Endocrine Control of Male Reproduction

1. Endocrine Control of Male Reproduction William Walker 383-8634 walkerw+@pitt.edu

2. Objectives 1. Understand the functions of the testis A. Secretion of testosterone B. Production of spermatozoa 2. Understand the endocrine and paracrine regulation of the testis

3. Human Semen Abnormalities Azoospermia No spermatozoa in the ejaculate Oligospermia Sperm concentration < 20 million/ml Asthenozoospermia Less than 50% of spermatozoa have normal mobility or less than 25% have any motility Teratozoospermia Less than 30% of spermatozoa have normal morphology One or more of these abnormalities are found in 90% of infertile males. Treatments: In vitro fertilization Intracytoplasmic sperm injection

4. Lecture Outline Testis structure Testosterone production and action Regulation of testosterone secretion Germ cell development (spermatogenesis) Regulation of sperm output Sperm transport

6. Rhesus Testis

7. Testis Structure

8. Testis Cross Section Showing The Spermatogenic and Steroidigenic Units

9. Lecture Outline Testis structure Testosterone production and action Regulation of testosterone secretion Germ cell development (spermatogenesis) Regulation of sperm output Sperm transport

10. Testosterone Synthesis

11. Binding of Testosterone by TEBG Testosterone levels: Peripheral blood- 4 ng/ml Testis- 100-600 ng/ml

12. Male Testosterone Levels

13. Physiological Actions of Androgen In utero: External genitalia development Wolffian Duct development Pubertal: External genitalia Hair growth Linear growth Accessory sex organs Voice Pyche (aggressive attitudes, sexual potency) Muscle mass increase Initiation of spermatogenesis Adult: Hair growth, baldness Phyche (sexual potency) Maintenance of bone mass Maintenance of spermatogenesis

14. The Androgen Signaling Pathway Testosterone h s p 9 0 + A R h s p 7 0 C o a c t i v a t o r C o m p l e x A R A R S R C - 1 RNA Pol I I DHT A R A R A R E A A A A Testosterone A l t e r e d P r o t e i n C e l l u l a r F u n c t i o n Target tissues: Testosterone- muscle, testis DHT-external genitalia, reproductive tract, skin

15. Testicular Feminization (tfm) Androgen Insensitivity

16. DHT and Estrogen Synthesis Growth regulation Bone mass maintenance

17. Estrogen Regulates the Pubertal Growth Spurt in Men

18. Lecture Outline Testis structure Testosterone production and action Regulation of testosterone secretion Germ cell development (spermatogenesis) Regulation of sperm output Sperm transport

19. Regulation of the Hypothalamic-Pituitary-Testis Axis Negative Feedback (GnRH) Negative Feedback (LH) Negative Feedback (FSH)

20. A c R C G s R C CREB cAMP dependent kinase LH Binding to Receptors on Leydig Cells Induces the cAMP-Dependent Protein Kinase Signaling Pathway Leydigcell CYTOPLASM NUCLEUS R LH ATP cAMP P TRANSCRIPTION TGACGTCA downstream effector genes

21. Hypogonadal Male

22. Regulation of the Hypothalamic-Pituitary-Testis Axis Negative Feedback (GnRH) Negative Feedback (LH) Negative Feedback (FSH)

23. Kallmann’s Syndrome (GnRH deficiency) Symptoms: Hypogonadotropic, hypogonadal, aspermic, cryptorchid, absence of puberty, Defective sense of smell Defective KAL locus on X chromosome that encodes the anosmin protein Anosmin is a neural adhesion molecule Required for the correct migration of GnRH neurons Therapy: Androgen replacement-virilization Gonadotropin therapy-restore fertility

24. Pulsatile GnRH secretion is required for FSH and LH production

25. Serum LH concentrations in normal and hypogonadal men Normal ng/ml Hypogonadal ng/ml

26. Testosterone Treatment Decreases LH Secretion Frequency In Hypogonadal Men

27. Lecture Outline Testis structure Testosterone production and action Regulation of testosterone secretion Germ cell development (spermatogenesis) Regulation of sperm output Sperm transport

28. Testis Cross Section

29. Human Spermatogenesis Spermatogonia Spermatocytes Meiosis Spermiogenesis Spermiation Time to complete =70 days

30. Cell Divisions During Human Spermatogenesis Spermatogenesis potential Human: 1 type A spermatogonia = 8 spermatids Rat: 1 type A spermatogonia = 4,096 spermatids?

31. Germ Cells Form Cytoplasmic Bridges Due to Incomplete Cytokinesis Result: Clonal development of germ cell cohort Synchronization of germ cell maturation

32. Cell Divisions During Human Spermatogenesis 3 phases of Spermatogenesis Stem Cell Renewal Proliferation of spermatogonia and spermatocytes Spermiogenesis Spermatogenesis requires 70-75 days in humans

33. Spermatogenic Wave

34. Lecture Outline Testis structure Testosterone production and action Regulation of testosterone secretion Germ cell development (spermatogenesis) Regulation of sperm output Sperm transport

35. Sperm production: 800 million /day 5 million/10 minutes Regulation of Sperm Output: 1. Apoptosis 2. Toxic chemicals 3. Nutrition (Vit A) 4. Sertoli cell number 5. Testosterone and FSH

37. Sertoli Tight Junctions Form a Blood Barrier

38. Sertoli cells are the targets for testosterone and FSH regulation of spermatogenesis Sertoli cells form a blood-testis barrier Nothing larger than 1 kDa can pass into the seminiferous tubule The germ cells develop in a protected microenvironment Sertoli cells must provide all growth factors and nutrients for germ cells FSH and testosterone regulate Sertoli cell gene expression and protein production

39. A c R C G s R C CREB cAMP dependent kinase FSH Binding to Receptors on Sertoli Cells Induces the cAMP-Dependent Protein Kinase Signaling Pathway CYTOPLASM NUCLEUS R FSH cAMP ATP P TRANSCRIPTION TGACGTCA Sertoli cell downstream effector genes

40. FSH Activated Genes In Sertoli Cells Transferrin Androgen Binding Protein Pyruvate dehydrogenase Lactate dehydrogenase Androgen Receptor Inhibin

41. Inhibin Suppresses FSH Secretion

42. Effects of Decreased FSH Action 1. Mouse FSHb gene knockout Sperm number reduced 75% Motile sperm reduced 45% 2. Mouse FSH receptor gene knockout 33% lower litter size Delayed sexual maturity Sperm number decreased 36% 2.6-fold increase in aberrant sperm 3. FSHb mutation in men 3 of 3 have azoospermia- infertile 4. FSH receptor mutation in men (C566T) Oligozoospermia (<1 x 106/ml) 1 of 3 are childless

43. Testosterone can maintain spermatogenesis after hypophysectomy 1 0 0 7 5 % of normal sperm count 5 0 2 5 0 FSH T FSH + T

44. FSH and Testosterone Synergy Testosterone concentration

45. Spermatogenesis is Regulated by Testosterone and FSH Testosterone and FSH act through Sertoli cell receptors. Testosterone: Can independently maintain spermatogenesis Required to complete meiosis Induces protein secretion from Sertoli cells Mechanism is unknown FSH: Not essential to maintain spermatogenesis Increases spermatogenesis efficiency Increases the number of Sertoli cells Induces factors supporting spermatogenesis

46. Paracrine Factors Produced by Sertoli and Germ Cells Stem Cell Factor Activin IL-1 Nerve growth factor IGF-1 TNF-a Sertoli cell Germ Cell

47. Do Sertoli cells or germ cells determine the timing of germ cell development? Use the info that rat and mouse germ cells mature at different rates. Experiment: Use drugs or radiation to eliminate only germ cells in mouse testis. Transplant rat spermatogonia to mouse testis. Do rat germ cells mature on a rat or mouse schedule?

48. Lecture Outline Testis structure Testosterone production and action Regulation of testosterone secretion Germ cell development (spermatogenesis) Regulation of sperm output Sperm transport

49. Rete Testis

50. Male Accessory Glands