Oral Virtual Presentation (Virtual only) ESA-SRB-ANZBMS 2021

Human INHBB gene variant (c.1079T>C:p.Met360Thr) alters testis germ cell content, but does not impact fertility in a mouse model (#200)

Brendan J Houston 1 2 , Anne E O'Connor 1 2 , Degang Wang 1 3 , Georgia Goodchild 1 , D Jo Merriner 1 2 , Haitong Luan 1 , Don F Conrad 4 5 , Kenneth I Aston 5 6 , Sabine Kliesch 7 , Margot J. Wyrwoll 8 , Corinna Friedrich 8 , Frank Tüttelmann 8 , Craig A Harrison 1 , Moira K O'Bryan 1 2 , Kelly Walton 1
  1. Monash University, Clayton, VIC, Australia
  2. School of BioSciences and Bio21 Institute, Faculty of Science, University of Melbourne , Melbourne , Victoria, Australia
  3. The Affiliated Zhongshan Boai Hospital of Southern Medical University, Guangdong, China
  4. Oregon National Primate Research Center , Oregon Health and Science University, Beaverton, Oregon, USA
  5. Genetics of Male Infertility Initiative, GEMINI, Portland, USA
  6. Department of Surgery, University of Utah School of Medicine, Utah, USA
  7. Department of Clinical and Surgical Andrology, Centre of Reproductive Medicine and Andrology, University Hospital Münster, Münster, Germany
  8. Institute of Reproductive Genetics, University of Münster, Münster, Germany

Testicular derived inhibin B (α/βB dimers) acts in an endocrine manner to suppress pituitary production of follicle stimulating hormone (FSH), by blocking the actions of activins (βA/B/βA/B dimers). This hypothalamic-pituitary-gonadal (HPG) axis is integral to reproductive function, and consequently, imbalances in inhibin/activin can impact gonadal function and fertility. In a recent study, we identified a homozygous genetic variant (c.1079T>C:p.Met360Thr) arising from uniparental disomy of chromosome 2 in the INHBB gene (encoding the βB-subunit of inhibin B and activin B) in a man suffering from infertility (azoospermia). In this study, we aimed to test the causality of the p.Met360Thr variant in INHBB and male infertility. Here, we used CRISPR/Cas-9 technology to generate InhbbM364T/M364Tmice, where mouse INHBB amino acid p.Met364 corresponds with human p.Met360. Surprisingly, it was found that the testes of male InhbbM364T/M364Tmutant mice were significantly larger compared with those of aged-matched wildtype littermates at 12 and 24 weeks of age. This was attributed to a significant increase in Sertoli cell and round spermatid number and, consequently, seminiferous tubule area, in InhbbM364T/M364Tmales compared to wildtype males. Despite this testis phenotype, male InhbbM364T/M364Tmutant mice retained normal fertility, daily sperm production levels, and sperm motility. Serum hormone analyses however, indicated that the InhbbM364Tvariant resulted in reduced circulating levels of activin B, but did not have significant consequences for FSH production. We also examined the effect of this p.Met360Thr, and an additional INHBB variant (c.314C>T: p.Thr105Met) found in another infertile man, on inhibin B and activin B in vitro biosynthesis. Intriguingly, it was found that both INHBB variants resulted in a significant disruption to activin B in vitro biosynthesis. Together, this analysis supports that INHBB variants that limit activin B production have consequences for testis composition in males.