Importance of Uterine Cell Death, Renewal, and Their Hormonal Regulation in Hamsters that Show Progesterone-Dependent Implantation

Abstract

This study was initiated to investigate the significance of uterine cell death and proliferation during the estrous cycle and early pregnancy and their correlation with sex steroids in hamsters where blastocyst implantation occurs in only progesterone-primed uteri. The results obtained in hamsters were also compared with mice where blastocyst implantation occurs in progesterone-primed uteri if estrogen is provided. Apoptotic cells in the uterus were detected by using terminal deoxynucleotide transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL) technique. Uterine cell proliferation was determined by 5-bromo-2'-deoxyuridine labeling followed by immunohistochemistry and methyl-tritiated [(3)H]thymidine labeling. Active caspase-3, an executor protein of cell death, expression was assayed by immunohistochemistry/immunofluorescence. Our results demonstrate that epithelial proliferation on the second day after mating marks the initiation of pregnancy-related uterine changes in both species despite their differences in hormonal requirements. Hamsters and mice showed subtle differences in uterine proliferative and apoptotic patterns during early pregnancy and in response to steroids. There existed almost a direct correlation between apoptosis and caspase-3 expression, suggesting uterine cell death mostly involves the caspase pathway. Consistent with these findings, we showed, for the first time, that execution of uterine epithelial cell apoptosis by caspase-3 is important for blastocyst implantation because a caspsase-3 inhibitor N-acetyl-DEVD-CHO when instilled inside the uterine lumen on d 3 of pregnancy inhibits implantation in hamsters and mice. The overall results indicate that uterine cell apoptosis and proliferation patterns are highly ordered cell-specific phenomena that play an important role in maintaining the sexual cycle and pregnancy-associated uterine changes.

Uterine RAC1 via Pak1-ERM signaling directs normal luminal epithelial integrity conducive to on-time embryo implantation in mice

“…This luminal epithelial cell death is identified as apoptosis and is executed by Caspase 3, because a Caspase 3 inhibitor N-acetyl-DEVD-CHO inhibits implantation. 15 Opposite to our initial assumption that a premature decrease of epithelial polarity in the absence of Rac1 would lead to increased epithelial cell death, we found that Rac1 is essential for timely luminal epithelial degradation within the implantation chamber; its null mutation results in a persistent epithelial layer surrounding the implantation blastocyst even on day 6 of pregnancy. However, unlike previous observations in Klf5 null mice, 5 these retained epithelial layers in the Rac1 null implantation chamber is not due to a reduced Cox2 expression.…”

“…14 There is early evidence that Caspase 3 is an executor of uterine epithelial apoptotic death and loss of Klf5 in mice leads to impaired epithelial cell elimination at postimplantation. 5,15 However, it remained largely elusive regarding the underlying mechanisms governing luminal epithelial cell death after blastocyst-uterus attachment.…”

Leukemia inhibitory factor ligand-receptor signaling is important for uterine receptivity and implantation in golden hamsters (Mesocricetus auratus)

“…Female hamsters that showed three consecutive estrous cycles were placed with fertile males on the evening of the proestrous day for mating. Microscopic finding of spermatozoa in the vaginal discharge the next morning was designated day 1 of pregnancy (Wang et al 2002, 2004, Zhang & Paria 2006. Female mice were mated with fertile male to induce pregnancy (day 1 of pregnancyZvaginal plug; Paria et al 1993, Zhang & Paria 2006.…”

“…The preparation of a receptive uterus for supporting embryo implantation in mice and rats is achieved by sequential effects of ovarian progesterone (P 4 ) and estrogen (E; Yoshinaga & Adams 1966, Psychoyos 1973, Paria et al 1993. However, uterine receptivity is regulated only by ovarian P 4 in hamsters (Prasad et al 1960, Orsini & Meyer 1962, Harper et al 1969, Wang et al 2002, 2004, Zhang & Paria 2006. Studies in the mouse, rat, and agricultural species suggest that cytokines and growth factors produced by the uterine cells in response to ovarian steroids help in preimplantation embryo development and implantation (Carson et al 2000, Modric et al 2000.…”

“…In contrast, dating of the time of ovulation, chronological development of the secretory endometrium, and the timing of implantation cannot be accurately predicted in humans. It has been demonstrated that in the majority of species, such as the hamster, rabbit, pig, guinea pig, monkey, and human, luteal estrogen is not required to initiate the process of implantation (Deanesly 1960, Prasad et al 1960, Orsini & Meyer 1962, Harper et al 1969, Meyer et al 1969, Perry et al 1973, George & Wilson 1978, Heap et al 1981, Hoversland et al 1982, Ghosh et al 1994, Zegers-Hochschild & Altieri 1995, Wang et al 2002, 2004, Zhang & Paria 2006. A comprehensive study has not been done on the relative involvement and functions of uterine Lif in species where implantation is dependent on ovarian P 4 , but not E. Thus, the present experiments were undertaken to study the expression of Lif and its receptors during the periimplantation period and their hormonal and embryonic regulation in hamsters.…”