Implicación de las microvesículas endoteliales en el desarrollo de daño vascular

Résumé

Cardiovascular disease (CVD) is a pathology commonly associated with chronic kidney disease (CKD) that represents the main cause of morbidity and mortality in this group. This high incidence of CVD occurs as a result of endothelial dysfunction caused by different factors present in patients with CKD. In addition, these patients frequently show vascular calcifications (CV) that hinder the treatment of CVD and its prognosis. This fact has led to propose the identification of early biomarkers of endothelial damage and vascular calcification that could be a key factor to palliate CVD associated with CKD. The immune system has been proposed as a mechanism to explain endothelial dysfunction in CKD; specifically it has been associated with the rise of an activated monocytes subpopulation in the uremic patient’s serum, CD14+ CD16++ monocytes. These cells are increased in the peripheral blood of uremic patients, even when there is a lack of clinical data related to an active inflammatory process, or without an increase in other inflammatory markers such as PCR or pro-inflammatory cytokines in peripheral blood. Furthermore, a direct link has been found between this subpopulation of monocytes and the appearance of cardiovascular events it. Microvesicles (MV) were originally described as structures produced by different activated cells; they have been considered as indicative markers of cellular activation and / or apoptosis and reflect cellular damage. It has been shown that high levels of endothelial microvesicles (EMV) in plasma can be considered as an indicator of endothelial damage in pathological situations; however, low levels of EMV are also observed in the plasma of subjects without vascular pathology. The role as a barriers of the endothelial cells (EC) constantly exposes them to the stimuli and attacks from the blood torrent, so a relatively small number of these cells are destroyed continuously. In order to maintain vascular homeostasis, damaged endothelial cells are replaced by endothelial progenitor cells (EPC), originated in bone marrow, and they circulate in a low percentage in peripheral blood. These precursor cells will differentiate and replace damaged EC, returning the vascular integrity and balance. EVM produced by EC works as stimulation for the EPC differentiation so the EMV could act as "messengers” between reparative cells and mature cells. Based on these premises, the main objective of the thesis has been to characterize the role of EMV produced in response to different harmful agents to the vascular endothelium related to CKD, determining the functionality of these microvesicles in the regulation of endothelial damage / repair balance. The results obtained suggest: 1.- In patients with CKD, there is an increase in EMV that is associated with a decrease in the number of EPC, which suggests an imbalance between the processes of endothelial damage and repair in patients with CKD, mainly those with CV. The MV of CKD patients induce the expression of osteocalcin, a procalcifying molecule, in vascular smooth muscle cells, fibroblasts and EPC. Our results suggest that EPC stimulated with MV, through the expression of OCN, can participate directly in the VC process. 2.- Patients with hemodialysis remain in an inflammatory state and suffer endothelial alterations that can be identified using quantifiable early markers in peripheral blood. In particular, MVs, which measure 400-1000 nm, have a possible predictive value in the prevention of CVD in patients with HD. In addition, diabetes mellitus alters these factors of inflammatory and endothelial damage. 3.- The indoxyl sulfate, is able to induce EC vesiculation and produce MVE with different characteristics of membrane, miRNA content and other molecules, which means that the maintenance of the vascular homeostasis of EPC is not completely functional. These specific features of the EMV might be used like new biomarkers for the CVD diagnosis and prognosis.