Abstract
Bovine oocytes and blastocysts produced in vitro are frequently of lower quality and less cryotolerant than those produced in vivo, and greater accumulation of lipids in the cytoplasm has been pointed out as one of the reasons. In human adipocytes cGMP signaling through the activation of PKG appears to be involved in lipid metabolism, and components of this pathway have been detected in bovine cumulus-oocyte complexes (COCs). The aim of this study was to investigate the influence of this pathway on the lipid content in oocytes and expression of PLIN2 (a lipid metabolism-related gene) in cumulus cells. COCs were matured in vitro for 24 h with different stimulators of cGMP synthesis. The activation of soluble guanylyl cyclase (sGC) by Protoporphyrin IX reduced lipid content (22.7 FI) compared to control oocytes (36.45 FI; P <0.05). Stimulation of membrane guanylyl cyclase (mGC) with natriuretic peptides precursors A and C (NPPA and NPPC) had no effect (36.5 FI; P>0.05). When the PKG inhibitor KT5823 was associated with Protoporphyrin IX, its effect was reversed and lipid contents increased (52.71 FI; P<0.05). None of the stimulators of cGMP synthesis affected the expression of PLIN2 in cumulus cells. In conclusion, stimulation of sGC for cGMP synthesis promotes lipolytic activities in bovine oocytes matured in vitro and such effect is mediated by PKG. However, such effect may vary depending on the stimulus received and/or which synthesis enzyme was activated, as stimulation of mGC had no effects.
Highlights
Throughout the years, the in vitro production of embryos (IVP) has been increasing its importance as an assisted reproduction technology and is employed worldwide in animal production to accelerate the production of genetically superior animals (Perry, 2015)
Oocytes from cumulus-oocyte complexes (COCs) matured in the presence of fetal calf serum (FCS) had a higher lipid content (39.73 fluorescence intensity (FI)) compared to the control group (PVA, 26.96 FI; P
Different agents to stimulate cyclic guanosine 3'5'-monophosphate (cGMP) synthesis were tested for oocyte nuclear maturation after the in vitro maturation (IVM) period, to assure treatments would not negatively interfere on oocyte nuclear maturation
Summary
Throughout the years, the in vitro production of embryos (IVP) has been increasing its importance as an assisted reproduction technology and is employed worldwide in animal production to accelerate the production of genetically superior animals (Perry, 2015). Bovine oocytes and blastocysts produced in vitro are inferior in quality compared to those produced in vivo as they present more swollen blastomeres, slower growth rate (Fair et al, 2001), morphological, biochemical and metabolic alterations (Lonergan et al, 2006), and darker cytoplasm as a consequence of higher lipid accumulation (Pollard and Leibo, 1994). This last characteristic has been associated with lower quality of embryos produced in vitro and to their higher sensitivity to cryopreservation (Rizos at al., 2002).
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