Examining inflammation in the CNS: from inflammatory molecules to in vitro models

Abstract

Studies of CNS inflammation typically focus mostly on microglia cells or co-cultures of CNS cells, and not on how each CNS cell type alone can contribute to an inflamed environment. To address this deficiency, the current study investigated the inflammatory potential and in-vitro responses of CNS cells following treatment with pro-inflammatory stimuli (lipopolysaccharide (LPS); Interferon-γ (IFN-γ)). To determine cells’ potentials for responding to these stimuli, expression of their cognate receptors was determined using qPCR, while inflammatory responses were determined using immunoassays to measure the secretion of inflammatory and regulatory cytokines. For non-microglial CNS cells, despite expression of TLR-4 and IFNγR1 being detectable, limited responsiveness to LPS or IFNγ was observed.

In order to study microglia, microglia(-like) cell models are often used; these are generally produced through complicated methodologies involving multiple steps. The current study aimed to develop a novel (and simpler) procedure for generating an in-vitro model for microglia-like cells. Specifically, a one-step process was developed and optimised, by which monocytic THP-1 cells were differentiated into microglia-like ‘mgTHP-1’ cells. The microglia-like nature of mgTHP-1 cells was confirmed using a panel of microglial markers, while their molecular and functional properties, and aspects of their metabolism and epigenetics, were also investigated. mgTHP-1 cells were shown to be capable of pro-inflammatory M1-like responses, as indicated by significant secretion of pro-inflammatory cytokines when challenged with LPS or IFN-γ. Conversely, pre-treatment with the anti-inflammatory flavonoid Vicenin-2 significantly reduced IFNγ- or LPS-triggered secretion of pro-inflammatory cytokines, and increased secretion of anti-inflammatory cytokines, indicating that mgTHP1 cells can also shift towards an M2-like anti-inflammatory phenotype.

In conclusion, this study reports the establishment of a novel protocol for generating microglia-like (mgTHP-1) cells, and demonstrates that CNS cells have significantly varying inflammatory response profiles in-vitro, which may be associated with their physiological roles in-vivo.