| Objective: To investigate the effect and mechanism of JAK2/STAT3 pathway on myocardial protection of tetrodotoxin (TTX) cardioplegia in rat hearts.Methods: 24 Wistar rats were randomly divided into Group Control, Group TTX and Group TTX+AG490 (n=8). The left ventricular samples in Group Control were collected as pre-ischemia control through thoracotomy. After isolated heart Langendorff and Neely models were established the rat hearts in Group TTX were continuously perfused with Krebs-Henseleit (K-H) buffer solution for 30 minutes, arrested by TTX cardioplegia (4℃) for 60 minutes, underwent reperfusion with K-H buffer solution for 60 minutes, and then the left ventricular samples were collected for detections. The rat hearts in Group TTX+AG490 were perfused and reperfused with JAK2 inhibitor AG490 (5μmol/L) and K-H buffer solution under the same procedure as Group TTX. The protein expression indexes (PEI) of phosphorylated-STAT3 (p-STAT3), B-cell lymphoma-2 (Bcl-2) and heat shock protein 70 (HSP70) in myocardium were detected by immunohistochemical assay (IHC). In addition, p-STAT3 protein expression was detected by Western blot (WB). Both the activity of superoxide dismutase (SOD) and the content of maleic dialdehyde (MDA) in myocardial tissue homogenate were detected by colorimetry. The apoptosis index (AI) of cardiomyocyte was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL).Results: The PEI of p-STAT3 in Group Control, Group TTX and Group TTX+AG490 was 2.65±0.15%, 18.19±1.68% and 6.91±1.03% respectively. Arrested by TTX cardioplegia, the PEI of p-STAT3 in Group TTX and Group TTX+AG490 was higher than that in Group Control (P<0.05); treated with AG490, the PEI of p-STAT3 in Group TTX+AG490 was lower than that in Group TTX (P<0.05). The result of p-STAT3 protein expression detected by WB was similar to that by IHC.Arrested by TTX cardioplegia, the PEI of Bcl-2 in Group TTX (23.40±1.19%) and Group TTX+AG490 (11.47±1.15%) was higher than that (2.96±0.69%) in Group Control (P<0.05); treated with AG490, the PEI of Bcl-2 in Group TTX+AG490 was lower than that in Group TTX (P<0.05).Arrested by TTX cardioplegia, the PEI of HSP70 in Group TTX (22.63±1.15%) and Group TTX+AG490 (14.40±1.20%) was higher than that (2.52±0.58%) in Group Control (P<0.05); treated with AG490, the PEI of HSP70 in Group TTX+AG490 was lower than that in Group TTX (P<0.05).The PEI of Bcl-2 had a positive correlation with the PEI of p-STAT3 (r=0.743, P<0.05), and the PEI of HSP70 had also a positive correlation with that of p-STAT3 (r=0.826, P<0.05).The activity of SOD (U/mgprot) in Group Control, Group TTX and Group TTX+AG490 was 6.55±0.81, 20.56±1.16 and 13.55±1.17 respectively; and the content of MDA (nmol/mgprot) was 3.13±0.31, 8.55±0.53 and 15.52±1.04 respectively. Arrested by TTX cardioplegia, the activity of SOD and the content of MDA in Group TTX and Group TTX+AG490 were higher than those in Group Control (P<0.05); treated with AG490, the activity of SOD in Group TTX+AG490 was lower than that in Group TTX (P<0.05), but the content of MDA was higher than that in Group TTX (P<0.05).Arrested by TTX cardioplegia, AI in Group TTX (6.92±1.11%) and Group TTX+AG490 (16.21±1.40%) was higher than that (1.31±0.11%) in Group Control (P<0.05); treated with AG490, AI in Group TTX+AG490 was higher than that in Group TTX (P<0.05).Conclusions: It was suggested that JAK2/STAT3 pathway mediated myocardial protection of TTX cardioplegia in rat hearts. TTX could activiate JAK2/STAT3 pathway and alleviate myocardial ischemia/reperfusion injury through activating STAT3, upregulating the protein expressions of Bcl-2 and HSP70, and reducing apoptotic cardiomyocytes; meanwhile enhancing the activity of SOD, and decreasing the content of MDA.
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