Abstract Body: Background: After suffering myocardial infarction (MI), the heart can develop excessive scarring, interstitial fibrosis, and reduced cardiac function which together promotes adverse remodeling of the heart. The main culprit responsible is the cardiac fibroblast which upon injury activates and transitions to myofibroblasts. Thus, there is great interest in studying how cardiac fibroblast activation is perpetuated as a means of understanding how we can attenuate adverse cardiac scarring. Previous studies in our lab have shown that conditional knockout (cKO) of Yap and Wwtr1 in myofibroblasts results in improved cardiac function and reduced MI induced fibrosis and cardiac scarring following MI. We identified CCN3, a secreted extracellular matrix factor, as one of the top downregulated genes in Yap/Wwtr1 cKO mice. We then demonstrated administration of exogenous human recombinant CCN3 (hCCN3) resulted in increased cardiac fibrosis compared to mice treated with PBS post MI. Collectively this led to our hypothesis: Myofibroblast CCN3 expression contributes to adverse remodeling outcomes following MI.

Methods: We used a Cre-lox system to delete CCN3 specifically in myofibroblasts. We then compared cardiac scarring, fibrosis, and function, of CCN3 cKO mice with control mice post MI. We performed single cell RNA sequencing and western blotting to confirm that CCN3 is downregulated specifically in myofibroblasts. We administered hCCN3 to animals without injury and immediately following injury at 0dpi or 3dpi to determine if hCCN3 was inherently deleterious or deleterious in a time specific window and compared cardiac function of CCN3 treated mice with PBS treated mice.

Results: Our data demonstrate that knockout of myofibroblast CCN3 post MI results in reduced cardiac fibrosis, reduced scarring, and preserved cardiac function compared to Cre-positive and Cre-negative mice. Previously, we found hCCN3 administration worsened cardiac function and fibrosis when administered 3x weekly after MI injury. We demonstrate that hCCN3 is only deleterious, if administered to injured hearts within 3 days following injury.

Conclusions: Together these data suggest that myofibroblast expression of CCN3 promotes cardiac fibrosis in an injury and time dependent manner. We aim to determine pathways CCN3 specifically upregulates or downregulates immediately post MI to provide insight into novel therapeutic targets which only need to be administered within the first few days post MI.