The N-terminal segment of protein AA determines its fibrillogenic property

Emerging Biosensing Methods to Monitor Lung Cancer Biomarkers in Biological Samples: A Comprehensive Review

Lung cancer is the most commonly diagnosed of all cancers and one of the leading causes of cancer deaths among men and women worldwide, causing 1.5 million deaths every year. Despite developments in cancer treatment technologies and new pharmaceutical products, high mortality and morbidity remain major challenges for researchers. More than 75% of lung cancer patients are diagnosed in advanced stages, leading to poor prognosis. Lung cancer is a multistep process associated with genetic and epigenetic abnormalities. Rapid, accurate, precise, and reliable detection of lung cancer biomarkers in biological fluids is essential for risk assessment for a given individual and mortality reduction. Traditional diagnostic tools are not sensitive enough to detect and diagnose lung cancer in the early stages. Therefore, the development of novel bioanalytical methods for early-stage screening and diagnosis is extremely important. Recently, biosensors have gained tremendous attention as an alternative to conventional methods because of their robustness, high sensitivity, inexpensiveness, and easy handling and deployment in point-of-care testing. This review provides an overview of the conventional methods currently used for lung cancer screening, classification, diagnosis, and prognosis, providing updates on research and developments in biosensor technology for the detection of lung cancer biomarkers in biological samples. Finally, it comments on recent advances and potential future challenges in the field of biosensors in the context of lung cancer diagnosis and point-of-care applications.

Influences of amino-terminal modifications on amyloid fibril formation of human serum amyloid A

Human serum amyloid A (SAA) is a precursor protein involved in AA amyloidosis. The N-terminal region of the SAA molecule is crucial for amyloid fibril formation, and therefore modifications in this region are considered to influence the pathogenesis of AA amyloidosis. In the present study, using the N-terminal peptide corresponding to the putative first helix region of the SAA molecule, we investigated the influences of N-terminal modifications on amyloid fibril formation. Spectroscopic analyses revealed that carbamoylation of the N-terminal amino group delayed the onset of amyloid fibril formation. From transmission electron microscopic observations, the N-terminal carbamoylated aggregate showed remarkably different morphologies from the unmodified control. In contrast, acetylation of the N-terminal amino group or truncation of N-terminal amino acid(s) considerably diminished amyloidogenic properties. Furthermore, we also tested the cell toxicity of each peptide aggregate on cultured cells by two cytotoxic assays. Irrespective of carbamoylation or acetylation, MTT assay revealed that SAA peptides reduced the reductive activity of MTT on cells, whereas no apparent increase in LDH release was observed during an LDH assay. In contrast, N-terminal truncation did not affect either MTT reduction or LDH release. These results suggest that N-terminal modification of SAA molecules can act as a switch to regulate susceptibility to AA amyloidosis.

Hydrogels from the Assembly of SAA/Elastin-Inspired Peptides Reveal Non-Canonical Nanotopologies

Peptide-based hydrogels are of great interest in the biomedical field according to their biocompatibility, simple structure and tunable properties via sequence modification. In recent years, multicomponent assembly of peptides have expanded the possibilities to produce more versatile hydrogels, by blending gelating peptides with different type of peptides to add new features. In the present study, the assembly of gelating P5 peptide SFFSF blended with P21 peptide, SFFSFGVPGVGVPGVGSFFSF, an elastin-inspired peptides or, alternatively, with FF dipeptide, was investigated by oscillatory rheology and different microscopy techniques in order to shed light on the nanotopologies formed by the self-assembled peptide mixtures. Our data show that, depending on the added peptides, cooperative or disruptive assembly can be observed giving rise to distinct nanotopologies to which correspond different mechanical properties that could be exploited to fabricate materials with desired properties.

Interconversion between Serum Amyloid A Native and Fibril Conformations

Overexpression of serum amyloid A (SAA) can lead to a form of amyloidosis where the fibrils are made of SAA fragments, most often SAA1-76. Using Replica Exchange with Tunneling, we study the conversion of a SAA1-76 chain between the folded conformation and a fibril conformation. We find that the basins in the free energy landscape corresponding to the two motifs are separated by barriers of only about 2-3 k B T. Crucial for the assembly into the fibril structure is the salt bridge 26E-34K that provides a scaffold for forming the fibril conformation.

Post-translational modification of amyloid a protein in patients with AA amyloidosis

AA amyloidosis is a disease caused by extracellular deposition of insoluble β-pleated sheet fibrils composed of amyloid A (AA) protein, an amino (N)-terminal fragment of serum amyloid A (SAA). The deposits disrupt tissue structure and compromise organ function. Although the disease is systemic, deposition in kidney glomeruli is the most common manifestation. The leading cause of AA amyloidosis is sustained or recurrent inflammation accompanied by elevated levels of SAA. Factors determining the conversion of SAA to AA amyloid fibrils have yet to be fully resolved. Herein, we present liquid chromatography tandem-mass spectrometry (LC-MS/MS) analysis of AA proteins purified from eight patients with AA amyloidosis. For the first time, post-translational modifications (PTM), including carbamylation, acetylation and oxidation, were identified on AA peptides; all eight samples showed some degree of PTM. The amyloid in 6 samples comprised peptides derived from SAA1 with few or none from SAA2, while the other two samples contained both SAA1- and SAA2-derived peptides. N-terminal AA peptides beginning with Arg1 as well as AA peptides starting with Ser2 were present in five of the eight samples, while all or nearly all of the N-terminal peptides in the other three samples lacked Arg1. These data demonstrate that multiple species of AA amyloid proteins can comprise the subunits in amyloid fibrils and raise the possibility that PTM may play a role in fibrillogenesis.

Cryo-EM demonstrates the in vitro proliferation of an ex vivo amyloid fibril morphology by seeding

Several studies showed that seeding of solutions of monomeric fibril proteins with ex vivo amyloid fibrils accelerated the kinetics of fibril formation in vitro but did not necessarily replicate the seed structure. In this research we use cryo-electron microscopy and other methods to analyze the ability of serum amyloid A (SAA)1.1-derived amyloid fibrils, purified from systemic AA amyloidosis tissue, to seed solutions of recombinant SAA1.1 protein. We show that 98% of the seeded fibrils remodel the full fibril structure of the main ex vivo fibril morphology, which we used for seeding, while they are notably different from unseeded in vitro fibrils. The seeded fibrils show a similar proteinase K resistance as ex vivo fibrils and are substantially more stable to proteolytic digestion than unseeded in vitro fibrils. Our data support the view that the fibril morphology contributes to determining proteolytic stability and that pathogenic amyloid fibrils arise from proteolytic selection.

MTADV 5-MER peptide suppresses chronic inflammations as well as autoimmune pathologies and unveils a new potential target-Serum Amyloid A

Despite the existence of potent anti-inflammatory biological drugs e.g., anti-TNF and anti IL-6 receptor antibodies, for treating chronic inflammatory and autoimmune diseases, these are costly and not specific. Cheaper oral available drugs remain an unmet need. Expression of the acute phase protein Serum Amyloid A (SAA) is dependent on release of pro-inflammatory cytokines IL-1, IL-6 and TNF-α during inflammation. Conversely, SAA induces pro-inflammatory cytokine secretion, including Th17, leading to a pathogenic vicious cycle and chronic inflammation. 5- MER peptide (5-MP) MTADV (methionine-threonine-alanine-aspartic acid-valine), also called Amilo-5MER, was originally derived from a sequence of a pro-inflammatory CD44 variant isolated from synovial fluid of a Rheumatoid Arthritis (RA) patient. This human peptide displays an efficient anti-inflammatory effects to ameliorate pathology and clinical symptoms in mouse models of RA, Inflammatory Bowel Disease (IBD) and Multiple Sclerosis (MS). Bioinformatics and qRT-PCR revealed that 5-MP, administrated to encephalomyelytic mice, up-regulates genes contributing to chronic inflammation resistance. Mass spectrometry of proteins that were pulled down from an RA synovial cell extract with biotinylated 5-MP, showed that it binds SAA. 5-MP disrupted SAA assembly, which is correlated with its pro-inflammatory activity. The peptide MTADV (but not scrambled TMVAD) significantly inhibited the release of pro-inflammatory cytokines IL-6 and IL-1β from SAA-activated human fibroblasts, THP-1 monocytes and peripheral blood mononuclear cells. 5-MP suppresses the pro-inflammatory IL-6 release from SAA-activated cells, but not from non-activated cells. 5-MP could not display therapeutic activity in rats, which are SAA deficient, but does inhibit inflammations in animal models of IBD and MS, both are SAA-dependent, as shown by others in SAA knockout mice. In conclusion, 5-MP suppresses chronic inflammation in animal models of RA, IBD and MS, which are SAA-dependent, but not in animal models, which are SAA-independent.

Dietary Intake of Rosmarinic Acid Increases Serum Inhibitory Activity in Amyloid A Aggregation and Suppresses Deposition in the Organs of Mice

Serum amyloid A (SAA) is one of the most important precursor amyloid proteins and plays a vital step in AA amyloidosis, although the underlying aggregation mechanism has not been elucidated. Since SAA aggregation is a key step in this pathogenesis, inhibitors are useful to prevent and treat AA amyloidosis, serving as tools to investigate the pathogenic mechanism. In this study, we showed that rosmarinic acid (RA), which is a well-known inhibitor of the aggregation of amyloid β (Aβ), displayed inhibitory activity against SAA aggregation in vitro using a microliter-scale high-throughput screening (MSHTS) system with quantum-dot nanoprobes. Therefore, we evaluated the amyloid aggregation inhibitory activity of blood and the deposition of SAA in organs by feeding mice with Melissa officinalis extract (ME) containing RA as an active substance. Interestingly, the inhibitory activity of ME-fed mice sera for SAA and Aβ aggregation, measured with the MSHTS system, was higher than that of the control group. The amount of amyloid deposition in the organs of ME-fed mice was lower than that in the control group, suggesting that the SAA aggregation inhibitory activity of serum is associated with SAA deposition. These results suggest that dietary intake of RA-containing ME enhanced amyloid aggregation inhibitory activity of blood and suppressed SAA deposition in organs. This study also demonstrated that the MSHTS system could be applied to in vitro screening and to monitor comprehensive activity of metabolized foods adsorbed by blood.

Labeling of Nanofiber-Forming Peptides by Site-Directed Bioconjugation: Effect of Spacer Length on Self-Assembly

BACKGROUND

The conjugation of small organic molecules to self-assembling peptides is a versatile tool to decorate nanostructures with original functionalities. Labeling with chromophores or fluorophores, for example, creates optically active fibers with potential interest in photonic devices.

AIM AND OBJECTIVE

In this work, we present a rapid and effective labeling procedure for a self-assembling peptide able to form nanofibers. Rapid periodate oxidation of the N-terminal serine residue of the peptide and subsequent conjugation with dansyl moiety generated fluorophore-decorated peptides.

RESULTS

Three dansyl-conjugated self-assembling peptides with variable spacer-length were synthesized and characterized and the role of the size of the linker between fluorophore and peptide in self-assembling was investigated. Our results show that a short linker can alter the self-assembly in nanofibers of the peptide.

CONCLUSIONS

Herein we report on an alternative strategy for creating functionalized nanofibrils, able to expand the toolkit of chemoselective bioconjugation strategies to be used in site-specific decoration of self-assembling peptides.

Serum amyloid A: A potential biomarker of lung disorders

Serum amyloid A is an acute-phase protein with multiple immunological functions. Serum amyloid A is involved in lipid metabolism, inflammatory reactions, granuloma formation, and cancerogenesis. Additionally, serum amyloid A is involved in the pathogenesis of different autoimmune lung diseases. The levels of serum amyloid A has been evaluated in biological fluids of patients with different lung diseases, including autoimmune disorders, chronic obstructive pulmonary diseases, obstructive sleep apnea syndrome, sarcoidosis, asthma, lung cancer, and other lung disorders, such as idiopathic pulmonary fibrosis, tuberculosis, radiation pneumonitis, and cystic fibrosis. This review focuses on the cellular and molecular interactions of serum amyloid A in different lung diseases and suggests this acute-phase protein as a prognostic marker.

Short to ultrashort peptide-based hydrogels as a platform for biomedical applications

Short peptides have attracted significant attention from researchers in the past few years due to their easy design, synthesis and characterization, diverse functionalisation possibilities, low cost, possibility to make a large range of hierarchical nanostructures and most importantly their high biocompatibility and biodegradability. Generally, short peptides are also relatively more stable than their longer variants, non-immunogenic in nature and many of them self-assemble to provide an exciting range of nanostructures, including hydrogels. Thus, the development of short peptide-based hydrogels has become an area of intense investigation. Although these hydrogels have a water content of greater than 90%, they are surprisingly highly stable structures, and thus have been used for various biomedical applications, including cell therapeutics, drug delivery, tissue engineering and regeneration, contact lenses, biosensors, and wound healing, by different researchers. Herein, we review the progress of research in the rapidly expanding field of short to ultrashort peptide-based hydrogels and their possible applications. Special attention is paid to address and review this field with regard to the stability of peptide-based hydrogels, particularly to enzymatic degradation.

Designed Two- and Three-Dimensional Protein Nanocage Networks Driven by Hydrophobic Interactions Contributed by Amyloidogenic Motifs

Precise manipulation of protein self-assembly by noncovalent interactions into programmed networks to mimic naturally occurring nanoarchitectures in living organisms is a challenge due to its structural heterogeneity, flexibility, and complexity. Herein, by taking advantage of both the hydrophobic forces contributed by the "GLMVG" motif, a kind of amyloidogenic motif (AM), and the high symmetry of protein nanocages, we have built an effective protein self-assembly strategy for the construction of two-dimensional (2D) or three-dimensional (3D) protein nanocage arrays. According to this strategy, "GLMVG" AMs from β-amyloid 42 were grafted onto the outer surface of a 24-mer ferritin nanocage close to its C₄ symmetry channels, initially resulting in the production of subgrade 2D nanocage arrays and ultimately generating 3D highly ordered arrays with a simple cubic packing pattern as the reaction time increases. More importantly, the reversibility and the formation rate of these protein arrays can be modulated by pH. This work provides a de novo design strategy for accurate control over 2D or 3D protein self-assemblies.

Cryo-EM fibril structures from systemic AA amyloidosis reveal the species complementarity of pathological amyloids

Systemic AA amyloidosis is a worldwide occurring protein misfolding disease of humans and animals. It arises from the formation of amyloid fibrils from the acute phase protein serum amyloid A. Here, we report the purification and electron cryo-microscopy analysis of amyloid fibrils from a mouse and a human patient with systemic AA amyloidosis. The obtained resolutions are 3.0 Å and 2.7 Å for the murine and human fibril, respectively. The two fibrils differ in fundamental properties, such as presence of right-hand or left-hand twisted cross-β sheets and overall fold of the fibril proteins. Yet, both proteins adopt highly similar β-arch conformations within the N-terminal ~21 residues. Our data demonstrate the importance of the fibril protein N-terminus for the stability of the analyzed amyloid fibril morphologies and suggest strategies of combating this disease by interfering with specific fibril polymorphs.

Systemic AA amyloidosis is caused by misfolding of the acute phase protein serum amyloid A1. Here the authors present the cryo-EM structures of murine and human AA amyloid fibrils that were isolated from tissue samples and describe how the fibrils differ in their fundamental structural properties.

Acute phase reactant serum amyloid A in inflammation and other diseases

Acute-phase reactant serum amyloid A (A-SAA) plays an important role in acute and chronic inflammation and is used in clinical laboratories as an indicator of inflammation. Although both A-SAA and C-reactive protein (CRP) are acute-phase proteins, the detection of A-SAA is more conclusive than the detection of CRP in patients with viral infections, severe acute pancreatitis, and rejection reactions to kidney transplants. A-SAA has greater clinical diagnostic value in patients who are immunosuppressed, patients with cystic fibrosis who are treated with corticoids, and preterm infants with late-onset sepsis. Nevertheless, for the assessment of the inflammation status and identification of viral infection in other pathologies, such as bacterial infections, the combinatorial use of A-SAA and other acute-phase proteins (APPs), such as CRP and procalcitonin (PCT), can provide more information and sensitivity than the use of any of these proteins alone, and the information generated is important in guiding antibiotic therapy. In addition, A-SAA-associated diseases and the diagnostic value of A-SAA are discussed. However, the relationship between different A-SAA isotypes and their human diseases are mostly derived from research laboratories with limited clinical samples. Thus, further clinical evaluations are necessary to confirm the clinical significance of each A-SAA isotype. Furthermore, the currently available A-SAA assays are based on polyclonal antibodies, which lack isotype specificity and are associated with many inflammatory diseases. Therefore, these assays are usually used in combination with other biomarkers in the clinic.

Tuning of hydrogel stiffness using a two-component peptide system for mammalian cell culture

Self-assembling peptide hydrogels (SAPHs) represent emerging cell cultures systems in several biomedical applications. The advantages of SAPHs are mainly ascribed to the absence of toxic chemical cross-linkers, the presence of ECM-like fibrillar structures and the possibility to produce hydrogels with a large range of different mechanical properties. We will present a two-component peptide system with tuneable mechanical properties, consisting of a small pentapeptide (SFFSF-NH2 , SA5N) that acts as a gelator and a larger 21-mer peptide (SFFSF-GVPGVGVPGVG-SFFSF, SA21) designed as a physical cross-linker. The hydrogels formed by different mixtures of the two peptides are made up mainly of antiparallel β-sheet nanofibers entangling in an intricate network. The effect of the addition of SA21 on the morphology of the hydrogels was investigated by atomic force microscopy and transmission electron microscopy and correlated to the mechanical properties of the hydrogel. Finally, the biocompatibility of the hydrogels using 2D cell cultures was tested. © 2018 The Authors. journal Of Biomedical Materials Research Part A Published By Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 535-544, 2019.

Variation of amino acid sequences of serum amyloid a (SAA) and immunohistochemical analysis of amyloid a (AA) in Japanese domestic cats

Amyloid A (AA) amyloidosis, a fatal systemic amyloid disease, occurs secondary to chronic inflammatory conditions in humans. Although persistently elevated serum amyloid A (SAA) levels are required for its pathogenesis, not all individuals with chronic inflammation necessarily develop AA amyloidosis. Furthermore, many diseases in cats are associated with the elevated production of SAA, whereas only a small number actually develop AA amyloidosis. We hypothesized that a genetic mutation in the SAA gene may strongly contribute to the pathogenesis of feline AA amyloidosis. In the present study, genomic DNA from four Japanese domestic cats (JDCs) with AA amyloidosis and from five without amyloidosis was analyzed using polymerase chain reaction (PCR) amplification and direct sequencing. We identified the novel variation combination of 45R-51A in the deduced amino acid sequences of four JDCs with amyloidosis and five without. However, there was no relationship between amino acid variations and the distribution of AA amyloid deposits, indicating that differences in SAA sequences do not contribute to the pathogenesis of AA amyloidosis. Immunohistochemical analysis using antisera against the three different parts of the feline SAA protein—i.e., the N-terminal, central, and C-terminal regions—revealed that feline AA contained the C-terminus, unlike human AA. These results indicate that the cleavage and degradation of the C-terminus are not essential for amyloid fibril formation in JDCs.

Influence of C-terminal truncation of murine Serum amyloid A on fibril structure

Amyloid A (AA) amyloidosis is a systemic protein misfolding disease affecting humans and other vertebrates. While the protein precursor in humans and mice is the acute-phase reactant serum amyloid A (SAA) 1.1, the deposited fibrils consist mainly of C-terminally truncated SAA fragments, termed AA proteins. For yet unknown reasons, phenotypic variations in the AA amyloid distribution pattern are clearly associated with specific AA proteins. Here we describe a bacterial expression system and chromatographic strategies to obtain significant amounts of C-terminally truncated fragments of murine SAA1.1 that correspond in truncation position to relevant pathological AA proteins found in humans. This enables us to investigate systematically structural features of derived fibrils. All fragments form fibrils under nearly physiological conditions that show similar morphological appearance and amyloid-like properties as evident from amyloid-specific dye binding, transmission electron microscopy and infrared spectroscopy. However, infrared spectroscopy suggests variations in the structural organization of the amyloid fibrils that might be derived from a modulating role of the C-terminus for the fibril structure. These results provide insights, which can help to get a better understanding of the molecular mechanisms underlying the different clinical phenotypes of AA amyloidosis.

Carbamylation of the amino-terminal residue (Gly1) of mouse serum amyloid A promotes amyloid formation in a cell culture model

Amyloid A (AA) amyloidosis is a fatal protein deposition disease afflicting a small percentage of patients with chronic inflammation. Factors other than inflammation that determine development of AA amyloidosis remain largely unknown. The subunit protein comprising AA amyloid fibrils is derived from serum amyloid A (SAA), specifically its amino-terminal portion. In this in vitro study, carbamylation of residues in this region (primarily Gly1 but also Lys24) was shown to markedly increase amyloid-forming propensity as judged by extensive accumulation of amyloid in cell cultures. Contrastingly, no amyloid deposition occurred in cultures given SAA having a noncarbamylated amino terminus. Carbamylation, known to occur during uremia or inflammation, merits investigation as a potential determinant of AA amyloid fibril formation.

Electrostatic Interactions at N- and C-Termini Determine Fibril Polymorphism in Serum Amyloid A Fragments

Amyloid polymorphism presents a challenge to physical theories of amyloid formation and stability. The amyloidogenic protein serum amyloid A (SAA) exhibits complex and unexplained structural polymorphism in its N-terminal fragments: the N-terminal 11-residue peptide (SAA1-11) forms left-handed helical fibrils, while extension by one residue (SAA1-12) produces a rare right-handed amyloid. In this study, we use a combination of vibrational spectroscopy and ultramicroscopy to examine fibrils of these peptides and their terminally acetylated and amidated variants, in an effort to uncover the physical basis for this effect. Raman spectroscopy and atomic force microscopy provide evidence that SAA1-12 forms a β-helical fibril architecture, while SAA1-11 forms more typical stacked β-sheets. Importantly, N-terminal acetylation blocks fibril formation by SAA1-12 with no effect on SAA1-11, while C-terminal amidation has nearly the opposite effect. Together, these data suggest distinct electrostatic interactions at the N- and C-termini stabilize the two fibril structures; we propose model fibril structures in which C-terminal extension changes the favored intermolecular interaction between peptide monomers from an Arg1-C-terminus charge pair to an N-terminus-C-terminus charge pair. This model suggests a general mechanism for charge-mediated amyloid polymorphism and may inform strategies for design of peptide-based nanomaterials stabilized by engineered intermolecular contacts.

Structural requirements of glycosaminoglycans for facilitating amyloid fibril formation of human serum amyloid A

Serum amyloid A (SAA) is a precursor protein of amyloid fibrils. Given that heparan sulfate (HS), a glycosaminoglycan (GAG), is detected in amyloid deposits, it has been suggested that GAG is a key component of amyloid fibril formation. We previously reported that heparin (an analog of HS) facilitates the fibril formation of SAA, but the structural requirements remain unknown. In the present study, we investigated the structural requirements of GAGs for facilitating the amyloid fibril formation of SAA. Spectroscopic analyses using structurally diverse GAG analogs suggested that the fibril formation of SAA was facilitated irrespective of the backbone structure of GAGs; however, the facilitating effect was strongly correlated with the degree of sulfation. Microscopic analyses revealed that the morphologies of SAA aggregates were modulated by the GAGs. The HS molecule, which is less sulfated than heparin but contains highly sulfated domains, exhibited a relatively high potential to facilitate fibril formation compared to other GAGs. The length dependence of fragmented heparins on the facilitating effect suggested that a high density of sulfate groups is also required. These results indicate that not only the degree of sulfation but also the lengths of sulfated domains in GAG play important roles in fibril formation of SAA.

Designing peptidic inhibitors of serum amyloid A aggregation process

Amyloid A amyloidosis is a life-threatening complication of a wide range of chronic inflammatory, infectious and neoplastic diseases, and the most common form of systemic amyloidosis worldwide. It is characterized by extracellular tissue deposition of fibrils that are composed of fragments of serum amyloid A protein (SAA), a major acute-phase reactant protein, produced predominantly by hepatocytes. Currently, there are no approved therapeutic agents directed against the formation of fibrillar SAA assemblies. We attempted to develop peptidic inhibitors based on their similarity and complementarity to the regions critical for SAA self-association, which they should interact with and block their assembly into amyloid fibrils. Inh1 and inh4 which are comprised of the residues from the amyloidogenic region of SAA1.1 protein and Aβ peptide, respectively, were found by us as capable to significantly suppress aggregation of the SAA1-12 peptide. It was chosen as an aggregation model that mimicks the amyloidogenic nucleus of SAA protein. We suppose that aromatic interactions may be responsible for inhibitory activity of both compounds. We also recognized that aromatic residues are involved in self-association of SAA1-12.

Systemic Amyloid A Amyloidosis in Island Foxes (Urocyon littoralis): Severity and Risk Factors

Systemic amyloid A (AA) amyloidosis is highly prevalent (34%) in endangered island foxes (Urocyon littoralis) and poses a risk to species recovery. Although elevated serum AA (SAA) from prolonged or recurrent inflammation predisposes to AA amyloidosis, additional risk factors are poorly understood. Here we define the severity of glomerular and medullary renal amyloid and identify risk factors for AA amyloidosis in 321 island foxes necropsied from 1987 through 2010. In affected kidneys, amyloid more commonly accumulated in the medullary interstitium than in the glomeruli (98% [n= 78 of 80] vs 56% [n= 45], respectively;P< .0001), and medullary deposition was more commonly severe (19% [n= 20 of 105]) as compared with glomeruli (7% [n= 7];P= .01). Univariate odds ratios (ORs) of severe renal AA amyloidosis were greater for short- and long-term captive foxes as compared with free-ranging foxes (ORs = 3.2, 3.7, respectively; overall P= .05) and for females as compared with males (OR = 2.9;P= .05). Multivariable logistic regression revealed that independent risk factors for amyloid development were increasing age class (OR = 3.8;P< .0001), San Clemente Island subspecies versus San Nicolas Island subspecies (OR = 5.3;P= .0003), captivity (OR = 5.1;P= .0001), and nephritis (OR = 2.3;P= .01). The increased risk associated with the San Clemente subspecies or captivity suggests roles for genetic as well as exogenous risk factors in the development of AA amyloidosis.

Probing the role of aromatic residues in the self-assembly of Aβ(16-22) in fluorinated alcohols and their aqueous mixtures

The Aβ(16–22) sequence KLVFFAE spans the hydrophobic core of the Aβ peptide and plays an important role in its self-assembly. Apart from forming amyloid fibrils, Aβ(16–22) can self-associate into highly ordered nanotubes and ribbon-like structures depending on the composition of solvent used for dissolution. The Aβ(16–22) sequence which has FF at the 19th and 20th positions would be a good model to investigate peptide self-assembly in the context of aromatic interactions. In this study, self-assembly of Aβ(16–22) and its aromatic analogs obtained by replacement of F19, F20 or both by Y or W was examined after dissolution in fluorinated alcohols and their aqueous mixtures in solvent cluster forming conditions. The results indicate that the presence of aromatic residues Y and W and their position in the sequence plays an important role in self-assembly. We observe the formation of amyloid fibrils and other self-assembled structures such as spheres, rings and beads. Our results indicate that 20% HFIP is more favourable for amyloid fibril formation as compared to 20% TFE, when F is replaced with Y or W. The dissolution of peptides in DMSO followed by evaporation of solvent and dissolution in water appears to greatly influence peptide conformation, morphology and cross-β content of self-assembled structures. Our study shows that positioning of aromatic residues F, Y and W have an important role in directing self-assembly of the peptides.

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Effect of fluorinated alcohols on the aggregation of Aβ(16–22) and analogs was investigated.

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Replacement of F by Y and W in the Aβ(16–22) sequence modulates self-assembly.

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Positions of F, Y, W in Aβ(16–22) plays an important role in self-assembly.

Identification of a Serum amyloid A gene and the association of SNPs with Vibrio-resistance and growth traits in the clam Meretrix meretrix

Serum amyloid A (SAA), an acute response protein as well as an apolipoprotein, is considered to play crucial roles in both innate immunity and lipid metabolism. In this study, a SAA gene (MmSAA) was identified in the clam Meretrix meretrix. The full length DNA of MmSAA was 1407bp, consisting of three exons and two introns. The distribution of MmSAA in clam tissues was examined with the highest expression in hepatopancreas. In response to the Vibrio parahaemolyticus challenge, MmSAA mRNA showed significantly higher expression at 24 h post-challenge in experimental clams (P < 0.05). Forty-eight single nucleotide polymorphisms (SNPs) in the DNA partial sequence of MmSAA were discovered and examined for their association with Vibrio-resistance and growth traits, respectively. The single SNP association analysis indicated that five single SNPs (g.42, g.72, g.82, g.147 and g.165) were significantly associated with Vibrio-resistance (P < 0.05). Haplotype analysis produced additional support for association with the Chi-square values 6.393 (P = 0.012). Among the five selected SNPs, the effect of a missense mutation (g.82, A → G) was detected by site-directed mutagenesis with fusion expression of protein assay, and the result showed that the recombinant plasmids containing wild-type pET30a-MmSAA had more inhibition effect than the mutant ones on the growth rate of the host bacteria. In addition, four growth traits of the clams in 09G3SPSB population were recorded and the SNP g.176 was found to be significantly associated with the growth traits with the Global score value 0.790 (P = 0.015). Our findings suggested that common genetic variation in MmSAA might contribute to the risk of susceptibility to Vibrio infection and might be associated with the growth traits in the clams M. meretrix, and more works are still needed to validate these SNPs as potential markers for actual selective breeding.

Serum amyloid a truncations in type 2 diabetes mellitus

Serum Amyloid A (SAA) is an acute phase protein complex consisting of several abundant isoforms. The N- terminus of SAA is critical to its function in amyloid formation. SAA is frequently truncated, either missing an arginine or an arginine-serine dipeptide, resulting in isoforms that may influence the capacity to form amyloid. However, the relative abundance of truncated SAA in diabetes and chronic kidney disease is not known.

Nanospheres from the self-assembly of an elastin-inspired triblock peptide

The self-assembly of an elastin-inspired triblock peptide into nanospheres highlights the important role of conformational flexibility and π–π stacking.

Intrinsic Stability, Oligomerization, and Amyloidogenicity of HDL-Free Serum Amyloid A

Serum amyloid A (SAA) is an acute-phase reactant protein predominantly bound to high-density lipoprotein in serum and presumed to play various biological and pathological roles. Upon tissue trauma or infection, hepatic expression of SAA increases up to 1,000 times the basal levels. Prolonged increased levels of SAA may lead to amyloid A (AA) amyloidosis, a usually fatal systemic disease in which the amyloid deposits are mostly comprised of the N-terminal 1-76 fragment of SAA. SAA isoforms may differ across species in their ability to cause AA amyloidosis, and the mechanism of pathogenicity remains poorly understood. In vitro studies have shown that SAA is a marginally stable protein that folds into various oligomeric species at 4 °C. However, SAA is largely disordered at 37 °C, reminiscent of intrinsically disordered proteins. Non-pathogenic murine (m)SAA2.2 spontaneously forms amyloid fibrils in vitro at 37 °C whereas pathogenic mSAA1.1 has a long lag (nucleation) phase, and eventually forms fibrils of different morphology than mSAA2.2. Remarkably, human SAA1.1 does not form mature fibrils in vitro. Thus, it appears that the intrinsic amyloidogenicity of SAA is not a key determinant of pathogenicity, and that other factors, including fibrillation kinetics, ligand binding effects, fibril stability, nucleation efficiency, and SAA degradation may play key roles. This chapter will focus on the known structural and biophysical properties of SAA and discuss how these properties may help better understand the molecular mechanism of AA amyloidosis.

Proteomic analysis of highly prevalent amyloid A amyloidosis endemic to endangered island foxes

Amyloid A (AA) amyloidosis is a debilitating, often fatal, systemic amyloid disease associated with chronic inflammation and persistently elevated serum amyloid A (SAA). Elevated SAA is necessary but not sufficient to cause disease and the risk factors for AA amyloidosis remain poorly understood. Here we identify an extraordinarily high prevalence of AA amyloidosis (34%) in a genetically isolated population of island foxes (Urocyon littoralis) with concurrent chronic inflammatory diseases. Amyloid deposits were most common in kidney (76%), spleen (58%), oral cavity (45%), and vasculature (44%) and were composed of unbranching, 10 nm in diameter fibrils. Peptide sequencing by mass spectrometry revealed that SAA peptides were dominant in amyloid-laden kidney, together with high levels of apolipoprotein E, apolipoprotein A-IV, fibrinogen-α chain, and complement C3 and C4 (false discovery rate ≤ 0.05). Reassembled peptide sequences showed island fox SAA as an 111 amino acid protein, most similar to dog and artic fox, with 5 unique amino acid variants among carnivores. SAA peptides extended to the last two C-terminal amino acids in 5 of 9 samples, indicating that near full length SAA was often present in amyloid aggregates. These studies define a remarkably prevalent AA amyloidosis in island foxes with widespread systemic amyloid deposition, a unique SAA sequence, and the co-occurrence of AA with apolipoproteins.

AA amyloidosis: pathogenesis and targeted therapy

The understanding of why and how proteins misfold and aggregate into amyloid fibrils has increased considerably during recent years. Central to amyloid formation is an increase in the frequency of the β-sheet structure, leading to hydrogen bonding between misfolded monomers and creating a fibril that is comparably resistant to degradation. Generation of amyloid fibrils is nucleation dependent, and once formed, fibrils recruit and catalyze the conversion of native molecules. In AA amyloidosis, the expression of cytokines, particularly interleukin 6, leads to overproduction of serum amyloid A (SAA) by the liver. A chronically high plasma concentration of SAA results in the aggregation of amyloid into cross-β-sheet fibrillar deposits by mechanisms not fully understood. Therefore, AA amyloidosis can be thought of as a consequence of long-standing inflammatory disease. This review summarizes current knowledge about AA amyloidosis. The systemic amyloidoses have been regarded as intractable conditions, but improvements in the understanding of fibril composition and pathogenesis over the past decade have led to the development of a number of different therapeutic approaches with promising results.

Self-assembling properties of peptides derived from TDP-43 C-terminal fragment

Two highly fibrillogenic peptide sequences (MNFGAFSINP and EDLIIKGISV) were previously reported in the C-terminal fragment (CTF) of TDP-43 (220-414), a protein recently implicated in neuro-degenerative diseases such as amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD-U). It was observed that the sequences MNFGAFS and EDLIIKG harbor their respective fibrillogenic domains. Here, the self-assembling properties of peptides obtained by systematic deletion of residues from these two sequences were investigated with the help of light scattering, thioflavin T fluorescence, transmission electron microscopy, and circular dichroism spectroscopy. It was found that the pentapeptide NFGAF and the tetrapeptide DLII are the shortest fibrillogenic sequences from MNFGAFS and EDLIIKG, respectively. Structure function studies revealed that self-assembly of the peptides is largely governed by hydrophobic interactions. Both NFGAF and DLII formed hydrogels based on a complex fibrillar network, at relatively low concentrations, and of remarkable strength and stability. Of particular interest was DLII, a rare aliphatic tetrapeptide that formed a hydrogel at a concentration of 1 mg/mL in less than an hour. Interestingly, various other tetrapeptides based on DLII (YLII, KLII, NLII, and LIID) also formed hydrogels of comparable physical properties, suggesting that an amphipathic peptide design based on the hydrophobic LII motif and a single residue polar terminus is highly favorable for hydrogelation. Peptides discovered in this study, especially DLII and its variants, are some of the shortest ever reported to show such structural and functional features, suggesting that they can be useful templates for the design of peptide-based soft materials.

Inhibiting toxic aggregation of amyloidogenic proteins: a therapeutic strategy for protein misfolding diseases

BACKGROUND

The deposition of self-assembled amyloidogenic proteins is associated with multiple diseases, including Alzheimer's disease, Parkinson's disease and type 2 diabetes mellitus. The toxic misfolding and self-assembling of amyloidogenic proteins are believed to underlie protein misfolding diseases. Novel drug candidates targeting self-assembled amyloidogenic proteins represent a potential therapeutic approach for protein misfolding diseases.

SCOPE OF REVIEW

In this perspective review, we provide an overview of the recent progress in identifying inhibitors that block the aggregation of amyloidogenic proteins and the clinical applications thereof.

MAJOR CONCLUSIONS

Compounds such as polyphenols, certain short peptides, and monomer- or oligomer-specific antibodies, can interfere with the self-assembly of amyloidogenic proteins, prevent the formation of oligomers, amyloid fibrils and the consequent cytotoxicity.

GENERAL SIGNIFICANCE

Some inhibitors have been tested in clinical trials for treating protein misfolding diseases. Inhibitors that target the aggregation of amyloidogenic proteins bring new hope to therapy for protein misfolding diseases.

Characterization of the oligomerization and aggregation of human Serum Amyloid A

The fibrillation of Serum Amyloid A (SAA) – a major acute phase protein – is believed to play a role in the disease Amyloid A (AA) Amyloidosis. To better understand the amyloid formation pathway of SAA, we characterized the oligomerization, misfolding, and aggregation of a disease-associated isoform of human SAA – human SAA1.1 (hSAA1.1) – using techniques ranging from circular dichroism spectroscopy to atomic force microscopy, fluorescence spectroscopy, immunoblot studies, solubility measurements, and seeding experiments. We found that hSAA1.1 formed alpha helix-rich, marginally stable oligomers in vitro on refolding and cross-beta-rich aggregates following incubation at 37°C. Strikingly, while hSAA1.1 was not highly amyloidogenic in vitro, the addition of a single N-terminal methionine residue significantly enhanced the fibrillation propensity of hSAA1.1 and modulated its fibrillation pathway. A deeper understanding of the oligomerization and fibrillation pathway of hSAA1.1 may help elucidate its pathological role.

Why working with porcine circulating serum amyloid A is a pig of a job

Serum amyloid A (SAA) is a major acute phase protein in most species, and is widely employed as a health marker. Systemic SAA isoforms (SAA1, and SAA2) are apolipoproteins synthesized by the liver which associate with high density lipoproteins (HDL). Local SAA (SAA3) isoforms are synthesized in other tissues and are present in colostrums, mastitic milk and mammary dry secretions. Of systemic SAA the bulk is monomeric and bound to HDL, and a small proportion is found in serum in a multimeric form with a buried HDL binding site. In most species, systemic SAA could easily be studied by purifying it from serum of diseased individuals by hydrophobic interaction chromatography methods. For years, we were not able to isolate systemic pig SAA using the latter methods, and found that the bulk of pig SAA did not reside in the HDL-rich serum fractions but in the soluble protein fraction mainly as a multimeric protein. Based on these surprising results, we analysed in silico the theoretical properties and predicted the secondary structure of pig SAA by using the published pig primary SAA amino acid sequence. Results of the analysis confirmed that systemic pig SAA had the highest homology with local SAA3 which in other species is the isoform associated with non-hepatic production in tissues such as mammary gland and intestinal epithelium. Furthermore, the primary sequence of the pig SAA N-terminal HDL binding site did differ considerably from SAA1/2. Secondary structure analysis of the predicted alpha-helical structure of this HDL binding site showed a considerable reduction in hydrophobicity compared to SAA1/2. Based on these results, it is argued that systemic acute phase SAA in the pig has the structural properties of locally produced SAA (SAA3). It is proposed that in pig SAA multimers the charged N-terminal sequence is buried, which would explain their different properties. It is concluded that pig systemic SAA is unique compared to other species, which raises questions about the proposed importance of acute phase SAA in HDL metabolism during inflammation in this species.

Influence of the carboxy terminus of serum amyloid A on protein oligomerization, misfolding, and fibril formation

The fibrillar deposition of serum amyloid A (SAA) has been linked to the disease amyloid A (AA) amyloidosis. We have used the SAA isoform, SAA2.2, from the CE/J mouse strain, as a model system to explore the inherent structural and biophysical properties of SAA. Despite its nonpathogenic nature in vivo, SAA2.2 spontaneously forms fibrils in vitro, suggesting that SAA proteins are inherently amyloidogenic. However, whereas the importance of the amino terminus of SAA for fibril formation has been well documented, the influence of the proline-rich and presumably disordered carboxy terminus remains poorly understood. To clarify the inherent role of the carboxy terminus in the oligomerization and fibrillation of SAA, we truncated the proline-rich final 13 residues of SAA2.2. We found that unlike full-length SAA2.2, the carboxy-terminal truncated SAA2.2 (SAA2.2ΔC) did not oligomerize to a hexamer or octamer, but formed a high molecular weight soluble aggregate. Moreover, SAA2.2ΔC also exhibited a pronounced decrease in the rate of fibril formation. Intriguingly, when equimolar amounts of denatured SAA2.2 and SAA2.2ΔC were mixed and allowed to refold together, the mixture formed an octamer and exhibited rapid fibrillation kinetics, similar to those for full-length SAA2.2. These results suggest that the carboxy terminus of SAA, which is highly conserved among SAA sequences in all vertebrates, might play important structural roles, including modulating the folding, oligomerization, misfolding, and fibrillation of SAA.

Identification of regions responsible for heparin-induced amyloidogenesis of human serum amyloid A using its fragment peptides

Human serum amyloid A (SAA) is a precursor protein of amyloid fibrils. Although several studies have been performed, a detailed understanding of the molecular mechanism for SAA fibrillation remains elusive. Glycosaminoglycans such as heparin are suggested to serve as scaffolds in amyloid fibril formation in some cases. In the present study, amyloidogenic properties of synthetic fragment peptides corresponding to the N-terminal (residues 1-27), central (residues 43-63), and C-terminal (residues 77-104) regions of SAA molecule induced by heparin were examined using fluorescence, circular dichroism (CD), and electron microscopy. Fluorescence and CD measurements demonstrated that SAA (1-27) peptide is evidently involved in heparin-induced amyloidogenesis. Correspondingly, relatively minor changes in fluorescence and a quite different pattern in the CD spectrum were observed in SAA (43-63) peptide. In contrast, SAA (77-104) peptide did not show any changes induced by heparin. Transmission electron microscopy indicated that SAA (1-27) peptide forms short and straight fibrils, whereas SAA (43-63) peptide forms much longer and seemingly elastic fibrils. These results suggest that the N-terminal region plays a crucial role as a rigid core and the central region facilitates the elongation of fibrils in heparin-induced amyloidogenesis of SAA molecule.

Acute phase response in Chinese soft-shelled turtle (Trionyx sinensis) with Aeromonas hydrophila infection

Chinese soft-shelled turtle (Trionyx sinensis) is an important culture reptile. However, little is known about its acute phase response (APR) caused by bacteria. Serum amyloid A (SAA) is a major acute phase protein (APP). In this study, a turtle SAA homologue was identified and described in reptiles. The full-length cDNA of turtle SAA was 554 bp and contained a 381 bp open reading frame (ORF) coding for a protein of 127 aa. Similar to other known SAA genes, the turtle SAA gene contained three exons and two introns. The promoter region of turtle SAA gene contained the consensus binding sites for nuclear factor (NF)-κB and c-Rel. The turtle SAA amino acid sequence shared the highest identity to avian SAA sequences. Meantime, we present the first systematic study with expression levels of five genes encoding APPs in immune response caused by Aeromonas hydrophila infection. After infection, turtle SAA mRNA was induced in liver at 8h, then increased more than 1200-fold at 2d; in spleen and kidney, the SAA mRNAs were also induced during 8h-7d, but the level was far lower than that in the liver. The complement 3 (C3), fibrinogen-gamma chain (Fb-G) and cathepsin L (CathL) mRNAs were increased in liver at 2d, whereas the albumin (ALB) mRNA was significantly decreased during 8h-7d. Our studies suggest that the APR in turtle with A. hydrophila infection is similar to that in mammals, and SAA is a major indicator of bacterial infection, especially at early stage, in reptiles. Additionally, the different expression patterns of five APP genes observed in present studies could provide clues for understanding the innate immune mechanisms in the APR of reptiles.

Impact on the replacement of Phe by Trp in a short fragment of Aβ amyloid peptide on the formation of fibrils

Aβ(16-22) (Ac-KLVFFAE-NH(2) ) is one of the shortest amyloid fibril-forming sequences identified in β-amyloid peptide. At neutral pH, the peptide forms fibrils in the concentration range of 0.2-2.0 mM after ≥ 10 days of incubation. Structures of the fibrils proposed based on solid-state NMR and MD simulations studies suggest antiparallel arrangement of β-strands and aromatic interactions between the Phe residues. In an effort to examine the role of aromatic interactions between two Phe residues in Aβ(16-22) , we have studied the self-assembly of Aβ(16-22) (AβFF) and two of its variants, Ac-KLVFWAE-NH(2) (AβFW) and Ac-KLVWFAE-NH(2) (AβWF). The peptides were dissolved in methanol (MeOH) at a concentration of 1 mM and in water (AβFW and AβWF, 1 mM; AβFF, 330 µM). Peptide solutions (100 µM) were prepared in 50 mM sodium phosphate buffer at pH 7 by diluting from MeOH and water stock solutions. AβFW forms amyloid-like fibrils immediately from MeOH, as indicated by atomic force microscopy. Dilution of AβFW into phosphate buffer from stock solution prepared in MeOH results in fibrils, but with different morphology and dimensions. The secondary structure potentiated by MeOH seems to be important for the self-assembly of AβFW, as fibrils are not formed from water where the peptide is unordered. On the other hand, AβFF and AβWF do not form amyloid fibrils rapidly from any of the solvents used for dissolution. However, drying of AβWF from MeOH on mica surface gives rod-like and fibrous structures. Our study indicates that positioning of the aromatic residues F and W has an important role to play in promoting self-assembly of the Aβ(16-22) peptides.

Interactions in the native state of monellin, which play a protective role against aggregation

A series of recent studies have provided initial evidence about the role of specific intra-molecular interactions in maintaining proteins in their soluble state and in protecting them from aggregation. Here we show that the amino acid sequence of the protein monellin contains two aggregation-prone regions that are prevented from initiating aggregation by multiple non-covalent interactions that favor their burial within the folded state of the protein. By investigating the behavior of single-chain monellin and a series of five of its mutational variants using a variety of biochemical, biophysical and computational techniques, we found that weakening of the non-covalent interaction that stabilizes the native state of the protein leads to an enhanced aggregation propensity. The lag time for fibrillation was found to correlate with the apparent midpoint of thermal denaturation for the series of mutational variants, thus showing that a reduced thermal stability is associated with an increased aggregation tendency. We rationalize these findings by showing that the increase in the aggregation propensity upon mutation can be predicted in a quantitative manner through the increase in the exposure to solvent of the amyloidogenic regions of the sequence caused by the destabilization of the native state. Our findings, which are further discussed in terms of the structure of monellin and the perturbation by the amino acid substitutions of the contact surface between the two subdomains that compose the folded state of monellin, provide a detailed description of the specific intra-molecular interactions that prevent aggregation by stabilizing the native state of a protein.

Conformational preferences of non-polar amino acid residues: an additional factor in amyloid formation

Amyloid consists of β-sheet polymers and is associated with disease and with functional assemblies. Amyloid-forming proteins differ widely in native structures and sequences. We describe here how conformational preferences of non-polar amino acid residues can affect amyloid formation. The most non-polar residues promote either β-strands (Val, Ile, Phe, and Cys, VIFC) or α-helices (Leu, Ala, and Met, LAM), while the most polar residues promote only α-helices. For 12 proteins associated with disease, the localizations of the amyloid core regions are known. Eleven of these contain segments that are biased for VIFC, but essentially lack segments that are biased for LAM. For the amyloid β-peptide associated with Alzheimer's disease and an amyloidogenic fragment of the prion protein, observed effects of mutations support that VIFC bias favors formation of β-sheet aggregates and amyloid, while LAM bias prevents it. VIFC and LAM profiles combine information on secondary structure propensities and polarity, and add a simple criterion to the prediction of amyloidogenic regions.

An orphan dermaseptin from frog skin reversibly assembles to amyloid-like aggregates in a pH-dependent fashion

Dermaseptin PD-3-7 (aDrs) from frog skin contains three aspartic acid residues resulting in a negative net charge at neutral pH, as opposed to numerous other dermaseptins which are cationic helical antimicrobial peptides. Still, this peptide can be fitted into an amphipathic alpha helix by an Edmundson wheel projection. However, folding to the proposed helix was induced to only a low extent by zwitterionic vesicles or even detergents. Furthermore, no evidence of antibacterial or cytotoxic activity from soluble aDrs could be obtained. The peptide has an inherent propensity to an extended conformation in aqueous solution and self-assembles into amyloid fibrils in a reversible pH-controlled fashion, which was studied in some detail; above pH 5, the amyloid fibrils disassemble in a cooperative manner. This is probably caused by deprotonation of both side chain and terminal carboxyl groups, which results in intermolecular electrostatic repulsion. At neutral pH, this process proceeds instantaneously to the soluble form. Within the transition interval (pH 5-6.5), however, 'backward' granular aggregates, 10-500 nm in size, are formed. Such metastable amorphous aggregates, which are quickly released from an amyloid depot by a shift in pH, can mediate a strong cytotoxic effect. This activity does not involve lysis or interference with the cellular redox status, but apparently acts via an as yet unidentified mechanism. In this study, we present a new member of an emerging class of self-assembling frog skin peptides with extraordinary self-aggregation properties, which may potentially be relevant for biological processes. Structured digital abstract: * MINT-7256467: Dermaseptin (uniprotkb:O93455) and Dermaseptin (uniprotkb:O93455) bind (MI:0407) by circular dichroism (MI:0016) * MINT-7255686: Dermaseptin (uniprotkb:O93455) and Dermaseptin (uniprotkb:O93455) bind (MI:0407) by biophysical (MI:0013) * MINT-7256439: Dermaseptin (uniprotkb:O93455) and Dermaseptin (uniprotkb:O93455) bind (MI:0407) by fluorescence microscopy (MI:0416) * MINT-7256449: Dermaseptin (uniprotkb:O93455) and Dermaseptin (uniprotkb:O93455) bind (MI:0407) by electron microscopy (MI:0040) * MINT-7256430: Dermaseptin (uniprotkb:O93455) and Dermaseptin (uniprotkb:O93455) bind (MI:0407) by fluorescence technologies (MI:0051).

Animal models of human amyloidoses: are transgenic mice worth the time and trouble?

The amyloidoses are the prototype gain of toxic function protein misfolding diseases. As such, several naturally occurring animal models and their inducible variants provided some of the first insights into these disorders of protein aggregation. With greater analytic knowledge and the increasing flexibility of transgenic and gene knockout technology, new models have been generated allowing the interrogation of phenomena that have not been approachable in more reductionist systems, i.e. behavioral readouts in the neurodegenerative diseases, interactions among organ systems in the transthyretin amyloidoses and taking pre-clinical therapeutic trials beyond cell culture. The current review describes the features of both transgenic and non-transgenic models and discusses issues that appear to be unresolved even when viewed in their organismal context.

Cathepsin D activity protects against development of type AA amyloid fibrils

BACKGROUND

The extracellular, fibrillar deposits of reactive (secondary) amyloidosis are composed of amyloid A (AA) protein, a proteolytically derived fragment of the acute phase protein serum amyloid A (SAA). While complete degradation of SAA precludes amyloid formation, limited cleavage which generates AA protein is considered part of the pathogenic mechanism.

MATERIALS AND METHODS

In this study, we investigated SAA degradation by lysosomal enzymes cathepsins B, D, and K, and assessed the impact of cathepsin activity on AA amyloid formation in a cell culture model using peripheral blood mononuclear cells from healthy volunteers.

RESULTS

Lysates of human mononuclear cells were capable of degrading SAA. Degradation was significantly reduced by inhibition of cathepsin D with pepstatin A. Inhibition of cathepsin B or cathepsin K, however, had no effect. The SAA fragment pattern generated by mononuclear cell lysates was similar to that produced by incubating SAA with purified human cathepsin D. Consistent with in vitro findings, amyloid formation in human monocyte cultures was increased by 43% when cathepsin D was inhibited, but remained unaffected by inhibition of cathepsin B or cathepsin K.

CONCLUSION

These data provide evidence that cathepsin D but not cathepsin B or cathepsin K is physiologically important in SAA degradation and hence in preventing SAA from accumulating and serving as precursor of AA amyloid fibrils.

Diffusible amyloid oligomers trigger systemic amyloidosis in mice

AA (amyloid protein A) amyloidosis in mice is markedly accelerated when the animals are given, in addition to an inflammatory stimulus, an intravenous injection of protein extracted from AA-laden mouse tissue. Previous findings affirm that AA fibrils can enhance the in vivo amyloidogenic process by a nucleation seeding mechanism. Accumulating evidence suggests that globular aggregates rather than fibrils are the toxic entities responsible for cell death. In the present study we report on structural and morphological features of AEF (amyloid-enhancing factor), a compound extracted and partially purified from amyloid-laden spleen. Surprisingly, the chief amyloidogenic material identified in the active AEF was diffusible globular oligomers. This partially purified active extract triggered amyloid deposition in vital organs when injected intravenously into mice. This implies that such a phenomenon could have been inflicted through the nucleation seeding potential of toxic oligomers in association with altered cytokine induction. In the present study we report an apparent relationship between altered cytokine expression and AA accumulation in systemically inflamed tissues. The prevalence of serum AA monomers and proteolytic oligomers in spleen AEF is consistent to suggest that extrahepatic serum AA processing might lead to local accumulation of amyloidogenic proteins at the serum AA production site.