Regulation of inflammatory processes by ceramide kinase and phosphatidylethanolamine N-methyltransferase in lung cells, adipocytes and liver tissue

Resumen

Nowadays, around 60% of the world¿s population dies due to chronic inflammatory conditions, such as chronic respiratory diseases, obesity, fatty liver disease and cancer. All these pathologies are associated to alterations in sphingolipid metabolism. Thus, understanding the mechanisms responsible for the establishment and evolution of those diseases may be useful for developing novel strategies to control their development and progression. In this thesis, we demonstrate that ROCK1 is a key regulatory enzyme necessary for cigarette smoke extract (CSE)-induced monocyte chemoattractant protein-1 (MCP-1) release in lung epithelial cells, and that AKT2 and the Ceramide Kinase (CerK)/ ceramide 1-phosphate (C1P) axis elicit the opposite effects, pointing to an anti-inflammatory role of C1P in the lungs. We also provide evidence suggesting that adipogenesis is associated with an increase in phosphatidylethanolamine N-methyltransferase-2 (PEMT-2) protein expression, whose depletion leads to impaired adipocyte differentiation, as seen by a reduced expression of adipogenic markers, as well as reduced lipid droplet formation, triglyceride (TG) content and leptin release. Moreover, we demonstrate that the inhibition of adipocyte differentiation by exogenous C1P occurs by modulating PEMT expression. Besides, we havealso found an abnormal sphingolipid metabolism in Pemt-/- mice fed a HFD (a well-known non-alcoholic fatty liver disease mouse model), with elevation of ceramides, sphingomyelin, sphinganine, sphingosine, 1-deoxyceramides, and C26:1 C1P as well as higher expression of mRNAs for acid ceramidase (Asah1) and ceramide kinase (CerK). Treatment with vitamin E (0.5 g/kg) for 3 weeks improved VLDL-TG secretion and normalized cholesterol metabolism, but failed to reduce hepatic TG content. Moreover, vitamin E treatment was able to reduce hepatic oxidative stress, inflammation and fibrosis, and restored Asah1 and CerK mRNA and sphingolipid levels, showing that vitamin E treatment efficiently prevents the progression from simple steatosis to steatohepatitis in mice lacking PEMT, and that sphingolipid metabolites and Asah1 and CerK may be important factors in this action.