STING1 deficiency ameliorates immune-mediated crescentic glomerulonephritis in mice.

Rapidly progressive/crescentic glomerulonephritis (RPGN/CGN) involves the formation of glomerular crescents by maladaptive differentiation of parietal epithelial cells that leads to rapid loss of renal function. The molecular mechanisms of crescent formation are poorly understood. Therefore, new insights into molecular mechanisms could identify alternative therapeutic targets for RPGN/CGN. Analysis of kidney biopsies from patients with RPGN revealed increased interstitial, glomerular, and tubular expression of STING1, an accessory protein of the c-GAS-dependent DNA-sensing pathway, which was also observed in murine nephrotoxic nephritis induced by an anti-GBM antibody. STING1 was expressed by key cell types involved in RPGN and crescent formation such as glomerular parietal epithelial cells, and tubular cells as well as by inflammation accessory cells. In functional in vivo studies, Sting1-/- mice with nephrotoxic nephritis had lower kidney cytokine expression, milder kidney infiltration by innate and adaptive immune cells, and decreased disease severity. Pharmacological STING1 inhibition mirrored these findings. Direct STING1 agonism in parietal and tubular cells activated the NF-κB-dependent cytokine response and the interferon-induced genes (ISGs) program. These responses were also triggered in a STING1-dependent manner by the pro-inflammatory cytokine TWEAK. These results identify STING1 activation as a pathological mechanism in RPGN/CGN and TWEAK as an activator of STING1. Pharmacological strategies targeting STING1, or upstream regulators may therefore be potential alternatives to treat RPGN. © 2023 The Pathological Society of Great Britain and Ireland.

The transcription factor Fosl1 preserves Klotho expression and protects from acute kidney injury.

Increased expression of AP-1 transcription factor components has been reported in acute kidney injury (AKI). However, the role of specific components, such as Fosl1, in tubular cells or AKI is unknown. Upstream regulator analysis of murine nephrotoxic AKI transcriptomics identified AP-1 as highly upregulated. Among AP-1 canonical components, Fosl1 was found to be upregulated in two transcriptomics datasets from nephrotoxic murine AKI induced by folic acid or cisplatin and from proximal tubular cells exposed to TWEAK, a cytokine mediator of AKI. Fosl1 was minimally expressed in the kidneys of control uninjured mice. Increased Fosl1 protein was localized to proximal tubular cell nuclei in AKI. In human AKI, FOSL1 was found present in proximal tubular cells in kidney sections and in urine along with increased urinary FOSL1 mRNA. Selective Fosl1 deficiency in proximal tubular cells (Fosl1Δtub) increased the severity of murine cisplatin- or folate-induced AKI as characterized by lower kidney function, more severe kidney inflammation and Klotho downregulation. Indeed, elevated AP-1 activity was observed after cisplatin-induced AKI in Fosl1Δtub mice compared to wild-type mice. More severe Klotho downregulation preceded more severe kidney dysfunction. The Klotho promoter was enriched in Fosl1 binding sites and Fosl1 bound to the Klotho promoter in cisplatin-AKI. In cultured proximal tubular cells, Fosl1 targeting increased the proinflammatory response and downregulated Klotho. In vivo, recombinant Klotho administration protected Fosl1Δtub mice from cisplatin-AKI. Thus, increased proximal tubular Fosl1 expression during AKI is an adaptive response, preserves Klotho, and limits the severity of tubular cell injury and AKI.

CCN2 (Cellular Communication Network Factor 2) Deletion Alters Vascular Integrity and Function Predisposing to Aneurysm Formation.

BACKGROUND: CCN2 (cellular communication network factor 2) is a matricellular protein involved in cell communication and microenvironmental signaling responses. CCN2 is known to be overexpressed in several cardiovascular diseases, but its role is not completely understood. METHODS: Here, CCN2 involvement in aortic wall homeostasis and response to vascular injury was investigated in inducible <i>Ccn2</i>-deficient mice, with induction of vascular damage by infusion of Ang II (angiotensin II; 15 days), which is known to upregulate CCN2 expression in the aorta. RESULTS: Ang II infusion in CCN2-silenced mice lead to 60% mortality within 10 days due to rapid development and rupture of aortic aneurysms, as evidenced by magnetic resonance imaging, echography, and histological examination. <i>Ccn2</i> deletion decreased systolic blood pressure and caused aortic structural and functional changes, including elastin layer disruption, smooth muscle cell alterations, augmented distensibility, and increased metalloproteinase activity, which were aggravated by Ang II administration. Gene ontology analysis of RNA sequencing data identified aldosterone biosynthesis as one of the most enriched terms in CCN2-deficient aortas. Consistently, treatment with the mineralocorticoid receptor antagonist spironolactone before and during Ang II infusion reduced aneurysm formation and mortality, underscoring the importance of the aldosterone pathway in Ang II-induced aorta pathology. CONCLUSIONS: CCN2 is critically involved in the functional and structural homeostasis of the aorta and in maintenance of its integrity under Ang II-induced stress, at least, in part, by disruption of the aldosterone pathway. Thus, this study opens new avenues to future studies in disorders associated to vascular pathologies.

Ferrostatin-1 modulates dysregulated kidney lipids in acute kidney injury.

Ferroptosis, a form of regulated necrosis characterized by peroxidation of lipids such as arachidonic acid-containing phosphatidylethanolamine (PE), contributes to the pathogenesis of acute kidney injury (AKI). We have characterized the kidney lipidome in an experimental nephrotoxic AKI induced in mice using folic acid and assessed the impact of the ferroptosis inhibitor Ferrostatin-1. Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) was used to assess kidney lipidomics and it discriminated between glomeruli, medulla, and cortex in control kidneys, AKI kidneys, and AKI + Ferrostatin-1 kidneys. Out of 139 lipid species from 16 classes identified, 29 (20.5%) showed significant differences between control and AKI at 48 h. Total PE and lyso-sulfatide species decreased, while phosphatidylinositol (PI) species increased in AKI. Dysregulated mRNA levels for Pemt, Pgs1, Cdipt, and Tamm41, relevant to lipid metabolism, were in line with the lipid changes observed. Ferrostatin-1 prevented AKI and some AKI-associated changes in lipid levels, such as the decrease in PE and lyso-sulfatide species, without changing the gene expression of lipid metabolism enzymes. In conclusion, changes in the kidney lipid composition during nephrotoxic AKI are associated with differential gene expression of lipid metabolism enzymes and are partially prevented by Ferrostatin-1. © 2022 The Pathological Society of Great Britain and Ireland.

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.

Urinary Growth Differentiation Factor-15 (GDF15) levels as a biomarker of adverse outcomes and biopsy findings in chronic kidney disease.

BACKGROUND: Growth Differentiation Factor-15 (GDF15) is a member of the TGF-ß superfamily. Increased serum GDF15 has been associated with increased risk of chronic kidney disease (CKD) progression. However, no prior studies have addressed the significance of urinary GDF15 in adult CKD. METHODS: We measured serum and urinary GDF15 in a prospective cohort of 84 patients who underwent kidney biopsy and assessed their association with outcomes (survival, kidney replacement therapy) during a follow-up of 29 ± 17 months. RESULTS: There was a statistically significant correlation between serum and urine GDF15 values. However, while serum GDF15 values increased with decreasing glomerular filtration rate, urinary GDF15 did not. Immunohistochemistry located kidney GDF15 expression mainly in tubular cells, and kidney GDF15 staining correlated with urinary GDF15 values. Urine GDF15 was significantly higher in patients with a histologic diagnosis of diabetic nephropathy than in diabetic patients without diabetic nephropathy. This was not the case for serum GDF15. Both serum and urine GDF15 were negatively associated with patient survival in multivariate models. However, when both urine and serum GDF15 were present in the model, lower urine GDF15 predicted patient survival [B coefficient (SEM) - 0.395 (0.182) p 0.03], and higher urine GDF15 predicted a composite of mortality or kidney replacement therapy [0.191 (0.06) p 0.002], while serum GDF15 was not predictive. Decision tree analysis yielded similar results. The area under the curve (AUC) of the receiver operating curve (ROC) for urine GDF15 as a predictor of mortality was 0.95 (95% CI 0.89-1.00, p < 0.001). CONCLUSIONS: In conclusion, urinary GDF15 is associated with kidney histology patterns, mortality and the need for renal replacement therapy (RRT) in CKD patients who underwent a kidney biopsy.

Podocyte and tubular involvement in AngioJet-induced kidney injury.

The AngioJet technique combines localized thrombolysis and percutaneous mechanical thrombectomy (PMT). However, PMT may cause acute kidney injury (AKI), which has been ascribed to severe mechanical haemolysis, although no renal biopsies have been reported. We now report the first renal biopsy in a patient with AKI following PMT. There is histological evidence of haemoglobin (Hb)-induced tubular injury and podocyte stress characterized by intracellular Hb and staining for ferritin and hemo-oxygenase-1, suggestive of an adaptive response to oxidative stress. This confirms that Hb is involved in kidney cell injury and supports the existence of several different kidney cellular targets.

Fracaso renal agudo anúrico persistente en paciente infectado con Plasmodium malariae: la importancia de la biopsia renal / Persistent acute renal failure in a patient infected with Plasmodium malariae: The importance of renal biopsy

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Interleukin 17A Participates in Renal Inflammation Associated to Experimental and Human Hypertension.

Hypertension is now considered as an inflammatory disease, and the kidney is a key end-organ target. Experimental and clinical studies suggest that interleukin 17A (IL-17A) is a promising therapeutic target in immune and chronic inflammatory diseases, including hypertension and kidney disease. Elevated circulating IL-17A levels have been observed in hypertensive patients. Our aim was to investigate whether chronically elevated circulating IL-17A levels could contribute to kidney damage, using a murine model of systemic IL-17A administration. Blood pressure increased after 14 days of IL-17A infusion in mice when compared with that in control mice, and this was associated to kidney infiltration by inflammatory cells, including CD3+ and CD4+ lymphocytes and neutrophils. Moreover, proinflammatory factors and inflammatory-related intracellular mechanisms were upregulated in kidneys from IL-17A-infused mice. In line with these findings, in the model of angiotensin II infusion in mice, IL-17A blockade, using an anti-IL17A neutralizing antibody, reduced kidney inflammatory cell infiltrates and chemokine overexpression. In kidney biopsies from patients with hypertensive nephrosclerosis, IL-17A positive cells, mainly Th17 and γδ T lymphocytes, were found. Overall, the results support a pathogenic role of IL-17A in hypertensive kidney disease-associated inflammation. Therapeutic approaches targeting this cytokine should be explored to prevent hypertension-induced kidney injury.

Positive/retained SDHB immunostaining in renal cell carcinomas associated to germline SDHB-deficiency: case report.

BACKGROUND: According to WHO, succinate dehydrogenase (SDH)-deficient renal cell carcinoma is characterized by negative immunostaining for SDHB, which remains positive in non-tumor tissue despite germline mutations in the SDHB gene. We now report a patient with a SDHB mutation, c.166_170del (p.Pro56Tyrfs*5) who developed renal cell carcinomas with characteristic morphological features of SDH-deficient renal cell carcinoma but had positive SDHB immunostaining. CASE PRESENTATION: Within a 6-year period, the patient developed two different renal cell carcinomas, which had characteristic morphological features of SDH-deficient renal cell carcinoma (uniform cells characteristically displaying eosinophilic granular material intermixed with fewer cells exhibiting clear intracytoplasmic inclusions and bland centered nuclei) but displayed immunohistochemistry for SDHB with a cytoplasmic granular positivity (mitochondrial pattern) in tumor cells. For the second case, this was initially interpreted as positive by IHC, but on review some subtle differences were identified. CONCLUSIONS: SDHB immunostaining may be positive in renal cell carcinoma associated to germline SDHB deficiency which have other typical morphological features. Immunohistochemistry interpretation may be complex.

PGC-1α deficiency causes spontaneous kidney inflammation and increases the severity of nephrotoxic AKI.

PGC-1α (peroxisome proliferator-activated receptor gamma coactivator-1α, PPARGC1A) regulates the expression of genes involved in energy homeostasis and mitochondrial biogenesis. Here we identify inactivation of the transcriptional regulator PGC-1α as a landmark for experimental nephrotoxic acute kidney injury (AKI) and describe the in vivo consequences of PGC-1α deficiency over inflammation and cell death in kidney injury. Kidney transcriptomic analyses of WT mice with folic acid-induced AKI revealed 1398 up- and 1627 downregulated genes. Upstream transcriptional regulator analyses pointed to PGC-1α as the transcription factor potentially driving the observed expression changes with the highest reduction in activity. Reduced PGC-1α expression was shared by human kidney injury. Ppargc1a-/- mice had spontaneous subclinical kidney injury characterized by tubulointerstitial inflammation and increased Ngal expression. Upon AKI, Ppargc1a-/- mice had lower survival and more severe loss of renal function, tubular injury, and reduction in expression of mitochondrial PGC-1α-dependent genes in the kidney, and an earlier decrease in mitochondrial mass than WT mice. Additionally, surviving Ppargc1a-/- mice showed higher rates of tubular cell death, compensatory proliferation, expression of proinflammatory cytokines, NF-κB activation, and interstitial inflammatory cell infiltration. Specifically, Ppargc1a-/- mice displayed increased M1 and decreased M2 responses and expression of the anti-inflammatory cytokine IL-10. In cultured renal tubular cells, PGC-1α targeting promoted spontaneous cell death and proinflammatory responses. In conclusion, PGC-1α inactivation is a key driver of the gene expression response in nephrotoxic AKI and PGC-1α deficiency promotes a spontaneous inflammatory kidney response that is magnified during AKI. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

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.

Reproducibility of the Oxford classification of immunoglobulin A nephropathy, impact of biopsy scoring on treatment allocation and clinical relevance of disagreements: evidence from the VALidation of IGA study cohort.

BACKGROUND: The VALidation of IGA (VALIGA) study investigated the utility of the Oxford Classification of immunoglobulin A nephropathy (IgAN) in 1147 patients from 13 European countries. Methods. Biopsies were scored by local pathologists followed by central review in Oxford. We had two distinct objectives: to assess how closely pathology findings were associated with the decision to give corticosteroid/immunosuppressive (CS/IS) treatments, and to determine the impact of differences in MEST-C scoring between central and local pathologists on the clinical value of the Oxford Classification. We tested for each lesion the associations between the type of agreement (local and central pathologists scoring absent, local present and central absent, local absent and central present, both scoring present) with the initial clinical assessment, as well as long-term outcomes in those patients who did not receive CS/IS. RESULTS: All glomerular lesions (M, E, C and S) assessed by local pathologists were independently associated with the decision to administer CS/IS therapy, while the severity of tubulointerstitial lesions was not. Reproducibility between local and central pathologists was moderate for S (segmental sclerosis) and T (tubular atrophy/interstitial fibrosis), and poor for M (mesangial hypercellularity), E (endocapillary hypercellularity) and C (crescents). Local pathologists found statistically more of each lesion, except for the S lesion, which was more frequent with central review. Disagreements were more likely to occur when the proportion of glomeruli affected was low. The M lesion, assessed by central pathologists, correlated better with the severity of the disease at presentation and discriminated better with outcomes. In contrast, the E lesion, evaluated by local pathologists, correlated better with the clinical presentation and outcomes when compared with central review. Both C and S lesions, when discordant between local and central pathologists, had a clinical phenotype intermediate to double absent lesions (milder disease) and double present (more severe). CONCLUSION: We conclude that differences in the scoring of MEST-C criteria between local pathologists and a central reviewer have a significant impact on the prognostic value of the Oxford Classification. Since the decision to offer immunosuppressive therapy in this cohort was intimately associated with the MEST-C score, this study indicates a need for a more detailed guidance for pathologists in the scoring of IgAN biopsies.

[Aggressive variants of castration resistant prostate cancer (CRPC): neuroendocrine prostate cancer.] / Variantes agresivas de cáncer de próstata resistente a la castracion (CPRC): cáncer de próstata neuroendocrino.

Castration resistant prostate cancer (CRPC) is characterized by an important molecular, pathological and clinical heterogeneity. Although most of them present androgen receptor (AR) signal dependence, there are independent phenotypes. Neuroendocrine prostate cancer (NEPC) is a rare histologic subtype with adverse prognosis due to late diagnosis, heterogeneous clinical features and lack of effective systemic treatments. Platinum based chemotherapy is the standard treatment, presenting short limited responses. There are pure forms or mixed with adenocarcinoma component. De novo diagnosis is unusual, being more frequent in advanced stages of prostate cancer, as a consequence of the inhibition of androgen receptor performed by various treatments. Thus, it could represent an aggressive evolution from carcinoma through a NEEpithelial transdifferentiation. Development of preclinical studies has permitted characterization of molecular and genomic alterations associated with this evolution and they may help to develop new therapeutic targets. Over the last years, there have been important advances in identification and characterization of clinical and pathological CRPC variants. NEPC is one of the most aggressive subtypes. A better knowledge of the disease biology is necessary to develop new treatments and biomarkers that help to manage this aggressive variant of PC.

Variantes agresivas de cáncer de próstata resistente a la castración (cprc): cáncer de próstata neuroendocrino / Recommendations for follow up in castration resistant prostate cancer

El cáncer de próstata resistente a la castración (CPRC) se caracteriza por una importante heterogeneidad molecular, patológica y clínica. Aunque la mayoría presentan dependencia a la señal del receptor androgénico (RA), existen fenotipos independientes a ésta. El cáncer de próstata neuroendocrino (CPNE) es un subtipo histológico poco frecuente y de pronóstico adverso debido al diagnóstico tardío, características clínicas heterogéneas y a la falta de tratamientos sistémicos efectivos. El tratamiento estándar es la quimioterapia (QT) basada en platino, presentando respuestas de escasa duración. Existen formas puras o mixtas con un componente de adenocarcinoma. Es raro su diagnóstico de novo, siendo más frecuente su aparición en estados avanzados del cáncer de próstata (CP), como consecuencia de la inhibición del receptor androgénico (RA) realizada por diversos tratamientos. Así, podría representar una evolución agresiva desde un adenocarcinoma (CPAD) a través de un mecanismo de transdiferenciación epitelio-NE. El desarrollo de estudios preclínicos han permitido la determinación de alteraciones moleculares y genómicas asociadas a esta evolución y que pueden ayudar al desarrollo de nuevas dianas terapéuticas. En los últimos años se han producido importantes avances en la identificación y caracterización de variantes clínicas y patológicas del CPRC. El CPNE es uno de los subtipos más agresivos. Un mayor conocimiento de la biología de la enfermedad es necesario para desarrollar nuevos tratamientos y biomarcadores que ayuden al manejo de esta variante agresiva del CP

Castration resistant prostate cancer (CRPC) is characterized by an important molecular, pathological and clinical heterogeneity. Although most of them present androgen receptor (AR) signal dependence, there are independent phenotypes. Neuroendocrine prostate cancer (NEPC) is a rare histologic subtype with adverse prognosis due to late diagnosis, heterogeneous clinical features and lack of effective systemic treatments. Platinum based chemotherapy is the standard treatment, presenting short limited responses. There are pure forms or mixed with adenocarcinoma component. De novo diagnosis is unusual, being more frequent in advanced stages of prostate cancer, as a consequence of the inhibition of androgen receptor performed by various treatments. Thus, it could represent an aggressive evolution from carcinoma through a NEEpithelial transdifferentiation. Development of preclinical studies has permitted characterization of molecular and genomic alterations associated with this evolution and they may help to develop new therapeutic targets. Over the last years, there have been important advances in identification and characterization of clinical and pathological CRPC variants. NEPC is one of the most aggressive subtypes. A better knowledge of the disease biology is necessary to develop new treatments and biomarkers that help to manage this aggressive variant of PC

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 and RIPK1 mediate a second wave of cell death during AKI.

Acute kidney injury (AKI) is characterized by necrotic tubular cell death and inflammation. The TWEAK/Fn14 axis is a mediator of renal injury. Diverse pathways of regulated necrosis have recently been reported to contribute to AKI, but there are ongoing discussions on the timing or molecular regulators involved. We have now explored the cell death pathways induced by TWEAK/Fn14 activation and their relevance during AKI. In cultured tubular cells, the inflammatory cytokine TWEAK induces apoptosis in a proinflammatory environment. The default inhibitor of necroptosis [necrostatin-1 (Nec-1)] was protective, while caspase inhibition switched cell death to necroptosis. Additionally, folic acid-induced AKI in mice resulted in increased expression of Fn14 and necroptosis mediators, such as receptor-interacting protein kinase 1 (RIPK1), RIPK3, and mixed lineage domain-like protein (MLKL). Targeting necroptosis with Nec-1 or by genetic RIPK3 deficiency and genetic Fn14 ablation failed to be protective at early time points (48 h). However, a persistently high cell death rate and kidney dysfunction (72-96 h) were dependent on an intact TWEAK/Fn14 axis driving necroptosis. This was prevented by Nec-1, or MLKL, or RIPK3 deficiency and by Nec-1 stable (Nec-1s) administered before or after induction of AKI. These data suggest that initial kidney damage and cell death are amplified through recruitment of inflammation-dependent necroptosis, opening a therapeutic window to treat AKI once it is established. This may be relevant for clinical AKI, since using current diagnostic criteria, severe injury had already led to loss of renal function at diagnosis.

Bcl3: a regulator of NF-κB inducible by TWEAK in acute kidney injury with anti-inflammatory and antiapoptotic properties in tubular cells.

Acute kidney injury (AKI) is characterized by tubular cell death and interstitial inflammation. TWEAK promotes experimental kidney injury and activates the transcription factor NF-κB, a key regulator of genes involved in cell survival and inflammatory response. In search of potential therapeutic targets for AKI, we compared a transcriptomics database of NF-κB-related genes from murine AKI-kidneys with a transcriptomics database of TWEAK-stimulated cultured tubular cells. Four out of twenty-four (17%) genes were significantly upregulated (false discovery rate, FDR<0.05), while nine out of twenty-four (37%) genes were significantly upregulated at FDR <0.1 in both databases. Bcl3 was the top upregulated NF-κB-related gene in experimental AKI and one of the most upregulated genes in TWEAK-stimulated tubular cells. Quantitative reverse transcription PCR (qRT-PCR), western blot and immunohistochemistry confirmed Bcl3 upregulation in both experimental conditions and localized increased Bcl3 expression to tubular cells in AKI. Transcriptomics database analysis revealed increased Bcl3 expression in numerous experimental and human kidney conditions. Furthermore, systemic TWEAK administration increased kidney Bcl3 expression. In cultured tubular cells, targeting Bcl3 by siRNA resulted in the magnification of TWEAK-induced NF-κB transcriptional activity, chemokine upregulation and Klotho downregulation, and in the sensitization to cell death induced by TWEAK/TNFα/interferon-γ. In contrast, Bcl3 overexpression decreased NF-κB transcriptional activity, inflammatory response and cell death while dampening the decrease in Klotho expression. In conclusion, Bcl3 expressed in response to TWEAK stimulation decreases TWEAK-induced inflammatory and lethal responses. Therefore, therapeutic upregulation of Bcl3 activity should be explored in kidney disease because it has advantages over chemical inhibitors of NF-κB that are known to prevent inflammatory responses but can also sensitize the cells to apoptosis.