Abstract 1617: Modulating MDM2 - P53 Pathway by Postconditioning
Background: Ischemia reperfusion has been shown to be associated with P53 activation in different organs and tissues, including myocardium. Postconditioning (postcon) protects the heart by reducing both necrotic and apoptotic cell death. However, the molecular mechanisms responsible for this protection are still under extensive research. The role of MDM2-P53 pathway in postcon has not been investigated. Hypothesis: Postcon protects the heart by modulating MDM2 - P53 pathway via regulation of MDM2, P53 expression and their interaction.
Methods: In anesthetized open-chest rats, the left coronary artery (LCA) was occluded for 30 min and reperfused for 3 hours. Rats were randomly assigned to 4 groups:
Control: saline vehicle;
Postcon: three cycles of 10-s reperfusion followed by 10-s re-occlusion during the first minute of reperfusion;
Nutlin-3 ( a blocker of MDM2 and P53 binding) 0.5 mg/Kg 5 min before Postcon;
Nutlin-3 0.5 mg/Kg alone.
Another set of experiment was performed in the 4 groups for expression of P53, MDM2 and phospho-MDM2 in AAR tissue by Western blot. Immunoprecipiation was performed to show MDM2 and P53 binding.
Results: The area at risk by LCA occlusion, expressed as a percentage of left ventricular mass (AAR/LV) was comparable among groups. Infarct size, expressed as a percentage of the area at risk (AN/AAR), was significantly reduced in the Postcon group (42.4 ± 1.6% vs control 58.9 ± 4.1%, P<0.05). Interestingly, Nutlin-3 given before postcon reversed the infarct size reduction (54.3 ± 1.5%) and Ntlin-3 alone had no effect on infarct size (55.4 ± 3.8%) . Western blot analysis showed that postcon significantly reduced P53 expression, but increased phospho-MDM2 (ser 166) and phospho-BAD expression in AAR tissue compared to control. MDM2 and P53 interaction with immunoprecipitation was significantly increased in postcon group, accordingly Nutlin-3 given before postcon attenuated MDM2 binding with P53.
Postcon reduces P53 expression and increases MDM2-P53 binding;
inhibition of MDM2 and P53 binding blocked the cardioprotection of postcon.
Therefore, modulating MDM2-P53 pathway plays a role in cardioprotection of postcon.