# Flow-induced Klf4-Akt signaling links EC cycling to mural cell defects in arterial-venous malformations

## TL;DR

This study shows how disrupted blood flow causes abnormal cell growth and weakens blood vessel walls in a genetic disorder called Hereditary Hemorrhagic Telangiectasia.

## Contribution

The paper identifies a new signaling pathway (Klf4-Akt) linking endothelial cell cycling to mural cell defects in arterial-venous malformations.

## Key findings

- AVM endothelium shows excessive KLF4-Akt activation and sustained cell proliferation under pathological flow.
- Hyperproliferation suppresses PDGFB, leading to pericyte loss and mural cell remodeling.
- Inhibiting KLF4, Akt, or CDK4/6, or using thalidomide to induce PDGFB, reduces AVM burden in models.

## Abstract

Fluid shear stress (FSS) safeguards vascular homeostasis, coordinating endothelial cell (EC) behavior and endothelial - mural cell communication. Disrupted flow sensing driving excessive proliferation contribute to arterial-venous malformations (AVMs) in Hereditary Hemorrhagic Telangiectasia (HHT) vascular disorder. Yet, how flow-dependent cell cycle regulation intersects with mural cell remodeling in HHT remains unclear.

We used a combination between in vitro shear stress assays and in vivo analyses of multiple murine HHT models, including endothelial-specific loss of Activin-like kinase 1 (Alk1) or Smad4 and bone morphogenic factor 9/10 (BMP9/10) ligand blockade. Retinal vasculature and human nasal mucosal biopsies from HHT2 patients were examined for pathway conservation. Endothelial - mural cell crosstalk was evaluated using transwell and three-dimensional flow-dependent co-culture assays. Loss and gain of function studies were employed to define disease mechanisms.

Across all studied murine HHT models and in HHT2 telangiectasias, AVM endothelium exhibited excessive flow-induced Krüpper-like 4 (KLF4) - Akt pathway activation, sustained EC proliferation, and abolition of FSS-mediated cyclin-dependent kinases 2/6 (CDK2/6) inhibition. The hyperproliferative state suppressed the expression of endothelial platelet-derived growth factor B (PDGFB) leading to pericyte loss, and and mural cell remodeling in AVMs. Restoration of endothelial quiescence via inhibition of KLF4, Akt or CDK4/6 rescued FSS-induced PDGFB expression. Pharmacological PDGFB induction with thalidomide restored mural cell coverage, and significantly reduced AVM burden in vivo.

Our study establishes EC cycle state as the upstream determinant of mural cell stability under pathological flow and provides the mechanistic reasoning for why distinct therapeutic strategies (e.g., CDK4/6 inhibition, Akt modulation, or thalidomide-induced PDGFB upregulation) converge on AVM stabilization.