Alterations of renal phenotype and gene expression profiles due to protein overload in NOD-related mouse strains

Manifestation of rs1888747 polymorphisms in the FRMD3 gene in diabetic kidney disease and diabetic retinopathy in type 2 diabetes patients

Background

FRMD3 polymorphisms has suggested that they could be an alternative test to differentiate diabetic nephropathy (DN) from nondiabetic renal disease (NDRD) in type 2 diabetes mellitus (DM) patients. This study was performed to investigate the relationship between the FRMD3 gene and clinical characteristics of DN.

Methods

Patients who already had renal pathologic results were tested for FRMD3 polymorphisms. The subjects were classified into three groups; DN with diabetic retinopathy (DR), DN without DR, and DM with NDRD. FRMD3 polymorphisms were analyzed in each group.

Results

The prevalence of GG, CG, and CC was 44.4%, 42.2%, and 13.3% respectively. There was no significant difference in clinical parameters, which consisted of disease duration, proteinuria, and complications in DN with or without DR and DM with NDRD. The G allele was mainly found in DN with DR patients (50.8%) whereas the C allele was found in DM with NDRD patients (43.5%) (p = 0.02). There was a significant association between the CC genotype in NDRD when compared to GG (p = 0.001). In addition, the C allele was 2.10-fold more often associated with NDRD than the G allele (p = 0.03). The CC genotype was correlated with risk for NDRD than the GG and GC genotypes, with odds ratios of 6.89 and 4.91, respectively (p = 0.02).

Conclusion

C allele presentation, especially homozygous CC, was associated with NDRD pathology in patients with overt proteinuria. Hence, kidney biopsy is suggested in those with the C allele or homozygous CC genotype, regardless of retinopathy manifestations.

Genetic analysis of intracapillary glomerular lipoprotein deposits in aging mice

BACKGROUND

Renal aging is characterized by functional and structural changes like decreased glomerular filtration rate, and glomerular, tubular and interstitial damage. To gain insight in pathways involved in renal aging, we studied aged mouse strains and used genetic analysis to identify genes associated with aging phenotypes.

METHODS

Upon morphological screening in kidneys from 20-month-old mice from 26 inbred strains we noted intracapillary PAS-positive deposits. The severity of these deposits was quantified by scoring of a total of 50 glomeruli per section (grade 0-4). Electron microscopy and immunohistochemical staining for apoE, apoB, apoA-IV and perilipin-2 was performed to further characterize the lesions. To identify loci associated with these PAS-positive intracapillary glomerular deposits, we performed haplotype association mapping.

RESULTS

Six out of 26 mouse strains showed glomerular PAS-positive deposits. The severity of these deposits varied: NOD(0.97), NZW(0.41), NON(0.30), B10(0.21), C3 H(0.9) and C57BR(0.7). The intracapillary deposits were strongly positive for apoE and weakly positive for apoB and apoA-IV. Haplotype association mapping showed a strong association with a 30-Kb haplotype block on Chr 1 within the Esrrg gene. We investigated 1 Mb on each site of this region, which includes the genes Spata17, Gpatch2, Esrrg, Ush2a and Kctd3.

CONCLUSIONS

By analyzing 26 aged mouse strains we found that some strains developed an intracapillary PAS and apoE-positive lesion and identified a small haplotype block on Chr 1 within the Esrrg gene to be associated with these lipoprotein deposits. The region spanning this haplotype block contains the genes Spata17, Gpatch2, Esrrg, Ush2a and Kctd3, which are all highly expressed in the kidney. Esrrg might be involved in the evolvement of these glomerular deposits by influencing lipid metabolism and possibly immune reponses.

The evolution of blood pressure and the rise of mankind

Why is it that only human beings continuously perform acts of heroism? Looking back at our evolutionary history can offer us some potentially useful insight. This review highlights some of the major steps in our evolution-more specifically, the evolution of high blood pressure. When we were fish, the first kidney was developed to create a standardized internal 'milieu' preserving the primordial sea within us. When we conquered land as amphibians, the evolution of the lung required a low systemic blood pressure, which explains why early land vertebrates (amphibians, reptiles) are such low performers. Gaining independence from water required the evolution of an impermeable skin and a water-retaining kidney. The latter was accomplished twice with two different solutions in the two major branches of vertebrate evolution: mammals excrete nitrogenous waste products as urea, which can be utilized by the kidney as an osmotic agent to produce more concentrated urine. Dinosaurs and birds have a distinct nitrogen metabolism and excrete nitrogen as water-insoluble uric acid-therefore, their kidneys cannot use urea to concentrate as well. Instead, some birds have developed the capability to reabsorb water from their cloacae. The convergent development of a separate small circulation of the lung in mammals and birds allowed for the evolution of 'high blood-pressure animals' with better capillarization of the peripheral tissues allowing high endurance performance. Finally, we investigate why mankind outperforms any other mammal on earth and why, to this day, we continue to perform acts of heroism on our eternal quest for personal bliss.

Discovery of genes related to diabetic nephropathy in various animal models by current techniques

One of the major problems facing clinical nephrology currently throughout the world is an exponential increase in patients with end-stage renal disease (ESRD), which is largely related to a high incidence of diabetic nephropathy. The latter is characterized by a multitude of metabolic and signaling events following excessive channeling of glucose, which leads to an increased synthesis of extracellular matrix (ECM) glycoproteins resulting in glomerulosclerosis, interstitial fibrosis and ultimately ESRD. With the incidence of nephropathy at pandemic levels and a high rate of ESRD, physicians around the world must treat a disproportionately large number of diabetic patients with upto-date innovative measures. In this regard, identification of genes that are crucially involved in the progression of diabetic nephropathy would enhance the discovery of new biomarkers and could also promote the development of novel therapeutic strategies. Over the last decade, we focused on the recent methodologies of high-throughput and genome-wide screening for identification of relevant genes in various animal models, which included the following: (1) single nucleotide polymorphism-based genome- wide screening; (2) the transcriptome approach, such as differential display reverse transcription polymerase chain reaction (DDRT-PCR), representational difference analysis of cDNA (cDNA-RDA)/suppressive subtractive hybridization, SAGE (serial analysis of gene expression) and DNA Microarray; and (3) the proteomic approach and 2- dimensional polyacrylamide gel electrophoresis (2D- PAGE) coupled with mass spectroscopic analysis. Several genes, such as Tim44 (translocase of inner mitochondrial membrane- 44), RSOR/MIOX (renal specific oxidoreductase/myo-inositol oxygenase), UbA52, Rap1b (Ras-related GTPase), gremlin, osteopontin, hydroxysteroid dehydrogenase- 3β isotype 4 and those of the Wnt signaling pathway, were identified as differentially expressed genes in kidneys of diabetic rodents. Functional analysis of these genes and the subsequent translational research in the clinical settings would be very valuable in the prevention and treatment of diabetic nephropathy. Future trends for identification of the biomarkers and therapeutic target genes should also include genome scale DNA/histonemethylation profiling, metabolomic approaches (e.g. metabolic phenotyping by 1H spectroscopy) and lectin microarray for glycan profiling along with the development of robust data-mining strategies.

Role of ClC-5 in renal endocytosis is unique among ClC exchangers and does not require PY-motif-dependent ubiquitylation

Inactivation of the mainly endosomal 2Cl(-)/H(+)-exchanger ClC-5 severely impairs endocytosis in renal proximal tubules and underlies the human kidney stone disorder Dent's disease. In heterologous expression systems, interaction of the E3 ubiquitin ligases WWP2 and Nedd4-2 with a "PY-motif" in the cytoplasmic C terminus of ClC-5 stimulates its internalization from the plasma membrane and may influence receptor-mediated endocytosis. We asked whether this interaction is relevant in vivo and generated mice in which the PY-motif was destroyed by a point mutation. Unlike ClC-5 knock-out mice, these knock-in mice displayed neither low molecular weight proteinuria nor hyperphosphaturia, and both receptor-mediated and fluid-phase endocytosis were normal. The abundances and localizations of the endocytic receptor megalin and of the Na(+)-coupled phosphate transporter NaPi-2a (Npt2) were not changed, either. To explore whether the discrepancy in results from heterologous expression studies might be due to heteromerization of ClC-5 with ClC-3 or ClC-4 in vivo, we studied knock-in mice additionally deleted for those related transporters. Disruption of neither ClC-3 nor ClC-4 led to proteinuria or impaired proximal tubular endocytosis by itself, nor in combination with the PY-mutant of ClC-5. Endocytosis of cells lacking ClC-5 was not impaired further when ClC-3 or ClC-4 was additionally deleted. We conclude that ClC-5 is unique among CLC proteins in being crucial for proximal tubular endocytosis and that PY-motif-dependent ubiquitylation of ClC-5 is dispensable for this role.

Gene expression profiles stratified according to type 1 diabetes mellitus susceptibility regions

The MHC region (6p21) aggregates the major genes that contribute to susceptibility to type 1 diabetes (T1D). Three additional relevant susceptibility regions mapped on chromosomes 1p13 (PTPN22), 2q33 (CTLA-4), and 11p15 (insulin) have also been described by linkage studies. To evaluate the contribution of these susceptibility regions and the chromosomes that house these regions, we performed a large-scale differential gene expression on lymphomononuclear cells of recently diagnosed T1D patients, pinpointing relevant modulated genes clustered in these regions and their respective chromosomes. A total of 4608 cDNAs from the IMAGE library were spotted onto glass slides using robotic technology. Statistical analysis was carried out using the SAM program, and data regarding gene location and biological function were obtained at the SOURCE, NCBI, and FATIGO programs. Three induced genes were observed spanning around the MHC region (6p21-6p23), and seven modulated genes (5 repressed and 2 repressed) were seen spanning around the 6q21-24 region. Additional modulated genes were observed in and around the 1p13, 2q33, and 11p15 regions. Overall, modulated genes in these regions were primarily associated with cellular metabolism, transcription factors and signaling transduction. The differential gene expression characterization may identify new genes potentially involved with diabetes pathogenesis.

Inducible rodent models of acquired podocyte diseases

Glomerular diseases remain the leading cause of chronic and end-stage kidney disease. Significant advances in our understanding of human glomerular diseases have been enabled by the development and better characterization of animal models. Diseases of the glomerular epithelial cells (podocytes) account for the majority of proteinuric diseases. Rodents have been extensively used experimentally to better define mechanisms of disease induction and progression, as well as to identify potential targets and therapies. The development of podocyte-specific genetically modified mice has energized the research field to better understand which animal models are appropriate to study acquired podocyte diseases. In this review we discuss inducible experimental models of acquired nondiabetic podocyte diseases in rodents, namely, passive Heymann nephritis, puromycin aminonucleoside nephrosis, adriamycin nephrosis, liopolysaccharide, crescentic glomerulonephritis, and protein overload nephropathy models. Details are given on the model backgrounds, how to induce each model, the interpretations of the data, and the benefits and shortcomings of each. Genetic rodent models of podocyte injury are excluded.