The interaction of heparan sulfate proteoglycans with endothelial transglutaminase-2 limits VEGF ₁₆₅ -induced angiogenesis

Abstract

Sprouting angiogenesis is stimulated by vascular endothelial growth factor (VEGF165) that is localized in the extracellular matrix (ECM) and binds to heparan sulfate (HS)-bearing proteins known as heparan sulfate proteoglycans (HSPGs). VEGF165 presentation by HSPGs enhances VEGF receptor-2 (VEGFR2) signaling. We investigated the effect of TG2, which binds to HSPGs, on the interaction between VEGF165 and HS and angiogenesis. Mice with tg2 deficiency showed transiently enhanced retina vessel formation and increased vascularization of VEGF165-containing Matrigel implants. In addition, endothelial cells in which TG2 was knocked down exhibited enhanced VEGF165-induced sprouting and migration, which was associated with increased phosphorylation of VEGFR2 at Tyr(951) and its targets Src and Akt. TG2 knockdown did not affect the phosphorylation of VEGFR2 at Tyr(1175) or cell proliferation in response to VEGF165 and sprouting or signaling in response to VEGF121. Decreased phosphorylation of VEGFR2 at Tyr(951) was due to ECM-localized TG2, which reduced the binding of VEGF165 to endothelial ECM in a manner that required its ability to bind to HS but not its catalytic activity. Surface plasmon resonance assays demonstrated that TG2 impeded the interaction between VEGF165 and HS. These results show that TG2 controls the formation of VEGF165-HSPG complexes and suggest that this regulation could be pharmacologically targeted to modulate developmental and therapeutic angiogenesis.

Vascular ageing and endothelial cell senescence: Molecular mechanisms of physiology and diseases

“…TG2, transglutaminase 2; VEGF165, vascular endothelial growth factor isoform 165; VEGFR2, vascular endothelial growth factor receptor2; HSPG, heparan sulfate proteoglycans. This scheme follows recent findings described in Beckouche et al (2015).…”

“…TG2 stabilize ECM by it cross-linking activity and interact with beta1-integrin, fibronectin, endostatin and HSPGs. In mice lacking TG2 Beckouche et al (2015) found increased retinal angiogenesis and sprouting of endothelial capillaries in response to this VEGF isoform, indicating that TG2, limiting VEGF165-mediated angiogenesis, acts as negative regulator. Among the vasculature changes in ageing there is an increase in vascular stiffness, associated with increased collagen deposition and elastin fracture/fragmentation in the ECM (Vaikevicius et al, 1993).…”

“…Reduced TG2 expression results in inhibition of fibronectin deposition in HUVEC, paralleled by a reduction in matrix-bound VEGFA and its down-stream effectors. Recently, in vivo studies using TG2KO mice, instead, found that TG2 prevented a specific VEGF isoform (VEGF165) from binding to HSPGs (Beckouche et al, 2015), (Fig. 2).…”

“…Proteins of the vascular endothelial growth factor (VEGF) family are key angiogenic factors. Selected VEGF isoforms bind the receptor VEGFR2 and heparan sulfate proteoglycans to stimulate angiogenesis, recently it has been shown that transglutaminase 2 (TG2) enzyme play a role in VEGF165-heparan sulfate proteoglycans interaction (Beckouche et al, 2015). TG2 is a Ca2+-dependent cross-linking enzyme that catalyzes the formation of -␥-glutamyl isopeptide bonds between peptide-bounds glutamine and lysine (Candi et al, 2005;De Laurenzi and Melino, 2001;Liu et al, 2002;Myneni et al, 2015;Rossin et al, 2015;Shrestha et al, 2015).…”

Essential Role of Transglutaminase 2 in Vascular Endothelial Growth Factor–Induced Vascular Leakage in the Retina of Diabetic Mice

“…However, whether extracellular TGase2 is involved in VEGF-induced vascular leakage is not clear. It was recently reported that extracellular TGase2 inhibits VEGF-induced angiogenesis by impeding the interaction of VEGF with heparan sulfate proteoglycans and subsequent VEGF receptor-2 signaling independent of its transamidating activity (39). There are, however, contradictory reports on the involvement of extracellular TGase2 activity in VEGF-mediated angiogenesis (40).…”