Myenteric neuronal loss in rats with experimental colitis: Role of tissue transglutaminase-induced apoptosis

Background and Aims. Transglutaminases are tissue enzymes involved in different neuronal processes including maintenance and signalling. However, their up-regulation elicited by a variety of noxae contributes to neurodegeneration. This study tested the hypothesis that experimental inflammation evoked transglutaminase up-regulation in myenteric neurons and that this event had an impact on neuronal survival. Methods. Rats with or without trinitro-benzene-sulphonic acid-induced colitis were used. One week after colitis induction, longitudinal muscle-myenteric plexus preparations were obtained from left colon to assess tissue-transglutaminase activity, protein and mRNA expression. Double labelling immunofluorescence using antibodies to neuron-specific enolase and transglutaminase was performed to identify myenteric neurons expressing transglutatninase. Additional sets of experiments evaluated the involvement of transglutaminase in the apoptotic process of cultured myenteric neurons. Results. Compared to controls, rats with colitis showed several tranglutaminase/neuron-specific enolase positive myenteric neurons. Western blot analysis and RT-PCR confirmed that in rats with colitis, the increased neuronal transglutaminase-immunoreactivity was associated with an increased enzyme expression. Similarly, transglutaminase activity was significantly higher than in controls (1100 +/- 280 mU/g vs. 725 +/- 119 mU/g, p<0.05). In cultured myenteric neurons incubation with the specific transglutaminase inducer, retinoic acid, significantly increased neuronal apoptosis, whereas the presence of cystamine significantly reduced the number of apoptotic neurons. Conclusions. Experimental colitis evoked transglutaminase up-regulation and increased activity in myenteric neurons. This mechanism enhances neuronal susceptibility to apoptosis and could contribute to neuropathic changes during gut inflammation. (C) 2008 Editrice Gastroenterologica Italian. S.r.l. Published by Elsevier Ltd. All rights reserved.