The Neuroepithelial Body Microenvironment as a Postnatal Airway Epithelial Stem Cell Niche: Critical Role for BMP Signaling

Abstract

Main objective was to develop models that enable exploring the stem cell characteristics of pulmonary neuroepithelial bodies (NEBs) in postnatal mouse lungs. The NEB microenvironment (ME) consists of innervated groups of pulmonary neuroepithelial endocrine cells, covered by socalled Clara‐like cells (CLCs). Epithelial cells of intrapulmonary conductive airways typically show a very low turn‐over rate in healthy postnatal lungs. Own and literature data point out that the NEB ME is important during development and for adult lung epithelial repair after total ablation, and that CLCs may act as stem cells under these circumstances. However, the absence of a model to physiologically induce selective cell proliferation in the healthy NEB ME, has so far hampered the identification of signaling processes to support their characterization as a quiescent postnatal stem cell niche involved in postnatal airway epithelial homeostasis.We developed a laser microdissection (LMD)‐based method that is compatible with high‐end PCR techniques to selectively isolate the NEB ME and compare its gene expression with control airway epithelium (CAE) [1]. To identify genes that may be involved in signaling mechanisms in the NEB ME, as a potential postnatal stem cell niche, pooled NEB and CAE samples were collected using LMD and gene expression was compared using a panel of stem cell related PCR Arrays. Expression of stem cell ‘signature’ genes in the NEB ME was confirmed and quantified by qPCR [1].Since inhibition of bone morphogenetic protein (BMP) signaling has been reported to induce proliferation of basal progenitor cells in the mouse trachea [2], and members of the BMP pathway showed a high expression in the NEB ME in multiple PCR arrays, their possible involvement in the stem cell characteristics of the NEB ME was further evaluated. Localization of BMP2, BMP7 and BMP receptors in the NEB ME could be confirmed by multiple immunofluorescent labeling.Additionally, mild transient acute lung injury (ALI), induced by a single low‐dose intratracheal lipopolysaccharide (LPS) challenge, was shown to induce a remarkable selective proliferation of CLCs in the NEB ME. It also resulted in a strongly decreased expression of BMP ligands in the NEB ME, indicating that stem cell activation by ALI might involve inhibition of the BMP pathway. Treating mice with LDN‐193189, a small molecule inhibitor of BMP type I receptors, recently revealed that compromising BMP signaling on its own appears to cause cell proliferation in the NEB ME that is reminiscent of what was seen after LPS treatment.In conclusion, a highly reproducible mild ALI model was generated for the selective activation of a quiescent postnatal airway stem cell population in the NEB ME, creating novel opportunities for unraveling the mechanisms that are involved. So far, combined LMD, gene and protein expression analysis, and specific inhibition of BMP signaling strongly suggest the involvement of BMP in silencing cell proliferation in the non‐activated stem cell niche of the NEB ME.Support or Funding InformationSupported by UA grant GOA BOF 2015 (30729 to DA).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.