Cathepsin-D: protein moonlighting as a pathological mechanism in COPD-associated pulmonary hypertension

• Applicant: Marija Gredic, Ph.D.
• Subject Area: Pneumology, Thoracic Surgery ; Pathology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 564838617

Chronic obstructive pulmonary disease (COPD) is an incurable condition with increasing prevalence and the third most common cause of death worldwide. In addition to respiratory tract pathology, the majority of COPD patients have pulmonary vascular abnormalities and pulmonary hypertension (PH). Even mild to moderate elevation of pulmonary arterial pressure (PAP) is associated with higher mortality in COPD patients. Moreover, current evidence suggests that pulmonary vascular alterations precede emphysema, possibly contributing to its development and/or progression. We recently demonstrated that cross-talk between interstitial macrophages and adjacent pulmonary artery smooth muscle cells (PASMCs) drives pulmonary vascular remodeling in COPD. Moreover, we provided evidence that these described events are largely hypoxia-independent and rely on a smoke-specific signaling cascade that has not been fully characterized. Cathepsin D (Cts-D) is a ubiquitously expressed lysosomal aspartic protease, abundantly present in macrophages. In certain pathological conditions such as cancer, this enzyme is secreted in its inactive form into the intercellular environment, where it triggers the proliferation of cancer cells and stromal fibroblasts. Our preliminary data revealed that CtsD expression is strongly upregulated in remodeled pulmonary vasculature in the lungs of smoke-exposed mice and COPD patients, whereas no such regulation can be observed in mice exposed to chronic hypoxia. In vitro, co-culturing of PASMCs and macrophages, which promotes PASMC proliferation, is accompanied by the secretion of Cts-D into medium. Importantly, addition of recombinant pro-Cts-D in culturing medium augments the proliferation of PASMCs, while the knockout of this protein exerts the opposite effect. Intriguingly, presence of Cts-D in PASMC culturing medium induces phosphorylation of ERK-1/2, a kinase previously involved in the pro-proliferative cross-talk with adjacent macrophages and resulting pulmonary vascular remodeling. Based on these results, we want to decipher the exact cellular mechanism through which Cts-D potentiates proliferation of PASMCs. Moreover, we plan to test in vivo the relevance of this signaling pathway for the development and reversal of cigarette smoke-induced PH in mice, using the cell type-specific CtsD knockout and CtsD neutralizing antibodies. Finally, we will validate findings from animal studies in human material and evaluate circulating Cts-D as a potential biomarker for COPD-PH severity. Our overall goal is to delineate the signaling pathway(s) mediating macrophage-induced PASMC proliferation and investigate the possible involvement of Cts-D in this process, in order to design therapeutic concepts to halt the further progression of COPD-PH and reverse the established disease.

• DFG Programme: Research Grants