P0675LEUCOCYTE PODOSOME FORMATION AND ADHESION TO ENDOTHELIUM IS MEDIATED BY INTEGRIN LINKED KINASE IN CHRONIC KIDNEY DISEASE (CKD)
Authors: Campillo de Blas Sofía , Bohorquez Magro Lourdes , Gutiérrez-Calabrés Elena , García Ayuso Diego , Vaillo David , Griera-Merino Mercedes , De Frutos García Sergio , Rodríguez-Puyol Manuel , Rodríguez-Puyol Diego , Calleros Laura 
Published: June 2020

Abstract

Background and Aims
Patients with CKD have a higher risk of developing cardiovascular diseases. Protein-bound uremic toxins, such as p-cresol (pc) and indoxyl-sulfate (IS), are retention solutes, poorly removed during hemodialysis. They lead to endothelial dysfunction inducing the expression of adhesion molecules and leucocyte adhesion to endothelium. Monocyte extravasation can be carried out by dynamic adhesion structures called podosomes. Integrin-linked kinase (ILK), a kinase and an intracellular scaffold protein, links the cell-adhesion receptors, integrins and growth factors to the actin cytoskeleton and to a range of signalling pathways. We demonstrate the role of ILK in the accumulation of integrin-associated proteins inside the podosomes. The aim of this study was to investigate if ILK is involved in uremic toxin-induced leucocyte podosome formation and adhesion under uremic conditions that simulate CKD.

Method
In vitro experiments were carried out in human cell line of leukemic monocytes, THP-1. We tested the effect of uremic toxins on cell viability and ILK expression levels or activation by performing dose and time-response experiments. Cells were exposed to IS (25-100 µg ml-1) plus pc (10-100 µg ml-1) both combined, for different times. ILK expression levels were determined by Western Blot and RT-qPCR and its kinase activity was tested by its downstream effector GSK-3β phosphorylated levels. Cell adhesion of THP-1 cells stained with cell tracker to a monolayer of human endothelial cells (EA.hy926) and podosome formation and cell adhesion of THP-1 cells stained with phalloidin to a fibronectin extracellular matrix, was determined by fluorescence confocal microscopy. ILK co-localization with podosome specific protein cortactin was assessed by fluorescence confocal microscopy. For ex vivo experiments in ILK conditional-knockdown mice (cKD-ILK), male CRE-LOX mice were injected with tamoxifen (cKD-ILK) or vehicle (wild-type, WT), to induce ILK deletion. Peripheral blood mononuclear cells (PBMCs) were obtained and treated with uremic toxins. Cell adhesion to a fibronectin extracellular matrix was determined by cell count of the percentage of attached cells against the total cells collected.

Results
Our data suggests that uremic toxins did not induce toxicity in THP-1 cells. Furthermore, ILK was activated by uremic toxins both at low and high concentrations, without changes in the protein expression. In the cell adhesion assay to the endothelium, uremic toxins induces an increase of THP-1 cells adhesion, which is completely abolished when ILK is knocked down by ILK siRNA, both at low and high toxins concentrations. Similar results were obtained from the cell adhesion assay to the fibronectin extracellular matrix. Moreover, uremic toxins induced podosome formation in THP-1 cells, even at low concentrations, compared to the control, while ILK knockdown abrogated almost completely fibronectin adhesion and podosome formation in uremic toxin-treated cells. Interestingly, we tested that ILK co-localize with cortactin in podosomes, which confirmed the implication of ILK in podosome structures formation induced by uremic toxins. In cKD-ILK PBMC mice the transgenic ILK depletion significantly decrease non-excised ILK mRNA levels. These cKD-ILK PBMC mice exhibited a lower adhesion to the fibronectin extracellular matrix compared to WT. By last, uremic toxins induced a significant increase of mice PBMCs adhesion in WT animals compared to the control that was significantly lower in PBMCs of cKD-ILK animals.

Conclusion
These data suggest that ILK plays a critical role in the required processes for leukocyte extravasation. ILK deletion may prevent podosome formation and adhesion of leucocytes, decreasing the endothelial and vascular damage caused by the accumulation of uremic toxins in CKD. Therefore, ILK could be a potential therapeutic target for the treatment of vascular damage associated with CKD.