Reparative effect of mesenchymal stromal cells on endothelial cells after ischemic and inflammatory injury

Background & Aim Renal endothelium is damaged by ischemia reperfusion injury (IRI) during transplantation as a result of the hypoxic metabolism and the resumption of oxygen supply after reperfusion. It has been shown that mesenchymal stromal cells (MSC) are effective in enhancing kidney function after IRI. However, the cellular targets and mechanisms of action behind MSC effects are still poorly understood. Therefore, our objective was to evaluate the role of MSC in repairing injured endothelium as it is the first tissue with which they interact after infusion and to determine the specific interactions involved in this process. The role of physical communication and cytokine secretion in the reparative action of MSC was studied as well as its molecular mechanisms. Methods, Results & Conclusion Human umbilical vein endothelial cells (HUVEC) were submitted to hypoxic and inflammatory insult (TNF-a). This increased the expression of activation molecules such as CD54, CD62e and HLA-II on HUVEC's cell surface. Consequently, an increase of almost 20% in the adherence of MSC to HUVEC was observed in comparison to untreated HUVEC. Moreover, an increase of around 20% in the migratory capacity of MSC towards injured HUVEC was observed. MSC showed a 15 to 20% increase in their ability to transmigrate through injured HUVEC monolayers. Once MSC were in contact with HUVEC, the oxidative stress of HUVEC decreased as observed by a decrease in reactive oxygen species levels, their proliferative status improved and MSC restored the angiogenic potential to levels close to those from healthy HUVEC. To determine whether physical interaction or soluble factors released by MSC are fundamental for MSC regenerative capacity, a Boyden chamber system experiment was performed and we observed that both were required to achieve the full reparative effect of MSC. Moreover, we observed an increase in the expression of CD44 and CD29 adhesion molecules on MSC membrane after co-culture with injured HUVEC, as well as their ligands CD62e and CD106 on HUVEC membrane. We conclude that MSC are able to repair the injury caused by ischemic and inflammatory injury on HUVEC via a mechanism that requires both physical and paracrine interaction between MSC and HUVEC. We are currently studying the specific effector molecules involved in MSC and HUVEC cell-to-cell interaction which will allow targeted modification to improve the regenerative effects of MSC therapy.