Dissecting the interplay between the kynurenine pathway and extracellular vesicle signaling in schizophrenia

Increased levels of the kynurenine pathway (KP) metabolites L-kynurenine (KYN) and kynurenic acid (KYNA) have been found in the brains of patients with schizophrenia, and have been linked to cognitive impairment in these individuals. KYN and KYNA can bind and activate the transcription factor aryl hydrocarbon receptor (AHR), which has key roles in inflammation and cancer. Activation of the AHR by other ligands has been shown to induce extracellular vesicle (EV) release, in particular the release of small exosome-like vesicles from cells in vitro. However, the release of EVs from microglia and neurons - critical cell types in KP physiology - in response to AHR activation by KP metabolites has not been previously examined. We hypothesise that KP metabolites modulate the release of EVs from microglia and neurons, and that these EVs can then be transferred between cell types to regulate gene expression and modify cellular functions - ultimately impacting schizophrenia pathogenesis . For the initial part of this project we therefore propose to characterise the release of EVs from microglial cells and neurons in response to kynurenine and KYNA, and examine the involvement of AHR and downstream signalling pathways.
We also will examine the miRNA and protein content of the released EVs, as activation of cells with different stimuli can result in the differential loading of cargo into EVs. This not only potentially alters the outcome of EV uptake on the function of the recipient cells, but also makes EVs useful biomarkers of disease as their miRNA or protein content reflects that of the cells they were released from. Therefore, this study will examine the cargo of the released EVs, the transfer of EVs between microglia and neurons and their effects on cellular functions such as cell survival/apoptosis and the regulation of gene expression. Cell-type specific responses such as the release of inflammatory cytokines from microglia, and dendrite formation and neurotransmitter receptor expression in primary neurons will also be assessed.
Promising findings from this work validated in neuronally-enriched EVs derived from the plasma of individuals with schizophrenia and controls arising from ongoing work in the Giorgini group. This will permit us to refine/extend our current work and validate findings from the proposed project in a translationally relevant manner.