Role For Inflammatory Cytokines In Neurodegeneration

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Chemokines have been shown to be involved in brain development, in the maintenance of normal brain homeostasis, and in the migration, differentiation, and proliferation of glial and neuronal cells. Chemokine and chemokine receptor expression can be increased by inflammatory mediators and have been associated with a number of neuroinflammatory and neurological disorders including multiple sclerosis, trauma, stroke, Alzheimer's disease, tumor progression, and AIDS dementia. An emerging area of interest for chemokine action is represented by the communication between the neuroendocrine and the immune system. It is now evident that chemokines and their receptors represent a multifunctional pluripotent family of proteins whose actions on the CNS are not restricted to neuroinflammation. These molecules constitute crucial regulators of cellular communication in physiological and developmental processes. We have previously shown that human neuronal cells express a number of cell surface chemokine receptors, which appear to mediate neuronal cell migration and increases in intracellular calcium. In addition, we have found that SDF-1a and the HIV protein, gp120, are able to bind to CXCR4 on the surface of neurons resulting in a programmed neuronal cell death. Despite these findings, there is still very little known about the biological role of other chemokine receptors on the surface of neurons and glia cells. In this study, we have examined the direct and indirect effects of a variety of chemokines, more specifically here MCP-1 and MIP-2 (for which we have demonstrated the presence of cell surface receptors on neurons), to induce neuronal cell death or survival. We have found that the MCP-1 and MIP-2 directly and specifically induce differentiated hippocampal neuron death via specific cell surface chemokine receptors, through the generation of reactive oxygen species production (e.g., nitric oxide or NO), through caspase activation, and glutamate release. In addition, we have also found that these chemokines directly activate astrocytes to produce a number of inflammatory cytokines and molecules that appear to be toxic to human and rodent differentiated neurons. In fact, chemokine-induced astrocyte neurotoxicity appears to be partially due to the release of glutamate by metabolically active astrocytes and microglia. We believe that CNS chemokines play an important role in the genesis of neuroinflammation and the various pathological sequelae associated with trauma and neurological diseases. Whether there are common underlying biochemical and molecular mechanisms in which chemokines mediate their effects in both acute and chronic neurodegenerative and neuroinflammatory processes remains to be determined. Additional studies have focused on chemokines and various inflammatory mediators in the development of Alzheimers Disease (AD). The hallmark pathological feature of this disease is the accumulation of b-amyloid (Ab) plaques, the ensuing neurodegeneration and neuroinflammation within the brains of AD patients. There are several forms of Ab, including Ab1-40 and 1-42, each exhibiting differing cellular associations as well as neurotoxic potency. For example, Ab 1-40 is primarily associated with reactive astrocytes, while Ab 1-42 is associated with activated microglia/macrophages and exhibits greater neurotoxic potency than Ab 1-40. The presence of activated glia in both cases results in the production of chemokines and inflammatory cytokines, which we believe may mediate as well as exacerbate Ab-induced neurotoxicity. Using cDNA microarray technology, we have analyzed the effect of the two forms of Ab peptide on neuronal and astroglial populations and their ability to induce differential gene expression. A number of proinflammatory (including chemokines and several CCRs), apoptotic, and glutamate receptor-associated genes were found to be upregulated in human astrocytes and neuronal cells. We are currently examining the specific role of these genes in Ab-mediated activation and cell death as well as examining histological sections of control aged and AD brain tissue for the RNA and protein expression of the genes in question. We believe these studies may elucidate the pathways via which glia cells may directly and indirectly mediate neuroinflammation, neurodegeneration and AD pathology. In addition to the work above, we have recently acquired highly defined hippocampal tissue from AD patients along with age-matched counterparts with the hope of building a model defining the inflammatory mechanisms of AD as well as Ab- and chemokine-induced neurotoxicity and astrocyte activation. The goals of this project are to characterize and compare the gene expression profile of CNS tissue obtained from acute (trauma) and chronic (AD) disease-injury processes using cDNA microarray analysis. We have already performed these studies and are currently processing the data. Immunohistological analyses and PCR confirmations are currently underway to confirm our findings. Overall, we believe there are common underlying biochemical and molecular mechanisms involved in both acute and chronic neurodegenerative and neuroinflammatory processes. The ultimate goals of this project are: 1) to characterize and compare the genetic profile of CNS tissue obtained from acute (trauma) and chronic (AD) disease-injury processes using cDNA microarray analysis; 2) to determine whether specific inflammatory markers are modulated during acute and chronic phases of neurodegeneration that may be diagnostic or phenotypic; and 3) to determine whether specific signaling pathways are being utilized in various neurodegenerative processes with specific emphasis on neuroglia.