Whole mount immunofluorescence analysis of placentas from normotensive versus preeclamptic pregnancies

Placental cell type deconvolution reveals that cell proportions drive preeclampsia gene expression differences

The placenta mediates adverse pregnancy outcomes, including preeclampsia, which is characterized by gestational hypertension and proteinuria. Placental cell type heterogeneity in preeclampsia is not well-understood and limits mechanistic interpretation of bulk gene expression measures. We generated single-cell RNA-sequencing samples for integration with existing data to create the largest deconvolution reference of 19 fetal and 8 maternal cell types from placental villous tissue (n = 9 biological replicates) at term (n = 40,494 cells). We deconvoluted eight published microarray case-control studies of preeclampsia (n = 173 controls, 157 cases). Preeclampsia was associated with excess extravillous trophoblasts and fewer mesenchymal and Hofbauer cells. Adjustment for cellular composition reduced preeclampsia-associated differentially expressed genes (log2 fold-change cutoff = 0.1, FDR < 0.05) from 1154 to 0, whereas downregulation of mitochondrial biogenesis, aerobic respiration, and ribosome biogenesis were robust to cell type adjustment, suggesting direct changes to these pathways. Cellular composition mediated a substantial proportion of the association between preeclampsia and FLT1 (37.8%, 95% CI [27.5%, 48.8%]), LEP (34.5%, 95% CI [26.0%, 44.9%]), and ENG (34.5%, 95% CI [25.0%, 45.3%]) overexpression. Our findings indicate substantial placental cellular heterogeneity in preeclampsia contributes to previously observed bulk gene expression differences. This deconvolution reference lays the groundwork for cellular heterogeneity-aware investigation into placental dysfunction and adverse birth outcomes.

Lymphatic mimicry in maternal endothelial cells promotes placental spiral artery remodeling

Molecular heterogeneity of endothelial cells underlies their highly specialized functions during changing physiological conditions within diverse vascular beds. For example, placental spiral arteries (SAs) undergo remarkable remodeling to meet the ever-growing demands of the fetus - a process which is deficient in preeclampsia. The extent to which maternal endothelial cells coordinate with immune cells and pregnancy hormones to promote SA remodeling remains largely unknown. Here we found that remodeled SAs expressed the lymphatic markers PROX1, LYVE1, and VEGFR3, mimicking lymphatic identity. Uterine natural killer (uNK) cells, which are required for SA remodeling and secrete VEGFC, were both sufficient and necessary for VEGFR3 activation in vitro and in mice lacking uNK cells, respectively. Using Flt4Chy/+ mice with kinase inactive VEGFR3 and Vegfcfl/fl Vav1-Cre mice, we demonstrated that SA remodeling required VEGFR3 signaling, and that disrupted maternal VEGFR3 signaling contributed to late-gestation fetal growth restriction. Collectively, we identified a novel instance of lymphatic mimicry by which maternal endothelial cells promote SA remodeling, furthering our understanding of the vascular heterogeneity employed for the mitigation of pregnancy complications such as fetal growth restriction and preeclampsia.

Elucidating the Pathogenesis of Pre-eclampsia Using In Vitro Models of Spiral Uterine Artery Remodelling

PURPOSE OF REVIEW

The aim of the study is to perform a critical assessment of in vitro models of pre-eclampsia using complementary human and cell line-based studies. Molecular mechanisms involved in spiral uterine artery (SUA) remodelling and trophoblast functionality will also be discussed.

RECENT FINDINGS

A number of proteins and microRNAs have been implicated as key in SUA remodelling, which could be explored as early biomarkers or therapeutic targets for prevention of pre-eclampsia. Various 2D and 3D in vitro models involving trophoblast cells, endothelial cells, immune cells and placental tissue were discussed to elucidate the pathogenesis of pre-eclampsia. Nevertheless, pre-eclampsia is a multifactorial disease, and the mechanisms involved in its pathogenesis are complex and still largely unknown. Further studies are required to provide better understanding of the key processes leading to inappropriate placental development which is the root cause of pre-eclampsia. This new knowledge could identify novel biomarkers and treatment strategies.

VEGF and VEGFR1 levels in different regions of the normal and preeclampsia placentae

Altered placental angiogenesis is implicated in the pathophysiology of preeclampsia. We have earlier reported placental regional differences in oxidative stress markers and neurotrophins. Oxidative stress and neurotrophins are reported to regulate angiogenesis. This study aims to examine protein and mRNA levels of vascular endothelial growth factor (VEGF) and VEGF receptor 1 (VEGFR1) in four regions [central maternal (CM), central fetal (CF), peripheral maternal (PM), and peripheral fetal (PF)] of the placenta in normotensive control (NC) women (n = 51) and women with preeclampsia (PE) (n = 43) [18 delivered at term (T-PE) and 25 delivered preterm (PT-PE)]. In all groups, CF region reported highest VEGF protein levels compared to all other regions. VEGF mRNA level was higher in CF region as compared to CM region in PE group (p < 0.05). VEGF levels were lower in all regions of PE, T-PE, and PT-PE groups (p < 0.05) as compared to their respective regions in NC group. VEGFR1 levels were lower in CF (p < 0.05) and PF (p < 0.01) regions as compared to CM region only in control. However, VEGFR1 levels were higher in CF (p < 0.05) and PF (p < 0.01) regions of PT-PE group as compared to control. VEGFR1 mRNA level was higher in PM region of PE group and T-PE group (p < 0.05 for both) as compared to control. VEGF levels in the PF region were positively associated with birth weight and placental weight. This study describes placental regional changes in angiogenic factors particularly highlighting increased VEGF in CF region possibly in response to hypoxic conditions prevailing in placenta.

Coordinated lymphangiogenesis is critical in lymph node development and maturation

BACKGROUND

Lymph node (LN) formation requires multiple but coordinated signaling from intrinsic and extrinsic cellular components during embryogenesis. However, the contribution and role of lymphatic vessels (LVs) in LN formation and maturation are poorly defined. Here, using lymphatic-specific reporters, Prox1-GFP mice and Vegfc^+/LacZ mice, we analyzed migration, assembly, and ingrowth of lymphatic endothelial cells (LECs) in LNs during pre- and postnatal development.

RESULTS

Prox1⁺ LECs form string-like connections rather than lymph sac-like structures until E14.5, but the LEC coverage around LN anlagen completes before birth. Compared to wild-type littermates, Vegfc^+/LacZ mice had markedly smaller LNs in neonates and adults, presumably due to the decrease in LTi cell clusters and migrating Prox1⁺ LECs during embryogenesis. In addition, Vegfc-haploinsufficiency or inhibition of VEGFR3 signaling led to an impairment of LN LV ingrowth, resulting in a significant decrease in LN volume. These data indicate that VEGF-C/VEGFR3 signaling plays a substantial role in normal LN formation through proper migration and organization of LECs.

CONCLUSIONS

Taken together, our results provide compelling evidence that the contribution of LVs through VEGF-C/VEGFR3 signaling is critical in LN development and maturation. Developmental Dynamics 245:1189-1197, 2016. © 2016 Wiley Periodicals, Inc.