A109-12 MCEMP1-SPP1 Axis Orchestrates Myeloid-Fibrotic Crosstalk in Pulmonary Fibrosis

Abstract Rationale Idiopathic pulmonary fibrosis (IPF) lacks survival-improving therapies. Building on a validated peripheral blood mononuclear cell (PBMC) mortality signature, we investigated whether MCEMP1 is both a prognostic marker and a mechanistic driver of fibrogenesis. Methods PBMC microarrays (Pittsburgh, n = 75; Chicago, n = 45) were analyzed by GAP-adjusted Cox models. CRISPR Mcemp1 knockout (KO) and Rosa26CAG-Mcemp1-tdTomato/Cx3cr1CreER knock-in (KI) mice underwent oropharyngeal bleomycin (survival analysis: 1.5 U/kg; readout experiments: 1.0 U/kg). Outcomes included weight, survival, histology (Ashcroft, trichrome, picrosirius red), hydroxyproline, serum TGFβ, RT-qPCR, and Western blot. Lung and bone marrow were profiled by scRNA-seq with Milo differential abundance and CellRank fate mapping. Bone-marrow-derived macrophage migration was tested by scratch assay. BAL immunofluorescence and proximity ligation assay (PLA) assessed Mcemp1-Spp1 interaction. THP-1 perturbations (MCEMP1 knockdown/overexpression ± TGFβ) probed SPP1 regulation. Results Higher PBMC MCEMP1 predicted greater IPF mortality (Pittsburgh HR:2.28, 95%CI 1.04-5.01, p=0.03; Chicago HR:3.70, 95%CI1.17-11.66, p=0.02). At 1.5 U/kg bleomycin, WT mortality exceeded KO (58% vs 28%; HR:2.05, 95%CI1.09-3.83, p=0.0378). At 1.0 U/kg, KO mice showed improved trajectories: less weight deficit by D21 (WT 8% vs KO 1.5%, p0.01), reduced fibrosis (Ashcroft −43%, trichrome −22%, picrosirius −42%), and lower collagen and TGFβ (hydroxyproline 0.43-fold; TGFβ 0.51-fold). Profibrotic transcripts were reduced in KO (Col1a1 0.51-fold, p0.05; Col1a2 0.53-fold, p0.001; Fn1 0.35-fold, p0.001), with lower Col1a1 protein vs WT-bleomycin (0.64-fold, p0.01). scRNA-seq showed fewer fibrotic fibroblasts, AT2 restoration, and enrichment of non-classical monocytes in KO; treatment-driven DEG were markedly lower in KO fibrotic cells (WT 756 vs KO 2). Myeloid KO lungs downregulated Spp1, Ccr2, Mmp12; protein levels were reduced (Spp1 0.30-fold, Mmp12 0.29-fold, Ccr2 0.50-fold). KI mice worsened: greater early weight loss (−66% and −137% by D7; p0.001), higher fibrosis (trichrome 1.43-fold; picrosirius 1.83-fold vs KI-vehicle-bleomycin; p0.01), and increased transcripts/proteins (Col1a1 1.8-fold, p0.05; Col1a2 1.72-fold, p0.05; Fn1 2.26-fold, p0.02; hydroxyproline 7.34-fold vs saline and 2.08-fold vs vehicle, p0.01; Mcemp1 9.28-fold, Spp1 2.16-fold, Mmp12 5.38-fold, Ccr2 15.76-fold, all p0.05). Migration was bidirectionally controlled: KO-bleomycin decreased (0.8- and 0.5-fold at 24/48 h, p0.001), KI-tamoxifen-bleomycin increased (1.23- and 1.75-fold, p0.001). THP-1: MCEMP1 knockdown reduced SPP1 (0.74-fold), overexpression increased SPP1 (3.32-fold). BAL co-localization and PLA confirmed Mcemp1-Spp1 interaction in vivo. Conclusions MCEMP1 links patient mortality risk to causation in mice through an MCEMP1-SPP1-CCR2/MMP12 axis that governs myeloid recruitment, epithelial repair, and collagen deposition. Targeting MCEMP1-SPP1 may reduce SPP1+ macrophages, attenuate fibrosis, and improve outcomes in IPF. This abstract is funded by: Ubben funds