Live imaging of wound angiogenesis reveals macrophage orchestrated vessel sprouting and regression

Abstract

Wound angiogenesis is an integral part of tissue repair and is impaired in many pathologies of healing. Here, we investigate the cellular interactions between innate immune cells and endothelial cells at wounds that drive neoangiogenic sprouting in real time and in vivo. Our studies in mouse and zebrafish wounds indicate that macrophages are drawn to wound blood vessels soon after injury and are intimately associated throughout the repair process and that macrophage ablation results in impaired neoangiogenesis. Macrophages also positively influence wound angiogenesis by driving resolution of anti‐angiogenic wound neutrophils. Experimental manipulation of the wound environment to specifically alter macrophage activation state dramatically influences subsequent blood vessel sprouting, with premature dampening of tumour necrosis factor‐α expression leading to impaired neoangiogenesis. Complementary human tissue culture studies indicate that inflammatory macrophages associate with endothelial cells and are sufficient to drive vessel sprouting via vascular endothelial growth factor signalling. Subsequently, macrophages also play a role in blood vessel regression during the resolution phase of wound repair, and their absence, or shifted activation state, impairs appropriate vessel clearance.

Parathyroid Hormone Remodels Bone Transitional Vessels and the Leptin Receptor-Positive Pericyte Network in Mice

“…In nontumoral processes, vascular remodeling takes place after angiogenesis to produce a functional network. This process, referred to as post‐angiogenesis or vascular maturation, involves an integrated series of vascular activities, including inter alia, arteriovenous specification, vessel pruning, new vessel coverage by mature pericytes, and, in some tissues, the formation of a hierarchical network of vessels based on diameters . Although angiogenesis stricto sensu has been extensively studied, especially in cancer, post‐angiogenesis is not fully understood.…”

“…This process, referred to as post-angiogenesis or vascular maturation, involves an integrated series of vascular activities, including inter alia, arteriovenous specification, vessel pruning, new vessel coverage by mature pericytes, and, in some tissues, the formation of a hierarchical network of vessels based on diameters. (9,10) Although angiogenesis stricto sensu has been extensively studied, especially in cancer, post-angiogenesis is not fully understood. In retina development or during skin wound repair, this process is characterized by a complex cascade of events involving an array of genes such as PDGF-BB/PDGF-R alpha signaling, which controls pericyte recruitment to the vessel wall, or increase in angiopoietin2/angiopoietin1 ratio.…”

Osteoimmunology: Inflammatory osteolysis and regeneration of the alveolar bone

“…The contribution of macrophages to wound healing and bone regeneration involves angiogenesis. In mouse models, macrophages positively influence angiogenesis by driving resolution of anti‐angiogenic wound neutrophils (Gurevich et al., ). Macrophages also contribute to wound healing by their expression of IL10.…”

Live imaging the Foreign Body Response reveals how dampening inflammation reduces fibrosis

“…An effective angiogenic response is pivotal for both wound healing (Eming et al, 2014) and biomaterial integration (Spiller et al, 2015). Our previous work has indicated that proinflammatory macrophages expressing tumour necrosis factor α (tnfα) are critical in driving sprouting angiogenesis during tissue repair, but that macrophages must switch to an antiinflammatory, tnfα negative state at later stages to enable appropriate subsequent vessel remodelling and regression (Gurevich et al, 2018). We have used our suture implantation model to observe the dynamic changes that occur with respect to both tissue inflammation and angiogenesis during a FBR.…”

“…We have developed a genetically tractable and translucent model of the FBR that allows for transgenic fluorescent marking of various cells and tissues, enabling the real-time visualisation of immune cell-foreign body interaction over time in a non-invasive manner (Witherel et al, 2017). Aside from external fibrin clot formation, most steps of mammalian wound repair appear to be well conserved in zebrafish and have previously been extensively characterised (Gurevich et al, 2018;Mathias et al, 2009;Renshaw et al, 2006;Richardson et al, 2013); all the initial tissue interactions that are believed to contribute to the development of FBR are known to be present. By fluorescently labelling leukocytes, inflammatory markers and blood vessels, we are able to study the dynamic activities of cells in response to the implanted biomaterials, observing the interactions between these cells and the subsequent fibrotic encapsulation, and how these interactions can be modulated to reduce fibrosis and improve integration of biomaterials.…”