Prevention of allograft rejection in heart transplantation through concurrent gene silencing of TLR and Kinase signaling pathways

Potential Immunoregulatory Mechanism of Plant Saponins: A Review

Saponins are extracted from different parts of plants such as seeds, roots, stems, and leaves and have a variety of biological activities including immunomodulatory, anti-inflammatory effects, and hypoglycemic properties. They demonstrate inherent low immunogenicity and possess the capacity to effectively regulate both the innate and adaptive immune responses. Plant saponins can promote the growth and development of the body's immune organs through a variety of signaling pathways, regulate the activity of a variety of immune cells, and increase the secretion of immune-related cytokines and antigen-specific antibodies, thereby exerting the role of immune activity. However, the chemical structure of plant saponins determines its certain hemolytic and cytotoxicity. With the development of science and technology, these disadvantages can be avoided or reduced by certain technical means. In recent years, there has been a significant surge in interest surrounding the investigation of plant saponins as immunomodulators. Consequently, the objective of this review is to thoroughly examine the immunomodulatory properties of plant saponins and elucidate their potential mechanisms, with the intention of offering a valuable point of reference for subsequent research and advancement within this domain.

Urinary Exosomal Cystatin C and Lipopolysaccharide Binding Protein as Biomarkers for Antibody−Mediated Rejection after Kidney Transplantation

We aimed to discover and validate urinary exosomal proteins as biomarkers for antibody−mediated rejection (ABMR) after kidney transplantation. Urine and for-cause biopsy samples from kidney transplant recipients were collected and categorized into the discovery cohort (n = 36) and a validation cohort (n = 65). Exosomes were isolated by stepwise ultra-centrifugation for proteomic analysis to discover biomarker candidates for ABMR (n = 12). Of 1820 exosomal proteins in the discovery cohort, four proteins were specifically associated with ABMR: cystatin C (CST3), serum paraoxonase/arylesterase 1, retinol-binding protein 4, and lipopolysaccharide−binding protein (LBP). In the validation cohort, the level of urinary exosomal LBP was significantly higher in the ABMR group (n = 25) compared with the T-cell-mediated rejection (TCMR) group and the no major abnormality (NOMOA) group. Urinary exosomal CST3 level was significantly higher in the ABMR group compared with the control and NOMOA groups. Immunohistochemical staining showed that LBP and CST3 in the glomerulus were more abundant in the ABMR group compared with other groups. The combined prediction probability of urinary exosomal LBP and CST3 was significantly correlated with summed LBP and CST3 intensity scores in the glomerulus and peritubular capillary as well as Banff g + ptc scores. Urinary exosomal CST3 and LBP could be potent biomarkers for ABMR after kidney transplantation.

MiRNA-122 Promotes Ischemia-Reperfusion Injury after Lung Transplantation via the Toll-like Receptor Signaling Pathway

OBJECTIVE

MiRNAs have been recently implicated in the pathogenesis of ischemia-reperfusion (IR) injury. This study aimed to investigate the miRNA expression profiles in the early stages after lung transplantation (LT) and to study the involvement of the Toll-like receptor (TLR) signaling pathway in lung IR injury following LT.

METHODS

We established the left LT model in mice and selected the miRNA-122 as a research target. The mice were injected with a miRNA-122-specific inhibitor, following which pathological changes in the lung tissue were studied using different lung injury indicators. In addition, we performed deep sequencing of transplanted lung tissues to identify differentially expressed (DE) miRNAs and their target genes. These target genes were used to further perform gene ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis.

RESULTS

A total of 12 DE miRNAs were selected, and 2476 target genes were identified. The GO enrichment analysis predicted 6063 terms, and the KEGG analysis predicted 1554 biological pathways. Compared with the control group, inhibiting the expression of miRNA-122 significantly reduced the lung injury and lung wet/dry ratio (P<0.05). In addition, the activity of myeloperoxidase and the expression levels of tumor necrosis factor-alpha and TLR2/4 were decreased (P<0.05); whereas the expression of interleukin-10 was increased (P<0.05). Furthermore, the inhibition of miRNA-122 suppressed the IR injury-induced activation of the TLR signaling pathway.

CONCLUSION

Our findings showed the differential expression of several miRNAs in the early inflammatory response following LT. Of these, miRNA-122 promoted IR injury following LT, whereas its inhibition prevented IR injury in a TLR-dependent manner.

Impact of Graft-Resident Leucocytes on Treg Mediated Skin Graft Survival

The importance and exact role of graft-resident leucocytes (also referred to as passenger leucocytes) in transplantation is controversial as these cells have been reported to either initiate or retard graft rejection. T cell activation to allografts is mediated via recognition of intact or processed donor MHC molecules on antigen-presenting cells (APC) as well as through interaction with donor-derived extracellular vesicles. Reduction of graft-resident leucocytes before transplantation is a well-known approach for prolonging organ survival without interfering with the recipient's immune system. As previously shown by our group, injecting mice with IL-2/anti-IL-2 complexes (IL-2cplx) to augment expansion of CD4 T regulatory cells (Tregs) induces tolerance towards islet allografts, and also to skin allografts when IL-2cplx treatment is supplemented with rapamycin and a short-term treatment of anti-IL-6. In this study, we investigated the mechanisms by which graft-resident leucocytes impact graft survival by studying the combined effects of IL-2cplx-mediated Treg expansion and passenger leucocyte depletion. For the latter, effective depletion of APC and T cells within the graft was induced by prior total body irradiation (TBI) of the graft donor. Surprisingly, substantial depletion of donor-derived leucocytes by TBI did not prolong graft survival in naïve mice, although it did result in augmented recipient leucocyte graft infiltration, presumably through irradiation-induced nonspecific inflammation. Notably, treatment with the IL-2cplx protocol prevented early inflammation of irradiated grafts, which correlated with an influx of Tregs into the grafts. This finding suggested there might be a synergistic effect of Treg expansion and graft-resident leucocyte depletion. In support of this idea, significant prolongation of skin graft survival was achieved if we combined graft-resident leucocyte depletion with the IL-2cplx protocol; this finding correlated along with a progressive shift in the composition of T cells subsets in the grafts towards a more tolerogenic environment. Donor-specific humoral responses remained unchanged, indicating minor importance of graft-resident leucocytes in anti-donor antibody development. These results demonstrate the importance of donor-derived leucocytes as well as Tregs in allograft survival, which might give rise to new clinical approaches.

Toll-like receptor 3 is an endogenous sensor of cell death and a potential target for induction of long-term cardiac transplant survival

Inflammation posttransplant is directly linked to cell death programs including apoptosis and necrosis. Cell death leads to the release of cellular contents which can promote inflammation. Targeting of these pathways should be an effective strategy to prevent transplant rejection. Toll-like receptor 3 (TLR3) is emerging as a major endogenous sensor of inflammation. In this study, we assessed the role of TLR3 on cell death and transplant rejection. We showed that TLR3 is highly expressed on mouse microvascular endothelial cell (ECs) and the endothelium of cardiac grafts. We demonstrated that TLR3 interacting with dsRNA or self-RNA triggered apoptosis and necroptosis in ECs. Interestingly, TLR3-induced necroptosis led mitochondrial damage. Inhibition of the mitochondrial membrane permeability molecule Cyclophilin D prevented necroptosis in ECs. In vivo, endothelium damage and activities of caspase-3 and mixed lineage kinase domain-like protein were inhibited in TLR3-/- cardiac grafts compared with C57BL/6 grafts posttransplant (n = 5, p < .001). Importantly, TLR3-/- cardiac grafts had prolonged survival in allogeneic BALB/c mice (mean survival = 121 ± 67 vs. 31 ± 6 days of C57BL/6 grafts, n = 7, p = .002). In summary, our study suggests that TLR3 is an important cell death inducer in ECs and cardiac grafts and thus a potential therapeutic target in preventing cardiac transplant rejection.

Rethinking peripheral T cell tolerance: checkpoints across a T cell's journey

Following their exit from the thymus, T cells are endowed with potent effector functions but must spare host tissue from harm. The fate of these cells is dictated by a series of checkpoints that regulate the quality and magnitude of T cell-mediated immunity, known as tolerance checkpoints. In this Perspective, we discuss the mediators and networks that control the six main peripheral tolerance checkpoints throughout the life of a T cell: quiescence, ignorance, anergy, exhaustion, senescence and death. At the naive T cell stage, two intrinsic checkpoints that actively maintain tolerance are quiescence and ignorance. In the presence of co-stimulation-deficient T cell activation, anergy is a dominant hallmark that mandates T cell unresponsiveness. When T cells are successfully stimulated and reach the effector stage, exhaustion and senescence can limit excessive inflammation and prevent immunopathology. At every stage of the T cell's journey, cell death exists as a checkpoint to limit clonal expansion and to terminate unrestrained responses. Here, we compare and contrast the T cell tolerance checkpoints and discuss their specific roles, with the aim of providing an integrated view of T cell peripheral tolerance and fate regulation.

Dendritic cells with METTL3 gene knockdown exhibit immature properties and prolong allograft survival

Maturation of dendritic cells (DCs) initiates adaptive immune responses and thereby provokes allograft rejection. Here, this study aimed to explore the effect of Methyltransferase-like protein 3 (METTL3) silencing on DC function and the role of METTL3-silencing donor DCs in the immune response after mouse heart transplantation. Bone marrow-derived DCs from donor BALB/c mice were infected with lentiviruses expressing METTL3-specific short hairpin RNA (LV-METTL3 shRNA) to silence METTL3. Then METTL3-silencing DCs were treated with lipopolysaccharide (LPS) for another 48 h to induce DC maturation. Recipient C57BL/6 mice were injected with phosphate-buffered saline (PBS), immature DCs, and METTL3 shRNA-DCs prior to the cardiac transplantation involving the transfer of hearts from donor BALB/c mice to recipient C57BL/6 mice. In vitro we demonstrated that METTL3-silencing DCs had lower expression of MHCII, costimulatory molecules (CD80, CD86), and DC-related cytokines (IFN-γ, IL-12) as well as lower ability to activate T-cell proliferation, which were consistent with the characteristics of tolerogenic DCs. In vivo we found that METTL3-silencing donor DCs induced immune tolerance after mouse heart transplantation and prolonged the allograft survival, which might be associated with Th1/Th2 immune deviation. In summary, METTL3-silencing DCs exhibit immature properties and prolong allograft survival.

RNA interference therapeutics in organ transplantation: The dawn of a new era

RNA interference (RNAi) is a natural process through which double-stranded RNA molecules can silence the gene carrying the same code as the particular RNA of interest. In 2006, the discovery of RNAi was awarded the Nobel Prize in Medicine and its success has accumulated since. Gene silencing through RNAi has been used successfully in a broad range of diseases, and, more recently, this technique has gained interest in the field of organ transplantation. Here, genes related to ischemia-reperfusion injury (IRI) or graft rejection may be silenced to improve organ quality after transplantation. Several strategies have been used to deliver siRNA, and pretransplant machine perfusion presents a unique opportunity to deliver siRNA to the target organ during ex situ preservation. In this review, the potential of RNAi in the field of organ transplantation will be discussed. A brief overview on the discovery of RNAi, its mechanism, and limitations are included. In addition, studies using RNAi to target genes related to IRI in liver, kidney, lung, and heart transplantation are discussed.

Is There a Positive Side to T Cell Exhaustion?

T cell “exhaustion” describes a state of late-stage differentiation usually associated with active prevention of functionality via ligation of negative signaling receptors on the cell surface, and which can be reversed by blocking these interactions. This contrasts with T cell “senescence,” which has been defined as a state that is maintained by intrinsic internal cell signaling (caused by DNA damage or other stresses) and which can be reversed pharmacologically. Interventions to alleviate these two different categories of inhibitory pathways may be desirable in immunotherapy for cancer and possibly certain infectious diseases, but reciprocally inducing and maintaining these states, or some properties thereof, may be beneficial in organ transplantation and autoimmunity. Even under physiological non-pathological conditions, T cell exhaustion and senescence may play a role in the retention of T cell clones required for immunosurveillance, and prevent their loss via elimination at the Hayflick limit. This essay briefly reviews T cell exhaustion in contrast to replicative senescence, and circumstances under which their modulation may be beneficial.

Eugenol protects the transplanted heart against ischemia/reperfusion injury in rats by inhibiting the inflammatory response and apoptosis

The aim of the present study was to investigate the protective effect of eugenol on the transplanted heart and explore its mechanisms of action. Male Sprague-Dawley rats were randomly divided into a sham group (n=10), a eugenol group (n=10 pairs, donors and recipients) and a control group (n=10 pairs, donors and recipients). The recipients in the eugenol group received an intraperitoneal injection of eugenol (20 mg/kg/day). The sham group and the control group received equal volumes of physiological saline by intraperitoneal injection. After 15 days the recipients in the control and eugenol groups underwent abdominal heterotopic heart transplantation, while the sham group received only a coeliotomy. The orthotopic hearts in the sham group and the heterotopic hearts in the eugenol and control groups, as well as the peripheral blood samples from all three groups were taken 3 h post operation for biochemical, histopathological, molecular and apoptosis analyses. Compared with the control group, the eugenol treatment significantly reduced the myocardial malondialdehyde content, serum cardiac troponin I, creatine kinase-MB, tumor necresis factor-α and interleukin-6 levels (P<0.05) and significantly alleviated myocardial injury. Western blot analysis demonstrated that the protein expression of cleaved Poly (ADP-ribose) polymerase 1, BAX and active caspase-3 in the eugenol group were significantly decreased, while B-cell lymphoma 2 expression was significantly increased compared with the control group (P<0.05). The myocardial apoptosis rate of the eugenol group was significantly decreased compared with the control group (P<0.05). In conclusion eugenol treatment significantly reduced myocardial injury and demonstrated protective effects for the transplanted heart.

Differential T Cell Signaling Pathway Activation by Tacrolimus and Belatacept after Kidney Transplantation: Post Hoc Analysis of a Randomised-Controlled Trial

Pharmacokinetic immunosuppressive drug monitoring poorly correlates with clinical outcomes after solid organ transplantation. A promising method for pharmacodynamic monitoring of tacrolimus (TAC) in T cell subsets of transplant recipients might be the measurement of (phosphorylated) p38MAPK, ERK1/2 and Akt (activated downstream of the T cell receptor) by phospho-specific flow cytometry. Here, blood samples from n = 40 kidney transplant recipients (treated with either TAC-based or belatacept (BELA)-based immunosuppressive drug therapy) were monitored before and throughout the first year after transplantation. After transplantation and in unstimulated samples, p-p38MAPK and p-Akt were inhibited in CD8⁺ T cells and p-ERK in CD4⁺ T cells but only in patients who received TAC-based therapy. After activation with PMA/ionomycin, p-p38MAPK and p-AKT were significantly inhibited in CD4⁺ and CD8⁺ T cells when TAC was given, compared to pre-transplantation. Eleven BELA-treated patients had a biopsy-proven acute rejection, which was associated with higher p-ERK levels in both CD4⁺ and CD8⁺ T cells compared to patients without rejection. In conclusion, phospho-specific flow cytometry is a promising tool to pharmacodynamically monitor TAC-based therapy. In contrast to TAC-based therapy, BELA-based immunosuppression does not inhibit key T cell activation pathways which may contribute to the high rejection incidence among BELA-treated transplant recipients.