Application of FTY720 (a synthetic analogue structurally similar to sphingosine) induced Pak1 activation and restrained the development of CH in wild type mice with pressure overload stress, but not in Pak1-deficient mice (Pak1cko) mice with pressure overload stress, suggesting the anti-hypertrophic effect of FTY720 was likely due to its effect on activation of Pak1[6]. This evidence concerns the gene PAK1 and cyclic hematopoiesis.