Placenta NAD⁺ Depletion: A Mechanism Through Which Gestational Obesity Contributes to Placenta Dysfunction
Creators: name: Poisson, Hannah
Publisher: name: Université d'Ottawa | University of Ottawa
Year: 2024
Subjects: Placenta
Gestational Obesity
Mitochondria
Chronic Inflammation
Nicotinamide Adenine Dinucleotide (NAD+)
Poly-ADP Ribose Polymerases (PARPs)
Nicotinamide Riboside (NR)

description: Introduction: Gestational obesity is a metabolic disease on the rise in Canadian individuals of reproductive age which increases the risk of adverse pregnancy and fetal health outcomes. Although the exact mechanisms underlying these poor health consequences are currently unknown, chronic inflammation is a key contributor. Nicotinamide adenine dinucleotide (NAD⁺) depletion is a hallmark of many chronic inflammatory pathophysiologies in non-pregnant individuals, leading to mitochondrial dysfunction and metabolic stress. Considerable reduction in NAD⁺ content has likewise been found to play an important role in the establishment of placental dysfunction and poor fetal growth in the context of inflammation-mediated preeclampsia - a hypertensive disorder of pregnancy. Interestingly, boosting placental NAD⁺ levels via nicotinamide riboside (NR) supplementation improved placental structure/function and fetal growth profiles in a rodent model of this inflammatory disease. Considering that gestational obesity is a chronic inflammatory disease of pregnancy, this thesis seeks to determine if NAD⁺ depletion and mitochondrial impairment are also present, and if these factors contribute to poor placental/fetal health outcomes. This was explored using a high-fat high-sugar (HFHS) diet-induced gestational obesity murine model, with and without supplementation of NAD⁺ boosting treatment. Methods: Six-week-old C57BL/6N female mice were placed on a HFHS western diet or control (CTRL) diet for 12-15 weeks prior to pregnancy. During pregnancy, mice were maintained on the same diet and additionally received either water (H₂O; CTRL-H₂O = 11, HFHS-H₂O = 7) or the NAD+ supplement nicotinamide riboside (NR; 400 mg/kg/day; CTRL-NR = 10, HFHS-NR = 9) daily. Dams were sacrificed at gestational day (E)18.5 and placentas and fetuses were weighed and measured, with one half of each placenta fixed for histomorphology and the other half flash-frozen for RNA and protein analysis. Samples were pooled by fetal sex per litter, and data presented as litter average. Results: Fetuses from HFHS mothers were 0.23 g +/- 0.05 g smaller in mass and 3.37 mm +/- 0.74 mm smaller in length, and their placentas demonstrated reduced efficiencies and evidence of increased inflammation. Placental expression of PARP proteins (PARP-1, PARP-2) was elevated in placentas from obese dams. A trend towards elevated protein PARylation was observed in placentas from obese dams. NAD⁺ was found to be significantly reduced in these placentas, as well as total NAD. Interestingly, placentas from obese dams also demonstrated dysregulated OXPHOS protein levels, indicative of mitochondrial impairment. Unexpectedly, the use of NR supplementation across pregnancy did not increase NAD⁺ levels in the placenta, nor did it alter placental PARP/PARylation levels, mitochondrial dysfunction, and detriments to placental/fetal health. Conclusion: This thesis provides evidence that PARP-mediated NAD⁺ depletion and subsequent mitochondrial dysfunction may be components of placental pathophysiology in the context of gestational obesity - providing insight on future targets to rescue harmful effects to the placenta and fetus in pregnant populations with obesity. However, further research focused on optimizing modalities to therapeutically target placental NAD⁺ signaling is warranted.