Statins Directly Activate Erk5 and Reduce Endothelial Dysfunction and Acute Allograft Rejection

Rationale: The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, or statins, are principal therapeutic agents for the treatment of hypercholesteremia. Statins, however, appear to also exert cholesterol-independent pleiotropic effects, such as improvement of endothelial (EC) function, stabilization of fibrous plaques, and decrease vascular inflammation. It is now well established that statins are beneficial in the prevention of cardiovascular disease and also widely used for suppressing cardiac allograft rejection. Previously, we have reported anti-inflammatory effect of ERK5 kinase in ECs. Methods and Results: In this study, we screened small molecules that activate ERK5 using high throughput screening, and identified statins as strong activators of the transcriptional activity of ERK5. In particular, we have found that pitavastatin increases ERK5 transcriptional activity, KLF2 promoter activity, and eNOS mRNA expression in ECs. These effects are abolished by the depletion of ERK5, but not its direct upstream kinase, MEK5. In addition, pitavastatin directly and dose-dependently activates ERK5 kinase activity in an in vitro kinase reaction assay, suggesting that ERK5 is a direct target of this statin. To examine the functional role of EC ERK5 activation by the statin in vivo, we utilized inducible endothelial ERK5 knock out (EC-ERK5-KO) mice and evaluated the effect of pitavastatin on EC function and acute allograft rejection. Depletion of ERK5 in ECs resulted in significant EC inflammation and dysfunction in vivo. Although pitavastatin reduced leukocyte rolling and vascular reactivity in mesebteruc microvessels of diabetic mice and prolonged allograft survival in a full allomismatch combination model, these protective effects were lost in EC-ERK5-KO mice. Conclusion: These data suggest the crucial role of ERK5 in pleiotropic effects of statins on EC dysfunction and allograft rejection in vivo.