Neutrophils in cisplatin AKI-mediator or marker?

Inflammation is an important mediator of most forms of acute kidney injury (AKI). Although neutrophils are prominent components of the inflammatory cascade, the precise role of neutrophils in AKI and the mechanisms by which they contribute to AKI remain controversial. In this issue, Deng et al. identify an important cross talk between renal epithelial cells and neutrophils involving the production and action of leukotriene B4 in mediating cisplatin AKI. We discuss the possible explanations for the discrepant findings that have been reported for neutrophils in cisplatin AKI.

NODding off in acute kidney injury with progranulin?

Zhou et al. identify progranulin (PGRN) as a protective mediator that limits inflammation in murine models of acute kidney injury (AKI) and reduces its severity. Deficiency of PGRN was associated with increased inflammation and increased injury in ischemic and nephrotoxic models of AKI. Exogenous PGRN reduced AKI even when administered after AKI was established. Interference in NOD2 pathways is suggested as a possible mechanism for protection. PGRN-based therapeutics might have application in the treatment or prevention of AKI.

TNF-α mediates increased susceptibility to ischemic AKI in diabetes.

Diabetes is a risk factor for the development of acute kidney injury (AKI) in humans and rodents. However, the mechanistic basis for this observation is unknown. The present studies evaluated the role of inflammation and TNF-α in ischemic AKI in a model of type 2 diabetes mellitus (DM). Diabetic (db/db) and nondiabetic (db/+) littermates were subjected to 20 min of bilateral renal ischemia. The nondiabetic mice developed only mild and transient renal dysfunction. In contrast, the equivalent ischemic insult provoked severe and sustained renal dysfunction in the db/db mice. The expression of TNF-α and Toll-like receptor 4 (TLR4) mRNA was measured in the kidneys of diabetic mice before and after renal ischemia; db/db mice exhibited greater increases in TNF-α and TLR4 mRNA expression following ischemia than did db/+. In addition, urinary excretion of TNF-α after ischemia was higher in db/db mice than in db/+ mice. To determine the possible role of TNF-α in mediating the enhanced susceptibility of diabetic mice to ischemic injury, db/db mice were injected with either a neutralizing anti-mouse TNF-α antibody or nonimmune globulin and then subjected to 20 min of bilateral renal ischemia. Treatment of the db/db mice with the TNF-α antibody provided significant protection against the ischemic injury. These data support the view that diabetes increases the susceptibility to ischemia-induced renal dysfunction. This increased susceptibility derives from a heightened inflammatory response involving TNF-α and perhaps TLR4 signaling.

Endogenous IL-10 attenuates cisplatin nephrotoxicity: role of dendritic cells.

Sterile inflammation is associated with tissue injury and organ failure. Recent studies indicate that certain endogenous cytokines and immune cells may limit tissue injury by reducing immune-mediated inflammatory responses. Cisplatin is a commonly used anticancer chemotherapeutic agent but causes acute kidney injury and dysfunction. In a recent study, we showed that renal dendritic cells attenuate cisplatin-induced kidney injury by reducing inflammation. In this study, we investigated the effect of endogenous IL-10 and dendritic cell IL-10 in cisplatin-mediated kidney injury. Cisplatin treatment caused increases in renal IL-10R1 expression and STAT3 phosphorylation. In response to cisplatin treatment, IL-10 knockout mice showed more rapid and greater increases in blood urea nitrogen and serum creatinine compared with wild-type mice, indicating that endogenous IL-10 ameliorates kidney injury in cisplatin nephrotoxicity. Renal infiltration of IFN-γ-producing neutrophils was markedly increased in IL-10 knockout mice compared with wild-type mice. However, IFN-γ neutralization had no impact on renal dysfunction, suggesting IFN-γ-independent mechanisms of tissue injury in cisplatin nephrotoxicity. Renal dendritic cells showed high expression of IL-10 in response to cisplatin treatment. We further investigated the effect of dendritic cell-derived IL-10 in cisplatin nephrotoxicity using a conditional cell ablation approach. Mixed bone marrow chimeric mice lacking IL-10 in dendritic cells showed moderately greater renal dysfunction than chimeric mice positive for IL-10 in dendritic cells. These data demonstrate that endogenous IL-10 reduces cisplatin nephrotoxicity and associated inflammation. Moreover, IL-10 produced by dendritic cells themselves accounts for a portion of the protective effect of dendritic cells in cisplatin nephrotoxicity.

Netrin-1 regulates Th1/Th2/Th17 cytokine production and inflammation through UNC5B receptor and protects kidney against ischemia-reperfusion injury.

Overwhelming evidence suggests that ischemia-reperfusion injury of the kidney is an inflammatory disease mediated by innate and adoptive immune systems. The neuronal guidance molecule netrin-1 was shown to modulate inflammatory responses. Given that ischemic kidney is particularly prone to reperfusion-elicited inflammation, we sought to determine the function of netrin-1 and its receptor UNC5B in ischemia-reperfusion-induced inflammation. Renal ischemia-reperfusion caused a rapid decrease in serum netrin-1 levels. Administration of recombinant netrin-1 before or after renal ischemia-reperfusion reduced kidney injury, apoptosis, monocyte and neutrophil infiltration, and cytokine (IL-6, IL-1beta, and TNF-alpha) and chemokine (MCP-1, macrophage-derived cytokine, monokine-induced IFN-gamma, keratinocyte-derived chemokine, and chemokine with 6 cysteines) production. Analysis for different netrin-1 receptors on leukocytes showed very high expression of UNC5B but not UNC5C, UNC5D, neogenin, or deleted in colorectal cancer. Expression of UNC5A was low. Neutralization of UNC5B receptor reduced netrin-1-mediated protection against renal ischemia-reperfusion injury, and it increased monocyte and neutrophil infiltration, as well as serum and renal cytokine and chemokine production, with increased kidney injury and renal tubular cell apoptosis. Finally, investigation into netrin-1's effect on CD4 T cell stimulation showed suppression of Th1/Th2/Th17 cytokine (IL-2, IL-6, IL-10, IL-13, IL-17, IFN-gamma, IL-4, and TNF-alpha) production in vitro. Our studies demonstrate that netrin-1 acting through UNC5B receptor reduces renal ischemia-reperfusion injury and its associated renal inflammation.

Renal dendritic cells ameliorate nephrotoxic acute kidney injury.

Inflammation contributes to the pathogenesis of acute kidney injury. Dendritic cells (DCs) are immune sentinels with the ability to induce immunity or tolerance, but whether they mediate acute kidney injury is unknown. Here, we studied the distribution of DCs within the kidney and the role of DCs in cisplatin-induced acute kidney injury using a mouse model in which DCs express both green fluorescence protein and the diphtheria toxin receptor. DCs were present throughout the tubulointerstitium but not in glomeruli. We used diphtheria toxin to deplete DCs to study their functional significance in cisplatin nephrotoxicity. Mice depleted of DCs before or coincident with cisplatin treatment but not at later stages experienced more severe renal dysfunction, tubular injury, neutrophil infiltration and greater mortality than nondepleted mice. We used bone marrow chimeric mice to confirm that the depletion of CD11c-expressing hematopoietic cells was responsible for the enhanced renal injury. Finally, mixed bone marrow chimeras demonstrated that the worsening of cisplatin nephrotoxicity in DC-depleted mice was not a result of the dying or dead DCs themselves. After cisplatin treatment, expression of MHC class II decreased and expression of inducible co-stimulator ligand increased on renal DCs. These data demonstrate that resident DCs reduce cisplatin nephrotoxicity and its associated inflammation.

IL-10 from dendritic cells but not from T regulatory cells protects against cisplatin-induced nephrotoxicity.

Interleukin-10 (IL-10), a cytokine with anti-inflammatory effects, is produced by renal parenchymal cells and bone marrow derived cells. Both endogenous and exogenous IL-10 are protective in cisplatin-induced acute kidney injury. However, the source of endogenous IL-10 in cisplatin-induced nephrotoxicity is not clear. Bone marrow chimera experiments in IL10-KO mice indicated that bone marrow derived cells were the primary source of IL-10 in cisplatin nephrotoxicity. Cell specific deletion of IL-10 in T regulatory cells and dendritic cells was accomplished using Foxp3 and CD11c driven cre recombination in IL10flox/flox mice, respectively. Upon treatment with cisplatin, both the IL10flox/flox and the Foxp3YFP-Cre x IL10flox/flox mice developed similar degrees of kidney injury. However, mice with the dendritic cell deletion of IL-10 showed more severe structural and functional changes in the kidney compared to the IL10flox/flox mice. These results indicate that IL-10 from dendritic cells but not from T regulatory cells offers significant endogenous protection against cisplatin induced nephrotoxicity.

Modulation of Inflammatory Responses by Wnt/ß-Catenin Signaling in Dendritic Cells: A Novel Immunotherapy Target for Autoimmunity and Cancer.

The Wnt/ß-catenin pathway is an evolutionarily conserved signaling pathway critical for several biological processes. An aberrant Wnt/ß-catenin signaling is linked to several human diseases. Emerging studies have highlighted the regulatory role of the Wnt/ß-catenin signaling pathway in normal physiological processes of parenchymal and hematopoietic cells. Recent studies have shown that the activation of Wnt/ß-catenin pathway in dendritic cells (DCs) play a critical role in mucosal tolerance and suppression of chronic autoimmune pathologies. Alternatively, tumors activate Wnt/ß-catenin pathway in DCs to induce immune tolerance and thereby evade antitumor immunity through suppression of effector T cell responses and promotion of regulatory T cell responses. Here, we review our work and current understanding of how Wnt/ß-catenin signaling in DCs shapes the immune response in cancer and autoimmunity and discuss how Wnt/ß-catenin pathway can be targeted for successful therapeutic interventions in various human diseases.

Dendritic Cell Protection from Cisplatin Nephrotoxicity Is Independent of Neutrophils.

Cisplatin is a very effective chemotherapeutic agent used against a wide range of solid tumors. A major adverse effect of cisplatin therapy is acute kidney injury (AKI). Neutrophils are reported to infiltrate and exacerbate injury in a wide range of sterile inflammatory models of tissue injury. Here, we studied the kinetics of neutrophil infiltration into kidneys and their role in cisplatin-mediated AKI. Mice treated with cisplatin showed an increase in circulating neutrophils 24 and 48 h after cisplatin administration. Cisplatin treatment caused an increase in kidney leukocytes with neutrophils accounting for the majority of the infiltrating leukocytes. The extent of neutrophil infiltration coincided with the severity of kidney injury and renal dysfunction. To examine the functional relevance of infiltrating neutrophils in cisplatin nephrotoxicity, we depleted neutrophils using a neutrophil-specific antibody (anti-Ly-6G). This antibody resulted in greater than 90% depletion of neutrophils in both the blood and kidney. Of note, depletion of neutrophils had no impact on the extent of cisplatin-induced AKI as compared to non-depleted mice. Earlier, we reported that dendritic cell depletion in CD11c-DTRtg mice causes exacerbation of AKI and a dramatic increase in renal neutrophils. Thus, we also examined the role of neutrophils in dendritic cell-depleted mice treated with cisplatin. Dendritic cell depletion exacerbated AKI in spite of neutrophil depletion. These data demonstrate that cisplatin nephrotoxicity is not mediated by neutrophils and that dendritic cells protect kidneys via neutrophil-independent mechanisms.

TRPM2 mediates ischemic kidney injury and oxidant stress through RAC1.

Ischemia is a leading cause of acute kidney injury. Kidney ischemia is associated with loss of cellular ion homeostasis; however, the pathways that underlie ion homeostasis dysfunction are poorly understood. Here, we evaluated the nonselective cation channel transient receptor potential melastatin 2 (TRPM2) in a murine model of kidney ischemia/reperfusion (I/R) injury. TRPM2-deficient mice were resistant to ischemic injury, as reflected by improved kidney function, reduced histologic damage, suppression of proapoptotic pathways, and reduced inflammation. Moreover, pharmacologic TRPM2 inhibition was also protective against I/R injury. TRPM2 was localized mainly in kidney proximal tubule epithelial cells, and studies in chimeric mice indicated that the effects of TRPM2 are due to expression in parenchymal cells rather than hematopoietic cells. TRPM2-deficient mice had less oxidative stress and lower levels of NADPH oxidase activity after ischemia. While RAC1 is a component of the NADPH oxidase complex, its relation to TRPM2 and kidney ischemic injury is unknown. Following kidney ischemia, TRPM2 promoted RAC1 activation, with active RAC1 physically interacting with TRPM2 and increasing TRPM2 expression at the cell membrane. Finally, inhibition of RAC1 reduced oxidant stress and ischemic injury in vivo. These results demonstrate that TRPM2-dependent RAC1 activation increases oxidant stress and suggest that therapeutic approaches targeting TRPM2 and/or RAC1 may be effective in reducing ischemic kidney injury.

Mechanisms of Cisplatin nephrotoxicity.

Cisplatin is a widely used and highly effective cancer chemotherapeutic agent. One of the limiting side effects of cisplatin use is nephrotoxicity. Research over the past 10 years has uncovered many of the cellular mechanisms which underlie cisplatin-induced renal cell death. It has also become apparent that inflammation provoked by injury to renal epithelial cells serves to amplify kidney injury and dysfunction in vivo. This review summarizes recent advances in our understanding of cisplatin nephrotoxicity and discusses how these advances might lead to more effective prevention.