The effects of cooling human oocytes

Area of Science:

• Reproductive Biology
• Cell Biology
• Cryobiology

Background:

• Human oocyte cryopreservation is crucial for fertility treatments.
• Understanding the effects of low temperatures on oocyte structure is vital for improving cryopreservation success rates.

Purpose of the Study:

• To investigate the impact of cooling on the meiotic spindle and overall structure of preovulatory human oocytes.
• To evaluate the cryoprotective efficacy of dimethyl sulfoxide (DMSO) against cooling-induced damage.

Main Methods:

• Human oocytes were cooled to 0°C at 1°C/min, with or without DMSO.
• Oocytes were held at 0°C for 20 or 60 minutes.
• Transmission electron microscopy (TEM) was used to examine oocyte structure and meiotic spindles at 0°C or 8°C, with controls at 22°C or 37°C.

Main Results:

• Cooling to 0°C caused significant disassembly of meiotic spindles due to microtubule depolymerization, irrespective of DMSO presence.
• DMSO offered minimal stabilization; cooled oocytes showed disorganized spindles and abnormal chromosome arrangement.
• Other cellular components like endoplasmic reticulum and mitochondria were also adversely affected in some cooled oocytes and cumulus cells.

Conclusions:

• Human oocyte meiotic spindles are highly sensitive to simple cooling, even at 0°C.
• Dimethyl sulfoxide (DMSO) does not provide substantial stabilization to meiotic spindles during cooling.
• These findings highlight the vulnerability of oocytes to thermal stress and inform strategies for improving oocyte cryopreservation.