Nitric oxide synthase isoforms and the effect of their inhibition on meiotic maturation of porcine oocytes

Abstract

In this paper we assessed: (i) the change in nitric oxide synthase (NOS) isoforms' expression and intracellular localization and in NOS mRNA in porcine oocytes during meiotic maturation; (ii) the effect of NOS inhibition by N(omega)-nitro-l-arginine methyl ester (l-NAME) and aminoguanidine (AG) on meiotic maturation of cumulus-oocyte complexes (COC) as well as denuded oocytes (DO); and (iii) nitric oxide (NO) formation in COC. All three NOS isoforms (eNOS, iNOS and nNOS) and NOS mRNA (eNOS mRNA, iNOS mRNA and nNOS mRNA) were found in both porcine oocytes and their cumulus cells except for nNOS mRNA, which was not detected in the cumulus cells. NOS isoforms differed in their intracellular localization in the oocyte: while iNOS protein was dispersed in the oocyte cytoplasm, nNOS was localized in the oocyte cytoplasm and in germinal vesicles (GV) and eNOS was present in dots in the cytoplasm, GV and was associated with meiotic spindles. l-NAME inhibitor significantly suppressed metaphase (M)I to MII transition (5.0 mM experimental group: 34.9% MI, control group: 9.5% MI) and at the highest concentration (10.0 mM) also affected GV breakdown (GVBD); in contrast also AG inhibited primarily GVBD. The majority of the oocytes (10.0 mM experimental group: 60.8%, control group: 1.2%) was not able to resume meiosis. AG significantly inhibited GVBD in DO, but l-NAME had no significant effect on the GVBD of these cells. During meiotic maturation, NO is formed in COC and the NO formed by cumulus cells is necessary for the process of GVBD.

Reduction of nitric oxide level leads to spontaneous resumption of meiosis in diplotene-arrested rat oocytes cultured in vitro

“…Few studies suggest that high level of NO induces meiotic resumption from diplotene arrest in mouse, 7,15 rat, 16 porcine, 9,17,18 and murine oocytes. 13 On the other hand, NO inhibits meiotic resumption from diplotene arrest in rat .................................................................................................................. 41 and a reduced level of NO triggers meiotic resumption from diplotene arrest in rat oocytes cultured in vitro.…”

The role of nitric oxide synthase isoforms in aged porcine oocytes

“…NOS isoforms play an essential part in meiotic maturation (Tao et al, 2005;Chmelíková et al, 2010). Our experiments highlight the role of NOS during prolonged cultivation of porcine oocytes.…”

“…The reason for the various rates of isoform decrease is uncertain. Due to the fact that nNOS and iNOS levels in oocytes were relatively low and eNOS indicated a higher-intensity signal, the differences in the signal decrease rate may have resulted from diverse levels of specific isoforms (Kim et al, 2005;Chmelíková et al, 2010). Accordingly, detectable iNOS and nNOS signals in oocytes have yet to be observed (Kim et al, 2005;Hattori and Tabata, 2006).…”

Inhibition of germinal vesicle breakdown by antioxidants and the roles of signaling pathways related to nitric oxide and cGMP during meiotic resumption in oocytes of a marine worm

“…However, analyses of mammalian oocytes have sometimes presented conflicting data regarding the functions of NO and its common downstream mediator, cGMP (LaPolt 2002), particularly during the resumption of meiotic maturation, as the oocyte undergoes nuclear disassembly (germinal vesicle breakdown (GVBD)); Downs 2010. Thus, mammalian GVBD is often stimulated by antioxidants that can counteract the effects of RNS and reactive oxygen species (ROS;Sun et al 2000, Tao et al 2004a, 2010, Nadri et al 2009, and consistent with these findings, GVBD is prevented or delayed by treatments that elevate intraoocytic NO/cGMP levels (Törnell et al 1990, Faerge et al 2001, Tao et al 2005, Zhang et al 2005, Viana et al 2007, Sela-Abramovich et al 2008. Conversely, in other studies of mammals, antioxidants block GVBD (Takami et al 1999), and pathways involving NO and cGMP promote GVBD (Hubbard & Price 1988, Jablonka-Shariff & Olson 2000, Sengoku et al 2001, Tao et al 2004b, Huo et al 2005, Chmelikova et al 2010, Amale et al 2011. Although species-specific differences might account for some of these discrepancies, both inhibitory and stimulatory effects of NO signaling have been reported for the same oocytes (Bu et al 2003, Bilodeau-Goeseels 2007.…”