Thromboxane receptor (TPr) activity is elevated in diabetes and contributes to complications of diabetic kidney disease (DKD). TPr blockade appears to have therapeutic potential. Several rodent models of DKD show attenuation of renal damage and proteinuria upon administration of the TPr antagonist, S18886. However, the cellular targets that underlie the injurious effects of TPr activation in DKD remain to be elucidated. A pilot study in our laboratory subjected a conditionally-immortalized mouse podocyte cell line to high glucose (25 mM D-glucose) and equibiaxial mechanical stretch (an in vitro simulator of increased glomerular capillary pressure associated with glomerular hyperfiltration in early diabetes). qRT-PCR revealed that exposure of podocytes to mechanical stretch (10% elongation) and high glucose for 6 hours yielded a 9-fold increase in TPr mRNA levels vs. controls (non-stretch, 5mM D-glucose + 25mM L-glucose) (p<0.05, n=5). We hypothesized that TPr expression and activity are increased in podocytes during the onset of DKD resulting in maladaptive effects on this key glomerular filtration barrier cell type. We showed that enhanced TPr signaling threatens podocytes viablility. Cultured podocytes treated with the TPr agonist, U-46619 (1 μM) for 24 hours are more vulnerable to apoptosis as quantified by Hoescht 33342 (20% cell death p<0.001, n=3) , TUNEL (30-fold increase, ns, n=3) and Annexin-V labeling (3-fold increase, p <0.001, n=3). To further support these in vitro findings, we developed a transgenic mouse with podocyte-specific overexpression of TPr. A construct consisting of a desensitization resistant mutant of the human TPr with both N- and C-terminal HA-epitope tags under the control of an 8.3 kb fragment of the immediate 5’ mouse NPHS1 promoter was cloned, isolated and injected into FVB/n oocytes that were implanted into pseudopregnant CD1 females. Founders were characterized for TPr transgene expression, and TPr transgene mRNA levels were detected by qRT-PCR. Our in vitro results suggest that increased TPr expression in podocytes of diabetic mice may contribute to filtration barrier damage and have important implications in the development and progression of DKD.

Glomerular diseases are the leading cause of end stage kidney disease worldwide. Podocyte injury plays a key role in the initiation and development of such diseases, which follow a progressive course due to the limited capacity of podocytes to regenerate. Podocytes are highly specialised, terminally differentiated cells, which play a vital role in the glomerular filtration barrier. They are also the main sites of expression of the Wilms Tumour Suppressor gene, WT1, in the adult. WT1 is a complex gene, which plays an essential role in renal development by controlling the process of mesenchymal to epithelial transition that forms the nephron. Adult podocytes maintain both epithelial and mesenchymal features and continue to express high levels of WT1. Little is known about the role of WT1 in adult podocytes as previous studies have been limited due to the confounding developmental effects and embryonic lethality of existing animal models. This thesis sought to investigate the hypothesis that WT1 is an essential gene in adult kidney and plays a fundamental role in the adult podocyte. Given its role in nephron development, WT1 loss was hypothesised to result in dedifferentiation and an alteration of the epithelial-mesenchymal balance in the podocyte, affecting its specialised function. Using an inducible, conditional animal model of Wt1 loss, Wt1 was deleted from the adult, confirming its essential role in adult kidney. Wt1 deletion resulted in severe podocyte injury and failure of the glomerular filtration barrier, as well as loss of expression of key podocyte genes. Preliminary analysis suggests this was not simply due to podocyte apoptosis and/or detachment, supporting a role for Wt1 in podocyte differentiation. This was corroborated by in vitro studies that demonstrated a requirement for Wt1 for podocyte differentiation. Significantly, Wt1 loss resulted in a marked change in the expression of epithelial and mesenchymal markers in podocytes, with upregulation of mesenchymal characteristics, in keeping with a transitional stage consistent with an earlier developmental form. To investigate the mechanism behind these findings a conditionally immortalised podocyte cell line was generated as a model of Wt1 loss in vitro. In order to confirm and specifically analyse the podocyte phenotype, BAC recombineering was utilised to produce a promoter-reporter transgene construct to attempt to generate a fluorescent-labelled, podocyte specific animal model of Wt1 loss. The findings of this thesis establish that Wt1 is essential for adult podocyte function, and appears to be a key upstream regulator of podocyte differentiation. Extension of this work may allow the identification of potential targets to promote podocyte differentiation and/or regeneration in the setting of acquired and progressive glomerular disease.

Background: Nephrotic syndrome (NS) occurs when the glomerular filtration barrier becomes abnormally permeable, leading to the clinical triad of proteinuria, massive oedema, and hypoalbuminaemia. Historically, NS has been thought to result from dysregulation of the immune system, although recent evidence suggests the glomerular podocyte plays a central role in disease pathogenesis. Children with NS are generally treated with an empiric course of glucocorticoid (Gc) therapy; a class of steroids which are activating ligands for the glucocorticoid receptor (GR) transcription factor. A major factor limiting the clinical utility of these agents is the marked variation observed in response to treatment. Although Gc-therapy has been the cornerstone of NS management for several decades, the mechanism of action, and target cell, remain poorly understood. Hypothesis and aims: The central hypothesis for this thesis states that glucocorticoids act directly on the podocyte to produce clinically useful effects without involvement of the immune system. Findings: Using a wild-type human podocyte cell line, I demonstrated that the basic GR-signalling mechanism is intact in the podocyte, and that glucocorticoids produce a direct, protective effect on the podocyte without immune cell involvement, by using electrical resistance across a podocyte monolayer as a surrogate marker for barrier integrity. To understand potential mechanisms underpinning this direct effect I defined the podocyte GR cistrome (using a combination of chromatin immunoprecipitation followed by massively parallel DNA sequencing and transcriptomic analysis) as well as total cell proteomics. Subsequent gene ontology analysis revealed that Gc treatment had prominent effects on podocyte motility, and these findings were validated with live-cell imaging. To gain mechanistic insight, I investigated the role of the pro-migratory small GTPase regulator Rac1, and demonstrated that treatment with Gc reduced Rac1 activity. Furthermore, the Rac1 inhibitor EHT 1864 had a direct, protective effect on the podocyte. To create a model to study the role of podocyte GR in vivo I generated a mouse line with a podocyte-specific GR deletion. Impact: Gc exposure produces potentially clinically-relevant effects directly on the podocyte, and Gc-induced podocyte hypomobility may underlie the clinical efficacy of these agents. Future animal studies investigating the consequences of GR deletion in the podocyte and the anti-proteinuric effects of Rac1 inhibition are warranted.

Thromboxane receptor (TPr) activity is elevated in diabetes and contributes to complications of diabetic kidney disease (DKD). TPr blockade appears to have therapeutic potential. Several rodent models of DKD show attenuation of renal damage and proteinuria upon administration of the TPr antagonist, S18886. However, the cellular targets that underlie the injurious effects of TPr activation in DKD remain to be elucidated. A pilot study in our laboratory subjected a conditionally-immortalized mouse podocyte cell line to high glucose (25 mM D-glucose) and equibiaxial mechanical stretch (an in vitro simulator of increased glomerular capillary pressure associated with glomerular hyperfiltration in early diabetes). qRT-PCR revealed that exposure of podocytes to mechanical stretch (10% elongation) and high glucose for 6 hours yielded a 9-fold increase in TPr mRNA levels vs. controls (non-stretch, 5mM D-glucose + 25mM L-glucose) (p<0.05, n=5). We hypothesized that TPr expression and activity are increased in podocytes during the onset of DKD resulting in maladaptive effects on this key glomerular filtration barrier cell type. We showed that enhanced TPr signaling threatens podocytes viablility. Cultured podocytes treated with the TPr agonist, U-46619 (1 μM) for 24 hours are more vulnerable to apoptosis as quantified by Hoescht 33342 (20% cell death p<0.001, n=3) , TUNEL (30-fold increase, ns, n=3) and Annexin-V labeling (3-fold increase, p <0.001, n=3). To further support these in vitro findings, we developed a transgenic mouse with podocyte-specific overexpression of TPr. A construct consisting of a desensitization resistant mutant of the human TPr with both N- and C-terminal HA-epitope tags under the control of an 8.3 kb fragment of the immediate 5’ mouse NPHS1 promoter was cloned, isolated and injected into FVB/n oocytes that were implanted into pseudopregnant CD1 females. Founders were characterized for TPr transgene expression, and TPr transgene mRNA levels were detected by qRT-PCR. Our in vitro results suggest that increased TPr expression in podocytes of diabetic mice may contribute to filtration barrier damage and have important implications in the development and progression of DKD.

京都大学 / 新制・課程博士 / 博士(医学) / 甲第23096号 / 医博第4723号 / 新制||医||1050(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 長船 健二, 教授 小川 修, 教授 藤田 恭之 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

Glomerular podocytes are epithelial cells that are attached to outer glomerular basement memberane (GBM) by foot processes, and blood filtration occurs through podocytes, GBM, and endothelial cells. Podocytes are under constant mechanical stress due to their location around outside of glomerular capillaries, which can be associated with glomerular hypertension. It is important for podocytes to maintain their mechanical integrity, since podocyte adhesion to GBM is crucial to prevent podocyte loss, detachment, and associated alteration in cell adhesive properties, and further progression of glomerular disease. In this study, we examined the role of stiffness in podocyte function with hypothesis that increasing substrate stiffness would promote development of cell structural features that are associated with stronger adhesion. In order to test this, polyacrylamide substrates with different stiffness ranged from 3750 Pa to 152600 Pa were generated and immortalized mouse podocytes were cultured on these substrates. Then we measured how substrate stiffness affects cell morphology and several structural proteins distribution. We found that the size and the number of attached cells increased with longer actin filaments as stiffness of substrate increased. Since proteinuria or glomerulosclerosis can be associated with podocyte actin cytoskeleton defect, we suggest podocytes in a "softer" environment are vulnerable to glomerular diseases, since stress fibers were shorter and less organized as substrates decreased stiffness. Our results relating to the presence and distribution of certain proteins in cells were somewhat inconclusive, since intensity of synaptopodin and vinculin did not correspond to the changes of stiffness, due to the possibility of other underway mechanisms that interfere with podocyte adhesion. There was no clear relationship between YAP and the changes of substrate stiffness, and one possible explanation could be due to the optical irregularities in the substrate. Overall, this study was able to show that increased substrate stiffness promoted cell structural feature development in podocytes. However, further studies are needed to better understand how changes in substrate mechanical properties can affect structural protein distribution in these cells.

Chronic kidney disease (CKD), defined as an irreversible reduction in glomerular filtration rate, is a large public health concern. Dissecting the genetic components of CKD is required to improve our understanding of disease pathogenesis. Researchers have identified that SHROOM3, has very high associations with kidney disease and function. Shroom3 encodes an actin-binding protein important in regulating cell and tissue morphogenesis. However, there is a lack of evidence supporting a role for Shroom3 in kidney function or disease. Here, I investigated the developmental and functional role of Shroom3 in the mammalian kidney. For the first time, I described the expression pattern of Shroom3 in the embryonic and adult mouse kidneys. By performing in situ hybridization and immunohistochemistry, I demonstrated that Shroom3 is expressed in the condensing mesenchyme, podocytes, and collecting ducts. I further showed that Shroom3 protein is localized in the foot processes of podocytes, utilizing immunogold labeling and transmission electron microscopy. In order to uncover a potential role of Shroom3 in the kidney, we utilized Shroom3 knockout mice. Shroom3 mutants demonstrated marked glomerular abnormalities including cystic and degenerating glomeruli, and reduced glomerular number. Scanning and transmission electron microscopic analyses of Shroom3 mutant glomeruli revealed disruptions in podocyte morphology characterized by disorganized foot processes with less interdigitation and segmental foot processes effacement. Furthermore, immunofluorescence analysis of mutant kidneys revealed aberrant distribution of podocyte actin-associated proteins. Elucidating the underlying molecular mechanism of this abnormal podocyte architecture; v we demonstrated that in the absence of Shroom3, Rho kinase is mislocalized in the apical membrane of podocytes. As a result, mislocalized Rho kinase failed to phosphorylate non-muscle myosin and induce actomyosin contraction resulting in a patchy granular distribution of actin in the podocytes of Shroom3 mutants. Taken together, our findings established that Shroom3 is essential for proper actin organization in the podocytes through interaction with Rock. Furthermore, we took advantage of a haploinsufficiency phenotype of Shroom3 heterozygote adult mice and demonstrated these mice develop glomerulosclerosis and proteinuria. In conclusion, our studies provided evidence to support a role for Shroom3 in kidney development and disease and support the GWAS studies that suggested a correlation between SHROOM3 variants and kidney function in humans. / Thesis / Master of Science (MSc)

No description available.

Le Syndrome Néphrotique à Lésions Glomérulaires Minimes (SNLGM) et la glomérulonéphrite extra membraneuse (GEM) sont deux podocytopathies primitives d'origine immunitaire associant des altérations immunes et des atteintes podocytaires à l'origine d'un syndrome néphrotique. Cependant, bien que l'origine dysimmunitaire soit confortée par de nombreux arguments cliniques, les mécanismes impliqués restent obscurs. Initialement identifié dans les lymphocytes T (LT) de patients en phase de poussée de SNLGM, le gène c-mip est également exprimé dans les podocytes de patients atteints de SNLGM et de GEM, alors qu'il est physiologiquement réprimé. Ainsi, les objectifs de ce travail étaient : 1) appréhender le rôle de c-mip dans le LT d'une part à travers l'étude d'un modèle murin transgénique (Tg), et 2) comprendre la fonction de c-mip au niveau du podocyte grâce au modèle expérimental de GEM humaine induit chez le rat.Le modèle murin Tg Lck-cmip surexprime spécifiquement c-mip dans les LT matures périphériques. Cette surexpression est à l'origine d'un phénotype lymphocytaire altéré marqué par une accumulation de LT naïf, et une inhibition de la synthèse de cytokines de type TH1 et TH2, après une activation T spécifique ex vivo. Cette régulation négative est associée à une accumulation des formes inactives des kinases de la famille des Src et un blocage du recrutement des lipids rafts nécessaire à la formation de la synapse immunologique. Ces résultats suggèrent donc que c-mip est un régulateur négatif de l'activation T impliqué dans la signalisation proximale lymphocytaire et pourrait être impliqué dans l'hyporéactivité lymphocytaire observée chez les patients atteints de SNLGM actif.L'étude de la néphrite de Heymann passive, un modèle expérimental de GEM humaine, montre que l'induction podocytaire de c-mip coïncide avec l'apparition de la protéinurie. Cette surexpression est associée d'une part, à une diminution des taux de synaptopodine qui engendre une diminution de l'activité RhoA, à l'origine d'une désorganisation du cytosquelette podocytaire, et d'autre part à une induction de DAPK (death-associated protein kinase) et ILK (Integrin Linked Kinase) impliquées dans des phénomènes pro-apoptotiques. La cyclosporine A en inhibant l'expression de c-mip restaure les taux de DAPK et ILK ainsi que l'activité RhoA. Ainsi dans le podocyte, c-mip semble impliquer dans les troubles de la signalisation podocytaire aboutissant à une protéinurie néphrotique.C-mip semble donc jouer un rôle crucial dans les perturbations podocytaires et lymphocytaires observées chez les patients atteints de podocytopathies primitives et représente à ce titre une cible thérapeutique.Mots clefs :C-mip, Syndrome Néphrotique à Lésions Glomérulaires Minimes, Glomerulonéphrite Extra Membraneuse, signalisation proximale, lymphocyte T, podocyte, cytosquelette / Minimal Change Nephrotic Syndrome (MCNS) and Membranous Nephropathy (MN) are two primitive immune podocytopathies associating immune alterations and podocyte damage ultimately leading to proteinuria. Although the immune origin of the disease is corroborated by numerous clinical data, the mechanisms involved are still unknown. In previous works by the team, the c-mip protein was found expressed in T lymphocytes (TL) from patients with MCNS relapse, and in podocytes from MCNS and MN patients, while it is physiologically repressed. The aims of the present work were: firstly, to investigate the rôle of c-mip in TL by the study of Lck-cmip transgenic mice (Tg); secondly, to understand c-mip function in podocyte using a rat experimental model of human MN (Heymann nephritis).Transgenic mice overexpressed specifically c-mip in peripheral mature TL. This expression led to an altered TL phenotype characterized by accumulation of naïve LT associated with inhibition of TH1's and TH2's cytokines, after T-specific activation ex vivo. This negative regulation was correlated with an increase in the inactive forms of Src kinases and a blockage of the lipid raft clustering required for immunological synapse formation. These results suggest that (i) c-mip is a negative regulator of the proximal signaling events associated with TL activation involved in proximal signaling and (ii) it could be involved in the TL hyporeactivity described in SNLGM patients.In the study based on passive Heymann Nephritis, the experimental model of MN, the results highlight a correlation between podocyte expression of c-mip and proteinuria. This expression is associated, on the one hand, with a decrease in synaptopodin levels, which generate a decrease of RhoA activity resulting in podocyte cytoskeleton disorganization, and on the other hand with DAPK (Death Associated Protein Kinase) and ILK (Integrin Linked Kinase) induction, known to be involved in pro-apoptotic mechanisms. Cyclosporin A inhibited c-mip expression and restored the basal levels of DAPK, ILK and Rhoa activity. These results suggest that in podocyte, c-mip could be involved in proximal signaling alterations leading to nephrotic proteinuria.In conclusion, c-mip could play a crucial rôle in both the lymphocyte and podocyte alterations observed in patients suffering from primitive podocytopathies, strongly suggesting its potential as a therapeutic target in these disorders.Key words :C-mip, MCNS, MN, proximal signaling, Src kinase, T lymphocyte, podocyte, cytoskeleton

The actin cytoskeleton is critical to the proper function of cells and its misregulation can lead to human disease states. As a consequence, actin dynamics is tightly controlled. To gain further insight into the mechanisms controlling actin dynamics, my studies have focused on two families of proteins implicated in actin regulation. The Nck proteins act as molecular adaptors in signal propagation by linking upstream mediators, which they recognize through the Nck SH2 domain, to downstream effectors, which bind the Nck SH3 domains. I have found that Nck is required in podocyte cells for proper foot process formation, a process involving actin cytoskeletal reorganization, and therefore for proper kidney function. Furthermore, I show that Nck links the podocyte adhesion protein nephrin to actin polymerization. In cell-based assays, nephrin-induced actin polymerization is dependent on an interaction with functional Nck, which occurs through binding of three phosphorylated tyrosine sites within the cytoplasmic tail of nephrin to the Nck SH2 domain. Finally, I demonstrate that the enteropathogenic E.coli protein Tir reorganizes the cytoskeleton by molecular-mimicry of nephrin-like signaling. The srGAP proteins are GTPase activating proteins that attenuate the activity Rho GTPases, proteins directly involved in actin cytoskeletal control. The regulatory mechanisms that control srGAP activity are unclear. I have found that the srGAP family members srGAP1, srGAP2, and srGAP3 interact, through their carboxy-terminal region with 14-3-3 proteins, and that this interaction is dependent on protein kinase C-induced phosphorylation of srGAP. 14-3-3 binding does not affect the activity of srGAP2, as determined using cell-based GAP assays. Further studies are required to clarify the biological significance of this interaction to srGAP regulation. The data presented in this thesis furthers our understanding of signaling networks that control the actin cytoskeleton, and brings us closer to the goal of fully understanding actin dynamics and cellular signaling.