Phosphorylation-state dependent intraneuronal sorting of Aß differentially impairs autophagy and the endo-lysosomal system.

ABBREVIATIONS: AD: Alzheimer disease; APP: amyloid beta precursor protein; ATG: autophagy related; Aß: amyloid-ß; CTSD: cathepsin D; DAPI: 4',6-diamidino-2-phenylindole; EEA1: early endosome antigen 1; FA: formic acid; GFP: green fluorescent protein; LAMP2: lysosomal-associated membrane protein 2; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MAP2: microtubule-associated protein 2; nmAß: non-modified amyloid-ß; npAß: non-phosphorylated amyloid-ß; pAß: phosphorylated amyloid-ß; p-Ser26Aß: amyloid-ß phosphorylated at serine residue 26; p-Ser8Aß: amyloid-ß phosphorylated at serine residue 8; RAB: RAB, member RAS oncogene family; RFP: red fluorescent protein; SQSTM1/p62: sequestome 1; YFP: yellow fluorescent protein.

Spatio-Temporal Autophagy Tracking with a Cell-Permeable, Water-Soluble, Peptide-Based, Autophagic Vesicle-Targeted Sensor.

Autophagy is an essential cellular degradation process. Impaired autophagy has been linked to multiple disorders, including cancer and neurodegeneration. Tracking the autophagic flux in living cells will provide mechanistic insights into autophagy and will allow rapid screening of autophagy modulators as potential therapeutics. Imaging autophagy to track the autophagic flux demands a cell-permeable probe that can specifically target autophagic vesicles and report on the extent of autophagy. Existing fluorescent protein-based probes for imaging autophagy target autophagic vesicles but are cell-impermeable and degrade with the progress of autophagy resulting in ambiguous information on the later stages of autophagy. Although small-molecule-based autophagy probes can be cell-permeable, they are mostly water-insoluble and often target lysosomes instead of autophagic vesicles leading to incomplete evidence of the early stages of the process. Hence, there is a major gap in the ability to link the imaging data obtained by applying fluorescent sensors to the real extent of autophagy in living cells. To address these challenges, we have combined the desirable features of targetability and cell permeability to develop a novel water-soluble, cell-permeable, visible-light excitable, peptide-based, fluorescent sensor, HCFP, for imaging autophagy and tracking the autophagic flux. The probe readily enters living cells within 30 min of incubation, distinctly targets autophagic vesicles, and spatio-temporally tracks the entire autophagy pathway in living cells via a ratiometric pH-sensitive detection scheme. The salient features of the probe combining targetability with cell permeability should provide an edge in high-throughput screening of autophagy modulators by tracking autophagy live.

Modified histidine containing amphipathic ultrashort antifungal peptide, His[2-p-(n-butyl)phenyl]-Trp-Arg-OMe exhibits potent anticryptococcal activity.

In pursuit of ultrashort peptide-based antifungals, a new structural class, His(2-aryl)-Trp-Arg is reported. Structural changes were investigated on His-Trp-Arg scaffold to demonstrate the impact of charge and lipophilic character on the biological activity. The presence and size of the aryl moiety on imidazole of histidine modulated overall amphiphilic character, and biological activity. Peptides exhibited IC50 of 0.37-9.66 µg/mL against C. neoformans. Peptide 14f [His(2-p-(n-butyl)phenyl)-Trp-Arg-OMe] exhibited two-fold potency (IC50 = 0.37 µg/mL, MIC = 0.63 µg/mL) related to amphotericin B, without any cytotoxic effects up to 10 µg/mL. Peptide 14f act by nuclear fragmentation, membranes permeabilization, disruption and pore formations in the microbial cells as determined by the mechanistic studies employing Trp-quenching, CLSM, SEM, and HR-TEM. The amalgamation of short sequence, presence of appropriate aryl group on l-histidine, potent anticryptococcal activity, no cytotoxicity, and detailed mechanistic studies directed to the identification of 14f as a new antifungal structural lead.

Structural and mechanistic insights into the inhibition of amyloid-ß aggregation by Aß39-42 fragment derived synthetic peptides.

The inhibition of amyloid-ß (Aß) aggregation is a promising approach towards therapeutic intervention for Alzheimer's disease (AD). Thirty eight tetrapeptides based upon Aß39-42C-terminus fragment of the parent Aß peptide were synthesized. The sequential replacement/modification employing unnatural amino acids imparted scaffold diversity, augmented activity, enhanced blood brain barrier permeability and offered proteolytic stability to the synthetic peptides. Several peptides exhibited promising protection against Aß aggregation-mediated-neurotoxicity in PC-12 cells at doses ranged between 10 µM and 0.1 µM, further confirmed by the thioflavin-T fluorescence assay. CD study illustrate that these peptides restrict the ß-sheet formation, and the non-appearance of Aß42 fibrillar structures in the electron microscopy confirm the inhibition of Aß42 aggregation. HRMS and ANS fluorescence spectroscopic analysis provided additional mechanistic insights. Two selected lead peptides 5 and 16 depicted enhanced blood-brain penetration and stability against serum and proteolytic enzyme. Structural insights into ligand-Aß interactions on the monomeric and proto-fibrillar units of Aß were computationally studied. Promising inhibitory potential and short sequence of the lead peptides offers new avenues for the advancement of peptide-derived therapeutics for AD.

Exploring the potential of pyrazoline containing molecules as Aß aggregation inhibitors in Alzheimer's disease.

Objectives Alzheimer's disease (AD) is a chronic and progressive neurodegenerative disease in which one of the most prominent pathological features is accumulation of amyloid (Aß) plaques. This occurs due to the process of aggregation from monomeric to polymeric forms of Aß peptide and thus represents one of the attractive targets to treat AD. Methods After initial evaluation of a set of molecules containing N-acetylpyrazoline moiety flanked by aromatic rings on both sides as Aß aggregation inhibitors, the most potent molecules were further investigated for mechanistic insights. These were carried out by employing techniques such as circular dichroism (CD) spectroscopy, transmission electron microscopy (TEM), in vitro PAMPA-BBB (Blood-Brain Barrier) assay and cytotoxicity evaluation. Results Two molecules among the exploratory set displayed Aß aggregation inhibition comparable to standard curcumin. Among the follow-up molecules, several molecules displayed more inhibition than curcumin. These molecules displayed good inhibitory activity even at lower concentrations. CD and TEM confirmed the mechanism of Aß aggregation. These molecules were found to alleviate Aß induced cytotoxicity. BBB penetration studies highlighted the potential of these molecules to reach central nervous system (CNS). Conclusions Thus, several promising Aß-aggregation inhibitors were obtained as a result of this study.

Novel Phosphorylation-State Specific Antibodies Reveal Differential Deposition of Ser26 Phosphorylated Aß Species in a Mouse Model of Alzheimer's Disease.

Aggregation and deposition of amyloid-ß (Aß) peptides in extracellular plaques and in the cerebral vasculature are prominent neuropathological features of Alzheimer's disease (AD) and closely associated with the pathogenesis of AD. Amyloid plaques in the brains of most AD patients and transgenic mouse models exhibit heterogeneity in the composition of Aß deposits, due to the occurrence of elongated, truncated, and post-translationally modified Aß peptides. Importantly, changes in the deposition of these different Aß variants are associated with the clinical disease progression and considered to mark sequential phases of plaque and cerebral amyloid angiopathy (CAA) maturation at distinct stages of AD. We recently showed that Aß phosphorylated at serine residue 26 (pSer26Aß) has peculiar characteristics in aggregation, deposition, and neurotoxicity. In the current study, we developed and thoroughly validated novel monoclonal and polyclonal antibodies that recognize Aß depending on the phosphorylation-state of Ser26. Our results demonstrate that selected phosphorylation state-specific antibodies were able to recognize Ser26 phosphorylated and non-phosphorylated Aß with high specificity in enzyme-linked immunosorbent assay (ELISA) and Western Blotting (WB) assays. Furthermore, immunofluorescence analyses with these antibodies demonstrated the occurrence of pSer26Aß in transgenic mouse brains that show differential deposition as compared to non-phosphorylated Aß (npAß) or other modified Aß species. Notably, pSer26Aß species were faintly detected in extracellular Aß plaques but most prominently found intraneuronally and in cerebral blood vessels. In conclusion, we developed new antibodies to specifically differentiate Aß peptides depending on the phosphorylation state of Ser26, which are applicable in ELISA, WB, and immunofluorescence staining of mouse brain tissues. These site- and phosphorylation state-specific Aß antibodies represent novel tools to examine phosphorylated Aß species to further understand and dissect the complexity in the age-related and spatio-temporal deposition of different Aß variants in transgenic mouse models and human AD brains.

Effect of C-terminus amidation of Aß39-42 fragment derived peptides as potential inhibitors of Aß aggregation.

The C-terminus fragment (Val-Val-Ile-Ala) of amyloid-ß is reported to inhibit the aggregation of the parent peptide. In an attempt to investigate the effect of sequential amino-acid scan and C-terminus amidation on the biological profile of the lead sequence, a series of tetrapeptides were synthesized using MW-SPPS. Peptide D-Phe-Val-Ile-Ala-NH2 (12c) exhibited high protection against ß-amyloid-mediated-neurotoxicity by inhibiting Aß aggregation in the MTT cell viability and ThT-fluorescence assay. Circular dichroism studies illustrate the inability of Aß42 to form ß-sheet in the presence of 12c, further confirmed by the absence of Aß42 fibrils in electron microscopy experiments. The peptide exhibits enhanced BBB permeation, no cytotoxicity along with prolonged proteolytic stability. In silico studies show that the peptide interacts with the key amino acids in Aß, which potentiate its fibrillation, thereby arresting aggregation propensity. This structural class of designed scaffolds provides impetus towards the rational development of peptide-based-therapeutics for Alzheimer's disease (AD).