Introduction: Age-related chronic lung diseases are characterized by a progressive lung function decline. Increased levels of senescence markers were reported in the epithelium of COPD and IPF lungs. Recently, the chronic activation of WNT/?-catenin signaling was linked with cellular senescence in epithelial progenitors. Leucin-rich repeat-containing G-protein-coupled receptor 6 (LGR6), a known enhancer of the WNT/?-catenin pathway, was found to be expressed in lung epithelial progenitors. Here, we investigated the contribution of LGR6 to senescence in progenitor cells in COPD and IPF.

Methods: We applied multiplex immunofluorescent staining using the Multiple Iterative Labeling by Antibody Neodeposition (MILAN) methodology for LGR6, RSPO2, RSPO3, P21, KRT5, KRT17, STFPC, RAGE, CD68 on the parenchyma from a COPD and an IPF explanted lungs.

Results: Within 17,420 analyzed cells, five main distinct cell clusters (basal, ATI, ATII, intermediate ATII-to-ATI, macrophages) were identified on the basis of the above-described phenotypic markers. High LGR6 levels were observed in basal and ATII populations located in fibrotic regions and in areas of inflammatory infiltration in COPD and IPF lungs. Within the LGR6^pos basal, ATII and intermediate ATII-to-ATI cells (versus LGR6^neg) populations the senescence marker P21 was increased (p < 0.05).

Conclusions: LGR6 levels are mainly increased in basal, ATII cells and intermediate alveolar progenitor populations in COPD and IPF lungs. Moreover, LGR6 protein expression was associated with increased P21 levels, suggesting that LGR6 likely contributes to senescence in fibrotic regions in chronic lung diseases.