Comparative Studies in the A30P and A53T α-Synuclein C. elegans Strains to Investigate the Molecular Origins of Parkinson's Disease

2-Butoxytetrahydrofuran, Isolated from Holothuria scabra, Attenuates Aggregative and Oxidative Properties of α-Synuclein and Alleviates Its Toxicity in a Transgenic Caenorhabditis elegans Model of Parkinson's Disease

Aggregative α-synuclein and incurring oxidative stress are pivotal cascading events, leading to dopaminergic (DAergic) neuronal loss and contributing to clinical manifestations of Parkinson's disease (PD). Our previous study demonstrated that 2-butoxytetrahydrofuran (2-BTHF), isolated from Holothuria scabra (H. scabra), could inhibit amyloid-β aggregation and its ensuing toxicity, which leads to Alzheimer's disease. In the present study, we found that 2-BTHF also attenuated the aggregative and oxidative activities of α-synuclein and lessened its toxicity in a transgenic Caenorhabditis elegans (C. elegans) PD model. Such worms treated with 100 μM of 2-BTHF showed substantial reductions in α-synuclein accumulation and DAergic neurodegeneration. Mechanistically, 2-BTHF, at this concentration, significantly decreased aggregation of monomeric α-synuclein and restored locomotion and dopamine-dependent behaviors. Molecular docking exhibited potential bindings of 2-BTHF to HSF-1 and DAF-16 transcription factors. Additionally, 2-BTHF significantly increased the mRNA transcripts of genes encoding proteins involved in proteostasis, including the molecular chaperones hsp-16.2 and hsp-16.49, the ubiquitination/SUMOylation-related ubc-9 gene, and the autophagy-related genes atg-7 and lgg-1. Transcriptomic profiling revealed an additional mechanism of 2-BTHF in α-synuclein-expressing worms, which showed upregulation of PPAR signaling cascades that mediated fatty acid metabolism. 2-BTHF significantly restored lipid deposition, upregulated the fat-7 gene, and enhanced gcs-1-mediated glutathione synthesis in the C. elegans PD model. Taken together, this study demonstrated that 2-BTHF could abrogate aggregative and oxidative properties of α-synuclein and attenuate its toxicity, thus providing a possible therapeutic application for the treatment of α-synuclein-induced PD.

Exploring Caenorhabditis elegans as Parkinson's Disease Model: Neurotoxins and Genetic Implications

Parkinson's disease (PD) is the second most common neurodegenerative disease in the world, the first being Alzheimer's disease. Patients with PD have a loss of dopaminergic neurons in the substantia nigra of the basal ganglia, which controls voluntary movements, causing a motor impairment as a result of dopaminergic signaling impairment. Studies have shown that mutations in several genes, such as SNCA, PARK2, PINK1, DJ-1, ATP13A2, and LRRK2, and the exposure to neurotoxic agents can potentially increase the chances of PD development. The nematode Caenorhabditis elegans (C. elegans) plays an important role in studying the risk factors, such as genetic factors, aging, exposure to chemicals, disease progression, and drug treatments for PD. C. elegans has a conserved neurotransmission system during evolution; it produces dopamine, through the eight dopaminergic neurons; it can be used to study the effect of neurotoxins and also has strains that express human α-synuclein. Furthermore, the human PD-related genes, LRK-1, PINK-1, PDR-1, DJR-1.1, and CATP-6, are present and functional in this model. Therefore, this review focuses on highlighting and discussing the use of C. elegans an in vivo model in PD-related studies. Here, we identified that nematodes exposed to the neurotoxins, such as 6-OHDA, MPTP, paraquat, and rotenone, had a progressive loss of dopaminergic neurons, dopamine deficits, and decreased survival rate. Several studies have reported that expression of human LRRK2 (G2019S) caused neurodegeneration and pink-1, pdr-1, and djr-1.1 deletion caused several effects PD-related in C. elegans, including mitochondrial dysfunctions. Of note, the deletion of catp-6 in nematodes caused behavioral dysfunction, mitochondrial damage, and reduced survival. In addition, nematodes expressing α-synuclein had neurodegeneration and dopamine-dependent deficits. Therefore, C. elegans can be considered an accurate animal model of PD that can be used to elucidate to assess the underlying mechanisms implicated in PD to find novel therapeutic targets.

Application of serum peptidomics for Parkinson's disease in SNCA-A30P mice

Intraneuronal inclusions of alpha-synuclein (α-synuclein, α-syn) are commonly found in the brain of patients with Parkinson's disease (PD). The pathogenesis of the abundant α-syn protein in the blood has been extensively studied to understand its properties better. In recent years, peptidome analysis has received increasing attention. In this study, we identified and analyzed serum peptides from wild-type (WT) and the (Thy-1)-h[A30P] alpha-synuclein transgenic mice (SNCA-A30P mice) using liquid chromatography-tandem mass spectrometry (LC-MS/MS). One thousand eight hundred fifty-six peptides from 771 proteins were analyzed. Among them, 151 peptides from 107 proteins were significantly differentially expressed. The glycoprotein VI platelet pathway (GP6) was the pathway's most significant differentially expressed signaling pathway. Cleavage sites of the differentially expressed peptides may reflect protease distribution and activity. We selected the most significantly differentially expressed peptide, VGGDPI, and found that it contained cathepsin K (Ctsk) and trypsin-1 cleavage sites, suggesting that Ctsk and trypsin-1 may be key peptidases in PD. α-syn is a protein associated with the pathogenesis of PD. mutations in several genes, including SNCA, which encodes α-syn, are associated with the development of PD. Bioinformatics analysis of the physiological pathways related to SNCA genes and apoptosis genes found the five most markedly up-regulated proteins: formin homology 2 domain-containing 1 (FHOD1), insulin receptor substrate 1(IRS1), TRPM8 channel-associated factor 1 (TCAF1), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), and interleukin-16 (IL-16). Therefore, the differentially expressed peptides in the five precursor protein domains may be potential bioactive peptides associated with α-syn and apoptosis. This study provides a validated peptidomics profile of SNCA-A30P mice and identifies potentially bioactive peptides linked to α-syn and apoptosis.

Animal models of Parkinson's disease: bridging the gap between disease hallmarks and research questions

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by motor and non-motor symptoms. More than 200 years after its first clinical description, PD remains a serious affliction that affects a growing proportion of the population. Prevailing treatments only alleviate symptoms; there is still neither a cure that targets the neurodegenerative processes nor therapies that modify the course of the disease. Over the past decades, several animal models have been developed to study PD. Although no model precisely recapitulates the pathology, they still provide valuable information that contributes to our understanding of the disease and the limitations of our treatment options. This review comprehensively summarizes the different animal models available for Parkinson's research, with a focus on those induced by drugs, neurotoxins, pesticides, genetic alterations, α-synuclein inoculation, and viral vector injections. We highlight their characteristics and ability to reproduce PD-like phenotypes. It is essential to realize that the strengths and weaknesses of each model and the induction technique at our disposal are determined by the research question being asked. Our review, therefore, seeks to better aid researchers by ensuring a concrete discernment of classical and novel animal models in PD research.

Can Allostery Be a Key Strategy for Targeting PTP1B in Drug Discovery? A Lesson from Trodusquemine

Protein tyrosine phosphatase 1B (PTP1B) is an enzyme crucially implicated in aberrations of various signaling pathways that underlie the development of different human pathologies, such as obesity, diabetes, cancer, and neurodegenerative disorders. Its inhibition can prevent these pathogenetic events, thus providing a useful tool for the discovery of novel therapeutic agents. The search for allosteric PTP1B inhibitors can represent a successful strategy to identify drug-like candidates by offering the opportunity to overcome some issues related to catalytic site-directed inhibitors, which have so far hampered the development of drugs targeting this enzyme. In this context, trodusquemine (MSI-1436), a natural aminosterol that acts as a non-competitive PTP1B inhibitor, appears to be a milestone. Initially discovered as a broad-spectrum antimicrobial agent, trodusquemine exhibited a variety of unexpected properties, ranging from antidiabetic and anti-obesity activities to effects useful to counteract cancer and neurodegeneration, which prompted its evaluation in several preclinical and clinical studies. In this review article, we provide an overview of the main findings regarding the activities and therapeutic potential of trodusquemine and their correlation with PTP1B inhibition. We also included some aminosterol analogues and related structure-activity relationships that could be useful for further studies aimed at the discovery of new allosteric PTP1B inhibitors.

Development of a Systematic Strategy toward Promotion of α-Synuclein Aggregation Using 2-Hydroxyisophthalamide-Based Systems

Establishing a potent scheme against α-synuclein aggregation involved in Parkinson's disease has been evaluated as a promising route to identify compounds that either inhibit or promote the aggregation process of α-synuclein. In the last two decades, this perspective has guided a dramatic increase in the efforts, focused on developing potent drugs either for retardation or promotion of the self-assembly process of α-synuclein. To address this issue, using a chemical kinetics platform, we developed a strategy that enabled a progressively detailed analysis of the molecular events leading to protein aggregation at the microscopic level in the presence of a recently synthesized 2-hydroxyisophthalamide class of small organic molecules based on their binding affinity. Furthermore, qualitatively, we have developed a strategy of disintegration of α-synuclein fibrils in the presence of these organic molecules. Finally, we have shown that these organic molecules effectively suppress the toxicity of α-synuclein oligomers in neuron cells.

A Brain-Permeable Aminosterol Regulates Cell Membranes to Mitigate the Toxicity of Diverse Pore-Forming Agents

The molecular composition of the plasma membrane plays a key role in mediating the susceptibility of cells to perturbations induced by toxic molecules. The pharmacological regulation of the properties of the cell membrane has therefore the potential to enhance cellular resilience to a wide variety of chemical and biological compounds. In this study, we investigate the ability of claramine, a blood–brain barrier permeable small molecule in the aminosterol class, to neutralize the toxicity of acute biological threat agents, including melittin from honeybee venom and α-hemolysin from Staphylococcus aureus. Our results show that claramine neutralizes the toxicity of these pore-forming agents by preventing their interactions with cell membranes without perturbing their structures in a detectable manner. We thus demonstrate that the exogenous administration of an aminosterol can tune the properties of lipid membranes and protect cells from diverse biotoxins, including not just misfolded protein oligomers as previously shown but also biological protein-based toxins. Our results indicate that the investigation of regulators of the physicochemical properties of cell membranes offers novel opportunities to develop countermeasures against an extensive set of cytotoxic effects associated with cell membrane disruption.

Anti-α-synuclein Toxicity and Anti-neurodegenerative Role of Chrysin in Transgenic Caenorhabditis elegans Models of Parkinson's Disease

Parkinson's disease (PD) is the second most progressive neurodegenerative disorder of the central nervous system in the elderly, causing motor impediments and cognitive dysfunctions. Dopaminergic (DA) neuron degeneration and α-synuclein (α-Syn) accumulation in substantia nigra pars compacta are the major contributors to this disease. At present, PD remains untreatable with a huge burden on the quality of life. Therefore, we attempt to explore novel treatment strategies by detecting effective drugs that stop or arrest PD's progression via modifying disease-specific pathways. Chrysin is a flavonoid derived from passion flowers and possesses anti-cancer, anti-inflammatory, anti-oxidant, and anti-depression properties. In the present study, we assessed the neuroprotective potential of chrysin in transgenic Caenorhabditis elegans models of PD. We observed that chrysin reduced the aggregative toxicity of α-Syn and diminished DA neuron degeneration induced by 6-hydroxydopamine (6-OHDA), reduced food-sensing behavioral disabilities, and expanded the nematodes' lifespan. Moreover, chrysin augmented the ubiquitin-like proteasome and superoxide dismutase activities in transgenic C. elegans models. Further, we observed the anti-oxidative role of chrysin by reducing the internal cellular reactive oxygen species levels in 6-OHDA-intoxicated C. elegans. Together, these findings supported chrysin as a possible treatment for PD and encouraged further investigation of chrysin's mechanism of action as a neuroprotective medicine in the future.

From Marine Metabolites to the Drugs of the Future: Squalamine, Trodusquemine, Their Steroid and Triterpene Analogues

This review comprehensively describes the recent advances in the synthesis and pharmacological evaluation of steroid polyamines squalamine, trodusquemine, ceragenins, claramine, and their diverse analogs and derivatives, with a special focus on their complete synthesis from cholic acids, as well as an antibacterial and antiviral, neuroprotective, antiangiogenic, antitumor, antiobesity and weight-loss activity, antiatherogenic, regenerative, and anxiolytic properties. Trodusquemine is the most-studied small-molecule allosteric PTP1B inhibitor. The discovery of squalamine as the first representative of a previously unknown class of natural antibiotics of animal origin stimulated extensive research of terpenoids (especially triterpenoids) comprising polyamine fragments. During the last decade, this new class of biologically active semisynthetic natural product derivatives demonstrated the possibility to form supramolecular networks, which opens up many possibilities for the use of such structures for drug delivery systems in serum or other body fluids.

Pathogenic D76N Variant of β2-Microglobulin: Synergy of Diverse Effects in Both the Native and Amyloid States

Simple Summary

Elevated β₂-microglobulin (β2m) serum levels cause serious complications in patients on long-term kidney dialysis by depositing in the form of amyloid fibrils in the osteoarticular system. Recently, a hereditary systemic amyloidosis was discovered, caused by a naturally occurring D76N β2m mutant exhibiting normal serum levels and a distinct, visceral deposition pattern. D76N β2m showed a structure remarkably similar to the wild-type (WT) protein, albeit with decreased thermodynamic stability and increased amyloidogenicity. Despite the extensive research, the molecular bases of the aberrant aggregation of β2m in vivo remains elusive. Here, using a variety of biophysical techniques, we investigated the role of the pathogenic D76N mutation in the amyloid formation of β2m by point mutations affecting the stabilizing ion-pairs of β2m. We found that, relative to WT β2m, the exceptional amyloidogenicity of the pathogenic D76N β2m variant is realized by the synergy of diverse effects of destabilized native structure, higher sensitivity to negatively charged amphiphilic molecules and polyphosphate, more effective fibril nucleation, higher conformational stability of fibrils, and elevated affinity for extracellular matrix proteins. Understanding the underlying molecular mechanisms might help to find target points for effective treatments against diseases associated with the deleterious aggregation of proteins.

Abstract

β₂-microglobulin (β2m), the light chain of the MHC-I complex, is associated with dialysis-related amyloidosis (DRA). Recently, a hereditary systemic amyloidosis was discovered, caused by a naturally occurring D76N β2m variant, which showed a structure remarkably similar to the wild-type (WT) protein, albeit with decreased thermodynamic stability and increased amyloidogenicity. Here, we investigated the role of the D76N mutation in the amyloid formation of β2m by point mutations affecting the Asp76-Lys41 ion-pair of WT β2m and the charge cluster on Asp38. Using a variety of biophysical techniques, we investigated the conformational stability and partial unfolding of the native state of the variants, as well as their amyloidogenic propensity and the stability of amyloid fibrils under various conditions. Furthermore, we studied the intermolecular interactions of WT and mutant proteins with various binding partners that might have in vivo relevance. We found that, relative to WT β2m, the exceptional amyloidogenicity of the pathogenic D76N β2m variant is realized by the deleterious synergy of diverse effects of destabilized native structure, higher sensitivity to negatively charged amphiphilic molecules (e.g., lipids) and polyphosphate, more effective fibril nucleation, higher conformational stability of fibrils, and elevated affinity for extracellular components, including extracellular matrix proteins.

Squalamine and trodusquemine: two natural products for neurodegenerative diseases, from physical chemistry to the clinic

Covering: 1993 to 2021 (mainly 2017-2021)Alzheimer's and Parkinson's diseases are neurodegenerative conditions affecting over 50 million people worldwide. Since these disorders are still largely intractable pharmacologically, discovering effective treatments is of great urgency and importance. These conditions are characteristically associated with the aberrant deposition of proteinaceous aggregates in the brain, and with the formation of metastable intermediates known as protein misfolded oligomers that play a central role in their aetiology. In this Highlight article, we review the evidence at the physicochemical, cellular, animal model and clinical levels on how the natural products squalamine and trodusquemine offer promising opportunities for chronic treatments for these progressive conditions by preventing both the formation of neurotoxic oligomers and their interaction with cell membranes.

Squalamine and Its Derivatives Modulate the Aggregation of Amyloid-β and α-Synuclein and Suppress the Toxicity of Their Oligomers

The aberrant aggregation of proteins is a key molecular event in the development and progression of a wide range of neurodegenerative disorders. We have shown previously that squalamine and trodusquemine, two natural products in the aminosterol class, can modulate the aggregation of the amyloid-β peptide (Aβ) and of α-synuclein (αS), which are associated with Alzheimer's and Parkinson's diseases. In this work, we expand our previous analyses to two squalamine derivatives, des-squalamine and α-squalamine, obtaining further insights into the mechanism by which aminosterols modulate Aβ and αS aggregation. We then characterize the ability of these small molecules to alter the physicochemical properties of stabilized oligomeric species in vitro and to suppress the toxicity of these aggregates to varying degrees toward human neuroblastoma cells. We found that, despite the fact that these aminosterols exert opposing effects on Aβ and αS aggregation under the conditions that we tested, the modifications that they induced to the toxicity of oligomers were similar. Our results indicate that the suppression of toxicity is mediated by the displacement of toxic oligomeric species from cellular membranes by the aminosterols. This study, thus, provides evidence that aminosterols could be rationally optimized in drug discovery programs to target oligomer toxicity in Alzheimer's and Parkinson's diseases.