| Purpose. In most tissues, physiological stress upregulates specific members of heat shock family of proteins. The enhanced expression of these proteins has been shown protect cells from future injury, while autoimmune reactions to these proteins may contribute to cellular degeneration. The aim of this study was to evaluate changes in retinal expression of three heat shock proteins, Hsp-27, Hsp-70 and Hsp-90, in rats with elevated IOPs. Methods. IOP in Sprague Dawley rats (100-150g) was elevated unilaterally by cauterization of three episcleral veins. IOPs were monitored twice weekly using a Tonopen. Rats were euthanized at 10, 20, or 60 days following the induction of ocular hypertension, retinas dissected free and total RNA and protein isolated. RNA was used for the northern blot analysis and probed with cDNAs for specific Hsp. Protein was used for western blot analysis and probed with specific Hsp antibodies. Northern and western blots were normalized to 18s ribosomal RNA and b-actin levels, respectively. Results. In treated eyes, IOP ranged from 27 to 35 mm of Hg throughout the study. In contralateral control eyes, IOP ranged from 12 to 17mm of Hg. In retinas from control eyes, Hsp-27, Hsp-70 and Hsp 90 were each constitutively expressed. Ten days following the induction of ocular hypertension expression of Hsp-27 mRNA in the retina 205% above control levels. At 20 and 60 days hsp-27 mRNA levels were 250% and 195% above control levels, respectively. Western blot analysis demonstrated that Hsp-27 protein levels in the retinas from were elevated as much as 285% at 10, 20 and 60 days following the induction of ocular hypertension. No changes in mRNA or protein levels were observed for Hsp-70 or Hsp-90 in retinas from ocular hypertensive eyes. Conclusions. These results demonstrate that the stress protein Hsp-27 is upregulated in retinas from ocular hypertensive rats. As no changes in Hsp-70 or Hsp-90 were observed, the upregulation in Hsp-27 appears to be a gene specific event associated with elevated IOP and not a general increase in transcription. |
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