Interferon-γ production by tubulointerstitial human CD56bright natural killer cells contributes to renal fibrosis and chronic kidney disease progression

Interferon-γ induces combined pyroptotic angiopathy and APOL1 expression in human kidney disease

Elevated interferon (IFN) signaling is associated with kidney diseases including COVID-19, HIV, and apolipoprotein-L1 (APOL1) nephropathy, but whether IFNs directly contribute to nephrotoxicity remains unclear. Using human kidney organoids, primary endothelial cells, and patient samples, we demonstrate that IFN-γ induces pyroptotic angiopathy in combination with APOL1 expression. Single-cell RNA sequencing, immunoblotting, and quantitative fluorescence-based assays reveal that IFN-γ-mediated expression of APOL1 is accompanied by pyroptotic endothelial network degradation in organoids. Pharmacological blockade of IFN-γ signaling inhibits APOL1 expression, prevents upregulation of pyroptosis-associated genes, and rescues vascular networks. Multiomic analyses in patients with COVID-19, proteinuric kidney disease, and collapsing glomerulopathy similarly demonstrate increased IFN signaling and pyroptosis-associated gene expression correlating with accelerated renal disease progression. Our results reveal that IFN-γ signaling simultaneously induces endothelial injury and primes renal cells for pyroptosis, suggesting a combinatorial mechanism for APOL1-mediated collapsing glomerulopathy, which can be targeted therapeutically.

Obesity-related glomerulopathy: recent advances in inflammatory mechanisms and related treatments

Obesity-related glomerulopathy, which is an obesity-triggered kidney damage, has become a significant threat to human health. Several studies have recently highlighted the critical role of inflammation in obesity-related glomerulopathy development. Additionally, excess adipose tissue and adipocytes in patients with obesity produce various inflammatory factors that cause systemic low-grade inflammation with consequent damage to vascular endothelial cells, exacerbating glomerular injury. Therefore, we conducted a comprehensive review of obesity-related glomerulopathy and addressed the critical role of obesity-induced chronic inflammation in obesity-related glomerulopathy pathogenesis and progression, which leads to tubular damage and proteinuria, ultimately impairing renal function. The relationship between obesity and obesity-related glomerulopathy is facilitated by a network of various inflammation-associated cells (including macrophages, lymphocytes, and mast cells) and a series of inflammatory mediators (such as tumor necrosis factor α, interleukin 6, leptin, adiponectin, resistin, chemokines, adhesion molecules, and plasminogen activator inhibitor 1) and their inflammatory pathways. Furthermore, we discuss a recently discovered relationship between micronutrients and obesity-related glomerulopathy inflammation and the important role of micronutrients in the body's anti-inflammatory response. Therefore, assessing these inflammatory molecules and pathways will provide a strong theoretical basis for developing therapeutic strategies based on anti-inflammatory effects to prevent or delay the onset of kidney injury.

Immune-Modulating Effects of Low-Carbohydrate Ketogenic Foods in Healthy Canines

Background

Ketogenic foods limit digestible carbohydrates but contain high fat, and have antioxidant and anti-inflammatory effects as well as improving mitochondrial function. β-Hydroxybutyrate (BHB), 1 of the ketone bodies, reduces the proinflammatory NLR family pyrin domain containing 3 inflammasomes, as well as chemokines in cultures.

Objectives

We assessed the immune-modulating effects of 2 low-carbohydrate (LoCHO) foods varying in protein and fat and compared their effects with a food replete with high-carbohydrate (HiCHO) in healthy canines.

Methods

Dogs were fed control food [HiCHO; ketogenic ratio (KR: 0.46) followed by LoCHO_PROT (KR: 0.97), then LoCHO_FAT (KR: 1.63) or LoCHO_FAT followed by LoCHO_PROT. Each food was fed for 5 wk, with collections in the 5th wk; 15 wk feeding total. Gene expression for circulating inflammatory cytokines from 10 dogs was assessed using the Canine RT2 Profiler polymerase chain reaction array, and fold changes were calculated using the ΔΔCt method.

Results

LoCHO_FAT significantly increased circulating β-hydroxybutyrate compared with both HiCHO and LoCHO_PROT. When compared with HiCHO, there was a significant decrease in several proinflammatory cytokines/chemokines in LoCHO_PROT and LoCHO_FAT groups, including chemokine (C-C motif) ligand (CCL)1, CCL8, CCL13, CCL17, CCL24, chemokine (C-X3-C motif) ligand 1, chemokine (C-X-C motif) receptor 1, Interleukin-10 receptor alpha ((IL)-10RA), IL-1 receptor antagonist, IL-5, and secreted phosphoprotein 1 (all P < 0.05). Interestingly, a subset of inflammatory proteins that decreased in LoCHO_PROT but not in LoCHO_FAT included IL-33, IL-6 receptor, IL-7, IL-8, Nicotinamide phosphoribosyltransferase, and tumor necrosis factor (TNF) receptor superfamily member 11B. In contrast, the decrease in inflammatory markers in LoCHO_FAT, but not in LoCHO_PROT, included complement component 5, granulocyte colony-stimulating factor or G-CSF, interferon-γ, IL-3, IL-10RB, IL-17C, Tumor necrosis factor superfamily (TNFSF)13, TNFSF13B, and TNFSF14. Decreased concentrations of selected cytokines indicate that both low-carbohydrate foods exert an anti-inflammatory effect and provide a strong rationale for testing their efficacy in dogs with inflammatory conditions.

Conclusions

Both LoCHO_PROT and LoCHO_FAT foods might be important as part of immune-modulating therapeutic nutritional strategies to reduce inflammation to maintain health in canines. Our study identifies several inflammatory genes that are reduced when fed ketogenic food that were not previously reported.

Natural Killer Lymphocytes Mediate Renal Fibrosis Due to Acute Cardiorenal Syndrome

Key Points

Natural killer cells infiltrate the kidney after cardiac arrest and medial renal fibrosis Granzyme A is produced by natural killer cells and causes mesenchymal cell expansion and fibrosis in type 1 cardiorenal syndrome

Background

The AKI to CKD transition presents an opportunity for intervention to prevent CKD. Our laboratory developed a novel murine model of AKI-CKD transition and cardiac arrest/cardiopulmonary resuscitation (CA/CPR), in which all animals develop CKD at 7 weeks. The purpose of this study was to identify potential immune drivers of fibrosis after CA/CPR.

Methods

Cardiac arrest was induced by potassium chloride, and mice were resuscitated with chest compressions and epinephrine. The kidney immune landscape after CA/CPR was profiled using 11-color flow cytometry analysis and immunofluorescence. Immune cell-derived mediators of fibrosis were identified by analyzing data from three previously published single-cell or single-nuclear RNA sequencing studies. NRK49F fibroblasts were treated with granzyme A (GzA) in vitro , and then cell proliferation was quantified using 5-ethynyl-2′-deoxyuridine. GzA was pharmacologically inhibited both in vitro and in vivo .

Results

Immune cells infiltrated the kidney after CA/CPR, consisting primarily of innate immune cells, including monocytes/macrophages, neutrophils, and natural killer (NK) cells. NK cell infiltration immediately preceded mesenchymal cell expansion, which occurred starting 7 days after CA/CPR. Immune cells colocalized with mesenchymal cells, accumulating in the areas of fibrosis. Analysis of previously published single-cell or single-nuclear RNA sequencing data revealed GzA as a potential mediator of immune to mesenchymal communication. GzA administration to fibroblasts in vitro induced cell growth and proliferation. Pharmacologic blockade of GzA signaling in vivo attenuated fibrosis and improved renal function after CA/CPR.

Conclusions

Renal inflammation occurs during cardiorenal syndrome, which correlates with mesenchymal cell expansion. GzA, produced by NK cells, presents a novel therapeutic target to prevent the transition to CKD after AKI.

Physical exercise as a friend not a foe in acute kidney diseases through immune system modulation

Regular and moderate exercise is being used for therapeutic purposes in treating several diseases, including cancer, cardiovascular diseases, arthritis, and even chronic kidney diseases (CKDs). Conversely, extenuating physical exercise has long been pointed out as one of the sources of acute kidney injury (AKI) due to its severe impact on the body's physiology. AKI development is associated with increased tubular necrosis, which initiates a cascade of inflammatory responses. The latter involves cytokine production, immune cell (macrophages, lymphocytes, and neutrophils, among others) activation, and increased oxidative stress. AKI can induce prolonged fibrosis stimulation, leading to CKD development. The need for therapeutic alternative treatments for AKI is still a relevant issue. In this context arises the question as to whether moderate, not extenuating, exercise could, on some level, prevent AKI. Several studies have shown that moderate exercise can help reduce tissue damage and increase the functional recovery of the kidneys after an acute injury. In particular, the immune system can be modulated by exercise, leading to a better recovery from different pathologies. In this review, we aimed to explore the role of exercise not as a trigger of AKI, but as a modulator of the inflammatory/immune system in the prevention or recovery from AKI in different scenarios. In AKI induced by ischemia and reperfusion, sepsis, diabetes, antibiotics, or chemotherapy, regular and/or moderate exercise could modulate the immune system toward a more regulatory immune response, presenting, in general, an anti-inflammatory profile. Exercise was shown to diminish oxidative stress, inflammatory markers (caspase-3, lactate dehydrogenase, and nitric oxide), inflammatory cytokines (interleukin (IL)-1b, IL-6, IL-8, and tumor necrosis factor-α (TNF-α)), modulate lymphocytes to an immune suppressive phenotype, and decrease tumor necrosis factor-β (TGF-β), a cytokine associated with fibrosis development. Thus, it creates an AKI recovery environment with less tissue damage, hypoxia, apoptosis, or fibrosis. In conclusion, the practice of regular moderate physical exercise has an impact on the immune system, favoring a regulatory and anti-inflammatory profile that prevents the occurrence of AKI and/or assists in the recovery from AKI. Moderate exercise should be considered for patients with AKI as a complementary therapy.

Interferon lambda modulates proinflammatory cytokines production in PBMCs from patients with chronic kidney disease

BACKGROUND

CKD is a major cause of morbidity and mortality worldwide. Considerable evidence now indicates that renal inflammation plays a central role in the initiation and progression of CKD. Recent investigations have demonstrated that IFNλ plays an important role in the pathogenesis of autoimmune and inflammatory diseases. However, the association of IFNλ with CKD is still poorly understood.

OBJECTIVE

To analyze the correlation between IFNλ levels and pro-inflammatory cytokines, and to investigate the effect of IFNλ on PBMCs in patients with CKD.

METHODS

PBMCs were harvested from patients with CKD and healthy controls for measuring the expression level of inflammatory cytokines by RT-qPCR. Spearman correlation test was used to analyze correlation between IFNλ and cytokines as well as eGFR. PBMCs from healthy individuals and CKD patients were subjected to IFNλ protein stimulation. IL6, TNFα, IL10, ISG15 and MX1 mRNA level were measured by RT-PCR, STAT1 and phosphorylated STAT1 protein level were measured by Western blot.

RESULTS

Patients with CKD showed higher levels of IFNλ in PBMCs compared to healthy controls. IFNλ mRNA levels were associated with cytokines and eGFR. The transcription of IL6, TNFα, and IL10 was significantly increased in healthy human PBMCs after IFNλ stimulation. In addition, IFNλ acts on PBMCs by p-STAT1 and ISG15 as well as MX1.

CONCLUSION

High expression of IFNλ was found in CKD patients and was associated with eGFR and disease-related cytokines. More importantly, IFNλ promoted the expression of pro-inflammatory cytokines in PBMCs, suggesting a potential pro-inflammatory role of IFNλ in CKD.

Causal effects of systemic inflammatory regulators on chronic kidney diseases and renal function: a bidirectional Mendelian randomization study

Background

While targeted systemic inflammatory modulators show promise in preventing chronic kidney disease (CKD) progression, the causal link between specific inflammatory factors and CKD remains uncertain.

Methods

Using a genome-wide association study of 41 serum cytokines from 8,293 Finnish individuals, we conducted a bidirectional two-sample Mendelian randomization (MR) analysis. In addition, we genetically predicted causal associations between inflammatory factors and 5 phenotypes, including CKD, estimated glomerular filtration rate (eGFR), dialysis, rapid progression of CKD, and rapid decline in eGFR. Inverse variance weighting (IVW) served as the primary MR method, while MR-Egger, weighted median, and MR-pleiotropy residual sum and outlier (MR-PRESSO) were utilized for sensitivity analysis. Cochrane's Q test for heterogeneity. Leave-one-out method ensured stability of MR results, and Bonferroni correction assessed causal relationship strength.

Results

Seventeen cytokines were associated with diverse renal outcomes. Among them, after Bonferroni correction test, higher tumor necrosis factor alpha levels were associated with a rapid decrease in eGFR (OR = 1.064, 95% CI 1.028 - 1.103, P = 0.001), higher interleukin-4 levels were associated with an increase in eGFR (β = 0.003, 95% CI 0.001 - 0.005, P = 0.002), and higher growth regulated oncogene alpha (GROα) levels were associated with an increased risk of CKD (OR=1.035, 95% CI 1.012 - 1.058, P = 0.003). In contrast, genetic susceptibility to CKD was associated with an increase in GROa, and a decrease in eGFR may lead to an increase in stem cell factor. We did not find the presence of horizontal pleiotropy during the analysis.

Conclusion

We discovered causally related inflammatory factors that contribute to the initiation and progression of CKD at the genetic prediction level.

Protective and pathogenic functions of innate lymphoid cells in transplantation

Innate lymphoid cells (ILCs) are a family of lymphocytes with essential roles in tissue homeostasis and immunity. Along with other tissue-resident immune populations, distinct subsets of ILCs have important roles in either promoting or inhibiting immune tolerance in a variety of contexts, including cancer and autoimmunity. In solid organ and hematopoietic stem cell transplantation, both donor and recipient-derived ILCs could contribute to immune tolerance or rejection, yet understanding of protective or pathogenic functions are only beginning to emerge. In addition to roles in directing or regulating immune responses, ILCs interface with parenchymal cells to support tissue homeostasis and even regeneration. Whether specific ILCs are tissue-protective or enhance ischemia reperfusion injury or fibrosis is of particular interest to the field of transplantation, beyond any roles in limiting or promoting allograft rejection or graft-versus host disease. Within this review, we discuss the current understanding of ILCs functions in promoting immune tolerance and tissue repair at homeostasis and in the context of transplantation and highlight where targeting or harnessing ILCs could have applications in novel transplant therapies.

Natural Killer Cells, as the Rising Point in Tissues, Are Forgotten in the Kidney

Natural killer (NK) cells are members of a rapidly expanding family of innate lymphoid cells (ILCs). NK cells play roles in the spleen, periphery, and in many tissues, such as the liver, uterine, lung, adipose, and so on. While the immunological functions of NK cells are well established in these organs, comparatively little is known about NK cells in the kidney. Our understanding of NK cells is rapidly rising, with more and more studies highlighting the functional significance of NK cells in different types of kidney diseases. Recent progress has been made in translating these findings to clinical diseases that occur in the kidney, with indications of subset-specific roles of NK cells in the kidney. For the development of targeted therapeutics to delay kidney disease progression, a better understanding of the NK cell with respect to the mechanisms of kidney diseases is necessary. In order to promote the targeted treatment ability of NK cells in clinical diseases, in this paper we demonstrate the roles that NK cells play in different organs, especially the functions of NK cells in the kidney.

Kidney fibrosis: from mechanisms to therapeutic medicines

Chronic kidney disease (CKD) is estimated to affect 10-14% of global population. Kidney fibrosis, characterized by excessive extracellular matrix deposition leading to scarring, is a hallmark manifestation in different progressive CKD; However, at present no antifibrotic therapies against CKD exist. Kidney fibrosis is identified by tubule atrophy, interstitial chronic inflammation and fibrogenesis, glomerulosclerosis, and vascular rarefaction. Fibrotic niche, where organ fibrosis initiates, is a complex interplay between injured parenchyma (like tubular cells) and multiple non-parenchymal cell lineages (immune and mesenchymal cells) located spatially within scarring areas. Although the mechanisms of kidney fibrosis are complicated due to the kinds of cells involved, with the help of single-cell technology, many key questions have been explored, such as what kind of renal tubules are profibrotic, where myofibroblasts originate, which immune cells are involved, and how cells communicate with each other. In addition, genetics and epigenetics are deeper mechanisms that regulate kidney fibrosis. And the reversible nature of epigenetic changes including DNA methylation, RNA interference, and chromatin remodeling, gives an opportunity to stop or reverse kidney fibrosis by therapeutic strategies. More marketed (e.g., RAS blockage, SGLT2 inhibitors) have been developed to delay CKD progression in recent years. Furthermore, a better understanding of renal fibrosis is also favored to discover biomarkers of fibrotic injury. In the review, we update recent advances in the mechanism of renal fibrosis and summarize novel biomarkers and antifibrotic treatment for CKD.

Novel Aspects of the Immune Response Involved in the Peritoneal Damage in Chronic Kidney Disease Patients under Dialysis

Chronic kidney disease (CKD) incidence is growing worldwide, with a significant percentage of CKD patients reaching end-stage renal disease (ESRD) and requiring kidney replacement therapies (KRT). Peritoneal dialysis (PD) is a convenient KRT presenting benefices as home therapy. In PD patients, the peritoneum is chronically exposed to PD fluids containing supraphysiologic concentrations of glucose or other osmotic agents, leading to the activation of cellular and molecular processes of damage, including inflammation and fibrosis. Importantly, peritonitis episodes enhance peritoneum inflammation status and accelerate peritoneal injury. Here, we review the role of immune cells in the damage of the peritoneal membrane (PM) by repeated exposure to PD fluids during KRT as well as by bacterial or viral infections. We also discuss the anti-inflammatory properties of current clinical treatments of CKD patients in KRT and their potential effect on preserving PM integrity. Finally, given the current importance of coronavirus disease 2019 (COVID-19) disease, we also analyze here the implications of this disease in CKD and KRT.

Plasma Galectin-9 Is a Useful Biomarker for Predicting Renal Function in Patients Undergoing Native Kidney Biopsy

CONTEXT.—

Galectin-9 reduces tissue damage in certain immune-mediated glomerular diseases. However, its role in structural and functional renal changes in patients with varying types of chronic kidney disease (CKD) is less clear.

OBJECTIVE.—

To investigate the association between plasma galectin-9 levels, proteinuria, tubulointerstitial lesions, and renal function in different CKD stages.

DESIGN.—

We measured plasma galectin-9 levels in 243 patients undergoing renal biopsy for determining the CKD etiology. mRNA and protein expression levels of intrarenal galectin-9 were assessed by quantitative real-time polymerase chain reaction and immunostaining. Relationships between plasma galectin-9, clinical characteristics, and tubulointerstitial damage were analyzed with logistic regression. We investigated galectin-9 expression patterns in vitro in murine J774 macrophages treated with differing stimuli.

RESULTS.—

To analyze the relationship between galectin-9 and clinical features, we divided the patients into 2 groups according to median plasma galectin-9 levels. The high galectin-9 group tended to be older and to have decreased renal function, higher proteinuria, and greater interstitial fibrosis. After multivariable adjustment, elevated plasma galectin-9 levels were independently associated with stage 3b or higher CKD. An analysis of gene expression in the tubulointerstitial compartment in the biopsy samples showed a significant positive correlation between intrarenal galectin-9 mRNA expression and plasma galectin-9 levels. Immunohistochemistry confirmed increased galectin-9 expression in the renal interstitium of patients with advanced CKD, and most galectin-9-positive cells were macrophages, as determined by double-immunofluorescence staining. In vitro experiments showed that galectin-9 expression in macrophages was significantly increased after interferon-γ stimulation.

CONCLUSIONS.—

Our findings suggest that plasma galectin-9 is a good biomarker for diagnosing advanced CKD.

Peripheral blood persistence and expansion of transferred non-genetically modified Natural Killer cells might not be necessary for clinical activity

Natural killer (NK) cells are innate lymphocytes that react without previous exposition to virus infected or malignant cells and stimulate adaptive immune response to build a long-lasting immunity against it. To that end, tissue resident NK cells are predominantly regulatory as opposed to cytotoxic. In the hematopoietic stem cell transplant (HSCT) setting, which curative potential relies on the graft versus leukemia effect, NK cells are known to play a significant role. This knowledge has paved the way to the active investigation on its anti-tumor effect outside the stem cell transplant scenario. Based on the relevant literature on the adoptive transfer of non-genetically modified NK cells for the treatment of relapsed/refractory acute leukemia and on our own experience, we discuss the role of donor cell peripheral blood persistence and expansion and its lack of correlation with anti-leukemia activity.

T cells and their products in diabetic kidney disease

Diabetic kidney disease (DKD) is the most common cause of end-stage renal disease and has gradually become a public health problem worldwide. DKD is increasingly recognized as a comprehensive inflammatory disease that is largely regulated by T cells. Given the pivotal role of T cells and T cells-producing cytokines in DKD, we summarized recent advances concerning T cells in the progression of type 2 diabetic nephropathy and provided a novel perspective of immune-related factors in diabetes. Specific emphasis is placed on the classification of T cells, process of T cell recruitment, function of T cells in the development of diabetic kidney damage, and potential treatments and therapeutic strategies involving T cells.

Temporal Profile of Kynurenine Pathway Metabolites in a Rodent Model of Autosomal Recessive Polycystic Kidney Disease

Autosomal recessive polycystic kidney disease (ARPKD) is an early onset genetic disorder characterized by numerous renal cysts resulting in end stage renal disease. Our study aimed to determine if metabolic reprogramming and tryptophan (Trp) metabolism via the kynurenine pathway (KP) is a critical dysregulated pathway in PKD. Using the Lewis polycystic kidney (LPK) rat model of PKD and Lewis controls, we profiled temporal trends for KP metabolites in plasma, urine, and kidney tissues from 6- and 12-week-old mixed sex animals using liquid and gas chromatography, minimum n = 5 per cohort. A greater kynurenine (KYN) concentration was observed in LPK kidney and plasma of 12-week rats compared to age matched Lewis controls (P ⩽ .05). LPK kidneys also showed an age effect (P ⩽ .05) with KYN being greater in 12-week versus 6-week LPK. The metabolites xanthurenic acid (XA), 3-hydroxykynurenine (3-HK), and 3-hydroxyanthranilic acid (3-HAA) were significantly greater in the plasma of 12-week LPK rats compared to age matched Lewis controls (P ⩽ .05). Plasma XA and 3-HK also showed an age effect (P ⩽ .05) being greater in 12-week versus 6-week LPK. We further describe a decrease in Trp levels in LPK plasma and kidney (strain effect P ⩽ .05). There were no differences in KP metabolites in urine between cohorts. Using the ratio of product and substrates in the KP, a significant age-strain effect (P ⩽ .05) was observed in the activity of the KYN/Trp ratio (tryptophan-2,3-dioxygenase [TDO] or indoleamine-2,3-dioxygenase [IDO] activity), kynurenine 3-monooxygenase (KMO), KAT A (kynurenine aminotransferase A), KAT B, total KAT, total KYNU (kynureninase), KYNU A, KYNU B, and total KYNU within LPK kidneys, supporting an activated KP. Confirmation of the activation of these enzymes will require verification through orthogonal techniques. In conclusion, we have demonstrated an up-regulation of the KP in alignment with progression of renal impairment in the LPK rat model, suggesting that KP activation may be a critical contributor to the pathobiology of PKD.

Metabolic signatures of immune cells in chronic kidney disease

Immune cells play a key role in maintaining renal dynamic balance and dealing with renal injury. The physiological and pathological functions of immune cells are intricately connected to their metabolic characteristics. However, immunometabolism in chronic kidney disease (CKD) is not fully understood. Pathophysiologically, disruption of kidney immune cells homeostasis causes inflammation and tissue damage via triggering metabolic reprogramming. The diverse metabolic characteristics of immune cells at different stages of CKD are strongly associated with their different pathological effect. In this work, we reviewed the metabolic characteristics of immune cells (macrophages, natural killer cells, T cells, natural killer T cells and B cells) and several non-immune cells, as well as potential treatments targeting immunometabolism in CKD. We attempt to elaborate on the metabolic signatures of immune cells and their intimate correlation with non-immune cells in CKD.

Identification of Unique Genetic Biomarkers of Various Subtypes of Glomerulonephritis Using Machine Learning and Deep Learning

(1) Objective: Identification of potential genetic biomarkers for various glomerulonephritis (GN) subtypes and discovering the molecular mechanisms of GN. (2) Methods: four microarray datasets of GN were downloaded from Gene Expression Omnibus (GEO) database and merged to obtain the gene expression profiles of eight GN subtypes. Then, differentially expressed immune-related genes (DIRGs) were identified to explore the molecular mechanisms of GN, and single-sample gene set enrichment analysis (ssGSEA) was performed to discover the abnormal inflammation in GN. In addition, a nomogram model was generated using the R package "glmnet", and the calibration curve was plotted to evaluate the predictive power of the nomogram model. Finally, deep learning (DL) based on a multilayer perceptron (MLP) network was performed to explore the characteristic genes for GN. (3) Results: we screened out 274 common up-regulated or down-regulated DIRGs in the glomeruli and tubulointerstitium. These DIRGs are mainly involved in T-cell differentiation, the RAS signaling pathway, and the MAPK signaling pathway. ssGSEA indicates that there is a significant increase in DC (dendritic cells) and macrophages, and a significant decrease in neutrophils and NKT cells in glomeruli, while monocytes and NK cells are increased in tubulointerstitium. A nomogram model was constructed to predict GN based on 7 DIRGs, and 20 DIRGs of each subtype of GN in glomeruli and tubulointerstitium were selected as characteristic genes. (4) Conclusions: this study reveals that the DIRGs are closely related to the pathogenesis of GN and could serve as genetic biomarkers in GN. DL further identified the characteristic genes that are essential to define the pathogenesis of GN and develop targeted therapies for eight GN subtypes.

Shenkang injection protects against renal fibrosis by reducing perforin expression through the STING/TBK1/IRF3 signaling pathways in natural killer cells

BACKGROUND

Immune activation, chronic inflammation, and renal interstitial fibrosis (RIF) are associated with chronic kidney disease (CKD). The herbal formula, Shenkang injection (SKI), has been reported to attenuate RIF. However, the mechanisms by which SKI alleviates renal fibrosis, especially the role of natural killer (NK) cells, are unknown and require exploration.

PURPOSE

This study aimed to determine the mechanisms by which SKI alleviates RIF.

METHODS

Differential gene expression between CKD mice and control groups was explored using bioinformatics analysis. To reveal how SKI reduces RIF in CKD, a CKD mouse model was established using folic acid for in vivo studies, and human kidney-2 cells were used for in vitro experiments. The effects of various SKI doses were then determined. Immunohistochemical staining, Enzyme-linked immunosorbent assay, western blotting, and quantitative real-time PCR were used for pathological and molecular expression detection.

RESULTS

We first investigated the potential immune dysfunction in CKD using bioinformatics analysis. Some differentially expressed genes were enriched in immune-related functions. The expressions of perforin and interferon (IFN)-γ, which are mainly released by NK cells, were significantly higher in patients with CKD (p< 0.05). In vivo experiments showed that SKI alleviated renal fibrosis in a folic acid-induced renal fibrosis model. Serum creatinine and blood urea nitrogen levels were reduced in the high-dose SKI-treated group. Additionally, the mRNA and protein expression levels of type IV collagen and alpha-spinal muscular atrophy were reduced. Biochemical detection showed that SKI could also downregulate the activity of NK cells (by decreasing the expressions of perforin and IFN-γ). Increased levels of stimulator of interferon genes (STING)/TANK-binding kinase 1 (TBK1)/IFN regulatory factor 3 (IRF3), phosphorylation of TBK1, and IRF3 in FA-induced RIF mice were alleviated by SKI treatment, which was consistent with the results of in vitro experiments.

CONCLUSION

These results demonstrated that SKI could decrease the activation of NK cells via the STING/TBK1/IRF3 signaling pathway, thereby alleviating RIF and protecting renal function in CKD. This may provide valuable evidence supporting the clinical use of SKI in the treatment of patients with CKD.

Kynurenine Pathway-An Underestimated Factor Modulating Innate Immunity in Sepsis-Induced Acute Kidney Injury?

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection, and it accounts for about half of the cases of acute kidney injury (AKI). Although sepsis is the most frequent cause of AKI in critically ill patients, its pathophysiological mechanisms are not well understood. Sepsis has the ability to modulate the function of cells belonging to the innate immune system. Increased activity of indoleamine 2,3-dioxygenase 1 (IDO1) and production of kynurenines are the major metabolic pathways utilized by innate immunity cells to maintain immunological tolerance. The activation of the kynurenine pathway (KP) plays a dual role in sepsis—in the early stage, the induction of IDO1 elicits strong proinflammatory effects that may lead to tissue damage and septic shock. Afterwards, depletion of tryptophan and production of kynurenines contribute to the development of immunosuppression that may cause the inability to overpower opportunistic infections. The presented review provides available data on the various interdependencies between elements of innate immunity and sepsis-induced AKI (SAKI) with particular emphasis on the immunomodulatory significance of KP in the above processes. We believe that KP activation may be one of the crucial, though underestimated, components of a deregulated host response to infection during SAKI.

Annexin A2 (ANXA2) regulates the transcription and alternative splicing of inflammatory genes in renal tubular epithelial cells

Background

Renal inflammation plays a crucial role during the progression of Chronic kidney disease (CKD), but there is limited research on hub genes involved in renal inflammation. Here, we aimed to explore the effects of Annexin A2 (ANXA2), a potential inflammatory regulator, on gene expression in human proximal tubular epithelial (HK2) cells. RNA-sequencing and bioinformatics analysis were performed on ANXA2-knockdown versus control HK2 cells to reveal the differentially expressed genes (DEGs) and regulated alternative splicing events (RASEs). Then the DEGs and RASEs were validated by qRT-PCR.

Results

A total of 220 upregulated and 171 downregulated genes related to ANXA2 knockdown were identified. Genes enriched in inflammatory response pathways, such as interferon-mediated signaling, cytokine-mediated signaling, and nuclear factor κB signaling, were under global transcriptional and alternative splicing regulation by ANXA2 knockdown. qRT-PCR confirmed ANXA2-regulated transcription of chemokine gene CCL5, as well as interferon-regulating genes ISG15, IFI6, IFI44, IFITM1, and IRF7, in addition to alternative splicing of inflammatory genes UBA52, RBCK1, and LITAF.

Conclusions

The present study indicated that ANXA2 plays a role in inflammatory response in HK2 cells that may be mediated via the regulation of transcription and alternative splicing of inflammation-related genes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08748-6.

Molecular Mechanisms of Epigenetic Regulation, Inflammation, and Cell Death in ADPKD

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder, which is caused by mutations in the PKD1 and PKD2 genes, characterizing by progressive growth of multiple cysts in the kidneys, eventually leading to end-stage kidney disease (ESKD) and requiring renal replacement therapy. In addition, studies indicate that disease progression is as a result of a combination of factors. Understanding the molecular mechanisms, therefore, should facilitate the development of precise therapeutic strategies for ADPKD treatment. The roles of epigenetic modulation, interstitial inflammation, and regulated cell death have recently become the focuses in ADPKD. Different epigenetic regulators, and the presence of inflammatory markers detectable even before cyst growth, have been linked to cyst progression. Moreover, the infiltration of inflammatory cells, such as macrophages and T cells, have been associated with cyst growth and deteriorating renal function in humans and PKD animal models. There is evidence supporting a direct role of the PKD gene mutations to the regulation of epigenetic mechanisms and inflammatory response in ADPKD. In addition, the role of regulated cell death, including apoptosis, autophagy and ferroptosis, have been investigated in ADPKD. However, there is no consensus whether cell death promotes or delays cyst growth in ADPKD. It is therefore necessary to develop an interactive picture between PKD gene mutations, the epigenome, inflammation, and cell death to understand why inherited PKD gene mutations in patients may result in the dysregulation of these processes that increase the progression of renal cyst formation.

Spatially Resolved Transcriptomes of Mammalian Kidneys Illustrate the Molecular Complexity and Interactions of Functional Nephron Segments

Available transcriptomes of the mammalian kidney provide limited information on the spatial interplay between different functional nephron structures due to the required dissociation of tissue with traditional transcriptome-based methodologies. A deeper understanding of the complexity of functional nephron structures requires a non-dissociative transcriptomics approach, such as spatial transcriptomics sequencing (ST-seq). We hypothesize that the application of ST-seq in normal mammalian kidneys will give transcriptomic insights within and across species of physiology at the functional structure level and cellular communication at the cell level. Here, we applied ST-seq in six mice and four human kidneys that were histologically absent of any overt pathology. We defined the location of specific nephron structures in the captured ST-seq datasets using three lines of evidence: pathologist's annotation, marker gene expression, and integration with public single-cell and/or single-nucleus RNA-sequencing datasets. We compared the mouse and human cortical kidney regions. In the human ST-seq datasets, we further investigated the cellular communication within glomeruli and regions of proximal tubules–peritubular capillaries by screening for co-expression of ligand–receptor gene pairs. Gene expression signatures of distinct nephron structures and microvascular regions were spatially resolved within the mouse and human ST-seq datasets. We identified 7,370 differentially expressed genes (p_adj < 0.05) distinguishing species, suggesting changes in energy production and metabolism in mouse cortical regions relative to human kidneys. Hundreds of potential ligand–receptor interactions were identified within glomeruli and regions of proximal tubules–peritubular capillaries, including known and novel interactions relevant to kidney physiology. Our application of ST-seq to normal human and murine kidneys confirms current knowledge and localization of transcripts within the kidney. Furthermore, the generated ST-seq datasets provide a valuable resource for the kidney community that can be used to inform future research into this complex organ.

Tissue-Dependent Adaptations and Functions of Innate Lymphoid Cells

Tissue-resident immune cells reside in distinct niches across organs, where they contribute to tissue homeostasis and rapidly respond to perturbations in the local microenvironment. Innate lymphoid cells (ILCs) are a family of innate immune cells that regulate immune and tissue homeostasis. Across anatomical locations throughout the body, ILCs adopt tissue-specific fates, differing from circulating ILC populations. Adaptations of ILCs to microenvironmental changes have been documented in several inflammatory contexts, including obesity, asthma, and inflammatory bowel disease. While our understanding of ILC functions within tissues have predominantly been based on mouse studies, development of advanced single cell platforms to study tissue-resident ILCs in humans and emerging patient-based data is providing new insights into this lymphocyte family. Within this review, we discuss current concepts of ILC fate and function, exploring tissue-specific functions of ILCs and their contribution to health and disease across organ systems.

Conventional NK Cells and Type 1 Innate Lymphoid Cells Do Not Influence Pathogenesis of Experimental Glomerulonephritis

Innate lymphoid cells (ILCs) that express NK cell receptors (NCRs) and the transcription factor T-bet populate nonlymphoid tissues and are crucial in immune responses against viral infections and malignancies. Recent studies highlighted the heterogeneity of this ILC population and extended their functional spectrum to include important roles in tissue homeostasis and autoimmunity. In this article, we provide detailed profiling of NCR+T-bet+ ILC populations in the murine kidney, identifying conventional NK (cNK) cells and type 1 ILCs (ILC1s) as the two major subsets. Induction of renal inflammation in a mouse model of glomerulonephritis did not substantially influence abundance or phenotype of cNK cells or ILC1s in the kidney. For functional analyses in this model, widely used depletion strategies for total NCR+ ILCs (anti-NK1.1 Ab application) and cNK cells (anti-asialoGM1 serum application) were unreliable tools, because they were accompanied by significant off-target depletion of kidney NKT cells and CD8+ T cells, respectively. However, neither depletion of cNK cells and ILC1s in NKT cell–deficient mice nor specific genetic deletion of cNK cells in Ncr1Cre/wt × Eomesfl/fl mice altered the clinical course of experimental glomerulonephritis. In summary, we show in this article that cNK cells and ILC1s are dispensable for initiation and progression of immune-mediated glomerular disease and advise caution in the use of standard Ab depletion methods to study NCR+ ILC function in mouse models.

Curcumin Supplementation (Meriva®) Modulates Inflammation, Lipid Peroxidation and Gut Microbiota Composition in Chronic Kidney Disease

Chronic kidney disease (CKD) subjects suffer from high risk of cardiovascular mortality, and any intervention preventing the progression of CKD may have an enormous impact on public health. In the last decade, there has been growing awareness that the gut microbiota (GM) can play a pivotal role in controlling the pathogenesis of systemic inflammatory state and CKD progression. To ameliorate the quality of life in CKD subjects, the use of dietary supplements has increased over time. Among those, curcumin has demonstrated significant in vitro anti-inflammatory properties. In this pilot study, 24 CKD patients and 20 healthy volunteers were recruited. CKD patients followed nutritional counselling and were supplemented with curcumin (Meriva^®) for six months. Different parameters were evaluated at baseline and after 3-6 months: uremic toxins, metagenomic of GM, and nutritional, inflammatory, and oxidative status. Curcumin significantly reduced plasma pro-inflammatory mediators (CCL-2, IFN-γ, and IL-4) and lipid peroxidation. Regarding GM, after 6 months of curcumin supplementation, Escherichia-Shigella was significantly lower, while Lachnoclostridium was significant higher. Notably, at family level, Lactobacillaceae spp. were found significantly higher in the last 3 months of supplementation. No adverse events were observed in the supplemented group, confirming the good safety profile of curcumin phytosome after long-term administration.

Differential Kat3 Usage Orchestrates the Integration of Cellular Metabolism with Differentiation

Simple Summary

The coupling of metabolism with cellular status is critically important and highly evolutionarily conserved. However, how cells coordinate metabolism with transcription as they change their status is not clear. Utilizing multiomic and functional studies, we now demonstrate the dichotomous roles of the Kat3 coactivators CBP and p300 and, in particular, their extreme N-termini, in coordinating cellular metabolism with cell differentiation. Using multiple in vitro and in vivo systems, our study sheds new light on metabolic regulation in homeostasis and disease, including cancer.

Abstract

The integration of cellular status with metabolism is critically important and the coupling of energy production and cellular function is highly evolutionarily conserved. This has been demonstrated in stem cell biology, organismal, cellular and tissue differentiation and in immune cell biology. However, a molecular mechanism delineating how cells coordinate and couple metabolism with transcription as they navigate quiescence, growth, proliferation, differentiation and migration remains in its infancy. The extreme N-termini of the Kat3 coactivator family members, CBP and p300, by far the least homologous regions with only 66% identity, interact with members of the nuclear receptor family, interferon activated Stat1 and transcriptionally competent β-catenin, a critical component of the Wnt signaling pathway. We now wish to report based on multiomic and functional investigations, utilizing p300 knockdown, N-terminal p300 edited and p300 S89A edited cell lines and p300 S89A knockin mice, that the N-termini of the Kat3 coactivators provide a highly evolutionarily conserved hub to integrate multiple signaling cascades to coordinate cellular metabolism with the regulation of cellular status and function.

Kidney disease risk factors do not explain impacts of low dietary protein on kidney function and structure

The kidneys balance many byproducts of the metabolism of dietary components. Previous studies examining dietary effects on kidney health are generally of short duration and manipulate a single macronutrient. Here, kidney function and structure were examined in C57BL/6J mice randomized to consume one of a spectrum of macronutrient combinations (protein [5%–60%], carbohydrate [20%–75%], and fat [20%–75%]) from weaning to late-middle age (15 months). Individual and interactive impacts of macronutrients on kidney health were modeled. Dietary protein had the greatest influence on kidney function, where chronic low protein intake decreased glomerular filtration rates and kidney mass, whereas it increased kidney immune infiltration and structural injury. Kidney outcomes did not align with cardiometabolic risk factors including glucose intolerance, overweight/obesity, dyslipidemia, and hypertension in mice with chronic low protein consumption. This study highlights that protein intake over a lifespan is an important determinant of kidney function independent of cardiometabolic changes.

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Chronic high macronutrient intake from any source increases kidney function (GFR)

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Low protein intake led to greater kidney tubular structural injury and inflammation

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Lower protein intake decreased kidney mass and glomerular filtration capacity

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Kidney outcomes did not align with longevity or cardiometabolic outcomes

Taking the road less traveled - the therapeutic potential of CBP/β-catenin antagonists

AREAS COVERED

This perspective discusses the challenges of targeting the Wnt signaling cascade, the safety, efficacy, and therapeutic potential of specific CBP/β-catenin antagonists and a rationale for the pleiotropic effects of CBP/β-catenin antagonists beyond Wnt signaling.

EXPERT OPINION

CBP/β-catenin antagonists can correct lineage infidelity, enhance wound healing, both normal and aberrant (e.g. fibrosis) and force the differentiation and lineage commitment of stem cells and cancer stem cells by regulating enhancer and super-enhancer coactivator occupancy. Small molecule CBP/β-catenin antagonists rebalance the equilibrium between CBP/β-catenin versus p300/β-catenin dependent transcription and may be able to treat or prevent many diseases of aging, via maintenance of our somatic stem cell pool, and regulating mitochondrial function and metabolism involved in differentiation and immune cell function.

Human NK cells: From development to effector functions

NK cells are the major lymphocyte subset of the innate immune system that mediates antiviral and anti-tumor responses. It is well established that they develop mechanisms to distinguish self from non-self during the process of NK cell education. Unlike T and B cells, natural killer cells lack clonotypic receptors and are activated after recognizing their target via germline-encoded receptors through natural cytotoxicity, cytokine stimulation, and Ab-dependent cellular cytotoxicity. Subsequently, they utilize cytotoxic granules, death receptor ligands, and cytokines to perform their effector functions. In this review, we provide a general overview of human NK cells, as opposed to murine NK cells, discussing their ontogeny, maturation, receptor diversity, types of responses, and effector functions. Furthermore, we also describe recent advances in human NK cell biology, including tissue-resident NK cell populations, NK cell memory, and novel approaches used to target NK cells in cancer immunotherapy.

Mechanisms of Peritoneal Fibrosis: Focus on Immune Cells-Peritoneal Stroma Interactions

Peritoneal fibrosis is characterized by abnormal production of extracellular matrix proteins leading to progressive thickening of the submesothelial compact zone of the peritoneal membrane. This process may be caused by a number of insults including pathological conditions linked to clinical practice, such as peritoneal dialysis, abdominal surgery, hemoperitoneum, and infectious peritonitis. All these events may cause acute/chronic inflammation and injury to the peritoneal membrane, which undergoes progressive fibrosis, angiogenesis, and vasculopathy. Among the cellular processes implicated in these peritoneal alterations is the generation of myofibroblasts from mesothelial cells and other cellular sources that are central in the induction of fibrosis and in the subsequent functional deterioration of the peritoneal membrane. Myofibroblast generation and activity is actually integrated in a complex network of extracellular signals generated by the various cellular types, including leukocytes, stably residing or recirculating along the peritoneal membrane. Here, the main extracellular factors and the cellular players are described with emphasis on the cross-talk between immune system and cells of the peritoneal stroma. The understanding of cellular and molecular mechanisms underlying fibrosis of the peritoneal membrane has both a basic and a translational relevance, since it may be useful for setup of therapies aimed at counteracting the deterioration as well as restoring the homeostasis of the peritoneal membrane.

PD-1 immunobiology in glomerulonephritis and renal cell carcinoma

BACKGROUND

Programmed cell death protein (PD)-1 receptors and ligands on immune cells and kidney parenchymal cells help maintain immunological homeostasis in the kidney. Dysregulated PD-1:PD-L1 binding interactions occur during the pathogenesis of glomerulopathies and renal cell carcinoma (RCC). The regulation of these molecules in the kidney is important to PD-1/PD-L1 immunotherapies that treat RCC and may induce glomerulopathies as an adverse event.

METHODS

The expression and function of PD-1 molecules on immune and kidney parenchymal cells were reviewed in the healthy kidney, PD-1 immunotherapy-induced nephrotoxicity, glomerulopathies and RCC.

RESULTS

PD-1 and/or its ligands are expressed on kidney macrophages, dendritic cells, lymphocytes, and renal proximal tubule epithelial cells. Vitamin D3, glutathione and AMP-activated protein kinase (AMPK) regulate hypoxic cell signals involved in the expression and function of PD-1 molecules. These pathways are altered in kidney disease and are linked to the production of vascular endothelial growth factor, erythropoietin, adiponectin, interleukin (IL)-18, IL-23, and chemokines that bind CXCR3, CXCR4, and/or CXCR7. These factors are differentially produced in glomerulonephritis and RCC and may be important biomarkers in patients that receive PD-1 therapies and/or develop glomerulonephritis as an adverse event CONCLUSION: By comparing the functions of the PD-1 axis in glomerulopathies and RCC, we identified similar chemokines involved in the recruitment of immune cells and distinct mediators in T cell differentiation. The expression and function of PD-1 and PD-1 ligands in diseased tissue and particularly on double-negative T cells and parenchymal kidney cells needs continued exploration. The possible regulation of the PD-1 axis by vitamin D3, glutathione and/or AMPK cell signals may be important to kidney disease and the PD-1 immunotherapeutic response.

SARS-CoV-2 and Viral Sepsis: Immune Dysfunction and Implications in Kidney Failure

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causal agent of coronavirus disease 2019 (COVID-19), first emerged in Wuhan, China. The clinical manifestations of patients infected with COVID-19 include fever, cough, and dyspnea, up to acute respiratory distress syndrome (ARDS) and acute cardiac injury. Thus, a lot of severe patients had to be admitted to intensive care units (ICU). The pathogenic mechanisms of SARS-CoV-2 infection are mediated by the binding of SARS-CoV-2 spikes to the human angiotensin-converting enzyme 2 (ACE-2) receptor. The overexpression of human ACE-2 is associated with the disease severity in SARS-CoV-2 infection, demonstrating that viral entry into cells is a pivotal step. Although the lung is the organ that is most commonly affected by SARS-CoV-2 infection, acute kidney injury (AKI), heart dysfunction and abdominal pain are the most commonly reported co-morbidities of COVID-19. The occurrence of AKI in COVID-19 patients might be explained by several mechanisms that include viral cytopathic effects in renal cells and the host hyperinflammatory response. In addition, kidney dysfunction could exacerbate the inflammatory response started in the lungs and might cause further renal impairment and multi-organ failure. Mounting recent evidence supports the involvement of cardiovascular complications and endothelial dysfunction in COVID-19 syndrome, in addition to respiratory disease. To date, there is no vaccine, and no specific antiviral medicine has been shown to be effective in preventing or treating COVID-19. The removal of pro-inflammatory cytokines and the shutdown of the cytokine storm could ameliorate the clinical outcome in severe COVID-19 cases. Therefore, several interventions that inhibit viral replication and the systemic inflammatory response could modulate the severity of the renal dysfunction and increase the probability of a favorable outcome.

Recent Advances in the Role of Natural Killer Cells in Acute Kidney Injury

Growing evidence is revealing a central role for natural killer (NK) cells, cytotoxic cells belonging to the broad family of innate lymphoid cells (ILCs), in acute and chronic forms of renal disease. NK cell effector functions include both the recognition and elimination of virus-infected and tumor cells and the capability of sensing pathogens through Toll-like receptor (TLR) engagement. Notably, they also display immune regulatory properties, exerted thanks to their ability to secrete cytokines/chemokines and to establish interactions with different innate and adaptive immune cells. Therefore, because of their multiple functions, NK cells may have a major pathogenic role in acute kidney injury (AKI), and a better understanding of the molecular mechanisms driving NK cell activation in AKI and their downstream interactions with intrinsic renal cells and infiltrating immune cells could help to identify new potential biomarkers and to select clinically valuable novel therapeutic targets. In this review, we discuss the current literature regarding the potential involvement of NK cells in AKI.

The Role of Natural Killer Cells in the Immune Response in Kidney Transplantation

Natural killer cells (NK) represent a population of lymphocytes involved in innate immune response. In addition to their role in anti-viral and anti-tumor defense, they also regulate several aspects of the allo-immune response in kidney transplant recipients. Growing evidence suggests a key role of NK cells in the pathogenesis of immune-mediated graft damage in kidney transplantation. Specific NK cell subsets are associated with operational tolerance in kidney transplant patients. On the other side, allo-reactive NK cells are associated with chronic antibody-mediated rejection and graft loss. Moreover, NK cells can prime the adaptive immune system and promote the migration of other immune cells, such as dendritic cells, into the graft leading to an increased allo-immune response and, eventually, to chronic graft rejection. Finally, activated NK cells can infiltrate the transplanted kidney and cause a direct graft damage. Interestingly, immunosuppression can influence NK cell numbers and function, thus causing an increased risk of post-transplant neoplasia or infection. In this review, we will describe how these cells can influence the innate and the adaptive immune response in kidney transplantation and how immunosuppression can modulate NK behavior.

Tissue-resident natural killer cells exacerbate tubulointerstitial fibrosis by activating transglutaminase 2 and syndecan-4 in a model of aristolochic acid-induced nephropathy

Despite reports suggesting that tissue-resident natural killer (trNK) cells cause ischemic kidney injury, their contribution to the development of tubulointerstitial fibrosis has not been determined. This study hypothesized that the depletion of trNK cells may ameliorate renal fibrosis by affecting transglutaminase 2/syndecan-4 interactions. Aristolochic acid nephropathy (AAN) was induced in C57BL/6 mice as an experimental model of kidney fibrosis. The mice were treated with anti-asialo GM1 (ASGM1) or anti-NK1.1 antibodies to deplete NK cells. Although both ASGM1 and NK1.1 antibodies suppressed renal NKp46⁺DX5⁺ NK cells, renal NKp46⁺DX5⁻ cells were resistant to suppression by ASGM1 or NK1.1 antibodies during the development of tubulointerstitial fibrosis in the AAN-induced mouse model. Western blot analysis showed that both antibodies increased the expression of fibronectin, transglutaminase 2, and syndecan-4. These findings indicate that trNK cells played an exacerbating role in tubulointerstitial fibrosis by activating transglutaminase 2 and syndecan-4 in the AAN-induced mouse model.

Effector γδ T cells in human renal fibrosis and chronic kidney disease

Background

γδ T cells are effector lymphocytes recognized as key players during chronic inflammatory processes. Mouse studies suggest a pathological role for γδ T cells in models of kidney disease. Here we evaluated γδ T cells in human native kidneys with tubulointerstitial fibrosis, the pathological hallmark of chronic kidney disease.

Methods

γδ T cells were extracted from human kidney tissue and enumerated and phenotyped by multicolour flow cytometry. Localization and cytokine production by γδ T cells was examined by immunofluorescent microscopy.

Results

We detected significantly elevated numbers of γδ T cells in diseased biopsies with tubulointerstitial fibrosis compared with diseased biopsies without fibrosis and healthy kidney tissue. At a subset level, only numbers of Vδ1+ γδ T cells were significantly elevated in fibrotic kidney tissue. Expression levels of cluster of differentiation 161 (CD161), a marker of human memory T cells with potential for innate-like function and interleukin (IL)-17A production, were significantly elevated on γδ T cells from fibrotic biopsies compared with nonfibrotic kidney tissue. Flow cytometric characterization of CD161+ γδ T cells in fibrotic biopsies revealed significantly elevated expression of natural killer (NK) cell-associated markers CD56, CD16 and CD336 (NKp44) compared with CD161- γδ T cells, indicative of a cytotoxic phenotype. Immunofluorescent analysis of fibrotic kidney tissue localized the accumulation of γδ T cells within the tubulointerstitium, with γδ T cells identified, for the first time, as a source of pro-inflammatory cytokine IL-17A.

Conclusions

Collectively, our data suggest that human effector γδ T cells contribute to the fibrotic process and thus progression to chronic kidney disease.

Identification of CD2, CCL5 and CCR5 as potential therapeutic target genes for renal interstitial fibrosis

Background

We aimed to explore potential gene biomarkers of renal interstitial fibrosis (RIF) due to a lack of effective and non-invasive methods for diagnosis.

Methods

Three data sets (GSE22459, GSE76882 and GSE57731) including 350 samples were acquired from Gene Expression Omnibus (GEO) database. We used bioconductor limma package to perform background adjustment. Cluster analysis was conducted by 'edgeR' package to identify the differentially expressed genes (DEGs). We generated heat maps with using heatmap package in R software. Function annotation of genes was performed by Gene Ontology (GO) enrichment analysis. STRING (Search Tool for the Retrieval of Interacting Genes) database was employed to construct the protein-protein interaction (PPI) network and the results were visualized by Cytoscape 3.6.1. At last, we applied Graphpad Prism 7.0. to explore the correlation between three hub genes and pathological degrees of RIF.

Results

By applying the "edgeR" package in R, we detected 116 DEGs with three data sets. These genes were enriched in 19 GO biological process categories. Three main hub genes (CD2, CCL5 and CCR5) were identified after construction of PPI network. In Pearson correlation coefficient, CD2, CCL5 and CCR5 was found to hold higher expression patterns in RIF samples based on independent data set GSE57731. Besides, their gene expression levels were found significantly positive correlation with the degree of RIF (CD2: P<0.05, r=0.29; CCL5: P<0.05, r=0.31; CCR5: P<0.05, r=0.38).

Conclusions

CD2, CCL5 and CCR5 might serve as potential early biomarkers of RIF. The mechanism between these genes and RIF remains to be further studied.

Complement C1r serine protease contributes to kidney fibrosis

We have previously reported that complement activation precedes the development of kidney fibrosis; however, little is known about the cellular mechanisms involved in this transition. We hypothesized that increased expression of C1 complex protease C1r, the initiator of complement activation, contributes to tubulointerstitial fibrosis and tested this idea in mice with global deletion of C1r. Although expression of C1r in untreated wild-type (WT) mice was higher in the liver compared with kidney tissue, administration of folic acid (FA) led to upregulation of C1r mRNA and protein levels only in kidney tissue. Immunohistochemistry and in situ hybridization experiments localized increased expression of C1r and C1s proteases to renal tubular epithelial cells. C1r-null mice had reduced acute tubular injury and inflammation measured 2 days after FA administration compared with WT mice. C1r deletion reduced expression of C1s, C3 fragment formation, and organ fibrosis measured 14 days after FA administration. Differential gene expression performed in kidney tissue demonstrated that C1r-null mice had reduced expression of genes associated with the acute phase response, complement, proliferation of connective tissue cells (e.g., platelet-derived growth factor receptor-β), and reduced expression of genes associated with inflammation compared with FA-treated WT mice. In vitro experiments in renal epithelial cells demonstrated that C1s expression is dependent on increased C1r expression and that interferon-γ induces the expression of these two proteases. We conclude that increased expression of C1 complex proteases is associated with increased tissue inflammation and complement C3 formation and represents an important pathogenic mechanism leading to FA-mediated tubulointerstitial fibrosis.

Specialized Roles of Human Natural Killer Cell Subsets in Kidney Transplant Rejection

Background: Human natural killer (NK) cells are key functional players in kidney transplant rejection. However, the respective contributions of the two functionally distinct human NK cell subsets (CD56bright cytokine-producing vs. CD56dim cytotoxic effector) in episodes of allograft rejection remain uncertain, with current immunohistochemical methods unable to differentiate these discrete populations. We report the outcomes of an innovative multi-color flow cytometric-based approach to unequivocally define and evaluate NK cell subsets in human kidney allograft rejection. Methods: We extracted renal lymphocytes from human kidney transplant biopsies. NK cell subsets were identified, enumerated, and phenotyped by multi-color flow cytometry. Dissociation supernatants were harvested and levels of soluble proteins were determined using a multiplex bead-based assay. Results were correlated with the histopathological patterns in biopsies-no rejection, borderline cellular rejection, T cell-mediated rejection (TCMR), and antibody-mediated rejection (AMR). Results: Absolute numbers of only CD56bright NK cells were significantly elevated in TCMR biopsies. In contrast, both CD56bright and CD56dim NK cell numbers were significantly increased in biopsies with histopathological evidence of AMR. Notably, expression of the activation marker CD69 was only significantly elevated on CD56dim NK cells in AMR biopsies compared with no rejection biopsies, indicative of a pathogenic phenotype for this cytotoxic NK cell subset. In line with this, we detected significantly elevated levels of cytotoxic effector molecules (perforin, granzyme A, and granulysin) in the dissociation supernatants of biopsies with a histopathological pattern of AMR. Conclusions: Our results indicate that human NK cell subsets are differentially recruited and activated during distinct types of rejection, suggestive of specialized functional roles.

Human Tissue-Resident Mucosal-Associated Invariant T (MAIT) Cells in Renal Fibrosis and CKD

BACKGROUND

Mucosal-associated invariant T (MAIT) cells represent a specialized lymphocyte population associated with chronic inflammatory disorders. Little is known, however, about MAIT cells in diseases of the kidney, including CKD.

METHODS

To evaluate MAIT cells in human native kidneys with tubulointerstitial fibrosis, the hallmark of CKD, we used multicolor flow cytometry to identify, enumerate, and phenotype such cells from human kidney tissue biopsy samples, and immunofluorescence microscopy to localize these cells. We cocultured MAIT cells and human primary proximal tubular epithelial cells (PTECs) under hypoxic (1% oxygen) conditions to enable examination of mechanistic tubulointerstitial interactions.

RESULTS

We identified MAIT cells (CD3+ TCR Vα7.2+ CD161hi) in healthy and diseased kidney tissues, detecting expression of tissue-resident markers (CD103/CD69) on MAIT cells in both states. Tissue samples from kidneys with tubulointerstitial fibrosis had significantly elevated numbers of MAIT cells compared with either nonfibrotic samples from diseased kidneys or tissue samples from healthy kidneys. Furthermore, CD69 expression levels, also an established marker of lymphocyte activation, were significantly increased on MAIT cells from fibrotic tissue samples. Immunofluorescent analyses of fibrotic kidney tissue identified MAIT cells accumulating adjacent to PTECs. Notably, MAIT cells activated in the presence of human PTECs under hypoxic conditions (modeling the fibrotic microenvironment) displayed significantly upregulated expression of CD69 and cytotoxic molecules perforin and granzyme B; we also observed a corresponding significant increase in PTEC necrosis in these cocultures.

CONCLUSIONS

Our findings indicate that human tissue-resident MAIT cells in the kidney may contribute to the fibrotic process of CKD via complex interactions with PTECs.

Roles of Natural Killer T Cells and Natural Killer Cells in Kidney Injury

Mouse natural killer T (NKT) cells and natural killer (NK) cells are innate immune cells that are highly abundant in the liver. In addition to their already-known antitumor and antimicrobial functions, their pathophysiological roles in the kidney have recently become evident. Under normal circumstances, the proportion of activated NKT cells in the kidney increases with age. Administration of a synthetic sphingoglycolipid ligand (alpha-galactosylceramide) further activates NKT cells, resulting in injury to renal vascular endothelial cells via the perforin-mediated pathway and tubular epithelial cells via the TNF-α/Fas ligand pathway, causing acute kidney injury (AKI) with hematuria. Activation of NKT cells by common bacterial DNA (CpG-ODN) also causes AKI. In addition, NKT cells together with B cells play significant roles in experimental lupus nephritis in NZB/NZW F1 mice through their Th2 immune responses. Mouse NK cells are also assumed to be involved in various renal diseases, and there may be complementary roles shared between NKT and NK cells. Human CD56⁺ T cells, a functional counterpart of mouse NKT cells, also damage renal cells through a mechanism similar to that of mice. A subpopulation of human CD56⁺ NK cells also exert strong cytotoxicity against renal cells and contribute to the progression of renal fibrosis.

Natural Killer and Natural Killer T Cells in Juvenile Systemic Lupus Erythematosus: Relation to Disease Activity and Progression

The contribution of innate immune cells, including natural killer (NK) and natural killer T (NKT) cells, in systemic lupus erythematosus (SLE) is still unclear. Herein, we examined the frequency of peripheral NK cells, CD56^dim and CD56^bright NK cells, and NKT cells in patients with juvenile SLE and their potential relations to SLE-related clinical and laboratory parameters. The study included 35 SLE children and 20 apparently healthy controls. After baseline clinical and lab work, SLE Disease Activity Index (SLEDAI-2K) and Pediatric Systemic Lupus International Collaborative Clinics/American College of Rheumatology (SLICC/ACR) Damage Index (Ped-SDI) scores were assessed. The frequency of peripheral NK cells, CD56^dim and CD56^bright NK cells, and NKT cells was examined using flow cytometry. SLE patients showed significantly lower frequency of NK cells and NKT cells and higher frequency of CD56^bright NK cells compared to controls. Disease activity, urea, and creatinine correlated negatively with NK, but positively with CD56^bright NK cells. NK and NKT cells exhibited inverse correlation with the renal biopsy activity index; however, CD56^bright NK cells showed direct correlations with both activity and chronicity indices. Regarding Ped-SDI, renal, neuropsychiatry disorders, and growth failure correlated inversely with NK but directly with CD56^bright NK cells. NKT cell inversely correlated with renal damage and delayed puberty. In conclusion, low frequency of NK and NKT and expansion of CD56^bright NK cells are marked in juvenile SLE, particularly with activity. These changes have direct effect on renal impairment and growth failure, reflecting their potential influence on disease progression.

Abnormalities of quantities and functions of CD56bright natural killer cells in non-severe aplastic Anemia

OBJECTIVES

The mechanism of non-severe aplastic anemia (NSAA) is not clear. It may be different from severe aplastic anemia (SAA). CD56bright NK cells (regulatory NK cells) is a subgroup of NK cells that produce immunoregulatory cytokines and express high-affinity IL-2 receptor. To investigate CD56bright NK cells quantities and function in patients with NSAA and to explore how CD56bright NK cells participate in the progress of this disease.

METHODS

In this study, we analyzed the quantitative and functional changes of CD56bright NK cells in peripheral blood of patients with NSAA by using Flow Cytometry (FCM) before and after immunosuppressive therapy (IST). The expressions of activating receptor (NKG2D, NKp46, NKp44), inhibitory receptor (NKG2A, CD158a, CD158b) and perforin and granzyme B were detected by FCM. IL-2 and IL-18 levels in serum were detected by ELISA. The correlation between these parameters and clinical indicators of patients were evaluated.

RESULTS

We found that the percentage of CD56bright NK cells in newly diagnosed NSAA patients was higher than that in normal controls (p = .011, p < .05). The median expression of NKG2D in patients with NSAA was higher compared to that in normal controls (p = .021, p < .05), and the expression of CD158a was lower (p = .047, p < .05). The concentrations of IL-2 and IL-18 in the serum of patients with NSAA were higher than those in normal group.

CONCLUSION

These findings suggest that increased and activated CD56bright NK cells might play a protective role in the pathogenesis of NSAA.

Natural Killer Cells in Kidney Health and Disease

Natural killer (NK) cells are a specialized population of innate lymphocytes that have a major effector function in local immune responses. While their immunological functions in many inflammatory diseases are well established, comparatively little is still known about their roles in kidney homeostasis and disease. Our understanding of kidney NK cells is rapidly evolving, with murine studies highlighting the functional significance of NK cells in acute and chronic forms of renal disease. Recent progress has been made in translating these murine findings to human kidneys, with indications of NK cell subset-specific roles in disease progression in both native and allograft kidneys. Clearly, a better understanding of the molecular mechanisms driving NK cell activation and importantly, their downstream interactions with intrinsic renal cells and infiltrating immune cells is necessary for the development of targeted therapeutics to halt disease progression. In this review, we discuss the properties and potential functions of kidney NK cells.

Renal tubular epithelial cells: the neglected mediator of tubulointerstitial fibrosis after injury

Renal fibrosis, especially tubulointerstitial fibrosis, is the inevitable outcome of all progressive chronic kidney diseases (CKDs) and exerts a great health burden worldwide. For a long time, interests in renal fibrosis have been concentrated on fibroblasts and myofibroblasts. However, in recent years, growing numbers of studies have focused on the role of tubular epithelial cells (TECs). TECs, rather than a victim or bystander, are probably a neglected mediator in renal fibrosis, responding to a variety of injuries. The maladaptive repair mechanisms of TECs may be the key point in this process. In this review, we will focus on the role of TECs in tubulointerstitial fibrosis. We will follow the fate of a tubular cell and depict the intracellular changes after injury. We will then discuss how the repair mechanism of tubular cells becomes maladaptive, and we will finally discuss the intercellular crosstalk in the interstitium that ultimately proceeds tubulointerstitial fibrosis.

Identification and Quantitation of Leukocyte Populations in Human Kidney Tissue by Multi-parameter Flow Cytometry

Inflammatory immune cells play direct pathological roles in cases of acute kidney injury (AKI) and chronic kidney disease (CKD). However, the identification and characterization of distinct populations of leukocytes in human kidney biopsies have been confounded by the limitations of immunohistochemical (IHC)-based techniques used to detect them. This methodology is not amenable to the combinations of multiple markers necessary to unequivocally define discrete immune cell populations. We have developed a multi-parameter, flow cytometric-based approach that addresses the need for panels of cell-specific markers in the identification of immune cell populations, allowing both the accurate detection and quantitation of leukocyte subpopulations from a single, clinical kidney biopsy specimen. In this approach, fresh human kidney tissue is dissociated into a single cell suspension followed by antibody-labeling and flow cytometric-based acquisition and analysis. This novel technique provides a major step forward in identifying and enumerating immune cell subpopulations in human kidney disease and is a powerful platform to complement traditional histopathological examinations of clinical kidney biopsies.

Renal fibrosis: Primacy of the proximal tubule

Tubulointerstitial fibrosis (TIF) is the hallmark of chronic kidney disease and best predictor of renal survival. Many different cell types contribute to TIF progression including tubular epithelial cells, myofibroblasts, endothelia, and inflammatory cells. Previously, most of the attention has centered on myofibroblasts given their central importance in extracellular matrix production. However, emerging data focuses on how the response of the proximal tubule, a specialized epithelial segment vulnerable to injury, plays a central role in TIF progression. Several proximal tubular responses such as de-differentiation, cell cycle changes, autophagy, and metabolic changes may be adaptive initially, but can lead to maladaptive responses that promote TIF both through autocrine and paracrine effects. This review discusses the current paradigm of TIF progression and the increasingly important role of the proximal tubule in promoting TIF both in tubulointerstitial and glomerular injuries. A better understanding and appreciation of the role of the proximal tubule in TIF has important implications for therapeutic strategies to halt chronic kidney disease progression.

Activated natural killer T cells in mice induce acute kidney injury with hematuria through possibly common mechanisms shared by human CD56+ T cells

Although activation of mouse natural killer T (NKT) cells by α-galactosylceramide (α-GalCer) causes failure of multiple organs, including the kidneys, the precise mechanisms underlying kidney injury remain unclear. Here, we showed that α-GalCer-activated mouse NKT cells injured both kidney vascular endothelial cells and tubular epithelial cells in vitro, causing acute kidney injury (AKI) with hematuria in middle-aged mice. The perforin-mediated pathway was mainly involved in glomerular endothelial cell injury, whereas the TNF-α/Fas ligand pathway played an important role in the injury of tubular epithelial cells. Kidney injury in young mice was mild but could be significantly exacerbated if NKT cells were strongly activated by NK cell depletion alone or in combination with IL-12 pretreatment. When stimulated by a combination of IL-2 and IL-12, human CD56⁺ T cells, a functional counterpart of mouse NKT cells, also damaged both glomerular endothelial cells and tubular epithelial cells, with the former being affected in a perforin-dependent manner. These data suggest that both mouse NKT cells and human CD56⁺ T cells are integral to the processes that mediate AKI. Targeting CD56⁺ T cells may, therefore, be a promising approach to treat AKI.

Natural killers: the bad guys in fibrosis?

Immune cells infiltrating the tubulointerstitium critically contribute to the progression of chronic kidney disease. In this issue of Kidney international, Law et al. provide first evidence for a role of natural killer cells in the perpetuation of tubulointerstitial fibrosis in human renal disease. By detailed flow cytometric characterization of leukocytes isolated from kidney biopsies of chronic kidney disease patients, they define accumulation of natural killer cells as a feature of fibrotic kidney tissue and provide insight into potential mechanisms of how these cells might promote chronic kidney inflammation.