Tubular Epithelial Cells Research Articles

The Role of Urinary Extracellular Vesicles in Kidney Cancer: Diagnostic and Therapeutic Potential

Renal cancer ranks as the 14th most common cancer globally, with renal cell carcinoma (RCC) being the primary variant, arising from renal tubular epithelial cells; clear cell RCC constitutes about 80% of cases. Despite their limitations, surgery and targeted therapy remain the mainstays of RCC treatment. Regardless of advancements in RCC research, substantial obstacles continue to exist, such as delayed diagnosis, advanced distant metastasis, and drug resistance. As urine is an easily accessible biofluid, the identification of EVs has paved the way for novel biomarker research. Urinary extracellular vesicles (uEVs) are a novel source of biomarkers with potential applications in cancer detection and management, utilizing a less invasive approach. New data indicate that uEVs are crucial in several areas of RCC, containing tumor development, metastasis, immune evasion, and response to drugs. These vesicles facilitate intercellular communication by transporting a variety of bioactive substances, including RNA, DNA, proteins, and lipids, and are released into the extracellular space by the majority of cell types. uEVs RNAs and proteins are presently being investigated for their possible application as diagnostic biomarkers for different types of kidney cancer. This review summarizes the most recent research examining the potential of uEVs cargo as a biomarker for the diagnosis, prognosis, and treatment of renal cancer.

Comprehensive analysis and validation of TP73 as a biomarker for calcium oxalate nephrolithiasis using machine learning and in vivo and in vitro experiments.

Calcium oxalate (CaOx) nephrolithiasis constitutes approximately 75% of nephrolithiasis cases, resulting from the supersaturation and deposition of CaOx crystals in renal tissues. Despite their prevalence, precise biomarkers for CaOx nephrolithiasis are lacking. With advances in high-throughput sequencing, we aimed to identify biomarkers of CaOx nephrolithiasis by combining twoCaOx nephrolithiasis datasets (GSE73680 and GSE117518). Utilizing weighted gene co-expression network analysis (WGCNA) and four machine learning, we identified six hub genes (DLK2, BHLHA15, C12orf5, ICMT, LOXHD1, and TP73) as potential biomarkers. Additionally, CIBERSORT immune infiltration analysis suggested that these core genes may influence immune cell recruitment and infiltration in CaOx nephrolithiasis. Then, TP73 emerged as a significant hub gene in CaOx nephrolithiasis via receiver operating characteristic (ROC) analysis (AUC = 0.885). Furthermore, the role of TP73 was validated in CaOx nephrolithiasis rat models induced by 1% ethylene glycol, as well as clinical samples and renal tubular epithelial cell models treated with 1mM oxalate. Immunohistochemistry, RNA-Sequencing, and RT-qPCR experiments demonstrated an increased expression of TP73 in CaOx nephrolithiasis rat models and clinical samples. After transfection with TP73 lentivirus, CCK-8 assays suggested that TP73 could inhibit the proliferation of HK-2 and NRK-52E cells. In oxalate-induced cell models, dihydroethidium staining and flow cytometry apoptosis assays indicated that TP73 could enhance ROS levels and cell apoptosis. In summary, our study preliminarily identified TP73 as a diagnostic biomarker and elucidated the promoting role of TP73 in CaOx nephrolithiasis, providing a deeper understanding of the clinical diagnosis and pathogenesis.

Nanoparticle Transport in Proximal Tubules with Rhabdomyolysis‐Induced Necrosis

AbstractRenal‐clearable engineered nanoparticles are being explored for their potential to deliver therapeutic agents for kidney disease treatment. A fundamental understanding of how these nanoparticles accumulate in diseased kidneys at the cellular level is essential to enhance their effectiveness and minimize side effects on adjacent healthy tissues. Herein, we report that the accumulation of glutathione‐coated, near‐infrared emitting gold nanoparticles (GS‐AuNPs) correlates strongly with the necrotic stages of injured proximal tubular cells. Using a rhabdomyolysis‐induced acute kidney injury (AKI) mouse model, we observed that GS‐AuNPs were significantly accumulated in the extracellular lumen of proximal tubular epithelial cells (PTECs) at advanced necrotic stage, where cellular debris and released intracellular contents impeded their clearance. In contrast, during early necrosis, GS‐AuNPs were still cleared through the unobstructed lumen. Additionally, intracellular uptake of GS‐AuNPs was significantly reduced across all necrotic stages. These findings underscore the need for new strategies to design nanoparticles that can effectively target and be taken up by the diseased tubular cells before extensive necrosis occurs; so that nanoparticle‐mediated drug delivery for kidney disease treatment can be achieved with desired efficacy and precision.

A novel role of peroxiredoxin 2 in diabetic kidney disease progression by activating the classically activated macrophages.

Diabetic kidney disease (DKD) is the main cause of deaths due to diabetes mellitus (DM). Due to the complexity of its onset, it is difficult to achieve accurate prevention and treatment. The classically activated macrophage (M1) polarization is a crucial proinflammatory mechanism of DKD, while the interaction and cascade effects of oxidative stress and inflammatory response remain to be elucidated. A urine proteomic analysis of patients with DM indicated that peroxiredoxin 2 (PRDX2) had the higher abundance in DKD. We recently found that PRDX of parasitic protozoa Entamoeba histolytica, which was similar to human PRDX2 in amino acid sequence and spatial structure, could activate the inflammatory response of macrophages through toll-like receptor 4 (TLR4). Hence, our study was designed to explore the role of PRDX2 in chronic inflammation during DKD. Combined with in vivo and in vitro experiments, results showed that the PRDX2 was positively correlated with DKD progression and upregulated by high glucose or recombinant tumor necrosis factor-α in renal tubular epithelial cells; Besides, recombinant PRDX2 could promote M1 polarization of macrophages, and enhance the migration as well as phagocytic ability of macrophages through TLR4. In summary, our study has explored the novel role of PRDX2 in DKD to provide a basis for further research on the diagnosis and treatment of DKD.

Nanoparticle Transport in Proximal Tubules with Rhabdomyolysis-Induced Necrosis.

Renal-clearable engineered nanoparticles are being explored for their potential to deliver therapeutic agents for kidney disease treatment. A fundamental understanding of how these nanoparticles accumulate in diseased kidneys at the cellular level is essential to enhance their effectiveness and minimize side effects on adjacent healthy tissues. Herein, we report that the accumulation of glutathione-coated, near-infrared emitting gold nanoparticles (GS-AuNPs) correlates strongly with the necrotic stages of injured proximal tubular cells. Using a rhabdomyolysis-induced acute kidney injury (AKI) mouse model, we observed that GS-AuNPs were significantly accumulated in the extracellular lumen of proximal tubular epithelial cells (PTECs) at advanced necrotic stage, where cellular debris and released intracellular contents impeded their clearance. In contrast, during early necrosis, GS-AuNPs were still cleared through the unobstructed lumen. Additionally, intracellular uptake of GS-AuNPs was significantly reduced across all necrotic stages. These findings underscore the need for new strategies to design nanoparticles that can effectively target and be taken up by the diseased tubular cells before extensive necrosis occurs; so that nanoparticle-mediated drug delivery for kidney disease treatment can be achieved with desired efficacy and precision.

Activating PPARβ/δ-Mediated Fatty Acid β-Oxidation Mitigates Mitochondrial Dysfunction Co-induced by Environmentally Relevant Levels of Molybdenum and Cadmium in Duck Kidneys.

Cadmium (Cd) and high molybdenum (Mo) pose deleterious effects on health. Prior studies have indicated that exposure to Mo and Cd leads to damage in duck kidneys, but limited studies have explored this damage from the perspective of fatty acid metabolism. In this study, 40 healthy 8-day-old ducks were randomly assigned to four groups and fed a basic diet containing Cd (4mg/kg Cd) or Mo (100mg/kg Mo) or both. Kidney tissues were harvested on the 16th week. Results demonstrated that Cd and/or Mo inhibited mitochondrial fatty acid β-oxidation and disrupted mitochondrial dynamics, along with significant suppression of peroxisome proliferator-activated receptor β/δ (PPARβ/δ) protein in duck kidneys. In vitro study, duck renal tubular epithelial cells were exposed for 12h to either Mo (480μM Mo), Cd (2.5μM Cd), and GW0742 (0.3μM, a potent agonist of PPARβ/δ) alone or in combination. The results demonstrated that Cd and/or Mo led to marked fatty acid oxidation deficiency and mitochondrial dysfunction and that PPARβ/δ protein was involved in the process. Altogether, this study found that activating PPARβ/δ-mediated fatty acid β-oxidation mitigates mitochondrial dysfunction co-induced by Mo and Cd in duck kidneys.

Ulinastatin attenuates renal fibrosis by regulating AMPK/HIF-1α signaling pathway-mediated glycolysis.

Renal fibrosis is a common outcome of chronic kidney diseases and glycolysis drives the development of renal fibrosis in damaged kidneys. Ulinastatin (UTI) is a broad-spectrum protease inhibitor with anti-inflammatory and antioxidant properties with anti-fibrosis effects. In this study, we aimed to verify whether UTI could exert anti-renal fibrosis effects by inhibiting glycolysis and explored the potential mechanisms. Renal fibrosis was induced in mice via unilateral ureteral obstruction (UUO). Transforming growth factor-β1 stimulates human kidney proximal tubular epithelial cells to undergo fibrotic changes. Histopathological staining was used to observe the pathological changes in the kidneys. The levels of fibrosis biomarkers, glycolytic enzymes, and key signaling molecules were determined using gene and protein assays. Cellular energy metabolism was measured using Seahorse XF24 analyzer. Modulated the activity of adenylate-activated protein kinase (AMPK) and hypoxia-inducible factor-1α (HIF-1α) to confirm that AMPK can regulate HIF-1α-mediated glycolysis. Furthermore, UTI and AMPK knockdown were combined to verify whether UTI could attenuate glycolysis via the AMPK pathway. UTI pretreatment improved UUO-induced renal injury and fibrosis. The expression of fibrosis biomarkers and glycolytic enzymes was reduced by UTI at both mRNA and protein levels. UTI treatment decreased the rate of glycolysis and the production of glycolytic intermediates in fibrotic cells and tissues. Furthermore, AMPK can regulate HIF-1α-mediated glycolysis in renal tubular epithelial cells. Finally, the attenuation of glycolysis by UTI was related to AMPK/HIF-1α pathway, and this effect was inhibited by knockdown AMPK. UTI can effectively alleviate renal fibrosis, which may be partly attributed to the reduction of glycolysis by regulating AMPK/HIF-1α pathway.

VEGFC Overexpression in Kidney Progenitor Cells Is a Model of Renal Lymphangiectasia.

Lymphangiogenesis is believed to be a protective response in the setting of multiple forms of kidney injury and mitigates the progression of interstitial fibrosis. To augment this protective response, promoting kidney lymphangiogenesis is being investigated as a potential treatment to slow the progression of kidney disease. As injury-related lymphangiogenesis is driven by signaling from the receptor VEGFR3 (vascular endothelial growth factor receptor 3) in response to the cognate growth factor VEGF (vascular endothelial growth factor)-C released by tubular epithelial cells, this signaling pathway is a candidate for future kidney therapeutics. However, the consequences to kidney development and function to targeting this signaling pathway remain poorly defined. We generated a new mouse model expressing Vegfc under regulation of the nephron progenitor Six2Cre driver strain (Six2Vegfc). Mice underwent a detailed phenotypic evaluation. Whole kidneys were processed for histology and 3-dimensional imaging. Six2Vegfc mice had reduced body weight and kidney function compared with littermate controls. Six2Vegfc kidneys demonstrated large peripelvic fluid-filled lesions with distortion of the pelvicalcyceal system which progressed in severity with age. Three-dimensional imaging showed a 3-fold increase in total cortical vascular density. Histology confirmed a substantial increase in LYVE1+ (lymphatic vessel endothelial hyaluronan receptor-1)/PDPN+ (podoplanin)/VEGFR3+ lymphatic capillaries extending alongside EMCN+ (endomucin) peritubular capillaries. There was no change in EMCN+ peritubular capillary density. Kidney lymphatic density was robustly increased in the Six2Vegfc mice. There were no changes in peritubular blood capillary density despite these endothelial cells also expressing VEGFR3. The model resulted in malformation of the lymphatic hilar plexus, resulting in severe hydronephrosis that resembled a human condition termed renal lymphangiectasia. This study defines the vascular consequences of augmenting VEGFC signaling during kidney development and provides new insight into human renal lymphatic malformations.

Cell Division Cycle 42 Improves Renal Functions, Fibrosis, Th1/Th17 Infiltration and Inflammation to Some Degree in Diabetic Nephropathy.

Our two previous studies observed that cell division cycle 42 (CDC42) was lower and correlated with improved renal function and inflammation in diabetic nephropathy (DN) patients, and CDC42 inhibited renal tubular epithelial cell fibrosis and inflammation under high glucose condition. Sequentially, this current study aimed to investigate the effect of CDC42 on improving renal function, fibrosis, and inflammation in DN mice, and its interaction with T cell receptor (TCR) related pathways. Mice were treated by streptozotocin to construct early-stage DN model, then transfected with CDC42 overexpression adenovirus, followed by simultaneous treatment of LY294002 (PI3K/AKT inhibitor) and CI-1040 (ERK inhibitor), respectively. CDC42 reduced blood glucose, creatinine, and 24h urine protein in DN mice, but only showed a tendency to decrease blood urea nitrogen without statistical significance. Hematoxylin&eosin staining revealed that CDC42 descended the glomerular volume, basement membrane thickness, and inflammatory cell infiltration in kidney. Meanwhile, CDC42 lowered fibronectin, TGF-β1, and Collagen I expressions in kidney, but not decreased α-SMA significantly. Besides, CDC42 decreased T-helper (Th) 1 and Th17 cells in kidney, and reduced serum IFN-γ, IL-1β, IL-17A, and TNF-α but not IL-6. Regarding TCR-related pathways, CDC42 activated AKT and ERK pathways but not JNK pathway. However, the treatment of LY294002 and CI-1040 had limited effect on attenuating CDC42's functions on renal function and fibrotic markers. CDC42 improves renal functions, fibrosis, Th1/Th17 infiltration and inflammation to some degree in DN mice, these functions may be independent to AKT and ERK pathways.

Clinical, histological, molecular, and toxicokinetic renal outcomes of per-/polyfluoroalkyl substances (PFAS) exposure: Systematic review and meta-analysis.

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals present in the environment that can negatively affect health. Kidney is the major target organ of PFAS exposure, yet the renal impact of PFAS is not completely understood. Here we review the effects of PFAS exposure on kidney health to identify gaps in our understanding and mark potential avenues for future research. PubMed and SCOPUS databases were searched for studies that examined the association between PFAS exposure and kidney-related outcomes. We included all epidemiological, animal, and cell studies and categorized outcomes into four categories: clinical, histological, molecular and toxicokinetic. We identified 169 studies, including 51 on clinical outcomes, 28 on histological changes, 42 on molecular mechanisms, and 68 on toxicokinetics. Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) exposure were associated with kidney dysfunction, chronic kidney diseases, and increased risk of kidney cancer. Various histological changes were reported, especially in tubular epithelial cells, and the etiology of PFAS-induced kidney injury included various molecular mechanisms. Although PFOA and PFOS are not considered genotoxic, they exhibit several characteristics of carcinogens. Toxicokinetics of PFOA and PFOS differed significantly between species, with renal elimination influenced by various factors such as sex, age, and structure of the compound. Evidence suggests that PFAS, especially PFOA and PFOS, negatively affects kidney health, though gaps in our understanding of such effects call for further research.

Metabolic Chaos in Kidney Disease: Unraveling Energy Dysregulation

Background: Acute kidney injury (AKI) and chronic kidney disease (CKD) share a fundamental disruption: metabolic dysfunction. Methods: A literature review was performed to determine the metabolic changes that occur in AKI and CKD as well as potential therapeutic targets related to these changes. Results: In AKI, increased energy demand in proximal tubular epithelial cells drives a shift from fatty acid oxidation (FAO) to glycolysis. Although this shift offers short-term support, it also heightens cellular vulnerability to further injury. As AKI progresses to CKD, metabolic disruption intensifies, with both FAO and glycolysis becoming downregulated, exacerbating cellular damage and fibrosis. These metabolic alterations are governed by shifts in gene expression and protein signaling pathways, which can now be precisely analyzed through advanced omics and histological methods. Conclusions: This review examines these metabolic disturbances and their roles in disease progression, highlighting therapeutic interventions that may restore metabolic balance and enhance kidney function. Many metabolic changes that occur in AKI and CKD can be utilized as therapeutic targets, indicating a need for future studies related to the clinical utility of these therapeutics.

Monocyte/macrophage pyroptosis and C5b-9-induced cyst enlargement in Pkd1-/- mice.

The levels of C5b-9, terminal products of complement activation, were significantly elevated in autosomal dominant polycystic kidney disease (ADPKD). However, the precise mechanisms by which C5b-9 facilitates cyst growth remain incompletely elucidated. Three groups of chronic-onset Pkd1-/- mice were established: one group received intravenous injections of 0.5 mg/kg C5b-9, another was administered 1.0 mg/kg monoclonal anti-C9 antibodies, and a control group received 1 mg/kg IgG isotype control (IC). All treatments were administered biweekly for two months (postnatal day [PD] 180-240). Renal macrophages from distinct subsets were sorted using fluorescence-activated cell sorting (FACS). To deplete macrophages, liposome clodronate (LC) was injected intraperitoneally. Sublethal irradiation followed by bone marrow (BM) reconstruction was performed in Pkd1-/- mice to evaluate the role of BM-derived macrophages (BMDMs) in ADPKD progression. (1) In vitro, sublytic C5b-9 did not affect the viability of renal tubular epithelial cells (RTECs), but significantly induced M1-like polarization and pyroptosis of BMDMs. (2) In vivo, C5b-9 notably triggered pyroptosis of Ly6C+ monocytes and a reduction in circulating monocyte numbers as cysts enlarged. (3) Residual Ly6C+ monocytes infiltrated renal tissues and differentiated into Ly6C+ macrophages, which exhibited a greater susceptibility to pyroptosis compared to Ly6C- macrophages. (4) Although limited evidence has recently suggested that Ly6C- monocytes may also be affected by C5b-9, upregulation of CCR2 in Ly6C- macrophages was observed in C5b-9-treated Pkd1-/- mice, implying that Ly6C- monocytes could represent a significant source of M2 macrophages. C5b-9 infusion promoted RTEC proliferation by inducing pyroptosis of Ly6C+ monocytes/macrophages, contributing to progressive cyst enlargement in chronic-onset PKD mice.

New Therapeutic Method for Alleviating Damage of Acute Kidney Injury Through BCL-2 Gene Promoter I-Motif

Acute kidney injury (AKI) is a global public health problem with its pathogenesis not fully understood. Excessive apoptosis of renal tubular epithelial cells is an important feature of AKI patients, and therefore an anti-apoptotic approach could be used in the treatment for AKI. Up-regulation of B-cell lymphoma-2 (BCL-2) gene and protein has been found to be correlated with anti-apoptosis of cells. It has been found that the presence of the C-rich sequence on the upstream region of the BCL-2 gene promoter could form DNA secondary i-motif structure, and its stabilization by small molecules could up-regulate gene transcription and translation. In the present study, we constructed AKI models through folic acid (FA) induction. With these in vitro and in vivo models, we demonstrated that the acridone derivative A22 could up-regulate the expression of BCL-2 by targeting its gene promoter i-motif to reduce renal tubular epithelial cell apoptosis and improve renal function in many ways. A22 could alleviate FA-induced oxidative stress injury, inflammatory response, and endoplasmic reticulum stress in mouse kidneys. Our results provided a potentially new anti-apoptotic approach for the treatment of early stages of AKI. Our employed model focused on its short-term effect on AKI, while its long-term efficacy and safety, particularly regarding the regeneration of renal tubular epithelial cells, require further investigation before clinical application. This study further demonstrated that promoter i-motif could be targeted for up-regulating BCL-2 expression for the treatment of important diseases caused by excessive apoptosis.

Single-cell RNA-sequencing of BK polyomavirus replication in primary human renal proximal tubular epithelial cells identifies specific transcriptome signatures and a novel mitochondrial stress pattern.

BK polyomavirus (BKPyV) contributes to premature renal failure in 10%-20% of kidney transplant recipients. Current treatment relies on reducing immunosuppression to regain BKPyV-specific immune control. Subsequently, declining allograft function may result from persisting viral cytopathology, BKPyV-specific immune reconstitution, or alloimmunity/rejection, all being poorly distinguishable by current histological or molecular approaches. To reduce the complexity encountered in BKPyV-replicating kidneys, we analyzed differentially expressed genes (DEGs) in primary human renal proximal tubular epithelial cells at 24 and 48 h post-infection (hpi) using single-cell RNA-sequencing (10x-Genomics-3´ kit). At 24 hpi, viral transcript reads predominantly mapped to the early viral gene region (EVGR) and shifted to >100-fold higher late viral gene region (LVGR) levels at 48 hpi, matching the sequential bi-directional viral protein expression from the circular double-stranded BKPyV-DNA genome. Besides expected coverage "hills" at viral 3´-poly-A sites, unexpected "spike" and "pulse" reads resulted from off-target TSO priming. "Spike" and "pulse" patterns were rare for the mostly unidirectional reads mapping to the circular mitochondrial genome. Bioinformatic curation removed "spikes" and "pulses" and reclassified 10% of DEGs in renal proximal tubular epithelial cells (RPTECs). Up-regulated gene ontologies included S and G2/M phase, double-stranded DNA repair, proximal tubulopathy, and renal tubular dysfunction, whereas allograft rejection, antigen presentation, innate immunity, translation, and autophagy were down-regulated. BKPyV-LVGR expression induced a novel mitochondrial cell stress pattern consisting of discordant up-regulation and down-regulation of mitochondria-encoded and nucleus-encoded mitochondrial genes, respectively. We explored which top-scoring gene sets of late-phase BKPyV-replicating RPTECs can identify BKPyV-associated nephropathy in kidney transplant biopsies. The results should facilitate distinguishing BKPyV-associated pathology from other entities in kidney transplant biopsies.IMPORTANCEBK polyomavirus (BKPyV) infects more than 90% of the general population and then persists in the reno-urinary tract. Subsequently, low-level urinary shedding is seen in 10% of healthy BKPyV-seropositive persons, indicating that BKPyV replication occurs despite the presence of virus-specific cellular and humoral immunity. Notably, transplantation of donor kidneys with low-level BKPyV replication is a risk factor for progression to high-level BKPyV viruria, new-onset BKPyV-DNAemia and biopsy-proven BKPyV nephropathy. Here, we identify a short list of robust up- and down-regulated nucleus-encoded differentially expressed genes potentially allowing to discriminate viral from allograft immune damage. By carefully curating viral and mitochondrial transcriptomes, we identify a novel virus-associated mitochondrial stress pattern of up-regulated mitochondria-encoded and down-regulated nucleus-encoded mitochondrial transcripts which heralds the BKPyV-agnoprotein-mediated immune escape by breakdown of the mitochondrial membrane potential and network and mitophagy. The results may prove useful when assessing the role of BKPyV replication in kidney transplant patients with suspected acute rejection and/or BKPyV nephropathy.

Inhibiting SIRT2 Attenuates Sepsis-Induced Acute Kidney Injury via FOXO1 Acetylation-Mediated Autophagy Activation.

Sepsis-associated acute kidney injury (SAKI), a common complication in intensive care units (ICUs), is linked to high morbidity and mortality. Sirtuin 2 (SIRT2), an NAD+-dependent deacetylase, has been shown to have distinct effects on autophagy regulation compared to other sirtuins, but its role in SAKI remains unclear. This study explored the potential of SIRT2 as a therapeutic target for SAKI. We found that inhibition of SIRT2 with the antagonist AGK2 improved the survival of septic mice. SIRT2 inhibition reduced kidney injury, as indicated by lower levels of KIM-1, NGAL, serum creatinine (Scr), blood urea nitrogen (BUN), and proinflammatory cytokines following cecal ligation and puncture (CLP). Pretreatment with AGK2 in septic mice increased autophagosome and autolysosome formation in renal tubular epithelial cells (RTECs) and upregulated LC3 II expression in the renal cortex. Consistent with in vivo findings, SIRT2 gene silencing promoted autophagy in LPS-treated HK-2 cells, whereas SIRT2 overexpression inhibited it. Mechanistically, SIRT2 inhibition increased FOXO1 acetylation, inducing its nuclear-to-cytoplasmic translocation, which promoted kidney autophagy and alleviated SAKI. Our study suggests SIRT2 as a potential target for SAKI therapy.

Observation of neutrophil extracellular traps in the development of diabetic nephropathy using diabetic murine models.

Diabetic nephropathy (DN) is a progressive complication among patients with diabetes and the most common cause of end-stage kidney disease. Neutrophil extracellular traps (NETs) are known to play a role in kidney disease, thus this study aimed to determine their role in the development of diabetic kidney disease using diabetic murine models. Protein and histological analyses revealed that db/db mice and streptozotocin DN models expressed no significant NET-related proteins, myeloperoxidase, citrullinated histone H3 (citH3), neutrophil elastase, and lymphocyte antigen 6 complex locus G6D (Ly6G). However, the inflamed individuals in the DN model showed that citH3 and Ly6G were highly deposited in the renal system based on immunohistochemistry images. In vitro, NET treatment did not induce apoptosis in glomerular endothelial and renal tubular epithelial cells. NET inhibition by DNase administration demonstrated no significant changes in cell apoptosis. NET-related proteins were only expressed in the DN model with tubulointerstitial inflammation. Our study revealed that NETs are only induced in mice with hyperglycemia-induced inflammation.

CXCL5 inhibition ameliorates acute kidney injury and prevents the progression from acute kidney injury to chronic kidney disease.

Acute kidney injury (AKI) increases the risk of chronic kidney disease (CKD). CXCL5 is upregulated in kidney diseases. We aimed to investigate the direct effect of CXCL5 on the pathology of AKI. Serum and renal expression of CXCL5 were increased in animals with renal ischemia-reperfusion injury or unilateral ureteral obstruction. CXCL5-knockout mice exhibited reduced systemic oxidative stress and preserved renal function in the acute and chronic phases of AKI, as evidenced by reductions in serum BUN and creatinine levels, the urinary albumin-to-creatinine ratio, and the kidney-to-body weight ratio. CXCL5-knockout mice improved AKI-induced tubular injury and fibrosis, reduced renal macrophage infiltration, and reduced expression of NADPH oxidase and inflammatory and fibrotic proteins. CXCL5 activated p47 to upregulate ROS generation and induce cellular damages through CXCR2. CXCL5 knockdown exerted antioxidative, anti-inflammatory, anti-fibrotic, and anti-apoptotic effects on hypoxia-reoxygenation-stimulated renal proximal tubular epithelial cells. Clinical data indicated elevated circulating and renal CXCL5 in CKD patients, and renal CXCL5 was correlated with increased renal fibrosis and decreased estimated glomerular filtration rate. Altogether, CXCL5 levels increased in experimental AKI and clinical CKD, and in vivo and in vitro CXCL5 inhibition may reduce acute tubular injury and prevent the subsequent progression from AKI to CKD.

Sirtuin1 Suppresses Calcium Oxalate Nephropathy via Inhibition of Renal Proximal Tubular Cell Ferroptosis Through PGC-1α-mediated Transcriptional Coactivation.

Calcium oxalate (CaOx) crystals induce renal tubular epithelial cell injury and subsequent nephropathy. However, the underlying mechanisms remain unclear. In the present study, single-cell transcriptome sequencing is performed on kidney samples from mice with CaOx nephrocalcinosis. Renal proximal tubular cells are identified as the most severely damaged cell population and are accompanied by elevated ferroptosis. Further studies demonstrated that sirtuin1 (Sirt1) effectively reduced ferroptosis and CaOx crystal-induced kidney injury in a glutathione peroxidase 4 (GPX4)-dependent manner. Mechanistically, Sirt1 relies on peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α) to promote resistance to ferroptosis in the tubular epithelium, and PGC-1α can recruit nuclear factor erythroid 2-related factor 2 (NRF2) to the promoter region of GPX4 and co-activate GPX4 transcription. This work provides new insight into the mechanism of CaOx crystal-induced kidney injury and identifies Sirt1 and PGC-1α as potential preventative and therapeutic targets for crystal nephropathies.

Nuclear translocation of SIRT4 mediates deacetylation of U2AF2 to modulate renal fibrosis through alternative splicing-mediated upregulation of CCN2.

TGF-β stimulates CCN2 expression which in turn amplifies TGF-β signaling. This process promotes extracellular matrix production and accelerates the pathological progression of fibrotic diseases. Alternative splicing plays an important role in multiple disease development, while U2 small nuclear RNA auxiliary factor 2 (U2AF2) is an essential factor in the early steps of pre-mRNA splicing. However, the molecular mechanism underlying abnormal CCN2 expression upon TGF-β stimulation remains unclear. This study elucidates that SIRT4 acts as a master regulator for CCN2 expression in response to TGF-β by modulating U2AF2-mediated alternative splicing. Analyses of renal biopsy specimens from patients with CKD and mouse fibrotic kidney tissues revealed marked nuclear accumulation of SIRT4. The tubulointerstitial fibrosis was alleviated by global deletion or tubular epithelial cell (TEC)-specific knockout of Sirt4, and aggravated by adeno-associated virus-mediated SIRT4 overexpression in TECs. Furthermore, SIRT4 was found to translocate from the mitochondria to the cytoplasm through the BAX/BAK pore under TGF-β stimulation. In the cytoplasm, TGF-β activated the ERK pathway and induced the phosphorylation of SIRT4 at Ser36, which further promoted its interaction with importin α1 and subsequent nuclear translocation. In the nucleus, SIRT4 was found to deacetylate U2AF2 at K413, facilitating the splicing of CCN2 pre-mRNA to promote CCN2 protein expression. Importantly, exosomes containing anti-SIRT4 antibodies were found to effectively mitigate the UUO-induced kidney fibrosis in mice. Collectively, these findings indicated that SIRT4 plays a role in kidney fibrosis by regulating CCN2 expression via the pre-mRNA splicing.

Nuclear translocation of SIRT4 mediates deacetylation of U2AF2 to modulate renal fibrosis through alternative splicing-mediated upregulation of CCN2

TGF-β stimulates CCN2 expression which in turn amplifies TGF-β signaling. This process promotes extracellular matrix production and accelerates the pathological progression of fibrotic diseases. Alternative splicing plays an important role in multiple disease development, while U2 small nuclear RNA auxiliary factor 2 (U2AF2) is an essential factor in the early steps of pre-mRNA splicing. However, the molecular mechanism underlying abnormal CCN2 expression upon TGF-β stimulation remains unclear. This study elucidates that SIRT4 acts as a master regulator for CCN2 expression in response to TGF-β by modulating U2AF2-mediated alternative splicing. Analyses of renal biopsy specimens from patients with CKD and mouse fibrotic kidney tissues revealed marked nuclear accumulation of SIRT4. The tubulointerstitial fibrosis was alleviated by global deletion or tubular epithelial cell (TEC)-specific knockout of Sirt4, and aggravated by adeno-associated virus-mediated SIRT4 overexpression in TECs. Furthermore, SIRT4 was found to translocate from the mitochondria to the cytoplasm through the BAX/BAK pore under TGF-β stimulation. In the cytoplasm, TGF-β activated the ERK pathway and induced the phosphorylation of SIRT4 at Ser36, which further promoted its interaction with importin α1 and subsequent nuclear translocation. In the nucleus, SIRT4 was found to deacetylate U2AF2 at K413, facilitating the splicing of CCN2 pre-mRNA to promote CCN2 protein expression. Importantly, exosomes containing anti-SIRT4 antibodies were found to effectively mitigate the UUO-induced kidney fibrosis in mice. Collectively, these findings indicated that SIRT4 plays a role in kidney fibrosis by regulating CCN2 expression via the pre-mRNA splicing.