Combination of histochemical analyses and micro-MRI reveals regional changes of the murine cervix in preparation for labor

Antara Chatterjee,Anna Dorogin,Rojan Saghian,John G Sled,Lindsay S Cahill,Oksana Shynlova,Stephen Lye

doi:10.1038/s41598-021-84036-9

Abstract

The cervix is responsible for maintaining pregnancy, and its timely remodeling is essential for the proper delivery of a baby. Cervical insufficiency, or “weakness”, may lead to preterm birth, which causes infant morbidities and mortalities worldwide. We used a mouse model of pregnancy and term labor, to examine the cervical structure by histology (Masson Trichome and Picrosirius Red staining), immunohistochemistry (Hyaluronic Acid Binding Protein/HABP), and ex-vivo MRI (T2-weighted and diffusion tensor imaging), focusing on two regions of the cervix (i.e., endocervix and ectocervix). Our results show that mouse endocervix has a higher proportion of smooth muscle cells and collagen fibers per area, with more compact tissue structure, than the ectocervix. With advanced gestation, endocervical changes, indicative of impending delivery, are manifested in fewer smooth muscle cells, expansion of the extracellular space, and lower presence of collagen fibers. MRI detected three distinctive zones in pregnant mouse endocervix: (1) inner collagenous layer, (2) middle circular muscular layer, and (3) outer longitudinal muscular layer. Diffusion MRI images detected changes in tissue organization as gestation progressed suggesting the potential application of this technique to non-invasively monitor cervical changes that precede the onset of labor in women at risk for preterm delivery.

Highlights

The cervix is responsible for maintaining pregnancy, and its timely remodeling is essential for the proper delivery of a baby
We applied an Magnetic resonance imaging (MRI) technique called diffusion tensor imaging (DTI), which is sensitive to cellular scale restriction of water movement, and is used to infer orientation of fibers or the organization of tissue structure
We found that mouse endocervix from NP, GD15, and GD18 animals contains three well-defined zones, with specific orientation of structurally organized fibers

Summary

Introduction

The cervix is responsible for maintaining pregnancy, and its timely remodeling is essential for the proper delivery of a baby. Diffusion MRI images detected changes in tissue organization as gestation progressed suggesting the potential application of this technique to non-invasively monitor cervical changes that precede the onset of labor in women at risk for preterm delivery. Two measured quantities from DTI images are mean diffusivity (MD) (B) and fractional anisotropy (FA) (C) and values are compared for outer and middle layers at the endocervix and ectocervix for non-pregnant and pregnant mice at two gestational time points (15GD and 18GD). The non-pregnant cervix in women and mice is a small, yet firm, cylinder with a canal inside surrounded by region-specific cervical lumen[25], separated from the uterus and vagina by two physical openings, the internal os and external os, with well-defined endocervix and ectocervix sub-regions[26,27,28]. Recent literature has shown that the cervix is a specialized organ and its transformation during pregnancy is a complex molecular p rocess[20,36,37]

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