PP2Cm overexpression alleviates MI/R injury mediated by a BCAA catabolism defect and oxidative damagein T2DM mice

[GW30-e0056]

Authors: Kun Lian, Ling Tao

Department of Cardiology, Xijing Hospital, Fourth Military Medical University

OBJECTIVES Diabetic patients are more sensitive tomyocardial ischemia-reperfusion (MI/R) injury. Branched-chain amino acids (BCAA) catabolism is defective and mitochondrial phosphatase 2C (PP2Cm) expression is reduced in the diabetic state. However, the role of PP2Cm and BCAA in diabetes with MI/R injury remains unclear. This study aims to determine the mechanism of reduced PP2Cm expression and investigate whether PP2Cm and BCAA have a cardioprotective effect in diabetes with MI/R injury.

METHODS C57BL/6 mice were fed a high-fat diet (HFD) and injected intraperitoneally with a dose of streptozotocin (25 mg/kg) twice to generate T2DM model mice. C57BL/6 mice (WT), type 2 diabetes (T2DM), PP2Cm–/– mice, were used in this study. For T2DM mice, PP2Cm-specific adenovirus was delivered to generate diabetic mice with PP2Cm overexpression. The T2DM mice were also treated with with BDK inhibitor BT2, while the PP2Cm–/– mice were treated with MnTBAP (manganese (III) tetrakis (4-benzoic acid)porphyrin chloride). Myocardial infarction/reperfusion (MI/R) was produced simultaneously in all types of mice. Additionally, WT and PP2Cm–/– mice treated with BT2 and expressing adenovirus were analyzed. H9C2 cells were treated with BCAA and BCKA. After H9C2 cells were treated with BCKA and underwent simulated ischemia-reperfusion (SI/R), BT2 and MnTBAP were added. Cardiac function, apoptosis, BCAA metabolism and oxidative damage were assayed.

RESULTS PP2Cm protein levels were significantly decreased in the diabetic heart. Under PP2Cm-overexpressing T2DM mice injury, cardiac function was improved due to a decrease of myocardial infarct size and the increase of LVEF. The Apoptosis rate was decreased as evidenced by Caspase-3 activity and the number of TUNEL positive cardiomyocytes. Cardiac BCAA and BCKA levels, as well as the ratio of p-BCKDE1α/BCKDE1α significantly increased (P<0.01) and BCKD activity significantly decreased (P<0.01) in T2DM mice. After BT2 treatment in T2DM mice with MI/R injury, the BCAA cataboliam defect was alleviated. At the same time, an improvement of Cardiac function and reduction of apoptosis was observed. In PP2Cm–/– mice, aBCAA catabolism defect and MI/R injury was observed. After PP2Cm overexpression and BT2 treatment, BCAA catabolism defect and MI/R injury was obviously alleviated. In PP2Cm–/– mice, oxidative damage was observed evident as an the increases in superoxide concentration, a decrease of MnSOD, complex I and III activities, and ATP levels as well as mitochondrial damage. Supplementation with MnTBAP obviously ameliorated this oxidative damage and MI/R injury in PP2Cm–/– mice. Treatment with BCKA (1.5-3 mM) resulted in significant decreases cell viability, and significant increases in the percentage of LDH release, apoptosis in H9C2 cells with SI/R injury. After BT2 and MnTBAP treatment, these effects were obviously alleviated.

CONCLUSIONS T2DM induced a downregulation of PP2Cm and reduced the defect of BCAA metabolism. PP2Cm directly mediated the defect of BCAA catabolism and oxidative damage. Overexpression PP2Cm alleviated MI/R injury by reducing the catabolism of BCAA and oxidative damage.