FABP4 activates the JAK2/STAT2 pathway via Rap1a in the homocysteine-induced macrophage inflammatory response in ApoE-/- mice atherosclerosis.

Atherosclerosis is a chronic inflammatory vascular disease, and inflammation plays a critical role in its formation and progression. Elevated serum homocysteine (Hcy) is an independent risk factor for atherosclerosis. Previous studies have shown that fatty acid binding protein 4 (FABP4) plays an important role in macrophage inflammation and lipid metabolism in atherosclerosis induced by Hcy. However, the underlying molecular mechanism of FABP4 in Hcy-induced macrophage inflammation remains unknown. In this study, we found that FABP4 activated the Janus kinase 2/signal transducer and activator of transcription 2 (JAK2/STAT2) pathway in macrophage inflammation induced by Hcy. Of note, we further observed that ras-related protein Rap-1a (Rap1a) induced the Tyr416 phosphorylation and membrane translocation of non-receptor tyrosine kinase (c-Src) to activate the JAK2/STAT2 pathway. In addition, the suppressor of cytokine signaling 1 (SOCS1)—a transcriptional target of signal transducer and activator of transcription (STATs) inhibited the JAK2/STAT2 pathway and Rap1a expression via a negative feedback loop. In summary, these results demonstrated that FABP4 promotes c-Src phosphorylation and membrane translocation via Rap1a to activate the JAK2/STAT2 pathway, contributing to Hcy-accelerated macrophage inflammation in ApoE−/− mice. A proposed regulatory model of FABP4 in Hcy-induced macrophage inflammation in atherosclerosis of ApoE−/− mice. FABP4 activates the JAK2/STAT2 pathway via Rap1a in Hcy-induced macrophage inflammatory response and atherosclerosis in ApoE−/− mice, which is attributed to Rap1a-dependent promotion of the c-Src phosphorylation at Tyr416 and membrane translocation. SOCS1 has a negative regulatory role in FABP4-dependent activation of the JAK2/STAT2 pathway and Rap1a in macrophage inflammatory response induced by Hcy.