Abstract 12299: Rejuvenation of the Bone Marrow-Derived Cardiac Resident Sca-1+ Stem Cell Subset Improved Healing of the Aged Heart

Abstract

Introduction: We previously reported that bone marrow (BM) reconstitution with young BM cells into aged recipients restored progenitors in both the BM and the myocardium and improved functional recovery post-injury. Here, our goal was to identify the specific cell type responsible for the improved cardiac regeneration and to restore that capacity in aged individuals after myocardial infarction (MI). Methods and Results: We reconstituted old mice with BM cells from young or old GFP+ mice to generate young chimeras and old chimeras. The number of BM-derived Sca-1+ progenitors homing to the heart was significantly greater in young chimeras compared to old ones (7.14±0.32/field for young vs 2.48±0.78/field for old, P<0.01, 5 high-powered fields/section, 3 sections/heart, 3 animals/group). We then separated Sca-1+ from Sca-1- young donor BM cells using magnetic cell sorting and transplanted them into lethally-irradiated old recipients to generate Sca-1+ and Sca-1- chimeras. Quantification by flow cytometry of heart tissue revealed: 1) the Sca-1+ chimeras had more BM-derived cells that co-expressed PDGFRβ (1.65±0.13% for Sca-1+ vs 0.52±0.09% for Sca-1-, P<0.05, n=4/group) and 2) the number of GFP+ PDGFRβ+ cells was greater in the Sca-1+ chimeric hearts than the Sca-1- chimeric hearts after MI (3.77±0.55% for Sca-1+ vs 0.85±0.106% for Sca-1-, P<0.05, n=3/group). The BM-derived cells that homed to the heart in the Sca-1+ chimeras actively proliferated, stimulated proliferation of the host’s aged progenitors and improved ventricular function after MI. BM chimerism with Sca-1+ cells in aged mice restored the regenerative capability of cardiac resident progenitors and improved functional healing of the aged heart. Conclusions: BM Sca-1+ cells that homed to the heart in aged recipients proliferated and stimulated the propagation of host aged progenitor cells post-MI. This improved regeneration involved activation of the PDGFRβ/Akt/p27Kip1 signaling pathway. The number of BM-derived Sca-1+ progenitor cells in the aged myocardium was the major determinant for successful cardiac functional recovery. Restoration of the Sca-1 subset of stem cells by BM reconstitution improved cardiac repair and prevented heart failure.