Leptin

Question 1

How do neurotransmitters/modulators affect LTP?

Answer 1

Change either

• the threshold for LTP
• magnitude of LTP
• duration of LTP

Question 2

What is leptin?

Answer 2

A 16 kDa protein that acts as an endocrine hormone

Question 3

Which gene encodes for leptin?

Answer 3

Ob gene

Question 4

What is leptin mostly made by?

Answer 4

White adipose tissue

Question 5

What is the amount of circulating leptin proportional to?

Answer 5

Body weight

Question 6

What is the main role of leptin?

Answer 6

To regulate energy homeostasis

Question 7

Which gene encodes of the leptin receptor?

Answer 7

db gene

diabetes gene

Question 8

Which receptor superfamily is leptin a member of?

Answer 8

Class I cytokine receptor superfamily

Question 9

Name the leptin receptor (ObR) isoforms

Answer 9

ObR a-f

Question 10

Which is thought to be the most competent signalling ObR isoform?

Answer 10

ObR(b)

Has lotsa tyrosine residues

Question 11

Phosphorylation of WHAT occurs at the C terminal of the leptin receptor?

Answer 11

Tyrosine reside phosphorylation by JAK

Question 12

What occurs after JAK activation?

Answer 12

STAT3 activation

Question 13

What is the main function of the JAK-STAT pathway?

Answer 13

Regulate gene transcription

Question 14

What other pathways does ObR binding activate?

Answer 14

RAS > RAF signalling

PI3K

Question 15

Where are high levels of Ob-R mRNA expressed?

Answer 15

Hippocampus
Cerebellum
Brainstem
Amygdala

Question 16

What is the main route for leptin into the brain?

Answer 16

Via a sturable transport system regulated by triglycerides and other factors

Question 17

Where do shorter ObR isoforms get expressed in the brain?

Answer 17

On brain microvessels

Question 18

Which other route does leptin take into the brain?

Answer 18

via CSF

Question 19

How can we see where leptin is in the hippocampus?

Answer 19

Fix and permeablise them then 4% paraformaldehyde and 0.1% Triton X-100

Insert primary Ab and secondary Ab

Visual with laser scanning confocal microscope

Question 20

Which antibodies are used to in the immunocytochemical determination of leptin location?

Answer 20

Primary - polyclonal goat anti-Ob-R

Secondary - Alexa 488 conjugated donkey anti-goat

Question 21

Where in the hippocampus are leptin receptors highly expressed?

Answer 21

At synapses

Shanley et al 2002
O’Malley et al 2007

Question 22

How do we know that Ob-Rs are highly expressed at synapses?

Answer 22

Ob-R tagged with green Ab
Synapses with red synapsin-1
Overlap them and see

Shanley et al 2002
O’Malley et al 2007

Question 23

Which excitatory receptor type is most active at CA1 neurons?

Answer 23

AMPAR

Question 24

How does the presence of leptin change theta-burst stimulation respnose?

Answer 24

Theta burst stimulation causes STP (for approx. 30 mins)
In the presence of 50nM leptin, theta burst stimulation causes potentiation of the cell for at least 90 mins - LTP

Shanley et al 2001

Question 25

What effect does leptin have on NMDAR transmission?

Answer 25

Enhancement of NMDA action --> more NMDAR function (Doesn't occur in the absence of ObR) Shanley et al 2001

Question 26

How can we monitor NMDAR function with leptin?

Answer 26

Digital epifluoroescence This picks up changes in intracellular Ca2+ and since NMDAR are Ca2+ permeable, it monitors their function

Question 27

How does Leptin modulate NMDAR function?

Answer 27

via PI3K and MAPK

Question 28

Outline the composition of NMDARs

Answer 28

At least one NR1 subunit One or more NR2 subunits With/without NR3

Question 29

Where are the different types of NR2 subunit expressed?

Answer 29

NRA - synaptic | NR2B - extrasynaptic

Question 30

How does leptin affect NMDA trafficking?

Answer 30

Increases Can be seen through immunocytochemical methods again Harvey et al 2005

Question 31

In which age group does leptin have the most effect on rodent hippocampal functioning?

Answer 31

Adults

Question 32

Outline the composition of AMPARs

Answer 32

Tetrameric complexes of 4 subunits | GluA1-4

Question 33

Which AMPAR subunits have long C-terminal tails?

Answer 33

GluA1 and 4

Question 34

How does leptin affect GluA1 surface expression?

Answer 34

Increases it - seen via immunocytochemical techniques Moult et al 2010

Question 35

What are the most common AMPAR subunits in the hippocampus?

Answer 35

GluA1 and 2

Question 36

Which AMPAR subunits are Ca2+ permeable?

Answer 36

GluA1

Question 37

How does leptin affect LTP via AMPARs?

Answer 37

Increases insertion of GluA2 lacking AMPARs into synapses Increases GluA1 surface expression (More Ca2+, more excitation) Moult et al 2010

Question 38

What does PI3K do?

Answer 38

Phosphorylates phosphoinositides on the 3' position

Question 39

What accompanies leptin-induced GluA1 surface receptor increase?

Answer 39

Increase in PIP3 Moul et al 2010

Question 40

How does leptin increase PI3K activity?

Answer 40

Increases PI3K activity This increases conversion of PI(4,5)P3 to PI(3,4,5)3 Also decreases PTEN activity This reduces the reverse from happening

Question 41

What happens to LTP in leptin insensitive rats? (fa/fa rats)

Answer 41

Impaired LTP in hippocampus, basal transmission is fine

Question 42

Which type of memory is impaired in Zucker fa/fa rats?

Answer 42

Spatial

Question 43

In which disease may leptin be helpful?

Answer 43

AD

Question 44

Why do we think leptin will be helpful in this disease?

Answer 44

Circulating leptin low in patients and in transgenic mice Leptin administration decreases beta-amyloid levels (and they have opposing actions) Leptin improves memory in mouse models of b-amyloid toxicity

Question 45

Why is leptin implicated in this disease?

Answer 45

AD patients have less body weight and imbalance in leptin levels

Question 46

Which study showed that leptin prevents amyloid beta induced internalisation of AMPARs?

Answer 46

Doherty et al 2013

Question 47

Which leptin fragment mimics the action of leptin?

Answer 47

Leptin 116-130 Malekizadeh et al 2017

Question 48

What is the role of leptin in brain regions outwith the hypothalamus?

Answer 48

Unsure

Question 49

What occurs upon leptin binding to shorter isoforms?

Answer 49

Internalisation of leptin

Question 50

Inhibition of which compound mimics the action of leptin?

Answer 50

PTEN phosphatase Moult et al 2010