Oral Presentation ESA-SRB-APEG-NZSE 2022

Blockade of both canonical and alternate androgen biosynthetic pathways reveals a third androgen-production pathway in mice (#94)

Ben M Lawrence 1 2 , Liza O'Donnell 1 , Lee B Smith 1 3 , Diane Rebourcet 1 2
  1. The University of Newcastle, Callaghan, NSW, Australia
  2. HMRI Infertility and Reproduction Research Program, Newcastle, NSW, Australia
  3. Griffith University, Gold Coast, QLD, Australia

Androgen deficiency in males is associated with disorders of sexual development, infertility, increased risk of cardiovascular disease and diabetes and premature mortality1. Exogenous testosterone therapy is widely prescribed, yet side-effects persist, and long-term risk remains unclear. An alternative approach would be to develop safer strategies supporting endogenous androgen production in men, that remains self-regulating under negative feedback control2. Testosterone is essential for spermatogenesis and is synthesised by testicular Leydig cells via the “canonical” pathway of androgen biosynthesis, however, testosterone can be converted to the more potent androgen dihydrotestosterone. Dihydrotestosterone can also be produced via the “alternate” pathway, utilising androsterone as a substrate instead of testosterone. Both pathways are essential for human male sexual development, yet how these pathways co-operate, especially to support androgen action in adulthood, remains unknown3,4.

 

To dissect the roles and interactions of these pathways, we generated a double knockout (KO) mouse model, where genes essential for the canonical (Hsd17b3) and alternate (Srd5a1) pathways were disrupted. We validated these mutations at the DNA, transcript and protein level.

 

Surprisingly, double KO male mice showed normal development of reproductive organs and remained fertile. Precursor steroidogenic enzyme mRNA and protein levels in testis were increased, suggesting disrupted Leydig cell function and steroidogenic compensation. This increase was apparent in Hsd17b3 single KO mice, but was further increased in double KO mice. Circulating and intratesticular hormone levels are currently being measured.

 

We conclude a third compensatory androgen production pathway may exist in mice that maintains androgen production in absence of HSD17B3 and SRD5A1. We have identified candidate steroidogenic enzymes that could support this pathway and are testing their involvement using similar approaches. Our mouse models are defining the pathways that co-operate to maintain androgen production and will in turn enable us to define therapies to support healthy androgen production across the life course.

  1. Fantus, R.J., et al., Serum Total Testosterone and Premature Mortality Among Men in the USA. Eur Urol Open Sci, 2021. 29: p. 89-92.
  2. Khodamoradi, K., et al., Exogenous testosterone replacement therapy versus raising endogenous testosterone levels: current and future prospects. F S Rev, 2021. 2(1): p. 32-42.
  3. Geissler, W.M., et al., Male pseudohermaphroditism caused by mutations of testicular 17β–hydroxysteroid dehydrogenase 3. Nature genetics, 1994. 7(1): p. 34-39.
  4. Flück, C.E., et al., Why boys will be boys: two pathways of fetal testicular androgen biosynthesis are needed for male sexual differentiation. The American Journal of Human Genetics, 2011. 89(2): p. 201-218.