C26-18 Early Monocyte Recruitment and Cathepsin D-Mediated Macrophage Signaling Drive Pulmonary Vascular Remodeling in Smoke-Induced COPD

Rationale Patients with chronic obstructive pulmonary disease (COPD) frequently develop pulmonary hypertension (PH) and cor pulmonale. Importantly, even mild PH affects patient survival. We previously showed that pulmonary vascular remodeling in COPD-PH critically depends on cross-talk between pulmonary artery smooth muscle cells (PASMCs) and adjacent macrophages. However, the early events in this pathological cascade, including the timing and nature of factors governing monocyte recruitment, survival, and differentiation into macrophages, as well as the phenotypic changes influencing communication with PASMCs, remain largely unresolved. Methods We profiled chemokines in lungs and bronchoalveolar lavage (BAL) fluid from smoke-exposed and control mice, and tested the role of upregulated chemokines and their receptors in guiding bone marrow-derived monocyte (BMMo) chemotaxis in vitro. In parallel, we analyzed transcriptomic changes in BMMo and smoke-recruited lung macrophages. Finally, we confirmed upregulation of uncovered targets in human and mouse lungs on a protein level and investigated in vitro functional relevance of their elevated expression. Results Macrophage recruitment and accumulation in perivascular areas were evident after one month of smoke exposure, coinciding with increased pulmonary vascular cell proliferation. Among tested chemokines, Ccl3 was consistently upregulated at early (1 month) and later (3 and 8 months) time points. Neutralizing antibodies against Ccl3, as well as inhibition of its receptors, abolished BMMo chemotaxis toward BAL fluid from smoke-exposed lungs. While smoke-induced transcriptomic changes in BMMo were generally subtle and reflected heightened metabolic activity, bulk and single cell sequencing of lung recruited macrophages revealed a smoke-specific macrophage population, less abundant in a mouse line resistant to smoke-induced PH. Those macrophages expressed factors implicated in cell proliferation and extracellular matrix remodeling, particularly Cathepsin D (Cts-D), previously described as a paracrine pro-proliferative signal in various cancers. Cts-D expression was upregulated in the lungs and sera of COPD patients, as well as in the lungs of smoke-exposed mice. In vitro, Cts-D was secreted in co-cultures of macrophages and PASMCs, and the addition of recombinant Cts-D to PASMC culture medium increased cellular proliferation. Conclusions Together, our findings indicate that early monocyte recruitment to smoke-exposed lungs and the acquisition of a distinct macrophage phenotype are critical drivers of pulmonary vascular remodeling and the subsequent development of PH in COPD. Cts-D appears to be one of the pro-proliferative factors secreted by these macrophages, promoting PASMC proliferation and contributing to pulmonary vascular remodeling. This abstract is funded by: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 564838617 to M.G. and CPI