Differential effects of axotomy on the in vivo synthesis of the stress-inducible and constitutive 70-kDa heat-shock proteins in rat dorsal root ganglia.

The purpose of this study was to the test the hypothesis that heat-shock protein expression is upregulated (or induced) in dorsal root ganglia (DRG) following axotomy. To test this hypothesis, DRG or sciatic nerve (SN) proteins were pulse-labelled in vivo with [35S]methionine and the metabolic synthesis of two major 70-kDa heat-shock proteins, the constitutive species (hsc70) and stress-inducible species (hsp68), were analyzed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and fluorography. Results showed that DRG hsp68 expression was absent (or barely detectable) under normal (sham-axotomy) conditions. However, following long-range axotomy (35 mm from DRG), there was a delayed (> 12 h post-axotomy) and transient upregulation of DRG hsp68 metabolic synthesis. Control studies demonstrated that, although DRG hsp68 was upregulated, hsp68 was not induced in SN regions proximal to the crush site. In contrast to DRG hsp68 expression, there was abundant DRG hsc70 synthesis under normal conditions that did not significantly change following axotomy. These results suggest that a specific stress protein response is induced in DRG following axotomy.