Download Gn-RH-R - FertilityCenter

Seconda Università degli Studi di Napoli
Dipartimento di Scienze della Vita
SUNfert
Gn-RH
and
Gn-RH receptors
Fertility Center Cardito
Dr. Vincenzo Volpicelli
Hypothalamic anatomy
 Hypothalamus is a pars of
diencephalon
 Under thalamus
 Is floor of the third ventriculus
Hypothalamic anatomy
Optic Chiasm
 Mammillary bodies
 Median eminence
 Infundibulum

Neurotransductor effects
on Gn-RH release
Legenda: b- END = b-endorfine; CRF = Corticotropin Releasing Factor; OT = Somatostatina; DA = Dopamina; GABA = Acido g-AminoButirrico; ACh = Acetilcolima; NPY = Neuropeptide Y; NA = Noradrenalina
leptine
 Modulates NY

 Gn-RH secretion
Leptin bioactivity
Leptine
ng/ml
leptine serum levels
16
14
12
10
8
6
4
2
0
1
3
6
9
12
15
cycle days
18
21
24
27
30
medial eminence (ME)
ventromedial nucleus
(VM)
Hypothalamic
arcuate nucleus (AR)
nuclei
hypothalamic nuclei
Region
Medial Area
Lateral Area
Anterior
Medial preoptic nucleus
Supraoptic nucleus
Paraventricular nucleus
Anterior nucleus
Suprachiasmatic nucleus
Lateral preoptic nucleus
Lateral nucleus
Part of supraoptic nucleus
Tuberal
Posterior
Dorsomedial nucleus
Ventromedial nucleus
Arcuate nucleus
Mammillary nuclei (part of
mammillary bodies)
Posterior nucleus
Lateral nucleus
Lateral tuberal nuclei
Lateral nucleus
Hormones of the hypothalamus
o Corticotropin-releasing hormone (CRH)
o Dopamine (DA)
o Gonadotropin-releasing hormone (Gn-RH)
o Growth hormone releasing hormone (GH-RH)
o Somatostatin (ST)
o Thyrotropin-releasing hormone (TRH)
o Antidiuretic Hormone (ADH)
Gn-RH
Human
Luteinizing
hormone-releasing
hormone gene (LH-RH) is located on short
arm of chromosome 8 (region 8p11.2 → p21) *

Gn-RH neurons are inside the mediumbasal hypothalamus (arcuate nucleus and
median eminence)

Lately scientists showed Gn-RH syntesis
in pituitary gland too.
Teresa L. Yang-Feng, Peter H. Seeburg and Uta Francke: Somatic Cell and Molecular
Gn-RH
 Gn-RH is considered a neurohormone
 produced in a specific neural cell and released at its neural terminal
 A key area for production of Gn-RH1 is the preoptic area of the
hypothalamus, that contains most of the Gn-RH1-secreting neurons.
 Gn-RH1 is secreted in the hypophysial portal bloodstream at the
median eminence
 The portal blood carries the Gn-RH1 to the pituitary gland, which
contains the gonadotrope cells, where Gn-RH1 activates its own
receptor, gonadotropin-releasing hormone receptor (Gn-RH-R),
located in the cell membrane
Gn-RH
 Gn-RH
neurons are closely
connected with noradrenergic,
dopaminergic, serotoninergic,
oppioid ones.
Gn-RH frequency
•Low frequency Gn-RH pulses lead to
FSH release
•high frequency Gn-RH pulses
stimulate LH release
Gn-RH-r
 Gn-RH-r is a member of the seven-transmembrane,
G-protein coupled receptor (GPCR) family
 It is expressed on the surface of pituitary gonadotrope
cells*
* as well as lymphocytes, breast, ovary, and prostate
Gn-RH-r Function
 Following binding of Gn-RH activate a
phosphatidylinositol (PtdIns)-calcium second
messenger system.
 Activation of GNRH-r ultimately causes the
release of FSH and LH
Gn-RH
 Gn-RH is considered a neurohormone
 produced in a specific neural cell and released at its neural terminal
 A key area for production of GN-RH1 is the preoptic area of the
hypothalamus, that contains most of the GNRH1-secreting neurons.
 GN-RH1 is secreted in the hypophysial portal bloodstream at the
median eminence
 The portal blood carries the GN-RH1 to the pituitary gland, which
contains the gonadotrope cells, where GN-RH1 activates its own
receptors, gonadotropin-releasing hormone receptors (GN-RH-R),
located in the cell membrane
Gn-RH

Gn-RH neurons are closely connected
with noradrenergic, dopaminergic,
serotoninergic, oppioid ones.
Males/females Gn-RH secretion
• in males, Gn-RH1 is secreted in pulses at a
constant frequency
• in females the frequency of the pulses varies
during the menstrual cycle
• there is a large surge of GNRH1 just before
ovulation
Proteolysis
Gn-RH is degraded by
proteolysis within a
few minutes
 Proteolysis is the
directed degradation
(digestion) of
proteins by cellular
enzymes called
protease or by
intramolecular
digestion.
Control of FSH and LH
At the pituitary, Gn-RH1 stimulates
the synthesis and secretion of FSH
and LH
These processes are controlled by:


the size and frequency of Gn-RH1 pulses,
feedback from androgens and estrogens
Gn-RH-R Function
Following binding of Gn-RH activate a
phosphatidylinositol(PtdIns)-calcium second
messenger system.
Activation of Gn-RH-R ultimately causes the
release of FSH and LH
receptors
 Hormones and active metabolites bind to
different types of receptors. Water-soluble
molecules (i.e., insulin) cannot pass through the
lipid membrane of a cell and thus rely on cell
surface receptors to transmit messages to the
interior of the cell. In contrast, lipid-soluble
molecules (i.e., certain active metabolites) are
able to diffuse through the lipid membrane to
communicate messages directly to the nucleus
Gn-RH-R
Gn-RH-R
is
transmembrane,
(GPCR) family.
a member of the sevenG-protein coupled receptor
It is expressed on the surface of pituitary
gonadotrope cells*
* as well as lymphocytes, breast, ovary, and prostate.
Gn-RH biochemistry
a decapeptide (10 amino
acids) in mammals.
This chain is represented
by: pyroGlu-His-Tyr-SerGly-Leu-Arg-Pro-Gly-NH2
previously called LH-RH
The identity of GN-RH1 was
clarified by the 1977 Nobel
Laureates Roger Guillemin and
Andrew V. Schally
Gn-RH
Gn-RH is considered a neurohormone
produced in a specific neural cell and released at its neural terminal.
A key area for production of Gn-RH1 is the preoptic area of the
hypothalamus, that contains most of the Gn-RH1-secreting neurons.
Gn-RH1 is secreted in the hypophysial portal bloodstream at the
median eminence.
The portal blood carries the Gn-RH1 to the pituitary gland, which
contains the gonadotrope cells, where Gn-RH1 activates its own
receptor (Gn-RH-R), located in the cell membrane.
Gn-RH neural junctions

Gn-RH neurons are closely connected
with:




noradrenergic,
dopaminergic,
serotoninergic,
oppioid ones.
Gn-Receptors
 Upon binding Hormone externally to the
membrane, a transduction of the signal
takes place that activates the G protein
 that is bound to the receptor internally
Gn-Receptors
 With Hormone attached, the receptor
shifts conformation
 mechanically activates the G protein,
which detaches from the receptor and
activates the cAMP system.
G Protein System
Alfred G. Gilman
and
Martin Rodbell
received the 1994 Nobel Prize in
Medicine and Physiology for the
discovery of the G Protein System
Gn-RH-R Function
 Following binding of Gn-RH activate a
phosphatidylinositol (PtdIns)-calcium second
messenger system.
 Activation of Gn-RH-R ultimately causes the
release of FSH and LH
Gonadotropin-releasing
hormone receptor
 Gn-RH-R is a member of the seven-
transmembrane, G-protein coupled
receptor (GPCR) family.
 It is expressed on the surface of pituitary
gonadotrope cells*
* as well as lymphocytes, breast, ovary, and prostate.
The seven transmembrane α-helix structure of
a G protein-coupled receptor
hormone receptor*
 I° messenger: hormone
 Hormone + Receptor
G-Protein activation:
•Adhesion H-R complex
•Scission H-R complex
•Subunit a production
* A protein on the surface of a cell to which a specific hormone binds
hormone receptors
 a subunit activates

 intracellular effectors (enzymes)
 adenyl-ciclases  cAMP
(II° messenger) guanil-cyclase  cGMP
phospholipase  DAG*, IP3 *
 ionic ducts
 (K+ , Ca++)
*Diacilglicerolo, Inositolo trifosfato
PO4 by cAMP-dependent PKA
 II°
messenger

activates Protein kinasi (PKA)

activates Phosphorylation (PO4) of:
•citoplasmatic protein
•nuclear transcription factors (cAMP
Responsive Element Binding Protein,
CREB).
DNA transcription
CREB
modulates
transcription of genes
interacting directely with
specific DNA string
hormone receptors
Control of FSH and LH
 At the pituitary, Gn-RH1 stimulates the
synthesis and secretion of FSH and LH
 These processes are controlled by:



the size and frequency of GN-RH1 pulses
feedback from androgens and estrogens
Gn-receptors wholeness
Control of FSH and LH
•Low frequency Gn-RH pulses lead to
FSH release
•high frequency Gn-RH pulses
stimulate LH release
Gn-RH secretion males/females
in males, GN-RH1 is secreted in pulses at a
constant frequency
• in females the frequency of the pulses varies
during the menstrual cycle
• there is a large surge of GN-RH1 just before
ovulation
Gn-RH proteolysis
 Proteolysis is the
Gn-RH is degraded
by proteolysis
within a few
minutes
directed degradation
(digestion) of
proteins by cellular
enzymes called
protease or by
intramolecular
digestion.
Gn-RH-a
A
gonadotropin-releasing
hormone
agonist (GnRH agonist) is a synthetic
peptide modeled after the hypothalamic
neurohormone GnRH that interacts with
the gonadotropin-releasing hormone
receptor to elicit its biologic response,
the release of the pituitary hormones
FSH and LH
Gn-RH-a
Aminoacid sequence
name
act
Gn-RH
1
Leuproreline*
Buserelin * *
15
20
triptor * * *
Goserelin* * * *
1
Pyroglu
2
His
3
Trp
4
se
ro
to
nin
5
6
10
for
Leu
GlyNH2
iv
D-Leu
NEtNH2
sc, im
NEtNH2
sc, im
Tyr
7
Leu
D-Ser
8
Arg
9
Pro
D-Trip
100
D-Ser
sc, im
AzGlyNH2
* Enantone 3.75, 11.25 mg fl s.c. im; Enantone die 1 mg/die (0.2 ml) fl s.c.;
* * Suprefact 5.5 ml fl s.c.; Suprefact spray nasale 10 gr (1 buff = 200 mg)
* * * Decapeptyl 3.75, 11.25 mg fl s.c. im; Decapeptyl die 0.1 mg fl s.c.
* * * * Zoladex 3.6, 10.8 mg fl s.c. im
Triptorelin is an agonist with only a single substitution at position 6.
depot sc
Gn-RH-a administration mode
 These medications can be administered
 intranasally,
 by injection,
 or by implant.
 Injectables
have been formulated for daily,
monthly, and quarterly use; and implants can last
from 1 to 3 months.
Gn-RH-a Downregulation
 after their initial stimulating action – termed a
“flare” effect -, eventually caused a paradoxical
and sustained drop in gonadotropin secretion.
 This second effect was termed “downregulation”
and can be observed after about 10 days.
 While this phase is reversible it can be
maintained with further GnRH agonist use for a
long time.
Gn-RH-a Downregulation
 refers to the decrease in the number of receptor sites.
 This can be accomplished by metabolizing bound LH-R
sites.
 The bound LCGR complex is brought by lateral migration
to a “coated pit” where such units are concentrated and
then stabilized by a framework of clathrins.
 A pinched-off coated pit is internalized and degraded by
lysosomes. Proteins may be metabolized or the receptor
can be recycled. Use of long-acting agonists will
downregulate the receptor population.
Gn-RH-a Desensitization
 The LH-Rs become desensitized when exposed to LH for
some time.
 A key reaction of this downregulation is the
phosphorylation of the intracellular receptor domain by
protein kinases
 This process uncouples Gs protein from the LH-R
 Another way to desensitize is to uncouple the regulatory
and catalytic units of the cAMP system.
Gn-RH antagonist
 GnRH antagonists are also derivates of the natural GnRH
decapeptide with multiple amino acid substitutions
 A gonadotropin-releasing hormone antagonist (GnRH
antagonist) is an analogue that blocks the GnRH receptor
resulting in an immediate drop in gonadotropin (FSH, LH)
secretion
 The Gn-RH antagonist is primarily used in IVF treatments
to block premature surge of LH
Gn-RH antagonist
 These substitutions modify the agent so that it
blocks the receptor and decreases FSH and LH
secretions within hours
 In contrast to GnRH agonists, antagonists have
no flare effect, thus their therapeutic effect is
immediately apparent
 However, their action is short-lived and daily
injections are necessary to maintain their effect
Gn-RH antagonist
 Typically endogenous FSH and LH activity returns
about 40 hours after cessation of GnRH
antagonist administration, although with a higher
dose the return to normal pituitary function will be
postponed for longer.
 Unlike the GnRH agonists, long acting or depot
forms of the agent are not currently available, thus
GnRH antagonists are not used in the long term
therapy
receptors activation
a
receptor
molecule
exists
in
a
conformational equilibrium between active
and inactive states.
 The binding of LH (or FSH) to the receptor
shifts the equilibrium between active and
inactive receptors.
 Gn-RH-a shift the equilibrium in favor of
active states;
 Gn-RH antagonists shift the equilibrium in
favor of inactive states.
THE END