Citations

The progression of autosomal dominant polycystic kidney disease (ADPKD), an inherited kidney disease, is associated with renal interstitial inflammation and fibrosis. CD74 has been known not only as a receptor of macrophage migration inhibitory factor (MIF) it can also have MIF independent functions. In this study, we report unknown roles and function of CD74 in ADPKD. We show that knockout of CD74 delays cyst growth in Pkd1 mutant kidneys. Knockout and knockdown of CD74 (1) normalize PKD associated signaling pathways, including ERK, mTOR and Rb to decrease Pkd1 mutant renal epithelial cell proliferation, (2) decrease the activation of NF-κB and the expression of MCP-1 and TNF-alpha (TNF-α) which decreases the recruitment of macrophages in Pkd1 mutant kidneys, and (3) decrease renal fibrosis in Pkd1 mutant kidneys. We show for the first time that CD74 functions as a transcriptional factor to regulate the expression of fibrotic markers, including collagen I (Col I), fibronectin, and α-smooth muscle actin (α-SMA), through binding on their promoters. Interestingly, CD74 also regulates the transcription of MIF to form a positive feedback loop in that MIF binds with its receptor CD74 to regulate the activity of intracellular signaling pathways and CD74 increases the expression of MIF in ADPKD kidneys during cyst progression. We further show that knockout of MIF and targeting MIF with its inhibitor ISO-1 not only delay cyst growth but also ameliorate renal fibrosis through blocking the activation of renal fibroblasts and CD74 mediated the activation of TGF-β-Smad3 signaling, supporting the idea that CD74 is a key and novel upstream regulator of cyst growth and interstitial fibrosis. Thus, targeting MIF-CD74 axis is a novel therapeutic strategy for ADPKD treatment.

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disorder worldwide and progresses to end-stage renal disease (ESRD). However, its precise mechanism is not fully understood. In recent years, epigenetic reprogramming has drawn increasing attention regarding its effect on cyst growth. However, considering the complexity of epigenetic mechanisms and the broad range of alterations of epigenetic components in ADPKD, identifying more specific epigenetic factors and understanding how they are mechanistically linked to promote cyst growth is relevant for the development of treatment for ADPKD. Here, we find that the histone methyltransferase SMYD3, which activates gene transcription via histone H3 lysine 4 trimethylation (H3K4me3), is upregulated in PKD1 mutant mouse and human ADPKD kidneys. Genetic knockout of SMYD3 in a PKD1 knockout mouse model delayed cyst growth and improved kidney function compared with PKD1 single knockout mouse kidneys. Immunostaining and Western blot assays indicated that SMYD3 regulated PKD1-associated signaling pathways associated with proliferation, apoptosis, and cell cycle effectors in PKD1 mutant renal epithelial cells and tissues. In addition, we found that SMYD3 localized to the centrosome and regulated mitosis and cytokinesis via methylation of α-tubulin at lysine 40. In addition, SMYD3 regulated primary cilia assembly in PKD1 mutant mouse kidneys. In summary, our results demonstrate that overexpression of SMYD3 contributes to cyst progression and suggests targeting SMYD3 as a potential therapeutic strategy for ADPKD.

AbstractBackgroundAutosomal dominant polycystic kidney disease (ADPKD) is the most prevalent monogenic renal disease progressing to end‐stage renal disease. There is a pressing need for the identification of early ADPKD biomarkers to enable timely intervention and the development of effective therapeutic approaches. Here, we profiled human urinary extracellular vesicles small RNAs by small RNA sequencing in patients with ADPKD and compared their differential expression considering healthy control individuals to identify dysregulated small RNAs and analyze downstream interaction to gain insight about molecular pathophysiology.MethodsThis is a cross‐sectional study where urine samples were collected from a total of 23 PKD1‐ADPKD patients and 28 healthy individuals. Urinary extracellular vesicles were purified, and small RNA was isolated and sequenced. Differentially expressed Small RNA were identified and functional enrichment analysis of the critical miRNAs was performed to identify driver genes and affected pathways.ResultsmiR‐320b, miR‐320c, miR‐146a‐5p, miR‐199b‐3p, miR‐671‐5p, miR‐1246, miR‐8485, miR‐3656, has_piR_020497, has_piR_020496 and has_piR_016271 were significantly upregulated in ADPKD patient urine extracellular vesicles and miRNA‐29c was significantly downregulated. Five ‘driver’ target genes (FBRS, EDC3, FMNL3, CTNNBIP1 and KMT2A) were identified.ConclusionsThe findings of the present study make significant contributions to the understanding of ADPKD pathogenesis and to the identification of novel biomarkers and potential drug targets aimed at slowing disease progression in ADPKD.

ABSTRACT Introduction Our main objective was to identify baseline prognostic factors predictive of rapid disease progression in a large unselected clinical autosomal dominant polycystic kidney disease (ADPKD) cohort. Methods A cross-sectional analysis was performed in 618 consecutive ADPKD patients assessed and followed-up for over a decade. A total of 123 patients (19.9%) had reached kidney failure by the study date. Data were available for the following: baseline eGFR (n = 501), genotype (n = 549), baseline ultrasound mean kidney length (MKL, n = 424) and height-adjusted baseline MKL (HtMKL, n = 377). Rapid disease progression was defined as an annualized eGFR decline (∆eGFR) of >2.5 mL/min/year by linear regression over 5 years (n = 158). Patients were further divided into slow, rapid and very rapid ∆eGFR classes for analysis. Genotyped patients were classified into several categories: PKD1 (T, truncating; or NT, non-truncating), PKD2, other genes (non-PKD1 or -PKD2), no mutation detected or variants of uncertain significance. Results A PKD1-T genotype had the strongest influence on the probability of reduced baseline kidney function by age. A multivariate logistic regression model identified PKD1-T genotype and HtMKL (>9.5 cm/m) as independent predictors for rapid disease progression. The combination of both factors increased the positive predictive value for rapid disease progression over age 40 years and of reaching kidney failure by age 60 years to 100%. Exploratory analysis in a subgroup with available total kidney volumes showed higher positive predictive value (100% vs 80%) and negative predictive value (42% vs 33%) in predicting rapid disease progression compared with the Mayo Imaging Classification (1C–E). Conclusion Real-world longitudinal data confirm the importance of genotype and kidney length as independent variables determining ∆eGFR. Individuals with the highest risk of rapid disease progression can be positively selected for treatment based on this combination.

Background Autosomal Dominant Polycystic Kidney Disease (PKD) is the most frequent hereditary renal disease and the fourth leading cause of end‐stage renal disease. However, the exact mechanisms of cystogenesis and disease progression remain to be elucidated. Recent evidence suggests that a metabolic reprograming may underlie the dysregulation of several signaling pathways known to be affected in PKD. To identify the metabolic pathways associated with cystogenesis in the PKD kidney, we characterized the urinary, plasma, and tissue metabolome of PCK (a well established model of PKD) compared to Sprague‐Dawley (SD) wild‐type rats. Methods Male and female PCK and SD rats were treated with dDAVP (PCK‐D, n=16 or SD‐D, n=12) to aggravate the cystic phenotype and achieve animals with different degrees of disease severity for a given age, or saline solution (PCK‐S, n=16 or SD‐S, n=12) as controls. Total kidney volume (TKV) gold standard to assess disease severity, were measured by MRI, and urinary, plasma, and tissue metabolites by proton nuclear magnetic resonance, 1H‐NMR. Kidney metabolites identified from renal tissues collected at euthanasia were correlated with TKV. Mitochondrial structure was assessed by electron microscopy in proximal tubules (PT), medullary thick ascending limb (mTAL), distal tubules (DT), and collecting ducts (CD). Results Consistent with previously published data, administration of dDAVP significantly aggravated the disease in PCK rats (TKV) without inducing a cystic phenotype in SD rats (). Analysis of PCK and SD metabolomes by Partial least squares‐discriminant analysis (PLS‐DA) score plots showed a significant separation between the groups (). Integration of tissue, urine and plasma analysis revealed 5 metabolites (α‐ketoglutarate, fumarate, malate, citrate, and hippurate) consistently differentially expressed, among which 4 participate in the mitochondrial tricarboxylic acid (TCA) cycle (). Moreover, tissue TCA cycle metabolites correlated directly with TKV (). Mitochondrial area and matrix density were preserved in PT, mTAL, and DT of PCK rats, yet disruption of cristae membranes, swelling, and decreased matrix density were observed in their CD cystic cells (). Conclusions Comprehensive multilevel metabolomics analysis showed significant dysregulations of several mitochondrial TCA cycle metabolites in PCK rats, which further aggravated with the more severe phenotype. Notably, these changes were associated with mitochondrial structural abnormalities in the CD. Our observations suggest that mitochondrial damage and metabolic dysregulations may be implicated in cystogenesis, and position mitochondria as important therapeutic targets in PKD. Support or Funding Information This study was supported by the Mayo Translational Polycystic Kidney Disease Center (NIDDK P30 DK090728) and an endowment from Robert M. and Billie J. Pirnie for Kidney Research

Dent disease I is a rare X‐linked recessive chronic kidney disorder caused by mutations of the CLCN5 gene, which encodes the electrogenic Cl−/H+ exchanger (transporter) ClC‐5. CLC‐5 protein has been localized to the apical membrane and endosomal vesicles of the kidney in the proximal tubule as well as other tubule segments. Clinical manifestations of patients with Dent disease include low molecular weight proteinuria (LMWP), hypercalciuria, nephrocalcinosis, nephrolithiasis, bone disease (rickets), and often progressive renal failure. While it is known that the CLC‐5 protein functions in the formation and maturation of endosomes, the etiology of the nephrocalcinosis and kidney stones often observed in Dent disease patients is not known. Therefore, in this project we investigated the effects of several CLC‐5 mutations identified in Dent disease patients, including S244L, Q629X, and R345W, on cellular processing of calcium oxalate (CaOx) crystals. Monolayers of renal proximal tubular cells (LLC‐PK1) and renal cortical tubular epithelial cells (RCTE) transfected with GFP tagged WT and mutated CLC‐5 were subjected to a CaOx crystal adhesion/agglomeration assay for thirty minutes then imaged by DIC and epifluorescence microscopy. The total area of CaOx crystal formation around each transfected cell within a 35, 55, and 75 μm diameter concentric circle was analyzed using ImageJ, and compared to adjacent un‐transfected cells which served as an internal control. A significant increase in CaOx aggregation was observed around cells expressing CLC‐5 mutants compared to wild type cells, especially for S244L. In LLC‐PK1 cells crystal adhesion/agglomeration decreased in this order: S224L > R345W > Q629X = WT; while in RCTE it decreased in this order: S224L = Q629X > R345W = WT. These findings support the hypothesis that mutated CLC‐5 proteins alter the apical surface of epithelial nephron cells and encourage CaOx aggregation/adhesion. It is also possible that decreased internalization and dissolution of CaOx crystals which form on the cell surface plays a role, as the greatest crystal adhesion/agglomeration was found within the 35 μm diameter circle around cells transfected with mutated CLC‐5 (35 μm > 55 μm > 75 μm). Further investigation into the impact of specific CLC‐5 mutation of protein structure and function, including protein‐protein interactions, is needed. Support or Funding Information Supported by O'Brien Urology Research Center U54‐DK100227 summer student supplement and the Rare Kidney Stone Consortium (U54‐DK083908)

Dent disease 1, an X‐linked inherited kidney disease caused by mutations in the CLCN5 gene, is characterized by low molecular weight proteinuria (LMWP), hypercalciuria, nephrocalcinosis, nephrolithiasis, rickets, and progressive renal failure. CLCN5 encodes the CLC‐5 protein found at the apical membrane in the kidney proximal tubule as well as endosome membranes of other tubule segments. Approximately 80 human mutations of the CLCN5 gene have been identified consisting of nonsense, missense, splice site, insertion and deletion mutations. However, the genotype and phenotype correlation are poor, and the mechanisms of CLC‐5 dysfunction that cause disease are still unclear. Moreover, there has been a lack of systematic study of CLC‐5 mutational effects on Cl − /H + exchanger activity. To address this need we used ion selective microelectrodes to monitor intracellular pH (pH i ) and intracellular Cl − concentration ([Cl i ]) of Xenopus oocytes expressing WT and mutant CLC‐5 while clamping at +40 mV. Common and novel mutations were identified in Dent patients by collaborators in the Rare Kidney Stone Consortium. The apparent H + :Cl − coupling ratio through the CLC‐5 protein was calculated using the Gibbs‐free energy equation. Cellular localization and protein trafficking of WT and mutant CLC‐5 in renal epithelial cells were also examined by immunofluorescence microscopy using eGFP/HA double‐tagged CLC‐5 and organelle‐specific markers and quantified by flow cytometry. In the presence of 104 mM Cl − (ND96), the pH i and [Cl − ] i of the CLC‐5 WT increased 340 ± 59 ×10 −4 pH unit/min and 2.8 ± 0.5 mM/min, respectively. T657S increased at a similar rate as WT, while there was a significant decrease in the rate of pH i and [Cl − ] i change for S244L, R345W, and Q629X compared to WT. Decreasing extracellular chloride to 5 mM decreased WT ClC‐5 pH i and [Cl − ] i by reversing transport: −7 ± 65 ×10 −4 pH unit/min and −0.2 ± 0.2 mM/min, respectively. Using these measurements, the stoichiometry of WT CLC‐5 was calculated to be 1.80 ± 0.02 (nCl − :H + ) in ND96, similar to the stoichiometry estimated for T657S. However, the stoichiometry was significantly altered for S244L, R345W, and Q629X. WT ClC‐5 acts as Cl − /H + exchanger at +40mV with 104 mM Cl − in the extracellular solution. Lowering extracellular Cl − reverses the transport direction, and the ClC‐5 exchanger functions at a significantly slower rate. Although S244L has normal surface expression, S244L and R345W mutations have significantly decreased pH and Cl − exchange rates in response to solution manipulations, suggesting these mutations have an altered ion exchange coupling ratio (stoichiometry). Interestingly, while R345W was retained in the ER suggesting defective protein maturation, R345W surface localization was rescued by lowering the incubation temperature from 37 to 30°C. Q629X was retained in the ER, not localized in early endosomes, and also has abolished Cl − /H + exchange activity, suggesting that Q629X affects protein maturation and trafficking while T657S is a benign, non‐disease causing mutation. These data suggest studying CLC‐5 mutational effects on both transport function and cellular localization is essential to better understand divergent phenotypes in Dent disease. Support or Funding Information NIH DK101405, U54KD083908, U54DK100227, Mayo O'Brien Urology Research Center, Mayo Clinic Rare Kidney Stone Consortium

Genetic testing in nephrology is becoming increasingly important to diagnose patients and to provide appropriate care. This is especially true for autosomal dominant polycystic kidney disease (ADPKD) because this is a common cause of kidney failure and genetically complex. In addition to the major genes, PKD1 and PKD2 , there are at least six minor loci, and phenotypic, and in some cases, genetic overlap with other cystic disorders. Targeted next-generation sequencing, a low-cost, high-throughput technique, has made routine genetic testing viable in nephrology clinics. Appropriate pre- and post-testing genetic counseling is essential to the testing process. Carefully assessing variants is also critical, with the genetic report classifying variants in accordance with American College of Medical Genetics and Genomics guidelines. However, variant of uncertain significance (VUSs) may pose a significant challenge for the ordering clinician. In ADPKD, and particularly within PKD1 , there is high allelic heterogeneity; no single variant is present in more than 2% of families. The Mayo/Polycystic Kidney Disease Foundation variant database, a research tool, is the best current database of PKD1 and PKD2 variants containing over 2300 variants identified in individuals with polycystic kidney disease, but novel variants are often identified. In patients with a high pretest probability of ADPKD on the basis of clinical criteria, but no finding of a pathogenic (P) or likely pathogenic (LP) variant in a cystic kidney gene, additional evaluation of cystic gene VUS can be helpful. In this case-based review, we propose an algorithm for the assessment of such variants in a clinical setting and show how some can be reassigned to a diagnostic grouping. When assessing the relevance of a VUS, we consider both patient/family-specific and allele-related factors using population and variant databases and available prediction tools, as well as genetic expertise. This analysis plus further family studies can aid in making a genetic diagnosis.

There is a broad phenotypic spectrum of monogenic polycystic kidney diseases (PKDs). These disorders often involve cilia-related genes and lead to the development of fluid-filled cysts and eventual kidney function decline and failure. Preimplantation genetic testing for monogenic (PGT-M) disorders has moved into the clinical realm. It allows prospective parents to avoid passing on heritable diseases to their children, including monogenic PKD. The PGT-M process involves embryo generation through in vitro fertilization, with subsequent testing of embryos and selective transfer of those that do not harbor the specific disease-causing variant(s). There is a growing body of literature supporting the success of PGT-M for autosomal-dominant and autosomal-recessive PKD, although with important technical limitations in some cases. This technology can be applied to many other types of monogenic PKD and ciliopathies despite the lack of existing reports in the literature. PGT-M for monogenic PKD, like other forms of assisted reproductive technology, raises important ethical questions. When considering PGT-M for kidney diseases, as well as the potential to avoid disease in future generations, there are regulatory and ethical considerations. These include limited government regulation and unstandardized consent processes, potential technical errors, high cost and equity concerns, risks associated with pregnancy for mothers with kidney disease, and the impact on all involved in the process, including the children who were made possible with this technology.