PSAT1 modified mRNA induces cardiac repair post-ischemic heart injury - Cardiovascular diseases (CVD) are the leading causes of death worldwide. Although diagnosis and treatment approaches have improved, the prognosis of heart failure (HF) patients remains poor. After myocardial infarction (MI), there is a permanent loss of functional cardiomyocytes (CMs), and as the mammalian heart has limited regenerative capacity, it leads to HF and death. Lower organisms like zebrafish, newts, and even 1-day mice and pig can regenerate their heart post-injury by inducing CM proliferation. Attempts have been made to transiently reconstitute embryonic signaling in adult hearts, including overexpression of cell cycle activating and proliferative genes, with limited success. Existing gene therapy approaches for the heart have significant challenges like short-term, low, or uncontrolled expression and genome insertion, resulting in insufficient CM proliferation and cardiac repair. Recently we have shown that modified mRNA (modRNA) delivery is a safe, efficient, transient, non-immunogenic, local, and dose-controlled gene delivery platform for the heart. Induced pluripotent stem cells (iPSC)-derived extracellular vesicles (EV)/exosomes have been shown to improve cardiac function. However, the mechanism of iPSC-EV mediated cardiac regeneration remains unclear. In our preliminary studies, using a hiPSC-extracellular proteomic approach combined with a developmentally restricted gene database of mouse hearts, we identified for the first time that Phosphoserine Aminotransferase 1 (PSAT1) protein is expressed exclusively in hiPSC-EVs, and PSAT1 mRNA expression is significantly downregulated quickly after the postnatal period in mice hearts. Myocardial delivery of PSAT1 modRNA induced CM proliferation, improves cardiac function and mice survival post-MI. Furthermore, we showed that YAP1 is a transactivator of PSAT1 and induces its expression, and in turn, PSAT1 induces β-catenin nuclear translocation to induce CM proliferation. We found a novel YAP1-PSAT1-β-catenin molecular signaling axis in cardiac regeneration. Moreover, PSAT1 induced serine synthesis pathway (SSP), nucleotide synthesis and inhibited oxidative stress and DNA damage response post-MI. This proposal will determine a local and short pulse of cmsPSAT1 (CM-specific PSAT1) or PSAT1 modRNA is sufficient for the induction of cardiac regeneration and reversal of cardiac remodeling post-MI and HF, respectively, and will study the pleiotropic effects of PSAT1 through novel molecular mechanisms on activating YAP1-β-catenin molecular axis and downstream signaling pathways. Finally, determine the involvement of SSP in PSAT1 induced CMs proliferation and cardiac regeneration post-MI. The highly translatable nature of our proposed modRNA platform and our integrative, multi-disciplinary experimental plan are ultimately geared towards clinical applicability for ischemic heart diseases.
