Abstract Body: Funding: The INSIGHT Registry is funded by Penumbra.

Introduction
Rapid and precise determination of the etiology of acute ischemic stroke is crucial in long-term management and prevention of recurrence. Identification of etiology-associated molecular biomarkers following thrombectomy may allow for personalized intervention. Here, we examine the transcriptomics of cardioembolic thrombi as a result of atrial fibrillation, identifying a distinct transcriptomic signature relative to other causes of ischemic stroke.

Methods
The INSIGHT registry is a prospective, multicenter, multi-omic registry focused on elucidating the molecular underpinnings of stroke from analysis of clot and interarterial blood. RNA sequencing of 10,990 genes from 292 thrombi from patients undergoing thrombectomy was analyzed using edgeR, sva, and limma/voom. 111 patients had a determined etiology of atrial fibrillation. Controls had unknown, atheroembolic, or coagulopathy stroke etiology. Significant association of thrombus gene expression with atrial fibrillation was conducted using the Wilcoxon Rank Sum test using Benjamini-Hochberg multiple testing correction (FDR <5%). Gene set enrichment was performed using FGSEA using Gene Ontology biological processes gene sets. Co-expression modules were detected using WGCNA and analyzed using cytoscape.

Results
33 genes (27 upregulated, 6 downregulated) within thrombi were significantly associated with atrial fibrillation etiology. These included upregulated endothelial cell markers associated with cardiac endothelial cells (e.g. KDR, AMDHD2, IL18BP) compared to thrombi of other etiologies. In addition, upregulated genes were associated with oxidative stress (FDR= 8.46x10^-8) and metabolism (1.04x10^-6), while adaptive T-cell immunity was downregulated (FDR= 7.52x10^-3). Co-expressed gene networks upregulated by atrial fibrillation-associated thrombi included a module implicated in innate immune signaling and cytotoxic granule release (p=0.02), which included key hub genes GZMH and TBX21.

Conclusion
Cardioembolic thrombi possess a distinct transcriptomic signature consistent with collection and retainment of cardiac endothelial tissue at origin, and display immunomodulatory activity associated with innate vs adaptive immune balance. This signature suggests the active role thrombi likely play in the vascular microenvironment and may ultimately be used to identify atrial fibrillation as an etiology in strokes of unknown origin.