Abstract 16085: Nucleostemin Antagonizes Senescence of Cardiac Progenitor Cells
Functional decline in stem cell regenerative potential contributes to aging associated with onset of cellular senescence in the c-kit+ cardiac progenitor cell (CPC) pool. Clinical implementation of autologous cell based therapy using CPCs with elderly patients would benefit tremendously from understanding phenotypic and molecular characteristics of senescent stem cells with a goal of antagonizing cellular aging. Nucleostemin (NS) is a nucleolar protein that regulates stem cell proliferation and pluripotency that decreases in expression with cardiac aging. This study demonstrates that NS antagonizes senescence in CPCs. NS expression drops (-63%, p<0.05), while the percentage of senescent cells increase in CPCs isolated from old mice (OCPC) relative to CPCs isolated from young mice (YCPC). OCPCs are characterized by flat, round cells with increased multinucleation (p<0.05) relative to YCPCs in vitro and in vivo (p<0.01). Loss of NS recapitulates the phenotype observed in OCPCs, as silencing NS in YCPCs induces flattening of cells, increases % of senescent and multinucleated cells (p<0.01), decreases proliferation by inhibiting S phase progression (p<0.05), decreases expression of pro-proliferative Cyclin D1 (-41%), Aurora B (-60%) and c-kit (-42%) while upregulating cell cycle inhibitors p53 and p16 (1.9, 2 fold, respectively). NS heterozygous knockout mice increase cardiac p53 expression by 1 month of age (2 fold, p<0.05) indicative of premature senescence. NS-mediated regulation of CPC senescence is p53 dependent, as silencing p53 partly inhibits acquisition of senescent phenotype induced by NS-silencing. Mechanistically, NS is induced by Pim-1 kinase-mediated stabilization of transcription factor c-Myc. Pim-1 is required for NS regulation in vitro and in vivo (p<0.05). However, in the absence of c-Myc, Pim-1 mediated regulation of NS is blunted. Engineering OCPCs with NS antagonizes senescence, as observed by decreased percentage of senescent and multinucleated cells (p<0.01), increased proliferation and restored morphology. In conclusion, NS expression induced by Pim-1 inhibits senescence and maintains youth of CPCs consistent with cumulative evidence that Pim-1-mediated cardiac regeneration is dependent in part upon NS.
- © 2013 by American Heart Association, Inc.