Collagen turnover is dominated by fibrogenesis in lung adenocarcinoma and fibrolysis in lung squamous cell carcinomas

The tumor stroma in non-small cell lung cancer (NSCLC) is highly desmoplastic/fibrotic and is emerging as a key regulator of tumor progression, immune evasion and therapy resistance. Tumor fibrosis is characterized by the aberrant accumulation of collagen. However, our understanding of collagen turnover and its potential dependence on the histologic subtype is very limited. Here, we combined transcriptional profiling and ELISA-based assays for neoepitope collagen fragments to analyze collagen production (fibrogenesis) and degradation (fibrolysis) in tumor-associated fibroblasts (TAFs) and in tumor samples from the major NSCLC histologic subtypes: lung adenocarcinoma (LUAD) and lung squamous cell carcinoma (LUSC). In culture, LUSC-TAFs exhibited enhanced collagen turnover with increased markers of both production (exPRO-C1, PRO-C3 and PRO-C6) and degradation (C1M, C3M, C6M). Consistently, LUSC-TAFs exhibited higher RNA levels of both fibrillar collagens and collagenolytic MMPs, whereas TIMP-1 (a natural inhibitor of major collagenolytic MMPs) showed opposite patterns at the RNA and secreted protein levels. Consistent hystotype-dependent collagen-turnover signatures were observed in bulk RNA-seq data (TCGA) and in histologic analyses of TMAs from surgical specimens. Our results indicate that fibrogenesis is favored in LUAD through increased production of TIMP-1 and lower levels of collagenolytic MMPs, whereas fibrolysis is dominant in LUSC through increased production of collagenolytic MMPs (notably MMP1) and reduced production of TIMP-1. Mechanistically, TGF-beta1 is a major driver of tumor fibrosis, and knocking-down SMAD2 or SMAD3 in normal fibroblasts -to mimic previously reported histotype-specific SMAD2/3 expression patterns in lung TAFs (Ikemori et al, Cancer Res 2020) - was sufficient to recapitulate key differential features of collagen turnover between LUAD and LUSC. Together, these data reveal opposite collagen-turnover programs in NSCLC, in which LUAD are predominantly fibrogenic, whereas LUSC are largely fibrolytic through histotype-dependent regulatory processes. Targeting these divergent programs may help revert pathologic fibrosis and improve responses to chemotherapy and/or immunotherapy in NSCLC.