A 3D tri-culture system reveals that activin receptor-like kinase 5 and connective tissue growth factor drive human glomerulosclerosis

Glomerular scarring, known as glomerulosclerosis, occurs in many chronic kidney diseases and involves interaction between glomerular endothelial cells (GECs), podocytes, and mesangial cells (MCs), leading to signals that promote extracellular matrix deposition and endothelial cell dysfunction and loss. We describe a 3D tri-culture system to model human glomerulosclerosis. In 3D monoculture, each cell type alters its phenotype in response to TGFβ, which has been implicated as an important mediator of glomerulosclerosis. GECs form a lumenized vascular network, which regresses in response to TGFβ. MCs respond to TGFβ by forming glomerulosclerotic-like nodules with matrix deposition. TGFβ treatment of podocytes does not alter cell morphology but increases connective tissue growth factor (CTGF) expression. BMP7 prevents TGFβ-induced GEC network regression, whereas TGFβ-induced MC nodule formation is prevented by SMAD3 siRNA knockdown or ALK5 inhibitors but not BMP7, and increased phospho-SMAD3 was observed in human glomerulosclerosis. In 3D tri-culture, GECs, podocytes, and MCs form a vascular network in which GECs and podocytes interact intimately within a matrix containing MCs. TGFβ treatment induces formation of nodules, but combined inhibition of ALK5 and CTGF is required to prevent TGFβ-induced nodule formation in tri-cellular cultures. Identification of therapeutic targets for glomerulosclerosis depends on the 3D culture of all three glomerular cells. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

NADPH Oxidase Nox5 Accelerates Renal Injury in Diabetic Nephropathy

NADPH oxidase-derived excessive production of reactive oxygen species (ROS) in the kidney plays a key role in mediating renal injury in diabetes. Pathological changes in diabetes include mesangial expansion and accumulation of extracellular matrix (ECM) leading to glomerulosclerosis. There is a paucity of data about the role of the Nox5 isoform of NADPH oxidase in animal models of diabetic nephropathy since Nox5 is absent in the mouse genome. Thus, we examined the role of Nox5 in human diabetic nephropathy in human mesangial cells and in an inducible human Nox5 transgenic mouse exposed to streptozotocin-induced diabetes. In human kidney biopsies, Nox5 was identified to be expressed in glomeruli, which appeared to be increased in diabetes. Colocalization demonstrated Nox5 expression in mesangial cells. In vitro, silencing of Nox5 in human mesangial cells was associated with attenuation of the hyperglycemia and TGF-β1-induced enhanced ROS production, increased expression of profibrotic and proinflammatory mediators, and increased TRPC6, PKC-α, and PKC-β expression. In vivo, vascular smooth muscle cell/mesangial cell-specific overexpression of Nox5 in a mouse model of diabetic nephropathy showed enhanced glomerular ROS production, accelerated glomerulosclerosis, mesangial expansion, and ECM protein (collagen IV and fibronectin) accumulation as well as increased macrophage infiltration and expression of the proinflammatory chemokine MCP-1. Collectively, this study provides evidence of a role for Nox5 and its derived ROS in promoting progression of diabetic nephropathy.

Alterations in the long non‑coding RNA transcriptome in mesangial cells treated with aldosterone in vitro

Clinical and experimental reports indicate that aldosterone (ALD) contributes to the progression of renal failure independent of its hemodynamic effects. However, the mechanisms remain to be completely elucidated. The aim of the present study was to investigate the alterations of long non-coding RNA (lncRNA) in mesangial cells (MCs) treated with ALD. The present study used MCs treated with 10⁻⁶ M ALD as experimental cells. Microarray techniques performed by Agilent Technologies were used to identify the profiles of differentially expressed lncRNAs between the ALD group and the control group. Pathway and gene ontology analysis were applied to determine the roles of the differentially expressed lncRNAs. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used to quantify the differentially expressed lncRNAs. A total of 8,459 lncRNA and 13,214 mRNAs with differential expression between MCs treated with and without ALD were identified. The expression of lncRNAs was confirmed by RT-qPCR and the results were consistent with the lncRNA array. The biological functions of lncRNAs are associated with responding to external stimuli, positive regulation of biological and apoptotic processes, cell division, mitosis and nuclear division. The pathways include cell cycle and peroxisome proliferator-activated receptor signaling pathways. The present study revealed distinct sets of lncRNA expressed in MCs treated with ALD, suggesting that this class of transcripts may be involved in the pathogenesis of chronic kidney diseases.

Trifluoperazine Inhibits Mesangial Cell Proliferation by Arresting Cell Cycle-Dependent Mechanisms

Background

It has been reported that trifluoperazine (TFP) inhibits proliferation of cancer cells, however, the effects of TFP in renal proliferation diseases are still unclear. This study examined the effects of TFP on proliferation of human renal mesangial cells and analyzed the underlying mechanisms.

Material/Methods

Cell proliferation in vivo was determined by HE staining, immunohistochemistry of proliferating cell nuclear antigen (PCNA), and Western blot analysis (Ki-67 and PCNA). Effects of different TFP concentrations and treatment duration on cell proliferation and cell cycle were analyzed using the MTT assay and flow cytometry. Expression of G₀/G₁ phase cell cycle-related proteins and TFP-induced MAPK and PI3K/AKT signaling pathways was estimated with Western blot analysis.

Results

Our findings suggest that TFP inhibits cell proliferation in a dose- and time-dependent manner and decreased PCNA and Ki-67 levels in lupus MRL/lpr mice. TFP arrested the cell cycle in the G₀/G₁ phase, down-regulating cyclin D1, CDK2, and CDK4, and up-regulating p21 expression in a dose-dependent manner. In addition, TFP inhibited p-AKT and p-JNK, possibly by suppressing the activation of PI3K/AKT and JNK/MAPK signaling pathways. TFP treatment remarkably reduced the levels of serum creatinine (Cr) in lupus mice.

Conclusions

TFP exhibits inhibitory activity against mesangial cells in vivo and in vitro, which is associated with G1 cell cycle arrest by inactivation of PI3K/AKT and JNK/MAPK signaling pathways. These results suggest the potential of TFP in treatment of mesangial proliferative diseases.

Structure and Function of the Kidney in Septic Shock. A Prospective Controlled Experimental Study

RATIONALE

It is unclear how septic shock causes acute kidney injury (AKI) and whether this is associated with histological change.

OBJECTIVES

We aimed to determine the nature and extent of changes in renal structure and function over time in an ovine model of septic shock.

METHODS

Fifteen sheep were instrumented with a renal artery flow probe and renal vein cannula. Ten were given intravenous Escherichia coli to induce septic shock, and five acted as controls. Animals were mechanically ventilated for 48 hours, while receiving protocol-guided parenteral fluids and a norepinephrine infusion to maintain mean arterial pressure. Renal biopsies were taken every 24 hours or whenever animals were oliguric for 2 hours. A renal pathologist, blinded to tissue source, systematically quantified histological appearance by light and electron microscopy for 31 prespecified structural changes.

MEASUREMENTS AND MAIN RESULTS

Sheep given E. coli developed septic shock, oliguria, increased serum creatinine, and reduced creatinine clearance (AKI), but there were no changes over time in renal blood flow between groups (P > 0.30) or over time within groups (P > 0.50). Renal oxygen consumption increased only in nonseptic animals (P = 0.01), but there was no between-group difference in renal lactate flux (P > 0.50). There was little structural disturbance in all biopsies and, although some cellular appearances changed over time, the only difference between septic and nonseptic animals was mesangial expansion on electron microscopy.

CONCLUSIONS

In an intensive care-supported model of gram-negative septic shock, early AKI was not associated with changes in renal blood flow, oxygen delivery, or histological appearance. Other mechanisms must contribute to septic AKI.

Persistent and inducible neogenesis repopulates progenitor renin lineage cells in the kidney

Renin lineage cells (RLCs) serve as a progenitor cell reservoir during nephrogenesis and after renal injury. The maintenance mechanisms of the RLC pool are still poorly understood. Since RLCs were also identified as a progenitor cell population in bone marrow we first considered that these may be their source in the kidney. However, transplantation experiments in adult mice demonstrated that bone marrow-derived cells do not give rise to RLCs in the kidney indicating their non-hematopoietic origin. Therefore we tested whether RLCs develop in the kidney through neogenesis (de novo differentiation) from cells that have never expressed renin before. We used a murine model to track neogenesis of RLCs by flow cytometry, histochemistry, and intravital kidney imaging. During nephrogenesis RLCs first appear at e14, form a distinct population at e16, and expand to reach a steady state level of 8-10% of all kidney cells in adulthood. De novo differentiated RLCs persist as a clearly detectable population through embryogenesis until at least eight months after birth. Pharmacologic stimulation of renin production with enalapril or glomerular injury induced the rate of RLC neogenesis in the adult mouse kidney by 14% or more than three-fold, respectively. Thus, the renal RLC niche is constantly filled by local de novo differentiation. This process could be stimulated consequently representing a new potential target to beneficially influence repair and regeneration after kidney injury.

LY333531, a PKCβ inhibitor, attenuates glomerular endothelial cell apoptosis in the early stage of mouse diabetic nephropathy via down-regulating swiprosin-1

Glomerular endothelial cell (GEC) injury plays an important role in the early stage of diabetic nephropathy (DN). Previous studies show that a PKCβ inhibitor is effective for treating DN. In the current study we further explored the effects and molecular mechanisms of PKCβ inhibitors on GEC apoptosis in DN in streptozotocin-induced diabetic mice in vivo and high glucose- or PMA-treated human renal glomerular endothelial cells (HRGECs) in vitro. In the diabetic mice, hyperglycemia caused aggravated nephropathy and GEC apoptosis accompanied by significantly increased expression of swiprosin-1, a potentally pro-apoptotic protein. Administration of LY333531 (1 mg·kg^-1·d^-1 for 8 weeks) significantly attenuated both GEC apoptosis and swiprosin-1 upregulation in the diabetic mice. Similar results were observed in high glucose- or PMA-treated HRGECs in vitro. The pro-apoptotic role of swiprosin-1 was further examined using HRGECs treated with lentivirus mediating RNA interference or over-expression and swiprosin-1-knockout mice. Over-expression of swiprosin-1 in HRGECs resulted in increases in apoptosis and in caspase-9, caspase-3 and Bax expression. In contrast, knockdown of swiprosin-1 attenuated high glucose- or PMA-induced HRGECs apoptosis. Furthermore, over-expression of swiprosin-1 promoted interaction between swiprosin-1 and caspase-9 and increased the formation of apoptosomes. In diabetic swiprosin-1^-/- mice, the kidney/body weight, urinary albumin, glomerular hypertrophy, mitochondrial apoptotic-associated proteins and GEC apoptosis were significantly attenuated as compared with those in diabetic swiprosin-1^+/+ mice. These results demonstrate that swiprosin-1 is up-regulated by PKCβ in the early stage of DN, and that PKCβ facilitates GEC apoptosis through the mitochondrial-dependent pathway.

Increased glomerular filtration rate and impaired contractile function of mesangial cells in TRPC6 knockout mice

The present study was conducted to determine if TRPC6 regulates glomerular filtration rate (GFR) and the contractile function of glomerular mesangial cells (MCs). GFR was assessed in conscious TRPC6 wild type and knockout mice, and in anesthetized rats with and without in vivo knockdown of TRPC6 in kidneys. We found that GFR was significantly greater, and serum creatinine level was significantly lower in TRPC6 deficient mice. Consistently, local knockdown of TRPC6 in kidney using TRPC6 specific shRNA construct significantly attenuated Ang II-induced GFR decline in rats. Furthermore, Ang II-stimulated contraction and Ca²⁺ entry were significantly suppressed in primary MCs isolated from TRPC6 deficient mice, and the Ca²⁺ response could be rescued by re-introducing TRPC6. Moreover, inhibition of reverse mode of Na⁺-Ca²⁺ exchange by KB-R7943 significantly reduced Ca²⁺ entry response in TRPC6-expressing, but not in TRPC6-knocked down MCs. Ca²⁺ entry response was also significantly attenuated in Na⁺ free solution. Single knockdown of TRPC6 and TRPC1 resulted in a comparable suppression on Ca²⁺ entry with double knockdown of both. These results suggest that TRPC6 may regulate GFR by modulating MC contractile function through multiple Ca²⁺ signaling pathways.

Sodium glucose cotransporter 2 in mesangial cells and retinal pericytes and its implications for diabetic nephropathy and retinopathy

Retinopathy and nephropathy are life-threatening diabetic complications that decrease patient quality of life. Although the mechanisms underlying these conditions have been extensively studied, they remain unknown. Recent reports have demonstrated the presence of sodium glucose cotransporter 2 (SGLT2) in retinal pericytes and mesangial cells. Hyperglycemia results in functional and morphological changes in these cells, but these effects are attenuated by phlorizin, a nonselective SGLT inhibitor. Based on these findings, we hypothesized that SGLT2 plays a pivotal role in the development of diabetic nephropathy and retinopathy and that SGLT2 inhibitors may directly protect against these complications.

Polydatin promotes Nrf2-ARE anti-oxidative pathway through activating CKIP-1 to resist HG-induced up-regulation of FN and ICAM-1 in GMCs and diabetic mice kidneys

Our previous study indicated that Casein kinase 2 interacting protein-1 (CKIP-1) could promote the activation of the nuclear factor E2-related factor 2 (Nrf2)/ antioxidant response element (ARE) pathway, playing a significant role in inhibiting the fibrosis of diabetic nephropathy (DN). Polydatin (PD) has been shown to possess strong resistance effects on renal fibrosis which is closely related to activating the Nrf2/ARE pathway, too. Whereas, whether PD could resist DN through regulating CKIP-1 and consequently promoting the activation of Nrf2-ARE pathway needs further investigation. Here, we found that PD significantly reversed the down-regulation of CKIP-1 and attenuated fibronectin (FN) and intercellular cell adhesion molecule-1 (ICAM-1) in glomerular mesangial cells (GMCs) exposed to high glucose (HG). Moreover, PD could decrease Keap1 expression and promote the nuclear content, ARE-binding ability, and transcriptional activity of Nrf2. The activation of Nrf2-ARE pathway by PD eventually led to the quenching of hydrogen peroxide (H₂O₂) and superoxide overproduction boosted by HG. Depletion of CKIP-1 blocked the Nrf2-ARE pathway activation and reversed FN and ICAM-1 down-regulation induced by PD in GMCs challenged with HG. PD increased CKIP-1 and Nrf2 levels in the kidney tissues as well as improved the anti-oxidative effect and renal dysfunction of diabetic mice, which eventually reversed the up-regulation of FN and ICAM-1. Experiments above suggested that PD could increase the CKIP-1-Nrf2-ARE pathway activation to prevent the OSS-induced insult in GMCs and diabetic mice which effectively postpone the diabetic renal fibrosis and the up-regulation of CKIP-1 is probably a novel mechanism in this process.

Single-cell RNA-sequence analysis of mouse glomerular mesangial cells uncovers mesangial cell essential genes

Mesangial cells are essential for the structure and function of glomeruli, but the mechanisms underlying these roles are not well understood. Here, we performed a single-cell RNA-sequence (RNA-seq) analysis of mouse mesangial cells using the Fluidigm C1 platform. We found that gene expression in individual mesangial cells was tremendously heterogeneous, with mean correlation coefficients of 0.20, and most mesangial genes were actually expressed in only a portion of mesangial cells and are therefore presumably dispensable. In contrast, 1,045 genes were expressed in every single mesangial cell and were considered mesangial cell essential genes. A gene ontology analysis revealed a significant enrichment of genes associated with the endothelium, supporting the inference that mesangial cells function as pericytes. Among 58 endothelium-associated genes, 18 encode proteins that are secreted and may be directly involved in endothelial homeostasis. Importantly, 11 (Angpt2, Anxa5, Axl, Ecm1, Eng, Fn1, Mfge8, Msn, Nrp1, Serpine2, and Sparc) were upregulated, while 2 (Apoe and Fgf1) were downregulated in various glomerulopathies. The enrichment of genes associated with other reported functions of mesangial cells was also found. Furthermore, we identified 173 genes specifically expressed in every mesangial cell in glomeruli from the mesangial cell essential gene list. Finally, based on single mesangial cell RNA-seq results, we found that commonly used glomerular cell type markers, including Fhl2, Igfbp5, Wt1, Tek/Tie2, Kdr/Flk1, Flt1/Vegfr1, and Cd34, are actually not specific. Thus, single mesangial cell RNA-seq analysis has provided insights into the functions and underlying mechanisms of mesangial cells.

Negative regulation of Smad1 pathway and collagen IV expression by store-operated Ca2+ entry in glomerular mesangial cells

Collagen IV (Col IV) is a major component of expanded glomerular extracellular matrix in diabetic nephropathy and Smad1 is a key molecule regulating Col IV expression in mesangial cells (MCs). The present study was conducted to determine if Smad1 pathway and Col IV protein abundance were regulated by store-operated Ca²⁺ entry (SOCE). In cultured human MCs, pharmacological inhibition of SOCE significantly increased the total amount of Smad1 protein. Activation of SOCE blunted high-glucose-increased Smad1 protein content. Treatment of human MCs with ANG II at 1 µM for 15 min, high glucose for 3 days, or TGF-β1 at 5 ng/ml for 30 min increased the level of phosphorylated Smad1. However, the phosphorylation of Smad1 by those stimuli was significantly attenuated by activation of SOCE. Knocking down Smad1 reduced, but expressing Smad1 increased, the amount of Col IV protein. Furthermore, activation of SOCE significantly attenuated high-glucose-induced Col IV protein production, and blockade of SOCE substantially increased the abundance of Col IV. To further verify those in vitro findings, we downregulated SOCE specifically in MCs in mice using small-interfering RNA (siRNA) against Orai1 (the channel protein mediating SOCE) delivered by the targeted nanoparticle delivery system. Immunohistochemical examinations showed that expression of both Smad1 and Col IV proteins was significantly greater in the glomeruli with positively transfected Orai1 siRNA compared with the glomeruli from the mice without Orai1 siRNA treatment. Taken together, our results indicate that SOCE negatively regulates the Smad1 signaling pathway and inhibits Col IV protein production in MCs.

Caveolin-1 in the Pathogenesis of Diabetic Nephropathy: Potential Therapeutic Target?

PURPOSE OF REVIEW

Diabetic nephropathy, a major microvascular complication of diabetes and the most common cause of end-stage renal disease, is characterized by prominent accumulation of extracellular matrix. The membrane microdomains caveolae, and their integral protein caveolin-1, play critical roles in the regulation of signal transduction. In this review we discuss current knowledge of the contribution of caveolin-1/caveolae to profibrotic signaling and the pathogenesis of diabetic kidney disease, and assess its potential as a therapeutic target.

RECENT FINDINGS

Caveolin (cav)-1 is key to facilitating profibrotic signal transduction induced by several stimuli known to be pathogenic in diabetic nephropathy, including the most prominent factors hyperglycemia and angiotensin II. Phosphorylation of cav-1 on Y14 is an important regulator of these responses. In vivo studies support a pathogenic role for caveolae in the progression of diabetic nephropathy. Targeting caveolin-1/caveolae would enable inhibition of multiple profibrotic pathways, representing a novel and potentially potent therapeutic option for diabetic nephropathy.

miR302 regulates SNAI1 expression to control mesangial cell plasticity

Cell fate decisions are controlled by the interplay of transcription factors and epigenetic modifiers, which together determine cellular identity. Here we elaborate on the role of miR302 in the regulation of cell plasticity. Overexpression of miR302 effected silencing of the TGFβ type II receptor and facilitated plasticity in a manner distinct from pluripotency, characterized by increased expression of Snail. miR302 overexpressing mesangial cells also exhibited enhanced expression of EZH2 coincident with Snail upregulation. esiRNA silencing of each component suggest that Smad3 and EZH2 are part of a complex that regulates plasticity and that miR302 regulates EZH2 and Snail independently. Subsequent manipulation of miR302 overexpressing cells demonstrated the potential of using this approach for reprogramming as evidenced by de novo expression of the tight junction components ZO-1 and E-cadherin and the formation of ZO-1 containing tight junctions. Understanding the processes through which dynamic epigenetic silencing is controlled in adults cells will allow us to address the epigenetic state of acquired disease and whether original states, regenerative in nature, can be restored with therapy.

Crucial Role of Mesangial Cell-derived Connective Tissue Growth Factor in a Mouse Model of Anti-Glomerular Basement Membrane Glomerulonephritis

Connective tissue growth factor (CTGF) coordinates the signaling of growth factors and promotes fibrosis. Neonatal death of systemic CTGF knockout (KO) mice has hampered analysis of CTGF in adult renal diseases. We established 3 types of CTGF conditional KO (cKO) mice to investigate a role and source of CTGF in anti-glomerular basement membrane (GBM) glomerulonephritis. Tamoxifen-inducible systemic CTGF (Rosa-CTGF) cKO mice exhibited reduced proteinuria with ameliorated crescent formation and mesangial expansion in anti-GBM nephritis after induction. Although CTGF is expressed by podocytes at basal levels, podocyte-specific CTGF (pod-CTGF) cKO mice showed no improvement in renal injury. In contrast, PDGFRα promoter-driven CTGF (Pdgfra-CTGF) cKO mice, which predominantly lack CTGF expression by mesangial cells, exhibited reduced proteinuria with ameliorated histological changes. Glomerular macrophage accumulation, expression of Adgre1 and Ccl2, and ratio of M1/M2 macrophages were all reduced both in Rosa-CTGF cKO and Pdgfra-CTGF cKO mice, but not in pod-CTGF cKO mice. TGF-β1-stimulated Ccl2 upregulation in mesangial cells and macrophage adhesion to activated mesangial cells were decreased by reduction of CTGF. These results reveal a novel mechanism of macrophage migration into glomeruli with nephritis mediated by CTGF derived from mesangial cells, implicating the therapeutic potential of CTGF inhibition in glomerulonephritis.

Hyperfiltration-associated biomechanical forces in glomerular injury and response: Potential role for eicosanoids

Hyperfiltration is a well-known risk factor in progressive loss of renal function in chronic kidney disease (CKD) secondary to various diseases. A reduced number of functional nephrons due to congenital or acquired cause(s) results in hyperfiltration in the remnant kidney. Hyperfiltration-associated increase in biomechanical forces, namely pressure-induced tensile stress and fluid flow-induced shear stress (FFSS) determine cellular injury and response. We believe the current treatment of CKD yields limited success because it largely attenuates pressure-induced tensile stress changes but not the effect of FFSS on podocytes. Studies on glomerular podocytes, tubular epithelial cells and bone osteocytes provide evidence for a significant role of COX-2 generated PGE₂ and its receptors in response to tensile stress and FFSS. Preliminary observations show increased urinary PGE₂ in children born with a solitary kidney. FFSS-induced COX2-PGE₂-EP₂ signaling provides an opportunity to identify targets and, for developing novel agents to complement currently available treatment.

Diabetes-Induced Reactive Oxygen Species: Mechanism of Their Generation and Role in Renal Injury

Diabetes induces the onset and progression of renal injury through causing hemodynamic dysregulation along with abnormal morphological and functional nephron changes. The most important event that precedes renal injury is an increase in permeability of plasma proteins such as albumin through a damaged glomerular filtration barrier resulting in excessive urinary albumin excretion (UAE). Moreover, once enhanced UAE begins, it may advance renal injury from progression of abnormal renal hemodynamics, increased glomerular basement membrane (GBM) thickness, mesangial expansion, extracellular matrix accumulation, and glomerulosclerosis to eventual end-stage renal damage. Interestingly, all these pathological changes are predominantly driven by diabetes-induced reactive oxygen species (ROS) and abnormal downstream signaling molecules. In diabetic kidney, NADPH oxidase (enzymatic) and mitochondrial electron transport chain (nonenzymatic) are the prominent sources of ROS, which are believed to cause the onset of albuminuria followed by progression to renal damage through podocyte depletion. Chronic hyperglycemia and consequent ROS production can trigger abnormal signaling pathways involving diverse signaling mediators such as transcription factors, inflammatory cytokines, chemokines, and vasoactive substances. Persistently, increased expression and activation of these signaling molecules contribute to the irreversible functional and structural changes in the kidney resulting in critically decreased glomerular filtration rate leading to eventual renal failure.

Pathophysiology of IgA Nephropathy

Immunoglobulin (Ig)A nephropathy is the most prevalent primary chronic glomerular disease in the world. Studies of molecular and cellular interactions involved in the pathogenesis of IgA nephropathy have revealed several inherent abnormalities in the production and subsequent handling of IgA1. In patients with this disease, altered glycan structures in the unique hinge region of the heavy chains of IgA1 molecules lead to the exposure of antigenic determinants, which are recognized by naturally occurring antiglycan antibodies of the IgG and/or IgA1 isotype. In addition, due to a homing abnormality there is a gradual shift of mucosal IgA1 producing lymphoplasma cells from mucosal lymphoid tissue to bone marrow resulting in excess production of mucosal-type IgA1 in the systemic circulation. As a result, nephritogenic immune complexes form in the circulation and deposit in the glomerular mesangium. Deposited immune complexes induce proliferation of resident mesangial cells with increased production of extracellular matrix proteins. A number of inflammatory cytokines produced by the mesangial cells damage the filtration barrier resulting in hematuria and proteinuria ultimately leading to progressive renal damage.

Regulation of Nephrin Phosphorylation in Diabetes and Chronic Kidney Injury

Diabetes is the leading cause of microalbuminuria and end-stage renal failure in industrial countries. Disruption of the filtration barrier, seen in almost all nephrotic diseases and diabetes, is the result of the loss or effacement of the podocyte foot process, notably damage of proteins within the slit diaphragm such as nephrin. For many years, nephrin has been viewed as a structural component of the slit diaphragm. It is now well recognized that nephrin contains several tyrosine residues in its cytoplasmic domain, which influences the development of glomerular injury. In this review, we propose an overview of nephrin signaling pathways in kidney injury.

Connexin43 regulates high glucose-induced expression of fibronectin, ICAM-1 and TGF-β1 via Nrf2/ARE pathway in glomerular mesangial cells

Nrf2/ARE signaling pathway is a crucial cellular defense system to cope with oxidative stress, which is adaptively activated, in diabetic condition that is not efficient enough to resist the oxidative stress provoked by hyperglycemia. We have previously demonstrated that Connexin43 (Cx43) attenuates renal fibrosis through c-Src. However, the underlying mechanisms need to be further clarified. It has been reported that Cx43 possesses the ability of anti-oxidative. The current study aimed to determine if Cx43 exerts protective effects on renal fibrosis in diabetes via activation of Nrf2/ARE pathway and explore the underlying molecular mechanisms. The following findings were observed: (1) Cx43 expression decreased and c-Src activity increased in kidneys of diabetic animals; (2) Over-expressed Cx43 in high glucose treated GMCs inhibited protein levels of FN, ICAM-1 and TGF-β1; (3) Nrf2/ARE signaling adaptively responded to high glucose treatment in GMCs; (4) Cx43 reduced ROS generation by boost Nrf2/ARE signaling under high glucose condition; (5) Inhibition of c-Src activity promoted nucleus accumulation of Nrf2; (6) Over-expressed Cx43 inhibited c-Src activity and the interaction between c-Src and Nrf2 in GMCs cultured in high glucose. Thus we propose that Cx43 might enhance the activation of Nrf2/ARE pathway by means of inhibiting c-Src activity to hinder the nuclear export of Nrf2, and then reduce expression of FN, ICAM-1 and TGF-β1, ultimately attenuating renal fibrosis in diabetes.

Podocyte and Parietal Epithelial Cell Interactions in Health and Disease

The glomerulus has 3 resident cells namely mesangial cells that produce the mesangial matrix, endothelial cells that line the glomerular capillaries, and podocytes that cover the outer surface of the glomerular basement membrane. Parietal epithelial cells (PrECs), which line the Bowman's capsule are not part of the glomerular tuft but may have an important role in the normal function of the glomerulus. A significant progress has been made in recent years regarding our understanding of the role and function of these cells in normal kidney and in kidneys with various types of glomerulopathy. In crescentic glomerulonephritis necrotizing injury of the glomerular tuft results in activation and leakage of fibrinogen which provides the trigger for excessive proliferation of PrECs giving rise to glomerular crescents. In cases of collapsing glomerulopathy, podocyte injury causes collapse of the glomerular capillaries and activation and proliferation of PrECs, which accumulate within the urinary space in the form of pseudocrescents. Many of the noninflammatory glomerular lesions such as focal segmental glomerulosclerosis and global glomerulosclerosis also result from podocyte injury which causes variable loss of podocytes. In these cases podocyte injury leads to activation of PrECs that extend on to the glomerular tuft where they cause segmental and/or global sclerosis by producing excess matrix, resulting in obliteration of the capillary lumina. In diabetic nephropathy, in addition to increased matrix production in the mesangium and glomerular basement membranes, increased loss of podocytes is an important determinant of long-term prognosis. Contrary to prior belief there is no convincing evidence for an active podocyte proliferation in any of the above mentioned glomerulopathies.

Betulinic acid ameliorates experimental diabetic-induced renal inflammation and fibrosis via inhibiting the activation of NF-κB signaling pathway

Diabetic nephropathy (DN) is the leading cause of end-stage renal failure and is characterized by excessive deposition of extracellular matrix (ECM) proteins such as fibronectin (FN), in the glomerular mesangium and tubulointerstitium. Betulinic acid (BA), a pentacyclic triterpene derived from the bark of the white birch tree, has been demonstrated to have many pharmacological activities. However, the effect of BA on DN has not been fully elucidated. To explore the possible anti-inflammatory effects of BA and their underlying mechanisms, we used streptozotocin-induced diabetic rat kidneys and high glucose-treated glomerular mesangial cells. Our study showed BA could inhibit the degradation of IκBα and the activity of NF-κB in diabetic rat kidneys and high glucose-induced mesangial cells, resulting in reduction of FN expression. In addition, BA suppressed the DNA binding activity and transcriptional activity of NF-κB in high glucose-induced glomerular mesangial cells (GMCs). Furthermore, BA enhanced the interaction between IκBα and β-arrestin2 in mesangial cells. Taken together, our data suggest BA inhibits NF-κB activation through stabilizing NF-κB inhibitory protein IκBα, thereby preventing diabetic renal fibrosis.

Human kidney pericytes produce renin

Pericytes, perivascular cells embedded in the microvascular wall, are crucial for vascular homeostasis. These cells also play diverse roles in tissue development and regeneration as multi-lineage progenitors, immunomodulatory cells and as sources of trophic factors. Here, we establish that pericytes are renin producing cells in the human kidney. Renin was localized by immunohistochemistry in CD146 and NG2 expressing pericytes, surrounding juxtaglomerular and afferent arterioles. Similar to pericytes from other organs, CD146⁺CD34^–CD45^–CD56^– renal fetal pericytes, sorted by flow cytometry, exhibited tri-lineage mesodermal differentiation potential in vitro. Additionally, renin expression was triggered in cultured kidney pericytes by cyclic AMP as confirmed by immuno-electron microscopy, and secretion of enzymatically functional renin, capable of generating angiotensin I. Pericytes derived from second trimester human placenta also expressed renin in an inducible fashion although the renin activity was much lower than in renal pericytes. Thus, our results confirm and extend the recently discovered developmental plasticity of microvascular pericytes, and may open new perspectives to the therapeutic regulation of the renin-angiotensin system.

Research review on the pharmacological effects of astragaloside IV

Astragalus membranaceus Bunge has been used to treat numerous diseases for thousands of years. As the main active substance of Astragalus membranaceus Bunge, astragaloside IV (AS-IV) also demonstrates the potent protective effect on focal cerebral ischemia/reperfusion, cardiovascular disease, pulmonary disease, liver fibrosis, and diabetic nephropathy. Based on studies published during the past several decades, the current state of AS-IV research and the pharmacological effects are detailed, elucidated, and summarized. This review systematically summarizes the pharmacological effects, metabolism mechanism, and the toxicity of AS-IV. AS-IV has multiple pharmacologic effects, including anti-inflammatory, antifibrotic, antioxidative stress, anti-asthma, antidiabetes, immunoregulation, and cardioprotective effect via numerous signaling pathways. According to the existing studies and clinical practices, AS-IV possesses potential for broad application in many diseases.

Usp2-69 overexpression slows down the progression of rat anti-Thy1.1 nephritis

Mesangial proliferative glomerulonephritis is characterized by proliferation of mesangial cells (MCs) and transforming growth factor-β (TGF-β)-dependent stimulation of abnormal extracellular matrix (ECM) accumulation. We previously showed that Decorin--a leucine-rich proteoglycan inhibiting the progression of glomerulonephritis and glomerular sclerosis--can be degraded by the ubiquitin-proteasome pathway and deubiquitinated and stabilized by ubiquitin-specific processing protease 2-69(Usp2-69). Usp2-69 is highly expressed in the kidney and has been implicated in the regulation of cell proliferation and apoptosis. However, its role in mesangial proliferative glomerulonephritis remains unclear. Here, we explored the effect of Usp2-69 on MC proliferation and ECM deposition by transfecting Usp2-69 plasmid into rat anti-Thy1.1 nephritis model and into cultured MCs, as well as detected Usp2-69 and Decorin in rat anti-Thy1.1 nephritis model by western blot. Overexpressing Usp2-69 at the early stage, but not advanced stage, of anti-Thy1.1 nephritis alleviated cell proliferation and ECM deposition, which was shown by decreased Ki-67, Collagen IV and Fibronectin detected by immunohistochemistry. Overexpression also increased Decorin and decreased TGF-β1 and Collagen IV both in vitro and in vivo. In conclusion, our findings suggest that Usp2-69 overexpression alleviates the progression of rat anti-Thy1.1 nephritis and, therefore, that exogenous plasmid injection via the renal artery enhanced by electrotransfer technology could be a promising avenue for glomerular disease research.

The Players: Cells Involved in Glomerular Disease

Glomerular diseases are common and important. They can arise from systemic inflammatory or metabolic diseases that affect the kidney. Alternately, they are caused primarily by local glomerular abnormalities, including genetic diseases. Both intrinsic glomerular cells and leukocytes are critical to the healthy glomerulus and to glomerular dysregulation in disease. Mesangial cells, endothelial cells, podocytes, and parietal epithelial cells within the glomerulus all play unique and specialized roles. Although a specific disease often primarily affects a particular cell type, the close proximity, and interdependent functions and interactions between cells mean that even diseases affecting one cell type usually indirectly influence others. In addition to those cells intrinsic to the glomerulus, leukocytes patrol the glomerulus in health and mediate injury in disease. Distinct leukocyte types and subsets are present, with some being involved in different ways in an individual glomerular disease. Cells of the innate and adaptive immune systems are important, directing systemic immune and inflammatory responses, locally mediating injury, and potentially dampening inflammation and facilitating repair. The advent of new genetic and molecular techniques, and new disease models means that we better understand both the basic biology of the glomerulus and the pathogenesis of glomerular disease. This understanding should lead to better diagnostic techniques, biomarkers, and predictors of prognosis, disease severity, and relapse. With this knowledge comes the promise of better therapies in the future, directed toward halting pathways of injury and fibrosis, or interrupting the underlying pathophysiology of the individual diseases that lead to significant and progressive glomerular disease.

Gata3 Hypomorphic Mutant Mice Rescued with a Yeast Artificial Chromosome Transgene Suffer a Glomerular Mesangial Cell Defect

GATA3 is a zinc finger transcription factor that plays a crucial role in embryonic kidney development, while its precise functions in the adult kidney remain largely unexplored. Here, we demonstrate that GATA3 is specifically expressed in glomerular mesangial cells and plays a critical role in the maintenance of renal glomerular function. Newly generated Gata3 hypomorphic mutant mice exhibited neonatal lethality associated with severe renal hypoplasia. Normal kidney size was restored by breeding the hypomorphic mutant with a rescuing transgenic mouse line bearing a 662-kb Gata3 yeast artificial chromosome (YAC), and these animals (termed G3YR mice) survived to adulthood. However, most of the G3YR mice showed degenerative changes in glomerular mesangial cells, which deteriorated progressively during postnatal development. Consequently, the G3YR adult mice suffered severe renal failure. We found that the 662-kb Gata3 YAC transgene recapitulated Gata3 expression in the renal tubules but failed to direct sufficient GATA3 activity to mesangial cells. Renal glomeruli of the G3YR mice had significantly reduced amounts of platelet-derived growth factor receptor (PDGFR), which is known to participate in the development and maintenance of glomerular mesangial cells. These results demonstrate a critical role for GATA3 in the maintenance of mesangial cells and its absolute requirement for prevention of glomerular disease.

High glucose-induced cytoplasmic translocation of Dnmt3a contributes to CTGF hypo-methylation in mesangial cells

Connective tissue growth factor (CTGF) plays an essential role in the pathogenesis of diabetic nephropathy and we have previously identified that high glucose induced the expression of CTGF by decreasing DNA methylation. The aim of the present study was to investigate the underlying mechanisms of the high glucose-induced CTGF hypo-methylation. Human glomerular mesangial cells (hMSCs) were treated with low glucose (5 mM), mannitol (30 mM) or high glucose (30 mM) respectively. Immunofluorescence staining, real-time quantitative PCR and western blotting were performed to determine the subcellular distribution and expression of CTGF and Dnmt3a. ChIP-PCR assay was applied to investigate the capability of Dnmt3a to bind the CpG island of CTGF. Our results showed that high glucose induced both mRNA and protein expressions of CTGF, and led to increased cytoplasmic translocation of Dnmt3a in cultured hMSCs. The nuclear Dnmt3a protein was significantly reduced after high glucose treatment, although the expression of total Dnmt3a protein was not altered. We further discovered that ERK/MAPK signalling contributed to the high glucose-induced cytoplasmic translocation of Dnmt3a. Consequently, less Dnmt3a protein was bound to the CpG island of CTGF promoter, which induced an increase in CTGF expression by epigenetic regulation in the presence of high glucose. In conclusion, high glucose induces cytoplasmic translocation of Dnmt3a, possibly through activating ERK/MAPK signalling pathway, which contributes to the decreased binding of Dnmt3a on CTGF promoter and the subsequent CTGF hypo-methylation in diabetic nephropathy.

TRPC6 channel activation promotes neonatal glomerular mesangial cell apoptosis via calcineurin/NFAT and FasL/Fas signaling pathways

Glomerular mesangial cell (GMC) proliferation and death are involved in the pathogenesis of glomerular disorders. The mechanisms that control GMC survival are poorly understood, but may include signal transduction pathways that are modulated by changes in intracellular Ca²⁺ ([Ca²⁺]_i) concentration. In this study, we investigated whether activation of the canonical transient receptor potential (TRPC) 6 channels and successive [Ca²⁺]_i elevation alter neonatal GMC survival. Hyperforin (HF)-induced TRPC6 channel activation increased [Ca²⁺]_i concentration, inhibited proliferation, and triggered apoptotic cell death in primary neonatal pig GMCs. HF-induced neonatal GMC apoptosis was not associated with oxidative stress. However, HF-induced TRPC6 channel activation stimulated nuclear translocation of the nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1). HF also increased cell death surface receptor Fas ligand (FasL) level and caspase-8 activity in the cells; effects mitigated by [Ca²⁺]_i chelator BAPTA, calcineurin/NFAT inhibitor VIVIT, and TRPC6 channel knockdown. Accordingly, HF-induced neonatal GMC apoptosis was attenuated by BAPTA, VIVIT, Fas blocking antibody, and a caspase-3/7 inhibitor. These findings suggest that TRPC6 channel-dependent [Ca²⁺]_i elevation and the ensuing induction of the calcineurin/NFAT, FasL/Fas, and caspase signaling cascades promote neonatal pig GMC apoptosis.

Enhanced detection with spectral imaging fluorescence microscopy reveals tissue- and cell-type-specific compartmentalization of surface-modified polystyrene nanoparticles

BACKGROUND

Precisely targeted nanoparticle delivery is critically important for therapeutic applications. However, our knowledge on how the distinct physical and chemical properties of nanoparticles determine tissue penetration through physiological barriers, accumulation in specific cells and tissues, and clearance from selected organs has remained rather limited. In the recent study, spectral imaging fluorescence microscopy was exploited for precise and rapid monitoring of tissue- and cell-type-specific distribution of fluorescent polystyrene nanoparticles with chemically distinct surface compositions.

METHODS

Fluorescent polystyrene nanoparticles with 50-90 nm diameter and with carboxylated- or polyethylene glycol-modified (PEGylated) surfaces were delivered into adult male and pregnant female mice with a single intravenous injection. The precise anatomical distribution of the particles was investigated by confocal microscopy after a short-term (5 min) or long-term (4 days) distribution period. In order to distinguish particle-fluorescence from tissue autofluorescence and to enhance the detection-efficiency, fluorescence spectral detection was applied during image acquisition and a post hoc full spectrum analysis was performed on the final images.

RESULTS

Spectral imaging fluorescence microscopy allowed distinguishing particle-fluorescence from tissue-fluorescence in all examined organs (brain, kidney, liver, spleen and placenta) in NP-treated slice preparations. In short-time distribution following in vivo NP-administration, all organs contained carboxylated-nanoparticles, while PEGylated-nanoparticles were not detected in the brain and the placenta. Importantly, nanoparticles were not found in any embryonic tissues or in the barrier-protected brain parenchyma. Four days after the administration, particles were completely cleared from both the brain and the placenta, while PEGylated-, but not carboxylated-nanoparticles, were stuck in the kidney glomerular interstitium. In the spleen, macrophages accumulated large amount of carboxylated and PEGylated nanoparticles, with detectable redistribution from the marginal zone to the white pulp during the 4-day survival period.

CONCLUSIONS

Spectral imaging fluorescence microscopy allowed detecting the tissue- and cell-type-specific accumulation and barrier-penetration of polystyrene nanoparticles with equal size but chemically distinct surfaces. The data revealed that polystyrene nanoparticles are retained by the reticuloendothelial system regardless of surface functionalization. Taken together with the increasing production and use of nanoparticles, the results highlight the necessity of long-term distribution studies to estimate the potential health-risks implanted by tissue-specific nanoparticle accumulation and clearance.

Unraveling the immunopathogenesis of glomerular disease

Immune-mediated damage to glomerular structures is largely responsible for the pathology associated with the majority of glomerular diseases. Therefore, a detailed understanding of the basic immune mechanisms responsible for glomerular damage is needed to inform the design of novel intervention strategies. Glomerular injury of immune origin is complex and involves both inflammatory and non-inflammatory processes driven by elements of the innate and adaptive immune system. This review summarizes the basic immune mechanisms that cause glomerular injury leading to the nephritic and nephrotic syndromes. A major focus of the review is to highlight the mechanisms by which antibodies cause glomerular injury through their interactions with glomerular cells, complement proteins, phagocytes bearing complement and Fcγ receptors, and dendritic cells expressing the neonatal receptor for IgG, FcRn.

Immunoglobulin A nephropathy: a pathophysiology view

BACKGROUND AND AIM

IgA nephropathy is one of the leading causes of primary glomerulonephritis worldwide and an important etiology of renal disease in young adults. IgA nephropathy is considered an immune complex-mediated disease.

METHODS

This review article summarizes recent evidence on the pathophysiology of IgA nephropathy.

RESULTS

Current studies indicate an ordered sequence of multi-hits as fundamental to disease occurrence. Altered glycan structures in the hinge region of the heavy chains of IgA1 molecules act as auto-antigens, potentially triggering the production of glycan-specific autoantibodies. Recognition of novel epitopes by IgA and IgG antibodies leads to the formation of immune complexes galactose deficient-IgA1/anti-glycan IgG or IgA. Immune complexes of IgA combined with FcαRI/CD89 have also been implicated in disease exacerbation. These nephritogenic immune complexes are formed in the circulation and deposited in renal mesangium. Deposited immune complexes ultimately induce glomerular injury, through the release of pro-inflammatory cytokines, secretion of chemokines and the resultant migration of macrophages into the kidney. The TfR1/CD71 receptor has a pivotal role in mesangial cells. New signaling intracellular mechanisms have also been described.

CONCLUSION

The knowledge of the whole pathophysiology of this disease could provide the rational bases for developing novel approaches for diagnosis, for monitoring disease activity, and for disease-specific treatment.

The chemokine (C-C motif) ligand protein synthesis inhibitor bindarit prevents cytoskeletal rearrangement and contraction of human mesangial cells

Intraglomerular mesangial cells (MCs) maintain structural and functional integrity of renal glomerular microcirculation and homeostasis of mesangial matrix. Following different types of injury, MCs change their phenotype upregulating the expression of α-smooth muscle actin (α-SMA), changing contractile abilities and increasing the production of matrix proteins, chemokines and cytokines. CCL2 is a chemokine known to be involved in the pathogenesis of renal diseases. Its glomerular upregulation correlates with the extent of renal damage. Bindarit is an indazolic derivative endowed with anti-inflammatory activity when tested in experimental diseases. It selectively inhibits the synthesis of inflammatory C-C chemokines including CCL2, CCL7 and CCL8. This work aims to analyse bindarit effects on ET1-, AngII- and TGFβ-induced mesangial cell dysfunction. Bindarit significantly reduced AngII-, ET1- and TGFβ-induced α-SMA upregulation. In a collagen contraction assay, bindarit reduced AngII-, ET1- and TGFβ-induced HRMC contraction. Within 3-6h stimulation, vinculin organization and phosphorylation was significantly impaired by bindarit in AngII-, ET1- and TGFβ-stimulated cells without any effect on F-actin distribution. Conversely, p38 phosphorylation was not significantly inhibited by bindarit. Our data strengthen the importance of CCL2 on ET-1, AngII- and TGFβ-induced mesangial cell dysfunction, adding new insights into the cellular mechanisms responsible of bindarit protective effects in human MC dysfunction.

Obesity-related glomerulopathy: clinical and pathologic characteristics and pathogenesis

The prevalence of obesity-related glomerulopathy is increasing in parallel with the worldwide obesity epidemic. Glomerular hypertrophy and adaptive focal segmental glomerulosclerosis define the condition pathologically. The glomerulus enlarges in response to obesity-induced increases in glomerular filtration rate, renal plasma flow, filtration fraction and tubular sodium reabsorption. Normal insulin/phosphatidylinositol 3-kinase/Akt and mTOR signalling are critical for podocyte hypertrophy and adaptation. Adipokines and ectopic lipid accumulation in the kidney promote insulin resistance of podocytes and maladaptive responses to cope with the mechanical forces of renal hyperfiltration. Although most patients have stable or slowly progressive proteinuria, up to one-third develop progressive renal failure and end-stage renal disease. Renin-angiotensin-aldosterone blockade is effective in the short-term but weight loss by hypocaloric diet or bariatric surgery has induced more consistent and dramatic antiproteinuric effects and reversal of hyperfiltration. Altered fatty acid and cholesterol metabolism are increasingly recognized as key mediators of renal lipid accumulation, inflammation, oxidative stress and fibrosis. Newer therapies directed to lipid metabolism, including SREBP antagonists, PPARα agonists, FXR and TGR5 agonists, and LXR agonists, hold therapeutic promise.

Polydatin attenuates AGEs-induced upregulation of fibronectin and ICAM-1 in rat glomerular mesangial cells and db/db diabetic mice kidneys by inhibiting the activation of the SphK1-S1P signaling pathway

We previously demonstrated that activation of sphingosine kinase 1 (SphK1)- sphingosine 1- phosphate (S1P) signaling pathway by high glucose (HG) plays a pivotal role in increasing the expression of fibronectin (FN), an important fibrotic component, by promoting the DNA-binding activity of transcription factor activator protein 1 (AP-1) in glomerular mesangial cells (GMCs) under diabetic conditions. As a multi-target anti-oxidative drug, polydatin (PD) has been shown to have renoprotective effects on experimental diabetes. However, whether PD could resist diabetic nephropathy (DN) by regulating SphK1-S1P signaling pathway needs further investigation. Here, we found that PD significantly reversed the upregulated FN and ICAM-1 expression in GMCs exposed to AGEs. Simultaneously, PD dose-dependently inhibited SphK1 levels at the protein expression and kinase activity and attenuated S1P production under AGEs treatment conditions. In addition, PD reduced SphK activity in GMCs transfected with wild-type SphK(WT) plasmid and significantly suppressed SphK1-mediated increase of FN and ICAM-1 levels under normal conditions. Furthermore, we found that the AGEs-induced upregulation of phosphorylation of c-Jun at Ser63 and Ser73 and c-Fos at Ser32, DNA-binding activity and transcriptional activity of AP-1 were blocked by PD. In comparison with db/db model group, PD treatment suppressed SphK1 levels (mRNA, protein expression, and activity) and S1P production, reversed the upregulation of FN, ICAM-1, c-Jun, and c-Fos in the kidney tissues of diabetic mice, and finally ameliorated renal injury in db/db mice. These findings suggested that the downregulation of SphK1-S1P signaling pathway is probably a novel mechanism by which PD suppressed AGEs-induced FN and ICAM-1 expression and improved renal dysfunction of diabetic models.

Spontaneous one-kidney rats are more susceptible to develop hypertension by DOCA-NaCl and subsequent kidney injury compared with uninephrectomized rats

There is little clinical data of how hypertension may influence individuals with nephron deficiency in the context of being born with a single kidney. We recently developed a new rat model (the heterogeneous stock-derived model of unilateral renal agenesis rat) that is born with a single kidney and exhibits progressive kidney injury and decline in kidney function with age. We hypothesized that DOCA-salt would induce a greater increase in blood pressure and therefore accelerate the progression of kidney injury in rats born with a solitary kidney compared with rats that have undergone unilateral nephrectomy. Time course evaluation of blood pressure, kidney injury, and renal hemodynamics was performed in the following six groups of animals from weeks 13 to 18: 1) DOCA-treated rats with a solitary kidney (DOCA+S group), 2) placebo-treated rats with a solitary kidney, 3) DOCA-treated control rats with two kidneys (DOCA+C group), 4) placebo-treated control rats with two kidneys, 5) DOCA-treated rats with two kidneys that underwent uninephrectomy (DOCA+UNX8 group), and 6) placebo-treated rats with two kidneys that underwent uninephrectomy. DOCA+S rats demonstrated a significant rise (P < 0.05) in blood pressure (192 ± 4 mmHg), proteinuria (205 ± 31 mg/24 h), and a decline in glomerular filtration rate (600 ± 42 μl·min(-1)·g kidney weight(-1)) relative to the DOCA+UNX8 (173 ± 3 mmHg, 76 ± 26 mg/24 h, and 963 ± 36 μl·min(-1)·g kidney weight(-1)) and DOCA+C (154 ± 2 mmHg, 7 ± 1 mg/24 h, and 1,484 ± 121 μl·min(-1)·g kidney weight(-1)) groups. Placebo-treated groups showed no significant change among the three groups. An assessment of renal injury markers via real-time PCR/Western blot analysis and histological analysis was concordant with the measured physiological parameters. In summary, congenital solitary kidney rats are highly susceptible to the induction of hypertension compared with uninephrectomized rats, suggesting that low nephron endowment is an important driver of elevated blood pressure, hastening nephron injury through the transmission of elevated systemic blood pressure and thereby accelerating decline in kidney function.

Exosomes from high glucose-treated glomerular endothelial cells activate mesangial cells to promote renal fibrosis

The interaction between glomerular endothelial cells (GECs) and glomerular mesangial cells (GMCs) is an essential aspect of diabetic nephropathy (DN). Therefore, understanding how GECs communicate with GMCs in the diabetic environment is crucial for the development of new targets for the prevention and treatment of DN. Exosomes, nanometer-sized extracellular membrane vesicles secreted by various cell types, play important roles in cell-to-cell communication via the transfer of mRNA, microRNA and protein. In this study, we demonstrate that high glucose (HG)-treated GECs secrete a higher number of exosomes highly enriched in TGF-β1 mRNA compared with normal glucose (NG)-treated GECs. Exosomes released by HG-treated GECs can promote α-smooth muscle actin (α-SMA) expression, proliferation and extracellular matrix protein overproduction in GMCs through the TGF-β1/Smad3 signaling pathway. Thus, we provide new insights into the pathogenesis of DN that involves intercellular transfer of TGF-β1 mRNA in the GEC-to-GMC direction via exosomes.

Summary: In this study, we demonstrate that TGF-β1-containing exosomes from high glucose-treated glomerular endothelial cells can activate glomerular mesangial cells to promote renal fibrosis.

Mesangial cells from patients with IgA nephropathy have increased susceptibility to galactose-deficient IgA1

Background

IgA nephropathy (IgAN) is the most common glomerulonephritis in the world, affecting close to a million people. Circulating galactose-deficient IgA (gd-IgA), present in patients with IgAN, form immune complex deposits in the glomerular mesangium causing local proliferation and matrix expansion. Intriguing though, individuals having gd-IgA deposits in the kidneys do not necessarily have signs of glomerular disease. Recurrence of IgAN only occurs in less than half of transplanted patients with IgAN, indicating that gd-IgA is not the only factor driving the disease. We hypothesize that, in addition to IgA complexes, patients with IgAN possess a subtype of mesangial cells highly susceptible to gd-IgA induced cell proliferation.

Methods

To test the hypothesis, we designed a technique to culture primary mesangial cells from renal biopsies obtained from IgAN patients and controls. The cell response to gd-IgA treatment was then measured both on gene and protein level and the proliferation rate of the cells in response to PDGF was investigated.

Results

When treated with gd-IgA, mesangial cells from patients with IgAN express and release more PDGF compared to controls. In addition, the mesangial cells from patients with IgAN were more responsive to treatment with PDGF resulting in an increased proliferation rate of the cells compared to control. Mesangial cells cultured from patients with IgAN expressed and released more IL-6 than controls and had a higher expression of matrix genes. Both mesangial cells derived from patients with IgAN and controls increased their expressed TGFβ1 and CCL5 when treated with gd-IgA.

Conclusion

We conclude that mesangial cells derived from IgAN patients have a mesangioproliferative phenotype with increased reactivity to IgA and that these cellular intrinsic properties may be important for the development of IgA nephropathy.

Crosstalk in glomerular injury and repair

PURPOSE OF REVIEW

The glomerulus is a unique structure required for filtration of blood, while retaining plasma proteins based on size and charge selectivity. Distinct cell types form the structural unit that creates the filtration barrier. Structurally, fenestrated endothelial cells line the capillary loops and lie in close contact with mesangial cells. Podocytes are connected by specialized intercellular junctions known as slit diaphragms and separated from the endothelial compartment by the glomerular basement membrane. In order for this highly specialized structure to function, cross-communication between these cells must occur.

RECENT FINDINGS

Although classical studies have established key roles for vascular endothelial and platelet-derived growth factors in glomerular cross-communication, novel paracrine signaling pathways within the glomerulus have recently been identified. In addition, unique cellular pathways of established signaling cascades have been identified that are important for maintaining glomerular barrier function in health and disease.

SUMMARY

Here, we will review our current understanding of the processes of cross-communication between the unique cellular constituents forming the glomerular filtration unit. We will highlight recent findings of cellular crosstalk via signaling pathways that regulate glomerular barrier function in pathophysiological conditions.

Lipoprotein X Causes Renal Disease in LCAT Deficiency

Human familial lecithin:cholesterol acyltransferase (LCAT) deficiency (FLD) is characterized by low HDL, accumulation of an abnormal cholesterol-rich multilamellar particle called lipoprotein-X (LpX) in plasma, and renal disease. The aim of our study was to determine if LpX is nephrotoxic and to gain insight into the pathogenesis of FLD renal disease. We administered a synthetic LpX, nearly identical to endogenous LpX in its physical, chemical and biologic characteristics, to wild-type and Lcat-/- mice. Our in vitro and in vivo studies demonstrated an apoA-I and LCAT-dependent pathway for LpX conversion to HDL-like particles, which likely mediates normal plasma clearance of LpX. Plasma clearance of exogenous LpX was markedly delayed in Lcat-/- mice, which have low HDL, but only minimal amounts of endogenous LpX and do not spontaneously develop renal disease. Chronically administered exogenous LpX deposited in all renal glomerular cellular and matrical compartments of Lcat-/- mice, and induced proteinuria and nephrotoxic gene changes, as well as all of the hallmarks of FLD renal disease as assessed by histological, TEM, and SEM analyses. Extensive in vivo EM studies revealed LpX uptake by macropinocytosis into mouse glomerular endothelial cells, podocytes, and mesangial cells and delivery to lysosomes where it was degraded. Endocytosed LpX appeared to be degraded by both human podocyte and mesangial cell lysosomal PLA2 and induced podocyte secretion of pro-inflammatory IL-6 in vitro and renal Cxl10 expression in Lcat-/- mice. In conclusion, LpX is a nephrotoxic particle that in the absence of Lcat induces all of the histological and functional hallmarks of FLD and hence may serve as a biomarker for monitoring recombinant LCAT therapy. In addition, our studies suggest that LpX-induced loss of endothelial barrier function and release of cytokines by renal glomerular cells likely plays a role in the initiation and progression of FLD nephrosis.

A computational model of flow and species transport in the mesangium

A variety of macromolecules accumulate in the glomerular mesangium in many different diseases, but the physics of the transport of these molecules within the mesangial matrix has not been extensively studied. We present a computational model of convection and diffusion within the porous mesangial matrix and apply this model to the specific instance of immunoglobulin A (IgA) transport in IgA nephropathy. We examine the influence of physiological factors including glomerular basement membrane (GBM) thickness and mesangial matrix density on the total accumulation of IgA. Our results suggest that IgA accumulation can be understood by relating convection and diffusion, thus demonstrating the importance of intrinsic glomerular factors.

Obesity-Related Chronic Kidney Disease-The Role of Lipid Metabolism

Obesity is an independent risk factor for chronic kidney disease (CKD). The mechanisms linking obesity and CKD include systemic changes such as high blood pressure and hyperglycemia, and intrarenal effects relating to lipid accumulation. Normal lipid metabolism is integral to renal physiology and disturbances of renal lipid and energy metabolism are increasingly being linked with kidney disease. AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase (ACC) are important regulators of fatty acid oxidation, which is frequently abnormal in the kidney with CKD. A high fat diet reduces renal AMPK activity, thereby contributing to reduced fatty acid oxidation and energy imbalance, and treatments to activate AMPK are beneficial in animal models of obesity-related CKD. Studies have found that the specific cell types affected by excessive lipid accumulation are proximal tubular cells, podocytes, and mesangial cells. Targeting disturbances of renal energy metabolism is a promising approach to addressing the current epidemic of obesity-related kidney disease.