Possible Function of Molecular Chaperones in Diseases Caused by Propagating Amyloid Aggregates

Membrane protein chaperone and sodium chloride modulate the kinetics and morphology of amyloid beta aggregation

Protein aggregation is a biological phenomenon caused by the accumulation of misfolded proteins. Amyloid beta (Aβ) peptides are derived from the cleavage of a larger membrane protein molecule and accumulate to form plaques extracellularly. According to the amyloid hypothesis, accumulation of Aβ aggregates in the brain is primarily responsible for the pathogenesis of Alzheimer's disease (AD). Therefore, the disassembly of Aβ aggregates may provide opportunities for alleviating or treating AD. Here, we show that the novel protein targeting machinery from chloroplast, chloroplast signal recognition particle 43 (cpSRP43), is an ATP-independent membrane protein chaperone that can both prevent and reverse Aβ aggregation effectively. Using of thioflavin T dye, we obtained the aggregation kinetics of Aβ aggregation and determined that the chaperone prevents Aβ aggregation in a concentration-dependent manner. Size exclusion chromatography and sedimentation assays showed that 10-fold excess of cpSRP43 can keep Aβ in the soluble monomeric form. Electron microscopy showed that the fibril structure was disrupted in the presence of this chaperone. Importantly, cpSRP43 utilizes the binding energy to actively remodel the preformed Aβ aggregates without assistance by a co-chaperone and ATP, emphasizing its unique function among protein chaperones. Moreover, when sodium chloride concentration is higher than 25 mm, the Aβ aggregation rate increases drastically to form tightly associated aggregates and generate more oligomers. Our results demonstrate that the presence of cpSRP43 and low NaCl levels inhibit or retard Aβ peptide aggregation, potentially opening new avenues to strategically develop an effective treatment for AD.

Chaperone Activity and Protective Effect against Aβ-Induced Cytotoxicity of Artocarpus camansi Blanco and Amaranthus dubius Mart. ex Thell Seed Protein Extracts

Alzheimer's disease (AD) is the most common type of dementia and is listed as the sixth-leading cause of death in the United States. Recent findings have linked AD to the aggregation of amyloid beta peptides (Aβ), a proteolytic fragment of 39-43 amino acid residues derived from the amyloid precursor protein. AD has no cure; thus, new therapies to stop the progression of this deadly disease are constantly being searched for. In recent years, chaperone-based medications from medicinal plants have gained significant interest as an anti-AD therapy. Chaperones are responsible for maintaining the three-dimensional shape of proteins and play an important role against neurotoxicity induced by the aggregation of misfolded proteins. Therefore, we hypothesized that proteins extracted from the seeds of Artocarpus camansi Blanco (A. camansi) and Amaranthus dubius Mart. ex Thell (A. dubius) could possess chaperone activity and consequently may exhibit a protective effect against Aβ_1-40-induced cytotoxicity. To test this hypothesis, the chaperone activity of these protein extracts was measured using the enzymatic reaction of citrate synthase (CS) under stress conditions. Then, their ability to inhibit the aggregation of Aβ_1-40 using a thioflavin T (ThT) fluorescence assay and DLS measurements was determined. Finally, the neuroprotective effect against Aβ_1-40 in SH-SY5Y neuroblastoma cells was evaluated. Our results demonstrated that A. camansi and A. dubius protein extracts exhibited chaperone activity and inhibited Aβ_1-40 fibril formation, with A. dubius showing the highest chaperone activity and inhibition at the concentration assessed. Additionally, both protein extracts showed neuroprotective effects against Aβ_1-40-induced toxicity. Overall, our data demonstrated that the plant-based proteins studied in this research work can effectively overcome one of the most important characteristics of AD.

Combination of a Chaperone Synthesis Inducer and an Inhibitor of GAPDH Aggregation for Rehabilitation after Traumatic Brain Injury: A Pilot Study

The recovery period after traumatic brain injury (TBI) is often complicated by secondary damage that may last for days or even months after trauma. Two proteins, Hsp70 and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), were recently described as modulating post-traumatic processes, and in this study, we test them as targets for combination therapy using an inhibitor of GAPDH aggregation (derivative of hydrocortisone RX624) and an inducer of Hsp70 synthesis (the pyrrolylazine derivative PQ-29). The protective effect of the combination on C6 rat glioblastoma cells treated with the cerebrospinal fluid of traumatized animals resulted in an increase in the cell index and in a reduced level of apoptosis. Using a rat weight drop model of TBI, we found that the combined use of both drugs prevented memory impairment and motor deficits, as well as a reduction of neurons and accumulation of GAPDH aggregates in brain tissue. In conclusion, we developed and tested a new approach to the treatment of TBI based on influencing distinct molecular mechanisms in brain cells.

Indolylazine Derivative Induces Chaperone Expression in Aged Neural Cells and Prevents the Progression of Alzheimer's Disease

The risk of progression of most sporadic neurodegenerative diseases, including Alzheimer's disease, increases with age. Traditionally, this is associated with a decrease in the efficiency of cell protection systems, in particular, molecular chaperones. Thus, the development of small molecules able to induce the synthesis of chaperones is a promising therapeutic approach to prevent neural diseases associated with ageing. Here, we describe a new compound IA-50, belonging to the class of indolylazines and featured by a low size of topological polar surface area, the property related to substances with potentially high membrane-penetrating activity. We also estimated the absorption, distribution, metabolism and excretion characteristics of IA-50 and found the substance to fit the effective drug criteria. The new compound was found to induce the synthesis and accumulation of Hsp70 in normal and aged neurons and in the hippocampi of young and old mice. The transgenic model of Alzheimer's disease, based on 5xFAD mice, confirmed that the injection of IA-50 prevented the formation of β-amyloid aggregates, loss of hippocampal neurons and the development of memory impairment. These data indicate that this novel substance may induce the expression of chaperones in neural cells and brain tissues, suggesting its possible application in the therapy of ageing-associated disorders.

The HSP40 chaperone Ydj1 drives amyloid beta 42 toxicity

Amyloid beta 42 (Abeta42) is the principal trigger of neurodegeneration during Alzheimer's disease (AD). However, the etiology of its noxious cellular effects remains elusive. In a combinatory genetic and proteomic approach using a yeast model to study aspects of intracellular Abeta42 toxicity, we here identify the HSP40 family member Ydj1, the yeast orthologue of human DnaJA1, as a crucial factor in Abeta42-mediated cell death. We demonstrate that Ydj1/DnaJA1 physically interacts with Abeta42 (in yeast and mouse), stabilizes Abeta42 oligomers, and mediates their translocation to mitochondria. Consequently, deletion of YDJ1 strongly reduces co-purification of Abeta42 with mitochondria and prevents Abeta42-induced mitochondria-dependent cell death. Consistently, purified DnaJ chaperone delays Abeta42 fibrillization in vitro, and heterologous expression of human DnaJA1 induces formation of Abeta42 oligomers and their deleterious translocation to mitochondria in vivo. Finally, downregulation of the Ydj1 fly homologue, Droj2, improves stress resistance, mitochondrial morphology, and memory performance in a Drosophila melanogaster AD model. These data reveal an unexpected and detrimental role for specific HSP40s in promoting hallmarks of Abeta42 toxicity.

Synthetic Sulfated Polymers Control Amyloid Aggregation of Ovine Prion Protein and Decrease Its Toxicity

Amyloid aggregation, including aggregation and propagation of prion protein, is a key factor in numerous human diseases, so-called amyloidosis, with a very poor ability for treatment or prevention. The present work describes the effect of sulfated or sulfonated polymers (sodium dextran sulfate, polystyrene sulfonate, polyanethole sulfonate, and polyvinyl sulfate) on different stages of amyloidogenic conversion and aggregation of the prion protein, which is associated with prionopathies in humans and animals. All tested polymers turned out to induce amyloid conversion of the ovine prion protein. As suggested from molecular dynamics simulations, this effect probably arises from destabilization of the native prion protein structure by the polymers. Short polymers enhanced its further aggregation, whereas addition of high-molecular poly(styrene sulfonate) inhibited amyloid fibrils formation. According to the seeding experiments, the protein–polymer complexes formed after incubation with poly(styrene sulfonate) exhibited significantly lower amyloidogenic capacity compared with the control fibrils of the free prion protein. The cytotoxicity of soluble oligomers was completely inhibited by treatment with poly(styrene sulfonate). To summarize, sulfonated polymers are a promising platform for the formulation of a new class of anti-prion and anti-amyloidosis therapeutics.

Synthesis and approbation of new neuroprotective chemicals of pyrrolyl- and indolylazine classes in a cell model of Alzheimer's disease

One of the major causes of neurodegeneration in the pathogenesis of Alzheimer's disease is the accumulation of cytotoxic amyloid species within the intercellular compartments of the brain. The efficacy of the anti-proteotoxic mechanism based on the molecular chaperones Hsp70 and Hsp90 in numerous types of neurons is often low, while its pharmacological enhancement has been shown to ameliorate the physiological and cognitive functions of the brain. Suggesting that the chemicals able to induce heat shock protein synthesis and therefore rescue neural cells from cytotoxicity associated with amyloid, we have synthesized a group of pyrrolyl- and indolylazines that cause the accumulation of heat shock proteins, using a novel method of photocatalysis that is employed in green chemistry. The selected compounds were tested in a cell model of Alzheimer's disease and demonstrated a pronounced neuroprotective effect. These substances increased the survival of neurons, blocked the activation of β-galactosidase, and prevented apoptosis in neurons cultured in the presence of β-amyloid.

Proteotoxicity: A Fatal Consequence of Environmental Pollutants-Induced Impairments in Protein Clearance Machinery

A tightly regulated protein quality control (PQC) system maintains a healthy balance between correctly folded and misfolded protein species. This PQC system work with the help of a complex network comprised of molecular chaperones and proteostasis. Any intruder, especially environmental pollutants, disrupt the PQC network and lead to PQCs disruption, thus generating damaged and infectious protein. These misfolded/unfolded proteins are linked to several diseases such as Parkinson's disease, Alzheimer's disease, Huntington's disease, and cataracts. Numerous studies on proteins misfolding and disruption of PQCs by environmental pollutants highlight the necessity of detailed knowledge. This review represents the PQCs network and environmental pollutants' impact on the PQC network, especially through the protein clearance system.

Motifs and interface amino acid-mediated regulation of amyloid biogenesis in microbes to humans: potential targets for intervention

Amyloids are linked to many debilitating diseases in mammals. Some organisms produce amyloids that have a functional role in the maintenance of their biological processes. Microbes utilize functional bacterial amyloids (FuBA) for pathogenicity and infections. Amyloid biogenesis is regulated differentially in various systems to avoid its toxic accumulation. A familiar feature in the process of amyloid biogenesis from humans to microbes is its regulation by protein-protein interactions (PPI). The spatial arrangement of amino acid residues in proteins generates topologies like flat interface and linear motif, which participate in protein interactions. Motifs and interface residue-mediated interactions have a direct or an indirect impact on amyloid secretion and assembly. Some motifs undergo post-translational modifications (PTM), which effects interactions and dynamics of the amyloid biogenesis cascade. Interaction-induced local changes stimulate global conformational transitions in the PPI complex, which indirectly affects amyloid formation. Perturbation of such motifs and interface residues results in amyloid abolishment. Interface residues, motifs and their respective interactive protein partners could serve as potential targets for intervention to inhibit amyloid biogenesis.

Pyrrolylquinoxaline-2-One Derivative as a Potent Therapeutic Factor for Brain Trauma Rehabilitation

Traumatic brain injury (TBI) often causes massive brain cell death accompanied by the accumulation of toxic factors in interstitial and cerebrospinal fluids. The persistence of the damaged brain area is not transient and may occur within days and weeks. Chaperone Hsp70 is known for its cytoprotective and antiapoptotic activity, and thus, a therapeutic approach based on chemically induced Hsp70 expression may become a promising approach to lower post-traumatic complications. To simulate the processes of secondary damage, we used an animal model of TBI and a cell model based on the cultivation of target cells in the presence of cerebrospinal fluid (CSF) from injured rats. Here we present a novel low molecular weight substance, PQ-29, which induces the synthesis of Hsp70 and empowers the resistance of rat C6 glioma cells to the cytotoxic effect of rat cerebrospinal fluid taken from rats subjected to TBI. In an animal model of TBI, PQ-29 elevated the Hsp70 level in brain cells and significantly slowed the process of the apoptosis in acceptor cells in response to cerebrospinal fluid action. The compound was also shown to rescue the motor function of traumatized rats, thus proving its potential application in rehabilitation therapy after TBI.

Alpha-Synuclein Amyloid Aggregation Is Inhibited by Sulfated Aromatic Polymers and Pyridinium Polycation

The effect of a range of synthetic charged polymers on alpha-synuclein aggregation and amyloid formation was tested. Sulfated aromatic polymers, poly(styrene sulfonate) and poly(anethole sulfonate), have been found to suppress the fibril formation. In this case, small soluble complexes, which do not bind with thioflavin T, have been formed in contrast to the large stick-type fibrils of free alpha-synuclein. Sulfated polysaccharide (dextran sulfate), as well as sulfated vinylic polymer (poly(vinyl sulfate)) and polycarboxylate (poly(methacrylic acid)), enhanced amyloid aggregation. Conversely, pyridinium polycation, poly(N-ethylvinylpyridinium), switched the mechanism of alpha-synuclein aggregation from amyloidogenic to amorphous, which resulted in the formation of large amorphous aggregates that do not bind with thioflavin T. The obtained results are relevant as a model of charged macromolecules influence on amyloidosis development in humans. In addition, these results may be helpful in searching for new approaches for synucleinopathies treatment with the use of natural polymers.

New HSF1 inducer as a therapeutic agent in a rodent model of Parkinson's disease

Molecular chaperone HSP70 (HSPA1A) has therapeutic potential in conformational neurological diseases. Here we evaluate the neuroprotective function of the chaperone in a rat model of Parkinson's disease (PD). We show that the knock-down of HSP70 (HSPA1A) in dopaminergic neurons of the Substantia nigra causes an almost 2-fold increase in neuronal death and multiple motor disturbances in animals. Conversely, pharmacological activation of HSF1 transcription factor and enhanced expression of inducible HSP70 with the echinochrome derivative, U-133, reverses the process of neurodegeneration, as evidenced by а increase in the number of tyrosine hydroxylase-containing neurons, and prevents the motor disturbances that are typical of the clinical stage of the disease. The neuroprotective effect caused by the elevation of HSP70 in nigral neurons is due to the ability of the chaperone to prevent α-synuclein aggregation and microglia activation. Our findings support the therapeutic relevance of HSP70 induction for the prevention and/or deceleration of PD-like neurodegeneration.

Hsp70 Inhibits the Nucleation and Elongation of Tau and Sequesters Tau Aggregates with High Affinity

As a key player of the protein quality control network of the cell, the molecular chaperone Hsp70 inhibits the aggregation of the amyloid protein tau. To date, the mechanism of this inhibition and the tau species targeted by Hsp70 remain unknown. This is partly due to the inherent difficulty of studying amyloid aggregates because of their heterogeneous and transient nature. Here, we used ensemble and single-molecule fluorescence measurements to dissect how Hsp70 counteracts the self-assembly process of the K18 ΔK280 tau variant. We found that Hsp70 blocks the early stages of tau aggregation by suppressing the formation of tau nuclei. Additionally, Hsp70 sequesters oligomers and mature tau fibrils with nanomolar affinity into a protective complex, efficiently neutralizing their ability to damage membranes and seed further tau aggregation. Our results provide novel insights into the molecular mechanisms by which the chaperone Hsp70 counteracts the formation, propagation, and toxicity of tau aggregates.

Misfolding and aggregation of nascent proteins: a novel mode of toxic cadmium action in vivo

Cadmium is a highly poisonous metal and a human carcinogen, but the molecular mechanisms underlying its cellular toxicity are not fully understood. Recent findings in yeast cells indicate that cadmium exerts its deleterious effects by inducing widespread misfolding and aggregation of nascent proteins. Here, we discuss this novel mode of toxic heavy metal action and propose a mechanism by which molecular chaperones may reduce the damaging effects of heavy metal ions on protein structures.