Neuroblastoma suppressor of tumorigenicity 1 is a circulating protein associated with progression to end-stage kidney disease in diabetes

Circulating proteins associated with transforming growth factor-β (TGF-β) signaling are implicated in the development of diabetic kidney disease (DKD). It remains to be comprehensively examined which of these proteins are involved in the pathogenesis of DKD and its progression to end-stage kidney disease (ESKD) in humans. Using the SOMAscan proteomic platform, we measured concentrations of 25 TGF-β signaling family proteins in four different cohorts composed in total of 754 Caucasian or Pima Indian individuals with type 1 or type 2 diabetes. Of these 25 circulating proteins, we identified neuroblastoma suppressor of tumorigenicity 1 (NBL1, aliases DAN and DAND1), a small secreted protein known to inhibit members of the bone morphogenic protein family, to be most strongly and independently associated with progression to ESKD during 10-year follow-up in all cohorts. The extent of damage to podocytes and other glomerular structures measured morphometrically in 105 research kidney biopsies correlated strongly with circulating NBL1 concentrations. Also, in vitro exposure to NBL1 induced apoptosis in podocytes. In conclusion, circulating NBL1 may be involved in the disease process underlying progression to ESKD, and its concentration in circulation may identify subjects with diabetes at increased risk of progression to ESKD.

A dominant negative ADIPOQ mutation in a diabetic family with renal disease, hypoadiponectinemia, and hyperceramidemia

Adiponectin, encoded by ADIPOQ, is an insulin-sensitizing, anti-inflammatory, and renoprotective adipokine that activates receptors with intrinsic ceramidase activity. We identified a family harboring a 10-nucleotide deletion mutation in ADIPOQ that cosegregates with diabetes and end-stage renal disease. This mutation introduces a frameshift in exon 3, resulting in a premature termination codon that disrupts translation of adiponectin's globular domain. Subjects with the mutation had dramatically reduced circulating adiponectin and increased long-chain ceramides levels. Functional studies suggest that the mutated protein acts as a dominant negative through its interaction with non-mutated adiponectin, decreasing circulating adiponectin levels, and correlating with metabolic disease.

Results of untargeted analysis using the SOMAscan proteomics platform indicates novel associations of circulating proteins with risk of progression to kidney failure in diabetes

This study applies a large proteomics panel to search for new circulating biomarkers associated with progression to kidney failure in individuals with diabetic kidney disease. Four independent cohorts encompassing 754 individuals with type 1 and type 2 diabetes and early and late diabetic kidney disease were followed to ascertain progression to kidney failure. During ten years of follow-up, 227 of 754 individuals progressed to kidney failure. Using the SOMAscan proteomics platform, we measured baseline concentration of 1129 circulating proteins. In our previous publications, we analyzed 334 of these proteins that were members of specific candidate pathways involved in diabetic kidney disease and found 35 proteins strongly associated with risk of progression to kidney failure. Here, we examined the remaining 795 proteins using an untargeted approach. Of these remaining proteins, 11 were significantly associated with progression to kidney failure. Biological processes previously reported for these proteins were related to neuron development (DLL1, MATN2, NRX1B, KLK8, RTN4R and ROR1) and were implicated in the development of kidney fibrosis (LAYN, DLL1, MAPK11, MATN2, endostatin, and ROR1) in cellular and animal studies. Specific mechanisms that underlie involvement of these proteins in progression of diabetic kidney disease must be further investigated to assess their value as targets for kidney-protective therapies. Using multivariable LASSO regression analysis, five proteins (LAYN, ESAM, DLL1, MAPK11 and endostatin) were found independently associated with risk of progression to kidney failure. Thus, our study identified proteins that may be considered as new candidate prognostic biomarkers to predict risk of progression to kidney failure in diabetic kidney disease. Furthermore, three of these proteins (DLL1, ESAM, and MAPK11) were selected as candidate biomarkers when all SOMAscan results were evaluated.

Association of Coding Variants in Hydroxysteroid 17-beta Dehydrogenase 14 (HSD17B14) with Reduced Progression to End Stage Kidney Disease in Type 1 Diabetes

BACKGROUND

Rare variants in gene coding regions likely have a greater impact on disease-related phenotypes than common variants through disruption of their encoded protein. We searched for rare variants associated with onset of ESKD in individuals with type 1 diabetes at advanced kidney disease stage.

METHODS

Gene-based exome array analyses of 15,449 genes in five large incidence cohorts of individuals with type 1 diabetes and proteinuria were analyzed for survival time to ESKD, testing the top gene in a sixth cohort (n=2372/1115 events all cohorts) and replicating in two retrospective case-control studies (n=1072 cases, 752 controls). Deep resequencing of the top associated gene in five cohorts confirmed the findings. We performed immunohistochemistry and gene expression experiments in human control and diseased cells, and in mouse ischemia reperfusion and aristolochic acid nephropathy models.

RESULTS

Protein coding variants in the hydroxysteroid 17-β dehydrogenase 14 gene (HSD17B14), predicted to affect protein structure, had a net protective effect against development of ESKD at exome-wide significance (n=4196; P value=3.3 × 10^-7). The HSD17B14 gene and encoded enzyme were robustly expressed in healthy human kidney, maximally in proximal tubular cells. Paradoxically, gene and protein expression were attenuated in human diabetic proximal tubules and in mouse kidney injury models. Expressed HSD17B14 gene and protein levels remained low without recovery after 21 days in a murine ischemic reperfusion injury model. Decreased gene expression was found in other CKD-associated renal pathologies.

CONCLUSIONS

HSD17B14 gene is mechanistically involved in diabetic kidney disease. The encoded sex steroid enzyme is a druggable target, potentially opening a new avenue for therapeutic development.

Comprehensive Search for Novel Circulating miRNAs and Axon Guidance Pathway Proteins Associated with Risk of ESKD in Diabetes

BACKGROUND

Mechanisms underlying the pro gression of diabetic kidney disease to ESKD are not fully understood.

METHODS

We performed global microRNA (miRNA) analysis on plasma from two cohorts consisting of 375 individuals with type 1 and type 2 diabetes with late diabetic kidney disease, and targeted proteomics analysis on plasma from four cohorts consisting of 746 individuals with late and early diabetic kidney disease. We examined structural lesions in kidney biopsy specimens from the 105 individuals with early diabetic kidney disease. Human umbilical vein endothelial cells were used to assess the effects of miRNA mimics or inhibitors on regulation of candidate proteins.

RESULTS

In the late diabetic kidney disease cohorts, we identified 17 circulating miRNAs, represented by four exemplars (miR-1287-5p, miR-197-5p, miR-339-5p, and miR-328-3p), that were strongly associated with 10-year risk of ESKD. These miRNAs targeted proteins in the axon guidance pathway. Circulating levels of six of these proteins-most notably, EFNA4 and EPHA2-were strongly associated with 10-year risk of ESKD in all cohorts. Furthermore, circulating levels of these proteins correlated with severity of structural lesions in kidney biopsy specimens. In contrast, expression levels of genes encoding these proteins had no apparent effects on the lesions. In in vitro experiments, mimics of miR-1287-5p and miR-197-5p and inhibitors of miR-339-5p and miR-328-3p upregulated concentrations of EPHA2 in either cell lysate, supernatant, or both.

CONCLUSIONS

This study reveals novel mechanisms involved in progression to ESKD and points to the importance of systemic factors in the development of diabetic kidney disease. Some circulating miRNAs and axon guidance pathway proteins represent potential targets for new therapies to prevent and treat this condition.

Circulating proteins protect against renal decline and progression to end-stage renal disease in patients with diabetes

Diabetic kidney disease (DKD) and its major clinical manifestation, progressive renal decline that leads to end-stage renal disease (ESRD), are a major health burden for individuals with diabetes. The disease process that underlies progressive renal decline comprises factors that increase risk as well as factors that protect against this outcome. Using untargeted proteomic profiling of circulating proteins from individuals in two independent cohorts with type 1 and type 2 diabetes and varying stages of DKD followed for 7 to 15 years, we identified three elevated plasma proteins-fibroblast growth factor 20 (OR, 0.69; 95% CI, 0.54 to 0.88), angiopoietin-1 (OR, 0.72; 95% CI, 0.57 to 0.91), and tumor necrosis factor ligand superfamily member 12 (OR, 0.75; 95% CI, 0.59 to 0.95)-that were associated with protection against progressive renal decline and progression to ESRD. The combined effect of these three protective proteins was demonstrated by very low cumulative risk of ESRD in those who had baseline concentrations above median for all three proteins, whereas the cumulative risk of ESRD was high in those with concentrations below median for these proteins at the beginning of follow-up. This protective effect was shown to be independent from circulating inflammatory proteins and clinical covariates and was confirmed in a third cohort of diabetic individuals with normal renal function. These three protective proteins may serve as biomarkers to stratify diabetic individuals according to risk of progression to ESRD and might also be investigated as potential therapeutics to delay or prevent the onset of ESRD.

Effect of TNFα stimulation on expression of kidney risk inflammatory proteins in human umbilical vein endothelial cells cultured in hyperglycemia

We recently identified a kidney risk inflammatory signature (KRIS), comprising 6 TNF receptors (including TNFR1 and TNFR2) and 11 inflammatory proteins. Elevated levels of these proteins in circulation were strongly associated with risk of the development of end-stage kidney disease (ESKD) during 10-year follow-up. It has been hypothesized that elevated levels of these proteins in circulation might reflect (be markers of) systemic exposure to TNFα. In this in vitro study, we examined intracellular and extracellular levels of these proteins in human umbilical vein endothelial cells (HUVECs) exposed to TNFα in the presence of hyperglycemia. KRIS proteins as well as 1300 other proteins were measured using the SOMAscan proteomics platform. Four KRIS proteins (including TNFR1) were down-regulated and only 1 protein (IL18R1) was up-regulated in the extracellular fraction of TNFα-stimulated HUVECs. In the intracellular fraction, one KRIS protein was down-regulated (CCL14) and 1 protein was up-regulated (IL18R1). The levels of other KRIS proteins were not affected by exposure to TNFα. HUVECs exposed to a hyperglycemic and inflammatory environment also showed significant up-regulation of a distinct set of 53 proteins (mainly in extracellular fraction). In our previous study, circulating levels of these proteins were not associated with progression to ESKD in diabetes.

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.

A signature of circulating inflammatory proteins and development of end-stage renal disease in diabetes

Chronic inflammation is postulated to be involved in development of end stage renal disease (ESRD) in diabetes, but which specific circulating inflammatory proteins contribute to this risk remains unknown. To study this we examined 194 circulating inflammatory proteins in subjects from three independent cohorts with Type 1 and Type 2 diabetes. In each cohort we identified an extremely robust Kidney Risk Inflammatory Signature (KRIS) consisting of 17 novel proteins enriched for TNF Receptor Superfamily members that was associated with a 10-year risk of ESRD. All these proteins had a systemic, non-kidney source. Our prospective study findings provide strong evidence that KRIS proteins contribute to the inflammatory process underlying ESRD development in both types of diabetes. These proteins may be used as new therapeutic targets, new prognostic tests for high risk of ESRD and as surrogate outcome measures where changes in KRIS levels during intervention can reflect the tested therapy’s effectiveness.

Proteomic profiling of circulating proteins in subjects from three independent cohorts with type 1 and type 2 diabetes, identified an extremely robust inflammatory signature, consisting of 17 proteins enriched for TNF Receptor Superfamily members that was associated with a 10-year risk of end-stage renal disease.

Variations in Risk of End-Stage Renal Disease and Risk of Mortality in an International Study of Patients With Type 1 Diabetes and Advanced Nephropathy

OBJECTIVE

Patients with type 1 diabetes and diabetic nephropathy are targets for intervention to reduce high risk of end-stage renal disease (ESRD) and deaths. This study compares risks of these outcomes in four international cohorts.

RESEARCH DESIGN AND METHODS

In the 1990s and early 2000s, Caucasian patients with type 1 diabetes with persistent macroalbuminuria in chronic kidney disease stages 1-3 were identified in the Joslin Clinic (U.S., 432), Finnish Diabetic Nephropathy Study (FinnDiane) (Finland, 486), Steno Diabetes Center Copenhagen (Denmark, 368), and INSERM (France, 232) and were followed for 3-18 years with annual creatinine measurements to ascertain ESRD and deaths unrelated to ESRD.

RESULTS

During 15,685 patient-years, 505 ESRD cases (rate 32/1,000 patient-years) and 228 deaths unrelated to ESRD (rate 14/1,000 patient-years) occurred. Risk of ESRD was associated with male sex; younger age; lower estimated glomerular filtration rate (eGFR); higher albumin/creatinine ratio, HbA_1c, and systolic blood pressure; and smoking. Risk of death unrelated to ESRD was associated with older age, smoking, and higher baseline eGFR. In adjusted analysis, ESRD risk was highest in Joslin versus reference FinnDiane (hazard ratio [HR] 1.44, P = 0.003) and lowest in Steno (HR 0.54, P < 0.001). Differences in eGFR slopes paralleled risk of ESRD. Mortality unrelated to ESRD was lowest in Joslin (HR 0.68, P = 0.003 vs. the other cohorts). Competing risk did not explain international differences in the outcomes.

CONCLUSIONS

Despite almost universal renoprotective treatment, progression to ESRD and mortality in patients with type 1 diabetes with advanced nephropathy are still very high and differ among countries. Finding causes of these differences may help reduce risk of these outcomes.

A Genome-Wide Association Study of Diabetic Kidney Disease in Subjects With Type 2 Diabetes

Identification of sequence variants robustly associated with predisposition to diabetic kidney disease (DKD) has the potential to provide insights into the pathophysiological mechanisms responsible. We conducted a genome-wide association study (GWAS) of DKD in type 2 diabetes (T2D) using eight complementary dichotomous and quantitative DKD phenotypes: the principal dichotomous analysis involved 5,717 T2D subjects, 3,345 with DKD. Promising association signals were evaluated in up to 26,827 subjects with T2D (12,710 with DKD). A combined T1D+T2D GWAS was performed using complementary data available for subjects with T1D, which, with replication samples, involved up to 40,340 subjects with diabetes (18,582 with DKD). Analysis of specific DKD phenotypes identified a novel signal near GABRR1 (rs9942471, P = 4.5 × 10^-8) associated with microalbuminuria in European T2D case subjects. However, no replication of this signal was observed in Asian subjects with T2D or in the equivalent T1D analysis. There was only limited support, in this substantially enlarged analysis, for association at previously reported DKD signals, except for those at UMOD and PRKAG2, both associated with estimated glomerular filtration rate. We conclude that, despite challenges in addressing phenotypic heterogeneity, access to increased sample sizes will continue to provide more robust inference regarding risk variant discovery for DKD.

Circulating miRNA Profiles Associated With Hyperglycemia in Patients With Type 1 Diabetes

We investigated plasma microRNA (miRNA) profiles associated with variation of hyperglycemia, measured as hemoglobin A_1c (HbA_1c), in two panels of patients with type 1 diabetes (T1D). Using the HTG Molecular Diagnostics EdgeSeq platform, 2,083 miRNAs were measured in plasma from 71 patients included in a screening panel. Quantitative real-time PCR was used to measure the candidate miRNAs in plasma from 95 patients included in an independent replication panel. We found 10 miRNAs replicated in both panels and 4 with high statistical significance. The strongest positive correlations with HbA_1c were found with miR-125b-5p (r_s = 0.40, P = 6.0 × 10^-5) and miR-365a-3p (r_s = 0.35, P = 5.9 × 10^-4). The strongest negative correlations were found with miR-5190 (r_s = -0.30, P = 0.003) and miR-770-5p (r_s = -0.27, P = 0.008). Pathway analysis revealed that 50 Kyoto Encyclopedia of Genes and Genomes pathways were significantly enriched by genes targeted by these four miRNAs. The axon guidance signaling pathway was enriched (P < 1 × 10^-7) by genes targeted by all four miRNAs. In addition, three other pathways (Rap1 signaling, focal adhesion, and neurotrophin signaling) were also significantly enriched but with genes targeted by only by three of the identified miRNAs. In conclusion, our study identified four circulating miRNAs that were influenced by variation in hyperglycemia. Dysregulation of these miRNAs, which are associated with hyperglycemia in patients with T1D, may contribute to the development of diabetes complications. However, there are multitudes of possible mechanisms/pathways through which dysregulation of these miRNAs may impact risk of diabetes complications.

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.

Fast renal decline to end-stage renal disease: an unrecognized feature of nephropathy in diabetes

A new model of diabetic nephropathy in type 1 diabetes emerged from our studies of Joslin Clinic patients. The dominant feature is progressive renal decline, not albuminuria. This decline is a unidirectional process commencing while patients have normal renal function and, in the majority, progressing steadily (linearly) to end-stage renal disease (ESRD). While an individual's rate of renal decline is constant, the estimated glomerular filtration rate (eGFR) slope varies widely among individuals from -72 to -3.0 ml/min/year. Kidney Disease: Improving Global Outcomes guidelines define rapid progression as rate of eGFR declines > 5 ml/min/year, a value exceeded by 80% of patients in Joslin's type 1 diabetes ESRD cohort. The extraordinary range of slopes within the rapid progression category prompted us to partition it into "very fast," "fast" and "moderate" decline. We showed, for the first time, that very fast and fast decline from normal eGFR to ESRD within 2 to 10 years constitutes 50% of the Joslin cohort. In this review we present data about frequency of fast decliners in both diabetes types, survey some mechanisms underlying fast renal decline, discuss methods of identifying patients at risk and comment on the need for effective therapeutic interventions. Whether the initiating mechanism of fast renal decline affects glomerulus, tubule, interstitium or vasculature is unknown. Since no animal model mimics progressive renal decline, studies in humans are needed. Prospective studies searching for markers predictive of the rate of renal decline yield findings that may make detection of fast decliners feasible. Identifying such patients will be the foundation for developing effective individualized methods to prevent or delay onset of ESRD in diabetes.

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.

Circulating Modified Metabolites and a Risk of ESRD in Patients With Type 1 Diabetes and Chronic Kidney Disease

OBJECTIVE

Patients with type 1 diabetes (T1D) with impaired renal function are at increased risk for end-stage renal disease (ESRD). Although the rate of progression varies, determinants and mechanisms of this variation are unknown.

RESEARCH DESIGN AND METHODS

We examined serum metabolomic profiles associated with variation in renal function decline in participants with T1D (the Joslin Kidney Study prospective cohort). One hundred fifty-eight patients with proteinuria and chronic kidney disease stage 3 were followed for a median of 11 years to determine estimated glomerular filtration rate slopes from serial measurements of serum creatinine and to ascertain time to onset of ESRD. Baseline serum samples were subjected to global metabolomic profiling.

RESULTS

One hundred ten amino acids and purine and pyrimidine metabolites were detected in at least 80% of participants. Serum levels of seven modified metabolites (C-glycosyltryptophan, pseudouridine, O-sulfotyrosine, N-acetylthreonine, N-acetylserine, N6-carbamoylthreonyladenosine, and N6-acetyllysine) were associated with renal function decline and time to ESRD (P < 0.001) independent of the relevant clinical covariates. The significant metabolites correlated with one another and with the indices of tubular injury.

CONCLUSIONS

This prospective cohort study in participants with T1D, proteinuria, and impaired renal function at baseline demonstrated that patients with increased circulating levels of certain modified metabolites experience faster renal function decline, leading to ESRD. Whether some of these candidate metabolites are risk factors or just prognostic biomarkers of progression to ESRD in T1D needs to be determined.

Patterns of Estimated Glomerular Filtration Rate Decline Leading to End-Stage Renal Disease in Type 1 Diabetes

OBJECTIVE

The patterns of estimated glomerular filtration rate (eGFR) decline to end-stage renal disease (ESRD) in patients with type 1 diabetes has not been conclusively described. Decline could be linearly progressive to ESRD but with a variable rate. Conversely, decline may be linear but interrupted by periods of plateaus or improvements.

RESEARCH DESIGN AND METHODS

This observational study included 364 patients with type 1 diabetes attending the Joslin Clinic who developed ESRD between 1991 and 2013. We retrieved serum creatinine measurements from clinic visits or research examinations up to 24 years (median 6.7 years) preceding the onset of ESRD. Using serial measurements of serum creatinine to estimate renal function (eGFR), we used regression-based spline methods and a data smoothing approach to characterize individual trajectories of eGFR over time for the 257 patients with five or more data points.

RESULTS

The rate of eGFR decline per year ranged widely, from -72 to -2 mL/min/1.73 m² (median -8.5). The trajectories, as characterized with linear regression-based spline models, were linear or nearly so for 87% of patients, accelerating for 6%, and decelerating for 7%. Smoothed trajectories evaluated by a Bayesian approach did not significantly depart from a linear fit in 76%.

CONCLUSIONS

The decline of eGFR in type 1 diabetes is predominantly linear. Deviations from linearity are small, with little effect on the expected time of ESRD. A single disease process most likely underlies renal decline from its initiation and continues with the same intensity to ESRD. Linearity of renal decline suggests using slope reduction as the measure of effectiveness of interventions to postpone ESRD.

Tumor necrosis factor receptors 1 and 2 are associated with early glomerular lesions in type 2 diabetes

Elevated serum tumor necrosis factor receptor 1 (TNFR1) and 2 (TNFR2) concentrations are strongly associated with increased risk of end-stage renal disease in type 2 diabetes. However, little is known about the early glomerular structural lesions that develop in patients when these markers are elevated. Here we examined the relationships between TNFRs and glomerular structure in 83 American Indians with type 2 diabetes. Serum TNFRs and glomerular filtration rates (GFR, iothalamate) were measured during a research exam performed within a median of 0.9 months from a percutaneous kidney biopsy. Associations of TNFRs with glomerular structural variables were quantified by Spearman's correlations and by multivariable linear regression after adjustment for age, gender, diabetes duration, hemoglobin A1c, body mass index, and mean arterial pressure. The baseline mean age was 46 years, median GFR 130 ml/min, median albumin/creatinine ratio 26 mg/g, median TNFR1 1500 pg/ml, and median TNFR2 3284 pg/ml. After multivariable adjustment, TNFR1 and TNFR2 significantly correlated inversely with the percentage of endothelial cell fenestration and the total filtration surface per glomerulus. There were significant positive correlations with mesangial fractional volume glomerular basement membrane width, podocyte foot process width, and percent of global glomerular sclerosis. Thus, TNFRs may be involved in the pathogenesis of early glomerular lesions in diabetic nephropathy.

Circulating TGF-β1-Regulated miRNAs and the Risk of Rapid Progression to ESRD in Type 1 Diabetes

We investigated whether circulating TGF-β1-regulated miRNAs detectable in plasma are associated with the risk of rapid progression to end-stage renal disease (ESRD) in a cohort of proteinuric patients with type 1 diabetes (T1D) and normal eGFR. Plasma specimens obtained at entry to the study were examined in two prospective subgroups that were followed for 7-20 years (rapid progressors and nonprogressors), as well as a reference panel of normoalbuminuric T1D patients. Of the five miRNAs examined in this study, let-7c-5p and miR-29a-3p were significantly associated with protection against rapid progression and let-7b-5p and miR-21-5p were significantly associated with the increased risk of ESRD. In logistic analysis, controlling for HbA1c and other covariates, let-7c-5p and miR-29a-3p were associated with more than a 50% reduction in the risk of rapid progression (P ≤ 0.001), while let-7b-5p and miR-21-5p were associated with a >2.5-fold increase in the risk of ESRD (P ≤ 0.005). This study is the first prospective study to demonstrate that circulating TGF-β1-regulated miRNAs are deregulated early in T1D patients who are at risk for rapid progression to ESRD.

Cardiac autonomic neuropathy and early progressive renal decline in patients with nonmacroalbuminuric type 1 diabetes

BACKGROUND AND OBJECTIVES

Cardiac autonomic neuropathy predicts future adverse renal outcomes in the general population. This study sought to determine its relationship with early progressive renal decline in type 1 diabetes.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A subset of participants with normoalbuminuria (n=204) or microalbuminuria (n=166) from the First Joslin Kidney Study underwent assessment for cardiac autonomic neuropathy using heart rate variability during baseline visits performed from January 1991 to April 1992. Cardiac autonomic neuropathy was defined as an R-R variation (mean circular resultant) <20. Participants also had baseline and follow-up measurement of eGFR. Early progressive renal decline was evaluated according to two definitions: early GFR loss (slope of eGFR estimated by cystatin C <-3.3%/year) and incident advanced CKD (stage ≥3, defined by eGFR [calculated by Modification of Diet in Renal Disease method] <60 ml/min per 1.73 m(2)). Association with baseline cardiac autonomic neuropathy was assessed by adjusted logistic regression and Cox proportional hazards.

RESULTS

Among the 370 participants, 47 (13%) had baseline cardiac autonomic neuropathy, 51 (14%) had early GFR loss, and 68 (18%) had incident advanced CKD over a median 14-year follow-up. Early GFR loss occurred in 15 (32%) of the 47 patients with baseline autonomic neuropathy and in 32 (10%) of the 323 without baseline autonomic neuropathy (P<0.001). Baseline autonomic neuropathy was strongly associated with odds of early GFR loss (adjusted odds ratio, 4.09; 95% confidence interval, 1.65 to 10.12; P=0.002). Incident advanced CKD was observed in 22 (47%) of those with baseline autonomic neuropathy and 46 (14%) of those without baseline autonomic neuropathy (P<0.001). Autonomic neuropathy was independently associated with incident advanced CKD (adjusted hazard ratio, 2.76; 95% confidence interval, 1.44 to 5.30; P=0.002).

CONCLUSIONS

Cardiac autonomic neuropathy was a strong independent predictor of the long-term risk of early progressive renal decline in type 1 diabetes. Future research should explore the mechanisms by which autonomic neuropathy may be associated with renal function loss.

Progressive renal decline: the new paradigm of diabetic nephropathy in type 1 diabetes

On the basis of extensive studies in Joslin Clinic patients over 25 years, we propose a new model of diabetic nephropathy in type 1 diabetes. In this model, the predominant clinical feature of both early and late stages of diabetic nephropathy is progressive renal decline, not albuminuria. Progressive renal decline (estimated glomerular filtration rate loss >3.5 mL/min/year) is a unidirectional process that develops while patients have normal renal function. It progresses at an almost steady rate until end-stage renal disease is reached, albeit at widely differing rates among individuals. Progressive renal decline precedes the onset of microalbuminuria, and as it continues, it increases the risk of proteinuria. Therefore, study groups ascertained for microalbuminuria/proteinuria are enriched for patients with renal decline (decliners). We found prevalences of decliners in 10%, 32%, and 50% of patients with normoalbuminuria, microalbuminuria, and proteinuria, respectively. Whether the initial lesion of progressive renal decline is in the glomerulus, tubule, interstitium, or vasculature is unknown. Similarly unclear are the initiating mechanism and the driver of progression. No animal model mimics progressive renal decline, so etiological studies must be conducted in humans with diabetes. Prospective studies searching for biomarkers predictive of the onset and rate of progression of renal decline have already yielded positive findings that will help to develop not only accurate methods for early diagnosis but also new therapeutic approaches. Detecting in advance which patients will have rapid, moderate, or minimal rates of progression to end-stage renal disease will be the foundation for developing personalized methods of prevention and treatment of progressive renal decline in type 1 diabetes.

Differential Gene Expression in Diabetic Nephropathy in Individuals With Type 1 Diabetes

CONTEXT

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease (ESRD) in the United States.

OBJECTIVE

The aim of this study was to determine whether there were skin fibroblast gene expression differences between subjects with type 1 diabetes (T1D) with or without DN.

SETTING

This was a cross-sectional study conducted in the University of Minnesota.

PATIENTS

Study volunteers were 100 former participants of Genetics of Kidneys in Diabetes: 40 were diabetic nephropathy (DN) Controls, normoalbuminuric after ≥ 15 years of T1D; and 60 were DN Cases, 25 with proteinuria and 35 with ESRD.

INTERVENTION(S)

Skin fibroblasts were grown in high glucose (HG) for five passages (approximately 6 weeks).

MAIN OUTCOME MEASURE(S)

SF gene expression was assessed by transcriptome sequencing using the Illumina HiSeq 2000 platform. Pathway analyses tested directionally consistent group differences within the Kyoto Encyclopedia of Genes and Genomes pathways.

RESULTS

Eight pathways, all related to cell cycle and repair, were up-regulated in the DN Controls vs the DN Cases. These pathways markedly overlapped with the pathways up-regulated by HG in T1D monozygotic twins (MZT), but not in their non-T1D MZT. DN Cases showed statistical trends toward up-regulation of these pathways vs non-T1D MZT, but much less so than the DN Controls.

CONCLUSIONS

Together, these data suggest that SF from T1D patients undergo epigenetic modifications resulting in increased expression of genes in healing and repair pathways. These responses, much more robust in patients protected from DN, suggest that epigenetic factors are important in DN risk.

Elevation of circulating TNF receptors 1 and 2 increases the risk of end-stage renal disease in American Indians with type 2 diabetes

In Caucasians with type 2 diabetes, circulating TNF receptors 1 (TNFR1) and 2 (TNFR2) predict end-stage renal disease (ESRD). Here we examined this relationship in a longitudinal cohort study of American Indians with type 2 diabetes with measured glomerular filtration rate (mGFR, iothalamate) and urinary albumin-to-creatinine ratio (ACR). ESRD was defined as dialysis, kidney transplant, or death attributed to diabetic kidney disease. Age-gender-adjusted incidence rates and incidence rate ratios of ESRD were computed by Mantel-Haenszel stratification. The hazard ratio of ESRD was assessed per interquartile range increase in the distribution of each TNFR after adjusting for baseline age, gender, mean blood pressure, HbA1c, ACR, and mGFR. Among the 193 participants, 62 developed ESRD and 25 died without ESRD during a median follow-up of 9.5 years. The age-gender-adjusted incidence rate ratio of ESRD was higher among participants in the highest versus lowest quartile for TNFR1 (6.6, 95% confidence interval (CI) 3.3-13.3) or TNFR2 (8.8, 95% CI 4.3-18.0). In the fully adjusted model, the risk of ESRD per interquartile range increase was 1.6 times (95% CI 1.1-2.2) as high for TNFR1 and 1.7 times (95% CI 1.2-2.3) as high for TNFR2. Thus, elevated serum concentrations of TNFR1 or TNFR2 are associated with increased risk of ESRD in American Indians with type 2 diabetes after accounting for traditional risk factors including ACR and mGFR.

Synergism between circulating tumor necrosis factor receptor 2 and HbA(1c) in determining renal decline during 5-18 years of follow-up in patients with type 1 diabetes and proteinuria

OBJECTIVE

We studied the serum concentration of tumor necrosis factor receptor 2 (TNFR2) and the rate of renal decline, a measure of the intensity of the disease process leading to end-stage renal disease (ESRD).

RESEARCH DESIGN AND METHODS

A cohort of 349 type 1 diabetic patients with proteinuria was followed for 5-18 years. Serum TNFR2, glycated hemoglobin A1c (HbA1c), and other characteristics were measured at enrollment. We used a novel analytic approach, a joint longitudinal-survival model, fitted to serial estimates of glomerular filtration rate (eGFR) based on serum creatinine (median seven per patient) and time to onset of ESRD (112 patients) to estimate the rate of renal decline (eGFR loss).

RESULTS

At enrollment, all patients had chronic kidney disease stage 1-3. The mean (±SD) rate of eGFR loss during 5-18 years of follow-up was -5.2 (±4.9) mL/min/1.73 m(2)/year. Serum TNFR2 was the strongest determinant of renal decline and ESRD risk (C-index 0.79). The rate of eGFR loss became steeper with rising concentration of TNFR2, and elevated HbA1c augmented the strength of this association (P = 0.030 for interaction). In patients with HbA1c ≥10.1% (87 mmol/mol), the difference in the rate of eGFR loss between the first and fourth quartiles of TNFR2 was 5.4 mL/min/1.73 m(2)/year, whereas it was only 1.9 in those with HbA1c <7.9% (63 mmol/mol).

CONCLUSIONS

Circulating TNFR2 is a major determinant of renal decline in patients with type 1 diabetes and proteinuria. Elevated HbA1c magnifies its effect. Although the mechanisms of this synergism are unknown, our findings allow us to stratify patients according to risk of ESRD.

Progressive renal decline as the major feature of diabetic nephropathy in type 1 diabetes

Despite almost universal implementation of renoprotective therapies over the past 25 years, the risk of end-stage renal disease (ESRD) in type 1 diabetes (T1D) is not decreasing, and ESRD remains the major cause of excess morbidity and premature mortality [1]. Such a state of affairs prompts a call to action. In this review we re-evaluated the proteinuria-centric model of diabetic nephropathy and showed its deficiencies. On the basis of extensive studies that we have been conducting on the patients attending the Joslin Clinic, we propose that progressive renal decline, not abnormalities in urinary albumin excretion, should be considered as the major feature of disease processes leading to ESRD in T1D. The etiology of diabetic nephropathy should be reconsidered in light of our new findings so our perspective can be broadened regarding new therapeutic targets available for interrupting the progressive renal decline in T1D. Reduction in the loss of glomerular filtration rate, not reduction of albumin excretion rate, should become the measure for evaluating the effectiveness of new therapeutic interventions. We need new accurate methods for early diagnosis of patients at risk of progressive renal decline or, better still, for detecting in advance which patients will have rapid, moderate or minimal rate of progression to ESRD.

Improved glycemic control and risk of ESRD in patients with type 1 diabetes and proteinuria

Most patients with type 1 diabetes (T1D) and proteinuria have poor glycemic control and a high risk of ESRD. We investigated whether long-term improvement of glycemic control reduces risk of ESRD in a prospective 7- to 15-year follow-up observation of 349 patients with CKD stages 1-3 enrolled in the Joslin Proteinuria Cohort of adults with T1D. All patients developed proteinuria between 1990 and 2004 and were followed until 2011 to ascertain onset of ESRD and deaths unrelated to ESRD. Furthermore, we analyzed data from 279 patients with ≥3 years of clinic follow-up available to assess the level of glycemic control after enrollment. Average HbA1c during the 5 years before study enrollment (prebaseline) was compared with HbA1c (postbaseline) averaged during the first half of follow-up (median, 5.1 years). Median prebaseline HbA1c was 9.3%, decreasing to 8.7% postbaseline. Cumulative risk of ESRD after 15 years was significantly lower for patients whose HbA1c decreased than for those whose HbA1c increased or remained poor (29% versus 42%; P<0.001). The difference between these groups was not visible at 5 years of follow-up but became visible at 10 and 15 years of follow-up. In multivariate Cox regression analysis of ESRD risk, the hazard ratio corresponding to a 1-percentage point improvement in postbaseline HbA1c was 0.76 (95% confidence interval, 0.63 to 0.91; P=0.003). In conclusion, results of this study suggest that long-term sustained improvement in HbA1c decelerates eGFR loss and delays the onset of ESRD in patients with T1D and proteinuria.

Blood kidney injury molecule-1 is a biomarker of acute and chronic kidney injury and predicts progression to ESRD in type I diabetes

Currently, no blood biomarker that specifically indicates injury to the proximal tubule of the kidney has been identified. Kidney injury molecule-1 (KIM-1) is highly upregulated in proximal tubular cells following kidney injury. The ectodomain of KIM-1 is shed into the lumen, and serves as a urinary biomarker of kidney injury. We report that shed KIM-1 also serves as a blood biomarker of kidney injury. Sensitive assays to measure plasma and serum KIM-1 in mice, rats, and humans were developed and validated in the current study. Plasma KIM-1 levels increased with increasing periods of ischemia (10, 20, or 30 minutes) in mice, as early as 3 hours after reperfusion; after unilateral ureteral obstruction (day 7) in mice; and after gentamicin treatment (50 or 200 mg/kg for 10 days) in rats. In humans, plasma KIM-1 levels were higher in patients with AKI than in healthy controls or post-cardiac surgery patients without AKI (area under the curve, 0.96). In patients undergoing cardiopulmonary bypass, plasma KIM-1 levels increased within 2 days after surgery only in patients who developed AKI (P<0.01). Blood KIM-1 levels were also elevated in patients with CKD of varous etiologies. In a cohort of patients with type 1 diabetes and proteinuria, serum KIM-1 level at baseline strongly predicted rate of eGFR loss and risk of ESRD during 5-15 years of follow-up, after adjustment for baseline urinary albumin-to-creatinine ratio, eGFR, and Hb1Ac. These results identify KIM-1 as a blood biomarker that specifically reflects acute and chronic kidney injury.

Role of podocyte B7-1 in diabetic nephropathy

Podocyte injury and resulting albuminuria are hallmarks of diabetic nephropathy, but targeted therapies to halt or prevent these complications are currently not available. Here, we show that the immune-related molecule B7-1/CD80 is a critical mediator of podocyte injury in type 2 diabetic nephropathy. We report the induction of podocyte B7-1 in kidney biopsy specimens from patients with type 2 diabetes. Genetic and epidemiologic studies revealed the association of two single nucleotide polymorphisms at the B7-1 gene with diabetic nephropathy. Furthermore, increased levels of the soluble isoform of the B7-1 ligand CD28 correlated with the progression to ESRD in individuals with type 2 diabetes. In vitro, high glucose conditions prompted the phosphatidylinositol 3 kinase-dependent upregulation of B7-1 in podocytes, and the ectopic expression of B7-1 in podocytes increased apoptosis and induced disruption of the cytoskeleton that were reversed by the B7-1 inhibitor CTLA4-Ig. Podocyte expression of B7-1 was also induced in vivo in two murine models of diabetic nephropathy, and treatment with CTLA4-Ig prevented increased urinary albumin excretion and improved kidney pathology in these animals. Taken together, these results identify B7-1 inhibition as a potential therapeutic strategy for the prevention or treatment of diabetic nephropathy.

Early progressive renal decline precedes the onset of microalbuminuria and its progression to macroalbuminuria

OBJECTIVE Progressive decrease in the glomerular filtration rate (GFR), or renal decline, in type 1 diabetes (T1D) is observed in patients with macroalbuminuria. However, it is unknown whether this decline begins during microalbuminuria (MA) or normoalbuminuria (NA). RESEARCH DESIGN AND METHODS The study group (second Joslin Kidney Study) comprises patients with T1D and NA (n = 286) or MA (n = 248) who were followed for 4-10 years (median 8 years). Serial measurements (median 6, range 3-16) of serum creatinine and cystatin C were used jointly to estimate GFR (eGFRcr-cys) and assess its trajectories during follow-up. RESULTS Renal decline (progressive eGFRcr-cys loss of at least 3.3% per year) occurred in 10% of the NA and 35% of the MA (P < 0.001). In both groups, the strongest determinants of renal decline were baseline serum concentrations of uric acid (P < 0.001) and tumor necrosis factor receptor 1 or 2 (TNFR-1 or -2, P < 0.001). Other significant risk factors included baseline HbA1c, age/diabetes duration, and systolic blood pressure. Relative impacts of these determinants were similar in NA and MA. Renal decline was not associated with sex or baseline serum concentration of TNF-α, IL-6, IL-8, IP-10, MCP-1, VCAM, ICAM, Fas, or FasL. CONCLUSIONS Renal decline in T1D begins during NA and it is determined by multiple factors, similar to MA. Thus, this early decline is the primary disease process leading to impaired renal function in T1D. Changes in albumin excretion rate, such as the onset of MA or its progression to macroalbuminuria, are either caused by or develop in parallel to the early renal decline.

Association between a genetic variant related to glutamic acid metabolism and coronary heart disease in individuals with type 2 diabetes

IMPORTANCE

Diabetes is associated with an elevated risk of coronary heart disease (CHD). Previous studies have suggested that the genetic factors predisposing to excess cardiovascular risk may be different in diabetic and nondiabetic individuals.

OBJECTIVE

To identify genetic determinants of CHD that are specific to patients with diabetes.

DESIGN, SETTING, AND PARTICIPANTS

We studied 5 independent sets of CHD cases and CHD-negative controls from the Nurses' Health Study (enrolled in 1976 and followed up through 2008), Health Professionals Follow-up Study (enrolled in 1986 and followed up through 2008), Joslin Heart Study (enrolled in 2001-2008), Gargano Heart Study (enrolled in 2001-2008), and Catanzaro Study (enrolled in 2004-2010). Included were a total of 1517 CHD cases and 2671 CHD-negative controls, all with type 2 diabetes. Results in diabetic patients were compared with those in 737 nondiabetic CHD cases and 1637 nondiabetic CHD-negative controls from the Nurses' Health Study and Health Professionals Follow-up Study cohorts. Exposures included 2,543,016 common genetic variants occurring throughout the genome.

MAIN OUTCOMES AND MEASURES

Coronary heart disease--defined as fatal or nonfatal myocardial infarction, coronary artery bypass grafting, percutaneous transluminal coronary angioplasty, or angiographic evidence of significant stenosis of the coronary arteries.

RESULTS

A variant on chromosome 1q25 (rs10911021) was consistently associated with CHD risk among diabetic participants, with risk allele frequencies of 0.733 in cases vs 0.679 in controls (odds ratio, 1.36 [95% CI, 1.22-1.51]; P = 2 × 10(-8)). No association between this variant and CHD was detected among nondiabetic participants, with risk allele frequencies of 0.697 in cases vs 0.696 in controls (odds ratio, 0.99 [95% CI, 0.87-1.13]; P = .89), consistent with a significant gene × diabetes interaction on CHD risk (P = 2 × 10(-4)). Compared with protective allele homozygotes, rs10911021 risk allele homozygotes were characterized by a 32% decrease in the expression of the neighboring glutamate-ammonia ligase (GLUL) gene in human endothelial cells (P = .0048). A decreased ratio between plasma levels of γ-glutamyl cycle intermediates pyroglutamic and glutamic acid was also shown in risk allele homozygotes (P = .029).

CONCLUSION AND RELEVANCE

A single-nucleotide polymorphism (rs10911021) was identified that was significantly associated with CHD among persons with diabetes but not in those without diabetes and was functionally related to glutamic acid metabolism, suggesting a mechanistic link.

From single nucleotide polymorphism to transcriptional mechanism: a model for FRMD3 in diabetic nephropathy

Genome-wide association studies have proven to be highly effective at defining relationships between single nucleotide polymorphisms (SNPs) and clinical phenotypes in complex diseases. Establishing a mechanistic link between a noncoding SNP and the clinical outcome is a significant hurdle in translating associations into biological insight. We demonstrate an approach to assess the functional context of a diabetic nephropathy (DN)-associated SNP located in the promoter region of the gene FRMD3. The approach integrates pathway analyses with transcriptional regulatory pattern-based promoter modeling and allows the identification of a transcriptional framework affected by the DN-associated SNP in the FRMD3 promoter. This framework provides a testable hypothesis for mechanisms of genomic variation and transcriptional regulation in the context of DN. Our model proposes a possible transcriptional link through which the polymorphism in the FRMD3 promoter could influence transcriptional regulation within the bone morphogenetic protein (BMP)-signaling pathway. These findings provide the rationale to interrogate the biological link between FRMD3 and the BMP pathway and serve as an example of functional genomics-based hypothesis generation.

High risk of ESRD in type 1 diabetes: new strategies are needed to retard progressive renal function decline

Care of patients with type 1 diabetes (T1D) has changed during the past 30 years. Tools to control hyperglycemia have improved and it was shown that improvement in glycemic control diminished the risk of late diabetic complications, including nephropathy. Moreover, in patients with impaired renal function, aggressive treatment of hypertension and renoprotective blockade of the renin-angiotensin system were shown to postpone end-stage renal disease (ESRD), albeit for a short while. Despite these achievements, the incidence of ESRD caused by T1D in the US population has not decreased but rather has increased over the past 20 years, although it now occurs at slightly older ages. This state of affairs is a call to action. This should begin with adopting a new model of diabetic nephropathy in human beings. In that model, instead of microalbuminuria or proteinuria, the focus should be on diagnosis and treatment of progressive renal function decline that leads to ESRD. Such a model has received significant support in clinical and epidemiologic studies. Investigation of mechanisms of such progressive renal function decline should help in the identification of new therapeutic targets and the development of new interventions. To evaluate these interventions, accurate diagnostic algorithms are needed so T1D patients will be stratified according to time to onset to ESRD. Consistent with concepts of personalized medicine, the new interventions should be tailored to and evaluated in patients predicted to have rapid, moderate, or even slow progression to ESRD.

Family-based association analysis confirms the role of the chromosome 9q21.32 locus in the susceptibility of diabetic nephropathy

A genome-wide association scan of type 1 diabetic patients from the GoKinD collections previously identified four novel diabetic nephropathy susceptibility loci that have subsequently been shown to be associated with diabetic nephropathy in unrelated patients with type 2 diabetes. To expand these findings, we examined whether single nucleotide polymorphisms (SNPs) at these susceptibility loci were associated with diabetic nephropathy in patients from the Joslin Study of Genetics of Nephropathy in Type 2 Diabetes Family Collection. Six SNPs across the four loci identified in the GoKinD collections and 7 haplotype tagging SNPs, were genotyped in 66 extended families of European ancestry. Pedigrees from this collection contained an average of 18.5 members, including 2 to 14 members with type 2 diabetes. Among diabetic family members, the 9q21.32 locus approached statistical significance with advanced diabetic nephropathy (P = 0.037 [adjusted P = 0.222]). When we expanded our definition of diabetic nephropathy to include individuals with high microalbuminuria, the strength of this association improved significantly (P = 1.42×10⁻³ [adjusted P = 0.009]). This same locus also trended toward statistical significance with variation in urinary albumin excretion in family members with type 2 diabetes (P = 0.032 [adjusted P = 0.192]) and in analyses expanded to include all relatives (P = 0.019 [adjusted P = 0.114]). These data increase support that SNPs identified in the GoKinD collections on chromosome 9q21.32 are true diabetic nephropathy susceptibility loci.

Transcriptome analysis of proximal tubular cells (HK-2) exposed to urines of type 1 diabetes patients at risk of early progressive renal function decline

Background

In patients with Type 1 Diabetes (T1D) who develop microalbuminuria, progressive decline in glomerular filtration rate (GFR) may be initiated by leakage into the urine of toxic proteins (txUPs). This study tested this hypothesis.

Methods

After archiving baseline urine, we followed T1D patients with microalbuminuria for 8–12 years to distinguish those in whom GFR declined (Decliners) and those in whom it remained stable (Non-decliners). Human proximal tubular cells (HK-2 cells) were grown in serum-free medium enriched with pooled urines from Decliners or Non-decliners. We determined genome-wide expression profiles in extracted mRNA.

Results

The two pooled urines induced differential expression of 312 genes. In terms of gene ontology, molecular functions of the 119 up-regulated genes were enriched for protein binding and peptidase inhibitor activities. Their biologic processes were enriched for defense response, responses to other organisms, regulation of cellular processes, or response to stress or stimulus, and programmed cell death. The 195 down-regulated genes were disproportionately represented in molecular functions of cation binding, hydrolase activity, and DNA binding. They were disproportionately represented in biological processes for regulation of metabolic processes, nucleic acid metabolic processes, cellular response to stress and macromolecule biosynthesis. The set of up-regulated genes in HK-2 cells overlaps significantly with sets of over-expressed genes in tubular and interstitial compartments of kidney biopsies from patients with advanced DN (33 genes in one study and 25 in the other compared with 10.3 expected by chance, p<10⁻⁹ and p<10⁻⁴, respectively). The overlap included genes encoding chemokines and cytokines. Overlap of down-regulated genes was no more than expected by chance.

Conclusions

Molecular processes in tubules and interstitium seen in advanced diabetic nephropathy can be induced in vitro by exposure to urine from patients with minimal microalbuminuria who subsequently developed progressive renal function decline, presumably due to putative txUPs.

Plasma kininogen and kininogen fragments are biomarkers of progressive renal decline in type 1 diabetes

The ability of microalbuminuria to predict early progressive renal function decline in type-1 diabetic patients has been questioned. To resolve this, we determined the plasma proteome differences between microalbuminuric patients with type-1 diabetes and stable renal function (controls) and patients at risk for early progressive renal function decline (cases) and asked whether these differences have value as surrogate biomarkers. Mass spectrometry was used to analyze small (less than 3 kDa) plasma peptides isolated from well-matched case and control plasma obtained at the beginning of an 8-12 year follow-up period. Spearman analysis of plasma peptide abundance and the rate of renal function decline during follow-up identified seven masses with a significant negative correlation with early progressive renal function decline. Tandem mass spectrometry identified three fragments of high molecular weight kininogen. Increased plasma high molecular weight kininogen in the cases was confirmed by immunoblot. One peptide, des-Arg9-BK(1-8), induced Erk1/2 phosphorylation when added apically to two proximal tubular cell lines grown on permeable inserts. Thus, we have identified plasma protein fragments, some of which have biological activity with moderate to strong correlation, with early progressive renal function decline in microalbuminuric patients with type-1 diabetes. Other peptides are candidates for validation as candidate biomarkers of diabetes-associated renal dysfunction.

The genetic risk of kidney disease in type 2 diabetes

For more than 20 years, evidence in favor of a genetic basis for the susceptibility of DN in T2D has provided a foundation for studies aimed at identifying the causal genes responsible for its development. During this period, strategies used to map genes for DN have been driven by our understanding of variation across our genome and the technologies available to interrogate it; as both have evolved, so to have our approaches. The advent of next-generation sequencing technology and increased interest in the search for rare variants has begun to swing the pendulum of these efforts away from population-based studies and back to studies of pedigrees. As the field moves forward, family based approaches should greatly facilitate efforts to identify variants in genes that have a major affect on the risk of DN in T2D. To be successful, the ascertainment and comprehensive study of families with multiple affected members is critical.

Serum concentration of cystatin C and risk of end-stage renal disease in diabetes

OBJECTIVE

Patients with diabetes have a high risk of end-stage renal disease (ESRD). We examined whether prediction of this outcome, according to chronic kidney disease (CKD) staging by creatinine-based estimates of the glomerular filtration rate (eGFRcreat), is improved by further staging with serum cystatin C-based estimates (eGFRcyst).

RESEARCH DESIGN AND METHODS

Patients with diabetes in CKD stages 1-3 were selected from three cohorts: two from Joslin Diabetes Center, one with type 1 diabetes (N = 364) and one with type 2 diabetes (N = 402), and the third from the Finnish Diabetic Nephropathy (FinnDiane) Study of type 1 (N = 399). Baseline serum concentrations of creatinine and cystatin C were measured in all patients. Follow-up averaged 8-10 years and onsets of ESRD (n = 246) and death unrelated to ESRD (n = 159) were ascertained.

RESULTS

Although CKD staging by eGFRcyst was concordant with that by eGFRcreat for 62% of Joslin patients and 73% of FinnDiane patients, those given a higher stage by eGFRcyst than eGFRcreat had a significantly higher risk of ESRD than those with concordant staging in all three cohorts (hazard ratio 2.3 [95% CI 1.8-3.1]). Similarly, patients at a lower stage by eGFRcyst than by eGFRcreat had a lower risk than those with concordant staging (0.30 [0.13-0.68]). Deaths unrelated to ESRD followed the same pattern, but differences were not as large.

CONCLUSIONS

In patients with diabetes, CKD staging based on eGFRcyst significantly improves ESRD risk stratification based on eGFRcreat. This conclusion can be generalized to patients with type 1 and type 2 diabetes and to diabetic patients in the U.S. and Finland.

Serum levels of advanced glycation endproducts and other markers of protein damage in early diabetic nephropathy in type 1 diabetes

Objective

To determine the role of markers of plasma protein damage by glycation, oxidation and nitration in microalbuminuria onset or subsequent decline of glomerular filtration rate (termed “early GFR decline”) in patients with type 1 diabetes.

Methods

From the 1^st Joslin Kidney Study, we selected 30 patients with longstanding normoalbuminuria and 55 patients with new onset microalbuminuria. Patients with microalbuminuria had 8–12 years follow-up during which 33 had stable GFR and 22 early GFR decline. Mean baseline GFR_{CYSTATIN C} was similar between the three groups. Glycation, oxidation and nitration markers were measured in protein and ultrafiltrate at baseline by liquid chromatography-tandem mass spectrometry using the most reliable methods currently available.

Results

Though none were significantly different between patients with microalbuminuria with stable or early GFR decline, levels of 6 protein damage adduct residues of plasma protein and 4 related free adducts of plasma ultrafiltrate were significantly different in patients with microalbuminuria compared to normoalbuminuria controls. Three protein damage adduct residues were decreased and 3 increased in microalbuminuria while 3 free adducts were decreased and one increased in microalbuminuria. The most profound differences were of N-formylkynurenine (NFK) protein adduct residue and N_ω-carboxymethylarginine (CMA) free adduct in which levels were markedly lower in microalbuminuria (P<0.001 for both).

Conclusions

Complex processes influence levels of plasma protein damage and related proteolysis product free adducts in type 1 diabetes and microalbuminuria. The effects observed point to the possibility that patients who have efficient mechanisms of disposal of damaged proteins might be at an increased risk of developing microalbuminuria but not early renal function decline. The findings support the concept that the mechanisms responsible for microalbuminuria may differ from the mechanisms involved in the initiation of early renal function decline.

Elevated urinary excretion of immunoglobulins in nonproteinuric patients with type 1 diabetes

Increased albuminuria is a hallmark of early diabetic nephropathy, whereas the role of immunoglobulins (Igs), such as IgG (its 1-4 subtypes), IgA, and IgM, different in charge and size, has not been examined in early nephropathy in the past due to lack of a sensitive and reliable method. Our study group consisted of subjects with type 1 diabetes (T1D) and normoalbuminuria (n = 78), microalbuminuria (n = 78), and of 75 healthy subjects (HS). A Luminex-based immunoassay (1,000 time more sensitive than nephelometry-based method) was validated for the urine matrix and used for the measurements of IgG1-4, IgA, and IgM in our study groups. The Luminex-based assay detected Igs in 87% of HS subjects and in 100% of T1D subjects. Recovery of known amounts of Igs added to urine was 92-118%. In the normoalbuminuria group, urinary concentrations of albumin, IgG2, IgA, and IgM were significantly higher than in HS, whereas in the microalbuminuria, further elevation of IgG2, IgG4, and IgA was the most pronounced. In all three groups, fractional excretion of Igs was at least 100 times lower than that of albumin. Fractional excretion of IgG2 was the highest among all Igs. We validated a sensitive method for measuring Igs in urine using Luminex. We found that elevated concentrations of Igs, particularly in IgG2 and IgA, is present in subjects with T1D and no proteinuria. Elevation of those particular Ig subtypes suggests a contribution of novel mechanisms in early diabetic nephropathy, different from charge and size barrier impairment.

Circulating TNF receptors 1 and 2 predict ESRD in type 2 diabetes

Levels of proinflammatory cytokines associate with risk for developing type 2 diabetes but whether chronic inflammation contributes to the development of diabetic complications, such as ESRD, is unknown. In the 1990s, we recruited 410 patients with type 2 diabetes for studies of diabetic nephropathy and recorded their characteristics at enrollment. During 12 years of follow-up, 59 patients developed ESRD (17 per 1000 patient-years) and 84 patients died without ESRD (24 per 1000 patient-years). Plasma markers of systemic inflammation, endothelial dysfunction, and the TNF pathway were measured in the study entry samples. Of the examined markers, only TNF receptors 1 and 2 (TNFR1 and TNFR2) associated with risk for ESRD. These two markers were highly correlated, but ESRD associated more strongly with TNFR1. The cumulative incidence of ESRD for patients in the highest TNFR1 quartile was 54% after 12 years but only 3% for the other quartiles (P<0.001). In Cox proportional hazard analyses, TNFR1 predicted risk for ESRD even after adjustment for clinical covariates such as urinary albumin excretion. Plasma concentration of TNFR1 outperformed all tested clinical variables with regard to predicting ESRD. Concentrations of TNFRs moderately associated with death unrelated to ESRD. In conclusion, elevated concentrations of circulating TNFRs in patients with type 2 diabetes at baseline are very strong predictors of the subsequent progression to ESRD in subjects with and without proteinuria.

Circulating TNF receptors 1 and 2 predict stage 3 CKD in type 1 diabetes

Elevated plasma concentrations of TNF receptors 1 and 2 (TNFR1 and TNFR2) predict development of ESRD in patients with type 2 diabetes without proteinuria, suggesting these markers may contribute to the pathogenesis of renal decline. We investigated whether circulating markers of the TNF pathway determine GFR loss among patients with type 1 diabetes. We followed two cohorts comprising 628 patients with type 1 diabetes, normal renal function, and no proteinuria. Over 12 years, 69 patients developed estimated GFR less than 60 mL/min per 1.73 m(2) (16 per 1000 person-years). Concentrations of TNFR1 and TNFR2 were strongly associated with risk for early renal decline. Renal decline was associated only modestly with total TNFα concentration and appeared unrelated to free TNFα. The cumulative incidence of estimated GFR less than 60 mL/min per 1.73 m(2) for patients in the highest TNFR2 quartile was 60% after 12 years compared with 5%-19% in the remaining quartiles. In Cox proportional hazards analysis, patients with TNFR2 values in the highest quartile were threefold more likely to experience renal decline than patients in the other quartiles (hazard ratio, 3.0; 95% confidence interval, 1.7-5.5). The risk associated with high TNFR1 values was slightly less than that associated with high TNFR2 values. TNFR levels were unrelated to baseline free TNFα level and remained stable over long periods within an individual. In conclusion, early GFR loss in patients with type 1 diabetes without proteinuria is strongly associated with circulating TNF receptor levels but not TNFα levels (free or total).

Genetic variation in the matrix metalloproteinase genes and diabetic nephropathy in type 1 diabetes

Genetic data support the notion that polymorphisms in members of the matrix metalloproteinase (MMP) family of genes play an important role in extracellular matrix remodeling and contribute to the pathogenesis of vascular disease. To identify novel genetic markers for diabetic nephropathy (DN), we examined the relationship between MMP gene polymorphisms and DN in the Genetics of Kidneys in Diabetes (GoKinD) population. Genotypic data from the Genetic Association Information Network (GAIN) type 1 DN project were analyzed for associations across 21 MMP genes in 1705 individual with type 1 diabetes, including 885 normoalbuminuric control subjects and 820 advanced DN case subjects. In total, we investigated the role of 1283 SNPs (198 genotyped SNPs and 1085 imputed SNPs) mapping to the MMP genes. We identified associations at several correlated SNPs across a 29.2kb interval on chromosome 11q at the MMP-3/MMP-12 locus. The strongest associations occurred at 2 highly-correlated SNPs, rs610950 (OR=0.50, P=1.6×10(-5)) and rs1277718 (OR=0.50, P=2.1×10(-5)). Further examination of this locus identified 17 SNPs (2 genotyped SNPs and 15 imputed SNPs) in complete linkage disequilibrium associated with DN (P-values<2.5×10(-4)), including a non-synonymous SNP (rs652438, Asn357Ser) located in exon 8 of MMP-12 that significantly reduced the risk of DN among carriers of the serine substitution relative to homozygous carriers of asparagine (OR=0.51; 95% CI=0.37-0.71, P=6.2×10(-5)). Taken together, our study suggests that genetic variations within the MMP-3/MMP-12 locus influence susceptibility of DN in type 1 diabetes.