Spinal cord injury (SCI) triggers a neuroinflammatory reaction that can aggravate tissue injury (e.g., neuronal death, axonal injury, demyelination) and promote repair (e.g., axon regeneration, remyelination, revascularization). The cellular and molecular mechanisms that underlie this functional dichotomy are poorly defined. We have hypothesized that CNS macrophages (microglia and hematogenous macrophages) exert divergent effects on tissue injury and repair after SCI as a result of microenvironmental factors that are specific to location (i.e., region within the spinal cord) and time post-injury. Studies in Aim 1 will use lasercapture microdissection in combination with microarray analysis to define gene expression patterns specific to resident and recruited CNS macrophages after SCI. It is likely these studies will reveal target genes that can be manipulated to modulate CNS macrophage function after SCI. Preliminary data suggest that activation of macrophages via Toll-like receptors (TLRs) can positively and negatively affect neuron/glial survival. Using rat and knockout mouse models of SCI, studies in Aim 2 will evaluate the anatomical and functional consequences of activating CNS macrophages via TLR2 or TLR4.
In Aim 3, CX3CR1 and CD200 knock-out mice will be used to determine how removal of these endogenous macrophage regulatory proteins influences anatomical and functional recovery after SCI. The studies in this application should facilitate the development of molecular-based therapies designed to antagonize or promote macrophage-specific functions after SCI. For example, any significant functional and/or anatomical changes that are observed after SCI using knockout mice (Aims 2 or 3) can be traced back to a single gene product (e.g., fractalkine, CD200) that could be manipulated to improve functional recovery. Also, if specific genes are found to be regulated in macrophages after SCI (Aim 1), the promoter regions of those genes could be used to drive local and regulated production of growth factors or neurotrophins. In this way, CNS macrophages could be used as vehicles for drug delivery. ? ?
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