Epithelial Cell–Derived Secreted and Transmembrane 1a Signals to Activated Neutrophils during Pneumococcal Pneumonia

Abstract

Airway epithelial cell responses are critical to the outcome of lung infection. In this study, we aimed to identify unique contributions of epithelial cells during lung infection. To differentiate genes induced selectively in epithelial cells during pneumonia, we compared genome-wide expression profiles from three sorted cell populations: epithelial cells from uninfected mouse lungs, epithelial cells from mouse lungs with pneumococcal pneumonia, and nonepithelial cells from those same infected lungs. Of 1,166 transcripts that were more abundant in epithelial cells from infected lungs compared with nonepithelial cells from the same lungs or from epithelial cells of uninfected lungs, 32 genes were identified as highly expressed secreted products. Especially strong signals included two related secreted and transmembrane (Sectm) 1 genes, Sectm1a and Sectm1b. Refinement of sorting strategies suggested that both Sectm1 products were induced predominantly in conducting airway epithelial cells. Sectm1 was induced during the early stages of pneumococcal pneumonia, and mutation of NF-κB RelA in epithelial cells did not diminish its expression. Instead, type I IFN signaling was necessary and sufficient for Sectm1 induction in lung epithelial cells, mediated by signal transducer and activator of transcription 1. For target cells, Sectm1a bound to myeloid cells preferentially, in particular Ly6G(bright)CD11b(bright) neutrophils in the infected lung. In contrast, Sectm1a did not bind to neutrophils from uninfected lungs. Sectm1a increased expression of the neutrophil-attracting chemokine CXCL2 by neutrophils from the infected lung. We propose that Sectm1a is an epithelial product that sustains a positive feedback loop amplifying neutrophilic inflammation during pneumococcal pneumonia.

Expression of Piwi protein MIWI2 defines a distinct population of multiciliated cells

“…These studies have revealed a more complex population of lung epithelial cells than had been previously appreciated (2). A recent study from our group revealed the unanticipated finding that epithelial cells from lungs with bacterial pneumonia exhibited higher expression of the mRNA encoding the Piwi protein MIWI2 during pneumococcal pneumonia (3).…”

“…Specific cell sources of Miwi2 expression were interrogated in mice infected with S. pneumoniae using a previously described protocol for isolating purified cell populations recovered from whole lung enzymatic digests and bronchoalveolar lavage fluid (3,16 ized in the cytoplasm, and restricted to airway cells ( Figure 1E). To determine whether the increase in Miwi2 mRNA correlated with increased MIWI2 protein expression, tissue sections isolated from uninfected or infected lungs were quantitatively compared, and demonstrated that the number of MIWI2-positive cells was significantly increased as a result of infection ( Figure 1F).…”

“…Lung digestion. Lung digests for isolation of epithelial cells were performed using elastase, as previously described (3,16). Briefly, after euthanasia, lungs were perfused with 10 ml HBSS via the right ventricle through the pulmonary artery.…”

Pathogenesis of severe pneumonia

“…A protective action observed was the induction of CXCL5 by epithelial cells (10), advancing prior studies that suggested this was an epithelial-specific product during pneumonia that elicits neutrophil recruitment (12, 13). Transcriptional profiling experiments in mice with pneumococcal pneumonia have now revealed that CXCL5 is only one of many hundreds of genes that are induced preferentially in epithelial cells during infection, dozens of which are secreted products like CXCL5 that can mediate immune cell cross-talk (14). Another epithelial-specific product was identified as a neutrophil activator, secreted and transmembrane 1 (Sectm1), which stimulates recruited neutrophils to make more of the neutrophil-attracting chemokine, CXCL2, thereby amplifying the positive feedback of inflammation within the infected lung (14).…”

“…Transcriptional profiling experiments in mice with pneumococcal pneumonia have now revealed that CXCL5 is only one of many hundreds of genes that are induced preferentially in epithelial cells during infection, dozens of which are secreted products like CXCL5 that can mediate immune cell cross-talk (14). Another epithelial-specific product was identified as a neutrophil activator, secreted and transmembrane 1 (Sectm1), which stimulates recruited neutrophils to make more of the neutrophil-attracting chemokine, CXCL2, thereby amplifying the positive feedback of inflammation within the infected lung (14). Harnessing the power of epithelial innate immunity, pharmacologically triggering these cells is being pursued as a means to provide protection against diverse respiratory infections (15), and it now appears that this can be effective even in mice modeling leukemia patients, despite profound immune dysregulation due to both leukemia and leukemia treatment (16).…”