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

## TL;DR

Deleting the Tie2 receptor in heart endothelial cells boosts their growth and sprouting, which could help treat heart diseases.

## Contribution

This study shows that Tie2 deletion specifically enhances cardiac endothelial cell proliferation and sprouting without causing unwanted blood vessel growth.

## Key findings

- Deleting Tie2 increases cardiac endothelial cell proliferation and sprouting.
- Tie2 deletion leads to expression of tip cell markers like Angpt2 and Esm1 in heart endothelial cells.
- Tie2 deletion promotes migration of cultured endothelial cells.

## Abstract

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.

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 Tie1fl/fl, Tie2fl/fl, and Tie1fl/fl;Tie2fl/fl mice, in which vascular endothelial cadherin-driven CreERT2 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.

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.

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.

The online version contains supplementary material available at 10.1007/s10456-025-10028-2.