Local and systemic control of gonadal function

Human: 1 oocyte – 150 million sperm

Semen analysis results vary considerably even in the normal fertile population. CONSECUTIVE SEMEN DONOR CONCENTRATIONS OVER FOUR YEARS

Cooper T G et al. Hum. Reprod. Update 2010;16: © World Health Organization [2009]. All rights reserved. The World Health Oragnization has granted Oxford University Press permission for the reproduction of this article

The association of age and semen quality in healthy men B.Eskenazi Human Reproduction Vol.18, pp , 2003 Semen volume Concentration Count Motility Progressive motility The likelihood of semen sample being graded as “clinically” abnormal or unhealthy: Age 22 25% 3040% 4060% 6085%

So where are we going now? So many sperm? Why? How? Environmental pollutants and male fertility?

3.Cervical mucus. a) penetration characteristics b) “filter” for immotile sperm 1. Human: Vaginal deposition of semen 2. Human: 99% of sperm lost through retrograde transport 150,000,000

3.Cervical mucus. a) penetration characteristics b) “filter” for immotile sperm 1. Human: Vaginal deposition of semen 2. Human: 99% of sperm lost through retrograde transport 4. Transport through uterus; phagocytosis 150,000,000

Dog sperm in contact with uterine epithelial cells Courtesy: Gary England

3.Cervical mucus. a) penetration characteristics b) “filter” for immotile sperm 1. Human: Vaginal deposition of semen 2. Human: 99% of sperm of sperm lost through retrograde transport 4. Transport through uterus due to muscular contractions; phagocytosis 5. Utero-tubal junction 6. Fallopian tube 150,000,000

The journey? 2. Human: 99% of sperm of sperm lost through retrograde transport 5. Utero-tubal junction 6. Fallopian tube From Wheater’s Functional Histology, 4 th ed., Sperm bound to ciliated epithelial cells – slow release

Spermatogenesis: How much do you need? Body weight: 44 kg Testis size: 120 gm Body weight: 170 kg Testis size: 30 gm Many males mate with same female: competition! i.e. 16 x more testicular tissue/kg body wt

Take home message: the more testicular tissue, the more sperm.

Body weight Testis weight Man Multi-male breeding system Monogamous

~ 8 cm Why so many sperm? 50 um/sec = 3 mm/min = ~30 min

Take home message: variability in reproduction often correlates with competition between males/sperm

Stahlberg et al (2000) pig experiment Semen from 2 boars was pooled in equal numbers and inseminated (32 females) DNA analysis was used to identify paternity of offspring and embryos Theriogenology (2000) 53, Take home message: there is competition between sperm!

What controls testicular size/ sperm production?

Each Sertoli cell has a fixed capacity for the number of germ cells that it can support. Therefore, the number of Sertoli cells in the adult testis determines (testis size) daily sperm production.

Sharpe, Reproduction(2003) 125, 769–784 The distribution profile of Sertoli cell number in a population of men: i.e. it is very variable

Sertoli cell number Final terminal differentiation – losing ability to divide, but switching on spermatogenic support function Hypothesis: Disturbances in testicular development will affect male fertility. Proliferation during fetal and neonatal life Proliferation peripubertally.

Testis Spermatozoa Hypothalamus Pituitary FSHLH + + GnRH + Testosterone Negative feedback Inhibin The “TEXT BOOK” control of the testis and spermatogenesis

Testis Spermatozoa Hypothalamus Pituitary FSHLH + + GnRH + Testosterone Suppress FSH/LH GnRH antagonist? Increase feedback: Give testosterone Negative feedback Observation: The 1 st large scale trials in 1990s - highly effective in reducing sperm counts in most men, BUT a small % of men failed to show sufficient suppression of sperm – even when gonadotrophin levels were undetectable. The difficulty of getting a male contraceptive..

Normal testes “wild type” Small testes, but still fertile But in the FSH “knockout” Conclusion: FSH is NOT essential for spermatogenesis… For many years, FSH had been seen as the main driving force in spermatogenesis… FSH Sertoli cells FSH receptors

Is the same true for man? Yes - very similar! Men with an inactivating mutation of the FSH receptor are fertile despite having small testes. Conclusion: FSH is not essential for spermatogenesis… – but does seem to be important in determining testicular size

No Spermatozoa Hypothalamus Pituitary FSHLH + + GnRH + Testosterone Prepubertal boys Negative feedback Small testes

Spermatozoa Hypothalamus Pituitary FSHLH + + GnRH + Testosterone Prepubertal boys Negative feedback Small testes Spermatogenesis can occur in testes with Leydig cell tumours in pre-pubertal boys Perhaps local steroids may be important in spermatogenesis? TESTOSTERONE Perhaps this explains the small % of men who failed to show sufficient suppression of sperm – even when gonadotrophin levels were undetectable – in the contraceptive trials

Intra-Testicular Circulation T nmol/L E pmol/L Local steroids may be important in spermatogenesis?

Are local steroids really important? Leydig cells Sertoli cells Peritubular cells AR AR null AR Location of androgen receptors Androgen receptor knockout (AR null) WT

Direct evidence that testosterone acting via Sertoli cells is important for later stages of spermatogenesis.

Are local steroids really important? Leydig cells Sertoli cells AR Location of androgen receptors Peritubular cells

Where are the steroids acting? Small testes AR-null Leydig cells Sertoli cells Peritubular cells Androgen receptor knock-out in Sertoli cells only AR Result: Spermatogenesis becomes arrested during meiosis

Testosterone ↑↑ later stages of spermatogenesis FSH ↑ Leydig cell no. ↑↑ early Sertoli cell proliferation ↑↑ later Sertoli cell proliferation Initiates spermatogenesis ↑↑ Spermatogonia no. LH AR Conclusion: Sequential, coordinated actions of LH, FSH and androgens are required. Conclusion: Sequential, coordinated actions of LH, FSH and androgens are required. Leydig cell development Peri-tubular cells

By end of 1 st year, few Leydig cells left 2 nd wave of Leydig cells (peaks at 3 mo ) + T surge 1 st wave of Leydig cells. T production stimulated by hCG Adult Leydig cells differentiate from undifferentiated precursors Sertoli cell number Leydig cells

Men: m sperm each day The no. of sperm determined by no. of Sertoli cells. Sperm count (10 6 /ml) Sperm count (10 6 /ejaculate) Daily sperm production (10 6 /testis) % men % becoming pregnant per cycle. Sertoli cell number/testis (m) Fertility The number of Sertoli cells is fixed by puberty. Largely determined by rate of proliferation in fetus and 1-9 months post-natal. The number of Sertoli cells is fixed by puberty. Largely determined by rate of proliferation in fetus and 1-9 months post-natal. Therefore, factors affecting no. of Sertoli cells in early life will influence sperm counts in adulthood. The sperm count in men varies. Normally, m sperm each day If sperm count is too low, fertility declines FSH Testosterone from fetal Leydig cells Endocrine disrupting compounds