Receptor interacting protein kinase 1 (RIPK1) is a cytosolic multidomain protein that controls cell life and death. While RIPK1 promotes cell death through its kinase activity, it also functions as a scaffold protein to promote cell survival by inhibiting FADD-caspase 8-dependent apoptosis and RIPK3-MLKL-dependent necroptosis. This pro-survival function is highlighted by excess cell death and perinatal lethality in Ripk1−/− mice. Recently, loss of function mutation of RIPK1 was found in patients with immunodeficiency and inflammatory bowel diseases. Hematopoietic stem cell transplantation restored not only immunodeficiency but also intestinal inflammatory pathology, indicating that RIPK1 in hematopoietic cells is critical to maintain intestinal immune homeostasis. Here, we generated dendritic cell (DC)-specific Ripk1−/− mice in a genetic background with loss of RIPK1 kinase activity and found that the mice developed spontaneous colonic inflammation characterized by increased neutrophil and Ly6C+ monocytes. In addition, these mice were highly resistant to injury-induced colitis. The increased colonic inflammation and the resistance to colitis were restored by dual inactivation of RIPK3 and FADD, but not by inhibition of RIPK3, MLKL, or ZBP1 alone. Altogether, these results reveal a scaffold activity-dependent role of RIPK1 in DC-mediated maintenance of colonic immune homeostasis.

Carminic acid (CA) is a major component of cochineal dye used in food additives, cosmetics, and pharmaceuticals. CA and its isomers, 2-C-α-glucofuranoside and 2-C-β-glucofuranoside of kermesic acid (DCIV and DCVII, respectively), were isolated from cochineal dye and the equilibrium constants (K) between CA, DCIV and DCVII were investigated. DCIV was partially converted to CA and DCVII, and DCVII was converted to CA and DCIV, whereas CA was very stable and only very slightly converted to DCIV and DCVII. Most of the DCIV and DCVII was converted to CA under aqueous conditions. The kinetic rate constants (k) for the degradation of DCIV within the first day of incubation at 24°C was determined to be 0.901 d 1 and for the degradation of DCVII it was determined to be 1.102 d 1 . The k value for the formation of CA from the remaining DCIV was calculated to be 0.146 d 1 and for the formation of CA from the produced DCVII it was found to be 0.148 d 1 . The K values were calculated as 1.22 10 7, 2.61 10 3 and 2.36 10 3 mol/L for CA, DCIV and DCVII, respectively. These findings will be helpful for ensuring the safety and for aiding the quality assurance of cochineal dye products.

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Receptor interacting protein kinase 1 (RIPK1) is a cytosolic multidomain protein that controls cell life and death. While RIPK1 promotes cell death through its kinase activity, it also functions as a scaffold protein to promote cell survival by inhibiting FADD-caspase 8-dependent apoptosis and RIPK3-MLKL-dependent necroptosis. This pro-survival function is highlighted by excess cell death and a perinatal lethality in Ripk1-/- mice. Recently, loss of function mutation of RIPK1 was found in patients with immunodeficiency and inflammatory bowel diseases. Hematopoietic stem cell transplantation restored not only immunodeficiency but also intestinal inflammatory pathology, indicating that RIPK1 in hematopoietic cells is critical to maintain intestinal immune homeostasis. Here, we generated dendritic cell (DC)-specific Ripk1-/- mice in a genetic background with loss of RIPK1 kinase activity and found that the mice developed spontaneous colonic inflammation characterized by increased neutrophil infiltration. In addition, these mice were highly resistant to injury-induced colitis. The increased neutrophil infiltration in the colon and the resistance to colitis were restored by dual inactivation of RIPK3 and FADD, but not by inhibition of RIPK3, MLKL, or ZBP1 alone. Altogether, these results reveal a scaffold activity-dependent role of RIPK1 in protecting colonic DCs from apoptotic insults and maintenance of colonic immune homeostasis.