Microglial cell hyperactivation following hypoxic brain injury, and their release of neurotoxic inflammatory mediators into the CNS contributes to inflammation and damage. Hence, modulation of microglial cell activity is of great interest to decrease or prevent neuronal damage following brain injury from stroke, heart or lung disease and breathing disorders. Extracellular adenine nucleotides are important modulators of microglial cell inflammatory capacity, and they are abundant following brain injury. Although much work has been done elucidating the mechanisms involved in ATP stimulation of microglial inflammatory cytokines, little is known about their complementary inhibitory effects on microglial inflammatory mediator production. The fundamental hypothesis guiding this proposal is that extracellular adenine nucleotides exert neuroprotective effects in the brain by interacting with purinergic receptor signal transduction pathways to decrease microglial cell activation. We will investigate the molecular mechanisms underlying adenine nucleotide mediated neuroprotection in microglial cell cultures using two models of microglial activation: bacterial lipopolysaccharide (LPS) or hypoxia.
Four specific aims are proposed to test mechanisms by which purinergic receptors influence microglial production of neurotoxic/inflammatory mediators, focusing on purinergic receptor MAP kinase pathways and transcription factor activation profiles. Purinergic receptor activation decreases microglial cell activity in response to several microglial activators, suggesting that purinergic receptors interact with signaling pathways common to different stimuli. However, purinergic receptor activation can cause deleterious effects in some situations, implying that therapeutic modulation of certain purinergic receptors may result in different effects depending upon the pre-existing microglial activation status. Results of this work will aid in the identification of new pharmacologic targets that may be exploited therapeutically to control microglial activation in response to several stimuli including hypoxia.
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