Identification of amyloidogenic proteins in the microbiomes of a rat Parkinson's disease model and wild-type rats

Biofilm-associated proteins: from the gut biofilms to neurodegeneration

Human microbiota form a biofilm with substantial consequences for health and disease. Numerous studies have indicated that microbial communities produce functional amyloids as part of their biofilm extracellular scaffolds. The overlooked interplay between bacterial amyloids and the host may have detrimental consequences for the host, including neurodegeneration. This work gives an overview of the biofilm-associated amyloids expressed by the gut microbiota and their potential role in neurodegeneration. It discusses the biofilm-associated proteins (BAPs) of the gut microbiota, maps the amyloidogenic domains of these proteins, and analyzes the presence of bap genes within accessory genomes linked with transposable elements. Furthermore, the evidence supporting the existence of amyloids in the gut are presented. Finally, it explores the potential interactions between BAPs and α-synuclein, extending the literature on amyloid cross-kingdom interactions. Based on these findings, this study propose that BAP amyloids act as transmissible catalysts, facilitating the misfolding, accumulation, and spread of α-synuclein aggregates. This review contributes to the understanding of complex interactions among the microbiota, transmissible elements, and host, which is crucial for developing novel therapeutic approaches to combat microbiota-related diseases and improve overall health outcomes.

Parkinson's disease and gut microbiota metabolites: The dual impact of vitamins and functional amyloids

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the abnormal accumulation of alpha-synuclein (α-Syn). Recent research emphasizes the significant role of the gut microbiota, the diverse community of microbes living in the intestines, in modulating α-Syn pathology. This review explores the bi-directional communication along the microbiota-gut-brain axis, highlighting the paradoxical impact of two gut microbiota metabolites-functional bacterial amyloids (FuBA) and vitamins-on neurodegenerative diseases, particularly PD. FuBA contributes to PD pathogenesis by promoting α-Syn aggregation, while vitamins offer neuroprotection through their anti-amyloidogenic, antioxidant, and anti-inflammatory properties. Understanding these processes could lead to precision clinical approaches and novel strategies for managing and preventing PD.

Interactions between pathological and functional amyloid: A match made in Heaven or Hell?

The amyloid state of proteins occurs in many different contexts in Nature and in modern society, ranging from the pathological kind (neurodegenerative diseases and amyloidosis) via man-made forms (food processing and - to a much smaller extent - protein biologics) to functional versions (bacterial biofilm, peptide hormones and signal transmission). These classes all come together in the human body which endogenously produces amyloidogenic protein able to form pathological human amyloid (PaHA), hosts a microbiome which continuously makes functional bacterial amyloid (FuBA) and ingests food which can contain amyloid. This can have grave consequences, given that PaHA can spread throughout the body in a "hand-me-down" fashion from cell to cell through small amyloid fragments, which can kick-start growth of new amyloid wherever they encounter monomeric amyloid precursors. Amyloid proteins can also self- and cross-seed across dissimilar peptide sequences. While it is very unlikely that ingested amyloid plays a role in this crosstalk, FuBA-PaHA interactions are increasingly implicated in vivo amyloid propagation. We are now in a position to understand the structural and bioinformatic basis for this cross-talk, thanks to the very recently obtained atomic-level structures of the two major FuBAs CsgA (E. coli) and FapC (Pseudomonas). While there are many reports of homology-driven heterotypic interactions between different PaHA, the human proteome does not harbor significant homology to CsgA and FapC. Yet we and others have uncovered significant cross-stimulation (and in some cases inhibition) of FuBA and PaHA both in vitro and in vivo, which we here rationalize based on structure and sequence. These interactions have important consequences for the transmission and development of neurodegenerative diseases, not least because FuBA and PaHA can come into contact via the gut-brain interface, recurrent infections with microbes and potentially even through invasive biofilm in the brain. Whether FuBA and PaHA first interact in the gut or the brain, they can both stimulate and block each other's aggregation as well as trigger inflammatory responses. The microbiome may also affect amyloidogenesis in other ways, e.g. through their own chaperones which recognize and block growth of both PaHA and FuBA as we show both experimentally and computationally. Heterotypic interactions between and within PaHA and FuBA both in vitro and in vivo are a vital part of the amyloid phenomenon and constitute a vibrant and exciting frontier for future research.

Young rat microbiota extracts strongly inhibit fibrillation of α-synuclein and protect neuroblastoma cells and zebrafish against α-synuclein toxicity

The clinical manifestations of Parkinson's disease (PD) are driven by aggregation of α-Synuclein (α-Syn) in the brain. However, there is increasing evidence that PD may be initiated in the gut and thence spread to the brain, eg, via the vagus nerve. Many studies link PD to changes in the gut microbiome, and bacterial amyloid has been shown to stimulate α-Syn aggregation. Yet, we are not aware of any studies reporting on a direct connection between microbiome components and α-Syn aggregation. Here, we report that soluble extract from the gut microbiome of the rats, particularly young rats transgenic for PD, shows a remarkably strong ability to inhibit in vitro α-Syn aggregation and keep it natively unfolded and monomeric. The active component(s) are heat-labile molecule(s) of around 30- to 100-kDa size, which are neither nucleic acid nor lipid. Proteomic analysis identified several proteins whose concentrations in different rat samples correlated with the samples' anti-inhibitory activity, while a subsequent pull-down assay linked the protein chaperone DnaK with the inhibitory activity of young rat's microbiome, confirmed in subsequent in vitro assays. Remarkably, the microbiome extracts also protected neuroblastoma SH-SY5Y cells and zebrafish embryos against α-Syn toxicity. Our study sheds new light on the gut microbiome as a potential source of protection against PD and opens up for new microbiome-based therapeutic strategies.

Functional Amyloids: The Biomaterials of Tomorrow?

Functional amyloid (FAs), particularly the bacterial proteins CsgA and FapC, have many useful properties as biomaterials: high stability, efficient, and controllable formation of a single type of amyloid, easy availability as extracellular material in bacterial biofilm and flexible engineering to introduce new properties. CsgA in particular has already demonstrated its worth in hydrogels for stable gastrointestinal colonization and regenerative tissue engineering, cell-specific drug release, water-purification filters, and different biosensors. It also holds promise as catalytic amyloid; existing weak and unspecific activity can undoubtedly be improved by targeted engineering and benefit from the repetitive display of active sites on a surface. Unfortunately, FapC remains largely unexplored and no application is described so far. Since FapC shares many common features with CsgA, this opens the window to its development as a functional scaffold. The multiple imperfect repeats in CsgA and FapC form a platform to introduce novel properties, e.g., in connecting linkers of variable lengths. While exploitation of this potential is still at an early stage, particularly for FapC, a thorough understanding of their molecular properties will pave the way for multifunctional fibrils which can contribute toward solving many different societal challenges, ranging from CO2 fixation to hydrolysis of plastic nanoparticles.

Trans-seeding of Alzheimer-related tau protein by a yeast prion

Abnormal tau protein aggregates constitute a hallmark of Alzheimer's disease. The mechanisms underlying the initiation of tau aggregation in sporadic neurodegeneration remain unclear. Here we investigate whether a non-human prion can seed tau aggregation. Due to their structural similarity with tau aggregates, we chose Sup35NM yeast prion domain fibrils for explorative tau seedings. Upon in vitro incubation with tau monomers, Sup35NM fibrils promoted the formation of morphologically distinct tau fibril strains. In vivo, intrahippocampal inoculation of Sup35NM fibrils accentuated tau pathology in P301S tau transgenic mice. Thus, our results provide first in vivo evidence for heterotypic cross-species seeding of a neurodegenerative human prion-like protein by a yeast prion. This opens up the conceptual perspective that non-mammalian prions present in the human microbiome could be involved in the initiation of protein misfolding in neurodegenerative disorders, a mechanism for which we propose the term "trans-seeding."

Co-Aggregation of S100A9 with DOPA and Cyclen-Based Compounds Manifested in Amyloid Fibril Thickening without Altering Rates of Self-Assembly

The amyloid cascade is central for the neurodegeneration disease pathology, including Alzheimer’s and Parkinson’s, and remains the focus of much current research. S100A9 protein drives the amyloid-neuroinflammatory cascade in these diseases. DOPA and cyclen-based compounds were used as amyloid modifiers and inhibitors previously, and DOPA is also used as a precursor of dopamine in Parkinson’s treatment. Here, by using fluorescence titration experiments we showed that five selected ligands: DOPA-D-H-DOPA, DOPA-H-H-DOPA, DOPA-D-H, DOPA-cyclen, and H-E-cyclen, bind to S100A9 with apparent K_d in the sub-micromolar range. Ligand docking and molecular dynamic simulation showed that all compounds bind to S100A9 in more than one binding site and with different ligand mobility and H-bonds involved in each site, which all together is consistent with the apparent binding determined in fluorescence experiments. By using amyloid kinetic analysis, monitored by thioflavin-T fluorescence, and AFM imaging, we found that S100A9 co-aggregation with these compounds does not hinder amyloid formation but leads to morphological changes in the amyloid fibrils, manifested in fibril thickening. Thicker fibrils were not observed upon fibrillation of S100A9 alone and may influence the amyloid tissue propagation and modulate S100A9 amyloid assembly as part of the amyloid-neuroinflammatory cascade in neurodegenerative diseases.

Identification of amyloidogenic proteins in the microbiomes of a rat Parkinson's disease model and wild-type rats

Cross seeding between amyloidogenic proteins in the gut is receiving increasing attention as a possible mechanism for initiation or acceleration of amyloid formation by aggregation-prone proteins such as αSN, which is central in the development of Parkinson's disease (PD). This is particularly pertinent in view of the growing number of functional (i.e., benign and useful) amyloid proteins discovered in bacteria. Here we identify two amyloidogenic proteins, Pr12 and Pr17, in fecal matter from PD transgenic rats and their wild type counterparts, based on their stability against dissolution by formic acid (FA). Both proteins show robust aggregation into ThT-positive aggregates that contain higher-order β-sheets and have a fibrillar morphology, indicative of amyloid proteins. In addition, Pr17 aggregates formed in vitro showed significant resistance against FA, suggesting an ability to form highly stable amyloid. Treatment with proteinase K revealed a protected core of approx. 9 kDa. Neither Pr12 nor Pr17, however, affected αSN aggregation in vitro. Thus, amyloidogenicity does not per se lead to an ability to cross-seed fibrillation of αSN. Our results support the use of proteomics and FA to identify amyloidogenic protein in complex mixtures and suggests that there may be numerous functional amyloid proteins in microbiomes.