Insulin

Question 1

What is the main action of insulin?

Answer 1

Enhances uptake, utilisation and storage of glucose

Question 2

Describe an insulin receptor (IR)

Answer 2

Its one large transmembrane glycoprotein complex

With two alpha and two beta subunits linked by disulphide bridges

Question 3

Describe the alpha subunit in the insulin receptor (IR)

Answer 3

Extracellular

Insulin binding domain

Question 4

Describe the beta subunit in the insulin receptor (IR)

Answer 4

Transmembrane proteins with intrinsic tyrosine kinase activity

Question 5

Which methods can be used to determine IR expression in CNS?

Answer 5

Immunocytochemistry
In situ hybridisation
Western blots & PCR

Question 6

Outline in situ hybridisation

Answer 6

Labelled anti-sense oligonucleotide probes inserted which are specific to IR subunits
Detects mRNA

Question 7

How does peripheral insulin get into the brain?

Answer 7

Active transport across the BBB via a regulated, saturable insulin transporter

Question 8

How may insulin be released locally from the CNS?

Answer 8

Depolarisation of insulin mRNA expressing neurons should cause insulin relase

Question 9

What is the main role of insulin in the CNS?

Answer 9

Mediate cerebral glucose uptake in glial cells

Question 10

Hyper-insulinaemia is a risk factor for Parkinson’s disease

True/False

Answer 10

False

risk factor for dementia

Question 11

How does insulin administration affect memory formation?

Answer 11

Improves it

Craft et al 1999

Question 12

Why doe we think that insulin is relevant to learning and memory?

Answer 12

IRs concentrated in brain regions involved in learning and memory
Hippocampus and amygdala

Question 13

How does insulin affect synaptic strength?

Answer 13

Increases synaptic strength of excitatory synapses

Man et al 2000

Question 14

What is streptozotocin?

Answer 14

A diabetic inducing agent

Question 15

What effect does streptozotocin have on memory?

Answer 15

Memory impairment

Question 16

Which NMDAR features does insulin enhance?

Answer 16

NMDAR single channel currents

NMDAR mediated synaptic transmission

Question 17

Which isoforms of NMDAR does insulin enhance?

Answer 17

NR1-NR2A and NR1-NR2B

These are prominent in the hippocampus!

Question 18

Outline insulin receptor signal transduction

Answer 18

Binds to alpha subunit
Causes autophosphorylation of beta subunits
Stimulates intrinsic tyrosine kinase activity
Phosphorylation then triggers the activation of other signalling cascades

Question 19

Phosphorylation of IR causes activation of which signalling cascades?

Answer 19

IRS proteins and Src proteins (PI3K)

Shc protein

Question 20

What does Shc protein do?

Answer 20

Mediates association of IR with Grb-2-SOS complex

Activates Ras-Raf-MAPK

Question 21

Which inhibitors block insulin action?

Answer 21

IR tyrosine kinase inhibitors eg tyrphostin (Skeberdis 2001)
PKC inhibitors (Liao 1999)
Src TK inhibitors (Liao and Leonard 1999)

Question 22

How does insulin effect NMDAR surface expression?

Answer 22

Increases exocytosis

Inhibits endocytosis

Question 23

How does insulin increase NMDAR expression and how do we know?

Answer 23

Via SNAP-25 dependent exocytosis

Botox injections cleave SNAP-25 and prevents this exocytosis
With botox there is reduced NDMAR current
Skeberdis 2001

Question 24

How does SNAP-25 driven insulin receptor exocytosis work?

Answer 24

IR activated
Activates IRS proteins
Activates PI3K
Then activates abnormal protein kinase C
This increases SNAP-25 activity which then causes the receptors exocytosis

Question 25

Through which signalling pathways does insulin increase NMDA responses?

Answer 25

PI3K and MAPK Because application of inhibitors of these stop the increase in current

Question 26

How may insulin modulate LTD?

Answer 26

Depressing AMPAR mediated EPSCs in hippocampal neurons by reducing surface AMPAR expression Man et all 2000

Question 27

Low concentrations of insulin induce LTP | True/false

Answer 27

False Low conc produces transient synaptic depression High conc induces LTD

Question 28

Insulin decreases NMDAR EPSCs | T/F

Answer 28

F | Depresses AMPAR EPSCs but not NMDARs

Question 29

Which AMPAR subunit does insulin supress?

Answer 29

GluA2 | But not GluA1

Question 30

How do we know insulin affects AMPAR subunits?

Answer 30

Immunocytochemistry shows less of them | Man et all 2000

Question 31

How does hypertonic sucrose affect insulin mediated subunit endocytosis?

Answer 31

Inhibits clathrin coating the vesicle which means it cant endocytose

Question 32

What can be given to block insulin-mediated endocytosis of AMPAR?

Answer 32

Hypertonic sucrose | Post-synaptic dialysis with Anti-IR Abs

Question 33

Why do we think insulin and memory are linked?

Answer 33

In rodents, MWM training upregulated IR mRNA and protein in CA1 region Increase in IR staining also observed Zhao et al 1999

Question 34

What biochemical changes were observed following training in the MWM?

Answer 34

Increased tyrosine phosphorylation in 52 and 66 kDa proteins Increase in Shc-66 Accumulation of Grb (52kDa) Increase in active MAPK Zhao et al 1999

Question 35

Which neurodegenerative disorder is insulin linked to?

Answer 35

AD

Question 36

How may insulin be useful in AD treatment?

Answer 36

Prevents Ab derived diffusible ligands (ADDL) induced synapse loss

Question 37

Which signalling pathway does insulin enhance NMDA via?

Answer 37

PI3K-MAPK | when this is blocked u dont get insulin mediated increase in NMDARs

Question 38

What is insulin induced LTD dependent on?

Answer 38

Postsynaptic IR activation