Cross-talk between amyloidogenic proteins in type-2 diabetes and Parkinson's disease

Mechanistic Insights Behind the Self-Assembly of Human Insulin under the Influence of Surface-Engineered Gold Nanoparticles

Elucidating the underlying principles of amyloid protein self-assembly at nanobio interfaces is extremely challenging due to the diversity in physicochemical properties of nanomaterials and their physical interactions with biological systems. It is, therefore, important to develop nanoscale materials with dynamic features and heterogeneities. In this work, through engineering of hierarchical polyethylene glycol (PEG) structures on gold nanoparticle (GNP) surfaces, tailored nanomaterials with different surface properties and conformations (GNPs-PEG) are created for modulating the self-assembly of a widely studied protein, insulin, under amyloidogenic conditions. Important biophysical studies including thioflavin T (ThT) binding, circular dichroism (CD), surface plasmon resonance (SPR), and atomic force microscopy (AFM) showed that higher-molecular weight GNPs-PEG triggered the formation of amyloid fibrils by promoting adsorption of proteins at nanoparticle surfaces and favoring primary nucleation rate. Moreover, the modulation of fibrillation kinetics reduces the overall toxicity of insulin oligomers and fibrils. In addition, the interaction between the PEG polymer and amyloidogenic insulin examined using MD simulations revealed major changes in the secondary structural elements of the B chain of insulin. The experimental findings provide molecular-level descriptions of how the PEGylated nanoparticle surface modulates protein adsorption and drives the self-assembly of insulin. This facile approach provides a new avenue for systematically altering the binding affinities on nanoscale surfaces by tailoring their topologies for examining adsorption-induced fibrillogenesis phenomena of amyloid proteins. Together, this study suggests the role of nanobio interfaces during surface-induced heterogeneous nucleation as a primary target for designing therapeutic interventions for amyloid-related neurodegenerative disorders.

The comorbidity profiles and medication issues of patients with multiple system atrophy: a systematic cross-sectional analysis

BACKGROUND

Multiple system atrophy (MSA) is a complex and fatal neurodegenerative movement disorder. Understanding the comorbidities and drug therapy is crucial for MSA patients' safety and management.

OBJECTIVES

To investigate the pattern of comorbidities and aspects of drug therapy in MSA patients.

METHODS

Cross-sectional data of MSA patients according to Gilman et al. (2008) diagnostic criteria and control patients without neurodegenerative diseases (non-ND) were collected from German, multicenter cohorts. The prevalence of comorbidities according to WHO ICD-10 classification and drugs administered according to WHO ATC system were analyzed. Potential drug-drug interactions were identified using AiDKlinik®.

RESULTS

The analysis included 254 MSA and 363 age- and sex-matched non-ND control patients. MSA patients exhibited a significantly higher burden of comorbidities, in particular diseases of the genitourinary system. Also, more medications were prescribed MSA patients, resulting in a higher prevalence of polypharmacy. Importantly, the risk of potential drug-drug interactions, including severe interactions and contraindicated combinations, was elevated in MSA patients. When comparing MSA-P and MSA-C subtypes, MSA-P patients suffered more frequently from diseases of the genitourinary system and diseases of the musculoskeletal system and connective tissue.

CONCLUSIONS

MSA patients face a substantial burden of comorbidities, notably in the genitourinary system. This, coupled with increased polypharmacy and potential drug interactions, highlights the complexity of managing MSA patients. Clinicians should carefully consider these factors when devising treatment strategies for MSA patients.

The Contribution of Type 2 Diabetes to Parkinson's Disease Aetiology

Type 2 diabetes (T2D) and Parkinson's disease (PD) are chronic disorders that have a significant health impact on a global scale. Epidemiological, preclinical, and clinical research underpins the assumption that insulin resistance and chronic inflammation contribute to the overlapping aetiologies of T2D and PD. This narrative review summarises the recent evidence on the contribution of T2D to the initiation and progression of PD brain pathology. It also briefly discusses the rationale and potential of alternative pharmacological interventions for PD treatment.

The Inhibition Effect of Epigallocatechin-3-Gallate on the Co-Aggregation of Amyloid-β and Human Islet Amyloid Polypeptide Revealed by Replica Exchange Molecular Dynamics Simulations

Alzheimer's disease and Type 2 diabetes are two epidemiologically linked diseases which are closely associated with the misfolding and aggregation of amyloid proteins amyloid-β (Aβ) and human islet amyloid polypeptide (hIAPP), respectively. The co-aggregation of the two amyloid proteins is regarded as the fundamental molecular mechanism underlying their pathological association. The green tea extract epigallocatechin-3-gallate (EGCG) has been extensively demonstrated to inhibit the amyloid aggregation of Aβ and hIAPP proteins. However, its potential role in amyloid co-aggregation has not been thoroughly investigated. In this study, we employed the enhanced-sampling replica exchange molecular dynamics simulation (REMD) method to investigate the effect of EGCG on the co-aggregation of Aβ and hIAPP. We found that EGCG molecules substantially diminish the β-sheet structures within the amyloid core regions of Aβ and hIAPP in their co-aggregates. Through hydrogen-bond, π-π and cation-π interactions targeting polar and aromatic residues of Aβ and hIAPP, EGCG effectively attenuates both inter-chain and intra-chain interactions within the co-aggregates. All these findings indicated that EGCG can effectively inhibit the co-aggregation of Aβ and hIAPP. Our study expands the potential applications of EGCG as an anti-amyloidosis agent and provides therapeutic options for the pathological association of amyloid misfolding disorders.

Association between falls and nonmotor symptoms in patients with Parkinson's disease

INTRODUCTION

Parkinson's disease (PD) is a chronic neurodegenerative disorder. Falls are common in patients with PD and can lead to disability, bedridden status, and death. The mechanisms of falls induced by symptoms of PD have not been fully clarified. We investigated the association between falls and nonmotor symptoms in PD patients.

METHODS

A total of 361 patients with Parkinson's disease were included. Whether the patients had fallen in the past half a year was recorded. Nonmotor symptoms were assessed by 30 items from the nonmotor symptom questionnaire (NMS Quest), Parkinson's Disease Sleep Scale (PDSS), Hamilton Depression Scale (HAMD), Hamilton Anxiety Scale (HAMA), and Montreal Cognitive Assessment Scale (MOCA).

RESULTS

A total of 63 patients experienced falls in the past six months, with an incidence of 17.5%. The patients with falls were elderly, had severe motor symptoms and disease severity, and the proportion of diabetic patients who experienced falls was higher. Adjusted for the above factors, the results showed that patients with falls had higher PD-NMS, HAMD and HAMA scores, but there was no significant difference in the total score and subscores of the MoCA scale between the two groups. The risk factors related to falling included age, history of diabetes, depression (HAMD), HAMD cognitive impairment, NMS urinary tract and NMS postural hypotension.

CONCLUSIONS

Falls were a common symptom in patients with PD and were not only related to motor symptoms but also closely related to nonmotor symptoms. urinary tract symptoms, postural hypotension, depression and HAMD cognitive impairment were risk factors related to falling in patients with PD.

How should we be using biomarkers in trials of disease modification in Parkinson's disease?

The recent validation of the α-synuclein seed amplification assay as a biomarker with high sensitivity and specificity for the diagnosis of Parkinson's disease has formed the backbone for a proposed staging system for incorporation in Parkinson's disease clinical studies and trials. The routine use of this biomarker should greatly aid in the accuracy of diagnosis during recruitment of Parkinson's disease patients into trials (as distinct from patients with non-Parkinson's disease parkinsonism or non-Parkinson's disease tremors). There remain, however, further challenges in the pursuit of biomarkers for clinical trials of disease modifying agents in Parkinson's disease, namely: optimizing the distinction between different α-synucleinopathies; the selection of subgroups most likely to benefit from a candidate disease modifying agent; a sensitive means of confirming target engagement; and the early prediction of longer-term clinical benefit. For example, levels of CSF proteins such as the lysosomal enzyme β-glucocerebrosidase may assist in prognostication or allow enrichment of appropriate patients into disease modifying trials of agents with this enzyme as the target; the presence of coexisting Alzheimer's disease-like pathology (detectable through CSF levels of amyloid-β42 and tau) can predict subsequent cognitive decline; imaging techniques such as free-water or neuromelanin MRI may objectively track decline in Parkinson's disease even in its later stages. The exploitation of additional biomarkers to the α-synuclein seed amplification assay will, therefore, greatly add to our ability to plan trials and assess the disease modifying properties of interventions. The choice of which biomarker(s) to use in the context of disease modifying clinical trials will depend on the intervention, the stage (at risk, premotor, motor, complex) of the population recruited and the aims of the trial. The progress already made lends hope that panels of fluid biomarkers in tandem with structural or functional imaging may provide sensitive and objective methods of confirming that an intervention is modifying a key pathophysiological process of Parkinson's disease. However, correlation with clinical progression does not necessarily equate to causation, and the ongoing validation of quantitative biomarkers will depend on insightful clinical-genetic-pathophysiological comparisons incorporating longitudinal biomarker changes from those at genetic risk with evidence of onset of the pathophysiology and those at each stage of manifest clinical Parkinson's disease.

An Innate Host Defense Protein β2-Microglobulin Keeps a Check on α-Synuclein amyloid Assembly: Implications in Parkinson's Disease

Amyloid formation due to protein misfolding has gained significant attention due to its association with neurodegenerative diseases. α-Synuclein (α-syn) is one such protein that undergoes a profound conformational switch to form higher order cross-β-sheet structures, resulting in amyloid formation, which is linked to the pathophysiology of Parkinson's disease (PD). The present status of research on α-syn aggregation and PD reveals that the disease progression may be linked with many other diseases, such as kidney-related disorders. Unraveling the link between PD and non-neurological diseases may help in early detection and a better understanding of PD progression. Herein, we investigated the modulation of α-syn in the presence of β2-microglobulin (β2m), a structural protein associated with dialysis-related amyloidosis. We took a multi-disciplinary approach to establish that β2m mitigates amyloid formation by α-syn. Our fluorescence, microscopy and toxicity data demonstrated that sub-stoichiometric ratio of β2m drives α-syn into off-pathway non-toxic aggregates incompetent of transforming into amyloids. Using AlphaFold2 and all-atom MD simulation, we showed that the β-strand segments (β1 and β2) of α-synuclein, which frequently engage in interactions within amyloid fibrils, interact with the last β-strand at the C-terminal of β2m. The outcome of this study will unravel the yet unknown potential linkage of PD with kidney-related disorders. Insights from the cross-talk between two amyloidogenic proteins will lead to early diagnosis and new therapeutic approaches for treating Parkinson's disease. Finally, disruption of the nucleation process of α-syn amyloids by targeting the β1-β2 region will constitute a potential therapeutic approach for inhibiting amyloid formation.

Nucleation of α-Synuclein Amyloid Fibrils Induced by Cross-Interaction with β-Hairpin Peptides Derived from Immunoglobulin Light Chains

Heterologous interactions between different amyloid-forming proteins, also called cross-interactions, may have a critical impact on disease-related amyloid formation. β-hairpin conformers of amyloid-forming proteins have been shown to affect homologous interactions in the amyloid self-assembly process. Here, we applied two β-hairpin-forming peptides derived from immunoglobulin light chains as models to test how heterologous β-hairpins modulate the fibril formation of Parkinson's disease-associated protein α-synuclein (αSyn). The peptides SMAhp and LENhp comprise β-strands C and C' of the κ4 antibodies SMA and LEN, which are associated with light chain amyloidosis and multiple myeloma, respectively. SMAhp and LENhp bind with high affinity to the β-hairpin-binding protein β-wrapin AS10 according to isothermal titration calorimetry and NMR spectroscopy. The addition of SMAhp and LENhp affects the kinetics of αSyn aggregation monitored by Thioflavin T (ThT) fluorescence, with the effect depending on assay conditions, salt concentration, and the applied β-hairpin peptide. In the absence of agitation, substoichiometric concentrations of the hairpin peptides strongly reduce the lag time of αSyn aggregation, suggesting that they support the nucleation of αSyn amyloid fibrils. The effect is also observed for the aggregation of αSyn fragments lacking the N-terminus or the C-terminus, indicating that the promotion of nucleation involves the interaction of hairpin peptides with the hydrophobic non-amyloid-β component (NAC) region.

The yeast prion protein Sup35 initiates α-synuclein pathology in mouse models of Parkinson's disease

Parkinson's disease (PD) is characterized by the pathologic aggregation and prion-like propagation of α-synuclein (α-syn). Emerging evidence shows that fungal infections increase the incidence of PD. However, the molecular mechanisms by which fungi promote the onset of PD are poorly understood. Here, we show that nasal infection with Saccharomyces cerevisiae (S. cerevisiae) in α-syn A53T transgenic mice accelerates the aggregation of α-syn. Furthermore, we found that Sup35, a prion protein from S. cerevisiae, is the key factor initiating α-syn pathology induced by S. cerevisiae. Sup35 interacts with α-syn and accelerates its aggregation in vitro. Notably, injection of Sup35 fibrils into the striatum of wild-type mice led to α-syn pathology and PD-like motor impairment. The Sup35-seeded α-syn fibrils showed enhanced seeding activity and neurotoxicity compared with pure α-syn fibrils in vitro and in vivo. Together, these observations indicate that the yeast prion protein Sup35 initiates α-syn pathology in PD.

Recent research progress on metabolic syndrome and risk of Parkinson's disease

Parkinson's disease (PD) is one of the most widespread neurodegenerative diseases. PD is associated with progressive loss of substantia nigra dopaminergic neurons, including various motor symptoms (e.g., bradykinesia, rigidity, and resting tremor), as well as non-motor symptoms (e.g., cognitive impairment, constipation, fatigue, sleep disturbance, and depression). PD involves multiple biological processes, including mitochondrial or lysosomal dysfunction, oxidative stress, insulin resistance, and neuroinflammation. Metabolic syndrome (MetS), a collection of numerous connected cerebral cardiovascular conditions, is a common and growing public health problem associated with many chronic diseases worldwide. MetS components include central/abdominal obesity, systemic hypertension, diabetes, and atherogenic dyslipidemia. MetS and PD share multiple pathophysiological processes, including insulin resistance, oxidative stress, and chronic inflammation. In recent years, MetS has been linked to an increased risk of PD, according to studies; however, the specific mechanism remains unclear. Researchers also found that some related metabolic therapies are potential therapeutic strategies to prevent and improve PD. This article reviews the epidemiological relationship between components of MetS and the risk of PD and discusses the potentially relevant mechanisms and recent progress of MetS as a risk factor for PD. Furthermore, we conclude that MetS-related therapies are beneficial for the prevention and treatment of PD.

Thiadiazolidinone (TDZD) Analogs Inhibit Aggregation-Mediated Pathology in Diverse Neurodegeneration Models, and Extend C. elegans Life- and Healthspan

Chronic, low-grade inflammation has been implicated in aging and age-dependent conditions, including Alzheimer's disease, cardiomyopathy, and cancer. One of the age-associated processes underlying chronic inflammation is protein aggregation, which is implicated in neuroinflammation and a broad spectrum of neurodegenerative diseases such as Alzheimer's, Huntington's, and Parkinson's diseases. We screened a panel of bioactive thiadiazolidinones (TDZDs) from our in-house library for rescue of protein aggregation in human-cell and C. elegans models of neurodegeneration. Among the tested TDZD analogs, PNR886 and PNR962 were most effective, significantly reducing both the number and intensity of Alzheimer-like tau and amyloid aggregates in human cell-culture models of pathogenic aggregation. A C. elegans strain expressing human Aβ1-42 in muscle, leading to AD-like amyloidopathy, developed fewer and smaller aggregates after PNR886 or PNR962 treatment. Moreover, age-progressive paralysis was reduced 90% by PNR886 and 75% by PNR962, and "healthspan" (the median duration of spontaneous motility) was extended 29% and 62%, respectively. These TDZD analogs also extended wild-type C. elegans lifespan by 15-30% (p < 0.001), placing them among the most effective life-extension drugs. Because the lead drug in this family, TDZD-8, inhibits GSK3β, we used molecular-dynamic tools to assess whether these analogs may also target GSK3β. In silico modeling predicted that PNR886 or PNR962 would bind to the same allosteric pocket of inactive GSK3β as TDZD-8, employing the same pharmacophore but attaching with greater avidity. PNR886 and PNR962 are thus compelling candidate drugs for treatment of tau- and amyloid-associated neurodegenerative diseases such as AD, potentially also reducing all-cause mortality.

Interaction of Proteins Involved in Neuronal Proteinopathies

Proteinopathy is characterized by the accumulation of aggregates of a specific protein in a target organ, tissue, or cell. The aggregation of the same protein can cause different pathologies as single protein can adopt various amyloidogenic, disease-specific conformations. The conformation governs the interaction of amyloid aggregates with other proteins that are prone to misfolding and, thus, determines disease-specific spectrum of concomitant pathologies. In this regard, a detailed description of amyloid protein conformation as well as spectrum of its interaction with other proteins become a key point for drafting of precise description of the disease. The majority of clinical cases of neuronal proteinopathies is caused by the aggregation of rather limited range of amyloidogenic proteins. Here, we provided the characterization of pathologies, related to the aggregation of amyloid β peptide, tau protein, α-synuclein, TDP-43, and amylin, giving a short description of pathologies themselves, recent advances in elucidation of misfolded protein conformation, with emphasis on those protein aggregates extracted from biological samples, what is known about the interaction of this proteins, and the influence of this interaction on the progression of underlying disease and comorbidities.

The Aβ42 Peptide and IAPP Physically Interact in a Yeast-Based Assay

Numerous studies have demonstrated that people with type 2 diabetes mellitus (associated with IAPP peptide aggregation) show an increased incidence of Alzheimer's disease (associated with Aβ aggregation), but the mechanism responsible for this correlation is presently unknown. Here, we applied a yeast-based model to study the interactions of IAPP with PrP (associated with TSEs) and with the Aβ42 peptide. We demonstrated that fluorescently tagged IAPP forms detergent-resistant aggregates in yeast cells. Using the FRET approach, we showed that IAPP and Aβ aggregates co-localize and physically interact in yeast cells. We also showed that this interaction is specific and that there is no interaction between IAPP and PrP in the yeast system. Our data confirmed a direct physical interaction between IAPP and Aβ42 aggregates in a living cell. Based on these findings, we hypothesize that this interaction may play a crucial role in seeding Aβ42 aggregation in T2DM patients, thereby promoting the development of AD.

Brain Hydrophobic Peptides Antagonists of Neurotoxic Amyloid β Peptide Monomers/Oligomers-Protein Interactions

Amyloid β (Aβ) oligomers have been linked to Alzheimer's disease (AD) pathogenesis and are the main neurotoxic forms of Aβ. This review focuses on the following: (i) the Aβ(1-42):calmodulin interface as a model for the design of antagonist Aβ peptides and its limitations; (ii) proteolytic degradation as the major source of highly hydrophobic peptides in brain cells; and (iii) brain peptides that have been experimentally demonstrated to bind to Aβ monomers or oligomers, Aβ fibrils, or Aβ plaques. It is highlighted that the hydrophobic amino acid residues of the COOH-terminal segment of Aβ(1-42) play a key role in its interaction with intracellular protein partners linked to its neurotoxicity. The major source of highly hydrophobic endogenous peptides of 8-10 amino acids in neurons is the proteasome activity. Many canonical antigen peptides bound to the major histocompatibility complex class 1 are of this type. These highly hydrophobic peptides bind to Aβ and are likely to be efficient antagonists of the binding of Aβ monomers/oligomers concentrations in the nanomolar range with intracellular proteins. Also, their complexation with Aβ will protect them against endopeptidases, suggesting a putative chaperon-like physiological function for Aβ that has been overlooked until now. Remarkably, the hydrophobic amino acid residues of Aβ responsible for the binding of several neuropeptides partially overlap with those playing a key role in its interaction with intracellular protein partners that mediates its neurotoxicity. Therefore, these latter neuropeptides are also potential candidates to antagonize Aβ peptides binding to target proteins. In conclusion, the analysis performed in this review points out that hydrophobic endogenous brain neuropeptides could be valuable biomarkers to evaluate the risk of the onset of sporadic AD, as well as for the prognosis of AD.

Are fibrinaloid microclots a cause of autoimmunity in Long Covid and other post-infection diseases?

It is now well established that the blood-clotting protein fibrinogen can polymerise into an anomalous form of fibrin that is amyloid in character; the resultant clots and microclots entrap many other molecules, stain with fluorogenic amyloid stains, are rather resistant to fibrinolysis, can block up microcapillaries, are implicated in a variety of diseases including Long COVID, and have been referred to as fibrinaloids. A necessary corollary of this anomalous polymerisation is the generation of novel epitopes in proteins that would normally be seen as 'self', and otherwise immunologically silent. The precise conformation of the resulting fibrinaloid clots (that, as with prions and classical amyloid proteins, can adopt multiple, stable conformations) must depend on the existing small molecules and metal ions that the fibrinogen may (and is some cases is known to) have bound before polymerisation. Any such novel epitopes, however, are likely to lead to the generation of autoantibodies. A convergent phenomenology, including distinct conformations and seeding of the anomalous form for initiation and propagation, is emerging to link knowledge in prions, prionoids, amyloids and now fibrinaloids. We here summarise the evidence for the above reasoning, which has substantial implications for our understanding of the genesis of autoimmunity (and the possible prevention thereof) based on the primary process of fibrinaloid formation.

Melatonin as a Chronobiotic/Cytoprotective Agent in REM Sleep Behavior Disorder

Dream-enactment behavior that emerges during episodes of rapid eye movement (REM) sleep without muscle atonia is a parasomnia known as REM sleep behavior disorder (RBD). RBD constitutes a prodromal marker of α-synucleinopathies and serves as one of the best biomarkers available to predict diseases such as Parkinson disease, multiple system atrophy and dementia with Lewy bodies. Most patients showing RBD will convert to an α-synucleinopathy about 10 years after diagnosis. The diagnostic advantage of RBD relies on the prolonged prodromal time, its predictive power and the absence of disease-related treatments that could act as confounders. Therefore, patients with RBD are candidates for neuroprotection trials that delay or prevent conversion to a pathology with abnormal α-synuclein metabolism. The administration of melatonin in doses exhibiting a chronobiotic/hypnotic effect (less than 10 mg daily) is commonly used as a first line treatment (together with clonazepam) of RBD. At a higher dose, melatonin may also be an effective cytoprotector to halt α-synucleinopathy progression. However, allometric conversion doses derived from animal studies (in the 100 mg/day range) are rarely employed clinically regardless of the demonstrated absence of toxicity of melatonin in phase 1 pharmacological studies with doses up to 100 mg in normal volunteers. This review discusses the application of melatonin in RBD: (a) as a symptomatic treatment in RBD; (b) as a possible disease-modifying treatment in α-synucleinopathies. To what degree melatonin has therapeutic efficacy in the prevention of α-synucleinopathies awaits further investigation, in particular multicenter double-blind trials.

Islet Amyloid Polypeptide Triggers α-synuclein Pathology in Parkinson's Disease

Pathologic aggregation and prion-like propagation of α-synuclein (α-syn) are the hallmarks of Parkinson's disease (PD). Emerging evidence shows that type 2 diabetes mellitus (T2DM) is a risk factor for PD. Interestingly, T2DM is characterized by the amyloid deposition of islet amyloid polypeptide (IAPP) in the pancreas. Although T2DM and PD share pathological similarities, the underlying molecular mechanisms bridging these two diseases remain unknown. Here, we report that IAPP co-deposits with α-syn in the brains of PD patients. IAPP interacts with α-syn and accelerates its aggregation. In addition, the IAPP-seeded α-syn fibrils show enhanced seeding activity and neurotoxicity compared with pure α-syn fibrils in vitro and in vivo. Strikingly, intravenous injection of IAPP fibrils into α-syn A53T transgenic mice or human SNCA transgenic mice accelerated the aggregation of α-syn and PD-like motor deficits. Taken together, these findings support that IAPP acts as a trigger of α-syn pathology in PD, and provide a mechanistic explanation for the increased risk and faster progression of PD in patients with T2DM.

Type 2 Diabetes (T2DM) and Parkinson's Disease (PD): a Mechanistic Approach

Growing evidence suggest that there is a connection between Parkinson's disease (PD) and insulin dysregulation in the brain, whilst the connection between PD and type 2 diabetes mellitus (T2DM) is still up for debate. Insulin is widely recognised to play a crucial role in neuronal survival and brain function; any changes in insulin metabolism and signalling in the central nervous system (CNS) can lead to the development of various brain disorders. There is accumulating evidence linking T2DM to PD and other neurodegenerative diseases. In fact, they have a lot in common patho-physiologically, including insulin dysregulation, oxidative stress resulting in mitochondrial dysfunction, microglial activation, and inflammation. As a result, initial research should focus on the role of insulin and its molecular mechanism in order to develop therapeutic outcomes. In this current review, we will look into the link between T2DM and PD, the function of insulin in the brain, and studies related to impact of insulin in causing T2DM and PD. Further, we have also highlighted the role of various insulin signalling pathway in both T2DM and PD. We have also suggested that T2DM-targeting pharmacological strategies as potential therapeutic approach for individuals with cognitive impairment, and we have demonstrated the effectiveness of T2DM-prescribed drugs through current PD treatment trials. In conclusion, this investigation would fill a research gap in T2DM-associated Parkinson's disease (PD) with a potential therapy option.

Recent advances in the modulation of amyloid protein aggregation using the supramolecular host-guest approaches

Misfolding of proteins is associated with many incurable diseases in human beings. Understanding the process of aggregation from monomers to fibrils, the characterization of all intermediate species, and the origin of toxicity is very challenging. Extensive research including computational and experimental shed some light on these tricky phenomena. Non-covalent interactions between amyloidogenic domains of proteins play a major role in their self-assembly which can be disrupted by designed chemical tools. This will lead to the development of inhibitors of detrimental amyloid formations. In supramolecular host-guest chemistry approaches, different macrocycles function as hosts for encapsulating hydrophobic guests, i.e. phenylalanine residues of proteins, in their hydrophobic cavities via non-covalent interactions. In this way, they can disrupt the interactions between adjacent amyloidogenic proteins and prevent their self-aggregation. This supramolecular approach has also emerged as a prospective tool to modify the aggregation of several amyloidogenic proteins. In this review, we discussed recent supramolecular host-guest chemistry-based strategies for the inhibition of amyloid protein aggregation.

PPARs and Their Neuroprotective Effects in Parkinson's Disease: A Novel Therapeutic Approach in α-Synucleinopathy?

Parkinson's disease (PD) is the most common α-synucleinopathy worldwide. The pathognomonic hallmark of PD is the misfolding and propagation of the α-synuclein (α-syn) protein, observed in post-mortem histopathology. It has been hypothesized that α-synucleinopathy triggers oxidative stress, mitochondrial dysfunction, neuroinflammation, and synaptic dysfunction, leading to neurodegeneration. To this date, there are no disease-modifying drugs that generate neuroprotection against these neuropathological events and especially against α-synucleinopathy. Growing evidence suggests that peroxisome proliferator-activated receptor (PPAR) agonists confer neuroprotective effects in PD, however, whether they also confer an anti-α-synucleinopathy effect is unknown. Here we analyze the reported therapeutic effects of PPARs, specifically the gamma isoform (PPARγ), in preclinical PD animal models and clinical trials for PD, and we suggest possible anti-α-synucleinopathy mechanisms acting downstream from these receptors. Elucidating the neuroprotective mechanisms of PPARs through preclinical models that mimic PD as closely as possible will facilitate the execution of better clinical trials for disease-modifying drugs in PD.

Type 2 Diabetes and Parkinson's Disease: A Focused Review of Current Concepts

Highly reproducible epidemiological evidence shows that type 2 diabetes (T2D) increases the risk and rate of progression of Parkinson's disease (PD), and crucially, the repurposing of certain antidiabetic medications for the treatment of PD has shown early promise in clinical trials, suggesting that the effects of T2D on PD pathogenesis may be modifiable. The high prevalence of T2D means that a significant proportion of patients with PD may benefit from personalized antidiabetic treatment approaches that also confer neuroprotective benefits. Therefore, there is an immediate need to better understand the mechanistic relation between these conditions and the specific molecular pathways affected by T2D in the brain. Although there is considerable evidence that processes such as insulin signaling, mitochondrial function, autophagy, and inflammation are involved in the pathogenesis of both PD and T2D, the primary aim of this review is to highlight the evidence showing that T2D-associated dysregulation of these pathways occurs not only in the periphery but also in the brain and how this may facilitate neurodegeneration in PD. We also discuss the challenges involved in disentangling the complex relationship between T2D, insulin resistance, and PD, as well as important questions for further research. © 2022 International Parkinson and Movement Disorder Society.

Studies on alpha-synuclein and islet amyloid polypeptide interaction

Introduction: Parkinson's disease and type 2 diabetes have both elements of local amyloid depositions in their pathogenesis. In Parkinson's disease, alpha-synuclein (aSyn) forms insoluble Lewy bodies and Lewy neurites in brain neurons, and in type 2 diabetes, islet amyloid polypeptide (IAPP) comprises the amyloid in the islets of Langerhans. In this study, we assessed the interaction between aSyn and IAPP in human pancreatic tissues, both ex vivo and in vitro. Material and Methods: The antibody-based detection techniques, proximity ligation assay (PLA), and immuno-TEM were used for co-localization studies. Bifluorescence complementation (BiFC) was used for interaction studies between IAPP and aSyn in HEK 293 cells. The Thioflavin T assay was used for studies of cross-seeding between IAPP and aSyn. ASyn was downregulated with siRNA, and insulin secretion was monitored using TIRF microscopy. Results: We demonstrate intracellular co-localization of aSyn with IAPP, while aSyn is absent in the extracellular amyloid deposits. ASyn reactivity is present in the secretory granules of β-cells and some α-cells in human islets. The BiFC-expression of aSyn/aSyn and IAPP/IAPP in HEK293 cells resulted in 29.3% and 19.7% fluorescent cells, respectively, while aSyn/IAPP co-expression resulted in ∼10% fluorescent cells. Preformed aSyn fibrils seeded IAPP fibril formation in vitro, but adding preformed IAPP seeds to aSyn did not change aSyn fibrillation. In addition, mixing monomeric aSyn with monomeric IAPP did not affect IAPP fibril formation. Finally, the knockdown of endogenous aSyn did not affect β cell function or viability, nor did overexpression of aSyn affect β cell viability. Discussion: Despite the proximity of aSyn and IAPP in β-cells and the detected capacity of preformed aSyn fibrils to seed IAPP in vitro, it is still an open question if an interaction between the two molecules is of pathogenic significance for type 2 diabetes.

Cysteine-Derived Chiral Carbon Quantum Dots: A Fibrinolytic Activity Regulator for Plasmin to Target the Human Islet Amyloid Polypeptide for Type 2 Diabetes Mellitus

The fibrillization and deposition of the human islet amyloid polypeptide (hIAPP) are the pathological hallmark of type 2 diabetes mellitus (T2DM), and these insoluble fibrotic depositions of hIAPP are considered to strongly affect insulin secretion by inducing toxicity toward pancreatic islet β-cells. The current strategy of preventing amyloid aggregation by nanoparticle-assisted inhibitors can only disassemble fibrotic amyloids into more toxic oligomers and/or protofibrils. Herein, for the first time, we propose a type of cysteine-derived chiral carbon quantum dot (CQD) that targets plasmin, a core natural fibrinolytic protease in humans. These CQDs can serve as fibrinolytic activity regulators for plasmin to cleave hIAPP into nontoxic polypeptides or into even smaller amino acid fragments, thus alleviating hIAPP's fibrotic amyloid-induced cytotoxicity. Our experiments indicate that chiral CQDs have opposing effects on plasmin activity. The l-CQDs promote the cleavage of hIAPP by enhancing plasmin activity at a promotion ratio of 23.2%, thus protecting β-cells from amyloid-induced toxicity. In contrast, the resultant d-CQDs significantly inhibit proteolysis, decreasing plasmin activity by 31.5% under the same reaction conditions. Second harmonic generation (SHG) microscopic imaging is initially used to dynamically characterize hIAPP before and after proteolysis. The l-CQD promotion of plasmin activity thus provides a promising avenue for the hIAPP-targeted treatment of T2DM to treat low fibrinolytic activity, while the d-CQDs, as inhibitors of plasmin activity, may improve patient survival for hyperfibrinolytic conditions, such as those existing during surgeries and traumas.

Amyloid Protein Cross-Seeding Provides a New Perspective on Multiple Diseases In Vivo

Amyloid protein cross-seeding is a peculiar phenomenon of cross-spreading among different diseases. Unlike traditional infectious ones, diseases caused by amyloid protein cross-seeding are spread by misfolded proteins instead of pathogens. As a consequence of the interactions among misfolded heterologous proteins or polypeptides, amyloid protein cross-seeding is considered to be the crucial cause of overlapping pathological transmission between various protein misfolding disorders (PMDs) in multiple tissues and cells. Here, we briefly review the phenomenon of cross-seeding among amyloid proteins. As an interesting example worth mentioning, the potential links between the novel coronavirus pneumonia (COVID-19) and some neurodegenerative diseases might be related to the amyloid protein cross-seeding, thus may cause an undesirable trend in the incidence of PMDs around the world. We then summarize the theoretical models as well as the experimental techniques for studying amyloid protein cross-seeding. Finally, we conclude with an outlook on the challenges and opportunities for basic research in this field. Cross-seeding of amyloid opens up a new perspective in our understanding of the process of amyloidogenesis, which is crucial for the development of new treatments for diseases. It is therefore valuable but still challenging to explore the cross-seeding system of amyloid protein as well as to reveal the structural basis and the intricate processes.

Association between prediabetes and cognitive function in Parkinson's disease

INTRODUCTION

It remains largely unknown whether prediabetes is related to cognitive impairment in Parkinson's disease (PD). This study aimed to assess the association between prediabetes and cognitive function in PD patients.

METHODS

In this cross-sectional study, 262 PD patients (age, 69.8 ± 10.3 years; Hoehn-Yahr stage, 2.3 ± 0.8) were classified into diabetes (glycated hemoglobin [HbA1c] ≥6.5% or previously diagnosed, n = 76), prediabetes (5.7%-6.4%, n = 90), or diabetes free (≤5.6%, n = 96) groups. Cognitive function was measured using the Montreal Cognitive Assessment (MoCA) test.

RESULTS

Both the diabetes and prediabetes groups had significantly lower MoCA scores (17.0 ± 6.6 and 18.0 ± 6.1, respectively) than the diabetes free group (20.0 ± 5.7), even after adjusting for potential confounders (p = .002 and p = .008, respectively). In the combined group of prediabetes and diabetes free patients, higher HbA1c levels significantly correlated with lower MoCA scores (p = .031). There was a significant interaction of diabetes status with age, but not with the duration of PD, on cognitive function.

CONCLUSION

In addition to diabetes, prediabetes may negatively affect cognitive function in PD patients. Further prospective longitudinal studies are necessary to clarify the impact of prediabetes on the cognitive trajectory of these patients.

Association between Parkinson's Disease and Diabetes Mellitus: From Epidemiology, Pathophysiology and Prevention to Treatment

Diabetes mellitus (DM) and Parkinson's disease (PD) are both age-related diseases of global concern being among the most common chronic metabolic and neurodegenerative diseases, respectively. While both diseases can be genetically inherited, environmental factors play a vital role in their pathogenesis. Moreover, DM and PD have common underlying molecular mechanisms, such as misfolded protein aggregation, mitochondrial dysfunction, oxidative stress, chronic inflammation, and microbial dysbiosis. Recently, epidemiological and experimental studies have reported that DM affects the incidence and progression of PD. Moreover, certain antidiabetic drugs have been proven to decrease the risk of PD and delay its progression. In this review, we elucidate the epidemiological and pathophysiological association between DM and PD and summarize the antidiabetic drugs used in animal models and clinical trials of PD, which may provide reference for the clinical translation of antidiabetic drugs in PD treatment.

Crossroads between copper ions and amyloid formation in Parkinson's disease

Copper (Cu) ion dys-homeostasis and α-synclein amyloid deposits are two hallmarks of Parkinson's disease (PD). Here, I will discuss the connections between these features, with a major focus on the role of Cu in the α-synuclein (aS) amyloid formation process. The structurally disordered aS monomer can bind to both redox states of Cu (i.e., oxidized Cu(II) and reduced Cu(I)) with high affinity in vitro. Notably, the presence of Cu(II) (in absence of aS N-terminal acetylation) and Cu(I) (when in complex with the copper chaperone Atox1) modulate aS assembly into β-structured amyloids in opposite directions in vitro. Albeit the link to biological relevance is not fully unraveled, existing observations clearly emphasize the need for more knowledge on this interplay and its consequences to eventually combat destructive reactions that promote PD.

Exposure to the environmentally toxic pesticide maneb induces Parkinson's disease-like neurotoxicity in mice: A combined proteomic and metabolomic analysis

Maneb is a typical dithiocarbamate fungicide that has been extensively used worldwide. Epidemiological evidence shows that exposure to maneb is an environmental risk factor for Parkinson's disease (PD). However, the mechanisms underlying maneb-induced neurotoxicity have yet to be elucidated. In this study, we exposed SH-SY5Y cells to maneb at environmentally relevant concentrations (0, 0.1, 5, 10 mg/L) and found that maneb dose-dependently decreased the cell viability. Furthermore, maneb (60 mg/kg) induced PD-like motor impairment in α-synuclein A53T transgenic mice. The results of tandem mass tag (TMT) proteomics and metabolomics studies of mouse brain and serum revealed significant changes in proteins and metabolites in the pathways involved in the neurotransmitter system. The omics results were verified by targeted metabolomics and Western blot analysis, which demonstrated that maneb induced disturbance of the PD-related pathways, including the phenylalanine and tryptophan metabolism pathways, dopaminergic synapse, synaptic vesicle cycle, mitochondrial dysfunction, and oxidative stress. In addition, the PD-like phenotype induced by maneb was attenuated by the asparagine endopeptidase (AEP) inhibitor compound #11 (CP11) (10 mg/kg), indicating that AEP may play a role in maneb-induced neurotoxicity. To the best of our knowledge, this is the first study to investigate the molecular mechanisms underlying maneb-induced PD-like phenotypes using multiomics analysis, which identified novel therapeutic targets for PD associated with pesticides and other environmental pollutants.

Type 2 diabetes mellitus augments Parkinson's disease risk or the other way around: Facts, challenges and future possibilities

About 10% of the adult population is living with type 2 diabetes mellitus (T2DM) and 1% of the population over 60 years of age is suffering from Parkinson's disease (PD). A school of thought firmly believes that T2DM, an age-related disease, augments PD risk. Such relationship is reflected from the severity of PD symptoms in drug naive subjects possessing T2DM. Onset of Parkinsonian feature in case controls possessing T2DM corroborates the role of hyperglycemia in PD. A few cohort, meta-analysis and animal studies have shown an increased PD risk owing to insulin resistance. High fat diet and role of insulin signaling in the regulation of sugar metabolism, oxidative stress, α-synuclein aggregation and accumulation, inflammatory response and mitochondrial function in PD models and sporadic PD further connect the two. Although little is reported about the implication of PD in hyperglycemia and T2DM, a few studies have also contradicted. Ameliorative effect of anti-diabetic drugs on Parkinsonian symptoms and vague outcome of anti-PD medications in T2DM patients also suggest a link. The article reviews the literature supporting augmented risk of one by the other, analysis of proof of the concept, facts, challenges, future possibilities and standpoint on the subject.

Targeting hIAPP fibrillation: A new paradigm to prevent β-cell death?

Loss of pancreatic β-cell mass is deleterious for type 2 diabetes patients since it reduces insulin production, critical for glucose homeostasis. The main research axis developed over the last few years was to generate new pancreatic β-cells or to transplant pancreatic islets as occurring for some specific type 1 diabetes patients. We evaluate here a new paradigm consisting in preservation of β-cells by prevention of human islet amyloid polypeptide (hIAPP) oligomers and fibrils formation leading to pancreatic β-cell death. We review the hIAPP physiology and the pathology that contributes to β-cell destruction, deciphering the various cellular steps that could be involved. Recent progress in understanding other amyloidosis such as Aβ, Tau, α-synuclein or prion, involved in neurodegenerative processes linked with inflammation, has opened new research lines of investigations to preserve neuronal cells. We evaluate and estimate their transposition to the pancreatic β-cells preservation. Among them is the control of reactive oxygen species (ROS) production occurring with inflammation and the possible implication of the mitochondrial translocator protein as a diagnostic and therapeutic target. The present review also focuses on other amyloid forming proteins from molecular to physiological and physiopathological points of view that could help to better decipher hIAPP-induced β-cell death mechanisms and to prevent hIAPP fibril formation.

Mechanisms behind the Fibrillation and Toxicity of Insulin Fibrils on Neuron Cells by Engineered Curcumin Analogs

Among foods, the use of plant derivatives as promising drugs and/or excipients has been considered from various perspectives. In the present study, curcumin, which is one of the most important plant derivatives for biological uses, and four curcumin-based pyrido[2,3-d]pyrimidine analogs (C2-C5) were used for investigating the mechanism of insulin fibrillation and evaluating the cytotoxicity of insulin fibrils. The synthesized analogs differed in terms of hydrophobicity and electrostatic charge. The analogs with more hydrophobicity (C1 and C4) in both acidic and neutral environments were able to reduce the rate of insulin fibrillation and the degree of cross-linking in the produced fibrils. Additionally, the toxicity of these fibrils for neural cells (N2a cell line) was very low. However, they did not show any significant effects on the toxicity of non-neural cells (HEK293 cell line), indicating the effect of the biochemical surface diversity on determining the vulnerability to fibrils and even the mechanism of action of additives on cell line survival. Although negatively charged analogs were able to reduce insulin fibrillation in the acidic environment, they indicated an opposite effect in the neutral environment. The resultant fibrils in the acidic medium appeared with a well-distinguished filament, but they were very close at neutral pH levels. Moreover, such fibrils indicated very poor toxicity against the N2a cell line and had no significant effects on HEK293 cells. Considering the docking studies, by creatively using the size exclusion chromatography, it was suggested that analogs C2 and C3 were capable of binding to the C-terminal end of the insulin B chain (low affinity) and His^B10 (high affinity). Hence, it was suggested that different compounds could play different protecting and/or destroying roles in cell toxicity by blocking some ligands at the surface of neuron cells.

The Impact of Type 2 Diabetes in Parkinson's Disease

BACKGROUND

Type 2 diabetes (T2DM) is an established risk factor for developing Parkinson's disease (PD), but its effect on disease progression is not well understood.

OBJECTIVE

The aim of this study was to investigate the influence of T2DM on aspects of disease progression in PD.

METHODS

We analyzed data from the Tracking Parkinson's study to examine the effects of comorbid T2DM on PD progression and quality of life by comparing symptom severity scores assessing a range of motor and nonmotor symptoms.

RESULTS

We identified 167 (8.7%) patients with PD and T2DM (PD + T2DM) and 1763 (91.3%) patients with PD without T2DM (PD). After controlling for confounders, patients with T2DM had more severe motor symptoms, as assessed by Movement Disorder Society Unified Parkinson's Disease Rating Scale, Part III (25.8 [0.9] vs. 22.5 [0.3] P = 0.002), and nonmotor symptoms, as assessed by Non-Motor Symptoms Scale total (38.4 [2.5] vs. 31.8 [0.7] P < 0.001), and were significantly more likely to report loss of independence (odds ratio, 2.08; 95% confidence interval [CI]: 1.34-3.25; P = 0.001) and depression (odds ratio, 1.62; CI: 1.10-2.39; P = 0.015). Furthermore, over time, patients with T2DM had significantly faster motor symptom progression (P = 0.012), developed worse mood symptoms (P = 0.041), and were more likely to develop substantial gait impairment (hazard ratio, 1.55; CI: 1.07-2.23; P = 0.020) and mild cognitive impairment (hazard ratio, 1.7; CI: 1.24-2.51; P = 0.002) compared with the PD group.

CONCLUSIONS

In the largest study to date, T2DM is associated with faster disease progression in Parkinson's, highlighting an interaction between these two diseases. Because it is a potentially modifiable metabolic state, with multiple peripheral and central targets for intervention, it may represent a target for alleviating parkinsonian symptoms and slowing progression to disability and dementia. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Nutrient-sensing amyloid metastasis

Amyloids are organized suprastructural polypeptide arrangements. The prevalence of amyloid-related processes of pathophysiological relevance has been linked to aging-related degenerative diseases. Besides the role of genetic polymorphisms on the relative risk of amyloid diseases, the contributions of nongenetic ontogenic cluster of factors remain elusive. In recent decades, mounting evidences have been suggesting the role of essential micronutrients, in particular transition metals, in the regulation of amyloidogenic processes, both directly (such as binding to amyloid proteins) or indirectly (such as regulating regulatory partners, processing enzymes, and membrane transporters). The features of transition metals as regulatory cofactors of amyloid proteins and the consequences of metal dyshomeostasis in triggering amyloidogenic processes, as well as the evidences showing amelioration of symptoms by dietary supplementation, suggest an exaptative role of metals in regulating amyloid pathways. The self- and cross-talk replicative nature of these amyloid processes along with their systemic distribution support the concept of their metastatic nature. The role of amyloidosis as nutrient sensors would act as intra- and transgenerational epigenetic metabolic programming factors determining health span and life span, viability, which could participate as an evolutive selective pressure.

Linking hIAPP misfolding and aggregation with type 2 diabetes mellitus: a structural perspective

There are over 40 identified human disorders that involve certain proteins folding incorrectly, accumulating in the body causing damage to cells and organs and causing disease. Type 2 Diabetes Mellitus (T2DM) is one of these protein misfolding disorders (PMDs) and involves human islet amyloid polypeptide (hIAPP) misfolding and accumulating in parts of the body, primarily in the pancreas, causing damage to islet cells and affecting glucose regulation. In this review, we have summarised our current understanding of what causes hIAPP to misfold, what conformations are found in different parts of the body with a particular focus on what is known about the structure of hIAPP and how this links to T2DM. Understanding the molecular basis behind these misfolding events is essential for understanding the role of hIAPP to develop better therapeutics since type 2 diabetes currently affects over 4.9 million people in the United Kingdom alone and is predicted to increase as our population ages.

Linking Alzheimer’s Disease and Type 2 Diabetes: Characterization and Inhibition of Cytotoxic Aβ and IAPP Hetero-Aggregates

The cytotoxic self-aggregation of β-amyloid (Aβ) peptide and islet amyloid polypeptide (IAPP) is implicated in the pathogenesis of Alzheimer’s disease (AD) and Type 2 diabetes (T2D), respectively. Increasing evidence, particularly the co-deposition of Aβ and IAPP in both brain and pancreatic tissues, suggests that Aβ and IAPP cross-interaction may be responsible for a pathological link between AD and T2D. Here, we examined the nature of IAPP-Aβ40 co-aggregation and its inhibition by small molecules. In specific, we characterized the kinetic profiles, morphologies, secondary structures and toxicities of IAPP-Aβ40 hetero-assemblies and compared them to those formed by their homo-assemblies. We demonstrated that monomeric IAPP and Aβ40 form stable hetero-dimers and hetero-assemblies that further aggregate into β-sheet-rich hetero-aggregates that are toxic (cell viability <50%) to both PC-12 cells, a neuronal cell model, and RIN-m5F cells, a pancreatic cell model for β-cells. We then selected polyphenolic candidates to inhibit IAPP or Aβ40 self-aggregation and examined the inhibitory effect of the most potent candidate on IAPP-Aβ40 co-aggregation. We demonstrated that epigallocatechin gallate (EGCG) form inter-molecular hydrogen bonds with each of IAPP and Aβ40. We also showed that EGCG reduced hetero-aggregate formation and resulted in lower β-sheets content and higher unordered structures in IAPP-Aβ40-EGCG samples. Importantly, we showed that EGCG is highly effective in reducing the toxicity of IAPP-Aβ40 hetero-aggregates on both cell models, specifically at concentrations that are equivalent to or are 2.5-fold higher than the mixed peptide concentrations. To the best of our knowledge, this is the first study to report the inhibition of IAPP-Aβ40 co-aggregation by small molecules. We conclude that EGCG is a promising candidate to prevent co-aggregation and cytotoxicity of IAPP-Aβ40, which in turn, contribute to the pathological link between AD and T2D.

Molecular Mechanisms of Amylin Turnover, Misfolding and Toxicity in the Pancreas

Amyloidosis is a common pathological event in which proteins self-assemble into misfolded soluble and insoluble molecular forms, oligomers and fibrils that are often toxic to cells. Notably, aggregation-prone human islet amyloid polypeptide (hIAPP), or amylin, is a pancreatic hormone linked to islet β-cells demise in diabetics. The unifying mechanism by which amyloid proteins, including hIAPP, aggregate and kill cells is still matter of debate. The pathology of type-2 diabetes mellitus (T2DM) is characterized by extracellular and intracellular accumulation of toxic hIAPP species, soluble oligomers and insoluble fibrils in pancreatic human islets, eventually leading to loss of β-cell mass. This review focuses on molecular, biochemical and cell-biology studies exploring molecular mechanisms of hIAPP synthesis, trafficking and degradation in the pancreas. In addition to hIAPP turnover, the dynamics and the mechanisms of IAPP–membrane interactions; hIAPP aggregation and toxicity in vitro and in situ; and the regulatory role of diabetic factors, such as lipids and cholesterol, in these processes are also discussed.

A new strategy to reconcile amyloid cross-seeding and amyloid prevention in a binary system of α-synuclein fragmental peptide and hIAPP

Amyloid cross-seeding and amyloid inhibition are two different research subjects being studied separately for different pathological purposes, in which amyloid cross-seeding targets to study the co-aggregation of different amyloid proteins and potential molecular links between different neurodegenerative diseases, while amyloid inhibition aims to design different molecules for preventing amyloid aggregation. While both amyloid cross-seeding and amyloid inhibition are critical for better understanding the pathological causes of different neurodegenerative diseases including Parkinson disease (PD) and Type 2 diabetes (T2D), less efforts have been made to reconcile the two phenomena. Herein, we proposed a new preventive strategy to demonstrate (a) the cross-seeding of octapeptide TKEQVTNV from α-synuclein (associated with PD) with hIAPP (associated with T2D) and (b) the cross-seeding-promoted hIAPP fibrillization and cross-seeding-reduced hIAPP toxicity. Collective results confirmed that TKEQVTNV can indeed cross-seed with hIAPP monomers and oligomers, not protofibrils, to form β-structure-rich fibrils and to accelerate hIAPP fibrillization. Moreover, such cross-seeding-induced promotion effect by TKEQVTNV also rescued the pancreatic cells from hIAPP-induced cytotoxicity by increasing cell viability and reducing cell apoptosis simultaneously. This work provides a new angle to discover amyloid fragments and use them as amyloid modulators (inhibitors or promotors) to interfere with amyloid aggregation of other amyloid proteins, as well as sequence/structure basis to explore the amyloid cross-seeding between different amyloid proteins that may help explain a potential molecular talk between different neurodegenerative diseases.

Parkinson's disease and diabetes mellitus: common mechanisms and treatment repurposing

In the last decade, attention has become greater to the relationship between neurodegeneration and abnormal insulin signaling in the central nervous system, as insulin in the brain is implicated in neuronal survival, plasticity, oxidative stress and neuroinflammation. Diabetes mellitus and Parkinson’s disease are both aging-associated diseases that are turning into epidemics worldwide. Diabetes mellitus and insulin resistance not only increase the possibility of developing Parkinson’s disease but can also determine the prognosis and progression of Parkinsonian symptoms. Today, there are no available curative or disease modifying treatments for Parkinson’s disease, but the role of insulin and antidiabetic medications in neurodegeneration opens a door to treatment repurposing to fight against Parkinson’s disease, both in diabetic and nondiabetic Parkinsonian patients. Furthermore, it is essential to comprehend how a frequent and treatable disease such as diabetes can influence the progression of neurodegeneration in a challenging disease such as Parkinson’s disease. Here, we review the present evidence on the connection between Parkinson’s disease and diabetes and the consequential implications of the existing antidiabetic molecules in the severity and development of Parkinsonism, with a particular focus on glucagon-like peptide-1 receptor agonists.

Insulin-releasing or insulin-sensitizing drugs in Parkinson's disease? Choosing a pathway

There are several reports in the literature showing an epidemiological and clinical association between type 2 diabetes mellitus and Parkinson's disease (PD). This notwithstanding, many aspects of the pathophysiological links between both diseases remain elusive. Filling this knowledge gap is important to address issues such as whether some antidiabetic drugs can be potential disease-modifying agents in PD.

Islet amyloid toxicity: From genesis to counteracting mechanisms

Islet amyloid polypeptide (IAPP or amylin) is a hormone co-secreted with insulin by pancreatic β-cells and is the major component of islet amyloid. Islet amyloid is found in the pancreas of patients with type 2 diabetes (T2D) and may be involved in β-cell dysfunction and death, observed in this disease. Thus, investigating the aspects related to amyloid formation is relevant to the development of strategies towards β-cell protection. In this sense, IAPP misprocessing, IAPP overproduction, and disturbances in intra- and extracellular environments seem to be decisive for IAPP to form islet amyloid. Islet amyloid toxicity in β-cells may be triggered in intra- and/or extracellular sites by membrane damage, endoplasmic reticulum stress, autophagy disruption, mitochondrial dysfunction, inflammation, and apoptosis. Importantly, different approaches have been suggested to prevent islet amyloid cytotoxicity, from inhibition of IAPP aggregation to attenuation of cell death mechanisms. Such approaches have improved β-cell function and prevented the development of hyperglycemia in animals. Therefore, counteracting islet amyloid may be a promising therapy for T2D treatment.

β-Hairpin Peptide Mimics Decrease Human Islet Amyloid Polypeptide (hIAPP) Aggregation

Amyloid diseases are degenerative pathologies, highly prevalent today because they are closely related to aging, that have in common the erroneous folding of intrinsically disordered proteins (IDPs) which aggregate and lead to cell death. Type 2 Diabetes involves a peptide called human islet amyloid polypeptide (hIAPP), which undergoes a conformational change, triggering the aggregation process leading to amyloid aggregates and fibers rich in β-sheets mainly found in the pancreas of all diabetic patients. Inhibiting the aggregation of amyloid proteins has emerged as a relevant therapeutic approach and we have recently developed the design of acyclic flexible hairpins based on peptidic recognition sequences of the amyloid β peptide (Aβ_1–42) as a successful strategy to inhibit its aggregation involved in Alzheimer’s disease. The present work reports the extension of our strategy to hIAPP aggregation inhibitors. The design, synthesis, conformational analyses, and biophysical evaluations of dynamic β-hairpin like structures built on a piperidine-pyrrolidine β-turn inducer are described. By linking to this β-turn inducer three different arms (i) pentapeptide, (ii) tripeptide, and (iii) α/aza/aza/pseudotripeptide, we demonstrate that the careful selection of the peptide-based arms from the sequence of hIAPP allowed to selectively modulate its aggregation, while the peptide character can be decreased. Biophysical assays combining, Thioflavin-T fluorescence, transmission electronic microscopy, capillary electrophoresis, and mass spectrometry showed that the designed compounds inhibit both the oligomerization and the fibrillization of hIAPP. They are also capable to decrease the aggregation process in the presence of membrane models and to strongly delay the membrane-leakage induced by hIAPP. More generally, this work provides the proof of concept that our rational design is a versatile and relevant strategy for developing efficient and selective inhibitors of aggregation of amyloidogenic proteins.

Living with the enemy: from protein-misfolding pathologies we know, to those we want to know

Conformational diseases are caused by the aggregation of misfolded proteins. The risk for such pathologies develops years before clinical symptoms appear, and is higher in people with alpha-1 antitrypsin (AAT) polymorphisms. Thousands of people with alpha-1 antitrypsin deficiency (AATD) are underdiagnosed. Enemy-aggregating proteins may reside in these underdiagnosed AATD patients for many years before a pathology for AATD fully develops. In this perspective review, we hypothesize that the AAT protein could exert a new and previously unconsidered biological effect as an endogenous metal ion chelator that plays a significant role in essential metal ion homeostasis. In this respect, AAT polymorphism may cause an imbalance of metal ions, which could be correlated with the aggregation of amylin, tau, amyloid beta, and alpha synuclein proteins in type 2 diabetes mellitus (T2DM), Alzheimer's and Parkinson's diseases, respectively.

Macromolecular crowding modulates α-synuclein amyloid fiber growth

The crowdedness of living cells, hundreds of milligrams per milliliter of macromolecules, may affect protein folding, function, and misfolding. Still, such processes are most often studied in dilute solutions in vitro. To assess consequences of the in vivo milieu, we here investigated the effects of macromolecular crowding on the amyloid fiber formation reaction of α-synuclein, the amyloidogenic protein in Parkinson's disease. For this, we performed spectroscopic experiments probing individual steps of the reaction as a function of the macromolecular crowding agent Ficoll70, which is an inert sucrose-based polymer that provides excluded-volume effects. The experiments were performed at neutral pH at quiescent conditions to avoid artifacts due to shaking and glass beads (typical conditions for α-synuclein), using amyloid fiber seeds to initiate reactions. We find that both primary nucleation and fiber elongation steps during α-synuclein amyloid formation are accelerated by the presence of 140 and 280 mg/mL Ficoll70. Moreover, in the presence of Ficoll70 at neutral pH, secondary nucleation appears favored, resulting in faster overall α-synuclein amyloid formation. In contrast, sucrose, a small-molecule osmolyte and building block of Ficoll70, slowed down α-synuclein amyloid formation. The ability of cell environments to modulate reaction kinetics to a large extent, such as severalfold faster individual steps in α-synuclein amyloid formation, is an important consideration for biochemical reactions in living systems.

Challenges in sample preparation and structure determination of amyloids by cryo-EM

Amyloids share a common architecture but play disparate biological roles in processes ranging from bacterial defense mechanisms to protein misfolding diseases. Their structures are highly polymorphic, which makes them difficult to study by X-ray diffraction or NMR spectroscopy. Our understanding of amyloid structures is due in large part to recent advances in the field of cryo-EM, which allows for determining the polymorphs separately. In this review, we highlight the main stepping stones leading to the substantial number of high-resolution amyloid fibril structures known today as well as recent developments regarding automation and software in cryo-EM. We discuss that sample preparation should move closer to physiological conditions to understand how amyloid aggregation and disease are linked. We further highlight new approaches to address heterogeneity and polymorphism of amyloid fibrils in EM image processing and give an outlook to the upcoming challenges in researching the structural biology of amyloids.

Role of Liquid-Liquid Separation in Endocrine and Living Cells

Context

Recent studies have revealed that every eukaryotic cell contains several membraneless organelles created via liquid–liquid phase separation (LLPS). LLPS is a physical phenomenon that transiently compartmentalizes the subcellular space and thereby facilitates various biological reactions. LLPS is indispensable for cellular functions; however, dysregulated LLPS has the potential to cause irreversible protein aggregation leading to degenerative disorders. To date, there is no systematic review on the role of LLPS in endocrinology.

Evidence acquisition

We explored previous studies which addressed roles of LLPS in living cells, particularly from the viewpoint of endocrinology. To this end, we screened relevant literature in PubMed published between 2009 and 2021 using LLPS-associated keywords including “membraneless organelle,” “phase transition,” and “intrinsically disordered,” and endocrinological keywords such as “hormone,” “ovary,” “androgen,” and “diabetes.” We also referred to the articles in the reference lists of identified papers.

Evidence synthesis

Based on 67 articles selected from 449 papers, we provided a concise overview of the current understanding of LLPS in living cells. Then, we summarized recent articles documenting the physiological or pathological roles of LLPS in endocrine cells.

Conclusions

The discovery of LLPS in cells has resulted in a paradigm shift in molecular biology. Recent studies indicate that LLPS contributes to male sex development by providing a functional platform for SOX9 and CBX2 in testicular cells. In addition, dysregulated LLPS has been implicated in aberrant protein aggregation in pancreatic β-cells, leading to type 2 diabetes. Still, we are just beginning to understand the significance of LLPS in endocrine cells.

Diabetes, insulin and new therapeutic strategies for Parkinson's disease: Focus on glucagon-like peptide-1 receptor agonists

Parkinson's disease and diabetes mellitus are two chronic disorders associated with aging that are becoming increasingly prevalent worldwide. Parkinson is a multifactorial progressive condition with no available disease modifying treatments at the moment. Over the last few years there is growing interest in the relationship between diabetes (and impaired insulin signaling) and neurodegenerative diseases, as well as the possible benefit of antidiabetic treatments as neuroprotectors, even in non-diabetic patients. Insulin regulates essential functions in the brain such as neuronal survival, autophagy of toxic proteins, synaptic plasticity, neurogenesis, oxidative stress and neuroinflammation. We review the existing epidemiological, experimental and clinical evidence that supports the interplay between insulin and neurodegeneration in Parkinson's disease, as well as the role of antidiabetic treatments in this disease.

Necessity of regulatory guidelines for the development of amyloid based biomaterials

Amyloid diseases are caused due to protein homeostasis failure where incorrectly folded proteins/peptides form cross-β-sheet rich amyloid fibrillar structures. Besides proteins/peptides, small metabolite assemblies also exhibit amyloid-like features. These structures are linked to several human and animal diseases. In addition, non-toxic amyloids with diverse physiological roles are characterized as a new functional class. This finding, along with the unique properties of amyloid like stability and mechanical strength, led to a surge in the development of amyloid-based biomaterials. However, the usage of these materials by humans and animals may pose a health risk such as the development of amyloid diseases and toxicity. This is possible because amyloid-based biomaterials and their fragments may assist seeding and cross-seeding mechanisms of amyloid formation in the body. This review summarizes the potential uses of amyloids as biomaterials, the concerns regarding their usage, and a prescribed workflow to initiate a regulatory approach.

Prediabetes, type 2 diabetes mellitus and risk of Parkinson's disease: A population-based cohort study

BACKGROUND

Association of type 2 diabetes mellitus (T2D) with subsequent Parkinson's disease (PD) has supported the link between glucose metabolism and PD. We assessed the risk of PD not only in T2D but also in prediabetes.

METHODS

We conducted a retrospective cohort study of the population attended in primary care centres of the Catalan Health Institute in Catalonia between 2006 and 2018. The data were obtained from the Information System for Research in Primary Care (SIDIAP). We created a cohort of T2D and prediabetes patients (HbA1c ≥ 5.7-6.4% without antidiabetic drugs or previous T2D diagnosis) and compared to a reference cohort. The outcome was PD diagnosis and we excluded PD before or during the first year of follow-up. We used multivariate Cox regression models to calculate hazard ratios (HR) and 95% confidence intervals (95%CI). We excluded subjects with atypical and secondary parkinsonisms.

RESULTS

The exposed cohorts comprised of 281.153 patients with T2D and 266.379 with prediabetes and a reference cohort of 2.556.928 subjects. T2D and prediabetes were associated with higher risk of PD (HRadjusted 1.19, 95%CI 1.13-1.25, and 1.07, 1.00-1.14; respectively). In analyses stratified by sex, prediabetes was only associated with PD risk in women (1.12, 1.03-1.22 vs. 1.01, 0.99-1.10 in men). When analysis was stratified by age, T2D and prediabetes were associated with a greater PD risk both in women (2.36, 1.96-2.84 and 2.10, 1.70-2.59 respectively) and men (1.74, 1.52-2.00 and 1.90, 1.57-2.30 respectively) below 65 years-old.

CONCLUSIONS

We report for the first time that prediabetes increases the odds of subsequent PD and replicate the association with established T2D. Both associations predominate in women and young individuals.

Linking Parkinson's Disease and Melanoma: Interplay Between α-Synuclein and Pmel17 Amyloid Formation

Parkinson's disease (PD) is a neurodegenerative disorder associated with the death of dopaminergic neurons within the substantia nigra of the brain. Melanoma is a cancer of melanocytes, pigmented cells that give rise to skin tone, hair, and eye color. Although these two diseases fundamentally differ, with PD leading to cell degeneration and melanoma leading to cell proliferation, epidemiological evidence has revealed a reciprocal relationship where patients with PD are more susceptible to melanoma and patients with melanoma are more susceptible to PD. The hallmark pathology observed in PD brains is intracellular inclusions, of which the primary component is proteinaceous α-synuclein (α-syn) amyloid fibrils. α-Syn also has been detected in cultured melanoma cells and tissues derived from patients with melanoma, where an inverse correlation exists between α-syn expression and pigmentation. Although this has led to the prevailing hypothesis that α-syn inhibits enzymes involved in melanin biosynthesis, we recently reported an alternative hypothesis in which α-syn interacts with and modulates the aggregation of Pmel17, a functional amyloid that serves as a scaffold for melanin biosynthesis. In this perspective, we review the literature describing the epidemiological and molecular connections between PD and melanoma, presenting both the prevailing hypothesis and our amyloid-centric hypothesis. We offer our views of the essential questions that remain unanswered to motivate future investigations. Understanding the behavior of α-syn in melanoma could not only provide novel approaches for treating melanoma but also could reveal insights into the role of α-syn in PD. © 2021 International Parkinson and Movement Disorder Society.