The neuroprotective efficacy of alpha-crystallin against acute inflammation in mice

Extracellular vesicles from Trichinella spiralis: Proteomic analysis and protective immunity

Trichinella spiralis (T. spiralis) derived extracellular vesicles (EVs) have been proposed to play a key role in regulating the host immune responses. In this study, we provided the first investigation of EVs proteomics released by T. spiralis muscle larvae (ML). T. spiralis ML EVs (Ts-ML-EVs) were successfully isolated and characterized by transmission electron microscopy (TEM) and western blotting. Using liquid chromatograph mass spectrometer (LC-MS/MS) analysis, we identified 753 proteins in the Ts-ML-EVs proteome and annotated by gene ontology (GO). These proteins were enriched in different categories by GO, kyoto encyclopedia of genes and genomes (KEGG) and domain analysis. GO enrichment analysis indicated association of protein deglutathionylation, lysosomal lumen and serine-type endopeptidase inhibitor activity with proteins which may be helpful during parasite-host interaction. Moreover, KEGG enrichment analysis revealed involvement of Ts-ML-EVs proteins in other glycan degradation, complement and coagulation cascades, proteasome and various metabolism pathways. In addition, BALB/c mice were immunized by subcutaneous injection of purified Ts-ML-EVs. Ts-ML-EVs group demonstrated a 23.4% reduction in adult worms and a 43.7% reduction in ML after parasite challenge. Cellular and humoral immune responses induced by Ts-ML-EVs were detected, including the levels of specific antibodies (IgG, IgM, IgE, IgG1 and IgG2a) as well as cytokines (IL-12, IFN-γ, IL-4 and IL-10) in serum. The results showed that Ts-ML-EVs could induce a Th1/Th2 mixed immune response with Th2 predominant. This study revealed a potential role of Ts-ML-EVs in T. spiralis biology, particularly in the interaction with host. This work provided a critical step to against T. spiralis infection based on Ts-ML-EVs.

Extracellular vesicles (EVs) play an important role in cell-cell communication. They can transport functional molecules to target tissues and cells. During parasite infection, EVs provide suitable diagnostic makers and vaccine antigens for as well as inducing host immune responses. In Trichinella spiralis (T. spiralis), we previous proved that Ts-ML-EVs exerted immunomodulatory effect that inhibited experimental colitis in mice. Based on these results, we tested the protein composition of Ts-ML-EVs and the immune protective effect of Ts-ML-EVs. Our study showed that Ts-ML-EVs contained a number of immune-related proteins and it could be potential vaccine antigen for preventing T. spiralis infection.

Therapeutic Potential of α-Crystallins in Retinal Neurodegenerative Diseases

The chaperone and anti-apoptotic activity of α-crystallins (αA- and αB-) and their derivatives has received increasing attention due to their tremendous potential in preventing cell death. While originally known and described for their role in the lens, the upregulation of these proteins in cells and animal models of neurodegenerative diseases highlighted their involvement in adaptive protective responses to neurodegeneration associated stress. However, several studies also suggest that chronic neurodegenerative conditions are associated with progressive loss of function of these proteins. Thus, while external supplementation of α-crystallin shows promise, their potential as a protein-based therapeutic for the treatment of chronic neurodegenerative diseases remains ambiguous. The current review aims at assessing the current literature supporting the anti-apoptotic potential of αA- and αB-crystallins and its potential involvement in retinal neurodegenerative diseases. The review further extends into potentially modulating the chaperone and the anti-apoptotic function of α-crystallins and the use of such functionally enhanced proteins for promoting neuronal viability in retinal neurodegenerative disease.

HspB4/αA-Crystallin Modulates Neuroinflammation in the Retina via the Stress-Specific Inflammatory Pathways

PURPOSE

We have previously demonstrated that HspB4/αA-crystallin, a molecular chaperone, plays an important intrinsic neuroprotective role during diabetes, by its phosphorylation on residue 148. We also reported that HspB4/αA-crystallin is highly expressed by glial cells. There is a growing interest in the potential causative role of low-grade inflammation in diabetic retinopathy pathophysiology and retinal Müller glial cells' (MGCs') participation in the inflammatory response. MGCs indeed play a central role in retinal homeostasis via secreting various cytokines and other mediators. Hence, this study was carried out to delineate and understand the regulatory function of HspB4/αA-crystallin in the inflammatory response associated with metabolic stresses.

METHODS

Primary MGCs were isolated from knockout HspB4/αA-crystallin mice. These primary cells were then transfected with plasmids encoding either wild-type (WT), phosphomimetic (T148D), or non-phosphorylatable mutants (T148A) of HspB4/αA-crystallin. The cells were exposed to multiple metabolic stresses including serum starvation (SS) or high glucose with TNF-alpha (HG + T) before being further evaluated for the expression of inflammatory markers by qPCR. The total protein expression along with subcellular localization of NF-kB and the NLRP3 component was assessed by Western blot.

RESULTS

Elevated levels of IL-6, IL-1β, MCP-1, and IL-18 in SS were significantly diminished in MGCs overexpressing WT and further in T148D as compared to EV. The HG + T-induced increase in these inflammatory markers was also dampened by WT and even more significantly by T148D overexpression, whereas T148A was ineffective in either stress. Further analysis revealed that overexpression of WT or the T148D, also led to a significant reduction of Nlrp3, Asc, and caspase-1 transcript expression in serum-deprived MGCs and nearly abolished the NF-kB induction in HG + T diabetes-like stress. This mechanistic effect was further evaluated at the protein level and confirmed the stress-dependent regulation of NLRP3 and NF-kB by αA-crystallin.

CONCLUSIONS

The data gathered in this study demonstrate the central regulatory role of HspB4/αA-crystallin and its modulation by phosphorylation on T148 in retinal MGCs. For the first time, this study demonstrates that HspB4/αA-crystallin can dampen the stress-induced expression of pro-inflammatory cytokines through the modulation of multiple key inflammatory pathways, therefore, suggesting its potential as a therapeutic target for the modulation of chronic neuroinflammation.

Comparative analysis of excretory-secretory products of muscle larvae of three isolates of Trichinella pseudospiralis by the iTRAQ method

Trichinella pseudospiralis is a non-encapsulated intracellular parasitic nematode that can possess a strong ability to modulate the host immune response. Here, we compared the differentially expressed proteins of excretory-secretory (ES) products in three isolates of T. pseudospiralis muscle larvae (ML) [from Russia (RUS), United States of America (USA) and Australia (AUS)] using isobaric tags for relative and absolute quantification (iTRAQ)-based technology. A total of 2591 nonredundant proteins were identified, of which 65 (146), 72 (98) and 43 (103) significantly upregulated (downregulated) differentially expressed proteins were detected among pairwise comparisons (T4RUS vs T4USA, T4AUS vs T4USA and T4RUS vs T4AUS). In addition, GO annotation, KEGG and STRING analyses were carried out on the screened differentially altered proteins. The main biological processes involved included carbohydrate metabolic processes, DNA metabolic processes, cellular protein modification processes and homeostatic processes. The majority of KEGG pathways were found to be related to the metabolic pathways, lysosome pathway and protein processing in endoplasmic reticulum. Moreover, all ES protein expression levels involved in the lysosome pathway were significantly higher in the T4USA isolate than in the other two isolates. We also found differences in the expression of some important immunoregulatory proteins, such as protein disulfide-isomerase, thioredoxin protein and deoxyribonuclease-2-alpha, between different isolates of T. pseudospiralis ML. Flow cytometry was used to detect the increase in the CD4+/CD8 + T-cell ratio in pig peripheral blood and to verify the effect of T. pseudospiralis on the Th1/Th2 polarization of the host. Quantitative real-time PCR analysis also confirmed that the changes in the transcriptional level of genes were consistent with those at the proteomic level. These findings reveal the possible role of significantly differentially expressed proteins in ES products of the different isolates of T. pseudospiralis in antagonizing and participating in the regulation of the host immune response and maintaining a stable growth environment.

Evidence of the involvement of spinal αB-crystallin in the maintenance of bone cancer pain in rats

BACKGROUND

αB-crystallin (CRYAB) is a small heat shock protein that is able to inhibit neuroinflammatory responses under various pathological conditions. Some studies have proven that neuroinflammatory mechanisms play important roles in bone cancer pain (BCP). However, whether CRYAB participates in the maintenance of BCP has not yet been examined.

METHODS

Walker256 tumour cells were inoculated into the tibia to induce a rat model of BCP. Von Frey hairs were used to measure mechanical allodynia. Immunohistochemistry and western blotting were used to examine the expression level of CRYAB in the spinal dorsal horn.

RESULTS

The gradual development of mechanical allodynia was induced by the injection of Walker256 cells into the tibia. The downregulation of spinal CRYAB expression was found in BCP rats. The intrathecal administration of CRYAB (from days 9 to 15 post-inoculation) dose-dependently alleviated mechanical allodynia in BCP rats. Additionally, there were concomitant increases in spinal CRYAB expression and decreases in TNF-α expression.

CONCLUSIONS

Spinal CRYAB may participate in the maintenance of BCP in rats. The findings will help to identify new drugs for the management of BCP.

Anti-inflammatory and Oto-Protective Effect of the Small Heat Shock Protein Alpha B-Crystallin (HspB5) in Experimental Pneumococcal Meningitis

Sensorineural hearing loss is the most common long-term deficit after pneumococcal meningitis (PM), occurring in up to 30% of surviving patients. The infection and the following overshooting inflammatory host response damage the vulnerable sensory cells of the inner ear, resulting in loss of hair cells and spiral ganglion neurons, ultimately leading to elevated hearing thresholds. Here, we tested the oto-protective properties of the small heat shock protein alpha B-crystallin (HspB5) with previously reported anti-inflammatory, anti-apoptotic and neuroprotective functions, in an experimental model of PM-induced hearing loss. We analyzed the effect of local and systemic delivery of HspB5 in an infant rat model of PM, as well as ex vivo, using whole mount cultures. Cytokine secretion profile, hearing thresholds and inner ear damage were assessed at predefined stages of the disease up to 1 month after infection. PM was accompanied by elevated pro-inflammatory cytokine concentrations in the cerebrospinal fluid (CSF), leukocyte and neutrophil infiltration in the perilymphatic spaces of the cochlea with neutrophils extracellular trap formation during the acute phase of the disease. Elevated hearing thresholds were measured after recovery from meningitis. Intracisternal but not intraperitoneal administration of HspB5 significantly reduced the levels of TNF-α, IL-6 IFN-γ and IL-10 in the acute phase of the disease. This resulted in a greater outer hair cell survival, as well as improved hearing thresholds at later stages. These results suggest that high local concentrations of HspB5 are needed to prevent inner ear damage in acute PM. HspB5 represents a promising therapeutic option to improve the auditory outcome and counteract hearing loss after PM.

Suppression of astrocytic autophagy by αB-crystallin contributes to α-synuclein inclusion formation

Background

Parkinson’s disease (PD) is characterized by a chronic loss of dopaminergic neurons and the presence of proteinaceous inclusions (Lewy bodies) within some remaining neurons in the substantia nigra. Recently, astroglial inclusion body has also been found in some neurodegenerative diseases including PD. However, the underlying molecular mechanisms of how astroglial protein aggregation forms remain largely unknown. Here, we investigated the contribution of αB-crystallin (CRYAB), a small heat shock protein, in α-synuclein inclusion formation in astrocytes.

Methods

Small interfering RNA (siRNA)-mediated CRYAB (siCRYAB) knockdown or CRYAB overexpression was performed to investigate the impact of CRYAB on the autophagy in human glioblastoma cell line U251 cells. Co-immunoprecipitation (co-IP) and immunoblotting were used to dissect the interaction among multiple proteins. The clearance of α-synuclein in vitro was evaluated by immunocytochemistry. CRYAB transgenic mice and transgenic mice overexpressing A30P mutant form of human α-synuclein were used to examine the influence of CRYAB to α-synuclein accumulation in vivo.

Results

We found that knockdown of CRYAB in U251 cells or primary cultured astrocytes resulted in a marked augmentation of autophagy activity. In contrast, exogenous CRYAB disrupted the assembly of the BAG3-HSPB8-HSC70 complex via binding with BAG3, thereby suppressing the autophagy activity. Furthermore, CRYAB-regulated autophagy has relevance to PD pathogenesis. Knockdown of CRYAB remarkably promoted cytoplasmic clearance of α-synuclein preformed fibrils (PFFs). Conversely, selective overexpression of CRYAB in astrocytes markedly suppressed autophagy leading to the accumulation of α-synuclein aggregates in the brain of transgenic mice expressing human α-synuclein A30P mutant.

Conclusions

This study reveals a novel function for CRYAB as a natural inhibitor of astrocytic autophagy and shows that knockdown of CYRAB may provide a therapeutic target against proteinopathies such as synucleinopathies.

Extracellular small heat shock proteins: exosomal biogenesis and function

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

The small heat shock proteins, especially HspB4 and HspB5 are promising protectants in neurodegenerative diseases

Small heat shock proteins (sHsps) are a group of proteins with molecular mass between 12 and 43 kDa. Currently, 11 members of this family have been classified, namely HspB1 to HspB11. HspB1, HspB2, HspB5, HspB6, HspB7, and HspB8, which are expressed in brain have been observed to be related to the pathology of neurodegenerative diseases, including Parkinson's, Alzheimer's, Alexander's disease, multiple sclerosis, and human immunodeficiency virus-associated dementia. Specifically, sHsps interact with misfolding and damaging protein aggregates, like Glial fibrillary acidic protein in AxD, β-amyloid peptides aggregates in Alzheimer's disease, Superoxide dismutase 1 in Amyotrophic lateral sclerosis and cytosine-adenine-guanine/polyglutamine (CAG/PolyQ) in Huntington's disease, Spinocerebellar ataxia type 3, Spinal-bulbar muscular atrophy, to reduce the toxicity or increase the clearance of these protein aggregates. The degree of HspB4 expression in brain is still debated. For neuroprotective mechanisms, sHsps attenuate mitochondrial dysfunctions, reduce accumulation of misfolded proteins, block oxidative/nitrosative stress, and minimize neuronal apoptosis and neuroinflammation, which are molecular mechanisms commonly accepted to mirror the progression and development of neurodegenerative diseases. The increasing incidence of the neurodegenerative diseases enhanced search for effective approaches to rescue neural tissue from degeneration with minimal side effects. sHsps have been found to exert neuroprotective functions. HspB5 has been emphasized to reduce the paralysis in a mouse model of experimental autoimmune encephalomyelitis, providing a therapeutic basis for the disease. In this review, we discuss the current understanding of the properties and the mechanisms of protection orchestrated by sHsps in the nervous system, highlighting the promising therapeutic role of sHsps in neurodegenerative diseases.

Involvement of Astrocytes in Alzheimer's Disease from a Neuroinflammatory and Oxidative Stress Perspective

Alzheimer disease (AD) is a frequent and devastating neurodegenerative disease in humans, but still no curative treatment has been developed. Although many explicative theories have been proposed, precise pathophysiological mechanisms are unknown. Due to the importance of astrocytes in brain homeostasis they have become interesting targets for the study of AD. Changes in astrocyte function have been observed in brains from individuals with AD, as well as in AD in vitro and in vivo animal models. The presence of amyloid beta (Aβ) has been shown to disrupt gliotransmission, neurotransmitter uptake, and alter calcium signaling in astrocytes. Furthermore, astrocytes express apolipoprotein E and are involved in the production, degradation and removal of Aβ. As well, changes in astrocytes that precede other pathological characteristics observed in AD, point to an early contribution of astroglia in this disease. Astrocytes participate in the inflammatory/immune responses of the central nervous system. The presence of Aβ activates different cell receptors and intracellular signaling pathways, mainly the advanced glycation end products receptor/nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway, responsible for the transcription of pro-inflammatory cytokines and chemokines in astrocytes. The release of these pro-inflammatory agents may induce cellular damage or even stimulate the production of Aβ in astrocytes. Additionally, Aβ induces the appearance of oxidative stress (OS) and production of reactive oxygen species and reactive nitrogen species in astrocytes, affecting among others, intracellular calcium levels, NADPH oxidase (NOX), NF-κB signaling, glutamate uptake (increasing the risk of excitotoxicity) and mitochondrial function. Excessive neuroinflammation and OS are observed in AD, and astrocytes seem to be involved in both. The Aβ/NF-κB interaction in astrocytes may play a central role in these inflammatory and OS changes present in AD. In this paper, we also discuss therapeutic measures highlighting the importance of astrocytes in AD pathology. Several new therapeutic approaches involving phenols (curcumin), phytoestrogens (genistein), neuroesteroids and other natural phytochemicals have been explored in astrocytes, obtaining some promising results regarding cognitive improvements and attenuation of neuroinflammation. Novel strategies comprising astrocytes and aimed to reduce OS in AD have also been proposed. These include estrogen receptor agonists (pelargonidin), Bambusae concretio Salicea, Monascin, and various antioxidatives such as resveratrol, tocotrienol, anthocyanins, and epicatechin, showing beneficial effects in AD models.

The Small Heat Shock Protein α-Crystallin B Shows Neuroprotective Properties in a Glaucoma Animal Model

Glaucoma is a neurodegenerative disease that leads to irreversible retinal ganglion cell (RGC) loss and is one of the main causes of blindness worldwide. The pathogenesis of glaucoma remains unclear, and novel approaches for neuroprotective treatments are urgently needed. Previous studies have revealed significant down-regulation of α-crystallin B as an initial reaction to elevated intraocular pressure (IOP), followed by a clear but delayed up-regulation, suggesting that this small heat-shock protein plays a pathophysiological role in the disease. This study analyzed the neuroprotective effect of α-crystallin B in an experimental animal model of glaucoma. Significant IOP elevation induced by episcleral vein cauterization resulted in a considerable impairment of the RGCs and the retinal nerve fiber layer. An intravitreal injection of α-crystallin B at the time of the IOP increase was able to rescue the RGCs, as measured in a functional photopic electroretinogram, retinal nerve fiber layer thickness, and RGC counts. Mass-spectrometry-based proteomics and antibody-microarray measurements indicated that a α-crystallin injection distinctly up-regulated all of the subclasses (α, β, and γ) of the crystallin protein family. The creation of an interactive protein network revealed clear correlations between individual proteins, which showed a regulatory shift resulting from the crystallin injection. The neuroprotective properties of α-crystallin B further demonstrate the potential importance of crystallin proteins in developing therapeutic options for glaucoma.

Crystallins and neuroinflammation: The glial side of the story

BACKGROUND

There is an abundance of evidence to support the association of damaging neuroinflammation and neurodegeneration across a multitude of diseases. One of the links between these pathological phenomena is the role of chaperone proteins as both neuroprotective and immune-regulatory agents.

SCOPE OF REVIEW

Chaperone proteins are highly expressed at sites of neuroinflammation both in glial cells and in the injured neurons that initiate the immune response. For this reason, the use of chaperones as treatment for various diseases associated with neuroinflammation is a highly active area of investigation. This review explores the various ways that the small heat shock protein chaperones, α-crystallins, can affect glial cell function with a specific focus on their implication in the inflammatory response associated with neurodegenerative disorders, and their potential as therapeutic treatment.

MAJOR CONCLUSIONS

Although the mechanisms are still under investigation, a clear link has now been established between alpha-crystallins and neuroinflammation, especially through their roles in microglial and macroglial cells. Interestingly, similar to inflammation in itself, crystallins can have a beneficial or detrimental impact on the CNS based on the context and duration of the condition.

GENERAL SIGNIFICANCE

Overall this review points out the novel roles that chaperones such as alpha-crystallins can play outside of the classical protein folding pathways, and their potential in the development of new therapies for the treatment of neuroinflammatory/neurodegenerative diseases. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.

Upregulation of alphaB-crystallin expression in the substantia nigra of patients with Parkinson's disease

Parkinson's disease (PD) is one of the most devastating neurodegenerative disorders. The underlying mechanisms of the characteristic neurodegeneration in the substantia nigra (SN) are still not fully understood. To better understand the molecular events occurring in the SN of PD brain, we used the culture-derived isotope tag-based quantitative proteomics to compare the protein expression profiles in the nigral tissue of PD patients and control subjects. We identified a total of 11 differentially expressed proteins, including alphaB-crystallin (Cryab). Both the levels and pattern of Cryab expression in the SN were validated. It was revealed that Cryab was markedly upregulated in the SN of PD brain. Cryab expression was also upregulated in reactive astrocytes and microglia in a neurotoxin-induced mouse PD model. Moreover, we showed increased expression of Cryab in cytoplasmic inclusions in a subset of glial cells in Parkinsonian brain. Thus, we identified Cryab that is highly expressed in the SN of PD brain and may be involved in the glial pathology during dopaminergic neuron degeneration in PD.

Extracellular heat shock proteins: a new location, a new function

The expression of heat shock proteins (HSPs) is a basic and well-conserved cellular response to an array of stresses. These proteins are involved in the repair of cellular damage induced by the stress, which is necessary for the salutary resolution from the insult. Moreover, they confer protection from subsequent insults, which has been coined stress tolerance. Because these proteins are expressed in subcellular compartments, it was thought that their function during stress conditions was circumscribed to the intracellular environment. However, it is now well established that HSPs can also be present outside cells where they appear to display a function different than the well-understood chaperone role. Extracellular HSPs act as alert stress signals priming other cells, particularly of the immune system, to avoid the propagation of the insult and favor resolution. Because the majority of HSPs do not possess a secretory peptide signal, they are likely to be exported by a nonclassic secretory pathway. Different mechanisms have been proposed to explain the export of HSPs, including translocation across the plasma membrane and release associated with lipid vesicles, as well as the passive release after cell death by necrosis. Extracellular HSPs appear in various flavors, including membrane-bound and membrane-free forms. All of these variants of extracellular HSPs suggest that their interactions with cells may be quite diverse, both in target cell types and the activation signaling pathways. This review addresses some of our current knowledge about the release and relevance of extracellular HSPs.

CRYAB modulates the activation of CD4+ T cells from relapsing-remitting multiple sclerosis patients

BACKGROUND

Suppression of activation of pathogenic CD4(+) T cells is a potential therapeutic intervention in multiple sclerosis (MS). We previously showed that a small heat shock protein, CRYAB, reduced T cell proliferation, pro-inflammatory cytokine production and clinical signs of experimental allergic encephalomyelitis, a model of MS.

OBJECTIVE

We assessed whether the ability of CRYAB to reduce the activation of T cells translated to the human disease.

METHODS

CD4(+) T cells from healthy controls and volunteers with MS were activated in vitro in the presence or absence of a CRYAB peptide (residues 73-92). Parameters of activation (proliferation rate, cytokine secretion) and tolerance (anergy, activation-induced cell death, microRNAs) were evaluated.

RESULTS

The secretion of pro-inflammatory cytokines by CD4(+) T cells was decreased in the presence of CRYAB in a subset of relapsing-remitting multiple sclerosis (RRMS) participants with mild disease severity while no changes were observed in healthy controls. Further, there was a correlation for higher levels of miR181a microRNA, a marker upregulated in tolerant CD8(+) T cells, in CD4(+) T cells of MS patients that displayed suppressed cytokine production (responders).

CONCLUSION

CRYAB may be capable of suppressing the activation of CD4(+) T cells from a subset of RRMS patients who appear to have less disability but similar age and disease duration.

Novel roles for α-crystallins in retinal function and disease

α-Crystallins are key members of the superfamily of small heat shock proteins that have been studied in detail in the ocular lens. Recently, novel functions for α-crystallins have been identified in the retina and in the retinal pigmented epithelium (RPE). αB-Crystallin has been localized to multiple compartments and organelles including mitochondria, golgi apparatus, endoplasmic reticulum and nucleus. α-Crystallins are regulated by oxidative and endoplasmic reticulum stress, and inhibit apoptosis-induced cell death. α-Crystallins interact with a large number of proteins that include other crystallins, and apoptotic, cytoskeletal, inflammatory, signaling, angiogenic, and growth factor molecules. Studies with RPE from αB-crystallin deficient mice have shown that αB-crystallin supports retinal and choroidal angiogenesis through its interaction with vascular endothelial growth factor. αB-Crystallin has also been shown to have novel functions in the extracellular space. In RPE, αB-crystallin is released from the apical surface in exosomes where it accumulates in the interphotoreceptor matrix and may function to protect neighboring cells. In other systems administration of exogenous recombinant αB-crystallin has been shown to be anti-inflammatory. Another newly described function of αB-crystallin is its ability to inhibit β-amyloid fibril formation. α-Crystallin minichaperone peptides have been identified that elicit anti-apoptotic function in addition to being efficient chaperones. Generation of liposomal particles and other modes of nanoencapsulation of these minipeptides could offer great therapeutic advantage in ocular delivery for a wide variety of retinal degenerative, inflammatory and vascular diseases including age-related macular degeneration and diabetic retinopathy.

Small heat shock protein αA-crystallin prevents photoreceptor degeneration in experimental autoimmune uveitis

The small heat shock protein, αA-crystallin null (αA−/−) mice are known to be more prone to retinal degeneration than the wild type mice in Experimental Autoimmune Uveoretinitis (EAU). In this report we demonstrate that intravenous administration of αA preserves retinal architecture and prevents photoreceptor damage in EAU. Interestingly, only αA and not αB-crystallin (αB), a closely related small heat shock protein works, pointing to molecular specificity in the observed retinal protection. The possible involvement of αA in retinal protection through immune modulation is corroborated by adaptive transfer experiments, (employing αA−/− and wild type mice with EAU as donors and Rag2−/− as the recipient mice), which indicate that αA protects against the autoimmune challenge by modulating the systemic B and T cell immunity. We show that αA administration causes marked reduction in Th1 cytokines (TNF-α, IL-12 and IFN-γ), both in the retina and in the spleen; notably, IL-17 was only reduced in the retina suggesting local intervention. Importantly, expression of Toll-like receptors and their associated adaptors is also inhibited suggesting that αA protection, against photoreceptor loss in EAU, is associated with systemic suppression of both the adaptive and innate immune responses.

The link between small heat shock proteins and the immune system

There is now compelling evidence that members of the family of small heat shock proteins (HSP) can be secreted by a variety of different types of cells. Secretion of small HSP may at times represent altruistic delivery of supporting and stabilizing factors from one cell to another. A probably more general effect of extracellular small HSP, however, is exerted by their ability to activate macrophages and macrophage-like cells. When doing so, small HSP induce an immune-regulatory state of activation, stimulating macrophages to suppress inflammation. For this reason, small HSP deserve consideration as broadly applicable therapeutic agents for inflammatory disorders. In one particular case, however, adaptive immune responses to the small HSP itself may subvert the protective quality of the innate immune response it triggers. This situation only applies to alpha B-crystallin, and is unique for humans as well. In this special case, local concentrations of alpha B-crystallin determine the balance between protective innate responses and destructive adaptive responses, the latter of which are held responsible for the development of multiple sclerosis lesions. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.

Methionine sulfoxide reductase A: Structure, function and role in ocular pathology

Methionine is a highly susceptible amino acid that can be oxidized to S and R diastereomeric forms of methionine sulfoxide by many of the reactive oxygen species generated in biological systems. Methionine sulfoxide reductases (Msrs) are thioredoxin-linked enzymes involved in the enzymatic conversion of methionine sulfoxide to methionine. Although MsrA and MsrB have the same function of methionine reduction, they differ in substrate specificity, active site composition, subcellular localization, and evolution. MsrA has been localized in different ocular regions and is abundantly expressed in the retina and in retinal pigment epithelial (RPE) cells. MsrA protects cells from oxidative stress. Overexpression of MsrA increases resistance to cell death, while silencing or knocking down MsrA decreases cell survival; events that are mediated by mitochondria. MsrA participates in protein-protein interaction with several other cellular proteins. The interaction of MsrA with α-crystallins is of utmost importance given the known functions of the latter in protein folding, neuroprotection, and cell survival. Oxidation of methionine residues in α-crystallins results in loss of chaperone function and possibly its antiapoptotic properties. Recent work from our laboratory has shown that MsrA is co-localized with αA and αB crystallins in the retinal samples of patients with age-related macular degeneration. We have also found that chemically induced hypoxia regulates the expression of MsrA and MsrB2 in human RPE cells. Thus, MsrA is a critical enzyme that participates in cell and tissue protection, and its interaction with other proteins/growth factors may provide a target for therapeutic strategies to prevent degenerative diseases.

Growth factor signals in neural cells: coherent patterns of interaction control multiple levels of molecular and phenotypic responses

Individual neurons express receptors for several different growth factors that influence the survival, growth, neurotransmitter phenotype, and other properties of the cell. Although there has been considerable progress in elucidating the molecular signal transduction pathways and physiological responses of neurons and other cells to individual growth factors, little is known about if and how signals from different growth factors are integrated within a neuron. In this study, we determined the interactive effects of nerve growth factor, insulin-like growth factor 1, and epidermal growth factor on the activation status of downstream kinase cascades and transcription factors, cell survival, and neurotransmitter production in neural cells that express receptors for all three growth factors. We document considerable differences in the quality and quantity of intracellular signaling and eventual phenotypic responses that are dependent on whether cells are exposed to a single or multiple growth factors. Dual stimulations that generated the greatest antagonistic or synergistic actions, compared with a theoretically neutral summation of their two activities, yielded the largest eventual change of neuronal phenotype indicated by the ability of the cell to produce norepinephrine or resist oxidative stress. Combined activation of insulin-like growth factor 1 and epidermal growth factor receptors was particularly notable for antagonistic interactions at some levels of signal transduction and norepinephrine production, but potentiation at other levels of signaling and cytoprotection. Our findings suggest that in true physiological settings where multiple growth factors are present, activation of one receptor type may result in molecular and phenotypic responses that are different from that observed in typical experimental paradigms in which cells are exposed to only a single growth factor at a time.

Nuclear localization of ataxin-3 is required for the manifestation of symptoms in SCA3: in vivo evidence

Spinocerebellar ataxia type 3 (SCA3) is an autosomal dominantly inherited neurodegenerative disorder caused by the expansion of a CAG repeat in the MJD1 gene resulting in an expanded polyglutamine repeat in the ataxin-3 protein. To study the course of the disease, we generated transgenic mice for SCA3 using full-length ataxin-3 constructs containing 15, 70, or 148 CAG repeats, respectively. Control mice (15 CAGs) were phenotypically normal and had no neuropathological findings. However, mice transgenic for ataxin-3 with expanded polyglutamine repeats were severely affected by a strong neurological phenotype with tremor, behavioral deficits, strongly reduced motor and exploratory activity, a hunchback, and premature death at 3 to 6 months of age. Neuropathological examination by immunohistochemical staining revealed ubiquitin- and ataxin-3-positive intranuclear inclusion bodies in a multitude of neurons. Directing ataxin-3 with 148 CAGs to the nucleus revealed an even more pronounced phenotype with more inclusions and earlier death, whereas mice transgenic with the same construct but attached to a nuclear export signal developed a milder phenotype with less inclusions. These studies indicate that nuclear localization of ataxin-3 is required for the manifestation of symptoms in SCA3 in vivo.

Molecular chaperone alpha-crystallin prevents detrimental effects of neuroinflammation

Silver nitrate administration stimulates immune activation, inflammation and deterioration in cell function. It is well established that hippocampal and cortical tissue are susceptible to degeneration in responses to insult such as oxidative stress or infection. This study was designed to investigate the prophylactic effect of alpha-crystallin, a major chaperone lens protein comprising of alpha-A and alpha-B subunits in inflammation induced mice. Mice were divided into three groups (n=6 in each), control, inflammation and alpha-crystallin treated. Our result shows that alpha-crystallin pretreatment effectively diminished systemic inflammation induced glial fibrillary acidic protein (GFAP) and nuclear factor kappa B (NFkappaB) expression in the mice neocortex, reversed elevated intracellular calcium levels, acetylcholine esterase activity and depletion of glucose. Furthermore it also significantly prevented nitric oxide (P<0.05) and lipid peroxide production in the plasma, liver, neocortex and hippocampus of the inflammation-induced mice. In order to demonstrate the direct *OH and nitric oxide radical scavenging ability of alpha-crystallin, an In vitro experiment using primary astrocyte culture subjected to lipopolysaccharide (LPS), a well-known inflammatory stimuli were also carried out. This study reiterates that alpha-crystallin therapy may serve as a potent pharmacological agent in neuroinflammation.