Abstract 12967: Tlr Accessory Molecule RP105 (CD180) Modulates Monocyte Activation and Moderates Arteriogenesis
Introduction: TLR4 plays an important role in arteriogenesis. RP105 (CD180) is a homolog and physiological negative regulator specific of TLR4-signaling. The role of RP105 in arteriogenesis is still unknown.
Methods and Results: We demonstrate that mRNA expression pattern of RP105 mirrors that of TLR4 in both adductor and calf muscle after the surgical induction of hindlimb ischemia in wildtype (WT) mice. RP105 deficiency does result in a pro-inflammatory cytokine response. Ex vivo whole blood stimulation with LPS (as TLR4 ligand) shows a dose-dependent exaggerated TNFα response in RP105−/− mice compared to wildtype (WT) mice, measured by ELISA. Also in vivo, RP105−/− mice produce significantly more TNFα in response to LPS. Blood flow recovery after hindlimb ischemia is significantly impaired in RP105−/− mice up to four weeks. Also the smooth muscle actin positive vessels in the adductor muscle of RP105−/− mice show a reduced increase in growth. FACS analysis demonstrates equal numbers of monocytes (CD11b+Ly6G-CD115+) in WT and RP105−/− mice. Whole blood LPS stimulation shows a different activation state of circulating monocytes, measured by mean fluorescence intensity of CD11b. In particular the (pro-inflammatory) Ly6Chi monocyte population is significantly more activated in the RP105−/− mice at baseline and after LPS stimulation. Also in the ischemic muscle tissue (1 day after surgery) the Ly6Chi monocytes show a more activated phenotype in the RP105−/− mice and less infiltration of these overactivated Ly6Chi monocytes is observed. These data suggest a premature or overactivated immune system in RP105−/− mice. To test this in more detail we investigated whether the beneficial effect of LPS on arteriogenesis is absent in RP105−/− mice. Hindlimb ischemia was induced in both WT and RP105−/− mice and mice were injected with saline or LPS at day 3 after hindlimb ischemia induction. LPS injection enhanced blood flow recovery in WT mice but showed no additional effect in RP105−/− mice.
Conclusion: We conclude that RP105 plays an important role in blood flow recovery after hindlimb ischemia and that the hampered blood flow recovery in RP105−/− mice is a result of premature activated Ly6Chi monocytes which infiltrate less in ischemic tissue.
- © 2011 by American Heart Association, Inc.