Genome-wide analysis of WT1-controlled gene expression in podocytes
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ABSTRACT: We identified binding sites of the Wilms' tumor suppressor protein WT1 in the mouse podocyte genome in vivo by ChIP-seq. Furthermore, we provide a podocyte transcriptome derived from primary podocytes that were isolated by FACS on mouse glomeruli. In short, we show that WT1 activates a highly specific podocyte transcriptome by binding to putative podocyte-specific enhancers and TSS of target genes. Genes bound by WT1 in podocytes include the majority of genes mutated in hereditary podocytopathies as well as components of the slit diaphragm, actin cytoskeleton, extracellular matrix, and within endocytosis pathways. Furthermore, we infer a podocyte TF network from DNA-binding motifs enriched at WT1-bound loci that includes Tead, Lmx1b, Mafb, Tcf21, and Fox-class transcription factors. Examination of transcription factor binding sites for WT1 by ChIP-seq. Transcriptome analysis of podocytes by RNA-seq.
Project description:We identified binding sites of the Wilms' tumor suppressor protein WT1 in the mouse podocyte genome in vivo by ChIP-seq. Furthermore, we provide a podocyte transcriptome derived from primary podocytes that were isolated by FACS on mouse glomeruli. In short, we show that WT1 activates a highly specific podocyte transcriptome by binding to putative podocyte-specific enhancers and TSS of target genes. Genes bound by WT1 in podocytes include the majority of genes mutated in hereditary podocytopathies as well as components of the slit diaphragm, actin cytoskeleton, extracellular matrix, and within endocytosis pathways. Furthermore, we infer a podocyte TF network from DNA-binding motifs enriched at WT1-bound loci that includes Tead, Lmx1b, Mafb, Tcf21, and Fox-class transcription factors.
Project description:The transcription factor MafB is essential for differentiation and foot process formation of podocytes. In order to identify the downstream targets of MafB, we analyzed the Mafb-deficient podocyte by RNA-seq. We found slit diaphragm-related protein (Nphs1, Magi2), Rho GTPase-activating protein (Arhgap24, Iqgap2) and podocyte-specific transcription factor (Tcf21) were significantly reduced in MafB cKO glomeruli. This indicates that one of these factors might be directly regulated by MafB to maintain its function in podocyte maintenance.
Project description:In the context of human disease, the mechanisms whereby transcription factors reprogram gene expression in reparative responses to injury are not well understood. We have studied the mechanisms of transcriptional reprogramming in disease using murine kidney podocytes as a model for tissue injury. Podocytes are a crucial component of glomeruli, the filtration units of each nephron. Podocyte injury is the initial event in many processes that lead to End Stage Kidney Disease. FOXC2 is a transcription factor known to regulate gene expression in podocytes. FOXC2 and WT1 are both required for podocyte differentiation. Using murine models and human kidney organoids, we investigated FOXC2-mediated transcriptional reprogramming during the course of podocyte injury. Correlating FOXC2 and WT1 ChIP-seq analyses demonstrated that they co-bind many genes expressed in podocytes. Reprogramming the transcriptome involved highly dynamic changes in the binding of FOXC2 and WT1 to target genes during a reparative injury response.
Project description:Podocytes are essential cells of the renal blood filter. They structurally compose the renal blood filter by interdigitating with neighboring podocytes by the means of a modified adherens junction, the slit membrane. In podocyte injury, loss of podocytes is a common feature. Podocyte loss could be mediated by the cleavage of podocyte cell adhesion molecules through the A Disintegrin and Metalloproteinase 10 (ADAM10). Here we show that ADAM10 is highly abundant at the site of blood filtration, namely at podocyte foot processes. Podocyte-expressed ADAM10 is not required for the development of the renal filter but plays a major role in podocyte injury. Following antibody-mediated injury, ADAM10 is upregulated in humans and mice. ADAM10 activity results in the cleavage of cell-cell adhesion molecules. This cleavage paves the way for an activation of the injury related Wnt/-catenin signaling pathway and for podocyte loss. We therefore conclude that ADAM10-mediated ectodomain shedding of injury-related cadherins drives podocyte injury. As part of this project, we have analyzed the membrane proteome of murin podocytes to evaluate the abundance of membrane bound proteases.
Project description:Kidney podocytes and their slit diaphragms contribute to prevent urinary protein loss. T cell from patients with systemic lupus erythematosus display increased expression of calcium/calmodulin kinase IV (CaMKIV). Here we evaluated the functional role of CaMKIV in lupus nephritis (LN) using kidney biopsy specimens and human podocyte cell line (AB8/13). We found that exposure of podocytes to IgG from LN patients resulted in entry of IgG into the cytoplasm. CaMKIV expression was found to be increased in podocytes of LN kidney biopsy specimens and exposure to IgG from LN patients. IgG entered podocytes using the FcRn receptor because when podocytes where treated with FcRn siRNA less IgG was found in the cytoplasm. The DNA microarray studies of podocytes exposed to LN IgG revealed that genes that are related to the activation of immune cells or podocyte damage were upregulated. These genes included CD86, CaMKIV, PTPN22, PDE5A, CD47 and MALT1. Interestingly, CD86 expression decreased after silencing CaMKIV in podocytes. Also, in situ hybridization experiments showed that the expression of CD86 was reduced in podocytes from MRL/lpr.camkivM-bM-^HM-^R/M-bM-^HM-^R mice. IgG from LN patients may enter podocytes through the FcRn and causes the upregulation of a distinct set of genes which may alter podocyte function. Upregulation of CaMKIV appears to precede that of genes known to be linked to podocyte damage such as CD86. These findings may indicate that inhibition of CaMKIV may prove of clinical use in patients with LN. IgG Purification Kits (Dojindo Molecular Technologies, Inc.) are used for isolation and purification of immunoglobulin G of healthy and normal individual according to the manufacturerM-bM-^@M-^Ys protocol. Flow through the column was used for non IgG binding samples. Cultured human podocytes with IgG purified from sera of normal individuals and LN patient for 24 hr were collected for RNA.
Project description:We profiled Wt1, a key transcription factor, in purified murine podocytes based on ChIP-seq during the time course of podocyte injury by ADR.
Project description:The Wilms tumor-suppressor gene WT1, a key player in renal development, also has a crucial role in maintenance of the glomerulus in the mature kidney. However, molecular pathways orchestrated by WT1 in podocytes, where it is highly expressed, remain unknown. Their defects are thought to modify the cross-talk between podocytes and other glomerular cells and ultimately lead to glomerular sclerosis, as observed in diffuse mesangial sclerosis (DMS) a nephropathy associated with WT1 mutations. To identify podocyte WT1 targets, we generated a novel DMS mouse line, performed gene expression profiling in isolated glomeruli, and identified excellent candidates that may modify podocyte differentiation and growth factor signalling in glomeruli. Scel, encoding sciellin, a protein of the cornified envelope in the skin, and sulf1, encoding a 6-O endosulfatase, are shown to be expressed in wild type podocytes and to be strongly down-regulated in mutants. Co-expression of Wt1, Scel and Sulf1 was also found in a mesonephric cell line, and siRNA-mediated knockdown of WT1 decreased Scel and Sulf1 mRNAs and proteins. By ChIP we show that Scel and Sulf1 are direct WT1 targets. Cyp26a1, encoding an enzyme involved in the degradation of retinoic acid, is shown to be up-regulated in mutant podocytes. Cyp26a1 may play a role in the development of glomerular lesions but does not seem to be regulated by WT1. These results provide novel clues in our understanding of normal glomerular function and early events involved in glomerulosclerosis. Experiment Overall Design: Isolation of glomeruli from mutant (FVB-N4 Wt1+/R394W) and wild-type (FVB-N4 Wt1+/+) was performed after cardiac Dynabead perfusion. GeneChip analysis of glomeruli from 5 Wt1+/R394W mice and 5 Wt1+/+ littermates (N4-FVB) were performed independently. Animals were unweaned 27-day-old males. The Wt1+/R394W mice used were showing little albuminuria (<3 ug/ul on Coomassie blue stained SDS-PAGE gel) and no evidence of mesangial lesions by light microscopy.
Project description:The Wilms tumor-suppressor gene WT1, a key player in renal development, also has a crucial role in maintenance of the glomerulus in the mature kidney. However, molecular pathways orchestrated by WT1 in podocytes, where it is highly expressed, remain unknown. Their defects are thought to modify the cross-talk between podocytes and other glomerular cells and ultimately lead to glomerular sclerosis, as observed in diffuse mesangial sclerosis (DMS) a nephropathy associated with WT1 mutations. To identify podocyte WT1 targets, we generated a novel DMS mouse line, performed gene expression profiling in isolated glomeruli, and identified excellent candidates that may modify podocyte differentiation and growth factor signalling in glomeruli. Scel, encoding sciellin, a protein of the cornified envelope in the skin, and sulf1, encoding a 6-O endosulfatase, are shown to be expressed in wild type podocytes and to be strongly down-regulated in mutants. Co-expression of Wt1, Scel and Sulf1 was also found in a mesonephric cell line, and siRNA-mediated knockdown of WT1 decreased Scel and Sulf1 mRNAs and proteins. By ChIP we show that Scel and Sulf1 are direct WT1 targets. Cyp26a1, encoding an enzyme involved in the degradation of retinoic acid, is shown to be up-regulated in mutant podocytes. Cyp26a1 may play a role in the development of glomerular lesions but does not seem to be regulated by WT1. These results provide novel clues in our understanding of normal glomerular function and early events involved in glomerulosclerosis.
Project description:Podocytes are cells of the visceral epithelium in the kidneys and form a crucial component of the glomerular filtration barrier, contributing to size selectivity and maintaining a massive filtration surface. We are interested in pursuing a microarray analysis to identify the glycosylation-related genes that are modulated in podocytes during insulin and glucose stimulation. As such, we propose to isolate RNA from cultured AB 8/13 human podocyte cell line in their normal state and treated with different concentrations of insulin and glucose. Initially, we would like to analyze 12 samples (Normal control, 2 Starved controls, Insulin experiments 1-4, and glucose experiments 1-5). These experiments would give us information on the gene regulation changes in different healthy and diabetic conditions. In addition to providing possible identification of the unknown proteins involved with diabetic nephropathy, such analysis would provide novel information about early responses by podocytes in response to insulin and glucose level changes in vitro. The results from this analysis will be utilized to focus our research with regard to glycosylation of the proteins in the podocyte slit diaphragm.
Project description:The most common genetic causes of steroid-resistant nephrotic syndrome (SRNS) are mutations in the NPHS2 gene, which encodes the lipid-binding protein podocin. Mass spectrometry and cDNA sequencing revealed the existence of a second shorter isoform in the human kidney in addition to the well-studied canonical full-length protein. Distinct subcellular localization of the shorter isoform that lacks part of the conserved PHB domain suggested a physiological role. Here we analyzed whether this protein can substitute for the canonical full-length protein. The short isoform of podocin is not found in other organisms except humans. We therefore now analysed a mouse line expressing the equivalent podocin isoform (podocinΔexon5) by CRISPR/Cas-mediated genome editing. We characterized the phenotype of these mice expressing podocinΔexon5 and used targeted mass spectrometry and qPCR to compare protein and RNA levels of podocinwildtype and podocinΔexon. After immunolabeling slit diaphragm components, STED microscopy was applied to visualize alterations of the podocytes’ foot process morphology. Mice homozygous for podocinΔexon5 were born heavily albuminuric and did not survive past the first 24 hours after birth. Targeted mass spectrometry revealed massively decreased protein levels of podocinΔexon5, whereas RNA abundance was not different from the canonical form of podocin. STED microscopy revealed the complete absence of podocin at the podocytes’ slit diaphragm and severe morphological alterations of podocyte foot processes. Mice heterozygous for podocinΔexon5 were phenotypically and morphologically unaffected despite decreased podocin and nephrin protein levels.The murine equivalent to the human short isoform of podocin cannot stabilize the lipid-protein complex at the podocyte slit diaphragm. Reduction of podocin levels at the site of the slit diaphragm complex has a detrimental effect on podocyte function and morphology. It is associated with decreased protein abundance of nephrin, the central component of the filtration-slit forming slit diaphragm protein complex.