Abstract 19546: Retinoblastoma Regulates Cardiac and Mesenchymal Stem Cell Niches during Adult Heart Regeneration
Introduction: Cardiac (CSCs) and mesenchymal stem cells (MSCs) stimulate cardiac repair, both primarily and secondarily by stimulating endogenous cardiac regeneration; however, the mechanisms underlying successful cardiac repair remain elusive and controversial. We addressed this issue in a porcine model of cell therapy by quantifying levels of Ser-608 hyperphosphorylated retinoblastoma (Rbser608+), which marks actively regenerating cardiomyocytes (CM) in adult newt hearts, and Ink4aARF (alternate reading frame of Ink4a), which inhibits cell cycle. Hypothesis: Interactions between CSCs and MSCs regulate Rbser608 and Ink4aARF expression in endogenous progenitors and CM to enhance cardiac regeneration.
Methods: Twenty adult swine underwent myocardial infarction (MI), followed 2 weeks later by intramyocardial injection of 200M human (h)MSCs (n=5), 1M hCSCs (n=5), 200M hMSC plus 1M hCSC (MCC, n=5) or placebo (n=5). Tissue from immunosuppressed animals were analyzed 4 weeks later for exogenous cell engraftment (human Alu). Ink4aARF and Rbser608 were assessed in GATA4+ progenitors and mitotic CMs (phosphoH3+).
Results: In situ hybridization demonstrated Alu+ cells in all groups. Engraftment was ∼7-fold greater in the MCC group compared to hCSCs or hMSCs (7.8±4.6, 0.2±0.2, 1.4±0.7 Alu+/cm3 respectively, p=0.0003) and infarct size was reduced 2-fold in MCC vs either cell type alone. Interestingly, Rbser608+ was expressed both in porcine GATA4+ progenitors as well as mature CM. There were 3 times as many Rbser608+/GATA4+ progenitors (150M/cm3) in the MCC hearts compared to the other 3 groups (p<0.0001). In addition ∼20% of the CM were Rbser608+/Ink4a(-), suggesting that the MCC hearts contained CM capable of completing the cell-cycle (p<0.0001). There was also a 46-fold increase in mitotic CMs in MCC hearts vs. either cell alone (P<0.0001). Importantly, MCC recipients contained a subpopulation of Ink4aARF(−)/phosphoH3+ CM, supporting the existence of transient amplifying CM with the capacity to undergo multiple cell divisions.
Conclusions: Together these findings demonstrate a novel mechanism of heart regeneration, where hMSC and hCSC interactions propagate Rbser608 in CM and CSCs to regulate cell-cycle and stem cell fate decisions.
- © 2012 by American Heart Association, Inc.