Slide 1

Trafficking and processing of APP and -secretase Slide 2 Intracellular trafficking of APP: relation to its physiological function? Slide 3 APP NH 2 5A3/1G7 TMD APP localizes to the plasma membrane, Golgi and endosomes Pastorino, unpublished data Slide 4 COOH APP NH 2 5A3/1G7 TMD APP internalizes from the plasma membrane into intracellular compartments, endosomes and Golgi Koo and Squazzo, 1994 Slide 5 Protein trafficking and endocytosis Slide 6 APP co-localizes with the endosomes Pastorino et al., 2006 Slide 7 Because, the intracellular localization of APP INFLUENCES the production of Amyloid peptide Why we want to study the trafficking of APP? Slide 8 Processing of APP -secretase Protective non-amyloidogenic pathway Pathogenic amyloidogenic pathway APP TMD s APPs C83 s APPs C99 -secretase NH2 COOH AA AICD p3 AICD -secretase -secretase -secretase -secretase -secretase Slide 9 Intracellular compartments and processing of APP -secretase activity: in the plasma membrane (where metalloproteases, known to have like TACE and ADAM10/ADAM17, reside). -secretase activity: mostly in the endosomes, possible also in the ER and Golgi -secretase activity: mostly in the ER, also in lysosomes and possible at the plasma membrane (still under debate). Slide 10 Trafficking of APP -secretase activity -secretase activity -secretase activity APP C83 APP C99 APPs APP AICD C99 AA Slide 11 APP retained @ plasma membrane = Internalization of full length APP = GOOD!! BAD!!! Protective non-amyloidogenic processing pathogenic amyloidogenic processing Slide 12 Products dowstream of non-amyloidogenic processing: APPs: soluble stub of APP deriving from the -secretase cleavage : possible neurotrophic function p3: c-terminal truncated portion of the sequence of b-amyloid, deriving from the subsequent action of - and -secretase. DOES NOT aggregate. Unknown function. AICD: APP Intra Cellular Domain, deriving from the cleavage of - secretase. Known regulation of transcriptional activity. Slide 13 Products downstream of the amyloidogenic processing: APPs: soluble stub of APP deriving from the -secretase cleavage : unknown function C99: c-terminal stub containing the entire intact sequence of the - amyloid peptide, deriving from the action of -secretase. It is the substrate from where -amyloid peptides derive. -Amyloid peptides: generated by the subsequent action of - and - secretases. At very low concentration could be neurotrophic, however, when forming aggregates they are VERY TOXIC and lead to the formation of the core of the -amyloid plaque in AD AICD: APP Intra Cellular Domain, deriving from the cleavage of - secretase. Known regulation of transcriptional activity. Slide 14 Alpha-secretase: ADAM10, ADAM17, TACE Slide 15 ADAM10 and ADAM17 expression: colocalization with APP and BACE Higher expression in the brain Slide 16 ADAM10s expression profile is similar to the one of BACE and APP Slide 17 ADAM10 and ADAM17 have a protective role: Implication in AD and cell growth Slide 18 ADAM10 is essential for non-amyloidogenic processing of APP: Evidences in vitro Slide 19 Slide 20 Characterization of ADAM10 transgenic mice Slide 21 18 weeks old ADAM10 regulates non-amyloidogenic APP processing in vivo Slide 22 10 months old ADAM10 protects from plaque deposition in APPTg V717I (Indiana) mice Slide 23 17-19 months old in an age-dependent fashion ADAM10XAPPtg ADAM10 DN XAPPtg Slide 24 Overexpression of ADAM10 in double transgenic mice ADAM10 X APPV717I rescues behavioral impairment Slide 25 Could ADAM10 levels decrease during aging causing AD? Slide 26 Sirtuins levels are reduced in aging DO sirtuins regulate ADAM10 expression and/or activity? Slide 27 Sirtuin: deacetylation and control on protein transcription Slide 28 SIRT1 Tg AD mice show reduced plaque and Abeta load Slide 29 Sirt1 expression in AD mice regulates non-amyloidogenic processing of APP Slide 30 ..and also levels of the -secretase ADAM10 in AD mice both as protein. Slide 31 and as mRNA Slide 32 Loss of non-amyloidogenic activity as a possible way to develop AD? Slide 33 Alzheimers pathology and depression Slide 34 Selective Serotonin reuptake inhibitors (SSRI) reduce ISF Abeta Slide 35 and activate protective pathways Slide 36 Chronic SSRI treatment reduces the load of Abeta plaques in AD mice 4 months treatment Slide 37 Chronic SSRI treatment reduces the load of Abeta peptides in AD mice Slide 38 and increases alpha-secretase activity Slide 39 Use of antidepressant associates with reduced PIB uptake in humans Slide 40 Activation of serotoninergic receptors leads to increased non-amyloidogenic pathway Slide 41 Activation of non-amyloidogenic pathway as protective from AD! Slide 42 The aspartyl protease BACE -Amyloid cleaving enzyme Slide 43 BACE is expressed mostly in the brain Vassar et al., 1999 Slide 44 In the cell, BACE localizes to Golgi apparatus and Endosomes Slide 45 1-In vitro, BACE is mostly active at an acidic pH range between 4.5- 5.5. 2-BACE is supposed to be mostly active in the endosomes, due to BACE co-localization and to the acidic pH of these organelles. Although in vivo, interaction between BACE and APP was observed at the plasma membrane and in the endosomes, in cell culture, BACE was active also in the ER and in the Golgi apparatus. BACE activity Slide 46 Slide 47 BACE KO mice lack amyloidgenic processing of APP Slide 48 Abeta levels are reduced in BACE KO mice Slide 49 Levels of BACE protein are increased in AD Slide 50 BACE enzymatic activity is increased in AD brain Slide 51 BACE Domains and trafficking TM Propeptide sequence DTGDSG DDISLLK furin 1 501 aa460-476 Regulation of BACE Trafficking Abeta? Slide 52 The LL motif, but not the S (that can be phoshorylated) regulates the amount of BACE retained at the plasma membrane.. Pastorino et al., MCN 2002 Slide 53 BACE LL motif determines lysosomal colocalization for degradation Koh et al., 2005 Slide 54 GGA proteins: a crucial role in the regulation of BACE trafficking and degradation through BACE LL domain Slide 55 Do GGA3 and BACE levels change during neurodegenerative pathologies? Slide 56 Tesco et al., Neuron. 2007 Jun 7;54(5):721-37. Ischemic patients have increased levels of BACE in the brain Slide 57 Tesco et al., Neuron. 2007 Jun 7;54(5):721-37. and decreased levels of GGA3 Slide 58 Tesco et al., Neuron. 2007 Jun 7;54(5):721-37. AD patients have increased levels of BACE and decreased levels of GGA3 in the brain Slide 59 Tesco et al., Neuron. 2007 Jun 7;54(5):721-37. GGA3 siRNA causes increase of BACE expression and accumulation of C99 Slide 60 What happens during apoptosis? Slide 61 Tesco et al., Neuron. 2007 Jun 7;54(5):721-37. APP contains caspase cleavage sites in its sequence However, although apoptosis increases C99 and A levels, this effects do not depend on caspase-mediated cleavage of APP (Tesco et al., 2003). Slide 62 Tesco et al., Neuron. 2007 Jun 7;54(5):721-37. Apoptosis increases levels of C99.. Slide 63 Tesco et al., Neuron. 2007 Jun 7;54(5):721-37. and BACE Slide 64 Tesco et al., Neuron. 2007 Jun 7;54(5):721-37. During apoptosis GGA3 levels are destabilized Slide 65 Apoptotic mechanisms associated with neurodegeneration stabilize BACE via the inhibition of GGA3, therefore inhibiting GGA3-mediated BACE degradation Slide 66 Vassar, Neuron. 2007 Jun 7;54(5):671-3. Review. Model of BACE stabilization during apoptosis