Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (p. [104]-108).

No description available.

published_or_final_version / Pharmacology / Doctoral / Doctor of Philosophy

published_or_final_version / Medicine / Master / Master of Philosophy

No description available.

Thesis (Ph. D.)--Lehigh University, 2001. / Includes vita. Includes bibliographical references (leaves 127-165).

published_or_final_version / Pharmacology and Pharmacy / Doctoral / Doctor of Philosophy

Endothelial senescence represents one of the major characteristics of vascular aging contributing to the development of cardiovascular diseases. SIRT1 is a NAD+-dependent enzyme catalyzing the deacetylation reaction of various signaling molecules and exerts beneficial effects against aging-associated pathologies. SIRT1 is a potent regulator antagonizing endothelial senescence. Both expression and activity of SIRT1 are down-regulated in senescent endothelial cells. However, the molecular mechanisms underlying the loss-of-SIRT1 function during the occurrence of endothelial senescence remain unknown. The present study reveals that phosphorylation at serine 47(S47) contributes to the loss-of-SIRT1 function during endothelial senescence. In both replicative and premature senescent endothelial cells, increased phosphorylation of SIRT1 at S47 was closely associated with the severity of cellular senescence. Replacing serine 47 residue with a phospho-mimicking aspartic acid residue impaired the anti-senescence activity of this protein. In addition, phosphorylation of SIRT1 at serine 47 inhibited its nuclear-cytoplasmic shuttling and protein-protein interactions with LKB1, a senescence-promoting kinase and telomeric repeat-binding factor 2–interacting protein 1, a telomere and inflammation regulator. As a result, the anti-inflammatory function of SIRT1 was also abolished by phosphorylation at serine 47. Cyclin dependent kinase 5 (CDK5) was identified as an upstream kinase responsible for phosphorylation of SIRT1 at serine 47. During the endothelial senescence, the activity of this kinase was up-regulated which was attributed to the augmented P25, a regulatory subunit of CDK5. Inhibition of this kinase by roscovitine, a CDK5 inhibitor, decreased the phosphorylation of SIRT1 at serine 47, reduced cellular senescence, promoted the cytoplasmic translocation of SIRT1 and attenuated the inflammation in endothelial cells triggered by tumor necrosis factor α. Moreover, the kinase activity of CDK5 was significantly elevated in aorta tissues of apolipoprotein E–deficient mice. Chronic administration of roscovitine alleviated endothelial senescence, vascular inflammation and the development of arterial atherosclerosis. These results collectively suggest that CDK 5 is responsible for the phosphorylation of SIRT1 at serine 47, which impairs the anti-senescence activity of enzyme and contributes to loss-of-SIRT1 function during vascular aging. By inhibiting this kinase, SIRT1 function can be improved, in turn preventing the development of endothelial senescence and slowing down the process of vascular aging. In addition to phosphorylation, I have also performed a preliminary study on the ubiquitination of SIRT1. The results demonstrated that SIRT1 ubiquitination was mediated by a Cullin-1-RING E3 ligase complex. Knocking down of cullin-1 enhanced SIRT1 protein expression, promoted proliferation and inhibited senescence in endothelial cells. This discovery may provide novel insights on the anti-vascular aging therapeutic development based on SIRT1 modification. / published_or_final_version / Pharmacology and Pharmacy / Doctoral / Doctor of Philosophy

In blood vessel of mature animal, endothelial cells remain quiescent for years, before apoptosis and being replaced by newly generated endothelial cells. During aging, this turnover process is accelerated and the fast generated endothelial cells become dysfunctional. Endothelial dysfunction in blood vessel is characterized by the imbalanced production of endothelium-dependent relaxing factors (EDRF) and endothelium-dependent contracting factors (EDCF). The NAD-dependent deacetylase SIRT1 is an anti-aging protein with therapeutic potential for aging related cardiovascular diseases. Endothelium-specific over-expression of human SIRT1 promotes endothelium-dependent vasodilatation and endothelium-selective inhibition of human SIRT1 inhibit it. It is accepted that SIRT1 plays a protective role in endothelium dysfunction. However, the underlying mechanisms remain unclear. In the present study, the endothelial functions of a transgenic mouse model with endothelium-selective over-expression of human SIRT1 (hSIRT1) were evaluated and compared with those of wild type mice. Aging-induced deterioration in endothelium-dependent vasodilatation was observed in wild type but not hSIRT1 mice. Endothelium-specific over-expression of SIRT1 prevented aging-induced reduction of NO bioavailability in aortae, without changing endothelial nitric oxide synthase (eNOS) expression levels. Enhanced phosphorylation of eNOS at serine 1177 was detected in hSIRT1 mice aorta. In the presence of Nω-Nitro-L-arginine methyl ester (L-NAME), the nitric oxide synthase (NOS) inhibitor, EDCF induced contraction to acetylcholine was significantly decreased in carotid arteries of hSIRT1 mice. Cyclooxygenase-2 (COX-2) expression was induced by aging in wild-type mice but not in hSIRT1 mice. Thus, both the augmented NO bioavailability and the reduced production of COX-2-derived EDCF in hSIRT1 mice enhanced their endothelial function. To further explore the eNOS-independent mechanism underlying the vasoprotective role of SIRT1, the eNOS deficient and hSIRT1 endothelium-specific over-expression (eNOS-hSIRT1) mice was generated. Decreased endothelium-dependent contraction to acetylcholine was observed in both the carotid artery and aorta of eNOS-hSIRT1 mice, when compared to the controlled eNOS deficient mice. Besides, ATP induced endothelium-dependent contraction, which was COX-dependent, was also decreased in aortae of eNOS-hSIRT1 mice. Thus, the improved endothelial function induced by the endothelium-selective overexpression of SIRT1 was partly attributed to the reduced COX function, independent of eNOS signaling pathway. In summary, endothelium-selective overexpression of human SIRT1 prevented aging-induced impairment of endothelial function via both eNOS dependent and independent mechanisms. / published_or_final_version / Pharmacology and Pharmacy / Master / Master of Philosophy

published_or_final_version / Pharmacology / Master / Master of Philosophy