A revised airway epithelial hierarchy includes CFTR-expressing ionocytes

Abstract

The airways of the lung are the primary sites of disease in asthma and cystic fibrosis. Here we study the cellular composition and hierarchy of the mouse tracheal epithelium by single-cell RNA-sequencing (scRNA-seq) and in vivo lineage tracing. We identify a rare cell type, the Foxi1 pulmonary ionocyte; functional variations in club cells based on their location; a distinct cell type in high turnover squamous epithelial structures that we term 'hillocks'; and disease-relevant subsets of tuft and goblet cells. We developed 'pulse-seq', combining scRNA-seq and lineage tracing, to show that tuft, neuroendocrine and ionocyte cells are continually and directly replenished by basal progenitor cells. Ionocytes are the major source of transcripts of the cystic fibrosis transmembrane conductance regulator in both mouse (Cftr) and human (CFTR). Knockout of Foxi1 in mouse ionocytes causes loss of Cftr expression and disrupts airway fluid and mucus physiology, phenotypes that are characteristic of cystic fibrosis. By associating cell-type-specific expression programs with key disease genes, we establish a new cellular narrative for airways disease.

Lessons learned from lung and liver in-vivo gene therapy: implications for the future

“…In CF, lung disease begins in the small airways where the CFTR protein is primarily expressed [26,27]. In contrast, for treatment of surfactant protein deficiencies, the target cells are located in the parenchyma, mainly in alveolar type 2 (AT-2) cells.…”

“…As mentioned before, alternate genetic lung diseases may originate from different cell types and in different regions of the lung [26,27]. This represents a challenge to develop platform gene therapies for multiple diseases, since both the vector tropism and delivery method will have to be fine-tuned to meet specific disease needs.…”

“…CD34 + cells), the same cannot often be said for in-vivo gene therapy for lung or liver. Although there is currently no consensus on the identity of a single ‘lung stem cell’ [26,27], once identified, that stem cell will still require a vector capable of transducing it in an in-vivo setting. The profound differences in developmental and adult lung biology between mice and humans [89] have not made the development of suitable vectors for in-vivo stem cell targeting any easier.…”

Tracheal brush cells release acetylcholine in response to bitter tastants for paracrine and autocrine signaling

“…However, absence or very low levels of inflammation indicate the presence of innate sensing mechanisms that can either signal "keep calm" or initiate protective responses such as secretion of antimicrobial peptides, a boost in mucociliary clearance (MC) or neurogenic inflammation. 4,[9][10][11] In a bacterial artificial chromosome (BAC)-transgenic mouse model expressing eGFP under control of the promoter for the acetylcholine (ACh) synthesizing enzyme choline acetyltransferase (ChAT) and utilizing ChAT-antisera, eG-FP-fluorescent tracheal epithelial cells were identified as BC. In recent years, brush cells (BC), a less abundant epithelial cell type with a characteristic tuft of apical microvilli and elusive function for more than 60 years after their discovery, were identified as specialized chemosensory cells serving as sentinels in various organs including the airway epithelium.…”

Reaction combination opens up 3D molecular diversity for drug discovery

“…The power of these reactions has been demonstrated in numerous syntheses of complex natural products 1,2 . However, the scope of cycloadditions is limited to certain combinations of starting materials, which has restricted their use for making libraries of compounds in drugdiscovery programs 3 .…”