OSR1 and SPAK cooperatively modulate Sertoli cell support of mouse spermatogenesis

We investigated the role of oxidative stress-responsive kinase-1 (OSR1) and STE20 (sterile 20)/SPS1-related proline/alanine-rich kinase (SPAK), upstream regulators of the Na⁺-K⁺-2Cl^- cotransporter (NKCC1)-essential for spermatogenesis-in mouse models of male fertility. Global OSR1^+/- gene mutations, but not global SPAK^-/- or Sertoli cell (SC)-specific OSR1 gene knockout (SC-OSR1^-/-), cause subfertility with impaired sperm function and are associated with reduced abundance of phosphorylated (p)-NKCC1 but increased p-SPAK expression in testicular tissue and spermatozoa. To dissect further in a SC-specific manner the compensatory effect of OSR1 and SPAK in male fertility, we generated SC-OSR1^-/- and SPAK^-/- double knockout (DKO) male mice. These are infertile with defective spermatogenesis, presenting a SC-only-like syndrome. Disrupted meiotic progression and increased germ cell apoptosis occurred in the first wave of spermatogenesis. The abundance of total and p-NKCC1 was significantly decreased in the testicular tissues of DKO mice. These results indicate that OSR1 and SPAK cooperatively regulate NKCC1-dependent spermatogenesis in a SC-restricted manner.