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 signaling domain and acts a TLR accessory molecule and physiological inhibitor of TLR4-signaling. The role of RP105 in vascular remodeling, in particular postinterventional 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 RP1052/2 mice resulting in a higher proliferation rate. In RP1052/2 mice femoral artery cuff placement resulted in an increase in neointima formation as compared to WT mice (49826974 mm2 vs.19476278 mm2,p = 0.0014). Local LPS application augmented neointima formation in both groups, but in RP1052/2 mice this effect was more pronounced (1031661243 mm2 vs.42086555 mm2,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 (25006573 vs.658161894 mm2,p,0.05), whereas expression of the single factors RP105 or MD1 had no effect.