Ceramide synthase 2 deficiency aggravates AOM-DSS-induced colitis in mice: role of colon barrier integrity

Abstract

Loss of intestinal barrier functions is a hallmark of inflammatory bowel disease like ulcerative colitis. The molecular mechanisms are not well understood, but likely involve dysregulation of membrane composition, fluidity, and permeability, which are all essentially regulated by sphingolipids, including ceramides of different chain length and saturation. Here, we used a loss-of-function model (CerS2 and CerS2 mice) to investigate the impact of ceramide synthase 2, a key enzyme in the generation of very long-chain ceramides, in the dextran sodium salt (DSS) evoked model of UC. CerS2 mice developed more severe disease than CerS2 mice in acute DSS and chronic AOM/DSS colitis. Deletion of CerS2 strongly reduced very long-chain ceramides (Cer24:0, 24:1) but concomitantly increased long-chain ceramides and sphinganine in plasma and colon tissue. In naive CerS2 mice, the expression of tight junction proteins including ZO-1 was almost completely lost in the colon epithelium, leading to increased membrane permeability. This could also be observed in vitro in CerS2 depleted Caco-2 cells. The increase in membrane permeability in CerS2 mice did not manifest with apparent clinical symptoms in naive mice, but with slight inflammatory signs such as an increase in monocytes and IL-10. AOM/DSS and DSS treatment alone led to a further deterioration of membrane integrity and to severe clinical symptoms of the disease. This was associated with stronger upregulation of cytokines in CerS2 mice and increased infiltration of the colon wall by immune cells, particularly monocytes, CD4 and Th17 T-cells, and an increase in tumor burden. In conclusion, CerS2 is crucial for the maintenance of colon barrier function and epithelial integrity. CerS2 knockdown, and associated changes in several sphingolipids such as a drop in very long-chain ceramides/(dh)-ceramides, an increase in long-chain ceramides/(dh)-ceramides, and sphinganine in the colon, may weaken endogenous defense against the endogenous microbiome.

Beyond Immune Cell Migration: The Emerging Role of the Sphingosine-1-phosphate Receptor S1PR4 as a Modulator of Innate Immune Cell Activation

“…Here, S1P primarily acts as a cofactor. Besides, ceramide synthase 2 is directly inhibited by S1P [ 13 ], which may either enhance or suppress inflammation [ 14 , 15 ]. Despite these intracellular targets, S1P appears to exert the majority of its functions in immunity by activating its 5 specific G protein-coupled receptors.…”

Knockout of Ceramide Kinase Aggravates Pathological and Lethal Responses in Mice with Experimental Colitis

“…In the colons of DSS-treated WT mice, occludin and epithelial (E)-cadherin levels were significantly decreased, while those of β-catenin were slightly decreased, as previously reported. 11,27) The levels of these three adhesion proteins in the colon were not affected by the depletion of CerK, and the DSS treatment reduced their levels to a similar extent in both mice under the experimental conditions employed in the pres-ent study.…”

“…A ceramide synthase-2 deficiency was shown to exacerbate DSSinduced colitis. 11,12) Thus, sphingolipids and/or their metabolic enzymes may have distinct roles in colitis that depend on their molecules, enzyme subtypes, and cell/tissue types. To the best of our knowledge, the role of ceramide kinase (CerK), an enzyme involved in the formation of ceramide-1-phosphate (C1P) from ceramide, in experimental colitis has not yet been elucidated.…”

Reproduction of inflammatory bowel diseases in experiment

“…ТНБС-індукований коліт супроводжується втратою маси тіла тваринами, кривавою діареєю тощо [9]. ТНБС також викликає достовірні зміни морфологічних характеристик, механічних властивостей і фармакологічної відповіді циркулярного м'язового шару дистального відділу кишківника [10]. ТНБС викликає локальне підвищення синтезу прозапальних медіаторів, що пов'язано з нейтрофільною відповіддю [11], внаслідок чого виникають глибокі деструктивні зміни в дистальних відділах кишківника, завдяки чому використання даного препарату доцільніше для відтворення ХК [1].…”

“…Оскільки ЗЗК є мультифакторіальними захворюваннями, розвиток яких пов'язують з комбінацією внутрішніх та зовнішніх чинників, досить поширеною є комбінація хімічно індукованої моделі коліту з використанням генетично модифікованих тварин з метою максимально наблизити викликані морфо-функціональні зміни до таких при захворюваннях у людини, наприклад, комбінація оксазолону чи ДСН з імунокомпромісними NOD2-мишами [6,10].…”