Transcript No Slide Title

Body growth- effects by the
hypothalamus-pituitary.
John-Olov Jansson
Content
•
Body growth – general
•
Body growth - endocrine regulation
•
What are the effects of the GH- IGF-1 axis?
•
How is the GH- IGF-1 axis regulated ?
•
What are the mechanisms of action
of GH- IGF-1?
•
What can go wrong with GH – IGF-1?
Body growth - general
Size obtain (as % adult size)
Organ growth (% of size at age 20)
LYMPHOID
BRAIN & HEAD
GENERAL
REPRODUCTIVE
Factors that affect growth
1. Genetic
2. Environmental: nutrition, illness, stress
Hormones:
growth hormone,
insulin-like growth factor 1 and 2, insulin
 thyroid hormones
Androgens - estrogens,
 glucocorticoids – inhibitory.
Growth in humans
Growth is not continuous - it is episodic.
Two periods of physiological rapid growth:
 In infancy
 Late in puberty (just before growth stops)
In addition patophysiological:
 (After illness “catch-up”
growth occurs.)
Recovery
from illness
Growth velocity in boys & girls
25
20
Height
gain
(cm/yr)
15
Growth spurt
10
GIRLS
BOYS
Why are men taller?
5
0
0
2
4 6
8 10 12 14 16 18 20
Age in years
Body growthendocrine regulation
Endocrine control of
postnatal and prenatal growth
1. Postnatal
Thyroid hormones
Growth hormone  ↑ IGF-1
25
Gonadal steroids
Estradiol
Testosterone  Estradiol
=> ERα =>↑ GH =>↑ IGF-1)
20
Height
gain
(cm/yr)
15
10
GIRLS
BOYS
5
0
0
2
4 6
8 10 12 14 16 18 20
Age in years
2. Prenatal (trimester 2 and 3):
 Nutrients (dose response)
 Insulin
 IGF-1
 IGF-2
 Thyroid hormone
 Not GH.
Induction of growth plate closure by
steroids in men and women
Aromatase
E2
TE2
Same hormones that cause
The growth
spurt, acts
but later!
Females:
Estradiol
on ERα in growth
plate.
Males: Testosterone  Estradiol acts on ERα
in growth plate.
Growth hormone
Endogenous produced by:
 anterior pituitary GH-N, GH gene (somatotrophs) – pulsatile
 placenta - GH variant – continuous, 3rd trimester, secretion to mother.
not fetus, may increase B-glucose in mother  more nutrients for
fetus?.
GH-N
(pit)
GH-V
(placenta)
(In addition 3 placental
lactogen genes)
GH therapy:
Human GH protein (192 amino acids, 4 -helices)
must be injected.
GH structure
Without GH proportional dwarf 110 cm.
GH tumour: Giant if not adult. 270 cm.  Wide dose
response! (maybe also for IGF-1.)
Body growthEffects by the GH
- IGF-1 axis
What does GH do?
One opinion
What does GH do?
Where is Belitze
located?
Belize (former British Honduras) –
Where Dr Klatz got his MD
GH is anabolic, lipolytic and
diabetogenic
anabolic
Bone growth
lipolytic
Local IGF-1
production
GH
?
FFAs
 fat mass
 Protein synthesis
 Amino acid uptake
anabolic
 Lean body mass
glycogenolysis
Liver-derived
IGF1
 blood glucose
 glucose uptake
(insulin resistance)
diabetogenic
GH therapy reduces visceral adiposity in GH-deficiency:
Influence on risk cardiovascular diseases?
GH-deficient patient
before GH therapy
GH-deficient patient
after 26 weeks
GH therapy
Bengtsson et al 1993
J. Clin. Endocrinol. Metab. 76:309
Body growth:
Regulation of
GH - IGF-1 axis
Physiological control of GH secretion
Exercise
Fasting
Aging
+
_
+
Arginine
+ +
GH
_
_
Stress
Sleep
+
+
_
Glucose
Lipids
Gonadal
steroids
GH/IGF-1
Control of GH secretion
Hypothalamus
+
somatostatin
GHRH
_
_
Portal vessels
Anterior pituitary
_
Growth Hormone
Liver
IGF-1
Insulin-like growth factor-1
Nutrient control of GH secretion in relation to GH
effects
GH
_
_
+
+
Amino acids
(Arginine)
Lipids (FFA)
Glucose
+
_
Implications of pulsatile GH secretion
Single GH blood samples
not good enough
How to destinguish?
GH levels
GH prod
tumor
X
X
Normal GH
pattern
GH deficiency
X
Time
• 24 h GH pattern
(golden standard)
• Serum IGF-1 as marker
of mean 24 h GH
• Stimulators or inhibitors
Effect of arginine on plasma GH
hGH µg/ml
100
Arginine can be
used as a
provocactive test
for GH release
80
60
40
20
Arg
0
-10 0
30
60
90
Time (minutes)
Normal
GH deficient
120
Glucose tolerance test
Acromegaly (nonresponsive to glucose)
35
GH 6
mU/ml
3
Normal
0
0
Glucose
2
Hours
4
GH secretion is increased by gonadal steroids during
growth spurt, then declines
Age 7 years
Age 13 years
Serum GH
(mU/L)
(Due to E2 in girls,
due to T  E2 in boys)
Age 20 years
Age 30 years
CLOCK TIME
GH secretion during sleep
STAGE
ClockSWS
time
Plasma
GH g/l
SWS= slow
wave sleep
Clock time
Fasting increases GH secretion in man
Effects:
•Keep B-glucose up
•Lipolysis
•Does NOT increase
growth
Bergendahl et al, 1999
GH, IGF-1 and fasting
 B-glucose
IGF-1 stimulated by GH and Nutrition (partly via insulin).
FASTING
 GH
 Lipolysis
  Body growth
 IGF-1
Needed for IGF-1 synthesis:
GH and food!
Fasting blocks GH effects
on body growth and IGF-1
 Appropriate response
to fasting
Somatotrophs: GHRH and somatostatin
Regulates GH synthesis & release +
cell replication
Somatostatin
GHRH
G-prot +
AC
cAMP
CREB
-
PKA
CREB P
Pit-1
Pit-1
Pituitary
somatotroph
1 GH synthesis
GH
3 Proliferation
GH
2 GH Secretion
Taken from: PhD thesis of
Tanya Gilbert, MRC NIMR,
London
Ghrelin – pharmacologic
regulator of GH
•
•
•
•
•
•
•
A peptide – fatty acid hybride (see below)
Ghrelin treatement stimulates GH release.
Ghrelin knockout mice lean but not small!
Released from the empty stomach between meals
Increases appetite
Increases fat mass
Decreases fat burning (increased RQ)
Ghrelin receptors: In GHRH (growth)
And NPY (body fat) neurons
in arcuate nucleus (ARC)
Ghrelin: a centrally active hormone
from the empty stomach
Hypothalamus
 Fat mass
 Food intake
Pituitary
Ghrelin
-
Positive
Energy
Balance
 Growth hormone
+
Negative
Energy
Balance
Stomach
(oxyntic
glands)
Possible mechanism for adiposity:
Ghrelin =>  RQ ( Fat/CHO burning)
Respiratory quotient (RQ)
1.05
1.00
Ghrelin
0.95
Vehicle
0.90
0.85
Control Ghrelin
analog
0.80
0
4
8
12
16
20 24
Dark Photo Period
Lall et al, 2001, BBRC 280:132-138)
Tschöp et al, 2000, Nature 407:908
Body growthMechanisms
GH – IGF-1 axis
Growth of long bones before epiphyseal
plate closure
Epiphyseal
plate
Geminal
Proliferative
Hypertrophic
Chondrocytes
Calcifying
Endochondral
growth
Oestrogens induce closure
of the growth plate via ERα.
Somatomedin (IGF-1) hypothesis of GH action on
bone
Salmon & Daughaday, 1957
GH actions to stimulate
bone growth are
mediated by insulin-like
growth factor 1 (IGF-1),
produced by the liver.
IGF-1 - previously called
somatomedin C.
GH
IGF-1
Challenge to the somatomedin
hypothesis - I
Experiment:
Administration of GH to growth
plate of one leg.
GH acts locally within the
epiphyseal plate to
promote growth. No
effect via liver IGF-1 on
Contralateral leg
GH
NaCl
Direct action of GH?
Locally produced IGF-1
needed
Olle Isakssson and coworkers, Science 1982
Challenge to the somatomedin
hypothesis - II
Additional Experiment:
IGF-1 antiserum (removes IGF- GH plus
1) + GH to growth plate of one IGF antiserum
leg.
Result: No increase in growth
of injected leg.
Conclusion: GH actions require
the presence of IGF-1.
IGF-1 may be produced locally.
NaCl
Challenge to the somatomedin
hypothesis - II
Liver IGF-1 knockout
Control
24
20
Body
16
Weight
(g) 12
Liver-derived IGF-1
may not be important
for growth.
8
0
Normal body
growth in liverspecific IGF-1knockout mice.

0
10
20
30
40
50
Days after induction of knockout
Sjögren K, Ohlsson C
et al, PNAS 1999
Modified somatomedin (IGF-1)
hypothesis
Green et al, 1985
The local
actions of
GH within
the growth
plate require
Needed
the for growth:
1. presence
Direct GHofeffect.
and
IGF-1
GH
GH
GH-R
Prechondrocyte
IGF1 mRNA
Differentiation
Early chondrocyte
IGF1
Clonal expansion
Epiphyseal
growth
plate
2. IGF-1 (liver or
local)
•
IGF-1 can not
replace GH if GHD.
• GH no effect in Long bone
IGF-1 knockout mice
IGF1
Maturing
chondrocytes
Revised GH action on bone
GH actions to stimulate
bone growth are direct on
the bone.
The effects are partly
mediated by local IGF-1.
GH
GH
IGF-1
IGF-1
GH receptor dimerization for
biological effect
GH
GH
receptor
inactive
inactive
active
GH antagonist
(pegvisomant,
No proper dimerisation)
inactive
GH Receptor signaling:
Active STAT dimer to nucleus
GH
GH
receptor
P
JAK2
P
Nucleus
Nucleus
STAT5b
Phosphotyrosine
Binding domain
STAT : signal transducer and
activator of transcription
Serum IGF-1 levels determine sizes of dog
breeds
IGF-I
IGF-I
IGF-I
IGF-I
IGF-I
Polymorphism near IGF-I
gene associated with
body size of dog breeds
Comparisons between
IGF-1, IGF-2, and insulin
The ligands bind mainly
to their own receptors ,
but also to others with
lower affinity
Scavenger receptor?
* Insulin- and IGF-I–
Receptors 
Biological signaling
* IGF-II Receptors 
Scavenging of ligand.
Derek LeRoith NEJM 1997
The insulin-like growth factor (IGF) system
ALS
ALS
IGF-I
insulin
IGFBP-1
IGFBP-2 IGFBP-3 IGFBP-4 IGFBP-5 IGFBP-6
IGF-II

IGFBP-3 – ALS binds
most of all IGF-1 in serum.
IGFBP proteases
P
P
P
P
IGF-IR
P
P
P
P
Insulin-R
IGF-IIR
Courtesy of Dr Ricarda Granata
Interactions between IGF-1, IGF-BP3, ALS and BP3
protease
BP3 Protease (=Prostate
Specific Antigen PSA)
IGF-BP3
IGF-1
Rec
IGF-1
ALS
ALS: “acid labile subunit”
(old term)
Beware of IGF-1? 1): tumors
IGF-1 stimulated proliferation
 IGF-1 inhibits apoptosis.
 In epidemiologic studies: High S-IGF-1 predictor
of breast cancer, prostate cancer, colon cancer…
Low S-IGF-BP3 predictor of cancer.
PSA (IGF BP3 protease) a clinical marker of
prostate cancer
IGF-1 is still approved by FDA for the indication
Low growth in children, irrespective of cause. Caution!
Beware of IGF-1? 2) longevity.
↑ Longivity
2/3 ↓ food
intake
Genetic
growth
defects
?
↓GH effect
↓ S-IGF-1 &
insulin
Animals with ↓ IGF-1 that all live longer (15-30%!)
1) Semi-starved animals, 2) Growth mutants (GHRH-/- (Little) mice, ames
dwarf mice, GHR-/-, IGF-1+/- etc.)
Body growthGH - IGF-1 axis pathology
Gigantism
Excessive GH production
in childhood, or before the
epiphyseal growth plates
have fused
Dose-response 110-270 cm!
Cause:
Pituitary tumour that
start from a
somatotrophic cell.
Acromegaly
Excessive GH production
in adulthood after the
epiphyseal growth plates
have fused. Growth of
“the tips of the body”.
Cause:
Pituitary tumor that
starts from a
somatotrophic cell.
Clinical features of acromegaly
Large nose
Thick lips
Growth of
mandible
Prominent
cheek bones
Osteoarthritic
vertabral changes
Enlarged
hand &
feet
Visual field
defects
(bitemporal
hemianopia)
Hirsutism
Barrel chest
Often caused by
Lack of GTPase
activity in G-protein
(see next slide)
Excessive
sweating
Molecular cause of acromegaly in a
somatotroph
40% of acromegaly
in Europeans.
GHRH receptor
Active
Inactive
GsGDP
GDP
GTP
XGTPase
P
GsGTP
+
Adenylate
cyclase
cAMP
Arg201 in G-protein changed 
No dephosphorylisation by GTPase  No signal termination 
1 GH prod, 2 GH release, 3 Somatotroph proliferation
Kända genetiska defekter med proportionerliga
tillväxtrubbningar
• Pit-1 defekt. Snell (dw/dw) Anläggning GH, TSH, PRL celler.
Prop-1 ”Prophet of Pit” defekt. Ames (df/df) GH, TSH, PRL +LH +FSH
Dvärgmöss, Master genes. Människor också.  Livslängd??
• GHRH receptor gen ”little” mus. Människor Bangla Desh, Sydamerika.
• GH gen. Antikroppar mot GH!
• GH receptor gen. Laron dvärgar. IGF-1 behandlig delvis effektiv.
• STAT5b gen. IGF-1 behandlig delvis effektiv.
• IGF-1 gen. Mental retardation, hörselpåverkan. IGF-1 behandling.
• IGF-1 receptor gen. Som IGF-1 defekt. Ej effekt av IGF-1.
• (Fibroblast growth factor-receptor 3 (FGFR3) gen. Achondroplasi, korta armar
och ben, alltså EJ proportionerlig.)
Monogenetic causes of
dwarfism: Defective GH axis
Ghrelin-R
Mutation?
somatostatin
GHRH
Defective development
of somatotrophs
GHRH-R
Defective GH gene
GH-R
Mutation
GH
GH-R
 IGF-1
synthesis & release
GHRH-R
Mutation
“Little”
Dwarfism
Laron Dwarfism
IGF1-R mutations
IGF-1
Target organs
IGF1-R
Dwarf mice and human equivalents:
defective pituitary master genes
GH
Stem cell
PRL
Stem cell
TSH
LH, FSH
Prop-1
Defect:
Ames Dwarf mice
Human dwarfs
(Krk)
Pit-1
Defect:
Snell Dwarf mice
Human dwarfs
Pit-1 :
1. Mediator of GHRH effect
on GH production postnatally
2. Inducer of pituitary
development prenatally
Defect earlier in development,
(e g Prop-1 instead of Pit-1)
 More hormones lacking.
Evidence that the GHRH-receptor, and not downstream pathways, is nonfunctional in dwarf “little”
mice
GHRH
Forskolin
40
G-prot
AC
cAMP
GH secretion
(% of cell
content)
Little mice
Wild type
30
Cholera toxin
20
GH Secretion
10
Control
dbcAMP
Forskolin Cholera toxin
GHRH
GH secretion from pituitaries of Little mice is decreased after GHRH compared to Wild type mice.
In contrast, stimulation of the down stream G-protein –adenylate cyclase (AC) – cAMP signal
pathway by cholera toxin, forskolin or dbcAMP can all stimulate GH secretion in little mice
(Adapted from Jansson et al Science 1986)
Dwarfism due to mutations
of human GHRH receptor
little mouse
-/- and -/+ littermates
Brazil (intron 1 splice donor)
Little mouse
AspGlu
P
H
H M
E
C
D
F
I
Effect of Sindh
Mutation (AlaGlu)
T
P
V
P C A V
P Y
P
L
E
L
L
A
E
E
E
S
Y
F
S
T
V
K
I I Y
H GV T
S I S
L AV I
FVA
L I T I
VA L
R
R L
Leu
His
Spain
USA
D
S
H
F
L
A
A
D
K
LF
GRV
AK L
T F I
T F L
H T Q
V
LY N
R
P
H C
E
Q L R E D
P
F
D T D H
P
L
G C P A T
T T L
W
P N
D
M
E
G
A E
A
L
Q
D
I
A C WD
E
F
A
L
K
CS V
T GT W
F L V
GL P
WG A
WLV L
WFA
R
R
S
S
A
S T S P
S
G
W
Glu Stop
L
D
D
T
S
P
Glu Phe Cys
USA
L
C
W
P
E
V
GS E
T
S S F H
S F F D P CPL
L G I
R
G
A
L
N
P
D
L
Y WW
E LG
P L
F NF
GK I I
SGL
P I V
F QG
I I Y
GV S L
V I F
GI H
VN F
A I L
F LP
Y F L G
FCY
L
F L I
LT S
N I I
L NQ
R
K
E
I
S
V
L
L
R
V
R
T
R
E
W
K
I
Y
L
S
Q
E
R
P
S
K
Q
A
W
Q
C MS T L
G S L H T
H
V KA
A S R
G
S P T
H
T W
D
KA R
T RW A P L L E P
Pakistan
Little mouse
T
A
G
Sindh
T C
DR
KV
A
C
S
F
S
T
V
L
C
K
V SV
HS AA
F A T
FN TM
S
SWL
A EA L
V YL
N
C
L
L
Ala
COOH
C
S A
E S
WG
T I
Gly
Asp
NH2
D4
Japan
GH receptor deficiency
(Laron dwarfism)
GH
X X
GH
receptor
inactive
• GH treatment ineffective
• IGF-1 only small effect
(lack of cells with IGF-1 rec
in growth plate when no GH?)
IGF-1 and IGF-1 receptor deficiency
IGF-1 gene defect
Intrauterine
growth defect
IGF-1 receptor gene defect
Intrauterine
growth defect
Chernausek
Chernausek SS et
et al
al NEJM
NEJM 2003
2003
Woods
Woods KA
KA et
et al
al NEJM
NEJM 1996
1996
Causes of dwarfism unrelated to GHIGF axis
• Thyroid hormone deficiency in childhood (Cretinism).
Retardation of mental development & growth.
Thyroid hormones are permissive for growth.
• Excess glucocorticoids - stunts growth.
Glucocorticoids are permissive for growth, but inhibitory
in high doses.
• Genetic diseases:
Pygmy mouse, HMGA2 (high-mobility group A2), a
transcription factor for e g cycline A.
Human SNP 0.5 cm height.
 Achondroplasia (next slide)
Achondroplasia: Selective shortening of
long bones in dogs and humans.
Diego Velázquez (1599-1660).
Museo del Prado, Madrid
Not responsive to GH or IGF-1 treatment.
Hypothesis: Gain of function mutation in fibroblast growth
factor receptor-3 (FGFR-3). FGFR3 prevents stem cell
proliferation and differentiation.
(Autosomal dominant disease. Logical.)
Transmembrane mutation G380A causes
over-activation of FGFR3
1. Constitutive dimerisation and activation of
50% of FGFR3.
(Stronger signal.)
2. Less degradation by
lysosomes
↓
 Inhibition of stemcell
proliferation and
differentiation
(Horton WA 2006,
Growth Genetics &
Hormones. Vol 4)
Summary
•
Prenatal, postnatal and pubertal body growth is
regulated by different hormons.
•
Postnatal longitudinal body growth is regulated by a
hypothalamus – pituitary – liver – bone axis.
•
GH is dibetogenic and lipolytic in addition to
growth promoting.
•
GH- IGF-1 is axis regulated by feeding, amino acids,
lipids and glucose.
•
GH- IGF-1 in relation to tumor growth is a
concern, but few alarming data at present.
•
Dwarfism can be due to defects of various hormones
and receptors in the GHRH - GH- IGF-1 – FGFR3 axis. Diagnos
for right treatment.
Effects of GH and IGF-1 on different nutrients
_
GH
TÄNK IGENOM!
BRA ATT HA MED??
FÖRE FASTEBILDEN?
 Growth/Protein
anabolism 
 B-glucose 
 Lipolysis

IGF-1
+
+
+
Nutrition
GH and IGF-1 both stimulate growth, but have different effects
on fat and sugar.
Elevated GH following ectopic GHRH
secretion
Plasma GH and GHRH in acromegaly
GH
40
30
ng/ml
20
10
GHRH
10.00 14.00 18.00 22.00 02.00 06.00
Hours
Vance et al, 1985
Ghrelin treatment elevates pulsatile GH secretion
in the elderly
However: Uncertain if endogenous ghrelin is important for GH secretion
in humans. (Not important in mice. Ghrelin KO mice normal growth.)
Molecular cause of acromegaly
Arg201 in G-protein changed 
GTP hydrolysis activitity disrupted. 
No signal termination 
G-protein-alpha-GTP and adenylate
cyclase (AC) remains active.  cAMP 
• Somatotroph growth
• GH prod
• GH release.
(GTPase)
Active AC
cAMP
Cause of 40% of acromegaly
in Europeans.
(Cholera Toxin ADP-ribosylates Arg201
 GTPase activity in gut: diarrhoea.)
little mouse
-/- and -/+ littermates
-NH2
Asp60 to Gly
% of Maximum cAMP
100
Wild-Type
80
60
40
20
little
0 l
0 10 -10
10 -9
10 -8
10 -7
10 -6
Concentration of Mouse GHRH (M)
COOH-
Courtesy of Dr Kelly Mayo
Northwestern University
Chicago
GH Receptor signaling II
P
P
Nucleus
STAT3 with phosphotyrosines forms dimer and
goes to the nucleus