Everolimus Inhibits Anti-HLA I Antibody-Mediated Endothelial Cell Signaling, Migration and Proliferation More Potently Than Sirolimus

Abstract

Antibody (Ab) crosslinking of HLA I molecules on the surface of endothelial cells triggers proliferative and pro-survival intracellular signaling, which is implicated in the process of chronic allograft rejection, also known as transplant vasculopathy. The purpose of this study was to investigate the role of mammalian target of rapamycin (mTOR) in HLA I antibody-induced signaling cascades. Everolimus provides a tool to establish how the mTOR signal network regulates HLA I-mediated migration, proliferation, and survival. We found that everolimus inhibits mTORC1 by disassociating Raptor from mTOR, thereby preventing class I-induced phosphorylation of mTOR, p70S6K, S6RP, and 4E-BP1, and resultant class I-stimulated cell migration and proliferation. Furthermore, we found that everolimus inhibits class I-mediated mTORC2 activation (1) by disassociating Rictor and Sin1 from mTOR; (2) by preventing class I-stimulated Akt phosphorylation; and (3) by preventing class I-mediated ERK phosphorylation. These results suggest that everolimus is more effective than sirolimus at antagonizing both mTORC1 and mTORC2, the latter of which is critical in endothelial cell functional changes leading to transplant vasculopathy in solid organ transplantation after HLA I crosslinking. Our findings point to a potential therapeutic effect of everolimus in prevention of chronic antibody-mediated rejection.

Strategies to improve outcome of patients with hepatocellular carcinoma receiving a liver transplantation

“…In addition the analysis of the Scientific Registry of Transplant Recipients (SRTR) database (n = 26414) showed an increased risk of all-cause mortality in patients with hepatitis C treated with sirolimus (HR = 1.29; 95%CI: 1.08-1.55) [134] . Everolimus has a selective effect on mTOR complex 1, and it has been proposed to be more potent than sirolimus [135] , and with an improved metabolic profile [136] . Unfortunately the evidence linking everolimus and HCC recurrence after LT is lacking.…”

Antibody-mediated rejection across solid organ transplants: manifestations, mechanisms, and therapies

“…HLA antibodies promote activation of intracellular signaling in vitro and in animal models (141)(142)(143)(144)(145)(146)(147). Several studies have demonstrated that detection of phosphorylated signaling molecules that are activated downstream of HLA cross-linking, including S6 ribosomal protein and S6 kinase, aids in detection of AMR in cardiac allografts (101,102,148).…”

“…Extensive in vitro evidence points to an intrinsic role for HLA signaling within the graft vasculature that promotes angiogenic and inflammatory responses (Figure 2). For example, cross-linking of HLA class I with bivalent antibodies mimics trans interactions with T cell receptors, triggering phosphorylation of Src and focal adhesion kinases (FAKs), mTOR, ERK, and S6 ribosomal protein in endothelial and smooth muscle cells (143,145,146). These signaling pathways promote cytoskeletal rearrangements, as well as increased wound healing and cell growth (143,145,146).…”

“…For example, cross-linking of HLA class I with bivalent antibodies mimics trans interactions with T cell receptors, triggering phosphorylation of Src and focal adhesion kinases (FAKs), mTOR, ERK, and S6 ribosomal protein in endothelial and smooth muscle cells (143,145,146). These signaling pathways promote cytoskeletal rearrangements, as well as increased wound healing and cell growth (143,145,146). Activation of these signaling molecules during AMR has been substantiated in vivo in a murine model (147) as well as in human cardiac allografts (101,102).…”

“…This is likely partly attributable to general antiproliferative properties, since mTOR inhibitors also reduce neointimal hyperplasia in other vascular injury models (189). We have proposed that mTOR inhibition may also ameliorate progrowth signaling in the vasculature triggered by HLA antibodies (143). Recently, antibody-mediated TV in murine recipients capable of mounting a de novo antibody response against renal allografts was reported (190).…”