The Human Airway Epithelial Basal Cell Transcriptome

The human airway epithelium consists of 4 major cell types: ciliated, secretory, columnar and basal cells. During natural turnover and in response to injury, the airway basal cells function as stem/progenitor cells for the other airway cell types. The objective of this study is to better understand human airway epithelial basal cell biology by defining the gene expression signature of this cell population.. The basal cell signature displayed overlap with genes expressed in basal-like cells from other human tissues and with that of murine airway basal cells. Consistent with self-modulation as well as signaling to other airway cell types, the human airway basal cell signature was characterized by genes encoding extracellular matrix components, growth factors and growth factor receptors, including genes related to the EGF and VEGF pathways. Interestingly, while the basal cell signature overlaps that of basal-like cells of other organs, the human airway basal cell signature has features not previously associated with this cell type, including a unique pattern of genes encoding extracellular matrix components, G protein-coupled receptors, neuroactive ligands and receptors, and ion channels.The human airway epithelial basal cell signature identified in the present study provides novel insights into the molecular phenotype and biology of the stem/progenitor cells of the human airway epithelium

RNA-Seq quantification of the human small airway epithelium transcriptome

<p>Abstract</p> <p>Background</p> <p>The small airway epithelium (SAE), the cell population that covers the human airway surface from the 6^thgeneration of airway branching to the alveoli, is the major site of lung disease caused by smoking. The focus of this study is to provide quantitative assessment of the SAE transcriptome in the resting state and in response to chronic cigarette smoking using massive parallel mRNA sequencing (RNA-Seq).</p> <p>Results</p> <p>The data demonstrate that 48% of SAE expressed genes are ubiquitous, shared with many tissues, with 52% enriched in this cell population. The most highly expressed gene, SCGB1A1, is characteristic of Clara cells, the cell type unique to the human SAE. Among other genes expressed by the SAE are those related to Clara cell differentiation, secretory mucosal defense, and mucociliary differentiation. The high sensitivity of RNA-Seq permitted quantification of gene expression related to infrequent cell populations such as neuroendocrine cells and epithelial stem/progenitor cells. Quantification of the absolute smoking-induced changes in SAE gene expression revealed that, compared to ubiquitous genes, more SAE-enriched genes responded to smoking with up-regulation, and those with the highest basal expression levels showed most dramatic changes. Smoking had no effect on SAE gene splicing, but was associated with a shift in molecular pattern from Clara cell-associated towards the mucus-secreting cell differentiation pathway with multiple features of cancer-associated molecular phenotype.</p> <p>Conclusions</p> <p>These observations provide insights into the unique biology of human SAE by providing quantit-ative assessment of the global transcriptome under physiological conditions and in response to the stress of chronic cigarette smoking.</p

Microbial Patterns Signaling via Toll-Like Receptors 2 and 5 Contribute to Epithelial Repair, Growth and Survival

Epithelial cells (ECs) continuously interact with microorganisms and detect their presence via different pattern-recognition receptors (PRRs) including Toll-like receptors (TLRs). Ligation of epithelial TLRs by pathogens is usually associated with the induction of pro-inflammatory mediators and antimicrobial factors. In this study, using human airway ECs as a model, we found that detection of microbial patterns via epithelial TLRs directly regulates tissue homeostasis. Staphylococcus aureus (S. aureus) and microbial patterns signaling via TLR2 and TLR5 induce a set of non-immune epithelial responses including cell migration, wound repair, proliferation, and survival of primary and cancerous ECs. Using small interfering RNA (siRNA) gene targeting, receptor-tyrosine kinase microarray and inhibition studies, we determined that TLR and the epidermal growth factor receptor (EGFR) mediate the stimulating effect of microbial patterns on epithelial repair. Microbial patterns signaling via Toll-like receptors 2 and 5 contribute to epithelial repair, growth and survival. This effect is independent of hematopoietic and other cells as well as inflammatory cytokines suggesting that epithelia are able to regulate their integrity in an autonomous non-inflammatory manner by sensing microbes directly via TLRs

Co-operative regulation of epithelial homeostasis and immunity

Epithelium of barrier organs plays a primary host defense function. In the lung, airway epithelium protects from respiratory pathogens routinely present in the air without development of excessive inflammation or tissue injury. We hypothesized that such a barrier function might be achieved due to a co-operation of immunoregulatory and tissue repair mechanisms. Consistent with such a concept, in the present study we identified multiple links between innate immunity and epithelial homeostasis using airway epithelium as a model. First, we found that, at physiologically relevant concentrations, the endogenous antimicrobial peptide LL-37 exerts protective effects on airway mucosal cells by inducing epithelial cell (EC) migration, proliferation, wound closure, and by regulation of inflammatory responses of ECs and dendritic cells (DCs) induced by microbial signals. High concentrations of LL-37 (> 20 μg/ml) were toxic for airway ECs. Second, innate immune recognition of microbial patterns by airway ECs initiated repair (cell migration, wound closure) and growth (cell proliferation, survival) events in epithelium independently on cells of myeloid origin. Microbial patterns signaling via toll-like receptor (TLR) – MyD88 – NF-kappa B pathway showed the most prominent effect on epithelial homeostasis. Epidermal growth factor receptor (EGFR) is involved in epithelial repair responses induced by LL-37 or epithelial TLR signals. Particular sensitivity of epithelial cancer cells to growth-promoting effects of TLR agonists suggests that epithelial TLRs might be involved in autonomous cancer cell growth. Finally, in an in vitro model of interaction of DCs with differentiated airway epithelium, ECs were able to control DC activation by prevention of a direct contact with bacteria and / or due to the regulatory properties of soluble factors which are released by ECs. DCs “educated” within airway epithelial microenvironment were substantially less sensitive to stimulation with microbial factors. Prolonged presence of monocyte-derived DCs beneath airway epithelium significantly increased epithelial permeability, suggesting that bidirectional interactions between ECs and DCs exist and may potentially modulate epithelial barrier function and mucosal tissue homeostasis. Taken together, epithelial homeostasis and innate immunity are closely connected, and their co-operative regulation is involved in the maintenance of tissue integrity and immune balance. Understanding of such a mechanism might be important for further progress in the development of novel therapeutic approaches to chronic diseases (asthma, interstitial lung diseases, inflammatory bowel disease, cancer and others), which are associated with concomitant immune dysregulation and epithelial tissue injury

Co-operative regulation of epithelial homeostasis and immunity

Epithelium of barrier organs plays a primary host defense function. In the lung, airway epithelium protects from respiratory pathogens routinely present in the air without development of excessive inflammation or tissue injury. We hypothesized that such a barrier function might be achieved due to a co-operation of immunoregulatory and tissue repair mechanisms. Consistent with such a concept, in the present study we identified multiple links between innate immunity and epithelial homeostasis using airway epithelium as a model. First, we found that, at physiologically relevant concentrations, the endogenous antimicrobial peptide LL-37 exerts protective effects on airway mucosal cells by inducing epithelial cell (EC) migration, proliferation, wound closure, and by regulation of inflammatory responses of ECs and dendritic cells (DCs) induced by microbial signals. High concentrations of LL-37 (> 20 μg/ml) were toxic for airway ECs. Second, innate immune recognition of microbial patterns by airway ECs initiated repair (cell migration, wound closure) and growth (cell proliferation, survival) events in epithelium independently on cells of myeloid origin. Microbial patterns signaling via toll-like receptor (TLR) – MyD88 – NF-kappa B pathway showed the most prominent effect on epithelial homeostasis. Epidermal growth factor receptor (EGFR) is involved in epithelial repair responses induced by LL-37 or epithelial TLR signals. Particular sensitivity of epithelial cancer cells to growth-promoting effects of TLR agonists suggests that epithelial TLRs might be involved in autonomous cancer cell growth. Finally, in an in vitro model of interaction of DCs with differentiated airway epithelium, ECs were able to control DC activation by prevention of a direct contact with bacteria and / or due to the regulatory properties of soluble factors which are released by ECs. DCs “educated” within airway epithelial microenvironment were substantially less sensitive to stimulation with microbial factors. Prolonged presence of monocyte-derived DCs beneath airway epithelium significantly increased epithelial permeability, suggesting that bidirectional interactions between ECs and DCs exist and may potentially modulate epithelial barrier function and mucosal tissue homeostasis. Taken together, epithelial homeostasis and innate immunity are closely connected, and their co-operative regulation is involved in the maintenance of tissue integrity and immune balance. Understanding of such a mechanism might be important for further progress in the development of novel therapeutic approaches to chronic diseases (asthma, interstitial lung diseases, inflammatory bowel disease, cancer and others), which are associated with concomitant immune dysregulation and epithelial tissue injury