Esculetin Provides Neuroprotection against Mutant Huntingtin-Induced Toxicity in Huntington’s Disease Models

Huntington’s disease (HD) is a neurodegenerative disorder caused by an abnormal CAG trinucleotide repeat expansion within exon 1 of the huntingtin (HTT) gene. This mutation leads to the production of mutant HTT (mHTT) protein which triggers neuronal death through several mechanisms. Here, we investigated the neuroprotective effects of esculetin (ESC), a bioactive phenolic compound, in an inducible PC12 model and a transgenic Drosophila melanogaster model of HD, both of which express mHTT fragments. ESC partially inhibited the progression of mHTT aggregation and reduced neuronal death through its ability to counteract the oxidative stress and mitochondria impairment elicited by mHTT in the PC12 model. The ability of ESC to counteract neuronal death was also confirmed in the transgenic Drosophila model. Although ESC did not modify the lifespan of the transgenic Drosophila, it still seemed to have a positive impact on the HD phenotype of this model. Based on our findings, ESC may be further studied as a potential neuroprotective agent in a rodent transgenic model of HD.

Pain is so close to pleasure: the same dopamine neurons can mediate approach and avoidance in Drosophila

In mammals, dopamine is considered a central neuromodulator involved in all kinds of rewarding experiences ('common currency' hypothesis). In insects, the role of dopaminergic neurons in aversive stimuli was discovered before dopaminergic neurons were found to also be involved in processing appetitive stimuli. Here, we screened about 50 transgenic Drosophila lines, representing different subpopulations of dopaminergic neurons for their ability to sustain approach or avoidance behavior, when activated optogenetically in four different operant self-stimulation paradigms. None of the lines sustain consistent behavioral valence in all experiments. Individual lines sustain approach in one experiment and avoidance in another. One line mediated strong avoidance early in the experiment and weak approach in later stages. The evidence presented here appears to contradict a 'common currency' dopamine function in flies. Instead, different dopaminergic neurons convey valence in a context-dependent and flexible manner, reflecting the genetic heterogeneity of the dopaminergic neuronal population.

Gut bacteria regulate the pathogenesis of Huntington's disease in Drosophila

Changes in the composition of gut microbiota are implicated in the pathogenesis of several neurodegenerative disorders. Here, we investigated whether gut bacteria affect the hallmarks of Huntington's disease (HD) in transgenic Drosophila melanogaster (fruit fly) models expressing human full-length or N-terminal fragments of mutant huntingtin (HTT) protein, here referred to as HD flies. We find that elimination of commensal gut bacteria by antibiotics reduces the aggregation of amyloidogenic N-terminal fragments of HTT and delays the development of motor defects. Conversely, colonization of HD flies with Escherichia coli (E. coli), a known pathobiont of human gut, accelerates HTT aggregation, aggravates immobility and shortens life span. Similar to antibiotics, treatment of HD flies with compounds such as luteolin, a flavone, or crocin a beta-carotenoid, ameliorates disease phenotypes and promotes survival. Crocin prevents colonization of E. coli in the HD flies gut and alters the levels of commensal bacteria, which may be linked to its protective effects. The opposing effects of E. coli and crocin on HTT aggregation, motor defects and survival in transgenic Drosophila support the involvement of gut-brain networks in the pathogenesis of HD.

Peptide-based inhibitors of Tau aggregation as a potential therapeutic for Alzheimer's disease and other Tauopathies

There are currently no disease altering drugs available for Tauopathies such as Alzheimer's disease, which alone is predicted to affect ~88 million people worldwide by 2050. As Tau aggregation underpins its toxicity, aggregation inhibitors are likely to have disease-modifying potential. Guided by in-silico mutagenesis studies, we developed a potent retro-inverso peptide inhibitor of Tau aggregation, RI-AG03 [AcrrrrrrrrGpkyk( ac)iqvGr-NH2], based on the 306VQIVYK311 hotspot. Aggregation of recombinant Tau was reduced by >90% with equimolar RI-AG03 and no fibrils were observed by EM. When added during the growth phase, RI-AG03 blocked seeded aggregation. Fluorescein-tagged RI-AG03 efficiently penetrated HEK-293 cells over 24 hours and was non-toxic at doses up to 30 μM. In transgenic Drosophila, RI-AG03 significantly improves neurodegenerative and behavioural phenotypes caused by expression of human Tau. Collectively this shows that RI-AG03 can effectively reduce Tau aggregation in vitro and block aggregationdependent phenotypes in vivo, raising possibilities for exploring its translational potential.

Lemon grass extract alleviates oxidative stress and delayed the loss of climbing ability in transgenic Drosophila model of Parkinson’s disease

Background: Parkinson’s Disease (PD) is characterized by the aggregation of α-synuclein, formation of Lewy bodies and the selective loss of dopaminergic neurons of mesencephalic substantia nigra pars compacta (SNC) with the debilitating motor symptoms. Introduction: The available treatment for PD provides symptomatic relief with no control on the progression of the disease. The treatment is also associated with several side effects. As the neurodegeneration in PD is also associated with the oxidative stress, antioxidants from plants could play an important role in reducing the PD symptoms. With this aim we decided to study the effect of Lemon grass extract (LGE) on the transgenic Drosophila model of PD expressing human alpha synuclein in the neurons. Methods: The PD flies allowed were allowed to feed on different doses of LGE established in diet for 24 days and then assayed for climbing ability and oxidative stress markers. The molecular docking study was also performed for citral (the component of the extract) and human α-synuclein. Results and discussion: A dose dependent significant improvement in the climbing ability and reduction in oxidative stress was observed in the PD flies exposed to LGE. In our earlier study on LGE, citral was found to be the main component of the extract by GC-MS analysis. The docking results also support the positive interaction between citral and human α-synuclein. Conclusion: The results suggests that LGE is potemnt in reducing the PD symptoms being mimicked in transgenic Drosophila.