Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Neuroscience

Supervisor

Laviolette, Steven R

Abstract

Prenatal hypoxia during fetal development is a significant environmental risk factor linked to schizophrenia (SCZ) vulnerability. However, hypoxia’s impact on human brain development at the cellular level remains unclear. Our laboratory has developed human cerebral organoids using induced pluripotent stem cells (iPSCs) derived from healthy control or SCZ patient cell lines to address these questions. This creates a platform that allows for the investigation into the pathophysiology of SCZ and hypoxia in tandem. Organoids were exposed to hypoxic conditions at one month of development, mimicking the early stages of cortical growth in the human fetus. Results reveal innate differences in neuronal development markers in SCZ organoids at the transcriptomic and protein level. In response to hypoxia, SCZ organoids exhibit dysregulation of mitochondrial-associated proteins and genes required for normal metabolism and growth. Our findings highlight critical differences in the expression of vital neuronal markers in SCZ and highlight hypoxia’s further impacts on neurodevelopmental pathophysiology related to SCZ risk.

Summary for Lay Audience

Schizophrenia (SCZ) is a mental disorder illness usually characterized by delusions, hallucinations, disordered thought, and diminished emotional expression. During pregnancy, fetuses that experience a lack of oxygen, termed hypoxia, are at an increased risk of developing schizophrenia later in life. However, how low oxygen negatively impacts brain development at a cellular level is not fully understood. Moreover, how an individual’s genetic risk for SCZ interacts with hypoxia has yet to be fully elucidated. To study both factors together, our laboratory grows ‘mini-brains in a dish,’ termed cerebral organoids, that mimic different aspects of early fetal brain development across various stages of pregnancy. These 3D sphere-like structures are grown from cells obtained from patients with SCZ or healthy individuals. At a period of growth reflecting the cusp of the first and second trimester of pregnancy, organoids were exposed to low-oxygen (hypoxic) conditions. Using various investigative techniques, we examined differences between SCZ and control organoids and the impact of hypoxia on both types of organoids. In response to hypoxia exposure, all organoids show an increased expression in proteins known to increase in response to low oxygen conditions. As expected with cell stress, we see increases in cell death due to hypoxia. Further investigation of the organoids revealed SCZ organoids show reductions in proteins and genes required for normal brain development compared to healthy controls. We also looked at proteins and genes in mitochondria, the powerhouse of the cell, as they need constant inputs of oxygen to produce energy for cells. Non-optimal functioning of mitochondria is also related to SCZ pathology as SCZ patient samples show differences in mitochondria shape and function compared to healthy individuals. RNA-Sequencing is used to determine which genes are up- and downregulated in samples. In the SCZ hypoxia-exposed organoids, there are changes in the expression of genes in mitochondria required to break down sugars into energy. Hypoxia also impacts the expression of proteins required for proper metabolism within cells in both control and SCZ organoids. This project reveals innate differences in brain development markers in SCZ and the impact of hypoxia on development via mitochondrial dysfunction and cellular stress responses.

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