MO684A CO-CULTURE MODEL FOR TESTING EFFECTS OF CYTOPROTECTIVE ADDITIVES IN PD FLUIDS ON THE SECRETOME OF MESOTHELIAL AND ENDOTHELIAL CELLS
Authors: Sacnun Juan Manuel , Herzog Rebecca , Kratochwill Klaus 
Published: May 2021

Abstract

Background and Aims
The composition of all currently available peritoneal dialysis fluids (PDF) triggers morphological and functional changes in the peritoneal membrane. Periodic exposure leads to vasculopathy, hypervascularization, and diabetes-like damage of vessels of the peritoneal membrane, eventually leading to technique failure. Patients undergoing dialysis generally, have a high risk of cardiovascular events. It is currently unclear if there is a mechanistic link between peritoneal membrane failure and cardiovascular risk. In vitro and in vivo studies have shown that cytoprotective additives (e.g. dipeptide alanyl-glutamine (AlaGln) or kinase inhibitor lithium chloride (LiCl)) to PDF reduce peritoneal damage. Here, we developed an experimental model for investigating effects of such additives on secretome-mediated signalling between cell-types of the peritoneal membrane which are relevant in the cardiovascular context.

Method
For modelling the peritoneal membrane in vitro, mesothelial (MC) and endothelial cells (EC) were co-cultured in transwell plates. MC were grown in the upper compartment and primary microvascular cells were grown in the lower compartment. MC were exposed to PDF with or without cytoprotective compounds (8 mM AlaGln in glucose-based PDF 3.86% or 10 mM LiCl in icodextrin-based PDF), while EC below were kept in medium. Cell damage was assessed by quantification of lactate-dehydrogenase (LDH) release, neutral red uptake and cell morphology. Proteome and secretome profiles were analysed for both cell-types in co-culture or separately with an isobaric-tag labelling approach with a multiplexed liquid chromatography/mass spectrometry (LC-MS) approach. Prior to analysis of the secretome a bead-based equalizer approach based on a combinatorial peptide ligand library (CPLL) was performed to enrich low abundant proteins.

Results
EC injury after PD-fluid exposure of MC was decreased with the addition of AlaGln or LiCl, showing a link between the individual cell outcomes. Proteome analysis revealed perturbation of major cellular processes including regulation of cell death and cytoskeleton re-organization, which characterize PDF cytotoxicity. Selected markers of angiogenesis, oxidative stress, cell junctions and transdifferentiation were counter-regulated by the additives. Co-cultured cells yielded differently regulated pathways following PDF exposure compared to separate culture. We were able to identify and quantify 334 secreted proteins in the co-culture system. The secretome analysis showed variation in several clinically relevant proteins and important extracellular processes such as extracellular matrix reorganization, vesicle transport or collagen deposition. Comparison to previously published abundance profiles of omental arteriolar proteins from paediatric PD patient and age-matched controls confirmed overlapping protein regulation between endothelial cells in vitro and in vivo.

Conclusion
This study shows that harmful effects of PDF-stressed MC also affect EC and elucidates potential mechanisms by which cytoprotective additives may counteract the signalling axis between local peritoneal damage and systemic vasculopathy. An in vitro co-culture system may be an attractive approach to simulate the close proximity of different cell types in the peritoneal membrane for testing direct and indirect effects of cytoprotective additives. Characterisation of PD-induced perturbations may allow identifying molecular mechanisms linking the peritoneal and cardiovascular context, offering therapeutic targets to reduce current limitations of PD and ultimately decreasing cardiovascular risk of dialysis patients.