Abstract 5413: Constitutive Cox-2 Activity In Cardiomyocytes Confers Permanent Cardioprotection. Role Of Arachidonic Acid Depletion
Different lines of evidence suggest that COX-2 could play a cardioprotective role but direct data is lacking. The aim of this study was to determine the effect of constitutive expression of COX-2 on cardiomyocyte tolerance to ischemia-reperfusion injury and its molecular mechanisms.
Methods and Results: We generated new transgenic mice (B6D2-Tg (MHC-PTGS2)17Upme) that constitutively express functional human COX-2 in cardiomyocytes under the control of the α-myosin heavy chain promoter. COX-2 expression and activity in cardiomyocytes was confirmed by immunoblotting, immunofluorescence and by increased levels of PGE2 and PGI2. Histological and echocardiographic analysis revealed no differences in the phenotype of transgenic mice (TgCOX-2) with respect to wild type (Wt) mice. Isolated TgCOX-2 hearts reperfused after 40 min of ischemia improved functional recovery (32.9±6.2% vs. 9.45±4.4%, P=0.004) and reduced cell death assessed by LDH release (43%, P<0.001) and triphenyltetrazolium staining (41%, P=0.002). Tolerance to ischemia/reperfusion was not further increased by ischemic preconditioning. Pretreatment of mice with the COX-2 inhibitor DFU resulted in a 61% reduction of PGE2 levels, abolished PGI2 increase and attenuated cardioprotection. No differences in myocardial cAMP levels were detected between Wt and TgCOX-2 mice. H+-NMR spectroscopy of TgCOX-2 hearts showed a marked reduction in unsaturated fatty acids. H+-H+ correlation spectra revealed that this reduction is attributable to unsterified arachidonic acid.
Conclusions: This study demonstrates that constitutive expression of COX-2 in cardiomyocytes confers a permanent cardioprotective state to the heart against reperfusion injury of magnitude similar to that obtained with ischemic preconditioning and without functional or inflammatory consequences. This effect appears to be related to increased PGE2 synthesis and reduced arachidonic acid content.