Autism sensory dysfunction in an evolutionarily conserved system

There is increasing evidence for a strong genetic basis for autism, with many genetic models being developed in an attempt to replicate autistic symptoms in animals. However, current animal behaviour paradigms rarely match the social and cognitive behaviours exhibited by autistic individuals. Here we instead assay another functional domain – sensory processing – known to be affected in autism to test a novel genetic autism model in Drosophila melanogaster. We show similar visual response alterations and a similar development trajectory in Nhe3 mutant flies (total N=72) and in autistic human participants (total N=154). We report a dissociation between first- and second-order electrophysiological visual responses to steady-state stimulation in adult mutant fruit flies that is strikingly similar to the response pattern in human adults with ASD as well as that of a large sample of neurotypical individuals with high numbers of autistic traits. We explain this as a genetically driven, selective signalling alteration in transient visual dynamics. In contrast to adults, autistic children show a decrease in the first-order response that is matched by the fruit fly model, suggesting that a compensatory change in processing occurs during development. Our results provide the first animal model of autism comprising a differential developmental phenotype in visual processing

Vitamin B12 modulates Parkinson’s disease LRRK2 kinase activity through allosteric regulation and confers neuroprotection

Missense mutations in Leucine-Rich Repeat Kinase 2 (LRRK2) cause the majority of familial and some sporadic forms of Parkinson’s disease (PD). The hyperactivity of LRRK2 kinase induced by the pathogenic mutations underlies neurotoxicity, promoting the development of LRRK2 kinase inhibitors as therapeutics. Many potent and specific small molecule LRRK2 inhibitors have been reported with promise. However, nearly all inhibitors are ATP competitive – some with unwanted side effects and unclear clinical outcome - alternative types of LRRK2 inhibitors are lacking. Herein we find 5’-deoxyadenosylcobalamin (AdoCbl), a physiological form of the essential micronutrient vitamin B12 as a mixed-type allosteric inhibitor of LRRK2 kinase activity. Multiple assays show that AdoCbl directly binds LRRK2, leading to the alterations of protein conformation and ATP binding in LRRK2. STD-NMR analysis of a LRRK2 homologous kinase reveals the contact sites in AdoCbl that interface with the kinase domain. Furthermore, we provide evidence that AdoCbl modulates LRRK2 activity through disruption of LRRK2 dimerization. Treatment with AdoCbl inhibits LRRK2 kinase activity in cultured cells and brain tissue, and importantly prevents neurotoxicity in primary rodent cultures as well as in transgenic C. elegans and D. melanogaster expressing LRRK2 disease variants. Finally, AdoCbl alleviates deficits in dopamine release sustainability caused by LRRK2 disease variants in mouse models. Our study uncovers vitamin B12 as a novel class of LRRK2 kinase modulator with a distinct mechanism, which can be harnessed to develop new LRRK2-based PD therapeutics in the futur

Interaction of LRRK2-G2019S with Rab GTPases in vivo

Previously, we identified an excitotoxic mechanism by which expression of mutant forms of LRRK2 in the dopaminergic neurons increased visual signalling in young flies, followed by the complete loss of visual response in old flies. We used this assay to screen for Rabs which interact with LRRK2. Our top hit is Rab10. In young flies, expressing both Rab10 and LRRK2-G2019S increases the lamina neural response ~20 fold. These changes in the neural response are independent of photoreception. Knockdown of Rab10 ameliorates the neurodegeneration seen in the visual system of old flies expressing LRRK2-G2019S in their dopamine neurons. GFP expression/antibody staining suggests that the dopamine neurons innervating the visual system (lobes and lamina) and suboesophageal zone (controlling the proboscis extension response) are Rab10+, but in other dopamine neurons (e.g. those controlling sleep/wake/circadian patterns) Rab10 is undetectable. We therefore tested dopaminergic knockdown of Rab10 and found it rescues movement G2019S-induced deficits in the proboscis movement. Neither LRRK2-G2019S nor Rab10-RNAi affect the circadian pattern. In dopaminergic neurons, not all Rabs are equal: Rab3 and Rab32 (the fly homolog of Rab29) affect LRRK2 in other ways. Neither are found in visual neurons. We conclude that differences in neurodegeneration between groups of dopaminergic neurons may be the consequence of their palette of Rab proteins