Circulating biomarkers reflecting type III, IV and VI collagen remodeling are present in lung tissue of patients with pulmonary fibrosis and non-fibrotic controls

Abstract Background The extracellular matrix (ECM) is a dynamic network that provides structural support and maintains tissue homeostasis. Collagens are the main structural components of the ECM, occupying distinct tissue compartments and serving specialized roles. Dysregulated ECM remodeling involves an imbalance between collagen production and degradation, generating neoepitope-specific fragments that can be released into circulation. Serological measurements of these fragments can be used as biomarkers of disease and have been associated with progression and mortality in different fibrotic diseases, including pulmonary fibrosis (PF). This study aimed to investigate whether these systemic biomarkers originate from human lung tissue in patients with PF and non-fibrotic controls. Methods Lung tissue was collected from patients with PF (n = 21) and non-fibrotic controls (n = 21) and processed in parallel as formalin-fixed paraffin-embedded or snap-frozen samples. Serum samples were collected from patients with PF and healthy controls (n = 21). Neoepitope-specific biomarkers reflecting type III, IV, and VI collagen production (PRO-C3, PRO-C4, and PRO-C6) and degradation (C3M, C4M, C4Ma3, and C6M) were quantified in serum and proteolytically degraded lung tissue, and their spatial distribution was assessed by immunohistochemistry in lung tissue sections. Results All collagen remodeling biomarkers were significantly increased in serum of patients with PF compared with healthy controls (PRO-C3: p = 0.0006, all others: p < 0.0001). Collagen degradation fragments (C3M, C4M, and C6M) could be generated and released from both non-fibrotic and fibrotic human lung tissue following proteolytic cleavage with pepsin, collagenase, and/or MMP-9. All biomarkers were detected in lung tissue by immunohistochemical staining, with widespread distribution of type III and IV collagen fragments, whereas type VI collagen (PRO-C6) production showed a more compartment-specific pattern. Conclusions These findings demonstrated that neoepitope-specific collagen remodeling biomarkers, usually detected in circulation, are present and can be released from human lung tissue. Their spatial distribution suggests that ECM remodeling is heterogeneous and differs according to collagen type and distinct tissue compartments. Collectively, our findings support the use of collagen remodeling biomarkers as tools to assess ECM remodeling in pulmonary disease.