TLR4 and cardiovascular disorder: Norseen et al. (2012) found that RBP4 induced macrophage pro-inflammatory cytokine secretion and expression through activation of C-Jun N-terminal protein kinase (JNK) and Toll-like receptor 4 (TLR4)-dependent signaling pathways (Figure 1). Similarly, RBP4 was found to mediate vascular endothelial cell inflammatory responses via NADPH oxidase and NF-κB-dependent pathways (Farjo et al., 2012). In addition to endothelial cells, RBP4 also increases the proliferation of vascular smooth muscle cells through MAPK pathway and increases the risk of cardiovascular diseases (Li et al., 2015).