Drosophila mutants of the kynurenine pathway as a model for ageing studies

LIM-kinase 1 effects on memory abilities and male courtship song in Drosophila depend on the neuronal type

The signal pathway of actin remodeling, including LIM-kinase 1 (LIMK1) and its substrate cofilin, regulates multiple processes in neurons of vertebrates and invertebrates. Drosophila melanogaster is widely used as a model object for studying mechanisms of memory formation, storage, retrieval and forgetting. Previously, active forgetting in Drosophila was investigated in the standard Pavlovian olfactory conditioning paradigm. The role of specific dopaminergic neurons (DAN) and components of the actin remodeling pathway in different forms of forgetting was shown. In our research, we investigated the role of LIMK1 in Drosophila memory and forgetting in the conditioned courtship suppression paradigm (CCSP). In the Drosophila brain, LIMK1 and p-cofilin levels appeared to be low in specific neuropil structures, including the mushroom body (MB) lobes and the central complex. At the same time, LIMK1 was observed in cell bodies, such as DAN clusters regulating memory formation in CCSP. We applied GAL4 × UAS binary system to induce limk1 RNA interference in different types of neurons. The hybrid strain with limk1 interference in MB lobes and glia showed an increase in 3-h short-term memory (STM), without significant effects on long-term memory. limk1 interference in cholinergic neurons (CHN) impaired STM, while its interference in DAN and serotoninergic neurons (SRN) also dramatically impaired the flies' learning ability. By contrast, limk1 interference in fruitless neurons (FRN) resulted in increased 15-60 min STM, indicating a possible LIMK1 role in active forgetting. Males with limk1 interference in CHN and FRN also showed the opposite trends of courtship song parameters changes. Thus, LIMK1 effects on the Drosophila male memory and courtship song appeared to depend on the neuronal type or brain structure.

cd1 Mutation in Drosophila Affects Phenoxazinone Synthase Catalytic Site and Impairs Long-Term Memory

Being involved in development of Huntington's, Parkinson's and Alzheimer's diseases, kynurenine pathway (KP) of tryptophan metabolism plays a significant role in modulation of neuropathology. Accumulation of a prooxidant 3-hydroxykynurenine (3-HOK) leads to oxidative stress and neuronal cell apoptosis. Drosophila mutant cardinal (cd¹) with 3-HOK excess shows age-dependent neurodegeneration and short-term memory impairments, thereby presenting a model for senile dementia. Although cd gene for phenoxazinone synthase (PHS) catalyzing 3-HOK dimerization has been presumed to harbor the cd¹ mutation, its molecular nature remained obscure. Using next generation sequencing, we have shown that the cd gene in cd¹ carries a long deletion leading to PHS active site destruction. Contrary to the wild type Canton-S (CS), cd¹ males showed defective long-term memory (LTM) in conditioned courtship suppression paradigm (CCSP) at days 5-29 after eclosion. The number of dopaminergic neurons (DAN) regulating fly locomotor activity showed an age-dependent tendency to decrease in cd¹ relative to CS. Thus, in accordance with the concept "from the gene to behavior" proclaimed by S. Benzer, we have shown that the aberrant PHS sequence in cd¹ provokes drastic LTM impairments and DAN alterations.

Cas9-mediated maternal-effect and derived resistance alleles in a gene-drive strain of the African malaria vector mosquito, Anopheles gambiae

CRISPR/Cas9 technologies are important tools for the development of gene-drive systems to modify mosquito vector populations to control the transmission of pathogens that cause diseases such as malaria. However, one of the challenges for current Cas9-based drive systems is their ability to produce drive-resistant alleles resulting from insertions and deletions (indels) caused principally by nonhomologous end-joining following chromosome cleavage. Rapid increases in the frequency of such alleles may impair gene-drive dynamics. We explored the generation of indels in the germline and somatic cells in female gene-drive lineages using a series of selective crosses between a gene-drive line, AgNosCd-1, and wild-type mosquitoes. We find that potential drive-resistant mutant alleles are generated largely during embryonic development, most likely caused by deposition of the Cas9 endonuclease and guide RNAs in oocytes and resulting embryos by homozygous and hemizygous gene-drive mothers.

3-Hydroxykynurenine as a Potential Ligand for Hsp70 Proteins and Its Effects on Drosophila Memory After Heat Shock

Kynurenine products of tryptophan metabolism are modifiers of the nervous activity and oxidative processes in mammals and invertebrates. 3-Hydroxykynurenine (3HOK) in moderate concentrations is a lipid peroxidation inhibitor. However, its accumulation and oxidative auto-dimerization lead to oxidative stress development manifested in age-related neurodegenerative diseases (NDD) and neurological disorders provoked by acute stress. Different forms of stress, the mostly studied being heat shock response, rely on functioning of heat shock proteins of the Hsp70 superfamily. Since kynurenines are called "kids of stress," we performed computational estimation of affinity of 3HOK and other kynurenines binding to predicted ATP site of Drosophila melanogaster Hsp cognate 71 protein (Dhsp71) using AutoDock Vina. The binding energy of 3HOK dimer is - 9.4 kcal/mol; its orientation within the active site is close to that of ATP. This might be a new mechanism of producing a competitive inhibitor of Hsp70 chaperones that decreases organism ability to adapt to heat shock. We also showed that the Drosophila cardinal (cd¹) mutant with 3HOK excess, serving as a model for Huntington's disease (HD), manifests severe defects of short-term memory after heat shock applied either in adults or at the prepupal stage.

The effects of high-monosaccharide diets on development and biochemical composition of white-eyed mutant strain of house cricket (Acheta domesticus)

Tryptophan (TRP) is one of the essential amino acids in the animal body. Its exogenicity and low concentrations mean that it can be regarded as one of the key regulatory molecules at the cellular as well as physiological level. It has been shown to have a number of essential functions, such as in the production of other biologically active molecules. The main objective of this project was to investigate the effects of a high monosaccharide diet (HMD) on a hemimetabolic insect-house cricket (Acheta domesticus) and a mutant strain with impaired visual pigment synthesis (closely related to the tryptophan and kynurenine (KYN) metabolic pathway)-white eye. This study was aimed at determining the effects of glucose and fructose on cricket development and biochemical composition. A parallel goal was to compare the response of both cricket strains to HMD. ELISA assays indicated dysfunction of the TRP-KYN pathway in white strain insects and an elevated KYN/TRP ratio. Biochemical analyses demonstrated the effects of HMD mainly on fat and glycogen content. A decrease in food intake was also observed in the groups on HMD. However, no changes in imago body weight and water content were observed. The results of the study indicate a stronger response of the white strain to HMD compared to the wild-type strain. At the same time, a stronger detrimental effect of fructose than of glucose was apparent. Sex was found to be a modulating factor in the response to HMD.

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.

Enzymatic and non-enzymatic pathways of kynurenines' dimerization: the molecular factors for oxidative stress development

Kynurenines, the products of tryptophan oxidative degradation, are involved in multiple neuropathologies, such as Huntington's chorea, Parkinson's disease, senile dementia, etc. The major cause for hydroxykynurenines's neurotoxicity is the oxidative stress induced by the reactive oxygen species (ROS), the by-products of L-3-hydroxykynurenine (L-3HOK) and 3-hydroxyanthranilic acid (3HAA) oxidative self-dimerization. 2-aminophenol (2AP), a structural precursor of L-3HOK and 3HAA, undergoes the oxidative conjugation to form 2-aminophenoxazinone. There are several modes of 2AP dimerization, including both enzymatic and non-enzymatic stages. In this study, the free energies for 2AP, L-3HOK and 3HAA dimerization stages have been calculated at B3LYP/6-311G(d,p)//6-311+(O)+G(d) level, both in the gas phase and in heptane or water solution. For the intermediates, ionization potentials and electron affinities were calculated, as well as free energy and kinetics of molecular oxygen interaction with several non-enzymatically formed dimers. H-atom donating power of the intermediates increases upon the progress of the oxidation, making possible generation of hydroperoxyl radical or hydrogen peroxide from O2 at the last stages. Among the dimerization intermediates, 2-aminophenoxazinole derivatives have the lowest ionization potential and can reduce O2 to superoxide anion. The rate for O-H homolytic bond dissociation is significantly higher than that for C-H bond in non-enzymatic quinoneimine conjugate. However, the last reaction passes irreversibly, reducing O2 to hydroperoxyl radical. The inorganic ferrous iron and the heme group of Drosophila phenoxazinone synthase significantly reduce the energy cost of 2AP H-atom abstraction by O2. We have also shown experimentally that total antioxidant capacity decreases in Drosophila mutant cardinal with L-3HOK excess relative to the wild type Canton-S, and lipid peroxidation decreases in aged cardinal. Taken together, our data supports the conception of hydroxykynurenines' dual role in neurotoxicity: serving as antioxidants themselves, blocking lipid peroxidation by H-atom donation, they also can easily generate ROS upon dimerization, leading to the oxidative stress development.

Assessing and Modulating Kynurenine Pathway Dynamics in Huntington's Disease: Focus on Kynurenine 3-Monooxygenase

The link between disturbances in kynurenine pathway (KP) metabolism and Huntington's disease (HD) pathogenesis has been explored for a number of years. Several novel genetic and pharmacological tools have recently been developed to modulate key regulatory steps in the KP such as the reaction catalyzed by the enzyme kynurenine 3-monooxygenase (KMO). This insight has offered new options for exploring the mechanistic link between this metabolic pathway and HD, and provided novel opportunities for the development of candidate drug-like compounds. Here, we present an overview of the field, focusing on some novel approaches for interrogating the pathway experimentally.

Immunological Relevance of the Coevolution of IDO1 and AHR

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor initially identified because of its role in controlling the cellular response to environmental molecules. More recently, AHR has been shown to play a crucial role in controlling innate and adaptive immune responses through several mechanisms, one of which is the regulation of tryptophan metabolism. Indoleamine-2,3-dioxygenase (IDO) and tryptophan-2,3-dioxygenase (TDO) are considered rate-limiting enzymes in the tryptophan catabolism and play important roles in the regulation of the immunity. Moreover, AHR and IDO/TDO are closely interconnected: AHR regulates IDO and TDO expression, and kynurenine produced by IDO/TDO is an AHR agonist. In this review, we propose to examine the relationship between AHR and IDO/TDO and its relevance for the regulation of the immune response in health and disease.

Extension of life span of Drosophila melanogaster by the inhibitors of tryptophan-kynurenine metabolism

Upregulation of kynurenine (KYN) formation from tryptophan (TRY) was associated with aging in animal and human studies. TRY - KYN metabolism is affected by the activities of TRY 2,3-dioxygenase 2 (TDO) and ATP-binding cassette (ABC) transporter regulating TRY access to intracellular TDO. We studied the effects of TDO inhibitor, alpha-methyl tryptophan (aMT), and ABC transported inhibitor, 5-methyl tryptophan (5MT), on the life span of wild strain female Drosophila flies (Oregon-R). aMT and 5MT prolonged mean and maximum life span (by 27% and 43%, and 21% and 23%, resp.). The present results are the first observation of the extension of life span of Drosophila melanogaster by inhibitors of TRY - KYN metabolism, and in line with literature and previous studies on prolonged life span of TDO- and ABC-deficient female Drosophila mutants. Inhibition of TDO and ABC transporter activity might offer the new target for anti-aging and anti-AAMPD interventions.

The extended life span of Drosophila melanogaster eye-color (white and vermilion) mutants with impaired formation of kynurenine

Animal and human studies suggest that aging is associated with increased formation of kynurenine (KYN) from tryptophan (TRY). The rate-limiting factors of TRY-KYN metabolism are transmembrane transport of TRY, and activity of enzyme, TRY 2,3-dioxygenase (TDO2). Eye-color mutants, white (w1118) (impaired TRY transport) and vermilion (v48a and v2) (deficient TDO activity), were compared with wild-type Oregon-R (Ore-R) strain of Drosophila melanogaster. Female 1-day-old adult flies maintained on a standard medium, and acclimatized to 12-h light:12-h dark cycle were collected, and then regularly transferred to fresh medium every 3-4 days. The number of dead flies was recorded at the time of transfer. Forty flies were studied in each experimental group. The life span of w1118 (mean = 45.5 days), and v48a (mean = 47.6 days) and v2 (mean = 43.8 days), were significantly longer than of wild-type Ore-R flies (27.1 days) (p < 0.001, Logrank test). There were no differences in life span between w1118 and v48a and v2 mutants. Present results suggest that prolongation of life span may be associated with slow rate of KYN formation from TRY.

Metabolomic signatures of inbreeding at benign and stressful temperatures in Drosophila melanogaster

While the population genetics of inbreeding is fairly well understood, the effects of inbreeding on the physiological and biochemical levels are not. Here we have investigated the effects of inbreeding on the Drosophila melanogaster metabolome. Metabolite fingerprints in males from five outbred and five inbred lines were studied by nuclear magnetic resonance spectroscopy after exposure to benign temperature, heat stress, or cold stress. In both the absence and the presence of temperature stress, metabolite levels were significantly different among inbred and outbred lines. The major effect of inbreeding was increased levels of maltose and decreased levels of 3-hydroxykynurenine and a galactoside [1-O-(4-O-(2-aminoethyl phosphate)-beta-d-galactopyranosyl)-x-glycerol] synthesized exclusively in the paragonial glands of Drosophila species, including D. melanogaster. The metabolomic effect of inbreeding at the benign temperature was related to gene expression data from the same inbred and outbred lines. Both gene expression and metabolite data indicate that fundamental metabolic processes are changed or modified by inbreeding. Apart from affecting mean metabolite levels, inbreeding led to an increased between-line variation in metabolite profiles compared to outbred lines. In contrast to previous observations revealing interactions between inbreeding and environmental stress on gene expression patterns and life-history traits, the effect of inbreeding on the metabolite profile was similar across the different temperature treatments.