Leptin Receptor Signalling in Hypothalamic Circuits (Prof Ashford)

Question 1

Describe the 5 different pathways leptin has an impact on in reference to energy homeostasis

Answer 1

1) Feeding: Eating to survive
2) Anorexia: Starvation
3) Hedonic feeding: Motivation to eat
4) Energy expenditure: Thermoregulation
5) Glucose homeostasis: Insulin sensitivity

Question 2

What pathway allows leptin to change feeding

Answer 2

Leptin allows less melanocortin (NPY) pathway and switches to PVN/LHA (POMC)

Question 3

What pathway allows leptin to impact anorexia

Answer 3

Leptin acts on AgRP GABA pathway (not the melanocortin)

Question 4

How does leptin impact fasting

Answer 4

Less leptin and this activates dopaminergic neurons in ventral tegmental area

Question 5

How does leptin impact glucose homeostasis

Answer 5

It alters sympathetic and parasympathetic (vagal) output which in turn acts to modify hepatic glucose production and peripheral glucose uptake (increases insulin sensitivity)

Question 6

Which neurons inhibit which. NPY or POMC

Answer 6

NPY inhibits POMC when activated

Question 7

Can single gene deletion of NPY or AgRP genes have an impact on energy homeostasis?

Answer 7

No single gene deletion does not have an effect but ablation of all neurons does

Question 8

How did they go about ablating NPY/AgRP/POMC neurons in mice?

Answer 8

Mice do not have diphtheria receptors and therefore do not react to the diphtheria toxin. NPY and POMC neurons were selected for cell targeted expression of diphtheria toxin receptors. When the toxin is added it destroyed all of the NPY or POMC neurons.

Question 9

What results did ablating of the NPY/POMC neurons

Answer 9

NPY ablation: Hypophagia

POMC ablation: Hyperphagia

Question 10

What two sets of neurons are used in immunohistochemistry and why?

Answer 10

AgRP and POMC as they are discrete (mainly all present in hypothalamus) whereas NPY neurons are present in many brain locations

Question 11

How many amino acids in ghrelin?

Answer 11

28

Question 12

Is ghrelin anorexigenic or orexigenic

Answer 12

Orexigenic

Question 13

Where is ghrelin produced

Answer 13

Endocrine cells lining the stomach and duodenum

Question 14

When does ghrelin become biologically active?

Answer 14

When phosphorylated with a n-octanoyl group by the enzyme ghrelin-o-acyltransferase (GOAT)

Question 15

What receptor does ghrelin bind to?

Answer 15

GHS-R

Question 16

When do ghrelin levels rise and fall in relation to meal time

Answer 16

Rise before meal and fall after (appetite stimulating)

Question 17

What does systemic and i.c.v. administration of ghrelin do to rodents in terms of food intake, energy expenditure and body weight

Answer 17

Increases food intake, decreases energy expenditure and increases body weight.

Question 18

What does ghrelin do to NPY/AgRP and POMC mRNA

Answer 18

Increases NPY/AgRP mRNA synthesis but does not have a direct impact on POMC mRNA (indirectly as NPY neurons inhibit POMC neurons)

Question 19

What does chronic ghrelin infusion to the CNS result in in terms of lipogenesis, lipid oxidation, blood glucose and insulin secretion

Answer 19

Increases lipogenesis, decreases lipid oxidation, increases blood glucose and decreases insulin secretion.

Question 20

Describe anorexia nervosa

Answer 20

Reduced dietary intake leading to weight loss

Question 21

Describe cachexia

Answer 21

Increased energy expenditure in patients often despite reduced energy intake

Question 22

Central administration of what can suppress cachexia

Answer 22

AgRP or other MC3/4R antagonists

Question 23

What happens to ghrelin in DIO

Answer 23

Reduced ghrelin secretion, reduced plasma ghrelin, reduced GOAT mRNA and reduced transport across BBB

Question 24

What potentially life-threatening thing does ghrelin prevent during fasting

Answer 24

Hypoglycaemia

Question 25

How many amino acids does LEAP2 have

Answer 25

40

Question 26

Where is LEAP2 expressed

Answer 26

The liver

Question 27

What does LEAP2 do

Answer 27

Is a reverse agonist of the GHS-R (antagonist of ghrelin)

Question 28

List some key signalling pathways of the leptin receptor

Answer 28

JAK-STAT, PI3K-Fox01, Shp-MAPK and AMPK

Question 29

What are the three important tyrosine residues on LEP-Rb

Answer 29

Y985, Y1077 and Y1138

Question 30

What can JAK2 phosphorylate (generally)

Answer 30

Itself and a partner