eNOS Activity Is Reduced in Senescent Human Endothelial Cells

Abstract

Abstract-Advanced age is associated with endothelial dysfunction and increased risk for atherosclerosis. However, the mechanisms for these observed effects are not clear. To clarify the association between aging and loss of endothelial function, young human aortic endothelial cells (HAECs), senescent HAECs transfected with control vector, and immortalized HAECs containing human telomerase reverse transcriptase (hTERT) were compared for expression of endothelial nitric oxide synthase (eNOS) and production of NO. To investigate a specific function modulated by endothelial NO, adhesion of monocytes under basal conditions as well as after exposure to TNF-␣ was assessed. A decrease in eNOS mRNA, protein, and activity was observed in endothelial cells at senescence as compared with young HAEC; this effect was blunted in hTERT cells. In all cells, shear stress induced a greater increase in the expression of eNOS protein with the final result being higher levels in hTERT compared with senescent cells. Basal monocyte binding was significantly elevated on aged endothelial cells compared with parental and hTERT cells. Exposure of TNF-␣ resulted in a 2-fold increase in monocyte adhesion in senescent cells, whereas this effect was reduced in cells transfected with hTERT. Prior exposure to fluid flow significantly reduced subsequent monocyte adhesion in all groups. These studies demonstrate that replicative aging results in decreased endothelial expression of eNOS accompanied by enhanced monocyte binding. Key Words: aging Ⅲ telomerase Ⅲ atherosclerosis Ⅲ nitric oxide Ⅲ shear stress V ascular endothelial cells play an important role in maintaining normal vascular homeostasis by producing a balance of paracrine factors such as nitric oxide (NO) and angiotensin II. Many of these factors are known not only to play an important role in the regulation of vessel tone, but also have dramatic effects on vascular structure. Nitric oxide, for example, is not only a potent vasodilator, but it also inhibits platelet adhesion and reactivity, smooth muscle proliferation, and leukocyte adhesion. 1 Because each of these processes is thought to be important in the development of atherosclerosis, nitric oxide is hypothesized to be an important endogenous antiatherogenic molecule.Nitric oxide is produced from the conversion of L-arginine to L-citrulline by the enzyme nitric oxide synthase (NOS). 2 In endothelial cells, the constitutive isoform, eNOS (NOSIII) is responsible for endothelium-derived NO production. In vivo, the predominant physiological stimulus for NO is wall shear stress. 3 NO is produced in response to not only the specific level of shear but also to acute changes in blood flow.Interestingly, eNOS expression is also shear responsive with increasing levels of laminar shear stress resulting in enhanced eNOS mRNA and protein. 4 Because NO has important regulatory function in atherogenesis, increased eNOS expression by laminar shear stress has been hypothesized to be a factor in the resistance of specific vascular segments to atheros...

Flow, NO, and atherogenesis

“…In human iliac arteries, endothelial cells at the bifurcation have shorter telomeres, consistent with a focal acceleration of senescence (3). Senescent human endothelial cells produce less nitric oxide (NO ⅐ ), generate more superoxide anion (O 2 ⅐-), and are more adhesive for monocytes, effects that can be reversed by transfection with the gene encoding telomerase (4).…”

FOXOs and Sirtuins in Vascular Growth, Maintenance, and Aging

“…This decline in NO availability is a consequence of an impaired eNOS activity as well as of a progressive NO inactivation through increasing levels of superoxide anions. 108,109 As a result, aged vessels exhibit compromised vasodilatory properties that cause increased vascular resistance and impaired perfusion. Moreover, reduced NO bioavailability prompts vascular inflammation and atherogenesis and impedes endothelial repair.…”

Endothelial dysfunction and hypertension in aging

“…127,128 Decreases in both NO production and eNOS activity in human umbilical vein endothelial cells and human aortic endothelial cells (HAECs) are associated with aging. 129,130 Matsushita et al 130 demonstrated that shear stress-induced increase in NO production was diminished in senescent HAECs and that stable expression of TERT restored the decreased eNOS expression and NO production associated with aging. Minamino et al 131 reported that HAECs from human atherosclerotic lesions presented phenotypes of senescent cells and decreases in eNOS expression and eNOS activity.…”