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Todd E Golde

Publications and source records attributed to Todd E Golde.

At least 37 records · Page 2Linked to original sources
PubMed2005

Diverse compounds mimic Alzheimer disease-causing mutations by augmenting Abeta42 production.

Increased Abeta42 production has been linked to the development of Alzheimer disease. We now identify a number of compounds that raise Abeta42. Among the more potent Abeta42-raising agents identified are fenofibrate, an antilipidemic agent, and celecoxib, a COX-2-selective NSAID. Many COX-2-selective NSAIDs tested raised Abeta42, including multiple COX-2-selective derivatives of two Abeta42-lowering NSAIDs. Compounds devoid of COX activity and the endogenous isoprenoids FPP and GGPP also raised Abeta42. These compounds seem to target the gamma-secretase complex, increasing gamma-secretase-catalyzed production of Abeta42 in vitro. Short-term in vivo studies show that two Abeta42-raising compounds increase Abeta42 levels in the brains of mice. The elevations in Abeta42 by these compounds are comparable to the increases in Abeta42 induced by Alzheimer disease-causing mutations in the genes encoding amyloid beta protein precursor and presenilins, raising the possibility that exogenous compounds or naturally occurring isoprenoids might increase Abeta42 production in humans.

Alzheimer Disease↗
PubMed2005

Homing in on intracellular Abeta?

In this issue of Neuron, a study by Billings et al. points to intracellular Abeta as a possible cause of neuronal dysfunction. In a mouse model of Alzheimer's disease, Billings et al. link appearance of intraneuronal Abeta to cognitive impairments and then show that "clearance" of intraneuronal Abeta by anti-Abeta antibodies restores cognitive deficits.

Alzheimer Disease↗
PubMed2005

The Abeta hypothesis: leading us to rationally-designed therapeutic strategies for the treatment or prevention of Alzheimer disease.

In recent years the amyloid cascade hypothesis of Alzheimer disease (AD) has been increasingly referred to as the amyloid beta protein (Abeta) cascade hypothesis. This subtle rephrasing reflects the acknowledgment that there is debate within the field as to whether Abeta aggregates other than Abeta deposited as classic amyloid fibrils could trigger the pathological cascade that results in neuronal dysfunction and neurodegeneration. Despite this semantic shift, which highlights one enigmatic aspects of AD, the evidence supporting the Abeta hypothesis of AD is extensive. More importantly the Abeta hypothesis of AD has led and will continue to lead to the development of rationale therapeutic strategies that are likely to either prevent or treat this devastating disease. In this review, the evidence supporting the Abeta hypothesis and the recent advances in anti-Abeta therapy are discussed.

Alzheimer Disease↗
PubMed2005

Inhibitors of gamma-secretase block in vivo and in vitro T helper type 1 polarization by preventing Notch upregulation of Tbx21.

Notch receptors are processed by gamma-secretase acting in synergy with T cell receptor signaling to sustain peripheral T cell activation. Activated CD4+ T cells differentiate into T helper type 1 (TH1) or TH2 subsets. Molecular cues directing TH1 differentiation include expression of the TH1-specific transcription factor T-bet, encoded by Tbx21. However, the regulation of Tbx21 remains incompletely defined. Here we report that Notch1 can directly regulate Tbx21 through complexes formed on the Tbx21 promoter. In vitro, gamma-secretase inhibitors extinguished expression of Notch, interferon-gamma and Tbx21 in TH1-polarized CD4+ cells, whereas ectopic expression of activated Notch1 restored Tbx21 transcription. In vivo, administration of gamma-secretase inhibitors substantially impeded TH1-mediated disease progression in the mouse experimental autoimmune encephalomyelitis model of multiple sclerosis. Thus, using gamma-secretase inhibitors to modulate Notch signaling may prove beneficial in treating TH1-mediated autoimmunity.

Amyloid Precursor Protein Secretases↗
PubMed2004

Presenilin regulates capacitative calcium entry dependently and independently of gamma-secretase activity.

Mutations in presenilin-1 and 2 (PS) lead to increased intracellular calcium stores and an attenuation in the refilling mechanism known as capacitative calcium entry (CCE). Previous studies have shown that the mechanism by which PS modulates intracellular calcium signaling is dependent on gamma-secretase activity. Although the modulation of intracellular calcium signaling can lead to alterations in CCE, it is plausible that PS can also directly affect CCE independent of the effect it exerts on intracellular stores. To investigate this possibility, we studied the effects of the dominant negative variant of PS1 known as DeltaTM1-2, which lacks the first two transmembrane domains of PS1 and in which gamma-secretase activity is abrogated. We demonstrate that, like other dominant negative isoforms of PS1, DeltaTM1-2 expression leads to reduced intracellular calcium. However, unlike other dominant negative isoforms, DeltaTM1-2 leads to a deficit rather than a potentiation of CCE. These data suggest that changes in the structural components of presenilin can modulate CCE independent of its function in gamma-secretase activity and intracellular calcium stores.

Amyloid Precursor Protein Secretases↗
PubMed2004

A signal peptide peptidase (SPP) reporter activity assay based on the cleavage of type II membrane protein substrates provides further evidence for an inverted orientation of the SPP active site relative to presenilin.

Signal peptide peptidase (SPP) is an intramembrane-cleaving protease identified by its cleavage of several type II membrane signal peptides after signal peptidase cleavage. Here we describe a novel, quantitative, cell-based SPP reporter assay. This assay utilizes a substrate consisting of the NH2 terminus of the ATF6 transcription factor fused to a transmembrane domain susceptible to SPP cleavage in vitro. In cells, cleavage of the substrate releases ATF6 from the membrane. This cleavage can be monitored by detection of an epitope that is unmasked in the cleaved substrate or by luciferase activity induced by the cleaved ATF6 substrate binding to and activating an ATF6 luciferase reporter construct. Using this assay we show that (i) SPP is the first aspartyl intramembrane-cleaving protease whose activity increases proportionally to its overexpression and (ii) selectivity of various SPP and gamma-secretase inhibitors can be rapidly evaluated. Because this assay was designed based on data suggesting that SPP has an orientation distinct from presenilin and cleaves type II membrane proteins, we determined whether the segment of SPP located between the two presumptive catalytic aspartates was in the lumen or cytoplasm. Using site-directed mutagenesis to insert an N-linked glycosylation site we show that a portion of this region is present in the lumen. These data provide strong evidence that although the SPP and presenilin active sites have some similarities, their presumptive catalytic domains are inverted. This assay should prove useful for additional functional studies of SPP as well as evaluation of SPP and gamma-secretase inhibitors.

Activating Transcription Factor 6↗
PubMed2004

Signal peptide peptidase forms a homodimer that is labeled by an active site-directed gamma-secretase inhibitor.

Presenilin (PS) is the presumptive catalytic component of the intramembrane aspartyl protease gamma-secretase complex. Recently a family of presenilin homologs was identified. One member of this family, signal peptide peptidase (SPP), has been shown to be a protease, which supports the hypothesis that PS and presenilin homologs are related intramembrane-cleaving aspartyl proteases. SPP has been reported as a glycoprotein of approximately 45 kDa. Our initial characterization of SPP isolated from human brain and cell lines demonstrated that SPP is primarily present as an SDS-stable approximately 95-kDa protein on Western blots. Upon heating or treatment of this approximately 95-kDa SPP band with acid, a approximately 45-kDa band could be resolved. Co-purification of two different epitope-tagged forms of SPP from a stably transfected cell line expressing both tagged versions demonstrated that the approximately 95-kDa band is a homodimer of SPP. Pulse-chase metabolic labeling studies demonstrated that the SPP homodimer assembles rapidly and is metabolically stable. In a glycerol velocity gradient, SPP sedimented from approximately 100-200 kDa. Significantly the SPP homodimer was specifically labeled by an active site-directed photoaffinity probe (III-63) for PS, indicating that the active sites of SPP and PS/gamma-secretase are similar and providing strong evidence that the homodimer is functionally active. Collectively these data suggest that SPP exists in vivo as a functional dimer.

Amyloid Precursor Protein Secretases↗
PubMed2003

Amyloid-beta immunization effectively reduces amyloid deposition in FcRgamma-/- knock-out mice.

Direct immunization with amyloid beta protein (Abeta) and passive transfer of anti-Abeta antibodies reduce Abeta accumulation and attenuate cognitive deficits in transgenic models of Alzheimer's disease (AD). The reduction in Abeta deposition has been proposed to involve microglial phagocytosis of Abeta immune complexes via Fc receptors (FcRs). We have examined the efficacy of Abeta immunization in amyloid precursor protein (APP) transgenic mice crossed into FcR-gamma chain knock-out mice (FcRgamma-/-). As might be expected from previous studies on macrophages, phagocytosis of Abeta immune complexes via FcR was completely impaired in microglia cells isolated from FcRgamma-/- mice. Thus, we immunized APP Tg2576 transgenic mice that were crossed in the FcRgamma-/- background with Abeta1-42 and then analyzed the effect on Abeta accumulation. In APP Tg2576 transgenic mice crossed to FcRgamma-/-, Abeta1-42 immunization significantly attenuated Abeta deposition, as assessed by both biochemical and immunohistological methods. The reduction in Abeta accumulation was equivalent to the reduction in deposition seen in Abeta1-42 immunized, age-matched, FcR-sufficient Tg2576 mice. We conclude that after Abeta immunization, the effects of anti-Abeta antibodies on Abeta deposition in APP Tg2576 transgenic mice are not dependent on FcR-mediated phagocytic events.

Age Factors↗
PubMed2003

TCR-mediated Notch signaling regulates proliferation and IFN-gamma production in peripheral T cells.

Notch genes encode membrane receptors that regulate cell fate decisions in metazoa. Notch receptors and ligands are expressed in developing lymphoid tissue and mature lymphocytes and the role of Notch signaling in early T and B cell development has been studied extensively. However, its contribution to mature T cell function is unknown. TCR-mediated T cell activation is a fundamental process of the adaptive immune system that has been studied for decades; however, the details of this process are incompletely understood. In this study, we present evidence that Notch is required for TCR-mediated activation of peripheral T cells. Inhibition of Notch activation dramatically decreases T cell proliferation in both CD4 and CD8 cells and blocks both NF-kappaB activity and IFN-gamma production in peripheral T cells. Our data reveal a new, nondevelopmental function of Notch as a previously unknown key link in peripheral T cell activation and cytokine secretion.

Amyloid Precursor Protein Secretases↗
PubMed2003

Intramembrane-cleaving aspartic proteases and disease: presenilins, signal peptide peptidase and their homologs.

Recent studies demonstrate that presenilins (PSs) and signal peptide peptidase (SPP) are members of a novel protease family of integral membrane proteins that may utilize a catalytic mechanism similar to classic aspartic proteases such as pepsin, renin and cathepsin D. The defining features of the PSs and SPP are their ability to cleave substrate polypeptides within a transmembrane region, the presence of two active site aspartate residues in adjacent membrane-spanning regions and a conserved PAL motif near their COOH-terminus. PSs appear to be the catalytic subunit of multiprotein complexes that possess gamma-secretase activity. Because this activity generates the amyloid beta peptide (Abeta) deposited in the brain of patients with Alzheimer's disease (AD), PSs are considered therapeutic targets in AD. In contrast to PSs that are not active unless part of a larger complex, SPP does not appear to require protein co-factors. Because of its requirement for hepatitis C virus maturation and a possible immune modulatory role, SPP is also considered a potential therapeutic target. Four additional PS/SPP homologs have been identified in humans; yet, their functions have not been elucidated. Herein, we will review the recent advances in our understanding of the PS/SPP family of proteases as well as discuss aspects of intramembrane cleavage that are not well understood.

Amino Acid Sequence↗
PubMed2003

Triple-transgenic model of Alzheimer's disease with plaques and tangles: intracellular Abeta and synaptic dysfunction.

The neuropathological correlates of Alzheimer's disease (AD) include amyloid-beta (Abeta) plaques and neurofibrillary tangles. To study the interaction between Abeta and tau and their effect on synaptic function, we derived a triple-transgenic model (3xTg-AD) harboring PS1(M146V), APP(Swe), and tau(P301L) transgenes. Rather than crossing independent lines, we microinjected two transgenes into single-cell embryos from homozygous PS1(M146V) knockin mice, generating mice with the same genetic background. 3xTg-AD mice progressively develop plaques and tangles. Synaptic dysfunction, including LTP deficits, manifests in an age-related manner, but before plaque and tangle pathology. Deficits in long-term synaptic plasticity correlate with the accumulation of intraneuronal Abeta. These studies suggest a novel pathogenic role for intraneuronal Abeta with regards to synaptic plasticity. The recapitulation of salient features of AD in these mice clarifies the relationships between Abeta, synaptic dysfunction, and tangles and provides a valuable model for evaluating potential AD therapeutics as the impact on both lesions can be assessed.

Alzheimer Disease↗
PubMed2003

The non-cyclooxygenase targets of non-steroidal anti-inflammatory drugs, lipoxygenases, peroxisome proliferator-activated receptor, inhibitor of kappa B kinase, and NF kappa B, do not reduce amyloid beta 42 production.

Epidemiological evidence suggests that chronic use of non-steroidal anti-inflammatory drugs (NSAIDs) reduces the risk of Alzheimer's disease. Recently, NSAIDs have been shown to decrease amyloid pathology in a transgenic mouse model of Alzheimer's disease. This benefit may be partially attributable to the ability of NSAIDs to selectively reduce production of the amyloidogenic A beta 42 peptide in both cultured cells and transgenic mice. Although this activity does not appear to require the action of cyclooxygenases in cultured cells, it is not known whether other NSAID-sensitive targets contribute to this A beta 42 effect. In this study, we have used both pharmacological and genetic means to determine if other known cellular targets of NSAIDs could mediate the reduction in A beta 42 secretion from cultured cells. We find that altered arachidonic acid metabolism via NSAID action on cyclooxygenases and lipoxygenases does not alter A beta 42 production. Furthermore, we demonstrate that alterations in activity of peroxisome proliferator-activated receptors, I kappa B kinase beta or nuclear factor kappa B do not affect A beta 42 production. Thus, NSAIDs do not appear to alter A beta 42 production indirectly through previously identified cellular targets and may interact directly with the gamma-secretase complex itself to affect amyloid production.

Amyloid beta-Peptides↗
PubMed2003

Evidence that nonsteroidal anti-inflammatory drugs decrease amyloid beta 42 production by direct modulation of gamma-secretase activity.

Chronic use of nonsteroidal anti-inflammatory drugs (NSAIDs) is associated with a lower risk of developing Alzheimer's disease. Recent evidence indicates that some NSAIDs specifically inhibit secretion of the amyloidogenic A beta 42 peptide in cultured cells and mouse models of Alzheimer's disease. The reduction of A beta 42 peptides is not mediated by inhibition of cyclooxygenases (COX) but the molecular mechanism underlying this novel activity of NSAIDs has not been further defined. We now demonstrate that NSAIDs efficiently reduce the intracellular pool of A beta 42 in cell-based studies and selectively decrease A beta 42 production in a cell-free assay of gamma-secretase activity. Moreover, we find that presenilin-1 (PS1) mutations, which affect gamma-secretase activity, differentially modulate the cellular A beta 42 response to NSAID treatment. Overexpression of the PS1-M146L mutation enhances the cellular drug response to A beta 42 lowering NSAIDs as compared with cells expressing wild-type PS1. In contrast, expression of the PS1-Delta Exon9 mutation strongly diminishes the A beta 42 response, showing that PS1 mutations can modulate the cellular drug response to NSAID treatment both positively and negatively. Enhancement of the NSAID drug response was also observed with overexpression of the APP V717F mutation but not with Swedish mutant APP, which affects beta-secretase cleavage. In sum, these results strongly suggest that NSAIDs represent a founding group of compounds that lower A beta 42 production by direct modulation of gamma-secretase activity or its substrate.

Amyloid Precursor Protein Secretases↗
PubMed2003

Peptide-based, irreversible inhibitors of gamma-secretase activity.

The characterization of the enzymes responsible for amyloid beta-peptide (Abeta) production is considered to be a primary goal towards the development of future therapeutics for the treatment of Alzheimer's disease. Inhibitors of gamma-secretase activity were critical in demonstrating that the presenilins (PSs) likely comprised at least part of the active site of the gamma-secretase enzyme complex, with two highly conserved membrane aspartates presumably acting as catalytic residues. However, whether or not these aspartates are actually the catalytic residues of the enzyme complex or are merely essential for normal PS function and/or maturation is still unknown. In this paper, we report the development of reactive inhibitors of gamma-secretase activity that are functionally irreversible. Since such inhibitors have been shown to bind catalytic residues in other aspartyl proteases (e.g., HIV protease), they might be used to determine if the transmembrane aspartates of PSs are involved directly in substrate cleavage.

Amyloid Precursor Protein Secretases↗
PubMed2003

Abeta42-lowering nonsteroidal anti-inflammatory drugs preserve intramembrane cleavage of the amyloid precursor protein (APP) and ErbB-4 receptor and signaling through the APP intracellular domain.

Epidemiological studies indicate that long term use of nonsteroidal anti-inflammatory drugs (NSAIDs) confers protection from Alzheimer's disease, and some NSAIDs were shown to specifically decrease production of the amyloidogenic Abeta42 peptide, most likely by direct modulation of gamma-secretase activity. In contrast to gamma-secretase inhibitors, Abeta42-lowering NSAIDs do not impair S3 cleavage in the NOTCH receptor and release of the NOTCH intracellular domain, a finding with conceptual implications for the development of safer drugs targeting Abeta production through gamma-secretase modulation. Intramembrane cleavage and release of an intracellular signaling domain has recently been demonstrated in a number of additional gamma-secretase substrates. We now show in cell-based assays that intramembrane cleavage of APP and ErbB-4 receptor is not impaired by the Abeta42-lowering NSAIDs, sulindac sulfide and ibuprofen. Generation of the APP intracellular domain (AICD) was further not inhibited in a cell-free assay at concentrations far exceeding those effective in reducing Abeta42 production. Closer inspection of AICD signaling showed that stabilization of the AICD peptide by FE65 and AICD-mediated transcription were also retained at Abeta42-lowering concentrations. These results demonstrate that S3-like/intramembrane cleavage is preserved by Abeta42-lowering NSAIDs in at least three substrates of gamma-secretase APP, ErbB-4, and NOTCH and underline the striking specificity by which these drugs target Abeta42 production.

Amino Acid Sequence↗
PubMed2003

Overexpression of nicastrin increases Abeta production.

Gamma-secretase cleavage is the final proteolytic step that releases the amyloid beta-peptide (Abeta) from the amyloid beta-protein precursor (APP). Significant evidence indicates that the presenilins (PS) are catalytic components of a high molecular weight gamma-secretase complex. The glycoprotein nicastrin was recently identified as a functional unit of this complex based on 1) binding to PS and 2) the ability to modulate Abeta production following mutation of a conserved DYIGS region. In contrast to the initial report, we find that overexpression of wild-type (WT) nicastrin increases Abeta production, whereas DYIGS mutations (MT) have little or no effect. The increase in Abeta production is associated with an increase in gamma-secretase activity but not with a detectable increase in PS1 levels. Subcellular fractionation studies show that WT but not MT nicastrin matures into buoyant membrane fractions enriched in gamma-secretase activity. These data support the hypothesis that nicastrin is an essential component of the gamma-secretase complex. The finding that WT nicastrin overexpression can increase gamma-secretase activity without altering levels of the presumed catalytic component (PS) of the enzyme may point to a role for nicastrin in facilitating cleavage by regulating substrate interactions with the gamma-secretase complex.

Amyloid Precursor Protein Secretases↗
PubMed2003

Physiologic and pathologic events mediated by intramembranous and juxtamembranous proteolysis.

Intramembranous proteolysis (IP) is a recently recognized mechanism for transmembrane signal transduction that involves proteolysis of transmembrane proteins within their membrane-spanning domains. Juxtamembranous proteolysis (JP) is similar, but proteolytic cleavage of a transmembrane protein occurs at a site close to, but not within, the transmembrane domain of the target protein. In both IP and JP, a soluble domain of a transmembrane protein is released from its membrane tether. This domain can then transmit a signal either locally or at some distance from the site of cleavage. In certain signaling pathways, JP and IP are linked. JP on one side of the membrane results in secondary IP, which then releases a signaling domain from the membrane. Whereas well-characterized proteases such as caspases, the proteasome, and metalloprotease disintegrins, have been implicated in JP, three families of multipass membrane proteases (MpMPs) have now been shown to carry out IP. Recent studies of events mediated by IP and JP indicate that they regulate key cellular signaling events including pathways involved in sterol regulation, cell fate selection, and growth regulation. Moreover, IP and JP have important roles in certain diseases such as Alzheimer's disease. Because some of the proteases mediating IP and JP can be selectivity inhibited, inhibitors targeting these proteases are likely to alter both physiologic and pathologic events triggered by IP and JP.

Alzheimer Disease↗