Presence of melatonin‐catabolizing non‐specific enzymes myeloperoxidase and indoleamine 2,3‐dioxygenase in the ram reproductive tract

Abstract

The melatonin catabolism is very complex and not completely understood. Melatonin can be metabolized by free radical interaction, but also pseudo‐enzymatically or by enzymatic pathways. We have previously detected the existence of melatonin‐synthesizing enzymes and melatonin receptors MT1 and MT2 in the ram reproductive tract; thus, in order to start to elucidate melatonin catabolism in these organs, we have investigated the presence of the melatonin‐catabolizing enzymes indoleamine 2,3‐dioxygenase (IDO, both IDO1 and IDO2 isoforms) and myeloperoxidase (MPO) in testis, epididymis and accessory glands. Gene expression analyses by real‐time PCR showed the presence of MPO, IDO1 and IDO2 in all the organs of the ram reproductive tract and revealed that MPO is the main melatonin‐catabolizing enzyme, which is mainly expressed in the testis and the bulbourethral glands (p < .05). These results were further corroborated by immunohistochemical staining, and by Western blot. Likewise, MPO was also evidenced in epididymal and ejaculated spermatozoa by indirect immunofluorescence and Western blot. In conclusion, melatonin‐catabolizing enzymes MPO, IDO1 and IDO2 are expressed in the ram reproductive tract, and MPO is the most expressed one, mainly in the testis and the bulbourethral glands. The presented results warrant further studies on the function of these enzymes and their melatonin‐metabolizing activity.

Melatonin affects red deer spermatozoa motility and physiology in capacitating and non‐capacitating conditions

“…Melatonin is a widespread and pleiotropic molecule (Hardeland et al., 2011 ). Widely studied as a hormone regulating the circadian cycle and seasonality, evidence has mounted on its paracrine activity in reproductive organs (Gonzalez‐Arto et al., 2016 ; Martínez‐Marcos et al., 2019 ) and its membrane receptors MT 1 and MT 2 are present in spermatozoa (González‐Arto et al., 2016 , 2017 ). Melatonin affects sperm survival, capacitation and chemotaxis (Casao et al., 2012 ; Cebrián‐Pérez et al., 2014 ; Espino et al., 2011 ).…”

Characterization of Myeloperoxidase in the Healthy Equine Endometrium

“…In a healthy, non-inflamed mare uterus, only few neutrophils may be found in the endometrium during estrus, while during diestrus, they are practically non-existent [42]. For a long time, it was accepted that MPO gene expression, and consequently its biosynthesis, was exclusively associated with myeloid precursors [9], but recently the enzyme has been localized in some non-myeloid cells in inflammatory and physiological conditions in different organs [10][11][12][13]. For the first time, our study shows the immunohistochemical expression of MPO in equine endometrial cells.…”

“…The synthesis and expression of MPO have been exclusively related to myeloid cells, mainly neutrophils [9]. However, MPO has recently been described to be contained in non-myeloid cells [10][11][12][13]. Non-inflammatory cells are able to capture MPO from the extracellular medium [14,15], and through direct contact with neutrophils [16].…”

“…Non-inflammatory cells are able to capture MPO from the extracellular medium [14,15], and through direct contact with neutrophils [16]. More interestingly, the capacity of non-myeloid cells to express endogenous MPO has been demonstrated in cells of the reproductive tract of rams and human neurons under physiological conditions [10,11], as well as in human endothelial cells as a response to oxidative stress [17].…”

Genotyping of rams based on melatonin receptor 1A gene polymorphisms: a tool in sire selection?

“…Melatonin can influence ovine reproduction through mechanisms other than photoperiod translation. It can also be synthesised in ram testes (Martínez-Marcos et al 2019) and is present in seminal plasma (Casao et al 2010). Moreover, both melatonin receptors, MT1 and MT2, have been found in the ram reproductive tract (González-Arto et al 2017) and the plasma membrane of ovine spermatozoa (Casao et al 2012;González-Arto et al 2016).…”