Identification of CD44 as a senescence-induced cell adhesion gene responsible for the enhanced monocyte recruitment to senescent endothelial cells.

The mechanism that is responsible for progression of atherosclerosis seen with increasing age remains controversial. This issue was addressed in the present study, by searching for genes that are uniquely expressed in senescent endothelial cells and functionally involved in inflammatory leukocyte adhesion recognized as a critical step in the initiation of atherogenesis. Senescent human umbilical vein endothelial cells (HUVECs) prepared by continuous subculturing in vitro showed higher binding affinity for monocytes (THP-1 cells, human acute monocytic leukemia cell line) compared with young cells. Gene expression profiles between young and senescent endothelial cells were compared by the cDNA microarray method, and CD44 was identified as one of the "senescence-induced cell adhesion genes" whose expression was upregulated in senescent cells and whose gene ontology annotation indicated their role in cell adhesion. The enhanced gene expression of CD44 in senescent endothelial cells was verified both at the mRNA and protein levels. Adhesion of monocytes to senescent endothelial cells was significantly reduced following pretreatment of endothelial cells with the CD44 antibody or small-interfering RNA, thus reinforcing the critical role of CD44 in the inflammatory event. Exogenous expression of CD44 in young HUVECs and in human aortic endothelial cells led to an increase in monocyte adhesion. CD44 expression levels in the rat aorta endothelium were found to increase in an age-dependent manner, as determined by immunohistochemistry and Western blotting. CD44 and other senescence-induced cell adhesion genes identified in this study may provide the novel targets for the prevention of inflammatory leukocyte adhesion leading to the development atherosclerosis.