5BBL0210 Control of Testicular Function and Sperm Physiology PDF

5BBL0210 Control of testicular function and sperm physiology James Bowe King’s College London [email protected]  Topics covered The HPG axis and testosterone Spermatogenesis and its control Sperm journey: production to fertilisation Abnormalities of spermatoge...

5BBL0210 Control of testicular function and sperm physiology James Bowe King’s College London [email protected]  Topics covered The HPG axis and testosterone Spermatogenesis and its control Sperm journey: production to fertilisation Abnormalities of spermatogenesis  Testes The testes have 2 main physiological functions Production and release of testosterone Spermatogenesis  Testes The testes have 2 main physiological functions Production and release of testosterone Spermatogenesis Both are controlled by the hypothalamic-pituitary-gonadal axis  The hypothalamic-pituitary-gonadal (HPG) axis Hypothalamus -ve GnRH Anterior +ve pituitary Testosterone -ve FSH LH +ve Testis Sperm  Hypothalamus Hypothalamus  Hypothalamus Hypothalamus  Hypothalamus GnRH neurons: GnRH neurones Cell bodies in the Preoptic area of the hypothalamus extend to the median eminence and release GnRH into the pituitary portal blood system.  Hypothalamus GnRH neurons: GnRH neurones Cell bodies in the Preoptic area of the hypothalamus extend to the median eminence and release GnRH into the pituitary portal blood system. GnRH is released in regular pulses.  Pituitary GnRH neurons: GnRH neurones Cell bodies in the Preoptic area of the hypothalamus extend to the median eminence and release GnRH into the pituitary portal blood system. GnRH is released in regular pulses. LH and FSH: Released from gonadotroph cells in the anterior pituitary in response to GnRH. LH and FSH released Also released as regular pulses. from Gonadotroph cells in anterior pituitary  The hypothalamic-pituitary-gonadal (HPG) axis Luteinising Hormone (LH) and Follicle Stimulating Hormone (FSH) are released together into the circulation from the anterior pituitary in response to GnRH Luteinising Hormone Male: Stimulates production of testosterone in the testes Female: Controls the reproductive cycle and ovulation, stimulates oestrogen Follicle Stimulating Hormone Male: Stimulates the growth and maturation of the testes and spermatogenesis Female: Stimulates the growth and maturation of ovarian follicles  The hypothalamic-pituitary-gonadal (HPG) axis Luteinising Hormone (LH) and Follicle Stimulating Hormone (FSH) are released together into the circulation from the anterior pituitary in response to GnRH Luteinising Hormone Male: Stimulates production of testosterone in the testes Female: Controls the reproductive cycle and ovulation, stimulates oestrogen Follicle Stimulating Hormone Male: Stimulates the growth and maturation of the testes and spermatogenesis Female: Stimulates the growth and maturation of ovarian follicles  The hypothalamic-pituitary-gonadal (HPG) axis Hypothalamus -ve GnRH Anterior +ve pituitary Testosterone -ve FSH LH +ve Testis Sperm Anatomy of male genitalia Anatomy of testes Anatomy of testes Anatomy of testes Seminiferous tubules Leydig cells Leydig Cells LH stimulates the synthesis and release of testosterone and other androgens from Leydig cells. LH Cholesterol +ve Cholesterol desmolase Pregnenolone Leydig Cells Pregnenolone is the main precursor for testosterone. Plasma testosterone Testis vol. profiles 12.5 Testis volume is directly linked to plasma testosterone levels 5.9 Increased testosterone 3.8 released from the growing testes drives the formation of secondary sexual 2 characteristics, e.g. facial 1.6 hair, voice breaking.  Effects of Testosterone Male hormone - anabolic Primary and secondary sexual characters Libido and sexual behaviour Stimulates spermatogenesis Anatomy of testes Seminiferous tubules Leydig cells  Seminiferous tubules Spermatogenesis occurs within the seminifous tubules  Seminiferous tubules Spermatogenesis occurs within the seminifous tubules Seminiferous tubules contain both sertoli cells and spermatogonial stem cells  Seminiferous tubules Spermatogonial stem cells Sperm production Sertoli cells Support Nutrition Protection Regulation  Spermatogenesis Starts at puberty Maintains species Mitosis followed by Meiosis 120 million sperm / day or 1,500 / sec  Spermatogenesis Spermatocytogenesis: Spermatogonial stem cells (diploid cells – 46 chromosomes) divide by mitosis to replace themselves and produce spermatocytes, cells that go on to become sperm.  Spermatogenesis Spermatocytogenesis: Spermatogonial stem cells (diploid cells – 46 chromosomes) divide by mitosis to replace themselves and produce spermatocytes, cells that go on to become sperm. 3 subtypes: Type A(d): Replicate by mitosis to provide a constant supply of Type A(d) and Type A(p) cells.  Spermatogenesis Spermatocytogenesis: Spermatogonial stem cells (diploid cells – 46 chromosomes) divide by mitosis to replace themselves and produce spermatocytes, cells that go on to become sperm. 3 subtypes: Type A(d): Replicate by mitosis to provide a constant supply of Type A(d) and Type A(p) cells. Type A(p): Divide by mitosis to provide Type B cells.  Spermatogenesis Spermatocytogenesis: Spermatogonial stem cells (diploid cells – 46 chromosomes) divide by mitosis to replace themselves and produce spermatocytes, cells that go on to become sperm. 3 subtypes: Type A(d): Replicate by mitosis to provide a constant supply of Type A(d) and Type A(p) cells. Type A(p): Divide by mitosis to provide Type B cells. Type B: Divide by mitosis into primary spermatocytes.  Spermatogenesis Spermatidogenesis: Primary spermatocytes produce spermatids through meiosis. Spermatids (23 chromosomes, haploid) Meiosis II Secondary Spermatocyte (23 chromosomes, haploid) Meiosis I Interphase Primary Spermatocyte (46 chromosomes, diploid)  Spermiogenesis Spermiogenesis is a 4-phase process that converts the symmetrical spermatids into mature sperm.  Spermiogenesis Golgi phase Golgi phase The golgi apparatus creates a vesicle of enzymes around the nucleus. Mitochondria start to move to the other side of the cell. The centriole starts to form an axoneme, the cytoskeletal core of the tail.  Spermiogenesis Golgi phase Cap phase Cap phase Spermatid DNA is condensed in the nucleus. The golgi apparatus surrounds the nucleus and the enzyme vesicle forming the acrosomal cap.  Spermiogenesis Golgi phase Cap phase Acrosome phase Acrosome phase The axoneme extends to become the tail of the sperm. Temporary cytoskeleton structures called manchettes support the growing tail.  Spermiogenesis Golgi phase Cap phase Acrosome phase Maturation phase Maturation phase Excess cytoplasm is phagocytosed by Sertoli cells to produce mature sperm.  Mature sperm Though mature, sperm in the seminiferous tubules are not motile. Non-motile Sperm are transported to the epididymis where they are stored and gain motility.  Sertoli cells The Sertoli cells are regulated by FSH and are essential for spermatogenesis Multiple functions Form the blood-testis barrier  Sertoli cells The Sertoli cells are regulated by FSH and are essential for spermatogenesis Multiple functions Form the blood-testis barrier Release androgen-binding protein  Sertoli cells The Sertoli cells are regulated by FSH and are essential for spermatogenesis Multiple functions Form the blood-testis barrier Release androgen-binding protein Release inhibin for feedback on the pituitary  Sertoli cells The Sertoli cells are regulated by FSH and are essential for spermatogenesis Multiple functions Form the blood-testis barrier Release androgen-binding protein Release inhibin for feedback on the pituitary Secrete supporting fluid into the lumen  Sertoli cells The Sertoli cells are regulated by FSH and are essential for spermatogenesis Multiple functions Form the blood-testis barrier Release androgen-binding protein Release inhibin for feedback on the pituitary Secrete supporting fluid into the lumen Phagocytose residual cytoplasm from spermiogenesis  Sertoli cells The Sertoli cells are regulated by FSH and are essential for spermatogenesis Multiple functions Form the blood-testis barrier Release androgen-binding protein Release inhibin for feedback on the pituitary Secrete supporting fluid into the lumen Phagocytose residual cytoplasm from spermiogenesis Release of a range of other proteins such as GDNF and anti-müllerian hormone.  Sertoli cells The Sertoli cells are regulated by FSH and are essential for spermatogenesis Multiple functions Form the blood-testis barrier Release androgen-binding protein Release inhibin for feedback on the pituitary Secrete supporting fluid into the lumen Phagocytose residual cytoplasm from spermiogenesis Release of a range of other proteins such as GDNF and anti-müllerian hormone. Blood-testis barrier Tight junctions between Sertoli cells forms a barrier between the lumen of the seminiferous tubules and the blood vessels. Allows the Sertoli cells to control the environment within the lumen. Protects developing sperm from any toxins. Separates the developing sperm from the immune system which would otherwise mount an autoimmune response.  Sertoli cells The Sertoli cells are regulated by FSH and are essential for spermatogenesis Multiple functions Form the blood-testis barrier Release androgen-binding protein Release inhibin for feedback on the pituitary Secrete supporting fluid into the lumen Phagocytose residual cytoplasm from spermiogenesis Release of a range of other proteins such as GDNF and anti-müllerian hormone. Androgen-binding protein (ABP) Spermatogenesis requires very high levels of testosterone around the developing sperm. ABP binds to testosterone in the lumen, making testosterone less lipophilic. Concentrates testosterone in the lumen, increasing fertility.  Sertoli cells The Sertoli cells are regulated by FSH and are essential for spermatogenesis Multiple functions Form the blood-testis barrier Release androgen-binding protein Release inhibin for feedback on the pituitary Secrete supporting fluid into the lumen Phagocytose residual cytoplasm from spermiogenesis Release of a range of other proteins such as GDNF and anti-müllerian hormone.  The hypothalamic-pituitary-gonadal (HPG) axis Hypothalamus -ve GnRH Anterior +ve pituitary Testosterone -ve FSH LH +ve Testis Sperm  The hypothalamic-pituitary-gonadal (HPG) axis Hypothalamus LH stimulates the interstitial Leydig cells -ve GnRH to produce Anterior +ve testosterone. pituitary Testosterone FSH stimulates the -ve Sertoli cells to produce LH FSH +ve +ve ABP and inhibin. Converted into Oestradiol and other androgens Leydig Sertoli cells cells Stem Testis cells  The hypothalamic-pituitary-gonadal (HPG) axis Hypothalamus ABP binds to testosterone to -ve GnRH stimulate Anterior +ve spermatogenesis. pituitary Testosterone Testosterone also -ve feeds back to LH FSH +ve +ve suppress LH secretion. Converted into Oestradiol and other androgens Testosterone Leydig Sertoli cells cells ABP Stem Testis cells Mature sperm  The hypothalamic-pituitary-gonadal (HPG) axis Hypothalamus Inhibin is produced by the Sertoli cells. It -ve GnRH feeds back to Anterior +ve suppress FSH pituitary Inhibin secretion Testosterone -ve -ve LH FSH +ve +ve Converted into Oestradiol and other androgens Testosterone Leydig Sertoli cells cells ABP Stem Testis cells Mature sperm The role for prolactin Prolactin released from the pituitary also affects male fertility. Increases LH receptor expression on the Leydig cells resulting in increased testosterone release and increased spermatogenesis. The hypothalamic-pituitary-gonadal (HPG) axis Hypothalamus -ve GnRH Anterior +ve pituitary Inhibin Testosterone -ve -ve LH FSH Prolactin +ve Converted into Oestradiol and +ve other androgens Testosterone Leydig Sertoli cells cells ABP Stem Testis cells Mature sperm  Seminiferous tubules The Leydig cells and the seminiferous tubules work closely together to maintain reproductive function. Leydig cells  Sperm transport Ejaculation: deposition of sperm in vagina (acidic). Cervix: mucous barrier and crypts as sperm reservoirs – sperm motility is important. Uterus and fallopian tubes: mild contraction to propel the sperm towards egg Fertilisation occurs in the ampullary region of the tube.  Sperm capacitation Takes place in the uterus. Cholesterol and glycoproteins are removed from the sperm cell surface by enzymes such as heparin in the uterus. “Switching on” of sperm through increased calcium influx. HYPERACTIVITY – Increased motility. Ca2  Acrosome reaction Triggered by contact with oocyte. Interaction with ZP3 protein on oocyte membrane prevents cross-species fertilisation. Acrosome releases hyaluronidase and acrosin enzymes break through egg coating allowing fertilisation.  Oocyte activation Following fertilisation cortical granules are released – Oocyte membrane becomes impermeable to other sperm. Formation of the male and female pronuclei.  Disturbances in testes function Genetic level, e.g. Klinefelter syndrome  Klinefelter syndrome A genetic disorder in which a male with X and Y chromosomes also has an additional X chromosome. Individuals will have 47 chromosomes instead of the normal 46 with XXY. Effects vary between individuals, many people will not show any symptoms, but it can result in hypogonadism and reduced fertility. Affects between 1:500 and 1:1000 males  Disturbances in testes function Genetic level, e.g. Klinefelter syndrome Hypothalamic level, e.g. Kallman syndrome  Kallman syndrome The GnRH neurones originate from the olfactory region of the brain. Genetic mutations affecting the olfactory bulb also stop GnRH neurones developing. Lack of GnRH neurons results in no reproductive function. Kallman syndrome also causes a loss of sense of smell. Affects around 1:10,000 males.  Disturbances in testes function Genetic level, e.g. Klinefelter syndrome Hypothalamic level, e.g. Kallman syndrome Pituitary level, e.g. Hyperprolactinaemia  Hyperprolactinaemia Abnormally high levels of circulating prolactin which inhibits GnRH. Can be caused by pituitary tumours. Also often a side-effect of various prescription drugs that affect dopamine. In males symptoms include decreased libido and reduced fertility.  Disturbances in testes function Genetic level, e.g. Klinefelter syndrome Hypothalamic level, e.g. Kallman syndrome Pituitary level, e.g. Hyperprolactinaemia Target tissue level, e.g. Androgen insensitivity syndrome  Androgen insensitivity syndrome Genetic defects in the androgen receptors reduce sensitivity to testosterone and other androgens. The extent of androgen insensitivity can vary resulting in a wide range of severity. Sometimes only very mild effects, but complete androgen insensitivity can result in female body development despite XY chromosomes. Factors affecting sperm production - hormones Male contraceptive  Factors affecting sperm production - hormones Use of steroids will suppress the HPG axis and reduce fertility  Non-hormonal factors Environment  Non-hormonal factors Environment  Non-hormonal factors Environment  Non-hormonal factors Environment  Non-hormonal factors Environment Climate (heat)  Non-hormonal factors Environment Climate (heat) Radiation  Non-hormonal factors Environment Climate (heat) Radiation Air pollution  Non-hormonal factors Environment Climate (heat) Radiation Air pollution Food chain pollution  Non-hormonal factors Environment Climate (heat) Radiation Air pollution Food chain pollution Stress Mechanism  Take home message Testicular function depends on delicate interaction between the 2 testicular compartments. Control is mainly via the HPG axis. Disturbance of testicular function can occur at genetic, hypothalamic, pituitary or end-organ level. Environmental factors could also affect testicular function.