COL5A2-mediated endoplasmic reticulum stress promotes macrophage M2 polarization in lung adenocarcinoma

Collagen is a major component of the extracellular matrix. Type V collagen α2 (COL5A2), a common collagen subtype, plays a crucial role in immune regulation, angiogenesis, and tumor metastasis. It is highly expressed in various malignancies, but its mechanistic role in lung adenocarcinoma (LUAD) remains unclear. Therefore, this study aims to investigate the regulatory mechanism of COL5A2 in mediating macrophage M2 polarization in LUAD. We analyzed COL5A2 expression in LUAD samples from the TCGA-LUAD database. Using GSEA, we sought to identify the signaling pathways influenced by COL5A2 expression. mRNA levels of COL5A2, TGF-β, and IL-10 were quantified via qPCR analysis, and protein levels of COL5A2, PD-L1, and endoplasmic reticulum (ER) stress-related proteins (GRP78 and CHOP) were assessed using western blot. Immunofluorescence assay detected the fluorescence signal of CD206 in M2 macrophages, while flow cytometry assessed the M2 macrophage marker CD206, flow cytometry determined the positive rates for CD68 and CD206. Exosome uptake by macrophages was examined using confocal microscopy, and cell viability was measured with cell counting kit-8. KI-67 protein expression was analyzed by immunohistochemistry, and in vivo assays in animals verified our findings. The results showed that elevated COL5A2 levels in LUAD were found to correlate with a shift toward M2 macrophage polarization. Specifically, the overexpression of COL5A2 amplified ER stress, which led to an increase in PD-L1 exosome release and macrophage uptake of PD-L1, thus driving the M2 phenotype. In conclusion, COL5A2 in LUAD induces ER stress, which is associated with elevated PD-L1 exosome secretion and macrophage PD-L1 uptake, ramping up M2 polarization in macrophages.