A20 () and ABIN-1 () are candidate susceptibility genes for inflammatory bowel disease and other autoimmune or inflammatory diseases, but it is unclear how these proteins interact in vivo to prevent disease. Here we show that intestinal epithelial cell (IEC)-specific deletion of either A20 or ABIN-1 alone leads to negligible IEC loss, whereas simultaneous deletion of both A20 and ABIN-1 leads to rapid IEC death and mouse lethality. Deletion of both A20 and ABIN-1 from enteroids causes spontaneous cell death in the absence of microbes or hematopoietic cells. Studies with enteroids reveal that A20 and ABIN-1 synergistically restrict death by inhibiting TNF-induced caspase 8 activation and RIPK1 kinase activity. Inhibition of RIPK1 kinase activity alone, or caspase inhibition combined with RIPK3 deletion, abrogates IEC death by blocking both apoptosis and necroptosis in A20 and ABIN-1 double-deficient cells. These data show that the disease susceptibility proteins A20 and ABIN-1 synergistically prevent intestinal inflammation by restricting IEC death and preserving tissue integrity.

Untreated Human Immunodeficiency Virus (HIV) infection is characterized by intestinal epithelial barrier dysfunction and chronic inflammation, related features that are attenuated to variable degrees by suppressive antiretroviral therapy (ART). Specific mediators of intestinal epithelial cell (IEC) dysfunction and restoration during HIV disease and treatment have yet to be identified. We studied IECs isolated from intestinal biopsies by RNAseq and found that mRNA levels for the ubiquitin-modifying enzyme, A20, are upregulated in ART-treated individuals and are positively correlated with markers of epithelial function (e.g., CTNNB, CLDN4, and TJP1). In a murine intestinal organoid model, A20 expression was suppressed by interferon-alpha (IFNα), which is highly expressed during HIV viremia and induces IFN-mediated signaling. Notably, A20 deletion rendered intestinal organoids more susceptible to cell death and inhibition of barrier-related genes mediated by interferon-gamma (IFNγ), a cytokine also present at elevated levels during untreated infection. Furthermore, A20 specifically restricted expression of IL-17A-induced inflammatory genes in organoids. Finally, ART-suppressed chronically infected individuals treated with pegylated IFNα2a for five weeks demonstrated reduced expression of A20 in peripheral blood mononuclear cells. Our results are thus consistent with a model in which enhanced type I interferons suppress A20 levels, leading to IFNγ-mediated dysfunction. As such, variation in A20 expression during the course of HIV infection could underlie both the development of epithelial dysfunction before the initiation of ART and the recovery of intestinal epithelial integrity thereafter.Trial registrationClinicalTrials.gov Clinical Trial NCT00594880

Anti-TNF antibodies are effective for treating patients with inflammatory bowel disease (IBD), but many patients fail to respond to anti-TNF therapy, highlighting the importance of TNF-independent disease. We previously demonstrated that acute deletion of two IBD susceptibility genes, A20 (Tnfaip3) and Abin-1 (Tnip1), in intestinal epithelial cells (IECs) sensitized mice to both TNF-dependent and TNF-independent death. Here we show that TNF-independent IEC death after A20 and Abin-1 deletion was rescued by germ-free derivation or deletion of MyD88, while deletion of Trif provided only partial protection. Combined deletion of Ripk3 and Casp8, which inhibits both apoptotic and necroptotic death, completely protected against death after acute deletion of A20 and Abin-1 in IECs. A20 and Abin-1-deficient IECs were sensitized to TNF-independent, TNFR-1-mediated death in response to lymphotoxin alpha (LT⍺) homotrimers. Blockade of LT⍺ in vivo reduced weight loss and improved survival when combined with partial deletion of MyD88. Biopsies of inflamed colon mucosa from patients with IBD exhibited increased LTA and IL1B expression, including a subset of patients with active colitis on anti-TNF therapy. These data show that microbial signals, MyD88, and LT⍺ all contribute to TNF-independent intestinal injury.Anti-TNF therapy remains one of the most effective approaches for treating Crohn's disease (CD) and ulcerative colitis (UC), but roughly one-third of patients have no response and one-third of patients lose response over time (46)(47)(48)(49). Therefore, understanding the gene products that control TNF-independent IEC injury could have significant translational relevance for anti-TNF non-responders. To better understand the pathways leading to TNF-independent IEC injury we performed in vivo and in vitro analysis of IECs after acute simultaneous deletion of A20 and Abin-1. RESULTS Germ-free A20/Abin-1 T-ΔIEC Tnf -/mice are protected from TNF-independent IEC deathMice with floxed A20 (A20 fl/fl ) and floxed Abin-1 (Abin-1 fl/fl ) on a Vil-cre-ER T2+ background (A20/Abin-1 T-ΔIEC ) undergo acute deletion of A20 and Abin-1 in IECs upon treatment with tamoxifen, culminating in spontaneous apoptotic IEC death, severe enterocolitis, and rapid mouse lethality ( 9). This death occurs on a Tnf +/+ or Tnf -/background, demonstrating the important role of TNF-independent death in this model. Tamoxifen delivery by intraperitoneal (i.p.) oil injection has been reported to cause peritoneal inflammation, foam cell formation, and depletion of resident macrophages (50). To exclude the possibility that sterile peritonitis contributes to TNFindependent death in A20/Abin-1 T-ΔIEC Tnf -/mice, we treated mice with tamoxifen by oral gavage rather than i.p. A higher dose of tamoxifen was required to delete A20 and Abin-1 in IECs from the small intestine and colon by oral gavage (Supplemental Figure 1A), and with this approach A20/Abin-1 T-ΔIEC Tnf -/mice died with similar kinetics as A20/Abin-1 T-ΔIEC mice (Figure 1A). Enteroids derived from A2...

Background Rectourethral fistula (RUF) is an uncommon serious condition with various etiologies including neoplasm, radiation therapy, and surgery. Treatment for RUF remains problematic with a high recurrence rate. Although studies have suggested the recurrence rate of RUF is lower after surgical repair using a gracilis flap, outcomes have varied and the studies were small and inadequately controlled. Here, we compare outcomes of RUF repair with and without gracilis flap to evaluate its efficacy in preventing fistula recurrence and identify risk factors for recurrence. Methods We retrospectively reviewed patients who had undergone surgical repair for RUF between 2007 and 2018 at our institution and had at least 30 days of follow-up. Patient demographics, comorbidities, and surgical outcomes were recorded and compared for patients who had gracilis flap repair and those who did not (controls). Single variable logistic regression analysis was used to identify risk factors for recurrence. Results The gracilis group (n = 24) and control group (n = 12) had similar demographics and comorbidities. Fistula recurrence was far less frequent in the gracilis group (8% vs 50%, P = 0.009). There were no significant differences in other outcomes including length of hospitalization and surgical complications. When recurrent RUF was treated with a muscle flap (gracilis or inferior gluteus), 83% of the group had no additional fistula recurrence. In the control group, history of radiation (P = 0.04) and urinary incontinence (P = 0.015) were associated with fistula recurrence. Conclusions We recommend using a gracilis flap for RUF repair given its association with lower recurrence without increased surgical complications.

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