# Downregulation of the Long Non-Coding RNA KLRK1-AS1 Disturbs Endothelial Barrier Integrity and Promotes Angiogenic Sprouting

## TL;DR

This study shows that reducing the lncRNA KLRK1-AS1 weakens blood vessel barriers but boosts new blood vessel growth in endothelial cells.

## Contribution

Identifies KLRK1-AS1 as a novel regulator of endothelial barrier integrity and angiogenic behavior.

## Key findings

- KLRK1-AS1 knockdown reduced endothelial barrier integrity by 44%.
- Loss of KLRK1-AS1 increased angiogenic sprouting by 62%.
- KLRK1-AS1 supports a stable, quiescent endothelial phenotype.

## Abstract

Endothelial integrity is essential for cardiovascular health, and circulating endothelial progenitor cells, particularly endothelial colony-forming cells (ECFCs), are key contributors to vascular repair and maintenance. Long non-coding RNAs (lncRNAs) have emerged as novel epigenetic regulators of endothelial physiology and pathology. Building on our previous work identifying the lncRNA KLRK1-AS1 as a positive modulator of ECFC wound healing, we aimed to elucidate its role in endothelial biology. Cord blood-derived ECFCs were subjected to siRNA-mediated silencing of KLRK1-AS1, followed by blinded evaluations of monolayer morphology, barrier stability using ECIS impedance measurements, assessments of proliferation, and spheroid-based angiogenic activity. SiRNA-mediated silencing of KLRK1-AS1 induced detectable alterations in ECFC monolayer morphology (p = 0.047), while proliferation remained unaffected. Notably, KLRK1-AS1 knockdown significantly compromised endothelial barrier integrity, resulting in a 44% reduction in impedance after 48 h (p < 0.001), suggesting weakened intercellular contacts. In contrast, loss of KLRK1-AS1 enhanced angiogenic behaviour, demonstrated by an increased number of sprouts (+62%, p = 0.031). Together, these findings indicate that KLRK1-AS1 supports a quiescent, stable endothelial phenotype, with intact barrier function, while its depletion shifts ECFCs toward a more angiogenic, activated state. Our results identify KLRK1-AS1 as a previously unrecognised regulator of endothelial function.