The Expression Of TRAIL/TRAILR And Its Role In The Rejection Of Graft After Renal Transplantation

TNF-related apoptosis-inducing ligand (TRAIL), a novel member of the TNF superfamily, is a cytokine capable of inducing apoptotic cell death in a variety of cell types. There are five distinct receptors, death receptor 4 (DR4), DR5, decoy receptor 1 (DcRl), DcR2, and Osteoprotegerin (OPG), for TRAIL ligand. Among them DR4 and DR5 contain death domains (DD) in their cytoplasmic region and can mediate cell apoptosis upon ligation with membrane form TRAIL or soluble TRAIL. In contrast, DcRl and DcR2 contain no DD or incomplete death domain lacking the ability to induce apoptotic signal and have been hypothesized as protective receptors, either by acting as "decoy" receptors or via transduction of an antiapoptotic signal. OPG is a soluble antagonist receptor of TRAIL and may prevent the transduction of apoptotic signal through DR4 and DR5.Renal transplantation is the best way for the treatmentof some end-stage renal diseases. Unfortunately not every transplant is successful due to the rejection or disfunction of transplanted kidney. It is well known that many cytokines participate in the rejection of graft via inducing inflammation or cell apoptosis. In this study the expression of TRAIL, DR4 and DR5 in rejected renal tissue, serum soluble TRAIL (sTRAIL) levels of patients with kidney rejection were investigated by immunohistochemical staining and sandwich ELISA respectively. The results showed that the expression of TRAIL, DR4, DR5 and serum sTRAIL levels were markedly up-regulated in patients received renal transplantation. Since both membrane and soluble form of TRAIL could induce apoptosis of DR4/DR5-expressing cells via recruiting FADD and caspase 8, elevated TRAIL and its receptors may participate in the rejection of graft after renal transplantation.It has been confirmed that a number of membrane molecules exist their soluble forms either shedded from the membrane form by proteolysis or generated by direct secretion from the cell due to the alternative splicing of mRNA. These soluble forms play important roles in the regulation of immunological function and some of them are found to be related to the pathogenesis of certain diseases.TRAIL is a 32. 5 kDa type II transmembrane glycoprotein. The primary structure of this protein contains 281 amino acids with an N-terminal cytosolic domain of 14 residues that precedes a stretch of 26 hydrophobic residues characteristic of type II transmembrane protein. The extracelullar regionof TRAIL exhibits significant homology with that of other TNF superfamily members, such as FasL (28% identity), TNF-a (23% identity). The extracellular domain of TRAIL can be shed from the membrane and form a soluble form about 19 kDa. Soluble TRAIL can form dimeric or trimeric structure with molecule masses of 48 kDa and 66 kDa respectively. A zinc ion coordinated by three cysteines at the position 230aa of each subunit and stabilizes the homotrimeric structure of TRAIL. The trimeric structure of sTRAIL make it possible to establish a sandwich ELISA using just a single mAb acting both capture antibody and detection antibody. In this study, we estalished a sandwich ELISA for quantitating sTRAIL with the detection limitation of 60pg/ml.The distrubution of TRAIL and its receptors DR4, DR5, DcRl and DcR2 in the heart tissue of heathy persons was investigated by immunohistochemical staining. The results showed that all the heart tissues studied expressed TRAIL and its receptors which were localized in cytoplasm mostly and some on the membrane. Interestingly, among TRAIL receptors not only decoy receptors DcRl and DcR2,but also death receptor DR5 were expressed in normal heart equally strong. These results suggested that TRAIL and its receptors may be involved in apoptosis of cardiac myocytes under some pathological situations.