Identification of heat shock protein 10 within the equine embryo, endometrium, and maternal peripheral blood mononuclear cells

Early pregnancy factor has been identified as a 10-kDa extracellular homolog of heat shock protein 10 (Hsp10). Hsp10 has been detected during early pregnancy in serum of mice, sheep, pigs, horses, cows, and humans by the rosette inhibition test. Hsp10 has also been associated with several neoplastic and autoimmune diseases. The goal of the present study was to determine if Hsp10 could be detected in the early equine embryo through the use of immunohistochemistry and quantitative real-time PCR. Additionally, analysis of systemically harvested peripheral blood mononuclear cells (PBMCs) from both pregnant and nonpregnant mares was evaluated to determine expression levels of HSP10. Embryos were collected from Quarter Horse mares by uterine lavage at either 8 or 25 days after ovulation. Collection and separation of PBMCs occurred on Day 8 for both pregnant and nonpregnant mares. Immunohistochemistry revealed cytoplasmic localization of HSP10 throughout the single layer of ectodermal cells forming the trophoblast in Day-8 embryos. Day-25 embryos demonstrated intense localization focally along the apical border of ectodermal cells forming the trophoblast layer of the developing chorion. There was no nuclear staining in either embryonic population. Quantitative real-time PCR detected the presence of mRNA for HSP10 in both 8- and 25-day equine embryos. Day-25 embryos exhibited an elevated degree of expression (P = 0.006) compared with the 8-day embryos for HSP10. Endometrial samples did not display any significant difference in degree of expression for HSP10 (P = 0.10). Finally, PBMCs from pregnant mares demonstrated elevated (P = 0.03) expression of HSP10 compared to the nonpregnant mares on Day 8 of the estrous cycle. This study confirmed the presence of HSP10 protein and mRNA expression of HSP10 in equine embryos at two maturation stages. Additionally, the presence of increased gene expression within PBMCs of pregnant mares suggests communication, possibly leading to necessary immunomodulatory effects between the embryo and mare.