# Targeting sorting nexin 3 to treat pulmonary fibrosis by dual modulating Wnt/β-catenin signaling

## TL;DR

This study shows that targeting SNX3, a protein involved in Wnt/β-catenin signaling, can reduce lung fibrosis and suggests a new treatment strategy using a drug delivery system.

## Contribution

The study identifies SNX3 as a dual regulator of Wnt/β-catenin signaling in pulmonary fibrosis and proposes a novel therapeutic strategy using TDN-LC4.

## Key findings

- SNX3 is upregulated in PF and regulates Wnt/β-catenin signaling through two distinct pathways.
- Genetic ablation of SNX3 reduces fibrosis, while overexpression worsens it.
- TDN-LC4 delivery system improves LC4 efficiency and reduces off-target effects in treating PF.

## Abstract

Pulmonary fibrosis (PF) is a chronic progressive lung disorder characterized by overactivation of Wnt/β-catenin signaling and limited therapeutic efficacy. This study identifies sorting nexin 3 (SNX3), a retromer-associated protein, as a dual regulator of PF pathogenesis through coordinated molecular mechanisms. SNX3 is significantly upregulated in PF patients’ lungs and bleomycin-induced murine fibrotic models, with predominant localization in alveolar type 2 (AT2) epithelial cells correlating with β-catenin hyperactivation and fibrotic progression. Genetic ablation of SNX3 in AT2 cells attenuated Wnt/β-catenin signaling, collagen deposition, and pulmonary dysfunction, while SNX3 overexpression exacerbated these phenotypes. Mechanistic studies further elucidated two distinct SNX3-driven regulatory pathways. Wls is rescued by SNX3 from lysosomal degradation to sustain Wnt ligand secretion and canonical pathway activation. In addition to Wls, casein kinase 1α (CK-1α) is identified as a novel cargo protein for SNX3, which mediates its plasma membrane recruitment via Rab5a-dependent endosomal recycling, bypassing the β-catenin destruction complex, ultimately suppressing proteasomal degradation of β-catenin. This dual regulatory mechanism positions SNX3 as a master coordinator of both Wnt-dependent and -independent β-catenin signaling in PF. Furthermore, we screened inhibitors targeting SNX3 and identified a novel small molecule, LC4, which effectively ameliorated pulmonary dysfunction and reversed pulmonary fibrosis. Tetrahedral framework nucleic acids (TDNs), known for their excellent biocompatibility and drug delivery capacity, were utilized to develop a multifunctional nanodrug delivery system (TDN-LC4) to enhance the treatment of PF. By optimizing this loading approach, we improved LC4 delivery efficiency, enhanced its therapeutic potential, and minimized off-target effects. Our findings reveal SNX3 as a master coordinator of dual Wnt-dependent and -independent β-catenin activation, and propose TDN-LC4 as a potential therapeutic strategy to disrupt pathogenic signaling redundancy in PF pathogenesis.