Regulators of Complement System Activation Increase with Placental Ischemia‐induced Hypertension in Rat
Authors: Strehlke Megan E , Elmquist Barbara J , Bemis Lynne T , Gilbert Jeffrey S , Regal Jean F 
Published: November 2023

Preeclampsia is characterized by new onset hypertension, reduced placental perfusion, and increased activation of complement, part of the innate immune system. In a rat model of placental ischemia‐induced hypertension, our previous work was the first to demonstrate the importance of complement activation, particularly activation products C3a and C5a, in mediating maternal hypertension. In this model circulating C3a increases, suggesting either increased activation of complement through C3 and/or insufficient changes in endogenous regulators to limit complement activation. In preeclampsia, complement regulators CD55 and CD59 have been shown to increase in placenta compared to normal pregnancy, indicating upregulation to control excessive complement activation. In addition, excessive complement activation in kidney has been demonstrated in preeclampsia. Thus, we hypothesized that increased complement activation following placental ischemia in rat leads to an increase in complement regulators in kidney and placenta. On gestation day (GD) 14, rats underwent either Sham surgery or clip placement on ovarian arteries and abdominal aorta to reduce uterine perfusion pressure (RUPP) resulting in increased maternal blood pressure on GD19. On GD19, mean arterial pressure (MAP) was measured via arterial catheter, and serum and plasma collected. Serum C3a and soluble C5b‐9 were measured as indicators of complement activation using Western Blot and ELISA assay, respectively. Membrane bound complement regulators investigated included: 1) CD55 and Crry which limit complement activation through C3 and C5, and 2) CD59 which limits formation of C5b‐9 membrane attack complex. Kidney cortex and placenta were collected, mRNA extracted, and quantitative RT‐PCR used to measure mRNA for complement regulators CD55, CD59, and Crry using β‐actin as a housekeeping gene. As expected, MAP significantly increased (p<0.05) in RUPP (109±3 mmHg, n=9) vs. Sham (95±3 mmHg, n=7) animals, with a corresponding increase in C3a (0.49±0.14 units/ul, RUPP; 0.22±0.09 units/ul, Sham). Soluble C5b‐9 did not significantly differ in plasma of RUPP vs. Sham animals. In placenta, mRNA for CD55, CD59, or Crry did not significantly change with placental ischemia. However, in kidney cortex CD59 mRNA significantly increased in RUPP vs. Sham with a 1.16±0.04 fold change (p<0.05). A slight increase in CD55 mRNA was noted (1.21±0.09 fold change; p= 0.07) in RUPP vs. Sham kidney cortex, and no change in Crry mRNA was detected. Thus, our data demonstrate increased CD59 mRNA in kidney following placental ischemia with a minor increase in CD55, without upregulation of either molecule in placenta. The minor increase in CD55 in kidney and lack of change in Crry in either placenta or kidney following placental ischemia suggests inadequate regulation at the level of C3 and C5 activation resulting in increased C3a. However, increased CD59 in kidney following placental ischemia limits production of soluble C5b‐9. Thus, placental ischemia alone in the rat does not change complement regulators in the placenta. However, these data suggest a feedback mechanism is present in kidney that adequately limits circulating C5b‐9 but is insufficient to limit excessive C3a production.

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NIH HL109843