Ephrin-B1 localizes at the slit diaphragm of the glomerular podocyte

14-3-3 Proteins stabilize actin and vimentin filaments to maintain processes in renal glomerular podocyte

14-3-3 proteins are a ubiquitously expressed family of adaptor proteins. Despite exhibiting high sequence homology, several 14-3-3 isoforms have isoform-specific binding partners and roles. We reported that 14-3-3β interacts with FKBP12 and synaptopodin to maintain the structure of actin fibers in podocytes. However, the precise localization and differential role of 14-3-3 isoforms in kidneys are unclear. Herein, we showed that 14-3-3β in glomeruli was restricted in podocytes, and 14-3-3σ in glomeruli was expressed in podocytes and mesangial cells. Although 14-3-3β was dominantly co-localized with FKBP12 in the foot processes, a part of 14-3-3β was co-localized with Par3 at the slit diaphragm. 14-3-3β interacted with Par3, and FKBP12 bound to 14-3-3β competitively with Par3. Deletion of 14-3-3β enhanced the interaction of Par3 with Par6 in podocytes. Gene silencing for 14-3-3β altered the structure of actin fibers and process formation. 14-3-3β and synaptopodin expression was decreased in podocyte injury models. In contrast, 14-3-3σ in podocytes was expressed in the primary processes. 14-3-3σ interacted with vimentin but not with the actin-associated proteins FKBP12 and synaptopodin. Gene silencing for 14-3-3σ altered the structure of vimentin fibers and process formation. 14-3-3σ and vimentin expression was increased in the early phase of podocyte injury models but was decreased in the late stage. Together, the localization of 14-3-3β at actin cytoskeleton plays a role in maintaining the foot processes and the Par complex in podocytes. In contrast, 14-3-3σ at vimentin cytoskeleton is essential for maintaining primary processes.

Alterations in the Circulating Proteome Associated with Albuminuria

SIGNIFICANCE STATEMENT

We describe circulating proteins associated with albuminuria in a population of African American Study of Kidney Disease and Hypertension with CKD (AASK) using the largest proteomic platform to date: nearly 7000 circulating proteins, representing approximately 2000 new targets. Findings were replicated in a subset of a general population cohort with kidney disease (ARIC) and a population with CKD Chronic Renal Insufficiency Cohort (CRIC). In cross-sectional analysis, 104 proteins were significantly associated with albuminuria in the Black group, of which 67 of 77 available proteins were replicated in ARIC and 68 of 71 available proteins in CRIC. LMAN2, TNFSFR1B, and members of the ephrin superfamily had the strongest associations. Pathway analysis also demonstrated enrichment of ephrin family proteins.

BACKGROUND

Proteomic techniques have facilitated understanding of pathways that mediate decline in GFR. Albuminuria is a key component of CKD diagnosis, staging, and prognosis but has been less studied than GFR. We sought to investigate circulating proteins associated with higher albuminuria.

METHODS

We evaluated the cross-sectional associations of the blood proteome with albuminuria and longitudinally with doubling of albuminuria in the African American Study of Kidney Disease and Hypertension (AASK; 38% female; mean GFR 46; median urine protein-to-creatinine ratio 81 mg/g; n =703) and replicated in two external cohorts: a subset of the Atherosclerosis Risk in Communities (ARIC) study with CKD and the Chronic Renal Insufficiency Cohort (CRIC).

RESULTS

In cross-sectional analysis, 104 proteins were significantly associated with albuminuria in AASK, of which 67 of 77 available proteins were replicated in ARIC and 68 of 71 available proteins in CRIC. Proteins with the strongest associations included LMAN2, TNFSFR1B, and members of the ephrin superfamily. Pathway analysis also demonstrated enrichment of ephrin family proteins. Five proteins were significantly associated with worsening albuminuria in AASK, including LMAN2 and EFNA4, which were replicated in ARIC and CRIC.

CONCLUSIONS

Among individuals with CKD, large-scale proteomic analysis identified known and novel proteins associated with albuminuria and suggested a role for ephrin signaling in albuminuria progression.

Tacrolimus ameliorates podocyte injury by restoring FK506 binding protein 12 (FKBP12) at actin cytoskeleton

FKBP12 was identified as a binding protein of tacrolimus (Tac). Tac binds to FKBP12 and exhibits immunosuppressive effects in T cells. Although it is reported that Tac treatment directly ameliorates the dysfunction of the podocyte in nephrotic syndrome, the precise pharmacological mechanism of Tac is not well understood yet. It is also known that FKBP12 functions independently of Tac. However, the localization and the physiological function of FKBP12 are not well elucidated. In this study, we observed that FKBP12 is highly expressed in glomeruli, and the FKBP12 in glomeruli is restricted in podocytes. FKBP12 in cultured podocytes was expressed along the actin cytoskeleton and associated with filamentous actin (F-actin). FKBP12 interacted with the actin-associated proteins 14-3-3 and synaptopodin. RNA silencing for FKBP12 reduced 14-3-3 expression, F-actin staining, and process formation in cultured podocytes. FKBP12 expression was decreased in the nephrotic model caused by adriamycin (ADR) and the cultured podocyte treated with ADR. The process formation was deteriorated in the podocytes treated with ADR. Tac treatment ameliorated these decreases. Tac treatment to the normal cells increased the expression of FKBP12 at F-actin in processes and enhanced process formation. Tac enhanced the interaction of FKBP12 with synaptopodin. These observations suggested that FKBP12 at actin cytoskeleton participates in the maintenance of processes, and Tac treatment ameliorates podocyte injury by restoring FKBP12 at actin cytoskeleton.

Key role for EphB2 receptor in kidney fibrosis

Erythropoietin producing hepatocellular (Eph)-Eph receptor interacting (Ephrin) receptor-ligand signaling has been implicated in the development of tissue fibrosis, though it has not been well defined in the kidney. We detected substantial up-regulation of expression and phosphorylation of the EphB2 receptor tyrosine kinase in fibrotic kidney tissue obtained both from mice subjected to the unilateral renal ischemia-reperfusion (IR) model at 14 days and in patients suffering from chronic kidney disease (CKD). Knockout (KO) mice lacking EphB2 expression exhibited a normal renal structure and function, indicating no major role for this receptor in kidney development or action. Although IR injury is well-known to cause tissue damage, fibrosis, and renal dysfunction, we found that kidneys from EphB2KO mice showed much less renal tubular injury and retained a more preserved renal function. IR-injured kidneys from EphB2 KOs exhibited greatly reduced fibrosis and inflammation compared with injured wildtype (WT) littermates, and this correlated with a significant reduction in renal expression of profibrotic molecules, inflammatory cytokines, NADPH oxidases, and markers for cell proliferation, tubular epithelial-to-mesenchymal transition (EMT), myofibroblast activation, and apoptosis. A panel of 760 fibrosis-associated genes were further assessed, revealing that 506 genes in WT mouse kidney following IR injury changed their expression. However, 70.9% of those genes were back to or close to normal in expression when EphB2 was deleted. These data indicate that endogenous EphB2 expression and signaling are abnormally activated after kidney injury and subsequently contribute to the development of renal fibrosis via regulation of multiple profibrotic pathways.

Synbindin Downregulation Participates in Slit Diaphragm Dysfunction

INTRODUCTION

Synbindin, originally identified as a neuronal cytoplasmic molecule, was found in glomeruli. The cDNA subtractive hybridization technique showed the mRNA expression of synbindin in glomeruli was downregulated in puromycin aminonucleoside (PAN) nephropathy, a mimic of minimal-change nephrotic syndrome.

METHODS

The expression of synbindin in podocytes was analyzed in normal rats and 2 types of rat nephrotic models, anti-nephrin antibody-induced nephropathy, a pure slit diaphragm injury model, and PAN nephropathy, by immunohistochemical analysis and RT-PCR techniques. To elucidate the function of synbindin, a gene silencing study with human cultured podocytes was performed.

RESULTS

Synbindin was mainly expressed at the slit diaphragm area of glomerular epithelial cells (podocytes). In both nephrotic models, decreased mRNA expression and the altered staining of synbindin were already detected at the early phase when proteinuria and the altered staining of nephrin, a key molecule of slit diaphragm, were not detected yet. Synbindin staining was clearly reduced when severe proteinuria was observed. When the cultured podocytes were treated with siRNA for synbindin, the cell changed to a round shape, and filamentous actin structure was clearly altered. The expression of ephrin-B1, a transmembrane protein at slit diaphragm, was clearly lowered, and synaptic vesicle-associated protein 2B (SV2B) was upregulated in the synbindin knockdown cells.

CONCLUSION

Synbindin participates in maintaining foot processes and slit diaphragm as a downstream molecule of SV2B-mediated vesicle transport. Synbindin downregulation participates in slit diaphragm dysfunction. Synbindin can be an early marker to detect podocyte injury.

Nephrin-Ephrin-B1-Na+/H+ Exchanger Regulatory Factor 2-Ezrin-Actin Axis Is Critical in Podocyte Injury

Ephrin-B1 is one of the critical components of the slit diaphragm of kidney glomerular podocyte. However, the precise function of ephrin-B1 is unclear. To clarify the function of ephrin-B1, ephrin-B1-associated molecules were studied. RNA-sequencing analysis suggested that Na⁺/H⁺ exchanger regulatory factor 2 (NHERF2), a scaffolding protein, is associated with ephrin-B1. NHERF2 was expressed at the apical area and the slit diaphragm, and interacted with the nephrin-ephrin-B1 complex at the slit diaphragm. The nephrin-ephrin-B1-NHERF2 complex interacted with ezrin bound to F-actin. NHERF2 bound ephrin-B1 via its first postsynaptic density protein-95/disks large/zonula occludens-1 domain, and podocalyxin via its second postsynaptic density protein-95/disks large/zonula occludens-1 domain. Both in vitro analyses with human embryonic kidney 293 cells and in vivo study with rat nephrotic model showed that stimulaiton of the slit diaphragm, phosphorylation of nephrin and ephrin-B1, and dephosphorylation of NHERF2 and ezrin, disrupted the linkages of ephrin-B1-NHERF2 and NHERF2-ezrin. It is conceivable that the linkage of nephrin-ephrin-B1-NHERF2-ezrin-actin is a novel critical axis in the podocytes. Ephrin-B1 phosphorylation also disrupted the linkage of an apical transmembrane protein, podocalyxin, with NHERF2-ezrin-actin. The phosphorylation of ephrin-B1 and the consequent dephosphorylation of NHERF2 are critical initiation events leading to podocyte injury.

The receptor tyrosine kinase EPHB6 regulates catecholamine exocytosis in adrenal gland chromaffin cells

The erythropoietin-producing human hepatocellular receptor EPH receptor B6 (EPHB6) is a receptor tyrosine kinase that has been shown previously to control catecholamine synthesis in the adrenal gland chromaffin cells (AGCCs) in a testosterone-dependent fashion. EPHB6 also has a role in regulating blood pressure, but several facets of this regulation remain unclear. Using amperometry recordings, we now found that catecholamine secretion by AGCCs is compromised in the absence of EPHB6. AGCCs from male knockout (KO) mice displayed reduced cortical F-actin disassembly, accompanied by decreased catecholamine secretion through exocytosis. This phenotype was not observed in AGCCs from female KO mice, suggesting that testosterone, but not estrogen, contributes to this phenotype. Of note, reverse signaling from EPHB6 to ephrin B1 (EFNB1) and a 7-amino acid-long segment in the EFNB1 intracellular tail were essential for the regulation of catecholamine secretion. Further downstream, the Ras homolog family member A (RHOA) and FYN proto-oncogene Src family tyrosine kinase (FYN)-proto-oncogene c-ABL-microtubule-associated monooxygenase calponin and LIM domain containing 1 (MICAL-1) pathways mediated the signaling from EFNB1 to the defective F-actin disassembly. We discuss the implications of EPHB6's effect on catecholamine exocytosis and secretion for blood pressure regulation.

New insight into podocyte slit diaphragm, a therapeutic target of proteinuria

Dysfunction of slit diaphragm, a cell–cell junction of glomerular podocytes, is involved in the development of proteinuria in several glomerular diseases. Slit diaphragm should be a target of a novel therapy for proteinuria. Nephrin, NEPH1, P-cadherin, FAT, and ephrin-B1 were reported to be extracellular components forming a molecular sieve of the slit diaphragm. Several cytoplasmic proteins such as ZO-1, podocin, CD2AP, MAGI proteins and Par-complex molecules were identified as scaffold proteins linking the slit diaphragm to the cytoskeleton. In this article, new insights into these molecules and the pathogenic roles of the dysfunction of these molecules were introduced. The slit diaphragm functions not only as a barrier but also as a signaling platform transfer the signal to the inside of the cell. For maintaining the slit diaphragm function properly, the phosphorylation level of nephrin is strictly regulated. The recent studies on the signaling pathway from nephrin, NEPH1, and ephrin-B1 were reviewed. Although the mechanism regulating the function of the slit diaphragm had remained unclear, recent studies revealed TRPC6 and angiotensin II-regulating mechanisms play a critical role in regulating the barrier function of the slit diaphragm. In this review, recent investigations on the regulation of the slit diaphragm function were reviewed, and a strategy for the establishment of a novel therapy for proteinuria was proposed.

Partitioning-Defective-6-Ephrin-B1 Interaction Is Regulated by Nephrin-Mediated Signal and Is Crucial in Maintaining Slit Diaphragm of Podocyte

Ephrin-B1 plays a critical role at slit diaphragm. Partitioning-defective (Par)-6 is down-regulated in podocyte of ephrin-B1 knockout mouse, suggesting that Par-6 is associated with ephrin-B1. Par polarity complex, consisting of Par-6, Par-3, and atypical protein kinase C, is essential for tight junction formation. In this study, the expression of Par-6 was analyzed in the normal and nephrotic syndrome model rats, and the molecular association of Par-6, Par-3, ephrin-B1, and nephrin was assessed with the human embryonic kidney 293 cell expression system. Par-6 was concentrated at slit diaphragm. Par 6 interacted with ephrin-B1 but not with nephrin, and Par-3 interacted with nephrin but not with ephrin-B1. The complexes of Par-6-ephrin-B1 and Par-3-nephrin were linked via extracellular sites of ephrin-B1 and nephrin. The Par-6-ephrin-B1 complex was delinked from the Par-3-nephrin complex, and Par-6 and ephrin-B1 were clearly down-regulated already at early phase of nephrotic model. The alteration of Par-6/ephrin-B1 advanced that of Par-3/nephrin. Stimulation to nephrin phosphorylated not only nephrin but also ephrin-B1, and consequently inhibited the interaction between ephrin-B1 and Par-6. Par-6 appeared at presumptive podocyte of early developmental stage and moved to basal area at capillary loop stage to participate in slit diaphragm formation at the final stage. Par-6-ephrin-B1 interaction is crucial for formation and maintenance of slit diaphragm of podocyte.

The zinc fingers and homeoboxes 2 protein ZHX2 and its interacting proteins regulate upstream pathways in podocyte diseases

Zinc fingers and homeoboxes (ZHX) proteins are heterodimeric transcriptional factors largely expressed at the cell membrane in podocytes in vivo. We found ZHX2-based heterodimers in podocytes, with ZHX2-ZHX1 predominantly at the cell membrane of the podocyte cell body, and ZHX2-ZHX3 at the slit diaphragm. In addition to changes in overall ZHX2 expression, there was increased podocyte nuclear ZHX3 and ZHX2 in patients with focal segmental glomerulosclerosis, and increased podocyte nuclear ZHX1 in patients with minimal change disease. Zhx2 deficient mice had increased podocyte ZHX1 and ZHX3 expression. Zhx2 deficient mice and podocyte specific Zhx2 overexpressing transgenic rats develop worse experimental focal segmental glomerulosclerosis than controls, with increased nuclear ZHX3 and ZHX2, respectively. By contrast, podocyte specific Zhx2 overexpressing transgenic rats develop lesser proteinuria during experimental minimal change disease due to peripheral sequestration of ZHX1 by ZHX2. Using co-immunoprecipitation, the interaction of ZHX2 with aminopeptidase A in the podocyte body cell membrane, and EPHRIN B1 in the slit diaphragm were noted to be central to upstream events in animal models of minimal change disease and focal segmental glomerulosclerosis, respectively. Mice deficient in Enpep, the gene for aminopeptidase A, and Efnb1, the gene for ephrin B1 developed worse albuminuria in glomerular disease models. Targeting aminopeptidase A in Zhx2 deficient mice with monoclonal antibodies induced albuminuria and upregulation of the minimal change disease mediator angiopoietin-like 4 through nuclear entry of ZHX1. Thus, podocyte ZHX2 imbalance is a critical factor in human glomerular disease, with minimal change disease disparities mediated mostly through ZHX1, and focal segmental glomerulosclerosis deviations through ZHX3 and ZHX2.

Genome-wide association study identifies novel loci for type 2 diabetes-attributed end-stage kidney disease in African Americans

BACKGROUND

End-stage kidney disease (ESKD) is a significant public health concern disproportionately affecting African Americans (AAs). Type 2 diabetes (T2D) is the leading cause of ESKD in the USA, and efforts to uncover genetic susceptibility to diabetic kidney disease (DKD) have had limited success. A prior genome-wide association study (GWAS) in AAs with T2D-ESKD was expanded with additional AA cases and controls and genotypes imputed to the higher density 1000 Genomes reference panel. The discovery analysis included 3432 T2D-ESKD cases and 6977 non-diabetic non-nephropathy controls (N = 10,409), followed by a discrimination analysis in 2756 T2D non-nephropathy controls to exclude T2D-associated variants.

RESULTS

Six independent variants located in or near RND3/RBM43, SLITRK3, ENPP7, GNG7, and APOL1 achieved genome-wide significant association (P < 5 × 10-8) with T2D-ESKD. Following extension analyses in 1910 non-diabetic ESKD cases and 908 non-diabetic non-nephropathy controls, a meta-analysis of 5342 AA all-cause ESKD cases and 6977 AA non-diabetic non-nephropathy controls revealed an additional novel all-cause ESKD locus at EFNB2 (rs77113398; P = 9.84 × 10-9; OR = 1.94). Exclusion of APOL1 renal-risk genotype carriers identified two additional genome-wide significant T2D-ESKD-associated loci at GRAMD3 and MGAT4C. A second variant at GNG7 (rs373971520; P = 2.17 × 10-8, OR = 1.46) remained associated with all-cause ESKD in the APOL1-negative analysis.

CONCLUSIONS

Findings provide further evidence for genetic factors associated with advanced kidney disease in AAs with T2D.

Making Connections: Guidance Cues and Receptors at Nonneural Cell-Cell Junctions

The field of axon guidance was revolutionized over the past three decades by the identification of highly conserved families of guidance cues and receptors. These proteins are essential for normal neural development and function, directing cell and axon migration, neuron-glial interactions, and synapse formation and plasticity. Many of these genes are also expressed outside the nervous system in which they influence cell migration, adhesion and proliferation. Because the nervous system develops from neural epithelium, it is perhaps not surprising that these guidance cues have significant nonneural roles in governing the specialized junctional connections between cells in polarized epithelia. The following review addresses roles for ephrins, semaphorins, netrins, slits and their receptors in regulating adherens, tight, and gap junctions in nonneural epithelia and endothelia.

Analysis of the association of EPHB6, EFNB1 and EFNB3 variants with hypertension risks in males with hypogonadism

Several members of the EPH kinase family and their ligands are involved in blood pressure regulation, and such regulation is often sex- or sex hormone-dependent, based on animal and human genetic studies. EPHB6 gene knockout (KO) in mice leads to hypertension in castrated males but not in un-manipulated KO males or females. To assess whether this finding in mice is relevant to human hypertension, we conducted a human genetic study for the association of EPHB6 and its two ligands, EFNB1 and EFNB3, with hypertension in hypogonadic patients. Seven hundred and fifty hypertensive and 750 normotensive Han Chinese patients, all of whom were hypogonadic, were genotyped for single nucleotide polymorphisms (SNPs) within the regions of the genes, plus an additional 50 kb 5′ of the genes for EPHB6, EFNB1 and EFNB3. An imputed insertion/deletion polymorphism, rs35530071, was found to be associated with hypertension at p-values below the Bonferroni-corrected significance level of 0.0024. This marker is located 5′ upstream of the EFNB3 gene start site. Previous animal studies showed that while male EFNB3 gene knockout mice were normotensive, castration of these mice resulted in hypertension, corroborating the results of the human genetic study. Considering the significant associations of EFNB3 SNPs with hypertension in hypogonadic males and supporting evidence from castrated EFNB3 KO mice, we conclude that loss-of-function variants of molecules in the EPHB6 signaling pathway in the presence of testosterone are protective against hypertension in humans.

Nephrin-Binding Ephrin-B1 at the Slit Diaphragm Controls Podocyte Function through the JNK Pathway

Background B-type ephrins are membrane-bound proteins that maintain tissue function in several organs. We previously reported that ephrin-B1 is localized at the slit diaphragm of glomerular podocytes. However, the function of ephrin-B1 at this location is unclear.Methods We analyzed the phenotype of podocyte-specific ephrin-B1 knockout mice and assessed the molecular association of ephrin-B1 and nephrin, a key molecule of the slit diaphragm, in HEK293 cells and rats with anti-nephrin antibody-induced nephropathy.Results Compared with controls, ephrin-B1 conditional knockout mice displayed altered podocyte morphology, disarrangement of the slit diaphragm molecules, and proteinuria. Ephrin-B1 expressed in HEK293 cells immunoprecipitated with nephrin, which required the basal regions of the extracellular domains of both proteins. Treatment of cells with an anti-nephrin antibody promoted the phosphorylation of nephrin and ephrin-B1. However, phosphorylation of ephrin-B1 did not occur in cells expressing a mutant nephrin lacking the ephrin-B1 binding site or in cells treated with an Src kinase inhibitor. The phosphorylation of ephrin-B1 enhanced the phosphorylation of nephrin and promoted the phosphorylation of c-Jun N-terminal kinase (JNK), which was required for ephrin-B1-promoted cell motility in wound-healing assays. Notably, phosphorylated JNK was detected in the glomeruli of control mice but not ephrin-B1 conditional knockout mice. In rats, the phosphorylation of ephrin-B1, JNK, and nephrin occurred in the early phase (24 hours) of anti-nephrin antibody-induced nephropathy.Conclusions Through interactions with nephrin, ephrin-B1 maintains the structure and barrier function of the slit diaphragm. Moreover, phosphorylation of ephrin-B1 and, consequently, JNK are involved in the development of podocyte injury.

Evidence from single nucleotide polymorphism analyses of ADVANCE study demonstrates EFNB3 as a hypertension risk gene

EPH kinases and their ligands, ephrins (EFNs), have vital and diverse biological functions. We recently reported that Efnb3 gene deletion results in hypertension in female but not male mice. These data suggest that EFNB3 regulates blood pressure in a sex- and sex hormone-dependent way. In the present study, we conducted a human genetic study to assess the association of EFNB3 single nucleotide polymorphisms with human hypertension risks, using 3,448 patients with type 2 diabetes from the ADVANCE study (Action in Diabetes and Vascular Disease: Peterax and Diamicron MR Controlled Evaluation). We have observed significant association between 2 SNPs in the 3′ untranslated region or within the adjacent region just 3′ of the EFNB3 gene with hypertension, corroborating our findings from the mouse model. Thus, our investigation has shown that EFNB3 is a hypertension risk gene in certain individuals.

The role of GRIP1 and ephrin B3 in blood pressure control and vascular smooth muscle cell contractility

Several erythropoietin-producing hepatocellular receptor B family (EPHB) and their ligands, ephrinBs (EFNBs), are involved in blood pressure regulation in animal models. We selected 528 single nucleotide polymorphisms (SNPs) within the genes of EPHB6, EFNB2, EFNB3 and GRIP1 in the EPH/EFN signalling system to query the International Blood Pressure Consortium dataset. A SNP within the glutamate receptor interacting protein 1 (GRIP1) gene presented a p-value of 0.000389, approaching the critical p-value of 0.000302, for association with diastolic blood pressure of 60,396 individuals. According to echocardiography, we found that Efnb3 gene knockout mice showed enhanced constriction in the carotid arteries. In vitro studies revealed that in mouse vascular smooth muscle cells, siRNA knockdown of GRIP1, which is in the EFNB3 reverse signalling pathway, resulted in increased contractility of these cells. These data suggest that molecules in the EPHB/EFNB signalling pathways, specifically EFNB3 and GRIP1, are involved blood pressure regulation.

Role of calcineurin (CN) in kidney glomerular podocyte: CN inhibitor ameliorated proteinuria by inhibiting the redistribution of CN at the slit diaphragm

Although calcineurin (CN) is distributed in many cell types and functions in regulating cell functions, the precise roles of CN remained in each type of the cells are not well understood yet. A CN inhibitor (CNI) has been used for steroid‐resistant nephrotic syndrome. A CNI is assumed to ameliorate proteinuria by preventing the overproduction of T‐cell cytokines. However, recent reports suggest that CNI has a direct effect on podocyte. It is accepted that a slit diaphragm (SD), a unique cell–cell junction of podocytes, is a critical barrier preventing a leak of plasma protein into urine. Therefore, we hypothesized that CNI has an effect on the SD. In this study, we analyzed the expression of CN in physiological and in the nephrotic model caused by the antibody against nephrin, a critical component of the SD. We observed that CN is expressed at the SD in normal rat and human kidney sections and has an interaction with nephrin. The staining of CN at the SD was reduced in the nephrotic model, while CN activity in glomeruli was increased. We also observed that the treatment with tacrolimus, a CNI, in this nephrotic model suppressed the redistribution of CN, nephrin, and other SD components and ameliorated proteinuria. These observations suggested that the redistribution and the activation of CN may participate in the development of the SD injury.

Reduced blood pressure after smooth muscle EFNB2 deletion and the potential association of EFNB2 mutation with human hypertension risk

Ephrin B2 (EFNB2) is a ligand for erythropoietin-producing hepatocellular kinases (EPH), the largest family of receptor tyrosine kinases. It has critical functions in many biological systems, but is not known to regulate blood pressure. We generated mice with a smooth muscle cell (SMC)-specific deletion of EFNB2 and investigated its roles in blood pressure regulation and vascular SMC (VSMC) contractility. Male Efnb2 knockout (KO) mice presented reduced blood pressure, whereas female KO mice had no such reduction. Both forward signaling from EFNB2 to EPHs and reverse signaling from EPHs to EFNB2 were involved in regulating VSMC contractility, with EPHB4 serving as a critical molecule for forward signaling, based on crosslinking studies. We also found that a region from aa 313 to aa 331 in the intracellular tail of EFNB2 was essential for reverse signaling regulating VSMC contractility, based on deletion mutation studies. In a human genetic study, we identified five SNPs in the 3' region of the EFNB2 gene, which were in linkage disequilibrium and were significantly associated with hypertension for male but not female subjects, consistent with our findings in mice. The coding (minor) alleles of these five SNPs were protective in males. We have thus discovered a previously unknown blood pressure-lowering mechanism mediated by EFNB2 and identified EFNB2 as a gene associated with hypertension risk in humans.

Retina-derived POU domain factor 1 coordinates expression of genes relevant to renal and neuronal development

Retina-derived POU domain Factor 1 (RPF-1), a member of POU transcription factor family, is encoded by POU6F2 gene, addressed by interstitial deletions at chromosome 7p14 in Wilms tumor (WT). Its expression has been detected in developing kidney and nervous system, suggesting an early role for this gene in regulating development of these organs. To investigate into its functions and determine its role in transcriptional regulation, we generated an inducible stable transfectant from HEK293 cells. RPF-1 showed nuclear localization, elevated stability, and transactivation of promoters featuring POU consensus sites, and led to reduced cell proliferation and in vivo tumor growth. By addressing the whole transcriptome regulated by its induction, we could detect a gross alteration of gene expression that is consistent with promoter occupancy predicted by genome-wide Chip-chip analysis. Comparison of bound regulatory regions with differentially expressed genes allowed identification of 217 candidate targets. Enrichment of divergent octamers in predicted regulatory regions revealed promiscuous binding to bipartite POUS and POUH consensus half-sites with intervening spacers. Gel-shift competition assay confirmed the specificity of RPF-1 binding to consensus motifs, and demonstrated that the Ser-rich region upstream of the POU domain is indispensable to achieve DNA-binding. Promoter-reporter activity addressing a few target genes indicated a dependence by RPF-1 on transcriptional response. In agreement with its expression in developing kidney and nervous system, the induced transcriptome appears to indicate a function for this protein in early renal differentiation and neuronal cell fate, providing a resource for understanding its role in the processes thereby regulated.

Bidirectional signalling between EphA2 and ephrinA1 increases tubular cell attachment, laminin secretion and modulates erythropoietin expression after renal hypoxic injury

Acute kidney injury (AKI) is common in hospitalized patients and has a poor prognosis, the severity of AKI being linked to progression to chronic kidney disease. This stresses the need to search for protective mechanisms during the acute phase. We investigated kidney repair after hypoxic injury using a rat model of renal artery branch ligation, which led to an oxygen gradient vertical to the corticomedullary axis. Three distinct zones were observed: tubular necrosis, infarction border zone and preserved normal tissue. EphA2 is a receptor tyrosine kinase with pivotal roles in cell architecture, migration and survival, upon juxtacrine contact with its membrane-bound ligand EphrinA1. Following hypoxia, EphA2 was up-regulated in cortical and medullary tubular cells, while EphrinA1 was up-regulated in interstitial cells adjacent to peritubular capillaries. Moreover, erythropoietin (EPO) messenger RNA (mRNA) was strongly expressed in the border zone of infarcted kidney within the first 6 h. To gain more insight into the biological impact of EphA2 and EphrinA1 up-regulation, we activated the signalling pathways in vitro using recombinant EphrinA1/Fc or EphA2/Fc proteins. Stimulation of EphA2 forward signalling in the proximal tubular cell line HK2 increased cell attachment and laminin secretion at the baso-lateral side. Conversely, activation of reverse signalling through EphrinA1 expressed by Hep3B cells promoted EPO production at both the transcriptional and protein level. Strikingly, in co-culture experiments, juxtacrine contact between EphA2 expressing MDCK and EphrinA1 expressing Hep3B was sufficient to induce a significant up-regulation of EPO mRNA production in the latter cells, even in the absence of hypoxic conditions. The synergistic effects of EphA2 and hypoxia led to a 15-20-fold increase of EPO expression. Collectively, our results suggest an important role of EphA2/EphrinA1 signalling in kidney repair after hypoxic injury through stimulation of (i) tubular cell attachment, (ii) secretion of basal membrane proteins and (iii) EPO production. These findings could thus pave the way to new therapeutic approaches.

Eph/ephrin signaling in the kidney and lower urinary tract

Development and homeostasis of the highly specialized cell types and tissues that constitute the organs of the urinary system, the kidneys and ureters, the bladder, and the urethra, require the tightly regulated exchange of signals in and between these tissues. Eph/ephrin signaling is a bidirectional signaling pathway that has been functionally implicated in many developmental and homeostatic contexts, most prominently in the vascular and neural system. Expression and knockout analyses have now provided evidence that Eph/ephrin signaling is of crucial relevance for cell and tissue interactions in the urinary system as well. A clear requirement has emerged in the formation of the vesicoureteric junction, in urorectal septation and glomerulogenesis during embryonic development, in maintenance of medullary tubular cells and podocytes in homeostasis, and in podocyte and glomerular injury responses. Deregulation of Eph/ephrin signaling may also contribute to the formation and progression of tumors in the urinary system, most prominently bladder and renal cell carcinoma. While in the embryonic contexts Eph/ephrin signaling regulates adhesion of epithelial cells, in the adult setting, cell-shape changes and cell survival seem to be the primary cellular processes mediated by this signaling module. With progression of the genetic analyses of mice conditionally mutant for compound alleles of Eph receptor and ephrin ligand genes, additional essential functions are likely to arise in the urinary system.

Estrogen and testosterone in concert with EFNB3 regulate vascular smooth muscle cell contractility and blood pressure

EPH kinases and their ligands, ephrins (EFNs), have vital and diverse biological functions, although their function in blood pressure (BP) control has not been studied in detail. In the present study, we report that Efnb3 gene knockout (KO) led to increased BP in female but not male mice. Vascular smooth muscle cells (VSMCs) were target cells for EFNB3 function in BP regulation. The deletion of EFNB3 augmented contractility of VSMCs from female but not male KO mice, compared with their wild-type (WT) counterparts. Estrogen augmented VSMC contractility while testosterone reduced it in the absence of EFNB3, although these sex hormones had no effect on the contractility of VSMCs from WT mice. The effect of estrogen on KO VSMC contractility was via a nongenomic pathway involving GPER, while that of testosterone was likely via a genomic pathway, according to VSMC contractility assays and GPER knockdown assays. The sex hormone-dependent contraction phenotypes in KO VSMCs were reflected in BP in vivo. Ovariectomy rendered female KO mice normotensive. At the molecular level, EFNB3 KO in VSMCs resulted in reduced myosin light chain kinase phosphorylation, an event enhancing sensitivity to Ca(2+)flux in VSMCs. Our investigation has revealed previously unknown EFNB3 functions in BP regulation and show that EFNB3 might be a hypertension risk gene in certain individuals.

Human Induced Pluripotent Stem Cell-Derived Podocytes Mature into Vascularized Glomeruli upon Experimental Transplantation

Glomerular podocytes express proteins, such as nephrin, that constitute the slit diaphragm, thereby contributing to the filtration process in the kidney. Glomerular development has been analyzed mainly in mice, whereas analysis of human kidney development has been minimal because of limited access to embryonic kidneys. We previously reported the induction of three-dimensional primordial glomeruli from human induced pluripotent stem (iPS) cells. Here, using transcription activator-like effector nuclease-mediated homologous recombination, we generated human iPS cell lines that express green fluorescent protein (GFP) in the NPHS1 locus, which encodes nephrin, and we show that GFP expression facilitated accurate visualization of nephrin-positive podocyte formation in vitro These induced human podocytes exhibited apicobasal polarity, with nephrin proteins accumulated close to the basal domain, and possessed primary processes that were connected with slit diaphragm-like structures. Microarray analysis of sorted iPS cell-derived podocytes identified well conserved marker gene expression previously shown in mouse and human podocytes in vivo Furthermore, we developed a novel transplantation method using spacers that release the tension of host kidney capsules, thereby allowing the effective formation of glomeruli from human iPS cell-derived nephron progenitors. The human glomeruli were vascularized with the host mouse endothelial cells, and iPS cell-derived podocytes with numerous cell processes accumulated around the fenestrated endothelial cells. Therefore, the podocytes generated from iPS cells retain the podocyte-specific molecular and structural features, which will be useful for dissecting human glomerular development and diseases.

Role of EFNB1 and EFNB2 in Mouse Collagen-Induced Arthritis and Human Rheumatoid Arthritis

OBJECTIVE

EFNB1 and EFNB2 are ligands for Eph receptor tyrosine kinases. This study was undertaken to investigate how the expression of Efnb1 and Efnb2 on murine T cells influences the pathogenesis of collagen-induced arthritis (CIA) and to assess correlations between the T cell expression of these 2 molecules and measures of disease activity in patients with rheumatoid arthritis (RA).

METHODS

CIA was studied in mice with T cell-specific deletion (double gene knockout [dKO]) of both Efnb1 and Efnb2. Expression of EFNB1 and EFNB2 messenger RNA (mRNA) in peripheral blood T cells from patients with RA was determined by quantitative reverse transcription- polymerase chain reaction.

RESULTS

In dKO mice, clinical scores of arthritis were reduced compared to those in wild-type (WT) control mice. Serum collagen-specific antibody titers in dKO mice were lower than those in WT mice. In analyses based on equal cell numbers, dKO mouse T cells, as compared to WT mouse T cells, provided vastly inferior help to B cells in the production of collagen-specific antibodies in vitro. T cells from dKO mice were compromised in their ability to migrate to the arthritic paws in vivo and in their ability to undergo chemotaxis toward CXCL12 in vitro. Deletion mutation of Efnb1 and Efnb2 intracellular tails revealed critical regions in controlling T cell chemotaxis. T cells from RA patients expressed higher EFNB1 mRNA levels, which correlated with RA symptoms and laboratory findings.

CONCLUSION

Efnb1 and Efnb2 in T cells are essential for pathogenic antibody production and for T cell migration to the inflamed paws in mice with CIA. These findings suggest that the expression of EFNB1 in T cells might be a useful parameter for monitoring RA disease activity and treatment responses.

Cells of renin lineage are adult pluripotent progenitors in experimental glomerular disease

Modified vascular smooth muscle cells of the kidney afferent arterioles have recently been shown to serve as progenitors for glomerular epithelial cells in response to glomerular injury. To determine whether such cells of renin lineage (CoRL) serve as progenitors for other cells in kidney disease characterized by both glomerular and tubulointerstitial injury, permanent genetic cell fate mapping of adult CoRL using Ren1cCreER × Rs-tdTomato-R reporter mice was performed. TdTomato-labeled CoRL were almost completely restricted to the juxtaglomerular compartment in healthy kidneys. Following 2 wk of antibody-mediated focal segmental glomerulosclerosis (FSGS) or 16 wk of ⅚ nephrectomy-induced chronic kidney diseases, tdTomato-mapped CoRL were identified in both interstitial and glomerular compartments. In the interstitium, PDGFβ receptor (R)-expressing cells significantly increased, and a portion of these expressed tdTomato. This was accompanied by a decrease in native pericyte number, but an increase in the number of tdTomato cells that coexpressed the pericyte markers PDGFβ-R and NG2. These cells surrounded vessels and coexpressed the pericyte markers CD73 and CD146, but not the endothelial marker ERG. Within glomeruli of reporter mice with the ⅚ nephrectomy model, a subset of labeled CoRL migrated to the glomerular tuft and coexpressed podocin and synaptopodin. By contrast, labeled CoRL were not detected in glomerular or interstitial compartments following uninephrectomy. These observations indicate that in addition to supplying new adult podocytes to glomeruli, CoRL have the capacity to become new adult pericytes in the setting of interstitial disease. We conclude that CoRL have the potential to function as progenitors for multiple adult cell types in kidney disease.

Alteration in the podoplanin-ezrin-cytoskeleton linkage is an important initiation event of the podocyte injury in puromycin aminonucleoside nephropathy, a mimic of minimal change nephrotic syndrome

Podoplanin was identified as a protein associated with the transformation of arborized foot processes of glomerular epithelial cells (podocytes) to flat feet. However, the function of podoplanin in the podocyte is not yet fully clarified. In this study, we analyzed the molecular nature of podoplanin, and its expression in rat nephrotic models and patients with minimal change nephrotic syndrome (MCNS). We demonstrated here that podoplanin has two forms: one contains abundant sialic acid and the other a lesser amount of sialic acid. Podoplanin bound ezrin to interact with the cytoskeleton. The silencing of podoplanin in cultured podocytes caused a change in the cell shape and the distribution of ezrin and actin. The expression of podoplanin was clearly reduced before the onset of proteinuria in puromycin aminonucleoside (PAN) nephropathy, a mimic of MCNS, and the decrease in the expression of podoplanin became more evident at the proteinuric stage. Podoplanin was detected in normal urine samples, and the amount of urinary podoplanin markedly increased on day 1 of PAN nephropathy. Urinary ezrin was also detected. The amount of the phosphorylated ezrin was reduced, while the amount of the podoplanin-interacting ezrin increased. The podoplanin expression was reduced in a patient with active-phase MCNS. It is conceivable that the alteration of the podoplanin-ezrin-cytoskeleton linkage is an important event of the podocyte injury in MCNS.

EPHB4 Protein Expression in Vascular Smooth Muscle Cells Regulates Their Contractility, and EPHB4 Deletion Leads to Hypotension in Mice

EPH kinases are the largest family of receptor tyrosine kinases, and their ligands, ephrins (EFNs), are also cell surface molecules. This work presents evidence that EPHB4 on vascular smooth muscle cells (VSMCs) is involved in blood pressure regulation. We generated gene KO mice with smooth muscle cell-specific deletion of EPHB4. Male KO mice, but not female KO mice, were hypotensive. VSMCs from male KO mice showed reduced contractility when compared with their WT counterparts. Signaling both from EFNBs to EPHB4 (forward signaling) and from EPHB4 to EFNB2 (reverse signaling) modulated VSMC contractility. At the molecular level, the absence of EPHB4 in VSMCs resulted in compromised signaling from Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) to myosin light chain kinase (MLCK) to myosin light chain, the last of which controls the contraction force of motor molecule myosin. Near the cell membrane, an adaptor protein GRIP1, which can associate with EFNB2, was found to be essential in mediating EPHB4-to-EFNB reverse signaling, which regulated VSMC contractility, based on siRNA gene knockdown studies. Our research indicates that EPHB4 plays an essential role in regulating small artery contractility and blood pressure.

Therapeutic target for nephrotic syndrome: Identification of novel slit diaphragm associated molecules

The slit diaphragm bridging the neighboring foot processes functions as a final barrier of glomerular capillary wall for preventing the leak of plasma proteins into primary urine. It is now accepted that the dysfunction of the sit diaphragm contributes to the development of proteinuria in several glomerular diseases. Nephrin, a gene product of NPHS1, a gene for a congenital nephrotic syndrome of Finnish type, constitutes an extracellular domain of the slit diaphragm. Podocin was identified as a gene product of NPHS2, a gene for a familial steroid-resistant nephrotic syndrome of French. Podocin binds the cytoplasmic domain of nephrin. After then, CD2 associated protein, NEPH1 and transient receptor potential-6 were also found as crucial molecules of the slit diaphragm. In order to explore other novel molecules contributing to the development of proteinuria, we performed a subtraction hybridization assay with a normal rat glomerular RNA and a glomerular RNA of rats with a puromycin aminonucleoside nephropathy, a mimic of a human minimal change type nephrotic syndrome. Then we have found that synaptic vesicle protein 2B, ephrin-B1 and neurexin were already downregulated at the early stage of puromycin aminonucleoside nephropathy, and that these molecules were localized close to nephrin. It is conceivable that these molecules are the slit diaphragm associated molecules, which participate in the regulation of the barrier function. These molecules could be targets to establish a novel therapy for nephrotic syndrome.

Signal transduction in podocytes--spotlight on receptor tyrosine kinases

The mammalian kidney filtration barrier is a complex multicellular, multicomponent structure that maintains homeostasis by regulating electrolytes, acid-base balance, and blood pressure (via maintenance of salt and water balance). To perform these multiple functions, podocytes--an important component of the filtration apparatus--must process a series of intercellular signals. Integrating these signals with diverse cellular responses enables a coordinated response to various conditions. Although mature podocytes are terminally differentiated and cannot proliferate, they are able to respond to growth factors. It is possible that the initial response of podocytes to growth factors is beneficial and protective, and might include the induction of hypertrophic cell growth. However, extended and/or uncontrolled growth factor signalling might be maladaptive and could result in the induction of apoptosis and podocyte loss. Growth factors signal via the activation of receptor tyrosine kinases (RTKs) on their target cells and around a quarter of the 58 RTK family members that are encoded in the human genome have been identified in podocytes. Pharmacological inhibitors of many RTKs exist and are currently used in experimental and clinical cancer therapy. The identification of pathological RTK-mediated signal transduction pathways in podocytes could provide a starting point for the development of novel therapies for glomerular disorders.

Molecular understanding of the slit diaphragm

Glomerular filtration has always attracted the interest of nephrologists and renal researchers alike. Although several key questions on the structure and function of the kidney filter may have been answered within the last 40 years of intense research, there still remain crucial questions to be solved. The following article attempts to give a brief overview of recent developments in glomerular research highlighting particular advances in our understanding of the slit diaphragm.

Signaling from the podocyte intercellular junction to the actin cytoskeleton

Observations of hereditary glomerular disease support the contention that podocyte intercellular junction proteins are essential for junction formation and maintenance. Genetic deletion of most of these podocyte intercellular junction proteins results in foot process effacement and proteinuria. This review focuses on the current understanding of molecular mechanisms by which podocyte intercellular junction proteins such as the nephrin-neph1-podocin-receptor complex coordinate cytoskeletal dynamics and thus intercellular junction formation, maintenance, and injury-dependent remodeling.

T cell-specific deletion of EFNB2 minimally affects T cell development and function

BACKGROUND

Eph kinases and their ephrin ligands (EFN) are all cell surface molecules, capable of transmitting signals in both directions (1, 2). Such bidirectional signaling is called forward (from EFNs to Ephs) and reverse (from Ephs to EFNs) signaling. Eph family kinases have 15 members, divided into A and B subfamilies. Ephrin ligands have 9 members, also classified into A and B families. Ephs and ephrins interact promiscuously, but EphAs mainly interact with EFNAs, and EphBs with EFNBs. EphB family kinases and their ephrin ligands (EFN) are expressed in the T cell compartment.

RESULTS

In this study, using mice with T cell-specific EFNB2 gene knockout (EFNB2 KO mice), we investigated T cell development and function after EFNB2 deletion. EFNB2 KO mice presented normal thymus weight and cellularity. Their thymocyte subpopulations, such as CD4CD8 double positive cells and CD4 and CD8 single positive cells, were normally distributed, but there was a significant relative increase of CD4CD8 double negative cells. Flow cytometry analysis revealed that there was a moderate increase in the DN3 subpopulation. This augmented percentage of DN cells was further confirmed in competitive repopulation chimeras, suggesting that EFNB2 is involved in thymocyte development. The EFNB2 KO mice had normal T cell numbers and percentages in the spleen, and the T cells were able to be activated and to proliferate normally upon TCR ligation. Further, EFNB2 KO naïve CD4 cells were capable of differentiating into Th1, Th2, Th17 and Treg cells similar to WT naïve CD4 cells.

CONCLUSIONS

Our results suggest the involvement of EFNB2 in thymocyte development. However, heavy redundancy among Eph/EFN family members prevents the occurrence of detrimental phenotypes in the T cell compartment caused by T cell-specific EFNB2 gene null mutation.

Podocyte EphB4 signaling helps recovery from glomerular injury

Eph receptor tyrosine kinases and their ligands (ephrins) have a pivotal role in the homeostasis of many adult organs and are widely expressed in the kidney. Glomerular diseases beginning with mesangiolysis can recover, with podocytes having a critical role in this healing process. We studied here the role of Eph signaling in glomerular disease recovery following mesangiolytic Thy1.1 nephritis in rats. EphB4 and ephrinBs were expressed in healthy glomerular podocytes and were upregulated during Thy1.1 nephritis, with EphB4 strongly phosphorylated around day 9. Treatment with NPV-BHG712, an inhibitor of EphB4 phosphorylation, did not cause glomerular changes in control animals. Nephritic animals treated with vehicle did not have morphological evidence of podocyte injury or loss; however, application of this inhibitor to nephritic rats induced glomerular microaneurysms, podocyte damage, and loss. Prolonged NPV-BHG712 treatment resulted in increased albuminuria and dysregulated mesangial recovery. Additionally, NPV-BHG712 inhibited capillary repair by intussusceptive angiogenesis (an alternative to sprouting angiogenesis), indicating a previously unrecognized role of podocytes in regulating intussusceptive vessel splitting. Thus, our results identify EphB4 signaling as a pathway allowing podocytes to survive transient capillary collapse during glomerular disease.

Possible role of Efnb1 protein, a ligand of Eph receptor tyrosine kinases, in modulating blood pressure

Eph kinases constitute the largest receptor tyrosine kinase family, and their ligands, ephrins (Efns), are also cell surface molecules. Although they are ligands, Efns can transduce signals reversely into cells. We have no prior knowledge of the role played by any members of this family of kinases or their ligands in blood pressure (BP) regulation. In the present studies, we investigated the role of Efnb1 in vascular smooth muscle cell (VSMC) contractility and BP regulation. We revealed that reverse signaling through Efnb1 led to a reduction of RhoA activation and VSMC contractility in vitro. Consistent with this finding, ex vivo, there was an increase of RhoA activity accompanied by augmented myosin light chain phosphorylation in mesenteric arteries from mice with smooth muscle-specific conditional Efnb1 gene knock-out (KO). Small interfering RNA knockdown of Grip1, a molecule associated with the Efnb1 intracellular tail, partially eliminated the effect of Efnb1 on VSMC contractility and myosin light chain phosphorylation. In support of these in vitro and ex vivo results, Efnb1 KO mice on a high salt diet showed a statistically significant heightened increment of BP at multiple time points during stress compared with wild type littermates. Our results demonstrate that Efnb1 is a previously unknown negative regulator of VSMC contractility and BP and that it exerts such effects via reverse signaling through Grip1.

Receptor tyrosine kinase Ephb6 regulates vascular smooth muscle contractility and modulates blood pressure in concert with sex hormones

Eph kinases constitute the largest receptor tyrosine kinase family, and their ligands, ephrins (Efns), are also cell surface molecules. Our study is the first to assess the role of Ephb6 in blood pressure (BP) regulation. We observed that EphB6 and all three of its Efnb ligands were expressed on vascular smooth muscle cells (VSMC) in mice. We discovered that small arteries from castrated Ephb6 gene KO males showed increased contractility, RhoA activation, and constitutive myosin light chain phosphorylation ex vivo compared with their WT counterparts. Consistent with this finding, castrated Ephb6 KO mice presented heightened BP compared with castrated WT controls. In vitro experiments in VSMC revealed that cross-linking Efnbs but not Ephb6 resulted in reduced VSMC contractions, suggesting that reverse signaling through Efnbs was responsible for the observed BP phenotype. The reverse signaling was mediated by an adaptor protein Grip1. Additional experiments demonstrated decreased 24-h urine catecholamines in male Ephb6 KO mice, probably as a compensatory feedback mechanism to keep their BP in the normal range. After castration, however, such compensation was abolished in Ephb6 KO mice and was likely the reason why BP increased overtly in these animals. It suggests that Ephb6 has a target in the nervous/endocrine system in addition to VSMC, regulating a testosterone-dependent catecholamine compensatory mechanism. Our study discloses that Ephs and Efns, in concert with testosterone, play a critical role in regulating small artery contractility and BP.

The effect of conditional EFNB1 deletion in the T cell compartment on T cell development and function

BACKGROUND

Eph kinases are the largest family of cell surface receptor tyrosine kinases. The ligands of Ephs, ephrins (EFNs), are also cell surface molecules. Ephs interact with EFNs transmitting signals in both directions, i.e., from Ephs to EFNs and from EFNs to Ephs. EFNB1 is known to be able to co-stimulate T cells in vitro and to modulate thymocyte development in a model of foetal thymus organ culture. To further understand the role of EFNB1 in T cell immunity, we generated T-cell-specific EFNB1 gene knockout mice to assess T cell development and function in these mice.

RESULTS

The mice were of normal size and cellularity in the thymus and spleen and had normal T cell subpopulations in these organs. The bone marrow progenitors from KO mice and WT control mice repopulated host spleen T cell pool to similar extents. The activation and proliferation of KO T cells was comparable to that of control mice. Naïve KO CD4 cells showed an ability to differentiate into Th1, Th2, Th17 and Treg cells similar to control CD4 cells.

CONCLUSIONS

Our results suggest that the function of EFNB1 in the T cell compartment could be compensated by other members of the EFN family, and that such redundancy safeguards the pivotal roles of EFNB1 in T cell development and function.

Efnb1 and Efnb2 proteins regulate thymocyte development, peripheral T cell differentiation, and antiviral immune responses and are essential for interleukin-6 (IL-6) signaling

Erythropoietin-producing hepatocellular kinases (Eph kinases) constitute the largest family of cell membrane receptor tyrosine kinases, and their ligand ephrins are also cell surface molecules. Because of promiscuous interaction between Ephs and ephrins, there is considerable redundancy in this system, reflecting the essential roles of these molecules in the biological system through evolution. In this study, both Efnb1 and Efnb2 were null-mutated in the T cell compartment of mice through loxP-mediated gene deletion. Mice with this double conditional mutation (double KO mice) showed reduced thymus and spleen size and cellularity. There was a significant decrease in the DN4, double positive, and single positive thymocyte subpopulations and mature CD4 and CD8 cells in the periphery. dKO thymocytes and peripheral T cells failed to compete with their WT counterparts in irradiated recipients, and the T cells showed compromised ability of homeostatic expansion. dKO naive T cells were inferior in differentiating into Th1 and Th17 effectors in vitro. The dKO mice showed diminished immune response against LCMV infection. Mechanistic studies revealed that IL-6 signaling in dKO T cells was compromised, in terms of abated induction of STAT3 phosphorylation upon IL-6 stimulation. This defect likely contributed to the observed in vitro and in vivo phenotype in dKO mice. This study revealed novel roles of Efnb1 and Efnb2 in T cell development and function.

Nephrin expression in adult rodent central nervous system and its interaction with glutamate receptors

Nephrin is an immunoglobulin-like adhesion molecule first discovered as a major component of the podocyte slit diaphragm, where its integrity is essential to the function of the glomerular filtration barrier. Outside the kidney, nephrin has been shown in other restricted locations, most notably in the central nervous system (CNS) of embryonic and newborn rodents. With the aim of better characterizing nephrin expression and its role in the CNS of adult rodents, we studied its expression pattern and possible binding partners in CNS tissues and cultured neuronal cells and compared these data to those obtained in control renal tissues and podocyte cell cultures. Our results show that, besides a number of locations already found in embryos and newborns, endogenous nephrin in adult rodent CNS extends to the pons and corpus callosum and is expressed by granule cells and Purkinje cells of the cerebellum, with a characteristic alternating expression pattern. In primary neuronal cells we find nephrin expression close to synaptic proteins and demonstrate that nephrin co-immunoprecipitates with Fyn kinase, glutamate receptors and the scaffolding molecule PSD95, an assembly that is reminiscent of those made by synaptic adhesion molecules. This role seems to be confirmed by our findings of impaired maturation and reduced glutamate exocytosis occurring in Neuro2A cells upon nephrin silencing. Of note, we disclose that the very same nephrin interactions occur in renal glomeruli and cultured podocytes, supporting our hypothesis that podocytes organize and use similar molecular intercellular signalling modules to those used by neuronal cells.

Neurexin-1, a presynaptic adhesion molecule, localizes at the slit diaphragm of the glomerular podocytes in kidneys

The slit diaphragm connecting the adjacent foot processes of glomerular epithelial cells (podocytes) is the final barrier of the glomerular capillary wall and serves to prevent proteinuria. Podocytes are understood to be terminally differentiated cells and share some common features with neurons. Neurexin is a presynaptic adhesion molecule that plays a role in synaptic differentiation. Although neurexin has been understood to be specifically expressed in neuronal tissues, we found that neurexin was expressed in several organs. Several forms of splice variants of neurexin-1α were detected in the cerebrum, but only one form of neurexin-1α was detected in glomeruli. Immunohistochemical study showed that neurexin restrictedly expressed in the podocytes in kidneys. Dual-labeling analyses showed that neurexin was colocalized with CD2AP, an intracellular component of the slit diaphragm. Immunoprecipitation assay using glomerular lysate showed that neurexin interacted with CD2AP and CASK. These observations indicated that neurexin localized at the slit diaphragm area. The staining intensity of neurexin in podocytes was clearly lowered, and their staining pattern shifted to a more discontinuous patchy pattern in the disease models showing severe proteinuria. The expression and localization of neurexin in these models altered more clearly and rapidly than that of other slit diaphragm components. We propose that neurexin is available as an early diagnostic marker to detect podocyte injury. Neurexin coincided with nephrin, a key molecule of the slit diaphragm detected in a presumptive podocyte of the developing glomeruli and in the glomeruli for which the slit diaphragm is repairing injury. These observations suggest that neurexin is involved in the formation of the slit diaphragm and the maintenance of its function.

Angiogenesis and chronic kidney disease

The number of patients requiring renal replacement therapy due to end-stage renal disease (ESRD) is increasing worldwide. The prevalence of chronic kidney disease (CKD), and the importance of CKD as a risk factor in development of ESRD and in complicating cardiovascular disease (CVD) have been confirmed. In recent years, the involvement of angiogenesis-related factors in the progression of CKD has been studied, and the potential therapeutic effects on CKD of modulating these factors have been identified. Vascular endothelial growth factor (VEGF)-A, a potent pro-angiogenic factor, is involved in the development of the kidney, in maintenance of the glomerular capillary structure and filtration barrier, and in the renal repair process after injury. VEGF-A is also involved in the development of early diabetic nephropathy, demonstrated by the therapeutic effects of anti-VEGF-A antibody. Angiopoietin (Ang)-1 induces the maturation of newly formed blood vessels, and the therapeutic effects of Ang-1 in diabetic nephropathy have been described. In experimental models of diabetic nephropathy, the therapeutic effects of angiogenesis inhibitors, including angiostatin, endostatin and tumstatin peptides, the isocoumarin NM-3, and vasohibin-1, have been reported.

Further analysis of the involvement of angiogenesis-related factors in the development of CKD is required. Determining the disease stage at which therapy is most effective and developing an effective drug delivery system targeting the kidney will be essential for pro-or anti-angiogenic strategies for patients with CKD.

Identification of EphrinB1 expression in prostatic mesenchyme and a role for EphB-EphrinB signalling in prostate development

Paracrine signalling from mesenchyme to epithelium plays a key role in regulating prostate organogenesis and it is important to identify the mesenchymally expressed molecules that regulate organ growth, though currently few such molecules are known. Tyrosine kinase signalling via EphB receptors has been characterised in many developmental processes, and EphB3 mRNA expression was detected in prostate inductive mesenchyme in previous gene profiling studies. This led us to examine the expression and function of EphrinB signalling in prostate development, to determine if EphrinB ligands might function as mesenchymal paracrine regulators of prostate growth. Using PCR, wholemount in situ hybridisation, and immunohistochemistry we examined the expression of EphB receptors and EphrinB ligands in rat prostate during development to determine which showed mesenchymal expression. EphB3 and EphrinB1 transcripts and proteins were expressed in the mesenchyme of developing prostate and in female urogenital mesenchyme and smooth muscle. The function of EphrinB signalling was examined using in vitro organ culture assays of ventral prostate (VP), which were treated with EphB3-Fc and EphrinB1-Fc proteins to inhibit or augment Ephrin signalling. Addition of recombinant EphB3-Fc resulted in a significant decrease in VP organ size, while recombinant EphrinB1-Fc resulted in a significant increase in VP organ size and epithelial proliferation. Additionally, EphrinB1-Fc reduced the degree of epithelial branching in VP organs and increased ductal tip size, though without disrupting normal differentiation. We have identified expression of EphrinB1 in prostatic mesenchyme and suggest that the EphrinB signalling system acts as a regulator of prostate growth. EphrinB-EphB signalling may function as an autocrine regulator of mesenchyme and/or as a paracrine regulator of epithelia.

Slit diaphragm dysfunction in proteinuric states: identification of novel therapeutic targets for nephrotic syndrome

Several recent studies have demonstrated that the slit diaphragm of the glomerular epithelial cell (podocyte) is the structure likely to be the principal barrier in the glomerular capillary wall. Nephrin identified as a gene product mutated in congenital nephrotic syndrome located at the outer leaflet of plasma membranes of the slit diaphragm. The anti-nephrin antibody is capable of inducing massive proteinuria, which indicates that nephrin is a key functional molecule in the slit diaphragm. Expression of nephrin was reduced in glomeruli of minimal change nephrotic syndrome. Some recent studies demonstrated that podocin, CD2-associated protein and NEPH1 are also functional molecules in the slit diaphragm, and their expressions are altered in membranous nephropathy and also in focal glomerulosclerosis. These observations suggested that the alteration of the molecular arrangement in the slit diaphragm is involved in the development of proteinuria in several kinds of glomerular diseases. Recent studies of our group have demonstrated that type 1 receptor-mediated angiotensin II action reduced the expression of the slit diaphragm-associated molecules and that type 1 receptor blockade ameliorated proteinuria by preventing the function of angiotensin II on the slit diaphragm. By the subtraction hybridization techniques using glomerular cDNA of normal and proteinuric rats, we detected that synaptic vesicle protein 2B and ephrin B1 are involved in the maintenance of the barrier function of the slit diaphragm.

Eph/ephrin signaling in epithelial development and homeostasis

Eph receptors and ephrin ligands are widely expressed during embryonic development with well-defined functions in directing neuronal and vascular network formation. Over the last decade, evidence has mounted that Ephs and ephrins are also actively involved in prenatal and postnatal development of epithelial tissues. Their functions beyond developmental settings are starting to be recognized as well. The diverse functions of Eph/ephrin are largely related to the complementary expression pattern of the Eph receptors and corresponding ephrin ligands that are expressed in adjacent compartments, although overlapping expression pattern also exists in epithelial tissue. The interconnection between Ephs or ephrins and classical cell junctional molecules suggests they may function coordinately in maintaining epithelial structural integrity and homeostasis. This review will highlight cellular and molecular evidence in current literature that support a role of Eph/ephrin systems in regulating epithelial cell development and physiology.

Association analysis of the ephrin-B2 gene in African-Americans with end-stage renal disease

BACKGROUND

Genome scans in African-Americans with end-stage renal disease (ESRD) identified linkage on chromosome 13q33 in the region containing the ephrin-B2 ligand (EFNB2) genes. Interactions between the ephrin-B2 receptor and ephrin-B2 ligand play essential roles in renal angiogenesis, blood vessel maturation, and kidney disease.

METHODS

The EFNB2 gene was evaluated as a positional candidate for non-diabetic and diabetic ESRD susceptibility in 1,071 unrelated African-American subjects; 316 with non-diabetic etiologies of ESRD, 394 with type 2 diabetes-associated ESRD and 361 healthy controls. Single nucleotide polymorphism (SNP) genotyping was performed on the Sequenom Mass Array System. Statistical analyses were computed using Dandelion version 1.26, Snpaddmix version 1.4 and Haploview version 3.32.

RESULTS

Twenty-eight HapMap tag SNPs were genotyped spanning the 39 kilobases (kb) of the EFNB2 coding region, with average spacing of 1.43 kb. Analysis of 710 ESRD patient samples and 361 controls provided no evidence of single SNP associations in either diabetic or non-diabetic ESRD; although nominal evidence of association with all-cause ESRD was observed with a two SNP (p = 0.022) and three SNP (p = 0.023) haplotype, both containing SNPs rs7490924 and rs2391335 in intron 1.

CONCLUSIONS

Although an attractive positional candidate gene, polymorphisms in the EFNB2 gene do not appear to contribute in a substantial way to non-diabetic, diabetic or all-cause ESRD susceptibility in African-Americans. Additional genes within the chromosome 13q33 linkage interval are likely contributors to African-American non-diabetic ESRD.

Irradiation prolongs survival of Alport mice

Alport syndrome is a hereditary nephropathy that results in irreversible, progressive renal failure. Recent reports suggested that bone marrow transplantation (BMT) has a beneficial, short-term effect on renal injury in Alport (Col4a3(-/-)) mice, but its long-term effects, especially with regard to survival, are unknown. In this study, Alport mice received a transplant of either wild-type or Col4a3(-/-) bone marrow cells. Surprising, laboratory evaluations and renal histology demonstrated similar findings in both transplanted groups. Transplanted cells accounted for >10% of glomerular cells at 8 wk, but type IV collagen alpha3 chains were not detected in glomerular basement membranes of either group by immunofluorescence or Western blot analysis, although Col4a3 mRNA in the kidney could be amplified by reverse transcription-PCR in knockout mice that received a transplant of wild-type bone marrow. Both transplanted groups, however, survived approximately 1.5 times longer than untreated knockout mice (log rank P < 0.05). These data suggested that irradiation, which preceded BMT, may have conferred a survival benefit; therefore, the survival time of knockout mice was assessed after sublethal irradiation (3, 6, and 7 Gy) without subsequent BMT. A strong positive correlation between irradiation dosage and survival time was identified (P < 0.0001). In conclusion, the improved survival observed in Alport mice that received a transplant of wild-type bone marrow might be primarily attributed to as-yet-unidentified effects of irradiation.

Eph-ephrin bidirectional signaling in physiology and disease

Receptor tyrosine kinases of the Eph family bind to cell surface-associated ephrin ligands on neighboring cells. The ensuing bidirectional signals have emerged as a major form of contact-dependent communication between cells. New findings reveal that Eph receptors and ephrins coordinate not only developmental processes but also the normal physiology and homeostasis of many adult organs. Imbalance of Eph/ephrin function may therefore contribute to a variety of diseases. The challenge now is to better understand the complex and seemingly paradoxical signaling mechanisms of Eph receptors and ephrins, which will enable effective strategies to target these proteins in the treatment of diseases such as diabetes and cancer.