PubMed Health⌕ Search

Biomedical subjects

Sam Gandy

Publications and source records attributed to Sam Gandy.

At least 19 recordsLinked to original sources
PubMed2006

Physiological mouse brain Abeta levels are not related to the phosphorylation state of threonine-668 of Alzheimer's APP.

BACKGROUND: Amyloid-beta peptide species ending at positions 40 and 42 (Abeta40, Abeta42) are generated by the proteolytic processing of the Alzheimer's amyloid precursor protein (APP). Abeta peptides accumulate in the brain early in the course of Alzheimer's disease (AD), especially Abeta42. The cytoplasmic domain of APP regulates intracellular trafficking and metabolism of APP and its carboxyl-terminal fragments (CTFalpha, CTFbeta). The role of protein phosphorylation in general, and that of the phosphorylation state of APP at threonine-668 (Thr668) in particular, has been investigated in detail by several laboratories (including our own). Some investigators have recently proposed that the phosphorylation state of Thr668 plays a pivotal role in governing brain Abeta levels, prompting the current study. METHODOLOGY: In order to evaluate whether the phosphorylation state of Thr668 controlled brain Abeta levels, we studied the levels and subcellular distributions of holoAPP, sAPPalpha, sAPPbeta, CTFalpha, CTFbeta, Abeta40 and Abeta42 in brains from "knock-in" mice in which a non-phosphorylatable alanyl residue had been substituted at position 668, replacing the threonyl residue present in the wild-type protein. CONCLUSIONS: The levels and subcellular distributions of holoAPP, sAPPalpha, sAPPbeta, CTFalpha, CTFbeta, Abeta40 and Abeta42 in the brains of Thr668Ala mutant mice were identical to those observed in wild-type mice. These results indicate that, despite speculation to the contrary, the phosphorylation state of APP at Thr668 does not play an obvious role in governing the physiological levels of brain Abeta40 or Abeta42 in vivo.

Alzheimer Disease↗
PubMed2006

Sorting through the cell biology of Alzheimer's disease: intracellular pathways to pathogenesis.

During the first 100 years of Alzheimer's disease research, this devastating and intractable disorder has been characterized at the clinical, histological, and molecular levels. Nevertheless, many key mechanistic questions remain unanswered. Here we will emphasize the importance of the cell biology of Alzheimer's disease, reviewing the relevant literature that has expanded our mechanistic understanding, with a particular focus on pathways regulating protein sorting. Accumulated evidence indicates that sorting pathways may be uniquely vulnerable to disease pathogenesis, and recent studies have begun to reveal disease-related defects in the regulation of protein sorting.

Alzheimer Disease↗
PubMed2005

Brain neprilysin activity and susceptibility to transgene-induced Alzheimer amyloidosis.

Neprilysin (NEP) is a zinc metalloproteinase that degrades enkephalins, endothelins, and the Alzheimer's disease amyloid beta (Abeta) peptides. NEP-deficient mice possess increased levels of brain Abeta(1-40) and Abeta(1-42). The objective of this study was to determine whether tissue NEP specific activity differs according to age and/or across mouse strains, especially those strains predisposed toward formation of Abeta-amyloid plaques following overexpression of the human Alzheimer amyloid precursor protein (APP). The C57Bl/6J mouse strain appears to be relatively susceptible to cerebral amyloidosis, whereas the Swiss Webster (SW) strain appears more resistant. We investigated whether NEP specific activity in brain and kidney homogenates from SW and C57 mice of 6, 40, and 80 weeks old varied according to mouse strain, age, and gender. Among the variables tested, NEP specific activity varied most dramatically across mouse strain, with the kidney and brain of SW mice displaying the highest activities. Aging was associated with a reduction in brain NEP specific activity in both strains. Gender-specific differences were identified in kidney but not in brain. We conclude that aging- and strain-dependent differences in NEP specific activity may play a role in the differential susceptibility of some mouse strains for developing cerebral amyloidosis following human APP overexpression.

Age Factors↗
PubMed2005

Emerging prospects for the disease-modifying treatment of Alzheimer's disease.

The currently approved therapies for Alzheimer's disease (AD) in the US are designed to modify the function of specific neurotransmitter systems in the brain. While these palliative treatments can benefit some patients for a period of time, they do not halt the relentless cognitive and behavioral deterioration that characterize this neurodegenerative disorder. Consequently, much current research on AD is directed toward illuminating the disease process itself, particularly the abnormal accumulation of certain proteins in brain: the amyloid-beta protein (Abeta) in senile plaques and cerebral blood vessels, and the tau protein in neurofibrillary tangles. Genetic, biochemical and pathologic evidence now favors a primary role of Abeta aggregation in the Alzheimer proteopathic cascade, and studies in mice indicate that lowering the amount of this protein in brain can be beneficial. Recently, Abeta-immunization therapy has emerged as a particularly promising therapeutic option for treating Alzheimer's disease, but unexpected treatment-related side-effects are an overriding issue. These adverse events were not anticipated from preclinical studies with rodents; hence, more biologically relevant models, such as nonhuman primates, are needed to test the safety and efficacy of novel therapies for Alzheimer's disease.

Alzheimer Disease↗
PubMed2005

Modulation of statin-activated shedding of Alzheimer APP ectodomain by ROCK.

BACKGROUND: Statins are widely used cholesterol-lowering drugs that act by inhibiting HMGCoA reductase, the rate-limiting enzyme in cholesterol biosynthesis. Recent evidence suggests that statin use may be associated with a decreased risk for Alzheimer disease, although the mechanisms underlying this apparent risk reduction are poorly understood. One popular hypothesis for statin action is related to the drugs' ability to activate alpha-secretase-type shedding of the alpha-secretase-cleaved soluble Alzheimer amyloid precursor protein ectodomain (sAPP(alpha)). Statins also inhibit the isoprenoid pathway, thereby modulating the activities of the Rho family of small GTPases-Rho A, B, and C-as well as the activities of Rac and cdc42. Rho proteins, in turn, exert many of their effects via Rho-associated protein kinases (ROCKs). Several cell-surface molecules are substrates for activated alpha-secretase-type ectodomain shedding, and regulation of shedding typically occurs via activation of protein kinase C or extracellular-signal-regulated protein kinases, or via inactivation of protein phosphatase 1 or 2A. However, the possibility that these enzymes play a role in statin-stimulated shedding has been excluded, leading us to investigate whether the Rho/ROCK1 protein phosphorylation pathway might be involved. METHODS AND FINDINGS: We found that both atorvastatin and simvastatin stimulated sAPP(alpha) shedding from a neuroblastoma cell line via a subcellular mechanism apparently located upstream of endocytosis. A farnesyl transferase inhibitor also increased sAPP(alpha) shedding, as did a dominant negative form of ROCK1. Most conclusively, a constitutively active ROCK1 molecule inhibited statin-stimulated sAPP(alpha) shedding. CONCLUSION: Together, these data suggest that statins exert their effects on shedding of sAPP(alpha) from cultured cells, at least in part, by modulation of the isoprenoid pathway and ROCK1.

Alzheimer Disease↗
PubMed2005

The role of cerebral amyloid beta accumulation in common forms of Alzheimer disease.

For approximately 80 years following Alzheimer's description of the disease that bears his name, a gulf divided researchers who believed that extracellular deposits of the amyloid beta (Abeta) peptide were pathogenic from those who believed that the deposits were secondary detritus. Since 1990, the discoveries of missense mutations in the Abeta peptide precursor (APP) and the APP-cleaving enzyme presenilin 1 (PS1) have enabled much progress in understanding the molecular, cellular, and tissue pathology of the aggregates that accumulate in the interstices of the brains of patients with autosomal dominant familial Alzheimer disease (AD). Clarification of the molecular basis of common forms of AD has been more elusive. The central questions in common AD focus on whether cerebral and cerebrovascular Abeta accumulation is (a) a final neurotoxic pathway, common to all forms of AD; (b) a toxic by-product of an independent primary metabolic lesion that, by itself, is also neurotoxic; or (c) an inert by-product of an independent primary neurotoxic reaction. Antiamyloid medications are entering clinical trials so that researchers can evaluate whether abolition of cerebral amyloidosis can mitigate, treat, or prevent the dementia associated with common forms of AD. Successful development of antiamyloid medications is critical for elucidating the role of Abeta in common AD.

Alzheimer Disease↗
PubMed2004

Similar promotion of Abeta1-42 fibrillogenesis by native apolipoprotein E epsilon3 and epsilon4 isoforms.

The apolipoprotein E epsilon4 allele contributes to the genetic susceptibility underlying a large proportion (~40-60%) of typical, sporadic Alzheimer disease. Apolipoprotein E deficient mice made transgenic for human apolipoprotein E epsilon4 accumulate excess cerebral amyloid when compared to similarly prepared mice expressing human apolipoprotein E epsilon3. Therefore, it is important to search for relevant interactions(s) between apolipoprotein E epsilon4 and Abeta in order to clarify the biological role for apolipoprotein E epsilon4 in Alzheimer disease. Using a thioflavine T (ThT)-based assay, we have investigated the effects of native human apolipoprotein E isoforms on the kinetics of Abeta fibrillogenesis. No obvious profibrillogenic activity was detected in Abeta1-40-based assays of any native apolipoprotein E isoform. However, when ThT assays were repeated using Abeta1-42, modest, but statistically significant, profibrillogenic activity was detected in both apolipoprotein E epsilon3- and apolipoprotein E epsilon4-containing media and was similar in magnitude for the two isoforms. These data demonstrate that native apolipoprotein E possesses "pathological chaperone"-type activity for Abeta: in other words, the data indicate that a chaperone-like misfolding reaction can occur between native apolipoprotein E and Abeta. However, the equipotent activities of the apolipoprotein E epsilon3 and epsilon4 isoforms suggests the possibility that either extended co-incubation of apolipoprotein E and Abeta, or, perhaps, the inclusion in the reaction of other fibrillogenesis-modulation co-factors (such as metal ions, or inflammatory mediators such as reactive oxygen species, alpha2-macroglobulin, apolipoprotein J, etc.) may be required for modeling in vitro the apolipoprotein E-isoform-specific-regulation of extracellular Abeta accumulation that occurs in vivo. Alternatively, other events, such as differential apolipoprotein E-isoform-mediated clearance of Abeta or of apolipoprotein E/Abeta complexes may underlie apolipoprotein E-isoform-dependent Abeta accumulation.

Journal Article↗
PubMed2004

Toward modeling hemorrhagic and encephalitic complications of Alzheimer amyloid-beta vaccination in nonhuman primates.

The potential of amyloid-beta (Abeta) immunization as a disease-modifying therapy for Alzheimer's disease is limited by the occurrence of encephalitic side effects in a subset of treated patients. The encephalitis was not predicted from immunization studies in transgenic, Abeta-depositing mice. More recently, studies in these same mice indicate that passive immunization with certain anti-Abeta antibodies can induce microhemorrhage. Cerebral amyloid angiopathy (CAA) may play a key role in determining the risk for these complications. Because aged nonhuman primates (NHPs) have a more human-like immune system than rodents, and because NHPs naturally develop senile plaques and CAA with age, NHPs appear to be important, adjunctive models for assessing the efficacy and safety of immunotherapeutics for Alzheimer's disease. Conversely, the ability to model the complications of Abeta immunotherapy will be important for elucidating the bases of these complications, and for developing protocols that minimize or eliminate the risks of these serious adverse effects.

Alzheimer Disease↗
PubMed2004

Differential preservation of AMPA receptor subunits in the hippocampi of Alzheimer's disease patients according to Braak stage.

The Alzheimer's disease (AD) brain, characterized pathologically by the presence of senile plaques and neurofibrillary tangles, contains regions that are differentially prone toward development of AD pathology. Within these "vulnerable" regions, specific cell populations appear to be selectively affected; the pyramidal cells of the hippocampal subiculum subfield constitute such a vulnerable region. This study investigated whether the AMPA receptor subunit content (GluR1, GluR2, GluR2/3) within "vulnerable" vs. "resistant" sectors of the hippocampus is quantitatively altered with increasing AD neuropathology, as determined by Braak staging. We hypothesize that the glutamate-mediated vulnerability is highly influenced by the repertoire of glutamate receptors expressed on hippocampal neurons. Our results indicate that AMPA receptor subunit proteins are relatively spared across all Braak stages in resistant subfields (CA2/CA3/Dentate Gyrus). However, within vulnerable sectors, i.e., subiculum, GluR2, and GluR2/3 protein levels decreased 63.77% and 60.60%, respectively, in association with Braak stages I-II and stages III-IV, respectively. In Braak stages V-VI, GluR2 and GluR2/3 protein levels were similar to those of Braak stages I-II. In contrast to GluR2 and GluR2/3, GluR1 protein levels were unchanged within vulnerable sectors throughout all stages of the disease. In interpreting these data, it may be relevant to consider that the GluR2 subunit impedes the flow of Ca(+2) through the AMPA receptor ion channel. Thus, we hypothesize that in resistant sectors, the presence of the GluR2 subunit may provide a neuroprotective role by limiting the flow of extracellular Ca(+2), whereas in vulnerable regions, the reduction of GluR2 may contribute to the vulnerability via a mechanism involving an increase in intracellular Ca(+2) and destabilization of intracellular Ca(+2) homeostasis.

Aged↗
PubMed2004

Alzheimer's Abeta vaccination of rhesus monkeys (Macaca mulatta).

Recent preliminary data suggest that vaccination with Alzheimer's Abeta might reduce senile plaque load and stabilize cognitive decline in human Alzheimer's disease. To examine the mechanisms and consequences of anti-Abeta-antibody formation in a species more closely related to humans, rhesus monkeys (Macaca mulatta) were vaccinated with aggregated Abeta(1-42). Immunized monkeys developed anti-Abeta titers exceeding 1:1000, and their plasma Abeta levels were 5-10-fold higher than the plasma Abeta levels observed in monkeys vaccinated with aggregated amylin. These data support the use of non-human primates to model certain phenomena associated with vaccination of humans with aggregated Alzheimer's Abeta.

Aging↗
PubMed2004

Atorvastatin-induced activation of Alzheimer's alpha secretase is resistant to standard inhibitors of protein phosphorylation-regulated ectodomain shedding.

Studies of metabolism of the Alzheimer amyloid precursor protein (APP) have focused much recent attention on the biology of juxta- and intra-membranous proteases. Release or 'shedding' of the large APP ectodomain can occur via one of two competing pathways, the alpha- and beta-secretase pathways, that are distinguished both by subcellular site of proteolysis and by site of cleavage within APP. The alpha-secretase pathway cleaves within the amyloidogenic Abeta domain of APP, precluding the formation of toxic amyloid aggregates. The relative utilization of the alpha- and beta-secretase pathways is controlled by the activation of certain protein phosphorylation signal transduction pathways including protein kinase C (PKC) and extracellular signal regulated protein kinase [ERK/mitogen-activated protein kinase (MAP kinase)], although the relevant substrates for phosphorylation remain obscure. Because of their apparent ability to decrease the risk for Alzheimer disease, the effects of statins (HMG CoA reductase inhibitors) on APP metabolism were studied. Statin treatment induced an APP processing phenocopy of PKC or ERK activation, raising the possibility that statin effects on APP processing might involve protein phosphorylation. In cultured neuroblastoma cells transfected with human Swedish mutant APP, atorvastatin stimulated the release of alpha-secretase-released, soluble APP (sAPPalpha). However, statin-induced stimulation of sAPPalpha release was not antagonized by inhibitors of either PKC or ERK, or by the co-expression of a dominant negative isoform of ERK (dnERK), indicating that PKC and ERK do not play key roles in mediating the effect of atorvastatin on sAPPalpha secretion. These results suggest that statins may regulate alpha-secretase activity either by altering the biophysical properties of plasma membranes or by modulating the function of as-yet unidentified protein kinases that respond to either cholesterol or to some intermediate in the cholesterol metabolic pathway. A 'phospho-proteomic' analysis of N2a cells with and without statin treatment was performed, revealing changes in the phosphorylation state of several protein kinases plausibly related to APP processing. A systematic evaluation of the possible role of these protein kinases in statin-regulated APP ectodomain shedding is underway.

Amyloid Precursor Protein Secretases↗
PubMed2004

Aging, gender and APOE isotype modulate metabolism of Alzheimer's Abeta peptides and F-isoprostanes in the absence of detectable amyloid deposits.

Aging and apolipoprotein E (APOE) isoform are among the most consistent risks for the development of Alzheimer's disease (AD). Metabolic factors that modulate risk have been elusive, though oxidative reactions and their by-products have been implicated in human AD and in transgenic mice with overt histological amyloidosis. We investigated the relationship between the levels of endogenous murine amyloid beta (Abeta) peptides and the levels of a marker of oxidation in mice that never develop histological amyloidosis [i.e. APOE knockout (KO) mice with or without transgenic human APOEepsilon3 or human APOEepsilon4 alleles]. Aging-, gender-, and APOE-genotype-dependent changes were observed for endogenous mouse brain Abeta40 and Abeta42 peptides. Levels of the oxidized lipid F2-isoprostane (F2-isoPs) in the brains of the same animals as those used for the Abeta analyses revealed aging- and gender-dependent changes in APOE KO and in human APOEepsilon4 transgenic KO mice. Human APOEepsilon3 transgenic KO mice did not exhibit aging- or gender-dependent increases in F2-isoPs. In general, the changes in the levels of brain F2-isoPs in mice according to age, gender, and APOE genotype mirrored the changes in brain Abeta levels, which, in turn, paralleled known trends in the risk for human AD. These data indicate that there exists an aging-dependent, APOE-genotype-sensitive rise in murine brain Abeta levels despite the apparent inability of the peptide to form histologically detectable amyloid. Human APOEepsilon3, but not human APOEepsilon4, can apparently prevent the aging-dependent rise in murine brain Abeta levels, consistent with the relative risk for AD associated with these genotypes. The fidelity of the brain Abeta/F2-isoP relationship across multiple relevant variables supports the hypothesis that oxidized lipids play a role in AD pathogenesis, as has been suggested by recent evidence that F2-isoPs can stimulate Abeta generation and aggregation.

Aging↗
PubMed2003

Altered Abeta formation and long-term potentiation in a calsenilin knock-out.

Calsenilin has been identified as a presenilin-binding protein, a transcription factor regulating dynorphin expression, and a beta-subunit of Kv4 channels and could, thus, be a multifunctional protein. To study these functions of calsenilin in vivo and to determine the neuroanatomical expression pattern of calsenilin, we generated mice with a disruption of the calsenilin gene by the targeted insertion of the beta-galactosidase gene. We found that calsenilin expression (as represented by beta-galactosidase activity) is very restricted but overlaps better with that of presenilins and Kv4 channels than with dynorphin, suggesting that calsenilin may regulate presenilin and Kv4 channels in brain. Abeta peptide levels are reduced in calsenilin knock-out mice, demonstrating that calsenilin affects presenilin-dependent gamma-cleavage in vivo. Furthermore, long-term potentiation (LTP) in dentate gyrus of hippocampus, in which calsenilin is strongly and selectively expressed, is enhanced in calsenilin knock-out mice. This enhancement of LTP coincides with a downregulation of the Kv4 channel-dependent A-type current and can be mimicked in wild-type animals by a Kv4 channel blocker. The data presented here show that lack of calsenilin affects both Abeta formation and the A-type current. We suggest that these effects are separate events, caused by a common mechanism possibly involving protein transport.

Amyloid beta-Peptides↗