THE MOLECULAR SIGNATURE OF CSCS SOURCED FROM AGED DONORS WITH ISCHEMIC CARDIOMYOPATHY IMPAIRS CELL CYCLE CONTROL AND REPAIR

Abstract

Aging reduces the ability of organs to maintain homeostasis and respond to stressors. Previously, we have shown that aging increases the production of pro-inflammatory cytokines by ex vivo proliferated cardiac stem cells (CSCs) while ischemic aged CSCs have shorter telomere lengths, higher levels of oxidative stress and are less capable of repairing injured myocardium after transplantation. In this study, we explore the fundamental mechanisms underlying these changes. Young (YM; 8 wks) and old (OM; 52 wks) C57/BL6 mice were randomized to receive no intervention (n=20 YM and n=19 OM) or surgical ligation of the left anterior descending artery (n=20 YM and n=17 OM). Following establishment of ischemic cardiomyopathy (ICM) (+4 week ejection fraction: 27±2% and 30±2% for OM and YM, respectively, p=0.24), CSCs were cultured from plated ICM or age matched myocardial biopsies. After exposure to low serum hypoxic (1% oxygen) stress conditions designed to mirror the remodeled ICM heart, flow cytometry demonstrated that while aging alone had little negligible effects on CSC viability, aging and a history of ICM combined to increase the number of apoptotic CSCs by 1.5±0.2 fold (p=0.01). Consistent with these findings, microarray profiling revealed that aging alone prompted the differential expression of 245 genes (≥2 fold change; false discovery rate (FDR) ≤0.05) that resulted in up-regulation of pro-inflammatory pathways including NF-КB, TREM1, Toll-like receptor and death receptor signaling. A history of ICM resulted in the differential expression of 924 and 773 genes in OM and YM donors, respectively (≥2 fold change; FDR≤0.05). ICM resulted in CSCs sourced from YM donors up-regulating transcripts responsible for cell migration, proliferation, survival within the Protein Kinase A, NRF2-mediated oxidative stress response and PPAR signalling pathways. In contrast, a history of ICM in OM donors increased stimulation within pathways responsible for IL-6, NF-КB, TNFR2, TREM1 and p38 MAPK signaling. Most interestingly, aging alone promoted the differential expression of 145 genes in ICM CSCs (≥2 fold change; FDR≤0.05) which modify many of the pathways responsible for effective cell cycle control and DNA damage/repair. Although advanced donor age biases ex vivo proliferated CSCs to adopt a pro-inflammatory molecular signature, a history of ICM promotes the expression of pro-survival pro-cardiogenic transcripts- suggestive of a tendency towards enhanced cardiac repair. In contrast, CSCs from aged donors with a history of ICM exhibit transcripts underlying an attenuated capacity for cardiac repair through impaired cell cycle control and repair.