Lecture 14 - Pathophysiology of GH/IGF axis in postnatal life II

Question 1

GH/IGF abnormalities: how may they affect puberty and what treatments exist?

Answer 1

Too little – puberty delayed; common in catabolic states - GH/IGF or testosterone
Too much – puberty advanced; clinical & animal studies implicate IGF-1 - GnRH agonists/antagonists to suppress FSH/LH production

Affected characteristics:
* Height
* Genitalial development
* Secondary sexual characteristics
* Psychosocial development

Question 2

GH/IGF abnormalities: what may they be caused by?

Answer 2

• Genetic factors
• Epigenetic factors?
• Nutritional status
• Adiposity?

Question 3

Gonaodotrophs: what axis are they involved in and what do each stage do?

Answer 3

Hypothalamus - Gonadotrophin Releasing Hormone (GnRH)
Anterior pituitary - Gonadotrophs
Gonads - affects gametes/sex steroids

Question 4

Puberty: by what mechanism is it initiated?

Answer 4

Pre-puberty:
* GnRH inhibited by dynorphin
* GnRH in a quiescent state (juvenile pause)

Multiple mechanisms of activating puberty:
* IGF-1 levels increase as the liver produces more (as a response to nutrition/caloric intake), activates KNDy cells
* KNDy cells produce neruokinin B which suppresses dynorphin
* Dynorphin effect is decreased
* Inhibition of GnRH neurons is stopped and GnRH is produced and secreted

• IGF-1 levels increase, activates KNDy cells
• KNDy cells produce kisspeptin
• Kisspeptin activates GnRH neurones and GnRH is produced and secreted
• IGF-1 levels increase and promote adipose tissue formation
• Leptin is produced by adipose tissue and travels to the KNDy neuron, activating it
• KNDy neurons activate gonadotrophin-releasing hormone (GnRH) neurons in the hypothalamus
• Hypothalamus releases gonadotrophin-releasing hormone (GnRH)
• IGF-1 levels increase and act on neighbouring glial cells near the GnRH neurones
• These cells produce prostaglandin which promotes GnRH production

GnRH effects:
* GnRH causes Gn release (FSH/LH) from the anterior pituitary
* FSH/LH affect the ovaries and cause oocyte development and ovulation

Question 5

KNDy neuron: what is it, what does it do, and what is it activated and inhibited by?

Answer 5

Kisspeptin-neurokinin-dynorphin neuron

Produces signalling molecules (dynorphin and kisspeptin/neruokinin B) which control the timing of puberty by either inhibiting or activating GnRH neurones -

• Leptin
• IGF-1
• Gonadotrophins (negative feedbacl)

Question 6

Menstrual cycle: what two parts of it are there?

Answer 6

• Uterine cycle
• Ovarian cycle

Question 7

Uterine cycle

Answer 7

• Menstrual phase - ~5 days
• Proliferative phase - ~9 days
• Secretory phase - ~14 days

Question 8

Ovarian cycle

Answer 8

• Follicular phase - ~14 days
• Luteal phase - ~14 days

Question 9

Dominant follicle: how is it produced?

Answer 9

One of the tertiary follicles will become the dominant follicle

IGF-1 required

Question 10

IGF: what is it, what is its role in follicle development and ovulation, and how is it regulated?

Answer 10

Insulin-like growth factor

• Produced as a response to estradiol production
• Stimulates steroidogenesis - directly and also by augmenting gonadotropin action
• Stimulate granulose cell proliferation and survival

IGFBPs

Question 11

Follicular development: what causes it to occur, and what are the stages?

Answer 11

Gonadotrophin-dependent initially

• Primordial follicles
• Primary follicles
• Secondary follicles
• Tertiary follicles

Question 12

Primordial follicles: what are they, what stage of meiosis development are the oocytes in, and what are their granulosa cells like?

Answer 12

Structure containing an immature oocyte and a layer of granulosa cells

1st meiotic prophase

Single-layer, flat

Question 13

Primary follicles: what are they, what are their key features, what stage of meiosis development are the oocytes in, and what are their granulosa cells like?

Answer 13

Follicle containing a developing oocyte and a cuboidal layer of granulosa cells

• FSH receptor expression
• Oocyte growth and differentiation
• Zona pellucida
• Theca

1st meiotic prophase

Single-layer, cuboidal

Question 14

Secondary follicles: what are they, what are their key features, what stage of meiosis development are the oocytes in, and what are their granulosa cells like?

Answer 14

Follicle containing a developing oocyte and a multi-layer cuboidal layer of granulosa cells

• Oocyte growth and differentiation
• Zona pellucida
• Theca - internal and external
• Follicular fluid

1st meiotic prophase

Multi-layer, cuboidal

Question 15

Tertiary follicles: what are they, what are their key features, what stage of meiosis development are the oocytes in, and what are their granulosa cells like?

Answer 15

An ovarian follicle that has reached a late stage of development

• Zona pellucida
• Theca – interna & externa
• Antral cavity
• Sex steroids

1st meiotic prophase

Multi-layer, cuboidal

Question 16

Granulosa cells: what are they and what do they do?

Answer 16

Cells in the ovarian follicles that support oocyte development

Question 17

Theca cells: what are they and what do they do?

Answer 17

Endocrine cells in the interfollicular stroma that affect reproduction and fertility

Question 18

IGF-I production: what gonadotroph may it be stimulated by and by what mechanism may this occur?

Answer 18

Estradiol

• LH stimulates thecal cell
• Thecal cell produces androgens
• Androgens and FSH promote granulosa cells aromatise androgens to secrete estradiol-17β
• Estradiol acts back on granulosa cells to produce IGF-I

Question 19

IGFBPs: what are they, what do they do, and what are they inhibited by?

Answer 19

IGF binding proteins

Bind to IGFs, inhibiting their activity

• FSH - stimulates IGFBP protease activity and suppresses IGFBP production
• Kallikreins - proteases that cleave IGFBPs
• MMPs (matrix metalloproteases) - breaks IGFBPs down
• PAPP-A (Pregnancy-associated plasma protein A) - cleaves IGFBPs

Question 20

How do stromal and epithelial cells communicate?

Answer 20

Originally thought to potentially be:
* Paracrine factor?
* EGF
* FGF
* TGF

Evidence suggests that it is IGF - IGF is stimulated by estrogen and results in endometrium epithelial cell proliferation

Question 21

IGF-I receptor inhibition: what causes it and what does it cause to happen?

Answer 21

PPP

Prevents estrogen-induced proliferation

Question 22

E: what is it, what does it do, and what is it inhibited by?

Answer 22

Estrogen

Stimulates IGF-1 expression in stroma

Inhibition of the IGF-1 receptor

Question 23

PPP: what is it and what does it do?

Answer 23

Picropodophyllin - an IGF-I receptor inhibitor

• PPP (in uterine lumen) blocks E-mediated activation of IGF-1 receptor
• PPP inhibits E-stimulated epithelial proliferation

Question 24

IGF/IGF1R and cancer: what is their relationship?

Answer 24

May promote:
* Angiogenesis
* Epithelial to mesenchymal transition (EMT)
* ECM invasion
* Immune escape
* Maintenance of cancer stem cells

High IGF levels and IGF1R activity cause a higher risk of cancer

Question 25

IGF/IGF1R and cancer: what evidence is there to support their relationship?

Answer 25

In vitro - IGF1R –ve cells resistant to transformation but growth not impaired Animal models: * lid mouse (reduced circulating IGF-I levels) – resistant to tumour induction * Caloric restriction – reduced incidence and growth of various tumours * Overexpression of IGF-1R leads to tumour formation Epidemiological studies: * Physicians Health & Nurses Health Studies Measured IGF-I levels 7 or 2 years before the onset of cancer * Risk increased (2-fold) if IGF-I level upper end of the normal range

Question 26

Acromegaly: since IGF-I overexpression causes an increased cancer risk, does this also occur in those with acromegaly?

Answer 26

Acromegaly is not associated with an increased risk of prostate/breast cancer

Question 27

IGF-I: what is the treatment of those with high levels?

Answer 27

Licenced & unlicensed use of GH & IGF-I

Question 28

Treatment with IGF-1: what are the potential issues?

Answer 28

No cases of malignancy reported to date but current data from a small population and short time frame so more follow-up needed

Question 29

GH usage: what studies have occurred to investigate the potential relationship with cancer and what was found?

Answer 29

Follow-up of children treated with GH: * In general, no increase in cancer risk (but lifelong surveillance is necessary) * Slight increase in risk for those with a history of malignancy 2012 – EU SAGhE study * 1st study: increased mortality, particularly in those receiving the highest dose * 2nd study: no deaths from cancer * Appropriate control group in either study - not using "normal kids", instead use GH-deficient children (a group that can't ethically exist)? 2018 – EU SAGhE study – results inconclusive: * Follow-up of adults treated with GH * Not well-studied * Available data suggests no risk

Question 30

IGF axis: is it a good target for cancer treatment, what is the mechanism behind this process, what are the existing treatments, and how promising are they?

Answer 30

Potentially * Down-regulate signalling through the type 1 IGF receptor * Decreased receptor expression * Decreased receptor activation Selective tyrosine kinase inhibitors: * Some compounds had toxicity in pre-clinical testing * Phase I and II trials ongoing Monoclonal antibodies: * Block ligand binding (e.g. Figitumumab) * Well tolerated * Promising results in (rare) Ewing sarcoma * Phase II results discouraging in cancers of “corporate” interest (most common cancers) * several trials stopped early because interim data provided no evidence of beneficial effect

Question 31

Anti-IGF-I therapy: why is it not as good as one would expect and how could this be fixed in future treatments?

Answer 31

* Reduced negative feedback, therefore increased GH/IGF release? * Tumours have heterogeneous IGF1R expression? Future: * Need biomarker to identify appropriate people to treat * IGF1R as an adjuvant or secondary target? * target IR as well

Question 32

Improved stress resistance: by what mechanism may GH/IGF k/o result in this?

Answer 32

Ames dwarf mice: * Mutation in Prop-1 (prevents differentiation of somatotrophs) * males & females live 49% & 64% longer * Given Diquat (50mg/kg) – potent inducer of oxidative stress - GH/IGF k/o's tolerate it way better

Question 33

GH/IGF: how may they affect lifespan?

Answer 33

Reduction in GH / IGF-I signalling extends lifespan: * Mutations & caloric restriction * Analysis of human IGF1R gene: over-representation of heterozygous mutations associated with reduced receptor activity in centenarians (those over 100yrs olf) * Some controversies but broadly supported in worms, flies mice & humans; * Improved stress resistance * Improved insulin sensitivity - decreased pancreatic mass, beta cell mass, insulin levels, and then insulin sensitivity * Adipose function - increased adiposity and adiponectin - anti-inflammatory and insulin sensitivity effects * Decreased tumor formation

Question 34

GH/IGF: how may they affect healthspan?

Answer 34

GH & IGF-I levels decrease with advancing age – somatopause: * Correlates with increased fat / decreased muscle mass & physical fitness * GH therapy as an anti-ageing regimen? * Short-term trials in older men suggest favourable effects on lean muscle mass but little evidence of improved muscle strength/performance or quality of life * Longer studies needed

Question 35

hGH: what is it and what does it do?

Answer 35

“hGH is the anti-ageing serum rejuvenating every cell in your body”