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Luminal microbes promote monocyte-stem cell interactions across a healthy colonic epithelium.

ABSTRACT: The intestinal epithelium forms a vital barrier between luminal microbes and the underlying mucosal immune system. Epithelial barrier function is maintained by continuous renewal of the epithelium and is pivotal for gut homeostasis. Breaching of the barrier causes mobilization of immune cells to promote epithelial restitution. However, it is not known whether microbes at the luminal surface of a healthy epithelial barrier influence immune cell mobilization to modulate tissue homeostasis. Using a mouse colonic mucosal explant model, we demonstrate that close proximity of luminal microbes to a healthy, intact epithelium results in rapid mucus secretion and movement of Ly6C(+)7/4(+) monocytes closer to epithelial stem cells. These early events are driven by the epithelial MyD88-signaling pathway and result in increased crypt cell proliferation and intestinal stem cell number. Over time, stem cell number and monocyte-crypt stem cell juxtapositioning return to homeostatic levels observed in vivo. We also demonstrate that reduced numbers of tissue Ly6C+ monocytes can suppress Lgr5EGFP+ stem cell expression in vivo and abrogate the response to luminal microbes ex vivo. The functional link between monocyte recruitment and increased crypt cell proliferation was further confirmed using a crypt-monocyte coculture model. This work demonstrates that the healthy gut epithelium mediates communication between luminal bacteria and monocytes, and monocytes can modulate crypt stem cell number and promote crypt cell proliferation to help maintain gut homeostasis.

SUBMITTER: Skoczek DA

PROVIDER: S-EPMC4067517 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Background Bronchioalveolar stem cells (BASCs) located at the bronchioalveolar-duct junction (BADJ) are stem cells residing in alveoli and terminal bronchioles that can self-renew and differentiate into alveolar type (AT)-1 cells, AT-2 cells, club cells, and ciliated cells. Following terminal-bronchiole injury, BASCs increase in number and promote repair. However, whether BASCs can be differentiated from mouse-induced pluripotent stem cells (iPSCs) remains unreported, and the therapeutic potential of such cells is unclear. We therefore sought to differentiate BASCs from iPSCs and examine their potential for use in the treatment of epithelial injury in terminal bronchioles. Methods BASCs were induced using a modified protocol for differentiating mouse iPSCs into AT-2 cells. Differentiated iPSCs were intratracheally transplanted into naphthalene-treated mice. The engraftment of BASCs into the BADJ and their subsequent ability to promote repair of injury to the airway epithelium were evaluated. Results Flow cytometric analysis revealed that BASCs represented ~?7% of the cells obtained. Additionally, ultrastructural analysis of these iPSC-derived BASCs via transmission electron microscopy showed that the cells containing secretory granules harboured microvilli, as well as small and immature lamellar body-like structures. When the differentiated iPSCs were intratracheally transplanted in naphthalene-induced airway epithelium injury, transplanted BASCs were found to be engrafted in the BADJ epithelium and alveolar spaces for 14 days after transplantation and to maintain the BASC phenotype. Notably, repair of the terminal-bronchiole epithelium was markedly promoted after transplantation of the differentiated iPSCs. Conclusions Mouse iPSCs could be differentiated in vitro into cells that display a similar phenotype to BASCs. Given that the differentiated iPSCs promoted epithelial repair in the mouse model of naphthalene-induced airway epithelium injury, this method may serve as a basis for the development of treatments for terminal-bronchiole/alveolar-region disorders.

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Luminal microbes promote monocyte-stem cell interactions across a healthy colonic epithelium.

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