(907) Mouse model of cesarean section wound: model validation and basic characteristics of the scar.

Objective:
Placenta accreta spectrum (PAS) is a highly morbid pregnancy complication that results from abnormal adherence of the placenta to the uterine wall, usually in the area of prior cesarean section or other uterine injury. Molecular mechanisms driving the abnormal placental implantation and trophoblast invasion are still unclear. The aim of this study was to improve and better characterize the mouse model of cesarean section wound and to further analyze the cellular and molecular features of resultant scar tissues.

Study Design:
On postpartum day 1 C57BL6 mice underwent a unilateral longitudinal full thickness injury (Fig.1A). Mice were sacrificed 4-6 weeks later, and uteri (injured and uninjured) were fixed to prepare tissue sections. H&E staining was performed to assess histological architecture. Immunofluorescent (IF) staining for alpha smooth muscle actin and COL1A2 was performed to characterize the myometrial structure and collagen composure of the scar.

Results:
Gross appearance of the injured uterine horn varies from unremarkable to dilated with some uterine distortion and adhesions (Fig 1B). Injured uteri consistently demonstrated a defect in the circumferential and longitudinal myometrial layers of various width (Fig. 1C,D). The scar was consistently covered by endometrial epithelium, but the thickness of underlying stroma varied. IF confirmed consistent incomplete healing of both myometrial layers with areas of disorganized myometrial fibers and abnormal collagen deposition in the scar (Fig.2).

Conclusion:
We characterized a mouse model of uterine injury which recapitulates cesarean section injury in humans. Full thickness longitudinal uterine injury results in permanent disruption of both layers of myometrium and development of the scar, characterized by various amount of type I collage deposition. This model can be used to further understand post-cesarean section healing process and the role of the scar in PAS formation.