Deletion of the angiopoietin receptor Tie2 enhances proliferation and sprouting of cardiac endothelial cells

Abstract Background Endothelial cells (ECs) of the heart proliferate and form new vessels in response to vascular endothelial growth factor (VEGF), but VEGF has not benefited the therapy of cardiac ischemia because of its side effects. Here, we explored if deletion of the vascular steady-state homeostasis maintaining Tie1 and Tie2 receptor tyrosine kinases affects the proliferation and sprouting of cardiac ECs. Methods We analyzed EC proliferation and histological and immunohistochemical stainings by confocal microscopy, plus scRNA and qPCR analyses of gene expression in the heart, kidneys, and lungs of Tie1 fl/fl , Tie2 fl/fl , and Tie1 fl/fl ; Tie2 fl/fl mice, in which vascular endothelial cadherin-driven CreER T2 recombinase was used to delete Tie1 , Tie2 or both receptors. These analyses were also performed in mice subjected to transverse aortic constriction (TAC). Boyden chamber assays were performed to assess the migration of cultured ECs in cultures with or without TIE receptor silencing. Results Genetic deletion of Tie1 , Tie2 , or Tie1/Tie2 in mice increased significantly the proliferation of cardiac but not renal or pulmonary ECs, as measured by EdU incorporation into DNA and quantification of the cell cycle marker cyclin D1. Tie1/Tie2 or Tie2 deletion, but not Tie1 deletion alone, induced EC sprouting in coronary vasculature and expression of endothelial tip cell markers, including expression of the FOXO1-regulated Angpt2 and Esm1 genes in cardiac versus kidney or lung ECs. Consistent with these findings, silencing of TIE2 , but not TIE1 , in cultured ECs resulted in increased migration of ECs. Similar results were obtained in mice subjected to TAC. Conclusion Deletion of Tie2 alone or together with Tie1 increases the proliferation and sprouting of cardiac, but not renal or pulmonary ECs, without to neovessel formation in the heart.