Parkinson’s disease (PD) is recognized as the second most common neurodegenerative disease (Du et al., 2020; Serratos et al., 2022) and is part of a heterogeneous group of disorders, so-called synucleinopathies, that include dementia with Lewy bodies (DLB), multiple system atrophy (MSA) (So and Watts, 2023) among others. As referred to by their name, a common hallmark of these disorders is the abnormal accumulation of α-synuclein (α-syn) (encoded by the SNCA gene), in neurons and neurites, glia, and presynaptic terminals (Kramer and Schulz-Schaeffer, 2007). In these, α-syn accumulates as inclusions in the form of Lewy bodies (LB) and Lewy neurites (LN) collectively referred to as Lewy pathology (LP) (Spillantini et al., 1997; Goedert et al., 2017; Killinger et al., 2022). Whereas in MSA, the inclusions found in oligodendrocytes are called glial cell inclusions (GCIs) (Kramer and Schulz-Schaeffer, 2007).

Identifying genetic defects related to the α-syn gene, such as mutations and copy number variations in families with hereditary disorders, reinforces its significance (SNCA Gene: MedlinePlus Genetics, 2021). Consequently, it is well-established that α-syn is the central protein involved in the pathology of several neurodegenerative diseases, including PD and other synucleinopathies (Lee and Trojanowski, 2006; Poulopoulos et al., 2012; Goedert, 2015; Ugalde et al., 2016; Cremades et al., 2017; Meade et al., 2019; Du et al., 2020). The presence of α-syn inclusions is a defining feature of these conditions, and research has primarily focused on the pathological (aggregated) forms of α-syn as the main factor in neurodegeneration, a conclusion that remains well-supported today. Despite this, the fundamental aspects that concern α-syn and its role in the underlying pathogenesis of PD and other synucleinopathies remain unknown, and the details about how α-syn mediates toxicity are not fully elucidated. Furthermore, growing evidence indicates a significant variability in clinical and pathological manifestations between different synucleinopathies, and, more strikingly, this variability also exists within the same disease entity (So and Watts, 2023). To reveal what could be a potential reason for such inconsistency among a group of disorders caused by the same protein, we will collect the current knowledge with particular attention to the environmental factors and conditions that may contribute to α-syn structural re-arrangement, leading to the formation of various strains of α-syn aggregates, with differential toxicity patterns. Furthermore, we will also focus on exploring the abnormal formation of a phenomenon called liquid–liquid phase separation (LLPS), cellular stress leading to chronic neuroinflammation and immune dysregulation, as well as the potential role of LLPS in α-syn pathology. We will also aim to explore how the variability of the α-syn aggregate might be related to pathological manifestations at the cellular level. This information is vital to understanding the current experimental models and ongoing development of disease-modifying and diagnostic tools.

Numerous studies indicate that the hallmark pathological features of synucleinopathies primarily arise from the abnormal folding of α-syn and its subsequent aggregation into intracellular inclusions (Grosso Jasutkar et al., 2022). This process contributes to the formation of potentially toxic α-syn species, which may also have the capacity to propagate throughout the brain in a prion-like neuron-to-neuron manner (Jan et al., 2021). Consequently, understanding the various structural modifications of α-syn is crucial for elucidating the onset and progression of these diseases. Under abnormal conditions, native monomeric and soluble α-syn undergoes a conformational shift from a random coil to a β-sheet structure. This transition leads to the formation of non-filamentous α-syn species that are on-pathway to further polymerization and aggregation, resulting in oligomers and protofibrils. The accumulation of these species promotes self-assembly and subsequent aggregation, ultimately leading to the formation of highly ordered, cross-β-sheet insoluble fibrils, as reviewed by Goedert (2015); Cremades and Dobson (2018); Du et al. (2020), and So and Watts (2023).The insoluble fibrils, together with crowded organelle components such as lipids, vesicular structures, damaged lysosomes, mitochondria, and other proteins within dying neurons eventually form the characteristic inclusions, such as Lewy pathology (LP) (Cremades et al., 2012; Shahmoradian et al., 2019; Fanning et al., 2020; Scheiblich et al., 2021).

The aggregation of α-syn follows a mechanism of nucleation-dependent polymerization pathway, with sigmoidal growth kinetics (Wood et al., 1999). This process consists of three separate phases (Figure 1). First, the lag phase where events are mainly thermodynamically unfavorable due to a high free energy barrier for abnormal aggregation. During this phase, native soluble and monomeric α-syn slowly polymerizes to form aggregation-competent species called nuclei. When α-syn nuclei reach a critical size, it acts as a seed that nucleates the aggregation pathway. At this stage, intermolecular interactions within the α-syn assemblies promote stability and prevent their dissolution. The second phase is the elongation or exponential growth in which the α-syn nuclei rapidly convert into oligomers, protofibrils, and fibrils by attaching monomeric α-syn onto them. Interestingly, the fibril growth involves different mechanisms, such as surface-mediated secondary nucleation which is templated by already formed fibrils catalyzing the aggregation process; fibril fragmentation, a process that generates multiple short fibrils that can template misfolding and assembly, as well as elongation (Gaspar et al., 2017). The third phase, the stationary phase, is where most of the soluble α-syn has been converted into insoluble amyloid-like fibrils and a steady state equilibrium is achieved between the fibrils and the monomers (Gaspar et al., 2017). It is important to mention that the initial misfolding and transformation of α-syn is poorly understood. However, it is quite established that the structural transition from random coil to β-sheet-rich insoluble fibrils relates to pathology and can happen in a sequence of events or through ramifications of the classical aggregation pathway, as reviewed in (Miraglia et al., 2018).

It is widely accepted that intermediates, both non-filamentous species such as oligomers, and filamentous intermediates, known as protofibrils are the toxic species that lead to neuronal death (Sharon et al., 2003; Karpinar et al., 2009; Winner et al., 2012; Cremades et al., 2017; Cremades and Dobson, 2018; Vicario et al., 2018; Ugalde et al., 2019; Meade et al., 2019; Lövestam et al., 2021; Emin et al., 2022; Gadhe et al., 2022). These species exist in a thermodynamically metastable environment where they can be kinetically trapped (with a minimum local free energy) and are prone to transform into different structural conformations (Ghosh and Ranjan, 2020) (Figure 2). However, they must overcome an energy barrier to achieve a stable and highly ordered conformation, and this transformation does not occur spontaneously depending on various environmental conditions, such as α-syn posttranslational modifications (PTM) and mutations, alternative splicing of the coding exons, chaperone proteins, lipids, and other factors. These conditions help to reduce the kinetic barrier, accelerating α-syn aggregation (Vidović and Rikalovic, 2022). Additionally, during the formation of different α-syn conformational states, only those sufficiently stable will persist and grow to form filaments (Peelaerts et al., 2018). This metastable character is the reason why these α-syn intermediate species can quickly change their morphological and biochemical properties (surface properties), forming a short-lived transient population that coexists as heterogeneous conformations (structurally unique aggregates), more commonly called strains. The existence of this short-lived and transient population also explains why their structural characterization is extremely complicated (Meade et al., 2019; Du et al., 2020; Han et al., 2024).

Intermediate species such as α-syn oligomers have been described as soluble (as opposed to fibrils) although they possess a varying degree of hydrophobicity (Chen et al., 2015; Lee et al., 2018). Some oligomers can have different sizes, structures, and morphologies (Emin et al., 2022), for instance spherical, cylindrical or annular, chain-shaped, and also tubular (Miraglia et al., 2018). Some oligomers have an intermediate β-sheet content between monomers and fibrils (Hong et al., 2008; Chen et al., 2015). In addition, some of these can adopt a β-sheet structure with an antiparallel arrangement (stabilized oligomers-kinetically trapped) (Chen et al., 2015) that differs from the classical β-sheet geometry. This could influence oligomer toxicity (Celej et al., 2012) or monomer binding capacity, as species with antiparallel arrangements are less stable and less efficient at elongating (Chen et al., 2015). Other evidence supports the hypothesis that these heterogeneous conformations show toxic disparity depending on the different structures [reviewed by Meade et al. (2019); Du et al. (2020), So and Watts (2023), and Han et al. (2024)]. For instance, ultrastructural analysis has shown that oligomers with cylindrical or donut-shaped conformation may interact favorably with hydrophobic membranes contributing to toxicity (Chen et al., 2015; Meade et al., 2019). Although small oligomers are kinetically unstable and can dissociate into monomeric forms (Chen et al., 2015; Meade et al., 2019), some evidence suggests that this less stable form of α-syn induces greater toxicity when compared to other species (Chen et al., 2015; Meade et al., 2019). Conversely, fibrillar forms of α-syn, that are recognized to be kinetically more stable compared to oligomeric and intermediate species (Chen et al., 2015; Bisi et al., 2021), can sequester toxic oligomers and eventually convert them into more thermodynamically stable fibrils, leading to potential beneficial outcomes for cells [as reviewed Gadhe et al. (2022)].

Although α-syn fibrils are generally considered less toxic than their intermediate species, their pathological role remains significant [as recently reviewed by Bigi et al. (2023)]. For instance, small α-syn fibrils are known to bind efficiently to cell surface receptors, such as heparin sulfate proteoglycans (Holmes et al., 2013) and possess a strong capacity to disrupt cellular membranes and other processes, including mitochondrial function [reviewed by Domingues et al. (2022)]. Moreover, α-syn fibrils are highly prone to fragmentation within cells, leading to the formation of numerous small structures. These fragments act as potent seeds, facilitating the propagation of toxic, misfolded α-syn aggregates to neighboring brain regions (Luk et al., 2012; Masuda-Suzukake et al., 2013; Volpicelli-Daley et al., 2011, 2014; Thakur et al., 2017; Cascella et al., 2021; Bigi et al., 2021, 2022). These findings underscore the pivotal role of prion-like behavior and propagation in the clinical manifestations of human diseases [as reviewed by Bigi et al. (2023) and Gadhe et al. (2022)]. Determination of α-syn conformational strains has been linked more frequently to fibrils, as small oligomeric species lack ordered structures and stable conformations. Therefore, studying their properties using common methods, such as cryo-electron microscopy (cryo-EM) (Schweighauser et al., 2020; Yang et al., 2022) or solid-state NMR spectroscopy (Heise et al., 2005; Gath et al., 2014; Tuttle et al., 2016; Li et al., 2018a; Li et al., 2018b; Cao et al., 2019; Kollmer et al., 2019) is complicated. However, α-syn fibrillar forms have been well characterized based on diameter, proto-filament packing, number of twists and side chain interactions, and relative resistance to proteolytic enzymes (Gath et al., 2014; Li et al., 2018b; Guerrero-Ferreira et al., 2019).

An increasing number of observations report the presence of different conformational strains of endogenous α-syn in postmortem brains of patients suffering from PD, MSA, and DLB [as reviewed in Peelaerts et al. (2018) and more recently in Wojewska et al. (2023)]. This leads to the hypothesis that α-syn may adopt different disease-causing conformations that determine the destiny of pathology and may manifest in individual clinical phenotypes (Figure 3) (Peelaerts et al., 2015; Peng et al., 2018b; Peng et al., 2018a; Rey et al., 2019; Lau et al., 2020; Shahnawaz et al., 2020; Holec et al., 2022; Khedmatgozar et al., 2024). Supporting this hypothesis, it has been reported that various conformations of α-syn inclusions generated in vitro (referred by the authors as fibrils, ribbons, fibrils-91, fibrils-65, and fibrils-110) lead to differential binding and clustering in the neuronal membrane (Shrivastava et al., 2020). This results in distinct patterns of synaptic receptor redistribution in primary neuronal cultures and organotypic cultures of hippocampal slices from wild-type mice (Shrivastava et al., 2020). Furthermore, conformation-dependent seeding activity and alteration in neuronal network activity after seeded α-syn aggregation were also observed, affecting neuronal homeostasis through the redistribution of synaptic proteins (Shrivastava et al., 2020). In MSA patients, immuno-EM and cryo-EM analysis revealed the existence of two distinct α-syn filament types, characterized by the asymmetric packing of the two protofilaments that compose them, in addition to an extended N-terminal arm and a compact C-terminal body. More interestingly, both structures show a central cavity that incorporates non-protein molecules, suggesting the involvement of various factors and co-factors during their formation. The two reported MSA aggregates are distinct from those isolated from the brains of PD, Parkinson’s disease dementia (PDD), and DLB patients, where a single untwisted protofilament typically forms fibrillar inclusions (Tarutani et al., 2018; Schweighauser et al., 2020). However, a subpopulation of twisted aggregates has also been described in DLB (Yang et al., 2022). These MSA structures also differ from those obtained in vitro using recombinant α-syn (Schweighauser et al., 2020). Aggregates from PD, PDD, and DLB patients have a unique structural feature known as the Lewy fold, characterized by a salt bridge between residues E35 and K80. In contrast, MSA structures exhibit a salt bridge between residues E46 and K80 (So and Watts, 2023).

As different structural features between distinct conformations, some biochemical characteristics could also define these strains among human synucleinopathies. For instance, the exposure of recognition sites of proteins to enzymatic digestion agents generates various proteolytic fragments. Differences in protease resistance (PK and TL digestion) have been reported in α-syn fibrils isolated from LB (LB-α-syn) and MSA brains (GCI-α-syn), the latter being the more resistant to protease digestion (Peng et al., 2018a). A recent study reported that α-syn fibrils isolated from MSA brains gradually disappear after PK treatment but are not digested into small fragments as seen in filaments from PDD and DLB. This suggests that α-syn fibrils from MSA brains are more easily digestible and exhibit characteristic biochemical instability (Lee et al., 2024). This is important because greater resistance could be related to a slower degradation rate of α-syn species, potentially leading to a more efficient propagation of α-syn pathology in MSA (So and Watts, 2023). These propagation properties are related to the high ability of α-syn species to act as seeds that can be taken up by cells and template the misfolding of monomeric α-syn (So and Watts, 2023). It has been demonstrated that MSA-related aggregates are more potent than Lewy body inclusions (LB-α-syn) in seeding α-syn aggregation and maintain their high seeding activity when propagated in neurons (Peng et al., 2018a). This is in line with other findings showing that α-syn inclusions from MSA brains are less resistant to denaturation by detergents such as guanidine hydrochloride (GdnHCl) (Lau et al., 2020; Martinez-Valbuena et al., 2022; Lee et al., 2024) and sodium dodecyl sulfate (SDS) (Campbell et al., 2001) compared to α-syn fibrils from both DLB (Lau et al., 2020; Martinez-Valbuena et al., 2022; Lee et al., 2024) and PD (Lau et al., 2020; Martinez-Valbuena et al., 2022). Detergents such as GdnHCl, can act as chaotropic agents and denature through interactions with the polar regions of α-syn. Therefore, greater resistance to strong detergents suggests greater stability or less polar interactions within the protein. This is supported by previous observations in which upon exposure of human samples to SDS, more insoluble species are generated in DLB and PD than in MSA samples (Campbell et al., 2001) α-syn fibrils from MSA are smaller and more fragile as well as both more compact (in terms of packaging) and prone to recruit native α-syn molecules to form aggregates and filaments (seeding activity) compared to other filaments (So and Watts, 2023), such as LB human brains (Prusiner et al., 2015; Woerman et al., 2015; Peng et al., 2018b; Yamasaki et al., 2019). MSA fibrils are more easily fragmented by detergents (due to less conformational stability). Fragmentation of α-syn fibrils produces newly formed nuclei that can then catalyze additional misfolding and aggregation of monomeric α-syn, resulting in an exponential amplification of the original seed. This in turn may increase their propensity to seed and spread its aggregation (Peng et al., 2018a; Peng et al., 2018b). This is supported by the more rapid progression as well as the poor prognosis of MSA (Foubert-Samier et al., 2020; So and Watts, 2023; Wojewska et al., 2023). These findings are consistent with the notion that different α-syn strains underlie PD and MSA (Yamasaki et al., 2019) and highlight the importance of conformational stability as a possible explanation for the more rapid rates of disease progression in MSA compared to PD (So and Watts, 2023). This also supports the hypothesis that both the onset and progression of the disease are specific to each strain (as recently reviewed by Khedmatgozar et al., 2024). These stages are determined by the amount of energy required for the α-syn monomer to transform into a certain conformation which varies across different pathologies, such as MSA and PD (Khedmatgozar et al., 2024). The α-syn protein misfolding cyclic amplification (PMCA) method, known as α-syn-PMCA assay (Shahnawaz et al., 2020) or α-syn-RT-QuIC assay (Fairfoul et al., 2016; Groveman et al., 2018; Nakagaki et al., 2021) have been used to discriminate between cerebrospinal fluid samples from patients diagnosed with PD and MSA and is based on the seeding-nucleation mechanism to amplify small amounts of α-syn oligomers to facilitate their detection by other biological methods. The use of α-syn-PMCA assay has contributed to generating additional evidence indicating that α-syn aggregates associated with PD and MSA correspond to different conformational strains of α-syn (Shahnawaz et al., 2020). These studies highlight that the various forms of α-syn involved in synucleinopathies may lead to distinct pathological manifestations due to their conformational differences. Therefore, it is crucial to understand, how the surrounding environment influences the conformational properties of α-syn and the events that trigger its aggregation and inclusion formation.

Increasing evidence highlights that oligomers and protofilaments are the most neurotoxic species responsible for dopaminergic neurodegeneration in PD (Sharon et al., 2003; Karpinar et al., 2009; Cremades et al., 2017; Gadhe et al., 2022). To unravel the mechanisms behind α-syn pathology in neurodegeneration, it is crucial to comprehend the events that initiate the transformation of monomeric α-syn into its pathological forms. However, the key processes driving this transformation, and the subsequent onset of pathology remain poorly understood. Recent emerging evidence suggests that a phenomenon called liquid–liquid phase separation (LLPS) occurs as an early event preceding the aggregation of α-syn associated with neurodegeneration (Elbaum-Garfinkle, 2019; Ray et al., 2020; Zbinden et al., 2020). LLPS is a physiological, spontaneous, and reversible process through which various components, such as proteins and nucleic acids, organize into membrane-less bodies resembling liquids, known as biomolecular condensates (Banani et al., 2016; Wegmann et al., 2018). LLPS enables the formation of distinct compartments that are isolated from the surrounding environment, facilitating specialized functions and biochemical reactions within these compartments (Banani et al., 2016; Boeynaems et al., 2018; Alberti et al., 2019; Wang et al., 2021; Gouveia et al., 2022; Hou et al., 2023). Although LLPS formation has been described under normal physiological conditions, this phenomenon has also been observed in relevant neurodegenerative disorders (Wegmann et al., 2018; Borcherds et al., 2021; Darling and Shorter, 2021; Hardenberg et al., 2021; Kanaan et al., 2020; Ray et al., 2020; Sprunger and Jackrel, 2021; Ziaunys et al., 2024). For this reason, the formation of LLPS has recently been proposed as a mechanism potentially underlying PD and other neurodegenerative diseases (Hou et al., 2023; Mukherjee et al., 2023; Han et al., 2024).

Studies have shown that soluble α-syn can undergo LLPS to form droplets, which result from interactions between its negatively charged regions and positively charged molecules in the environment (Mukherjee et al., 2023). These droplets might act as intermediates in the transition from native α-syn to its aggregated disease-associated form. Over time, the droplets can undergo a liquid-to-solid phase transition, eventually forming a gel-like structure with embedded oligomers and filaments (Ray et al., 2020; Mukherjee et al., 2023; Han et al., 2024; Ziaunys et al., 2024). LLPS and condensate formation have been proposed as an alternative aggregation mechanism and may potentially underlie the basis of neurodegenerative diseases (Figure 4) (Hou et al., 2023; Mukherjee et al., 2023; Han et al., 2024). Furthermore, this alternative mechanism could be key to understand the factors that trigger α-syn misfolding and conformational changes with the development of pathology, influenced by environmental conditions. Specifically, this aggregation pathway is affected by the crowded nature of the cellular environment (Mukherjee et al., 2023). Additionally, different aggregation routes can explain the diverse conformational strains of α-syn, which in turn may account for the varying clinical presentations of PD and other synucleinopathies (Lashuel et al., 2013; Koga et al., 2021). Recent research supports this hypothesis by comparing α-syn aggregates formed under conditions that either promote or inhibit LLPS (Ziaunys et al., 2024). A study found that when LLPS was encouraged, using a crowding agent and high protein concentrations, α-syn formed a diverse range of structures with various shapes and secondary structures. Conversely, in conditions that inhibit LLPS, such as low protein concentration and no crowding agents, different aggregate forms were observed (Ziaunys et al., 2024). The authors highlight the relevance that this could have in the context of LLPs formed in vivo, given the abundance and rapid formation of these aggregates. This process may play an important role in both the onset and progression of these disorders (Ziaunys et al., 2024) which can be extrapolated to the severity of the pathological manifestations. Furthermore, some of these structures could have greater toxicity and more efficiently catalyze the conversion of native α-syn protein, compared to aggregates formed through a different pathway. Additionally, this study suggests that the formation of LLPS and condensate could be a critical event in the appearance of conformational strains. Another research team developed a cell model to explore how fibrillary seeds interact with synthetic α-syn condensates, shedding light on their role in driving prion-like disease progression (Piroska et al., 2023). Interestingly, the presence of pre-formed condensates prompts the transition of α-syn (exogenous fibrillary seeds) from a liquid to a solid-like state through phase separation, resulting in the formation of needle-shaped amyloid structures within the condensates in cells (Piroska et al., 2023). This finding supports the idea that α-syn condensates may play a crucial role in initiating pathology and potentially drive its subsequent spread. Additionally, the study observed that different strains of α-syn fibrils lead to a remodeling of these condensates over time (Piroska et al., 2023).

As discussed previously, electrostatic, and hydrophobic interactions are important in the aggregation process, likewise, these interactions can also modulate the formation of LLPS (Gallardo et al., 2020; Sawner et al., 2021; Huang et al., 2022). For example, metal ions can influence the progression of α-syn phase separation, while this process can be reversed by metal ion chelators (Ray et al., 2020; Sawner et al., 2021; Huang et al., 2022; Xu et al., 2022b). Similarly, α-syn protein modifications, such as A53T and E46K mutations, may contribute to the modulation of α-syn LLPS and fibril formation (Ray et al., 2020). PTMs also mediate α-syn LLPS modulation. For example, S129 phosphorylation accelerates α-syn LLPS and its amyloid transition (Ray et al., 2020; Hou et al., 2023). In contrast, N-terminal acetylation increases protein solubility and delays α-syn LLPS (Ray et al., 2020). Binding to negatively charged lipids promotes the folding of α-syn into a tighter conformation leading to the rapid formation of filaments (Fusco et al., 2017) and LLPS. Although the α-syn LLPS formation has been recently established as a potential factor in pathology, the mechanism underlying its toxicity remains unknown. It has recently been proposed that under physiological conditions droplets could be highly regulated by cellular machinery. In contrast, alterations in proteostasis in an environment appropriate for the development of the disease could trigger irreversible and aberrant phase separation that leads to subsequent aggregation and pathology (Hou et al., 2023).

In the next section, we will now attempt to briefly explore the potential relationship between α-syn, the LLPS phenomenon, and relevant cellular processes such as mitophagy regulation, which plays an essential role in the pathogenesis of PD.

A variety of studies have explored strategies targeting α-syn to treat human synucleinopathies (McFarthing et al., 2023; Price et al., 2018; Wagner et al., 2013; Perni et al., 2017; Staats et al., 2020; Chia et al., 2023), highlighting their potential to generate encouraging results. Thus, α-syn-targeting therapies based on active immunization (Poewe et al., 2021; Volc et al., 2020; Eijsvogel et al., 2024), passive immunization (Lang et al., 2022; Pagano et al., 2022) as well as the use of α-syn aggregation inhibitors (Wagner et al., 2013; Smit et al., 2022; Prince et al., 2023) have achieved promising results in recent years. Despite this, their clinical relevance remains to be determined [as reviewed in Calabresi et al. (2023)]. So far, treatment with a small molecule called Minzasolmin (UCB0599) stands out as a potential disease-modifying therapy, which reduces the formation of α-syn aggregates (as oligomers) (Wagner et al., 2013; Smit et al., 2022; Prince et al., 2023). This treatment is currently being tested in phase 2 clinical trials in patients with early PD, and its clinical efficacy is expected to be published in the upcoming years.

While these strategies clearly have the potential to treat human synucleinopathies, their use is still limited, and significant obstacles remain, given the complexity of the disease itself [as reviewed in Calabresi et al. (2023), McFarthing et al. (2023), and Otzen (2024)]. A potential limitation, for instance, is that the mechanisms of action of certain therapies may lack full specificity for the relevant pathogenic α-syn species due to the extensive heterogeneity of aggregates and diverse conformational strains in which α-syn can polymerize. This variability complicates the development of highly specific therapeutic approaches, making it challenging to target a single pathogenic species precisely. Therefore, recognizing the disease-relevant conformation of α-syn (atomic conformation) with high specificity could represent a new opportunity for developing methods that accurately replicate the relevant strains causing human diseases in the appropriate study models. This unlocks a new paradigm for identifying specifically designed and personalized therapies to interfere with developing and propagating disease-specific α-syn aggregates in the brain. In addition, it provides the foundation to develop methods to recognize individual α-syn strains in a personalized manner, which could improve the stratification of patient populations for clinical trials and the development of efficient diagnostic tools.

Another challenge to overcome is the chemical modification to which α-syn is exposed, which can impact α-syn’s biochemical characteristics and biological activities. Since α-syn can interact with other molecules, some may cause negative effects (such as interaction with other proteins, membranes, and other molecules). Despite this, understanding the mechanisms underlying α-syn conformational modifications upon interactions with the surrounding environment could also lead to opportunities to inhibit and neutralize α-syn aggregation and fibril formation or even generate alternative species with less toxicity (Han et al., 2024). For example, research has shown that the post-translational modification of α-syn monomers with O-GlcNAc leads to the formation of α-syn amyloid-like fibrils [called α-syn (gS87)], which possess distinct structural characteristics that significantly diminish their seeding potential in both in vitro and rodent PD models (Balana et al., 2024). This finding opens up new avenues for exploring innovative therapeutic strategies for treating synucleinopathies, highlighting the potential for targeted interventions that leverage these unique modifications.

A more comprehensive understanding of α-syn in the context of pathology, along with the challenges associated with developing effective therapies, has stimulated the exploration of new aggregation mechanisms, such as condensation (Mitrea et al., 2022; Vendruscolo and Fuxreiter, 2022; Han et al., 2024). Consequently, approaches previously employed to identify small molecules that stabilize and inhibit α-syn aggregation via conventional mechanisms can now be adapted to enhance stability through the condensation pathway (Xu et al., 2022a; Dada et al., 2024; Li et al., 2024). As an example, a recent study reported that the aminosterol claramine could stabilize α-syn condensates as well as inhibit the primary nucleation of α-syn within the condensates, both in vitro and in a Caenorhabditis elegans PD model (Dada et al., 2024). This is especially important considering that LLPS formation could be the mechanism potentially underlying PD and other neurodegenerative diseases. Thus, additional studies exploring this approach would be very informative and may significantly impact drug development.

Growing evidence supports the promising and valuable potential of targeting α-syn to develop clinically effective therapeutic strategies. However, it also highlights the importance of thoroughly understanding the mechanisms underlying α-syn conformational modifications and their interactions with the surrounding environment.

Evidence suggests that intermediate species of α-syn aggregates are responsible for cell death in PD. However, the molecular events involved in α-syn aggregation and its relationship with disease onset and progression are not fully understood. However, the molecular events involved in α-syn aggregation and their relationship to disease initiation and progression are not fully understood. Current research is exploring LLPS and condensate formation, which have been proposed as alternative mechanisms that might not only underlie α-syn pathology but also contribute to heterogeneity in synucleinopathies. Cellular stress and pathological conditions may affect α-syn monomeric structure, aggregation, and LLPS behavior, potentially leading to the formation of aberrant structures within LLPS and condensates that result in toxicity. Therefore, it is reasonable to hypothesize that these factors may influence the dynamic interactions of monomer conformers and affect specific aggregation pathways, which could have a significant impact on the onset and progression of the disease.