Evaluation of Pro-Angiogenic Activity of Factor XIII (FXIII) in Ischemic Tissue, Heart Transplantation and FXIII-Deficient Mice.
Authors: Inbal Aida , Leor Jonathan , Skutelsky Ehud , Castel David , Holbova Radka , Schibi Ganet , Goldberg Iris , Eskaraev Regina , Dardik Rima 
Published: April 2020

Abstract
FXIII, the last factor of the coagulation cascade, is a plasma transglutaminase that stabilizes fibrin clots by cross-linking fibrin chains. In addition to its role in coagulation, FXIII is essential for embryo implantation and wound healing - processes that involve angiogenesis. In our previous work (Dardik et al., Arterioscler. Thromb. Vasc. Biol., 2003:23: 1472) we showed that thrombin-activated FXIII (FXIIIa) exhibits pro-angiogenic activity that is associated with downregulation of thrombospondin (TSP-1). We next shoowed that the proangiogenic effect of FXIIIa is mediated by the phosphorylation and activation of VEGFR-2 receptor. Activated VEGFR-2 then initiates a signaling cascade leading to upregulation of cyclin D-1, Egr-1 and c-Jun, and downregulation of TSP-1 induced by c-Jun via WT-1 (submitted). In the current study we evaluated the pro-angiogenic effect of FXIIIa on cardiac ischemia (using rat myocardial ischemia model) or transplantation (usig murine neonatal cardiac allograft into pinnae ear transplant model). In addition, angiogenesis in FXIII-deficient mice was studied using in vivo Matrigel model. Following myocardial ischemia, a significant increase in new vessel formation was observed in the FXIIIa-injected as compared to saline-injected rats: 142±15/mm2 vs 64±15/mm2; respectively, p = &lt;0.001. The increase in new vessel formation in the bFGF-treated animals (positive control) was similar to that observed in FXIIIa-treated mice (144±22/mm2; p = 0.6). Similarly, in the neonatal cardiac allograft transplant model the number of new vessels was higher in FXIIIa-treated animals than in controls 31.7±3.3 vs. 21.1±5.7; p&lt;0.003. Moreover the function of the transplanted tissue as reflected by % heart beating area was significantly increased in FXIIIa-treated hearts than in the controls 64.7±14.9 vs. 40.3±21.2, respectively; p = 0.04.. In addition, the number of mice with &gt;80% beating area was significantly higher in the FXIIIa-treated group that in the control: 46% vs 17%, respectively; p = 0.038. Histological analysis of the matrigel sections from FXIII-deficient mice showed significantly decreased number of new vessels compared to that of the control mice and the number of the vessels increased after treatment with FXIII (5.9±1.9 vr. 8.8±2.4 vr. 7.4±2.9, respectively, P=0.004). Similarly, the values of hemoglobin measured in the matrigel tissue were significantly higher in the control group as compared to that of the FXIII-deficient - group, increasding after treatment with FXIII (4.6 ± 2.5 mg/mg matrigel vs 1.3 ± 1.0 mg/mg matrigel vs. 4.4±0.6 mg/mg matrigel, respectively; p = 0.01. The results of this study confirm the pro-angiogenic activity of FXIIIa in ischemic tissues and clarify its role in tissue remodeling, thus, opening new therapeutic options for this compound with regard to clinical conditions where perfusion via development of new vessels is crucial.