Osteopontin expression in prepubertal and adult dog testes and the effect of slow-release deslorelin implants (Suprelorin® 4.7 mg)

Osteopontin (OPN) is a highly phosphorylated glycoprotein expressed in several cells, tissues, and tissue fluids, including the male reproductive system. Recent studies have indicated that OPN may be a potential fertility marker in male dogs. However, OPN expression and localization during testicular growth are still unclear, and the effect of pharmacological castration on testicular OPN expression in male dogs has not been studied to date. This study aimed to investigate and compare the expression and protein immunolocalization of OPN in the prepubertal (PRE) and adult dog (AD) testes, while also evaluating whether treatment of adult dogs (DES) with gonadotropin-releasing hormone (GnRH)-agonist deslorelin (Suprelorin® 4.7 mg implant) could alter the expression of testicular OPN. A significantly elevated OPN gene expression (p ≤ 0.007) was detected in the PRE dogs' testes than in AD and DES dogs. In addition, OPN mRNA expression was higher in DES dogs than in AD (p = 0.002). OPN-immunoreactivity was observed in all groups as granular staining in Sertoli and Leydig cell cytoplasm. Furthermore, in AD dogs, one or sometimes two OPN-positive granules were observed in round spermatids at stage V, and in elongating and elongated spermatids at stages I-III and VI-VIII of the spermatogenic cycle. Our results confirm the presence of OPN in the testes of prepubertal, adult, and deslorelin-induced spermatogenic and steroidogenic arrest dogs and reveal that infertile status, either developmental in PRE or induced in DES, affects testicular OPN expression.