D29-10 Targeting Macrophage Secreted Phosphoprotein 1 in Pulmonary Fibrosis

Abstract Rationale Secreted phosphoprotein 1 (SPP1) is a multifunctional glycoprotein involved in stress responses and immunomodulation. SPP1 is highly expressed by macrophages in idiopathic pulmonary fibrosis (IPF), yet the upstream pathways regulating its expression and its functional role in fibrosis remain incompletely defined. Methods Single-cell RNA sequencing was performed on explanted IPF lungs and non-fibrotic donor lungs. Differentially expressed genes (DEGs) are identified using the MAST statistical framework and the Seurat analysis pipeline. Altered intercellular communication networks are assessed using CellChat. Pseudotime analysis is performed using Slingshot. Precision-cut lung slices (PCLS) were used as an ex vivo model of lung fibrosis. Bronchoalveolar lavage fluid (BALF) from IPF patients and healthy controls was analyzed to validate key findings. To assess the role of macrophage-derived SPP1 in vivo, Spp1fl/fl-Cx3cr1-CreER mice were generated by crossing Spp1fl/fl mice with Cx3cr1-CreER mice. Results Single-cell RNA-sequencing confirmed that SPP1 is highly enriched in monocyte-derived macrophages (MDMs) in IPF lungs, predominantly originating from classical monocytes. BALF SPP1 levels were elevated in IPF compared with healthy controls. In bleomycin-injured mice, BALF SPP1 levels correlated with the temporal trajectory of fibrosis development (peaked on day 21) and resolution (returned to baseline by day 56). In PCLS derived from non-fibrotic lungs, IPF BALF induced increased expression of the profibrotic marker CTHRC1, whereas SPP1-neutralizing antibody attenuated CTHRC1 induction. Moreover, tamoxifen-treated Spp1fl/fl-Cx3cr1-CreER mice exhibited reduced pulmonary fibrosis after bleomycin injury compared with vehicle-treated controls, demonstrating a functional role for macrophage-derived SPP1 in fibrosis progression. Conclusions SPP1 is highly expressed by IPF-associated MDMs, primarily derived from classical monocytes, and plays a functional role in fibroproliferation. Targeting SPP1 or its upstream regulatory pathways may represent a promising therapeutic strategy for pulmonary fibrosis. Funding: Supported by NIH K08HL163406 (to C.H.) This abstract is funded by: NIH K08HL163406