Nonerythroid hemoglobin promotes human cumulus cell viability and the developmental capacity of the human oocyte

Abstract

Objective: To determine the relationship between the levels of cumulus cell (CC) hemoglobin messenger ribonucleic acid (mRNA) and the developmental potential of the associated oocyte and whether hemoglobin protects the CCs from oxidative stress-induced apoptosis.

Design: Laboratory-based study.

Setting: University laboratory and university-affiliated in vitro fertilization center.

Patient(s): Cumulus cells from the oocytes of patients who underwent in vitro fertilization with intracytoplasmic sperm injection with and without preimplantation genetic testing between 2018 and 2020.

Intervention(s): Studies on individual and pooled CCs collected at the time of oocyte retrieval or cultured under 20% or 5% O₂.

Main outcome measure(s): Quantitative polymerase chain reaction analysis of individual and pooled patient CC samples were used to monitor the hemoglobin mRNA levels. Reverse transcription-polymerase chain reaction arrays were used to assess genes that regulate oxidative stress in CCs associated with aneuploid and euploid blastocysts. Studies were conducted to assess the effect of oxidative stress on the rate of apoptosis, level of reactive oxygen species, and gene expression in CCs in vitro.

Result(s): Compared with CCs associated with arrested and aneuploid blastocysts, the mRNA levels encoding the alpha and beta chains of hemoglobin increased by 2.9- and 2.3-fold in CCs associated with euploid blastocysts, respectively. The mRNA levels encoding the alpha and beta chains of hemoglobin also increased by 3.8- and 4.5-fold in CCs cultured under 5% O₂ vs. 20% O₂, respectively, and multiple regulators of oxidative stress were overexpressed in cells cultured under 20% O₂ compared with those under 5% O₂. However, the rate of apoptosis and amount of mitochondrial reactive oxidative species increased by 1.25-fold in CCs cultured under 20% O₂ compared with those under 5% O₂. Variable amounts of the alpha and beta chains of hemoglobin were also detected within the zona pellucida and oocytes.

Conclusion(s): Higher levels of nonerythroid hemoglobin in CCs are associated with oocytes that result in euploid blastocysts. Hemoglobin may protect CCs from oxidative stress-induced apoptosis, which may enhance cumulus-oocyte interactions. Moreover, CC-derived hemoglobin may be transferred to the oocytes and protect it from the adverse effects of oxidative stress that occurs in vivo and in vitro.

Keywords: Aneuploidy; cumulus cells; hemoglobin; invitro fertilization; oxidative stress.