SPINK2 deficiency causes infertility by inducing sperm defects in heterozygotes and azoospermia in homozygotes

Abstract

Azoospermia, characterized by the absence of spermatozoa in the ejaculate, is a common cause of male infertility with a poorly characterized etiology. Exome sequencing analysis of two azoospermic brothers allowed the identification of a homozygous splice mutation in SPINK2, encoding a serine protease inhibitor believed to target acrosin, the main sperm acrosomal protease. In accord with these findings, we observed that homozygous Spink2 KO male mice had azoospermia. Moreover, despite normal fertility, heterozygous male mice had a high rate of morphologically abnormal spermatozoa and a reduced sperm motility. Further analysis demonstrated that in the absence of Spink2, protease‐induced stress initiates Golgi fragmentation and prevents acrosome biogenesis leading to spermatid differentiation arrest. We also observed a deleterious effect of acrosin overexpression in HEK cells, effect that was alleviated by SPINK2 coexpression confirming its role as acrosin inhibitor. These results demonstrate that SPINK2 is necessary to neutralize proteases during their cellular transit toward the acrosome and that its deficiency induces a pathological continuum ranging from oligoasthenoteratozoospermia in heterozygotes to azoospermia in homozygotes.

The seminal acrosin‐inhibitor ClTI1/SPINK2 is a fertility‐associated marker in the chicken

“…We found the turkey acrosin‐like specific peptide (SLQEYVEPYRVLQEAKVQLIDL) in the chicken acrosin sequence. Recently by coexpression of acrosin and SPINK2 proteins in human cell line HEK293, it was demonstrated that SPINK2 prevents cell proliferation arrest induced by proacrosin (Kherraf et al, ). We thus conclude that, in the chicken, like in the mouse, SPINK2 regulates the activity of acrosin to prevent uncontrolled/deleterious sperm proteolysis and too early acrosome reactions.…”

“…In mouse, Spink2 genomic invalidation demonstrated the importance of the protein at the gonadic level. SPINK2 allowed spermatid differentiation and acrosome formation during spermatogenesis and was still present on the acrosome of mature sperm of mouse and human to protect it from proteolysis (Kherraf et al, ). In the present study, we demonstrated a role of SPINK2 at the postgonadic level.…”

“…In semen, SPINK2 levels are reduced in specific pathological conditions (men azoospermia, specific reduced SPINK2 mutant mice (Kherraf et al, ; Lee et al, ; Rockett, Patrizio, Schmid, Hecht, & Dix, ). SPINK2 protein was recently identified as essential for acrosome biogenesis during mouse spermatogenesis (Kherraf et al, ). However, postgonadic SPINK2 biochemical and physiological functions in nonpathological conditions have been poorly explored and make part of the aim of the present study using the chicken model.…”

The dynamics of gene expression during and post meiosis sets the sperm agenda

“…The Mgat1 gene encodes the enzyme N‐acetylglucosaminyltransferase that regulates ERK signaling (Biswas, Batista, Sundaram, & Stanley, ), which is indispensable for spermatogenesis and Mgat1 deletion in spermatogonia did not produce any sperm (Batista, Lu, Williams, & Stanley, ). Likewise, spink2 deficient mouse have increased serine protease activity, disrupted spermatogenesis, and germ cell apoptosis (B. Lee et al, ), while the spink2 knockout homozygous male mice are azoospermic (Kherraf et al, ). The Slc16a7 (monocarboxylate transporter‐2) that transports lactate from Sertoli to germ cells was previously reported predominantly in spermatocytes and spermatids (Yadav et al, ) and genetic variations in MCT‐2 have clinical relevance in male infertility (J. Lee, Lee, & Lee, ).…”

Proteomics Analysis of Testis of Rats Fed a High-Fat Diet

“…However, only Spink2 is expressed in testes. Thus, it is considered essential for spermatogenesis [16, 17]. Moreover, Spink2 is necessary to inactivate acrosin during its transit through the endoplasmic reticulum and the Golgi apparatus.…”