Metabolic Rewiring and Communication: An Integrative View of Kidney Proximal Tubule Function.

The kidney proximal tubule is a key organ for human metabolism. The kidney responds to stress with altered metabolite transformation and perturbed metabolic pathways, an ultimate cause for kidney disease. Here, we review the proximal tubule's metabolic function through an integrative view of transport, metabolism, and function, and embed it in the context of metabolome-wide data-driven research. Function (filtration, transport, secretion, and reabsorption), metabolite transformation, and metabolite signaling determine kidney metabolic rewiring in disease. Energy metabolism and substrates for key metabolic pathways are orchestrated by metabolite sensors. Given the importance of renal function for the inner milieu, we also review metabolic communication routes with other organs. Exciting research opportunities exist to understand metabolic perturbation of kidney and proximal tubule function, for example, in hypertension-associated kidney disease. We argue that, based on the integrative view outlined here, kidney diseases without genetic cause should be approached scientifically as metabolic diseases.

Hepatorenal Syndrome in Cirrhosis.

Hepatorenal syndrome (HRS) is a form of kidney dysfunction that characteristically occurs in liver cirrhosis. It is characterized by a marked impairment of kidney function in response to circulatory and hemodynamic alterations that occur in advanced stages of liver cirrhosis, aggravated by systemic inflammation and bacterial translocation. The classical definitions of the types of HRS have been recently revisited and 2 forms of HRS have been redefined: the acute form, referred to as acute kidney injury (HRS-AKI), and the chronic form, referred to as chronic kidney disease. HRS-AKI is one of the most severe forms of AKI in patients with cirrhosis and it consists of an abrupt impairment of kidney function, frequently triggered by an infection, appearing in the setting of advanced decompensated cirrhosis. Differential diagnosis with other causes of AKI is crucial because HRS-AKI requires a specific treatment. Differential diagnosis with AKI-acute tubular necrosis may be challenging and kidney biomarkers may be useful in this setting. Treatment of HRS-AKI is based on the administration of vasoconstrictor drugs in combination with volume expansion with albumin. Prognosis of HRS-AKI is poor, and the ideal definitive treatment consists of liver transplantation or simultaneous liver-kidney transplantation. HRS-AKI has a big impact on patients' quality of life. Management of HRS-AKI remains challenging in specific situations such as alcohol-associated hepatitis or metabolic-associated steatotic liver disease cirrhosis. Developing preventive measures for HRS-AKI, improving its early identification, discovering new biomarkers for differential diagnosis, and improving the response to therapy are some of the unmet needs in the field of HRS-AKI.

Proximal tubular MBD2 promotes autophagy to drive the progression of AKI caused by vancomycin via regulation of miR-597-5p/S1PR1 axis.

Our recent investigation has indicated that the global deletion of MBD2 can mitigate the progression of AKI induced by VAN. Nevertheless, the role and regulatory mechanisms of proximal tubular MBD2 in this pathophysiological process have yet to be elucidated. Our preceding investigation revealed that autophagy played a crucial role in advancing AKI induced by VAN. Consequently, we postulated that MBD2 present in the proximal tubule could upregulate the autophagic process to expedite the onset of AKI. In the present study, we found for the first time that MBD2 mediated the autophagy production induced by VAN. Through the utilization of miRNA chip analysis, we have mechanistically demonstrated that MBD2 initiates the activation of miR-597-5p through promoter demethylation. This process leads to the suppression of S1PR1, which results in the induction of autophagy and apoptosis in renal tubular cells. Besides, PT-MBD2-KO reduced autophagy to attenuate VAN-induced AKI via regulation of the miR-597-5p/S1PR1 axis, which was reversed by rapamycin. Finally, the overexpression of MBD2 aggravated the diminished VAN-induced AKI in autophagy-deficient mice (PT-Atg7-KO). These data demonstrate that proximal tubular MBD2 facilitated the process of autophagy via the miR-597-5p/S1PR1 axis and subsequently instigated VAN-induced AKI through the induction of apoptosis. The potentiality of MBD2 being a target for AKI was established.

Discovery and verification of mmu_Circ_26986/hsa_Circ_0072463 as a potential biomarker and intervention target for sepsis-associated acute kidney injury.

Approximately 60% of septic patients developed acute kidney injury (AKI). The mortality rate of septic AKI (SA-AKI) is two to three times higher than that of septic without AKI (SA-non-AKI). The actual functions and mechanisms of CircRNAs in the pathophysiology of SA-AKI remain incompletely understood. Herein, we observed that the mmu_Circ_26986 could be induced by lipopolysaccharide (LPS) and cecum ligation and puncture (CLP) in BUMPT cell line and C57BL/6 mouse kidney, respectively. Functionally, mmu_Circ_26986 suppressed BUMPT cell apoptosis induced by LPS. Mechanistically, mmu_Circ_26986 sponged miRNA-29b-1-5p to upregulate the expression of PAK7. Overexpression of mmu_Circ_26986 ameliorated the progression of CLP-stimulated AKI through miRNA-29b-1-5p/PAK7 axis. In addition, we found that hsa_Circ_0072463, homologous to mmu_Circ_26986, suppressed LPS-induced HK-2 cells apoptosis via regulation of miRNA-29b-1-5p/PAK7 axis. Furthermore, sepsis patients with AKI had a higher level of hsa_Circ_0072463 compared to those without AKI. The sensitivity, specificity and AUC of hsa_Circ_0072463 were 78.8%, 87.9% and 0.866, respectively. Spearman's test indicated a noticeable positive correlation between plasma hsa_Circ_0072463 and serum creatinine in sepsis patients (r = 0.725). In summary, this study reveals that the mmu_Circ_26986/hsa_Circ_0072463 miRNA-29b-1-5p/PAK7 axis mediates septic AKI, and hsa_Circ_0072463 is a potential diagnostic marker for septic AKI.

TIMP2 protects against sepsis-associated acute kidney injury by cAMP/NLRP3 axis-mediated pyroptosis.

The tissue inhibitor of metalloproteinases 2 (TIMP2) has emerged as a promising biomarker for predicting the risk of sepsis-associated acute kidney injury (SA-AKI). However, its exact role in SA-AKI and the underlying mechanism remains unclear. In this study, we investigated the impact of kidney tubule-specific Timp2 knockout mice on kidney injury and inflammation. Our findings demonstrated that Timp2-knockout mice exhibited more severe kidney injury than wild-type mice, along with elevated levels of pyroptosis markers NOD-like receptor protein 3 (NLRP3), Caspase1, and gasdermin D (GSDMD) in the early stage of SA-AKI. Conversely, the expression of exogenous TIMP2 in TIMP2-knockout mice still protected against kidney damage and inflammation. In in vitro experiments, using recombinant TIMP2 protein, TIMP2 knockdown demonstrated that exogenous TIMP2 inhibited pyroptosis of renal tubular cells stimulated by lipopolysaccharide (LPS). Mechanistically, TIMP2 promoted the ubiquitination and autophagy-dependent degradation of NLRP3 by increasing intracellular cyclic adenosine monophosphate (cAMP), which mediated NLRP3 degradation through recruiting the E3 ligase MARCH7, attenuating downstream pyroptosis, and thus alleviating primary tubular cell damage. These results revealed the renoprotective role of extracellular TIMP2 in SA-AKI by attenuating tubular pyroptosis, and suggested that exogenous administration of TIMP2 could be a promising therapeutic intervention for SA-AKI treatment.NEW & NOTEWORTHY Tissue inhibitor of metalloproteinase 2 (TIMP-2) has been found to be the best biomarker for predicting the risk of sepsis-associated acute kidney injury (SA-AKI). However, its role and the underlying mechanism in SA-AKI remain elusive. The authors demonstrated in this study using kidney tubule-specific knockout mice model of SA-AKI and primary renal tubule cells stimulated with lipopolysaccharide (LPS) that extracellular TIMP-2 promoted NOD-like receptor protein 3 (NLRP3) ubiquitination and autophagy-dependent degradation by increasing intracellular cyclic adenosine monophosphate (cAMP), thus attenuated pyroptosis and alleviated renal damage.

Unveiling Pathophysiological Insights: Serum Metabolic Dysregulation in Acute Respiratory Distress Syndrome Patients with Acute Kidney Injury.

Acute respiratory distress syndrome (ARDS) is associated with high mortality rates, which are further exacerbated when accompanied by acute kidney injury (AKI). Presently, there is a lack of comprehensive studies thoroughly elucidating the metabolic dysregulation in ARDS patients with AKI leading to poor outcomes. We hypothesized that metabolomics can be a potent tool to highlight the differences in the metabolic profile unraveling unidentified pathophysiological mechanisms of ARDS patients with and without AKI. 1H nuclear magnetic resonance spectroscopy was used to identify key metabolites in the serum samples of 75 patients. Distinct clusters of both groups were obtained as the study's primary outcome using multivariate analysis. Notable alternations in the levels of nine metabolites were identified. Pathway analysis revealed the dysregulation of five significant cycles, which resulted in various complications, such as hyperammonemia, higher energy requirements, and mitochondrial dysfunction causing oxidative stress. Identified metabolites also showed a significant correlation with clinical scores, indicating severity. This study shows the alterations in the metabolite concentration highlighting the difference in the pathophysiology of both patient groups and its association with outcome, pointing in the direction of a personalized medicine approach and holding significant promise for application in critical care settings to improve clinical outcomes.

Berberine alleviates contrast-induced nephropathy by activating Akt/Foxo3a/Nrf2 signalling pathway.

Contrast-induced nephropathy (CIN) is a condition that causes kidney damage in patients receiving angiography with iodine-based contrast agents. This study investigated the potential protective effects of berberine (BBR) against CIN and its underlying mechanisms. The researchers conducted both in vivo and in vitro experiments to explore BBR's renal protective effects. In the in vivo experiments, SD rats were used to create a CIN model, and different groups were established. The results showed that CIN model group exhibited impaired renal function, severe damage to renal tubular cells and increased apoptosis and ferroptosis. However, BBR treatment group demonstrated improved renal function, decreased apoptosis and ferroptosis. Similar results were observed in the in vitro experiments using HK-2 cells. BBR reduced ioversol-induced apoptosis and ferroptosis, and exerted its protective effects through Akt/Foxo3a/Nrf2 signalling pathway. BBR administration increased the expression of Foxo3a and Nrf2 while decreasing the levels of p-Akt and p-Foxo3a. In conclusion, this study revealed that BBR effectively inhibited ioversol-induced apoptosis and ferroptosis in vivo and in vitro. The protective effects of BBR were mediated through the modulation of Akt/Foxo3a/Nrf2 signalling pathway, leading to the alleviation of CIN. These findings suggest that BBR may have therapeutic potential for protecting against CIN in patients undergoing angiography with iodine-based contrast agents.

Galectin-3 protects distal convoluted tubules in rhabdomyolysis-induced kidney injury.

Advanced glycation endproducts (AGEs) contribute to cellular damage of various pathologies, including kidney diseases. Acute kidney injury (AKI) represents a syndrome seldom characterized by a single, distinct pathophysiological cause. Rhabdomyolysis-induced acute kidney injury (RIAKI) constitutes roughly 15% of AKI cases, yet its underlying pathophysiology remains poorly understood. Using a murine model of RIAKI induced by muscular glycerol injection, we observed elevated levels of AGEs and the AGE receptor galectin-3 (LGALS3) in the kidney. Immunofluorescence localized LGALS3 to distal nephron segments. According to transcriptomic profiling via next-generation sequencing, RIAKI led to profound changes in kidney metabolism, oxidative stress, and inflammation. Cellular stress was evident in both proximal and distal tubules, as shown by kidney injury markers KIM-1 and NGAL. However, only proximal tubules exhibited overt damage and apoptosis, as detected by routine morphology, active Caspase-3, and TUNEL assay, respectively. In vitro, distal convoluted tubule (DCT) cells challenged with AGEs underwent apoptosis, which was markedly enhanced by Lgals3 siRNA treatment. Thus, in RIAKI, the upregulation of LGALS3 may protect the distal nephron from AGE-mediated damage, while proximal tubules lacking LGALS3 stay at risk. Thus, stimulating LGALS3 in the proximal nephron, if achievable, may attenuate RIAKI.

Renal-specific loss of ferroportin disrupts iron homeostasis and attenuates recovery from acute kidney injury.

Chronic kidney disease is increasing at an alarming rate and correlates with the increase in diabetes, obesity, and hypertension that disproportionately impact socioeconomically disadvantaged communities. Iron plays essential roles in many biological processes including oxygen transport, mitochondrial function, cell proliferation, and regeneration. However, excess iron induces the generation and propagation of reactive oxygen species, which lead to oxidative stress, cellular damage, and ferroptosis. Iron homeostasis is regulated in part by the kidney through iron resorption from the glomerular filtrate and exports into the plasma by ferroportin (FPN). Yet, the impact of iron overload in the kidney has not been addressed. To test more directly whether excess iron accumulation is toxic to kidneys, we generated a kidney proximal tubule-specific knockout of FPN. Despite significant intracellular iron accumulation in FPN mutant tubules, basal kidney function was not measurably different from wild type kidneys. However, upon induction of acute kidney injury (AKI), FPN mutant kidneys exhibited significantly more damage and failed recovery, evidence for ferroptosis, and increased fibrosis. Thus, disruption of iron export in proximal tubules, leading to iron overload, can significantly impair recovery from AKI and can contribute to progressive renal damage indicative of chronic kidney disease. Understanding the mechanisms that regulate iron homeostasis in the kidney may provide new therapeutic strategies for progressive kidney disease and other ferroptosis-associated disorders.NEW & NOTEWORTHY Physiological iron homeostasis depends in part on renal resorption and export into the plasma. We show that specific deletion of iron exporters in the proximal tubules sensitizes cells to injury and inhibits recovery. This can promote a chronic kidney disease phenotype. Our paper demonstrates the need for iron balance in the proximal tubules to maintain and promote healthy recovery after acute kidney injury.

Distinct developmental reprogramming footprint of macrophages during acute kidney injury across species.

Acute kidney injury (AKI) is a common finding in hospitalized patients, particularly those who are critically ill. The development of AKI is associated with several adverse outcomes including mortality, morbidity, progression to chronic kidney disease, and an increase in healthcare expenditure. Despite the well-established negative impact of AKI and rigorous efforts to better define, identify, and implement targeted therapies, the overall approach to the treatment of AKI continues to principally encompass supportive measures. This enduring challenge is primarily due to the heterogeneous nature of insults that activate many independent and overlapping molecular pathways. Consequently, it is evident that the identification of common mechanisms that mediate the pathogenesis of AKI, independent of etiology and engaged pathophysiological pathways, is of paramount importance and could lead to the identification of novel therapeutic targets. To better distinguish the commonly modulated mechanisms of AKI, we explored the transcriptional characteristics of human kidney biopsies from patients with acute tubular necrosis (ATN), and acute interstitial nephritis (AIN) using a NanoString inflammation panel. Subsequently, we used publicly available single-cell transcriptional resources to better interpret the generated transcriptional findings. Our findings identify robust acute kidney injury (AKI-induced) developmental reprogramming of macrophages (MΦ) with the expansion of C1Q+, CD163+ MΦ that is independent of the etiology of AKI and conserved across mouse and human species. These results would expand the current understanding of the pathophysiology of AKI and potentially offer novel targets for additional studies to enhance the translational transition of AKI research.NEW & NOTEWORTHY Our findings identify robust acute kidney injury (AKI)-induced developmental reprogramming of macrophages (MΦ) with the expansion of C1Q+, CD163+ MΦ that is independent of the etiology of AKI and conserved across mouse and human species.

VCAM-1 mediates proximal tubule-immune cell crosstalk in failed tubule recovery during AKI-to-CKD transition.

Studies in animal models suggest a linkage between inflammatory response to injury and subsequent nephron loss during acute kidney injury (AKI) to chronic kidney disease (CKD) transition. Failure of normal repair during CKD transition correlates with de novo expression of vascular cell adhesion protein-1 (VCAM-1) by a subset of injured proximal tubule cells. This study identifies the role of VCAM-1 expression in promoting the failed repair state. Single-cell transcriptome analysis of patients with AKI and CKD, and whole kidney RNA and protein analyses of mouse models of CKD, confirmed a marked increase of VCAM-1 expression in the proximal tubules of injured kidneys. In immortalized mouse proximal tubular (MPT) cells and primary cultured renal cells (PCRCs), VCAM-1 expression was induced by proinflammatory cytokines including TNFα and IL-1ß. Analyses of bulk RNA sequencing of TNFα-treated PCRCs or pseudo-bulk RNA sequencing of biopsies from the Kidney Precision Medicine Project (KPMP) datasets indicated activation of NF-κB and an enrichment of inflammatory response and cell adhesion pathways in VCAM-1-positive cells. Pharmacologic inhibition of NF-κB signaling or genetic deletion of myeloid differentiation factor 88 (Myd88) and TIR-domain-containing adapter-inducing interferon-ß (Trif) suppressed TNFα- and IL-1ß-induced VCAM-1 expression in vitro. TNFα stimulation or overexpression of VCAM-1 significantly increased splenocyte adhesion to the MPT monolayer in culture. These results demonstrate that persistence of proinflammatory cytokines after AKI can induce NF-κB-dependent VCAM-1 expression by proximal tubule cells, mediating increased immune cell adhesion to the tubule and thus promoting further tubule injury and greater risk of progression from AKI to CKD.

Role of CDKL1-SOX11 signaling axis in Acute Kidney Injury.

The biology of CDKL (Cyclin-Dependent Kinase-Like) kinase family remains enigmatic. Contrary to their nomenclature, CDKLs do not rely on cyclins for activation and are not involved in cell cycle regulation. Instead, they share structural similarities with MAPKs (Mitogen-Activated Protein Kinases) and GSK3 (glycogen synthase kinase 3), though their specific functions and associated signaling pathways are still unknown. Previous studies have shown that the activation of CDKL5 kinase contributes to the development of acute kidney injury (AKI) by suppressing the protective SOX9-dependent transcriptional program in tubular epithelial cells. In the current study, we measured the functional activity of all the five CDKL kinases and discovered that, in addition to CDKL5, CDKL1 is also activated in tubular epithelial cells during AKI. To explore the role of CDKL1, we generated a germline knockout mouse which exhibited no abnormalities under normal conditions. Notably, when these mice were challenged with bilateral ischemia reperfusion and rhabdomyolysis, they were found to be protected from AKI. Further mechanistic investigations revealed that CDKL1 phosphorylates and destabilizes SOX11, contributing to tubular dysfunction. In summary, these studies have unveiled a previously unknown CDKL1-SOX11 axis that drives tubular dysfunction during AKI.

Visualization of intracellular ATP dynamics in different nephron segments under pathophysiological conditions using the kidney slice culture system.

ATP depletion plays a central role in the pathogenesis of kidney diseases. Recently, we reported spatiotemporal intracellular ATP dynamics during ischemia reperfusion (IR) using GO-ATeam2 mice systemically expressing an ATP biosensor. However, observation from the kidney surface did not allow visualization of deeper nephrons or accurate evaluation of ATP synthesis pathways. Here, we established a novel ATP imaging system using slice culture of GO-ATeam2 mouse kidneys, evaluated the ATP synthesis pathway, and analyzed intracellular ATP dynamics using an ex vivo IR-mimicking model and a cisplatin nephropathy model. Proximal tubules (PTs) were found to be strongly dependent on oxidative phosphorylation (OXPHOS) using the inhibitor oligomycin A, whereas podocytes relied on both OXPHOS and glycolysis using phloretin an active transport inhibitor of glucose. We also confirmed that an ex vivo IR-mimicking model could recapitulate ATP dynamics in vivo; ATP recovery in PTs after reoxygenation varied depending on anoxic time length, whereas ATP in distal tubules (DTs) recovered well even after long-term anoxia. After cisplatin administration, ATP levels in PTs decreased first, followed by a decrease in DTs. An organic cation transporter 2 inhibitor, cimetidine, suppressed cisplatin uptake in kidney slices, leading to better ATP recovery in PTs, but not in DTs. Finally, we confirmed that a mitochondria protection reagent (Mitochonic Acid 5) delayed the cisplatin-induced ATP decrease in PTs. Thus, our novel system may provide new insights into the energy dynamics and pathogenesis of kidney disease.

Development of PD in lower-income countries: a rational solution for the management of AKI and ESKD.

It is estimated that >50% of patients with end-stage kidney disease (ESKD) in low-resource countries are unable to access dialysis. When hemodialysis is available, it often has high out-of-pocket expenditure and is seldom delivered to the standard recommended by international guidelines. Hemodialysis is a high-cost intervention with significant negative effects on environmental sustainability, especially in resource-poor countries (the ones most likely to be affected by resultant climate change). This review discusses the rationale for peritoneal dialysis (PD) as a more resource and environmentally efficient treatment with the potential to improve dialysis access, especially to vulnerable populations, including women and children, in lower-resource countries. Successful initiatives such as the Saving Young Lives program have demonstrated the benefit of PD for acute kidney injury. This can then serve as a foundation for later development of PD services for end-stage kidney disease programs in these countries. Expansion of PD programs in resource-poor countries has proven to be challenging for various reasons. It is hoped that if some of these issues can be addressed, PD will be able to permit an expansion of end-stage kidney disease care in these countries.

Antibiotic-induced intestinal microbiota depletion can attenuate the acute kidney injury to chronic kidney disease transition via NADPH oxidase 2 and trimethylamine-N-oxide inhibition.

Intestinal microbiota and their metabolites affect systemic inflammation and kidney disease outcomes. Here, we investigated the key metabolites associated with the acute kidney injury (AKI)-to chronic kidney disease (CKD) transition and the effect of antibiotic-induced microbiota depletion (AIMD) on this transition. In 61 patients with AKI, 59 plasma metabolites were assessed to determine the risk of AKI-to-CKD transition. An AKI-to-CKD transition murine model was established four weeks after unilateral ischemia-reperfusion injury (IRI) to determine the effects of AIMD on the gut microbiome, metabolites, and pathological responses related to CKD transition. Human proximal tubular epithelial cells were challenged with CKD transition-related metabolites, and inhibitory effects of NADPH oxidase 2 (NOX2) signals were tested. Based on clinical metabolomics, plasma trimethylamine N-oxide (TMAO) was associated with a significantly increased risk for AKI-to-CKD transition [adjusted odds ratio 4.389 (95% confidence interval 1.106-17.416)]. In vivo, AIMD inhibited a unilateral IRI-induced increase in TMAO, along with a decrease in apoptosis, inflammation, and fibrosis. The expression of NOX2 and oxidative stress decreased after AIMD. In vitro, TMAO induced fibrosis with NOX2 activation and oxidative stress. NOX2 inhibition successfully attenuated apoptosis, inflammation, and fibrosis with suppression of G2/M arrest. NOX2 inhibition (in vivo) showed improvement in pathological changes with a decrease in oxidative stress without changes in TMAO levels. Thus, TMAO is a key metabolite associated with the AKI-to-CKD transition, and NOX2 activation was identified as a key regulator of TMAO-related AKI-to-CKD transition both in vivo and in vitro.

Pseudogene GSTM3P1 derived long non-coding RNA promotes ischemic acute kidney injury by target directed microRNA degradation of kidney-protective mir-668.

Long non-coding RNAs (lncRNAs) are a group of epigenetic regulators that have been implicated in kidney diseases including acute kidney injury (AKI). However, very little is known about the specific lncRNAs involved in AKI and the mechanisms underlying their pathologic roles. Here, we report a new lncRNA derived from the pseudogene GSTM3P1, which mediates ischemic AKI by interacting with and promoting the degradation of mir-668, a kidney-protective microRNA. GSTM3P1 and its mouse orthologue gstm2-ps1 were induced by hypoxia in cultured kidney proximal tubular cells. In mouse kidneys, gstm2-ps1 was significantly upregulated in proximal tubules at an early stage of ischemic AKI. This transient induction of gstm2-ps1 depends on G3BP1, a key component in stress granules. GSTM3P1 overexpression increased kidney proximal tubular apoptosis after ATP depletion, which was rescued by mir-668. Notably, kidney proximal tubule-specific knockout of gstm2-ps1 protected mice from ischemic AKI, as evidenced by improved kidney function, diminished tubular damage and apoptosis, and reduced kidney injury biomarker (NGAL) induction. To test the therapeutic potential, gstm2-ps1 siRNAs were introduced into cultured mouse proximal tubular cells or administered to mice. In cultured cells, gstm2-ps1 knockdown suppressed ATP depletion-associated apoptosis. In mice, gstm2-ps1 knockdown ameliorated ischemic AKI. Mechanistically, both GSTM3P1 and gstm2-ps1 possessed mir-668 binding sites and downregulated the mature form of mir-668. Specifically, GSTM3P1 directly bound to mature mir-668 to induce its decay via target-directed microRNA degradation. Thus, our results identify GSTM3P1 as a novel LncRNA that promotes kidney tubular cell death in AKI by binding mir-668 to inducing its degradation.

Critical roles of tubular mitochondrial ATP synthase dysfunction in maleic acid-induced acute kidney injury.

Maleic acid (MA) induces renal tubular cell dysfunction directed to acute kidney injury (AKI). AKI is an increasing global health burden due to its association with mortality and morbidity. However, targeted therapy for AKI is lacking. Previously, we determined mitochondrial-associated proteins are MA-induced AKI affinity proteins. We hypothesized that mitochondrial dysfunction in tubular epithelial cells plays a critical role in AKI. In vivo and in vitro systems have been used to test this hypothesis. For the in vivo model, C57BL/6 mice were intraperitoneally injected with 400 mg/kg body weight MA. For the in vitro model, HK-2 human proximal tubular epithelial cells were treated with 2 mM or 5 mM MA for 24 h. AKI can be induced by administration of MA. In the mice injected with MA, the levels of blood urea nitrogen (BUN) and creatinine in the sera were significantly increased (p < 0.005). From the pathological analysis, MA-induced AKI aggravated renal tubular injuries, increased kidney injury molecule-1 (KIM-1) expression and caused renal tubular cell apoptosis. At the cellular level, mitochondrial dysfunction was found with increasing mitochondrial reactive oxygen species (ROS) (p < 0.001), uncoupled mitochondrial respiration with decreasing electron transfer system activity (p < 0.001), and decreasing ATP production (p < 0.05). Under transmission electron microscope (TEM) examination, the cristae formation of mitochondria was defective in MA-induced AKI. To unveil the potential target in mitochondria, gene expression analysis revealed a significantly lower level of ATPase6 (p < 0.001). Renal mitochondrial protein levels of ATP subunits 5A1 and 5C1 (p < 0.05) were significantly decreased, as confirmed by protein analysis. Our study demonstrated that dysfunction of mitochondria resulting from altered expression of ATP synthase in renal tubular cells is associated with MA-induced AKI. This finding provides a potential novel target to develop new strategies for better prevention and treatment of MA-induced AKI.

Emodin inhibits M1 macrophage activation that related to acute and chronic kidney injury through EGFR/MAPK pathway.

BACKGROUND: Macrophages are the main inflammatory cells involved in kidney injury and play a significant role in the development of acute kidney injury (AKI) and progression of chronic kidney disease (CKD). Emodin is believed to stabilize macrophage homeostasis under pathological conditions. The objective of this study aimed to explore the underlying mechanisms and effects of Emodin on M1 macrophages. METHODS: Network pharmacology methods were used to predict target proteins associated with renal injury and identify the pathways affected by emodin. RAW264.7 macrophages were induced into M1 polarization using LPS and then treated with emodin at 20, 40, and 80 µM. The effects of emodin on cell viability, cytokines (IL-1ß, IL-6, TNF-α), M1 macrophage markers (F4/80 + CD86+), and the EGFR/MAPK pathway were evaluated. Additionally, we transfected RAW264.7 cells with an EGFR shRNA interference lentivirus to assess its effects on RAW264.7 cells function and MAPK pathway. After RAW264.7 cells were passaged to expanded culture and transfected with EGFR-interfering plasmid, macrophages were induced to polarize towards M1 with LPS and then treated with 80 µM emodin. CKD modeling was performed to test how emodin is regulated during CKD. RESULTS: There are 15 common targets between emodin and kidney injury, of which the EGFR/MAPK pathway is the pathway through which emodin affects macrophage function. Emodin significantly reduced the levels of IL-6, IL-1ß and TNF-α (p < 0.05) and the ratio of M1 macrophage surface markers F4/80 + CD86+ (p < 0.01) in the supernatant of RAW264.7 cells in a dose-dependent manner. Furthermore, the inhibitory effect of emodin on RAW264.7 cells was achieved by interfering with the EGFR/MAPK pathway. Moreover, emodin also affected the mRNA and protein expression of EGFR and Ras, leading to a decrease in the rate of M1 macrophages, thus inhibiting the pro-inflammatory effect of M1 macrophages. The addition of emodin reduced the rate of M1 macrophages in CKD and inhibited the further polarization of M1 macrophages, thus maintaining the pro-inflammatory and anti-inflammatory homeostasis in CKD, and these effects were achieved by emodin through the control of the EGRF/ERK pathway. CONCLUSION: Emodin attenuates M1 macrophage polarization and pro-inflammatory responses via the EGFR/MAPK signalling pathway. And the addition of emodin maintains pro- and anti-inflammatory homeostasis, which is important for maintaining organ function and tissue repair.

Clinical features associated with immune checkpoint inhibitor nephritis: a single-center clinical case series.

BACKGROUND: Acute kidney injury (AKI) has been well described as a complication of immune checkpoint inhibitor therapy. We present a series of patients, the majority with lung adenocarcinoma, who developed AKI while actively receiving immune checkpoint inhibitors. METHODS: This is a retrospectively analyzed clinical case series of six patients treated at City of Hope Comprehensive Cancer Center. Data were collected on gender, age, ethnicity, comorbidities, concomitant medications, type of malignancy, treatments, and renal function. All patients underwent renal biopsy for classification of the mechanism of AKI. Comprehensive genomic profiling (CGP) was performed on tumor tissue for all patients. RESULTS: Patterns of AKI included acute interstitial nephritis and acute tubular necrosis. Contributing factors included the use of concomitant medications known to contribute to AKI. All but two patients had full resolution of the AKI with the use of steroids. There were several mutations found on CGP that was notable including an Exon 20 insertion as well as multiple NF1 and TP53 mutations. There was high PD-L1 expression on tumor tissue noted in two out of six patients. In addition to AKI, a subset of patients had proteinuria with biopsies revealing corresponding glomerular lesions of minimal change disease and focal and segmental glomerulosclerosis. CONCLUSIONS: Our case series demonstrates that AKI from immune checkpoint inhibitors has a variable presentation that may require an individualized treatment approach. Further studies are needed to identify biomarkers that may help identify those at risk and guide the management of this condition.

AKI-Pro score for predicting progression to severe acute kidney injury or death in patients with early acute kidney injury after cardiac surgery.

BACKGROUND: No reliable clinical tools exist to predict acute kidney injury (AKI) progression. We aim to explore a scoring system for predicting the composite outcome of progression to severe AKI or death within seven days among early AKI patients after cardiac surgery. METHODS: In this study, we used two independent cohorts, and patients who experienced mild/moderate AKI within 48 h after cardiac surgery were enrolled. Eventually, 3188 patients from the MIMIC-IV database were used as the derivation cohort, while 499 patients from the Zhongshan cohort were used as external validation. The primary outcome was defined by the composite outcome of progression to severe AKI or death within seven days after enrollment. The variables identified by LASSO regression analysis were entered into logistic regression models and were used to construct the risk score. RESULTS: The composite outcome accounted for 3.7% (n = 119) and 7.6% (n = 38) of the derivation and validation cohorts, respectively. Six predictors were assembled into a risk score (AKI-Pro score), including female, baseline eGFR, aortic surgery, modified furosemide responsiveness index (mFRI), SOFA, and AKI stage. And we stratified the risk score into four groups: low, moderate, high, and very high risk. The risk score displayed satisfied predictive discrimination and calibration in the derivation and validation cohort. The AKI-Pro score discriminated the composite outcome better than CRATE score, Cleveland score, AKICS score, Simplified renal index, and SRI risk score (all P < 0.05). CONCLUSIONS: The AKI-Pro score is a new clinical tool that could assist clinicians to identify early AKI patients at high risk for AKI progression or death.