Expression of pro-inflammatory cytokines in mouse blastocysts during implantation: modulation by steroid hormones

Expression and hormonal regulation of pro-inflammatory cytokines and their role in blastocyst activation and implantation is poorly known. The present study is aimed at analysing the expression and hormonal modulation of two pro-inflammatory cytokines [interleukin-1alpha (IL-1alpha) and IL-6] in mouse blastocysts during implantation.

Blastocyst-uterine interactions are inhibited by progesterone during implantation and subsequent treatment with oestrogen triggers events that allow implantation to begin. Using this delayed implantation mouse model, dormant and activated blastocysts were recovered from mice treated with progesterone alone and progesterone plus oestrogen therapy, respectively. Expression of IL-1alpha and IL-6 messenger RNA (mRNA) was analysed in normal, dormant and activated blastocysts by in situ hybridization using specific labelled sense and antisense RNA probes, and the protein expression of the same was analysed by immunocytochemistry.

In situ hybridization revealed IL-1alpha and IL-6 mRNA localization in normal, dormant and activated blastocysts and a differential expression was observed in relation to the exposure to progesterone and oestrogen. There was less expression in the dormant blastocysts as compared with the normal and activated ones, and the pattern was similar for both cytokines. Immunocytochemistry also revealed a similar pattern of protein expression to that of the mRNA expression for both the cytokines.

Using a delayed implantation model, we show that mouse blastocysts express both IL-1alpha and IL-6 mRNA as well as their respective proteins. Both mRNA and the protein levels of IL-1alpha and IL-6 seem to be hormonally modulated in mouse blastocysts during implantation.