A peptide that mimics the C-terminal sequence of SNAP-25 inhibits secretory vesicle docking in chromaffin cells

Preparation and efficacy verification of three-dimensional printed partitioned multi-effect precision-care gel facial mask

OBJECTIVE

A partition multi-effect precision-care gel facial mask conforming to facial skin characteristics was prepared using three-dimensional (3D) printing technology.

METHODS

First, the hydrogel matrix and humectant of a 3D-printed gel for facial masks were screened, and three 3D-printed gels of arbutin, hexapeptide, and salicylic acid were prepared with whitening, wrinkle removal, and oil control functions, respectively. Skin irritation tests were performed on the gels. Physicochemical properties such as pH, heat and cold tolerance were evaluated. The efficacy of three 3D-printed gels was assessed by measuring melanin value, wrinkle depression score, and oil secretion. Finally, the facial mask model design and printing parameters were studied, and a partition multi-effect precision-care gel facial mask was printed in line with facial skin characteristics.

RESULTS

For the 3D-printed facial mask, the gel prescription with 2% hydroxyethyl cellulose gel as matrix and 7% glycerol as humectant was the best. The prepared 3D-printed gel did not irritate the human skin, and its physicochemical properties met the Chinese facial mask industry standard (QB/T2872-2017). We showed that three types of 3D-printed gels containing arbutin, hexapeptide, and salicylic acid could be applied to the corresponding parts of the face to solve different problems, such as facial skin dullness, wrinkles, and oil secretion. Therefore, according to facial physiological characteristics, the facial mask model was designed for the forehead and nasolabial fold, which needs to be anti-wrinkled; the cheek, which needs to be whitened; and the nose and chin, which need oil control. The optimal printing parameters were 0.26 mm nozzle diameter, 90 mm/s printing speed, 30% filling density, 140% wire extrusion ratio, and 0.25 mm layer height. Different skin care effects can be achieved using a three-nozzle printer to print arbutin, hexapeptide, or salicylic acid gel on the mask's forehead and nasolabial fold, cheek, and nose and chin, respectively.

CONCLUSION

The 3D-printed partition multi-effect care gel facial mask prepared according to the skin features of different parts of the face can overcome the problem of the single skincare effect of the mass-produced facial masks.

Anti-ageing peptides and proteins for topical applications: a review

Skin ageing is a cumulative result of oxidative stress, predominantly caused by reactive oxygen species (ROS). Respiration, pollutants, toxins, or ultraviolet A (UVA) irradiation produce ROS with 80% of skin damage attributed to UVA irradiation. Anti-ageing peptides and proteins are considered valuable compounds for removing ROS to prevent skin ageing and maintenance of skin health. In this review, skin ageing theory has been illustrated with a focus on the mechanism and relationship with anti-ageing peptides and proteins. The effects, classification, and transport pathways of anti-ageing peptides and proteins across skin are summarized and discussed. Over the last decade, several novel formulations and advanced strategies have been developed to overcome the challenges in the dermal delivery of proteins and peptides for skin ageing. This article also provides an in-depth review of the latest advancements in the dermal delivery of anti-ageing proteins and peptides. Based on these studies, this review prospected several semi-solid dosage forms to achieve topical applicability for anti-ageing peptides and proteins.

Argireline: Needle-Free Botox as Analytical Challenge

Argireline-containing cosmetics attract public interest due to their confirmed reduction of facial wrinkles. Argireline is a peptide that works by inhibiting the release of neurotransmitters in the neuromuscular junction, producing a botox-like effect. Therefore, it is used as a safe needle-free alternative to botox treatment. In this work we investigated the presence of Argireline in cosmetic creams and sera by application of reversed phase liquid chromatography and tandem mass spectrometry (RP-HPLC/MS and MS/MS). The analysis revealed the presence of argireline and its oxidized form in several different cosmetics. The methionine residue in Argireline sequence was indicated as oxidation point according to neutral loss MS studies. The developed sample preparation strategy minimizes and monitors methionine oxidation, bringing to our attention the question of impact of ingredients on the stability of cosmetic product.

Method development for acetyl octapeptide-3 analysis by liquid chromatography-tandem mass spectrometry

Background

Acetyl octapeptide-3 (SNAP-8) is an antiaging peptide that is more effective than acetyl hexapeptide-3, which is more stable than botulinum toxin and effectively relieves facial wrinkles. Products containing SNAP-8 such as patch are producing, but analytical method has not been reported to determination of SNAP-8.

Method

Mobile phase, collision energy, and desolvation line temperature were optimized, and mass spectral data set for SNAP-8 was newly constructed by liquid chromatography-triple quadrupole mass spectrometer in multiple reaction monitoring mode.

Results

The developed method showed good linearity (r ≥ 0.9971) with limit of quantification of 0.0125 ng/mL, repeatability (% relative standard deviation = 0.02 to 0.12) and accuracy (% relative error = − 1.68 to 1.44) under optimal conditions. This method was successfully applied to a biodegradable microneedle patch loaded with SNAP-8.

Conclusion

The present method for the quantification of SNAP-8 may be useful for quality control in the cosmetic fields.

SNAP25/syntaxin4/VAMP2/Munc18-1 Complexes in Spinal Dorsal Horn Contributed to Inflammatory Pain

Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) have been implicated in the trafficking of postsynaptic glutamate receptors, including N-methyl-d-aspartate (NMDA)-subtype glutamate receptors (NMDARs) that are critical for nociceptive plasticity and behavioral sensitization. However, the components of SNAREs complex involved in spinal nociceptive processing remain largely unknown. Here we found that SNAP25, syntaxin4, VAMP2 and Munc18-1 were localized at postsynaptic sites and formed the complex in the superficial lamina of spinal cord dorsal horn of rats. The complex formation between these SNAREs components were accelerated after intraplantar injection of complete Freund's adjuvant (CFA), pharmacological removal of GABAergic inhibition or activation of NMDAR in intact rats. The increased SNAP25/syntaxin4/VAMP2/Munc18-1 interaction facilitated the surface delivery and synaptic accumulation of NMDAR during inflammatory pain. Disruption of the molecular interaction between SNAP25 with its SNARE partners by using a blocking peptide derived from the C-terminus of SNAP25 effectively repressed the surface and synaptic accumulation of GluN2B-containing NMDARs in CFA-injected rats. This peptide also alleviated inflammatory mechanical allodynia and thermal hypersensitivity. These data suggested that SNAREs complex assembly in spinal cord dorsal horn was involved in the inflammatory pain hypersensitivity through promoting NMDAR synaptic trafficking.

Anti-Wrinkle Efficacy of Cross-Linked Hyaluronic Acid-Based Microneedle Patch with Acetyl Hexapeptide-8 and Epidermal Growth Factor on Korean Skin

Background

Hyaluronic acid (HA)-based microneedle patch has recently been studied for wrinkle improvement. Cross-linked HA (CLHA) is widely used in dermal fillers. Acetyl hexapeptide-8 (AHP-8) and epidermal growth factor (EGF) are used for cosmetic ingredients.

Objective

This study aimed to verify the efficacy of the CLHA/HA-based patch with microstructure (microneedle patch) containing AHP-8 or EGF.

Methods

A total of 52 Korean females were enrolled in a double-blind, randomized, controlled, split-face trial. The subjects were divided into 3 groups: (1) microneedle patch alone, (2) microneedle patch/AHP-8, and (3) microneedle patch/EGF. The treatment was applied on the periorbital and nasolabial fold area for 4 hours to completely dissolve the microstructures once per week for 29 days. Evaluations, including photodamage scoring, image analysis with Antera 3D® (Miravex, Ireland), skin hydration measurement, and adverse effect assessments, were performed at each visit.

Results

Fifty subjects (96.2%) completed this clinical study. On day 29 after application, statistically significant improvements in wrinkle and skin hydration were observed in all groups (p<0.01). Treatment with microneedle patch/AHP-8 and microneedle patch/EGF showed statistically significant improvements in wrinkle compared with microneedle patch alone (p<0.05). No serious adverse effects were noted.

Conclusion

Combination of CLHA-based microneedle patch and functional cosmetic ingredients can improve wrinkle with minimal discomfort.

A mechanism for exocytotic arrest by the Complexin C-terminus

ComplexinII (CpxII) inhibits non-synchronized vesicle fusion, but the underlying mechanisms have remained unclear. Here, we provide evidence that the far C-terminal domain (CTD) of CpxII interferes with SNARE assembly, thereby arresting tonic exocytosis. Acute infusion of a CTD-derived peptide into mouse chromaffin cells enhances synchronous release by diminishing premature vesicle fusion like full-length CpxII, indicating a direct, inhibitory function of the CTD that sets the magnitude of the primed vesicle pool. We describe a high degree of structural similarity between the CpxII CTD and the SNAP25-SN1 domain (C-terminal half) and show that the CTD peptide lowers the rate of SDS-resistant SNARE complex formation in vitro. Moreover, corresponding CpxII:SNAP25 chimeras do restore complexin's function and even 'superclamp' tonic secretion. Collectively, these results support a so far unrecognized clamping mechanism wherein the CpxII C-terminus hinders spontaneous SNARE complex assembly, enabling the build-up of a release-ready pool of vesicles for synchronized Ca²⁺-triggered exocytosis.

Soluble N-Ethylmaleimide-Sensitive Factor Attachment Protein Receptor-Derived Peptides for Regulation of Mast Cell Degranulation

Vesicle-associated V-soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins and target membrane-associated T-SNAREs (syntaxin 4 and SNAP-23) assemble into a core trans-SNARE complex that mediates membrane fusion during mast cell degranulation. This complex plays pivotal roles at various stages of exocytosis from the initial priming step to fusion pore opening and expansion, finally resulting in the release of the vesicle contents. In this study, peptides with the sequences of various SNARE motifs were investigated for their potential inhibitory effects against SNARE complex formation and mast cell degranulation. The peptides with the sequences of the N-terminal regions of vesicle-associated membrane protein 2 (VAMP2) and VAMP8 were found to reduce mast cell degranulation by inhibiting SNARE complex formation. The fusion of protein transduction domains to the N-terminal of each peptide enabled the internalization of the fusion peptides into the cells equally as efficiently as cell permeabilization by streptolysin-O without any loss of their inhibitory activities. Distinct subsets of mast cell granules could be selectively regulated by the N-terminal-mimicking peptides derived from VAMP2 and VAMP8, and they effectively decreased the symptoms of atopic dermatitis in mouse models. These results suggest that the cell membrane fusion machinery may represent a therapeutic target for atopic dermatitis.

Peptide therapeutics from venom: Current status and potential

Peptides are recognized as being highly selective, potent and relatively safe as potential therapeutics. Peptides isolated from the venom of different animals satisfy most of these criteria with the possible exception of safety, but when isolated as single compounds and used at appropriate concentrations, venom-derived peptides can become useful drugs. Although the number of venom-derived peptides that have successfully progressed to the clinic is currently limited, the prospects for venom-derived peptides look very optimistic. As proteomic and transcriptomic approaches continue to identify new sequences, the potential of venom-derived peptides to find applications as therapeutics, cosmetics and insecticides grows accordingly.

Sphingomimetic multiple sclerosis drug FTY720 activates vesicular synaptobrevin and augments neuroendocrine secretion

Neurotransmission and secretion of hormones involve a sequence of protein/lipid interactions with lipid turnover impacting on vesicle trafficking and ultimately fusion of secretory vesicles with the plasma membrane. We previously demonstrated that sphingosine, a sphingolipid metabolite, promotes formation of the SNARE complex required for membrane fusion and also increases the rate of exocytosis in isolated nerve terminals, neuromuscular junctions, neuroendocrine cells and in hippocampal neurons. Recently a fungi-derived sphingosine homologue, FTY720, has been approved for treatment of multiple sclerosis. In its non-phosphorylated form FTY720 accumulates in the central nervous system, reaching high levels which could affect neuronal function. Considering close structural similarity of sphingosine and FTY720 we investigated whether FTY720 has an effect on regulated exocytosis. Our data demonstrate that FTY720 can activate vesicular synaptobrevin for SNARE complex formation and enhance exocytosis in neuroendocrine cells and neurons.

In vitro skin penetration of acetyl hexapeptide-8 from a cosmetic formulation

There is a concern that peptides in cosmetic creams marketed as anti-aging/anti-wrinkle may penetrate into the deep layers of the skin and potentially stimulate biological activity. Claims for one cosmetic peptide, acetyl hexapeptide-8 (Ac-EEMQRR-amide), suggest interference with neuromuscular signaling as its anti-wrinkle mechanism of action. Therefore, the skin penetration of commercially available Ac-EEMQRR-amide from a cosmetic formulation (oil-in-water (O/W) emulsion) was determined in hairless guinea pig (HGP) and human cadaver skin assembled into in vitro diffusion cells. An O/W emulsion containing 10% Ac-EEMQRR-amide was applied to skin at a dose of 2 mg/cm(2). After a 24-h exposure, the skin surface was washed to remove unabsorbed peptide. Skin disks were tape stripped to determine the amount of peptide in the stratum corneum. Removal of the stratum corneum layers was verified by confocal microscopy. The epidermis was heat separated from the dermis and each skin fraction was homogenized. Skin penetration of Ac-EEMQRR-amide was measured in skin layers by hydrophilic interaction liquid chromatography with tandem mass spectrometry using electrospray ionization (ESI) in the positive mode. Stable isotopically labeled hexapeptides were used as internal standards for the quantitation of native hexapeptides to correct for matrix effects associated with ESI. The results (percent of applied dose) showed that the majority of the Ac-EEMQRR-amide was washed from the surface of both HGP and human skin. Ac-EEMQRR-amide that penetrated skin remained mostly in the stratum corneum of HGP (0.54%) and human (0.22%) with the peptide levels decreasing as each layer was removed by tape stripping. Total Ac-EEMQRR-amide found in the epidermis of HGP and human skin was similar at 0.01%. No peptide was detected in the dermis or buffer collected underneath the skin for both human and HGP. There was no hexapeptide metabolite (H2N-EEMQRR-amide) detected in any layers of HGP skin, human skin or buffer collected underneath the skin. This skin penetration data will be useful for evaluating the safety of cosmetic products containing small peptide cosmetic ingredients.

Lipid metabolites enhance secretion acting on SNARE microdomains and altering the extent and kinetics of single release events in bovine adrenal chromaffin cells

Lipid molecules such as arachidonic acid (AA) and sphingolipid metabolites have been implicated in modulation of neuronal and endocrine secretion. Here we compare the effects of these lipids on secretion from cultured bovine chromaffin cells. First, we demonstrate that exogenous sphingosine and AA interact with the secretory apparatus as confirmed by FRET experiments. Examination of plasma membrane SNARE microdomains and chromaffin granule dynamics using total internal reflection fluorescent microscopy (TIRFM) suggests that sphingosine production promotes granule tethering while arachidonic acid promotes full docking. Our analysis of single granule release kinetics by amperometry demonstrated that both sphingomyelinase and AA treatments enhanced drastically the amount of catecholamines released per individual event by either altering the onset phase of or by prolonging the off phase of single granule catecholamine release kinetics. Together these results demonstrate that the kinetics and extent of the exocytotic fusion pore formation can be modulated by specific signalling lipids through related functional mechanisms.

The anti wrinkle efficacy of synthetic hexapeptide (Argireline) in Chinese Subjects

Abstract Background: This is the first multicenter clinical and experimental study of the anti wrinkle efficacy of Argireline in Chinese subjects. Objective: To evaluate the safety and efficacy of Argireline in the treatment of periorbital lines in Chinese subjects, and to observe the effect of Argireline on microstructural changes of the skin in the aged mice induced by D-galactose. Methods: The study was comprised of two parts: i) Clinical study: A total of 60 subjects received a single treatment in a 3:1 randomization ratio of Argireline: placebo. Argireline or placebo was applied to their periorbital wrinkles twice daily for 4 weeks, evaluations were made for the improvements in wrinkles. ii) Animal study: Argireline was applied to the aged mice twice daily for 6 weeks and the histopathological changes of skin tissue were evaluated. Results: In humans, the total anti wrinkle efficiency in the Argireline group was 48.9%, the depth of the wrinkles was notably reduced(P<0.01). In the aged mice, there was improvements in the morphology of skin tissue, the amount of typeⅠcollagen fibers increased(P<0.01) while type Ⅲ collagen fibers decreased (P<0.05). Conclusions: The studies revealed that Argireline had significant anti wrinkle effects in Chinese subjects.

Persistence of Botulinum neurotoxin inactivation of nerve function

The extraordinary persistence of intoxication occurring after exposure to some Botulinum neurotoxin (BoNT) serotypes is both a therapeutic marvel and a biodefense nightmare. Understanding the mechanisms underlying BoNT persistence will offer new strategies for improving the efficacy and extending the applications of BoNT therapeutic agents as well as for treating the symptoms of botulism. Research indicates that the persistence of BoNT intoxication can be influenced both by the ability of the toxin protease or its cleaved soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein substrate to resist turnover. Protease turnover seems to be mediated in part by the ubiquitin-proteasome system (UPS) and efforts to manipulate the UPS may prove to be an effective strategy for improving therapeutic utility of BoNT products and in the development of botulism antidotes.

The anti-wrinkle efficacy of argireline, a synthetic hexapeptide, in Chinese subjects: a randomized, placebo-controlled study

BACKGROUND

Argireline is a synthetic peptide that is patterned from the N-terminal end of the protein SNAP-25 and has been shown to reduce the degree of facial wrinkles. It is reported to inhibit vesicle docking by preventing formation of the ternary SNARE complex and by interfering in catecholamine release. The anti-wrinkle efficacy of argireline has not been studied in Chinese subjects.

OBJECTIVE

The objective of the study was to evaluate the safety and efficacy of argireline in the treatment of peri-orbital wrinkles in Chinese subjects.

METHODS

A total of 60 subjects received a randomized treatment of argireline or placebo in a ratio of 3:1. Argireline or placebo was applied to their peri-orbital wrinkles twice daily for 4 weeks, and then evaluations were made for the improvements in wrinkles. In the subjective evaluation, Daniell's classification and Seeman's standard were applied to make a global assessment of changes in the appearance of peri-orbital lines. In the objective evaluation, silicone replicas of the skin at the application area were made before and after the treatment, which were analyzed by a wrinkle-analysis apparatus.

RESULTS

In the subjective evaluation, the total anti-wrinkle efficacy in the argireline group was 48.9 %, compared with 0 % in the placebo group. In the objective evaluation, the parameters of roughness were all decreased in the argireline group (p < 0.01), while no decrease was obvious in the placebo group (p > 0.05).

CONCLUSIONS

This study showed that argireline had a significant anti-wrinkle effect in Chinese subjects.

The anti-wrinkle efficacy of Argireline

BACKGROUND

Argireline, a synthetic peptide, which is patterned from the N-terminal end of the protein SNAP-25, can both reduce the degree of existing facial wrinkles and demonstrate effectively against their development. In our past studies, we found out that Argireline had a significant anti-wrinkle effect in Chinese subjects and that it was safe and well tolerated.

OBJECTIVE

To observe the effect of Argireline on histological changes in the skin in the aged mice induced by D-galactose.

METHODS

Argireline was applied to the aged mice twice daily for 6 weeks. The histological changes in skin tissue were evaluated using hematoxylin-eosin (HE) and picrosirius-polarization (PSP) stains. The amount of type I and of type III collagen fibers were also semi-quantitatively compared using software Image-ProPlus.

RESULTS

There was an improvement in the histological structure of skin tissue in the aged mice; the amount of type I collagen fibers increased (P < 0.01), while that of type III collagen fibers decreased (P < 0.05).

CONCLUSIONS

This study revealed that Argireline could improve the histological structure of skin tissue and rejuvenate the aging skin.

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.

Trafficking of gap junction channels at a vertebrate electrical synapse in vivo

Trafficking and turnover of transmitter receptors required to maintain and modify the strength of chemical synapses have been characterized extensively. In contrast, little is known regarding trafficking of gap junction components at electrical synapses. By combining ultrastructural and in vivo physiological analysis at identified mixed (electrical and chemical) synapses on the goldfish Mauthner cell, we show here that gap junction hemichannels are added at the edges of GJ plaques where they dock with hemichannels in the apposed membrane to form cell-cell channels and, simultaneously, that intact junctional regions are removed from centers of these plaques into either presynaptic axon or postsynaptic dendrite. Moreover, electrical coupling is readily modified by intradendritic application of peptides that interfere with endocytosis or exocytosis, suggesting that the strength of electrical synapses at these terminals is sustained, at least in part, by fast (in minutes) turnover of gap junction channels. A peptide corresponding to a region of the carboxy terminus that is conserved in Cx36 and its two teleost homologs appears to interfere with formation of new gap junction channels, presumably by reducing insertion of hemichannels on the dendritic side. Thus, our data indicate that electrical synapses are dynamic structures and that their channels are turned over actively, suggesting that regulated trafficking of connexons may contribute to the modification of gap junctional conductance.

The F-actin cortical network is a major factor influencing the organization of the secretory machinery in chromaffin cells

We have studied how the F-actin cytoskeleton is involved in establishing the heterogeneous intracellular Ca(2+) levels ([Ca(2+)](i)) and in the organization of the exocytotic machinery in cultured bovine chromaffin cells. Simultaneous confocal visualization of [Ca(2+)](i) and transmitted light studies of the cytoskeleton showed that, following cell stimulation, the maximal signal from the Ca(2+)-sensitive fluorescent dye Fluo-3 was in the empty cytosolic spaces left by cytoskeletal cages. This was mostly due to the accumulation of the dye in spaces devoid of cytoskeletal components, as shown by the use of alternative Ca(2+)-insensitive fluorescent cytosolic markers. In addition to affecting the distribution of such compounds in the cytosol, the cytoskeleton influenced the location of L- and P-Q-type Ca(2+) channel clusters, which were associated with the borders of cytoskeletal cages in resting and stimulated cells. Indeed, syntaxin-1 and synaptotagmin-1, which are components of the secretory machinery, were present in the same location. Furthermore, granule exocytosis took place at these sites, indicating that the organization of the F-actin cytoskeletal cortex shapes the preferential sites for secretion by associating the secretory machinery with preferential sites for Ca(2+) entry. The influence of this cortical organization on the propagation of [Ca(2+)](i) can be modelled, illustrating how it serves to define rapid exocytosis.

Targeted secretion inhibitors-innovative protein therapeutics

Botulinum neurotoxins are highly effective therapeutic products. Their therapeutic success results from highly specific and potent inhibition of neurotransmitter release with a duration of action measured in months. These same properties, however, make the botulinum neurotoxins the most potent acute lethal toxins known. Their toxicity and restricted target cell activity severely limits their clinical utility. Understanding the structure-function relationship of the neurotoxins has enabled the development of recombinant proteins selectively incorporating specific aspects of their pharmacology. The resulting proteins are not neurotoxins, but a new class of biopharmaceuticals, Targeted Secretion Inhibitors (TSI), suitable for the treatment of a wide range of diseases where secretion plays a major role. TSI proteins inhibit secretion for a prolonged period following a single application, making them particularly suited to the treatment of chronic diseases. A TSI for the treatment of chronic pain is in clinical development.

Targeting botulinum neurotoxin persistence by the ubiquitin-proteasome system

Botulinum neurotoxins (BoNTs) are the most potent natural toxins known. The effects of BoNT serotype A (BoNT/A) can last several months, whereas the effects of BoNT serotype E (BoNT/E), which shares the same synaptic target, synaptosomal-associated protein 25 (SNAP25), last only several weeks. The long-lasting effects or persistence of BoNT/A, although desirable for therapeutic applications, presents a challenge for medical treatment of BoNT intoxication. Although the mechanisms for BoNT toxicity are well known, little is known about the mechanisms that govern the persistence of the toxins. We show that the recombinant catalytic light chain (LC) of BoNT/E is ubiquitylated and rapidly degraded in cells. In contrast, BoNT/A LC is considerably more stable. Differential susceptibility of the catalytic LCs to ubiquitin-dependent proteolysis therefore might explain the differential persistence of BoNT serotypes. In this regard we show that TRAF2, a RING finger protein implicated in ubiquitylation, selectively associates with BoNT/E LC and promotes its proteasomal degradation. Given these data, we asked whether BoNT/A LC could be targeted for rapid proteasomal degradation by redirecting it to characterized ubiquitin ligase domains. We describe chimeric SNAP25-based ubiquitin ligases that target BoNT/A LC for degradation, reducing its duration in a cellular model for toxin persistence.

SNAP-25 is a target of protein kinase C phosphorylation critical to NMDA receptor trafficking

Protein kinase C (PKC) enhances NMDA receptor (NMDAR)-mediated currents and promotes NMDAR delivery to the cell surface via SNARE-dependent exocytosis. Although the mechanisms of PKC potentiation are established, the molecular target of PKC is unclear. Here we show that synaptosomal-associated protein of 25 kDa (SNAP-25), a SNARE protein, is functionally relevant to PKC-dependent NMDAR insertion, and identify serine residue-187 as the molecular target of PKC phosphorylation. Constitutively active PKC delivered via the patch pipette potentiated NMDA (but not AMPA) whole-cell currents in hippocampal neurons. Expression of RNAi targeting SNAP-25 or mutant SNAP-25(S187A) and/or acute disruption of the SNARE complex by treatment with BoNT A, BoNT B or SNAP-25 C-terminal blocking peptide abolished NMDAR potentiation. A SNAP-25 peptide and function-blocking antibody suppressed PKC potentiation of NMDA EPSCs at mossy fiber-CA3 synapses. These findings identify SNAP-25 as the target of PKC phosphorylation critical to PKC-dependent incorporation of synaptic NMDARs and document a postsynaptic action of this major SNARE protein relevant to synaptic plasticity.

Automatic detection of large dense-core vesicles in secretory cells and statistical analysis of their intracellular distribution

Analyzing the morphological appearance and the spatial distribution of large dense-core vesicles (granules) in the cell cytoplasm is central to the understanding of regulated exocytosis. This paper is concerned with the automatic detection of granules and the statistical analysis of their spatial locations in different cell groups. We model the locations of granules of a given cell as a realization of a finite spatial point process and the point patterns associated with the cell groups as replicated point patterns of different spatial point processes. First, an algorithm to segment the granules using electron microscopy images is proposed. Second, the relative locations of the granules with respect to the plasma membrane are characterized by two functional descriptors: the empirical cumulative distribution function of the distances from the granules to the plasma membrane and the density of granules within a given distance to the plasma membrane. The descriptors of the different cells for each group are compared using bootstrap procedures. Our results show that these descriptors and the testing procedure allow discriminating between control and treated cells. The application of these novel tools to studies of secretion should help in the analysis of diseases associated with dysfunctional secretion, such as diabetes.

Inhibition of SNARE-driven neuroexocytosis by plant extracts

Neuronal soluble N-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor (SNARE) proteins mediate membrane fusion between synaptic vesicle and presynaptic membrane, resulting in neurotransmitter release. SNARE proteins are specific substrates of botulinum neurotoxins (BoNT) which are now widely used for therapeutic and cosmetic purposes. While BoNT blocks neuroexocytosis by cleaving SNAREs, inhibiting SNARE assembly process might exert the same effect on neurotransmission. In the present study, some extracts of 100 plants reduced neurotransmitter release by inhibiting SNARE complex formation in neuronal cells. The extracts effectively paralyzed muscle of rat phrenic nerve-hemidiaphragm preparation. Our results raise the possibility that SNARE folding inhibitors from natural resources might replace some special BoNT application fields.

A search for synthetic peptides that inhibit soluble N-ethylmaleimide sensitive-factor attachment receptor-mediated membrane fusion

Soluble N-ethylmaleimide sensitive-factor attachment receptor (SNARE) proteins have crucial roles in driving exocytic membrane fusion. Molecular recognition between vesicle-associated (v)-SNARE and target membrane (t)-SNARE leads to the formation of a four-helix bundle, which facilitates the merging of two apposing membranes. Synthetic peptides patterned after the SNARE motifs are predicted to block SNARE complex formation by competing with the parental SNAREs, inhibiting neuronal exocytosis. As an initial attempt to identify the peptide sequences that block SNARE assembly and membrane fusion, we created thirteen 17-residue synthetic peptides derived from the SNARE motifs of v- and t-SNAREs. The effects of these peptides on SNARE-mediated membrane fusion were investigated using an in vitro lipid-mixing assay, in vivo neurotransmitter release and SNARE complex formation assays in PC12 cells. Peptides derived from the N-terminal region of SNARE motifs had significant inhibitory effects on neuroexocytosis, whereas middle- and C-terminal-mimicking peptides did not exhibit much inhibitory function. N-terminal mimicking peptides blocked N-terminal zippering of SNAREs, a rate-limiting step in SNARE-driven membrane fusion. Therefore, the results suggest that the N-terminal regions of SNARE motifs are excellent targets for the development of drugs to block SNARE-mediated membrane fusion and neurotransmitter release.

Long-term potentiation selectively expressed by NMDA receptors at hippocampal mossy fiber synapses

The mossy fiber to CA3 pyramidal cell synapse (mf-CA3) provides a major source of excitation to the hippocampus. Thus far, these glutamatergic synapses are well recognized for showing a presynaptic, NMDA receptor-independent form of LTP that is expressed as a long-lasting increase of transmitter release. Here, we show that in addition to this "classical" LTP, mf-CA3 synapses can undergo a form of LTP characterized by a selective enhancement of NMDA receptor-mediated transmission. This potentiation requires coactivation of NMDA and mGlu5 receptors and a postsynaptic calcium rise. Unlike classical LTP, expression of this mossy fiber LTP is due to a PKC-dependent recruitment of NMDA receptors specifically to the mf-CA3 synapse via a SNARE-dependent process. Having two mechanistically different forms of LTP may allow mf-CA3 synapses to respond with more flexibility to the changing demands of the hippocampal network.

Cosmeceutical peptides

Peptide cosmeceuticals are one of the new, popular options to treat aging skin. There are three main categories of cosmeceutical peptides: signal peptides, neurotransmitter-affecting peptides and carrier peptides. Although their benefits currently may not be as rigorously tested as most FDA-regulated drugs, the evidence to support their use is growing. This article attempts to review the various current popular cosmeceutical peptides, the published studies on their theoretical effects, and their practical use in dermatology.

Botulinum neurotoxin A and neurotoxin E cleavage products of synaptosome-associated protein of 25 kd exhibit distinct actions on pancreatic islet beta-cell Kv2.1 channel gating

OBJECTIVES

Synaptosome-associated protein of 25 kd (SNAP-25) regulates pancreatic islet beta-cell-delayed rectifier K channels (Kv2.1) in addition to insulin exocytosis. Botulinum neurotoxin A (BoNT/A) and E (BoNT/E) cleavage and presumed deletion of SNAP-25 have been used to examine SNAP-25 function. We hypothesized that proteolytic products of SNAP-25 (206 amino acids) resulting from BoNT/A and BoNT/E cleavage, SNAP-25(1-197) and SNAP-25(1-180), have independent actions on beta-cell Kv gating.

METHODS

We examined by confocal microscopy and immunoblotting BoNT/A and BoNT/E cleavage of SNAP-25 to these N-terminal fragments, and the consequent effects of these BoNTs and SNAP-25 fragments on Kv currents in rat beta cells and MIN6 cells by patch clamp electrophysiology.

RESULTS

Confocal microscopy and immunoblotting showed that MIN6 cells transfected with BoNT/A or BoNT/E generated SNAP-25(1-197) and SNAP-25(1-180) fragments that were retained in the cytosol. Both BoNTs caused increased rate of channel activation and slowed channel inactivation, mimicked by these SNAP-25 fragments, but not full-length SNAP-25. These SNAP-25 fragments potentiated tetraethylammonium block of beta-cell Kv currents.

CONCLUSIONS

BoNT/A or BoNT/E treatment of beta cells generates N-terminal SNAP-25 fragments that are retained in beta cells to directly influence Kv channel gating in a manner distinct from full-length SNAP-25, contributing to overall actions of these BoNTs on insulin secretion.

Vesicle movements are governed by the size and dynamics of F-actin cytoskeletal structures in bovine chromaffin cells

Dense vesicles can be observed in live bovine chromaffin cells using fluorescent reflection confocal microscopy. These vesicles display a similar distribution, cytoplasmic density and average size as the chromaffin granules visualized by electron microscopy. In addition, the acidic vesicles labeled with Lysotracker Red comprised a subpopulation of the vesicles that are visualized by reflection fluorescence. A combination of fluorescence reflection and transmitted light images permitted the movements of vesicles in relation to the cortical cytoskeleton to be studied. The movement of vesicles located on the outside of this structure was restricted, with an apparent diffusion coefficient of 1.0+/-0.4 x 10(-4) microm(2)/s. In contrast, vesicles located in the interior moved much more freely and escaped from the visual confocal plane. Lysotracker labeling was more appropriate to study the movement of the faster moving vesicles, whose diffusion coefficient was five times higher. Using this type of labeling we confirmed the restriction on cortical movement and showed a clear relationship between vesicle mobility and the kinetics of cytoskeletal movement on both sides of the cortical cytoskeleton. This relationship was further emphasized by studying cytoskeletal organization and kinetics. Indeed, an estimate of the size of the cytoskeletal polygonal cages present in the cortical region and in the cell interior agreed well with the calculation of the theoretical radius of the cages imprisoning vesicle movement. Therefore, these data suggest that the structure and kinetics of the cytoskeleton governs vesicle movements in different regions of chromaffin cells.

Cleavage of neuronal synaptosomal-associated protein of 25 kDa by exogenous matrix metalloproteinase-7

Matrix metalloproteinases (MMPs) belong to a family of zinc dependent enzymes best studied for their role in cancer and inflammation. Though MMPs typically target extracellular proteins, here we show that MMP-7, an MMP family member which lacks a C-terminal hemopexin-like domain, can cleave an intraneuronal protein that is critical to vesicular fusion and neurotransmitter release, synaptosomal-associated protein of 25 kDa (SNAP-25). Western blot analysis using an N-terminal specific antibody on extracts from cultured neurons suggests that cleavage occurs towards the C-terminal portion of SNAP 25. Additional studies with recombinant SNAP-25 demonstrate that cleavage occurs at amino acid 129. The ability of MMP-7 to cleave SNAP-25 is diminished by chlorpromazine and phenylarsine oxide, inhibitors of clathrin dependent endocytosis. Together, these results imply that exogenous MMP-7 can access an intraneuronal substrate and suggest that additional studies may be warranted to determine if SNAP function is impaired with brain inflammation.

Cosmeceuticals

The aging population and a desire to maintain a youthful appearance have propelled the recent surge in the U.S. cosmeceuticals market. The rapidly growing number of products claiming to diminish fine lines and wrinkles, decrease redness, smooth texture, and fade discoloration has lead to much confusion and misinformation among dermatologists and consumers alike. Cosmeceuticals can be a useful adjunct to prescription medications and office procedures. Therefore, it behooves us as dermatologists to understand the science behind these products to better educate ourselves and our patients. We present an update of the following categories of cosmeceuticals: antioxidants, growth factors, peptides, anti-inflammatories/botanicals, polysaccharides, and pigment-lightening agents.

Botulinum neurotoxin structure, engineering, and novel cellular trafficking and targeting

Botulinum neurotoxins are multifaceted molecules, which are truly unique not only in their mode of action, but also their utility as a drug carrier either across the gut wall or to the nerve terminals. The molecule is divided in clear functional domains that can operate independently. This feature can be used to employ them as cargo carrier by linking other drugs or vaccines with the binding and translocation domains of BoNT. While the domain structures are largely independent of each other, the dynamic structure of these domains, especially that of the enzymatic domain (L chain), is quite different from the reported crystal structures for several BoNT serotypes and their enzymatic domain. This review discusses the comparative structures of BoNT in crystal and solution for their relevance to the molecular mechanism of BoNT action, especially in view of our recent discovery that the enzymatically active structure of the BoNT exists as a molten-globule and that of the endopeptidase domain as a novel PRIME conformation. Finally, a non-exhaustive discussion has been included to explain the long-lasting biological effects of certain serotypes of BoNT, based on the current knowledge of the structure-function of different serotypes of botulinum neurotoxins.

Modulation of Kv2.1 channel gating and TEA sensitivity by distinct domains of SNAP-25

Distinct domains within the SNARE (soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptor) proteins, STX1A (syntaxin 1A) and SNAP-25 (synaptosome-associated protein-25 kDa), regulate hormone secretion by their actions on the cell's exocytotic machinery, as well as voltage-gated Ca2+ and K+ channels. We examined the action of distinct domains within SNAP-25 on Kv2.1 (voltage gated K+ 2.1) channel gating. Dialysis of N-terminal SNAP-25 domains, S197 (SNAP-25(1-197)) and S180 (SNAP-25(1-180)), but not S206 (full-length SNAP-25(1-206)) increased the rate of Kv2.1 channel activation and slowed channel inactivation. Remarkably, these N-terminal SNAP-25 domains, acting on the Kv2.1 cytoplasmic N-terminus, potentiated the external TEA (tetraethylammonium)-mediated block of Kv2.1. To further examine whether these are effects of the channel pore domain, internal K+ was replaced with Na+ and external K+ was decreased from 4 to 1 mM, which decreased the IC50 of the TEA block from 6.8+/-0.9 mM to >100 mM. Under these conditions S180 completely restored TEA sensitivity (7.9+/-1.5 mM). SNAP-25 C-terminal domains, SNAP-25(198-206) and SNAP-25(181-197), had no effect on Kv2.1 gating kinetics. We conclude that different domains within SNAP-25 can form distinct complexes with Kv2.1 to execute a fine allosteric regulation of channel gating and the architecture of the outer pore structure in order to modulate cell excitability.

Cosmeceutical Peptides

BACKGROUND

Cosmeceuticals are skin care products that lie in a gray area between cosmetics and drugs. The desire for the improvement of aging skin has resulted in a plethora of products designed to improve the appearance beyond the simple camouflage of cosmetics. Many ingredients have been added to these products based on theoretical benefits discovered from in vitro studies on wound healing and other metabolic processes.

OBJECTIVE

To help the practicing dermatologist who is often the source of information for patients regarding the benefits of available cosmeceuticals.

METHODS AND MATERIALS

This article is a compilation of published studies on the effects and the practical applications of peptides as topical agents for skin improvement.

RESULTS

There does seem to be science that shows that these peptide cosmeceuticals have the potential to improve the appearance of aging skin. It is important to remember, however, that for benefit to be realized, the final product must be stable in formula, absorbed into the skin, and biologically active at the target for clinical benefit.

CONCLUSION

This article will provide dermatologists with more background to answer pressing questions from patients on this subject.

SNARE complexes and neuroexocytosis: how many, how close?

Regulated secretion is an essential process in all eukaryotic cells. The release of molecules contained inside exocytic granules and synaptic vesicles is mediated by the assembly of a SNARE complex formed by the coil-coiling of three proteins: SNAP-25, syntaxin and VAMP/synaptobrevin. It seems that SNARE complexes assemble together in rosette-shaped super-complexes but there is controversy on the actual number (N) of copies of SNARE complexes that are necessary to mediate exocytosis. We discuss attempts to determine the value of N and suggest that N varies with the type of exocytic vesicles. In addition, we propose that the N value in neuroexocytosis can be estimated by the comparative use of different types of botulinum neurotoxins.

Small peptides patterned after the N-terminus domain of SNAP25 inhibit SNARE complex assembly and regulated exocytosis

Synthetic peptides patterned after the C-terminus of synaptosomal associated protein of 25 kDa (SNAP25) efficiently abrogate regulated exocytosis. In contrast, the use of SNAP25 N-terminal-derived peptides to modulate SNAP receptors (SNARE) complex assembly and neurosecretion has not been explored. Here, we show that the N-terminus of SNAP25, specially the segment that encompasses 22Ala-44Ile, is essential for the formation of the SNARE complex. Peptides patterned after this protein domain are potent inhibitors of SNARE complex formation. The inhibitory activity correlated with their propensity to adopt an alpha-helical secondary structure. These peptides abrogated SNARE complex formation only when added previous to the onset of aggregate assembly. Analysis of the mechanism of action revealed that these peptides disrupted the binary complex formed by SNAP25 and syntaxin. The identified peptides inhibited Ca2+-dependent exocytosis from detergent-permeabilized excitable cells. Noteworthy, these amino acid sequences markedly protected intact hippocampal neurones against hypoglycaemia-induced, glutamate-mediated excitotoxicity with a potency that rivalled that displayed by botulinum neurotoxins. Our findings indicate that peptides patterned after the N-terminus of SNAP25 are potent inhibitors of SNARE complex formation and neuronal exocytosis. Because of their activity in intact neurones, these cell permeable peptides may be hits for antispasmodic and analgesic drug development.

Identification of SNARE complex modulators that inhibit exocytosis from an alpha-helix-constrained combinatorial library

Synthetic peptides patterned after the proteins involved in vesicle fusion [the so-called SNARE (soluble N -ethylmaleimide-sensitive fusion protein attachment protein receptor) proteins] are potent inhibitors of SNARE complex assembly and neuronal exocytosis. It is noteworthy that the identification of peptide sequences not related to the SNARE proteins has not been accomplished yet; this is due, in part, to the structural constraints and the specificity of the protein interactions that govern the formation of the SNARE complex. Here we have addressed this question and used a combinatorial approach to identify peptides that modulate the assembly of the SNARE core complex and inhibit neuronal exocytosis. An alpha-helix-constrained, mixture-based, 17-mer combinatorial peptide library composed of 137180 sequences was synthesized in a positional scanning format. Peptide mixtures were assayed for their ability to prevent the formation of the in vitro -reconstituted SDS-resistant SNARE core complex. Library deconvolution identified eight peptides that inhibited the assembly of the SNARE core complex. Notably, the most potent 17-mer peptide (acetyl-SAAEAFAKLYAEAFAKG-NH2) abolished both Ca2+-evoked catecholamine secretion from detergent-permeabilized chromaffin cells and L-glutamate release from intact hippocampal primary cultures. Collectively, these findings indicate that amino acid sequences that prevent SNARE complex formation are not restricted to those that mimic domains of SNARE proteins, thus expanding the diversity of molecules that target neuronal exocytosis. Because of the implication of neurosecretion in the aetiology of several human neurological disorders, these newly identified peptides may be considered hits for the development of novel anti-spasmodic drugs.

Complete DNA sequences of the botulinum neurotoxin complex of Clostridium botulinum type A-Hall (Allergan) strain

BOTOX is manufactured with the purified native 900-kDa type A neurotoxin complex from Clostridium botulinum type A-Hall (Allergan) strain. This complex is composed of the botulinum neurotoxin (BoNT) and several toxin associated proteins known as the hemagglutinins (HAs) and the non-toxic non-hemagglutinin protein (NTNH). We describe here the complete gene sequences of the BoNT complex of type A-Hall (Allergan) strain. Using a polymerase chain reaction-based approach, we sequenced six open reading frames (ORFs) encoding BoNT (1296 amino acids), the toxin-associated proteins: HA70, 625 aa; HA17, 147 aa; HA34, 291 aa; NTNH, 1193 aa; and the regulatory component botR/OrfX, 178 aa. Comparative alignments of the amino acid sequence of BoNT/A shows a 98-100% sequence identity among different strains of the type A, except for the Kyoto-F strain (90%), whereas the sequence identity between BoNT/A and other toxin serotypes is only 30.4-39.1%. Similar to the neurotoxin, the toxin-associated proteins and botR from type A-Hall strain also share more than 95% identity to the homologous proteins found in type A-NCTC2916 strain. Among all the toxin associated proteins, NTNHs and HA70s are the most conserved with 65-87% identity across different serotypes. On the other hand, HA34s, present only in serotypes A-D, show greater diversity than all other toxin-associated proteins; HA34/A has 90% identity to HA34/B and only approximately 35% identity to HA34/C and HA34/D. Relatively higher sequence identity ( approximately 60%) is seen in HA17 and botR of Hall A when compared to their counterparts in serotypes C or D. Of all proteins within the toxin complex, NTNH and HA70 have the highest degree of conservation across serotypes and this may underscore a critical role for these proteins in the formation of the complexes. Physiologically, different duration of action in different serotypes may be due to different modifications of toxins by neuronal enzymes, which lead to different compartmentalization of different toxins. Computer-assisted motif analysis reveals that toxins contain several potential sites for phosphorylation by casein kinase II, protein kinase C, tyrosine kinases, glycogen synthase kinase 3, cGMP dependent protein kinase (PKG) that are well conserved. The reported sequence information for type A-Hall strain will potentially facilitate elucidation of the toxin interactions with the nontoxin proteins in the complex.

Revisiting the role of SNAREs in exocytosis and membrane fusion

For over a decade SNARE hypotheses have been proposed to explain the mechanism of membrane fusion, yet the field still lacks sufficient evidence to conclusively identify the minimal components of native fusion. Consequently, debate concerning the postulated role(s) of SNAREs in membrane fusion continues. The focus of this review is to revisit original literature with a current perspective. Our analysis begins with the earliest studies of clostridial toxins, leading to various cellular and molecular approaches that have been used to test for the roles of SNAREs in exocytosis. We place much emphasis on distinguishing between specific effects on membrane fusion and effects on other critical steps in exocytosis. Although many systems can be used to study exocytosis, few permit selective access to specific steps in the pathway, such as membrane fusion. Thus, while SNARE proteins are essential to the physiology of exocytosis, assay limitations often prevent definitive conclusions concerning the molecular mechanism of membrane fusion. In all, the SNAREs are more likely to function upstream as modulators or priming factors of fusion.

Differential participation of actin- and tubulin-based vesicle transport systems during secretion in bovine chromaffin cells

The role of cytoskeletal elements in vesicle transport occurring during exocytosis was examined in adrenal medullary bovine chromaffin cells maintained in culture. Amperometric determination of depolarization-dependent catecholamine release from individual intact cells treated with actin or myosin inhibitors showed alterations in the fast and slow phases of secretion when compared with untreated cells. In contrast, microtubule disassemblers or stabilizers have a moderate effect on secretion, only affecting the release of slow secretory components. In experiments using confocal dynamic microscopy we have observed the drastic effect of actin and myosin inhibitors in abolishing vesicle movement throughout the cytoplasm, and the inhibition of granule mobility in deep perinuclear regions caused by the microtubule stabilizers. Following loss of mobility, vesicles were associated with filaments of F-actin or microtubules. In addition, the mobility of cortical vesicles was affected by actin-myosin inhibitors but not by microtubule inhibitors. The study of cortical cytoskeleton in living cells showed vesicles associated with dense tubular F-actin structures, with microtubules appearing as low density networks. These findings suggest that the distribution and density of both cytoskeletal elements in the cortical region may influence the recruitment of vesicle pools during secretion.

Inhibition of neurotransmitter release by peptides that mimic the N-terminal domain of SNAP-25

Botulinum neurotoxin serotypes A and E (BoNT/A and BoNT/E) block neurotransmitter release by cleaving the 206-amino-acid SNARE protein, SNAP-25. For each BoNT serotype, cleavage of SNAP-25 results in the loss of intact protein, the production of an N-terminal truncated protein, and the generation of a small C-terminal peptide. Peptides that mimic the C-terminal fragments of SNAP-25 following BoNT/A or BoNT/E cleavage were shown to depress transmitter release in bovine chromaffin cells and in Aplysia buccal ganglion cells. Similarly, the N-terminal-truncated SNAP-25 resulting from BoNT/A or BoNT/E cleavage has been found to inhibit transmitter exocytosis in various systems. With one exception, however, the inhibitory action of truncated SNAP-25 has not been demonstrated at a well-defined cholinergic synapse. The goal of the current study was to determine the level of inhibition of neurotransmitter release by N-terminal BoNT/A- or BoNT/E-truncated SNAP-25 in two different neuronal systems: cholinergically coupled Aplysia neurons and rat hippocampal cell cultures. Both truncated SNAP-25 products inhibited depolarization-dependent glutamate release from hippocampal cultures and depressed synaptic transmission in Aplysia buccal ganglion cells. These results suggest that truncated SNAP-25 can compete with endogenous SNAP-25 for binding with other SNARE proteins involved in transmitter release, thus inhibiting neurotransmitter exocytosis.

Modifications in the C terminus of the synaptosome-associated protein of 25 kDa (SNAP-25) and in the complementary region of synaptobrevin affect the final steps of exocytosis

Fusion proteins made of green fluorescent protein coupled to SNAP-25 or synaptobrevin were overexpressed in bovine chromaffin cells in order to study the role of critical protein domains in exocytosis. Point mutations in the C-terminal domain of SNAP-25 (K201E and L203E) produced a marked inhibition of secretion, whereas single (Q174K, Q53K) and double mutants (Q174K/Q53K) of amino acids from the so-called zero layer only produced a moderate alteration in secretion. The importance of the SNAP-25 C-terminal domain in exocytosis was also confirmed by the similar effect on secretion of mutations in analogous residues of synaptobrevin (A82D, L84E). The effects on the initial rate and magnitude of secretion correlated with the alteration of single vesicle fusion kinetics since the amperometric spikes from cells expressing SNAP-25 L203E and K201E and synaptobrevin A82D and L84E mutants had lower amplitudes and larger half-width values than the ones from controls, suggesting slower neurotransmitter release kinetics than that found in cells expressing the wild-type proteins or zero layer mutants of SNAP-25. We conclude that a small domain of the SNAP-25 C terminus and its counterpart in synaptobrevin play an essential role in the final membrane fusion step of exocytosis.

Co-localization of vesicles and P/Q Ca2+-channels explains the preferential distribution of exocytotic active zones in neurites emitted by bovine chromaffin cells

We have taken advantage of the differences between the preferential localization of secretion in the terminals of neurite-emitting bovine chromaffin cells in contrast with the random distribution secretion in spherical cells to study the possible molecular factors determining such localization by using immunofluorescence and confocal microscopy techniques. By analyzing the distribution of dopamine beta-hydroxylase present in the membrane of chromaffin granules, we found that vesicles migrate and accumulate in dense packages in the terminals of neurite processes. Neither members of the fusion core complex such as SNAP-25, nor nicotinic receptors are preferentially located in the terminals as would be expected from elements defining sites of release, thereby suggesting the presence of additional factors. Interestingly, we observed a preferential distribution of the P/Q subtype of Ca2+ channels in these neurite terminals and co-localization with vesicles present in these structures, in sharp contrast with the overall distribution of the L subtype channels. Using the same immunofluorescence techniques we were unable to detect N-type calcium channels. In addition, omega-agatoxin IVA was able to block 70% of the exocytotic release occurring into the neurites, whereas L-type blockers had a weak effect. Taken together our results strongly indicate that the co-localization of vesicles and clusters of P/Q Ca2+ channels may explain the precise localization of exocytotic sites in the terminals of neurite-emitting chromaffin cells, whereas the distribution of secretory sites in round cells may arise from the random presence of these factors as indicated by their partial co-localization.

The role of the synaptic protein snap-25 in the potency of botulinum neurotoxin type A

Botulinum neurotoxin serotype A (BoNT/A) is distinguished from BoNT/E by longer duration of paralysis and greater potency. The proteolytic activity of BoNT/A in cultures of dissociated spinal cord neurons persists beyond 80 days, whereas BoNT/E activity persists for less than 1 day (Keller, J. E., Neale, E. A. Oyler, G., and Adler, M. (1999) FEBS Lett. 456, 137-142). This single quality of toxin activity can account for the differences observed in the duration of muscle block. In the present work we sought to understand the basis for the apparent greater potency of BoNT/A. BoNT/E cleaves a 26-amino acid fragment from the C terminus of the synaptic protein SNAP-25 whereas BoNT/A removes only nine residues creating a 197-amino acid fragment (P197) that is 95% the length of SNAP-25. We show that inhibition of neurotransmitter release by BoNT/E is equivalent to the damage caused to SNAP-25. However, synaptic blockade by BoNT/A is greater than the extent of SNAP-25 proteolysis. These findings can be explained if P197 produces an inhibitory effect on neurotransmitter release. A mathematical model of the experimentally determined relationship between SNAP-25 damage and blockade of neurotransmission supports this interpretation. Furthermore, neurotransmitter release following complete cleavage of SNAP-25 can be achieved by P197, but with about 5-fold less sensitivity to external Ca(2+). In this case, vesicular release is restored by increasing intracellular Ca(2+). These data demonstrate that P197 competes with intact SNAP-25, but is unable to initiate normal synaptic vesicle fusion in physiological concentrations of Ca(2+).