Chronic intestinal inflammation in mice expressing viral Flip in epithelial cells

Abstract

Viruses are present in the intestinal microflora and are currently discussed as a potential causative mechanism for the development of inflammatory bowel disease. A number of viruses, such as Human Herpesvirus-8, express homologs to cellular FLIPs, which are major contributors for the regulation of epithelial cell death. In this study we analyzed the consequences of constitutive expression of HHV8-viral FLIP in intestinal epithelial cells (IECs) in mice. Surprisingly, expression of vFlip disrupts tissue homeostasis and induces severe intestinal inflammation. Moreover vFlip mice showed reduced Paneth cell numbers, associated with excessive necrotic cell death. On a molecular level vFlip expression altered classical and alternative NFκB activation. Blocking of alternative NFκB signaling by deletion of Ikka in vivo largely protected mice from inflammation and Paneth cell loss induced by vFLIP. Collectively, our data provide functional evidence that expression of a single viral protein in IECs can be sufficient to disrupt epithelial homeostasis and to initiate chronic intestinal inflammation.

Viral FLIP blocks Caspase-8 driven apoptosis in the gut in vivo

“…In accordance to our previous study [6], all control mice survived the indicated time period of treatment whereas all cFlip iΔIEC mice showed dramatic weight loss and died within 5 days (Fig 2A and 2B). As expected, all of the vFlip iIEC-tg mice survived, as even mice with a constitutive vFlip expression in IECs were viable [16]. Strikingly, cFlip iΔIEC x vFlip iIEC-tg mice were characterized by a significantly higher survival rate as compared to cFlip iΔIEC mice and most of the animals could recover from severe body weight loss around day 8 (Fig 2A and 2B).…”

“…These cytokines could further activate other signaling pathways beside NFκB, that regulate cFlip expression in cells adjacent to epithelial cells. Beside constitutive activation of NFκB, constitutive expression of vFlip in IECs moreover induced the spontaneous development of intestinal inflammation accompanied by Paneth cell loss and increased epithelial cell death [16]. However, the phenotype of vFlip IEC-tg mice was not completely identical to mice with a constitutive activation of NFκB in IECs [30,31], which were not characterized by increased cell death.…”

“…These mice are characterized by intestinal inflammation, Paneth cell loss and increased cell death, suggesting that vFLIP, similar to cFLIP short , inhibits Caspase-8 maturation and activation. However, in contrast to Casp8 ΔIEC mice, cell death in vFlip IEC-tg mice was not dependent on RIPK3, suggesting that IECs did not die due to classical RIPK3-mediated necroptosis [5,16]. The aim of the present study was to investigate if viral FLIP can compensate for cFLIP in IECs by undertaking its Caspase-8-regulating functions.…”

“…Previous results generated by our group showed that mice which express HHV8-vFlip in intestinal epithelial cells (vFlip IEC-tg mice) are characterized by spontaneous intestinal inflammation accompanied by Paneth cell loss, in addition to massive epithelial cell death and constitutive activation of the NFκB pathway [16]. Although the cFlip gene was described to be a target of the NFκB pathway [21,22], vFlip IEC-tg mice showed a significantly decreased cFlip gene expression in the small intestine as compared to controls ( Fig 1A).…”

“…The generation of Rosa26.vFLIP, vFlip IEC-tg , cFlip iΔIEC and VillinCreERT2 mice was described earlier [6,[16][17][18]. To generate vFlip iIEC-tg mice with an inducible vFlip expression in IECs, Rosa26.vFLIP mice were crossed to VillinCreERT2 mice.…”