The role of phosphatidylcholine 34:1 in the occurrence, development and treatment of ulcerative colitis

Abstract

Lipid homeostasis is considered to be related to intestinal metabolic balance, while its role in the pathogenesis and treatment of ulcerative colitis (UC) remains largely unexplored. The present study aimed to identify the target lipids related to the occurrence, development and treatment of UC by comparing the lipidomics of UC patients, mice and colonic organoids with the corresponding healthy controls. Here, multi-dimensional lipidomics based on LC-QTOF/MS, LC-MS/MS and iMScope systems were constructed and used to decipher the alteration of lipidomic profiles. The results indicated that UC patients and mice were often accompanied by dysregulation of lipid homeostasis, in which triglycerides and phosphatidylcholines were significantly reduced. Notably, phosphatidylcholine 34:1 (PC34:1) was characterized by high abundance and closely correlation with UC disease. Our results also revealed that down-regulation of PC synthase PCYT1α and Pemt caused by UC modeling was the main factor leading to the reduction of PC34:1, and exogenous PC34:1 could greatly enhance the fumarate level via inhibiting the transformation of glutamate to N-acetylglutamate, thus exerting an anti-UC effect. Collectively, our study not only supplies common technologies and strategies for exploring lipid metabolism in mammals, but also provides opportunities for the discovery of therapeutic agents and biomarkers of UC.

Keywords: Fumarate; Lipidomics; Metabonomics; PC34:1; Ulcerative colitis.

Graphical abstract

Figure 1

Identification of differential lipids in UC patients. (A) Heatmap of PCs in serum of healthy controls and UC patients. (B) 16 differential PCs between healthy controls and UC patients. (C) Univariate analysis of lipids. (D) Relative abundance of 16 differential PCs in serum of healthy controls and UC patients. ∗∗∗P < 0.001, ∗∗P < 0.01, ∗P < 0.05.

Figure 2

Identification of differential lipids in UC mice and colonic organoid. (A) PCA analysis of mouse serum lipidome. (B) PCA analysis of mouse colon lipidome. (C) Relative abundance of differential PCs in mouse serum. (D) Relative abundance of differential PCs in mouse colon. n = 6, ∗∗∗P < 0.001, ∗∗P < 0.01, ∗P < 0.05 vs. model group; ^###P < 0.001, ^##P < 0.01, ^#P < 0.05 acute group vs. recovery group.

Figure 3

MS imaging for PC34:1 and PC34:2 in mouse colon acquired using iMScope. (A) Colon MS imaging of colon in control mice. (B) Colon MS imaging of colon in UC model mice at acute stage.

Figure 4

Identification of differential lipids in colonic organoid and the expression of metabolic enzymes related to PC synthesis. (A) Representative images of colonic organoids cultured with or without the treatment of Salmonella typhimurium. (B) Heatmap of PCs. (C) Relative levels of differential PCs. (D) PCYT1α. (E) Pemt. (F) Chkα. (G) Chkβ. (H) Cept1. n = 6, ∗∗P < 0.01.

Figure 5

Influence of exogenous PC34:1 on UC mice. (A) Influence of PC34:1 on colon length. (B) IL-1β level. (C) IL-6 level. (D) HE-stained and Alcian blue-stained colon tissue sections. (E) Influence of PC34:1 on mouse weight. (F) Heatmap of colonic PCs. n = 6, ∗∗P < 0.01 vs. control group; ^##P < 0.01, ^#P < 0.05 vs. model group.

Figure 6

Regulation of PC34:1 on metabolome in UC mice. (A) Heatmap of metabonomics. (B) PCA analysis. (C) KEGG pathway analysis. (D) Representative metabolites with significant differences. (E) Regulation of PC34:1 on enzymes of fumarate synthesis. (F) Expression of Nags. n = 6, ∗∗P < 0.01, ∗P < 0.05.

Figure 7

Identification of differential metabonomics in UC patients. (A) PCA analysis. (B) Heatmap of metabonomics in healthy volunteers and UC patients. (C) KEGG pathway analysis. (D) Representative small molecule metabolites. ∗∗∗P < 0.001, ∗∗P < 0.01, ∗P < 0.05.

Figure 8

Influence of exogenous fumarate on UC. (A) Effect of fumarate administered intragastrically at a dose of 100 mg/kg on body weight of UC mice. (B) Influence of fumarate (100 mg/kg) on colon length. (C) HE-stained colon tissue sections. (D) Level of proinflammatory cytokines and enhanced ROS, AST and ALT levels. (E) Influence of fumarate on the production of NO in LPS-induced inflammatory RAW264.7 cells. (F) Influence of fumarate (100 μg/mL) on the proinflammatory factors. n = 6, ∗∗∗P < 0.001, ∗∗P < 0.01, ∗P < 0.05 vs. the control group; ^###P < 0.001, ^##P < 0.01, ^#P < 0.05 vs. the model group.