Out of the TWEAKlight: Elucidating the Role of Fn14 and TWEAK in Acute Kidney Injury

Serum and urinary levels of MIF, CD74, DDT and CXCR4 among patients with type 1 diabetes mellitus, type 2 diabetes and healthy individuals: Implications for further research

Background

Macrophage migration inhibitory factor (MIF) is a highly conserved cytokine with pleiotropic properties, mainly pro-inflammatory. MIF seems to exert its pro-inflammatory features by binding to its transmembrane cellular receptor CD74. MIF also has CXCR4, which acts as a co-receptor in this inflammatory process. Apart from MIF, D-dopachrome tautomerase (DDT) or MIF2, which belongs to the MIF superfamily, also binds to receptor CD74. Therefore, these molecules, MIF, CD74, DDT and CXCR4 are suggested to work together orchestrating an inflammatory process. Diabetes mellitus is characterised by chronic low-grade inflammation. Therefore, the aim of the present study was to evaluate serum and urinary levels of the aforementioned molecules among patients with type 1 diabetes mellitus (T1DM), type 2 diabetes mellitus (T2DM) and among healthy controls.

Methods

We enrolled 13 patients with T1DM, 74 patients with T2DM and 25 healthy individuals as controls. Levels of CD74, CXCR4, DDT, and MIF were measured using ELISA Kits according to the manufacturer's instructions.

Results

We documented increased serum MIF levels together with higher urinary CD74 levels among patients with T1DM, when compared to patients with T2DM and healthy adults. In particular, patients with T1DM showed significantly increased levels of MIF compared to T2DM (p = 0.011) and healthy controls (p = 0.0093). CD74 in urine were significantly higher in patients with T1DM compared to those affected with T2DM (p = 0.0302) and healthy group (p = 0.0099). On the contrary, serum CD74 were similar among the three groups. No statistical differences were identified in CXCR4 levels both in serum and in urine of all groups. Patients with T2DM and overweight/obesity had increased urinary levels of CD74, when compared to lean patients with T2DM.

Conclusion

The increased serum MIF levels and urinary CD74 levels among patients with T1DM may be attributed to the autoimmune milieu, which characterises patients with T1DM, when compared to patients with T2DM. These two findings merit further attention as they could pave the way for further research regarding the potential beneficial effects of inhibitors of MIF among patients with T1DM, especially in the early stages of T1DM. Finally, the role of inhibitors of MIF could be further explored in the context of obesity among patients with T2DM.

Combined Plasma Olink Proteomics and Transcriptomics Identifies CXCL1 and TNFRSF12A as Potential Predictive and Diagnostic Inflammatory Markers for Acute Kidney Injury

Acute kidney injury (AKI) poses a significant global public health challenge. Current methods for detecting AKI rely on monitoring changes in serum creatinine (Scr), blood urea nitrogen (BUN), urinary output and some commonly employed biomarkers. However, these indicators are usually neither specific nor sensitive to AKI, especially in cases of mild kidney injury. AKI is accompanied by severe inflammatory reactions, resulting in the upregulation of numerous inflammation-associated proteins in the plasma. Plasma biomarkers are a noninvasive method for detecting kidney injury, and to date, plasma inflammation-associated cytokines have not been adequately studied in AKI patients. The objective of our research was to identify novel inflammatory biomarkers for AKI. We utilized Olink proteomics to analyze the alterations in plasma inflammation-related proteins in the serum of healthy mice (n = 2) or mice treated with cisplatin (n = 6). Additionally, transcriptome datasets for the lipopolysaccharide (LPS), cisplatin, and ischemia‒reperfusion injury (IRI) groups were obtained from the National Center of Biotechnology Information (NCBI) Gene Expression Omnibus (GEO) database. We calculated the intersection of differentially expressed proteins (DEPs) and genes (DEGs) from both datasets. In the Olink proteomics analysis, the AKI group had significantly greater levels of 11 DEPs than did the control group. In addition, 56 common upregulated DEGs were obtained from the transcriptome dataset. The expression of CXCL1 and TNFRSF12A overlapped across all the datasets. The transcription and protein expression levels of CXCL1 and TNFRSF12A were detected in vivo. The gene and protein levels of CXCL1 and TNFRSF12A were significantly increased in different AKI mouse models and clinical patients, suggesting that these genes and proteins could be potential specific biomarkers for the identification of AKI.

Targeting the TWEAK-Fn14 pathway prevents dysfunction in cardiac calcium handling after acute kidney injury

Heart and kidney have a closely interrelated pathophysiology. Acute kidney injury (AKI) is associated with significantly increased rates of cardiovascular events, a relationship defined as cardiorenal syndrome type 3 (CRS3). The underlying mechanisms that trigger heart disease remain, however, unknown, particularly concerning the clinical impact of AKI on cardiac outcomes and overall mortality. Tumour necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor fibroblast growth factor-inducible 14 (Fn14) are independently involved in the pathogenesis of both heart and kidney failure, and recent studies have proposed TWEAK as a possible therapeutic target; however, its specific role in cardiac damage associated with CRS3 remains to be clarified. Firstly, we demonstrated in a retrospective longitudinal clinical study that soluble TWEAK plasma levels were a predictive biomarker of mortality in patients with AKI. Furthermore, the exogenous application of TWEAK to native ventricular cardiomyocytes induced relevant calcium (Ca2+ ) handling alterations. Next, we investigated the role of the TWEAK-Fn14 axis in cardiomyocyte function following renal ischaemia-reperfusion (I/R) injury in mice. We observed that TWEAK-Fn14 signalling was activated in the hearts of AKI mice. Mice also showed significantly altered intra-cardiomyocyte Ca2+ handling and arrhythmogenic Ca2+ events through an impairment in sarcoplasmic reticulum Ca2+ -adenosine triphosphatase 2a pump (SERCA2a ) and ryanodine receptor (RyR2 ) function. Administration of anti-TWEAK antibody after reperfusion significantly improved alterations in Ca2+ cycling and arrhythmogenic events and prevented SERCA2a and RyR2 modifications. In conclusion, this study establishes the relevance of the TWEAK-Fn14 pathway in cardiac dysfunction linked to CRS3, both as a predictor of mortality in patients with AKI and as a Ca2+ mishandling inducer in cardiomyocytes, and highlights the cardioprotective benefits of TWEAK targeting in CRS3. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Evolution of diagnosis and treatment for lupus nephritis in Spain

Lupus nephritis (LN) is a serious manifestation of systemic lupus erythematosus that can lead to end-stage renal disease. Many clinical and prognostic data on which our therapeutic decisions are based come from international cohorts, which have important ethnic and prognostic differences. To identify clinical and prognostic data from patients with LN in Spain, we undertook a bibliographic search of NL-related papers by Spanish authors and published in national and international journals between 2005 and 2022. According to the selected references, renal biopsy is not only essential for LN diagnosis but its repetition can be useful for the follow-up. Regarding LN treatment, standard strategy consists of an induction phase and a maintenance phase. However, as new drugs have been released, a new paradigm of treatment in a single, continuing and personalized phase has been proposed.

Biotherapy of experimental acute kidney injury: emerging novel therapeutic strategies

Acute kidney injury (AKI) is a complex and heterogeneous disease with high incidence and mortality, posing a serious threat to human life and health. Usually, in clinical practice, AKI is caused by crush injury, nephrotoxin exposure, ischemia-reperfusion injury, or sepsis. Therefore, most AKI models for pharmacological experimentation are based on this. The current research promises to develop new biological therapies, including antibody therapy, non-antibody protein therapy, cell therapy, and RNA therapy, that could help mitigate the development of AKI. These approaches can promote renal repair and improve systemic hemodynamics after renal injury by reducing oxidative stress, inflammatory response, organelles damage, and cell death, or activating cytoprotective mechanisms. However, no candidate drugs for AKI prevention or treatment have been successfully translated from bench to bedside. This article summarizes the latest progress in AKI biotherapy, focusing on potential clinical targets and novel treatment strategies that merit further investigation in future pre-clinical and clinical studies.

Emerging significance and therapeutic targets of ferroptosis: a potential avenue for human kidney diseases

Kidney diseases remain one of the leading causes of human death and have placed a heavy burden on the medical system. Regulated cell death contributes to the pathology of a plethora of renal diseases. Recently, with in-depth studies into kidney diseases and cell death, a new iron-dependent cell death modality, known as ferroptosis, has been identified and has attracted considerable attention among researchers in the pathogenesis of kidney diseases and therapeutics to treat them. The majority of studies suggest that ferroptosis plays an important role in the pathologies of multiple kidney diseases, such as acute kidney injury (AKI), chronic kidney disease, and renal cell carcinoma. In this review, we summarize recently identified regulatory molecular mechanisms of ferroptosis, discuss ferroptosis pathways and mechanisms of action in various kidney diseases, and describe the protective effect of ferroptosis inhibitors against kidney diseases, especially AKI. By summarizing the prominent roles of ferroptosis in different kidney diseases and the progress made in studying ferroptosis, we provide new directions and strategies for future research on kidney diseases. In summary, ferroptotic factors are potential targets for therapeutic intervention to alleviate different kidney diseases, and targeting them may lead to new treatments for patients with kidney diseases.

Ginkgolide A downregulates transient receptor potential (melastatin) 2 to protect cisplatin-induced acute kidney injury in rats through the TWEAK/Fn14 pathway: Ginkgolide A improve acute renal injury

PURPOSE

In order to seek effective drugs for treating cisplatin-induced acute renal injury and explore the corresponding potential mechanism.

METHODS

Mouse kidney injury model was established by intraperitoneal injection of 20 mg/kg cisplatin. The temporal expression of TRPM2 and the regulation of Ginkgolide A on its expression were analyzed by western blot. In order to perform the mechanical analysis, we used TRPM2-KO knockout mice. In this study, we evaluated the repair effect of GA on acute kidney injury through renal function factors, inflammatory factors and calcium and potassium content. Pathological injury and cell apoptosis were detected by H&E and TUNEL, respectively.

RESULT

Ginkgolide A inhibited inflammatory reaction and excessive oxidative stress, reduced renal function parameters, and improved pathological injury. Meanwhile, we also found that the repair effect of Ginkgolide A on renal injury is related to TRPM2, and Ginkgolide A downregulated TRPM2 expression and inactivated TWEAK/Fn14 pathway in cisplatin-induced renal injury model. We also found that inhibition of TWEAK/Fn14 pathway was more effective in TRPM2-KO mice than TRPM2-WT mice.

CONCLUSION

Ginkgolide A was the effective therapeutic drug for cisplatin-induced renal injury through acting on TRPM2, and TWEAK/Fn14 pathway was the downstream pathway of Ginkgolide A in acute renal injury, and Ginkgolide A inhibited TWEAK/Fn14 pathway in cisplatin-induced renal injury model.

Bone Marrow-Derived RIPK3 Mediates Kidney Inflammation in Acute Kidney Injury

BACKGROUND

Receptor-interacting protein kinase 3 (RIPK3), a component of necroptosis pathways, may have an independent role in inflammation. It has been unclear which RIPK3-expressing cells are responsible for the anti-inflammatory effect of overall Ripk3 deficiency and whether Ripk3 deficiency protects against kidney inflammation occurring in the absence of tubular cell death.

METHODS

We used chimeric mice with bone marrow from wild-type and Ripk3-knockout mice to explore RIPK3's contribution to kidney inflammation in the presence of folic acid-induced acute kidney injury AKI (FA-AKI) or absence of AKI and kidney cell death (as seen in systemic administration of the cytokine TNF-like weak inducer of apoptosis [TWEAK]).

RESULTS

Tubular and interstitial cell RIPK3 expressions were increased in murine AKI. Ripk3 deficiency decreased NF-κB activation and kidney inflammation in FA-AKI but did not prevent kidney failure. In the chimeric mice, RIPK3-expressing bone marrow-derived cells were required for early inflammation in FA-AKI. The NLRP3 inflammasome was not involved in RIPK3's proinflammatory effect. Systemic TWEAK administration induced kidney inflammation in wild-type but not Ripk3-deficient mice. In cell cultures, TWEAK increased RIPK3 expression in bone marrow-derived macrophages and tubular cells. RIPK3 mediated TWEAK-induced NF-κB activation and inflammatory responses in bone marrow-derived macrophages and dendritic cells and in Jurkat T cells; however, in tubular cells, RIPK3 mediated only TWEAK-induced Il-6 expression. Furthermore, conditioned media from TWEAK-exposed wild-type macrophages, but not from Ripk3-deficient macrophages, promoted proinflammatory responses in cultured tubular cells.

CONCLUSIONS

RIPK3 mediates kidney inflammation independently from tubular cell death. Specific targeting of bone marrow-derived RIPK3 may limit kidney inflammation without the potential adverse effects of systemic RIPK3 targeting.

Ischemia-Reperfusion Injury in Peripheral Artery Disease and Traditional Chinese Medicine Treatment

Peripheral artery disease (PAD) is a serious public health issue, characterized by circulation disorder of the lower extreme that reduces the physical activity of the lower extremity muscle. The artery narrowed by atherosclerotic lesions initiates limb ischemia. In the progression of treatment, reperfusion injury is still inevitable. Ischemia-reperfusion injury induced by PAD is responsible for hypoxia and nutrient deficiency. PAD triggers hindlimb ischemia and reperfusion (I/R) cycles through various mechanisms, mainly including mitochondrial dysfunction and inflammation. Alternatively, mitochondrial dysfunction plays a central role. The I/R injury may cause cells' injury and even death. However, the mechanism of I/R injury and the way of cell damage or death are still unclear. We review the pathophysiology of I/R injury, which is majorly about mitochondrial dysfunction. Then, we focus on the cell damage and death during I/R injury. Further comprehension of the progress of I/R will help identify biomarkers for diagnosis and therapeutic targets to PAD. In addition, traditional Chinese medicine has played an important role in the treatment of I/R injury, and we will make a brief introduction.

Ferroptosis and Necroptosis in the Kidney

In the last decade, the role of apoptosis in the pathophysiology of acute kidney injury (AKI) and AKI to chronic kidney disease (CKD) progression has been revisited as our understanding of ferroptosis and necroptosis has emerged. A growing body of evidence, reviewed here, ascribes a central pathophysiological role for ferroptosis and necroptosis to AKI, nephron loss, and acute tubular necrosis. We will introduce concepts to the non-cell-autonomous manner of kidney tubular injury during ferroptosis, a phenomenon that we refer to as a "wave of death." We hypothesize that necroptosis might initiate cell death propagation through ferroptosis. The remaining necrotic debris requires effective removal processes to prevent a secondary inflammatory response, referred to as necroinflammation. Open questions include the differences in the immunogenicity of ferroptosis and necroptosis, and the specificity of necrostatins and ferrostatins to therapeutically target these processes to prevent AKI-to-CKD progression and end-stage renal disease.

TWEAK-Fn14 as a common pathway in the heart and the kidneys in cardiorenal syndrome

There is a complex relationship between cardiac and renal disease, often referred to as the cardiorenal syndrome. Heart failure adversely affects kidney function, and both acute and chronic kidney disease are associated with structural and functional changes to the myocardium. The pathological mechanisms and contributing interactions that surround this relationship remain poorly understood, limiting the opportunities for therapeutic intervention. The cytokine tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor, fibroblast growth factor-inducible 14 (Fn14), are abundantly expressed in injured kidneys and heart. The TWEAK-Fn14 axis promotes responses that drive tissue injury such as inflammation, proliferation, fibrosis, and apoptosis, while restraining the expression of tissue protective factors such as the anti-aging factor Klotho and the master regulator of mitochondrial biogenesis peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α). High levels of TWEAK induce cardiac remodeling, and promote inflammation, tubular and podocyte injury and death, fibroblast proliferation, and, ultimately, renal fibrosis. Accordingly, targeting the TWEAK-Fn14 axis is protective in experimental kidney and heart disease. TWEAK has also emerged as a biomarker of kidney damage and cardiovascular outcomes and has been successfully targeted in clinical trials. In this review, we update our current knowledge of the roles of the TWEAK-Fn14 axis in cardiovascular and kidney disease and its potential contribution to the cardiorenal syndrome. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

New insights into the pathophysiological mechanisms underlying cardiorenal syndrome

Communication between the heart and kidney occurs through various bidirectional pathways. The heart maintains continuous blood flow through the kidney while the kidney regulates blood volume thereby allowing the heart to pump effectively. Cardiorenal syndrome (CRS) is a pathologic condition in which acute or chronic dysfunction of the heart or kidney induces acute or chronic dysfunction of the other organ. CRS type 3 (CRS-3) is defined as acute kidney injury (AKI)-mediated cardiac dysfunction. AKI is common among critically ill patients and correlates with increased mortality and morbidity. Acute cardiac dysfunction has been observed in over 50% of patients with severe AKI and results in poorer clinical outcomes than heart or renal dysfunction alone. In this review, we describe the pathophysiological mechanisms responsible for AKI-induced cardiac dysfunction. Additionally, we discuss current approaches in the management of patients with CRS-3 and the development of targeted therapeutics. Finally, we summarize current challenges in diagnosing mild cardiac dysfunction following AKI and in understanding CRS-3 etiology.

Epigenetic Modifiers as Potential Therapeutic Targets in Diabetic Kidney Disease

Diabetic kidney disease is one of the fastest growing causes of death worldwide. Epigenetic regulators control gene expression and are potential therapeutic targets. There is functional interventional evidence for a role of DNA methylation and the histone post-translational modifications-histone methylation, acetylation and crotonylation-in the pathogenesis of kidney disease, including diabetic kidney disease. Readers of epigenetic marks, such as bromodomain and extra terminal (BET) proteins, are also therapeutic targets. Thus, the BD2 selective BET inhibitor apabetalone was the first epigenetic regulator to undergo phase-3 clinical trials in diabetic kidney disease with an endpoint of kidney function. The direct therapeutic modulation of epigenetic features is possible through pharmacological modulators of the specific enzymes involved and through the therapeutic use of the required substrates. Of further interest is the characterization of potential indirect effects of nephroprotective drugs on epigenetic regulation. Thus, SGLT2 inhibitors increase the circulating and tissue levels of β-hydroxybutyrate, a molecule that generates a specific histone modification, β-hydroxybutyrylation, which has been associated with the beneficial health effects of fasting. To what extent this impact on epigenetic regulation may underlie or contribute to the so-far unclear molecular mechanisms of cardio- and nephroprotection offered by SGLT2 inhibitors merits further in-depth studies.

MAGE genes in the kidney: identification of MAGED2 as upregulated during kidney injury and in stressed tubular cells

BACKGROUND

Mutations in Melanoma Antigen-encoding Gene D2 (MAGED2) promote tubular dysfunction, suggesting that MAGE proteins may play a role in kidney pathophysiology. We have characterized the expression and regulation of MAGE genes in normal kidneys and during kidney disease.

METHODS

The expression of MAGE genes and their encoded proteins was explored by systems biology multi-omics (kidney transcriptomics and proteomics) in healthy adult murine kidneys and following induction of experimental acute kidney injury (AKI) by a folic acid overdose. Changes in kidney expression during nephrotoxic AKI were validated by quantitative reverse transcription-polymerase chain reaction (qRT-PCR), western blot and immunohistochemistry. Factors regulating gene expression were studied in cultured tubular cells.

RESULTS

Five MAGE genes (MAGED1, MAGED2, MAGED3, MAGEH1, MAGEE1) were expressed at the mRNA level in healthy adult mouse kidneys, as assessed by RNA-Seq. Additionally, MAGED2 was significantly upregulated during experimental AKI as assessed by array transcriptomics. Kidney proteomics also identified MAGED2 as upregulated during AKI. The increased kidney expression of MAGED2 mRNA and protein was confirmed by qRT-PCR and western blot, respectively, in murine folic acid- and cisplatin-induced AKI. Immunohistochemistry located MAGED2 to tubular cells in experimental and human kidney injury. Tubular cell stressors [serum deprivation and the inflammatory cytokine tumour necrosis factor-like weak inducer of apoptosis (TWEAK)] upregulated MAGED2 in cultured tubular cells.

CONCLUSIONS

MAGED2 is upregulated in tubular cells in experimental and human kidney injury and is increased by stressors in cultured tubular cells. This points to a role of MAGED2 in tubular cell injury during kidney disease that should be dissected by carefully designed functional approaches.

Chronodisruption: A Poorly Recognized Feature of CKD

Multiple physiological variables change over time in a predictable and repetitive manner, guided by molecular clocks that respond to external and internal clues and are coordinated by a central clock. The kidney is the site of one of the most active peripheral clocks. Biological rhythms, of which the best known are circadian rhythms, are required for normal physiology of the kidneys and other organs. Chronodisruption refers to the chronic disruption of circadian rhythms leading to disease. While there is evidence that circadian rhythms may be altered in kidney disease and that altered circadian rhythms may accelerate chronic kidney disease (CKD) progression, there is no comprehensive review on chronodisruption and chronodisruptors in CKD and its manifestations. Indeed, the term chronodisruption has been rarely applied to CKD despite chronodisruptors being potential therapeutic targets in CKD patients. We now discuss evidence for chronodisruption in CKD and the impact of chronodisruption on CKD manifestations, identify potential chronodisruptors, some of them uremic toxins, and their therapeutic implications, and discuss current unanswered questions on this topic.

Regulation of Fn14 stability by SCFFbxw7α during septic acute kidney injury

Acute kidney injury (AKI) initiated by sepsis remains a thorny problem despite recent advancements in its clinical management. Having been found to be activated during AKI, fibroblast growth factor-inducible molecule 14 (Fn14) may be a potential therapeutic target because of its involvement in the molecular basis of injury. Here, we report that LPS induces apoptosis of mouse cortical tubule cells mediated by Fn14, for which simultaneous Toll-like receptor (TLR)4 activation is required. Mechanistically, TLR4 activation by lipopolysaccharide, through disassociating E3 ligase SCFFbxw7α from Fn14, dismantles Lys48-linked polyubiquitination of Fn14 and stabilizes it. Pharmacological deactivation of Fn14 with monoclonal antibody ITEM-2 provides effective protection against lethal sepsis and AKI in mice. Our study underscores an adaptive mechanism whereby TLR4 regulates SCFFbxw7α-dependent Fn14 stabilization during inflammatory tubular damage and further supports investigation of targeting Fn14 in clinical trials of patients with septic AKI.

TRAIL, OPG, and TWEAK in kidney disease: biomarkers or therapeutic targets?

Ligands and receptors of the tumor necrosis factor (TNF) superfamily regulate immune responses and homeostatic functions with potential diagnostic and therapeutic implications. Kidney disease represents a global public health problem, whose prevalence is rising worldwide, due to the aging of the population and the increasing prevalence of diabetes, hypertension, obesity, and immune disorders. In addition, chronic kidney disease is an independent risk factor for the development of cardiovascular disease, which further increases kidney-related morbidity and mortality. Recently, it has been shown that some TNF superfamily members are actively implicated in renal pathophysiology. These members include TNF-related apoptosis-inducing ligand (TRAIL), its decoy receptor osteoprotegerin (OPG), and TNF-like weaker inducer of apoptosis (TWEAK). All of them have shown the ability to activate crucial pathways involved in kidney disease development and progression (e.g. canonical and non-canonical pathways of the transcription factor nuclear factor-kappa B), as well as the ability to regulate cell proliferation, differentiation, apoptosis, necrosis, inflammation, angiogenesis, and fibrosis with double-edged effects depending on the type and stage of kidney injury. Here we will review the actions of TRAIL, OPG, and TWEAK on diabetic and non-diabetic kidney disease, in order to provide insights into their full clinical potential as biomarkers and/or therapeutic options against kidney disease.

NFκB and Kidney Injury

The global burden of chronic kidney disease will increase during the next century. As NFκB, first described more than 30 years ago, plays a major role in immune and non-immune-mediated diseases and in inflammatory and metabolic disorders, this review article summarizes current knowledge on the role of NFκB in in vivo kidney injury and describes the new and so far not completely understood crosstalk between canonical and non-canonical NFκB pathways in T-lymphocyte activation in renal disease.

Increased Serum Concentrations of TNF-Like Weak Inducer of Apoptosis Predict Higher 28-Day Mortality in Patients with Sepsis

We performed the current study to explore potential predictive value of serum Tumor Necrosis Factor- (TNF-) like weak inducer of apoptosis (TWEAK) concentrations for 28-day mortality in patients with sepsis. Adult septic patients (age≥18 years) admitted to a general ICU between November 2016 and October 2017 were consecutively included in our prospective observational study. TWEAK concentrations were detected in septic patients and healthy controls. Dynamic changes of TWEAK concentrations between 1st day and 3rd day of admission to ICU (ΔTWEAK concentrations) were also measured. A total of 79 septic patients were included and 19 of them (24.1%) died after a follow-up period of 28 days. We identified arterial lactate, NT-proBNP, and male gender as independent factors for 28-day mortality of patients with sepsis. The serum levels of TWEAK were significantly lower in septic patients compared to controls (417.4 ± 196.7 pg/ml versus 1243.8 ± 174.3 pg/ml, p<0.001). We found a positive correlation between TWEAK concentrations and SOFA score (Spearman correlation coefficient 0.235, p=0.037). Area under the receiver operating characteristic curve (AUROC) of ΔTWEAK concentrations for 28-day mortality was 0.754 (95% CI 0.645-0.844). We also evaluated the diagnostic performance of combinative index (ΔTWEAK concentrations and lactate) and obtained an AUROC of 0.860 (95% CI 0.763-0.928). In conclusion, our study found lower TWEAK concentrations in septic patients than those in healthy controls. Furthermore, the increased TWEAK concentrations during disease process predict higher 28-day mortality in septic patients. Dynamic changes of TWEAK should be an important supplement for current prognostic markers.

Fn14 Deficiency Ameliorates Anti-dsDNA IgG-Induced Glomerular Damage in SCID Mice

Many studies have demonstrated that anti-dsDNA IgG is closely associated with lupus nephritis. Recently, it was found that activation of the fibroblast growth factor-inducible 14 (Fn14) signaling pathway damages glomerular filtration barrier in MRL/lpr lupus-prone mice. However, MRL/lpr mice have high titers of serum autoantibodies other than anti-dsDNA IgG. The aim of this study was to further explore the effect of Fn14 deficiency on anti-dsDNA IgG-induced glomerular damage in severe combined immunodeficiency (SCID) mice that have no endogenous IgG. Fn14 deficiency was generated in SCID mice. The murine hybridoma cells producing control IgG or anti-dsDNA IgG were intraperitoneally injected into mice. In two weeks, the urine, serum, and kidney tissue samples were harvested from mice at sacrifice. It showed that the injection of anti-dsDNA IgG, but not control IgG hybridoma cells, induced proteinuria and glomerular damage in SCID mice. Between the wild-type (WT) and knockout (KO) mice injected with anti-dsDNA IgG hybridoma cells, the latter showed a decrease in both proteinuria and glomerular IgG deposition. The histopathological changes, inflammatory cell infiltration, and proinflammatory cytokine production were also attenuated in the kidneys of the Fn14-KO mice upon anti-dsDNA IgG injection. Therefore, Fn14 deficiency effectively protects SCID mice from anti-dsDNA IgG-induced glomerular damage.

Immunopathogenesis of Acute Kidney Injury

Pathophysiologically, the classification of acute kidney injury (AKI) can be divided into three categories: (1) prerenal, (2) intrinsic, and (3) postrenal. Emerging evidence supports the involvement of renal tubular epithelial cells and the innate and adaptive arms of the immune system in the pathogenesis of intrinsic AKI. Pro-inflammatory damage-associated molecular patterns, pathogen-associated molecular patterns, hypoxia inducible factors, toll-like receptors, complement system, oxidative stress, adhesion molecules, cell death, resident renal dendritic cells, neutrophils, T and B lymphocytes, macrophages, natural killer T cells, cytokines, and secreted chemokines contribute to the immunopathogenesis of AKI. However, other immune cells and pathways such as M2 macrophages, regulatory T cells, progranulin, and autophagy exhibit anti-inflammatory properties and facilitate kidney tissue repair after AKI. Thus, therapies for AKI include agents such as anti-inflammatory (e.g., recombinant alkaline phosphatase), antioxidants (iron chelators), and apoptosis inhibitors. In preclinical toxicity studies, drug-induced kidney injury can be seen after exposure to a nephrotoxicant test article due to immune mechanisms and dysregulation of innate, and/or adaptive cellular immunity. The focus of this review will be on intrinsic AKI, as it relates to the immune and renal systems cross talks focusing on the cellular and pathophysiologic mechanisms of AKI.

The clinical relevance of necroinflammation-highlighting the importance of acute kidney injury and the adrenal glands

Necroinflammation is defined as the inflammatory response to necrotic cell death. Different necrotic cell death pathways exhibit different immune reponses, despite a comparable level of intracellular content release (referred to as damage associated molecular patterns or DAMPs). In addition to DAMP release, which is inevitably associated with necrotic cell death, the active production of pro/anti-inflammatory cytokines characterizes certain necrotic pathways. Necroptosis, ferroptosis and pyroptosis, therefore, are immunogenic to a different extent. In this review, we discuss the clinical relevance of necroinflammation highlighting potential human serum markers. We focus on the role of the adrenal glands and the lungs as central organs affected by systemic and/or local DAMP release and underline their role in intensive care medicine. In addition, data from models of acute kidney injury (AKI) and kidney transplantation have significantly shaped the field of necroinflammation and may be helpful for the understanding of the potential role of dialysis and plasma exchange to treat ongoing necroinflammation upon intensive care unit (ICU) conditions. In conclusion, we are only beginning to understand the importance of necroinflammation in diseases and transplantation, including xenotransplantation. However, given the existing efforts to develop inhibitors of necrotic cell death (ferrostatins, necrostatins, etc), we consider it likely that interference with necroinflammation reaches clinical routine in the near future.

CCL20 blockade increases the severity of nephrotoxic folic acid-induced acute kidney injury

The chemokine CCL20 activates the CCR6 receptor and has been implicated in the pathogenesis of glomerular injury. However, it is unknown whether it contributes to acute kidney injury (AKI). We identified CCL20 as upregulated in a systems biology strategy combining transcriptomics of kidney tissue from experimental toxic folic acid-induced AKI and from stressed cultured tubular cells and have explored the expression and function of CCL20 in experimental and clinical AKI. CCL20 upregulation was confirmed in three models of kidney injury induced by a folic acid overdose, cisplatin or unilateral ureteral obstruction. In injured kidneys, CCL20 was expressed by tubular, endothelial, and interstitial cells, and was also upregulated in human kidneys with AKI. Urinary CCL20 was increased in human AKI and was associated with severity. The function of CCL20 in nephrotoxic folic acid-induced AKI was assessed by using neutralising anti-CCL20 antibodies or CCR6-deficient mice. CCL20/CCR6 targeting increased the severity of kidney failure and mortality. This was associated with more severe histological injury, nephrocalcinosis, capillary rarefaction, and fibrosis, as well as higher expression of tubular injury-associated genes. Surprisingly, mice with CCL20 blockade had a lower tubular proliferative response and a higher number of cells in the G2/M phase, suggesting impaired repair mechanisms. This may be related to a lower influx of Tregs, despite a milder inflammatory response in terms of chemokine expression and infiltration by IL-17⁺ cells and neutrophils. In conclusion, CCL20 has a nephroprotective role during AKI, both by decreasing tissue injury and by facilitating repair. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

TWEAK increases CD74 expression and sensitizes to DDT proinflammatory actions in tubular cells

CD74 is a multifunctional protein and a receptor for Macrophage Migration Inhibitory Factor (MIF) and MIF-2 / D-dopachrome tautomerase (DDT) cytokines, upregulated in diabetic kidney disease. However, the drivers of CD74 expression and DDT function in kidney cells are poorly characterized. TWEAK is a proinflammatory cytokine that promotes kidney injury. We have now identified CD74 gene expression as upregulated in the kidneys in response to systemic TWEAK administration in mice, and have characterized the in vivo CD74 expression and the functional consequences in cultured cells. TWEAK administration to mice resulted in a progressive time-dependent (up to 24h) upregulation of kidney CD74 mRNA (RT-PCR) and protein (Western blot). Furthermore, the CD74 ligands MIF and DDT were also upregulated at the protein level 24h after TWEAK administration. Immunohistochemistry localized the increased CD74, MIF and DDT expression to tubular cells. In cultured tubular cells, TWEAK increased CD74 mRNA and protein expression dose-dependently, with a temporal pattern similar to in vivo. TWEAK-induced CD74 localized to the cell membrane, where it can function as a cytokine receptor. For the first time, we explored the actions of DDT in tubular cells and found that DDT amplified the increase in MCP-1 and RANTES expression in response to TWEAK. By contrast, DDT did not significantly modify TWEAK-induced Klotho downregulation. In conclusion, TWEAK upregulates CD74 and its ligands MIF and DDT in renal tubular cells. This may have functional consequences for kidney injury since DDT amplified the inflammatory response to TWEAK.

Sirt6 deficiency results in progression of glomerular injury in the kidney

Aging is associated with an increased incidence and prevalence of renal glomerular diseases. Sirtuin (Sirt) 6, a nicotinamide adenine dinucleotide (NAD)-dependent histone deacetylase, has been shown to protect against multiple age-associated phenotypes; however it is unknown whether Sirt6 has a direct pathophysiologic role in the kidney. In the present study, we demonstrate that Sirt6 is expressed in the kidney and aging Sirt6-deficient mice exhibit renal hypertrophy with glomerular enlargement. Sirt6 deletion induces podocyte injury, including decreases in slit diaphragm proteins, foot process effacement, and cellular loss, resulting in proteinuria. Knockdown of Sirt6 in cultured primary murine podocytes induces shape changes with loss of process formation and cell apoptosis. Moreover, Sirt6 deficiency results in progressive renal inflammation and fibrosis. Collectively, these data provide compelling evidence that Sirt6 is important for podocyte homeostasis and maintenance of glomerular function, and warrant further investigation into the role of Sirt6 in age-associated kidney dysfunction.

Targeting of regulated necrosis in kidney disease

The term acute tubular necrosis was thought to represent a misnomer derived from morphological studies of human necropsies and necrosis was thought to represent an unregulated passive form of cell death which was not amenable to therapeutic manipulation. Recent advances have improved our understanding of cell death in acute kidney injury. First, apoptosis results in cell loss, but does not trigger an inflammatory response. However, clumsy attempts at interfering with apoptosis (e.g. certain caspase inhibitors) may trigger necrosis and, thus, inflammation-mediated kidney injury. Second, and most revolutionary, the concept of regulated necrosis emerged. Several modalities of regulated necrosis were described, such as necroptosis, ferroptosis, pyroptosis and mitochondria permeability transition regulated necrosis. Similar to apoptosis, regulated necrosis is modulated by specific molecules that behave as therapeutic targets. Contrary to apoptosis, regulated necrosis may be extremely pro-inflammatory and, importantly for kidney transplantation, immunogenic. Furthermore, regulated necrosis may trigger synchronized necrosis, in which all cells within a given tubule die in a synchronized manner. We now review the different modalities of regulated necrosis, the evidence for a role in diverse forms of kidney injury and the new opportunities for therapeutic intervention.