Amorphous protein aggregates stimulate plasminogen activation, leading to release of cytotoxic fragments that are clients for extracellular chaperones

Agglomeration: when folded proteins clump together

Protein self-association is a widespread phenomenon that results in the formation of multimeric protein structures with critical roles in cellular processes. Protein self-association can lead to finite protein complexes or open-ended, and potentially, infinite structures. This review explores the concept of protein agglomeration, a process that results from the infinite self-assembly of folded proteins. We highlight its differences from other better-described processes with similar macroscopic features, such as aggregation and liquid-liquid phase separation. We review the sequence, structural, and biophysical factors influencing protein agglomeration. Lastly, we briefly discuss the implications of agglomeration in evolution, disease, and aging. Overall, this review highlights the need to study protein agglomeration for a better understanding of cellular processes.

Clusterin is a Potential Therapeutic Target in Alzheimer's Disease

In recent years, Clusterin, a glycosylated protein with multiple biological functions, has attracted extensive research attention. It is closely associated with the physiological and pathological states within the organism. Particularly in Alzheimer's disease (AD) research, Clusterin plays a significant role in the disease's occurrence and progression. Numerous studies have demonstrated a close association between Clusterin and AD. Firstly, the expression level of Clusterin in the brain tissue of AD patients is closely related to pathological progression. Secondly, Clusterin is involved in the deposition and formation of β-amyloid, which is a crucial process in AD development. Furthermore, Clusterin may affect the pathogenesis of AD through mechanisms such as regulating inflammation, controlling cell apoptosis, and clearing pathological proteins. Therefore, further research on the relationship between Clusterin and AD will contribute to a deeper understanding of the etiology of this neurodegenerative disease and provide a theoretical basis for developing early diagnostic and therapeutic strategies for AD. This also makes Clusterin one of the research focuses as a potential biomarker for AD diagnosis and treatment monitoring.

Characterization of extracellular matrix deposited by segmental trabecular meshwork cells

PURPOSE

Biophysical and biochemical attributes of the extracellular matrix are major determinants of cell fate in homeostasis and disease. Ocular hypertension and glaucoma are diseases where the trabecular meshwork tissue responsible for aqueous humor egress becomes stiffer accompanied by changes in its matrisome in a segmental manner with regions of high or low flow. Prior studies demonstrate these alterations in the matrix are dynamic in response to age and pressure changes. The underlying reason for segmentation or differential response to pressure and stiffening are unknown. This is largely due to a lack of appropriate models (in vitro or ex vivo) to study this phenomena.

METHODS

Primary trabecular meshwork cells were isolated from segmental flow regions, and cells were cultured for 4 weeks in the presence or absence or dexamethasone to obtain cell derived matrices (CDM). The biomechanical attributes of the CDM, composition of the matrisome, and incidence of crosslinks were determined by atomic force microscopy and mass spectrometry.

RESULTS

Data demonstrate that matrix deposited by cells from low flow regions are stiffer and exhibit a greater number of immature and mature crosslinks, and that these are exacerbated in the presence of steroid. We also show a differential response of high or low flow cells to steroid via changes observed in the matrix composition. However, no correlations were observed between elastic moduli and presence or absence of mature and immature crosslinks in the CDMs.

CONCLUSION

Regardless of a direct correlation between matrix stiffness and crosslinks, we observed distinct differences in the composition and mechanics of the matrices deposited by segmental flow cells. These results suggest distinct differences in cellular identify and likely a basis for mechanical memory post isolation and culture. Nevertheless, we conclude that although a mechanistic basis for matrix stiffness was undetermined in this study, it is a viable tool to study cell-matrix interactions and further our understanding of trabecular meshwork pathobiology.

Characterization of extracellular matrix deposited by segmental trabecular meshwork cells

Biophysical and biochemical attributes of the extracellular matrix are major determinants of cell fate in homeostasis and disease. Ocular hypertension and glaucoma are diseases where the trabecular meshwork tissue responsible for aqueous humor egress becomes stiffer accompanied by changes in its matrisome in a segmental manner with regions of high or low flow. Prior studies demonstrate these alterations in the matrix are dynamic in response to age and pressure changes. The underlying reason for segmentation or differential response to pressure and stiffening are unknown. This is largely due to a lack of appropriate models ( in vitro or ex vivo ) to study this phenomena. In this study, we characterize the biomechanical attributes, matrisome, and incidence of crosslinks in the matrix deposited by primary cells isolated from segmental flow regions and when treated with glucocorticosteroid. Data demonstrate that matrix deposited by cells from low flow regions are stiffer and exhibit a greater number of immature and mature crosslinks, and that these are exacerbated in the presence of steroid. We also show a differential response of high or low flow cells to steroid via changes observed in the matrix composition. We conclude that although a mechanistic basis for matrix stiffness was undetermined in this study, it is a viable tool to study cell-matrix interactions and further our understanding of trabecular meshwork pathobiology.

Extracellular protein homeostasis in neurodegenerative diseases

The protein homeostasis (proteostasis) system encompasses the cellular processes that regulate protein synthesis, folding, concentration, trafficking and degradation. In the case of intracellular proteostasis, the identity and nature of these processes have been extensively studied and are relatively well known. By contrast, the mechanisms of extracellular proteostasis are yet to be fully elucidated, although evidence is accumulating that their age-related progressive impairment might contribute to neuronal death in neurodegenerative diseases. Constitutively secreted extracellular chaperones are emerging as key players in processes that operate to protect neurons and other brain cells by neutralizing the toxicity of extracellular protein aggregates and promoting their safe clearance and disposal. Growing evidence indicates that these extracellular chaperones exert multiple effects to promote cell viability and protect neurons against pathologies arising from the misfolding and aggregation of proteins in the synaptic space and interstitial fluid. In this Review, we outline the current knowledge of the mechanisms of extracellular proteostasis linked to neurodegenerative diseases, and we examine the latest understanding of key molecules and processes that protect the brain from the pathological consequences of extracellular protein aggregation and proteotoxicity. Finally, we contemplate possible therapeutic opportunities for neurodegenerative diseases on the basis of this emerging knowledge.

A guide to studying protein aggregation

Disrupted protein folding or decreased protein stability can lead to the accumulation of (partially) un- or misfolded proteins, which ultimately cause the formation of protein aggregates. Much of the interest in protein aggregation is associated with its involvement in a wide range of human diseases and the challenges it poses for large-scale biopharmaceutical manufacturing and formulation of therapeutic proteins and peptides. On the other hand, protein aggregates can also be functional, as observed in nature, which triggered its use in the development of biomaterials or therapeutics as well as for the improvement of food characteristics. Thus, unmasking the various steps involved in protein aggregation is critical to obtain a better understanding of the underlying mechanism of amyloid formation. This knowledge will allow a more tailored development of diagnostic methods and treatments for amyloid-associated diseases, as well as applications in the fields of new (bio)materials, food technology and therapeutics. However, the complex and dynamic nature of the aggregation process makes the study of protein aggregation challenging. To provide guidance on how to analyse protein aggregation, in this review we summarize the most commonly investigated aspects of protein aggregation with some popular corresponding methods.

The Role of Proteolysis in Amyloidosis

Amyloidoses are a group of diseases associated with deposits of amyloid fibrils in different tissues. So far, 36 different types of amyloidosis are known, each due to the misfolding and accumulation of a specific protein. Amyloid deposits can be found in several organs, including the heart, brain, kidneys, and spleen, and can affect single or multiple organs. Generally, amyloid-forming proteins become prone to aggregate due to genetic mutations, acquired environmental factors, excessive concentration, or post-translational modifications. Interestingly, amyloid aggregates are often composed of proteolytic fragments, derived from the degradation of precursor proteins by yet unidentified proteases, which display higher amyloidogenic tendency compared to precursor proteins, thus representing an important mechanism in the onset of amyloid-based diseases. In the present review, we summarize the current knowledge on the proteolytic susceptibility of three of the main human amyloidogenic proteins, i.e., transthyretin, β-amyloid precursor protein, and α-synuclein, in the onset of amyloidosis. We also highlight the role that proteolytic enzymes can play in the crosstalk between intestinal inflammation and amyloid-based diseases.

The Emerging Roles of Extracellular Chaperones in Complement Regulation

The immune system is essential to protect organisms from internal and external threats. The rapidly acting, non-specific innate immune system includes complement, which initiates an inflammatory cascade and can form pores in the membranes of target cells to induce cell lysis. Regulation of protein homeostasis (proteostasis) is essential for normal cellular and organismal function, and has been implicated in processes controlling immunity and infection. Chaperones are key players in maintaining proteostasis in both the intra- and extracellular environments. Whilst intracellular proteostasis is well-characterised, the role of constitutively secreted extracellular chaperones (ECs) is less well understood. ECs may interact with invading pathogens, and elements of the subsequent immune response, including the complement pathway. Both ECs and complement can influence the progression of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis, as well as other diseases including kidney diseases and diabetes. This review will examine known and recently discovered ECs, and their roles in immunity, with a specific focus on the complement pathway.

Direct Analysis of Mitochondrial Damage Caused by Misfolded/Destabilized Proteins

Protein quality control is essential for cellular homeostasis. In this study, we examined the effect of improperly folded proteins that do not form amyloid fibrils on mitochondria, which play important roles in ATP production and cell death. First, we prepared domain 3 of the dengue envelope protein in wild type and four mutants with widely different biophysical properties in misfolded/aggregated or destabilized states. The effects of the different proteins were detected using fluorescence microscopy and Western blotting, which revealed that three of the five proteins disrupted both inner and outer membrane integrity, while the other two proteins, including the wild type, did not. Next, we examined the common characteristics of the proteins that displayed toxicity against mitochondria by measuring oligomer size, molten globule-like properties, and thermal stability. The common feature of all three toxic proteins was thermal instability. Therefore, our data strongly suggest that thermally unstable proteins generated in the cytosol can cause cellular damage by coming into direct contact with mitochondria. More importantly, we revealed that this damage is not amyloid-specific.

The Influence of Clusterin Glycosylation Variability on Selected Pathophysiological Processes in the Human Body

The present review gathers together the most important information about variability in clusterin molecular structure, its profile, and the degree of glycosylation occurring in human tissues and body fluids in the context of the utility of these characteristics as potential diagnostic biomarkers of selected pathophysiological conditions. The carbohydrate part of clusterin plays a crucial role in many biological processes such as endocytosis and apoptosis. Many pathologies associated with neurodegeneration, carcinogenesis, metabolic diseases, and civilizational diseases (e.g., cardiovascular incidents and male infertility) have been described as causes of homeostasis disturbance, in which the glycan part of clusterin plays a very important role. The results of the discussed studies suggest that glycoproteomic analysis of clusterin may help differentiate the severity of hippocampal atrophy, detect the causes of infertility with an immune background, and monitor the development of cancer. Understanding the mechanism of clusterin (CLU) action and its binding epitopes may enable to indicate new therapeutic goals. The carbohydrate part of clusterin is considered necessary to maintain its proper molecular conformation, structural stability, and proper systemic and/or local biological activity. Taking into account the wide spectrum of CLU action and its participation in many processes in the human body, further studies on clusterin glycosylation variability are needed to better understand the molecular mechanisms of many pathophysiological conditions. They can also provide the opportunity to find new biomarkers and enrich the panel of diagnostic parameters for diseases that still pose a challenge for modern medicine.

Serpin Signatures in Prion and Alzheimer's Diseases

Serpins represent the most broadly distributed superfamily of proteases inhibitors. They contribute to a variety of physiological functions and any alteration of the serpin-protease equilibrium can lead to severe consequences. SERPINA3 dysregulation has been associated with Alzheimer's disease (AD) and prion diseases. In this study, we investigated the differential expression of serpin superfamily members in neurodegenerative diseases. SERPIN expression was analyzed in human frontal cortex samples from cases of sporadic Creutzfeldt-Jakob disease (sCJD), patients at early stages of AD-related pathology, and age-matched controls not affected by neurodegenerative disorders. In addition, we studied whether Serpin expression was dysregulated in two animal models of prion disease and AD.Our analysis revealed that, besides the already observed upregulation of SERPINA3 in patients with prion disease and AD, SERPINB1, SERPINB6, SERPING1, SERPINH1, and SERPINI1 were dysregulated in sCJD individuals compared to controls, while only SERPINB1 was upregulated in AD patients. Furthermore, we analyzed whether other serpin members were differentially expressed in prion-infected mice compared to controls and, together with SerpinA3n, SerpinF2 increased levels were observed. Interestingly, SerpinA3n transcript and protein were upregulated in a mouse model of AD. The SERPINA3/SerpinA3nincreased anti-protease activity found in post-mortem brain tissue of AD and prion disease samples suggest its involvement in the neurodegenerative processes. A SERPINA3/SerpinA3n role in neurodegenerative disease-related protein aggregation was further corroborated by in vitro SerpinA3n-dependent prion accumulation changes. Our results indicate SERPINA3/SerpinA3n is a potential therapeutic target for the treatment of prion and prion-like neurodegenerative diseases.

HDL Accessory Proteins in Parkinson’s Disease—Focusing on Clusterin (Apolipoprotein J) in Regard to Its Involvement in Pathology and Diagnostics—A Review

Parkinson’s disease (PD)—a neurodegenerative disorder (NDD) characterized by progressive destruction of dopaminergic neurons within the substantia nigra of the brain—is associated with the formation of Lewy bodies containing mainly α-synuclein. HDL-related proteins such as paraoxonase 1 and apolipoproteins A1, E, D, and J are implicated in NDDs, including PD. Apolipoprotein J (ApoJ, clusterin) is a ubiquitous, multifunctional protein; besides its engagement in lipid transport, it modulates a variety of other processes such as immune system functionality and cellular death signaling. Furthermore, being an extracellular chaperone, ApoJ interacts with proteins associated with NDD pathogenesis (amyloid β, tau, and α-synuclein), thus modulating their properties. In this review, the association of clusterin with PD is delineated, with respect to its putative involvement in the pathological mechanism and its application in PD prognosis/diagnosis.

Identifying new molecular players in extracellular proteostasis

Proteostasis refers to a delicately tuned balance between the processes of protein synthesis, folding, localization, and the degradation of proteins found inside and outside cells. Our understanding of extracellular proteostasis is rather limited and largely restricted to knowledge of 11 currently established extracellular chaperones (ECs). This review will briefly outline what is known of the established ECs, before moving on to discuss experimental strategies used to identify new members of this growing family, and an examination of a group of putative new ECs identified using one of these approaches. An observation that emerges from an analysis of the expanding number of ECs is that all of these proteins are multifunctional. Strikingly, the armory of activities each possess uniquely suit them as a group to act together at sites of tissue damage, infection, and inflammation to restore homeostasis. Lastly, we highlight outstanding questions to guide future research in this field.

Clusterin, other extracellular chaperones, and eye disease

Proteostasis refers to all the processes that maintain the correct expression level, location, folding and turnover of proteins, essential to organismal survival. Both inside cells and in body fluids, molecular chaperones play key roles in maintaining proteostasis. In this article, we focus on clusterin, the first-recognized extracellular mammalian chaperone, and its role in diseases of the eye. Clusterin binds to and inhibits the aggregation of proteins that are misfolded due to mutations or stresses, clears these aggregating proteins from extracellular spaces, and facilitates their degradation. Clusterin exhibits three main homeostatic activities: proteostasis, cytoprotection, and anti-inflammation. The so-called "protein misfolding diseases" are caused by aggregation of misfolded proteins that accumulate pathologically as deposits in tissues; we discuss several such diseases that occur in the eye. Clusterin is typically found in these deposits, which is interpreted to mean that its capacity as a molecular chaperone to maintain proteostasis is overwhelmed in the disease state. Nevertheless, the role of clusterin in diseases involving such deposits needs to be better defined before therapeutic approaches can be entertained. A more straightforward case can be made for therapeutic use of clusterin based on its proteostatic role as a proteinase inhibitor, as well as its cytoprotective and anti-inflammatory properties. It is likely that clusterin works together in this way with other extracellular chaperones to protect the eye from disease, and we discuss several examples. We end this article by predicting future steps that may lead to development of clusterin as a biological drug.

In Vitro and In Vivo Effects of SerpinA1 on the Modulation of Transthyretin Proteolysis

Transthyretin (TTR) proteolysis has been recognized as a complementary mechanism contributing to transthyretin-related amyloidosis (ATTR amyloidosis). Accordingly, amyloid deposits can be composed mainly of full-length TTR or contain a mixture of both cleaved and full-length TTR, particularly in the heart. The fragmentation pattern at Lys48 suggests the involvement of a serine protease, such as plasmin. The most common TTR variant, TTR V30M, is susceptible to plasmin-mediated proteolysis, and the presence of TTR fragments facilitates TTR amyloidogenesis. Recent studies revealed that the serine protease inhibitor, SerpinA1, was differentially expressed in hepatocyte-like cells (HLCs) from ATTR patients. In this work, we evaluated the effects of SerpinA1 on in vitro and in vivo modulation of TTR V30M proteolysis, aggregation, and deposition. We found that plasmin-mediated TTR proteolysis and aggregation are partially inhibited by SerpinA1. Furthermore, in vivo downregulation of SerpinA1 increased TTR levels in mice plasma and deposition in the cardiac tissue of older animals. The presence of TTR fragments was observed in the heart of young and old mice but not in other tissues following SerpinA1 knockdown. Increased proteolytic activity, particularly plasmin activity, was detected in mice plasmas. Overall, our results indicate that SerpinA1 modulates TTR proteolysis and aggregation in vitro and in vivo.

Transthyretin: From Structural Stability to Osteoarticular and Cardiovascular Diseases

Transthyretin (TTR) is a tetrameric protein transporting hormones in the plasma and brain, which has many other activities that have not been fully acknowledged. TTR is a positive indicator of nutrition status and is negatively correlated with inflammation. TTR is a neuroprotective and oxidative-stress-suppressing factor. The TTR structure is destabilized by mutations, oxidative modifications, aging, proteolysis, and metal cations, including Ca2+. Destabilized TTR molecules form amyloid deposits, resulting in senile and familial amyloidopathies. This review links structural stability of TTR with the environmental factors, particularly oxidative stress and Ca2+, and the processes involved in the pathogenesis of TTR-related diseases. The roles of TTR in biomineralization, calcification, and osteoarticular and cardiovascular diseases are broadly discussed. The association of TTR-related diseases and vascular and ligament tissue calcification with TTR levels and TTR structure is presented. It is indicated that unaggregated TTR and TTR amyloid are bound by vicious cycles, and that TTR may have an as yet undetermined role(s) at the crossroads of calcification, blood coagulation, and immune response.

Conformational consequences of NPM1 rare mutations: An aggregation perspective in Acute Myeloid Leukemia

Often proteins association is a physiological process used by cells to regulate their growth and to adapt to different stress conditions, including mutations. In the case of a subtype of Acute Myeloid Leukemia (AML), mutations of nucleophosmin 1 (NPM1) protein cause its aberrant cytoplasmatic mislocalization (NPMc+). We recently pointed out an amyloidogenic propensity of protein regions including the most common mutations of NPMc+ located in the C-terminal domain (CTD): they were able to form, in vitro, amyloid cytotoxic aggregates with fibrillar morphology. Herein, we analyzed the conformational characteristics of several peptides including rare AML mutations of NPMc+. By means of different spectroscopic, microscopic and cellular assays we evaluated the importance of amino acid composition, among rare AML mutations, to determine amyloidogenic propensity. This study could add a piece of knowledge to the structural consequences of mutations in cytoplasmatic NPM1c+.

The Dual Roles of Clusterin in Extracellular and Intracellular Proteostasis

Clusterin (CLU) was the first reported secreted mammalian chaperone and impacts on serious diseases associated with inappropriate extracellular protein aggregation. Many studies have described intracellular CLU in locations outside the secretory system and recent work has shown that CLU can be released into the cytosol during cell stress. In this article, we critically evaluate evidence relevant to the proposed origins of cellular CLU found outside the secretory system, and advance the hypothesis that the cytosolic release of CLU induced by stress serves to facilitate the trafficking of misfolded proteins to the proteasome and autophagy for degradation. We also propose future research directions that could help establish CLU as a unique chaperone performing critical and synergic roles in both intracellular and extracellular proteostasis.

Modulation of the Mechanisms Driving Transthyretin Amyloidosis

Transthyretin (TTR) amyloidoses are systemic diseases associated with TTR aggregation and extracellular deposition in tissues as amyloid. The most frequent and severe forms of the disease are hereditary and associated with amino acid substitutions in the protein due to single point mutations in the TTR gene (ATTRv amyloidosis). However, the wild type TTR (TTR wt) has an intrinsic amyloidogenic potential that, in particular altered physiologic conditions and aging, leads to TTR aggregation in people over 80 years old being responsible for the non-hereditary ATTRwt amyloidosis. In normal physiologic conditions TTR wt occurs as a tetramer of identical subunits forming a central hydrophobic channel where small molecules can bind as is the case of the natural ligand thyroxine (T₄). However, the TTR amyloidogenic variants present decreased stability, and in particular conditions, dissociate into partially misfolded monomers that aggregate and polymerize as amyloid fibrils. Therefore, therapeutic strategies for these amyloidoses may target different steps in the disease process such as decrease of variant TTR (TTRv) in plasma, stabilization of TTR, inhibition of TTR aggregation and polymerization or disruption of the preformed fibrils. While strategies aiming decrease of the mutated TTR involve mainly genetic approaches, either by liver transplant or the more recent technologies using specific oligonucleotides or silencing RNA, the other steps of the amyloidogenic cascade might be impaired by pharmacologic compounds, namely, TTR stabilizers, inhibitors of aggregation and amyloid disruptors. Modulation of different steps involved in the mechanism of ATTR amyloidosis and compounds proposed as pharmacologic agents to treat TTR amyloidosis will be reviewed and discussed.

Plasmin-Induced Activation of Human Platelets Is Modulated by Thrombospondin-1, Bona Fide Misfolded Proteins and Thiol Isomerases

Inflammatory processes are triggered by the fibrinolytic enzyme plasmin. Tissue-type plasminogen activator, which cleaves plasminogen to plasmin, can be activated by the cross-β-structure of misfolded proteins. Misfolded protein aggregates also represent substrates for plasmin, promoting their degradation, and are potent platelet agonists. However, the regulation of plasmin-mediated platelet activation by misfolded proteins and vice versa is incompletely understood. In this study, we hypothesize that plasmin acts as potent agonist of human platelets in vitro after short-term incubation at room temperature, and that the response to thrombospondin-1 and the bona fide misfolded proteins Eap and SCN^--denatured IgG interfere with plasmin, thereby modulating platelet activation. Plasmin dose-dependently induced CD62P surface expression on, and binding of fibrinogen to, human platelets in the absence/presence of plasma and in citrated whole blood, as analyzed by flow cytometry. Thrombospondin-1 pre-incubated with plasmin enhanced these plasmin-induced platelet responses at low concentration and diminished them at higher dose. Platelet fibrinogen binding was dose-dependently induced by the C-terminal thrombospondin-1 peptide RFYVVMWK, Eap or NaSCN-treated IgG, but diminished in the presence of plasmin. Blocking enzymatically catalyzed thiol-isomerization decreased plasmin-induced platelet responses, suggesting that plasmin activates platelets in a thiol-dependent manner. Thrombospondin-1, depending on the concentration, may act as cofactor or inhibitor of plasmin-induced platelet activation, and plasmin blocks platelet activation induced by misfolded proteins and vice versa, which might be of clinical relevance.

Reversible Oligomerization and Reverse Hydrophobic Effect Induced by Isoleucine Tags Attached at the C-Terminus of a Simplified BPTI Variant

Protein amorphous aggregation has become the focus of great attention, as it can impair the ability of cells to function properly. Here, we evaluated the effects of three peptide tags, consisting of one, three, and five consecutive isoleucines attached at the C-terminus end of a simplified bovine pancreatic trypsin inhibitor (BPTI) variant, BPTI-19A, on the thermal stability and oligomerization by circular dichroism spectrometry and differential scanning calorimetry in detail. All of the BPTI-19A variants exhibited a reversible and apparently two-state thermal transition like BPTI-19A at pH 4.7. The thermal transition of the five-isoleucine-tagged variant showed clear protein-concentration dependence, where the apparent denaturation temperature decreased as the protein concentration increased. Quantitative analysis indicated that this phenomenon originated from the presence of reversibly oligomerized (RO) states at high temperatures. The results also illustrated that the thermodynamic stability difference between the native and the monomeric denatured state in all the proteins was destabilized by the hydrophobic tags and was well explained by the reverse hydrophobic effect due to the tags. The existence of the RO states was confirmed by both analytical ultracentrifugation and dynamic light scattering. This indicated that the five-isoleucine hydrophobic tag is strong enough to induce intermolecular hydrophobic contact among the denatured molecules leading to oligomerization, and even one- or three-isoleucine tags are effective enough to generate intramolecular hydrophobic contact, thus provoking denaturation through the reverse hydrophobic effect.

7B2 chaperone knockout in APP model mice results in reduced plaque burden

Impairment of neuronal proteostasis is a hallmark of Alzheimer's and other neurodegenerative diseases. However, the underlying molecular mechanisms leading to pathogenic protein aggregation, and the role of secretory chaperone proteins in this process, are poorly understood. We have previously shown that the neural-and endocrine-specific secretory chaperone 7B2 potently blocks in vitro fibrillation of Aβ42. To determine whether 7B2 can function as a chaperone in vivo, we measured plaque formation and performed behavioral assays in 7B2-deficient mice in an hAPPswe/PS1dE9 Alzheimer's model mouse background. Surprisingly, immunocytochemical analysis of cortical levels of thioflavin S- and Aβ-reactive plaques showed that APP mice with a partial or complete lack of 7B2 expression exhibited a significantly lower number and burden of thioflavin S-reactive, as well as Aβ-immunoreactive, plaques. However, 7B2 knockout did not affect total brain levels of either soluble or insoluble Aβ. While hAPP model mice performed poorly in the Morris water maze, their brain 7B2 levels did not impact performance. Since 7B2 loss reduced amyloid plaque burden, we conclude that brain 7B2 can impact Aβ disposition in a manner that facilitates plaque formation. These results are reminiscent of prior findings in hAPP model mice lacking the ubiquitous secretory chaperone clusterin.