CoCl2 Pretreatment Protects the Retina From Ischemic Injury in the Rat

Abstract

Abstract: : Purpose: Ischemic preconditioning (IPC) of the retina can offer both structural and functional protection from ischemic retinal injury. The mechanisms behind this protection are not yet fully understood. Previous work from our lab has shown that the upregulation of retinal Hsp27 acts as a key cytoprotective factor in preventing retinal ischemic damage. Recent studies have provided evidence that the hypoxia mimicker CoCl₂ can stimulate Hsp27 expression in a rat retinal ganglion cell line. The purpose of this study was to determine if CoCl₂ pretreatment could protect the retina from ischemic injury. Methods: Baseline ERGs were measured in Brown Norway rats. Rats then received a subcutaneous (SQ) injection of CoCl₂ (60mg/kg) or 0.9% NaCl (control). Twenty-four hours following the injection, the rats were anaesthetized and the IOP of their right eyes was elevated to 160 mm Hg for 45 minutes to create a complete retinal ischemia. Rats were then allowed to recover for 72 hours at which time ERG recordings were again measured. The contralateral eye was used as an internal control. The ERG results were compared to corresponding baseline ERG readings. Western blot analysis of retinas isolated from rats 24 hours following CoCl₂ or saline injections was done to assess stress protein levels. Results: In rats receiving saline injections, 45 minutes of complete retinal ischemia resulted in a nearly 40% decrease (p< 0.05) in b-wave amplitudes 72 hours after the ischemia; however, no significant change in a-wave amplitudes was observed. In rats receiving CoCl₂ injections, ERG measurements 72 hours following 45 minutes of retinal ischemia found that neither a-wave nor b-wave measurements were significantly altered from baseline measurements. The administration of CoCl₂ alone did not significantly alter ERG a-wave or b-wave measurements in control (non-ischemic) eyes. Twenty-four hours following CoCl₂ treatment, retinal Hsp27 protein levels were elevated by 69% over control retina levels. In contrast, levels of inducible Hsp70 protein levels were not altered in retinas from CoCl₂ treated animals. Conclusion: These results demonstrate that CoCl₂ treatment can protect the retina from ischemic injury, and this protection may be related to the specific induction of retinal Hsp27. The use of CoCl₂ should be a valuable tool in understanding the protective events that underlie IPC.

Keywords: ischemia • neuroprotection • retinal degenerations: cell biology