Effect of Maternal Age on Hippo Pathway Related Gene Expressions and Protein Localization Pattern in Human Embryos

The Hippo pathway plays an important role in embryo development, and separation of trophectoderm (TE) and inner cell mass (ICM) cell lines. Therefore, this study investigated effect of maternal age on activity of Hippo pathway in human embryos.

In this experimental study, the developed up embryos to the blastocyst stage and the embryos whose growth stopped at the morula stage were collected from women aged 20-30 years old (young group, 94 embryos) and >37 years (old group, 89 embryos). Expression of OCT4, SOX2, CDX2, GATA3, YAP genes and the relevant proteins, in the both groups were evaluated using respectively quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and immunofluorescence methods.

There was no significant difference in the expression level of OCT4, SOX2, CDX2, GATA3 and YAP genes in blastocyst and morula stages, between the two groups. However, SOX2 and CDX2 gene expressions in morula stage embryos of the old group was statistically lower than that of the young group (P=0.007 and P=0.008, respectively). Additionally, in the embryos collected from women with >37 years of age, at the blastocyst stage, phospho-YAP (p-YAP) protein was found to be accumulated in the TE, but it was almost disappeared from the ICM. Additionally, in the old group, contrary to the expectation, YAP protein was expressed in the ICM, rather than TE.

The results of this study showed that YAP and P-YAP among the Hippo signalling pathway may be altered by increasing age.