Placental Ischemia Leads to Regional Astrocyte Activation: Role of TNFα

Abstract

Preeclampsia, a hypertensive disorder of pregnancy, can quickly progress to eclampsia when seizure develops in the peri-partum period. We have shown that the preclinical rat model of preeclampsia, induced by surgical reduction of uterine perfusion pressure (RUPP), has reduced latency to drug induced seizures and cerebral edema. The increased seizure sensitivity was associated with increased cerebrospinal fluid (CSF) cytokines, an indicator of tissue inflammation and potential activation of neuroglial cells. Moreover, other labs have shown that treatment of brain slices with serum from pregnant women induced increased neuronal activity and neuro-inflammation through TNFα. Thus, we tested the hypothesis that placental ischemia induces regional astrocyte activation that can be reversed by pharmacological blockade of TNFα. On GD14, time pregnant rats were randomly assigned to normal pregnant (NP, n=6) or RUPP (n=6) groups and further assigned to no treatment or etanercept injection (0.8 mg/kg, sc) on GD18. RUPP rats underwent surgery on GD14 to induce placental ischemia by inserting silver clips around the abdominal aorta and each of the uterine artery branches. Normal pregnant rats did not undergo surgery. Brains were harvested on GD19 and processed for immunofluorescence staining. Anterior brain was cut into 20 μm thick sections and stained for glial fibrillary acidic protein (GFAP), an astrocyte marker. Z-stacks (0.5 μm steps) were obtained and percent area of GFAP positive astrocytes was analyzed using Image J in the anterior commissure, corpus callosum, cortex, and caudate putamen. Two-Way Analysis of Variance revealed a significant increase in the percent area of astrocytes in the caudate putamen in RUPP rats [RUPP: 5.05 ± 1.09%; NP: 1.32 ± 0.28% (P = 0.01)] which was reduced by etanercept (2.11 ± 0.85%). There were no significant changes in % area in the anterior commissure, corpus callosum, or cortex (P> 0.05). Increased astrocyte area in the caudate putamen was associated with higher number of astrocytes [NP: 7 ± 1; RUPP: 13 ± 1 (p<0.01)] which was unchanged by etanercept (12 ± 3 cells). Our results are consistent with the hypothesis that placental ischemia induces cytotoxic edema (cell swelling) in the anterior cerebrum through regional astrocyte activation (caudate putamen). Moreover, increased circulating TNFα in placental ischemic rats may contribute to astrocyte activation, and in turn induce the release of TNFα and other pro-inflammatory cytokines, increasing seizure susceptibility and cytotoxic edema. Additional analyses of astrocytic morphology are ongoing and the direct role of pro-inflammatory cytokines on seizure susceptibility during pregnancy are areas of future study. Support or Funding Information NIH K99/R00HL129192, COBRE Pilot Grant, P20GM104357, P01HL051971 Representative images of GFAP+ astrocytes in the Caudate Putamen (CP) taken at 60X. Graph shows % area covered by astrocytes for each group. Individual points represent average data per section (1–3 images - 2 sections per rat). NP-normal pregnant, RUPP - reduced uterine perfusion pressure. *p<0.05, **p<0.01. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.