Phase Separation of TRIM21 Modulates PTPN14 Stability to Drive Flow‐Dependent Endothelial Activation and Atherogenesis

Local flow patterns determine the uneven distribution of atherosclerotic lesions, yet the underlying mechanism remains poorly defined. We previously reported that protein tyrosine phosphatase nonreceptor type 14 (PTPN14) is implicated in atherosclerosis. Its role in flow-dependent endothelial dysfunction and the upstream regulatory mechanisms remain incompletely understood. Here, we show that PTPN14 functions as a flow-sensitive regulator in endothelial cells, with its protein stability reduced under disturbed flow. Endothelial-specific deletion of PTPN14 led to exacerbated endothelial inflammation and atherosclerosis in vivo. We further identify TRIM21 as a critical E3 ubiquitin ligase that binds PTPN14 via its SPRY domain and promotes K48-linked polyubiquitination at lysine 956, resulting in proteasomal degradation of PTPN14. Notably, disturbed flow induced TRIM21 LLPS in a cytoskeleton-dependent manner, facilitating the recruitment of PTPN14 into co-condensates and enhancing its ubiquitination. Endothelial-specific TRIM21 overexpression aggravated disturbed flow-induced endothelial inflammation and atherosclerosis. In contrast, endothelial-specific TRIM21 deficiency attenuated induced endothelial activation and atherosclerosis; importantly, this atheroprotective effect was abolished by concomitant PTPN14 deletion, establishing a functional TRIM21-PTPN14 regulatory axis in vivo. Together, these findings uncover phase separation-dependent ubiquitin signaling as a mechanistic link between hemodynamic forces and endothelial dysfunction and suggest the TRIM21-PTPN14 pathway as a potential therapeutic target in atherosclerosis.