The Role of Estrogen Receptor α in the Development and Maintenance of Uterine Epithelium in Mice

The uterus is composed of uterine cervix and uterine body. The cervical lumen is lined by the K14+/p63+/K8- squamous and K14-/p63-/K8+ columnar epithelium, which are demarcated at the squamocolumnar junction (SCJ). Location of SCJ changes depending on several factors, including ovarian hormones, vaginal acidity, and age in women. The epithelial region that the SCJ moves is called the transformation zone (TZ), where most cervical cancers occur. In K14E7 mice expressing HPV16 E7, SCJ shifts towards the uterine epithelium in an estrogen/ERα-dependent manner. We observed that SCJ moves toward the ectocervical epithelium in estrogen-depleted ovariectomized mice. (i.e., retraction of squamous epithelium). Estrogen administration expanded the squamous epithelium. These results suggest that HPV and estrogen/ERα promote squamous differentiation in the cervix. To better understand the role of ERα in this process, I first characterized genesis of cervical squamous epithelium and SCJ in postnatal mice. At birth, the entire cervical epithelium was composed of K14-/p63-/K8+ cells. Several K14+/p63+/K8- epithelial cells appeared underneath K14-/p63-/K8+ epithelial cells in the endocervix at postnatal day 6 (P6). They expanded to the posterior part of the cervix as aging. At P16 onwards, the endocervical epithelium became stratified. The location and epithelial marker expression of SCJ at P16 was similar to that in ovariectomized adults, indicating that squamous epithelium development was complete at P16. ERα expression pattern in the cervical epithelium at postnatal age coincided with expansion of K14+/p63+ cells. To study the role of epithelial ERα in squamous differentiation and SCJ formation, I used Wnt7aCre/Esr1f/f mice lacking expression of ERα specifically in the epithelium of the female reproductive tract including the cervix-they will be referred to as ER epithelium deletion (ED). Interestingly, ED mice had a delay in formation of SCJ. The location of SCJ in both ED and ERα knockout (Esr1-/-) mice at prepubertal age (P21) was similar to that in wild-type mice. However, junction location was impaired in ED but not in Esr1-/- mice at adult age, suggesting that balance between epithelial and stromal ERα is required for maintenance of SCJ at adult age. I found that, in epithelial ERα-deficient ED mice, K14+/p63+/K8- basal cells were present underneath the columnar epithelium in the entire uterus at adult age. I found that, although rare, these cells were also present in wild-type mice as early as postnatal day 14. Uterine basal cells expressed proteins that are not expressed in the other epithelial cell types in the cervix and uterine body. I found that K14 and p63 were expressed in human endometrium at the mRNA level. I did cell lineage tracing experiments in Krt5CreER/+/ROSA26mTmG/+ mice and found that uterine basal cells contribute to the columnar epithelium. Traced cells were mostly in the glandular epithelium. My results showed that the number of glands decreased in in ED mice but not in Esr1-/- mice. My results suggest that the balance between epithelial and stromal ERα signaling is crucial for the development and maintenance of cervical SCJ and uterine glandular genesis.