Renal ischemia-reperfusion injury: new implications of dendritic cell-endothelial cell interactions

Impaired immunoproteasomal function exacerbates renal ischemia-reperfusion injury

Oxidative stress caused by reactive oxygen species (ROS) is involved in the pathogenesis of renal ischemia-reperfusion injury (I/R injury), a major cause of acute kidney injury and delayed graft function (DGF). DGF is an early transplant complication that worsens graft prognosis and patient survival, but the underlying molecular changes are unclear. The proteasome is a multicatalytic enzyme complex that degrades both normal and damaged proteins, and recent studies have revealed that the immunoproteasome, a specific proteasome isoform whose proteolytic activity enhances the generation of antigenic peptides, plays critical roles in the cellular response against oxidative stress. In this study, we demonstrate the impact of the immunoproteasome in human DGF and in a mouse model of I/R injury. In patients with DGF, the expression of β5i, a specific immunoproteasome subunit, was decreased in vascular endothelial cells. In a mouse model, β5i knockout (KO) exacerbated renal I/R injury. KO mice showed greater inflammation, oxidative stress, and endothelial damage compared with wild-type mice. Impaired immunoproteasomal activity also caused increased cell death, ROS production, and expression of inflammatory factors in mouse renal vascular endothelial cells under conditions of hypoxia and reoxygenation. In conclusion, reduced expression of the immunoproteasomal catalytic subunit β5i exacerbates renal I/R injury in vivo, potentially increasing the risk of DGF. Further research targeting β5i expression in DGF could lead to the development of novel therapeutic strategies and biomarkers.

Indoleamine 2,3 Dioxygenase 1-The Potential Link between the Innate Immunity and the Ischemia-Reperfusion-Induced Acute Kidney Injury?

Ischemia-reperfusion injury (IRI) is of the most common causes of acute kidney injury (AKI); nevertheless, the mechanisms responsible for both early kidney injury and the reparative phase are not fully recognised. The inflammatory response following ischemia is characterised by the crosstalk between cells belonging to the innate immune system-dendritic cells (DCs), macrophages, neutrophils, natural killer (NK) cells, and renal tubular epithelial cells (RTECs). A tough inflammatory response can damage the renal tissue; it may also have a protective effect leading to the repair after IRI. Indoleamine 2,3 dioxygenase 1 (IDO1), the principal enzyme of the kynurenine pathway (KP), has a broad spectrum of immunological activity from stimulation to immunosuppressive activity in inflamed areas. IDO1 expression occurs in cells of the innate immunity and RTECs during IRI, resulting in local tryptophan (TRP) depletion and generation of kynurenines, and both of these mechanisms contribute to the immunosuppressive effect. Nonetheless, it is unknown if the above mechanism can play a harmful or preventive role in IRI-induced AKI. Despite the scarcity of literature in this field, the current review attempts to present a possible role of IDO1 activation in the regulation of the innate immune system in IRI-induced AKI.

Dendritic Cells: Versatile Players in Renal Transplantation

Dendritic cells (DCs) induce and regulate adaptive immunity through migrating and maturing in the kidney. In this procedure, they can adopt different phenotypes—rejection-associated DCs promote acute or chronic injury renal grafts while tolerogenic DCs suppress the overwhelmed inflammation preventing damage to renal functionality. All the subsets interact with effector T cells and regulatory T cells (Tregs) stimulated by the ischemia–reperfusion procedure, although the classification corresponding to different effects remains controversial. Thus, in this review, we discuss the origin, maturation, and pathological effects of DCs in the kidney. Then we summarize the roles of divergent DCs in renal transplantation: taking both positive and negative stages in ischemia–reperfusion injury (IRI), switching phenotypes to induce acute or chronic rejection, and orchestrating surface markers for allograft tolerance via alterations in metabolism. In conclusion, we prospect that multidimensional transcriptomic analysis will revolute researches on renal transplantation by addressing the elusive mononuclear phagocyte classification and providing a holistic view of DC ontogeny and subpopulations.

Kidney dendritic cells: fundamental biology and functional roles in health and disease

Dendritic cells (DCs) are chief inducers of adaptive immunity and regulate local inflammatory responses across the body. Together with macrophages, the other main type of mononuclear phagocyte, DCs constitute the most abundant component of the intrarenal immune system. This network of functionally specialized immune cells constantly surveys its microenvironment for signs of injury or infection, which trigger the initiation of an immune response. In the healthy kidney, DCs coordinate effective immune responses, for example, by recruiting neutrophils for bacterial clearance in pyelonephritis. The pro-inflammatory actions of DCs can, however, also contribute to tissue damage in various types of acute kidney injury and chronic glomerulonephritis, as DCs recruit and activate effector T cells, which release toxic mediators and maintain tubulointerstitial immune infiltrates. These actions are counterbalanced by DC subsets that promote the activation and maintenance of regulatory T cells to support resolution of the immune response and allow kidney repair. Several studies have investigated the multiple roles for DCs in kidney homeostasis and disease, but it has become clear that current tools and subset markers are not sufficient to accurately distinguish DCs from macrophages. Multidimensional transcriptomic analysis studies promise to improve mononuclear phagocyte classification and provide a clearer view of DC ontogeny and subsets.

Intermedin protects HUVECs from ischemia reperfusion injury via Wnt/β-catenin signaling pathway

Intermedin (IMD) is a member of the calcitonin gene-related peptide (CGRP) superfamily and a pro-angiogenic factor. In the present study, we identified activation of the Wnt/β-catenin signaling pathway by IMD. Adding CoCl₂ HUVECs was used to establish an in vitro model. The migration of HUVECs was measured by wound healing assays and transwell migration assays. Capillary formation was measured using tube formation assays. Immunocytochemistry (ICC) analysis was used to evaluate VEGF and RAMP2 expression in HUVECs. The relevant signaling molecules were detected with western blot. Our study shows that IMD could promote H/R impaired HUVECs migration and tube formation in vitro. On the other hand, inhibition of Wnt/β-catenin signaling led to the suppression of this promotion of migration and tube formation. This result suggests that Wnt/β-catenin signaling is correlated to IMD induced angiogenesis. Analysis of results from ICC assays indicated that IMD works through increasing levels of VEGF and RAMP2. Meanwhile, the Wnt/β-catenin signaling specific inhibitor IWR-1-endo was shown to down-regulate VEGF and RAMP2 expression. Western blot results further confirmed the signaling mechanism by which IMD promotes angiogenesis. Thus, Wnt/β-catenin signaling plays an important role in IMD induced neovascularization. The data further suggest that the PI3K axis contributes positively downstream.

Enhanced renal ischemia-reperfusion injury in aging and diabetes

The incidence and severity of acute kidney injury is increased in patients with diabetes and with aging. However, the mechanisms involved have not been clearly established. The present study examined the effects of aging and diabetes on the severity of renal ischemia-reperfusion (IR) injury in Sprague-Dawley (SD) and type 2 diabetic (T2DN) rats. T2DN rats develop diabetes at 3 mo of age and progressive proteinuria and diabetic nephropathy as they age from 6 to 18 mo. Plasma creatinine levels after bilateral IR were significantly higher (3.4 ± 0.1 mg/dl) in 18-mo-old elderly T2DN rats than in middle-aged (12 mo) T2DN rats with less severe diabetic nephropathy or young (3 mo) and elderly (18 mo) control SD rats (1.5 ± 0.2, 1.8 ± 0.1, and 1.7 ± 0.1 mg/dl, respectively). Elderly T2DN rats exhibited a greater fall in medullary blood flow 2 h following renal IR and a more severe and prolonged decline in glomerular filtration rate than middle-aged T2DN and young or elderly SD rats. The basal expression of the adhesion molecules ICAM-1 and E-selectin and the number of infiltrating immune cells was higher in the kidney of elderly T2DN than age-matched SD rats or young and middle-aged T2DN rats before renal IR. These results indicate that elderly T2DN rats with diabetic nephropathy are more susceptible to renal IR injury than diabetic animals with mild injury or age-matched control animals. This is associated with increased expression of ICAM-1, E-selectin and immune cell infiltration, renal medullary vasocongestion, and more prolonged renal medullary ischemia.

The Role of Dendritic and Endothelial Cells in Cardiorenal Syndrome

BACKGROUNDS

Dendritic cells (DCs) are antigen-presenting cells that play a central role in innate and adaptive immune responses; however, the cross talk between cardiac and renal DCs in cardiorenal syndrome (CRS) has not yet been fully elucidated. In this setting, endothelial cells (ECs) also contribute to immune responses.

SUMMARY

DC and EC activation and dysfunction have a central role in the pathogenesis of CRS. Regarding immune responses in CRS, it is unknown whether ECs may serve as antigen-presenting cells or act synergistically with DCs to actively participate in innate and adaptive immune responses. This review first focuses on the burden of concomitant heart and renal DCs in the context of CRS; it examines what is known of DCs in animal models, and proposes a central role for DCs in all types of CRS. Second, this review briefly describes the role of ECs in the context of CRS. Key Messages: Understanding the role of DCs and ECs in immune response could lead to the development of novel therapies for the prevention and treatment of CRS.

Vitamin C Attenuates Hemorrhagic Shock-induced Dendritic Cell-specific Intercellular Adhesion Molecule 3-grabbing Nonintegrin Expression in Tubular Epithelial Cells and Renal Injury in Rats

BACKGROUND

The expression of dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN) in renal tubular epithelial cells has been thought to be highly correlated with the occurrence of several kidney diseases, but whether it takes place in renal tissues during hemorrhagic shock (HS) is unknown. The present study aimed to investigate this phenomenon and the inhibitory effect of Vitamin C (VitC).

METHODS

A Sprague-Dawley rat HS model was established in vivo in this study. The expression level and location of DC-SIGN were observed in kidneys. Also, the degree of histological damage, the concentrations of tumor necrosis factor-μ and interleukin-6 in the renal tissues, and the serum concentration of blood urea nitrogen and creatinine at different times (2-24 h) after HS (six rats in each group), with or without VitC treatment before resuscitation, were evaluated.

RESULTS

HS induced DC-SIGN expression in rat tubular epithelial cells. The proinflammatory cytokine concentration, histological damage scores, and functional injury of kidneys had increased. All these phenomena induced by HS were relieved when the rats were treated with VitC before resuscitation.

CONCLUSIONS

The results of the present study illustrated that HS could induce tubular epithelial cells expressing DC-SIGN, and the levels of proinflammatory cytokines in the kidney tissues improved correspondingly. The results also indicated that VitC could suppress the DC-SIGN expression in the tubular epithelial cells induced by HS and alleviate the inflammation and functional injury in the kidney.

Hypothermic Oxygenated Perfusion (HOPE) downregulates the immune response in a rat model of liver transplantation

OBJECTIVE

To evaluate the impact of a novel oxygenated perfusion approach on rejection after orthotopic liver transplantation (OLT).

BACKGROUND

Hypothermic oxygenated perfusion (HOPE) was designed to prevent graft failure after OLT. One of the mechanisms is downregulation of Kupffer cells (in situ macrophages). We, therefore, designed experiments to test the effects of HOPE on the immune response in an allogeneic rodent model of nonarterialized OLT.

METHODS

Livers from Lewis rats were transplanted into Brown Norway rats to induce liver rejection in untreated recipients within 4 weeks. Next, Brown Norway recipients were treated with tacrolimus (1 mg/kg), whereas in a third group, liver grafts from Lewis rats underwent HOPE or deoxygenated machine perfusion for 1 hour before implantation, but recipients received no immunosuppression. In a last step, low-dose tacrolimus treatment (0.3 mg/kg) was assessed with and without HOPE.

RESULTS

Allogeneic OLT without immunosuppression led to death within 3 weeks after nonarterialized OLT due to severe acute rejection. Full-dose tacrolimus prevented rejection, whereas low-dose tacrolimus led to graft fibrosis within 4 weeks. HOPE treatment without immunosuppression also protected from lethal rejection. The combination of low-dose tacrolimus and 1-hour HOPE resulted in 100% survival within 4 weeks without any signs of rejection.

CONCLUSIONS

We demonstrate that allograft treatment by HOPE not only protects against preservation injury but also impressively downregulates the immune system, blunting the alloimmune response. Therefore, HOPE may offer many beneficial effects, not only to rescue marginal grafts but also by preventing rejection and the need for immunosuppression.

Slit2-Robo signaling in inflammation and kidney injury

Acute kidney injury is an increasingly common global health problem and is associated with severe morbidity and mortality. In addition to facing high mortality rates, the survivors of acute kidney injury are at increased risk of developing chronic kidney disease and end-stage renal disease. Renal ischemia-reperfusion injury (IRI) is the most common cause of acute kidney injury, and results from impaired delivery of oxygen and nutrients to the kidney. Massive leukocyte influx into the post-ischemic kidney is one of the hallmarks of IRI. The recruited leukocytes exacerbate tissue damage and, if uncontrolled, initiate the progressive changes that lead to renal fibrosis and chronic kidney disease. Early on, recruitment and activation of platelets promotes microthrombosis in the injured kidney, further exacerbating kidney damage. The diversity, complexity, and multiplicity of pathways involved in leukocyte recruitment and platelet activation make it extremely challenging to control these processes, and past efforts have met with limited success in human trials. A generalized strategy to inhibit infiltration of inflammatory leukocytes and platelets, thereby reducing inflammation and injury, may prove to be more beneficial. In this review, we summarize recent findings demonstrating that the neuronal guidance cues, Slit and Roundabout (Robo), prevent the migration of multiple leukocyte subsets towards diverse inflammatory chemoattractants, and have potent anti-platelet functions in vitro and in vivo. These properties uniquely position Slit2 as a novel therapeutic that could be used to prevent acute kidney injury associated with IRI.

Immune cells in experimental acute kidney injury

Acute kidney injury (AKI) prolongs hospital stay and increases mortality in various clinical settings. Ischaemia-reperfusion injury (IRI), nephrotoxic agents and infection leading to sepsis are among the major causes of AKI. Inflammatory responses substantially contribute to the overall renal damage in AKI. Both innate and adaptive immune systems are involved in the inflammatory process occurring in post-ischaemic AKI. Proinflammatory damage-associated molecular patterns, hypoxia-inducible factors, adhesion molecules, dysfunction of the renal vascular endothelium, chemokines, cytokines and Toll-like receptors are involved in the activation and recruitment of immune cells into injured kidneys. Immune cells of both the innate and adaptive immune systems, such as neutrophils, dendritic cells, macrophages and lymphocytes contribute to the pathogenesis of renal injury after IRI, and some of their subpopulations also participate in the repair process. These immune cells are also involved in the pathogenesis of nephrotoxic AKI. Experimental studies of immune cells in AKI have resulted in improved understanding of the immune mechanisms underlying AKI and will be the foundation for development of novel diagnostic and therapeutic targets. This Review describes what is currently known about the function of the immune system in the pathogenesis and repair of ischaemic and nephrotoxic AKI.

A novel mechanism of anti-T-lymphocyte globulin mediated by fractalkine in renal ischemia-reperfusion injury in rats

BACKGROUND

Ischemia-reperfusion injury (IRI) is among the main challenges in kidney transplantation. It causes delayed graft function and graft loss in long-term follow-up studies. Anti-T lymphocyte globulin (ATG), a common induction immunosuppressive, has been used in kidney transplantation to prevent rejection. Fractalkine (FKN) is among the main chemokines involved in IRI. This study was designed to identify the relationship between ATG and FKN after warm ischemia in rat kidneys.

METHODS

Rats were divided into three groups: Control, IRI+normal saline(NS) and IRI+ATG. After IRI was initiated, rats received a dose of ATG or NS during surgery as well as two more doses at 24 and 48 hours after surgery. All rats were humanely killed at 72 hours.

RESULTS

The concentration of FKN as well as dendritic cells (DC) and macrophages were lower in both peripheral blood and the injured kidney among ATG-treated versus control rats. Additionally cell necrosis, cytoplasmic vacuolization, cast formation, and tubular dilatation were improved among ATG-treated rats. Serum creatinine levels were lower in rats that received ATG.

CONCLUSION

ATG depleted the concentration of FKN, which inhibits migrations of DCs and macrophages into the kidney, and reduces IRI-related pathology.

Nephroprotective effects of TVP1022, a non-MAO inhibitor S-isomer of rasagiline, in an experimental model of diabetic renal ischemic injury

Ischemic acute kidney injury (iAKI) in diabetes mellitus is associated with a rapid deterioration of kidney function, more than in nondiabetic subjects. TVP1022, a non-MAO inhibitor S-isomer of rasagiline, possesses antioxidative and antiapoptotic activities. The current study examines the effects of TVP1022 and tempol on iAKI in diabetic rats. Diabetes was induced by streptozotocin. iAKI was induced by clamping the left renal artery for 30 min in both diabetic and nondiabetic rats. The right intact kidney served as a control. Forty-eight hours following ischemia, urinary flow (V), sodium excretion (UNaV), and glomerular filtration rate (GFR) in both ischemic and nonischemic kidneys were determined. The nephroprotective effects of tempol and TVP1022 were examined in these rats. Hematoxylin and eosin staining, 4-hydroxynonenal (4-HNE) immunofluorescence, and nitrotyrosine immunohistochemistry were performed on renal tissues of the various experimental groups. Compared with normoglycemic rats, iAKI in diabetic animals caused more profound reductions in V, UNaV, and GFR. Tempol and TVP1022 treatment increased GFR two- and four-fold in diabetic ischemic kidney, respectively. Besides hemodynamic perturbations, iAKI markedly increased renal immunoreactive 4-HNE and nitrotyrosine staining in both diabetic and nondiabetic rats. Moreover, iAKI increased medullary necrosis, congestion, and casts. Noteworthy, these increases were to a larger extent in ischemic diabetic kidneys. TVP1022, and to a lesser extent tempol, decreased nitrotyrosine and 4-HNE immunoreactivities and necrosis and cast formation in the renal medulla. TVP1022 treatment improves renal dysfunction and histological changes in an iAKI diabetic model and suggests a role for TVP1022 therapy in kidney injury.

Endothelial cell preservation at hypothermic to normothermic conditions using clinical and experimental organ preservation solutions

INTRODUCTION

Endothelial barrier function is pivotal for the outcome of organ transplantation. Since hypothermic preservation (gold standard) is associated with cold-induced endothelial damage, endothelial barrier function may benefit from organ preservation at warmer temperatures. We therefore assessed endothelial barrier integrity and viability as function of preservation temperature and perfusion solution, and hypothesized that endothelial cell preservation at subnormothermic conditions using metabolism-supporting solutions constitute optimal preservation conditions.

METHODS

Human umbilical vein endothelial cells (HUVEC) were preserved at 4-37°C for up to 20 h using Ringer's lactate, histidine-tryptophan-ketoglutarate solution, University of Wisconsin (UW) solution, Polysol, or endothelial cell growth medium (ECGM). Following preservation, the monolayer integrity, metabolic capacity, and ATP content were determined as positive parameters of endothelial cell viability. As negative parameters, apoptosis, necrosis, and cell activation were assayed. A viability index was devised on the basis of these parameters.

RESULTS

HUVEC viability and barrier integrity was compromised at 4°C regardless of the preservation solution. At temperatures above 20°C, the cells' metabolic demands outweighed the preservation solutions' supporting capacity. Only UW maintained HUVEC viability up to 20°C. Despite high intracellular ATP content, none of the solutions were capable of sufficiently preserving HUVEC above 20°C except for ECGM.

CONCLUSION

Optimal HUVEC preservation is achieved with UW up to 20°C. Only ECGM maintains HUVEC viability at temperatures above 20°C.

Therapeutic potential of 7,8-dimethoxycoumarin on cisplatin- and ischemia/reperfusion injury-induced acute renal failure in rats

This study was designed to investigate the role of 7,8-dimethoxycoumarin on cisplatin- and ischemia/reperfusion (I/R)-induced acute renal failure in rats. Acute renal failure was induced in rats by administration of a single dose of cisplatin (CP) (6 mg/kg, intraperitoneally on day 6) and occlusion of the left renal artery for 45 min (I) and opened for the next 24 h (R). The drug samples of 7,8-dimethoxycoumarin (DMC, 50, 75, and 100 mg/kg) and cyclosporin A (50 μM/kg) were administered orally for six consecutive days. Administration of a single dose of cisplatin and I/R event has significantly raised blood urea nitrogen and creatinine, N-acetyl beta-D: -glucosaminidase, and thiobarbituric acid reactive substances but decreased FrNa, creatinine clearance, reduced glutathione (GSH), mitochondrial cytochrome c oxidase, and adenosine triphosphate levels. Further, pretreatment of DMC (50, 75, and 100 mg/kg, p.o., for six consecutive days) has ameliorated the CP- and I/R-induced biochemical and histopathological changes in a dose-dependent manner. Furthermore, 75 and 100 mg/kg of 7,8-dimethoxycoumarin has shown to possess the significant renoprotective effect similar to that of the cyclosporin A-treated group which served as positive control. Based on the results of the present study, it has been concluded that 7,8-dimethoxycoumarin protects the kidney against the CP and I/R injury via antioxidant, anti-inflammatory, and inactivation of mitochondrial permeability transition pore opening.

Role of dendritic cells in cardiovascular diseases

Dendritic cells (DCs) are potent antigen-presenting cells that bridge innate and adaptive immune responses. Recent work has elucidated the DC life cycle, including several important stages such as maturation, migration and homeostasis, as well as DC classification and subsets/locations, which provided etiological insights on the role of DCs in disease processes. DCs have a close relationship to endothelial cells and they interact with each other to maintain immunity. DCs are deposited in the atherosclerotic plaque and contribute to the pathogenesis of atherosclerosis. In addition, the necrotic cardiac cells induced by ischemia activate DCs by Toll-like receptors, which initiate innate and adaptive immune responses to renal, hepatic and cardiac ischemia reperfusion injury (IRI). Furthermore, DCs are involved in the acute/chronic rejection of solid organ transplantation and mediate transplant tolerance as well. Advancing our knowledge of the biology of DCs will aid development of new approaches to treat many cardiovascular diseases, including atherosclerosis, cardiac IRI and transplantation.

Kidney dendritic cells in acute and chronic renal disease

Dendritic cells are not only the master regulators of adaptive immunity, but also participate profoundly in innate immune responses. Much has been learned about their basic immunological functions and their roles in various diseases. Comparatively little is still known about their role in renal disease, despite their obvious potential to affect immune responses in the kidney, and immune responses that are directed against renal components. Kidney dendritic cells form an abundant network in the renal tubulointerstitium and constantly survey the environment for signs of injury or infection, in order to alert the immune system to the need to initiate defensive action. Recent studies have identified a role for dendritic cells in several murine models of acute renal injury and chronic nephritis. Here we summarize the current knowledge on the role of kidney dendritic cells that has been obtained from the study of murine models of renal disease.

Increased asymmetric dimethylarginine serum levels are associated with acute rejection in kidney transplant recipients

Asymmetric dimethylarginine (ADMA) has been identified as a marker of endothelial dysfunction and an independent risk factor for cardiovascular events in uremic subjects. This study evaluated ADMA plasma levels in kidney transplant recipients. ADMA levels were serially measured during the first year posttransplantation in 41 recipients treated with cyclosporine regimen (CY), sirolimus (SIR), or low-dose cyclosporine plus everolimus (E). Homocysteine, C reactive protein (CRP), nitric oxide (NO), and standard routine laboratory analyses were determined serially. ADMA significantly increased at 6 months posttransplantation, but was significantly lower among patients on SIR or E. NO was only slightly reduced in patients with increased ADMA levels. Interestingly, ADMA was significantly increased during the first 4 days posttransplantation in patients who experienced acute rejection during the first 6 months after transplantation. The same group of patients demonstrated higher levels of CRP and systolic blood pressure before transplantation. Our results demonstrated that ADMA was increased in patients on CY at 6 months. When increased soon after transplantation ADMA may be associated with episodes of acute rejection in kidney transplant recipients. The presence of elevated systolic blood pressure, as well as CRP and ADMA levels, suggested a role for endothelial dysfunction in the development of acute rejection episodes among deceased donor kidney transplant recipients.

Modulation of inflammatory response by selective inhibition of cyclooxygenase-1 and cyclooxygenase-2 in acute kidney injury

OBJECTIVE AND DESIGN

This work explored the role of inhibition of cyclooxygenases (COXs) in modulating the inflammatory response triggered by acute kidney injury.

MATERIAL

C57Bl/6 mice were used.

TREATMENT

Animals were treated or not with indomethacin (IMT) prior to injury (days -1 and 0).

METHODS

Animals were subjected to 45 min of renal pedicle occlusion and sacrificed at 24 h after reperfusion. Serum creatinine and blood urea nitrogen, reactive oxygen species (ROS), kidney myeloperoxidase (MPO) activity, and prostaglandin E2 (PGE(2)) levels were analyzed. Tumor necrosis factor (TNF)-alpha, t-bet, interleukin (IL)-10, IL-1beta, heme oxygenase (HO)-1, and prostaglandin E synthase (PGES) messenger RNA (mRNA) were studied. Cytokines were quantified in serum.

RESULTS

IMT-treated animals presented better renal function with less acute tubular necrosis and reduced ROS and MPO production. Moreover, the treatment was associated with lower expression of TNF-alpha, PGE(2), PGES, and t-bet and upregulation of HO-1 and IL-10. This profile was mirrored in serum, where inhibition of COXs significantly decreased interferon (IFN)-gamma, TNF-alpha, and IL-12 p70 and upregulated IL-10.

CONCLUSIONS

COXs seem to play an important role in renal ischemia and reperfusion injury, involving the secretion of pro-inflammatory cytokines, activation of neutrophils, and ROS production. Inhibition of COX pathway is intrinsically involved with cytoprotection.

The interaction between ischemia-reperfusion and immune responses in the kidney

Kidney ischemia-reperfusion injury (IRI) engages both the innate and adaptive immune responses. Cellular mediators of immunity, such as dendritic cells, neutrophils, macrophages, natural killer T, T, and B cells, contribute to the pathogenesis of renal injury after IRI. Postischemic kidneys express increased levels of adhesion molecules on endothelial cells and toll-like receptors on tubular epithelial cells. Soluble components of the immune system, such as complement activation proteins and cytokines, also participate in injury/repair of postischemic kidneys. Experimental studies on the immune response in kidney IRI have resulted in better understanding of the mechanisms underlying IRI and led to the discovery of novel therapeutic and diagnostic targets.

The innate immune response in ischemic acute kidney injury

Kidney ischemia reperfusion injury is a major cause of morbidity in both allograft and native kidneys. Ischemia reperfusion-induced acute kidney injury is characterized by early, alloantigen-independent inflammation. Major components of the innate immune system are activated and participate in the pathogenesis of acute kidney injury, plus prime the allograft kidney for rejection. Soluble members of innate immunity implicated in acute kidney injury include the complement system, cytokines, and chemokines. Toll-like receptors (TLRs) are also important contributors. Effector cells that participate in acute kidney injury include the classic innate immune cells, neutrophils and macrophages. Recent data has unexpectedly identified lymphocytes as participants of early acute kidney injury responses. In this review, we will focus on immune mediators that participate in the pathogenesis of ischemic acute kidney injury.

Endothelial cells in allograft rejection

In organ transplantation, blood borne cells and macromolecules (e.g., antibodies) of the host immune system are brought into direct contact with the endothelial cell lining of graft vessels. In this location, graft endothelial cells play several roles in allograft rejection, including the initiation of rejection responses by presentation of alloantigen to circulating T cells; the development of inflammation and thrombosis; and as targets of injury and agents of repair.

Endothelial cells in allograft rejection

In organ transplantation, blood borne cells and macromolecules (e.g., antibodies) of the host immune system are brought into direct contact with the endothelial cell lining of graft vessels. In this location, graft endothelial cells play several roles in allograft rejection, including the initiation of rejection responses by presentation of alloantigen to circulating T cells; the development of inflammation and thrombosis; and as targets of injury and agents of repair.

Renal ischemia: does sex matter?

Renal ischemia is a common complication in the perioperative period that leads to a high rate of morbidity and mortality. As in other forms of ischemia (i.e., cardiac, neurologic), the incidence and outcome of renal ischemia is strikingly sex-specific. Sexual dimorphism in response to renal injury has been noted for many years, but is now the subject of both clinical and experimental research. Clinically, women experience a lower incidence of perioperative acute renal failure, with the exception of cardiac surgery. Experimental science is now producing tantalizing clues that sex steroids, both male and female, play a role in the kidney's response to ischemia. In this review, we evaluated sex differences in perioperative renal failure and in the pathophysiology of renal ischemia/reperfusion injury. Although much work remains to characterize the biological mechanisms involved, the data are sufficient to support consideration of gender and the use of medications that impact steroid availability in the perioperative plan of care.

Targeted disruption of the meprin metalloproteinase beta gene protects against renal ischemia-reperfusion injury in mice

Meprins are membrane-bound and secreted metalloproteinases consisting of alpha- and/or beta-subunits that are highly expressed in mouse kidney proximal tubules. Previous studies have implied that the meprin alpha/beta-isoform is deleterious when renal tissue is subjected to ischemia-reperfusion (I/R). To delineate the roles of the meprin isoforms in renal disease, we subjected mice deficient in meprin-beta (KO) and their wild-type (WT) counterparts to I/R. WT mice were markedly more susceptible to renal injury after I/R than the meprin-beta KO mice as determined by blood urea nitrogen levels. Urinary levels of inflammatory cytokines IL-6 and KC (CXCL1) were significantly higher in WT compared with meprin-beta KO mice by 6 h post-I/R. At 96 h postischemia, kidney mRNA expression levels for tumor necrosis factor-alpha, transforming growth factor-beta, inducible nitric oxide synthase, and heat shock protein-27 were significantly higher in the WT than meprin-beta KO mice. For WT mice subjected to I/R, there was a rapid (3 h) redistribution of meprin beta-subunits in cells in S3 segments of proximal tubules, followed by shedding of apical cell membrane and detachment of cells. These studies indicate that meprin-beta is important in the pathogenesis of renal injury following I/R and that the redistribution of active meprin-alpha/beta is a major contributor to renal injury and subsequent inflammation.

Ischemia-reperfusion and immediate T cell responses

The pathogenesis of ischemia-reperfusion injury (IRI) is complex and not well understood. Inflammation plays an important role in IRI, with involvement of leukocytes, adhesion molecules, chemokines and cytokines. Emerging data suggest a role of T cells as mediators of IRI both in renal and extra-renal organs. Divergent roles of T cell subsets have also been elucidated, suggesting a more complicated role of T cells in the different phases of IRI. This review presents recent evidence from various animal models that advances our understanding of the role T cells play in IRI. These findings entertain the possibility of using immunotherapeutic agents for the prevention and treatment of IRI.

Characterization of donor dendritic cells and enhancement of dendritic cell efflux with CC-chemokine ligand 21: a novel strategy to prolong islet allograft survival

Dendritic cells (DCs) are the most potent antigen-presenting cells, yet little data are available on the differential characteristics of donor and recipient DCs (dDCs and rDCs, respectively) during the process of islet allograft rejection. DTR-GFP-DC mice provide a novel tool to monitor DC trafficking and characteristics during allograft rejection. We show rapid migration of dDCs to recipient lymphoid tissues as early as 3 h post-islet allotransplantation. Compared with rDCs, dDCs express different patterns of chemokine receptors, display differential proliferative capacity, and exhibit a higher level of maturity; these findings could be attributed to the effects of injury that dDCs undergo during islet cell preparation and engraftment. Intriguingly, we detected dDCs in the spleen of recipients long after rejection of islet allografts. Given that dDCs express high levels of CCR7, islets were cultured before transplant with the ligand for CCR7 (CCL21). This novel method, which enabled us to enhance the efflux of dDCs from islet preparations, resulted in a prolongation of islet allograft survival in immunocompetent recipients. This study introduces dDCs and rDCs as two distinct types of DCs and provides novel data with clinical implications to use chemokine-based DC-depleting strategies to prolong islet allograft survival.