AKI-CKD Transition Research Articles

Urinary Cytokeratin 20 as a Biomarker for AKI-CKD Transition among Patients with Acute Decompensated Heart Failure and AKI.

Predicting the risk of AKI-CKD transition remains a major challenge in management of acute decompensated heart failure and AKI. This study investigated the clinical utility of urinary cytokeratin 20 (CK20), a novel biomarker reflecting severity of histological acute tubular injury, for identifying patients at risk of AKI-CKD progression. This prospective cohort study included a Test set comprising 279 consecutive hospitalized patients with acute decompensated heart failure and AKI in 5 centers and a Validation set enrolling 206 similar patients at an external center. Urinary CK20 and seven reported renal tubular injury biomarkers at the time of AKI diagnosis were measured. The primary outcome was a composite of AKI-CKD transition 90 days after AKI or all-cause death within 90 days. The secondary outcome was AKI-CKD progression 90 days after AKI. In the Test set, 115 (41%) patients reached the primary endpoint. Concentrations of urinary CK20 peaked on the day of AKI diagnosis and remained elevated 14 days after AKI. After multivariable adjustment, the highest tertile of urinary CK20 was associated with 21-fold higher risk of the primary outcome and 29-fold higher risk of the secondary outcome. For predicting the primary and the secondary outcomes, urinary CK20 at the time of AKI diagnosis had area under the receiver-operating characteristic curves (AUC) of 0.82 (95% confidence interval [CI], 0.77-0.87) and 0.81 (95% CI, 0.75-0.87), and outperformed other reported biomarkers reflecting acute tubular injury and the risk of CKD. Adding urinary CK20 to the clinical variables improved the ability for predicting the primary outcome with an AUC of 0.90 (95% CI, 0.85-0.94), and largely improved the risk reclassification. The ability of urinary CK20 in predicting AKI-CKD transition was further confirmed in the Validation set. Urinary CK20 improved prediction of the risk for transition from AKI to CKD in patients with acute decompensated heart failure and AKI.

CGS-21680 defers cisplatin-induced AKI-CKD transition in C57/BL6 mice

Acute kidney injury (AKI), with a high mortality and morbidity, is known as a risk factor for developing progressive chronic kidney disease (CKD). Targeting transition of AKI to CKD displays an excellent therapeutic potential. This study aims at investigating the role of CGS-21680, selective A2AR agonist, in deferring Cis-induced AKI-CKD transition. The AKI-CKD transition model was induced in C57/BL6 mice by repeated low doses of Cis (2.5 mg/kg i.p for 5 consecutive days in two cycles with a recovery phase of 16 days between two cycles). CGS-21680 was administered daily for 6 weeks (0.1 mg/kg, i.p). Urine, blood, and kidney were collected at three different time points to track the disease progression. CGS-21680 administration preserved kidney function and attenuated tubular damage as evidenced by hematoxylin-eosin (H&E) histopathology. CGS-21680 significantly restored oxidative status as reflected by reduced malondialdehyde (MDA) content and increased total antioxidant capacity (TAC). CGS-21680 showed anti-inflammatory effect as indicated by decreased TNF-α and iNOS. Additionally, CGS-21680 ameliorated endothelial dysfunction and enhanced renal vasodilation as evidenced by upregulation of endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) expression and down regulation of endothelin-1 (ET-1) and its receptor endothelin-A (ET-A) receptor expression. CGS-21680 also attenuated renal fibrosis as reflected by the reduction of percentage of fibrosis in Masson's trichome-stained renal sections and down regulation of transforming growth factor beta1 (TGF-β1) protein expression in IHC-stained renal sections. In conclusion, CGS-21680 could defer Cis-induced AKI-CKD transition via its vasodilatory, antioxidant, anti-inflammatory, and anti-fibrotic effects.

Molecular mechanism of ALKBH5-mediated m6A demethylation regulating lipopolysaccharide-induced epithelial-mesenchymal transition in sepsis-induced acute kidney injury.

This study explored the mechanism by which the m6A demethylase ALKBH5 mediates epithelial-mesenchymal transition (EMT) in sepsis-associated acute kidney injury (SA-AKI) and AKI-chronic kidney disease (CKD) transition. HK-2 cells were stimulated with lipopolysaccharide (LPS) to establish an in vitro model of SA-AKI. ALKBH5 expression was reduced through the transfection of si-ALKBH5. Cell viability, apoptosis, and migration were detected by CCK-8 assay, TUNEL staining, and Transwell. The levels of TNF-α, IL-1β, and IL-6 were measured by enzyme-linked immunosorbent assay. Quantitative real-time polymerase chain reaction or Western blotting was performed to determine the expressionsof ALKBH5, miR-205-5p, DDX5, E-cadherin, and α-SMA. The m6A level was quantitatively analyzed. The expression of pri-miR-205 bound to DGCR8 and m6A-modified pri-miR-205 after intervention with ALKBH5 expression was detected by RNA immunoprecipitation. A dual-luciferase assay confirmed the binding between miR-205-5p and DDX5. ALKBH5 was highly expressed in LPS-induced HK-2 cells. Inhibition of ALKBH5 increased cell viability, repressed apoptosis, and reduced EMT. Inhibition of ALKBH5 increased the m6A modification level, thereby promoting DGCR8 binding to pri-miR-205 to increase miR-205-5p expression and eventually targeting DDX5 expression. Low expression of miR-205-5p or overexpression of DDX5 partially abolished the inhibitory effect of ALKBH5 silencing on EMT. In conclusion, ALKBH5 represses miR-205-5p expression by removing m6A modification to upregulate DDX5 expression, thereby promoting EMT and AKI-CKD transition after SA-AKI.

Rodent models of AKI and AKI-CKD transition: an update in 2024.

Despite known drawbacks, rodent models are essential tools in the research of renal development, physiology, and pathogenesis. In the past decade, rodent models have been developed and used to mimic different etiologies of acute kidney injury (AKI), AKI to chronic kidney disease (CKD) transition or progression, and AKI with comorbidities. These models have been applied for both mechanistic research and preclinical drug development. However, current rodent models have their limitations, especially since they often do not fully recapitulate the pathophysiology of AKI in human patients, and thus need further refinement. Here, we discuss the present status of these rodent models, including the pathophysiologic compatibility, clinical translational significance, key factors affecting model consistency, and their main limitations. Future efforts should focus on establishing robust models that simulate the major clinical and molecular phenotypes of human AKI and its progression.

GSDMD and GSDME synergy in the transition of acute kidney injury to chronic kidney disease.

Acute kidney injury (AKI) could progress to chronic kidney disease (CKD) and the AKI-CKD transition has major clinical significance. A growing body of evidence has unveiled the role of pyroptosis in kidney injury. We postulate that GSDMD and GSDME exert cumulative effects on the AKI-CKD transition by modulating different cellular responses. We established an AKI-CKD transition model induced by folic acid in wildtype (WT), Gsdmd-/-, Gsdme-/-, and Gsdmd-/-Gsdme-/- mice. Tubular injury, renal fibrosis and inflammatory responses were evaluated. In vitro studies were conducted to investigate the interplay among tubular cells, neutrophils, and macrophages. Double deletion of Gsdmd and Gsdme conferred heightened protection against AKI, mitigating inflammatory responses, including the formation of neutrophil extracellular traps (NETs), macrophage polarization and differentiation, and ultimately renal fibrosis, compared with wildtype mice and mice with single deletion of either Gsdmd or Gsdme. Gsdme, but not Gsdmd deficiency, shielded tubular cells from pyroptosis. GSDME-dependent tubular cell death stimulated NETs formation and prompted macrophage polarization towards a pro-inflammatory phenotype. Gsdmd deficiency suppressed NETs formation and subsequently hindered NETs-induced macrophage-to-myofibroblast transition (MMT). GSDMD and GSDME collaborate to contribute to AKI and subsequent renal fibrosis induced by folic acid. Synchronous inhibition of GSDMD and GSDME could be an innovative therapeutic strategy for mitigating the AKI-CKD transition.

Natural Killer Lymphocytes Mediate Renal Fibrosis Due to Acute Cardiorenal Syndrome.

The acute kidney injury (AKI) to chronic kidney disease (CKD) transition presents an opportunity for intervention to prevent CKD. Our lab developed a novel murine model of AKI-CKD transition, cardiac arrest and cardiopulmonary resuscitation (CA/CPR), in which all animals develop CKD at 7 weeks. The purpose of this study was to identify potential immune drivers of fibrosis after CA/CPR. Cardiac arrest was induced by potassium chloride and mice were resuscitated with chest compressions and epinephrine. The kidney immune landscape after CA/CPR was profiled using 11-color flow cytometry analysis and immunofluorescence. Immune cell-derived mediators of fibrosis were identified by analyzing data from three previously published single cell or single nuclear RNA sequencing (sc/snRNASeq) studies. NRK49F fibroblasts were treated with granzyme A (GzA) in vitro, then cell proliferation was quantified using 5-ethynyl-2'-deoxyuridine. GzA was pharmacologically inhibited both in vitro and in vivo. Immune cells infiltrated the kidney after CA/CPR, consisting primarily of innate immune cells, including monocytes/macrophages, neutrophils, and natural killer (NK) cells. NK cell infiltration immediately preceded mesenchymal cell expansion, which occurred starting 7 days after CA/CPR. Immune cells colocalized with mesenchymal cells, accumulating in areas of fibrosis. Analysis of previously published sc/snRNASeq data revealed GzA as a potential mediator of immune to mesenchymal communication. GzA administration to fibroblasts in vitro induced cell growth and proliferation. Pharmacologic blockade of GzA signaling in vivo attenuated fibrosis and improved renal function after CA/CPR. Renal inflammation occurs during cardiorenal syndrome, which correlates with mesenchymal cell expansion. GzA, produced by NK cells, presents a novel therapeutic target to prevent the transition to CKD after AKI.

Tweak/Fn14 system is involved in rhabdomyolysis-induced acute kidney injury

BackgroundRhabdomyolysis is a severe clinical syndrome associated to acute kidney injury (AKI) and chronic kidney disease (CKD). TWEAK/Fn14 signaling axis regulates renal inflammation and tubular cell death. However, the functional role of TWEAK/Fn14 in rhabdomyolysis remains unknown. MethodsRhabdomyolysis was induced in wild-type, TWEAK- and Fn14-deficient mice or mice treated with TWEAK blocking antibody. Renal injury, inflammation, fibrosis and cell death were assessed. Additionally, we performed in vivo and in vitro studies to explore the possible signalling pathways involved in Fn14 regulation. FindingsFn14 renal expression was increased in mice with rhabdomyolysis, correlating with decline of renal function. Mechanistically, myoglobin (Mb) induced Fn14 expression via ERK and p38 pathway, whereas Nrf2 activation diminished Mb-mediated Fn14 upregulation in cultured renal cells. TWEAK or Fn14 genetic depletion ameliorated rhabdomyolysis-associated loss of renal function, histological damage, tubular cell death, inflammation, and expression of both tubular and endothelial injury markers. Deficiency of TWEAK or Fn14 also decreased long-term renal inflammation and fibrosis in mice with rhabdomyolysis. Finally, pharmacological treatment with a blocking TWEAK antibody diminished the expression of acute renal injury markers and cell death and lessened residual kidney fibrosis and chronic inflammation in rhabdomyolysis. InterpretationTWEAK/Fn14 axis participates in the pathogenesis of rhabdomyolysis-AKI and subsequent AKI-CKD transition. Blockade of this signaling pathway may represent a promising therapeutic strategy for reducing rhabdomyolysis-mediated renal injury. FundingSpanish Ministry of Science and Innovation, ISCIII and Junta de Andalucía.

HDAC3 aberration-incurred GPX4 suppression drives renal ferroptosis and AKI-CKD progression

Acute kidney injury (AKI) progression to chronic kidney disease (CKD) represents a unique renal disease setting characterized by early renal cellular injury and regulated cell death, and later renal fibrosis, of which the critical role and nature of ferroptosis are only partially understood. Here, we report that renal tubular epithelial ferroptosis caused by HDAC3 (histone deacetylase 3) aberration and the resultant GPX4 suppression drives AKI-CKD progression. In mouse models of AKI-CKD transition induced by nephrotoxic aristolochic acid (AA) and folic acid (FA), renal tubular epithelial ferroptosis occurred early that coincided with preferential HDAC3 elevation and marked suppression of a core anti-ferroptosis enzyme GPX4 (glutathione peroxidase 4). Intriguingly, genetic Hdac3 knockout or administration of a HDAC3-selective inhibitor RGFP966 effectively mitigated the GPX4 suppression, ferroptosis and the fibrosis-associated renal functional loss. In cultured tubular epithelial cells, HDAC3 over-expression or inhibition inversely affected GPX4 abundances. Further analysis revealed that Gpx4 promoter contains a typical binding motif of transcription factor KLF5 (Kruppel-like factor 5). HDAC3 and KLF5 inducibly associated and bound to Gpx4 promoter upon AA treatment, leading to local histone hypoacetylation and GPX4 transactivation inhibition, which was blocked by RGFP966 and a KLF5 inhibitor ML264, respectively, suggesting that KLF5 co-regulated the HDAC3-incurred Gpx4 transcription inhibition. More importantly, in AKI-CKD mice receiving a GPX4 inactivator RSL3, the anti-ferroptosis and renoprotective effects of RGFP966 were largely abrogated, indicating that GPX4 is an essential downstream mediator of the HDAC3 aberration and renal ferroptosis during AKI-CKD transition. Together, our study identified a critical epigenetic pathway of ferroptosis during AKI-CKD transition and suggested that the strategies preserving GPX4 by HDAC3 inhibition are potentially effective to reduce renal ferroptosis and slow AKI-CKD progression.

Longitudinal tracking of acute kidney injury reveals injury propagation along the nephron

Acute kidney injury (AKI) is an important risk factor for chronic kidney disease (CKD), but the underlying mechanisms of failed tubule repair and AKI-CKD transition are incompletely understood. In this study, we aimed for dynamic tracking of tubule injury and remodeling to understand if focal injury upon AKI may spread over time. Here, we present a model of AKI, in which we rendered only half of the kidney ischemic. Using serial intravital 2-photon microscopy and genetic identification of cycling cells, we tracked dynamic tissue remodeling in post- and non-ischemic kidney regions simultaneously and over 3 weeks. Spatial and temporal analysis of cycling cells relative to initial necrotic cell death demonstrated pronounced injury propagation and expansion into non-necrotic tissue regions, which predicted tubule atrophy with epithelial VCAM1 expression. In summary, our longitudinal analyses of tubule injury, remodeling, and fate provide important insights into AKI pathology.

Loss of FUT8 in renal tubules ameliorates ischemia-reperfusion injury-induced renal interstitial inflammation transition to fibrosis via the TLR3-NF-κB pathway.

Renal ischemia-reperfusion injury (IRI) is a common reason of acute kidney injury (AKI). AKI can progress to chronic kidney disease (CKD) in some survivors. Inflammation is considered the first-line response to early-stage IRI. We previously reported that core fucosylation (CF), specifically catalyzed by α-1,6 fucosyltransferase (FUT8), exacerbates renal fibrosis. However, the FUT8 characteristics, role, and mechanism in inflammation and fibrosis transition remain unclear. Considering renal tubular cells are the trigger cells that initiate the fibrosis in the AKI-to-CKD transition in IRI, we targeted CF by generating a renal tubular epithelial cell (TEC)-specific FUT8 knockout mouse and measured FUT8-driven and downstream signaling pathway expression and AKI-to-CKD transition. During the IRI extension phase, specific FUT8 deletion in the TECs ameliorated the IRI-induced renal interstitial inflammation and fibrosis mainly via the TLR3 CF-NF-κB signaling pathway. The results firstly indicated the role of FUT8 in the transition of inflammation and fibrosis. Therefore, the loss of FUT8 in TECs may be a novel potential strategy for treating AKI-CKD transition.

#3971 INJURY INDUCED RENAL FIBROSIS PROMOTES CYSTOGENESIS AND CYST GROWTH IN ADULT MICE WITH AUTOSOMAL DOMINANT POLYCYSTIC KIDNEY DISEASE

Abstract Background and Aims Acute kidney injury (AKI) is not a merely transient event, which can lead to a subsequent progression to chronic kidney disease (CKD). Autosomal dominant polycystic kidney disease (ADPKD) is the most frequent inherited kidney disease caused by mutations in PKD1 or PKD2 gene. Previous studies showed that acute kidney injuries promote cystogenesis in adult mice with ADPKD. Fibrosis is a hallmark of AKI to CKD (AKI-CKD) transition, and positively correlated with renal cyst growth in humans. All these data imply a role of AKI-CKD transition in ADPKD.In this study, we aimed to determine the role of AKI-CKD transition in the ADPKD. Method We established AKI-CKD transition model by toxic or surgical injuries, and Pkd gene inactivation in adult mice was performed in different time point of AKI-CKD transition. The progression of renal fibrosis was shown by Western blotting analysis in toxic or surgical injury induced AKI-CKD transition model. Results We showed that renal injury before or after Pkd gene inactivation can both induce renal cyst formation in adult Pkd1 or Pkd2 mice, and the extent of cyst formation was correlated with the initial fibrosis level of three hits (injury and gene inactivation). Inactivation of Pkd1 gene at fibrosis recovery stage in surgery induced less cyst formation in adult Pkd1 mice. Enhanced renal fibrosis by repeated toxic injuries before gene inactivation accelerated renal cyst growth in Pkd1 mice. We further showed that the speed of cyst growth at the early stage in adult Pkd1 mice was decided by the baseline of renal fibrosis. Finally, we showed that conditional knockout of Ezh2 gene attenuated renal fibrosis and cyst growth in adult Pkd1 mice with established renal fibrosis. Conclusion Fibrotic responses in AKI-CKD transition is a driving force for renal cyst formation and growth in adult kidneys and inhibition of renal fibrosis through targeting EZH2 might be new therapeutic strategy for adult ADPKD.

#4668 CITRATE SYNTHASE LACTYLATION PROMOTES THE TRANSITION FROM ACUTE KIDNEY INJURY TO CHRONIC KIDNEY DISEASE BY ACTIVATING NLRP3 INFLAMMASOME

Abstract Background and Aims Renal interstitial inflammation has been postulated to play a critical role in the acute kidney injury (AKI) to chronic kidney disease (CKD) transition. Recent studies have shown that protein lactylation caused by lactate accumulation can regulate chronic organ injury. The purpose of this study was to investigated the role and mechanism of protein lactlylation in AKI-CKD transition. Method Severe renal ischemia-reperfusion(I/R) injury (severe AKI) was constructed by bilateral renal ischemia for 35min. The lactylation enhancer rotenone and the lactylation inhibitor oxamate were used to verify the effect of protein lactylation. Lactylated proteomics was used to detect the changes of lactylated proteins in renal cortex at different time points (day 0, 3, and 7), and the lactylated proteins related to kidney injury were screened for verification. Results The pathological staining results showed that the severe AKI mice were most severely injuried at day 3, partially recovered at day 7, and developed renal interstitial fibrosis at day 28. The Serum creatinine (SCr) levels did not return to baseline at day 28 after I/R injury. The levels of lactate and protein lactylation modification detected by Elisa and western blot analysis showed the same tendency as the above pathological injury, indicating that protein lactylation might contribute to the chronic transition of severe AKI. The renal injury score was significantly increased at day 3 and the percentage of renal interstitial fibrosis was significantly increased at day 28 after treatment with protein lactylation enhancer. IL-1b and IL-18 were found to be the most significantly enhanced inflammatory cytokines in the blood of mice, and the NLRP3 inflammasome activation was significantly enhanced in renal tissue at 3 days. The in vitro results further confirmed these findings. We found that protein lactylation might activate the NLRP3 inflammasome, therefore leading to AKI-CKD transition. Meanwhile, lactylation inhibitor had a protective effect on AKI-CKD transition. Lactylated proteins were detected by lactylated proteomics analysis at day 0, 3 and 7 after I/R, and the enrichment of differential lactylated proteins was analyzed. The results showed that the differential proteins with significant difference mainly existed in the tricarboxylic acid cycle. One of them is citrate synthase (CS), a key rate-limiting enzyme in the tricarboxylic acid cycle. Citrate synthase lactylation level increased significantly on day 3 after AKI. Among the three lactylation sites of CS, the further screening revealed that CS-K370 is the most significant. We constructed mutations of CS-K370 lactylation sites to verify its effects on the enzyme activity and function. Results showed in hypoxia/reoxygenation(H/R) model for mice renal tubular epithelial cells (mRTECs), compared with control group, the enzyme activity of CS in K370T group (modified status) decreased significantly, while in K370R group (unmodified status) did not decrease significantly. Moreover, the lactylation modification of CS-K370 can lead to the activation of NLRP3 inflammasome. The above results indicated that the lactylation of CS-K370 site inhibited the enzyme activity of CS and activated NLRP3 inflammasome. Conclusion Renal protein lactylation promotes activation of NLRP3 inflammasome, leading to AKI-CKD transition. Citrate synthase may be the key lactylated protein.

#5645 SHORT-CHAIN FATTY ACIDS, PROPIONATE AND BUTYRATE, RESEMBLE THE BENEFICIAL EFFECTS OF VITAMIN D DURING ACUTE KIDNEY DAMAGE

Abstract Background and Aims The vitamin D receptor (VDR) is a nuclear receptor that acts as a ligand-induced transcription factor regulating the renal expression of numerous genes with anti-inflammatory and anti-fibrotic effects, among others. For that, VDR requires the binding of its ligand, 1,25 (OH)2D3, to further heterodimerize with its co-activator, RXR, and translocate into the nucleus. Vitamin D deficiency in patients with renal disease leads to a decrease in VDR-mediated signaling and, consequently, of its beneficial functions. Additionally, these patients have intestinal dysbiosis, which leads to alterations in the production of microbial metabolites. Short-chain fatty acids (SCFAs) are metabolites with a clear anti-inflammatory and immunoregulatory role. Until now, some studies have studied their role as regulators of the inflammation and oxidative stress during the renal damage.1,2 However, their role in the VDR-mediated signaling in the kidney and the potential consequences to prevent the progression of the disease have not yet been explored in detail. Method The tubular epithelial cell line, HK2, was used to analyze the effect of the SCFAs, Propionate (Prop,1-15mM) and Butyrate (But, 0.5-3 mM), in the VDR expression and their target-genes. In vitro treatment with histone deacetylases (HDACs) inhibitors and specific HDAC1 and HDAC3 siRNAs were used to determine the role of both SCFAs as epigenetic remodelers. The binding of VDR to HDAC1/3 and RXR was determined by ChIP and co-immunoprecipitation assays. The in vivo effect of these SCFAs was evaluated in an acute kidney injury mice model induced by folic acid (250 mg/kg) and administration of Prop (200mg/kg) or But (500mg/kg) at different time points. The expression of VDR and its target genes, inflammatory cell infiltration, renal damage markers and renal function parameters were evaluated at shorter (24h) and longer times (40 days). Results Treatment of tubular cells with Prop and But induces, in a dose-dependent manner, the VDR gene transcription. This effect is similar to the one obtained by using specific inhibitors and siRNA treatments against HDAC1/3. We determine using ChIP assay, that HDAC1/3 are recruited to the promoter regions of the VDR gene, blocking its expression. In presence of Prop and But, these HDACs are displaced, increasing the acetylation levels and VDR transcription. Moreover, Prop and But prevent the degradation of VDR by the proteasome, increasing its stability and enhancing VDR protein levels. In the presence of both SCFAs, VDR dimerizes with RXR initiating its translocation to the nucleus and allowing the transcription of its dependent genes, such as Cyp24a1 and E-cadherin. Of note, VDR activation by Prop and But is additive to the effect achieved by the vitamin D alone. In vivo studies reported that administration of Prop or But prevents the loss of VDR expression 24h after induction of the damage, leading to its activation and to the expression of its target genes. Additionally, a decrease in the recruitment of neutrophils to the kidney was observed associated to a reduced expression of IL-6. These changes are accompanied by a decrease of the kidney damage markers (KIM-1 and NGAL) and a significant reduction of the creatinine and blood urea nitrogen serum levels. In a second model of AKI-to CKD transition, administration of both SCFAs shows a decrease in the inflammatory (Ccl20, Ccl2, Lif, Ltb, Csf2SF2, Il18, Ccl5, Tnf-α) and pro-fibrotic markers (Fsp1, α-Sma, Col1a1, Fn1) and a partial recovery of the glomerular filtration rate at long term. Conclusion Propionate and Butyrate, not only induce the VDR gene transcription in renal tubular cells but are also able to stabilize and activate the VDR protein. Accordingly, both metabolites are able to restore the loosed expression and activation of VDR due to induced renal damage, reduce the infiltration of immune cells, and partially recover the renal function. Thus, strategies aimed to increase the propionate and butyrate levels with postbiotics could be useful to ameliorate the AKI renal damage and CKD transition.

The role of the SGK3/TOPK signaling pathway in the transition from acute kidney injury to chronic kidney disease.

Introduction: Profibrotic phenotype of renal tubular epithelial cells (TECs) featured with epithelial to mesenchymal transition (EMT) and profibrotic factors secretion, and aberrant accumulation of CD206+ M2 macrophages are the key points in the transition from acute kidney injury (AKI) to chronic kidney disease (CKD). Nevertheless, the underlying mechanisms involved remain incompletely understood. Serum and glucocorticoid-inducible kinase (SGK) is a serine/threonine protein kinase, required for intestinal nutrient transport and ion channels modulation. T-LAK-cell-originated protein kinase (TOPK) is a member of the mitogen activated protein kinase family, linked to cell cycle regulation. However, little is known about their roles in AKI-CKD transition. Methods: In this study, three models were constructed in C57BL/6 mice: low dose and multiple intraperitoneal injection of cisplatin, 5/6 nephrectomy and unilateral ureteral obstruction model. Rat renal tubular epithelial cells (NRK-52E) were dealt with cisplatin to induce profibrotic phenotype, while a mouse monocytic cell line (RAW264.7) were cultured with cisplatin or TGF-β1 to induce M1 or M2 macrophage polarization respectively. And co-cultured NRK-52E and RAW264.7 through transwell plate to explore the interaction between them. The expression of SGK3 and TOPK phosphorylation were detected by immunohistochemistry, immunofluorescence and western blot analysis. Results: In vivo, the expression of SGK3 and p-TOPK were gradually inhibited in TECs, but enhanced in CD206+ M2 macrophages. In vitro, SGK3 inhibition aggravated epithelial to mesenchymal transition through reducing the phosphorylation state of TOPK, and controlling TGF-β1 synthesis and secretion in TECs. However, SGK3/TOPK axis activation promoted CD206+ M2 macrophage polarization, which caused kidney fibrosis by mediating macrophage to myofibroblast transition (MMT). When co-cultured, the TGF-β1 from profibrotic TECs evoked CD206+ M2 macrophage polarization and MMT, which could be attenuated by SGK3/TOPK axis inhibition in macrophages. Conversely, SGK3/TOPK signaling pathway activation in TECs could reverse CD206+ M2 macrophages aggravated EMT. Discussion: We revealed for the first time that SGK3 regulated TOPK phosphorylation to mediate TECs profibrotic phenotype, macrophage plasticity and the crosstalk between TECs and macrophages during AKI-CKD transition. Our results demonstrated the inverse effect of SGK3/TOPK signaling pathway in profibrotic TECs and CD206+ M2 macrophages polarization during the AKI-CKD transition.

Tracing causes of tubule atrophy in vivo

Acute kidney injury (AKI) is a known risk factor for chronic kidney disease (CKD). The mechanisms for AKI-CKD transition may involve failed tubule repair and progressive interstitial fibrosis but are incompletely understood. Which events lead to failed tubule repair? Can injury spread over time? And are these processes steered by myofibroblasts and fibrotic tissue remodeling?Here, we combined serial intravital 2-photon microscopy and a novel model of partial ischemia-reperfusion injury (partial IRI), which allowed us to investigate injured tissue alongside uninjured tissue in the same kidney and over time. Thus, we occluded only one branch of the left renal artery for 21 min, rendering half the kidney ischemic. We then tracked tubule necrosis and remodeling alongside myofibroblast dynamics for up to 3 weeks. Necrotic cell death was detected by in vivo propidium iodide staining. PDGFRβ-CreERT2-Salsa6F mice (N=5) identified main myofibroblast precursor cells, by tdTomato-expression. Myofibroblast-differentiation was confirmed by ex vivo αSMA staining. Proximal tubule (PT) function was assessed by in vivo uptake of fluorescent albumin.Necrotic cell death was solely detectable upon reperfusion. Border areas in between post-ischemic and non-ischemic tissue presented severely necrotic PTs alongside uninjured PTs. From 1 day after partial IRI, we observed formation of granular casts in the lumen of necrotic tubules, which 1-2 days later also appeared in initially non-necrotic PTs downstream. Tubule necrosis and granular cast accumulation preceded thinned epithelium that lacked albumin endocytosis (day 3-7) and recruitment of myofibroblasts (peaking D4-10). Of note, non-necrotic tubules, without granular cast accumulation, didn’t remodel nor recruit myofibroblasts.Among all remodeling tubule segments, 24% turned atrophic. Importantly, preceding necrotic cell death was higher in atrophic than in recovering tubules (55±13% vs. 39±18% necrotic cells/total segment cell number, (mean±SD), p<.0001). Preceding granular casts accounted for 38±15% vs. 12±11% (mean ±SD) of the luminal area in atrophic and recovering tubules, respectively (p<.0001). Ex vivo staining for pro-fibrotic VCAM-1 demonstrated selective positivity in atrophic tubules, which appeared scattered at D8 while at D21, entire atrophic tubules stained positive (n=3, each). Consistently, we detected persistent myofibroblast enclosure of atrophic tubule, while recruitment around recovered PTs resolved by day 14 (50±21% vs. 23±18% of coverage, p<.001).Tracking the same tubules in vivo and over time, we demonstrated early proximal tubule necrosis, which induced luminal granular cast formation and injury propagation. These events preceded myofibroblast accumulation and predicted tubule atrophy. We further documented de novo expression of pro-inflammatory VCAM-1 and persistent myofibroblast recruitment selectively in atrophic tubules, suggesting an active role of this tubule state in AKI-CKD transition. Novo Nordisk Foundation, Augustinus Foundation, Aarhus University Research Foundation (AUFF) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Bibliometric and visualization analysis of kidney repair associated with acute kidney injury from 2002 to 2022.

Background: Renal repair is closely related to the prognosis of acute kidney injury (AKI) and has attracted increasing attention in the research field. However, there is a lack of a comprehensive bibliometric analysis in this research area. This study aims at exploring the current status and hotspots of renal repair research in AKI from the perspective of bibliometrics. Methods: Studies published between 2002 and 2022 related to kidney repair after AKI were collected from Web of Science core collection (WoSCC) database. Bibliometric measurement and knowledge graph analysis to predict the latest research trends in the field were performed using bibliometrics software CiteSpace and VOSviewer. Results: The number of documents related to kidney repair after AKI has steadily increased over 20 years. The United States and China contribute more than 60% of documents and are the main drivers of research in this field. Harvard University is the most active academic institution that contributes the most documents. Humphreys BD and Bonventre JV are the most prolific authors and co-cited authors in the field. The American Journal of Physiology-Renal Physiology and Journal of the American Society of Nephrology are the most popular journals in the field with the greatest number of documents. "exosome", "macrophage polarization", "fibroblast", and" aki-ckd transition" are high-frequency keywords in this field in recent years. Extracellular vesicles (including exosomes), macrophage polarization, cell cycle arrest, hippo pathway, and sox9 are current research hotspots and potential targets in this field. Conclusion: This is the first comprehensive bibliometric study on the knowledge structure and development trend of AKI-related renal repair research in recent years. The results of the study comprehensively summarize and identify research frontiers in AKI-related renal repair.

Tubular Epithelial Cell HMGB1 Promotes AKI-CKD Transition by Sensitizing Cycling Tubular Cells to Oxidative Stress: A Rationale for Targeting HMGB1 during AKI Recovery.

Cells undergoing necrosis release extracellular high mobility group box (HMGB)-1, which triggers sterile inflammation upon AKI in mice. Neither deletion of HMGB1 from tubular epithelial cells, nor HMGB1 antagonism with small molecules, affects initial ischemic tubular necrosis and immediate GFR loss upon unilateral ischemia/reperfusion injury (IRI). On the contrary, tubular cell-specific HMGB1 deficiency, and even late-onset pharmacological HMGB1 inhibition, increased functional and structural recovery from AKI, indicating that intracellular HMGB1 partially counters the effects of extracellular HMGB1. In vitro studies indicate that intracellular HMGB1 decreases resilience of tubular cells from prolonged ischemic stress, as in unilateral IRI. Intracellular HMGB1 is a potential target to enhance kidney regeneration and to improve long-term prognosis in AKI. Late diagnosis is a hurdle for treatment of AKI, but targeting AKI-CKD transition may improve outcomes. High mobility group box-1 (HMGB1) is a nuclear regulator of transcription and a driver of necroinflammation in AKI. We hypothesized that HMGB1 would also modulate AKI-CKD transition in other ways. We conducted single-cell transcriptome analysis of human and mouse AKI and mouse in vivo and in vitro studies with tubular cell-specific depletion of Hmgb1 and HMGB1 antagonists. HMGB1 was ubiquitously expressed in kidney cells. Preemptive HMGB1 antagonism with glycyrrhizic acid (Gly) and ethyl pyruvate (EP) did not affect postischemic AKI but attenuated AKI-CKD transition in a model of persistent kidney hypoxia. Consistently, tubular Hmgb1 depletion in Pax8 rtTA, TetO Cre, Hmgb1fl/fl mice did not protect from AKI, but from AKI-CKD transition. In vitro studies confirmed that absence of HMGB1 or HMGB1 inhibition with Gly and EP does not affect ischemic necrosis of growth-arrested differentiated tubular cells but increased the resilience of cycling tubular cells that survived the acute injury to oxidative stress. This effect persisted when neutralizing extracellular HMGB1 with 2G7. Consistently, late-onset HMGB1 blockade with EP started after the peak of ischemic AKI in mice prevented AKI-CKD transition, even when 2G7 blocked extracellular HMGB1. Treatment of AKI could become feasible when ( 1 ) focusing on long-term outcomes of AKI; ( 2 ) targeting AKI-CKD transition with drugs initiated after the AKI peak; and ( 3 ) targeting with drugs that block HMGB1 in intracellular and extracellular compartments.

Depletion of macrophages with clodronate liposomes partially attenuates renal fibrosis on AKI–CKD transition

Clodronate liposomes are bisphosphonates encapsulated by liposomes that are known to induce macrophage depletion in vivo. In a previous study, clodronate liposomes improved renal ischemia/reperfusion (I/R) injury in mice, which may be due to effects on macrophage phenotypes. However, how inflammatory cytokines secretion participates is unknown. In this study, we investigated the effect of macrophages in the I/R kidney by depleting macrophages with clodronate liposomes and changing inflammatory cytokines. C57BL/6 mice underwent I/R injury with or without clodronate liposomes administration on Days 5 and 15. Tubular injury, collagen deposition, and fibrosis were detected and analyzed by histological staining, immunocytochemistry (IHC), flow cytometry (FACS), and reverse transcription–polymerase chain reaction (RT–PCR). Inflammatory cytokines were detected and analyzed by Western blotting and RT–PCR. We found that clodronate liposomes alleviated renal fibrosis and tissue damage on both Days 5 and 15. KIM-1, IL-10, and TGF-β were reduced significantly in the clodronate liposomes treatment group. However, TNF-α was not different between the clodronate liposomes treatment group and the phosphate-buffered saline treatment group on either Day 5 or Day 15. Thus, clodronate liposomes can alleviate renal fibrosis and tissue damage and reduce the inflammatory cytokines IL-10 and TGF-β, suggesting that clodronate liposomes alleviate renal fibrosis may because of M1/M2 polarization.

Mechanisms of Difference in AKI-CKD Transition due to Acute Cardiorenal Syndrome and Ischemia-Reperfusion Injury

Mechanisms of Difference in AKI-CKD Transition due to Acute Cardiorenal Syndrome and Ischemia-Reperfusion Injury

Tubular cell polyploidy protects from lethal acute kidney injury but promotes consequent chronic kidney disease

Acute kidney injury (AKI) is frequent, often fatal and, for lack of specific therapies, can leave survivors with chronic kidney disease (CKD). We characterize the distribution of tubular cells (TC) undergoing polyploidy along AKI by DNA content analysis and single cell RNA-sequencing. Furthermore, we study the functional roles of polyploidization using transgenic models and drug interventions. We identify YAP1-driven TC polyploidization outside the site of injury as a rapid way to sustain residual kidney function early during AKI. This survival mechanism comes at the cost of senescence of polyploid TC promoting interstitial fibrosis and CKD in AKI survivors. However, targeting TC polyploidization after the early AKI phase can prevent AKI-CKD transition without influencing AKI lethality. Senolytic treatment prevents CKD by blocking repeated TC polyploidization cycles. These results revise the current pathophysiological concept of how the kidney responds to acute injury and identify a novel druggable target to improve prognosis in AKI survivors.