BACKGROUNDProteinuria is considered an unfavorable clinical condition that accelerates renal and cardiovascular disease. However, it is not clear whether all forms of proteinuria are damaging. ...Mutations in CUBN cause Imerslund-Gräsbeck syndrome (IGS), which is characterized by intestinal malabsorption of vitamin B12 and in some cases proteinuria. CUBN encodes for cubilin, an intestinal and proximal tubular uptake receptor containing 27 CUB domains for ligand binding.METHODSWe used next-generation sequencing for renal disease genes to genotype cohorts of patients with suspected hereditary renal disease and chronic proteinuria. CUBN variants were analyzed using bioinformatics, structural modeling, and epidemiological methods.RESULTSWe identified 39 patients, in whom biallelic pathogenic variants in the CUBN gene were associated with chronic isolated proteinuria and early childhood onset. Since the proteinuria in these patients had a high proportion of albuminuria, glomerular diseases such as steroid-resistant nephrotic syndrome or Alport syndrome were often the primary clinical diagnosis, motivating renal biopsies and the use of proteinuria-lowering treatments. However, renal function was normal in all cases. By contrast, we did not found any biallelic CUBN variants in proteinuric patients with reduced renal function or focal segmental glomerulosclerosis. Unlike the more N-terminal IGS mutations, 37 of the 41 proteinuria-associated CUBN variants led to modifications or truncations after the vitamin B12-binding domain. Finally, we show that 4 C-terminal CUBN variants are associated with albuminuria and slightly increased GFR in meta-analyses of large population-based cohorts.CONCLUSIONCollectively, our data suggest an important role for the C-terminal half of cubilin in renal albumin reabsorption. Albuminuria due to reduced cubilin function could be an unexpectedly common benign condition in humans that may not require any proteinuria-lowering treatment or renal biopsy.FUNDINGATIP-Avenir program, Fondation Bettencourt-Schueller (Liliane Bettencourt Chair of Developmental Biology), Agence Nationale de la Recherche (ANR) Investissements d'avenir program (ANR-10-IAHU-01) and NEPHROFLY (ANR-14-ACHN-0013, to MS), Steno Collaborative Grant 2018 (NNF18OC0052457, to TSA and MS), Heisenberg Professorship of the German Research Foundation (KO 3598/5-1, to AK), Deutsche Forschungsgemeinschaft (DFG) Collaborative Research Centre (SFB) KIDGEM 1140 (project 246781735, to CB), and Federal Ministry of Education and Research (BMB) (01GM1515C, to CB).
Cisplatin nephrotoxicity is a critical limitation of solid cancer treatment. Until now, the complex interplay of various pathophysiological mechanisms leading to proximal tubular cell apoptosis after ...cisplatin exposure has not been fully understood. In our study, we assessed the role of the autophagy-related protein BECLIN1 (ATG6) in cisplatin-induced acute renal injury (AKI)-a candidate protein involved in autophagy and with putative impact on apoptosis by harboring a B-cell lymphoma 2 (BCL2) interaction site of unknown significance. By using mice with heterozygous deletion of
, we demonstrate that reduced intracellular content of BECLIN1 does not impact renal function or autophagy within 12 months. However, these mice were significantly sensitized towards cisplatin-induced AKI, and by using
mice with subsequent primary cell analysis, we confirmed that nephrotoxicity depends on proximal tubular BECLIN1 content. Mechanistically, BECLIN1 did not impact autophagy or primarily the apoptotic pathway. In fact, a lack of BECLIN1 sensitized mice towards cisplatin-induced ER stress. Accordingly, the ER stress inhibitor tauroursodeoxycholic acid (TUDCA) blunted cisplatin-induced cell death in
heterozygosity. In conclusion, our data first highlight a novel role of BECLIN1 in protecting against cellular ER stress independent from autophagy. These novel findings open new therapeutic avenues to intervene in this important intracellular stress response pathway with a promising impact on future AKI management.
Polat et al. report that mice with a podocyte-specific expression of a constitutively active Rac1 form displayed similar injury and albuminuria, regardless of transient receptor potential canonical 5 ...activity. This article confirms the pathogenic role of deregulated Rac1 and challenges models involving the role of transient receptor potential canonical 5 in podocytes. We learned from this study and propose a roadmap for this controversial field to help new drug candidates succeed in clinical trials and safely reach patients.
The molecular mechanisms that maintain podocytes and consequently, the integrity of the glomerular filtration barrier are incompletely understood. Here, we show that the class III phosphoinositide ...3-kinase vacuolar protein sorting 34 (Vps34) plays a central role in modulating endocytic pathways, maintaining podocyte homeostasis. In mice, podocyte-specific conditional knockout of Vps34 led to early proteinuria, glomerular scarring, and death within 3-9 weeks of age. Vps34-deficient podocytes exhibited substantial vacuolization and foot process effacement. Although the formation of autophagosomes and autophagic flux were impaired, comparisons between podocyte-specific Vps34-deficient mice, autophagy-deficient mice, and doubly deficient mice suggested that defective autophagy was not primarily responsible for the severe phenotype caused by the loss of Vps34. In fact, Rab5-positive endosomal compartments, endocytosis, and fluid-phase uptake were severely disrupted in Vps34-deficient podocytes. Vps34 deficiency in nephrocytes, the podocyte-like cells of Drosophila melanogaster, resulted in a block between Rab5- and Rab7-positive endosomal compartments. In summary, these data identify Vps34 as a major regulator of endolysosomal pathways in podocytes and underline the fundamental roles of endocytosis and fluid-phase uptake for the maintenance of the glomerular filtration barrier.
Staphylococcus aureus is frequently detected in patients with sepsis and thus represents a major health burden worldwide. CD4+ T helper cells are involved in the immune response to S. aureus by ...supporting antibody production and phagocytosis. In particular, Th1 and Th17 cells secreting IFN-γ and IL-17A, are involved in the control of systemic S. aureus infections in humans and mice. To investigate the role of T cells in severe S. aureus infections, we established a mouse sepsis model in which the kidney was identified to be the organ with the highest bacterial load and abundance of Th17 cells. In this model, IL-17A but not IFN-γ was required for bacterial control. Using Il17aCre × R26YFP mice we could show that Th17 fate cells produce Th17 and Th1 cytokines, indicating a high degree of Th17 cell plasticity. Single cell RNA-sequencing of renal Th17 fate cells uncovered their heterogeneity and identified a cluster with a Th1 expression profile within the Th17 cell population, which was absent in mice with T-bet/Tbx21-deficiency in Th17 cells (Il17aCre x R26eYFP x Tbx21-flox). Blocking Th17 to Th1 transdifferentiation in Th17 fate cells in these mice resulted in increased S. aureus tissue loads. In summary, we highlight the impact of Th17 cells in controlling systemic S. aureus infections and show that T-bet expression by Th17 cells is required for bacterial clearance. While targeting the Th17 cell immune response is an important therapeutic option in autoimmunity, silencing Th17 cells might have detrimental effects in bacterial infections.
Abstract
Mucosal-associated invariant T (MAIT) cells have been implicated in various inflammatory diseases of barrier organs, but so far, their role in kidney disease is unclear. Here we report that ...MAIT cells that recognize their prototypical ligand, the vitamin B2 intermediate 5-OP-RU presented by MR1, reside in human and mouse kidneys. Single cell RNAseq analysis reveals several intrarenal MAIT subsets, and one, carrying the genetic fingerprint of tissue-resident MAIT17 cells, is activated and expanded in a murine model of crescentic glomerulonephritis (cGN). An equivalent subset is also present in kidney biopsies of patients with anti-neutrophil cytoplasmatic antibody (ANCA)-associated cGN. MAIT cell-deficient MR1 mice show aggravated disease, whereas B6-MAIT
CAST
mice, harboring higher MAIT cell numbers, are protected from cGN. The expanded MAIT17 cells express anti-inflammatory mediators known to suppress cGN, such as CTLA-4, PD-1, and TGF-β. Interactome analysis predicts CXCR6 – CXCL16-mediated cross-talk with renal mononuclear phagocytes, known to drive cGN progression. In line, we find that cGN is aggravated upon CXCL16 blockade. Finally, we present an optimized 5-OP-RU synthesis method which we apply to attenuating cGN in mice. In summary, we propose that CXCR6
+
MAIT cells might play a protective role in cGN, implicating them as a potential target for anti-inflammatory therapies.
Melanoma differentiation-associated gene 5 (MDA5) positive dermatomyositis is a rare systemic autoimmune disease that is associated with life-threatening rapidly progressive interstitial lung ...disease. We report the case of a 19-year-old male patient with a life-threatening disease course caused by rapidly progressive interstitial lung disease that caused respiratory failure despite intensive immunosuppression with multiple agents (steroids, IV immunoglobulins, tofacitinib, cyclophosphamide, mycophenolate mofetil, ciclosporin and rituximab). Rescue therapy with daratumumab, an anti-CD38-antibody, was initiated. Significant pulmonary improvement was noticed after 4 weekly injections of 1,800 mg. After 6 months of follow up, stable disease remission with significant pulmonary improvement and persistent depletion of CD38+ plasma cells and MDA5-antibody titers were seen. This is the first report of the successful use of daratumumab in dermatomyositis. It highlights the potential of CD38 targeted therapies for severe antibody-mediated autoimmune diseases such as dermatomyositis.
Podocyte maintenance and stress resistance are exquisitely based on high basal rates of autophagy making these cells a unique model to unravel mechanisms of autophagy regulation. Polyamines have key ...cellular functions such as proliferation, nucleic acid biosynthesis and autophagy. Here we test whether endogenous spermidine signaling is a driver of basal and dynamic autophagy in podocytes by using genetic and pharmacologic approaches to interfere with different steps of polyamine metabolism. Translational studies revealed altered spermidine signaling in focal segmental glomerulosclerosis in vivo and in vitro. Exogenous spermidine supplementation emerged as new treatment strategy by successfully activating autophagy in vivo via inhibition of EP300, a protein with an essential role in controlling cell growth, cell division and prompting cells to differentiate to take on specialized functions. Surprisingly, gas chromatography-mass spectroscopy based untargeted metabolomics of wild type and autophagy deficient primary podocytes revealed a positive feedback mechanism whereby autophagy itself maintains polyamine metabolism and spermidine synthesis. The transcription factor MAFB acted as an upstream regulator of polyamine metabolism. Thus, our data highlight a novel positive feedback loop of autophagy and spermidine signaling allowing maintenance of high basal levels of autophagy as a key mechanism to sustain the filtration barrier. Hence, spermidine supplementation may emerge as a new therapeutic to restore autophagy in glomerular disease.
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Renal proximal tubular cells constantly recycle nutrients to ensure minimal loss of vital substrates into the urine. Although most of the transport mechanisms have been discovered at the molecular ...level, little is known about the factors regulating these processes. Here, we show that mTORC1 and mTORC2 specifically and synergistically regulate PTC endocytosis and transport processes. Using a conditional mouse genetic approach to disable nonredundant subunits of mTORC1, mTORC2, or both, we showed that mice lacking mTORC1 or mTORC1/mTORC2 but not mTORC2 alone develop a Fanconi-like syndrome of glucosuria, phosphaturia, aminoaciduria, low molecular weight proteinuria, and albuminuria. Interestingly, proteomics and phosphoproteomics of freshly isolated kidney cortex identified either reduced expression or loss of phosphorylation at critical residues of different classes of specific transport proteins. Functionally, this resulted in reduced nutrient transport and a profound perturbation of the endocytic machinery, despite preserved absolute expression of the main scavenger receptors, MEGALIN and CUBILIN. Our findings highlight a novel mTOR-dependent regulatory network for nutrient transport in renal proximal tubular cells.
Nephron number is a major determinant of long-term renal function and cardiovascular risk. Observational studies suggest that maternal nutritional and metabolic factors during gestation contribute to ...the high variability of nephron endowment. However, the underlying molecular mechanisms have been unclear.
We used mouse models, including DNA methyltransferase (
and
) knockout mice, optical projection tomography, three-dimensional reconstructions of the nephrogenic niche, and transcriptome and DNA methylation analysis to characterize the role of DNA methylation for kidney development.
We demonstrate that DNA hypomethylation is a key feature of nutritional kidney growth restriction
and
and that DNA methyltransferases
and
are highly enriched in the nephrogenic zone of the developing kidneys. Deletion of
in nephron progenitor cells (in contrast to deletion of
or
) mimics nutritional models of kidney growth restriction and results in a substantial reduction of nephron number as well as renal hypoplasia at birth. In
-deficient mice, optical projection tomography and three-dimensional reconstructions uncovered a significant reduction of stem cell niches and progenitor cells. RNA sequencing analysis revealed that global DNA hypomethylation interferes in the progenitor cell regulatory network, leading to downregulation of genes crucial for initiation of nephrogenesis,
and its target
Derepression of germline genes, protocadherins,
genes, and endogenous retroviral elements resulted in the upregulation of IFN targets and inhibitors of cell cycle progression.
These findings establish DNA methylation as a key regulatory event of prenatal renal programming, which possibly represents a fundamental link between maternal nutritional factors during gestation and reduced nephron number.
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