Human INHBB Gene Variant (c.1079T>C:p.Met360Thr) Alters Testis Germ Cell Content, but Does Not Impact Fertility in Mice

• Published in: Endocrinology (Philadelphia) 2022-03, Vol.163 (3), p.1
• Main Authors: Houston, Brendan J, O’Connor, Anne E, Wang, Degang, Goodchild, Georgia, Merriner, D Jo, Luan, Haitong, Conrad, Don F, Nagirnaja, Liina, Aston, Kenneth I, Kliesch, Sabine, Wyrwoll, Margot J, Friedrich, Corinna, Tüttelmann, Frank, Harrison, Craig, O’Bryan, Moira K, Walton, Kelly
• Format: Article
• Language: English
• Subjects: Activin; Activins - biosynthesis; Activins - genetics; Amino acids; Analysis; Animals; Azoospermia - genetics; Biosynthesis; Chromosome 2; CRISPR; CRISPR-Associated Protein 9; Dimers; Endocrinology; Fertility; Follicle Stimulating Hormone - metabolism; Follicle-stimulating hormone; Genetic diversity; Genetic variance; Humans; Infertility; Infertility, Male - genetics; Infertility, Male - physiopathology; INHBB gene; Inhibin; Inhibin-beta Subunits - genetics; Inhibin-beta Subunits - physiology; Inhibins - biosynthesis; Inhibins - genetics; Male; Males; Mice; Mice, Inbred C57BL; Mutants; Mutation; Phenotypes; Pituitary; Seminiferous tubule; Sertoli Cells; Sperm Count; Spermatogenesis - genetics; Spermatogonia; Testes; Testis - chemistry; Testis - cytology; Testis - physiopathology; Uniparental disomy
• ISSN: 0013-7227; 1945-7170
• DOI: 10.1210/endocr/bqab269

Testicular-derived inhibin B (α/β B dimers) acts in an endocrine manner to suppress pituitary production of follicle-stimulating hormone (FSH), by blocking the actions of activins (β A/B/β A/B dimers). Previously, we identified a homozygous genetic variant (c.1079T>C:p.Met360Thr) arising from uniparental disomy of chromosome 2 in the INHBB gene (β B-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 testis function. Here, we used CRISPR/Cas9 technology to generate InhbbM364T/M364T mice, where mouse INHBB p.Met364 corresponds with human p.Met360. Surprisingly, we found that the testes of male InhbbM364T/M364T mutant 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/M364T males compared to wildtype males. Despite this testis phenotype, male InhbbM364T/M364T mutant mice retained normal fertility. Serum hormone analyses, however, indicated that the InhbbM364T variant resulted in reduced circulating levels of activin B but did not affect 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. We 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.