Heat shock protein 27 delays Ca2+-induced cell death in a caspase-dependent and -independent manner in rat retinal ganglion cells.

PURPOSE Hsp27 is a well-characterized and studied antiapoptotic protein. A recent study reported that Hsp27 is upregulated in the retina after retinal ischemic preconditioning. The timing of this upregulation of Hsp27 correlates with the protective effects of the treatment. It was the goal of the current study to determine what role Hsp27 plays in this protection. METHODS The rat homologue of Hsp27 (rHsp27) was overexpressed in a transformed rat retinal ganglion cell line and subjected to ischemic stress and calcium overload. RESULTS The overexpression of rHsp27 increased cell survival and inhibited caspase-3 activation. However, the inhibition of caspase-3 alone had no effect on cell survival. Proteomic analysis after Ca(2+) overload identified four proteins that were repeatedly associated with rHsp27. These proteins include actin, Hsp70, eEF-1alpha, and SPIN-2. No association with cytochrome c or any caspase enzymes was detected. CONCLUSIONS The results indicate that Hsp27 protects the retinal cells by both caspase-dependent and -independent mechanisms.