Effects of Familial Alzheimer's Disease Mutations on the Assembly of a ß-Hairpin Peptide Derived from Aß16-36.

Familial Alzheimer's disease (FAD) is associated with mutations in the ß-amyloid peptide (Aß) or the amyloid precursor protein (APP). FAD mutations of Aß were incorporated into a macrocyclic peptide that mimics a ß-hairpin to study FAD point mutations K16N, A21G, E22Δ, E22G, E22Q, E22K, and L34V and their effect on assembly, membrane destabilization, and cytotoxicity. The X-ray crystallographic structures of the four E22 mutant peptides reveal that the peptides assemble to form the same compact hexamer. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) experiments reveal that the mutant FAD peptides assemble as trimers or hexamers, with peptides that have greater positive charge assembling as more stable hexamers. Mutations that increase the positive charge also increase the cytotoxicity of the peptides and their propensity to destabilize lipid membranes.

Macrocyclic Peptides Derived from Familial Alzheimer's Disease Mutants Show Charge-Dependent Oligomeric Assembly and Toxicity.

This work probes the role of charge in the oligomeric assembly, toxicity, and membrane destabilization of a series of peptides derived from Aß and the E22Q and E22K familial mutants. In the mutant Aß peptides, an acidic residue (E) is replaced with either a neutral or basic residue (Q or K), thus altering the net charge of the peptide. Acetylation at peripheral positions permits modulation of charge of the peptides and allows investigation of the role of charge in their oligomeric assembly, cytotoxicity, and membrane disruption. Peptides with the same net charge generally behave similarly even if the amino acid residue at position 22 differs. As the net charge of the peptide decreases, so does the extent of assembly, cytotoxicity, and membrane destabilization, which were determined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, lactate dehydrogenase (LDH)-release assays with SH-SY5Y cells, and dye leakage assays using liposomes. These findings suggest that the charge of the amino acid side chain, rather than its size or hydrophobicity, accounts for the differences in the oligomeric assembly and toxicity of the E22 familial mutants of Aß.

Anaphylaxis Induced by Peptide Coupling Agents: Lessons Learned from Repeated Exposure to HATU, HBTU, and HCTU.

Peptide coupling agents pose a special hazard because they are immune sensitizers. Here, we present a case study of anaphylaxis induced by three uronium coupling agents, HATU, HBTU, and HCTU, as a cautionary note for researchers who handle peptide coupling agents frequently. We also include recommendations for handling coupling agents more safely in the research laboratory.

A Hexamer of a Peptide Derived from Aß16-36.

The absence of high-resolution structures of amyloid oligomers constitutes a major gap in our understanding of amyloid diseases. A growing body of evidence indicates that oligomers of the ß-amyloid peptide Aß are especially important in the progression of Alzheimer's disease. In many Aß oligomers, the Aß monomer components are thought to adopt a ß-hairpin conformation. This paper describes the design and study of a macrocyclic ß-hairpin peptide derived from Aß16-36. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and size exclusion chromatography studies show that the Aß16-36 ß-hairpin peptide assembles in solution to form hexamers, trimers, and dimers. X-ray crystallography reveals that the peptide assembles to form a hexamer in the crystal state and that the hexamer is composed of dimers and trimers. Lactate dehydrogenase release assays show that the oligomers formed by the Aß16-36 ß-hairpin peptide are toxic toward neuronally derived SH-SY5Y cells. Replica-exchange molecular dynamics demonstrates that the hexamer can accommodate full-length Aß. These findings expand our understanding of the structure, solution-phase behavior, and biological activity of Aß oligomers and may offer insights into the molecular basis of Alzheimer's disease.

A critical role for dendritic cells in the evolution of IL-1ß-mediated murine airway disease.

Chronic airway inflammation and fibrosis, known as airway remodeling, are defining features of chronic obstructive pulmonary disease and are refractory to current treatments. How and whether chronic inflammation contributes to airway fibrosis remain controversial. In this study, we use a model of chronic obstructive pulmonary disease airway disease utilizing adenoviral delivery of IL-1ß to determine that adaptive T cell immunity is required for airway remodeling because mice deficient in α/ß T cells (tcra(-/-)) are protected. Dendritic cells (DCs) accumulate around chronic obstructive pulmonary disease airways and are critical to prime adaptive immunity, but they have not been shown to directly influence airway remodeling. We show that DC depletion or deficiency in the crucial DC chemokine receptor ccr6 both protect from adenoviral IL-1ß-induced airway adaptive T cell immune responses and fibrosis in mice. These results provide evidence that chronic airway inflammation, mediated by accumulation of α/ß T cells and driven by DCs, is critical to airway fibrosis.

Selective targeting of TGF-ß activation to treat fibroinflammatory airway disease.

Airway remodeling, caused by inflammation and fibrosis, is a major component of chronic obstructive pulmonary disease (COPD) and currently has no effective treatment. Transforming growth factor-ß (TGF-ß) has been widely implicated in the pathogenesis of airway remodeling in COPD. TGF-ß is expressed in a latent form that requires activation. The integrin αvß8 (encoded by the itgb8 gene) is a receptor for latent TGF-ß and is essential for its activation. Expression of integrin αvß8 is increased in airway fibroblasts in COPD and thus is an attractive therapeutic target for the treatment of airway remodeling in COPD. We demonstrate that an engineered optimized antibody to human αvß8 (B5) inhibited TGF-ß activation in transgenic mice expressing only human and not mouse ITGB8. The B5 engineered antibody blocked fibroinflammatory responses induced by tobacco smoke, cytokines, and allergens by inhibiting TGF-ß activation. To clarify the mechanism of action of B5, we used hydrodynamic, mutational, and electron microscopic methods to demonstrate that αvß8 predominantly adopts a constitutively active, extended-closed headpiece conformation. Epitope mapping and functional characterization of B5 revealed an allosteric mechanism of action due to locking-in of a low-affinity αvß8 conformation. Collectively, these data demonstrate a new model for integrin function and present a strategy to selectively target the TGF-ß pathway to treat fibroinflammatory airway diseases.

The K(+) channel GIRK2 is both necessary and sufficient for peripheral opioid-mediated analgesia.

The use of opioid agonists acting outside the central nervous system (CNS) is a promising therapeutic strategy for pain control that avoids deleterious central side effects such as apnea and addiction. In human clinical trials and rat models of inflammatory pain, peripherally restricted opioids have repeatedly shown powerful analgesic effects; in some mouse models however, their actions remain unclear. Here, we investigated opioid receptor coupling to K(+) channels as a mechanism to explain such discrepancies. We found that GIRK channels, major effectors for opioid signalling in the CNS, are absent from mouse peripheral sensory neurons but present in human and rat. In vivo transgenic expression of GIRK channels in mouse nociceptors established peripheral opioid signalling and local analgesia. We further identified a regulatory element in the rat GIRK2 gene that accounts for differential expression in rodents. Thus, GIRK channels are indispensable for peripheral opioid analgesia, and their absence in mice has profound consequences for GPCR signalling in peripheral sensory neurons.