FGF23 excess is associated with morbidity and mortality, but the role of excessive circulating FGF23 concentrations as a causative factor of pathology is controversial. Here, we investigated the consequences of FGF23 excess in kidney disease. This study used three disease models: anti-glomerular basement membrane (anti-GBM) disease, Adriamycin nephropathy, and adenine-containing diets. Anti-GBM and Adriamycin mice and matched control mice received recombinant FGF23 (1 µg) or vehicle for six days (anti-GBM) or once (Adriamycin model), with dissection 24 h after the last injection. We established precision-cut kidney slices (PCKS) in adenine nephropathy for 24 h of treatment with recombinant FGF23 or vehicle. We assessed serum cytokines, biochemistry, and renal transcriptomes and histology of mice and patients with IgA nephropathy. RNA-Seq data and published transcriptomes underwent gene set enrichment, bulk ligand-receptor interaction analysis, and cell-type decomposition. Experimental anti-GBM disease caused decreased glomerular filtration rate, albuminuria, and renal tubular casts. FGF23 treatment increased phosphaturia and circulating soluble tumor necrosis factor receptor 1. The anti-GBM model showed FGF23-driven proinflammatory transcriptional signatures and Vcam1, Pdgfrb, and chemokine signaling, which were absent in FGF23-treated healthy mice. FGF23 increased renal macrophage content by transcriptome deconvolution and by immunofluorescence. In Adriamycin-induced nephropathy and in PCKS from adenine nephropathy, short-term FGF23 excess increased proinflammatory transcripts. Human data revealed associations between circulating FGF23 and renal immune cell infiltration. We found FGF23-driven renal patterns of proinflammatory gene and protein expression or leukocyte overabundance. The present data provide evidence that excess FGF23 directly drives inflammation in kidney disease and may serve as a therapeutic target.

Chronic kidney disease (CKD) is a strong risk factor for cardiovascular mortality and morbidity. We hypothesized that a senescent phenotype instigated by uremic toxins could account for early vascular aging (EVA) and vascular dysfunctions of microvasculature in end stage kidney disease (ESKD) patients which ultimately lead to increased cardiovascular complication. To test this hypothesis, we utilized both in vivo, and ex vivo approaches to study endothelial and smooth muscle function and structure, and characterized markers related to EVA in 82 ESKD patients (eGFR <15 ml/min) and 70 non-CKD controls. In vivo measurement revealed no major difference in endothelial function between ESKD and control group, aside from higher stiffness detected in the microcirculation of ESKD participants. In contrast, ex vivo measurements revealed a notable change in the contribution of endothelium-derived factors and increased stiffness in ESKD patients vs. controls. In support, we demonstrated that ex vivo exposure of arteries to uremic toxins such as Trimethylamine N-oxide, Phenylacetylglutamine, or extracellular vesicles from CKD patients impaired endothelial function via diminishing the contribution of endothelium-derived relaxing factors such as nitric oxide and endothelium derived hyperpolarizing factor. Uremic arteries displayed elevated expression of senescence markers (p21CIP1, p16INK4a, and SA-β-gal), calcification marker (RUNX2), and reduced expression of Ki67, sirtuin1, Nrf2, and MHY11 markers, indicating the accumulation of senescent cells and EVA phenotype. Correspondingly, treating uremic vessel rings ex vivo with senolytic agents (Dasatinib + Quercetin) effectively reduced the senescence-associated secretory phenotype and changed the origin of extracellular vesicles. Notably, sex differences exist for certain abnormalities suggesting the importance of biological sex in the pathogenesis of vascular complications. In conclusion, the uremic microvasculature is characterized by a "senescence signature", which may contribute to EVA and cardiovascular complications in ESKD patients and could be alleviated by treatment with senolytic agents.

Early vascular aging plays a central role in chronic kidney disease (CKD), but its molecular causes remain unclear. Somatic mutations accumulate in various cells with age, yet their functional contribution to aging tissues is not well understood. Here we found progerin, the protein responsible for the premature aging disease Hutchinson-Gilford progeria syndrome, steadily recurring in vascular smooth muscle cells of patients with CKD. Notably, the most common progeria-causing mutation, LMNA c.1824C>T, was identified as a somatic mutation in CKD arteries. Clusters of proliferative progerin-expressing cells in CKD arteries and in vivo lineage-tracing in mice revealed clonal expansion capacity of mutant cells. Mosaic progerin expression contributed to genomic damage, endoplasmic reticulum stress and senescence in CKD arteries and resulted in vascular aging phenotypes in vivo. These findings suggest that certain somatic mutations may be clonally expanded in the arterial wall, contributing to the disease-related functional decline of the tissue.

Patients with chronic kidney disease (CKD) face an increased risk of early vascular aging, progressive vascular calcification, and premature death. With increasing age, mitochondrial function and mitochondrial DNA copy number (mtDNA-cn) decline. This has been identified as an independent predictor of frailty and mortality in cardiovascular diseases (CVDs) and cancer. However, the relationship between mtDNA-cn and vascular calcification in the context of a uremic milieu remains ambiguous. We hypothesize that a lower mtDNA-cn is associated with medial calcification, as both are linked to impaired vascular health and accelerated aging. mtDNA-cn was analyzed in 211 CKD5 patients undergoing renal transplantation (RTx) and 196 healthy controls using quantitative PCR (qPCR) for three mtDNA genes (mtND1, mtND4, and mtCOX1) and single-locus nuclear gene hemoglobin beta (HbB). In 32 patients, mtDNA-cn was also quantified one year after RTx. The association between mtDNA-cn and vascular calcification scores, circulatory cell-free (ccf) mtDNA in plasma, and the surrogate marker of biological aging (skin autofluorescence) and CVD risk was assessed. mtDNA-cn was significantly lower in CKD5 patients than in controls and correlated with biological age, vascular calcification, and CVD risk. One year after RTx there was a significant recovery of mtDNA-cn in male patients compared to baseline levels. mtDNA-cn and ccf-mtDNA were inversely correlated. This prospective study provides novel insights into the link between low mtDNA-cn and vascular aging. It demonstrates that RTx restores mtDNA levels and may improve oxidative phosphorylation capacity in CKD. Further investigation is warranted to evaluate mtDNA as a biologically relevant biomarker and a potential therapeutic target for early vascular aging in the uremic environment.

A common observation in diabetic kidney disease is lipid accumulation, but the mechanism(s) underlying this pathology is unknown. Inhibition of Vascular endothelial growth factor B (VEGF-B) signaling was shown to prevent glomerular lipid accumulation and ameliorated diabetic kidney disease in experimental models. Here, we examined kidney biopsies from patients with Type 2 (84%) and Type 1 diabetes (16%), combined with data mining of RNA-seq dataset analyses in patients with diabetic kidney disease. In glomeruli, mesangial cell-derived VEGF-B expression was increased, and glomerular lipid accumulation positively correlated with impaired kidney function. Tubular lipid accumulation also associated with kidney dysfunction but was independent of tubular-derived VEGF-B expression. In vitro, the uptake of the fatty acid analogue, BODIPY-FA, was quantified. VEGF-B treatment increased BODIPY-FA uptake in endothelial cells, whilst pre-incubation with neutralizing antibodies against VEGF-B and its receptor VEGFR1 abolished this uptake. Transcriptome analyses of kidney and white adipose tissue from diabetic macaques showed that VEGF-B expression was higher in white adipose tissue than in kidney, and expression of VEGF-B was increased in white adipose tissue from patients with diabetic kidney disease. Analyses in diabetic transgenic mice demonstrated that expression of VEGF-B in adipocytes determined the lipolytic activity, dyslipidemia, kidney lipid accumulation and the development of diabetic kidney disease. Overall, VEGF-B is a regulator of kidney lipotoxicity in diabetic kidney disease, by controlling white adipose tissue lipolysis as well as endothelial fatty acid transport in glomeruli. Our data propose that assessment of kidney lipid accumulation, and VEGF-B expression can serve as biomarkers for early diabetic kidney disease.

Previous cross-sectional transcriptomics studies on diabetic kidney disease (DKD) kidney tissue have shown correlations between gene expression and both disease status and kidney function at the time of biopsy; however, longitudinal data are scarce. We utilized clinical follow-up data up to five years post-biopsy, linking the transcriptomes of diagnostic kidney biopsies to progression rates and outcomes in 19 patients with DKD. Patients were stratified into “rapid progressors” and “non-rapid progressors” based on clinical parameters (eGFR slope, CKD stage advancement, degree of albuminuria, composite outcome of kidney failure or 40

Key PointsInflammation and immune response pathways were enriched in IgA nephropathy/IgA vasculitis with nephropathy compared with living donors.The transcriptomic profile differed significantly between adults and children with the disease.BackgroundDisease manifestations and progression of IgA nephropathy vary widely between individuals, particularly between children and adults. To further understand these differences, we examined the transcriptional profiles in kidney biopsies from both adult and pediatric patients with IgA nephropathy or IgA vasculitis with nephropathy in relation to normal kidneys.MethodsKidney biopsies from 95 participants, 71 adults and 13 children with histopathologically verified IgA nephropathy or IgA vasculitis with nephropathy as well as 11 living donors, were microdissected into glomerular and tubulointerstitial fractions and subjected to RNA sequencing. Differential gene expression analysis was performed across groups, and functional enrichment analyses were conducted using gene ontology and Kyoto Encyclopedia of Genes and Genomes. Histopathological grading (Oxford and part of the Banff classifications) and clinical data (at time of biopsy and up to 5 years of follow-up) were analyzed in relation to normalized RNA counts.ResultsDifferentially expressed genes obtained from all patients versus living donors, both glomerular and tubulointerstitial fractions, were enriched for immune system and complement activation pathways. When comparing adults with children within the IgA nephropathy/IgA vasculitis with nephropathy group, 5562 and 3539 differentially expressed genes in each fraction were identified, which were enriched in pathways related to the endoplasmic reticulum and mitochondrial activity (glomeruli), as well as T-cell activation (tubulointerstitium).ConclusionsDistinct transcriptional profiles with enrichment of inflammation and immune response pathways were revealed in patients compared with living donors. However, the transcriptomic signatures across adult and pediatric patients were not consistent, highlighting differences in pathways involved in endoplasmic reticular, mitochondrial, and T-cell activity.

Chronic kidney disease (CKD) is an age-related disease that displays multiple features of accelerated ageing. It is currently unclear whether the two treatment options for end-stage kidney disease (dialysis and kidney transplantation [KT]) ameliorate the accelerated uremic ageing process. Data on clinical variables and blood DNA methylation (DNAm) from CKD stage G3–G5 patients were used to estimate biological age based on blood biomarkers (phenotypic age [PA], n  = 333), skin autofluorescence (SAF age, n  = 199) and DNAm (Horvath, Hannum and PhenoAge clocks, n  = 47). In the DNAm cohort, we also measured the change in biological age 1 year after the KT or initiation of dialysis. Healthy subjects recruited from the general population were included as controls. All three DNAm clocks indicated an increased biological age in CKD G5. However, PA and SAF age tended to produce implausibly large estimates of biological age in CKD G5. By contrast, DNAm age was 4.9 years ( p  = 0.005) higher in the transplantation group and 5.9 years ( p  = 0.001) higher in the dialysis group compared to controls. This age acceleration was significantly reduced 1 year after KT, but not after 1 year of dialysis. Kidney failure patients displayed an increased biological age as estimated by DNAm clocks compared to population-based controls. Our results suggest that KT, but not dialysis, partially reduces the age acceleration.

In today's industrialized society food consumption has changed immensely toward heightened red meat intake and use of artificial sweeteners instead of grains and vegetables or sugar, respectively. These dietary changes affect public health in general through an increased incidence of metabolic diseases like diabetes and obesity, with a further elevated risk for cardiorenal complications. Research shows that high red meat intake and artificial sweeteners ingestion can alter the microbial composition and further intestinal wall barrier permeability allowing increased transmission of uremic toxins like p-cresyl sulfate, indoxyl sulfate, trimethylamine n-oxide and phenylacetylglutamine into the blood stream causing an array of pathophysiological effects especially as a strain on the kidneys, since they are responsible for clearing out the toxins. In this review, we address how the burden of the Western diet affects the gut microbiome in altering the microbial composition and increasing the gut permeability for uremic toxins and the detrimental effects thereof on early vascular aging, the kidney per se and the blood-brain barrier, in addition to the potential implications for dietary changes/interventions to preserve the health issues related to chronic diseases in future.

Background Ischemia-reperfusion injury (IRI) inevitably occurs during kidney transplantation and extended ischemia is associated with delayed graft function and poor outcomes. Remote ischemic preconditioning (RIPC) is a simple, noninvasive procedure aimed at reducing IRI and improving graft function. Experimental studies have implicated the kynurenine pathway as a protective mechanism behind RIPC. Methods First, paired biopsies from 11 living kidney donors were analyzed to characterize the acute transcriptomic response to IRI. Second, 16 living kidney donors were subjected to either RIPC (n = 9) or no pretreatment (n = 7) to evaluate the impact of RIPC on the transcriptomic response to IRI. Finally, the effect of RIPC on plasma metabolites was analyzed in 49 healthy subjects. Results There was a robust immediate response to IRI in the renal transcriptomes of living-donor kidney transplantation, including activation of the mitogen-activated protein kinase (MAPK) and epidermal growth factor receptor (EGFR) pathways. Preconditioning with RIPC did not significantly alter the transcriptomic response to IRI or the concentration of plasma metabolites. Conclusions The present data validate living-donor kidney transplantation as a suitable model for mechanistic studies of IRI in human kidneys. The failure of RIPC to alter transcriptomic responses or metabolites in the kynurenine pathway raises the question of the robustness of the standard procedure used to induce RIPC, and might explain the mixed results in clinical trials evaluating RIPC as a method to attenuate IRI.

Abstract Background and Aims Chronic kidney disease (CKD) is an irreversible decline in renal function where kidney transplantation (KT) is the optimal therapeutic intervention. We aim to investigate the role and activation of the uremic toxin receptor aryl hydrocarbon receptor (AhR) in the microvasculature, particularly its implication in the blood-brain barrier impairment. We will also explore the potential role of growth hormone-releasing hormone (GHRH) as a biomarker reflecting the resolution of uremia-induced inflammation, early vascular ageing (EVA) phenotype, and potential enhancement in central nervous system (CNS) function post-KT. Method Resistance arteries from KT patients and non-CKD controls were isolated and expression of AhR was analysed by immunohistochemistry. The study used plasma samples from 60 KT patients, and levels of GHRH were measured at baseline and two years after transplantation using ELISA. Results Following KT, our initial findings indicate a decrease in levels of DBP, Lp(a), creatinine, homocysteine, phosphate, and troponin T among KT patients. Conversely, there was an increase in albumin, HBA1c, calcium and NfL post-transplantation. The expression of AhR in the resistance arteries of KT patients (2.6%) was notably lower compared to non-CKD controls (9.7%). Plasma concentrations of GHRH were significantly higher (p < 0.0001) in CKD-5 patients two years post-KT (2.94 ng/mL, IQR 2.60-3.43) compared to baseline (2.32 mg/L, IQR 1.84-3.24). This elevated trend in GHRH levels post-KT was observed in both sexes, with males (p < 0.0001) and females (p 0.0084) showing higher levels—males (3.0 ng/mL, IQR 2.6-3.5) and females (2.8 ng/mL, IQR 2.4-3.5)—compared to baseline level of males (2.4 ng/mL, IQR 1.8-3.2) and females (2.2 ng/mL, 1.9-3.3). No significant difference in GHRH levels was observed when assessing extreme EVA phenotypes based on the presence or absence of calcification or fibrosis. Conclusion Contrary to our initial expectation, the preliminary results indicate a downregulation in AhR expression within resistance vessels of CKD patients, implying modifications in AhR signaling within the uremic environment. The observed alteration in GHRH levels presents a promising avenue for further investigation focusing on its possible application as a biomarker for assessing CNS status in CKD patients undergoing KT. Prospective clinical application could involve the administration of GHRH agonists as a protective measure against cognitive impairment, considering its deficiency in CKD. Such supplementation holds promise to prevent further cognitive morbidity. The modulation in the levels of this hormone has the potential to significantly influence the treatment trajectory of CKD patients and enhance clinical outcomes.

Abstract Background and Aims Chronic kidney disease (CKD) and kidney failure are connected to increased oxidative stress and vascular calcification, which are indicators for development of comorbidities and mortality outcome. Mitochondrial (mt)DNA copy number has been reported as independent predictor for frailty and mortality outcome of various cardiovascular diseases (CVD) and cancer. We aimed that mtDNA copy number in whole blood of kidney failure patients can be correlated to coronary artery media calcification score and coronary artery calcium (CAC) score and be used as an independent predictor for comorbidities and mortality outcome. Method Quantitative PCR (qPCR) with TaqMan® probes for three mtDNA genes (mtND1, mtND4 and mtCOX1) and two single locus genes on nuclear DNA (hemoglobin subunit beta and 18S), for normalization, is performed on DNA samples isolated from collected blood of 196 kidney transplant donors and 211 recipients at basal timepoint and 32 at 1-year-follow-up timepoint, included in the KaroKidney biobank. Resulting mtDNA copy number is investigated for correlation to CAC score, patient mortality outcome, biological age determined by skin autofluorescence and other clinical parameters. Results In our Swedish kidney transplant cohort we can see statistically significant difference in mtDNA copy number between kidney failure patients (recipients) and healthy controls (donors). No obvious difference between females and males was observed. mtDNA copy number correlates to biological age determined by skin autofluorescence, CAC score and Framingham CVD risk score. In the 32 1-year-follow-up samples we could see significant increase/recovery of mtDNA copy number for male patients compared to their baseline before receiving a transplant. Conclusion In this study we show that mtDNA copy number in kidney failure patients correlates to biological age and CAC score, affirming mtDNA copy number as an independent predictor of frailty in this Swedish cohort of CKD patients. Additionally, we can see that a kidney transplant can lead to a significant increase of mtDNA copy number in blood one year later, suggesting a general increase in health quality.

BackgroundChronic kidney disease (CKD) is an age-related disease that displays multiple features of accelerated ageing. It is currently unclear whether the two treatment options for end-stage kidney disease (dialysis and kidney transplantation [KT]) ameliorate the accelerated uremic ageing process.MethodsData on clinical variables and blood DNA methylation (DNAm) from CKD stage G3-G5 patients were used to estimate biological age based on blood biomarkers (phenotypic age [PA], n = 333), skin autofluorescence (SAF age, n = 199) and DNAm (Horvath, Hannum and PhenoAge clocks, n = 47). In the DNAm cohort, we also measured the change in biological age 1 year after the KT or initiation of dialysis. Healthy subjects recruited from the general population were included as controls.ResultsAll three DNAm clocks indicated an increased biological age in CKD G5. However, PA and SAF age tended to produce implausibly large estimates of biological age in CKD G5. By contrast, DNAm age was 4.9 years (p = 0.005) higher in the transplantation group and 5.9 years (p = 0.001) higher in the dialysis group compared to controls. This age acceleration was significantly reduced 1 year after KT, but not after 1 year of dialysis.ConclusionsKidney failure patients displayed an increased biological age as estimated by DNAm clocks compared to population-based controls. Our results suggest that KT, but not dialysis, partially reduces the age acceleration. image

The pathophysiology of vascular disease is linked to accelerated biological aging and a combination of genetic, lifestyle, biological, and environmental risk factors. Within the scenario of uncontrolled artery wall aging processes, CKD (chronic kidney disease) stands out as a valid model for detailed structural, functional, and molecular studies of this process. The cardiorenal syndrome relates to the detrimental bidirectional interplay between the kidney and the cardiovascular system. In addition to established risk factors, this group of patients is subjected to a plethora of other emerging vascular risk factors, such as inflammation, oxidative stress, mitochondrial dysfunction, vitamin K deficiency, cellular senescence, somatic mutations, epigenetic modifications, and increased apoptosis. A better understanding of the molecular mechanisms through which the uremic milieu triggers and maintains early vascular aging processes, has provided important new clues on inflammatory pathways and emerging risk factors alike, and to the altered behavior of cells in the arterial wall. Advances in the understanding of the biology of uremic early vascular aging opens avenues to novel pharmacological and nutritional therapeutic interventions. Such strategies hold promise to improve future prevention and treatment of early vascular aging not only in CKD but also in the elderly general population.

Previous cross-sectional transcriptomics studies have shown associations between kidney gene expression and concomitant kidney function in patients with diabetic kidney disease (DKD) as well as in other chronic kidney disease (CKD) etiologies. However, studies of longitudinal design are lacking. We hypothesized that certain intra-renal gene expression patterns associated with progressive glomerular filtration rate (GFR) decrease in DKD may reveal important disease drivers and prognostic factors.

Morphological alterations at the kidney filtration barrier increase intrinsic capillary wall permeability resulting in albuminuria. However, automated, quantitative assessment of these morphological changes has not been possible with electron or light microscopy. Here we present a deep learning-based approach for segmentation and quantitative analysis of foot processes in images acquired with confocal and super-resolution fluorescence microscopy. Our method, Automatic Morphological Analysis of Podocytes (AMAP), accurately segments podocyte foot processes and quantifies their morphology. AMAP applied to a set of kidney diseases in patient biopsies and a mouse model of focal segmental glomerulosclerosis allowed for accurate and comprehensive quantification of various morphometric features. With the use of AMAP, detailed morphology of podocyte foot process effacement was found to differ between categories of kidney pathologies, showed detailed variability between diverse patients with the same clinical diagnosis, and correlated with levels of proteinuria. AMAP could potentially complement other readouts such as various omics, standard histologic/electron microscopy and blood/urine assays for future personalized diagnosis and treatment of kidney disease. Thus, our novel finding could have implications to afford an understanding of early phases of kidney disease progression and may provide supplemental information in precision diagnostics.

ABSTRACT Background Immunoglobulin A nephropathy (IgAN) and its systemic variant IgA vasculitis (IgAV) damage the glomeruli, resulting in proteinuria, hematuria and kidney impairment. Dendrin is a podocyte-specific protein suggested to be involved in the pathogenesis of IgAN. Upon cell injury, dendrin translocates from the slit diaphragm to the nucleus, where it is suggested to induce apoptosis and cytoskeletal changes, resulting in proteinuria and accelerated disease progression in mice. Here we investigated gene and protein expression of dendrin in relation to clinical and histopathological findings to further elucidate its role in IgAN/IgAV. Methods Glomerular gene expression was measured using microarray on 30 IgAN/IgAV patients, 5 patients with membranous nephropathy (MN) and 20 deceased kidney donors. Dendrin was spatially evaluated on kidney tissue sections by immunofluorescence (IF) staining (IgAN patients, n = 4; nephrectomized kidneys, n = 3) and semi-quantified by immunogold electron microscopy (IgAN/IgAV patients, n = 21; MN, n = 5; living kidney donors, n = 6). Histopathological grading was performed according to the Oxford and Banff classifications. Clinical data were collected at the time of biopsy and follow-up. Results Dendrin mRNA levels were higher (P = .01) in IgAN patients compared with MN patients and controls and most prominently in patients with preserved kidney function and fewer chronic histopathological changes. Whereas IF staining did not differ between groups, immunoelectron microscopy revealed that a higher relative nuclear dendrin concentration in IgAN patients was associated with a slower annual progression rate and milder histopathological changes. Conclusion Dendrin messenger RNA levels and relative nuclear protein concentrations are increased and associated with a more benign phenotype and progression in IgAN/IgAV patients.