Wnts heal by restraining angiogenesis

CD301b+ macrophages mediate angiogenesis of calcium phosphate bioceramics by CaN/NFATc1/VEGF axis

Calcium phosphate (CaP) bioceramics are important for tissue regeneration and immune response, yet how CaP bioceramics influence these biological processes remains unclear. Recently, the role of immune cells in biomaterial-mediated regeneration, especially macrophages, has been well concerned. CD301b⁺ macrophages were a new subset of macrophages we have discovered, which were required for bioceramics-mediated bone regeneration. Nevertheless, the impact of CD301b⁺ macrophages on angiogenesis, which is a vital prerequisite to bone formation is yet indistinct. Herein, we found that CD301b⁺ macrophages were closely correlated to angiogenesis of CaP bioceramics. Additionally, depletion of CD301b⁺ macrophages led to the failure of angiogenesis. We showed that store-operated Ca²⁺ entry and calcineurin signals regulated the VEGF expression of CD301b⁺ macrophages via the NFATc1/VEGF axis. Inhibition of calcineurin effectively impaired angiogenesis via decreasing the infiltration of CD301b⁺ macrophages. These findings provided a potential immunomodulatory strategy to optimize the integration of angiogenesis and bone tissue engineering scaffold materials.

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BCP bioceramics need the involvement of CD301b⁺ macrophages to promote angiogenesis.

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Surrounding BCP, CD301b⁺ macrophages are controlled by CaN and SOCE to express VEGF.

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BCP bioceramics direct CD301b⁺ macrophages' infiltration partly through calcineurin.

Identification of different macrophage subpopulations with distinct activities in a mouse model of oxygen-induced retinopathy

The aim of the present study was to characterize the phenotypic shift, quantity and role changes in different subgroups of retinal macrophages in a mouse model of oxygen-induced retinopathy (OIR). The mRNA expression levels of macrophage M1 and M2 subgroup marker genes and polarization-associated genes were analyzed by RT-qPCR. The number of M1 and M2 macrophages in our mouse model of OIR was analyzed by flow cytometry at different time points during the progression of OIR. Immunofluorescence whole mount staining of the retinas of mice with OIR was performed at different time points to examine the influx of macrophages, as well as the morphological characteristics and roles of M1 and M2 macrophages. An increased number of macrophages was recruited during the progression of angiogenesis in the retinas of mice with OIR due to the pro-inflammatory microenvironment containing high levels of cell adhesion and leukocyte transendothelial migration molecules. RT-qPCR and flow cytometric analysis at different time points revealed a decline in the number of M1 cells from a significantly high level at post-natal day (P)13 to a relatively normal level at P21, as well as an increase in the number of M2 cells from P13 to P21 in the mice with OIR, implicating a shift of macrophage polarization towards the M2 subtype. Immunofluorescence staining suggested that the M1 cells interacted with endothelial tip cells at the vascular front, while M2 cells embraced the emerging vessels and bridged the neighboring vessel sprouts. Thus, our data indicate that macrophages play an active role in OIR by contributing to the different steps of neovascularization. Our findings indicate that tissue macrophages may be considered as a potential target for the anti-angiogenic therapy of ocular neovascularization disease.

Immunohistochemical Expression of MCAM/CD146 in Canine Melanoma

MCAM/CD146 (melanoma cell adhesion molecule/CD146) is a transmembrane immunoglobulin superfamily cell adhesion molecule involved in transendothelial migration and signal transduction. It is expressed in melanoma, squamous cell carcinoma, prostatic, ovarian, cervical and endometrial cancers and promotes tumour growth, angiogenesis and metastasis. Melanoma is the most common malignant oral tumour of dogs and also arises in the skin, nail bed and footpad. The aim of this study was to investigate the immunohistochemical expression of MCAM/CD146 in 51 canine melanomas, including oral, cutaneous and ocular tumours. Seventeen of the 51 (33.3%) cases were negative, eight (15.7%) were weakly positive, seven (13.7%) were moderately positive and 19 (37.3%) were strongly positive. MCAM/CD146 was expressed by both oral and cutaneous melanomas; however, the intensity and the extent of the immunoreactivity was higher in oral (P = 0.009) than in cutaneous tumours (P = 0.058). Most ocular melanomas did not express MCAM/CD146 (P = 0.256). Expression of MCAM/CD146 by canine melanomas may suggest the molecule as a target for treatment, especially in oral melanomas.

Delivery strategies to control inflammatory response: Modulating M1-M2 polarization in tissue engineering applications

Macrophages are key players in many physiological scenarios including tissue homeostasis. In response to injury, typically the balance between macrophage sub-populations shifts from an M1 phenotype (pro-inflammatory) to an M2 phenotype (anti-inflammatory). In tissue engineering scenarios, after implantation of any device, it is desirable to exercise control on this M1-M2 progression and to ensure a timely and smooth transition from the inflammatory to the healing stage. In this review, we briefly introduce the current state of knowledge regarding macrophage function and nomenclature. Next, we discuss the use of controlled release strategies to tune the balance between the M1 and M2 phenotypes in the context of tissue engineering applications. We discuss recent literature related to the release of anti-inflammatory molecules (including nucleic acids) and the sequential release of cytokines to promote a timely M1-M2 shift. In addition, we describe the use of macrophages as controlled release agents upon stimulation by physical and/or mechanical cues provided by scaffolds. Moreover, we discuss current and future applications of "smart" implantable scaffolds capable of controlling the cascade of biochemical events related to healing and vascularization. Finally, we provide our opinion on the current challenges and the future research directions to improve our understanding of the M1-M2 macrophage balance and properly exploit it in tissue engineering and regenerative medicine applications.

CD146 acts as a novel receptor for netrin-1 in promoting angiogenesis and vascular development

Angiogenesis, a process that newly-formed blood vessels sprout from pre-existing ones, is vital for vertebrate development and adult homeostasis. Previous studies have demonstrated that the neuronal guidance molecule netrin-1 participates in angiogenesis and morphogenesis of the vascular system. Netrin-1 exhibits dual activities in angiogenesis: either promoting or inhibiting angiogenesis. The anti-angiogenic activity of netrin-1 is mediated by UNC5B receptor. However, how netrin-1 promotes angiogenesis remained unclear. Here we report that CD146, an endothelial transmembrane protein of the immunoglobulin superfamily, is a receptor for netrin-1. Netrin-1 binds to CD146 with high affinity, inducing endothelial cell activation and downstream signaling in a CD146-dependent manner. Conditional knockout of the cd146 gene in the murine endothelium or disruption of netrin-CD146 interaction by a specific anti-CD146 antibody blocks or reduces netrin-1-induced angiogenesis. In zebrafish embryos, downregulating either netrin-1a or CD146 results in vascular defects with striking similarity. Moreover, knocking down CD146 blocks ectopic vascular sprouting induced by netrin-1 overexpression. Together, our data uncover CD146 as a previously unknown receptor for netrin-1 and also reveal a functional ligand for CD146 in angiogenesis, demonstrating the involvement of netrin-CD146 signaling in angiogenesis during vertebrate development.

Macrophages modulate engineered human tissues for enhanced vascularization and healing

Tissue engineering is increasingly based on recapitulating human physiology, through integration of biological principles into engineering designs. In spite of all progress in engineering functional human tissues, we are just beginning to develop effective methods for establishing blood perfusion and controlling the inflammatory factors following implantation into the host. Functional vasculature largely determines tissue survival and function in vivo. The inflammatory response is a major regulator of vascularization and overall functionality of engineered tissues, through the activity of different types of macrophages and the cytokines they secrete. We discuss here the cell-scaffold-bioreactor systems for harnessing the inflammatory response for enhanced tissue vascularization and healing. To this end, inert scaffolds that have been considered for many decades a "gold standard" in regenerative medicine are beginning to be replaced by a new generation of "smart" tissue engineering systems designed to actively mediate tissue survival and function.

Macrophages modulate adult zebrafish tail fin regeneration

Neutrophils and macrophages, as key mediators of inflammation, have defined functionally important roles in mammalian tissue repair. Although recent evidence suggests that similar cells exist in zebrafish and also migrate to sites of injury in larvae, whether these cells are functionally important for wound healing or regeneration in adult zebrafish is unknown. To begin to address these questions, we first tracked neutrophils (lyzC⁺, mpo⁺) and macrophages (mpeg1⁺) in adult zebrafish following amputation of the tail fin, and detailed a migratory timecourse that revealed conserved elements of the inflammatory cell response with mammals. Next, we used transgenic zebrafish in which we could selectively ablate macrophages, which allowed us to investigate whether macrophages were required for tail fin regeneration. We identified stage-dependent functional roles of macrophages in mediating fin tissue outgrowth and bony ray patterning, in part through modulating levels of blastema proliferation. Moreover, we also sought to detail molecular regulators of inflammation in adult zebrafish and identified Wnt/β-catenin as a signaling pathway that regulates the injury microenvironment, inflammatory cell migration and macrophage phenotype. These results provide a cellular and molecular link between components of the inflammation response and regeneration in adult zebrafish.

The role of macrophage phenotype in vascularization of tissue engineering scaffolds

Angiogenesis is crucial for the success of most tissue engineering strategies. The natural inflammatory response is a major regulator of vascularization, through the activity of different types of macrophages and the cytokines they secrete. Macrophages exist on a spectrum of diverse phenotypes, from "classically activated" M1 to "alternatively activated" M2 macrophages. M2 macrophages, including the subsets M2a and M2c, are typically considered to promote angiogenesis and tissue regeneration, while M1 macrophages are considered to be anti-angiogenic, although these classifications are controversial. Here we show that in contrast to this traditional paradigm, primary human M1 macrophages secrete the highest levels of potent angiogenic stimulators including VEGF; M2a macrophages secrete the highest levels of PDGF-BB, a chemoattractant for stabilizing pericytes, and also promote anastomosis of sprouting endothelial cells in vitro; and M2c macrophages secrete the highest levels of MMP9, an important protease involved in vascular remodeling. In a murine subcutaneous implantation model, porous collagen scaffolds were surrounded by a fibrous capsule, coincident with high expression of M2 macrophage markers, while scaffolds coated with the bacterial lipopolysaccharide were degraded by inflammatory macrophages, and glutaraldehyde-crosslinked scaffolds were infiltrated by substantial numbers of blood vessels, accompanied by high levels of M1 and M2 macrophages. These results suggest that coordinated efforts by both M1 and M2 macrophages are required for angiogenesis and scaffold vascularization, which may explain some of the controversy over which phenotype is the angiogenic phenotype.