Potential role of orexin A binding the receptor 1 for orexins in normal and cryptorchid dogs

Abstract

BackgroundCryptorchidism is one of the most common birth disorders of the male reproductive system identified in dogs and other mammals. This condition is characterised by the absence of one (unilateral) or both (bilateral) gonads from the scrotum. The peptides orexin A (OxA) and B (OxB) were obtained by post-transcriptional proteolytic cleavage of a precursor molecule, called prepro-orexin. These substances bind two types of G-coupled receptors called receptor 1 (OX1R) and 2 (OX2R) for orexins. OX1R is specific to OxA while OX2R binds the two peptides with equal affinity. Orexins modulate a great variety of body functions, such as the reproductive mechanism. The purpose of the present research was to study the presence of OxA and its receptor 1 and their possible involvement in the canine testis under healthy and pathological conditions.MethodsThis study was performed using adult male normal dogs and male dogs affected by unilateral cryptorchidism. Tissue samples were collected from testes and were divided into three groups: normal, contralateral and cryptic. The samples were used for immunohistochemistry, Western blot and in vitro tests for testosterone evaluation in normal and pathological conditions.ResultsOxA-immunoreactivity (IR) was described in interstitial Leydig cells of the normal gonad, and Leydig, Sertoli cells and gonocytes in the cryptic gonad. In the normal testis, OX1R-IR was described in Leydig cells, in pachytene and second spermatocytes and in immature and mature spermatids throughout the stages of the germ developing cycle of the male gonad. In the cryptic testis OX1R-IR was distributed in Leydig and Sertoli cells. The presence of prepro-orexin and OX1R was demonstrated by Western blot analysis. The incubation of fresh testis slices with OxA caused the stimulation of testosterone synthesis in the normal and cryptic gonad while the steroidogenic OxA-induced effect was cancelled by adding the selective OX1R antagonist SB-408124.ConclusionsThese results led us to hypothesise that OxA binding OX1R might be involved in the modulation of spermatogenesis and steroidogenesis in canine testis in healthy and pathological conditions.

Orexin A-Mediated Modulation of Reproductive Activities in Testis of Normal and Cryptorchid Dogs: Possible Model for Studying Relationships Between Energy Metabolism and Reproductive Control

“…Furthermore, E levels decrease in the presence of OxA, demonstrating an inhibitory effect of OxA on E synthesis. A possible role of OxA in these mechanisms was suggested in previous studies demonstrating the presence and expression of OxA in the testis of several species (25, 28, 31), according to which OxA induces T secretion via binding OX1R. OxA is also involved in down-regulating estrogen secretion.…”

“…Western blotting analysis confirmed immunohistochemical results and identified two antibody-specific bands at ~51–53 and 49 kDa in agreement with previous results from Lambard et al (56). We previously demonstrated the presence and expression of OxA and OxA receptor 1 in testis from normal and cryptorchid dogs (31). OxA was seen in both the interstitial and tubular compartments.…”

“…The peptides OxA and orexin B (OxB) are derived from the proteolytic cleavage of a prepro-orexin precursor and bind the receptors orexin receptor 1 (OX1R) and orexin receptor 2 (OX2R). Prepro-orexin, OxA, and OX1R have been identified in rat testis and epididymis (23–27), alpacas ( Vicugna pacos ) (28, 29), mouse testis (21, 30), the normal and cryptorchid male gonads (31), and the urethro-prostatic complex of cattle (32), and in the normal, hyperplastic, and neoplastic prostate of human males (33–35). The effects of OxA on testis function and glucose homeostasis may find useful extrapolations by considering male infertility conditions like cryptorchidism (36).…”

Ingestive Peptides – An Emerging Tool for Diagnostics and Therapeutics: A Review

“…The orexinic system can engage in placental growth and development and in the regulation of its steroidogenic capacity through endocrine, paracrine and/or autocrine mechanisms (Dall'Aglio et al 2012). In canine testis, Orexin-A can modulate the spermatogenesis and the steroidogenesis in healthy and pathological states (Liguori et al 2018).…”

Does Orexin B-Binding Receptor 2 for Orexins Regulate Testicular and Epididymal Functions in Normal and Cryptorchid Dogs?

“…Notoriously, OXA—by binding OX1R—has been demonstrated to have a steroidogenic effect in the testes of rats ( 5 ), alpaca ( 8 ), and normal and cryptorchid dogs ( 9 ). The mechanisms as to how OXA-binding OX1R regulates testicular steroidogenesis has been well-demonstrated in adult mice by Joshi et al ( 12 ).…”