Type IV Collagen Induces Podocytic Features in Bone Marrow Stromal Stem CellsIn Vitro

Stem/progenitor cell in kidney: characteristics, homing, coordination, and maintenance

Renal failure has a high prevalence and is becoming a public health problem worldwide. However, the renal replacement therapies such as dialysis are not yet satisfactory for its multiple complications. While stem/progenitor cell-mediated tissue repair and regenerative medicine show there is light at the end of tunnel. Hence, a better understanding of the characteristics of stem/progenitor cells in kidney and their homing capacity would greatly promote the development of stem cell research and therapy in the kidney field and open a new route to explore new strategies of kidney protection. In this review, we generally summarize the main stem/progenitor cells derived from kidney in situ or originating from the circulation, especially bone marrow. We also elaborate on the kidney-specific microenvironment that allows stem/progenitor cell growth and chemotaxis, and comment on their interaction. Finally, we highlight potential strategies for improving the therapeutic effects of stem/progenitor cell-based therapy. Our review provides important clues to better understand and control the growth of stem cells in kidneys and develop new therapeutic strategies.

High glucose inhibits osteogenic differentiation of bone marrow mesenchymal stem cells via regulating miR-493-5p/ZEB2 signalling

Diabetic osteoporosis (DOP) is attributed to the aberrant physiological function of bone marrow mesenchymal stem cells (BMSCs) under high glucose (HG) environment. MicroRNAs (miRNAs) are involved in the pathological processes of DOP. We aimed to explore the underlying mechanism of miRNA in DOP. BMSCs were cultured in osteogenic medium with HG to induce osteogenic differentiation, and the interaction between miR-493-5p and ZEB2 was assessed by luciferase assay. Herein, we found miR-493-5p is gradually reduced during osteogenic differentiation in BMSCs. HG treatment inhibits osteogenic differentiation and induces an up-regulation of miR-493-5p leading to reduced level of its downstream target ZEB2. Inhibition of miR-493-5p attenuates HG-induced osteogenic differentiation defects by upregulation of ZEB2. Mechanistically, miR-493-5p/ZEB2 signalling mediates HG-inhibited osteogenic differentiation by inactivation of Wnt/β-catenin signalling. More importantly, knockdown of miR-493-5p therapeutically alleviated the DOP condition in mice. HG prevents BMSCs osteogenic differentiation via up-regulation of miR-493-5p, which results in reduced level of ZEB2 by directly targeting its 3'-untranslated region of mRNA. Thus, miR-493-5p/ZEB2 is a potential therapeutic target and provides novel strategy for the treatment and management of DOP.

From Infancy to Fancy: A Glimpse into the Evolutionary Journey of Podocytes in Culture

Podocytes are critical components of the filtration barrier and responsible for maintaining healthy kidney function. An assault on podocytes is generally associated with progression of chronic glomerular diseases. Therefore, podocyte pathophysiology is a favorite research subject for nephrologists. Despite this, podocyte research has lagged because of the unavailability of techniques for culturing such specialized cells ex vivo in quantities that are adequate for mechanistic studies. In recent years, this problem was circumvented by the efforts of researchers, who successfully developed several in vitro podocyte cell culture model systems that paved the way for incredible discoveries in the field of nephrology. This review sets us on a journey that provides a comprehensive insight into the groundbreaking breakthroughs and novel technologic advances made in the field of podocyte cell culture so far, beginning from its inception, evolution, and progression. In this study, we also describe in detail the pros and cons of different models that are being used to culture podocytes. Our extensive and exhaustive deliberation on the status of podocyte cell culture will facilitate researchers to choose wisely an appropriate model for their own research to avoid potential pitfalls in the future.

miR-124a enhances therapeutic effects of bone marrow stromal cells transplant on diabetic nephropathy-related epithelial-to-mesenchymal transition and fibrosis

BACKGROUND

Epithelial-to-mesenchymal transition (EMT) has been gradually considered as one of the major pathways that causes the production of interstitial myofibroblasts in diseased kidneys.

MATERIALS AND METHODS

The study was done to investigate the effect of a bone marrow stromal cell (BMSCs) transplant on rat podocytes and diabetic nephropathy (DN) rats in high-glucose concentration, and to explore the effect of miR-124a on BMSC therapy. High glucose-injured podocytes and streptozotocin-induced DN rats have been respectively used as injury models in in vitro and in vivo studies. Podocyte viability was measured using the Cell Counting Kit-8 assay. Renal pathological examination was observed by HE staining and Masson staining. The messenger RNA and protein levels were determined via real-time polymerase chain reaction and Western blotting, respectively.

RESULTS

By mediating the activation of caveolin-1 (cav-1) and β-catenin and affecting the expression levels of EMT biomarkers including p-cadherin, synaptopodin, fibroblast-specific protein-1, α-smooth muscle actin and snail, our in vitro study confirmed that miR-124a played a significant role in the treatment of high glucose-induced podocyte injury by BMSCs. The therapeutic effects of the BMSC transplant on DN rats were also proved to be further enhanced by miR-124a overexpression in BMSCs, and such a phenomenon was accompanied by the improvement of renal fibrosis and mitigation of DN-related kidney impairment. Regulation of fibronectin, collagen1, and EMT-related proteins was closely implicated with the mechanism, and the activation of cav-1 and β-catenin was also possibly involved.

CONCLUSION

The study demonstrated the pivotal effect of miR-124a on BMSC therapy for DN rats via mitigating EMT and fibrosis. Our results provide a novel insight into how therapeutic effects of BMSCs can be improved at the posttranscriptional level.

Combination with miR-124a improves the protective action of BMSCs in rescuing injured rat podocytes from abnormal apoptosis and autophagy

This in vitro study was performed to identify the role of miR-124a in bone marrow stromal stem cells (BMSCs) therapy for H₂ O₂ -induced rat podocyte injury, and determine whether combination treatment with miR-124a could improve the protective effect of BMSCs. Cell viability of podocytes was detected by CCK-8 assay. Detection of ROS level, apoptotic rate, and autophagy rate was carried out using flow cytometry assays. Oxidative stress parameters were analyzed using the ELISA assays. MiR-124a and mRNA levels were determined using real-time PCR. Protein expression was detected using Western blotting. Our study revealed a pivotal role of miR-124a in the protective action of BMSCs on podocyte injury driven by oxidative stress. BMSCs could rescue injured podocytes from aberrant apoptosis and autophagy by regulating cleaved caspase-3, Bax, Bcl-2, LC3-II/I, and p62. Suppression of the PI3 K/Akt/mTOR signaling pathway is likely one of the main mechanisms underlying the protective action of BMSCs transfected with miR-124a. Our study revealed that miR-124a further improves the protective effect of BMSCs in injured podocytes. Thus, the combination of BMSCs and microRNAs could be a beneficial treatment for renal diseases in the near future.

Structure and Function of Basement Membranes

Basement membranes (BMs) are present in every tissue of the human body. All epithelium and endothelium is in direct association with BMs. BMs are a composite of several large glycoproteins and form an organized scaffold to provide structural support to the tissue and also offer functional input to modulate cellular function. While collagen I is the most abundant protein in the human body, type IV collagen is the most abundant protein in BMs. Matrigel is commonly used as surrogate for BMs in many experiments, but this is a tumor-derived BM–like material and does not contain all of the components that natural BMs possess. The structure of BMs and their functional role in tissues are unique and unlike any other class of proteins in the human body. Increasing evidence suggests that BMs are unique signal input devices that likely fine tune cellular function. Additionally, the resulting endothelial and epithelial heterogeneity in human body is a direct contribution of cell-matrix interaction facilitated by the diverse compositions of BMs.

Kidney transplantation, bioengineering and regeneration: an originally immunology-based discipline destined to transition towards ad hoc organ manufacturing and repair

Kidney transplantation (KT), as a modality of renal replacement therapy (RRT), has been shown to be both economically and functionally superior to dialysis for the treatment of end-stage renal disease (ESRD). Progress in KT is limited by two major barriers: a) a chronic and burgeoning shortage of transplantable organs and b) the need for chronic immunosuppression following transplantation. Although ground-breaking advances in transplant immunology have improved patient survival and graft durability, a new pathway of innovation is needed in order to overcome current obstacles. Regenerative medicine (RM) holds the potential to shift the paradigm in RRT, through organ bioengineering. Manufactured organs represent a potentially inexhaustible source of transplantable grafts that would bypass the need for immunosuppressive drugs by using autologous cells to repopulate extracellular matrix (ECM) scaffolds. This overview discusses the current status of renal transplantation while reviewing the most promising innovations in RM therapy as applied to RRT.

Prospect for kidney bioengineering: shortcomings of the status quo

INTRODUCTION

Dialysis and renal transplantation are the only two therapeutic options offered to patients affected by end-stage kidney disease; however, neither treatment can be considered definitive. In fact, dialysis is able to replace only the filtration function of the kidney without substituting its endocrine and metabolic roles, and dramatically impacts on patient's quality of life. On the other hand, kidney transplantation is severely limited by the shortage of transplantable organs, the need for immunosuppressive therapies and a narrow half-life. Regenerative medicine approaches are promising tools aiming to improve this condition.

AREAS COVERED

Cell therapies, bioartificial kidney, organ bioengineering, 3D printer and kidney-on-chip represent the most appealing areas of research for the treatment of end-stage kidney failure. The scope of this review is to summarize the state of the art, limits and directions of each branch.

EXPERT OPINION

In the future, these emerging technologies could provide definitive, curative and theoretically infinite options for the treatment of end-stage kidney disease. Progress in stem cells-based therapies, decellularization techniques and the more recent scientific know-how for the use of the 3D printer and kidney-on-chip could lead to a perfect cellular-based therapy, the futuristic creation of a bioengineered kidney in the lab or to a valid bioartificial alternative.

Podocyte Number in Children and Adults: Associations with Glomerular Size and Numbers of Other Glomerular Resident Cells

Increases in glomerular size occur with normal body growth and in many pathologic conditions. In this study, we determined associations between glomerular size and numbers of glomerular resident cells, with a particular focus on podocytes. Kidneys from 16 male Caucasian-Americans without overt renal disease, including 4 children (≤3 years old) to define baseline values of early life and 12 adults (≥18 years old), were collected at autopsy in Jackson, Mississippi. We used a combination of immunohistochemistry, confocal microscopy, and design-based stereology to estimate individual glomerular volume (IGV) and numbers of podocytes, nonepithelial cells (NECs; tuft cells other than podocytes), and parietal epithelial cells (PECs). Podocyte density was calculated. Data are reported as medians and interquartile ranges (IQRs). Glomeruli from children were small and contained 452 podocytes (IQR=335-502), 389 NECs (IQR=265-498), and 146 PECs (IQR=111-206). Adult glomeruli contained significantly more cells than glomeruli from children, including 558 podocytes (IQR=431-746; P<0.01), 1383 NECs (IQR=998-2042; P<0.001), and 367 PECs (IQR=309-673; P<0.001). However, large adult glomeruli showed markedly lower podocyte density (183 podocytes per 10(6) µm(3)) than small glomeruli from adults and children (932 podocytes per 10(6) µm(3); P<0.001). In conclusion, large adult glomeruli contained more podocytes than small glomeruli from children and adults, raising questions about the origin of these podocytes. The increased number of podocytes in large glomeruli does not match the increase in glomerular size observed in adults, resulting in relative podocyte depletion. This may render hypertrophic glomeruli susceptible to pathology.

Regeneration and bioengineering of the kidney: current status and future challenges

The prevalence of chronic kidney disease continues to outpace the development of effective treatment strategies. For patients with advanced disease, renal replacement therapies approximate the filtration functions of the kidney at considerable cost and inconvenience, while failing to restore the resorptive and endocrine functions. Allogeneic transplantation remains the only restorative treatment, but donor shortage, surgical morbidity and the need for lifelong immunosuppression significantly limit clinical application. Emerging technologies in the fields of regenerative medicine and tissue engineering strive to address these limitations. We review recent advances in cell-based therapies, primordial allografts, bio-artificial organs and whole-organ bioengineering as they apply to renal regeneration. Collaborative efforts across these fields aim to produce a bioengineered kidney capable of restoring renal function in patients with end-stage disease.

A novel source of cultured podocytes

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

The protective effects of erythropoietin on rat glomerular podocytes in culture are modulated by extracellular matrix proteins

BACKGROUND/AIMS

Podocytes are typically cultured on collagen I; however, collagen I is absent from healthy glomerular basement membranes. Erythropoietin (EPO) is thought to protect podocytes in vivo. Here, we studied how various types of extracellular matrix (ECM) proteins and EPO affect podocytes in culture.

METHODS

Primary rat podocytes were replated on collagen I, collagen IV, whole ECM extract, laminin, or bare plastic. Cellular adhesion (8 hours after plating), proliferation (5 days, 10 % serum), and resistance to serum deprivation (3 days, 0.5 % serum) were assessed. BrdU incorporation and expression of podocyte-specific markers were employed as measures of cellular proliferation and differentiation, respectively. qPCR was used to verify expression of EPO receptor in cultured podocytes.

RESULTS

Cellular adhesion was similar on all ECM proteins and unaffected by EPO. Proliferation was accelerated by laminin and the ECM extract, but the final cell density was similar on all ECM surfaces. Collagen IV supported the serum-deprived cells better than the other ECM proteins. EPO (2-20 ng/ml) improved viability of serum-deprived podocytes on collagen I, collagen IV, and ECM, but not on laminin or bare plastic. The cells expressed mRNA for EPO receptor.

CONCLUSION

The physiological ECM proteins are more supportive of primary podocytic cultures compared with collagen I. The protective effects of EPO during serum deprivation are modulated by the cultivation surface.

Polymorphisms in the non-muscle myosin heavy chain gene (MYH9) are associated with lower glomerular filtration rate in mixed ancestry diabetic subjects from South Africa

Objective

Though single nucleotide polymorphisms (SNPs) in the non-muscle myosin gene (MYH9) have been reported to explain most of the excess risk of nondiabetic chronic kidney disease (CKD), in African-Americans, some studies have also shown associations with diabetic end-stage renal disease. We investigated the association of MYH9 SNPs with renal traits in a mixed-ancestry South African population prone to diabetes.

Research Design and Methods

Three SNPs known to be associated with CKD (rs4821480, rs5756152 and rs12107) were genotyped using Taqman assay in 716 adults (198 with diabetes) from the Bellville-South community, Cape Town. Glomerular filtration rate was estimated (eGFR) and urinary albumin/creatinine ratio (ACR) assessed. Multivariable regressions were used to relate the SNPs with renal traits.

Results

Mean age was 53.6 years, with the expected differences observed in characteristics by diabetic status. Significant associations were found between rs575152 and serum creatinine, and eGFR in the total population, and in diabetic participants (all p≤0.003), but not in non-diabetics (all p≥0.16), with significant interactions by diabetes status (interaction-p≤0.009). The association with ACR was borderline in diabetic participants (p = 0.05) and non-significant in non-diabetics (p = 0.85), with significant interaction (interaction p = 0.02). rs12107 was associated with fasting-, 2-hour glucose and HbA1c in diabetic participants only (interaction-p≤0.003), but not with renal traits.

Conclusion

MYH9 SNPs were associated with renal traits only in diabetic participants in this population. Our findings and other studies suggest that MYH9 may have a broader genetic risk effect on kidney diseases.

Mesenchymal stem cell injection ameliorates chronic renal failure in a rat model

CKD (chronic kidney disease) has become a public health problem. The therapeutic approaches have been able to reduce proteinuria, but have not been successful in limiting disease progression. In this setting, cell therapies associated with regenerative effects are attracting increasing interest. We evaluated the effect of MSC (mesenchymal stem cells) on the progression of CKD and the expression of molecular biomarkers associated with regenerative effects. Adult male Sprague-Dawley rats subjected to 5/6 NPX (nephrectomy) received a single intravenous infusion of 0.5×106 MSC or culture medium. A sham group subjected to the same injection was used as the control. Rats were killed 5 weeks after MSC infusion. Dye tracking of MSC was followed by immunofluorescence analysis. Kidney function was evaluated using plasma creatinine. Structural damage was evaluated by H&E (haematoxylin and eosin) staining, ED-1 abundance (macrophages) and interstitial α-SMA (α-smooth muscle actin). Repairing processes were evaluated by functional and structural analyses and angiogenic/epitheliogenic protein expression. MSC could be detected in kidney tissues from NPX animals treated with intravenous cell infusion. This group presented a marked reduction in plasma creatinine levels and damage markers ED-1 and α-SMA (P<0.05). In addition, treated rats exhibited a significant induction in epitheliogenic [Pax-2, bFGF (basic fibroblast growth factor) and BMP-7 (bone morphogenetic protein-7)] and angiogenic [VEGF (vascular endothelial growth factor) and Tie-2] proteins. The expression of these biomarkers of regeneration was significantly related to the increase in renal function. Many aspects of the cell therapy in CKD remain to be investigated in more detail: for example, its safety, low cost and the possible need for repeated cell injections over time. Beyond the undeniable importance of these issues, what still needs to be clarified is whether MSC administration has a real effect on the treatment of this pathology. It is precisely to this point that the present study aims to contribute.

Bone marrow-derived progenitor cells do not contribute to podocyte turnover in the puromycin aminoglycoside and renal ablation models in rats

A key event in the progression of glomerular disease is podocyte loss that leads to focal and segmental glomerulosclerosis (FSGS). Because adult podocytes are postmitotic cells, podocyte replacement by bone marrow-derived progenitors could prevent podocytopenia and FSGS. This study uses double immunofluorescence for Wilms' tumor-1 and enhanced green fluorescent protein (eGFP) to examine whether an eGFP-positive bone marrow transplant can replace podocytes under normal circumstances and in 3 different rat models of FSGS: puromycin aminoglycoside nephropathy, subtotal nephrectomy, and uninephrectomy. Bone marrow engraftment was successful, with more than 70% eGFP-positive cells and virtually normal histologic findings. No bone marrow transplant-derived podocytes were found in four control rats after transplantation, in nine rats at up to 10 weeks after puromycin aminoglycoside nephropathy induction, in three rats 23 days after subtotal nephrectomy, and in six rats up to 21 days after uninephrectomy. A total of 2200 glomeruli with 14,474 podocytes were evaluated in all groups. Thus, podocyte replacement by bone marrow-derived cells does not contribute to podocyte turnover in rats, even in models of podocyte damage. This is in contrast to previous studies in mice, in which bone marrow-derived podocytes were found. Further studies will address this discrepancy, which could be explained by species differences or by predominant podocyte regeneration from a parietal epithelial cell niche.

MYH9 genetic variants associated with glomerular disease: what is the role for genetic testing?

Genetic variation in MYH9, encoding nonmuscle myosin IIA heavy chain, has been associated recently with increased risk for kidney disease. Previously, MYH9 missense mutations have been shown to cause the autosomal-dominant MYH9 (ADM9) spectrum, characterized by large platelets, leukocyte Döhle bodies, and, variably, sensorineural deafness, cataracts, and glomerulopathy. Genetic testing is indicated for familial and sporadic cases that fit this spectrum. By contrast, the MYH9 kidney risk variant is characterized by multiple intronic single nucleotide polymorphisms, but the causative variant has not been identified. Disease associations include human immunodeficiency virus-associated collapsing glomerulopathy, focal segmental glomerulosclerosis, hypertension-attributed end-stage kidney disease, and diabetes-attributed end-stage kidney disease. One plausible hypothesis is that the MYH9 kidney risk variant confers a fragile podocyte phenotype. In the case of hypertension-attributed kidney disease, it remains unclear if the hypertension is a contributing cause or a consequence of glomerular injury. The MYH9 kidney risk variant is strikingly more common among individuals of African descent, but only some will develop clinical kidney disease in their lifetime. Thus, it is likely that additional genes and/or environmental factors interact with the MYH9 kidney risk variant to trigger glomerular injury. A preliminary genetic risk stratification scheme, using two single nucleotide polymorphisms, may estimate lifetime risk for kidney disease. Nevertheless, at present, no role has been established for genetic testing as part of personalized medicine, but testing should be considered in clinical studies of glomerular diseases among populations of African descent. Such studies will address critical questions pertaining to MYH9-associated kidney disease, including mechanism, course, and response to therapy.

Tissue engineered human tracheas for in vivo implantation

Two years ago we performed the first clinical successful transplantation of a fully tissue engineered trachea. Despite the clinically positive outcome, the graft production took almost 3 months, a not feasible period of time for patients with the need of an urgent transplantation. We have then improved decellularization process and herein, for the first time, we completely describe and characterize the obtainment of human tracheal bioactive supports. Histological and molecular biology analysis demonstrated that all cellular components and nuclear material were removed and quantitative PCR confirmed it. SEM analysis revealed that the decellularized matrices retained the hierarchical structures of native trachea, and biomechanical tests showed that decellularization approach did not led to any influence on tracheal morphological and mechanical properties. Moreover immunohistological staining showed the preservation of angiogenic factors and angiogenic assays demonstrated that acellular human tracheal scaffolds exert an in vitro chemo-active action and induce strong in vivo angiogenic response (CAM analysis). We are now able to obtained, in a short and clinically useful time (approximately 3 weeks), a bioengineered trachea that is structurally and mechanically similar to native trachea, which exert chemotactive and pro-angiogenic properties and which could be successfully used for clinical tissue engineered airway clinical replacements.

Isolation and characterization of resident mesenchymal stem cells in human glomeruli

In humans, renal resident stem cells were identified within the interstitium, the tubular cells, and the Bowman's capsule. The aim of the present study was to investigate whether multipotent stem cells are present also in the adult human-decapsulated glomeruli and whether they represent a resident population. We found that human glomeruli deprived of the Bowman's capsule contain a population of CD133+CD146+ cells and a population of CD133-CD146+ cells expressing mesenchymal stem cell (MSC) markers and renal stem cell markers CD24 and Pax-2. The CD133+CD146+ cells differed from those previously isolated from Bowman's capsule as they co-expressed endothelial markers, such as CD31 and von Willebrand factor (vWF), were CD24-negative and were not clonogenic, suggesting an endothelial commitment. The glomerular mesenchymal CD133-CD146+ population (Gl-MSC) exhibited self-renewal capability, clonogenicity, and multipotency. In addition to osteogenic, adipogenic, and chondrogenic differentiation, these cells were able to differentiate to endothelial cells and epithelial cells expressing podocytes markers such as nephrin, podocin, and synaptopodin. Moreover, Gl-MSC when cultured in appropriate conditions, acquired mesangial cell markers such as alpha-smooth muscle actin (alpha-SMA) and angiotensin II (AT-II) receptor I. The expression of the embryonic organ-specific PAX-2 gene and protein and of donor sex identity when isolated from glomeruli of a renal allograft suggested these cells to be a tissue resident population. In conclusion, these results indicate the presence of a multipotent mesenchymal cell population resident in human glomeruli that may have a role in the physiological cell turnover and/or in response to glomerular injury.

Cellular origins of type IV collagen networks in developing glomeruli

Laminin and type IV collagen composition of the glomerular basement membrane changes during glomerular development and maturation. Although it is known that both glomerular endothelial cells and podocytes produce different laminin isoforms at the appropriate stages of development, the cellular origins for the different type IV collagen heterotrimers that appear during development are unknown. Here, immunoelectron microscopy demonstrated that endothelial cells, mesangial cells, and podocytes of immature glomeruli synthesize collagen alpha 1 alpha 2 alpha1(IV). However, intracellular labeling revealed that podocytes, but not endothelial or mesangial cells, contain collagen alpha 3 alpha 4 alpha 5(IV). To evaluate the origins of collagen IV further, we transplanted embryonic kidneys from Col4a3-null mutants (Alport mice) into kidneys of newborn, wildtype mice. Hybrid glomeruli within grafts containing numerous host-derived, wildtype endothelial cells never expressed collagen alpha 3 alpha 4 alpha 5(IV). Finally, confocal microscopy of glomeruli from infant Alport mice that had been dually labeled with anti-collagen alpha 5(IV) and the podocyte marker anti-GLEPP1 showed immunolabeling exclusively within podocytes. Together, these results indicate that collagen alpha 3 alpha 4 alpha 5(IV) originates solely from podocytes; therefore, glomerular Alport disease is a genetic defect that manifests specifically within this cell type.

Cellular origins of type IV collagen networks in developing glomeruli

Laminin and type IV collagen composition of the glomerular basement membrane changes during glomerular development and maturation. Although it is known that both glomerular endothelial cells and podocytes produce different laminin isoforms at the appropriate stages of development, the cellular origins for the different type IV collagen heterotrimers that appear during development are unknown. Here, immunoelectron microscopy demonstrated that endothelial cells, mesangial cells, and podocytes of immature glomeruli synthesize collagen alpha 1 alpha 2 alpha1(IV). However, intracellular labeling revealed that podocytes, but not endothelial or mesangial cells, contain collagen alpha 3 alpha 4 alpha 5(IV). To evaluate the origins of collagen IV further, we transplanted embryonic kidneys from Col4a3-null mutants (Alport mice) into kidneys of newborn, wildtype mice. Hybrid glomeruli within grafts containing numerous host-derived, wildtype endothelial cells never expressed collagen alpha 3 alpha 4 alpha 5(IV). Finally, confocal microscopy of glomeruli from infant Alport mice that had been dually labeled with anti-collagen alpha 5(IV) and the podocyte marker anti-GLEPP1 showed immunolabeling exclusively within podocytes. Together, these results indicate that collagen alpha 3 alpha 4 alpha 5(IV) originates solely from podocytes; therefore, glomerular Alport disease is a genetic defect that manifests specifically within this cell type.

COL4A3/COL4A4 mutations link familial hematuria and focal segmental glomerulosclerosis. glomerular epithelium destruction via basement membrane thinning?

The recent description of multiple gene defects in hereditary podocytopathies and in hereditary glomerular basement membrane diseases has dramatically improved the current state of our knowledge on the renal glomerular filtration barrier. Recently described mutations in collagen IV and laminin in patients with hematuria and severe nephrotic syndrome add to other experimental data supporting the hypothesis that the glomerular basement membrane (GBM) may also have a significant role in protein filtration, a function previously attributed exclusively to the podocytes. Collagen IV heterozygous mutations were thought to cause only a mild form of renal disease (thin basement membrane nephropathy--TBMN). However, data from our laboratory show that many patients who carry such mutations may later on in life develop focal and segmental glomerulosclerosis, on top of the TBMN and the microscopic hematuria, a situation that frequently progresses to chronic renal failure or even end-stage renal disease. The role of unknown modifier genes may explain the heterogeneity of symptoms in TBMN and other glomerular diseases and in particular the selected development of chronic renal failure. The molecular communication between GBM and podocytes may also be a key factor in the search for these major genetic modifiers while their understanding may improve novel drug design for glomerular diseases.

Immigrating progenitor cells contribute to human podocyte turnover

Podocyte depletion is a critical event in glomerular diseases in general and in the development of focal segmental glomerulosclerosis in particular. Progenitor cell immigration is a possible mechanism of podocyte replacement for the preservation of nephron function since, with rare exception, mature podocytes are thought to be incapable of replication. We examined eight paraffin-embedded renal biopsies from six male recipients of female transplant kidneys for receiver-derived podocytes. Fluorescent in situ hybridization for the Y chromosome was combined with immunofluorescence for the podocyte marker, Wilms tumor-1 antigen. Recipient-derived podocytes were found in 4 of 8 biopsies representing 3 of the 6 patients. Overall, 5 of the 740 podocytes examined in the female-donated kidneys were male derived. Our study suggests that immigrating progenitor cells are able to replace podocytes in humans; however, the importance of this process in physiologic and pathologic conditions is unknown.

The intermediate filament nestin is highly expressed in normal human podocytes and podocytes in glomerular disease

The intermediate protein nestin is expressed in proliferating embryonic tissues and adult tissues undergoing repair. Recently this protein been identified in rodent podocytes. Its role in this cell is unknown, since podocytes are believed to be terminally differentiated and nondividing. We report the first study of nestin in human kidney. Nestin expression in normal mature human glomeruli was confined to podocytes. In developing kidney, nestin was detected in metanephric blastema and in podocytic cells at all stages of glomerular development. Nestin co-localized with vimentin but not with actin or heavy chain myosin IIA, using a mouse podocyte cell line. Knockdown of nestin in a murine podocyte cell line failed to produce any obvious phenotypic change or alteration in vimentin distribution but was associated with increased cell cycling. A survey of glomerular diseases failed to identify any condition lacking nestin, indicating that the protein is critical for some aspect of podocyte function. Perhaps through an association with vimentin, nestin serves to bolster the mechanical strength of these cells that experience high tensile stress during glomerular filtration. Nestin was also expressed in podocytes that are reported to be 'dysregulated' (lacking podocyte markers). Thus, nestin has a potential as a reliable podocyte marker, even for podocytes that are not completely differentiated (for example, during development) or 'dedifferentiated' in glomerular disease.

Culture methods of glomerular podocytes

Podocytes (glomerular visceral epithelial cells) cover the exterior surface of the glomerular capillaries and contribute to the glomerular filtration membrane. Failure of podocyte function is involved in the progression of chronic glomerular disease; accordingly, research interest into podocyte biology is driven by the need for better protection and perhaps recovery of these cells in renal diseases. This review aims at summarizing available techniques for podocyte cell cultures from both the past and present, with special attention to the currently used methods. The establishment of classical primary cultures is based on isolation of glomeruli by differential sieving. Plating of glomeruli onto a collagen surface is followed by an outgrowth of cobblestone-like cells that, after replating, differentiate into arborized, mature podocytes. Currently, the majority of research studies use immortalized podocytic cell lines most often derived from transgenic mice bearing a conditional immortalizing gene. The podocytes can also be collected and cultured from healthy or diseased animal or patient urine. The urinary podocytes obtained from subjects with active glomerulopathies display higher proliferation potential and viability in vitro, perhaps due to disease-induced transdifferentiation. Finally, a list of phenotypic markers useful for identification and characterization of the cultured podocytic elements is provided.

Alport syndrome and thin basement membrane nephropathy

Both Alport syndrome and thin basement membrane nephropathy (TBMN) can be considered as genetic diseases of the GBM involving the alpha3/alpha4/alpha5 network of type IV collagen. Mutations in any of the COL4A3, COL4A4 or COL4A5 genes can lead to total or partial loss of this network. Males with mutations in the X-linked COL4A5 gene develop Alport syndrome with progressive renal disease and sometimes extra-renal disease. Females who are heterozygous for a COL4A5 mutation are considered to be carriers for X-linked Alport syndrome. Although their clinical course and GBM ultrastructural changes can sometimes mimic TBMN, more often it tends to be more progressive than usually seen in TBMN. Males or females who are heterozygous for COL4A3 or COL4A4 mutations usually manifest as TBMN, with nonprogressive hematuria, while those who are homozygous or combined heterozygotes develop autosomal-recessive Alport syndrome. Thus, individuals with TBMN can be considered to be carriers for autosomal-recessive Alport syndrome, but there remain some exceptions in which patients heterozygous for COL4A3 or COL4A4 mutations develop autosomal-dominant Alport syndrome. Distinguishing between all these groups of patients requires a combination of family history and a renal biopsy for electron microscopic examination of the GBM and immunohistochemical staining of the GBM for the alpha3, alpha4 and alpha5 chains of type IV collagen. Mutational analysis of the COL4A3, COL4A4, and COL4A5 genes, whenever it becomes available, will be a valuable adjunct to the diagnostic workup in these patients. Novel therapeutic approaches may one day provide a treatment or cure for these patients, avoiding the need for transplantation and dialysis.

Bone marrow-derived cells contribute to podocyte regeneration and amelioration of renal disease in a mouse model of Alport syndrome

In a model of autosomally recessive Alport syndrome, mice that lack the alpha3 chain of collagen IV (Col4alpha3(-/-)) develop progressive glomerular damage leading to renal failure. The proposed mechanism is that podocytes fail to synthesize normal glomerular basement membrane, so the collagen IV network is unstable and easily degraded. We used this model to study whether bone marrow (BM) transplantation can rectify this podocyte defect by correcting the deficiency in Col4alpha3. Female C57BL/6 Col4alpha3(-/-) (-/-) mice were transplanted with whole BM from male wild-type (+/+) mice. Control female -/- mice received BM from male -/- littermates. Serum urea and creatinine levels were significantly lower in recipients of +/+ BM compared with those of -/- BM 20 weeks post-transplant. Glomerular scarring and interstitial fibrosis were also significantly decreased. Donor-derived cells were detected by in situ hybridization (ISH) for the Y chromosome, and fluorescence and confocal microscopy indicated that some showed an apparent podocyte phenotype in mice transplanted with +/+ BM. Glomeruli of these mice showed small foci of staining for alpha3(IV) protein by immunofluorescence. alpha3(IV) mRNA was detectable by reverse transcription-polymerase chain reaction and ISH in some mice transplanted with +/+ BM but not -/- BM. However, a single injection of mesenchymal stem cells from +/+ mice to irradiated -/- recipients did not improve renal disease. Our data show that improved renal function in Col4alpha3(-/-) mice results from BM transplantation from wild-type donors, and the mechanism by which this occurs may in part involve generation of podocytes without the gene defect.