The expression of placental soluble fms-like tyrosine kinase 1 in mouse placenta varies significantly across different litters from normal pregnant mice

Current State of Preeclampsia Mouse Models: Approaches, Relevance, and Standardization

Preeclampsia (PE) is a multisystemic, pregnancy-specific disorder and a leading cause of maternal and fetal death. PE is also associated with an increased risk for chronic morbidities later in life for mother and offspring. Abnormal placentation or placental function has been well-established as central to the genesis of PE; yet much remains to be determined about the factors involved in the development of this condition. Despite decades of investigation and many clinical trials, the only definitive treatment is parturition. To better understand the condition and identify potential targets preclinically, many approaches to simulate PE in mice have been developed and include mixed mouse strain crosses, genetic overexpression and knockout, exogenous agent administration, surgical manipulation, systemic adenoviral infection, and trophoblast-specific gene transfer. These models have been useful to investigate how biological perturbations identified in human PE are involved in the generation of PE-like symptoms and have improved the understanding of the molecular mechanisms underpinning the human condition. However, these approaches were characterized by a wide variety of physiological endpoints, which can make it difficult to compare effects across models and many of these approaches have aspects that lack physiological relevance to this human disorder and may interfere with therapeutic development. This report provides a comprehensive review of mouse models that exhibit PE-like symptoms and a proposed standardization of physiological characteristics for analysis in murine models of PE.

Effect of placental growth factor in models of experimental pre-eclampsia and trophoblast invasion

Placental growth factor (PlGF) is decreased in early gestation of pregnant women who subsequently develop pre-eclampsia. In this study, pre-emptive treatment with PlGF to prevent pre-eclampsia was evaluated in an in vivo rodent model of experimental pre-eclampsia (EPE) induced by TNF-α and in an in vitro model of human first-trimester trophoblast invasion. Pregnant C57/BL6 mice were treated with recombinant mouse placental growth factor-2 (rmPlGF-2) 100 μg/kg/day IP from gestational day (gd) 10. Animals had EPE induced by continuous TNF-α infusion on gd 13 and were subject to either continuous blood pressure monitoring by radiotelemetry throughout pregnancy or live placenta T₂ -weighted magnetic resonance imaging (MRI) to demonstrate placental function on gd 17. There was no difference in BP (P > .99), proteinuria (P = .9) or T₂ values on MRI (P = .9) between control and rmPlGF-2-treated animals. On gd 13, animals treated with rmPlGF-2 demonstrated increased placenta PlGF (P = .01) and Toll-like receptor-3 (P = .03) mRNA expression as compared with controls. Fluorescent-labelled human uterine microvascular endothelial cells and HTR8/SVNeo cells were co-cultured on Matrigel^™ and treated with recombinant human PlGF (rhPlGF) (10 ng/mL) and/or TNF-α (0.5 ng/mL). Trophoblast integration into endothelial networks was reduced by added TNF-α (P = .006), as was rhPlGF concentration in conditioned media (P < .0001). Cell integration was not ameliorated by addition of rhPlGF (P > .9). Although TNF-α-induced EPE was not reversed with pre-emptive rmPlGF-2, a further trial of pre-emptive rhPlGF in vivo is required to determine whether the absence of effect of rhPlGF demonstrated in vitro precludes PlGF as a preventative therapy for pre-eclampsia.

Characterisation of the Selective Reduced Uteroplacental Perfusion (sRUPP) Model of Preeclampsia

Preeclampsia is a complication of pregnancy characterised by gestational hypertension, proteinuria and/or end organ disease. The reduced uteroplacental perfusion (RUPP) model, via partial occlusion of the lower abdominal aorta, mimics insufficient placental perfusion as a primary causal characteristic of preeclampsia. However, a major limitation of the RUPP model is that perfusion is reduced to the entire hindquarters of the rat resulting in hindlimb ischemia. We hypothesised that clipping the uterine and ovarian arteries in the selective (s)RUPP model would provoke signs of preeclampsia while avoiding systemic ischemia. Sham, RUPP or sRUPP procedures were performed in pregnant Sprague Dawley rats on gestational day (GD)14. On GD21 uterine blood flow was significantly reduced in both the RUPP and sRUPP models while aortic flow was reduced only in RUPP. Both models resulted in increased MAP, increased vascular oxidative stress (superoxide generation), increased pro-inflammatory (RANTES) and reduced pro-angiogenic (endoglin) mediators. Vascular compliance and constriction were unaltered in either RUPP or sRUPP groups. In summary, refinements to the RUPP model simultaneously maintain the characteristic phenotype of preeclampsia and avoid peripheral ischemia; providing a useful tool which may be used to increase our knowledge and bring us closer to a solution for women affected by preeclampsia.

Placental Regulation of Inflammation and Hypoxia after TNF-α Infusion in Mice

PROBLEM

Increased levels of inflammatory cytokines are demonstrated in the serum of women with pre-eclampsia. TNF-α infusion in animal models induces proteinuric hypertension similar to human pre-eclampsia. The effect of TNF-α on regulation of the immune and hypoxic pathways in the developing placenta and their relationship with experimental pre-eclampsia remains unexamined.

METHOD OF STUDY

TNF-α was infused into pregnant mice, and the effects on maternal hypertension, proteinuria, circulating levels of sFlt-1 and corresponding placental changes in molecules responding to inflammation (TLR-3 and TLR-4) and hypoxia (HIF-1α) were examined.

RESULTS

TNF-α infusion resulted in maternal hypertension and proteinuria. Molecular changes in the placenta involved upregulation of TLR-3, TLR-4 and HIF-1α. Serum levels of sFlt-1 were high in pregnant animals, but not further upregulated by TNF-α infusion.

CONCLUSION

A role for maladaptive regulation of TLR and HIF-1α induced by an imbalance in inflammatory cytokines is implicated in the pathogenesis of pre-eclampsia.

Ouabain inhibits placental sFlt1 production by repressing HSP27-dependent HIF-1α pathway

Up-regulation of placental soluble fms-like tyrosine kinase 1 (sFlt1) contributes to the pathogenesis of preeclampsia. To evaluate novel upstream pathways that regulate placental sFlt1 production, we screened a library of natural compounds (n=502) in human placental cell lines. Here, we report 3 compounds in the cardiac glycoside family, ouabain, gitoxigenin, and digitoxin, that inhibit placental sFlt1 production at nanomolar concentrations in vitro. We further characterized ouabain and demonstrated that it inhibits sFlt1 mRNA and protein expression in human placental cytotrophoblasts and explant cultures in a dose- and time-dependent manner. Ouabain down-regulated sFlt1 production by inhibiting hypoxia-inducible factor 1 (HIF-1α) protein expression in the placenta. Furthermore, we found that phosphorylation of heat-shock protein 27 (HSP27) was necessary for ouabain to inhibit HIF-1α translation. In a rat model of pregnancy-induced hypertension, ouabain reduced mean arterial pressure and enhanced placental HSP27 phosphorylation without any adverse effects on pups. Further studies are needed to explore the usefulness of targeting HIF-1α/HSP27 pathway in preeclampsia.