Mesenchymal stem cells (MSCs) reside in the perivascular niche of many organs, including kidney, lung, liver, and heart, although their roles in these tissues are poorly understood. Here, we ...demonstrate that Gli1 marks perivascular MSC-like cells that substantially contribute to organ fibrosis. In vitro, Gli1+ cells express typical MSC markers, exhibit trilineage differentiation capacity, and possess colony-forming activity, despite constituting a small fraction of the platelet-derived growth factor-β (PDGFRβ)+ cell population. Genetic lineage tracing analysis demonstrates that tissue-resident, but not circulating, Gli1+ cells proliferate after kidney, lung, liver, or heart injury to generate myofibroblasts. Genetic ablation of these cells substantially ameliorates kidney and heart fibrosis and preserves ejection fraction in a model of induced heart failure. These findings implicate perivascular Gli1+ MSC-like cells as a major cellular origin of organ fibrosis and demonstrate that these cells may be a relevant therapeutic target to prevent solid organ dysfunction after injury.
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•Gli1 marks a perivascular network of MSC-like cells across major organs•Gli1+ cells are a CFU-F enriched fraction of the interstitial PDGFRβ+ population•Upon organ injury resident Gli1+ cells expand and become myofibroblasts•Genetic ablation of Gli1+ cells ameliorates fibrosis and rescues organ function
The cellular origins of fibrosis in different tissues are unclear. Kramann et al. show that Gli1 marks a network of perivascular mesenchymal-stem-cell-like cells that generate myofibroblasts and play a central role in organ fibrosis after injury, and ablating these cells ameliorates fibrosis and rescues organ function.
Failure of the glomerular filtration barrier, primarily by loss of slit diaphragm architecture, underlies nephrotic syndrome in minimal change disease. The etiology remains unknown. The efficacy of B ...cell-targeted therapies in some patients, together with the known proteinuric effect of anti-nephrin antibodies in rodent models, prompted us to hypothesize that nephrin autoantibodies may be present in patients with minimal change disease.
We evaluated sera from patients with minimal change disease, enrolled in the Nephrotic Syndrome Study Network (NEPTUNE) cohort and from our own institutions, for circulating nephrin autoantibodies by indirect ELISA and by immunoprecipitation of full-length nephrin from human glomerular extract or a recombinant purified extracellular domain of human nephrin. We also evaluated renal biopsies from our institutions for podocyte-associated punctate IgG colocalizing with nephrin by immunofluorescence.
In two independent patient cohorts, we identified circulating nephrin autoantibodies during active disease that were significantly reduced or absent during treatment response in a subset of patients with minimal change disease. We correlated the presence of these autoantibodies with podocyte-associated punctate IgG in renal biopsies from our institutions. We also identified a patient with steroid-dependent childhood minimal change disease that progressed to end stage kidney disease; she developed a massive post-transplant recurrence of proteinuria that was associated with high pretransplant circulating nephrin autoantibodies.
Our discovery of nephrin autoantibodies in a subset of adults and children with minimal change disease aligns with published animal studies and provides further support for an autoimmune etiology. We propose a new molecular classification of nephrin autoantibody minimal change disease to serve as a framework for instigation of precision therapeutics for these patients.
Acute kidney injury predisposes patients to the development of both chronic kidney disease and end-stage renal failure, but the molecular details underlying this important clinical association remain ...obscure. We report that kidney injury molecule-1 (KIM-1), an epithelial phosphatidylserine receptor expressed transiently after acute injury and chronically in fibrotic renal disease, promotes kidney fibrosis. Conditional expression of KIM-1 in renal epithelial cells (Kim1(RECtg)) in the absence of an injury stimulus resulted in focal epithelial vacuolization at birth, but otherwise normal tubule histology and kidney function. By 4 weeks of age, Kim1(RECtg) mice developed spontaneous and progressive interstitial kidney inflammation with fibrosis, leading to renal failure with anemia, proteinuria, hyperphosphatemia, hypertension, cardiac hypertrophy, and death, analogous to progressive kidney disease in humans. Kim1(RECtg) kidneys had elevated expression of proinflammatory monocyte chemotactic protein-1 (MCP-1) at early time points. Heterologous expression of KIM-1 in an immortalized proximal tubule cell line triggered MCP-1 secretion and increased MCP-1-dependent macrophage chemotaxis. In mice expressing a mutant, truncated KIM-1 polypeptide, experimental kidney fibrosis was ameliorated with reduced levels of MCP-1, consistent with a profibrotic role for native KIM-1. Thus, sustained KIM-1 expression promotes kidney fibrosis and provides a link between acute and recurrent injury with progressive chronic kidney disease.
The genomic region encoding the miR-17-92 microRNA (miRNA) cluster is often amplified in lymphoma and other cancers, and cancer cells carrying this amplification have higher expression of miRNA in ...this cluster. Retroviral expression of miR-17-92 accelerates c-Myc-induced lymphoma development, but precisely how higher expression of miR-17-92 promotes lymphomagenesis remains unclear. Here we generated mice with higher expression of miR-17-92 in lymphocytes. These mice developed lymphoproliferative disease and autoimmunity and died prematurely. Lymphocytes from these mice showed more proliferation and less activation-induced cell death. The miR-17-92 miRNA suppressed expression of the tumor suppressor PTEN and the proapoptotic protein Bim. This mechanism probably contributed to the lymphoproliferative disease and autoimmunity of miR-17-92-transgenic mice and contributes to lymphoma development in patients with amplifications of the miR-17-92 coding region.
Tubulointerstitial abnormalities are predictive of the progression of diabetic kidney disease (DKD), and their targeting may be an effective means for prevention. Proximal tubular (PT) expression of ...kidney injury molecule (KIM)-1, as well as blood and urinary levels, are increased early in human diabetes and can predict the rate of disease progression. Here, we report that KIM-1 mediates PT uptake of palmitic acid (PA)-bound albumin, leading to enhanced tubule injury with DNA damage, PT cell-cycle arrest, interstitial inflammation and fibrosis, and secondary glomerulosclerosis. Such injury can be ameliorated by genetic ablation of the KIM-1 mucin domain in a high-fat-fed streptozotocin mouse model of DKD. We also identified TW-37 as a small molecule inhibitor of KIM-1-mediated PA-albumin uptake and showed in vivo in a kidney injury model in mice that it ameliorates renal inflammation and fibrosis. Together, our findings support KIM-1 as a new therapeutic target for DKD.
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•KIM-1 is expressed in proximal tubules of humans with diabetic kidney disease•KIM-1 mediates the endocytic uptake of palmitic acid (PA)-bound albumin•KIM-1-mediated PA-albumin uptake leads to interstitial inflammation and fibrosis•TW-37 prevents KIM-1-mediated PA-albumin uptake and ameliorates tubular injury
Mori et al. report that during diabetic kidney disease KIM-1 mediates proximal tubular uptake of palmitic acid-bound albumin, leading to enhanced tubule injury with interstitial inflammation and fibrosis, as well as secondary glomerulosclerosis. Further, they identify a small molecule inhibitor of KIM-1, TW-37, that can ameliorate the injury.
Phagocytosis of apoptotic cells by both professional and semi‐professional phagocytes is required for resolution of organ damage and maintenance of immune tolerance. KIM‐1/TIM‐1 is a ...phosphatidylserine receptor that is expressed on epithelial cells and can transform the cells into phagocytes. Here, we demonstrate that KIM‐1 phosphorylation and association with p85 results in encapsulation of phagosomes by lipidated LC3 in multi‐membrane organelles. KIM‐1‐mediated phagocytosis is not associated with increased ROS production, and NOX inhibition does not block LC3 lipidation. Autophagy gene expression is required for efficient clearance of apoptotic cells and phagosome maturation. KIM‐1‐mediated phagocytosis leads to pro‐tolerogenic antigen presentation, which suppresses CD4 T‐cell proliferation and increases the percentage of regulatory T cells in an autophagy gene‐dependent manner. Taken together, these data reveal a novel mechanism of epithelial biology linking phagocytosis, autophagy and antigen presentation to regulation of the inflammatory response.
Synopsis
This study reveals how KIM‐1/TIM‐1‐mediated phagocytosis down‐modulates inflammation through ATG5 and ULK1‐dependent autophagic processing of phagocytosed material to MHC I and MHC II.
Phagocytosis of apoptotic cells by KIM‐1, a non‐myeloid phagocytosis receptor, induces LC3 lipidation of resulting phagosomes.
Autophagy protein expression, ATG5, ULK1 and Beclin1, are required for LC3 targeting to phagosomes and efficient phagosome acidification and maturation.
KIM‐1 signaling via the PI3 kinase subunit p85 promotes LC3 lipidation and accumulation on phagosomes.
Phagocytosed material processed through autophagy is presented to MHC I and MHC II.
Enhanced antigen presentation resulting from autophagic processing results in a pro‐tolerogenic milieu, reducing the percentage of CD4 effector T cells while increasing the percentage of regulatory T cells.
Phosphatidylserine receptor KIM‐1/TIM‐1‐mediated phagocytosis and autophagic processing of apoptotic cells promote antigen presentation in epithelial cells to modulate inflammation.
Focal segmental glomerulosclerosis (FSGS) is a pattern of kidney injury observed either as an idiopathic finding or as a consequence of underlying systemic conditions. Several genes have been ...identified that, when mutated, lead to inherited FSGS and/or the related nephrotic syndrome. These findings have accelerated the understanding of glomerular podocyte function and disease, motivating our search for additional FSGS genes. Using linkage analysis, we identified a locus for autosomal-dominant FSGS susceptibility on a region of chromosome 14q. By sequencing multiple genes in this region, we detected nine independent nonconservative missense mutations in INF2, which encodes a member of the formin family of actin-regulating proteins. These mutations, all within the diaphanous inhibitory domain of INF2, segregate with FSGS in 11 unrelated families and alter highly conserved amino acid residues. The observation that alterations in this podocyte-expressed formin cause FSGS emphasizes the importance of fine regulation of actin polymerization in podocyte function.
The number of glomeruli and glomerulosclerosis evaluated on kidney biopsy slides constitute standard components of a renal pathology report. Prevailing methods for glomerular assessment remain ...manual, labor intensive, and nonstandardized. We developed a deep learning framework to accurately identify and segment glomeruli from digitized images of human kidney biopsies.
Trichrome-stained images (
= 275) from renal biopsies of 171 patients with chronic kidney disease treated at the Boston Medical Center from 2009 to 2012 were analyzed. A sliding window operation was defined to crop each original image to smaller images. Each cropped image was then evaluated by at least 3 experts into 3 categories: (i) no glomerulus, (ii) normal or partially sclerosed (NPS) glomerulus, and (iii) globally sclerosed (GS) glomerulus. This led to identification of 751 unique images representing nonglomerular regions, 611 images with NPS glomeruli, and 134 images with GS glomeruli. A convolutional neural network (CNN) was trained with cropped images as inputs and corresponding labels as output. Using this model, an image processing routine was developed to scan the test images to segment the GS glomeruli.
The CNN model was able to accurately discriminate nonglomerular images from NPS and GS images (performance on test data: Accuracy: 92.67% ± 2.02% and Kappa: 0.8681 ± 0.0392). The segmentation model that was based on the CNN multilabel classifier accurately marked the GS glomeruli on the test data (Matthews correlation coefficient = 0.628).
This work demonstrates the power of deep learning for assessing complex histologic structures from digitized human kidney biopsies.
Primary membranous nephropathy is a leading cause of adult nephrotic syndrome. The field took a major step forward with the identification of phospholipase A2 receptor (PLA2R) as a target antigen in ...the majority of cases and with the ability to measure circulating autoantibodies to PLA2R. Since then, the existence of additional target antigens such as thrombospondin type-1 domain–containing 7A, exostosin 1 and 2, neural EGFL like 1, and semaphorin 3B has been demonstrated. The ability to detect and monitor levels of circulating autoantibodies has opened a new window onto the humoral aspect of primary membranous nephropathy. Clinicians now rely on clinical parameters such as proteinuria, as well as levels of circulating autoantibodies against PLA2R and the results of immunofluorescence staining for PLA2R within kidney biopsy tissue, to guide the management of this disease. The relationship between immunologic and clinical disease course is consistent, but not necessarily intuitive. In addition, kidney biopsy provides only a single snapshot of disease that needs to be interpreted in light of changing clinical and serological findings. A clear understanding of these dynamic parameters is essential for staging, treatment, and management of this disease. This review aims to shed light on current knowledge regarding the development and time course of changes in the serum levels of autoantibodies against PLA2R, proteinuria, and histological findings that underlie the pathophysiology of primary membranous nephropathy.
Chronic kidney damage is routinely assessed semiquantitatively by scoring the amount of fibrosis and tubular atrophy in a renal biopsy sample. Although image digitization and morphometric techniques ...can better quantify the extent of histologic damage, we need more widely applicable ways to stratify kidney disease severity.
We leveraged a deep learning architecture to better associate patient-specific histologic images with clinical phenotypes (training classes) including chronic kidney disease (CKD) stage, serum creatinine, and nephrotic-range proteinuria at the time of biopsy, and 1-, 3-, and 5-year renal survival. Trichrome-stained images processed from renal biopsy samples were collected on 171 patients treated at the Boston Medical Center from 2009 to 2012. Six convolutional neural network (CNN) models were trained using these images as inputs and the training classes as outputs, respectively. For comparison, we also trained separate classifiers using the pathologist-estimated fibrosis score (PEFS) as input and the training classes as outputs, respectively.
CNN models outperformed PEFS across the classification tasks. Specifically, the CNN model predicted the CKD stage more accurately than the PEFS model (κ = 0.519 vs. 0.051). For creatinine models, the area under curve (AUC) was 0.912 (CNN) versus 0.840 (PEFS). For proteinuria models, AUC was 0.867 (CNN) versus 0.702 (PEFS). AUC values for the CNN models for 1-, 3-, and 5-year renal survival were 0.878, 0.875, and 0.904, respectively, whereas the AUC values for PEFS model were 0.811, 0.800, and 0.786, respectively.
The study demonstrates a proof of principle that deep learning can be applied to routine renal biopsy images.
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