Antidepressant fluoxetine rewires astrocyte metabolism and increases cAMP signalling via independent pathways

Abstract

Depression has a substantial socioeconomic burden as the leading cause of disability globally, affecting 5% of the adult population. 30% of patients, though, do not respond to antidepressant therapy. Hence, there remains a significant unmet need for more effective treatment options for those living with depression.

Commonly prescribed antidepressants, including Fluoxetine (FLX), inhibit the reuptake of monoamines at the synapse, increasing synaptic monoamine levels. Interestingly, changes to monoamine levels are not required for FLX’s therapeutic effects. Consequently, other mechanisms of action are likely to be involved. Notably, FLX enhances the release of astrocytic lactate, a metabolite and signalling molecule vital for regulating emotional behaviour. Individuals with depression have altered brain lactate, and lactate administration acts like an antidepressant in rodent models. However, the mechanism underlying FLX-triggered lactate release is not fully understood.

This thesis aimed to better elucidate the mechanism by which FLX increases lactate release, thus identifying a pathway through which FLX exerts its therapeutic effect.

The results demonstrate that FLX increases intracellular cAMP, by 22%, determined using confocal live imaging with the cAMP FRET sensor in primary rat astrocytes. Furthermore, this was mediated via both the adenosine A2B receptors (A2BR) and 5-HT2B receptors (5-HT2BR), as well as adenylate cyclase signalling. However, the FLX-potentiated lactate release (59%), quantified with a fluorometric assay, was independent of both A2B and 5-HT2B receptors. FLX decreased mitochondria respiration and ATP production while increasing glycolysis independently of cAMP signalling as measured in the Seahorse assay. FLX restored mitochondria respiration following inhibition of glycogen recruitment while blocking glucose uptake abolished FLX-mediated changes to metabolism.

Together, these results indicate that FLX increases lactate production by attenuating mitochondrial respiration while enhancing glycolysis in a cAMP-independent manner. Thus, offering a plausible, novel mechanism for FLX’s antidepressant action.

Date of Award	18 Mar 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Valentina Mosienko (Supervisor) & Anja G Teschemacher (Supervisor)