Thrombospondin-1 aggravates colonic mucosal inflammatory injuries via promoting the differentiation of CD11c+ macrophages with lysosomal activity limited in colitis

Background: Increased CD11c⁺ Mφ aggravates colonic mucosal injuries in ulcerative colitis (UC) with TSP1 protein increased. The thrombospondin-1 (TSP1) protein which could activate Mφ is closely related to the colonic mucosal damage in UC. Here, we investigated the role of TSP1 in the differentiation of CD11c⁺ Mφ and the mechanism.

Methods: We analyzed the population characteristics of TSP1 genes using the Genotype-Tissue Expression (GTEx) database, and human serum TSP1 protein was detected with ELISA. DSS-induced colitis rats were used to explore the effects of TSP1 on colonic mucosal inflammation. We analyzed the serum cytokines and tissue histopathology to evaluate the severity of UC. Furthermore, we analysed the main source of TSP1 in colon tissue. In vitro, lamina propria mononuclear cells (LPMC) and CD11c⁺ lamina propria macrophages (LPMP) was isolated from model rats in vivo. The target of TSP1 protein was assessed by LSKL, CD36 and CD47 interfering plasmids. The proteins, the lysosome, lysosomal activity and Cathepsin E activity, and the migration were detected by western blotting, test kits and Transwell.

Results: The expression of TSP1 was significantly higher in younger, male, and in the rectum and sigmoid than that in older, females, and colon tissues, and was closely related to the severity of UC. Compared with normal rats, the worse disease activity index (DAI) score, more histological damage, CD11c⁺ Mφ infiltration, and increased expression of several proinflammatory cytokines was displayed in colitis rats with the elevation of serum TSP1 protein. In vitro, TSP1 protein derived from cmMφ and endothelial cells promoted the migration and the differentiation of CD11c⁺ Mφ via binding on CD36, rather than the cell proliferation. Furthermore, PRKCQ/NF-κB signaling pathway was activated by CD36. However, the effect of TSP1 protein could be reversed by LSKL in vivo, and LSKL and anti-TSP1 antibody in vitro.

Conclusions: TSP1 promotes the migration and the differentiation of CD11c⁺ LPMP with lysosomal activity limited via activating the CD36-PRKCQ/NF-κB signaling pathway, which aggravates the colonic mucosal inflammatory injuries in UC.