Transmembrane protein 196-mediated regulation of CatSper channel through STAT3 phosphorylation influences sperm motility in mammals

The progressive decline in sperm motility is a major contributor to male infertility. The cation channel of sperm (CatSper) complex is a sperm-specific calcium (Ca2+) channel that plays a crucial role in regulating sperm motility. However, the molecular mechanisms governing CatSper regulation remain incompletely understood. This study found that the expression level of transmembrane protein 196 (TMEM196) positively influences human sperm quality and Ca2+ concentration. TMEM196-null male mice showed reduced fertility, characterized by fewer offspring and decreased sperm Ca2+ concentration. Sperm quality analysis revealed that TMEM196 deficiency led to reduced sperm concentration, impaired hyperactivation, and decreased motility in male mice. Further investigations demonstrated that the reduction in sperm motility in TMEM196-null mice was associated with decreased sperm Ca2+ concentration and was independent of hormone levels. Considering the essential role of CatSper in regulating sperm Ca2+ homeostasis, we examined the expression of CatSper subunits and observed significantly reduced protein levels of CatSper1-4 in the testes of TMEM196-null mice. In vitro, overexpression of TMEM196 in GC2 cells enhanced Ca2+ signaling and upregulated CatSper-related protein expression. Mechanistically, TMEM196 promoted the transcription of CatSper-related genes by enhancing the phosphorylation of signal transducer and activator of transcription 3 (STAT3). Collectively, these results identify TMEM196 as a novel regulator of the sperm-specific CatSper Ca2+ channel and demonstrate its critical role in modulating sperm motility.