HTRA3 expression in non-pregnant rhesus monkey ovary and endometrium, and at the maternal-fetal interface during early pregnancy.

Background: HTRA3 is a recently identified member of the mammalian serine protease family HTRA (high temperature requirement factor A). In both the rodent and the human HTRA3 is transcribed into two mRNA species (long and short) through alternative splicing. We have previously shown that HTRA3 is expressed in the mature rat ovary and may be involved in folliculogenesis and luteinisation. HTRA3 is also upregulated during mouse and human placental development. The current study investigated whether HTRA3 is also localised in the primate ovary (rhesus monkey n = 7). In addition, we examined the non-pregnant rhesus monkey endometrium (n = 4) and maternal-fetal interface during early pregnancy (n = 5) to further investigate expression of HTRA3 in primate endometrium and placentation.

Methods: HTRA3 mRNA levels in several rhesus monkey tissues was determined by semiquantitative RT-PCR. Protein expression and localisation of HTRA3 was determined by immunohistochemistry.

Results: Long and short forms of HTRA3 mRNA were detected in the ovary, aorta, bladder, small intestine, skeletal muscle, heart and uterus but not the liver nor the kidney. HTRA3 protein was immunolocalised to the oocyte of all follicular stages in the rhesus monkey ovary. Protein expression in mural and cumulus granulosa cells of late secondary follicles increased significantly compared to granulosa cells of primordial, primary and secondary follicles. Mural and cumulus granulosa cells of antral follicles also showed a significant increase in expression. Staining intensity was higher in the granulosa-lutein cells compared to the theca-lutein cells of corpora lutea (n = 3). In the non-pregnant monkey endometrium, HTRA3 was detected in the glandular epithelium. The basalis endometrial glands showed higher staining intensity than functionalis endometrial glands. During early pregnancy, strong staining for HTRA3 protein was seen in both maternal decidual cells and glands.

Conclusion: We propose that HTRA3 may be involved in folliculogenesis and luteinisation in the primate ovary. Furthermore, similar to previous findings in the human, HTRA3 is possibly a factor involved in and potentially important for primate placentation.