Metabolomics reveals signature of mitochondrial dysfunction in diabetic kidney disease.

Diabetic kidney disease is the leading cause of ESRD, but few biomarkers of diabetic kidney disease are available. This study used gas chromatography-mass spectrometry to quantify 94 urine metabolites in screening and validation cohorts of patients with diabetes mellitus (DM) and CKD(DM+CKD), in patients with DM without CKD (DM-CKD), and in healthy controls. Compared with levels in healthy controls, 13 metabolites were significantly reduced in the DM+CKD cohorts (P≤0.001), and 12 of the 13 remained significant when compared with the DM-CKD cohort. Many of the differentially expressed metabolites were water-soluble organic anions. Notably, organic anion transporter-1 (OAT1) knockout mice expressed a similar pattern of reduced levels of urinary organic acids, and human kidney tissue from patients with diabetic nephropathy demonstrated lower gene expression of OAT1 and OAT3. Analysis of bioinformatics data indicated that 12 of the 13 differentially expressed metabolites are linked to mitochondrial metabolism and suggested global suppression of mitochondrial activity in diabetic kidney disease. Supporting this analysis, human diabetic kidney sections expressed less mitochondrial protein, urine exosomes from patients with diabetes and CKD had less mitochondrial DNA, and kidney tissues from patients with diabetic kidney disease had lower gene expression of PGC1α (a master regulator of mitochondrial biogenesis). We conclude that urine metabolomics is a reliable source for biomarkers of diabetic complications, and our data suggest that renal organic ion transport and mitochondrial function are dysregulated in diabetic kidney disease.

Chronic renin inhibition with aliskiren improves glucose tolerance, insulin sensitivity, and skeletal muscle glucose transport activity in obese Zucker rats.

We have demonstrated previously that overactivity of the renin-angiotensin system (RAS) is associated with whole body and skeletal muscle insulin resistance in obese Zucker (fa/fa) rats. Moreover, this obesity-associated insulin resistance is reduced by treatment with angiotensin-converting enzyme inhibitors or angiotensin receptor (type 1) blockers. However, it is currently unknown whether specific inhibition of renin itself, the rate-limiting step in RAS functionality, improves insulin action in obesity-associated insulin resistance. Therefore, the present study assessed the effect of chronic, selective renin inhibition using aliskiren on glucose tolerance, whole body insulin sensitivity, and insulin action on the glucose transport system in skeletal muscle of obese Zucker rats. Obese Zucker rats were treated for 21 days with either vehicle or aliskiren (50 mg/kg body wt ip). Renin inhibition was associated with a significant lowering (10%, P < 0.05) of resting systolic blood pressure and induced reductions in fasting plasma glucose (11%) and free fatty acids (46%) and homeostatic model assessment for insulin resistance (13%). Glucose tolerance (glucose area under the curve) and whole body insulin sensitivity (inverse of the glucose-insulin index) during an oral glucose tolerance test were improved by 15% and 16%, respectively, following chronic renin inhibition. Moreover, insulin-stimulated glucose transport activity in isolated soleus muscle of renin inhibitor-treated animals was increased by 36% and was associated with a 2.2-fold greater Akt Ser(473) phosphorylation. These data provide evidence that chronic selective inhibition of renin activity leads to improvements in glucose tolerance and whole body insulin sensitivity in the insulin-resistant obese Zucker rat. Importantly, chronic renin inhibition is associated with upregulation of insulin action on skeletal muscle glucose transport, and it may involve improved Akt signaling. These data support the strategy of targeting the RAS to improve both blood pressure regulation and insulin action in conditions of insulin resistance.

Sustainability and Justice: Challenges and Opportunities for an Open STEM Education.

Open educational resources, or OER, are teaching materials that reside in the public domain and are available under an open license. While the creation of high-quality materials and cyberinfrastructure to share these resources is important, OER are much more than static resource repositories. Vibrant OER communities function as collaboration hubs and often include librarians, instructional technologists, instructors, education researchers, funders, open-source software developers, and college administrators. Together, these individuals work as a community to respond to changes in the education landscape, support student learning impacts both in terms of cost savings and student retention, and solve issues related to broadly sharing open resources on the web. This essay provides general information about OER, describes communities developing OER for science, technology, engineering, and mathematics education, and presents insights about sustainability challenges. The sustainability challenges are organized according to multiple dimensions: cultural and social, economic and financial, and technological and environmental. In addition, OER provide important opportunities to address and promote social justice and open and accessible education philosophies. Knowing more about the OER landscape, sustainability challenges, and educational justice opportunities can help instructors use and contribute to this growing movement to reshape the landscape of undergraduate education.

Role of the USF1 transcription factor in diabetic kidney disease.

The predominant transcription factors regulating key genes in diabetic kidney disease have not been established. The transcription factor upstream stimulatory factor 1 (USF1) is an important regulator of glucose-mediated transforming growth factor (TGF)-ß1 expression in mesangial cells; however, its role in the development of diabetic kidney disease has not been evaluated. In the present study, wild-type (WT; USF1 +/+), heterozygous (USF1 +/-), and homozygous (USF1 -/-) knockout mice were intercrossed with Akita mice (Ins2/Akita) to induce type 1 diabetes. Mice were studied up to 36 wk of age. The degree of hyperglycemia and kidney hypertrophy were similar in all groups of diabetic mice; however, the USF1 -/- diabetic mice had significantly less albuminuria and mesangial matrix expansion than the WT diabetic mice. TGF-ß1 and renin gene expression and protein were substantially increased in the WT diabetic mice but not in USF1 -/- diabetic mice. The underlying pathway by which USF1 is regulated by high glucose was investigated in mesangial cell culture. High glucose inhibited AMP-activated protein kinase (AMPK) activity and increased USF1 nuclear translocation. Activation of AMPK with AICAR stimulated AMPK activity and reduced nuclear accumulation of USF1. We thus conclude that USF1 is a critical transcription factor regulating diabetic kidney disease and plays a critical role in albuminuria, mesangial matrix accumulation, and TGF-ß1 and renin stimulation in diabetic kidney disease. AMPK activity may play a key role in high glucose-induced regulation of USF1.

Midkine, a heparin-binding protein, is increased in the diabetic mouse kidney postmenopause.

Estrogen is thought to protect against the development of chronic kidney disease, and menopause increases the development and severity of diabetic kidney disease. In this study, we used streptozotocin (STZ) to induce diabetes in the 4-vinylcyclohexene diepoxide (VCD)-treated mouse model of menopause. DNA microarrays were used to identify gene expression changes in the diabetic kidney postmenopause. An ANOVA model, CARMA, was used to isolate the menopause effect between two groups of diabetic mice, diabetic menopausal (STZ/VCD) and diabetic cycling (STZ). In this diabetic study, 8,864 genes of the possible 15,600 genes on the array were included in the ANOVA; 99 genes were identified as demonstrating a >1.5-fold up- or downregulation between the STZ/VCD and STZ groups. We randomly selected genes for confirmation by real-time PCR; midkine (Mdk), immediate early response gene 3 (IEX-1), mitogen-inducible gene 6 (Mig6), and ubiquitin-specific protease 2 (USP2) were significantly increased in the kidneys of STZ/VCD compared with STZ mice. Western blot analysis confirmed that Mdk and IEX-1 protein abundance was significantly increased in the kidney cortex of STZ/VCD compared with STZ mice. In a separate study, DNA microarrays and CARMA analysis were used to identify the effect of menopause on the nondiabetic kidney; VCD-treated mice were compared with cycling mice. Of the possible 15,600 genes on the array, 9,142 genes were included in the ANOVA; 20 genes were identified as demonstrating a >1.5-fold up- or downregulation; histidine decarboxylase and vanin 1 were among the genes identified as differentially expressed in the postmenopausal nondiabetic kidney. These data expand our understanding of how hormone status correlates with the development of diabetic kidney disease and identify several target genes for further studies.

Critical role of the transient activation of p38 MAPK in the etiology of skeletal muscle insulin resistance induced by low-level in vitro oxidant stress.

Increased cellular exposure to oxidants may contribute to the development of insulin resistance and type 2 diabetes. Skeletal muscle is the primary site of insulin-dependent glucose disposal in the body; however, the effects of oxidative stress on insulin signaling and glucose transport activity in mammalian skeletal muscle are not well understood. We therefore studied the effects of a low-level in vitro oxidant stress (30-40 µM H2O2) on basal and insulin-stimulated (5 mU/ml) glucose transport activity and insulin signaling at 2, 4, and 6 h in isolated rat soleus muscle. H2O2 increased basal glucose transport activity at 2 and 4 h, but not at 6 h. This low-level oxidant stress significantly impaired insulin-stimulated glucose transport activity at all time points, and was associated with inhibition of insulin-stimulated phosphorylation of Akt Ser473 and GSK-3ß Ser9. In the presence of insulin, H2O2 decreased total protein expression of IRS-1 at 6 h and IRS-2 at 4 and 6 h. Phosphorylation of p38 MAPK Thr180/Tyr182 was transiently increased by H2O2 in the presence and absence of insulin at 2 and 4 h, but not at 6 h. Selective inhibition of p38 MAPK with A304000 partially rescued the H2O2-induced reduction in insulin-stimulated glucose transport activity. These results indicate that direct in vitro exposure of isolated mammalian skeletal muscle to a low-level oxidant stress impairs distal insulin signaling and insulin-stimulated glucose transport activity, at least in part, due to a p38 MAPK-dependent mechanism.

Vasopressin increases expression of UT-A1, UT-A3, and ER chaperone GRP78 in the renal medulla of mice with a urinary concentrating defect.

Activation of V2 receptors (V2R) during antidiuresis increases the permeability of the inner medullary collecting duct to urea and water. Extracellular osmolality is elevated as the concentrating capacity of the kidney increases. Osmolality is known to contribute to the regulation of collecting duct water (aquaporin-2; AQP2) and urea transporter (UT-A1, UT-A3) regulation. AQP1KO mice are a concentrating mechanism knockout, a defect attributed to the loss of high interstitial osmolality. A V2R-specific agonist, deamino-8-D-arginine vasopressin (dDAVP), was infused into wild-type and AQP1KO mice for 7 days. UT-A1 mRNA and protein abundance were significantly increased in the medullas of wild-type and AQP1KO mice following dDAVP infusion. The mRNA and protein abundance of UT-A3, the basolateral urea transporter, was significantly increased by dDAVP in both wild-type and AQP1KO mice. Semiquantitative immunoblots revealed that dDAVP infusion induced a significant increase in the medullary expression of the endoplasmic reticulum (ER) chaperone GRP78. Immunofluorescence studies demonstrated that GRP78 expression colocalized with AQP2 in principal cells of the papillary tip of the renal medulla. Using immunohistochemistry and immunogold electron microscopy, we demonstrate that vasopressin induced a marked apical targeting of GRP78 in medullary principal cells. Urea-sensitive genes, GADD153 and ATF4 (components of the ER stress pathway), were significantly increased in AQP1KO mice by dDAVP infusion. These findings strongly support an important role of vasopressin in the activation of an ER stress response in renal collecting duct cells, in addition to its role in activating an increase in UT-A1 and UT-A3 abundance.

Loss of ovarian function in the VCD mouse-model of menopause leads to insulin resistance and a rapid progression into the metabolic syndrome.

Factors comprising the metabolic syndrome occur with increased incidence in postmenopausal women. To investigate the effects of ovarian failure on the progression of the metabolic syndrome, female B(6)C(3)F(1) mice were treated with 4-vinylcyclohexene diepoxide (VCD) and fed a high-fat (HF) diet for 16 wk. VCD destroys preantral follicles, causing early ovarian failure and is a well-characterized model for the gradual onset of menopause. After 12 wk on a HF diet, VCD-treated mice had developed an impaired glucose tolerance, whereas cycling controls were unaffected [12 wk AUC HF mice 13,455 +/- 643 vs. HF/VCD 17,378 +/- 1140 mg/dl/min, P < 0.05]. After 16 wk on a HF diet, VCD-treated mice had significantly higher fasting insulin levels (HF 5.4 +/- 1.3 vs. HF/VCD 10.1 +/- 1.4 ng/ml, P < 0.05) and were significantly more insulin resistant (HOMA-IR) than cycling controls on a HF diet (HF 56.2 +/- 16.7 vs. HF/VCD 113.1 +/- 19.6 mg/dl x microU/ml, P < 0.05). All mice on a HF diet gained more weight than mice on a standard diet, and weight gain in HF/VCD mice was significantly increased compared with HF cycling controls. Interestingly, even without a HF diet, progression into VCD-induced menopause caused a significant increase in cholesterol and free fatty acids. Furthermore, in mice fed a standard diet (6% fat), insulin resistance developed 4 mo after VCD-induced ovarian failure. Insulin resistance following ovarian failure (menopause) was prevented by estrogen replacement. Studies here demonstrate that ovarian failure (menopause) accelerates progression into the metabolic syndrome and that estrogen replacement prevents the onset of insulin resistance in VCD-treated mice. Thus, the VCD model of menopause provides a physiologically relevant means of studying how sex hormones influence the progression of the metabolic syndrome.

Mass Spectrometry Imaging Reveals Elevated Glomerular ATP/AMP in Diabetes/obesity and Identifies Sphingomyelin as a Possible Mediator.

AMP-activated protein kinase (AMPK) is suppressed in diabetes and may be due to a high ATP/AMP ratio, however the quantitation of nucleotides in vivo has been extremely difficult. Via matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) to localize renal nucleotides we found that the diabetic kidney had a significant increase in glomerular ATP/AMP ratio. Untargeted MALDI-MSI analysis revealed that a specific sphingomyelin species (SM(d18:1/16:0)) accumulated in the glomeruli of diabetic and high-fat diet-fed mice compared with wild-type controls. In vitro studies in mesangial cells revealed that exogenous addition of SM(d18:1/16:0) significantly elevated ATP via increased glucose consumption and lactate production with a consequent reduction of AMPK and PGC1α. Furthermore, inhibition of sphingomyelin synthases reversed these effects. Our findings suggest that AMPK is reduced in the diabetic kidney due to an increase in the ATP/AMP ratio and that SM(d18:1/16:0) could be responsible for the enhanced ATP production via activation of the glycolytic pathway.

AMPK dysregulation promotes diabetes-related reduction of superoxide and mitochondrial function.

Diabetic microvascular complications have been considered to be mediated by a glucose-driven increase in mitochondrial superoxide anion production. Here, we report that superoxide production was reduced in the kidneys of a steptozotocin-induced mouse model of type 1 diabetes, as assessed by in vivo real-time transcutaneous fluorescence, confocal microscopy, and electron paramagnetic resonance analysis. Reduction of mitochondrial biogenesis and phosphorylation of pyruvate dehydrogenase (PDH) were observed in kidneys from diabetic mice. These observations were consistent with an overall reduction of mitochondrial glucose oxidation. Activity of AMPK, the major energy-sensing enzyme, was reduced in kidneys from both diabetic mice and humans. Mitochondrial biogenesis, PDH activity, and mitochondrial complex activity were rescued by treatment with the AMPK activator 5-aminoimidazole-4-carboxamide-1-ß-D-ribofuranoside (AICAR). AICAR treatment induced superoxide production and was linked with glomerular matrix and albuminuria reduction in the diabetic kidney. Furthermore, diabetic heterozygous superoxide dismutase 2 (Sod2(+/-)) mice had no evidence of increased renal disease, and Ampka2(-/-) mice had increased albuminuria that was not reduced with AICAR treatment. Reduction of mitochondrial superoxide production with rotenone was sufficient to reduce AMPK phosphorylation in mouse kidneys. Taken together, these results demonstrate that diabetic kidneys have reduced superoxide and mitochondrial biogenesis and activation of AMPK enhances superoxide production and mitochondrial function while reducing disease activity.

Sugar, sex, and TGF-ß in diabetic nephropathy.

TGF-ß is well known to play a critical role in diabetic kidney disease, and ongoing clinical studies are testing the potential therapeutic promise of inhibiting TGF-ß production and action. An aspect of TGF-ß action that has not received much attention is its potential role in explaining sex-related proclivity for kidney disease. In this review, we discuss recent studies linking TGF-ß signaling to sex-related effects in diabetic kidney disease and suggest targets for future studies.

Contribution of the serine kinase c-Jun N-terminal kinase (JNK) to oxidant-induced insulin resistance in isolated rat skeletal muscle.

The specific and direct contribution of the stress-activated serine kinase c-Jun N-terminal kinase (JNK) in the development of oxidative stress-induced insulin resistance of the glucose transport system in mammalian skeletal muscle is not fully understood. We assessed the specific role of JNK in the development of insulin resistance caused by in vitro exposure of rat soleus muscle to low levels (30-40 µM) of the oxidant hydrogen peroxide (H(2)O(2)) for up to 6 h. Oxidant exposure caused significant (p < 0.05) decreases in insulin-stimulated glucose transport activity (up to 42%) and Akt Ser(473) phosphorylation (up to 67%), and increased (up to 74%) phosphorylation (Thr(183)/Tyr(185)) of JNK1 and JNK2/3 isoforms. Importantly, insulin-stimulated glucose transport activity in the presence of H(2)O(2) was moderately improved with the selective JNK inhibitor SP600125. These results indicate that activation of the serine kinase JNK contributes, at least in part, to oxidative stress-induced insulin resistance in isolated mammalian skeletal muscle.

Oxidative stress and the etiology of insulin resistance and type 2 diabetes.

The condition of oxidative stress arises when oxidant production exceeds antioxidant activity in cells and plasma. The overabundance of oxidants is mechanistically connected to the multifactorial etiology of insulin resistance, primarily in skeletal muscle tissue, and the subsequent development of type 2 diabetes. Two important mechanisms for this oxidant excess are (1) the mitochondrial overproduction of hydrogen peroxide and superoxide ion under conditions of energy surplus and (2) the enhanced activation of cellular NADPH oxidase via angiotensin II receptors. Several recent studies are reviewed that support the concept that direct exposure of mammalian skeletal muscle to an oxidant stress (including hydrogen peroxide) results in stimulation of the serine kinase p38 mitogen-activated protein kinase (p38 MAPK), and that the engagement of this stress-activated p38 MAPK signaling is mechanistically associated with diminished insulin-dependent stimulation of insulin signaling elements and glucose transport activity. The beneficial interactions between the antioxidant α-lipoic acid and the advanced glycation end-product inhibitor pyridoxamine that ameliorate oxidant stress-associated defects in whole-body and skeletal-muscle insulin action in the obese Zucker rat, a model of prediabetes, are also addressed. Overall, this review highlights the importance of oxidative stress in the development of insulin resistance in mammalian skeletal muscle tissue, at least in part via a p38-MAPK-dependent mechanism, and indicates that interventions that reduce this oxidative stress and oxidative damage can improve insulin action in insulin-resistant animal models. Strategies to prevent and ameliorate oxidative stress remain important in the overall treatment of insulin resistance and type 2 diabetes.

Direct inhibition by angiotensin II of insulin-dependent glucose transport activity in mammalian skeletal muscle involves a ROS-dependent mechanism.

No previous study has investigated how the vaso-constrictive peptide Ang II impacts insulin action in isolated mammalian skeletal muscle. We investigated the molecular actions of Ang II on insulin signalling and glucose transport in skeletal muscle from lean Zucker rats. Soleus strips were incubated with insulin (5 mU/ml) and/or Ang II (500 nM) for 2 hours. Ang II caused significant (p < 0.05) inhibition of insulin-stimulated glucose transport (39%) and decreased phosphorylation of Akt Ser(473) (37%) and glycogen synthase kinase-3beta Ser(9) (42%) without affecting phosphorylation of IRS-1 Ser(307) or p38 MAPK. We used the superoxide dismutase mimetic, tempol (1 mM), to determine if reactive oxygen species (ROS) contribute to Ang II-mediated insulin resistance. Tempol partially reversed (42%) Ang II-induced inhibition of insulin-stimulated glucose transport. These results indicate that Ang II inhibits distal insulin signalling and insulin-stimulated glucose transport in isolated mammalian skeletal muscle, and that this effect is partially mediated by ROS.