Interleukin-1 Receptor and Receptor Antagonist Gene Expression After Focal Stroke in Rats

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Abstract
Background and Purpose The expression of interleukin-1β (IL-1β) is upregulated after focal brain ischemia, and previous work has demonstrated its involvement in ischemic injury. The IL-1 receptor antagonist (IL-1ra), a natural competitive antagonist of IL-1 receptors (IL-1Rs), has been demonstrated to play a role in attenuating brain ischemic injury. To hypothesize the involvement of the IL-1 system in ischemic injury, we examined other IL-1 components, including IL-1ra, IL-1RI, and IL-1RII for their mRNA expression after focal stroke. Methods Quantitative reverse transcription and polymerase chain reaction (RT-PCR) technique was used to examine the mRNA expression profile of IL-1ra and two IL-1R isoforms in a temporal fashion (n=4 for each time point) after permanent occlusion of the middle cerebral artery (MCAO) in spontaneously hypertensive rats. IL-1ra and IL-1R mRNA expression was confirmed by Northern blot analysis using poly(A) RNA isolated after 2 and 12 hours of MCAO. Results Very low levels of IL-1ra mRNA were detected in sham-operated or nonischemic cortex. IL-1ra mRNA in ischemic cortex was greatly increased at 12 hours (16.5-fold increase over sham samples, P<.001) and remained elevated for up to 5 days (17.2-fold increase, P<.01) after MCAO. IL-1RI mRNA was relatively highly expressed in normal cortex and was further elevated late after ischemic injury (3.3-fold increase at day 5, P<.001). In contrast, the low basal expression of IL-1RII mRNA was remarkably elevated at 6 hours (5.3-fold increase, P<.05), reaching peak levels 12 hours (10.3-fold increase, P<.001) after MCAO. Conclusions Differential expression of IL-1β, IL-1ra, IL-1RI, and IL-1RII mRNAs after focal stroke may suggest a distinct role(s) for each component of the IL-1 system in ischemic injury. The data also stress the importance of evaluating all the components of a given cytokine system (eg, agonist, receptors, and natural antagonist) after focal stroke.