Characterisation of immunometabolic responses in astrocytes

Abstract

Astrocytes play a role in the central nervous system (CNS) inflammatory response. In many immune cell types cellular inflammation and metabolism are linked, a phenomenon termed ‘immunometabolism’. This has led to attempts to reduce chronic inflammation through manipulating cellular metabolism. Proteins of interest for this approach include transcription factor nuclear factor-kappa B (NF-κB) and mitochondrial protein ‘translocator protein (18 kDa)’ (TSPO). TSPO is of particular interest as a therapy for CNS disease as many TSPO ligands can access the CNS and have been demonstrated to have anti-inflammatory effects. However, immunometabolism has not been well described in astrocytes, and the function of TSPO is currently disputed. In this thesis, mouse primary astrocytes were used to characterise immunometabolic responses following treatment with the pro-inflammatory stimulus lipopolysaccharide (LPS). An initial increase in glycolytic metabolism was measured, prior to a shift towards oxidative phosphorylation and away from glucose metabolism, in part mediated by a decrease in glucose transporter GLUT1 expression. Pharmacological inhibition of NF-κB signalling demonstrated that this pathway is important in mediating the cellular metabolic response to inflammation in astrocytes, and may play a role in maintaining basal metabolic function in these cells. Pharmacological or genetic modulation of TSPO signalling in human astroglioma (U373) cells and/or mouse primary astrocytes demonstrated that while TSPO suppressed fatty acid oxidation and promoted glycolytic metabolism, this did not appear to acutely alter the inflammatory response of these cells after LPS treatment; however, the longer term effects remain to be explored. Together these data demonstrate that inflammation and metabolism are intrinsically linked in astrocytes and TSPO plays an important role in regulating metabolism in these cells.