Alzheimer Disease: Hooper NM

Griffiths HH, Morten IJ, Hooper NM. · University of Leeds, Proteolysis Research Group, Institute of Molecular and Cellular Biology, Faculty of Biological Sciences and Leeds Institute of Genetics, Health and Therapeutics, Leeds LS2 9JT, UK. · Expert Opin Ther Targets. · Pubmed #18479216 No free full text.

Abstract: BACKGROUND: The amyloid beta (Abeta) peptide is critical to the development of Alzheimer's disease (AD), the major neurodegenerative disease of the elderly for which there is currently no cure. OBJECTIVE: To review the literature on emerging treatments and potential therapeutic strategies for AD. METHODS: Available published literature and information from pharmaceutical companies was utilised. RESULTS/CONCLUSION: Several of the current treatments to combat AD are aimed at inhibiting the production, blocking the oligomerisation/aggregation or enhancing the degradation of Abeta. In our opinion, albeit based on limited available data, a future potential therapeutic strategy is to mimic the mechanism by which the normal cellular form of the prion protein inhibits the beta-secretase beta-site amyloid precursor protein cleaving enzyme-1 (BACE1), and hence the production of Abeta.

Taylor DR, Hooper NM. · Proteolysis Research Group, Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, and Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds LS2 9JT, UK. · Semin Cell Dev Biol. · Pubmed #17822928 No free full text.

Abstract: The conformational conversion of the cellular form of the prion protein (PrP C) into the infectious form (PrP Sc) and the proteolytic processing of the amyloid-beta (Abeta) peptide are central pathogenetic events in the prion diseases and Alzheimer's disease, respectively. Cholesterol- and sphingolipid-rich lipid rafts have emerged as important sites for the conversion of PrP C into PrP Sc, and for the proteolytic production, degradation and aggregation of Abeta. Here, we discuss these findings and their implications for our understanding of these disease processes. In addition, the potential for rafts as sites for therapeutic intervention in prion diseases and Alzheimer's disease is considered.

Vardy ER, Hussain I, Hooper NM. · University of Leeds, Academic Unit of Molecular Vascular Medicine, Leeds Institute of Genetics, Health and Therapeutics, Clarendon Way, Leeds LS2 9JT, UK. · Expert Rev Neurother. · Pubmed #16734517 No free full text.

Abstract: Alzheimer's disease (AD) is the most common form of dementia, with prevalence and the accompanying socioeconomic impact set to increase over the coming decades. Currently available medications result, at best, in modest cognitive improvement. With increasing understanding of the underlying pathology, new therapeutic targets are being identified at an ever-increasing rate. The key pathological events in the AD brain are deposition of insoluble amyloid-beta peptide (Abeta), formation of neurofibrillary tangles and neuroinflammation leading, ultimately, to neuronal cell death. Each of these will be considered, in detail, in terms of the variety of therapeutic approaches currently being investigated and mechanisms that may prove amenable to intervention in the future.

Cordy JM, Hooper NM, Turner AJ. · Proteolysis Research Group, Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, UK. · Mol Membr Biol. · Pubmed #16611586 No free full text.

Abstract: The amyloidogenesis occurring in Alzheimer's disease represents a fundamental membrane-related pathology involving a membrane-bound substrate metabolized by integral membrane proteases (secretases). Thus, the amyloid-beta peptide (Abeta), which accumulates extracellularly as plaques in the brains of Alzheimer's disease patients, is derived by sequential proteolytic cleavage of the integral transmembrane amyloid precursor protein (APP). Beta-Secretase or BACE-1 (beta-site APP cleaving enzyme) is a transmembrane aspartic protease responsible for the first of these cleavage events, generating the soluble APP ectodomain sAPPbeta, and a C-terminal fragment CTFbeta. CTFbeta is subsequently cleaved by the ?gamma-secretase complex, of which presenilin is the catalytic core, to produce Ass. A variety of studies indicate that cholesterol is an important factor in the regulation of Ass production, with high cholesterol levels being linked to increased Ass generation and deposition. However, the mechanism(s) underlying this effect are unclear at present. Recent evidence suggests that amyloidogenic APP processing may preferentially occur in the cholesterol-rich regions of membranes known as lipid rafts, and that changes in cholesterol levels could exert their effects by altering the distribution of APP-cleaving enzymes within the membrane. Rafts may be involved in the aggregation of Ass and also in its clearance by amyloid-degrading enzymes such as plasmin or possibly neprilysin (NEP).

Vardy ER, Catto AJ, Hooper NM. · Academic Unit of Molecular Vascular Medicine, Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Clarendon Way, Leeds LS2 9JT, UK. · Trends Mol Med. · Pubmed #16153892 No free full text.

Abstract: The accumulation of the amyloid-beta peptide, the main constituent of the "amyloid plaque", is widely considered to be the key pathological event in Alzheimer's disease. Amyloid-beta is produced from the amyloid precursor protein through the action of the proteases beta-secretase and gamma-secretase. Alternative cleavage of amyloid precursor protein by the enzyme alpha-secretase precludes amyloid-beta production. In addition, several proteases are involved in the degradation of amyloid-beta. This review focuses on the proteolytic mechanisms of amyloid-beta metabolism. An increasingly detailed understanding of proteolysis in both amyloid-beta deposition and clearance has identified some of these proteases as potential therapeutic targets for Alzheimer's disease. A more complex knowledge of these proteases takes us one step closer to developing "disease-modifying" therapies, but these advances also emphasize that significant challenges must be overcome before clinically effective drugs to treat Alzheimer's disease become a reality.

Hooper NM. · Proteolysis Research Group, School of Biochemistry and Microbiology, Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds LS2 9JT, UK. · Biochem Soc Trans. · Pubmed #15787600 No free full text.

Abstract: In the amyloidogenic pathway, the APP (amyloid precursor protein) is proteolytically processed by the beta- and gamma-secretases to release the Abeta (amyloid-beta) peptide that is neurotoxic and aggregates in the brains of patients suffering from Alzheimer's disease. In the non-amyloidogenic pathway, APP is cleaved by alpha-secretase within the Abeta domain, precluding deposition of intact Abeta peptide. The cellular form of the PrP(C) (prion protein) undergoes reactive oxygen species-mediated beta-cleavage within the copper-binding octapeptide repeats or, alternatively, alpha-cleavage within the central hydrophobic neurotoxic domain. In addition, PrP(C) is shed from the membrane by the action of a zinc metalloprotease. Members of the ADAM (a disintegrin and metalloproteinase) family of zinc metalloproteases, notably ADAM10 and TACE (ADAM17) display alpha-secretase activity towards APP and appear to be responsible for the alpha-cleavage of PrP(C). The amyloidogenic cleavage of APP by the beta- and gamma-secretases appears to occur preferentially in cholesterol-rich lipid rafts, while the conversion of PrP(C) into the infectious form PrP(Sc) also appears to occur in these membrane domains.

Allinson TM, Parkin ET, Turner AJ, Hooper NM. · Proteolysis Research Group, School of Biochemistry and Molecular Biology, University of Leeds, Leeds, United Kingdom. · J Neurosci Res. · Pubmed #14598310 No free full text.

Abstract: In the non-amyloidogenic pathway, the Alzheimer's amyloid precursor protein (APP) is cleaved within the amyloid-beta domain by alpha-secretase precluding deposition of intact amyloid-beta peptide. The large ectodomain released from the cell surface by the action of alpha-secretase has several neuroprotective properties. Studies with protease inhibitors have shown that alpha-secretase is a zinc metalloproteinase, and several members of the adamalysin family of proteins, tumour necrosis factor-alpha convertase (TACE, ADAM17), ADAM10, and ADAM9, all fulfil some of the criteria required of alpha-secretase. We review the evidence for each of these ADAMs acting as the alpha-secretase. What seems to be emerging from numerous studies, including those with mice in which each of the ADAMs has been knocked out, is that there is a team of zinc metalloproteinases able to cleave APP at the alpha-secretase site. We also discuss how upregulation of alpha-secretase activity by muscarinic agonists, cholesterol-lowering drugs, steroid hormones, non-steroidal anti-inflammatory drugs, and metal ions may explain some of the therapeutic actions of these agents in Alzheimer's disease.

Hooper NM, Turner AJ. · Proteolysis Research Group, School of Biochemistry and Molecular Biology, University of Leeds, UK. · Curr Med Chem. · Pubmed #12052175 No free full text.

Abstract: In the nonamyloidogenic processing pathway the Alzheimer s amyloid precursor protein (APP) is proteolytically cleaved by alpha-secretase. As this cleavage occurs at the Lys16-Leu17 bond within the amyloid beta domain, it prevents deposition of intact amyloidogenic peptide. In addition, the large ectodomain (sAPP(alpha)) released by the action of alpha-secretase has several neuroprotective properties. Studies with a range of hydroxamic acid-based compounds, such as batimastat, indicate that alpha-secretase is a zinc metalloproteinase, and members of the adamalysin family of proteins, TACE, ADAM10 and ADAM9, all fulfil some of the criteria required of alpha-secretase. APP is constitutively cleaved by alpha-secretase in most cell lines. However, on stimulation with muscarinic agonists or activators of protein kinase C, such as phorbol esters, the alpha-secretase cleavage of APP is up-regulated. The constitutive alpha-secretase activity is primarily at the cell surface, while the regulated activity is predominantly located within the Golgi. The beneficial action of cholinesterase inhibitors may in part be due to activation of muscarinic receptors, resulting in an up-regulation of alpha-secretase. Other agents can also increase the nonamyloidogenic cleavage of APP including estrogen, testosterone, various neurotransmitters and growth factors. As the alpha-secretase cleavage of APP both precludes the deposition of the amyloid beta peptide and releases the neuroprotective sAPP(alpha), pharmacological up-regulation of alpha-secretase may provide alternative therapeutic approaches for Alzheimer s disease.

Hooper NM, Turner AJ. · Proteolysis Research Group, School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS2 9JT, U.K. · Biochem Soc Trans. · Pubmed #10961936 No free full text.

Abstract: Angiotensin-converting enzyme (ACE) and the Alzheimer's disease amyloid precursor protein are two examples of membrane-bound proteins that are released in a soluble form by a post-translational proteolytic cleavage event involving a secretase. Site-specific antibodies and matrix-assisted laser desorption ionization-time-of-flight ('MALDI-TOF') MS have been used to map the secretase cleavage site in somatic ACE to Arg-1203/Ser-1204, 24 residues proximal to the membrane-anchoring domain. Trypsin, which can solubilize ACE from the membrane, cleaves the protein at the same site. The use of structurally related hydroxamic acid-based zinc metalloproteinase inhibitors indicate that tumour necrosis factor-alpha convertase, a member of the ADAMs ('a disintegrin and metalloproteinase') family of proteins, is not involved in the proteolytic release of ACE, or in the constitutive or regulated alpha-secretase release of the amyloid precursor protein from a human neuronal cell line.

Hooper NM, Trew AJ, Parkin ET, Turner AJ. · School of Biochemistry and Molecular Biology, University of Leeds, UK. · Adv Exp Med Biol. · Pubmed #10849764 No free full text.

Abstract: Alzheimer's disease is characterised by the progressive deposition of the 4 kDa beta-amyloid peptide (A beta) in extracellular senile plaques in the brain. A beta is derived by proteolytic cleavage of the amyloid precursor protein (APP) by various proteinases termed secretases. alpha-Secretase is inhibited by hydroxamate-based zinc metalloproteinase inhibitors such as batimastat with I50 values in the low micromolar range, and displays many properties in common with the secretase that releases angiotensin converting enzyme. A cell impermeant biotinylated derivative of one such inhibitor completely blocked the release of APP from the surface of neuronal cells, indicating that alpha-secretase cleaves APP at the cell-surface. A range of hydroxamate-based compounds have been used to distinguish between alpha-secretase and tumour necrosis factor-alpha convertase, a member of the ADAMs (a disintegrin and metalloproteinase-like) family of zinc metalloproteinases. Recent data suggests that the presenilins may be aspartyl proteinases with the specificity of gamma-secretase. Although APP and the presenilins are present in detergent-insoluble, cholesterol- and glycosphingolipid-rich lipid rafts, they do not behave as typical lipid raft proteins, and thus it is unclear whether these membrane domains are the sites for proteolytic processing of APP.

Vardy ER, Rice PJ, Bowie PC, Holmes JD, Catto AJ, Hooper NM. · Divison of Cardiovascular and Diabetes Research, Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds, UK. · J Alzheimers Dis. · Pubmed #19276555 No free full text.

Abstract: The insertion allele in the gene encoding angiotensin-converting enzyme (ACE) is a risk factor for Alzheimer's disease (AD) and ACE is one of several peptidases that have the ability to degrade the neurotoxic amyloid-beta peptide. ACE is a membrane-bound peptidase that is also present in a soluble form in plasma as a result of a zinc metalloprotease-mediated shedding event. Here we aimed to determine whether there is a difference in ACE in the plasma of late-onset clinically diagnosed AD patients (n = 94) as compared to age-matched non-demented control subjects (n = 188). Plasma ACE was lower in the AD subjects as compared to the controls both at baseline (p = 0.072) and after two years (p = 0.05). There was a greater reduction in plasma ACE in the AD subjects as compared to the control subjects over the two years. Plasma ACE did not correlate with cognitive function. The observed reduction in plasma ACE in AD may reflect a general decrease in the zinc metalloprotease-mediated shedding of a subset of membrane-bound proteins.

Hooper NM, Turner AJ. · Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Leeds, UK. · Trends Biochem Sci. · Pubmed #18343669 No free full text.

Abstract: Alzheimer's disease is a major neurodegenerative disease of the brain, the incidence of which increases dramatically in old age. Currently, no drugs are available to halt or slow the progression of this disease, which poses an ever-expanding burden on health services, families and society. The prion protein has become infamous owing to its role as the causative agent of the transmissible spongiform encephalopathies such as Creutzfeldt-Jakob disease in humans. However, our view of the prion protein as an unwanted, harmful entity has been challenged recently. New data indicate that the normal cellular form of the prion protein might have a crucial role in suppressing the production of the amyloid-beta peptide, the neurotoxic molecule involved in the pathogenesis of Alzheimer's disease.

Vardy ER, Rice PJ, Bowie PC, Holmes JD, Grant PJ, Hooper NM. · Academic Unit of Molecular Vascular Medicine, Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds, LS2 9JT, UK. · J Alzheimers Dis. · Pubmed #18198415 No free full text.

Abstract: BACKGROUND: Insulin-like growth factor (IGF)-1 has been implicated in the pathogenesis of Alzheimer's disease (AD). METHODS: We compared the level of circulating total and bioavailable IGF-1, by simultaneous measurements of IGF-1 and IGF binding protein (IGFBP)-3, between 87 patients diagnosed with AD and 126 age and sex matched control subjects without cognitive impairment. Blood samples were collected and IGF-1 and IGFBP-3 measured by ELISA. Subjects were also genotyped for apolipoprotein E. RESULTS: Total circulating IGF-1 levels were significantly raised in the AD group as compared to the control group (p=0.022). There was no significant difference in the circulating level of IGFBP-3 between the two groups. When the IGF-1 levels were ratioed against IGFBP-3 levels as an indicator of unbound, bioavailable circulating IGF-1, there was a significant increase in the molar IGF-1:IGFBP-3 ratio in the AD subjects (0.181 +/- 0.006) as compared to the controls (0.156 +/- 0.004) (p< 0.001). Logistic regression analysis revealed that an increase in the IGF-1:IGFBP-3 molar ratio increased the risk of AD significantly. CONCLUSION: The results of increased total and free circulating IGF-1 support the hypothesis that in its early stages late-onset AD reflects a state of resistance to IGF-1.

Parkin ET, Watt NT, Hussain I, Eckman EA, Eckman CB, Manson JC, Baybutt HN, Turner AJ, Hooper NM. · Proteolysis Research Group, Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, and Leeds Institute of Genetics, Health and Therapeutics, University of Leeds, Leeds LS2 9JT, United Kingdom. · Proc Natl Acad Sci U S A. · Pubmed #17573534 links to  free full text

Abstract: Proteolytic processing of the amyloid precursor protein (APP) by beta-secretase, beta-site APP cleaving enzyme (BACE1), is the initial step in the production of the amyloid beta (Abeta) peptide, which is involved in the pathogenesis of Alzheimer's disease. The normal cellular function of the prion protein (PrP(C)), the causative agent of the transmissible spongiform encephalopathies such as Creutzfeldt-Jakob disease in humans, remains enigmatic. Because both APP and PrP(C) are subject to proteolytic processing by the same zinc metalloproteases, we tested the involvement of PrP(C) in the proteolytic processing of APP. Cellular overexpression of PrP(C) inhibited the beta-secretase cleavage of APP and reduced Abeta formation. Conversely, depletion of PrP(C) in mouse N2a cells by siRNA led to an increase in Abeta peptides secreted into the medium. In the brains of PrP knockout mice and in the brains from two strains of scrapie-infected mice, Abeta levels were significantly increased. Two mutants of PrP, PG14 and A116V, that are associated with familial human prion diseases failed to inhibit the beta-secretase cleavage of APP. Using constructs of PrP, we show that this regulatory effect of PrP(C) on the beta-secretase cleavage of APP required the localization of PrP(C) to cholesterol-rich lipid rafts and was mediated by the N-terminal polybasic region of PrP(C) via interaction with glycosaminoglycans. In conclusion, this is a mechanism by which the cellular production of the neurotoxic Abeta is regulated by PrP(C) and may have implications for both Alzheimer's and prion diseases.

Plant LD, Boyle JP, Thomas NM, Hipkins NJ, Benedikz E, Hooper NM, Henderson Z, Vaughan PF, Peers C, Cowburn RF, Pearson HA. · School of Biomedical Sciences, University of Leeds, Leeds, UK. · Neuroreport. · Pubmed #12218704 No free full text.

Abstract: Mutations in presenilin 1 (PS1) are the major cause of autosomal dominant Alzheimer's disease. We have measured the voltage-gated K+ current in the human neuroblastoma cell line SH-SY5Y using whole-cell patch-clamp. When cells were stably transfected to over-express PS1, no change in K+ current was observed. However, over-expression of a deletion mutation (deltaE9) in PS1 led to a decreased K+ current. These changes were channel specific since no change in the Na+ current could be observed in the same cells. Confocal microscopy revealed that the K(V)3.1 K+ channel subunit had a diminished plasma membrane distribution when the deltaE9 over-expressing cells were compared to control cells. Intracellular retention of Kv3.1 is consistent with the notion that PS1 can modulate the activity and trafficking of ion channels in central neurones and implicates a compromise in electrical signalling as an underlying factor in the pathogenesis of familial Alzheimer's disease.

Canet-Aviles RM, Anderton M, Hooper NM, Turner AJ, Vaughan PF. · Academic Unit of Cardiovascular Medicine, University of Leeds, Leeds, UK. · Brain Res Mol Brain Res. · Pubmed #12191495 No free full text.

Abstract: The signalling pathways by which muscarine and epidermal growth factor (EGF) regulate the secretion of the alpha-secretase cleavage product (sAPPalpha) of the amyloid precursor protein (APP) were examined in the human neuroblastoma SH-SY5Y. Using specific inhibitors it was found that over 80% of sAPPalpha secretion, enhanced by muscarine, occurred via the extracellular signal-regulated kinase (ERK1/2) member of the mitogen-activated protein kinase (MAPK) family and was dependent on protein kinase Calpha (PKCalpha) and a member of the Src family of non-receptor tyrosine kinases (Src-TK). In contrast the stimulation of sAPPalpha secretion by EGF was not affected by inhibitors of PKC nor Src-TK but was dependent on ERK1/2. In addition muscarine-enhanced sAPPalpha secretion and ERK1/2 activation were inhibited 60 and 80%, respectively, by micromolar concentrations of the phosphatidylinositol 3 kinase (PI-3K) inhibitor wortmannin. In comparison wortmannin decreased EGF stimulation of sAPPalpha secretion and ERK 1/2 activation by approximately 40%. Unexpectedly, U73122, an inhibitor of phosphoinositide-specific phospholipase C, did not inhibit muscarine enhancement of sAPPalpha secretion. These data are discussed in relation to a pathway for the enhancement of sAPPalpha secretion by muscarine which involves the activation of a Src-TK by G-protein beta/gamma-subunits leading to activation of PKCalpha, and ERK1/2 by a mechanism not involving phospholipase C.

Parvathy S, Hussain I, Karran EH, Turner AJ, Hooper NM. · School of Biochemistry and Molecular Biology, University of Leeds, U.K. · Biochemistry. · Pubmed #10423252 No free full text.

Abstract: The amyloid precursor protein (APP) is proteolytically processed predominantly by alpha-secretase to release the ectodomain (sAPPalpha). In this study, we have addressed the cellular location of the constitutive alpha-secretase cleavage of endogenous APP in a neuronal cell line. Incubation of the neuroblastoma cell line IMR32 at 20 degrees C prevented the secretion into the medium of soluble wild-type APP cleaved by alpha-secretase as revealed by both immunoelectrophoretic blot analysis with a site-specific antibody and immunoprecipitation following metabolic labeling of the cells. No sAPPalpha was detected in the cell lysates following incubation of the cells at 20 degrees C, indicating that alpha-secretase does not cleave APP in the secretory pathway prior to or within the trans-Golgi network. Parallel studies using an antibody that recognizes specifically the neoepitope revealed on soluble APP cleaved by beta-secretase indicated that this enzyme was acting intracellularly. alpha-Secretase is a zinc metalloproteinase susceptible to inhibition by hydroxamate-based compounds such as batimastat [Parvathy, S., et al. (1998) Biochemistry 37, 1680-1685]. Incubation of the cells with a cell-impermeant, biotinylated hydroxamate inhibitor inhibited the release of sAPPalpha by >92%, indicating that alpha-secretase is cleaving APP almost exclusively at the cell surface. The observation that alpha-secretase cleaves APP at the cell surface, while beta-secretase can act earlier in the secretory pathway within the neuronal cell line indicates that there must be strict control mechanisms in place to ensure that APP is normally cleaved primarily by alpha-secretase in the nonamyloidogenic pathway to produce the neuroprotective sAPPalpha.

Parkin ET, Hussain I, Karran EH, Turner AJ, Hooper NM. · School of Biochemistry and Molecular Biology, University of Leeds, England, UK. · J Neurochem. · Pubmed #10098859 No free full text.

Abstract: Many cases of early-onset familial Alzheimer's disease have been linked to mutations within two genes encoding the proteins presenilin-1 and presenilin-2. The presenilins are 48-56-kDa proteins that can be proteolytically cleaved to generate an N-terminal fragment (approximately 25-35 kDa) and a C-terminal fragment (approximately 17-20 kDa). The N- and C-terminal fragments of presenilin-1, but not full-length presenilin-1, were readily detected in both human and mouse cerebral cortex and in neuronal and glioma cell lines. In contrast, presenilin-2 was detected almost exclusively in cerebral cortex as the full-length molecule with a molecular mass of 56 kDa. The association of the presenilins with detergent-insoluble, low-density membrane microdomains, following the isolation of these structures from cerebral cortex by solubilization in Triton X-100 and subsequent sucrose density gradient centrifugation, was also examined. A minor fraction (10%) of both the N- and C-terminal fragments of presenilin-1 was associated with the detergent-insoluble, low-density membrane microdomains, whereas a considerably larger proportion of full-length presenilin-2 was present in the same membrane microdomains. In addition, a significant proportion of full-length presenilin-2 was present in a high-density, detergent-insoluble cytoskeletal pellet enriched in beta-actin. The presence of the presenilins in detergent-insoluble, low-density membrane microdomains indicates a possible role for these specialized regions of the membrane in the lateral separation of Alzheimer's disease-associated proteins within the lipid bilayer and/or in the distinct functions of these proteins.