Placental Ischemia Stimulated Natural Killer Cells Play a Direct Role in Causing Hypertension and Intrauterine Growth Restriction in Pregnant Rats
Authors: Travis Olivia K. , Baik Cedar , Tardo Geilda A. , Amaral Lorena , Jackson Carmilya , Greer Mallory , Giachelli Chelsea , Williams Jan M. , Cornelius Denise C. 
Published: April 2020

Preeclampsia (PE) is a multisystem pregnancy disorder characterized by maternal hypertension (HTN), intrauterine growth restriction (IUGR), and immune activation, including increased cytolytic natural killer cells (cNKs). The
Reduced
Uterine
Perfusion
Pressure (RUPP) rat model of placental ischemia recapitulates many of these characteristics, and we have previously demonstrated that depletion of NK cells (NKs) in RUPP rats improves maternal and fetal outcomes. In this study we tested the hypotheses that (1) RUPP stimulated NKs play a direct role in causing maternal HTN and IUGR in pregnant rats and (2) normal pregnant control (Sham) NKs attenuate maternal HTN and IUGR in RUPP rats. NKs were isolated from the placentas of Sham and RUPP rats on gestation day (GD) 19 and assessed for cytotoxicity. RUPP NKs demonstrated a 5‐fold increase in cytotoxicity vs Sham NKs (p<0.05 vs Sham). On GD14, vehicle or 5x106 RUPP NKs were infused i.v. into a subset of Sham rats (Sham n=8, Sham+RUPP NK, n=7), and vehicle or 5x106 Sham NKs were infused i.v. into a subset of RUPP rats (RUPP n=8, RUPP+ Sham NK, n=7). On GD18, Uterine Artery Resistance Index (UARI) was measured via Doppler Ultrasound. On GD19, cNKs were quantified via flow cytometry, MAP, fetal and placental weights, and placental oxidative stress (ROS) were measured. Placental cNKs (%gated) were 3±1% in Sham and increased to 19±5% in RUPP and 21±4% in Sham+RUPP NK (p<0.05 vs Sham). This was reduced to 3±1% in RUPP+Sham NK (p<0.05 vs RUPP). Similarly, circulating cNKs (% gated) were 5±1% in Sham, increased to 20±3% in RUPP and 21±3% in Sham+RUPP NK (p<0.05 vs Sham) and decreased to 5±1% in RUPP+Sham NK (p<0.05 vs RUPP). MAP increased from 102±1 mmHg in Sham to 130±2 mmHg in RUPP and 121±2 mmHg in Sham+RUPP NK (p<0.05 vs Sham), but this was blunted to 113±1 mmHg in RUPP+Sham NK (p<0.05 vs RUPP). Mean fetal weight decreased from 2.4±0.04g in Sham to 2.1±0.07g in RUPP and 2.1±0.03g in Sham+RUPP NK (p<0.05 vs Sham); however, this was normalized to 2.3±0.03g in RUPP+Sham NK (p<0.05 vs RUPP). Similarly, placental weight decreased from 0.56±0.02g in Sham, to 0.47±0.02g in RUPP and 0.45±0.02g in Sham +RUPP NK (p<0.05 vs Sham) and increased to 0.53±0.01g in RUPP+Sham NK (p<0.05 vs RUPP). Placental ROS (RLUs/min/mg) was 35±2 in Sham, increased to 63±6 in RUPP and 70±12 in Sham +RUPP NK (p<0.05 vs Sham), and remained elevated at 60±5 in RUPP+Sham NK (p<0.05 vs Sham). UARI was 0.59±0.03 in Sham (n=3), 0.73±0.03 in RUPP (n=3; p=0.15 vs Sham), and 0.61±0.02 in RUPP+Sham NK (n=5; p>0.05 vs RUPP). UARI increased to 0.76±0.05 in Sham+RUPP NK (n=5; p<0.05 vs Sham). In conclusion, we observed that infusion of RUPP NKs led to HTN, IUGR, increased placental ROS, and increased UARI in pregnant rats, while Sham NK infusion improved the pathophysiology observed in RUPP rats. These data demonstrate a direct role for cNKs in causing PE pathophysiology and a role for normal NKs to promote positive maternal and fetal outcomes. Our study identifies cNKs as a therapeutic target in PE and suggests that strategies to normalize polarization of NKs represents a novel therapeutic approach to improve maternal and fetal outcomes associated with PE.Support or Funding InformationR00HL130456, T32HL105324