A susceptibility gene for kidney disease in an obese mouse model of type II diabetes maps to chromosome 8

Alx3 deficiency disrupts energy homeostasis, alters body composition, and impairs hypothalamic regulation of food intake

The coordination of food intake, energy storage, and expenditure involves complex interactions between hypothalamic neurons and peripheral tissues including pancreatic islets, adipocytes, muscle, and liver. Previous research shows that deficiency of the transcription factor Alx3 alters pancreatic islet-dependent glucose homeostasis. In this study we carried out a comprehensive assessment of metabolic alterations in Alx3 deficiency. We report that Alx3-deficient mice exhibit decreased food intake without changes in body weight, along with reduced energy expenditure and altered respiratory exchange ratio. Magnetic resonance imaging reveals increased adiposity and decreased muscle mass, which was associated with markers of motor and sympathetic denervation. By contrast, Alx3-deficient mice on a high-fat diet show attenuated weight gain and improved insulin sensitivity, compared to control mice. Gene expression analysis demonstrates altered lipogenic and lipolytic gene profiles. In wild type mice Alx3 is expressed in hypothalamic arcuate nucleus neurons, but not in major peripheral metabolic organs. Functional diffusion-weighted magnetic resonance imaging reveals selective hypothalamic responses to fasting in the arcuate nucleus of Alx3-deficient mice. Additionally, altered expression of proopiomelanocortin and melanocortin-3 receptor mRNA in the hypothalamus suggests impaired regulation of feeding behavior. This study highlights the crucial role for Alx3 in governing food intake, energy homeostasis, and metabolic nutrient partitioning, thereby influencing body mass composition.

Mouse and human studies support DSTYK loss of function as a low-penetrance and variable expressivity risk factor for congenital urinary tract anomalies

PURPOSE

Previous work identified rare variants in DSTYK associated with human congenital anomalies of the kidney and urinary tract (CAKUT). Here, we present a series of mouse and human studies to clarify the association, penetrance, and expressivity of DSTYK variants.

METHODS

We phenotypically characterized Dstyk knockout mice of 3 separate inbred backgrounds and re-analyzed the original family segregating the DSTYK c.654+1G>A splice-site variant (referred to as "SSV" below). DSTYK loss of function (LOF) and SSVs were annotated in individuals with CAKUT, epilepsy, or amyotrophic lateral sclerosis vs controls. A phenome-wide association study analysis was also performed using United Kingdom Biobank (UKBB) data.

RESULTS

Results demonstrate ∼20% to 25% penetrance of obstructive uropathy, at least, in C57BL/6J and FVB/NJ Dstyk-/- mice. Phenotypic penetrance increased to ∼40% in C3H/HeJ mutants, with mild-to-moderate severity. Re-analysis of the original family segregating the rare SSV showed low penetrance (43.8%) and no alternative genetic causes for CAKUT. LOF DSTYK variants burden showed significant excess for CAKUT and epilepsy vs controls and an exploratory phenome-wide association study supported association with neurological disorders.

CONCLUSION

These data support causality for DSTYK LOF variants and highlights the need for large-scale sequencing studies (here >200,000 cases) to accurately assess causality for genes and variants to lowly penetrant traits with common population prevalence.

Catalpol alleviates renal damage by improving lipid metabolism in diabetic db/db mice

OBJECTIVE

To evaluate the protective effect of catalpol against diabetic nephropathy in db/db mouse.

METHODS

8 week old C57BLKS/J db/db mice (type 2 diabetic mouse model) were divided into three groups to feed for 16 weeks on chow diet with or without catalpol supplementation. Their food intake, water consumption, body weight, and fasting glucose levels were recorded every 4 weeks. At the end of study, urine and blood samples were examined for several metabolic variables, and kidneys were harvested for structural characterization and microarray analysis.

RESULTS

Catalpol efficiently lowers the fasting glucose and the 24 h urinary albumin excretion rate. Catalpol significantly lowers serum triglycerides, increases high-density lipoproteins, and improves serum creatinine and urea nitrogen. Catalpol-fed mice preserve their kidney structure and renal function better than chow fed db/db mice. Microarray data indicates that lipid metabolism is a potential target of catalpol in exerting protective effect.

CONCLUSION

Catalpol has a renal protective effect in diabetic db/db mice.

Kidney disease models: tools to identify mechanisms and potential therapeutic targets

Acute kidney injury (AKI) and chronic kidney disease (CKD) are worldwide public health problems affecting millions of people and have rapidly increased in prevalence in recent years. Due to the multiple causes of renal failure, many animal models have been developed to advance our understanding of human nephropathy. Among these experimental models, rodents have been extensively used to enable mechanistic understanding of kidney disease induction and progression, as well as to identify potential targets for therapy. In this review, we discuss AKI models induced by surgical operation and drugs or toxins, as well as a variety of CKD models (mainly genetically modified mouse models). Results from recent and ongoing clinical trials and conceptual advances derived from animal models are also explored.

Immunologic and endocrine functions of adipose tissue: implications for kidney disease

Excess adiposity can induce adverse sequelae in multiple cell types and organ systems. The transition from the lean to the obese state is characterized by fundamental cellular changes at the level of the adipocyte. These changes affect the local microenvironment within the respective adipose tissue but can also affect nonadipose systems. Adipocytes within fat pads respond to chronic nutrient excess through hyperplasia or hypertrophy, which can differentially affect interorgan crosstalk between various adipose depots and other organs. This crosstalk is dependent on the unique ability of the adipocyte to coordinate metabolic adjustments throughout the body and to integrate responses to maintain metabolic homeostasis. These actions occur through the release of free fatty acids and metabolites during times of energy need - a process that is altered in the obese state. In addition, adipocytes release a wide array of signalling molecules, such as sphingolipids, as well as inflammatory and hormonal factors (adipokines) that are critical for interorgan crosstalk. The interactions of adipose tissue with the kidney - referred to as the adipo-renal axis - are important for normal kidney function as well as the response of the kidney to injury. Here, we discuss the mechanistic basis of this interorgan crosstalk, which clearly has great therapeutic potential given the increasing rates of chronic kidney disease secondary to obesity and type 2 diabetes mellitus.

Modelling diabetic nephropathy in mice

Diabetic nephropathy (DN) is a leading cause of end-stage renal disease in the developed world. Accordingly, an urgent need exists for new, curative treatments as well as for biomarkers to stratify risk of DN among individuals with diabetes mellitus. A barrier to progress in these areas has been a lack of animal models that faithfully replicate the main features of human DN. Such models could be used to define the pathogenesis, identify drug targets and test new therapies. Owing to their tractability for genetic manipulation, mice are widely used to model human diseases, including DN. Questions have been raised, however, about the general utility of mouse models in human drug discovery. Standard mouse models of diabetes typically manifest only modest kidney abnormalities, whereas accelerated models, induced by superimposing genetic stressors, recapitulate key features of human DN. Incorporation of systems biology approaches and emerging data from genomics and metabolomics studies should enable further model refinement. Here, we discuss the current status of mouse models for DN, their limitations and opportunities for improvement. We emphasize that future efforts should focus on generating robust models that reproduce the major clinical and molecular phenotypes of human DN.

GSK-3β inhibitor attenuates urinary albumin excretion in type 2 diabetic db/db mice, and delays epithelial-to-mesenchymal transition in mouse kidneys and podocytes

The mechanism underlying epithelial‑to‑mesenchymal transition (EMT) caused by high glucose (HG) stimulation in diabetic nephropathy (DN) remains to be fully elucidated. The present study investigated the effects of HG on EMT and the activity of glycogen synthase kinase 3β (GSK‑3β) in podocytes and the kidneys of db/db mice, and assessed the effects of (2'Z, 3'E)‑6‑bromoindirubin‑3'‑oxime (BIO), an inhibitor of GSK‑3β, on EMT and glomerular injury. The resulting data showed that the activity of GSK‑3β was upregulated by HG and downregulated by BIO in the podocytes and the renal cortex. The expression levels of epithelial markers, including nephrin, podocin and synaptopodin, were decreased by HG and increased by BIO, whereas the reverse were true for mesenchymal markers, including α‑smooth muscle actin (α‑SMA) and fibronectin. The expression levels of β‑catenin and Snail, in contrast to current understanding of the Wnt signaling pathway, were increased by HG and decreased by BIO. In addition, expression of the vitamin D receptor (VDR) was decreased by HG and increased by BIO. In conclusion, the present study revealed that the mechanism by which BIO inhibited HG‑mediated EMT in podocytes and the renal cortex was primarily due to the VDR. Treatment with BIO protected renal function by maintaining the integrity of the filtration membrane and decreasing UAE, but not by regulating blood glucose. Therefore, GSK‑3β may be used as a sensitive biomarker of DN, and its inhibition by BIO may be effective in the treatment of DN.

Epigenetic Histone Modifications Involved in Profibrotic Gene Regulation by 12/15-Lipoxygenase and Its Oxidized Lipid Products in Diabetic Nephropathy

AIMS

Epigenetic mechanisms, including histone post-translational modifications and DNA methylation, are implicated in the pathogenesis of diabetic nephropathy (DN), but the mediators are not well known. Moreover, although dyslipidemia contributes to DN, epigenetic changes triggered by lipids are unclear. In diabetes, increased expression of 12/15-lipoxygenase (12/15-LO) enhances oxidized lipids such as 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], which promote oxidant stress, glomerular and mesangial cell (MC) dysfunction, and fibrosis, and mediate the actions of profibrotic growth factors. We hypothesized that 12/15-LO and its oxidized lipid products can regulate epigenetic mechanisms mediating profibrotic gene expression related to DN.

RESULTS

12(S)-HETE increased profibrotic gene expression and enrichment of permissive histone lysine modifications at their promoters in MCs. 12(S)-HETE also increased protein levels of SET7, a histone H3 lysine 4 methyltransferase, and promoted its nuclear translocation and enrichment at profibrotic gene promoters. Furthermore, SET7 (Setd7) gene silencing inhibited 12(S)-HETE-induced profibrotic gene expression. 12/15-LO (Alox15) gene silencing or genetic knockout inhibited transforming growth factor-β1 (TGF-β1)-induced expression of Setd7 and profibrotic genes and histone modifications in MCs. Furthermore, 12/15-LO knockout in mice ameliorated key features of DN and abrogated increases in renal SET7 and profibrotic genes. Additionally, 12/15-LO siRNAs in vivo blocked increases in renal SET7 and profibrotic genes in diabetic mice.

INNOVATION AND CONCLUSION

These novel results demonstrate for the first time that 12/15-LO-derived oxidized lipids regulate histone modifications associated with profibrotic gene expression in MCs, and 12/15-LO can mediate similar actions of TGF-β1 and diabetes. Targeting 12/15-LO might be a useful strategy to inhibit key epigenetic mechanisms involved in DN.

An Update on the Use of Animal Models in Diabetic Nephropathy Research

In the current review, we discuss limitations and recent advances in animal models of diabetic nephropathy (DN). As in human disease, genetic factors may determine disease severity with the murine FVB and DBA/2J strains being more susceptible to DN than C57BL/6J mice. On the black and tan, brachyuric (BTBR) background, leptin deficient (ob/ob) mice develop many of the pathological features of human DN. Hypertension synergises with hyperglycemia to promote nephropathy in rodents. Moderately hypertensive endothelial nitric oxide synthase (eNOS(-/-)) deficient diabetic mice develop hyaline arteriosclerosis and nodular glomerulosclerosis and induction of renin-dependent hypertension in diabetic Cyp1a1mRen2 rats mimics moderately severe human DN. In addition, diabetic eNOS(-/-) mice and Cyp1a1mRen2 rats recapitulate many of the molecular pathways activated in the human diabetic kidney. However, no model exhibits all the features of human DN; therefore, researchers should consider biochemical, pathological, and transcriptomic data in selecting the most appropriate model to study their molecules and pathways of interest.

Oxidative/Nitrative Stress and Inflammation Drive Progression of Doxorubicin-Induced Renal Fibrosis in Rats as Revealed by Comparing a Normal and a Fibrosis-Resistant Rat Strain

Chronic renal fibrosis is the final common pathway of end stage renal disease caused by glomerular or tubular pathologies. Genetic background has a strong influence on the progression of chronic renal fibrosis. We recently found that Rowett black hooded rats were resistant to renal fibrosis. We aimed to investigate the role of sustained inflammation and oxidative/nitrative stress in renal fibrosis progression using this new model. Our previous data suggested the involvement of podocytes, thus we investigated renal fibrosis initiated by doxorubicin-induced (5 mg/kg) podocyte damage. Doxorubicin induced progressive glomerular sclerosis followed by increasing proteinuria and reduced bodyweight gain in fibrosis-sensitive, Charles Dawley rats during an 8-week long observation period. In comparison, the fibrosis-resistant, Rowett black hooded rats had longer survival, milder proteinuria and reduced tubular damage as assessed by neutrophil gelatinase-associated lipocalin (NGAL) excretion, reduced loss of the slit diaphragm protein, nephrin, less glomerulosclerosis, tubulointerstitial fibrosis and matrix deposition assessed by periodic acid–Schiff, Picro-Sirius-red staining and fibronectin immunostaining. Less fibrosis was associated with reduced profibrotic transforming growth factor-beta, (TGF-β1) connective tissue growth factor (CTGF), and collagen type I alpha 1 (COL-1a1) mRNA levels. Milder inflammation demonstrated by histology was confirmed by less monocyte chemotactic protein 1 (MCP-1) mRNA. As a consequence of less inflammation, less oxidative and nitrative stress was obvious by less neutrophil cytosolic factor 1 (p47^phox) and NADPH oxidase-2 (p91^phox) mRNA. Reduced oxidative enzyme expression was accompanied by less lipid peroxidation as demonstrated by 4-hydroxynonenal (HNE) and less protein nitrosylation demonstrated by nitrotyrosine (NT) immunohistochemistry and quantified by Western blot. Our results demonstrate that mediators of fibrosis, inflammation and oxidative/nitrative stress were suppressed in doxorubicin nephropathy in fibrosis-resistant Rowett black hooded rats underlying the importance of these pathomechanisms in the progression of renal fibrosis initiated by glomerular podocyte damage.

A transcriptional network underlies susceptibility to kidney disease progression

The molecular networks that control the progression of chronic kidney diseases (CKD) are poorly defined. We have recently shown that the susceptibility to development of renal lesions after nephron reduction is controlled by a locus on mouse chromosome 6 and requires epidermal growth factor receptor (EGFR) activation. Here, we identified microphthalmia-associated transcription factor A (MITF-A), a bHLH-Zip transcription factor, as a modifier of CKD progression. Sequence analysis revealed a strain-specific mutation in the 5' UTR that decreases MITF-A protein synthesis in lesion-prone friend virus B NIH (FVB/N) mice. More importantly, we dissected the molecular pathway by which MITF-A modulates CKD progression. MITF-A interacts with histone deacetylases to repress the transcription of TGF-α, a ligand of EGFR, and antagonizes transactivation by its related partner, transcription factor E3 (TFE3). Consistent with the key role of this network in CKD, Tgfa gene inactivation protected FVB/N mice from renal deterioration after nephron reduction. These data are relevant to human CKD, as we found that the TFE3/MITF-A ratio was increased in patients with damaged kidneys. Our study uncovers a novel transcriptional network and unveils novel potential prognostic and therapeutic targets for preventing human CKD progression.

Diabetic kidney disease in FVB/NJ Akita mice: temporal pattern of kidney injury and urinary nephrin excretion

Akita mice are a genetic model of type 1 diabetes. In the present studies, we investigated the phenotype of Akita mice on the FVB/NJ background and examined urinary nephrin excretion as a marker of kidney injury. Male Akita mice were compared with non-diabetic controls for functional and structural characteristics of renal and cardiac disease. Podocyte number and apoptosis as well as urinary nephrin excretion were determined in both groups. Male FVB/NJ Akita mice developed sustained hyperglycemia and albuminuria by 4 and 8 weeks of age, respectively. These abnormalities were accompanied by a significant increase in systolic blood pressure in 10-week old Akita mice, which was associated with functional, structural and molecular characteristics of cardiac hypertrophy. By 20 weeks of age, Akita mice developed a 10-fold increase in albuminuria, renal and glomerular hypertrophy and a decrease in the number of podocytes. Mild-to-moderate glomerular mesangial expansion was observed in Akita mice at 30 weeks of age. In 4-week old Akita mice, the onset of hyperglycemia was accompanied by increased podocyte apoptosis and enhanced excretion of nephrin in urine before the development of albuminuria. Urinary nephrin excretion was also significantly increased in albuminuric Akita mice at 16 and 20 weeks of age and correlated with the albumin excretion rate. These data suggest that: 1. FVB/NJ Akita mice have phenotypic characteristics that may be useful for studying the mechanisms of kidney and cardiac injury in diabetes, and 2. Enhanced urinary nephrin excretion is associated with kidney injury in FVB/NJ Akita mice and is detectable early in the disease process.

Identification of the nephropathy-susceptibility locus HIVAN4

HIVAN1, HIVAN2, and HIVAN3 are nephropathy-susceptibility loci previously identified in the HIV-1 transgenic mouse, a model of collapsing glomerulopathy. The HIVAN1 and HIVAN2 loci modulate expression of Nphs2, which encodes podocin and several other podocyte-expressed genes. To identify additional loci predisposing to nephropathy, we performed a genome-wide scan in 165 backcross mice generated between the nephropathy-sensitive HIV-1-transgenic FVB/NJ (TgFVB) strain and the resistant Balb/cJ (BALB) strain. We identified a major susceptibility locus (HIVAN4) on chromosome 6 G3-F3, with BALB alleles conferring a twofold reduction in severity (peak LOD score = 4.0). Similar to HIVAN1 and HIVAN2, HIVAN4 modulated expression of Nphs2, indicating a common pathway underlying these loci. We independently confirmed the HIVAN4 locus in a sister TgFVB colony that experienced a dramatic loss of nephropathy subsequent to a breeding bottleneck. In this low-penetrance line, 3% of the genome was admixed with BALB alleles, suggesting a remote contamination event. The admixture localized to discrete segments on chromosome 2 and at the HIVAN4 locus. HIVAN4 candidate genes include killer lectin-like receptor genes as well as A2m and Ptpro, whose gene products are enriched in the glomerulus and interact with HIV-1 proteins. In summary, these data identify HIVAN4 as a major quantitative trait locus for nephropathy and a transregulator of Nphs2. Furthermore, similar selective breeding strategies may help identify further susceptibility loci.

Mouse models and the interpretation of human GWAS in type 2 diabetes and obesity

Within the last 3 years, genome-wide association studies (GWAS) have had unprecedented success in identifying loci that are involved in common diseases. For example, more than 35 susceptibility loci have been identified for type 2 diabetes and 32 for obesity thus far. However, the causal gene and variant at a specific linkage disequilibrium block is often unclear. Using a combination of different mouse alleles, we can greatly facilitate the understanding of which candidate gene at a particular disease locus is associated with the disease in humans, and also provide functional analysis of variants through an allelic series, including analysis of hypomorph and hypermorph point mutations, and knockout and overexpression alleles. The phenotyping of these alleles for specific traits of interest, in combination with the functional analysis of the genetic variants, may reveal the molecular and cellular mechanism of action of these disease variants, and ultimately lead to the identification of novel therapeutic strategies for common human diseases. In this Commentary, we discuss the progress of GWAS in identifying common disease loci for metabolic disease, and the use of the mouse as a model to confirm candidate genes and provide mechanistic insights.

The molecular pathogenesis of HIV-1 associated nephropathy: recent advances

HIV-1-associated nephropathy (HIVAN) is a major complication of HIV-1 infection, frequently resulting in kidney failure. HIVAN arises due to HIV-1-induced dysregulation of podocytes, the glomerular epithelial cells that establish and maintain the kidney filtration barrier. Host genetic factors are important for the development of HIVAN. The risk of HIVAN is greatest in populations of African ancestry, and is attributable to a genetic variation at the APOL1 locus on chromosome 22. Mouse models of HIVAN enable delineation of dysregulated pathways underlying disease. Identification of HIVAN susceptibility loci in a mouse model, combined with expression quantitative trait locus mapping, has demonstrated that murine HIVAN loci transregulate podocyte gene expression. HIV-1 induces perturbations in podocyte expression response, suggesting that HIV-1 potentially interferes with compensatory pathways that normally restore cellular homeostasis in the face of genetic mutations. These findings present a framework for identification of podocyte transregulators and reconstruction of the molecular networks connecting susceptibility genes to the development of nephropathy.

Recent insights into diabetic renal injury from the db/db mouse model of type 2 diabetic nephropathy

The db/db mouse is the most widely used animal model of type 2 diabetic nephropathy. Recent studies have utilized genetic backcrossing with transgenic mouse strains to create novel db/db strains that either lack or overexpress specific genes. These novel strains [ICAM-1-/-, CCL2-/-, MKK3-/-, osteopontin-/-, plasminogen activator inhibitor-1 (PAI-1)-/-, endothelial nitric oxide synthase-/-, SOD-Tg, rCAT-Tg] have provided valuable insights into the molecular mechanisms which promote diabetic renal injury. In addition, surgical removal of one kidney has been shown to accelerate injury in the remaining kidney of diabetic db/db mice. A number of novel therapeutic agents have also been tested in db/db mice, including inhibitors of inflammation (chemokine receptor antagonists, anti-CCL2 RNA aptamer, anti-c-fms antibody); oxidative stress (oxykine, biliverdin); the renin-angiotensin-aldosterone system (aliskiren, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, eplerenone); advanced glycation end products (AGE; pyridoxamine, alagebrium, soluble AGE receptor); angiogenesis (NM-3, anti-CXCL12 RNA aptamer, soluble Flt-1); lipid accumulation (statins, farnesoid X receptor agonists, Omacor); intracellular signaling pathways (PKC-β or JNK inhibitors); and fibrosis [transforming growth factor (TGF)-β antibody, TGF-βR kinase inhibitor, soluble betaglycan, SMP-534, CTGF-antisense oligonucleotide, mutant PAI-1, pirfenidone], which have identified potential therapeutic targets for clinical translation. This review summarizes the advances in knowledge gained from studies in genetically modified db/db mice and treatment of db/db mice with novel therapeutic agents.

Susceptible mice: identifying a diabetic nephropathy disease locus using a murine model

Diabetic nephropathy is a common, complex disease with a clear genetic predisposition. Human gene association studies are beginning to bear fruit by identifying gene loci that increase diabetic nephropathy risk. Chua et al. report a similar study in diabetic mice that reveals a major nephropathy locus on chromosome 8. Could this be a human nephropathy gene? Time will tell, but such findings will at least improve the use of mouse models of human kidney disease.