Oxidative stress regulated expression of Ubiquitin Carboxyl-terminal Hydrolase-L1: Role in cell survival

Abolishing UCHL1's hydrolase activity exacerbates ischemia-induced axonal injury and functional deficits in mice

Ubiquitin C-terminal hydrolase L1 (UCHL1) is a neuronal protein important in maintaining axonal integrity and motor function and may be important in the pathogenesis of many neurological disorders. UCHL1 may ameliorate acute injury and improve recovery after cerebral ischemia. In the current study, the hypothesis that UCHL1's hydrolase activity underlies its effect in maintaining axonal integrity and function is tested after ischemic injury. Hydrolase activity was inhibited by treatment with a UCHL1 hydrolase inhibitor or by employing knockin mice bearing a mutation in the hydrolase active site (C90A). Ischemic injury was induced by oxygen-glucose deprivation (OGD) in brain slice preparations and by transient middle cerebral artery occlusion (tMCAO) surgery in mice. Hydrolase activity inhibition increased restoration time and decreased the amplitude of evoked axonal responses in the corpus callosum after OGD. Mutation of the hydrolase active site exacerbated white matter injury as detected by SMI32 immunohistochemistry, and motor deficits as detected by beam balance and cylinder testing after tMCAO. These results demonstrate that UCHL1 hydrolase activity ameliorates white matter injury and functional deficits after acute ischemic injury and support the hypothesis that UCHL1 activity plays a significant role in preserving white matter integrity and recovery of function after cerebral ischemia.

Osteopontin depletion in macrophages perturbs proteostasis via regulating UCHL1-UPS axis and mitochondria-mediated apoptosis

Introduction

Osteopontin (OPN; also known as SPP1), an immunomodulatory cytokine highly expressed in bone marrow-derived macrophages (BMMΦ), is known to regulate diverse cellular and molecular immune responses. We previously revealed that glatiramer acetate (GA) stimulation of BMMΦ upregulates OPN expression, promoting an anti-inflammatory, pro-healing phenotype, whereas OPN inhibition triggers a pro-inflammatory phenotype. However, the precise role of OPN in macrophage activation state is unknown.

Methods

Here, we applied global proteome profiling via mass spectrometry (MS) analysis to gain a mechanistic understanding of OPN suppression versus induction in primary macrophage cultures. We analyzed protein networks and immune-related functional pathways in BMMΦ either with OPN knockout (OPNKO) or GA-mediated OPN induction compared with wild type (WT) macrophages. The most significant differentially expressed proteins (DEPs) were validated using immunocytochemistry, western blot, and immunoprecipitation assays.

Results and discussion

We identified 631 DEPs in OPNKO or GA-stimulated macrophages as compared to WT macrophages. The two topmost downregulated DEPs in OPNKO macrophages were ubiquitin C-terminal hydrolase L1 (UCHL1), a crucial component of the ubiquitin-proteasome system (UPS), and the anti-inflammatory Heme oxygenase 1 (HMOX-1), whereas GA stimulation upregulated their expression. We found that UCHL1, previously described as a neuron-specific protein, is expressed by BMMΦ and its regulation in macrophages was OPN-dependent. Moreover, UCHL1 interacted with OPN in a protein complex. The effects of GA activation on inducing UCHL1 and anti-inflammatory macrophage profiles were mediated by OPN. Functional pathway analyses revealed two inversely regulated pathways in OPN-deficient macrophages: activated oxidative stress and lysosome-mitochondria-mediated apoptosis (e.g., ROS, Lamp1-2, ATP-synthase subunits, cathepsins, and cytochrome C and B subunits) and inhibited translation and proteolytic pathways (e.g., 60S and 40S ribosomal subunits and UPS proteins). In agreement with the proteome-bioinformatics data, western blot and immunocytochemical analyses revealed that OPN deficiency perturbs protein homeostasis in macrophages-inhibiting translation and protein turnover and inducing apoptosis-whereas OPN induction by GA restores cellular proteostasis. Taken together, OPN is essential for macrophage homeostatic balance via the regulation of protein synthesis, UCHL1-UPS axis, and mitochondria-mediated apoptotic processes, indicating its potential application in immune-based therapies.

Role of UCHL1 in the pathogenesis of neurodegenerative diseases and brain injury

UCHL1 is a multifunctional protein expressed at high concentrations in neurons in the brain and spinal cord. UCHL1 plays important roles in regulating the level of cellular free ubiquitin and redox state as well as the degradation of select proteins. This review focuses on the potential role of UCHL1 in the pathogenesis of neurodegenerative diseases and brain injury and recovery. Subjects addressed in the review include 1) Normal physiological functions of UCHL1. 2) Posttranslational modification sites and splice variants that alter the function of UCHL1 and mouse models with mutations and deletions of UCHL1. 3) The hypothesized role and pathogenic mechanisms of UCHL1 in neurodegenerative diseases and brain injury. 4) Potential therapeutic strategies targeting UCHL1 in these disorders.

Ubiquitin C-terminal hydrolase 1 is increased in migraine attack

OBJECTIVE

This study aimed to determine the serum level of Ubiquitin C-terminal hydrolase 1 enzyme during a migraine attack and after its treatment.

METHODS

Blood samples of 43 patients and 30 healthy controls who presented to the emergency department with migraine attacks were analysed. Study sample was classified into three groups: Group 1 (patients presenting with migraine attack), Group 2 (4thhour after dexketoprofen treatment) and Group 3 (healthy control). Demographic data of patients, visual analogue scale and Ubiquitin C-terminal hydrolase 1 levels were analysed.

RESULTS

Median (IQR) Ubiquitin C-terminal hydrolase 1 levels were 13.70 (10.75-18.92) in Group 1, 9.45 (6.95-11.56) in Group 2 and 6.04 (3.88-8.72) ng/mL in Group 3; the Kruskal-Wallis test result showed a significant difference between the groups (P<0.001). Following the Kruskal-Wallis test, the post-hoc Dunn test was performed for binary comparison between the groups, which revealed significant differences between all groups (Group 1-Group 2, Group 1-Group 3 and Group 2-Group 3 with P=0.001, P<0.001 and P=0.008, respectively). Moreover, a significant positive correlation was found between VAS score and UCHL1 levels before treatment (r=0.884, P<0.001).

CONCLUSION

UCHL1 levels of patients with migraine increase during acute attack and they can be used to assess the severity of attack and response to treatment.

Chlorogenic acid modulates the ubiquitin-proteasome system in stroke animal model

BACKGROUND

Chlorogenic acid, a phenolic compound, has potent antioxidant and neuroprotective properties. The ubiquitin-proteasome system is an important regulators of neurodevelopment and modulators of neuronal function. This system is associated with neurodevelopment and neurotransmission through degradation and removal of damaged proteins. Activation of the ubiquitin-proteasome system is a critical factor in preventing cell death. We have previously reported a decrease in the activity of the ubiquitin-proteasome system during cerebral ischemia. This study investigated whether chlorogenic acid regulates the ubiquitin-proteasome system in an animal stroke model. In adult rats, middle cerebral artery occlusion (MCAO) surgery was performed to induce focal cerebral ischemia. Chlorogenic acid (30 mg/kg) or normal saline was injected into the abdominal cavity 2 h after MCAO surgery, and cerebral cortex tissues were collected 24 h after MCAO damage.

RESULTS

Chlorogenic acid attenuated neurobehavioral disorders and histopathological changes caused by MCAO damage. We identified the decreases in ubiquitin C-terminal hydrolase L1, ubiquitin thioesterase OTUB1, proteasome subunit α type 1, proteasome subunit α type 3, and proteasome subunit β type 4 expression using a proteomics approach in MCAO animals. The decrease in these proteins was alleviated by chlorogenic acid. In addition, the results of reverse transcription-polymerase chain reaction confirmed these changes. The identified proteins were markedly reduced in MCAO damage, while chlorogenic acid prevented these reductions induced by MCAO. The decrease of ubiquitin-proteasome system proteins in ischemic damage was associated with neuronal apoptosis.

CONCLUSIONS

Our results showed that chlorogenic acid regulates ubiquitin-proteasome system proteins and protects cortical neurons from neuronal damage. These results provide evidence that chlorogenic acid has neuroprotective effects and maintains the ubiquitin-proteasome system in ischemic brain injury.

The intricate interplay between HIFs, ROS, and the ubiquitin system in the tumor hypoxic microenvironment

Alterations in protein ubiquitination and hypoxia-inducible factor (HIF) signaling both contribute to tumorigenesis and tumor progression. Ubiquitination is a dynamic process that is coordinately regulated by E3 ligases and deubiquitinases (DUBs), which have emerged as attractive therapeutic targets. HIF expression and transcriptional activity are usually increased in tumors, leading to poor clinical outcomes. Reactive oxygen species (ROS) are upregulated in tumors and have multiple effects on HIF signaling and the ubiquitin system. A growing body of evidence has shown that multiple E3 ligases and UBDs function synergistically to control the expression and activity of HIF, thereby allowing cancer cells to cope with the hypoxic microenvironment. Conversely, several E3 ligases and DUBs are regulated by hypoxia and/or HIF signaling. Hypoxia also induces ROS production, which in turn modulates the stability or activity of HIF, E3 ligases, and DUBs. Understanding the complex networks between E3 ligase, DUBs, ROS, and HIF will provide insights into the fundamental mechanism of the cellular response to hypoxia and help identify novel molecular targets for cancer treatment. We review the current knowledge on the comprehensive relationship between E3 ligase, DUBs, ROS, and HIF signaling, with a particular focus on the use of E3 ligase or DUB inhibitors in cancer.

Retinoic acid regulates the ubiquitin-proteasome system in a middle cerebral artery occlusion animal model

Background

Retinoic acid is a major metabolite of vitamin A and exerts beneficial effects including anti-oxidant and anti-inflammatory activities in neurons. The ubiquitin–proteasome system is an important biological system that regulates cell survival. Ubiquitination regulates protein degradation and plays an important role in oxidative stress. Deubiquitinating enzymes cleave ubiquitin from proteins and control ubiquitination-induced degradation. We detected decreases in ubiquitin carboxy-terminal hydrolase L1, ubiquitin thioesterase OTUB1, and proteasome subunit alpha types 1 and 3 in cerebral ischemic damage. In this study, we investigated whether retinoic acid regulates the expression of deubiquitinating enzymes ubiquitin carboxy-terminal hydrolase L1, ubiquitin thioesterase OTUB1, and proteasome subunit alpha types 1 and 3 in cerebral ischemic injury. Right middle cerebral artery occlusion (MCAO) was performed to induce cerebral ischemic damage in male rats. Retinoic acid (5 mg/kg) or vehicle was intraperitoneally injected every day from 4 days before surgery. Neurological behavioral tests were performed 24 h after MCAO, and right cerebral cortical tissues were collected.

Results

MCAO damage caused neurological behavioral dysfunction, and retinoic acid alleviated these deficits. The identified proteins decreased in MCAO animals with vehicle, while retinoic acid treatment attenuated these decreases. The results of proteomic study were confirmed by a reverse transcription-PCR technique. Expressions of ubiquitin carboxy-terminal hydrolase L1, ubiquitin thioesterase OTUB1, and proteasome subunit alpha types 1 and 3 were decreased in MCAO animals treated with vehicle. Retinoic acid treatment alleviated these MCAO-induced reductions. The ubiquitin–proteasome system plays an essential role in maintaining cell function and preserving cell shape against ischemic damage.

Conclusions

These findings suggest that retinoic acid regulates ubiquitin- and proteasome-related proteins including ubiquitin carboxy-terminal hydrolase L1, ubiquitin thioesterase OTUB1, and proteasome subunit alpha types 1 and 3 in a brain ischemia model. Changes in these proteins are involved in the neuroprotective effects of retinoic acid.

Redox regulation of DUBs and its therapeutic implications in cancer

Reactive oxygen species (ROS) act as a double-edged sword in cancer, where low levels of ROS are beneficial but excessive accumulation leads to cancer progression. Elevated levels of ROS in cancer are counteracted by the antioxidant defense system. An imbalance between ROS generation and the antioxidant system alters gene expression and cellular signaling, leading to cancer progression or death. Post-translational modifications, such as ubiquitination, phosphorylation, and SUMOylation, play a critical role in the maintenance of ROS homeostasis by controlling ROS production and clearance. Recent evidence suggests that deubiquitinating enzymes (DUBs)-mediated ubiquitin removal from substrates is regulated by ROS. ROS-mediated oxidation of the catalytic cysteine (Cys) of DUBs, leading to their reversible inactivation, has emerged as a key mechanism regulating DUB-controlled cellular events. A better understanding of the mechanism by which DUBs are susceptible to ROS and exploring the ways to utilize ROS to pharmacologically modulate DUB-mediated signaling pathways might provide new insight for anticancer therapeutics. This review assesses the recent findings regarding ROS-mediated signaling in cancers, emphasizes DUB regulation by oxidation, highlights the relevant recent findings, and proposes directions of future research based on the ROS-induced modifications of DUB activity.

Mutation of a Ubiquitin Carboxy Terminal Hydrolase L1 Lipid Binding Site Alleviates Cell Death, Axonal Injury, and Behavioral Deficits After Traumatic Brain Injury in Mice

Ubiquitin carboxy terminal hydrolase L1 (UCHL1) is a protein highly expressed in neurons that may play important roles in the ubiquitin proteasome pathway (UPP) in neurons, axonal integrity, and motor function after traumatic brain injury (TBI). Binding of reactive lipid species to cysteine 152 of UCHL1 results in unfolding, aggregation, and inactivation of the enzyme. To test the role of this mechanism in TBI, mice bearing a cysteine to alanine mutation at site 152 (C152A mice) that renders UCHL1 resistant to inactivation by reactive lipids were subjected to the controlled cortical impact model (CCI) of TBI and compared to wild type (WT) controls. Alterations in protein ubiquitination and activation of autophagy pathway markers in traumatized brain were detected by immunoblotting. Cell death and axonal injury were determined by histological assessment and anti-amyloid precursor protein (APP) immunohistochemistry. Behavioral outcomes were determined using the beam balance and Morris water maze tests. C152A mice had reduced accumulation of ubiquitinated proteins, decreased activation of the autophagy markers Beclin-1 and LC3B, a decreased number of abnormal axons, decreased CA1 cell death, and improved motor and cognitive function compared to WT controls after CCI; no significant change in spared tissue volume was observed. These results suggest that binding of lipid substrates to cysteine 152 of UCHL1 is important in the pathogenesis of injury and recovery after TBI and may be a novel target for future therapeutic approaches.

Loss of Ubiquitin Carboxy-Terminal Hydrolase L1 Impairs Long-Term Differentiation Competence and Metabolic Regulation in Murine Spermatogonial Stem Cells

Spermatogonia are stem and progenitor cells responsible for maintaining mammalian spermatogenesis. Preserving the balance between self-renewal of spermatogonial stem cells (SSCs) and differentiation is critical for spermatogenesis and fertility. Ubiquitin carboxy-terminal hydrolase-L1 (UCH-L1) is highly expressed in spermatogonia of many species; however, its functional role has not been identified. Here, we aimed to understand the role of UCH-L1 in murine spermatogonia using a Uch-l1^−/− mouse model. We confirmed that UCH-L1 is expressed in undifferentiated and early-differentiating spermatogonia in the post-natal mammalian testis. The Uch-l1^−/− mice showed reduced testis weight and progressive degeneration of seminiferous tubules. Single-cell transcriptome analysis detected a dysregulated metabolic profile in spermatogonia of Uch-l1^−/− compared to wild-type mice. Furthermore, cultured Uch-l1^−/− SSCs had decreased capacity in regenerating full spermatogenesis after transplantation in vivo and accelerated oxidative phosphorylation (OXPHOS) during maintenance in vitro. Together, these results indicate that the absence of UCH-L1 impacts the maintenance of SSC homeostasis and metabolism and impacts the differentiation competence. Metabolic perturbations associated with loss of UCH-L1 appear to underlie a reduced capacity for supporting spermatogenesis and fertility with age. This work is one step further in understanding the complex regulatory circuits underlying SSC function.

Deubiquitinases: Modulators of Different Types of Regulated Cell Death

The mechanisms and physiological implications of regulated cell death (RCD) have been extensively studied. Among the regulatory mechanisms of RCD, ubiquitination and deubiquitination enable post-translational regulation of signaling by modulating substrate degradation and signal transduction. Deubiquitinases (DUBs) are involved in diverse molecular pathways of RCD. Some DUBs modulate multiple modalities of RCD by regulating various substrates and are powerful regulators of cell fate. However, the therapeutic targeting of DUB is limited, as the physiological consequences of modulating DUBs cannot be predicted. In this review, the mechanisms of DUBs that regulate multiple types of RCD are summarized. This comprehensive summary aims to improve our understanding of the complex DUB/RCD regulatory axis comprising various molecular mechanisms for diverse physiological processes. Additionally, this review will enable the understanding of the advantages of therapeutic targeting of DUBs and developing strategies to overcome the side effects associated with the therapeutic applications of DUB modulators.

Cross-over Loop Cysteine C152 Acts as an Antioxidant to Maintain the Folding Stability and Deubiquitinase Activity of UCH-L1 Under Oxidative Stress

Redox-dependent inactivation of deubiquitinases (DUBs) is a critical factor for attenuating their DUB activity in response to cellular oxidative stress. Ubiquitin C-terminal hydrolase isoform (UCH-L1) is an important DUB that is highly expressed in human neuronal cells and is implicated in a myriad of human diseases such as neurodegenerative diseases and cancer. Increasing evidence suggests an important role of UCH-L1 in redox regulation and the protection of neuronal cells from oxidative stress. In this study, we examined the molecular basis of how UCH-L1 responds to oxidation in a reversible manner. Using H₂O₂ as a model oxidant, we showed by mass spectrometry that a subset of methionine and cysteine residues, namely (M1, M6, M12, C90, and C152) were more susceptible to oxidation. Spectroscopic analysis showed that oxidation of C90 can lead to profound structural changes in addition to the loss of function. Importantly, we further demonstrated that C152, which is located at the substrate recognition cross-over loop, serves as a reactive oxygen species (ROS) scavenger to protect catalytic C90 from oxidation under moderate oxidative conditions. Hydrogen-deuterium exchange mass spectrometry analysis provided detailed structural mapping of the destabilizing effect of H₂O₂-mediated oxidation, which resulted in global destabilization far beyond the oxidation sites. These perturbations may be responsible for irreversible aggregation when subject to prolonged oxidative stress.

Autophagy and Redox Homeostasis in Parkinson's: A Crucial Balancing Act

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated primarily from endogenous biochemical reactions in mitochondria, endoplasmic reticulum (ER), and peroxisomes. Typically, ROS/RNS correlate with oxidative damage and cell death; however, free radicals are also crucial for normal cellular functions, including supporting neuronal homeostasis. ROS/RNS levels influence and are influenced by antioxidant systems, including the catabolic autophagy pathways. Autophagy is an intracellular lysosomal degradation process by which invasive, damaged, or redundant cytoplasmic components, including microorganisms and defunct organelles, are removed to maintain cellular homeostasis. This process is particularly important in neurons that are required to cope with prolonged and sustained operational stress. Consequently, autophagy is a primary line of protection against neurodegenerative diseases. Parkinson's is caused by the loss of midbrain dopaminergic neurons (mDANs), resulting in progressive disruption of the nigrostriatal pathway, leading to motor, behavioural, and cognitive impairments. Mitochondrial dysfunction, with associated increases in oxidative stress, and declining proteostasis control, are key contributors during mDAN demise in Parkinson's. In this review, we analyse the crosstalk between autophagy and redoxtasis, including the molecular mechanisms involved and the detrimental effect of an imbalance in the pathogenesis of Parkinson's.

Elevated CCL2 causes Leydig cell malfunction in metabolic syndrome

Metabolic syndrome (MetS), which is associated with chronic inflammation, predisposes males to hypogonadism and subfertility. The underlying mechanism of these pathologies remains poorly understood. Homozygous leptin-resistant obese db/db mice are characterized by small testes, low testicular testosterone, and a reduced number of Leydig cells. Here we report that IL-1β, CCL2 (also known as MCP-1), and corticosterone concentrations were increased in the testes of db/db mice relative to those in WT controls. Cultured murine and human Leydig cells responded to cytokine stress with increased CCL2 release and apoptotic signals. Chemical inhibition of CCL2 rescued Leydig cell function in vitro and in db/db mice. Consistently, we found that Ccl2-deficient mice fed with a high-energy diet were protected from testicular dysfunction compared with similarly fed WT mice. Finally, a cohort of infertile men with a history of MetS showed that reduction of CCL2 plasma levels could be achieved by weight loss and was clearly associated with recovery from hypogonadism. Taken together, we conclude that CCL2-mediated chronic inflammation is, to a large extent, responsible for the subfertility in MetS by causing damage to Leydig cells.

MCP-1/CCL2 upregulation associates with metabolic syndrome–induced male subfertility in both mice and men.

Gene Expression Profiling of B Cell Lymphoma in Dogs Reveals Dichotomous Metabolic Signatures Distinguished by Oxidative Phosphorylation

Gene expression profiling has revealed molecular heterogeneity of diffuse large B cell lymphoma (DLBCL) in both humans and dogs. Two DLBCL subtypes based on cell of origin are generally recognized, germinal center B (GCB)-like and activated B cell (ABC)-like. A pilot study to characterize the transcriptomic phenotype of 11 dogs with multicentric BCL yielded two molecular subtypes distinguished on the basis of genes important in oxidative phosphorylation. We propose a metabolic classification of canine BCL that transcends cell of origin and shows parallels to a similar molecular phenotype in human DLBCL. We thus confirm the validity of this classification scheme across widely divergent mammalian taxa and add to the growing body of literature suggesting cellular and molecular similarities between human and canine non-Hodgkin lymphoma. Our data support a One Health approach to the study of DLBCL, including the advancement of novel therapies of relevance to both canine and human health.

Unraveling oxidative stress response in the cestode parasite Echinococcus granulosus

Cystic hydatid disease (CHD) is a worldwide neglected zoonotic disease caused by Echinococcus granulosus. The parasite is well adapted to its host by producing protective molecules that modulate host immune response. An unexplored issue associated with the parasite's persistence in its host is how the organism can survive the oxidative stress resulting from parasite endogenous metabolism and host defenses. Here, we used hydrogen peroxide (H₂O₂) to induce oxidative stress in E. granulosus protoescoleces (PSCs) to identify molecular pathways and antioxidant responses during H₂O₂ exposure. Using proteomics, we identified 550 unique proteins; including 474 in H₂O₂-exposed PSCs (H-PSCs) samples and 515 in non-exposed PSCs (C-PSCs) samples. Larger amounts of antioxidant proteins, including GSTs and novel carbonyl detoxifying enzymes, such as aldo-keto reductase and carbonyl reductase, were detected after H₂O₂ exposure. Increased concentrations of caspase-3 and cathepsin-D proteases and components of the 26S proteasome were also detected in H-PSCs. Reduction of lamin-B and other caspase-substrate, such as filamin, in H-PSCs suggested that molecular events related to early apoptosis were also induced. We present data that describe proteins expressed in response to oxidative stress in a metazoan parasite, including novel antioxidant enzymes and targets with potential application to treatment and prevention of CHD.

Downregulated UCHL1 Accelerates Gentamicin-Induced Auditory Cell Death via Autophagy

The clinical use of aminoglycoside antibiotics is partly limited by their ototoxicity. The pathogenesis of aminoglycoside-induced ototoxicity still remains unknown. Here, RNA-sequencing was conducted to identify differentially expressed genes in rat cochlear organotypic cultures treated with gentamicin (GM), and 232 and 43 genes were commonly up- and downregulated, respectively, at day 1 and 2 after exposure. Ubiquitin carboxyl-terminal hydrolase isozyme L1 (Uchl1) was one of the downregulated genes whose expression was prominent in spiral ganglion cells (SGCs), lateral walls, as well as efferent nerve terminal and nerve fibers. We further investigated if a deficit of Uchl1 in organotypic cochlea and the House Ear Institute-Organ of Corti 1 (HEI-OC1) cells accelerates ototoxicity. We found that a deficit in Uchl1 accelerated GM-induced ototoxicity by showing a decreased number of SGCs and nerve fibers in organotypic cochlear cultures and HEI-OC1 cells. Furthermore, Uchl1-depleted HEI-OC1 cells revealed an increased number of autophagosomes accompanied by decreased lysosomal fusion. These data indicate that the downregulation of Uchl1 following GM treatment is deleterious to auditory cell survival, which results from the impaired autophagic flux. Our results provide evidence that UCHL1-dependent autophagic flux may have a potential as an otoprotective target for the treatment of GM-induced auditory cell death.

Ubiquitin C-terminal hydrolase L1 (UCH-L1) loss causes neurodegeneration by altering protein turnover in the first postnatal weeks

Ubiquitin C-terminal hydrolase L1 (UCH-L1) is one of the most abundant and enigmatic enzymes of the CNS. Based on existing UCH-L1 knockout models, UCH-L1 is thought to be required for the maintenance of axonal integrity, but not for neuronal development despite its high expression in neurons. Several lines of evidence suggest a role for UCH-L1 in mUB homeostasis, although the specific in vivo substrate remains elusive. Since the precise mechanisms underlying UCH-L1-deficient neurodegeneration remain unclear, we generated a transgenic mouse model of UCH-L1 deficiency. By performing biochemical and behavioral analyses we can show that UCH-L1 deficiency causes an acceleration of sensorimotor reflex development in the first postnatal week followed by a degeneration of motor function starting at periadolescence in the setting of normal cerebral mUB levels. In the first postnatal weeks, neuronal protein synthesis and proteasomal protein degradation are enhanced, with endoplasmic reticulum stress, and energy depletion, leading to proteasomal impairment and an accumulation of nondegraded ubiquitinated protein. Increased protein turnover is associated with enhanced mTORC1 activity restricted to the postnatal period in UCH-L1-deficient brains. Inhibition of mTORC1 with rapamycin decreases protein synthesis and ubiquitin accumulation in UCH-L1-deficient neurons. Strikingly, rapamycin treatment in the first 8 postnatal days ameliorates the neurological phenotype of UCH-L1-deficient mice up to 16 weeks, suggesting that early control of protein homeostasis is imperative for long-term neuronal survival. In summary, we identified a critical presymptomatic period during which UCH-L1-dependent enhanced protein synthesis results in neuronal strain and progressive loss of neuronal function.

Role of UCHL1 in axonal injury and functional recovery after cerebral ischemia

Many neuroprotective strategies have failed to translate to clinical trials, perhaps because of a failure to preserve white matter function. Ubiquitin C-terminal hydrolase L1 (UCHL1), a neuron-specific protein essential for axonal function, is deactivated by reactive lipids produced after cerebral ischemia. Mutation of the cysteine residue 152-reactive lipid-binding site of UCHL1 decreased axonal injury after hypoxia and ischemia in vitro and in vivo, preserved axonal conductance and synaptic function, and improved motor behavior after ischemia in mice. These results suggest that UCHL1 may play an important role in maintaining axonal function after cerebral ischemia. Restoration of UCHL1 activity or prevention of degradation of UCHL1 activity by preventing binding of substrates to cysteine residue 152 could be useful approaches for treatment of stroke.

Ubiquitin C-terminal hydrolase L1 (UCHL1) is a unique brain-specific deubiquitinating enzyme. Mutations in and aberrant function of UCHL1 have been linked to many neurological disorders. UCHL1 activity protects neurons from hypoxic injury, and binding of stroke-induced reactive lipid species to the cysteine 152 (C152) of UCHL1 unfolds the protein and disrupts its function. To investigate the role of UCHL1 and its adduction by reactive lipids in inhibiting repair and recovery of function following ischemic injury, a knock-in (KI) mouse expressing the UCHL1 C152A mutation was generated. Neurons derived from KI mice had less cell death and neurite injury after hypoxia. UCHL1 C152A KI and WT mice underwent middle cerebral artery occlusion (MCAO) or sham surgery. White matter injury was significantly decreased in KI compared with WT mice 7 d after MCAO. Histological analysis revealed decreased tissue loss at 21 d after injury in KI mice. There was also significantly improved sensorimotor recovery in postischemic KI mice. K63- and K48-linked polyubiquitinated proteins were increased in penumbra of WT mouse brains but not in KI mouse brains at 24 h post MCAO. The UCHL1 C152A mutation preserved excitatory synaptic drive to pyramidal neurons and their excitability in the periinfarct zone; axonal conduction velocity recovered by 21 d post MCAO in KI mice in corpus callosum. These results demonstrate that UCHL1 activity is an important determinant of function after ischemia and further demonstrate that the C152 site of UCHL1 plays a significant role in functional recovery after stroke.

Altered Expression of Umbilical Cord Blood Levels of miR-181b and Its Downstream Target mUCH-L1 in Infants with Moderate and Severe Neonatal Hypoxic-Ischaemic Encephalopathy

Hypoxic-ischaemic encephalopathy (HIE) remains one of the leading causes of neurological disability worldwide. No blood biomarker capable of early detection and classification of injury severity in HIE has been identified. This study aimed to investigate the potential of miRNA-181b (miR-181b) and its downstream target, ubiquitin C-terminal hydrolase-L1 (UCH-L1), to predict the severity of HIE. Full-term infants with perinatal asphyxia were recruited at birth and observed for the development of HIE, along with healthy controls. Levels of miR-181b and messenger UCH-L1 (mUCH-L1) in umbilical cord blood were determined using qRT-PCR. In total, 131 infants; 40 control, 50 perinatal asphyxia without HIE (PA) and 41 HIE, recruited across two separate cohorts (discovery and validation) were included in this study. Significant and consistent downregulation of miR-181b was observed in infants with moderate/severe HIE compared to all other groups in both cohorts: discovery 0.25 (0.16-0.32) vs 0.61 (0.26-1.39), p = 0.027 and validation 0.33 (0.15-1.78) vs 1.2 (0.071-2.09), p = 0.035. mUCH-L1 showed increased expression in infants with HIE in both cohorts. The expression ratio of miR-181b to mUCH-L1 was reduced in those infants with moderate/severe HIE in both cohorts: discovery cohort 0.23 (0.06-0.44) vs 1.59 (0.46-2.54), p = 0.01 and validation cohort 0.41 (0.10-0.81) vs 1.38 (0.59-2.56) in all other infants, p = 0.009. We have validated consistent patterns of altered expression in miR-181b/mUCH-L1 in moderate/severe neonatal HIE which may have the potential to guide therapeutic intervention in HIE.

UCHL1/PGP 9.5 Dynamic in Neuro-Immune-Cutaneous Milieu: Focusing on Axonal Nerve Terminals and Epidermal Keratinocytes in Psoriatic Itch

Psoriasis is an immunogenetic skin disease manifesting as plaque lesions on the skin. Patients with psoriasis frequently suffer from itch, an unpleasant sensation causing a desire to scratch. Psoriatic itch is mainly transmitted by unmyelinated C-fibers; however, the exact molecular mechanism of psoriatic itch is still unexplained. Protein gene product 9.5 (PGP 9.5) is a panneurological marker commonly used for analysis of peripheral peptidergic and nonpeptidergic nerves and identification of cutaneous neuro-immune-endocrine cells. However, some studies suggested that nonneuronal cells, like keratinocytes, may also express PGP 9.5. This phenomenon might be linked with impaired axonal transport, keratinocyte injury, or dysfunctions of neuro-immune-cutaneous connections. The aim of this study was to analyze the expression of PGP 9.5 in psoriatic skin. We observed significantly altered density of PGP 9.5-positive axonal nerve terminals in pruritic lesional (p=0.04) and nonlesional psoriatic skin (p>0.001) compared with controls. In contrast, no significant differences were observed between psoriatic skin without itch and controls. Furthermore, PGP 9.5 expression by suprabasal keratinocytes (SBKs) was significantly increased in itchy skin lesions (p=0.007) compared to skin without itch, and a positive correlation was observed between PGP 9.5 expression and itch intensity (r=0.64; p=0.02). Our findings indicate changes in peripheral innervations and psoriatic keratinocytes, which may influence neuro-immune-cutaneous homeostasis and modulate itch transmission.

Proteomic Analysis of Hippocampus in a Mouse Model of Depression Reveals Neuroprotective Function of Ubiquitin C-terminal Hydrolase L1 (UCH-L1) via Stress-induced Cysteine Oxidative Modifications

Chronic physical restraint stress increases oxidative stress in the brain, and dysregulation of oxidative stress can be one of the causes of major depressive disorder. To understand the underlying mechanisms, we undertook a systematic proteomic analysis of hippocampus in a chronic restraint stress mouse model of depression. Combining two-dimensional gel electrophoresis (2D-PAGE) for protein separation with nanoUPLC-ESI-q-TOF tandem mass spectrometry, we identified sixty-three protein spots that changed in the hippocampus of mice subjected to chronic restraint stress. We identified and classified the proteins that changed after chronic stress, into three groups respectively functioning in neural plasticity, metabolic processes and protein aggregation. Of these, 5 proteins including ubiquitin C-terminal hydrolase L1 (UCH-L1), dihydropyrimidinase-related protein 2 (DPYL2), haloacid dehalogenase-like hydrolase domain-containing protein 2 (HDHD2), actin-related protein 2/3 complex subunit 5 (ARPC5) and peroxiredoxin-2 (PRDX2), showed pI shifts attributable to post-translational modifications. Further analysis indicated that UCH-L1 underwent differential oxidations of 2 cysteine residues following chronic stress. We investigated whether the oxidized form of UCH-L1 plays a role in stressed hippocampus, by comparing the effects of UCH-L1 and its Cys mutants on hippocampal cell line HT-22 in response to oxidative stress. This study demonstrated that UCH-L1 wild-type and cysteine to aspartic acid mutants, but not its cysteine to serine mutants, afforded neuroprotective effects against oxidative stress; there were no discernible differences between wild-type UCH-L1 and its mutants in the absence of oxidative stress. These findings suggest that cysteine oxidative modifications of UCH-L1 in the hippocampus play key roles in neuroprotection against oxidative stress caused in major depressive disorder.

Integrated transcriptomic and proteomic analyses reveal potential mechanisms linking thermal stress and depressed disease resistance in the turbot Scophthalmus maximus

A worldwide increase in the reports of diseases affecting marine organisms has paralleled the climate warming over the past few decades. In this study, we applied omics to explore the mechanisms underlying thermo-linked epizootics, by comparing both the transcriptome- and proteome-wide response of turbots to a mimic pathogen (poly I:C) between high temperature and low temperature using a time-course approach. Our results showed that myeloperoxidase (MPO) and insulin were differentially expressed transcripts shared by all five time-points post poly I:C-injection between high and low temperature and also had a consistent expression trend as differentially expressed proteins at 24 h post injection. Combined with other data, it was suggested that the elevated temperature enhanced neutrophil-mediated immunity and the resultant MPO-mediated oxidative stress, which lasted for at least 5 days. The contents of malondialdehyde and protein carbonyls, markers of oxidative damage for lipids and proteins, respectively, were compared between different temperature groups, and the results further implied the emergence of oxidative damage under high temperature. It was also suggested that metabolism disorder likely occur considering the sustained expression changes of insulin. Hence, prolonged MPO-mediated oxidative stress and metabolic disorder might be involved in the thermo-linked epizootic.

Ubiquitin C-terminal hydrolase L1 (UCH-L1): structure, distribution and roles in brain function and dysfunction

Ubiquitin C-terminal hydrolase L1 (UCH-L1) is an extremely abundant protein in the brain where, remarkably, it is estimated to make up 1–5% of total neuronal protein. Although it comprises only 223 amino acids it has one of the most complicated 3D knotted structures yet discovered. Beyond its expression in neurons UCH-L1 has only very limited expression in other healthy tissues but it is highly expressed in several forms of cancer. Although UCH-L1 is classed as a deubiquitinating enzyme (DUB) the direct functions of UCH-L1 remain enigmatic and a wide array of alternative functions has been proposed. UCH-L1 is not essential for neuronal development but it is absolutely required for the maintenance of axonal integrity and UCH-L1 dysfunction is implicated in neurodegenerative disease. Here we review the properties of UCH-L1, and how understanding its complex structure can provide new insights into its roles in neuronal function and pathology.

In vivo transduction of neurons with TAT-UCH-L1 protects brain against controlled cortical impact injury

Many mechanisms or pathways are involved in secondary post-traumatic brain injury, such as the ubiquitin-proteasome pathway (UPP), axonal degeneration and neuronal cell apoptosis. UCH-L1 is a protein that is expressed in high levels in neurons and may have important roles in the UPP, autophagy and axonal integrity. The current study aims to evaluate the role of UCH-L1 in post-traumatic brain injury (TBI) and its potential therapeutic effects. A novel protein was constructed that fused the protein transduction domain (PTD) of trans-activating transduction (TAT) protein with UCH-L1 (TAT-UCH-L1) in order to promote neuronal transduction. The TAT-UCH-L1 protein was readily detected in brain by immunoblotting and immunohistochemistry after i.p. administration in mice. TBI was induced in mice using the controlled cortical impact (CCI) model. TAT-UCH-L1 treatment significantly attenuated K48-linkage polyubiquitin (polyUb)-protein accumulation in hippocampus after CCI compared to vehicle controls, but had no effects on K65-linkage polyUb-protein. TAT-UCH-L1 treatment also attenuated expression of Beclin-1 and LC3BII after CCI. TAT-UCH-L1-treated mice had significantly increased spared tissue volumes and increased survival of CA3 neurons 21 d after CCI compared to control vehicle-treated mice. Axonal injury, detected by APP immunohistochemistry, was reduced in thalamus 24 h and 21 d after CCI in TAT-UCH-L1-treated mice. These results suggest that TAT-UCH-L1 treatment improves function of the UPP and decreases activation of autophagy after CCI. Furthermore, TAT-UCH-L1 treatment also attenuates axonal injury and increases hippocampal neuronal survival after CCI. Taken together these results suggest that UCH-L1 may play an important role in the pathogenesis of cell death and axonal injury after TBI.

Role of the Ubiquitin C-Terminal Hydrolase L1-Modulated Ubiquitin Proteasome System in Auditory Cortex Senescence

BACKGROUND/AIMS

According to recent studies, central auditory impairments are closely related to neurodegenerative diseases. However, the mechanism of central presbycusis remains unclear. Ubiquitin C-terminal hydrolase L1 (UCHL1) is important in maintaining proteasomal activity; however, the detailed mechanism has not yet been fully elucidated. This study aims to investigate the molecular alterations involved in UCHL1 regulation during auditory cortex aging.

METHODS

D-Galactose (D-gal) induces oxidative stress and senescence in the auditory cortex, as reported in our previous studies. Primary auditory cortex cells were treated with D-gal for 72 h or 5 days. The proteins related to the ubiquitin proteasome system (UPS) and proteasomal activities were evaluated. UCHL1 was overexpressed, and the effects of UCHL1 on the UPS and proteasomal activity were analyzed.

RESULTS

Proteasomal activity was elevated at 72 h and decreased at 5 days in D-gal-treated primary auditory cortex cells. We also found that overexpression of UCHL1 increased the UPS-related proteins UBE1, PSMA7, ubiquitinated proteins, and monoubiquitin, and proteasomal activity.

CONCLUSION

The results suggest that UCHL1 may modify the aging process in the auditory cortex by regulating UPS- related proteins.

Life and death in the trash heap: The ubiquitin proteasome pathway and UCHL1 in brain aging, neurodegenerative disease and cerebral Ischemia

The ubiquitin proteasome pathway (UPP) is essential for removing abnormal proteins and preventing accumulation of potentially toxic proteins within the neuron. UPP dysfunction occurs with normal aging and is associated with abnormal accumulation of protein aggregates within neurons in neurodegenerative diseases. Ischemia disrupts UPP function and thus may contribute to UPP dysfunction seen in the aging brain and in neurodegenerative diseases. Ubiquitin carboxy-terminal hydrolase L1 (UCHL1), an important component of the UPP in the neuron, is covalently modified and its activity inhibited by reactive lipids produced after ischemia. As a result, degradation of toxic proteins is impaired which may exacerbate neuronal function and cell death in stroke and neurodegenerative diseases. Preserving or restoring UCHL1 activity may be an effective therapeutic strategy in stroke and neurodegenerative diseases.

It Is All about (U)biquitin: Role of Altered Ubiquitin-Proteasome System and UCHL1 in Alzheimer Disease

Free radical-mediated damage to macromolecules and the resulting oxidative modification of different cellular components are a common feature of aging, and this process becomes much more pronounced in age-associated pathologies, including Alzheimer disease (AD). In particular, proteins are particularly sensitive to oxidative stress-induced damage and these irreversible modifications lead to the alteration of protein structure and function. In order to maintain cell homeostasis, these oxidized/damaged proteins have to be removed in order to prevent their toxic accumulation. It is generally accepted that the age-related accumulation of “aberrant” proteins results from both the increased occurrence of damage and the decreased efficiency of degradative systems. One of the most important cellular proteolytic systems responsible for the removal of oxidized proteins in the cytosol and in the nucleus is the proteasomal system. Several studies have demonstrated the impairment of the proteasome in AD thus suggesting a direct link between accumulation of oxidized/misfolded proteins and reduction of this clearance system. In this review we discuss the impairment of the proteasome system as a consequence of oxidative stress and how this contributes to AD neuropathology. Further, we focus the attention on the oxidative modifications of a key component of the ubiquitin-proteasome pathway, UCHL1, which lead to the impairment of its activity.

Cardiac sympathetic innervation and PGP9.5 expression by cardiomyocytes after myocardial infarction: effects of central MR blockade

Central mechanisms involving mineralocorticoid receptor (MR) activation contribute to an increase in sympathetic tone after myocardial infarction (MI). We hypothesized that this central mechanism also contributes to cardiac sympathetic axonal sprouting and that central MR blockade reduces cardiac sympathetic hyperinnervation post-MI. Post-MI, tyrosine hydroxylase (TH) and norepinephrine transporter protein content in the noninfarcted base of the heart remained unaltered. In contrast, protein gene product (PGP)9.5 protein was increased twofold in the base of the heart and sixfold in the peri-infarct area at 1 wk post-MI and was associated with increased ubiquitin expression. These changes persisted to a lesser extent at 4 wk post-MI and were no longer present at 12 wk. Cardiac myocytes rather than sympathetic axons were the main source of this elevated PGP9.5 expression. At 7–10 days post-MI, in the peri-infarct area, sympathetic hyperinnervation was observed with a fourfold increase in growth-associated protein 43, a twofold increase in TH, and a 50% increase in PGP9.5-positive fibers compared with the epicardial side of the left ventricle in sham rats. Central infusion of the MR blocker eplerenone markedly attenuated these increases in nerve densities but did not affect overall cardiac PGP9.5 and ubiquitin protein overexpression. We conclude that central MR activation contributes to sympathetic hyperinnervation, possibly by decreasing cardiac sympathetic activity post-MI, or by affecting other mechanisms, such as the expression of nerve growth factor. Marked PGP9.5 expression occurs in cardiomyocytes early post-MI, which may contribute to the increase in ubiquitin.

Proteomic analysis of testicular ischemia-reperfusion injury in rats

Testicular torsion is a urological emergency that leads to serious testicular damage and male infertility. We performed this study to identify specific proteins that are differentially expressed in response to testicular torsion and detorsion-induced ischemia-reperfusion (I-R) injury. Adult male rats were divided into two groups: a sham-operated group and a testicular I-R group. Testicular torsion was induced by rotating the left testis 720° in a clockwise direction for 1 hr, and then, detorsion was performed for 24 hr. After this testicular tissues were collected, protein analysis was performed using two-dimensional gel electrophoresis and Western blot analyses. Testicular I-R injury resulted in serious histopathologic damage to the germinal cells in the seminiferous tubules and increased the number of TUNEL-positive cells in testicular tissue. Specific protein spots with a greater than 2.5-fold change in intensity between the sham-operated and testicular I-R groups were identified by mass spectrometry. Among these proteins, levels of peroxiredoxin 6, thioredoxin, heterogeneous nuclear ribonucleoproteins, ubiquitin carboxyl terminal hydrolase isozyme L5 and zinc finger AN1-type domain 3 were decreased in the testicular I-R group compared to the sham-operated group. Moreover, Western blot analysis clearly showed the decrease of these proteins in the testicular I-R group. These proteins have spermatogenesis and anti-oxidative functions. These findings suggest that testicular I-R results in cell death due to altered expression of several proteins with spermatogenesis and anti-oxidation functions.

Urea transporter UT-B deletion induces DNA damage and apoptosis in mouse bladder urothelium

BACKGROUND

Previous studies found that urea transporter UT-B is abundantly expressed in bladder urothelium. However, the dynamic role of UT-B in bladder urothelial cells remains unclear. The objective of this study is to evaluate the physiological roles of UT-B in bladder urothelium using UT-B knockout mouse model and T24 cell line.

METHODOLOGY/PRINCIPAL FINDINGS

Urea and NO measurement, mRNA expression micro-array analysis, light and transmission electron microscopy, apoptosis assays, DNA damage and repair determination, and intracellular signaling examination were performed in UT-B null bladders vs wild-type bladders and in vitro T24 epithelial cells. UT-B was highly expressed in mouse bladder urothelium. The genes, Dcaf11, MCM2-4, Uch-L1, Bnip3 and 45 S pre rRNA, related to DNA damage and apoptosis were significantly regulated in UT-B null urothelium. DNA damage and apoptosis highly occurred in UT-B null urothelium. Urea and NO levels were significantly higher in UT-B null urothelium than that in wild-type, which may affect L-arginine metabolism and the intracellular signals related to DNA damage and apoptosis. These findings were consistent with the in vitro study in T24 cells that, after urea loading, exhibited cell cycle delay and apoptosis.

CONCLUSIONS/SIGNIFICANCE

UT-B may play an important role in protecting bladder urothelium by balancing intracellular urea concentration. Disruption of UT-B function induces DNA damage and apoptosis in bladder, which can result in bladder disorders.

Sustained resistance to acute MPTP toxicity by hypothalamic dopamine neurons following chronic neurotoxicant exposure is associated with sustained up-regulation of parkin protein

Hypothalamic tuberoinfundibular dopamine (TIDA) neurons remain unaffected in Parkinson disease (PD) while there is significant degeneration of midbrain nigrostriatal dopamine (NSDA) neurons. A similar pattern of susceptibility is observed following acute exposure to the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and the resistance of TIDA neurons to MPTP is associated with increased expression of parkin and ubiquitin carboxy-terminal hydrolase L-1 (UCHL-1). In the present study, the response of TIDA and NSDA neurons to acute MPTP administration following chronic MPTP exposure was examined. Mice were treated with ten injections of either MPTP (20mg/kg; s.c.; every 3.5 days) or saline vehicle (10 ml/kg; s.c.; every 3.5 days). Following a 21 day recovery period, chronic saline- and MPTP-treated mice received an additional injection of either saline (10 ml/kg; s.c.) or MPTP (20mg/kg; s.c.) and were sacrificed 24h later. NSDA neurons displayed significant axon terminal degeneration (as reflected by decreases in DA, tyrosine hydroxylase (TH) and DA transporter concentrations in the striatum) as well as loss of TH-immunoreactive (IR) neurons in the substantia nigra (SN) following MPTP, whereas TIDA neurons revealed no overt axon terminal pathology or loss of TH-IR cell bodies. NSDA neuronal pathology was associated with transient decreases in concentrations of parkin and UCHL-1 protein in the SN, which returned to normal levels by 21 days following cessation of chronic neurotoxicant exposure. Resistance of TIDA neurons to MPTP toxicity was correlated with a transient increase in UCHL-1 and a sustained elevation in parkin in the arcuate nucleus. TIDA neurons represent a DA neuron population with a unique and inherent ability to adapt to acute and chronic toxicant administration with a sustained elevation of the neuroprotective protein parkin. The correlation between the ability to increase parkin and UCHL-1 expression and the resistance of DA neurons to neurotoxicant exposure is consistent with a functional link between these features and an underlying differential susceptibility to toxicant-associated neurodegeneration.

Increased EID1 nuclear translocation impairs synaptic plasticity and memory function associated with pathogenesis of Alzheimer's disease

Though loss of function in CBP/p300, a family of CREB-binding proteins, has been causally associated with a variety of human neurological disorders, such as Rubinstein-Taybi syndrome, Huntington's disease and drug addiction, the role of EP300 interacting inhibitor of differentiation 1 (EID1), a CBP/p300 inhibitory protein, in modulating neurological functions remains completely unknown. Through the examination of EID1 expression and cellular distribution, we discovered that there is a significant increase of EID1 nuclear translocation in the cortical neurons of Alzheimer's disease (AD) patient brains compared to that of control brains. To study the potential effects of EID1 on neurological functions associated with learning and memory, we generated a transgenic mouse model with a neuron-specific expression of human EID1 gene in the brain. Overexpression of EID1 led to an increase in its nuclear localization in neurons mimicking that seen in human AD brains. The transgenic mice had a disrupted neurofilament organization and increase of astrogliosis in the cortex and hippocampus. Furthermore, we demonstrated that overexpression of EID1 reduced hippocampal long-term potentiation and impaired spatial learning and memory function in the transgenic mice. Our results indicated that the negative effects of extra nuclear EID1 in transgenic mouse brains are likely due to its inhibitory function on CBP/p300 mediated histone and p53 acetylation, thus affecting the expression of downstream genes involved in the maintenance of neuronal structure and function. Together, our data raise the possibility that alteration of EID1 expression, particularly the increase of EID1 nuclear localization that inhibits CBP/p300 activity in neuronal cells, may play an important role in AD pathogenesis.

A novel neuron-enriched protein SDIM1 is down regulated in Alzheimer's brains and attenuates cell death induced by DNAJB4 over-expression in neuro-progenitor cells

BACKGROUND

Molecular changes in multiple biological processes contribute to the development of chronic neurodegeneration such as late onset Alzheimer's disease (LOAD). To discover how these changes are reflected at the level of gene expression, we used a subtractive transcription-based amplification of mRNA procedure to identify novel genes that have altered expression levels in the brains of Alzheimer's disease (AD) patients. Among the genes altered in expression level in AD brains was a transcript encoding a novel protein, SDIM1, that contains 146 amino acids, including a typical signal peptide and two transmembrane domains. Here we examined its biochemical properties and putative roles in neuroprotection/neurodegeneration.

RESULTS

QRT-PCR analysis of additional AD and control post-mortem human brains showed that the SDIM1 transcript was indeed significantly down regulated in all AD brains. SDIM1 is more abundant in NT2 neurons than astrocytes and present throughout the cytoplasm and neural processes, but not in the nuclei. In NT2 neurons, it is highly responsive to stress conditions mimicking insults that may cause neurodegeneration in AD brains. For example, SDIM1 was significantly down regulated 2 h after oxygen-glucose deprivation (OGD), though had recovered 16 h later, and also appeared significantly up regulated compared to untreated NT2 neurons. Overexpression of SDIM1 in neuro-progenitor cells improved cells' ability to survive after injurious insults and its downregulation accelerated cell death induced by OGD. Yeast two-hybrid screening and co-immunoprecipitation approaches revealed, both in vitro and in vivo, an interaction between SDIM1 and DNAJB4, a heat shock protein hsp40 homolog, recently known as an enhancer of apoptosis that also interacts with the mu opioid receptor in human brain. Overexpression of DNAJB4 alone significantly reduced cell viability and SDIM1 co-overexpression was capable of attenuating the cell death caused DNAJB4, suggesting that the binding of SDIM1 to DNAJB4 might sequester DNAJB4, thus increasing cell viability.

CONCLUSION

Taken together, we have identified a small membrane protein, which is down regulated in AD brains and neuronal cells exposed to injurious insults. Its ability to promote survival and its interaction with DNAJB4 suggest that it may play a very specific role in brain cell survival and/or receptor trafficking.

The tumor suppressor UCHL1 forms a complex with p53/MDM2/ARF to promote p53 signaling and is frequently silenced in nasopharyngeal carcinoma

PURPOSE

Nasopharyngeal carcinoma is prevalent in southern China and Southeast Asia, with distinct geographic and ethnic distribution. One candidate susceptibility locus has been identified at 4p11-14, with the associated candidate gene(s) not identified yet. This study investigated the role of ubiquitin carboxyl-terminal hydrolase L1 (UCHL1) in nasopharyngeal carcinoma pathogenesis.

EXPERIMENTAL DESIGN

UCHL1 expression and methylation were examined in nasopharyngeal carcinoma. Furthermore, the mechanism of its tumor-suppressive function was elucidated in nasopharyngeal carcinoma cells.

RESULTS

Through genomewide expression profiling, we identified UCHL1, a 4p14 gene normally expressed in normal upper respiratory tract tissues, being silenced in all nasopharyngeal carcinoma cell lines. Its silencing is mediated by CpG methylation because UCHL1 promoter methylation was detected in all silenced cell lines, and pharmacologic demethylation reactivated UCHL1 expression along with concomitant promoter demethylation. UCHL1 methylation was also frequently detected in primary tumors but only weakly detected in few normal nasopharyngeal tissues, indicating that the methylation-mediated silencing of UCHL1 is important in nasopharyngeal carcinoma pathogenesis. Ectopic UCHL1 expression dramatically inhibited the growth of nasopharyngeal carcinoma cells through promoting tumor cell apoptosis. We further found that UCHL1 formed a complex with p53/p14(ARF)/Mdm2 p53 binding protein homolog (mouse), MDM2 and activated the p53 signaling pathway. UCHL1 expression extended p53 and p14(ARF) protein half-life and shortened MDM2 protein half-life.

CONCLUSIONS

These results indicate that UCHL1 could deubiquitinate p53 and p14(ARF) and ubiquitinate MDM2 for p53 stabilization to promote p53 signaling, thus involved in nasopharyngeal carcinoma pathogenesis, whereas it is frequently silenced in this tumor.

Proteomic analysis of focal cerebral ischemic injury in male rats

The present study identified the proteins that are differentially expressed during ischemic brain injury. Adult male rats were performed a middle cerebral artery occlusion (MCAO) to induce cerebral ischemia, and brains were collected at 24 hr after MCAO. Protein analysis was performed on the cerebral cortex using two-dimensional gel electrophoresis. Protein spots with a greater than 3 fold change in intensity between the sham and MCAO groups were identified by mass spectrometry. Among these proteins, 60 kDa heat shock protein, dehydropyrimidinase-related protein 2, t-complex protein 1, and Rho GDP dissociation inhibitor levels were significantly increased in MCAO group compared to those of the sham group. In contrast, thioredoxin, peroxiredoxin-2, stathmin, ubiquitin carboxy-terminal hydrolase L1, guanine nucleotide-binding protein alpha, pyridoxal-5'-phosphate phosphatase, and apoplipoprotein A-I levels were significantly decreased in MCAO group. These results suggest that cerebral ischemia induces neuronal cells death by changing expression levels of several proteins.

Expression and functional studies of ubiquitin C-terminal hydrolase L1 regulated genes

Deubiquitinating enzymes (DUBs) have been increasingly implicated in regulation of cellular processes, but a functional role for Ubiquitin C-terminal Hydrolases (UCHs), which has been largely relegated to processing of small ubiquitinated peptides, remains unexplored. One member of the UCH family, UCH L1, is expressed in a number of malignancies suggesting that this DUB might be involved in oncogenic processes, and increased expression and activity of UCH L1 have been detected in EBV-immortalized cell lines. Here we present an analysis of genes regulated by UCH L1 shown by microarray profiles obtained from cells in which expression of the gene was inhibited by RNAi. Microarray data were verified with subsequent real-time PCR analysis. We found that inhibition of UCH L1 activates genes that control apoptosis, cell cycle arrest and at the same time suppresses expression of genes involved in proliferation and migration pathways. These findings are complemented by biological assays for apoptosis, cell cycle progression and migration that support the data obtained from microarray analysis, and suggest that the multi-functional molecule UCH L1 plays a role in regulating principal pathways involved in oncogenesis.

Alteration of NRSF expression exacerbating 1-methyl-4-phenyl-pyridinium ion-induced cell death of SH-SY5Y cells

Neuron-restrictive silencer factor (NRSF)/neuronal repressor element-1 silencing transcription factor (REST) and its neuron-specific truncated form REST4 participates in the pathological processes of nervous system diseases, such as global ischemia, epilepsy, Huntington disease and so on. In this paper, we investigated the changes of NRSF and REST4 in a cellular model of Parkinson's disease (PD). Our results showed that neurotoxin 1-methyl-4-phenyl-pyridinium ion (MPP(+)) treatment triggered the mRNA and protein expression of NRSF and REST4, and caused both NRSF and REST4 proteins relocalized between the nucleus and cytoplasm in human dopaminergic SH-SY5Y cells. Redistribution of NRSF and REST4 derepressed the expression of target genes at late time points. Furthermore, alteration of NRSF and REST4 expression by overexpression or RNAi techniques elicited deleterious effects on cell viability of SH-SY5Y treated with toxic MPP(+).

Identification of proteins differentially expressed by melatonin treatment in cerebral ischemic injury--a proteomics approach

We previously reported that melatonin protects neuronal cells against ischemic brain damage. In this study, we identified proteins that were differentially expressed by melatonin treatment during ischemic brain injury. Rats were subjected to cerebral ischemia by middle cerebral artery occlusion (MCAO). Adult male rats were treated with melatonin (5 mg/kg) or vehicle prior to MCAO and brains were collected at 24 hr after MCAO. Proteins derived from the cerebral cortex were analyzed using two-dimensional gel electrophoresis. Protein spots with a greater than 2.5-fold change in intensity were identified by mass spectrometry. Among these proteins, gamma-enolase, stathmin, thioredoxin, peroxiredoxin-6, hippocalcin, protein phosphatase 2A, adenosylhomocysteinase, ubiquitin carboxy-terminal hydrolase L1, and NAD-specific isocitrate dehydrogenase subunit alpha were significantly decreased in the vehicle-treated group in comparison to the melatonin-treated group. The identified proteins consist of cell differentiation and stabilization proteins, as well as an antioxidant enzyme. In contrast, dehydroprimidinase-related protein 2 (DRP-2), a target of protein oxidation in neurodegeneration, was significantly increased in vehicle-treated animals, while melatonin prevented the injury-induced increase of DRP-2. Thus, the results of this study suggest that melatonin prevents cell death resulting from ischemic brain injury and that its neuroprotective effects are mediated by both the up- and down-regulation of various proteins.

Multifarious proteomic signatures and regional heterogeneity in glioblastomas

To investigate the underlying intratumoral diversity of molecular profiles in glioblastomas, a proteomic approach was introduced to compare samples from regions of different histological grade. Using two-dimensional gel electrophoresis (2DE) with matrix-assisted laser-desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), we compared prospectively collected tissue samples of different histological grade areas of three glioblastoma patients. Consistent results showing relatively high expression of ubiquitin carboxyl-terminal esterase L1 in low-histological-grade areas (Grade 2 > Grades 3 and 4) and high expression of transthyretin in high-histological-grade areas (Grade 2 < Grades 3 and 4) were demonstrated. These results were confirmed by western blot (WB) analysis and immunohistochemical staining. This study provided the evidence of multifarious proteomic signatures according to regional and histological heterogeneity in glioblastomas.

A novel brain-enriched E3 ubiquitin ligase RNF182 is up regulated in the brains of Alzheimer's patients and targets ATP6V0C for degradation

Background

Alterations in multiple cellular pathways contribute to the development of chronic neurodegeneration such as a sporadic Alzheimer's disease (AD). These, in turn, involve changes in gene expression, amongst which are genes regulating protein processing and turnover such as the components of the ubiquitin-proteosome system. Recently, we have identified a cDNA whose expression was altered in AD brains. It contained an open reading frame of 247 amino acids and represented a novel RING finger protein, RNF182. Here we examined its biochemical properties and putative role in brain cells.

Results

RNF182 is a low abundance cytoplasmic protein expressed preferentially in the brain. Its expression was elevated in post-mortem AD brain tissue and the gene could be up regulated in vitro in cultured neurons subjected to cell death-inducing injuries. Subsequently, we have established that RNF182 protein possessed an E3 ubiquitin ligase activity and stimulated the E2-dependent polyubiquitination in vitro. Yeast two-hybrid screening, overexpression and co-precipitation approaches revealed, both in vitro and in vivo, an interaction between RNF182 and ATP6V0C, known for its role in the formation of gap junction complexes and neurotransmitter release channels. The data indicated that RNF182 targeted ATP6V0C for degradation by the ubiquitin-proteosome pathway. Overexpression of RNF182 reduced cell viability and it would appear that by itself the gene can disrupt cellular homeostasis.

Conclusion

Taken together, we have identified a novel brain-enriched RING finger E3 ligase, which was up regulated in AD brains and neuronal cells exposed to injurious insults. It interacted with ATP6V0C protein suggesting that it may play a very specific role in controlling the turnover of an essential component of neurotransmitter release machinery.

The c-Jun-N-terminal kinase is involved in the neurotoxic effect of azaspiracid-1

AIMS

Azaspiracids (AZAs) are marine phycotoxins with an unknown mechanism of action, recently implicated in human intoxications. The predominant analog in nature, AZA-1 targets several organs in vivo, including the central nervous system and exhibits high neurotoxicity in vitro.

METHODS

We used pharmacological tools to inhibit the cytotoxic effect of the toxin in primary cultured neurons. Immunocytochemical techniques in combination with confocal microscopy were employed to examine the cellular mechanisms involved in the neurotoxic effect of AZA-1.

RESULTS

Several targets for azaspiracid-induced neurotoxicity, specifically the cAMP pathway, or protein kinase C and phosphatidylinositol 3-kinase activation were excluded. Interestingly, the specific c-Jun-N-terminal protein kinase (JNK) inhibitor SP 600125 protected cultured neurons against AZA-induced cytotoxicity. Immunocytochemistry experiments showed that AZA-1 increased the amount of phosphorylated JNK and caused nuclear translocation of the active protein that was prevented by SP 600125.

CONCLUSION

Our data constitute the relationship between azaspiracid-induced cytotoxicity and specific modifications in cellular transduction signals, specifically we found that JNK activation is associated with the cytotoxic effect of the toxin. These results should provide the basis to identify the mechanism of action of this group of toxins.

Gene encoding a deubiquitinating enzyme is mutated in artesunate- and chloroquine-resistant rodent malaria parasites

Artemisinin- and artesunate-resistant Plasmodium chabaudi mutants, AS-ART and AS-ATN, were previously selected from chloroquine-resistant clones AS-30CQ and AS-15CQ respectively. Now, a genetic cross between AS-ART and the artemisinin-sensitive clone AJ has been analysed by Linkage Group Selection. A genetic linkage group on chromosome 2 was selected under artemisinin treatment. Within this locus, we identified two different mutations in a gene encoding a deubiquitinating enzyme. A distinct mutation occurred in each of the clones AS-30CQ and AS-ATN, relative to their respective progenitors in the AS lineage. The mutations occurred independently in different clones under drug selection with chloroquine (high concentration) or artesunate. Each mutation maps to a critical residue in a homologous human deubiquitinating protein structure. Although one mutation could theoretically account for the resistance of AS-ATN to artemisinin derivates, the other cannot account solely for the resistance of AS-ART, relative to the responses of its sensitive progenitor AS-30CQ. Two lines of Plasmodium falciparum with decreased susceptibility to artemisinin were also selected. Their drug-response phenotype was not genetically stable. No mutations in the UBP-1 gene encoding the P. falciparum orthologue of the deubiquitinating enzyme were observed. The possible significance of these mutations in parasite responses to chloroquine or artemisinin is discussed.

Testicular germ cell sensitivity to TRAIL-induced apoptosis is dependent upon p53 expression and is synergistically enhanced by DR5 agonistic antibody treatment

The ability of the TRAIL/DR5 signaling pathway to induce apoptosis has generally been limited to tumor cells. Here we report that in primary testis explants, addition of TRAIL (0.5 mug/ml) caused a three-fold increase in germ cell apoptosis. Furthermore, exposure of C57BL/6 mice to the testicular toxicant, mono-(2-ethylhexyl) phthalate (MEHP), caused an increased p53 stability and elevated DR5 mRNA levels coincident with increases in the levels of apoptosis in spermatocytes. To further assess the mechanisms responsible for the sensitivity of germ cells to undergo TRAIL/DR5-mediated apoptosis, we used the germ cell lines GC-1spg and GC-2spd(ts) (a temperature sensitive spermatocyte-like cell line that allows for p53 nuclear localization at 32 degrees C but not 37 degrees C). Addition of TRAIL and the anti-DR5 monoclonal antibody, MD5-1, triggered a robust synergistic increase of apoptosis in p53 permissive GC-2 cells (32 degrees C) but not in GC-1 cells. In addition, DR5 levels on the plasma membrane of permissive cells were considerably enhanced concomitant with p53 expression and after MD5-1 treatment. These data represent the first indication that testicular germ cells, specifically spermatocytes, can undergo TRAIL-mediated apoptosis and the clinically relevant observation that pretreatment with a DR5 monoclonal antibody can greatly sensitize their apoptotic response to TRAIL.