IL1 and hypoxic-ischemic insults

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DESCRIPTION (provided by applicant): Injury to the brain caused by cerebral ischemia (i.e. stroke) is a major public health concern. As much as 50% of the brain damage incurred by stroke occurs outside of the primary focus of damage with the process of tissue destruction continuing for hours to days. It is now apparent that inflammatory factors contribute to this delayed pathophysiology. Specifically, studies demonstrate that the cytokine, interleukin 1beta (IL-1beta), is upregulated following experimental and clinical stroke while additional studies implicate it in the progression of injury. However, the cellular and molecular pathway(s) by which IL-1beta contributes to neuronal cell death have yet to be identified. This is largely due to the lack of suitable in vitro models in which to assess these mechanisms. Therefore, we developed a reliable and reproducible in vitro model system utilizing mixed neuronal/astrocyte cortical cell cultures. In this model, endogenous production of IL-1beta is simulated by exogenous addition of IL-1beta and neuronal injury induced by depriving cells of oxygen. We found that pre-treatment - but not concurrent or post-treatment - with this cytokine dramatically potentiated neuronal cell death induced by depriving mixed murine cortical cell cultures of oxygen. The effect of IL-1beta was concentration-dependent and could be completely inhibited by the recombinant IL-1 receptor antagonist, indicating that signaling through the IL-1 receptor type I (IL1R1) was involved. Further, we found this IL-1beta -mediated enhancement of hypoxic-neuronal injury can be completely prevented by pharmacological antagonism of metabotropic glutamate receptor 1 (but not mGluR5). This is in stark contrast to a pure hypoxic neuronal injury which is unaffected by mGluR1 receptor antagonism. Finally, we found that the enhancement of injury induced by IL-1beta was dependent on astrocytic expression of IL1R1 whereas loss of signaling in neurons had no effect. Thus, the objectives of this five year research plan are to 1) determine the molecular mechanism(s) by which IL1beta signaling functionally synergizes with mGluR1 signaling to enhance hypoxic neuronal injury; 2) to determine the astrocytic factor or factors responsible for mediating the IL-1beta enhancing effect; and 3) to assess whether removal of IL-1beta signaling can effectively prevent/ameliorate hippocampal injury in vivo induced by direct hippocampal injection of NMDA and/or middle cerebral artery occlusion. Improved definition of these events could lead to the development of new therapeutic strategies designed to attenuate the progression of neuronal destruction following stroke.