Abstract Body: Introduction: Endothelial cells (ECs) are highly plastic and undergo transformations, such as endothelial-to-mesenchymal transition (EndMT). This process involves a multistage transition from an early-activated, proinflammatory state to a fibroblast-like phenotype. Recognized as essential for atherosclerosis stability, low shear stress (SS) mainly triggers early EndMT. We identified the interleukin-1 receptor (IL-1R1) as an upstream regulator of SS-induced EndMT, but the downstream mediators remain poorly understood.
Hypothesis: SS causes pathological endothelial reprogramming into a proinflammatory mesenchymal-like state, leading to atherosclerosis progression via activating IL-1R1 downstream kinases (IRAK1/4).
Methods: scRNA sequencing of human unstable atherosclerosis used an online dataset, validated by coronary lesions from Nebraska Cardiovascular Biobank, along with bulk RNA sequencing of human ECs under SS (± 2 dynes/cm²). Male mice were studied on a 16-week high-fat diet (HFD) and a partial carotid ligation (PCL) to induce SS, with n=12 per group. In vitro studies included 4 independent experiments, and data were analyzed as mean ± SEM.
Results: Unstable human coronary atherosclerosis revealed that levels of active IRAK1 are significantly higher in the activated EndMT population than in stable lesions, while IRAK4 is upregulated in granulocytes. Genetic silencing of IRAK1 markedly reduced the expression of EndMT-related genes by SS (p<0.01, n=4). In contrast, IRAK4 deletion did not significantly affect EndMT. In vivo, in PCL- and HFD-induced atherosclerosis, the therapeutic use of an IRAK1-specific inhibitor or IRAK1-specific EC knockout in inducible lineage-tracing mice resulted in a markedly reduced atherosclerotic burden (p<0.001). This was associated with notably less macrophage infiltration and increased smooth muscle cell incorporation compared to controls. IRAK1 inhibition significantly decreased the subset of active EndMT while increasing fibrous cap thickness and collagen content. Bulk RNA sequencing demonstrated IRAK1’s direct involvement in pathways related to EC-to-EndMT, which occurs independently of IL-1 stimulation, suggesting a direct role for IRAK1 in low shear-induced EndMT.
Conclusions: These findings identify a new function for endothelial IRAK1 in EndMT and atherosclerosis development, making IRAK1 a promising therapeutic target to lessen activated EndMT in unstable atheromas and preserve lesion stability in atherosclerosis.