3-Hydroxykynurenine in Regulation of Drosophila Behavior: The Novel Mechanisms for Cardinal Phenotype Manifestations

Dysfunctions of kynurenine pathway of tryptophan metabolism (KPTM) are associated with multiple neuropathologies in vertebrates and invertebrates. Drosophila mutants with altered content of kynurenines are model objects for studying the molecular processes of neurodegeneration and senile dementia. The mutant cardinal (cd¹) with accumulation of the redox stress inductor 3-hydroxykynurenine (3-HOK) shows age-dependent impairments of the courtship song and middle-term memory. The molecular mechanisms for 3-HOK accumulation in cd¹ are still unknown. Here, we have studied age-dependent differences in spontaneous locomotor activity (SLA) for the wild type strain Canton-S (CS), cd¹, and cinnabar (cn¹) with an excess of neuroprotective kynurenic acid (KYNA). We have also estimated the level and distribution of protein-bound 3-HOK (PB-3-HOK) in Drosophila brains (Br) and head tissues. The middle-age cd¹ show the higher running speed and lower run frequency compared to CS, for cn¹ the situation is the opposite. There is a decrease in the index of activity for 40-day-old cd¹ that seems to be an effect of the oxidative stress development. Surprisingly, PB-3-HOK level in Drosophila heads, brains, and head capsules (HC) is several times lower for cd¹ compared to CS. This complements the traditional hypothesis that cd¹ phenotype results from a mutation in phenoxazinone synthase (PHS) gene governing the brown eye pigment xanthommatin synthesis. In addition to 3-HOK dimerization, cd¹ mutation affects protein modification by 3-HOK. The accumulation of free 3-HOK in cd¹ may result from the impairment of 3-HOK conjugation with some proteins of the brain and head tissues.