FGF-2 Induces Neuronal Death through Upregulation of System xc-

The cystine/glutamate antiporter (system xc-) transports cystine into cell in exchange for glutamate. Fibroblast growth factor-2 (FGF-2) upregulates system xc- selectively on astrocytes, which leads to increased cystine uptake, the substrate for glutathione production, and increased glutamate release. While increased intracellular glutathione can limit oxidative stress, the increased glutamate release can potentially lead to excitotoxicity to neurons. To test this hypothesis, mixed neuronal and glial cortical cultures were treated with FGF-2. Treatment with FGF-2 for 48 h caused a significant neuronal death in these cultures. Cell death was not observed in neuronal-enriched cultures, or astrocyte-enriched cultures, suggesting the toxicity was the result of neuron-glia interaction. Blocking system xc- eliminated the neuronal death as did the AMPA/kainate receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline-2,3-dione (NBQX), but not the NMDA receptor antagonist memantine. When cultures were exposed directly to glutamate, both NBQX and memantine blocked the neuronal toxicity. The mechanism of this altered profile of glutamate receptor mediated toxicity by FGF-2 is unclear. The selective calcium permeable AMPA receptor antagonist 1-naphthyl acetyl spermine (NASPM) failed to offer protection. The most likely explanation for the results is that 48 h FGF-2 treatment induces AMPA/kainate receptor toxicity through increased system xc- function resulting in increased release of glutamate. At the same time, FGF-2 alters the sensitivity of the neurons to glutamate toxicity in a manner that promotes selective AMPA/kainate receptor mediated toxicity

Regulation of System XC- and its Contribution to Cell Death

The main focus of the studies in this thesis involves examining the role of cystine/glutamate exchange (system xC-) in neuronal death in primary cortical cell culture, with an emphasis on how glial function affects neuronal cell death. System xC- is a sodium-independent transporter that mediates cystine uptake and glutamate release. It accounts for most of the cystine uptake in astrocytes in mature cultures, providing the rate limiting substrate for synthesis of the main endogenous antioxidant glutathione. The glutamate released by system xC- may lead to excessive extracellular glutamate and cause excitotoxicity. β-N-methylamino-L-alanine (BMAA) is a non-protein amino acid that may be involved in neurodegenerative diseases. We found that BMAA induced oxidative stress by competing with cystine at system xC- leading to depletion of glutathione. BMAA also drives system xC- mediated glutamate release, which may contribute to its induction of excitotoxicity. Fibroblast growth factor-2 (FGF-2) is involved in multiple processes in the central nervous system, including plasticity, neurogenesis, differentiation, and neuronal survival. Also, alterations in FGF-2 and its signaling have been implicated in neurodegenerative diseases and psychiatric disorders. We found that FGF-2 greatly increased cystine uptake through system xC- in astrocyte-enriched primary cultures, but not in neuronal or microglial cultures. Our data showed that FGF-2 increased cystine uptake by upregulating system xC- by acting on FGFR1, and signaling through the PI3K/Akt and MEK/ERK pathways. FGF-2 treatment for 48 hours caused significant neuronal death only in mixed neuronal and glial cultures, but not in neuronal-enriched or astrocyte-enriched cultures. Blocking system xC-, or AMPA/kainate receptors, eliminated the neuronal death induced by FGF-2 treatment. Therefore, it is likely that 48 hour FGF-2 treatment induces AMPA receptor mediated toxicity through increased glutamate release from astrocytes due to increased system xC- function. However, we cannot exclude the possibility that FGF-2 treatment sensitizes the neurons to normal system xC- mediated glutamate release. Together the results indicate that 1) competitive substrates of system xC-, such as BMAA, that do not lead to glutathione production are particularly toxic; and 2) upregulation of system xC- on astrocytes may be toxic to surrounding neurons

Glutathione-Mediated Neuroprotection Against Methylmercury Neurotoxicity in Cortical Culture is Dependent on MRP1

Methylmercury (MeHg) exposure at high concentrations poses significant neurotoxic threat to humans worldwide. The present study investigated the mechanisms of glutathione-mediated attenuation of MeHg neurotoxicity in primary cortical culture. MeHg (5 μM) caused depletion of mono- and disulfide glutathione in neuronal, glial and mixed cultures. Supplementation with exogenous glutathione, specifically glutathione monoethyl ester (GSHME) protected against the MeHg induced neuronal death. MeHg caused increased reactive oxygen species (ROS) formation measured by dichlorodihydrofluorescein (DCF) fluorescence with an early increase at 30 min and a late increase at 6 h. This oxidative stress was prevented by the presence of either GSHME or the free radical scavenger, trolox. While trolox was capable of quenching the ROS, it showed no neuroprotection. Exposure to MeHg at subtoxic concentrations (3 μM) caused an increase in system xc− mediated 14C-cystine uptake that was blocked by the protein synthesis inhibitor, cycloheximide (CHX). Interestingly, blockade of the early ROS burst prevented the functional upregulation of system xc−. Inhibition of multidrug resistance protein-1 (MRP1) potentiated MeHg neurotoxicity and increased cellular MeHg. Taken together, these data suggest glutathione offers neuroprotection against MeHg toxicity in a manner dependent on MRP1-mediated efflux

Self-supervised Pretraining for Decision Foundation Model: Formulation, Pipeline and Challenges

Decision-making is a dynamic process requiring perception, memory, and reasoning to make choices and find optimal policies. Traditional approaches to decision-making suffer from sample efficiency and generalization, while large-scale self-supervised pretraining has enabled fast adaptation with fine-tuning or few-shot learning in language and vision. We thus argue to integrate knowledge acquired from generic large-scale self-supervised pretraining into downstream decision-making problems. We propose Pretrain-Then-Adapt pipeline and survey recent work on data collection, pretraining objectives and adaptation strategies for decision-making pretraining and downstream inference. Finally, we identify critical challenges and future directions for developing decision foundation model with the help of generic and flexible self-supervised pretraining

The state through its mirrors : an anthropological study of a 'Respect-the-Elderly Home' in rural China at the turn of the 21st century

This thesis represents an endeavour to study and rethink bureaucracy through an ethnography of the bureaucratic organisation called ‘Respect-the-Elderly Home’ (REH) in rural China in the first decade of the 21st century. Its contextual concern is to examine the phenomenon of old age support being transferred from primary groups (family and village) to the state in the processes of modern state formation, a context in which elderly support is portrayed by both the Chinese government and mainstream academic discourse as a symptom of family dysfunction and moral crisis; and a state project to build up REHs to host the welfare category of ‘Five-Guarantee Elderly’ is hailed to be practically therapeutic and ideologically significant. Based on long term fieldwork in one REH in southwestern China and more REHs generally (April 2010 – June 2011), this thesis reveals a secret function of this organisation, namely, ‘accommodative inversion’, and argues for a heterotopian looking-glass perspective to conceptualise it. The first chapter outlines the fieldwork setting in a way that its heterotopian qualities are simultaneously presented. The following chapters are divided into two parts. The first part delineates the realities of the institution-defined order and disorders of dining, spatial layout and temporal orientation, and explores the mechanisms which make the presumable incompatibility of these distinct orders practically irrelevant. The second part explores the dialectics of state and family in service delivery, guarantee and deprivation, and the condition of the residents as the served and the serving, and explains why structural inversions are inevitable through institutional processes beyond individual intention. This research brings the myth of our era – of bureaucracy and in particular of the Chinese bureaucracy – into a dialogue with the literature on bureaucratic organisation that has emerged in social science since the 1960s. More significantly, by disclosing and expounding the violent nature of state welfare, it presents a fundamental challenge to conventional understandings of benefactor and beneficiary in state provision

PART I: ASYMMETRIC SYNTHESIS OF SIX MEMBERED N-HETEROCYCLIC RINGS MEDIATED BY BIFUNCTIONAL THIOUREA CATALYSTS PART II: EXPLORATION OF DNA CLEAVAGE ACTIVITIES BY CERTAIN SMALL ORGANIC MOLECULES

Ph.DDOCTOR OF PHILOSOPH