PRSS55 is a novel potential causative gene for human male infertility

Testis-specific PRSS55 is a chymotrypsin-like serine protease that is highly conserved among mammalian species. The essential role of Prss55 in mouse male fertility has been established. What is the role of PRSS55 in human reproduction? Whole exome sequencing was used to identify the genetic cause in an infertile male with teratozoospermia. Papanicolaou staining, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to explore morphological defects in the patient's spermatozoa. Immunofluorescence staining and western blot analysis were conducted to assess the pathogenicity of the identified variant. Intracytoplasmic sperm injection (ICSI) was used to assist the patient with fertilization. Sanger sequencing of the pedigree demonstrated that the infertile man carried a novel homozygous mutation in PRSS55 (c.575C>T [p.A192V]). Morphological defects in the sperm head, neck, midpiece and tail were demonstrated by Papanicolaou staining, SEM and TEM. Immunofluorescence staining and western blotting of the patient's spermatozoa showed that the point mutation changed the conformation of PRSS55 and caused a sharp decrease in the PRSS55 protein concentration. The expression and subcellular localization of PRSS55 in the testis and spermatozoa of mice and humans showed that PRSS55 was expressed in the head and flagella of spermatids and epididymal spermatozoa. Moreover, ICSI treatment for this kind of infertile patient was shown to be effective. These findings revealed a novel mutation in PRSS55 in an infertile patient, suggesting for the first time the crucial role of PRSS55 in human fertility. This study provides new insight into genetic counselling diagnoses and subsequent treatment for male infertility.