Small Heat Shock Protein Family Research Articles

The major inducible small heat shock protein HSP20-3 in the tardigrade Ramazzottius varieornatus forms filament-like structures and is an active chaperone.

The tardigrade Ramazzottius varieornatus has remarkable resilience to a range of environmental stresses. In this study, we have characterised two members of the small heat shock protein (sHSP) family in R. varieornatus, HSP20-3 and HSP20-6. These are the most highly upregulated sHSPs in response to a 24h heat shock at 35 0C of adult tardigrades with HSP20-3 being one of the most highly upregulatedgene in the whole transcriptome. Both R. varieornatus sHSPs and the human sHSP, CRYAB (HSPB5), were produced recombinantly for comparative structure-function studies. HSP20-3 exhibited a superior chaperone activity than human CRYAB in a heat-induced protein aggregation assay. Both tardigrade sHSPs also formed larger oligomers than CRYAB as assessed by size exclusion chromatography and transmission electron microscopy of negatively stained samples. Whilst both HSP20-3 and HSP20-6 formed particles that were variable in size and larger than the particles formed by CRYAB, only HSP20-3 formed filament-like structures. The particles and filament-like structures formed by HSP20-3 appear inter-related as the filament-like structures often had particles located at their ends. Sequence analyses identified two unique features; an insertion in the middle region of the N-terminal domain (NTD) and preceding the critical-sequence identified in CRYAB, as well as a repeated QNTN-motif located in the C-terminal domain of HSP20-3. The NTD insertion is expected to affect protein-protein interactions and subunit oligomerisation. Removal of the repeated QNTN-motif abolished HSP20-3 chaperone activity and also affected the assembly of the filament-like structures. We discuss the potential contribution of HSP20-3 to protein condensate formation.

Phosphorylated Hsp27 promotes adriamycin resistance in breast cancer cells through regulating dual phosphorylation of c-Myc

Chemotherapy resistance of breast cancer cells is one of the major factors affecting patient survival rate. Heat shock protein 27 (Hsp27) is a member of the small heat shock protein family that has been reported to be associated with chemotherapy resistance in tumor cells, but the exact mechanism is not fully understood. Here, we explored the regulation of Hsp27 in adriamycin-resistant pathological conditions of breast cancer in vitro and in vivo. We found that overexpression of Hsp27 in MCF-7 breast cancer cells reversed DNA damage induced by adriamycin, and thereby reduced subsequent cell apoptosis. Non-phosphorylated Hsp27 accelerated ubiquitin-mediated degradation of c-Myc under normal physiological conditions. After stimulation with adriamycin, Hsp27 was phosphorylated and translocated from the cytoplasm into the nucleus, where phosphorylated Hsp27 upregulated c-Myc and Nijmegen breakage syndrome 1 (NBS1) protein levels thus leading to ATM activation. We further showed that phosphorylated Hsp27 promoted c-Myc nuclear import and stabilization by regulating T58/S62 phosphorylation of c-Myc through a protein phosphatase 2A (PP2A)-dependent mechanism. Collectively, the data presented in this study demonstrate that Hsp27, in its phosphorylation state, plays a critical role in adriamycin-resistant pathological conditions of breast cancer cells.

Association between HSP-Specific T-Cell Counts and Retinal Nerve Fiber Layer Thickness in Patients with Primary Open-Angle Glaucoma.

Previous laboratory reports implicate heat shock protein (HSP)-specific T-cell responses in glaucoma pathogenesis; here, we aimed to provide direct clinical evidence by correlating systemic HSP-specific T-cell levels with glaucoma severity in patients with primary open-angle glaucoma (POAG). Cross-sectional case-control study. Thirty-two adult patients with POAG and 38 controls underwent blood draw and optic nerve imaging. Peripheral blood monocytes (PBMC) were stimulated in culture with HSP27, α-crystallin, a member of the small HSP family, or HSP60. Both interferon-γ (IFN-γ)+ CD4+ T helper type 1 cells (Th1) and transforming growth factor-β1 (TGF-β1)+ CD4+ regulatory T cells (Treg) were quantified by flow cytometry and presented as a percentage of total PBMC counts. Relevant cytokines were measured using enzyme-linked immunosorbent assays. Retinal nerve fiber layer thickness (RNFLT) was measured with OCT. Pearson's correlation (r) was used to assess correlations. Correlations of HSP-specific T-cell counts, and serum levels of corresponding cytokine levels with RNFLT. Patients with POAG (visual field mean deviation, -4.7 ± 4.0 dB) and controls were similar in age, gender, and body mass index. Moreover, 46.9% of POAG and 60.0% of control subjects had prior cataract surgery (P= 0.48). Although no significant difference in total nonstimulated CD4+ Th1 or Treg cells was detected, patients with POAG exhibited significantly higher frequencies of Th1 cells specific for HSP27, α-crystallin, or HSP60 than controls (7.3 ± 7.9% vs. 2.6 ± 2.0%, P= 0.004; 5.8 ± 2.7% vs. 1.8 ± 1.3%, P < 0.001; 13.2 ± 13.3 vs. 4.3 ± 5.2, P= 0.01; respectively), but similar Treg specific for the same HSPs compared with controls (P ≥ 0.10 for all). Concordantly, the serum levels of IFN-γ were higher in POAG than in controls (36.2 ± 12.1 pg/ml vs. 10.0 ± 4.3 pg/ml; P < 0.001), but TGF-β1 levels did not differ. Average RNFLT of both eyes negatively correlated with HSP27- and α-crystallin-specific Th1 cell counts, and IFN-γ levels in all subjects after adjusting for age (partial correlation coefficient r= -0.31, P= 0.03; r= -0.52, p= 0.002; r= -0.72, P < 0.001, respectively). Higher levels of HSP-specific Th1 cells are associated with thinner RNFLT in patients with POAG and control subjects. The significant inverse relationship between systemic HSP-specific Th1 cell count and RNFLT supports the role of these T cells in glaucomatous neurodegeneration. Proprietary or commercial disclosure may be found after the references.

Regulation of rat HspB5/alphaB-Crystallin by microRNAs miR-101a-3p, miR-140-5p, miR-330-5p, and miR-376b-3p

HspB5/alphaB-crystallin is an ubiquitously expressed member of the small heat shock protein family which help cells to survive cellular stress conditions and are also implicated in neurodegenerative diseases. MicroRNAs are small non-coding RNAs fine-tuning protein expression mainly by inhibiting the translation of target genes. Our earlier finding of an increase in HspB5/alphaB-crystallin protein amount after heat shock in rat hippocampal neurons without a concomitant increase of mRNA prompted us to look for microRNAs as a posttranscriptional regulatory mechanism. Microarray miRNA expression data of rat hippocampal neurons under control and stress conditions in combination with literature search, miRNA binding site prediction and conservation of target sites yielded nine candidate microRNAs. Of these candidates, five (miR-101a-3p, miR-129-2-3p, miR-330-5p, miR-376b-3p, and miR-491-5p) were able to convey a downregulation by binding to the HspB5 3′- or 5′-UTR in a luciferase reporter gene assay while one (miR-140-5p) led to an upregulation. Overexpression of these six microRNAs in C6 glioma cells showed that three of them (miR-101a-3p, miR-140-5p, and miR-376b-3p) regulated endogenous HspB5 protein amount significantly in the same direction as in the reporter gene assay. In addition, overexpression of miR-330-5p and miR-491-5p in C6 cells resulted in regulation of HspB5 in the opposite direction as expected from the luciferase assay. Analysis of miRNA expression in rat hippocampal neurons after cellular stress by qPCR showed that miR-491-5p was not expressed in these cells. In total, we therefore identified four microRNAs, namely miR-101a-3p, miR-140-5p, miR-330-5p, and miR-376b-3p, which can regulate rat HspB5 directly or indirectly.

Characterization of Hsp17, a Novel Small Heat Shock Protein, in Sphingomonas melonis TY under Heat Stress.

Bacteria are constantly exposed to a variety of environmental stresses. Temperature is considered one of the most important environmental factors affecting microbial growth and survival. As ubiquitous environmental microorganisms, Sphingomonas species play essential roles in the biodegradation of organic contaminants, plant protection, and environmental remediation. Understanding the mechanism by which they respond to heat shock will help further improve cell resistance by applying synthetic biological strategies. Here, we assessed the transcriptomic and proteomic responses of Sphingomonas melonis TY to heat shock and found that stressful conditions caused significant changes in functional genes related to protein synthesis at the transcriptional level. The most notable changes observed were increases in the transcription (1,857-fold) and protein expression (11-fold) of Hsp17, which belongs to the small heat shock protein family, and the function of Hsp17 in heat stress was further investigated in this study. We found that the deletion of hsp17 reduced the capacity of the cells to tolerate high temperatures, whereas the overexpression of hsp17 significantly enhanced the ability of the cells to withstand high temperatures. Moreover, the heterologous expression of hsp17 in Escherichia coli DH5α conferred to the bacterium the ability to resist heat stress. Interestingly, its cells were elongated and formed connected cells following the increase in temperature, while hsp17 overexpression restored their normal morphology under high temperature. In general, these results indicate that the novel small heat shock protein Hsp17 greatly contributes to maintaining cell viability and morphology under stress conditions. IMPORTANCE Temperature is generally considered the most important factor affecting metabolic functions and the survival of microbes. As molecular chaperones, small heat shock proteins can prevent damaged protein aggregation during abiotic stress, especially heat stress. Sphingomonas species are widely distributed in nature, and they can frequently be found in various extreme environments. However, the role of small heat shock proteins in Sphingomonas under high-temperature stress has not been elucidated. This study greatly enhances our understanding of a novel identified protein, Hsp17, in S. melonis TY in terms of its ability to resist heat stress and maintain cell morphology under high temperature, leading to a broader understanding of how microbes adapt to environmental extremes. Furthermore, our study will provide potential heat resistance elements for further enhancing cellular resistance as well as the synthetic biological applications of Sphingomonas.

In silico Characterization of Heat Shock Protein HSP27 in Mammals

Dairy animals have a significant role in every country’s agricultural economy. Livestock is the major sub-sector of the agricultural industry and the value of dairy products is increasing globally. Under pathological circumstances heat shock proteins (HSPs) promote protein repair, folding, refolding of misfolded peptides, and possible breakdown of irreparable proteins. Heat shock protein 27 (HSP27) is a member of the small heat shock protein family (sHSPs) also called HSPB1. HSP27 is crucial in the regulation and progression of different types of tumors and also acts as an oncotherapeutic target in humans and other mammals especially sheep. By using computational tools, a detailed in silico investigation of HSP27 sequences from humans and sheep has been examined with respect to their structural, functional, expression and phylogenetic properties. An extensive study has been made to compare the human protein with that of other mammals using computational tools. However, the sequences of HSP27 in humans and sheep are closely linked with each other. Although the sequences of HSP27 vary, their structural characteristics and functional properties remain the same. In this study, hydrophilic proteins with an average molecular weight of 27kDa were discovered both in humans and sheep. This study helps to understand the economic worth of dairy animals worldwide. HSP27 phosphorylation has been predicted as an anticancer agent. Recent research shows that new strategies have been developed for cancer treatment based on therapy of HSP27. This research will highlight the characterization and significant role of HSP27 in sheep.

PINK1 and Parkin Ameliorate the Loss of Motor Activity and Mitochondrial Dysfunction Induced by Peripheral Neuropathy-Associated HSPB8 Mutants in Drosophila Models

Charcot-Marie-Tooth disease (CMT) is a group of inherited peripheral nerve disorders characterized by progressive muscle weakness and atrophy, sensory loss, foot deformities and steppage gait. Missense mutations in the gene encoding the small heat shock protein HSPB8 (HSP22) have been associated with hereditary neuropathies, including CMT. HSPB8 is a member of the small heat shock protein family sharing a highly conserved α-crystallin domain that is critical to its chaperone activity. In this study, we modeled HSPB8 mutant-induced neuropathies in Drosophila. The overexpression of human HSPB8 mutants in Drosophila neurons produced no significant defect in fly development but led to a partial reduction in fly lifespan. Although these HSPB8 mutant genes failed to induce sensory abnormalities, they reduced the motor activity of flies and the mitochondrial functions in fly neuronal tissue. The motor defects and mitochondrial dysfunction were successfully restored by PINK1 and parkin, which are Parkinson's disease-associated genes that have critical roles in maintaining mitochondrial function and integrity. Consistently, kinetin riboside, a small molecule amplifying PINK1 activity, also rescued the loss of motor activity in our HSPB8 mutant model.

Client-induced elongation, expansion, and co-aggregation of the lens alpha-crystallins.

The long-lived nature of the eye lens presents unique challenges to the maintenance of protein stability and function. Age-related accumulation of chemical modifications to proteins in the lens promote the formation of light-scattering aggregates that disrupt vision, leading to cataract: a leading cause of blindness worldwide. To counteract these effects, ∼40% of the lens cytosol is composed of α-crystallins (αAc and αBc isoforms): ATP-independent chaperone “holdases” that work to prevent formation of protein aggregates capable of scattering light. Like other members of the small heat shock protein (sHSP) family of chaperones, the α-crystallins form large and polydisperse oligomeric assemblies that recognize and sequester destabilized proteins, through the formation of soluble chaperone/client complexes. Over time, saturating conditions of unfolding clientele overwhelm lens chaperone capacity, leading to light-scattering co-aggregates. A mechanistic basis for the chaperone/client co-aggregation pathway is not well understood. Here, we applied single-particle electron microscopy and other biophysical techniques to define the morphological transitions associated with chaperone/client co-aggregation, using the model client lysozyme. We observe a mechanism where αAc and αBc chaperone/client sequestration progresses through an “initiation complex” (∼15–20 nm diameter, akin to apo-state α-crystallins), and proceeds through an intermediate elongation/expansion stage where co-aggregates reach dimensions of 50–200 nm. Ultimately, under saturating client conditions, the elongation/expansion complexes appear to cluster (or collapse) to form large light-scattering aggregates (microns in diameter). Ensemble and single-particle analysis techniques show αAc and αBc adopt a similar overall mechanism of expansion/elongation, while some unique isoform-specific features may be attributed to characteristic differences in activity toward lysozyme client. Overall, this work provides a mechanistic basis for understanding how α-crystallins (and perhaps other sHSP's) accommodate destabilized clients and depicts a potential client-induced co-aggregation pathway leading to lens opacification and age-related vision loss.

Evaluation of the Small Heat Shock Protein Family Members HSPB2 and HSPB3 in Bladder Cancer Prognosis and Progression.

Bladder cancer (BlCa) represents the sixth most commonly diagnosed type of male malignancy. Due to the clinical heterogeneity of BlCa, novel markers would optimize treatment efficacy and improve prognosis. The small heat shock proteins (sHSP) family is one of the major groups of molecular chaperones responsible for the maintenance of proteome functionality and stability. However, the role of sHSPs in BlCa remains largely unknown. The present study aimed to examine the association between HSPB2 and HSPB3 expression and BlCa progression in patients, and to investigate their role in BlCa cells. For this purpose, a series of experiments including reverse transcription-quantitative PCR, Western blotting, MTT assay and flow cytometry were performed. Initial analyses revealed increased vs. human transitional carcinoma cells, expression levels of the HSPB2 and HSPB3 genes and proteins in high grade BlCa cell lines. Therefore, we then evaluated the clinical significance of the HSPB2 and HSPB3 genes expression levels in bladder tumor samples and matched adjusted normal bladder specimens. Total RNA from 100 bladder tumor samples and 49 paired non-cancerous bladder specimens were isolated, and an accurate SYBR-Green based real-time quantitative polymerase chain reaction (qPCR) protocol was developed to quantify HSPB2 and HSPB3 mRNA levels in the two cohorts of specimens. A significant downregulation of the HSPB2 and HSPB3 genes expression was observed in bladder tumors as compared to matched normal urothelium; yet, increased HSPB2 and HSPB3 levels were noted in muscle-invasive (T2-T4) vs. superficial tumors (TaT1), as well as in high-grade vs. low-grade tumors. Survival analyses highlighted the significantly higher risk for post-treatment disease relapse in TaT1 patients poorly expressing HSPB2 and HSPB3 genes; this effect tended to be inverted in advanced disease stages (muscle-invasive tumors) indicating the biphasic impact of HSPB2, HSPB3 genes in BlCa progression. The pro-survival role of HSPB2 and HSPB3 in advanced tumor cells was also evident by our finding that HSPB2, HSPB3 genes expression silencing in high grade BlCa cells enhanced doxorubicin toxicity. These findings indicate that the HSPB2, HSPB3 chaperone genes have a likely pro-survival role in advanced BlCa; thus, they can be targeted as novel molecular markers to optimize treatment efficacy in BlCa and to limit unnecessary interventions.

HY5-HDA9 orchestrates the transcription of HsfA2 to modulate salt stress response in Arabidopsis.

Integration of light signaling and diverse abiotic stress responses contribute to plant survival in a changing environment. Some reports have indicated that light signals contribute a plant's ability to deal with heat, cold, and stress. However, the molecular link between light signaling and the salt-response pathways remains unclear. We demonstrate here that increasing light intensity elevates the salt stress tolerance of plants. Depletion of HY5, a key component of light signaling, causes Arabidopsis thaliana to become salinity sensitive. Interestingly, the small heat shock protein (sHsp) family genes are upregulated in hy5-215 mutant plants, and HsfA2 is commonly involved in the regulation of these sHsps. We found that HY5 directly binds to the G-box motifs in the HsfA2 promoter, with the cooperation of HISTONE DEACETYLASE 9 (HDA9), to repress its expression. Furthermore, the accumulation of HDA9 and the interaction between HY5 and HDA9 are significantly enhanced by salt stress. On the contrary, high temperature triggers HY5 and HDA9 degradation, which leads to dissociation of HY5-HDA9 from the HsfA2 promoter, thereby reducing salt tolerance. Under salt and heat stress conditions, fine tuning of protein accumulation and an interaction between HY5 and HDA9 regulate HsfA2 expression. This implies that HY5, HDA9, and HsfA2 play important roles in the integration of light signaling with salt stress and heat shock response.

Mycobacterium leprae hsp18 promoter-EGFP transcriptional fusion construct: Environmental stress and strain-specific expression

The Hsp18 protein is a major T-cell antigen of Mycobacterium leprae belonging to the family of small heat-shock proteins. The protein is specifically regulated at post-translational level during the intracellular growth of M. leprae within macrophages due to auto-phosphorylation, indicating its importance in the survival of the bacterium. The promoter and regulatory sequences that control hsp18 expression are located within a 256-bp sequence upstream of the translation start site. However, there are no studies describing either characterization of the hsp18 promoter or its genetic regulation. Therefore, we constructed an hsp18-EGFP transcriptional fusion in an E. coli–Mycobacterium shuttle vector. A 168-bp sequence comprising the hsp18 promoter was cloned upstream of the EGFP gene and transformed in M. smegmatis, and the integration of the construct was confirmed by Southern hybridization. hsp18 promoter activity was measured by analyzing EGFP expression in M. smegmatis and Escherichia coli grown under different environmental stress conditions normally encountered by M. leprae in vivo. We found that the 168-bp upstream sequence of hsp18 could function as a promoter, and the regulation of hsp18 expression was host-, environmental stress-, and temperature-dependent. Appreciable EGFP expression was detected in M. smegmatis grown under normal conditions, and theexpression was significantly increased by environmental stress. However, EGFP expression was observed in E. coli only under stress conditions. Comparative sequence analysis revealed the putative sigma factor C (SigC)-binding site within the 168-bp promoter sequence of hsp18, which might be involved in the regulation of hsp18 expression during stress conditions in M. leprae. Thus, our data demonstrated the transcriptional regulation of hsp18 expression in response to different environmental stress conditions, possibly through SigC in Mycobacterium. Further, this shuttle vector could be used for the functional characterization of M. leprae genes in heterologous systems.

Genetic polymorphism in HSPB6 gene and their association with heat tolerance in Sahiwal cattle

Heat shock proteins (HSPs) are known to modulate cellular response during summer stress in dairy cattle. Among different classes of HSPs, heat shock protein 20 (HSPB6) is a member of the small HSP family protein, the role of which has not been fully characterized in the context of heat stress in cattle. This study identified single nucleotide polymorphisms (SNPs) in the HSPB6 gene in Sahiwal cattle and their associations with heat tolerance traits (RR, RT and HTC). Three SNPs (SNP 1-3) were reported, which included two transitions, viz. SNP1-g.436G&gt;A (Intron 1) and SNP2-g.2152A&gt;G (3′-UTR) and one transversion, viz. SNP3-g.2417A&gt;T (3′-UTR). The association analysis revealed that SNPs loci, viz. SNP1-g.436G&gt;A and SNP2-g.2152A&gt;G were significantly associated with heat tolerance traits. The GG genotype of SNP2-g.2152A&gt;G was significantly associated with heat tolerance traits in Sahiwal cattle. The association analysis of four available haplotypes, viz. Hap1 (GGA), Hap2 (AAA), Hap3 (GAA), and Hap4 (AAT) of HSPB6 gene with heat tolerance traits did not differ significantly with any haplotype in Sahiwal cattle. This study provides the first association analyses between the SNPs of HSPB6 gene and heat tolerance traits in Sahiwal cattle, which could be used as effective SNP markers in genetic selection for heat tolerance in cattle breeding programs.

Heat shock protein 20 suppresses breast carcinogenesis by inhibiting the MAPK and AKT signaling pathways.

Heat shock protein (HSP) 20 belongs to the small HSP family and exhibits diverse functions, including tumor suppression, in addition to being a molecular chaperon, which is the classical property of HSPs. The present study aimed to examine the association between HSP20 expression and breast cancer (BC) progression in patients, and to explore the possible role of HSP20 in malignant phenotypes of BC cells. A series of experiments, including reverse transcription-quantitative PCR, western blotting, Cell Counting Kit-8 and flow cytometry, were performed. Data from Gene Expression Omnibus and Kaplan-Meier Plotter revealed that HSP20 expression was significantly downregulated in BC tissues, and patients with BC with lower HSP20 expression exhibited poorer recurrence-free survival. The data revealed that HSP20 was closely associated with the pathological tumor stage (P=0.015) and pathological tumor node metastasis (P=0.031) of patients with BC. Additionally, HSP20 expression was markedly decreased in BC cell lines. Exogenous overexpression of HSP20 inhibited proliferation and accelerated apoptosis of BC cells. These cells exhibited decreased migration and invasion when HSP20 was overexpressed. Furthermore, HSP20 overexpression suppressed the MAPK and AKT signaling pathways, as evidenced by the reduced phosphorylation levels of AKT, ERK, JNK and p38. Knockdown of HSP20 exerted the opposite effects. Notably, the AKT agonist, SC79, and the ERK agonist, LM22B-10, reversed the decrease in cell proliferation and migration induced by HSP20 overexpression. Overall, the data suggest that the decreased expression of HSP20 in BC tissues may be associated with disease progression. HSP20 also attenuated the malignant phenotype of BC cells and the inhibition of MAPK and AKT signaling may be associated with this effect. Therefore, HSP20 may be a potential prognostic marker or a candidate therapeutic target for BC.

Small Heat Shock Proteins Collaborate with FAIM to Prevent Accumulation of Misfolded Protein Aggregates.

Cells and tissues are continuously subject to environmental insults, such as heat shock and oxidative stress, which cause the accumulation of cytotoxic, aggregated proteins. We previously found that Fas Apoptosis Inhibitory Molecule (FAIM) protects cells from stress-induced cell death by preventing abnormal generation of protein aggregates similar to the effect of small heat shock proteins (HSPs). Protein aggregates are often associated with neurodegenerative diseases, including Alzheimer’s disease (AD). In this study, we sought to determine how FAIM protein dynamics change during cellular stress and how FAIM prevents the formation of amyloid-β aggregates/fibrils, one of the pathological hallmarks of AD. Here, we found that the majority of FAIM protein shifts to the detergent-insoluble fraction in response to cellular stress. A similar shift to the insoluble fraction was also observed in small heat shock protein (sHSP) family molecules, such as HSP27, after stress. We further demonstrate that FAIM is recruited to sHSP-containing complexes after cellular stress induction. These data suggest that FAIM might prevent protein aggregation in concert with sHSPs. In fact, we observed the additional effect of FAIM and HSP27 on the prevention of protein aggregates using an in vitro amyloid-β aggregation model system. Our work provides new insights into the interrelationships among FAIM, sHSPs, and amyloid-β aggregation.

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.

Conformational Changes of α-Crystallin Proteins Induced by Heat Stress.

α-crystallin is a major structural protein in the eye lenses of vertebrates that is composed of two relative subunits, αA and αB crystallin, which function in maintaining lens transparency. As a member of the small heat-shock protein family (sHsp), α-crystallin exhibits chaperone-like activity to prevent the misfolding or aggregation of critical proteins in the lens, which is associated with cataract disease. In this study, high-purity αA and αB crystallin proteins were expressed from E. coli and purified by affinity and size-exclusion chromatography. The size-exclusion chromatography experiment showed that both αA and αB crystallins exhibited oligomeric complexes in solution. Here, we present the structural characteristics of α-crystallin proteins from low to high temperature by combining circular dichroism (CD) and small-angle X-ray scattering (SAXS). Not only the CD data, but also SAXS data show that α-crystallin proteins exhibit transition behavior on conformation with temperature increasing. Although their protein sequences are highly conserved, the analysis of their thermal stability showed different properties in αA and αB crystallin. In this study, taken together, the data discussed were provided to demonstrate more insights into the chaperone-like activity of α-crystallin proteins.

HSPB8 Overexpression Ameliorates Cognitive Impairment in Diabetic Mice via Inhibiting NLRP3 Inflammation Activation

Type 2 diabetes mellitus (T2DM) is associated with an elevated risk of cognitive impairment. And the underlying mechanism remains unillustrated. HSPB8 is a member of the small heat shock protein family. In this study, we found that the expression of HSPB8 was upregulated in the hippocampus of high − fat diet (HFD) + streptozotocin (STZ) − induced diabetic mice and N2a cells exposed to high glucose. Overexpression of HSPB8 relieved cognitive decline in DM mice. Mechanically, HSPB8 overexpression in the hippocampus of diabetic mice inhibited NOD-like receptor protein 3 (NLRP3) inflammasome activation via dephosphorylating mitochondrial fission-associated protein dynamin-related protein 1 (DRP1) at the phosphorylated site Ser616 (p-Drp1S616). Furthermore, HSPB8 overexpression increased mitochondrial membrane potential (MMP) and reduced oxidative stress. These results indicate a protective effect of HSPB8 in the hippocampus of diabetic mice and N2a cells exposed to high glucose. Overexpression of HSPB8 might be a useful strategy for treating T2DM-related cognitive decline.

TAT-HSP27 Peptide Improves Neurologic Deficits via Reducing Apoptosis After Experimental Subarachnoid Hemorrhage.

Cell apoptosis plays an important role in early brain injury (EBI) after subarachnoid hemorrhage (SAH). Heat shock protein 27 (HSP27), a member of the small heat shock protein (HSP) family, is induced by various stress factors and exerts protective role on cells. However, the role of HSP27 in brain injury after SAH needs to be further clarified. Here, we reported that HSP27 level of cerebrospinal fluid (CSF) is increased obviously at day 1 in patients with aneurysmal SAH (aSAH) and related to the grades of Hunt and Hess (HH), World Federation of Neurological Surgeons (WFNS), and Fisher score. In rat SAH model, HSP27 of CSF is first increased and then obviously declined; overexpression of HSP27, not knockdown of HSP27, attenuates SAH-induced neurological deficit and cell apoptosis in the basal cortex; and overexpression of HSP27 effectively suppresses SAH-elevated activation of mitogen-activated protein Kinase Kinase 4 (MKK4), the c-Jun N-terminal kinase (JNK), c-Jun, and caspase-3. In an in vitro hemolysate-damaged cortical neuron model, HSP2765−90 peptide effectively inhibits hemolysate-induced neuron death. Furthermore, TAT-HSP2765−90 peptide, a fusion peptide consisting of trans-activating regulatory protein (TAT) of HIV and HSP2765−90 peptide, effectively attenuates SAH-induced neurological deficit and cell apoptosis in the basal cortex of rats. Altogether, our results suggest that TAT-HSP27 peptide improves neurologic deficits via reducing apoptosis.

Small HSPs play an important role in crosstalk between HSF-HSP and ROS pathways in heat stress response through transcriptomic analysis in lilies (Lilium longiflorum)

BackgroundHigh temperature seriously limits the annual production of fresh cut lilies, which is one of the four major cut flowers in the global cut flower market. There were few transcriptomes focused on the gene expression of lilies under heat stress. In order to reveal the potential heat response patterns in bulbous plants and provide important genes for further genetic engineering techniques to improve thermotolerance of lily, RNA sequencing of lilies under heat treatments were conducted.ResultsIn this study, seedlings of Lilium longiflorum ‘White Heaven’ were heat-treated at 37 °C for different lengths of time (0 h, 0.5 h, 1 h, 3 h, 6 h, and 12 h with a 12 h-light/12 h-dark cycle). The leaves of these lily seedlings were immediately collected after heat treatments and quickly put into liquid nitrogen for RNA sequencing. 109,364,486–171,487,430 clean reads and 55,044 unigenes including 21,608 differentially expressed genes (DEGs) (fold change ≥2) were obtained after heat treatment. The number of DEGs increased sharply during the heat treatments of 0.5 h–1 h and 1 h–3 h compared to that of other periods. Genes of the heat stress transcription factor (HSF) family and the small heat shock proteins (small HSPs, also known as HSP20) family responded to heat stress early and quickly. Compared to that of the calcium signal and hormone pathways, DEGs of the HSF-HSP pathway and reactive oxygen species (ROS) pathway were significantly and highly induced. Moreover, they had the similar expression pattern in response to heat stress. Small HSPs family genes were the major components in the 50 most highly induced genes at each heat stress treatment and involved in ROS pathway in the rapid response to heat stress. Furthermore, the barley stripe mosaic virus induced gene silencing (BSMV-VIGS) of LlHsfA2 caused a significantly reduced thermotolerance phenotype in Lilium longiflorum ‘White Heaven’, meanwhile decreasing the expression of small HSPs family genes and increasing the ROS scavenging enzyme ascorbate peroxidase (APX) genes, indicating the potential interplay between these two pathways.ConclusionsBased on our transcriptomic analysis, we provide a new finding that small HSPs play important roles in crosstalk between HSF-HSP and ROS pathways in heat stress response of lily, which also supply the groundwork for understanding the mechanism of heat stress in bulbous plants.

Heat Shock Proteins: Central Players in Oncological and Immuno-Oncological Tracks.

Heat shock proteins (HSPs) are a group of proteins that promote protein folding, inhibit denaturation of cellular proteins, and maintain other proteins' functional activities when cells are subjected to stress and/or high temperature. HSP classification is generally based on their molecular weights into large and small HSP. The family of small HSPs includes HSPs 27, 40, 60, 70, and 90. The potential rolesof HSP27 and HSP70 are quite evident in different solid malignancies, including breast, colorectal, pancreatic, and liver cancers. In this chapter, the authors focus on HSP27 and HSP70 signaling in oncology and their role in different solid malignancies as well as they shed light on the novel role of HSP70 and HSP90 in the immune-oncology field.