Critical differences in responses to stress exist between the central (CNS) and peripheral nervous systems (PNS). In contrast to the CNS, where sustained cellular perturbation, such as that due to accumulated amyloid- beta peptide (Abeta), leads to eventual neuronal loss, in the peripheral nervous system, an appropriately limited inflammatory response effectively promotes neuronal regeneration after injury, in the peripheral nervous system, an appropriately-limited inflammatory response effectively promotes neuronal regeneration after injury. An initial inflammatory response in segments distal to the injured nerve provides an environment for axonal regeneration. Monocyte-derived macrophages promote removal of damaged myelin sheaths and elaborate key mediators which redirect Schwann cell and neuronal function from homeostatic myelination and transmission modes, to proliferative/non-myelinating and growth phenotypes, respectively. Recent findings have implicated ligands of the receptor RAGE in macrophage recruitment and activation, and neurite outgrowth and extension. EN-RAGEs (Extracellular Newly- identified RAGE binding proteins), members of the S100/calgranulin family synthesized and/or released by damaged Schwann cells, interact with RAGE to stimulate macrophage chemotaxis and activation. EN- RAGEs may also mediate neurite outgrowth via engagement of neuronal chemotaxis and activation. EN-RAGEs may also mediate neurite outgrowth via engagement of neuronal RAGE, a function shared with amphoterin, another RAGE ligand. Our pilot studies display the proximity of these mediators and RAGE-bearing cells in injured peripheral nerve, and upon unilateral crush of the sciatic nerve in mice, administration of blocking F(ab')s derived from anti-RAGE, anti-EN- RAGE or anti-amphoterin IgG, but not non-immune (Fab') s, impairs removal of myelin and diminishes regeneration. We hypothesize that rapid release of EN-RAGEs by perturbed Schwann cells triggers RAGE- dependent macrophage recruitment and activation critical to initiation of reparative mechanisms. Subsequently, EN-RAGEs and amphoterin target neuronal RAGE thereby promoting axonal growth into approximately prepared distal nerve stumps. We speculate that these processes are suppressed in aged mice. The goal of Project 2 is to dissect the role of RAGE in peripheral nerve injury utilizing novel transgenic models with targeted expression of a dominant-negative RAGE, a form of the receptor lacking the cytosolic tail which blocks RAGE signaling, in macrophages and/or neurons. Project 2 will work closely with Project 1, and will obtain technical assistance from Core B. Collaborative interactions include: exchange of reagents regarding RAGE biology (Project 1), evaluation of cellular stress (Projects 1, 3, and 4), and mouse breeding (Core B).
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