Toll‐like receptor 4 activated ceramide kinase mediates inflammatory responses in vascular smooth muscle cells.

Lipopolysaccharide (LPS) signaling is critical for the innate immune response to gram‐negative bacteria through the toll‐like receptor 4 (TLR4). TLR4 is essential for LPS‐induced cytosolic phospholipase A 2 (cPLA 2 ) activation, lipid release, and production of pro‐inflammatory lipid mediators (Qi et al, JBC , 2005, 280(47): 38969–75). Ceramide‐1‐phosphate (C1P) is a phosphorylated bioactive sphingolipid that has been shown to specifically activate cPLA 2 (Chalfant et al, J Cell Sci, 2005, 118:) and to regulate many physiological processes, including cell proliferation, phagocytosis, and inflammation. C1P is formed by the phosphorylation of ceramide by ceramide kinase (CERK). We thus hypothesized that LPS‐induced activation of TLR4 may lead to activation of CERK and production of C1P leading to pro‐inflammatory angiogenic or restenotic vascular disease. We now demonstrate that LPS addition leads to elevated mRNA and protein levels of CERK, and that the increased expression of CERK correlates with increased C1P lipid mass in A7r5 rat aorta vascular smooth muscle cells (VSM). We also show that VSM responds to LPS or C1P with increased proliferation, positive remodeling, and production of inflammatory mediators. Inhibition of CERK‐generated C1P may be an ideal pharmacological target for the development of anti‐angiogenic or anti‐restenotic therapies. The abstract was funded, in part, by NIH R01 HL076789 to MK.