Spatiotemporal increases in epidermal growth factor receptors following peripheral nerve injury

Abstract

Non-neuronal cells of peripheral nerve respond to axonal injury with a series of cellular changes that facilitate neuronal regeneration. To characterize the potential role of the epidermal growth factor (EGF) family of proteins in this response, we monitored the expression of EGF receptor mRNA and protein in the injured rat sciatic nerve. EGF receptor mRNA is synthesized in both primary cultured fibroblasts and Schwann cells, and Schwann cells express EGF receptor-like immunoreactivity. In situ hybridization and immunocytochemistry revealed that EGF receptor mRNA and protein are expressed in Schwann cells and fibroblasts of the sciatic nerve in vivo, and that receptor levels increase following nerve injury. Thirty-six hours postlesion, EGF receptors were expressed in gradients along the nerve both proximal and distal to the lesion, with the highest levels localized adjacent to the transection site. By 72 hr, receptor levels were maintained in a gradient in the proximal segment, but were uniformly increased throughout the portions of the distal segment that were analyzed. These changes were similar to those observed for low-affinity NGF receptor mRNA and protein, with transection causing increased expression in both Schwann cells and fibroblasts. Northern blots confirmed that primary cultured fibroblasts express low-affinity NGF receptor mRNA. To determine whether spatiotemporal gradients were a general characteristic of the nerve injury response, we monitored expression of the mRNA encoding the major myelin protein P0. Levels of P0 mRNA decreased initially in cells immediately adjacent to the transection site and, by 72 hr, were uniformly decreased throughout the distal segment. These data suggest that members of the EGF family of proteins may play a role in the peripheral nerve response to injury, and demonstrate a generalized gradient of cellular responses that commence at the transection site and progress distally in the nerve in the absence of intact axons.