Sa1721 Spontaneous Intestinal Inflammation in Mice Lacking Geranylgeranylation in Epithelial Cells Due to RhoA-Mediated Cytoskeleton Alterations and Breakdown of Gut Homeostasis

Abstract

Background and Aims: Recently it could be demonstrated that mice lacking caspase8 expression in the intestinal epithelium (Casp8ΔIEC) showed a high amount of RIPmediated cell death. Casp8ΔIEC mice spontaneously developed inflammatory lesions in the terminal ileum. Furthermore they lacked Paneth cells and showed a reduced number of Goblet cells, indicating dysregulated antimicrobial immune cell functions of the intestinal epithelium. Consequently a tightly regulated caspase-8 activity is indispensable for gut homeostasis. The caspase-8 activity can be regulated by cellular FLIPs, which are expressed in two different isoforms, cFLIPlong and cFLIPshort. Interestingly certain poxviruses and herpesviruses express a viral FLIP (vFLIP) which shares structural similarities with cFLIPshort. To elucidate the ability of vFLIP to influence the caspase-8 activity and the homeostasis in the gut, we analyze mice, which express vFLIP only in the intestinal epithelial cells (IECs). Methods: We generated mice which express a vFLIP only in the intestinal epithelium (vFLIPVillinCre-tg). vFLIPVillinCre-tg and control mice were histologically analyzed by immuno¬histochemistry. The gene expression pattern of IECs of vFLIPVillinCre-tg mice was analyzed by quantitative PCR. Furthermore we analyzed the protein expression of IECs from vFLIPVillinCre-tg mice. Results: Our data show that expression of vFLIP in the intestinal epithelium leads to spontaneous development of inflammatory lesions in the small intestine. Immunohistochemical staining revealed a high amount of immune cell infiltration and quantitative PCR analysis showed increased levels of proinflammatory markers. Moreover vFLIPVillinCre-tg mice demonstrated a reduction in Paneth cell number and a high amount of cell death in the small intestine. Furthermorewe could discover a dysregulation of theNFκB pathway by western blot and immunohistochemical staining. Conclusions: vFLIPVillinCre-tg mice show a dramatic phenotype which shares similarities with the phenotype of Casp8ΔIEC mice. The expression of vFLIP leads to the development of spontaneous inflammatory lesions and a reduction in the Paneth cell number, indicating a dysregulation in the immune defence. The observation of the high amount of cell death in the small intestine suggests that vFLIP might affect the caspase-8 activity and therefore interact with the cell death protein platform.