alphaB-Crystallin-coated MAP microtubule resists nocodazole and calcium-induced disassembly

Direct observation of chaperone-modulated talin mechanics with single-molecule resolution

Talin as a critical focal adhesion mechanosensor exhibits force-dependent folding dynamics and concurrent interactions. Being a cytoplasmic protein, talin also might interact with several cytosolic chaperones; however, the roles of chaperones in talin mechanics remain elusive. To address this question, we investigated the force response of a mechanically stable talin domain with a set of well-known unfoldase (DnaJ, DnaK) and foldase (DnaKJE, DsbA) chaperones, using single-molecule magnetic tweezers. Our findings demonstrate that chaperones could affect adhesion proteins’ stability by changing their folding mechanics; while unfoldases reduce their unfolding force from ~11 pN to ~6 pN, foldase shifts it upto ~15 pN. Since talin is mechanically synced within 2 pN force ranges, these changes are significant in cellular conditions. Furthermore, we determined that chaperones directly reshape the energy landscape of talin: unfoldases decrease the unfolding barrier height from 26.8 to 21.7 k_BT, while foldases increase it to 33.5 k_BT. We reconciled our observations with eukaryotic Hsp70 and Hsp40 and observed their similar function of decreasing the talin unfolding barrier. Quantitative mapping of this chaperone-induced talin folding landscape directly illustrates that chaperones perturb the adhesion protein stability under physiological force, thereby, influencing their force-dependent interactions and adhesion dynamics.

Chakraborty et al. uses single-molecule magnetic tweezers to investigate the chaperone-modulated talin protein mechanics. The results showed that chaperones are involved in the regulation of talin folding/unfolding under mechanical force with some chaperones stabilizing talin and increasing the force, whereas others destabilize it and reduce the force.

Nucleosomal association and altered interactome underlie the mechanism of cataract caused by the R54C mutation of αA-crystallin

BACKGROUND

αA-crystallin plays an important role in eye lens development. Its N-terminal domain is implicated in several important biological functions. Mutations in certain conserved arginine residues in the N-terminal region of αA-crystallin lead to cataract with characteristic cytoplasmic/nuclear aggregation of the mutant protein. In this study, we attempt to gain mechanistic insights into the congenital cataract caused by the R54C mutation in human αA-crystallin.

METHODS

We used several spectroscopic techniques to investigate the structure and function of the wild-type and R54CαA-crystallin. Immunoprecipitation, chromatin-enrichment followed by western blotting, immunofluorescence and cell-viability assay were performed to study the interaction partners, chromatin-association, stress-like response and cell-death caused by the mutant.

RESULTS

Although R54CαA-crystallin exhibited slight changes in quaternary structure, its chaperone-like activity was comparable to that of wild-type. When expressed in lens epithelial cells, R54CαA-crystallin exhibited a speckled appearance in the nucleus rather than cytoplasmic localization. R54CαA-crystallin triggered a stress-like response, resulting in nuclear translocation of αB-crystallin, disassembly of cytoskeletal elements and activation of caspase 3, leading to apoptosis. Analysis of the "interactome" revealed an increase in interaction of the mutant protein with nucleosomal histones, and its association with chromatin.

CONCLUSIONS

The study shows that alteration of "interactome" and nucleosomal association, rather than loss of chaperone-like activity, is the molecular basis of cataract caused by the R54C mutation in αA-crystallin.

GENERAL SIGNIFICANCE

The study provides a novel mechanism of cataract caused by a mutant of αA-crystallin, and sheds light on the possible mechanism of stress and cell death caused by such nuclear inclusions.

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

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

Dynamin 1 is important for microtubule organization and stabilization in glomerular podocytes

Dynamin 1 is a neuronal endocytic protein that participates in vesicle formation by scission of invaginated membranes. Dynamin 1 is also expressed in the kidney; however, its physiological significance to this organ remains unknown. Here, we show that dynamin 1 is crucial for microtubule organization and stabilization in glomerular podocytes. By immunofluorescence and immunoelectron microscopy, dynamin 1 was concentrated at microtubules at primary processes in rat podocytes. By immunofluorescence of differentiated mouse podocytes (MPCs), dynamin 1 was often colocalized with microtubule bundles, which radially arranged toward periphery of expanded podocyte. In dynamin 1-depleted MPCs by RNAi, α-tubulin showed a dispersed linear filament-like localization, and microtubule bundles were rarely observed. Furthermore, dynamin 1 depletion resulted in the formation of discontinuous, short acetylated α-tubulin fragments, and the decrease of microtubule-rich protrusions. Dynamins 1 and 2 double-knockout podocytes showed dispersed acetylated α-tubulin and rare protrusions. In vitro, dynamin 1 polymerized around microtubules and cross-linked them into bundles, and increased their resistance to the disassembly-inducing reagents Ca²⁺ and podophyllotoxin. In addition, overexpression and depletion of dynamin 1 in MPCs increased and decreased the nocodazole resistance of microtubules, respectively. These results suggest that dynamin 1 supports the microtubule bundle formation and participates in the stabilization of microtubules.

Proteomic study of hypothalamus in pigs exposed to heat stress

Background

With evidence of warming climates, it is important to understand the effects of heat stress in farm animals in order to minimize production losses. Studying the changes in the brain proteome induced by heat stress may aid in understanding how heat stress affects brain function. The hypothalamus is a critical region in the brain that controls the pituitary gland, which is responsible for the secretion of several important hormones. In this study, we examined the hypothalamic protein profile of 10 pigs (15 ± 1 kg body weight), with five subjected to heat stress (35 ± 1 °C; relative humidity = 90%) and five acting as controls (28 ± 3 °C; RH = 90%).

Result

The isobaric tags for relative and absolute quantification (iTRAQ) analysis of the hypothalamus identified 1710 peptides corresponding to 360 proteins, including 295 differentially expressed proteins (DEPs), 148 of which were up-regulated and 147 down-regulated, in heat-stressed animals. The Ingenuity Pathway Analysis (IPA) software predicted 30 canonical pathways, four functional groups, and four regulatory networks of interest. The DEPs were mainly concentrated in the cytoskeleton of the pig hypothalamus during heat stress.

Conclusions

In this study, heat stress significantly increased the body temperature and reduced daily gain of body weight in pigs. Furthermore, we identified 295 differentially expressed proteins, 147 of which were down-regulated and 148 up-regulated in hypothalamus of heat stressed pigs. The IPA showed that the DEPs identified in the study are involved in cell death and survival, cellular assembly and organization, and cellular function and maintenance, in relation to neurological disease, metabolic disease, immunological disease, inflammatory disease, and inflammatory response. We hypothesize that a malfunction of the hypothalamus may destroy the host physical and immune function, resulting in decreased growth performance and immunosuppression in heat stressed pigs.

Dynamic localization of αB-crystallin at the microtubule cytoskeleton network in beating heart cells

αB-crystallin is highly expressed in the heart and slow skeletal muscle; however, the roles of αB-crystallin in the muscle are obscure. Previously, we showed that αB-crystallin localizes at the sarcomere Z-bands, corresponding to the focal adhesions of cultured cells. In myoblast cells, αB-crystallin completely colocalizes with microtubules and maintains cell shape and adhesion. In this study, we show that in beating cardiomyocytes α-tubulin and αB-crystallin colocalize at the I- and Z-bands of the myocardium, where it may function as a molecular chaperone for tubulin/microtubules. Fluorescence recovery after photobleaching (FRAP) analysis revealed that the striated patterns of GFP-αB-crystallin fluorescence recovered quickly at 37°C. FRAP mobility assay also showed αB-crystallin to be associated with nocodazole-treated free tubulin dimers but not with taxol-treated microtubules. The interaction of αB-crystallin and free tubulin was further confirmed by immunoprecipitation and microtubule sedimentation assay in the presence of 1-100 μM calcium, which destabilizes microtubules. Förster resonance energy transfer analysis showed that αB-crystallin and tubulin were at 1-10 nm apart from each other in the presence of colchicine. These results suggested that αB-crystallin may play an essential role in microtubule dynamics by maintaining free tubulin in striated muscles, such as the soleus or cardiac muscles.

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.

Modulation of Protein Quality Control and Proteasome to Autophagy Switch in Immortalized Myoblasts from Duchenne Muscular Dystrophy Patients

The maintenance of proteome integrity is of primary importance in post-mitotic tissues such as muscle cells; thus, protein quality control mechanisms must be carefully regulated to ensure their optimal efficiency, a failure of these processes being associated with various muscular disorders. Duchenne muscular dystrophy (DMD) is one of the most common and severe forms of muscular dystrophies and is caused by mutations in the dystrophin gene. Protein quality control modulations have been diversely observed in degenerating muscles of patients suffering from DMD or in animal models of the disease. In this study, we investigated whether modulations of protein quality control mechanisms already pre-exist in undifferentiated myoblasts originating from DMD patients. We report for the first time that the absence of dystrophin in human myoblasts is associated with protein aggregation stress characterized by an increase of protein aggregates. This stress is combined with BAG1 to BAG3 switch, NFκB activation and up-regulation of BAG3/HSPB8 complexes that ensure preferential routing of misfolded/aggregated proteins to autophagy rather than to deficient 26S proteasome. In this context, restoration of pre-existing alterations of protein quality control processes might represent an alternative strategy for DMD therapies.

Muscle plasticity related to changes in tubulin and αB-crystallin levels induced by eccentric contraction in rat skeletal muscles

We used the model of eccentric contraction of the hindlimb muscle by Ochi et al. to examine the role of eccentric contraction in muscle plasticity. This model aims to focus on stimulated skeletal muscle responses by measuring tissue weights and tracing the quantities of αB-crystallin and tubulin. The medial gastrocnemius muscle (GCM) responded to electrically induced eccentric contraction (EIEC) with significant increases in tissue weight (p < 0.01) and the ratio of tissue weight to body weight (p < 0.05); however, there was a decrease in soleus muscle weight after EIEC. EIEC in the GCM caused contractile-induced sustenance of the traced proteins, but the soleus muscle exhibited a remarkable decrease in α-tubulin and a 19% decrease in αB-crystallin. EIEC caused fast-to-slow myosin heavy chain (MHC) isoform type-oriented shift within both the GCM and soleus muscle. These results have shown that different MHC isoform type-expressing slow and fast muscles commonly undergo fast-to-slow type MHC isoform transformation. This suggests that different levels of EIEC affected each of the slow and fast muscles to induce different quantitative changes in the expression of αB-crystallin and α-tubulin.

Small Heat Shock Protein αB-Crystallin Controls Shape and Adhesion of Glioma and Myoblast Cells in the Absence of Stress

Cell shape and adhesion and their proper controls are fundamental for all biological systems. Mesenchymal cells migrate at an average rate of 6 to 60 μm/hr, depending on the extracellular matrix environment and cell signaling. Myotubes, fully differentiated muscle cells, are specialized for power-generation and therefore lose motility. Cell spreading and stabilities of focal adhesion are regulated by the critical protein vinculin from immature myoblast to mature costamere of differentiated myotubes where myofibril Z-band linked to sarcolemma. The Z-band is constituted from microtubules, intermediate filaments, cell adhesion molecules and other adapter proteins that communicate with the outer environment. Mesenchymal cells, including myoblast cells, convert actomyosin contraction forces to tension through mechano-responsive adhesion assembly complexes as Z-band equivalents. There is growing evidence that microtubule dynamics are involved in the generation of contractile forces; however, the roles of microtubules in cell adhesion dynamics are not well determined. Here, we show for the first time that αB-crystallin, a molecular chaperon for tubulin/microtubules, is involved in cell shape determination. Moreover, knockdown of this molecule caused myoblasts and glioma cells to lose their ability for adhesion as they tended to behave like migratory cells. Surprisingly, αB-crystallin knockdown in both C6 glial cells and L6 myoblast permitted cells to migrate more rapidly (2.7 times faster for C6 and 1.3 times faster for L6 cells) than dermal fibroblast. On the other hand, overexpression of αB-crystallin in cells led to an immortal phenotype because of persistent adhesion. Position of matured focal adhesion as visualized by vinculin immuno-staining, stress fiber direction, length, and density were clearly αB-crystallin dependent. These results indicate that the small HSP αB-crystallin has important roles for cell adhesion, and thus microtubule dynamics are necessary for persistent adhesion.

Selective and compartmentalized myelin expression of HspB5

In the present study, we reveal myelin-specific expression and targeting of mRNA and biochemical pools of HspB5 in the mouse CNS. Our observations are based on in situ hybridization, electron microscopy and co-localization with 2',3'-Cyclic-Nucleotide 3'-Phosphodiesterase (CNPase), reinforcing this myelin-selective expression. HspB5 mRNA might be targeted to these structures based on its presence in discrete clusters resembling RNA granules and the presence of a putative RNA transport signal. Further, sub-cellular fractionation of myelin membranes reveals a distinct sub-compartment-specific association and detergent solubility of HspB5. This is akin to other abundant myelin proteins and is consistent with HspB5's association with cytoskeletal/membrane assemblies. Oligodendrocytes have a pivotal role in supporting axonal function via generating and segregating the ensheathing myelin. This specialization places extreme structural and metabolic demands on this glial cell type. Our observations place HspB5 in oligodendrocytes which may require selective and specific chaperone capabilities to maintain normal function and neuronal support.

BILBO1 is a scaffold protein of the flagellar pocket collar in the pathogen Trypanosoma brucei

The flagellar pocket (FP) of the pathogen Trypanosoma brucei is an important single copy structure that is formed by the invagination of the pellicular membrane. It is the unique site of endo- and exocytosis and is required for parasite pathogenicity. The FP consists of distinct structural sub-domains with the least explored being the annulus/horseshoe shaped flagellar pocket collar (FPC). To date the only known component of the FPC is the protein BILBO1, a cytoskeleton protein that has a N-terminus that contains an ubiquitin-like fold, two EF-hand domains, plus a large C-terminal coiled-coil domain. BILBO1 has been shown to bind calcium, but in this work we demonstrate that mutating either or both calcium-binding domains prevents calcium binding. The expression of deletion or mutated forms of BILBO1 in trypanosomes and mammalian cells demonstrate that the coiled-coil domain is necessary and sufficient for the formation of BILBO1 polymers. This is supported by Yeast two-hybrid analysis. Expression of full-length BILBO1 in mammalian cells induces the formation of linear polymers with comma and globular shaped termini, whereas mutation of the canonical calcium-binding domain resulted in the formation of helical polymers and mutation in both EF-hand domains prevented the formation of linear polymers. We also demonstrate that in T. brucei the coiled-coil domain is able to target BILBO1 to the FPC and to form polymers whilst the EF-hand domains influence polymers shape. This data indicates that BILBO1 has intrinsic polymer forming properties and that binding calcium can modulate the form of these polymers. We discuss whether these properties can influence the formation of the FPC.

Trypanosoma brucei avoids destruction by, in part, changing its surface glycoprotein coat, which is trafficked onto the cell surface via an invagination of the cell surface called the flagellar pocket. The pocket is essential for pathogenicity. The distal membrane of the pocket is anchored to a cytoskeleton structure called the flagellar pocket collar (FPC). The FPC is a ring/horseshoe shaped structure, which itself is attached to the single copy flagellum of the parasite. How the “ring” shape of the collar is formed is not understood. Moreover, the only known protein component of the FPC is the protein BILBO1. BILBO1 is modular and has a distinct N-terminal domain, two EF-hand calcium-binding domains and a large C-terminal coiled-coil domain. Here we demonstrate that mutating the EF hand domains prevent calcium binding and that the coiled-coil domain is not only sufficient to target to the collar, but can also form polymers in mammalian cells. Mutating either or both calcium-binding domains of BILBO1 influences polymer formation and type when expressed in mammalian and trypanosome cells. Our premise is that BILBO1 has intrinsic polymer forming properties that are essential for the flagellar pocket collar making the pocket a target for intervention.

Gravitational Effects on Human Physiology

Physical working capacity decreases with age and also in microgravity. Regardless of age, increased physical activity can always improve the physical adaptability of the body, although the mechanisms of this adaptability are unknown. Physical exercise produces various mechanical stimuli in the body, and these stimuli may be essential for cell survival in organisms. The cytoskeleton plays an important role in maintaining cell shape and tension development, and in various molecular and/or cellular organelles involved in cellular trafficking. Both intra and extracellular stimuli send signals through the cytoskeleton to the nucleus and modulate gene expression via an intrinsic property, namely the "dynamic instability" of cytoskeletal proteins. αB-crystallin is an important chaperone for cytoskeletal proteins in muscle cells. Decreases in the levels of αB-crystallin are specifically associated with a marked decrease in muscle mass (atrophy) in a rat hindlimb suspension model that mimics muscle and bone atrophy that occurs in space and increases with passive stretch. Moreover, immunofluorescence data show complete co-localization of αB-crystallin and the tubulin/microtubule system in myoblast cells. This association was further confirmed in biochemical experiments carried out in vitro showing that αB-crystallin acts as a chaperone for heat-denatured tubulin and prevents microtubule disassembly induced by calcium. Physical activity induces the constitutive expression of αB-crystallin, which helps to maintain the homeostasis of cytoskeleton dynamics in response to gravitational forces. This relationship between chaperone expression levels and regulation of cytoskeletal dynamics observed in slow anti-gravitational muscles as well as in mammalian striated muscles, such as those in the heart, diaphragm and tongue, may have been especially essential for human evolution in particular. Elucidation of the intrinsic properties of the tubulin/microtubule and chaperone αB-crystallin protein complex systems is expected to provide valuable information for high-pressure bioscience and gravity health science.

Small heat shock proteins: Role in cellular functions and pathology

Small heat shock proteins (sHsps) are conserved across species and are important in stress tolerance. Many sHsps exhibit chaperone-like activity in preventing aggregation of target proteins, keeping them in a folding-competent state and refolding them by themselves or in concert with other ATP-dependent chaperones. Mutations in human sHsps result in myopathies, neuropathies and cataract. Their expression is modulated in diseases such as Alzheimer's, Parkinson's and cancer. Their ability to bind Cu2+, and suppress generation of reactive oxygen species (ROS) may have implications in Cu2+-homeostasis and neurodegenerative diseases. Circulating αB-crystallin and Hsp27 in the plasma may exhibit immunomodulatory and anti-inflammatory functions. αB-crystallin and Hsp20 exhitbit anti-platelet aggregation: these beneficial effects indicate their use as potential therapeutic agents. sHsps have roles in differentiation, proteasomal degradation, autophagy and development. sHsps exhibit a robust anti-apoptotic property, involving several stages of mitochondrial-mediated, extrinsic apoptotic as well as pro-survival pathways. Dynamic N- and C-termini and oligomeric assemblies of αB-crystallin and Hsp27 are important factors for their functions. We propose a "dynamic partitioning hypothesis" for the promiscuous interactions and pleotropic functions exhibited by sHsps. Stress tolerance and anti-apoptotic properties of sHsps have both beneficial and deleterious consequences in human health and diseases. Conditional and targeted modulation of their expression and/or activity could be used as strategies in treating several human disorders. The review attempts to provide a critical overview of sHsps and their divergent roles in cellular processes particularly in the context of human health and disease.

α-B-Crystallin as a Tissue Marker of Epileptic Foci in Paediatric Resections

Background:

We studied α-B-crystallin, a small heat shock chaperone protein upregulated by various “stresses”, as an immunocytochemical tissue marker of epileptic foci.

Methods:

We examined 45 resected brain tissues of epileptic patients, 16 months to 23 years. Postmortem brains of 2 epileptic children and 20 normal fetuses and neonates of 10-41 weeks gestation similarly were studied. Immunocytochemical demonstration of α-B-crystallin was supplemented by neuronal, glial and inflammatory cell markers and electron microscopy (EM) in surgical cases. Autopsy brain tissue of children without epilepsy or neurological disease served as controls.

Results:

In all resections, α-B-crystallin was overexpressed in astrocytes and oligodendrocytes, including satellite cells adherent to neurons, and occasionally in neurons of neocortex, hippocampus and amygdala. In six cases, reactivity was most intense at or near the epileptic focus, with a diminishing gradient of intensity for 2-3 cm; similar focal expression was seen in autopsy cases. Presence or absence of histological structural lesions was independent of α-B-crystallin expression. Balloon cells and giant atypical cells in tuberous sclerosis were intensely reactive. Reactivity was present in DNETs. No correlation occurred with microglial activation, inflammation or gliosis; no ultrastructural alterations were seen. No expression was seen in fetal brains at any age.

Conclusions:

Immunoreactive α-B-crystallin is a reliable tissue marker of epileptic foci, regardless of presence or absence of structural lesions; at times it maps the extent of a focus.

Microtubules and their role in cellular stress in cancer

Microtubules are highly dynamic structures, which consist of α- and β-tubulin heterodimers, and are involved in cell movement, intracellular trafficking, and mitosis. In the context of cancer, the tubulin family of proteins is recognized as the target of the tubulin-binding chemotherapeutics, which suppress the dynamics of the mitotic spindle to cause mitotic arrest and cell death. Importantly, changes in microtubule stability and the expression of different tubulin isotypes as well as altered post-translational modifications have been reported for a range of cancers. These changes have been correlated with poor prognosis and chemotherapy resistance in solid and hematological cancers. However, the mechanisms underlying these observations have remained poorly understood. Emerging evidence suggests that tubulins and microtubule-associated proteins may play a role in a range of cellular stress responses, thus conferring survival advantage to cancer cells. This review will focus on the importance of the microtubule-protein network in regulating critical cellular processes in response to stress. Understanding the role of microtubules in this context may offer novel therapeutic approaches for the treatment of cancer.

Changes in αB-crystallin, tubulin, and MHC isoforms by hindlimb unloading show different expression patterns in various hindlimb muscles

[Purpose]

αB-crystallin is a small heat shock protein that acts as a molecular chaperone under various stress conditions. Microtubules, which consist of tubulin, are related to maintain the intracellular organelles and cellular morphology. These two proteins have been shown to be related to the properties of different types of myofibers based on their contractile properties. The response of these proteins during muscular atrophy, which induces a myofibril component change, is not clearly understood.

[Methods]

We performed 15 days of hindlimb unloading on rats to investigate the transitions of these proteins by analyzing their absolute quantities. Protein contents were analyzed in the soleus, plantaris, and gastrocnemius muscles of the unloading and control groups (N = 6).

[Results]

All three muscles were significantly atrophied by hindlimb unloading (P < 0.01): soleus (47.5%), plantaris (16.3%), and gastrocnemius (21.3%) compared to each control group. αB-crystallin was significantly reduced in all three examined unloaded hindlimb muscles compared to controls (P < 0.01) during the transition of the myosin heavy chain to fast twitch muscles. α-Tubulin responded only in the unloaded soleus muscle. Muscle atrophy induced the reduction of αB-crystallin and α-tubulin expressions in plantar flexor muscles with a shift to the fast muscle fiber compared to the control.

[Conclusion]

The novel finding of this study is that both proteins, αB-crystallin and α-tubulin, were downregulated in slow muscles (P < 0.01); However, α-tubulin was not significantly reduced compared to the control in fast muscles (P < 0.01).

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 proteins are necessary for heart migration and laterality determination in zebrafish

Small heat shock proteins (sHsps) regulate cellular functions not only under stress, but also during normal development, when they are expressed in organ-specific patterns. Here we demonstrate that two small heat shock proteins expressed in embryonic zebrafish heart, hspb7 and hspb12, have roles in the development of left-right asymmetry. In zebrafish, laterality is determined by the motility of cilia in Kupffer's vesicle (KV), where hspb7 is expressed; knockdown of hspb7 causes laterality defects by disrupting the motility of these cilia. In embryos with reduced hspb7, the axonemes of KV cilia have a 9+0 structure, while control embyros have a predominately 9+2 structure. Reduction of either hspb7 or hspb12 alters the expression pattern of genes that propagate the signals that establish left-right asymmetry: the nodal-related gene southpaw (spaw) in the lateral plate mesoderm, and its downstream targets pitx2, lefty1 and lefty2. Partial depletion of hspb7 causes concordant heart, brain and visceral laterality defects, indicating that loss of KV cilia motility leads to coordinated but randomized laterality. Reducing hspb12 leads to similar alterations in the expression of downstream laterality genes, but at a lower penetrance. Simultaneous reduction of hspb7 and hspb12 randomizes heart, brain and visceral laterality, suggesting that these two genes have partially redundant functions in the establishment of left-right asymmetry. In addition, both hspb7 and hspb12 are expressed in the precardiac mesoderm and in the yolk syncytial layer, which supports the migration and fusion of mesodermal cardiac precursors. In embryos in which the reduction of hspb7 or hspb12 was limited to the yolk, migration defects predominated, suggesting that the yolk expression of these genes rather than heart expression is responsible for the migration defects.

Study of αB-crystallin expression in Gerbil BCAO model of transient global cerebral ischemia

αB-crystallin (α-BC), the fifth member of mammalian small heat shock protein family (HspB5), is known to be expressed in many tissues and has a distinctive interaction with cytoskeleton components. In this study, we investigated that α-BC and microtubule-associated protein-2 (MAP-2), a neuron-specific cytoskeleton protein, were coexpressed in neurons of Gerbil cortex, while in subcortex Gerbil brains, we found that several MAP-2-negative glia cells also express α-BC. When subjected to 10-minute bilateral carotid artery occlusion (BCAO), an increment was observed in α-BC-positive cells after 6-hour reperfusion and peaked at around 7 days after. In the same circumstances, the number and the staining concentration of MAP-2 positive neurons significantly decreased immediately after 6-hour reperfusion, followed by a slow recovery, which is consistent with the increase of α-BC. Our results suggested that α-BC plays an important role in brain ischemia, providing the early protection of neurons by giving intracellular supports through the maintenance of cytoskeleton and extracellular supports through the protection of glia cells.

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.

Alteration of protein folding and degradation in motor neuron diseases: Implications and protective functions of small heat shock proteins

Motor neuron diseases (MNDs) are neurodegenerative disorders that specifically affect the survival and function of upper and/or lower motor neurons. Since motor neurons are responsible for the control of voluntary muscular movement, MNDs are characterized by muscle spasticity, weakness and atrophy. Different susceptibility genes associated with an increased risk to develop MNDs have been reported and several mutated genes have been linked to hereditary forms of MNDs. However, most cases of MNDs occur in sporadic forms and very little is known on their causes. Interestingly, several molecular mechanisms seem to participate in the progression of both the inherited and sporadic forms of MNDs. These include cytoskeleton organization, mitochondrial functions, DNA repair and RNA synthesis/processing, vesicle trafficking, endolysosomal trafficking and fusion, as well as protein folding and protein degradation. In particular, accumulation of aggregate-prone proteins is a hallmark of MNDs, suggesting that the protein quality control system (molecular chaperones and the degradative systems: ubiquitin-proteasome-system and autophagy) are saturated or not sufficient to allow the clearance of these altered proteins. In this review we mainly focus on the MNDs associated with disturbances in protein folding and protein degradation and on the potential implication of a specific class of molecular chaperones, the small heat shock proteins (sHSPs/HSPBs), in motor neuron function and survival. How boosting of specific HSPBs may be a potential useful therapeutic approach in MNDs and how mutations in specific HSPBs can directly cause motor neuron degeneration is discussed.

Dynamic subunit exchange and the regulation of microtubule assembly by the stress response protein human alphaB crystallin

Background

The small heat shock protein (sHSP), human αB crystallin, forms large, polydisperse complexes that modulate the tubulin-microtubule equilibrium using a dynamic mechanism that is poorly understood. The interactive sequences in αB crystallin for tubulin are surface exposed, and correspond to interactive sites for the formation of αB crystallin complexes.

Methodology/Principal Findings

There is sequence homology between tubulin and the interactive domains in the β8-strand of the core domain and the C-terminal extension of αB crystallin. This study investigated the hypothesis that the formation of tubulin and αB crystallin quaternary structures was regulated through common interactive domains that alter the dynamics of their assembly. Size exclusion chromatography (SEC), SDS-PAGE, microtubule assembly assays, aggregation assays, multiple sequence alignment, and molecular modeling characterized the dynamic response of tubulin assembly to increasing concentrations of αB crystallin. Low molar ratios of αB crystallin∶tubulin were favorable for microtubule assembly and high molar ratios of αB crystallin∶tubulin were unfavorable for microtubule assembly. Interactions between αB crystallin and unassembled tubulin were observed using SEC and SDS-PAGE.

Conclusions/Significance

Subunits of αB crystallin that exchange dynamically with the αB crystallin complex can interact with tubulin subunits to regulate the equilibrium between tubulin and microtubules.

The interaction of alphaB-crystallin with mature alpha-synuclein amyloid fibrils inhibits their elongation

αB-Crystallin is a small heat-shock protein (sHsp) that is colocalized with α-synuclein (αSyn) in Lewy bodies—the pathological hallmarks of Parkinson's disease—and is an inhibitor of αSyn amyloid fibril formation in an ATP-independent manner in vitro. We have investigated the mechanism underlying the inhibitory action of sHsps, and here we establish, by means of a variety of biophysical techniques including immunogold labeling and nuclear magnetic resonance spectroscopy, that αB-crystallin interacts with αSyn, binding along the length of mature amyloid fibrils. By measurement of seeded fibril elongation kinetics, both in solution and on a surface using a quartz crystal microbalance, this binding is shown to strongly inhibit further growth of the fibrils. The binding is also demonstrated to shift the monomer-fibril equilibrium in favor of dissociation. We believe that this mechanism, by which a sHsp interacts with mature amyloid fibrils, could represent an additional and potentially generic means by which at least some chaperones protect against amyloid aggregation and limit the onset of misfolding diseases.

Comparative proteomic profile of rat sciatic nerve and gastrocnemius muscle tissues in ageing by 2-D DIGE

Ageing induces a progressive morphological change and functional decline in muscles and in nerves. Light and electron microscopy, 2-D DIGE and MS, were applied to profile the qualitative and quantitative differences in the proteome and morphology of rat gastrocnemius muscle and sciatic nerve, in healthy 22-month-old rats. At muscle level, morphological changes are associated to fibre atrophy accompanied by myofibrillar loss and degeneration, disappearance of sarcomeres and sarcoplasmic reticulum dilatation, internal migration of nuclei, longitudinal fibre splitting, increment of subsarcolemmal mitochondria aggregates and increment of lipofuscin granules. Sciatic nerve shows myelin abnormalities like enfoldings, invaginations, onion bulbs, breakdowns and side axonal atrophy. Proteomic analysis identified changes correlated to morphological abnormalities in metabolic, contractile and cytoskeletal proteins, deregulation of iron homeostasis, change of Ca(2+) balance and stress response proteins, accompanied by a deregulation of myelin membrane adhesion protein and proteins regulating the neuronal caliber. By comparing proteomic results from the two tissues, 16 protein isoforms showed the same up and down regulation trend suggesting that there are changes implying a general process which may act as a signal event of degeneration. Only beta enolase and tropomyosin 1alpha were differentially expressed in the tissues.

Proteomic analysis of microtubule-associated proteins during macrophage activation

Classical activation of macrophages induces a wide range of signaling and vesicle trafficking events to produce a more aggressive cellular phenotype. The microtubule (MT) cytoskeleton is crucial for the regulation of immune responses. In the current study, we used a large scale proteomics approach to analyze the change in protein composition of the MT-associated protein (MAP) network by macrophage stimulation with the inflammatory cytokine interferon-gamma and the endotoxin lipopolysaccharide. Overall the analysis identified 409 proteins that bound directly or indirectly to MTs. Of these, 52 were up-regulated 2-fold or greater and 42 were down-regulated 2-fold or greater after interferon-gamma/lipopolysaccharide stimulation. Bioinformatics analysis based on publicly available binary protein interaction data produced a putative interaction network of MAPs in activated macrophages. We confirmed the up-regulation of several MAPs by immunoblotting and immunofluorescence analysis. More detailed analysis of one up-regulated protein revealed a role for HSP90beta in stabilization of the MT cytoskeleton during macrophage activation.

Significant roles of microtubules in mature striated muscle deduced from the correlation between tubulin and its molecular chaperone alphaB-crystallin in rat muscles

To elucidate the significance of cytoskeletal microtubule networks in striated muscles, we analyzed correlation between the content of tubulin (building block of microtubules) and alphaB-crystallin (a molecular chaperone for tubulin) in a variety of striated muscles expressing different myosin heavy-chain (MHC) isoforms. The content of both tubulin and alphaB-crystallin was larger in MHC-I dominant soleus muscle and in MHC-alpha dominant cardiac (atrium and ventricle) muscles; intermediate in MHC-IId dominant masseter, tongue, and diaphragm muscles; and smaller in MHC-IIb dominant plantaris, gastrocnemius, psoas, extensor digitorum longus, and tibialis anterior muscles. Since the muscles of slow-type MHC (MHC-I/alpha) show the most economical features in their function and metabolism, which suit for continuous activity required to sustain posture and blood pumping, the present results afforded additional support to our hypothesis that microtubule networks transduce mechanical environmental demands to morphological and biochemical responses that eventually evolve adaptive transformation in the function and metabolism of the mature muscles. The comparison of tubulin/alphaB-crystalline ratios across the muscles of varied MHC isoforms further suggested that mechanical stress fluctuating at the rhythmic frequency of walking and breathing efficiently activates the hypothesized dynamic function of microtubules.

Confocal fluorescence microscopy study of interaction between lens MIP26/AQP0 and crystallins in living cells

MIP26/AQP0 is the major lens fiber membrane protein and has been reported to interact with many other lens components including crystallins, lipid, and cytoskeletal proteins. Regarding crystallins, many previous reports indicate that MIP26/AQP0 interacts with either only alpha-crystallin or some specific gamma-crystallins. Considering the possibly important role of MIP26/AQP0 in the reduction of light scattering in the lenses, we have further investigated its interaction with crystallins using confocal fluorescence resonance energy transfer (FRET) microscopy. Specifically, we used MIP26 tagged with a green fluorescence protein (GFP) as a donor and a crystallin (alphaA-, alphaB-, betaB2-, or gammaC-crystallin) tagged with a red fluorescence protein (RFP) as an acceptor. The two plasmids were cotransfected to HeLa cells. After culture, laser scattering microscopy images were taken in each of the three channels: GFP, RFP, and FRET. The net FRET images were then obtained by removing the contribution of spectral bleed-through. The pixels of net FRET were normalized with those of GFP. The results show the presence of measurable interactions between MIP26 and all crystallins, with the extent of interactions decreasing from alphaA- and alphaB-crystallin to betaB2- and gammaC-crystallin. Competitive interaction study using untagged alphaA-crystallin shows decreased net FRET, indicating specificity of the interactions between MIP26 and alphaA-crystallin. We conclude that all crystallins interact with MIP26, the physiological significance of which may be a reduction in the difference of refractive index between membrane and cytoplasm.

Small heat shock proteins Hsp27 or alphaB-crystallin and the protein components of neurofibrillary tangles: tau and neurofilaments

The heat-shock proteins (HSPs) Hsp27 and alphaB-crystallin are up-regulated in Alzheimer's disease (AD), but the extent of this and the consequences are still largely unknown. The HSPs are involved in protein degradation and protection against protein aggregation, and they interact with several cytoskeletal components such as microtubules (MT) and neurofilaments (NF). AD pathology includes aggregated proteins (tau, NF), decreased protein degradation, and cytoskeletal disruption. It is thus of interest to investigate more closely the possible roles of the HSPs in AD pathology. The expressions of Hsp27 and alphaB-crystallin in AD brain samples were significantly increased (by approximately 20% and approximately 30%, respectively) and correlated significantly with phosphorylated tau and NF proteins. To investigate the consequences of increased HSP levels on tau and NF regulation, N2a cells were transfected with Hsp27 or alphaB-crystallin constructs, and overexpression of the HSPs was confirmed in the cells. Increased tau phosphorylation at the Ser262 site in the N2a cells was regulated by Hsp27 overexpression (possibly through p70S6k), whereas the overexpression of alphaB-crystallin resulted in decreased levels of phosphorylated tau, NF, and GSK-3beta. It was also shown that overexpression of HSPs causes an increase in the percentage of cells present in the G(1) phase. The results presented suggest that a cellular defense against dysregulated proteins, in the form of Hsp27 and alphaB-crystallin, might contribute to the cell cycle reentry seen in AD cells. Furthermore, Hsp27 might also be involved in AD pathology by aggravating MT disruption by tau phosphorylation.

Effect of thermal stress on early and late passaged mouse lens epithelial cells

Cataract is an age related disease of protein aggregation. It has been suggested that aging affects the cells ability to protect protein integrity. The protein integrity, which is essential for cellular homeostasis, is maintained by a complex system of refolding or degradation of damaged proteins. The heat shock proteins (hsps) are the major contributors in the maintenance of protein integrity. The heat shock transcription factor (HSF-1) is the master regulator of all hsp synthesis in response to stress. This investigation examined the role of HSF-1 in the regulation of hsp synthesis in early and late passaged alphaTN-4 cells. Data collected in this study revealed that the nucleotide sequence of HSF-1 mRNA obtained from early and late passaged alphaTN-4 cells were identical. When early and late passaged cell were exposed to thermal stress, their hsp expression were also similar. HSP-40 expression was detected after 2 h of heat stress, whereas HSP-70 and low molecular weight heat shock protein alphabeta crystallin showed significantly increased synthesis 18 h post heat stress. The late passaged alphaTN-4 cells ability to upregulate hsps in response to heat stress could be due to its high replicative activities. The data presented here suggests a relationship between the presence of functional HSF-1 and sustained proliferative activities of the late passaged alphaTN-4 cell.

Analysis of the alphaB-crystallin domain responsible for inhibiting tubulin aggregation

The cytoskeleton has a unique property such that changes of conformation result in polymerization into a filamentous form. alphaB-Crystallin, a small heat shock protein (sHsp), has chaperone activities for various substrates, including proteins constituting the cytoskeleton, such as actin; intermediate filament; and tubulin. However, it is not clear whether the "alpha-crystallin domain" common to sHsps also has chaperone activity for the protein cytoskeleton. To investigate the possibility that the C-terminal alpha-crystallin domain of alpha-crystallin has the aggregation-preventing ability for tubulin, we constructed an N-terminal domain deletion mutant of alphaB-crystallin. We characterized its structural properties and chaperone activities. Far-ultraviolet (UV) circular dichroism measurements showed that secondary structure in the alpha-crystallin domain of the deletion mutant is maintained. Ultracentrifuge analysis of molecular masses indicated that the deletion mutant formed smaller oligomers than did the full-length protein. Chaperone activity assays demonstrated that the N-terminal domain deletion mutant suppressed heat-induced aggregation of tubulin well. Comparison of chaperone activities for 2 other substrates (citrate synthase and alcohol dehydrogenase) showed that it was less effective in the suppression of their aggregation. These results show that alphaB-crystallin recognizes a variety of substrates and especially that alpha-crystallin domain binds free cytoskeletal proteins. We suggest that this feature would be advantageous in its functional role of holding or folding multiple proteins denatured simultaneously under stress conditions.

Interactive domains in the molecular chaperone human alphaB crystallin modulate microtubule assembly and disassembly

Background

Small heat shock proteins regulate microtubule assembly during cell proliferation and in response to stress through interactions that are poorly understood.

Methodology

Novel functions for five interactive sequences in the small heat shock protein and molecular chaperone, human αB crystallin, were investigated in the assembly/disassembly of microtubules and aggregation of tubulin using synthetic peptides and mutants of human αB crystallin.

Principal Findings

The interactive sequence ₁₁₃FISREFHR₁₂₀ exposed on the surface of αB crystallin decreased microtubule assembly by ∼45%. In contrast, the interactive sequences, ₁₃₁LTITSSLSSDGV₁₄₂ and ₁₅₆ERTIPITRE₁₆₄, corresponding to the β8 strand and the C-terminal extension respectively, which are involved in complex formation, increased microtubule assembly by ∼34–45%. The αB crystallin peptides, ₁₁₃FISREFHR₁₂₀ and ₁₅₆ERTIPITRE₁₆₄, inhibited microtubule disassembly by ∼26–36%, and the peptides ₁₁₃FISREFHR₁₂₀ and ₁₃₁LTITSSLSSDGV₁₄₂ decreased the thermal aggregation of tubulin by ∼42–44%. The ₁₃₁LTITSSLSSDGV₁₄₂ and ₁₅₆ERTIPITRE₁₆₄ peptides were more effective than the widely used anti-cancer drug, Paclitaxel, in modulating tubulin↔microtubule dynamics. Mutagenesis of these interactive sequences in wt human αB crystallin confirmed the effects of the αB crystallin peptides on microtubule assembly/disassembly and tubulin aggregation. The regulation of microtubule assembly by αB crystallin varied over a narrow range of concentrations. The assembly of microtubules was maximal at αB crystallin to tubulin molar ratios between 1∶4 and 2∶1, while molar ratios >2∶1 inhibited microtubule assembly.

Conclusions and Significance

Interactive sequences on the surface of human αB crystallin collectively modulate microtubule assembly through a dynamic subunit exchange mechanism that depends on the concentration and ratio of αB crystallin to tubulin. These are the first experimental results in support of the functional importance of the dynamic subunit model of small heat shock proteins.

Age-Related Increase of Insoluble, Phosphorylated Small Heat Shock Proteins in Human Skeletal Muscle

Among mammalian heat shock proteins (Hsps), small Hsps (sHsps) are constitutively expressed in skeletal muscles. We investigated age-related changes of phosphorylation and cellular distribution of representative sHsps (Hsp27 and alphaB-crystallin) in human vastus lateralis muscle under resting conditions. We also examined upstream kinases which may be responsible for phosphorylation of sHsps, namely p38 mitogen-activated protein kinase (MAPK), MAPK-activated protein kinase-2, and extracellular signal-regulated kinase-1/2. The study groups consisted of nine young (15-38 years old) and nine aged (51-79 years old) patients who underwent orthopedic surgery. sHsps protein levels were higher in the insoluble fraction of aged muscles. The phosphorylated states of sHsps were enhanced in both the soluble and insoluble fraction of aged patients. The phosphorylated form of each upstream kinase was elevated in aged patients. Ubiquitinated proteins accumulated in the insoluble fractions of aged muscles. Aging mechanisms may affect the activation process of MAPKs, and the phosphorylation and accumulation of sHsps.

Differences in expression of retinal proteins between diabetic and normal rats

AIM: To compare and identify the differences in expression of retinal proteins between normal and diabetic rats, and to analyze the molecular pathogenetic mechanisms of retinal diseases caused by diabetes.

METHODS: Changes in protein expression of retinal tissues from diabetic and normal rats were observed using 2-dimensional polyacrylamide gel electrophoresis (2-DE). Some protein spots exhibiting statistically significant variations (P < 0.05) were selected randomly and identified by tandem mass spectrometry and analyzed by bioinformatics.

RESULTS: 2-DE showed that the expression was up-regulated in 5 retinal proteins, down-regulated in 23 retinal proteins, and disappeared in 8 retinal proteins. Eight spots were identified from the 36 spots by tandem mass spectrometry (MS/MS) and analyzed by bioinformatics. Guanylate kinase 1, triosephosphate isomerase 1, ATP synthase subunit d, albumin and dimethylarginine dimethylaminohydrolase 2 played an important role in signal transduction. Triosephosphate isomerase 1, crystallin alpha B, ATP synthase subunit d and peroxiredoxin 6 were involved in energy metabolism of retinal tissues. Guanylate kinase 1 played an important role in photoexcitation of retinal rod photoreceptor cells. Whether crystallin beta A1 plays a role in diabetic retinas is unknown so far.

CONCLUSION: There are differences in expression of retinal proteins between diabetic and normal rats. These proteins may be involved in the mechanisms and prognosis of retinal diseases caused by diabetes.

Crystallins in the eye: Function and pathology

Crystallins are the predominant structural proteins in the lens that are evolutionarily related to stress proteins. They were first discovered outside the vertebrate eye lens by Bhat and colleagues in 1989 who found alphaB-crystallin expression in the retina, heart, skeletal muscles, skin, brain and other tissues. With the advent of microarray and proteome analysis, there is a clearer demonstration that crystallins are prominent proteins both in the normal retina and in retinal pathologies, emphasizing the importance of understanding crystallin functions outside of the lens. There are two main crystallin gene families: alpha-crystallins, and betagamma-crystallins. alpha-crystallins are molecular chaperones that prevent aberrant protein interactions. The chaperone properties of alpha-crystallin are thought to allow the lens to tolerate aging-induced deterioration of the lens proteins without showing signs of cataracts until older age. alpha-crystallins not only possess chaperone-like activity in vitro, but can also remodel and protect the cytoskeleton, inhibit apoptosis, and enhance the resistance of cells to stress. Recent advances in the field of structure-function relationships of alpha-crystallins have provided the first clues to their underlying roles in tissues outside the lens. Proteins of the betagamma-crystallin family have been suggested to affect lens development, and are also expressed in tissues outside the lens. The goal of this paper is to highlight recent work with lens epithelial cells from alphaA- and alphaB-crystallin knockout mice. The use of lens epithelial cells suggests that crystallins have important cellular functions in the lens epithelium and not just the lens fiber cells as previously thought. These studies may be directly relevant to understanding the general cellular functions of crystallins.

The molecular chaperone HSP47 rapidly senses gravitational changes in myoblasts

Skeletal muscle unloading induced by spaceflight or bed rest leads to muscle atrophy. It is unclear how muscle atrophy is caused and how muscles respond to microgravity. We addressed the response of collagen and its chaperone system to gravitational forces. We show here that expression of HSP47, a collagen-specific molecular chaperone, responds to gravitational changes, including microgravity and hypergravity in vitro and in vivo. By using the method hindlimb suspension of rats, which mimics microgravity conditions, we demonstrated that the expression of Hsp47 mRNA decreased within 1 day and the mRNA levels of collagen types I and IV were subsequently reduced. In contrast, hypergravity stimulated HSP47 expression. HSP47 and collagen types I and IV were localized intracellularly in the endoplasmic reticulum and/or Golgi apparatus of myoblasts, as expected. Intriguingly, Hsp47 mRNA levels in cultured myoblasts increased significantly with hypergravity treatment at 40G for 2 h, and decreased with microgravity treatment at almost 0G for 1-2 h. Collagen mRNA levels were also altered, although changes were slower and less pronounced compared with those for HSP47. The gravity-regulated HSP47 may play a role in the maintenance of the extracellular matrix by modulating collagen production at the primary stage of adaptation.

Thermally induced and developmentally regulated expression of a small heat shock protein in Trichinella spiralis

A cDNA encoding a small heat shock protein of Trichinella spiralis, Ts-sHsp, was cloned and expressed and is herein characterized. This cDNA encoded a predicted protein of 165 amino acids, which had a high sequence identity in alpha crystallin domain with various small heat shock proteins of other organisms. A Western blot analysis indicated that anti-Ts-sHsp recombinant antibody recognized the protein of adults and larvae migrating at about 19 kDa. An in situ localization study showed the protein to be abundantly present in the body wall muscle cells, hypodermis, stichocytes, and esophagus of muscle larvae. The Ts-sHsp recombinant protein possessed chaperone activity to suppress the thermally-induced aggregation of citrate synthase. This sHsp was expressed at various developmental stages of T. spiralis, but at different levels. A high level was observed in mature muscle larvae (infective larvae), which was much higher than the levels seen in adults, newborn larvae, or immature muscle larvae. The expression of the sHsp gene was thermal inducible, thus responding to both cold (0 degrees C) and heat shock (43 degrees C) stress; however, at different patterns. The expression of Ts-sHsp increased gradually from 3 to 72 h after cold stress, while the expression was elevated to its highest after 3 h heat stress and then decreased. These results suggest that this small heat shock protein likely plays a role in the tolerance to both chemical and physical stresses, thereby enhancing the survival ability of Trichinella muscle larvae.

Association of αB-Crystallin, a Small Heat Shock Protein, with Actin: Role in Modulating Actin Filament Dynamics in Vivo

Disruption of cytoskeletal assembly is one of the early effects of any stress that can ultimately lead to cell death. Stabilization of cytoskeletal assembly, therefore, is a critical event that regulates cell survival under stress. alphaB-crystallin, a small heat shock protein, has been shown to associate with cytoskeletal proteins under normal and stress conditions. Earlier reports suggest that alphaB-crystallin could prevent stress-induced aggregation of actin in vitro. However, the molecular mechanisms by which alphaB-crystallin stabilizes actin filaments in vivo are not known. Using the H9C2 rat cardiomyoblast cell line as a model system, we show that upon heat stress, alphaB-crystallin preferentially partitions from the soluble cytosolic fraction to the insoluble cytoskeletal protein-rich fraction. Confocal microscopic analysis shows that alphaB-crystallin associates with actin filaments during heat stress and the extent of association increases with time. Further, immunoprecipitation experiments show that alphaB-crystallin interacts directly with actin. Treatment of heat-stressed H9C2 cells with the actin depolymerzing agent, cytochalasin B, failed to disorganize actin. We show that this association of alphaB-crystallin with actin is dependent on its phosphorylation status, as treatment of cells with MAPK inhibitors SB202190 or PD98059 results in abrogation of this association. Our results indicate that alphaB-crystallin regulates actin filament dynamics in vivo and protects cells from stress-induced death. Further, our studies suggest that the association of alphaB-crystallin with actin helps maintenance of pinocytosis, a physiological function essential for survival of cells.

Chaperone-mediated inhibition of tubulin self-assembly

Molecular chaperones are known to play an important role in facilitating the proper folding of many newly synthesized proteins. Here, we have shown that chaperone proteins exhibit another unique property to inhibit tubulin self-assembly efficiently. Chaperones tested include alpha-crystallin from bovine eye lenses, HSP16.3, HSP70 from Mycobacterium tuberculosis and alpha (s)-casein from milk. All of them inhibit polymerization in a dose-dependent manner independent of assembly inducers used. The critical concentration of MTP polymerization increases with increasing concentration of HSP16.3. Increase in chaperone concentration lowers the extent of polymerization and increases the lag time of self-assembly reaction. Although the addition of a chaperone at the early stage of elongation phase shows no effect on polymerization, the same concentration of chaperone inhibits polymerization completely when added before the initiation of polymerization. Bindings of HSP16.3 and alpha (s)-casein to tubulin have been confirmed using isothermal titration calorimetry. Affinity constants of tubulin are 5.3 xx 10(4) and 9.8 xx 10(5) M(-1) for HSP16.3 and alpha (s)-casein, respectively. Thermodynamic parameters indicate favourable entropy and enthalpy changes for both chaperones-tubulin interactions. Positive entropy change suggests that the interaction is hydrophobic in nature and desolvation occurring during formation of tubulin-chaperone complex. On the basis of thermodynamic data and observations made upon addition of chaperone at early elongation phase or before the initiation of polymerization, we hypothesize that chaperones bind tubulin at the protein-protein interaction site involved in the nucleation phase of self-assembly.

Cell signaling pathways to αB-crystallin following stresses of the cytoskeleton

Small heat shock proteins (sHSPs) act as chaperone, but also in protecting the different cytoskeletal components. Recent results suggest that alphaB-crystallin, a member of sHSPs family, might regulate actin filament dynamics, stabilize them in a phosphorylation dependent manner, and protect the integrity of intermediate filaments (IF) against extracellular stress. We demonstrate that vinblastin and cytochalasin D, which respectively disorganize microtubules and actin microfilaments, trigger the activation of the p38/MAPKAP2 kinase pathway and lead to the specific alphaB-crystallin phosphorylation at serine 59. Upstream of p38, we found that RhoK, PKC and PKA are selectively involved in the activation of p38 and phosphorylation of alphaB-crystallin, depending on the cytoskeletal network disorganized. Moreover, we demonstrate that chronic perturbations of IF network result in the same activation of p38 MAPK and alphaB-crystallin phosphorylation, as with severe disorganization of other cytoskeletal networks. Finally, we also show that Ser 59 phosphorylated alphaB-crystallin colocalizes with cytoskeletal components. Thus, disturbance of cytoskeleton leads by converging signaling pathways to the phosphorylation of alphaB-crystallin, which probably acts as a protective effector of the cytoskeleton.

Aberrantly regulated proteins in frontotemporal dementia

Non-Alzheimer's disease of the frontal type, or frontotemporal dementia (FTD), is the second most common form of dementia. Yet, a detailed characterization of the disease has been especially limiting. To identify mechanisms possibly involved in disease pathology or progression, a proteomic analysis of proteins isolated from human frontal cortex with frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) was performed. We used 2D gel electrophoresis and MALDI-TOF to identify a total of 24 proteins differentially expressed in FTDP-17. We identified a ubiquitin C-terminal hydrolase, UCHL1, as well as several proteins involved in oxidative stress to be differentially expressed. Data presented implicate UCHL1 and ubiquitin-mediated degradation as well as oxidative stress response in disease pathology or progression.

αB-Crystallin Maintains Skeletal Muscle Myosin Enzymatic Activity and Prevents its Aggregation under Heat-shock Stress

Here, we provide functional and direct structural evidence that alphaB-crystallin, a member of the small heat-shock protein family, suppresses thermal unfolding and aggregation of the myosin II molecular motor. Chicken skeletal muscle myosin was thermally unfolded at heat-shock temperature (43 degrees C) in the absence and in the presence of alphaB-crystallin. The ATPase activity of myosin at 25 degrees C was used as a parameter to monitor its unfolding. Myosin retained only 65% and 8% of its ATPase activity when incubated at heat-shock temperature for 15 min and 30 min, respectively. However, 84% and 58% of the myosin ATPase activity was maintained when it was incubated with alphaB-crystallin under the same conditions. Furthermore, actin-stimulated ATPase activity of myosin was reduced by approximately 90%, when myosin was thermally unfolded at 43 degrees C for 30 min, but was reduced by only approximately 42% when it was incubated with alphaB-crystallin under the same conditions. Light-scattering assays and bound thioflavin T fluorescence indicated that myosin aggregates when incubated at 43 degrees C for 30 min, while alphaB-crystallin suppressed this thermal aggregation. Photo-labeled bis-ANS alphaB-crystallin fluorescence studies confirmed the transient interaction of alphaB-crystallin with myosin. These findings were further supported by electron microscopy of rotary shadowed molecules. This revealed that approximately 94% of myosin molecules formed inter and intra-molecular aggregates when incubated at 43 degrees C for 30 min. alphaB-Crystallin, however, protected approximately 48% of the myosin molecules from thermal aggregation, with protected myosin appearing identical to unheated molecules. These results are the first to show that alphaB-crystallin maintains myosin enzymatic activity and prevents the aggregation of the motor under heat-shock conditions. Thus, alphaB-crystallin may be critical for nascent myosin folding, promoting myofibrillogenesis, maintaining cytoskeletal integrity and sustaining muscle performance, since heat-shock temperatures can be produced during multiple stress conditions or vigorous exercise.

Alpha‐crystallin expression affects microtubule assembly and prevents their aggregation

The molecular chaperones alphaA- and alphaB-crystallins are important for cell survival and genomic stability and associate with the tubulin cytoskeleton. The mitotic spindle is abnormally assembled in a number of alphaA-/- and alphaB-/- lens epithelial cells. However, no report to date has studied the effect of alpha-crystallin expression on tubulin/microtubule assembly in lens epithelial cells. In the current work we tested the hypothesis that the absence of alphaA- and alphaB-crystallins alters microtubule assembly. Microtubules were reconstituted from freshly dissected explants of wild-type, alphaA-/-, alphaB-/-, and alpha(A/B) -/- (DKO) mouse lens epithelia and examined by electron microscopic and biochemical analyses. The wild-type microtubules were 4 mum long and approximately 25 nm wide and had a characteristic protofilament structure, but alphaB-/- microtubules were 2.5-fold longer. Microtubule-associated proteins (MAPs) extracted from microtubules by washing with salt included transketolase, alpha-enolase, and betaB2-crystallin. In DKO lens epithelial microtubules but not in wild-type, alphaA-/- or alphaB-/- microtubules, extraction of the MAPs gave very long (14-20 microm) "polyfilament" assemblies that were tightly bundled. Addition of exogenous alpha-crystallin (alphaA+ alphaB) was ineffective in preventing polyfilament formation. However, normal microtubule structure could be restored by including MAPs derived from wild-type lens epithelial cells during microtubule reconstitution. Intriguingly, these data suggest that alpha-crystallin may interact with MAPs to inhibit aggregation of microtubules in lens epithelial cells. Sedimentation analysis and 90 degrees light scattering measurements showed that alpha-crystallin suppressed tubulin assembly in vitro. Alpha-crystallin did not have a strong effect on the GTPase activity of purified tubulin. SDS-PAGE analysis showed that alpha-crystallin prevented heat-induced aggregation of tubulin, suggesting that alpha-crystallin may affect microtubule assembly by maintaining the pool of unassembled tubulin.

Dietary modulation of lens zeaxanthin in quail

Although higher dietary intake of lutein/zeaxanthin has been associated with reduced risk for cataracts, the impact of dietary supplements on lens lutein (L) or zeaxanthin (Z) has not been examined. If higher lens carotenoids do reduce risk for cataract, it would be essential to know whether dietary carotenoids can elevate carotenoids in the adult vertebrate lens. In this study, a covey of Japanese quail were hatched and raised 6 months on carotenoid-deficient diet, then switched to deficient diet supplemented with low or high 3R,3R'-zeaxanthin (5 or 35 mgkg(-1) food) or beta-carotene (50 mgkg(-1) food). Controls included a group of covey-mates that remained on the deficient diet and another raised from birth on the high Z (35 mg Zkg(-1)) diet. At 1 year of age, carotenoids and tocopherols in the lens and in the serum were analysed by HPLC, and compared by analysis of variance. Serum Z was significantly elevated in deficient birds fed the lower or higher Z supplement for 6 months (P<0.0001 for each). Serum Z in birds maintained on the higher Z supplement for 1 year was much higher than that in deficient birds (P<0.0001), but not different from deficient birds given the higher Z supplement. As in humans, the predominant lens carotenoids were lutein (L) and zeaxanthin (Z), and the total carotenoid concentration was of lower magnitude than the concentration of alpha-tocopherol. Responses to Z supplementation were sex-related. Female quail had 5-10 times higher serum concentrations of both Z and L than males (P<0.0001, <0.001), and they also had higher lens Z concentrations than males (P<0.0006); possible effects of estrogen on lens carotenoids are discussed. Lens Z concentration was strongly and positively correlated with serum Z in females (r=0.77; P<0.002). Deficient adult females supplemented with the 35 mgkg(-1) dose of Z for 6 months had a mean lens Z concentration (0.252+/-0.06 microgg(-1) protein) close to that in females fed with the supplement from birth (0.282+/-0.15 microgg(-1) protein). Birds fed with the higher dietary Z supplement for 6 or 12 months had significantly higher lens Z than birds fed lower or no dietary Z (P<0.0001). Lens L was not altered by dietary supplementation with either Z or beta-carotene. beta-Carotene supplements did not result in detectable lens beta-carotene, and had no effect on lens Z. Neither Z nor beta-carotene supplementation had a significant effect on serum or lens tocopherol concentrations. These studies in quail provide the first experimental evidence that lens carotenoids in adult vertebrates can be manipulated by dietary Z supplements.

Nuclear import of {alpha}B-crystallin is phosphorylation-dependent and hampered by hyperphosphorylation of the myopathy-related mutant R120G

Phosphorylation modulates the functioning of alphaB-crystallin as a molecular chaperone. We here explore the role of phosphorylation in the nuclear import and cellular localization of alphaB-crystallin in HeLa cells. Inhibition of nuclear export demonstrated that phosphorylation of alphaB-crystallin is required for import into the nucleus. As revealed by mutant analysis, phosphorylation at Ser-59 is crucial for nuclear import, and phosphorylation at Ser-45 is required for speckle localization. Co-immunoprecipitation experiments suggested that the import of alphaB-crystallin is possibly regulated by its phosphorylation-dependent interaction with the survival motor neuron (SMN) protein, an important factor in small nuclear ribonucleoprotein nuclear import and assembly. This interaction was supported by co-localization of endogenous phosphorylated alphaB-crystallin with SMN in nuclear structures. The cardiomyopathy-causing alphaB-crystallin mutant R120G was found to be excessively phosphorylated, which disturbed SMN interaction and nuclear import, and resulted in the formation of cytoplasmic inclusions. Like for other protein aggregation disorders, hyperphosphorylation appears as an important aspect of the pathogenicity of alphaB-crystallin R120G.

Insights into Hydrophobicity and the Chaperone-like Function of αA- and αB-crystallins

Alpha-crystallin, composed of two subunits, alphaA and alphaB, has been shown to function as a molecular chaperone that prevents aggregation of other proteins under stress conditions. The exposed hydrophobic surfaces of alpha-crystallins have been implicated in this process, but their exact role has not been elucidated. In this study, we quantify the hydrophobic surfaces of alphaA- and alphaB-crystallins by isothermal titration calorimetry using 8-anilino-1-napthalenesulfonic acid (ANS) as a hydrophobic probe and analyze its correlation to the chaperone potential of alphaA- and alphaB-crystallins under various conditions. Two ANS binding sites, one with low and another with high affinity, were clearly detected, with alphaB showing a higher number of sites than alphaA at 30 degrees C. In agreement with the higher number of hydrophobic sites, alphaB-crystallin demonstrated higher chaperone activity than alphaA at this temperature. Thermodynamic analysis of ANS binding to alphaA- and alphaB-crystallins indicates that high affinity binding is driven by both enthalpy and entropy changes, with entropy dominating the low affinity binding. Interestingly, although the number of ANS binding sites was similar for alphaA and alphaB at 15 degrees C, alphaA was more potent than alphaB in preventing aggregation of the insulin B-chain. Although there was no change in the number of high affinity binding sites of alphaA and alphaB for ANS upon preheating, there was an increase in the number of low affinity sites of alphaA and alphaB. Preheated alphaA, in contrast to alphaB, exhibited remarkably enhanced chaperone activity. Our results indicate that although hydrophobicity appears to be a factor in determining the chaperone-like activity of alpha-crystallins, it does not quantitatively correlate with the chaperone function of alpha-crystallins.

The decrease of the cytoskeleton tubulin follows the decrease of the associating molecular chaperone alphaB-crystallin in unloaded soleus muscle atrophy without stretch

The cytoskeletal component tubulin/microtubule commonly allows the cell to respond mechanically to the environment. The concentration of free tubulin dimer is autoregulated in the balance of free dimer and polymeric forms of microtubule (MT) protein, having an intrinsic property of "dynamic instability", and through cotranslational beta-tubulin mRNA degradation. Recently, we have demonstrated that alphaB-crystallin is a key molecule of muscle atrophy, since alphaB-crystallin has a chaperone-like-activity that suppresses tubulin aggregation and protects the MT disassembly against both Ca2+ and depolymelizing alkaloid in vitro. Most of the small heat-shock proteins (sHsps), including alphaB-crystallin, are expressed in skeletal muscle. However, no report to date has studied the changes of tubulin/MT during muscle adaptation. Here, we examined changes in tubulin content in rat soleus muscles after hindlimb suspension (HS) with/without passive stretch and the recovery. HS induced rapid decreases of soleus muscle mass, most Hsps (alphaB-crystallin, Hsp90, Hsp70, Hsp27, and p20) and tubulin contents in soleus muscle, while heat-shock cognate 70-kDa protein (Hsc70) did not decrease. Soleus muscle mass, most Hsps, and tubulin were maintained with passive stretch. After 5 days' recovery, the levels of tubulin and Hsps, but not Hsc70, were restored to control levels. The interactions of alphaB-crystallin and tubulin/MT were observed with immunoprecipitation with an anti-alpha-tubulin antibody and taxol-dependent MT assembly. Other sHsps were also associated with alphaB-crystallin and MT, whereas Hsp90 and Hsp70 did not co-precipitate with them. These data imply an interaction and close relationship between alphaB-crystallin and tubulin/MTs in muscle tissues. The amount of mRNA of alphaB-crystallin decreased with the muscle atrophy level, whereas the gene expression level of betaI-tubulin was maintained during HS. This means a significant role of post-transcriptional regulation in tubulin/MT system in muscle adaptation, whereas alphaB-crystallin and most sHsps are regulated at the transcriptional level. Additional functional contribution of alphaB-crystallin to tubulin/MTs during myotube formation was examined using C2C12 myoblast cultured cells, the alphaB-crystallin expression of which was decreased or increased. It indicated the necessity of alphaB-crystallin during microtubule reorganization. In conclusion, tubulin/MTs were revealed to be one of the substrates of alphaB-crystallin, and also serial decreases of alphaB-crystallin and tubulin/MT in early soleus muscle atrophy suggest that the chaperone effect of alphaB-crystallin on the cytoskeleton, which may be also dynamically regulated in the muscle cell, is a key mechanism for muscle adaptation and protection of the atrophy and also muscle differentiation.