The role of enteric glial cells in inflammatory diseases of the bowel
Objective: Enteric glial cells (EGCs) are recognized as a heterogeneous population capable of interacting with all major intestinal cell types to ensure tissue homeostasis. According to central nervous system (CNS) astrocytes, the subpopulation of EGCs expressing the glial fibrillary acidic protein (GFAP) is assigned to exert immunomodulatory functions. However, the mechanisms of such immunocompetence are largely unknown. Previously, much attention has been paid to changes within the enteric nervous system in chronic inflammatory bowel diseases (IBD). In IBD, an inappropriate mucosal immune response causes a persisting state of tissue inflammation, influencing structure as well as function of the ENS. Here, we focus our attention on acute inflammatory conditions and their impact on ENS function with emphasis on the GFAP-expressing glial subpopulation and their contribution to the inflammatory microenvironment. Method: In our ongoing study we experimentally induced intestinal inflammation in hGFAP-eGFP transgenic mice to specifically study the physiological responses of GFAP-glia. Colon samples were analyzed employing advanced techniques such as 3D light sheet fluorescence microscopy (LSFM). We correlated the in vivo findings of GFAP-glia physiology to in vitro experiments, in which we cultured flow cytometrysorted GFAP-glia as gliospheres and stimulated the mono-cultures with lipopolysaccharide (LPS). Additionally, we are currently setting up co-culture models incorporating primary ENS cells with lamina propria immune cells to develop suitable in vitro test systems for acute inflammatory stimuli. Results: LSFM of inflamed murine colon samples revealed the close proximity of GFAP-glia to lamina propria immune cells. When directly stimulated with LPS in vitro, hGFAP-eGFP transgenic murine EGCs boosted the expression of genes associated with immunomodulatory capacities, such as immune responses, cell locomotion and metabolism. Both, microarray analysis and multiplex protein profiling identified an increased production and secretion of proinflammatory cytokines. Employing the in vivo model we aim to further characterize the physiological potential of EGCs to modulate a pro-inflammatory microenvironment. Conclusion: With a better understanding of the potential of EGCs to fuel the inflammatory microenvironment in intestinal disorders it will be necessary and promising to consider the enteric nervous system in the development of new therapeutic strategies.