Features Of Diabetic Kidney Disease Research Articles

The Familiality of Rapid Renal Decline in Diabetes.

Sustained and rapid loss of glomerular filtration rate (GFR) is the predominant clinical feature of diabetic kidney disease and a requisite for the development of end-stage renal disease. Although GFR trajectories have been studied in several cohorts with diabetes and without diabetes, whether rapid renal decline clusters in families with diabetes has not been examined. To determine this, we estimated GFR (eGFR) from serum creatinine measurements obtained from 15,612 patients with diabetes at the University of Utah Health Sciences Center and established their renal function trajectories. Patients with rapid renal decline (eGFR slope < -5 mL/min/1.73 m2/year) were then mapped to pedigrees using extensive genealogical records from the Utah Population Database to identify high-risk rapid renal decline pedigrees. We identified 2,127 (13.6%) rapid decliners with a median eGFR slope of -8.0 mL/min/1.73 m2/year and 51 high-risk pedigrees (ranging in size from 1,450 to 24,501 members) with excess clustering of rapid renal decline. Familial analysis showed that rapid renal decline aggregates in these families and is associated with its increased risk among first-degree relatives. Further study of these families is necessary to understand the magnitude of the influence of shared familial factors, including environmental and genetic factors, on rapid renal decline in diabetes.

Triptolide Restores Autophagy to Alleviate Diabetic Renal Fibrosis through the miR-141-3p/PTEN/Akt/mTOR Pathway.

Fibrosis is the major pathological feature of diabetic kidney disease (DKD). Autophagy, a process to maintain metabolic homeostasis, is obviously inhibited in DKD. Triptolide (TP) is a traditional Chinese medicine extract known for immune suppression and anti-inflammatory and anti-cancer activities. In this study, we investigated the effects of TP on autophagy and fibrosis in DKD. TP restored autophagy and alleviated fibrosis in DKD rats and high-glucose-incubated human mesangial cells. After we applied 3-methyladenine (an autophagy inhibitor) and autophagy-related gene 5-small interfering RNA (siRNA), we found that the improvement of fibrosis on TP was related to the restoration of autophagy. In addition, miR-141-3p levels were increased under high glucose but reduced after TP treatment. miR-141-3p overexpression aggravated the fibrosis and restrained the autophagy further, while miR-141-3p inhibition imitated the effects of TP. As an action target, phosphatase and tensin homolog (PTEN) showed corresponding opposite changes. After PTEN-siRNA transfection, the effects of TP on autophagy and fibrosis were inhibited. PTEN levels were downregulated, with downstream phosphorylated protein kinase B (Akt) and the mammalian target of rapamycin (mTOR) upregulated in high glucose, which were reversed by TP treatment. These findings indicate that TP alleviates fibrosis by restoring autophagy through the miR-141-3p/PTEN/Akt/mTOR pathway and is a novel therapeutic option for DKD.

Podocyte-specific knockout of cyclooxygenase 2 exacerbates diabetic kidney disease.

Enhanced expression of cyclooxygenase 2 (COX2) in podocytes contributes to glomerular injury in diabetic kidney disease, but some basal level of podocyte COX2 expression might be required to promote podocyte attachment and/or survival. To investigate the role of podocyte COX2 expression in diabetic kidney disease, we deleted COX2 specifically in podocytes in a mouse model of Type 1 diabetes mellitus (Akita mice). Podocyte-specific knockout (KO) of COX2 did not affect renal morphology or albuminuria in nondiabetic mice. Albuminuria was significantly increased in wild-type (WT) and KO Akita mice compared with nondiabetic controls, and the increase in albuminuria was significantly greater in KO Akita mice compared with WT Akita mice at both 16 and 20 wk of age. At the 20-wk time point, mesangial expansion was also increased in WT and KO Akita mice compared with nondiabetic animals, and these histologic abnormalities were not improved by KO of COX2. Tubular injury was seen only in diabetic mice, but there were no significant differences between groups. Thus, KO of COX2 enhanced albuminuria and did not improve the histopathologic features of diabetic kidney disease. These data suggest that 1) KO of COX2 in podocytes does not ameliorate diabetic kidney disease in Akita mice, and 2) some basal level of podocyte COX2 expression in podocytes is necessary to attenuate the adverse effects of diabetes on glomerular filtration barrier function.

Berberine activates Nrf2 nuclear translocation and inhibits apoptosis induced by high glucose in renal tubular epithelial cells through a phosphatidylinositol 3-kinase/Akt-dependent mechanism.

Apoptosis of tubular epithelial cells is a major feature of diabetic kidney disease, and hyperglycemia triggers the generation of free radicals and oxidant stress in tubular cells. Berberine (BBR) is identified as a potential anti-diabetic herbal medicine due to its beneficial effects on insulin sensitivity, glucose metabolism and glycolysis. In this study, the underlying mechanisms involved in the protective effects of BBR on high glucose-induced apoptosis were explored using cultured renal tubular epithelial cells (NRK-52E cells) and human kidney proximal tubular cell line (HK-2 cells). We identified the pivotal role of phosphatidylinositol 3-kinase (PI3K)/Akt in BBR cellular defense mechanisms and revealed the novel effect of BBR on nuclear factor (erythroid-derived 2)-related factor-2 (Nrf2) and heme oxygenase (HO)-1 in NRK-52E and HK-2 cells. BBR attenuated reactive oxygen species production, antioxidant defense (GSH and SOD) and oxidant-sensitive proteins (Nrf2 and HO-1), which also were blocked by LY294002 (an inhibitor of PI3K) in HG-treated NRK-52E and HK-2 cells. Furthermore, BBR improved mitochondrial function by increasing mitochondrial membrane potential. BBR-induced anti-apoptotic function was demonstrated by decreasing apoptotic proteins (cytochrome c, Bax, caspase3 and caspase9). All these findings suggest that BBR exerts the anti-apoptosis effects through activation of PI3K/Akt signal pathways and leads to activation of Nrf2 and induction of Nrf2 target genes, and consequently protecting the renal tubular epithelial cells from HG-induced apoptosis.

Augmenting podocyte injury promotes advanced diabetic kidney disease in Akita mice

To determine if augmenting podocyte injury promotes the development of advanced diabetic nephropathy (DN), we created mice that expressed the enzyme cytosine deaminase (CD) specifically in podocytes of diabetic Akita mice (Akita-CD mice). In these mice, treatment with the prodrug 5-flucytosine (5-FC) causes podocyte injury as a result of conversion to the toxic metabolite 5-fluorouracil (5-FU). We found that treatment of 4–5week old Akita mice with 5-FC for 5days caused robust albuminuria at 16 and 20weeks of age compared to 5-FC treated Akita controls, which do not express CD (Akita CTLs). By 20weeks of age, there was a significant increase in mesangial expansion in Akita-CD mice compared to Akita CTLs, which was associated with a variable increase in glomerular basement membrane (GBM) width and interstitial fibrosis. At 20weeks of age, podocyte number was similarly reduced in both groups of Akita mice, and was inversely correlated with the albuminuria and mesangial expansion. Thus, enhancing podocyte injury early in the disease process promotes the development of prominent mesangial expansion, interstitial fibrosis, increased GBM thickness and robust albuminuria. These data suggest that podocytes play a key role in the development of advanced features of diabetic kidney disease.

Combined acute hyperglycemic and hyperinsulinemic clamp induced profibrotic and proinflammatory responses in the kidney

Increase in matrix protein content in the kidney is a cardinal feature of diabetic kidney disease. While renal matrix protein content is increased by chronic hyperglycemia, whether it is regulated by acute elevation of glucose and insulin has not been addressed. In this study, we aimed to evaluate whether short duration of combined hyperglycemia and hyperinsulinemia, mimicking the metabolic environment of prediabetes and early type 2 diabetes, induces kidney injury. Normal rats were subjected to either saline infusion (control, n = 4) or 7 h of combined hyperglycemic-hyperinsulinemic clamp (HG+HI clamp; n = 6). During the clamp, plasma glucose and plasma insulin were maintained at about 350 mg/dl and 16 ng/ml, respectively. HG+HI clamp increased the expression of renal cortical transforming growth factor-β (TGF-β) and renal matrix proteins, laminin and fibronectin. This was associated with the activation of SMAD3, Akt, mammalian target of rapamycin (mTOR) complexes, and ERK signaling pathways and their downstream target events in the initiation and elongation phases of mRNA translation, an important step in protein synthesis. Additionally, HG+HI clamp provoked renal inflammation as shown by the activation of Toll-like receptor 4 (TLR4) and infiltration of CD68-positive monocytes. Urinary F2t isoprostane excretion, an index of renal oxidant stress, was increased in the HG+HI clamp rats. We conclude that even a short duration of hyperglycemia and hyperinsulinemia contributes to activation of pathways that regulate matrix protein synthesis, inflammation, and oxidative stress in the kidney. This finding could have implications for the control of short-term rises in blood glucose in diabetic individuals at risk of developing kidney disease.

Diabetes and renal tubular cell apoptosis

Apoptosis contributes to the development of diabetic nephropathy, but the mechanism by which high glucose induces apoptosis is not fully understood. Apoptosis of tubular epithelial cells is a major feature of diabetic kidney disease, and hyperglycemia triggers the generation of free radicals and oxidant stress in tubular cells. Hyperglycemia and high glucose in vitro also lead to apoptosis, a form of programmed cell death. High glucose similar to those seen with hyperglycemia in people with diabetes mellitus, lead to accelerated apoptosis, a form of programmed cell death characterized by cell shrinkage, chromatin condensation and DNA fragmentation, in variety of cell types, including renal proximal tubular epithelial cells.

MicroRNA-21 Orchestrates High Glucose-induced Signals to TOR Complex 1, Resulting in Renal Cell Pathology in Diabetes

Hyperglycemia induces a wide array of signaling pathways in the kidney that lead to hypertrophy and matrix expansion, eventually culminating in progressive kidney failure. High glucose-induced reduction of the tumor suppressor protein phosphatase and tensin homolog deleted in chromosome 10 (PTEN) contributes to renal cell hypertrophy and matrix expansion. We identified microRNA-21 (miR-21) as the molecular link between high glucose and PTEN suppression. Renal cortices from OVE26 type 1 diabetic mice showed significantly elevated levels of miR-21 associated with reduced PTEN and increased fibronectin content. In renal mesangial cells, high glucose increased the expression of miR-21, which targeted the 3'-UTR of PTEN mRNA to inhibit PTEN protein expression. Overexpression of miR-21 mimicked the action of high glucose, which included a reduction in PTEN expression and a concomitant increase in Akt phosphorylation. In contrast, expression of miR-21 Sponge, to inhibit endogenous miR-21, prevented down-regulation of PTEN and phosphorylation of Akt induced by high glucose. Interestingly, high glucose-stimulated miR-21 inactivated PRAS40, a negative regulator of TORC1. Finally, miR-21 enhanced high glucose-induced TORC1 activity, resulting in renal cell hypertrophy and fibronectin expression. Thus, our results identify a previously unrecognized function of miR-21 that is the reciprocal regulation of PTEN levels and Akt/TORC1 activity that mediate critical pathologic features of diabetic kidney disease.

Evaluation of Renal Hypoxia in Diabetic Mice by BOLD MRI

Renal hypoxia has been proposed to be a pathophysiologic feature of diabetic kidney disease but it has been difficult to demonstrate in vivo, particularly in mouse models of diabetes. The objective of this work was to examine the sensitivity of blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) to assess renal oxygenation in vivo in a mouse model of diabetic kidney disease, the db/db mice. Kidney BOLD MRI studies were performed on a 3.0 T scanner using multiple gradient echo sequence with a custom-designed surface coil to acquire T2*-weighted images. Studies were performed in 10-week-old db/db mice (n = 7) and db/m controls (n = 6). R2* is a measure of the tissue deoxyhemoglobin concentration and higher values of R2* are associated with hypoxia. The db/db mice had higher medullary (43.1 ± 5.1 s⁻¹ vs. 32.3 ± 3.7⁻¹ s, P = 0.001) and cortical R2* (31.7 ± 3.1 s⁻¹ vs. 27.1 ± 4.1 s⁻¹, P = 0.04) values. Using pimonidazole staining as a marker of kidney hypoxia, in kidney sections from 10-week-old db/db mice neither cortex nor medulla had significant differences as compared with 10-week-old db/m mice (cortex: db/db 2.14 ± 0.05 vs. db/m 2.02 ± 0.28, medulla: db/db 2.81 ± 0.08 vs. db/m 2.6 ± 0.08). The db/db mice demonstrated further increased cortical and medullary hypoxia when scanned again at 15 weeks of age. The report shows that renal BOLD MRI is a sensitive method for the in vivo evaluation of renal hypoxia in a mouse model of diabetic kidney disease where progressive renal hypoxia can be documented over time. BOLD MRI may be useful to monitor therapeutic interventions that may improve tissue hypoxia in the diabetic kidney.

Diabetic Kidney Disease in the Older Adult: An Update

The kidneys are among the most prominent body organs affected by the process of aging, as both kidney morphology and function are known to change with age. However, special challenges emerge when the elderly patient also has diabetes complicated by kidney disease. Cases frequently progress from the early stages of diabetic nephropathy to advanced kidney impairment and end-stage renal disease, and the majority of patients suffer cardiovascular complications. However, many elderly patients with diabetes will lack the classic clinical features of diabetic kidney disease. Neither the efficacy nor safety of general treatment goals such as glycemic control, hypertension management and renin–angiotensin blockade have been adequately addressed in the aging diabetic kidney patient. These basic treatments for diabetic kidney disease are extrapolated from studies of mostly middle-aged individuals. Diabetic kidney guidelines do not adequately distinguish between age groups. Aggressive management must be measured against life expectancy in the elderly. The physician should be aware of these risks. Unfortunately, many elderly diabetic chronic kidney disease/end-stage renal disease patients are not prescribed the treatments that are available. Over a third of new end-stage renal disease cases among the elderly are due to diabetic kidney disease. Prognosis is poor, even for those who receive a kidney transplant.

Trophic factors and cytokines in early diabetic glomerulopathy.

The intent of this review is to focus on recent advances in the understanding of the factors responsible for the progressive pathologic features of diabetic kidney disease, with special attention to various growth factors and cytokines that appear to be important in this process. In addition, emphasis is centered on relatively early stages of the disease, because animal models have been most helpful to date in understanding this stage of the disease process. Although tubulointerstitial changes are of critical importance in the progression of diabetic nephropathy, especially in the evolution to end-stage renal disease, there is a general consensus that glomerular pathology occurs first. Therefore, attention is limited to factors that may be important in the development of early diabetic glomerulopathy, including transforming growth factor-beta (TGF-β), insulin-like growth factor (IGF)-I, vascular endothelial growth factor (VEGF)-A, and connective tissue growth factor (CTGF).

Premature senescence of skin fibroblasts from insulin-dependent diabetic patients with kidney disease

Diabetic glomerulopathy develops in a subset only of patients with insulin-dependent diabetes (IDDM) and early, in its course, is characterized by cell hypertrophy and by excessive extracellular matrix production. These observations suggest that an alteration in the control of cell growth processes may contribute to its pathogenesis and be related to the susceptibility to kidney disease. We therefore investigated whether the development of diabetic nephropathy is associated with abnormalities of cell growth and morphology. Cultured skin fibroblasts from 14 IDDM patients with nephropathy (DN) were compared with those of 10 IDDM patients without nephropathy (D) and of 14 control non-diabetic subjects (C). Cell volume (in arbitrary units) and total protein content (microgram/10, 000 cells) were increased in serially passaged skin fibroblasts of IDDM patients with nephropathy (DN = 809.5 +/- 33.1 and 1.93 +/- 0.38 vs. D = 764.4 +/- 31.5 and 1.5 +/- 0.37, P = 0.005 and P = 0.03, respectively; vs. C = 756.2 +/- 36.3 and 1.5 +/- 0.38, P = 0.0006 and P = 0.03, respectively). These hypertrophic cells had a tendency to a slower duplication rate and exhibited a dissociation of the DNA and cytoplasmic cell-cycles, resulting in a higher proportion of tetraploid cells (DN = 25 +/- 15% vs. D = 6 +/- 4%, P = 0.005; and vs. C = 10 +/- 8%, P = 0.04). The frequency of terminally differentiated post-mitotic fibrocytes, cells specialized for extracellular matrix production, was higher in patients with nephropathy compared to that of patients without nephropathy and normal controls (DN = 34 +/- 14% vs. D = 21 +/- 10%, P = 0.02; and vs. C = 19 +/- 12%, P = 0.008). That early differentiation was a specific feature of cells derived from patients with diabetic nephropathy was confirmed by the study of cell life-span which demonstrated that these cells aged prematurely (log rank test, chi 2 = 10,012; P = 0.0067). We conclude that an acceleration of cell aging is a peculiar feature of diabetic kidney disease and may contribute to its pathological tissue changes.