Kidney International

Abstract Background. Tuberous Sclerosis Complex (TSC) is caused by inactivating mutations in either the TSC1 or TSC2 genes, leading to activation of the mammalian target of rapamycin complex 1 (mTORC1) and unhindered cell growth and proliferation. The epithelium of TSC renal cysts in both mice and humans is composed of proliferating A-intercalated (A-IC) cells. The exact molecular mechanism of kidney cystogenesis in TSC remains speculative. Hypothesis.Superfluous cell proliferation driven by mTORC1 activation increases metabolic demand, causing oxidative stress and excess reactive oxygen species. If unchecked, this overwhelms antioxidant defenses and causes cell death. In TSC kidney cystogenesis, Nuclear Factor Erythroid 2-Related Factor 2 (NFE2L2), also known as NRF2, serves as the "master regulator" of antioxidant and anti-inflammatory responses, enabling cells to survive and proliferate by clearing the toxic environment and supplying nutrients and fuel. Results. RNA-seq and proteomics, along with western blot analysis, showed robust downregulation of Fumarate Hydrase 1 (FH1) and upregulation of NRF2, STAT3, and HIF1 in kidneys from TSC mice with moderate or heavy cyst burden. Confocal microscopy and immunohistochemical staining on kidney sections, and/or western blot studies on nuclear and cytoplasmic fractions, showed nuclear localization of NRF2, STAT3, and HIF1. In cyst-lining cells in TSC mouse models, FH1 downregulation was associated with inactivating succination of KEAP1 in immunoprecipitation experiments, promoting NRF2 nuclear localization in A-IC cells lining the cysts. NRF2 nuclear localization was associated with ectopic induction of the glutamine transporter SLC38A3 (SNAT3) on the basolateral membrane and activation of the NH3/NH4+ transporters RHCG and RHBG in A-IC cells lining the cysts. Twenty-four h urine NH3/NH4+ excretion rates increased significantly in Tsc1 KO vs. WT mice. The activation of NRF2, STAT3, and HIF1 can drive metabolic reprogramming and activate survival genes in proliferating cells. Together with SLC38A3 induction and upregulation of other glutamine and NH3/NH4+ transporters, these factors activate glutaminolysis and aerobic glycolysis, supplying nutrients to proliferating cystic epithelial cells and supporting cyst expansion in TSC. Consistent with this central role for glutaminolysis in kidney cystic epithelium and TSC cystogenesis, we find a significant reduction in kidney cyst burden in Tsc1 KO mice on a glutamine-free diet. Conclusions. NRF2 plays a critical role in antioxidant defense. Along with STAT3 and HIF1, NRF2 is a key player in metabolic reprogramming through glutaminolysis, which supplies nutrients to proliferating cystic epithelial cells and supports cyst expansion in TSC. These findings suggest that inhibiting or inactivating NRF2, alone or in combination with HIF1 or STAT3, may represent a potential treatment strategy for kidney lesions in TSC.

Abstract Endothelial cell (EC) injury is central to the pathogenesis of various renal disorders, highlighting the critical importance of vascular repair for restoring organ health. However, due to limited access to human tissue during active regeneration, the exact reparative processes remain largely unknown. This study aimed to investigate regeneration mechanisms specifically within the glomerular microvasculature by utilizing a selective endothelial cell injury (ECI) model in mice.Lineage tracing identified the origin of regenerating ECs. To uncover the transcriptional dynamics driving these reparative changes, we combined single-cell RNA sequencing and Xenium spatial transcriptomics (ST), mapping distinct glomerular EC (gEC) subpopulations across different phases of injury and recovery. Apold1 emerged as a key regulatory candidate within this process. To functionally validate this gene's specific role during the regenerative phase, Apold1-deficient (Apold1-/-) mice underwent the ECI model. After showing that gECs regenerate primarily from local, pre-existing renal ECs, our transcriptomic analysis identified 10 distinct gEC subpopulations and revealed a complex temporal pattern of regeneration. This process begins with the expression of genes associated with inflammation, followed sequentially by endothelial cell (EC) migration, the activation of immediate early genes, vascular remodeling and cellular proliferation. Within this dynamic process, the EC-specific gene Apold1 was identified as a key regulatory candidate. Apold1-/- mice exhibited impaired endothelial regeneration, characterized by increased endothelial activation and greater immune cell infiltration seven days post-ECI. To our knowledge, this is the first study to elucidate the spatiotemporal mechanisms of glomerular endothelial cell regeneration. By identifying local gECs as the primary source of repair, and stablishing the change in their expression pattern during regeneration, as well as identifying Apold1 as an intrinsic regulator, we have laid the groundwork for future research on renal microvascular disorders.

Kidney disease affects over 850 million people and leads to degradation of the kidney cortical compartments and kidney failure. Interstitial fibrosis and tubular atrophy (IFTA) is a universal feature of chronic kidney disease, yet the sequence of tubulointerstitial matrix protein (matrisome) changes that underlie the development and progression of IFTA are not fully understood. In particular, post-translational modifications which may stabilize key matrisome components and result in irreversible and functionally detrimental interstitial fibrosis or tubular basement membrane thickening, have yet to be characterized. Post-translational modifications (e.g., acetylation) have been shown to contribute to kidney diseases, yet they have not been investigated in chronic kidney disease progression. Herein, we established feasibility of matrisome protein quantification in the tubulointerstitium, with concurrent matrisome protein post-translational modification quantification, in archived diagnostic human kidney biopsies, using laser capture microdissection, liquid chromatography tandem mass spectrometry (LC-MS/MS), and bioinformatics analysis. In this pilot study, we focused on two conditions associated with IFTA progression: diabetic nephropathy and kidney transplantation. We examined both healthy and chronically damaged tubulointerstitium in two human kidney biopsies, one representing each condition. We identified signature protein markers of tubulointerstitium (e.g., UMOD, SLC12A1) in abundance, confirming sample composition, and observed uniformity in protein abundance across replicates from the same biopsies. We found increases in certain collagen isoforms (COL1A1, COL6A3) and other ancillary proteins in areas of IFTA. We also successfully quantified post-translational modifications, confirming that hydroxylproline was the most abundant modification in healthy tubulointerstitium from the kidney transplant biopsy, and that hydroxyllysine was also highly abundant and could be confidently quantitated on two collagen isoforms (COL1A1, COL4A2). Lastly, we performed power analysis to determine the required sample size to achieve significant power and false discovery rate. Several proteins exhibited large Hedge effect sizes in the tubulointerstitium (ANPEP, PRODH2), indicating their potential usefulness as fibrosis signatures. Our study is a first step toward comprehensive characterization of tubulointerstitial matrisome changes, including post-translational modifications seen with IFTA progression. Subsequent studies will potentially reveal new molecular markers of key early events in chronic kidney disease progression, and new therapeutic targets for mitigating this process. Data are available via ProteomeXchange identifier PXD079025.

Certain glomerulopathies (GN) feature impaired protein homeostasis in the endoplasmic reticulum (ER) of podocytes. Protein misfolding causing ER stress activates the unfolded protein response (UPR), a protective signaling network. Mesencephalic astrocyte-derived neurotrophic factor (MANF) and ERdj3/DNAJB11 are ER chaperones that may be secreted from cells during the UPR. In rats with membranous nephropathy (MN) and focal segmental glomerulosclerosis (FSGS), secretion of MANF or ERdj3 from podocytes into urine identified glomerular ER stress/UPR activation. We address the biomarker potential of MANF and ERdj3 in human MN and FSGS. Glomerular gene expression of MANF and ERdj3 was increased in human MN and FSGS. Urinary MANF and ERdj3 were increased in proteinuric MN and FSGS compared to MN and FSGS in remission (low proteinuria), as well as other GNs, polycystic kidney disease, hypertension and healthy controls. In individuals with proteinuric MN or FSGS, amounts of urinary MANF and ERdj3 correlated weakly with proteinuria; correlation of MANF with ERdj3 was moderate. Males represented ~60% of persons in each group. eGFR in proteinuric MN and FSGS was >40 ml/min/1.73 m2. In MN, there were no significant differences in urinary MANF and ERdj3 between anti-PLA2R positive and negative individuals. In conclusion, proteinuric MN and FSGS show increased glomerular expression of MANF and ERdj3. High urinary levels of these ER chaperones correlate only weakly with proteinuria. In these GNs, urinary ER chaperones are thus non-invasive biomarkers of glomerular/podocyte ER stress. Such biomarkers may eventually be useful in identifying patients for therapies targeting ER protein misfolding.

Sickle cell disease (SCD) causes heterogeneous mineral imbalances including variable degrees of hypocalcemia. The kidney controls systemic calcium by reabsorbing calcium from the glomerular filtrate via paracellular transport and transcellular transport in the nephron tubules, yet it is unknown whether these processes are modulated by genetic or environmental factors or disrupted in SCD. Using SCD mouse models and single-cell multiomics, we identify the distal convoluted tubule (DCT) as the nephron segment most susceptible to calcium reabsorption dysfunction in SCD, mainly via reduction of calcium buffer protein calbindin 1 (CALB1). We show that CALB1 and its encoding mRNA are decreased in DCT cells in SCD, alongside decreased Klotho (KL)-dependent fibroblast growth factor (FGF) 23 signaling and intracellular calcium signaling. Dietary iron restriction reduces CALB1, KL, and calcium exporter SLC8A1 levels in SCD kidneys. Loss of CALB1 shifts DCT cells toward energy-inefficient glycolysis with the metabolite 2,3-diphosphoglycerate impairing KL-dependent FGF23 signaling to create a feed-forward loop suppressing calcium reabsorption. Analysis of gene expression and protein quantitative trait loci data from kidneys of genetically diverse mice revealed that Calb1 expression levels are highly heritable and co-regulated with Slc8a1, identifying a genetic axis that dictates differential capacities for calcium buffering and trafficking toward blood in the kidney. Together, these findings support a model in which genetic variation, dietary iron status, and FGF23 signaling converge on DCT calcium buffering to reduce renal calcium reabsorption in the SCD kidney. This points to personalized, genotype- and iron-dependent strategies for managing mineral metabolism in SCD patients.

Importance. Plasma phosphorylated tau 217 (p-tau217) is entering clinical use with fixed diagnostic threshold that do not account for kidney function. Chronic kidney disease (defined as estimated glomerular filtration rate (eGFR) below 60 mL/min/1.73 m2), raises plasma p-tau217 concentrations and can produce false positive results. It remains unclear whether milder reductions in kidney function, above the CKD threshold, have the same effect. Objective. To determine whether plasma p-tau217 is elevated with mildly reduced kidney function, above the chronic kidney disease threshold, in adults without neurological disease. Design. Cross-sectional analysis of a cohort enrolled between 2023 and 2025 and biomarker analysis blinded to clinical data. Setting. Two private psychiatric inpatient facilities in Australia. Participants. Adults admitted with psychiatric disorders and free of neurological disease. Exposures. eGFR calculated from serum creatinine using the CKD-EPI 2021 equation. Main Outcomes and Measures. Plasma p-tau217, neurofilament light chain (NfL), and glial fibrillary acidic protein (GFAP), measured on the Simoa platform. Multivariable linear regression compared eGFR groups (< 60, 60 to 90, and [&ge;] 90 mL/min/1.73 m2), adjusted for age, BMI, and sex. Results. Among 180 participants (median age, 50.5 years [IQR, 38.0-61.5]; 94 [52%] female), eGFR was [&ge;] 90 mL/min/1.73 m2 in 106 (59%), 60 to 90 in 61 (34%), and < 60 in 13 (7.2%). Compared with an eGFR [&ge;] 90, plasma p-tau217 was 36% higher in both the 60 to < 90 group ({beta} = 0.42 [95% CI: 0.11, 0.74]; P = .008) and 116% higher in the < 60 group ({beta} = 1.05 [95% CI: 0.43, 1.72]; P = .002). Plasma NfL and GFAP were elevated in the < 60 group but differences in the 60 to < 90 group did not reach significance. Modelled continuously, plasma p-tau217 was 9.5% lower per 10 mL/min/1.73 m2 higher eGFR (95% CI: 3.3%, 15.4%). Conclusions and Relevance. Plasma p-tau217 was elevated in adults with mildly reduced kidney function, above the CKD threshold, in a cohort free of neurological disease. Kidney function across its full range should be incorporated into plasma p-tau217 reference ranges and clinical interpretation to reduce false positive and false negative results.

Protein O-mannosylation in the endoplasmic reticulum (ER) regulates the maturation and function of extracellular proteins, yet the substrate spectrum and biological functions of individual O-mannosyltransferases remain incompletely understood. TMEM260 is an ER-resident O-mannosyltransferase that modifies immunoglobulin-like, plexins, transcription factors (IPT) domains. Here, we identify fibrocystin and fibrocystin-L, encoded by PKHD1 and PKHD1L1, respectively, as novel TMEM260-mediated O-mannosylated proteins. By combining screening of human proteomic datasets with mass spectrometry-based analysis of IPT domains expressed in TMEM260-deficient HEK293 cells, we demonstrate that multiple IPT domains of fibrocystin and fibrocystin-L are modified by TMEM260. Our findings expand the known substrate requirements of TMEM260 by revealing tolerance of substantial sequon variation and demonstrating serine as an alternative acceptor residue within IPT domains. In humans, loss-of-function variants in TMEM260 cause structural heart defects and renal anomalies (SHDRA) syndrome, whereas pathogenic variants in fibrocystin cause autosomal recessive polycystic kidney disease (ARPKD). Notably, patients with SHDRA and ARPKD share overlapping renal phenotypes, suggesting that impaired TMEM260 function may phenocopy aspects of fibrocystin-associated diseases. Given that fibrocystin is a substrate protein for TMEM260-mediated O-mannosylation, these findings raise the possibility that functional impairment of TMEM260 causes aberrant O-mannosylation of fibrocystin. Thereby fibrocystin function might be compromised leading to the renal phenotype observed in patients with TMEM260 mutations. To directly assess the functional relevance of this modification, we expressed recombinant fibrocystin fragments in TMEM260-deficient cells complemented with either wild-type TMEM260 or a catalytically inactive TMEM260 mutant. Further, we investigate the O-mannosylation of the threonine residue directly C-terminal to the ARPKD-associated patient mutation L1407R. Strikingly, substitution of leucine L1407 by the patient-associated arginine residue, completely abolished O-mannosylation of the adjacent threonine, demonstrating that this disease-associated mutation directly disrupts a TMEM260-dependent O-mannosylation site. Together, our findings establish fibrocystin and fibrocystin-L as TMEM260-dependent O-mannosylated proteins and reveal a potential molecular mechanism linking defective TMEM260-mediated O-mannosylation to the renal phenotype of SHDRA, which overlaps with PKHD1-associated ARPKD.

Background: Genomic reassessment may reveal clinically relevant diagnoses in patients with young-onset kidney failure despite established clinical diagnostic labels. We evaluated this approach after excluding clinically apparent polycystic kidney disease (PKD). Methods: Among 1,139 patients receiving maintenance dialysis at participating Japanese facilities, 355 had initiated dialysis at age [&le;]50 years. After excluding 17 patients with clinically apparent PKD, 108 of 338 eligible patients underwent whole-genome sequencing through voluntary, nonrandom enrollment. Analysis included 465 nuclear candidate genes, mitochondrial DNA, and copy-number/structural variants. Clinically concordant diagnoses were adjudicated using integrated clinical and genetic evidence, with a separate pathogenic/likely pathogenic (P/LP)-supported subset. Results: Diagnoses were identified in 10/108 participants (9.3%; 95% confidence interval, 5.1-16.2), comprising seven renal and three systemic/metabolic diagnoses. Nine diagnoses were P/LP-supported (8.3%; 95% confidence interval, 4.4-15.1). The remaining diagnosis was phenotype-based clinical Dent disease associated with a CLCN5 variant of uncertain significance. Diagnoses occurred across diabetic kidney disease, nephrosclerosis, chronic glomerulonephritis, unknown-cause, and other clinical categories. In a post hoc analysis excluding three participants with low target coverage, the integrated and P/LP-supported proportions were 9/105 (8.6%) and 8/105 (7.6%). Six exploratory findings were excluded from both diagnostic numerators. Gitelman syndrome was included as a clinically manifest renal disorder, although its contribution to kidney failure remained uncertain. Conclusions: Integrated genomic assessment can uncover renal and systemic/metabolic diagnoses across conventional labels in young-onset kidney failure after exclusion of clinically apparent PKD. Nonrandom enrollment and variable sequencing coverage limit generalizability and interpretation of negative results.

Background: Noninvasive biomarkers capable of detecting kidney allograft injury and distinguishing rejection from infection remain an important clinical need. Torque teno virus (TTV) reflects host immune status, but its utility in urine has not been well established. We evaluated urinary TTV, total cell-free DNA (cfDNA), cfDNA fragmentation, and BK polyomavirus (BKV) as potential biomarkers of kidney transplant rejection and BK polyomavirus-associated nephropathy (BKPyVAN). Methods: Urine samples from 334 kidney transplant recipients were analyzed in association with kidney biopsies performed within 30 days of sample collection. TTV and cfDNA were measured by multiplex quantitative PCR (qPCR), with a subset analyzed by digital PCR (dPCR), and BKV was quantified by qPCR. Associations with biopsy results were evaluated using group comparisons and nominal logistic regression. Changes associated with outcomes of consecutive biopsies were assessed by matched pairs analysis. Results: Among 544 unique urine samples, the urinary TTV/cfDNA ratio was significantly lower in rejection than in non-rejection samples (P<0.0001). Logistic regression adjusted for demographic factors confirmed an inverse association between the qPCR-derived TTV/cfDNA metric and rejection (adjusted odds ratio per delta Cq, 0.91; 95% CI, 0.88-0.94; P<0.00001). Significant differences were observed for all types of rejection. Association was confirmed by dPCR: higher TTV was associated with lower rejection odds, whereas higher cfDNA was associated with greater rejection odds. A nominal logistic model incorporating dPCR measurements achieved an AUROC of 0.76 (95% CI, 0.69-0.82). Matched pairs analysis showed a significant decrease in TTV/cfDNA when rejection developed and an increase following recovery from rejection, with no significant changes when biopsy status remained unchanged. BKV levels were strongly associated with BKPyVAN. No correlation between TTV and BKV was observed. Nominal logistic regression integrating TTV, cfDNA, and BKV measurements yielded AUROCs of 0.75, 0.97, and 0.73 for rejection, BKPyVAN, and non-rejection, respectively. Conclusions: A reduced urinary TTV/cfDNA ratio is associated with biopsy-defined kidney transplant rejection, and changes in the ratio correlate with transitions in biopsy results. Combined TTV, cfDNA, and BKV measurements showed differential associations with rejection and BKPyVAN, supporting further evaluation as complementary urinary biomarkers.

Nephrotic syndrome, the leading cause of chronic kidney disease worldwide, is associated with injury and eventual loss of podocytes, the specialized epithelial cells that form the final layer of the kidney's filtration apparatus. The progression from injury to loss is largely irreversible. However, some forms of nephrotic syndrome undergo remission, suggesting that injured podocytes may retain a capacity for repair, the structural basis of which remains unknown. Podocytes respond to injury by the stereotypical morphological change known as foot process effacement (FPE), which can be visualized using transmission electron microscopy. Using modified ultrastructure expansion microscopy (U-ExM) protocol combined with super-resolution microscopy, we discovered that injured podocytes exhibit a three-stage progression of FPE maturation, with kinetics determined by the degree of actomyosin contractility. Through longitudinal study of adriamycin-induced nephropathy in mice, we identified three sequential stages of actomyosin reorganization within the sarcomere-like structures (SLSs) that define the injury response: focal infiltration of myosin IIA into synaptopodin-rich foot processes (Stage 1), disordered intermingling of synaptopodin/myosin IIA (Stage 2), and the formation of highly organized periodic contractile arrays oriented perpendicular to the direction of capillary blood flow (Stage 3). Longitudinal quantification revealed predictable temporal dynamics, with mature Stage 3 predominating by day 7-9 post-injury. To determine whether this sequence is conserved in human disease, we analyzed kidney biopsies from patients with minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, and diabetic nephropathy. The same three stages were present across all four diseases, and their distribution tracked disease course: acute podocytopathies exhibited heterogeneous early-stage patterns, whereas chronic injuries converged on uniform, mature SLS organization. These findings demonstrate that podocyte injury is a graded, potentially reversible process rather than a binary switch. They identify structured actomyosin remodeling as a conserved wound response across mechanistically distinct kidney diseases and suggest that therapeutic strategies targeting specific stages of this progression could alter the trajectory of diverse glomerular diseases.

Background: Cardiovascular-kidney-metabolic (CKM) syndrome integrates cardiac, renal, and metabolic abnormalities that drive multi-organ injury. In pulmonary arterial hypertension (PAH), CKM manifests as systemic metabolic derangements, right ventricular dysfunction, and renal compromise. Renal dysfunction strongly predicts mortality in PAH, yet current therapies provide little renal benefit. Moreover, the mechanisms driving PAH nephropathy remain poorly understood, limiting our ability to effectively treat PAH-CKM. Methods: Single-nucleus RNA sequencing identified cell-type-specific transcriptional alterations in autopsy-derived kidneys from control (n=5) and PAH (n=4) patients. Mitochondrial, cytoplasmic, and phosphoproteomic analyses profiled proteomic alterations. AlphaFold 3/ChimeraX modeling defined the predicted structural consequences of altered protein phosphorylation. Histological analysis assessed renal fibrosis, glomerular structure, immune cell infiltration, and nephron segment density. Results: 3 of 4 PAH patients exhibited renal impairment, with a cohort mean estimated glomerular filtration rate of 61 plus or minus 36 mL/min/1.73m squared. snRNA-seq identified a distinct cellular architecture in PAH kidneys, marked by an increase in thick ascending limb, proximal tubule, and immune cell nuclei and depletion of collecting duct nuclei. Transcriptional profiling demonstrated proximal tubule and thick ascending limb cells both upregulated fatty acid oxidation, ferroptosis, and cuproptosis pathways. PAH lymphocytes displayed heightened T87 cell receptor signaling, natural killer cell-mediated cytotoxicity, and Th17 differentiation. Histological analyses demonstrated increased perivascular fibrosis, glomerular T-cell infiltration, and a reduction in glomerular basement membrane density in PAH kidneys. Mitochondrial and cytoplasmic proteomics revealed broad metabolic dysfunction characterized by impaired {beta}-oxidation, TCA cycle activity, amino acid metabolism, transsulfuration, and urea cycle pathways. Phosphoproteomics predicted increased GSK3{beta}, STK, and casein kinase activity in PAH kidneys. Finally, using the totality of our data, we nominated multiple druggable targets that could be evaluated to counteract PAH nephropathy. Conclusions: Integrated multi-omic profiling demonstrates PAH nephropathy is defined by glomerular structural remodeling, proximal nephron ferroptotic and cuproptotic signaling, amino acid metabolic dysregulation, and innate and adaptive leukocyte activation. Future studies intervening on these pathways could lead to the development of novel therapeutics to augment renal function in PAH.

Understanding the shared and disease-specific mechanisms that drive glomerular injury remains a major unmet need for developing more precise and effective treatments for glomerular diseases. Here, we integrate histology-guided spatial transcriptomics with trajectory inference and cell-state deconvolution to resolve glomerular injury across Membranous Nephropathy, Focal Segmental Glomerulosclerosis, and Lupus Nephritis. Herein, we show that glomerular diseases arising from distinct initiating mechanisms converge on common pathways during progressive loss of kidney function. We used spatial transcriptomics to analyze kidney biopsies from 59 individuals with glomerular diseases and controls and identified 792 glomeruli, including structurally injured glomeruli missed by transcriptomic clustering alone. Glomeruli shared interferon- and complement- associated inflammatory programs together with suppression of oxidative and lipid metabolic pathways, while retaining disease-preferential transcriptional features. Increased pseudotime correlated with lower estimated glomerular filtration rate, and cell- state deconvolution linked progression to podocyte loss and cellular remodeling. Parallel analysis of passive Heymann nephritis, a rat model of membranous nephropathy, recapitulated complement activation and localized complement activity to multiple renal cell populations extending into the periglomerular niche. These findings define a spatially resolved, cross-disease continuum of glomerular injury and identify coordinated local complement activation as a convergent feature of progressive glomerular damage.

Metabolic disturbance is a key feature in acute kidney injury (AKI) and chronic kidney disease (CKD). The kidney highly depends on fatty acid metabolism; how renal cells rewire metabolism upon AKI and CKD transition remained unclear. Here, we combine spatial transcriptomics with biochemical analyses to characterize metabolic changes and intercellular interactions during AKI to CKD transition. Using aristolochic acid model of CKD, we spatio-temporally correlated changes in structure and function with metabolic profile during AKI to CKD transition. Surprisingly, keto-gluconeogenic metabolic axis was highly enriched in healthy kidney and paralleled injury phase transitions. Intercellular interaction analysis associated a subtype of macrophage with the drift to chronicity. Online scRNAseq datasets analysis confirmed altered keto-gluconeogenic metabolic pathways in ischemia-reperfusion injured mouse kidneys and AKI and CKD human kidney biopsies compared to healthy controls. This study identifies a metabolic axis transcriptionally mirroring renal homeostasis and injury responses, and tubulo-interstitial interactions that can be targeted to mitigate AKI to CKD transition.

Introduction: Kidney volume is associated with renal function, but conventional whole-organ measurements may miss regional changes in kidney substructures. We used magnetic resonance imaging (MRI) to test whether kidney substructure volumes and three-dimensional (3D) thickness phenotypes are associated with disease, adiposity, and incident outcomes. Methods: Automated abdominal MRI segmentations from 70,270 UK Biobank participants were used to quantify left and right kidney cortex, medulla, and parenchyma volumes and mesh-based thickness maps. Mass univariate regression generated statistical parametric maps linking regional thickness to anthropometric traits and disease (CKD, type-2 diabetes [T2D], hypertension). Bidirectional causal mediation analyses were performed using kidney substructure volumetric, thickness PCs and kidney adiposity. Longitudinal changes were assessed in 2,610 participants with repeat imaging. Cox proportional hazards models tested the associations between kidney volumes and principal component (PC) scores of thickness and incident CKD, T2D, hypertension, cardiovascular disease (CVD), and mortality. Results: CKD was associated with thinning of the parenchyma and most pronounced in the medulla (87.7% left, 72.8% right), whereas associations in the cortex were mixed. In contrast, T2D and hypertension were predominantly associated with increased thickness, most extensively in the cortex (T2D: 84.39% left, 96.35% right; hypertension: 94.8% left, 99.9% right). Age-disease interactions were associated with reduced thickness across all conditions. Smaller medulla volume and lower cortical thickness mediated the association between CKD and renal sinus fat. Kidney substructure volume was inversely associated with incident CKD across all substructures and both kidney sides (p<0.05), but positively associated with incident hypertension and mortality (p<0.05). Thickness PC scores also predicted outcomes independently of volume, with PC3 in the left cortex (HR 0.91 [0.84-0.98]), reflecting inferior pole/hilar thickness, associated with incident CKD. Conclusions: MRI-derived kidney substructure volumes and 3D thickness maps provide complementary, spatially-resolved markers of kidney morphology, that are mechanistically linked to renal adiposity and future disease risk.

Background: Chronic kidney disease (CKD) is a major risk factor for cardiovascular morbidity, promoting left ventricular hypertrophy (LVH) prior to overt heart failure. The mechanisms underlying early cardiac remodeling in CKD remain incompletely understood. The IL-23/Th17/IL-17A inflammatory axis has emerged as a key mediator of cardiovascular pathology; however, its role in CKD-associated cardiac remodeling remains unclear. This study aimed to elucidate the contribution of this pathway to the early cardiac changes in CKD. Methods: Using a 5/6 nephrectomy (5/6Nx) mouse model of CKD, we evaluated cardiac structure, mitochondrial function, and inflammatory signaling. Cardiomyocyte transcriptomes were analyzed by RamDA-seq to identify molecular alterations. Circulating cytokines were profiled longitudinally, and IL-17A neutralization experiments were performed to assess causality. In addition, serum IL-12p40 concentrations were measured in patients with CKD and correlated with their renal function and cardiac remodeling indices. Results: At 16 weeks post-5/6Nx, mice developed LVH with preserved systolic function, accompanied by increased oxidative stress and mitochondrial structural abnormalities, but without significant myocardial fibrosis. Transcriptomic analysis identified oxidative phosphorylation as the most significantly downregulated pathway in cardiomyocytes. Despite increased mitochondrial DNA copy number and elevated PGC-1 expression, ATP production and mitochondrial respiratory chain proteins were reduced, indicating mitochondrial dysfunction. Circulating IL-12p40 and IL-23 levels increased progressively, concurrent with expansion of splenic Th17 cells and elevated cardiac IL-17A expression. Recombinant IL-17A directly impaired mitochondrial respiration in cultured cardiomyocytes. In vivo, IL-17A neutralization attenuated LVH, reduced oxidative stress, and partially restored mitochondrial protein expression without improving renal function. In patients with CKD, serum IL-12p40 levels correlated inversely with estimated glomerular filtration rate and positively with left ventricular mass index, supporting clinical relevance. Conclusions: Activation of the systemic IL-23/Th17/IL-17A axis contributes to early CKD-associated cardiac remodeling by promoting oxidative stress and mitochondrial dysfunction. Circulating IL-12p40 may serve as a biomarker of cardiorenal remodeling, and the IL-23/IL-17A pathway represents a potential therapeutic target.

Obesity is a major risk factor for interrelated cardiorenal metabolic diseases including type 2 diabetes, heart failure and chronic kidney disease (1-4). Although obesity develops when energy intake chronically exceeds energy expenditure, individuals vary markedly in the amount of adiposity and metabolic dysfunction that develop in response to comparable caloric excess. Controlled overfeeding studies demonstrate several-fold variation in weight gain between individuals (5), while susceptibility to metabolic dysfunction also differs substantially between populations (6), suggesting considerable variation in how excess nutrients are partitioned. Energy balance is conventionally considered in terms of intake and expenditure, yet energy-containing nutrients can also be eliminated from the body. The kidney is uniquely positioned to regulate this third component of energy balance by determining whether filtered metabolites are reabsorbed or excreted. The metabolic benefits of SGLT2 inhibition demonstrate that reducing renal nutrient reabsorption can favourably alter systemic metabolic function (7,8), but whether naturally occurring variation in renal nutrient conservation contributes to metabolic disease susceptibility remains unknown. Here, screening eleven genetically divergent mouse strains identified BXD34 mice as strikingly resistant to diet-induced obesity, ectopic lipid accumulation and insulin resistance despite increased caloric intake. Mechanistically, this protection was associated with widespread urinary nutrient loss accompanied by coordinated suppression of renal solute transport, but came at the cost of profound susceptibility to acute kidney injury. Together, these findings identify renal nutrient conservation as an underappreciated determinant of whole-body metabolism and reveal a renometabolic trade-off in which protection from obesity is achieved at the expense of renal resilience.

Methylmalonic aciduria (MMA) is caused by deficiency of methylmalonyl-CoA mutase (MMUT), which catalyses the final step of propionate catabolism and fuels the tricarboxylic acid cycle for energy production. Previous studies reported disrupted mitochondrial homeostasis in MMA, including reduced mitochondrial membrane potential and increased oxidative stress, especially in energetically demanding and chronically affected tissues like brain and kidneys. However, how these changes impact mitochondrial energy production remains unclear. Here, we systematically investigated mitochondrial energy production using extracellular flux analysis in cellular models of MMA, including 293T cells, patient-derived fibroblasts, urine-derived epithelial kidney cells and induced pluripotent stem cells (iPSCs) as well as iPSC-derived neurons harbouring either complete loss (knockout, KO) or pathogenic missense variants in MMUT. We found no impact on mitochondrial energy production in MMUT-KO 293T cells and fibroblasts compared to controls. In contrast, fibroblasts and 293T cells expressing the pathogenic MMUT-p.N219Y variant showed decreased energy production. This corresponds to the altered mitochondrial membrane potential in 293T cells, but contrasts with their unchanged mitochondrial abundance. Depletion of glucose, glutamine and pyruvate from the media or provision of each individually as sole fuel source exacerbated the phenotype of MMUT-p.N219Y clones, but did not induce a phenotype in MMUT-KO 293T cells. Finally, we confirmed reduced mitochondrial energy production in patient-derived kidney cells but found no evidence in MMUT-p.N219Y iPSCs and their derived neurons. Overall, our work suggests that the impact of MMUT-deficiency on mitochondrial energy production is cell type- and variant-dependent. Further investigations should clarify molecular mechanisms and their clinical impact.

Background: Chronic kidney disease (CKD) imposes persistent metabolic stress, yet whether metabolic organization can be preserved under sustained renal stress remains unclear. Essential trace elements support redox defense, mitochondrial function, and intermediary metabolism, and their homeostasis is disturbed in CKD; however, single-element supplementation has yielded heterogeneous results. We examined whether a defined multi-element formulation preserves metabolic resilience in CKD. Methods: In a randomized, double-blind, placebo-controlled trial, 80 maintenance dialysis patients received standard care alone (n = 40) or plus a trace element cocktail (TEX, 20 mL/day; n = 40). Longitudinal trajectories were analyzed with linear mixed-effects models; endpoint plasma metabolomics and fecal metagenomics were profiled in subsets. A 5/6 nephrectomy mouse model was used to quantify plasma tryptophan-pathway branches and renal spatial metabolism by MALDI imaging mass spectrometry. Results: TEX was well tolerated, with no treatment-related safety signal, and was associated with modestly more favorable creatinine and eGFR trajectories. Supplementation constrained, rather than erased, CKD-associated metabolic displacement (median |Cohen's d|, 0.25 versus 2.09 for disease effects), selectively realigning circulating metabolism toward the healthy state. The host kynurenine branch responded most strongly, whereas microbial indole metabolism and gut community structure changed little. Renal metabolic remodeling was region-specific, with preservation of selected tubular and antioxidant features. Conclusions: Trace element supplementation preserved metabolic resilience in CKD, limiting metabolic displacement without complete restoration. Preservation of metabolic organization may represent a complementary dimension of therapeutic response in CKD. Trial registration: International Traditional Medicine Clinical Trial Registry, ITMCTR2026000263 (registered 3 February 2026).

Background Delayed graft function (DGF) is among the most used metrics in transplant medicine, yet its prevailing definition-dialysis requirement within the first seven postoperative days lacks granularity and fails to capture the dynamic nature of graft recovery. It reflects a treatment decision rather than graft biology, varies by centre practice, and offers no temporal information about the pace or pattern of recovery. This study proposes a trajectory-based framework using serial serum creatinine measurements across three biologically defined time windows to capture the dynamic nature of early renal recovery. Methods We retrospectively analysed 205 adult kidney transplant recipients at Cleveland Clinic Weston Hospital in 2025. Donor groups included living donors, donation after brain death (DBD), donation after circulatory death with normothermic regional perfusion (DCD-NRP), and DCD without NRP. Creatinine slopes were estimated for Days 1-7, 7-30, and 30-90 using ordinary least-squares regression. Logistic regression assessed the predictive performance of each trajectory window for DGF, adjusting for Kidney Donor Profile Index, cold ischemia time, BMI, and donor type. Results DCD non-NRP kidneys showed negligible early creatinine decline (slope +0.02) compared to DBD (-0.71) and DCD-NRP (-0.57) grafts during Days 1-7. During Days 7-30, DCD-NRP kidneys showed accelerated recovery and converged toward DBD-level trajectories, whereas DCD non-NRP grafts remained sluggish. Predictive modelling identified the Day 7-30 trajectory had the strongest discrimination for DGF, with AUC 0.83, pseudo-R2 0.25, and the lowest AIC (181.73), outperforming Days 1-7 (AUC 0.75) and 30-90 (AUC 0.79). DGF rates were 0% in living donors, 25.5% in DBD, 20.7% in DCD-NRP, and 58.9% in DCD non-NRP recipients. Conclusions A trajectory-based creatinine model provides more informative prognostic value than the conventional binary DGF definition The Day 7-30 window periods offers the highest discriminatory power, and normothermic regional perfusion appears to favourably shift DCD kidney recovery trajectories in a manner the binary definition fails to detect.

Protein misfolding in the endoplasmic reticulum (ER) of podocytes/glomerular epithelial cells (GECs) induces ER stress and contributes to the pathogenesis of glomerular disease. Activation of IRE1 and consequently the unfolded protein response (UPR) and autophagy sustains proteostasis. The present study examines the role of Surf4 and collagen IV-5 (COL4A5) trafficking in podocyte proteostasis. Glomerular Surf4 protein expression increased in IRE1-replete mice with experimental focal segmental glomerulosclerosis (FSGS) compared to podocyte-IRE1 knockout mice with FSGS and control mice. Glomerular Surf4 gene expression was greater in human FSGS and membranous nephropathy compared to healthy controls. In cultured GECs, basal Surf4 expression was greater in IRE1-replete (control) compared to IRE1 knockout GECs, although ER stress (tunicamycin treatment) did not increase Surf4 despite activating the UPR. Tunicamycin enhanced autophagy (LC3-II) in an IRE1-dependent manner, and the amount of Surf4 localized in autophagosomes. In GECs, tunicamycin increased the amount and colocalization of endogenous COL4A5 or ectopically-expressed COL4A5-wild type (WT) and Surf4 in autophagosomes. Compared to COL4A5-WT, the human COL4A5-C1567R mutant (which is misfolded) showed enhanced basal colocalization with Surf4 in autophagosomes; colocalization was similar to COL4A5-WT after tunicamycin treatment. Degradation of COL4A5-C1567R was more rapid compared to COL4A5-WT and was comparable to degradation of COL4A5-WT in the presence of tunicamycin. Thus, during ER stress, subsets of Surf4 and COL4A5 are redirected from the secretory pathway to autophagy. Surf4 may help deliver misfolded ER cargo, such as COL4A5 for autosomal degradation, thereby sustaining proteostasis in podocytes.