Author(s): García Cassani, Bethania
Date: 2017
Persistent ID: http://hdl.handle.net/10451/28400
Origin: Repositório da Universidade de Lisboa
Subject(s): Neuroglia; Neurotransmissores; Linfócitos; Intestinos; Imunologia; Teses de doutoramento - 2017; Domínio/Área Científica::Ciências Médicas::Medicina Básica
Tese de doutoramento, Ciências Biomédicas (Imunologia), Universidade de Lisboa, Faculdade de Medicina, 2017
In this thesis we demonstrate that three distinct players form a novel multi-tissue defence unit in the intestinal wall: group 3 of innate lymphoid cells (ILC3s), intestinal epithelial cells and enteric glial cells (EGCs). This interplay reveals a neuro-immune interaction unit that regulates epithelial homeostasis and mucosal defense. ILC3s are major regulators at mucosal surfaces being critical in tissue repair and in the maintenance of gut homeostasis. Intestinal ILC3 – that mainly aggregate into cryptopatches - integrate environmental signals leading to the production of the proinflammatory cytokines IL-22 and IL-17. IL-22 in turn induces intestinal epithelial cells to produce antimicrobial peptides and mucus. We found that ILC3s express high levels of RET, a neuroregulatory receptor for GDNF family ligands (GFLs). In order to address the effect of RET in ILC3s development and function RET-deficient mice foetal liver chimeras were analyzed. Interestingly a decrease of IL-22 expressing ILC3s was observed when compared to WT controls. In addition a RET gain of function model (RetMEN2B) resulted in increased IL-22 expressing ILC3s. In line with these experiments, cell-autonomous ablation of RET in Rorγt expressing cells was performed. RorγtCreRetfl/fl, (RetΔ) mice had decrease IL-22 expressing ILC3s and a reduction of epithelial reactivity genes such as mucins and defensins comparing with their littermate controls. Upon infection with the attaching and effacing bacteria Citrobacter rodentium, RetΔ mice had marked gut inflammation, reduced IL-22 producing ILC3, increased C. rodentium infection and translocation, reduced epithelial reactivity genes, increased weight loss and reduced survival. All these data together, suggest that RET cell autonomous ILC3 signals regulate IL-22 production. Signals downstream of Ret were regulated via GFLs which directly controled rapid phosphorylation of the p38 MAPK/ERK-AKT cascade and STAT3 activation in ILC3s. In turn, STAT3 bound to the Il22 promoter to induce transcription. Finally, we found that enteric glial cells integrated commensal and environmental signals to produce GFLs that control IL-22 production. Physical localization of glial cells in the vicinity of ILC3 was observed taking advantage of double reporter mice for GFAP (glial fibrillary acidic protein) and RET. Enteric glial cells had a stellate shape morphology, projecting into cryptopatches. In vitro co-culture studies showed EGCs capacity to produce GFLs in response to TLR2 and TLR4 activation and IL-1β and IL-33 stimulation, promoting IL-22 production by ILC3s. In vivo studies with DSS induced colitis in glial specific Myd88 deficient mice (Gfap-Cre.Myd88Δ) showed an increase of gut inflammation and weight loss along with a reduced expression of intestinal GFLs and ILC3-derived IL-22 levels compared with their littermate controls. When infected with Citrobacter Rodentium Myd88 deficient mice exhibited a pronounced susceptibility to bowel inflammation and infection. In summary, we were able to show that the enteric glial cells sense environmental cues through MYD88 to produce GFLs that in turn activate RET expressing ILC3s and via MAP kinase and STAT3 induce the transcription of Il22. The production of IL-22 promotes the expression of defence and repair genes. Thus, this novel glial-ILC3 epithelial unit is critical in the maintenance of intestinal homeostasis providing protection and repairing the epithelial barrier after injury.
