Lecture 15 - IGF regulation of placental & fetal growth

Question 1

IGF system: how does it affect different species in their pregnancies?

Answer 1

• Mice - lacking placental-specific transcript of IGF-2 have reduced placental and fetal growth
• Rodent - overcome maternal constraint on growth
• Sheep - increases glucose & amino acid uptake to fetus, increases placental production of lactate
• Guinea pig - increases placental transport & fetal weight
• Humans - some studies show a correlation with birth weight - rate of increase in maternal IGF correlates with placental mass

Question 2

Development of maternal/fetal exchange barrier

Answer 2

• Cytotrophoblast proliferation
• Cytotrophoblast differentiation & syncytial fusion
• Maturation/apoptosis of syncytial nuclei
• Extrusion of apoptotic nuclei

Question 3

IGF: what role does it have in placental growth, how do we know this, what receptor is present in the placenta, and which is the main functional one?

Answer 3

Promotes proliferation (observed using BrdU or Ki67 staining) and inhibits apoptosis (observed using TUNEL staining)

Both IGF receptors are present in the placenta - staining results in mass staining not localised

• Inhibition of IGF1R reduces IGF-stimulated proliferation - main IGF receptor
• IGF2R knockdown does not reduce IGF-stimulated proliferation

Question 4

IGF signalling pathways

Answer 4

• IGF binds to IGF-1 receptor
• IRS1/2, SHC, GRB2, GAB1, and SOS complex
• Activates Ras
• Ras - Raf1 - MEK1/2 - ERK1/2 - RSK, ERK1/2 and RSK act as TF, promoting proliferation
• Ras - PI3K - PDK-1 - Akt, Akt acts as a TF, promoting proliferation

Question 5

PPP: what does it do to IGF?

Answer 5

Inhibits type 1 IGF-1 receptors

Question 6

SiRNA: what does it do to IGF?

Answer 6

Inhibits type 2 IGF-1 receptors

Question 7

PD98059: what does it do to IGF?

Answer 7

Inhibit MEK1/2/, inhibiting the MEK/ERK IGF signalling pathway

Question 8

LYS294002: what does it do to IGF?

Answer 8

Inhibits PI3K, inhibiting the PI3K/Akt IGF signalling pathway

Question 9

What evidence is there of the role of IGF in placental growth?

Answer 9

• MAPK inhibition reduces IGF-stimulated proliferation
• PI3K inhibition reduces IGF protection from apoptosis
• Inhibition of IGF1R reduces IGF-stimulated proliferation
• IGF-1/2 k/o reduces fetal size
• IGF-2 k/o have small placentas

Question 10

Can we manipulate the IGF axis to influence placental and fetal growth?

Answer 10

• Deliver IGF to placenta via maternal circulation - quantum dots
• Enhance IGF signalling in placenta
• Increase activation of IGF1R
• Increase activation of MAPK pathway

Question 11

IGF-1 with quantum dots: what are quantum dots, how can they affect IGF-1-derived placental growth, and how do we ensure it only goes to the placenta?

Answer 11

Quantum dots are tiny biomolecules that can bind biotin and a molecule of interest

By using this, we can activate signalling in placental explants

Using a targeting/homing peptide

Question 12

IGFR2: what is it, what does its k/o do in mice, and what is its mechanism?

Answer 12

IGF-2 receptor

• Elevated IGF-II
• Somatic overgrowth
• Enlarged placentas

Endogenous IGF-2 binds to the IGF-1 receptor causing the typical IGF-1 effects of reduced apoptosis and increased proliferation

Question 13

IGF-2 analogues: what is an example, what can they do, and what has research found them to do?

Answer 13

Leu27 IGF-2 - a high-affinity IGFR2 binder (able to displace and/or block IGFR2)

Bind to IGFR2, causing endogenous IGF-2 to bind to the IGFR1 and promote proliferation and inhibit apoptosis

IGF-II analogue reduces the number of small pups in a mouse model of FGR

Question 14

microRNA: what is it, what does it do, what are some key enzymes in its synthesis, and how does it regulate IGF signalling pathways?

Answer 14

Endogenous RNA that targets mRNA for either degradation or repression

DICER/TREBP - cleaving it

• Results in reduced IGF-stimulated cytotrophoblast proliferation
• Dampens signalling molecules downstream of IGF to reduce its proliferative/anti-apoptotic effects - MAPK

Question 15

DICER: how does it get k/o, what does this result in, and what effects does it have on IGF signalling?

Answer 15

k/o of dicer using SiRNA

Reduced microRNA production

Less inhibition of IGF signalling pathway:
* Results in higher IGF-stimulated cytotrophoblast proliferation
* less dampening of signalling molecules downstream of IGF to reduce its proliferative/anti-apoptotic effects - MAPK

Question 16

What considerations would have to be used when using microRNA to affect IGF function in the placenta?

Answer 16

• Which microRNAs target MAPK?
• Can they be manipulated to increase MAPK signalling?

Question 17

IGF1R: what modifications does it undergo before it becomes functional, how necessary is it, and what investigations have investigated this?

Answer 17

N-terminal glycosylation

Required for receptor processing and cell surface expression

Glycosylation inhibitors:
* Affect IGF receptor processing
* Reduce IGFR cell surface expression
* Blocks IGF-stimulated trophoblast proliferation

Question 18

Glycosylation: can we give glycosylation inhibitors to pregnant women, why, what else are we able to use, and why? How can we block glycosylation clinically?

Answer 18

No - glycosylation is a key process in various parts of not only the body but the placenta, its indiscriminate inhibition would cause various serious adverse effects

Statins

• Statins affect IGF receptor processing
• Statins inhibit IGF-stimulated trophoblast proliferation in human 1st trimester placental explants