Establishment and application of a novel in vitro model of microglial activation in traumatic brain injury.

Mechanical impact-induced primary injury after traumatic brain injury (TBI) leads to acute microglial pro-inflammatory activation and consequently mediates neurodegeneration, which is a major secondary brain injury mechanism. However, the detailed pathological cascades have not been fully elucidated, partially due to the pathological complexity in animal TBI models. Although there are several in vitro TBI models, none of them closely mimic post-TBI microglial activation. In the present study, we aimed to establish an in vitro TBI model, specifically reconstituting the pro-inflammatory activation and associated neurodegeneration following TBI. We proposed three sets of experiments. Firstly, we established a needle scratch injured neuron (NSN)-induced microglial activation and neurodegeneration in vitro model of TBI. Secondly, we compared microglial pro-inflammatory cytokines profiles between the in vitro TBI model and TBI in male mice. Additionally, we validated the role of injured neurons-derived damage-associated molecular patterns (DAMPs) in amplifying microglial pro-inflammatory pathways using the in vitro TBI model. Thirdly, we applied the in vitro model for the first time to characterize the cellular metabolic profile of needle scratch injured-neuron-activated microglia (NCAM), and define the role of metabolic reprogramming in mediating pro-inflammatory microglial activation and mediated neurodegeneration. Our results showed we successfully established a novel in vitro TBI model, which closely mimics primary neuronal injury-triggered microglial pro-inflammatory activation and mediated neurodegeneration after TBI. This in vitro model provides an advanced and highly translational platform for dissecting interactions in the pathological processes of neuronal injury-microglial activation-neuronal degeneration cascade, and elucidating the detailed underlying cellular and molecular insights after TBI. SIGNIFICANCE STATEMENT: Microglial activation is a key component of acute neuroinflammation that leads to neurodegeneration and long-term neurological outcome deficits after TBI. However, it is not feasible to truly dissect primary neuronal injury-induced microglia activation, and consequently mediated neurodegeneration in vivo Furthermore, there is currently lacking of in vitro TBI models closely mimic the TBI primary injury-mediated microglial activation. In this study, we successfully established and validated a novel in vitro TBI model of microglial activation, and for the first time, characterized the cellular metabolic profile of microglia in this model. This novel microglial activation in vitro TBI model will help in elucidating microglial inflammatory activation and consequently associated neurodegeneration after TBI.