Lysosomal dysfunction in the brain of a mouse model with intraneuronal accumulation of carboxyl terminal fragments of the amyloid precursor protein (original) (raw)
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Evidence for lysosomal processing of amyloid β-protein precursor in cultured cells
Neurochemical Research, 1989
Amyloid β-protein precursor (ABPP) of Alzheimer's disease (AD) represents a family of proteins which includes the parent protein which generates a small (4 kD) fragment that self-assembles to form amyloid fibrils in AD. Thus, the normal and abnormal proteolysis of ABPP may be directly relevant to AD pathogenesis. We have examined the accumulation of ABPP in cultured rodent and human neuronal cell lines in the presence and absence of a battery of protease inhibitors using immunohistochemistry and Western blot analysis. Here we present evidence for a lysosomal pathway for the turnover of ABPP and discuss the relevance of these results to plaque pathology and abnormal ABPP immunostaining in AD.
Evidence for lysosomal processing of amyloid ?-protein precursor in cultured cells
Neurochemical Research, 1989
Amyloid β-protein precursor (ABPP) of Alzheimer's disease (AD) represents a family of proteins which includes the parent protein which generates a small (4 kD) fragment that self-assembles to form amyloid fibrils in AD. Thus, the normal and abnormal proteolysis of ABPP may be directly relevant to AD pathogenesis. We have examined the accumulation of ABPP in cultured rodent and human neuronal cell lines in the presence and absence of a battery of protease inhibitors using immunohistochemistry and Western blot analysis. Here we present evidence for a lysosomal pathway for the turnover of ABPP and discuss the relevance of these results to plaque pathology and abnormal ABPP immunostaining in AD.
Endo-lysosomal and autophagic dysfunction: a driving factor in Alzheimer's disease?
Journal of Neurochemistry
Alzheimer's disease (AD) is the most common cause of dementia, and its prevalence will increase significantly in the coming decades. Although important progress has been made, fundamental pathogenic mechanisms as well as most hereditary contributions to the sporadic form of the disease remain unknown. In this review, we examine the now substantial links between AD pathogenesis and lysosomal biology. The lysosome hydrolyses and processes cargo delivered by multiple pathways, including endocytosis and autophagy. The endo-lysosomal and autophagic networks are central to clearance of cellular macromolecules, which is important given there is a deficit in clearance of amyloid-b in AD. Numerous studies show prominent lysosomal dysfunction in AD, including perturbed trafficking of lysosomal enzymes and accumulation of the same substrates that accumulate in lysosomal storage disorders. Examination of the brain in lysosomal storage disorders shows the accumulation of amyloid precursor protein metabolites, which further links lysosomal dysfunction with AD. This and other evidence leads us to hypothesise that genetic variation in lysosomal genes modifies the disease course of sporadic AD.
Neurodegenerative lysosomal disorders: A continuum from development to late age
Autophagy, 2008
Neuronal survival requires continuous lysosomal turnover of cellular constituents delivered by autophagy and endocytosis. Primary lysosomal dysfunction in inherited congenital "lysosomal storage" disorders is well known to cause severe neurodegenerative phenotypes associated with accumulations of lysosomes and autophagic vacuoles (AVs). Recently, the number of inherited adult-onset neurodegenerative diseases caused by proteins that regulate protein sorting and degradation within the endocytic and autophagic pathways has grown considerably. In this Perspective, we classify a group of neurodegenerative diseases across the lifespan as disorders of lysosomal function, which feature extensive autophagic-endocytic-lysosomal neuropathology and may share mechanisms of neurodegeneration related to degradative failure and lysosomal destabilization. We highlight Alzheimer's disease as a disease within this group and discuss how each of the genes and other risk factors promoting this disease contribute to progressive lysosomal dysfunction and neuronal cell death.
Lysosomal Network Proteins as Potential Novel CSF Biomarkers for Alzheimer’s Disease
NeuroMolecular Medicine, 2014
The success of future intervention strategies for Alzheimer's disease (AD) will likely rely on the development of treatments starting early in the disease course, before irreversible brain damage occurs. The pre-symptomatic stage of AD occurs at least one decade before the clinical onset, highlighting the need for validated biomarkers that reflect this early period. Reliable biomarkers for AD are also needed in research and clinics for diagnosis, patient stratification, clinical trials, monitoring of disease progression and the development of new treatments. Changes in the lysosomal network, i.e., the endosomal, lysosomal and autophagy systems, are among the first alterations observed in an AD brain. In this study, we performed a targeted search for lysosomal network proteins in human cerebrospinal fluid (CSF). Thirty-four proteins were investigated, and six of them, early endosomal antigen 1 (EEA1), lysosomal-associated membrane proteins 1 and 2 (LAMP-1, LAMP-2), microtubule-associated protein 1 light chain 3 (LC3), Rab3 and Rab7, were significantly increased in the CSF from AD patients compared with neurological controls. These results were confirmed in a validation cohort of CSF samples, and patients with no neurochemical evidence of AD, apart from increased total-tau, were found to have EEA1 levels corresponding to the increased total-tau levels. These findings indicate that increased levels of LAMP-1, LAMP-2, LC3, Rab3 and Rab7 in the CSF might be specific for AD, and increased EEA1 levels may be a sign of general neurodegeneration. These six lysosomal network proteins are potential AD biomarkers and may be used to investigate lysosomal involvement in AD pathogenesis.
Journal of Alzheimer's Disease
This work provides new insight into the age-related basis of Alzheimer's disease (AD), the composition of intraneuronal amyloid (iA), and the mechanism of an age-related increase in iA in adult AD-model mouse neurons. A new end-specific antibody for A 45 and another for aggregated forms of A provide new insight into the composition of iA and the mechanism of accumulation in old adult neurons from the 3xTg-AD model mouse. iA levels containing aggregates of A 45 increased 30-50-fold in neurons from young to old age and were further stimulated upon glutamate treatment. iA was 8 times more abundant in 3xTg-AD than non-transgenic neurons with imaged particle sizes following the same log-log distribution, suggesting a similar snowball mechanism of intracellular biogenesis. Pathologically misfolded and mislocalized Alz50 tau colocalized with iA and rapidly increased following a brief metabolic stress with glutamate. APP-CTF, A 45 , and aggregated A colocalized most strongly with mitochondria and endosomes and less with lysosomes and autophagosomes. Differences in iA by sex were minor. These results suggest that incomplete carboxyl-terminal trimming of long As by gamma-secretase produced large intracellular deposits which limited completion of autophagy in aged neurons. Understanding the mechanism of age-related changes in iA processing may lead to application of countermeasures to prolong dementia-free health span.
PLOS ONE, 2016
Proper function of lysosomes is particularly important in neurons, as they cannot dilute accumulated toxic molecules and aggregates by cell division. Thus, impairment of lysosomal function plays an important role in neuronal degeneration and in the pathogenesis of numerous neurodegenerative diseases. In this work we analyzed how inhibition and/or loss of the major lysosomal proteases, the cysteine cathepsins B and L (CtsB/L), affects lysosomal function, cholesterol metabolism and degradation of the key Alzheimer's disease (AD) proteins. Here, we show that cysteine CtsB/L, and not the aspartyl cathepsin D (CtsD), represent a major lysosomal protease(s) that control lysosomal function, intracellular cholesterol trafficking and AD-like amyloidogenic features. Intriguingly, accumulation of free cholesterol in late endosomes/lysosomes upon CtsB/L inhibition resembled a phenotype characteristic for the rare neurodegenerative disorder Niemann-Pick type C (NPC). CtsB/L inhibition and not the inhibition of CtsD led to lysosomal impairment assessed by decreased degradation of EGF receptor, enhanced LysoTracker staining and accumulation of several lysosomal proteins LC3II, NPC1 and NPC2. By measuring the levels of NPC1 and ABCA1, the two major cholesterol efflux proteins, we showed that CtsB/L inhibition or genetic depletion caused accumulation of the NPC1 in lysosomes and downregulation of ABCA1 protein levels and its expression. Furthermore, we revealed that CtsB/L are involved in degradation of the key Alzheimer's proteins: amyloid-β peptides (Aβ) and C-terminal fragments of the amyloid precursor protein (APP) and in degradation of β-secretase (BACE1). Our results imply CtsB/L as major regulators of lysosomal function and demonstrate that CtsB/L may play an important role in intracellular cholesterol trafficking and in degradation of the key AD proteins. Our findings implicate that enhancing the activity or levels of CtsB/L could provide a promising and a common strategy for maintaining lysosomal function and for preventing and/or treating neurodegenerative diseases.
Journal of Neuroscience, 2012
Alterations in the lipid composition of endosomal-lysosomal membranes may constitute an early event in Alzheimer's disease (AD) pathogenesis. In this study, we investigated the possibility that GM2 ganglioside accumulation in a mouse model of Sandhoff disease might be associated with the accumulation of intraneuronal and extracellular proteins commonly observed in AD. Our results show intraneuronal accumulation of amyloid- peptide (A)-like, ␣-synuclein-like, and phospho-tau-like immunoreactivity in the brains of -hexosaminidase knockout (HEXB KO) mice. Biochemical and immunohistochemical analyses confirmed that at least some of the intraneuronal A-like immunoreactivity (iA-LIR) represents amyloid precursor protein C-terminal fragments (APP-CTFs) and/or A. In addition, we observed increased levels of A40 and A42 peptides in the lipid-associated fraction of HEXB KO mouse brains, and intraneuronal accumulation of ganglioside-bound A (GA) immunoreactivity in a brain region-specific manner. Furthermore, ␣-synuclein and APP-CTFs and/or A were found to accumulate in different regions of the substantia nigra, indicating different mechanisms of accumulation or turnover pathways. Based on the localization of the accumulated iA-LIR to endosomes, lysosomes, and autophagosomes, we conclude that a significant accumulation of iA-LIR may be associated with the lysosomal-autophagic turnover of A and fragments of APP-containing A epitopes. Importantly, intraneuronal GA immunoreactivity, a proposed prefibrillar aggregate found in AD, was found to accumulate throughout the frontal cortices of postmortem human GM1 gangliosidosis, Sandhoff disease, and Tay-Sachs disease brains. Together, these results establish an association between the accumulation of gangliosides, autophagic vacuoles, and the intraneuronal accumulation of proteins associated with AD.