Abstract Body: Background:
Slit guidance ligand 2 (Slit2) was recently identified in epicardium-derived cardiac fibroblasts (cFBs) to promote angiogenesis during development. In the postnatal heart, Slit2 is enriched in cFBs relative to cardiomyocytes (CMs) and was transiently upregulated 7 days (D) after myocardial infarction (MI). Overexpression of Slit2 in the myocardium improved cardiac function and increased vessel density following MI. These findings suggest that Slit2 may be a promising therapeutic target for recovery after MI, though the mechanisms that regulate Slit2's cardioprotective functions during ischemia remain unclear.

Objective:
This study aims to elucidate the mechanistic role of Slit2 in cFBs to post-infarct recovery.

Methods:
The Tcf21-MerCreMer mouse strain was used to conditionally delete Slit2 in resident Tcf21⁺ cFBs of adult mice (Slit2-iKO). Sham surgery or permanent artery ligation to induce MI was performed two weeks after tamoxifen. Cardiac systolic and diastolic function were measured longitudinally using echocardiography up to 28D post-MI. Immunohistochemistry and fluorescence in situ hybridization (FISH) assays were used to evaluate cellular remodeling.

Results:
Control and Slit2-iKO mice following sham surgery did not show significant differences in cardiac function, morphology, or fibrosis. Following MI, Slit2-iKO mice showed a reduction in ejection fraction, reaching heart failure by 14D post-surgery compared to controls. Interestingly, Slit2-iKO mice showed reduced fibrosis at 28D post-MI compared with control mice. This observation was further validated by the inability of Tcf21-lineage cells lacking Slit2 to efficiently differentiate into Postn+ myofibroblasts (myoFBs), as assessed by qRT-PCR and FISH at 7 and 28D post-MI.

Conclusions:
Our data indicate that Slit2 plays a critical role in the transition of resident cFBs to myoFBs following MI, thereby preventing scar maturation and accelerating pathological remodeling. Studies currently underway include the deletion of Slit2 in Postn⁺ myoFBs, providing a complementary cellular approach to understanding Slit2's function in fibroblast activation under ischemic conditions. Understanding the regulators of transitional fibrotic repair may yield new therapeutic avenues.