Comparative analysis of high field MRI and histology for ex vivo whole organ imaging: assessment of placental functional morphology in a murine model.

OBJECTIVES: The purpose of our study was to evaluate MRI as a tool to examine placental morphology in a murine model in comparison to classical histology techniques. METHODS: Assessment of placental samples (n = 24) from C57Bl/6 J mice was performed using MR imaging and histomorphological analyses. To optimize image contrast for MRI, a protocol for gadolinium-mediated enhancement of placental tissue was established. To test method sensitivity, placental zone assessment with MRI and histology was applied to a model of prenatal stress exposure known to affect placental morphology (n = 10). Mean data acquisition time for both methods was estimated. Difference between groups was calculated using the Mann-Whitney U test. RESULTS: Tissue fixation with formaldehyde and staining with gadolinium resulted in the best image quality. Placental functional zones were identified and measured with both MRI and histology. MRI and histology were able to detect changes in the L/Jz ratio upon a prenatal stress challenge (p = 0.001; p = 0.003). Data acquisition time was shorter using MRI assessment. CONCLUSIONS: Ex vivo MRI analyses of murine placental functional morphology with MRI are feasible and results are comparable to time-consuming histology. Both MRI and histology allow the detection of experimentally induced morphological tissue alterations.

DCE MRI reveals early decreased and later increased placenta perfusion after a stress challenge during pregnancy in a mouse model.

OBJECTIVES: Stress during pregnancy is known to have negative effects on fetal outcome. The purpose of this exploratory study was to examine placental perfusion alterations after stress challenge during pregnancy in a mouse model. MATERIAL AND METHODS: Seven Tesla MRI was performed on pregnant mice at embrionic day (ED) 14.5 and 16.5. Twenty dams were exposed to an established acoustic stress challenge model while twenty non-exposed dams served as controls. Placental perfusion was analyzed in dynamic contrast-enhanced (DCE) MRI using the steepest slope model. The two functional placental compartments, the highly vascularized labyrinth and the endocrine junctional zone, were assessed separately. RESULTS: Statistical analysis revealed decreased perfusion levels in the stress group at ED 14.5 compared to controls in both placenta compartments. On ED 16.5, the perfusion level increased significantly in the stress group while placenta perfusion in controls remained similar or even slightly decreased leading to an overall increased perfusion in the stress group on ED 16.5 compared to controls. CONCLUSION: MR imaging allows noninvasive placenta perfusion assessment in this fetal stress mimicking animal model. In this exploratory study, we demonstrated that stress challenge during pregnancy leads to an initial reduction followed by an increase of placenta perfusion.

Neutralization of LPS or blockage of TLR4 signaling prevents stress-triggered fetal loss in murine pregnancy.

Maternal stress can cause loss of both histocompatible (syngeneic) and histoincompatible (semiallogeneic) embryos in pregnant mice. Stress increases abortogenic Th1 cytokines and reduces levels of anti-abortogenic Th2 cytokines, progesterone levels, and T regulatory cell activity. While physiological levels of interferon-γ promote vascular remodeling at the feto-maternal interface, an overshooting Th1 cytokine response requires a Toll-like receptor (TLR)-mediated "danger signal" such as lipopolysaccharide (LPS). Interestingly, stress can enhance permeability of mucosal membranes to entry of bacterial products and promote transmucosal migration of commensal bacteria. We hypothesized that bacterial component such as LPS may provide the danger signal through which stress triggers maternal immune activation, subsequently resulting in fetal rejection. Blocking the TLR4 receptor for LPS or neutralization of LPS using bactericidal permeability increasing protein abrogate fetal loss due to sonic stress challenge in DBA/2J-mated CBA/J mice. These treatments prevented stress-triggered immune responses in the decidua, upregulated Treg cells, and reduced the frequency of mature dendritic cells in uterine-draining lymph nodes but not in the uterus. Interestingly, anti-TLR4 treatment only partly ameliorated stress-induced endocrine responses, such as increased hypothalamic corticotropin releasing hormone and vasopressin mRNA expression but not decrease of serum progesterone. Galectin-1 knock-out mice were more susceptible to stress-triggered complete implantation failure rather than fetal loss, which was also abolished by LPS neutralization. Insights provided in this paper shed new light on the mechanisms by which stress affects pregnancy outcome and introduce microbial-derived LPS as a mediator within the cascade of stress-triggered immune and endocrine events during pregnancy.