Prostacyclin Mitigates Renal Fibrosis by Activating Fibroblast Prostaglandin I 2 Receptor

SIGNIFICANCE STATEMENT

Renal fibrosis is a common pathologic process of progressive CKD. We have provided strong evidence that PGI 2 is an important component in the kidney injury/repairing process by reducing fibrosis and protecting renal function from declining. In our study, administration of a PGI 2 analog or selective PTGIR agonist after the acute injury ameliorated renal fibrosis. Our findings provide new insights into the role of PGI 2 in kidney biology and suggest that targeting PGI 2 /PTGIR may be a potential therapeutic strategy for CKD.

BACKGROUND

Prostanoids have been demonstrated to be important modulators to maintain tissue homeostasis in response to physiologic or pathophysiologic stress. Prostacyclin (PGI 2 ) is a member of prostanoids. While limited studies have shown that PGI 2 is involved in the tissue injury/repairing process, its role in renal fibrosis and CKD progression requires further investigation.

METHODS

Prostacyclin synthase ( Ptgis )-deficient mice, prostaglandin I 2 receptor ( Ptgir )-deficient mice, and an oral PGI 2 analog and selective PTGIR agonist were used to examine the role of PGI 2 in renal fibrosis in mouse models. We also analyzed the single-cell RNA-Seq data to examine the PTGIR -expressing cells in the kidneys of patients with CKD.

RESULTS

Increased PTGIS expression has been observed in fibrotic kidneys in both humans and mice. Deletion of the PTGIS gene aggravated renal fibrosis and decline of renal function in murine models. A PGI 2 analog or PTGIR agonist that was administered after the acute injury ameliorated renal fibrosis. PTGIR, the PGI 2 receptor, deficiency blunted the protective effect of the PGI 2 analog. Fibroblasts and myofibroblasts were the major cell types expressing PTGIR in the kidneys of patients with CKD. Deletion of PTGIR in collagen-producing fibroblastic cells aggravated renal fibrosis. The protective effect of PGI 2 was associated with the inhibition of fibroblast activation through PTGIR-mediated signaling.

CONCLUSIONS

PGI 2 is an important component in the kidney injury/repairing process by preventing the overactivation of fibroblasts during the repairing process and protecting the kidney from fibrosis and decline of renal function. Our findings suggest that PGI 2 /PTGIR is a potential therapeutic target for CKD.

Unbiased kidney-centric molecular categorization of chronic kidney disease as a step towards precision medicine

Current classification of chronic kidney disease (CKD) into stages using indirect systemic measures (estimated glomerular filtration rate (eGFR) and albuminuria) is agnostic to the heterogeneity of underlying molecular processes in the kidney thereby limiting precision medicine approaches. To generate a novel CKD categorization that directly reflects within kidney disease drivers we analyzed publicly available transcriptomic data from kidney biopsy tissue. A Self-Organizing Maps unsupervised artificial neural network machine-learning algorithm was used to stratify a total of 369 patients with CKD and 46 living kidney donors as healthy controls. Unbiased stratification of the discovery cohort resulted in identification of four novel molecular categories of disease termed CKD-Blue, CKD-Gold, CKD-Olive, CKD-Plum that were replicated in independent CKD and diabetic kidney disease datasets and can be further tested on any external data at kidneyclass.org. Each molecular category spanned across CKD stages and histopathological diagnoses and represented transcriptional activation of distinct biological pathways. Disease progression rates were highly significantly different between the molecular categories. CKD-Gold displayed rapid progression, with significant eGFR-adjusted Cox regression hazard ratio of 5.6 [1.01-31.3] for kidney failure and hazard ratio of 4.7 [1.3-16.5] for composite of kidney failure or a 40% or more eGFR decline. Urine proteomics revealed distinct patterns between the molecular categories, and a 25-protein signature was identified to distinguish CKD-Gold from other molecular categories. Thus, patient stratification based on kidney tissue omics offers a gateway to non-invasive biomarker-driven categorization and the potential for future clinical implementation, as a key step towards precision medicine in CKD.

Mapping the single-cell transcriptomic response of murine diabetic kidney disease to therapies

Diabetic kidney disease (DKD) occurs in ∼40% of patients with diabetes and causes kidney failure, cardiovascular disease, and premature death. We analyzed the response of a murine DKD model to five treatment regimens using single-cell RNA sequencing (scRNA-seq). Our atlas of ∼1 million cells revealed a heterogeneous response of all kidney cell types both to DKD and its treatment. Both monotherapy and combination therapies targeted differing cell types and induced distinct and non-overlapping transcriptional changes. The early effects of sodium-glucose cotransporter-2 inhibitors (SGLT2i) on the S1 segment of the proximal tubule suggest that this drug class induces fasting mimicry and hypoxia responses. Diabetes downregulated the spliceosome regulator serine/arginine-rich splicing factor 7 (Srsf7) in proximal tubule that was specifically rescued by SGLT2i. In vitro proximal tubule knockdown of Srsf7 induced a pro-inflammatory phenotype, implicating alternative splicing as a driver of DKD and suggesting SGLT2i regulation of proximal tubule alternative splicing as a potential mechanism of action for this drug class.

Profibrotic Circulating Proteins and Risk of Early Progressive Renal Decline in Patients With Type 2 Diabetes With and Without Albuminuria

OBJECTIVE

The role of fibrosis in early progressive renal decline in type 2 diabetes is unknown. Circulating WFDC2 (WAP four-disulfide core domain protein 2) and matrix metalloproteinase 7 (MMP-7; Matrilysin) are postulated to be biomarkers of renal fibrosis. This study examined an association of circulating levels of these proteins with early progressive renal decline.

RESEARCH DESIGN AND METHODS

Individuals with type 2 diabetes enrolled in the Joslin Kidney Study with an estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m² were monitored for 6-12 years to ascertain fast early progressive renal decline, defined as eGFR loss ≥5 mL/min/1.73 m²/year.

RESULTS

A total of 1,181 individuals were studied: 681 without and 500 with albuminuria. Median eGFR and albumin-to-creatinine ratio (ACR) at baseline were 97 mL/min/1.73 m² and 24 mg/g, respectively. During follow-up, 152 individuals experienced fast early progressive renal decline: 6.9% in those with normoalbuminuria and 21% with albuminuria. In both subgroups, the risk of renal decline increased with increasing baseline levels of WFDC2 (P < 0.0001) and MMP-7 (P < 0.0001). After adjustment for relevant clinical characteristics and known biomarkers, an increase by one quartile in the fibrosis index (combination of levels of WFDC2 and MMP-7) was associated with higher risk of renal decline (odds ratio 1.63; 95% CI 1.30-2.04). The association was similar and statistically significant among patients with and without albuminuria.

CONCLUSIONS

Elevation of circulating profibrotic proteins is associated with the development of early progressive renal decline in type 2 diabetes. This association is independent from albuminuria status and points to the importance of the fibrotic process in the development of early renal decline.

The Use of Genomics to Drive Kidney Disease Drug Discovery and Development

As opposed to diseases such as cancer, autoimmune disease, and diabetes, identifying drugs to treat CKD has proven significantly more challenging. Over the past 2 decades, new potential therapeutic targets have been identified as genetically altered proteins involved in rare monogenetic kidney diseases. Other possible target genes have been implicated through common genetic polymorphisms associated with CKD in the general population. Significant challenges remain before translating these genetic insights into clinical therapies for CKD. This paper will discuss how genetic variants may be leveraged to develop drugs and will especially focus on those genes associated with CKD to exemplify the value and challenges in including genetic information in the drug development pipeline.

Targeting VE-PTP phosphatase protects the kidney from diabetic injury

Diabetic nephropathy is a leading cause of kidney failure. VE-PTP phosphatase expression is increased in the endothelium of rodents with diabetes and hypertension. Genetic deletion of VE-PTP reduces kidney injury in diabetic mice, suggesting it may be a therapeutic target.

Diabetic nephropathy is a leading cause of end-stage kidney failure. Reduced angiopoietin-TIE2 receptor tyrosine kinase signaling in the vasculature leads to increased vascular permeability, inflammation, and endothelial cell loss and is associated with the development of diabetic complications. Here, we identified a mechanism to explain how TIE2 signaling is attenuated in diabetic animals. Expression of vascular endothelial protein tyrosine phosphatase VE-PTP (also known as PTPRB), which dephosphorylates TIE2, is robustly up-regulated in the renal microvasculature of diabetic rodents, thereby reducing TIE2 activity. Increased VE-PTP expression was dependent on hypoxia-inducible factor transcriptional activity in vivo. Genetic deletion of VE-PTP restored TIE2 activity independent of ligand availability and protected kidney structure and function in a mouse model of severe diabetic nephropathy. Mechanistically, inhibition of VE-PTP activated endothelial nitric oxide synthase and led to nuclear exclusion of the FOXO1 transcription factor, reducing expression of pro-inflammatory and pro-fibrotic gene targets. In sum, we identify inhibition of VE-PTP as a promising therapeutic target to protect the kidney from diabetic injury.

Nonselective Cyclooxygenase Inhibition Retards Cyst Progression in a Murine Model of Autosomal Dominant Polycystic Kidney Disease

Aim: Autosomal dominant polycystic kidney disease is one of the most common genetic renal diseases. Cyclooxygenase plays an important role in epithelial cell proliferation and may contribute to the mechanisms underlying cyst formation. The aim of the present study was to evaluate the role of cyclooxygenase inhibition in the cyst progression in polycystic kidney disease. Method: Pkd2^WS25/- mice, a murine model which harbors a compound cis-heterozygous mutation of the Pkd2 gene were used. Cyclooxygenase expression was assessed in both human and murine kidney specimens. Pkd2^WS25/- mice were treated with Sulindac (a nonselective cyclooxygenase inhibitor) or vehicle for 8 months starting at three weeks age, and then renal cyst burden was assessed by kidney weight and volume. Results: Cyclooxygenase-2 expression was up-regulated compared to control kidneys as shown by RNase protection in human polycystic kidneys and immunoblot in mouse Pkd2^WS25/- kidneys. Cyclooxygenase-2 expression was up-regulated in the renal interstitium as well as focal areas of the cystic epithelium (p<0.05). Basal Cyclooxygenase-1 levels were unchanged in both immunohistochemistry and real-time PCR. Administration of Sulindac to Pkd2^WS25/- mice and to control mice for 8 months resulted in reduced kidney weights and volume in cystic mice. Renal function and electrolytes were not significantly different between groups. Conclusion: Thus treatment of a murine model of polycystic kidney disease with Sulindac results in decreased kidney cyst burden. These findings provide additional implications for the use of Cyclooxygenase inhibition as treatment to slow the progression of cyst burden in patients with polycystic kidney disease.

Pathological and Transcriptome Changes in the ReninAAV db/db uNx Model of Advanced Diabetic Kidney Disease Exhibit Features of Human Disease

The ReninAAV db/db uNx model of diabetic kidney disease (DKD) exhibits hallmarks of advanced human disease, including progressive elevations in albuminuria and serum creatinine, loss of glomerular filtration rate, and pathological changes. Microarray analysis of renal transcriptome changes were more similar to human DKD when compared to db/db eNOS−/− model. The model responds to treatment with arterial pressure lowering (lisinopril) or glycemic control (rosiglitazone) at early stages of disease. We hypothesized the ReninAAV db/db uNx model with advanced disease would have residual disease after treatment with lisinopril, rosiglitazone, or combination of both. To test this, ReninAAV db/db uNx mice with advanced disease were treated with lisinopril, rosiglitazone, or combination of both for 10 weeks. All treatment groups showed significant lowering of urinary albumin to creatinine ratio compared to baseline; however, only combination group exhibited lowering of serum creatinine. Treatment improved renal pathological scores compared to baseline values with residual disease evident in all treatment groups when compared to db/m controls. Gene expression analysis by TaqMan supported pathological changes with increased fibrotic and inflammatory markers. The results further validate this model of DKD in which residual disease is present when treated with agents to lower arterial pressure and glycemic control.

Markers of early progressive renal decline in type 2 diabetes suggest different implications for etiological studies and prognostic tests development

To identify determinants of early progressive renal decline in type 2 diabetes a range of markers was studied in 1032 patients enrolled into the 2nd Joslin Kidney Study. eGFR slopes estimated from serial measurements of serum creatinine during 5-12 years of follow-up were used to define early renal decline. At enrollment, all patients had normal eGFR, 58% had normoalbuminuria and 42% had albuminuria. Early renal decline developed in 6% and in 18% patients, respectively. As determinants, we examined baseline values of clinical characteristics, circulating markers: TNFR1, KIM-1, and FGF23, and urinary markers: albumin, KIM-1, NGAL, MCP-1, EGF (all normalized to urinary creatinine) and the ratio of EGF to MCP-1. In univariate analysis, all plasma and urinary markers were significantly associated with risk of early renal decline. When analyzed together, systolic blood pressure, TNFR1, KIM-1, the albumin to creatinine ratio, and the EGF/MCP-1 ratio remained significant with the latter having the strongest effect. Integration of these markers into a multi-marker prognostic test resulted in a significant improvement of discriminatory performance of risk prediction of early renal decline, compared with the albumin to creatinine ratio and systolic blood pressure alone. However, the positive predictive value was only 50% in albuminuric patients. Thus, markers in plasma and urine indicate that the early progressive renal decline in Type 2 diabetes has multiple determinants with strong evidence for involvement of tubular damage. However, new, more informative markers are needed to develop a better prognostic test for such decline that can be used in a clinical setting.

Progressive Renal Disease Established by Renin-Coding Adeno-Associated Virus-Driven Hypertension in Diverse Diabetic Models

Progress in research and developing therapeutics to prevent diabetic kidney disease (DKD) is limited by a lack of animal models exhibiting progressive kidney disease. Chronic hypertension, a driving factor of disease progression in human patients, is lacking in most available models of diabetes. We hypothesized that superimposition of hypertension on diabetic mouse models would accelerate DKD. To test this possibility, we induced persistent hypertension in three mouse models of type 1 diabetes and two models of type 2 diabetes by adeno-associated virus delivery of renin (ReninAAV). Compared with LacZAAV-treated counterparts, ReninAAV-treated type 1 diabetic Akita/129 mice exhibited a substantial increase in albumin-to-creatinine ratio (ACR) and serum creatinine level and more severe renal lesions. In type 2 models of diabetes (C57BKLS db/db and BTBR ob/ob mice), compared with LacZAAV, ReninAAV induced significant elevations in ACR and increased the incidence and severity of histopathologic findings, with increased serum creatinine detected only in the ReninAAV-treated db/db mice. The uninephrectomized ReninAAV db/db model was the most progressive model examined and further characterized. In this model, separate treatment of hyperglycemia with rosiglitazone or hypertension with lisinopril partially reduced ACR, consistent with independent contributions of these disorders to renal disease. Microarray analysis and comparison with human DKD showed common pathways affected in human disease and this model. These results identify novel models of progressive DKD that provide researchers with a facile and reliable method to study disease pathogenesis and support the development of therapeutics.

A Novel Aldosterone Antagonist Limits Renal Injury in 5/6 Nephrectomy

Aldosterone antagonists slow the progression of chronic kidney disease (CKD), but their use is limited by hyperkalemia, especially when associated with RAS inhibitors. We examined the renoprotective effects of Ly, a novel non-steroidal mineralocorticoid receptor (MR) blocker, through two experimental protocols: In Protocol 1, male Munich-Wistar rats underwent 5/6 renal ablation (Nx), being divided into: Nx+V, receiving vehicle, Nx+Eple, given eplerenone, 150 mg/kg/day, and Nx+Ly, given Ly, 20 mg/kg/day. A group of untreated sham-operated rats was also studied. Ly markedly raised plasma renin activity (PRA) and aldosterone, and exerted more effective anti-albuminuric and renoprotective action than eplerenone. In Protocol 2, Nx rats remained untreated until Day 60, when they were divided into: Nx+V receiving vehicle; Nx+L treated with losartan, 50 mg/kg/day; Nx+L+Eple, given losartan and eplerenone, and Nx+L+Ly, given losartan and Ly. Treatments lasted for 90 days. As an add-on to losartan, Ly normalized blood pressure and albuminuria, and prevented CKD progression more effectively than eplerenone. This effect was associated with strong stimulation of PRA and aldosterone. Despite exhibiting higher affinity for the MR than either eplerenone or spironolactone, Ly caused no hyperkalemia. Ly may become a novel asset in the effort to detain the progression of CKD.

Role of TGF-alpha in the progression of diabetic kidney disease

Transforming growth factor-alpha (TGFA) has been shown to play a role in experimental chronic kidney disease associated with nephron reduction, while its role in diabetic kidney disease (DKD) is unknown. We show here that intrarenal TGFA mRNA expression, as well as urine and serum TGFA, are increased in human DKD. We used a TGFA neutralizing antibody to determine the role of TGFA in two models of renal disease, the remnant surgical reduction model and the uninephrectomized (uniNx) db/db DKD model. In addition, the contribution of TGFA to DKD progression was examined using an adeno-associated virus approach to increase circulating TGFA in experimental DKD. In vivo blockade of TGFA attenuated kidney disease progression in both nondiabetic 129S6 nephron reduction and Type 2 diabetic uniNx db/db models, whereas overexpression of TGFA in uniNx db/db model accelerated renal disease. Therapeutic activity of the TGFA antibody was enhanced with renin angiotensin system inhibition with further improvement in renal parameters. These findings suggest a pathologic contribution of TGFA in DKD and support the possibility that therapeutic administration of neutralizing antibodies could provide a novel treatment for the disease.

Improved clinical trial enrollment criterion to identify patients with diabetes at risk of end-stage renal disease

Design of Phase III trials for diabetic nephropathy currently requires patients at a high risk of progression defined as within three years of a hard end point (end-stage renal disease, 40% loss of estimated glomerular filtration rate, or death). To improve the design of these trials, we used natural history data from the Joslin Kidney Studies of chronic kidney disease in patients with diabetes to develop an improved criterion to identify such patients. This included a training cohort of 279 patients with type 1 diabetes and 134 end points within three years, and a validation cohort of 221 patients with type 2 diabetes and 88 end points. Previous trials selected patients using clinical criteria for baseline urinary albumin-to-creatinine ratio and estimated glomerular filtration rate. Application of these criteria to our cohort data yielded sensitivities (detection of patients at risk) of 70-80% and prognostic values of only 52-63%. We applied classification and regression trees analysis to select from among all clinical characteristics and markers the optimal prognostic criterion that divided patients with type 1 diabetes according to risk. The optimal criterion was a serum tumor necrosis factor receptor 1 level over 4.3 ng/ml alone or 2.9-4.3 ng/ml with an albumin-to-creatinine ratio over 1900 mg/g. Remarkably, this criterion produced similar results in both type 1 and type 2 diabetic patients. Overall, sensitivity and prognostic value were high (72% and 81%, respectively). Thus, application of this criterion to enrollment in future clinical trials could reduce the sample size required to achieve adequate statistical power for detection of treatment benefits.

Developing Treatments for Chronic Kidney Disease in the 21st Century

Chronic kidney disease (CKD) is a lethal and rapidly increasing burden on society. Despite this, there are relatively few therapies in development for the treatment of CKD. Several recent costly phase 3 trials have failed to provide improved renal outcomes, diminishing interest in pharmaceutical investment. Furthermore, poor patient, physician, and payer awareness of CKD as a diagnosis has contributed to slow trial enrollment and successful implementation of these trials. Nevertheless, several therapeutics remain in development for the treatment of CKD, including mineralocorticoid-receptor antagonists, sodium/glucose cotransporter 2 inhibitors, anti-inflammatory drugs, and drugs that mitigate oxidative injury. Success of future CKD therapeutic trials will depend not only on improved understanding of disease pathogenesis, but also on improved trial enrollment rates, through increasing awareness of this disease by the public, policy makers, and the greater medical community.

From bench to patient: model systems in drug discovery

Model systems, including laboratory animals, microorganisms, and cell- and tissue-based systems, are central to the discovery and development of new and better drugs for the treatment of human disease. In this issue, Disease Models & Mechanisms launches a Special Collection that illustrates the contribution of model systems to drug discovery and optimisation across multiple disease areas. This collection includes reviews, Editorials, interviews with leading scientists with a foot in both academia and industry, and original research articles reporting new and important insights into disease therapeutics. This Editorial provides a summary of the collection's current contents, highlighting the impact of multiple model systems in moving new discoveries from the laboratory bench to the patients' bedsides.

Drug Discovery Collection: This Editorial introduces the new DMM Special Collection entitled ‘From bench to patient: model systems in drug discovery’, providing a summary of its contents and highlighting the impact of multiple model systems in moving new discoveries from bench to patient.

Prostaglandin-dependent modulation of dopaminergic neurotransmission elicits inflammation-induced aversion in mice

Systemic inflammation causes malaise and general feelings of discomfort. This fundamental aspect of the sickness response reduces the quality of life for people suffering from chronic inflammatory diseases and is a nuisance during mild infections like common colds or the flu. To investigate how inflammation is perceived as unpleasant and causes negative affect, we used a behavioral test in which mice avoid an environment that they have learned to associate with inflammation-induced discomfort. Using a combination of cell-type–specific gene deletions, pharmacology, and chemogenetics, we found that systemic inflammation triggered aversion through MyD88-dependent activation of the brain endothelium followed by COX1-mediated cerebral prostaglandin E2 (PGE2) synthesis. Further, we showed that inflammation-induced PGE2 targeted EP1 receptors on striatal dopamine D1 receptor–expressing neurons and that this signaling sequence induced aversion through GABA-mediated inhibition of dopaminergic cells. Finally, we demonstrated that inflammation-induced aversion was not an indirect consequence of fever or anorexia but that it constituted an independent inflammatory symptom triggered by a unique molecular mechanism. Collectively, these findings demonstrate that PGE2-mediated modulation of the dopaminergic motivational circuitry is a key mechanism underlying the negative affect induced by inflammation.

Overcoming Barriers in Kidney Health-Forging a Platform for Innovation

Innovation in kidney diseases is not commensurate with the effect of these diseases on human health and mortality or innovation in other key therapeutic areas. A primary cause of the dearth in innovation is that kidney diseases disproportionately affect a demographic that is largely disenfranchised, lacking sufficient advocacy, public attention, and funding. A secondary and likely consequent cause is that the existing infrastructure supporting nephrology research pales in comparison with those for other internal medicine specialties, especially cardiology and oncology. Citing such inequities, however, is not enough. Changing the status quo will require a coordinated effort to identify and redress the existing deficits. Specifically, these deficits relate to the need to further develop and improve the following: understanding of the disease mechanisms and pathophysiology, patient engagement and activism, clinical trial infrastructure, and investigational clinical trial designs as well as coordinated efforts among critical stakeholders. This paper identifies potential solutions to these barriers, some of which are already underway through the Kidney Health Initiative. The Kidney Health Initiative is unique and will serve as a current and future platform from which to overcome these barriers to innovation in nephrology.

Viral transduction of renin rapidly establishes persistent hypertension in diverse murine strains

Mice provide a unique platform to dissect disease pathogenesis, with the availability of recombinant inbred strains and diverse genetically modified strains. Leveraging these reagents to elucidate the mechanisms of hypertensive tissue injury has been hindered by difficulty establishing persistent hypertension in these inbred lines. ANG II infusion provides relatively short-term activation of the renin-angiotensinogen system (RAS) with concomitant elevated arterial pressure. Longer-duration studies using renin transgenic mice are powerful models of chronic hypertension, yet are limited by the genetic background on which the transgene exists and the exposure throughout development. The present studies characterized hypertension produced by transduction with a renin-coding adeno-associated virus (ReninAAV). ReninAAV mice experienced elevated circulating renin with concurrent elevations in arterial pressure. Following a single injection of ReninAAV, arterial pressure increased on average +56 mmHg, an increase that persisted for at least 12 wk in three distinct and widely used strains of adult mice: 129/S6, C56BL/6, and DBA/2J. This was accomplished without surgical implantation of pumps or complex breeding and backcrossing. In addition, ReninAAV mice developed pathophysiological changes associated with chronic hypertension, including increased heart weight and albuminuria. Thus ReninAAV provides a unique tool to study the onset of and effects of persistent hypertension in diverse murine models. This model should facilitate our understanding of the pathogenesis of hypertensive injury.

Estimated glomerular filtration rate progression in UK primary care patients with type 2 diabetes and diabetic kidney disease: a retrospective cohort study

AIMS

To examine the rates of diabetic kidney disease (DKD) progression and associated factors, we undertook a study of estimated glomerular filtration rate (eGFR) in a historical cohort of UK primary care patients with type 2 diabetes mellitus (T2DM) and associated DKD from the Clinical Practice Research Datalink.

METHODS

Our eligible population were patients with definitive T2DM from a recorded diagnostic code with either a diagnosis of chronic kidney disease (CKD) or renal function test values and renal abnormalities consistent with a CKD diagnosis, identified between 1 October 2006 and 31 December 2011. Only patients with albuminuria results reported in mg/l were used for the longitudinal statistical analyses of the eGFR rate of change using multilevel models.

RESULTS

We identified 111,030 patients with T2DM. Among them 58.6% (95% confidence interval (CI): 58.3-58.9) had CKD and 37.2% (95% CI: 36.9-37.5%) had presumed DKD at baseline. Only 19.4% of patients had urinary albumin test results expressed as mg/l in the year prior to index date. Almost two-thirds (63.8%) of patients with T2DM and presumed DKD received prescriptions for angiotensin-converting enzyme (ACE) inhibitors or angiotensin type 1 receptor blockers (ARB) or both. Time-dependent variables that predict subsequent eGFR decline include increased albuminuria, time from index date and older age.

CONCLUSION

Only a minority of diabetic patients with DKD had quantitative albuminuria assessments. The relatively low proportion of DKD patients with ACEi or ARB prescriptions suggests a gap between healthcare practice and available scientific evidence during the study period. Increased albuminuria and older age were the most consistent predictors of subsequent eGFR decline.

Abstract 5439: Metabolomic study of EGFR drug resistance mechanisms

Therapies targeting EGFR often fail after certain period of treatment due to development of resistance. There are many causes of resistance such as genetic mutations of KRAS, BRAF, etc.. Overexpression of other receptor tyrosine kinases can also lead to resistance of EGFR therapies. A therapeutic targeting metabolic phenotypes that can overcome multiple resistance mechanisms is highly desired. In order to identify the Achilles heel of resistant cell metabolism, we investigated the metabolic effects of the current EGFR targeting agents as well as the metabolic differences between sensitive and resistant cancer cells.

Citation Format: Yang Zhao, Bo Tan, Ming-Shang Kuo, Ling Liu, Matthew D. Breyer. Metabolomic study of EGFR drug resistance mechanisms. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5439. doi:10.1158/1538-7445.AM2014-5439

Improving productivity of modern-day drug discovery

The pharmaceutical industry is confronted by increasing costs of clinical development and diminishing productivity. The most challenging aspect of drug development has been the failure of therapeutics in expensive Phase II or III trials, and this is most commonly due to lack of efficacy. More can be done during the drug discovery phase to optimize efficacy-testing in animal models by expending resources to explore the congruence of the animal model with the human disease. Historically, relatively little attention has been paid to validation of these models, but access to molecular mRNA and genetic profiling offers a new lens through which the similarity of these disease models to human diseases can be examined and their utility for exploring therapeutic efficacy can be optimized. Exploring congruent experimental end points in clinical and preclinical experiments will also increase confidence of success in late phase clinical development. The expense of this investment is trivial compared to the costs of a failed clinical trial, more than justifying this endeavor.

Generation of a tenascin-C-CreER2 knockin mouse line for conditional DNA recombination in renal medullary interstitial cells

Renal medullary interstitial cells (RMIC) are specialized fibroblast-like cells that exert important functions in maintaining body fluid homeostasis and systemic blood pressure. Here, we generated a RMIC specific tenascin-C promoter driven inducible CreER2 knockin mouse line with an EGFP reporter. Similar as endogenous tenascin-C expression, the reporter EGFP expression in the tenascin-C-CreER2(+/-) mice was observed in the inner medulla of the kidney, and co-localized with COX2 but not with AQP2 or AQP1, suggesting selective expression in RMICs. After recombination (tenascin-C-CreER2(+/-)/ROSA26-lacZ(+/-) mice + tamoxifen), β-gal activity was restricted to the cells in the inner medulla of the kidney, and didn't co-localize with AQP2, consistent with selective Cre recombinase activity in RMICs. Cre activity was not obvious in other major organs or without tamoxifen treatment. This inducible RMIC specific Cre mouse line should therefore provide a novel tool to manipulate genes of interest in RMICs.

Increased dietary sodium induces COX2 expression by activating NFκB in renal medullary interstitial cells

High salt diet induces renal medullary cyclooxygenase 2 (COX2) expression. Selective blockade of renal medullary COX2 activity in rats causes salt-sensitive hypertension, suggesting a role for renal medullary COX2 in maintaining systemic sodium balance. The present study characterized the cellular location of COX2 induction in the kidney of mice following high salt diet and examined the role of NFκB in mediating this COX2 induction in response to increased dietary salt. High salt diet (8 % NaCl) for 3 days markedly increased renal medullary COX2 expression in C57Bl/6 J mice. Co-immunofluorescence using a COX2 antibody and antibodies against aquaporin-2, ClC-K, aquaporin-1, and CD31 showed that high salt diet-induced COX2 was selectively expressed in renal medullary interstitial cells. By using NFκB reporter transgenic mice, we observed a sevenfold increase of luciferase activity in the renal medulla of the NFκB-luciferase reporter mice following high salt diet, and a robust induction of enhanced green fluorescent protein (EGFP) expression mainly in renal medullary interstitial cells of the NFκB-EGFP reporter mice following high salt diet. Treating high salt diet-fed C57Bl/6 J mice with selective IκB kinase inhibitor IMD-0354 (8 mg/kg bw) substantially suppressed COX2 induction in renal medulla, and also significantly reduced urinary prostaglandin E2 (PGE2). These data therefore suggest that renal medullary interstitial cell NFκB plays an important role in mediating renal medullary COX2 expression and promoting renal PGE2 synthesis in response to increased dietary sodium.

Diabetic nephropathy: a national dialogue

The National Institute of Diabetes and Digestive and Kidney Diseases-supported Kidney Research National Dialogue (KRND) asked the scientific community to formulate and prioritize research objectives that would improve our understanding of kidney function and disease. Several high-priority objectives for diabetic nephropathy were identified in data and sample collection, hypothesis generation, hypothesis testing, and translation promotion. The lack of readily available human samples linked to comprehensive phenotypic, clinical, and demographic data remains a significant obstacle. With data and biological samples in place, several possibilities exist for using new technologies to develop hypotheses. Testing novel disease mechanisms with state-of-the-art tools should continue to be the foundation of the investigative community. Research must be translated to improve diagnosis and treatment of people. The objectives identified by the KRND provide the research community with future opportunities for improving the prevention, diagnosis, and treatment of diabetic nephropathy.

Abstract 1866: Stable isotope resolved metabolomics of colorectal cancer cells treated with inhibitor of monocarboxylate transporter-1

The rationale of this cell based study was to examine the metabolic effects of a synthetic monocarboxylate transporter 1 (MCT1) inhibitor (AR-C155858) on multiple cellular metabolites in colorectal tumor cells using [1,2,3,4,5,6-13C6]-D-glucose or [1,2,3,4,5-13C5]-D-glutamine as the single precursor metabolic tracer. DiFi colorectal cancer cells were cultured for 24 hrs in the presence of 0.1% DMSO (vehicle control) or 100 nM of MCT-1 inhibitor. Intracellular glycolysis intermediates measured by liquid chromatography/mass spectrometry (LC/MS) included phosphoenolpyruvate (PEP), phosphoglycerate (PG), fructose 1,6 bisphosphate (FBP), Glucose-6-phosphate (G6P), Gluconate-6-phosphate, glyceraldehydes 3-phosphate (G3P), ribose-5-phosphate (R5P), seduheptulose-7-phosphate (S7P), pyruvate, and lactate. TCA cycle intermediates measured included malate, α-ketoglutarate, succinate, fumarate, and citrate. Both glutamine and glutamate were also measured. Increases in PEP, PG3, G6P, Gluconate-6-phosphate, G3P, S7P, pyruvate, and lactate were induced by MCT1 inhibitor when traced with 13C6 glucose. When traced with 13C5 glutamine, PEP, G6P, S7P, pyruvate, and lactate were increased by MCT1 inhibitor. In contrast, decreases in α-ketoglutarate and glutamate were seen with both tracers.

Citation Format: Bo Tan, Ming-Shang Kuo, Matthew D. Breyer, Ling Liu, Yang Zhao. Stable isotope resolved metabolomics of colorectal cancer cells treated with inhibitor of monocarboxylate transporter-1. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1866. doi:10.1158/1538-7445.AM2013-1866

Drug discovery for diabetic nephropathy: trying the leap from mouse to man

Diabetic nephropathy is the single major cause of kidney failure in the industrialized world and given the emerging global pandemic of diabetes mellitus, its prevalence is expected to only increase. Because of the lack of dynamic biomarkers that define the rate of kidney function loss, there are few proof-of-concept clinical trials for new therapeutics to treat diabetic nephropathy. A molecular understanding of the pathogenesis of diabetic nephropathy also is lacking. These deficiencies are magnified by the fact that most mouse models of diabetic nephropathy fail to show progressive kidney disease. Recently, some mouse models that showed requisite phenotypic changes of diabetic nephropathy have been identified. Validation of results obtained in these experimental models, and showing whether they accurately can predict clinical response to therapeutics in human diabetic nephropathy, must now be established.

SOD1, but not SOD3, deficiency accelerates diabetic renal injury in C57BL/6-Ins2(Akita) diabetic mice

Superoxide dismutase (SOD) is a major defender against excessive superoxide generated under hyperglycemia. We have recently reported that renal SOD1 (cytosolic CuZn-SOD) and SOD3 (extracellular CuZn-SOD) isoenzymes are remarkably down-regulated in KK/Ta-Ins2(Akita) diabetic mice, which exhibit progressive diabetic nephropathy (DN), but not in DN-resistant C57BL/6- Ins2(Akita) (C57BL/6-Akita) diabetic mice. To determine the role of SOD1 and SOD3 in DN, we generated C57BL/6-Akita diabetic mice with deficiency of SOD1 and/or SOD3 and investigated their renal phenotype at the age of 20 weeks. Increased glomerular superoxide levels were observed in SOD1(-/-)SOD3(+/+) and SOD1(-/-)SOD3(-/-) C57BL/6-Akita mice but not in SOD1(+/+)SOD3(-/-) C57BL/6-Akita mice. The SOD1(-/-)SOD3(+/+) and SOD1(-/-)SOD3(-/-) C57BL/6-Akita mice exhibited higher glomerular filtration rate, increased urinary albumin levels, and advanced mesangial expansion as compared with SOD1(+/+)SOD3(+/+) C57BL/6-Akita mice, yet the severity of DN did not differ between the SOD1(-/-)SOD3(+/+) and SOD1(-/-)SOD3(-/-) C57BL/6-Akita groups. Increased renal mRNA expression of transforming growth factor-β1 (TGF-β1) and connective tissue growth factor (CTGF), reduced glomerular nitric oxide (NO), and increased renal prostaglandin E2 (PGE2) production were noted in the SOD1(-/-)SOD3(+/+) and SOD1(-/-)SOD3(-/-) C57BL/6-Akita mice. This finding indicates that such renal changes in fibrogenic cytokines, NO, and PGE2, possibly caused by superoxide excess, would contribute to the development of overt albuminuria by promoting mesangial expansion, endothelial dysfunction, and glomerular hyperfiltration. The present results demonstrate that deficiency of SOD1, but not SOD3, increases renal superoxide in the setting of diabetes and causes overt renal injury in nephropathy-resistant diabetic mice, and that SOD3 deficiency does not provide additive effects on the severity of DN in SOD1-deficient C57BL/6-Akita mice.

Circulating αKlotho influences phosphate handling by controlling FGF23 production

The FGF23 coreceptor αKlotho (αKL) is expressed as a membrane-bound protein (mKL) that forms heteromeric complexes with FGF receptors (FGFRs) to initiate intracellular signaling. It also circulates as an endoproteolytic cleavage product of mKL (cKL). Previously, a patient with increased plasma cKL as the result of a translocation [t(9;13)] in the αKLOTHO (KL) gene presented with rickets and a complex endocrine profile, including paradoxically elevated plasma FGF23, despite hypophosphatemia. The goal of this study was to test whether cKL regulates phosphate handling through control of FGF23 expression. To increase cKL levels, mice were treated with an adeno-associated virus producing cKL. The treated groups exhibited dose-dependent hypophosphatemia and hypocalcemia, with markedly elevated FGF23 (38 to 456 fold). The animals also manifested fractures, reduced bone mineral content, expanded growth plates, and severe osteomalacia, with highly increased bone Fgf23 mRNA (>150 fold). cKL activity in vitro was specific for interactions with FGF23 and was FGFR dependent. These results demonstrate that cKL potently stimulates FGF23 production in vivo, which phenocopies the KL translocation patient and metabolic bone syndromes associated with elevated FGF23. These findings have important implications for the regulation of αKL and FGF23 in disorders of phosphate handling and biomineralization.

Inactivation of the E-prostanoid 3 receptor attenuates the angiotensin II pressor response via decreasing arterial contractility

OBJECTIVE

The present studies aimed at elucidating the role of prostaglandin E(2) receptor subtype 3 (E-prostanoid [EP] 3) in regulating blood pressure.

METHODS AND RESULTS

Mice bearing a genetic disruption of the EP3 gene (EP(3)(-/-)) exhibited reduced baseline mean arterial pressure monitored by both tail-cuff and carotid arterial catheterization. The pressor responses induced by EP3 agonists M&B28767 and sulprostone were markedly attenuated in EP3(-/-) mice, whereas the reduction of blood pressure induced by prostaglandin E(2) was comparable in both genotypes. Vasopressor effect of acute or chronic infusion of angiotensin II (Ang II) was attenuated in EP3(-/-) mice. Ang II-induced vasoconstriction in mesenteric arteries decreased in EP3(-/-) group. In mesenteric arteries from wild-type mice, Ang II-induced vasoconstriction was inhibited by EP3 selective antagonist DG-041 or L798106. The expression of Arhgef-1 is attenuated in EP3 deficient mesenteric arteries. EP3 antagonist DG-041 diminished Ang II-induced phosphorylation of myosin light chain 20 and myosin phosphatase target subunit 1 in isolated mesenteric arteries. Furthermore, in vascular smooth muscle cells, Ang II-induced intracellular Ca(2+) increase was potentiated by EP3 agonist sulprostone but inhibited by DG-041.

CONCLUSIONS

Activation of the EP3 receptor raises baseline blood pressure and contributes to Ang II-dependent hypertension at least partially via enhancing Ca(2+) sensitivity and intracellular calcium concentration in vascular smooth muscle cells. Selective targeting of the EP3 receptor may represent a potential therapeutic target for the treatment of hypertension.

Generation of a conditional allele for the mouse endothelial nitric oxide synthase gene

Mice with endothelial nitric oxide synthase (eNOS) deletions have defined the crucial role of eNOS in vascular development, homeostasis, and pathology. However, cell specific eNOS function has not been determined, although an important role of eNOS has been suggested in multiple cell types. Here, we have generated a floxed eNOS allele in which exons 9-12, encoding the sites essential to eNOS activity, are flanked with loxP sites. Mice homozygous for the floxed allele showed normal eNOS protein levels and no overt phenotype. Conversely, homozygous mice with Cre-deleted alleles displayed truncated eNOS protein, lack of vascular NO production, and exhibited similar phenotype to eNOS knockout mice, including hypertension, low heart rate, and focal renal scarring. These findings demonstrate that the floxed allele is normal and it can be converted to a non-functional eNOS allele through Cre recombination. This mouse will allow time- and cell-specific eNOS deletion.

EP1(-/-) mice have enhanced osteoblast differentiation and accelerated fracture repair

As a downstream product of cyclooxygenase 2 (COX-2), prostaglandin E(2) (PGE(2)) plays a crucial role in the regulation of bone formation. It has four different receptor subtypes (EP1 through EP4), each of which exerts different effects in bone. EP2 and EP4 induce bone formation through the protein kinase A (PKA) pathway, whereas EP3 inhibits bone formation in vitro. However, the effect of EP1 receptor signaling during bone formation remains unclear. Closed, stabilized femoral fractures were created in mice with EP1 receptor loss of function at 10 weeks of age. Healing was evaluated by radiographic imaging, histology, gene expression studies, micro-computed tomographic (µCT), and biomechanical measures. EP1(-/-) mouse fractures have increased formation of cartilage, increased fracture callus, and more rapid completion of endochondral ossification. The fractures heal faster and with earlier fracture callus mineralization with an altered expression of genes involved in bone repair and remodeling. Fractures in EP1(-/-) mice also had an earlier appearance of tartrate-resistant acid phosphatase (TRAcP)-positive osteoclasts, accelerated bone remodeling, and an earlier return to normal bone morphometry. EP1(-/-) mesenchymal progenitor cells isolated from bone marrow have higher osteoblast differentiation capacity and accelerated bone nodule formation and mineralization in vitro. Loss of the EP1 receptor did not affect EP2 or EP4 signaling, suggesting that EP1 and its downstream signaling targets directly regulate fracture healing. We show that unlike the PGE(2) receptors EP2 and EP4, the EP1 receptor is a negative regulator that acts at multiple stages of the fracture healing process. Inhibition of EP1 signaling is a potential means to enhance fracture healing.

A maladaptive role for EP4 receptors in podocytes

Inhibition of p38 mitogen-activated protein kinase and cyclooxygenase-2 reduces albuminuria in models of chronic kidney disease marked by podocyte injury. Previously, we identified a feedback loop in podocytes whereby an in vitro surrogate for glomerular capillary pressure (i.e., mechanical stretch) along with prostaglandin E(2) stimulation of its EP4 receptor induced cyclooxygenase-2 in a p38-dependent manner. Here we asked whether stimulation of EP4 receptors would exacerbate glomerulopathies associated with enhanced glomerular capillary pressure. We generated mice with either podocyte-specific overexpression or depletion of the EP4 receptor (EP4(pod+) and EP4(pod-/-), respectively). Glomerular prostaglandin E(2)-stimulated cAMP levels were eightfold greater for EP4(pod+) mice compared with nontransgenic (non-TG) mice. In contrast, EP4 mRNA levels were >50% lower, and prostaglandin E(2)-induced cAMP synthesis was absent in podocytes isolated from EP4(pod-/-) mice. Non-TG and EP4(pod+) mice underwent 5/6 nephrectomy and exhibited similar increases in systolic BP (+25 mmHg) by 4 weeks compared with sham-operated controls. Two weeks after nephrectomy, the albumin-creatinine ratio of EP4(pod+) mice (3438 μg/mg) was significantly higher than that of non-TG mice (773 μg/mg; P < 0.0001). Consistent with more severe renal injury, the survival rate for nephrectomized EP4(pod+) mice was significantly lower than that for non-TG mice (14 versus 67%). In contrast, 6 weeks after nephrectomy, the albumin-creatinine ratio of EP4(pod-/-) mice (753 μg/mg) was significantly lower than that of non-TG mice (2516 μg/mg; P < 0.05). These findings suggest that prostaglandin E(2), acting via EP4 receptors contributes to podocyte injury and compromises the glomerular filtration barrier.

Better nephrology for mice--and man

The use of creatinine to estimate glomerular filtration rate in patients is prone to well-described artifacts that impact its interpretation. Eisner et al. now show that the impact of creatinine secretion on creatinine clearance is even larger in mice than in humans, raising questions regarding the utility of creatinine for measuring glomerular filtration rate in mice.

Sirt1 activation protects the mouse renal medulla from oxidative injury

Sirtuin 1 (Sirt1) is a NAD+-dependent deacetylase that exerts many of the pleiotropic effects of oxidative metabolism. Due to local hypoxia and hypertonicity, the renal medulla is subject to extreme oxidative stress. Here, we set out to investigate the role of Sirt1 in the kidney. Our initial analysis indicated that it was abundantly expressed in mouse renal medullary interstitial cells in vivo. Knocking down Sirt1 expression in primary mouse renal medullary interstitial cells substantially reduced cellular resistance to oxidative stress, while pharmacologic Sirt1 activation using either resveratrol or SRT2183 improved cell survival in response to oxidative stress. The unilateral ureteral obstruction (UUO) model of kidney injury induced markedly more renal apoptosis and fibrosis in Sirt1+/- mice than in wild-type controls, while pharmacologic Sirt1 activation substantially attenuated apoptosis and fibrosis in wild-type mice. Moreover, Sirt1 deficiency attenuated oxidative stress-induced COX2 expression in cultured mouse renal medullary interstitial cells, and Sirt1+/- mice displayed reduced UUO-induced COX2 expression in vivo. Conversely, Sirt1 activation increased renal medullary interstitial cell COX2 expression both in vitro and in vivo. Furthermore, exogenous PGE2 markedly reduced apoptosis in Sirt1-deficient renal medullary interstitial cells following oxidative stress. Taken together, these results identify Sirt1 as an important protective factor for mouse renal medullary interstitial cells following oxidative stress and suggest that the protective function of Sirt1 is partly attributable to its regulation of COX2 induction. We therefore suggest that Sirt1 provides a potential therapeutic target to minimize renal medullary cell damage following oxidative stress.

Mouse models of diabetic nephropathy

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

Effects of global or targeted deletion of the EP4 receptor on the response of osteoblasts to prostaglandin in vitro and on bone histomorphometry in aged mice

Because global deletion of the prostaglandin EP4 receptor results in neonatal lethality, we generated a mouse with targeted EP4 receptor deletion using Cre-LoxP methodology and a 2.3 kb collagen I a1 promoter driving Cre recombinase that is selective for osteoblastic cells. We compared wild type (WT), global heterozygote (G-HET), targeted heterozygote (T-HET) and knockout (KO) mice. KO mice had one targeted and one global deletion of the EP4 receptor. All mice were in a mixed background of C57BL/6 and CD-1. Although there were one third fewer G-HET or KO mice at weaning compared to WT and T-HET mice, G-HET and KO mice appeared healthy. In cultures of calvarial osteoblasts, prostaglandin E(2) (PGE(2)) increased alkaline phosphatase (ALP) activity in cells from WT mice, and this effect was significantly decreased in cells from either G-HET or T-HET mice and further decreased in cells from KO mice. A selective agonist for EP4 receptor increased ALP activity and osteocalcin mRNA levels in cells from WT but not KO mice. A selective COX-2 inhibitor, NS-398, decreased osteoblast differentiation in WT but not KO cells. At 15 to 18 months of age there were no differences in serum creatinine, calcium, PTH, body weight or bone mineral density among the different genotypes. Static and dynamic histomorphometry showed no consistent changes in bone volume or bone formation. We conclude that expression of the EP4 receptor in osteoblasts is critical for anabolic responses to PGE(2) in cell culture but may not be essential for maintenance of bone remodeling in vivo.

Reduction of renal superoxide dismutase in progressive diabetic nephropathy

Superoxide excess plays a central role in tissue damage that results from diabetes, but the mechanisms of superoxide overproduction in diabetic nephropathy (DN) are incompletely understood. In the present study, we investigated the enzyme superoxide dismutase (SOD), a major defender against superoxide, in the kidneys during the development of murine DN. We assessed SOD activity and the expression of SOD isoforms in the kidneys of two diabetic mouse models (C57BL/6-Akita and KK/Ta-Akita) that exhibit comparable levels of hyperglycemia but different susceptibility to DN. We observed down-regulation of cytosolic CuZn-SOD (SOD1) and extracellular CuZn-SOD (SOD3), but not mitochondrial Mn-SOD (SOD2), in the kidney of KK/Ta-Akita mice which exhibit progressive DN. In contrast, we did not detect a change in renal SOD expression in DN-resistant C57BL/6-Akita mice. Consistent with these findings, there was a significant reduction in total SOD activity in the kidney of KK/Ta-Akita mice compared with C57BL/6-Akita mice. Finally, treatment of KK/Ta-Akita mice with a SOD mimetic, tempol, ameliorated the nephropathic changes in KK/Ta-Akita mice without altering the level of hyperglycemia. Collectively, these results indicate that down-regulation of renal SOD1 and SOD3 may play a key role in the pathogenesis of DN.

Measurement of glomerular filtration rate in conscious mice

Glomerular filtration rate (GFR) is an important index of renal function and routinely used in patient care and basic research to evaluate progression of renal diseases or test the efficacy of novel therapeutic strategies. Determination of GFR in mouse models has been mostly practiced in anesthetized animals, which is not suitable for serial monitoring of GFR in the individual mouse. In this chapter, we outline two approaches for determining GFR in conscious mice including 1) determination of urinary excretion of fluorescein-labelled inulin (FITC-inulin), and 2) determination of plasma FITC-inulin decay following a single bolus injection. The GFR values determined using these two methods are comparable. The sensitivity of the methods in reflecting renal function was validated in nephrectomized mice and early stage diabetic mice. The effects of inbred mouse genetic background on GFR values are also discussed in this chapter.

Macrophage EP4 deficiency increases apoptosis and suppresses early atherosclerosis

Prostaglandin (PG) E(2), a major product of activated macrophages, has been implicated in atherosclerosis and plaque rupture. The PGE(2) receptors, EP2 and EP4, are expressed in atherosclerotic lesions and are known to inhibit apoptosis in cancer cells. To examine the roles of macrophage EP4 and EP2 in apoptosis and early atherosclerosis, fetal liver cell transplantation was used to generate LDLR(-/-) mice chimeric for EP2(-/-) or EP4(-/-) hematopoietic cells. After 8 weeks on a Western diet, EP4(-/-) --> LDLR(-/-) mice, but not EP2(-/-) --> LDLR(-/-) mice, had significantly reduced aortic atherosclerosis with increased apoptotic cells in the lesions. EP4(-/-) peritoneal macrophages had increased sensitivity to proapoptotic stimuli, including palmitic acid and free cholesterol loading, which was accompanied by suppression of activity of p-Akt, p-Bad, and NF-kappaB-regulated genes. Thus, EP4 deficiency inhibits the PI3K/Akt and NF-kappaB pathways compromising macrophage survival and suppressing early atherosclerosis, identifying macrophage EP4-signaling pathways as molecular targets for modulating the development of atherosclerosis.

Markers of glycemic control in the mouse: comparisons of 6-h- and overnight-fasted blood glucoses to Hb A1c

The present studies examined the relationship between fasting blood glucose and Hb A(1c) in C57BL/6J, DBA/2J, and KK/HlJ mice with and without diabetes mellitus. Daily averaged blood glucose levels based on continuous glucose monitoring and effects of 6-h vs. overnight fasting on blood glucose were determined. Daily averaged blood glucose levels were highly correlated with Hb A(1c), as determined with a hand-held automated device using an immunodetection method. R(2) values were 0.90, 0.95, and 0.99 in KK/HIJ, C57BL/6J, and DBA/2J, respectively. Six-hour fasting blood glucose correlated more closely with the level of daily averaged blood glucose and with Hb A(1c) than did blood glucose following an overnight fast. To validate the immunoassay-determined Hb A(1c), we also measured total glycosylated hemoglobin using boronate HPLC. Hb A(1c) values correlated well with total glycosylated hemoglobin in all three strains but were relatively lower than total glycosylated hemoglobin in diabetic DBA/2J mice. These results show that 6-h fasting glucose provides a superior index of glycemic control and correlates more closely with Hb A(1c) than overnight-fasted blood glucose in these strains of mice.

Single amino acid substitution in aquaporin 11 causes renal failure

A screen of recessive mutations generated by the chemical mutagen n-ethyl-n-nitrosourea (ENU) mapped a new mutant locus (5772SB) termed sudden juvenile death syndrome (sjds) to chromosome 7 in mice. These mutant mice, which exhibit severe proximal tubule injury and formation of giant vacuoles in the renal cortex, die from renal failure, a phenotype that resembles aquaporin 11 (Aqp11) knockout mice. In this report, the ENU-induced single-nucleotide variant (sjds mutation) is identified. To determine whether this variant, which causes an amino acid substitution (Cys227Ser) in the predicted E-loop region of aquaporin 11, is responsible for the sjds lethal renal phenotype, Aqp11-/sjds compound heterozygous mice were generated from Aqp11 +/sjds and Aqp11 +/- intercrosses. The compound heterozygous Aqp11 -/sjds offspring exhibited a lethal renal phenotype (renal failure by 2 wk), similar to the Aqp11 sjds/sjds and Aqp11-/- phenotypes. These results demonstrate that the identified mutation causes renal failure in Aqp11 sjds/sjds mutant mice, providing a model for better understanding of the structure and function of aquaporin 11 in renal physiology.