Toll-like receptor4 as a modulator of fertilization and subsequent pre-implantation development following in vitro maturation in mice.

PROBLEM: The use of in vitro maturation (IVM) as an alternative approach to the conventional assisted reproductive technique in clinical practice is limited due to low fertilization rate. The expression of Toll-like receptors (TLRs) as members of an innate immune system in cumulus cells are thought to affect fertilization. This study was aimed to evaluate the effect of IVM on TLR4 gene expression and fertilization rate in oocytes derived from IVM in comparison with in vivo matured one.

METHOD OF STUDY: Cumulus cells are collected from oocytes derived IVM and in vivo. The expression level of Tlr4 in cumulus cells of both groups was assessed by quantitative real-time PCR. To examine the protein expression level of TLR4, immunocytochemistry and Western blotting techniques were carried out. TLR4 receptor functions were also confirmed by blockade assay and TLR4 receptor activation with lipopolysaccharide.

RESULT: There was a substantial decrease in fertilization and blastulation rate in the IVM group in comparison with the in vivo one. The mRNA expression and protein levels of TLR4 declined in cumulus cells following IVM. Anti-TLR4 blocking antibody dramatically decreased the rate of fertilization and blastocyst formation compared to the in vivo group. In contrast, the fertilization rate was enhanced significantly in the presence of LPS as a TLR4 ligand compared to the control group.

CONCLUSION: Low expression level of Tlr4 following IVM and higher fertilization rate through TLR4 receptor activation with LPS proposed that alteration in TLR4 expression and subsequent cytokine section could be a possible cause of low fertilization rate in IVM-derived oocytes.