Strain differences rather than hyperglycemia determine the severity of glomerulosclerosis in mice

The genetic background significantly impacts the severity of kidney cystic disease in the Pkd1RC/RC mouse model of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD), primarily due to PKD1 or PKD2 mutations, causes progressive kidney cyst development and kidney failure. There is significant intrafamilial variability likely due to the genetic background and environmental/lifestyle factors; variability that can be modeled in PKD mice. Here, we characterized mice homozygous for the PKD1 hypomorphic allele, p.Arg3277Cys (Pkd1^RC/RC), inbred into the BALB/cJ (BC) or the 129S6/SvEvTac (129) strains, plus F1 progeny bred with the previously characterized C57BL/6J (B6) model; F1(BC/B6) or F1(129/B6). By one-month cystic disease in both the BC and 129 Pkd1^RC/RC mice was more severe than in B6 and continued with more rapid progression to six to nine months. Thereafter, the expansive disease stage plateaued/declined, coinciding with increased fibrosis and a clear decline in kidney function. Greater severity correlated with more inter-animal and inter-kidney disease variability, especially in the 129-line. Both F1 combinations had intermediate disease severity, more similar to B6 but progressive from one-month of age. Mild biliary dysgenesis, and an early switch from proximal tubule to collecting duct cysts, was seen in all backgrounds. Preclinical testing with a positive control, tolvaptan, employed the F1(129/B6)-Pkd1^RC/RC line, which has moderately progressive disease and limited isogenic variability. Magnetic resonance imaging was utilized to randomize animals and provide total kidney volume endpoints; complementing more traditional data. Thus, we show how genetic background can tailor the Pkd1^RC/RC model to address different aspects of pathogenesis and disease modification, and describe a possible standardized protocol for preclinical testing.

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.

Pharmacologic control of oxidative stress and inflammation determines whether diabetic glomerulosclerosis progresses or decreases: A pilot study in sclerosis-prone mice

Diabetic kidney disease (DKD) is characterized by progressive glomerulosclerosis (GS). ROP mice have a sclerosis-prone phenotype. However, they develop severe, rapidly progressive GS when rendered diabetic. Since GS also develops in aged C57Bl6 mice, and can be reversed using bone marrow from young mice which have lower oxidative stress and inflammation (OS/Infl), we postulated that this might also apply to DKD. Therefore, this pilot study asked whether reducing OS/Infl in young adult sclerosis-prone (ROP) diabetic mice leads to resolution of existing GS in early DKD using safe, FDA-approved drugs.After 4 weeks of stable streptozotocin-induced hyperglycemia 8-12 week-old female mice were randomized and treated for 22 weeks as follows: 1) enalapril (EN) (n = 8); 2) pyridoxamine (PYR)+EN (n = 8); 3) pentosan polysulfate (PPS)+EN (n = 7) and 4) PPS+PYR+EN (n = 7). Controls were untreated (non-DB, n = 7) and hyperglycemic (DB, n = 8) littermates. PPS+PYR+EN reduced albuminuria and reversed GS in DB. Treatment effects: 1) Anti-OS/Infl defenses: a) PPS+PYR+EN increased the levels of SIRT1, Nrf2, estrogen receptor α (ERα) and advanced glycation endproduct-receptor1 (AGER1) levels; and b) PYR+EN increased ERα and AGER1 levels. 2) Pro-OS/Infl factors: a) PPS+PYR+EN reduced sTNFR1, b) all except EN reduced MCP1, c) RAGE was reduced by all treatments. In summary, PYR+PPS+EN modulated GS in sclerosis-prone hyperglycemic mice. PYR+PPS+EN also decreased albuminuria, OS/Infl and the sclerosis-prone phenotype. Thus, reducing OS/Infl may reverse GS in early diabetes in patients, and albuminuria may allow early detection of the sclerosis-prone phenotype.

Assessment of Kidney Function in Mouse Models of Glomerular Disease

The use of murine models to mimic human kidney disease is becoming increasingly common. Our research is focused on the assessment of glomerular function in diabetic nephropathy and podocyte-specific VEGF-A knock-out mice; therefore, this protocol describes the full kidney work-up used in our lab to assess these mouse models of glomerular disease, enabling a vast amount of information regarding kidney and glomerular function to be obtained from a single mouse. In comparison to alternative methods presented in the literature to assess glomerular function, the use of the method outlined in this paper enables the glomerular phenotype to be fully evaluated from multiple aspects. By using this method, the researcher can determine the kidney phenotype of the model and assess the mechanism as to why the phenotype develops. This vital information on the mechanism of disease is required when examining potential therapeutic avenues in these models. The methods allow for detailed functional assessment of the glomerular filtration barrier through measurement of the urinary albumin creatinine ratio and individual glomerular water permeability, as well as both structural and ultra-structural examination using the Periodic Acid Schiff stain and electron microscopy. Furthermore, analysis of the genes dysregulated at the mRNA and protein level enables mechanistic analysis of glomerular function. This protocol outlines the generic but adaptable methods that can be applied to all mouse models of glomerular disease.

Combining streptozotocin and unilateral nephrectomy is an effective method for inducing experimental diabetic nephropathy in the 'resistant' C57Bl/6J mouse strain

Diabetic nephropathy (DN) is the leading cause of chronic kidney disease. Animal models are essential tools for designing new strategies to prevent DN. C57Bl/6 (B6) mice are widely used for transgenic mouse models, but are relatively resistant to DN. This study aims to identify the most effective method to induce DN in a type 1 (T1D) and a type 2 diabetes (T2D) model in B6 mice. For T1D-induced DN, mice were fed a control diet, and randomised to streptozotocin (STZ) alone, STZ+unilateral nephrectomy (UNx), or vehicle/sham. For T2D-induced DN, mice were fed a western (high fat) diet, and randomised to either STZ alone, STZ+UNx, UNx alone, or vehicle/sham. Mice subjected to a control diet with STZ +UNx developed albuminuria, glomerular lesions, thickening of the glomerular basement membrane, and tubular injury. Mice on control diet and STZ developed only mild renal lesions. Furthermore, kidneys from mice on a western diet were hardly affected by diabetes, UNx or the combination. We conclude that STZ combined with UNx is the most effective model to induce T1D-induced DN in B6 mice. In our hands, combining western diet and STZ treatment with or without UNx did not result in a T2D-induced DN model in B6 mice.

Vascular Endothelial Growth Factor-A165b Restores Normal Glomerular Water Permeability in a Diphtheria-Toxin Mouse Model of Glomerular Injury

BACKGROUND/AIMS

Genetic cell ablation using the human diphtheria toxin receptor (hDTR) is a new strategy used for analysing cellular function. Diphtheria toxin (DT) is a cytotoxic protein that leaves mouse cells relatively unaffected, but upon binding to hDTR it ultimately leads to cell death. We used a podocyte-specific hDTR expressing (Pod-DTR) mouse to assess the anti-permeability and cyto-protective effects of the splice isoform vascular endothelial growth factor (VEGF-A165b).

METHODS

The Pod-DTR mouse was crossed with a mouse that over-expressed VEGF-A165b specifically in the podocytes (Neph-VEGF-A165b). Wild type (WT), Pod-DTR, Neph-VEGF-A165b and Pod-DTR X Neph-VEGF-A165b mice were treated with several doses of DT (1, 5, 100, and 1,000 ng/g bodyweight). Urine was collected and the glomerular water permeability (LpA/Vi) was measured ex vivo after 14 days. Structural analysis and podocyte marker expression were also assessed.

RESULTS

Pod-DTR mice developed an increased glomerular LpA/Vi 14 days after administration of DT (all doses), which was prevented when the mice over-expressed VEGF-A165b. No major structural abnormalities, podocyte ablation or albuminuria was observed in Pod-DTR mice, indicating this to be a mild model of podocyte disease. However, a change in expression and localisation of nephrin within the podocytes was observed, indicating disruption of the slit diaphragm in the Pod-DTR mice. This was prevented in the Pod-DTR X Neph-VEGF-A165b mice.

CONCLUSION

Although only a mild model of podocyte injury, over-expression of the anti-permeability VEGF-A165b isoform in the podocytes of Pod-DTR mice had a protective effect. Therefore, this study further highlights the therapeutic potential of VEGF-A165b in glomerular disease.

VEGF-A165 b protects against proteinuria in a mouse model with progressive depletion of all endogenous VEGF-A splice isoforms from the kidney

Key points

Progressive depletion of all vascular endothelial growth factor A (VEGF‐A) splice isoforms from the kidney results in proteinuria and increased glomerular water permeability, which are both rescued by over‐expression of VEGF‐A₁₆₅b only.

VEGF‐A₁₆₅b rescues the increase in glomerular basement membrane and podocyte slit width, as well as the decrease in sub‐podocyte space coverage, produced by VEGF‐A depletion.

VEGF‐A₁₆₅b restores the expression of platelet endothelial cell adhesion molecule in glomerular endothelial cells and glomerular capillary circumference.

VEGF‐A₁₆₅b has opposite effects to VEGF‐A₁₆₅ on the expression of genes involved in endothelial cell migration and proliferation.

Abstract

Chronic kidney disease is strongly associated with a decrease in the expression of vascular endothelial growth factor A (VEGF‐A). However, little is known about the contribution of VEGF‐A splice isoforms to kidney physiology and pathology. Previous studies suggest that the splice isoform VEGF‐A₁₆₅b (resulting from alternative usage of a 3′ splice site in the terminal exon) is protective for kidney function. In the present study, we show, in a quad‐transgenic model, that over‐expression of VEGF‐A₁₆₅b alone is sufficient to rescue the increase in proteinuria, as well as glomerular water permeability, in the context of progressive depletion of all VEGF‐A isoforms from the podocytes. Ultrastructural studies show that the glomerular basement membrane is thickened, podocyte slit width is increased and sub‐podocyte space coverage is reduced when VEGF‐A is depleted, all of which are rescued in VEGF‐A₁₆₅b over‐expressors. VEGF‐A₁₆₅b restores the expression of platelet endothelial cell adhesion molecule‐1 in glomerular endothelial cells and glomerular capillary circumference. Mechanistically, it increases VEGF receptor 2 expression both in vivo and in vitro and down‐regulates genes involved in migration and proliferation of endothelial cells, otherwise up‐regulated by the canonical isoform VEGF‐A₁₆₅. The results of the present study indicate that manipulation of VEGF‐A splice isoforms could be a novel therapeutic avenue in chronic glomerular disease.

Progressive depletion of all vascular endothelial growth factor A (VEGF‐A) splice isoforms from the kidney results in proteinuria and increased glomerular water permeability, which are both rescued by over‐expression of VEGF‐A₁₆₅b only.

VEGF‐A₁₆₅b rescues the increase in glomerular basement membrane and podocyte slit width, as well as the decrease in sub‐podocyte space coverage, produced by VEGF‐A depletion.

VEGF‐A₁₆₅b restores the expression of platelet endothelial cell adhesion molecule in glomerular endothelial cells and glomerular capillary circumference.

VEGF‐A₁₆₅b has opposite effects to VEGF‐A₁₆₅ on the expression of genes involved in endothelial cell migration and proliferation.

Mild systemic thermal therapy ameliorates renal dysfunction in a rodent model of chronic kidney disease

Thermal therapy has become a nonpharmacological therapy in clinical settings, especially for cardiovascular diseases. However, the practical role of thermal therapy on chronic kidney disease remains elusive. We performed the present study to investigate whether a modified thermal protocol, repeated mild thermal stimulation (MTS), could affect renal damages in chronic kidney disease using a mouse renal ablation model. Mice were subjected to MTS or room temperature (RT) treatment once daily for 4 wk after subtotal nephrectomy (Nx) or sham operation (Sh). We revealed that MTS alleviated renal impairment as indicated by serum creatinine and albuminuria in Nx groups. In addition, the Nx + MTS group showed attenuated tubular histological changes and reduced urinary neutrophil gelatinase-associated lipocalin excretion approximately by half compared with the Nx + RT group. Increased apoptotic signaling, such as TUNEL-positive cell count and cleavage of caspase 3, as well as enhanced oxidative stress were significantly reduced in the Nx + MTS group compared with the Nx + RT group. These changes were accompanied with the restoration of kidney Mn-SOD levels by MTS. Heat shock protein 27, a key molecular chaperone, was phosphorylated by MTS only in Nx kidneys rather than in Sh kidneys. MTS also tended to increase the phosphorylation of p38 MAPK and Akt in Nx kidneys, possibly associated with the activation of heat shock protein 27. Taken together, these results suggest that modified MTS can protect against renal injury in a rodent model of chronic kidney disease.

A mouse model recapitulating human monoclonal heavy chain deposition disease evidences the relevance of proteasome inhibitor therapy

Randall-type heavy chain deposition disease (HCDD) is a rare disorder characterized by glomerular and peritubular amorphous deposits of a truncated monoclonal immunoglobulin heavy chain (HC) bearing a deletion of the first constant domain (CH1). We created a transgenic mouse model of HCDD using targeted insertion in the immunoglobulin κ locus of a human HC extracted from a HCDD patient. Our strategy allows the efficient expression of the human HC in mouse B and plasma cells, and conditional deletion of the CH1 domain reproduces the major event underlying HCDD. We show that the deletion of the CH1 domain dramatically reduced serum HC levels. Strikingly, even with very low serum level of truncated monoclonal HC, histologic studies revealed typical Randall-type renal lesions that were absent in mice expressing the complete human HC. Bortezomib-based treatment resulted in a strong decrease of renal deposits. We further demonstrated that this efficient response to proteasome inhibitors mostly relies on the presence of the isolated truncated HC that sensitizes plasma cells to bortezomib through an elevated unfolded protein response (UPR). This new transgenic model of HCDD efficiently recapitulates the pathophysiologic features of the disease and demonstrates that the renal damage in HCDD relies on the production of an isolated truncated HC, which, in the absence of a LC partner, displays a high propensity to aggregate even at very low concentration. It also brings new insights into the efficacy of proteasome inhibitor-based therapy in this pathology.

Development of a Model of Chronic Kidney Disease in the C57BL/6 Mouse with Properties of Progressive Human CKD

Chronic kidney disease (CKD) is a major healthcare problem with increasing prevalence in the population. CKD leads to end stage renal disease and increases the risk of cardiovascular disease. As such, it is important to study the mechanisms underlying CKD progression. To this end, an animal model was developed to allow the testing of new treatment strategies or molecular targets for CKD prevention. Many underlying risk factors result in CKD but the disease itself has common features, including renal interstitial fibrosis, tubular epithelial cell loss through apoptosis, glomerular damage, and renal inflammation. Further, CKD shows differences in prevalence between the genders with premenopausal women being relatively resistant to CKD. We sought to develop and characterize an animal model with these common features of human CKD in the C57BL/6 mouse. Mice of this genetic background have been used to produce transgenic strains that are commercially available. Thus, a CKD model in this strain would allow the testing of the effects of numerous genes on the severity or progression of CKD with minimal cost. This paper describes such a mouse model of CKD utilizing angiotensin II and deoxycorticosterone acetate as inducers.

Rodent animal models: from mild to advanced stages of diabetic nephropathy

Diabetic nephropathy (DN) is a secondary complication of both type 1 and type 2 diabetes, resulting from uncontrolled high blood sugar. 30-40% of diabetic patients develop DN associated with a poor life expectancy and end-stage renal disease, causing serious socioeconomic problems. Although an exact pathogenesis of DN is still unknown, several factors such as hyperglycemia, hyperlipidemia, hypertension and proteinuria may contribute to the progression of renal damage in diabetic nephropathy. DN is confirmed by measuring blood urea nitrogen, serum creatinine, creatinine clearance and proteinuria. Clinical studies show that intensive control of hyperglycemia and blood pressure could successfully reduce proteinuria, which is the main sign of glomerular lesions in DN, and improve the renal prognosis in patients with DN. Diabetic rodent models have traditionally been used for doing research on pathogenesis and developing novel therapeutic strategies, but have limitations for translational research. Diabetes in animal models such as rodents are induced either spontaneously or by using chemical, surgical, genetic, or other techniques and depicts many clinical features or related phenotypes of the disease. This review discusses the merits and demerits of the models, which are used for many reasons in the research of diabetes and diabetic complications.

Inhibition of inflammation by pentosan polysulfate impedes the development and progression of severe diabetic nephropathy in aging C57B6 mice

Inflammation has a key role in diabetic nephropathy (DN) progression. Pentosan polysulfate (PPS) has been shown to decreases interstitial inflammation and glomerulosclerosis in 5/6 nephrectomized rats. Since PPS has an excellent long-term safety profile in interstitial cystitis treatment, and we recently found that old diabetic C57B6 mice develop DN characterized by extensive tubulointerstitial inflammatory lesions that mimics human DN, we examined the effect of PPS on old diabetic mice. We also examined the anti-inflammatory properties of PPS in renal cells in vitro. Diabetes was induced with streptozotocin in 18 months female (early aging) C57B6 mice. Mice were then randomized to receive oral PPS (25 mg/kg/day) or water for 4 months. The effect of PPS on NF-κB activation and on TNFα, high glucose or advanced glycation end products (AGEs) stimulated proinflammatory gene expression in renal cells was examined. We found that PPS treatment preserved renal function, significantly reduced albuminuria, and markedly decreased the severity of renal lesions, including tubulointerstitial inflammation. PPS also reduced upregulation of TNFα and proinflammatory genes in aging diabetic kidneys. Furthermore, PPS suppressed NF-κB, decreased the proinflammatory actions of TNFα, and decreased high glucose and AGEs stimulated MCP-1 production in vitro. Finally, PPS decreased TNFα-induced increase in albumin permeability in podocyte monolayers. In conclusion, PPS treatment largely prevents the development/progression of nephropathy in aging diabetic mice. As this may be mediated by suppression of TNFα, high glucose, and AGE-stimulated NF-κB activation and inflammation in vitro, the in vivo blockade of DN may be due to the anti-inflammatory properties of PPS.

Renal programming: cause for concern?

Development of the kidney can be altered in utero in response to a suboptimal environment. The intrarenal factors that have been most well characterized as being sensitive to programming events are kidney mass/nephron endowment, the renin-angiotensin system, tubular sodium handling, and the renal sympathetic nerves. Newborns that have been subjected to an adverse intrauterine environment may thus begin life at a distinct disadvantage, in terms of renal function, at a time when the kidney must take over the primary role for extracellular fluid homeostasis from the placenta. A poor beginning, causing renal programming, has been linked to increased risk of hypertension and renal disease in adulthood. However, although a cause for concern, increasingly, evidence demonstrates that renal programming is not a fait accompli in terms of future cardiovascular and renal disease. A greater understanding of postnatal renal maturation and the impact of secondary factors (genes, sex, diet, stress, and disease) on this process is required to predict which babies are at risk of increased cardiovascular and renal disease as adults and to be able to devise preventative measures.

Induction of diabetes in aged C57B6 mice results in severe nephropathy: an association with oxidative stress, endoplasmic reticulum stress, and inflammation

Kidney aging is a slowly progressive process that is postulated to be accelerated by intervening diseases, such as diabetes, due in part to the addition of excessive stress and inflammation from the intervening disease to the underlying aging process. This hypothesis was tested by inducing diabetes with streptozotocin in 18-month-old, aging mice. After 4 months of diabetes, these mice developed severe albuminuria, elevated creatinine levels, and renal lesions including extensive apoptotic cell death, glomerulosclerosis, afferent and efferent hyalinosis, and tubulointerstitial inflammation and fibrosis. These symptoms were associated with elevated oxidative stress. The presence of endoplasmic reticulum (ER) stress in 22-month-old diabetic kidneys resulted in up-regulation of C/EBP homologous protein (CHOP), which may play a role in increasing kidney lesions because CHOP-deficient proximal tubular cells were resistant to ER stress-induced cell death, and CHOP-deficient mice were protected from diabetic nephropathy. Moreover, CHOP-deficient mice did not develop albuminuria as they aged. Inflammation, another key component of progressive diabetic nephropathy, was prominent in 22-month-old diabetic kidneys. The expression of tumor-necrosis factor-alpha in 22-month-old diabetic kidneys may play a role in inflammation, ER stress, and apoptosis. Thus, diabetes may accelerate the underlying kidney aging process present in old mice.

Chronic kidney disease induced in mice by reversible unilateral ureteral obstruction is dependent on genetic background

Chronic kidney disease (CKD) begins with renal injury; the progression thereafter depends upon a number of factors, including genetic background. Unilateral ureteral obstruction (UUO) is a well-described model of renal fibrosis and as such is considered a model of CKD. We used an improved reversible unilateral ureteral obstruction (rUUO) model in mice to study the strain dependence of development of CKD after obstruction-mediated injury. C57BL/6 mice developed CKD after reversal of three or more days of ureteral obstruction as assessed by blood urea nitrogen (BUN) measurements (>40 mg/dl). In contrast, BALB/c mice were resistant to CKD with up to 10 days ureteral obstruction. During rUUO, C57BL/6 mice exhibited pronounced inflammatory and intrinsic proliferative cellular responses, disruption of renal architecture, and ultimately fibrosis. By comparison, BALB/c mice had more controlled and measured extrinsic and intrinsic responses to injury with a return to normal within several weeks after release of ureteral obstruction. Our findings provide a model that allows investigation of the genetic basis of events during recovery from injury that contribute to the development of CKD.

Short-term intermittent PTH 1-34 administration enhances bone formation in SCID/Beige mice

The anabolic effect of intermittent PTH on bone is variable depending on the species studied, duration/mode of administration, and location of skeletal response investigated. We tested the hypothesis low dose, short term, intermittent PTH 1-34 administration is sufficient to enhance bone formation without altering bone resorption. To test our hypothesis, mice were treated intermittently with one of three concentrations of PTH 1-34 (1 microg/kg; low, 10 microg/kg, or 20 microg/kg; high) for three weeks. The skeletal response was identified by quantifying: serum markers of bone turnover, cancellous bone parameters in distal femur, proximal tibia, and lumbar vertebrae by microCT, and number of osteoblasts and osteoclasts in distal femur. Mice receiving 20 microg/kg of PTH 1-34 demonstrated a 30% increase in serum osteocalcin, but no differences in serum calcium, type I collagen teleopeptides, or TRACP 5b. For all bones, microCT analysis suggested mice receiving 20 microg/kg of PTH 1-34 had increased cancellous bone mineral density, trabecular thickness and spacing, but decreased trabecular number. A 60% increase in the number of alkaline phosphatase positive osteoblasts in the distal femur was also observed in tissue sections; however, the number of TRAP positive osteoclasts was not different between test and control groups. While animals administered 10 microg/kg demonstrated similar trends for all bone turnover indices, such alterations were not observed in animals administered PTH 1-34 at 1 microg/kg per day. Thus, PTH 1-34, administered intermittently for three weeks at 20 microg/kg is sufficient to enhance bone formation without enhancing resorption.

Oxidative stress-induced JNK activation contributes to proinflammatory phenotype of aging diabetic mesangial cells

Chronic inflammation and increased oxidative stress (OS) play an important role in diabetic nephropathy progression. Herein, we show that mesangial cells from streptozotocin-induced aging diabetic mice, a model of progressive diabetic nephropathy, exhibited increased OS and a proinflammatory phenotype characterized by elevated chemokines and ICAM-1 expression. This phenotypic change was consistent with the extensive inflammatory lesions present in aging diabetic kidneys and was not found in mesangial cells from old and young controls or young diabetic mice. Activation of the c-Jun NH(2)-terminal kinase (JNK) pathway was a likely contributor to the proinflammatory phenotype of aging diabetic mesangial cells since 1) phosphorylated JNK levels and JNK kinase activity were increased in these cells, 2) suppression of JNK significantly decreased monocyte chemoattractant protein-1 (MCP-1) production in these cells, and 3) activation of JNK in normal mesangial cells induced inflammation. Elevated OS in aging diabetic mesangial cells may be a cause of JNK activation and inflammation, because antioxidant treatment decreased JNK phosphorylation and MCP-1 production. Additionally, decreased expression of mitogen-activated protein kinase phosphatase 5 (MKP5) may also contribute to increased JNK and inflammation in aging diabetic mesangial cells since overexpression of MKP5 in these cells normalized phosphorylated JNK levels and reversed the proinflammatory phenotype. Moreover, knocking down of MKP5 expression in old control mesangial cells resulted in JNK activation and MCP-1 production, a phenotype seen in aging diabetic mesangial cells. Interestingly, MKP5 phosphatase activity was diminished by free radicals in vitro. Thus, OS may induce inflammation in mesangial cells by activating JNK through either a direct activation of JNK or indirectly by suppression of MKP5 activity. Proinflammatory phenotype of mesangial cells may contribute to chronic inflammatory lesions and disease progression of aging diabetic mice.

Overexpression of calmodulin in pancreatic beta cells induces diabetic nephropathy

Recently, endothelial dysfunction induced by an uncoupling of vascular endothelial growth factor (VEGF) and nitric oxide has been implicated in the pathogenesis of diabetic nephropathy (DN). Investigating the pathogenesis of DN has been limited, however, because of the lack of animal models that mimic the human disease. In this report, pancreatic beta cell-specific calmodulin-overexpressing transgenic (CaMTg) mice, a potential new model of DN, are characterized with particular emphasis on VEGF and related molecules. CaMTg mice developed hyperglycemia at 3 wk and persistent proteinuria by 3 mo. Morphometric analysis showed considerable increases in the glomerular and mesangial areas with deposition of type IV collagen. Moreover, the pathologic hallmarks of human DN (mesangiolysis, Kimmelstiel-Wilson-like nodular lesions, exudative lesions, and hyalinosis of afferent and efferent arteries with neovascularization) were observed. In addition, increased VEGF expression was associated with an increased number of peritubular capillaries. Expression of endothelial nitric oxidase synthase was reduced and that of VEGF was markedly elevated in CaMTg mice kidney compared with nontransgenic mice. No differences in VEGF receptor-1 or VEGF receptor-2 expression were observed between CaMTg mice and nontransgenic kidneys. In summary, CaMTg mice develop most of the distinguishing lesions of human DN, and the elevated VEGF expression in the setting of diminished endothelial nitric oxide synthase expression may lead to endothelial proliferation and dysfunction. This model may prove useful in the study of the pathogenesis and treatment of DN.

Dynamic blood pressure load and nephropathy in the ZSF1 (fa/facp) model of type 2 diabetes

Diabetes and increased blood pressure (BP) are believed to interact synergistically in the pathogenesis and progression of diabetic nephropathy. The present studies were performed to examine if there were differences in BP load and/or protective renal autoregulatory capacity between the obese diabetic Zucker fatty /spontaneously hypertensive heart failure F1 hybrid (ZSF1) ( fa/ facp) rats and their lean controls. By ∼26 wk of age, ZSF1 ( n = 13) but not their lean controls ( n = 16) had developed substantial proteinuria (180 ± 19 vs. 16 ± 1.4 mg/24 h) and glomerulosclerosis (19 ± 2.4 vs. 0.6 ± 0.2%; P < 0.001). However, average ambient systolic BP by radiotelemetry (12–26 wk of age) was modestly lower in ZSF1 than in lean controls (130 ± 1.4 vs. 137 ± 1.7 mmHg, P < 0.002), although the 24-h BP power spectra showed a mild increase at frequencies <0.1 Hz in the ZSF1. Autoregulatory capacity under anesthesia in response to step changes in perfusion pressure between 100 and 140 mmHg was similarly well preserved in both ZSF1 and lean controls at 16–18 wk of age [autoregulatory indexes (AI) <0.1]. Similarly, differences were not observed for dynamic autoregulation in conscious rats [transfer functions between BP (input) and renal blood flow (output) using chronic Transonic flow probes]. Collectively, these data indicate that the pathogenesis of nephropathy in the ZSF1 model of type 2 diabetic nephropathy is largely independent of differences in systemic BP and/or its potential renal transmission. However, these data do not exclude the possibility that the diabetic milieu may alter the glomerular capillaries in the ZSF1, such that there is an enhanced local susceptibility to injury with even normal glomerular pressures.

Genetics of diabetic nephropathy: lessons from mice

Although diabetic nephropathy occurs only in a minority of diabetic patients (approximately 30%), it is the major single cause of end-stage renal disease in the United States. Hyperglycemia and hypertension are important factors predisposing patients to nephropathy, however, accumulating evidence points to critical genetic factors that predispose only a subset of diabetic patients to nephropathy. Defining the genes responsible for nephropathy risk in human populations has proven challenging. Comparative genomics using the robust genetic reagents available in the laboratory mouse should provide a complementary approach to defining genes that may predispose to diabetic nephropathy in mice and human beings. In this article we review studies that have started to identify genetic risk factors for diabetic nephropathy in mice and the multiple approaches that may be used to elucidate the genetic pathogenesis of this disorder.

Doxycycline: a pilot study to reduce diabetic proteinuria

BACKGROUND

Activity of matrix metalloproteinases (MMPs), the enzymes primarily responsible for the deposition of extracellular matrix proteins, contributes to the pathogenesis of diabetic proteinuria. We evaluated the effect of doxycycline, a potent nonselective MMPs inhibitor, on reduction of proteinuria in diabetic patients.

MATERIAL AND METHODS

In a self-control clinical trial, 35 patients with overt diabetic nephropathy (proteinuria >300 mg/24 h) received oral doxycycline 100 mg/day for 2 months. Twenty-four-hour urine volume, Cr and protein excretion were measured at baseline, after 1 and 2 months of treatment, and after 4 months of its discontinuation. Treatment-related side effects were closely monitored and documented.

RESULTS

Mean (+/-SD) 24-hour urine protein was 888 +/- 419 mg at baseline, 884 +/- 368 mg after 1 month, and 643 +/- 386 mg after the 2 months of doxycycline treatment. There was statistically significant reduction in proteinuria at 2 months of treatment vs. at the baseline (p < 0.001). Mean 24-hour urine protein excretion increased to 1,021 +/- 422 mg 4 months after doxycycline was discontinued. The changes in serum sodium, potassium, BUN and Cr concentrations, and blood pressure measurements during the 2 months of treatment and follow-up period were not statistically significant.

CONCLUSION

Proteinuria in patients with diabetic nephropathy can be reduced with low dose doxycycline therapy over a 2-month period of drug administration. Further studies are necessary to determine the long-term effect, the optimal dose, and the optimal duration of this potentially novel therapy.

Diabetic nephropathy: leveraging mouse genetics

PURPOSE OF REVIEW

Advances in mouse genetics have made this species particularly useful as a model for human disease. This review will summarize recent advances regarding the pathogenesis of diabetic nephropathy discovered in mice.

RECENT FINDINGS

Diabetic nephropathy has been characterized in novel genetic models of murine diabetes including the Akita, Ove26, and ICER-Igamma mice. Mutagenesis resources targeting every gene of the genome and the importance of inbred genetic background are discussed.

SUMMARY

Through the use of these resources mouse models should provide new insight into the pathogenesis of diabetic nephropathy, and complement human studies and validate the identity of candidate genes contributing to diabetic nephropathy.

Spontaneously reduced blood pressure load in the rat streptozotocin-induced diabetes model: potential pathogenetic relevance

The rat streptozotocin (STZ)-induced diabetes model is widely used to investigate the pathogenesis of diabetic nephropathy. However, overt nephropathy is inexplicably slow to develop in this model compared with renal mass reduction (RMR) models. To examine whether blood pressure (BP) differences correlated with the time course of glomerulosclerosis (GS), BP was measured continuously throughout the course by radiotelemetry in control (n = 17), partially insulin-treated STZ-diabetes (average blood glucose 364 +/- 15 mg/dl; n = 15), and two normotensive RMR models (systolic BP <140 mmHg)--uninephrectomy (UNX; n = 16) and 3/4 RMR by surgical excision [right nephrectomy + excision of both poles of left kidney (RK-NX); n = 12] in Sprague-Dawley rats. Proteinuria and GS were assessed at approximately 16-20 wk (all groups) and at 36-40 wk (all groups except RK-NX). At 16 wk, significantly greater proteinuria and GS had developed in the RK-NX group compared with the other three groups (not different from each other). By 36-40 wk, substantial proteinuria and GS had also developed in the UNX group, but both the control and the STZ-diabetic rats exhibited comparable modest proteinuria and minimal GS. Systolic BP (mmHg) was significantly reduced in the STZ-diabetic rats (116 +/- 1.1) compared with both control (124 +/- 1.0) and RMR (128 +/- 1.2 and 130 +/- 3.0) groups (P < 0.01). Similarly, "BP load" as estimated by BP power spectral analysis was also lower in the STZ-diabetic rats. Given the known protective effects of BP reductions on the progression of diabetic nephropathy, it is likely that this spontaneous reduction in ambient BP contributes to the slow development of GS in the STZ-diabetes model compared with the normotensive RMR models.

Cis and trans regulatory elements in NPHS2 promoter: implications in proteinuria and progression of renal diseases

Podocin (NPHS2) expression in podocytes is associated with variable degrees of proteinuria and progression to renal failure in different glomerular diseases that suggests different expression profiles in NPHS2 promoter. Three functional polymorphisms in NPHS2 promoter (-51T, -116T, and -535 insCTTTTTT(3)) were found determining strong downregulation (-73, -59, and -82%, respectively) of the reporter gene expression when transfected in podocytes. Electrophoretic mobility shift assay experiments showed that all wild-type variants (-51G, -116C, and -535 insCTTTTTT(2)) formed specific DNA-protein complexes with podocyte nuclear extracts that were abolished by the presence of the rare forms (-51T, -116T, and -535 insCTTTTTT(3)). In the case of -51G, upstream stimulatory factor-1 (USF1) was identified as the specific trans element in accord to binding inhibition experiments and USF1 RNAi silencing. Haplotype analysis of 204 normal controls and 545 patients with renal diseases (308 immunoglobulin (Ig)A nephropathy and 237 focal segmental glomerulosclerosis) evidenced that -116/-51 and -535/P2OL formed two blocks in strong linkage disequilibrium in both normal and pathological cohorts. The high NPHS2 promoter profile -116C/-51G haplotype was more frequent in patients with IgA nephropathy (P-value=0.005) and was associated with a better clinical outcome in terms of proteinuria and creatinine levels. Overall our study describes functional variants of NPHS2 promoter and characterizes trans-acting elements that modulate podocin expression in the kidney. High producer NPHS2 promoter haplotypes seem protective in patients with chronic glomerular diseases.

Growth factor midkine is involved in the pathogenesis of diabetic nephropathy

Diabetic nephropathy is a life-threatening disease associated with diabetes mellitus. Longstanding hyperglycemia induces pathological reactions of glomerular mesangial cells, such as overproduction of extracellular matrix, which finally lead to nephropathy. However, the mechanisms underlying its pathogenesis have not been completely elucidated. Using the Streptozotocin-induced model of diabetes, we report that mice deficient in the growth factor midkine (Mdk-/-) exhibited strikingly milder nephropathy than Mdk+/+ mice, even though both mice showed similar extents of hyperglycemia after Streptozotocin injection. Midkine expression was induced in the glomerular mesangium of Mdk+/+ mice with diabetic nephropathy and in primary cultured mesangial cells exposed to high glucose. Mdk-/- mesangial cells exhibited reduced phosphorylation of protein kinase C and extracellular signal-regulated kinase as well as reduced production of transforming growth factor-beta(1) on high glucose loading. Addition of exogenous midkine restored extracellular signal-regulated kinase phosphorylation in Mdk-/- cells under high glucose conditions, whereas a midkine antisense oligodeoxynucleotide suppressed midkine in Mdk+/+ cells. Therefore, this study identifies midkine as a key molecule in diabetic nephropathy and suggests that midkine accelerates the intracellular signaling network evoked by hyperglycemia in nephropathy.

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.

The effect of intrauterine environment and low glomerular number on the histological changes in diabetic glomerulosclerosis

AIMS/HYPOTHESIS

We tested the hypothesis that diabetic glomerulosclerosis would develop more rapidly in animals with fewer glomeruli.

METHODS

We studied the female offspring of Wistar rats that had been fed a low-protein diet (LPD) containing 6% protein or a normal-protein diet (NPD) containing 18% protein during pregnancy. Streptozotocin diabetes was induced at 12 weeks and animals were killed at 40 weeks.

RESULTS

Non-diabetic LPD offspring were of lower birthweight than the NPD offspring (5.19+/-0.64 vs 6.45+/-0.67 g, p<0.001) and had fewer glomeruli (27,402+/-3,137 vs 34,203+/-6,471, p<0.05). Glomerular volume correlated inversely with glomerular number (r=-0.64, p=0.035), but total glomerular filtration surface area was reduced in the LPD animals (4,770+/-541 vs 5,779+/-1,302 mm(2), p=0.05). Other renal structural and functional parameters were similar. In LPD and NPD diabetic animals, glomerular volume and basement membrane width were significantly increased compared to their respective controls. Podocyte density was lowest in the LPD diabetic animals (not significant), and the area covered by each podocyte was greater in the LPD diabetic group (2.40+/-0.693 x10(-3) mm(2)) than in the LPD control group (1.68+/-0.374 x10(-3) mm(2), p<0.001) and in the NPD diabetic animals (1.71+/-0.291 x 10(-3) mm(2), p<0.05). There was no difference in any other structural or functional parameter between the LPD and NPD diabetic animals.

CONCLUSIONS/INTERPRETATION

A decrease in glomerular number was not deleterious to renal structure and function over 40 weeks in this animal model. Further work in models with progressive renal impairment and hypertension is necessary to clarify the impact of glomerular number on the development of renal disease.

In mice, proteinuria and renal inflammatory responses to albumin overload are strain-dependent

BACKGROUND

The availability of genetically modified mice has increased the need for relevant mouse models of renal disease, but widely used C57BL/6 mice often show resistance to proteinuria. 129/Sv mice are considered more sensitive to certain renal models. Albumin overload, an important model of proteinuric disease, induces marked proteinuria in rats but barely in C57BL/6 mice. We hypothesized that albumin overload would induce more proteinuria in 129S2/Sv than C57BL/6J mice.

METHODS

Male and female C57BL/6J and 129S2/Sv mice received bovine serum albumin (BSA) for 11 days. Control groups received saline injections. Injected BSA was immunohistochemically localized to study intrarenal handling of overloaded protein. Renal macrophage infiltration (F4/80 immuno-staining) and glomerular ultrastructure (electron microscopy) were assessed.

RESULTS

The BSA-treated groups were similarly hyperproteinemic at Day 11 (D11). Proteinuria differed widely. In C57BL/6J mice, it remained unchanged in females but significantly, though mildly, increased in males (from 3+/-1 to 8+/-2 mg/day, P < 0.05). In 129S2/Sv, proteinuria was marked in both males and females (4+/-1 to 59+/-14, and 0.6+/-0.2 to 29+/-9 mg/day, respectively, both P < 0.01). Proteinuria was accompanied by tubulo-interstitial macrophage infiltration in 129S2/Sv mice. Injected BSA was visualized within glomeruli in both strains and in the urinary space and tubules of 129S2/Sv but not C57BL/6J mice, indicating much greater glomerular leakage in the former. No glomerular macrophages or ultra-structural differences were detected.

CONCLUSION

There are major strain differences in the proteinuria and renal inflammatory response of mice to albumin overload, which are not due to structural variation in the filtration barrier but possibly to functional differences in glomerular protein permeability.

Plasminogen activator inhibitor-1 gene deficiency attenuates TGF-β1-induced kidney disease

BACKGROUND

Transforming growth factor-beta1 (TGF-beta1) stimulates the deposition of extracellular matrix (ECM), which is a hallmark in end-stage renal disease. The importance of TGF-beta1-induced changes in protease activity in this process is not fully elucidated. TGF-beta1 up-regulates plasminogen activator inhibitor type 1 (PAI-1), which lowers matrix degradation. Our aim was to investigate the importance of PAI-1 in TGF-beta1-induced kidney disease.

METHODS

TGF-beta1 transgenic mice were bred with PAI-1 gene deficient mice. The effect of PAI-1 gene knockout on TGF-beta1-induced glomerular disease was investigated by measuring morphologic changes in the glomeruli. Interstitial changes were assessed by measurement of total collagen content and expression and localization of ECM components. Finally, protease activity was evaluated by plasmin activity measurement and by gel and in situ gelatin zymography.

RESULTS

TGF-beta1 elevated PAI-1 expression fourfold. PAI-1 gene deficiency attenuated the TGF-beta1-induced mesangial expansion and basement membrane thickening. Furthermore, PAI-1 knockout diminished collagen accumulation in TGF-beta1-positive mice. The expression of both collagen type I and III were reduced. Interestingly, no difference in protease activity could be ascertained as cause of the decreased ECM accumulation.

CONCLUSION

We show that PAI-1 gene deficiency attenuates TGF-beta1-induced kidney disease, decreasing both glomerular and interstitial ECM deposition. Thus, PAI-1 mediates some of the biological effects of TGF-beta1 in vivo. However, we could not find evidence supporting the notion that the effect was mediated through increased protease activity.

Establishment of a diabetic mouse model with progressive diabetic nephropathy

Although diabetic animal models exist, no single animal model develops renal changes identical to those seen in humans. Here we show that transgenic mice that overexpress inducible cAMP early repressor (ICER Igamma) in pancreatic beta cells are a good model to study the pathogenesis of diabetic nephropathy. Although ICER Igamma transgenic mice exhibit extremely high blood glucose levels throughout their lives, they survive long enough to develop diabetic nephropathy. Using this model we followed the progress of diabetic renal changes compared to those seen in humans. By 8 weeks of age, the glomerular filtration rate (GFR) was already increased, and glomerular hypertrophy was prominent. At 20 weeks, GFR reached its peak, and urine albumin excretion rate was elevated. Finally, at 40 weeks, diffuse glomerular sclerotic lesions were prominently accompanied by increased expression of collagen type IV and laminin and reduced expression of matrix metalloproteinase-2. Nodular lesions were absent, but glomerular basement membrane thickening was prominent. At this point, GFR declined and urinary albumin excretion rate increased, causing a nephrotic state with lower serum albumin and higher serum total cholesterol. Thus, similar to human diabetic nephropathy, ICER Igamma transgenic mice exhibit a stable and progressive phenotype of diabetic kidney disease due solely to chronic hyperglycemia without other modulating factors.

Development of diabetic nephropathy in the Milan normotensive strain, but not in the Milan hypertensive strain: possible permissive role of hemodynamics

BACKGROUND

Rats of the Milan normotensive strain develop spontaneous glomerulosclerosis, whereas those of the Milan hypertensive strain are resistant to renal disease, possibly due to intrarenal artery hypertrophy protecting from systemic hypertension. To assess the role of hemodynamic versus metabolic factors in diabetic nephropathy, we investigated whether streptozotocin-induced diabetes accelerates glomerulosclerosis in Milan normotensive and/or removes (the hemodynamic) protection in Milan hypertensive rats by reducing preglomerular vascular resistance.

METHODS

Diabetic and nondiabetic Milan normotensive, hypertensive, and progenitor Wistar rats were followed for 6 months for the assessment of renal function and structure.

RESULTS

Proteinuria increased in nondiabetic and diabetic normotensive and, to a lesser extent, in diabetic Wistar, but not hypertensive rats. Serum creatinine increased and creatinine clearance decreased in nondiabetic and diabetic normotensive rats at 6 months. At 1.5 months, diabetic normotensive, but not hypertensive rats showed increased glomerular filtration rate and filtration fraction, suggesting glomerular hypertension. Diabetic nephropathy was detected in diabetic normotensive and Wistar, but not hypertensive rats. Glomerular extracellular matrix and TGF-beta mRNA levels increased with diabetes (and age) in normotensive, but not hypertensive rats. Arterioles and interlobular arteries showed increased media thickness in hypertensive versus normotensive rats, with diabetes reducing it only in the normotensive.

CONCLUSION

These data show that Milan hypertensive rats are not susceptible to diabetic nephropathy, at variance with glomerulosclerosis-prone Milan normotensive rats, thus indicating the importance of genetic background. Our study suggests that the nature of this (genetic) protection might be hemodynamic, with intrarenal artery hypertrophy preventing diabetes-induced loss of autoregulation.

Identification of podocin (NPHS2) gene mutations in African Americans with nondiabetic end-stage renal disease

BACKGROUND

Podocin, encoded by NPHS2 and mapped to 1q25.2, is an integral membrane protein exclusively expressed in glomerular podocytes. Mutations in the NPHS2 gene cause autosomal-recessive nephrotic syndrome and have been associated with proteinuria in several populations. Evidence for linkage of end-stage renal disease (ESRD) to chromosome 1q25-31 in the region of NPHS2 has been identified in a genome-wide scan in African American (AA) siblings.

METHODS

To investigate the potential role of this gene in ESRD, we sequenced all coding regions and approximately 2 kb of upstream promoter sequence of NPHS2 in 96 unrelated AA nondiabetic ESRD cases and 96 healthy population-based AA controls, and assessed several single nucleotide polymorphisms (SNPs) for association in a larger case-control sample.

RESULTS

Fifty-five variants were identified with minor allele frequencies ranging from <1% to 44%. Twenty-three polymorphisms were located in the promoter region, 11 were exonic, 13 were intronic, and 8 were in the 5' and 3'- untranslated regions. Two novel nonsynonymous coding SNPs were identified (A44E and A61V). An insertion polymorphism in intron 3, IVS3+9insA, was detected in 6 ESRD patients and in no controls. This variant, and 4 other common SNPs, were evaluated in a larger sample of 288 AA ESRD cases and 278 AA controls. The overall minor allele frequencies for the insertion allele were 0.018 in cases and 0.002 in controls. Significant evidence of association of IVS3+9insA was observed (P= 0.012), and the haplotype containing the insertion allele in cases was also associated.

CONCLUSION

These results suggest that uncommon variants of the NPHS2 gene may play a role in the development of nondiabetic ESRD in AAs.

Characterization of susceptibility of inbred mouse strains to diabetic nephropathy

Differential susceptibility to diabetic nephropathy has been observed in humans, but it has not been well defined in inbred strains of mice. The present studies characterized the severity of diabetic nephropathy in six inbred mouse strains including C57BL/6J, DBA/2J, FVB/NJ, MRL/MpJ, A/J, and KK/HlJ mice. Diabetes mellitus was induced using low-dose streptozotocin injection. Progression of renal injury was evaluated by serial measurements of urinary albumin excretion, glomerular filtration rate (GFR), and terminal assessment of renal morphology over 25 weeks. Despite comparable levels of hyperglycemia, urinary albumin excretion and renal histopathological changes were dramatically different among strains. DBA/2J and KK/HlJ mice developed significantly more albuminuria than C57BL/6J, MRL/MpJ, and A/J mice. Severe glomerular mesangial expansion, nodular glomerulosclerosis, and arteriolar hyalinosis were observed in diabetic DBA/2J and KK/HlJ mice. Glomerular hyperfiltration was observed in all diabetic strains studied except A/J. The significant decline in GFR was not evident over the 25-week period of study, but diabetic DBA/2J mice exhibited a tendency for GFR to decline. Taken together, these results indicate that differential susceptibility to diabetic nephropathy exists in inbred mice. DBA/2J and KK/HlJ mice are more prone to diabetic nephropathy, whereas the most widely used C57BL/6J mice are relatively resistant to development of diabetic nephropathy.

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.

Expression of Mediators of Renal Injury in the Remnant Kidney of ROP Mice Is Attenuated by Cyclooxygenase-2 Inhibition

To investigate the effects of cyclooxygenase-2 (COX-2) inhibition on renal injury of mice, ROP mice were subjected to subtotal ablation ('remnant'). A subset of the remnant group was treated with a selective COX-2 inhibitor, SC58236, in the drinking water. At 12 weeks the remnant group developed significant albuminuria (181.3 +/- 15.8 microg/24 h), which was blunted by SC58236 treatment (138.9 +/- 17.1; p < 0.05 compared to remnant). SC58236 did not alter systemic blood pressure or GFR significantly. Immunoreactive COX-2 was upregulated in remnant (1.88 +/- 0.35 fold sham, n = 8, p < 0.05), which was blunted by SC58236 (to 1.26 +/- 0.31 fold sham). Collagen IV mRNA increased significantly in remnant kidneys (2.69 +/- 0.34 fold sham, n = 8, p < 0.05), and this increase was inhibited by SC58236 treatment (to 1.84 +/- 0.32 fold control). Immunoreactive TGF-beta1, connective tissue growth factor, HGF receptor, c-Met, and fibronectin all increased in remnant (2.85 +/- 0.51, 3.83 +/- 0.55, 2.56 +/- 0.31, and 2.80 +/- 0.39 fold sham respectively, n = 4-8, p < 0.05), and SC58236 blunted the increases (to 1.45 +/- 0.34, 1.85 +/- 0.13, 1.75 +/- 0.30, and 1.60 +/- 0.32 fold sham). Immunohistochemistry indicated that the major localization for these progression factors was in the tubulointerstitium, especially in the scar area, which is in agreement with the expression of a macrophage marker, F4/80. Therefore, these results indicate that in a mouse model of subtotal renal ablation, COX-2 inhibition blocks expression of mediators of renal tubulointerstitial injury.

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.

Renal phenotype is exacerbated in Os and lpr double mutant mice

BACKGROUND

ROP-Os/+ mice are born with oligosyndactyly and oligonephronia and develop renal dysfunction, which includes renal tubular epithelial cell (RTC) Fas-dependent apoptosis and tubular atrophy. MRL/lpr mice harbor a Fas-inactivating mutation and develop glomerulonephritis, whereas mice expressing lpr on a C3H background demonstrate no renal phenotype. We hypothesized that crossing ROP-Os/+ with CH3-lpr/lpr mice would rescue the Os/+ renal phenotype by reducing Fas-dependent RTC apoptosis.

METHODS

ROP-Os/+ mice were intercrossed with C3H-lpr/lpr mice and F(2) generation animals were phenotyped by kidney weight, serum creatinine, and albuminuria. Kidney sections were scored for histopathology and apoptosis. Univariate and multivariate analyses were used to examine additive effects of Os and lpr on renal phenotype.

RESULTS

By 16 weeks, F(2)Os/+ lpr/lpr mice developed significantly more albuminuria, glomerulosclerosis, and interstitial inflammation compared to Os/++/+ mice. Glomerular cell apoptosis was increased in Os/+ lpr/lpr compared to Os/++/+ mice, with no significant difference in RTC apoptosis. A statistically significant Os-lpr effect on renal phenotype was demonstrated by multivariate analysis, which exceeded the combined independent effects if Os and lpr, indicating a biologic interaction exists between Os and lpr.

CONCLUSION

Os/+ mice with a superimposed lpr mutation displayed a more severe renal phenotype, rather than phenotype rescue, suggesting that Fas pathway activation is necessary to delete cells resulting from Os-dependent injury. We further propose that an Os-lpr gene interaction and/or mixed ROP-C3H genetic background regulated the renal phenotype, consistent with the concept that chronic renal disease pathogenesis reflects effects of multiple nephropathy susceptibility alleles.

Hyperlipidemia aggravates renal disease in B6.ROP Os/+ mice

INTRODUCTION

Reduction of renal mass is frequently associated with progressive loss of kidney function. We examined the effects of hyperlipidemia on renal pathology and mediators of tissue damage in B6.ROP Os/+ mice, a model of reduced renal mass.

METHODS

C57BL/6 control mice and B6.ROP Os/+ mice were fed normal rodent chow or a high fat, high cholesterol (HFHC) diet for 12 weeks. Kidney function and renal pathology were assessed.

RESULTS

Hyperlipidemia led to a decline in kidney function in C57BL/6 mice. Renal pathology was characterized by an increase in glomerular matrix and cellularity, glomerular and tubulointerstitial macrophage influx, and increased tubular epithelial cell turnover. Chow-fed B6.ROP Os/+ animals demonstrated glomerular hypertrophy with an increase in mesangial matrix and cellularity that was characterized by macrophage influx and increased proliferation. The tubulointerstitium showed increased macrophages as well as tubular atrophy and dilation. Renal pathology was accompanied by an increase in blood urea nitrogen (BUN) and proteinuria. Hyperlipidemia in B6.ROP Os/+ mice resulted in increased plasma BUN compared to chow-fed B6.ROP Os/+ animals and aggravated renal pathology by further increasing glomerular matrix and glomerular hypercellularity. Glomerular hypercellularity was associated with increased expression of platelet-derived growth factor-B (PDGF B) and its receptor beta. Glomerular transforming growth factor-beta (TGF-beta) mRNA expression was increased in B6.ROP Os/+ mice, hyperlipidemic C57BL/6 mice and hyperlipidemic B6.ROP Os/+ animals compared to controls and correlated with the amount of mesangial matrix.

CONCLUSION

This study demonstrates that hyperlipidemia worsens renal pathology in B6.ROP Os/+ mice with a decline in renal function mediated at least in part through increased renal expression of the cytokines PDGF B and TGF-beta.

Initial characterization of a rat model of diabetic nephropathy

The lack of an appropriate animal model that spontaneously develops diabetic nephropathy has been a significant limitation in the search for genetic factors underlying this disease and the development of new therapeutic strategies to prevent progressive renal disease in diabetes. We introgressed the mitochondria and some passenger loci from the FHH/EurMcwi rat into the genetic background of diabetic GK rats, creating a new rat strain, T2DN (T2DN/Mcwi). Despite the high degree of genetic similarity between T2DN and GK rats (97% at 681 loci), diabetes ensues earlier and progresses more severely in T2DN rats. T2DN rats exhibit proteinuria by 6 months of age, accompanied by renal histologic abnormalities such as focal glomerulosclerosis, mesangial matrix expansion, and thickening of basement membranes. These characteristics progress over time, and nearly all T2DN rats exhibit diffuse global glomerulosclerosis with nodule formation and arteriolar hyalinosis by 18 months of age. The histologic changes in the kidney of T2DN rats closely mimic the changes seen in the kidney of patients with diabetes. These results indicate that the T2DN rat is a suitable model for investigating diabetic nephropathy. Here we report the initial genetic and physiological characterization of this new rat model of diabetic nephropathy.

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.

Repeated Streptozotocin Injections Cause Early Onset of Glomerulosclerosis in Mice

Diabetic nephropathy (DN), a major cause of end-stage chronic renal failure, is histologically characterized by glomerulosclerosis. To investigate the molecular mechanisms of DN, it is important to establish a stable model of glomerulosclerosis in mice, because genomic manipulation techniques (such as gene destruction or transgene insertion) are well established in rodent species. In this study, we found that repeated administrations of streptozotocin led to early onset of glomerular sclerotic lesions in C57BL/6 mice, accompanied with renal dysfunction. During the natural course of DN, glomerular endothelial cells decreased at 10 weeks after the start of streptozotocin-injections, whereas myofibroblastic mesangial cells became evident. Our results provide an animal tool to elucidate the molecular mechanisms of DN, for example to investigate vascular pathology in diabetic glomerular diseases.

Glucose induces clonal selection and reversible dinucleotide repeat expansion in mesangial cells isolated from glomerulosclerosis-prone mice

Clonal selection has been proposed as a pathogenetic mechanism in various chronic diseases, such as scleroderma, hypertension, pulmonary fibrosis, interstitial fibrosis of the kidney, atherosclerosis, and uterine leiomyomatosis. We previously found that mesangial cells from ROP mice prone to develop glomerulosclerosis changed their phenotype in response to high glucose concentrations. Here, we investigate whether clonal selection might contribute to this phenotype change. We found that in ROP mice at least two distinct mesangial cell clones exist. They are characterized by a different length of the d(CA) repeat in the MMP-9 promoter and exhibit a significantly different gene expression profile. Exposure of ROP mesangial cells to 25 mmol/l glucose for 35 days induces both clonal selection and reversible dinucleotide repeat expansion. None of these findings were present in mesangial cells isolated from C57BL/6 mice, which are not sclerosis-prone. We conclude that mesangial cell michrochimerism may be a marker for the susceptibility to glomerulosclerosis, that dinucleotide repeat expansion may be a novel mechanism for glucose-induced changes in gene expression, and that clonal selection may partially explain the change in mesangial cell phenotype in diabetes.

Intercellular adhesion molecule-1-deficient mice are resistant against renal injury after induction of diabetes

Diabetic nephropathy is a leading cause of end-stage renal failure. Several mechanisms, including activation of protein kinase C, advanced glycation end products, and overexpression of transforming growth factor (TGF)-beta, are believed to be involved in the pathogenesis of diabetic nephropathy. However, the significance of inflammatory processes in the pathogenesis of diabetic microvascular complications is poorly understood. Accumulation of macrophages and overexpression of leukocyte adhesion molecules and chemokines are prominent in diabetic human kidney tissues. We previously demonstrated that intercellular adhesion molecule (ICAM)-1 mediates macrophage infiltration into the diabetic kidney. In the present study, to investigate the role of ICAM-1 in diabetic nephropathy, we induced diabetes in ICAM-1-deficient (ICAM-1(-/-)) mice and ICAM-1(+/+) mice with streptozotocin and examined the renal pathology over a period of 6 months. The infiltration of macrophages was markedly suppressed in diabetic ICAM-1(-/-) mice compared with that of ICAM-1(+/+) mice. Urinary albumin excretion, glomerular hypertrophy, and mesangial matrix expansion were significantly lower in diabetic ICAM-1(-/-) mice than in diabetic ICAM-1(+/+) mice. Moreover, expressions of TGF-beta and type IV collagen in glomeruli were also suppressed in diabetic ICAM-1(-/-) mice. These results suggest that ICAM-1 is critically involved in the pathogenesis of diabetic nephropathy.

The molecular basis of age-related kidney disease

Renal disease affects 11% of people in the United States over the age of 65, not including those with diabetes or hypertension. Although glomerular disease is the most common underlying etiology of age-related renal dysfunction, the cause of glomerular disease and whether it is the only contributor to renal failure are not known. Our studies in female mice show that renal disease in the postmenopausal period is associated with progressive glomerular enlargement and scarring, as well as abnormal renal function. To study the underlying causes of aging-related glomerular disease, we isolated and characterized glomerular smooth muscle (mesangial) cells from female mice of various ages. We found that the cells from older mice exhibit a variety of phenotypic changes, including increased concentrations of p27, a protein that serves to inhibit progression from the G1 to the S phase of the cell cycle. Because the bone marrow (BM) contains mesangial cell progenitors that can transfer the donor glomerular phenotype (normal or diseased) to recipients, we exchanged BM between postmenopausal and premenopausal mice and found that aging-related glomerular enlargement and scarring are transferred to young recipient glomeruli. In addition, BM from normal, young donors led to the regression of aging-related glomerular disease in postmenopausal recipients; namely, both glomerular enlargement and scarring were reduced. Thus, aging-related glomerular disease is an entity distinct from all other causes of renal disease, is characterized by phenotypic changes in mesangial cell progenitors, and is reversible when the phenotype of the progenitors is returned to normal.

Linkage analysis of candidate loci for end-stage renal disease due to diabetic nephropathy

Diabetic nephropathy (DN), a major cause of ESRD, is undoubtedly multifactorial and is caused by environmental and genetic factors. To identify a genetic basis for DN susceptibility, we are collecting multiplex DN families in the Caucasian (CA) and African-American (AA) populations for whole genome scanning and candidate gene analysis. A candidate gene search of diabetic sibs discordantly affected, concordantly affected and concordantly unaffected for DN was performed with microsatellite markers in genomic regions suspected to harbor nephropathy susceptibility loci. Regions examined were at human chromosome 10p,10q (orthologous to the rat renal susceptibility Rf-1 locus), and at NPHS1 (nephrin), CD2AP, Wilms tumor (WT1), and NPHS2 (podocin) loci. Linkage analyses were conducted using model-free methods (SIBPAL, S.A.G.E.) for AA, CA, and the combined sample. Allele frequencies and the identity by descent sharing were estimated separately for AA and CA, and race was included as a covariate in the final linkage analysis. To date, we have collected 212 sib pairs from 46 CA and 50 AA families. The average age of diabetes onset was 46.8 yr versus 36.2 yr for CA and 39.5 yr versus 40.2 yr for AA, in males versus females respectively. Genotyping data were available for 106 sib pairs (43 CA, 63 AA) from 27 CA (44% male probands) and 38 AA families (43% male probands). Average AA and CA sibship size was 2.73. Singlepoint and multipoint linkage analyses indicate that marker D10S1654 on chromosome 10p is potentially linked to DN (CA only multipoint P = 4 x 10(-3)). Interestingly, the majority of the linkage evidence derives from the CA sib pairs. We are now adding sib pairs and increasing marker density on chromosome 10. We have excluded linkage with candidate regions for nephrin, CD2AP, WT1, and podocin in this sample. In conjunction with previous reports, our data support evidence for a DN susceptibility locus on chromosome 10.

Model of robust induction of glomerulosclerosis in mice: importance of genetic background

BACKGROUND

Increasing evidence suggests that genetic background plays an important role in the development of progressive glomerulosclerosis. The remnant kidney model (RKM) of progressive renal disease has been used extensively in rats. However, C57BL/6 mice are resistant to glomerulosclerosis with RKM induced by either pole amputation or renal artery ligation. A pole resection protocol, applied in 129/Sv mice, induced only mild glomerulosclerosis. We present here a highly reproducible, modified RKM approach to successfully establish a glomerulosclerosis model in mice.

METHODS

Male C57BL/6 (N = 17), 129/Sv (N = 20) and Swiss-Webster (N = 3) mice underwent RKM as follows: the lower branch of the left renal artery was ligated to produce about one third infarct; the upper pole of the left kidney (about one third kidney size) was removed by cautery and the right kidney was nephrectomized to induce a total 5/6 nephrectomy (Nx). In some C57BL/6 mice, 7/8 nephrectomy was induced by removing additional renal mass from the upper pole of the left kidney by cautery. Systolic blood pressure (BP) was measured in conscious mice using a tail-cuff blood pressure monitor and animals were sacrificed at 9, 12, 18, and 24 weeks after nephrectomy. Kidneys were harvested for morphologic analysis.

RESULTS

BP in C57BL/6 mice increased slightly after 5/6 nephrectomy over time without significant difference compared to baseline blood pressure except at 8 weeks (blood pressure at week 0, 98 +/- 1 mm Hg; week 4, 105 +/- 2 mm Hg; week 8, 113 +/- 4 mm Hg; and week 12, 110 +/- 3 mm Hg). Blood presssure remained normal in C57BL/6 mice at 18 weeks after 7/8 nephrectomy (103 +/- 2 mm Hg). Blood pressure in 129/Sv mice increased significantly after 5/6 nephrectomy from 4 to 12 weeks (week 0, 112 +/- 3 mm Hg; week 4, 161 +/- 9 mm Hg; week 8, 166 +/- 5 mm Hg; and week 12, 176 +/- 5 mm Hg; P < 0.01 weeks 4, 8, and 12 vs. week 0 blood pressure). Urine protein excretion in C57BL/6 mice increased only at 4 weeks after 5/6 nephrectomy, and was back to normal at 8 and 12 weeks (week 0, 13.2 +/- 1.4 mg/24 hours; week 4, 20.5 +/- 1.8 mg/24 hours; week 8, 18.8 +/- 1.6 mg/24 hours; and week 12, 17.2 +/- 1.2 mg/24 hours, P < 0.05 week 4 vs. week 0). 129/Sv mice developed significant proteinuria 12 weeks after 5/6 nephrectomy compared to their baseline and to levels achieved in C57BL/6 mice (week 0, 17.2 +/- 1 mg/24 hours; week 4, 14.9 +/- 1.8 mg/24 hours; week 8, 23.8 +/- 6.7 mg/24 hours; and week 12, 36.3 +/- 6.6 mg/24 hours, P < 0.01 week 12 vs. week 0; P < 0.01 129/Sv vs. C57BL/6 at week 12). Mortality varied in response to nephrectomy injury in the different strains. Ten percent of C57BL/6 and 43% of 129/Sv died within 12 weeks after 5/6 nephrectomy. Although 50% of C57BL/6 mice died by 12 weeks after 7/8 nephrectomy, there was only mild glomerulosclerosis (<5%) in C57BL/6 mice even at 24 weeks after 5/6 nephrectomy or 18 weeks after 7/8 nephrectomy. In contrast, glomerulosclerosis was marked in both 129/Sv mice and Swiss-Webster mice as early as 9 weeks after 5/6 nephrectomy: 42% of glomeruli showed sclerosis in 129/Sv mice [average sclerosis index (SI), 0 to 4+ scale, 1.08] vs. 24% in Swiss-Webster mice (average SI, 0.57). Tubulointerstitial fibrosis developed in parallel with glomerulosclerosis in both 129/Sv and Swiss-Webster mice.

CONCLUSION

We conclude that genetic background is one of the important factors determining the susceptibility to the development of glomerulosclerosis in mice. We speculate that the superior effects of renal artery ligation plus cautery to produce glomerulosclerosis may result from higher blood pressure responses due to local ischemia activating the renin-angiotensin system.

Estrogen deficiency accelerates progression of glomerulosclerosis in susceptible mice

Estrogen deficiency may contribute to the development and progression of glomerulosclerosis in postmenopausal women. The responsiveness to estrogens could be controlled by genetic traits related to those that determine the susceptibility to glomerular scarring. This study was undertaken to determine whether the intensity of the sclerotic response was modified by the estrogen status in sclerosis-prone ROP Os/+ mice. Ovariectomized ROP Os/+ mice developed more severe renal dysfunction and glomerulosclerosis than intact, ie, estrogen sufficient age-matched female mice. Ovariectomized ROP Os/+ exhibited increased accumulation of extracellular matrix, predominantly of laminin, and a marked distortion of the glomerular architecture. We found an increase in macrophage infiltration in the mesangium of ovariectomized ROP Os/+. Estrogen deficiency decreased glomerular estrogen receptor expression in ROP Os/+ mice, which we had previously found to be low in the parental ROP strain. Thus, although physiological estrogen levels in young ROP Os/+ mice could not prevent the development of glomerulosclerosis, estrogen deficiency accelerated the progression of glomerular scarring in this mouse strain. This suggests that estrogen replacement will slow but not prevent the progression of glomerulosclerosis. It underscores the importance of the genetic composition of individuals that determines the susceptibility to diseases as well as the response to treatment.

Resistance to glomerulosclerosis in B6 mice disappears after menopause

The frequency of chronic renal failure increases with age, especially in women after menopause. Glomerulosclerosis is a common cause of chronic renal failure in aging. We reported that pre-menopausal female C57BL6 (B6) mice are resistant to glomerulosclerosis, irrespective of the type of injury. However, we now show that B6 mice develop progressive glomerulosclerosis after menopause. Glomerular lesions, first recognized in 18-month-old mice, consisted of hypertrophy, vascular pole sclerosis, and mesangial cell proliferation. Diffuse but moderate mesangial sclerosis and more marked hypertrophy were present at 22 months. At 28 to 30 months the glomerulosclerosis was diffuse and increased levels of type I and type IV collagen and transforming growth factor-beta 1 mRNA were present. Urine albumin excretion was significantly increased in 30-month-old mice. Mesangial cells isolated from 28-month-old mice retained their sclerotic phenotype in vitro. Comparison of the effects of uninephrectomy (Nx) in 20-month-old and 2.5-month-old mice revealed a 1.7-fold increase in urine albumin excretion, accelerated glomerulosclerosis, and renal function insufficiency in 20-month-old Nx mice, but not in 2.5-month-old Nx mice. Glycemic levels, glucose, insulin tolerance, and blood pressure were normal at all ages. Thus, B6 mice model the increased frequency of chronic renal failure in postmenopausal women and provide a model for studying the mechanism(s) of glomerulosclerosis in aging women.