C3 Deficiency Leads to Increased Angiogenesis and Elevated Pro-Angiogenic Leukocyte Recruitment in Ischemic Muscle Tissue

Abstract

The complement system is a potent inflammatory trigger, activator, and chemoattractant for leukocytes, which play a crucial role in promoting angiogenesis. However, little information is available about the influence of the complement system on angiogenesis in ischemic muscle tissue. To address this topic and analyze the impact of the complement system on angiogenesis, we induced muscle ischemia in complement factor C3 deficient (C3−/−) and wildtype control mice by femoral artery ligation (FAL). At 24 h and 7 days after FAL, we isolated the ischemic gastrocnemius muscles and investigated them by means of (immuno-)histological analyses. C3−/− mice showed elevated ischemic damage 7 days after FAL, as evidenced by H&E staining. In addition, angiogenesis was increased in C3−/− mice, as demonstrated by increased capillary/muscle fiber ratio and increased proliferating endothelial cells (CD31+/BrdU+). Moreover, our results showed that the total number of leukocytes (CD45+) was increased in C3−/− mice, which was based on an increased number of neutrophils (MPO+), neutrophil extracellular trap formation (MPO+/CitH3+), and macrophages (CD68+) displaying a shift toward an anti-inflammatory and pro-angiogenic M2-like polarized phenotype (CD68+/MRC1+). In summary, we show that the deficiency of complement factor C3 increased neutrophil and M2-like polarized macrophage accumulation in ischemic muscle tissue, contributing to angiogenesis.

MEFV, IRF8, ADA, PEPD, and NBAS gene variants and elevated serum cytokines in a patient with unilateral sporadic Meniere's disease and vascular congestion over the endolymphatic sac

“…C3 and C4 are important opsonins that bind to and facilitate the clearance of immune complexes and apoptotic debris, which would otherwise promote inflammation and autoimmune diseases. Angiogenesis was found to be increased in C3 −/− mice, as demonstrated by an increased capillary/muscle fiber ratio and increased proliferating endothelial cells ( Gotz et al., 2021 ). Complete C4 deficiency was reported in SLE patients who finally developed fatal central nervous system vasculitis ( Rupert et al., 2002 ).…”

C3‐dependent effector functions of complement

“…In a model of retinopathy of prematurity, C3−/− mice displayed increased neovascularization, 36 and in a model of muscle ischemia, angiogenesis was associated with increased neutrophil and macrophage infiltration. 37 C3 has a large number of direct and indirect downstream functions, the molecular details of which are discussed in the coming sections. Before that, to highlight the double-edged sword of C3 activation, we will give an overview of the deleterious effects of C3 activation.…”

Fibrinogen and Antifibrinolytic Proteins: Interactions and Future Therapeutics

“…Deficiencies in proteins of the complement system are usually hereditary and associated with increased susceptibility to infections [118]. Recent animal studies have revealed an association between C3 deficiency and increased angiogenesis, which may have implications for vascular occlusive disease [119,120].…”