Potentially amyloidogenic fragment of 50 kDa and intracellular processing of amyloid precursor protein in cells cultured under leupeptin

Conformational altered p53 affects neuronal function: relevance for the response to toxic insult and growth-associated protein 43 expression

The role of p53 in neurodegenerative diseases is essentially associated with neuronal death. Recently an alternative point of view is emerging, as altered p53 conformation and impaired protein function have been found in fibroblasts and blood cells derived from Alzheimer's disease patients. Here, using stable transfected SH-SY5Y cells overexpressing APP751wt (SY5Y-APP) we demonstrated that the expression of an unfolded p53 conformation compromised neuronal functionality. In particular, these cells showed (i) augmented expression of amyloid precursor protein (APP) and its metabolites, including the C-terminal fragments C99 and C83 and β-amyloid peptide (ii) high levels of oxidative markers, such as 4-hydroxy-2-nonenal Michael-adducts and 3-nitro-tyrosine and (iii) altered p53 conformation, mainly due to nitration of its tyrosine residues. The consequences of high-unfolded p53 expression resulted in loss of p53 pro-apoptotic activity, and reduction of growth-associated protein 43 (GAP-43) mRNA and protein levels. The role of unfolded p53 in cell death resistance and lack of GAP-43 transcription was demonstrated by ZnCl₂ treatment. Zinc supplementation reverted p53 wild-type tertiary structure, increased cells sensitivity to acute cytotoxic injury and GAP-43 levels in SY5Y-APP clone.

Statins Reduce Amyloid-β Production through Inhibition of Protein Isoprenylation

Epidemiological evidence suggests that long term treatment with hydroxymethylglutaryl-CoA reductase inhibitors, or statins, decreases the risk for developing Alzheimer disease (AD). However, statin-mediated AD protection cannot be fully explained by reduction of cholesterol levels. In addition to their cholesterol lowering effects, statins have pleiotropic actions and act to lower the concentrations of isoprenoid intermediates, such as geranylgeranyl pyrophosphate and farnesyl pyrophosphate. The Rho and Rab family small G-proteins require addition of these isoprenyl moieties at their C termini for normal GTPase function. In neuroblastoma cell lines, treatment with statins inhibits the membrane localization of Rho and Rab proteins at statin doses as low as 200 nm, without affecting cellular cholesterol levels. In addition, we show for the first time that at low, physiologically relevant, doses statins preferentially inhibit the isoprenylation of a subset of GTPases. The amyloid precursor protein (APP) is proteolytically cleaved to generate beta-amyloid (Abeta), which is the major component of senile plaques found in AD. We show that inhibition of protein isoprenylation by statins causes the accumulation of APP within the cell through inhibition of Rab family proteins involved in vesicular trafficking. Moreover, inhibition of Rho family protein function reduces levels of APP C-terminal fragments due to enhanced lysosomal dependent degradation. Statin inhibition of protein isoprenylation results in decreased Abeta secretion. In summary, we show that statins selectively inhibit GTPase isoprenylation at clinically relevant doses, leading to reduced Abeta production in an isoprenoid-dependent manner. These studies provide insight into the mechanisms by which statins may reduce AD pathogenesis.

Pilot tolerability studies of hydroxychloroquine and colchicine in Alzheimer disease

Anti-inflammatory drugs may be useful in the treatment of Alzheimer disease (AD). In preparation for therapeutic trials, we conducted pilot feasibility studies of hydroxychloroquine alone and in combination with colchicine in subjects with AD. A total of 20 subjects with probable AD were treated with hydroxychloroquine 200 mg twice daily for 11 weeks, or hydroxychloroquine 200 mg twice daily plus colchicine 0.6 mg twice daily for 12 weeks; subjects were monitored for adverse medical, cognitive, or behavioral effects. Neither regimen caused adverse effects on cognitive or behavioral assessment scores. There were no significant side effects in subjects receiving hydroxychloroquine alone; 2 subjects receiving the two drugs together experienced diarrhea. We conclude that these regimens of anti-inflammatory therapy are well tolerated in subjects with AD, indicating the feasibility of large-scale therapeutic trials of these agents.

Transthyretin binds amyloid beta peptides, Abeta1-42 and Abeta1-40 to form complex in the autopsied human kidney - possible role of transthyretin for abeta sequestration

The deposition of amyloid beta protein (Abeta), a proteolytic cleavage product of amyloid precursor protein (APP), is an invariable pathological feature of the Alzheimer's disease brain, while APP gene is widely expressed in all neuronal and non-neuronal tissues with the highest levels of expression in the brain, and kidney. To understand the role transthyretin (TTR) plays in the sequestration mechanism of Abeta in the kidney, we have investigated interactions of TTR with Abeta1-40 and Abeta1-42 molecules by an immunoprecipitation method, in vitro binding studies, and overlay assay. These in vivo and in vitro biochemical experiments showed that TTR bound Abeta1-42 preferentially, and Abeta1-40 only to a limited extent, to form TTR-monomer and -dimer-Abeta complexes in the normal human kidney. We provide new evidence supporting the hypothesis that TTR, an Abeta binding protein, plays an important role in the sequestration of Abeta and prevents amyloid formation in the kidney.

Advanced glycation end products in Alzheimer's disease and other neurodegenerative diseases

Advanced glycation end products (AGEs) have been implicated in the chronic complications of diabetes mellitus and have been reported to play an important role in the pathogenesis of Alzheimer's disease. In this study, we examined the immunohistochemical localization of AGEs, amyloid beta protein (A beta), apolipoprotein E (ApoE), and tau protein in senile plaques, neurofibrillary tangles (NFTs), and cerebral amyloid angiopathy (CAA) in Alzheimer's disease and other neurodegenerative diseases (progressive supranuclear palsy, Pick's disease, and Guamanian amyotrophic lateral sclerosis/Parkinsonism-dementia complex). In most senile plaques (including diffuse plaques) and CAA from Alzheimer's brains, AGE and ApoE were observed together. However, approximately 5% of plaques were AGE positive but A beta negative, and the vessels without CAA often showed AGE immunoreactivity. In Alzheimer's disease, AGEs were mainly present in intracellular NFTs, whereas ApoE was mainly present in extracellular NFTs. Pick's bodies in Pick's disease and granulovacuolar degeneration in various neurodegenerative diseases were also AGE positive. In non-Alzheimer neurodegenerative diseases, senile plaques and NFTs showed similar findings to those in Alzheimer's disease. These results suggest that AGE may contribute to eventual neuronal dysfunction and death as an important factor in the progression of various neurodegenerative diseases, including Alzheimer's disease.

Evidence for presenilin-1 involvement in amyloid angiopathy in the Alzheimer's disease-affected brain

Presenilin-1 (PS-1) has been identified as the protein encoded by the chromosome 14 locus that, when mutated, leads to familial Alzheimer's disease (FAD). The role PS-1 plays in the pathogenesis of Alzheimer's disease (AD) remains unclear. Using a set of antibodies raised against PS-1 synthetic peptides, polyclonal antibody to amyloid beta protein (Abeta) and end-specific antibodies against Abeta40, and Abeta42, immunohistochemical studies were performed on brain sections obtained from AD cases and controls. The PS-1 antibodies clearly stained amyloid angiopathies in AD-affected brains, but no recognizable immunoreactions were observed in any other vessels free from amyloid involvement in either AD-affected brains or controls. Abeta antibodies and the end-specific antibody against Abeta40 also decorated amyloid angiopathies, showing localization similar to that of PS-1. Western blot analyses predominantly detected protein band polypeptide species of a 50 kDa, band, presumably full-length PS-1 protein with N-terminus antisera, since these antibodies turned out to recognize a 50-kDa full-length band in cell lysate of transfected HeLa cell overexpressing PS-1. In addition, we recognized 30, 27 and 25 kDa proteins in both AD and control brain homogenate with these antibodies. In microvessel fractions extracted from brain homogenates, the 50, and 27 kDa fragments were observed in AD-affected brains but not in those of controls. C-terminus rabbit antisera reacted strongly with the 33 and 27 kDa bands, and additionally detected a small amount of full-length PS-1 protein in extracts from AD and control brains. Our present data indicate that PS-1 might be involved in the pathogenesis of amyloid angiopathy in the AD brain.

Amyloid precursor protein, A beta and amyloid-associated proteins involved in chloroquine retinopathy in rats--immunopathological studies

To understand the retinal changes in Alzheimer disease (AD) patients, pathological and immunocytochemical studies were performed on retinal cells in the chloroquine-treated rats at 0, 4, 8, 12, 16, 20, and 24 weeks after the initial injection, using anti-amyloid precursor protein (APP), -amyloid beta protein (A beta), -apolipoprotein E (apoE), -ubiquitin, and -cathepsin D antibodies. Pathological alterations consistent with chloroquine retinopathy were recognized in the ganglion cells of the ganglion cell layer (GCL) and the inner plexiform layer (IPL) 4 weeks after initial chloroquine injection. Rat retinal changes appear to have a direct relationship to the duration of chloroquine administration. Intense immunoreactivities for anti-APP, A beta, apoE (an associated protein), and ubiquitin co-localized in the swollen ganglion cells and Muller cells by 20-24 weeks together with the lysosomal enzyme cathepsin D. The present data indicate that the endosomal/lysosomal pathway plays an important role in the processing of APP in rat retina. This experimental model is considered to be a suitable neural model to understand retinal pathology and the processing of APP in terms of the pathogenesis of AD, whereas chloroquine-induced myopathy is a useful extra neuronal model.

Interaction of apolipoprotein J-amyloid beta-peptide complex with low density lipoprotein receptor-related protein-2/megalin. A mechanism to prevent pathological accumulation of amyloid beta-peptide

Apolipoprotein J (apoJ) has been shown to be the predominant amyloid beta-peptide (Abeta)-binding protein in cerebrospinal fluid. We have previously demonstrated that the endocytic receptor low density lipoprotein receptor-related protein-2/megalin (LRP-2), which is expressed by choroid plexus epithelium and ependymal cells lining the brain ventricles and neural tube, binds and mediates cellular uptake of apoJ (Kounnas, M. Z., Loukinova, E. B., Stefansson, S., Harmony, J. A., Brewer, B., Strickland, D. K., and Argraves, W. S. (1995) J. Biol. Chem. 270, 13070-13075). In the present study, we evaluated the ability of apoJ to mediate binding of Abeta1-40-apoJ complex to LRP-2 in vitro. Immunoblot analysis showed that incubation of apoJ with Abeta1-40 resulted in the formation of Abeta1-40-apoJ complex and the inhibition of the formation of Abeta1-40 aggregates. Using an enzyme-linked immunosorbent assay, an estimated dissociation constant (Kd) of 4.8 nM was derived for the interaction between Abeta1-40 and apoJ. Enzyme-linked immunosorbent assay was also used to study the interaction of the Abeta1-40-apoJ complex with LRP-2. The results showed that Abeta alone did not bind directly to LRP-2; however, when Abeta1-40 was combined with apoJ to form a complex, binding to LRP-2 took place. The binding interaction could be blocked by inclusion of the receptor-associated protein, an antagonist of apoJ binding to LRP-2. When LRP-2-expressing cells were given 125I-Abeta1-40, cellular uptake of the radiolabeled peptide was promoted by co-incubation with apoJ. When the cells were provided purified 125I-Abeta1-40-apoJ complex, the complex was internalized and degraded, and both processes were inhibited with polyclonal LRP-2 antibodies. Furthermore, chloroquine treatment inhibited the cellular degradation of the complex. The data indicate that apoJ facilitates Abeta1-40 binding to LRP-2 and that the receptor mediates cellular clearance of Abeta1-40-apoJ complex leading to lysosomal degradation of Abeta1-40. The findings support the possibility that LRP-2 can act in vivo to mediate clearance of the complex from biological fluids such as cerebrospinal fluid and thereby play a role in the regulation of Abeta accumulation.

Effects of acidosis on the distribution of processing of the beta-amyloid precursor protein in cultured hippocampal neurons

Reported increases in brain lactate production in Alzheimer disease led us to test the hypothesis that lactic acid acidosis alters the processing of the beta-amyloid precursor protein, beta PP, in neurons. To test this proposition, embryonic rat hippocampal neurons were first cultures for 4 d in serum-free B27/neurobasal medium. Lactic acid at 0.5 and 1 mg/mL (pH 7.1 and, 6.9, respectively) caused a dose-dependent increase in cellular beta-amyloid immunoreactivity detected with antibody 4G8. Acidosis did not affect secretion of beta PP or its derivatives into the medium. The cytoplasmic production of beta PP was slightly reduced by acidosis without a differential effect on maturation or proteolytic processing. In the substrate-bound material, which was insoluble in nonionic detergent, acidosis caused increases in an N-terminal 75-kDa band, a C-terminal 72-kDa band, and potentially amyloidogenic bands at 35 and 38 kDa. Processing to the 4-kDa amyloid beta protein was not observed in these early pure rat neuronal cultures. These results suggest that mild acidosis id sufficient to alter neuronal processing to the amyloid precursor protein into potentially amyloidogenic forms and increase certain beta PP fragments bound to the substrate. If a similar process occurs in the presence of other cell types in the aging brain, acidosis may stimulate an extracellular deposition of amyloid and contribute to the pathogenesis of Alzheimer disease.

Effect of alkalizing agents on the processing of the beta-amyloid precursor protein

We investigated the processing pathway of the amyloid precursor protein (APP) to the secretion of beta A4 under the treatment of ammonium chloride (NH4Cl), bafilomycin A1 (bafA1), or chloroquine, all three agents thought to raise the pH in acidic compartments. HEK-293 cells expressing wild-type APP (APPwt) and APP carrying the Swedish double mutation (APPswe) were affected in a different manner: while cells expressing APPswe decreased the secretion of beta A4 after treatment with bafA1 and NH4Cl, cells expressing APPwt compensated the drug-induced decrease in beta A4 by an increased generation of alternative beta A4-related peptides. Within cells APP accumulated, while the formation of a C-terminal fragment of APP generated by beta-secretase was completely inhibited. Thus, BafA1 and NH4Cl reduced the secretion of beta A4 by inhibiting beta-secretase. Treatment with chloroquine did not alter beta A4 secretion but, strikingly, resulted in an accumulation of intracellular beta A4. The effect of reduced APP endocytosis was studied by expressing APP molecules lacking the cytoplasmic domain (APPwt.delta. APPswe.delta). Truncation of APP reduced beta A4 secretion from APPwt but not from APPswe. BafA1 and NH4Cl treatment inhibited the formation of beta A4 in cells expressing APPswe.delta but not APPwt.delta. With these constructs, chloroquine had no effect and no accumulation of intracellular beta A4 was observed. Since alkalizing agents still affected endocytosis-deficient APP containing the Swedish double mutation, we suggest that the formation of beta A4 from this mutated APP takes place mainly in an acidic compartment along the constitutive secretory pathway. Much in contrast to this, beta A4 generation from APPwt appears to occur also in the endosomal/lysosomal compartment.

The possible place of cathepsins and cystatins in the puzzle of Alzheimer disease: a review

Lysosomal proteinases (cathepsins) and their endogenous inhibitors (cystatins) have been found to be closely associated with senile plaques, cerebrovascular amyloid deposits, and neurofibrillary tangles in Alzheimer disease (AD). Further, profound changes in the lysosomal system seem to be an early event in "at-risk" neurons of AD brains. There is an ongoing controversy as to whether lysosome-associated proteolytic mechanisms are causally related to the development and/or further progression of the disease. The present article deals with some arguments "pro" and "contra" an involvement of the endosomal/lysosomal pathway in amyloidogenesis as a cardinal process in AD. Other putative targets of acidic proteinases and their natural inhibitors in the pathogenesis of AD (such as formation of neurofibrillary tangles and regulation of apolipoprotein E) are also discussed.

The significance of glucose turnover in the brain in the pathogenetic mechanisms of Alzheimer's disease

This paper presents a comprehensive survey of the pathogenesis and pathophysiology of Alzheimer's disease (AD). Two mechanisms are of etiological importance in the development of a degenerative dementing brain disease: 1. Lesions in the mitochondrial genome that are caused by free radicals. Primary degenerative AD is characterized by a tendency to acquire random lesions within mitochondrial DNA that are produced by free radicals. The consequence of these lesions is a decrease in glucose turnover and a decline in oxidative phosphorylation. Point mutations on chromosome 21 are hypothesized to increase the susceptibility of mitochondrial DNA to lesions created by free radicals. 2. Ischemic brain lesions as well as traumatic brain damage cause an increase in the release of excitotoxic amino acids (glutamate, aspartate, etc.). These neurotransmitters increase CA(+2) influx into the nerve cell and significantly lower energy production. From a pathogenetic point of view, AD is characterized by a decrease in glucose turnover in the brain. The progression of AD can be monitored by F18- deoxyglucose PET studies. This technique also allows the recognition of patients who are prone to develop AD. The actual development of a cognitive deficit is a threshold phenomenon that occurs if glucose turnover in the hippocampus or temporoparietal cortex drops below a critical level of about 40% of the level of age-matched controls. The low glucose turnover in AD causes a cholinergic deficit by decreasing the synthesis of AcCoA, which is used by choline acetyltransferase in the acetylation of choline to acetylcholine. The decrease in glucose turnover also reduces oxidative phosphorylation. The resulting decrease in ATP triggers the hyperphosphorylation of tau protein by activating protein kinase 40erk. The hyperphosphorylation leads to the development of paired helical filaments. The generation of beta amyloid and the loss of neuronal synapses are also caused by a decrease in oxidative phosphorylation, since beta amyloid precursor proteins are not inserted into the membranes of nerve cells in the absence of a sufficient amount of ATP. This results in the generation of intact beta amyloid molecules and leads to amyloidosis in the brains of patients with Alzheimer's disease.

Amyloid beta protein in rat soleus muscle in chloroquine-induced myopathy using end-specific antibodies for A beta 40 and A beta 42: immunohistochemical evidence for amyloid beta protein

Previous immunohistochemical studies from this laboratory demonstrated that monoclonal antibodies raised against various regions of amyloid precursor protein (APP) (i.e., N-terminus, amyloid beta protein (A beta), and C-terminus) strongly labeled vacuoles in chloroquine-induced myopathy-affected muscle in rats. In this study, we used antibodies end specific for the A beta 40 and A beta 42 species, and a monoclonal antibody to A beta 1-9 which reacts with APP and A beta. Most vacuoles clearly reacted with anti-A beta 1-9, while about half reacted with anti-A beta 42, and only a few reacted with anti-A beta 40. These results demonstrate that vacuoles in chloroquine-induced myopathy-affected muscle contain cleaved A beta, and that distribution of the two major A beta species is similar to what is observed in A beta deposition in Alzheimer's disease (AD)-affected brain. This provides further evidence that chloroquine-induced myopathy in rats provides a suitable model to understand APP processing into A beta, and the role of APP in terms of the pathogenesis of AD.

Co-localization of amyloid-associated proteins with amyloid beta in rat soleus muscle in chloroquine-induced myopathy: a possible model for amyloid beta formation in Alzheimer's disease

Chloroquine, a potent lysosomotropic agent, induces myopathy in experimental animals similar to rimmed vacuole (RV) myopathy in humans. The abnormal accumulation of amyloid beta protein (A beta), which is the invariable pathological alterations in the brains affected by Alzheimer's disease (AD), has been demonstrated in denervated soleus muscle fibers in chloroquine-induced myopathy in rats. In AD affected brains, a variety of additional proteins are associated with the extracellular deposition of A beta, which leads to the intracellular accumulation of neurofibrillary tangles and finally to neuronal death. In this study, we demonstrate that amyloid-associated proteins, alpha 1-antichymotrypsin, apolipoprotein E, SP-40,40 and ubiquitin co-localize with A beta in vacuolated muscle fibers in chloroquine-induced myopathy. There are striking similarities in immunopathology between experimental RV myopathy and AD. Chloroquine-induced myopathy in rats provides a suitable model not only to obtain insight into the basic mechanisms underlying RV formation in muscle, but also to understand amyloid precursor protein processing into A beta, and the role of amyloid-associated proteins in terms of the pathogenesis of AD.

Immunohistochemical evidence for amyloid beta in rat soleus muscle in chloroquine-induced myopathy

Deposition of amyloid beta (A beta) is one of the pathological hallmarks of brains affected with Alzheimer's disease (AD). The accumulation of A beta have been observed in human myopathies with rimmed vacuoles (RVs) which might involve lysosomal function. Chloroquine, a potent lysosomotropic agent, induces muscle pathology in experimental animals similar to myopathy with RV. In this study, we demonstrate, for the first time, immunohistochemical evidence that A beta and cathepsin D, a lysosomal enzyme, accumulate in vacuolated rat soleus muscle due to chloroquine-induced myopathy. These data indicate that lysosomes are important in the metabolism of amyloid precursor protein to generate A beta. This experimental system seems to be useful not only to study basic mechanisms underlying RV myopathy but also to understand processing of amyloid precursor protein to A beta in AD.