Gene expression in the dorsal root ganglion and the role of PAI-1 and amphiregulin during regeneration

Abstract: This thesis is concerned with two aspects of peripheral nerve injury. First the early changes in the gene expression of the dorsal root ganglion (DRG) in response to sciatic nerve injury as revealed by micro-array analysis. Second an examination of the effect of PAI-1 and amphiregulin on survival and axonal outgrowth from DRG. Based on the micro-array analysis, performed on DRG 12 h and 24 h post sciatic nerve injury in vivo, we conclude that important changes in gene expression include the upregulation of several transcription factors, of which some have not been previously reported in the DRG, and an increased signaling via IL-6 and TGF-beta. Two of the upregulated proteins from the micro-array analysis, PAI-1 and amphiregulin, were chosen for further in vitro studies concerning their role in regeneration. When PAI-1 was added to organ cultured adult DRG we found that axonal elongation was unaffected while Schwann cell migration was impaired. In similar experiments with amphiregulin we found an increase in axonal outgrowth and neuronal survival and that this effect was mediated via the EGFR. In adult mouse DRG addition of TGF-alpha and EGF had no effect. Investigations of amphiregulins role in neuronal DRG development revealed that amphiregulin inhibited axonal outgrowth and increased neuronal cell death in late embryogenesis. In this case TGF-alpha was stimulating axonal outgrowth and neuronal survival of the DRG while EGF yet again had no effect. Altogether this indicates that amphiregulin has properties of a neurotrophic factor in the adult DRG and a switch occurs in the requirement for different EGF-family members during the DRG development.