Abstract Body: Background: Myocardial infarction (MI) is caused by coronary artery obstruction, leading to ischemia and localized cardiomyocyte death. The border zone (BZ) refers to “at-risk” tissue directly adjacent to the necrotic core of an infarcted heart, and is regarded as a promising target for therapy during the initial weeks after MI. Although next generation sequencing has greatly enhanced our understanding of the heterogeneity within the BZ, efforts to elucidate the contributions of BZ cardiomyocytes to post-MI remodeling have been hindered by a lack of tools to isolate and examine this niche. Using spatial transcriptomics, we recently identified Small Proline Rich Protein (Sprr1a) as a specific and transient marker of BZ cardiomyocytes
Methods: Here, we describe the development of two novel transgenic mouse lines that harbor membrane bound green fluorescent protein (mGFP) or tamoxifen-inducible Cre recombinase (CreERT2) at the endogenous Sprr1a locus. We interrogate cell type specificity of Sprr1a upregulation after MI using immunofluorescence and flow cytometry. We perform fluorescent activated cell sorting (FACS) to isolate GFP+ and GFP- myocytes post-MI for bulk RNA sequencing. We use Cre-dependent lineage tracing to investigate whether border zone myocytes persist after ischemia-reperfusion (I/R) and MI.
Results: Sprr1a expression was transiently induced in troponin-positive BZ cardiomyocytes after MI. Cardiomyocytes were identified as the predominant Sprr1a+ cell type at 5 days post-MI. Isolation of GFP+ BZ cardiomyocytes revealed distinct transcriptional signatures compared to remote zone cardiomyocytes, including previously established markers such as Nppa, Uchl1, Des, and Ankrd1. Lineage tracing demonstrated that Sprr1a+ cardiomyocytes persist up to 1-month following both I/R and MI.
Conclusions: These data establish Sprr1a as a novel biomarker that defines a transcriptionally distinct and persistent population of border zone cardiomyocytes. The novel Sprr1a-GFP and Sprr1a-CreERT2 mouse lines enable direct interrogation of BZ cardiomyocyte fate and function. Future studies will further establish BZ characteristics and identify cardioprotective factors that could be harnessed to improve post-MI repair.