Abstract-Senescence of endothelial cells (ECs) may contribute to age-associated cardiovascular diseases, including atherosclerosis and hypertension. The functional and gene expression changes associated with cellular senescence are poorly understood. Here, we have analyzed the expression, during EC senescence, of 2 different isoforms (L, long; S, short) of endoglin, an auxiliary transforming growth factor (TGF)- receptor involved in vascular remodeling and angiogenesis. As evidenced by RT-PCR, the S/L ratio of endoglin isoforms was increased during senescence of human ECs in vitro, as well as during aging of mice in vascularized tissues. Next, the effect of S-endoglin protein on the TGF- receptor complex was studied. As revealed by coimmunoprecipitation assays, S-endoglin was able to interact with both TGF- type I receptors, ALK5 and ALK1, although the interaction with ALK5 was stronger than with ALK1. S-endoglin conferred a lower proliferation rate to ECs and behaved differently from L-endoglin in relation to TGF--responsive reporters with ALK1 or ALK5 specificities, mimicking the behavior of the endothelial senescence markers Id1 and plasminogen activator inhibitor-1. In situ hybridization studies demonstrated the expression of S-endoglin in the endothelium from human arteries. Transgenic mice overexpressing S-endoglin in ECs showed hypertension, decreased hypertensive response to NO inhibition, decreased vasodilatory response to TGF- 1 administration, and decreased endothelial nitric oxide synthase expression in lungs and kidneys, supporting the involvement of S-endoglin in the NO-dependent vascular homeostasis. Taken together, these results suggest that S-endoglin is induced during endothelial senescence and may contribute to age-dependent vascular pathology. Key Words: endothelial cells Ⅲ hypertension Ⅲ TGF- receptors Ⅲ aging Ⅲ endoglin C ardiovascular repair mechanisms become progressively impaired with age, and advanced age is itself a significant risk factor for cardiovascular disease. 1 Defects in age-associated remodeling of the vascular wall are, in part, attributable to the declining of endothelial function. 2,3 Thus, vascular processes such as angiogenesis, nutrient trafficking, vascular repair, and homeostasis are impaired because of attenuation of endothelial cell (EC) proliferation, migration, or dilator responses. EC proliferation diminishes with age, entering in an irreversible senescent state. 4 Senescent cells undergo growth arrest in the G 1 phase and a change in morphology and metabolism. Some of the senescence-associated changes include cellular enlargement, altered response to growth factors such as transforming growth factor (TGF)- 1 , and expression of senescence-associated -galactosidase (SA--gal). 5 Also, alterations in the expression and/or activity of the endothelial nitric oxide synthase (eNOS) are critical for the attenuation of the endothelium-dependent dilatory responses with age. 6,7 Unfortunately, most of the functional and gene expression changes associated with...