Drosophila melanogaster Genetic Model of Parkinson’s Disease: phytotherapy approach for a new and more sustainable pre-clinical investigation

Drosophila melanogaster (Dm) is a valuable genetic model for exploring molecular, genetic and cellular aspects of neurodegeneration in Parkinson's disease (PD), for further understanding its etiology and pathogenesis and making valid contributions to drug screening. This study used two loss-of-function Dm mutants, PINK1B9 and LRRK2WD40 (deletion of WD40 domain), that both express essential phenotypic characteristics of PD in humans, albeit with a different biochemical mechanism and pathways. Since therapeutic treatments to limit the onset of PD are not yet available and the common approach to treating patients is to intervene by relieving symptoms, I sought to investigate the effects of two natural methanolic extracts of Mucuna pruriens (Mpe; a L-Dopa-containing herbal) and Withania somnifera Dunal (Wse). Both plants have been known and used for centuries in Ayurvedic medicine for their anti-oxidant, anti-inflammatory properties and protective features against neurodegeneration. The two extracts were tested on both male mutants at different concentrations and different physiological states (as adult L-/A+ or as larvae and adult L+/A+). The parameters considered were lifespan, motor activity, olfactory response, synaptic protein expression, mitochondria and synaptic active zone morphology; both in treated and untreated flies. The overall results indicate that Mpe shows a significant effect on PINK1B9 mutants while Wse acts mostly on LRRK2WD40 ones. The two phytochemical extracts tested were able to counteract the motor and non-motor dysfunctions as well as the mitochondrial impairment, although to different extents depending on PD variance (Mpe-PINK1B9 vs Wse-LRRK2WD40). Additional investigations are necessary to further understand the specific characteristics of the different effects in the two types of mutants. In detail: a) the administration of 0.1% Mpe L+/A+ on PINK1B9 significantly extended lifespan, overcame the olfactory deficit and improved climbing behavior of the PD mutant. Furthermore, TEM analysis of antennal lobes and thoracic ganglia revealed that Mpe administration prevented the loss of synaptic active zones (T-bars) and reduced the number of damaged mitochondria. Lastly, western blot analysis showed restored bruchpilot (BRP) and tyrosine hydroxylase (TH) expression, referred to WT control levels. The results highlight multiple sites of action of Mpe and suggest that its effects cannot depend only upon its L-Dopa content; b) the effect of 1% Wse L-/A+ administration on LRRK2WD40 caused a recovery of dysfunctions in locomotor activity, in muscle electrophysiological response to stimuli and in mitochondria degeneration. In contrast, the administration of Wse to Dm LRRK2WD40 as L+/A+, independent of the concentration, worsened lifespan and determined the appearance of increased endosomal activity in the thoracic ganglia. In conclusion, this study strengthens the relevance of using PINK1B9 Dm and LRRK2WD40 Dm as a translational model in studying the properties of both Mucuna pruriens and Withania somnifera for PD treatment.