The overall goal of this project is to improve our understanding of the role of astrocytes in the etiology of AIDS in the CNS. Astrocytes comprise about 25% of the cellular mass of the brain. They function in a variety of essential roles, including ionic homeostasis, removal of neurotransmitters from the extracellular fluid, and the transport of nutrients between neurons and the microvasculature. In addition, recent studies indicate that astrocytes are able to generate action potentials, a capability which raises the possibility of important new roles for these cells in intercellular communication. Although astrocytes can be infected by HIV, the extent of astrocytic involvement in AIDS Dementia Complex appears to greatly exceed the level of astrocytic infection. Purified GP120, the HIV coat protein, has been shown to have both toxic and protective actions on neurons, but its effects on astrocytes are as yet unknown. The experiments described here are designed to test the hypothesis that some of the effects of HIV on astrocytes may be mediated by the interaction of GP120 with the astrocyte plasma membrane. We will test the hypothesis that astrocytes are sensitive to vasoactive intestinal peptide (VIP) and to anti-CD4 antibody, both of which have been shown to be closely related to the cellular actions of GP120. For these studies we will use UC-11MG cells, a human astrocytoma derived which we have extensively characterized. These cells exhibit essentially all the features of mature, well-differentiated human astrocytes. We will test our hypothesis by exposing UC-11MG cells to GP120, VIP, and anti-CD4, either singly or in combination and monitoring the cells for changes in a number parameters that may be a part of the early response to HIV. These parameters include: (i) changes in morphology, viability, and growth rate; (ii) changes in the levels of intracellular second messengers; and (iii) changes in membrane electrical characteristics. Because some of these changes can be measured in individual cells, we should be able to identify even a relatively small subpopulation of responsive cells. After response to GP120, VIP, or anti-CD4 has been identified, attention will be focused on defining the relation of the induced response to alterations in specific astrocyte functions. Among the functions to be examined are regulation of ionic homeostasis, uptake of neurotransmitters, and modulation of the growth and activity of neurons. These studies are of potential significance in two ways. First, they may help to elucidate some of the mechanisms by which HIV affects an important population of cells in the CNS. Second, they should provide an important new model system for the in vitro testing of agents to block the effects of HIV on CNS cells. Grant=RO1NS27849 Tissue damage after treatment brain injury (TBI) results, in part, from a delayed series of interrelated biochemical and metabolic events. Based upon recent studies, we have suggested that changes in tissue magnesium (Mg2+) and release of excitatory amino acids (EAA) contribute to such secondary injury following central nervous system trauma. In the proposed studies we plan to utilize complementary biochemical techniques, including magnetic resonance spectroscopy (MRS) and microdialysis as well as pharmacological and anatomical methods, to further examine the role of EAA and Mg2+ in the pathophysiology of TBI. These experiments are intended to address the following hypotheses: MRS and microdialysis provide powerful complementary techniques for evaluating biochemical changes after TBI; EAA are released after TBI and contribute to secondary tissue damage through effects at N-methyl-D-aspartate (NMDA) receptors; changes in EAA are related to injury severity and are closely linked to changes in Mg2+; changes in Mg2+ are associated with abnormal mitochondrial function and decreased cellular bioenergetic state; competitive and non-competitive NMDA antagonists limit tissue damage and improve outcome after TBI; and magnesium supplementation enhances the effectiveness of both competitive and non-competitive NMDA antagonists in TBI.
Specific aims are: (1) to measure changes in amino acids (AA) in tissue and the extracellular space (microdialysis) after TBI is as a function of time posttrauma and injury severity; (2) to compare changes in EAA with alterations in level of ions (sodium, potassium, chlorine, calcium and magnesium) and water content after injury; (3) to correlate changes in EAA with metabolic and neurochemical alterations shown by 31P MRS (free Mg2+ concentration and cellular bioenergetic state); (4) to compare the temporal profile of biochemical changes to alterations in mitochondrial function; (5) to evaluate the effects of magnesium depletion and NMDA agonist administration on the response to trauma (behavioral, anatomical, biochemical); to examine the effects of treatment with NMDA antagonists, with and without magnesium supplementation, as well as magnesium treatment alone, on behavioral outcome and biochemical and anatomical correlates of trauma.
