The NAD+ precursor NMN activates dSarm to trigger axon degeneration in Drosophila.

Axon degeneration contributes to the disruption of neuronal circuit function in diseased and injured nervous systems. Severed axons degenerate following the activation of an evolutionarily conserved signaling pathway, which culminates in the activation of SARM1 in mammals to execute the pathological depletion of the metabolite NAD+. SARM1 NADase activity is activated by the NAD+ precursor nicotinamide mononucleotide (NMN). In mammals, keeping NMN levels low potently preserves axons after injury. However, it remains unclear whether NMN is also a key mediator of axon degeneration and dSarm activation in flies. Here, we demonstrate that lowering NMN levels in Drosophila through the expression of a newly generated prokaryotic NMN-Deamidase (NMN-D) preserves severed axons for months and keeps them circuit-integrated for weeks. NMN-D alters the NAD+ metabolic flux by lowering NMN, while NAD+ remains unchanged in vivo. Increased NMN synthesis by the expression of mouse nicotinamide phosphoribosyltransferase (mNAMPT) leads to faster axon degeneration after injury. We also show that NMN-induced activation of dSarm mediates axon degeneration in vivo. Finally, NMN-D delays neurodegeneration caused by loss of the sole NMN-consuming and NAD+-synthesizing enzyme dNmnat. Our results reveal a critical role for NMN in neurodegeneration in the fly, which extends beyond axonal injury. The potent neuroprotection by reducing NMN levels is similar to the interference with other essential mediators of axon degeneration in Drosophila.

Novel Curcumin-Diethyl Fumarate Hybrid as a Dualistic GSK-3ß Inhibitor/Nrf2 Inducer for the Treatment of Parkinson's Disease.

Common copathogenic factors, including oxidative stress and neuroinflammation, are found to play a vital role in the development of neurodegenerative disorders, including Alzheimer's disease (AD) and Parkinson's disease (PD). Nowadays, owing to the multifactorial character of the diseases, no effective therapies are available, thus underlying the need for new strategies. Overexpression of the enzyme GSK-3ß and downregulation of the Nrf2/ARE pathway are responsible for a decrease in antioxidant defense effects. These pieces of evidence underline the usefulness of dual GSK-3ß inhibitors/Nrf2 inducers. In this regard, to design a dual modulator, the structures of a curcumin-based analogue, as GSK-3ß inhibitor, and a diethyl fumarate fragment, as Nrf2 inducer, were combined. Among the hybrids, 5 and 6 proved to effectively inhibit GSK-3ß, while 4 and 5 showed a marked ability to activate Nrf2 together to increase the neuronal resistance to oxidative stress. These last pieces of evidence translated into specific neuroprotective effects of 4 and 5 against PD pathological events including neurotoxicity elicited by α-synuclein aggregates and 6-hydroxydopamine. Hybrid 5 also showed neuroprotective effects in a C. elegans model of PD where the activation of GSK-3ß is intimately involved in Nrf2 regulation. In summary, 5 emerged as an interesting multitarget derivative, valuable to be exploited in a multitarget PD perspective.

Morphological and Functional Evaluation of Axons and their Synapses during Axon Death in Drosophila melanogaster.

Axon degeneration is a shared feature in neurodegenerative disease and when nervous systems are challenged by mechanical or chemical forces. However, our understanding of the molecular mechanisms underlying axon degeneration remains limited. Injury-induced axon degeneration serves as a simple model to study how severed axons execute their own disassembly (axon death). Over recent years, an evolutionarily conserved axon death signaling cascade has been identified from flies to mammals, which is required for the separated axon to degenerate after injury. Conversely, attenuated axon death signaling results in morphological and functional preservation of severed axons and their synapses. Here, we present three simple and recently developed protocols that allow for the observation of axonal morphology, or axonal and synaptic function of severed axons that have been cut-off from the neuronal cell body, in the fruit fly Drosophila. Morphology can be observed in the wing, where a partial injury results in axon death side-by-side of uninjured control axons within the same nerve bundle. Alternatively, axonal morphology can also be observed in the brain, where the whole nerve bundle undergoes axon death triggered by antennal ablation. Functional preservation of severed axons and their synapses can be assessed by a simple optogenetic approach coupled with a post-synaptic grooming behavior. We present examples using a highwire loss-of-function mutation and by over-expressing dnmnat, both capable of delaying axon death for weeks to months. Importantly, these protocols can be used beyond injury; they facilitate the characterization of neuronal maintenance factors, axonal transport, and axonal mitochondria.

Co-occurring WARS2 and CHRNA6 mutations in a child with a severe form of infantile parkinsonism.

OBJECTIVE: To investigate the molecular cause(s) underlying a severe form of infantile-onset parkinsonism and characterize functionally the identified variants. METHODS: A trio-based whole exome sequencing (WES) approach was used to identify the candidate variants underlying the disorder. In silico modeling, and in vitro and in vivo studies were performed to explore the impact of these variants on protein function and relevant cellular processes. RESULTS: WES analysis identified biallelic variants in WARS2, encoding the mitochondrial tryptophanyl tRNA synthetase (mtTrpRS), a gene whose mutations have recently been associated with multiple neurological phenotypes, including childhood-onset, levodopa-responsive or unresponsive parkinsonism in a few patients. A substantial reduction of mtTrpRS levels in mitochondria and reduced OXPHOS function was demonstrated, supporting their pathogenicity. Based on the infantile-onset and severity of the phenotype, additional variants were considered as possible genetic modifiers. Functional assessment of a selected panel of candidates pointed to a de novo missense mutation in CHRNA6, encoding the α6 subunit of neuronal nicotinic receptors, which are involved in the cholinergic modulation of dopamine release in the striatum, as a second event likely contributing to the phenotype. In silico, in vitro (Xenopus oocytes and GH4C1 cells) and in vivo (C. elegans) analyses demonstrated the disruptive effects of the mutation on acetylcholine receptor structure and function. CONCLUSION: Our findings consolidate the association between biallelic WARS2 mutations and movement disorders, and suggest CHRNA6 as a genetic modifier of the phenotype.

A Caenorhabditis elegans model to study dopamine transporter deficiency syndrome.

Dopamine transporter deficiency syndrome (DTDS) is a novel autosomal recessive disorder caused by mutations in the dopamine transporter (DAT), which leads to the partial or total loss of function of the protein. DTDS is a pharmacoresistant syndrome and very little is known about its neurobiology, in part due to the lack of relevant animal models. The objective of this study was to establish the first animal model for DTDS with strong construct validity, using Caenorhabditis elegans, and to investigate the in vivo role played by DTDS-related mutations found in human DAT (hDAT). We took advantage of a C. elegans knockout for the hDAT orthologue, cedat-1, to obtain genetically humanized animals bearing hDAT, in the wild type and in two mutated forms (399delG and 941C>T), in a null background. In C. elegans transgenic animals expressing the human wild-type form, we observed a rescue of the knockout phenotype, as assessed using two well-established paradigms, known to be regulated by the endogenous uptake of dopamine or 6-hydroxydopamine (6-OHDA) by DAT. The less severe mutation (941C>T) was able to partially rescue only one of the knockout phenotypes, whereas the 399delG mutation impaired DAT function in both phenotypic paradigms. Our in vivo phenotypic findings demonstrate a functional conservation between human and nematode DAT and validate previous in vitro indications of the loss of function of hDAT in carriers of DTDS-related mutations. Taken together, these observations establish C. elegans as a novel animal model for fast and inexpensive screening of hDAT mutations in functional and in vivo tests.