Proteasomal processing of albumin by renal dendritic cells generates antigenic peptides

Abatacept Decreases Renal T-cell Infiltration and Renal Inflammation and Ameliorates Progressive Renal Injury in Obese Dahl Salt-sensitive Rats Before Puberty

ABSTRACT

Prepubertal obesity is growing at an alarming rate and is now considered a risk factor for renal injury. Recently, we reported that the early development of renal injury in obese Dahl salt-sensitive (SS) leptin receptor mutant (SS LepR mutant) rats was associated with increased T-cell infiltration and activation before puberty. Therefore, the current study investigated the effect of inhibiting T-cell activation with abatacept on the progression of renal injury in young obese SS LepR mutant rats before puberty. Four-week-old SS and SS LepR mutant rats were treated with IgG or abatacept (1 mg/kg; ip, every other day) for 4 weeks. Abatacept reduced the renal infiltration of T cells by almost 50% in SS LepR mutant rats. Treatment with abatacept decreased the renal expression of macrophage inflammatory protein-3 alpha while increasing IL-4 in SS LepR mutant rats without affecting SS rats. While not having an impact on blood glucose levels, abatacept reduced hyperinsulinemia and plasma triglycerides in SS LepR mutant rats without affecting SS rats. We did not observe any differences in the mean arterial pressure among the groups. Proteinuria was markedly higher in SS LepR mutant rats than in SS rats throughout the study, and treatment with abatacept decreased proteinuria by about 40% in SS LepR mutant rats without affecting SS rats. We observed significant increases in glomerular and tubular injury and renal fibrosis in SS LepR mutant rats versus SS rats, and chronic treatment with abatacept significantly reduced these renal abnormalities in SS LepR mutant rats. These data suggest that renal T-cell activation contributes to the early progression of renal injury associated with prepubertal obesity.

New-Onset Acute Interstitial Nephritis Post-SARS-CoV-2 Infection and COVID-19 Vaccination: A Panoramic Review

The 2019 coronavirus disease (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) has posed a considerable challenge to global healthcare. Acute interstitial nephritis (AIN) post SARS-CoV-2 infection and vaccination has been reported, but its clinical features and pathogenesis remained unclear. We reviewed so far the largest 22 cases of AIN post SARS-CoV-2 infection and 36 cases of AIN following COVID-19 vaccination. The onset of AIN was mainly related to messenger RNA vaccines (52.8%). Apart from fever, proteinuria (45.5%) was the main manifestation of AIN post SARS-CoV-2 infection, left acute kidney injury (AKI, 63.9%) in patients post COVID-19 vaccination. The potential mechanism of vaccination induced AIN was conjugating vaccines with proteins to form a hapten, which activated dendritic cells and promoted a cascade immunological reaction leading to AIN.

Metformin reduces insulin resistance and attenuates progressive renal injury in prepubertal obese Dahl salt-sensitive rats

Prepubertal obesity is currently an epidemic and is considered as a major risk factor for renal injury. Previous studies have demonstrated that insulin resistance contributes to renal injury in obesity, independent of diabetes. However, studies examining the relationship between insulin resistance and renal injury in obese children are lacking. Recently, we reported that progressive renal injury in Dahl salt-sensitive (SS) leptin receptor mutant (SSLepRmutant) rats was associated with insulin resistance before puberty. Therefore, the aim of the present study was to examine whether decreasing insulin resistance with metformin will reduce renal injury in SSLepRmutant rats. Four-wk-old SS and SSLepRmutant rats were separated into the following two groups: 1) vehicle and 2) metformin (300 mg/kg/day) via chow diet for 4 wk. Chronic administration of metformin markedly reduced insulin resistance and dyslipidemia in SSLepRmutant rats. We did not detect any differences in mean arterial pressure between vehicle and metformin-treated SS and SSLepRmutant rats. Proteinuria was significantly greater in SSLepRmutant rats versus SS rats throughout the study, and metformin administration significantly reduced proteinuria in SSLepRmutant rats. At the end of the protocol, metformin prevented the renal hyperfiltration observed in SSLepRmutant rats versus SS rats. Glomerular and tubular injury and renal inflammation and fibrosis were significantly higher in vehicle-treated SSLepRmutant rats versus SS rats, and metformin reduced these parameters in SSLepRmutant rats. These data suggest that reducing insulin resistance with metformin prevents renal hyperfiltration and progressive renal injury in SSLepRmutant rats before puberty and may be therapeutically useful in managing renal injury during prepubertal obesity.NEW & NOTEWORTHY Childhood/prepubertal obesity is a public health concern that is associated with early signs of proteinuria. Insulin resistance has been described in obese children. However, studies investigating the role of insulin resistance during childhood obesity-associated renal injury are limited. This study provides evidence of an early relationship between insulin resistance and renal injury in a rat model of prepubertal obesity. These data also suggest that reducing insulin resistance with metformin may be renoprotective in obese children.

Tolerogenic dendritic cells protect against acute kidney injury

Ischemia reperfusion injury is a common precipitant of acute kidney injury that occurs following disrupted perfusion to the kidney. This includes blood loss and hemodynamic shock, as well as during retrieval for deceased donor kidney transplantation. Acute kidney injury is associated with adverse long-term clinical outcomes and requires effective interventions that can modify the disease process. Immunomodulatory cell therapies such as tolerogenic dendritic cells remain a promising tool, and here we tested the hypothesis that adoptively transferred tolerogenic dendritic cells can limit kidney injury. The phenotypic and genomic signatures of bone marrow-derived syngeneic or allogeneic, Vitamin-D3/IL-10-conditioned tolerogenic dendritic cells were assessed. These cells were characterized by high PD-L1:CD86, elevated IL-10, restricted IL-12p70 secretion and a suppressed transcriptomic inflammatory profile. When infused systemically, these cells successfully abrogated kidney injury without modifying infiltrating inflammatory cell populations. They also provided protection against ischemia reperfusion injury in mice pre-treated with liposomal clodronate, suggesting the process was regulated by live, rather than reprocessed cells. Co-culture experiments and spatial transcriptomic analysis confirmed reduced kidney tubular epithelial cell injury. Thus, our data provide strong evidence that peri-operatively administered tolerogenic dendritic cells have the ability to protect against acute kidney injury and warrants further exploration as a therapeutic option. This technology may provide a clinical advantage for bench-to-bedside translation to affect patient outcomes.

Nutritional Treatment as a Synergic Intervention to Pharmacological Therapy in CKD Patients

Nutritional and pharmacological therapies represent the basis for non-dialysis management of CKD patients. Both kinds of treatments have specific and unchangeable features and, in certain cases, they also have a synergic action. For instance, dietary sodium restriction enhances the anti-proteinuric and anti-hypertensive effects of RAAS inhibitors, low protein intake reduces insulin resistance and enhances responsiveness to epoetin therapy, and phosphate restriction cooperates with phosphate binders to reduce the net phosphate intake and its consequences on mineral metabolism. It can also be speculated that a reduction in either protein or salt intake can potentially amplify the anti-proteinuric and reno-protective effects of SGLT2 inhibitors. Therefore, the synergic use of nutritional therapy and medications optimizes CKD treatment. Quality of care management is improved and becomes more effective when compared to either treatment alone, with lower costs and fewer risks of unwanted side effects. This narrative review summarizes the established evidence of the synergistic action carried out by the combination of nutritional and pharmacological treatments, underlying how they are not alternative but complementary in CKD patient care.

Attenuation of renal injury by depleting cDC1 and by repurposing Flt3 inhibitor in anti-GBM disease

Previous studies found cDC1s to be protective in early stage anti-GBM disease through Tregs, but pathogenic in late stage Adriamycin nephropathy through CD8⁺ T cells. Flt3 ligand is a growth factor essential for cDC1 development and Flt3 inhibitors are currently used for cancer treatment. We conducted this study to clarify the role and mechanisms of effects of cDC1s at different time points in anti-GBM disease. In addition, we aimed to utilize drug repurposing of Flt3 inhibitors to target cDC1s as a treatment of anti-GBM disease. We found that in human anti-GBM disease, the number of cDC1s increased significantly, proportionally more than cDC2s. The number of CD8⁺ T cells also increased significantly and their number correlated with cDC1 number. In XCR1-DTR mice, late (day 12-21) but not early (day 3-12) depletion of cDC1s attenuated kidney injury in mice with anti-GBM disease. cDC1s separated from kidneys of anti-GBM disease mice were found to have a pro-inflammatory phenotype (i.e. express high level of IL-6 and IL-12) in late but not early stage. In the late depletion model, the number of CD8⁺ T cells was also reduced, but not Tregs. CD8⁺ T cells separated from kidneys of anti-GBM disease mice expressed high levels of cytotoxic molecules (granzyme B and perforin) and inflammatory cytokines (TNF-α and IFN-γ), and their expression reduced significantly after cDC1 depletion with diphtheria toxin. These findings were reproduced using a Flt3 inhibitor in wild type mice. Therefore, cDC1s are pathogenic in anti-GBM disease through activation of CD8⁺ T cells. Flt3 inhibition successfully attenuated kidney injury through depletion of cDC1s. Repurposing Flt3 inhibitors has potential as a novel therapeutic strategy for anti-GBM disease.

Kidney-Targeted Drug Delivery System Based on Metformin-Grafted Chitosan for Renal Fibrosis Therapy

Our previous study demonstrated that metformin plays an anti-fibrotic role in addition to its hypoglycemic effect. Worryingly, it often requires more than 5 times the hypoglycemic dose to achieve a satisfactory anti-fibrotic effect, which greatly increases the risk of systemic acidosis caused by metformin overdose. Low-molecular-weight chitosan (LMWC) has natural kidney-targeting properties and good biocompatibility and degradability. Thus, we synthesized a novel carrier metformin-grafted chitosan (CS-MET) based on an imine reaction between oxidized chitosan and metformin. Then, GFP was recruited to form GFP-loaded CS-MET nanoparticles (CS-MET/GFP NPs) with controllable particle size. We hypothesized that CS-MET/GFP NPs would enrich in the kidney and be absorbed by HK-2 cells via megalin-mediated endocytosis by intravenous injection, which may avoid systemic acidosis caused by metformin overdose. Subsequently, the nanoparticle ruptures and releases metformin to exert its anti-apoptotic, anti-inflammatory, and anti-fibrotic effects. Our results showed that CS-MET/GFP NPs have great transfection efficiency and could enter HK-2 cells mainly through megalin-mediated endocytosis. Compared to the free metformin, CS-MET/GFP NPs showed similar anti-apoptotic ability but better therapeutic effects on cellular inflammation and fibrosis in vitro. On the other hand, CS-MET/GFP NPs showed great kidney-targeting ability and superior anti-apoptotic, anti-inflammatory, and anti-fibrotic effects in vivo.

Pathogenic T-Cell Responses in Immune-Mediated Glomerulonephritis

Glomerulonephritis (GN) comprises a group of immune-mediated kidney diseases affecting glomeruli and the tubulointerstitium. Glomerular crescent formation is a histopathological characteristic of severe forms of GN, also referred to as crescentic GN (cGN). Based on histological findings, cGN includes anti-neutrophil cytoplasmic antibody (ANCA)-associated GN, a severe form of ANCA-associated vasculitis, lupus nephritis associated with systemic lupus erythematosus, Goodpasture’s disease, and IgA nephropathy. The immunopathogenesis of cGN is associated with activation of CD4+ and CD8+ T cells, which particularly accumulate in the periglomerular and tubulointerstitial space but also infiltrate glomeruli. Clinical observations and functional studies in pre-clinical animal models provide evidence for a pathogenic role of Th1 and Th17 cell-mediated immune responses in cGN. Emerging evidence further argues that CD8+ T cells have a role in disease pathology and the mechanisms of activation and function of recently identified tissue-resident CD4+ and CD8+ T cells in cGN are currently under investigation. This review summarizes the mechanisms of pathogenic T-cell responses leading to glomerular damage and renal inflammation in cGN. Advanced knowledge of the underlying immune mechanisms involved with cGN will enable the identification of novel therapeutic targets for the replacement or reduction in standard immunosuppressive therapy or the treatment of refractory disease.

Antigen Cross-Presentation by Murine Proximal Tubular Epithelial Cells Induces Cytotoxic and Inflammatory CD8+ T Cells

Immune-mediated glomerular diseases are characterized by infiltration of T cells, which accumulate in the periglomerular space and tubulointerstitium in close contact to proximal and distal tubuli. Recent studies described proximal tubular epithelial cells (PTECs) as renal non-professional antigen-presenting cells that stimulate CD4⁺ T-cell activation. Whether PTECs have the potential to induce activation of CD8⁺ T cells is less clear. In this study, we aimed to investigate the capacity of PTECs for antigen cross-presentation thereby modulating CD8⁺ T-cell responses. We showed that PTECs expressed proteins associated with cross-presentation, internalized soluble antigen via mannose receptor-mediated endocytosis, and generated antigenic peptides by proteasomal degradation. PTECs induced an antigen-dependent CD8⁺ T-cell activation in the presence of soluble antigen in vitro. PTEC-activated CD8⁺ T cells expressed granzyme B, and exerted a cytotoxic function by killing target cells. In murine lupus nephritis, CD8⁺ T cells localized in close contact to proximal tubuli. We determined enhanced apoptosis in tubular cells and particularly PTECs up-regulated expression of cleaved caspase-3. Interestingly, induction of apoptosis in the inflamed kidney was reduced in the absence of CD8⁺ T cells. Thus, PTECs have the capacity for antigen cross-presentation thereby inducing cytotoxic CD8⁺ T cells in vitro, which may contribute to the pathology of immune-mediated glomerulonephritis.

pepsickle rapidly and accurately predicts proteasomal cleavage sites for improved neoantigen identification

MOTIVATION

Proteasomal cleavage is a key component in protein turnover, as well as antigen processing and presentation. Although tools for proteasomal cleavage prediction are available, they vary widely in their performance, options, and availability.

RESULTS

Herein we present pepsickle, an open-source tool for proteasomal cleavage prediction with better in vivo prediction performance (AUC) and computational speed than current models available in the field and with the ability to predict sites based on both constitutive and immunoproteasome profiles. Post-hoc filtering of predicted patient neoepitopes using pepsickle significantly enriches for immune-responsive epitopes and may improve current epitope prediction and vaccine development pipelines.

AVAILABILITY

pepsickle is open source and available at https://github.com/pdxgx/pepsickle.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Role of Dendritic Cell in Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the most significant microvascular complications in diabetic patients. DN is the leading cause of end-stage renal disease, accounting for approximately 50% of incident cases. The current treatment options, such as optimal control of hyperglycemia and elevated blood pressure, are insufficient to prevent its progression. DN has been considered as a nonimmune, metabolic, or hemodynamic glomerular disease initiated by hyperglycemia. However, recent studies suggest that DN is an inflammatory disease, and immune cells related with innate and adaptive immunity, such as macrophage and T cells, might be involved in its development and progression. Although it has been revealed that kidney dendritic cells (DCs) accumulation in the renal tissue of human and animal models of DN require activated T cells in the kidney disease, little is known about the function of DCs in DN. In this review, we describe kidney DCs and their subsets, and the role in the pathogenesis of DN. We also suggest how to improve the kidney outcomes by modulating kidney DCs optimally in the patients with DN.

Amplification of Salt-Sensitive Hypertension and Kidney Damage by Immune Mechanisms

Humans with salt-sensitive (SS) hypertension demonstrate increased morbidity, increased mortality, and renal end-organ damage when compared with normotensive subjects or those with salt-resistant hypertension. Increasing evidence indicates that immune mechanisms play an important role in the full development of SS hypertension and associated renal damage. Recent experimental advances and studies in animal models have permitted a greater understanding of the mechanisms of activation and action of immunity in this disease process. Evidence favors a role of both innate and adaptive immune mechanisms that are triggered by initial, immune-independent alterations in blood pressure, sympathetic activity, or tissue damage. Activation of immunity, which can be enhanced by a high-salt intake or by alterations in other components of the diet, leads to the release of cytokines, free radicals, or other factors that amplify renal damage and hypertension and mediate malignant disease.

SHROOM3, the gene associated with chronic kidney disease, affects the podocyte structure

Chronic kidney disease is a public health burden and it remains unknown which genetic loci are associated with kidney function in the Japanese population, our genome-wide association study using the Biobank Japan dataset (excluding secondary kidney diseases, such as diabetes mellitus) clearly revealed that almost half of the top 50 single nucleotide polymorphisms associated with estimated glomerular filtration rate are located in the SHROOM3 gene, suggesting that SHROOM3 will be responsible for kidney function. Thus, to confirm this finding, supportive functional analyses were performed on Shroom3 in mice using fullerene-based siRNA delivery, which demonstrated that Shroom3 knockdown led to albuminuria and podocyte foot process effacement. The in vitro experiment shows that knockdown of Shroom3 caused defective formation of lamellipodia in podocyte, which would lead to the disruption of slit diaphragm. These results from the GWAS, in vivo and in vitro experiment were consistent with recent studies reporting that albuminuria leads to impairment of kidney function.

Immune mechanisms of salt-sensitive hypertension and renal end-organ damage

Immune mechanisms have been recognized to have a role in the pathogenesis of hypertension, vascular disease and kidney damage in humans and animals for many decades. Contemporary advances in experimentation have permitted a deeper understanding of the mechanisms by which inflammation and immunity participate in cardiovascular disease, and multiple observations have demonstrated strong correlations between the discoveries made in animals and those made in patients with hypertension. Of note, striking phenotypic similarities have been observed in the infiltration of immune cells in the kidney and the development of end-organ damage in patients and animal models with sodium-sensitive hypertension. The available data suggest that an initial salt-induced increase in renal perfusion pressure, which is likely independent of immune mechanisms, induces the infiltration of immune cells into the kidney. The mechanisms mediating immune cell infiltration in the kidney are not well understood but likely involve tissue damage, the direct influence of salt to stimulate immune cell activation, sympathetic nerve stimulation or other factors. The infiltrating cells then release cytokines, free radicals and other factors that contribute to renal damage as well as increased retention of sodium and water and vascular resistance, which lead to the further development of hypertension.

New Understanding on the Role of Proteinuria in Progression of Chronic Kidney Disease

Proteinuria is identified as an important marker and risk factor of progression in chronic kidney disease. However, the precise mechanism of action in the progress of chronic kidney disease is still unclear. Mesangial toxicity from specific filtered compounds such as albumin-bound fatty acids and transferrin/iron, tubular overload and hyperplasia, and induction of proinflammatory molecules such as MCP-1 and inflammatory cytokines are some of the proposed mechanisms. Reversing intraglomerular hypertension with protein restriction or antihypertensive therapy may be beneficial both by diminishing hemodynamic injury to the glomeruli and by reducing protein filtration. Therefore, understanding proteinuria and its role in renal tubular interstitial inflammation and fibrosis is of great significance for the study of renal protective therapy, such as antiproteinuric treatments, and delaying the progression of chronic renal disease.

Exosomal CCL2 from Tubular Epithelial Cells Is Critical for Albumin-Induced Tubulointerstitial Inflammation

Albuminuria is a key instigator of tubulointerstitial inflammation associated with CKD, but the mechanism through which filtered albumin propagates renal injury remains unclear. In this study, we explored the role in this process of exosome mRNA released from tubular epithelial cells (TECs). Compared with control mice, acute and chronic kidney injury models had more exosomes containing inflammatory cytokine mRNA, particularly the chemokine CCL2, in kidneys and urine. In vitro stimulation of TECs with BSA recapitulated this finding. Notably, the internalization of purified TEC exosomes by cultured macrophages increased if TECs were exposed to BSA. Macrophage internalization of exosomes from BSA-treated TECs led to an enhanced inflammatory response and macrophage migration, but CCL2 silencing in TECs prevented these effects. Using a GFP-CCL2 fusion mRNA construct, we observed direct transfer of CCL2 mRNA from TEC exosomes to macrophages. Mice subjected to tail vein injection of purified BSA-treated TEC exosomes developed tubular injury with renal inflammatory cell infiltration. However, injection of exosomes from BSA-treated CCL2-deficient TECs induced less severe kidney inflammation. Finally, in patients with IgA nephropathy, the increase of proteinuria correlated with augmented urinary excretion of exosomes with exaggerated expression of CCL2 mRNA. Moreover, the level of CCL2 mRNA in urinary exosomes correlated closely with levels of renal interstitial macrophage infiltration in these patients. Our studies demonstrate that the increasing release of exosomes that transfer CCL2 mRNA from TECs to macrophages constitutes a critical mechanism of albumin-induced tubulointerstitial inflammation.

Disposition and clinical implications of protein-bound uremic toxins

In patients with chronic kidney disease (CKD), adequate renal clearance is compromised, resulting in the accumulation of a plethora of uremic solutes. These uremic retention solutes, also named uremic toxins, are a heterogeneous group of organic compounds with intrinsic biological activities, many of which are too large to be filtered and/or are protein bound. The renal excretion of protein-bound toxins depends largely on active tubular secretion, which shifts the binding and allows for active secretion of the free fraction. To facilitate this process, renal proximal tubule cells are equipped with a range of transporters that co-operate in basolateral uptake and luminal excretion. Many of these transporters have been characterized as mediators of drug disposition, but have recently been recognized for their importance in the proximal renal tubular transport of uremic toxins as well. This also indicates that during uremia, drug disposition may be severely affected as a result of drug–uremic toxin interaction. In addition, CKD patients receive various drugs to treat their complications potentially resulting in drug–drug interactions (DDIs), also for drugs that are non-renally excreted. This review discusses the current knowledge on formation, disposition and removal of protein-bound uremic toxins. Furthermore, implications associated with drug treatment in kidney failure, as well as innovative renal replacement therapies targetting the protein-bound uremic toxins are being discussed. It will become clear that the complex problems associated with uremia warrant a transdisciplinary approach that unites research experts in the area of fundamental biomedical research with their colleagues in clinical nephrology.

Renal recruitment of B lymphocytes exacerbates tubulointerstitial fibrosis by promoting monocyte mobilization and infiltration after unilateral ureteral obstruction

Renal fibrosis is a significant threat to public health globally. Diverse primary aetiologies eventually result in chronic kidney disease (CKD) and immune cells influence this process. The roles of monocytes/macrophages, T cells, and mast cells have been carefully examined, whilst only a few studies have focused on the effect of B cells. We investigated B‐cell function in tubulointerstitial fibrosis induced by unilateral ureteral obstruction (UUO), using genetic B‐cell‐deficient μMT mice or CD20 antibody‐mediated B‐cell‐depleted mice. Obstructed kidneys of μMT and anti‐CD20‐treated mice showed lower levels of monocyte/macrophage infiltration and collagen deposition compared to wild‐type mice. Mechanistically, anti‐CD20 attenuated UUO‐induced alterations of renal tumour necrosis factor‐α (TNF‐α), vascular cell adhesion molecule 1 (VCAM‐1) pro‐inflammatory genes, and CC chemokine ligand‐2 (CCL2) essential for monocyte recruitment; B cells were one of the main sources of CCL2 in post‐UUO kidneys. Neutralization of CCL2 reduced monocyte/macrophage influx and fibrotic changes in obstructed kidneys. Therefore, early‐stage accumulation of B cells in the kidney accelerated monocyte/macrophage mobilization and infiltration, aggravating the fibrosis resulting from acutely induced kidney nephropathy. © 2016 The Authors. Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Novel adaptive and innate immunity targets in hypertension

Hypertension is a worldwide epidemic and global health concern as it is a major risk factor for the development of cardiovascular diseases. A relationship between the immune system and its contributing role to the pathogenesis of hypertension has been long established, but substantial advancements within the last few years have dissected specific causal molecular mechanisms. This review will briefly examine these recent studies exploring the involvement of either innate or adaptive immunity pathways. Such pathways to be discussed include innate immunity factors such as antigen presenting cells and pattern recognition receptors, adaptive immune elements including T and B lymphocytes, and more specifically, the emerging role of T regulatory cells, as well as the potential of cytokines and chemokines to serve as signaling messengers connecting innate and adaptive immunity. Together, we summarize these studies to provide new perspective for what will hopefully lead to more targeted approaches to manipulate the immune system as hypertensive therapy.

Mechanisms of Drug-Induced Interstitial Nephritis

Drug-induced acute interstitial nephritis (DI-AIN) is a drug hypersensitivity reaction (DHR) that manifests 7 to 10 days after exposure to the culprit drug. DHRs account for fewer than 15% of reported adverse drug reactions. The kidneys are susceptible to DHR because: (1) the high renal blood flow whereby antigens are filtered, secreted, or concentrated, and (2) it is a major site of excretion for drugs and drug metabolites. More than 250 different drugs from various classes have been incriminated as causative agents of DI-AIN, the third most common cause of acute kidney injury in the hospital. DI-AIN must be differentiated from drug-induced nephrotoxic acute tubular necrosis because of their differing pathophysiology and treatment. DI-AIN begins with antigen processing and presentation to local dendritic cells. The dendritic cells activate T cells, and the subsequent effector phase of the immune response is mediated by various cytokines. Incriminated antigenic mechanisms include response to a conjugation product of the drug or its metabolite with a host protein (eg, beta-lactam or sulfonamide antibiotic) or the direct binding of the drug to a particular host allele to elicit a hypersensitivity response (eg, certain anti-epileptic drugs). If the offending drug is not identified and discontinued in a timely manner, irreversible fibrosis and chronic kidney disease will occur. The core structure of each drug or its metabolite is an antigenic determinant, and the host interaction is termed the structure-activity relationship. Differing structure-activity relationships accounts for effect, hypersensitivity, and cross-reactivity among and between classes. The essence of management of DI-AIN lies with the four sequential steps: anticipation, diagnosis, treatment, and prevention. Corticosteroids are used in the treatment of DI-AIN because of their potent anti-inflammatory effects on T cells and eosinophils. Anticipation and prevention require notifying the patient that DI-AIN is an idiosyncratic, hypersensitivity reaction that recurs on re-exposure, and the drug should be avoided.

The Tubulointerstitial Pathophysiology of Progressive Kidney Disease

Accumulating evidence suggests that the central locus for the progression of CKD is the renal proximal tubule. As injured tubular epithelial cells dedifferentiate in attempted repair, they stimulate inflammation and recruit myofibroblasts. At the same time, tissue loss stimulates remnant nephron hypertrophy. Increased tubular transport workload eventually exceeds the energy-generating capacity of the hypertrophied nephrons, leading to anerobic metabolism, acidosis, hypoxia, endoplasmic reticulum stress, and the induction of additional inflammatory and fibrogenic responses. The result is a vicious cycle of injury, misdirected repair, maladaptive responses, and more nephron loss. Therapy that might be advantageous at one phase of this progression pathway could be deleterious during other phases. Thus, interrupting this downward spiral requires narrowly targeted approaches that promote healing and adequate function without generating further entry into the progression cycle.

IL-36 Signaling Facilitates Activation of the NLRP3 Inflammasome and IL-23/IL-17 Axis in Renal Inflammation and Fibrosis

IL-36 cytokines are proinflammatory and have an important role in innate and adaptive immunity, but the role of IL-36 signaling in renal tubulointerstitial lesions (TILs), a major prognostic feature of renal inflammation and fibrosis, remains undetermined. In this study, increased IL-36α expression detected in renal biopsy specimens and urine samples from patients with renal TILs correlated with renal function impairment. We confirmed the increased expression of IL-36α in the renal tubular epithelial cells of a mouse model of unilateral ureteral obstruction (UUO) and related cell models using mechanically induced pressure, oxidative stress, or high mobility group box 1. In contrast, the kidneys of IL-36 receptor (IL-36R) knockout mice exhibit attenuated TILs after UUO. Compared with UUO-treated wild-type mice, UUO-treated IL-36 knockout mice exhibited markedly reduced NLRP3 inflammasome activation and macrophage/T cell infiltration in the kidney and T cell activation in the renal draining lymph nodes. In vitro, recombinant IL-36α facilitated NLRP3 inflammasome activation in renal tubular epithelial cells, macrophages, and dendritic cells and enhanced dendritic cell-induced T cell proliferation and Th17 differentiation. Furthermore, deficiency of IL-23, which was diminished in IL-36R knockout UUO mice, also reduced renal TIL formation in UUO mice. In wild-type mice, administration of an IL-36R antagonist after UUO reproduced the results obtained in UUO-treated IL-36R knockout mice. We propose that IL-36 signaling contributes to the pathogenesis of renal TILs through the activation of the NLRP3 inflammasome and IL-23/IL-17 axis.

Liraglutide Reduces Both Atherosclerosis and Kidney Inflammation in Moderately Uremic LDLr-/- Mice

Chronic kidney disease (CKD) leads to uremia. CKD is characterized by a gradual increase in kidney fibrosis and loss of kidney function, which is associated with a progressive increase in risk of atherosclerosis and cardiovascular death. To prevent progression of both kidney fibrosis and atherosclerosis in uremic settings, insight into new treatment options with effects on both parameters is warranted. The GLP-1 analogue liraglutide improves glucose homeostasis, and is approved for treatment of type 2 diabetes. Animal studies suggest that GLP-1 also dampens inflammation and atherosclerosis. Our aim was to examine effects of liraglutide on kidney fibrosis and atherosclerosis in a mouse model of moderate uremia (5/6 nephrectomy (NX)). Uremic (n = 29) and sham-operated (n = 14) atherosclerosis-prone low density lipoprotein receptor knockout mice were treated with liraglutide (1000 μg/kg, s.c. once daily) or vehicle for 13 weeks. As expected, uremia increased aortic atherosclerosis. In the remnant kidneys from NX mice, flow cytometry revealed an increase in the number of monocyte-like cells (CD68⁺F4/80^-), CD4⁺, and CD8⁺ T-cells, suggesting that moderate uremia induced kidney inflammation. Furthermore, markers of fibrosis (i.e. Col1a1 and Col3a1) were upregulated, and histological examinations showed increased glomerular diameter in NX mice. Importantly, liraglutide treatment attenuated atherosclerosis (~40%, p < 0.05) and reduced kidney inflammation in NX mice. There was no effect of liraglutide on expression of fibrosis markers and/or kidney histology. This study suggests that liraglutide has beneficial effects in a mouse model of moderate uremia by reducing atherosclerosis and attenuating kidney inflammation.

Partial Epithelial-to-Mesenchymal Transition and Other New Mechanisms of Kidney Fibrosis

Kidney fibrosis is the unavoidable consequence of chronic kidney disease irrespective of the primary underlying insult. It is a complex phenomenon governed by the interplay between different cellular components and intricate networks of signaling pathways, which together lead to loss of renal functionality and replacement of kidney parenchyma with scar tissue. An immense effort has recently been made to understand the molecular and cellular mechanisms leading to kidney fibrosis. The cellular protagonists of this process include myofibroblasts, tubular epithelial cells, endothelial cells, and immune cells. We discuss here the most recent findings, including partial epithelial-to-mesenchymal transition (EMT), in the initiation and progression of tissue fibrosis and chronic kidney disease (CKD). A deep understanding of these mechanisms will allow the development of effective therapies.

T cell infiltration is associated with kidney injury in patients with anti-glomerular basement membrane disease

Cell-mediated autoimmunity, particularly that involving autoreactive T cells, participates in mediating anti-glomerular basement membrane (GBM) disease. However, direct kidney injury mediated by renal infiltrated T cells has not been clearly elucidated in humans. The T cell profile (CD3, CD4, CD8, IL-17, and foxp3) and macrophage (CD68) were examined by immunohistochemistry on renal biopsy tissues from 13 patients with anti-GBM disease. The correlation between cell infiltration and clinical data was also analyzed. We found that the distribution of T cell infiltration was predominant in the peri-glomerular and interstitial areas. CD³⁺ T cell infiltratrion around the glomeruli with cellular crescent formations was significantly higher than that around the glomeruli with mild mesangial proliferation. CD⁸⁺ T cells significantly accumulated around the glomeruli with cellular crescents without IgG deposits compared to those with IgG deposits. The prevalence of infiltrating CD⁸⁺ T cells was correlated with the percentage of ruptured Bowman's capsules. In conclusion, cellular immunity may play a crucial role in the inflammatory kidney injury in anti-GBM patients. The periglomerular infiltration of T cells, especially CD⁸⁺ T cells, may participate in the pathogenic mechanism of glomerular damage.

Guanidinylations of albumin decreased binding capacity of hydrophobic metabolites

AIM

As post-translational modifications of proteins may have an impact on the pathogenesis of diseases such as atherosclerosis, diabetes mellitus and chronic kidney disease (CKD), post-translational modifications are currently gaining increasing interest. In this study, a comprehensive method for analysis of these post-translational modifications is established for the clinical diagnostic routine.

METHODS

Here, we analysed albumin - the most abundant plasma protein in human - isolated from patients with CKD and healthy controls by chromatographic steps and identified by MALDI mass spectrometry. Post-translational modifications of albumin were identified after digestion by analysing mass signal shifts of albumin peptides using pertinent mass databases.

RESULTS

Albumin isolated from plasma of patients with CKD but not from healthy control subjects was specifically post-translationally modified by guanidinylation of lysines at positions 249, 468, 548, 565 and 588. After identification of guanidinylations as post-translational modifications of albumin isolated from patients with CKD, these modifications were quantified by mass spectrometry demonstrating a significant increase in the corresponding mass signal intensities in patients with CKD compared to healthy controls. The relative amount of guanidinylation of lysine at position 468 in patients with CKD was determined as 63 ± 32% (N = 3). Subsequently, we characterized the pathophysiological impact of the post-translational guanidinylation on the binding capacity of albumin for representative hydrophobic metabolic waste products. In vitro guanidinylation of albumin from healthy control subjects caused a decreased binding capacity of albumin in a time-dependent manner. Binding of indoxyl sulphate (protein-bound fraction) decreased from 82 ± 1% of not post-translationally modified albumin to 56 ± 1% after in vitro guanidinylation (P < 0.01), whereas the binding of tryptophan decreased from 20 to 4%. These results are in accordance with the binding of indoxyl sulphate to albumin from healthy control subjects and patients with CKD (88 ± 3 vs. 74 ± 10, P < 0.01). Thus, in vitro post-translational guanidinylation of albumin had a direct effect on the binding capacity of hydrophobic metabolites such as indoxyl sulphate and tryptophan.

CONCLUSION

We used a mass spectrometry-based method for the characterization of post-translational modification and demonstrated the pathophysiological impact of a representative post-translational modification of plasma albumin. The data described in this study may help to elucidate the pathophysiological role of protein modifications.

Immunization with an ApoB-100 Related Peptide Vaccine Attenuates Angiotensin-II Induced Hypertension and Renal Fibrosis in Mice

Recent studies suggest the potential involvement of CD8+ T cells in the pathogenesis of murine hypertension. We recently reported that immunization with apoB-100 related peptide, p210, modified CD8+ T cell function in angiotensin II (AngII)-infused apoE (-/-) mice. In this study, we hypothesized that p210 vaccine modulates blood pressure in AngII-infused apoE (-/-) mice. Male apoE (-/-) mice were immunized with p210 vaccine and compared to unimmunized controls. At 10 weeks of age, mice were subcutaneously implanted with an osmotic pump which released AngII for 4 weeks. At 13 weeks of age, p210 immunized mice showed significantly lower blood pressure response to AngII compared to controls. CD8+ T cells from p210 immunized mice displayed a different phenotype compared to CD8+ T cells from unimmunized controls. Serum creatinine and urine albumin to creatinine ratio were significantly decreased in p210 immunized mice suggesting that p210 vaccine had renal protective effect. At euthanasia, inflammatory genes IL-6, TNF-α, and MCP-1 in renal tissue were down-regulated by p210 vaccine. Renal fibrosis and pro-fibrotic gene expression were also significantly reduced in p210 immunized mice. To assess the role of CD8+ T cells in these beneficial effects of p210 vaccine, CD8+ T cells were depleted by CD8 depleting antibody in p210 immunized mice. p210 immunized mice with CD8+ T cell depletion developed higher blood pressure compared to mice receiving isotype control. Depletion of CD8+ T cells also increased renal fibrotic gene expression compared to controls. We conclude that immunization with p210 vaccine attenuated AngII-induced hypertension and renal fibrosis. CD8+ T cells modulated by p210 vaccine could play an important role in the anti-hypertensive, anti-fibrotic and renal-protective effect of p210 vaccine.

Albuminuria Is an Appropriate Therapeutic Target in Patients with CKD: The Pro View

The presence of elevated levels of albuminuria is associated with an increased risk of progressive renal function loss over time. This association is found in various pathophysiological conditions, including diabetic nephropathy, hypertensive nephropathy, and various primary renal diseases, but also, the general, otherwise healthy population. Emerging data report that elevated albuminuria causes tubulointerstitial damage through activation of proinflammatory mediators, which ultimately leads to a progressive decline in renal function. Nowadays, various drugs are available that decrease the rate of GFR loss in patients with kidney disease. Well known are renin-angiotensin-aldosterone system inhibitors, but there are also other drugs and interventions, like intensive glucose control, anti-inflammatory agents (pentoxifylline), or a low-protein diet. These interventions have an additional effect beyond their original target, namely lowering albuminuria. Analyses from clinical trials show that the reduction in albuminuria observed during the first months of treatment with these drugs correlates with the degree of long-term renal protection: the larger the initial reduction in albuminuria, the lower the risk of ESRD during treatment. In addition, in treated patients, residual albuminuria is again the strongest risk marker for renal disease progression. These observations combined provide a strong argument that albuminuria is an appropriate therapeutic target in patients with CKD.

Dendritic cells and macrophages in the kidney: a spectrum of good and evil

Renal dendritic cells (DCs) and macrophages represent a constitutive, extensive and contiguous network of innate immune cells that provide sentinel and immune-intelligence activity; they induce and regulate inflammatory responses to freely filtered antigenic material and protect the kidney from infection. Tissue-resident or infiltrating DCs and macrophages are key factors in the initiation and propagation of renal disease, as well as essential contributors to subsequent tissue regeneration, regardless of the aetiological and pathogenetic mechanisms. The identification, and functional and phenotypic distinction of these cell types is complex and incompletely understood, and the same is true of their interplay and relationships with effector and regulatory cells of the adaptive immune system. In this Review, we discuss the common and distinct characteristics of DCs and macrophages, as well as key advances that have identified the renal-specific functions of these important phagocytic, antigen-presenting cells, and their roles in potentiating or mitigating intrinsic kidney disease. We also identify remaining issues that are of priority for further investigation, and highlight the prospects for translational and therapeutic application of the knowledge acquired.

Key fibrogenic mediators: old players. Renin-angiotensin system

Interstitial fibrosis represents the final common pathway of any form of progressive renal disease. The severity of tubular interstitial damage is highly correlated to the degree of decline of renal function, even better than the glomerular lesions do. Angiotensin II (Ang II), the main effector of the renin-angiotensin system, is a critical promoter of fibrogenesis. It represents a nexus among glomerular capillary hypertension, barrier dysfunction, and renal tubular injury caused by abnormally filtered proteins. Transforming growth factor (TGF)-β1 and reactive oxygen species (ROS) are the key mediators of the pro-fibrotic effect of Ang II causing apoptosis and epithelial-to-mesenchymal transition of the renal tubular epithelium. Recent studies link fibrosis to changes of microRNA (miRNA) modulated by Ang II through TGF-β1, unraveling that antifibrotic action of Ang II antagonism is attributable to epigenetic control of fibrosis-associated genes. Other mechanisms of Ang II-induced fibrosis include ROS-dependent activation of hypoxia-inducible factor-1. Finally, Ang II via angiotensin type 1 receptor regulates the activation and transdifferentiation of pericytes and fibrocytes into scar-forming myofibroblasts. Detachment and phenotypic changes of the former can lead to the loss of peritubular capillaries and also contribute to hypoxia-dependent fibrosis.

What is the best way to measure renal fibrosis?: A pathologist's perspective

Interstitial fibrosis is a hallmark structural correlate of progressive and chronic kidney disease. There remain many uncertainties about how to best measure interstitial fibrosis both in research settings and in evaluations of renal biopsies performed for management of individual patients. Areas of uncertainty include determination of the composition of the matrix in a fibrotic parenchyma, the definition of how the interstitium is involved by fibrosing injuries, the choice of histologic stains for evaluation of renal fibrosis, and the reproducibility and robustness of measures currently employed by pathologists, both with and without the assistance of computerized imaging and assessments. In this review, we address some of these issues while citing the key studies that illustrate these difficulties. We point to future approaches that may allow a more accurate and meaningful assessment of renal interstitial fibrosis.

Acute interstitial nephritis - a reappraisal and update

Acute interstitial nephritis (AIN) is an under recognized and under diagnosed cause of acute kidney injury (AKI). It is estimated to account for 15 - 20% of cases of AKI; it is the reported diagnosis in 2.8% of all kidney biopsies, and 13.5% of biopsies done specifically for acute renal failure. Considerable evidence implicates antigen initiated cell-mediated injury in the pathogenesis of AIN. Drugs account for 70% of all cases, with over 150 different agents incriminated. The remaining cases are due to infections, autoimmune diseases, and rarely idiopathic. The central component of renal injury in AIN is altered tubular function, which usually precedes decrements in filtration rate. The key to early diagnosis is vigilance for the presence of tubular dysfunction in non-oliguric individuals, especially in patients with modest but gradual increments in creatinine level. The utility of urinary biomarkers to diagnose AIN in its early nascent and potentially reversible stage remains to be determined. Prompt recognition, elimination of the offending source of antigen, and use of a limited course of steroid therapy where indicated, will result in complete resolution in ~ 65% of cases, partial resolution in up to 20%, and irreversible damage in the rest.

Progression of renal injury toward interstitial inflammation and glomerular sclerosis is dependent on abnormal protein filtration

Chronic proteinuric renal diseases, independent from the type of the initial insult, have in common a loss of selectivity of the glomerular barrier to protein filtration. Glomerular sclerosis is the progressive lesion affecting the glomerular capillary wall, the primary site at which the protein filtration is abnormally enhanced by disease. Dysfunction of podocytes, that serve to maintain the intact barrier, is a central event in lesion development. However, glomerular injury is signalled to tubular and interstitial structures largely in advance of nephron destruction. Glomerular ultrafiltration of excessive amounts of plasma-derived proteins and associated factors incites tubulointerstitial damage and might amplify an inherent susceptibility of the kidney to become dysfunctional in several disease conditions. Thus, noxious substances in the proteinuric ultrafiltrate promote apoptotic responses and multiple changes in the phenotype of tubule cells with generation of inflammatory and fibrogenic mediators. The severity of tubular interstitial damage has long been recognized to be highly correlated to the degree of deterioration of renal failure even better than glomerular lesions. This review focuses on pathways of tubular injury and apoptosis that in turn promote nephron-by-nephron degeneration and interstitial fibrosis during proteinuria contributing to multifaceted processes of kidney scarring and function loss.

Infiltrating immune cells in the kidney in salt-sensitive hypertension and renal injury

The importance of the immune system in hypertension, vascular disease, and renal disease has been appreciated for over 50 years. Recent experimental advances have led to a greater appreciation of the mechanisms whereby inflammation and immunity participate in cardiovascular disease. In addition to the experimental data, multiple studies in patients have demonstrated a strong correlation between the observations made in animals and humans. Of great interest is the development of salt-sensitive hypertension in humans with the concurrent increase in albumin excretion rate. Experiments in our laboratory have demonstrated that feeding a high-NaCl diet to Dahl salt-sensitive (SS) rats results in a significant infiltration of T lymphocytes into the kidney that is accompanied by the development of hypertension and renal disease. The development of disease in the Dahl SS closely resembles observations made in patients; studies were therefore performed to investigate the pathological role of infiltrating immune cells in the kidney in hypertension and renal disease. Pharmacological and genetic studies indicate that immune cell infiltration into the kidney amplifies the disease process. Further experiments demonstrated that infiltrating T cells may accentuate the Dahl SS phenotype by increasing intrarenal ANG II and oxidative stress. From these and other data, we hypothesize that infiltrating immune cells, which surround the blood vessels and tubules, can serve as a local source of bioactive molecules which mediate vascular constriction, increase tubular sodium reabsorption, and mediate the retention of sodium and water to amplify sodium-sensitive hypertension. Multiple experiments remain to be performed to refine and clarify this hypothesis.

Pathophysiology of proteinuria and its value as an outcome measure in chronic kidney disease

Chronic kidney diseases share common pathogenic mechanisms that, independently from the initial injury, lead to glomerular hyperfiltration, proteinuria, and progressive renal scarring and function loss. Consistent experimental evidence supports the crucial role of proteinuria in accelerating kidney disease progression to end-stage renal failure through multiple pathways, including induction of tubular chemokine expression and complement activation. These events, in turn, lead to inflammatory cell infiltration in the interstitium and sustained fibrogenesis. The extent of proteinuria is widely recognized as a marker of the severity of chronic kidney disease and as a predictor of future decline in glomerular filtration rate. More importantly, a reduction in proteinuria invariably translates into a protection from renal function decline in patients with diabetic and non-diabetic renal disease. Recent evidence also showed the existence of a relationship between proteinuria levels and cardiovascular risk, which extends to the range of urinary albumin excretion that was previously thought 'normal'. Thus, proteinuria should be considered a valuable surrogate end point for clinical trials in patients with chronic renal diseases and a target for reno- and cardioprotecive strategies.

Increased tubulointerstitial recruitment of human CD141(hi) CLEC9A(+) and CD1c(+) myeloid dendritic cell subsets in renal fibrosis and chronic kidney disease

Dendritic cells (DCs) play critical roles in immune-mediated kidney diseases. Little is known, however, about DC subsets in human chronic kidney disease, with previous studies restricted to a limited set of pathologies and to using immunohistochemical methods. In this study, we developed novel protocols for extracting renal DC subsets from diseased human kidneys and identified, enumerated, and phenotyped them by multicolor flow cytometry. We detected significantly greater numbers of total DCs as well as CD141(hi) and CD1c(+) myeloid DC (mDCs) subsets in diseased biopsies with interstitial fibrosis than diseased biopsies without fibrosis or healthy kidney tissue. In contrast, plasmacytoid DC numbers were significantly higher in the fibrotic group compared with healthy tissue only. Numbers of all DC subsets correlated with loss of kidney function, recorded as estimated glomerular filtration rate. CD141(hi) DCs expressed C-type lectin domain family 9 member A (CLEC9A), whereas the majority of CD1c(+) DCs lacked the expression of CD1a and DC-specific ICAM-3-grabbing nonintegrin (DC-SIGN), suggesting these mDC subsets may be circulating CD141(hi) and CD1c(+) blood DCs infiltrating kidney tissue. Our analysis revealed CLEC9A(+) and CD1c(+) cells were restricted to the tubulointerstitium. Notably, DC expression of the costimulatory and maturation molecule CD86 was significantly increased in both diseased cohorts compared with healthy tissue. Transforming growth factor-β levels in dissociated tissue supernatants were significantly elevated in diseased biopsies with fibrosis compared with nonfibrotic biopsies, with mDCs identified as a major source of this profibrotic cytokine. Collectively, our data indicate that activated mDC subsets, likely recruited into the tubulointerstitium, are positioned to play a role in the development of fibrosis and, thus, progression to chronic kidney disease.

The immune system and kidney disease: basic concepts and clinical implications

The kidneys are frequently targeted by pathogenic immune responses against renal autoantigens or by local manifestations of systemic autoimmunity. Recent studies in rodent models and humans have uncovered several underlying mechanisms that can be used to explain the previously enigmatic immunopathology of many kidney diseases. These mechanisms include kidney-specific damage-associated molecular patterns that cause sterile inflammation, the crosstalk between renal dendritic cells and T cells, the development of kidney-targeting autoantibodies and molecular mimicry with microbial pathogens. Conversely, kidney failure affects general immunity, causing intestinal barrier dysfunction, systemic inflammation and immunodeficiency that contribute to the morbidity and mortality of patients with kidney disease. In this Review, we summarize the recent findings regarding the interactions between the kidneys and the immune system.

Proteomic peptide profiling for preemptive diagnosis of acute graft-versus-host disease after allogeneic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation is one curative treatment for hematological malignancies, but is compromised by life-threatening complications, such as severe acute graft-versus-host disease (aGvHD). Prediction of severe aGvHD as early as possible is crucial to allow timely initiation of treatment. Here we report on a multicentre validation of an aGvHD-specific urinary proteomic classifier (aGvHD_MS17) in 423 patients. Samples (n=1106) were collected prospectively between day +7 and day +130 and analyzed using capillary electrophoresis coupled on-line to mass spectrometry. Integration of aGvHD_MS17 analysis with demographic and clinical variables using a logistic regression model led to correct classification of patients developing severe aGvHD 14 days before any clinical signs with 82.4% sensitivity and 77.3% specificity. Multivariate regression analysis showed that aGvHD_MS17 positivity was the only strong predictor for aGvHD grade III or IV (P<0.0001). The classifier consists of 17 peptides derived from albumin, β2-microglobulin, CD99, fibronectin and various collagen α-chains, indicating inflammation, activation of T cells and changes in the extracellular matrix as early signs of GvHD-induced organ damage. This study is currently the largest demonstration of accurate and investigator-independent prediction of patients at risk for severe aGvHD, thus allowing preemptive therapy based on proteomic profiling.

Mononuclear phagocyte system in kidney disease and repair

The mononuclear phagocyte system is comprised of circulating monocytes, tissue macrophages and dendritic cells (DCs) that play key roles in tissue homeostasis, immune surveillance, and immune and non-immune-mediated tissue injury and repair. This review summarizes the various subsets within this system that exhibit significant functional and phenotypic diversity that can adapt to their surrounding microenvironments during inflammation and in response to colony-stimulating factor (CSF)-1. The current understanding of the co-ordination of monocyte infiltration into the homeostatic and diseased kidney through adhesion molecules, chemokines and chemokine receptors, and cytokines are described. Furthermore, the significant confusion and controversy associated with monocyte differentiation into renal macrophages and DCs following infiltration into the kidney, the considerable functional and phenotypic overlap between both tissue populations and their respective roles in immune and non-immune-mediated renal is also discussed. Understanding the factors that control the activation and recruitment of cells from the mononuclear phagocyte system during renal injury may offer an avenue for the development of new cellular and growth factor-based therapies in combination with existing therapies as an alternative treatment option for patients with renal disease.

Batf3-dependent dendritic cells in the renal lymph node induce tolerance against circulating antigens

Although the spleen is a major site where immune tolerance to circulating innocuous antigens occurs, the kidney also contributes. Circulating antigens smaller than albumin are constitutively filtered and concentrated in the kidney and reach the renal lymph node by lymphatic drainage, where resident dendritic cells (DCs) capture them and induce tolerance of specific cytotoxic T cells through unknown mechanisms. Here, we found that the coinhibitory cell surface receptor programmed death 1 (PD-1) on cytotoxic T cells mediates to their tolerance. Renal lymph node DCs of the CD8(+) XCR1(+) subset, which depend on the transcription factor Batf3, expressed the PD-1 cognate ligand PD-L1. Batf3-dependent DCs in the renal lymph node presented antigen that had been concentrated in the kidney and used PD-L1 to induce apoptosis of cytotoxic T cells. In contrast, T cell tolerance in the spleen was independent of PD-1, PD-L1, and Batf3. In summary, these results clarify how the kidney/renal lymph node system tolerizes the immune system against circulating innocuous antigens.

Diabetic nephropathy: the role of inflammation in fibroblast activation and kidney fibrosis

Kidney disease associated with diabetes mellitus is a major health problem worldwide. Although established therapeutic strategies, such as appropriate blood glucose control, blood pressure control with renin-angiotensin system blockade, and lipid lowering with statins, are used to treat diabetes, the contribution of diabetic end-stage kidney disease to the total number of cases requiring hemodialysis has increased tremendously in the past two decades. Once renal function starts declining, it can result in a higher frequency of renal and extra-renal events, including cardiovascular events. Therefore, slowing renal function decline is one of the main areas of focus in diabetic nephropathy research, and novel strategies are urgently needed to prevent diabetic kidney disease progression. Regardless of the type of injury and etiology, kidney fibrosis is the commonly the final outcome of progressive kidney diseases, and it results in significant destruction of normal kidney structure and accompanying functional deterioration. Kidney fibrosis is caused by prolonged injury and dysregulation of the normal wound-healing process in association with excess extracellular matrix deposition. Kidney fibroblasts play an important role in the fibrotic process, but the origin of the fibroblasts remains elusive. In addition to the activation of residential fibroblasts, other important sources of fibroblasts have been proposed, such as pericytes, fibrocytes, and fibroblasts originating from epithelial-to-mesenchymal and endothelial-to-mesenchymal transition. Inflammatory cells and cytokines play a vital role In the process of fibroblast activation. In this review, we will analyze the contribution of inflammation to the process of tissue fibrosis, the type of fibroblast activation and the therapeutic strategies targeting the inflammatory pathways in an effort to slow the progression of diabetic kidney disease.

Renal interstitial fibrosis: mechanisms and evaluation

PURPOSE OF REVIEW

Tubulointerstitial injury in the kidney is complex, involving a number of independent and overlapping cellular and molecular pathways, with renal interstitial fibrosis and tubular atrophy (IFTA) as the final common pathway. Furthermore, there are multiple ways to assess IFTA.

RECENT FINDINGS

Cells involved include tubular epithelial cells, fibroblasts, fibrocytes, myofibroblasts, monocyte/macrophages, and mast cells with complex and still incompletely characterized cell-molecular interactions. Molecular mediators involved are numerous and involve pathways such as transforming growth factor (TGF)-β, bone morphogenic protein (BMP), platelet-derived growth factor (PDGF), and hepatocyte growth factor (HGF). Recent genomic approaches have shed insight into some of these cellular and molecular pathways. Pathologic evaluation of IFTA is central in assessing the severity of chronic disease; however, there are a variety of methods used to assess IFTA. Most assessment of IFTA relies on pathologist assessment of special stains such as trichrome, Sirius Red, and collagen III immunohistochemistry. Visual pathologist assessment can be prone to intra and interobserver variability, but some methods employ computerized morphometery, without a clear consensus as to the best method.

SUMMARY

IFTA results from on orchestration of cell types and molecular pathways. Opinions vary on the optimal qualitative and quantitative assessment of IFTA.

Novel insights into the relationship between glomerular pathology and progressive kidney disease

Both glomerular and tubulointerstitial damage are important factors in the pathophysiology and progression of nephropathy. Glomerular injury is associated with tubulointerstitial inflammation, and many studies show that tubulointerstitial changes correlate well with progressive renal functional decline. Strong evidence supports the concept that once established, proteinuric glomerular injury can cause tubular injury. This review briefly summarizes the pathophysiological consequences of glomerular damage that are responsible for tubulointerstitial injury. It further focuses on tubule-derived renal injury biomarkers that may be used to monitor the progression of kidney disease. This monitoring is predicted to become increasingly useful as novel therapeutic interventions preventing progressive renal damage are introduced. In particular, biomarkers of kidney dysfunction, such as urinary podocytes, kidney injury molecule-1, neutrophil gelatinase-associated lipocalin, hematopoietic growth factor-inducible neurokinin 1, or periostin, might be useful in the diagnosis or detection of early nephropathy and risk assessment of kidney disease. However, these biomarkers require further study before they are used in routine screening or in guiding patient therapy.