The C5a/C5a receptor 1 axis controls tissue neovascularization through CXCL4 release from platelets

Abstract

Platelets contribute to the regulation of tissue neovascularization, although the specific factors underlying this function are unknown. Here, we identified the complement anaphylatoxin C5a-mediated activation of C5a receptor 1 (C5aR1) on platelets as a negative regulatory mechanism of vessel formation. We showed that platelets expressing C5aR1 exert an inhibitory effect on endothelial cell functions such as migration and 2D and 3D tube formation. Growth factor- and hypoxia-driven vascularization was markedly increased in C5ar1−/− mice. Platelet-specific deletion of C5aR1 resulted in a proangiogenic phenotype with increased collateralization, capillarization and improved pericyte coverage. Mechanistically, we found that C5a induced preferential release of CXC chemokine ligand 4 (CXCL4, PF4) from platelets as an important antiangiogenic paracrine effector molecule. Interfering with the C5aR1-CXCL4 axis reversed the antiangiogenic effect of platelets both in vitro and in vivo.In conclusion, we identified a mechanism for the control of tissue neovascularization through C5a/C5aR1 axis activation in platelets and subsequent induction of the antiangiogenic factor CXCL4.

Platelet and Megakaryocyte Roles in Innate and Adaptive Immunity

“…90 Platelets can also be activated through the C5a/C5aR axis and C5a activated platelets inhibit endothelial migration and tube formation. 91 Mechanistically, C5aR-activated platelets exert their antiangiogenic activity on endothelial cells through PF4 secretion. 91 Lack of C5aR on platelets allows for more collateral artery formation and pericyte coverage.…”

“…91 Mechanistically, C5aR-activated platelets exert their antiangiogenic activity on endothelial cells through PF4 secretion. 91 Lack of C5aR on platelets allows for more collateral artery formation and pericyte coverage. 91 It has been proposed that the insertion of the C5b-C9 complex in the platelet membrane can trigger platelet-microparticle formation and release.…”

Platelet depletion does not alter long-term functional outcome after cerebral ischaemia in mice

“…Various studies investigating vascularisation provide conflictive results on the contribution of platelets. Indeed, platelet-derived microparticles (PMP) similar to other platelet-derived factors appeared to be positive regulators of neovascularisation ( Hayon et al, 2012 , 2013 ; Packham et al, 2014 ), although these findings still remain controversial ( Nording et al, 2021 ). Hence, we performed light sheet fluorescent microscopy (LSFM) analysis using brains 28 days after stroke to further identify a potential effect of platelet depletion in vascularisation.…”

“…In a muscle overload in vivo study, inhibition or depletion of platelets resulted in decreased sprouting and longitudinal splitting of vessels ( Packham et al, 2014 ), underscoring the involvement of platelet-derived factors in angiogenesis. Conversely, platelet-secreted PF4 negatively regulated neovascularisation in part by inhibiting endothelial cell functions such as tube formation and migration in vitro and in vivo after hind limb ischaemia ( Nording et al, 2021 ).…”

“…These protective effects were retained in aged and comorbid mice ( Kraft et al, 2015 ) and even in combination with thrombolysis via rt-PA ( Schuhmann et al, 2019 ). In particular, platelets appear to modify post-stroke neuroinflammation and angiogenesis through interaction with various immune cells ( Nording et al, 2021 ; Packham et al, 2014 ; Schuhmann et al, 2020 ).…”