Elucidating the mechanisms of α-Synuclein-lipid interactions using site-directed mutagenesis.

α-Synuclein (α-syn) is a small protein that is involved in cell vesicle trafficking in neuronal synapses. A progressive aggregation of this protein is the expected molecular cause of Parkinson's disease, a disease that affects millions of people around the world. A growing body of evidence indicates that phospholipids can strongly accelerate α-syn aggregation and alter the toxicity of α-syn oligomers and fibrils formed in the presence of lipid vesicles. This effect is attributed to the presence of high copies of lysines in the N-terminus of the protein. In this study, we performed site-directed mutagenesis and replaced one out of two lysines at each of the five sites located in the α-syn N-terminus. Using several biophysical and cellular approaches, we investigated the extent to which six negatively charged fatty acids (FAs) could alter the aggregation properties of K10A, K23A, K32A, K43A, and K58A α-syn. We found that FAs uniquely modified the aggregation properties of K43A, K58A, and WT α-syn, as well as changed morphology of amyloid fibrils formed by these mutants. At the same time, FAs failed to cause substantial changes in the aggregation rates of K10A, K23A, and K32A α-syn, as well as alter the morphology and toxicity of the corresponding amyloid fibrils. Based on these results, we can conclude that K10, K23, and K32 amino acid residues play a critical role in protein-lipid interactions since their replacement on non-polar alanines strongly suppressed α-syn-lipid interactions.

Elucidation of molecular mechanisms by which amyloid ß1-42 fibrils exert cell toxicity.

Abrupt aggregation of amyloid ß1-42 (Aß1-42) peptide in the frontal lobe is the expected underlying cause of Alzheimer's disease (AD). ß-Sheet-rich oligomers and fibrils formed by Aß1-42 exert high cell toxicity. A growing body of evidence indicates that lipids can uniquely alter the secondary structure and toxicity of Aß1-42 aggregates. At the same time, underlying molecular mechanisms that determine this difference in toxicity of amyloid aggregates remain unclear. Using a set of molecular and biophysical assays to determine the molecular mechanism by which Aß1-42 aggregates formed in the presence of cholesterol, cardiolipin, and phosphatidylcholine exert cell toxicity. Our findings demonstrate that rat neuronal cells exposed to Aß1-42 fibrils formed in the presence of lipids with different chemical structure exert drastically different magnitude and dynamic of unfolded protein response (UPR) in the endoplasmic reticulum (ER) and mitochondria (MT). We found that the opposite dynamics of UPR in MT and ER in the cells exposed to Aß1-42: cardiolipin fibrils and Aß1-42 aggregates formed in a lipid-free environment. We also found that Aß1-42: phosphatidylcholine fibrils upregulated ER UPR simultaneously downregulating the UPR response of MT, whereas Aß1-42: cholesterol fibrils suppressed the UPR response of ER and upregulated UPR response of MT. We also observed progressively increasing ROS production that damages mitochondrial membranes and other cell organelles, ultimately leading to cell death.

Diagnosing arsenic-mediated biochemical responses in rice cultivars using Raman spectroscopy.

Rice (Oryza sativa) is the primary crop for nearly half of the world's population. Groundwater in many rice-growing parts of the world often has elevated levels of arsenite and arsenate. At the same time, rice can accumulate up to 20 times more arsenic compared to other staple crops. This places an enormous amount of people at risk of chronic arsenic poisoning. In this study, we investigated whether Raman spectroscopy (RS) could be used to diagnose arsenic toxicity in rice based on biochemical changes that were induced by arsenic accumulation. We modeled arsenite and arsenate stresses in four different rice cultivars grown in hydroponics over a nine-day window. Our results demonstrate that Raman spectra acquired from rice leaves, coupled with partial least squares-discriminant analysis, enabled accurate detection and identification of arsenic stress with approximately 89% accuracy. We also performed high-performance liquid chromatography (HPLC)-analysis of rice leaves to identify the key molecular analytes sensed by RS in confirming arsenic poisoning. We found that RS primarily detected a decrease in the concentration of lutein and an increase in the concentration of vanillic and ferulic acids due to the accumulation of arsenite and arsenate in rice. This showed that these molecules are detectable indicators of biochemical response to arsenic accumulation. Finally, a cross-correlation of RS with HPLC and ICP-MS demonstrated RS's potential for a label-free, non-invasive, and non-destructive quantification of arsenic accumulation in rice.

Plasmalogens Alter the Aggregation Rate of Transthyretin and Lower Toxicity of Transthyretin Fibrils.

Heart tissue can experience a progressive accumulation of transthyretin (TTR), a small four subunit protein that transports holoretinol binding protein and thyroxine. This severe pathology is known as transthyretin amyloid cardiomyopathy. Numerous experimental studies indicated that the aggregation rate and toxicity of TTR fibrils could be altered by the presence of lipids; however, the role of plasmalogens in this process remains unknown. In this study, we investigate the effect of choline plasmalogens (CPs) with different lengths and saturations of fatty acids (FAs) on TTR aggregation. We found that CPs with saturated and unsaturated FAs strongly suppressed TTR aggregation. We also found that CPs with saturated FAs did not change the morphology of TTR fibrils; however, much thicker fibrillar species were formed in the presence of CPs with unsaturated FAs. Finally, we found that CPs with C16:0, C18:0, and C18:1 FAs substantially lowered the cytotoxicity of TTR fibrils that were formed in their presence.

Macrophages and Natural Killers Degrade α-Synuclein Aggregates.

Amyloid oligomers and fibrils are protein aggregates that exert a high cell toxicity. Efficient degradation of these protein aggregates can minimize the spread and progression of neurodegeneration. In this study, we investigate the properties of natural killer (NK) cells and macrophages in the degradation of α-synuclein (α-Syn) aggregates grown in a lipid-free environment and in the presence of phosphatidylserine and cholesterol (PS/Cho), which are lipids that are directly associated with the onset and progression of Parkinson's disease. We found that both types of α-Syn aggregates were endocytosed by neurons, which caused strong damage to cell endosomes. Our results also indicated that PS/Cho vesicles drastically increased the toxicity of α-Syn fibrils formed in their presence compared to the toxicity of α-Syn aggregates grown in a lipid-free environment. Both NK cells and macrophages were able to degrade α-Syn and α-Syn/Cho monomers, oligomers, and fibrils. Quantitative analysis of protein degradation showed that macrophages demonstrated substantially more efficient internalization and degradation of amyloid aggregates in comparison to NK cells. We also found that amyloid aggregates induced the proliferation of macrophages and NK cells and significantly changed the expression of their cytokines and chemokines.

Using surface-enhanced Raman spectroscopy to probe artificial dye degradation on hair buried in multiple soils for up to eight weeks.

The discovery of clandestine burials poses unique challenges for forensic specialists, requiring diverse expertise to analyze remains in various states. Bones, teeth, and hair often endure the test of time, with hair particularly exposed to the external environment. While existing studies focus on the degradation of virgin hair influenced by soil pH and decomposition fluids, the interaction between artificial dyes on hair and soil remains underexplored. This paper introduces a novel approach to forensic hair analysis that is based on high-throughput, nondestructive, and non-invasive surface-enhanced Raman spectroscopy (SERS) and machine learning. Using this approach, we investigated the reliability of the detection and identification of artificial dyes on hair buried in three distinct soil types for up to eight weeks. Our results demonstrated that SERS enabled the correct prediction of 97.9% of spectra for five out of the eight dyes used within the 8 weeks of exposure. We also investigated the extent to which SERS and machine learning can be used to predict the number of weeks since burial, as this information may provide valuable insights into post-mortem intervals. We found that SERS enabled highly accurate exposure intervals to soils for specific dyes. The study underscores the high achievability of SERS in extrapolating colorant information from dyed hairs buried in diverse soils, with the suggestion that further model refinement could enhance its reliability in forensic applications.

Length and saturation of choline plasmalogens alter the aggregation rate of α-synuclein but not the toxicity of amyloid fibrils.

Plasmalogens comprise a large fraction of the total phospholipids in plasma membranes. These molecules modulate membrane fluidity, produce inflammatory mediators mitigating effects of metabolic stresses. A growing body of evidence suggests that an onset of Parkinson's disease (PD), a severe neurodegenerative pathology, can be triggered by metabolic changes in plasma membranes. However, the role of plasmalogens in the aggregation of α-synuclein (α-syn), an expected molecular cause of PD, remains unclear. In this study we examine the effect of choline plasmalogens (CPs), unique phospholipids that have a vinyl ether linkage at the sn-1 position of glycerol, on the aggregation rate of α-syn. We found that the length and saturation of fatty acids (FAs) in CPs change rates of protein aggregation. We also found drastic changes in the morphology of α-syn fibrils formed in the presence of different CPs compared to α-syn fibrils grown in the lipid-free environment. At the same time, we did not observe substantial changes in the secondary structure and toxicity of α-syn fibrils formed in the presence of different CPs. These results indicate that the length and saturation of FAs in CPs present in the plasma membrane can alter α-syn stability and modulate its aggregation properties, which, in turn can accelerate or delay the onset of PD.

Large Unilamellar Vesicles of Phosphatidic Acid Reduce the Toxicity of α-Synuclein Fibrils.

Parkinson's disease (PD) is a severe pathology that is caused by a progressive degeneration of dopaminergic neurons in substantia nigra pars compacta as well as other areas in the brain. These neurodegeneration processes are linked to the abrupt aggregation of α-synuclein (α-syn), a small protein that is abundant at presynaptic nerve termini, where it regulates cell vesicle trafficking. Due to the direct interactions of α-syn with cell membranes, a substantial amount of work was done over the past decade to understand the role of lipids in α-syn aggregation. However, the role of phosphatidic acid (PA), a negatively charged phospholipid with a small polar head, remains unclear. In this study, we examined the effect of PA large unilamellar vesicles (LUVs) on α-syn aggregation. We found that PA LUVs with 16:0, 18:0, and 18:1 FAs drastically reduced the toxicity of α-syn fibrils if were present in a 1:1 molar ratio with the protein. Our results also showed that the presence of these vehicles changed the rate of α-syn aggregation and altered the morphology and secondary structure of α-syn fibrils. These results indicate that PA LUVs can be used as a potential therapeutic strategy to reduce the toxicity of α-syn fibrils formed upon PD.

Elucidation of sex from mature Palmer amaranth (Amaranthus palmeri) leaves using a portable Raman spectrometer.

Palmer amaranth (Amaranthus palmeri) is a pervasive and troublesome weed species that poses significant challenges to agriculture in the United States. Identifying the sex of Palmer amaranth plants is crucial for developing tailored control measures due to the distinct characteristics and reproductive strategies exhibited by male and female plants. Traditional methods for sex determination are expensive and time-consuming, but recent advancements in spectroscopic techniques offer new possibilities. This study explores the potential of portable Raman spectroscopy for determining the sex of mature Palmer amaranth plants in-field. Raman analysis of the plant leaves reveals spectral differences associated with nitrate salts, lipids, carotenoids, and terpenoids, allowing for high accuracy and reliable identification of the plant's sex; male plants had higher concentrations of these compounds compared to females. It was also found that male plants had higher concentrations of these compounds compared to the females. Raman spectra were analyzed using a machine learning tool, partial least squares discriminant analysis (PLS-DA), to generate accuracies of no less than 83.7% when elucidating sex from acquired spectra. These findings provide insights into the sex-specific characteristics of Palmer amaranth and suggest that Raman analysis, combined with PLS-DA, can be a promising, non-destructive, and efficient method for sex determination in field settings. This approach has implications for developing sex-specific management strategies to monitor and control this invasive weed in real-world environments, benefiting farmers, agronomists, researchers, and master gardeners.

Near-infrared excitation Raman analysis of Underlying colorants on redyed fabric.

Forensic analysis of fabric is often critically important to establish a relationship between a suspect and a crime scene or demonstrate the absence of such connections. Most of commercially available fabric is colored with primarily organic colorants. These dye substances are highly fluorescent, which limits the use to conventional Raman spectroscopy for the analysis of the colorant content of fabric. At the same time, elucidation of the chemical composition of dyes in fabrics can be used to advance the importance of this physical piece of evidence for forensic research. Our recent findings showed that near-infrared excitation Raman spectroscopy (NIeRS) could be used to overcome this limitation. However, it remains unclear to what extent NIeRS could be used to identify the presence of several different colorants on fabric, as well as utilize for the analysis of dyes on fabric contaminated with paints. In this study, we utilized a hand-held NIeRS instrument to ex-amine re-colored cotton fabric and cotton fabric with household paints applied on it. Our results indicate that NIeRS coupled with chemometrics highly accurately identify the presence of several colorants on cotton. We also found that the presence of paint fully obscures the ability of NIeRS to extract the information about the dye content of the fabric. These results expand our understanding of the use of NIeRS in the forensic analysis of colored fabric.

The influence of zwitterionic and anionic phospholipids on protein aggregation.

The progressive aggregation of misfolded proteins is the underlying molecular cause of numerous pathologies including Parkinson's disease and injection and transthyretin amyloidosis. A growing body of evidence indicates that protein deposits detected in organs and tissues of patients diagnosed with such pathologies contain fragments of lipid membranes. In vitro experiments also showed that lipid membranes could strongly change the aggregation rate of amyloidogenic proteins, as well as alter the secondary structure and toxicity of oligomers and fibrils formed in their presence. In this review, the effect of large unilamellar vesicles (LUVs) composed of zwitterionic and anionic phospholipids on the aggregation rate of insulin, lysozyme, transthyretin (TTR) and α- synuclein (α-syn) will be discussed. The manuscript will also critically review the most recent findings on the lipid-induced changes in the secondary structure of protein oligomers and fibrils, as well as reveal the extent to which lipids could alter the toxicity of protein aggregates formed in their presence.

Species identification of adult ixodid ticks by Raman spectroscopy of their feces.

BACKGROUND: Ticks and tick-borne diseases pose significant challenges to cattle production, thus the species identification of ticks and knowledge on their presence, abundance, and dispersal are necessary for the development of effective control measures. The standard method of inspection for the presence of ticks is the visual and physical examination of restrained animals, but the limitations of human sight and touch can allow larval, nymphal, and unfed adult ticks to remain undetected due to their small size and site of attachment. However, Raman spectroscopy, an analytical tool widely used in agriculture and other sectors, shows promise for the identification of tick species in infested cattle. Raman spectroscopy is a non-invasive and efficient method that employs the interaction between molecules and light for the identification of the molecular constituents of specimens. METHODS: Raman spectroscopy was employed to analyze the structure and composition of tick feces deposited on host skin and hair during blood-feeding. Feces of 12 species from a total of five genera and one subgenus of ixodid ticks were examined. Spectral data were subjected to partial least squares discriminant analysis, a machine-learning model. We also used Raman spectroscopy and the same analytical procedures to compare and evaluate feces of the horn fly Haematobia irritans after it fed on cattle. RESULTS: Five genera and one sub-genus at overall true prediction rates ranging from 92.3 to 100% were identified from the Raman spectroscopy data of the tick feces. At the species level, Dermacentor albipictus, Dermacentor andersoni and Dermacentor variabilis at overall true prediction rates of 100, 99.3 and 100%, respectively, were identified. There were distinct differences between horn fly and tick feces with respect to blood and guanine vibrational frequencies. The overall true prediction rate for the separation of tick and horn fly feces was 98%. CONCLUSIONS: Our findings highlight the utility of Raman spectroscopy for the reliable identification of tick species from their feces, and its potential application for the identification of ticks from infested cattle in the field.

Phospholipids and Cholesterol Determine Molecular Mechanisms of Cytotoxicity of α-Synuclein Oligomers and Fibrils.

Progressive loss of dopaminergic (DA) neurons in the substantia nigra pars compacta, hypothalamus, and thalamus is a hallmark of Parkinson's disease. Neuronal death is linked to the abrupt aggregation of α-synuclein (α-Syn), a small membrane protein that regulates cell vesicle trafficking. α-Syn aggregation rate, as well as the secondary structure and toxicity of α-Syn fibrils, could be uniquely altered by lipids. However, molecular mechanisms that determine such a remarkable difference in the toxicity of α-Syn fibrils formed in the presence of lipids remain unclear. In this study, we used a set of molecular assays to determine the molecular mechanism by which α-Syn fibrils formed in the presence of phosphatidylcholine (PC), cardiolipin (CL), and cholesterol (Cho) exert cell toxicity. We found that rat dopaminergic cells exposed to α-Syn fibrils formed in the presence of different lipids exert drastically different magnitudes and dynamics of unfolded protein response (UPR) in the endoplasmic reticulum (ER) and mitochondria (MT). Specifically, α-Syn:CL were found to cause the strongest, whereas α-Syn fibrils formed in the absence of lipids had the lowest magnitude of the UPR cell response. We also found the opposite dynamics of the ER- and MT-UPR responses in rat dopaminergic cells exposed to protein aggregates. These results could suggest that facing severe ER stress, dopaminergic cells suppress MT-UPR response, enabling the maximal ATP production to restore their normal physiological function. These findings help to better understand complex mechanisms of cell toxicity of amyloid aggregates and ultimately find neuroprotective drug candidates that will be able to suppress the spread of Parkinson's disease.

Secondary structure and toxicity of lysozyme fibrils are determined by the length and unsaturation of phosphatidic acid.

A progressive aggregation of misfolded proteins is a hallmark of numerous pathologies including diabetes Type 2, Alzheimer's disease, and Parkinson's disease. As a result, highly toxic protein aggregates, which are known as amyloid fibrils, are formed. A growing body of evidence suggests that phospholipids can uniquely alter the secondary structure and toxicity of amyloid aggregates. However, the role of phosphatidic acid (PA), a unique lipid that is responsible for cell signaling and activation of lipid-gated ion channels, in the aggregation of amyloidogenic proteins remains unclear. In this study, we investigate the role of the length and degree of unsaturation of fatty acids (FAs) in PA in the structure and toxicity of lysozyme fibrils formed in the presence of this lipid. We found that both the length and saturation of FAs in PA uniquely altered the secondary structure of lysozyme fibrils. However, these structural differences in PA caused very little if any changes in the morphology of lysozyme fibrils. We also utilized cell toxicity assays to determine the extent to which the length and degree of unsaturation of FAs in PA altered the toxicity of lysozyme fibrils. We found that amyloid fibrils formed in the presence of PA with C18:0 FAs exerted significantly higher cell toxicity compared to the aggregates formed in the presence of PA with C16:0 and C18:1 FAs. These results demonstrated that PA can be an important player in the onset and spread of amyloidogenic diseases.

Long-Chain Polyunsaturated Fatty Acids Accelerate the Rate of Insulin Aggregation and Enhance Toxicity of Insulin Aggregates.

Long-chain polyunsaturated fatty acids (LCPUFAs) are essential components of a human diet. These molecules are critically important for cognitive attention and memory, mood states, coronary circulation, and cirrhosis. However, recently reported findings demonstrated that docosahexaenoic (DHA) and arachidonic acids (ARA), ω-3 and ω-6 LCPUFAs, accelerated the aggregation rates of insulin and α-synuclein, proteins that are directly linked to diabetes type 2 and Parkinson's disease, respectively. Furthermore, both DHA and ARA uniquely altered the structure and toxicity of the corresponding protein aggregates. Our objective is to ascertain whether other LCPUFAs, alongside long-chain unsaturated fatty acid (LCUFA) proteins, exhibit similar effects on amyloidogenic proteins. To explore this matter, we investigated the effect of 10 different LCPUFAs and LCUFAs on the rate of insulin aggregation. We found that all of the analyzed fatty acids strongly accelerated insulin aggregation. Moreover, we found that protein aggregates that were formed in the presence of these fatty acids exerted significantly higher cell toxicity compared with insulin fibrils grown in the lipid-free environment. These findings show that interactions between amyloid-associated proteins and LCPUFAs can be the underlying molecular cause of neurodegenerative diseases.

Raman-based diagnostics of drought, heat and light-induced stresses in three different varieties of hemp.

MAIN CONCLUSION: Hand-held Raman spectroscopy can be used for highly accurate differentiation between drought, heat and light-triggered stresses in hemp. The differentiation is based on the changes in the biochemistry of plants caused by such stresses. Hemp farming is a rapidly growing industry. This dioecious plant is primarily cultivated for its fibers, seeds, and cannabinoid-rich oils. The yield of these materials can be drastically lowered by many abiotic stresses, such as drought, heat and light. It becomes critically important to develop robust and reliable approaches that can be used to diagnose such abiotic stresses in hemp. In this study, we investigate the accuracy of Raman spectroscopy, an emerging tool within crop monitoring, in the confirmatory identification of drought, heat, and light-induced stresses in three varieties of hemp. Our results showed that mono, double and triple stresses uniquely alter plant biochemistry that results in small spectroscopic changes detected in the Raman spectra acquired from the hemp leaves. These changes could be used for the 80-100% accurate identification of individual abiotic stresses and their combinations in plants. These results demonstrate that a hand-held Raman spectrometer can be used for highly accurate, non-invasive, non-destructive, and label-free diagnostics of hemp stresses directly in the greenhouse or in the field.

Non-Destructive Identification of Dyes on Fabric Using Near-Infrared Raman Spectroscopy.

Fabric is a commonly found piece of physical evidence at most crime scenes. Forensic analysis of fabric is typically performed via microscopic examination. This subjective approach is primarily based on pattern recognition and, therefore, is often inconclusive. Most of the fabric material found at crime scenes is colored. One may expect that a confirmatory identification of dyes can be used to enhance the reliability of the forensic analysis of fabric. In this study, we investigated the potential of near-infrared Raman spectroscopy (NIRS) in the confirmatory, non-invasive, and non-destructive identification of 15 different dyes on cotton. We found that NIRS was able to resolve the vibrational fingerprints of all 15 colorants. Using partial-squared discriminant analysis (PLS-DA), we showed that NIRS enabled ~100% accurate identification of dyes based on their vibrational signatures. These findings open a new avenue for the robust and reliable forensic analysis of dyes on fabric directly at crime scenes. Main conclusion: a hand-held Raman spectrometer and partial least square discriminant analysis (PLS-DA) approaches enable highly accurate identification of dyes on fabric.

Nanoscale structural characterization of transthyretin aggregates formed at different time points of protein aggregation using atomic force microscopy-infrared spectroscopy.

Transthyretin (TTR) amyloidosis is a progressive disease characterized by an abrupt aggregation of misfolded protein in multiple organs and tissues TTR is a tetrameric protein expressed in the liver and choroid plexus. Protein misfolding triggers monomerization of TTR tetramers. Next, monomers assemble forming oligomers and fibrils. Although the secondary structure of TTR fibrils is well understood, there is very little if anything is known about the structural organization of TTR oligomers. To end this, we used nano-infrared spectroscopy, also known as atomic force microscopy infrared (AFM-IR) spectroscopy. This emerging technique can be used to determine the secondary structure of individual amyloid oligomers and fibrils. Using AFM-IR, we examined the secondary structure of TTR oligomers formed at the early (3-6 h), middle (9-12 h), and late (28 h) of protein aggregation. We found that aggregating, TTR formed oligomers (Type 1) that were dominated by α-helix (40%) and ß-sheet (~30%) together with unordered protein (30%). Our results showed that fibril formation was triggered by another type of TTR oligomers (Type 2) that appeared at 9 h. These new oligomers were primarily composed of parallel ß-sheet (55%), with a small amount of antiparallel ß-sheet, α-helix, and unordered protein. We also found that Type 1 oligomers were not toxic to cells, whereas TTR fibrils formed at the late stages of protein aggregation were highly cytotoxic. These results show the complexity of protein aggregation and highlight the drastic difference in the protein oligomers that can be formed during such processes.

Nano-infrared analysis of amyloid ß1-42 fibrils formed in the presence of lipids with unsaturated fatty acids.

Alzheimer's disease (AD) is characterized by progressive memory loss and serious impairment of cognitive abilities. AD is the most common cause of dementia, affecting more than 44 million people around the world. The hallmark of AD is amyloid plaques, extracellular deposits primarily found in the frontal lobe, that are composed of amyloid ß (Aß) aggregates. In this study, we utilized nano-infrared spectroscopy, also known as Atomic Force Microscopy Infrared (AFM-IR) spectroscopy to investigate the effect of unsaturated phospholipids on the rate of Aß1-42 aggregation. We found that unsaturated phosphatidylcholine, phosphatidylserine, and cardiolipin strongly suppressed aggregation of Aß1-42. Furthermore, Aß1-42 fibrils formed in the presence of such lipids exerted significantly lower cell toxicity compared to the protein aggregates formed in the lipid-free environment. These findings suggest that dietary changes linked to the increased consumption of unsaturated phospholipids could be considered as a potential therapeutic approach that can decelerate the progression of AD. These results also suggest that large unilamellar vesicles with unsaturated lipids can be used as potential therapeutics to delay the onset and decelerate the progression of AD.

Cholesterol and Sphingomyelin Uniquely Alter the Rate of Transthyretin Aggregation and Decrease the Toxicity of Amyloid Fibrils.

Transthyretin (TTR) is a small tetrameric protein that aggregates, forming highly toxic oligomers and fibrils. In the blood and cerebrospinal fluid, TTR can interact with various biomolecules, phospho- and sphingolipids, and cholesterol on the red blood cell plasma membrane. However, the role of these molecules in TTR aggregation remains unclear. In this study, we investigated the extent to which phosphatidylcholine (PC), sphingomyelin (SM), and cholesterol (Cho), important components of plasma membranes, could alter the rate of TTR aggregation. We found that PC and SM inhibited TTR aggregation whereas Cho strongly accelerated it. The presence of these lipids during the stage of protein aggregation uniquely altered the morphology and secondary structure of the TTR fibrils, which changed the toxicity of these protein aggregates. These results suggest that interactions of TTR with red blood cells, whose membranes are rich with these lipids, can trigger irreversible aggregation of TTR and cause transthyretin amyloidosis.