OBJECTIVETo explore the molecular mechanism of microRNA-21 in myocardial damage of rats in the early stage of severe scald injury by observing the expression of microRNA-21 and programmed cell death 4 (PDCD4) in myocardial tissue of rat and to validate the relationship between them in cell model.

METHODS(1) Forty SD rats were divided into sham injury group (n =8, sham injured) and scald injury group (n =32, inflicted with 30% TBSA full-thickness scald on the back) according to the random number table. The left ventricular tissue was collected from rats in sham injury group at post injury hour 1 without any fluid infusion. Rats in scald injury group were given an intraperitoneal injection of lactic acid Ringer's solution and 8 rats were respectively sacrificed at post injury hour 3, 6, 12, 24 to harvest left ventricular tissue. The expression of microRNA-21 in myocardial tissue was assessed by real-time fluorescent quantitative RT-PCR. The protein expression of PDCD4 in myocardial tissue was assessed by Western blotting. (2) Rat myocardial cell line H9C2 was divided into microRNA-21 inhibitor group (cells were transfected with microRNA-21 inhibitor) and negative transfection control group (cells were transfected with negative control of microRNA inhibitor) according to the random number table. At post transfection hour 48, real-time fluorescent quantitative RT-PCR and Western blotting were performed respectively to determine the mRNA and protein expression levels of PDCD4 in cells. Data were processed with one-way analysis of variance, LSD-t and two independent samples t test. The relationship between microRNA-21 expression and PDCD4 protein level in myocardial tissue of rats was assessed by linear correlation analysis.

RESULTS(1) The expression levels of microRNA-21 in myocardial tissue of rats in sham injury group at post injury hour 1 and in scald injury group at post injury hour 3, 6, 12, 24 were respectively 0. 96 ± 0. 13, 0. 44 ± 0. 08, 0. 42 ± 0. 10, 0.33 +0.07, and 0.61 0.10 (F = 27.331, P <0.001). Compared with that in myocardial tissue of rats in sham injury group at post injury hour 1, expression level of microRNA-21 was significantly decreased in scald injury group at post injury hour 3, 6, 12, 24 (with t values from 4. 558 to 9.410, P values below 0.01). The protein expression levels of PDCD4 in myocardial tissue of rats in sham injury group at post injury hour 1 and in scald injury group at post injury hour 3, 6, 12, 24 were respectively 0.44 ± 0.05, 0.60 ± 0.09, 0.92 ± 0. 15, 0. 86 ± 0.11, and 0.57 ± 0. 10 (F =8.622, P =0.003). Compared with that in sham injury group at post injury hour 1, protein expression level of PDCD4 was significantly increased in scald injury group at post injury hour 6 and 12 (with t values respectively 4. 968 and 4. 122, P values below 0.01). A significant negative correlation between the expression of microRNA-21 and PDCD4 protein in myocardial tissue of rats of scald injury group was observed at each time point (r = -0. 572, P = 0. 026). (2) The mRNA and protein expression levels of PDCD4 of myocardial cells in microRNA-21 inhibitor group were respectively 1.73 ± 0. 29 and 0. 38 ± 0. 08, which were significantly higher than those in negative transfection control group (0.95 ± 0.14 and 0.23 ± 0.03, with t values respectively 4. 857 and 3.356, P <0.05 or P <0.01).

CONCLUSIONSExpression of microRNA-21 was decreased, while expression of PDCD4 was increased, in myocardial tissue of rats in the early stage of severe scald injury. MicroRNA-21 might participate in myocardial damage in the early stage of scald injury by negatively regulating expression of PDCD4.