GM-CSF Promotes Macrophage Alternative Activation after Renal Ischemia/Reperfusion Injury

After kidney ischemia/reperfusion (I/R) injury, monocytes home to the kidney and differentiate into activated macrophages. Whereas proinflammatory macrophages contribute to the initial kidney damage, an alternatively activated phenotype can promote normal renal repair. The microenvironment of the kidney during the repair phase mediates the transition of macrophage activation from a proinflammatory to a reparative phenotype. In this study, we show that macrophages isolated from murine kidneys during the tubular repair phase after I/R exhibit an alternative activation gene profile that differs from the canonical alternative activation induced by IL-4–stimulated STAT6 signaling. This unique activation profile can be reproduced in vitro by stimulation of bone marrow-derived macrophages with conditioned media from serum-starved mouse proximal tubule cells. Secreted tubular factors were found to activate macrophage STAT3 and STAT5 but not STAT6, leading to induction of the unique alternative activation pattern. Using STAT3-deficient bone marrow-derived macrophages and pharmacologic inhibition of STAT5, we found that tubular cell-mediated macrophage alternative activation is regulated by STAT5 activation. Both in vitro and after renal I/R, tubular cells expressed GM-CSF, a known STAT5 activator, and this pathway was required for in vitro alternative activation of macrophages by tubular cells. Furthermore, administration of a neutralizing antibody against GM-CSF after renal I/R attenuated kidney macrophage alternative activation and suppressed tubular proliferation. Taken together, these data show that tubular cells can instruct macrophage activation by secreting GM-CSF, leading to a unique macrophage reparative phenotype that supports tubular proliferation after sterile ischemic injury.     

Kidney tubular epithelium is restored without replacement with bone marrow-derived cells during repair after ischemic injury

The kidney has the ability to restore the structural and functional integrity of the proximal tubule, which undergoes extensive epithelial cell death after prolonged exposure to ischemia. In order to study the role that adult bone marrow-derived stem cells might play in kidney remodeling after injury, we employed a murine model of ischemia/reperfusion (I/R) injury in which the degree of injury, dysfunction, repair, tubular cell proliferation and functional recovery have been characterized [Park KM, et al, J Biol Chem 276:11870-11876, 2001]. We generated chimeric mice using marrow from mice expressing the bacterial LacZ gene, or the enhanced green fluorescence protein (eGFP) gene, or from male mice transplanted into female mice. The establishment of chimerism was confirmed at 6 weeks following transplantation in each case. I/R injury was induced in chimeric mice by occluding the renal arteries and veins with microaneurysm clamps for 30 minutes. After functional recovery in the eGFP chimeras, although there were many interstitial cells, no tubular cells were derived from bone marrow cells. In the bacterial beta-galactosidase (beta-gal) chimeric mice we found evidence of mammalian (endogenous) beta-gal by 5-bomo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-gal) staining, but not bacterial beta-gal in tubule cells. Detection of the Y chromosome by fluorescence in situ hybridization (FISH) in the postischemic kidneys of gender-mismatched chimeras revealed Y chromosome positivity only in the nuclei of interstitial cells, when scrutinized by deconvolution microscopy. In our model of I/R injury there was a large amount of proliferation of surviving, injured tubular cells indicating that the injured tubule is repopulated by daughter cells of surviving tubular cells. Analysis of the phenotype of interstitial and vascular cells following I/R injury revealed small numbers of peritubular endothelial cells to be derived from bone marrow cells that may serve in the repair process.     

HCaRG accelerates tubular repair after ischemic kidney injury

The repair of the kidney after ischemia/reperfusion injury involves proliferation of proximal tubular epithelial cells as well as cell migration and differentiation. Immediately after reperfusion, expression of hypertension-related calcium-regulated gene (HCaRG/COMMD5) decreases, but its expression increases even higher than baseline during repair. HCaRG inhibits proliferation and accelerates wound healing and differentiation in cultured cells, but whether HCaRG can stimulate renal repair after ischemia/reperfusion injury is unknown. Here, transgenic mice overexpressing human HCaRG survived longer and recovered renal function faster than littermate controls after ischemia/reperfusion (64% versus 25% survival at 7 days). Proliferation of proximal tubular epithelial cells stopped earlier after ischemia/reperfusion injury, E-cadherin levels recovered more rapidly, and vimentin induction abated faster in transgenic mice. HCaRG overexpression also reduced macrophage infiltration and inflammation after injury. Taken together, these data suggest that HCaRG accelerates repair of renal proximal tubules by modulating cell proliferation of resident tubular epithelial cells and by facilitating redifferentiation.     

Direct targeting of fibroblast growth factor-inducible 14 protein protects against renal ischemia reperfusion injury

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is known to have pivotal roles in various inflammatory processes. The TWEAK receptor, fibroblast growth factor-inducible 14 (Fn14), has various unique functions under physiological and pathological conditions; however, the therapeutic potential of its direct targeting remains unknown. Here, we found that Fn14 expression was highly upregulated in ischemic renal tissues and tubular epithelial cells of patient biopsies and experimental animal models of renal injury. To clarify the function of Fn14 in ischemia reperfusion injury, we coincubated renal tubular cells with ITEM-2, an anti-Fn14 blocking monoclonal antibody, and found that it inhibited the production of proinflammatory cytokines and chemokines after injury. Furthermore, Fn14 blockade downregulated the local expression of several proinflammatory mediators, reduced accumulation of neutrophils and macrophages in ischemic tissues, and inhibited tubular cell apoptosis. Importantly, Fn14 blockade attenuated the development of chronic fibrosis after ischemia reperfusion injury and significantly prolonged the survival of lethally injured mice. Thus, we conclude that Fn14 is a critical mediator in the pathogenesis of ischemia reperfusion injury.     

Zag expression during aging suppresses proliferation after kidney injury

Recovery after acute kidney injury is impaired in the elderly, but mechanistic information regarding why this occurs is limited. In this study, aged mouse kidneys displayed a reduced epithelial proliferative reserve in vivo and in vitro. Microarray analysis identified increased expression of zinc-alpha (2)-glycoprotein (Zag) in aged proximal tubular cells. The addition of recombinant Zag to primary renal epithelial cell cultures decreased proliferation, whereas knockdown of Zag increased proliferation. In vivo, systemic small interference RNA suppressed expression of Zag in the mouse proximal tubule; this increased the rate of epithelial cell proliferation after renal ischemia/reperfusion in aged mice but also increased parenchymal fibrosis. These results demonstrate that increased Zag expression in the aged kidney acts to suppress the proliferative response to injury and introduce Zag as a modifier of the aging phenotype.     

Dedifferentiation and proliferation of surviving epithelial cells in acute renal failure

In contrast to the heart or brain, the kidney can completely recover from an ischemic or toxic insult that results in cell death. During recovery from ischemia/reperfusion injury, surviving tubular epithelial cells dedifferentiate and proliferate, eventually replacing the irreversibly injured tubular epithelial cells and restoring tubular integrity. Repair of the kidney parallels kidney organogenesis in the high rate of DNA synthesis and apoptosis and in patterns of gene expression. As has been shown by proliferating cell nuclear antigen and 5-bromo 2'-deoxyuridine labeling studies and, in unpublished studies, by counting mitotic spindles identified by labeling with antitubulin antibody, the proliferative response is rapid and extensive, involving many of the remaining cells of the proximal tubule. This extensive proliferative capacity is interpreted to reflect the intrinsic ability of the surviving epithelial cell to adapt to the loss of adjacent cells by dedifferentiating and proliferating. Adhesion molecules likely play important roles in the regulation of renal epithelial cell migration, proliferation, and differentiation, as do cytokines and chemokines. Better understanding of all of the characteristics resulting in dedifferentiation and proliferation of the proximal tubule epithelial cell and cell-cell and cell-matrix interactions important for this repair function will lead to novel approaches to therapies designed to facilitate the processes of recovery in humans.     

祖细胞样肾小管细胞在急性肾小管坏死修复中的作用

目的 观察大鼠缺血性急性肾小管坏死（ATN）后肾脏内溴脱氧尿嘧啶核苷（BrdU）及Pax2阳性细胞的动态变化,探讨祖细胞样肾小管细胞在ATN修复过程中的作用。 方法 钳夹SD大鼠左侧肾动脉60 min后再开放血流,建立缺血性ATN模型。给予细胞分裂增殖标记物BrdU负荷,分别于术后第1、3、5、7、14、21、28天收获肾脏标本,进行BrdU和肾源性标记物Pax2免疫组织化学染色,以及BrdU和Pax2、间充质细胞标记物波形蛋白（vimentin）、细胞凋亡标记物活化caspase-3的双重染色,观察BrdU阳性细胞的数量和分布变化。 结果 ATN组术后左肾出现明显的近端肾小管上皮细胞广泛性坏死,BrdU阳性细胞明显增加,第3天达到高峰,显著高于假手术对照组和右肾（P < 0.01）。而右肾BrdU阳性细胞亦显著高于假手术对照组（P < 0.01）。双重染色显示BrdU阳性细胞同时表达Pax2和波形蛋白,但未见同时表达活化的caspase-3。 结论 大鼠在经历缺血性ATN后,肾脏内祖细胞样小管细胞被动员。其修复可能是通过逆分化、增殖和再分化过程来完成的。而细胞因子可能在这过程中起着调控作用。     

Retinoic Acid Signaling Coordinates Macrophage-Dependent Injury and Repair after AKI

Retinoic acid (RA) has been used therapeutically to reduce injury and fibrosis in models of AKI, but little is known about the regulation of this pathway and what role it has in regulating injury and repair after AKI. In these studies, we show that RA signaling is activated in mouse and zebrafish models of AKI, and that these responses limit the extent of injury and promote normal repair. These effects were mediated through a novel mechanism by which RA signaling coordinated the dynamic equilibrium of inflammatory M1 spectrum versus alternatively activated M2 spectrum macrophages. Our data suggest that locally synthesized RA represses proinflammatory macrophages, thereby reducing macrophage-dependent injury post-AKI, and activates RA signaling in injured tubular epithelium, which in turn promotes alternatively activated M2 spectrum macrophages. Because RA signaling has an essential role in kidney development but is repressed in the adult, these findings provide evidence of an embryonic signaling pathway that is reactivated after AKI and involved in reducing injury and enhancing repair.     

TGR5/Cathepsin E signaling regulates macrophage innate immune activation in liver ischemia and reperfusion injury

The role and underlying mechanism of plasma membrane-bound G protein-coupled bile acid receptor (TGR5) in regulating macrophage innate immune activation during liver ischemia and reperfusion (IR) injury remains largely unclear. Here, we demonstrated that TGR5 depletion in myeloid cells aggravated liver injury with increased macrophage infiltration and enhanced inflammation in livers post-IR. While TGR5 deficiency enhanced mobility and proinflammatory M1 polarization of macrophages, TGR5 agonist enhanced the anti-inflammatory effect of TGR5 both in vivo and in vitro. Microarray profiling revealed that TGR5-deficient macrophages exhibited enhanced proinflammatory characteristics and cathepsin E (Cat E) was the most upregulated gene. Knockdown of Cat E abolished the enhanced mobility and shift of macrophage phenotypes induced by TGR5 depletion. Moreover, Cat E knockdown attenuated liver IR injury and liver inflammation in myeloid TGR5-deficient mice. In patients undergoing partial hepatectomy, IR stress promoted TGR5 activation of CD11b+ cells in peripheral blood mononuclear cells, correlating with the shift in macrophage M2 polarization. Ursodeoxycholic acid administration enhanced TGR5 activation and the trend in macrophage M2 polarization. Our results suggest that TGR5 attenuates proinflammatory immune activation by restraining macrophage migration and facilitating macrophage M2 polarization via suppression of Cat E and thereby protects against liver IR injury.     

Macrophage/monocyte depletion by clodronate, but not diphtheria toxin, improves renal ischemia/reperfusion injury in mice

The role of resident renal mononuclear phagocytes in acute kidney injury is controversial with experimental data suggesting both deleterious and protective functions. To help resolve this, we used mice transgenic for the human diphtheria toxin receptor under the control of the CD11b promoter and treated them with diphtheria toxin, or liposomal clodronate, or both to deplete monocyte/mononuclear phagocytes prior to renal ischemia/reperfusion injury. Although either system effectively depleted circulating monocytes and resident mononuclear phagocytes, depletion was most marked in diphtheria toxin-treated mice. Despite this, diphtheria toxin treatment did not protect from renal ischemia. In contrast, mice treated with clodronate exhibited reduced renal failure and acute tubular necrosis, suggesting key differences between these depletion strategies. Clodronate did not deplete CD206-positive renal macrophages and, unlike diphtheria toxin, left resident CD11c-positive cells unscathed while inducing dramatic apoptosis in hepatic and splenic mononuclear phagocyte populations. Abolition of the protected phenotype by administration of diphtheria toxin to clodronate-treated mice suggested that the protective effect of clodronate resulted from the presence of a cytoprotective intrarenal population of mononuclear phagocytes sensitive to diphtheria toxin-mediated ablation.     

Histological evaluation of proximal tubule cell injury in isolated perfused pig kidneys exposed to cold ischemia

BACKGROUND. Ischemic injury of the renal allograft before transplantation is a major cause of impaired graft function. Proton nuclear spectroscopy provides a useful technique for evaluating proximal tubular activity. In addition to this technique, we proposed a histological grading system for quantifying proximal tubule alterations. METHODS. The aim of this study was to evaluate the histological lesions of tubule epithelial cells in the model of isolated perfused pig kidneys following 48 to 72 h of cold storage in Euro-Collins solution. Normothermic isolated perfused pig kidneys were randomized in three experimental groups : Group 1, control group; cold flush with cold heparinized solution followed by immediate reperfusion (n = 6); Group 2, 48 h of cold storage in Euro-Collins followed by reperfusion (n = 6); Group 3, 72 h of cold storage in Euro-Collins followed by reperfusion (n = 6). Proton nuclear spectroscopy of urine and biochemical studies were performed for whole renal functional evaluation during reperfusion. Optical and electron microscopy analyses of the reperfused kidneys were performed by four investigators and the degree of cell injury was assessed using 8 different criteria in a 5-scale numerical score. RESULTS. Numerical scores corroborate the results from NMR spectroscopy and differed significantly between the three groups studied. The degree of proximal tubule cell damage was increased with prolonged cold ischemia as shown particularly in Group 3. CONCLUSION. The results from this study showed that analysis of cell injury based on an histological grading system in the model of isolated perfused kidney allows the quantification of the degree of proximal tubule injury. Thus, such morphological system analysis could be a useful method for quantifying tubule cell injuries observed under various physiopathological conditions.     

Tubular epithelial syndecan-1 maintains renal function in murine ischemia/reperfusion and human transplantation

Syndecan-1, a heparan sulfate proteoglycan, has an important role in wound healing by binding several growth factors and cytokines. As these processes are also crucial in damage and repair after renal transplantation, we examined syndecan-1 expression in human control kidney tissue, renal allograft protocol biopsies, renal allograft biopsies taken at indication, and non-transplant interstitial fibrosis. Syndecan-1 expression was increased in tubular epithelial cells in renal allograft biopsies compared with control. Increased epithelial syndecan-1 in allografts correlated with low proteinuria and serum creatinine, less interstitial inflammation, less tubular atrophy, and prolonged allograft survival. Knockdown of syndecan-1 in human tubular epithelial cells in vitro reduced cell proliferation. Selective binding of growth factors suggests that syndecan-1 may promote epithelial restoration. Bilateral renal ischemia/reperfusion in syndecan-1-deficient mice resulted in increased initial renal failure and tubular injury compared with wild-type mice. Macrophage and myofibroblast numbers, tubular damage, and plasma urea levels were increased, and tubular proliferation reduced in the kidneys of syndecan-1 deficient compared with wild-type mice 14 days following injury. Hence syndecan-1 promotes tubular survival and repair in murine ischemia/reperfusion injury and correlates with functional improvement in human renal allograft transplantation.     

Overexpression of stanniocalcin-1 inhibits reactive oxygen species and renal ischemia/reperfusion injury in mice

Reactive oxygen species, endothelial dysfunction, inflammation, and mitogen-activated protein kinases have important roles in the pathogenesis of ischemia/reperfusion kidney injury. Stanniocalcin-1 (STC1) suppresses superoxide generation in many systems through the induction of mitochondrial uncoupling proteins and blocks the cytokine-induced rise in endothelial permeability. Here we tested whether transgenic overexpression of STC1 protects from bilateral ischemia/reperfusion kidney injury. This injury in wild-type mice caused a halving of the creatinine clearance; severe tubular vacuolization and cast formation; increased infiltration of macrophages and T cells; higher vascular permeability; greater production of superoxide and hydrogen peroxide; and higher ratio of activated extracellular regulated kinase/activated Jun-N-terminal kinase and p38, all compared to sham-treated controls. Mice transgenic for human STC1 expression, however, had resistance to equivalent ischemia/reperfusion injury indicated as no significant change from controls in any of these parameters. Tubular epithelial cells in transgenic mice expressed higher mitochondrial uncoupling protein 2 and lower superoxide generation. Pre-treatment of transgenic mice with paraquat, a generator of reactive oxygen species, before injury restored the susceptibility to ischemia/reperfusion kidney injury, suggesting that STC1 protects by an anti-oxidant mechanism. Thus, STC1 may be a therapeutic target for ischemia/reperfusion kidney injury.     

Renoprotective effects of asialoerythropoietin in diabetic mice against ischaemia–reperfusion-induced acute kidney injury

Aim: Diabetic patients are at higher risk of failure to recover after acute kidney injury, however, the mechanism and therapeutic strategies remain unclear. Erythropoietin is cytoprotective in a variety of non‐haematopoietic cells. The aim of the present study was to clarify the mechanism of diabetes‐related acceleration of renal damage after ischaemia–reperfusion injury and to examine the therapeutic potential of asialoerythropoietin, a non‐haematopoietic erythropoietin derivative, against ischaemia–reperfusion‐induced acute kidney injury in diabetic mice. Methods: C57BL/6J mice with and without streptozotocin‐induced diabetes were subjected to 30 min unilateral renal ischaemia–reperfusion injury at 1 week after induction of diabetes. They were divided into four group: (i) non‐diabetic plus ischaemia–reperfusion injury; (ii) non‐diabetic plus ischaemia–reperfusion injury plus asialoerythropoietin (3000 IU/kg bodyweight); (iii) diabetic plus ischaemia–reperfusion injury; and (iv) diabetic plus ischemia–reperfusion injury plus asialoerythropoietin. Experiments were conducted at the indicated time periods after ischaemia–reperfusion injury. Results: Ischaemia–reperfusion injury of diabetic kidney resulted in significantly low protein expression levels of bcl‐2, an anti‐apoptotic molecule, and bone morphogenetic protein‐7 (BMP‐7), an anti‐fibrotic and pro‐regenerative factor, compared with non‐diabetic kidneys. Diabetic kidney subsequently showed severe damage including increased tubular cell apoptosis, tubulointerstitial fibrosis and decreased tubular proliferation, compared with non‐diabetic kidney. Treatment with asialoerythropoietin induced bcl‐2 and BMP‐7 expression in diabetic kidney and decreased tubular cell apoptosis, tubulointerstitial fibrosis and accelerated tubular proliferation. Conclusion: Reduced induction bcl‐2 and BMP‐7 may play a role in the acceleration of renal damage after ischaemia–reperfusion injury in diabetic kidney. The renoprotective effects of asialoerythropoietin on acute kidney injury may be mediated through the induction of bcl‐2 and BMP‐7.     

Polyethylene glycol reduces the inflammatory injury due to cold ischemia/reperfusion in autotransplanted pig kidneys

BACKGROUND: The conditions of storage of donor kidney may influence the deleterious consequences of ischemia/reperfusion injury (IRI) on delayed graft function. Since polyethylene glycol (PEG) can protect renal tubule cells against cold injury, we tested the effects of adding PEG 20 kD to ice-cold preservation solutions on the IRI of autotransplanted pig kidneys. METHODS: The pigs' left kidneys were removed, cold-flushed with University of Wisconsin (UW) or simplified high K+ or high Na+ solutions with or without 30 g/L PEG 20M and stored for 48 hours at 4 degrees C. The kidneys were then autotransplanted and the contralateral kidneys were removed. Kidney biopsies were then performed and renal function parameters were analyzed over 8 to 12 weeks following surgery. RESULTS: The kidneys cold-flushed with PEG-supplemented solutions on day 7 post-transplantation were better preserved and exhibited less marked nuclear tubular cell damage than the kidneys cold-flushed with the UW solution alone. PEG also almost completely inhibited the overexpression of major histocompatibility complex class II that was detected in epithelial tubule cells from kidneys cold-flushed with the UW solution. PEG also significantly reduced the number of CD4+ T lymphocytes and limited the infiltration of macrophages/monocytes and the progression of interstitial fibrosis in the 8- to 12-week post-transplanted kidneys. Moreover, pigs autotransplanted with kidneys flushed with PEG-supplemented solutions had the best renal function and the lowest levels of proteinuria. CONCLUSIONS: These findings indicate that PEG inhibits the early inflammatory response due to IRI, improves renal function, and may prevent the progression of interstitial fibrosis in the long-term autotransplanted pig kidney.     

IL-18 contributes to renal damage after ischemia-reperfusion

IL-18 is a proinflammatory cytokine produced by macrophages and other cell types present in the kidney during ischemia-reperfusion injury (IRI), but its role in this injury is unknown. Here, compared with wild-type mice, IL-18(-/-) mice subjected to kidney IRI demonstrated better kidney function, less tubular damage, reduced accumulation of neutrophils and macrophages, and decreased expression of proinflammatory molecules that are downstream of IL-18. For determination of the relative contributions of leukocytes and parenchymal cells to IL-18 production and subsequent kidney damage during IRI, bone marrow-chimeric mice were generated. Wild-type mice engrafted with IL-18(-/-) hemopoietic cells showed less kidney dysfunction and tubular damage than IL-18(-/-) mice engrafted with wild-type bone marrow. In vitro, macrophages produced IL-18 mRNA and protein in response to ischemia. These data suggest bone marrow-derived cells are the key contributors to IL-18-mediated effects of renal IRI. Finally, similar to IL-18(-/-) mice, pretreatment of wild-type mice with IL-18-binding protein was renoprotective in this model of IRI. In conclusion, IL-18, derived primarily from cells of bone marrow origin, contributes to the renal damage observed during IRI. IL-18-binding protein may have potential as a renoprotective therapy.     

Bcl-xL augmentation potentially reduces ischemia/reperfusion induced proximal and distal tubular apoptosis and autophagy

BACKGROUND: Apoptosis and autophagy may contribute to cell homeostasis in the kidney subjected to ischemia/reperfusion injury via mitochondrial injury. Ischemia/reperfusion induces differential sensitivity between proximal and distal tubules via a dissociated Bcl-xL expression. We hypothesized Bcl-xL augmentation in the proximal and distal tubules may potentially reduce ischemia/reperfusion induced renal dysfunction. METHODS: We augmented Bcl-xL protein expression in the kidney with intrarenal adenoviral bcl-xL gene transfer and evaluated the potential effect of Bcl-xL augmentation on ischemia/reperfusion induced renal oxidative stress, apoptosis, and autophagy in the rat. RESULTS: Intrarenal arterial Adv-bcl-xL administration augmented maximal Bcl-xL protein expression of rat kidney after 7 days of transfection. The primary location of Bcl-xL augmentation was found in proximal and distal tubules, but not in glomeruli. Ischemia/reperfusion increased mitochondrial cytochrome C release, renal O2(-*) level and renal 3-nitrosine and 4-hydroxyneonal accumulation, potentiated tubular apoptosis and autophagy, including increase in microtubule-associated protein 1 light chain 3 (LC-3) and Beclin-1 expression, Bax/Bcl-xL ratio, caspase 3 expression and poly-(ADP-ribose)-polymerase fragments, and subsequent proximal and distal tubular apoptosis/autophagy. However, Adv-bcl-xL administration significantly reduced ischemia/reperfusion enhanced mitochondrial cytochrome C release, O2(-*) production, 3-nitrotyrosine and 4-hydroxynonenal accumulation, Beclin-1 expression, Bax/Bcl-xL ratio, and proximal and distal tubular apoptosis/autophagy, consequently improving renal dysfunction. Further study showed that Bcl-xL augmentation was more efficiently than Bcl-2 augmentation in amelioration of ischemia/reperfusion induced proximal and distal tubular apoptosis and renal dysfunction. CONCLUSIONS: Our results suggest that Adv-bcl-xL gene transfer significantly improves ischemia/reperfusion-induced renal dysfunction via the downregulation of renal tubular apoptosis and autophagy.     

C3a and c5a promote renal ischemia-reperfusion injury

Renal ischemia reperfusion injury triggers complement activation, but whether and how the small proinflammatory fragments C3a and C5a contribute to the pathogenesis of this injury remains to be elucidated. Using C3aR-, C5aR-, or C3aR/C5aR-deficient mice and models of renal ischemia-reperfusion injury, we found that deficiency of either or both of these receptors protected mice from injury, but the C3aR/C5aR- and C5aR-deficient mice were most protected. Protection from injury was associated with less cellular infiltration and lower mRNA levels of kidney injury molecule-1, proinflammatory mediators, and adhesion molecules in postischemic kidneys. Furthermore, chimera studies showed that the absence of C3aR and C5aR on renal tubular epithelial cells or circulating leukocytes attenuated renal ischemia-reperfusion injury. In vitro, C3a and C5a stimulation induced inflammatory mediators from both renal tubular epithelial cells and macrophages after hypoxia/reoxygenation. In conclusion, although both C3a and C5a contribute to renal ischemia-reperfusion injury, the pathogenic role of C5a in this injury predominates. These data also suggest that expression of C3aR and C5aR on both renal and circulating leukocytes contributes to the pathogenesis of renal ischemia-reperfusion injury.     

IL-25 Elicits Innate Lymphoid Cells and Multipotent Progenitor Type 2 Cells That Reduce Renal Ischemic/Reperfusion Injury

IL-25 is an important immune regulator that can promote Th2 immune response-dependent immunity, inflammation, and tissue repair in asthma, intestinal infection, and autoimmune diseases. In this study, we examined the effects of IL-25 in renal ischemic/reperfusion injury (IRI). Treating IRI mice with IL-25 significantly improved renal function and reduced renal injury. Furthermore, IL-25 treatment increased the levels of IL-4, IL-5, and IL-13 in serum and kidney and promoted induction of alternatively activated (M2) macrophages in kidney. Notably, IL-25 treatment also increased the frequency of type 2 innate lymphoid cells (ILC2s) and multipotent progenitor type 2 (MPP^type2) cells in kidney. IL-25–responsive ILC2 and MPP^type2 cells produced greater amounts of Th2 cytokines that associated with the induction of M2 macrophages and suppression of classically activated (M1) macrophages in vitro. Finally, adoptive transfer of ILC2s or MPP^type2 cells not only reduced renal functional and histologic injury in IRI mice but also induced M2 macrophages in kidney. In conclusion, our data identify a mechanism whereby IL-25-elicited ILC2 and MPP^type2 cells regulate macrophage phenotype in kidney and prevent renal IRI.     

Renal cilia display length alterations following tubular injury and are present early in epithelial repair.

BACKGROUND: Renal cilia are flow sensors that are required for the maintenance of normal kidney architecture. Defects in this organelle are frequently associated with polycystic kidney disease, but the role of renal cilia during acute tubular injury has not been investigated. METHODS: We have analysed the presence and dimensions of renal cilia following renal ischaemia-reperfusion and ureteral obstruction injury in the mouse, and related these results to injury and repair of the renal tubule. The expression of genes encoding cilium-localized proteins was measured following ischaemia-reperfusion injury. RESULTS: Ischaemia-reperfusion injury was demonstrated to affect the length of cilia in the renal tubule and duct. The average length of renal cilia in the proximal tubule decreases 1 day (2.8 +/- 0.4 microm) and 2 days (3.0 +/- 0.2 microm) after injury, as compared to the control uninjured proximal tubule (4.2 +/- 0.3 microm). Later in the injury and repair process at 4 and 7 days, the average length of cilia increases in both the proximal (7 days = 6.2 +/- 0.3 microm) and distal tubule/collecting duct (4 days = 4.4 +/- 0.3 microm; 7 days = 5.5 +/- 0.4 microm; control 2.5 +/- 0.1 microm). The expression level of genes encoding cilium-localized products did not correlate with the increase in cilium length following ischaemia-reperfusion injury. Ureteral obstruction for 8 days also caused lengthening (8 days UUO = 5.8 +/- 0.3 microm; control 2.5 +/- 0.1 microm) of renal cilia in the distal tubule/collecting duct. During the repair process that follows ischaemia-reperfusion injury, cilia were present on the dedifferentiated cells that proliferate and adopt an epithelial phenotype to facilitate the repair of the ischaemic renal tubule. CONCLUSIONS: We propose roles for the renal cilium in responding to changes in the renal environment caused by injury, and in the repair process that re-establishes the epithelial layer of the damaged renal tubule.