Accumulation of the sigma‐1 receptor is common to neuronal nuclear inclusions in various neurodegenerative diseases

The sigma‐1 receptor (SIGMAR1) is now known to be one of the endoplasmic reticulum (ER) chaperones, which participate in the degradation of misfolded proteins in cells via the ER‐related degradation machinery linked to the ubiquitin‐proteasome pathway. Mutations of the SIGMAR1 gene are implicated in the pathogenesis of familial frontotemporal lobar degeneration and motor neuron disease. Involvement of ER dysfunction in the formation of inclusion bodies in various neurodegenerative diseases has also become evident. We performed immunohistochemical staining to clarify the localization of SIGMAR1 in the brains of patients with neurodegenerative disorders, including trans‐activation response DNA protein 43 (TDP‐43) proteinopathy, tauopathy, α‐synucleinopathy, polyglutamine disease and intranuclear inclusion body disease (INIBD). Double‐immunocytofluorescence and Western blot analyses of cultured cells were also performed to investigate the role of SIGMAR1 using a specific exportin 1 inhibitor, leptomycin B and an ER stress inducer, thapsigargin. SIGMAR1 was consistently shown to be co‐localized with neuronal nuclear inclusions in TDP‐43 proteinopathy, five polyglutamine diseases and INIBD, as well as in intranuclear Marinesco bodies in aged normal controls. Cytoplasmic inclusions in neurons and glial cells were unreactive for SIGMAR1. In cultured cells, immunocytofluorescent study showed that leptomycin B and thapsigargin were shown to sequester SIGMAR1 within the nucleus, acting together with p62. This finding was also supported by immunoblot analysis. These results indicate that SIGMAR1 might shuttle between the nucleus and the cytoplasm. Neurodegenerative diseases characterized by neuronal nuclear inclusions might utilize the ER‐related degradation machinery as a common pathway for the degradation of aberrant proteins.     

Aberrant neuronal differentiation and inhibition of dendrite outgrowth resulting from endoplasmic reticulum stress

Neural stem cells (NSCs) play an essential role in development of the central nervous system. Endoplasmic reticulum (ER) stress induces neuronal death. After neuronal death, neurogenesis is generally enhanced to repair the damaged regions. However, it is unclear whether ER stress directly affects neurogenesis‐related processes such as neuronal differentiation and dendrite outgrowth. We evaluated whether neuronal differentiation and dendrite outgrowth were regulated by HRD1, a ubiquitin ligase that was induced under mild conditions of tunicamycin‐induced ER stress. Neurons were differentiated from mouse embryonic carcinoma P19 cells by using retinoic acid. The differentiated cells were cultured for 8 days with or without tunicamycin and HRD1 knockdown. The ER stressor led to markedly increased levels of ER stress. ER stress increased the expression levels of neuronal marker βIII‐tubulin in 8‐day‐differentiated cells. However, the neurites of dendrite marker microtubule‐associated protein‐2 (MAP‐2)‐positive cells appeared to retract in response to ER stress. Moreover, ER stress markedly reduced the dendrite length and MAP‐2 expression levels, whereas it did not affect the number of surviving mature neurons. In contrast, HRD1 knockdown abolished the changes in expression of proteins such as βIII‐tubulin and MAP‐2. These results suggested that ER stress caused aberrant neuronal differentiation from NSCs followed by the inhibition of neurite outgrowth. These events may be mediated by increased HRD1 expression. © 2014 The Authors Journal of Neuroscience Research Published by Wiley Periodicals, Inc.     

Rab6 is increased in Alzheimer's disease brain and correlates with endoplasmic reticulum stress

Alzheimer's disease (AD) is characterized by deposits of aggregated proteins. Accumulation of aggregation-prone proteins activates protein quality control mechanisms, such as the unfolded protein response (UPR) in the endoplasmic reticulum (ER). We previously reported upregulation of the UPR marker BiP in AD brain. In this study, we investigated the small GTPase Rab6, which is involved in retrograde Golgi-ER trafficking and may function as a post-ER quality control system. Using immunohistochemistry and semiquantitative Western blotting, the expression of Rab6 was analysed in hippocampus, entorhinal and temporal cortex of 10 AD patients and six nondemented control subjects. Rab6 is upregulated in AD temporal cortex from Braak stage 3/4, the same stage that UPR activation is found. We observe increased neuronal Rab6 immunoreactivity in all brain areas examined. Although some neurones show colocalization of immunoreactivity for Rab6 and hyperphosphorylated tau, strong Rab6 staining does not colocalize with tangles. We find a highly significant correlation between the Rab6 and BiP levels. In vitro data show that Rab6 is not upregulated as a result of UPR activation or proteasome inhibition indicating an independent regulatory mechanism. Our data suggest that ER and post-ER protein quality control mechanisms are activated early in the pathology of AD.     

3‐[(2,4‐dimethoxy)benzylidene]‐anabaseine dihydrochloride protects against 6‐hydroxydopamine‐induced parkinsonian neurodegeneration through α7 nicotinic acetylcholine receptor stimulation in rats

To explore a novel therapy against Parkinson's disease through enhancement of α7 nicotinic acetylcholine receptor (nAChR), we evaluated the neuroprotective effects of 3‐[(2,4‐dimethoxy)benzylidene]‐anabaseine dihydrochloride (DMXBA; GTS‐21), a functionally selective α7 nAChR agonist, in a rat 6‐hydroxydopamine (6‐OHDA)‐induced hemiparkinsonian model. Microinjection of 6‐OHDA into the nigrostriatal pathway of rats destroys dopaminergic neurons selectively. DMXBA dose dependently inhibited methamphetamine‐stimulated rotational behavior and dopaminergic neuronal loss induced by 6‐OHDA. The protective effects were abolished by methyllycaconitine citrate salt hydrate, an α7 nAChR antagonist. Immunohistochemical study confirmed abundant α7 nAChR expression in the cytoplasm of dopaminergic neurons. These results indicate that DMXBA prevented 6‐OHDA‐induced dopaminergic neuronal loss through stimulating α7 nAChR in dopaminergic neurons. Injection of 6‐OHDA elevated immunoreactivities to glial markers such as ionized calcium binding adaptor molecule 1, CD68, and glial fibrillary acidic protein in the substantia nigra pars compacta of rats. In contrast, these immunoreactivities were markedly inhibited by comicroinjection of DMXBA. Microglia also expressed α7 nAChR in both resting and activated states. Hence, we hypothesize that DMXBA simultaneously affects microglia and dopaminergic neurons and that both actions lead to dopaminergic neuroprotection. The findings that DMXBA attenuates 6‐OHDA‐induced dopaminergic neurodegeneration and glial activation in a rat model of Parkinson's disease raisethe possibility that DMXBA could be a novel therapeutic compound to prevent Parkinson's disease development. © 2012 Wiley Periodicals, Inc.     

Neurodegerative dementias involving aberrant protein aggregation

Recently, it was shown that inclusion bodies consisting of aberrant protein aggregation are a common pathological finding in neurodegenerative dementias. It is also believed that the ubiquitin–proteasome system (UPS) is involved in these aberrant aggregations. Because the UPS is related to the unfolded protein response (UPR) in the endoplasmic reticulum (ER) through ER‐associated degradation (ERAD), we propose that the mechanism of neurodegeneration is as follows: (i) aberrant protein aggregation overloads the UPS; (ii) the disturbed UPS affects ERAD; (iii) disturbed ERAD impairs UPR; and (iv) prolonged UPR causes ER‐mediated apoptosis.     

Unfolded protein response and aggresome formation in hereditary reducing-body myopathy

Reducing-body myopathy (RBM) is a rare myopathy characterized by the presence of unique sarcoplasmic inclusions called reducing bodies (RBs). We characterized the aggresomal features of RBs that contained gamma-tubulin, ubiquitin, and endoplasmic reticulum (ER) chaperones, together with a set of membrane proteins, in a family with hereditary RBM. Increased messenger ribonucleic acid and protein levels of a molecular chaperone, glucose-related protein 78, were also observed. These results suggest that the unfolded protein response caused by the accumulation of misfolded proteins in the endoplasmic reticulum plays an important role in the formation of RBs.     

Low levels of mutant ubiquitin are degraded by the proteasome in vivo

The ubiquitin‐proteasome system fulfills a pivotal role in regulating intracellular protein turnover. Impairment of this system is implicated in the pathogenesis of neurodegenerative diseases characterized by ubiquitin‐ containing proteinaceous deposits. UBB⁺¹, a mutant ubiquitin, is one of the proteins accumulating in the neuropathological hallmarks of tauopathies, including Alzheimer's disease, and polyglutamine diseases. In vitro, UBB⁺¹ properties shift from a proteasomal ubiquitin‐fusion degradation substrate at low expression levels to a proteasome inhibitor at high expression levels. Here we report on a novel transgenic mouse line (line 6663) expressing low levels of neuronal UBB⁺¹. In these mice, UBB⁺¹ protein is scarcely detectable in the neuronal cell population. Accumulation of UBB⁺¹ commences only after intracranial infusion of the proteasome inhibitors lactacystin or MG262, showing that, at these low expression levels, the UBB⁺¹ protein is a substrate for proteasomal degradation in vivo. In addition, accumulation of the protein serves as a reporter for proteasome inhibition. These findings strengthen our proposition that, in healthy brain, UBB⁺¹ is continuously degraded and disease‐related UBB⁺¹ accumulation serves as an endogenous marker for proteasomal dysfunction. This novel transgenic line can give more insight into the intrinsic properties of UBB⁺¹ and its role in neurodegenerative disease. © 2010 Wiley‐Liss, Inc.     

Neuronal activity in the medial associative‐limbic and lateral motor part of the rat subthalamic nucleus and the effect of 6‐hydroxydopamine‐induced lesions of the dorsolateral striatum

Lesions of the rat nigrostriatal dopamine system by injection of 6‐hydroxydopamine (6‐OHDA) lead to abnormal neuronal activity in the basal ganglia (BG) motor loop similar to that found in Parkinson's disease (PD). In the BG motor loop the subthalamic nucleus (STN) represents an important structure, which, however, also comprises areas of the BG associative and limbic loops. We were interested whether neuronal activity would differ between the STN medial associative‐limbic and lateral motor part, and whether selective 6‐OHDA‐induced lesions of the dorsolateral striatum, the entrance region of the BG motor loop, would differently affect these subregions. In male Sprague–Dawley rats 6‐OHDA (n = 12) or vehicle (n = 10) was bilaterally injected in the dorsolateral striatum. Four weeks later extracellular single‐unit activity and local field potentials were recorded in medial and lateral STN neurons of urethane‐anesthetized rats. In sham‐lesioned rats the discharge rate and burst activity were higher in the lateral compared to the medial STN. Similar differences were found for other neuronal activity measures (coefficient of variation of interspike interval, skewness, kurtosis, approximate entropy). After 6‐OHDA injection neuronal burst activity was enhanced, while the discharge rate was not affected. In addition, in 6‐OHDA‐lesioned rats β‐band oscillatory activity was enhanced, with no difference between STN subregions. We found important differences of neuronal activity between STN subregions, indicating functional segregation. However, selective 6‐OHDA lesions of the dorsolateral striatum also had a pronounced effect on the medial STN subregion, indicating interaction between BG loops. J. Comp. Neurol. 521:3226–3240, 2013. © 2013 Wiley Periodicals, Inc.     

Conversion of psychological stress into cellular stress response: Roles of the sigma‐1 receptor in the process

Psychiatrists empirically recognize that excessive or chronic psychological stress can result in long‐lasting impairments of brain functions that partly involve neuronal cell damage. Recent studies begin to elucidate the molecular pathways activated/inhibited by psychological stress. Activation of the hypothalamic–pituitary–adrenal axis under psychological stress causes inflammatory oxidative stresses in the brain, in part due to elevation of cytokines. Psychological stress or neuropathological conditions (e.g., accumulation of β‐amyloids) trigger ‘cellular stress responses’, which promote upregulation of molecular chaperones to protect macromolecules from degradation. The unfolded protein response, the endoplasmic reticulum (ER)‐specific cellular stress response, has been recently implicated in the pathophysiology of neuropsychiatric disorders and the pharmacology of certain clinically used drugs. The sigma‐1 receptor is an ER protein whose ligands are shown to exert antidepressant‐like and neuroprotective actions. Recent studies found that the sigma‐1 receptor is a novel ligand‐operated ER chaperone that regulates bioenergetics, free radical generation, oxidative stress, unfolded protein response and cytokine signaling. The sigma‐1 receptor also regulates morphogenesis of neuronal cells, such as neurite outgrowth, synaptogenesis, and myelination, which can be perturbed by cellular stress. The sigma‐1 receptor may thus contribute to a cellular defense system that protects nervous systems against chronic psychological stress. Findings from sigma receptor research imply that not only cell surface monoamine effectors but also intracellular molecules, especially those at the ER, may provide novel therapeutic targets for future drug developments.     

Induction of GAP‐43 modulates neuroplasticity in PBSC (CD34+) implanted‐Parkinson's model

As a result of the progressive decrease in efficacy of drugs used to treat Parkinson's disease (PD) and the rapid development of motor complications, effective alternative treatments for PD are required. In a 6‐hydroxydopamine (6‐OHDA)‐induced Parkinson's rat model, intracerebral peripheral blood stem cell (CD34⁺) (PBSC) transplantation significantly protected dopaminergic neurons from 6‐OHDA‐induced neurotoxicity, enhanced neural repair of tyrosine hydroxylase neurons through up‐regulation of Bcl‐2, facilitated stem cell plasticity, and attenuated activation of microglia, in comparison with vehicle‐control rats. The 6‐OHDA‐lesioned hemi‐Parkinsonian rats receiving intrastriatal transplantation of PBSCs also showed: 1) enhanced glucose metabolism in the lesioned striatum and thalamus, demonstrated by [¹⁸F]fluoro‐2‐deoxyglucose positron emission tomography (FDG‐PET), 2) improved neurochemical activity as shown by proton magnetic resonance spectroscopy (¹H‐MRS), and 3) significantly reduced rotational behavior in comparison with control lesioned rats. These observations might be explained by an up‐regulation of growth‐associated protein 43 (GAP‐43) expression because improvements in neurological dysfunction were blocked by injection of MK‐801 in the PBSC‐treated group. In addition, a significant increase in neurotrophic factor expression was found in the ipsilateral hemisphere of the PBSC‐treated group. In summary, this protocol may be a useful strategy for the treatment of clinical PD. © 2009 Wiley‐Liss, Inc.     

The majority of newly generated cells in the adult mouse substantia nigra express low levels of Doublecortin,but their proliferation is unaffected by 6‐OHDA‐induced nigral lesion or Minocycline‐mediated inhibition of neuroinflammation

Parkinson's disease is characterized by a selective loss of dopaminergic neurons in the substantia nigra (SN). However, whether regenerative endogenous neurogenesis is taking place in the mammalian SN of parkinsonian and non‐parkinsonian brains remains of debate. Here, we tested whether proliferating cells in the SN and their neurogenic potential would be affected by anti‐inflammatory treatment under physiological conditions and in the 6‐hydroxy‐dopamine (6‐OHDA) Parkinson's disease mouse model. We report that the majority of newly generated nigral cells are positive for Doublecortin (Dcx), which is an often used marker for neural progenitor cells. Yet, Dcx expression levels in these cells were much lower than in neural progenitor cells of the subventricular zone and the dentate gyrus neural progenitor cells. Furthermore, these newly generated nigral cells are negative for neuronal lineage markers such as TuJ1 and NeuN. Therefore, their neuronal commitment is questionable. Instead, we found evidence for oligodendrogenesis and astrogliosis in the SN. Finally, neither short‐term nor long‐term inhibition of neuroinflammation by Minocycline‐ or 6‐OHDA‐induced lesion affected the numbers of newly generated cells in our disease paradigm. Our findings of adult generated Dcx⁺ cells in the SN add important data for understanding the cellular composition and consequently the regenerative capacity of the SN.     

Subthalamic nucleus stimulation and lesioning have distinct state‐dependent effects upon striatal dopamine metabolism

The mechanism by which deep brain stimulation (DBS) of the subthalamic nucleus (STN) achieves its effects in Parkinson's disease (PD) is not known. In animal models of PD, stimulation and lesioning of the STN have some effects which are the same, but others which differ, in reversing cellular and behavioral changes induced by dopamine depletion. We compared the effects of short‐term STN stimulation and lesions upon extracellular levels of dopamine and metabolites using in vivo microdialysis of the dorsal striatum of awake, intact and unilateral 6‐hydroxydopamine (6OHDA)‐lesioned rats. STN stimulation in control rats decreased striatal dopamine levels and caused a relative increase in dopamine metabolism, as expressed by HVA/dopamine and DOPAC/dopamine ratios. This suggests an increase in both vesicular dopamine release (metabolized to HVA), and release from the cytoplasmic dopamine pool (metabolized to DOPAC). STN lesions in control rats increased the HVA/dopamine ratio, also suggesting a relative increase in vesicular dopamine release. These results indicate that STN stimulation and lesioning can affect striatal dopamine metabolism in the intact system. In 6OHDA‐lesioned rats at baseline, metabolic ratios were markedly decreased as compared with controls. STN lesions of 6OHDA‐lesioned rats did not affect relative metabolic ratios as compared with baseline levels. In 6‐OHDA‐lesioned rats, STN stimulation decreased extracellular levels of dopamine, and, to a greater extent, metabolites, resulting in a decrease in metabolic ratios. This further decrease in dopamine turnover with STN stimulation would serve to maintain dopamine levels in the dopamine‐depleted striatum, and may account for the therapeutic benefit of DBS in Parkinson's disease. Synapse 63:136–146, 2009. Published 2008 Wiley‐Liss, Inc.     

5‐S‐cysteinyldopamine neurotoxicity: Influence on the expression of α‐synuclein and ERp57 in cellular and animal models of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder whose etiology is still unclear in spite of extensive investigations. It has been hypothesized that 5‐S‐cysteinyldopamine (CysDA), a catechol‐thioether metabolite of dopamine (DA), could be an endogenous parkinsonian neurotoxin. To gain further insight into its role in the neurodegenerative process, both CD1 mice and SH‐SY5Y neuroblastoma cells were treated with CysDA, and the data were compared with those obtained by the use of 6‐hydroxydopamine, a well‐known parkinsonian mimetic. Intrastriatal injection of CysDA in CD1 mice caused a long‐lasting depletion of DA, providing evidence of in vivo neurotoxicity of CysDA. Both in mice and in SH‐SY5Y cells, CysDA treatment induced extensive oxidative stress, as evidenced by protein carbonylation and glutathione depletion, and affected the expression of two proteins, α‐synuclein (α‐Syn) and ERp57, whose levels are modulated by oxidative insult. Real‐time PCR experiments support these findings, indicating an upregulation of both ERp57 and α‐Syn expression. α‐Syn aggregation was also found to be modulated by CysDA treatment. The present work provides a solid background sustaining the hypothesis that CysDA is involved in parkinsonian neurodegeneration by inducing extensive oxidative stress and protein aggregation. © 2013 Wiley Periodicals, Inc.     

Doxycycline restrains glia and confers neuroprotection in a 6‐OHDA Parkinson model

Neuron–glia interactions play a key role in maintaining and regulating the central nervous system. Glial cells are implicated in the function of dopamine neurons and regulate their survival and resistance to injury. Parkinson's disease is characterized by the loss of dopamine neurons in the substantia nigra pars compacta, decreased striatal dopamine levels and consequent onset of extrapyramidal motor dysfunction. Parkinson's disease is a common chronic, neurodegenerative disorder with no effective protective treatment. In the 6‐OHDA mouse model of Parkinson's disease, doxycycline administered at a dose that both induces/represses conditional transgene expression in the tetracycline system, mitigates the loss of dopaminergic neurons in the substantia nigra compacta and nerve terminals in the striatum. This protective effect was associated with: (1) a reduction of microglia in normal mice as a result of doxycycline administration per se; (2) a decrease in the astrocyte and microglia response to the neurotoxin 6‐OHDA in the globus pallidus and substantia nigra compacta, and (3) the astrocyte reaction in the striatum. Our results suggest that doxycycline blocks 6‐OHDA neurotoxicity in vivo by inhibiting microglial and astrocyte expression. This action of doxycycline in nigrostriatal dopaminergic neuron protection is consistent with a role of glial cells in Parkinson's disease neurodegeneration. The neuroprotective effect of doxycycline may be useful in preventing or slowing the progression of Parkinson's disease and other neurodegenerative diseases linked to glia function.     

Elevation of heme oxygenase‐1 by proteasome inhibition affords dopaminergic neuroprotection

Postmortem studies have shown that heme oxygenase‐1 (HO‐1) immunoreactivity is increased in patients with Parkinson disease. HO‐1 expression is highly upregulated by a variety of stress. Since the proteasome activity is decreased in patients with Parkinson disease, we investigated whether proteasome activity regulates HO‐1 content. MG‐132, a proteasome inhibitor, increased the amount of HO‐1 protein mainly in astrocytes of primary mesencephalic cultures. Quantitative RT‐PCR analysis revealed that lactacystin upregulated HO‐1 mRNA expression. Proteasome inhibition with MG132 also increased the cytomegalovirus promoter‐driven expression of Flag‐HO‐1 protein and resulted in an accumulation of ubiquitinated Flag‐HO‐1 in Flag‐HO‐1‐overexpressing PC12 cells. In addition, a cycloheximide chase assay demonstrated that the degradation of Flag‐HO‐1 protein was slowed by MG‐132. Next, the function of HO‐1 which was upregulated by proteasome inhibitors was examined. Proteasome inhibitors protected dopaminergic neurons from 6‐hydroxydopamine (6‐OHDA)‐induced toxicity and this neuroprotection was abrogated by co‐treatment with zinc protoporphyrin IX, a HO‐1 inhibitor. Furthermore, 6‐OHDA‐induced toxicity was blocked by bilirubin and carbon monoxide, products of the HO‐1‐catalyzed degradation of heme. These results suggest that mesencephalic HO‐1 protein level is regulated by proteasome activity and the elevation by proteasome inhibition affords neuroprotection. © 2010 Wiley‐Liss, Inc.     

Immunohistochemical localization of a ubiquitin ligase HRD1 in murine brain

HRD1 is an E3 ubiquitin ligase and plays an important role in endoplasmic reticulum-associated degradation (ERAD). Parkin-associated endothelin receptor-like receptor (Pael-R) is a substrate of the E3 ubiquitin ligase parkin, which has been implicated in ER stress-induced cell death in dopamine neurons in autosomal recessive juvenile parkinsonism (AR-JP). Recently, we demonstrated that endogenous HRD1 interacts with Pael-R, and that HRD1 promotes the degradation of Pael-R and protects cell death caused by the accumulation of Pael-R. Another group recently reported that HRD1 suppresses the toxicity of polyglutamine-expanded huntingtin. However, the topographical localization of HRD1 protein in the brain, especially related to neurodegenerative disease, is unclear. In this study, we used immunohistochemistry to investigate the topographical localization of HRD1 in the brain and demonstrated that HRD1 immunoreactivity was expressed widely in the substantia nigra pars compacta (SNC) containing dopaminergic neurons and was expressed in the cerebral cortex, hippocampus, dentate gyrus, striatum, globus pallidus, and Purkinje cells of the cerebellar cortex. Furthermore, HRD1 immunoreactivity was detected in the neuronal cells but not in the glial cells. These results suggest that HRD1 may play an important role in maintaining higher brain function, including motor function or learning and memory. In addition, HRD1 may have substrates other than Pael-R that are implicated in neurodegenerative disorders.     

Parkin reverses intracellular β‐amyloid accumulation and its negative effects on proteasome function

The significance of intracellular β‐amyloid (Aβ₄₂) accumulation is increasingly recognized in Alzheimer's disease (AD) pathogenesis. Aβ removal mechanisms that have attracted attention include IDE/neprilysin degradation and antibody‐mediated uptake by immune cells. However, the role of the ubiquitin‐proteasome system (UPS) in the disposal of cellular Aβ has not been fully explored. The E3 ubiquitin ligase Parkin targets several proteins for UPS degradation, and Parkin mutations are the major cause of autosomal recessive Parkinson's disease. We tested whether Parkin has cross‐function to target misfolded proteins in AD for proteasome‐dependent clearance in SH‐SY5Y and primary neuronal cells. Wild‐type Parkin greatly decreased steady‐state levels of intracellular Aβ₄₂, an action abrogated by proteasome inhibitors. Intracellular Aβ₄₂ accumulation decreased cell viability and proteasome activity. Accordingly, Parkin reversed both effects. Changes in mitochondrial ATP production from Aβ or Parkin did not account for their effects on the proteasome. Parkin knock‐down led to accumulation of Aβ. In AD brain, Parkin was found to interact with Aβ and its levels were reduced. Thus, Parkin is cytoprotective, partially by increasing the removal of cellular Aβ through a proteasome‐dependent pathway. © 2009 Wiley‐Liss, Inc.     

Involvement of endoplasmic reticulum stress in optic nerve degeneration after chronic high intraocular pressure in DBA/2J mice

DBA/2J mice are one of several animal strains used for experimental models of both intraocular hypertension and glaucoma. This study investigates the relationship between endoplasmic reticulum (ER) stress and optic nerve degeneration in DBA/2J mice. Intraocular pressure (IOP) was measured in DBA/2J mice between the ages of 6 and 15 months. Optic nerve damage was assessed at 15 months of age. The nerve was immunostained with antibodies to either neurofilament heavy chain (NFH) or phosphorylated NFH (pNFH), and optic nerve damage was assessed by performing NFH‐ and pNFH‐positive axon counts. Expression levels of the ER stress proteins 78‐kDa glucose‐regulated protein, also known as binding immunoglobulin protein, and C/EBP homologous protein were assayed with Western blotting. We also investigated ER stress localization in the optic nerve by double immunostaining with antibodies to ionized calcium‐binding adaptor molecule 1, myelin basic protein, and glial fibrillary acidic protein (GFAP). In DBA/2J mice, IOP began to rise at 8 months of age, and retinal degeneration was detected at 15 months of age. DBA/2J mice had fewer axons than controls at 15 months of age. ER stress‐related protein levels were higher in the optic nerves of DBA/2J mice and were colocalized with GFAP‐positive astrocytes. Our findings suggest that ER stress plays a role in optic nerve degeneration during chronic ocular hypertension. Furthermore, ER stress may be related in some way to astrocyte activation. © 2015 Wiley Periodicals, Inc.     

Role of ubiquitin–proteasome proteolysis in muscle fiber destruction in experimental chloroquine‐induced myopathy

Previous studies have documented the presence of rimmed vacuoles, atrophic fibers, and increased lysosomal cathepsin activity in skeletal muscle from animal models of chloroquine‐induced myopathy, suggesting that muscle fibers in this type of myopathy may be degraded via the lysosomal‐proteolysis pathway. Given recent evidence of abnormal ubiquitin accumulation in rimmed vacuoles, in this study we chose to examine the significance of the ubiquitin–proteasome proteolytic system in the process of muscle fiber destruction in experimental chloroquine myopathy. Expression of ubiquitin, 26S proteasome proteins, and ubiquitin ligases, such as muscle‐specific RING finger‐1 (MuRF‐1) and atrogin‐1/muscle atrophy F‐box protein (MAFbx), was analyzed in innervated and denervated rat soleus muscles after treatment with either saline or chloroquine. Abnormal accumulation of rimmed vacuoles was observed only in chloroquine‐treated denervated muscles. Ubiquitin and proteasome immunostaining, and ubiquitin, MuRF‐1, and atrogin‐1/MAFbx mRNAs were significantly increased in denervated soleus muscles from saline‐ and chloroquine‐treated rats when compared with contralateral innervated muscles. Further, ubiquitin and ubiquitin ligase mRNA levels were higher in denervated muscles from chloroquine‐treated rats when compared with saline‐treated rats. These data demonstrate increased proteasomes and ubiquitin in denervated muscles from chloroquine‐treated rats and suggest that the ubiquitin–proteasome proteolysis pathway as well as the lysosomal‐proteolysis pathway mediate muscle fiber destruction in experimental chloroquine myopathy. Muscle Nerve 39: 521–528, 2009