Intracellular degradation of misfolded proteins in polyglutamine neurodegenerative diseases

Glucoraphanin Triggers Rapid Antidepressant Responses in a Rat Model of Beta Amyloid-Induced Depressive-like Behaviour

Glucoraphanin (GRA) is a natural compound that has shown beneficial effects in chronic diseases and in central nervous system disorders. Moreover, GRA displayed antidepressant activity in preclinical models. We have previously demonstrated that a single intracerebroventricular administration of soluble amyloid-beta 1-42 (sAβ 1-42) in rat evokes a depressive-like phenotype by increasing immobility frequency in the forced swimming test (FST). The aim of this work was to investigate the effect of GRA in naïve and in sAβ-1-42-treated rats by using the FST. Behavioural analyses were accompanied by neurochemical and biochemical measurements in the prefrontal cortex (PFC), such as serotonin (5-HT), noradrenaline (NA), kynurenine (KYN), tryptophan (TRP), reactive oxygen species (ROS) and the transcription nuclear factor kappa B (NF-kB) levels. We reported that GRA administration in naïve rats at the dose of 50 mg/kg reduced the immobility frequency in the FST and increased 5-HT and NA levels in the PFC compared to controls. At the same dose, GRA reverted depressive-like effects of sAβ 1-42 administration, restored the 5-HT levels and reduced NF-kB, KYN and ROS levels in PFC. In conclusion, GRA rapidly reverting depressive-like behaviour, together with biochemical and neurochemical alterations, might represent a safe and natural candidate for the treatment of depression.

Protein Hydrolysate of Silkworm Pupa Prevents Memory Impairment Induced by Oxidative Stress in Scopolamine-Induced Mice via Modulating the Cholinergic Nervous System and Antioxidant Defense System

Silkworm pupae (Bombyx mori) is an edible insect that has been reported to contain high-quality proteins, lipids, minerals, and vitamins, and to possess high antioxidant activity. However, there have been no studies on the neuroprotective effects of silkworm pupae. Therefore, we investigated a water extract of silkworm pupae with protease (WSP) as a functional and therapeutic candidate for neurodegenerative disorders. First, we evaluated the effect of WSP on oxidative stress-induced mouse hippocampal neuronal cells (HT-22 cells). Cell viability diminished by addition of glutamate but was significantly recovered by WSP treatment. Furthermore, WSP significantly decreased the release of lactate dehydrogenase and generation of intracellular reactive oxygen species in oxidative stress-induced cells. In addition, in scopolamine-treated mice, WSP attenuated memory impairment, as demonstrated in the Morris water maze and passive avoidance tests, indicating protection of neuronal cells against oxidative damage. Moreover, WSP prevented scopolamine-induced increases in acetylcholinesterase activity and decreases in choline-acetyltransferase activity. Finally, treatment with WSP enhanced the antioxidant defense system by regulating the activities of antioxidant enzymes. Overall, this study showed that WSP exerted antioxidant and memory enhancing action against oxidative stress.

Neuroprotective Activity of Polyphenol-Rich Ribes diacanthum Pall against Oxidative Stress in Glutamate-Stimulated HT-22 Cells and a Scopolamine-Induced Amnesia Animal Model

Ribes diacanthum Pall, a native Mongolian medicinal plant, has been reported to show antioxidant activities due to its polyphenol and flavonoid content, and is especially rich in the ethyl acetate fraction from an 80% methanol extraction (RDP). We assessed the cytoprotective effect of RDP on glutamate-caused oxidative stress and apoptosis in mouse hippocampal neuronal cells (HT-22 cells). Cell viability was significantly recovered by RDP treatment. Also, RDP effectively decreased the glutamate-induced production of intracellular reactive oxygen species (ROS). In flow cytometric analysis, apoptotic cells and the mitochondrial membrane potential were suppressed by RDP. In the Western blotting analysis, we found that RDP not only decreased the release of apoptotic proteins but also recovered anti-apoptotic protein. Additionally, RDP enhanced the antioxidant defense system by regulating the expression of antioxidant enzymes. Furthermore, treatment with RDP activated the BDNF/TrkB pathway. In accordance with the in vitro results, RDP meliorated memory deficit by defending hippocampal neuronal cells against oxidative damage in scopolamine-injected mice. Taken together, our present study showed that RDP exerted antioxidant and neuroprotective actions against oxidative stress. Therefore, RDP might facilitate the development of candidates for functional health foods for neurodegenerative disorders.

Targeting Ubiquitin Proteasome Pathway with Traditional Chinese Medicine for Treatment of Spinocerebellar Ataxia Type 3

Nine autosomal dominant spinocerebellar ataxias (SCAs) are caused by an abnormal expansion of CAG trinucleotide repeats that encodes a polyglutamine (polyQ) tract within different genes. Accumulation of aggregated mutant proteins is a common feature of polyQ diseases, leading to progressive neuronal dysfunction and degeneration. SCA type 3 (SCA3), the most common form of SCA worldwide, is characterized by a CAG triplet expansion in chromosome 14q32.1 ATXN3 gene. As accumulation of the mutated polyQ protein is a possible initial event in the pathogenic cascade, clearance of aggregated protein by ubiquitin proteasome system (UPS) has been proposed to inhibit downstream detrimental events and suppress neuronal cell death. In this study, Chinese herbal medicine (CHM) extracts were studied for their proteasome-activating, polyQ aggregation-inhibitory and neuroprotective effects in GFP^u and ATXN3/Q 75 -GFP 293/SH-SY5Y cells. Among the 14 tested extracts, 8 displayed increased proteasome activity, which was confirmed by 20S proteasome activity assay and analysis of ubiquitinated and fused GFP proteins in GFP^u cells. All the eight extracts displayed good aggregation-inhibitory potential when tested in ATXN3/Q 75 -GFP 293 cells. Among them, neuroprotective effects of five selected extracts were shown by analyses of polyQ aggregation, neurite outgrowth, caspase 3 and proteasome activities, and ATXN3-GFP, ubiquitin, BCL2 and BAX protein levels in neuronal differentiated ATXN3/Q 75 -GFP SH-SY5Y cells. Finally, enhanced proteasome function, anti-oxidative activity and neuroprotection of catalpol, puerarin and daidzein (active constituents of Rehmannia glutinosa and Pueraria lobata) were demonstrated in GFP^u and/or ATXN3/Q 75 -GFP 293/SH-SY5Y cells. This study may have therapeutic implication in polyQ-mediated disorders.

Mutant Ataxin-1 Inhibits Neural Progenitor Cell Proliferation in SCA1

Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited neurodegenerative disease caused by the expansion of a polyglutamine (Q) repeat tract in the protein ataxin-1 (ATXN1). Beginning as a cerebellar ataxic disorder, SCA1 progresses to involve the cerebral cortex, hippocampus, and brainstem. Using SCA1 knock-in mice that mirror the complexity of the human disease, we report a significant decrease in the capacity of adult neuronal progenitor cells (NPCs) to proliferate. Remarkably, a decrease in NPCs proliferation can be observed in vitro, outside the degenerative milieu of surrounding neurons or glia, demonstrating that mutant ATXN1 acting cell autonomously within progenitor cells interferes with their ability to proliferate. Our findings suggest that compromised adult neurogenesis contributes to the progressive pathology of the disease particularly in areas such as the hippocampus and cerebral cortex where stem cells provide neurotropic factors and participate in adult neurogenesis. These findings not only shed light on the biology of the disease but also have therapeutic implications in any future stem cell-based clinical trials.

Cuprous oxide nanoparticles inhibit the growth of cervical carcinoma by inducing autophagy

Cervical carcinoma is one of the main causes of women's cancer, and substantial side effects from standard treatment including platinum-based chemotherapy limit the options for escalation. In this paper, using cervical cancer cell lines and tumor-bearing mice as models, we report that CONPs could inhibit the proliferation of cancer cells in vitro and in vivo. Especially CONPs could inhibit tumor growth as cisplatin without weight loss. CONPs could also induce autophagy through AKT/mTOR pathway, which demonstrates that CONPs has the potential clinical applications.

Topoisomerase 1 inhibitor topotecan delays the disease progression in a mouse model of Huntington's disease

Huntington's disease (HD) is a dominantly inherited progressive neurodegenerative disorder caused by the accumulation of polyglutamine expanded mutant huntingtin as inclusion bodies primarily in the brain. After the discovery of the HD gene, considerable progress has been made in understanding the disease pathogenesis and multiple drug targets have been identified, even though currently there is no effective therapy. Here, we demonstrate that the treatment of topotecan, a brain-penetrating topoisomerase 1 inhibitor, to HD transgenic mouse considerably improved its motor behavioural abnormalities along with a significant extension of lifespan. Improvement of behavioural deficits are accompanied with the significant rescue of their progressively decreased body weight, brain weight and striatal volume. Interestingly, topotecan treatment also significantly reduced insoluble mutant huntingtin load in the HD mouse brain. Finally, we show that topotecan treatment to HD mouse not only inhibits the expression of transgenic mutant huntingtin, but also at the same time induces the expression of Ube3a, an ubiquitin ligase linked to the clearance of mutant huntingtin. These findings suggest that topotecan could be a potential therapeutic molecule to delay the progression of HD.

Translational effects and coding potential of an upstream open reading frame associated with DOPA Responsive Dystonia

Upstream open reading frames (uORFs) have emerged as major post-transcriptional regulatory elements in eukaryotic species. In general, uORFs are initiated by a translation start codon within the 5' untranslated region of a gene (upstream ATG; uATG), and they are negatively correlated with translational efficiency. In addition to their translational regulatory role, some uORFs can code for biologically active short peptides. The importance of uATGs/uORFs is further underscored by human diseases associated with single nucleotide polymorphisms (SNPs), which disrupt existing uORFs or introduce novel uORFs. Although several functional proteins translated from naturally occurring uORFs have been described, the coding potential of uORFs created by SNPs has been ignored because of the a priori assumption that these proteins are short-lived with no likely impact on protein homeostasis. Thus, studies on SNP-created uORFs are limited to their translational effects, leaving unexplored the potential cellular consequences of a SNP/uORF-encoded protein. Here, we investigate functionality of a uATG/uORF introduced by a +142C>T SNP within the GCH1 gene and associated with a familial form of DOPA Responsive Dystonia. We report that the +142C>T SNP represses GCH1 translation, and introduces a short, frame shifted uORF that encodes a 73-amino acid peptide. This peptide is localized within the nucleus and compromises cell viability upon proteasome inhibition. Our work extends the list of uATG/uORF associated diseases and advances research on peptides translated from SNP-introduced uORFs, a neglected component of the proteome.

Rapamycin Loaded Solid Lipid Nanoparticles as a New Tool to Deliver mTOR Inhibitors: Formulation and in Vitro Characterization

Recently, the use of mammalian target of rapamycin (mTOR) inhibitors, in particular rapamycin (Rp), has been suggested to improve the treatment of neurodegenerative diseases. However, as Rp is a strong immunosuppressant, specific delivery to the brain has been postulated to avoid systemic exposure. In this work, we fabricated new Rp loaded solid lipid nanoparticles (Rp-SLN) stabilized with polysorbate 80 (PS80), comparing two different methods and lipids. The formulations were characterized by differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), wide angle X-ray scattering (WAXS), cryo-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS) and particle tracking. In vitro release and short-term stability were assessed. Biological behavior of Rp-SLN was tested in SH-SY5Y neuroblastoma cells. The inhibition of mTOR complex 1 (mTORC1) was evaluated over time by a pulse-chase study compared to free Rp and Rp nanocrystals. Compritol Rp-SLN resulted more stable and possessing proper size and surface properties with respect to cetyl palmitate Rp-SLN. Rapamycin was entrapped in an amorphous form in the solid lipid matrix that showed partial crystallinity with stable Lβ, sub-Lα and Lβ′ arrangements. PS80 was stably anchored on particle surface. No drug release was observed over 24 h and Rp-SLN had a higher cell uptake and a more sustained effect over a week. The mTORC1 inhibition was higher with Rp-SLN. Overall, compritol Rp-SLN show suitable characteristics and stability to be considered for further investigation as Rp brain delivery system.

Atypical ubiquitination by E3 ligase WWP1 inhibits the proteasome-mediated degradation of mutant huntingtin

Huntington's disease (HD) is caused by the expansion of CAG trinucleotide repeats in exon 1 of HD gene encoding huntingtin (Htt), which is characterized by aggregation and formation of mutant Htt containing expanded polyglutamine (polyQ) repeats. Dysfunction of the ubiquitin-proteasome system (UPS) plays a critical role in the pathogenesis of HD. As the linkage mediator between ubiquitin and specific target proteins, E3 ubiquitin ligases have been suggested to be involved in mHtt degradation and HD pathology. However, the potential involvement of the E3 ligase WWP1 in HD has not been explored. The present study determined whether WWP1 is involved in the development of HD in both in vivo and in vitro models. The results showed that in contrast to several other E3 ligases, expression of WWP1 is enhanced in mice and N2a cells expressing mutant Htt (160Q) and co-localized with mHtt protein aggregates. In addition, expression of WWP1 positively regulates mutan Htt levels, aggregate formation, and cell toxicity. Further analysis revealed that WWP1 ubiquitinated mHtt at an atypical position of Lys-63, which may have inhibited degradation of mutant Htt through the ubiquitin-proteasome pathway. In conclusion, these results suggested that the E3 ligase WWP1 is involved in the pathogenesis of HD; therefore, it may be a novel target for therapeutic intervention.

Curcumin modulates cell death and is protective in Huntington's disease model

Huntington’s disease (HD) is a progressive, dominantly inherited neurological disorder caused by an abnormal expansion of polyglutamine (polyQ) repeat within the Huntingtin (Htt) protein with no disease modifying treatments. In a Drosophila model of HD, expression of mutant Huntingtin (Htt) protein with expanded polyQ leads to formation of inclusion bodies (IBs), increase in cellular toxicity, progression of motor disabilities and reduced viability. Multiple cellular events such as oxidative stress, mitochondrial dysfunction, inflammation and transcriptional dysregulation are reported to contribute to pathology, however, till date there are no disease-modifying treatments with least side effects. Therefore, we investigated effect of the phytochemical curcumin on HD pathogenesis. Curcumin, a phytochemical and commonly used ingredient in Asian food has a wide spectrum of anti-oxidant, anti-inflammatory and anti-fibrilogenic properties. In this study, we provide evidence that curcumin significantly ameliorates disease symptoms in a Drosophila model of HD by suppressing cell death and can be a key to halting the progression of Huntington’s disease with least side effects.

The potential of lactulose and melibiose, two novel trehalase-indigestible and autophagy-inducing disaccharides, for polyQ-mediated neurodegenerative disease treatment

The unique property of trehalose encourages its pharmaceutical application in aggregation-mediated neurodegenerative disorders, including Alzheimer's, Parkinson's, and many polyglutamine (polyQ)-mediated diseases. However, trehalose is digested into glucose by trehalase and which reduced its efficacy in the disease target tissues. Therefore, searching trehalase-indigestible analogs of trehalose is a potential strategy to enhance therapeutic effect. In this study, two trehalase-indigestible trehalose analogs, lactulose and melibiose, were selected through compound topology and functional group analyses. Hydrogen-bonding network analyses suggest that the elimination of the hydrogen bond between the linker ether and aspartate 321 (D321) of human trehalase is the key for lactulose and melibiose to avoid the hydrolyzation. Using polyQ-mediated spinocerebellar ataxia type 17 (SCA17) cell and slice cultures, we found the aggregation was significantly prohibited by trehalose, lactulose, and melibiose, which may through up-regulating of autophagy. These findings suggest the therapeutic applications of trehalase-indigestible trehalose analogs in aggregation-associated neurodegenerative diseases.

Heat shock protein 70 regulates degradation of the mumps virus phosphoprotein via the ubiquitin-proteasome pathway

Mumps virus (MuV) infection induces formation of cytoplasmic inclusion bodies (IBs). Growing evidence indicates that IBs are the sites where RNA viruses synthesize their viral RNA. However, in the case of MuV infection, little is known about the viral and cellular compositions and biological functions of the IBs. In this study, pulldown purification and N-terminal amino acid sequencing revealed that stress-inducible heat shock protein 70 (Hsp72) was a binding partner of MuV phosphoprotein (P protein), which was an essential component of the IB formation. Immunofluorescence and immunoblotting analyses revealed that Hsp72 was colocalized with the P protein in the IBs, and its expression was increased during MuV infection. Knockdown of Hsp72 using small interfering RNAs (siRNAs) had little, if any, effect on viral propagation in cultured cells. Knockdown of Hsp72 caused accumulation of ubiquitinated P protein and delayed P protein degradation. These results show that Hsp72 is recruited to IBs and regulates the degradation of MuV P protein through the ubiquitin-proteasome pathway.

IMPORTANCE

Formation of cytoplasmic inclusion bodies (IBs) is a common characteristic feature in mononegavirus infections. IBs are considered to be the sites of viral RNA replication and transcription. However, there have been few studies focused on host factors recruited to the IBs and their biological functions. Here, we identified stress-inducible heat shock protein 70 (Hsp72) as the first cellular partner of mumps virus (MuV) phosphoprotein (P protein), which is an essential component of the IBs and is involved in viral RNA replication/transcription. We found that the Hsp72 mobilized to the IBs promoted degradation of the MuV P protein through the ubiquitin-proteasome pathway. Our data provide new insight into the role played by IBs in mononegavirus infection.

Structure prediction of polyglutamine disease proteins: comparison of methods

Background

The expansion of polyglutamine (poly-Q) repeats in several unrelated proteins is associated with at least ten neurodegenerative diseases. The length of the poly-Q regions plays an important role in the progression of the diseases. The number of glutamines (Q) is inversely related to the onset age of these polyglutamine diseases, and the expansion of poly-Q repeats has been associated with protein misfolding. However, very little is known about the structural changes induced by the expansion of the repeats. Computational methods can provide an alternative to determine the structure of these poly-Q proteins, but it is important to evaluate their performance before large scale prediction work is done.

Results

In this paper, two popular protein structure prediction programs, I-TASSER and Rosetta, have been used to predict the structure of the N-terminal fragment of a protein associated with Huntington's disease with 17 glutamines. Results show that both programs have the ability to find the native structures, but I-TASSER performs better for the overall task.

Conclusions

Both I-TASSER and Rosetta can be used for structure prediction of proteins with poly-Q repeats. Knowledge of poly-Q structure may significantly contribute to development of therapeutic strategies for poly-Q diseases.

Deficiency of Ube3a in Huntington's disease mice brain increases aggregate load and accelerates disease pathology

Huntington's disease (HD) is an inherited neurodegenerative disorder caused by abnormal expansion of CAG repeats in the gene encoding huntingtin. Mutant huntingtin undergoes proteolytic processing and its N-terminal fragment containing polyglutamine repeat accumulates as inclusion not only in nucleus but also in cytoplasm and neuronal processes. Here, we demonstrate that removal of ubiquitin ligase Ube3a selectively from HD mice brain resulted in accelerated disease phenotype and shorter lifespan in comparison with HD mice. The deficiency of Ube3a in HD mice brain also caused significant increase in global aggregates load, and these aggregates were less ubiquitinated when compared with age-matched HD mice. These Ube3a-maternal deficient HD mice also showed drastic reduction of DARPP-32, a dopamine-regulated phoshphoprotein in their striatum. These results emphasize the crucial role of Ube3a in the progression of HD and its immense potential as therapeutic target.

Maintenance of chaperone-mediated autophagy activity in cultured cells expressing mutant huntingtin

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease caused by mutant huntingtin (Htt) with an expanded polyglutamine tract. It has been reported that Htt regulates autophagy. However, it remains unclear whether mutant Htt affects chaperone-mediated autophagy (CMA). Our study aimed to investigate the effect of mutant Htt on CMA activity in cultured HEK293T cells. A HEK293T cell model of HD was produced by transient transfection of wild-type (20Q) or mutant (120Q) Htt plasmids. The effect of mutant Htt on two CMA components, lysosomal-associated membrane protein 2a (Lamp2a) and heat-shock cognate protein 70 (Hsc70), was determined by western blotting and immunofluorescent staining. We observed that mutant Htt did not significantly alter the expression of Lamp2a and Hsc70 when compared to normal Htt. These findings suggest that mutant Htt does not reduce CMA activity and that enhancing CMA activity to clear mutant Htt may be a novel strategy for the management of HD.

The Ginkgo biloba Extract EGb 761 Modulates Proteasome Activity and Polyglutamine Protein Aggregation

The standardized Ginkgo biloba extract EGb 761 has well-described antioxidative activities and effects on different cytoprotective signaling pathways. Consequently, a potential use of EGb 761 in neurodegenerative diseases has been proposed. A common characteristic feature of a variety of such disorders is the pathologic formation of protein aggregates, suggesting a crucial role for protein homeostasis. In this study, we show that EGb 761 increased the catalytic activity of the proteasome and enhanced protein degradation in cultured cells. We further investigated this effect in a cellular model of Huntington's disease (HD) by employing cells expressing pathologic variants of a polyglutamine protein (polyQ protein). We show that EGb 761 affected these cells by (i) increasing proteasome activity and (ii) inducing a more efficient degradation of aggregation-prone proteins. These results demonstrate a novel activity of EGb 761 on protein aggregates by enhancing proteasomal protein degradation, suggesting a therapeutic use in neurodegenerative disorders with a disturbed protein homeostasis.

ADSC Therapy in Neurodegenerative Disorders

Neurodegenerative disorders, chronic diseases that can severely affect the patient's daily life, include amyotrophic lateral sclerosis, Parkinson's, Alzheimer's, and Huntington's diseases. However, these diseases all have the common characteristic that they are due to degenerative irreversibility, and thus no efficient drugs or therapy methods can mitigate symptoms completely. Stem cell therapy, such as adipose tissue-derived stem cells (ADSCs), is a promising treatment for incurable disorders. In this review, we summarized the previous studies using ADSCs to treat neurodegenerative disorders, as well as their therapeutic mechanisms. We also suggested possible expectations for future human clinical trials involving minimized intracerebroventricular combined with intravenous administration, using different cell lineages to finish complementary therapy as well as change the extracellular matrix to create a homing niche. Depending on successful experiments in relevant neurodegenerative disorders models, this could form the theoretical basis for future human clinical trials.

Sulforaphane enhances proteasomal and autophagic activities in mice and is a potential therapeutic reagent for Huntington's disease

The ubiquitin proteasome system (UPS) is impaired in Huntington's disease, a devastating neurodegenerative disorder. Sulforaphane, a naturally occurring compound, has been shown to stimulate UPS activity in cell cultures. To test whether sulforaphane enhances UPS function in vivo, we treated UPS function reporter mice ubiquitously expressing the green fluorescence protein (GFP) fused to a constitutive degradation signal that promotes its rapid degradation in the conditions of a healthy UPS. The modified GFP is termed GFP UPS reporter (GFPu). We found that both GFPu and ubiquitinated protein levels were significantly reduced and the three peptidase activities of the proteasome were increased in the brain and peripheral tissues of the mice. Interestingly, sulforaphane treatment also enhanced autophagy activity in the brain and the liver. To further examine whether sulforaphane promotes mutant huntingtin (mHtt) degradation, we treated Huntington's disease cells with sulforaphane and found that sulforaphane not only enhanced mHtt degradation but also reduced mHtt cytotoxicity. Sulforaphane-mediated mHtt degradation was mainly through the UPS pathway as the presence of a proteasome inhibitor abolished this effect. Taken together, these data indicate that sulforaphane activates protein degradation machineries in both the brain and peripheral tissues and may be a therapeutic reagent for Huntington's disease and other intractable disorders. Accumulation of mutant huntingtin (mHtt) protein causes Huntington's disease (HD). Sulforaphane (SFN), a naturally occurring compound, increased proteasome and autophagy activities in vivo and enhanced mHtt turnover and cell survival in HD cell models. SFN-mediated mHtt degradation is mainly through the proteasome pathway. These data suggest that SFN can be a therapeutic reagent for treating HD and other intractable disorders.

Mechanisms mediating spinal and bulbar muscular atrophy: investigations into polyglutamine-expanded androgen receptor function and dysfunction

Spinal and bulbar muscular atrophy (SBMA, Kennedy’s disease), a late-onset neuromuscular disorder, is caused by expansion of the polymorphic polyglutamine tract in the androgen receptor (AR). The AR is a ligand-activated transcription factor, but plays roles in other cellular pathways. In SBMA, selective motor neuron degeneration occurs in the brainstem and spinal cord, thus the causes of neuronal dysfunction have been studied. However, pathogenic pathways in muscles may also be involved. Cultured cells, fly and mouse models are used to study the molecular mechanisms leading to SBMA. Both the structure of the polyglutamine-expanded AR (polyQ AR) and its interactions with other proteins are altered relative to the normal AR. The ligand-dependent translocation of the polyQ AR to the nucleus appears to be critical, as are interdomain interactions. The polyQ AR, or fragments thereof, can form nuclear inclusions, but their pathogenic or protective nature is unclear. Other data suggests soluble polyQ AR oligomers can be harmful. Post-translational modifications such as phosphorylation, acetylation, and ubiquitination influence AR function and modulate the deleterious effects of the polyQ AR. Transcriptional dysregulation is highly likely to be a factor in SBMA; deregulation of non-genomic AR signaling may also be involved. Studies on polyQ AR-protein degradation suggest inhibition of the ubiquitin proteasome system and changes to autophagic pathways may be relevant. Mitochondrial function and axonal transport may also be affected by the polyQ AR. Androgens, acting through the AR, can be neurotrophic and are important in muscle development; hence both loss of normal AR functions and gain of novel harmful functions by the polyQ AR can contribute to neurodegeneration and muscular atrophy. Thus investigations into polyQ AR function have shown that multiple complex mechanisms lead to the initiation and progression of SBMA.

Inhibition of autophagy via p53-mediated disruption of ULK1 in a SCA7 polyglutamine disease model

Spinocerebellar ataxia type 7 (SCA7) is one of nine neurodegenerative disorders caused by expanded polyglutamine domains. These so-called polyglutamine (polyQ) diseases are all characterized by aggregation. Reducing the level of aggregating polyQ proteins via pharmacological activation of autophagy has been suggested as a therapeutic approach. However, recently, evidence implicating autophagic dysfunction in these disorders has also been reported. In this study, we show that the SCA7 polyglutamine protein ataxin-7 (ATXN7) reduces the autophagic activity via a previously unreported mechanism involving p53-mediated disruption of two key proteins involved in autophagy initiation. We show that in mutant ATXN7 cells, an increased p53-FIP200 interaction and co-aggregation of p53-FIP200 into ATXN7 aggregates result in decreased soluble FIP200 levels and subsequent destabilization of ULK1. Together, this leads to a decreased capacity for autophagy induction via the ULK1-FIP200-Atg13-Atg101 complex. We also show that treatment with a p53 inhibitor, or a blocker of ATXN7 aggregation, can restore the soluble levels of FIP200 and ULK1, as well as increase the autophagic activity and reduce ATXN7 toxicity. Understanding the mechanism behind polyQ-mediated inhibition of autophagy is of importance if therapeutic approaches based on autophagy stimulation should be developed for these disorders.

Degradation of mutant huntingtin via the ubiquitin/proteasome system is modulated by FE65

An unstable expansion of the polyglutamine repeat within exon 1 of the protein Htt (huntingtin) causes HD (Huntington's disease). Mounting evidence shows that accumulation of N-terminal mutant Htt fragments is the source of disruption of normal cellular processes which ultimately leads to neuronal cell death. Understanding the degradation mechanism of mutant Htt and improving its clearance has emerged as a new direction in developing therapeutic approaches to treat HD. In the present study we show that the brain-enriched adaptor protein FE65 is a novel interacting partner of Htt. The binding is mediated through WW-polyproline interaction and is dependent on the length of the polyglutamine tract. Interestingly, a reduction in mutant Htt protein level was observed in FE65-knockdown cells, and the process requires the UPS (ubiquitin/proteasome system). Moreover, the ubiquitination level of mutant Htt was found to be enhanced when FE65 is knocked down. Immunofluroescence staining revealed that FE65 associates with mutant Htt aggregates. Additionally, we demonstrated that overexpression of FE65 increases mutant Htt-induced cell death both in vitro and in vivo. These results suggest that FE65 facilitates the accumulation of mutant Htt in cells by preventing its degradation via the UPS, and thereby enhances the toxicity of mutant Htt.

[Selective degradation of expanded polyglutamine proteins by their specific recognition with QBP1]

Protein misfolding and aggregation have been recognized as a common molecular pathogenesis of various neurodegenerative diseases including Alzheimer's, Parkinson's, and the polyglutamine (polyQ) diseases. The polyQ diseases, including Huntington's disease and various spinocerebellar ataxias, are caused by abnormal expansions of the polyQ stretch (>35-40) within disease-causative proteins. Recently, defects in protein degradation in the brain have been shown to cause neurodegeneration in genetically-engineered mice, highlighting two important roles of protein degradation systems in neurodegenerative diseases; 1) their dysfunction in the pathogenesis and 2) their activation as a therapy. However, it is indispensable to eliminate only the pathogenic proteins to avoid deleterious side effects. Aiming to selectively degrade the expanded polyQ proteins, we employed QBP1, a peptide which specifically binds to the expanded polyQ stretch. We designed a chimeric protein with the Hsc70 binding motif, a signal sequence for chaperone-mediated autophagy, fused to QBP1 (Hsc70BM-QBP1), and found that Hsc70BM-QBP1 accelerates the selective degradation of expanded polyQ proteins in cell culture. Gene therapy using a viral vector expressing Hsc70BM-QBP1 effectively ameliorates the motor dysfunction and premature death in polyQ disease model mice. We propose that our therapeutic strategy to selectively degrade the pathogenic proteins can also be applied to other neurodegenerative diseases.

The role of mTOR signaling in Alzheimer disease

The buildup of Abeta and tau is believed to directly cause or contribute to the progressive cognitive deficits characteristic of Alzheimer disease. However, the molecular pathways linking Abeta and tau accumulation to learning and memory deficits remain elusive. There is growing evidence that soluble forms of Abeta and tau can obstruct learning and memory by interfering with several signaling cascades. In this review, I will present data showing that the mammalian target of rapamycin (mTOR) may play a role in Abeta and tau induced neurodegeneration.

Polyglutamine aggregation in Huntington and related diseases

Polyglutamine (polyQ)-expansions in different proteins cause nine neurodegenerative diseases. While polyQ aggregation is a key pathological hallmark of these diseases, how aggregation relates to pathogenesis remains contentious. In this chapter, we review what is known about the aggregation process and how cells respond and interact with the polyQ-expanded proteins. We cover detailed biophysical and structural studies to uncover the intrinsic features of polyQ aggregates and concomitant effects in the cellular environment. We also examine the functional consequences ofpolyQ aggregation and how cells may attempt to intervene and guide the aggregation process.

Protein repertoire impact of Ubiquitin-Proteasome System impairment: insight into the protective role of beta-estradiol

The Ubiquitin-Proteasome System (UPS) and the Autophagy-Lysosome Pathways (ALP) are key mechanisms for cellular homeostasis sustenance and protein clearance. A wide number of Neurodegenerative Diseases (NDs) are tied with UPS impairment and have been also described as proteinopathies caused by aggregate-prone proteins, not efficiently removed by proteasome. Despite the large knowledge on proteasome biological role, molecular mechanisms associated with its impairment are still blur. We have pursued a comprehensive proteomic investigation to evaluate the phenotypic rearrangements in protein repertoires associated with a UPS blockage. Different functional proteomic approaches have been employed to tackle UPS impairment impact on human NeuroBlastoma (NB) cell lines responsive to proteasome inhibition by Epoxomicin. 2-Dimensional Electrophoresis (2-DE) separation combined with Mass Spectrometry and Shotgun Proteomics experiments have been employed to design a thorough picture of protein profile. Unsupervised meta-analysis of the collected proteomic data revealed that all the identified proteins relate each other in a functional network centered on beta-estradiol. Moreover we showed that treatment of cells with beta-estradiol resulted in aggregate removal and increased cell survival due to activation of the autophagic pathway. Our data may provide the molecular basis for the use of beta-estradiol in neurodegenerative disorders by induction of protein aggregate removal.

Dysfunction of constitutive and inducible ubiquitin-proteasome system in amyotrophic lateral sclerosis: implication for protein aggregation and immune response

The ubiquitin-proteasome system (UPS) is the major intracellular proteolytic mechanism controlling the degradation of misfolded/abnormal proteins. A common hallmark in amyotrophic lateral sclerosis (ALS) and in other neurodegenerative disorders is the accumulation of misfolded/abnormal proteins into the damaged neurons, leading to the formation of cellular inclusions that are mostly ubiquitin-positive. Although proteolysis is a complex mechanism requiring the participation of different pathways, the abundant accumulation of ubiquitinated proteins strongly suggests an important contribution of UPS to these neuropathological features. The use of cellular and animal models of ALS, particularly those expressing mutant SOD1, the gene mutation most represented in familiar ALS, has provided significant evidence for a role of UPS in protein inclusions formation and motor neuron death. This review will specifically discuss this piece of evidence and provide suggestions of potential strategies for therapeutic intervention. We will also discuss the finding that, unlike the constitutive proteasome subunits, the inducible subunits are overexpressed early during disease progression in SOD1 mice models of ALS. These subunits form the immunoproteasome and generate peptides for the major histocompatibility complex class I molecules, suggesting a role of this system in the immune responses associated with the pathological features of ALS. Since recent discoveries indicate that innate and adaptive immunity may influence the disease process, in this review we will also provide evidence of a possible connection between immune-inflammatory reactions and UPS function, in the attempt to better understand the etiopathology of ALS and to identify appropriate targets for novel treatment strategies of this devastating disease.

Overexpression of the autophagic beclin-1 protein clears mutant ataxin-3 and alleviates Machado-Joseph disease

Machado-Joseph disease, also known as spinocerebellar ataxia type 3, is the most common of the dominantly inherited ataxias worldwide and is characterized by mutant ataxin-3 misfolding, intracellular accumulation of aggregates and neuronal degeneration. Here we investigated the implication of autophagy, the major pathway for organelle and protein turnover, in the accumulation of mutant ataxin-3 aggregates and neurodegeneration found in Machado-Joseph disease and we assessed whether specific stimulation of this pathway could mitigate the disease. Using tissue from patients with Machado-Joseph disease, transgenic mice and a lentiviral-based rat model, we found an abnormal expression of endogenous autophagic markers, accumulation of autophagosomes and decreased levels of beclin-1, a crucial protein in the early nucleation step of autophagy. Lentiviral vector-mediated overexpression of beclin-1 led to stimulation of autophagic flux, mutant ataxin-3 clearance and overall neuroprotective effects in neuronal cultures and in a lentiviral-based rat model of Machado-Joseph disease. These data demonstrate that autophagy is a key degradation pathway, with beclin-1 playing a significant role in alleviating Machado-Joseph disease pathogenesis.

Sphingolipid storage affects autophagic metabolism of the amyloid precursor protein and promotes Abeta generation

Deposition of amyloid β peptides (Aβs) in extracellular amyloid plaques within the human brain is a hallmark of Alzheimer's disease (AD). Aβ derives from proteolytic processing of the amyloid precursor protein (APP) by β- and γ-secretases. The initial cleavage by β-secretase results in shedding of the APP ectodomain and generation of APP C-terminal fragments (APP-CTFs), which can then be further processed within the transmembrane domain by γ-secretase, resulting in release of Aβ. Here, we demonstrate that accumulation of sphingolipids (SLs), as occurs in lysosomal lipid storage disorders (LSDs), decreases the lysosome-dependent degradation of APP-CTFs and stimulates γ-secretase activity. Together, this results in increased generation of both intracellular and secreted Aβ. Notably, primary fibroblasts from patients with different SL storage diseases show strong accumulation of potentially amyloidogenic APP-CTFs. By using biochemical, cell biological, and genetic approaches, we demonstrate that SL accumulation affects autophagic flux and impairs the clearance of APP-CTFs. Thus, accumulation of SLs might not only underlie the pathogenesis of LSDs, but also trigger increased generation of Aβ and contribute to neurodegeneration in sporadic AD.

Polyphenolic compounds for treating neurodegenerative disorders involving protein misfolding

A diverse group of neurodegenerative diseases are characterized by progressive, age-dependent intracellular formation of misfolded protein aggregates. These include Alzheimer's disease, Huntington's disease, Parkinson's disease and a number of tau-mediated disorders. There is no effective treatment for any of these disorders; currently approved interventions are designed to treat disease symptoms and generally lead to modest modulation of clinical symptoms. None are known to mitigate underlying neuropathologic mechanisms and, thus, it is not unexpected that existing treatments appear ineffective in modulating disease progression. We note that these neurodegenerative disorders all share a common mechanistic theme in that depositions of misfolded protein in the brain is a key molecular feature underlying disease onset and/or progression. While previous studies have identified a number of drugs and nutraceuticals capable of interfering with the formation and/or stability of misfolded protein aggregates, none have been demonstrated to be effective in vivo for treating any of the neurodegenerative disorders. We hereby review accumulating evidence that a select nutraceutical grape-seed polyphenolic extract (GSPE) is effective in vitro and in vivo in mitigating certain misfolded protein-mediated neuropathologic and clinical phenotypes. We will also review evidence implicating bioavailability of GSPE components in the brain and the tolerability as well as safety of GSPE in animal models and in humans. Collectively, available information supports continued development of the GSPE for treating a variety of neurodegenerative disorders involving misfolded protein-mediated neuropathologic mechanisms.

Expression of Huntington's disease protein results in apoptotic neurons in the brains of cloned transgenic pigs

Neurodegeneration is a hallmark of many neurological diseases, including Alzheimer's, Parkinson's and the polyglutamine diseases, which are all caused by misfolded proteins that accumulate in neuronal cells of the brain. Although apoptosis is believed to contribute to neurodegeneration in these cases, genetic mouse models of these diseases often fail to replicate apoptosis and overt neurodegeneration in the brain. Using nuclear transfer, we generated transgenic Huntington's disease (HD) pigs that express N-terminal (208 amino acids) mutant huntingtin with an expanded polyglutamine tract (105Q). Postnatal death, dyskinesia and chorea-like movement were observed in some transgenic pigs that express mutant huntingtin. Importantly, the transgenic HD pigs, unlike mice expressing the same transgene, displayed typical apoptotic neurons with DNA fragmentation in their brains. Also, expression of mutant huntingtin resulted in more neurons with activated caspase-3 in transgenic pig brains than that in transgenic mouse brains. Our findings suggest that species differences determine neuropathology and underscore the importance of large mammalian animals for modeling neurological disorders.

Proteasomal and autophagic degradative activities in spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA or Kennedy's disease) is a fatal neurodegenerative disease characterized by the selective loss of motor neurons in the bulbar region of the brain and in the anterior horns of the spinal cord. The disease has been associated to an expansion of a CAG triplet repeat present in the first coding exon of the androgen receptor (AR) gene. SBMA was the first identified member of a large class of neurodegenerative diseases now known as CAG-related diseases, which includes Huntington's disease (HD), several types of spinocerebellar ataxia (SCAs), and dentatorubral and pallidoluysian atrophy (DRPLA). The expanded CAG tract is translated to an aberrantly long polyglutamine tract (ARpolyQ) in the N-terminal region of the AR protein. The elongated polyQ tract seems to confer a neurotoxic gain-of-function to the mutant AR, possibly via the generation of aberrant conformations (misfolding). Protein misfolding is thought to be a trigger of neurotoxicity, since it perturbs a wide variety of motor neuronal functions. The first event is the accumulation of the ARpolyQ into ubiquitinated aggregates in a ligand (testosterone) dependent manner. The mutant ARpolyQ also impairs proteasome functions. The autophagic pathway may be activated to compensate these aberrant events by clearing the mutant ARpolyQ from motor neuronal cells. This review illustrates the mechanisms at the basis of ARpolyQ degradation via the proteasomal and autophagic systems.

Clearance of mutant huntingtin

Mutant huntingtin (htt) carries an expanded polyglutamine (polyQ) repeat (> 36 glutamines) in its N-terminal region, which leads htt to become misfolded and kill neuronal cells in Huntington disease (HD). The cytotoxicity of N-terminal mutant htt fragments is evident by severe neurological phenotypes of transgenic mice that express these htt fragments. Clearance of mutant htt is primarily mediated by the ubiquitin-proteasomal sysmtem (UPS) and autophagy. However, the relative efficiency of these two systems to remove toxic forms of mutant htt has not been rigorously compared. Using cellular and mouse models of HD, we found that inhibiting the UPS leads to a greater accumulation of mutant htt than inhibiting autophagy. Moreover, N-terminal mutant htt fragments, but not full-length mutant htt, accumulate in the HD mouse brains after inhibiting the UPS. These findings suggest that the UPS is more efficient than autophagy to remove N-terminal mutant htt.

Inhibiting the ubiquitin-proteasome system leads to preferential accumulation of toxic N-terminal mutant huntingtin fragments

An expanded polyglutamine (polyQ) domain in the N-terminal region of huntingtin (htt) causes misfolding and accumulation of htt in neuronal cells and the subsequent neurodegeneration of Huntington's disease (HD). Clearing the misfolded htt is critical for preventing neuropathology, and this process is mediated primarily by both the ubiquitin-proteasome system (UPS) and autophagy. Although overexpression of mutant htt can inhibit UPS activity in cultured cells, mutant htt does not inhibit global UPS activity in the brains of HD transgenic mice. These findings underscore the importance of investigating the function of the UPS and autophagy in the brain when mutant proteins are not overexpressed. When cultured PC12 cells were treated with either UPS or autophagy inhibitors, more N-terminal mutant htt fragments accumulated via inhibition of the UPS. Furthermore, in HD CAG repeat knock-in mouse brain, inhibiting the UPS also resulted in a greater accumulation of N-terminal, but not full-length, mutant htt than inhibiting autophagy did. Our findings suggest that impairment of the UPS may be more important for the accumulation of N-terminal mutant htt and might therefore make an attractive therapeutic target.

Role of the ubiquitin–proteasome system and autophagy in polyglutamine neurodegenerative diseases

The accumulation of intracellular protein aggregates is a prominent feature of many late-onset neurodegenerative disorders, including polyglutamine neurodegenerative diseases. Appearance of aggregates of the misfolded mutant disease proteins indicate that the degradative pathways of the cell are failing to efficiently clear them and are being progressively overwhelmed, which could eventually lead to neuronal dysfunction and neurodegeneration. Cellular pathways for degrading misfolded and aggregated-prone proteins include the ubiquitin–proteasome system and autophagy. This article reviews recent studies that have shown a critical role of the ubiquitin–proteasome system and autophagy in the pathogenesis of polyglutamine diseases. Understanding the role of these two pathways in disease pathogenesis could open up a new attractive therapeutic avenue for polyglutamine and other related neurodegenerative disorders.

Molecular pathogenesis of protein misfolding diseases: pathological molecular environments versus quality control systems against misfolded proteins

Diverse human diseases, including various neurodegenerative disorders and amyloidoses, are thought to result from the misfolding and aggregation of disease-causative proteins, and thus are collectively called protein misfolding diseases. Natively folded disease-causative proteins generally undergo a beta-sheet conformational transition through an energetically unfavourable process, and further polymerize into amyloid fibrils. In the case of beta(2)-microglobulin-related amyloidosis, an extracellular protein misfolding disease, many kinds of biological molecules including glycosaminoglycans, proteoglycans and lipids partially unfold beta(2)-microglobulin and catalyse its subsequent nucleus formation. After amyloid fibrils are formed, these biological molecules stabilize the beta(2)-microglobulin fibrils. In the polyglutamine neurodegenerative diseases, an intracellular protein misfolding disease, molecular chaperones as well as the ubiquitin-proteasome and autophagy-lysosome protein degradation systems, which are called the protein quality control systems, strictly regulate protein misfolding, aggregation and disease progression. A family of extracellular chaperones also binds to misfolded proteins and inhibit amyloid fibril formation in the extracellular space. Protein misfolding and aggregation may be an ideal therapeutic target for protein misfolding diseases in general.

The ubiquitin-proteasome reporter GFPu does not accumulate in neurons of the R6/2 transgenic mouse model of Huntington's disease

Impairment of the ubiquitin-proteasome system (UPS) has long been considered an attractive hypothesis to explain the selective dysfunction and death of neurons in polyglutamine disorders such as Huntington's disease (HD). The fact that inclusion bodies in HD mouse models and patient brains are rich in ubiquitin and proteasome components suggests that the UPS may be hindered directly or indirectly by inclusion bodies or their misfolded monomeric or oligomeric precursors. However, studies into UPS function in various polyglutamine disease models have yielded conflicting results, suggesting mutant polyglutamine tracts may exert different effects on the UPS depending on protein context, expression level, subcellular localisation and cell-type. To investigate UPS function in a well-characterised mouse model of HD, we have crossed R6/2 HD mice with transgenic UPS reporter mice expressing the GFPu construct. The GFPu construct comprises GFP fused to a constitutive degradation signal (CL-1) that promotes its rapid degradation under conditions of a healthy UPS. Using a combination of immunoblot analysis, fluorescence and immunofluorescence microscopy studies, we found that steady-state GFPu levels were not detectably different between R6/2 and non-R6/2 brain. We observed no correlation between inclusion body formation and GFPu accumulation, suggesting no direct relationship between protein aggregation and global UPS inhibition in R6/2 mice. These findings suggest that while certain branches of the UPS can be impaired by mutant polyglutamine proteins, such proteins do not necessarily cause total blockade of UPS-dependent degradation. It is therefore likely that the relationship between mutant polyglutamine proteins and the UPS is more complex than originally anticipated.