The role of membranes in function and dysfunction of intrinsically disordered amyloidogenic proteins

Preclinical assessment of a ganglioside-targeted therapy for Parkinson's disease with the first-in-class adaptive peptide AmyP53

We propose a new concept for the treatment of Parkinson's disease (PD), which considers that its root cause, α-synuclein, is an intrinsically disordered protein (IDP) difficult to target by classic approaches. Upon binding to lipid raft gangliosides, α-synuclein shifts from random coil to α-helix, forming Ca2+-permeable oligomeric pores triggering a neurotoxicity cascade. We used the α-synuclein-ganglioside interaction as guideline to design a therapeutic peptide (AmyP53) that combines the respective flexible ganglioside-binding domains of α-synuclein and Alzheimer's β-amyloid protein. AmyP53 is an adaptive peptide, the first representant of a new therapeutic class. It acts as a competitive inhibitor of α-synuclein oligomer formation in brain cell membranes and prevents subsequent downstream synaptotoxicity, including the loss of dopaminergic neurons in an animal α-synuclein injection model of PD. It is active against both wild-type and mutant forms of α-synuclein. AmyP53 is administered intranasally without side effects. This new concept "target the target (gangliosides), not the arrow (IDP)" is distinct from classic α-synuclein centric approaches that did not cure PD so far.

Impact of Ca2+ on membrane catalyzed IAPP amyloid formation and IAPP induced vesicle leakage

Human islet amyloid polypeptide (hIAPP, also known as amylin) is a 37 amino acid pancreatic polypeptide hormone that plays a role in regulating glucose levels, but forms pancreatic amyloid in type-2 diabetes. The process of amyloid formation by hIAPP contributes to β-cell death in the disease. Multiple mechanisms of hIAPP induced toxicity of β-cells have been proposed including disruption of cellular membranes. However, the nature of hIAPP membrane interactions and the effect of ions and other molecules on hIAPP membrane interactions are not fully understood. Many studies have used model membranes with a high content of anionic lipids, often POPS, however the concentration of anionic lipids in the β-cell plasma membrane is low. Here we study the concentration dependent effect of Ca2+ (0 to 50 mM) on hIAPP membrane interactions using large unilamellar vesicles (LUVs) with anionic lipid content ranging from 0 to 50 mol%. We find that Ca2+ does not effectively inhibit hIAPP amyloid formation and hIAPP induced membrane leakage from binary LUVs with a low percentage of POPS, but has a greater effect on LUVs with a high percentage of POPS. Mg2+ had very similar effects, and the effects of Ca2+ and Mg2+ can be largely rationalized by the neutralization of POPS charge. The implications for hIAPP-membrane interactions are discussed.