Ischemia-reperfusion injury activates innate immunity in rat kidneys

Lymphocytes and innate immune cells in acute kidney injury and repair

Acute kidney injury (AKI) is a common and serious disease entity that affects native kidneys and allografts but for which no specific treatments exist. Complex intrarenal inflammatory processes driven by lymphocytes and innate immune cells have key roles in the development and progression of AKI. Many studies have focused on prevention of early injury in AKI. However, most patients with AKI present after injury is already established. Increasing research is therefore focusing on mechanisms of renal repair following AKI and prevention of progression from AKI to chronic kidney disease. CD4+ and CD8+ T cells, B cells and neutrophils are probably involved in the development and progression of AKI, whereas regulatory T cells, double-negative T cells and type 2 innate lymphoid cells have protective roles. Several immune cells, such as macrophages and natural killer T cells, can have both deleterious and protective effects, depending on their subtype and/or the stage of AKI. The immune system not only participates in injury and repair processes during AKI but also has a role in mediating AKI-induced distant organ dysfunction. Targeted manipulation of immune cells is a promising therapeutic strategy to improve AKI outcomes.

The Impact of Hematological Indices on the Occurrence of Delayed Graft Function (DGF) of Transplanted Kidney

BACKGROUND

to analyse the effect of haematological indices on the occurrence of Delayed Graft Function (DGF) in patients undergoing kidney transplantation and on the function of the transplanted kidney on the 7th postoperative day.

METHODS

365 recipients who underwent kidney transplantation from a donor with known brain death between 2010 and 2017 were included in this retrospective study. Information from patient medical records, donor medical records, and donation and transplantation protocols was used for analysis. Statistica 13 was used for statistical analysis.

RESULTS

In the study group, DGF occurred in 144 recipients (39.45%), and Non-Graft Function (NGF) occurred in 12 recipients (3.29%). Recipients who developed DGF had a significantly higher Neutrophil/Monocyte Ratio (NMR) before renal transplantation (p = 0.048), a lower NMR value on postoperative day 1 (p < 0.001), and a difference between the values on day 1 and before surgery (p < 0.001). In addition, they had a significantly lower Lymphocyte/Monocyte Ratio (LMR) on postoperative day 1 LMR 1 (p < 0.001). It was shown that the value of the indices based on the ROC curve-NMR1 > 29.29, NMR1-0 > 22.71, and LMR1 > 1.74 (respectively: AUC = 0.624; 95% CI 0.566-0.682; and p < 0.001/AUC = 0.622; 95% CI 0.563-0.680; and p < 0.001/AUC = 0.610; 95% CI 0.550-0.670; and p < 0.001)-can be used to identify recipients with a significant probability of DGF.

CONCLUSIONS

the NMR and LMR parameters on the first postoperative day and the difference between the NMR values on the first post-transplant day and the first pre-transplant day are predictive factors associated with the risk of DGF.

Toll-like receptors and nuclear factor kappa B signaling pathway involvement in hepatorenal oxidative damage induced by some food preservatives in rats

Chemical food preservatives are extensively found in various processed food products in the human environment. Hence, this study aimed to investigate the effect of long-term exposure to five food preservatives (potassium sorbate (PS), butylated hydroxyanisole (BHA), sodium benzoate (SB), calcium propionate (CP), and boric acid (BA)) on the liver and kidney in rats and the probable underlying mechanisms. For 90 days, sixty male albino rats were orally given either water (control), 0.09 mg/kg b.wt BHA, 4.5 mg/kg b.wt PS, 0.9 mg/kg b.wt SB, 0.16 mg/kg b.wt BA, or 0.18 mg/kg b.wt CP. Liver and kidney function tests were assessed. Hepatic and renal oxidative stress biomarkers were estimated. Histologic examination analysis of liver and kidney tissues was achieved. Toll-like receptors 2 and 4 (TLR-2 and TLR-4), tumor necrosis factor-alpha (TNF-α), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) mRNA expression levels were measured. The results revealed that long-term oral dosing of the five food preservatives resulted in significant increases in alkaline phosphatase, alanine transaminase, aspartate transaminase, urea, uric acid, and creatinine levels. There were significant reductions in hepatic and renal antioxidant enzymes, an increase in MDA concentrations, and pathological alterations in renal and hepatic tissues. The mRNA levels of TLR-4, TLR-2, NF-κB, and TNF-α were elevated in the food preservatives-exposed groups. Conclusively, the current findings revealed that long-term exposure to PS, BHA, SB, CP, and BA has a negative impact on liver and kidney function. Furthermore, these negative effects could be mediated via oxidative stress induction, inflammatory reactions, and cytokine production.

Toll-like Receptor 4 in Acute Kidney Injury

Acute kidney injury (AKI) is a common and devastating pathologic condition, associated with considerable high morbidity and mortality. Although significant breakthroughs have been made in recent years, to this day no effective pharmacological therapies for its treatment exist. AKI is known to be connected with intrarenal and systemic inflammation. The innate immune system plays an important role as the first defense response mechanism to tissue injury. Toll-like receptor 4 (TLR4) is a well-characterized pattern recognition receptor, and increasing evidence has shown that TLR4 mediated inflammatory response, plays a pivotal role in the pathogenesis of acute kidney injury. Pathogen-associated molecular patterns (PAMPS), which are the conserved microbial motifs, are sensed by these receptors. Endogenous molecules generated during tissue injury, and labeled as damage-associated molecular pattern molecules (DAMPs), also activate pattern recognition receptors, thereby offering an understanding of sterile types of inflammation. Excessive, uncontrolled and/or sustained activation of TLR4, may lead to a chronic inflammatory state. In this review we describe the role of TLR4, its endogenous ligands and activation in the inflammatory response to ischemic/reperfusion-induced AKI and sepsis-associated AKI. The potential regeneration signaling patterns of TLR4 in acute kidney injury, are also discussed.

Lipopolysaccharide from Rhodobacter spheroids modulate toll-like receptors expression and tissue damage in an animal model of bilateral renal ischemic reperfusion injury

Ischemic reperfusion injury (IRI) of the kidneys is a direct sequela of surgical procedures associated with the interruption of blood supply. The pathophysiology of IRI is complicated, and several inflammatories, apoptosis, and oxidative stress pathways are implicated. Among the major receptors directly involved in renal IRI are the toll-like receptors (TLRs), specifically TLR2 and TLR4. In this study, we investigated the effects of Lipopolysaccharide from Rhodobacter Sphaeroides (TLR2 and TLR4 antagonist, LPS-RS) and the ultrapure form (pure TLR4 antagonist, ULPS-RS) on the histopathological changes and TLRs expression in an animal model of bilateral renal IRI. Forty-eight adult male rats were allocated into six groups (N=8) as follows: sham group (negative control without IRI), control group (rats underwent bilateral renal ischemia for 30 minutes and 2 hours of reperfusion), vehicle group (IRI+ vehicle), LPS-RS group (IRI+ 0.5 mg/kg of LPS-RS), ULPS-RS group (IRI+ 0.1 mg/kg of ULPS-RS), ULPS-RSH group (IRI+ 0.2 mg/kg of ULPS-RS). Significant improvement in the histopathological damages induced by renal IRI was found in the ULPS-RS treated groups at both doses compared with the control group. The protective effect of ULPS-RS was associated with significantly reduced TLR4 expression without affecting TLR2. Regarding LPS-RS, the tested dose adversely affected the renal tissues as manifested by the histopathological findings, although it similarly affected TLRs expression as ULPS-RS. Our results demonstrated that ULPS-RS was renoprotective while LPS-RS had no protective effect against the tissue damages induced by renal IRI.

SCM-198 Can Regulate Autophagy Through the Bax/Bcl-2/TLR4 Pathway to Alleviate Renal Ischemia-Reperfusion Injury

Renal ischemia-reperfusion (I/R) injury is frequently observed in several clinical cases. In this study, we want to investigate that SCM-198 attenuates renal injury in the renal I/R model and find out the possible mechanisms. Wistar albino 40 male rats were classified into four groups (n=10): control, DMSO, I/R, and SCM-198 30 mg/kg. In the group 4, SCM-198 was administered intraperitoneally once at the doses of 30 mg/kg following the reperfusion. Glomerular associated proteins (PCX), tubular damage factors (NGAL, KIM-1), blood urea nitrogen (BUN), serum creatinine, inflammatory cytokines (IL-1β, IL-18, and TNF-α), Bax/Bcl-2, TLR4, LC3B, and Beclin-1 were evaluated. SCM-198 played an essential role in mitigating kidney damage. SCM-198 alleviated tubular damage and decreased IL-1β, IL-18, and TNF-α levels. SCM-198 reduced the apoptosis marker Bax/Bcl-2 ratio, immune system protein TLR4, and autophagy proteins LC3B and Beclin-1. In brief, our results support the notion that SCM-198 has protective effects on I/R-induced renal injury. SCM-198 therapy may be a new alternative for the prevention and treatment of renal I/R injury.

Systematic Understanding of Pathophysiological Mechanisms of Oxidative Stress-Related Conditions-Diabetes Mellitus, Cardiovascular Diseases, and Ischemia-Reperfusion Injury

Reactive oxygen species (ROS) plays a role in intracellular signal transduction under physiological conditions while also playing an essential role in diseases such as hypertension, ischemic heart disease, and diabetes, as well as in the process of aging. The influence of ROS has some influence on the frequent occurrence of cardiovascular diseases (CVD) in diabetic patients. In this review, we considered the pathophysiological relationship between diabetes and CVD from the perspective of ROS. In addition, considering organ damage due to ROS elevation during ischemia-reperfusion, we discussed heart and lung injuries. Furthermore, we have focused on the transient receptor potential (TRP) channels and L-type calcium channels as molecular targets for ROS in ROS-induced tissue damages and have discussed about the pathophysiological mechanism of the injury.

Toll-like receptor 4: An attractive therapeutic target for acute kidney injury

Acute kidney injury (AKI) is a progressive renal complication which significantly affects the patient's life with huge economic burden. Untreated acute kidney injury eventually progresses to a chronic form and end-stage renal disease. Although significant breakthroughs have been made in recent years, there are still no effective pharmacological therapies for the treatment of acute kidney injury. Toll-like receptor 4 (TLR4) is a well-characterized pattern recognition receptor, and increasing evidence has shown that TLR4 mediated inflammatory response plays a pivotal role in the pathogenesis of acute kidney injury. The expression of TLR4 has been seen in resident renal cells, including podocytes, mesangial cells, tubular epithelial cells and endothelial cells. Activation of TLR4 signaling regulates the transcription of numerous pro-inflammatory cytokines and chemokines, resulting in renal inflammation. Therefore, targeting TLR4 and its downstream effectors could serve as an effective therapeutic intervention to prevent renal inflammation and subsequent kidney damage. For the first time, this review summarizes the literature on acute kidney injury from the perspective of TLR4 from year 2010 to 2020. In the current review, the role of TLR4 signaling pathway in AKI with preclinical evidence is discussed. Furthermore, we have highlighted several compounds of natural and synthetic origin, which have the potential to avert the renal TLR4 signaling in preclinical AKI models and have shown protection against AKI. This scientific review provides new ideas for targeting TLR4 in the treatment of AKI and provides strategies for the drug development against AKI.

Toll-Like Receptors in Acute Kidney Injury

Acute kidney injury (AKI) is an important health problem, affecting 13.3 million individuals/year. It is associated with increased mortality, mainly in low- and middle-income countries, where renal replacement therapy is limited. Moreover, survivors show adverse long-term outcomes, including increased risk of developing recurrent AKI bouts, cardiovascular events, and chronic kidney disease. However, there are no specific treatments to decrease the adverse consequences of AKI. Epidemiological and preclinical studies show the pathological role of inflammation in AKI, not only at the acute phase but also in the progression to chronic kidney disease. Toll-like receptors (TLRs) are key regulators of the inflammatory response and have been associated to many cellular processes activated during AKI. For that reason, a number of anti-inflammatory agents targeting TLRs have been analyzed in preclinical studies to decrease renal damage during AKI. In this review, we updated recent knowledge about the role of TLRs, mainly TLR4, in the initiation and development of AKI as well as novel compounds targeting these molecules to diminish kidney injury associated to this pathological condition.

Activated mesangial cells acquire the function of antigen presentation

Mesangial cells (MCs), as resident cells of the kidneys, play an important role in maintaining glomerular function. MCs are located between the capillary loops of the glomeruli and mainly support the capillary plexus, constrict blood vessels, extracellular matrix components, produce cytokines, and perform phagocytosis and clearance of macromolecular substances. When the glomerular environment changes, MCs are often affected, which can lead to functional transformation. The immune response is involved in the occurrence and development of various kidney diseases, in these diseases, antigen-presenting cells (APCs) play an important role. APCs can present antigens to T lymphocytes, causing them to become activated and proliferate. Studies have shown that MCs have phagocytic function and express APC markers on the cell surface. Additionally, MCs are stimulated by or produce various inflammatory factors to participate in the renal inflammatory response. Therefore, MCs have potential antigen presentation function and participate in the pathological changes of various kidney diseases as APCs upon activation. In this paper, by reviewing MC phagocytic function, activated MC expression of APC surface markers, and MC participation in the inflammatory response and local renal immune response, we confirm that activated MCs can act as APCs in renal disease.

Review: Ischemia Reperfusion Injury-A Translational Perspective in Organ Transplantation

Thanks to the development of new, more potent and selective immunosuppressive drugs together with advances in surgical techniques, organ transplantation has emerged from an experimental surgery over fifty years ago to being the treatment of choice for many end-stage organ diseases, with over 139,000 organ transplants performed worldwide in 2019. Inherent to the transplantation procedure is the fact that the donor organ is subjected to blood flow cessation and ischemia during harvesting, which is followed by preservation and reperfusion of the organ once transplanted into the recipient. Consequently, ischemia/reperfusion induces a significant injury to the graft with activation of the immune response in the recipient and deleterious effect on the graft. The purpose of this review is to discuss and shed new light on the pathways involved in ischemia/reperfusion injury (IRI) that act at different stages during the donation process, surgery, and immediate post-transplant period. Here, we present strategies that combine various treatments targeted at different mechanistic pathways during several time points to prevent graft loss secondary to the inflammation caused by IRI.

New Insights Into the Molecular Mechanisms and Immune Control of Cytomegalovirus Reactivation

Cytomegalovirus (CMV) is a β-herpesvirus that establishes lifelong latency in infected hosts. Following transplantation of a latently infected organ, reactivation can occur and consists of a spectrum of clinically apparent syndromes from mild symptoms to tissue-invasive, resulting in both direct and indirect sequelae. Before the advent of effective antiviral agents, the primary treatment was reduction in immunosuppression (IS). While antiviral agents provide effective prophylaxis, there are several important caveats associated with their use, including drug toxicity and resistance. The traditional view attributes CMV reactivation and the ensuing clinical disease primarily to IS, either intrinsic to disease-related immune compromise or from the extrinsic administration of IS agents. However, previous data from both animal models and human subjects showed that inflammatory signals could induce upregulation of latent viral gene expression. New data demonstrate that ischemia/reperfusion is necessary and sufficient to induce CMV reactivation following murine transplantation of a latently infected graft. In this article, we review a growing body of evidence that suggests that reactivation of both human CMV and murine CMV is first triggered by molecular events that activate CMV gene expression and lytic infection and viral dissemination are then facilitated by IS. The initial activation of viral gene expression may be mediated by oxidative stress, DNA damage, or inflammatory cytokines, and these factors may act synergistically. New therapeutic approaches are needed to capture this complex array of targets.

Immunopathophysiology of trauma-related acute kidney injury

Physical trauma can affect any individual and is globally accountable for more than one in every ten deaths. Although direct severe kidney trauma is relatively infrequent, extrarenal tissue trauma frequently results in the development of acute kidney injury (AKI). Various causes, including haemorrhagic shock, rhabdomyolysis, use of nephrotoxic drugs and infectious complications, can trigger and exacerbate trauma-related AKI (TRAKI), particularly in the presence of pre-existing or trauma-specific risk factors. Injured, hypoxic and ischaemic tissues expose the organism to damage-associated and pathogen-associated molecular patterns, and oxidative stress, all of which initiate a complex immunopathophysiological response that results in macrocirculatory and microcirculatory disturbances in the kidney, and functional impairment. The simultaneous activation of components of innate immunity, including leukocytes, coagulation factors and complement proteins, drives kidney inflammation, glomerular and tubular damage, and breakdown of the blood-urine barrier. This immune response is also an integral part of the intense post-trauma crosstalk between the kidneys, the nervous system and other organs, which aggravates multi-organ dysfunction. Necessary lifesaving procedures used in trauma management might have ambivalent effects as they stabilize injured tissue and organs while simultaneously exacerbating kidney injury. Consequently, only a small number of pathophysiological and immunomodulatory therapeutic targets for TRAKI prevention have been proposed and evaluated.

Toll-Like Receptor as a Potential Biomarker in Renal Diseases

One of the major challenges faced by modern nephrology is the identification of biomarkers associated with histopathological patterns or defined pathogenic mechanisms that may assist in the non-invasive diagnosis of kidney disease, particularly glomerulopathy. The identification of such molecules may allow prognostic subgroups to be established based on the type of disease, thereby predicting response to treatment or disease relapse. Advances in understanding the pathogenesis of diseases, such as membranous nephropathy, minimal change disease, focal segmental glomerulosclerosis, IgA (immunoglobulin A) nephropathy, and diabetic nephropathy, along with the progressive development and standardization of plasma and urine proteomics techniques, have facilitated the identification of an increasing number of molecules that may be useful for these purposes. The growing number of studies on the role of TLR (toll-like receptor) receptors in the pathogenesis of kidney disease forces contemporary researchers to reflect on these molecules, which may soon join the group of renal biomarkers and become a helpful tool in the diagnosis of glomerulopathy. In this article, we conducted a thorough review of the literature on the role of TLRs in the pathogenesis of glomerulopathy. The role of TLR receptors as potential marker molecules for the development of neoplastic diseases is emphasized more and more often, as prognostic factors in diseases on several epidemiological backgrounds.

Depletion of miR-21 in dendritic cells aggravates renal ischemia-reperfusion injury

Dendritic cells (DCs) play an important role in the pathophysiology of renal ischemia-reperfusion injury (IRI). The mechanisms underlying DCs phenotypic modulation and their function are not fully understood. In this study, we examined the effect of miR-21 on the phenotypic modulation of DCs in vitro and in vivo, and further investigated the impact of miR-21-overexpression DC or miR-21-deficient DC on renal IRI. We found that treatment with hypoxia/reoxygenation (H/R) suppressed miR-21 expression in bone marrow-derived dendritic cells (BMDCs), and significantly increased the percentage of mature DCs (CD11c⁺ /MHC-II⁺ /CD80⁺ ). Using a selection of microRNA mimics, we successfully induced the upregulation of miR-21 in BMDCs, which induced immature DC phenotype and an anti-inflammatory DC response. However, deletion of miR-21 in BMDCs promoted maturation of DCs under H/R. Adoptive transfer of miR-21-overexpression BMDCs could alleviate renal IR-induced pro-inflammatory cytokines production and acute kidney injury (AKI). Mice with miR-21 deficiency in DCs subjected to renal IR showed more severe renal dysfunction and inflammatory response compared with wild-type mice. In addition, chemokine C receptor 7 (CCR7), a surface marker of mature DC, was a target gene of miR-21, and silencing of CCR7 in BMDCs led to reduced mature DCs under H/R. In conclusion, our findings highlight miR-21 as a key regulator of DCs subset phenotype and a potential therapeutic target in renal IRI.

Rapamycin Is Not Protective against Ischemic and Cisplatin-Induced Kidney Injury

Autophagy plays an important role in the pathogenesis of acute kidney injury (AKI). Although autophagy activation was shown to be associated with an increased lifespan and beneficial effects in various pathologies, the impact of autophagy activators, particularly, rapamycin and its analogues on AKI remains obscure. In our study, we explored the effects of rapamycin treatment in in vivo and in vitro models of ischemic and cisplatin-induced AKI. The impact of rapamycin on the kidney function after renal ischemia/reperfusion (I/R) or exposure to the nephrotoxic agent cisplatin was assessed by quantifying blood urea nitrogen and serum creatinine and evaluating the content of neutrophil gelatinase-associated lipocalin, a novel biomarker of AKI. In vitro experiments were performed on the primary culture of renal tubular cells (RTCs) that were subjected to oxygen-glucose deprivation (OGD) or incubated with cisplatin under various rapamycin treatment protocols. Cell viability and proliferation were estimated by the MTT assay and real-time cell analysis using an RTCA iCELLigence system. Although rapamycin inhibited mTOR (mammalian target of rapamycin) signaling, it failed to enhance the autophagy and to ameliorate the severity of AKI caused by ischemia or cisplatin-induced nephrotoxicity. Experiments with RTCs demonstrated that rapamycin exhibited the anti-proliferative effect in primary RTCs cultures but did not protect renal cells exposed to OGD or cisplatin. Our study revealed for the first time that the mTOR inhibitor rapamycin did not prevent AKI caused by renal I/R or cisplatin-induced nephrotoxicity and, therefore, cannot be considered as an ideal mimetic of the autophagy-associated nephroprotective mechanisms (e.g., those induced by caloric restriction), as it had been suggested earlier. The protective action of such approaches like caloric restriction might not be limited to mTOR inhibition and can proceed through more complex mechanisms involving alternative autophagy-related targets. Thus, the use of rapamycin and its analogues for the treatment of various AKI forms requires further studies in order to understand potential protective or adverse effects of these compounds in different contexts.

Immunomodulatory role of recombinant human erythropoietin in acute kidney injury induced by crush syndrome via inhibition of the TLR4/NF-κB signaling pathway in macrophages

Objective: The present study aimed to investigate whether recombinant human erythropoietin (rHuEPO) plays an immunomodulatory function by regulating the TLR4/NF-κB signaling pathway.Materials and methods: C57BL/6 mice were intraperitoneally injected with rHuEPO and, half an hour later, with 50% glycerol at the dose of 7.5 ml/kg to induce crush syndrome (CS)-acute kidney injury (AKI). The levels of TNF-α, IL-1β, IL-6, serum creatinine (Scr), and creatine kinase (CK) were measured. The kidney tissues were analyzed by HE staining, and macrophage infiltration was detected by immunohistochemistry. Double immunofluorescence staining, RT-qPCR, and western blotting were conducted to analyze TLR4/NF-κB p65 expression. Ferrous myoglobin was co-cultured with RAW264.7 cells to mimic crush injury and the production of proinflammatory cytokines. The expression levels of TLR4 and NF-κB p65 were measured.Results: In vivo study results revealed that rHuEPO ameliorated renal function, tissue damage, production of proinflammatory cytokines, and macrophage infiltration in the kidneys. The protein and mRNA expression levels of genes involved in the TLR4/NF-κB signaling pathway in CS-induced AKI mice were upregulated (p < .05). Meanwhile, the expression levels of TLR4, NF-κB p65, and proinflammatory cytokines in RAW264.7 cells were downregulated in CS-AKI mice injected with rHuEPO (p < .05).Conclusions: Our results demonstrated the immunomodulatory capacity of rHuEPO and confirmed that rHuEPO exerts protective effects against CS-induced AKI by regulating the TLR4/NF-κB signaling pathway in macrophages. Therefore, our findings highlight the therapeutic potential of rHuEPO in improving the prognosis of CS-AKI patients.

Ischemia and Reperfusion Injury in Kidney Transplantation: Relevant Mechanisms in Injury and Repair

Ischemia and reperfusion injury (IRI) is a complex pathophysiological phenomenon, inevitable in kidney transplantation and one of the most important mechanisms for non- or delayed function immediately after transplantation. Long term, it is associated with acute rejection and chronic graft dysfunction due to interstitial fibrosis and tubular atrophy. Recently, more insight has been gained in the underlying molecular pathways and signalling cascades involved, which opens the door to new therapeutic opportunities aiming to reduce IRI and improve graft survival. This review systemically discusses the specific molecular pathways involved in the pathophysiology of IRI and highlights new therapeutic strategies targeting these pathways.

Anti-donor MHC Class II Alloantibody Induces Glomerular Injury in Mouse Renal Allografts Subjected to Prolonged Cold Ischemia

BACKGROUND

The mechanisms underlying the effects of prolonged cold-ischemia storage on kidney allografts are poorly understood.

METHODS

To investigate effects of cold ischemia on donor-reactive immune responses and graft pathology, we used a mouse kidney transplantation model that subjected MHC-mismatched BALB/c kidney allografts to cold-ischemia storage for 0.5 or 6 hours before transplant into C57BL/6 mice.

RESULTS

At day 14 post-transplant, recipients of allografts subjected to 6 versus 0.5 hours of cold-ischemia storage had increased levels of anti-MHC class II (but not class I) donor-specific antibodies, increased donor-reactive T cells, and a significantly higher proportion of transplant glomeruli infiltrated with macrophages. By day 60 post-transplant, allografts with a 6 hour cold-ischemia time developed extensive glomerular injury compared with moderate pathology in allografts with 0.5 hour of cold-ischemia time. Pathology was associated with increased serum levels of anti-class 2 but not anti-class 1 donor-specific antibodies. Recipient B cell depletion abrogated early macrophage recruitment, suggesting augmented donor-specific antibodies, rather than T cells, increase glomerular pathology after prolonged cold ischemia. Lymphocyte sequestration with sphingosine-1-phosphate receptor 1 antagonist FTY720 specifically inhibited anti-MHC class II antibody production and abrogated macrophage infiltration into glomeruli. Adoptive transfer of sera containing anti-donor MHC class II antibodies or mAbs against donor MHC class II restored early glomerular macrophage infiltration in FTY720-treated recipients.

CONCLUSIONS

Post-transplant inflammation augments generation of donor-specific antibodies against MHC class II antigens. Resulting MHC class II-reactive donor-specific antibodies are essential mediators of kidney allograft glomerular injury caused by prolonged cold ischemia.

Epithelial innate immunity mediates tubular cell senescence after kidney injury

Acute kidney injury (AKI) is a common clinical condition of growing incidence. Patients who suffer severe AKI have a higher risk of developing interstitial fibrosis, chronic kidney disease, and end-stage renal disease later in life. Cellular senescence is a persistent cell cycle arrest and altered gene expression pattern evoked by multiple stressors. The number of senescent cells increases with age and even in small numbers these cells can induce chronic inflammation and fibrosis; indeed, in multiple organs including kidneys, the accumulation of such cells is a hallmark of aging. We hypothesized that cellular senescence might be induced in the kidney after injury and that this might contribute to progressive organ fibrosis. Testing this hypothesis, we found that tubular epithelial cells (TECs) in mice senesce within a few days of kidney injury and that this response is mediated by epithelial Toll-like and interleukin 1 receptors (TLR/IL-1R) of the innate immune system. Epithelial cell-specific inhibition of innate immune signaling in mice by knockout of myeloid differentiation 88 (Myd88) reduced fibrosis as well as damage to kidney tubules, and also prevented the accumulation of senescent TECs. Importantly, although inactivation of Myd88 after injury ameliorated fibrosis, it did not reduce damage to the tubules. Selectively induced apoptosis of senescent cells by two different approaches only partially reduced kidney fibrosis, without ameliorating damage to the tubules. Our data reveal a cell-autonomous role for epithelial innate immunity in controlling TEC senescence after kidney injury, and additionally suggest that early therapeutic intervention is required for effective reduction of long-term sequelae of AKI.

Rictor deficiency in dendritic cells exacerbates acute kidney injury

Dendritic cells (DCs) are critical initiators of innate immunity in the kidney and orchestrate inflammation following ischemia-reperfusion injury. The role of the mammalian/mechanistic target of rapamycin (mTOR) in the pathophysiology of renal ischemia-reperfusion injury has been characterized. However, the influence of DC-based alterations in mTOR signaling is unknown. To address this, bone marrow-derived mTORC2-deficient (Rictor^-/-) DCs underwent hypoxia-reoxygenation and then analysis by flow cytometry. Adoptive transfer of wild-type or Rictor^-/- DC to C57BL/6 mice followed by unilateral or bilateral renal ischemia-reperfusion injury (20 min ischemia) was used to assess their in vivo migratory capacity and influence on tissue injury. Age-matched male DC-specific Rictor^-/- mice or littermate controls underwent bilateral renal ischemia-reperfusion, followed by assessment of renal function, histopathology, and biomolecular and cell infiltration analysis. Rictor^-/- DCs expressed more costimulatory CD80/CD86 but less coinhibitory programmed death ligand 1 (PDL1), a pattern that was enhanced by hypoxia-reoxygenation. They also demonstrated enhanced migration to the injured kidney and induced greater tissue damage. Following ischemia-reperfusion, Rictor^-/- DC mice developed higher serum creatinine levels, more severe histological damage, and greater proinflammatory cytokine production compared to littermate controls. Additionally, a greater influx of both neutrophils and T cells was seen in Rictor^-/- DC mice, along with CD11c⁺MHCII⁺CD11b^hiF4/80⁺ renal DC, that expressed more CD86 but less PDL1. Thus, DC-targeted elimination of Rictor enhances inflammation and migratory responses to the injured kidney, highlighting the regulatory roles of both DCs and Rictor in the pathophysiology of acute kidney injury.

Complement Component C3 Promotes Cerebral Ischemia/Reperfusion Injury Mediated by TLR2/NFκB Activation in Diabetic Mice

Complement component C3 (C3), a key factor in the complement system, is heavily involved in various inflammation-associated diseases. However, it remains obscure for its role in the pathogenesis of cerebral ischemia/reperfusion (I/R) injury in diabetes. A transient middle cerebral artery occlusion (tMCAO) model was used for cerebral I/R injury in streptozotocin-induced diabetic mice. Cerebral infarct volume and neurological function were measured at different times of reperfusion. Complement C3 was measured by ELISA and western blotting. It was observed that complement C3 expression was increased in cerebral I/R injury of diabetic mice, whereas complement C3 deficiency abrogated the activation and injury. Furthermore, activating complement C3 promotes TLR2/NFκB activation after I/R injury in diabetic mice, which is inhibited by of the silencing of TLR2. Taken together, our data demonstrate that complement C3 promotes cerebral I/R injury via the TLR2/NFκB pathway in diabetic mice, and regulating the complement C3/TLR2/NFκB pathway may be a novel target for therapeutic intervention in diabetic stroke.

Nrf2 protects against acute lung injury and inflammation by modulating TLR4 and Akt signaling

Lung injury, which is associated with systemic inflammatory responses, is a common problem with significant morbidity and mortality. Here, we examined the involvement of toll-like receptor 4 (TLR4) and nuclear factor erythroid 2-related factor 2 (Nrf2) on intestinal ischemia-reperfusion (I/R)-induced lung injury in vivo and in vitro. Analysis of lung tissues in Nrf2-knockout mice by western blotting, immunohistochemistry, and TUNEL assay, and analysis of bronchoalveolar lavage fluid showed that Nrf2 deficiency upregulated TLR4, enhanced I/R-induced lung injury, apoptosis, inflammation, and autophagy, and increased the I/R-induced inactivation of Akt. In mouse lung epithelial cells subjected to oxygen and glucose deprivation/reperfusion (OGD/Rep), Nrf2 silencing increased the OGD/Rep-induced upregulation of TLR4 and MyD88 and downregulation of HO-1, and exacerbated OGD/Rep-induced apoptosis, autophagy, and the downregulation of phospho-Akt. TLR4 silencing and Akt inhibition experiments indicated that OGD/Rep-induced cell death by suppressing Akt signaling, and Nrf2 protected lung cells by modulating TLR4 and Akt signaling. These results indicated that the Nrf2/TLR4/Akt axis plays a role in inflammation-associated lung damage, suggesting potential therapeutic targets for the treatment of lung injury.

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.

Sessile Innate Immune Cells

In this chapter, sessile cells of the innate immune system are briefly introduced. Defined as cells equipped with diverse pattern recognition molecules capable of detecting MAMPs and DAMPs, they encompass cells such as epithelial cells, fibroblasts, vascular cells, chondrocytes, osteoblasts, and adipocytes. Located at the body surfaces, epithelial cells represent the first line of innate immune defense against invading microbial pathogens. They are significant contributors to innate mucosal immunity and generate various antimicrobial defense mechanisms. Also, epithelial cells critically contribute to tissue repair via the phenomenon of re-epithelialization. Fibroblasts operate as classical sentinel cells of the innate immune system dedicated to responding to MAMPs and DAMPs emitted upon any tissue injury. Typically, fibroblasts synthesize most of the extracellular matrix of connective tissues, thereby playing a crucial role in tissue repair processes. Vascular cells of the innate immune system represent an evolutionarily developed first-line defense against any inciting insult hitting the vessel walls from the luminal side including bacteria, viruses, microbial toxins, and chemical noxa such as nicotine. Upon such insults and following recognition of MAMPs and DAMPs, vascular cells react with an innate immune response to create an acute inflammatory milieu in the vessel wall aimed at curing the vascular injury concerned. Chondrocytes, osteoblasts, and osteoclasts represent other vital cells of the skeletal system acting as cells of the innate immune system in its wider sense. These cells mediate injury-promoted DAMP-induced inflammatory and regenerative processes specific for the skeletal systems. Finally, adipocytes are regarded as highly active cells of the innate immune system. As white, brown, and beige adipocytes, they operate as a dynamic metabolic organ that can secrete certain bioactive molecules which have endocrine, paracrine, and autocrine actions.

Acute toll-like receptor 4 activation impairs rat renal microvascular autoregulatory behaviour

AIM

Little is known about how toll-like receptor 4 (TLR4) influences the renal microvasculature. We hypothesized that acute TLR4 stimulation with lipopolysaccharide (LPS) impairs afferent arteriole autoregulatory behaviour, partially through reactive oxygen species (ROS).

METHODS

We assessed afferent arteriole autoregulatory behaviour after LPS treatment (1 mg kg^-1 ; i.p.) using the in vitro blood-perfused juxtamedullary nephron preparation. Autoregulatory behaviour was assessed by measuring diameter responses to stepwise changes in renal perfusion pressure. TLR4 expression was assessed by immunofluorescence, immunohistochemistry and Western blot analysis in the renal cortex and vasculature.

RESULTS

Baseline arteriole diameter at 100 mmHg averaged 15.2 ± 1.2 μm and 12.2 ± 1.0 μm for control and LPS groups (P < 0.05) respectively. When perfusion pressure was increased in 15 mmHg increments from 65 to 170 mmHg, arteriole diameter in control kidneys decreased significantly to 69 ± 6% of baseline diameter. In the LPS-treated group, arteriole diameter remained essentially unchanged (103 ± 9% of baseline), indicating impaired autoregulatory behaviour. Pre-treatment with anti-TLR4 antibody or the TLR4 antagonist, LPS-RS, preserved autoregulatory behaviour during LPS treatment. P2 receptor reactivity was normal in control and LPS-treated rats. Pre-treatment with Losartan (angiotensin type 1 receptor blocker; (AT₁ ) 2 mg kg^-1 ; i.p.) increased baseline afferent arteriole diameter but did not preserve autoregulatory behaviour in LPS-treated rats. Acute exposure to Tempol (10^-3 mol L^-1 ), a superoxide dismutase mimetic, restored pressure-mediated vasoconstriction in kidneys from LPS-treated rats.

CONCLUSION

These data demonstrate that TLR4 activation impairs afferent arteriole autoregulatory behaviour, partially through ROS, but independently of P2 and AT₁ receptor activation.

Oxidative Stress and Acute Kidney Injury in Critical Illness: Pathophysiologic Mechanisms-Biomarkers-Interventions, and Future Perspectives

Acute kidney injury (AKI) is a multifactorial entity that occurs in a variety of clinical settings. Although AKI is not a usual reason for intensive care unit (ICU) admission, it often complicates critically ill patients' clinical course requiring renal replacement therapy progressing sometimes to end-stage renal disease and increasing mortality. The causes of AKI in the group of ICU patients are further complicated from damaged metabolic state, systemic inflammation, sepsis, and hemodynamic dysregulations, leading to an imbalance that generates oxidative stress response. Abundant experimental and to a less extent clinical data support the important role of oxidative stress-related mechanisms in the injury phase of AKI. The purpose of this article is to present the main pathophysiologic mechanisms of AKI in ICU patients focusing on the different aspects of oxidative stress generation, the available evidence of interventional measures for AKI prevention, biomarkers used in a clinical setting, and future perspectives in oxidative stress regulation.

Activated Renal Dendritic Cells Cross Present Intrarenal Antigens After Ischemia-Reperfusion Injury

BACKGROUND

The healthy kidney contains an extensive population of renal mononuclear phagocytes (RMPs), with substantial phenotypic and functional diversity. However, how this diverse population is affected by ischemia-reperfusion injury (IRI), an obligate part of renal transplantation, is not yet well understood. The aim of this study was to characterize the phenotypic and functional alterations in RMPs induced by IRI.

METHODS

Renal mononuclear phagocytes were studied 24 and 72 hours after 30 minutes of renal ischemia or sham operation. Kidneys were digested and the phenotypes of renal leukocyte populations were analyzed via flow cytometry. Multiphoton microscopy was used to image renal dendritic cells (DCs) in vivo using CD11c reporter mice. The capacity of renal DCs to present antigen was examined by assessment of proliferation of ovalbumin-specific T cells in rat insulin promoter-membrane-bound ovalbumin transgenic mice after sham or IRI procedures.

RESULTS

Ischemia-reperfusion injury induced influx of monocytes, DCs, macrophages, and neutrophils into the kidney. Classification of RMP subpopulations based on CD11b/CD11c expression demonstrated that the RMPs that increased in response to IRI were predominantly newly recruited monocyte-derived inflammatory DCs. In vivo multiphoton imaging of CD11c-EYFP mice revealed that intrarenal DCs exhibited increased number and activity of dendrites in the postischemic period. Ischemia-reperfusion injury also promoted DC-dependent cross-presentation of renal antigens to CD8 T cells in the draining lymph node.

CONCLUSIONS

In response to renal IRI, RMP populations are skewed toward those derived from inflammatory monocyte precursors. In addition, renal DCs undergo functional activation, increasing their capacity to activate antigen-specific CD8 T cells in renal draining lymph nodes.

Innate Immune Response in Kidney Ischemia/Reperfusion Injury: Potential Target for Therapy

Acute kidney injury caused by ischemia and subsequent reperfusion is associated with a high rate of mortality and morbidity. Ischemia/reperfusion injury in kidney transplantation causes delayed graft function and is associated with more frequent episodes of acute rejection and progression to chronic allograft nephropathy. Alloantigen-independent inflammation is an important process, participating in pathogenesis of injurious response, caused by ischemia and reperfusion. This innate immune response is characterized by the activity of classical cells belonging to the immune system, such as neutrophils, macrophages, dendritic cells, lymphocytes, and also tubular epithelial cells and endothelial cells. These immune cells not only participate in inflammation after ischemia exerting detrimental influence but also play a protective role in the healing response from ischemia/reperfusion injury. Delineating of complex mechanisms of their actions could be fruitful in future prevention and treatment of ischemia/reperfusion injury. Among numerous so far conducted experiments, observed immunomodulatory role of adenosine and adenosine receptor agonists in complex interactions of dendritic cells, natural killer T cells, and T regulatory cells is emphasized as promising in the treatment of kidney ischemia/reperfusion injury. Potential pharmacological approaches which decrease NF-κB activity and antagonize mechanisms downstream of activated Toll-like receptors are discussed.

Protective Effects and Mechanisms of Shenhua Tablet () on Toll-Like Receptors in Rat Model of Renal Ischemia-Reperfusion Injury

OBJECTIVES

To investigate the protective effects and potential mechanisms of Shenhua Tablet (, SHT) on the toll-like receptors (TLRs)-mediated signaling pathways in a rat model of kidney ischemia-reperfusion injury (IRI).

METHODS

Sixty male Wistar rats were randomly divided into 5 groups: sham surgery, model control, astragaloside (150 mg•kg^-1•d^-1), low- and high-dose SHT (1.5 and 3.0 g•kg^-1•d^-1, repectively) groups. One week after drug treatment, rats underwent surgery to establish the IRI models. At 24 h and 72 h after the modeling, serum creatinine (Scr) and blood urea nitrogen (BUN) were analyzed; pathological damage were scored after periodic acid-Schiffstaining. TLR2, TLR4 and myeloid differentiation factor 88 (MyD88) protein and mRNA expressions were detected by inmmunohistochemistry, Western blot and qPCR. Tumor necrosis factor α (TNF-α) and interleukin-6 (IL-6) protein expressions were detected by enzyme linked immunosorbent assay.

RESULTS

Compared with the sham group, the model group exhibited severe change in renal function (Scr: 189.42±21.50, P<0.05), pathological damage (damage score: 4.50±0.55, P<0.05), and the expression levels of TLR2, TLR4, MyD88, TNF-α, IL-6 were significantly higher than other groups. Meanwhile, the levels of TLRs in model group showed upward tendency from 24 to 72 h, unparalleled with pathological and functional changes. The aforementioned parameters were alleviated to a certain extent, and, in addition to TLRs, presented the obvious downward trending from the 24 to 72 h after the intervention in the SHT and astragaloside groups relative to the model (P<0.05); in particular, the most significant mitigation of these changes was observed in the SHT-H group (P<0.05).

CONCLUSION

TLRs may be an important spot to treat and research in acute kidney injury. SHT could effectively mitigate renal injuries and promote recovery of IRI injuries through suppression of degeneration induced by up-regulation of TLR2 and TLR4 expression levels in the MyD88-dependent signaling pathway and exhibit some dose dependence.

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.

High Glucose Induces Mouse Mesangial Cell Overproliferation via Inhibition of Hydrogen Sulfide Synthesis in a TLR-4-Dependent Manner

Background/Aims: Overproliferation of mesangial cells was believed to play an important role in the progress of diabetic nephropathy, one of the primary complications of diabetes. Hydrogen sulfide (H2S), a well-known and pungent gas with the distinctive smell of rotten eggs, was discovered to play a protective role in diabetic nephropathy. Methods: MTT assay was used to examine the viability of mesangial cells. Small interfering RNA was used to knock down the expression of TLR4 while specific inhibitor LY294002 to suppress the function of PI3K. H2S generation rate was determined by a H2S micro-respiration sensor. Results: Glucose of 25mM induced significant mesangial cells proliferation, which was accomplished by significantly inhibited endogenous H2S synthesis. And exogenous H2S treatment by NaHS markedly mitigated the overproliferation of mouse mesangial cells. Furthermore, it was found that H2S deficiency could result in TLR4 activation. And H2S supplementation remarkably inhibited TLR4 expression and curbed the mesangial cell overproliferation. Besides, PI3K/Akt pathway inhibition also significantly ameliorated the cell overproliferation. Conclusion: High glucose (HG) induces mouse mesangial cell overproliferation via inhibition of hydrogen sulfide synthesis in a TLR-4-dependent manner. And PI3K/Akt pathway might also play a vital part in the HG-induced mesangial cell overproliferation.

Beneficial effect of low-level laser therapy in acute lung injury after i-I/R is dependent on the secretion of IL-10 and independent of the TLR/MyD88 signaling

The use of low-level laser for lung inflammation treatment has been evidenced in animal studies as well as clinical trials. The laser action mechanism seems to involve downregulation of neutrophil chemoattractants and transcription factors. Innate immune responses against microorganisms may be mediated by toll-like receptors (TLR). Intestinal ischemia and reperfusion (i-I/R) lead to bacterial product translocation, such as endotoxin, which consequently activates TLRs leading to intestinal and lung inflammation after gut trauma. Thus, the target of this study was to investigate the role of TLR activation in the laser (660 nm, 30 mW, 67.5 J/cm², 0.375 mW/cm², 5.4 J, 180 s, and spot size with 0.08 cm²) effect applied in contact with the skin on axillary lymph node in lung inflammation induced by i-I/R through a signaling adaptor protein known as myeloid differentiation factor 88 (MyD88). It is a quantitative, experimental, and laboratory research using the C57Bl/6 and MyD88^-/- mice (n = 6 mice for experimental group). Statistical differences were evaluated by ANOVA and the Tukey-Kramer multiple comparisons test to determine differences among groups. In order to understand how the absence of MyD88 can interfere in the laser effect on lung inflammation, MyD88^-/- mice were treated or not with laser and subjected to occlusion of the superior mesenteric artery (45 min) followed by intestinal reperfusion (4 h). In summary, the laser decreased the MPO activity and the lung vascular permeability, thickened the alveolar septa, reduced both the edema and the alveolar hemorrhage, as well as significantly decreased neutrophils infiltration in MyD88-deficient mice as well in wild-type mice. It noted a downregulation in chemokine IL-8 production as well as a cytokine IL-10 upregulation in these animals. The results also evidenced that in absence of IL-10, the laser effect is reversed. Based on these results, we suggest that the beneficial effect of laser in acute lung injury after i-I/R is dependent on the secretion of IL-10 and independent of the TLR/MyD88 signaling.

Hypoxia/reoxygenation-induced HMGB1 translocation and release promotes islet proinflammatory cytokine production and early islet graft failure through TLRs signaling

High-mobility group box 1 (HMGB1) translocation and release, which is involved in several tissue types of ischemia-reperfusion injuries, activate innate immunity by inducing proinflammatory cytokine production through its interaction with toll-like receptors (TLRs). Our objective was to determine the role of HMGB1 and the degree of activation of TLR-related signal transduction pathways in hypoxia/reoxygenation (H/R)-induced proinflammatory cytokine production and intra-islet graft inflammation. After islets are exposed to hypoxia-reoxygenation for 24h, TLR2/4 expression and TLR-mediated signaling was up-regulated in islets, and HMGB1 was translocated from the nucleus to the cytoplasm and released to the extracellular space. With H/R exposure, proinflammatory cytokine production (IL-1β and TNF-α) and islet injury were significantly increased, and these effects depend on TLR2/4 signaling pathways. Exogenous HMGB1 also induces islet inflammation and increases the phosphorylation of STAT3, p38 and IκBα in wild-type islets. TLR2 deficiency in TLR2-KO islets resulted in the inhibition of IL-1β production and STAT3/p38 phosphorylation after HMGB1 exposure. TLR4 deficiency in TLR4-KO islets resulted in the inhibition of TNF-α production and IκBα phosphorylation after HMGB1 exposure. Pre-incubation of the STAT3, p38, or NF-κB inhibitors significantly inhibited HMGB1-induced IL-1β or TNF-α production in islets, but the effect of HMGB1 or H/R-induced islet injury was not counteracted by a separate treatment of the STAT3 inhibitor, p38 inhibitor, or NF-κB inhibitors. HMGB1 inhibition by ethyl pyruvate or blockade by neutralizing antibodies significantly decreased the phosphorylation of STAT3, p38 and IκBα, the production of IL-1β and TNF-α, and the islet injury in wild-type islets after exposure to H/R and significantly improved early islet graft failure. Thus, our results suggest that HMGB1 released from H/R induced islets works in an autocrine manner to up-regulate STAT or p38 and augment IL-1β production via TLR2, and up-regulate NF-κB and augment TNF-α production via TLR4 in intra-islet, which are associated with H/R-induced islet injury and early graft failure.

Immune response and histology of humoral rejection in kidney transplantation

The adaptive immune response forms the basis of allograft rejection. Its weapons are direct cellular cytotoxicity, identified from the beginning of organ transplantation, and/or antibodies, limited to hyperacute rejection by preformed antibodies and not as an allogenic response. This resulted in allogenic response being thought for decades to have just a cellular origin. But the experimental studies by Gorer demonstrating tissue damage in allografts due to antibodies secreted by B lymphocytes activated against polymorphic molecules were disregarded. The special coexistence of binding and unbinding between antibodies and antigens of the endothelial cell membranes has been the cause of the delay in demonstrating the humoral allogenic response. The endothelium, the target tissue of antibodies, has a high turnover, and antigen-antibody binding is non-covalent. If endothelial cells are attacked by the humoral response, immunoglobulins are rapidly removed from their surface by shedding and/or internalization, as well as degrading the components of the complement system by the action of MCP, DAF and CD59. Thus, the presence of complement proteins in the membrane of endothelial cells is transient. In fact, the acute form of antibody-mediated rejection was not demonstrated until C4d complement fragment deposition was identified, which is the only component that binds covalently to endothelial cells. This review examines the relationship between humoral immune response and the types of acute and chronic histological lesion shown on biopsy of the transplanted organ.

Dioscin attenuates renal ischemia/reperfusion injury by inhibiting the TLR4/MyD88 signaling pathway via up-regulation of HSP70

We previously reported the effect of dioscin against hepatic ischemia/reperfusion injury (IRI) in rats. However, little is known concerning the role of dioscin in renal IRI. In the present study, rats were subjected to IRI and dioscin was intragastrically administered for seven consecutive days before surgery. In vitro models of hypoxia/reoxygenation were developed in NRK-52E and HK-2 cells, which were prophylactically treated with or without dioscin. The results showed that dioscin significantly decreased serum BUN and Cr levels, and markedly attenuated cell injury. Mechanistic studies showed that dioscin significantly increased HSP70 levels, decreased the levels of TLR4, MyD88, TRAF6, COX-2, JNK, ERK and p38 MAPK phosphorylation, suppressed the nuclear translocation of NF-κB and HMGB1, and subsequently decreased the mRNA levels of IL-1β, IL-6, TNF-α, ICAM-1 and IFN-γ. Moreover, HSP70 siRNA or TLR4 DNA reversed the nephroprotective effects of dioscin, while dioscin still significantly down-regulated the TLR4 signaling pathway. Furthermore, by inhibiting MyD88 with ST2825 (a MyD88 inhibitor), renal IRI was significantly attenuated, suggesting that the effect of dioscin against renal IRI depended on MyD88. Our results suggested that dioscin had a potent effect against renal IRI through suppressing the TLR4/MyD88 signaling pathway by up-regulating HSP70. These data provide new insights for investigating the natural product with the nephroprotective effect against IRI, which should be developed as a new therapeutic agent for the treatment of acute kidney injury in the future.

Clinical applications of remote ischaemic preconditioning in native and transplant acute kidney injury

Ischaemia-reperfusion (IR) injury is a composite of the injury sustained during a period of reduced or absent blood flow to a tissue or organ and the additional insult sustained upon reperfusion that limits the amount of tissue that can be salvaged. IR injury plays a central role in both native and transplant acute kidney injury (AKI). Native AKI is associated with increased morbidity and mortality in hospital inpatients, and transplant AKI contributes to graft dysfunction, ultimately limiting graft longevity. In this review, we discuss the potential therapeutic benefits of a cost-effective and low-risk intervention, remote ischaemic preconditioning (RIPC), and its applicability in the prevention and reduction of AKI.

Class-specific histone/protein deacetylase inhibition protects against renal ischemia reperfusion injury and fibrosis formation

Renal ischemia-reperfusion injury (IRI) is a common cause of renal dysfunction and renal failure. Histone/protein deacetylases (HDACs) regulate gene accessibility and higher order protein structures and may alter cellular responses to a variety of stresses. We investigated whether use of pan- and class-specific HDAC inhibitors (HDACi) could improve IRI tolerance in the kidney. Using a model of unilateral renal IRI, we investigated early renal function after IRI, and calculated fibrosis after IRI using an automated scoring system. We found that pan-HDAC inhibition using trichostatin (TSA) yielded significant renal functional benefit at 24-96 hours (p < 0.001). Treated mice developed significantly less fibrosis at 30 days (p < 0.0004). Class I HDAC inhibition with MS-275 yielded similar effects. Protection from fibrosis formation was also noted in a cold ischemia transplant model (p < 0.008) with a trend toward improved cold ischemic survival in TSA-treated mice. These effects were not accompanied by induction of typical ischemic tolerance pathways or by priming of heat shock protein expression. In fact, heat shock protein 70 deletion or overexpression did not alter renal ischemia tolerance. Micro-RNA 21, known to be enhanced in vitro in renal tubular cells that survive stress, was enhanced by treatment with HDACi, pointing to possible mechanism.

KIM-1-mediated phagocytosis reduces acute injury to the kidney

Kidney injury molecule 1 (KIM-1, also known as TIM-1) is markedly upregulated in the proximal tubule after injury and is maladaptive when chronically expressed. Here, we determined that early in the injury process, however, KIM-1 expression is antiinflammatory due to its mediation of phagocytic processes in tubule cells. Using various models of acute kidney injury (AKI) and mice expressing mutant forms of KIM-1, we demonstrated a mucin domain-dependent protective effect of epithelial KIM-1 expression that involves downregulation of innate immunity. Deletion of the mucin domain markedly impaired KIM-1-mediated phagocytic function, resulting in increased proinflammatory cytokine production, decreased antiinflammatory growth factor secretion by proximal epithelial cells, and a subsequent increase in tissue macrophages. Mice expressing KIM-1Δmucin had greater functional impairment, inflammatory responses, and mortality in response to ischemia- and cisplatin-induced AKI. Compared with primary renal proximal tubule cells isolated from KIM-1Δmucin mice, those from WT mice had reduced proinflammatory cytokine secretion and impaired macrophage activation. The antiinflammatory effect of KIM-1 expression was due to the interaction of KIM-1 with p85 and subsequent PI3K-dependent downmodulation of NF-κB. Hence, KIM-1-mediated epithelial cell phagocytosis of apoptotic cells protects the kidney after acute injury by downregulating innate immunity and inflammation.

Role of toll-like receptor-4 in lung ischemia-reperfusion injury

BACKGROUND

Toll-like receptor-4 has been implicated in modulating ischemia-reperfusion injury in cardiac, hepatic, renal, and cerebral models. However, its role in lung ischemia-reperfusion injury is unknown. We hypothesize that toll-like receptor-4 has a key role in initiating the inflammatory cascade in lung ischemia-reperfusion injury.

METHODS

We used toll-like receptor-4 specific short interference RNA to achieve toll-like receptor-4 knockdown in rats prior to undergoing ischemia and reperfusion. Lungs were explanted and studied for protein expression and markers of lung injury. Additional animals were evaluated for cellular uptake of toll-like receptor-4 short interference RNA. Toll-like receptor-4 short interference RNA localized to the alveolar macrophage.

RESULTS

In animals pretreated with toll-like receptor-4 short interference RNA, toll-like receptor-4 expression and mitogen-activated protein kinase phosphorylation were suppressed. Markers of lung injury including permeability index, myeloperoxidase content, and bronchoalveolar lavage inflammatory cell counts were all reduced with toll-like receptor-4 knockdown.

CONCLUSIONS

Toll-like receptor-4 is critical in the development of lung ischemia-reperfusion injury and its activation in the alveolar macrophage may be the initiating step.

Differential toll-like receptor activation in lung ischemia reperfusion injury

OBJECTIVE

The requirement for toll-like receptors (TLRs) in lung ischemia reperfusion injury (LIRI) has been demonstrated but not fully characterized. Previously, we reported that TLR-4 is required by alveolar macrophages but not pulmonary endothelial or epithelial cells for development of LIRI. Additionally, we demonstrated differential patterns of mitogen-activated protein kinase (MAPK) activation and cytokine release in these cell types during LIRI. Here, we sought to determine whether these differences in activation responses are related to cell-specific TLR activation requirements.

METHODS

Primary cultures of alveolar macrophages, pulmonary endothelial, and immortalized epithelial cells were pretreated with TLR-2 or TLR-4 short interference RNA (ribonucleic acid) before hypoxia and reoxygenation. Cell lysates and media were analyzed for receptor knockdown, MAPK activation, and cytokine production. Rats were pretreated with TLR-2 or TLR-4 short interference RNA before lung ischemia reperfusion and changes in lung vascular permeability were assessed.

RESULTS

Knockdown of TLR-2 in alveolar macrophages did not affect MAPK phosphorylation or cytokine secretion. Conversely, TLR-2 knockdown in pulmonary endothelial and epithelial cells demonstrated significant reductions in extracellular signal-regulated kinase 1/2 activation and cytokine secretion. The lung permeability index in LIRI was decreased by TLR-4 but not TLR-2.

CONCLUSIONS

Differential TLR signaling and MAPK activation in response to LIRI seem to be cell specific. Short interference RNA provides an outstanding tool for examination of the underlying mechanism.

Heme Oxygenase-1 Regulates Myeloid Cell Trafficking in AKI

Renal ischemia-reperfusion injury is mediated by a complex cascade of events, including the immune response, that occur secondary to injury to renal epithelial cells. We tested the hypothesis that heme oxygenase-1 (HO-1) expression, which is protective in ischemia-reperfusion injury, regulates trafficking of myeloid-derived immune cells in the kidney. Age-matched male wild-type (HO-1(+/+)), HO-1-knockout (HO-1(-/-)), and humanized HO-1-overexpressing (HBAC) mice underwent bilateral renal ischemia for 10 minutes. Ischemia-reperfusion injury resulted in significantly worse renal structure and function and increased mortality in HO-1(-/-) mice. In addition, there were more macrophages (CD45(+) CD11b(hi)F4/80(lo)) and neutrophils (CD45(+) CD11b(hi) MHCII(-) Gr-1(hi)) in HO-1(-/-) kidneys than in sham and HO-1(+/+) control kidneys subjected to ischemia-reperfusion. However, ischemic injury resulted in a significant decrease in the intrarenal resident dendritic cell (DC; CD45(+)MHCII(+)CD11b(lo)F4/80(hi)) population in HO-1(-/-) kidneys compared with controls. Syngeneic transplant experiments utilizing green fluorescent protein-positive HO-1(+/+) or HO-1(-/-) donor kidneys and green fluorescent protein-negative HO-1(+/+) recipients confirmed increased migration of the resident DC population from HO-1(-/-) donor kidneys, compared to HO-1(+/+) donor kidneys, to the peripheral lymphoid organs. This effect on renal DC migration was corroborated in myeloid-specific HO-1(-/-) mice subjected to bilateral ischemia. These mice also displayed impaired renal recovery and increased fibrosis at day 7 after injury. These results highlight an important role for HO-1 in orchestrating the trafficking of myeloid cells in AKI, which may represent a key pathway for therapeutic intervention.

The effect of ischemia/reperfusion on the kidney graft

PURPOSE OF REVIEW

Ischemia/reperfusion injury is an unavoidable companion after kidney transplantation and influences short-term as well as long-term graft outcome. Clinically ischemia/reperfusion injury is associated with delayed graft function, graft rejection, and chronic graft dysfunction. Ischemia/reperfusion affects many regulatory systems at the cellular level as well as in the renal tissue that eventually result in a distinct inflammatory reaction of the kidney graft.

RECENT FINDINGS

Underlying factors include energy metabolism, cellular changes of the mitochondria and cellular membranes, initiation of different forms of cell death-like apoptosis and necrosis together with a recently discovered mixed form termed necroptosis. Chemokines and cytokines together with other factors promote the inflammatory response leading to activation of the innate immune system as well as the adaptive immune system. If the inflammatory reaction continues within the graft tissue, a progressive interstitial fibrosis develops that impacts long-term graft outcome.

SUMMARY

It is of particular importance in kidney transplantation to understand the underlying mechanisms and effects of ischemia/reperfusion on the graft as this knowledge also opens strategies to prevent or treat ischemia/reperfusion injury after transplantation in order to improve graft outcome.