β-Amyloid induces nuclear protease-mediated lamin fragmentation independent of caspase activation

An expeditious and facile method of amyloid beta (1-42) purification

For the study of amyloid beta (Aβ) associated toxicity which is supposed to be the main pathological agent in Alzheimer's disease (AD), it is important to secure Aβ peptide with appropriate biological activity. However, commercial and synthetic Aβ often have some pitfalls like less cell toxicity, prompt aggregation and excess price, using recombinant technology, these issues can be resolved though the method also suffered from some problems such as low yield, aggregation and prolong time to purify. Thus, we previously developed an easy, economic and convenient method for Aβ42 purification using highly expressed GroES-Ubiquitin-Aβ42 fusion protein. The method was efficient, but further development was performed to improve the procedure and increase the yield. Focus was on the isolation of the fusion protein (GroES-Ubiquitin) from Aβ42 peptide. After a series of systematic testing with several chemicals, we found that methanol could precipitate efficiently the fusion protein, while the Aβ peptide was recovered in the supernatant. By this method, Aβ peptide was easily purified without tedious chromatographic steps which are main obstacles to purify the peptide in the previous method. This method yielded ~20 mg highly pure Aβ42 peptide from 1-liter bacterial culture. Different biophysical characterizations and bioactivity assays indicate that the peptide purified using this method was competitive with others which have been previously reported whereas considering the simplicity, final yield and time of purification, this method is the optimal solution.

DNA repair deficiencies and neurodegeneration

Neurodegenerative diseases are the second most prevalent cause of death in industrialized countries. Alzheimer's Disease is the most widespread and also most acknowledged form of dementia today. Together with Parkinson's Disease they account for over 90 % cases of neurodegenerative disorders caused by proteopathies. Far less known are the neurodegenerative pathologies in DNA repair deficiency syndromes. Such diseases like Cockayne - or Werner Syndrome are described as progeroid syndromes - diseases that cause the premature ageing of the affected persons, and there are clear implications of such diseases in neurologic dysfunction and degeneration. In this review, we aim to draw the attention on commonalities between proteopathy-associated neurodegeneration and neurodegeneration caused by DNA repair defects and discuss how mitochondria are implicated in the development of both disorder classes. Furthermore, we highlight how nematodes are a valuable and indispensable model organism to study conserved neurodegenerative processes in a fast-forward manner.

Inhibition of Pancreatic Cancer Cells by Different Amyloid Proteins Reveals an Inverse Relationship between Neurodegenerative Diseases and Cancer

Neurodegenerative diseases and cancers are considered to be two families of diseases caused by completely opposite cell-death mechanisms: the former caused by premature cell death, with the latter due to the increased resistance to cell death. Growing epidemiologic evidence appear to suggest an inverse correlation between neurodegenerative diseases and cancers. However, pathological links, particularly from a protein-cell interaction perspective, between these two families of diseases remains to be proven. Here, a fundamental study investigates the effects of three amyloid proteins of Aβ (associated with AD), hIAPP (associated with T2D), and hCT (associated with MTC) on pancreatic cancer (PANC-1) cells. Collective results demonstrate a general inhibitory activity of all of three amyloid proteins on cancer cell proliferation, but inhibition efficiencies are strongly dependent on amyloid sequence (Aβ, hIAPP, hCT), concentration (IC25, IC50, IC75), and aggregation states (monomers, oligomers). Amyloid proteins exhibit two pathways against cancer cells: amyloid monomer-induced ROS production to inhibit cell growth and amyloid oligomer-induced membrane disruption to kill cells. Collectively, the results demonstrate a general inhibition function of amyloid proteins to induce cancer cell death by preventing cell proliferation, suppressing cell migration, promoting reactive oxygen species production, and disrupting cell membranes.

Evidence for a Strong Relationship between the Cytotoxicity and Intracellular Location of β-Amyloid

β-Amyloid (Aβ) is a hallmark peptide of Alzheimer’s disease (AD). Herein, we explored the mechanism underlying the cytotoxicity of this peptide. Double treatment with oligomeric 42-amino-acid Aβ (Aβ42) species, which are more cytotoxic than other conformers such as monomers and fibrils, resulted in increased cytotoxicity. Under this treatment condition, an increase in intracellular localization of the peptide was observed, which indicated that the peptide administered extracellularly entered the cells. The cell-permeable peptide TAT-tagged Aβ42 (tAβ42), which was newly prepared for the study and found to be highly cell-permeable and soluble, induced Aβ-specific lamin protein cleavage, caspase-3/7-like DEVDase activation, and high cytotoxicity (5–10-fold higher than that induced by the wild-type oligomeric preparations). Oligomeric species enrichment and double treatment were not necessary for enhancing the cytotoxicity and intracellular location of the fusion peptide. Taiwaniaflavone, an inhibitor of the cytotoxicity of wild-type Aβ42 and tAβ42, strongly blocked the internalization of the peptides into the cells. These data imply a strong relationship between the cytotoxicity and intracellular location of the Aβ peptide. Based on these results, we suggest that agents that can reduce the cell permeability of Aβ42 are potential AD therapeutics.

Regulatory role of cathepsin L in induction of nuclear laminopathy in Alzheimer's disease

Experimental and clinical therapies in the field of Alzheimer's disease (AD) have focused on elimination of extracellular amyloid beta aggregates or prevention of cytoplasmic neuronal fibrillary tangles formation, yet these approaches have been generally ineffective. Interruption of nuclear lamina integrity, or laminopathy, is a newly identified concept in AD pathophysiology. Unraveling the molecular players in the induction of nuclear lamina damage may lead to identification of new therapies. Here, using 3xTg and APP/PS1 mouse models of AD, and in vitro model of amyloid beta42 (Aβ42) toxicity in primary neuronal cultures and SH‐SY5Y neuroblastoma cells, we have uncovered a key role for cathepsin L in the induction of nuclear lamina damage. The applicability of our findings to AD pathophysiology was validated in brain autopsy samples from patients. We report that upregulation of cathepsin L is an important process in the induction of nuclear lamina damage, shown by lamin B1 cleavage, and is associated with epigenetic modifications in AD pathophysiology. More importantly, pharmacological targeting and genetic knock out of cathepsin L mitigated Aβ42 induced lamin B1 degradation and downstream structural and molecular changes. Affirming these findings, overexpression of cathepsin L alone was sufficient to induce lamin B1 cleavage. The proteolytic activity of cathepsin L on lamin B1 was confirmed using mass spectrometry. Our research identifies cathepsin L as a newly identified lamin B1 protease and mediator of laminopathy observed in AD. These results uncover a new aspect in the pathophysiology of AD that can be pharmacologically prevented, raising hope for potential therapeutic interventions.

Engineering Amyloid Aggregation as a New Way to Eliminate Cancer Stem Cells by the Disruption of Iron Homeostasis

Cancer stem cells (CSCs) play crucial roles in tumor initiation. Amyloid β (Aβ), which is associated with Alzheimer's disease (AD), has been identified to induce cytotoxicity in tumor cells besides brain cells. Herein, we find that oligomeric Aβ1-42 and Aβ1-40 (OAβ1-42 and OAβ1-40) can repress the viability of breast CSCs. Intriguingly, OAβ1-42 and OAβ1-40 preferentially induce the growth arrest of breast CSCs by contrast with the bulk cancer cells. Further studies indicate that OAβ1-42 and OAβ1-40 disturb iron homeostasis, which results in iron accumulation in lysosomes. The iron in lysosomes then induces ROS production by Fenton reaction, leading to breast CSC death. In vivo experiments show that the tumorigenesis of breast CSCs pretreated with OAβ1-42 is inhibited. These results reveal that OAβ1-42 and OAβ1-40 are multifaceted players with the ability to eliminate CSCs. Our work may provide a new clue to better understand the biological functions of amyloid oligomers.

Differential involvement of caspase-6 in amyloid-β-induced fragmentation of lamin A and B

Amyloid-β (Aβ), a peptide implicated in Alzheimer's disease, was shown to cause specific fragmentation of lamin proteins, which was mediated by an unidentified protease named nuclear scaffold protease (NSP) independently of caspase-6. Because caspase-6 is responsible for the fragmentation process in many other damage-induced apoptosis, here we further investigated possible involvement of caspase-6 in Aβ-induced lamin fragmentation under various conditions. We found that lamin A fragment generated by NSP (named fragment b) disappeared in cells incubated with Aβ42 for prolonged periods and this product was preserved by a caspase-6 inhibitor. Furthermore, caspase-6 could remove fragment b in nuclei isolated from Aβ42-treated cells (ANU). Lamin B in ANU was fragmented by caspase-6 only after treatment with an alkaline phosphatase. The caspase-mediated fragmentation of lamin B was also achieved with nuclei isolated from cells incubated with Aβ42 plus a Cdk5 inhibitor. The results indicate that Aβ42 induces NSP-mediated fragmentation of lamin A and the following removal process of fragment b by caspase-6 and an Aβ-induced phosphorylation prevents the fragmentation of lamin B by caspase-6. The pathway leading to lamin protein fragmentation in this investigation appears to be specific for Aβ and thus the data will provide novel insights into the toxicity of the peptide.

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Aβ42 induces nuclear scaffold protease (NSP)-mediated fragmentation of lamin A.

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The produced fragment of lamin A is subsequently removed by caspase-6.

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Aβ42 also induced NSP-mediated lamin B fragmentation.

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Caspase-6-mediated fragmentation of lamin B protein is absent.

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The absence appears to be due to phosphorylation of lamin B.

Thioredoxin system as a gatekeeper in caspase-6 activation and nuclear lamina integrity: Implications for Alzheimer's disease

Recent reports in pathophysiology of neurodegenerative diseases (ND) have linked nuclear lamina degradation/deficits to neuronal cell death. Lamin-B1 damage is specifically involved in this process leading to nuclear envelope invagination and heterochromatin rearrangement. The underlying mechanisms involved in these events are not yet defined. In this study, while examining the effect of Thioredoxin-1(Trx1) inhibition on cell death in a model of oxidative stress, we noted robust nuclear invagination in SH-SY5Y cells. Evaluation of nuclear lamina proteins revealed lamin-B1 cleavage that was prevented by caspase-6 (CASP6) inhibitor and exacerbated after pharmacologic/genetic inhibition of Trx1 system, but not after glutathione depletion. Activation of CASP6 was upstream of CASP3/7 activation and its inhibition was sufficient to prevent cell death in our system. The effect of Trx1 redox status on CASP6 activation was assessed by administration of reduced/oxidized forms in cell-free nuclei preparation and purified enzymatic assays. Although reduced Trx1 decreased CASP6 enzymatic activity and lamin-B1 cleavage, the fully oxidized Trx1 showed opposite effects. The enhanced CASP6 activation was also associated with lower levels of DJ-1, a neuroprotective and master regulator of cellular antioxidants. The implication of our findings in ND pathophysiology was strengthened with detection of lower Trx1 levels in the hippocampi tissue of a mouse model of Alzheimer's disease. This coincided with higher CASP6 activation resulting in increased lamin-B1 and DJ-1 depletion. This study provides a first mechanistic explanation for the key regulatory role of Trx1 as a gatekeeper in activation of CASP6 and induction of nuclear invagination, an important player in ND pathophysiology.

Major compounds of red ginseng oil attenuate Aβ25-35-induced neuronal apoptosis and inflammation by modulating MAPK/NF-κB pathway

β-Amyloid (Aβ)-induced neuronal toxicity in Alzheimer's disease (AD) is associated with complex mechanisms. Thus, a multi-target approach might be suitable for AD treatment. Following our previous study on the neuroprotective effects of red ginseng oil extract, its major compounds, including linoleic acid (LA), β-sitosterol (BS), and stigmasterol (SS), were examined to elucidate the mechanism of anti-apoptosis and anti-inflammation in Aβ25-35-stimulated PC12 cells. The results showed that the three compounds mitigated Aβ25-35 toxicity by regulating oxidative stress, apoptotic responses, and pro-inflammatory mediators. LA and SS strongly regulated intrinsic apoptosis markers, such as mitochondrial membrane potential, intracellular Ca2+, Bax/Bcl-2 ratio, and caspases-9, -3, and -8. However, BS blocked only the intrinsic apoptotic pathway, particularly by suppressing Ca2+ accumulation. Furthermore, all three compounds downregulated iNOS and phospho-nuclear factor-κB, but only LA and SS inhibited the expression of cyclooxygenase-2 and phospho-IκB. In assays to evaluate MAPK expression for confirming upstream signal pathways, BS decreased the phosphorylation of p38 and ERK, but not JNK, while SS markedly decreased the phosphorylation of all three MAPKs, and LA clearly decreased the phosphorylation of ERK and JNK, but not p38. These results indicate that LA, BS, and SS act as neuroprotectives against Aβ25-35-induced injury by distinct molecular mechanisms, indicating their preventive and/or therapeutic potential to treat AD.

Protective effect of chloroform extract of Stereospermum chelonoides bark against amyloid beta42 induced cell death in SH-SY5Y cells and against inflammation in Swiss albino mice

Background This study was designed to evaluate the free radical scavenging property of chloroform extract of the bark of Stereospermum chelonoides (SCBC) and to investigate its potential in Alzheimer's disease and inflammation, two oxidative stress related disorders. Methods Preliminary phytochemical analysis and in vitro antioxidant potential of SCBC were evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay, ferric reducing antioxidant power (FRAP) assay, cupric reducing antioxidant capacity (CUPRAC) and total antioxidant capacity determination assay. Total phenol and total flavonoid contents were also determined. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) based cytotoxicity and cyto-protective assays were performed on human neuroblastoma SH-SY5Y cells. Thioflavin-T assay and caspase activation measurement assay were carried out to elucidate the mechanism of cytoprotection of SCBC observed here. In vivo anti-inflammatory potential was measured using croton oil and xylene induced ear edema tests. Results Phytochemical screening of SCBC revealed the presence of various phytoconstituents. Dose-dependent in vitro antioxidant activity was observed. The extract was enriched in flavonoids and polyphenolic compounds too. SCBC was found to inhibit amyloid-β peptide 1-42 (Aβ42) induced cell death in a dose-dependent manner. Encouraged by the cyto-protective effect, its effects on Aβ42 fibrillogenesis and caspase-3 activated apoptosis were observed. SCBC significantly slowed down the Aβ42 fibrillogenesis and caspase-3 activation in a concentration-dependent manner indicating its probable mechanism of rendering cyto-protection. SCBC has been able to reduce inflammation significantly in croton oil induced ear edema in both doses. Conclusions Thus, this study could form the basis for further study for the potential use of SCBC in oxidative stress associated cell death and inflammation.