TLR Accessory Molecule RP105 (CD180) Is Involved in Post-Interventional Vascular Remodeling and Soluble RP105 Modulates Neointima Formation

Background: RP105 (CD180) is TLR4 homologue lacking the intracellular TLR4 signalling domain and acts a TLR accessory molecule and physiological inhibitor of TLR4-signaling. The role of RP105 in vascular remodeling, in particular post-interventional remodeling is unknown. Methods and Results: TLR4 and RP105 are expressed on vascular smooth muscle cells (VSMC) as well as in the media of murine femoral artery segments as detected by qPCR and immunohistochemistry. Furthermore, the response to the TLR4 ligand LPS was stronger in VSMC from RP105(-/-) mice resulting in a higher proliferation rate. In RP105(-/-) mice femoral artery cuff placement resulted in an increase in neointima formation as compared to WT mice (4982 +/- 974 mu m(2) vs. 1947 +/- 278 mu m(2), p = 0.0014). Local LPS application augmented neointima formation in both groups, but in RP105(-/-) mice this effect was more pronounced (10316 +/- 1243 mu m(2) vs. 4208 +/- 555 mu m(2), p = 0.0002), suggesting a functional role for RP105. For additional functional studies, the extracellular domain of murine RP105 was expressed with or without its adaptor protein MD1 and purified. SEC-MALSanalysis showed a functional 2: 2 homodimer formation of the RP105-MD1 complex. This protein complex was able to block the TLR4 response in whole blood ex-vivo. In vivo gene transfer of plasmid vectors encoding the extracellular part of RP105 and its adaptor protein MD1 were performed to initiate a stable endogenous soluble protein production. Expression of soluble RP105-MD1 resulted in a significant reduction in neointima formation in hypercholesterolemic mice (2500 +/- 573 vs. 6581 +/- 1894 mu m(2), p < 0.05), whereas expression of the single factors RP105 or MD1 had no effect. Conclusion: RP105 is a potent inhibitor of post-interventional neointima formation.