Published online Sep 21, 2021. doi: 10.3748/wjg.v27.i35.5946
Peer-review started: March 5, 2021
First decision: April 5, 2021
Revised: April 7, 2021
Accepted: August 10, 2021
Article in press: August 10, 2021
Published online: September 21, 2021
Crohn’s disease (CD) is an incurable intestinal disorder with unclear etiology and pathogenesis. Currently, there is a lack of specific biomarkers and drug targets for CD in clinical practice. It is essential to identify the precise pathophysiological mechanism of CD and investigate new therapeutic targets.
To explore a new biomarker and therapeutic target for CD and verify its role in the CD pathological mechanism.
Proteomics was performed to quantify the protein profile in the plasma of 20 CD patients and 20 matched healthy controls. Hub genes among the selected differentially expressed proteins (DEPs) were detected via the MCODE plugin in Cytoscape software. The expression level of one hub gene with an immunoregulatory role that interested us was verified in the inflamed intestinal tissues of 20 CD patients by immunohistochemical analysis. After that, the effects of the selected hub gene on the intestinal inflammation of CD were identified in a CD cell model by examining the levels of proinflammatory cytokines by enzyme-linked immunosorbent assays and the expression of the NF-κB signalling pathway by quantitative real-time PCR analysis and Western blot assays.
Thirty-five DEPs were selected from 393 credible proteins identified by proteomic analysis. Among the DEPs, fibrinogen-like protein 1 (FGL1), which attracted our attention due to its function in the regulation of the immune response, had 1.722-fold higher expression in the plasma of CD patients and was identified as a hub gene by MCODE. Furthermore, the expression of FGL1 in the intestinal mucosal and epithelial tissues of CD patients was also upregulated (P < 0.05). In vitro, the mRNA levels of FGL1 and NF-κB; the protein expression levels of FGL1, IKKα, IKKβ, p-IKKα/β, p-IκBα, and p-p65; and the concentrations of the proinflammatory cytokines IL-1β, IL-6, IL-17, and TNF-α were increased (P < 0.05) after stimulation with lipopolysaccharide, which were reversed by knockdown of FGL1 with siRNA transfection (P < 0.05). Conversely, FGL1 overexpression enhanced the abovementioned results (P < 0.05).
FGL1 can induce intestinal inflammation by activating the canonical NF-κB signalling pathway, and it may be considered a potential biomarker and therapeutic target for CD.
Core Tip: In this study, fibrinogen-like protein 1 (FGL1) was identified to be significantly upregulated in the plasma and intestinal mucosa of Crohn’s disease (CD) patients. In vitro, silencing FGL1 downregulated the levels of the proinflammatory cytokines IL-1β, IL-6, IL-17, and TNF-α. Furthermore, FGL1 knockdown suppressed the mRNA expression of NF-κB and the protein levels of IKKα, IKKβ, p-IKKα/β, p-IκBα, and p-p65. These results could be reversed by the overexpression of FGL1. Taken together, these data suggest that FGL1 may induce intestinal inflammation by activating the canonical NF-κB signalling pathway and has the potential to be a therapeutic target for CD.