Alpha B crystallin and HSP28 are enhanced in the cerebral cortex of patients with Alzheimer's disease

Differential expression of molecular chaperones in brain of patients with Down syndrome

Heat shock proteins (HSPs) in their molecular capacity as chaperones have been reported to regulate the apoptotic pathway and also play a critical role in protein conformational diseases such as Alzheimer's disease (AD). As all Down syndrome (DS) brains display AD-like neuropathology, neuronal loss in DS was shown to be mediated by apoptosis. We decided to investigate the expression patterns of HSPs in seven brain regions of adults with DS using two-dimensional polyacrylamide gel electrophoresis (2-DE). Following 2-DE, approximately 120 protein spots were successfully identified by matrix-assisted laser desorption/ionization--mass spectrometry (MALDI-MS) followed by quantification of the identified proteins. We unambiguously identified and quantified nine different chaperone proteins. Accordingly, all but three chaperone proteins did exhibit a significant change in expression. HSP 70 RY, heat shock cognate (HSC) 71 and glucose-regulated protein (GRP) 75 showed a significant decrease (P < 0.05) in DS temporal cortex whereas HSP 70.1 and GRP 78 were significantly increased (P<0.05) in cerebellum. Whilst T-complex 1 (TCP-1) epsilon subunit showed a significant decrease (P< 0.05) in parietal cortex, a similar extent of increase (P<0.05) as that observed in cerebellum was obtained in parietal levels of GRP 78. Alpha-crystallin B, HSP 60 and GRP 94 did not show any detectable changes in expression patterns. This report presents the first approach to quantify nine different chaperones simultaneously at the protein level in different brain regions and provides evidence for aberrant chaperone expression patterns in DS. The relevance of this aberrant expression patterns are discussed in relation to the biochemical and neuropathological abnormalities in DS brain.

Delayed induction of alpha B-crystallin in activated glia cells of hippocampus in kainic acid-treated mouse brain

Small heat shock proteins have been implicated in playing a role in various cellular processes, including stress-induced cell death. In kainic acid (KA)-treated rat brain, the immunoreactivity of heat-shock protein 27 (HSP27) was markedly increased in glia cells of the limbic system. In the present study, we demonstrated that alpha B-crystallin, a member of the small heat-shock protein family, was strongly induced in reactive astrocytes in hippocampus after KA-induced seizure. The induction was localized mainly in the CA3 region of hippocampus, where massive neuronal loss occurred. We also demonstrated that the delayed induction of alpha B-crystallin and HSP27 immunoreactivities in the hippocampus of epileptic animals was repressed to the levels seen in control animals with preadministration of the selective nNOS inhibitor 7-nitroindazole (7-NI). This repression was reversed by coinjection of L-arginine, a substrate of NOS. Together, these data suggest a role for alpha B-crystallin and HSP27 in reactive gliosis and/or in delayed neuronal death proceeded after KA-induced seizure.

Modulation of HSP25 expression during anterior horn motor neuron degeneration in the paralysé mouse mutant

The paralysé spontaneous mutation in mice involves degeneration and death of anterior horn motor neurons. Mutant mice are not viable past postnatal day 16. At present, the mechanisms involved in motor neuron death are unknown. Here, we investigate the expression of the small heat shock protein Hsp25, in the spinal cord of paralysé at two different stages during postnatal development, i.e., day 11 and day 14. Western blot analysis reveals that the level of Hsp25 was strikingly different in paralysé as compared to control littermates. Hsp25 expression level in paralysé at day 11 was much lower than in control mice. At day 14, an opposite pattern was observed. Such pattern seems to be restricted to spinal cord, since level of Hsp25 in other tissues (lung, brain, liver, and heart) was quite similar. Immunofluorescence examination of the lumbar spinal cord sections reveals that in control mice, Hsp25 was expressed at high level in motor neurons located in the ventral horn at both day 11 and day 14. By contrast, in paralysé mice, Hsp25 staining within the motor neurons was barely detectable except as a spot in the nucleolus (day 11). At the end stage of the disease (day 14), not only was Hsp25 staining even less intense in motor neurons, but also a strong Hsp25 staining was observed in reactive astrocytes within the gray matter. Taken together, these data suggest that Hsp25 expression is differently modulated in neuronal and glial cells during neurodegenerative processes leading to motor neuron death.

Expression of R120G-alphaB-crystallin causes aberrant desmin and alphaB-crystallin aggregation and cardiomyopathy in mice

Upregulation of alphaB-crystallin (CryAB), a small heat shock protein, is associated with a variety of diseases, including the desmin-related myopathies. CryAB, which binds to both desmin and cytoplasmic actin, may participate as a chaperone in intermediate filament formation and maintenance, but the physiological consequences of CryAB upregulation are unknown. A mutation in CryAB, R120G, has been linked to a familial desminopathy. However, it is unclear whether the mutation is directly causative. We created multiple transgenic mouse lines that overexpressed either murine wild-type CryAB or the R120G mutation in cardiomyocytes. Overexpression of wild-type CryAB was relatively benign, with no increases in mortality and no induction of desmin-related cardiomyopathy even in a line in which CryAB mRNA expression was increased approximately 104-fold and the protein level increased by 11-fold. In contrast, lines expressing the R120G mutation were compromised, with a high-expressing line exhibiting 100% mortality by early adulthood. Modest expression levels resulted in a phenotype that was strikingly similar to that observed for the desmin-related cardiomyopathies. The desmin filaments in the cardiomyocytes were overtly affected, myofibril alignment was significantly impaired, and a hypertrophic response occurred at both the molecular and cellular levels. The data show that the R120G mutation causes a desminopathy, is dominant negative, and results in cardiac hypertrophy.

The relationship between alphaB-crystallin and neurofibrillary tangles in Alzheimer's disease

AlphaB-crystallin is known as a small heat shock protein with a cytoprotective function. This study was undertaken to investigate the relationship between alphaB-crystallin and changes seen in Alzheimer's disease. The distribution and immunohistochemical characteristics of alphaB-crystallin positive neurones in the cerebral cortices of 4 patients with Alzheimer's disease were examined. AlphaB-crystallin positive neurones were mainly distributed in the limbic and paralimbic regions, namely parahippocampal gyrus, fusiform gyrus, cingulate cortex, middle and superior frontal gyrus, and insular cortex, which corresponded to commonly affected regions in Alzheimer's disease. Moreover, such neurones were present predominantly in the III or V layer of the cerebral cortex. The number of alphaB-crystallin positive neurones increased in parallel with the neuronal loss. Logistic regression analysis revealed a significant relation between the density of alphaB-crystallin positive neurones and that of extracellular neurofibrillary tangles (NFTs), with a correlation coefficient (r) of 0.57 and P < 0.0001 in 14 regions of the cerebral cortex. In contrast, the relation was not statistically significant between the density of alphaB-crystallin positive neurones and that of classical senile plaques, diffuse plaques or intracellular NFTs. Modified Gallyas-Braak (GB) staining on alphaB-crystallin positive neurone demonstrated several patterns of the structures: faint GB positive structures in the swollen perikaryon with straight neurites, fine granules compressed and contorted into fuzzy bundles, intensely GB positive filamentous structures together with fine granules and very intensely GB positive ring-like NFTs in a swollen perikaryon with curved neurites. In positive neurones, the density of ring-like NFTs correlated with that of atrophic perikaryon, or bent neurites and a decrease in the immunoreactivity of alphaB-crystallin. These data suggest that a close relationship exists between the appearance of alphaB-crystallin in neurones, extracellular NFTs, and neurofibrillary formation in alphaB-crystallin positive neurones in Alzheimer brain.

Constitutive expression of the 27-kDa heat-shock protein in neurons and satellite cells in the peripheral nervous system of the rat

By use of reverse transcriptase-polymerase chain reaction, abundant expression of the mRNA of 27 kDa heat shock protein (Hsp27) was revealed in the sympathetic and parasympathetic ganglia as well as in the sensory ganglia of unstressed adult rats. In situ hybridization and immunohistochemistry further localized Hsp27 mRNA and protein to both neurons and satellite cells in all types of ganglia examined. Schwann cells in the ganglia and peripheral nerve fibers were devoid of Hsp27 signal. These results suggested that Hsp27 is constitutively expressed in neurons and satellite cells in the entire peripheral nervous system of the rat.

Ser-59 is the major phosphorylation site in alphaB-crystallin accumulated in the brains of patients with Alexander's disease

The phosphorylation state of alphaB-crystallin accumulated in the brains of two patients with Alexander's disease (one infantile and one juvenile type) was determined by means of SDS-PAGE or isoelectric focusing of soluble and insoluble fractions of brain extracts and subsequent western blot analysis with specific antibodies against alphaB-crystallin and each of three phosphorylated serine residues. The level of mammalian small heat shock protein of 25-28 kDa (Hsp27) in the same fraction was also estimated by western blot analysis. The majority of alphaB-crystallin was detected in the insoluble fraction of brain homogenates and phosphorylation was preferentially observed at Ser-59 in both cases. A significant level of phosphorylation at Ser-45 but not Ser-19 was also detected. Hsp27 was found at considerable levels in the insoluble fractions. alphaB-crystallin and phosphorylated forms were detected in the cerebrospinal fluid of patient with the juvenile type. AlphaB-crystallin and phosphorylated forms were also detectable at considerable levels in the insoluble fraction of brain homogenates from patients with Alzheimer's disease and aged controls. The phosphorylation site was mostly at Ser-59 in all cases. Immunohistochemically, alphaB-crystallin was stained in Rosenthal fibers in brains of patients with Alexander's disease and their peripheral portions were immunostained with antibodies recognizing phosphorylated Ser-59. These results indicate that the major phosphorylation site in alphaB-crystallin in brains of patients with Alexander's disease or Alzheimer's disease as well as in aged controls is Ser-59.

Deranged expression of molecular chaperones in brains of patients with Alzheimer's disease

Alzheimer's disease (AD) is one of the disorders caused by protein conformational changes and recent studies have shown that several chaperone proteins are involved in this process. As information of chaperone expression in AD brain is limited, we aimed to study the expressional pattern of chaperones in several brain regions, as this may be essential to understand how folding defects can lead to disease. We studied the concomitant expressional patterns of molecular chaperones in seven brain regions of adults with AD using two-dimensional polyacrylamide gel electrophoresis (2-DE) and matrix-associated laser desorption ionization mass spectroscopy (MALDI-MS). We unambiguously identified and quantified nine different chaperone proteins. Six chaperone proteins, heat shock protein 60 (HSP 60), HSP 70 RY, heat shock cognate (HSC) 71, alpha crystallin B chain, glucose regulated protein (GRP) 75, and GRP 94 showed aberrant expressional patterns depending on brain region. HSP 70.1, GRP 78 and T-complex 1 (TCP-1) epsilon subunit did not show any significant expressional change. These findings are compatible with neuropathological and biochemical abnormalities in AD brain and this report presents the first approach to quantify nine different chaperones simultaneously at the protein level in individual AD brain regions providing evidence for the relevance of aberrant chaperone expression to AD neuropathology.

Interaction between beta-amyloid and lens alphaB-crystallin

In Alzheimer's disease, beta-amyloid peptides (betaA(1-40) and betaA(1-42)) are deposited on the brain cell surfaces as neurotoxic plaques. Some reports indicate that small heat shock proteins, Hsp27 and alphaB-crystallin, colocalize in the plaques, but their functions are not known. Interaction between betaA and alphaB-crystallin must be determined in order to understand the role of alphaB-crystallin in betaA fibril formation. We used a pyrene (Pyr)-labeled betaA(1-40) in a fluorescence energy transfer experiment. Upon incubation together at 37 degrees C, energy transfer between Trp of alphaB-crystallin and Pyr of Pyr-labeled betaA was observed, indicating that betaA participated in subunit exchange of alphaB-crystallin, which promoted fibril formation.

Differential expression of small heat shock proteins in reactive astrocytes after focal ischemia: possible role of beta-adrenergic receptor

Small heat shock proteins (sHSPs), a family of HSPs, are known to accumulate in the CNS, mainly in astrocytes, in several pathological conditions such as Alexander's disease, Alzheimer's disease, and Creutzfeldt-Jakob disease. sHSPs may act not only as molecular chaperones, protecting against various stress stimuli, but may also play a physiological role in regulating cell differentiation and proliferation. In the present study, we have demonstrated that transient focal ischemia in rats dramatically induced HSP27 but not alpha B-crystallin (alphaBC), both of which are members of sHSPs, in reactive astrocytes. In contrast, in vitro chemical ischemic stress induced both HSP27 and alphaBC in cultured glial cells to the same extent. Dibutyryl cAMP (dBcAMP) and isoproterenol, a beta-adrenergic receptor (betaAR) agonist, enhanced HSP27 expression but suppressed alphaBC, and changed the shape of the cells to a stellate form. dBcAMP and isoproterenol inhibited cell proliferation under normal conditions. An increase in betaAR-like immunoreactivity was also observed in reactive astrocytes in vivo. These results, together with recent findings that betaAR plays an important role in glial scar formation in vivo, raise the possibility that betaAR activation modulates sHSP expression after focal ischemia and is involved in the transformation of astrocytes to their reactive form.

Glucocorticoids regulate the synthesis of HSP27 in rat brain slices

Using mild heat shock of rat brain slices as a model for cellular insult, corticosteroid-mediated regulation of protein synthesis has been investigated. Following a single in vivo injection of rats with corticosterone or the Type II glucocorticoid receptor agonist, RU-28362, synthesis of a 28 kDa protein is elevated in cerebellar slices which are subsequently incubated in vitro at 39 degrees C for 3 h. Immunoblotting of proteins subsequent to separation by two-dimensional gel electrophoresis has identified this glucocorticoid-sensitive protein to be the small molecular weight heat-shock protein, HSP27. Synthesis of the major heat-shock proteins, HSP70 and HSP90, is not glucocorticoid-sensitive. When animals are sacrificed at either 4 h following an aldosterone injection or at 24 h following a corticosterone injection, the synthesis of HSP27 in cerebellar slices is decreased. Treatment of adrenalectomized rats with either corticosterone, RU-28362 or aldosterone produces increased synthesis of HSP27. With duration of heat shock, there is a transient increase in the synthesis of HSP27 after 2 h at 39 degrees C in slices from the cerebral cortex, with a more sustained synthesis of HSP27 in cerebellar slices. In hippocampal slices, HSP27 is rarely present. The upregulated synthesis of HSP27 in the cerebellum following an acute exposure to stress-like elevations in corticosterone titers may contribute to the relative resistance of this brain region to cellular insults.

ATP and the core "alpha-Crystallin" domain of the small heat-shock protein alphaB-crystallin

Electrospray ionization mass spectrometry (ESI-LC/MS) of tryptic digests of human alphaB-crystallin in the presence and absence of ATP identified four residues located within the core "alpha-crystallin" domain, Lys(82), Lys(103), Arg(116), and Arg(123), that were shielded from the action of trypsin in the presence of ATP. In control experiments, chymotrypsin was used in place of trypsin. The chymotryptic fragments of human alphaB-crystallin produced in the presence and absence of ATP were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Seven chymotryptic cleavage sites, Trp(60), Phe(61), Phe(75), Phe(84), Phe(113), Phe(118), and Tyr(122), located near or within the core alpha-crystallin domain, were shielded from the action of chymotrypsin in the presence of ATP. Chemically similar analogs of ATP were less protective than ATP against proteolysis by trypsin or chymotrypsin. ATP had no effect on the enzymatic activity of trypsin and the K(m) for trypsin was 0.031 mM in the presence of ATP and 0.029 mM in the absence of ATP. The results demonstrated an ATP-dependent structural modification in the core alpha-crystallin domain conserved in nearly all identified small heat-shock proteins that act as molecular chaperones.

The molecular chaperone alphaB-crystallin enhances amyloid beta neurotoxicity

Amyloid beta (Abeta) is a 40- to 42-residue peptide that is implicated in the pathogenesis of Alzheimer's Disease (AD). As a result of conformational changes, Abeta assembles into neurotoxic fibrils deposited as 'plaques' in the diseased brain. In AD brains, the small heat shock proteins (sHsps) alphaB-crystallin and Hsp27 occur at increased levels and colocalize with these plaques. In vitro, sHsps act as molecular chaperones that recognize unfolding peptides and prevent their aggregation. The presence of sHsps in AD brains may thus reflect an attempt to prevent amyloid fibril formation and toxicity. Here we report that alphaB-crystallin does indeed prevent in vitro fibril formation of Abeta(1-40). However, rather than protecting cultured neurons against Abeta(1-40) toxicity, alphaB-crystallin actually increases the toxic effect. This indicates that the interaction of alphaB-crystallin with conformationally altering Abeta(1-40) may keep the latter in a nonfibrillar, yet highly toxic form.

Ectopic expression of alpha B-crystallin in Chinese hamster ovary cells suggests a nuclear role for this protein

alpha B-crystallin (alpha B) is known to be a cytosolic, small heat shock-like multimeric protein that has anti-aggregation, chaperone-like properties. The expression of the alpha B-crystallin gene is developmentally regulated and is induced by a variety of stress stimuli. Importantly, alpha B-crystallin expression is enhanced during oncogenic transformation of cells, in a number of tumors, and most notably, in many neurodegenerative disorders, including Alzheimer's disease and multiple sclerosis. Other than its perceived role as a structural protein in the ocular lens, the actual function of alpha B-crystallin in cellular physiology remains unknown. We have stably transfected CHO cells with an inducible alpha B-cDNA-MMTV-promoter construct that allows the synthesis of recombinant alpha B-crystallin only upon exposure of these cells to dexamethasone. Using immunostaining and conventional and confocal microscopy, we have examined the subcellular distribution of the ectopically expressed alpha B-crystallin. We find that in addition to being in the cytoplasm, the protein resides in the nuclear interior in the interphase nucleus. Double labeling with anti alpha B-crystallin and anti-tubulin, concanavallin, and wheat germ agglutinin, respectively, revealed that during cell division alpha B-crystallin is excluded from condensed chromatin and the nascent nuclei. However, the protein again appears in the newly formed nuclei after the completion of cytokinesis suggesting a conditional, regulatory role for alpha B-crystallin in the nucleus.

Proteasome inhibitors induce the association of Alzheimer's amyloid precursor protein with Hsc73

Amyloid precursor protein (APP) is a secretory membrane-bound protein that undergoes restrictive proteolysis and degradation with a short life span in the constitutive secretory pathway or in the endosomal/lysosomal compartment. The degradation machinery, including cellular trafficking and the restrictive cleavage of APP, is poorly understood. To gain further insight into the intracellular degradation mechanism of APP, we searched for effector proteins that interact with APP. We found that a cytosolic molecular chaperon, Hsc73, effectively interacts with the cytoplasmic domain of APP in the presence of proteasome inhibitors. Hsc73 binds to the cytoplasmic domain near the post-transmembrane region of APP and not to the KFERQ-related sequence, KFFEQ, at the C-terminal tail that is assumed to be the selective targeting signal for lysosomal proteolysis. The amounts of Hsc73 that bind to several APP species such as those found in pathological Familial Alzheimer's disease (FAD), Swedish, or Dutch type mutation, are almost identical, suggesting that an abnormal conformation around the secretory cleavage site or a pathological imbalance in APP processing are not irrelevant to the efficiency of Hsc73 binding.

Alpha B-crystallin in the mammalian inner ear

To study the distribution of alpha B-crystallin, formalin-fixed preparations of the inner ear of the rat, cynomolgus monkey, rhesus monkey and human were stained immunohistochemically for alpha B-crystallin. In all cochleae investigated, intense staining for alpha B-crystallin was found in the inner and outer pillars as well as in the cells of Hensen and Claudius. In the primate inner ear, alpha B-crystallin was also present in the polygonal epithelial cells of Reissner's membrane, the interdental cells and some fibrocytes of the spiral limbus, epithelial cells of the outer spiral sulcus and the Schwann cells of the 8th nerve. In the primate stria vascularis, alpha B-crystallin was mainly seen in the basal cell layer and the adjacent cells of the connective tissue layer. alpha B-crystallin was found to be present in a large variety of cells in the inner ear surrounding the scala media.

Amyloid precursor protein heat shock response in lymphoblastoid cell lines bearing presenilin-1 mutations

The amyloid precursor protein (APP) gene promoter contains a heat shock element. An abnormal APP heat shock response could increase accumulation of A beta, the APP metabolite found in Alzheimer's disease amyloid plaques. Since A beta production is affected by presenilin-1 (PS-1) mutations, we investigated whether basal APP levels or response to heat shock were altered in lymphoblastoid cell lines from 8 PS-1 mutation-bearers and 9 control members of Alzheimer's disease families. Lymphoblastoid cell lines were incubated at 42 degrees C for 35 min and allowed to recover at 37 degrees C for 1, 3, 8, 24 and 48 h. APP mRNA levels, quantified using RNA-RNA solution hybridisation, increased significantly at 1 and 3 h post-heat shock to between 123% and 163% of pre-heat shock (0 h) levels and returned to normal by 8 h. Semi-quantitative Western immunoblotting of cell lysates using the 22C11 antibody detected two major bands, migrating at approximately 145 and approximately 120 kDa. Band optical densities increased significantly at 3 h to approximately 155% of 0 h levels, following the increase in APP mRNA levels and showing a similar reversibility. APP mRNA and protein responses were comparable in the PS-1 mutation-bearing and control cell lines. This study shows that both APP mRNA and protein are induced in lymphoblastoid cell lines following heat shock and that this response is not affected by PS-1 mutations which are pathogenic for Alzheimer's disease.

Synthesis and accumulation of alphaB crystallin in C6 glioma cells is induced by agents that promote the disassembly of microtubules

When C6 cells in culture were exposed at 37 degrees C to 1 microM colchicine or to 1 microM colcemid, a tubulin-binding antimitotic alkaloid, levels of alphaB crystallin in cells began to increase after about 10 h, reaching a maximum of more than 1 microg/mg protein after 24 h. The level of alphaB crystallin returned to near the control level within two subsequent days of culture in the normal medium. Northern blot analysis showed that the accumulation of alphaB crystallin was preceded by an increase in the level of the mRNA for alphaB crystallin. Nuclear run-off transcription assays showed that colchicine induced new synthesis of mRNA for alphaB crystallin. Immunofluorescence staining revealed that alphaB crystallin accumulated in the peripheral areas of cells, as did the depolymerized tubulin, after several hours of treatment with colcemid, and then it gradually became more conspicuous in the cytoplasm. Vinblastine and nocodazole, which also promote the disassembly of microtubules by binding to tubulins, also induced the synthesis of alphaB crystallin. Furthermore, induction of alphaB crystallin by these drugs was observed in quiescent cells that had been cultured in serum-free medium. However, taxol, a microtubule-stabilizing antimitotic agent, did not stimulate the synthesis of alphaB crystallin, but rather, it suppressed the induction of synthesis of alphaB crystallin by the microtubule-disrupting drugs. Induction of alphaB crystallin by colchicine or by other drugs that promote the disassembly of microtubules was sensitive to staurosporine, an inhibitor of protein kinases, and the induction was completely suppressed in the presence of 10 nM staurosporine. These results suggest that the expression of alphaB crystallin is stimulated, via phosphorylation reactions that are sensitive to staurosporine, when the depolymerization of microtubules is enhanced.