Shock wave treatment after hindlimb ischaemia results in increased perfusion and M2 macrophage presence.

Background Shock wave therapy (SWT) has been shown to induce angiogenesis in ischemic muscle. However, the mechanism of action remains unknown. Macrophages are crucial for angiogenic responses after ischemic injury. The M2 macrophage subset enables tissue repair and induces angiogenesis. We hypothesized that the angiogenic effects of SWT are at least partly caused by enhanced macrophage recruitment. Methods C57BL/6 mice were subjected to hind limb ischemia with subsequent SWT or sham treatment. Muscles were analyzed via immunofluorescence staining, RT-PCR and western blot. Gene expression and proteins involved in macrophage recruitment was analyzed. Tissue sections were stained for macrophages including subsets, capillaries and arterioles. Laser Doppler perfusion imaging was performed to assess functional outcome. Results Treated muscles showed increased expression of the pivotal macrophage recruiting factor monocyte chemotactic protein 1 (MCP-1). Higher levels of macrophage marker CD14 were found. Increased numbers of macrophages after SWT could be confirmed in immunofluorescence stainings. The expression of the M2 polarization promoting chemokine IL-13 was significantly elevated in the treatment group. We found elevated mRNA expression of the M2 scavenger receptor CD163 after SWT. Immunofluorescence stainings confirmed increased numbers of M2 macrophages after treatment. SWT resulted in higher number of capillaries and arterioles. Assessment of functional outcome revealed significantly improved limb perfusion in treated animals. Conclusion SWT causes increased macrophage recruitment and enhanced polarization towards reparative M2 macrophages in ischemic muscle resulting in angiogenesis and improved limb perfusion. SWT represents a promising new treatment option for the treatment of ischemic heart disease.