Abstract 202: Early Reprogramming Derived Cocktail FIJs Supports Cardiomyocyte Proliferation for Heart Regeneration

Abstract

Although remnant cardiomyocytes (CMs) possess a certain degree of proliferative ability, their regenerative efficiency is too low for cardiac regeneration after injury. As terminally differentiated cells, CMs are considered difficult to successfully reprogram into iPSCs. In this study, a modified reprogramming method was employed to avoid damage to the CMs, and the resulting CM-derived iPSCs were characterized their pluripotency and differentiative abilities. During the early stages of reprogramming, we observed sequential morphological changes in both CMs and non-CMs, but alkaline phosphatase assay revealed that CMs demonstrate a time-delayed sequence of events compared to non-CMs. In order to identify the specific events preceding colony formation, total RNA was purified for microarray analysis on day 0, 2, 4, and 6 of the reprogramming process. There were several interesting changes revealing such as up-regulation of sterol synthesis in non-CMs and down-regulation of chemokines in CMs on day 2. Most importantly, we detected significant enhanced mitosis for CMs on day 2. Nevertheless, typical iPSC-like colonies were clearly observed after 6 days of reprogramming in both cell types. In the purpose of bringing CM back to regain proliferative ability for heart regeneration, the candidates were selected from the microarray results on day 2 of the reprogramming. Triple combined gene cocktail FIJs was determined supporting CM proliferation with 7 times higher Ki-67 + or H3P + population % in neonatal murine CMs in vitro . The same supportive role of FIJs was also confirmed in adult mice showing higher H3P + adult CMs in vivo . Furthermore, heart function detected by echocardiography was significantly improved and less fibrosis shown by trichrome staining after the triple gene cocktail treatment in adult mice suffering from myocardial infarction, and this improvement was owing to the enhanced CM proliferation. In conclusion, triple gene cocktail selected from CM reprogramming day 2 provides valuable information for inducing remnant CM proliferation for heart regeneration.