Endothelial-specific deficiency of Junctional Adhesion Molecule-C promotes vessel normalisation in proliferative retinopathy

Abstract

In proliferative retinopathies, like proliferative diabetic retinopathy and retinopathy of prematurity (ROP), the hypoxia response is sustained by the failure of the retina to revascularise its ischaemic areas. Non-resolving retina ischaemia/hypoxia results in upregulation of pro-angiogenic factors and pathologic neovascularisation with ectopic, fragile neovessels. Promoting revascularisation of the retinal avascular area could interfere with this vicious cycle and lead to vessel normalisation. Here, we examined the function of endothelial junctional adhesion molecule-C (JAM-C) in the context of ROP. Endothelial-specific JAM-C-deficient (EC-JAM-C KO) mice and littermate JAM-C-proficient (EC-JAM-C WT) mice were subjected to the ROP model. An increase in total retinal vascularisation was found at p17 owing to endothelial JAM-C deficiency, which was the result of enhanced revascularisation and vessel normalisation, thereby leading to significantly reduced avascular area in EC-JAM-C KO mice. In contrast, pathologic neovessel formation was not affected by endothelial JAM-C deficiency. Consistent with improved vessel normalisation, tip cell formation at the interface between vascular and avascular area was higher in EC-JAM-C KO mice, as compared to their littermate controls. Consistently, JAM-C inactivation in endothelial cells resulted in increased spreading on fibronectin and enhanced sprouting in vitro in a manner dependent on β1-integrin and on the activation of the small GTPase RAP1. Together, endothelial deletion of JAM-C promoted endothelial cell sprouting, and consequently vessel normalisation and revascularisation of the hypoxic retina without altering pathologic neovascularisation. Thus, targeting endothelial JAM-C may provide a novel therapeutic strategy for promoting revascularisation and vessel normalisation in the treatment of proliferative retinopathies.

The inner blood-retinal barrier: Cellular basis and development

“…JAM-A expression on monocytes facilitates its movement across the BBB (Williams, Anastos et al 2015), while JAM-A knockout and endothelial specific JAM-A deficient mice, prevent neutrophil transmigration (Woodfin, Reichel et al 2007). Further, although JAM-C and JAM-B are expressed at the junctions of the retinal pigment epithelium (RPE), JAM-C deficient animals showed increased JAM-A expression and enhanced retinal vascularization (Daniele, Adams et al 2007, Economopoulou, Avramovic et al 2015) suggesting a role for JAMs in retinal angiogenesis.…”

Dynamic trafficking and turnover of JAM-C is essential for endothelial cell migration

“…JAM-C is known to mediate a number of important biological processes, including angiogenesis [16,38–41] and leukocyte transmigration [8–12]. To determine how altering the ubiquitin-mediated trafficking of JAM-C affects its cellular function, we performed scratch wound assays.…”

Mechanisms Ensuring Endothelial Junction Integrity Beyond VE-Cadherin

“…In vitro tube formation and in vivo matrigel plug assay (Cao et al, 2009) No defect in endothelial junction integrity in KO mice (Duong et al, 2020) Enhanced effects of inflammation inducing agents upon blocking or depletion (Ferrero et al, 1995;Graesser et al, 2002;Carrithers et al, 2005;Maas et al, 2005;Liao et al, 2018) JAM-A Matrigel plug assays (Cooke et al, 2006); angiogenesis in corneal wound healing assays (Chatterjee et al, 2013) No defect in endothelial junction integrity in KO mice (Duong et al, 2020) Enhanced effects of inflammation inducing agents upon blocking or depletion (Mandell et al, 2006;Mitchell et al, 2015) JAM-C Antibodies and soluble JAM-C interfere with neovascularization in the retina (Lamagna et al, 2005;Hou et al, 2012;Economopoulou et al, 2015) Reduced effects of inflammation inducing agents upon blocking or depletion (Orlova et al, 2006;Li et al, 2009) ESAM Support of VE-cadherin function in anastomosis in zebrafish embryo (Sauteur et al, 2017); no role in mouse embryonic angiogenesis (Wegmann et al, 2006;Ueda et al, 2019), but tumor angiogenesis and matrigel plug assay (Ishida et al, 2003) Plasma leaks in lung, but not heart, skin and brain in KO mice (Duong et al, 2020); rupture of endothelial junctions in lung upon simultaneous block of ESAM and VE-cadherin (Duong et al, 2020) Reduced effects of inflammation inducing agents upon gene inactivation (Wegmann et al, 2006) Cldn5…”