A Multi-omics Insight into Hypoxia and Glucose Deprivation-Mediated Changes: Implications for Intrauterine Growth Restriction Development
Abstract
Intrauterine growth restriction (IUGR) is a condition in which a fetus fails to achieve its genetically determined growth potential, often due to insufficient nutrient and oxygen supply. IUGR development is multifactorial and the mechanisms underlying its development are poorly known. This thesis investigates how hypoxia and glucose deprivation contribute to IUGR. Using a non-human primate model and HepG2 cells, I found that maternal nutrient restriction (MNR), where overall food intake is reduced, induces fetal liver hypoxia and increases expression of hypoxia-inducible factor-1α (HIF-1α) and REDD1 (regulated in development and DNA damage-response-1). This activation inhibits mechanistic target of rapamycin (mTORC1) and enhances phosphorylation of insulin-like growth factor (IGF) binding protein-1 (IGFBP-1) at specific sites (Ser101/Ser119/Ser169), thereby reducing IGF-1 bioavailability, an important regulator of fetal growth. Depriving HepG2 cells of glucose similarly led to mTORC1 inhibition and increased IGFBP-1 phosphorylation, mediated by the activation of energy-sensing AMPK (AMP-activated kinase) and TSC2 (tuberous sclerosis protein 2). Increased IGFBP-1 phosphorylation decreases IGF-1 bioavailability, inhibiting growth signaling. Additionally, my work identified over 400 mRNAs and 140 miRNAs differentially expressed in hypoxic HepG2 cells. Key miRNAs like miR-197-3p and miR-766-3p were upregulated, targeting genes involved in lipid biosynthesis and metabolism, while downregulated miRNAs, including miR-33a-5p and miR-15a-5p, targeted glycolysis and lactate metabolism genes. I newly identified miR-6834 as a regulator of mTOR signaling and IGFBP-1 phosphorylation. Further, proteomic and phosphoproteomic analyses of hypoxia-treated HepG2 cells revealed increased glycolysis and altered carbohydrate metabolism to maintain energy homeostasis. Lipid metabolism and cell proliferation were concurrently inhibited, with potential induction of cell death through ferroptosis. The data presented in this thesis improve our understanding of the complex mechanisms involved in IUGR and provide an insight into how hypoxia and glucose deprivation disrupt critical metabolic pathways and cell proliferation. Key mediators of growth signaling provide possible avenues for targeted therapeutic interventions to restore appropriate fetal development.