Expression of small heat shock proteins HspB2, HspB8, Hsp20 and cvHsp in different tissues of the perinatal developing pig

Quantitative Proteomics Reveals Manganese Alleviates Heat Stress of Broiler Myocardial Cells via Regulating Nucleic Acid Metabolism

Heat stress threatens severely cardiac function by caused myocardial injury in poultry. Our previous study has showed that manganese (Mn) has a beneficial effect on heat-stress resistance of broiler. Therefore, we tried to confirm the alleviation mechanism through proteomic analysis after heat stress exposure to primary broiler myocardial cells pretreated with Mn. The experiment was divided into four groups: CON group (37 °C, cells without any treatment), HS group (43 °C, cells treatment with heat stress for 4 h), HS+MnCl2 group (cells treated with 20 μM MnCl2 before heat stress), and HS+Mn-AA group (cells treated with 20 μM Mn compound amino acid complex before heat stress). Proteome analysis using DIA identified 300 differentially expressed proteins (DEPs) between CON group and HS group; 93 and 121 DEPs were identified in inorganic manganese treatment group and organic manganese treatment group, respectively; in addition, there were 53 DEPs identified between inorganic and organic manganese group. Gene Ontology (GO) analysis showed that DEPs were mainly involved in binding, catalytic activity, response to stimulus, and metabolic process. DEPs of manganese pretreatment involved in a variety of biological regulatory pathways, and significantly influenced protein processing and repair in endoplasmic reticulum, apoptosis, and DNA replication and repair. These all seem to imply that manganese may help to resist cell damage induced by heat stress by regulating key node proteins. These findings contribute to a better understanding of the effects of manganese on overall protein changes during heat-stress and the possible mechanisms, as well as how to better use manganese to protect heart function in high temperature.

Dynamics and composition of small heat shock protein condensates and aggregates

Small heat shock proteins (sHSPs) are essential ATP-independent chaperones that protect the cellular proteome. These proteins assemble into polydisperse oligomeric structures, the composition of which dramatically affects their chaperone activity. The biomolecular consequences of variations in sHSP ratios, especially inside living cells, remain elusive. Here, we study the consequences of altering the relative expression levels of HspB2 and HspB3 in HEK293T cells. These chaperones are partners in a hetero-oligomeric complex, and genetic mutations that abolish their mutual interaction are associated with myopathic disorders. HspB2 displays three distinct phenotypes when co-expressed with HspB3 at varying ratios. Expression of HspB2 alone leads to formation of liquid nuclear condensates, while shifting the stoichiometry towards HspB3 resulted in the formation of large solid-like aggregates. Only cells co-expressing HspB2 with a limited amount of HspB3 formed fully soluble complexes that were distributed homogeneously throughout the nucleus. Strikingly, both condensates and aggregates were reversible, as shifting the HspB2:HspB3 balance in situ resulted in dissolution of these structures. To uncover the molecular composition of HspB2 condensates and aggregates, we used APEX-mediated proximity labelling. Most proteins interact transiently with the condensates and were neither enriched nor depleted in these cells. In contrast, we found that HspB2:HspB3 aggregates sequestered several disordered proteins and autophagy factors, suggesting that the cell is actively attempting to clear these aggregates. This study presents a striking example of how changes in the relative expression levels of interacting proteins affects their phase behavior. Our approach could be applied to study the role of protein stoichiometry and the influence of client binding on phase behavior in other biomolecular condensates and aggregates.

Transcriptome Profiling of Different Developmental Stages on Longissimus Dorsi to Identify Genes Underlying Intramuscular Fat Content in Wannanhua Pigs

Intramuscular fat (IMF) is a key index to measure the tenderness and flavor of pork. Wannanhua pig, a famous indigenous pig breed in Anhui Province, is renowned for its high lipid deposition and high genetic divergence, making it an ideal model for investigating the lipid position trait mechanisms in pigs. However, the regulatory mechanisms of lipid deposition and development in pigs remain unclear. Furthermore, the temporal differences in gene regulation are based on muscle growth and IMF deposition. The purpose of this study was to study the expression changes of longissimus dorsi (LD) at different growth stages of WH pigs at the molecular level, to screen the candidate genes and signaling pathways related to IMF during development by transcriptome sequencing technology, and to explore the transcriptional regulation mechanism of IMF deposition-related genes at different development stages. In total, 616, 485, and 1487 genes were differentially expressed between LD60 and LD120, LD120 and LD240, and LD60 and LD240, respectively. Numerous differentially expressed genes (DEGs) associated with lipid metabolism and muscle development were identified, and most of them were involved in IMF deposition and were significantly up-regulated in LD120 and LD240 compared to LD60. STEM (Short Time-series Expression Miner) analysis indicated significant variations in the mRNA expression across distinct muscle development stages. The differential expression of 12 selected DEGs was confirmed by RT-qPCR. The results of this study contribute to our understanding of the molecular mechanism of IMF deposition and provide a new way to accelerate the genetic improvement of pork quality.

The chaperone-assisted selective autophagy complex dynamics and dysfunctions

Each protein must be synthesized with the correct amino acid sequence, folded into its native structure, and transported to a relevant subcellular location and protein complex. If any of these steps fail, the cell has the capacity to break down aberrant proteins to maintain protein homeostasis (also called proteostasis). All cells possess a set of well-characterized protein quality control systems to minimize protein misfolding and the damage it might cause. Autophagy, a conserved pathway for the degradation of long-lived proteins, aggregates, and damaged organelles, was initially characterized as a bulk degradation pathway. However, it is now clear that autophagy also contributes to intracellular homeostasis by selectively degrading cargo material. One of the pathways involved in the selective removal of damaged and misfolded proteins is chaperone-assisted selective autophagy (CASA). The CASA complex is composed of three main proteins (HSPA, HSPB8 and BAG3), essential to maintain protein homeostasis in muscle and neuronal cells. A failure in the CASA complex, caused by mutations in the respective coding genes, can lead to (cardio)myopathies and neurodegenerative diseases. Here, we summarize our current understanding of the CASA complex and its dynamics. We also briefly discuss how CASA complex proteins are involved in disease and may represent an interesting therapeutic target.Abbreviation ALP: autophagy lysosomal pathway; ALS: amyotrophic lateral sclerosis; AMOTL1: angiomotin like 1; ARP2/3: actin related protein 2/3; BAG: BAG cochaperone; BAG3: BAG cochaperone 3; CASA: chaperone-assisted selective autophagy; CMA: chaperone-mediated autophagy; DNAJ/HSP40: DnaJ heat shock protein family (Hsp40); DRiPs: defective ribosomal products; EIF2A/eIF2α: eukaryotic translation initiation factor 2A; EIF2AK1/HRI: eukaryotic translation initiation factor 2 alpha kinase 1; GABARAP: GABA type A receptor-associated protein; HDAC6: histone deacetylase 6; HSP: heat shock protein; HSPA/HSP70: heat shock protein family A (Hsp70); HSP90: heat shock protein 90; HSPB8: heat shock protein family B (small) member 8; IPV: isoleucine-proline-valine; ISR: integrated stress response; KEAP1: kelch like ECH associated protein 1; LAMP2A: lysosomal associated membrane protein 2A; LATS1: large tumor suppressor kinase 1; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOC: microtubule organizing center; MTOR: mechanistic target of rapamycin kinase; NFKB/NF-κB: nuclear factor kappa B; NFE2L2: NFE2 like bZIP transcription factor 2; PLCG/PLCγ: phospholipase C gamma; polyQ: polyglutamine; PQC: protein quality control; PxxP: proline-rich; RAN translation: repeat-associated non-AUG translation; SG: stress granule; SOD1: superoxide dismutase 1; SQSTM1/p62: sequestosome 1; STUB1/CHIP: STIP1 homology and U-box containing protein 1; STK: serine/threonine kinase; SYNPO: synaptopodin; TBP: TATA-box binding protein; TARDBP/TDP-43: TAR DNA binding protein; TFEB: transcription factor EB; TPR: tetratricopeptide repeats; TSC1: TSC complex subunit 1; UBA: ubiquitin associated; UPS: ubiquitin-proteasome system; WW: tryptophan-tryptophan; WWTR1: WW domain containing transcription regulator 1; YAP1: Yes1 associated transcriptional regulator.

Role of Heat Shock Proteins in Atrial Fibrillation: From Molecular Mechanisms to Diagnostic and Therapeutic Opportunities

Heat shock proteins (HSPs) are endogenous protective proteins and biomarkers of cell stress response, of which examples are HSP70, HSP60, HSP90, and small HSPs (HSPB). HSPs protect cells and organs, especially the cardiovascular system, against harmful and cytotoxic conditions. More recent attention has focused on the roles of HSPs in the irreversible remodeling of atrial fibrillation (AF), which is the most common arrhythmia in clinical practice and a significant contributor to mortality. In this review, we investigated the relationship between HSPs and atrial remodeling mechanisms in AF. PubMed was searched for studies using the terms "Heat Shock Proteins" and "Atrial Fibrillation" and their relevant abbreviations up to 10 July 2022. The results showed that HSPs have cytoprotective roles in atrial cardiomyocytes during AF by promoting reverse electrical and structural remodeling. Heat shock response (HSR) exhaustion, followed by low levels of HSPs, causes proteostasis derailment in cardiomyocytes, which is the basis of AF. Furthermore, potential implications of HSPs in the management of AF are discussed in detail. HSPs represent reliable biomarkers for predicting and staging AF. HSP inducers may serve as novel therapeutic modalities in postoperative AF. HSP induction, either by geranylgeranylacetone (GGA) or by other compounds presently in development, may therefore be an interesting new approach for upstream therapy for AF, a strategy that aims to prevent AF whilst minimizing the ventricular proarrhythmic risks of traditional anti-arrhythmic agents.

Emerging therapeutic roles of small heat shock protein-derived mini-chaperones and their delivery strategies

The small heat shock protein (sHsp) family is a group of proteins in which some are induced in response to external stimuli, such as environmental and pathological stresses, while others are constitutively expressed. They show chaperone-like activity, protect cells from apoptosis, and maintain cytoskeletal architecture. Short sequences or fragments ranging from approximately 19-20 residues in sHsps were shown to display chaperone activity in vitro. These sequences are termed sHsp-derived mini-peptides/mini-chaperones. These peptides offer an advantage in providing protective and therapeutic effects over full-length proteins owing to their small molecular weight and easy uptake into the cells. Research on sHsp mini-chaperone therapy has recently received attention and advanced tremendously. sHsp mini-chaperones have shown a wide range of therapeutic effects, such as anti-aggregation of proteins, anti-apoptotic, anti-inflammatory, anti-oxidant, senolytic, and anti-platelet activity. The administration of mini-chaperones into the several disease animal models, including experimental autoimmune encephalomyelitis, cataract, age-related macular degeneration, glaucoma, and thrombosis through various routes reduced symptoms or prevented the progression of the disease. However, it was found that the therapeutic potential of sHsp mini-chaperones is limited by their short turnover and enzymatic degradation in circulation. Nonetheless, carrier molecules approach such as nanoparticles, cell penetration peptides, and extracellular vesicles increased their efficacy by enhancing the uptake, retention time, protection from enzymatic degradation, and site-specific delivery without altering their biological activity. In this context, this review highlights the recent advances in the therapeutic potential of sHsp-derived mini-chaperones, their effect in experimental animal models, and approaches for increasing their efficacy.

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.

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.

Cardio-Vascular Heat Shock Protein (cvHsp, HspB7), an Unusual Representative of Small Heat Shock Protein Family

HspB7 is one of ten human small heat shock proteins. This protein is expressed only in insulin-dependent tissues (heart, skeletal muscle, and fat tissue), and expression of HspB7 is regulated by many different factors. Single nucleotide polymorphism is characteristic for the HspB7 gene and this polymorphism correlates with cardio-vascular diseases and obesity. HspB7 has an unusual N-terminal sequence, a conservative α-crystallin domain, and very short C-terminal domain lacking conservative IPV tripeptide involved in a small heat shock proteins oligomer formation. Nevertheless, in the isolated state HspB7 forms both small oligomers (probably dimers) and very large oligomers (aggregates). HspB7 is ineffective in suppression of amorphous aggregation of model proteins induced by heating or reduction of disulfide bonds, however it is very effective in prevention of aggregation of huntingtin fragments enriched with Gln residues. HspB7 can be an effective sensor of electrophilic agents. This protein interacts with the contractile and cytoskeleton proteins (filamin C, titin, and actin) and participates in protection of the contractile apparatus and cytoskeleton from different adverse conditions. HspB7 possesses tumor suppressive activity. Further investigations are required to understand molecular mechanisms of HspB7 participation in numerous biological processes.

Tissue-specific small heat shock protein 20 activation is not associated with traditional autophagy markers in Ossabaw swine with cardiometabolic heart failure

The small heat shock protein 20 (HSPB6) emerges as a potential upstream mediator of autophagy. Although autophagy is linked to several clinical disorders, how HSPB6 and autophagy are regulated in the setting of heart failure (HF) remains unknown. The goal of this study was to assess the activation of the HSPB6 and its association with other well-established autophagy markers in central and peripheral tissues from a preclinical Ossabaw swine model of cardiometabolic HF induced by Western diet and chronic cardiac pressure overload. We hypothesized HSPB6 would be activated in central and peripheral tissues, stimulating autophagy. We found that autophagy in the heart is interrupted at various stages of the process in a chamber-specific manner. Protein levels of HSPB6, Beclin 1, and p62 are increased in the right ventricle, whereas only HSPB6 was increased in the left ventricle. Unlike the heart, samples from the triceps brachii long head showed only an increase in the protein level of p62, highlighting interesting central versus peripheral differences in autophagy regulation. In the right coronary artery, total HSPB6 protein expression was decreased and associated with an increase in LC3B-II/LC3B-I ratio, demonstrating a different mechanism of autophagy dysregulation in the coronary vasculature. Thus, contrary to our hypothesis, activation of HSPB6 was differentially regulated in a tissue-specific manner and observed in parallel with variable states of autophagy markers assessed by protein levels of LC3B, p62, and Beclin 1. Our data provide insight into how the HSPB6/autophagy axis is regulated in a preclinical swine model with potential relevance to heart failure with preserved ejection fraction.NEW & NOTEWORTHY Our study shows that the activation of HSPB6 is tissue specific and associated with variable states of downstream markers of autophagy in a unique preclinical swine model of cardiometabolic HF with potential relevance to HFpEF. These findings suggest that targeted approaches could be an important consideration regarding the development of drugs aimed at this intracellular recycling process.

Structural aspects of the human small heat shock proteins related to their functional activities

Small heat shock proteins function as chaperones by binding unfolding substrate proteins in an ATP-independent manner to keep them in a folding-competent state and to prevent irreversible aggregation. They play crucial roles in diseases that are characterized by protein aggregation, such as neurodegenerative and neuromuscular diseases, but are also involved in cataract, cancer, and congenital disorders. For this reason, these proteins are interesting therapeutic targets for finding molecules that could affect the chaperone activity or compensate specific mutations. This review will give an overview of the available knowledge on the structural complexity of human small heat shock proteins, which may aid in the search for such therapeutic molecules.

Structural and functional properties of proteins interacting with small heat shock proteins

Small heat shock proteins (sHsps) are ubiquitous molecular chaperones found in all domains of life, possessing significant roles in protein quality control in cells and assisting the refolding of non-native proteins. They are efficient chaperones against many in vitro protein substrates. Nevertheless, the in vivo native substrates of sHsps are not known. To better understand the functions of sHsps and the mechanisms by which they enhance heat resistance, sHsp-interacting proteins were identified using affinity purification under heat shock conditions. This paper aims at providing some insights into the characteristics of natural substrate proteins of sHsps. It seems that sHsps of prokaryotes, as well as sHsps of some eukaryotes, can bind to a wide range of substrate proteins with a preference for certain functional classes of proteins. Using Drosophila melanogaster mitochondrial Hsp22 as a model system, we observed that this sHsp interacted with the members of ATP synthase machinery. Mechanistically, Hsp22 interacts with the multi-type substrate proteins under heat shock conditions as well as non-heat shock conditions.

Skin Irritation Testing beyond Tissue Viability: Fucoxanthin Effects on Inflammation, Homeostasis, and Metabolism

UV light catalyzes the ozone formation from air pollutants, like nitrogen oxides. Since ozone reacts with cutaneous sebum lipids to peroxides and, thus, promotes inflammation, tumorigenesis, and aging, even broad-spectrum sunscreens cannot properly protect skin. Meanwhile, xanthophylls, like fucoxanthin, proved their antioxidant and cytoprotective functions, but the safety of their topical application in human cell-based models remains unknown. Aiming for a more detailed insight into the cutaneous fucoxanthin toxicity, we assessed the tissue viability according to OECD test guideline no. 439 as well as changes in inflammation (IL-1α, IL-6, IL-8), homeostasis (EGFR, HSPB1) and metabolism (NAT1). First, we proved the suitability of our 24-well-based reconstructed human skin for irritation testing. Next, we dissolved 0.5% fucoxanthin either in alkyl benzoate or in ethanol and applied both solutions onto the tissue surface. None of the solutions decreased RHS viability below 50%. In contrast, fucoxanthin ameliorated the detrimental effects of ethanol and reduced the gene expression of pro-inflammatory interleukins 6 and 8, while increasing NAT1 gene expression. In conclusion, we developed an organ-on-a-chip compatible RHS, being suitable for skin irritation testing beyond tissue viability assessment. Fucoxanthin proved to be non-irritant in RHS and already showed first skin protective effects following topical application.

Effect of heat-shock protein B7 on oxidative stress in adipocytes from preruminant calves

Dairy cows with ketosis display excessive lipolysis in adipose tissue. Heat-shock protein B7 (HSPB7), a small heat-shock protein, plays important roles in mediating cytoprotective responses to oxidative stress in rodent adipose tissue. Accordingly, it is assumed that HSPB7 may also play important roles in the antioxidant response in adipose tissue of ketotic cows. Therefore, the aim of this study is to investigate (1) the redox state of adipose tissue in ketotic cows and (2) the role and mechanism of HSPB7 on the regulation of oxidative stress in adipocytes from preruminant calves. An in vivo study consisting of 15 healthy and 15 clinically ketotic cows was performed to harvest subcutaneous adipose tissue and blood samples. In addition, adipocytes isolated from calves were treated with different concentrations of H₂O₂ (0, 12.5, 25, 50, 100, or 200 μM) for 2 h, transfected with adenovirus-mediated overexpression of HSPB7 for 48 h, or transfected with small interfering RNA of HSPB7 for 48 h followed by exposure to H₂O₂ (200 μM) for 2 h. Serum concentrations of nonesterified fatty acids and β-hydroxybutyrate were greater in cows with clinical ketosis, whereas serum concentration of glucose was lower. Compared with healthy cows, the malondialdehyde content was greater but the activity of glutathione peroxidase and superoxide dismutase was lower in adipose tissue of clinically ketotic cows. The abundance of HSPB7 and nuclear factor, erythroid 2 like 2 (NFE2L2) was greater in adipose tissue of clinically ketotic cows. In vitro, H₂O₂ treatment induced the overproduction of reactive oxygen species and malondialdehyde, and inhibited the activity of antioxidant enzymes glutathione peroxidase and superoxide dismutase in adipocytes from preruminant calves. The low concentration of H₂O₂ (12.5, 25, and 50 μM) increased the abundance of HSPB7 and NFE2L2, but high concentrations of H₂O₂ (100 or 200 μM) reduced the abundance of HSPB7 and NFE2L2. The overexpression of HSPB7 improved the H₂O₂-induced oxidative stress in adipocytes via increasing the abundance of NFE2L2 and its downstream target genes heme oxygenase-1 (HMOX1) and NADH quinone oxidoreductase 1 (NQO1). Knockdown of HSPB7 markedly inhibited the expression of NFE2L2, HMOX1, and NQO1 and further exacerbated H₂O₂-induced oxidative stress. Overall, these results indicate that activation of the HSPB7-NFE2L2 pathway increases cellular antioxidant capacity, thereby alleviating oxidative stress in bovine adipocytes.

The BAG3-dependent and -independent roles of cardiac small heat shock proteins

Small heat shock proteins (sHSPs) comprise an important protein family that is ubiquitously expressed, is highly conserved among species, and has emerged as a critical regulator of protein folding. While these proteins are functionally important for a variety of tissues, an emerging field of cardiovascular research reveals sHSPs are also extremely important for maintaining normal cardiac function and regulating the cardiac stress response. Notably, numerous mutations in genes encoding sHSPs have been associated with multiple cardiac diseases. sHSPs (HSPB5, HSPB6, and HSPB8) have been described as mediating chaperone functions within the heart by interacting with the cochaperone protein BCL-2-associated anthanogene 3 (BAG3); however, recent reports indicate that sHSPs (HSPB7) can perform other BAG3-independent functions. Here, we summarize the cardiac functions of sHSPs and present the notion that cardiac sHSPs function via BAG3-dependent or -independent pathways.

Exploring the multifaceted roles of heat shock protein B8 (HSPB8) in diseases

HSPB8 is a member of ubiquitous small heat shock protein (sHSP) family, whose expression is induced in response to a wide variety of unfavorable physiological and environmental conditions. Investigation of HSPB8 structure indicated that HSPB8 belongs to the group of so-called intrinsically disordered proteins and possesses a highly flexible structure. Unlike most other sHSPs, HSPB8 tends to form small-molecular-mass oligomers and exhibits substrate-dependent chaperone activity. In cooperation with BAG3, the chaperone activity of HSPB8 was reported to be involved in the delivery of misfolded proteins to the autophagy machinery. Through this way, HSPB8 interferes with pathological processes leading to neurodegenerative diseases. Accordingly, published studies have identified genetic links between mutations of HSPB8 and some kind of neuromuscular diseases, further supporting its important role in neurodegenerative disorders. In addition to their anti-aggregation properties, HSPB8 is indicated to interact with a wide range of client proteins, modulating their maturations and activities, and therefore, regulates a large repertoire of cellular functions, including apoptosis, proliferation, inflammation and etc. As a result, HSPB8 has key roles in cancer biology, autoimmune diseases, cardiac diseases and cerebral vascular diseases.

Heat shock proteins HSPB8 and DNAJC5B have HCV antiviral activity

Hepatitis C is a disease caused by the hepatitis C virus (HCV), and an estimated 3% of the world population is infected with the virus. During replication, HCV interacts with several cellular proteins. Studies have shown that several heat shock proteins (HSPs) have an altered expression profile in the presence of the virus, and some HSPs interact directly with HCV proteins. In the present study, we evaluated the expression levels of heat shock proteins in vitro in the presence and absence of HCV. The differential expression of 84 HSPs and chaperones was observed using a qPCR array, comparing HCV uninfected and infected Huh7.5 cells. To validate qPCR array, the differentially expressed genes were tested by real-time PCR in three different HCV models: subgenomic HCV replicon cells (SGR-JFH-1), JFH-1 infected cells (both genotype 2a) and subgenomic S52 cells (genotype 3). The HSPB8 gene showed increased expression in all three viral models. We silenced HSPB8 expression and observed an increase in viral replication. In contrast, when we increased the expression of HSPB8, a decrease in the HCV replication rate was observed. The same procedure was adopted for DNAJC5B, and HCV showed a similar replication pattern as that observed for HSPB8. These results suggest that HSPB8 may act as an intracellular factor against hepatitis C virus replication and that DNAJC5B has the same function, with more relevant results for genotype 3. We also evaluated the direct interactions between HCV and HSP proteins, and the IP experiments showed that the HCV NS4B protein interacts with HSPB8. These results contribute to a better understanding of the mechanisms involved in HCV replication.

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 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).

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.

Tissue-specific NETs alter genome organization and regulation even in a heterologous system

Different cell types exhibit distinct patterns of 3D genome organization that correlate with changes in gene expression in tissue and differentiation systems. Several tissue-specific nuclear envelope transmembrane proteins (NETs) have been found to influence the spatial positioning of genes and chromosomes that normally occurs during tissue differentiation. Here we study 3 such NETs: NET29, NET39, and NET47, which are expressed preferentially in fat, muscle and liver, respectively. We found that even when exogenously expressed in a heterologous system they can specify particular genome organization patterns and alter gene expression. Each NET affected largely different subsets of genes. Notably, the liver-specific NET47 upregulated many genes in HT1080 fibroblast cells that are normally upregulated in hepatogenesis, showing that tissue-specific NETs can favor expression patterns associated with the tissue where the NET is normally expressed. Similarly, global profiling of peripheral chromatin after exogenous expression of these NETs using lamin B1 DamID revealed that each NET affected the nuclear positioning of distinct sets of genomic regions with a significant tissue-specific component. Thus NET influences on genome organization can contribute to gene expression changes associated with differentiation even in the absence of other factors and overt cellular differentiation changes.

The Chaperone Activity and Substrate Spectrum of Human Small Heat Shock Proteins

Small heat shock proteins (sHsps) are a ubiquitous family of molecular chaperones that suppress the unspecific aggregation of miscellaneous proteins. Multicellular organisms contain a large number of different sHsps, raising questions as to whether they function redundantly or are specialized in terms of substrates and mechanism. To gain insight into this issue, we undertook a comparative analysis of the eight major human sHsps on the aggregation of both model proteins and cytosolic lysates under standardized conditions. We discovered that sHsps, which form large oligomers (HspB1/Hsp27, HspB3, HspB4/αA-crystallin, and HspB5/αB-crystallin) are promiscuous chaperones, whereas the chaperone activity of the other sHsps is more substrate-dependent. However, all human sHsps analyzed except HspB7 suppressed the aggregation of cytosolic proteins of HEK293 cells. We identified ∼1100 heat-sensitive HEK293 proteins, 12% of which could be isolated in complexes with sHsps. Analysis of their biochemical properties revealed that most of the sHsp substrates have a molecular mass from 50 to 100 kDa and a slightly acidic pI (5.4-6.8). The potency of the sHsps to suppress aggregation of model substrates is correlated with their ability to form stable substrate complexes; especially HspB1 and HspB5, but also B3, bind tightly to a variety of proteins, whereas fewer substrates were detected in complex with the other sHsps, although these were also efficient in preventing the aggregation of cytosolic proteins.

Small Heat Shock Proteins and Distal Hereditary Neuropathies

Classification of small heat shock proteins (sHsp) is presented and processes regulated by sHsp are described. Symptoms of hereditary distal neuropathy are described and the genes whose mutations are associated with development of this congenital disease are listed. The literature data and our own results concerning physicochemical properties of HspB1 mutants associated with Charcot-Marie-Tooth disease are analyzed. Mutations of HspB1, associated with hereditary motor neuron disease, can be accompanied by change of the size of HspB1 oligomers, by decreased stability under unfavorable conditions, by changes in the interaction with protein partners, and as a rule by decrease of chaperone-like activity. The largest part of these mutations is accompanied by change of oligomer stability (that can be either increased or decreased) or by change of intermonomer interaction inside an oligomer. Data on point mutation of HspB3 associated with axonal neuropathy are presented. Data concerning point mutations of Lys141 of HspB8 and those associated with hereditary neuropathy and different forms of Charcot-Marie-Tooth disease are analyzed. It is supposed that point mutations of sHsp associated with distal neuropathies lead either to loss of function (for instance, decrease of chaperone-like activity) or to gain of harmful functions (for instance, increase of interaction with certain protein partners).

Pharmacoinformatic and molecular docking studies reveal potential novel antidepressants against neurodegenerative disorders by targeting HSPB8

Charcot-Marie-Tooth (CMT) disease is an inherited peripheral neuromuscular disorder characterized by length-dependent and progressive degeneration of peripheral nerves, leading to muscular weakness. Research has shown that mutated HSPB8 may be responsible for depression, neurodegenerative disorders, and improper functioning of peripheral nerves, resulting in neuromuscular disorders like CMT. In the current work, a hybrid approach of virtual screening and molecular docking studies was followed by homology modeling and pharmacophore identification. Detailed screening analyses were carried out by 2-D similarity search against prescribed antidepressant drugs with physicochemical properties. LigandScout was employed to ascertain novel molecules and pharmacophore properties. In this study, we report three novel compounds that showed maximum binding affinity with HSPB8. Docking analysis elucidated that Met37, Ser57, Ser58, Trp60, Thr63, Thr114, Lys115, Asp116, Gly117, Val152, Val154, Leu186, Asp189, Ser190, Gln191, and Glu192 are critical residues for ligand-receptor interactions. Our analyses suggested paroxetine as a potent compound for targeting HSPB8. Selected compounds have more effective energy scores than the selected drug analogs. Additionally, site-directed mutagenesis could be significant for further analysis of the binding pocket. The novel findings based on an in silico approach may be momentous for potent drug design against depression and CMT.

Heat shock proteins in the retina: Focus on HSP70 and alpha crystallins in ganglion cell survival

Heat shock proteins (HSPs) belong to a superfamily of stress proteins that are critical constituents of a complex defense mechanism that enhances cell survival under adverse environmental conditions. Cell protective roles of HSPs are related to their chaperone functions, antiapoptotic and antinecrotic effects. HSPs' anti-apoptotic and cytoprotective characteristics, their ability to protect cells from a variety of stressful stimuli, and the possibility of their pharmacological induction in cells under pathological stress make these proteins an attractive therapeutic target for various neurodegenerative diseases; these include Alzheimer's, Parkinson's, Huntington's, prion disease, and others. This review discusses the possible roles of HSPs, particularly HSP70 and small HSPs (alpha A and alpha B crystallins) in enhancing the survival of retinal ganglion cells (RGCs) in optic neuropathies such as glaucoma, which is characterized by progressive loss of vision caused by degeneration of RGCs and their axons in the optic nerve. Studies in animal models of RGC degeneration induced by ocular hypertension, optic nerve crush and axotomy show that upregulation of HSP70 expression by hyperthermia, zinc, geranyl-geranyl acetone, 17-AAG (a HSP90 inhibitor), or through transfection of retinal cells with AAV2-HSP70 effectively supports the survival of injured RGCs. RGCs survival was also stimulated by overexpression of alpha A and alpha B crystallins. These findings provide support for translating the HSP70- and alpha crystallin-based cell survival strategy into therapy to protect and rescue injured RGCs from degeneration associated with glaucomatous and other optic neuropathies.

Expression of mRNA in the frontal cortex and hypothalamus in a rat model of acute carbon dioxide poisoning

Acute carbon dioxide (CO2) poisoning causes no specific features that are revealed upon autopsy, and the pathophysiological mechanism of this syndrome is unclear. To address this issue, in the present study, we exposed rats to CO2 concentrations ranging from 10% to 60% and determined the effects on mRNA expression. According to the results of Gene Ontology (GO) and cluster analyses of microarrays data, we selected the following genes for further analysis: alkylglycerone phosphate synthase (Agps), hypocretin (Hcrt), tyrosine hydroxylase (Th), heat shock protein beta 2 (Hspb2), and opioid receptor delta 1 (Oprd1) expressed in the frontal cortex and renin (Ren), pancreatic polypeptide (Ppy), corticotropin releasing hormone receptor 2 (Crhr2), carbonic anhydrase 1 (Car1), and hypocretin receptor 1 (Hcrtr1) expressed in the hypothalamus. We found significant differences between the expression levels of Agps and Hspb2 mRNAs in the frontal cortex and that of Ppy, Crhr2 mRNAs in the hypothalamus in the presence of high concentrations of CO2. Further investigation of these genes may clarify the pathophysiology of acute CO2 poisoning and facilitate the development of novel forensic tests that can diagnose the cause of death.

Hsp90, Hsp60 and sHsp families of heat shock protein genes in channel catfish and their expression after bacterial infections

Heat shock proteins (Hsps) are a suite of highly conserved proteins whose expressions are generally induced by elevated temperature. However, many Hsps play important roles in both innate and adaptive immunity. On the basis of our previous work on Hsp40 and Hsp70 gene families in channel catfish (Ictalurus punctatus), the objective of this study was to characterize Hsp90, Hsp60, Hsp10, and small Hsp genes, and to investigate their expression profiles after bacterial infections. A total of 20 Hsp genes were identified and annotated in the channel catfish genome, including five Hsp90 genes, one Hsp60 gene, one Hsp10 gene, and 13 sHsp genes. Six Hsp genes were differentially expressed after Edwardsiella ictaluri infection, and 12 were differentially expressed after Flavobacterium columnare infection. Although expression of these genes exhibited both temporal and spatial regulation, the induction of Hsp genes was observed soon after bacterial infection, while the suppression of Hsp genes was observed at later time-points, suggesting their distinct roles in immune responses and disease defenses. A pathogen-specific expression pattern of Hsp90 was observed. After F. columnare infection, all Hsp90 genes were found up-regulated except Hsp90ab1, which was not significantly regulated. However, after E. ictaluri infection, only one Hsp90 gene was found significantly down-regulated. Both pathogen-specific and tissue-specific pattern of expression were observed with small Hsps after E. ictaluri and F. columnare bacterial infections. These results suggested that most of Hsp genes may play important roles in immune response and/or disease defense in channel catfish.

Dual functions in response to heat stress and spermatogenesis: characterization of expression profile of small heat shock proteins 9 and 10 in goat testis

Small heat shock proteins 9 and 10 (HSPB9 and HSPB10) are two testis-specific expressed sHsps. The objective of this study was to investigate the mRNA expression profile of HSPB9 and HSPB10 in goat testis among the different seasons, ages, and environmental temperatures. Allocation of the two sHsps was also performed by immunohistochemistry. The results showed that the transcript levels of HSPB9 and HSPB10 were extremely high in the testis (P < 0.01). The relative expression of HSBP9 and HSPB10 in testis showed a tendency to increase with age and then is maintained at the constant level after sexual maturity. HSPB9 and HSPB10 have significantly higher expression in the breeding season  (P < 0.05) and hot season (P < 0.01). Both HSPB9 and HSPB10 were found to be upregulated by high-temperature stress in testis (P < 0.05), and the expressions of Hsp70 and Hsp90 were also increased simultaneously (P < 0.01). Immunohistochemistry analysis localized HSPB9 expressed in spermatogonia, spermatocytes, and round spermatids and HSPB10 expressed in the elongate spermatids. In epididymis, strongly staining signal of HSPB10 was detected in pseudostratified columnar epithelium. In conclusion, the two testis-specific sHsps are closely related to male reproduction and heat tolerance. The results could provide valuable data for the further studies on HSPB9 and HSPB10.

FTSJ2, a heat shock-inducible mitochondrial protein, suppresses cell invasion and migration

Ribosomal RNA large subunit methyltransferase J (RrmJ), an Escherichia coli heat shock protein, is responsible for 2′-O-ribose methylation in 23S rRNA. In mammals, three close homologs of RrmJ have been identified and have been designated as FTSJ1, FTSJ2 and FTSJ3; however, little is known about these genes. In this study, we characterized the mammalian FTSJ2, which was the most related protein to RrmJ in a phylogenetic analysis that had similar amino acid sequence features and tertiary protein structures of RrmJ. FTSJ2 was first identified in this study as a nucleus encoded mitochondrial protein that preserves the heat shock protein character in mammals in which the mRNA expressions was increased in porcine lung tissues and A549 cells after heat shock treatment. In addition, a recent study in non-small cell lung cancer (NSCLC) suggested that the FTSJ2 gene is located in a novel oncogenic locus. However, our results demonstrate that the expression of FTSJ2 mRNA was decreased in the more invasive subline (CL1-5) of the lung adenocarcinoma cells (CL1) compared with the less invasive subline (CL1-0), and overexpression of FTSJ2 resulted in the inhibition of cell invasion and migration in the rhabdomyosarcoma cell (TE671). In conclusion, our findings indicate that mammalian FTSJ2 is a mitochondrial ortholog of E. coli RrmJ and conserves the heat shock protein properties. Moreover, FTSJ2 possesses suppressive effects on the invasion and migration of cancer cells.

Contribution of small heat shock proteins to muscle development and function

Investigations undertaken over the past years have led scientists to introduce the concept of protein quality control (PQC) systems, which are responsible for polypeptide processing. The PQC system monitors proteostasis and involves activity of different chaperones such as small heat shock proteins (sHSPs). These proteins act during normal conditions as housekeeping proteins regulating cellular processes, and during stress conditions. They also mediate the removal of toxic misfolded polypeptides and thereby prevent development of pathogenic states. It is postulated that sHSPs are involved in muscle development. They could act via modulation of myogenesis or by maintenance of the structural integrity of signaling complexes. Moreover, mutations in genes coding for sHSPs lead to pathological states affecting muscular tissue functioning. This review focuses on the question how sHSPs, still relatively poorly understood proteins, contribute to the development and function of three types of muscle tissue: skeletal, cardiac and smooth.

Small heat shock protein expression and functions during development

The expression of small heat shock proteins is tightly regulated during development in multiple organisms. As housekeeping proteins, small heat shock proteins help protect cells from apoptosis, stabilize the cytoskeleton and contribute to proteostasis. Consistently, depletion of one small heat shock protein is usually not detrimental due to a certain level of redundancy between the functions of each small heat shock protein. However, while their stress-induced expression is regulated by heat shock factors, their constitutive expression is under the control of other specific transcription factors, suggesting the existence of very specialized functions. This review focuses on the expression patterns and functions of small heat shock proteins in various organisms during development. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.

Heterooligomeric complexes of human small heat shock proteins

Oligomeric association of human small heat shock proteins HspB1, HspB5, HspB6 and HspB8 was analyzed by means of size-exclusion chromatography, analytical ultracentrifugation and chemical cross-linking. Wild-type HspB1 and Cys mutants of HspB5, HspB6 and HspB8 containing a single Cys residue in position homologous to that of Cys137 of human HspB1 were able to generate heterodimers cross-linked by disulfide bond. Cross-linked heterodimers between HspB1/HspB5, HspB1/HspB6 and HspB5/HspB6 were easily produced upon mixing, whereas formation of any heterodimers with participation of HspB8 was significantly less efficient. The size of heterooligomers formed by HspB1/HspB6 and HspB5/HspB6 was different from the size of the corresponding homooligomers. Disulfide cross-linked homodimers of small heat shock proteins were unable to participate in heterooligomer formation. Thus, monomers can be involved in subunit exchange leading to heterooligomer formation and restriction of flexibility induced by disulfide cross-linking prevents subunit exchange.

Modulation of heat shock protein response in SH-SY5Y by mobile phone microwaves

AIM

To investigate putative biological damage caused by GSM mobile phone frequencies by assessing electromagnetic fields during mobile phone working.

METHODS

Neuron-like cells, obtained by retinoic-acid-induced differentiation of human neuroblastoma SH-SY5Y cells, were exposed for 2 h and 4 h to microwaves at 1800 MHz frequency bands.

RESULTS

Cell stress response was evaluated by MTT assay as well as changes in the heat shock protein expression (Hsp20, Hsp27 and Hsp70) and caspase-3 activity levels, as biomarkers of apoptotic pathway. Under our experimental conditions, neither cell viability nor Hsp27 expression nor caspase-3 activity was significantly changed. Interestingly, a significant decrease in Hsp20 expression was observed at both times of exposure, whereas Hsp70 levels were significantly increased only after 4 h exposure.

CONCLUSION

The modulation of the expression of Hsps in neuronal cells can be an early response to radiofrequency microwaves.

HspB2/myotonic dystrophy protein kinase binding protein (MKBP) as a novel molecular chaperone: structural and functional aspects

The small heat shock protein, human HspB2, also known as Myotonic Dystrophy Kinase Binding Protein (MKBP), specifically associates with and activates Myotonic Dystrophy Protein Kinase (DMPK), a serine/threonine protein kinase that plays an important role in maintaining muscle structure and function. The structure and function of HspB2 are not well understood. We have cloned and expressed the protein in E.coli and purified it to homogeneity. Far-UV circular dichroic spectrum of the recombinant HspB2 shows a β-sheet structure. Fluorescence spectroscopic studies show that the sole tryptophan residue at the 130^th position is almost completely solvent-exposed. Bis-ANS binding shows that though HspB2 exhibits accessible hydrophobic surfaces, it is significantly less than that exhibited by another well characterized small HSP, αB-crystallin. Sedimentation velocity measurements show that the protein exhibits concentration-dependent oligomerization. Fluorescence resonance energy transfer study shows that HspB2 oligomers exchange subunits. Interestingly, HspB2 exhibits target protein-dependent chaperone-like activity: it exhibits significant chaperone-like activity towards dithiothreitol (DTT)-induced aggregation of insulin and heat-induced aggregation of alcohol dehydrogenase, but only partially prevents the heat-induced aggregation of citrate synthase, co-precipitating with the target protein. It also significantly prevents the ordered amyloid fibril formation of α-synuclein. Thus, our study, for the first time, provides biophysical characterization on the structural aspects of HspB2, and shows that it exhibits target protein-dependent chaperone-like activity.

Developmental expression pattern of Hspb8 mRNA in the mouse brain: analysis through online databases

Hspb8 is a member of the Hspb family of chaperone-like proteins. It is involved in several neural disorders such as Alzheimer's disease, amyotrophic lateral sclerosis, hereditary distal motor neuropathy, and Charcot-Marie-Tooth's disease. In this work, we aimed to characterize its expression pattern in the mouse brain, by using the information available at online databases of high-throughput in situ hybridization. Therefore, we downloaded and analyzed the image series from these databases showing Hspb8 mRNA expression from embryonic to adult and aging stages. In early gestational embryos, Hspb8 was expressed in the hippocampal anlagen and in the ventricular layer of rhombomere 4. At perinatal stages, there appeared transitory expression in the dentate gyrus and the cerebellar cortex. From perinatal to aging stages, the neurons of the mesencephalic trigeminal nucleus and cranial motor nuclei displayed stable and strong Hspb8 expression. Additionally, along these stages there was moderate and relatively homogenous expression in the anterodorsal thalamic, lateral mammillary, arcuate hypothalamic and medial habenular nuclei, and in the locus coeruleus. In its turn, the basal ganglia, cerebellar inner granular layer and diverse sensory and reticular formation nuclei of the hindbrain contained scattered cells with strong expression. In conclusion, Hspb8 mRNA is constitutively expressed in specific brain structures across ontogeny, so that eventually they could be affected by the malfunction or deregulation of this molecule.

Large potentials of small heat shock proteins

Modern classification of the family of human small heat shock proteins (the so-called HSPB) is presented, and the structure and properties of three members of this family are analyzed in detail. Ubiquitously expressed HSPB1 (HSP27) is involved in the control of protein folding and, when mutated, plays a significant role in the development of certain neurodegenerative disorders. HSPB1 directly or indirectly participates in the regulation of apoptosis, protects the cell against oxidative stress, and is involved in the regulation of the cytoskeleton. HSPB6 (HSP20) also possesses chaperone-like activity, is involved in regulation of smooth muscle contraction, has pronounced cardioprotective activity, and seems to participate in insulin-dependent regulation of muscle metabolism. HSPB8 (HSP22) prevents accumulation of aggregated proteins in the cell and participates in the regulation of proteolysis of unfolded proteins. HSPB8 also seems to be directly or indirectly involved in regulation of apoptosis and carcinogenesis, contributes to cardiac cell hypertrophy and survival and, when mutated, might be involved in development of neurodegenerative diseases. All small heat shock proteins play important "housekeeping" roles and regulate many vital processes; therefore, they are considered as attractive therapeutic targets.

The Gln32Lys polymorphism in HSP22 of Zhikong scallop Chlamys farreri is associated with heat tolerance

Background

Heat shock protein 22 is a member of small heat shock proteins with molecular chaperone activity. Though their multiple functions have been well characterized, there is no report about the association between the polymorphisms of HSP22 and heat tolerance.

Methodology

Three single nucleotide polymorphisms were identified in HSP22 from scallop Chlamys farreri (CfHSP22), and the +94 C-A locus was found to be nonsynonymous. Three genotypes at locus +94, A/A, A/C and C/C, were revealed by using Bi-PASA PCR analysis, and their frequencies were 19.5%, 27.6% and 52.9% in the heat resistant stock, while 9.3%, 17.4% and 73.3% in the heat susceptible stock, respectively. The frequency differences of the three genotypes were significant (P<0.05) between the two stocks. After incubating at 30°C for 84 h, the cumulative mortality of scallops with +94 C/C genotype and +94 A/C genotypes was 95% and 90%, respectively, which was significantly higher (P<0.01) than that of scallops with +94 A/A genotype (70%). The molecular chaperone activity of two His-tagged fusion proteins, rCfHSP22Q with +94 C/C genotype and rCfHSP22K with +94 A/A genotype were analyzed by testing the ability of protecting citrate synthase (CS) against thermal inactivation in vitro. After incubated with rCfHSP22Q or rCfHSP22K at 38°C for 1 h, the activity of CS lost 50% and 45%, and then recovered to 89% and 95% of the original activity following 1 h restoration at 22°C, respectively, indicating that the mutation from Gln to Lys at this site might have an impact on molecular chaperone activities of CfHSP22.

Conclusions

These results implied that the polymorphism at locus +94 of CfHSP22 was associated with heat tolerance of scallop, and the +94 A/A genotype could be a potential marker available in future selection of Zhikong scallop with heat tolerance.

Small heat shock proteins induce a cerebral inflammatory reaction

More than 80% of Alzheimer's disease (AD) patients have some degree of cerebral amyloid angiopathy (CAA). In addition to arteries and veins, capillaries can also be affected. Capillary CAA (capCAA), rather than CAA in larger vessels, is associated with flame-like amyloid-beta (Aβ) deposits that may extend beyond the vessel wall and radiate into the neuropil, a phenomenon also known as "dyshoric angiopathy." Aβ deposits in AD, parenchymal as well as (cap)CAA and dyshoric angiopathy, are associated with a local inflammatory reaction, including activation of microglial cells and astrocytes that, among others, produce cytokines and reactive oxygen species. This neuroinflammatory reaction may account for at least part of the cognitive decline. In previous studies we observed that small heat shock proteins (sHsps) are associated with Aβ deposits in AD. In this study the molecular chaperones Hsp20, HspB8 and HspB2B3 were found to colocalize with CAA and capCAA in AD brains. In addition, Hsp20, HspB8 and HspB2B3 colocalized with intercellular adhesion molecule 1 (ICAM-1) in capCAA-associated dyshoric angiopathy. Furthermore, we demonstrated that Hsp20, HspB8 and HspB2B3 induced production of interleukin 8, soluble ICAM-1 and monocyte chemoattractant protein 1 by human leptomeningeal smooth muscle cells and human brain astrocytes in vitro and that Hsp27 inhibited production of transforming growth factor beta 1 and CD40 ligand. Our results suggest a central role for sHsps in the neuroinflammatory reaction in AD and CAA and thus in contributing to cognitive decline.

Ethanol-induced small heat shock protein genes in the differentiation of mouse embryonic neural stem cells

Neural stem cells (NSCs) of the neuroepithelium differentiate into one of three central nervous system (CNS) cell lineages: neurons, astrocytes, or oligodendrocytes. In this study, the differentiation potential of NSCs from the forebrain of embryonic day 15 (E15) mouse embryos was analyzed using immunocytochemistry. NSCs were differentiated early in the presence or absence of ethanol (50 mM), and gene expression patterns among NSCs, differentiated cells and ethanol-treated differentiated cells were assessed by microarray and real-time PCR analysis. Genes that were up-regulated in differentiated cells both in the presence and in the absence of ethanol when compared to NSCs were related to the Wnt signaling pathway, including Ctnna1, Wnt5a, Wnt5b, Wnt7a, Fzd3, and Fzd2; genes related to cell adhesion, including Cadm1, Ncam1, and Ncam2; and genes encoding small heat shock proteins, including HspB2, HspB7, and HspB8. In particular, the expression levels of HspB2 and HspB7 were elevated in ethanol-treated differentiated cells compared to non-treated differentiated cells. The gene expression patterns of various heat shock transcription factors (HSFs), proteins that regulate the transcription of heat shock genes, were also analyzed. The expression levels of HSF2 and HSF5 increased in differentiated cells in the presence and absence of ethanol when compared to NSCs. Of these two genes, HSF5 demonstrated an enhanced up-regulation, particularly in ethanol-treated differentiated cells compared to cells that were differentiated in the absence of ethanol. These results imply that HspB2 and HspB7, which are small heat shock proteins with tissue-restricted expression profiles, might be up-regulated by ethanol during the short-term differentiation of NSCs.

Abnormal interaction of motor neuropathy-associated mutant HspB8 (Hsp22) forms with the RNA helicase Ddx20 (gemin3)

A number of missense mutations in the two related small heat shock proteins HspB8 (Hsp22) and HspB1 (Hsp27) have been associated with the inherited motor neuron diseases (MND) distal hereditary motor neuropathy and Charcot-Marie-Tooth disease. HspB8 and HspB1 interact with each other, suggesting that these two etiologic factors may act through a common biochemical mechanism. However, their role in neuron biology and in MND is not understood. In a yeast two-hybrid screen, we identified the DEAD box protein Ddx20 (gemin3, DP103) as interacting partner of HspB8. Using co-immunoprecipitation, chemical cross-linking, and in vivo quantitative fluorescence resonance energy transfer, we confirmed this interaction. We also show that the two disease-associated mutant HspB8 forms have abnormally increased binding to Ddx20. Ddx20 itself binds to the survival-of-motor-neurons protein (SMN protein), and mutations in the SMN1 gene cause spinal muscular atrophy, another MND and one of the most prevalent genetic causes of infant mortality. Thus, these protein interaction data have linked the three etiologic factors HspB8, HspB1, and SMN protein, and mutations in any of their genes cause the various forms of MND. Ddx20 and SMN protein are involved in spliceosome assembly and pre-mRNA processing. RNase treatment affected the interaction of the mutant HspB8 with Ddx20 suggesting RNA involvement in this interaction and a potential role of HspB8 in ribonucleoprotein processing.

Developmental expression patterns of the zebrafish small heat shock proteins

Small heat shock proteins (sHSPs), or alpha-crystallins, are low-molecular weight proteins found in every kingdom and nearly every species examined to date. Many, if not all, sHSPs act as molecular chaperones. Several also have functions independent of their chaperone activity, and at least a few are expressed in specific spatiotemporal patterns during embryonic and/or juvenile stages, suggesting specific roles during development. To date, however, no one has systematically characterized the expression patterns of all of the sHSPs during development in any organism. We have characterized the normal heat shock-induced expression patterns of all 13 zebrafish sHSPs during development. Seven of the sHSPs are expressed in a tissue-specific manner during development, and five are upregulated by heat shock. The results of these studies provide a foundation for analysis of sHSP function during normal development and their roles in protecting cells from the effects environmental stressors.

Structure, properties, and functions of the human small heat-shock protein HSP22 (HspB8, H11, E2IG1): A critical review

The recently described human HSP22 belongs to the superfamily of small heat-shock proteins containing a conservative alpha-crystallin domain. HSP22 seems to be involved in regulation of cell proliferation, cardiac hypertrophy, apoptosis, and carcinogenesis, and expression of point mutants of HSP22 correlates with development of different neuromuscular diseases. Therefore, an investigation of the structure and properties of HSP22 is desirable for understanding its multiple functions. HSP22 seems to belong to the group of so-called intrinsically disordered proteins and possesses a highly flexible structure. HSP22 tends to form small-molecular-mass oligomers and interacts with biological membranes and many different proteins, among them glycolytic enzymes and different protein kinases. HSP22 possesses chaperonelike activity and prevents aggregation of denatured proteins both in vitro and in vivo. Depending on the cell type and its expression, HSP22 might have either pro- or anti-apoptotic effects. Chaperonelike activity seems to be important for antiapoptotic effects, whereas interaction with and regulation of certain protein kinases might be important for the proapoptotic effects of HSP22. Expression of K141N or K141E mutants of HSP22 correlates with development of distal hereditary motor neuropathy and/or Charcot-Marie-Tooth disease. These mutations destabilize the structure of HSP22, affect its interaction with other small heat-shock proteins, and decrease its chaperonelike activity. HSP22 decreases or prevents aggregation of Huntingtin fragments and amyloid-beta peptide 1-40 of the Dutch type. Thus, HSP22 seems to play an important role in the nervous system, and further investigations are needed to understand the molecular mechanisms of its functioning.

Insights into function and regulation of small heat shock protein 25 (HSPB1) in a mouse model with targeted gene disruption

The mammalian small heat shock protein (sHSPs) family is comprised of 10 members and includes HSPB1, which is proposed to play an essential role in cellular physiology, acting as a molecular chaperone to regulate diverse cellular processes. Whilst differential roles for sHSPs are suggested for specific tissues, the relative contribution of individual sHSP family members in cellular and organ physiology remains unclear. To address the function of HSPB1 in vivo and determine its tissue-specific expression during development and in the adult, we generated knock-in mice where the coding sequence of hspb1 is replaced by a lacZ reporter gene. Hspb1 expression marks myogenic differentiation with specific expression first confined to developing cardiac muscles and the vascular system, and later in skeletal muscles with specific expression at advanced stages of myoblast differentiation. In the adult, hspb1 expression was observed in other tissues, such as stratified squamous epithelium of skin, oronasal cavity, tongue, esophagus, and uterine cervix but its expression was most prominent in the musculature. Interestingly, in cardiac muscle hsbp1 expression was down-regulated during the neonatal period and maintained to a relatively low steady-level throughout adulthood. Despite this widespread expression, hspb1-/- mice were viable and fertile with no apparent morphological abnormalities in tissues under physiological conditions. However, at the cellular level and under stress conditions (heat challenge), HSPB1 act synergistically with the stress-induced HSPA1 (HSP70) in thermotolerance development, protecting cells from apoptosis. Our data thus indicate a nonessential role for HSPB1 in embryonic development and for maintenance of tissues under physiological conditions, but also shows that it plays an important role by acting synergistically with other HSPs during stress conditions to exert cytoprotection and anti-apoptotic effects.

Structure, function, property, and role in neurologic diseases and other diseases of the sHsp22

Small heat shock proteins are members of the heat shock proteins family. They share important identical features: 1) they form the conserved structure 'alpha-crystallin domain' with about 80-100 residues in the C-terminal part of the proteins; 2) they have monomeric molecular masses ranging in 12-43 kDa; 3) they associate into large oligomers consisting in many cases of subunits; 4) they increase expression under stress conditions; 5) they exhibit a highly dynamic structure; and 6) they play a chaperone-like role. Hsp22 (also known as HspB8, H11, and E2IG1) retains the structural motif of the 'alpha-crystallin' family of Hsps and is a member of the superfamily of sHsps. Hsp22 displays chaperone activity, autokinase activity, and trigger or block apoptosis activity. It differs from canonical family members existing as a monomer. A decrease in the HspB8 activity may contribute to the development of some neurologic diseases and others.