Role of autophagy in the clearance of mutant huntingtin: A step towards therapy?

Designed Nanodrugs for Ultrasonic Removal of Toxic Polyglutamine Aggregates from Neuron Cells

Clearing of toxic polyglutamine aggregates from neuronal cells is crucial for ameliorating Huntington's disease. However, such clearance is challenging, requiring the targeting of affected neuron cells in the brain, followed by the removal of polyglutamine from cells. Here we report a designed nanodrug that can be used for the ultrasound-based removal of toxic polyglutamine aggregates from neuron cells. The nanodrug is composed of a sonosensitizer molecule, chlorin e6- or protoporphyrin IX-loaded polymer micelle of 20-30 nm in size that rapidly delivers the sonosensitizer into the cell nucleus. Ultrasound exposure of these cells generates singlet oxygen in the nucleus/perinuclear region that induces strong autophagic flux and clears toxic polyglutamine aggregates from cells. It has been demonstrated that the nanodrug and ultrasound treatment can enhance the cell survival against polyglutamine aggregates by 4 times. This result suggests that the nanodrug can be designed for focused ultrasound-based wireless treatment of various neurodegenerative diseases.

Vitamin B6, B12 and folate modulate deregulated pathways and protein aggregation in yeast model of Huntington disease

Huntington's disease (HD) is an incurable and progressive neurodegenerative disease affecting the basal ganglia of the brain. HD is caused due to expansion of the polyglutamine tract in the protein Huntingtin resulting in aggregates. The increased PolyQ length results in aggregation of protein Huntingtin leading to neuronal cell death. Vitamin B6, B12 and folate are deficient in many neurodegenerative diseases. We performed an integrated analysis of transcriptomic, metabolomic and cofactor-protein network of vitamin B6, B12 and folate was performed. Our results show considerable overlap of pathways modulated by Vitamin B6, B12 and folate with those obtained from transcriptomic and metabolomic data of HD patients and model systems. Further, in yeast model of HD we showed treatment of B6, B12 or folate either alone or in combination showed impaired aggregate formation. Transcriptomic analysis of yeast model treated with B6, B12 and folate showed upregulation of pathways like ubiquitin mediated proteolysis, autophagy, peroxisome, fatty acid, lipid and nitrogen metabolism. Metabolomic analysis of yeast model shows deregulation of pathways like aminoacyl-tRNA biosynthesis, metabolism of various amino acids, nitrogen metabolism and glutathione metabolism. Integrated transcriptomic and metabolomic analysis of yeast model showed concordance in the pathways obtained. Knockout of Peroxisomal (PXP1 and PEX7) and Autophagy (ATG5) genes in yeast increased aggregates which is mitigated by vitamin B6, B12 and folate treatment. Taken together our results show a role for Vitamin B6, B12 and folate mediated modulation of pathways important for preventing protein aggregation with potential implications for HD.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03525-y.

Targeting autophagy in disease: established and new strategies

Macroautophagy/autophagy is an evolutionarily conserved pathway responsible for clearing cytosolic aggregated proteins, damaged organelles or invading microorganisms. Dysfunctional autophagy leads to pathological accumulation of the cargo, which has been linked to a range of human diseases, including neurodegenerative diseases, infectious and autoimmune diseases and various forms of cancer. Cumulative work in animal models, application of genetic tools and pharmacologically active compounds, has suggested the potential therapeutic value of autophagy modulation in disease, as diverse as Huntington, Salmonella infection, or pancreatic cancer. Autophagy activation versus inhibition strategies are being explored, while the role of autophagy in pathophysiology is being studied in parallel. However, the progress of preclinical and clinical development of autophagy modulators has been greatly hampered by the paucity of selective pharmacological agents and biomarkers to dissect their precise impact on various forms of autophagy and cellular responses. Here, we summarize established and new strategies in autophagy-related drug discovery and indicate a path toward establishing a more efficient discovery of autophagy-selective pharmacological agents. With this knowledge at hand, modern concepts for therapeutic exploitation of autophagy might become more plausible.

Abbreviations: ALS: amyotrophic lateral sclerosis; AMPK: AMP-activated protein kinase; ATG: autophagy-related gene; AUTAC: autophagy-targeting chimera; CNS: central nervous system; CQ: chloroquine; GABARAP: gamma-aminobutyric acid type A receptor-associated protein; HCQ: hydroxychloroquine; LYTAC: lysosome targeting chimera; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; NDD: neurodegenerative disease; PDAC: pancreatic ductal adenocarcinoma; PE: phosphatidylethanolamine; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PtdIns3K: class III phosphatidylinositol 3-kinase; PtdIns3P: phosphatidylinositol 3-phosphate; PROTAC: proteolysis-targeting chimera; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; SQSTM1/p62: sequestosome 1; ULK1: unc-51 like autophagy activating kinase 1.

Autophagy contributes to angiotensin II induced dysfunction of HUVECs

BACKGROUND

Signal transduction of Angiotensin II (Ang II) induced autophagy and its role in Ang II-induced dysfunction of HUVECs are still unclear.

METHODS

HUVECs are stimulated with different doses of Ang II (10-9-10-5 mol/L) for different time (6-48 hours). Autophagy-related protein markers: LC3, Beclin-1 and SQSTM1/p62 are measured by western blot.

RESULTS

Incubation with Ang II increases autophagic flux (Beclin-1, autophagosomes formation, and degradation of SQSTM1/p62, LC3-I). Increased autophagic levels are inhibited by pretreatment with Ang II type 1 receptor (AT1) blocker (Candesartan), NADPH Oxidase inhibitor (apocycin), mitochondrial K_ATP channels inhibitor (5-hydroxydecanoate, 5HD). 3-Methyladenine (inhibitors of autophagy) and rapamycin (activator of autophagy) respectively inhibits or activates Ang II-induced autophagy levels. Ang II decreases phosphorylation of endothelial nitric oxide synthase (eNOS) and NO production in HUVECs. L-NAME (NOS inhibitor) totally mimics the actions of Ang II on eNOS, NO production and autophagy levels. Rapamycin further decreases NO production combined with Ang II. Silence Atg5 completely reverses Ang II-activated autophagy levels.

CONCLUSIONS

Our results demonstrate that Ang II stimulation increases autophagy levels via AT1 receptor, NADPH oxidase, mitochondrial K_ATP channel, eNOS, Atg5 signal pathway in HUVECs, and activation of autophagy contributes to Ang II induced dysfunction of HUVECs.

The Novel Alpha-2 Adrenoceptor Inhibitor Beditin Reduces Cytotoxicity and Huntingtin Aggregates in Cell Models of Huntington's Disease

Huntington's disease (HD) is a monogenetic neurodegenerative disorder characterized by the accumulation of polyglutamine-expanded huntingtin (mHTT). There is currently no cure, and therefore disease-slowing remedies are sought to alleviate symptoms of the multifaceted disorder. Encouraging findings in Alzheimer's and Parkinson's disease on alpha-2 adrenoceptor (α2-AR) inhibition have shown neuroprotective and aggregation-reducing effects in cell and animal models. Here, we analyzed the effect of beditin, a novel α2- adrenoceptor (AR) antagonist, on cell viability and mHTT protein levels in cell models of HD using Western blot, time-resolved Foerster resonance energy transfer (TR-FRET), lactate dehydrogenase (LDH) and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) cytotoxicity assays. Beditin decreases cytotoxicity, as measured by TUNEL staining and LDH release, in a neuronal progenitor cell model (STHdh cells) of HD and decreases the aggregation propensity of HTT exon 1 fragments in an overexpression model using human embryonic kidney (HEK) 293T cells. α2-AR is a promising therapeutic target for further characterization in HD models. Our data allow us to suggest beditin as a valuable candidate for the pharmaceutical manipulation of α2-AR, as it is capable of modulating neuronal cell survival and the level of mHTT.

Acute manganese treatment restores defective autophagic cargo loading in Huntington's disease cell lines

The molecular etiology linking the pathogenic mutations in the Huntingtin (Htt) gene with Huntington's disease (HD) is unknown. Prior work suggests a role for Htt in neuronal autophagic function and mutant HTT protein disrupts autophagic cargo loading. Reductions in the bioavailability of the essential metal manganese (Mn) are seen in models of HD. Excess cellular Mn impacts autophagic function, but the target and molecular basis of these changes are unknown. Thus, we sought to determine if changes in cellular Mn status impact autophagic processes in a wild-type or mutant Htt-dependent manner. We report that the HD genotype is associated with reduced Mn-induced autophagy and that acute Mn exposure increases autophagosome induction/formation. To determine if a deficit in bioavailable Mn is mechanistically linked to the autophagy-related HD cellular phenotypes, we examined autophagosomes by electron microscopy. We observed that a 24 h 100 uM Mn restoration treatment protocol attenuated an established HD 'cargo-recognition failure' in the STHdh HD model cells by increasing the percentage of filled autophagosomes. Mn restoration had no effect on HTT aggregate number, but a 72 h co-treatment with chloroquine (CQ) in GFP-72Q-expressing HEK293 cells increased the number of visible aggregates in a dose-dependent manner. As CQ prevents autophagic degradation this indicates that Mn restoration in HD cell models facilitates incorporation of aggregates into autophagosomes. Together, these findings suggest that defective Mn homeostasis in HD models is upstream of the impaired autophagic flux and provide proof-of-principle support for increasing bioavailable Mn in HD to restore autophagic function and promote aggregate clearance.

Life, death, and autophagy in cancer: NF-κB turns up everywhere

Escaping programmed cell death is a hallmark of cancer. NF-κB transcription factors are key regulator of cell survival and aberrant NF-κB signaling has been involved in the pathogenesis of most human malignancies. Although NF-κB is best known for its antiapoptotic role, other processes regulating the life/death balance, such as autophagy and necroptosis, seem to network with NF-κB. This review discusses how the reciprocal regulation of NF-κB, autophagy and programmed cell death affect cancer development and progression.

Brain-penetrant PQR620 mTOR and PQR530 PI3K/mTOR inhibitor reduce huntingtin levels in cell models of HD

One of the pathological hallmarks of Huntington disease (HD) is accumulation of the disease-causing mutant huntingtin (mHTT), which leads to the disruption of a variety of cellular functions, ultimately resulting in cell death. Induction of autophagy, for example by the inhibition of mechanistic target of rapamycin (mTOR) signaling, has been shown to reduce HTT levels and aggregates. While rapalogs like rapamycin allosterically inhibit the mTOR complex 1 (TORC1), ATP-competitive mTOR inhibitors suppress activities of TORC1 and TORC2 and have been shown to be more efficient in inducing autophagy and reducing protein levels and aggregates than rapalogs. The ability to cross the blood-brain barrier of first generation catalytic mTOR inhibitors has so far been limited, and therefore sufficient target coverage in the brain could not be reached. Two novel, brain penetrant compounds - the mTORC1/2 inhibitor PQR620, and the dual pan-phosphoinositide 3-kinase (PI3K) and mTORC1/2 kinase inhibitor PQR530 - were evaluated by assessing their potential to induce autophagy and reducing mHTT levels. For this purpose, expression levels of autophagic markers and well-defined mTOR targets were analyzed in STHdh cells and HEK293T cells and in mouse brains. Both compounds potently inhibited mTOR signaling in cell models as well as in mouse brain. As proof of principle, reduction of aggregates and levels of soluble mHTT were demonstrated upon treatment with both compounds. Originally developed for cancer treatment, these second generation mTORC1/2 and PI3K/mTOR inhibitors show brain penetrance and efficacy in cell models of HD, making them candidate molecules for further investigations in HD.

Quantifying autophagy using novel LC3B and p62 TR-FRET assays

Autophagy is a cellular mechanism that can generate energy for cells or clear misfolded or aggregated proteins, and upregulating this process has been proposed as a therapeutic approach for neurodegenerative diseases. Here we describe a novel set of LC3B-II and p62 time-resolved fluorescence resonance energy transfer (TR-FRET) assays that can detect changes in autophagy in the absence of exogenous labels. Lipidated LC3 is a marker of autophagosomes, while p62 is a substrate of autophagy. These assays can be employed in high-throughput screens to identify novel autophagy upregulators, and can measure autophagy changes in cultured cells or tissues after genetic or pharmacological interventions. We also demonstrate that different cells exhibit varying autophagic responses to pharmacological interventions. Overall, it is clear that a battery of readouts is required to make conclusions about changes in autophagy.

An open-label study to assess the feasibility and tolerability of rilmenidine for the treatment of Huntington's disease

Preclinical data have shown that rilmenidine can regulate autophagy in models of Huntington's disease (HD), providing a potential route to alter the disease course in patients. Consequently, a 2-year open-label study examining the tolerability and feasibility of rilmenidine in mild-moderate HD was undertaken. 18 non-demented patients with mild to moderate HD took daily doses of 1 mg Rilmenidine for 6 months and 2 mg for a further 18 months followed by a 3-month washout period. The primary outcome was the number of withdrawals and serious adverse events. Secondary outcomes included safety parameters and changes in disease-specific variables, such as motor, cognitive and functional performance, structural MRI and serum metabolomic analysis. 12 patients completed the study; reasons for withdrawal included problems tolerating study procedures (MRI, and venepuncture), depression requiring hospital admission and logistical reasons. Three serious adverse events were recorded, including hospitalisation for depression, but none were thought to be drug-related. Changes in secondary outcomes were analysed as the annual rate of change in the study group. The overall change was comparable to changes seen in recent large observational studies in HD patients, though direct statistical comparisons to these studies were not made. Chronic oral administration of rilmenidine is feasible and well-tolerated and future, larger, placebo-controlled, studies in HD are warranted.

TRIAL REGISTRATION

EudraCT number 2009-018119-14.

The significance of Hsp70 subnetwork for Dengue virus lifecycle

Viruses hijack host machineries for replicating themselves efficiently. Host protein quality control machineries (QC) not only assist protein folding to form bona fide proteins with active functions but also get rid of un/misfolded proteins via degradation to maintain the protein homeostasis. Previous studies have reported that viruses utilize QC at various steps for their lifecycles. Recently we defined Hsp70s and their cochaperones, DnaJs functions on Dengue lifecycle. Here we summarize the significance of QC on Dengue virus.

Low cancer prevalence in polyglutamine expansion diseases

Objective:

Polyglutamine (PolyQ) diseases are dominantly transmitted neurologic disorders, caused by coding and expanded CAG trinucleotide repeats. Cancer was reported retrospectively to be rare in patients with PolyQ diseases and we aimed to investigate its prevalence in France.

Methods:

Consecutive patients with Huntington disease (HD) and spinocerebellar ataxia (SCA) were questioned about cancer, cardiovascular diseases, and related risk factors in 4 university hospitals in Paris, Toulouse, Strasbourg, and Montpellier. Standardized incidence ratios (SIR), based on age- and sex-adjusted rate of the French population, were assessed for different types of cancer.

Results:

We questioned 372 patients with HD and 134 patients with SCA. SIR showed significantly reduced risk of cancer in HD: 23 observed cases vs 111.05 expected ones (SIR 0.21, 95% confidence interval [CI] 0.13–0.31), as well as in SCA: 7 observed cases vs 34.73 expected (SIR 0.23, 95% CI 0.08–0.42). This was surprising since risk behavior for cancer was increased in these patients, with significantly greater tobacco and alcohol consumption in patients with HD vs patients with SCA (p < 0.0056). There was no association between CAG repeat size and cancer or cardiovascular disease. However, in patients with HD, skin cancers were more frequent than expected (5 vs 0.98, SIR 5.11, 95% CI 1.65–11.95).

Conclusions:

There was a decreased cancer rate in PolyQ diseases despite high incidence of risk factors. Intriguingly, skin cancer incidence was higher, suggesting a crosstalk between neurodegeneration and skin tumorigenesis.

Manganese and the Insulin-IGF Signaling Network in Huntington's Disease and Other Neurodegenerative Disorders

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease resulting in motor impairment and death in patients. Recently, several studies have demonstrated insulin or insulin-like growth factor (IGF) treatment in models of HD, resulting in potent amelioration of HD phenotypes via modulation of the PI3K/AKT/mTOR pathways. Administration of IGF and insulin can rescue microtubule transport, metabolic function, and autophagy defects, resulting in clearance of Huntingtin (HTT) aggregates, restoration of mitochondrial function, amelioration of motor abnormalities, and enhanced survival. Manganese (Mn) is an essential metal to all biological systems but, in excess, can be toxic. Interestingly, several studies have revealed the insulin-mimetic effects of Mn-demonstrating Mn can activate several of the same metabolic kinases and increase peripheral and neuronal insulin and IGF-1 levels in rodent models. Separate studies have shown mouse and human striatal neuroprogenitor cell (NPC) models exhibit a deficit in cellular Mn uptake, indicative of a Mn deficiency. Furthermore, evidence from the literature reveals a striking overlap between cellular consequences of Mn deficiency (i.e., impaired function of Mn-dependent enzymes) and known HD endophenotypes including excitotoxicity, increased reactive oxygen species (ROS) accumulation, and decreased mitochondrial function. Here we review published evidence supporting a hypothesis that (1) the potent effect of IGF or insulin treatment on HD models, (2) the insulin-mimetic effects of Mn, and (3) the newly discovered Mn-dependent perturbations in HD may all be functionally related. Together, this review will present the intriguing possibility that intricate regulatory cross-talk exists between Mn biology and/or toxicology and the insulin/IGF signaling pathways which may be deeply connected to HD pathology and, perhaps, other neurodegenerative diseases (NDDs) and other neuropathological conditions.

The P42 peptide and Peptide-based therapies for Huntington's disease

Huntington's disease (HD) is a progressive neurodegenerative hereditary disease clinically characterised by the presence of involuntary movements, behavioural problems and cognitive decline. The disease-onset is usually between 30 and 50 years of age. HD is a rare disorder affecting approximately 1.3 in 10,000 people in the European Union. It is caused by an expanded CAG repeat in the first exon of the Huntingtin (HTT) gene, leading to an abnormal form of the Huntingtin protein (Htt) (polyQHtt), containing N-terminus, enlarged polyglutamine strands of variable length that stick together to form aggregates and nuclear inclusions in the damaged brain cells. Treatments currently used for Huntington's disease are symptomatic and aimed at temporally relieving the symptoms of the disease; although some promising therapies are on study, there is no drug capable of stopping disease progression either in the form of delaying onset or slowing disability progression. The utilization of peptides interacting with polyQ stretches or with Htt protein to prevent misfolding and aggregation of the expanded polyQ protein is a fascinating idea, because of low potential toxicity and ability to target very initial steps in the pathophysiological cascade of the disease, such as aggregation or cleavage process. Indeed, several therapeutic peptides have been developed and were found to significantly slow down the progression of symptoms in experimental models of Huntington's disease. This review is essentially focusing on the latest development concerning peptide strategy. In particular, we focused on a 23aa peptide P42, which is a part of the Htt protein. It is expected to work principally by preventing the abnormal Htt protein from sticking together, thereby preventing pathological consequences of aggregation and improving the symptoms of the disease. In the meantime, as P42 is part of the Htt protein, some therapeutic properties might be linked to the physiological actions of the peptide itself, considered as a functional domain of the Htt protein.

PAWR-mediated suppression of BCL2 promotes switching of 3-azido withaferin A (3-AWA)-induced autophagy to apoptosis in prostate cancer cells

An active medicinal component of plant origin with an ability to overcome autophagy by inducing apoptosis should be considered a therapeutically active lead pharmacophore to control malignancies. In this report, we studied the effect of concentration-dependent 3-AWA (3-azido withaferin A) sensitization to androgen-independent prostate cancer (CaP) cells which resulted in a distinct switching of 2 interrelated conserved biological processes, i.e. autophagy and apoptosis. We have observed 3 distinct parameters which are hallmarks of autophagy in our studies. First, a subtoxic concentration of 3-AWA resulted in an autophagic phenotype with an elevation of autophagy markers in prostate cancer cells. This led to a massive accumulation of MAP1LC3B and EGFP-LC3B puncta coupled with gradual degradation of SQSTM1. Second, higher toxic concentrations of 3-AWA stimulated ER stress in CaP cells to turn on apoptosis within 12 h by elevating the expression of the proapoptotic protein PAWR, which in turn suppressed the autophagy-related proteins BCL2 and BECN1. This inhibition of BECN1 in CaP cells, leading to the disruption of the BCL2-BECN1 interaction by overexpressed PAWR has not been reported so far. Third, we provide evidence that pawr-KO MEFs exhibited abundant autophagy signs even at toxic concentrations of 3-AWA underscoring the relevance of PAWR in switching of autophagy to apoptosis. Last but not least, overexpression of EGFP-LC3B and DS-Red-BECN1 revealed a delayed apoptosis turnover at a higher concentration of 3-AWA in CaP cells. In summary, this study provides evidence that 3-AWA is a strong anticancer candidate to abrogate protective autophagy. It also enhanced chemosensitivity by sensitizing prostate cancer cells to apoptosis through induction of PAWR endorsing its therapeutic potential.

RTP801 Is Involved in Mutant Huntingtin-Induced Cell Death

RTP801 expression is induced by cellular stress and has a pro-apoptotic function in non-proliferating differentiated cells such as neurons. In several neurodegenerative disorders, including Parkinson's disease and Alzheimer's disease, elevated levels of RTP801 have been observed, which suggests a role for RTP801 in neuronal death. Neuronal death is also a pathological hallmark in Huntington's disease (HD), an inherited neurodegenerative disorder caused by a CAG repeat expansion in the huntingtin gene. Currently, the exact mechanisms underlying mutant huntingtin (mhtt)-induced toxicity are still unclear. Here, we investigated whether RTP801 is involved in (mhtt)-induced cell death. Ectopic exon-1 mhtt elevated RTP801 mRNA and protein levels in nerve growth factor (NGF)-differentiated PC12 cells and in rat primary cortical neurons. In neuronal PC12 cells, mhtt also contributed to RTP801 protein elevation by reducing its proteasomal degradation rate, in addition to promoting RTP801 gene expression. Interestingly, silencing RTP801 expression with short hairpin RNAs (shRNAs) blocked mhtt-induced cell death in NGF-differentiated PC12 cells. However, RTP801 protein levels were not altered in the striatum of Hdh(Q7/Q111) and R6/1 mice, two HD models that display motor deficits but not neuronal death. Importantly, RTP801 protein levels were elevated in both neural telencephalic progenitors differentiated from HD patient-derived induced pluripotent stem cells and in the putamen and cerebellum of human HD postmortem brains. Taken together, our results suggest that RTP801 is a novel downstream effector of mhtt-induced toxicity and that it may be relevant to the human disease.

Complex interplay between the length and composition of the huntingtin-derived peptides modulates the intracellular behavior of the N-terminal fragments of mutant huntingtin

Diverse subcellular localizations of the huntingtin-containing inclusion bodies are frequently suspected of reflecting crucial divisions between different cellular pathways contributing to the pathophysiology of Huntington's disease. Here, we use a panel of different N-terminal huntingtin fragments overexpressed in transfected neuronal and non-neuronal cells to demonstrate that it is the length of the N-terminal huntingtin fragments rather than a presence of any specific amino acid sequences that determines the ratio between the nuclear and cytoplasmic inclusion bodies. Importantly, the length of those fragments does also seem to strongly influence the folding of the aggregating huntingtin species, as indicated by the apparent differences in their accessibility for different antibodies directed against particular subdomains within the N-terminal part of huntingtin, although these differences do not correlate with the peptides' ability to efficiently aggregate within the cell nucleus. Furthermore, the relatively long huntingtin fragment containing 588 amino acids of the reference sequence shows intracellular behavior that is substantially different from that exhibited by its shorter counterparts (containing either 171, 120, 89 or 64 amino acids), as this rarely aggregating peptide is not only accumulating in cytoplasmic inclusions of slightly different morphology but is also most strongly affected by the FLAG-tagging procedure that unexpectedly induces (or enhances) autophagy-related processes. Together, our results reveal a significant heterogeneity of the huntingtin accumulation patterns that are observed at the cellular level. These patterns are not only strongly dependent on both the length and the amino acid composition of the N-terminal huntingtin peptides but also seem to engage different cellular mechanisms implicated in the pathogenesis of Huntington's disease, including the non-proteasomal degradation of potentially toxic huntingtin forms.

Viral capsid assembly as a model for protein aggregation diseases: Active processes catalyzed by cellular assembly machines comprising novel drug targets

Viruses can be conceptualized as self-replicating multiprotein assemblies, containing coding nucleic acids. Viruses have evolved to exploit host cellular components including enzymes to ensure their replicative life cycle. New findings indicate that also viral capsid proteins recruit host factors to accelerate their assembly. These assembly machines are RNA-containing multiprotein complexes whose composition is governed by allosteric sites. In the event of viral infection, the assembly machines are recruited to support the virus over the host and are modified to achieve that goal. Stress granules and processing bodies may represent collections of such assembly machines, readily visible by microscopy but biochemically labile and difficult to isolate by fractionation. We hypothesize that the assembly of protein multimers such as encountered in neurodegenerative or other protein conformational diseases, is also catalyzed by assembly machines. In the case of viral infection, the assembly machines have been modified by the virus to meet the virus' need for rapid capsid assembly rather than host homeostasis. In the case of the neurodegenerative diseases, it is the monomers and/or low n oligomers of the so-called aggregated proteins that are substrates of assembly machines. Examples for substrates are amyloid β peptide (Aβ) and tau in Alzheimer's disease, α-synuclein in Parkinson's disease, prions in the prion diseases, Disrupted-in-schizophrenia 1 (DISC1) in subsets of chronic mental illnesses, and others. A likely continuum between virus capsid assembly and cell-to-cell transmissibility of aggregated proteins is remarkable. Protein aggregation diseases may represent dysfunction and dysregulation of these assembly machines analogous to the aberrations induced by viral infection in which cellular homeostasis is pathologically reprogrammed. In this view, as for viral infection, reset of assembly machines to normal homeostasis should be the goal of protein aggregation therapeutics. A key basis for the commonality between viral and neurodegenerative disease aggregation is a broader definition of assembly as more than just simple aggregation, particularly suited for the crowded cytoplasm. The assembly machines are collections of proteins that catalytically accelerate an assembly reaction that would occur spontaneously but too slowly to be relevant in vivo. Being an enzyme complex with a functional allosteric site, appropriated for a non-physiological purpose (e.g. viral infection or conformational disease), these assembly machines present a superior pharmacological target because inhibition of their active site will amplify an effect on their substrate reaction. Here, we present this hypothesis based on recent proof-of-principle studies against Aβ assembly relevant in Alzheimer's disease.

Possible involvement of self-defense mechanisms in the preferential vulnerability of the striatum in Huntington's disease

HD is caused by a mutation in the huntingtin gene that consists in a CAG repeat expansion translated into an abnormal poly-glutamine (polyQ) tract in the huntingtin (Htt) protein. The most striking neuropathological finding in HD is the atrophy of the striatum. The regional expression of mutant Htt (mHtt) is ubiquitous in the brain and cannot explain by itself the preferential vulnerability of the striatum in HD. mHtt has been shown to produce an early defect in transcription, through direct alteration of the function of key regulators of transcription and in addition, more indirectly, as a result of compensatory responses to cellular stress. In this review, we focus on gene products that are preferentially expressed in the striatum and have down- or up-regulated expression in HD and, as such, may play a crucial role in the susceptibility of the striatum to mHtt. Many of these striatal gene products are for a vast majority down-regulated and more rarely increased in HD. Recent research shows that some of these striatal markers have a pro-survival/neuroprotective role in neurons (e.g., MSK1, A2A, and CB1 receptors) whereas others enhance the susceptibility of striatal neurons to mHtt (e.g., Rhes, RGS2, D2 receptors). The down-regulation of these latter proteins may be considered as a potential self-defense mechanism to slow degeneration. For a majority of the striatal gene products that have been identified so far, their function in the striatum is unknown and their modifying effects on mHtt toxicity remain to be experimentally addressed. Focusing on these striatal markers may contribute to a better understanding of HD pathogenesis, and possibly the identification of novel therapeutic targets.

iASPP is a novel autophagy inhibitor in keratinocytes

The protein iASPP (encoded by PPP1R13L) is an evolutionarily conserved p53 inhibitor, the expression of which is often upregulated in human cancers. We have recently shown that iASPP is a crucial regulator of epidermal homeostasis. Here, we report that iASPP also acts as autophagy inhibitor in keratinocytes. Our data show that depletion of iASPP protects keratinocytes from apoptosis by modulating the expression of Noxa (also known as PMAIP1). In our model, iASPP expression can affect the fission-fusion cycle, mass and shape of mitochondria. iASPP-silenced keratinocytes display disorganization of cytosolic compartments and increased metabolic stress caused by deregulation of mTORC1 signaling. Moreover, increased levels of lipidated LC3 protein confirmed the activation of autophagy in iASPP-depleted cells. We have identified a novel mechanism modulating autophagy in keratinocytes that relies upon iASPP expression specifically reducing the interaction of Atg5-Atg12 with Atg16L1, an interaction that is essential for autophagosome formation or maturation. Using organotypic culture, we further explored the link between autophagy and differentiation, and we showed that impairing autophagy affects epidermal terminal differentiation. Our data provide an alternative mechanism to explain how epithelial integrity is maintained against environmental stressors and might also improve the understanding of the etiology of skin diseases that are characterized by defects in differentiation and DNA damage responses.

Less is more: improving proteostasis by translation slow down

Protein homeostasis, or proteostasis, refers to a proper balance between synthesis, maturation, and degradation of cellular proteins. A growing body of evidence suggests that the ribosome serves as a hub for co-translational folding, chaperone interaction, degradation, and stress response. Accordingly, in addition to the chaperone network and proteasome system, the ribosome has emerged as a major factor in protein homeostasis. Recent work revealed that high rates of elongation of translation negatively affect both the fidelity of translation and the co-translational folding of nascent polypeptides. Accordingly, by slowing down translation one can significantly improve protein folding. In this review, we discuss how to target translational processes to improve proteostasis and implications in treating protein misfolding diseases.

Atg4b-dependent autophagic flux alleviates Huntington's disease progression

The accumulation of aggregated mutant huntingtin (mHtt) inclusion bodies is involved in Huntigton’s disease (HD) progression. Medium sized-spiny neurons (MSNs) in the corpus striatum are highly vulnerable to mHtt aggregate accumulation and degeneration, but the mechanisms and pathways involved remain elusive. Here we have developed a new model to study MSNs degeneration in the context of HD. We produced organotypic cortico-striatal slice cultures (CStS) from HD transgenic mice mimicking specific features of HD progression. We then show that induction of autophagy using catalytic inhibitors of mTOR prevents MSNs degeneration in HD CStS. Furthermore, disrupting autophagic flux by overexpressing Atg4b in neurons and slice cultures, accelerated mHtt aggregation and neuronal death, suggesting that Atg4b-dependent autophagic flux influences HD progression. Under these circumstances induction of autophagy using catalytic inhibitors of mTOR was inefficient and did not affect mHtt aggregate accumulation and toxicity, indicating that mTOR inhibition alleviates HD progression by inducing Atg4b-dependent autophagic flux. These results establish modulators of Atg4b-dependent autophagic flux as new potential targets in the treatment of HD.

Macrophage autophagy in atherosclerosis

Macrophages play crucial roles in atherosclerotic immune responses. Recent investigation into macrophage autophagy (AP) in atherosclerosis has demonstrated a novel pathway through which these cells contribute to vascular inflammation. AP is a cellular catabolic process involving the delivery of cytoplasmic contents to the lysosomal machinery for ultimate degradation and recycling. Basal levels of macrophage AP play an essential role in atheroprotection during early atherosclerosis. However, AP becomes dysfunctional in the more advanced stages of the pathology and its deficiency promotes vascular inflammation, oxidative stress, and plaque necrosis. In this paper, we will discuss the role of macrophages and AP in atherosclerosis and the emerging evidence demonstrating the contribution of macrophage AP to vascular pathology. Finally, we will discuss how AP could be targeted for therapeutic utility.

The first reported generation of several induced pluripotent stem cell lines from homozygous and heterozygous Huntington's disease patients demonstrates mutation related enhanced lysosomal activity

Neuronal disorders, like Huntington's disease (HD), are difficult to study, due to limited cell accessibility, late onset manifestations, and low availability of material. The establishment of an in vitro model that recapitulates features of the disease may help understanding the cellular and molecular events that trigger disease manifestations. Here, we describe the generation and characterization of a series of induced pluripotent stem (iPS) cells derived from patients with HD, including two rare homozygous genotypes and one heterozygous genotype. We used lentiviral technology to transfer key genes for inducing reprogramming. To confirm pluripotency and differentiation of iPS cells, we used PCR amplification and immunocytochemistry to measure the expression of marker genes in embryoid bodies and neurons. We also analyzed teratomas that formed in iPS cell-injected mice. We found that the length of the pathological CAG repeat did not increase during reprogramming, after long term growth in vitro, and after differentiation into neurons. In addition, we observed no differences between normal and mutant genotypes in reprogramming, growth rate, caspase activation or neuronal differentiation. However, we observed a significant increase in lysosomal activity in HD-iPS cells compared to control iPS cells, both during self-renewal and in iPS-derived neurons. In conclusion, we have established stable HD-iPS cell lines that can be used for investigating disease mechanisms that underlie HD. The CAG stability and lysosomal activity represent novel observations in HD-iPS cells. In the future, these cells may provide the basis for a powerful platform for drug screening and target identification in HD.

The identification of candidate genes and SNP markers for classical bovine spongiform encephalopathy susceptibility

Classical bovine spongiform encephalopathy is a transmissible prion disease that is fatal to cattle and is a human health risk due to its association with a strain of Creutzfeldt-Jakob disease (vCJD). Mutations to the coding region of the prion gene (PRNP) have been associated with susceptibility to transmissible spongiform encephalopathies in mammals including bovines and humans. Additional loci such as the retinoic acid receptor beta (RARB) and stathmin like 2 (STMN2) have also been associated with disease risk. The objective of this study was to refine previously identified regions associated with BSE susceptibility and to identify positional candidate genes and genetic variation that may be involved with the progression of classical BSE. The samples included 739 samples of either BSE infected animals (522 animals) or non-infected controls (207 animals). These were tested using a custom SNP array designed to narrow previously identified regions of importance in bovine genome. Thirty one single nucleotide polymorphisms were identified at p < 0.05 and a minor allele frequency greater than 5%. The chromosomal regions identified and the positional and functional candidate genes and regulatory elements identified within these regions warrant further research.

A novel approach to recovery of function of mutant proteins by slowing down translation

Protein homeostasis depends on a balance of translation, folding, and degradation. Here, we demonstrate that mild inhibition of translation results in a dramatic and disproportional reduction in production of misfolded polypeptides in mammalian cells, suggesting an improved folding of newly synthesized proteins. Indeed, inhibition of translation elongation, which slightly attenuated levels of a copepod GFP mutant protein, significantly enhanced its function. In contrast, inhibition of translation initiation had minimal effects on copepod GFP folding. On the other hand, mild suppression of either translation elongation or initiation corrected folding defects of the disease-associated cystic fibrosis transmembrane conductance regulator mutant F508del. We propose that modulation of translation can be used as a novel approach to improve overall proteostasis in mammalian cells, as well as functions of disease-associated mutant proteins with folding deficiencies.

Expression pattern and functions of autophagy-related gene atg5 in zebrafish organogenesis

The implications of autophagy-related genes in serious neural degenerative diseases have been well documented. However, the functions and regulation of the family genes in embryonic development remain to be rigorously studied. Here, we report on for the first time the important role of atg5 gene in zebrafish neurogenesis and organogenesis as evidenced by the spatiotemporal expression pattern and functional analysis. Using morpholino oligo knockdown and mRNA overexpression, we demonstrated that zebrafish atg5 is required for normal morphogenesis of brain regionalization and body plan as well as for expression regulation of neural gene markers: gli1, huC, nkx2.2, pink1, β-synuclein, xb51 and zic1. We further demonstrated that ATG5 protein is involved in autophagy by LC3-II/LC3I ratio and rapamycin-induction experiments, and that ATG5 is capable of regulating expression of itself gene in the manner of a feedback inhibition loop. In addition, we found that expression of another autophagy-related gene, atg12, is maintained at a higher constant level like a housekeeping gene. This indicates that the formation of the ATG12–ATG5 conjugate may be dependent on ATG5 protein generation and its splicing, rather than on ATG12 protein in zebrafish. Importantly, in the present study, we provide a mechanistic insight into the regulation and functional roles of atg5 in development of zebrafish nervous system.

Age-related changes in the function of autophagy in rat kidneys

Autophagy is a highly regulated intracellular process for the degradation of cytoplasmic components, especially protein aggregates and damaged organelles. It is essential for maintaining healthy cells. Impaired or deficient autophagy is believed to cause or contribute to aging and age-related disease. In this study, we investigated the effects of age on autophagy in the kidneys of 3-, 12-, and 24-month-old Fischer 344 rats. The results revealed that autophagy-related gene (Atg)7 was significantly downregulated in kidneys of increasing age. The protein expression level of the autophagy marker light chain 3/Atg8 exhibited a marked decline in aged kidneys. The levels of p62/SQSTM1 and polyubiquitin aggregates, representing the function of autophagy and proteasomal degradation, increased in older kidneys. The level of 8-hydroxydeoxyguanosine, a marker of mitochondrial DNA oxidative damage, was also increased in older kidneys. Analysis by transmission electron microscope demonstrated swelling and disintegration of cristae in the mitochondria of aged kidneys. These results suggest that autophagic function decreases with age in the kidneys of Fischer 344 rats, and autophagy may mediate the process of kidney aging, leading to the accumulation of damaged mitochondria.

Identification of novel potentially toxic oligomers formed in vitro from mammalian-derived expanded huntingtin exon-1 protein

Huntington disease is a genetic neurodegenerative disorder that arises from an expanded polyglutamine region in the N terminus of the HD gene product, huntingtin. Protein inclusions comprised of N-terminal fragments of mutant huntingtin are a characteristic feature of disease, though are likely to play a protective role rather than a causative one in neurodegeneration. Soluble oligomeric assemblies of huntingtin formed early in the aggregation process are candidate toxic species in HD. In the present study, we established an in vitro system to generate recombinant huntingtin in mammalian cells. Using both denaturing and native gel analysis, we have identified novel oligomeric forms of mammalian-derived expanded huntingtin exon-1 N-terminal fragment. These species are transient and were not previously detected using bacterially expressed exon-1 protein. Importantly, these species are recognized by 3B5H10, an antibody that recognizes a two-stranded hairpin conformation of expanded polyglutamine believed to be associated with a toxic form of huntingtin. Interestingly, comparable oligomeric species were not observed for expanded huntingtin shortstop, a 117-amino acid fragment of huntingtin shown previously in mammalian cell lines and transgenic mice, and here in primary cortical neurons, to be non-toxic. Further, we demonstrate that expanded huntingtin shortstop has a reduced ability to form amyloid-like fibrils characteristic of the aggregation pathway for toxic expanded polyglutamine proteins. Taken together, these data provide a possible candidate toxic species in HD. In addition, these studies demonstrate the fundamental differences in early aggregation events between mutant huntingtin exon-1 and shortstop proteins that may underlie the differences in toxicity.

Roles of AMP-activated protein kinase in Alzheimer's disease

AMP-activated protein kinase (AMPK), a master regulator of cellular energy homeostasis and a central player in glucose and lipid metabolism, is potentially implicated in the pathogenesis of Alzheimer's disease (AD). AMPK activity decreases in AD brain, indicating decreased mitochondrial biogenesis and function. Emerging evidence demonstrates that AMPK activation is a potential target for improving perturbed brain energy metabolism that is involved in the pathogenesis of AD. The roles of AMPK in the pathogenesis of AD include β-amyloid protein (Aβ) generation and tau phosphorylation. In particular, AMPK may regulate Aβ generation through modulating neuronal cholesterol and sphingomyelin levels and through regulating APP distribution in the lipid rafts. AMPK is activated by phosphorylation of Thr-172 by LKB1 complex in response to increase in the AMP/ATP ratio and by calmodulin-dependent protein kinase kinase-beta in response to elevated Ca(2+) levels, which contributes to regulating Aβ generation. AMPK is a physiological tau kinase and can increase the phosphorylation of tau at Ser-262. AMPK can also directly phosphorylate tau at Thr-231 and Ser-396/404. Furthermore, AMPK activation decreases mTOR signaling activity to facilitate autophagy and promotes lysosomal degradation of Aβ. However, AMPK activation has non-neuroprotective property and may lead to detrimental outcomes, including Aβ generation and tau phosphorylation. Therefore, it is still unclear whether AMPK could serve a potential therapeutic target for AD, and hence, further studies will be needed to clarify the role of AMPK in AD.

Mutant huntingtin, abnormal mitochondrial dynamics, defective axonal transport of mitochondria, and selective synaptic degeneration in Huntington's disease

Huntington's disease (HD) is a progressive, fatal neurodegenerative disease caused by expanded polyglutamine repeats in the HD gene. HD is characterized by chorea, seizures, involuntary movements, dystonia, cognitive decline, intellectual impairment and emotional disturbances. Research into mutant huntingtin (Htt) and mitochondria has found that mutant Htt interacts with the mitochondrial protein dynamin-related protein 1 (Drp1), enhances GTPase Drp1 enzymatic activity, and causes excessive mitochondrial fragmentation and abnormal distribution, leading to defective axonal transport of mitochondria and selective synaptic degeneration. This article summarizes latest developments in HD research and focuses on the role of abnormal mitochondrial dynamics and defective axonal transport in HD neurons. This article also discusses the therapeutic strategies that decrease mitochondrial fragmentation and neuronal damage in HD.

Alteration of protein folding and degradation in motor neuron diseases: Implications and protective functions of small heat shock proteins

Motor neuron diseases (MNDs) are neurodegenerative disorders that specifically affect the survival and function of upper and/or lower motor neurons. Since motor neurons are responsible for the control of voluntary muscular movement, MNDs are characterized by muscle spasticity, weakness and atrophy. Different susceptibility genes associated with an increased risk to develop MNDs have been reported and several mutated genes have been linked to hereditary forms of MNDs. However, most cases of MNDs occur in sporadic forms and very little is known on their causes. Interestingly, several molecular mechanisms seem to participate in the progression of both the inherited and sporadic forms of MNDs. These include cytoskeleton organization, mitochondrial functions, DNA repair and RNA synthesis/processing, vesicle trafficking, endolysosomal trafficking and fusion, as well as protein folding and protein degradation. In particular, accumulation of aggregate-prone proteins is a hallmark of MNDs, suggesting that the protein quality control system (molecular chaperones and the degradative systems: ubiquitin-proteasome-system and autophagy) are saturated or not sufficient to allow the clearance of these altered proteins. In this review we mainly focus on the MNDs associated with disturbances in protein folding and protein degradation and on the potential implication of a specific class of molecular chaperones, the small heat shock proteins (sHSPs/HSPBs), in motor neuron function and survival. How boosting of specific HSPBs may be a potential useful therapeutic approach in MNDs and how mutations in specific HSPBs can directly cause motor neuron degeneration is discussed.

Resveratrol and vitamin D: significant potential interpretative problems arising from their mutual processes, interactions and effects

The hypothesis is formulated and presented that resveratrol and vitamin D have important mutual processes, interactions and induced effects that if not taken into account could seriously jeopardize the interpretation of their current and future preclinical, epidemiological and clinical studies. In support of this hypothesis, evidence is presented that resveratrol and vitamin D mutually share some of the same biochemical processes and mechanisms as well as the fact that they can each affect some of the same diseases and maladies.

Decreased heat shock protein 27 expression and altered autophagy in human cells harboring A8344G mitochondrial DNA mutation

Mitochondrial DNA (mtDNA) mutations are responsible for human neuromuscular diseases caused by mitochondrial dysfunction. Myoclonus epilepsy associated with ragged-red fibers (MERRF) is a maternally inherited mitochondrial encephalomyopathy with various syndromes involving both muscular and nervous systems. The most common mutation in MERRF syndrome, A8344G mutation in mtDNA, has been associated with severe defects in protein synthesis. This defect impairs assembly of complexes in electron transport chain and results in decreased respiratory function of mitochondria. In this study, we showed a significant decrease of the heat shock protein 27 (Hsp27) in lymphoblastoid cells derived from a MERRF patient and in cybrid cells harboring MERRF A8344G mutation. However, normal cytoplasmic distributions of Hsp27 and normal heat shock responses were observed in both wild type and mutant cybrids. Furthermore, overexpression of wild type Hsp27 in mutant MERRF cybrids significantly decreased cell death under staurosporine (STS) treatment, suggesting a protective function of Hsp27 in cells harboring the A8344G mutation of mtDNA. Meanwhile, reverse transcriptase PCR showed no difference in the mRNA level between normal and mutant cybrids, indicating that alterations may occur at the protein level. Evidenced by the decreased levels of Hsp27 upon treatment with proteasome inhibitor, starvation and rapamycin and the accumulation of Hsp27 upon lysosomal inhibitor treatment; Hsp27 may be degraded by the autophagic pathway. In addition, the increased formation of LC3-II and autophagosomes was found in MERRF cybrids under the basal condition, indicating a constitutively-activated autophagic pathway. It may explain, at least partially, the faster turnover of Hsp27 in MERRF cybrids. This study provides information for us to understand that Hsp27 is degraded through the autophagic pathway and that Hsp27 may have a protective role in MERRF cells. Regulating Hsp27 and the autophagic pathway might help develop therapeutic solutions for treatment of MERRF syndrome in the future.

A compact beta model of huntingtin toxicity

Huntington disease results from an expanded polyglutamine region in the N terminus of the huntingtin protein. HD pathology is characterized by neuronal degeneration and protein inclusions containing N-terminal fragments of mutant huntingtin. Structural information is minimal, though it is believed that mutant huntingtin polyglutamine adopts β structure upon conversion to a toxic form. To this end, we designed mammalian cell expression constructs encoding compact β variants of Htt exon 1 N-terminal fragment and tested their ability to aggregate and induce toxicity in cultured neuronal cells. In parallel, we performed molecular dynamics simulations, which indicate that constructs with expanded polyglutamine β-strands are stabilized by main-chain hydrogen bonding. Finally, we found a correlation between the reactivity to 3B5H10, an expanded polyglutamine antibody that recognizes a compact β rich hairpin structure, and the ability to induce cell toxicity. These data are consistent with an important role for a compact β structure in mutant huntingtin-induced cell toxicity.

In vivo cellular adaptation to ER stress: survival strategies with double-edged consequences

Disturbances to the balance of protein synthesis, folding and secretion in the endoplasmic reticulum (ER) induce stress and thereby the ER stress signaling (ERSS) response, which alleviates this stress. In this Commentary, we review the emerging idea that ER stress caused by abnormal physiological conditions and/or mutations in genes that encode client proteins of the ER is a key factor underlying different developmental processes and the pathology of diverse diseases, including diabetes, neurodegeneration and skeletal dysplasias. Recent studies in mouse models indicate that the effect of ERSS in vivo and the nature of the cellular strategies induced to ameliorate pathological ER stress are crucial factors in determining cell fate and clinical disease features. Importantly, ERSS can affect cellular proliferation and the differentiation program; cells that survive the stress can become 'reprogrammed' or dysfunctional. These cell-autonomous adaptation strategies can generate a spectrum of context-dependent cellular consequences, ranging from recovery to death. Secondary effects can include altered cell-extracellular-matrix interactions and non-cell-autonomous alteration of paracrine signaling, which contribute to the final phenotypic outcome. Recent reports showing that ER stress can be alleviated by chemical compounds suggest the potential for novel therapeutic approaches.

Clearing the brain's cobwebs: the role of autophagy in neuroprotection

Protein aggregates or inclusion bodies are common hallmarks of age-related neurodegenerative disorders. Why these aggregates form remains unclear. Equally debated is whether they are toxic, protective, or simple by-products. Increasing evidence, however, supports the notion that in general aggregates confer toxicity and disturb neuronal function by hampering axonal transport, synaptic integrity, transcriptional regulation, and mitochondrial function. Thus, neuroscientists in search of effective treatments to slow neural loss during neurodegeneration have long been interested in finding new ways to clear inclusion bodies. Intriguingly, two studies using conditional neuron-specific gene ablations of autophagy regulators in mice revealed that autophagy loss elicits inclusion body formation and a neurodegenerative cascade.Such studies indicate autophagy may be a built-in defense mechanism to clear the nervous system of inclusion bodies.This new finding has implications for our understanding of aging and neurodegeneration and the development of new therapies. First, we discuss the pathways underlying autophagy and its controversial role in cell death and survival regulation.We then discuss the physiological role of autophagy in the aging process of the nervous system. In the final portion of this review, we discuss the therapeutic promise of inducing autophagy and the potential side effects of such treatments.

Starvation triggers Abeta42 generation from human umbilical vascular endothelial cells

Cerebral amyloid angiopathy is a common feature in Alzheimer's disease (AD), which is characterized by amyloid deposit around brain vessels including capillaries. The origin of the amyloid protein of CAA remains controversial. In our work, we provide data to show that primary umbilical vein endothelial cells (HUVEC) harbor APP processing secretases and can produce Abeta(42) under starvation. Starvation can increase the secretion of Abeta(42) by altering the expression of beta-secretases (BACE1) and gamma-secretases (APH and PEN2). This process is regulated by macroautophagy. Suppression of macroautophagy induction by 3MA further increased the level of Abeta(42) produced under starvation in HUVECs. These results suggest that starvation-induced Abeta(42) secretion might contribute to the formation of CAA and hence vascular degeneration in AD.

Genetic determinants at the interface of cancer and neurodegenerative disease

It has been hypothesized that oncogenesis and neurodegeneration may share common mechanistic foundations. Recent evidence now reveals a number of genes in which alteration leads to either carcinogenesis or neurodegeneration, depending on cellular context. Pathways that have emerged as having critical roles in both cancer and neurodegenerative disease include those involving genes such as PARK2, ATM, PTEN, PTPRD, and mTOR. A number of mechanisms have been implicated, and commonly affected cellular processes include cell cycle regulation, DNA repair, and response to oxidative stress. For example, we have recently shown that the E3 ubiquitin ligase PARK2 is mutated or deleted in many different human malignancies and helps drive loss on chromosome 6q25.2-27, a genomic region frequently deleted in cancers. Mutation in PARK2 is also the most common cause of juvenile Parkinson's disease. Mutations in PARK2 result in an upregulation of its substrate cyclin E, resulting in dysregulated entry into the cell cycle. In neurons, this process results in cell death, but in cycling cells, the result is a growth advantage. Thus, depending on whether the cell affected is a dividing cell or a post-mitotic neuron, responses to these alterations may differ, ultimately leading to varying disease phenotypes. Here, we review the substantial data implicating specific genes in both cancer and neurodegenerative disease.