Inhibition of SPI1 by ADAP regulates S100A8/A9 signaling in macrophages to control the development of colitis

Although the immune adapter protein ADAP (adhesion and degranulation protein adaptor protein) plays a critical role in regulating the inflammatory responses of macrophages, the impact of this regulation on intestinal inflammation remains elusive. This study reveals that mice with ADAP deficiency had an increased susceptibility to dextran sulfate sodium (DSS)-induced colitis. Furthermore, the absence of ADAP leads to increased expression of S100A8/A9 (also known as MRP8 and MRP14, respectively) both in vivo and in vitro, and increased susceptibility to intestinal inflammation. Mechanistically, we demonstrate that ADAP upregulates macrophage E3 ubiquitin ligase FBXW7 (F-box and WD repeat domain-containing 7), promoting proteasomal degradation of the transcription factor SPI1(SPI-1 proto-oncogene) and mediates this effect in macrophages during colitis. Whereas ADAP inhibits SPI1 expression in macrophages, ADAP deficiency promotes SPI1 expression and increases the binding of SPI1 to the S100A8/A9 promoter region. Blockade of SPI1 effectively prevents colitis-induced S100A8/A9 upregulation in macrophages. Thus, our findings highlight the potential link between ADAP and intestinal inflammation and pave the way for therapeutic interventions targeting the ADAP-SPI1-S100A8/A9 signaling axis in inflammatory colitis. Overall design: The mice were randomly grouped. The mice in the control group were given normal drinking water, whereas those in the DSS group were given fresh 3% DSS (Yeasen, 60316ES60, China) in their drinking-water. The DSS mixture was changed every two days and administered to the mice for seven consecutive days to induce ulcerative colitis. Each mouse was treated with 200 µL of clodronate liposomes (Yeasen, 40337ES08, China) via intraperitoneal injection on the first, second, and fifth day of DSS treatment. In the control group, 200 µL of liposomes were treated with control liposomes.After establishing the mouse model, the colon tissue was homogenized, and total RNA was extracted using TRIzol reagent (Sigma-Aldrich, T9424, USA).