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

Abstract

Orexin A (OxA) is a neuropeptide produced in the lateral hypothalamus that performs pleiotropic functions in different tissues, including involvement in energy homeostasis and reproductive neuroendocrine functions. The role of OxA is particularly important given the well-studied relationships between physiological mechanisms controlling energy balance and reproduction. The enzyme P450 aromatase (ARO) helps convert androgens to estrogens and has roles in steroidogenesis, spermatogenesis, and energy metabolism in several organs. The goal of this study was thus to investigate the role of OxA in ARO activity and the effects of this regulation on reproductive homeostasis in male gonads from healthy and cryptorchid dogs. The cryptorchidism is a specific condition characterized by altered reproductive and metabolic activities, the latter of which emerge from impaired glycolysis. OxA helps to stimulate testosterone (T) synthesis in the dog testis. We aimed to investigate OxA-mediated modulation of 17β-estradiol (17β-E) synthesis, ARO expression and metabolic indicators in testis of normal and cryptorchid dogs. Our results indicate putative effects of OxA on estrogen biosynthesis and ARO activity based on western blotting analysis and immunohistochemistry for ARO detection and in vitro tests. OxA triggered decrease in estrogen production and ARO activity inhibition; reduced ARO activity thus prevented the conversion of T to estrogens and increasing OxA-mediated synthesis of T. Furthermore, we characterized some metabolic and oxidative modulations in normal and cryptorchid dog's testis. The steroidogenic regulation by OxA and its modulation of ARO activity led us to hypothesize that OxA is a potential therapeutic target in pathological conditions associated with steroidogenic alterations and OxA possible involvement in metabolic processes in the male gonad.

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

“…The mechanisms as to how OXA-binding OX1R regulates testicular steroidogenesis has been well-demonstrated in adult mice by Joshi et al ( 12 ). These findings confirmed our recent papers in dogs, where OXA was demonstrated to significantly decrease basal 17βE secretion via a marked reduction in the aromatase (ARO) enzymic activity in normal and cryptorchid gonads, respectively ( 6 ). As it is known, ARO is responsible for the aromatization of androgens into estrogens ( 20 ).…”

“…Afterwards, the hormone was extracted with ether and left to dry at room temperature. 17βE determination was carried out using the residues of this extract through an ELISA immunoassay (EIA) kit as reported previously ( 6 ). The results were indicated as the 17βE content produced per gram of tissue/per hour.…”

“…Then, suspension of the tissue was treated with the above-reported substances followed by the addition of T (35 µM) dissolved in 100 µl of NADPH solution (3 mg/mL) and treated for 24 h at 37 • C. Afterwards, the hormone was extracted with ether and left to dry at room temperature. 17βE determination was carried out using the residues of this extract through an ELISA immunoassay (EIA) kit as reported previously (6). The results were indicated as the 17βE content produced per gram of tissue/per hour.…”

“…In the male genital tract, PPO, OXA, and OX1R were found in the testis and epididymis of different animal species, dogs included (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13), and in the human prostate (14). In contrast, the distribution of OXB and OX2R has been described in the testis of rats and alpaca (15,16) and rat epididymis (17), and OX2R mRNAs were detected in several male genitalia (18) and in the prostate of humans (19).…”

Aquaporins Are Differentially Regulated in Canine Cryptorchid Efferent Ductules and Epididymis

“…Regarding domestic animal species, studies on dogs have often been conducted regarding either testicular organization and function [40][41][42] or clinical problems related to the specific dysfunction of this tissue [43]. From the limited studies reported, data on the expression and possible role of AQPs in the canine male reproductive tract are limited to the testicular area [38,39,44]; the presence of AQP1 and AQP9 in different cell types in the testis [38,39,44]; and the presence of AQP3, 4, 7, and 9 at the level of the gubernaculum testis (GT) [45], suggesting the need for the further investigation of their roles using disease models of the reproductive system.…”