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  • br Introduction The cervix is

    2019-07-13


    Introduction The AS601245 weight is a poorly studied component of the mare’s reproductive tract. It has anatomical and biological defense mechanisms involved in the delicate balance between immunological tolerance, sperm transport and biological defense. Anatomically, the cervix is composed of epithelial cells, smooth muscle and stromal fibroblasts which are responsible for production of a resistant collagenous extracellular matrix (Huchzermeyer et al., 2005). The complexity of the cellular composition of the ovine cervix suggests that different cell types communicate in an autocrine or paracrine manner to modify the composition of the extracellular matrix (Schmitz et al., 2006). The cervix undergoes complex changes during the normal estrous cycle, pregnancy and parturition (Nallasamy and Mahendroo, 2017). During estrus in the ewe and mouse, there is slight relaxation and dilation which is partly due to the reorganization of collagen bundles and fibers that disperse and “soften” the extracellular matrix (Falchi et al., 2012, Yoshida et al., 2014, Nallasamy et al., 2017). This softening reduces the tensile strength of the ovine cervix, allowing the smooth muscle to dilate the cervical canal (Kershaw et al., 2007). In contrast, during murine pregnancy the cervix must remain tightly closed to exclude pathogens until near parturition, at which point the cervix profoundly relaxes to allow for delivery (Mahendroo, 2012). Yellon and coworkers have rightly referred to the cervix as the “gatekeeper for pregnancy” (Yellon et al., 2009). Although very little is known about the complex regulatory mechanisms of these changes, the cervix and extra-cervical tissues are influenced by a myriad of hormones, including estrogens, progestogens and prostaglandins (Larsen and Hwang, 2011, Nallasamy et al., 2017). In addition to their effect on mechanical changes, alterations in this hormonal milieu also affect the secretory phenotype of the human cervix, with changes seen throughout estrus and pregnancy (Moriyama et al., 1999). These changes in secretory proteins in the equine cervical mucus plug include both immunologically and gestationally related proteins such as lactoferrin, uteroglobin, uterine serpin 14 and uteroferrin, as well as mucins such as mucin 4 and mucin 5B (Loux et al., 2017). Both estrogen (E2) and progesterone (P4) have significant effects on the female reproductive tract in preparation for fertilization and implantation (Gipson et al., 2001). In humans and ewes, the cervix is a known target of E2 (Rodriguez-Pinon et al., 2008, Falchi and Scaramuzzi, 2013, Nallasamy et al., 2017), with normal cervical tissue containing specific, high-affinity estrogen receptors, including both α and β subtypes (ESR1 and ESR2) (Cao et al., 1983). Additional cervical changes are regulated by the action of progesterone receptor (PGR), while others are moderated by inflammatory mediators, enzymes like cyclooxygenases or peptide hormones from stromal or inflammatory cells (Larsen and Hwang, 2011). Prostaglandins (PGs) play a key role in the regulation of uterine and cervical activity. Different PGs play specific roles; for example, PGF2α aids in the initiation of parturition by stimulating contractions of the myometrium (Novy and Liggins, 1980), while PGE2 was related to cervical relaxation in the ewe (Kershaw et al., 2007) by dispersing the cervical extracellular matrix (Robinson et al., 2011). In fact, PGE2 is commonly used to ripen the cervix of diestrous (Volkmann et al., 1995) and pregnant mares (Rigby et al., 1998). Despite their physiological relevance, little is known about the gene expression and immunolocalization of sex-steroid receptors, prostaglandin E2 receptors (EP), and cyclooxygenases in the cervical mucosa and stroma of the mare. To better understand the hormonal regulation of cervical function, we examined the relative expression of estrogen receptor alpha (ESR1), estrogen receptor beta (ESR2), progesterone receptor (PGR), prostaglandin E2 type 2 (PTGER2) and type 4 (PTGER4) receptors as well as cyclooxygenase-1 (PTGS1) and -2 (PTGS2) in the equine cervical mucosa and stroma during estrus, diestrus and late pregnancy. Protein localization of ESR1, ESR2, PGR, PTGER2 and PTGER4 receptors by immunohistochemistry (IHC) was performed at the same time points.