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The mechanisms by which mitochondria convert nutrients into cellular energy have been described in intricate detail, and yet, the regulation and compartmentalization of such metabolic pathways are poorly understood. As a result, the underlying causes of mitochondrial dysfunction and bioenergetic deficiency in diseases such as amyotrophic lateral sclerosis (ALS) remain elusive. To address this longstanding gap in the field, we first sought to understand how the metabolism of glucose and glucose-derived pyruvate are regulated in the cell. Previous research has suggested that this metabolic regulation is mediated by specialized lipid raft domains of the endoplasmic reticulum (ER) in close contact with mitochondria, referred to as mitochondria-associated ER membranes (MAM). Using density gradient ultracentrifugation and immunoblotting techniques, we found that MAM domains play a role in the compartmentalization of glycolysis by recruiting and promoting the interaction of specific glycolytic enzymes. We then performed a series of bioenergetic, proteomic, and lipidomic analyses to determine how the establishment of ER-mitochondria contact sites at MAM affects the biology of mitochondria attached at these domains. We observed a novel distinction between mitochondria in contact with ER-MAM domains (MER) and those that are free from the ER (FM), with MER displaying a higher capacity for pyruvate-driven respiration and FM being specialized for fatty acid-driven energy production. Finally, using cell and mouse models of ALS with mutations in superoxide dismutase 1 (SOD1), we found that the glycolytic deficiency in ALS is a direct consequence of the progressive disruption of MAM structure and function, which thereby hinders the use of glucose-derived pyruvate as a mitochondrial fuel. This triggers a shift in mitochondrial substrate from pyruvate to fatty acids that, when sustained over time, contributes to the death of motor neurons and the progression of this fatal disease. Overall, this work aims to advance our understanding of metabolic compartmentalization, mitochondrial substrate specificity, and the relevance of both to ALS etiology.

Thesis: Sc. D., Massachusetts Institute of Technology, Department of Nuclear Engineering, 1980 / Bibliography: leaves 348-372. / by Kimberlee Jane Kearfott. / Sc. D. / Sc. D. Massachusetts Institute of Technology, Department of Nuclear Engineering

Pancreatic cancer is nearly asymptomatic, which can result in extensive grow and even metastasis to other organs before detection. When diagnosed at a late stage, the survival rate is 3%. Early detection is therefore the key to treating pancreatic cancer. Diabetes was identified as a risk factor for the development of pancreatic cancer, but the mechanism remains unknown. In this project, the objective was to delineate a link between diabetes and pancreatic cancer by examining their shared protein signaling pathways. In a previous study, hyper-activation of AKT1 resulted in a pre-diabetic phenotype and also increased upregulation of downstream phosphorylated mTOR and phosphorylated p70S6 kinase. More recently, mice with mutations that hyper-activated AKT1 and KRAS showed a significantly higher blood glucose level compared to littermate matched wild-type, mutant AKT1, or mutant KRAS mice. Interestingly, mice with a combination of mutations that hyper-activated AKT1 and KRAS also showed faster development of pancreatic cancer compared to these other groups of littermate mice. Toward determining a molecular basis for the crosstalk between AKT1 and KRAS, pancreas and liver tissues were collected from all four groups of mice including wild-type, mutant AKT1, mutant KRAS, and mice with dual AKT1/KRAS hyper-activation. One strategy was to examine expression and/or phosphorylation of downstream protein signaling crosstalk by analysis of p70S6K using Western Blots. Erk 1/2 proteins were also tested as downstream proteins of KRAS to provide a molecular view of the individual and cooperative roles of AKT1 and KRAS in the mouse models. A potential feedback mechanism to affect insulin receptor signaling in the pancreas was examined using enzyme-linked immunosorbent assays (ELISA). A significant decrease in insulin receptor phosphorylation, possibly contributing to insulin resistance, was found when mice had mutant hyper-activated KRAS. Contrary to the original expectations, mice with combined mutations of AKT1 and KRAS may contribute to the accentuated diabetic phenotype by targeting two different points in the AKT and KRAS protein signaling pathways. The information can help understand the relationship between glucose metabolism, diabetes, and pancreatic cancer development. By thoroughly studying the interactions between targets in the AKT1/KRAS signaling pathways, key molecular events that induce metabolic changes and potentially early biomarkers may lead to an improved understanding of risk and/or detection of pancreatic cancer.

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Glioblastomas continue to carry poor prognoses for patients despite advances in surgical, chemotherapeutic, and radiation regimens. One feature of glioblastoma associated with poor prognosis is the degree of hypoxia and elevated expression levels of hypoxia-inducible factor-1 á (HIF-1á). HIF-1á expression allows metabolic adaptation to low oxygen availability, partly through upregulation of vascular endothelial growth factor (VEGF) and increased tumor angiogenesis as well as induction of anaerobic glycolysis. In this study, we demonstrate an induced level of astrocyte-elevated gene-1 (AEG-1) by hypoxia in glioblastoma cells. AEG-1 has the capacity to promote anchorage-independent growth and cooperates with Ha-ras in malignant transformation. In addition, AEG-1 was recently demonstrated to serve as an oncogene and can induce angiogenesis and autophagy in glioblastoma. Results from in vitro studies show that hypoxic induction of AEG-1 is dependent on HIF-1á stabilization during hypoxia and that phosphatidylinositol 3-kinase (PI3K) inhibition abrogates AEG-1 induction during hypoxia through loss of HIF-1á stability. Furthermore, we show that AEG-1 is induced by glucose deprivation and that prevention of intracellular reactive oxygen species (ROS) production prevents this induction. Additionally, AEG-1 knockdown results in increased ROS production and increased glucose deprivation-induced cytotoxicity, whereas AEG-1 overexpression prevents ROS production and decreases glucose deprivation-induced cytotoxicity, indicating that AEG-1 induction is necessary for cells to survive this type of cell stress. From studies examining the expression of enzymes involved in glucose metabolism, we demonstrate that AEG-1 alters the tumor metabolic profile in a partially 5'-adenosine monophosphate (AMP)-activated protein kinase (AMPK)-dependent manner. Moreover, glycolytic inhibition modulates the metabolic effects induced by AEG-1, and AEG-1 knockdown reduces the growth and alters the metabolic phenotype of glioblastoma subcutaneous xenografts. These observations link AEG-1 overexpression observed in glioblastoma with hypoxia and glucose metabolic signaling, and targeting these physiological pathways may lead to therapeutic advances in the treatment of glioblastoma in the future. Recent studies have reported the detection of the human neurotropic virus, JC Virus (JCV), in a significant population of brain tumors, including medulloblastomas. Accordingly, expression of the JCV early protein, T-antigen, which has transforming activity in cell culture and in transgenic mice, results in the development of a broad range of tumors of neural crest and glial origin. Evidently, the association of T-antigen with a range of tumor-suppressor proteins, including p53 and pRb, and signaling molecules, such as â-catenin and IRS-1, play a role in the oncogenic function of JCV T-antigen. We demonstrate that T-antigen expression is suppressed by glucose deprivation in medulloblastoma cells that endogenously express T-antigen. Mechanistic studies indicate that glucose deprivation-mediated suppression of T-antigen is partly influenced by AMPK, a critical sensor of the AMP/ATP ratio in cells. We have found that AMPK activation inhibits T-antigen expression, whereas AMPK inhibition prevents glucose deprivation-mediated T-antigen suppression. In addition, glucose deprivation-induced cell cycle arrest in the G1 phase is blocked with AMPK inhibition, which also prevents T-antigen downregulation. Furthermore, T-antigen-expressing medulloblastoma cells, as compared to those which do not express T-antigen, exhibit less G1 arrest and an increased percentage of cells in the G2 phase of the cell cycle during glucose deprivation. On a functional level, T-antigen downregulation is partially dependent on ROS production during glucose deprivation. Additionally, studies indicate that T-antigen prevents ROS induction, loss of ATP production, and cytotoxicity induced by glucose deprivation. We have also found that T-antigen is downregulated by the glycolytic inhibitor, 2-deoxy-D-glucose (2-DG), and the pentose phosphate inhibitors, 6-aminonicotinamde (6-AN) and oxythiamine (OT). Enzyme expression studies also indicate that T-antigen upregulates the expression of the pentose phosphate enzyme, transaldolase-1 (TALDO1), demonstrating a potential link between T-antigen and glucose metabolic regulation. These studies highlight the potential involvement of JCV T-antigen in the proliferation and metabolic phenotype of medulloblastoma and may enhance our understanding of the role of viral proteins in tumor glycolytic metabolism, thus implicating these proteins as potential targets for the treatment of virus-associated tumors. / Biomedical Neuroscience

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