Abstract 18592: A Hmg-Coa Reductase Inhibitor (Statin) Directly Activates Endothelial Erk5 and Prevents Endothelial Dysfunction and Acute Cardiac Allograft Rejection

Background: Statins inhibit HMG-CoA reductase and are principal therapeutic agents for the treatment of hypercholesteremia. However, statins also have cholesterol-independent effects such as improving endothelial cell (EC) functions, preventing cardiovascular diseases and suppressing cardiac allograft rejection. How statins exert these cholesterol-independent effects is not known. Because ERK5 exerts beneficial effects on ECs and is anti-atherogenic, it may play a role in these statin effects. Methods and Results: We screened small molecules that activate ERK5 using high throughput screening and found that several statins were strong activators of ERK5 transcriptional activity. We found pitavastatin was especially effective. It increased ERK5 transcriptional activity and the promoter activity and mRNA expression of KLF2 and eNOS in ECs. These effects were abolished by the depletion of ERK5 but not its direct upstream kinase, MEK5. We found that pitavastatin dose-dependently activated ERK5 kinase activity in an in vitro kinase assay, suggesting that ERK5 is a direct target of statins. To examine roles of statin in EC ERK5 activation in vivo, we used inducible endothelial ERK5 knock out (EC-ERK5-KO) mice. When EC ERK5 was depleted, these mice exhibited significantly increased EC inflammation (increased leukocyte rolling) and dysfunction (impaired vascular reactivity), and these conditions could not be corrected by pitavastatin. However, when the EC inflammation and dysfunction were induced in wild type (WT) mice by STZ treatment (i.e. diabetic), their conditions were reversed by pitavastatin. Interestingly, the heart from EC-ERK5-EKO mice had significantly increased mRNA levels of inflammatory genes (TNFα, MCP1, IL-1, IL-6) and decreased expression of an anti-inflammatory cytokine, IL-10. Hearts from EC-ERK5-KO and littermate WT mice were used to perform prolonged allograft survival in a full allomismatch combination model. After 5 days of transplantation, a robust increase in inflammatory gene expression was inhibited by pitavastatin in WT but not in EC-ERK5-EKO hearts. Conclusion: These data suggest a crucial role of endothelial ERK5 in the pleiotropic effects of statins on EC dysfunction and allograft rejection.