Melatonin influences the sonic hedgehog signaling pathway in porcine cumulus oocyte complexes

<jats:title>Abstract</jats:title><jats:p>Melatonin, which is synthesized in the pineal gland and peripheral reproductive organs, has antioxidant properties and regulates physiological processes. It is well known that melatonin affects in vitro maturation (<jats:styled-content style="fixed-case">IVM</jats:styled-content>) of oocytes and embryonic development in many species. However, beneficial effects of melatonin on <jats:styled-content style="fixed-case">IVM</jats:styled-content> have been explained mainly by indirect antioxidant effects and little information is available on the underlying mechanism by which melatonin directly acts on porcine cumulus oocyte complexes (<jats:styled-content style="fixed-case">COC</jats:styled-content>s). Sonic hedgehog (Shh) signaling is important for follicle development, oocyte maturation, and embryo development, and there may be a relationship between melatonin and Shh signaling. To examine this, we designed three groups: (i) control, (ii) melatonin (10<jats:sup>−9</jats:sup> mol/L), and (iii) melatonin with cyclopamine (2 μmol/L; Shh signaling inhibitor). The aim of this study was to investigate the effects of these agents on cumulus expansion, oocyte maturation, embryo development after parthenogenetic activation (<jats:styled-content style="fixed-case">PA</jats:styled-content>), gene expression in cumulus cells, oocytes and blastocysts, and protein expression in <jats:styled-content style="fixed-case">COC</jats:styled-content>s. Melatonin significantly increased the proportion of <jats:styled-content style="fixed-case">COC</jats:styled-content>s exhibiting complete cumulus expansion (degree 4), <jats:styled-content style="fixed-case">PA</jats:styled-content> blastocyst formation rates, and total cell numbers, which were inhibited by addition of cyclopamine. Simultaneously, the expression of cumulus expansion‐related genes (<jats:italic>Ptgs1</jats:italic>,<jats:italic> Ptgs2,</jats:italic> and <jats:italic>Has2</jats:italic>) and Shh signaling‐related genes (<jats:italic>Shh</jats:italic>,<jats:italic> Pthc1</jats:italic>,<jats:italic> Smo,</jats:italic> and <jats:italic>Gli1</jats:italic>) and proteins (Ptch1, Smo, and Gli1) in cumulus cells was upregulated in the melatonin‐treated group, and these effects were also inhibited by cyclopamine. In conclusion, our results suggest that Shh signaling mediates effects of melatonin to improve porcine cumulus expansion and subsequent embryo development.</jats:p>