The relationship between PPAR-γ and PE
PPAR-γ plays an important role in pregnancy. In this study, mice treated with T0070907 developed key features of preeclampsia, including elevated mean arterial blood pressure, proteinuria, endothelial dysfunction. This is consistent with previous reports [
11‐
16].In addition, we found that the placental weight decreased and the pro-inflammatory factors increased in the antagonist group. The results indicated that PPAR-γ participates in the pathogenesis of PE.
Previous literature reports examination of the preeclamptic placenta reveals numerous placental infarcts and arterial sclerosis. Infarction may be due to maternal vascular malperfusion [
17,
18]. Placental hypoperfusion may lead to placental ischemia and contribute to the development of preeclampsia. In this study, we found a large number of infarcts in placental sections of mice treated with T0070907, which consistent with the symptoms of preeclampsia. The results indicated that PPAR-γ production was suppressed, leading to a reduction in the placental weight and necrotizing injury. Kubota et al. also showed that PPAR-γ deficiency resulted in abnormal placental development [
19].
In this study, the level of the proinflammatory cytokine IL-1β in the peripheral blood was significantly higher in the PPAR-γ antagonist group than in the other groups. This result indicated that suppression of PPAR-γ production resulted in higher levels of proinflammatory cytokines in the peripheral blood. At this lower level, PPAR-γ could not normally regulate inflammatory responses, eventually causing PE manifestations in the mice.
Significant amelioration of PPAR-γ antagonist-induced PE phenotypes by LDA
This study showed that LDA intervention significantly ameliorated hypertension treated by T0070907 in pregnant mice. In addition, the 24-h urine protein level and urine protein/creatinine ratio were significantly reduced in the LDA-treated groups than in the T0070907-treated group. Furthermore, LDA effectively decreased the production of proinflammatory factors and antiangiogenic factors, reducing the levels of these factors to levels observed in normal pregnancy. Pathological analysis of placental and kidney tissues from mice in the different treatment groups indicated that LDA significantly alleviated kidney and placenta infarcts treated by T0070907.
The mechanism of action of aspirin in the prevention of PE treated by T0070907 in mice
PPAR-γ mRNA expression in the placentas of mice treated by T0070907 was downregulated, which is consistent with previous research by McCarthy et al. [
11]. In our study, preventive administration of LDA significantly relieved the downregulation of PPAR-γ mRNA. In addition, LDA was significantly ameliorated the overexpression of antiangiogenic factors and inflammatory cytokines treated by T0070907 and pathological injury to the placenta and kidney. In summary, LDA significantly ameliorates the PE promoted by T0070907 through various pathways. Therefore, this study suggests that LDA prevents PE through the regulation of PPAR-γ expression.
A study by Lehmann et al. showed that nonsteroidal anti-inflammatory drugs (NSAIDs) can activate PPAR-γ [
20]. That study suggests that at certain concentrations, NSAIDs can inhibit or induce adipogenesis by activating the PPAR-γ pathway. So combined with this experiment, we propose the possibility that aspirin, as an NSAID, might exert biological effects at certain concentrations by activating the PPAR-γ pathway. However, further research is still needed.
PPAR-γ is a nuclear hormone receptor superfamily member that has many functions in the body. At the cellular level, PPAR-γ agonists have anti-inflammatory, anti-proliferative, anti-fibrotic, and anti-apoptotic functions. At the system level, PPAR-γ agonists can induce haemodynamic changes in humans and animals to produce anti-hypertensive effects [
9]. PPAR-γ might have the potential to relieve hypertensive disorders in pregnancy [
21]. McCarthy et al. found that application of the PPAR-γ agonist rosiglitazone to the reduced uterine perfusion pressure(RUPP) rats alleviated the PE-like pathological symptoms to a certain degree [
12]. Thus, this study proposes that PPAR-γ agonists might help relieve PE. In addition, McCarthy et al. found that PPAR-γ agonists improved pregnancy outcomes of mice with PE, mainly through the activation of haem oxygenase-1 (HO-1), which is consistent with a study by Cudmore et al. showing that PPAR-γ agonists reduced the production of ROS and sFlt-1 by upregulating HO-1 expression to reduce oxidative stress in the bodies of PE patients and restore the balance of angiogenic factors [
11,
22]. Other studies have confirmed that activation of PPAR-γ can restore nitric oxide (NO) bioavailability [
23]. Martens et al. showed that activation of PPAR-γ promoted NO production in human aortic endothelial cells [
24].
PPAR-γ agonists can not only interfere with oxidative stress and angiogenesis pathways but also effectively reduce the intensity of inflammation in the bodies of PE patients. Hofmann et al. showed that PPAR-γ activation in monocytes and macrophages reduced the production of cytokines such as tumour necrosis factor-α, IL-1β, and IL-6 [
25]. PPAR-γ activation can also inhibit the proinflammatory effect of platelets and suppress platelet aggregation and thromboxane A2 (TXA2) release [
26]. Therefore, PPAR-γ agonists could help to restore the balance of TXA2/PGI2 in PE patients.
It has been confirmed that PPAR-γ agonists have protective effects on the kidney and can effectively reduce proteinuria. Sugawara showed that PPAR-γ agonists could reduce blood pressure, protect vascular endothelial functions, cause vasodilation of the glomerular arterioles, and reduce proteinuria [
27]. PPAR-γ agonists were shown to protect podocytes in a rodent model of kidney disease and glomerular hypertension [
28]. Especially after podocyte injury, PPAR-γ activation plays a key protective role. Glomerular podocytes are key cells for the prevention of proteinuria, kidney failure, and cardiovascular disease.
In this study, LDA was administered to mice with PE treated by T0070907 and was found to significantly ameliorate hypertension and proteinuria. In addition, LDA effectively rescued the downregulation of PPAR-γ mRNA expression. Therefore, we believe that LDA could prevent PE by regulating PPAR-γ expression. PPAR-γ mRNA expression in the mouse placenta varied widely in the group that received preventive administration of LDA. This reflects the large individual differences that could confound the preventive use of LDA in clinical practice; therefore, more accurate confirmation of the target population for LDA treatment is clinically significant. Thus, whether LDA prevents PE through the activation of the PPAR-γ pathway and its specific action mechanism require further investigation.
Dose effect of aspirin
The results indicated that 20 mg/kg/d LDA has significant preventive effects against PE treated by T0070907. These results suggest that the preventive effect of aspirin on PE in mice was dose-dependent.
Precious observational study has also shown that daily administration of 100–160 mg LDA might be necessary to prevent PE and that 60–80 mg LDA might not be enough to prevent PE [
29]. The above views are all consistent with the conclusions of this study.