Cathepsin L is Required for Completion of Oocyte Meiotic Maturation in Mammals

Infertility is a major concern affecting a huge population worldwide. Aneuploidy is one of the leading causes of the infertility, usually originated from errors that happens in meiosis I as chromosomal misalignment and abnormal chromosomal segregation. Recent research showed that cathepsins family play an important role in affecting the oocytes developmental competence in many species. Cathepsin B inhibition improved bovine developmental competence of the oocytes, especially in the low-quality oocytes. Here, we are the first to introduce the significance of another member of this family, cathepsin L (CTSL) in the process of oocyte maturation using mouse oocyte model.  In this study we evaluated the expression of CTSL during oocyte meiotic maturation and the effect of CTSL inhibition using specific inhibitor “SCP110” on the subsequent maturation process. We found, CTSL is expressed in all stages of Meiosis I. In addition, inhibition of CTSL resulted in delaying the maturation time by elongation the time required for extrusion of the polar body (PBE). Moreover, CTSL inhibition reduced the maturation rate compared to the control group as we found a significant decrease in PBE percent. Trying to understand the reason of the lower maturation rates, we stained the chromosomes and spindles at metaphase I stage, we found a significant increase in chromosomal misalignment at metaphase plate. Finally, we evaluated matured oocytes quality after CTSL inhibition, importantly, aneuploidy incidence was increased significantly after CTSL inhibition. In summary, CTSL is required for normal meiosis completion in oocytes and production of healthy euploid egg.