Regulation of Telomerase Activation in Diabetic Vascular Complications

Cardiovascular disease is the leading cause of morbidity and mortality in patients with type 2 diabetes 1,2. With the evolving understanding of the mechanisms contributing to the development of cardiovascular diseases in diabetes, the nucear hormone receptor peroxisome proliferator-activated receptor (PPAR) y has emerged as key transcriptional regulator of gene expression in vascular cells 3-5. PPARy is the molecular target for thiazolidinediones (TZO) clinically used to treat insulin resistance in patients with type 2 diabetes 6. TZO PPARy ligands prevent the development of atherosclerosis and postangioplasty restenosis in preclinical and early clinical studies 7-10. Based on this evidence, elucidation of the molecular pathways utilized by PPARy to regulate gene expression is expected to facilitate the development of novel pharmacological approaches for the treatment of cardiovascular disease in type 2 diabetes. Proliferation of smooth muscle cells (SMC) plays a pivotal role in the pathogenesis of diabetic cardiovascular complications 11-13. Recent evidence has implicated telomerase activation as an important regulator of SMC proliferation 14,15. Interestingly, atherosclerosis development is decreased in telomerase deficient mice and inhibition of telomerase activity suppresses neointima formation indicating that telomerase may serve as a novel pharmacological target for the treatment of vascular diseases 16,17. Preliminary data presented in this application outline a previously unrecognized role for PPARy ligands to suppress telomerase activity in SMC. TZD PPARy ligands are in clinical use for the treatment of insulin resistance and are currently being investigated in large randomized trials for their efficacy to prevent cardiovascular disease. The experiments proposed in this application could identify inhibition of telomerase activity as an important novel mechanism by which PPARy ligands prevent the development of vascular complications of type II diabetes. Based on these findings, the central hypothesis of this proposal is that PPARy suppresses telomerase activity resulting in an inhibition of SMC proliferation and neointima formation following vascular injury in type 2 diabetes. To test this hypothesis, we propose the following aims: Specific Aim I: Determine the regulation of telomerase activity by PPARy and define the role of telomerase as molecular target for the antiproliferative activity of PPARy in SMC. Suppression of telomerase activity by PPARy ligands in SMC may constitute a novel mechanism by which these agents prevent diabetic vascular complications. Therefore, we propose to determine the regulation of telomerase activity by PPARy and to define the significance of telomerase inhibition for the antiproliferative efficacy of PPARy ligands in SMC. Specific Aim II: Determine the molecular mechanisms by which PPARy activation suppresses telomerase activity in SMC. Telomerase reverse transcriptase (TERT) constitutes the catalytic subunit of telomerase and suppression of TERT reduces SMC proliferation 15. Based on this evidence and our Preliminary Data demonstrating that PPARy ligands inhibit TERT expression, we propose to determine the transcriptional and posttranslational mechanisms by which ligand-induced and constitutive PPARy activation suppresses TERT expression in SMC. Specific Aim III: Determine the regulation of telomerase activation during neointima formation following vascular injury by PPARy in vivo. During the proliferative response following vascular injury telomerase is activated and required for SMC proliferation and subsequent neointima formation 14,16. Using a murine model of vascular injury in type 2 diabetic mice, we propose to determine whether TZD PPARy ligands inhibit vascular telomerase activity in response to injury in vivo. In addition, we will determine the relative effect of SMC-selective PPARy deficiency on neointima formation and telomerase activity and define whether the inhibition of both processes by TZD PPARy ligands is mediated through a receptor-dependent mechanism.