Apoptotic cell death in disease-Current understanding of the NCCD 2023

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

Cytoprotective remedies for ameliorating nephrotoxicity induced by renal oxidative stress

AIMS

Nephrotoxicity is the hallmark of anti-neoplastic drug metabolism that causes oxidative stress. External chemical agents and prescription drugs release copious amounts of free radicals originating from molecular oxidation and unless sustainably scavenged, they stimulate membrane lipid peroxidation and disruption of the host antioxidant mechanisms. This review aims to provide a comprehensive collection of potential cytoprotective remedies in surmounting the most difficult aspect of cancer therapy as well as preventing renal oxidative stress by other means.

MATERIALS AND METHODS

Over 400 published research and review articles spanning several decades were scrutinised to obtain the relevant data which is presented in 3 categories; sources, mechanisms, and mitigation of renal oxidative stress.

KEY-FINDINGS

Drug and chemical-induced nephrotoxicity commonly manifests as chronic or acute kidney disease, nephritis, nephrotic syndrome, and nephrosis. Renal replacement therapy requirements and mortalities from end-stage renal disease are set to rapidly increase in the next decade for which 43 different cytoprotective compounds which have the capability to suppress experimental nephrotoxicity are described.

SIGNIFICANCE

The renal system performs essential homeostatic functions that play a significant role in eliminating toxicants, and its accumulation and recurrence in nephric tissues results in tubular degeneration and subsequent renal impairment. Global statistics of the latest chronic kidney disease prevalence is 13.4 % while the end-stage kidney disease requiring renal replacement therapy is 4-7 million per annum. The remedial compounds discussed herein had proven efficacy against nephrotoxicity manifested consequent to impaired antioxidant mechanisms in preclinical models produced by renal oxidative stress activators.

TNFR2 as a Potential Biomarker for Early Detection and Progression of CKD

The inflammatory pathway driven by TNF-α, through its receptors TNFR1 and TNFR2, is a common feature in the pathogenesis of chronic kidney disease (CKD), regardless of the initial disease cause. Evidence correlates the chronic inflammatory status with decreased renal function. Our aim was to evaluate the potential of TNF receptors as biomarkers for CKD diagnosis and staging, as well as their association with the progression of renal lesions, in rat models of early and moderate CKD. We analyzed the circulating levels of inflammatory molecules—tumor necrosis factor-alpha (TNF-α), tumor necrosis factor receptor 1 (TNFR1) and 2 (TNFR2) and tissue inhibitor of metalloproteinase-1 (TIMP-1)—and studied their associations with TNFR1 and TNFR2 renal expression, glomerular and tubulointerstitial lesions, and with biomarkers of renal (dys)function. An increase in all inflammatory markers was observed in moderate CKD, as compared to controls, but only circulating levels of both TNFR1 and TNFR2 were significantly increased in the early disease; TNFR2 serum levels were negatively correlated with eGFR. However, only TNFR2 renal expression increased with CKD severity and showed correlations with the score of mild and advanced tubular lesions. Our findings suggest that renal TNFR2 plays a role in CKD development, and has potential to be used as a biomarker for the early detection and progression of the disease. Still, the potential value of this biomarker in disease progression warrants further investigation.

Targeting Differential Roles of Tumor Necrosis Factor Receptors as a Therapeutic Strategy for Glaucoma

Glaucoma is an irreversible sight-threatening disorder primarily due to elevated intraocular pressure (IOP), leading to retinal ganglion cell (RGC) death by apoptosis with subsequent loss of optic nerve fibers. A considerable amount of empirical evidence has shown the significant association between tumor necrosis factor cytokine (TNF; TNFα) and glaucoma; however, the exact role of TNF in glaucoma progression remains unclear. Total inhibition of TNF against its receptors can cause side effects, although this is not the case when using selective inhibitors. In addition, TNF exerts its antithetic roles via stimulation of two receptors, TNF receptor I (TNFR1) and TNF receptor II (TNFR2). The pro-inflammatory responses and proapoptotic signaling pathways predominantly mediated through TNFR1, while neuroprotective and anti-apoptotic signals induced by TNFR2. In this review, we attempt to discuss the involvement of TNF receptors (TNFRs) and their signaling pathway in ocular tissues with focus on RGC and glial cells in glaucoma. This review also outlines the potential application TNFRs agonist and/or antagonists as neuroprotective strategy from a therapeutic standpoint. Taken together, a better understanding of the function of TNFRs may lead to the development of a treatment for glaucoma.

Monocytes transition to macrophages within the inflamed vasculature via monocyte CCR2 and endothelial TNFR2

Monocytes undergo phenotypic and functional changes in response to inflammatory cues, but the molecular signals that drive different monocyte states remain largely undefined. We show that monocytes acquire macrophage markers upon glomerulonephritis and may be derived from CCR2+CX3CR1+ double-positive monocytes, which are preferentially recruited, dwell within glomerular capillaries, and acquire proinflammatory characteristics in the nephritic kidney. Mechanistically, the transition to immature macrophages begins within the vasculature and relies on CCR2 in circulating cells and TNFR2 in parenchymal cells, findings that are recapitulated in vitro with monocytes cocultured with TNF-TNFR2–activated endothelial cells generating CCR2 ligands. Single-cell RNA sequencing of cocultures defines a CCR2-dependent monocyte differentiation path associated with the acquisition of immune effector functions and generation of CCR2 ligands. Immature macrophages are detected in the urine of lupus nephritis patients, and their frequency correlates with clinical disease. In conclusion, CCR2-dependent functional specialization of monocytes into macrophages begins within the TNF-TNFR2–activated vasculature and may establish a CCR2-based autocrine, feed-forward loop that amplifies renal inflammation.

The Signaling Pathway of TNF Receptors: Linking Animal Models of Renal Disease to Human CKD

Chronic kidney disease (CKD) has been recognized as a global public health problem. Despite the current advances in medicine, CKD-associated morbidity and mortality remain unacceptably high. Several studies have highlighted the contribution of inflammation and inflammatory mediators to the development and/or progression of CKD, such as tumor necrosis factor (TNF)-related biomarkers. The inflammation pathway driven by TNF-α, through TNF receptors 1 (TNFR1) and 2 (TNFR2), involves important mediators in the pathogenesis of CKD. Circulating levels of TNFRs were associated with changes in other biomarkers of kidney function and injury, and were described as predictors of disease progression, cardiovascular morbidity, and mortality in several cohorts of patients. Experimental studies describe the possible downstream signaling pathways induced upon TNFR activation and the resulting biological responses. This review will focus on the available data on TNFR1 and TNFR2, and illustrates their contributions to the pathophysiology of kidney diseases, their cellular and molecular roles, as well as their potential as CKD biomarkers. The emerging evidence shows that TNF receptors could act as biomarkers of renal damage and as mediators of the disease. Furthermore, it has been suggested that these biomarkers could significantly improve the discrimination of clinical CKD prognostic models.

Context dependent induction of autoimmunity by TNF signaling deficiency

TNF inhibitors are widely used to treat inflammatory diseases; however, 30%–50% of treated patients develop new autoantibodies, and 0.5%–1% develop secondary autoimmune diseases, including lupus. TNF is required for formation of germinal centers (GCs), the site where high-affinity autoantibodies are often made. We found that TNF deficiency in Sle1 mice induced TH17 T cells and enhanced the production of germline encoded, T-dependent IgG anti-cardiolipin antibodies but did not induce GC formation or precipitate clinical disease. We then asked whether a second hit could restore GC formation or induce pathogenic autoimmunity in TNF-deficient mice. By using a range of immune stimuli, we found that somatically mutated autoantibodies and clinical disease can arise in the setting of TNF deficiency via extrafollicular pathways or via atypical GC-like pathways. This breach of tolerance may be due to defects in regulatory signals that modulate the negative selection of pathogenic autoreactive B cells.

Plasma Biomarkers of Tubular Injury and Inflammation Are Associated with CKD Progression in Children

BACKGROUND

After accounting for known risk factors for CKD progression in children, clinical outcomes among children with CKD still vary substantially. Biomarkers of tubular injury (such as KIM-1), repair (such as YKL-40), or inflammation (such as MCP-1, suPAR, TNF receptor-1 [TNFR-1], and TNFR-2) may identify children with CKD at risk for GFR decline.

METHODS

We investigated whether plasma KIM-1, YKL-40, MCP-1, suPAR, TNFR-1, and TNFR-2 are associated with GFR decline in children with CKD and in subgroups defined by glomerular versus nonglomerular cause of CKD. We studied participants of the prospective CKiD Cohort Study which enrolled children with an eGFR of 30-90 ml/min per 1.73 m² and then assessed eGFR annually. Biomarkers were measured in plasma collected 5 months after study enrollment. The primary endpoint was CKD progression, defined as a composite of a 50% decline in eGFR or incident ESKD.

RESULTS

Of the 651 children evaluated (median age 11 years; median baseline eGFR of 53 ml/min per 1.73 m²), 195 (30%) had a glomerular cause of CKD. Over a median follow-up of 5.7 years, 223 children (34%) experienced CKD progression to the composite endpoint. After multivariable adjustment, children with a plasma KIM-1, TNFR-1, or TNFR-2 concentration in the highest quartile were at significantly higher risk of CKD progression compared with children with a concentration for the respective biomarker in the lowest quartile (a 4-fold higher risk for KIM-1 and TNFR-1 and a 2-fold higher risk for TNFR-2). Plasma MCP-1, suPAR, and YKL-40 were not independently associated with progression. When stratified by glomerular versus nonglomerular etiology of CKD, effect estimates did not differ significantly.

CONCLUSIONS

Higher plasma KIM-1, TNFR-1, and TNFR-2 are independently associated with CKD progression in children.

Circulating Tumor Necrosis Factor Receptors: A Potential Biomarker for the Progression of Diabetic Kidney Disease

Despite considerable advancements in medicine, the optimal treatment for chronic kidney disease (CKD), especially diabetic kidney disease (DKD), remains a major challenge. More patients with DKD succumb to death due to cardiovascular events than due to progression to end-stage renal disease (ESRD). Moreover, patients with DKD and ESRD have remarkably poor prognosis. Current studies have appreciated the contribution of inflammation and inflammatory mediators, such as tumor necrosis factor (TNF)-related biomarkers, on the development/progression of DKD. The present review focuses on molecular roles, serum concentrations of TNF receptors (TNFRs), and their association with increased albuminuria, eGFR decline, and all-cause mortality in diabetes. Experimental studies have suggested that DKD progression occurs through the TNFα–TNFR2 inflammatory pathway. Moreover, serum TNFR levels were positively associated with albuminuria and negatively associated with estimated glomerular filtration rate (eGFR), while circulating levels of TNFRs exhibited an independent effect on all-cause mortality and eGFR decline, including ESRD, even after adjusting for existing risk factors. However, their precise function has yet to be elucidated and requires further studies.

Increased circulating cytokine levels in African American women with obesity and elevated HbA1c

PURPOSE

Obesity has emerged as one of the biggest health crisis and is the leading cause of death and disabilities around the world. BMI trends suggest that majority of the increase in T2D is resulting from the increased prevalence of obesity. In fact, 85.2% of people with T2D are overweight or obese. The highest prevalence for obesity is seen in non-Hispanic, African American women (56.6%). T2D is classified as an inflammatory disease because of elevated, circulating pro-inflammatory cytokines and acute-phase inflammatory proteins. This study was designed to determine how high HbA1c and serum glucose correlate with circulatory cytokine levels in obese, African American women.

METHODS

We investigated cytokine/chemokine serum levels using a multiplex assay. Then we used Pairwise Pearson Correlation Test to determine the relationship between clinical metabolic parameters and cytokine/chemokine serum levels.

RESULTS

The results indicated that participants with elevated HbA1c exhibited an up regulation of IL-3, IL-4, IL-7, TNF-α, IFN-α2 and CX3CL1 serum levels compared to participants with normal HbA1c. These cytokines were also correlated with several clinical metabolic parameters.

CONCLUSIONS

The results suggest that IL-3, IL-4, IL-7, TNF-α, IFN-α2 and CX3CL1 serum levels may contribute to the development and onset of type 2 diabetes.

Renal proximal tubular epithelial cells exert immunomodulatory function by driving inflammatory CD4+ T cell responses

In immune-mediated glomerular diseases like crescentic glomerulonephritis (cGN), inflammatory CD4⁺ T cells accumulate within the tubulointerstitial compartment in close contact to proximal and distal tubular epithelial cells and drive renal inflammation and tissue damage. However, whether renal epithelial cell populations play a role in the pathogenesis of cGN by modulating CD4⁺ T cell responses is less clear. In the present study, we aimed to investigate the potential of renal epithelial cells to function as antigen-presenting cells, thereby stimulating CD4⁺ T cell responses. Using a FACS-based protocol that allowed comparative analysis of cortical epithelial cell populations, we showed that particularly proximal tubular epithelial cells (PTECs) express molecules linked with antigen-presenting cell function, including major histocompatibility complex class II (MHCII), CD74, CD80, and CD86 in homeostasis and nephrotoxic nephritis, a murine model of cGN. Protein expression was visualized at the PTEC single cell level by imaging flow cytometry. Interestingly, we found inflammation-dependent regulation of epithelium-expressed CD74, CD80, and CD86, whereas MHCII expression was not altered. Antigen-specific stimulation of CD4⁺ T cells by PTECs in vitro supported CD4⁺ T cell survival and induced CD4⁺ T cell activation, proliferation, and inflammatory cytokine production. In patients with antineutrophil cytoplasmic antibody-associated glomerulonephritis, MHCII and CD74 were expressed by both proximal and distal tubules, whereas CD86 was predominantly expressed by proximal tubules. Thus, particularly PTECs have the potential to induce an inflammatory phenotype in CD4⁺ T cells in vitro, which might also play a role in the pathology of immune-mediated kidney disease.

Exclusive expression of transmembrane TNF aggravates acute glomerulonephritis despite reduced leukocyte infiltration and inflammation

Tumor necrosis factor-α (TNF) is a cytokine mediating inflammatory kidney diseases such as immune complex glomerulonephritis. Its two receptors, TNFR1 and TNFR2, play distinct roles in this process, with TNFR2 strongly required for induction of disease. In contrast to soluble TNF (sTNF), transmembrane TNF robustly activates TNFR2. Thus, we examined the functional role of transmembrane TNF by inducing heterologous nephrotoxic serum nephritis in wild-type and transgenic TNFΔ1-9,K11E knock-in mice expressing transmembrane TNF but no sTNF (memTNF mice). Compared to wild-type, nephritis was exacerbated in memTNF mice on day 5, indicated by increased albuminuria, higher serum urea levels, and more pronounced glomerular deposits, together with higher numbers of dying and proliferating glomerular cells. This was associated with greater loss of glomerular endothelial cells, increased podocyte stress, and signs of augmented necroptosis in memTNF kidneys. Aggravation of nephritis was dependent on transmembrane TNF expression in parenchymal cells, but not leukocytes. Surprisingly, increased kidney injury was associated with reduced renal leukocyte infiltration in memTNF mice, which correlated with decreased renal mRNA expression of pro-inflammatory mediators. This effect was also present in isolated memTNF glomeruli stimulated with interleukin-1β in vitro. Thus, uncleaved transmembrane TNF is an important mediator of renal tissue damage characterized by increased renal cell death and loss of glomerular endothelial cells in murine glomerulonephritis. In contrast, sTNF predominantly mediates renal leukocyte recruitment and inflammation. These findings highlight the importance of transmembrane TNF in inflammatory kidney disease as a possible therapeutic target.

Role of Kidney Biopsies for Biomarker Discovery in Diabetic Kidney Disease

Although estimated glomerular filtration rate and albuminuria are well-established biomarkers of diabetic kidney disease (DKD), additional biomarkers are needed, especially for the early stages of the disease when both albuminuria and estimated glomerular filtration rate may still be in the normal range and are less helpful for identifying those at risk of progression. Traditional biomarker studies for early DKD are challenging because of a lack of good early clinical end points, and most rely on changes in existing imprecise biomarkers to assess the value of new biomarkers. There are well-characterized changes in kidney structure, however, that are highly correlated with kidney function, always precede the clinical findings of DKD and, at preclinical stages, predict DKD progression. These structural parameters may thus serve as clinically useful end points for identifying new biomarkers of early DKD. In addition, investigators are analyzing tissue transcriptomic data to identify pathways involved in early DKD which may have associated candidate biomarkers measurable in blood or urine, and differentially expressed microRNAs and epigenetic modifications in kidney tissue are beginning to yield important observations which may be useful in identifying new clinically useful biomarkers. This review examines the emerging literature on the use of kidney tissue in biomarker discovery in DKD.

Inhibition of tumor necrosis factor signaling attenuates renal immune cell infiltration in experimental membranous nephropathy

Idiopathic membranous nephropathy (MN) is an autoimmune-mediated glomerulonephritis and the most common cause of idiopathic nephrotic syndrome in adult humans. A tumor necrosis factor α (TNF-α)-mediated inflammatory response via TNF receptor 1 (TNFR1) and TNFR2 has been proposed as a pathogenic factor. In this study, we assessed the therapeutic response to blocking TNF signaling in experimental MN. Murine MN was induced experimentally by cationic bovine serum albumin (cBSA); phosphate-buffered saline was used in control mice. In MN mice, TNF was inhibited by etanercept blocking of TNFR1/TNFR2 or the preligand assembly domain fusion protein (PLAD.Fc), a small fusion protein that can preferentially block TNFR1 signaling. Disease severity and possible mechanisms were assessed by analyzing the metabolic and histopathology profiles, lymphocyte subsets, immunoglobulin production, oxidative stress, and apoptosis. cBSA-induced MN mice exhibited typical nephrotic syndrome and renal histopathology. MN mice given etanercept or PLAD.Fc did not exhibit significant reduction of proteinuria, amelioration of glomerular lesions, or attenuation of immune complex deposition. Immune cell subsets, serum immunoglobulin levels, production of reactive oxygen species, and cell apoptosis in the kidney were not altered by TNF inhibition. By contrast, MN mice receiving etanercept or PLAD.Fc exhibited significantly decreased infiltration of immune cells into the kidney. These results show that the therapeutic effects of blocking TNFR1 and/or TNFR2 signaling in experimental MN are not clinically effective. However, TNF signaling inhibition significantly attenuated renal immune cell infiltration in experimental MN.

High levels of circulating TNFR1 increase the risk of all-cause mortality and progression of renal disease in type 2 diabetic nephropathy

BACKGROUND

Several studies have demonstrated that levels of circulating inflammatory markers such as tumour necrosis factorα (TNFα), are associated with early progression of diabetic nephropathy (DN). The aim of this study was to investigate whether there is an association between circulating TNFα receptor and disease progression in patients with advanced type 2 DN and severe proteinuria.

METHODS

Between 2006 and 2011, we measured levels of circulating soluble TNFα receptor 1 (TNFR1) and soluble TNFα receptor 2 (TNFR2) at baseline and 4 and 12 months in 101 patients included in a multicenter randomized controlled trial to compare the effect of optimal doses of renin-angiotensin system blockers in monotherapy or in combination (dual blockade) to slow progression of established type 2 DN. The primary composite endpoint was a >50% increase in baseline serum creatinine, end-stage renal disease, or death.

RESULTS

The median follow-up was 32 months (IQR, 18-48), during which time 28 patients (22.7%) achieved the primary endpoint. The TNFR1 level, but not the TNFR2 level, was correlated with other inflammatory markers. Cox regression analysis showed that the highest TNFR1 levels (HR, 2.60; 95%CI, 1.11-86.34) and baseline proteinuria (HR 1.32; 95%CI 1.15-1.52) were associated with the primary endpoint. The mixed model analysis revealed that TNFR1 and the TNFR2 levels did not change after starting treatment with renin-angiotensin system blockers.

CONCLUSIONS

Our results show that the highest levels of TNFR1 are independently associated with progression of renal disease and death in type 2 DN. The renin angiotensin blockers have no effect on these inflammatory markers.

Tumor necrosis factor superfamily ligand mRNA expression profiles differ between humans and mice during homeostasis and between various murine kidney injuries

BACKGROUND

Several tumour necrosis factor (TNF) based therapeutics have already been approved for human use and several others are emerging. Therefore, we determined the mRNA expression levels of the TNF superfamily ligands (TNFSF) - e.g. TNF-α, lymphotoxin (LT)-α, LT-β, Fas-L (CD95-L), TNF-related apoptosis-inducing ligand (TRAIL), TNF-related weak inducer of apoptosis (TWEAK), 4-1BBL, OX40-L (CD252) and amyloid precursor protein (APP) in healthy human and mouse solid organs.

METHODS

We used quantitative real time-PCR to analyse mRNA expression levels of TNFSF ligands. Murine models of acute ischemic renal injury, chronic oxalate nephropathy, and immune complex glomerulonephritis were used. Renal injury was assessed by PAS staining, and infiltrating immune cells were analysed by immunohistochemistry. Data was analysed using non-parametric ANOVA (non-parametric; Kruskal-Wallis test).

RESULTS

We observed significant differences in the mRNA expression levels of TNFSF ligands in human and mouse solid organs. Furthermore, we determined their mRNA expressions during acute and chronic kidney injuries in mice. Our data demonstrate that the mRNA expression levels of TNFSF vary depending on the type of tissue injury - for example, acute ischemic renal injury, chronic crystalline nephropathy, and immune complex glomerulonephritis. In addition, we observed that mRNA expressions of TNFSF ligands are differentially regulated during the course of a transient ischemic renal injury (IRI) and chronic kidney modelling. We observed that TNF-α, LT-β, and 4-1BBL were significantly upregulated during the progression of IRI and crystal-induced chronic kidney disease (CKD), whereas only 4-1BBL and TNF-α were significantly upregulated and LT-β was significantly downregulated during the progression of immune complex glomerulonephritis. The mRNA expression of Fas-L was higher during IRI whereas it decreased in a time dependent manner during the progression of crystal-induced CKD.

CONCLUSION

We conclude that the injury- and species-specific differences of TNFSF ligands must be considered in order to avoid the misinterpretation and wrong conclusions during data extrapolation between species.

Calcium/Calmodulin-Dependent Kinase IV Facilitates the Recruitment of Interleukin-17-Producing Cells to Target Organs Through the CCR6/CCL20 Axis in Th17 Cell-Driven Inflammatory Diseases

OBJECTIVE

The recruitment of interleukin-17 (IL-17)-producing T helper (Th17) cells to inflammatory sites has been implicated in the development of organ damage in inflammatory and autoimmune diseases including systemic lupus erythematosus (SLE). To define the mechanism of calcium/calmodulin-dependent kinase IV (CaMKIV) activation of Th17 cell recruitment to target tissues, we performed anti-glomerular basement membrane antibody-induced glomerulonephritis (AIGN) experiments in mice and studied samples from patients with SLE.

METHODS

We induced experimental AIGN in CaMKIV-sufficient or CaMKIV-deficient mice and compared histology, Th17 cell-related chemokine expression, and numbers of IL-17-producing cells in kidneys. We also evaluated the efficacy of the CaMKIV inhibitor KN-93 in AIGN-induced kidney disease. The expression of CCR6 in memory CD4+ T cells before AIGN induction was analyzed by flow cytometry. We investigated the correlation between CCR6 expression in peripheral blood and the severity of glomerulonephritis in patients with SLE.

RESULTS

CaMKIV-deficient mice displayed less glomerular injury after induction of AIGN. Kidney infiltration by IL-17-producing CD4+ T cells along with CCR6 and CCL20 expression were significantly decreased in CaMKIV-deficient mice. Similarly, treatment of mice with KN-93 improved clinical and pathologic outcomes. Expression and function of CCR6 in peripheral blood memory CD4+ T cells was decreased in CaMKIV-deficient mice. Expression of CCR6 correlated positively with severity of organ damage in SLE patients.

CONCLUSION

CaMKIV inhibition represents a novel therapeutic strategy for treatment of Th17 cell-mediated tissue damage in inflammatory diseases.

Circulating TNF receptors predict cardiovascular disease in patients with chronic kidney disease

Cardiovascular disease (CVD) is the main public health problem in patients with chronic kidney disease (CKD); however, there is no established biomarker for predicting CVD morbidity and mortality in CKD. The aim of this study was to evaluate the role of circulating tumor necrosis factor receptors (cTNFRs) in predicting CVD risk in CKD patients.We prospectively recruited 984 patients with CKD from 11 centers between 2006 and 2012. The levels of cTNFR1 and cTNFR2 were determined by performing an enzyme-linked immunosorbent assay. During the mean follow-up period of 4 years, 36 patients experienced a CVD event. The median serum concentrations of cTNFR1 and cTNFR2 were 2703.4 (225.6-13,057.7) and 5661.0 (634.9-30,599.6) pg/mL, respectively, and the cTNFR1 level was closely correlated with the cTNFR2 level (r = 0.86, P < .0001). The urinary protein-to-creatinine ratio (UPCR) and estimated glomerular filtration rate (eGFR) were significantly correlated with the cTNFR2 level (r = 0.21 for UPCR, r = -0.67 for eGFR; P < .001 for all). Similar correlations were observed for serum cTNFR1 (r = 0.21 for UPCR, r = -0.75 for eGFR; P < .001 for all). In the Cox proportional hazard analyses, cTNFR1 (hazard ratio [HR] 2.506, 95% confidence interval [CI] 1.186-5.295, P = .016) and cTNFR2 (HR 4.156, 95% CI 1.913-9.030, P < .001) predicted CVD risk even after adjustment for clinical covariates, such as UPCR, eGFR, and high-sensitivity C-reactive protein. cTNFR1 and 2 are associated with CVD and other risk factors in CKD, independently of eGFR and UPCR. Furthermore, cTNFRs could be relevant predictors of CVD in CKD patients.

Effect of tonsillectomy with steroid pulse therapy on circulating tumor necrosis factor receptors 1 and 2 in IgA nephropathy

BACKGROUND

High circulating levels of soluble tumor necrosis factor receptors (TNFRs: TNFR1, TNFR2) predict renal function decline in a variety of kidney diseases. Tonsillectomy with steroid pulse (TSP) therapy has been reported as a remission induction therapy in IgA nephropathy (IgAN), mainly in Japan. However, little is known about whether TNFR levels change after TSP therapy in patients with IgAN.

METHODS

Two hundred twenty-three patients with IgAN were stratified according to the estimated glomerular filtration rate (eGFR): Group I (eGFR ≥ 60 mL/min/1.73 m², n = 172) and Group II (eGFR < 60 mL/min/1.73 m², n = 51). We measured serum TNFR levels with immunoassay in all patients at the time of renal biopsy, and also in patients whose samples just before the first (after tonsillectomy) (n = 34) and/or the third steroid pulse therapy (n = 77) were available.

RESULTS

The TNFR levels were significantly higher in Group II than in Group I. A significant negative correlation was observed between TNFR levels and eGFR at baseline (TNFRs: r > -0.50). In multivariate logistic regression analysis, both TNFRs were associated with renal function decline, independent of age and uric acid levels. Proteinuria and hematuria remarkably improved after TSP therapy, as expected. In comparison with baseline TNFR levels, the levels of TNFR2, but not TNFR1, decreased significantly just before the third steroid pulse therapy, although both levels did not change after tonsillectomy.

CONCLUSIONS

The TNFR2 level did not change after tonsillectomy alone but decreased significantly after steroid pulse therapy in patients with IgAN.

Serum soluble tumour necrosis factor receptor-2 (sTNFR2) as a biomarker of kidney tissue damage and long-term renal outcome in lupus nephritis

OBJECTIVES

We investigated the performance of soluble tumour necrosis factor receptor-2 (sTNFR2) as a biomarker of renal activity, damage, treatment response, and long-term outcome in lupus nephritis (LN).

METHOD

Serum sTNFR2 levels were assessed in 64 LN patients (52 proliferative, 12 membranous) before and after induction treatment, and in 314 non-lupus controls. In LN patients, renal biopsies were performed at baseline and post-treatment. Patients with ≥ 50% reduced proteinuria, normal or improved estimated glomerular filtration rate (eGFR) by ≥ 25%, and inactive urinary sediment were considered clinical responders (CRs). Patients with ≥ 50% improved renal activity index were considered histopathological responders (HRs). Long-term renal outcome was determined using the chronic kidney disease (CKD) stage after a median follow-up of 11.3 years.

RESULTS

sTNFR2 levels were elevated in LN patients versus controls both at baseline (p < 0.001) and post-treatment (p < 0.001), and decreased following treatment (p < 0.001). Baseline sTNFR2 correlated with Chronicity Index scores in both baseline (r = 0.34, p = 0.006) and post-treatment (r = 0.43, p < 0.001) biopsies. In membranous LN, baseline sTNFR2 levels were higher in CRs (p = 0.048) and HRs (p = 0.03) than in non-responders, and decreased only in CRs (p = 0.03). Both baseline (p = 0.02) and post-treatment (p = 0.03) sTNFR2 levels were associated with decreasing eGFR throughout long-term follow-up, and post-treatment levels were higher in patients with long-term follow-up CKD stage ≥ 3 versus 1-2 (p = 0.008).

CONCLUSIONS

Our data suggest serum sTNFR2 as a marker of kidney tissue damage and a predictor of long-term prognosis in LN, and merit further evaluation of sTNFR2 as a predictor of clinical and histopathological treatment outcomes in membranous LN.

Genetics of Lupus Nephritis: Clinical Implications

Systemic lupus erythematosus is a heterogeneous autoimmune disease marked by the presence of pathogenic autoantibodies, immune dysregulation, and chronic inflammation that may lead to increased morbidity and early mortality from end-organ damage. More than half of all systemic lupus erythematosus patients will develop lupus nephritis. Genetic-association studies have identified more than 50 polymorphisms that contribute to lupus nephritis pathogenesis, including genetic variants associated with altered programmed cell death and defective immune clearance of programmed cell death debris. These variants may support the generation of autoantibody-containing immune complexes that contribute to lupus nephritis. Genetic variants associated with lupus nephritis also affect the initial phase of innate immunity and the amplifying, adaptive phase of the immune response. Finally, genetic variants associated with the kidney-specific effector response may influence end-organ damage and the progression to end-stage renal disease and death. This review discusses genetic insights of key pathogenic processes and pathways that may lead to lupus nephritis, as well as the clinical implications of these findings as they apply to recent advances in biologic therapies.

Increased concentration of plasma TNFR1 and TNFR2 in paediatric lupus nephritis

BACKGROUND

Juvenile-onset systemic lupus erythematous (JSLE) is a debilitating condition that frequently involves the kidneys (lupus nephritis; LN). Tumour necrosis factor alpha (TNF-α), an important pro-inflammatory cytokine, is expressed locally in the kidney and correlates with LN disease activity. The aim of this study was to ascertain whether soluble receptors for TNF-α (sTNFR1/sTNFR2) are significantly increased in children with LN.

METHODS

Plasma samples were collected from JSLE patients at routine review. Concentrations of sTNFR1 and sTNFR2 were measured (median; interquartile range, IQR) using enzyme-linked immunosorbent assay (ELISA) in 25 JSLE patients (seven LN) and 20 healthy controls (HCs).

RESULTS

sTNFR2 concentration was significantly increased in JSLE (5149 pg/dl, 3413-8561) compared to HCs (3858 pg/dl, 2254-5165; p = 0.049). sTNFR1 concentration was significantly increased in active LN (n = 7, 1765 pg/dl, IQR 1133-4167) compared to inactive LN (n = 18, 1104 pg/dl, 886-1272; p = 0.018). There was a non-significant increase in sTNFR2 concentration in active LN (9829 pg/dl, 3298-21271) compared to inactive LN (4595 pg/dl, 3345-6993; p = 0.146). sTNFR1 concentration correlated moderately with sTNFR2 (r = 0.66, p < 0.001). sTNFR2 demonstrated strong positive correlations with ESR (r = 0.941, p < 0.01) and anti-dsDNA antibodies (r = 0.998, p = 0.041). Both receptors also positively correlated with creatinine (TNFR1 r = 0.81, p < 0.001; TNFR2 r = 0.50, p = 0.015) and urinary albumin creatinine ratio (TNFR1 r = 0.64, p < 0.01; TNFR2 r = 0.63, p < 0.01).

CONCLUSIONS

These data indicate that sTNFR1 and sTNFR2 concentrations are elevated in LN and may reflect renal activity. These results provide basis for further investigation into the pathological pathways underlying LN.

The Changing Landscape of Renal Inflammation

Kidney inflammation is a major contributor to progressive renal injury, leading to glomerulonephritis (GN) and chronic kidney disease. We review recent advances in our understanding of leukocyte accumulation in the kidney, emphasizing key chemokines involved in GN. We discuss features of renal inflammation such as the evolving concept of immune cell plasticity. We also describe certain aspects of organ-specific tissue microenvironments in shaping immune cell responses, as well as the current knowledge of how regulatory T lymphocytes impact on other immune effector cell populations to control inflammation. It is clear that present and future research in these areas may contribute to the development of novel targeted therapeutics, with the hope of alleviating the burden of end-stage renal disease (ESRD).

The lymphotoxin β receptor is a potential therapeutic target in renal inflammation

Accumulation of inflammatory cells in different renal compartments is a hallmark of progressive kidney diseases including glomerulonephritis (GN). Lymphotoxin β receptor (LTβR) signaling is crucial for the formation of lymphoid tissue, and inhibition of LTβR signaling has ameliorated several non-renal inflammatory models. Therefore, we tested whether LTβR signaling could also have a role in renal injury. Renal biopsies from patients with GN were found to express both LTα and LTβ ligands, as well as LTβR. The LTβR protein and mRNA were localized to tubular epithelial cells, parietal epithelial cells, crescents, and cells of the glomerular tuft, whereas LTβ was found on lymphocytes and tubular epithelial cells. Human tubular epithelial cells, mesangial cells, and mouse parietal epithelial cells expressed both LTα and LTβ mRNA upon stimulation with TNF in vitro. Several chemokine mRNAs and proteins were expressed in response to LTβR signaling. Importantly, in a murine lupus model, LTβR blockade improved renal function without the reduction of serum autoantibody titers or glomerular immune complex deposition. Thus, a preclinical mouse model and human studies strongly suggest that LTβR signaling is involved in renal injury and may be a suitable therapeutic target in renal diseases.

Necroinflammation in Kidney Disease

The bidirectional causality between kidney injury and inflammation remains an area of unexpected discoveries. The last decade unraveled the molecular mechanisms of sterile inflammation, which established danger signaling via pattern recognition receptors as a new concept of kidney injury-related inflammation. In contrast, renal cell necrosis remained considered a passive process executed either by the complement-related membrane attack complex, exotoxins, or cytotoxic T cells. Accumulating data now suggest that renal cell necrosis is a genetically determined and regulated process involving specific outside-in signaling pathways. These findings support a unifying theory in which kidney injury and inflammation are reciprocally enhanced in an autoamplification loop, referred to here as necroinflammation. This integrated concept is of potential clinical importance because it offers numerous innovative molecular targets for limiting kidney injury by blocking cell death, inflammation, or both. Here, the contribution of necroinflammation to AKI is discussed in thrombotic microangiopathies, necrotizing and crescentic GN, acute tubular necrosis, and infective pyelonephritis or sepsis. Potential new avenues are further discussed for abrogating necroinflammation-related kidney injury, and questions and strategies are listed for further exploration in this evolving field.

Circulating Tumor Necrosis Factor α Receptors Predict the Outcomes of Human IgA Nephropathy: A Prospective Cohort Study

The circulating tumor necrosis factor receptors (TNFRs) could predict the long-term renal outcome in diabetes, but the role of circulating TNFRs in other chronic kidney disease has not been reported. Here, we investigated the correlation between circulating TNFRs and renal histologic findings on kidney biopsy in IgA nephropathy (IgAN) and assessed the notion that the circulating TNFRs could predict the clinical outcome. 347 consecutive biopsy-proven IgAN patients between 2006 and 2012 were prospectively enrolled. Concentrations of circulating TNFRs were measured using serum samples stored at the time of biopsy. The primary clinical endpoint was the decline of estimated glomerular filtration rate (eGFR; ≥ 30% decline compared to baseline). Mean eGFR decreased and proteinuria worsened proportionally as circulating TNFR1 and TNFR2 increased (P < 0.001). Tubulointerstitial lesions such as interstitial fibrosis and tubular atrophy were significantly more severe as concentrations of circulating TNFRs increased, regardless of eGFR levels. The risks of reaching the primary endpoint were significantly higher in the highest quartile of TNFRs compared with other quartiles by the Cox proportional hazards model (TNFR1; hazard ratio 7.48, P < 0.001, TNFR2; hazard ratio 2.51, P = 0.021). In stratified analysis according to initial renal function classified by the eGFR levels of 60 mL/min/1.73 m², TNFR1 and TNFR2 were significant predictors of renal progression in both subgroups. In conclusion, circulating TNFRs reflect the histology and clinical severity of IgAN. Moreover, elevated concentrations of circulating TNFRs at baseline are early biomarkers for subsequent renal progression in IgAN patients.

Absence of nicotinic acetylcholine receptor α7 subunit amplifies inflammation and accelerates onset of fibrosis: an inflammatory kidney model

Inflammation is regulated by endogenous mechanisms, including anti-inflammatory cytokines, adenosine, and the nicotinic acetylcholine receptor α7 subunit (α7nAChR). We investigated the role of α7nAChR in protection against the progression of tissue injury in a model of severe, macrophage-mediated, cytokine-dependent anti-glomerular basement membrane (GBM) glomerulonephritis (GN), in α7nAChR-deficient (α7(-/-)) mice . At d 7 after the injection of anti-GBM antibody, kidneys from α7(-/-) mice displayed severe glomeruli (P < 0.0001) and tubulointerstitial lesions (P < 0.001) compared to kidneys from WT mice. An important finding was the presence of severe glomerulosclerosis in α7(-/-) mice in this early phase of the disease. Kidneys of α7(-/-) mice showed greater accumulation of inflammatory cells and higher expression of chemokines and cytokines than did those of WT mice. In addition, in α7(-/-) fibrotic kidneys, the expression of fibrin, collagen, TGF-β, and tissue inhibitor of metalloproteinase (TIMP)-2 increased, and the expression of TIMP3 declined. The increase in counterregulatory responses to inflammation in α7(-/-) nephritic kidneys did not compensate for the lack of α7nAChR. These findings indicate that α7nAChR plays a key role in regulating the inflammatory response in anti-GBM GN and that disruption of the endogenous protective α7nAChR amplifies inflammation to accelerate kidney damage and fibrosis.

Elevation of circulating TNF receptors 1 and 2 increases the risk of end-stage renal disease in American Indians with type 2 diabetes

In Caucasians with type 2 diabetes, circulating TNF receptors 1 (TNFR1) and 2 (TNFR2) predict end-stage renal disease (ESRD). Here we examined this relationship in a longitudinal cohort study of American Indians with type 2 diabetes with measured glomerular filtration rate (mGFR, iothalamate) and urinary albumin-to-creatinine ratio (ACR). ESRD was defined as dialysis, kidney transplant, or death attributed to diabetic kidney disease. Age-gender-adjusted incidence rates and incidence rate ratios of ESRD were computed by Mantel-Haenszel stratification. The hazard ratio of ESRD was assessed per interquartile range increase in the distribution of each TNFR after adjusting for baseline age, gender, mean blood pressure, HbA1c, ACR, and mGFR. Among the 193 participants, 62 developed ESRD and 25 died without ESRD during a median follow-up of 9.5 years. The age-gender-adjusted incidence rate ratio of ESRD was higher among participants in the highest versus lowest quartile for TNFR1 (6.6, 95% confidence interval (CI) 3.3-13.3) or TNFR2 (8.8, 95% CI 4.3-18.0). In the fully adjusted model, the risk of ESRD per interquartile range increase was 1.6 times (95% CI 1.1-2.2) as high for TNFR1 and 1.7 times (95% CI 1.2-2.3) as high for TNFR2. Thus, elevated serum concentrations of TNFR1 or TNFR2 are associated with increased risk of ESRD in American Indians with type 2 diabetes after accounting for traditional risk factors including ACR and mGFR.

Tumor necrosis factor receptor 2 (TNFR2)·interleukin-17 receptor D (IL-17RD) heteromerization reveals a novel mechanism for NF-κB activation

TNF receptor 2 (TNFR2) exerts diverse roles in the pathogenesis of inflammatory and autoimmune diseases. Here, we report that TNFR2 but not TNFR1 forms a heteromer with interleukin-17 receptor D (IL-17RD), also named Sef, to activate NF-κB signaling. TNFR2 associates with IL-17RD, leading to mutual receptor aggregation and TRAF2 recruitment, which further activate the downstream cascade of NF-κB signaling. Depletion of IL-17RD impaired TNFR2-mediated activation of NF-κB signaling. Importantly, IL-17RD was markedly increased in renal tubular epithelial cells in nephritis rats, and a strong interaction of TNFR2 and IL-17RD was observed in the renal epithelia. The IL-17RD·TNFR2 complex in activation of NF-κB may explain the role of TNFR2 in inflammatory diseases including nephritis.

Inflammatory cytokines kinetics define the severity and phase of nephropathia epidemica

AIMS

Nephropathia epidemica (NE) is a form of hemorrhagic fever with renal syndrome associated with the Puumala virus species of Hantavirus. The pathogenesis of NE is not well understood; therefore, investigating the inflammatory cytokine response to infection may provide useful knowledge in deciphering the pathophysiology of NE.

MATERIALS & METHODS

Using Luminex and ELISA, we analyzed the serum of 137 NE cases and 44 controls to investigate if serum cytokines associate with different clinical presentations.

RESULTS

Serum levels of TNF-α and IL-1β are associated with disease severity while upregulation of IL-6, CXCL10, CCL2 and CCL3 are associated with clinical presentation.

CONCLUSION

Inflammatory cytokine kinetics associate with the severity and phase of NE. Our data support a role for inflammatory cytokines in the pathophysiology of NE.

TNF receptors: signaling pathways and contribution to renal dysfunction

Tumor necrosis factor (TNF), initially reported to induce tumor cell apoptosis and cachexia, is now considered a central mediator of a broad range of biological activities from cell proliferation, cell death and differentiation to induction of inflammation and immune modulation. TNF exerts its biological responses via interaction with two cell surface receptors: TNFR1 and TNFR2. (TNFRs). These receptors trigger shared and distinct signaling pathways upon TNF binding, which in turn result in cellular outputs that may promote tissue injury on one hand but may also induce protective, beneficial responses. Yet the role of TNF and its receptors specifically in renal disease is still not well understood. This review describes the expression of the TNFRs, the signaling pathways induced by them and the biological responses of TNF and its receptors in various animal models of renal diseases, and discusses the current outcomes from use of TNF biologics and TNF biomarkers in renal disorders.

Circulating TNF receptor 2 is closely associated with the kidney function in non-diabetic Japanese subjects

AIM

Chronic kidney disease (CKD) is associated with cardiovascular events. Tumor necrosis factor (TNF) and/or its receptors have been postulated to be involved in renal pathophysiology. It is unclear whether an increased TNF system activity is present before the development of apparent CKD.

METHODS

Four hundred and twenty non-diabetic Japanese subjects with an estimated GFR (eGFR) greater than 60 ml/min/1.73 m(2) were recruited for measurement of the HbA1c, insulin, TNF system activity (TNF-α, soluble TNF receptor 1 (sTNF-R1) and sTNF-R2) levels and various parameters, including the lipid, high-sensitivity C-reactive protein (hsCRP), high-molecular-weight (HMW) adiponectin and leptin levels. The subjects were stratified according to the eGFR: the G1 level (eGFR ≧90 ml/min/1.73 m(2)) and the G2 level (90 ＞eGFR ≧60 ml/min/1.73 m(2)).

RESULTS

Whereas no significant differences were observed in gender, body mass index (BMI), blood pressure, insulin, TNF-α, hsCRP, HMW adiponectin or leptin between the two groups, the values for age, HbA1c, triglycerides, sTNF-R1 and sTNF-R2 were significantly higher in the subjects with a G2 level of eGFR than in those with a G1 level. In contrast, the HDL cholesterol levels were significantly lower in the subjects with a G2 level than in those with a G1 level. Linear negative correlations were also observed between eGFR and age, BMI, HbA1c, triglycerides, sTNF-R1 and sTNFR2, respectively. A multiple logistic regression analysis revealed that only sTNF-R2 was associated with the presence of a G2 level of eGFR (Odds ratio 1.092, 95% CI 1.013-1.177, P=0.021).

CONCLUSIONS

The circulating sTNF-R2 level is closely associated with the kidney function in non-diabetic Japanese subjects.

Assaying NF-κB activation and signaling from TNF receptors

Tumor necrosis factor (TNF)-mediated activation of the NF-κB family of transcription factors is mediated by two receptors, TNFR1 and TNFR2. These two receptors have unique roles in response to TNF and have been the focus of new therapeutic strategies in a variety of diseases with an immune or an inflammatory component. This chapter describes in vitro methods to functionally identify which TNF receptor is initiating NF-κB activation. This will include antibody-mediated receptor blockade and RNAi-mediated gene silencing targeting the individual receptors. The NF-κB activation methods presented include standard, accepted assays for monitoring the sequential activation steps through the NF-κB signal transduction cascade, including IκBα degradation, NF-κB nuclear translocation, and transcriptional activation of gene expression.

Plasma apolipoprotein L1 levels do not correlate with CKD

Polymorphisms in APOL1 are associated with CKD, including HIV-related CKD, in individuals of African ancestry. The apolipoprotein L1 (APOL1) protein circulates and is localized in kidney cells, but the contribution of APOL1 location to CKD pathogenesis is unclear. We examined associations of plasma APOL1 levels with plasma cytokine levels, dyslipidemia, and APOL1 genotype in a nested case-control study (n=270) of HIV-infected African Americans enrolled in a multicenter prospective observational study. Patients were designated as having CKD when estimated GFR (eGFR) decreased to <60 ml/min per 1.73 m(2) (eGFR<60 cohort) or protein-to-creatinine ratios became >3.5 g/g (nephrotic proteinuria cohort). Circulating APOL1 levels did not associate with APOL1 genotype, CKD status, or levels of proinflammatory cytokines, but did correlate with fasting cholesterol, LDL cholesterol, and triglyceride levels. At ascertainment, CKD-associated polymorphisms (risk variants) in APOL1 associated with the eGFR<60 cohort, but not the nephrotic-range proteinuria cohort. Of note, in both the eGFR<60 and nephrotic proteinuria cohorts, CKD cases with two APOL1 risk variants had significant declines in eGFR over a median of 4 years compared with individuals with one or no risk variants. APOL1 risk genotype was not associated with changes in proteinuria. Higher circulating proinflammatory cytokine levels were independently associated with CKD but not APOL1 genotype. In conclusion, the function of variant APOL1 proteins derived from circulation or synthesized in the kidney, but not the level of circulating APOL1, probably mediates APOL1-associated kidney disease in HIV-infected African Americans.

The inflammation-lipocalin 2 axis may contribute to the development of chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is an important risk factor for coronary heart disease, and previous studies indicated the involvement of low-grade inflammation in the pathogenesis of CKD.

METHODS

The study was designed to (i) identify and confirm genes and their products upregulated in mesangial cells cocultured with endotoxin-stimulated macrophages and (ii) determine the clinical relevance of genes and proteins upregulated in mesangial cells under inflammatory conditions by an epidemiological approach.

RESULTS

DNA microarray analysis revealed upregulated expression of many genes and their products including several cytokines and chemokines, as well as the inflammatory marker, lipocalin 2 gene. The gene expression and protein upregulation of lipocalin 2 were synergistically affected by endotoxin and tumor necrosis factor (TNF)-α stimulation. In human studies, lipocalin 2 level was significantly associated with creatinine (r = 0.419, P < 0.001) and negatively associated with eGFR (r = -0.365, P < 0.001). Multiple logistic regression analysis revealed a significant association between lipocalin 2 and soluble tumor necrosis factor receptor 2 (sTNF-R2), eGFR and uric acid in general subjects attending regular annual medical check-up (n = 420). When subjects with diabetes were excluded from the analysis, lipocalin 2 remained associated with sTNF-R2, eGFR and uric acid.

CONCLUSIONS

Since an activated TNF system, as demonstrated by elevated sTNF-R2, and elevated uric acid were recently implicated in an elevated CKD risk, we conclude that inflammation could play an important role in the pathogenesis of CKD, and that lipocalin 2 is a potential universal marker for impaired kidney function. Furthermore, the results obtained by the current microarray analysis could improve the understanding of gene profiles associated with the pathophysiology of CKD under inflammatory conditions.

TNFR2 maintains adequate IL-12 production by dendritic cells in inflammatory responses by regulating endogenous TNF levels

Sepsis-induced immune reactions are reduced in TNF receptor 2 (TNFR2)-deficient mice as previously shown. In order to elucidate the underlying mechanisms, the functional integrity of myeloid cells of TNFR2-deficient mice was analyzed and compared to wild type (WT) mice. The capacity of dendritic cells to produce IL-12 was strongly impaired in TNF-deficient mice, mirroring impaired production of IL-12 by WT dendritic cells in sepsis or after LPS or TNF pre-treatment. In addition, TNFR2-deficient mice were refractory to LPS pre-treatment and also to hyper-sensitization by inactivated Propionibacterium acnes, indicating habituation to inflammatory stimuli by the immune response when TNFR2 is lacking. Constitutive expression of TNF mRNA in kidney, liver, spleen, colon and lung tissue, and the presence of soluble TNFR2 in urine of healthy WT mice supported the conclusion that TNF is continuously present in naïve mice and controlled by soluble TNFR2. In TNFR2-deficient mice endogenous TNF levels cannot be balanced and the continuous exposure to enhanced TNF levels impairs dendritic cell function. In conclusion, TNF pre-exposure suppresses secondary inflammatory reactions of myeloid cells; therefore, continuous control of endogenous TNF by soluble TNFR2 seems to be essential for the maintenance of adequate sensitivity to inflammatory stimuli.

Release of nonmuscle myosin II from the cytosolic domain of tumor necrosis factor receptor 2 is required for target gene expression

Tumor necrosis factor-α (TNF-α) elicits its biological activities through activation of TNF receptor 1 (TNFR1, also known as p55) and TNFR2 (also known as p75). The activities of both receptors are required for the TNF-α-induced proinflammatory response. The adaptor protein TNFR-associated factor 2 (TRAF2) is critical for either p55- or p75-mediated activation of nuclear factor κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling, as well as for target gene expression. We identified nonmuscle myosin II (myosin) as a binding partner of p75. TNF-α-dependent signaling by p75 and induction of target gene expression persisted substantially longer in cells deficient in myosin regulatory light chain (MRLC; a component of myosin) than in cells replete in myosin. In resting endothelial cells, myosin was bound constitutively to the intracellular region of p75, a region that overlaps with the TRAF2-binding domain, and TNF-α caused the rapid dissociation of myosin from p75. At early time points after exposure to TNF-α, p75 activated Rho-associated kinase 1 (ROCK1). Inhibition of ROCK1 activity blocked TNF-α-dependent phosphorylation of MRLC and the dissociation of myosin from p75. ROCK1-dependent release of myosin was necessary for the TNF-α-dependent recruitment of TRAF2 to p75 and for p75-specific activation of NF-κB and MAPK signaling. Thus, our findings have revealed a previously uncharacterized, noncanonical regulatory function of myosin in cytokine signaling.

Distinct contributions of TNF receptor 1 and 2 to TNF-induced glomerular inflammation in mice

TNF is an important mediator of glomerulonephritis. The two TNF-receptors TNFR1 and TNFR2 contribute differently to glomerular inflammation in vivo, but specific mechanisms of TNFR-mediated inflammatory responses in glomeruli are unknown. We investigated their expression and function in murine kidneys, isolated glomeruli ex vivo, and glomerular cells in vitro. In normal kidney TNFR1 and TNFR2 were preferentially expressed in glomeruli. Expression of both TNFRs and TNF-induced upregulation of TNFR2 mRNA was confirmed in murine glomerular endothelial and mesangial cell lines. In vivo, TNF exposure rapidly induced glomerular accumulation of leukocytes. To examine TNFR-specific inflammatory responses in intrinsic glomerular cells but not infiltrating leukocytes we performed microarray gene expression profiling on intact glomeruli isolated from wildtype and Tnfr-deficient mice following exposure to soluble TNF ex vivo. Most TNF-induced effects were exclusively mediated by TNFR1, including induced glomerular expression of adhesion molecules, chemokines, complement factors and pro-apoptotic molecules. However, TNFR2 contributed to TNFR1-dependent mRNA expression of inflammatory mediators in glomeruli when exposed to low TNF concentrations. Chemokine secretion was absent in TNF-stimulated Tnfr1-deficient glomeruli, but also significantly decreased in glomeruli lacking TNFR2. In vivo, TNF-induced glomerular leukocyte infiltration was abrogated in Tnfr1-deficient mice, whereas Tnfr2-deficiency decreased mononuclear phagocytes infiltrates, but not neutrophils. These data demonstrate that activation of intrinsic glomerular cells by soluble TNF requires TNFR1, whereas TNFR2 is not essential, but augments TNFR1-dependent effects. Previously described TNFR2-dependent glomerular inflammation may therefore require TNFR2 activation by membrane-bound, but not soluble TNF.

New model for adenine-induced chronic renal failure in mice, and the effect of gum acacia treatment thereon: comparison with rats

INTRODUCTION

This study aimed at comparing the effects of feeding mice and rats with adenine to induce a state of chronic renal failure (CRF), and to assess the effect of treatment with gum acacia (GA) thereon.

METHODS

We compared the outcome, in mice, of feeding adenine at three different doses (0.75%, 0.3%, and 0.2%, w/w). Biochemical and histopathological studies were conducted in plasma, urine and renal homogenates from both species.

RESULTS

When mice and rats were fed adenine (0.75%, w/w), all treated rats survived the treatment, but all treated mice died within 1-2 days. The dosage in mice was reduced to 0.3%, w/w, for 4 weeks, but again all treated mice died within 3-4 days. A further reduction in the dosage in mice to 0.2%, w/w, for 4 weeks resulted in no mortality, and produced alterations similar to those observed in rats fed adenine at a dose of 0.75%,w/w, for 4 weeks. Plasma creatinine, urea and urinary protein were significantly increased (P<0.001) in adenine-treated mice and rats, and this action was incompletely, but significantly (P<0.05), reversed by GA. Adenine significantly (P<0.001) reduced superoxide dismutase (SOD) activity and reduced glutathione (GSH) concentration in renal homogenates from both species, and these reductions were significantly (P<0.05) ameliorated by GA.

DISCUSSION

Our data suggest that mice are more sensitive to adenine than rats, and that a dose of adenine of 0.2%, w/w, for 4 weeks in mice is suggested as a model for CRF. In both models, GA (15%, w/v, in the drinking water for 4 weeks) given concomitantly with adenine ameliorated the severity of CRF to a similar extent.

Endothelial TNF receptor 2 induces IRF1 transcription factor-dependent interferon-β autocrine signaling to promote monocyte recruitment

Endothelial-dependent mechanisms of mononuclear cell influx are not well understood. We showed that acute stimulation of murine microvascular endothelial cells expressing the tumor necrosis factor receptors TNFR1 and TNFR2 with the soluble cytokine TNF led to CXCR3 chemokine generation. The TNF receptors signaled through interferon regulatory factor-1 (IRF1) to induce interferon-β (IFN-β) and subsequent autocrine signaling via the type I IFN receptor and the transcription factor STAT1. Both TNFR2 and TNFR1 were required for IRF1-IFNβ signaling and, in human endothelial cells TNFR2 expression alone induced IFN-β signaling and monocyte recruitment. In vivo, TNFR1 was required for acute renal neutrophil and monocyte influx after systemic TNF treatment, whereas the TNFR2-IRF1-IFN-β autocrine loop was essential only for macrophage accumulation. In a chronic model of proliferative nephritis, IRF1 and renal-expressed TNFR2 were essential for sustained macrophage accumulation. Thus, our data identify a pathway in endothelial cells that selectively recruits monocytes during a TNF-induced inflammatory response.

Tumor necrosis factor-α: regulation of renal function and blood pressure

Tumor necrosis factor-α (TNF-α) is a pleiotropic cytokine that becomes elevated in chronic inflammatory states such as hypertension and diabetes and has been found to mediate both increases and decreases in blood pressure. High levels of TNF-α decrease blood pressure, whereas moderate increases in TNF-α have been associated with increased NaCl retention and hypertension. The explanation for these disparate effects is not clear but could simply be due to different concentrations of TNF-α within the kidney, the physiological status of the subject, or the type of stimulus initiating the inflammatory response. TNF-α alters renal hemodynamics and nephron transport, affecting both activity and expression of transporters. It also mediates organ damage by stimulating immune cell infiltration and cell death. Here we will summarize the available findings and attempt to provide plausible explanations for such discrepancies.

TNF-α type 2 receptor mediates renal inflammatory response to chronic angiotensin II administration with high salt intake in mice

Tumor necrosis factor-alpha (TNF-α) has been implicated in salt-sensitive hypertension and renal injury (RI) induced by angiotensin II (ANG II). To determine the receptor type of TNF-α involved in this mechanism, we evaluated the responses to chronic ANG II infusion (25 ng/min by implanted minipump) given with high-salt diet (HS; 4% NaCl) for 2 wk in gene knockout mice for TNF-α receptor type 1 (TNFR1KO; n = 6) and type 2 (TNFR2KO; n = 6) and compared the responses with those in wild-type (WT; C57BL/6; n = 6) mice. Blood pressure in these mice was measured by implanted radiotelemetry as well as by tail-cuff plethysmography. RI responses were assessed by measuring macrophage cell infiltration (CD68(+) immunohistochemistry), glomerulosclerosis (PAS staining), and interstitial fibrosis (Gomori's trichrome staining) in renal tissues at the end of the treatment period. The increase in mean arterial pressure induced by ANG II + HS treatment was not different in these three groups of mice (TNFR1KO, 114 ± 1 to 161 ± 7 mmHg; TNFR2KO, 113 ± 1 to 161 ± 3 mmHg; WT, 110 ± 3 to 154 ± 3 mmHg). ANG II + HS-induced RI changes were similar in TNFR1KO mice but significantly less in TNFR2KO mice (macrophage infiltration, 0.02 ± 0.01 vs. 1.65 ± 0.45 cells/mm(2); glomerulosclerosis, 26.3 ± 2.6 vs. 35.7 ± 2.2% area; and interstitial fibrosis, 5.2 ± 0.6 vs. 8.1 ± 1.1% area) compared with the RI changes in WT mice. The results suggest that a direct activation of TNF-α receptors may not be required in inducing hypertensive response to chronic ANG II administration with HS intake, but the induction of inflammatory responses leading to renal injury are mainly mediated by TNF-α receptor type 2.

Circulating TNF receptor 2 is associated with the development of chronic kidney disease in non-obese Japanese patients with type 2 diabetes

AIMS

Chronic low-grade inflammation and/or obesity are suggested to induce chronic kidney disease (CKD) in patients with type 2 diabetes. This cross-sectional study was performed to investigate the relationship between inflammatory biomarkers and CKD in non-obese patients with type 2 diabetes.

METHODS

106 non-obese Japanese patients with type 2 diabetes were recruited for the measurement of GFR, TNF, HMW adiponectin, leptin, hsCRP and some variables including urinary albumin. BMI, serum creatinine, and urinary albumin levels were 22.2 ± 0.2 kg/m(2) (17.1-24.9 kg/m(2)), 0.76 ± 0.02 mg/dl (0.39-1.38 mg/dl), 40.4 ± 4.3mg/gCr (1.6-195.0mg/gCr), respectively. They were stratified into two groups based on the value of eGFR: low eGFR (eGFR<60 ml/min/1.73 m(2)) and normal eGFR (eGFR>60 ml/min/1.73 m(2)). Logistic regression analysis was used for statistical analysis.

RESULTS

Whereas univariate logistic regression analysis showed that gender, diabetes duration, triglyceride, HDL cholesterol, uric acid, urinary albumin, and soluble TNF receptors (sTNF-R1, sTNF-R2) are associated with the development of stage 3 CKD, multivariate logistic regression analysis revealed that sTNF-R2 (Odds ratio 1.003, 95% confidence interval 1.000 to 1.005, P=0.030) showed significant associations with the development of stage 3 CKD.

CONCLUSIONS

Circulating TNF receptor 2 is an independent risk factor for CKD in non-obese Japanese patients with type 2 diabetes.

Interleukin-17 cytokines are critical in development of fatal lupus glomerulonephritis

Systemic lupus erythematosus is a potentially fatal autoimmune disease. Although interleukin-17 (IL-17) has been linked to human lupus and mouse models of this disease, it has not been addressed whether this cytokine plays a critical role in fatal lupus pathology. Here we have demonstrated that increased production of IL-17 cytokines and their signaling via the adaptor protein CIKS (a.k.a. Traf3ip2, Act1) critically contributed to lethal pathology in an FcgammaR2b-deficient mouse model of lupus. Mice lacking IL-17 and especially those lacking CIKS showed greatly improved survival and were largely protected from development of glomerulonephritis. Importantly in this model, potential effects of IL-17 cytokines on antibody production could be distinguished from critical local contributions in kidneys, including recruitment of neutrophils and monocytes. These findings provide the proof of principle that signaling by IL-17 family cytokines mediated via CIKS presents promising therapeutic targets for the treatment of systemic lupus erythematosus, especially in cases with kidney involvement.

Tumor necrosis factor receptors: biology and therapeutic potential in kidney diseases

The major evolutionary advance represented in the human immune system is a mechanism of antigen-directed immunity in which tumor necrosis factor (TNF)-α and TNF receptors (TNFRs) play essential roles. Binding of TNF-α to the 55-kDa type I TNFR (TNFR1, TNFRSF1A, CD120a, p55) or the 75-kDa type II TNFR (TNFR2, TNFRSF1B, CD120b, p75) activates signaling pathways controlling inflammatory, immune and stress responses, as well as host defense and apoptosis. Multiple studies have investigated the role of TNFRs in the development of early and late renal failure (diabetic nephropathy, nephroangiosclerosis, acute kidney transplant rejection, renal cell carcinoma, glomerulonephritis, sepsis and obstructive renal injury). This article reviews the general characteristics, the analytical aspects and the biology of TNFRs in this domain. In addition, the potential therapeutic application of specific TNFR blockers is discussed.