Background P42 is a 23aa peptide lying within hHtt that prevents aggregate formation in HeLa cells and ameliorates axonal transport and motor performances in Drosophila HD models (Mugat et al., 2008; Arribat et al., 2013). Additionally, it reduces aggregate formation, weight loss, and brain atrophy, and ameliorates motor performances in R6/2 mouse model (Arribat et al., submitted). By mass spectroscopy we identified a shorter 14aa fragment, P42B, still present after three hours in P42TAT-containing brain extracts.

Aims To test whether the fragment P42B still harbours active properties in HeLa cells and Drosophila HD models.

Methods/techniques Cultured HeLa cells were co-transfected with GFP-hHtt171aa-138Q and cherry-P42 or cherry-P42B. P42 and P42B were tested alone, or combined to the transduction peptide TAT to increase cellular penetration. Transgenic flies expressing polyQ-hHtt in salivary glands (MS-1096-Gal4; UAS-HA-hHtt171aa-138Q/+) or eyes (GMR-Gal4; UAS-HA-hHtt67aa-93Q/+) were crossed with flies expressing UAS-P42GFP, UAS-P42TATGFP, UAS-P42BGFP, or UAS-GFP. MS-1096-Gal4; UAS-HA-hHtt171aa-138Q/+; +/+ flies were nourished since L1 with placebo, P42TAT or P42BTAT synthetic peptides containing yeast [0.2 mM] and sacrificed at L3. Aggregate formation was studied in L3 larval salivary glands by immunostaining and quantified with filter retardation assays. The eye degeneration was studied in adult Drosophila at day 0 and day 10.

Results/outcome P42B prevents aggregate formation in HeLa cells. In the salivary glands from L3 larvae, immunostaining and filter retardation assays show that P42B, either genetically or orally-administered, is not able to significantly hamper aggregate formation. On the contrary, P42B was clearly able to prevent the eye degeneration in adult flies.

Conclusions The efficacy of P42B is phenotype-dependent. This suggests either that the entire P42 peptide is required to fully hamper aggregate formation or that a threshold effects exists explaining the differences according to the phenotype.