Abstract 1064: Pellino-1: A Novel Candidate In Vegf/Flk-1/MKK2 Signaling In Ischemic Preconditioning Induced Cardioprotection: A Study Using Flk +/− and MKK2 −/− Knockout Mice.
VEGF modulates the complex process of angiogenesis and other various aspects of endothelial cell function through either of its two tyrosine kinase receptors, VEGFR1/Flt-1 or VEGFR2/Flk1/ KDR via its target protein MKK2. In the present study we used Flk1 +/− and MKK2 −/− knockout mice in an attempt to address an important clinical issue by identifying potential downstream candidates of VEGF signaling through Flk1 receptor that trigger cardioprotective signal during ischemic preconditioning (IP). Mouse hearts were subjected to 30 min of global ischemia and 2 hours of reperfusion (IR) in the Isolated Working Heart model. It is known that IP (4min of ischemia + 6min reperfusion, 4 cycles, before 30 min of ischemia) induces cardioprotection through the activation of the VEGF signaling cascade. The mice were randomly divided into 6 groups for both the gene knockout (KO) studies:
Wild Type-Baseline (WTBL),
FlkBL/ MKK2BL (KOBL),
Significant reduction in left ventricular functional recovery through out reperfusion (dp/dt = 605 vs 884), diminished coronary flow (1.9 vs 2.4) and aortic flow (0.16 vs 1.2) and increased infarct size (38.4% vs. 28.41%) after reperfusion were observed in FlkIR, compared to WTIR. As expected we observed disruption in IP induced cardioprotection in FlkIP compared to WTIP. Affymetrix gene chip analysis demonstrated significant downregulation of genes (Pellino-1, MKK2, NF-Î°B) which are thought to play important roles in cardioprotection after ischemic insults in the Flk +/− mice compared to WT. These results were further validated at the mRNA expression level with Real Time PCR. Pellino-1 (Pel-1) was found to be significantly downregulated in FlkBL (0.74 vs 1), FlkIR (1.29 vs 1.35) and FlkPC (1.35 vs 1.49) as compared to their respective controls. We further validated the mRNA levels of Pel-1using Real Time PCR and RT-PCR in the MKK2 −/− mice and found that it, remained unaffected in MKK2BL as compared to its WTBL, and increased as expected in MKK2PC as compared to both MKK2BL and FlkPC (2.48 vs 1.2 and 2.48 vs 1.35, respectively). Therefore this study validated for the first time that Pel-1 is a novel downstream mediator in VEGF/FLK1 signaling and it induces IP mediated cardioprotection via MKK2 signaling.