stress myocardial injury and its possible mechanisms of action. Adult female Sprague-Dawley (SD) rats were randomly divided into 5 groups: blank control group (NC), stress myocardial injury group (SMI), MLT low-dose group (MLTL), MLT medium-dose group (MLTM), and MLT high-dose group (MLTH), and 10 rats in each group were used to establish a stress myocardial injury model by the water immersion restraint method. We observed the changes in body weight and tail vein glucose of each group. Serum levels of corticosterone (Cort), creatine kinase isoenzyme (CK-MB), Troponin Ⅰ (Tn-Ⅰ) and activity of lactic acid dehydrogenase (LDH) were measured by ELISA. Transcriptome sequencing was used to find differentially expressed genes in the control and model groups and the results were verified by fluorescence quantitative RT-qPCR. HE staining was used to visualize the pathological changes in the heart tissue of each group and Western Blot was used to study the differences in protein expression in the cardiomyocytes of each group to further corroborate the results. The body weight growth rate of rats in the SMI group was significantly lower than that of the NC group (P < 0.01), and the body weight growth rate of rats in the MLTH group was significantly higher than that of the SMI group (P < 0.05) with no significant difference compared to the NC group rats. The mean blood glucose of rats in the SMI group was significantly higher compared to the NC group (P < 0.001), while the mean blood glucose of rats in the MLT administration groups was dose-dependently reduced compared to the SMI group. By RNA-seq and bioinformatics tools such as KEEG and GO, we found that the circadian clock-related genes Ciart, Arnt1, Per1, and Dbp were significantly down-regulated in the SMI group during water immersion stress, and differentially expressed genes were enriched in the p38MAPK signaling pathway and p53 signaling pathway. Moreover, genes related to inflammation and apoptosis were differentially expressed. ELISA results showed that Cort, CK-MB and Tn-Ⅰ levels were significantly higher in the SMI group compared to the NC group (p < 0.01) and that melatonin reduced the levels of Cort, CK-MB, and Tn-Ⅰ and decreased LDH activity in rat serum. HE staining results showed that melatonin could attenuate stress-generated myocardial injury. Western Blot showed that melatonin reduced the expression of p38MAPK, p53, Bax, and Caspase3 and increased the expression of Bcl-2 protein in rat heart. Melatonin can inhibit myocardial injury caused by water immersion, and its mechanism of action may be related to the regulation of the expression of circadian clock genes such as Ciart, Arnt1, Per1, and Dbp, the inhibition of the expression of pro-apoptotic proteins such as p38MAPK, p53, Bax and Caspase3, and the increase of the expression of Bcl-2 anti-apoptotic protein.