To investigate if the UPR could directly induce HMGCS2 downregulation in vivo, we injected tunicamycin in C57BL/6 wild type mice as well as in Xbp1ΔIEC mice, which display a defective UPR through the deletion of Xbp1 in IECs resulting in an ER associated spontaneous enteritis, but not colitis (5). This evidence concerns the gene XBP1 and colitis.