Trafficking and processing of APP a- and b -secretase

1. Trafficking and processing of APP a- and 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 APP TMD 5A3/1G7 NH2 APP localizes to the plasma membrane, Golgi and endosomes Pastorino, unpublished data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 5A3/1G7 NH2 APP internalizes from the plasma membrane into intracellular compartments, endosomes and Golgi COOH Koo and Squazzo, 1994

5. Protein trafficking and endocytosis

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

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

8. 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

9. 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).

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

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

12. 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.

13. 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.

14. Alpha-secretase: ADAM10, ADAM17, TACE

15. ADAM10 and ADAM17 expression: colocalization with APP and BACE Higher expression in the brain

16. ADAM10’s expression profile is similar to the one of BACE and APP

17. ADAM10 and ADAM17 have a protective role: Implication in AD and cell growth

18. ADAM10 is essential for non-amyloidogenic processing of APP: Evidences in vitro

20. Characterization of ADAM10 transgenic mice

21. ADAM10 regulates non-amyloidogenic APP processing in vivo 18 weeks old

22. ADAM10 protects from plaque deposition in APPTg V717I (Indiana) mice… 10 months old

23. …in an age-dependent fashion ADAM10XAPPtg 17-19 months old ADAM10 DN XAPPtg

24. Overexpression of ADAM10 in double transgenic mice ADAM10 X APPV717I rescues behavioral impairment

25. Could ADAM10 levels decrease during aging causing AD?

26. Sirtuins levels are reduced in aging DO sirtuins regulate ADAM10 expression and/or activity?

27. Sirtuin: deacetylation and control on protein transcription

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

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

30. ..and also levels of the a-secretase ADAM10 in AD mice both as protein….

31. …and as mRNA

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

33. Alzheimer’s pathology and depression

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

35. …and activate protective pathways

36. Chronic SSRI treatment reduces the load of Abeta plaques in AD mice 4 months treatment

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

38. …and increases alpha-secretase activity

39. Use of antidepressant associates with reduced PIB uptake in humans

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

41. Activation of non-amyloidogenic pathway as protective from AD!

42. The aspartyl protease BACE b-Amyloid cleaving enzyme

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

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

45. 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.

47. BACE KO mice lack amyloidgenic processing of APP

48. Abeta levels are reduced in BACE KO mice

49. Levels of BACE protein are increased in AD

50. BACE enzymatic activity is increased in AD brain