Regulated heat shock protein 27 expression in human retinal pigment epithelium

PURPOSE. To examine the expression and regulation of an injury-related prot ein, heat shock protein (Hsp) 27, in retinal pigment epithelium (RPE), sinc e RPE injury may be an important feature of age-related macular degeneratio n (ARMD). METHODS. Retinal cross sections from eyes of Lewis rats were examined for H sp27 in vivo by immunohistochemistry, and in vitro expression of Hsp27 in h uman ARPE-19 cells was determined by Northern and Western blot analysis. Ox idant-mediated injury was performed by exposing ARPE-19 cells to myeloperox idase and hydrogen peroxide. Cell lines stably expressing green fluorescent protein (GFP) targeted to the cell membrane were used to study injury-indu ced membrane blebbing, and XTT conversion was used to detect cell viability . RESULTS. High level of Hsp27 expression was detected in vivo in ganglion ce lls, RPE, and photoreceptor outer segments of rat retina. ARPE-19 cells als o expressed high levels of Hsp27 in vitro. Oxidative injury in ARPE-19 cell s resulted in transcriptional and translational activation of Hsp27 and ind uced extensive membrane blebbing. A high level of Hsp 27 protein was detect ed within membrane blebs. Increased expression of Hsp27 was also observed i n differentiated ARPE-19 cells when compared with dividing cells. Higher Hs p27 levels in differentiated RPE cells correlated with increased viability and phenotypically different blebbing after exposure to the injury stimulus . In addition, sublethal injury doses caused a moderate amount of membrane blebbing, which was well tolerated by differentiated ARPE-19 cells. CONCLUSIONS. These results indicate that Hsp27 may be an important componen t of the RPE injury response and may contribute to injury-induced membrane blebbing in differentiated RPE cells. It is hypothesized that Hsp27 levels may play a role in disease states in the retina, such as ARMD.