A mouse model of placenta accreta spectrum

Extracellular matrix induces trophoblast HtrA4 expression: Implications for the pathogenesis of placenta accreta spectrum

OBJECTIVE

To study whether the upregulation of HtrA4 expression in extravillous trophoblasts and the downregulation of HtrA1 expression in defective deciduae underlined the mechanisms of placenta accreta spectrum (PAS) development.

METHODS

Tissue samples from patients undergone cesarean hysterectomy because of postpartum hemorrhage due to PAS (n = 15) or uterine atony (control group; n = 10) were analyzed through immunostainings. The effect of extracellular matrix (ECM) on trophoblast HtrA4 expression, and HtrA4 in the alteration of trophoblast epithelial-to-mesenchymal transition, proliferation, invasion and HtrA1 inhibition were assessed.

RESULTS

ECM molecule collagen I, collagen IV, fibronectin, or laminin were highly expressed in decidua and myometrium. Culturing trophoblasts with these molecules induced HtrA4 expression. HtrA4 upregulated the expression of N-cadherin, vimentin, integrin β1, snail, and matrix metalloproteinase-2 but downregulated that of zonula occludens-1. HtrA4 knockdown inhibited these effects. HtrA4 knockdown or pretreatment with recombinant HtrA1 inhibited HtrA4-induced trophoblast invasion. HtrA4 promoted trophoblast proliferation. Numerous extravillous trophoblasts exhibiting strong HtrA4 expression invaded the myometrium at the villous adherence sites affected by PAS. Relatively few extravillous trophoblasts were observed at the nonadherence sites and in the control specimens; these trophoblasts exhibited weak or no HtrA4 expression. HtrA1 was primarily expressed over the decidua.

DISCUSSION

ECM in decidua and myometrium induced trophoblast HtrA4 expression. Decidual HtrA1 inhibited HtrA4-induced trophoblast invasion. Without the inhibition of HtrA1, HtrA4 expression and invasion was upregulated in the trophoblasts of patients with PAS. The reciprocal effects of HtrA4 and HtrA1 at the maternal-fetal interface may be involved in the pathogenesis of PAS.

Abnormal placental development induced by repeated cesarean sections: Investigating an animal model of placenta accreta spectrum disorders

INTRODUCTION

Placenta accreta spectrum (PAS) is a serious condition associated with severe postpartum hemorrhage, leading to emergency hysterectomy. Research has predominantly focused on clinical diagnosis and the prevention of adverse maternal outcomes, but the underlying pathological mechanisms remain poorly understood, partly due to the limitations of animal models.

METHODS

In this study, we conducted up to three cesarean sections (CS) on full-term pregnant mice, since a history of multiple CS is an independent risk factor for PAS. We evaluated pregnancy outcomes, placental development, morphology, trophoblast invasion, and angiogenesis at the maternal-fetal interface to assess the impact of repeated CS.

RESULTS

Following repeated CS, the model mice displayed adverse pregnancy outcomes, including placental dysplasia, incomplete remodeling of spiral arteries, deep trophoblast invasion at the maternal-fetal interface, and reduced placental perfusion. Additionally, the mice exhibited abnormal fetal development, imbalances in angiogenic and anti-angiogenic both within the placenta and in peripheral blood.

CONCLUSION

The pathological phenotypes of placenta and adverse pregnancy outcomes observed in mice with a history of three CSs closely resemble the clinical features of PAS. This model offers a valuable tool for studying the pathogenesis of PAS and could serve as a foundation for the development of early prevention strategies.

Uterine injury during diestrus leads to placental and embryonic defects in future pregnancies in mice†

Uterine injury from procedures such as Cesarean sections (C-sections) often have severe consequences on subsequent pregnancy outcomes, leading to disorders such as placenta previa, placenta accreta, and infertility. With rates of C-section at ~30% of deliveries in the USA and projected to continue to climb, a deeper understanding of the mechanisms by which these pregnancy disorders arise and opportunities for intervention are needed. Here we describe a rodent model of uterine injury on subsequent in utero outcomes. We observed three distinct phenotypes: increased rates of resorption and death, embryo spacing defects, and placenta accreta-like features of reduced decidua and expansion of invasive trophoblasts. We show that the appearance of embryo spacing defects depends entirely on the phase of estrous cycle at the time of injury. Using RNA-seq, we identified perturbations in the expression of components of the COX/prostaglandin pathway after recovery from injury, a pathway that has previously been demonstrated to play an important role in embryo spacing. Therefore, we demonstrate that uterine damage in this mouse model causes morphological and molecular changes that ultimately lead to placental and embryonic developmental defects.

Mouse Surgical Model of Mechanical Uterine Injury and Subsequent Embryo Defects

Uterine injury from procedures such as Cesarean sections (C-sections) often have severe consequences on subsequent pregnancies, leading to disorders such as uterine placenta previa, placenta accreta spectrum (PAS), and Cesarean scar pregnancy. With rates of C-section at ∼30% of deliveries in the US and projected to continue to climb, an understanding of the mechanisms by which these pregnancy disorders arise and opportunities for intervention are sorely needed. However, there are currently very few animal models of uterine injury and its subsequent impacts on maternal as well as in utero and postnatal fetal outcomes. Here, we describe a procedure for a novel model of surgically induced uterine injury in the genetically tractable laboratory mouse (Mus musculus). We describe preparatory steps for surgery, the induction of uterine injury itself, and post-surgical recovery. We then provide supporting information regarding downstream dissection of pregnant mice. Lastly, we include additional information regarding estrous cycle staging in order to perform surgeries and dissections at the relevant phase in non-pregnant mice. This procedure for incurring uterine injury in a mouse model presents an important step forward in understanding uterine damage and its associated pregnancy disorders. © 2024 Wiley Periodicals LLC. Basic Protocol 1: Preparation for surgery Basic Protocol 2: Surgery and induction of uterine injury Basic Protocol 3: Mating and dissection of pregnant mice as endpoint analyses Support Protocol: Estrous staging of animals.

Nanoparticle Contrast-enhanced MRI for Visualization of Retroplacental Clear Space Disruption in a Mouse Model of Placental Accreta Spectrum (PAS)

INTRODUCTION

Prior preclinical studies established the utility of liposomal nanoparticle blood-pool contrast agents in visualizing the retroplacental clear space (RPCS), a marker of normal placentation, while sparing fetuses from exposure because the agent does not cross the placental barrier. In this work, we characterized RPCS disruption in a mouse model of placenta accreta spectrum (PAS) using these agents.

MATERIALS AND METHODS

Contrast-enhanced MRI (CE-MRI) and computed tomography (CE-CT) using liposomal nanoparticles bearing gadolinium (liposomal-Gd) and iodine were performed in pregnant Gab3-/- and wild type (WT) mice at day 16 of gestation. CE-MRI was performed on a 1T scanner using a 2D T1-weighted sequence (100×100×600 µm3 voxels) and CE-CT was performed at a higher resolution (70×70×70 µm3 voxels). Animals were euthanized post-imaging and feto-placental units (FPUs) were harvested for histological examination. RPCS conspicuity was scored through blinded assessment of images.

RESULTS

Pregnant Gab3-/- mice showed elevated rates of complicated pregnancy. Contrast-enhanced imaging demonstrated frank infiltration of the RPCS of Gab3-/- FPUs. RPCS in Gab3-/- FPUs was smaller in volume, demonstrated a heterogeneous signal profile, and received lower conspicuity scores than WT FPUs. Histology confirmed in vivo findings and demonstrated staining consistent with a thinner RPCS in Gab3-/- FPUs.

DISCUSSION

Imaging of the Gab3-/- mouse model at late gestation with liposomal contrast agents enabled in vivo characterization of morphological differences in the RPCS that could cause the observed pregnancy complications. An MRI-based method for visualizing the RPCS would be valuable for early detection of invasive placentation.

Animal models of the placenta accreta spectrum: current status and further perspectives

Placenta accreta spectrum disorder (PAS) is a kind of disease of placentation defined as abnormal trophoblast invasion of part or all of the placenta into the myometrium, even penetrating the uterus. Decidual deficiency, abnormal vascular remodeling in the maternal-fetal interface, and excessive invasion by extravillous trophoblast (EVT) cells contribute to its onset. However, the mechanisms and signaling pathways underlying such phenotypes are not fully understood, partly due to the lack of suitable experimental animal models. Appropriate animal models will facilitate the comprehensive and systematic elucidation of the pathogenesis of PAS. Due to the remarkably similar functional placental villous units and hemochorial placentation to humans, the current animal models of PAS are based on mice. There are various mouse models induced by uterine surgery to simulate different phenotypes of PAS, such as excessive invasion of EVT or immune disturbance at the maternal-fetal interface, which could define the pathological mechanism of PAS from the perspective of the "soil." Additionally, genetically modified mouse models could be used to study PAS, which is helpful to exploring the pathogenesis of PAS from the perspectives of both "soil" and "seed," respectively. This review details early placental development in mice, with a focus on the approaches of PAS modeling. Additionally, the strengths, limitations and the applicability of each strategy and further perspectives are summarized to provide the theoretical foundation for researchers to select appropriate animal models for various research purposes. This will help better determine the pathogenesis of PAS and even promote possible therapy.

Uterine damage induces placenta accreta and immune imbalance at the maternal-fetal interface in the mouse

INTRODUCTION

Placenta accreta spectrum (PAS) disorder is one of the major complications resulting in maternal death and serious adverse pregnancy outcomes. Uterine damage - principally that associated with cesarean section - is the leading risk factor for the development of PAS. However, the underlying pathogenesis of PAS related to uterine damage remains unclear.

METHODS

For this study, we constructed a mouse PAS model using hysterotomy to simulate a cesarean section in humans. Pregnant mice were sacrificed on embryonic days 12.5 (E12.5) and E17.5. Trophoblast invasion and placental vascularization were analyzed using Hematoxylin-Eosin (H&E) staining and immunohistochemistry (IHC), and the proportions of immune cells at the maternal-fetal interface were analyzed using flow cytometry. We analyzed the expressions of genes in the decidua and placenta using RNA sequencing and subsequent validation by QPCR, and measured serum angiogenic factors by ELISA.

RESULTS

Uterine damage led to increased trophoblast invasion and placental vascularization, with extensive changes to the immune-cell profiles at the maternal-fetal interface. The proportions of T and NK cells in the deciduas diminished significantly, with the decidual NK cells and M - 2 macrophages showing the greatest decline. The expression of TNF-α and IL4 was upregulated in the deciduas, while that of IFN-γ and IL10 was downregulated significantly. The expression of Mmp2, Mmp9, Mmp3, and Dock4 was significantly elevated in the placenta, and the serum levels of anti-angiogenic factors were significantly attenuated.

DISCUSSION

Uterine damage can cause immune imbalance at the maternal-fetal interface, which may contribute to abnormal trophoblast invasion and enhanced vascularization of the mouse placenta.

Investigation of the pregnancy-induced muscle bundle dispersal of the inner myometrium of adult mouse uterus and its relationship to the metrial gland/MLAp

In the adult uterus of mice, rats and humans, the initially closely packed muscle bundles of the inner myometrium (muscular tissue that encircles the endometrium where the conceptus implants) undergo a pregnancy-induced dispersal that is clinically significant and hypothesized to regulate important pregnancy events. However, where, when and how this dispersal occurs, what its functions are, as well as its spatial relationship to the mouse metrial gland/mesometrial lymphoid aggregate of pregnancy (MG/MLAp), are unknown. The MG/MLAp, is a pregnancy-induced uterine structure required for successful rodent pregnancy located mesometrial to (above) the decidua basalis (pregnancy-modified mesometrial endometrium) and defined by its accumulation of maternal lymphocytes known as uterine Natural Killer (uNK) cells. To begin to understand how mouse inner myometrium dispersal (IMD) occurs, we spatiotemporally described it by observing the distribution of its muscle bundles and measuring their volume fraction (VF), as well as the VF of uNKs and stromal cells of inner myometrium. We discovered that (a) IMD (defined as reduction in VF of inner myometrium muscle bundles) is restricted to the mesometrial half of the uterus, is first evident at Embryonic day (E) 5.5 (early postimplantation) but not at E3.5 (preimplantation), further increases between E6.5 and E7.5 and remains unchanged from E7.5 to E10.5, (b) IMD initiation (observed between E3.5 and E5.5) occurs in the absence of uNKs and is associated with VF increases of pre-existing inner myometrium stromal cells and (c) the IMD observed between E6.5 and E7.5 is not associated with VF increases of uNKs or stromal cells. To get functional clues about IMD, we examined whether stromal cells between the dispersed muscle bundles undergo decidualization (important for correct fetomaternal interactions) and provide evidence that they do by E10.5, based on their production of Desmin (decidualization marker). Lastly, we examined whether mouse MG/MLAp only comprises the dispersed inner myometrium or additionally includes the mesometrial triangle (a triangular-like area mesometrial to the inner myometrium at the mesometrium-uterus attachment site), as is the case in rats. Our data supports that the dispersed inner myometrium is the only tissue that makes up the mouse MG/MLAp. In conclusion, we provide novel cellular and spatiotemporal insights about IMD that will contribute to understanding its mechanism and function and allow more informed inter-species comparisons about this process.

Placenta Accreta Spectrum

Placenta accreta spectrum (PAS) refers to the range of pathologic adherence of the placenta to the uterine myometrium, including the placenta accreta, increta, and percreta. The incidence of PAS is rising primarily because of an increase in related risk factors, such as the rate of cesarean deliveries and pregnancies resulting from assisted reproductive technology. The maternal risks associated with PAS are significant, including hemorrhage, hysterectomy, and death. Fetal and neonatal risks are primarily the result of premature delivery. Antenatal diagnosis via ultrasonography and magnetic resonance imaging remains imperfect. Management of PAS varies, however, and there is a clear improvement in maternal outcomes with an antenatal diagnosis compared with unexpected diagnosis at the time of delivery. Studies that evaluate the balance between maternal and fetal/neonatal risks of expectant management versus preterm delivery have found that planned delivery between 34 and 35 weeks' gestation optimizes outcomes. Multidisciplinary PAS care teams have become the norm and recommended approach to management, given the complexity of caring for this obstetrical condition. Although significant advances have been made over the years, large knowledge gaps remain in understanding the pathophysiology, diagnosis, and clinical management.