Expression of proteasome subunits low molecular mass polypeptide (LMP) 2 and LMP7 in the endometrium and placenta of rhesus monkey (Macaca mulatta) during early pregnancy

Abstract

Previous studies have demonstrated that the ubiquitin-proteasome pathway plays an important role in embryo implantation. Low molecular mass polypeptide (LMP) 2 and LMP7 are the two subunits of 20S proteasome, which are critical for proteasome activity. To further elucidate the roles of LMP2 and LMP7 in embryo implantation during early pregnancy, we cloned partial sequences of the LMP2 and LMP7 genes and studied the spatiotemporal expression of LMP2 and LMP7 in rhesus monkey (Macaca mulatta) uteri on Days 12, 18, and 26 of pregnancy. The results showed that the 349-base pair (bp) LMP2 fragment and the 340-bp LMP7 fragment were 97% and 99% identical, respectively, to those of human homologues. From the statistical results of reverse transcription-polymerase chain reaction, in situ hybridization, and immunohistochemistry, we found that the expression levels of LMP2 and LMP7 significantly increased with the elongation of pregnancy. The LMP2 and LMP7 mRNAs were mainly expressed in the luminal and glandular epithelium on Day 12 of pregnancy. On Days 18 and 26 of pregnancy, strong signals of LMP2 and LMP7 mRNAs were detected in the placental villi, trophoblastic column, and arterial endothelial cells close to the implantation site, and moderate expressions were found in the trophoblastic shell and glandular epithelium. The LMP2 and LMP7 mRNAs were extensively distributed in the stroma on Day 26 of pregnancy. The expression patterns of LMP2 and LMP7 proteins were similar to those of their transcripts, but weak immunostaining of LMP2 and LMP7 proteins was detected in stroma at all stages of pregnancy. These results suggest that LMP2 and LMP7 may be involved in some key processes of trophoblastic invasion, angiogenesis, degradation of the extracellular matrix, immune tolerance, and glandular secretion.