Glial expression of the 90-kDa heat shock protein (HSP90) and the 94-kDa glucose-regulated protein (GRP94) following an excitotoxic lesion in the mouse hippocampus

Heat Shock Protein 90 in Parkinson's Disease: Profile of a Serial Killer

Parkinson's disease (PD) is the second most common neurodegenerative disease, characterized by abnormal α-synuclein misfolding and aggregation, mitochondrial dysfunction, oxidative stress, as well as progressive death of dopaminergic neurons in the substantia nigra. Molecular chaperones play a role in stabilizing proteins and helping them achieve their proper structure. Previous studies have shown that overexpression of heat shock protein 90 (HSP90) can lead to the death of dopaminergic neurons associated with PD. Inhibiting HSP90 is considered a potential treatment approach for neurodegenerative disorders, as it may reduce protein aggregation and related toxicity, as well as suppress various forms of regulated cell death (RCD). This review provides an overview of HSP90 and its role in PD, focusing on its modulation of proteostasis and quality control of LRRK2. The review also explores the effects of HSP90 on different types of RCD, such as apoptosis, chaperone-mediated autophagy (CMA), necroptosis, and ferroptosis. Additionally, it discusses HSP90 inhibitors that have been tested in PD models. We will highlight the under-investigated neuroprotective effects of HSP90 inhibition, including modulation of oxidative stress, mitochondrial dysfunction, PINK/PARKIN, heat shock factor 1 (HSF1), histone deacetylase 6 (HDAC6), and the PHD2-HSP90 complex-mediated mitochondrial stress pathway. By examining previous literature, this review uncovers overlooked neuroprotective mechanisms and emphasizes the need for further research on HSP90 inhibitors as potential therapeutic strategies for PD. Finally, the review discusses the potential limitations and possibilities of using HSP90 inhibitors in PD therapy.

Preclinical Evaluation of [11C]YC-72-AB85 for In Vivo Visualization of Heat Shock Protein 90 in Brain and Cancer with Positron Emission Tomography

Aberrant Hsp90 has been implied in cancer and neurodegenerative disorders. The development of a suitable Hsp90 Positron emission tomography (PET) probe can provide in vivo quantification of the expression levels of Hsp90 as a biomarker for diagnosis and follow-up of cancer and central nervous system (CNS) disease progression. In this respect, [¹¹C]YC-72-AB85 was evaluated as an Hsp90 PET probe in B16.F10 melanoma bearing mice and its brain uptake was determined in rats and nonhuman primate. In vitro binding of [¹¹C]YC-72-AB85 to tissue slices of mouse B16.F10 melanoma, PC3 prostate carcinoma, and rodent brain was evaluated using autoradiography. Biodistribution of [¹¹C]YC-72-AB85 was evaluated in healthy and B16.F10 melanoma mice. In vivo brain uptake was assessed by μPET studies in rats and a rhesus monkey. In vitro binding was deemed Hsp90-specific by blocking studies with heterologous Hsp90 inhibitors onalespib and SNX-0723. Saturable Hsp90 binding was observed in brain, tumor, blood, and blood-rich organs in mice. In combined pretreatment and displacement studies, reversible and Hsp90-specific binding of [¹¹C]YC-72-AB85 was observed in rat brain. Dynamic μPET brain scans in baseline and blocking conditions in a rhesus monkey indicated Hsp90-specific binding. [¹¹C]YC-72-AB85 is a promising PET tracer for in vivo visualization of Hsp90 in tumor and brain. Clear differences of Hsp90 binding to blood and blood-rich organs were observed in tumor vs control mice. Further, we clearly demonstrate, for the first time, binding to a saturable Hsp90 pool in brain of rats and a rhesus monkey.

CircDYM ameliorates depressive-like behavior by targeting miR-9 to regulate microglial activation via HSP90 ubiquitination

Circular RNAs (circRNAs), highly expressed in the central nervous system, are involved in various regulatory processes and implicated in some pathophysiology. However, the potential role of circRNAs in psychiatric diseases, particularly major depressive disorder (MDD), remains largely unknown. Here, we demonstrated that circular RNA DYM (circDYM) levels were significantly decreased both in the peripheral blood of patients with MDD and in the two depressive-like mouse models: the chronic unpredictable stress (CUS) and lipopolysaccharide (LPS) models. Restoration of circDYM expression significantly attenuated depressive-like behavior and inhibited microglial activation induced by CUS or LPS treatment. Further examination indicated that circDYM functions as an endogenous microRNA-9 (miR-9) sponge to inhibit miR-9 activity, which results in a downstream increase of target-HECT domain E3 ubiquitin protein ligase 1 (HECTD1) expression, an increase of HSP90 ubiquitination, and a consequent decrease of microglial activation. Taken together, the results of our study demonstrate the involvement of circDYM and its coupling mechanism in depression, providing translational evidence that circDYM may be a novel therapeutic target for depression.

Inhibition of HSP90β by ganetespib blocks the microglial signalling of evoked pro-inflammatory responses to heat shock

Although microglial reaction to heat shock is considered to be protective, heat shock is still a potential hazard caused by high temperatures. Recent studies indicate that the inhibition of the 90-kDa heat shock protein (HSP90) increasing the protective heat shock response and suppressing inflammatory signalling pathways in several diseases. Nevertheless, the effects of heat shock on microglial pro-inflammatory responses are not completely identical. Here, we aim to investigate the effect of the HSP90 inhibitor ganetespib on microglial pro-inflammatory responses following heat shock. HSP90 isoforms were determined by transfecting N9 microglial cells (N9 cells) with enzymatically prepared siRNA (esiRNAs). We found that heat shock significantly increased the secretion of tumour necrosis factor alpha (TNF-α), interleukin (IL)-1β, IL-6 and nitric oxide (NO), and the phosphorylation of extracellular signal-regulated kinase (ERK), Janus-activated kinase 2 (JAK2), signal transducer and activator of transcription 3 (STAT3), nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor alpha (IκB-α) and p65 nuclear factor kappa-light-chain-enhancer of activated B cells (p65 NF-κB) in N9 cells. These increases, except for phospho-p65, were attenuated efficiently in a dose-dependent manner by ganetespib pretreatment. Furthermore, the suppression of heat shock-evoked cytokines and NO production, and the phosphorylation of ERK, JAK2 and STAT3 in cytosols and/or nuclei were also observed by administering esiRNA HSP90β, but not HSP90α, in heat shock-treated N9 cells. Taken together, our findings demonstrate that the HSP90 inhibitor ganetespib blocks pro-inflammatory responses in heat shock-treated N9 cells via a signalling mechanism involving HSP90β and STAT3.

Inhibition of Heat Shock Protein 90 by 17-AAG Reduces Inflammation via P2X7 Receptor/NLRP3 Inflammasome Pathway and Increases Neurogenesis After Subarachnoid Hemorrhage in Mice

Subarachnoid hemorrhage (SAH) is a life-threatening cerebrovascular disease that usually has a poor prognosis. Heat shock proteins (HSPs) have been implicated in the mechanisms of SAH-associated damage, including increased inflammation and reduced neurogenesis. The aim of this study was to investigate the effects of HSP90 inhibition on inflammation and neurogenesis in a mouse model of experimental SAH induced by endovascular surgery. Western blotting showed HSP90 levels to be decreased, while neurogenesis, evaluated by 5-bromo-2'-deoxyuridine (BrdU) immunohistochemistry, was decreased in the hippocampuses of SAH mice. SAH also induced pro-inflammatory factors such as interleukin-1β (IL-1β), capase-1 and the NLRP3 inflammasome. However, intraperitoneal administration of the specific HSP90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG) reduced the levels of HSP90, NLRP3, ASC, caspase-1 and IL-1β, while increasing the levels of brain-derived neurotrophic factor and doublecortin (DCX), as well as the number of BrdU-positive cells in SAH mice. In addition, 17-AGG improved short- and long-term neurobehavioral outcomes. The neuroprotective and anti-inflammatory effects of 17-AGG were reversed by recombinant HSP90 (rHSP90); this detrimental effect of HSP90 was inhibited by the specific P2X7 receptor (P2X7R) inhibitor A438079, indicating that SAH-induced inflammation and inhibition of neurogenesis were likely mediated by HSP90 and the P2X7R/NLRP3 inflammasome pathway. HSP90 inhibition by 17-AAG may be a promising therapeutic strategy for the treatment of SAH.

Pla2g6 Deficiency in Zebrafish Leads to Dopaminergic Cell Death, Axonal Degeneration, Increased β-Synuclein Expression, and Defects in Brain Functions and Pathways

This study aimed to gain insights into the pathophysiology underlying PLA2G6-associated neurodegeneration that is implicated in three different neurological disorders, suggesting that other, unknown genetic or environmental factors might contribute to its wide phenotypic expression. To accomplish this, we downregulated the function of pla2g6 in the zebrafish nervous system, performed parkinsonism-related phenotypic characterization, and determined the effects of gene regulation upon the loss of pla2g6 function by using RNA sequencing and downstream analyses. Pla2g6 deficiency resulted in axonal degeneration, dopaminergic and motor neuron cell loss, and increased β-synuclein expression. We also observed that many of the identified, differentially expressed genes were implicated in other brain disorders, which might explain the variable phenotypic expression of pla2g6-associated disease, and found that top enriched canonical pathways included those already known or suggested to play a major role in the pathogenesis of Parkinson's disease. Our data support that pla2g6 is relevant for cranial motor development with significant implications in the pathophysiology underlying Parkinson's disease.

Methylmercury alters the activities of Hsp90 client proteins, prostaglandin E synthase/p23 (PGES/23) and nNOS

Methylmercury (MeHg) is a persistent pollutant with known neurotoxic effects. We have previously shown that astrocytes accumulate MeHg and play a prominent role in mediating MeHg toxicity in the central nervous system (CNS) by altering glutamate signaling, generating oxidative stress, depleting glutathione (GSH) and initiating lipid peroxidation. Interestingly, all of these pathways can be regulated by the constitutively expressed, 90-kDa heat shock protein, Hsp90. As Hsp90 function is regulated by oxidative stress, we hypothesized that MeHg disrupts Hsp90-client protein functions. Astrocytes were treated with MeHg and expression of Hsp90, as well as the abundance of complexes of Hsp90-neuronal nitric oxide synthase (nNOS) and Hsp90-prostaglandin E synthase/p23 (PGES/p23) were assessed. MeHg exposure decreased Hsp90 protein expression following 12 h of treatment while shorter exposures had no effect on Hsp90 protein expression. Interestingly, following 1 or 6 h of MeHg exposure, Hsp90 binding to PGES/p23 or nNOS was significantly increased, resulting in increased prostaglandin E₂ (PGE₂) synthesis from MeHg-treated astrocytes. These effects were attenuated by the Hsp90 antagonist, geldanmycin. NOS activity was increased following MeHg treatment while cGMP formation was decreased. This was accompanied by an increase in •O₂⁻ and H₂O₂ levels, suggesting that MeHg uncouples NO formation from NO-dependent signaling and increases oxidative stress. Altogether, our data demonstrates that Hsp90 interactions with client proteins are increased following MeHg exposure, but over time Hsp90 levels decline, contributing to oxidative stress and MeHg-dependent excitotoxicity.

IQGAP1 expression in spared CA1 neurons after an excitotoxic lesion in the mouse hippocampus

Repeated seizures induce permanent alterations in the hippocampal circuits in experimental models with intractable temporal lobe epilepsy. Sprouting and synaptic reorganization induced by seizures has been well-studied in the mossy fiber pathway. However, studies investigating sprouting and synaptic reorganization beyond the mossy fiber pathway are limited. The present study examined the biochemical changes of CA1 pyramidal neurons undergoing morphological changes after excitotoxicity-induced hippocampal CA3 neuronal death. IQ-domain GTPase-activating proteins (IQGAP1), is an effector of Rac1 and Cdc42 and an actin-binding protein, was upregulated in CA1 pyramidal neurons after kainic acid-induced hippocampal CA3 neuronal degeneration. IQGAP1 + cells were colocalized with Nestin, but not in astrocytes or mature neurons. Furthermore, IQGAP1 did not originate from newly divided local precursors or NG2 + cells. IQGAP1 and adenomatous polyposis coli localized in CA1 pyramidal neurons, and Cdc42 activation was followed by IQGAP1 recruitment. These findings suggest that IQGAP1 is upregulated in pre-existed sparing neurons of the CA1 layer undergoing morphological changes after excitoxicity-induced hippocampal CA3 neuronal death. It demonstrates the utility of IQGAP1 as a possible marker for spared pyramidal neurons, which may contribute to structural and functional alternations responsible for the development of epilepsy.

Hsp90 inhibits α-synuclein aggregation by interacting with soluble oligomers

Aggregated α-synuclein is one of the main components of the pathological Lewy bodies associated with Parkinson's disease (PD). Many other proteins, including chaperones such as Hsp90 and Hsp70, have been found co-localized with Lewy bodies and the expression levels of Hsp90 have been found to be increased in brains of PD patients. Although the role of Hsp70 in the aggregation of α-synuclein has been extensively studied, relatively little is known about the effect of Hsp90 on this process. Here, we have investigated if Hsp90 can prevent the aggregation of the A53T pathological mutant of α-synuclein in vitro. A detailed study using many biophysical methods has revealed that Hsp90 prevents α-synuclein from aggregating in an ATP-independent manner and that it forms a strong complex with the transiently populated toxic oligomeric α-synuclein species formed along the aggregation pathway. We have also shown that, upon forming a complex with Hsp90, the oligomers are rendered harmless and nontoxic to cells. Thus, we have clear evidence that Hsp90 is likely to play an important role on these processes in vivo.

NFAT5-dependent expression of AQP4 in astrocytes

The maintenance of water homeostasis under pathological conditions is mediated by the aquaporin-4 (AQP4) channel in astrocytes. To clarify the transcriptional regulation for AQP4 under conditions of astrocytic swelling, we examined the role of nuclear factor of activated T cells 5 (NFAT5). We evaluated NFAT5 expression patterns after the induction of brain edema and following excitotoxic neuronal death by kainic acid injection. In injured hippocampi, NFAT5 expression increased in astrocytes from 12 h to 3 days post-injection. AQP4 was redistributed from perivascular to whole-cell processes in astrocytes. NFAT5 and AQP4 expression increased under astrocytic swelling induced by ammonia treatment, and NFAT5-targeted silencing significantly reduced AQP4 expression. The promoter region required for NFAT5 transcriptional activation was located between -49 and -38 bp of rat AQP4. The amount of NFAT5 bound to the promoter of AQP4 was increased in response to ammonia. Our data demonstrate that NFAT5 is necessary for the transcriptional regulation of AQP4 expression and for local astrocyte swelling with accompanying restriction of the neuropil extracellular space in vivo.

Expression of CD200 in alternative activation of microglia following an excitotoxic lesion in the mouse hippocampus

CD200 is a glycoprotein that is expressed on the surfaces of neurons and other cells. It interacts with its receptor, CD200R, which is expressed on cells of the myeloid lineage, including microglia. The interaction of CD200 with its receptor plays a significant role in maintaining microglia in a quiescent state; thus, a decrease in CD200 expression in the brain is associated with evidence of microglial activation. However, their roles in pathological progression remain unclear. We examined the expression of CD200 in kainic acid (KA)-induced neurodegeneration of the mouse hippocampus. Our quantitative analysis revealed that CD200 was constitutively expressed in the normal brain and transiently upregulated by KA treatment. At the cellular level, CD200 was expressed in neurons in control, and was upregulated primarily in the microglia of KA-treated mouse hippocampi. We examined the contribution of CD200 to both the classical and alternative activation of microglia in vitro using an adult microglia culture, which was exposed to interleukin-4 (IL-4) with and without lipopolysaccharide (LPS). CD200 expression was increased after exposure to IL-4, but not to LPS. These in vivo experiments demonstrated that CD200 was transiently expressed in microglia in a process mediated by the inflammatory response. Based on CD200R expression in microglia, it suggests that microglia is maintained in an activated state with autocrine signaling by interactions between microglial CD200 and its CD200R. Moreover, we suggest that CD200 may be expressed in the alternative activation of microglia and play a beneficial role in neuroinflammation.

Evidence for a role of heat shock protein-90 in toll like receptor 4 mediated pain enhancement in rats

Spinal cord microglial toll-like receptor 4 (TLR4) has been implicated in enhancing neuropathic pain and opposing morphine analgesia. The present study was initiated to explore TLR4-mediated pain modulation by intrathecal lipopolysaccharide, a classic TLR4 agonist. However, our initial study revealed that intrathecal lipopolysaccharide failed to induce low-threshold mechanical allodynia in naive rats, suggestive that TLR4 agonism may be insufficient to enhance pain. These studies explore the possibility that a second signal is required; namely, heat shock protein-90 (HSP90). This candidate was chosen for study given its known importance as a regulator of TLR4 signaling. A combination of in vitro TLR4 cell signaling and in vivo behavioral studies of pain modulation suggest that TLR4-enhancement of neuropathic pain and TLR4-suppression of morphine analgesia each likely require HSP90 as a cofactor for the effects observed. In vitro studies revealed that dimethyl sulfoxide (DMSO) enhances HSP90 release, suggestive that this may be a means by which DMSO enhances TLR4 signaling. While 2 and 100 microg lipopolysaccharide intrathecally did not induce mechanical allodynia across the time course tested, co-administration of 1 microg lipopolysaccharide with a drug that enhances HSP90-mediated TLR4 signaling now induced robust allodynia. In support of this allodynia being mediated via a TLR4/HSP90 pathway, it was prevented or reversed by intrathecal co-administration of a HSP90 inhibitor, a TLR4 inhibitor, a microglia/monocyte activation inhibitor (as monocyte-derived cells are the predominant cell type expressing TLR4), and interleukin-1 receptor antagonist (as this proinflammatory cytokine is a downstream consequence of TLR4 activation). Together, these results suggest for the first time that TLR4 activation is necessary but not sufficient to induce spinally mediated pain enhancement. Rather, the data suggest that TLR4-dependent pain phenomena may require contributions by multiple components of the TLR4 receptor complex.

Collagen I matrix contributes to determination of adult human stem cell lineage via differential, structural conformation-specific elicitation of cellular stress response

Previously, we reported that the conformational transition of collagen I matrix plays, along with differentiation stimuli, a regulatory role in determination of differentiation lineage of bone marrow stromal sells via distinct signaling pathways specific for the structural state of the matrix. The present study addresses mechanisms underlying differential structural conformation-specific effects of collagen matrices on differentiation into diverse lineages. The results obtained suggest that the pivotal player in the observed matrix conformation-mediated regulation is a differential cellular stress response elicited by the exposure to native but not to denatured collagen I matrix. The stress causing such a response appears to be generated by matrix contraction and mediated by Alpha2Beta1 integrins engaged on native but not on denatured collagen I matrix. The principal facet of the observed phenomenon is not the nature of a stress but general stress response: when cells on denatured collagen I matrix are subjected to thermal stress, osteogenic pathway shifts to that seen on native collagen I matrix. Importantly, cellular stress response might be commonly involved in determination of differentiation lineage. Indeed, distinct components of cellular stress response machinery appear to regulate differentiation into diverse lineages. Thus, augmentation of Hsp90 levels enables the operation of efficient Alpha1Beta1/Alpha2Beta1 integrin-driven ERK activation pathways hence facilitating osteogenesis and suppressing adipogenesis, whereas myogenesis of satellite stem cells appears to be promoted by native collagen I matrix-elicited activation and nuclear translocation of another stress response component, Beta-catenin, shown to be essential for skeletal myogenesis, and chondrogenesis may involve stress-mediated elevation of yet another stress response constituent, Hsp70, shown to be an interactive partner of the chondrogenic transcription factor SOX9. The proposed concept of the integral role of cellular stress response in tissue generation and maintenance suggests new therapeutic approaches and indicates novel tissue engineering strategies.

Modulation of stress proteins and apoptotic regulators in the anoxia tolerant turtle brain

Freshwater turtles survive prolonged anoxia and reoxygenation without overt brain damage by well-described physiological processes, but little work has been done to investigate the molecular changes associated with anoxic survival. We examined stress proteins and apoptotic regulators in the turtle during early (1 h) and long-term anoxia (4, 24 h) and reoxygenation. Western blot analyses showed changes within the first hour of anoxia; multiple stress proteins (Hsp72, Grp94, Hsp60, Hsp27, and HO-1) increased while apoptotic regulators (Bcl-2 and Bax) decreased. Levels of the ER stress protein Grp78 were unchanged. Stress proteins remained elevated in long-term anoxia while the Bcl-2/Bax ratio was unaltered. No changes in cleaved caspase 3 levels were observed during anoxia while apoptosis inducing factor increased significantly. Furthermore, we found no evidence for the anoxic translocation of Bax from the cytosol to mitochondria, nor movement of apoptosis inducing factor between the mitochondria and nucleus. Reoxygenation did not lead to further increases in stress proteins or apoptotic regulators except for HO-1. The apparent protection against cell damage was corroborated with immunohistochemistry, which indicated no overt damage in the turtle brain subjected to anoxia and reoxygenation. The results suggest that molecular adaptations enhance pro-survival mechanisms and suppress apoptotic pathways to confer anoxia tolerance in freshwater turtles.

Expression of L-serine biosynthetic enzyme 3-phosphoglycerate dehydrogenase (Phgdh) and neutral amino acid transporter ASCT1 following an excitotoxic lesion in the mouse hippocampus

The nonessential amino acid L-serine functions as a glia-derived trophic factor and strongly promotes the survival and differentiation of cultured neurons. The L-serine biosynthetic enzyme 3-phosphoglycerate dehydrogenase (Phgdh) and the small neutral amino acid transporter ASCT1 are preferentially expressed in specific glial cells in the brain. However, their roles in pathological progression remain unclear. We examined the expression of Phgdh and ASCT1 in kainic acid (KA)-induced neurodegeneration of the mouse hippocampus using immunohistochemistry and Western blots. Our quantitative analysis revealed that Phgdh and ASCT1 were constitutively expressed in the normal brain and transiently upregulated by KA-treatment. At the cellular level, Phgdh was expressed in astrocytes in control and in KA-treated mice while ASCT1 that was expressed primarily in the neurons of the normal brain appeared also in activated astrocytes in KA treated mouse brain. The preferential glial expression of ASCT1 was consistent with that of Phgdh. These results demonstrate injury-induced changes in Phgdh and ASCT1 expression. It is hypothesized that the secretion of L-serine is regulated by astrocytes in response to toxic molecules such as glutamate and free radicals that promote neurodegeneration, and may correspond to the level of L-serine needed for neuronal survival and glial activation during brain insults.

Analysis of FK506-mediated protection in an organotypic model of spinal cord damage: heat shock protein 70 levels are modulated in microglial cells

Functional loss after spinal cord injuries is originated by primary and secondary injury phases whose underlying mechanisms include massive release of excitatory amino acids to cytotoxic levels that contribute to neural death. Attenuation of this excitotoxicity is a key point for improving the functional outcome after injury. One of the drugs with potential neuroprotective actions is FK506, a molecule widely used as an immunosuppressant. FK506 may exert neuroprotection via inhibition of calcineurin by binding the FKBP12, or by binding other immunophilins such as FKBP52, leading to modulation of heat shock proteins (Hsp) 90 and 70. In the present study, we used an in vitro model of organotypic culture of rat spinal cord slices to assess whether FK506 is able to protect them against glutamate excitotoxicity. The results showed that FK506 promoted a significant protective effect on the spinal cord tissue at concentrations of 50 and 100 nM. Hsp70 induction was restricted to microglial cells in spinal cord slices treated with either glutamate or FK506. In contrast, the combination of both agents led to a transient reduction in Hsp70 levels in parallel to a marked reduction in IL-1beta precursor production by glial cells. The use of geldanamycin, which promotes persistent induction of Hsp70 in these cells as well as in motoneurons, did not produce tissue neuroprotection. These observations suggest that FK506 might protect spinal cord tissue by targeting on microglial cells and that transient downregulation of Hsp70 on these cells after excitotoxicity is a relevant mechanism of action of FK506.

Glial Expression of Interleukin-18 and its Receptor After Excitotoxic Damage in the Mouse Hippocampus

Interleukin (IL)-18, a member of the IL-1 cytokine family, is an important mediator of peripheral inflammation and host defence responses. However, although IL-1 is a key proinflammatory cytokine in the brain, little is known about IL-18 changes in glial cells under excitotoxic neurodegeneration. In this study, we characterized the expressions of IL-18 and IL-18 receptor (IL-18R) in kainic acid (KA)-induced excitotoxicity in mouse hippocampus by immunohistochemistry and Western blotting. IL-18 immunoreactivity was found in microglia whereas IL-18R immunoreactivity was observed in astrocytes. Levels of IL-18 and IL-18R in hippocampus homogenates increased progressively from day 1 post-KA and peaked at 3 days. This study demonstrates the cellular sources of IL-18 and IL-18R, and their temporal correlations after KA-insult, and suggests roles for IL-18 and IL-18R in glial cells in response to excitotoxic damage in the hippocampus.

Astrocytic Expressions of Phosphorylated Akt, GSK3β and CREB Following an Excitotoxic Lesion in the Mouse Hippocampus

Glycogen synthase kinase 3beta (GSK3beta) is believed to play important roles in the regulation of synaptic plasticity, cell survival and circadian rhythms in the mature CNS. However, although several studies have been focused on the GSK3beta, little is known about GSK3beta changes in glial cells under neuropathological conditions. In this study, we evaluated the expressions of molecules associated with the GSK3beta signaling pathway, following the induction of an excitotoxic lesion in mouse brain by kainic acid (KA) injection, which caused pyramidal cell degeneration in the hippocampal CA3 region. In injured hippocampi, Ser47-Akt (protein kinase B, PKB) phosphorylation increased from 4 h until 1 day post-injection (PI). Ser9-GSK3beta and Ser133-cAMP responsive element-binding protein (CREB) phosphorylations showed similar spatiotemporal patterns in hippocampi at 1 day until 3 days PI. Double immunohistochemistry also showed that these phosphorylated forms of Akt, GSK3beta and CREB were expressed in astrocytes. For the first time, our data demonstrate the injury-induced astrocytic changes in the levels of phosphorylation of Akt, -GSK3beta and -CREB in vivo, which may reflect mechanisms of glial cells protection or adaptive response to damage.

Induction of transcription factor A-myb expression in reactive astrocytes following an excitotoxic lesion in the mouse hippocampus

In the present study, we examined patterns of A-myb expression in the kainic acid (KA)-treated mouse hippocampus. Western blot analysis revealed that A-myb expression was dramatically increased in brain 3 days after KA treatment, and was sustained for more than 7 days. A-myb immunoreactivity was restricted to hippocampal neurons in control mice. Three days after KA treatment, strong A-myb immunoreactivity was observed in reactive astrocytes throughout the CA3 region. Thereafter, A-myb immunoreactive astrocytes gradually concentrated around the CA3 region in parallel with selective neuronal loss, and only a few A-myb immunoreactive astrocytes persisted in the CA3 region 14 days after KA treatment. These findings suggest that the A-myb plays a role in the reactive gliosis signaling pathway in KA-induced excitotoxic lesions.

Are heat shock proteins therapeutic target for Parkinson's disease?

Heat shock proteins (HSPs), known as molecular chaperone to assist protein folding, have recently become a research focus in Parkinson's disease (PD) because the pathogenesis of this disease is highlighted by the intracellular protein misfolding and inclusion body formation. The present review will focus on the functions of different HSPs and their protective roles in PD. It is postulated that HSPs may serve as protein folding machinery and work together with ubiquitin-proteasome system (UPS) to assist in decomposing aberrant proteins. Failure of UPS is thought to play a key role in the pathogenesis of PD. In addition, HSPs may possess anti-apoptotic effects and keep the homeostasis of dopaminergic neurons against stress conditions. The critical role of HSPs and recent discovery of some novel HSPs inducers suggest that HSPs may be potential therapeutic targets for PD and other neurodegenerative disorders.

Spinal nerve lesion alters blood-spinal cord barrier function and activates astrocytes in the rat

Alterations in the spinal cord microenvironment in a neuropathic pain model in rats comprising right L-4 spinal nerve lesion were examined following 1, 2, 4 and 10 weeks using albumin and glial fibrillary acidic protein (GFAP) immunoreactivity. Rats subjected to nerve lesion showed pronounced activation of GFAP indicating astrocyte activation, and exhibited marked leakage of albumin, suggesting defects of the blood-spinal cord barrier (BSCB) function in the corresponding spinal cord segment. The intensities of these changes were most prominent in the gray matter of the lesioned side compared to the contralateral cord in both the dorsal and ventral horns. The most marked changes in albumin and GFAP immunoreaction were seen after 2 weeks and persisted with mild intensities even after 10 weeks. Distortion of nerve cells, loss of neurons and general sponginess were evident in the gray matter of the spinal cord corresponding to the lesion side. These nerve cell and glial cell changes was mainly evident in the areas showing leakage of endogenous albumin in the spinal cord. These novel observations indicate that chronic nerve lesion has the capacity to induce a selective increase in local BSCB permeability that could be instrumental in nerve cell and glial cell activation. These findings may be relevant to our current understanding on the pathophysiology of neuropathic pain.