34. Biochemistry of Male Reproductive Hormones
Dangers of AAS by NIDA
stunt growth in adolescents reduced sperm count -- lower gonadotropins baldness -- andro receptors in skin breast development -- testosterone converted to estrogen changes in menstral cycles --> inhibits FSH and LH Deepened voice Reduction in HDLs
Dangers of AAS by NIDA con't
•Hormonal system disruptions. Reduced sperm production, shrinking of the testicles, impotence, and irreversible breast enlargement in boys and men. Decreased body fat and breast size, deepening of the voice, growth of excessive body hair, loss of scalp hair, and clitoral enlargement in girls and women. •Musculoskeletal system effects. Premature and permanent termination of growth among adolescents of both sexes. •Cardiovascular diseases. Heart attacks and strokes. •Liver diseases. Potentially fatal cysts and cancer. •Skin diseases. Acne and cysts. •Infections. In injecting steroid abusers, HIV/AIDS, hepatitis B and C, and infective endocarditis, a potentially fatal inflammation of the inner lining of the heart. •Behavioral effects. Increased aggressive behavior, particularly when high doses are taken. Depression, mood swings, fatigue, restlessness, loss of appetite, and reduced sex drive when steroid abuse is stopped.
*Describe the role of Sertoli cells.*
*FSH stimulates Sertoli cells* Sertoli cell proliferation and differentiation *ABP / SHBG* Spermatogenesis Aromatase Enzyme Inhibin-B --> Inhibits FSHβ subunit
GnRH and Puberty
*Increased GnRH hallmark of puberty* KiSS-1 neuron in arcuate nucleus (Arc) and anteroparaventricular nucleus (AVPV) releases KiSS-1 peptide (aka kisspeptin-10 or metastin) KiSS-1 peptide stimulates GnRH release from GnRH neuron. Kiss-1 peptide binds to GPR54 in GnRH neuron GPR54 is a G-protein coupled receptor.
*Know the key enzymes in the general biosynthetic pathway for sex steroid hormones.*
*P450scc, StAR*: Cholesterol to Pregnalone *3βHSD*: Pregnalone to Progesterone *P450c17* (CYP-17): Progesterone to 17-α Progesterone *P450c17* (CYP 17): 17-α Progesterone to Androstenedione *17βHSD*: Androstenedione to testosterone --*5α reductase*: testosterone to super testosterone (DHT) [cannot be turned into estrogen] OR --*CYP19 (aromatase)*: testosterone to estradiol-17β
*Define anabolic androgenic steroids and identify the consequences of their overuse in adolescents, men and women.*
*Reduced gonadotropins* Reduced sperm production, shrinking of the testicles, impotence, and irreversible breast enlargement in boys and men. Decreased body fat and breast size, deepening of the voice, growth of excessive body hair, loss of scalp hair, and clitoral enlargement in girls and women. •Premature and permanent termination of growth (adolescents) •Cardiovascular diseases •Liver diseases. Potentially fatal cysts and cancer. •Skin diseases. Acne and cysts. •Infections (In injecting steroid abusers) •Depression, mood swings, fatigue, restlessness, loss of appetite, and reduced sex drive when steroid abuse is stopped.
Hormone actions in the Testes
1. LH stimulates differentiation of Leydig cells & testosterone synthesis 2. *High intratesticular testosterone essential for spermatogenesis* Maintains germinal epithelium *SHBG maintains high intratesticular testosterone* (How?) 3. *FSH stimulates Differentiation of Sertoli cells, ABP (SHBG)*, inhibin-B, estradiol Factors for spermatogenesis: cytoskeletal element, transferrin Antimullerian hormone after birth In utero SOX9 stimulates AMH and regression of mullerian ducts*** 4. Germ cells express P450 aromatase. Epididymis and Ledyig cells express ER's
Which Androgens can NOT be converted to Estrogen?
5-alpha dihydrotestosterone Does not have an oxidized A ring
Sex steroid nuclear receptors and carrier proteins
> 1 Estrogen receptor, differ in transactivation domain, *can be selectively estrogen receptor modulated* (SERM) -- can have many different effects > 1 Progesterone receptors, differ in transactivation domain. 1 Androgen receptor (encoded on X-chromosome) Estrogen and Testosterone bind SHBG with different affinities (KD T < KD E) Estrogen + SHBG production (liver) Testosterone - SHBG production (liver) Testosterone/FSH + SHBG (aka ABP) production (Sertoli cell)
*Recall the causes and consequences of hypo-gonadism in men.*
A defect in the secretion or actions of testosterone. 1o Hypogonadism Defect in testes in testosterone synthesis or action e.g. androgen receptor 2o Hypogonadism Defect in pituitary 3o Hypogonadism Defect in hypothalamus
Male Hypogonadism
A defect in the secretion or actions of testosterone. 1o Hypogonadism Defect in testes in testosterone synthesis (SIP 17 = no androgens) or action e.g. or defect in androgen receptor 2o Hypogonadism Defect in pituitary 3o Hypogonadism Defect in hypothalamus
Testosterone Feedback Inhibition
Action on Hypothalamus *Testosterone inhibits GnRH release* By decreasing KiSS-1 peptide Action on Pituitary via 17β-estradiol *Testosterone converted to 17β-estradiol* *17β-estradiol inhibits FSH and LH* DHT no effect on Pituitary
Sex Steroid Intracrinology
Adrenal Gland (zona reticularis) Most abundant steroid except during pregnancy
*Sex hormone binding protein is the same as what?*
Androgen binding protein (ABP)
Metabolism of Testosterone
Androgens are estrogen precursors. Except DHT Estrogens 1,000X more potent than androgens Pubital growth spurt in men is due to estrogens
Biosynthesis of Androgens con't
Androgens precursors for Estrogens Must have oxidized A ring
Biosynthesis of Estrogens
Androgens precursors for Estrogens Must have oxidized A ring Androgen to Estrogen 19C to 18C Aromatic A ring Aromatase enzyme (CYP19) Estrone (carbonyl in D ring) From androstene dione 17β estradiol (alcohol in D ring) From testosterone DHT A & B rings reduced Can't be converted to estrogen
Sex Steroid Intracrinology Active Hormones
Binds receptors very well
*Recall the major actions of the Estrogen hormones in men.*
Brain -- Regulate GnRH, LH, FSH Stimulates GH Testes -- germ cell development? Bone -- Responsible for the pubertal growth spurt but also bone plate fusion, and inhibit bone erosion.
*Know the general biosynthetic pathway for sex steroid hormones.*
Cholesterol --> Pregnalone --> Progesterone --> 17-α Progesterone --> Androstenedione --> testosterone --> DHT [cannot be turned into estrogen] OR estradiol-17 Beta
*Biosynthesis of Sex Steroids*
Classify by # Carbons Rate-limiting Cholesterol to Pregnenolone P450scc, StaR Pregnenolone to Progesterone 3β hydroxysteroid dehydrogenase (3βHSD) oxidation of A ring Progesterone precursor for sex steroids.
Intacrinology of Sex Steroids
Conversion of sex steroids in peripheral target tissues from precursor steroids. Sex steroid producing tissues --Adrenal gland (Men and Women) --Testes (Men) --Ovary (Women) Peripheral Tissues Adipose (men and women) Brain Bone Skin Breast, Reproductive Tract Placenta Even in gonads, conversion of sex steroids in "peripheral" cells Male: Sertoli cells, Leydig cells, prostate, developing germ cells Female: Granulosa cell-Thecal cell
5α reductase (chromosome 2)
Converts testosterone to super testosterone (5-alpha dihydrotestosterone)
Function of Testosterone in development, puberty and adulthood
During *embryonic development* for normal development of the gonads in the male fetus. During *puberty* for initiation of sperm production, accessory gland secretion and development of secondary sex characteristics. During *adulthood* for maintenance of spermatogenesis, secondary sex characteristics and excurrent and accessory gland function.
What does Estrogen do to SHBG production in the liver?
Estrogen stimulates SHBG production (liver)
Major Function of Estrogens in Men
FSH --> sertoli cells Only cells with FSH receptor Estrogens are also made in brain cells, Fat cells, sperm cells, and bone cells.
Effects of FSH on Sertoli cells
FSH stimulates: Sertoli cell *proliferation and differentiation* (testicular size) Proteins for germ cell development Transferrin iron transport Cytoskeletal elements Androgen Binding Protein (ABP) Aka Sex Hormone Binding Globulin (SHBG) 17β-estradiol Aromatase Enzyme *Inhibin-B* -- index of spermatogenesis Inhibits FSHβ subunit --Transcription & Secretion Index of spermatogenesis
Testosterone Maintains Secondary Sex Characteristics
Facial, axillary, pubic hair Muscle mass, especially in shoulders "male" body habitus, broad shoulders Male pattern baldness (androgenic alopecia)
*Know the rate-limiting step of the biosynthetic pathway for sex steroid hormones .*
First step is side-chain removing step, it is the rate-limiting step. Cholesterol --P450scc,STaR--> Pregnalone
Why is *ABP / SHBG* in the intratesticular cells so important?
High levels of ABP / SHBG in the epithelium of the seminiferous tubules leads to High Intratesticular testosterone. Testesterone enters, is bound does not reach equilibrium with blood --> more testosterone enters. Need high testosterone for spermatogenesis
Steroid Hormone Action through Nuclear Receptors
Hormone-receptor complex regulates gene transcription +/- gene expression *Only free hormone enters cell* -- cannot be bound to carrier protein Steroid hormones bound to carrier protein Sex hormone binding globulin (SHBG aka ABP) regulate amount of free testosterone that enters cell.
*Recall the rationale for male hormonal contraceptives.* *Progestins*
How would *progestins* effect the male reproductive system? Bad -- works at level of hypothalamus, knocks everything out -- cannot maintain reproductive organs
What does testosterone and FSH do to SHBG (aka ABP) production in the testes?
Testosterone/FSH stimulates SHBG (aka ABP) production (Sertoli cell)
*Recall the rationale for male hormonal contraceptives.* *Supplemental Testosterone*
How would *testosterone* effect male reproductive system? Good -- Also works at level of hypothalamus, Eliminates ABP's (no spermatogenesis), would knock out leydig cell production of testosterone *BUT* the testosterone administered would make up for that, maintaining the reproductive organs
Male Hormonal Contraceptive Goal: Inhibit Sperm Production 2
How would progestins (analog of progesterone) effect the male reproductive system? Bad. It would "shut everything down", because it works at the level of the hypothalamus. No GnRH --> no FSH --> No spermatogenesis or LH --> not able to maintain male reproductive organs, no libido
Male Hormonal Contraceptive Goal: Inhibit Sperm Production 3
How would testosterone effect male reproductive system? Inhibit GnRH -- Inhibit FSH and LH --> no ABP (SHBG) --> no spermatogenesis --> would maintain reproductive organs Spermatogenesis requires high intratesticular testosterone. Intratesticular levels 50-100X levels in peripheral blood.
What stimulates leydig hormones in fetus? In Puberty?
Human Chorionic Gonaotropin (hCG) in fetus LH in puberty
*Describe the regulation of testosterone in Leydig cells.*
Hypothalamus: Testosterone inhibits GnRH release By decreasing KiSS-1 peptide Pituitary: Testosterone aromatized to 17β-estradiol 17β-estradiol inhibits FSH and LH *DHT no effect on Pituitary*
*CYP21 Defect*
In supplementary material
Overview of Male Endocrine System
Increased GnRH hallmark of puberty KiSS-1 peptide (aka metastin or kisspeptin-10) stimulates GnRH *Pulsatile GnRH stimulates FSH/LH* *LH pulsatile b/c short half life* *FSH not pulsatile b/c long half life* GnRH receptor in AP Gαq/phospholipase C/IP3/PKC/Ca2+ Transcription/secretion LHβ and FSHβ *Continuous GnRH inhibits FSH/LH* *Down regulates GnRH receptors and calcium channels.*
Male Endocrine Secretory Patterns
Increased GnRH triggers puberty onset. LH pulses follow GnRH pulses LH stimulates testosterone At Puberty, diurnal rhythm Nightly increases in GnRH/LH/testostosterone. Adulthood, ultradian pulses of GnRH and LH occur throughout the day.
*What happens if there is a defect in P450c21?
It causes a build up in 17-α Progesterone, which is a substrate for Androstenedione --> sex hormones (masculinization)
Progesterone in Men
LH --> leydig cells ACTH --> adrenal gland
Major Function of Androgens in Men
LH --> testosterone made in leydig cells ACTH --> DHEA in adrenal gland
Male Endocrine Signals in the Testes con't
LH stimulates Leydig cell (~puberty) *growth and differentiation of leydig* testosterone synthesis expression of steroid transforming enzymes such as 17βHSD especially P450c17 SER T estosterone converted to DHT in target tissue by 5α reductase II (prostate, reproductive organs) Testosterone stimulates 5α reductase II Testosterone stimulates Development of epididymis, vas deferens, seminal vesicle Growth and differentiation of external genitalia (dihydrotestosterone) Descent of the testes (inguinoscrotal phase)
Male Endocrine Signals in the Testes
LH stimulates Leydig cell (~puberty) growth and differentiation testosterone synthesis expression of steroid transforming enzymes such as 17βHSD especially P450c17 SER Testosterone converted to DHT in target tissue by 5α reductase II (prostate, reproductive organs) Testosterone stimulates 5α reductase II Testosterone stimulates Development of epididymis, vas deferens, seminal vesicle Growth and differentiation of external genitalia (dihydrotestosterone) Descent of the testes (inguinoscrotal phase)
*Describe the biosynthesis of testosterone in Leydig cells and the role of Sertoli cells.*
LH stimulates Leydig cell (~puberty) --> testosterone synthesis --> expression of 17βHSD and P450c17 Testosterone --> 5α reductase II synthesis --> DHT Testosterone --> Development of epididymis, vas deferens, seminal vesicle, Growth and differentiation of external genitalia, Descent of the testes
Timing of Prenatal Sexual Differentiation in the Male
Leydig cells of male fetus produce testosterone ~ 7weeks in utero. Stimulated by hCG (placenta), similar to LH *Male fetus produces own testosterone needed for sexual development in utero* Testosterone stimulates: --Development of wolffian ducts --Growth and differentiation of external genitalia (dihydrotestosterone) --Descent of the testes
*Recall the major actions of the Androgen hormones in men.*
Maintain/Develop internal and external reproductive organs Spermatogenesis Regulate GnRH Libido Increase Muscle mass Release Epo Acne, Hair Growth (body hair in puberty, hair loss in adulthood) Can be converted to an estrogen *Must have oxidized A ring to be converted to an estrogen*
Biochemistry of Male Reproductive Hormones Outline
Major functions of sex steroids in men. Biosynthesis of sex steroids Steroid hormone mechanism action Male pituitary gonadal axis and reproductive function Hormone actions in the testes Male hypogonadism Male hormonal contraceptives Anabolic steroids
*Recall the function of the pituitary axis in males, the feed back mechanisms and the role of gonadotropins on male reproductive function.*
Negative Feedback in the hypothalmic-pituitary axis in males is achieved by testosterone and inhibin. Testosterone (leydig cells) --> inhibits GnRH at hypothalamus and LH at Anterior Pituitary Inhibin (sertoli cells) --> inhibits FSH at the Anterior Pituitary *Presence of inhibin indicates functional Sertoli Cells. This suggests spermatogenic activity in the testes* (because sertoli cells also produce sperm).
Sex Steroid Intracrinology Biologically Inert
Not very active because they don't bind receptors very well
*Recall the causes and consequences of hyper-gonadism in men.*
Over-active androgen receptor Broad shoulders Hair Muscle Mass Lower voice
Male Hormonal Contraceptive Goal: Inhibit Sperm Production
Progesterone and testosterone inhibits GnRH release from the hypothalamus. Estradiol inhibits LH release from the anterior pituitary. Inhibin inhibits FSH release from the anterior pituitary.
*Biosynthesis of Androgens*
Progesterone precursor for androgenic steroids. Progesterone to Androgen 21C to 19C 2 step conversion with P450c17 (CYP17) P450c17 is a hyroxylase-lyase 1st: hydroxyl in D ring 2nd: remove 2C aldehyde Testosterone OH in D ring, 17βHSD DHT most potent androgen 5α reductase (chromosome 2) Reduction of A ring Androgens precursors for Estrogens Must have oxidized A ring
*Recall the major actions of the Progeterone hormones in men.*
Regulate GnRH, LH, FSH
Binding equilibria between SHBG, testosterone and estrogen Why is it important?
SHBG has a higher affinity for testosterone than for estrogen (still high for both though) SHBG_women > SHBG_men *More testosterone will be bound, less estrogen --> less free testosterone in plasma*
*How does SHBG maintain high intratesticular testosterone*
Sertoli cells make ABP in response to FSH More ABP (SHBG) in the tubules = more testosterone in the tubules
What does testosterone do to SHBG production in the liver?
Testosterone inhibits SHBG production (liver)
Important: Same enzyme in sex hormone synthesis unsed in creating cortisol
This means that the Zona Fasiculata must have *P450c17* to complete the cortisol reaction Progesterone --> 17-α Progesterone --> Cortisol *P450c17*: Progesterone to 17-α Progesterone *P450c21*: 17-α Progesterone to Cortisol