A 22-amino acid synthetic peptide corresponding to the second extracellular loop of rat occludin perturbs the blood-testis barrier and disrupts spermatogenesis reversibly in vivo.

When Sertoli cells were cultured in vitro on Matrigel-coated bicameral units, the assembly of the inter-Sertoli tight junction (TJ) permeability barrier correlated with an induction of occludin expression. Inclusion of a 22-amino acid peptide, NH(2)-GSQIYTICSQFYTPGGTGLYVD-COOH, corresponding to residues 209-230 in the second extracellular loop of rat occludin, at 0.2-4 microM into Sertoli cell cultures could perturb the assembly of Sertoli TJs dose-dependently and reversibly. This peptide apparently exerts its effects by interfering with the homotypic interactions of two occludin molecules between adjacent Sertoli cells at the sites of TJs, thereby disrupting TJs, which, in turn, causes a decline in transepithelial electrical resistance across the Sertoli cell epithelium. When similar experiments were performed using a 22-amino acid myotubularin peptide, NH(2)-TKVNERYELCDTYPALLAVPAN-COOH (residues 156-177), no effects on the assembly of inter-Sertoli TJs in vitro were noted. When a single dose of this synthetic occludin peptide was administered to adult rats intratesticularly at 1.5-10 mg/testis, germ cells began to deplete from the seminiferous epithelium within 8-16 days. By 27 days, virtually all tubules were devoid of germ cells. This antispermatogenic effect was reversible, because germ cells progressively repopulated the epithelium thereafter. Treated testes were indistinguishable from normal or control testes by 68 days post-occludin peptide treatment when assessed using histological analysis. In contrast, control rats receiving either no treatment, vehicle alone, or a 22-amino acid synthetic peptide of myotubularin displayed no changes in the testicular morphology at all time points. The occludin peptide-induced germ cell depletion was also accompanied by a disruption of the blood-testis barrier (BTB) when assessed by micropuncture techniques quantifying [(125)I]-BSA in rete testis fluid and seminiferous tubular fluid following i.v. administration of [(125)I]-BSA through the jugular vein. These results illustrate that the occludin peptide-induced disruption of the BTB may possibly affect the underlying adherens junctions, which causes premature release of germ cells from the epithelium and reversible infertility.