Unique glomerular lesion with spontaneous lipid deposition in glomerular capillary lumina in the NON strain of mice

Experimental animal models for diabetes and its related complications-a review

Diabetes mellitus, a very common and multifaceted metabolic disorder is considered as one of the fastest growing public health problems in the world. It is characterized by hyperglycemia, a condition with high glucose level in the blood plasma resulting from defects in insulin secretion or its action and in some cases both the impairment in secretion and also action of insulin coexist. Historically, animal models have played a critical role in exploring and describing malady pathophysiology and recognizable proof of targets and surveying new remedial specialists and in vivo medicines. In the present study, we reviewed the experimental models employed for diabetes and for its related complications. This paper reviews briefly the broad chemical induction of alloxan and streptozotocin and its mechanisms associated with type 1 and type 2 diabetes. Also we highlighted the different models in other species and other animals.

Revisiting Experimental Models of Diabetic Nephropathy

Diabetes prevalence is constantly increasing and, nowadays, it affects more than 350 million people worldwide. Therefore, the prevalence of diabetic nephropathy (DN) has also increased, becoming the main cause of end-stage renal disease (ESRD) in the developed world. DN is characterized by albuminuria, a decline in glomerular filtration rate (GFR), hypertension, mesangial matrix expansion, glomerular basement membrane thickening, and tubulointerstitial fibrosis. The therapeutic advances in the last years have been able to modify and delay the natural course of diabetic kidney disease (DKD). Nevertheless, there is still an urgent need to characterize the pathways that are involved in DN, identify risk biomarkers and prevent kidney failure in diabetic patients. Rodent models provide valuable information regarding how DN is set and its progression through time. Despite the utility of these models, kidney disease progression depends on the diabetes induction method and susceptibility to diabetes of each experimental strain. The classical DN murine models (Streptozotocin-induced, Akita, or obese type 2 models) do not develop all of the typical DN features. For this reason, many models have been crossed to a susceptible genetic background. Knockout and transgenic strains have also been created to generate more robust models. In this review, we will focus on the description of the new DN rodent models and, additionally, we will provide an overview of the available methods for renal phenotyping.

Animal Models of Diabetes-Associated Renal Injury

Diabetic nephropathy (DN) is the main factor leading to end-stage renal disease (ESRD) and subsequent morbidity and mortality. Importantly, the prevalence of DN is continuously increasing in developed countries. Many rodent models of type 1 and type 2 diabetes have been established to elucidate the pathogenesis of diabetes and examine novel therapies against DN. These models are developed by chemical, surgical, genetic, drug, and diet/nutrition interventions or combination of two or more methods. The main characteristics of DN including a decrease in renal function, albuminuria and mesangiolysis, mesangial expansion, and nodular glomerulosclerosis should be exhibited by an animal model of DN. However, a rodent model possessing all of the abovementioned features of human DN has not yet been developed. Furthermore, mice of different genetic backgrounds and strains show different levels of susceptibility to DN with respect to albuminuria and development of glomerular and tubulointerstitial lesions. Therefore, the type of diabetes, development of nephropathy, duration of the study, cost of maintaining and breeding, and animals' mortality rate are important factors that might be affected by the type of DN model. In this review, we discuss the pros and cons of different rodent models of diabetes that are being used to study DN.

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.

Identification of novel genes associated with renal tertiary lymphoid organ formation in aging mice

A hallmark of aging-related organ deterioration is a dysregulated immune response characterized by pathologic leukocyte infiltration of affected tissues. Mechanisms and genes involved are as yet unknown. To identify genes associated with aging-related renal infiltration, we analyzed kidneys from aged mice (≥20 strains) for infiltrating leukocytes followed by Haplotype Association Mapping (HAM) analysis. Immunohistochemistry revealed CD45⁺ cell clusters (predominantly T and B cells) in perivascular areas coinciding with PNAd⁺ high endothelial venules and podoplanin⁺ lymph vessels indicative of tertiary lymphoid organs. Cumulative cluster size increased with age (analyzed at 6, 12 and 20 months). Based on the presence or absence of clusters in male and female mice at 20 months, HAM analysis revealed significant associations with loci on Chr1, Chr2, Chr8 and Chr14 in male mice, and with loci on Chr4, Chr7, Chr13 and Chr14 in female mice. Wisp2 (Chr2) showed the strongest association (P = 5.00×10⁻¹³⁷) in male mice; Ctnnbip1 (P = 6.42×10⁻²⁶⁷) and Tnfrsf8 (P = 5.42×10⁻²⁴⁵) (both on Chr4) showed the strongest association in female mice. Both Wisp2 and Ctnnbip1 are part of the Wnt-signaling pathway and the encoded proteins were expressed within the tertiary lymphoid organs. In conclusion, this study revealed differential lymphocytic infiltration and tertiary lymphoid organ formation in aged mouse kidneys across different inbred mouse strains. HAM analysis identified candidate genes involved in the Wnt-signaling pathway that may be causally linked to tertiary lymphoid organ formation.

Mouse models of diabetic nephropathy

Diabetic nephropathy is a major cause of ESRD worldwide. Despite its prevalence, a lack of reliable animal models that mimic human disease has delayed the identification of specific factors that cause or predict diabetic nephropathy. The Animal Models of Diabetic Complications Consortium (AMDCC) was created in 2001 by the National Institutes of Health to develop and characterize models of diabetic nephropathy and other complications. This interim report and our online supplement detail the progress made toward that goal, specifically in the development and testing of murine models. Updates are provided on validation criteria for early and advanced diabetic nephropathy, phenotyping methods, the effect of background strain on nephropathy, current best models of diabetic nephropathy, negative models, and views of future directions. AMDCC investigators and other investigators in the field have yet to validate a complete murine model of human diabetic kidney disease. Nonetheless, the critical analysis of existing murine models substantially enhances our understanding of this disease process.

Animal models of obesity-associated chronic kidney disease

Dramatic advances in basic science have been made in the past 50 years on the basis of animal models of obesity and type II diabetes. Positional-cloning strategies in rodents with spontaneous obesity have enabled landmark scientific breakthroughs and defined the molecular scaffolding for the regulation of energy homeostasis. Recently, studies in the general population suggest that obesity is an independent risk factor for chronic kidney disease. To date, most of the animal studies that investigated chronic kidney disease associated with obesity and type II diabetes have largely been descriptive. We aim to provide an overview of animal models used to investigate the mechanisms of obesity-associated chronic kidney disease. Our overview is not meant to be an exhaustive list of all animal models in the literature on this subject, but rather to illustrate the experimental approaches. Because of space limitations, we have chosen to concentrate on rodent models. These animal models will provide excellent tools for in vivo testing of molecular mechanisms. Further hypothesis-driven research into the mechanism of chronic kidney disease and their progression by use of these models will provide important insights necessary to develop therapeutic strategies for this significant complication of the worldwide epidemic of obesity and type II diabetes.

Leukocyte recruitment and vascular injury in diabetic nephropathy

Different types of activated leukocytes play a crucial role in the pathogenesis of most kidney diseases from acute to chronic stages; however, diabetic nephropathy was not considered an inflammatory disease in the past. This view is changing now because there is a growing body of evidence implicating inflammatory cells at every stage of diabetic nephropathy. Renal tissue macrophages, T cells, and neutrophils produce various reactive oxygen species, proinflammatory cytokines, metalloproteinases, and growth factors, which modulate the local response and increase inflammation within the diabetic kidney. Although the precise mechanisms that direct leukocyte homing into renal tissues are not fully identified, it has been reported that intercellular adhesion molecule-1 and the chemokines CCL2 and CX3CL1 probably are involved in leukocyte migration in diabetic nephropathy. This review focuses on the molecular mechanisms of leukocyte recruitment into the diabetic kidney and the involvement of immigrated immune cells in the damage to renal tissues.

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

BACKGROUND

Despite multiple causes, Chronic Kidney Disease is commonly associated with proteinuria. A previous study on Non Obese Diabetic mice (NOD), which spontaneously develop type 1 diabetes, described histological and gene expression changes incurred by diabetes in the kidney. Because proteinuria is coincident to diabetes, the effects of proteinuria are difficult to distinguish from those of other factors such as hyperglycemia. Proteinuria can nevertheless be induced in mice by peritoneal injection of Bovine Serum Albumin (BSA). To gain more information on the specific effects of proteinuria, this study addresses renal changes in diabetes resistant NOD-related mouse strains (NON and NOD.B10) that were made to develop proteinuria by BSA overload.

METHODS

Proteinuria was induced by protein overload on NON and NOD.B10 mouse strains and histology and microarray technology were used to follow the kidney response. The effects of proteinuria were assessed and subsequently compared to changes that were observed in a prior study on NOD diabetic nephropathy.

RESULTS

Overload treatment significantly modified the renal phenotype and out of 5760 clones screened, 21 and 7 kidney transcripts were respectively altered in the NON and NOD.B10. Upregulated transcripts encoded signal transduction genes, as well as markers for inflammation (Calmodulin kinase beta). Down-regulated transcripts included FKBP52 which was also down-regulated in diabetic NOD kidney. Comparison of transcripts altered by proteinuria to those altered by diabetes identified mannosidase 2 alpha 1 as being more specifically induced by proteinuria.

CONCLUSION

By simulating a component of diabetes, and looking at the global response on mice resistant to the disease, by virtue of a small genetic difference, we were able to identify key factors in disease progression. This suggests the power of this approach in unraveling multifactorial disease processes.

Diabetic nephropathy: of mice and men

Accumulating evidence supports intrinsic genetic susceptibility as an important variable in the progression of diabetic nephropathy in people. Mice provide an experimental platform of unparalleled power for dissecting the genetics of mammalian diseases; however, phenotypic analysis of diabetic mice lags behind that already established for humans. Standardized benchmarks of hyperglycemia, albuminuria, and measurements of renal failure remain to be developed for different inbred strains of mice. The most glaring deficiency has been the lack of a diabetic mouse model that develops progressively worsening renal insufficiency, the sine qua non of diabetic nephropathy in humans. Differences in susceptibility of these inbred strains to complications of diabetes mellitus provide a possible avenue to dissect the genetic basis of diabetic nephropathy; however, the identification of those strains and/or mutants most susceptible to renal injury from diabetes mellitus is lacking. Identification of a mouse model that faithfully mirrors the pathogenesis of DN in humans will undoubtedly facilitate the development of new diagnostic and therapeutic interventions.

Mouse models of diabetic nephropathy

Mice provide an experimental model of unparalleled flexibility for studying mammalian diseases. Inbred strains of mice exhibit substantial differences in their susceptibility to the renal complications of diabetes. Much remains to be established regarding the course of diabetic nephropathy (DN) in mice as well as defining those strains and/or mutants that are most susceptible to renal injury from diabetes. Through the use of the unique genetic reagents available in mice (including knockouts and transgenics), the validation of a mouse model reproducing human DN should significantly facilitate the understanding of the underlying genetic mechanisms that contribute to the development of DN. Establishment of an authentic mouse model of DN will undoubtedly facilitate testing of translational diagnostic and therapeutic interventions in mice before testing in humans.

Gene expression profile in streptozotocin-induced diabetic mice kidneys undergoing glomerulosclerosis

BACKGROUND

To elucidate the molecular mechanism of diabetic nephropathy, a high-density DNA filter array was employed to survey the gene expression profile of streptozotocin-induced diabetic CD-1 (ICR) mouse kidneys.

METHODS

Ten-week-old CD-1 male mice were divided into four groups: (1) control, (2) unilaterally nephrectomized (UX) mice, (3) streptozotocin (STZ)-induced diabetic (STZ) mice, and (4) STZ mice with unilateral renal ablation (STZ-UX). Pathological changes were examined at 24 weeks after the induction. The gene expression profile was compared between the control and STZ mice by a Gene Discovery Array (GDA).

RESULTS

The glomeruli in UX mouse kidney showed prominent glomerular hypertrophy, while the accumulation of mesangial matrix was minimal. Both STZ and STZ + UX mice had significant glomerular hypertrophy and glomerulosclerosis, and the lesions were not enhanced by renal ablation. By comparison between control and STZ mice, 16 clones that increased in expression with the induction of diabetes and 65 clones that decreased in diabetic kidneys were identified. The 37 known genes were related to glucose and lipid metabolism, ion transport, transcription factors, signaling molecules, and extracellular matrix-related molecules. The genes known to be involved in cell differentiation and organogenesis in various tissues (that is, Unc-18 homolog, POU domain transcription factor 2, lunatic fringe gene homolog, fibrous sheath component 1, Sox-17, fibulin 2, and MRJ) were found to be differentially expressed in the early phase of diabetic kidneys.

CONCLUSIONS

Hyperglycemia is a major determinant of glomerulosclerosis in STZ-induced diabetic CD-1 mice, and the altered gene expression in the early phase of diabetic kidney may be critical for the development of diabetic nephropathy.

Progressive adriamycin nephropathy in mice: sequence of histologic and immunohistochemical events

BACKGROUND

As an experimental analogue of human focal glomerular sclerosis (FGS), adriamycin (ADR)-induced nephropathy is well-characterized in rats. Previously, this model has not been fully established in mice. The extension of this model to the mouse would be useful in the application of genetic and monoclonal antibody technology to characterize mechanisms of progressive renal disease. Herein, we describe a stable and reproducible murine model of chronic proteinuria induced by ADR.

METHODS

Male BALB/c mice were intravenously injected with a single dose of ADR (10 to 11 mg/kg). Seven mice were sacrificed at weeks 1, 2, 4, and 6. Renal function, quantitative morphometric analysis, and electron microscopic studies were performed. Peripheral CD4+ and CD8+ T cells were evaluated using flow cytometric analysis of splenocytes. The leukocytic inflammatory pattern was analyzed by immunohistochemical examination.

RESULTS

Overt proteinuria was observed from day 5 and remained significantly elevated throughout the study period. A focal increase in reabsorption droplets in tubular cells appeared at weeks 1 and 2, and numerous intraluminal casts were present after two weeks. Glomerular vacuolation and mild FGS appeared at week 4. At week 6, extensive focal and even global glomerular sclerosis, associated with moderate interstitial expansion and severe inflammation, were observed. A prominent macrophage infiltration appeared within both interstitium and glomeruli at week 2, followed by accumulation of both CD4+ and CD8+ T cells in interstitium but not glomeruli. There were almost no B lymphocytes seen at any time.

CONCLUSION

This model should be useful in unraveling the pathogenesis of glomerular and interstitial inflammation and fibrosis in chronic proteinuric renal disease.

Peculiar membranogranular glomerular deposits

Two patients with immune complex diseases, one with IgA nephropathy and the other with systemic lupus erythematosus, were found to have peculiar membranogranular deposits in the glomeruli in addition to typical immune complex deposits. There was no clinical indication of familial lipodosis in either case. The deposits were very similar to those seen in lecithin-cholesterol acyltransferase-deficient patients. The pathogenetic role of lipid deposits in the glomerulus is discussed.