GLUL and chronic obstructive pulmonary disease: While we did not observe the nuclear expression of proliferation marker Ki67 (Supplementary Figure S5A–F) and we excluded the presence of apoptotic events occurring in COPD and IPF tissues (Supplementary Figure S5K–N), we detected increased levels of Wnt-related markers total β-catenin and glutamine synthetase in lesions harbouring LGR6+ progenitors (Supplementary Figure S5G–J).