# ESRP1 drives epithelial-mesenchymal transition by activating EPAC-RAP1A signaling axis

## TL;DR

This study shows that ESRP1 promotes lung disease by triggering a key cell transformation process through a specific signaling pathway.

## Contribution

The study identifies ESRP1 as a novel upstream regulator of EMT via the EPAC-RAP1A signaling axis in IPF.

## Key findings

- ESRP1 is significantly upregulated in alveolar epithelial cells during IPF.
- ESRP1 promotes EMT by activating the EPAC-RAP1A signaling pathway.
- ESRP1 interacts with EPAC and RAP1A, establishing an upstream regulatory role.

## Abstract

Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease characterized by epithelial-mesenchymal transition (EMT) as a key pathological feature. The molecular mechanism of EMT is not fully understood. Hence, the current study aimed to investigate the pathogenesis of EMT, which focus on the function of Epithelial Splicing Regulatory Protein 1 (ESRP1) in regulating EMT.

The present study utilized bleomycin (BLM) to establish mouse models of IPF. Then, single-cell RNA sequencing (scRNA-seq) of entire lung tissue was employed to delineate transcriptional alterations in epithelial cells and to nominate prospective regulators of EMT. The target gene was subsequently validated in vivo and in vitro by qPCR, western blot, and immunofluorescence. Furthermore, an EMT model was established in TGF-β1–treated MLE-12 alveolar epithelial cells. Lentivirus or siRNA was hired to modulate the expression of target gene and elucidate its mechanistic contribution to EMT.

ScRNA-seq revealed marked up-regulation of the ESRP1 in alveolar epithelial cells compared with PBS-treated controls. Subsequent mechanistic interrogation in primary and MLE-12 alveolar epithelial cells demonstrated that knockdown of ESRP1 suppressed, whereas its overexpression potentiated, the expression of Epac, Rap1a, and N-cad which were key effectors of EMT. Importantly, Co-IP (Co-Immunoprecipitation) showed that there was interaction between ESRP1, Epac, and Rap1a. Silencing of either Epac or Rap1a did not reciprocally alter ESRP1 expression, confirming an upstream regulatory hierarchy.

Our findings demonstrate that ESRP1 upregulation in alveolar epithelial cells drives IPF progression by promoting EMT via the Epac–Rap1a axis.