A novel method for expression and purification of authentic amyloid-β with and without (15)N labels

TDP-43 interacts with amyloid-β, inhibits fibrillization, and worsens pathology in a model of Alzheimer's disease

TDP-43 inclusions are found in many Alzheimer’s disease (AD) patients presenting faster disease progression and greater brain atrophy. Previously, we showed full-length TDP-43 forms spherical oligomers and perturbs amyloid-β (Aβ) fibrillization. To elucidate the role of TDP-43 in AD, here, we examined the effect of TDP-43 in Aβ aggregation and the attributed toxicity in mouse models. We found TDP-43 inhibited Aβ fibrillization at initial and oligomeric stages. Aβ fibrillization was delayed specifically in the presence of N-terminal domain containing TDP-43 variants, while C-terminal TDP-43 was not essential for Aβ interaction. TDP-43 significantly enhanced Aβ’s ability to impair long-term potentiation and, upon intrahippocampal injection, caused spatial memory deficit. Following injection to AD transgenic mice, TDP-43 induced inflammation, interacted with Aβ, and exacerbated AD-like pathology. TDP-43 oligomers mostly colocalized with intracellular Aβ in the brain of AD patients. We conclude that TDP-43 inhibits Aβ fibrillization through its interaction with Aβ and exacerbates AD pathology.

TDP-43 inclusions are observed in Alzheimer’s disease. Here the authors show that TDP-43 interacts with amyloid-β and inhibits fibrillization in vitro and exacerbates Alzheimer’s disease pathology in animal models.

Expression and purification of amyloid β-protein, tau, and α-synuclein in Escherichia coli: a review

Misfolding and accumulation of amyloidogenic proteins into various forms of aggregated intermediates and insoluble amyloid fibrils is associated with more than 50 human diseases. Large amounts of high-quality amyloid proteins are required for better probing of their aggregation and neurotoxicity. Due to their intrinsic hydrophobicity, it is a challenge to obtain amyloid proteins with high yield and purity, and they have attracted the attention of researchers from all over the world. The rapid development of bioengineering technology provides technical support for obtaining large amounts of recombinant amyloidogenic proteins. This review discusses the available expression and purification methods for three amyloid proteins including amyloid β-protein, tau, and α-synuclein in microbial expression systems, especially Escherichia coli, and discusses the advantages and disadvantages of these methods. Importantly, these protocols can also be referred to for the expression and purification of other hydrophobic proteins.

Rationally designed divalent caffeic amides inhibit amyloid-β fibrillization, induce fibril dissociation, and ameliorate cytotoxicity

One of the pathologic hallmarks in Alzheimer's disease (AD) is extracellular senile plaques composed of amyloid-β (Aβ) fibrils. Blocking Aβ self-assembly or disassembling Aβ aggregates by small molecules would be potential therapeutic strategies to treat AD. In this study, we synthesized a series of rationally designed divalent compounds and examined their effects on Aβ fibrillization. A divalent amide (2) derived from two molecules of caffeic acid with a propylenediamine linker of ∼5.0 Å in length, which is close to the distance of adjacent β sheets in Aβ fibrils, showed good potency to inhibit Aβ(1-42) fibrillization. Furthermore, compound 2 effectively dissociated the Aβ(1-42) preformed fibrils. The cytotoxicity induced by Aβ(1-42) aggregates in human neuroblastoma was reduced in the presence of 2, and feeding 2 to Aβ transgenic C. elegans rescued the paralysis phenotype. In addition, the binding and stoichiometry of 2 to Aβ(1-40) were demonstrated by using electrospray ionization-traveling wave ion mobility-mass spectrometry, while molecular dynamic simulation was conducted to gain structural insights into the Aβ(1-40)-2 complex.

Glycation affects fibril formation of Aβ peptides

Increasing evidence shows that β-amyloid (Aβ) peptides, which are associated with Alzheimer disease (AD), are heavily glycated in patients, suggesting a role of this irreversible nonenzymatic post-translational modification in pathology. Previous reports have shown that glycation increases the toxicity of the Aβ peptides, although little is known about the mechanism. Here, we used the natural metabolic by-product methylglyoxal as a glycating agent and exploited various spectroscopic methods and atomic force microscopy to study how glycation affects the structures of the Aβ40 and Aβ42 peptides, the aggregation pathway, and the morphologies of the resulting aggregates. We found that glycation significantly slows down but does not prevent β-conversion to mature fibers. We propose that the previously reported higher toxicity of the glycated Aβ peptides could be explained by a longer persistence in an oligomeric form, usually believed to be the toxic species.

An Efficient Method for the Expression and Purification of Aβ(M1-42)

Advances in amyloid research rely on improved access to the β-amyloid peptide, Aβ. N-Terminal methionine-extended Aβ, Aβ(M1-42), is a readily expressed and widely used form of Aβ with properties comparable to those of the natural Aβ(1-42) peptide. Expression of Aβ(M1-42) is simple to execute and avoids an expensive and often difficult enzymatic cleavage step associated with expression and isolation of Aβ(1-42). This paper reports an efficient method for the expression and purification of Aβ(M1-42) and ¹⁵N-labeled Aβ(M1-42). This method affords the pure peptide at ∼19 mg/L of bacterial culture through simple and inexpensive steps in 3 days. This paper also reports a simple method for the construction of recombinant plasmids and the expression and purification of Aβ(M1-42) peptides containing familial mutations. We anticipate that these methods will enable experiments that would otherwise be hindered by insufficient access to Aβ.

Zinc ion rapidly induces toxic, off-pathway amyloid-β oligomers distinct from amyloid-β derived diffusible ligands in Alzheimer's disease

Alzheimer’s disease (AD) is the most prevalent neurodegenerative disease in the elderly. Zinc (Zn) ion interacts with the pathogenic hallmark, amyloid-β (Aβ), and is enriched in senile plaques in brain of AD patients. To understand Zn-chelated Aβ (ZnAβ) species, here we systematically characterized ZnAβ aggregates by incubating equimolar Aβ with Zn. We found ZnAβ40 and ZnAβ42 both form spherical oligomers with a diameter of ~12–14 nm composed of reduced β-sheet content. Oligomer assembly examined by analytical ultracentrifugation, hydrophobic exposure by BisANS spectra, and immunoreactivity of ZnAβ and Aβ derived diffusible ligands (ADDLs) are distinct. The site-specific ¹³C labeled solid-state NMR spectra showed that ZnAβ40 adopts β-sheet structure as in Aβ40 fibrils. Interestingly, removal of Zn by EDTA rapidly shifted the equilibrium back to fibrillization pathway with a faster kinetics. Moreover, ZnAβ oligomers have stronger toxicity than ADDLs by cell viability and cytotoxicity assays. The ex vivo study showed that ZnAβ oligomers potently inhibited hippocampal LTP in the wild-type C57BL/6JNarl mice. Finally, we demonstrated that ZnAβ oligomers stimulate hippocampal microglia activation in an acute Aβ-injected model. Overall, our study demonstrates that ZnAβ rapidly form toxic and distinct off-pathway oligomers. The finding provides a potential target for AD therapeutic development.

Highly efficient soluble expression, purification and characterization of recombinant Aβ42 fromEscherichia coli

Aggregation of amyloid-β protein (Aβ) is hypothesized to be a seminal neuropathological event in Alzheimer's disease (AD). Recombinant expression and purification of Aβ represents a common basis for investigating the molecular mechanisms of amyloid formation and toxicity. Herein, we report a novel high-yield expression and purification method for Aβ42 based on fusion with maltose binding protein (MBP) followed by the soluble polypeptide linker (NANP)₃ and a modified tobacco etch virus (TEV) cleavage site before the Aβ42. We obtained a final yield of ∼18 mg L⁻¹ of recombinant Aβ42 that was confirmed by SDS-PAGE, protein immunoblotting and MALDI-TOF. Finally, thioflavin T fluorescence and atomic force microscopy revealed that the recombinant Aβ42 aggregated into long, branched fibrils. Furthermore, the aggregates of the recombinant peptide had a strong cytotoxic effect on PC12 cells. The method described here can therefore be used to efficiently express the soluble fusion protein MBP-Aβ42 and obtain high-purity Aβ42 peptide, which can be used to understand the molecular mechanism of Aβ42 fibrillization and screen new candidate drugs for AD.

A novel high-yield expression and purification method for Aβ42 based on a fusion with maltose binding protein followed by the soluble polypeptide linker (NANP)₃ and a modified tobacco etch virus cleavage site before the Aβ42 was developed.

Alzheimer's amyloid-β A2T variant and its N-terminal peptides inhibit amyloid-β fibrillization and rescue the induced cytotoxicity

Alzheimer’s disease (AD) is the most common dementia affecting tens of million people worldwide. The primary neuropathological hallmark in AD is amyloid plaques composed of amyloid-β peptide (Aβ). Several familial mutations found in Aβ sequence result in early onset of AD. Previous studies showed that the mutations located at N-terminus of Aβ, such as the English (H6R) and Tottori (D7N) mutations, promote fibril formation and increase cytotoxicity. However, A2T mutant located at the very N-terminus of Aβ shows low-prevalence incidence of AD, whereas, another mutant A2V causes early onset of AD. To understand the molecular mechanism of the distinct effect and develop new potential therapeutic strategy, here, we examined the effect of full-length and N-terminal A2V/T variants to wild type (WT) Aβ40 by fibrillization assays and NMR studies. We found that full-length and N-terminal A2V accelerated WT fibrillization and induced large chemical shifts on the N-terminus of WT Aβ, whereas, full-length and N-terminal A2T retarded the fibrillization. We further examined the inhibition effect of various N-terminal fragments (NTFs) of A2T to WT Aβ. The A2T NTFs ranging from residue 1 to residue 7 to 10, but not 1 to 6 or shorter, are capable to retard WT Aβ fibrillization and rescue cytotoxicity. The results suggest that in the presence of full-length or specific N-terminal A2T can retard Aβ aggregation and the A2T NTFs can mitigate its toxicity. Our results provide a novel targeting site for future therapeutic development of AD.

A Robust and Efficient Production and Purification Procedure of Recombinant Alzheimers Disease Methionine-Modified Amyloid-β Peptides

An improved production and purification method for Alzheimer’s disease related methionine-modified amyloid-β 1–40 and 1–42 peptides is proposed, taking advantage of the formation of inclusion body in Escherichia coli. A Thioflavin-S assay was set-up to evaluate inclusion body formation during growth and optimize culture conditions for amyloid-β peptides production. A simple and fast purification protocol including first the isolation of the inclusion bodies and second, two cycles of high pH denaturation/ neutralization combined with an ultrafiltration step on 30-kDa cut-off membrane was established. Special attention was paid to purity monitoring based on a rational combination of UV spectrophotometry and SDS-PAGE analyses at the various stages of the process. It revealed that this chromatography-free protocol affords good yield of high quality peptides in term of purity. The resulting peptides were fully characterized and are appropriate models for highly reproducible in vitro aggregation studies.