Early ultrastructural glomerular alterations in neonatal nephrotic mice (ICGN strain)

Tensin 2-deficient nephropathy - mechanosensitive nephropathy, genetic susceptibility

Tensin 2 (TNS2), a focal adhesion protein, is considered to anchor focal adhesion proteins to β integrin as an integrin adaptor protein and/or serve as a scaffold to facilitate the interactions of these proteins. In the kidney, TNS2 localizes to the basolateral surface of glomerular epithelial cells, i.e., podocytes. Loss of TNS2 leads to the development of glomerular basement membrane lesions and abnormal accumulation of extracellular matrix in maturing glomeruli during the early postnatal stages. It subsequently results in podocyte foot process effacement, eventually leading to glomerulosclerosis. Histopathological features of the affected glomeruli in the middle stage of the disease include expansion of the mesangial matrix without mesangial cell proliferation. In this review, we provide an overview of TNS2-deficient nephropathy and discuss the potential mechanism underlying this mechanosensitive nephropathy, which may be applicable to other glomerulonephropathies, such as CD151-deficient nephropathy and Alport syndrome. The onset of TNS2-deficient nephropathy strictly depends on the genetic background, indicating the presence of critical modifier genes. A better understanding of molecular mechanisms of mechanosensitive nephropathy may open new avenues for the management of patients with glomerulonephropathies.

Genetic loci for resistance to podocyte injury caused by the tensin2 gene deficiency in mice

Background

Tensin2 is a focal adhesion-localized multidomain protein expressed in various tissues, and its dysfunction leads to alterations in podocytes. However, these podocyte-related manifestations are dependent on murine strain. Tensin2 dysfunction results in susceptible strains developing podocyte foot process effacement and massive albuminuria, whereas podocytes in resistant strains remain almost intact. In our previous studies, quantitative trait loci analysis and congenic analysis using resistant C57BL/6J and susceptible ICGN mice identified a modifier locus associated with podocyte injury caused by tensin2 dysfunction on chromosome 2. However, the effect of this modifier locus on chromosome 2 is insufficient to explain the resistance of C57BL/6J mice to tensin2 dysfunction, indicating the existence of other modifier genes.

Results

Whereas previous studies focused on the severity of chronic kidney disease, the present study focused on podocyte injury. We performed a genome-wide linkage analysis of backcrosses between two tensin2-deficient mouse strains, B6.ICGN-Tns2^nph and FVB.ICGN-Tns2^nph, and detected a novel major modifier locus on chromosome 10. The combined effect of the C57BL/6J alleles of the two loci on chromosomes 2 and 10 reduced the urinary albumin excretion caused by tensin2 dysfunction to a level comparable to that of C57BL/6J mice.

Conclusions

These data indicate that the resistance to podocyte injury caused by tensin2 dysfunction is mainly produced by the effects of the modifier genes on the two loci. The identification of these modifier genes is expected to help elucidate the mechanism underlying podocyte injury.

Electronic supplementary material

The online version of this article (10.1186/s12863-018-0611-1) contains supplementary material, which is available to authorized users.

Nephron, Wilms' tumor-1 (WT1), and synaptopodin expression in developing podocytes of mice

Newborn mouse glomeruli are still immature with a morphological feature of an early capillary loop stage, but infant mice do not manifest proteinuria. Little is known about the molecular mechanism whereby infant mice are resistant to proteinuria. Nephrin and synaptopodin are crucial for slit diaphragm and foot process (FP) formation for avoiding proteinuria. Nephrin tyrosine phosphorylation means a transient biological signaling required for FP repair or extension during nephrotic disease. Using an immunohistochemical technique, we examined the natural course of nephrin, Wilms’ tumor-1 (WT1) and synaptopodin at 16.5 days of embryonic age (E16.5d) and E19.5d, 7 days of post-neonatal age (P7d) and P42d during renal development of mice. As a result, nephrin and synaptopodin were detected at E19.5d in S-shaped bodies. WT1, a transcriptional factor for nephrin, was detected in nucleus in podocyte-like cells in all stages. Nephrin tyrosine phosphorylation was evident in glomeruli at P7d, and this was associated with an early-stage of FP extension. Inversely, nephrin phosphorylation became faint at P42d, along with maturated FP. Based on the present results, we suggest the sequential molecular mechanism to protect growing mice from proteinuria: (i) WT1-induced nephrin production by podocytes in S-shaped bodies at E19.5d; (ii) Synchronized induction of synaptopodin at the same period; and (iii) FP extension is initiated at a milk-suckling stage under a nephrin tyrosine-phosphorylated condition, while it is arrested at an adult stage, associated with a loss of nephrin-based signaling.

Mouse chromosome 2 harbors genetic determinants of resistance to podocyte injury and renal tubulointerstitial fibrosis

Background

Tensin2 deficiency results in alterations in podocytes and subsequent glomerular and tubulointerstitial injuries. However, this pathology is critically dependent on genetic background. While the Tensin2-deficient podocytes of resistant murine strains, including C57BL/6J mice, remain almost intact, susceptible murine strains with Tensin2 deficency, including ICGN mice, develop chronic kidney disease following alterations in the podocyte foot processes. In a previous study, genome-wide linkage analysis was utilized to identify the quantitative trait loci associated with the disease phenotypes on mouse chromosome 2. This study investigated the disease phenotypes of chromosome 2 consomic and subcongenic strains.

Results

ICGN consomic mice introgressed with chromosome 2 from the C57BL/6J mouse were generated and found to exhibit milder renal failure than that in ICGN mice. We developed 6 subcongenic strains that carry C57BL/6J-derived chromosomal segments from the consomic strain. One showed significantly milder albuminuria, another showed significantly milder tubulointerstitial injury, and the both showed significantly milder glomerular injury.

Conclusions

These data indicate that mouse chromosome 2 harbors two major genes associated with the severities of nephropathy induced by Tensin2 deficiency. The proximal region on chromosome 2 contributes to the resistance to tubulointerstitial fibrosis. In contrast, the distal region on chromosome 2 contributes to the resistance to podocyte injury. This study would be helpful to discover the biological mechanism underlying the renal injury, and may lead to the identification of therapeutic targets.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-016-0378-1) contains supplementary material, which is available to authorized users.

Spontaneous early-onset glomerulonephritis in a 8-week-old male Crj:CD1 (ICR) mouse

Glomerular lesions including membranoproliferative glomerulonephritis occur spontaneously in aged mice, but they are rare in young animals. In our laboratory, spontaneous glomerulonephritis was observed in an 8-week-old male Crj:CD1 (ICR) mouse. Macroscopically, the bilateral kidneys were discolored, but no edema or ascites was observed. Glomerular lesions were characterized by a thickening of capillary walls, a double-contoured basement membrane and mesangial expansion due to increased amounts of matrix. Ultrastructurally, mesangial interposition in the capillary wall and subendothelial deposition of basement membrane-like material were observed. No evidence of immune complex deposition or amyloid was found. On the basis of the observed clinical pathology and histopathology, a secondary form of glomerular lesion was excluded. The glomerular lesion was compatible with glomerulonephritis in a young Crj:CD1 (ICR) mouse.

A Decrease in Glomerular Endothelial Cells and Endothelial-mesenchymal Transition during Glomerulosclerosis in the Tensin2-deficient Mice (ICGN strain)

The ICR-derived glomerulonephritis (ICGN) mouse is a unique model of nephrotic syndrome, and albuminuria becomes evident in a neonatal stage, due to a genetic mutation of tensin2. We previously provided evidence that an apparent decrease in nephrin, caused by tensin2-deficiencient states, leads to podocytopathy, albuminuria and eventually, chronic renal failure. In general, glomerular endothelial cells (ECs) function as a barrier through tight attachment of glomerular basement membrane to podocytes, while decreased ECs can worsen renal failure. Nevertheless, it is still unknown whether glomerular ECs are altered under the tensin-2-deficient states during the manifestation of chronic renal failure. Herein, we examined the changes of glomerular ECs, with focus on the expression of PECAM-1 and VE-cadherin (EC-specific markers), or of α-SMA (myofibroblast marker) in this mouse model by histological methods. Compared with the non-nephrotic (+/nep) mice, the nephrotic (nep/nep) mice exhibited the reduced expression of PECAM-1, or of VE-cadherin, in glomerular area. Notably, some glomerular ECs showed the positive stainings for both PECAM-1 and α-SMA, suggesting endothelial-to-mesenchymal transition (EndoMT) during progression of glomerular sclerosis. This is the first report showing that a decrease in glomerular ECs, at least in part, via EndoMT is involved in tensin2-deficient pathological conditions.

Quantitative trait Loci for resistance to the congenital nephropathy in tensin 2-deficient mice

The ICR-derived glomerulonephritis (ICGN) mouse is a chronic kidney disease (CKD) model that is characterized histologically by glomerulosclerosis, vascular sclerosis and tubulointerstitial fibrosis, and clinically by proteinuria and anemia, which are common symptoms and pathological changes associated with a variety of kidney diseases. Previously, we performed a quantitative trait locus (QTL) analysis to identify the causative genes for proteinuria in ICGN mice, and found a deletion mutation of the tensin 2 gene (Tns2^nph, MGI no: 2447990). Interestingly, the congenic strain carrying the Tns2^nph mutation on a C57BL/6J (B6) genetic background exhibited milder phenotypes than did ICGN mice, indicating the presence of several modifier genes controlling the disease phenotype. In this study, to identify the modifier/resistant loci for CKD progression in Tns2-deficient mice, we performed QTL analysis using backcross progenies from susceptible ICGN and resistant B6 mice. We identified a significant locus on chromosome (Chr) 2 (LOD = 5.36; 31 cM) and two suggestive loci on Chrs 10 (LOD = 2.27; 64 cM) and X (LOD = 2.65; 67 cM) with linkage to the severity of tubulointerstitial injury. One significant locus on Chr 13 (LOD = 3.49; approximately 14 cM) and one suggestive locus on Chr 2 (LOD = 2.41; 51 cM) were identified as QTLs for the severity of glomerulosclerosis. Suggestive locus in BUN was also detected in the same Chr 2 region (LOD = 2.34; 51 cM). A locus on Chr 2 (36 cM) was significantly linked with HGB (LOD = 4.47) and HCT (LOD = 3.58). Four novel epistatic loci controlling either HGB or tubulointerstitial injury were discovered. Further genetic analysis should lead to identification of CKD modifier gene(s), aiding early diagnosis and providing novel approaches to the discovery of drugs for the treatment and possible prevention of kidney disease.

Gene expression analysis detected a low expression level of C1s gene in ICR-derived glomerulonephritis (ICGN) mice

BACKGROUND

ICR-derived glomerulonephritis (ICGN) strain is a novel inbred strain of mice with a hereditary nephrotic syndrome. Deletion mutation of tensin 2 (Tns2), a focal adhesion molecule, has been suggested to be responsible for nephrotic syndrome in ICGN mice; however, the existence of other associative factors has been suggested.

METHODS AND RESULTS

To identify additional associative factors and to better understand the onset mechanism of nephrotic syndrome in ICGN mice, we conducted a comprehensive gene expression analysis using DNA microarray. Immune-related pathways were markedly altered in ICGN mice kidney as compared with ICR mice. Furthermore, the gene expression level of complement component 1, s subcomponent (C1s), whose human homologue has been reported to associate with lupus nephritis, was markedly low in ICGN mouse kidney. Real-time quantitative reverse transcription-polymerase chain reaction confirmed a low expression level of C1s in ICGN mouse liver where the C1s protein is mainly synthesized. A high serum level of anti-dsDNA antibody and deposits of immune complexes were also detected in ICGN mice by enzyme-linked immunosorbent assay and immunohistochemical analyses, respectively.

CONCLUSION

Our results suggest that the immune system, especially the complement system, is associated with nephrotic syndrome in ICGN mice. We identified a low expression level of C1s gene as an additional associative factor for nephrotic syndrome in ICGN mice. Further studies are needed to elucidate the role of the complement system in the onset of nephrotic syndrome in ICGN mice.

Analysis of ultrastructural glomerular basement membrane lesions and podocytes associated with proteinuria and sclerosis in Osborne-Mendel rats with progressive glomerulonephropathy

The renal glomeruli of 12 male Osborne-Mendel (OM) rats 3 to 24 weeks old were examined by electron microscopy. Effacement of podocyte foot processes (FPs) developed at 3 weeks of age and became progressively worse over time. Loss or dislocation of the slit membrane was also found. Vacuoles and osmiophilic lysosomes appeared in the podocytes starting at 6 weeks of age. Podocyte detachment from the glomerular basement membrane (GBM) was apparent at 18 weeks of age. Laminated GBM was occasionally observed in all animals. These features might lead to the development of spontaneous proteinuria and glomerulosclerosis in OM rats.

Proteinuria-induced chronic kidney disease in the ICGN/Oa mice with a mutation of Tensin2 gene

ICGN/Oa mice are used to study the pathophysiological mechanisms underlying proteinuria-induced chronic kidney disease (CKD). Recently, a mutation of tensin2 gene (Tns2) was suggested to be responsible for proteinuria in the inbred ICGN mice. We identified the wild-type (+/+), heterozygous (+/nep), and homozygous (nep/nep) ICGN/Oa mice by PCR assay. The homozygotes developed proteinuria, resulting in nephrotic syndrome (NS) as early as 5 weeks and CKD by 15 weeks. However, the heterozygotes did not show the symptoms of these renal failures. These results indicate that the homozygous tensin2 mutation is necessary for the ICGN/Oa mice to develop proteinuria-induced CKD. Furthermore, we examined the time course of tubulointerstitial fibrosis and the kinetics of tubular epithelial cells (TECs) in the ICGN/Oa mice using immunohistochemical and TUNEL assays. In the renal parenchyma of the five-week-old homozygotes, the expression of alpha-SMA and type I collagen were higher than those in the age-matched wild-type. Additionally, increased TEC proliferation was found at 5 weeks, and increased TEC apoptosis was by 15 weeks in the homozygotes. Tubulointerstitial fibrosis precedes TEC apoptosis in the proteinuria-induced CKD model mice, and that tubulointerstitial fibrosis may be the triggering event of the disease.

Expression of macrophage metalloelastase (MMP-12) in podocytes of hereditary nephrotic mice (ICGN strain)

The Institute for Cancer Research (ICR)-derived glomerulonephritis (ICGN) mouse is a good model for renal fibrosis. In the glomeruli and tubulointerstitium of ICGN mouse kidneys, the components of the extracellular matrix (ECM) accumulated, and matrix metalloproteinases (MMPs) participated in this process. To clarify the mechanism of renal fibrosis, we investigated the expression and localization of macrophage metalloelastase (MMP-12), whose functions in kidney diseases are not fully understood, and its regulatory molecules, monocyte chemoattractive protein-1 (MCP-1) and CC chemokine receptor 2 (CCR2), in the kidneys of ICGN mice by RT-PCR, Western blotting and immunohistochemical staining, respectively. Extensive expression of MMP-12 mRNA and its protein was noted in ICGN mice with progressed nephrotic syndrome. The increase in MMP-12 expression occurred predominantly in podocytes. Furthermore, MCP-1 and CCR2 were also increased in podocytes of the ICGN strain. These results suggest that the expression of MMP-12 is involved in the progression of nephrotic syndrome in ICGN mice.

Deficiency of the tensin2 gene in the ICGN mouse: an animal model for congenital nephrotic syndrome

The ICGN mouse is a model for nephrotic syndrome (NS) which presents with proteinuria, hyperlipidemia, and edema. In this study we attempted to identify the gene(s) responsible for NS. By analyzing albuminuria in 160 (ICGN x MSM)F(1) x ICGN backcross progenies, we found that NS in the ICGN mouse is caused by more than one gene. We then performed a quantitative trait locus (QTL) analysis and detected a QTL with a very high LOD score peak in the telomeric region of Chr 15. By analyzing the nucleotide sequence of 22 genes located close to the QTL, we found that the tensin2 gene of the ICGN mouse possessed an 8-nucleotide deletion mutation in exon 18, leading to a frameshift and giving rise to a terminal codon at a premature position. Analyses of in situ hybridization and immunohistochemistry revealed that tensin2 was expressed in podocytes and tubular epithelial cells in normal mice but not in the ICGN mouse. These data raise the possibility that a mutation of the tensin2 gene is responsible for NS of the ICGN mouse and tensin2 is a prerequisite for the normal kidney function.

Transforming growth factor-β1 mediated up-regulation of lysyl oxidase in the kidneys of hereditary nephrotic mouse with chronic renal fibrosis

Lysyl oxidase (LOX), an extracellular enzyme, plays a key role in the post-translational modification of collagens and elastin, catalyzing inter- and intra-crosslinking reactions. Because the crosslinked extracellular matrices (ECMs) are highly resistant to degradative enzymes, it is considered that the over-expression of LOX may cause severe fibrotic degeneration. In the present study, we addressed the role of LOX-mediated crosslinking in chronic renal tubulointerstitial fibrosis using an animal model of hereditary nephrotic syndrome, the Institute of Cancer Research (ICR)-derived glomerulonephritis (ICGN) mouse. Ribonuclease protection assay (RPA) revealed that LOX mRNA expression was up-regulated in the kidneys of ICGN mice as compared with control ICR mice. High-level expression of LOX and transforming growth factor (TGF)-beta1 (an up-regulator of LOX) mRNA was detected in tubular epithelial cells of ICGN mouse kidneys by in situ hybridization. Type-I and -III collagens, major substrates for LOX, were accumulated in tubulointerstitium of ICGN mouse kidneys. The present findings imply that TGF-beta1 up-regulates the production of LOX in tubular epithelial cells of ICGN mouse kidneys, and the excessive LOX acts on interstitial collagens and catalyzes crosslinking reactions. As a result, the highly crosslinked collagens induce an irreversible progression of chronic renal tubulointerstitial fibrosis in the kidneys of ICGN mice.

Decreased expression of matrix metalloproteinases and tissue inhibitors of metalloproteinase in the kidneys of hereditary nephrotic (ICGN) mice

Matrix metalloporoteinases (MMPs), which are dominantly regulated by tissue inhibitors of metalloproteinase (TIMPs), play important roles in extracellular matrix (ECM) degradation and are involved in the progression of kidney diseases. In glomeruli and tubulointerstitum of hereditary nephrotic (ICR-derived glomerulonephritis: ICGN) mouse kidneys, hyper-accumulation of ECM components occurred, and MMP activity decreased. In the present study, because lower levels of MMP activity may contribute to the progression of renal fibrosis in ICGN mice, Western blotting analysis and immunohistochemical staining for MMPs and TIMPs were performed to verify the expression levels of these proteins. Levels of MMP-2, MMP-9, MT1-MMP, TIMP-1 and TIMP-2 in the kidneys were decreased in ICGN mice in comparison with normal ICR mice. These results indicate that small amounts and low levels of activity of MMPs cause the progression of renal fibrosis in ICGN mice.

Dysfunction of Erythropoietin-Producing Interstitial Cells in the Kidneys of ICR-derived Glomerulonephritis (ICGN) Mice

Anemia is a major secondary symptom in chronic renal disorder (CRD), but the precise cause of insufficient production of erythropoietin (EPO) remains unclear owing to the controversial localization of EPO-producing cells in the kidneys. The ICR-derived glomerulonephritis (ICGN) mouse, a new hereditary nephrotic mouse, is an appropriate model of anemia associated with CRD. By using an amplified in situ hybridization technique, we detected and counted the renal EPO-producing cells under both normoxic and hypoxic conditions. The expression levels of renal EPO mRNA were quantified and oxygen gradients were also assessed immunohistochemically. Amplified in situ hybridization clarified that EPO-producing cells were peritubular interstitial cells in the middle region of renal cortex in both ICR and ICGN mice. Hypoxia (7% O2) induced low oxygen tension in proximal tubular epithelial cells of renal cortex, and increased the expression of EPO mRNA and the number of EPO-producing cells in both ICR and ICGN mice. However, hypoxia did not increase the serum EPO levels in ICGN mice. The ICGN mouse is a good model for anemia associated with CRD, and the suppression of EPO protein production in the renal EPO-producing cells is considered to be a potential cause of anemia associated with CRD.

Improvement of anemia associated with chronic renal failure by recombinant human erythropoietin treatment in ICR-derived glomerulonephritis (ICGN) mice

The ICR-derived glomerulonephritis (ICGN) mouse, a novel inbred mouse strain with a hereditary nephrotic syndrome, develops severe anemia associated with chronic renal failure. To reveal the pathogenic mechanism of anemia in ICGN mice, we subcutaneously administered recombinant human erythropoietin (rhEPO; 5 IU/mouse/day) or saline for 5 days to ICGN mice. In terminal-stage ICGN mice with severe anemia, rhEPO significantly increased hematocrit (Ht), red blood cells (RBC) and hemoglobin levels. Endogenous EPO levels in peripheral blood were reduced by rhEPO injection. No histopathological changes in bone marrow and kidneys were induced by rhEPO injection. Insufficiency of EPO may cause anemia in ICGN mice.

Changes in the localization of type I, III and IV collagen mRNAs in the kidneys of hereditary nephritic (ICGN) mice with renal fibrosis

Renal fibrotic change, extreme accumulation of extracellular matrix (ECM) components in glomeruli and tubulointerstitum, is one of the characteristic features of ICR-derived glomerulonephritis (ICGN) mice. Decreased degradation of ECMs by matrixmetalloproteinases was demonstrated in kidneys of ICGN mice. To determine the balance between production and degradation of ECMs in kidneys of ICGN mice, we examined expression of mRNAs of ECMs in those. To demonstrate the localization of type I, III and IV collagen mRNAs in kidney sections of ICGN and control ICR mice, in situ hybridization using digoxigenin-labeled oligonucleotide antisense probes for procollagen-alpha(1) (I), -alpha(1) (III) and -alpha(1) (IV) mRNAs, respectively, was performed. Negative or trace expressions of type I and III collagen mRNAs were observed in the kidneys of control mice, but stronger expressions of those were seen in glomeruli and injured renal tubules of the kidneys of ICGN mice. Moderate expression of type IV collagen mRNA was demonstrated in a part of glomeruli and renal tubules of both control and ICGN mice, and no remarkable difference was seen between them. Severe renal fibrosis, extreme accumulation of interstitial type I and III collagens is caused by increased production and decreased degradation in the kidneys of ICGN mice. Thus, the profiles of metabolism between interstitial and membranous collagens may be different in the kidneys of ICGN mice, and excessive production of interstitial collagens may be the dominant cause of renal disease in them.

Anemia with Chronic Renal Disorder and Disrupted Metabolism of Erythropoietin in ICR-derived Glomerulonephritis (ICGN) Mice

The ICR-derived glomerulonephritis (ICGN) mouse, a new inbred mouse strain with a hereditary nephrotic syndrome, is considered to be a good model of human idiopathic nephrotic syndrome and notably exhibits proteinuria and hypoproteinemia from the neonatal stage. In chronic renal disorder (CRD), anemia is a major subsequent symptom (renal anemia). The precise cause of renal anemia remains unclear, primarily owing to the lack of appropriate spontaneous animal models for CRD. To establish adequate animal models for anemia with CRD, we examined the hematological-biochemical properties and histopathological characteristics. With the deterioration of renal function, ICGN mice developed a normochromic and normocytic anemia, and exhibited normochromic and microcytic at the terminal stage. The expression of erythropoietin (EPO) mRNA both in the kidneys and liver and the EPO leak into the urine were observed in ICGN mice, indicating a disrupted metabolism of EPO in ICGN mice. In addition, a lack of iron induced by the hemolysis in the spleen and the leak of transferrin into urine as proteinuria aggravated the anemic condition. In conclusion, the ICGN mouse is a good model for anemia with CRD.

Localization of extracellular matrix receptors in ICGN mice, a strain of mice with hereditary nephrotic syndrome

Fibrotic degeneration was examined in the kidneys of ICR-derived glomerulonephritis (ICGN) mice, a novel inbred mouse line with a hereditary nephrotic syndrome of unknown etiology considered to be a good model of human idiopathic nephrotic syndrome. In the present study, we histochemically revealed changes in accumulation of extracellular matrix (ECM) components and in localization of integrins, cellular receptors for ECM, in the kidneys of ICGN mice with the progression of renal failure. Excessive accumulation of basement membrane (laminin and collagen IV) and interstitial (type III collagen) ECM components were demonstrated in the glomeruli and tubulointerstitum of ICGN mice. Marked deposition of type I collagen and tenascin was seen only in the glomeruli of ICGN mice but not in those of ICR mice as normal controls. Increased expression of integrin alpha1-, alpha2-, alpha5- and beta1-subunits in glomeruli with fibrotic degeneration and abnormal distribution of alpha6-subunit were noted in the kidneys of ICGN mice. Excessive laminin, a ligand of alpha6beta1-integrin, was demonstrated on the tubular basement membrane, but alpha6-subunit diffusely disappeared on the basal side of the tubular epithelial cells. We presumed that abnormal integrin expression in renal tubules causes epithelial cell detachment, and consequently tubular nephropathy, and results in disorder of ECM metabolism causing excessive accumulation of ECM components in the kidneys of ICGN mice.

Localization of proliferative and apoptotic cells in the kidneys of ICR-derived glomerulonephritis (ICGN) mice

The ICR-derived glomerulonephritis (ICGN) mouse is a novel inbred mouse strain with a hereditary nephrotic syndrome, considered to be a good model of human idiopathic nephrotic syndrome and develops proteinuria, hypoproteinemia and anemia. In the present study, we compared the cell kinetics in the kidneys of ICGN mice with age-matched ICR mice as normal controls. The proliferating cells were visualized by 5-bromo-2'-deoxyuridine labeling, and apoptotic cells were determined by terminal deoxynucleotidyl transferase-mediated biotinylated deoxyuridine triphosphate nick end-labeling. Many proliferating epithelial cells of renal tubules, glomerular mesangial cells and tublointerstitial fibroblast-like cells were observed in the kidneys of ICGN mice, but no proliferating cells were seen in the kidneys of ICR mice. Apoptotic cells had round nuclei, and were observed only in the tubulointerstitium in the kidneys of ICGN mice but not in that of controls. The proliferation of renal tubular epithelial cells may represent a compensatory response, and that of mesangial and fibroblast-like cells may play a pathogenic role in nephrotic syndrome. Apoptosis in tubulointerstitial cells with round nuclei may have been erythropoietin-producing cells, and probably caused anemia.

Characteristic changes in carbohydrate profile in the kidneys of hereditary nephrotic mice (ICGN strain)

The ICR-derived glomerulonephritis (ICGN) mice consist of heterozygous and homozygous groups and are considered to be a good model for human idiopathic nephrotic syndrome. To reveal changes in cell-surface carbohydrate construction, 24 lectins were applied to kidney sections of 10-, 30- and 50-week-old male heterozygous and homozygous ICGN mice and age-matched male ICR mice. Bandeiraea simplicifolia lectin-I (BSL-I), which specifically binds to alpha-D-galactopyranosyl groups, showed positive staining in the glomeruli of ICGN mice, but not in those of ICR mice. Positive BSL-I staining was observed only in distal tubules of homozygous ICGN mice. Lectin blotting for BSL-I demonstrated characteristic glycoproteins (45, 58 and 64 kD) in ICGN but not in ICR mice, and the levels of these molecules augmented in homozygous ICGN mice with the progression of renal failure. Moreover, succinylated wheat germ agglutinin, Dolichos biflorus agglutinin, Aleuria aurantia lectin and Ulex europaeus agglutinin-I showed positive staining only in the glomeruli of homozygous ICGN mice, but not in those of heterozygous ICGN or ICR mice. The staining intensities of Ricinus communis agglutinin-I, Phaseolus vulgaris agglutinin-E and -L, Lens culinaris agglutinin and Erythrina cristagalli agglutinin (ECL) in the glomeruli of homozygous ICGN mice were stronger than those of heterozygous ICGN and ICR mice. In conclusion, lectin histochemistry provided useful information for the diagnosis and prognosis of nephrotic lesions. Characteristic BSL-I binding glycoproteins may be pathogenic factors which cause renal disease in ICGN mice and are good tools to investigate the molecular mechanism of renal disorders in ICGN mice.

Abnormalities of extracellular matrices and transforming growth factor beta1 localization in the kidney of the hereditary nephrotic mice (ICGN strain)

ICR-derived strain with glomerulonephritis (ICGN) is a strain of mice with hereditary nephrotic syndrome with an unidentified cause. Based on histopathological and biochemical data, ICGN mice are considered to be a good experimental model for human idiopathic nephrotic syndrome. In the present study, we histochemically investigated the changes in localization of extracellular matrix (ECM) components and transforming growth factor beta1 (TGF-beta1). Strong immunohistochemical staining of basal membrane ECM components (collagen IV and laminin) and interstitial ECM components (type III collagen and fibronectin) were demonstrated in glomeruli and tubulointerstitum of ICGN mice as compared with those of sex and age-matched ICR mice, used as normal healthy controls. Marked type I collagen and tenascin deposition, which were not detected in the glomeruli of ICR mice, were seen in the glomeruli of ICGN mice. A remarkable increase in active-TGF-beta1 was also detected only in glomeruli of ICGN mice, but not in those of ICR mice. Furthermore, strikingly increased alpha-smooth muscle actin, a marker of activated glomerular mesangial cells, was demonstrated in the glomeruli, mainly in the mesangial cells, of ICGN mice. These findings indicated that ECM components are increased in the glomerulus and tubulointerstitum of ICGN mice, and that active-TGF-beta1 induces such increases in ECM components. The present findings may contribute to elucidation of the pathogenic mechanisms of hereditary nephrotic syndrome in ICGN mice and, in future, human idiopathic nephrotic syndrome.

Preventive effect of ACE inhibitor on interstitial myofibroblast formation and matrix deposition in a nephrotic model

The nephrotic mouse (ICGN strain) is a useful model for progressive nephrotic syndrome (NS). In the present study, we demonstrated the preventive effects of enalapril, an angiotensin converting enzyme (ACE) inhibitor, on the progression of renal dysfunction and tubulo-interstitial fibrosis in the NS mice. Administration of enalapril (5 mg/dL in drinking water) to the 4-week-old NS mice for a 4-week-period did not improve their nephrotic symptoms such as albuminuria and hypoalbuminemia, but significantly suppressed the increases in blood urea nitrogen and serum creatinine levels. Renal histopathology demonstrated that the administration of the ACE inhibitor significantly attenuated the progression of the tubular and interstitial lesions (tubular dilatation, luminal cast accumulation and interstitial expansion) rather than the glomerular sclerotic changes. The suppression of the increase in blood urea nitrogen level by enalapril depended on the attenuated tubular injury rather than on the unchanged glomerular matrix deposition. Immunohistochemical examination revealed that the administration of the ACE inhibitor suppressed the formation of myofibroblasts, identified by the alpha-smooth muscle actin-positive cells, in the interstitial spaces. Consequently, interstitial matrix deposition was significantly reduced in the NS mice treated with enalapril. From the results obtained with the spontaneous nephrotic model, we emphasize a possibility that ACE inhibitor may be effective for attenuating progression of renal dysfunction and fibrosis in human NS, even if the ACE inhibitor fails to improve nephrotic symptoms such as albuminuria and hypoalbuminemia.

In vitro fertilization and microinsemination with round spermatids for propagation of nephrotic genes in mice

The ICGN is an inbred strain of mice with a hereditary nephrotic syndrome of an unknown cause. The disease progresses to renal failure, resulting in the deterioration of the systemic condition and in a drastic reduction of reproductive capacity. The present study was undertaken to determine if in vitro fertilization (IVF) and microinsemination using round spermatids could ameliorate the reduced fertility of ICGN mice. Mature oocytes (9.4 +/- 1.1 per mouse) were obtained from PMSG/hCG-primed females 2 to 5 mo of age. When spermatozoa from males aged 3 to 4 mo was used for IVF, a high fertilization rate (82.6%) was achieved and a high rate of embryos developed into blastocysts (92.6%). When spermatozoa from males aged 5 to 7 mo was used, the rates of fertilization and development to blastocysts were significantly lower (63.9 and 47.1%, respectively; P < 0.001). However, the production rate of offspring after embryo transfer was satisfactory irrespective of the age of males (59.1%). When males older than 9 mo were used, no fertilization was achieved due to the very poor motility of the spermatozoa. Microinsemination techniques with round spermatids (electrofusion and intracytoplasmic injection) resulted in the production of normal offspring from the older males, including one azoospermic case. These findings indicate that a conventional IVF technique and microinsemination using round spermatids can be used for propagating mutant genes which cause poor reproductive ability in mice.