Natural killer cells mediate pathophysiology in response to reduced uterine perfusion pressure

Abstract

Preeclampsia is associated with hypertension, small-for-gestational-age babies, and increased cytolytic natural killer (NK) cells. The specific role of cytolytic NK cells in the pathophysiology of preeclampsia has not been clearly defined. We hypothesized that Reduced Uterine Perfusion Pressure (RUPP) stimulates proliferation and cytolytic activation of NK cells, and that reducing NK cells in RUPP would prevent hypertension, intrauterine growth restriction, and inflammation in response to placental ischemia. RUPP was induced on gestation day (GD) 14 in pregnant rats. NK cells were depleted by i.p. administration of anti-asialo GM1 antibody on GDs 15 and 17. Placental and circulating NK cells were quantified via flow cytometry, mean arterial pressure (MAP), fetal weights, and cytokines were measured on GD 19. Total placental NK cells were 7.4 ± 2% of gated cells in normal pregnant (NP; n=10) and 16.5 ± 3% of gated cells in RUPP (n=10) rats. Furthermore, cytolytic placental NK cells also increased in RUPP. Depletion of NK cells in RUPP (RUPP + anti-ASGM1) significantly improved MAP and fetal weights. MAP was 108 ± 2 mmHg in NP, 125 ± 2 mmHg in RUPP, and 112 ± 2 mmHg in RUPP + anti-ASGM1 (n=12). Fetal weight was 2.32 ± 0.05 in NP, 1.8 ± 0.04g in RUPP, and increased to 2.0 ± 0.04g in RUPP + anti-ASGM1. Placental interferon-γ (IFN-γ) was 40.4 ± 5.2 pg/mg in NP, 72.17 ± 3.2 pg/mg in RUPP, and 44.0 ± 6.5 pg/mg in RUPP + anti-ASGM1 (P<0.05). Placental tumor necrosis factor-α (TNF-α) was 17.9 ± 1.7 pg/mg in NP, 23.9 ± 2.2 pg/mg in RUPP, and 12.9 ± 2.3 pg/mg in RUPP + anti-ASGM1 (P<0.05). Depletion of NK cells significantly lowered MAP, intrauterine growth restriction, and inflammation in RUPP rats indicating that cytolytic NK cells are important in preeclampsia pathophysiology.

Keywords: Hypertension; Inflammation; Intrauterine growth restriction; Natural Killer Cells; Preeclampsia; Pregnancy.

Figure 1. Natural killer cells are stimulated in response to placental ischemia

Total NK cells are increased in the placenta (A) and circulation (B) in response to reduced uterine perfusion pressure (RUPP) in pregnant rats. Cytolytic NK cells were significantly increased in the placenta (C) and circulation (D) of RUPP rats. Circulating and placental NK populations were significantly reduced after treatment with anti-asialo GM1 antibody on gestation days 15 and 17 (A–D); *P<0.05 versus NP, ^#P<0.05 versus RUPP.

Figure 2. Reduction in natural killer cells attenuates hypertension in RUPP rats

Blood pressure is increased in response to reduced uterine perfusion pressure (RUPP) in pregnant rats. Reduction of NK cells inhibited the blood pressure response to RUPP. Reduction of NK cells in NP rats had no effect on blood pressure; *P<0.05 versus NP, ^#P<0.05 versus RUPP.

Figure 3. Natural killer cell depletion significantly increased fetal weight in RUPP rats

Fetal and placental weights are decreased in response to placental ischemia in reduced uterine perfusion pressure (RUPP) rats (A and B); however, depletion of NK cells significantly improved weights of offspring in RUPP rats (A). *P<0.05 versus NP, ^#P<0.05 versus RUPP.

Figure 4. Circulating inflammatory cytokines are decreased with NK cell depletion in RUPP rats

Circulating levels of IFN-γ (A), TNF-α (B), and IL-17 (C) are significantly increased in response to reduced uterine perfusion pressure (RUPP) in pregnant rats. Reduction of NK cells inhibited the increase in circulating proinflammatory cytokines in RUPP rats; *P<0.05 versus NP, ^#P<0.05 versus RUPP.

Figure 5. Placental inflammatory cytokines are blunted after NK cell depletion in RUPP rats

Placental levels of IFN-γ (A) and TNF-α (B) are significantly increased in response to reduced uterine perfusion pressure (RUPP) in pregnant rats. Reduction of NK cells attenuated the increase in placental IFN-γ and TNF-α in RUPP rats; *P<0.05 versus NP, ^#P<0.05 versus RUPP.