#4950 CARNITINE ACETYLTRANSFERASE (CRAT) MODULATES MESOTHELIAL CELL RESPONSE TO FIBROTIC STRESS

Abstract

Abstract Background and Aims It has been shown that long-term exposure to the high glucose load of peritoneal dialysis (PD) fluids can induce peritoneal fibrosis causing loss of peritoneal ultrafiltration capacity. TGF-beta is a master regulator factor in the onset of peritoneal fibrosis and recent findings suggest that production of it is dependent on a hyper-glycolytic state caused by glucose-based PD solutions. Currently, a different class of bio-compatible PD solutions are under development; they are based on two synergistic strategies: reducing the amount of glucose, and using osmotic-metabolic agents that may provide metabolic benefits able to mitigate local and systemic glucose over-exposure [1, 2]. One such is L-carnitine [1]. The aim of the present study is to explore the role of L-carnitine and carnitine acetyltransferase (CrAT, a key enzyme in L-carnitine metabolism) on the modulation of TGF-beta pro-fibrotic effects. Method CrAT proved overexpressed in the human mesothelial cell line Met5A. Plasmid-coding CrAT ORF (Origene RG21296) was transfected by Lipofectamine 3000 and subsequently cells underwent antibiotic selection. Single clones were isolated, and CrAT expression was measured at the gene and protein level by real-time PCR and WB respectively. Metabolomic analyses were performed on WT and CrAT overexpressing mesothelial cells. WT and CrAT-overexpressing mesothelial cells were also treated with and without TGF-beta in the presence of physiological and supra-physiological L-carnitine concentrations (50 μM and 2 mM, respectively). The expression of fibrosis and inflammatory markers was analyzed. Results Gene and protein expression analyses confirmed CrAT overexpression in several clones and the two with the highest expression rate were used in subsequent analyses. WT and CrAT-overexpressing mesothelial cells displayed a different metabolic profile, as gleaned by unsupervised hierarchical clustering analysis of the top 50 significant metabolites employing ANOVA and partial least square-discriminant analysis (Figure 1). Most interestingly, they showed a different behavior in response to TGF-beta (Figure 2). In detail: treatment with TGF-beta significantly increased the expression of fibrotic markers alpha-smooth muscle actin (alpha-SMA) and vimentin (VIM) as well as that of pro-inflammatory markers interleukine-6 (IL-6) and interleukine-1β (IL-1β) at a physiological L-carnitine concentration (50 μM). Treatment with supra-physiological L-carnitine levels (2 mM) significantly reduced the up-regulation of the markers analyzed. Similarly, TGF-b was unable to modulate the expression of alpha-SMA, VIM, IL-6 and IL-1β in CrAT-overexpressing cells. Conclusion Studying CrAT-overexpressing mesothelial cells may prove to be a useful tool in elucidating how L-carnitine metabolism manages to keep in check the development of fibrosis and inflammation during PD. The use of L-carnitine as an osmo-metabolic agent in PD solutions could significantly slow down the progression of fibrosis in PD therapy.