The effect of anti-HLA class I antibodies on the immunological properties of human glomerular endothelial cells and their modification by mTOR inhibition or GCN2 kinase activation

In antibody-mediated rejection (ABMR), the graft endothelium is at the forefront of the kidney transplant against the assault from the recipient's humoral immune system, and is a target of the latter. The present study investigated the effect of antibodies against human leukocyte antigen (HLA) class I (anti-HLAI) on the immunological properties of human glomerular endothelial cells. Additionally, the effect of the mammalian target of rapamycin (mTOR) complex 1 (mTORC1) inhibitor (everolimus), or the general control nonderepressible 2 kinase (GCN2K) activator (halofuginone) on anti-HLAI antibody-mediated alterations was assessed. Cell integrity was examined, an lactate dehydrogenase (LDH) release assay was performed and cleaved caspase-3 levels were determined. Furthermore, cell proliferation was analyzed by performing a bromodeoxyuridine assay and the cellular proteins involved in signal transduction or immune effector mechanisms were assessed via western blotting. IL-8, monocyte chemoattractive protein-1 (MCP-1), von Willebrand factor (vWF) and transforming growth factor-beta 1 (TGF-β1) were assayed via ELISA. The results revealed that anti-HLAI triggered integrin signaling, activated mTOR and GCN2K, preserved cell integrity and promoted cell proliferation. Additionally, by increasing intercellular adhesion molecule 1 (ICAM-1), HLA-DR, IL-8 and MCP-1 levels, anti-HLAI enhanced the ability of immune cells to interact with endothelial cells thus facilitating graft rejection. Contrarily, by upregulating CD46 and CD59, anti-HLAI rendered the endothelium less vulnerable to complement-mediated injury. Finally, by enhancing vWF and TGF-β1, anti-HLAI may render the endothelium prothrombotic and facilitate fibrosis and graft failure, respectively. According to our results, mTORC1 inhibition and GCN2K activation may prove useful pharmaceutical targets, as they prevent cell proliferation and downregulate ICAM-1, IL-8, MCP-1 and TGF-β1. mTORC1 inhibition also decreases vWF.