Mild hypothermia and vitrification increase the mRNA expression of cold-inducible proteins in bovine oocytes and cumulus cells

Abstract

The cold-inducible RNA-binding protein (CIRBP) assists cells in adapting to new environmental conditions stabilizing specific mRNAs and promoting their translation. CIRBP participates in anti-apoptotic and anti-senescence processes, and its expression is induced by mild hypothermia, which may be advantageous to oocytes during vitrification. Several newly discovered small molecules, like zr17-2, mimic the effects of cold temperatures by increasing the expression of CIRBP at normothermia. This study aimed to evaluate the mRNA changes of a group of cold-inducible protein-encoding and apoptotic genes in response to exogenous supplementation of zr17-2 (experiment 1) or CIRBP (experiment 2) in vitro matured bovine oocytes and their cumulus cells. In experiment 1, cumulus-oocyte complexes (COCs) were randomly exposed to three concentrations of zr17-2 (1, 10, and 100 μM) during 24 h of in vitro maturation (IVM) under normothermia (38.5 °C) or mild hypothermia (34 °C) culture conditions. In experiment 2, COCs were randomly exposed to three concentrations of CIRBP (2, 4, and 6 μg/mL) or subjected to mild hypothermia (34 °C), followed by oocyte vitrification/warming after 20 h of IVM. The quantification of the selected gene transcript expression was performed separately in oocytes and cumulus cells by quantitative real-time PCR. We show that oocytes and cumulus cells exhibited similar mRNA expression responses to mild hypothermia and vitrification. However, minor differences were observed when COCs were exposed to exogenous supplementation with zr17-2 and CIRBP. In conclusion, the alterations observed in the mRNA expression in these experimental conditions may impact the quality of the cumulus-oocyte complexes in terms of vitrification and sublethal hypothermia challenges. In this sense, our results should complement other oocyte quality assessments for its application in future assisted reproductive techniques in the bovine species, including improving oocyte cryotolerance to vitrification.