Tryptophan metabolism and fruit fly behaviour: implications for psychosis

The kynurenine pathway of tryptophan degrades contains several neuroactive metabolites which have been implicated in the pathogenesis of psychotic and neurodegenerative disorders. The kynurenine pathway enzyme kynurenine 3-monooxigenase (KMO) plays a key role in maintaining balance of these neuroactive metabolites. Indeed, reduced KMO activity leads to elevated levels of kynurenic acid (KYNA), which antagonises both N-methyl-D-aspartate (NMDA) receptors and alpha7 nicotinic acetylcholine receptors. Decreased KMO activity and increased levels of KYNA have been observed in patients suffering from schizophrenia and other psychotic disorders.

Our recent work in KMO knockout mice suggests that increased levels of KYNA due to KMO impairment lead to altered behaviours which may have relevance to schizophrenia, including increased anxiety and impaired social interaction. It has also been observed that elevated KYNA levels in rats are associated with disruptions in sleep and impaired contextual memory. Although the KYNA-dependent effects observed in rodents are likely due to alterations in glutamatergic and cholinergic neurotransmission, the precise mechanisms underlying behavioural alterations arising from kynurenine pathway imbalances are not clear.

This project will employ the fruit fly Drosophila melanogaster, a powerful system for neurogenetic and kynurenine pathway analyses, to dissect these mechanisms via the following approaches:

1) Behavioural analyses: in order to confirm that modulation of the kynurenine pathway affects behaviour in flies, we will employ a panel of well-established behavioural paradigms, such as analysis of general activity, circadian rhythms, sleep, locomotion, social interactions, centrophobism, startle response and prepulse inhibition. The kynurenine pathway will be modulated by knockdown or overexpression of genes encoding key pathway enzymes such as KMO, tryptophan 2,3-dioxygenase (TDO) and kynurenine aminotransferase (KAT), as well as by the feeding of pathway metabolites and chemical inhibitors of these enzymes. Genes encoding key neurotransmitter receptors will also be targeted in order to dissect the signalling mechanisms underlying any effects.

2) Advanced imaging: confocal and electron microscopy will be employed to monitor effects on neurotransmission and structural alterations in the fly brain. For example, transgenic sensor constructs will be employed to measure second messengers (e.g. calcium, cAMP, dopamine) involved in physiology and neurotransmission.

3) Molecular analyses: alterations in gene and protein expression in the various paradigms above will be studied using RNA-Seq and mass spectrometry in order to understand the molecular changes resulting from the kynurenine pathway manipulations. Key findings will be validated by QPCR and immunoblotting and used as a starting point for further mechanistic analyses.

Techniques that will be undertaken during the project
- Microscopy techniques (confocal; electron)
- Drosophila genetics and husbandry
- Behavioural analyses with the fruit fly
- RNA-Seq (RNA isolation)
- Proteomics work (protein isolation, mass spectrometry)
- Relevant cell-based biochemical/molecular assays (QPCR, immunoblotting)

Available to UK/EU applicants only

Application information
https://www2.le.ac.uk/research-degrees/doctoral-training-partnerships/bbsrc