Cooperative inhibition of SNARE-mediated vesicle fusion by α-synuclein monomers and oligomers

The primary hallmark of Parkinson's disease (PD) is the generation of Lewy bodies of which major component is α-synuclein (α-Syn). Because of increasing evidence of the fundamental roles of α-Syn oligomers in disease progression, α-Syn oligomers have become potential targets for therapeutic interventions for PD. One of the potential toxicities of α-Syn oligomers is their inhibition of SNARE-mediated vesicle fusion by specifically interacting with vesicle-SNARE protein synaptobrevin-2 (Syb2), which hampers dopamine release. Here, we show that α-Syn monomers and oligomers cooperatively inhibit neuronal SNARE-mediated vesicle fusion. α-Syn monomers at submicromolar concentrations increase the fusion inhibition by α-Syn oligomers. This cooperative pathological effect stems from the synergically enhanced vesicle clustering. Based on this cooperative inhibition mechanism, we reverse the fusion inhibitory effect of α-Syn oligomers using small peptide fragments. The small peptide fragments, derivatives of α-Syn, block the binding of α-Syn oligomers to Syb2 and dramatically reverse the toxicity of α-Syn oligomers in vesicle fusion. Our findings demonstrate a new strategy for therapeutic intervention in PD and related diseases based on this specific interaction of α-Syn.

Synergistic effects of common schizophrenia risk variants

The mechanisms by which common risk variants of small effect interact to contribute to complex genetic disorders are unclear. Here, we apply a genetic approach, using isogenic human induced pluripotent stem cells, to evaluate the effects of schizophrenia (SZ)-associated common variants predicted to function as SZ expression quantitative trait loci (eQTLs). By integrating CRISPR-mediated gene editing, activation and repression technologies to study one putative SZ eQTL (FURIN rs4702) and four top-ranked SZ eQTL genes (FURIN, SNAP91, TSNARE1 and CLCN3), our platform resolves pre- and postsynaptic neuronal deficits, recapitulates genotype-dependent gene expression differences and identifies convergence downstream of SZ eQTL gene perturbations. Our observations highlight the cell-type-specific effects of common variants and demonstrate a synergistic effect between SZ eQTL genes that converges on synaptic function. We propose that the links between rare and common variants implicated in psychiatric disease risk constitute a potentially generalizable phenomenon occurring more widely in complex genetic disorders.

Ca2+-Triggered Synaptic Vesicle Fusion Initiated by Release of Inhibition

Recent structural and functional studies of the synaptic vesicle fusion machinery suggest an inhibited tripartite complex consisting of neuronal soluble N-ethylmaleimide sensitive factor attachment protein receptors (SNAREs), synaptotagmin, and complexin prior to Ca2+-triggered synaptic vesicle fusion. We speculate that Ca2+-triggered fusion commences with the release of inhibition by Ca2+ binding to synaptotagmin C2 domains. Subsequently, fusion is assisted by SNARE complex zippering and by active membrane remodeling properties of synaptotagmin. This additional, inhibitory role of synaptotagmin may be a general principle since other recent studies suggest that Ca2+ binding to extended synaptotagmin C2 domains enables lipid transport by releasing an inhibited state of the system, and that Munc13 may nominally be in an inhibited state, which is released upon Ca2+ binding to one of its C2 domains.

Characterization of SNARE proteins in human pituitary adenomas: targeted secretion inhibitors as a new strategy for the treatment of acromegaly?

CONTEXT

Targeted secretion inhibitors (TSIs), a new class of recombinant biotherapeutic proteins engineered from botulinum toxin, represent a novel approach for treating diseases with excess secretion. They inhibit hormone secretion from targeted cell types through cleavage of SNARE (soluble N-ethylmaleimide-sensitive factor-activating protein receptor) proteins. qGHRH-LH(N)/D is a TSI targeting pituitary somatotroph through binding to the GHRH-receptor and cleavage of the vesicle-associated membrane protein (VAMP) family of SNARE proteins.

OBJECTIVE

Our objective was to study SNARE protein expression in pituitary adenomas and to inhibit GH secretion from somatotropinomas using qGHRH-LH(N)/D.

DESIGN

We analyzed human pituitary adenoma analysis for SNARE expression and response to qGHRH-LH(N)/D treatment.

SETTING

The study was conducted in University Hospitals.

PATIENTS

We used pituitary adenoma samples from 25 acromegaly and 47 nonfunctioning pituitary adenoma patients.

OUTCOME

Vesicle-SNARE (VAMP1-3), target-SNARE (syntaxin1, SNAP-23, and SNAP-25), and GHRH-receptor detection with RT-qPCR, immunocytochemistry, and immunoblotting. Assessment of TSI catalytic activity on VAMPs and release of GH from adenoma cells.

RESULTS

SNARE proteins were variably expressed in pituitary samples. In vitro evidence using recombinant GFP-VAMP2&3 or pituitary adenoma lysates suggested sufficient catalytic activity of qGHRH-LH(N)/D to degrade VAMPs, but was unable to inhibit GH secretion in somatotropinoma cell cultures.

CONCLUSIONS

SNARE proteins are present in human pituitary somatotroph adenomas that can be targeted by TSIs to inhibit GH secretion. qGHRH-LH(N)/D was unable to inhibit GH secretion from human somatotroph adenoma cells. Further studies are required to understand how the SNARE proteins drive GH secretion in human somatotrophs to allow the development of novel TSIs with a potential therapeutic benefit.

A botulinum neurotoxin-like function of Potentilla chinensis extract that inhibits neuronal SNARE complex formation, membrane fusion, neuroexocytosis, and muscle contraction

CONTEXT

Botulinum neurotoxins (BoNTs) are popularly used to treat various diseases and for cosmetic purposes. They act by blocking neurotransmission through specific cleavage of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. Recently, several polyphenols were shown to interfere with SNARE complex formation by wedging into the hydrophobic core interface, thereby leading to reduced neuroexocytosis.

OBJECTIVE

In order to find industrially-viable plant extract that functions like BoNT, 71 methanol extracts of flowers were screened and BoNT-like activity of selected extract was evaluated.

MATERIALS AND METHODS

After evaluating the inhibitory effect of 71 flower methanol extracts on SNARE complex formation, seven candidates were selected and they were subjected to SNARE-driven membrane fusion assay. Neurotransmitter release from neuronal PC12 cells and SNARE complex formation inside the cell was also evaluated. Finally, the effect of one selected extract on muscle contraction and digit abduction score was determined.

RESULTS

The extract of Potentilla chinensis Ser. (Rosaceae)(Chinese cinquefoil) flower inhibited neurotransmitter release from neuronal PC12 cells by approximately 90% at a concentration of 10 μg/mL. The extract inhibited neuroexocytosis by interfering with SNARE complex formation inside cells. It reduced muscle contraction of phrenic nerve-hemidiaphragm by approximately 70% in 60 min, which is comparable to the action of the Ca²⁺-channel blocker verapamil and BoNT type A.

DISCUSSION AND CONCLUSION

While BoNT blocks neuroexocytosis by cleaving SNARE proteins, the Potentilla chinensis extract exhibited the same activity by inhibiting SNARE complex formation. The extract paralyzed muscle as efficiently as BoNT, suggesting the potential versatility in cosmetics and therapeutics.

SNARE-wedging polyphenols as small molecular botox

Most cosmetic and therapeutic applications of Clostridium botulinum neurotoxin (BoNT) are related to muscle paralysis caused by the blocking of neurotransmitter release at the neuromuscular junction. BoNT specifically cleaves SNARE proteins at the nerve terminal and impairs neuroexocytosis. Recently, we have shown that several polyphenols inhibit neurotransmitter release from neuronal PC12 cells by interfering with SNARE complex formation. Based on our previous result, we report here that myricetin, delphinidin, and cyanidin indeed paralyze muscle by inhibiting acetylcholine release at the neuromuscular junction. While the effect of myricetin on muscle paralysis was modest compared to BoNT/A, myricetin exhibited a shorter response time than BoNT/A. Intraperitoneally-injected myricetin at an extreme dose of 1000 mg/kg did not induce death of mice, alleviating the safety issue. Thus, these polyphenols might be useful in treating various human hypersecretion diseases for which BoNT/A has been the only option of choice.

Lipidic antagonists to SNARE-mediated fusion

SNARE proteins mediate the fusion of lipid bilayers by the directed assembly of coiled-coil domains arising from apposing membranes. We have utilized inverted cone-shaped lipids, antagonists of the necessary membrane deformation during fusion to characterize the extent and range of SNARE assembly up to the moment of stalk formation between bilayers. The inverted cone-shaped lipid family of acyl-CoAs specifically inhibits the completion of fusion in an acyl-chain length-dependent manner. Removal of acyl-CoA from the membrane relieves the inhibition and initiates a burst of membrane fusion with rates exceeding any point in the control curves lacking acyl-CoA. This burst indicates the accumulation of semi-assembled fusion complexes. These preformed complexes are resistant to cleavage by botulinum toxin B and thus appear to have progressed beyond the "loosely zippered" state of docked synaptic vesicles. Surprisingly, application of the soluble domain of VAMP2, which blocks SNARE assembly by competing for binding on the available t-SNAREs, blocks recovery from the acyl-CoA inhibition. Thus, complexes formed in the presence of a lipidic antagonist to fusion are incompletely assembled, suggesting that the formation of tightly assembled SNARE pairs requires progression all the way through to membrane fusion. In this regard, physiologically docked exocytic vesicles may be anchored by a highly dynamic and potentially even reversible SNAREpin.