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

Desmin and its molecular chaperone, the αB-crystallin: How post-translational modifications modulate their functions in heart and skeletal muscles?

Maintenance of the highly organized striated muscle tissue requires a cell-wide dynamic network through protein-protein interactions providing an effective mechanochemical integrator of morphology and function. Through a continuous and complex trans-cytoplasmic network, desmin intermediate filaments ensure this essential role in heart and in skeletal muscle. Besides their role in the maintenance of cell shape and architecture (permitting contractile activity efficiency and conferring resistance towards mechanical stress), desmin intermediate filaments are also key actors of cell and tissue homeostasis. Desmin participates to several cellular processes such as differentiation, apoptosis, intracellular signalisation, mechanotransduction, vesicle trafficking, organelle biogenesis and/or positioning, calcium homeostasis, protein homeostasis, cell adhesion, metabolism and gene expression. Desmin intermediate filaments assembly requires αB-crystallin, a small heat shock protein. Over its chaperone activity, αB-crystallin is involved in several cellular functions such as cell integrity, cytoskeleton stabilization, apoptosis, autophagy, differentiation, mitochondria function or aggresome formation. Importantly, both proteins are known to be strongly associated to the aetiology of several cardiac and skeletal muscles pathologies related to desmin filaments disorganization and a strong disturbance of desmin interactome. Note that these key proteins of cytoskeleton architecture are extensively modified by post-translational modifications that could affect their functional properties. Therefore, we reviewed in the herein paper the impact of post-translational modifications on the modulation of cellular functions of desmin and its molecular chaperone, the αB-crystallin.

Lens-specific βA3/A1-conditional knockout mice: Phenotypic characteristics and calpain activation causing protein degradation and insolubilization

βA3/A1-crystallin is a lens structural protein that plays an important role in maintaining lens transparency via interactions with other crystallins. While the function of βA3/A1-crystallin in the retina is well studied, its functions in the lens, other than as a structural protein, remain unclear. In the current study, we generated the lens-specific βA3/A1-crystallin conditional knockout mouse (named βA3/A1ckO) and explored phenotypic changes and the function of the crystallin in the lens. The βA3/A1ckO mice showed congenital cataract at birth and exhibited truncation of lens proteins. Several truncated protein fragments were recovered as a pellet during a low-speed centrifugation (800 rpm, 70 x g) followed by a relatively higher speed centrifugation (5000 rpm, 2744 x g). Mass spectrometric analysis of pellets recovered following the two centrifugations showed that among the fragments with Mr < 20 kDa, the majority of these were from β-tubulin, and some from phakinin, αA-crystallin, and calpain-3. Further, we observed that in vitro activation of calpain-3 by calcium treatment of the wild-type-lens homogenate resulted in the degradation of calpain-3, αA-crystallin and β-tubulin and insolubilization of these proteins. Based on these results, it was concluded that the activation of calpain 3 resulted in proteolysis of β-tubulin, which disrupted cellular microtubular structure, and caused proteolysis of other lens proteins (αA-crystallin and phakinin). These proteolyzed protein fragments become insoluble, and together with the disruption of microtubular structure, and could be the causative factors in the development of congenital nuclear cataract in βA3/A1cKO mice.

Electrical stimulated GLUT4 signalling attenuates critical illness-associated muscle wasting

BACKGROUND

Critical illness myopathy (CIM) is a debilitating condition characterized by the preferential loss of the motor protein myosin. CIM is a by-product of critical care, attributed to impaired recovery, long-term complications, and mortality. CIM pathophysiology is complex, heterogeneous and remains incompletely understood; however, loss of mechanical stimuli contributes to critical illness-associated muscle atrophy and weakness. Passive mechanical loading and electrical stimulation (ES) therapies augment muscle mass and function. While having beneficial outcomes, the mechanistic underpinning of these therapies is less known. Therefore, here we aimed to assess the mechanism by which chronic supramaximal ES ameliorates CIM in a unique experimental rat model of critical care.

METHODS

Rats were subjected to 8 days of critical care conditions entailing deep sedation, controlled mechanical ventilation, and immobilization with and without direct soleus ES. Muscle size and function were assessed at the single cell level. RNAseq and western blotting were employed to understand the mechanisms driving ES muscle outcomes in CIM.

RESULTS

Following 8 days of controlled mechanical ventilation and immobilization, soleus muscle mass, myosin : actin ratio, and single muscle fibre maximum force normalized to cross-sectional area (CSA; specific force) were reduced by 40-50% (P < 0.0001). ES significantly reduced the loss of soleus muscle fibre CSA and myosin : actin ratio by approximately 30% (P < 0.05) yet failed to effect specific force. RNAseq pathway analysis revealed downregulation of insulin signalling in the soleus muscle following critical care, and GLUT4 trafficking was reduced by 55% leading to an 85% reduction of muscle glycogen content (P < 0.01). ES promoted phosphofructokinase and insulin signalling pathways to control levels (P < 0.05), consistent with the maintenance of GLUT4 translocation and glycogen levels. AMPK, but not AKT, signalling pathway was stimulated following ES, where the downstream target TBC1D4 increased 3 logFC (P = 0.029) and AMPK-specific P-TBC1D4 levels were increased approximately two-fold (P = 0.06). Reduction of muscle protein degradation rather than increased synthesis promoted soleus CSA, as ES reduced E3 ubiquitin proteins, Atrogin-1 (P = 0.006) and MuRF1 (P = 0.08) by approximately 50%, downstream of AMPK-FoxO3.

CONCLUSIONS

ES maintained GLUT4 translocation through increased AMPK-TBC1D4 signalling leading to improved muscle glucose homeostasis. Soleus CSA and myosin content was promoted through reduced protein degradation via AMPK-FoxO3 E3 ligases, Atrogin-1 and MuRF1. These results demonstrate chronic supramaximal ES reduces critical care associated muscle wasting, preserved glucose signalling, and reduced muscle protein degradation in CIM.

Potential roles of neuronal nitric oxide synthase and the PTEN-induced kinase 1 (PINK1)/Parkin pathway for mitochondrial protein degradation in disuse-induced soleus muscle atrophy in adult rats

Excessive nitric oxide (NO) production and mitochondrial dysfunction can activate protein degradation in disuse-induced skeletal muscle atrophy. However, the increase in NO production in atrophied muscles remains controversial. In addition, although several studies have investigated the PTEN-induced kinase 1 (PINK1)/Parkin pathway, a mitophagy pathway, in atrophied muscle, the involvement of this pathway in soleus muscle atrophy is unclear. In this study, we investigated the involvement of neuronal nitric oxide synthase (nNOS) and the PINK1/Parkin pathway in soleus muscle atrophy induced by 14 days of hindlimb unloading (HU) in adult rats. HU lowered the weight of the soleus muscles. nNOS expression showed an increase in atrophied soleus muscles. Although HU increased malondialdehyde as oxidative modification of the protein, it decreased 6-nitrotryptophan, a marker of protein nitration. Additionally, the nitrosocysteine content and S-nitrosylated Parkin were not altered, suggesting the absence of excessive nitrosative stress after HU. The expression of PINK1 and Parkin was also unchanged, whereas the expression of heat shock protein 70 (HSP70), which is required for Parkin activity, was reduced in atrophied soleus muscles. Moreover, we observed accumulation and reduced ubiquitination of high molecular weight mitofusin 2, which is a target of Parkin, in atrophied soleus muscles. These results indicate that excessive NO is not produced in atrophied soleus muscles despite nNOS accumulation, suggesting that excessive NO dose not mediate in soleus muscle atrophy at least after 14 days of HU. Furthermore, the PINK1/Parkin pathway may not play a role in mitophagy at this time point. In contrast, the activity of Parkin may be downregulated because of reduced HSP70 expression, which may contribute to attenuated degradation of target proteins in the atrophied soleus muscles after 14 days of HU. The present study provides new insights into the roles of nNOS and a protein degradation pathway in soleus muscle atrophy.

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.

Remarkable Homeostasis of Protein Sialylation in Skeletal Muscles of Hibernating Daurian Ground Squirrels (Spermophilus dauricus)

As the most common post-translational protein modification, glycosylation is intimately linked to muscle atrophy. This study aimed to investigate the performance of protein glycosylation in the soleus muscle (SOL) in Daurian ground squirrels (Spermophilus dauricus) and to determine the potential role of protein glycosylation in the mechanism underlying disuse muscle atrophy prevention. The results showed that (1) seven glycan structures comprising sialic acid α2-3 galactose (SAα2-3Gal) were altered during hibernation; (2) alterations in the SAα2-3Gal structure during hibernation were based on changes in the expression levels of beta-galactoside alpha-2 and 3-sialyltransferases; and (3) α2-3–linked sialylated modifications of heat shock cognate 70 and pyruvate kinase and expression of 14-3-3 epsilon protein were oscillatorily changed during hibernation. Our findings indicate that the skeletal muscles of hibernating Daurian ground squirrels maintain protein sialylation homeostasis by restoring sialylation modification during periodic interbout arousal, which might protect the skeletal muscles against disuse atrophy.

Heat shock protein inducer GGA*-59 reverses contractile and structural remodeling via restoration of the microtubule network in experimental Atrial Fibrillation

BACKGROUND

Atrial Fibrillation (AF) is the most common progressive tachyarrhythmia. AF progression is driven by abnormalities in electrical impulse formation and contractile function due to structural remodeling of cardiac tissue. Previous reports indicate that structural remodeling is rooted in derailment of protein homeostasis (proteostasis). Heat shock proteins (HSPs) play a critical role in facilitating proteostasis. Hence, the HSP-inducing compound geranylgeranylacetone (GGA) and its derivatives protect against proteostasis derailment in experimental models for AF. Whether these compounds also accelerate reversibility from structural remodeling in tachypaced cardiomyocytes is unknown.

OBJECTIVE

To investigate whether the potent HSP inducer GGA*-59 restores structural remodeling and contractile dysfunction in tachypaced cardiomyocytes and explore the underlying mechanisms.

MATERIALS AND RESULTS

HL-1 cardiomyocytes post-treated with GGA*-59 or recombinant HSPB1 (rcHSPB1) revealed increased levels of HSPB1 expression and accelerated recovery from tachypacing (TP)-induced calcium transient (CaT) loss compared to non-treated cardiomyocytes. In addition, protein levels of the microtubule protein (acetylated) α-tubulin, and contractile proteins cardiac troponin I (cTnI) and troponin T (cTnT) were reduced after TP and significantly recovered by GGA*-59 or rcHSPB1 post-treatment. The mRNA levels of α-tubulin encoding genes, but not cardiac troponin genes, were reduced upon TP and during recovery, but significantly enhanced by GGA*-59 and rcHSPB1 post-treatment. In addition, TP increased calpain activity, which remained increased during recovery and GGA*-59 post-treatment. However, HDAC6 activity, which deacetylates α-tubulin resulting in microtubule disruption, was significantly increased after TP and during recovery, but normalized to control levels by GGA*-59 or rcHSPB1 post-treatment in HL-1 cardiomyocytes.

CONCLUSIONS

Our results imply that the HSP inducer GGA*-59 and recombinant HSPB1 accelerate recovery from TP-induced structural remodeling and contractile dysfunction in HL-1 cardiomyocytes. GGA*-59 increases HSPB1 levels, represses HDAC6 activity and restores contractile protein and microtubule levels after TP, indicating that HSP-induction is an interesting target to accelerate recovery from AF-induced remodeling.

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.

2D-DIGE proteomic analysis of vastus lateralis from COPD patients with low and normal fat free mass index and healthy controls

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is associated with several extra-pulmonary effects of which skeletal muscle wasting is one of the most common and contributes to reduced quality of life, increased morbidity and mortality. The molecular mechanisms leading to muscle wasting are not fully understood. Proteomic analysis of human skeletal muscle is a useful approach for gaining insight into the molecular basis for normal and pathophysiological conditions.

METHODS

To identify proteins involved in the process of muscle wasting in COPD, we searched differentially expressed proteins in the vastus lateralis of COPD patients with low fat free mass index (FFMI), as a surrogate of muscle mass (COPDL, n = 10) (FEV1 33 ± 4.3% predicted, FFMI 15 ± 0.2 Kg.m-2), in comparison to patients with COPD and normal FFMI (COPDN, n = 8) and a group of age, smoking history, and sex matched healthy controls (C, n = 9) using two-dimensional fluorescence difference in gel electrophoresis (2D-DIGE) technology, combined with mass spectrometry (MS). The effect of silencing DOT1L protein expression on markers of cell arrest was analyzed in skeletal muscle satellite cells (HSkMSCs) in vitro and assessed by qPCR and Western blotting.

RESULTS

A subset of 7 proteins was differentially expressed in COPDL compared to both COPDN and C. We found an increased expression of proteins associated with muscle homeostasis and protection against oxidative stress, and a decreased expression of structural muscle proteins and proteins involved in myofibrillogenesis, cell proliferation, cell cycle arrest and energy production. Among these was a decreased expression of the histone methyltransferase DOT1L. In addition, silencing of the DOT1L gene in human skeletal muscle satellite cells in vitro was significantly related to up regulation of p21 WAF1/Cip1/CDKN1A, a marker of cell arrest and ageing.

CONCLUSIONS

2D-DIGE coupled with MS identified differences in the expression of several proteins in the wasted vastus lateralis that are relevant to the disease process. Down regulation of DOT1L in the vastus lateralis of COPDL patients may mediate the muscle wasting process through up regulation of markers of cell arrest and senescence.

Altered nuclear dynamics in MDX myofibers

Duchenne muscular dystrophy (DMD) is a genetic disorder in which the absence of dystrophin leads to progressive muscle degeneration and weakness. Although the genetic basis is known, the pathophysiology of dystrophic skeletal muscle remains unclear. We examined nuclear movement in wild-type (WT) and muscular dystrophy mouse model for DMD (MDX) (dystrophin-null) mouse myofibers. We also examined expression of proteins in the linkers of nucleoskeleton and cytoskeleton (LINC) complex, as well as nuclear transcriptional activity via histone H3 acetylation and polyadenylate-binding nuclear protein-1. Because movement of nuclei is not only LINC dependent but also microtubule dependent, we analyzed microtubule density and organization in WT and MDX myofibers, including the application of a unique 3D tool to assess microtubule core structure. Nuclei in MDX myofibers were more mobile than in WT myofibers for both distance traveled and velocity. MDX muscle shows reduced expression and labeling intensity of nesprin-1, a LINC protein that attaches the nucleus to the microtubule and actin cytoskeleton. MDX nuclei also showed altered transcriptional activity. Previous studies established that microtubule structure at the cortex is disrupted in MDX myofibers; our analyses extend these findings by showing that microtubule structure in the core is also disrupted. In addition, we studied malformed MDX myofibers to better understand the role of altered myofiber morphology vs. microtubule architecture in the underlying susceptibility to injury seen in dystrophic muscles. We incorporated morphological and microtubule architectural concepts into a simplified finite element mathematical model of myofiber mechanics, which suggests a greater contribution of myofiber morphology than microtubule structure to muscle biomechanical performance.NEW & NOTEWORTHY Microtubules provide the means for nuclear movement but show altered organization in the muscular dystrophy mouse model (MDX) (dystrophin-null) muscle. Here, MDX myofibers show increased nuclear movement, altered transcriptional activity, and altered linkers of nucleoskeleton and cytoskeleton complex expression compared with healthy myofibers. Microtubule architecture was incorporated in finite element modeling of passive stretch, revealing a role of fiber malformation, commonly found in MDX muscle. The results suggest that alterations in microtubule architecture in MDX muscle affect nuclear movement, which is essential for muscle function.

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.

No-dependent signaling pathways in unloaded skeletal muscle

The main focus of the current review is the nitric oxide (NO)-mediated signaling mechanism in unloaded skeletal. Review of the published data describing muscles during physical activity and inactivity demonstrates that NO is an essential trigger of signaling processes, which leads to structural and metabolic changes of the muscle fibers. The experiments with modulation of NO-synthase (NOS) activity during muscle unloading demonstrate the ability of an activated enzyme to stabilize degradation processes and prevent development of muscle atrophy. Various forms of muscle mechanical activity, i.e., plantar afferent stimulation, resistive exercise and passive chronic stretch increase the content of neural NOS (nNOS) and thus may facilitate an increase in NO production. Recent studies demonstrate that NO-synthase participates in the regulation of protein and energy metabolism in skeletal muscle by fine-tuning and stabilizing complex signaling systems which regulate protein synthesis and degradation in the fibers of inactive muscle.

Proteomic analysis of mouse soleus muscles affected by hindlimb unloading and reloading

INTRODUCTION

Disuse muscle atrophy, induced by prolonged space flight, bed rest, or denervation, is a common process with obvious changes in slow-twitch soleus muscles.

METHODS

Proteomic analysis was performed on mouse soleus subjected to hindlimb unloading (HU) and hindlimb reloading (HR) to identify new dysregulated proteins.

RESULTS

Following HU, the mass and cross-sectional area of muscle fibers decreased, but they recovered after HR. Proteomic analyses revealed 9 down-regulated and 7 up-regulated proteins in HU, and 2 down-regulated and 5 up-regulated proteins in HR. The dysregulated proteins were mainly involved in energy metabolism, protein degradation, and cytoskeleton stability. Among the dysregulated proteins were fatty acid binding protein 3, α-B crystalline, and transthyretin.

CONCLUSIONS

These results indicate that muscle atrophy induced by unloading is related to activation of proteolysis, metabolic alterations toward glycolysis, destruction of myofibrillar integrity, and dysregulation of heat shock proteins (HSPs). The dysregulated proteins may play a role in muscle atrophy and the recovery process.

Effects of heat stimulation and l-ascorbic acid 2-phosphate supplementation on myogenic differentiation of artificial skeletal muscle tissue constructs

Although skeletal muscle tissue engineering has been extensively studied, the physical forces produced by tissue-engineered skeletal muscles remain to be improved for potential clinical utility. In this study, we examined the effects of mild heat stimulation and supplementation of a l-ascorbic acid derivative, l-ascorbic acid 2-phosphate (AscP), on myoblast differentiation and physical force generation of tissue-engineered skeletal muscles. Compared with control cultures at 37°C, mouse C2C12 myoblast cells cultured at 39°C enhanced myotube diameter (skeletal muscle hypertrophy), whereas mild heat stimulation did not promote myotube formation (differentiation rate). Conversely, AscP supplementation resulted in an increased differentiation rate but did not induce skeletal muscle hypertrophy. Following combined treatment with mild heat stimulation and AscP supplementation, both skeletal muscle hypertrophy and differentiation rate were enhanced. Moreover, the active tension produced by the tissue-engineered skeletal muscles was improved following combined treatment. These findings indicate that tissue culture using mild heat stimulation and AscP supplementation is a promising approach to enhance the function of tissue-engineered skeletal muscles. Copyright © 2015 John Wiley & Sons, Ltd.

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.

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.

Identification of a conserved set of upregulated genes in mouse skeletal muscle hypertrophy and regrowth

The purpose of this study was to compare the gene expression profile of mouse skeletal muscle undergoing two forms of growth (hypertrophy and regrowth) with the goal of identifying a conserved set of differentially expressed genes. Expression profiling by microarray was performed on the plantaris muscle subjected to 1, 3, 5, 7, 10, and 14 days of hypertrophy or regrowth following 2 wk of hind-limb suspension. We identified 97 differentially expressed genes (≥2-fold increase or ≥50% decrease compared with control muscle) that were conserved during the two forms of muscle growth. The vast majority (∼90%) of the differentially expressed genes was upregulated and occurred at a single time point (64 out of 86 genes), which most often was on the first day of the time course. Microarray analysis from the conserved upregulated genes showed a set of genes related to contractile apparatus and stress response at day 1, including three genes involved in mechanotransduction and four genes encoding heat shock proteins. Our analysis further identified three cell cycle-related genes at day and several genes associated with extracellular matrix (ECM) at both days 3 and 10. In conclusion, we have identified a core set of genes commonly upregulated in two forms of muscle growth that could play a role in the maintenance of sarcomere stability, ECM remodeling, cell proliferation, fast-to-slow fiber type transition, and the regulation of skeletal muscle growth. These findings suggest conserved regulatory mechanisms involved in the adaptation of skeletal muscle to increased mechanical loading.

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).

Masseter muscle myofibrillar protein synthesis and degradation in an experimental critical illness myopathy model

Critical illness myopathy (CIM) is a debilitating common consequence of modern intensive care, characterized by severe muscle wasting, weakness and a decreased myosin/actin (M/A) ratio. Limb/trunk muscles are primarily affected by this myopathy while cranial nerve innervated muscles are spared or less affected, but the mechanisms underlying these muscle-specific differences remain unknown. In this time-resolved study, the cranial nerve innervated masseter muscle was studied in a unique experimental rat intensive care unit (ICU) model, where animals were exposed to sedation, neuromuscular blockade (NMB), mechanical ventilation, and immobilization for durations varying between 6 h and 14d. Gel electrophoresis, immunoblotting, RT-PCR and morphological staining techniques were used to analyze M/A ratios, myofiber size, synthesis and degradation of myofibrillar proteins, and levels of heat shock proteins (HSPs). Results obtained in the masseter muscle were compared with previous observations in experimental and clinical studies of limb muscles. Significant muscle-specific differences were observed, i.e., in the masseter, the decline in M/A ratio and muscle fiber size was small and delayed. Furthermore, transcriptional regulation of myosin and actin synthesis was maintained, and Akt phosphorylation was only briefly reduced. In studied degradation pathways, only mRNA, but not protein levels of MuRF1, atrogin-1 and the autophagy marker LC3b were activated by the ICU condition. The matrix metalloproteinase MMP-2 was inhibited and protective HSPs were up-regulated early. These results confirm that the cranial nerve innervated masticatory muscles is less affected by the ICU-stress response than limb muscles, in accordance with clinical observation in ICU patients with CIM, supporting the model' credibility as a valid CIM model.

A new directionality tool for assessing microtubule pattern alterations

The cytoskeleton (microtubules, actin and intermediate filaments) has a cell type-specific spatial organization that is essential and reflects cell health. We are interested in understanding how changes in the organization of microtubules contribute to muscle diseases such as Duchenne muscular dystrophy (DMD). The grid-like immunofluorescence microtubule pattern of fast-twitch muscle fibers lends itself well to visual assessment. The more complicated pattern of other fibers does not. Furthermore, visual assessment is not quantitative. Therefore we have developed a robust software program for detecting and quantitating microtubule directionality. Such a tool was necessary because existing methods focus mainly on local image features and are not well suited for microtubules. Our tool, texture detection technique (TeDT), is based on the Haralick texture method and takes into account both local and global features with more weight on the latter. The results are expressed in a graphic form responsive to subtle variations in microtubule distribution, while a numerical score allows quantitation of directionality. Furthermore, the results are not affected by imaging conditions or post-imaging procedures. TeDT successfully assesses test images and microtubules in fast-twitch fibers of wild-type and mdx mice (a model for DMD); TeDT also identifies and quantitates microtubule directionality in slow-twitch fibers, in the fibers of young animals, and in other mouse models which could not be assessed visually. TeDT might also contribute to directionality assessments of other cytoskeletal components.

Frogs and estivation: transcriptional insights into metabolism and cell survival in a natural model of extended muscle disuse

Green-striped burrowing frogs (Cyclorana alboguttata) survive in arid environments by burrowing underground and entering into a deep, prolonged metabolic depression known as estivation. Throughout estivation, C. alboguttata is immobilized within a cast-like cocoon of shed skin and ceases feeding and moving. Remarkably, these frogs exhibit very little muscle atrophy despite extended disuse and fasting. Little is known about the transcriptional regulation of estivation or associated mechanisms that may minimize degradative pathways of atrophy. To investigate transcriptional pathways associated with metabolic depression and maintenance of muscle function in estivating burrowing frogs, we assembled a skeletal muscle transcriptome using next-generation short read sequencing and compared gene expression patterns between active and 4 mo estivating C. alboguttata. This identified a complex suite of gene expression changes that occur in muscle during estivation and provides evidence that estivation in burrowing frogs involves transcriptional regulation of genes associated with cytoskeletal remodeling, avoidance of oxidative stress, energy metabolism, the cell stress response, and apoptotic signaling. In particular, the expression levels of genes encoding cell cycle and prosurvival proteins, such as serine/threonine-protein kinase Chk1, cell division protein kinase 2, survivin, and vesicular overexpressed in cancer prosurvival protein 1, were upregulated during estivation. These data suggest that estivating C. alboguttata are able to regulate the expression of genes in several major cellular pathways critical to the survival and viability of cells, thus preserving muscle function while avoiding the deleterious consequences often seen in laboratory models of muscle disuse.

FSHD myotubes with different phenotypes exhibit distinct proteomes

Facioscapulohumeral muscular dystrophy (FSHD) is a progressive muscle disorder linked to a contraction of the D4Z4 repeat array in the 4q35 subtelomeric region. This deletion induces epigenetic modifications that affect the expression of several genes located in the vicinity. In each D4Z4 element, we identified the double homeobox 4 (DUX4) gene. DUX4 expresses a transcription factor that plays a major role in the development of FSHD through the initiation of a large gene dysregulation cascade that causes myogenic differentiation defects, atrophy and reduced response to oxidative stress. Because miRNAs variably affect mRNA expression, proteomic approaches are required to define the dysregulated pathways in FSHD. In this study, we optimized a differential isotope protein labeling (ICPL) method combined with shotgun proteomic analysis using a gel-free system (2DLC-MS/MS) to study FSHD myotubes. Primary CD56(+) FSHD myoblasts were found to fuse into myotubes presenting various proportions of an atrophic or a disorganized phenotype. To better understand the FSHD myogenic defect, our improved proteomic procedure was used to compare predominantly atrophic or disorganized myotubes to the same matching healthy control. FSHD atrophic myotubes presented decreased structural and contractile muscle components. This phenotype suggests the occurrence of atrophy-associated proteolysis that likely results from the DUX4-mediated gene dysregulation cascade. The skeletal muscle myosin isoforms were decreased while non-muscle myosin complexes were more abundant. In FSHD disorganized myotubes, myosin isoforms were not reduced, and increased proteins were mostly involved in microtubule network organization and myofibrillar remodeling. A common feature of both FSHD myotube phenotypes was the disturbance of several caveolar proteins, such as PTRF and MURC. Taken together, our data suggest changes in trafficking and in the membrane microdomains of FSHD myotubes. Finally, the adjustment of a nuclear fractionation compatible with mass spectrometry allowed us to highlight alterations of proteins involved in mRNA processing and stability.

Muscle composition slightly affects in vitro digestion of aged and cooked meat: identification of associated proteomic markers

Meat is an appropriate source of proteins and minerals for human nutrition. Technological treatments modify the physical-chemical properties of proteins, making them liable to decrease the nutritional potential of meat. To counteract this damage, antioxidants and chaperone proteins in muscle cells can prevent oxidation, restore the function of denatured proteins, and thus prevent aggregation. This study aimed to explore the impact of indoor vs outdoor-reared meat protein composition on digestion and to associate protein markers to in vitro digestion parameters. Indoor-reared meat tended to show less oxidation and denaturation than outdoor-reared meat and was characterised by an overexpression of contractile and chaperone proteins. Outdoor-reared meat showed amplification of antioxidant and detoxification metabolism defending against oxidised compounds. Impacts on digestion remained minor. Several protein markers of in vitro digestion parameters were found for aged and cooked meat, linked to the detoxification process and to muscle contraction.

Attenuation of unloading-induced rat soleus atrophy with the heat-shock protein inducer 17-(allylamino)-17-demethoxygeldanamycin

We hypothesized that pharmacological induction of HSP70 would attenuate soleus atrophy development under 3 d of rat hindlimb unloading. Male Wistar rats were divided into control (C; n=7), 3-d hindlimb unloading (HUL; n=7), HUL with HSP90 inducer administration, 17-allylamino-17-emethoxygeldanamycin (17-AAG; 60 mg/kg, HUL+17-AAG, n=8). The relative weight of soleus muscle to body weight [soleus wt (mg)/body wt (g)] in the HUL group was less than that of the C and HUL+17-AAG groups (P<0.05). We revealed HSP90, HSP70 mRNA decrease in the HUL group (but not the HUL+17-AAG group) vs. C (P<0.05). The unloading resulted in significant increases of μ-calpain and conjugated ubiquitin (Ub) levels (proteins as well as mRNAs) vs. the C group, whereas 17-AAG administration prevented these alterations (studied by SDS-PAGE and RT-PCR). pFOXO3 protein was decreased in the HUL group vs. C, but not in HUL+17-AAG. Content of E3-lygase (MuRF-1, MAFbx) mRNA was increased in both suspended groups. In summary, 17-AAG administration attenuates soleus muscle atrophy, μ-calpain, and Ub increases under hindlimb unloading as well as decrease of pFOXO3.

Inhalation of carbon monoxide reduces skeletal muscle injury after hind limb ischemia-reperfusion injury in mice

BACKGROUND

The purpose of this study was to determine if inhaled carbon monoxide (CO) can ameliorate skeletal muscle injury, modulate endogenous heme oxygenase-1 expression, and improve indexes of tissue integrity and inflammation after hind limb ischemia reperfusion.

METHODS

C57BL6 mice inhaling CO (250 ppm) or room air were subjected to 1.5 hours of ischemia followed by limb reperfusion for either 3 or 6 hours (total treatment time, 4.5 or 7.5 h). After the initial period of reperfusion, all mice breathed only room air until 24 hours after the onset of ischemia. Mice were killed at either the end of CO treatment or at 24 hours' reperfusion. Skeletal muscle was subjected to histologic and biochemical analysis.

RESULTS

CO treatment for 7.5 hours protected skeletal muscle from histologic and structural evidence of skeletal muscle injury. Serum and tissue cytokines were reduced significantly (P < .05) in mice treated with CO for 7.5 hours. Tubulin, heme oxygenase, and adenosine triphosphate levels were higher in CO-treated mice.

CONCLUSIONS

Inhaled CO protected muscle from structural injury and energy depletion after ischemia reperfusion.

HSP25 can modulate myofibrillar desmin cytoskeleton following the phosphorylation at Ser15 in rat soleus muscle

The main purpose of the present study was to investigate the role(s) of 25-kDa heat shock protein (HSP25) in the regulation and integration of myofibrillar Z-disc structure during down- or upregulation of the size in rat soleus muscle fibers. Hindlimb unloading by tail suspension was performed in adult rats for 7 days, and reloading was allowed for 5 days after the termination of suspension. Interaction of HSP25 and Z-disc proteins, phosphorylation status, distribution, and complex formation of HSP25 were investigated. Non- and single-phosphorylated HSP25s were generally expressed in the cytoplasmic fraction of normal muscle. The level of total HSP25, as well as the phosphorylation ratio, did not change significantly in response to atrophy. Increased expressions of HSP25, phosphorylated at serine 15 (p-Ser15) and dual-phosphorylated form, were noted, when atrophied muscles were reloaded. Myofibrillar HSP25 was also noted in reloaded muscle. Histochemical analysis further indicated the localization of p-Ser15 in the regions with disorganization of Z-disc structure in reloaded muscle fibers. HSP25 formed a large molecular complex in the cytoplasmic fraction of normal muscle, whereas dissociation of free HSP25 with Ser15 phosphorylation was noted in reloaded muscle. The interaction of p-Ser15 with desmin and actinin was detected in Z-discs by proximity ligation assay. Strong interaction between p-Ser15 and desmin, but not actinin, was noted in the disorganized areas. These results indicated that HSP25 contributed to the desmin cytoskeletal organization following the phosphorylation at Ser15 during reloading and regrowing of soleus muscle.

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.

Identification of cold-shock protein RBM3 as a possible regulator of skeletal muscle size through expression profiling

Changes in gene expression associated with skeletal muscle atrophy due to aging are distinct from those due to disuse, suggesting that the response of old muscle to inactivity may be altered. The goal of this study was to identify changes in muscle gene expression that may contribute to loss of adaptability of old muscle. Muscle atrophy was induced in young adult (6-mo) and old (32-mo) male Brown Norway/F344 rats by 2 wk of hindlimb suspension (HS), and soleus muscles were analyzed by cDNA microarrays. Overall, similar changes in gene expression with HS were observed in young and old muscles for genes encoding proteins involved in protein folding (heat shock proteins), muscle structure, and contraction, extracellular matrix, and nucleic acid binding. More genes encoding transport and receptor proteins were differentially expressed in the soleus muscle from young rats, while in soleus muscle from old rats more genes that encoded ribosomal proteins were upregulated. The gene encoding the cold-shock protein RNA-binding motif protein-3 (RBM3) was induced most highly with HS in muscle from old rats, verified by real-time RT-PCR, while no difference with age was observed. The cold-inducible RNA-binding protein (Cirp) gene was also overexpressed with HS, whereas cold-shock protein Y-box-binding protein-1 was not. A time course analysis of RBM3 mRNA abundance during HS showed that upregulation occurred after apoptotic nuclei and markers of protein degradation increased. We conclude that a cold-shock response may be part of a compensatory mechanism in muscles undergoing atrophy to preserve remaining muscle mass and that RBM3 may be a therapeutic target to prevent muscle loss.

Myopathy with tubulin-reactive inclusions in two cats

Many types of inclusions have been described in human myopathies including but not limited to nemaline rod bodies, cylindrical spirals, tubular aggregates, cytoplasmic bodies, reducing bodies, and fingerprint bodies, and hyaline inclusions in myofibrillar myopathy and inclusion body myositis. There are very few reports describing inclusions in spontaneously occurring myopathies in cats, and these reports are limited to nemaline rod myopathy. A myopathy with tubulin-reactive crystalline inclusions has recently been reported in a human patient with a clinical presentation of myalgia and fatigue. Similarly, a myopathy with chronic, slowly progressive muscle weakness has been identified here in two unrelated cats. Inclusions were the only pathological change in skeletal muscle biopsies and, ultrastructurally, groups of crystalline structures were evident that had a subsarcolemmal or central location, rhomboid or rectangular shapes, lacked orientation, and were not membrane bound. The crystalline structures reacted positively with an antibody against tubulin. This feline myopathy may be the equivalent of the human myopathy with tubulin-positive crystalline inclusions.

Iron load and redox stress in skeletal muscle of aged rats

Loss of skeletal muscle mass (sarcopenia) is a major contributor to disability in old age. We used two-dimensional gel electrophoresis and mass spectrometry to screen for changes in proteins, and cDNA profiling to assess transcriptional regulations in the gastrocnemius muscle of adult (4 months) and aged (30 months) male Sprague-Dawley rats. Thirty-five proteins were differentially expressed in aged muscle. Proteins and mRNA transcripts involved in redox homeostasis and iron load were increased, representing novel components that were previously not associated with sarcopenia. Tissue iron levels were elevated in senescence, paralleling an increase in transferrin. Proteins involved in redox homeostasis showed a complex pattern of changes with increased SOD1 and decreased SOD2. These results suggest that an elevated iron load is a significant component of sarcopenia with the potential to be exploited clinically, and that mitochondria of aged striated muscle may be more vulnerable to radicals produced in cell respiration.

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.

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.

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.

Small heat shock protein alphaB-crystallin binds to p53 to sequester its translocation to mitochondria during hydrogen peroxide-induced apoptosis

Apoptosis is a highly conserved procedure of cell death and occurs under various stimuli, including oxidative stress. A small heat shock protein, alphaB-crystallin, is found to process resistance to apoptosis in some cells and tissues. But the mechanisms under this protective role are not fully understood. In the present study, we reported the early protective role of alphaB-crystallin against hydrogen peroxide-induced apoptosis in mice myogenic C(2)C(12) cells. alphaB-Crystallin interacted with p53, a proapoptotic protein, during cell apoptosis and such protein interaction mainly occurred in the cytoplasm of the cells, suggesting that the interaction of alphaB-crystallin with p53 might prevent the translocation of p53 from cytoplasm to mitochondria. Hence, this study provides a hint that alphaB-crystallin affects on p53 mitochondrial translocation during oxidative stress-induced apoptosis.

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.