Stowell, M. H. B. | Search bioRxiv

bioRxiv2017

Synaptophysin is a β-Amyloid Target that Regulates Synaptic Plasticity and Seizure Susceptibility in an Alzhiemer’s Model

Intro/abstractAlzheimers disease (AD), a condition characterized by cognitive deficits and progressive loss of memory, is causally linked to the short amyloid peptide A{beta}42, which disrupts normal neurotransmission1,2. Neurotransmitter (NT) release from synaptic vesicles (SV) requires coordinated binding of the conserved core secretory machinery comprised of the soluble NSF attachment protein receptor (vSNARE) synaptobrevin 2 (VAMP2) on the SV and the cognate tSNAREs on the plasma membrane. Synaptophysin (SYP) is the most abundant SV protein3 and the major pre-fusion binding partner of VAMP24. A major challenge in understanding the etiology and prevention of AD is determining the proteins directly targeted by A{beta}42 and elucidating if these targets mediate disease phenotypes. Here we demonstrate that A{beta}42 binds to SYP with picomolar affinity and disrupts the SYP/VAMP2 complex resulting in inhibition of both neurotransmitter release and synaptic plasticity. While functionally redundant paralogs of SYP have masked its critical activity in knockout studies5,6, we now demonstrate a profound seizure susceptibility phenotype in SYP knockout mice that is recapitulated in an AD model mouse. Our studies imply a subtle yet critical role for SYP in the synaptic vesicle cycle and the etiology of AD.

neuroscience↗

bioRxiv2017

Identification of the primary peptide inhibitor contaminant of fibrillation and toxicity in synthetic Amyloid-β42

Understanding the pathophysiology of Alzheimer disease has relied upon the use of amyloid peptides from a variety of sources, but most predominantly synthetic peptides produced using t-butyloxycarbonyl (Boc) or 9-fluorenylmethoxycarbonyl (Fmoc) chemistry. These synthetic methods can lead to minor impurities which can have profound effects on the biological activity of amyloid peptides. Here we used a combination of cytotoxicity assays, fibrillation assays and high resolution mass spectrometry (MS) to identify impurities in synthetic amyloid preparations that inhibit both cytotoxicity and aggregation. We identify the A{beta}42{Delta}39 species as the major peptide contaminant responsible for limiting both cytotoxicity and fibrillation of the amyloid peptide. In addition, we demonstrate that the presence of this minor impurity inhibits the formation of a stable A{beta}42 dimer observable by MS in very pure peptide samples. These results highlight the critical importance of purity and provenance of amyloid peptides in Alzheimers research in particular, and biological research in general.

neuroscience↗