Melatonin and its cytoprotector effect on oocyte maturation in mice

Author(s)

Hugo Fernandes

• Document type: Master's Dissertation
• Press: Pirassununga.
• Institution: Universidade de São Paulo (USP). Faculdade de Zootecnica e Engenharia de Alimentos (FZE/BT)
• Defense date: 2015-10-02

Examining board members

Cláudia Lima Verde Leal; Heidge Fukumasu; Yeda Fumie Watanabe

• Advisor: Cláudia Lima Verde Leal

Abstract

Many factors are involved in the control of oocyte maturation and developmental competence. Melatonin (MEL) is a hormone showing varied functions including antioxidant and antiapoptotic activities, besides influencing many cell signaling pathways. There are few studies on the role of MEL in oocyte maturation and the mouse, due to its quick reproduction and lower maintencance cost, is an interesting model widely used for in vitro and particularly in vivo studies. The aim of this work was to study the effects of MEL on in vivo and in vitro maturation and its cytoprotective action (antioxidant/antiapoptotic) in murine cumulus-oocyte complexes (CCOs). In experiment one, mice received MEL injections at concentrations of 0 (control), 10 and 20 mg/kg/i.p./day for 4 days. CCOs were in vivo matured and recovered 17 hours after the last injection. In experiment 2, the animals received MEL in the same dosages of the previous experiment, but for 3 days. CCOs were collected 24 hours after the last injection and in vitro matured with follicle stimulating hormone (FSH). In experiment 3, CCOs were in vitro matured with three MEL concentrations (10-9, 10-6 e 10-3 M) or FSH (FSH control). Finally, in the fourth experiment, the best concentration of MEL (10-9 M) selected in experiment 3 was used alone or in association with hydrogen peroxide (300 µM; H2O2). CCOs were matured as in the previous experiment. For all four experiments maturation rates were evaluated by extrusion of the first polar body and the expression of genes related to apoptosis (Bax and Bcl2l1) and antioxidant enzymes (Gpx1, Sod1 and Sod2) by qPCR-RT both cumulus cells (CC), and for the oocytes (OO) were assessed as well. In experiment 1, treatment with 20 mg/kg MEL showed a higher rate of in vivo maturation of 80.3%, followed by the control (69.4%) and 10 mg/kg MEL (62.4%; P>0.05). No effect for gene expression treatments (P>0.05) was observed. In experiment 2, maturation rate ranged from 39 to 53.2% between treatments (P>0.05). In CC, the gene expression was reduced for Bcl2l1 and enhanced for Gpx1 in animals treated with 20 mg/kg MEL (P<0.05). For OO, only Gpx1 expression was increased for both MEL treatments (P<0.05). In experiment 3, the maturation rates were 48.9, 53.7, 56 e 57.3% for MEL 10-3, 10-6, 10-9 M and FSH, respectively (P>0.05). MEL concentrations of 10-6 and 10-9 M increased expression of Gpx1 and Sod1 genes in CC (P<0.05). For OO, only Bax increased the gene expression in 10-6 M MEL concentration (P<0.05). In the last experiment, there was no significant difference in maturation rate, ranging from 51.8 for H2O2 to 60% for FSH control (P>0.05). Gpx1 and Sod1 genes had their expression increased in all the treatments in CC (P<0.05). For Bcl2l1 gene, the expression was decreased in CC as well (P<0.05). Based on these data, we conclude that MEL treatment in vivo was unable to promote maturation rate in vivo and in vitro, but under in vitro conditions it induced meiosis progression in murine oocytes. In addition, Gpx1 and Sod1 antioxidant genes were more expressed in CC than OO in response to MEL treatments in vitro indicating induction of a possible protective effect against in vitro culture conditions. (AU)

• FAPESP's process: 12/13675-3 - Melatonin and its cytoprotector effect on oocyte maturation in mice
• Grantee: Hugo Fernandes
• Support Opportunities: Scholarships in Brazil - Master