2) Alzheimers: Amyloid plaque formation

chromosome 21

*APP*: -belongs to a family of transmembrane glycoproteins - large ectodomain and short cytoplasmic tail -*gene is on __________ (three copies in Downs' syndrome!)* -expressed in all mammalian cells - Multiple functions suggested, including that it might act as a receptor (ligand?)

Ab

1)*ER/Golgi*: much processing to _______ occurs APP is synthesized in the endoplasmic reticulum (ER) and then transported through the trans-Golgi network. Unprocessed APP is transported from trans-Golgi to plasma membrane in secretory vesicles.

cleavage

2) *Plasma membrane* ________ occurs Cell surface APP is re-internalized in endosomal vesicles.

secretases

A group of 3 proteases called ___________ *process APP*: *a-secretase*: several exist *b-secratase: BACE1* *y-secretase*: Multiprotein complex (*presenilin-1*, nicastrin, APH-1 and PEN-2) *Cleaves substrates within the membrane !*

proteolysis, amyloidogenic

Ab is produced from APP, but how? *by enzymatic procession (_________)* can be produced in 2 major modes: i) *amyloidogenic* and *non-amyloidogenic* (depending on proteases involved) Only __________ processing produces Ab

Amyloid Precursor Protein (APP)

Ab: Ab is a 40 or 42 amino acid protein fragment produced by the *proteolytic processing* of the _____________. Ab is normally present in CSF *function is unknown*

neprilysin IDE

Accumulation of Ab can be due to increased APP production, increased processing or reduced clearance (or both) *What clears Ab? Two proteases:* 1) __________ (zinc metalloendopeptidase) - Major protease for Ab 2) ___________ (insulin-degrading enzyme)

Ab

How are *amyloid plaques* formed? Either excessive production or reduced clearance of a protein called _____ in the brain, which subsequently aggregates.

*PS-1 and y-secretase* activity are necessary for processing of many other proteins, some of which (eg Notch) are essential during embryonic development.

If PS-1 serves to process APP but APP KO mice are normal, why do PS-1 KO mice die embryonically?

Amyloidogenic Non-amyloidogenic

Two modes of APP processing: 1) _________________: - Generates Ab - Involves only b- and y-secretase - Also generates sAPPb and AICD 2) ___________________: - Precludes Ab generation - Predominant processing pathway - Involves a-secretase (also y-secretase) - Also generates sAPPa and AICD

E/Golgi, plasma membrane, endosomes

Where does amyloidogenic processing of APP happen within a neuron? 3 locations: ________, ________, ________

Presenilins

Y-Secretase: _____________: -*Aspartyl protease. Two proteins (PS-1 and PS-2)*, structurally related (67% homology), ubiquitously expressed. - within cells, *localized mainly in the ER and Golgi membranes*. - *PS-1 knockout mice die embryonically*; PS-2 KO's are viable and fertile. - *80% of y-secretase activity is due to PS-1* - *PS-1 and PS-2 double-KO mice have no y-secretase activity; die embryonically.*

Presenilin-1 (PS1).

Y-Secretase: i) Catalytic core of g-secretase is the aspartyl protease, _______________

4

Y-Secretase: ii) *Active 7-secretase is a complex of (_#_) core proteins.* All proteins are necessary for enzymatic activity.

3

_______ APP isoforms expressed from the APP gene in mammals

nicastrin

_________ essential for PS1 activity KO mice die embryonically

y-secretase

__________cleaves APP within the membrane

Neurodegeneration

a) *transgenic mice*: *overexpressing human mutant APP* have been generated using different promoters - most display *age-associated and robust amyloid plaques* in the brain and some cognitive impairment. *But little to no ____________*!

no major problems

b) *APP knockout mice*: *display ____________ !!!* Compensation by APLP 1 or APLP2 ? Function unclear but based on minor problems in the KO mice - might regulate neuronal survival, neurite outgrowth, synaptic plasticity and cell adhesion