Pharmacology and Therapeutics - Research Publications
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ItemSex-dependent effects of amyloid precursor-like protein 2 in the SOD1-G37R transgenic mouse model of MND(SPRINGER BASEL AG, 2021-10)Motor neurone disease (MND) is a neurodegenerative disorder characterised by progressive destruction of motor neurons, muscle paralysis and death. The amyloid precursor protein (APP) is highly expressed in the central nervous system and has been shown to modulate disease outcomes in MND. APP is part of a gene family that includes the amyloid precursor-like protein 1 (APLP1) and 2 (APLP2) genes. In the present study, we investigated the role of APLP2 in MND through the examination of human spinal cord tissue and by crossing APLP2 knockout mice with the superoxide dismutase 1 (SOD1-G37R) transgenic mouse model of MND. We found the expression of APLP2 is elevated in the spinal cord from human cases of MND and that this feature of the human disease is reproduced in SOD1-G37R mice at the End-stage of their MND-like phenotype progression. APLP2 deletion in SOD1-G37R mice significantly delayed disease progression and increased the survival of female SOD1-G37R mice. Molecular and biochemical analysis showed female SOD1-G37R:APLP2-/- mice displayed improved innervation of the neuromuscular junction, ameliorated atrophy of muscle fibres with increased APP protein expression levels in the gastrocnemius muscle. These results indicate a sex-dependent role for APLP2 in mutant SOD1-mediated MND and further support the APP family as a potential target for further investigation into the cause and regulation of MND.
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ItemAmyloid precursor protein and amyloid precursor-like protein 2 have distinct roles in modulating myelination, demyelination, and remyelination of axons(WILEY, 2019-03)The identification of factors that regulate myelination provides important insight into the molecular mechanisms that coordinate nervous system development and myelin regeneration after injury. In this study, we investigated the role of amyloid precursor protein (APP) and its paralogue amyloid precursor-like protein 2 (APLP2) in myelination using APP and APLP2 knockout (KO) mice. Given that BACE1 regulates myelination and myelin sheath thickness in both the peripheral and central nervous systems, we sought to determine if APP and APLP2, as alternate BACE1 substrates, also modulate myelination, and therefore provide a better understanding of the events regulating axonal myelination. In the peripheral nervous system, we identified that adult, but not juvenile KO mice, have lower densities of myelinated axons in their sciatic nerves while in the central nervous system, axons within both the optic nerves and corpus callosum of both KO mice were significantly hypomyelinated compared to wild-type (WT) controls. Biochemical analysis demonstrated significant increases in BACE1 and myelin oligodendrocyte glycoprotein and decreased NRG1 and proteolipid protein levels in both KO brain tissue. The acute cuprizone model of demyelination/remyelination revealed that whereas axons in the corpus callosum of WT and APLP2-KO mice underwent similar degrees of demyelination and subsequent remyelination, the myelinated callosal axons in APP-KO mice were less susceptible to cuprizone-induced demyelination and showed a failure in remyelination after cuprizone withdrawal. These data identified APP and APLP2 as modulators of normal myelination and demyelination/remyelination conditions. Deletion of APP and APLP2 identifies novel interplays between the BACE1 substrates in the regulation of myelination.
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ItemMild Oxidative Stress Induces Redistribution of BACE1 in Non-Apoptotic Conditions and Promotes the Amyloidogenic Processing of Alzheimer's Disease Amyloid Precursor Protein(PUBLIC LIBRARY SCIENCE, 2013-04-17)BACE1 is responsible for β-secretase cleavage of the amyloid precursor protein (APP), which represents the first step in the production of amyloid β (Aβ) peptides. Previous reports, by us and others, have indicated that the levels of BACE1 protein and activity are increased in the brain cortex of patients with Alzheimer's disease (AD). The association between oxidative stress (OS) and AD has prompted investigations that support the potentiation of BACE1 expression and enzymatic activity by OS. Here, we have established conditions to analyse the effects of mild, non-lethal OS on BACE1 in primary neuronal cultures, independently from apoptotic mechanisms that were shown to impair BACE1 turnover. Six-hour treatment of mouse primary cortical cells with 10-40 µM hydrogen peroxide did not significantly compromise cell viability but it did produce mild oxidative stress (mOS), as shown by the increased levels of reactive radical species and activation of p38 stress kinase. The endogenous levels of BACE1 mRNA and protein were not significantly altered in these conditions, whereas a toxic H2O2 concentration (100 µM) caused an increase in BACE1 protein levels. Notably, mOS conditions resulted in increased levels of the BACE1 C-terminal cleavage product of APP, β-CTF. Subcellular fractionation techniques showed that mOS caused a major rearrangement of BACE1 localization from light to denser fractions, resulting in an increased distribution of BACE1 in fractions containing APP and markers for trans-Golgi network and early endosomes. Collectively, these data demonstrate that mOS does not modify BACE1 expression but alters BACE1 subcellular compartmentalization to favour the amyloidogenic processing of APP, and thus offer new insight in the early molecular events of AD pathogenesis.
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ItemInduction of integral membrane PAM expression in AtT-20 cells alters the storage and trafficking of POMC and PC1.(Rockefeller University Press, 1999-02-08)Peptidylglycine alpha-amidating monooxygenase (PAM) is an essential enzyme that catalyzes the COOH-terminal amidation of many neuroendocrine peptides. The bifunctional PAM protein contains an NH2-terminal monooxygenase (PHM) domain followed by a lyase (PAL) domain and a transmembrane domain. The cytosolic tail of PAM interacts with proteins that can affect cytoskeletal organization. A reverse tetracycline-regulated inducible expression system was used to construct an AtT-20 corticotrope cell line capable of inducible PAM-1 expression. Upon induction, cells displayed a time- and dose-dependent increase in enzyme activity, PAM mRNA, and protein. Induction of increased PAM-1 expression produced graded changes in PAM-1 metabolism. Increased expression of PAM-1 also caused decreased immunofluorescent staining for ACTH, a product of proopiomelanocortin (POMC), and prohormone convertase 1 (PC1) in granules at the tips of processes. Expression of PAM-1 resulted in decreased ACTH and PHM secretion in response to secretagogue stimulation, and decreased cleavage of PC1, POMC, and PAM. Increased expression of a soluble form of PAM did not alter POMC and PC1 localization and metabolism. Using the inducible cell line model, we show that expression of integral membrane PAM alters the organization of the actin cytoskeleton. Altered cytoskeletal organization may then influence the trafficking and cleavage of lumenal proteins and eliminate the ability of AtT-20 cells to secrete ACTH in response to a secretagogue.
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ItemSynthetic dityrosine-linked β-amyloid dimers form stable, soluble, neurotoxic oligomers(ROYAL SOC CHEMISTRY, 2013)