# Parathyroid hormone–related protein is a therapeutic target in idiopathic pulmonary fibrosis

## TL;DR

A protein called PTHrP1-34 from bronchial cells contributes to lung fibrosis and could be a new treatment target.

## Contribution

Identifies PTHrP1-34 as a novel therapeutic target in idiopathic pulmonary fibrosis.

## Key findings

- PTHrP1-34 is elevated in fibrotic lungs and activates fibroblasts to produce extracellular matrix.
- Blocking PTHrP1-34 reduced fibrosis in a mouse model using antibodies and gene silencing.
- PTHrP1-34 is primarily produced by bronchial epithelial cells in IPF patients.

## Abstract

The crosstalk between immune or alveolar epithelial cells and fibroblasts mediated by paracrine signaling molecules is associated with the pathogenesis of idiopathic pulmonary fibrosis (IPF). However, studies investigating the active involvement of soluble mediators derived from bronchial epithelial cells in fibroblast activation and the development of pulmonary fibrosis are limited. Reanalysis of bulk and single-cell RNA-sequencing data from human bronchus and IPF lung tissue revealed marked upregulation of parathyroid hormone–like hormone (PTHLH) in IPF lung tissue compared with normal tissue, with expression predominantly localized to bronchial epithelial cells. parathyroid hormone–related protein (PTHrP) translated from PTHLH was significantly increased in the bronchial epithelium of IPF patients and bleomycin-induced pulmonary fibrosis mice. Furthermore, the paracrine peptide PTHrP1-34, generated through post-translational processing of PTHrP, was elevated in lung homogenates and bronchoalveolar lavage fluid obtained from fibrotic lungs. Cell- and animal-based experiments showed that PTHrP1-34 activated fibroblasts and extracellular matrix production, resulting in the progression of pulmonary fibrosis. In a preclinical evaluation using a bleomycin-induced pulmonary fibrosis mouse model, attenuating effects against pulmonary fibrosis were observed using neutralizing antibodies, peptides, and gene silencing strategies targeting the PTHrP1-34/parathyroid hormone 1 receptor axis. In conclusion, our results suggest that PTHrP1-34 derived from bronchial epithelial cells is involved in the pathogenesis of IPF and is a promising target for alleviating disease progression.