Modelling neuroinflammation in a dish using murine iPSC-derived microglia and macrophages
24 September 2020
UAntwerp online - - - - -
Prof. P. Ponsaerts
PhD defence Alessandra Quarta - Faculty of Medicine and Health Sciences
Neuroinflammation is defined as the development of an inflammatory response in the central nervous system (CNS) upon trauma or disease. The post-insult neuroinflammatory environment is generally colonized by two myeloid cell populations: endogenous parenchymal microglia and blood-derived monocytes that infiltrate the CNS in response to a compromised blood-brain-barrier. Both these cell populations are characterized by multiple functional states and can either display highly pro-inflammatory properties or promote the resolution of inflammation and provide support for tissue regeneration. Steering the activation of microglia and CNS infiltrating monocytes in favour of the latter, hold great promises as a future treatment option for CNS pathologies. Our research group has previously demonstrated that local administration of the immune-modulating cytokine interleukin 13 (IL13) drives microglia and infiltrating monocytes toward the anti-inflammatory phenotype and improves disease outcome in several mouse models of CNS disease. Unfortunately, as the existing cell culture systems to evaluate microglia/monocyte immune properties often overlook the important contribution of CNS environmental signalling to neuroinflammatory processes, a comprehensive in vitro analysis of microglia and monocyte/macrophage behaviour was not possible. The main aim of this PhD research was to establish and validate a novel in vitro platform to investigate similarities and differences in immune reactivity for both microglia and monocytes under pro-inflammatory stimulation, as well as following immunomodulatory treatment with IL13.
In the first part of this doctoral thesis, cellular models of murine induced pluripotent stem cell (iPSC)-derived microglia and iPSC-derived macrophages were generated and characterized. Analysis of their transcriptome profile and evaluation of their phenotypical and functional properties following classical and alternative immune stimulation revealed strong similarities with endogenous microglia and brain-infiltrating monocytes/macrophages, respectively, thus confirming the cellular identity of in vitro differentiated iPSC-microglia and iPSC-macrophages. Furthermore, we provide evidence that a brain-like culture milieu strongly modulates the phenotypic and inflammatory properties of iPSC-microglia and iPSC-macrophages, suggesting that CNS-specific environmental cues play an important role in the restrained immune activation potential of murine microglia as compared to murine monocytes. These findings imply that the development of novel immunomodulating therapeutic approaches will need to (re)consider both cell types independently and in combination within a neural environment.
In the second part of this doctoral thesis, we aimed at unravelling the immune mechanism(s) responsible for the observed in vivo clinical and/or histopathological benefits following IL13-mediated therapeutic intervention. To this end, we explored how pro-inflammatory activation of iPSC-microglia and iPSC-macrophage can be modulated by IL13. Interestingly, our results indicate that IL13 has divergent signalling outcome in microglia as compared to macrophages. While iPSC-macrophages profoundly inhibited the release of pro-inflammatory mediators upon IL13 administration, iPSC-microglia cultures exacerbated inflammation-induced oxidative stress in the presence of IL13. This striking observation was additionally confirmed in vivo following intracerebral delivery of IL13, thus emphasizing that IL13 might operate through multiple and even opposite mechanisms within the inflamed CNS and not simply via a binary activation as previously postulated.
In conclusion, the technological and scientific findings reported in this doctoral thesis reveal the value of iPSC-derived neuro-immune cell culture models as an in vitro tool to unravel the different contribution of microglia and monocytes to the development and resolution of neuroinflammatory responses, as well as to investigate novel therapeutic interventions for inflammation-associated CNS injury or disease.