Spatio-temporal profile of small heat-shock protein Hsp27 induction in rat brain following fluid-percussion injury to the lateral parietotemporal cerebral cortex; involvement with beta actin

Abstract

Heat shock protein 27 (Hsp27) belongs to a group of small Hsps that perform a variety of functions including molecular chaperoning, regulation of actin dynamics and antioxidative activity, and inhibition of apoptosis. In adult rat brain, constitutive neuronal expression of Hsp27 is present in neurons and occasionally non-neuronal cells including astrocytes, ependymal cells and the choroid plexus. Since little is currently known of the involvement of Hsp27 in cerebral trauma, we have examined the effects of moderate fluid-percussion injury (FPI) on the spatio-temporal patterns of Hsp27 induction and potential interaction of Hsp27 with other structural proteins in rat brain. In the ipsilateral parieto-temporal cortex, Hsp27 protein levels were increased over 7-fold at 24 h following the insult compared to sham controls by immunoblotting (Figure 1A), and which persisted for up to 7 days post-trauma. Immunohistochemical assessment revealed a mainly astroglial pattern of staining for Hsp27 in the cortex, hippocampus, and thalamic nuclei ipsilateral to the injury with some immunoreactivity also extending into contralateral hippocampal structures. Immunoprecipitation studies using both injured and contralateral cortical brain tissue of 24 h post-injured rats showed that Hsp27 immunoprecipitated only from the injured, but not contralateral, cortex at 24 h post-injury (Figure 1B). In addition, Hsp27 immunoprecipitate from 24 h post-injured ipsilateral cortex coimmunoprecipitated with beta actin, and not GFAP (Figure 1C). Our results suggest that FPI produces a large, predominantly astroglial-specific induction of Hsp27 that is widespread in the injured hemisphere. Given its previously identified role as a chaperone protein, interaction of Hsp27 with actin may indicate an important function for this gene in stabilization of actin filaments in astroglia, a potentially valuable contributing factor to the known resistance of these cells to trauma-induced stress.