The Aachen Minipig: Phenotype, Genotype, Hematological and Biochemical Characterization, and Comparison to the Göttingen Minipig

BACKGROUND

The pig is one of the most frequently used large animal models for biomedical research, especially in the field of translational research and surgical models. While standard livestock breeds are used in short-term and acute studies, minipig breeds are the preferred breeds in long-term and chronic studies due to their limited growth and body weight.

OBJECTIVE

In consideration of the 3R principle (refinement, reduction, replacement) and the increasing demand, the aim of this study was to generate a new, robust, non-specific-pathogen-free minipig breed, the Aachen minipig.

METHODS

Phenotype, genotype, and hematological as well as clinical chemistry parameters were characterized, and reference values of the Aachen minipig were generated and compared to the values in the commonly used Göttingen minipig. Organ weights of the heart, kidney, liver, lung, spleen, and brain were determined using a laboratory balance. Blood samples were collected for hematology and clinical chemistry. Assessment of genetic diversity was performed by microsatellite markers. Nasal swabs were collected from 11 individual minipigs representing 6 races for DNA extraction. DNA was quantified and the identity and origin of the Aachen minipigs at the genomic level was determined by microsatellites.

RESULTS

The Aachen minipig established here is based on the Mini-LEWE breed and consists of the Vietnamese potbelly pig, the Schwäbisch Hällisch Landpig, the German Landrace, and the Minnesota minipig. Relative organ weights (lung, heart, kidneys, brain), hematology (hemoglobin, hematocrit, platelet count, mean corpuscular hemoglobin concentration, segmented neutrophils, lymphocytes, eosinophils, basophils), and clinical chemistry parameters (sodium, calcium, chloride, alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, gamma-glutamyl transferase, lactate dehydrogenase, triglycerides, blood urea nitrogen, creatinine, total bilirubin, total protein, creatine kinase) of the Aachen minipigs and the Göttingen minipigs were not significantly different. Significant differences where only seen in relative organ weights (liver, spleen), hematology (red blood cell count, mean corpuscular volume, mean corpuscular hemoglobin, white blood cell count, banded neutrophils, monocytes), and clinical chemistry parameters (inorganic phosphorus, potassium, glucose, cholesterol, albumin, amylase).

CONCLUSION

The Aachen minipig is a suitable model for research due to its similarity to other minipig breeds, especially the Göttingen minipig. The reference values established in this study may be used for the comparison of scientific data and encourage the use of the Aachen minipig as an animal model for biomedical research.

A molecular signature of proteinuria in glomerulonephritis

Proteinuria is the most important predictor of outcome in glomerulonephritis and experimental data suggest that the tubular cell response to proteinuria is an important determinant of progressive fibrosis in the kidney. However, it is unclear whether proteinuria is a marker of disease severity or has a direct effect on tubular cells in the kidneys of patients with glomerulonephritis. Accordingly we studied an in vitro model of proteinuria, and identified 231 “albumin-regulated genes” differentially expressed by primary human kidney tubular epithelial cells exposed to albumin. We translated these findings to human disease by studying mRNA levels of these genes in the tubulo-interstitial compartment of kidney biopsies from patients with IgA nephropathy using microarrays. Biopsies from patients with IgAN (n = 25) could be distinguished from those of control subjects (n = 6) based solely upon the expression of these 231 “albumin-regulated genes.” The expression of an 11-transcript subset related to the degree of proteinuria, and this 11-mRNA subset was also sufficient to distinguish biopsies of subjects with IgAN from control biopsies. We tested if these findings could be extrapolated to other proteinuric diseases beyond IgAN and found that all forms of primary glomerulonephritis (n = 33) can be distinguished from controls (n = 21) based solely on the expression levels of these 11 genes derived from our in vitro proteinuria model. Pathway analysis suggests common regulatory elements shared by these 11 transcripts. In conclusion, we have identified an albumin-regulated 11-gene signature shared between all forms of primary glomerulonephritis. Our findings support the hypothesis that albuminuria may directly promote injury in the tubulo-interstitial compartment of the kidney in patients with glomerulonephritis.

Renal gene and protein expression signatures for prediction of kidney disease progression

Although chronic kidney disease (CKD) is common, only a fraction of CKD patients progress to end-stage renal disease. Molecular predictors to stratify CKD populations according to their risk of progression remain undiscovered. Here we applied transcriptional profiling of kidneys from transforming growth factor-beta1 transgenic (Tg) mice, characterized by heterogeneity of kidney disease progression, to identify 43 genes that discriminate kidneys by severity of glomerular apoptosis before the onset of tubulointerstitial fibrosis in 2-week-old animals. Among the genes examined, 19 showed significant correlation between mRNA expression in uninephrectomized left kidneys at 2 weeks of age and renal disease severity in right kidneys of Tg mice at 4 weeks of age. Gene expression profiles of human orthologs of the 43 genes in kidney biopsies were highly significantly related (R(2) = 0.53; P < 0.001) to the estimated glomerular filtration rates in patients with CKD stages I to V, and discriminated groups of CKD stages I/II and III/IV/V with positive and negative predictive values of 0.8 and 0.83, respectively. Protein expression patterns for selected genes were successfully validated by immunohistochemistry in kidneys of Tg mice and kidney biopsies of patients with IgA nephropathy and CKD stages I to V, respectively. In conclusion, we developed novel mRNA and protein expression signatures that predict progressive renal fibrosis in mice and may be useful molecular predictors of CKD progression in humans.

Enhanced expression of Janus kinase-signal transducer and activator of transcription pathway members in human diabetic nephropathy

OBJECTIVE

Glomerular mesangial expansion and podocyte loss are important early features of diabetic nephropathy, whereas tubulointerstitial injury and fibrosis are critical for progression of diabetic nephropathy to kidney failure. Therefore, we analyzed the expression of genes in glomeruli and tubulointerstitium in kidney biopsies from diabetic nephropathy patients to identify pathways that may be activated in humans but not in murine models of diabetic nephropathy that fail to progress to glomerulosclerosis, tubulointerstitial fibrosis, and kidney failure.

RESEARCH DESIGN AND METHODS

Kidney biopsies were obtained from 74 patients (control subjects, early and progressive type 2 diabetic nephropathy). Glomerular and tubulointerstitial mRNAs were microarrayed, followed by bioinformatics analyses. Gene expression changes were confirmed by real-time RT-PCR and immunohistological staining. Samples from db/db C57BLKS and streptozotocin-induced DBA/2J mice, commonly studied murine models of diabetic nephropathy, were analyzed.

RESULTS

In human glomeruli and tubulointerstitial samples, the Janus kinase (Jak)-signal transducer and activator of transcription (Stat) pathway was highly and significantly regulated. Jak-1, -2, and -3 as well as Stat-1 and -3 were expressed at higher levels in patients with diabetic nephropathy than in control subjects. The estimated glomerular filtration rate significantly correlated with tubulointerstitial Jak-1, -2, and -3 and Stat-1 expression (R(2) = 0.30-0.44). Immunohistochemistry found strong Jak-2 staining in glomerular and tubulointerstitial compartments in diabetic nephropathy compared with control subjects. In contrast, there was little or no increase in expression of Jak/Stat genes in the db/db C57BLKS or diabetic DBA/2J mice.

CONCLUSIONS

These data suggest a direct relationship between tubulointerstitial Jak/Stat expression and progression of kidney failure in patients with type 2 diabetic nephropathy and distinguish progressive human diabetic nephropathy from nonprogressive murine diabetic nephropathy.

Maternal environment interacts with modifier genes to influence progression of nephrotic syndrome

Mutations in the NPHS2 gene, which encodes podocin, are responsible for some cases of sporadic and familial autosomal recessive steroid-resistant nephrotic syndrome. Inter- and intrafamilial variability in the progression of renal disease among patients bearing NPHS2 mutations suggests a potential role for modifier genes. Using a mouse model in which the podocin gene is constitutively inactivated, we sought to identify genetic determinants of the development and progression of renal disease as a result of the nephrotic syndrome. We report that the evolution of renal disease as a result of nephrotic syndrome in Nphs2-null mice depends on genetic background. Furthermore, the maternal environment significantly interacts with genetic determinants to modify survival and progression of renal disease. Quantitative trait locus mapping suggested that these genetic determinants may be encoded for by genes on the distal end of chromosome 3, which are linked to proteinuria, and on the distal end of chromosome 7, which are linked to a composite trait of urea, creatinine, and potassium. These loci demonstrate epistatic interactions with other chromosomal regions, highlighting the complex genetics of renal disease progression. In summary, constitutive inactivation of podocin models the complex interactions between maternal and genetically determined factors on the progression of renal disease as a result of nephrotic syndrome in mice.

The death ligand TRAIL in diabetic nephropathy

Apoptotic cell death contributes to diabetic nephropathy (DN), but its role is not well understood. The tubulointerstitium from DN biopsy specimens was microdissected, and expression profiles of genes related to apoptosis were analyzed. A total of 112 (25%) of 455 cell death-related genes were found to be significantly differentially regulated. Among those that showed the greatest changes in regulation were two death receptors, OPG (the gene encoding osteoprotegerin) and Fas, and the death ligand TRAIL. Glomerular and proximal tubular TRAIL expression, assessed by immunohistochemistry, was higher in DN kidneys than controls and was associated with clinical and histologic severity of disease. In vitro, proinflammatory cytokines but not glucose alone regulated TRAIL expression in the human proximal tubular cell line HK-2. TRAIL induced tubular cell apoptosis in a dosage-dependant manner, an effect that was more marked in the presence of high levels of glucose and proinflammatory cytokines. TRAIL also activated NF-kappaB, and inhibition of NF-kappaB sensitized cells to TRAIL-induced apoptosis. It is proposed that TRAIL-induced cell death could play an important role in the progression of human DN.

The death ligand TRAIL in diabetic nephropathy

Apoptotic cell death contributes to diabetic nephropathy (DN), but its role is not well understood. The tubulointerstitium from DN biopsy specimens was microdissected, and expression profiles of genes related to apoptosis were analyzed. A total of 112 (25%) of 455 cell death-related genes were found to be significantly differentially regulated. Among those that showed the greatest changes in regulation were two death receptors, OPG (the gene encoding osteoprotegerin) and Fas, and the death ligand TRAIL. Glomerular and proximal tubular TRAIL expression, assessed by immunohistochemistry, was higher in DN kidneys than controls and was associated with clinical and histologic severity of disease. In vitro, proinflammatory cytokines but not glucose alone regulated TRAIL expression in the human proximal tubular cell line HK-2. TRAIL induced tubular cell apoptosis in a dosage-dependant manner, an effect that was more marked in the presence of high levels of glucose and proinflammatory cytokines. TRAIL also activated NF-kappaB, and inhibition of NF-kappaB sensitized cells to TRAIL-induced apoptosis. It is proposed that TRAIL-induced cell death could play an important role in the progression of human DN.

A complex pattern of chemokine receptor expression is seen in osteosarcoma

Background

Osteosarcoma is the most frequent bone tumor in childhood and adolescence. Patients with primary metastatic disease have a poor prognosis. It is therefore important to better characterize the biology of this tumor to define new prognostic markers or therapeutic targets for tailored therapy. Chemokines and their receptors have been shown to be involved in the development and progression of malignant tumors. They are thought to be active participants in the biology of osteosarcoma. The function of specific chemokines and their receptors is strongly associated with the biological context and microenvironment of their expression. In this report we characterized the expression of a series of chemokine receptors in the complex environment that defines osteosarcoma.

Methods

The overall level of chemokine receptor mRNA expression was determined using TaqMan RT-PCR of microdissected archival patient biopsy samples. Expression was then verified at the protein level by immunohistochemistry using a series of receptor specific antibody reagents to elucidate the cellular association of expression.

Results

Expression at the RNA level was found for most of the tested receptors. CCR1 expression was found on infiltrating mononuclear and polynuclear giant cells in the tumor. Cells associated with the lining of intratumoral vessels were shown to express CCR4. Infiltrating mononuclear cells and tumor cells both showed expression of the receptor CCR5, while CCR7 was predominantly expressed by the mononuclear infiltrate. CCR10 was only very rarely detected in few scattered infiltrating cells.

Conclusion

Our data elucidate for the first time the cellular context of chemokine receptor expression in osteosarcoma. This is an important issue for better understanding potential chemokine/chemokine receptor function in the complex biologic processes that underlie the development and progression of osteosarcoma. Our data support the suggested involvement of chemokines and their receptors in diverse aspects of the biology of osteosarcoma, but also contradict aspects of previous reports describing the expression of these receptors in this tumor.

Interstitial vascular rarefaction and reduced VEGF-A expression in human diabetic nephropathy

Diabetic nephropathy (DN) is a frequent complication in patients with diabetes. Although the majority of DN models and human studies have focused on glomeruli, tubulointerstitial damage is a major feature of DN and an important predictor of renal dysfunction. This study sought to investigate molecular markers of pathogenic pathways in the renal interstitium of patients with DN. Microdissected tubulointerstitial compartments from biopsies with established DN and control kidneys were subjected to expression profiling. Analysis of candidate genes, potentially involved in DN on the basis of common hypotheses, identified 49 genes with significantly altered expression levels in established DN in comparison with controls. In contrast to some rodent models, the growth factors vascular endothelial growth factor A (VEGF-A) and epidermal growth factor (EGF) showed a decrease in mRNA expression in DN. This was validated on an independent cohort of patients with DN by real-time reverse transcriptase-PCR. Immunohistochemical staining for VEGF-A and EGF also showed a reduced expression in DN. The decrease of renal VEGF-A expression was associated with a reduction in peritubular capillary densities shown by platelet-endothelial cell adhesion molecule-1/CD31 staining. Furthermore, a significant inverse correlation between VEGF-A and proteinuria, as well as EGF and proteinuria, and a positive correlation between VEGF-A and hypoxia-inducible factor-1alpha mRNA was found. Thus, in human DN, a decrease of VEGF-A, rather than the reported increase as described in some rodent models, may contribute to the progressive disease. These findings and the questions about rodent models in DN raise a note of caution regarding the proposal to inhibit VEGF-A to prevent progression of DN.

Nitric oxide modulates expression of extracellular matrix genes linked to fibrosis in kidney mesangial cells

Mesangial cells are thought to be important mediators of glomerular inflammation and fibrosis. Studies have established a direct role for nitric oxide (NO) in the regulation of gene expression in mesangial cells. Representational difference analysis was used to investigate changes in gene expression elicited by the treatment of S-nitroso-L-glutathione in rat mesangial cells. Seven upregulated and 11 downregulated genes were identified. Four out of 11 downregulated genes (connective tissue growth factor, thrombospondin-1, collagen type I alpha1 and collagen type I alpha2) are known to be linked to inflammation and fibrosis. Results were verified across species in mesangial cells treated with a series of NO donors using Northern blot analysis, quantitative real-time PCR and protein analysis methods. Induction of endogenous NO production by cytokine stimulation also triggered regulation of the genes. One example gene, connective tissue growth factor, was studied at the promoter level. Promoter-reporter gene studies in mesangial cells demonstrated that NO acts at the transcriptional level to suppress gene expression. Our results reveal a complex role of NO in regulating gene expression in mesangial cells and suggest an antifibrotic potential for NO.

Induction of TRPC6 channel in acquired forms of proteinuric kidney disease

Injury to podocytes and their slit diaphragms typically leads to marked proteinuria. Mutations in the TRPC6 gene that codes for a slit diaphragm-associated, cation-permeable ion channel have been shown recently to co-segregate with hereditary forms of progressive kidney failure. Herein is shown that induced expression of wild-type TRPC6 is a common feature of human proteinuric kidney diseases, with highest induction observed in membranous nephropathy. Cultured podocytes that are exposed to complement upregulate TRPC6 protein. Stimulation of receptor-operated channels in puromycin aminonucleoside-treated podocytes leads to increased calcium influx in a time- and dosage-dependent manner. Mechanistically, it is shown that TRPC6 is functionally connected to the podocyte actin cytoskeleton, which is rearranged upon overexpression of TRPC6. Transient in vivo gene delivery of TRPC6 into mice leads to expression of TRPC6 protein at the slit diaphragm and causes proteinuria. These studies suggest the involvement of TRPC6 in the pathology of nongenetic forms of proteinuric disease.

Modular activation of nuclear factor-kappaB transcriptional programs in human diabetic nephropathy

Diabetic nephropathy (DN) is the leading cause of end-stage renal failure and a major risk factor for cardiovascular mortality in diabetic patients. To evaluate the multiple pathogenetic factors implicated in DN, unbiased mRNA expression screening of tubulointerstitial compartments of human renal biopsies was combined with hypothesis-driven pathway analysis. Expression fingerprints obtained from biopsies with histological diagnosis of DN (n = 13) and from control subjects (pretransplant kidney donors [n = 7] and minimal change disease [n = 4]) allowed us to segregate the biopsies by disease state and stage by the specific expression signatures. Functional categorization showed regulation of genes linked to inflammation in progressive DN. Pathway mapping of nuclear factor-kappaB (NF-kappaB), a master transcriptional switch in inflammation, segregated progressive from mild DN and control subjects by showing upregulation of 54 of 138 known NF-kappaB targets. The promoter regions of regulated NF-kappaB targets were analyzed using ModelInspector, and the NF-kappaB module NFKB_IRFF_01 was found to be specifically enriched in progressive disease. Using this module, the induction of eight NFKB_IRFF_01-dependant genes was correctly predicted in progressive DN (B2M, CCL5/RANTES, CXCL10/IP10, EDN1, HLA-A, HLA-B, IFNB1, and VCAM1). The identification of a specific NF-kappaB promoter module activated in the inflammatory stress response of progressive DN has helped to characterize upstream pathways as potential targets for the treatment of progressive renal diseases such as DN.

Expression of the chemokine receptor CXCR1 in human glomerular diseases

Leukocyte infiltration, a hallmark of renal diseases, is orchestrated in part by the actions of chemokines. The chemokine CXCL8/interleukin (IL)-8 is expressed during renal diseases and allograft rejection, whereas the corresponding receptor CXCR1 has not been described previously. Expression of CXCR1 was characterized in peripheral blood using multicolor fluorescence-activated cell sorter analysis (FACS). CXCR1 was localized in 81 formalin-fixed, paraffin-embedded renal specimens by immunohistochemistry using a monoclonal antibody against human CXCR1. Included were biopsies with crescentic glomerulonephritis (CGN, n = 22), immunoglobulin (Ig) A nephropathy (n = 15), membranoproliferative glomerulonephritis (MPGN, n = 17), lupus nephritis (n = 12), membranous nephropathy (n = 11), and non-involved parts of tumor nephrectomies (n = 4). Consecutive tissue sections of human tonsils, allograft explants, and renal biopsies were stained for CD15- and CD68-positive cells. Expression of CXCR1 and CXCL8/IL-8 mRNA was quantified by real-time reverse transcriptase-polymerse chain reaction of microdissected renal biopsies (n = 35) of the same disease entities. By FACS CXCR1 expression was found on polymorphonuclear CXCR1 expression by polymorphonuclear leukocytes (PMNs), natural killer cells, and a subpopulation of monocytes. By immunohistochemistry, CXCR1 expression was found on infiltrating inflammatory cells (predominantly PMNs), as well as on intrinsic renal cells (arterial smooth muscle cells, endothelial cells of peritubular capillaries). The distribution pattern of CXCR1 differed between disease entities. The highest numbers of glomerular CXCR1-positive cells were present in biopsies with MPGN, followed by lupus nephritis, and CGN. CXCR1 might be involved in the recruitment of PMNs to the glomerular tuft, which could be targeted by CXCR1-blocking agents.

Expression and regulation of Toll-like receptors in lupus-like immune complex glomerulonephritis of MRL-Fas(lpr) mice

BACKGROUND

How microbial infections exacerbate immune complex glomerulonephritis remains speculative. Toll-like receptors (TLRs) may be involved in this phenomenon, because TLRs have potent immunostimulatory functions when exposed to selected pathogen-associated molecules.

METHODS

We addressed this issue by characterizing the expression of TLR1-9 in MRLlpr/lpr mice that spontaneously develop immune complex glomerulonephritis as part of a systemic lupus-like autoimmune syndrome.

RESULTS

Five-week-old healthy MRLlpr/lpr mice expressed TLR3 mRNA in kidneys at comparable levels as in the spleen, while all other TLRs were expressed at low levels in the kidney. In 20-week-old nephritic MRLlpr/lpr mice, renal mRNA levels had increased for TLR1-9. Renal TLR mRNA originated at least in part from glomeruli as evidenced by real-time RT-PCR from laser capture microdissected glomeruli. Immunostaining for TLR3, TLR7 and TLR9 revealed their expression by F4/80-positive infiltrating macrophages in 20-week-old nephritic MRLlpr/lpr mice. In addition, TLR3 localized to glomerular mesangial cells. Cultured mesangial cells expressed TLR1-4 and TLR6, while murine macrophages expressed TLR1-9. TNF-alpha and IFN-gamma induced TLR2, TLR3 and TLR6 mRNA in mesangial cells, while they down-regulated TLR1-9 mRNA in macrophages. Stimulation of both cell types with ligands for TLR1-4, TLR5, TLR7 and TLR9 induced IL-6 production consistent with their respective TLR expression patterns. TNF-alpha and IFN-gamma enhanced ligand-induced IL-6 production in both cell types irrespective of their modulatory effect on respective TLR mRNA levels.

CONCLUSION

Thus, cell-type-specific expression and regulation of TLRs may be involved in infection-associated exacerbation of immune complex glomerulonephritis of MRLlpr/lpr mice.

Molecular approaches to chronic kidney disease

PURPOSE OF REVIEW

The progression of chronic kidney disease to terminal renal failure remains a major challenge in nephrology. Definition of the dynamic differences in gene regulation, protein interaction and protein function in this process might allow the development of rationally designed management strategies for the individual patient. Current approaches to identifying the molecular markers required to implement this 'personalized medicine' concept in progressive renal failure will be presented in this review.

RECENT FINDINGS

In small populations, molecular fingerprints derived from renal biopsies have allowed the definition of distinct patient subgroups. These parameters could be shown to correlate with the response to available therapies and, in chronic transplant failure, with the therapeutic toxicity of cyclosporine. Urine analysis for mRNA and protein markers is rapidly evolving as a non-invasive approach for molecular patient monitoring. As only a small fraction of these fingerprints have been evaluated in independent populations, studies to test marker sets in diverse cohorts for their clinical applicability are warranted.

SUMMARY

The genome-wide tools discussed in this review might define the molecular mechanism active in each single patient with progressive kidney disease. Reflecting the individuality of the disease process could result in a tailored therapy for the unique human being, contrasting with the 'one-size-fits-all' therapies currently employed in nephrology.

Gene expression profiling analysis in nephrology: towards molecular definition of renal disease

The increase in progressive kidney disease, resulting in a constantly rising prevalence of endstage renal disease (ESRD), urgently warrants the development of more effective strategies to diagnose, prevent, and intervene in renal disease. Histological information obtained by renal biopsies (RBx) is a cornerstone of the current management of kidney disease. Renal tissue can provide critical information on the disease process not available by nontissue-based approaches. However, insight gained by conventional histopathology remains limited and additional strategies to define renal disease on a molecular level are required. The sequencing of the human genome, together with recent advances in genome-wide profiling techniques, has provided the framework for a comprehensive analysis of renal disease-associated transcriptional programs. In this review, strategies to apply these technological advances towards the analysis of RBx will be described, with special emphasis on their potential impact on clinical management, but also on their inherent limitations. Finally, an outlook towards the emerging proteomic studies of renal disease will be given.

Podocyte-Specific Deletion of Integrin-Linked Kinase Results in Severe Glomerular Basement Membrane Alterations and Progressive Glomerulosclerosis

Alterations in glomerular podocyte cell-cell and cell-matrix contacts are key events in progressive glomerular failure. Integrin-linked kinase (ILK) has been implicated in podocyte cell-matrix interaction and is induced in proteinuria. For evaluation of ILK function in vivo, mice with a Cre-mediated podocyte-specific ILK inactivation were generated. These mice seemed normal at birth but developed progressive focal segmental glomerulosclerosis and died in terminal renal failure. The first ultrastructural lesions that are seen at onset of albuminuria are glomerular basement membrane (GBM) alterations with a significant increase in true harmonic mean GBM thickness. Podocyte foot process effacement and loss of slit diaphragm followed with progression to unselective proteinuria. No significant reduction of slit membrane molecules (podocin and nephrin), key GBM components (fibronectin, laminins, and collagen IV isoforms), or podocyte integrins could be observed at onset of proteinuria. However, alpha3-integrins were relocalized into a granular pattern along the GBM, consistent with altered integrin-mediated matrix assembly in ILK-deficient podocytes. As the increased GBM thickness precedes structural podocyte lesions and key components of the GBM were expressed at comparable levels to controls, these data suggest an essential role of ILK for the close interconnection of GBM structure and podocyte function.

Comparative promoter analysis allows de novo identification of specialized cell junction-associated proteins

Shared transcription factor binding sites that are conserved in distance and orientation help control the expression of gene products that act together in the same biological context. New bioinformatics approaches allow the rapid characterization of shared promoter structures and can be used to find novel interacting molecules. Here, these principles are demonstrated by using molecules linked to the unique functional unit of the glomerular slit diaphragm. An evolutionarily conserved promoter model was generated by comparative genomics in the proximal promoter regions of the slit diaphragm-associated molecule nephrin. Phylogenetic promoter fingerprints of known elements of the slit diaphragm complex identified the nephrin model in the promoter region of zonula occludens-1 (ZO-1). Genome-wide scans using this promoter model effectively predicted a previously unrecognized slit diaphragm molecule, cadherin-5. Nephrin, ZO-1, and cadherin-5 mRNA showed stringent coexpression across a diverse set of human glomerular diseases. Comparative promoter analysis can identify regulatory pathways at work in tissue homeostasis and disease processes.

Novel role of toll-like receptor 3 in hepatitis C-associated glomerulonephritis

Hepatitis C virus (HCV) infection is frequently complicated by glomerulonephritis with immune complexes containing viral RNA. We examined the potential influence of Toll-like receptors (TLRs), specifically TLR3 recognition of viral dsRNA exemplified by polyriboinosinic:polyribocytidylic acid [poly(I:C) RNA]. Normal human kidney stained positive for TLR3 on mesangial cells (MCs), vascular smooth muscle cells, and collecting duct epithelium. Cultured MCs have low TLR3 mRNA levels with predominant intracellular protein localization, which was increased by tumor necrosis factor-alpha, interleukin (IL)-1beta, interferon (IFN)-gamma, and the TLR3 ligand poly(I:C) RNA. Poly(I:C) RNA stimulation of MCs increased mRNA and protein synthesis of IL-6, IL-1beta, M-CSF, IL-8/CXCL8, RANTES/CCL5, MCP-1/CCL2, and ICAM-I; it also increased anti-proliferative and proapoptotic effects, the latter of which was decreased by inhibiting caspase-8. In microdissected glomeruli of normal and non-HCV membranoproliferative glomerulonephritis biopsies, TLR3 mRNA expression was low. In contrast TLR3 mRNA expression was significantly increased in hepatitis C-positive glomerulonephritis and was associated with enhanced mRNA for RANTES/CCL5 and MCP-1/CCL2. We hypothesize that immune complexes containing viral RNA activate mesangial TLR3 during HCV infection, thereby contributing to chemokine/cytokine release and effecting proliferation and apoptosis. Thus, TLR3 expression on renal cells, and especially MCs, may establish a link between viral infections and glomerular diseases.

Stereospecific and Redox-Sensitive Increase in Monocyte Adhesion to Endothelial Cells by Homocysteine

Objective— Previous studies have shown that elevated homocysteine (Hcy) levels promote the development of atherosclerotic lesions in atherosclerosis-prone animal models. There is evidence that oxidant stress contributes to Hcy’s deleterious effects on the vasculature. The accumulation and adhesion of monocytes to the vascular endothelium is a critical event in the development of atherosclerosis. We investigated the effects of Hcy on the interaction between human endothelial cells (EC) (EC line EA.hy 926 and primary human umbilical vein EC [HUVEC]) and the monocytic cell line THP-1, and the impact of vascular oxidant stress and redox-sensitive signaling pathways on these events.

Methods and Results— L-Hcy, but not D-Hcy, increases the production of reactive oxygen species inside EC, enhances nuclear factor(NF)-κB activation, and stimulates intercellular adhesion molecule-1 (ICAM-1) RNA transcription and cell surface expression. This leads to a time- and dose-dependent increase in monocyte adhesion to ECs. Pretreatment of ECs with superoxide scavengers (MnTBAP and Tiron) or with an inhibitor of NF-κB activation abolished Hcy-induced monocyte adhesion, ICAM-1 expression, and nuclear translocation of NF-κB.

Conclusions— These findings suggest that reactive oxygen species produced under hyperhomocysteinemic conditions may induce a proinflammatory situation in the vessel wall that initiates and promotes atherosclerotic lesion development.

Toll-like receptor-4: renal cells and bone marrow cells signal for neutrophil recruitment during pyelonephritis

BACKGROUND

The molecular mechanisms of pathogen recognition that initiate infective pyelonephritis are poorly understood. Toll-like receptor-4 (TLR4) mutant mice infected with uropathogenic Escherichia coli lack renal CXCL2 mRNA expression, subsequent neutrophil recruitment, and renal abscess formation.

METHODS

We used a bone marrow transplant approach in order to investigate the contribution of TLR4 in intrinsic renal cells or bone-marrow-derived immune cells to neutrophil recruitment during infective pyelonephritis.

RESULTS

Both chimera either expressing mutant tlr4 in intrinsic renal cells and wild-type tlr4 in bone marrow-derived cells or vice versa showed an impaired response to uropathogenic E. coli infection in terms of leukocyturia and renal abscess formation when compared to tlr4 wild-type mice with congenic bone marrow transplants.

CONCLUSION

These data suggest that TLR4 is required on both intrinsic renal cells (e.g., tubular epithelial cells) and bone marrow-derived immune cells for the control of ascending uropathogenic E. coli infection by initiating chemokine-driven renal neutrophil recruitment.

Polyomavirus DNA and RNA detection in renal allograft biopsies: results from a European multicenter study

Polyomavirus mediated nephropathy is an increasingly recognized complication in renal transplant recipients. In all, 362 renal biopsies collected from 15 European transplant centers were analyzed for presence of Polyomavirus nucleic acid (BK virus [BKV] and JC virus [JCV]). We evaluated 302 biopsies of patients with renal allograft dysfunction, including three with known BKV allograft nephropathy (BKVAN), and 60 native kidney biopsies. BKV DNA was detected in 8 of the 302 (2.6 %) biopsies obtained for transplant dysfunction, but in none of the controls. BKV RNA, indicating active viral replication, was found in all BKV DNA positive biopsies available for mRNA expression studies. Retrospective immunohistochemical staining was positive for SV40 large T antigen in all seven evaluated biopsies. BKV DNA and RNA were detected in biopsy tissues from patients with inconspicuous light microscopy for BKVAN. Further studies will evaluate the potential of intrarenal viral BKV RNA as an early predictor for BKVAN.

Expression of gremlin, a bone morphogenetic protein antagonist, in human diabetic nephropathy

BACKGROUND

We report the induction of gremlin, a bone morphogenetic protein antagonist, in cultured human mesangial cells exposed to high glucose and transforming growth factor beta (TGF-beta) levels in vitro and kidneys from diabetic rats in vivo.

METHODS

Gremlin expression was assessed in human diabetic nephropathy by means of in situ hybridization, immunohistochemistry, and real-time polymerase chain reaction and correlated with clinical and pathological indices of disease.

RESULTS

Gremlin was not expressed in normal human adult kidneys. Conversely, abundant gremlin expression was observed in human diabetic nephropathy. Although some gremlin expression was observed in occasional glomeruli, gremlin expression was most prominent in areas of tubulointerstitial fibrosis, where it colocalized with TGF-beta expression. Gremlin messenger RNA levels correlated directly with renal dysfunction, determined by means of serum creatinine level, but not with proteinuria level. There was a strong correlation between gremlin expression and tubulointerstitial fibrosis score.

CONCLUSION

In aggregate, these results indicate that the developmental gene gremlin reemerges in the context of tubulointerstitial fibrosis in diabetic nephropathy and suggests a role for TFG-beta as an inducer of gremlin expression in this context.

Human adult CD34- progenitor cells functionally express the chemokine receptors CCR1, CCR4, CCR7, CXCR5, and CCR10 but not CXCR4

The homing and tissue-specific recruitment of bone marrow-derived progenitor cells is a major issue in stem cell research and therapy. Chemokine biology plays a central role in the homing and trafficking of leukocytes. Here we show functional expression of the chemokine receptors CCR1, CCR4, CCR7, CCR10, and CXCR5 on primary isolates of CD34- mesenchymal progenitor cells as well as immortalized mesenchymal stem cell (MSC) lines. Although mRNA expression of CXCR4 was detected in both primary cells and immortalized clones, the receptor was not expressed on the cell surface. On the basis of this expression profile, the MSC could potentially home to secondary lymphatic organs (CCR7, CXCR5), skin (CCR4, CCR10), small intestine (CCR10), and salivary glands (CCR10). To study tissue-specific homing, murine CD34- MSC lines showing concordant chemokine receptor expression were either transiently labeled with CMFDA, or were stably transfected with green fluorescent protein (GFP) expression plasmids. The MSC were then injected into syngeneic healthy mice, and the distribution of the cells determined. The injected cells efficiently homed to spleen, thymus, and lymph nodes. In addition, cells were found in the mucosa of the small intestine, skin, and salivary gland. No significant recruitment to bone marrow, liver, or kidney was seen. Chemokine biology may play an important role in the homeostasis and potentially tissue recruitment of early adult progenitor cells.

Sam68-like mammalian protein 2, identified by digital differential display as expressed by podocytes, is induced in proteinuria and involved in splice site selection of vascular endothelial growth factor

Podocytes, the glomerular epithelial cells of the kidney, share important features with neuronal cells. In addition to phenotypical and functional similarities, a number of gene products have been found to be expressed exclusively or predominantly by both cell types. With the hypothesis of a common transcriptome shared by podocytes and neurons, digital differential display was used to identify novel podocyte-expressed gene products. Comparison of brain and kidney cDNA libraries with those of other organs identified Sam68-like mammalian protein 2 (SLM-2), a member of the STAR family of RNA processing proteins, as expressed by podocytes. SLM-2 expression was found to be restricted in the kidney to podocytes. In proteinuric diseases, SLM-2, a known regulator of neuronal mRNA splice site selection, was found significantly upregulated on mRNA and protein levels. Knockdown of SLM-2 by short interfering RNA in podocytes was performed to evaluate its biologic role. RNA splicing of vascular endothelial growth factor (VEGF), a key regulator of the filtration barrier and expressed as functionally distinct splice isoforms, was evaluated. VEGF(165) expression was found to be reduced by 25% after SLM-2 knockdown. In vivo, the glomerular expression of SLM-2 correlated with the mRNA levels of VEGF(165). This study demonstrates the power of digital differential display to predict cell type-specific gene expression by hypothesis-driven analysis of tissue cDNA libraries. SLM-2-dependent VEGF splicing indicates the importance of mRNA splice site selection for glomerular filtration barrier function.

CD20-positive infiltrates in human membranous glomerulonephritis

Membranous glomerulonephritis (MGN), histologically defined by subepithelial immune deposits, is the most common cause of nephrotic syndrome in Caucasian adults. The current hypothesis of the underlying disease mechanism postulates production of antibodies against podocyte-derived antigens. Respective antigens could be demonstrated in different animal models and recently in human neonatal MGN. Further support for this hypothesis was generated by the response of human MGN to therapeutic B cell depletion by rituximab. However, the role of B cells in this disease is not well defined. In this study, the interstitial expression of CD20 mRNA was determined in 31 MGN patients and controls (tumor nephrectomies (n = 4), minimal change disease (MCD, n = 10) and focal segmental glomerulosclerosis (n = 6)). CD20 mRNA expression was significantly higher in MGN patients compared to controls. By immunohistochemistry, a focal or diffuse interstitial B cell infiltration could be detected in MGN patients (n = 63), which was absent or minimal in patients with MCD (n = 11). These data suggest an involvement of B cells in the pathogenesis of MGN, possibly as antigen-presenting cells. Further studies should investigate the potential to predict the response to therapeutic B cell depletion by intrarenal CD20 quantification, a potential diagnostic basis for the selection of a specific therapy currently evolving for renal disease.

Viral Double-Stranded RNA Aggravates Lupus Nephritis through Toll-Like Receptor 3 on Glomerular Mesangial Cells and Antigen-Presenting Cells

How viral infections trigger autoimmunity is poorly understood. A role for Toll-like receptor 3 (TLR3) was hypothesized in this context as viral double-stranded RNA (dsRNA) activates dendritic cells to secrete type I interferons and cytokines that are known to be associated with the disease activity in systemic lupus erythematosus (SLE). Immunostaining of nephritic kidney sections of autoimmune MRL(lpr/lpr) mice revealed TLR3 expression in infiltrating antigen-presenting cells as well as in glomerular mesangial cells. TLR3-positive cultured mesangial cells that were exposed to synthetic polyinosinic-cytidylic acid (pI:C) RNA in vitro produced CCL2 and IL-6. pI:C RNA activated macrophages and dendritic cells, both isolated from MRL(lpr/lpr) mice, to secrete multiple proinflammatory factors. In vivo, a single injection of pI:C RNA increased serum IL-12p70, IL-6, and IFN-alpha levels. A course of 50 microg of pI:C RNA given every other day from weeks 16 to 18 of age aggravated lupus nephritis in pI:C-treated MRL(lpr/lpr) mice. Serum DNA autoantibody levels were unaltered upon systemic exposure to pI:C RNA in MRL(lpr/lpr) mice, as pI:C RNA, in contrast to CpG-DNA, failed to induce B cell activation. It therefore was concluded that viral dsRNA triggers disease activity of lupus nephritis by mechanisms that are different from those of bacterial DNA. In contrast to CpG-DNA/TLR9 interaction, pI:C RNA/TLR3-mediated disease activity is B cell independent, but activated intrinsic renal cells, e.g., glomerular mesangial cells, to produce cytokines and chemokines, factors that can aggravate autoimmune tissue injury, e.g., lupus nephritis.

Delayed chemokine receptor 1 blockade prolongs survival in collagen 4A3-deficient mice with Alport disease

Human Alport disease is caused by a lack of the alpha3-, 4-, or 5-chain of type IV collagen (COL4A). Affected humans and COL4A3-deficient mice develop glomerulosclerosis and progressive renal fibrosis in the presence of interstitial macrophages, but their contribution to disease progression is under debate. This question was addressed by treating COL4A3-deficient mice with BX471, an antagonist of chemokine receptor 1 (CCR1) that is known to block interstitial leukocyte recruitment. Treatment with BX471 from weeks 6 to 10 of life improved survival of COL4A3-deficient mice, associated with less interstitial macrophages, apoptotic tubular epithelial cells, tubular atrophy, interstitial fibrosis, and less globally sclerotic glomeruli. BX471 reduced total renal Cll5 mRNA expression by reducing the number of interstitial CCL5-positive cells in inflammatory cell infiltrates. Intravital microscopy of the cremaster muscle in male mice identified that BX471 or lack of CCR1 impaired leukocyte adhesion to activated vascular endothelium and transendothelial leukocyte migration, whereas leukocyte rolling and interstitial migration were not affected. Furthermore, in activated murine macrophages, BX471 completely blocked CCL3-induced CCL5 production. Thus, CCR1-mediated recruitment and local activation of macrophages contribute to disease progression in COL4A3-deficient mice. These data identify CCR1 as a potential therapeutic target for Alport disease or other progressive nephropathies associated with interstitial macrophage infiltrates.

Gene expression analysis of human renal biopsies: recent developments towards molecular diagnosis of kidney disease

PURPOSE OF REVIEW

The analysis of renal tissue from kidney biopsies by histology, electron microscopy and immunohistology represents the current standards used to establish a specific diagnosis in nephrology. Recent progress in gene expression-based tissue analysis may provide fundamentally novel information in renal biopsy interpretation. In this review, progress towards the routine application of this approach is summarized.

RECENT FINDINGS

Renal disease is characterized by closely interrelated mechanisms of inflammation, repair, scarring and atrophy affecting over 20 different intrinsic renal cell types. The renal biopsy sample represents a 'snapshot' of these dynamic processes. A central question for molecular diagnosis is whether specific gene expression patterns can adequately define segments of these disease processes. Can molecular markers be extracted as effectively as has been shown in oncology? Several studies have been able to correlate renal gene expression patterns with clinical parameters, renal histological findings and patient follow-up data. In small populations, molecular markers have been able to provide novel diagnostic, prognostic and differential therapeutic information beyond conventional histology.

SUMMARY

A growing number of renal gene expression projects are generating targets for the integration of molecular approaches into kidney biopsy evaluation. If these molecular makers can pass rigorous testing for their diagnostic value, they should become an indispensable part of the management of the renal patient.

Gene expression fingerprints in human tubulointerstitial inflammation and fibrosis as prognostic markers of disease progression

BACKGROUND

Gene expression profiling of nephropathies may facilitate development of diagnostic strategies for complex renal diseases as well as provide insight into the molecular pathogenesis of kidney diseases. To test molecular based renal disease categorization, differential gene expression profiles were compared between control and hydronephrotic kidneys showing varying degrees of inflammation and fibrosis.

METHODS

RNA expression profiles from 9 hydronephrotic and 3 control kidneys were analyzed using small macroarrays dedicated to genes involved in cell-cell contact, matrix turnover, and inflammation. In parallel, the degree of tubulointerstitial inflammation, fibrosis, and tubular atrophy using light microscopy and quantitative immunohistochemical parameters was determined.

RESULTS

Hierarchic clustering and self-organizing maps led to a gene expression dendrogram with three distinct nodes representing the control group, four kidneys with high inflammation, and five kidneys giving high fibrosis scores. To evaluate the clinical applicability of the marker set, the expression of nine genes (6Ckine, IL-8, MMP-9, MMP-3, MMP-7, urokinase R, CXCR5, integrin-beta4, and pleiotrophin) was tested in tubulointerstitial samples from routine renal biopsies. Seven mRNA markers showed differential regulation in inflammation and fibrosis in the biopsy population. Clinical follow-up revealed stringent correlation between gene expression data and progression of renal disease, and allowed segregation of the biopsies into progressive or stable disease course based on gene expression profiles.

CONCLUSION

This study suggests the feasibility of gene expression-based disease categorization in human nephropathies based on the extraction of marker gene sets.

Reduced intragraft mRNA expression of matrix metalloproteinases Mmp3, Mmp12, Mmp13 and Adam8, and diminished transplant arteriosclerosis in Ccr5-deficient mice

Experimental and human organ transplant studies suggest an important role for chemokine (C-C-motif) receptor-5 (CCR5) in the development of acute and chronic allograft rejection. Because early transplant damage can predispose allografts to chronic dysfunction, we sought to identify potential pathophysiologic mechanisms leading to allograft damage by using wild-type and Ccr5-deficient mice as recipients of fully MHC-mismatched heart and carotid-artery allografts. Gene expression in rejecting heart allografts was analyzed 2 and 6 days after transplantation using Affymetrix GeneChips. Microarray analysis led to identification of four metalloproteinase genes [matrix metalloproteinase (Mmp)3, Mmp12, Mmp13 and a disintegrin and metalloprotease domain (Adam)8] with significantly diminished intragraft mRNA expression in Ccr5-deficient mice at day 6. Accordingly, allografts from Ccr5-deficient mice showed less tissue remodeling and hence better preservation of the myocardial architecture compared with allografts from wild-type recipients. Moreover, survival of cardiac allografts was significantly increased in Ccr5-deficient mice. Carotid artery allografts from Ccr5-deficient recipients showed better tissue preservation, and significant reduction of neointima formation and CD3+ T cell infiltration. Ccr5 appears to play an important role in transplant-associated arteriosclerosis that may involve metalloproteinase-mediated vessel wall remodeling. We conclude that early tissue remodeling may be a critical feature in the predisposition of allografts to the development of chronic dysfunction.

Gene expression profiles of podocyte-associated molecules as diagnostic markers in acquired proteinuric diseases

For identifying potential diagnostic markers of proteinuric glomerulopathies, glomerular mRNA levels of molecules relevant for podocyte function (alpha-actinin-4, glomerular epithelial protein 1, Wilms tumor antigen 1, synaptopodin, dystroglycan, nephrin, podoplanin, and podocin) were determined by quantitative real-time RT-PCR from microdissected glomeruli. Biopsies from 83 patients with acquired proteinuric diseases were analyzed (minimal change disease [MCD; n = 13], benign nephrosclerosis [n = 16], membranous glomerulopathy [n = 31], focal and segmental glomerulosclerosis [FSGS; n = 9], and controls [n = 14]). Gene expression levels normalized to two different housekeeping transcripts (glyceraldehyde-3-phosphate-dehydrogenase and 18 S rRNA) did not allow a separation between proteinuric disease categories. However, a significant positive correlation between alpha-actinin-4, glomerular epithelial protein 1, synaptopodin, dystroglycan, Wilms tumor antigen 1, and nephrin was found in all analyzed glomeruli, whereas podocin mRNA expression did not correlate. Because varying amounts of housekeeper cDNA per glomerulus can confound expression ratios relevant for a subpopulation of cells, an "in silico" microdissection was performed using a podocyte-specific cDNA as a reference gene. Expression ratio of podocin to synaptopodin, the two genes with the most disparate expression, allowed a robust separation of FSGS from MCD and nephrosclerosis. Segregation of FSGS from MCD via this ratio was confirmed in an independent population of formaldehyde-fixed archival biopsies (MCD, n = 5; FSGS, n = 4) after glomerular laser capture microdissection. In addition, the expression marker was able to predict steroid responsiveness in diagnostically challenging cases of MCD versus FSGS (n = 6). As the above approach can be performed as an add-on diagnostic tool, these molecular diagnostic parameters could give novel information for the management of proteinuric diseases.

Early glomerular filtration defect and severe renal disease in podocin-deficient mice

Podocytes are specialized epithelial cells covering the basement membrane of the glomerulus in the kidney. The molecular mechanisms underlying the role of podocytes in glomerular filtration are still largely unknown. We generated podocin-deficient (Nphs2-/-) mice to investigate the function of podocin, a protein expressed at the insertion of the slit diaphragm in podocytes and defective in a subset of patients with steroid-resistant nephrotic syndrome and focal and segmental glomerulosclerosis. Nphs2-/- mice developed proteinuria during the antenatal period and died a few days after birth from renal failure caused by massive mesangial sclerosis. Electron microscopy revealed the extensive fusion of podocyte foot processes and the lack of a slit diaphragm in the remaining foot process junctions. Using real-time PCR and immunolabeling, we showed that the expression of other slit diaphragm components was modified in Nphs2-/- kidneys: the expression of the nephrin gene was downregulated, whereas that of the ZO1 and CD2AP genes appeared to be upregulated. Interestingly, the progression of the renal disease, as well as the presence or absence of renal vascular lesions, depends on the genetic background. Our data demonstrate the crucial role of podocin in the establishment of the glomerular filtration barrier and provide a suitable model for mapping and identifying modifier genes involved in glomerular diseases caused by podocyte injuries.

Eluate derived by extracorporal antibody-based immunoadsorption elevates the cytosolic Ca2+ concentration in podocytes via B2 kinin receptors

BACKGROUND/AIM

Patients with idiopathic focal segmental glomerulosclerosis (FSGS) often develop a recurrence of the disease after kidney transplantation. In a number of FSGS patients, plasmapheresis and immunoadsorption procedures have been shown to transiently reduce proteinuria and are thought to do this by eliminating a circulating factor. Direct cellular effects of eluates from immunoadsorption procedures on podocytes, the primary target of injury in FSGS, have not yet been reported.

METHODS

Eluates were derived from antibody-based immunoadsorption of a patient suffering from primary FSGS, a patient with systemic lupus erythematosus, and a healthy volunteer. The cytosolic free Ca(2+) concentration ([Ca(2+)](i)) of differentiated podocytes was measured by single-cell fura-2 microfluorescence measurements. Free and total immunoreactive kinin levels were measured by radioimmunoassay.

RESULTS

FSGS eluates increased the [Ca(2+)](i) levels concentration dependently (EC(50) 0.14 mg/ml; n = 3-19). 1 mg/ml eluate increased the [Ca(2+)](i) values reversibly from 82 +/- 12 to 1,462 +/- 370 nmol/l, and then they returned back to 100 +/- 16 nmol/l (n = 19). The eluate-induced increase of [Ca(2+)](i) consisted of an initial Ca(2+) peak followed by a Ca(2+) plateau which depended on the extracellular Ca(2+) concentration. The eluate-induced increase of [Ca(2+)](i) was inhibited by the specific B(2) kinin receptor antagonist Hoe 140 in a concentration-dependent manner (IC(50) 2.47 nmol/l). In addition, prior repetitive application of bradykinin desensitized the effect of eluate on [Ca(2+)](i). A colonic epithelial cell line not reacting to bradykinin did not respond to eluate either (n = 6). Similar to FSGS eluates, the eluate preparations of both the systemic lupus patient and the healthy volunteer led to a biphasic, concentration-dependent [Ca(2+)](i) increase in podocytes which again was inhibited by Hoe 140. Free kinins were detected in all eluate preparations.

CONCLUSION

The procedure of antibody-based immunoadsorption leads to kinin in the eluate which elevates the [Ca(2+)](i) level of podocytes via B(2) kinin receptors.

Glomerular podocytes possess the synaptic vesicle molecule Rab3A and its specific effector rabphilin-3a

Several recent studies have focused on similarities between glomerular podocytes and neurons because the two cells share a specialized cytoskeletal organization and several expression-restricted proteins, such as nephrin and synaptopodin. In neurons, the small guanosine triphosphatase Rab3A and its effector rabphilin-3A form a complex required for the correct docking of synaptic vesicles to their target membrane. Because rabphilin-3A binds in neurons to cytoskeletal proteins also important for podocyte homeostasis, and the complex rabphilin-3A-Rab3A has been demonstrated in neurons and neuroendocrine cells, the aim of our work was to investigate their possible expression and regulation in podocytes. Normal kidneys from mouse, rat, and human were studied by immunohistochemistry, Western blotting, and reverse transcriptase-polymerase chain reaction to evaluate the expression of Rab3A and rabphilin-3A. Double-staining immunohistochemistry and immunogold electron microscopy were then used to precisely localize the two proteins at the cellular and subcellular levels. Rab-3A and rabphilin-3A regulations in disease were then analyzed in growth hormone-transgenic mice, a well established model of focal and segmental glomerulosclerosis, and in human biopsies from proteinuric patients. Our results demonstrated that rabphilin-3A and Rab3A are present in normal mouse, rat, and human kidneys, with an exclusively glomerular expression and a comma-like pattern of positivity along the glomerular capillary wall, suggestive for podocyte staining. Co-localization of both molecules with synaptopodin confirmed their presence in podocytes. By immunogold electron microscopy both proteins were found around vesicles contained in podocyte foot processes. Their expression was increased in growth hormone-transgenic mice compared to their wild-type counterpart, and in a subset of biopsies from proteinuric patients. Our data, demonstrating the presence of two synaptic proteins in podocytes, further supports similarities between cytoskeletal and vesicular organization of podocytes and neurons. The altered expression observed in mouse and human proteinuric diseases suggests a possible role for these molecules in glomerulopathies.

Modification of the transcriptomic response to renal ischemia/reperfusion injury by lipoxin analog

BACKGROUND

Lipoxins are lipoxygenase-derived eicosanoids with anti-inflammatory and proresolution bioactivities in vitro and in vivo. We have previously demonstrated that the stable synthetic LXA4 analog 15-epi-16-(FPhO)-LXA4-Me is renoprotective in murine renal ischemia/reperfusion injury, as gauged by lower serum creatinine, attenuated leukocyte infiltration, and reduced morphologic tubule injury.

METHODS

We employed complementary oligonucleotide microarray and bioinformatic analyses to probe the transcriptomic events that underpin lipoxin renoprotection in this setting.

RESULTS

Microarray-based analysis identified three broad categories of genes whose mRNA levels are altered in response to ischemia/reperfusion injury, including known genes previously implicated in the pathogenesis of ischemia/reperfusion injury [e.g., intercellular adhesion molecule-1 (ICAM-1), p21, KIM-1], known genes not previously associated with ischemia/reperfusion injury, and cDNAs representing yet uncharacterized genes. Characterization of expressed sequence tags (ESTs) displayed on microarrays represents a major challenge in studies of global gene expression. A bioinformatic annotation pipeline successfully annotated a large proportion of ESTs modulated during ischemia/reperfusion injury. The differential expression of a representative group of these ischemia/reperfusion injury-modulated genes was confirmed by real-time polymerase chain reaction. Prominent among the up-regulated genes were claudin-1, -3, and -7, and ADAM8. Interestingly, the former response was claudin-specific and was not observed with other claudins expressed by the kidney (e.g., claudin-8 and -6) or indeed with other components of the renal tight junctions (e.g., occludin and junctional adhesion molecule). Noteworthy among the down-regulated genes was a cluster of transport proteins (e.g., aquaporin-1) and the zinc metalloendopeptidase meprin-1 beta implicated in renal remodeling.

CONCLUSION

Treatment with the lipoxin analog 15-epi-16-(FPhO)-LXA4-Me prior to injury modified the expression of many differentially expressed pathogenic mediators, including cytokines, growth factors, adhesion molecules, and proteases, suggesting a renoprotective action at the core of the pathophysiology of acute renal failure (ARF). Importantly, this lipoxin-modulated transcriptomic response included many genes expressed by renal parenchymal cells and was not merely a reflection of a reduced renal mRNA load resulting from attenuated leukocyte recruitment. The data presented herein suggest a framework for understanding drivers of kidney injury in ischemia/reperfusion and the molecular basis for renoprotection by lipoxins in this setting.

Validation of endogenous controls for gene expression analysis in microdissected human renal biopsies

BACKGROUND

The appropriate choice of an internal reference is critical for quantitative RNA analysis. However, no comparison of frequently used "housekeeping" genes is available for renal biopsy studies.

METHODS

Microdissected biopsies from 165 patients, including a wide range of histopathologic diagnoses, were analyzed [immunoglobulin A (IgA) nephritis, membranous glomerulopathy, rapid progressive glomerulonephritis, minimal change disease, focal segmental glomerulosclerosis (FSGS), nephrosclerosis, diabetic nephropathy, interstitial nephritis, and controls]. Expression of three frequently used housekeeping genes [glyceraldehyde-3-phosphate dehydrogenase (GAPDH), 18S rRNA, and cyclophilin A] was examined by real-time reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Absolute expression values of reference genes obtained from the renal biopsies were related to each other. In tubulointerstitial compartment, a positive correlation coefficient (r) of 0.96 was observed between 18S rRNA and cyclophilin A. However, a subset of samples showed lower expression levels for GAPDH in relation to 18S rRNA or cyclophilin A, resulting in a decrease to r = 0.77 and r = 0.73, respectively, consistent with considerable mRNA regulation of GAPDH. In glomerular samples, a comparable low correlation between GAPDH versus 18S rRNA (r = 0.75) was obtained.

CONCLUSION

Using a single housekeeper gene as reference for renal biopsy studies, differences in gene expression ratios may reflect regulation of the internal control rather than the mRNA under investigation. Relating the gene expression to several housekeepers in parallel (i.e., 18S rRNA and cyclophilin A) should result in robust expression data.

Identification of a signal transduction pathway that regulates MMP-9 mRNA expression in glomerular injury

Podocytes contribute to the filtration barrier within the kidney. The integrin-linked kinase (ILK) plays an important role in podocyte adhesion to the glomerular basement membrane, signal transduction and phenotype regulation. We demonstrate that ILK activity is also associated with upregulation of matrix metalloproteinase-9 (MMP-9) mRNA levels during podocyte stress. A synthetic ILK inhibitor blocked MMP-9 mRNA upregulation but showed no effect on TIMP-1 or MMP-2 mRNA expression. Interestingly, a corresponding increase in MMP-9 secretion was not observed, suggesting that MMP-9 mRNA production in podocytes is regulated via ILK, whereas additional signaling pathways may mediate the post-transcriptional regulation of MMP-9.

Repuncturing the renal biopsy: strategies for molecular diagnosis in nephrology

As has been exemplified by recent progress in the classification of cancer, future approaches to enhance the clinical diagnostic power of tissue biopsies may be based on gene expression profiles. A series of strategies to translate these approaches to the diagnosis of renal disease is here proposed. The theoretical and technical problems resulting from the small amount of starting material available from renal biopsies will be specifically addressed. A preliminary study with cDNA array-based expression data obtained from kidneys with tubulointerstitial inflammation and fibrosis suggests the feasibility of distinguishing molecular categories of renal disease. Finally, a combined conventional and molecular work-up of renal biopsies will be suggested. These approaches should add a new dimension to biopsy interpretation and provide novel information concerning renal pathogenesis, diagnosis, prognosis, and differential therapy. A coordinated effort from nephrologists and pathologists in large multicenter trials will be required to achieve this goal. It is hoped that this outlook will lead to stimulating discussions and the implementation of these innovative ideas in nephrology.

Acetylcholine increases the free intracellular calcium concentration in podocytes in intact rat glomeruli via muscarinic M(5) receptors

The effects of acetylcholine (ACh) on the free intracellular calcium concentration ([Ca2+](i)) of microdissected glomeruli were investigated using fura-2 fluorescence digital imaging and two-photon confocal microscopy. ACh caused a concentration-dependent [Ca2+](i) increases with an initial peak followed by a sustained plateau, which was suppressed by reduced extracellular Ca2+ concentrations. The [Ca2+](i) plateau was not affected by the L-type Ca2+ channel blocker nicardipine, whereas gadolinium and lanthanum (both at 1 microM) blocked the plateau. Diphenylacetoxy-N:-methylpiperidine methiodide (100 nM), an M(3)/M(5) receptor antagonist, and pirenzepine (1 microM), an M(1) receptor antagonist, completely inhibited the effect of ACh. [Ca2+](i) measurements using two-photon excitation of fluo-3 and staining of the cells with calcein/acetoxymethyl ester, for observation of the capillary network together with the glomerular cells, showed that [Ca2+](i) was increased in single podocytes. Immunohistochemical studies did not demonstrate M(3) receptor expression in glomerular cells. M(1) receptors could be detected only in the parietal sheet of Bowman's capsule, whereas M(5) receptors were found only in podocytes. The data show that ACh increases [Ca2+](i) in podocytes of intact glomeruli, most likely via muscarinic M(5) receptors.

Acid-base and endocrine effects of aldosterone and angiotensin II inhibition in metabolic acidosis in human patients

Chronic metabolic acidosis (CMA) in human beings is characterized by increased renin-angiotensin-aldosterone (RAA) activity and cortisol secretion as well as nitrogen wasting. The purpose of this study was to examine whether and to what extent increased RAA activity (i.e., angiotensin II or aldosterone) regulates acid-base equilibrium in CMA and thus might co-determine the severity of acidosis. CMA was induced in 8 normal subjects by oral NH4Cl administration (2.1 mmol/kg body weight per day) for 7 days, followed by a 7-day period of spironolactone (100 mg, 4 times a day by mouth), followed by a 4-day period of spironolactone and losartan (100 mg, every day by mouth). NH4Cl feeding was continued during all study periods. Spironolactone resulted in exacerbation of acidosis ((HCO3)p decreased from 19.8+/-0.4 mmol/L to 17.7+/-0.6 mmol/L, P<.005) because of a large increase in endogenous acid production, as evidenced by significant increases in net acid excretion (116 to 185 mmol/day, P<.005), urinary anion gap (+31 mEq/day, P<.05), and sulfate excretion (+32 mEq/day, P<.05). Plasma potassium increased from 4.2 to 4.6 mmol/L (P<.05) because of decreased urinary potassium excretion (from 108 to 92 mmol/day, P<.05). Plasma angiotensin II, cortisol, aldosterone, urinary aldosterone, urinary tetrahydrocortisol, free cortisol, and nitrogen excretion increased significantly. The subsequent addition of losartan to spironolactone administration resulted in further exacerbation of acidosis ((HCO3)p decreased to 15.7+/-0.4 mmol/L, P<.05) and hyperkalemia (5.0 mmol/L, P<.05) with no change in plasma anion gap. Renal potassium excretion decreased from 92 to 73 mmol/day (P<.05) on day 1. Exacerbation of acidosis was accounted for by a renal mechanism, as evidenced by the significant decrease in net acid excretion and unchanged urinary unmeasured anion and nitrogen excretion. We conclude the following: (1) AT-1 blockade by losartan exacerbates acidosis by inducing a distal-tubular acidification defect. Angiotensin II is an important modulator of the renal acid excretory response to CMA in human beings. (2) Inhibition of aldosterone action by spironolactone in CMA results in an increase in endogenous acid production and exacerbates acidosis by a non-renal mechanism that is mediated, at least in part, by exacerbated hyperglucocorticoidism.

Regulation of the Na+2Cl-K+ cotransporter in isolated rat colon crypts

The Na(+2)Cl(-)K+ cotransporter accepts NH4+ at its K+-binding site. Therefore, the rate of cytosolic acidification after NH4+ addition to the bath (20 mmol/l) measured by BCECF fluorescence can be used to quantify the rate of this cotransporter. In isolated colon crypts of rat distal colon (RCC) addition of NH4+ led to an initial alkalinization, corresponding to NH3 uptake. This was followed by an acidification, corresponding to NH4+ uptake. The rate of this uptake was quantified by exponential curve fitting and is given in arbitrary units (delta fluorescence ratio units/1000 s). In pilot experiments it was shown that the pH signal caused by the Na(+)2Cl(-)K+ co-transporter could be amplified if the experiments were carried out in the presence of bath Ba2+ to inhibit NH4+ uptake via K+ channels. Therefore all subsequent experiments were performed in the presence of 1 mmol/l Ba2+. In the absence of any secretagogue, preincubation of RCC in a low-Cl- solution (4 mmol/l) for 10 min enhanced the uptake rate significantly from 1.70+/-0.11 to 2.54+/-0.27 U/1000 s (n=20). The addition of 100 mmol/l mannitol (hypertonic solution) enhanced the rate significantly from 1.93+/-0.17 to 2.84+/-0.43 U/1000 s (n=5). Stimulation of NaCl secretion by a solution containing 100 micromol/l carbachol (CCH) led to a small but significant increase in NH4+ uptake rate from 2.06+/-0.34 to 2.40+/-0.30 U/1000 s (n= 11). The increase in uptake rate observed with stimulation of the cAMP pathway by isobutylmethylxanthine (IBMX) and forskolin (100 micromol/l and 5 micromol/l, respectively) was from 2.39+/-0.24 to 3.06+/-0.36 U/1000 s (n=24). Whatever the mechanism used to increase the NH4+ uptake rate, azosemide (500 micromol/l) always reduced this rate to control values. Hence three manoeuvres enhanced loop-diuretic-inhibitable uptake rates of the Na(+)2Cl(-)K+ cotransporter: (1) lowering of cytosolic Cl- concentration; (2) cell shrinkage; (3) activation of NaCl secretion by carbachol and (4) activation of NaCl secretion by cAMP. The common denominator of all four activation pathways may be a transient fall in cell volume.

Angiotensin II increases the intracellular calcium activity in podocytes of the intact glomerulus

Angiotensin II increases the intracellular calcium activity in podocytes of the intact glomerulus.

BACKGROUND

Knowledge about biological functions of podocytes in the glomerulus is limited because of its unique anatomical location. Here we introduce a new method for measuring the intracellular calcium activity ([Ca2+]i) in the podocyte in the intact glomerulus.

METHODS

With the help of fluorescence high-resolution digital imaging and a recently developed ultraviolet laser-scanning microscope, [Ca2+]i was measured in fura-2-loaded glomeruli and single podocytes of intact microdissected rat glomeruli.

RESULTS

Angiotensin II (Ang II) increased [Ca2+]i reversibly in a biphasic and concentration-dependent manner. In contrast to Ang II, bradykinin, thrombin, arginine vasopressin, and serotonin did not change [Ca2+]i in the glomerulus. At reduced extracellular Ca2+ activity, Ang II released [Ca2+]i from intracellular stores, but the second phase, corresponding to a Ca2+ influx from the extracellular space, was absent. The L-type Ca2+ channel blocker nicardipine did not influence the Ang II-mediated [Ca2+]i increase, and an increase of the extracellular K+ concentration did not change [Ca2+]i in the glomerulus. The angrotensin II type I (AT1) receptor antagonist losartan inhibited the Ang II-mediated [Ca2+]i increase. Confocal [Ca2+]i measurements using fura-2 or fluo-3 or fluo-4 on the single cell level show that some of the Ang II-mediated [Ca2+]i response originated from podocytes. Costaining with calcein allowed the identification of podocytes because of the characteristic morphology and location in relationship to the capillary network.

CONCLUSIONS

These data suggest that podocytes in the intact glomerulus respond to Ang II with an increase of [Ca2+]i via an AT1 receptor.

Polycations induce calcium signaling in glomerular podocytes

BACKGROUND

The neutralization of the polyanionic surface of the podocyte by perfusion of kidneys with polycations, such as protamine sulfate, leads to a retraction of podocyte foot processes and proteinuria. This study investigates the effects of protamine sulfate or anionic, neutral, or cationic dextrans on the cytosolic calcium activity ([Ca2+]i) in podocytes.

METHODS

[Ca2+]i was measured in single cultured differentiated mouse podocytes with the fluorescence dye fura-2/AM.

RESULTS

Protamine sulfate caused a concentration-dependent and partially reversible increase of [Ca2+]i (EC50 approximately 1.5 micromol/liter). Pretreatment of the cells with heparin (100 U/liter) inhibited the protamine sulfate-mediated increase of [Ca2+]i. Like protamine sulfate, diethylaminoethyl dextran (DEAE-dextran) concentration dependently increased [Ca2+]i in podocytes (EC50 approximately 20 nmol/liter), whereas dextran sulfate or uncharged dextran (both 10 micromol/liter) did not influence [Ca2+]i. A reduction of the extracellular Ca2+ concentration (from 1 mmol/liter to 1 micomol/liter) partially inhibited the protamine sulfate and the DEAE-dextran-induced [Ca2+]i response. Flufenamate (100 micromol/liter) or Gd3+ (10 micromol/liter), which are known to inhibit nonselective ion channels, did not influence the [Ca2+]i increase induced by protamine sulfate. In the presence of thapsigargin (50 nmol/liter), an inhibitor of the endoplasmic reticulum Ca2+-ATPase, both protamine sulfate and DEAE-dextran increased [Ca2+]i.

CONCLUSIONS

The data indicate that polycations increase podocyte [Ca2+]i. The increase of [Ca2+]i may be an early event in the pathogenesis of protamine sulfate-mediated retraction of podocyte foot processes.

Characterization of prostanoid receptors in podocytes

Prostaglandins participate in the regulation of important glomerular functions and are involved in the pathogenesis of glomerular diseases. This study investigates the influence of prostaglandins on membrane voltage, ion conductances, cAMP accumulation, and cytosolic calcium activity ([Ca2+]i) in differentiated podocytes. Prostaglandin E2 (PGE2) caused a concentration-dependent depolarization and an increase of the whole cell conductance in podocytes (EC50 approximately 50 nM). Compared with PGE2, the EP2/EP3/EP4 receptor agonist 11-deoxy-PGE1 caused an equipotent depolarization, whereas the DP receptor agonist BW 245 C, the EP1/EP3 receptor agonist sulprostone, and the IP receptor agonist iloprost were at least 100 to 1000 times less potent than PGE2. The EP2 receptor agonist butaprost did not change membrane voltage of podocytes. The depolarizing effect of PGE2 was increased in an extracellular solution with a reduced Cl- concentration (from 145 to 32 mM). PGE2 and the prostaglandin agonists, but not the IP receptor agonist iloprost and the EP2 receptor agonist butaprost, induced a time- and concentration-dependent cAMP accumulation in podocytes. In fura-2 fluorescence experiments, PGE2, sulprostone, PGF2alpha, fluprostenol (a potent FP agonist), and U-46619 (a selective thromboxane A2 agonist) induced a biphasic increase of [Ca2+]i in 60 to 80% of podocytes. In reverse transcription-PCR studies, podocyte mRNA for the EP1, EP4, FP, and TP receptor could be amplified. These data indicate that in podocytes, PGE2 regulates distinct cellular functions via the EP1 and EP4 receptor, thereby increasing [Ca2+]i and cAMP, respectively. Furthermore, PGF1alpha and U-46619 increase [Ca2+]i via their specific receptors.