Zhu-Xu Zhang

NK Cells Induce Apoptosis in Tubular Epithelial Cells and Contribute to Renal Ischemia-Reperfusion Injury

Renal ischemia-reperfusion injury (IRI) can result in acute renal failure with mortality rates of 50% in severe cases. NK cells are important participants in early-stage innate immune responses. However, their role in renal tubular epithelial cell (TEC) injury in IRI is currently unknown. Our data indicate that NK cells can kill syngeneic TEC in vitro. Apoptotic death of TEC in vitro is associated with TEC expression of the NK cell ligand Rae-1, as well as NKG2D on NK cells. In vivo following IRI, there was increased expression of Rae-1 on TEC. FACS analyses of kidney cell preparations indicated a quantitative increase in NKG2D-bearing NK cells within the kidney following IRI. NK cell depletion in wild-type C57BL/6 mice was protective, while adoptive transfer of NK cells worsened injury in NK, T, and B cell-null Rag2−/−γc−/− mice with IRI. NK cell-mediated kidney injury was perforin (PFN)-dependent as PFN−/− NK cells had minimal capacity to kill TEC in vitro compared with NK cells from wild-type, FasL-deficient (gld), or IFN-γ−/− mice. Taken together, these results demonstrate for the first time that NK cells can directly kill TEC and that NK cells contribute substantially to kidney IRI. NK cell killing may represent an important underrecognized mechanism of kidney injury in diverse forms of inflammation, including transplantation.

Immune Modulation and Tolerance Induction by RelB-Silenced Dendritic Cells through RNA Interference

Dendritic cells (DC), the most potent APCs, can initiate the immune response or help induce immune tolerance, depending upon their level of maturation. DC maturation is associated with activation of the NF-κB pathway, and the primary NF-κB protein involved in DC maturation is RelB, which coordinates RelA/p50-mediated DC differentiation. In this study, we show that silencing RelB using small interfering RNA results in arrest of DC maturation with reduced expression of the MHC class II, CD80, and CD86. Functionally, RelB-silenced DC inhibited MLR, and inhibitory effects on alloreactive immune responses were in an Ag-specific fashion. RelB-silenced DC also displayed strong in vivo immune regulation. An inhibited Ag-specific response was seen after immunization with keyhole limpet hemocyanin-pulsed and RelB-silenced DC, due to the expansion of T regulatory cells. Administration of donor-derived RelB-silenced DC significantly prevented allograft rejection in murine heart transplantation. This study demonstrates for the first time that transplant tolerance can be induced by means of RNA interference using in vitro-generated tolerogenic DC.

RIPK3-Mediated Necroptosis Promotes Donor Kidney Inflammatory Injury and Reduces Allograft Survival

Kidney transplant injury occurs with ischemia and alloimmunity. Members of the receptor interacting protein kinase family (RIPK1,3) are key regulators of “necroptosis,” a newly recognized, regulated form of necrosis. Necroptosis and apoptosis death appear to be counterbalanced as caspase‐8 inhibition can divert death from apoptosis to necrosis. Inhibition of necroptosis in donor organs to limit injury has not been studied in transplant models. In this study, necroptosis was triggered in caspase inhibited tubular epithelial cells (TEC) exposed to tumor necrosis factor alpha in vitro, while RIPK1 inhibition with necrostatin‐1 or use of RIPK3−/− TEC, prevented necroptosis. In vivo, short hairpin RNA silencing of caspase‐8 in donor B6 mouse kidneys increased necroptosis, enhanced high‐mobility group box 1 release, reduced renal function and accelerated rejection when transplanted into BALB/c recipients. Using ethidium homodimer perfusion to assess necrosis in vivo, necrosis was abrogated in RIPK3−/− kidneys postischemia. Following transplantation, recipients receiving RIPK3−/− kidneys had longer survival (p = 0.002) and improved renal function (p = 0.03) when compared to controls. In summary, we show for the first time that RIPK3‐mediated necroptosis in donor kidneys can promote inflammatory injury, and has a major impact on renal ischemia–reperfusion injury and transplant survival. We suggest inhibition of necroptosis in donor organs may similarly provide a major clinical benefit.

A novel in vivo siRNA delivery system specifically targeting dendritic cells and silencing CD40 genes for immunomodulation

Translation of small interfering RNA (siRNA)-based approaches into practical therapeutics is limited because of lack of an effective and cell-specific delivery system. Herein, we present a new method of selectively delivering siRNA to dendritic cells (DCs) in vivo using CD40 siRNA-containing immunoliposomes (siILs) that were decorated with DC-specific DEC-205 mAb. Administration of CD40 siILs resulted in DC-specific cell targeting in vitro and in vivo. On treatment with CD40 siILs, the expression of CD40 in DCs, as well allostimulatory activity was inhibited. In vivo administration resulted in selective siRNA uptake into immune organs and functional immune modulation as assessed using a model antigen. In conclusion, this is the first demonstration of DC-specific siRNA delivery and gene silencing in vivo, which highlights the potential of DC-mediated immune modulation and the feasibility of siRNA-based clinical therapy.

Osteopontin Expressed in Tubular Epithelial Cells Regulates NK Cell-Mediated Kidney Ischemia Reperfusion Injury

Renal ischemia reperfusion injury (IRI) occurs after reduced renal blood flow and is a major cause of acute injury in both native and transplanted kidneys. Studies have shown diverse cell types in both the innate and the adaptive immune systems participate in kidney IRI as dendritic cells, macrophages, neutrophils, B cells, CD4+ NK+ cells, and CD4+ T cells all contribute to this form of injury. Recently, we have found that NK cells induce apoptosis in tubular epithelial cells (TECs) and also contribute to renal IRI. However, the mechanism of NK cell migration and activation during kidney IRI remains unknown. In this study, we have identified that kidney TECs express a high level of osteopontin (OPN) in vitro and in vivo. C57BL/6 OPN-deficient mice have reduced NK cell infiltration with less tissue damage compared with wild-type C57BL/6 mice after ischemia. OPN can directly activate NK cells to mediate TEC apoptotic death and can also regulate chemotaxis of NK cells to TECs. Taken together, our study’s results indicate that OPN expression by TECs is an important factor in initial inflammatory responses that involves NK cells activity in kidney IRI. Inhibiting OPN expression at an early stage of IRI may be protective and preserve kidney function after transplantation.

Generation of therapeutic dendritic cells and regulatory T cells for preventing allogeneic cardiac graft rejection.

Tolerogenic dendritic cells (Tol-DCs) and regulatory T cells (Treg) are key factors in the induction and maintenance of transplantation tolerance. We previously demonstrated that ex vivo-isolated Tol-DCs promote Treg generation, and vice versa, in an in vitro co-culture system. Here we demonstrate the occurrence of such an immune regulatory feedback loop in vivo. Tol-DC generated in vitro by treatment with LF 15-0195 exhibited features of immature DC and express low levels of MHC class II, CD86 and CD40. These Tol-DCs were capable of augmenting CD4(+)CD25(+)CTLA4(+) and FoxP3(+) Treg cell numbers and activity in cardiac allograft recipients. On the other hand, Tol-DCs possessed an ability to generate Treg cells in vitro. The adoptive transfer of these in vitro-generated Treg cells resulted in an increase of Tol-DC in vivo, suggesting that an immune regulatory feedback loop, between Tol-DC and Treg, exists in vivo. Furthermore, the administration of in vitro-generated Tol-DCs or Treg cells prevented rejection of allografts. Co-administration of Tol-DC and Treg synergized efficacy of promoting allograft survival heart transplantation. The present study highlights the therapeutic potential of preventing allograft rejection using in vitro-generated Tol-DCs and Treg.

Adoptive transfer of double negative T regulatory cells induces B-cell death in vivo and alters rejection pattern of rat-to-mouse heart transplantation.

Abstract:  Background:  Antibody‐mediated hyperacute and acute graft rejection are major obstacles in achieving long‐term graft survival in xenotransplantation. It is well documented that regulatory T (Treg) cells play a very important role in regulating immune responses to self and non‐self antigens. Our previous studies have shown that TCRαβ+CD3+CD4−CD8− (double negative, DN)‐Treg cells can suppress anti‐donor T‐cell responses and prolong graft survival in allo‐ and xenotransplantation models. We have demonstrated that DN‐Treg cells can induce B‐cell apoptosis in vitro through a perforin‐dependent pathway.

IL-37 inhibits IL-18-induced tubular epithelial cell expression of pro-inflammatory cytokines and renal ischemia-reperfusion injury.

Cytokines and chemokines produced by tubular epithelial and infiltrating cells are critical to inflammation in renal ischemia-reperfusion injury. IL-37, a newly described IL-1 family member, inhibits IL-18-dependent pro-inflammatory cytokine production by its binding to IL-18 receptors and IL-18 binding protein. The potential role of IL-37 in renal ischemia-reperfusion injury is unknown. Here we found that exposure of tubular epithelial cells to exogenous IL-37 downregulated hypoxia and the IL-18-induced expression of TNFα, IL-6, and IL-1β. Importantly, human PT-2 tubular epithelial cells have inducible expression of IL-37. Moreover, pro-inflammatory cytokine expression was augmented in IL-37 mRNA-silenced tubular epithelial cells and inhibited by transfection with pCMV6-XL5-IL-37. In a mouse ischemic injury model, transgenic expression of human IL-37 inhibited kidney expression of TNFα, IL-6, and IL-1β and improved mononuclear cell infiltration, kidney injury, and function. Thus, human tubular epithelial cells express the IL-18 contra-regulatory protein IL-37 as an endogenous control mechanism to reduce inflammation. Augmenting kidney IL-37 may represent a novel strategy to suppress renal injury responses and promote kidney function after renal ischemic injury and transplantation.

RIPK3‐Mediated Necroptosis Regulates Cardiac Allograft Rejection

Cell death results in tissue damage and ultimately donor graft rejection and can occur as an active molecular process through apoptotic, necrotic and newly identified receptor interacting protein 1 and 3 kinase (RIPK1/3)‐mediated necroptotic pathways. Necroptosis leads to the release of inflammatory molecules which can activate host immune cells. This pathway has yet to be studied in heart transplantation. We have found that necroptosis was induced in murine cardiac microvascular endothelial cell (MVEC) under anti‐apoptotic condition following tumor necrosis factor alpha treatment. Necroptotic cell death and release of the danger molecule high mobility group box 1 (HMGB1) were inhibited by the RIPK1 inhibiting molecule necrostatin‐1 and by genetic deletion of RIPK3. In addition, tissue necrosis, release of HMGB1 and graft cell infiltrate were attenuated in RIPK3 null heart allografts following transplantation. Finally, a brief sirolimus treatment markedly prolonged RIPK3 null cardiac allograft survival in allogeneic BALB/c recipients as compared to WT C57BL/6 donor grafts (95 ± 5.8 vs. 24 ± 2.6 days, p < 0.05). This study has demonstrated that RIPK1/3 contributes to MVEC death and cardiac allograft survival through necroptotic death and the release of danger molecules. Our results suggest that targeting RIPK‐mediated necroptosis may be an important therapeutic strategy in transplantation.

Small interfering RNA targeting RelB protects against renal ischemia-reperfusion injury.

Background. Nuclear factor &kgr;B (NF-&kgr;B) has been found to be critical to the pathogenesis of renal ischemia-reperfusion injury (IRI). Using small interfering RNA (siRNA) to silence the expression of RelB, a component of the transcription factors Rel/nuclear factor &kgr;B, may protect renal IRI. Here, we report an siRNA-based treatment of preventing IRI. Methods. Renal IRI was induced in mice by clamping the left renal pedicle for 25 or 35 min. The therapeutic effects of siRNA were evaluated in renal function, histologic examination, and overall survival after lethal IRI. Results. A single injection of RelB siRNA resulted in knockdown of renal RelB expression. In comparison with control mice, levels of blood urea nitrogen and serum creatinine were significantly decreased in mice treated with siRNA. Pathologic examination demonstrated that tissue injury caused by IRI was markedly reduced as a result of RelB siRNA treatment. Additionally, with RelB siRNA treatment, immunohistochemistry showed a significant attenuation of tumor necrosis factor-&agr; expression. Furthermore, survival experiments revealed that more than 90% of control mice died from lethal IRI, whereas 80% of siRNA-pretreated mice survived until the end of the 8-day observation period. Conclusion. Silencing RelB, using siRNA, can significantly attenuate IRI-induced renal dysfunction and protect mice against lethal kidney ischemia, highlighting the potential for siRNA-based clinical therapy.