Enteric Glia Cells are Critical to Limiting the Intestinal Inflammatory Response After Injury
Author(s):
Simone Langness, UC San Diego; Brian Eliceiri, UC San Diego; Raul Coimbra, UC San Diego; Todd Costantini, UC San Diego
Background: Enteric glia cells (EGCs) have become increasingly recognized as key regulators of the gut inflammatory response to injury and are uniquely situated within the gut to interact with several target cells. We have demonstrated that vagal nerve stimulation (VNS) increases activation of EGCs that is associated with improved gut barrier function after injury. VNS has been shown to limit intestinal inflammation by altering the response of resident gut immune cells, however, no direct connection between vagal terminals and these resident immune cells has been identified.
Hypothesis: We hypothesize that EGCs modulate immune cell mobilization following injury and are required to relay vagal anti-inflammatory signals to the gut.
Methods: EGCs were selectively ablated from an isolated segment of distal bowel with topical application of benzalkonium chloride (BAC) in male C57 mice. 3 days following BAC application, mice were subjected to an ischemia-reperfusion injury (I/R) by superior mesenteric artery occlusion for 30 minutes. VNS was performed in a separate cohort of animals. EGC-ablated (EGC-) segments were compared to EGC-intact (EGC+) segments utilizing histology, flow cytometry and immunohistochemistry.
Results: Application of BAC resulted in a 39-77% decrease in the number of EGCs on flow cytometry compared to adjacent non-BAC treated segments (p<0.05). Enteric neurons were unaffected by BAC application. Following I/R injury, immune cell mobilization was increased in EGC- segments compared to EGC+ segments (20.6% vs. 13.1%, p<0.05). VNS significantly reduced immune cell mobilization after I/R injury in EGC+ segments only with cell percentages similar to sham (7.23 ± 1.4 vs. 5.98 ± 1.88, p=0.361). VNS failed to limit immune cell recruitment in EGC- segments (13.0 ± 2.3, p<0.05). Intestinal macrophages (MΦ) were the most affected immune cell subtype altered after EGC ablation, where VNS attenuated MΦ mobilization in EGC+ gut segments only. Histologic evidence of gut injury was diminished in animals treated with VNS when EGCs were intact, whereas segments with EGC ablation showed histologic features consistent with more severe gut tissue injury.
Conclusions: EGC ablation uncouples the protective effects of VNS after injury by altering the mobilization of immune cells in the gut. These findings support the importance of EGCs in transmitting vagal-mediated signals to effector cells, such as resident MΦ, to limit intestinal inflammation following injury.