Abstract 108: Il-1β Inhibition Promotes Fibrous Cap Thickening and Accumulation of Fibroblast Like Cells in Atheromas in Clonal Hematopoiesis

Clonal hematopoiesis (CH), a highly prevalent condition in the elderly, arises from somatic mutations that endow a survival advantage to hematopoietic stem cells. In CANTOS IL-1β inhibition was particularly beneficial in subjects with TET2 CH. Amongst the common genetic variants giving rise to CH, JAK2 V617F ( JAK2 VF ) gain of function and TET2 loss of function mutations have been shown to increase macrophage inflammasome activation and atherosclerosis in mice. We have shown that macrophages harboring Jak2 mutations have increased AIM2 inflammasome activation and pyroptosis which promoted features of unstable atherosclerotic lesions marked by prominent necrotic cores and an accumulation of inflammatory macrophages. Inflammasome inhibition led to a thickening of fibrous caps, indicating plaque stabilization. scRNA-Seq analysis of human carotid plaques indicates that myeloid cells were enriched for inflammasome components while endothelial, fibroblast, and smooth muscle cell (SMC) like cells were enriched for the IL-1 receptor suggesting IL-1-mediated cross-talk from myeloid cells to stromal cells. Here we investigated this cross-talk using IL-1β antibodies in mice modeling Jak2 VF or Tet2 CH and expressing Myh11-Cre/ZS-green in order to fate map SMC-derived cells. ScRNA-Sequencing of green and non-green cells revealed that IL-1β antagonism had minimal effects on SMC differentiation. However, in both Jak2 and Tet2 models non-SMC derived fibroblast like cells expanded more than two-fold following IL-1β inhibition and were primarily enriched for matrix genes like Col1a1 , Col1a2 , Lum , and Dcn . Histological analysis of the fibroblast enriched protein Decorin revealed increased expression and localization in fibrous cap region. Together these findings suggest that IL-1β inhibition may promotes cap thickening by promoting fibroblast like cell accumulation in lesions. These results provide a potential mechanistic explanation for why IL-1β therapy was beneficial in CANTOS.