Thesis Format
Integrated Article
Degree
Doctor of Philosophy
Program
Biochemistry
Supervisor
Han, Victor K.M.
Affiliation
Children's Health Research Institute, London, Canada; Department of Pediatrics, The University of Western Ontario
2nd Supervisor
Heinemann, Ilka U.
Co-Supervisor
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.
Summary for Lay Audience
Intrauterine growth restriction (IUGR), or low birth weight, is a condition in which a fetus does not grow to their full potential during pregnancy, usually because they do not receive enough nutrients or oxygen. Low birth weight babies have a higher chance of health problems soon after birth and later in life as children and adults. In this thesis, I investigated specific cell signals that cause IUGR and studied both lack of sugar and oxygen supply as instigators for growth restriction. We used a baboon model where pregnant mothers were given less food to mimic overall nutrient restriction. When food intake was limited, it caused the fetus’s liver to experience low oxygen levels, known as hypoxia. Human liver cells were also used to determine changes in protein synthesis. I found that hypoxia triggered the production of certain proteins that interfere with the ability to use growth factors important for normal growth. I was able to pinpoint specific proteins in both low oxygen and low glucose (sugar) conditions that disrupted these growth factors, therefore changing the activity of specific pathways that control growth and development. I further explored the roles of various microRNAs (miRNAs) and messenger RNAs (mRNAs), which are molecules that regulate how genes and proteins are expressed. Over 400 mRNAs and 140 miRNAs were affected by low oxygen levels. Some of these molecules are involved in energy production and cell growth, while others affect how cells manage nutrients under stress. Then, I did a proteomic analysis of liver cells exposed to hypoxia. Without oxygen, cells cannot make as much energy and to compensate, they shift their focus towards less efficient methods of making energy. Low energy reduced cellular growth and division, helping us understand how oxygen levels can affect a fetal growth. These findings provide valuable insights into what regulates IUGR development, as well as the specific proteins, mRNAs and miRNAs involved. Overall, this work provides suggestions for new potential biomarkers for early diagnosis based on biochemical mechanisms and highlights potential targets for therapies that could help improve IUGR conditions in babies, since there are currently no therapies.
Recommended Citation
Kakadia, Jenica, "A Multi-omics Insight into Hypoxia and Glucose Deprivation-Mediated Changes: Implications for Intrauterine Growth Restriction Development" (2024). Electronic Thesis and Dissertation Repository. 10631.
https://ir.lib.uwo.ca/etd/10631
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
