Targeting ACKR1+ Endothelial Cells Attenuates Pulmonary Fibrosis by Halting Monocytes Infiltration/Polarization and Endothelial-to-Mesenchymal Transition.

Abstract

While microvascular abnormalities drive idiopathic pulmonary fibrosis (IPF), the pathogenic endothelial subpopulations and their specific molecular networks are poorly understood. By integrating single-cell and spatial transcriptomics, we identified a pathologically expanded ACKR1+ endothelial cell (EC) subpopulation that correlates with pulmonary function decline and forms a pro-fibrotic endothelial-fibroblast niche in IPF. Within this niche, fibroblast-derived TGF-β upregulates endothelial ACKR1 transcription via the SMAD2 axis. We demonstrate that ACKR1+ ECs promote fibrosis through two distinct mechanisms. At the cellular level, interactome mapping shows ACKR1 drives endothelial-to-mesenchymal transition (EndMT) by competitively sequestering the endocytic adaptor NUMB, which prevents NOTCH1 lysosomal degradation and sustains Notch hyperactivation. In the microenvironment, ACKR1+ ECs mediate monocyte recruitment via CCL2 transcytosis and secrete IGFBP7, polarizing pro-fibrotic M2 macrophages through the CD93/PI3K/AKT signaling axis. Endothelial-specific deletion of Ackr1 protects against bleomycin-induced pulmonary fibrosis. Through structure-based virtual screening, we identified 1F-Fructofuranosylnystose as a direct ACKR1 inhibitor. Pharmacological blockade with 1F-Fructofuranosylnystose halted EndMT and pathogenic macrophage recruitment, preserving lung architecture and respiratory mechanics in murine models, ferret models, and human precision-cut lung slices. These findings establish the mechanistic basis of ACKR1+ ECs in fibrosis and highlight ACKR1 inhibition as a targeted therapeutic approach for IPF.