Bos taurus and Cervus elaphus as Non-Seasonal/Seasonal Models for the Role of Melatonin Receptors in the Spermatozoon

Abstract

Melatonin is crucial in reproduction due its antioxidant, hormonal, and paracrine action. Melatonin membrane receptors (MT1/MT2) have been confirmed on spermatozoa from several species, but functionality studies are scarce. To clarify their role in ruminants as reproductive models, bull (Bos taurus, non-seasonal) and red deer (Cervus elaphus, highly seasonal) spermatozoa were analyzed after 4 h of incubation (38 °C, capacitating media) in 10 nM melatonin, MT1/MT2 agonists (phenylmelatonin and 8M-PDOT), and antagonists (luzindole and 4P-PDOT). Motility and functionality (flow cytometry: viability, intracellular calcium, capacitation status, reactive oxygen species (ROS) production, and acrosomal and mitochondrial status) were assessed. In bull, MT1 was related to sperm viability preservation, whereas MT2 could modulate cell functionality to prevent excess ROS produced by the mitochondria; this action could have a role in modulating sperm capacitation. Deer spermatozoa showed resistance to melatonin and receptor activation, possibly because the samples were of epididymal origin and collected at the breeding season’s peak, with high circulating melatonin. However, receptors could be involved in mitochondrial protection. Therefore, melatonin receptors are functional in the spermatozoa from bull and deer, with different activities. These species offer models differing from traditional laboratory experimental animals on the role of melatonin in sperm biology.

Melatonin alleviates heat stress-induced testicular damage in dairy goats by inhibiting the PI3K/AKT signaling pathway

“…It is able to balance the mitochondrial membrane potential (Jauhari A, 2020 ) and is classified as a mitochondria-targeting antioxidant (Tan DX, 2020 ). Research shows that MT1 was found to have a variable distribution on the sperm head, depending on the spermatozoa and the individual male, whereas MT2 seems to be more restricted to the post-acrosomal and neck regions (Fernández-Alegre E, 2022 ), where are enriched with mitochondria. To address this point in more depth, in addition to exploring the mitochondrial morphology of HS and MT sperm, the link between them can be determined by comparing the proportion of different types of malformed sperm under different conditions, whether the typical heat-stressed malformed sperm is head, neck or tail malformed and which type of sperm is significantly reduced following melatonin treatment.…”