SynB3 Conjugated QBP1 Passes Blood-Brain Barrier Models and Inhibits PolyQ Protein Aggregation

Polyglutamine diseases are degenerative diseases in the central nervous system caused by CAG trinucleotide repeat expansion which encodes polyglutamine tracts, leading to the misfolding of pathological proteins. Small peptides can be designed to prevent polyglutamine diseases by inhibiting the polyglutamine protein aggregation, for example, polyglutamine binding peptide 1(QBP1). However, the transportation capability of polyglutamine binding peptide 1 across the blood-brain barrier is less efficient. We hypothesized whether its therapeutic effect could be improved by increasing the rate of membrane penetration.

The objective of the study was to explore whether polyglutamine binding peptide 1 conjugated cell-penetrating peptides could pass through the blood-brain barrier and inhibit the aggregation of polyglutamine proteins.

In order to investigate the toxic effects, we constructed a novel stable inducible PC12 cells to express Huntington protein that either has 11 glutamine repeats or 63 glutamine repeats to mimic wild type and polyglutamine expand Huntington protein, respectively. Both SynB3 and TAT conjugated polyglutamine binding peptide 1 was synthesized, respectively. We tested their capabilities to pass through a Trans-well system and subsequently studied the counteractive effects on polyglutamine protein aggregation.

The conjugation of cell-penetrating peptides to SynB3 and TAT enhanced the transportation of polyglutamine binding peptide 1 across the mono-cell layer and ameliorated polyglutamine-- expanded Huntington protein aggregation; moreover, SynB3 showed better delivery efficiency than TAT. Interestingly, it has been observed that polyglutamine binding peptide 1 specifically inhibited polyglutamine-expanded protein aggregation rather than affected other amyloidosis proteins, for example, β-Amyloid.

Our study indicated that SynB3 could be an effective carrier for polyglutamine binding peptide 1 distribution through the blood-brain barrier model and ameliorate the formation of polyglutamine inclusions; thus SynB3 conjugated polyglutamine binding peptide 1 could be considered as a therapeutic candidate for polyglutamine diseases.