Background: Atherosclerosis is a chronic inflammatory disease marked by lipid accumulation and immune cell infiltration in arterial walls. Macrophages contribute by internalizing oxidized low-density lipoprotein, forming foam cells, and driving inflammation. The ubiquitin-proteasome system regulates immune and inflammatory responses in atherosclerosis. This study investigated the protective role of TRIM31 (tripartite motif-containing 31), an E3 ubiquitin ligase, in macrophage lipid metabolism and inflammation through selective regulation of LOX-1 (lectin-like oxidized low-density lipoprotein receptor-1).
Methods: Transcriptomic profiling, macrophage-specific Trim31 knockout (Trim31fl/flLyz2cre) and overexpression (Trim31Lyz2-KI) mice, and LOX-1 knockout (Lox-1-/-) models were used to examine the impact of TRIM31 in vivo (n=8 per group). TRIM31 substrates were identified using single-cell RNA sequencing of atherosclerotic aortas and proteomic/immunoprecipitation-mass spectrometry analyses. Functional assays were performed in both mouse and human macrophages (n=5-6 per group). Ubiquitination mechanisms were clarified through immunoprecipitation and site-directed mutagenesis. Rescue experiments involved LOX-1 knockdown or reconstitution with wild-type and lysine 12 to arginine variant (K12R) LOX-1 and TRIM31 overexpression in Lox-1-/- or Apoe-/-Lox-1-/- mice to evaluate the functional importance of LOX-1 ubiquitination in vivo (n=8 per group) and in vitro (n=5 per group).
Results: TRIM31 was selectively upregulated in macrophages under oxidized low-density lipoprotein stimulation and in atherosclerosis plaques. TRIM31 deficiency exacerbated plaque burden, foam cell formation, and inflammatory signaling (n=8 per group). Single-cell analysis revealed enrichment of lipid transport and inflammatory pathways in TRIM31-deficient plaques. LOX-1 was identified as a key TRIM31 substrate. TRIM31 promoted K48-linked ubiquitination of LOX-1 at lysine 12, facilitating its degradation. The atheroprotective effects of TRIM31 were abolished in Lox-1-/- or K12R-variant rescue models. The TRIM31-LOX-1 axis was also confirmed by human macrophages in regulating lipid uptake and inflammation.
Conclusions: TRIM31, an inducible, macrophage-enriched protective factor in atherosclerosis, restricts foam cell formation and inflammation by targeting LOX-1 for proteasomal degradation. These findings position TRIM31 as a promising therapeutic target for macrophage-driven atherogenesis.
Keywords: atherosclerosis; foam cells; inflammation; macrophages; ubiquitination.