Review: autophagy and neurodegeneration: survival at a cost?

The Role of Autophagy in Excitotoxicity, Synaptic Mitochondrial Stress and Neurodegeneration

Brain and nervous system functions depend upon maintaining the integrity of synaptic structures over the lifetime. Autophagy, a key homeostatic quality control system, plays a central role not only in neuronal development and survival/cell death, but also in regulating synaptic activity and plasticity. Glutamate is the major excitatory neurotransmitter that activates downstream targets, with a key role in learning and memory. However, an excess of glutamatergic stimulation is pathological in stroke, epilepsy and neurodegeneration, triggering excitotoxic cell death or a sublethal process of excitatory mitochondrial calcium toxicity (EMT) that triggers dendritic retraction. Markers of autophagy and mitophagy are often elevated following excitatory neuronal injuries, with the potential to influence cell death or neurodegenerative outcomes of these injuries. Interestingly, leucine-rich repeat kinase 2 (LRRK2) and PTEN-induced kinase 1 (PINK1), two kinases linked to autophagy, mitophagy and Parkinson disease, play important roles in regulating mitochondrial calcium handling, synaptic density and function, and maturation of dendritic spines. Mutations in LRRK2, PINK1, or proteins linked to Alzheimer's disease perturb mitochondrial calcium handling to sensitize neurons to excitatory injury. While autophagy and mitophagy can play both protective and harmful roles, studies in various excitotoxicity and stroke models often implicate autophagy in a pathogenic role. Understanding the role of autophagic degradation in regulating synaptic loss and cell death following excitatory neuronal injuries has important therapeutic implications for both acute and chronic neurological disorders.

Mechanism of Decision Making between Autophagy and Apoptosis Induction upon Endoplasmic Reticulum Stress

Dynamic regulation of the cellular proteome is mainly controlled in the endoplasmic reticulum (ER). Accumulation of misfolded proteins due to ER stress leads to the activation of unfolded protein response (UPR). The primary role of UPR is to reduce the bulk of damages and try to drive back the system to the former or a new homeostatic state by autophagy, while an excessive level of stress results in apoptosis. It has already been proven that the proper order and characteristic features of both surviving and self-killing mechanisms are controlled by negative and positive feedback loops, respectively. The new results suggest that these feedback loops are found not only within but also between branches of the UPR, fine-tuning the response to ER stress. In this review, we summarize the recent knowledge of the dynamical characteristic of endoplasmic reticulum stress response mechanism by using both theoretical and molecular biological techniques. In addition, this review pays special attention to describing the mechanism of action of the dynamical features of the feedback loops controlling cellular life-and-death decision upon ER stress. Since ER stress appears in diseases that are common worldwide, a more detailed understanding of the behaviour of the stress response is of medical importance.

Endolysosome Iron Chelation Inhibits HIV-1 Protein-Induced Endolysosome De-Acidification-Induced Increases in Mitochondrial Fragmentation, Mitophagy, and Cell Death

People with human immunodeficiency virus-1 (PLWH) experience high rates of HIV-1-associated neurocognitive disorders (HANDs); clinical symptoms range from being asymptomatic to experiencing HIV-associated dementia. Antiretroviral therapies have effectively prolonged the life expectancy related to PLWH; however, the prevalence of HANDs has increased. Implicated in the pathogenesis of HANDs are two HIV-1 proteins, transactivator of transcription (Tat) and gp120; both are neurotoxic and damage mitochondria. The thread-like morphological features of functional mitochondria become fragmented when levels of reactive oxygen species (ROS) increase, and ROS can be generated via Fenton-like chemistry in the presence of ferrous iron (Fe2+). Endolysosomes are central to iron trafficking in cells and contain readily releasable Fe2+ stores. However, it is unclear whether the endolysosome store is sufficient to account for insult-induced increases in levels of ROS, mitochondrial fragmentation, autophagy, and cell death. Using U87MG astrocytoma and SH-SY5Y neuroblastoma cells, we determined that chloroquine (CQ), Tat, and gp120 all (1) de-acidified endolysosomes, (2) decreased endolysosome numbers and increased endolysosome sizes, (3) increased mitochondrial numbers (fragmentation), (4) increased autophagosome numbers, (5) increased autolysosome numbers, (6) increased mitochondrial fragments within endolysosomes, and (7) increased cell death. These effects were all blocked by the endolysosome-specific iron chelator deferoxamine (DFO). Thus, the endolysosome de-acidification-induced release of endolysosome Fe2+ is sufficient to account for inter-organellar signaling events and cell biology consequences of HIV-1 proteins, including mitochondrial fragmentation, autophagy, and cell death.

LncRNA RMRP accelerates autophagy-mediated neurons apoptosis through miR-3142/TRIB3 signaling axis in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a major neurodegenerative disorder. The functions of lncRNA RMRP have been characterized mainly in various human cancers. However, the functional network of RMRP in AD progression remains unknown.

METHODS

Human serum samples, AD transgenic (Tg) mice as well as SH-SY5Y cells were used in this study. The RNA expression patterns of RMRP, miR-3142 and TRIB3 were assessed by quantitative real-time PCR (qRT-PCR). Levels of apoptosis- or autophagy-associated biomarkers and TRIB3 level were evaluated using immunohistochemistry (IHC), western blotting or immunofluorescence assays, respectively. Bioinformatics methods and luciferase assays were used to predict and validate the interactions among RMRP, miR-3142, and TRIB3. Flow cytometry, TUNEL staining and EdU assays were used to examine the apoptosis and proliferation of neurons, respectively.

RESULTS

The elevated RMRP and TRIB3 expressions and activation of autophagy were observed in AD. Knockdown of RMRP restrained neuronal apoptosis and autophagy activation in vitro and in vivo. Interestingly, TRIB3 overexpression reversed the biological effects of RMRP silencing on Aβ_1-42-induced cell apoptosis and autophagy. Further mechanistic analysis showed RMRP acted as a sponge of miR-3142 to elevate TRIB3 level.

CONCLUSION

These data illustrated that knockdown of RMRP inhibited autophagy and apoptosis via regulating miR-3142/TRIB3 axis in AD, suggesting that inhibition of RMRP maybe a therapeutic strategy for AD.

Potential mechanisms underlying lithium treatment for Alzheimer's disease and COVID-19

Disruption of intracellular Ca2+ homeostasis plays an important role as an upstream pathology in Alzheimer's disease (AD), and correction of Ca2+ dysregulation has been increasingly proposed as a target of future effective disease-modified drugs for treating AD. Calcium dysregulation is also an upstream pathology for the COVID-19 virus SARS-CoV-2 infection and replication, leading to host cell damage. Clinically available drugs that can inhibit the disturbed intracellular Ca2+ homeostasis have been repurposed to treat COVID-19 patients. This narrative review aims at exploring the underlying mechanism by which lithium, a first line drug for the treatment of bipolar disorder, inhibits Ca2+ dysregulation and associated downstream pathology in both AD and COVID-19. It is suggested that lithium can be repurposed to treat AD patients, especially those afflicted with COVID-19.

Contribution of the Nrf2 Pathway on Oxidative Damage and Mitochondrial Failure in Parkinson and Alzheimer's Disease

The increase in human life expectancy has become a challenge to reduce the deleterious consequences of aging. Nowadays, an increasing number of the population suffer from age-associated neurodegenerative diseases including Parkinson's disease (PD) and Alzheimer's disease (AD). These disorders present different signs of neurodegeneration such as mitochondrial dysfunction, inflammation, and oxidative stress. Accumulative evidence suggests that the transcriptional factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2) plays a vital defensive role orchestrating the antioxidant response in the brain. Nrf2 activation promotes the expression of several antioxidant enzymes that exert cytoprotective effects against oxidative damage and mitochondrial impairment. In this context, several studies have proposed a role of Nrf2 in the pathogenesis of PD and AD. Thus, we consider it important to summarize the ongoing literature related to the effects of the Nrf2 pathway in the context of these diseases. Therefore, in this review, we discuss the mechanisms involved in Nrf2 activity and its connection with mitochondria, energy supply, and antioxidant response in the brain. Furthermore, we will lead our discussion to identify the participation of the Nrf2 pathway in mitochondrial impairment and neurodegeneration present in PD and AD. Finally, we will discuss the therapeutic effects that the Nrf2 pathway activation could have on the cognitive impairment, neurodegeneration, and mitochondrial failure present in PD and AD.

Astrocytes autophagy in aging and neurodegenerative disorders

Astrocytes can serve multiple functions in maintaining cellular homeostasis of the central nervous system (CNS), and normal functions for autophagy in astrocytes is considered to have very vital roles in the pathogenesis of aging and neurodegenerative diseases. Autophagy is a major intracellular lysosomal (or its yeast analog, vacuolar) clearance pathways involved in the degradation and recycling of long-lived proteins, oxidatively damaged proteins and dysfunctional organelles by lysosomes. Current evidence has shown that autophagy might influence inflammation, oxidative stress, aging and function of astrocytes. Although the interrelation between autophagy and inflammation, oxidative stress, aging or neurological disorders have been addressed in detail, the influence of astrocytes mediated-autophagy in aging and neurodegenerative disorders has yet to be fully reviewed. In this review, we will summarize the most up-to-date findings and highlight the role of autophagy in astrocytes and link autophagy of astrocytes to aging and neurodegenerative diseases. Due to the prominent roles of astrocytic autophagy in age-related neurodegenerative diseases, we believe that we can provide new suggestions for the treatment of these disorders.

Trehalose restores functional autophagy suppressed by high glucose

Autophagy is required for neurulation, and autophagy activators with minimal toxicity, such as the natural compound trehalose, a nonreducing disaccharide, possess high therapeutic value. To determine whether trehalose directly induces autophagy, FITC-labeled trehalose was used for tracing its presence in autophagosome complexes. Trehalose was as potent as rapamycin and starvation in inducing de novo autophagosome formation and increasing autophagosome flux in GFP-LC3 reporter cells and C17.2 neural stem cells. Trehalose effectively reversed high glucose-suppressed autophagy and reduced p62 protein expression. Trehalose abolished the disruption of autophagosome complexes under high glucose conditions in vitro and maternal diabetes in vivo. Autophagosomes induced by trehalose were functionally active, forming mitophagy and reticulophagy in removing damaged cellular organelles in neuroepithelial cells exposed to maternal diabetes. Thus, trehalose directly participated in functional autophagosome generation by incorporating itself into autophagosomes. These findings provide the mechanistic basis for the use of trehalose in preventing disruptive autophagy-associated pathogenesis.

Interplay between Autophagy and the Ubiquitin-Proteasome System and Its Role in the Pathogenesis of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a complex eye disease with many pathogenesis factors, including defective cellular waste management in retinal pigment epithelium (RPE). Main cellular waste in AMD are: all-trans retinal, drusen and lipofuscin, containing unfolded, damaged and unneeded proteins, which are degraded and recycled in RPE cells by two main machineries—the ubiquitin-proteasome system (UPS) and autophagy. Recent findings show that these systems can act together with a significant role of the EI24 (etoposide-induced protein 2.4 homolog) ubiquitin ligase in their action. On the other hand, E3 ligases are essential in both systems, but E3 is degraded by autophagy. The interplay between UPS and autophagy was targeted in several diseases, including Alzheimer disease. Therefore, cellular waste clearing in AMD should be considered in the context of such interplay rather than either of these systems singly. Aging and oxidative stress, two major AMD risk factors, reduce both UPS and autophagy. In conclusion, molecular mechanisms of UPS and autophagy can be considered as a target in AMD prevention and therapeutic perspective. Further work is needed to identify molecules and effects important for the coordination of action of these two cellular waste management systems.

The effect of rapamycin treatment on cerebral ischemia: A systematic review and meta-analysis of animal model studies

BACKGROUND

Amplifying endogenous neuroprotective mechanisms is a promising avenue for stroke therapy. One target is mammalian target of rapamycin (mTOR), a serine/threonine kinase regulating cell proliferation, cell survival, protein synthesis, and autophagy. Animal studies investigating the effect of rapamycin on mTOR inhibition following cerebral ischemia have shown conflicting results.

AIM

To conduct a systematic review and meta-analysis evaluating the effectiveness of rapamycin in reducing infarct volume in animal models of ischemic stroke.

SUMMARY OF REVIEW

Our search identified 328 publications. Seventeen publications met inclusion criteria (52 comparisons: 30 reported infarct size and 22 reported neurobehavioral score). Study quality was modest (median 4 of 9) with no evidence of publication bias. The point estimate for the effect of rapamycin was a 21.6% (95% CI, 7.6%-35.7% p < 0.01) improvement in infarct volume and 30.5% (95% CI 17.2%-43.8%, p < 0.0001) improvement in neuroscores. Effect sizes were greatest in studies using lower doses of rapamycin.

CONCLUSION

Low-dose rapamycin treatment may be an effective therapeutic option for stroke. Modest study quality means there is a potential risk of bias. We recommend further high-quality preclinical studies on rapamycin in stroke before progressing to clinical trials.

Amyloid precursor protein and endosomal-lysosomal dysfunction in Alzheimer's disease: inseparable partners in a multifactorial disease

Abnormalities of the endosomal-lysosomal network (ELN) are a signature feature of Alzheimer's disease (AD). These include the earliest known cytopathology that is specific to AD and that affects endosomes and induces the progressive failure of lysosomes, each of which are directly linked by distinct mechanisms to neurodegeneration. The origins of ELN dysfunction and β-amyloidogenesis closely overlap, which reflects their common genetic basis, the established early involvement of endosomes and lysosomes in amyloid precursor protein (APP) processing and clearance, and the pathologic effect of certain APP metabolites on ELN functions. Genes that promote β-amyloidogenesis in AD (APP, PSEN1/2, and APOE4) have primary effects on ELN function. The importance of primary ELN dysfunction to pathogenesis is underscored by the mutations in more than 35 ELN-related genes that, thus far, are known to cause familial neurodegenerative diseases even though different pathogenic proteins may be involved. In this article, I discuss growing evidence that implicates AD gene-driven ELN disruptions as not only the antecedent pathobiology that underlies β-amyloidogenesis but also as the essential partner with APP and its metabolites that drive the development of AD, including tauopathy, synaptic dysfunction, and neurodegeneration. The striking amelioration of diverse deficits in animal AD models by remediating ELN dysfunction further supports a need to integrate APP and ELN relationships, including the role of amyloid-β, into a broader conceptual framework of how AD arises, progresses, and may be effectively therapeutically targeted.-Nixon, R. A. Amyloid precursor protein and endosomal-lysosomal dysfunction in Alzheimer's disease: inseparable partners in a multifactorial disease.

Molecular definitions of autophagy and related processes

Over the past two decades, the molecular machinery that underlies autophagic responses has been characterized with ever increasing precision in multiple model organisms. Moreover, it has become clear that autophagy and autophagy-related processes have profound implications for human pathophysiology. However, considerable confusion persists about the use of appropriate terms to indicate specific types of autophagy and some components of the autophagy machinery, which may have detrimental effects on the expansion of the field. Driven by the overt recognition of such a potential obstacle, a panel of leading experts in the field attempts here to define several autophagy-related terms based on specific biochemical features. The ultimate objective of this collaborative exchange is to formulate recommendations that facilitate the dissemination of knowledge within and outside the field of autophagy research.

Resveratrol protects neuronal-like cells expressing mutant Huntingtin from dopamine toxicity by rescuing ATG4-mediated autophagosome formation

Parkinsonian-like motor deficits in Huntington's Disease (HD) patients are associated with abnormal dopamine neurotransmission in the striatum. Dopamine metabolism leads to the formation of oxidized dopamine quinones that exacerbates mitochondrial dysfunction with production of reactive oxygen species (ROS) that eventually lead to neuronal cell death. We have previously shown that dopamine-induced oxidative stress triggers apoptotic cell death in dopaminergic neuroblastoma SH-SY5Y cells hyper-expressing the mutant polyQ Huntingtin (polyQ-Htt) protein. Dopamine toxicity was paralleled by impaired autophagy clearance of the polyQ-Htt aggregates. In this study, we found that Dopamine affects the stability and function of ATG4, a redox-sensitive cysteine-protein involved in the processing of LC3, a key step in the formation of autophagosomes. Resveratrol, a dietary polyphenol with anti-oxidant and pro-autophagic properties, has shown neuroprotective potential in HD. Yet the molecular mechanism through which Resveratrol can protect HD cells against DA is not known. Here, we show that Resveratrol prevents the generation of ROS, restores the level of ATG4, allows the lipidation of LC3, facilitates the degradation of polyQ-Htt aggregates and protects the cells from Dopamine toxicity. The present findings provide a mechanistic explanation of the neuroprotective activity of Resveratrol and support its inclusion in a therapeutic regimen to slow down HD progression.

Comparative proteomics analyses for 139A and ME7 scrapie infected mice brains in the middle and terminal stages

PURPOSE

To analyze the proteomics patterns in the cortex regions of scrapie strains 139A- and ME7-infected mice collected in the middle and terminal stages.

EXPERIMENTAL DESIGN

Western Blot and immunohistochemistry methods are used to analyze the pathological changes in mice collected in the middle and terminal stages. The technique of iTRAQ and multidimensional LC and MS are used to analyze the proteomics patterns of mice in different stages.

RESULTS

In total, 2891 with 95% confidence interval are identified. The study here also demonstrates a similar protein expressions in the CNS tissues of two scrapie strains infected mice at the terminal stages, but markedly different one between the middle and terminal samples, not only in the numbers of differentially expressed proteins and involved gene ontologies and pathways but also in the relevant functional constitutions.

CONCLUSIONS

It may provide useful clue in exploring the abnormalities of biological functions at different time points of prion infections and in searching for potential therapeutic and diagnostic biomarkers for prion diseases.

Iron Deposition Leads to Neuronal α-Synuclein Pathology by Inducing Autophagy Dysfunction

Growing evidence has indicated that iron deposition in the substantia nigra plays an important role in Parkinson’s disease (PD). However, the underlying mechanism is still elusive. Using primary dopaminergic neurons and SH-SY5Y cells cultured in vitro, we observed that iron loading increased α-synuclein and reactive oxygen species (ROS) levels in these cells but did not affect the intracellular α-synuclein mRNA levels. Furthermore, iron loading significantly downregulated Beclin-1 levels and decreased the ratio of microtubule-associated protein 1 light chain 3 isoforms (LC3 II/LC3 I). However, a significant change in the levels of autophagy-related gene 5 (Atg5) was not observed in either neurons or SH-SY5Y cells after iron treatment. After treatment with rapamycin, the iron loading-induced increase in the α-synuclein level was significantly reversed and ROS generation was alleviated in both cultured neurons and SH-SY5Y cells. These results indicate that the inhibition of autophagy is critical for the pathological alterations in α-synuclein induced by iron loading. Moreover, treatment with vitamin E did not affect the increase in the α-synuclein levels but significantly eliminated the iron-induced ROS production. Together, our study shows that autophagy dysfunction contributes to iron-induced α-synuclein pathology.

PINK1 signaling in mitochondrial homeostasis and in aging (Review)

Mitochondrial dysfunction is involved in the pathology of Parkinson's disease, an age-associated neurodegenerative disorder. Phosphatase and tensin homolog (PTEN)-induced putative kinase protein 1 (PINK1) is responsible for the most common form of recessive Parkinson's disease. PINK1 is a mitochondrial kinase that is involved in mitrochondrial quality control and promotes cell survival. PINK1 has been shown to protect against neuronal cell death induced by oxidative stress. Accordingly, PINK1 deficiency is associated with mitochondrial dysfunction as well as increased oxidative cellular stress and subsequent neuronal cell death. In addition, several mitochondrial chaperone proteins have been shown to be substrates of the PINK1 kinase. In this review, we discuss recent studies concerning the signaling cascades and molecular mechanisms involved in the process of mitophagy, which is implicated in neurodegeneration and in related aging associated with oxidative stress. Particular attention will be given to the molecular mechanisms proposed to explain the effects of natural compounds and/or food ingredients against oxidative stress. Knowledge of the molecular mechanisms involved in this cellular protection could be critical for developing treatments to prevent and control excessive progression of neurodegenerative disorders.

Dopamine exacerbates mutant Huntingtin toxicity via oxidative-mediated inhibition of autophagy in SH-SY5Y neuroblastoma cells: Beneficial effects of anti-oxidant therapeutics

Neuronal cell death in Huntington's Disease (HD) is associated with the abnormal expansions of a polyglutamine (polyQ) tract in the huntingtin protein (Htt) at the N-terminus that causes the misfolding and aggregation of the mutated protein (mHtt). Autophagy-lysosomal degradation of Htt aggregates may protect the neurons in HD. HD patients eventually manifest parkinsonian-like symptoms, which underlie defects in the dopaminergic system. We hypothesized that dopamine (DA) exacerbates the toxicity in affected neurons by over-inducing an oxidative stress that negatively impinges on the autophagy clearance of mHtt and thus precipitating neuronal cell death. Here we show that the hyper-expression of mutant (>113/150) polyQ Htt is per se toxic to dopaminergic human neuroblastoma SH-SY5Y cells, and that DA exacerbates this toxicity leading to apoptosis and secondary necrosis. DA toxicity is mediated by ROS production (mainly anion superoxide) that elicits a block in the formation of autophagosomes. We found that the pre-incubation with N-Acetyl-l-Cysteine (a quinone reductase inducer) or Deferoxamine (an iron chelator) prevents the generation of ROS, restores the autophagy degradation of mHtt and preserves the cell viability in SH-SY5Y cells expressing the polyQ Htt and exposed to DA. The present findings suggest that DA-induced impairment of autophagy underlies the parkinsonism in HD patients. Our data provide a mechanistic explanation of the DA toxicity in dopaminergic neurons expressing the mHtt and support the use of anti-oxidative stress therapeutics to restore protective autophagy in order to slow down the neurodegeneration in HD patients.

Protective effects of salicylate on PKA inhibitor (H-89)-induced spatial memory deficit via lessening autophagy and apoptosis in rats

In this study, the effects of salicylate on spatial learning and memory, through its effects on autophagy and apoptosis, were evaluated in the presence of the PKA inhibitor H-89. Adult male Wistar rats were divided into experimental groups as follows: salicylate (30, 50, 100μg/0.5μl/side, intra-hippocampal; 400mg/kg, intra-peritoneal), donepezil (1mg/kg as a positive control for behavioral effects of salicylate), H-89 (1μl/side of 5 or 20μM), H-89 plus salicylate and H-89 plus donepezil. The Morris water maze test was used for evaluation of spatial learning and memory. The levels of different apoptotic and autophagic biomarkers were evaluated using the western blot technique. Salicylate (100μg/0.5μl/side) significantly reduced the escape latency on training days, increased the percentage of time spent in the target quadrant during the probe trial and reversed the inhibitory effects of H-89 during the process of spatial learning and memory. The behavioral efficacy of salicylate was comparable to that of donepezil. In addition, salicylate significantly decreased the levels of apoptotic proteins, Bax and caspase 3, and increased the Bcl2 levels in all groups. Furthermore, the levels of LC3II and Atg7 were decreased by salicylate. Our study revealed that both systemic and direct intra-hippocampal administration of salicylate can facilitate the spatial learning and memory. Additionally, intra-hippocampal administration of salicylate can reduce apoptotic and autophagic proteins. The antioxidant activity of salicylate might lead to increased pCREB via stimulation of signaling pathways, resulting in reduction of H-89-induced apoptosis and autophagy.

Tumor apelin, not serum apelin, is associated with the clinical features and prognosis of gastric cancer

BACKGROUND

To study the association between Apelin expression and the clinical features and postoperative prognosis in patients with gastric cancer (Int J Cancer 136:2388-2401, 2015).

METHODS

Tumor samples and matched adjacent normal tissues were collected from 270 patients with GC receiving surgical resection. The tumor and serum Apelin levels were determined by immunohistochemistry and ELISA methods, respectively. GC cell lines were cultured for migration and invasive assays.

RESULTS

Our data showed that tumor Apelin expression status, instead of serum Apelin level, was closely associated with more advance clinical features including tumor differentiation, lymph node and distant metastases. Moreover, patients with high tumor Apelin level had a significantly shorter overall survival period compared to those with low Apelin expression and those with or negative Apelin staining. Our in vitro study revealed that the Apelin regulated the migration and invasion abilities of GC cell lines, accompanied by up-regulations of a variety of cytokines associated with tumor invasiveness.

CONCLUSION

Our data suggest that tumor Apelin can be used as a marker to evaluate clinical characteristics and predict prognosis in GC patients.

Bexarotene targets autophagy and is protective against thromboembolic stroke in aged mice with tauopathy

Stroke is a highly debilitating, often fatal disorder for which current therapies are suitable for only a minor fraction of patients. Discovery of novel, effective therapies is hampered by the fact that advanced age, primary age-related tauopathy or comorbidities typical to several types of dementing diseases are usually not taken into account in preclinical studies, which predominantly use young, healthy rodents. Here we investigated for the first time the neuroprotective potential of bexarotene, an FDA-approved agent, in a co-morbidity model of stroke that combines high age and tauopathy with thromboembolic cerebral ischemia. Following thromboembolic stroke bexarotene enhanced autophagy in the ischemic brain concomitantly with a reduction in lesion volume and amelioration of behavioral deficits in aged transgenic mice expressing the human P301L-Tau mutation. In in vitro studies bexarotene increased the expression of autophagy markers and reduced autophagic flux in neuronal cells expressing P301L-Tau. Bexarotene also restored mitochondrial respiration deficits in P301L-Tau neurons. These newly described actions of bexarotene add to the growing amount of compelling data showing that bexarotene is a potent neuroprotective agent, and identify a novel autophagy-modulating effect of bexarotene.

MiR-299-5p regulates apoptosis through autophagy in neurons and ameliorates cognitive capacity in APPswe/PS1dE9 mice

Abnormalities of autophagy can result in neurodegenerative disorders such as Alzheimer's disease (AD). Nevertheless, the regulatory mechanisms of autophagy in AD are not well understood. Here, we describe our findings that microRNA (miR)-299-5p functions as an autophagy inhibitor by suppressing Atg5 and antagonizing caspase-dependent apoptosis. We observed decreased levels of miR-299-5p both in primary neurons under conditions of starvation and in hippocampi of APPswe/PS1dE9 mice. Additionally, low levels of miR-299-5p were observed in cerebrospinal fluid of AD patients. MiR-299-5p treatment resulted in attenuation of Atg5 and autophagy in primary neurons from APPswe/PS1dE9 mice, N2a cells and SH-SY5Y cells, whereas antagomiR-299-5p enhanced autophagy. Atg5 was verified as a direct target of miR-299-5p by dual luciferase reporter assays. Furthermore, transfection of miR-299-5p into primary hippocampal neurons caused the attenuation of caspase-mediated apoptosis, which was reversed upon starvation-induced autophagy. Inhibition of autophagy by shRNA knockdown of LC3β reduced apoptotic neuron death induced by antagomiR-299-5p. Injection of agomiR-299-5p into the cerebral ventricles of AD mice inhibited both autophagy and apoptosis and also improved the cognitive performance of mice. Overall, our results suggest that miR-299-5p modulates neuron survival programs by regulating autophagy. Thus, miR-299-5p serves as a potential neuroprotective factor in AD.

Baclofen mediates neuroprotection on hippocampal CA1 pyramidal cells through the regulation of autophagy under chronic cerebral hypoperfusion

GABA receptors play an important role in ischemic brain injury. Studies have indicated that autophagy is closely related to neurodegenerative diseases. However, during chronic cerebral hypoperfusion, the changes of autophagy in the hippocampal CA1 area, the correlation between GABA receptors and autophagy, and their influences on hippocampal neuronal apoptosis have not been well established. Here, we found that chronic cerebral hypoperfusion resulted in rat hippocampal atrophy, neuronal apoptosis, enhancement and redistribution of autophagy, down-regulation of Bcl-2/Bax ratio, elevation of cleaved caspase-3 levels, reduction of surface expression of GABAA receptor α1 subunit and an increase in surface and mitochondrial expression of connexin 43 (CX43) and CX36. Chronic administration of GABAB receptors agonist baclofen significantly alleviated neuronal damage. Meanwhile, baclofen could up-regulate the ratio of Bcl-2/Bax and increase the activation of Akt, GSK-3β and ERK which suppressed cytodestructive autophagy. The study also provided evidence that baclofen could attenuate the decrease in surface expression of GABAA receptor α1 subunit, and down-regulate surface and mitochondrial expression of CX43 and CX36, which might enhance protective autophagy. The current findings suggested that, under chronic cerebral hypoperfusion, the effects of GABAB receptors activation on autophagy regulation could reverse neuronal damage.

Role of autophagy in methylmercury-induced neurotoxicity in rat primary astrocytes

Autophagy is an evolutionarily conserved process in which cytoplasmic proteins and organelles are degraded and recycled for reuse. There are numerous reports on the role of autophagy in cell growth and death; however, the role of autophagy in methylmercury (MeHg)-induced neurotoxicity has yet to be identified. We studied the role of autophagy in MeHg-induced neurotoxicity in astrocytes. MeHg reduced astrocytic viability in a concentration- and time-dependent manner, and induced apoptosis. Pharmacological inhibition of autophagy with 3-methyladenine or chloroquine, as well as the silencing of the autophagy-related protein 5, increased MeHg-induced cytotoxicity and the ratio of apoptotic astrocytes. Conversely, rapamycin, an autophagy inducer, along with as N-acetyl-L-cysteine, a precursor of reduced glutathione, decreased MeHg-induced toxicity and the ratio of apoptotic astrocytes. These results indicated that MeHg-induced neurotoxicity was reduced, at least in part, through the activation of autophagy. Accordingly, modulation of autophagy may offer a new avenue for attenuating MeHg-induced neurotoxicity.

Exploring new pathways of neurodegeneration in ALS: the role of mitochondria quality control

Neuronal cells are highly dependent on mitochondria, and mitochondrial dysfunction is associated with neurodegenerative diseases. As perturbed mitochondrial function renders neurons extremely sensitive to a wide variety of insults, such as oxidative stress and bioenergetic defects, mitochondrial defects can profoundly affect neuronal fate. Several studies have linked ALS with mitochondrial dysfunction, stemming from observations of mitochondrial abnormalities, both in patients and in cellular and mouse models of familial forms of ALS. Mitochondrial changes have been thoroughly investigated in mutants of superoxide dismutase 1 (SOD1), one of the most common causes of familial ALS, for which excellent cellular and animal models are available, but recently evidence is emerging also in other forms of ALS, both familial and sporadic. Mitochondrial defects in ALS involve many critical physiopathological processes, from defective bioenergetics to abnormal calcium homeostasis, altered morphology and impaired trafficking. In this review, we summarize established evidence of mitochondrial dysfunction in ALS, especially in SOD1 mutant models of familial ALS. The main focus of the review is on defective mitochondrial quality control (MQC) in ALS. MQC operates at multiple levels to clear damaged proteins through proteostasis and to eliminate irreparably damaged organelles through mitophagy. However, since ALS motor neurons progressively accumulate damaged mitochondria, it is plausible that the MQC is ineffective or overwhelmed by excessive workload imposed by the chronic and extensive mitochondrial damage. This article is part of a Special Issue entitled ALS complex pathogenesis.

A new cellular model of pathological TDP-43: The neurotoxicity of stably expressed CTF25 of TDP-43 depends on the proteasome

The C-terminal fragments-25(CTF25) of TDP-43 is a fragment of TAR DNA-binding protein 43kDa (TDP-43), which is involved in RNA metabolism, neurite outgrowth, and neuronal development and stress granules. Not until recently did evidence suggest that CTF25 might play an important role in amyotrophic lateral sclerosis (ALS) pathogenesis. However, mechanical details on CTF25 causing motor neuron degeneration still remain unknown. To study the toxicity of CTF25 of TDP-43, we established a cellular model stably expressing CTF25 of TDP-43. Herein, we found that stably expressed CTF25 could induce significant oxidative stress and was mainly degraded by the proteasome pathway in cells. Furthermore, the neurotoxicity of CTF25 of TDP-43 was dependent on proteasome activity. In addition, electron microscopy showed mitochondrial swelling and cristae dilation in cells expressing CTF25 and that CTF25 aggregates were characterized by filamentous bundles and electron dense granular material. In conclusion, the new cellular model mimics classical toxic TDP-43 cellular model and interestingly the toxicity of CTF25 is dependent on the proteasome.

Involvement of p38 in signal switching from autophagy to apoptosis via the PERK/eIF2α/ATF4 axis in selenite-treated NB4 cells

Selenite has emerged as an optional chemotherapeutic agent for hematological malignancies. Autophagy and apoptosis are both engaged in selenite-induced cell death. In a previous report, we have identified heat shock protein 90 (Hsp90) as a critical modulator of the balance between autophagy and apoptosis in selenite-treated leukemia cells. However, the mechanisms by which selenite mediates the crosstalk between autophagy and apoptosis remain largely unknown. Herein, we demonstrate that the endoplasmic reticulum (ER) stress-related PERK/eIF2α/ATF4 pathway and p38 are core modules for the selenite-induced switch to apoptosis from autophagy. We found that selenite activated PERK and eIF2α/ATF4 downstream to promote apoptosis. During this progression, p38 was dissociated from PERK-inhibiting Hsp90 and became autophosphorylated. Then, activated p38 further enhanced the docking of activating transcription factor 4 (ATF4) onto the CHOP (CCAAT/enhancer-binding protein homologous protein) promoter via eIF2α to enhance apoptosis. We also found that activated p38 suppressed the phosphorylation of eIF4E that directed ATF4 to bind to the MAP1LC3B (microtubule-associated protein 1 light chain 3B) promoter. Because of the deactivation of eIF4E, the association of ATF4 with the MAP1LC3B promoter was inhibited, and autophagy was compromised. Intriguingly, p53 played important roles in mediating the p38-mediated regulation of eIF2α and eIF4E. When activated by p38, p53 induced the phosphorylation of eIF2α and the dephosphorylation of eIF4E, particularly in the nucleus where the ATF4 transcription factor was modulated, ultimately resulting in differential expression of CHOP and LC3. Moreover, selenite exhibited potent antitumor effects in vivo. In an NB4 cell xenograft model, selenite induced apoptosis and hampered autophagy. In addition, related signaling proteins demonstrated similar changes to those observed in vitro. These data suggest that selenite may be a candidate drug for leukemia therapy.

Autophagy and oxidative stress in gliomas with IDH1 mutations

IDH1 mutations in gliomas associate with longer survival. Prooxidant and antiproliferative effects of IDH1 mutations and its D-2-hydroxyglutarate (2-HG) product have been described in vitro, but inconsistently observed. It is also unclear whether overexpression of mutant IDH1 in wild-type cells accurately phenocopies the effects of endogenous IDH1-mutations on tumor apoptosis and autophagy. Herein we investigated the effects of 2-HG and mutant IDH1 overexpression on proliferation, apoptosis, oxidative stress, and autophagy in IDH1 wild-type glioma cells, and compared those results with patient-derived tumors. 2-HG reduced viability and proliferation of U87MG and LN18 cells, triggered apoptosis in LN18 cells, and autophagy in U87MG cells. In vitro studies and flank xenografts of U87MG cells overexpressing R132H IDH1 exhibited increased oxidative stress, including increases of both manganese superoxide dismutase (MnSOD) and p62. Patient-derived IDH1-mutant tumors showed no significant differences in apoptosis or autophagy, but showed p62 accumulation and actually trended toward reduced MnSOD expression. These data indicate that mutant IDH1 and 2-HG can induce oxidative stress, autophagy, and apoptosis, but these effects vary greatly according to cell type.

ERKed by LRRK2: a cell biological perspective on hereditary and sporadic Parkinson's disease

The leucine rich repeat kinase 2 (LRRK2/dardarin) is implicated in autosomal dominant familial and sporadic Parkinson's disease (PD); mutations in LRRK2 account for up to 40% of PD cases in some populations. LRRK2 is a large protein with a kinase domain, a GTPase domain, and multiple potential protein interaction domains. As such, delineating the functional pathways for LRRK2 and mechanisms by which PD-linked variants contribute to age-related neurodegeneration could result in pharmaceutically tractable therapies. A growing number of recent studies implicate dysregulation of mitogen activated protein kinases 3 and 1 (also known as ERK1/2) as possible downstream mediators of mutant LRRK2 effects. As these master regulators of growth, differentiation, neuronal plasticity and cell survival have also been implicated in other PD models, a set of common cell biological pathways may contribute to neuronal susceptibility in PD. Here, we review the literature on several major cellular pathways impacted by LRRK2 mutations--autophagy, microtubule/cytoskeletal dynamics, and protein synthesis--in context of potential signaling crosstalk involving the ERK1/2 and Wnt signaling pathways. Emerging implications for calcium homeostasis, mitochondrial biology and synaptic dysregulation are discussed in relation to LRRK2 interactions with other PD gene products. It has been shown that substantia nigra neurons in human PD and Lewy body dementia patients exhibit cytoplasmic accumulations of ERK1/2 in mitochondria, autophagosomes and bundles of intracellular fibrils. Both experimental and human tissue data implicate pathogenic changes in ERK1/2 signaling in sporadic, toxin-based and mutant LRRK2 settings, suggesting engagement of common cell biological pathways by divergent PD etiologies.

Reduction of synaptojanin 1 accelerates Aβ clearance and attenuates cognitive deterioration in an Alzheimer mouse model

Recent studies link synaptojanin 1 (synj1), the main phosphoinositol (4,5)-biphosphate phosphatase (PI(4,5)P2-degrading enzyme) in the brain and synapses, to Alzheimer disease. Here we report a novel mechanism by which synj1 reversely regulates cellular clearance of amyloid-β (Aβ). Genetic down-regulation of synj1 reduces both extracellular and intracellular Aβ levels in N2a cells stably expressing the Swedish mutant of amyloid precursor protein (APP). Moreover, synj1 haploinsufficiency in an Alzheimer disease transgenic mouse model expressing the Swedish mutant APP and the presenilin-1 mutant ΔE9 reduces amyloid plaque load, as well as Aβ40 and Aβ42 levels in hippocampus of 9-month-old animals. Reduced expression of synj1 attenuates cognitive deficits in these transgenic mice. However, reduction of synj1 does not affect levels of full-length APP and the C-terminal fragment, suggesting that Aβ generation by β- and γ-secretase cleavage is not affected. Instead, synj1 knockdown increases Aβ uptake and cellular degradation through accelerated delivery to lysosomes. These effects are partially dependent upon elevated PI(4,5)P2 with synj1 down-regulation. In summary, our data suggest a novel mechanism by which reduction of a PI(4,5)P2-degrading enzyme, synj1, improves amyloid-induced neuropathology and behavior deficits through accelerating cellular Aβ clearance.

Not on the menu: autophagy-independent clearance of prions

A common feature of neurodegenerative diseases is the accumulation of disease-specific, aggregated protein species in the nervous system. Transmissible spongiform encephalopathies are universally fatal neurodegenerative diseases involving the transconformation and aggregation of prion proteins. At the cellular level macroautophagy has been identified as an efficient pathway for the clearance of these toxic protein aggregates. Hence, recent research has focused on the pharmacological manipulation of autophagy as a potential treatment for neurodegenerative diseases. Independent of their effects on the estrogen receptor, tamoxifen and its metabolite 4-hydroxytamoxifen are well known inducers of autophagy. However, we recently reported that the ability of 4-hydroxytamoxifen to clear prion infection is independent of autophagy. In contrast, we provide a model whereby perturbation of cholesterol metabolism, and not autophagy, is the main mechanism whereby 4-hydroxytamoxifen is able to exert its anti-prion effects. Thus, while tamoxifen, a widely available pharmaceutical, may have applications in prion therapy, prions may also represent a special case and may require different pharmacological interventions than other proteinopathies.

ATF4 activation by the p38MAPK-eIF4E axis mediates apoptosis and autophagy induced by selenite in Jurkat cells

Previous studies have shown that selenite exerts pro-apoptosis and pro-autophagy effects and is associated with the activation of ER stress in T-cell acute lymphoblastic leukemia (T-ALL). Herein we demonstrate the underlying mechanisms by which the activation of p38MAPK plays essential roles in apoptosis and autophagy and the coordination of cellular metabolic processes during leukemia therapy. MKK3/6-dependent activation of p38MAPK is required for the phosphorylation of eIF4E, thus initiating the translation of ER stress-related transcription factor ATF4. Upregulated ATF4 results in the transcriptional initiation of the apoptosis-related chop gene and autophagy-related map1lc3b gene, through which selenite links ER stress to apoptosis and autophagy during leukemia treatment. Moreover, autophagy induction enhances cell apoptosis under this condition.

Arginine68 is an essential residue for the C-terminal cleavage of human Atg8 family proteins

Background

Autophagy is a conserved cellular process that degrades and recycles cytoplasmic components via a lysosomal pathway. The phosphatidylethanolamine (PE)-conjugation of the Atg8 protein plays an important role in the yeast autophagy process. In humans, six Atg8 homologs, including MAP1LC3A, MAP1LC3B, MAP1LC3C (refer to LC3A, LC3B, and LC3C hereafter), GABARAP, GABARAPL1, and GABARAPL2 have been reported. All of them can be conjugated to PE through a ubiquitin-like conjugation system, and be located to autophagosomes.

Results

In this study, we found 3 new alternative splicing isoforms in LC3B, GABARAP, and GABARAPL1, (designated as LC3B-a, GABARAP-a and GABARAPL1-a, respectively). None of them can go through the PE-conjugation process and be located to autophagosomes. Interestingly, compared with LC3B, LC3B-a has a single amino acid (Arg68) deletion due to the NAGNAG alternative splicing in intron 3. Through structural simulations, we found that the C-terminal tail of LC3B-a is less mobile than that of LC3B, thus affecting its C-terminal cleavage by human ATG4 family proteins. Furthermore, we found that Arg68 is an essential residue facilitating the interaction between human Atg8 family proteins and ATG4B by forming a salt bridge with Asp171 of ATG4B. Depletion of this salt bridge reduces autophagosomes formation and autophagic flux under both normal and nutrition starvation conditions.

Conclusions

These results suggest Arg68 is an essential residue for the C-terminal cleavage of Atg8 family proteins during the autophagy process.

After the banquet: mitochondrial biogenesis, mitophagy, and cell survival

Mitochondria are highly dynamic organelles of crucial importance to the proper functioning of neuronal, cardiac and other cell types dependent upon aerobic efficiency. Mitochondrial dysfunction has been implicated in numerous human conditions, to include cancer, metabolic diseases, neurodegeneration, diabetes, and aging. In recent years, mitochondrial turnover by macroautophagy (mitophagy) has captured the limelight, due in part to discoveries that genes linked to Parkinson disease regulate this quality control process. A rapidly growing literature is clarifying effector mechanisms that underlie the process of mitophagy; however, factors that regulate positive or negative cellular outcomes have been less studied. Here, we review the literature on two major pathways that together may determine cellular adaptation vs. cell death in response to mitochondrial dysfunction. Mitochondrial biogenesis and mitophagy represent two opposing, but coordinated processes that determine mitochondrial content, structure, and function. Recent data indicate that the capacity to undergo mitochondrial biogenesis, which is dysregulated in disease states, may play a key role in determining cell survival following mitophagy-inducing injuries. The current literature on major pathways that regulate mitophagy and mitochondrial biogenesis is summarized, and mechanisms by which the interplay of these two processes may determine cell fate are discussed. We conclude that in primary neurons and other mitochondrially dependent cells, disruptions in any phase of the mitochondrial recycling process can contribute to cellular dysfunction and disease. Given the emerging importance of crosstalk among regulators of mitochondrial function, autophagy, and biogenesis, signaling pathways that coordinate these processes may contribute to therapeutic strategies that target or regulate mitochondrial turnover and regeneration.

Longitudinal measures of proteostasis in live neurons: features that determine fate in models of neurodegenerative disease

Protein misfolding and proteostasis decline is a common feature of many neurodegenerative diseases. However, modeling the complexity of proteostasis and the global cellular consequences of its disruption is a challenge, particularly in live neurons. Although conventional approaches, based on population measures and single "snapshots", can identify cellular changes during neurodegeneration, they fail to determine if these cellular events drive cell death or act as adaptive responses. Alternatively, a "systems" cell biology approach known as longitudinal survival analysis enables single neurons to be followed over the course of neurodegeneration. By capturing the dynamics of misfolded proteins and the multiple cellular events that occur along the way, the relationship of these events to each other and their importance and role during cell death can be determined. Quantitative models of proteostasis dysfunction may yield unique insight and novel therapeutic strategies for neurodegenerative disease.

Function and characteristics of PINK1 in mitochondria

Mutations in phosphatase and tensin homologue-induced kinase 1 (PINK1) cause recessively inherited Parkinson's disease, a neurodegenerative disorder linked to mitochondrial dysfunction. Studies support the notion of neuroprotective roles for the PINK1, as it protects cells from damage-mediated mitochondrial dysfunction, oxidative stress, and cell apoptosis. PARL is a mitochondrial resident rhomboid serine protease, and it has been reported to mediate the cleavage of the PINK1. Interestingly, impaired mitophagy, an important autophagic quality control mechanism that clears the cells of damaged mitochondria, may also be an underlying mechanism of disease pathogenesis in patients for Parkinson's disease with the PARL mutations. Functional studies have revealed that PINK1 recruits Parkin to mitochondria to initiate the mitophagy. PINK1 is posttranslationally processed, whose level is definitely regulated in healthy steady state of mitochondria. As a consequence, PINK1 plays a pivotal role in mitochondrial healthy homeostasis.

4-hydroxytamoxifen leads to PrPSc clearance by conveying both PrPC and PrPSc to lysosomes independently of autophagy

Prion diseases are fatal neurodegenerative disorders involving the abnormal folding of a native cellular protein, named PrP(C), to a malconformed aggregation-prone state, enriched in beta sheet secondary structure, denoted PrP(Sc). Recently, autophagy has garnered considerable attention as a cellular process with the potential to counteract neurodegenerative diseases of protein aggregation such as Alzheimer's disease, Huntington's disease, and Parkinson's disease. Stimulation of autophagy by chemical compounds has also been shown to reduce PrP(Sc) in infected neuronal cells and prolong survival times in mouse models. Consistent with previous reports, we demonstrate that autophagic flux is increased in chronically infected cells. However, in contrast to recent findings we show that autophagy does not cause a reduction in scrapie burden. We report that in infected neuronal cells different compounds known to stimulate autophagy are ineffective in increasing autophagic flux and in reducing PrP(Sc). We further demonstrate that tamoxifen and its metabolite 4-hydroxytamoxifen lead to prion degradation in an autophagy-independent manner by diverting the trafficking of both PrP and cholesterol to lysosomes. Our data indicate that tamoxifen, a well-characterized, widely available pharmaceutical, may have applications in the therapy of prion diseases.

Nicotinamide forestalls pathology and cognitive decline in Alzheimer mice: evidence for improved neuronal bioenergetics and autophagy procession

Impaired brain energy metabolism and oxidative stress are implicated in cognitive decline and the pathologic accumulations of amyloid β-peptide (Aβ) and hyperphosphorylated tau in Alzheimer's disease (AD). To determine whether improving brain energy metabolism will forestall disease progress in AD, the impact of the β-nicotinamide adenine dinucleotide precursor nicotinamide on brain cell mitochondrial function and macroautophagy, bioenergetics-related signaling, and cognitive performance were studied in cultured neurons and in a mouse model of AD. Oxidative stress resulted in decreased mitochondrial mass, mitochondrial degeneration, and autophagosome accumulation in neurons. Nicotinamide preserved mitochondrial integrity and autophagy function, and reduced neuronal vulnerability to oxidative/metabolic insults and Aβ toxicity. β-Nicotinamide adenine dinucleotide biosynthesis, autophagy, and phosphatidylinositol-3-kinase signaling were required for the neuroprotective action of nicotinamide. Treatment of 3xTgAD mice with nicotinamide for 8 months resulted in improved cognitive performance, and reduced Aβ and hyperphosphorylated tau pathologies in hippocampus and cerebral cortex. Nicotinamide treatment preserved mitochondrial integrity, and improved autophagy-lysosome procession by enhancing lysosome/autolysosome acidification to reduce autophagosome accumulation. Treatment of 3xTgAD mice with nicotinamide resulted in elevated levels of activated neuroplasticity-related kinases (protein kinase B [Akt] and extracellular signal-regulated kinases) and the transcription factor cyclic adenosine monophosphate (AMP) response element-binding protein in the hippocampus and cerebral cortex. Thus, nicotinamide suppresses AD pathology and cognitive decline in a mouse model of AD by a mechanism involving improved brain bioenergetics with preserved functionality of mitochondria and the autophagy system.

Novel virostatic agents against bluetongue virus

Bluetongue virus (BTV), a member in the family Reoviridae, is a re-emerging animal disease infecting cattle and sheep. With its recent outbreaks in Europe, there is a pressing need for efficacious antivirals. We presented here the identification and characterization of a novel virostatic molecule against BTV, an aminothiophenecarboxylic acid derivative named compound 003 (C003). The virostatic efficacy of C003 could be improved via chemical modification, leading to a de novo synthesized compound 052 (C052). The 50% effective concentrations (EC(50)) of C003 and C052 were determined at 1.76 ± 0.73 µM and 0.27 ± 0.12 µM, respectively. The 50% cytotoxicity concentration (CC(50)) of C003 was over 100 µM and the CC(50) of C052 was at 82.69 µM. Accordingly, the 50% selective index (SI(50)) of C003 and C052 against BTV was over 57 and 306, respectively. The inhibitory effect of C003/C052 on BTV-induced apoptosis was also confirmed via the inhibition of caspase-3/-7 activation post BTV infection. C003/C052 could inhibit BTV induced CPE even when added as late as 24 h.p.i., indicating that they might act at late stage of viral life-cycle. C003/C052 could reduce over two-logs of both the progeny virus production and the number of genomic viral RNA copies. Interestingly, both the activation of host autophagy and viral protein expression were inhibited post BTV infection when cells were treated with C003 and C052, suggesting that C003/C052 might act as virostatic agents via inhibiting host autophagy activation. Although further investigations might be needed to pin down the exact mechanism of C003/C052, our finding suggested that these compounds might be potent lead compounds with potential novel mechanism of action against BTV.

The ubiquitin-proteasome system and the autophagic-lysosomal system in Alzheimer disease

As neurons age, their survival depends on eliminating a growing burden of damaged, potentially toxic proteins and organelles-a capability that declines owing to aging and disease factors. Here, we review the two proteolytic systems principally responsible for protein quality control in neurons and their important contributions to Alzheimer disease pathogenesis. In the first section, the discovery of paired helical filament ubiquitination is described as a backdrop for discussing the importance of the ubiquitin-proteasome system in Alzheimer disease. In the second section, we review the prominent involvement of the lysosomal system beginning with pathological endosomal-lysosomal activation and signaling at the very earliest stages of Alzheimer disease followed by the progressive failure of autophagy. These abnormalities, which result in part from Alzheimer-related genes acting directly on these lysosomal pathways, contribute to the development of each of the Alzheimer neuropathological hallmarks and represent a promising therapeutic target.

A homozygous mutation in KCTD7 links neuronal ceroid lipofuscinosis to the ubiquitin-proteasome system

Neuronal ceroid lipofuscinosis (NCL) is a genetically heterogeneous group of lysosomal diseases that collectively compose the most common Mendelian form of childhood-onset neurodegeneration. It is estimated that ∼8% of individuals diagnosed with NCL by conservative clinical and histopathologic criteria have been ruled out for mutations in the nine known NCL-associated genes, suggesting that additional genes remain unidentified. To further understand the genetic underpinnings of the NCLs, we performed whole-exome sequencing on DNA samples from a Mexican family affected by a molecularly undefined form of NCL characterized by infantile-onset progressive myoclonic epilepsy (PME), vision loss, cognitive and motor regression, premature death, and prominent NCL-type storage material. Using a recessive model to filter the identified variants, we found a single homozygous variant, c.550C>T in KCTD7, that causes a p.Arg184Cys missense change in potassium channel tetramerization domain-containing protein 7 (KCTD7) in the affected individuals. The mutation was predicted to be deleterious and was absent in over 6,000 controls. The identified variant altered the localization pattern of KCTD7 and abrogated interaction with cullin-3, a ubiquitin-ligase component and known KCTD7 interactor. Intriguingly, murine cerebellar cells derived from a juvenile NCL model (CLN3) showed enrichment of endogenous KCTD7. Whereas KCTD7 mutations have previously been linked to PME without lysosomal storage, this study clearly demonstrates that KCTD7 mutations also cause a rare, infantile-onset NCL subtype designated as CLN14.

Autophagy is induced through the ROS-TP53-DRAM1 pathway in response to mitochondrial protein synthesis inhibition

Mitoribosome in mammalian cells is responsible for synthesis of 13 mtDNA-encoded proteins, which are integral parts of four mitochondrial respiratory chain complexes (I, III, IV and V). ERAL1 is a nuclear-encoded GTPase important for the formation of the 28S small mitoribosomal subunit. Here, we demonstrate that knockdown of ERAL1 by RNA interference inhibits mitochondrial protein synthesis and promotes reactive oxygen species (ROS) generation, leading to autophagic vacuolization in HeLa cells. Cells that lack ERAL1 expression showed a significant conversion of LC3-I to LC3-II and an enhanced accumulation of autophagic vacuoles carrying the LC3 marker, all of which were blocked by the autophagy inhibitor 3-MA as well as by the ROS scavenger NAC. Inhibition of mitochondrial protein synthesis either by ERAL1 siRNA or chloramphenicol (CAP), a specific inhibitor of mitoribosomes, induced autophagy in HTC-116 TP53 (+/+) cells, but not in HTC-116 TP53 (-/-) cells, indicating that tumor protein 53 (TP53) is essential for the autophagy induction. The ROS elevation resulting from mitochondrial protein synthesis inhibition induced TP53 expression at transcriptional levels by enhancing TP53 promoter activity, and increased TP53 protein stability by suppressing TP53 ubiquitination through MAPK14/p38 MAPK-mediated TP53 phosphorylation. Upregulation of TP53 and its downstream target gene DRAM1, but not CDKN1A/p21, was required for the autophagy induction in ERAL1 siRNA or CAP-treated cells. Altogether, these data indicate that autophagy is induced through the ROS-TP53-DRAM1 pathway in response to mitochondrial protein synthesis inhibition.

Increased hippocampal accumulation of autophagosomes predicts short-term recognition memory impairment in aged mice

Constitutive macroautophagy involved in the turnover of defective long-lived proteins and organelles is crucial for neuronal homeostasis. We hypothesized that macroautophagic dysregulation in selective brain regions was associated with memory impairment in aged mice. We used the single-trial object recognition test to measure short-term memory in 18 aged mice compared to 22 young mice and employed immunohistochemistry to assess cellular distribution of proteins involved in the selective degradation of ubiquitinated proteins via macroautophagy. Values of the discrimination ratio (DR, a measure of short-term recognition memory performance) in aged mice were significantly lower than those in young mice (median, 0.54 vs. 0.67; p = 0.005, U test). Almost exclusively in aged mice, there were clusters of puncta immunoreactive for microtubule-associated protein 1 light chain 3 (LC3), ubiquitin- and LC3-binding protein p62, and ubiquitin in neuronal processes predominantly in the hippocampal formation, olfactory bulb/tubercle, and cerebellar cortex. The hippocampal burden of clustered puncta immunoreactive for LC3 and p62 exhibited inverse linear correlations with DR in aged mice (ρ = -0.48 and -0.55, p = 0.044 and 0.018, respectively, Spearman's rank correlation). These findings suggest that increased accumulation of autophagosomes within neuronal processes in selective brain regions is characteristic of aging. The dysregulation of macroautophagy can adversely affect the turnover of aggregate-prone proteins and defective organelles, which may contribute to memory impairment in aged mice.

Sporadic amyotrophic lateral sclerosis: new hypothesis regarding its etiology and pathogenesis suggests that astrocytes might be the primary target hosting a still unknown external agent

This article briefly describes the already known clinical features and pathogenic mechanisms underlying sporadic amyotrophic lateral sclerosis, namely excitoxicity, oxidative stress, protein damage, inflammation, genetic abnormalities and neuronal death. Thereafter, it puts forward the hypothesis that astrocytes may be the cells which serve as targets for the harmful action of a still unknown environmental agent, while neuronal death may be a secondary event following the initial insult to glial cells. The article also suggests that an emergent virus or a misfolded infectious protein might be potential candidates to accomplish this task.

Autophagy and cancer cell metabolism

Autophagy is a catabolic process involving lysosomal turnover of proteins and organelles for maintenance of cellular homeostasis and mitigation of metabolic stress. Autophagy defects are linked to diseases, such as liver failure, neurodegeneration, inflammatory bowel disease, aging and cancer. The role of autophagy in tumorigenesis is complex and likely context-dependent. Human breast, ovarian and prostate cancers have allelic deletions of the essential autophagy regulator BECN1 and Becn1(+/-) and other autophagy-deficient transgenic mice are tumor-prone, whereas tumors with constitutive Ras activation, including human pancreatic cancers, upregulate basal autophagy and are commonly addicted to this pathway for survival and growth; furthermore, autophagy suppression by Fip200 deletion compromises PyMT-induced mammary tumorigenesis. The double-edged sword function of autophagy in cancer has been attributed to both cell- and non-cell-autonomous mechanisms, as autophagy defects promote cancer progression in association with oxidative and ER stress, DNA damage accumulation, genomic instability and persistence of inflammation, while functional autophagy enables cancer cell survival under stress and likely contributes to treatment resistance. In this review, we will focus on the intimate link between autophagy and cancer cell metabolism, a topic of growing interest in recent years, which has been recognized as highly clinically relevant and has become the focus of intense investigation in translational cancer research. Many tumor-associated conditions, including intermittent oxygen and nutrient deprivation, oxidative stress, fast growth and cell death suppression, modulate, in parallel and in interconnected ways, both cellular metabolism and autophagy to enable cancer cells to rapidly adapt to environmental stressors, maintain uncontrolled proliferation and evade the toxic effects of radiation and/or chemotherapy. Elucidating the interplay between autophagy and tumor cell metabolism will provide unique opportunities to identify new therapeutic targets and develop synthetically lethal treatment strategies that preferentially target cancer cells, while sparing normal tissues.

Vid30 is required for the association of Vid vesicles and actin patches in the vacuole import and degradation pathway

When Saccharomyces cerevisiae is starved of glucose, the gluconeogenic enzymes fructose-1,6-bisphosphatase (FBPase), malate dehydrogenase (MDH2), isocitrate lyase (Icl1) and phosphoenolpyruvate carboxykinase (Pck1) are induced. However, when glucose is added to prolonged starved cells, these enzymes are degraded in the vacuole via the vacuole import and degradation (Vid) pathway. Recent evidence suggests that the Vid pathway merges with the endocytic pathway at actin patches where endocytic vesicles are formed. The convergence of the Vid pathway with the endocytic pathway allows cells to remove intracellular and extracellular proteins simultaneously. However, the genes that regulate this step of the convergence have not been identified previously. Here we show that VID30 plays a critical role for the association of Vid vesicles and actin patches. Vid30 is constitutively expressed and interacts with Vid vesicle proteins Vid24 and Sec28 but not with the cargo protein FBPase. In the absence of SEC28 or VID24, Vid30 association with actin patches was prolonged. In cells lacking the VID30 gene, FBPase and Vid24 were not localized to actin patches, suggesting that Vid30 has a role in the association of Vid vesicles and actin patches. Vid30 contains a LisH and a CTLH domain, both of which are required for FBPase degradation. When these domains were deleted, FBPase trafficking to the vacuole was impaired. We suggest that Vid30 also has a role in the Vid pathway at a later step in a process that is mediated by the LisH and CTLH domains.