Transglutaminase activity and transglutaminase mRNA transcripts in gerbil brain ischemia

Brain injury of the ischemia/reperfusion type induces neuronal damage, mainly by excitatory amino acid release, intracellular Ca(2+) overload and reactive oxygen species production. We have previously demonstrated that glutamate exposure increased transglutaminase activity and transglutaminase 2 expression in cultured cerebellar granule cells and astrocytes. The aim of this study is to evaluate changes in transglutaminase activity and expression using a gerbil model of global cerebral ischemia. Moreover, the distribution and amounts of different transglutaminase isoforms were examined. Transglutaminase activity was measured by incorporation of [(3)H]putrescine into dimethylcasein throughout 48 h of reperfusion following a 3 min occlusion. Compared to sham-operated brains, significant increases were found in the ischemic hippocampus at 24 h of reperfusion, while minor changes were observed in the cortex. RT-PCR demonstrated the presence of significant mRNA amounts of transglutaminase 2 and transglutaminase 1, both in the hippocampus and the cerebral cortex, while low levels were found for transglutaminase 3 transcripts. Interestingly, transglutaminase 2 and transglutaminase 1 mRNAs were 4-fold and 2-fold increased, respectively, in the ischemic hippocampus after 24 h of reperfusion. Western blot analysis of transglutaminase 2 expression confirmed a strong up-regulation in the ischemic hippocampus. However, it is possible to hypothesize that different expression rates of transglutaminase isoforms may be dependent on different responsiveness of their transcription regulatory elements to intracellular calcium overload following excitotoxic cell injury. Our results suggest that increases in transglutaminases may be part of the tissue stress response in global brain ischemia.