Extensive β-amyloid (Aβ) deposits in brain parenchyma
in the form of senile plaques and in blood vessels in the form of
amyloid angiopathy are pathological hallmarks of Alzheimer's
disease (AD). The mechanisms underlying Aβ deposition
remain unclear. Major efforts have focused on Aβ production,
but there is little to suggest that increased production of
Aβ plays a role in Aβ deposition, except for rare
familial forms of AD. Thus, other mechanisms must be involved in
the accumulation of Aβ in AD. Recent data shows that
impaired clearance may play an important role in Aβ
accumulation in the pathogenesis of AD. This review focuses on our
current knowledge of Aβ-degrading enzymes, including
neprilysin (NEP), endothelin-converting enzyme (ECE),
insulin-degrading enzyme (IDE), angiotensin-converting enzyme
(ACE), and the plasmin/uPA/tPA system as they relate to amyloid
deposition in AD.
As one of the dominant amyloid-β peptide (Aβ) proteases, neprilysin (NEP) plays a crucial role in maintaining a physiologic balance between Aβ production and catabolism. We have previously shown that NEP is modified by 4-hydroxynonenal (HNE) adducts, resulting in decreased activity in the brain of AD patients and cultured cells. In order to determine whether antioxidants can rescue NEP, SH-SY5Y cells were treated with HNE or Aβ, together with N-acetylcysteine for 24 hours, prior to analysis of NEP protein levels, activity, and oxidative modifications. Intracellular NEP developed HNE adducts after 24 hours of HNE or Aβ treatment as determined by immunoprecipitation, immunoblotting, and double immunofluorescence staining. N-acetylcysteine at 10 to 100 μM alleviated HNE adduction after HNE or Aβ treatment. In keeping with previous reports, HNE-modified NEP showed decreased catalytic activity. The present study demonstrates that antioxidants can be used to spare NEP from oxidative modification, suggesting a potential mechanism underlying the neuroprotective effects of antioxidants in aging or Alzheimer’s disease.
Alzheimer’s disease; amyloid-β; antioxidant; degradation; 4-hydroxynonenal; N-acetylcysteine; neprilysin; oxidative stress
The brain steady state level of Aβ is determined by the balance between its production and removal, the latter through egress across blood and CSF barriers as well as Aβ degradation. The major Aβ degrading enzymes are neprilysin (NEP), insulin degrading enzyme (IDE) and endothelin converting enzyme (ECE-1). Although evidence suggests that NEP is down-regulated in AD, the role of IDE and ECE in the Aβ accumulation in aging and dementia remains less certain. In this study, we examined mRNA and protein expression, as well as biological activity of NEP, IDE and ECE-1 in human frontal cortex by real-time RT-PCR for mRNA, immunoblotting for protein and highly sensitive and specific fluorescence assays for activity. The relationships between Aβ degrading enzymes and pathologic measures and clinical features were also assessed. The results showed that NEP mRNA, protein level and activity were decreased in AD compared with normal controls with no cognitive impairment (NCI). In contrast IDE activity was unchanged, but there was higher expression of IDE mRNA, indicating a possible compensatory reaction due to deficits in activity. ECE-1 expression in AD brain showed no significant difference compared to age-matched controls. Correlation analyses suggested that NEP expression was correlated with Aβ accumulation and clinical diagnosis, being lower in AD than in NCI. In contrast, neither IDE nor ECE-1 correlated with Aβ or clinical diagnosis. These findings provide additional support for NEP as the major protease involved in Aβ degradation and suggest its possible therapeutic targeting in AD.
Amyloid degrading enzymes; neprilysin (NEP); endothelin converting enzyme (ECE); insulin degrading enzyme (IDE); β-amyloid (Aβ); degradation; Alzheimer’s disease (AD); AD brain
Transactive response DNA-binding protein of 43 kDa (TDP-43), an RNA and DNA binding protein involved in transcriptional repression, RNA splicing and RNA metabolism during the stress response, is the major component of neuronal inclusions in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with ubiquitin inclusions, now referred to as FTLD-TDP. While initially thought to be relatively specific to ALS and FTLD-TDP, TDP-43 pathology has now been detected in a number of other neurodegenerative diseases, many associated with tau pathology, including Guam Parkinson dementia complex and Alzheimer's disease (AD). TDP-43 pathology is detected in 25% to 50% of AD cases, especially those with more severe clinical phenotype and greater Alzheimer type pathology, as well as AD cases with hippocampal sclerosis (HS). HS is characterized by selective neuronal loss affecting CA1 sector of the hippocampus, and most cases of HS, with or without AD, have TDP-43 pathology. Whether TDP-43 pathology is merely an incidental finding in AD or actually contributing to the more severe clinical phenotype remains unresolved. Presence of TDP-43 in normal elderly, who are at increased risk for AD, would strengthen the argument that it is not merely a secondary or incidental finding in end stage AD. Limited studies suggest that TDP-43 pathology is infrequent in neurologically normal elderly (3% or less). We provide an overview of what is known about TDP-43 in AD, normal aging and in other disorders and suggest that TDP-43 proteinopathies be considered in two classes - primary and secondary.
Alzheimer's disease (AD); amyotrophic lateral sclerosis (ALS); frontotemporal lobar degeneration (FTLD); neurofibrillary tangles (NFT); progranulin; tau; transactive response DNA-binding protein 43 (TDP-43)
The cerebral accumulation of amyloid-β (Aβ) is a consistent feature of and likely contributor to the development of Alzheimer’s disease (AD). In addition to dysregulated production, increasing experimental evidence suggests reduced catabolism plays an important role in Aβ accumulation. Although endothelin converting enzyme (ECE) and insulin degrading enzyme (IDE) degrade and thus contribute to regulating the steady-state levels of Aβ, how these enzymes are regulated remain poorly understood. In this study, we investigated the effects of 4-hydroxy-nonenal (HNE) and Aβ on the expression and activity of ECE-1 and IDE in human neuroblastoma SH-SY5Y cells. Treatment with HNE or Aβ upregulated ECE-1 mRNA and protein, while IDE was unchanged. Although both ECE-1 and IDE were oxidized within 24 h of HNE or Aβ treatment, ECE-1 catalytic activity was elevated while IDE specific activity was unchanged. The results demonstrated for the first time that both ECE-1 and IDE are substrates of HNE modification induced by Aβ. In addition, the results suggest complex mechanisms underlying the regulation of their enzymatic activity.
Alzheimer’s disease; amyloid-β; degradation; endothelin converting enzyme; 4-hydroxy-nonenal (HNE); insulin degrading enzyme; oxidative stress
The cerebral accumulation of β-amyloid (Aβ) is a consistent feature of and likely contributor to the development of Alzheimer’s Disease (AD). In addition to dysregulated production, increasing experimental evidence suggests reduced catabolism also plays an important role in Aβ accumulation. We have previously shown that neprilysin (NEP), the major protease which cleaves Aβ in vivo, is modified by 4-hydroxy-nonenal (HNE) adducts in the brain of AD patients. In order to determine if these changes affected Aβ, SH-SY5Y cells were treated with HNE or Aβ, and then NEP mRNA, protein levels, HNE adducted NEP, NEP activity and secreted Aβ levels were determined. Intracellular NEP developed HNE adducts after 24 h of HNE treatment as determined by immunoprecipitation, immunoblotting and double immunofluorescence staining. HNE-modified NEP showed decreased catalytic activity, which was associated with elevations in Aβ1-40 in SH-SY5Y and H4 APP695wt cells. Incubation of cells with Aβ1-42 also induced HNE adduction of NEP. In an apparent compensatory response, Aβ treated cells showed increased NEP mRNA and protein expression. Despite elevations in NEP protein, the activity was significantly lower compared to the NEP protein level. The present study demonstrates that NEP can be inactivated by HNE-adduction, which is associated with, at least partly, reduced Aβ cleavage and enhanced Aβ accumulation.
Neprilysin (NEP); 4-hydroxy-nonenal (HNE); oxidative stress; beta-amyloid; degradation; Alzheimer’s disease
Extensive protein cross-linking and aggregation are some of the most common molecular events in the pathogenesis of Alzheimer's disease (AD). Both β-amyloid (Aβ) plaques and neurofibrillary tangles, which are extracellular and intracellular proteinaceous aggregates, respectively, contribute to neuronal death and progressive cognitive decline. Although protein cross-linking has been recognized and extensively studied for many years, the underlying mechanisms are largely unknown. Recent data indicates that tissue transglutaminase (tTG), which catalyzes the cross-linking of a wide spectrum of proteins including Aβ, tau, α-synuclein and neurofilament proteins, may be involved in protein aggregation in AD. Many AD risk factors, such as trauma, inflammation, ischemia and stress, up-regulate tTG protein and activity levels. In this review, we summarize the evidence that tTG plays a role in AD, especially in cross-linking of Aβ, tau, α-synuclein and neurofilament proteins. An experimentally testable hypothesis is that tTG may play a central role in AD pathogenesis and that it provides a conceptual link between sporadic and familial AD through a shared pathogenic pathway.
Tissue transglutaminase (tTG, TG2); Alzheimer's disease; β-amyloid (Aβ); tau; α-synuclein; neurofilament proteins; protein cross-linking
Cognitive deficits in AD correlate with progressive synaptic dysfunction and loss. The Rho family of small GTPases, including Rho, Rac, and Cdc42, has a central role in cellular motility and cytokinesis. Acetylcholinesterase inhibitor has been found to protect cells against a broad range of reagents-induced injuries. Present studies examined if the effect of HupA on neurite outgrowth in Aβ-treated neuronal cells executed via regulating Rho-GTPase mediated axon guidance relative gene expression. Affymetrix cDNA microarray assay followed by real-time RT-PCR and Western Blotting analysis were used to elucidate and analyze the signaling pathway involved in Aβ and HupA’s effects. The effects of Aβ and HupA on the neurite outgrowth were further confirmed via immunofluorescence staining. Aβ up-regulated the mRNA expressions of NFAT5, LIMK1, EPHA1, NTN4 and RAC2 markedly in SH-SY5Y cells. Co-incubation of Aβ and HupA reversed or decreased the changes of NFAT5, NTN4, RAC2, CDC42 and SEMA4F. HupA treated alone increased NFAT5, LIMK1, NTN4 significantly. Following qRT-PCR validation showed that the correlation of the gene expression ratio between microarray and qRT-PCR is significant. Western blot result showed that the change of CDC42 protein is consistent with the mRNA level while RAC2 is not. The morphological results confirmed that HupA improved, or partly reversed, the Aβ-induced damage of neurite outgrowth. The protective effect of HupA from Aβ induced morphological injury might be correlative to, at least partially, regulating the network of neurite outgrowth related genes.
β-amyloid; axon guidance; neurite outgrowth; acetylcholinesterase inhibitor; huperzine A
The Vav family of proteins are guanine nucleotide exchange factors which have been shown to be deregulated in several types of human cancer. There are three members of the Vav family that have been identified which are members of the Dbl domain superfamily and have specificity towards Rho/Rac GTPases. The Vav family plays an important role in normal hematologic system development and homeostasis, and Vav1 is largely restricted to the hematologic system. While Vav1 was originally identified as a proto-oncogene, several recent studies have shown that Vav family deletion leads to the development of T-cell malignancies in mice. In addition, Vav1 has been shown to play a role in the ATRA-mediated differentiation of promyelocytic leukemia cells. In this concise review, the gene structure and normal function of Vav1, as well as a possible role for Vav1 in the development of hematologic and other malignancies is reviewed.
Vav1; guanine nucleotide exchange factor; lymphoma; leukemia
Central nervous system disorders, including cerebrovascular disease, neurodegenerative diseases and head trauma are the most common cause of severe disability in adults and share a number of pathophysiological features. The therapeutic strategy of neuroprotection has been well accepted as one of the promising approaches in treating such brain disorders, and searching for the effective neuroprotective agents is still an open-ended task for neurologists and neuro-pharmacologists. In this study, we report for the first time that the enzymatic hydrolysates from type-B porcine hide gelatin has potent neuroprotective activity against H2O2- or serum deprivation-induced injuries of cultured SH-SY5Y cells. The peptides used in this study were prepared from type-B porcine hide gelatin digested with pepsin and papain. The neuroprotective activity of the porcine hide gelatin hydrolysate (PHH) was evaluated using MTT reduction assay. From the pre-screening of PHH, we found that the whole porcine hide gelatin hydrolysate obtained from papain digestion (PHH-I) showed significant neuroprotective activities (P<0.05). After further separation of PPH-I through SP-Sephadex C-50 and Sephadex G-25, only the fraction with smaller molecular weight from Sephadex G-25 (PHH-Ic) demonstrated potent neuroprotective activities (P<0.01). The active fraction showed a molecular mass between 1,000–3,000Da in SDS-polyacrylamide gel electrophoresis, and was rich in Glycine, Proline and Hydroxyproline in amino acid composition, indicating that peptides with a spectrum of molecular sizes and certain amino acids are critical for the neuroprotective activities of gelatin peptides. The viability of cultured cells treated with gelatin peptides was significantly improved in a dose-dependent manner. Further studies are necessary to establish the neuroprotective activity of hydrolyzed peptides for the neurons in vivo.
Gelatin; hydrolysate; antioxidative; neuroprotective; neurotrophic
The rising worldwide prevalence of asthma has intensified interest in the natural history of asthma. An improved understanding of the genetic, environmental, and developmental factors contributing to the inception and exacerbation of asthma will be crucial to efforts to devise effective preventive and therapeutic interventions. There is increasing evidence that the complex interplay of early life respiratory viral infections and allergic sensitization is important in the development of asthma. Major causes of asthma exacerbations are respiratory viral infections and aeroallergen exposure, which may have interactive co-morbid effects. This review describes the potential role of thymic stromal lymphopoietin (TSLP) as a connection between the innate immune response to respiratory viral infections and the type-2 adaptive immune response in the development and exacerbation of asthma.
Thymic stromal lymphopoietin (TSLP); virus infection; atopy; asthma