Blood-testis barrier integrity depends on Pin1 expression in Sertoli cells

The conformation and function of a subset of serine and threonine-phosphorylated proteins are regulated by the prolyl isomerase Pin1 through isomerization of phosphorylated Ser/Thr-Pro bonds. Pin1 is intensely expressed in Sertoli cells, but its function in this post mitotic cell remains unclear. Our aim was to investigate the role of Pin1 in the Sertoli cells. Lack of Pin1 caused disruption of the blood-testis barrier. We next investigated if the activin pathways in the Sertoli cells were affected by lack of Pin1 through immunostaining for Smad3 protein in testis tissue. Indeed, lack of Pin1 caused reduced Smad3 expression in the testis tissue, as well as a reduction in the level of N-Cadherin, a known target of Smad3. Pin1^-/- testes express Sertoli cell marker mRNAs in a pattern similar to that seen in Smad3^+/- mice, except for an increase in Wt1 expression. The resulting dysregulation of N-Cadherin, connexin 43, and Wt1 targets caused by lack of Pin1 might affect the mesenchymal-epithelial balance in the Sertoli cells and perturb the blood-testis barrier. The effect of Pin1 dosage in Sertoli cells might be useful in the study of toxicant-mediated infertility, gonadal cancer, and for designing male contraceptives.