Leptin Flashcards
How do neurotransmitters/modulators affect LTP?
Change either
- the threshold for LTP
- magnitude of LTP
- duration of LTP
What is leptin?
A 16 kDa protein that acts as an endocrine hormone
Which gene encodes for leptin?
Ob gene
What is leptin mostly made by?
White adipose tissue
What is the amount of circulating leptin proportional to?
Body weight
What is the main role of leptin?
To regulate energy homeostasis
Which gene encodes of the leptin receptor?
db gene
diabetes gene
Which receptor superfamily is leptin a member of?
Class I cytokine receptor superfamily
Name the leptin receptor (ObR) isoforms
ObR a-f
Which is thought to be the most competent signalling ObR isoform?
ObR(b)
Has lotsa tyrosine residues
Phosphorylation of WHAT occurs at the C terminal of the leptin receptor?
Tyrosine reside phosphorylation by JAK
What occurs after JAK activation?
STAT3 activation
What is the main function of the JAK-STAT pathway?
Regulate gene transcription
What other pathways does ObR binding activate?
RAS > RAF signalling
PI3K
Where are high levels of Ob-R mRNA expressed?
Hippocampus
Cerebellum
Brainstem
Amygdala
What is the main route for leptin into the brain?
Via a sturable transport system regulated by triglycerides and other factors
Where do shorter ObR isoforms get expressed in the brain?
On brain microvessels
Which other route does leptin take into the brain?
via CSF
How can we see where leptin is in the hippocampus?
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
Which antibodies are used to in the immunocytochemical determination of leptin location?
Primary - polyclonal goat anti-Ob-R
Secondary - Alexa 488 conjugated donkey anti-goat
Where in the hippocampus are leptin receptors highly expressed?
At synapses
Shanley et al 2002
O’Malley et al 2007
How do we know that Ob-Rs are highly expressed at synapses?
Ob-R tagged with green Ab
Synapses with red synapsin-1
Overlap them and see
Shanley et al 2002
O’Malley et al 2007
Which excitatory receptor type is most active at CA1 neurons?
AMPAR
How does the presence of leptin change theta-burst stimulation respnose?
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
What effect does leptin have on NMDAR transmission?
Enhancement of NMDA action –> more NMDAR function
(Doesn’t occur in the absence of ObR)
Shanley et al 2001
How can we monitor NMDAR function with leptin?
Digital epifluoroescence
This picks up changes in intracellular Ca2+ and since NMDAR are Ca2+ permeable, it monitors their function
How does Leptin modulate NMDAR function?
via PI3K and MAPK
Outline the composition of NMDARs
At least one NR1 subunit
One or more NR2 subunits
With/without NR3
Where are the different types of NR2 subunit expressed?
NRA - synaptic
NR2B - extrasynaptic
How does leptin affect NMDA trafficking?
Increases
Can be seen through immunocytochemical methods again
Harvey et al 2005
In which age group does leptin have the most effect on rodent hippocampal functioning?
Adults
Outline the composition of AMPARs
Tetrameric complexes of 4 subunits
GluA1-4
Which AMPAR subunits have long C-terminal tails?
GluA1 and 4
How does leptin affect GluA1 surface expression?
Increases it - seen via immunocytochemical techniques
Moult et al 2010
What are the most common AMPAR subunits in the hippocampus?
GluA1 and 2
Which AMPAR subunits are Ca2+ permeable?
GluA1
How does leptin affect LTP via AMPARs?
Increases insertion of GluA2 lacking AMPARs into synapses
Increases GluA1 surface expression
(More Ca2+, more excitation)
Moult et al 2010
What does PI3K do?
Phosphorylates phosphoinositides on the 3’ position
What accompanies leptin-induced GluA1 surface receptor increase?
Increase in PIP3
Moul et al 2010
How does leptin increase PI3K activity?
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
What happens to LTP in leptin insensitive rats? (fa/fa rats)
Impaired LTP in hippocampus, basal transmission is fine
Which type of memory is impaired in Zucker fa/fa rats?
Spatial
In which disease may leptin be helpful?
AD
Why do we think leptin will be helpful in this disease?
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
Why is leptin implicated in this disease?
AD patients have less body weight and imbalance in leptin levels
Which study showed that leptin prevents amyloid beta induced internalisation of AMPARs?
Doherty et al 2013
Which leptin fragment mimics the action of leptin?
Leptin 116-130
Malekizadeh et al 2017
What is the role of leptin in brain regions outwith the hypothalamus?
Unsure
What occurs upon leptin binding to shorter isoforms?
Internalisation of leptin
Inhibition of which compound mimics the action of leptin?
PTEN phosphatase
Moult et al 2010
