Intermediate filament interactions can be altered by HSP27 and alphaB-crystallin

Understanding the structural and functional changes and biochemical pathomechanism of the cardiomyopathy-associated p.R123W mutation in human αB-crystallin

αB-crystallin, a member of the small heat shock protein (sHSP) family, is expressed in diverse tissues, including the eyes, brain, muscles, and heart. This protein plays a crucial role in maintaining eye lens transparency and exhibits holdase chaperone and anti-apoptotic activities. Therefore, structural and functional changes caused by genetic mutations in this protein may contribute to the development of disorders like cataract and cardiomyopathy. Recently, the substitution of arginine 123 with tryptophan (p.R123W mutation) in human αB-crystallin has been reported to trigger cardiomyopathy. In this study, human αB-crystallin was expressed in Escherichia coli (E. coli), and the missense mutation p.R123W was created using site-directed mutagenesis. Following purification via anion exchange chromatography, the structural and functional properties of both proteins were investigated and compared using a wide range of spectroscopic and microscopic methods. The p.R123W mutation induced significant alterations in the secondary, tertiary, and quaternary structures of human αB-crystallin. This pathogenic mutation resulted in an increased β-sheet structure and formation of protein oligomers with larger sizes compared to the wild-type protein. The mutant protein also exhibited reduced chaperone activity and lower thermal stability. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) demonstrated that the p.R123W mutant protein is more prone to forming amyloid aggregates. The structural and functional changes observed in the p.R123W mutant protein, along with its increased propensity for aggregation, could impact its proper functional interaction with the target proteins in the cardiac muscle, such as calcineurin. Our results provide an explanation for the pathogenic intervention of p.R123W mutant protein in the occurrence of hypertrophic cardiomyopathy (HCM).

Proximity Mapping of Desmosomes Reveals a Striking Shift in Their Molecular Neighborhood Associated With Maturation

Desmosomes are multiprotein adhesion complexes that link intermediate filaments to the plasma membrane, ensuring the mechanical integrity of cells across tissues, but how they participate in the wider signaling network to exert their full function is unclear. To investigate this, we carried out protein proximity mapping using biotinylation (BioID). The combined interactomes of the essential desmosomal proteins desmocollin 2a, plakoglobin, and plakophilin 2a (Pkp2a) in Madin-Darby canine kidney epithelial cells were mapped and their differences and commonalities characterized as desmosome matured from Ca2+ dependence to the mature, Ca2+-independent, hyper-adhesive state, which predominates in tissues. Results suggest that individual desmosomal proteins have distinct roles in connecting to cellular signaling pathways and that these roles alter substantially when cells change their adhesion state. The data provide further support for a dualistic concept of desmosomes in which the properties of Pkp2a differ from those of the other, more stable proteins. This body of data provides an invaluable resource for the analysis of desmosome function.

Desmin and its molecular chaperone, the αB-crystallin: How post-translational modifications modulate their functions in heart and skeletal muscles?

Maintenance of the highly organized striated muscle tissue requires a cell-wide dynamic network through protein-protein interactions providing an effective mechanochemical integrator of morphology and function. Through a continuous and complex trans-cytoplasmic network, desmin intermediate filaments ensure this essential role in heart and in skeletal muscle. Besides their role in the maintenance of cell shape and architecture (permitting contractile activity efficiency and conferring resistance towards mechanical stress), desmin intermediate filaments are also key actors of cell and tissue homeostasis. Desmin participates to several cellular processes such as differentiation, apoptosis, intracellular signalisation, mechanotransduction, vesicle trafficking, organelle biogenesis and/or positioning, calcium homeostasis, protein homeostasis, cell adhesion, metabolism and gene expression. Desmin intermediate filaments assembly requires αB-crystallin, a small heat shock protein. Over its chaperone activity, αB-crystallin is involved in several cellular functions such as cell integrity, cytoskeleton stabilization, apoptosis, autophagy, differentiation, mitochondria function or aggresome formation. Importantly, both proteins are known to be strongly associated to the aetiology of several cardiac and skeletal muscles pathologies related to desmin filaments disorganization and a strong disturbance of desmin interactome. Note that these key proteins of cytoskeleton architecture are extensively modified by post-translational modifications that could affect their functional properties. Therefore, we reviewed in the herein paper the impact of post-translational modifications on the modulation of cellular functions of desmin and its molecular chaperone, the αB-crystallin.

Unveiling the structural and functional consequences of the p.D109G pathogenic mutation in human αB-Crystallin responsible for restrictive cardiomyopathy and skeletal myopathy

αB-Crystallin (αB-Cry) is expressed in many tissues, and mutations in this protein are linked to various diseases, including cataracts, Alzheimer's disease, Parkinson's disease, and several types of myopathies and cardiomyopathies. The p.D109G mutation, which substitutes a conserved aspartate residue involved in the interchain salt bridges, with glycine leads to the development of both restrictive cardiomyopathy (RCM) and skeletal myopathy. In this study, we generated this mutation in the α-Cry domain (ACD) which is crucial for forming the active chaperone dimeric state, using site-directed mutagenesis. After inducing expression in the bacterial host, we purified the mutant and wild-type recombinant proteins using anion exchange chromatography. Various spectroscopic evaluations revealed significant changes in the secondary, tertiary, and quaternary structures of human αB-Cry caused by this mutation. Furthermore, this pathogenic mutation led to the formation of protein oligomers with larger sizes than those of the wild-type protein counterpart. The mutant protein also exhibited increased chaperone activity and decreased chemical, thermal, and proteolytic stability. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and fluorescence microscopy (FM) demonstrated that p.D109G mutant protein is more prone to forming amyloid aggregates. The misfolding associated with the p.D109G mutation may result in abnormal interactions of human αB-Cry with its natural partners (e.g., desmin), leading to the formation of protein aggregates. These aggregates can interfere with normal cellular processes and may contribute to muscle cell dysfunction and damage, resulting in the pathogenic involvement of the p.D109G mutant protein in restrictive cardiomyopathy and skeletal myopathy.

The potential mediation of hypoxia-inducible factor-1α in heat shock protein 27 translocations, caspase-3 and calpain activities and yak meat tenderness during postmortem aging

The present study aimed to characterize the influence of hypoxia-inducible factor-1α on heat shock protein 27 and cytochrome c translocation, yak meat microstructure destruction, and endogenous enzymes activities, refining the understanding of the tenderization process after slaughter. Postmortem yak longissimus thoracis et lumborum muscles were incubated with 0.9% saline or hypoxia-inducible factor-1α stabilizer dimethyloxaloylglycine at 4 °C for 6, 12, 24, 72, and 120 h. Results showed that hypoxia-inducible factor-1α activation promoted heat shock protein 27 migration and cytochrome c release, facilitating (P < 0.05) caspase-3 activity by mediating the heat shock protein 27/caspase-3 interaction but did not exert (P > 0.05) significant effects on the calpain-1 activity. Additionally, hypoxia-inducible factor-1α activation contributed to the mitochondrial apoptosis cascade, leading to a higher (P < 0.01) apoptosis rate. Therefore, these observations indicate that hypoxia-inducible factor-1α affects caspase-3 activity and tenderness of postmortem muscle through distinct regulatory mechanisms, possibly, in part, with heat shock protein 27 and cytochrome c mediation.

Desmin Reorganization by Stimuli Inducing Oxidative Stress and Electrophiles: Role of Its Single Cysteine Residue

The type III intermediate filament proteins vimentin and GFAP are modulated by oxidants and electrophiles, mainly through perturbation of their single cysteine residues. Desmin, the type III intermediate filament protein specific to muscle cells, is critical for muscle homeostasis, playing a key role in sarcomere organization and mitochondrial function. Here, we have studied the impact of oxidants and cysteine-reactive agents on desmin behavior. Our results show that several reactive species and drugs induce covalent modifications of desmin in vitro, of which its single cysteine residue, C333, is an important target. Moreover, stimuli eliciting oxidative stress or lipoxidation, including H2O2, 15-deoxy-prostaglandin J2, and CoCl2-elicited chemical hypoxia, provoke desmin disorganization in H9c2 rat cardiomyoblasts transfected with wild-type desmin, which is partially attenuated in cells expressing a C333S mutant. Notably, in cells lacking other cytoplasmic intermediate filaments, network formation by desmin C333S appears less efficient than that of desmin wt, especially when these proteins are expressed as fluorescent fusion constructs. Nevertheless, in these cells, the desmin C333S organization is also protected from disruption by oxidants. Taken together, our results indicate that desmin is a target for oxidative and electrophilic stress, which elicit desmin remodeling conditioned by the presence of its single cysteine residue.

The J Domain of Sacsin Disrupts Intermediate Filament Assembly

Autosomal Recessive Spastic Ataxia of the Charlevoix Saguenay (ARSACS) is caused by mutation in the SACS gene resulting in loss of function of the protein sacsin. A key feature is the formation of abnormal bundles of neurofilaments (NF) in neurons and vimentin intermediate filaments (IF) in cultured fibroblasts, suggesting a role of sacsin in IF homeostasis. Sacsin contains a J domain (SacsJ) homologous to Hsp40, that can interact with Hsp70 chaperones. The SacsJ domain resolved NF bundles in cultured Sacs^-/- neurons. Having studied the mechanism using NF assembled in vitro from purified NF proteins, we report that the SacsJ domain interacts with NF proteins to disassemble NFL filaments, and to inhibit their initial assembly. A cell-penetrating peptide derived from this domain, SacsJ-myc-TAT was efficient in disassembling NF bundles in cultured Sacs^-/- motor neurons, restoring the NF network; however, there was some loss of vimentin IF and NF in cultured Sacs^+/+ fibroblasts and motor neurons, respectively. These results suggest that sacsin through its SacsJ domain is a key regulator of NF and vimentin IF networks in cells.

The Role of Small Heat Shock Proteins in Protein Misfolding Associated Motoneuron Diseases

Motoneuron diseases (MNDs) are neurodegenerative conditions associated with death of upper and/or lower motoneurons (MNs). Proteostasis alteration is a pathogenic mechanism involved in many MNDs and is due to the excessive presence of misfolded and aggregated proteins. Protein misfolding may be the product of gene mutations, or due to defects in the translation process, or to stress agents; all these conditions may alter the native conformation of proteins making them prone to aggregate. Alternatively, mutations in members of the protein quality control (PQC) system may determine a loss of function of the proteostasis network. This causes an impairment in the capability to handle and remove aberrant or damaged proteins. The PQC system consists of the degradative pathways, which are the autophagy and the proteasome, and a network of chaperones and co-chaperones. Among these components, Heat Shock Protein 70 represents the main factor in substrate triage to folding, refolding, or degradation, and it is assisted in this task by a subclass of the chaperone network, the small heat shock protein (sHSPs/HSPBs) family. HSPBs take part in proteostasis by bridging misfolded and aggregated proteins to the HSP70 machinery and to the degradative pathways, facilitating refolding or clearance of the potentially toxic proteins. Because of its activity against proteostasis alteration, the chaperone system plays a relevant role in the protection against proteotoxicity in MNDs. Here, we discuss the role of HSPBs in MNDs and which HSPBs may represent a valid target for therapeutic purposes.

Effects of Alexander disease-associated mutations on the assembly and organization of GFAP intermediate filaments

Alexander disease is a primary genetic disorder of astrocytes caused by dominant mutations in the gene encoding glial fibrillary acidic protein (GFAP). How single-amino-acid changes can lead to cytoskeletal catastrophe and brain degeneration remains poorly understood. In this study, we have analyzed 14 missense mutations located in the GFAP rod domain to investigate how these mutations affect in vitro filament assembly. Whereas the internal rod mutants assembled into filaments that were shorter than those of wild type, the rod end mutants formed structures with one or more of several atypical characteristics, including short filament length, irregular width, roughness of filament surface, and filament aggregation. When transduced into primary astrocytes, GFAP mutants with in vitro assembly defects usually formed cytoplasmic aggregates, which were more resistant to biochemical extraction. The resistance of GFAP to solubilization was also observed in brain tissues of patients with Alexander disease, in which a significant proportion of insoluble GFAP were accumulated in Rosenthal fiber fractions. These findings provide clinically relevant evidence that link GFAP assembly defects to disease pathology at the tissue level and suggest that altered filament assembly and properties as a result of GFAP mutation are critical initiating factors for the pathogenesis of Alexander disease.

The Role of miR-20 in Health and Disease of the Central Nervous System

Current understanding of the mechanisms underlying central nervous system (CNS) injury is limited, and traditional therapeutic methods lack a molecular approach either to prevent acute phase or secondary damage, or to support restorative mechanisms in the nervous tissue. microRNAs (miRNAs) are endogenous, non-coding RNA molecules that have recently been discovered as fundamental and post-transcriptional regulators of gene expression. The capacity of microRNAs to regulate the cell state and function through post-transcriptionally silencing hundreds of genes are being acknowledged as an important factor in the pathophysiology of both acute and chronic CNS injuries. In this study, we have summarized the knowledge concerning the pathophysiology of several neurological disorders, and the role of most canonical miRNAs in their development. We have focused on the miR-20, the miR-17~92 family to which miR-20 belongs, and their function in the normal development and disease of the CNS.

Oxysterol Compounds in Mouse Mutant αA- and αB-Crystallin Lenses Can Improve the Optical Properties of the Lens

Purpose

To investigate how cataract-linked mutations affect the gradient refractive index (GRIN) and lens opacification in mouse lenses and whether there is any effect on the optics of the lens from treatment with an oxysterol compound.

Methods

A total of 35 mice including wild-type and knock-in mutants (Cryaa-R49C and Cryab-R120G) were used in these experiments: 26 mice were treated with topical VP1-001, an oxysterol, in one eye and vehicle in the other, and nine mice were untreated controls. Slit lamp biomicroscopy was used to analyze the lens in live animals and to provide apparent cataract grades. Refractive index in the lenses of 64 unfixed whole mouse eyes was calculated from measurements with X-ray phase tomography based on X-ray Talbot interferometry with a synchrotron radiation source.

Results

Heterozygous Cryaa-R49C lenses had slightly irregularly shaped contours in the center of the GRIN and distinct disturbances of the gradient index at the anterior and posterior poles. Contours near the lens surface were denser in homozygous Cryab-R120G lenses. Treatment with topical VP1-001, an oxysterol, showed an improvement in refractive index profiles in 61% of lenses and this was supported by a reduction in apparent lens opacity grade by 1.0 in 46% of live mice.

Conclusions

These results indicate that α-crystallin mutations alter the refractive index gradient of mouse lenses in distinct ways and suggest that topical treatment with VP1-001 may improve lens transparency and refractive index contours in some lenses with mutations.

Proteomic Technologies and their Application for Ensuring Meat Quality, Safety and Authenticity

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Proteomic tools were extensively used to understand the relationship between muscle proteome and conversion of muscle to meat, post-mortem proteolysis, meat texture, and variation in meat color. Developments in proteomic tools have also resulted in their application for addressing the safety and authenticity issues including meat species identification, detection of animal byproducts, non-meat ingredients and tissues in meat products, traceability, identification of genetically modified ingredients, chemical residues and other harmful substances. Proteomic tools are also being used in some of the potential areas like understanding the effect of animal transportation, stunning, slaughter stress, halal authentication and issues related to animal welfare. Emerging advances in proteomic and peptidomic technologies and their application in traceability, meat microbiology, safety and authentication are taking a major stride as an interesting and complementary alternative to DNA-based methods currently in use. Future research in meat science need to be linked to emerging metabolomic, lipidomic and other omic technologies for ensuring integrated meat quality and safety management. In this paper, a comprehensive overview of the use of proteomics for the assessment of quality and safety in the meat value chain and their potential application is discussed.

Insights on Human Small Heat Shock Proteins and Their Alterations in Diseases

The family of the human small Heat Shock Proteins (HSPBs) consists of ten members of chaperones (HSPB1-HSPB10), characterized by a low molecular weight and capable of dimerization and oligomerization forming large homo- or hetero-complexes. All HSPBs possess a highly conserved centrally located α-crystallin domain and poorly conserved N- and C-terminal domains. The main feature of HSPBs is to exert cytoprotective functions by preserving proteostasis, assuring the structural maintenance of the cytoskeleton and acting in response to cellular stresses and apoptosis. HSPBs take part in cell homeostasis by acting as holdases, which is the ability to interact with a substrate preventing its aggregation. In addition, HSPBs cooperate in substrates refolding driven by other chaperones or, alternatively, promote substrate routing to degradation. Notably, while some HSPBs are ubiquitously expressed, others show peculiar tissue-specific expression. Cardiac muscle, skeletal muscle and neurons show high expression levels for a wide variety of HSPBs. Indeed, most of the mutations identified in HSPBs are associated to cardiomyopathies, myopathies, and motor neuropathies. Instead, mutations in HSPB4 and HSPB5, which are also expressed in lens, have been associated with cataract. Mutations of HSPBs family members encompass base substitutions, insertions, and deletions, resulting in single amino acid substitutions or in the generation of truncated or elongated proteins. This review will provide an updated overview of disease-related mutations in HSPBs focusing on the structural and biochemical effects of mutations and their functional consequences.

Autoantibody-Specific Signalling in Pemphigus

Pemphigus is a severe autoimmune disease impairing barrier functions of epidermis and mucosa. Autoantibodies primarily target the desmosomal adhesion molecules desmoglein (Dsg) 1 and Dsg 3 and induce loss of desmosomal adhesion. Strikingly, autoantibody profiles in pemphigus correlate with clinical phenotypes. Mucosal-dominant pemphigus vulgaris (PV) is characterised by autoantibodies (PV-IgG) against Dsg3 whereas epidermal blistering in PV and pemphigus foliaceus (PF) is associated with autoantibodies against Dsg1. Therapy in pemphigus is evolving towards specific suppression of autoantibody formation and autoantibody depletion. Nevertheless, during the acute phase and relapses of the disease additional treatment options to stabilise desmosomes and thereby rescue keratinocyte adhesion would be beneficial. Therefore, the mechanisms by which autoantibodies interfere with adhesion of desmosomes need to be characterised in detail. Besides direct inhibition of Dsg adhesion, autoantibodies engage signalling pathways interfering with different steps of desmosome turn-over. With this respect, recent data indicate that autoantibodies induce separate signalling responses in keratinocytes via specific signalling complexes organised by Dsg1 and Dsg3 which transfer the signal of autoantibody binding into the cell. This hypothesis may also explain the different clinical pemphigus phenotypes.

Elevated GFAP isoform expression promotes protein aggregation and compromises astrocyte function

Alexander disease (AxD) caused by mutations in the coding region of GFAP is a neurodegenerative disease characterized by astrocyte dysfunction, GFAP aggregation, and Rosenthal fiber accumulation. Although how GFAP mutations cause disease is not fully understood, Rosenthal fibers could be induced by forced overexpression of human GFAP and this could be lethal in mice implicate that an increase in GFAP levels is central to AxD pathogenesis. Our recent studies demonstrated that intronic GFAP mutations cause disease by altering GFAP splicing, suggesting that an increase in GFAP isoform expression could lead to protein aggregation and astrocyte dysfunction that typify AxD. Here we test this hypothesis by establishing primary astrocyte cultures from transgenic mice overexpressing human GFAP. We found that GFAP-δ and GFAP-κ were disproportionately increased in transgenic astrocytes and both were enriched in Rosenthal fibers of human AxD brains. In vitro assembly studies showed that while the major isoform GFAP-α self-assembled into typical 10-nm filaments, minor isoforms including GFAP-δ, -κ, and -λ were assembly-compromised and aggregation prone. Lentiviral transduction showed that expression of these minor GFAP isoforms decreased filament solubility and increased GFAP stability, leading to the formation of Rosenthal fibers-like aggregates that also disrupted the endogenous intermediate filament networks. The aggregate-bearing astrocytes lost their normal morphology and glutamate buffering capacity, which had a toxic effect on neighboring neurons. In conclusion, our findings provide evidence that links elevated GFAP isoform expression with GFAP aggregation and impaired glutamate transport, and suggest a potential non-cell-autonomous mechanism underlying neurodegeneration through astrocyte dysfunction.

Charcot-Marie-Tooth disease type 2F associated with biallelic HSPB1 mutations

Objective

This work aims to expand knowledge regarding the genetic spectrum of HSPB1‐related diseases. HSPB1 is a gene encoding heat shock protein 27, and mutations in HSPB1 have been identified as the cause of axonal Charcot–Marie–Tooth (CMT) disease type 2F and distal hereditary motor neuropathy (dHMN).

Methods

Two patients with axonal sensorimotor neuropathy underwent detailed clinical examinations, neurophysiological studies, and next‐generation sequencing with subsequent bioinformatic prioritization of genetic variants and in silico analysis of the likely causal mutation.

Results

The HSPB1 p.S135F and p.R136L mutations were identified in homozygosis in the two affected individuals. Both mutations affect the highly conserved alpha‐crystallin domain and have been previously described as the cause of severe CMT2F/dHMN, showing a strictly dominant inheritance pattern.

Interpretation

Thus, we report for the first time two cases of biallelic HSPB1 p.S135F and p.R136L mutations in two families.

Energy transfer along Müller cell intermediate filaments isolated from porcine retina: I. Excitons produced by ADH1A dimers upon simultaneous hydrolysis of two ATP molecules

IR exciton propagation was explored in Müller cell (MC) intermediate filaments (IFs) filling a capillary matrix. These IFs have been isolated from porcine retina using different methods, while their properties were almost identical. Therefore, IFs isolated from the whole retinas were used presently. IR excitons were generated by IR radiation at 2 μm wavelength, or by enzymatic ATP hydrolysis, with the energy transferred to IFs. Excitons produced by ATP hydrolysis required simultaneous energy contribution of two ATP molecules, indicating simultaneous hydrolysis of two ATP molecules in the naturally dimeric human alcohol dehydrogenase enzyme (ADH1A). ATP hydrolysis was thus catalyzed by ADH1A…NAD⁺ enzymatic complexes absorbed at the IF extremities protruding out of the capillary matrix. The IR emission spectra of excitons were dependent on the exciton generation method. We believe this resulted from the exciton energy distribution varying in function of the generation method used. The latter seems reasonable, given the very long excited-state lifetimes, implying low nonradiative relaxation rates. The energy liberated by ATP hydrolysis has been measured directly in these experiments, for the first time. The results demonstrate that contrary to the predictions of equilibrium thermodynamics, the liberated energy is independent on the ATP/ADP concentration ratio, indicating that non-equilibrium reactions take place. Time-resolved experiments with excitons produced by pulsed IR radiation evaluated characteristic exciton propagation and emission times. For the first time, biexcitonic processes were observed in biological objects, whereby simultaneous hydrolysis of two ATP molecules bound to the same dimeric ADH1A molecule generated excitons carrying twice the energy liberated by hydrolysis of a single ATP molecule. The results reported indicate that ATP-liberated energy may be transmitted along natural polypeptide nanofibers in vivo, within and between live cells. These ideas could promote new understanding of the biophysics of life.

Cluster analyses of the TCGA and a TMA dataset using the coexpression of HSP27 and CRYAB improves alignment with clinical-pathological parameters of breast cancer and suggests different epichaperome influences for each sHSP

Our cluster analysis of the Cancer Genome Atlas for co-expression of HSP27 and CRYAB in breast cancer patients identified three patient groups based on their expression level combination (high HSP27 + low CRYAB; low HSP27 + high CRYAB; similar HSP27 + CRYAB). Our analyses also suggest that there is a statistically significant inverse relationship between HSP27 and CRYAB and known clinicopathological markers in breast cancer. Screening an unbiased 248 breast cancer patient tissue microarray (TMA) for the protein expression of HSP27 and phosphorylated HSP27 (HSP27-82pS) with CRYAB also identified three patient groups based on HSP27 and CRYAB expression levels. TMA24 also had recorded clinical-pathological parameters, such as ER and PR receptor status, patient survival, and TP53 mutation status. High HSP27 protein levels were significant with ER and PR expression. HSP27-82pS associated with the best patient survival (Log Rank test). High CRYAB expression in combination with wild-type TP53 was significant for patient survival, but a different patient outcome was observed when mutant TP53 was combined with high CRYAB expression. Our data suggest that HSP27 and CRYAB have different epichaperome influences in breast cancer, but more importantly evidence the value of a cluster analysis that considers their coexpression. Our approach can deliver convergence for archival datasets as well as those from recent treatment and patient cohorts and can align HSP27 and CRYAB expression to important clinical-pathological features of breast cancer.

HspB5/αB-crystallin phosphorylation at S45 and S59 is essential for protection of the dendritic tree of rat hippocampal neurons

Rarefaction of the dendritic tree leading to neuronal dysfunction is a hallmark of many neurodegenerative diseases and we have shown previously that heat shock protein B5 (HspB5)/αB-crystallin is able to increase dendritic complexity in vitro. The aim of this study was to investigate if this effect is also present in vivo, if HspB5 can counteract dendritic rarefaction under pathophysiological conditions and the impact of phosphorylation of HspB5 in this process. HspB5 and eight mutants inhibiting or mimicking phosphorylation at the three phosphorylation sites serine (S)19, S45, and S59 were over-expressed in cultured rat hippocampal neurons with subsequent investigation of the complexity of the dendritic tree. Sholl analysis revealed significant higher complexity of the dendritic tree after over-expression of wild-type HspB5 and the mutant HspB5-AEE. All other mutants showed no or minor effects. For in vivo investigation in utero electroporation of mouse embryos was applied. At embryonal day E15.5 the respective plasmids were injected, cornu ammonis 1 (CA1) pyramidal cells transfected by electroporation and their basal dendritic trees were analyzed at post-natal day P15. In vivo, HspB5 and HspB5-AEE led to an increase of total dendritic length as well as a higher complexity. Finally, the dendritic effect of HspB5 was investigated under a pathophysiological condition, that is, iron deficiency which reportedly results in dendritic rarefaction. HspB5 and HspB5-AEE but not the non-phosphorylatable mutant HspB5-AAA significantly counteracted the dendritic rarefaction. Thus, our data suggest that up-regulation and selective phosphorylation of HspB5 in neurodegenerative diseases may preserve dendritic morphology and counteract neuronal dysfunction.

Spatial organization and crosstalk of vimentin and actin stress fibers regulate the osteogenic differentiation of human adipose-derived stem cells

Human adipose-derived stem cells (hASCs) are ideal seed cells for tissue engineering due to their multidirectional differentiation potential. Microfilaments, microtubules, and intermediate filaments are responsible for supporting the intracellular space. Vimentin, a type III intermediate filament protein that is specifically expressed in cells of mesenchymal origin, can function as a scaffold and endow cells with tension and shear stress resistance. Actin stress fibers (ASF) act as an important physical device in stress signal transduction, providing stiffness for cells, and promoting osteogenesis. Through direct physical contact, cross-linkers, and spatial interactions, vimentin and actin networks exist as intersecting entities. Spatial interactions occur in the overlapping area of cytoskeleton subsystems, which could affect cell morphology, cell mechanics, and cell fate. However, how does the spatial organization between the cytoskeletal subsystems changed during osteogenesis, especially between vimentin and ASF, is still not understood, and its mechanism effect on cell fate remains unclear. In our study, WB experiment was used to detect the expression changes in Vimentin, ASF, and other proteins. Cells were reconstructed by three-dimensional scanning with fluorescence microscope, and the spatial thickness of vimentin and ASF cytoskeletons and the thickness of the overlapping area between them were calculated, respectively, so as to observe the spatial reorganization of vimentin and ASF in cells. Cytochalasin D (an inhibitor of actin polymerization) and vimentin upregulated/downregulated cells were used to verify the change in the spatial organization between vimentin and ASF and its influence on osteogenesis. Then, heat shock protein 27 (HSP27) was downregulated to illuminate the regulatory mechanisms of spatial organization between vimentin and ASF during osteogenesis. The amounts and the spatial positions of vimentin and actin stress fiber exhibited opposite trends during osteogenesis. Through controlling the anchor sites on the nucleus, intermediate filaments vimentin can reduce the spatial proportion of actin stress fibers, which can be regulated by HSP27. In addition, depolymerization of actin stress fibers lead to lower osteogenic differentiation ability, resulting in osteogenesis and lipogenesis existed simultaneously, that can be resisted by vimentin. Our data indicate that the spatial reorganization of vimentin and actin stress fibers is a key factor in the regulation of the differentiation state of hASCs. And their spatial overlapping area is detrimental to hASCs osteogenesis, providing a new perspective for further exploring the mechanism underlying hASCs osteogenesis.

Sarcoplasmic Proteome Profile and Internal Color of Beef Longissimus Lumborum Steaks Cooked to Different Endpoint Temperatures

The complex relationship between endpoint temperature, sarcoplasmic proteome, and internal color in cooked steaks is yet to be examined. The objective of the present study was to characterize the changes in sarcoplasmic proteome and their influence on the internal color of beef longissimus lumborum (LL) steaks cooked to different endpoint temperatures. Two 2.5-cm-thick LL steaks were fabricated from 9 beef strip loins and were cooked to an internal endpoint temperature of either 60°C (C-60) or 71°C (C-71). Cooked steaks were cooled and sliced parallel to the grilled surface, and internal color was evaluated instrumentally. Sarcoplasmic proteome from the interiors of the cooked steaks was analyzed using two-dimensional electrophoresis, and the gel images were digitally analyzed. The protein spots exhibiting more than 2-fold intensity differences (P &lt; 0.05) were subjected to in-gel tryptic digestion and were identified by tandem mass spectrometry. The C-60 steaks demonstrated greater (P &lt; 0.05) redness and color stability than the C-71 ones. Eleven differentially abundant protein spots were identified, and they belonged to 6 functional groups (transport proteins, enzymes in energy metabolism, chaperones, antioxidant proteins, enzymes in amino acid metabolism, and glycolytic enzymes). While 10 spots were overabundant (P &lt; 0.05) in C-60 steaks, 1 spot was overabundant (P &lt; 0.05) in C-71 steaks. The spot overabundant in C-71 samples was identified as myoglobin, suggesting the possible role of post-translational modifications in the heme protein’s thermal stability. The results indicated that the endpoint cooking temperature influenced sarcoplasmic proteome profile and internal color of cooked beef LL steaks. The overabundant proteins in steaks cooked to 60°C may be exploited as potential biomarkers for undercooked beef, which is a source for foodborne infections.

Regulation of small heat-shock proteins by hetero-oligomer formation

Small heat-shock proteins (sHsps) compose the most widespread family of molecular chaperones. The human genome encodes 10 different sHsps (HspB1-10). It has been shown that HspB1 (Hsp27), HspB5 (αB-crystallin), and HspB6 (Hsp20) can form hetero-oligomers in vivo However, the impact of hetero-oligomerization on their structure and chaperone mechanism remains enigmatic. Here, we analyzed hetero-oligomer formation in human cells and in vitro using purified proteins. Our results show that the effect of hetero-oligomer formation on the composition of the sHsp ensembles and their chaperone activities depends strongly on the respective sHsps involved. We observed that hetero-oligomer formation between HspB1 and HspB5 leads to an ensemble that is dominated by species larger than the individual homo-oligomers. In contrast, the interaction of dimeric HspB6 with either HspB1 or HspB5 oligomers shifted the ensemble toward smaller oligomers. We noted that the larger HspB1-HspB5 hetero-oligomers are less active and that HspB6 activates HspB5 by dissociation to smaller oligomer complexes. The chaperone activity of HspB1-HspB6 hetero-oligomers, however, was modulated in a substrate-specific manner, presumably due to the specific enrichment of an HspB1-HspB6 heterodimer. These heterodimeric species may allow the tuning of the chaperone properties toward specific substrates. We conclude that sHsp hetero-oligomerization exerts distinct regulatory effects depending on the sHsps involved.

Mechanism of Action of VP1-001 in cryAB(R120G)-Associated and Age-Related Cataracts

Purpose

We previously identified an oxysterol, VP1-001 (also known as compound 29), that partially restores the transparency of lenses with cataracts. To understand the mechanism of VP1-001, we tested the ability of its enantiomer, ent-VP1-001, to bind and stabilize αB-crystallin (cryAB) in vitro and to produce a similar therapeutic effect in cryAB(R120G) mutant and aged wild-type mice with cataracts. VP1-001 and ent-VP1-001 have identical physicochemical properties. These experiments are designed to critically evaluate whether stereoselective binding to cryAB is required for activity.

Methods

We compared the binding of VP1-001 and ent-VP1-001 to cryAB using in silico docking, differential scanning fluorimetry (DSF), and microscale thermophoresis (MST). Compounds were delivered by six topical administrations to mouse eyes over 2 weeks, and the effects on cataracts and lens refractive measures in vivo were examined. Additionally, lens epithelial and fiber cell morphologies were assessed via transmission electron microscopy.

Results

Docking studies suggested greater binding of VP1-001 into a deep groove in the cryAB dimer compared with ent-VP1-001. Consistent with this prediction, DSF and MST experiments showed that VP1-001 bound cryAB, whereas ent-VP1-001 did not. Accordingly, topical treatment of lenses with ent-VP1-001 had no effect, whereas VP1-001 produced a statistically significant improvement in lens clarity and favorable changes in lens morphology.

Conclusions

The ability of VP1-001 to bind native cryAB dimers is important for its ability to reverse lens opacity in mouse models of cataracts.

Quantum mechanism of light energy propagation through an avian retina

Taking into account the ultrastructure of the Pied Flycatcher foveal retina reported earlier and the earlier reported properties of Müller cell (MC) intermediate filaments (IFs) isolated from vertebrate retina, we proposed a quantum mechanism (QM) of light energy transfer from the inner limiting membrane level to visual pigments in the photoreceptor cells. This mechanism involves electronic excitation energy transfer in a donor-acceptor system, with the IFs excited by photons acting as energy donors, and visual pigments in the photoreceptor cells acting as energy acceptors. It was shown earlier that IFs with diameter 10 nm and length 117 μm isolated from vertebrate eye retina demonstrate properties of light energy guide, where exciton propagates along such IFs from MC endfeet area to photoreceptor cell area. The energy is mostly transferred via the contact exchange quantum mechanism. Our estimates demonstrate that energy transfer efficiencies in such systems may exceed 80-90%. Thus, the presently developed quantum mechanism of light energy transfer in the inverted retina complements the generally accepted classic optical mechanism and the mechanism whereby Müller cells transmit light like optical fibers. The proposed QM of light energy transfer in the inverted retina explains the high image contrast achieved in photopic conditions by an avian eye, being probably also active in other vertebrates.

Small heat shock proteins: multifaceted proteins with important implications for life

Small Heat Shock Proteins (sHSPs) evolved early in the history of life; they are present in archaea, bacteria, and eukaryota. sHSPs belong to the superfamily of molecular chaperones: they are components of the cellular protein quality control machinery and are thought to act as the first line of defense against conditions that endanger the cellular proteome. In plants, sHSPs protect cells against abiotic stresses, providing innovative targets for sustainable agricultural production. In humans, sHSPs (also known as HSPBs) are associated with the development of several neurological diseases. Thus, manipulation of sHSP expression may represent an attractive therapeutic strategy for disease treatment. Experimental evidence demonstrates that enhancing the chaperone function of sHSPs protects against age-related protein conformation diseases, which are characterized by protein aggregation. Moreover, sHSPs can promote longevity and healthy aging in vivo. In addition, sHSPs have been implicated in the prognosis of several types of cancer. Here, sHSP upregulation, by enhancing cellular health, could promote cancer development; on the other hand, their downregulation, by sensitizing cells to external stressors and chemotherapeutics, may have beneficial outcomes. The complexity and diversity of sHSP function and properties and the need to identify their specific clients, as well as their implication in human disease, have been discussed by many of the world's experts in the sHSP field during a dedicated workshop in Québec City, Canada, on 26-29 August 2018.

Chaperone-like activity of the N-terminal region of a human small heat shock protein and chaperone-functionalized nanoparticles

Small heat shock proteins (sHsps) are molecular chaperones employed to interact with a diverse range of substrates as the first line of defense against cellular protein aggregation. The N-terminal region (NTR) is implicated in defining features of sHsps; notably in their ability to form dynamic and polydisperse oligomers, and chaperone activity. The physiological relevance of oligomerization and chemical-scale mode(s) of chaperone function remain undefined. We present novel chemical tools to investigate chaperone activity and substrate specificity of human HspB1 (B1NTR), through isolation of B1NTR and development of peptide-conjugated gold nanoparticles (AuNPs). We demonstrate that B1NTR exhibits chaperone capacity for some substrates, determined by anti-aggregation assays and size-exclusion chromatography. The importance of protein dynamics and multivalency on chaperone capacity was investigated using B1NTR-conjugated AuNPs, which exhibit concentration-dependent chaperone activity for some substrates. Our results implicate sHsp NTRs in chaperone activity, and demonstrate the therapeutic potential of sHsp-AuNPs in rescuing aberrant protein aggregation.

Heat shock proteins are differentially expressed in brain and spinal cord: implications for multiple sclerosis

Multiple sclerosis (MS) is a chronic neurodegenerative disease characterized by demyelination, inflammation and neurodegeneration throughout the central nervous system. Although spinal cord pathology is an important factor contributing to disease progression, few studies have examined MS lesions in the spinal cord and how they differ from brain lesions. In this study we have compared brain and spinal cord white (WM) and grey (GM) matter from MS and control tissues, focusing on small heat shock proteins (HSPB) and HSP16.2. Western blotting was used to examine protein levels of HSPB1, HSPB5, HSPB6, HSPB8 and HSP16.2 in brain and spinal cord from MS and age-matched non-neurological controls. Immunohistochemistry was used to examine expression of the HSPs in MS spinal cord lesions and controls. Expression levels were quantified using ImageJ. Western blotting revealed significantly higher levels of HSPB1, HSPB6 and HSPB8 in MS and control spinal cord compared to brain tissues. No differences in HSPB5 and HSP16.2 protein levels were observed, although HSPB5 protein levels were higher in brain WM versus GM. In MS spinal cord lesions, increased HSPB1 and HSPB5 expression was observed in astrocytes, and increased neuronal expression of HSP16.2 was observed in normal-appearing GM and type 1 GM lesions. The high constitutive expression of several HSPBs in spinal cord and increased expression of HSPBs and HSP16.2 in MS illustrate differences between brain and spinal cord in health and upon demyelination. Regional differences in HSP expression may reflect differences in astrocyte cytoskeleton composition and influence inflammation, possibly affecting the effectiveness of pharmacological agents.

Effect of glutamine on heat-shock protein beta 1 (HSPB1) expression during myogenic differentiation in bovine embryonic fibroblast cells

The objective of this study was to examine the effects of glutamine on heat-shock protein beta 1 (HSPB1) expression in bovine embryonic fibroblast cells during myogenesis. First, to elucidate the role of glutamine on HSPB1 expression during myogenesis, we treated with glutamine in myogenic lineage determinant (MyoD) over-expressed bovine embryonic fibroblast cells (BEFS-MyoD cells). Second, knockdown of HSPB1 using small interference RNA was performed to evaluate whether muscle development by glutamine is dependent on HSPB1 in BEFS-MyoD cells. As a result, glutamine promoted the mRNA level of HSPB1, Myogenin, Desmin, and mTOR as well as myotube formation, and protein synthesis (p < 0.05). The inhibition of HSPB1 expression during myogenesis has shown to repress the expression of myogenic marker genes (MyoD, Myogenin, Desmin) (p < 0.01), formation of myotubes and protein synthesis (p < 0.05). According to the results, it is concluded that glutamine regulates HSPB1 expression during myogenesis.

Autoantibody Signaling in Pemphigus Vulgaris: Development of an Integrated Model

Pemphigus vulgaris (PV) is an autoimmune skin blistering disease effecting both cutaneous and mucosal epithelia. Blister formation in PV is known to result from the binding of autoantibodies (autoAbs) to keratinocyte antigens. The primary antigenic targets of pathogenic autoAbs are known to be desmoglein 3, and to a lesser extent, desmoglein 1, cadherin family proteins that partially comprise the desmosome, a protein structure responsible for maintaining cell adhesion, although additional autoAbs, whose role in blister formation is still unclear, are also known to be present in PV patients. Nevertheless, there remain large gaps in knowledge concerning the precise mechanisms through which autoAb binding induces blister formation. Consequently, the primary therapeutic interventions for PV focus on systemic immunosuppression, whose side effects represent a significant health risk to patients. In an effort to identify novel, disease-specific therapeutic targets, a multitude of studies attempting to elucidate the pathogenic mechanisms downstream of autoAb binding, have led to significant advancements in the understanding of autoAb-mediated blister formation. Despite this enhanced characterization of disease processes, a satisfactory explanation of autoAb-induced acantholysis still does not exist. Here, we carefully review the literature investigating the pathogenic disease mechanisms in PV and, taking into account the full scope of results from these studies, provide a novel, comprehensive theory of blister formation in PV.

Identification of periplakin as a major regulator of lung injury and repair in mice

Periplakin is a component of the desmosomes that acts as a cytolinker between intermediate filament scaffolding and the desmosomal plaque. Periplakin is strongly expressed by epithelial cells in the lung and is a target antigen for autoimmunity in idiopathic pulmonary fibrosis. The aim of this study was to determine the role of periplakin during lung injury and remodeling in a mouse model of lung fibrosis induced by bleomycin. We found that periplakin expression was downregulated in the whole lung and in alveolar epithelial cells following bleomycin-induced injury. Deletion of the Ppl gene in mice improved survival and reduced lung fibrosis development after bleomycin-induced injury. Notably, Ppl deletion promoted an antiinflammatory alveolar environment linked to profound changes in type 2 alveolar epithelial cells, including overexpression of antiinflammatory cytokines, decreased expression of profibrotic mediators, and altered cell signaling with a reduced response to TGF-β1. These results identify periplakin as a previously unidentified regulator of the response to injury in the lung.

Assembly and turnover of neurofilaments in growing axonal neurites

Neurofilaments (NFs) are thought to provide stability to the axon. We examined NF dynamics within axonal neurites of NB2a/d1 neuroblastoma by transient transfection with green fluorescent protein-tagged NF-heavy (GFP-H) under the control of a tetracycline-inducible promoter. Immunofluorescent and biochemical analyses demonstrated that GFP-H expressed early during neurite outgrowth associated with a population of centrally-situated, highly-phosphorylated crosslinked NFs along the length of axonal neurites (‘bundled NFs’). By contrast, GFP-H expressed after considerable neurite outgrowth displayed markedly reduced association with bundled NFs and was instead more evenly distributed throughout the axon. This differential localization was maintained for up to 2 weeks in culture. Once considerable neurite outgrowth had progressed, GFP that had previously associated with the NF bundle during early expression was irreversibly depleted by photobleaching. Cessation of expression allowed monitoring of NF turnover. GFP-H associated bundled NFs underwent slower decay than GFP-H associated with surrounding, less-phosphorylated NFs. Notably, GFP associated with bundled NFs underwent similar decay rates within the core and edges of this bundle. These results are consistent with previous demonstration of a resident NF population within axonal neurites, but suggest that this population is more dynamic than previously considered.

Summary: Immunofluorescent and radiolabel analyses demonstrate that neurofilaments establish a resident population within growing axonal neurites that undergoes exchange with a surrounding, transporting pool.

Getting Closer to an Effective Intervention of Ischemic Stroke: The Big Promise of Stem Cell

Stem cell therapy for ischemic stroke has widely been explored. Results from both preclinical and clinical studies have immensely supported the judicious use of stem cells as therapy. These provide an attractive means for preserving and replacing the damaged brain tissues following an ischemic attack. Since the past few years, researchers have used various types of stem cells to replenish insulted neuronal and glial cells in neurological disorders. In the present review, we discuss different types of stem cells employed for the treatment of ischemic stroke and mechanisms and challenges these cells face once introduced into the living system. Further, we also present different ways to maneuver and overcome challenges to translate the advances made at the preclinical level to clinics.

Interaction of small heat shock proteins with light component of neurofilaments (NFL)

The interaction of human small heat shock protein HspB1, its point mutants associated with distal hereditary motor neuropathy, and three other small heat shock proteins (HspB5, HspB6, HspB8) with the light component of neurofilaments (NFL) was analyzed by differential centrifugation, analytical ultracentrifugation, and fluorescent spectroscopy. The wild-type HspB1 decreased the quantity of NFL in pellets obtained after low- and high-speed centrifugation and increased the quantity of NFL remaining in the supernatant after high-speed centrifugation. Part of HspB1 was detected in the pellet of NFL after high-speed centrifugation, and at saturation, 1 mol of HspB1 monomer was bound per 2 mol of NFL. Point mutants of HspB1 associated with distal hereditary motor neuropathy (G84R, L99M, R140G, K141Q, and P182S) were almost as effective as the wild-type HspB1 in modulation of NFL assembly. At low ionic strength, HspB1 weakly interacted with NFL tetramers, and this interaction was increased upon salt-induced polymerization of NFL. HspB1 and HspB5 (αB-crystallin) decreased the rate of NFL polymerization measured by fluorescent spectroscopy. HspB6 (Hsp20) and HspB8 (Hsp22) were less effective than HspB1 (or HspB5) in modulation of NFL assembly. The data presented indicate that the small heat shock proteins affect NFL transition from tetramers to filaments, hydrodynamic properties of filaments, and their bundling and therefore probably modulate the formation of intermediate filament networks in neurons.

αB-crystallin is a sensor for assembly intermediates and for the subunit topology of desmin intermediate filaments

Mutations in the small heat shock protein chaperone CRYAB (αB-crystallin/HSPB5) and the intermediate filament protein desmin, phenocopy each other causing cardiomyopathies. Whilst the binding sites for desmin on CRYAB have been determined, desmin epitopes responsible for CRYAB binding and also the parameters that determine CRYAB binding to desmin filaments are unknown. Using a combination of co-sedimentation centrifugation, viscometric assays and electron microscopy of negatively stained filaments to analyse the in vitro assembly of desmin filaments, we show that the binding of CRYAB to desmin is subject to its assembly status, to the subunit organization within filaments formed and to the integrity of the C-terminal tail domain of desmin. Our in vitro studies using a rapid assembly protocol, C-terminally truncated desmin and two disease-causing mutants (I451M and R454W) suggest that CRYAB is a sensor for the surface topology of the desmin filament. Our data also suggest that CRYAB performs an assembly chaperone role because the assembling filaments have different CRYAB-binding properties during the maturation process. We suggest that the capability of CRYAB to distinguish between filaments with different surface topologies due either to mutation (R454W) or assembly protocol is important to understanding the pathomechanism(s) of desmin-CRYAB myopathies.

The functional roles of the unstructured N- and C-terminal regions in αB-crystallin and other mammalian small heat-shock proteins

Small heat-shock proteins (sHsps), such as αB-crystallin, are one of the major classes of molecular chaperone proteins. In vivo, under conditions of cellular stress, sHsps are the principal defence proteins that prevent large-scale protein aggregation. Progress in determining the structure of sHsps has been significant recently, particularly in relation to the conserved, central and β-sheet structured α-crystallin domain (ACD). However, an understanding of the structure and functional roles of the N- and C-terminal flanking regions has proved elusive mainly because of their unstructured and dynamic nature. In this paper, we propose functional roles for both flanking regions, based around three properties: (i) they act in a localised crowding manner to regulate interactions with target proteins during chaperone action, (ii) they protect the ACD from deleterious amyloid fibril formation and (iii) the flexibility of these regions, particularly at the extreme C-terminus in mammalian sHsps, provides solubility for sHsps under chaperone and non-chaperone conditions. In the eye lens, these properties are highly relevant as the crystallin proteins, in particular the two sHsps αA- and αB-crystallin, are present at very high concentrations.

The protective role of small heat shock proteins in cardiac diseases: key role in atrial fibrillation

Atrial fibrillation (AF) is the most common tachyarrhythmia which is associated with increased morbidity and mortality. AF usually progresses from a self-terminating paroxysmal to persistent disease. It has been recognized that AF progression is driven by structural remodeling of cardiomyocytes, which results in electrical and contractile dysfunction of the atria. We recently showed that structural remodeling is rooted in derailment of proteostasis, i.e., homeostasis of protein production, function, and degradation. Since heat shock proteins (HSPs) play an important role in maintaining a healthy proteostasis, the role of HSPs was investigated in AF. It was found that especially small heat shock protein (HSPB) levels get exhausted in atrial tissue of patients with persistent AF and that genetic or pharmacological induction of HSPB protects against cardiomyocyte remodeling in experimental models for AF. In this review, we provide an overview of HSPBs as a potential therapeutic target for normalizing proteostasis and suppressing the substrates for AF progression in experimental and clinical AF and discuss HSP activators as a promising therapy to prevent AF onset and progression.

The growing world of small heat shock proteins: from structure to functions

Small heat shock proteins (sHSPs) are present in all kingdoms of life and play fundamental roles in cell biology. sHSPs are key components of the cellular protein quality control system, acting as the first line of defense against conditions that affect protein homeostasis and proteome stability, from bacteria to plants to humans. sHSPs have the ability to bind to a large subset of substrates and to maintain them in a state competent for refolding or clearance with the assistance of the HSP70 machinery. sHSPs participate in a number of biological processes, from the cell cycle, to cell differentiation, from adaptation to stressful conditions, to apoptosis, and, even, to the transformation of a cell into a malignant state. As a consequence, sHSP malfunction has been implicated in abnormal placental development and preterm deliveries, in the prognosis of several types of cancer, and in the development of neurological diseases. Moreover, mutations in the genes encoding several mammalian sHSPs result in neurological, muscular, or cardiac age-related diseases in humans. Loss of protein homeostasis due to protein aggregation is typical of many age-related neurodegenerative and neuromuscular diseases. In light of the role of sHSPs in the clearance of un/misfolded aggregation-prone substrates, pharmacological modulation of sHSP expression or function and rescue of defective sHSPs represent possible routes to alleviate or cure protein conformation diseases. Here, we report the latest news and views on sHSPs discussed by many of the world's experts in the sHSP field during a dedicated workshop organized in Italy (Bertinoro, CEUB, October 12-15, 2016).

Glial fibrillary acidic protein exhibits altered turnover kinetics in a mouse model of Alexander disease

Mutations in the astrocyte-specific intermediate filament glial fibrillary acidic protein (GFAP) lead to the rare and fatal disorder, Alexander disease (AxD). A prominent feature of the disease is aberrant accumulation of GFAP. It has been proposed that this accumulation occurs because of an increase in gene transcription coupled with impaired proteasomal degradation, yet this hypothesis remains untested. We therefore sought to directly investigate GFAP turnover in a mouse model of AxD that is heterozygous for a disease-causing point mutation (Gfap^R236H/+) (and thus expresses both wild-type and mutant protein). Stable isotope labeling by amino acids in cell culture, using primary cortical astrocytes, indicated that the in vitro half-lives of total GFAP in astrocytes from wild-type and mutant mice were similar at ∼3-4 days. Surprisingly, results obtained with stable isotope labeling of mammals revealed that, in vivo, the half-life of GFAP in mutant mice (15.4 ± 0.5 days) was much shorter than that in wild-type mice (27.5 ± 1.6 days). These unexpected in vivo data are most consistent with a model in which synthesis and degradation are both increased. Our work reveals that an AxD-causing mutation alters GFAP turnover kinetics in vivo and provides an essential foundation for future studies aimed at preventing or reducing the accumulation of GFAP. In particular, these data suggest that elimination of GFAP might be possible and occurs more quickly than previously surmised.

Astrocytes release HspB1 in response to amyloid-β exposure in vitro

Although heat shock proteins are thought to function primarily as intracellular chaperones, the release and potential extracellular functions of heat shock proteins have been the focus of an increasing number of studies. Our particular interest is HspB1 (Hsp25/27) and as astrocytes are an in vivo source of HspB1 it is a reasonable possibility they could release HspB1 in response to local stresses. Using primary cultures of rat cortical astrocytes, we investigated the extracellular release of HspB1 with exposure to amyloid-β (Aβ). In order to assess potential mechanisms of release, we cotreated the cells with compounds that can modulate protein secretion including Brefeldin A, Methyl β-cyclodextrin, and MAP kinase inhibitors. Exposure to Aβ (0.1, 1.0, 2.0 μM) for 24-48 h resulted in a selective release of HspB1 that was insensitive to BFA treatment; none of the other inhibitors had any detectable influence. Protease protection assays indicated that some of the released HspB1 was associated with a membrane bound fraction, and analysis of exosomal preparations indicated the presence of HspB1 in exosomes. Finally, immunoprecipitation experiments demonstrated that the extracellular HspB1 was able to interact with extracellular Aβ. In summary, Aβ can stimulate release of HspB1 from astrocytes, this release is insensitive to Golgi or lipid raft disruption, and HspB1 can be found either free in the medium or associated with exosomes. This release suggests that there is a potential for extracellular HspB1 to be able to bind and sequester extracellular Aβ.

Desmin and αB-crystallin interplay in the maintenance of mitochondrial homeostasis and cardiomyocyte survival

The association of desmin with the α-crystallin Β-chain (αΒ-crystallin; encoded by CRYAB), and the fact that mutations in either one of them leads to heart failure in humans and mice, suggests a potential compensatory interplay between the two in cardioprotection. To address this hypothesis, we investigated the consequences of αΒ-crystallin overexpression in the desmin-deficient (Des^-/-) mouse model, which possesses a combination of the pathologies found in most cardiomyopathies, with mitochondrial defects as a hallmark. We demonstrated that cardiac-specific αΒ-crystallin overexpression ameliorates all these defects and improves cardiac function to almost wild-type levels. Protection by αΒ-crystallin overexpression is linked to maintenance of proper mitochondrial protein levels, inhibition of abnormal mitochondrial permeability transition pore activation and maintenance of mitochondrial membrane potential (Δψ_m). Furthermore, we found that both desmin and αΒ-crystallin are localized at sarcoplasmic reticulum (SR)-mitochondria-associated membranes (MAMs), where they interact with VDAC, Mic60 - the core component of mitochondrial contact site and cristae organizing system (MICOS) complex - and ATP synthase, suggesting that these associations could be crucial in mitoprotection at different levels.

HSPB3 protein is expressed in motoneurons and induces their survival after lesion-induced degeneration

The human small heat shock proteins (HSPBs) form a family of molecular chaperones comprising ten members (HSPB1-HSPB10), whose functions span from protein quality control to cytoskeletal dynamics and cell death control. Mutations in HSPBs can lead to human disease and particularly point mutations in HSPB1 and HSPB8 are known to lead to peripheral neuropathies. Recently, a missense mutation (R7S) in yet another member of this family, HSPB3, was found to cause an axonal motor neuropathy (distal hereditary motor neuropathy type 2C, dHMN2C). Until now, HSPB3 protein localization and function in motoneurons (MNs) have not yet been characterized. Therefore, we studied the endogenous HSPB3 protein distribution in the spinal cords of chicken and mouse embryos and in the postnatal nervous system (central and peripheral) of chicken, mouse and human. We further investigated the impact of wild-type and mutated HSPB3 on MN cell death via overexpressing these genes in ovo in an avian model of MN degeneration, the limb-bud removal. Altogether, our findings represent a first step for a better understanding of the cellular and molecular mechanisms leading to dHMN2C.

Regulation of lamin properties and functions: does phosphorylation do it all?

The main functions of lamins are their mechanical and structural roles as major building blocks of the karyoskeleton. They are also involved in chromatin structure regulation, gene expression, intracellular signalling pathway modulation and development. All essential lamin functions seem to depend on their capacity for assembly or disassembly after the receipt of specific signals, and after specific, selective and precisely regulated interactions through their various domains. Reversible phosphorylation of lamins is crucial for their functions, so it is important to understand how lamin polymerization and interactions are modulated, and which sequences may undergo such modifications. This review combines experimental data with results of our in silico analyses focused on lamin phosphorylation in model organisms to show the presence of evolutionarily conserved sequences and to indicate specific in vivo phosphorylations that affect particular functions.

Both monovalent cations and plectin are potent modulators of mechanical properties of keratin K8/K18 networks

Intermediate filament (IF) networks are a major contributor to cell rigidity and thus serve as vital elements to preserve the integrity of entire cell layers. Keratin K8 and K18 IFs are the basic constituents of the cytoskeleton of epithelial cells. The mechanical properties of K8/K18 networks depend on the structural arrangements of individual filaments within the network. This paper investigates the architecture of these networks in vitro under the influence of the monovalent cation potassium and that of the cytolinker protein plectin. Whereas increasing amounts of potassium ions lead to filament bundling, plectin interlinks filaments at filament intersection points but does not lead to bundle formation. The mechanics of the resulting networks are investigated by microrheology with assembled K8/K18 networks. It is shown that bundling induced by potassium ions significantly stiffens the network. Furthermore, our measurements reveal an increase in plectin-mediated keratin network rigidity as soon as an amount corresponding to more than 20% of the plectin present in cells is added to the keratin IF networks. In parallel, we investigated the influence of plectin on cell rigidity in detergent-extracted epithelial vulva carcinoma derived A431 cells in situ. These cytoskeletons, containing mostly IFs, actin filaments and associated proteins, exhibit a significantly decreased stiffness, when plectin is downregulated to ≈10% of the normal value. Therefore, we assume that plectin, via the formation of IF-IF connections and crosslinking of IFs to actin filaments, is an important contributor to cell stiffness.

The Invalidation of HspB1 Gene in Mouse Alters the Ultrastructural Phenotype of Muscles

Even though abundance of Hsp27 is the highest in skeletal muscle, the relationships between the expression of HspB1 (encoding Hsp27) and muscle characteristics are not fully understood. In this study, we have analysed the effect of Hsp27 inactivation on mouse development and phenotype. We generated a mouse strain devoid of Hsp27 protein by homologous recombination of the HspB1 gene. The HspB1^-/- mouse was viable and fertile, showing neither apparent morphological nor anatomical alterations. We detected a gender dimorphism with marked effects in males, a lower body weight (P < 0.05) with no obvious changes in the growth rate, and a lower plasma lipids profile (cholesterol, HDL and triglycerides, 0.001 < P< 0.05). The muscle structure of the animals was examined by optical microscopy and transmission electron microscopy. Not any differences in the characteristics of muscle fibres (contractile and metabolic type, shape, perimeter, cross-sectional area) were detected except a trend for a higher proportion of small fibres. Different myosin heavy chains electrophoretic profiles were observed in the HspB1^-/- mouse especially the presence of an additional isoform. Electron microscopy revealed ultrastructural abnormalities in the myofibrillar structure of the HspB1^-/- mouse mutant mice (e.g. destructured myofibrils and higher gaps between myofibrils) especially in the m. Soleus. Combined with our previous data, these findings suggest that Hsp27 could directly impact the organization of muscle cytoskeleton at the molecular and ultrastructural levels.