Effects of different stimulators of cGMP synthesis on lipid content in bovine oocytes matured in vitro

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.