Vascular Adaptations to Pregnancy in a Rat Model of Advanced Maternal Age: Endoplasmic Reticulum Stress as a Potential Target for Therapeutic Intervention
Creators: Pasha, Mazhar
Publisher: name: University of Alberta Library
Year: 2023

<p>Advanced maternal age (≥35 years) increases the risk of pregnancy-specific complications such as reduced fetal growth and preeclampsia. The Davidge laboratory previously showed poor pregnancy outcomes and vascular dysfunction in a rat model of advanced maternal age. However, vascular adaptations, molecular mechanisms, and potential interventions to improve vascular function and adverse pregnancy outcomes in aging were not studied. I hypothesize that in a rat model of advanced maternal age; 1) normal pregnancy-induced vascular adaptations are altered, causing adverse pregnancy outcomes, due to increased endoplasmic reticulum (ER) and oxidative<br>
stress via NADPH (NOX) oxidases in the vasculature and placenta and 2) that tauroursodeoxycholic acid (TUDCA) treatment (an ER stress inhibitor) by reducing ER and<br>
oxidative stress will improve pregnancy outcomes. In the first study, young (3-4 months) and aged (9-9.5 months; ~35 years in humans) non-pregnant and pregnant rats were used, in the second and third studies, young and aged dams with or without TUDCA treatment were studied on gestational day (GD) 20. A calculated dose (150 mg/kg/day) of TUDCA was provided in regular drinking water throughout pregnancy. On GD20 (non-pregnant rats were aged-matched), blood pressure<br>
was measured (tail-cuff plethysmography), pregnancy outcomes were recorded, vascular function in mesenteric and main uterine arteries (wire myography), and ER and oxidative stress markers<br>
(Western blotting) were assessed in systemic mesenteric arteries and placentas. Endothelium-dependent vasodilation response to methacholine (MCh) was studied in the presence or absence<br>
of pan-nitric oxide synthase (NOS) inhibitor (L-NAME), prostaglandin H-synthase (PGHS) inhibitor (meclofenamate), endothelium-dependent hyperpolarization (EDH) inhibitors (apamin and TRAM-34) or NOX inhibitor (apocynin). Vasoconstriction responses to big endothelin-1<br>
(bigET-1) were studied in the presence or absence of matrix metalloproteinases (MMPs) inhibitor (GM6001), endothelin converting enzyme-1 (ECE-1) inhibitor (CGS35066), chymase inhibitor (chymostatin), or neutral endopeptidase inhibitor (DL-Thiorphan), further, vascular response to ET-1 was also evaluated. <br>
In the first study, I observed adverse pregnancy outcomes in aged dams in comparison to young dams. Enhanced contribution of NO and EDH-mediated relaxation in aged dams compared<br>
to young dams. Increased blood pressure and enhanced contribution of NOX enzymes in aged nonpregnant<br>
rats compared to all the groups. In addition, aged groups demonstrated greater contractile responses to bigET-1 compared to young groups, independent of pregnancy. There was also increased contribution of ECE-1 in processing bigET-1 to ET-1 in aged groups, while no changes in the presence of other inhibitors (MMPs, chymase, or neutral endopeptidase). There were no differences in the sensitivity to ET-1 between the young and aged groups. In conclusion, reduced blood pressure and enhanced EDH-mediated contribution to vasodilation imply a compensatory beneficial adaptation in aged dams that were successful and able to maintain pregnancy.<br>
In the second study, the results recapitulated adverse pregnancy outcomes in the aged dams vs young dams. NO changes in the MCh responses were observed in mesenteric arteries,<br>
while reduced uterine artery relaxation was seen in aged dams vs young dams. Increased levels of phospho-eIF2α, CHOP, and NOX-4 were observed in the aged dams vs young dams. TUDCA<br>
treatment decreased blood pressure, improved fetal weight, tended to improve uterine artery vascular function, and reduced the expression of phospho-eIF2α, and CHOP proteins in aged dams vs control dams. In conclusion, this study highlighted the role of ER stress in pregnancy and highlighted the beneficial effect of TUDCA treatment in improving altered vascular function and pregnancy outcomes in advanced maternal age.<br>
In the third study, my data showed increased levels of ER stress proteins GRP78 (in the male labyrinth zone) and phospho-eIF2α (in male and female junctional zones) in aged dams vs<br>
young dams. Whereas TUDCA treatment reduced the levels of ER stress markers only in aged dams (GRP78, phospho-eIF2α, ATF-4, and CHOP) in the male labyrinth zone, and sXBP1 protein<br>
in both male and female junctional zones. Thus, TUDCA may have a cytoprotective role in maintaining ER stress proteins to basal levels in advanced maternal age. <br>
In conclusion, my PhD project emphasized the importance of vascular adaptive pathways in pregnancy that could compensate for advanced maternal age and highlighted the complexity of<br>
cellular ER stress responses in advanced maternal age that may be modulated in aged dams. Whereas TUDCA intervention, as a promising therapeutic option, may benefit pregnancy outcomes in complicated pregnancies such as advanced maternal age.</p>