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Gas6/TAM Signalling Negatively Regulates Inflammatory Induction of GM-CSF in Mouse Brain Microglia.

ABSTRACT: Microglia and astrocytes are the main CNS glial cells responsible for the neuroinflammatory response, where they release a plethora of cytokines into the CNS inflammatory milieu. The TAM (Tyro3, Axl, Mer) receptors and their main ligand Gas6 are regulators of this response, however, the underlying mechanisms remain to be determined. We investigated the ability of Gas6 to modulate the CNS glial inflammatory response to lipopolysaccharide (LPS), a strong pro-inflammatory agent, through a qPCR array that explored Toll-like receptor signalling pathway-associated genes in primary cultured mouse microglia. We identified the Csf2 gene, encoding granulocyte-macrophage colony-stimulating factor (GM-CSF), as a major Gas6 target gene whose induction by LPS was markedly blunted by Gas6. Both the Csf2 gene induction and the suppressive effect of Gas6 on this were emulated through measurement of GM-CSF protein release by cells. We found distinct profiles of GM-CSF induction in different glial cell types, with microglia being most responsive during inflammation. Also, Gas6 markedly inhibited the LPS-stimulated nuclear translocation of NF-κB p65 protein in microglia. These results illustrate microglia as a major resident CNS cellular source of GM-CSF as part of the neuroinflammatory response, and that Gas6/TAM signalling inhibits this response through suppression of NF-κB signalling.

SUBMITTER: Gilchrist SE

PROVIDER: S-EPMC8699038 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundAdministration of granulocyte-macrophage colony stimulating factor (GM-CSF) relieves symptoms in Crohn's disease (CD). It has been reported that reduced GM-CSF bioactivity is associated with more aggressive ileal behaviour and that GM-CSF-null mice exhibit ileal barrier dysfunction and develop a transmural ileitis following exposure to non-steroidal anti-inflammatory drugs (NSAIDs). STAT5 signalling is central to GM-CSF action. It was therefore hypothesised that GM-CSF signalling in non-haematopoietic cells is required for ileal homeostasis.MethodsBone marrow (BM) chimeras were generated by reconstituting irradiated GM-CSF receptor (gm-csfr) beta chain or GM-CSF (gm-csf) deficient mice with wild type BM (WTBM-->GMRKO and WTBM-->GMKO). Intestinal barrier function and the response to NSAID-induced ileal injury were examined. Expression of gm-csf, gm-csfr or stat5 in Caco-2 and HT-29 intestinal epithelial cell (IEC) lines was knocked down and the effect of GM-CSF signalling on IEC survival and proliferation was determined.ResultsElevated levels of GM-CSF autoantibodies in ileal CD were found to be associated with dysregulation of IEC survival and proliferation. GM-CSF receptor-deficient mice and WTBM-->GMRKO chimeras exhibited ileal hyperpermeability. NSAID exposure induced a transmural ileitis in GM-CSF receptor-deficient mice and WTBM-->GMRKO chimeras. Transplantation of wild type BM into GM-CSF-deficient mice prevented NSAID ileal injury and restored ileal barrier function. Ileal crypt IEC proliferation was reduced in WTBM-->GMRKO chimeras, while STAT5 activation in ileal IEC following NSAID exposure was abrogated in WTBM-->GMRKO chimeras. Following knock down of gm-csf, gm-csfr alpha or beta chain or stat5a/b expression in Caco-2 cells, basal proliferation was suppressed. GM-CSF normalised proliferation of Caco-2 cells exposed to NSAID, which was blocked by stat5a/b RNA interference.ConclusionsLoss of GM-CSF signalling in non-haematopoietic cells increases NSAID ileal injury; furthermore, GM-CSF signalling in non-haematopoietic cells regulates ileal epithelial homeostasis via the STAT5 pathway. The therapeutic use of GM-CSF may therefore be beneficial in chronic ileitis associated with CD.

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Gas6/TAM Signalling Negatively Regulates Inflammatory Induction of GM-CSF in Mouse Brain Microglia.

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