Leukocytes and Perfusion Recovery after Arterial Occlusion

The main topic of this thesis is arteriogenesis and the role circulating leukocytes play in this process of perfusion recovery. We have used clinically applicable inhibitors to increase leukocyte attraction and extravasation and discovered previously unknown factors which play a role in arteriogenesis. In chapter 2 we sought to further elucidate the systemic changes that occur in circulating leukocytes after arterial occlusion. We have shown that the total number of leukocytes did not change after arterial occlusion. However, leukocyte number within the different subsets changed dramatically and the emerging temporal patterns differed per leukocyte subset. In addition, the observed changes could be linked to the corresponding progenitor cells in the bone marrow. In chapter 3 we used the clinically available CD26 inhibitor Sitaglipin to improve perfusion recovery in atherosclerosis prone ApoE -/- mice. Daily doses of the CD26 inhibitor improved both short term (7 days) and long term (56 days) perfusion recovery. As previous pro-arteriogenic factors also proved to increase atherosclerosis we assessed plaque stability in ApoE -/- mice during CD26 inhibition. Plaque stability and plaque size were unaffected by CD26 inhibition indicating that CD26 inhibition might be a feasible therapeutic strategy to improve perfusion recovery in the clinic. In addition, recent results have shown that CD26 inhibition deters the progression of atherosclerosis in murine models[1,2]. To improve our understanding of the role that CD26 plays in human plaques we assessed CD26 content in chapter 4. We show that a higher CD26 content is correlated to a more atheromatous plaque in contrast to a more fibrous plaque. In addition, a higher CD26 content is related to a high number of macrophages, a larger lipid core and less smooth muscle cells. Our data indicates that CD26 is involved in the progression towards a more vulnerable plaque phenotype. However, based on our studies we cannot draw any conclusions on the mechanisms involved. In chapter 5 we explored the role of platelets in perfusion recovery. Platelet depleted mice were generated using a platelet depleting antibody. Platelet depleted mice show decreased perfusion recovery as well as reduced arterial remodeling. Macrophage numbers around growing collaterals were decreased and ex vivo models showed that leukocyte rolling was absent in blood from platelet depleted mice. Our results indicate that platelets are involved in the process of monocyte extravasation which is crucial for perfusion recovery. In chapter 6 we assessed differences in mRNA expression between leukocyte samples obtained at different time points after perfusion recovery. We assessed mRNA expression of CXCL10 which is a component of the TLR-pathway and found that its expression was down regulated. Using CXCL10 -/- mice we showed that mice lacking CXCL10 display a decrease in perfusion recovery when compared to WT mice. To elucidate the role of CXCL10 specifically in bone marrow derived cells we generated chimeric mice which lack CXCL10 in their bone marrow derived cells. These mice showed a similar decrease in perfusion recovery indicating that the expression of CXCL10 in leukocytes is of importance during perfusion recovery