Glomerular extracellular matrices and anionic sites in aging ddY mice: a morphometric study

Single-cell transcriptome atlas in C57BL/6 mice encodes morphological phenotypes in the aging kidneys

C57BL/6 mice are frequently utilized as murine models with the desired genetic background for altertion in multiple research contexts. So far, there is still a lack of comprehensive kidney morphology and single-cell transcriptome atlas at all stages of growth of C57BL/6 mice. To provide an interactive set of reference standards for the scientific community, we performed the current study to investigate the kidney's development throughout the capillary-loop stage until senescence. Eight groups, with five to six mice each, represented embryonic stage (embryos 18.5 days), suckling period (1 day after birth), juvenile stage (1 month old), adulthood (containing 3 months old, 6 months old and 10 months old), reproductive senescence stage (20 months old), and post-senescence stage (30 months old), respectively. With age, the thickness of the glomerular basement membrane (GBM) was increased. Notably, GBM knobs appeared at three months and became frequent with age. Using single-cell transcriptome data, we evaluated how various biological process appear in particular cell types and investigated the potential mechanism of formation of GBM konbs. In conclusion, having access to detailed kidney morphology and single-cell transcriptome maps from C57BL/6 mice at various developmental stages of C57BL/6 mice would be a novel and major resource for biological research and testing of prospective therapeutic approaches.

Knockout of aminopeptidase A in mice causes functional alterations and morphological glomerular basement membrane changes in the kidneys

Aminopeptidase A is one of the most potent enzymes within the renin-angiotensin system in terms of angiotensin II degradation. Here, we examined whether there is a kidney phenotype and any compensatory changes in other renin angiotensin system enzymes involved in the metabolism of angiotensin II associated with aminopeptidase A deficiency. Kidneys harvested from aminopeptidase A knockout mice were examined by light and electron microscopy, immunohistochemistry and immunofluorescence. Kidney angiotensin II levels and the ability of renin angiotensin system enzymes in the glomerulus to degrade angiotensin II ex vivo, their activities, protein and mRNA levels in kidney lysates were evaluated. Knockout mice had increased blood pressure and mild glomerular mesangial expansion without significant albuminuria. By electron microscopy, knockout mice exhibited a mild increase of the mesangial matrix, moderate thickening of the glomerular basement membrane but a striking appearance of knob-like structures. These knobs were seen in both male and female mice and persisted after the treatment of hypertension. In isolated glomeruli from knockout mice, the level of angiotensin II was more than three-fold higher as compared to wild type control mice. In kidney lysates from knockout mice angiotensin converting enzyme activity, protein and mRNA levels were markedly decreased possibly as a compensatory mechanism to reduce angiotensin II formation. Thus, our findings support a role for aminopeptidase A in the maintenance of glomerular structure and intra-kidney homeostasis of angiotensin peptides.

Pathological application of carbocyanine dye-based multicolour imaging of vasculature and associated structures

Simultaneous visualisation of vasculature and surrounding tissue structures is essential for a better understanding of vascular pathologies. In this work, we describe a histochemical strategy for three-dimensional, multicolour imaging of vasculature and associated structures, using a carbocyanine dye-based technique, vessel painting. We developed a series of applications to allow the combination of vessel painting with other histochemical methods, including immunostaining and tissue clearing for confocal and two-photon microscopies. We also introduced a two-photon microscopy setup that incorporates an aberration correction system to correct aberrations caused by the mismatch of refractive indices between samples and immersion mediums, for higher-quality images of intact tissue structures. Finally, we demonstrate the practical utility of our approach by visualising fine pathological alterations to the renal glomeruli of IgA nephropathy model mice in unprecedented detail. The technical advancements should enhance the versatility of vessel painting, offering rapid and cost-effective methods for vascular pathologies.

The podocyte-specific inactivation of Lmx1b, Ldb1 and E2a yields new insight into a transcriptional network in podocytes

Patients with nail-patella syndrome, which among other symptoms also includes podocyte-associated renal failure, suffer from mutations in the LMX1B gene. The disease severity among patients is quite variable and has given rise to speculations on the presence of modifier genes. Promising candidates for modifier proteins are the proteins interacting with LMX1B, such as LDB1 and E47. Since human kidney samples from patients are difficult to obtain, conventional Lmx1b knock-out mice have been extremely valuable to study the role of Lmx1b in podocyte differentiation. In contrast to findings in these mice, however, in which a downregulation of the Col4a3, Col4a4 and Nphs2 genes has been described, no such changes have been detected in kidney biopsies from patients. We now report on our results on the characterization of constitutive podocyte-specific Lmx1b, Ldb1 and E2a knock-out mice. Constitutive podocyte-specific Lmx1b knock-out mice survive for approximately 2 weeks after birth and do not present with a downregulation of the Col4a3, Col4a4 and Nphs2 genes, therefore they mimic the human disease more closely. The podocyte-specific Ldb1 knock-out mice survive longer, but then also succumb to renal failure, whereas the E2a knock-out mice show no renal symptoms for at least 6 months after birth. We conclude that LDB1, but not E2A is a promising candidate as a modifier gene in patients with nail-patella syndrome.

DDR1-deficient mice show localized subepithelial GBM thickening with focal loss of slit diaphragms and proteinuria

BACKGROUND

Type IV collagen in basement membranes is a ligand for the receptor tyrosine kinase discoidin domain receptor 1 (DDR1). DDR1 is expressed in renal cells and regulates cell adhesion and proliferation ex vivo. The interaction between type IV collagen and cell surface receptors is believed important for normal renal function as well as significant in chronic renal diseases and we therefore analyzed mice with a targeted deletion of DDR1.

METHODS

Homozygous DDR1 knockout mice were compared to heterozygous and wild-type animals. The quantitative and qualitative amount of proteinuria was measured by urine-microelectrophoresis. Structural changes of the kidneys were determined by immunohistochemistry, light microscopy, and electron microscopy.

RESULTS

Compared to heterozygous littermates, adult DDR1 knockout mice showed a selective middle- to high-molecular proteinuria of up to 0.3 g/L and urinary acanthocytes. There was no evidence of uremia with no change in serum urea in the first 9 months of age. Little apparent change in renal morphology was detected using light microscopy. However, electron microscopy showed a localized, subepithelial, mushroom-like isodense thickening of the glomerular basement membrane (GBM). Within these areas, a focal loss of the podocytic slit diaphragms occurred.

CONCLUSION

The loss of cell-matrix communication in DDR1-deficient podocytes appears to result in excess synthesis of basement membrane proteins leading to disturbed anchorage of foot processes and disruption of the slit diaphragm. Our data suggest that the interaction between type IV collagen and DDR1 plays an important role in maintaining the structural integrity of the GBM.

Special cytochemistry in cell biology

Cytochemistry is a science of localizing chemical components of cells and organelles on histological sections by using various techniques. We first aimed at studying cytochemistry by developing new techniques using various principles such as enzyme cytochemistry, microincineration, microspectrophotometry, radioautography, cryo-techniques, X-ray microanalysis and immunocytochemistry. We first concentrated on developing methodologies in the 1960s to 1970s. We then applied these special techniques to various kinds of cells in men and animals. Earlier, I proposed to classify these methods into three categories, i.e., chemical, physical, and biological techniques. The methodology has been well developed to form a new science which should be designated as "general cytochemistry" similarly to the general histology. On the other hand, these techniques should be applied to various cells in various organ systems, such as the skeletal, muscular, digestive, respiratory, urinary, reproductive, endocrine, circulatory, nervous and sensory systems similarly to the special histology or the histology of organs. I summarize the results of cytochemical studies on cells of various organs carried out in our laboratory during these 44 years since 1955. The results obtained from cytochemical studies applied to various cells in respective organ systems should be designated as "special cytochemistry."

Kidney disease in aging

There is an increasing number of elderly patients with glomerulonephritis. A number of reports regarding renal function [1-9] and morphology [10-13] in aged people have been published. However, few studies have been reported on the effect of glomerulonephritis on the kidneys of aged patients. Recently, some articles concerning renal function and histological changes in aged nephritic patients were reported [14]. Several reports about the effects of aging in an experimental kidney disease model [15-23] and on cultured renal cells [22, 24, 25] have been published. This review will focus mainly on the mechanisms of the decrease in renal function and morphological changes with aging.

Alteration of anionic sites in renal glomerular basement membrane of pigs

Ultrastructural alteration of anionic sites (ASs) in the glomerular basement membrane (GBM) was studied in 10 cases of swine mesangial proliferative glomerulonephritis using a cationic ultrastructural tracer, 0.5% polyethyleneimine (M.W. = 1,800). Glomerular ASs were seen as discrete electron-dense particles in the GBM, mesangial matrix and epithelial cell surfaces by electron microscopy. In the lamina rara externa (LRE) of the normal GBM, ASs were distributed regularly in a single layer. In those areas of the LRE that contained electron dense deposits or clusters of spherical microparticles (SMPs), however, a distinct reduction or loss of ASs was observed in all the pigs. Quantitative assessment of ASs in the LRE over 1,000 nm of the GBM revealed a significant reduction in ASs in one case with diffuse global thickening of the GBM as compared with the remaining nine pigs without GBM thickening (P < 0.001, Mann-Whitney's U-test). There were no ASs in the lamina densa (LD) of the normal GBM, but an irregular distribution of ASs was seen within the LD of the pig showing diffuse global thickening of the GBM. These results suggest that a disturbance of the charge-selective barrier in the GBM may be induced by electron-dense deposits or SMPs, in the LRE as well as thickening of the GBM in swine glomerulonephritis.

Enhanced production of glomerular extracellular matrix in a new mouse strain of high serum IgA ddY mice

To investigate the relationship between high serum levels of IgA and glomerular lesions, selective mating was performed in high serum IgA ddY mice, a murine model of spontaneously developing mesangioproliferative glomerulonephritis mimicking human IgA nephropathy. The selection and mating of high IgA ddY mice were accomplished when the mice were three to four months old. In the 12th generation of high IgA ddY (HIGA) mice, significantly higher levels of serum IgA from 10 age weeks to 60 weeks (P < 0.0002 to 0.0001) were observed in comparison with BALB/c mice. Relatively high proteinuria was observed at 40 weeks of age, although hematuria was consistently negative. Microscopic observations of renal tissue disclosed a marked glomerular mesangial matrix increase and a reduction of cell proliferation with age by both semiquantitative and morphometric analyses with moderate tubulointerstitial damage. These mesangial matrices were stained markedly by antisera for collagen type IV and by fibronectin, but not by collagen type I. Localization of TGF-beta protein was also detected in the mesangium of the HIGA mice. The positive mesangial IgA deposition was maintained consistently by this mating procedure and became more marked with age. Size analysis of IgA from ten pooled HIGA mice aged 50 to 60 weeks revealed dominant polymeric IgA in sera and dimeric IgA in glomerular eluates. Clonal analysis of serum IgA disclosed heterogeneous spectrotypes in a wide pH range (4.5 to 6.5), in contrast to very limited spectrotypes in the acidic pH range (4.5 to 5.2) of IgA in the glomerular eluates from these mice. The analyses of retroviral gp70 antigen involvement in the HIGA mice disclosed a significant increase of serum levels of gp70 anti-gp70 immune complexes with age, with no relationship to the severity of glomerular gp70 deposition. Northern blot analysis of renal tissue revealed markedly high mRNA expression of collagen type I, IV, fibronectin and TGF-beta even in 10-week-old HIGA mice in comparison with BALB/c mice. The expression became more significant in 60-week-old animals. The genetic background required to induce the expansion of IgA-producing B-cell clones is suggested to be closely related to the increased gene expression of TGF-beta, which induces enhanced glomerular extracellular matrix (especially fibronectin) accumulation in HIGA mice, being possibly mediated by the mesangial deposition of dimeric and highly acidic IgA. This newly established strain may provide a model for investigating the relationship between progressive glomerular sclerotic lesions and the induction of pathogenic IgA in human IgA nephropathy.

Increased peritoneal permeability to albumin in streptozotocin diabetic rats

The mechanism behind the increased peritoneal permeability to albumin in diabetics is still unclear. In this study, streptozotocin diabetic rats developed albuminuria and significantly increased D/P of albumin after the fourth week of disease, reaching peak levels at the end of the 24 week period of follow-up. Coincidentally, extravasation of albumin to the interstitial tissue was evaluated with the Evans-blue method. Age-matched control rats showed Evans-blue concentrations of 0.023 +/- 0.013 micrograms/100 mg of dry tissue, whereas in diabetics the numbers were 1.22 +/- 0.719 micrograms (P < 0.001). Perfusion with Ruthenium-Red (RR) done in control at zero time, and in age-matched intact as well as in diabetic rats after 24 weeks of disease showed that the density distribution of capillary subendothelial anionic sites was significantly lower for diabetics (13 +/- 3/microns basement membrane vs. 31 +/- 3 and 34 +/- 4 in control groups; P < 0.001). Similar findings were made on the mesenteric submesothelial basement membrane. Mean density of RR decorated anionic sites was 12 +/- 2/microns basement membrane in diabetics, whereas those observed in both control groups were 31 +/- 2 and 31 +/- 3/microns (P < 0.001). Therefore, this reduced density of microvascular and submesothelial negative charges, equivalent to that induced by diabetes in other capillary beds, appears to be at the origin of the decreased permselectivity of the diabetic peritoneum for anionic serum albumin.