The expression levels of NOS2, HMOX1 and VEGFC in cumulus cells are markers of oocyte maturation and fertilization rate

Abstract

PurposeWe aim to study whether the expression of genes related to hypoxia and ageing in cumulus cells (CC) is associated to reproductive results in in vitro fertilization cycles.MethodsCumulus cells (CC) were collected after ovum pick-up (OPU) from 94 women recruited undergoing controlled ovarian stimulation from 2018 to 2021; total RNA was extracted and reverse transcribed to cDNA using random hexamers. 14 genes affected by ageing in humans, and expressed in CC, were selected for testing. Expression levels of these genes were detected by qPCR and normalized against TATA-box binding protein (TBP) in CC. Expression levels were plotted against woman age, AFC, MII rate at OPU (MR), and fertilization rates (FR) and non-parametric Spearman’s correlation was applied.ResultsFrom the initial list of 423 candidate genes, we tested 14 genes related to hypoxia response via HIF1alpha activation, oxidative stress response, and angiogenic response. The expression of CLU, NOS2 and TXNIP had a positive correlation with age (rs=0.25, p=0.014; rs=0.31, p=0.0027; and rs=0.24, p=0.03; respectively). Additionally, NOS2 and HMOX1 expression correlated positively with the retrieval of immature oocytes (rs = 0.23228, p = 0.03242; rs = 0.38827, p = 0.01212; respectively). Moreover, VEGFC levels decreased overall with increasing fertilization rate, independently of age (rs=-0.29, p=0.026).ConclusionWe found that the fertilization potential of a cohort of oocytes is related to the ability of CC to respond to oxidative stress and hypoxia, pointing at NOS2, HMOX1 and VEGFC expression as markers for oocyte maturation and fertilization success.