Presentation

Background and Purpose: We previously identified soluble ST2 (sST2) as a biomarker of edema and inflammation in patients with large middle cerebral artery stroke. To establish a mechanistic link between sST2 and edema, we generated an sST2-knockout rat and examined edema formation and gene expression after middle cerebral artery occlusion (MCAO).

Methods: Experimental stroke was performed in sST2-knockout rats and littermate controls. We measured stroke size and swelling as a proportion of hemisphere volume using established methods. The cellular sources of sST2 and transmembrane ST2 (tmST2) were identified with qPCR and verified with in situ hybridization. To examine knockout-specific changes in microglial function, we used semi-automated morphological analysis using Iba1 immunohistochemistry and assessed gene expression using RNAseq.

Results: sST2 knockout significantly reduced swelling volume (4.0% vs 11.6%, p = 0.006). There were no differences in stroke volume based on sST2 expression (206mm^3 [IQR 100-248] in knockout vs 204mm^3 [89-307], p = 0.8). Accordingly, knockout was associated with reduced swelling even after adjustment for stroke volume (beta = -0.77, 95% CI -1.15 to -0.40, p < 0.001). Post-stroke upregulation of sST2 in wild type animals occurred primarily in endothelial cells (138±29-fold increase in expression) and tmST2 primarily in microglia (47±34-fold increase), which was confirmed with in situ hybridization. Morphometry identified a decrease in Iba1 process optical density in knockouts (3.19±0.05 vs 3.33±0.03, p = 0.025). Comparison of gene expression between wild type and knockout microglia identified significant changes in pathways related to blood-brain barrier integrity, including angiogenesis, extracellular matrix organization and cell-cell junction organization.

Conclusion: sST2 knockout reduces edema in a rat model of stroke. We propose that sST2 serves as a signal from injured brain endothelium to alter the microglial response and thereby influence edema formation. These findings set the stage for future study of the role of sST2 in regulating blood brain barrier integrity.