| dc.description.abstract | Astrocytes, a heterogeneous class of glial cells, play key roles in maintaining homeostasis in the central nervous system (CNS). This is achieved through multifaceted cellular responses; however, a growing body of evidence suggests that these are heavily associated with the capability of astrocytes to meet their energetic requirements. During CNS inflammation, a hallmark of many neuropathologies, astrocytes lose their homeostatic functions which correlates with significant alteration of their metabolic state. Related studies from the periphery indicate that modulating cellular metabolism may provide a tangible therapeutic target for inflammatory diseases, suggesting that this may represent a potential target for modulating astrocyte inflammatory responses to restore their homeostatic functions during CNS pathologies.
The 18-kilodalton translocator protein (TSPO) is a highly conserved outer mitochondrial membrane protein, expressed in glial cells such as astrocytes. Importantly, TSPO expression drastically increases during neuroinflammation in glial cells such as astrocytes. This has attracted much attention to the possibility of therapeutically modulating TSPO to treat CNS inflammation. However, to date this is hampered by the fact that the underlying function of TSPO remains unclear. An increasing body of evidence suggests that TSPO may regulate cellular metabolism, though this remains underexplored.
To test the overarching hypothesis that TSPO regulates cellular metabolism in astrocytes this study employed two distinct TSPO-deficient (TSPO-/-) cell models: an astrocytoma cell line (U373 cells) and mouse primary astrocytes (MPAs). This thesis explored the metabolic ramifications of TSPO deficiency in these CNS cell models, characterised changes to the bioenergetic responses of TSPO-/- MPAs to lipopolysaccharide-induced inflammation, and then attempted to pharmacologically recapitulate these studies with TSPO ligands.
TSPO deficiency modulated MPA and U373 cell metabolism, albeit resulting in different bioenergetic profiles, suggestive of altered fuel preference. Fatty acid oxidation (FAO) was increased in TSPO-/- MPAs, and studies in U373 cells indicated that the mechanistic basis for this may be an interaction between TSPO and carnitine palmitoyltransferase-1a (CPT1a) the rate-limiting enzyme of FAO. In response to inflammatory stimulation, TSPO-/- MPAs showed no significant differences in regulation of intracellular metabolic proteins, however secretion of the pro-inflammatory cytokine tumour necrosis factor from TSPO-/- MPAs was temporally modulated. Pharmacological recapitulation of these results was unsuccessful, however co-immunoprecipitation studies suggested that pharmacological inhibition of TSPO may modulate interactions between TSPO and other metabolic regulatory proteins. Taken together these studies have shown that TSPO acts as a regulator of cellular metabolism in astrocytes and may play a role in regulating cytokine release through a separate mechanism. These may represent two potential benefits following therapeutic modulation of TSPO that warrant further investigation. | en_GB |
