Aberrant proteolytic processing of amyloid precursor protein (APP) can alter amyloid-β (Aβ) peptide trafficking, with recent studies implicating MUC1-type O-glycosylation as a modulatory factor. In this study, we synthesized native and Swedish-mutated (Lys670Asn/Met671Leu) APP glycopeptides spanning the Aβ(1-23) region, including the β- and α-secretase cleavage sites, and introduced O-GalNAc moieties at Thr663, Ser667, and/or Tyr681. Circular dichroism (CD) revealed conformational changes governed by the glycosylation site and glycan density. Increased glycan valency favored the stabilization of β-turn-rich structures typically associated with oligomeric and prefibrillar intermediates. The Swedish mutation enhanced β-secretase (BACE1) cleavage, especially when Ser667 was glycosylated, while additional glycans favored α-secretase (ADAM10) processing. However, this shift was not sufficient to counterbalance the amyloidogenic pathway. Similarly, Ser667 glycosylation promoted fibril formation in coincubation assays with Aβ40, while di- and triglycosylated peptides disrupted fibril architecture and favored oligomer formation, as confirmed by ThT kinetics, AFM/TEM imaging, and dynamic light scattering. These findings highlight the critical role of mutation and site-specific glycosylation in shaping APP proteolytic processing, secondary structure, and aggregation behavior, underscoring their importance for understanding APP function in both healthy and diseased states.

Prion diseases are characterized by the self-association and amyloid formation of misfolded prion proteins. Developing effective inhibitors of protein aggregation is critical for therapeutic intervention. In this study, we systematically evaluated a range of polyphenolic compounds as potential inhibitors of amyloid fibril formation of PrP(106-128), a prion fragment crucially involved in prion aggregation and propagation. Our findings demonstrate that the basic aromatic backbone structure of flavone alone is insufficient to inhibit PrP(106-128) amyloid formation. Remarkably, flavone molecules containing adjacent hydroxyl groups on the phenolic B or A ring efficiently inhibited PrP(106-128) fibrillization, whereas compounds lacking vicinal hydroxyl groups were less effective in inhibiting amyloid formation. Epigallocatechin-3-gallate (EGCG) was one of the most potent inhibitors found in this study, with the gallate moiety playing an active role in the inhibitory function. Our findings indicate a structure-dependent inhibition activity of the phenolic small molecules, where the number and positioning of hydroxyl groups on the phenyl ring play a pivotal role in inhibiting the aggregation of the peptide. The auto-oxidation of the catechol or pyrogallol moieties to form quinone structures, followed by their reaction with amino acid side chains of the peptide to form covalent adducts, likely account for the inhibitory activity of these phenolic compounds on PrP(106-128) amyloidogenesis. These results will help the design of novel polyphenolic molecules with optimized structural features as potent inhibitors of amyloid formation of both PrP(106-128) and the full-length prion proteins.

Alzheimer’s disease (AD) is an extremely complex and heterogeneous pathology influenced by many factors contributing to its onset and progression, including aging, amyloid-beta (Aβ) plaques, tau fibril accumulation, inflammation, etc. Despite promising advances in drug development, there is no cure for AD. Although there have been substantial advancements in understanding the pathogenesis of AD, there have been over 200 unsuccessful clinical trials in the past decade. In recent years, immunotherapies have been at the forefront of these efforts. Immunotherapy alludes to the immunological field that strives to identify disease treatments via the enhancement, suppression, or induction of immune responses. Interestingly, immunotherapy in AD is a relatively new approach for non-infectious disease. At present, antibody therapy (passive immunotherapy) that targets anti-Aβ aimed to prevent the fibrillization of Aβ peptides and disrupt pre-existing fibrils is a predominant AD immunotherapy due to the continuous failure of active immunotherapy for AD. The most rational and safe strategies will be those targeting the toxic molecule without triggering an abnormal immune response, offering therapeutic advantages, thus making clinical trial design more efficient. This review offers a concise overview of immunotherapeutic strategies, including active and passive immunotherapy for AD. Our review encompasses approved methods and those presently under investigation in clinical trials, while elucidating the recent challenges, complications, successes, and potential treatments. Thus, immunotherapies targeting Aβ throughout the disease progression using a mutant oligomer-Aβ stimulated dendritic cell vaccine may offer a promising therapy in AD.

Misfolding and aggregation of cellular prion protein (PrPc) is a major molecular process involved in the pathogenesis of prion diseases. Here, we studied the aggregation properties of a prion fragment peptide PrP (106-128). The results show that the peptide aggregates in a concentration-dependent manner in an aqueous solution and that the aggregation is sensitive to pH and the preformed amyloid seeds. Furthermore, we show that the zwitterionic POPC liposomes moderately inhibit the aggregation of PrP(106-128), whereas POPC/cholesterol (8:2) vesicles facilitate peptide aggregation likely due to the increase of the lipid packing order and membrane rigidity in the presence of cholesterol. In addition, anionic lipid vesicles of POPG and POPG/cholesterol above a certain concentration accelerate the aggregation of the peptide remarkably. The strong electrostatic interactions between the N-terminal region of the peptide and POPG may constrain the conformational plasticity of the peptide, preventing insertion of the peptide into the inner side of the membrane and thus promoting fibrillation on the membrane surface. The results suggest that the charge properties of the membrane, the composition of the liposomes, and the rigidity of lipid packing are critical in determining peptide adsorption on the membrane surface and the efficiency of the membrane in catalyzing peptide oligomeric nucleation and amyloid formation. The peptide could be used as an improved model molecule to investigate the mechanistic role of the crucial regions of PrP in aggregation in a membrane-rich environment and to screen effective inhibitors to block key interactions between these regions and membranes for preventing PrP aggregation.

Tauopathies are neurodegenerative diseases characterized by the deposition of abnormal tau in the brain. To date, there are no disease-modifying therapies approved by the U.S. Food and Drug Administration (US FDA) for the treatment of tauopathies. In the past decades, extensive efforts have been provided to develop disease-modifying therapies to treat tauopathies. Specifically, exploring existing drugs with the intent of repurposing for the treatment of tauopathies affords a reasonable alternative to discover potent drugs for treating these formidable diseases. Drug repurposing will not only reduce formulation and development stage effort and cost but will also take a key advantage of the established toxicological studies, which is one of the main causes of clinical trial failure of new molecules. In this review, we provide an overview of the current treatment strategies for tauopathies and the recent progress in drug repurposing as an alternative approach to treat tauopathies.

Amyloid fibril formation is associated with protein-misfolding disorders and is a key pathway for the pathogenesis of Alzheimer’s disease (AD). The fibrillar structure of amyloid beta-protein (Aβ) is the hallmark of amyloid plaques in the brains of patients with Alzheimer’s disease (AD). The interaction between the cell membrane and the Aβ40 peptide may induce membrane disruption and membrane leakage and may be related to the toxicity in Alzheimer’s disease (AD). In this regard, we evaluated the competitive effects of different polyelectrolytes such as chitosan (CHT), N-trimethyl chitosan (TMC), heparin and dextran on peptide-phospholipid membrane interactions and Aβ40 fibrillation. The impact of polyelectrolytes on AB aggregation at membrane interface and fibrillation of Aβ40 peptide was evaluated by utilizing biophysical techniques such as ThT binding assays and atomic force microscopy. The polyelectrolytes and lipid membranes co-exist extensively in the cellular environment, we demonstrate that the interactions of polyelectrolytes and Aβ may substantially influence the role of the N-terminal charged region of Aβ in initiating and guiding adsorption and aggregation of the peptide on the membrane surface. Hence, there is a great deal of interest in polyelectrolytes that can bind to the Aβ40 peptide and interfere with the Aβ40 peptide-membrane interactions and manipulate amyloid formation in Alzheimer’s disease (AD).

The amyloid-β precursor protein (APP) undergoes proteolysis by β- and γ-secretases to form amyloid-β peptides (Aβ), which is a hallmark of Alzheimer's disease (AD). Recent findings suggest a possible role of O-glycosylation on APP's proteolytic processing and subsequent fate for AD-related pathology. We have previously reported that Tyr681-O-glycosylation and the Swedish mutation accelerate cleavage of APP model glycopeptides by β-secretase (amyloidogenic pathway) more than α-secretase (non-amyloidogenic pathway). Therefore, to further our studies, we have synthesized additional native and Swedish-mutated (glyco)peptides with O-GalNAc moiety on Thr663 and/or Ser667 to explore the role of glycosylation on conformation, secretase activity, and aggregation kinetics of Aβ40. Our results show that conformation is strongly dependent on external conditions such as buffer ions and solvent polarity as well as internal modifications of (glyco)peptides such as length, O-glycosylation, and Swedish mutation. Furthermore, the level of β-secretase activity significantly increases for the glycopeptides containing the Swedish mutation compared to their nonglycosylated and native counterparts. Lastly, the glycopeptides impact the kinetics of Aβ40 aggregation by significantly increasing the lag phase and delaying aggregation onset, however, this effect is less pronounced for its Swedish-mutated counterparts. In conclusion, our results confirm that the Swedish mutation and/or O-glycosylation can render APP model glycopeptides more susceptible to cleavage by β-secretase. In addition, this study sheds new light on the possible role of glycosylation and/or glycan density on the rate of Aβ40 aggregation.

Abnormal deposition of tau in neurons is a hallmark of Alzheimer's disease and several other neurodegenerative disorders. In the past decades, extensive efforts have been made to explore the mechanistic pathways underlying the development of tauopathies. Recently, the discovery of tau droplet formation by liquid-liquid phase separation (LLPS) has received a great deal of attention. It has been reported that tau condensates have a biological role in promoting and stabilizing microtubule (MT) assembly. Furthermore, it has been hypothesized that the transition of phase-separated tau droplets to a gel-like state and then to fibrils is associated with the pathology of neurodegenerative diseases. In this review, we outline LLPS, the structural disorder that facilitates tau droplet formation, the effects of posttranslational modification of tau on condensate formation, the physiological function of tau droplets, the pathways from droplet to toxic fibrils, and the therapeutic strategies for tauopathies that might evolve from toxic droplets. We expect a deeper understanding of tau LLPS will provide additional insights into tau physiology and tauopathies.