The small heat shock proteins and their role in human disease

High-Performance Workflow for Identifying Site-Specific Crosslinks Originating from a Genetically Incorporated, Photoreactive Amino Acid

In conventional crosslinking mass spectrometry, proteins are crosslinked using a highly selective, bifunctional chemical reagent, which limits crosslinks to residues that are accessible and reactive to the reagent. Genetically incorporating a photoreactive amino acid offers two key advantages: any site can be targeted, including those that are inaccessible to conventional crosslinking reagents, and photoreactive amino acids can potentially react with a broad range of interaction partners. However, broad reactivity imposes additional challenges for crosslink identification. In this study, we incorporate benzoylphenylalanine (BPA), a photoreactive amino acid, at selected sites in an intrinsically disordered region of the human protein HSPB5. We report and characterize a workflow for identifying and visualizing residue-level interactions originating from BPA. We routinely identify 30 to 300 crosslinked peptide spectral matches with this workflow, which is up to ten times more than existing tools for residue-level BPA crosslink identification. Most identified crosslinks are assigned to a precision of one or two residues, which is supported by a high degree of overlap between replicate analyses. Based on these results, we anticipate that this workflow will support the more general use of genetically incorporated, photoreactive amino acids for characterizing the structures of proteins that have resisted high-resolution characterization.

Modulation of Alzheimer's Disease Aβ40 Fibril Polymorphism by the Small Heat Shock Protein αB-Crystallin

Deposition of amyloid plaques in the brains of Alzheimer's disease (AD) patients is a hallmark of the disease. AD plaques consist primarily of the beta-amyloid (Aβ) peptide but can contain other factors such as lipids, proteoglycans, and chaperones. So far, it is unclear how the cellular environment modulates fibril polymorphism and how differences in fibril structure affect cell viability. The small heat-shock protein (sHSP) alpha-B-Crystallin (αBC) is abundant in brains of AD patients, and colocalizes with Aβ amyloid plaques. Using solid-state NMR spectroscopy, we show that the Aβ40 fibril seed structure is not replicated in the presence of the sHSP. αBC prevents the generation of a compact fibril structure and leads to the formation of a new polymorph with a dynamic N-terminus. We find that the N-terminal fuzzy coat and the stability of the C-terminal residues in the Aβ40 fibril core affect the chemical and thermodynamic stability of the fibrils and influence their seeding capacity. We believe that our results yield a better understanding of how sHSP, such as αBC, that are part of the cellular environment, can affect fibril structures related to cell degeneration in amyloid diseases.

αB-Crystallin Peptide Fused with Elastin-like Polypeptide: Intracellular Activity in Retinal Pigment Epithelial Cells Challenged with Oxidative Stress

BACKGROUND

Oxidative stress-induced retinal degeneration is among the main contributing factors of serious ocular pathologies that can lead to irreversible blindness. αB-crystallin (cry) is an abundant component of the visual pathway in the vitreous humor, which modulates protein and cellular homeostasis. Within this protein exists a 20 amino acid fragment (mini-cry) with both chaperone and antiapoptotic activity. This study fuses this mini-cry peptide to two temperature-sensitive elastin-like polypeptides (ELP) with the goal of prolonging its activity in the retina.

METHODS

The biophysical properties and chaperone activity of cry-ELPs were confirmed by mass spectrometry, cloud-point determination, and dynamic light scattering 'DLS'. For the first time, this work compares a simpler ELP architecture, cry-V96, with a previously reported ELP diblock copolymer, cry-SI. Their relative mechanisms of cellular uptake and antiapoptotic potential were tested using retinal pigment epithelial cells (ARPE-19). Oxidative stress was induced with H2O2 and comparative internalization of both cry-ELPs was made using 2D and 3D culture models. We also explored the role of lysosomal membrane permeabilization by confocal microscopy.

RESULTS

The results indicated successful ELP fusion, cellular association with both 2D and 3D cultures, which were enhanced by oxidative stress. Both constructs suppressed apoptotic signaling (cleaved caspase-3); however, cry-V96 exhibited greater lysosomal escape.

CONCLUSIONS

ELP architecture is a critical factor to optimize delivery of therapeutic peptides, such as the anti-apoptotic mini-cry peptide; furthermore, the protection of mini-cry via ELPs is enhanced by lysosomal membrane permeabilization.

Neurodegenerative Proteinopathies Induced by Environmental Pollutants: Heat Shock Proteins and Proteasome as Promising Therapeutic Tools

Environmental pollutants' (EPs) amount and diversity have increased in recent years due to anthropogenic activity. Several neurodegenerative diseases (NDs) are theorized to be related to EPs, as their incidence has increased in a similar way to human EPs exposure and they reproduce the main ND hallmarks. EPs induce several neurotoxic effects, including accumulation and gradual deposition of misfolded toxic proteins, producing neuronal malfunction and cell death. Cells possess different mechanisms to eliminate these toxic proteins, including heat shock proteins (HSPs) and the proteasome system. The accumulation and deleterious effects of toxic proteins are induced through HSPs and disruption of proteasome proteins' homeostatic function by exposure to EPs. A therapeutic approach has been proposed to reduce accumulation of toxic proteins through treatment with recombinant HSPs/proteasome or the use of compounds that increase their expression or activity. Our aim is to review the current literature on NDs related to EP exposure and their relationship with the disruption of the proteasome system and HSPs, as well as to discuss the toxic effects of dysfunction of HSPs and proteasome and the contradictory effects described in the literature. Lastly, we cover the therapeutic use of developed drugs and recombinant proteasome/HSPs to eliminate toxic proteins and prevent/treat EP-induced neurodegeneration.

Tardigrade small heat shock proteins can limit desiccation-induced protein aggregation

Small heat shock proteins (sHSPs) are chaperones with well-characterized roles in heat stress, but potential roles for sHSPs in desiccation tolerance have not been as thoroughly explored. We identified nine sHSPs from the tardigrade Hypsibius exemplaris, each containing a conserved alpha-crystallin domain flanked by disordered regions. Many of these sHSPs are highly expressed. Multiple tardigrade and human sHSPs could improve desiccation tolerance of E. coli, suggesting that the capacity to contribute to desicco-protection is a conserved property of some sHSPs. Purification and subsequent analysis of two tardigrade sHSPs, HSP21 and HSP24.6, revealed that these proteins can oligomerize in vitro. These proteins limited heat-induced aggregation of the model enzyme citrate synthase. Heterologous expression of HSP24.6 improved bacterial heat shock survival, and the protein significantly reduced heat-induced aggregation of soluble bacterial protein. Thus, HSP24.6 likely chaperones against protein aggregation to promote heat tolerance. Furthermore, HSP21 and HSP24.6 limited desiccation-induced aggregation and loss of function of citrate synthase. This suggests a mechanism by which tardigrade sHSPs promote desiccation tolerance, by limiting desiccation-induced protein aggregation, thereby maintaining proteostasis and supporting survival. These results suggest that sHSPs provide a mechanism of general stress resistance that can also be deployed to support survival during anhydrobiosis.

The Common Bean Small Heat Shock Protein Nodulin 22 from Phaseolus vulgaris L. Assembles into Functional High-Molecular-Weight Oligomers

Small heat shock proteins (sHsps) are present in all domains of life. These proteins are responsible for binding unfolded proteins to prevent their aggregation. sHsps form dynamic oligomers of different sizes and constitute transient reservoirs for folding competent proteins that are subsequently refolded by ATP-dependent chaperone systems. In plants, the sHsp family is rather diverse and has been associated with the ability of plants to survive diverse environmental stresses. Nodulin 22 (PvNod22) is an sHsp of the common bean (Phaseolus vulgaris L.) located in the endoplasmic reticulum. This protein is expressed in response to stress (heat or oxidative) or in plant roots during mycorrhizal and rhizobial symbiosis. In this work, we study its oligomeric state using a combination of in silico and experimental approaches. We found that recombinant PvNod22 was able to protect a target protein from heat unfolding in vitro. We also demonstrated that PvNod22 assembles into high-molecular-weight oligomers with diameters of ~15 nm under stress-free conditions. These oligomers can cluster together to form high-weight polydisperse agglomerates with temperature-dependent interactions; in contrast, the oligomers are stable regarding temperature.

A Charcot-Marie-Tooth-Causing Mutation in HSPB1 Decreases Cell Adaptation to Repeated Stress by Disrupting Autophagic Clearance of Misfolded Proteins

Charcot-Marie-Tooth (CMT) disease is the most common inherited neurodegenerative disorder with selective degeneration of peripheral nerves. Despite advances in identifying CMT-causing genes, the underlying molecular mechanism, particularly of selective degeneration of peripheral neurons remains to be elucidated. Since peripheral neurons are sensitive to multiple stresses, we hypothesized that daily repeated stress might be an essential contributor to the selective degeneration of peripheral neurons induced by CMT-causing mutations. Here, we mainly focused on the biological effects of the dominant missense mutation (S135F) in the 27-kDa small heat-shock protein HSPB1 under repeated heat shock. HSPB1S135F presented hyperactive binding to both α-tubulin and acetylated α-tubulin during repeated heat shock when compared with the wild type. The aberrant interactions with tubulin prevented microtubule-based transport of heat shock-induced misfolded proteins for the formation of perinuclear aggresomes. Furthermore, the transport of autophagosomes along microtubules was also blocked. These results indicate that the autophagy pathway was disrupted, leading to an accumulation of ubiquitinated protein aggregates and a significant decrease in cell adaptation to repeated stress. Our findings provide novel insights into the molecular mechanisms of HSPB1S135F-induced selective degeneration of peripheral neurons and perspectives for targeting autophagy as a promising therapeutic strategy for CMT neuropathy.

The role of heat shock proteins in metastatic colorectal cancer: A review

Heat shock proteins (HSPs) are a large molecular chaperone family classified by their molecular weights, including HSP27, HSP40, HSP60, HSP70, HSP90, and HSP110. HSPs are likely to have antiapoptotic properties and participate actively in various processes such as tumor cell proliferation, invasion, metastases, and death. In this review, we discuss comprehensively the functions of HSPs associated with the progression of colorectal cancer (CRC) and metastasis and resistance to cancer therapy. Taken together, HSPs have numerous clinical applications as biomarkers for cancer diagnosis and prognosis and potential therapeutic targets for CRC and its related metastases.

Effect of Betaine and Arginine on Interaction of αB-Crystallin with Glycogen Phosphorylase b

Protein-protein interactions (PPIs) play an important role in many biological processes in a living cell. Among them chaperone-client interactions are the most important. In this work PPIs of αB-crystallin and glycogen phosphorylase b (Phb) in the presence of betaine (Bet) and arginine (Arg) at 48 °C and ionic strength of 0.15 M were studied using methods of dynamic light scattering, differential scanning calorimetry, and analytical ultracentrifugation. It was shown that Bet enhanced, while Arg reduced both the stability of αB-crystallin and its adsorption capacity (AC0) to the target protein at the stage of aggregate growth. Thus, the anti-aggregation activity of αB-crystallin increased in the presence of Bet and decreased under the influence of Arg, which resulted in inhibition or acceleration of Phb aggregation, respectively. Our data show that chemical chaperones can influence the tertiary and quaternary structure of both the target protein and the protein chaperone. The presence of the substrate protein also affects the quaternary structure of αB-crystallin, causing its disassembly. This is inextricably linked to the anti-aggregation activity of αB-crystallin, which in turn affects its PPI with the target protein. Thus, our studies contribute to understanding the mechanism of interaction between chaperones and proteins.

Role of ATP-Small Heat Shock Protein Interaction in Human Diseases

Adenosine triphosphate (ATP) is an important fuel of life for humans and Mycobacterium species. Its potential role in modulating cellular functions and implications in systemic, pulmonary, and ocular diseases is well studied. Plasma ATP has been used as a diagnostic and prognostic biomarker owing to its close association with disease’s progression. Several stresses induce altered ATP generation, causing disorders and illnesses. Small heat shock proteins (sHSPs) are dynamic oligomers that are dominantly β-sheet in nature. Some important functions that they exhibit include preventing protein aggregation, enabling protein refolding, conferring thermotolerance to cells, and exhibiting anti-apoptotic functions. Expression and functions of sHSPs in humans are closely associated with several diseases like cataracts, cardiovascular diseases, renal diseases, cancer, etc. Additionally, there are some mycobacterial sHSPs like Mycobacterium leprae HSP18 and Mycobacterium tuberculosis HSP16.3, whose molecular chaperone functions are implicated in the growth and survival of pathogens in host species. As both ATP and sHSPs, remain closely associated with several human diseases and survival of bacterial pathogens in the host, therefore substantial research has been conducted to elucidate ATP-sHSP interaction. In this mini review, the impact of ATP on the structure and function of human and mycobacterial sHSPs is discussed. Additionally, how such interactions can influence the onset of several human diseases is also discussed.

Muscle-Related Plectinopathies

Plectin is a giant cytoskeletal crosslinker and intermediate filament stabilizing protein. Mutations in the human plectin gene (PLEC) cause several rare diseases that are grouped under the term plectinopathies. The most common disorder is autosomal recessive disease epidermolysis bullosa simplex with muscular dystrophy (EBS-MD), which is characterized by skin blistering and progressive muscle weakness. Besides EBS-MD, PLEC mutations lead to EBS with nail dystrophy, EBS-MD with a myasthenic syndrome, EBS with pyloric atresia, limb-girdle muscular dystrophy type R17, or EBS-Ogna. In this review, we focus on the clinical and pathological manifestations caused by PLEC mutations on skeletal and cardiac muscle. Skeletal muscle biopsies from EBS-MD patients and plectin-deficient mice revealed severe dystrophic features with variation in fiber size, degenerative myofibrillar changes, mitochondrial alterations, and pathological desmin-positive protein aggregates. Ultrastructurally, PLEC mutations lead to a disorganization of myofibrils and sarcomeres, Z- and I-band alterations, autophagic vacuoles and cytoplasmic bodies, and misplaced and degenerating mitochondria. We also summarize a variety of genetically manipulated mouse and cell models, which are either plectin-deficient or that specifically lack a skeletal muscle-expressed plectin isoform. These models are powerful tools to study functional and molecular consequences of PLEC defects and their downstream effects on the skeletal muscle organization.

Novel Proteome and N-Glycoproteome of the Thermophilic Fungus Chaetomium thermophilum in Response to High Temperature

Thermophilic fungi are eukaryotic species that grow at high temperatures, but little is known about the underlying basis of thermophily at cell and molecular levels. Here the proteome and N-glycoproteome of Chaetomium thermophilum at varying culture temperatures (30, 50, and 55°C) were studied using hydrophilic interaction liquid chromatography enrichment and high-resolution liquid chromatography–tandem mass spectroscopy analysis. With respect to the proteome, the numbers of differentially expressed proteins were 1,274, 1,374, and 1,063 in T50/T30, T55/T30, and T55/T50, respectively. The upregulated proteins were involved in biological processes, such as protein folding and carbohydrate metabolism. Most downregulated proteins were involved in molecular functions, including structural constituents of the ribosome and other protein complexes. For the N-glycoproteome, the numbers of differentially expressed N-glycoproteins were 160, 176, and 128 in T50/T30, T55/T30, and T55/T50, respectively. The differential glycoproteins were mainly involved in various types of N-glycan biosynthesis, mRNA surveillance pathway, and protein processing in the endoplasmic reticulum. These results indicated that an efficient protein homeostasis pathway plays an essential role in the thermophily of C. thermophilum, and N-glycosylation is involved by affecting related proteins. This is the novel study to reveal thermophilic fungi’s physiological response to high-temperature adaptation using omics analysis, facilitating the exploration of the thermophily mechanism of thermophilic fungi.

The involvement of small heat shock protein in chemoresistance in ovarian cancer - in vitro study

Ovarian cancer is the most deadly gynecologic malignancy worldwide. Although the primary response to chemotherapy is high, the majority of patients will develop resistance against applied treatment. In this study, we focused on resistance to cisplatin, a first-line drug used for the treatment of ovarian cancer. The mechanism of the resistance development process is widely described, but there is a lack of information about the involvement of members of small heat shock proteins (HSPs) and their transport via exosomes. In this study, we used two cell lines: A2780 and SKOV3, and their cisplatin-resistance variants: A2780 CDDP and SKOV3 CDDP. We have shown that the expression of three small HSPs (HSPB5, HSPB6, and HSPB8) in cisplatin-resistant cell lines differs from their sensitive counterparts. Further, we isolated exosomes and determined the small HSPs in their cargo. In A2780 WT we observed a low amount of HSPB5 and HSPB6. We did not observe the expression of small HSPs in the SKOV3 cell line in both sensitive and resistant variants. Our data suggest the involvement of small HSPs in drug resistance of ovarian cancer and their presence is not related to exosomal transport. Analysis of the biological consequences of the imbalance of small HSPs expression in cisplatin resistance needs further investigation.

Association of Alpha B-Crystallin Expression with Tumor Differentiation Grade in Colorectal Cancer Patients

Alpha B-crystallin (CRYAB, HSPB5) belongs to the small heat shock protein (HSP) family and is highly expressed in various human cancers, suggesting a crucial role in tumor progression. However, few studies have examined CRYAB expression in colorectal cancer (CRC). In the present study, we investigated the relationship between CRYAB expression and the clinicopathological features of CRC samples. We comparatively analyzed CRYAB protein expression in 111 CRC tissues and normal adjacent colonic tissue, observing that it was significantly lower in CRC tissues than in corresponding non-cancerous tissues. Moreover, immunohistochemical analysis showed a significant correlation between CRYAB expression and high histological grade G3 (p = 0.033). In summary, our results point to its possible application as a prognostic biomarker in CRC patients.

Heat Shock Proteins and Their Role in Pregnancy: Redefining the Function of "Old Rum in a New Bottle"

Pregnancy in humans is a multi-step complex physiological process comprising three discrete events, decidualization, implantation and placentation. Its overall success depends on the incremental advantage that each of the preceding stages passes on to the next. The success of these synchronized sequels of events is an outcome of timely coordination between them. The pregnancy events are coordinated and governed primarily by the ovarian steroid hormones, estrogen and progesterone, which are essentially ligand-activated transcription factors. It's well known that intercellular signaling of steroid hormones engages a plethora of adapter proteins that participate in executing the biological functions. This involves binding of the hormone receptor complex to the DNA response elements in a sequence specific manner. Working with Drosophila melanogaster, the heat shock proteins (HSPs) were originally described by Ferruccio Ritossa back in the early 1960s. Over the years, there has been considerable advancement of our understanding of these conserved families of proteins, particularly in pregnancy. Accumulating evidence suggests that endometrial and uterine cells have an abundance of HSP27, HSP60, HSP70 and HSP90, implying their possible involvement during the pregnancy process. HSPs have been found to be associated with decidualization, implantation and placentation, with their dysregulation associated with implantation failure, pregnancy loss and other feto-maternal complications. Furthermore, HSP is also associated with stress response, specifically in modulating the ER stress, a critical determinant for reproductive success. Recent advances suggest a therapeutic role of HSPs proteins in improving the pregnancy outcome. In this review, we summarized our latest understanding of the role of different members of the HSP families during pregnancy and associated complications based on experimental and clinical evidences, thereby redefining and exploring their novel function with new perspective, beyond their prototype role as molecular chaperones.

The effect of female sex hormones on Hsp27 phosphorylation and histological changes in prefrontal cortex after tMCAO

BACKGROUND

Female sex hormones are protective factors against many neurological disorders such as brain ischemia. Heat shock protein like HSP27 is activated after tissue injury. The main purpose of the present study is to determine the effect of a combined estrogen / progesterone cocktail on the morphology of astrocytes, neurons and Hsp27 phosphorylation after cerebral ischemia.

METHODS

One hour after the MCAO induction, a single dose of estrogen and progesterone was injected. The infarct volume was calculated by TTC staining 24 h after ischemia. Immunohistochemistry was used to show the effects of estrogen and progesterone on astrocyte and neuron morphology, as well as the Western blot technique used for the quantitation of phosphorylated Hsp27.

RESULTS

The combined dose of estrogen and progesterone significantly decreased astrocytosis after ischemia and increased neuron survival. There was a large increase in Hsp27 phosphorylation in the penumbra ischemic region after stroke, which was significantly reduced by hormone therapy.

CONCLUSION

Our results indicate that the neuroprotective effect of neurosteroids in the brain may be due to the modulation of heat shock proteins.

The p.Ala2430Val mutation in filamin C causes a "hypertrophic myofibrillar cardiomyopathy"

Hypertrophic cardiomyopathy (HCM) often leads to heart failure. Mutations in sarcomeric proteins are most frequently the cause of HCM but in many patients the gene defect is not known. Here we report on a young man who was diagnosed with HCM shortly after birth. Whole exome sequencing revealed a mutation in the FLNC gene (c.7289C > T; p.Ala2430Val) that was previously shown to cause aggregation of the mutant protein in transfected cells. Myocardial tissue from patients with this mutation has not been analyzed before and thus, the underlying etiology is not well understood. Myocardial tissue of our patient obtained during myectomy at the age of 23 years was analyzed in detail by histochemistry, immunofluorescence staining, electron microscopy and western blot analysis. Cardiac histology showed a pathology typical for myofibrillar myopathy with myofibril disarray and abnormal protein aggregates containing BAG3, desmin, HSPB5 and filamin C. Analysis of sarcomeric and intercalated disc proteins showed focally reduced expression of the gap junction protein connexin43 and Xin-positive sarcomeric lesions in the cardiomyocytes of our patient. In addition, autophagy pathways were altered with upregulation of LC3-II, WIPI1 and HSPB5, 6, 7 and 8. We conclude that the p.Ala2430Val mutation in FLNC most probably is associated with HCM characterized by abnormal intercalated discs, disarray of myofibrils and aggregates containing Z-disc proteins similar to myofibrillar myopathy, which supports the pathological effect of the mutation.

The role and therapeutic potential of Hsp90, Hsp70, and smaller heat shock proteins in peripheral and central neuropathies

Heat shock proteins (Hsps) are molecular chaperones that also play important roles in the activation of the heat shock response (HSR). The HSR is an evolutionary conserved and protective mechanism that is used to counter abnormal physiological conditions, stressors, and disease states, such as those exemplified in cancer and/or neurodegeneration. In normal cells, heat shock factor-1 (HSF-1), the transcription factor that regulates the HSR, remains in a dormant multiprotein complex that is formed upon association with chaperones (Hsp90, Hsp70, etc.), co-chaperones, and client proteins. However, under cellular stress, HSF-1 dissociates from Hsp90 and induces the transcriptional upregulation of Hsp70 to afford protection against the encountered cellular stress. As a consequence of both peripheral and central neuropathies, cellular stress occurs and results in the accumulation of unfolded and/or misfolded proteins, which can be counterbalanced by activation of the HSR. Since Hsp90 is the primary regulator of the HSR, modulation of Hsp90 by small molecules represents an attractive therapeutic approach against both peripheral and central neuropathies.

General Structural and Functional Features of Molecular Chaperones

Molecular chaperones are a group of structurally diverse and highly conserved ubiquitous proteins. They play crucial roles in facilitating the correct folding of proteins in vivo by preventing protein aggregation or facilitating the appropriate folding and assembly of proteins. Heat shock proteins form the major class of molecular chaperones that are responsible for protein folding events in the cell. This is achieved by ATP-dependent (folding machines) or ATP-independent mechanisms (holders). Heat shock proteins are induced by a variety of stresses, besides heat shock. The large and varied heat shock protein class is categorised into several subfamilies based on their sizes in kDa namely, small Hsps (HSPB), J domain proteins (Hsp40/DNAJ), Hsp60 (HSPD/E; Chaperonins), Hsp70 (HSPA), Hsp90 (HSPC), and Hsp100. Heat shock proteins are localised to different compartments in the cell to carry out tasks specific to their environment. Most heat shock proteins form large oligomeric structures, and their functions are usually regulated by a variety of cochaperones and cofactors. Heat shock proteins do not function in isolation but are rather part of the chaperone network in the cell. The general structural and functional features of the major heat shock protein families are discussed, including their roles in human disease. Their function is particularly important in disease due to increased stress in the cell. Vector-borne parasites affecting human health encounter stress during transmission between invertebrate vectors and mammalian hosts. Members of the main classes of heat shock proteins are all represented in Plasmodium falciparum, the causative agent of cerebral malaria, and they play specific functions in differentiation, cytoprotection, signal transduction, and virulence.

Single-molecule fluorescence-based approach reveals novel mechanistic insights into human small heat shock protein chaperone function

Small heat shock proteins (sHsps) are a family of ubiquitous intracellular molecular chaperones; some sHsp family members are upregulated under stress conditions and play a vital role in protein homeostasis (proteostasis). It is commonly accepted that these chaperones work by trapping misfolded proteins to prevent their aggregation; however, fundamental questions regarding the molecular mechanism by which sHsps interact with misfolded proteins remain unanswered. The dynamic and polydisperse nature of sHsp oligomers has made studying them challenging using traditional biochemical approaches. Therefore, we have utilized a single-molecule fluorescence-based approach to observe the chaperone action of human alphaB-crystallin (αBc, HSPB5). Using this approach we have, for the first time, determined the stoichiometries of complexes formed between αBc and a model client protein, chloride intracellular channel 1. By examining the dispersity and stoichiometries of these complexes over time, and in response to different concentrations of αBc, we have uncovered unique and important insights into a two-step mechanism by which αBc interacts with misfolded client proteins to prevent their aggregation.

Classifying the superfamily of small heat shock proteins by using g-gap dipeptide compositions

Small heat shock protein (sHSP) is a superfamily of molecular chaperone and is found from archaea to human. Recent researches have demonstrated that sHSPs participate in a series of biological processes and are even closely associated with serious diseases. Since sHSP is a very large superfamily and members from different superfamilies exhibit distinct functions, accurate classification of the subfamily of sHSP will be helpful for unrevealing its functions. In the present work, a support vector machine-based method was proposed to classify the subfamily of sHSPs. In the 10-fold cross validation test, an overall accuracy of 93.25% was obtained for classifying the subfamily of sHSPs. The superiority of the proposed method was also demonstrated by comparing it with the other methods. It is anticipated that the proposed method will become a useful tool for classifying the subfamily of sHSPs.

Proteinaceous Transformers: Structural and Functional Variability of Human sHsps

The proteostasis network allows organisms to support and regulate the life cycle of proteins. Especially regarding stress, molecular chaperones represent the main players within this network. Small heat shock proteins (sHsps) are a diverse family of ATP-independent molecular chaperones acting as the first line of defense in many stress situations. Thereby, the promiscuous interaction of sHsps with substrate proteins results in complexes from which the substrates can be refolded by ATP-dependent chaperones. Particularly in vertebrates, sHsps are linked to a broad variety of diseases and are needed to maintain the refractive index of the eye lens. A striking key characteristic of sHsps is their existence in ensembles of oligomers with varying numbers of subunits. The respective dynamics of these molecules allow the exchange of subunits and the formation of hetero-oligomers. Additionally, these dynamics are closely linked to the chaperone activity of sHsps. In current models a shift in the equilibrium of the sHsp ensemble allows regulation of the chaperone activity, whereby smaller oligomers are commonly the more active species. Different triggers reversibly change the oligomer equilibrium and regulate the activity of sHsps. However, a finite availability of high-resolution structures of sHsps still limits a detailed mechanistic understanding of their dynamics and the correlating recognition of substrate proteins. Here we summarize recent advances in understanding the structural and functional relationships of human sHsps with a focus on the eye-lens αA- and αB-crystallins.

Exercise modulates heat shock protein 27 activity in diabetic cardiomyopathy

AIMS

Heat shock protein 27 regulates homeostasis of skeletal and cardiac muscle proteins in various stressful states including diabetes and exercise. Aerobic exercise can inhibit or ameliorate cardiac structural abnormality and dysfunction in diabetic cardiomyopathy. The aim of this study was to evaluate the role of HSP27 in aerobic exercise improving cardiac diastolic dysfunction in type 2 diabetic rats.

METHODS

Forty male Sprague-Dawley rats were randomly divided into the following groups: control, control + aerobic exercise, diabetic, and diabetic + aerobic exercise. Diabetes was induced by feeding with a high-fat high-sugar diet for 7-weeks followed by a single intraperitoneal injection of streptozotocin (30 mg/kg) in male rats. Moderate aerobic exercise training was performed on a treadmill for 8 weeks after induction of diabetes.

KEY FINDINGS

Aerobic exercise increased left ventricular end-diastolic internal diameter, left ventricular end-diastolic volume, myocardial HSP27 protein expression, HSP27-S82 phosphorylation levels, pHSP27-titin binding and improved cardiac muscle fibre alignment in diabetic rats.

SIGNIFICANCE

Our study indicates that moderate aerobic exercise increases HSP27 activation, improves cardiomyocyte fibre alignment and restores cardiac diastolic function.

Molecular Chaperones in Neurodegeneration

Cellular chaperones are essential players to this protein quality control network that functions to prevent protein misfolding, refold misfolded proteins, or degrade them, thereby maintaining neuronal proteostasis. Moreover, overexpression of cellular chaperones is considered to inhibit protein aggregation and apoptosis in various experimental models of neurodegeneration. Alterations or downregulation of chaperone machinery by age-related decline, molecular crowding, or genetic mutations are regarded as key pathological hallmarks of neurodegenerative disorders like Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and Prion diseases. Therefore, chaperones may serve as potential therapeutic targets in these diseases. This chapter presents a generalized view of misfolding and aggregation of proteins in neurodegeneration and then critically analyses some of the known cellular chaperones and their role in several neurodegenerative disorders.

Heat shock protein beta 3 (HSPB3) is an unfavorable molecular biomarker in colorectal adenocarcinoma

Small heat shock proteins (sHSPs) participate in numerous cellular functions including cell signaling, differentiation, and apoptosis. Deregulation of the physiological expression level of sHSPs has been associated with several malignancies. Heat shock protein beta 3 (HSPB3) is the third member of the sHSP family in human and is mainly expressed in skeletal and smooth muscles. In this study, we investigated the potential prognostic significance of HSPB3 expression in colorectal adenocarcinoma, the most frequent type of colorectal cancer. For this purpose, we isolated total RNA from 188 colorectal adenocarcinoma specimens and 68 paired noncancerous ones. After reverse transcription of 2 μg total RNA, we quantified HSPB3 levels by using an in-house-developed real-time quantitative polymerase chain reaction method, based on the SYBR Green chemistry. Comparison of HSPB3 levels among 68 pairs of colorectal tumors and their adjacent noncancerous mucosae uncovered the downregulation of HSPB3 expression in the majority of malignant colorectal tumors. More importantly, high HSPB3 expression is associated with poor relapse-free survival (RFS) and overall survival (OS) of patients with colorectal adenocarcinoma. Multivariable Cox regression analysis revealed that HSPB3 overexpression could serve as an adverse prognostic biomarker in colorectal adenocarcinoma, independent of tumor location, histological grade, and TNM stage. Patients' stratification according to tumor location, histological grade, and TNM stage revealed that high HSPB3 messenger RNA expression retains its unfavorable prognostic potential regarding OS, in particular groups of patients with substantially different prognosis. In conclusion, high HSPB3 expression is associated with poor RFS and OS of patients with colorectal adenocarcioma, independently of clinicopathological prognosticators.

Dodecameric structure of a small heat shock protein from Mycobacterium marinum M

Small heat shock proteins (sHSPs) are ATP-independent molecular chaperones present ubiquitously in all kingdoms of life. Their low molecular weight subunits associate to form higher order structures. Under conditions of stress, sHSPs prevent aggregation of substrate proteins by undergoing rapid changes in their conformation or stoichiometry. Polydispersity and dynamic nature of these proteins have made structural investigations through crystallography a daunting task. In pathogens like Mycobacteria, sHSPs are immuno-dominant antigens, enabling survival of the pathogen within the host and contributing to disease persistence. We characterized sHSPs from Mycobacterium marinum M and determined the crystal structure of one of these. The protein crystallized in three different conditions as dodecamers, with dimers arranged in a tetrahedral fashion to form a closed cage-like architecture. Interestingly, we found a pentapeptide bound to the dodecamers revealing one of the modes of sHSP-substrate interaction. Further, we have observed that ATP inhibits the chaperoning activity of the protein.

Small heat shock proteins: Simplicity meets complexity

Small heat shock proteins (sHsps) are a ubiquitous and ancient family of ATP-independent molecular chaperones. A key characteristic of sHsps is that they exist in ensembles of iso-energetic oligomeric species differing in size. This property arises from a unique mode of assembly involving several parts of the subunits in a flexible manner. Current evidence suggests that smaller oligomers are more active chaperones. Thus, a shift in the equilibrium of the sHsp ensemble allows regulating the chaperone activity. Different mechanisms have been identified that reversibly change the oligomer equilibrium. The promiscuous interaction with non-native proteins generates complexes that can form aggregate-like structures from which native proteins are restored by ATP-dependent chaperones such as Hsp70 family members. In recent years, this basic paradigm has been expanded, and new roles and new cofactors, as well as variations in structure and regulation of sHsps, have emerged.

Small heat shock proteins and neurodegeneration: recent developments

Members of the small heat shock protein (sHSP) family are molecular chaperones with a critical role in the maintenance of cellular homeostasis under unfavorable conditions. The chaperone properties of sHSPs prevent protein aggregation, and sHSP deregulation underlies the pathology of several diseases, including neurodegenerative disorders. Recent evidence suggests that the clientele of sHSPs is broad, and the mechanisms of sHSP-mediated neuroprotection diverse. Nonetheless, the crosstalk of sHSPs with the neurodegeneration-promoting signaling pathways remains poorly understood. Here, we survey recent findings on the role and regulation of sHSPs in neurodegenerative diseases.

Chaperonomics in leptospirosis

INTRODUCTION

Knowledge of the function of molecular chaperones is required for a better understanding of cellular proteostasis. Nevertheless, such information is currently dispersed as most of previous studies investigated chaperones on a single-angle basis. Recently, a new subdiscipline of chaperonology, namely 'chaperonomics' (defined as 'systematic analysis of chaperone genes, transcripts, proteins, or their interaction networks using omics technologies'), has been emerging to better understand biological, physiological, and pathological roles of chaperones. Areas covered: This review provides broad overviews of bacterial chaperones, heat shock proteins (HSPs), and leptospirosis, and then focuses on recent progress of chaperonomics applied to define roles of HSPs in various pathogenic and saprophytic leptospiral species and serovars. Expert commentary: Comprehensive analysis of leptospiral chaperones/HSPs using a chaperonomics approach holds great promise for better understanding of functional roles of chaperones/HSPs in bacterial survival and disease pathogenesis. Moreover, this new approach may also lead to further development of chaperones/HSPs-based diagnostics and/or vaccine discovery for leptospirosis.

Engineering of a Polydisperse Small Heat-Shock Protein Reveals Conserved Motifs of Oligomer Plasticity

Small heat-shock proteins (sHSPs) are molecular chaperones that bind partially and globally unfolded states of their client proteins. Previously, we discovered that the archaeal Hsp16.5, which forms ordered and symmetric 24-subunit oligomers, can be engineered to transition to an ordered and symmetric 48-subunit oligomer by insertion of a peptide from human HspB1 (Hsp27). Here, we uncovered the existence of an array of oligomeric states (30-38 subunits) that can be populated as a consequence of altering the sequence and length of the inserted peptide. Polydisperse Hsp16.5 oligomers displayed higher affinity to a model client protein consistent with a general mechanism for recognition and binding that involves increased access of the hydrophobic N-terminal region. Our findings, which integrate structural and functional analyses from evolutionarily distant sHSPs, support a model wherein the modular architecture of these proteins encodes motifs of oligomer polydispersity, dissociation, and expansion to achieve functional diversity and regulation.

Extracellular small heat shock proteins: exosomal biogenesis and function

Small heat shock proteins (sHsps) belong to the family of heat shock proteins (Hsps): some are induced in response to multiple stressful events to protect the cells while others are constitutively expressed. Until now, it was believed that Hsps, including sHsps, are present inside the cells and perform intracellular functions. Interestingly, several groups recently reported the extracellular presence of Hsps, and sHsps have also been detected in sera/cerebrospinal fluids in various pathological conditions. Secretion into the extracellular milieu during many pathological conditions suggests additional or novel functions of sHsps in addition to their intracellular properties. Extracellular sHsps are implicated in cell-cell communication, activation of immune cells, and promoting anti-inflammatory and anti-platelet responses. Interestingly, exogenous administration of sHsps showed therapeutic effects in multiple disease models implying that extracellular sHsps are beneficial in pathological conditions. sHsps do not possess signal sequence and, hence, are not exported through the classical Endoplasmic reticulum-Golgi complex (ER-Golgi) secretory pathway. Further, export of sHsps is not inhibited by ER-Golgi secretory pathway inhibitors implying the involvement of a nonclassical secretory pathway in sHsp export. In lieu, lysoendosomal and exosomal pathways have been proposed for the export of sHsps. Heat shock protein 27 (Hsp27), αB-crystallin (αBC), and Hsp20 are shown to be exported by exosomes. Exosomes packaged with sHsps have beneficial effects in in vivo disease models. However, secretion mechanisms and therapeutic use of sHsps have not been elucidated in detail. Therefore, this review aimed at highlighting the current understanding of sHsps (Hsp27, αBC, and Hsp20) in the extracellular medium.

PDE4-Mediated cAMP Signalling

cAMP is the archetypal and ubiquitous second messenger utilised for the fine control of many cardiovascular cell signalling systems. The ability of cAMP to elicit cell surface receptor-specific responses relies on its compartmentalisation by cAMP hydrolysing enzymes known as phosphodiesterases. One family of these enzymes, PDE4, is particularly important in the cardiovascular system, where it has been extensively studied and shown to orchestrate complex, localised signalling that underpins many crucial functions of the heart. In the cardiac myocyte, cAMP activates PKA, which phosphorylates a small subset of mostly sarcoplasmic substrate proteins that drive β-adrenergic enhancement of cardiac function. The phosphorylation of these substrates, many of which are involved in cardiac excitation-contraction coupling, has been shown to be tightly regulated by highly localised pools of individual PDE4 isoforms. The spatial and temporal regulation of cardiac signalling is made possible by the formation of macromolecular “signalosomes”, which often include a cAMP effector, such as PKA, its substrate, PDE4 and an anchoring protein such as an AKAP. Studies described in the present review highlight the importance of this relationship for individual cardiac PKA substrates and we provide an overview of how this signalling paradigm is coordinated to promote efficient adrenergic enhancement of cardiac function. The role of PDE4 also extends to the vascular endothelium, where it regulates vascular permeability and barrier function. In this distinct location, PDE4 interacts with adherens junctions to regulate their stability. These highly specific, non-redundant roles for PDE4 isoforms have far reaching therapeutic potential. PDE inhibitors in the clinic have been plagued with problems due to the active site-directed nature of the compounds which concomitantly attenuate PDE activity in all highly localised “signalosomes”.

Heat Shock Proteins and Autophagy Pathways in Neuroprotection: from Molecular Bases to Pharmacological Interventions

Neurodegenerative diseases (NDDs) such as Alzheimer's disease, Parkinson's disease and Huntington's disease (HD), amyotrophic lateral sclerosis, and prion diseases are all characterized by the accumulation of protein aggregates (amyloids) into inclusions and/or plaques. The ubiquitous presence of amyloids in NDDs suggests the involvement of disturbed protein homeostasis (proteostasis) in the underlying pathomechanisms. This review summarizes specific mechanisms that maintain proteostasis, including molecular chaperons, the ubiquitin-proteasome system (UPS), endoplasmic reticulum associated degradation (ERAD), and different autophagic pathways (chaperon mediated-, micro-, and macro-autophagy). The role of heat shock proteins (Hsps) in cellular quality control and degradation of pathogenic proteins is reviewed. Finally, putative therapeutic strategies for efficient removal of cytotoxic proteins from neurons and design of new therapeutic targets against the progression of NDDs are discussed.

HSPB7 prevents cardiac conduction system defect through maintaining intercalated disc integrity

HSPB7 is a member of the small heat-shock protein (HSPB) family and is expressed in the cardiomyocytes from cardiogenesis onwards. A dramatic increase in HSPB7 is detected in the heart and blood plasma immediately after myocardial infarction. Additionally, several single-nucleotide polymorphisms of HSPB7 have been identified to be associated with heart failure caused by cardiomyopathy in human patients. Although a recent study has shown that HSPB7 is required for maintaining myofiber structure in skeletal muscle, its molecular and physiological functions in the heart remain unclear. In the present study, we generated a cardiac-specific inducible HSPB7 knockout mouse and demonstrated that the loss of HSPB7 in cardiomyocytes results in rapid heart failure and sudden death. The electrocardiogram showed cardiac arrhythmia with abnormal conduction in the HSPB7 mutant mice before death. In HSPB7 CKO cardiomyocytes, no significant defect was detected in the organization of contractile proteins in sarcomeres, but a severe structural disruption was observed in the intercalated discs. The expression of connexin 43, a gap-junction protein located at the intercalated discs, was downregulated in HSPB7 knockout cardiomyocytes. Mislocalization of desmoplakin, and N-cadherin, the intercalated disc proteins, was also observed in the HSPB7 CKO hearts. Furthermore, filamin C, the interaction protein of HSPB7, was upregulated and aggregated in HSPB7 mutant cardiomyocytes. In conclusion, our findings characterize HSPB7 as an intercalated disc protein and suggest it has an essential role in maintaining intercalated disc integrity and conduction function in the adult heart.

The intercalated disc is an indispensable structure that connects neighboring cardiomyocytes. It is also considered to be a single functional unit for cellular electric, mechanical, and signaling communication to maintain cardiomyocyte rigidity and synchrony. Mutation or defect in intercalated disc components usually results in distortions in the structure of intercalated discs and lethal cardiac abnormalities in patients. In this study, we found that the dynamic expression and subcellular location of HSPB7 are highly associated with intercalated disc component protein, N-cadherin, during the assembly and maturation of intercalated discs in cardiomyocytes. To identify the functional role of HSPB7 in the adult heart, we conducted a loss-of-function study of HSPB7 using a gene conditional knockout approach. We found that the loss of HSPB7 quickly results in the disruption of the intercalated disc structure, decreasing the expression of connexin 43 and mislocalization of N-cadherin and desmoplakin, and further inducing arrhythmic sudden death. In conclusion, our mouse model demonstrates that HSPB7 is required to maintain the structure and function of gap-junction complexes and intercalated discs, which has important implications for human heart disease.

The chloroplast-localized small heat shock protein Hsp21 associates with the thylakoid membranes in heat-stressed plants

The small heat shock protein (sHsp) chaperones are crucial for cell survival and can prevent aggregation of client proteins that partially unfold under destabilizing conditions. Most investigations on the chaperone activity of sHsps are based on a limited set of thermosensitive model substrate client proteins since the endogenous targets are often not known. There is a high diversity among sHsps with a single conserved β‐sandwich fold domain defining the family, the α‐crystallin domain, whereas the N‐terminal and C‐terminal regions are highly variable in length and sequence among various sHsps and conserved only within orthologues. The endogenous targets are probably also varying among various sHsps, cellular compartments, cell type and organism. Here we have investigated Hsp21, a non‐metazoan sHsp expressed in the chloroplasts in green plants which experience huge environmental fluctuations not least in temperature. We describe how Hsp21 can also interact with the chloroplast thylakoid membranes, both when isolated thylakoid membranes are incubated with Hsp21 protein and when plants are heat‐stressed. The amount of Hsp21 associated with the thylakoid membranes was precisely determined by quantitative mass spectrometry after metabolic ¹⁵N‐isotope labeling of either recombinantly expressed and purified Hsp21 protein or intact Arabidopsis thaliana plants. We found that Hsp21 is among few proteins that become associated with the thylakoid membranes in heat‐stressed plants, and that approximately two thirds of the pool of chloroplast Hsp21 is affected. We conclude that for a complete picture of the role of sHsps in plant stress resistance also their association with the membranes should be considered.

Specific sequences in the N-terminal domain of human small heat-shock protein HSPB6 dictate preferential hetero-oligomerization with the orthologue HSPB1

Small heat-shock proteins (sHSPs) are a conserved group of molecular chaperones with important roles in cellular proteostasis. Although sHSPs are characterized by their small monomeric weight, they typically assemble into large polydisperse oligomers that vary in both size and shape but are principally composed of dimeric building blocks. These assemblies can include different sHSP orthologues, creating additional complexity that may affect chaperone activity. However, the structural and functional properties of such hetero-oligomers are poorly understood. We became interested in hetero-oligomer formation between human heat-shock protein family B (small) member 1 (HSPB1) and HSPB6, which are both highly expressed in skeletal muscle. When mixed in vitro, these two sHSPs form a polydisperse oligomer array composed solely of heterodimers, suggesting preferential association that is determined at the monomer level. Previously, we have shown that the sHSP N-terminal domains (NTDs), which have a high degree of intrinsic disorder, are essential for the biased formation. Here we employed iterative deletion mapping to elucidate how the NTD of HSPB6 influences its preferential association with HSPB1 and show that this region has multiple roles in this process. First, the highly conserved motif RLFDQXFG is necessary for subunit exchange among oligomers. Second, a site ∼20 residues downstream of this motif determines the size of the resultant hetero-oligomers. Third, a region unique to HSPB6 dictates the preferential formation of heterodimers. In conclusion, the disordered NTD of HSPB6 helps regulate the size and stability of hetero-oligomeric complexes, indicating that terminal sHSP regions define the assembly properties of these proteins.

Protein Quality Control by Molecular Chaperones in Neurodegeneration

Protein homeostasis (proteostasis) requires the timely degradation of misfolded proteins and their aggregates by protein quality control (PQC), of which molecular chaperones are an essential component. Compared with other cell types, PQC in neurons is particularly challenging because they have a unique cellular structure with long extensions. Making it worse, neurons are postmitotic, i.e., cannot dilute toxic substances by division, and, thus, are highly sensitive to misfolded proteins, especially as they age. Failure in PQC is often associated with neurodegenerative diseases, such as Huntington's disease (HD), Alzheimer's disease (AD), Parkinson's disease (PD), and prion disease. In fact, many neurodegenerative diseases are considered to be protein misfolding disorders. To prevent the accumulation of disease-causing aggregates, neurons utilize a repertoire of chaperones that recognize misfolded proteins through exposed hydrophobic surfaces and assist their refolding. If such an effort fails, chaperones can facilitate the degradation of terminally misfolded proteins through either the ubiquitin (Ub)-proteasome system (UPS) or the autophagy-lysosome system (hereafter autophagy). If soluble, the substrates associated with chaperones, such as Hsp70, are ubiquitinated by Ub ligases and degraded through the proteasome complex. Some misfolded proteins carrying the KFERQ motif are recognized by the chaperone Hsc70 and delivered to the lysosomal lumen through a process called, chaperone-mediated autophagy (CMA). Aggregation-prone misfolded proteins that remain unprocessed are directed to macroautophagy in which cargoes are collected by adaptors, such as p62/SQSTM-1/Sequestosome-1, and delivered to the autophagosome for lysosomal degradation. The aggregates that have survived all these refolding/degradative processes can still be directly dissolved, i.e., disaggregated by chaperones. Studies have shown that molecular chaperones alleviate the pathogenic symptoms by neurodegeneration-causing protein aggregates. Chaperone-inducing drugs and anti-aggregation drugs are actively exploited for beneficial effects on symptoms of disease. Here, we discuss how chaperones protect misfolded proteins from aggregation and mediate the degradation of terminally misfolded proteins in collaboration with cellular degradative machinery. The topics also include therapeutic approaches to improve the expression and turnover of molecular chaperones and to develop anti-aggregation drugs.

Vps34 regulates myofibril proteostasis to prevent hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a common heart disease with a prevalence of 1 in 500 in the general population. Several mutations in genes encoding cardiac proteins have been found in HCM patients, but these changes do not predict occurrence or prognosis and the molecular mechanisms underlying HCM remain largely elusive. Here we show that cardiac expression of vacuolar protein sorting 34 (Vps34) is reduced in a subset of HCM patients. In a mouse model, muscle-specific loss of Vps34 led to HCM-like manifestations and sudden death. Vps34-deficient hearts exhibited abnormal histopathologies, including myofibrillar disarray and aggregates containing αB-crystallin (CryAB). These features result from a block in the ESCRT-mediated proteolysis that normally degrades K63-polyubiquitinated CryAB. CryAB deposition was also found in myocardial specimens from a subset of HCM patients whose hearts showed decreased Vps34. Our results identify disruption of the previously unknown Vps34-CryAB axis as a potentially novel etiology of HCM.

Effect of stress on heat shock protein levels, immune response and survival to fungal infection of Mamestra brassicae larvae

Although the utilisation of fungal biological control agents to kill insect pests is desirable, it is known that the outcome of infection may be influenced by a number of criteria, including whether or not the target insect is stressed. In the current work, topical treatment of larvae of the lepidopteran pest, Mamestra brassicae, with conidia of Beauveria bassiana, followed by a heat stress (HS; 37°C for 1h) 48h later, resulted in a similar level of larval survival to that occurring for no heat stress (No-HS), fungus-treated larvae. By contrast, when the HS was applied 24h after fungal treatment, larval survival was significantly increased, indicating that the HS is protecting the larvae from B. bassiana. Similarly, exposure of larvae to a HS provided protection against Metarhizium brunneum (V275) at 48h (but not 24h) after fungal treatment. To elucidate the mechanism(s) that might contribute to HS-induced increases in larval survival against fungal infection, the effects of a HS on key cellular and humoral immune responses and on the level of selected heat shock proteins (HSP) were assessed. When larvae were kept under control (No HS) conditions, there was no significant difference in the haemocyte number per ml of haemolymph over a 24h period. However, exposure of larvae to a HS, significantly increased the haemocyte density immediately after (t=0h) and 4h after HS compared to the No HS controls, whilst it returned to control levels at t=24h. In addition, in vitro assays indicated that haemocytes harvested from larvae immediately after (0h) and 4h (but not 24h) after a HS exhibited higher rates of phagocytosis of FITC-labelled B. bassiana conidia compared to haemocytes harvested from non-HS larvae. Interestingly, the HS did not appear to increase anti-fungal activity in larval plasma. Western blot analysis using antibodies which cross react with Drosophila melanogaster HSP, resulted in a relatively strong signal for HSP 70 and HSP 90 from extracts of 50,000 and 100,000haemocytes, respectively, harvested from No-HS larvae. By contrast, for HSP 60, a lysate derived from 200,000haemocytes resulted in a relatively weak signal. When larvae were exposed to a HS, the level of all three HSP increased compared to the No HS control 4h and 16h after the HS. However, 24h after treatment, any heat stress-mediated increase in HSP levels was minimal and not consistently detected. Similar results were obtained when HSP 90, 70, and 60 levels were assessed in fat body harvested from heat stressed and non-heat stressed larvae. With regard to HSP 27, no signal was obtained even when a lysate from 200,000haemocytes or three times the amount of fat body were processed, suggesting that the anti-HSP 27 antibody utilised does not cross-react with the M. brassicae HSP. The results suggest that a HS-mediated increase in haemocyte density and phagocytic activity, together with an upregulation of HSP 90 and 70, may contribute to increasing the survival of M. brassicae larvae treated with B. bassiana and M. brunneum (V275).

Chaperonopathies: Spotlight on Hereditary Motor Neuropathies

Distal hereditary motor neuropathies (dHMN) are a group of rare hereditary neuromuscular disorders characterized by an atrophy that affects peroneal muscles in the absence of sensory symptoms. To date, 23 genes are thought to be responsible for dHMN, four of which encode chaperones: DNAJB2, which encodes a member of the HSP40/DNAJ co-chaperone family; and HSPB1, HSPB3, and HSPB8, encoding three members of the small heat shock protein family. While around 30 different mutations in HSPB1 have been identified, the remaining three genes are altered in many fewer cases. Indeed, a mutation of HSPB3 has only been described in one case, whereas a few cases have been reported carrying mutations in DNAJB2 and HSPB8, most of them caused by a founder c.352+1G>A mutation in DNAJB2 and by mutations affecting the K141 residue in the HSPB8 chaperone. Hence, their rare occurrence makes it difficult to understand the pathological mechanisms driven by such mutations in this neuropathy. Chaperones can assemble into multi-chaperone complexes that form an integrated chaperone network within the cell. Such complexes fulfill relevant roles in a variety of processes, such as the correct folding of newly synthesized proteins, in which chaperones escort them to precise cellular locations, and as a response to protein misfolding, which includes the degradation of proteins that fail to refold properly. Despite this range of functions, mutations in some of these chaperones lead to diseases with a similar clinical profile, suggesting common pathways. This review provides an overview of the genetics of those dHMNs that share a common disease mechanism and that are caused by mutations in four genes encoding chaperones: DNAJB2, HSPB1, HSPB3, and HSPB8.

The function of small heat-shock proteins and their implication in proteostasis

All organisms rely on a conserved cellular machinery supporting and controlling the life cycle of proteins: the proteostasis network. Within this network, the main players that determine the fate of proteins are molecular chaperones, the ubiquitin–proteasome and the lysosome–autophagy systems. sHsps (small heat-shock proteins) represent one family of molecular chaperones found in all domains of life. They prevent irreversible aggregation of unfolded proteins and maintain proteostasis by stabilizing promiscuously a variety of non-native proteins in an ATP-independent manner. In the cellular chaperone network, sHsps act as the first line of defence and keep their substrates in a folding-competent state until they are refolded by downstream ATP-dependent chaperone systems. Besides this interaction with unfolding substrates upon stress, sHsps show a different mode of binding for specific clients which are also recognized under physiological conditions. In vertebrates, sHsps are especially needed to maintain the refractive index of the eye lens. Additionally, sHsps are linked to a broad variety of diseases such as myopathies and neuropathies. The most striking feature of sHsps is their ability to form dynamic ensembles of higher oligomers. The activity of sHsps is regulated by changes in the composition of the ensembles.

The small heat shock protein αA-crystallin negatively regulates pancreatic tumorigenesis

Our recent study has shown that αA-crystallin appears to act as a tumor suppressor in pancreas. Here, we analyzed expression patterns of αA-crystallin in the pancreatic tumor tissue and the neighbor normal tissue from 74 pancreatic cancer patients and also pancreatic cancer cell lines. Immunocytochemistry revealed that αA-crystallin was highly expressed in the normal tissue from 56 patients, but barely detectable in the pancreatic tumor tissue. Moreover, a low level of αA-crystallin predicts poor prognosis for patients with pancreatic duct adenocarcinoma (PDAC). In the 12 pancreatic cell lines analyzed, except for Capan-1 and Miapaca-2 where the level of αA-crystallin was about 80% and 65% of that in the control cell line, HPNE, the remaining pancreatic cancer cells have much lower αA-crystallin levels. Overexpression of αA-crystallin in MiaPaca-1 cells lacking endogenous αA-crystallin significantly decreased its tumorigenicity ability as shown in the colony formation and wound healing assays. In contrast, knockdown of αA-crystallin in the Capan-1 cells significantly increased its tumorigenicity ability as demonstrated in the above assays. Together, our results further demonstrate that αA-crystallin negatively regulates pancreatic tumorigenesis and appears to be a prognosis biomarker for PDAC.

HspB5/αB-crystallin increases dendritic complexity and protects the dendritic arbor during heat shock in cultured rat hippocampal neurons

The small heat shock protein ΗspΒ5 (αB-crystallin) exhibits generally cytoprotective functions and possesses powerful neuroprotective capacity in the brain. However, little is known about the mode of action of ΗspΒ5 or other members of the HspB family particularly in neurons. To get clues of the neuronal function of HspBs, we overexpressed several HspBs in cultured rat hippocampal neurons and investigated their effect on neuronal morphology and stress resistance. Whereas axon length and synapse density were not affected by any HspB, dendritic complexity was enhanced by HspB5 and, to a lesser extent, by HspB6. Furthermore, we could show that this process was dependent on phosphorylation, since a non-phosphorylatable mutant of HspB5 did not show this effect. Rarefaction of the dendritic arbor is one hallmark of several neurodegenerative diseases. To investigate if HspB5, which is upregulated at pathophysiological conditions, might be able to protect dendrites during such situations, we exposed HspB5 overexpressing neuronal cultures to heat shock. HspB5 prevented heat shock-induced rarefaction of dendrites. In conclusion, we identified regulation of dendritic complexity as a new function of HspB5 in hippocampal neurons.

The expression and function of hsp30-like small heat shock protein genes in amphibians, birds, fish, and reptiles

Small heat shock proteins (sHSPs) are a superfamily of molecular chaperones with important roles in protein homeostasis and other cellular functions. Amphibians, reptiles, fish and birds have a shsp gene called hsp30, which was also referred to as hspb11 or hsp25 in some fish and bird species. Hsp30 genes, which are not found in mammals, are transcribed in response to heat shock or other stresses by means of the heat shock factor that is activated in response to an accumulation of unfolded protein. Amino acid sequence analysis revealed that representative HSP30s from different classes of non-mammalian vertebrates were distinct from other sHSPs including HSPB1/HSP27. Studies with amphibian and fish recombinant HSP30 determined that they were molecular chaperones since they inhibited heat- or chemically-induced aggregation of unfolded protein. During non-mammalian vertebrate development, hsp30 genes were differentially expressed in selected tissues. Also, heat shock-induced stage-specific expression of hsp30 genes in frog embryos was regulated at the level of chromatin structure. In adults and/or tissue culture cells, hsp30 gene expression was induced by heat shock, arsenite, cadmium or proteasomal inhibitors, all of which enhanced the production of unfolded/damaged protein. Finally, immunocytochemical analysis of frog and chicken tissue culture cells revealed that proteotoxic stress-induced HSP30 accumulation co-localized with aggresome-like inclusion bodies. The congregation of damaged protein in aggresomes minimizes the toxic effect of aggregated protein dispersed throughout the cell. The current availability of probes to detect the presence of hsp30 mRNA or encoded protein has resulted in the increased use of hsp30 gene expression as a marker of proteotoxic stress in non-mammalian vertebrates.

Regulation of RANKL-Induced Osteoclastogenesis by 635-nm Light-Emitting Diode Irradiation Via HSP27 in Bone Marrow-Derived Macrophages

OBJECTIVE

This study was designed to investigate the effect of 635-nm irradiation from a light-emitting diode (LED) on osteoclastogenesis in receptor activator of nuclear factor kappa-B (NF-κB) ligand (RANKL)-stimulated mouse bone marrow-derived macrophages (BMMs). We determined whether 635-nm irradiation modulated the RANKL-induced osteoclastic signaling pathway in heat shock protein-27 (HSP27)-silenced cells and analyzed the functional cross talk between these factors in osteoclastic differentiation and activation.

BACKGROUND

HSP27, a member of the small HSP family, regulates oxidative stress. Clinical reports suggest that low-level laser therapy or LED therapy (LEDT) could be an effective alternative treatment for osteolytic bone disease.

METHODS

In control or HSP27-siRNA-treated BMMs, the effects of LED irradiation with 635 nm and 5 mW/cm² on RANKL-induced osteoclastic differentiation and activity were assessed by measuring tartrate-resistant acid phosphatase (TRAP) and resorption pit formation. Quantitative real-time polymerase chain reaction and western blot assays were carried out to assess the mRNA expression of osteoclastogenesis-related genes and phosphorylation of c-Jun-N-terminal kinase (JNK), extracellular signal-regulated kinase 1/2 (ERK1/2), AKT, and p38, respectively. Intracellular reactive oxygen species (ROS) generation was measured using the 2',7'-dichlorodihydrofluorescein diacetate (H₂DCF-DA) detection method.

RESULTS

The 635-nm irradiation treatment significantly increased HSP27 expression and decreased intracellular ROS generation, as well as p38 and AKT phosphorylation, leading to reductions in the expression of c-fos, NFATc1, and DC-STAMP and TRAP activation and osteoclastic bone resorption in RANKL-induced BMMs. However, in HSP27-silenced BMMs, no change was observed.

CONCLUSIONS

Thus, 635-nm irradiation modulates RANKL-induced osteoclastogenesis via HSP27 in BMMs. Thus, HSP27 may play a role in regulating the osteoclastic response to LEDT.

Cloning & sequence identification of Hsp27 gene and expression analysis of the protein on thermal stress in Lucilia cuprina

Hsp27, a highly conserved small molecular weight heat shock protein, is widely known to be developmentally regulated and heat inducible. Its role in thermotolerance is also implicated. This study is a sequel of our earlier studies to understand the molecular organization of heat shock genes/proteins and their role in development and thermal adaptation in a sheep pest, Lucilia cuprina (blowfly), which exhibits unusually high adaptability to a variety of environmental stresses, including heat and chemicals. In this report our aim was to understand the evolutionary relationship of Lucilia hsp27 gene/protein with those of other species and its role in thermal adaptation. We sequence characterized the Lchsp27 gene (coding region) and analyzed its expression in various larval and adult tissues under normal as well as heat shock conditions. The nucleotide sequence analysis of 678 bps long-coding region of Lchsp27 exhibited closest evolutionary proximity with Drosophila (90.09%), which belongs to the same order, Diptera. Heat shock caused significant enhancement in the expression of Lchsp27 gene in all the larval and adult tissues examined, however, in a tissue specific manner. Significantly, in Malpighian tubules, while the heat-induced level of hsp27 transcript (mRNA) appeared increased as compared to control, the protein level remained unaltered and nuclear localized. We infer that Lchsp27 may have significant role in the maintenance of cellular homeostasis, particularly, during summer months, when the fly remains exposed to high heat in its natural habitat.

Expression and localization of the Xenopus laevis small heat shock protein, HSPB6 (HSP20), in A6 kidney epithelial cells

Small heat shock proteins (sHSPs) are molecular chaperones that bind to unfolded protein, inhibit the formation of toxic aggregates and facilitate their refolding and/or degradation. Previously, the only sHSPs that have been studied in detail in the model frog system, Xenopus laevis, were members of the HSP30 family and HSPB1 (HSP27). We now report the analysis of X. laevis HSPB6, an ortholog of mammalian HSPB6. X. laevis HSPB6 cDNA encodes a 168 aa protein that contains an α-crystallin domain, a polar C-terminal extension and some possible phosphorylation sites. X. laevis HSPB6 shares 94% identity with a X. tropicalis HSPB6, 65% with turtle, 59% with humans, 49% with zebrafish and only 50% and 43% with X. laevis HSPB1 and HSP30C, respectively. Phylogenetic analysis revealed that X. laevis HSPB6 grouped more closely with mammalian and reptilian HSPB6s than with fish HSPB6. X. laevis recombinant HSPB6 displayed molecular chaperone properties since it had the ability to inhibit heat-induced aggregation of citrate synthase. Immunoblot analysis determined that HSPB6 was present constitutively in kidney epithelial cells and that heat shock treatment did not upregulate HSPB6 levels. While treatment with the proteasomal inhibitor, MG132, resulted in a 2-fold increase in HSPB6 levels, exposure to cadmium chloride produced a slight increase in HSPB6. These findings were in contrast to HSP70, which was enhanced in response to all three stressors. Finally, immunocytochemical analysis revealed that HSPB6 was present in the cytoplasm in the perinuclear region with some in the nucleus.

Can heat shock protein 32 be used for the early diagnosis of acute mesenteric ischemia?

OBJECTIVE

Acute mesenteric ischemia is a challenging and fatal disease. The aim of this study was to detect the heat shock protein 32 (HSP32) response in intestinal tissue and systemic blood to intestinal ischemia and ischemia/reperfusion to define a tool for the early diagnosis of acute mesenteric ischemia.

MATERIAL AND METHODS

Thirty female Wistar albino rats were equally divided into 3 groups. Group 1 rats underwent simple laparotomy and closure (control). In Group 2 rats, 1-hour intestinal ischemia followed by 5-hour reperfusion was performed, and Group 3 rats were subjected to 6-hour intestinal ischemia. The experiment was repeated with a 24-hour waiting period. At the end of the waiting period, blood was withdrawn from the tail veins of the rats and the rats were sacrificed via cardiac puncture. Re-laparotomy was subsequently performed and intestinal tissue and luminal samples were obtained for biochemical and pathological investigations. The HSP32 levels of intestinal tissues, luminal contents and blood levels were compared among the groups.

RESULTS

At the end of the 24-hour waiting period, the median tissue HSP32 levels were 0.43 (0-6.6) ng/mL for Group 1, 9.51 (2.5-49.9) ng/mL for Group 2 and 43.13 (6.3-121.3) ng/mL for Group 3 (p=0.001). The median blood HSP32 levels were 0.11 (0.1-1.4) ng/mL for Group 1, 0.42 (0.1-0.7) ng/mL for Group 2, and 0.25 (0.1-1.2) ng/mL for Group 3 (p=0.047). The HSP levels in the luminal contents were undetectable.

CONCLUSION

Both ischemia and ischemia/reperfusion significantly raised intestinal tissue HSP32 levels in comparison with the control group. However, this change was not reflected in the circulating blood or luminal contents.