Hypertension produced by placental ischemia in pregnant rats is associated with increased soluble endoglin expression

Abstract

Recent clinical studies indicate that an excess of angiostatic factors, such as soluble endoglin (sEng), is related to the occurrence of preeclampsia. Although recent clinical studies report that sEng is increased in preeclamptic women, the mechanisms underlying its overexpression remain unclear. Evidence suggests that hypoxia and induction of heme oxygenase-1 have opposing effects on sEng expression, the former stimulatory and the latter inhibitory. Hence, we hypothesized that placental ischemia because of reduced uterine perfusion pressure (RUPP) in the pregnant rat would increase sEng expression and decrease heme oxygenase-1. Mean arterial pressure was obtained via arterial catheter, and serum and placental proteins were measured by Western blot. Mean arterial pressure was increased (132+/-3 mm Hg versus 102+/-2 mm Hg; P<0.001), and fetal (2.35+/-0.05 g versus 1.76+/-0.08 g; P<0.001) and placental weight were decreased (0.47+/-0.04 g versus 0.58+/-0.03 g; P<0.01) in the RUPP compared with normal pregnant controls. Serum sEng (0.10+/-0.02 arbitrary pixel units [apu] versus 0.05+/-0.01 apu; P<0.05) and placental endoglin (4.7+/-2.3 apu versus 1.45+/-0.42 apu; P<0.05) were increased along with placental hypoxia inducible factor-1 alpha (1.42+/-0.25 apu versus 0.68+/-0.09 apu; P<0.05) expression in the RUPP versus the normal pregnant dams. Placental HO-1 (1.4+/-0.3 apu versus 2.5+/-0.1 apu; P<0.05) expression decreased in the RUPP compared with normal pregnant dams. The present findings support our hypothesis that placental ischemia because of RUPP increases the expression of sEng and shifts the balance of angiogenic factors in the maternal circulation toward an angiostatic state. The present study provides further evidence that placental ischemia is a strong in vivo stimulus of angiostatic factors during pregnancy.

Figure 1. Blood pressure (A) and fetal weight (B) during late gestation

Resting mean arterial pressure (MAP) was increased (P < 0.001; panel A) in the reduced uterine perfusion pressure (RUPP, n = 12) dams when contrasted to the normal pregnant (NP, n = 10) dams. RUPP (n = 12) fetuses were 25% lighter (P < 0.05) than fetuses from NP (n = 10) dams fetal (panel B).

Figure 2. Effect of placental ischemia on expression of serum sEng

Circulating sEng was increased in the serum of reduced uterine perfusion pressure (RUPP, n = 12) compared to the normal pregnant (NP, n = 10) dams. sEng blot data is expressed relative to the 67 kDa band corresponding to albumin on Ponceau stained membranes.

Figure 3. Effect of placental ischemia on expression of sEng and Eng in placenta

Figure 3A shows that placental Eng and Figure 3B illustrates that immunoreactive sEng relative to the 67 kDa band corresponding to albumin on Ponceau stained membranes was increased in the reduced uterine perfusion pressure (RUPP, n = 12) compared to the normal pregnant (NP, n = 10) control placentas.

Figure 4. Effect of placental ischemia on expression of placental HIF-1α

Figure 4 shows that immunoreactive placental HIF1-α relative to the 67 kDa band corresponding to albumin on Ponceau stained membranes were increased in the reduced uterine perfusion pressure (RUPP, n = 12) vs. the normal pregnant (NP, n = 10) dams.

Figure 5. Effect of placental ischemia on expression of placental HO-1

Reduced uterine perfusion pressure (RUPP, n = 12) dams had reduced (P<0.05) immunoreactive HO-1 relative to the 67 kDa band corresponding to albumin on Ponceau stained membranes in placental lysates than did normal pregnant (NP, n = 10) control rats with respect to the expression of HO-1 in the placenta.