The spatially resolved transcriptome signatures of glomeruli in chronic kidney disease.

Here, we used digital spatial profiling (DSP) to describe the glomerular transcriptomic signatures that may characterize the complex molecular mechanisms underlying progressive kidney disease in Alport syndrome, focal segmental glomerulosclerosis, and membranous nephropathy. Our results revealed significant transcriptional heterogeneity among diseased glomeruli, and this analysis showed that histologically similar glomeruli manifested different transcriptional profiles. Using glomerular pathology scores to establish an axis of progression, we identified molecular pathways with progressively decreased expression in response to increasing pathology scores, including signal recognition particle-dependent cotranslational protein targeting to membrane and selenocysteine synthesis pathways. We also identified a distinct signature of upregulated and downregulated genes common to all the diseases investigated when compared with nondiseased tissue from nephrectomies. These analyses using DSP at the single-glomerulus level could help to increase insight into the pathophysiology of kidney disease and possibly the identification of biomarkers of disease progression in glomerulopathies.

C3aR-initiated signaling is a critical mechanism of podocyte injury in membranous nephropathy.

The deposition of antipodocyte autoantibodies in the glomerular subepithelial space induces primary membranous nephropathy (MN), the leading cause of nephrotic syndrome worldwide. Taking advantage of the glomerulus-on-a-chip system, we modeled human primary MN induced by anti-PLA2R antibodies. Here we show that exposure of primary human podocytes expressing PLA2R to MN serum results in IgG deposition and complement activation on their surface, leading to loss of the chip permselectivity to albumin. C3a receptor (C3aR) antagonists as well as C3AR gene silencing in podocytes reduced oxidative stress induced by MN serum and prevented albumin leakage. In contrast, inhibition of the formation of the membrane-attack-complex (MAC), previously thought to play a major role in MN pathogenesis, did not affect permselectivity to albumin. In addition, treatment with a C3aR antagonist effectively prevented proteinuria in a mouse model of MN, substantiating the chip findings. In conclusion, using a combination of pathophysiologically relevant in vitro and in vivo models, we established that C3a/C3aR signaling plays a critical role in complement-mediated MN pathogenesis, indicating an alternative therapeutic target for MN.

Mitochondria Transplantation Mitigates Damage in an In Vitro Model of Renal Tubular Injury and in an Ex Vivo Model of DCD Renal Transplantation.

OBJECTIVES: To test whether mitochondrial transplantation (MITO) mitigates damage in 2 models of acute kidney injury (AKI). BACKGROUND: MITO is a process where exogenous isolated mitochondria are taken up by cells. As virtually any morbid clinical condition is characterized by mitochondrial distress, MITO may find a role as a treatment modality in numerous clinical scenarios including AKI. METHODS: For the in vitro experiments, human proximal tubular cells were damaged and then treated with mitochondria or placebo. For the ex vivo experiments, we developed a non-survival ex vivo porcine model mimicking the donation after cardiac death renal transplantation scenario. One kidney was treated with mitochondria, although the mate organ received placebo, before being perfused at room temperature for 24 hours. Perfusate samples were collected at different time points and analyzed with Raman spectroscopy. Biopsies taken at baseline and 24 hours were analyzed with standard pathology, immunohistochemistry, and RNA sequencing analysis. RESULTS: In vitro, cells treated with MITO showed higher proliferative capacity and adenosine 5'-triphosphate production, preservation of physiological polarization of the organelles and lower toxicity and reactive oxygen species production. Ex vivo, kidneys treated with MITO shed fewer molecular species, indicating stability. In these kidneys, pathology showed less damage whereas RNAseq analysis showed modulation of genes and pathways most consistent with mitochondrial biogenesis and energy metabolism and downregulation of genes involved in neutrophil recruitment, including IL1A, CXCL8, and PIK3R1. CONCLUSIONS: MITO mitigates AKI both in vitro and ex vivo.

Identification and Characterization of the Wilms Tumor Cancer Stem Cell.

A nephrogenic progenitor cell (NP) with cancer stem cell characteristics driving Wilms tumor (WT) using spatial transcriptomics, bulk and single cell RNA sequencing, and complementary in vitro and transplantation experiments is identified and characterized. NP from WT samples with NP from the developing human kidney is compared. Cells expressing SIX2 and CITED1 fulfill cancer stem cell criteria by reliably recapitulating WT in transplantation studies. It is shown that self-renewal versus differentiation in SIX2+CITED1+ cells is regulated by the interplay between integrins ITGß1 and ITGß4. The spatial transcriptomic analysis defines gene expression maps of SIX2+CITED1+ cells in WT samples and identifies the interactive gene networks involved in WT development. These studies define SIX2+CITED1+ cells as the nephrogenic-like cancer stem cells of WT and points to the renal developmental transcriptome changes as a possible driver in regulating WT formation and progression.

Generation of a Glomerular Filtration Barrier on a Glomerulus-on-a-Chip Platform.

Despite an enormous investment of clinical and financial resources, chronic kidney disease (CKD) remains a global health threat. The lack of reliable in vitro systems that can efficiently mimic the renal and glomerular environment has hampered our ability to successfully develop novel and more renal specific drugs. Even though some success in generating in vitro tubule analogues and kidney organoids has been described, a major challenge remains for the in vitro assembly of the filtration unit of the kidney, the glomerulus. We have recently developed a novel glomerulus-on-a-chip system that mimics the characteristic and functionality of the glomerular filtration barrier, including its response to injury. This system recapitulates the functions and structure of the in vivo glomerulus, including permselectivity; indeed, we have confirmed free diffusion of insulin as well as impermeability to physiological concentrations of albumin. Exposure to nephrotoxic agents like puromycin aminonucleoside leads to a significant increase in albumin leakage. When exposed to sera from patients with anti-podocyte autoantibodies, the chip shows albumin leakage to an extent proportional to in vivo clinical data, phenomenon not observed with sera from either healthy controls, confirming functional response to injury. We describe here the detailed procedure to obtain a glomerulus-on-a-chip system that replicates both phenotypically and functionally the in vivo glomerular microenvironment.

Intravital imaging reveals glomerular capillary distension and endothelial and immune cell activation early in Alport syndrome.

Alport syndrome (AS) is a genetic disorder caused by mutations in type IV collagen that lead to defective glomerular basement membrane, glomerular filtration barrier (GFB) damage, and progressive chronic kidney disease. While the genetic basis of AS is well known, the molecular and cellular mechanistic details of disease pathogenesis have been elusive, hindering the development of mechanism-based therapies. Here, we performed intravital multiphoton imaging of the local kidney tissue microenvironment in a X-linked AS mouse model to directly visualize the major drivers of AS pathology. Severely distended glomerular capillaries and aneurysms were found accompanied by numerous microthrombi, increased glomerular endothelial surface layer (glycocalyx) and immune cell homing, GFB albumin leakage, glomerulosclerosis, and interstitial fibrosis by 5 months of age, with an intermediate phenotype at 2 months. Renal histology in mouse or patient tissues largely failed to detect capillary aberrations. Treatment of AS mice with hyaluronidase or the ACE inhibitor enalapril reduced the excess glomerular endothelial glycocalyx and blocked immune cell homing and GFB albumin leakage. This study identified central roles of glomerular mechanical forces and endothelial and immune cell activation early in AS, which could be therapeutically targeted to reduce mechanical strain and local tissue inflammation and improve kidney function.

Emerging Technologies to Study the Glomerular Filtration Barrier.

Kidney disease is characterized by loss of glomerular function with clinical manifestation of proteinuria. Identifying the cellular and molecular changes that lead to loss of protein in the urine is challenging due to the complexity of the filtration barrier, constituted by podocytes, glomerular endothelial cells, and glomerular basement membrane. In this review, we will discuss how technologies like single cell RNA sequencing and bioinformatics-based spatial transcriptomics, as well as in vitro systems like kidney organoids and the glomerulus-on-a-chip, have contributed to our understanding of glomerular pathophysiology. Knowledge gained from these studies will contribute toward the development of personalized therapeutic approaches for patients affected by proteinuric diseases.

Loss of decay-accelerating factor triggers podocyte injury and glomerulosclerosis.

Kidney glomerulosclerosis commonly progresses to end-stage kidney failure, but pathogenic mechanisms are still poorly understood. Here, we show that podocyte expression of decay-accelerating factor (DAF/CD55), a complement C3 convertase regulator, crucially controls disease in murine models of adriamycin (ADR)-induced focal and segmental glomerulosclerosis (FSGS) and streptozotocin (STZ)-induced diabetic glomerulosclerosis. ADR induces enzymatic cleavage of DAF from podocyte surfaces, leading to complement activation. C3 deficiency or prevention of C3a receptor (C3aR) signaling abrogates disease despite DAF deficiency, confirming complement dependence. Mechanistic studies show that C3a/C3aR ligations on podocytes initiate an autocrine IL-1ß/IL-1R1 signaling loop that reduces nephrin expression, causing actin cytoskeleton rearrangement. Uncoupling IL-1ß/IL-1R1 signaling prevents disease, providing a causal link. Glomeruli of patients with FSGS lack DAF and stain positive for C3d, and urinary C3a positively correlates with the degree of proteinuria. Together, our data indicate that the development and progression of glomerulosclerosis involve loss of podocyte DAF, triggering local, complement-dependent, IL-1ß-induced podocyte injury, potentially identifying new therapeutic targets.

Circulating B Cells With Memory and Antibody-Secreting Phenotypes Are Detectable in Pediatric Kidney Transplant Recipients Before the Development of Antibody-Mediated Rejection.

Development of anti-human leukocyte antigen donor-specific antibodies (DSAs) is associated with antibody-mediated rejection (AMR) and reduced allograft survival in kidney transplant recipients. Whether changes in circulating lymphocytes anticipate DSA or AMR development is unclear. METHODS: We used time-of-flight mass cytometry to analyze prospectively collected peripheral blood mononuclear cells (PBMC) from pediatric kidney transplant recipients who developed DSA (DSA-positive recipients [DSAPOS], n = 10). PBMC were obtained at 2 months posttransplant, 3 months before DSA development, and at DSA detection. PBMC collected at the same time points posttransplant from recipients who did not develop DSA (DSA-negative recipients [DSANEG], n = 11) were used as controls. RESULTS: DSAPOS and DSANEG recipients had similar baseline characteristics and comparable frequencies of total B and T cells. Within DSAPOS recipients, there was no difference in DSA levels (mean fluorescence intensity [MFI]: 13 687 ± 4159 vs 11 375 ± 1894 in DSAPOSAMR-positive recipients (AMRPOS) vs DSAPOSAMR-negative recipients (AMRNEG), respectively; P = 0.630), C1q binding (5 DSAPOSAMRPOS [100%] vs 4 DSAPOSAMRNEG [80%]; P = 1.000), or C3d binding (3 DSAPOSAMRPOS [60%] vs 1 DSAPOSAMRNEG [20%]; P = 0.520) between patients who developed AMR and those who did not. However, DSAPOS patients who developed AMR (n = 5; 18.0 ± 3.6 mo post-DSA detection) had increased B cells with antibody-secreting (IgD-CD27+CD38+; P = 0.002) and memory (IgD-CD27+CD38-; P = 0.003) phenotypes compared with DSANEG and DSAPOSAMRNEG recipients at DSA detection. CONCLUSIONS: Despite the small sample size, our comprehensive phenotypic analyses show that circulating B cells with memory and antibody-secreting phenotypes are present at DSA onset, >1 year before biopsy-proven AMR in pediatric kidney transplant recipients.

Author Correction: A glomerulus-on-a-chip to recapitulate the human glomerular filtration barrier.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

A glomerulus-on-a-chip to recapitulate the human glomerular filtration barrier.

In this work we model the glomerular filtration barrier, the structure responsible for filtering the blood and preventing the loss of proteins, using human podocytes and glomerular endothelial cells seeded into microfluidic chips. In long-term cultures, cells maintain their morphology, form capillary-like structures and express slit diaphragm proteins. This system recapitulates functions and structure of the glomerulus, including permselectivity. When exposed to sera from patients with anti-podocyte autoantibodies, the chips show albuminuria proportional to patients' proteinuria, phenomenon not observed with sera from healthy controls or individuals with primary podocyte defects. We also show its applicability for renal disease modeling and drug testing. A total of 2000 independent chips were analyzed, supporting high reproducibility and validation of the system for high-throughput screening of therapeutic compounds. The study of the patho-physiology of the glomerulus and identification of therapeutic targets are also feasible using this chip.

Amniotic fluid cells: current progress and emerging challenges in renal regeneration.

Amniotic fluid (AF) contains a heterogeneous population of cells that have been identified to possess pluripotent and progenitor-like characteristics. These cells have been applied in various regenerative medicine applications ranging from in vitro cell differentiation to tissue engineering to cellular therapies for different organs including the heart, the liver, the lung, and the kidneys. In this review, we examine the different methodologies used for the derivation of amniotic fluid stem cells and renal progenitors, and their application in renal repair and regeneration. Moreover, we discuss the recent achievements and newly emerging challenges in our understanding of their biology, their immunoregulatory characteristics, and their paracrine-mediated therapeutic potential for the treatment of acute and chronic kidney diseases.

Direct Isolation and Characterization of Human Nephron Progenitors.

Mature nephrons originate from a small population of uninduced nephrogenic progenitor cells (NPs) within the cap mesenchyme. These cells are characterized by the coexpression of SIX2 and CITED1. Many studies on mouse models as well as on human pluripotent stem cells have advanced our knowledge of NPs, but very little is known about this population in humans, since it is exhausted before birth and strategies for its direct isolation are still limited. Here we report an efficient protocol for direct isolation of human NPs without genetic manipulation or stepwise induction procedures. With the use of RNA-labeling probes, we isolated SIX2+ CITED1+ cells from human fetal kidney for the first time. We confirmed their nephrogenic state by gene profiling and evaluated their nephrogenic capabilities in giving rise to mature renal cells. We also evaluated the ability to culture these cells without complete loss of SIX2 and CITED1 expression over time. In addition to defining the gene profile of human NPs, this in vitro system facilitates studies of human renal development and provides a novel tool for renal regeneration and bioengineering purposes. Stem Cells Translational Medicine 2017;6:419-433.

A step towards clinical application of acellular matrix: A clue from macrophage polarization.

The outcome of tissue engineered organ transplants depends on the capacity of the biomaterial to promote a pro-healing response once implanted in vivo. Multiple studies, including ours, have demonstrated the possibility of using the extracellular matrix (ECM) of animal organs as platform for tissue engineering and more recently, discarded human organs have also been proposed as scaffold source. In contrast to artificial biomaterials, natural ECM has the advantage of undergoing continuous remodeling which allows adaptation to diverse conditions. It is known that natural matrices present diverse immune properties when compared to artificial biomaterials. However, how these properties compare between diseased and healthy ECM and artificial scaffolds has not yet been defined. To answer this question, we used decellularized renal ECM derived from WT mice and from mice affected by Alport Syndrome at different time-points of disease progression as a model of renal failure with extensive fibrosis. We characterized the morphology and composition of these ECMs and compared their in vitro effects on macrophage activation with that of synthetic scaffolds commonly used in the clinic (collagen type I and poly-L-(lactic) acid, PLLA). We showed that ECM derived from Alport kidneys differed in fibrous protein deposition and cytokine content when compared to ECM derived from WT kidneys. Yet, both WT and Alport renal ECM induced macrophage differentiation mainly towards a reparative (M2) phenotype, while artificial biomaterials towards an inflammatory (M1) phenotype. Anti-inflammatory properties of natural ECMs were lost when homogenized, hence three-dimensional structure of ECM seems crucial for generating an anti-inflammatory response. Together, these data support the notion that natural ECM, even if derived from diseased kidneys promote a M2 protolerogenic macrophage polarization, thus providing novel insights on the applicability of ECM obtained from discarded organs as ideal scaffold for tissue engineering.

Decellularized Renal Matrix and Regenerative Medicine of the Kidney: A Different Point of View.

Over the past years, extracellular matrix (ECM) obtained from whole organ decellularization has been investigated as a platform for organ engineering. The ECM is composed of fibrous and nonfibrous molecules providing structural and biochemical support to the surrounding cells. Multiple decellularization techniques, including ours, have been optimized to maintain the composition, microstructure, and biomechanical properties of the native renal ECM that are difficult to obtain during the generation of synthetic substrates. There are evidences suggesting that in vivo implanted renal ECM has the capacity to induce formation of vasculature-like structures, but long-term in vivo transplantation and filtration activity by these tissue-engineered constructs have not been investigated or reported. Therefore, even if the process of renal decellularization is possible, the repopulation of the renal matrix with functional renal cell types is still very challenging. This review aims to summarize the current reports on kidney tissue engineering with the use of decellularized matrices and addresses the challenges in creating functional kidney units. Finally, this review discusses how future studies investigating cell-matrix interaction may aid the generation of a functional renal unit that would be transplantable into patients one day.

Renal Extracellular Matrix Scaffolds From Discarded Kidneys Maintain Glomerular Morphometry and Vascular Resilience and Retains Critical Growth Factors.

BACKGROUND: Extracellular matrix (ECM) scaffolds, obtained through detergent-based decellularization of native kidneys, represent the most promising platform for investigations aiming at manufacturing kidneys for transplant purposes. We previously showed that decellularization of the human kidney yields renal ECM scaffolds (hrECMs) that maintain their basic molecular components, are cytocompatible, stimulate angiogenesis, and show an intact innate vasculature. However, evidence that the decellularization preserves glomerular morphometric characteristics, physiological parameters (pressures and resistances of the vasculature bed), and biological properties of the renal ECM, including retention of important growth factors (GFs), is still missing. METHODS: To address these issues, we studied the morphometry and resilience of hrECMs' native vasculature with resin casting at electronic microscopy and pulse-wave measurements, respectively. Moreover, we determined the fate of 40 critical GFs post decellularization with a glass chip-based multiplex enzyme-linked immunosorbent assay array and in vitro immunofluorescence. RESULTS: Our method preserves the 3-dimensional conformation of the native glomerulus. Resin casting and pulse-wave measurements, showed that hrECMs preserves the microvascular morphology and morphometry, and physiological function. Moreover, GFs including vascular endothelial growth factor and its receptors are retained within the matrices. CONCLUSIONS: Our results indicate that discarded human kidneys are a suitable source of renal scaffolds because they maintain a well-preserved structure and function of the vasculature, as well as GFs that are fundamental to achieve a satisfying recellularization of the scaffold in vivo due to their angiogenic properties.

Prolonged fasting reduces IGF-1/PKA to promote hematopoietic-stem-cell-based regeneration and reverse immunosuppression.

Immune system defects are at the center of aging and a range of diseases. Here, we show that prolonged fasting reduces circulating IGF-1 levels and PKA activity in various cell populations, leading to signal transduction changes in long-term hematopoietic stem cells (LT-HSCs) and niche cells that promote stress resistance, self-renewal, and lineage-balanced regeneration. Multiple cycles of fasting abated the immunosuppression and mortality caused by chemotherapy and reversed age-dependent myeloid-bias in mice, in agreement with preliminary data on the protection of lymphocytes from chemotoxicity in fasting patients. The proregenerative effects of fasting on stem cells were recapitulated by deficiencies in either IGF-1 or PKA and blunted by exogenous IGF-1. These findings link the reduced levels of IGF-1 caused by fasting to PKA signaling and establish their crucial role in regulating hematopoietic stem cell protection, self-renewal, and regeneration.

Amniotic fluid stem cells prevent ß-cell injury.

BACKGROUND AIMS: The contribution of amniotic fluid stem cells (AFSC) to tissue protection and regeneration in models of acute and chronic kidney injuries and lung failure has been shown in recent years. In the present study, we used a chemically induced mouse model of type 1 diabetes to determine whether AFSC could play a role in modulating ß-cell injury and restoring ß-cell function. METHODS: Streptozotocin-induced diabetic mice were given intracardial injection of AFSC; morphological and physiological parameters and gene expression profile for the insulin pathway were evaluated after cell transplantation. RESULTS: AFSC injection resulted in protection from ß-cell damage and increased ß-cell regeneration in a subset of mice as indicated by glucose and insulin levels, increased islet mass and preservation of islet structure. Moreover, ß-cell preservation/regeneration correlated with activation of the insulin receptor/Pi3K/Akt signaling pathway and vascular endothelial growth factor-A expression involved in maintaining ß-cell mass and function. CONCLUSIONS: Our results suggest a therapeutic role for AFSC in preserving and promoting endogenous ß-cell functionality and proliferation. The protective role of AFSC is evident when stem cell transplantation is performed before severe hyperglycemia occurs, which suggests the importance of early intervention. The present study demonstrates the possible benefits of the application of a non-genetically engineered stem cell population derived from amniotic fluid for the treatment of type 1 diabetes mellitus and gives new insight on the mechanism by which the beneficial effect is achieved.

A novel source of cultured podocytes.

Amniotic fluid is in continuity with multiple developing organ systems, including the kidney. Committed, but still stem-like cells from these organs may thus appear in amniotic fluid. We report having established for the first time a stem-like cell population derived from human amniotic fluid and possessing characteristics of podocyte precursors. Using a method of triple positive selection we obtained a population of cells (hAKPC-P) that can be propagated in vitro for many passages without immortalization or genetic manipulation. Under specific culture conditions, these cells can be differentiated to mature podocytes. In this work we compared these cells with conditionally immortalized podocytes, the current gold standard for in vitro studies. After in vitro differentiation, both cell lines have similar expression of the major podocyte proteins, such as nephrin and type IV collagen, that are characteristic of mature functional podocytes. In addition, differentiated hAKPC-P respond to angiotensin II and the podocyte toxin, puromycin aminonucleoside, in a way typical of podocytes. In contrast to immortalized cells, hAKPC-P have a more nearly normal cell cycle regulation and a pronounced developmental pattern of specific protein expression, suggesting their suitability for studies of podocyte development for the first time in vitro. These novel progenitor cells appear to have several distinct advantages for studies of podocyte cell biology and potentially for translational therapies.

ß-Cell regeneration mediated by human bone marrow mesenchymal stem cells.

Bone marrow mesenchymal stem cells (BMSCs) have been shown to ameliorate diabetes in animal models. The mechanism, however, remains largely unknown. An unanswered question is whether BMSCs are able to differentiate into ß-cells in vivo, or whether BMSCs are able to mediate recovery and/or regeneration of endogenous ß-cells. Here we examined these questions by testing the ability of hBMSCs genetically modified to transiently express vascular endothelial growth factor (VEGF) or pancreatic-duodenal homeobox 1 (PDX1) to reverse diabetes and whether these cells were differentiated into ß-cells or mediated recovery through alternative mechanisms. Human BMSCs expressing VEGF and PDX1 reversed hyperglycemia in more than half of the diabetic mice and induced overall improved survival and weight maintenance in all mice. Recovery was sustained only in the mice treated with hBMSCs-VEGF. However, de novo ß-cell differentiation from human cells was observed in mice in both cases, treated with either hBMSCs-VEGF or hBMSCs- PDX1, confirmed by detectable level of serum human insulin. Sustained reversion of diabetes mediated by hBMSCs-VEGF was secondary to endogenous ß-cell regeneration and correlated with activation of the insulin/IGF receptor signaling pathway involved in maintaining ß-cell mass and function. Our study demonstrated the possible benefit of hBMSCs for the treatment of insulin-dependent diabetes and gives new insight into the mechanism of ß-cell recovery after injury mediated by hBMSC therapy.