Abstract 2513: Intraventricular Administration of Cystatin C Attenuates White Matter Injury In Rat Chronic Ischemia

Abstract

Background and Purpose Cerebral white matter lesions (WMLs) contribute to elderly cognitive deterioration and are usually caused by chronic ischemic insult. Experimental studies have shown that proteases are highly expressed in activated astrocyte and microglia, which are thought to be crucial in the development of WMLs. Cystatin C (CSTC) functions as a major extracellular cysteine protease inhibitor in mammals. Since the concentration of CSTC is 5 times higher in CSF than in plasma, CSTC is thought to be a major inhibitor of cysteine proteases in the central nervous system. We have shown that polymorphisms in the CSTC gene, which results in a decrease of plasma CSTC level, are significantly associated with prevalence of WMLs. However, direct impact of CSTC on the development of WMLs has not been elucidated yet. Here we studied whether direct administration of CSTC into brain has a protective effect on the pathophysiology of WMLs produced by chronic cerebral hypoperfusion in a rat model of permanent bilateral common carotid artery occlusion. Methods Adult Wister rats underwent ligation of bilateral common carotid arteries (LBCCA) and were divided into three groups; the CSTC group in which CSTC was injected continuously into the ventricle 14 consecutive days after LBCCA (n=10), the PBS group in which PBS was injected continuously into the ventricle 14 consecutive days after LBCCA (n=10), and the sham group (n=10). All rats were perfused on 14 days after LBCCA. The severity of WMLs and accumulation of microglia and astrocytes in the corpus callosum (CC) and optic nerve (ON) were evaluated. Furthermore, the activity of cathepsin B, one of the major proteases, was measured in the tissue lysates of CC and ON using the assay kit. Results Continuous intraventricular infusion of CSTC significantly reduced the severity of WMLs (CC; p<0.001 vs. PBS, ON; p<0.001 vs. PBS) and inhibited the accumulation and activation of microglia (CC; p=0.03 vs. PBS, ON; p<0.001 vs. PBS) and astrocytes (CC; p=0.003 vs. PBS, ON; p=0.04 vs. PBS) both in CC and ON. There were no alterations in cathepsin B activity in these regions. Conclusions The present study indicates that CSTC could suppress chronic ischemia-induced WMLs and the inhibition of proteases other than cathepsin B may be implicated in this beneficial effect.