Abstract 17434: Shelterin Complex Influenced by Pim-1 Preserves Telomeres in Cardiac Progenitor Cells
Telomere shortening has been implicated in the pathogenesis of heart disease associated with myocardial aging. Telomeres are the distal ends of chromosomes that consist of nucleotide repeats that function to protect important DNA from damage. The nucleoprotein complex known as the shelterin complex consists of several telomere-associated proteins (TRF1, TRF2, POT1, TIN2, and PTOP) and is essential to protect the telomere from degradation and regulate access of telomerase (TERT), the enzyme responsible for telomere elongation. Here we demonstrate that enhanced cardiac progenitor cell (CPC) proliferation observed with activation of Pim-1, a cardioprotective kinase, leads to preservation of telomeres consistent with a young phenotype. CPCs lentivirally engineered to stably overexpress Pim-1 (CPC-Pim) have significantly longer telomeres compared to GFP engineered CPCs (1.59 fold, p<0.05) when analyzed by quantitative fluorescent in situ hybridization. Telomere related protein analysis revealed an increase TRF1, TRF2, POT1, Tankyrase ½, and Ku86 (1.4, 2.6, 3.11, 1.82. 1.41, and 2.52 fold, respectively), while PTOP, PARP, and TERT levels are reduced dramatically (30%, 88%, and 82%, respectively). Nuclear TRF1 and TRF2 are diminished (50.4% and 24%), while proteins associated with protecting the telomere from attrition Ku86 and DNA pK are significantly upregulated in the nucleus (2.3 and 2.9 fold) upon subcellular fractionation and immunocytochemistry analysis. Cytoplasmic TRF2, TRF1, and Fbx4, a TRF1 specific ubiquitin ligase were significantly upregulated (1.8, 1.24, and 2.67 fold, respectively), suggesting proteins known to antagonize telomere lengthening are exiting the nucleus. Interestingly, nuclear TERT protein is more abundant in CPC-Pim fractions (1.73 fold), and was found to have enhanced activity upon subsequent activity assays (1.46 fold). These findings demonstrate the unique ability of Pim-1 kinase to modify the shelterin complex in order to preserve telomere length and represents a novel mechanism to antagonize age-associated senescence and extend the replicative lifespan of CPCs.
- © 2010 by American Heart Association, Inc.