# Targeting Smad3 Phosphorylation Attenuates Anastomotic Intimal Hyperplasia and Perigraft Fibrosis in Decellularized Tissue-Engineered Vascular Grafts

## TL;DR

This study shows that targeting Smad3 phosphorylation can reduce harmful tissue growth and fibrosis in engineered blood vessel grafts without harming their regenerative benefits.

## Contribution

A targeted Smad3 inhibition strategy is introduced to selectively alleviate anastomotic intimal hyperplasia and perigraft fibrosis in tissue-engineered vascular grafts.

## Key findings

- M2 macrophage infiltration in dTEVGs is linked to increased anastomotic intimal hyperplasia and perigraft fibrosis.
- Smad3 phosphorylation inhibition reduces AIH and PGF without affecting M2 macrophage recruitment.
- IL-4-loaded delivery systems enhance M2 macrophage polarization but contribute to fibrosis through TGF-β1/Smad3 signaling.

## Abstract

Traditional polymer-based arteriovenous grafts (AVGs) for hemodialysis access suffer from poor long-term patency, high reintervention rates, and susceptibility to infection. In contrast, decellularized tissue-engineered vascular grafts (dTEVGs) demonstrate improved patency, long-term durability, and resistance to infection. However, vascular stenosis and occlusion caused by anastomotic intimal hyperplasia (AIH), as well as vascular stiffening and calcification from excessive perigraft fibrosis (PGF), remain major challenges in the clinical use of dTEVGs for AVGs. M2 macrophage infiltration plays a key role in the biological processes of pro-regeneration and the clinical application of dTEVGs. However, in elastin-rich dTEVGs commonly used clinically, the elastic fiber layers form a barrier to cell infiltration, potentially limiting their biological functions. Therefore, the specific impact of M2 macrophage infiltration on dTEVGs in AVGs remains unclear. Through parallel analysis of human explants and a rat dTEVG-AVG model, we found that M2 macrophage infiltration predominates in dTEVGs, and this infiltration is associated with AIH and PGF. Furthermore, IL-4-loaded poly(lactic-co-glycolic acid)/gelatin methacryloyl delivery systems selectively enhanced M2 macrophage polarization, while sustained M2 macrophage infiltration triggered TGF-β1/Smad3-dependent myofibroblast activation, leading to increased AIH and PGF. Pharmacological inhibition of Smad3 phosphorylation selectively alleviated AIH and PGF without affecting M2 macrophage recruitment or other associated biological functions. These findings reveal the dual role of M2 macrophages in dTEVGs for AVGs, which, while promoting pro-regeneration, unexpectedly accelerate AIH and PGF. A targeted Smad3 inhibition strategy selectively alleviates AIH and PGF caused by M2 macrophage infiltration, without compromising M2 macrophage-associated functions.