1 / 72

Trafficking and processing of APP b -secretase

Trafficking and processing of APP b -secretase. Intracellular trafficking of APP: relation to its physiological function?. APP. TMD. 5A3/1G7. NH 2. APP localizes to the plasma membrane, Golgi and endosomes. Pastorino, unpublished data. APP. TMD. C-term APP Ab. NH 2.

mirit
Download Presentation

Trafficking and processing of APP b -secretase

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Trafficking and processing of APP b-secretase

  2. Intracellular trafficking of APP: relation to its physiological function?

  3. APP TMD 5A3/1G7 NH2 APP localizes to the plasma membrane, Golgi and endosomes Pastorino, unpublished data

  4. APP TMD C-term APP Ab NH2 Staining for C-term domain of APP is detected also in the nucleus Pastorino, unpublished data

  5. APP TMD 5A3/1G7 NH2 APP internalizes from the plasma membrane into intracellular compartments, endosomes and Golgi COOH Koo and Squazzo, 1994

  6. Protein trafficking and endocytosis

  7. APP co-localizes with the endosomes Pastorino et al., 2006

  8. Why we want to study the trafficking of APP? Because, the intracellular localization of APP INFLUENCES the production of b-Amyloid peptide

  9. Processing of APP a-secretase g-secretase b-secretase APP TMD NH2 COOH b-secretase a-secretase saAPPs C99 C83 sbAPPs g-secretase g-secretase Ab p3 AICD AICD Pathogenic amyloidogenic pathway Protective non-amyloidogenic pathway

  10. Intracellular compartments and processing of APP a-secretase activity: in the plasma membrane (where metalloproteases, known to have like TACE and ADAM10/ADAM17, reside). b-secretase activity: mostly in the endosomes, possible also in the ER and Golgi g-secretase activity: mostly in the ER, also in lysosomes and possible at the plasma membrane (still under debate).

  11. Trafficking of APP aAPP APP a-secretase activity APP C83 C99 b-secretase activity bAPPs AICD C99 Ab g-secretase activity

  12. GOOD!! APP retained @ plasma membrane = Internalization of full length APP =  Protective non-amyloidogenic processing BAD!!!  pathogenic amyloidogenic processing

  13. Products dowstream of non-amyloidogenic processing: aAPPs: soluble stub of APP deriving from the a-secretase cleavage : possible neurotrophic function p3: c-terminal truncated portion of the sequence of b-amyloid, deriving from the subsequent action of a- and g-secretase. DOES NOT aggregate. Unknown function. AICD: APP Intra Cellular Domain, deriving from the cleavage of g-secretase. Known regulation of transcriptional activity.

  14. Products downstream of the amyloidogenic processing: bAPPs: soluble stub of APP deriving from the b-secretase cleavage : unknown function C99: c-terminal stub containing the entire intact sequence of the b-amyloid peptide, deriving from the action of b-secretase. It is the substrate from where b-amyloid peptides derive. b-Amyloid peptides: generated by the subsequent action of b- and g-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 b-amyloid plaque in AD AICD:APP Intra Cellular Domain, deriving from the cleavage of g-secretase. Known regulation of transcriptional activity.

  15. Loss of non-amyloidogenic activity as a possible way to develop AD?

  16. Alzheimer’s pathology and depression

  17. Selective Serotonin reuptake inhibitors (SSRI) reduce ISF Abeta…

  18. …and activate protective pathways

  19. Chronic SSRI treatment reduces the load of Abeta plaques in AD mice

  20. Chronic SSRI treatment reduces the load of Abeta peptides in AD mice…

  21. …and increases alpha-secretase activity

  22. Use of antidepressant associates to reduced PIB uptake in humans

  23. Activation of serotoninergic receptors leads to increased non-amyloidogenic pathway

  24. Activation of non-amyloidogenic pathway as protective from AD?

  25. Sirtuin: deacetylation and control on protein transcription

  26. Sirtuins are involved in different diseases

  27. Sirtuins may protect from AD

  28. Sirtuins levels are reduced in aging Is sirtuins activity lost in AD? Could their activity be protective?

  29. SIRT1 Tg AD mice show reduced plaque and Abeta load

  30. Sirt1 expression regulates non-amyloidogenic processing of APP in AD mice

  31. Sirt1 expression regulates levels of the a-secretase ADAM10 in AD mice both as protein….

  32. …and as mRNA

  33. SIRT1 regulates ADAM10 expression by deacetylating Retinoic Acid Receptor beta (RARb)

  34. Levels of the transcription factor HES1 are regulated by SIRT1

  35. Model: SIRT1 controls expression of ADAM10

  36. The aspartyl protease BACE b-Amyloid cleaving enzyme

  37. BACE is expressed mostly in the brain Vassar et al., 1999

  38. In the cell, BACE localizes to Golgi apparatus and Endosomes Vassar et al., 1999

  39. BACE activity 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.

  40. It was previously reported that BACE interacts with GGAs in yeast two hybrid system GGA1, 2 and 3 are monomeric adaptors that are recruited to the trans-Golgi network. GGAs’ function relates to regulation of the trafficking and degradation of proteins GGA consists of 4 distinct domains: VHS domain that binds DxxxLL residue in proteins GAT domain which binds Arf:GTP Hinge region to recruit clathrin A gamma adapton ear homology domain Tesco et al., Neuron. 2007 Jun 7;54(5):721-37.

  41. BACE co-localizes and is degraded within lysosomes Koh et al., 2005

  42. APP contains caspase cleavage sites in its sequence Tesco et al., Neuron. 2007 Jun 7;54(5):721-37. However, although apoptosis increases C99 and Ab levels, this effects do not depend on caspase-mediated cleavage of APP (Tesco et al., 2003).

  43. Does apoptosis lead to increased amyloidogenic processing of APP up-regulating BACE?

  44. In this paper: Apoptosis increases levels of BACE and C99 in different cell lines These effects are reverted by the apoptosis inhibitor zVAD. Apoptosis regulates levels of BACE affecting its degradation not its synthesis, suggesting a post-translational mechanism. During apoptosis GGA3 is cleaved generating a Dominant Negative fragment that further affects BACE trafficking and degradation.

  45. Apoptosis increases levels of C99….. Tesco et al., Neuron. 2007 Jun 7;54(5):721-37.

  46. …and BACE Tesco et al., Neuron. 2007 Jun 7;54(5):721-37.

  47. Apoptosis regulates levels of BACE affecting its degradation not its synthesis The BACE trafficking molecule GGA3 is cleaved during apoptosis A dominant negative truncated form of GGA3 is generated under apoptotic stimuli, increasing levels of Ab and BACE

  48. What happens reducing the levels of GGA3?

More Related