The Library Derived 4554W Peptide Inhibits Primary Nucleation of α-Synuclein

Misfolded protein oligomers: mechanisms of formation, cytotoxic effects, and pharmacological approaches against protein misfolding diseases

The conversion of native peptides and proteins into amyloid aggregates is a hallmark of over 50 human disorders, including Alzheimer's and Parkinson's diseases. Increasing evidence implicates misfolded protein oligomers produced during the amyloid formation process as the primary cytotoxic agents in many of these devastating conditions. In this review, we analyze the processes by which oligomers are formed, their structures, physicochemical properties, population dynamics, and the mechanisms of their cytotoxicity. We then focus on drug discovery strategies that target the formation of oligomers and their ability to disrupt cell physiology and trigger degenerative processes.

Peptide-based approaches to directly target alpha-synuclein in Parkinson's disease

Peptides and their mimetics are increasingly recognised as drug-like molecules, particularly for intracellular protein-protein interactions too large for inhibition by small molecules, and inaccessible to larger biologics. In the past two decades, evidence associating the misfolding and aggregation of alpha-synuclein strongly implicates this protein in disease onset and progression of Parkinson's disease and related synucleinopathies. The subsequent formation of toxic, intracellular, Lewy body deposits, in which alpha-synuclein is a major component, is a key diagnostic hallmark of the disease. To reach their therapeutic site of action, peptides must both cross the blood-brain barrier and enter dopaminergic neurons to prevent the formation of these intracellular inclusions. In this review, we describe and summarise the current efforts made in the development of peptides and their mimetics to directly engage with alpha-synuclein with the intention of modulating aggregation, and importantly, toxicity. This is a rapidly expanding field with great socioeconomic impact; these molecules harbour significant promise as therapeutics, or as early biomarkers during prodromal disease stages, or both. As these are age-dependent conditions, an increasing global life expectancy means disease prevalence is rising. No current treatments exist to either prevent or slow disease progression. It is therefore crucial that drugs are developed for these conditions before health care and social care capacities become overrun.

Citrus Flavonoid Hesperetin Inhibits α-Synuclein Fibrillogenesis, Disrupts Mature Fibrils, and Reduces Their Cytotoxicity: In Vitro and In Vivo Studies

Misfolding and subsequent fibrillogenesis of α-synuclein (αSN) significantly influence the development of Parkinson's disease (PD). This study reports the inhibitory effect of citrus flavonoid hesperetin (Hst) on αSN fibrillation. Based on thioflavin T fluorometry and atomic force microscopy studies, Hst inhibited αSN fibrillation by interfering with initial nucleation and slowing the elongation rate. Furthermore, the inhibitory effect was concentration-dependent with a half-maximal inhibitory concentration of 24.4 μM. Cytotoxicity experiments showed that 100 μM Hst significantly reduced the cytotoxicity of αSN aggregates and maintained 98.4% cell activity. In addition, Hst disassembled the preprepared αSN fibrils into smaller and less-toxic aggregates. Excitingly, supplementation with 100 μM Hst inhibited the accumulation of 36.3% αSN in NL5901 and restored the amyloid-induced reduction in NL5901 lipid abundance, extending the mean lifespan of NL5901 to 23 d. These findings could support the use of Hst as a dietary supplement to regulate αSN fibrillation and prevent the development of PD.

Development of a hydroxyflavone-labelled 4554W peptide probe for monitoring αS aggregation

Parkinson's is the second most common neurodegenerative disease, with the number of individuals susceptible due to increase as a result of increasing life expectancy and a growing worldwide population. However, despite the number of individuals affected, all current treatments for PD are symptomatic-they alleviate symptoms, but do not slow disease progression. A major reason for the lack of disease-modifying treatments is that there are currently no methods to diagnose individuals during the earliest stages of the disease, nor are there any methods to monitor disease progression at a biochemical level. Herein, we have designed and evaluated a peptide-based probe to monitor αS aggregation, with a particular focus on the earliest stages of the aggregation process and the formation of oligomers. We have identified the peptide-probe K1 as being suitable for further development to be applied to number of applications including: inhibition of αS aggregation; as a probe to monitor αS aggregation, particularly at the earliest stages before Thioflavin-T is active; and a method to detect early-oligomers. With further development and in vivo validation, we anticipate this probe could be used for the early diagnosis of PD, a method to evaluate the effectiveness of potential therapeutics, and as a tool to help in the understanding of the onset and development of PD.

Alpha Synuclein: Neurodegeneration and Inflammation

Alpha-Synuclein (α-Syn) is one of the most important molecules involved in the pathogenesis of Parkinson's disease and related disorders, synucleinopathies, but also in several other neurodegenerative disorders with a more elusive role. This review analyzes the activities of α-Syn, in different conformational states, monomeric, oligomeric and fibrils, in relation to neuronal dysfunction. The neuronal damage induced by α-Syn in various conformers will be analyzed in relation to its capacity to spread the intracellular aggregation seeds with a prion-like mechanism. In view of the prominent role of inflammation in virtually all neurodegenerative disorders, the activity of α-Syn will also be illustrated considering its influence on glial reactivity. We and others have described the interaction between general inflammation and cerebral dysfunctional activity of α-Syn. Differences in microglia and astrocyte activation have also been observed when in vivo the presence of α-Syn oligomers has been combined with a lasting peripheral inflammatory effect. The reactivity of microglia was amplified, while astrocytes were damaged by the double stimulus, opening new perspectives for the control of inflammation in synucleinopathies. Starting from our studies in experimental models, we extended the perspective to find useful pointers to orient future research and potential therapeutic strategies in neurodegenerative disorders.

Anionic lipid vesicles have differential effects on the aggregation of early onset-associated α-synuclein missense mutants

α-synuclein (αS) is the key component of synucleinopathies such as Parkinson's disease (PD), dementia with Lewy bodies, and multiple system atrophy. αS was first linked to PD through the identification of point mutations in the SNCA gene, causing single amino acid substitutions within αS and familial autosomal dominant forms of PD that profoundly accelerated disease onset by up to several decades. At least eight single-point mutations linked to familial PD (A30G/P, E46K, H50Q, G51D, and A53T/E/V) are located in proximity of the region preceding the non-β amyloid component (preNAC) region, strongly implicating its pathogenic role in αS-mediated cytotoxicity. Furthermore, lipids are known to be important for native αS function, where they play a key role in the regulation of synaptic vesicle docking to presynaptic membranes and dopamine transmission. However, the role of lipids in the function of mutant αS is unclear. Here, we studied αS aggregation properties of WT αS and five of the most predominant single-point missense mutants associated with early onset PD in the presence of anionic 1,2-dimyristoyl-sn-glycero-3-phospho-l-serine lipid vesicles. Our results highlight significant differences between aggregation rates, the number of aggregates produced, and overall fibril morphologies of WT αS and the A30P, E46K, H50Q, G51D, and A53T missense mutants in the presence of lipid vesicles. These findings have important implications regarding the interplay between the lipids required for αS function and the individual point mutations known to accelerate PD and related diseases.

Library-Derived Peptide Aggregation Modulators of Parkinson's Disease Early-Onset α-Synuclein Variants

Parkinson's Disease (PD) is characterized by the accumulation of Lewy bodies in dopaminergic neurons. The main protein component of Lewy bodies, α-synuclein (αS), is also firmly linked to PD through the identification of a number of single point mutations that are autosomal dominant for early-onset disease. Consequently, the misfolding and subsequent aggregation of αS is thought to be a key stage in the development and progression of PD. Therefore, modulating the aggregation pathway of αS is an attractive therapeutic target. Owing to the fact that all but one of the familial mutations is located in the preNAC 45-54 region of αS, we previously designed a semi-rational library using this sequence as a design scaffold. The 45-54 peptide library was screened using a protein-fragment complementation assay approach, leading to the identification of the 4554W peptide. The peptide was subsequently found to be effective in inhibiting primary nucleation of αS, the earliest stage of the aggregation pathway. Here, we build upon this previous work by screening the same 45-54 library against five of the known αS single-point mutants that are associated with early-onset PD (A30P, E46K, H50Q, G51D, and A53T). These point mutations lead to a rapid acceleration of PD pathology by altering either the rate or type of aggregates formed. All ultimately lead to earlier disease onset and were therefore used to enforce increased assay stringency during the library screening process. The ultimate aim was to identify a peptide that is effective against not only the familial αS variant from which it has been selected but that is also effective against WT αS. Screening resulted in five peptides that shared common residues at some positions, while deviating at others. All reduced aggregation of the respective target, with several also identified to be effective at reducing aggregation when incubated with other variants. In addition, our results demonstrate that a previously optimized peptide, 4554W(N6A), is highly effective against not only WT αS but also several of the single-point mutant forms and hence is a suitable baseline for further work toward a PD therapeutic.

A Thermodynamic Model for Interpreting Tryptophan Excitation-Energy-Dependent Fluorescence Spectra Provides Insight Into Protein Conformational Sampling and Stability

It is now over 30 years since Demchenko and Ladokhin first posited the potential of the tryptophan red edge excitation shift (REES) effect to capture information on protein molecular dynamics. While there have been many key efforts in the intervening years, a biophysical thermodynamic model to quantify the relationship between the REES effect and protein flexibility has been lacking. Without such a model the full potential of the REES effect cannot be realized. Here, we present a thermodynamic model of the tryptophan REES effect that captures information on protein conformational flexibility, even with proteins containing multiple tryptophan residues. Our study incorporates exemplars at every scale, from tryptophan in solution, single tryptophan peptides, to multitryptophan proteins, with examples including a structurally disordered peptide, de novo designed enzyme, human regulatory protein, therapeutic monoclonal antibodies in active commercial development, and a mesophilic and hyperthermophilic enzyme. Combined, our model and data suggest a route forward for the experimental measurement of the protein REES effect and point to the potential for integrating biomolecular simulation with experimental data to yield novel insights.

A Downsized and Optimised Intracellular Library-Derived Peptide Prevents Alpha-Synuclein Primary Nucleation and Toxicity Without Impacting Upon Lipid Binding

Misfolding and aggregation of alpha-synuclein (αS) within dopaminergic neurons is a key factor in the development and progression of a group of age-related neurodegenerative diseases, termed synucleinopathies, that include Parkinson's disease (PD). We previously derived a peptide inhibitor from a 209,952-member intracellular library screen by employing the preNAC region (45-54) as a design template. At least six single-point mutations firmly linked to early-onset Parkinson's disease (E46K, H50Q, G51D, A53T/E/V) are located within this region, strongly implicating a pathogenic role within αS that leads to increased cytotoxicity. A library-derived ten residue peptide, 4554W, was consequently shown to block αS aggregation at the point of primary nucleation via lipid induction, inhibiting its conversion into downstream cytotoxic species. Here we couple truncation with a full alanine scan analysis, to establish the effect upon the αS aggregation pathway relative to 4554W. This revealed the precise residues responsible for eliciting inhibitory interaction and function, as well as those potentially amenable to modification or functionalisation. We find that modification N6A combined with N-terminal truncation results in a peptide of significantly increased efficacy. Importantly, our data demonstrate that the peptide does not directly disrupt αS lipid-binding, a desirable trait since antagonists of αS aggregation and toxicity should not impede association with small synaptic neurotransmitter vesicles, and thus not disrupt dopaminergic vesicle fusion and recycling. This work paves the way toward the major aim of deriving a highly potent peptide antagonist of αS pathogenicity without impacting on native αS function.

Regulation of diurnal energy balance by mitokines

The mammalian system of energy balance regulation is intrinsically rhythmic with diurnal oscillations of behavioral and metabolic traits according to the 24 h day/night cycle, driven by cellular circadian clocks and synchronized by environmental or internal cues such as metabolites and hormones associated with feeding rhythms. Mitochondria are crucial organelles for cellular energy generation and their biology is largely under the control of the circadian system. Whether mitochondrial status might also feed-back on the circadian system, possibly via mitokines that are induced by mitochondrial stress as endocrine-acting molecules, remains poorly understood. Here, we describe our current understanding of the diurnal regulation of systemic energy balance, with focus on fibroblast growth factor 21 (FGF21) and growth differentiation factor 15 (GDF15), two well-known endocrine-acting metabolic mediators. FGF21 shows a diurnal oscillation and directly affects the output of the brain master clock. Moreover, recent data demonstrated that mitochondrial stress-induced GDF15 promotes a day-time restricted anorexia and systemic metabolic remodeling as shown in UCP1-transgenic mice, where both FGF21 and GDF15 are induced as myomitokines. In this mouse model of slightly uncoupled skeletal muscle mitochondria GDF15 proved responsible for an increased metabolic flexibility and a number of beneficial metabolic adaptations. However, the molecular mechanisms underlying energy balance regulation by mitokines are just starting to emerge, and more data on diurnal patterns in mouse and man are required. This will open new perspectives into the diurnal nature of mitokines and action both in health and disease.