Authors: Evelina Vågesjö, Kristel Parv, David Ahl, Cédric Seignez, Carmen Herrera Hidalgo, Antoine Giraud, Catarina Amoêdo-Leite, Olle Korsgren, Håkan Wallén, Greta Juusola, Harri H Hakovirta, Helene Rundqvist, Magnus Essand, Lena Holm, Randall Johnson, Charlotte Thålin, Petra Korpisalo, Gustaf Christoffersson, Mia Phillipson
Summary: Rationale: Ischemic injuries remain a leading cause of mortality and morbidity worldwide, and restoration of functional blood perfusion is vital to limit tissue damage and support healing.
Objective: To reveal a novel role of macrophages in reestablishment of functional tissue perfusion following ischemic injury that can be targeted to improve tissue restoration.
Methods and Results: Using intravital microscopy of ischemic hind limb muscle in mice, and confocal microscopy of human tissues from amputated legs, we found that macrophages accumulated perivascularly in ischemic muscles, where they expressed high levels of iNOS. Genetic depletion of iNOS specifically in macrophages (Cx3cr1-CreERT2;Nos2fl/fl or LysM-Cre;Nos2fl/fl) did not affect vascular architecture but highly compromised blood flow regulation in ischemic but not healthy muscle, which resulted in aggravated ischemic damage. Thus, the ability to upregulate blood flow was shifted from eNOS (endothelial)-dependence in healthy muscles to completely rely on macrophage-derived iNOS during ischemia. Macrophages in ischemic muscles expressed high levels of CXCR4 and CCR2, and local overexpression by DNA plasmids encoding the corresponding chemokines CXCL12 or CCL2 increased macrophage numbers, while CXCL12 but not CCL2 induced their perivascular positioning. As a result, CXCL12-overexpression increased the number of perfused blood vessels in the ischemic muscles, improved functional muscle perfusion in a macrophage-iNOS-dependent manner, and ultimately restored limb function.
Conclusions: This study establishes a new function for macrophages during tissue repair, as they regulate blood flow through the release of iNOS-produced NO. Further, we demonstrate that macrophages can be therapeutically targeted to improve blood flow regulation and functional recovery of ischemic tissues.
Source: Circulation Research, 2021