Altered endothelial nitric oxide synthase targeting and conformation and caveolin-1 expression in the diabetic kidney

Diabetic Nephropathy and Gaseous Modulators

Diabetic nephropathy (DN) remains the leading cause of vascular morbidity and mortality in diabetes patients. Despite the progress in understanding the diabetic disease process and advanced management of nephropathy, a number of patients still progress to end-stage renal disease (ESRD). The underlying mechanism still needs to be clarified. Gaseous signaling molecules, so-called gasotransmitters, such as nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), have been shown to play an essential role in the development, progression, and ramification of DN depending on their availability and physiological actions. Although the studies on gasotransmitter regulations of DN are still emerging, the evidence revealed an aberrant level of gasotransmitters in patients with diabetes. In studies, different gasotransmitter donors have been implicated in ameliorating diabetic renal dysfunction. In this perspective, we summarized an overview of the recent advances in the physiological relevance of the gaseous molecules and their multifaceted interaction with other potential factors, such as extracellular matrix (ECM), in the severity modulation of DN. Moreover, the perspective of the present review highlights the possible therapeutic interventions of gasotransmitters in ameliorating this dreaded disease.

Vitamin D regulates insulin and ameliorates apoptosis and oxidative stress in pancreatic tissues of rats with streptozotocin-induced diabetes

This study was designed to evaluate the potential therapeutic efficacy of vitamin D (Vit D) in averting the harmful effects of type 2 diabetes mellitus (T2D). Forty male Wistar rats were allotted into four groups: (1) the control, (2) Vit D, (3) streptozotocin (STZ), and (4) STZ + Vit D groups. Rats co-treated with Vit D had significantly (p < 0.05) decreased levels of cortisol; proinflammatory cytokines, including interleukin-6 (IL-6); and malondialdehyde (MDA). Meanwhile, the levels of insulin significantly (p < 0.05) increased, whereas the activity of the antioxidant system, including glutathione (GSH), superoxide dismutase (SOD), catalase, and total antioxidant capacity (TAC), significantly (p < 0.05) decreased. Histopathological examination revealed the destruction of beta cells in the islets of Langerhans in rats with diabetes. Meanwhile, immunoexpression revealed an increase in the immunoreactivity of caspase-3 and endothelial nitric oxide synthase and a reduction in the immunoreactivity of insulin in rats with diabetes. In conclusion, Vit D ameliorated the harmful biochemical impact of diabetes mellitus, probably by increasing insulin secretion and sensitivity, ameliorating β-cell function, and decreasing cortisol levels; also, the anti-inflammatory effect of Vit D reduces the number of proinflammatory cytokines (e.g., IL-6) and increases the activity of the antioxidant system, such as GSH, SOD, TAC, and catalase while reducing lipid peroxidation enzymes (e.g., MDA).

Metabolomic Analysis of Serum and Tear Samples from Patients with Obesity and Type 2 Diabetes Mellitus

Metabolomics strategies are widely used to examine obesity and type 2 diabetes (T2D). Patients with obesity (n = 31) or T2D (n = 26) and sex- and age-matched controls (n = 28) were recruited, and serum and tear samples were collected. The concentration of 23 amino acids and 10 biogenic amines in serum and tear samples was analyzed. Statistical analysis and Pearson correlation analysis along with network analysis were carried out. Compared to controls, changes in the level of 6 analytes in the obese group and of 10 analytes in the T2D group were statistically significant. For obesity, the energy generation, while for T2D, the involvement of NO synthesis and its relation to insulin signaling and inflammation, were characteristic. We found that BCAA and glutamine metabolism, urea cycle, and beta-oxidation make up crucial parts of the metabolic changes in T2D. According to our data, the retromer-mediated retrograde transport, the ethanolamine metabolism, and, consequently, the endocannabinoid signaling and phospholipid metabolism were characteristic of both conditions and can be relevant pathways to understanding and treating insulin resistance. By providing potential therapeutic targets and new starting points for mechanistic studies, our results emphasize the importance of complex data analysis procedures to better understand the pathomechanism of obesity and diabetes.

Histone deacetylase 3 inhibition alleviates type 2 diabetes mellitus-induced endothelial dysfunction via Nrf2

BACKGROUND

The mechanism underlying endothelial dysfunction leading to cardiovascular disease in type 2 diabetes mellitus (T2DM) remains unclear. Here, we show that inhibition of histone deacetylase 3 (HDAC3) reduced inflammation and oxidative stress by regulating nuclear factor-E2-related factor 2 (Nrf2), which mediates the expression of anti-inflammatory- and pro-survival-related genes in the vascular endothelium, thereby improving endothelial function.

METHODS

Nrf2 knockout (Nrf2 KO) C57BL/6 background mice, diabetic db/db mice, and control db/m mice were used to investigate the relationship between HDAC3 and Nrf2 in the endothelium in vivo. Human umbilical vein endothelial cells (HUVECs) cultured under high glucose-palmitic acid (HG-PA) conditions were used to explore the role of Kelch-like ECH-associated protein 1 (Keap1) -Nrf2-NAPDH oxidase 4 (Nox4) redox signaling in the vascular endothelium in vitro. Activity assays, immunofluorescence, western blotting, qRT-PCR, and immunoprecipitation assays were used to examine the effect of HDAC3 inhibition on inflammation, reactive oxygen species (ROS) production, and endothelial impairment, as well as the activity of Nrf2-related molecules.

RESULTS

HDAC3 activity, but not its expression, was increased in db/db mice. This resulted in de-endothelialization and increased oxidative stress and pro-inflammatory marker expression in cells treated with the HDAC3 inhibitor RGFP966, which activated Nrf2 signaling. HDAC3 silencing decreased ROS production, inflammation, and damage-associated tube formation in HG-PA-treated HUVECs. The underlying mechanism involved the Keap1-Nrf2-Nox4 signaling pathway.

CONCLUSION

The results of this study suggest the potential of HDAC3 as a therapeutic target for the treatment of endothelial dysfunction in T2DM. Video Abstract.

Caveolin-1 stabilizes ATP7A, a copper transporter for extracellular SOD, in vascular tissue to maintain endothelial function

Caveolin-1 (Cav-1) is a scaffolding protein and a major component of caveolae/lipid rafts. Previous reports have shown that endothelial dysfunction in Cav-1-deficient (Cav-1-/-) mice is mediated by elevated oxidative stress through endothelial nitric oxide synthase (eNOS) uncoupling and increased NADPH oxidase. Oxidant stress is the net balance of oxidant generation and scavenging, and the role of Cav-1 as a regulator of antioxidant enzymes in vascular tissue is poorly understood. Extracellular SOD (SOD3) is a copper (Cu)-containing enzyme that is secreted from vascular smooth muscle cells/fibroblasts and subsequently binds to the endothelial cells surface, where it scavenges extracellular [Formula: see text] and preserves endothelial function. SOD3 activity is dependent on Cu, supplied by the Cu transporter ATP7A, but whether Cav-1 regulates the ATP7A-SOD3 axis and its role in oxidative stress-mediated vascular dysfunction has not been studied. Here we show that the activity of SOD3, but not SOD1, was significantly decreased in Cav-1-/- vessels, which was rescued by re-expression of Cav-1 or Cu supplementation. Loss of Cav-1 reduced ATP7A protein, but not mRNA, and this was mediated by ubiquitination of ATP7A and proteasomal degradation. ATP7A bound to Cav-1 and was colocalized with SOD3 in caveolae/lipid rafts or perinucleus in vascular tissues or cells. Impaired endothelium-dependent vasorelaxation in Cav-1-/- mice was rescued by gene transfer of SOD3 or by ATP7A-overexpressing transgenic mice. These data reveal an unexpected role of Cav-1 in stabilizing ATP7A protein expression by preventing its ubiquitination and proteasomal degradation, thereby increasing SOD3 activity, which in turn protects against vascular oxidative stress-mediated endothelial dysfunction.

Dysregulation of TRPV4, eNOS and caveolin-1 contribute to endothelial dysfunction in the streptozotocin rat model of diabetes

Endothelial dysfunction is a common complication in diabetes in which endothelium-dependent vasorelaxation is impaired. The aim of this study was to examine the involvement of the TRPV4 ion channel in type 1 diabetic endothelial dysfunction and the possible association of endothelial dysfunction with reduced expression of TRPV4, endothelial nitric oxide synthase (eNOS) and caveolin-1. Male Wistar rats (350-450 g) were injected with 65 mg/kg i.p. streptozotocin (STZ) or vehicle. Endothelial function was investigated in aortic rings and mesenteric arteries using organ bath and myograph, respectively. TRPV4 function was studied with fura-2 calcium imaging in endothelial cells cultured from aortas from control and STZ treated rats. TRPV4, caveolin-1 and eNOS expression was investigated in these cells using immunohistochemistry. STZ-treated diabetic rats showed significant endothelial dysfunction characterised by impaired muscarinic-induced vasorelaxation (aortic rings: STZ-diabetics: Emax = 29.6 ± 9.3%; control: Emax = 77.2 ± 2.5% P˂0.001), as well as significant impairment in TRPV4-induced vasorelaxation (aortic rings, 4αPDD STZ-diabetics: Emax = 56.0 ± 5.5%; control: Emax = 81.1 ± 2.1% P˂0.001). Furthermore, STZ-diabetic primary aortic endothelial cells showed a significant reduction in TRPV4-induced intracellular calcium elevation (P˂0.05) compared with the control group. This was associated with significantly lower expression of TRPV4, caveolin-1 and eNOS and this was reversed by insulin treatment of the endothelial cultures from STZ -diabetic rats. Taken together, these data are consistent with the hypothesis that signalling through TRPV4, caveolin-1, and eNOS is downregulated in STZ-diabetic aortic endothelial cells and restored by insulin treatment.

Molecular regulation and clinical significance of caveolin-1 methylation in chronic lung diseases

Chronic lung diseases represent a largely global burden whose pathogenesis remains largely unknown. Research increasingly suggests that epigenetic modifications, especially DNA methylation, play a mechanistic role in chronic lung diseases. DNA methylation can affect gene expression and induce various diseases. Of the caveolae in plasma membrane of cell, caveolin-1 (Cav-1) is a crucial structural constituent involved in many important life activities. With the increasingly advanced progress of genome-wide methylation sequencing technologies, the important impact of Cav-1 DNA methylation has been discovered. The present review overviews the biological characters, functions, and structure of Cav-1; epigenetic modifications of Cav-1 in health and disease; expression and regulation of Cav-1 DNA methylation in the respiratory system and its significance; as well as clinical potential as disease-specific biomarker and targets for early diagnosis and therapy.

Astragaloside IV protects against diabetic nephropathy via activating eNOS in streptozotocin diabetes-induced rats

BACKGROUND

Astragaloside IV (AS-IV) was reported to play a role in improving diabetic nephropathy (DN), however, the underlying mechanisms still remain unclear. The aim of the present study is to investigate whether AS-IV ameliorates DN via the regulation of endothelial nitric oxide synthase (eNOS).

METHODS

DN model was induced in Sprague-Dawley (SD) male rats by intraperitoneal injection of 65 mg/kg streptozotocin (STZ). Rats in the AS-IV treatment group were orally gavaged with 5 mg/kg/day or 10 mg/kg/day AS-IV for eight consecutive weeks. Body weight, blood glucose, blood urea nitrogen (BUN), Serum creatinine (Scr), proteinuria and Glycosylated hemoglobin (HbA1c) levels were measured. Hematoxylin-Eosin (HE) and Periodic Acid-Schiff (PAS) staining were used to detect the renal pathology. The apoptosis status of glomerular cells was measured by TUNEL assay. The phosphorylation and acetylation of eNOS were detected by western blot. The effects of AS-IV on high-glucose (HG)-induced apoptosis and eNOS activity were also investigated in human renal glomerular endothelial cells (HRGECs) in vitro.

RESULTS

Treatment with AS-IV apparently reduced DN symptoms in diabetic rats, as evidenced by reduced BUN, Scr, proteinuria, HbA1c levels and expanding mesangial matrix. AS-IV treatment also promoted the synthesis of nitric oxide (NO) in serum and renal tissues and ameliorated the phosphorylation of eNOS at Ser 1177 with decreased eNOS acetylation. Moreover, HG-induced dysfunction of HRGECs including increased cell permeability and apoptosis, impaired eNOS phosphorylation at Ser 1177, and decreased NO production, were all reversed by AS-IV treatment.

CONCLUSIONS

These novel findings suggest that AS-IV ameliorates functional abnormalities of DN through inhibiting acetylation of eNOS and activating its phosphorylation at Ser 1177. AS-IV could be served as a potential therapeutic drug for DN.

Investigation of the Mechanism Underlying Calcium Dobesilate-Mediated Improvement of Endothelial Dysfunction and Inflammation Caused by High Glucose

Background/Aims

Diabetic kidney disease (DKD) is a leading cause of end-stage renal disease. Calcium dobesilate (CaD) is widely used to treat diabetic retinopathy. Recent studies have demonstrated that CaD exerts protective effects against diabetic nephropathy. The aim of this study was to elucidate the molecular and cellular mechanisms underlying the protective effects of CaD.

Methods

Human umbilical vein endothelial cells (HUVECs) were cultured with different D-glucose concentrations to determine the effects of high glucose on HUVEC gene expression. HUVECs were also incubated with CaD (25 μM, 50 μM, and 100 μM) for 3 days to determine the effects of CaD on HUVEC viability. db/db mice were treated with CaD. 2-[(Aminocarbonyl)amino]-5-(4-fluorophenyl)-3-thiophenecarboxamide (TPCA-1) blocked the nuclear factor-κB (NF-κB) pathway in HUVECs. A pentraxin 3 (PTX3) small interfering RNA (siRNA) intervention experiment was performed in the cells. An adenovirus-encapsulated PTX3 siRNA intervention experiment was performed in db/db mice. Western blot and real-time PCR analyses were used to detect PTX3, p-IKBa/IKBa (I-kappa-B-alpha), and p-eNOS/eNOS (endothelial nitric oxide synthase) expression in mice and HUVECs. Hematoxylin-eosin (HE) staining and periodic acid-Schiff (PAS) staining were used to observe renal tissue damage in mice. PTX3 expression was observed by immunohistochemical staining.

Results

CaD downregulated the expression of PTX3 and p-IKBa/IKBa and upregulated the expression of p-eNOS/eNOS in vitro. When TPCA-1 was used, high glucose induced high PTX3 expression, and the expression of p-eNOS/eNOS increased. After PTX3 gene silencing, the expression of p-eNOS/eNOS also increased. In vivo, CaD reduced the expression of PTX3 and p-IKBa/IKBa in the kidneys of db/db mice and increased the expression of p-eNOS/eNOS. After PTX3 gene silencing, the urine protein and renal function of db/db mice were ameliorated, the glomerular extracellular matrix was decreased, and the expression of p-eNOS/eNOS was increased.

Conclusions

Our results suggested that CaD may inhibit the expression of PTX3 by altering the IKK/IKB/NF-κB pathway, thereby improving endothelial dysfunction in HUVECs. PTX3 may be a potential therapeutic target for DKD.

Endothelial Toxicity of High Glucose and its by-Products in Diabetic Kidney Disease

Alterations of renal endothelial cells play a crucial role in the initiation and progression of diabetic kidney disease. High glucose per se, as well as glucose by-products, induce endothelial dysfunction in both large vessels and the microvasculature. Toxic glucose by-products include advanced glycation end products (AGEs), a group of modified proteins and/or lipids that become glycated after exposure to sugars, and glucose metabolites produced via the polyol pathway. These glucose-related endothelio-toxins notably induce an alteration of the glomerular filtration barrier by increasing the permeability of glomerular endothelial cells, altering endothelial glycocalyx, and finally, inducing endothelial cell apoptosis. The glomerular endothelial dysfunction results in albuminuria. In addition, high glucose and by-products impair the endothelial repair capacities by reducing the number and function of endothelial progenitor cells. In this review, we summarize the mechanisms of renal endothelial toxicity of high glucose/glucose by-products, which encompass changes in synthesis of growth factors like TGF-β and VEGF, induction of oxidative stress and inflammation, and reduction of NO bioavailability. We finally present potential therapies to reduce endothelial dysfunction in diabetic kidney disease.

Caveolin-1 regulation of Sp1 controls production of the antifibrotic protein follistatin in kidney mesangial cells

BACKGROUND

We previously showed that caveolin-1 (cav-1), an integral membrane protein, is required for the synthesis of matrix proteins by glomerular mesangial cells (MC). In a previous study to understand how cav-1 is involved in regulating matrix production, we had identified significant upregulation of the antifibrotic protein follistatin in cav-1 knockout MC. Follistatin inhibits the profibrotic effects of several members of the transforming growth factor beta superfamily, in particular the activins. Here, we characterize the molecular mechanism through which cav-1 regulates the expression of follistatin.

METHODS

Kidneys from cav-1 wild type and knockout (KO) mice were analyzed and primary cultures of MC from cav-1 wild-type and KO mice were utilized. FST promoter deletion constructs were generated to determine the region of the promoter important for mediating FST upregulation in cav-1 KO MC. siRNA-mediated down-regulation and overexpression of Sp1 in conjunction with luciferase activity assays, immunoprecipitation, western blotting and ChiP was used to assess the role of Sp1 in transcriptionally regulating FST expression. Pharmacologic kinase inhibitors and specific siRNA were used to determine the post-translational mechanism through which cav-1 affects Sp1 activity.

RESULTS

Our results establish that follistatin upregulation occurs at the transcript level. We identified Sp1 as the critical transcription factor regulating activation of the FST promoter in cav-1 KO MC through binding to a region within 123 bp of the transcription start site. We further determined that the lack of cav-1 increases Sp1 nuclear levels and transcriptional activity. This occurred through increased phosphoinositide 3-kinase (PI3K) activity and downstream protein kinase C (PKC) zeta-mediated phosphorylation and activation of Sp1.

CONCLUSIONS

These findings shed light on the transcriptional mechanism by which cav-1 represses the expression of a major antifibrotic protein, and can inform the development of novel antifibrotic treatment strategies.

Hydrogen Sulfide Protects Hyperhomocysteinemia-Induced Renal Damage by Modulation of Caveolin and eNOS Interaction

The accumulation of homocysteine (Hcy) during chronic kidney failure (CKD) can exert toxic effects on the glomeruli and tubulo-interstitial region. Among the potential mechanisms, the formation of highly reactive metabolite, Hcy thiolactone, is known to modify proteins by N-homocysteinylation, leading to protein degradation, stress and impaired function. Previous studies documented impaired nitric oxide production and altered caveolin expression in hyperhomocysteinemia (HHcy), leading to endothelial dysfunction. The aim of this study was to determine whether Hhcy homocysteinylates endothelial nitric oxide synthase (eNOS) and alters caveolin-1 expression to decrease nitric oxide bioavailability, causing hypertension and renal dysfunction. We also examined whether hydrogen sulfide (H₂S) could dehomocysteinylate eNOS to protect the kidney. WT and Cystathionine β-Synthase deficient (CBS+/-) mice representing HHcy were treated without or with sodium hydrogen sulfide (NaHS), a H₂S donor (30 µM), in drinking water for 8 weeks. Hhcy mice (CBS+/-) showed low levels of plasma H₂S, elevated systolic blood pressure (SBP) and renal dysfunction. H₂S treatment reduced SBP and improved renal function. Hhcy was associated with homocysteinylation of eNOS, reduced enzyme activity and upregulation of caveolin-1 expression. Further, Hhcy increased extracellular matrix (ECM) protein deposition and disruption of gap junction proteins, connexins. H₂S treatment reversed the changes above and transfection of triple genes producing H₂S (CBS, CSE and 3MST) showed reduction of vascular smooth muscle cell proliferation. We conclude that during Hhcy, homocysteinylation of eNOS and disruption of caveolin-mediated regulation leads to ECM remodeling and hypertension, and H₂S treatment attenuates renovascular damage.

Sevoflurane postconditioning is not mediated by ferritin accumulation and cannot be rescued by simvastatin in isolated streptozotocin-induced diabetic rat hearts

Sevoflurane postconditioning (sevo postC) is an attractive and amenable approach that can protect the myocardium against ischemia/reperfusion (I/R)-injury. Unlike ischemic preconditioning (IPC), sevo postC does not require additional induced ischemic periods to a heart that is already at risk. IPC was previously shown to generate myocardial protection against I/R-injury through regulation of iron homeostasis and de novo ferritin synthesis, a process found to be impaired in the diabetic state. The current study investigated whether alterations in iron homeostasis and ferritin mRNA and protein accumulation are also involved in the cardioprotective effects generated by sevo postC. It was also investigated whether the protective effects of sevo postC in the diabetic state can be salvaged by simvastatin, through inducing nitric oxide (NO) bioavailability/activity, in isolated streptozotocin (STZ)-induced diabetic hearts (DH). Isolated rat hearts from healthy Controls and diabetic animals were retrogradely perfused using the Langendorff configuration and subjected to prolonged ischemia and reperfusion, with and without (2.4 and 3.6%) sevo postC and/or pre-treatment with simvastatin (0.5 mg/kg). Sevo postC significantly reduced infarct size and improved myocardial function in healthy Controls but not in isolated DH. The sevo postC mediated myocardial protection against I/R-injury was not associated with de novo ferrtin synthesis. Furthermore, simvastatin aggravated myocardial injury after sevo postC in STZ-induced DHs, likely due to increasing NO levels. Despite the known mechanistic overlaps between PC and postC stimuli, distinct differences underlie the cardioprotective interventions against myocardial I/R-injury and are impaired in the DH. Sevo postC mediated cardioprotection, unlike IPC, does not involve de novo ferritin accumulation and cannot be rescued by simvastatin in STZ-induced DHs.

Diabetic dyslipidaemia is associated with alterations in eNOS, caveolin-1, and endothelial dysfunction in streptozotocin treated rats

BACKGROUND

Diabetes is a complex progressive disease characterized by chronic hyperglycaemia and dyslipidaemia associated with endothelial dysfunction. Oxidized LDL (Ox-LDL) is elevated in diabetes and may contribute to endothelial dysfunction. The aim of this study was to relate the serum levels of Ox-LDL with endothelial dysfunction in streptozotocin (STZ)-diabetic rats and to further explore the changes in endothelial nitric oxide synthase (eNOS) and caveolin-1 (CAV-1) expression in primary aortic endothelial cells.

METHODS

Diabetes was induced with a single intraperitoneal injection of STZ in male Wistar rats. During the hyperglycaemic diabetes state serum lipid markers, aortic relaxation and aortic endothelial cell eNOS and CAV-1 protein expressions were measured.

RESULTS

Elevated serum Ox-LDL (STZ 1486 ± 78.1 pg/mL vs control 732.6 ± 160.6 pg/mL, P < .05) was associated with hyperglycaemia (STZ 29 ± 0.9 mmol/L vs control: 7.2 ± 0.2 mmol/L, P < .001) and hypertriglyceridaemia (STZ 9.0 ± 1.5 mmol/L vs control: 3.0 ± 0.3 mmol/L, P < .01) in diabetic rats. A significant reduction was observed in STZ-diabetic aortic endothelial cell eNOS and CAV-1 of 40% and 30%, respectively, accompanied by a compromised STZ-diabetic carbachol-induced vasodilation (STZ 29.6 ± 9.3% vs control 77.2 ± 2.5%, P < .001).

CONCLUSIONS

The elevated serum Ox-LDL in hyperglycaemic STZ-diabetic rats may contribute to diabetic endothelial dysfunction, possibly through downregulation of endothelial CAV-1 and eNOS.

Caveolin 1 Promotes Renal Water and Salt Reabsorption

Caveolin-1 (Cav1) is essential for the formation of caveolae. Little is known about their functional role in the kidney. We tested the hypothesis that caveolae modulate renal salt and water reabsorption. Wild-type (WT) and Cav1-deficient (Cav1−/−) mice were studied. Cav1 expression and caveolae formation were present in vascular cells, late distal convoluted tubule and principal connecting tubule and collecting duct cells of WT but not Cav1−/− kidneys. Urinary sodium excretion was increased by 94% and urine flow by 126% in Cav1−/− mice (p < 0.05). A decrease in activating phosphorylation of the Na-Cl cotransporter (NCC) of the distal convoluted tubule was recorded in Cav1−/− compared to WT kidneys (−40%; p < 0.05). Isolated intrarenal arteries from Cav1−/− mice revealed a fourfold reduction in sensitivity to phenylephrine (p < 0.05). A significantly diminished maximal contractile response (−13%; p < 0.05) was suggestive of enhanced nitric oxide (NO) availability. In line with this, the abundance of endothelial NO synthase (eNOS) was increased in Cav1−/− kidneys +213%; p < 0.05) and cultured caveolae-deprived cells showed intracellular accumulation of eNOS, compared to caveolae-intact controls. Our results suggest that renal caveolae help to conserve water and electrolytes via modulation of NCC function and regulation of vascular eNOS.

Sex-specific eNOS activity and function in human endothelial cells

Clinical and epidemiological data show that biological sex is one of the major determinants for the development and progression of cardiovascular disease (CVD). Impaired endothelial function, characterized by an imbalance in endothelial Nitric Oxide Synthase (eNOS) activity, precedes and accelerates the development of CVD. However, whether there is any sexual dimorphism in eNOS activity and function in endothelial cells (ECs) is still unknown. Here, by independently studying human male and female ECs, we found that female ECs expressed higher eNOS mRNA and protein levels both in vitro and ex vivo. The increased eNOS expression was associated to higher enzymatic activity and nitric oxide production. Pharmacological and genetic inhibition of eNOS affected migratory properties only in female ECs. In vitro angiogenesis experiments confirmed that sprouting mostly relied on eNOS-dependent migration in female ECs. At variance, capillary outgrowth from male ECs was independent of eNOS activity but required cell proliferation. In this study, we found sex-specific differences in the EC expression, activity, and function of eNOS. This intrinsic sexual dimorphism of ECs should be further evaluated to achieve more effective and precise strategies for the prevention and therapy of diseases associated to an impaired endothelial function such as CVD and pathological angiogenesis.

Caveolin-1 in the Pathogenesis of Diabetic Nephropathy: Potential Therapeutic Target?

PURPOSE OF REVIEW

Diabetic nephropathy, a major microvascular complication of diabetes and the most common cause of end-stage renal disease, is characterized by prominent accumulation of extracellular matrix. The membrane microdomains caveolae, and their integral protein caveolin-1, play critical roles in the regulation of signal transduction. In this review we discuss current knowledge of the contribution of caveolin-1/caveolae to profibrotic signaling and the pathogenesis of diabetic kidney disease, and assess its potential as a therapeutic target.

RECENT FINDINGS

Caveolin (cav)-1 is key to facilitating profibrotic signal transduction induced by several stimuli known to be pathogenic in diabetic nephropathy, including the most prominent factors hyperglycemia and angiotensin II. Phosphorylation of cav-1 on Y14 is an important regulator of these responses. In vivo studies support a pathogenic role for caveolae in the progression of diabetic nephropathy. Targeting caveolin-1/caveolae would enable inhibition of multiple profibrotic pathways, representing a novel and potentially potent therapeutic option for diabetic nephropathy.

Caveolin1/protein arginine methyltransferase1/sirtuin1 axis as a potential target against endothelial dysfunction

Endothelial dysfunction (ED), an established response to cardiovascular risk factors, is characterized by increased levels of soluble molecules secreted by endothelial cells (EC). Evidence suggest that ED is an independent predictor of cardiac events and that it is associated with a deficiency in production or bioavailability of nitric oxide (NO) and/or an imbalance in the relative contribution of endothelium-derived relaxing and contracting factors. ED can be reversed by treating cardiovascular risk factors, hence, beyond ambiguity, ED contributes to initiation and progression of atherosclerotic disease. Majority of cardiovascular risk factors act by a common pathway, oxidative stress (OS), characterized by an imbalance in bioavailability of NO and reactive oxygen species (ROS). Enhanced ROS, through several mechanisms, alters competence of EC that leads to ED, reducing its potential to maintain homeostasis and resulting in development of cardiovascular disease (CVD). Influential mechanisms that have been implicated in the development of ED include (i) presence of elevated levels of NOS inhibitor, asymmetric dimethylarginine (ADMA) due to augmented enzyme activity of protein arginine methyl transferase-1 (PRMT1); (ii) decrease in NO generation by endothelial nitric oxide synthase (eNOS) uncoupling, or by reaction of NO with free radicals and (iii) impaired post translational modification of protein (PTM) such as eNOS, caveolin-1 (cav1) and sirtuin-1 (SIRT1). However, the inter-related mechanisms that concur to developing ED is yet to be understood. The events that possibly overlay include OS-induced sequestration of SIRT1 to caveolae facilitating cav1-SIRT1 association; potential increase in lysine acetylation of enzymes such as eNOS and PRMT1 leading to enhanced ADMA formation; imbalance in acetylation-methylation ratio (AMR); diminished NO generation and ED. Here we review current literature from research showing interdependent association between cav1-PRMT1-SIRT1 to the outcomes of experimental and clinical research aiming to preserve endothelial function with gene- or pharmaco-therapy.

Effects of xanthine oxidase inhibition with febuxostat on the development of nephropathy in experimental type 2 diabetes

BACKGROUND AND PURPOSE

Elevated serum uric acid (UA) is a risk factor for the development of kidney disease. Inhibitors of xanthine oxidase (XOi), an enzyme involved in UA synthesis, have protective effects at early stages of experimental diabetic nephropathy (DN). However, long-term effects of XOi in models of DN remain to be determined.

EXPERIMENTAL APPROACH

The development of albuminuria, renal structure and molecular markers of DN were studied in type 2 diabetic Zucker obese (ZO) rats treated for 18 weeks with the XOi febuxostat and compared with vehicle-treated ZO rats, ZO rats treated with enalapril or a combination of both agents, and lean Zucker rats without metabolic defects.

RESULTS

Febuxostat normalized serum UA and attenuated the development of albuminuria, renal structural changes, with no significant effects on BP, metabolic control or systemic markers of oxidative stress (OS). Most of these actions were comparable with those of enalapril. Combination treatment induced marked decreases in BP and was more effective in ameliorating structural changes, expression of profibrotic genes and systemic OS than either monotherapy. Febuxostat attenuated renal protein expression of TGF-ß, CTGF, collagen 4, mesenchymal markers (FSP1 and vimentin) and a tissue marker of OS nitrotyrosine. Moreover, febuxostat attenuated TGF-ß- and S100B-induced increased expression of fibrogenic molecules in renal tubular cells in vitro in UA-free media in an Akt kinase-dependent manner.

CONCLUSIONS AND IMPLICATIONS

Febuxostat is protective and enhances the actions of enalapril in experimental DN. Multiple mechanisms might be involved, such as a reduction of UA, renal OS and inhibition of profibrotic signalling.

The Protective Effect of Antioxidants Consumption on Diabetes and Vascular Complications

Obesity and diabetes is generally accompanied by a chronic state of oxidative stress, disequilibrium in the redox balance, implicated in the development and progression of complications such as micro- and macro-angiopathies. Disorders in the inner layer of blood vessels, the endothelium, play an early and critical role in the development of these complications. Blunted endothelium-dependent relaxation and/or contractions are quietly associated to oxidative stress. Thus, preserving endothelial function and oxidative stress seems to be an optimization strategy in the prevention of vascular complications associated with diabetes. Diet is a major lifestyle factor that can greatly influence the incidence and the progression of type 2 diabetes and cardiovascular complications. The notion that foods not only provide basic nutrition but can also prevent diseases and ensure good health and longevity is now attained greater prominence. Some dietary and lifestyle modifications associated to antioxidative supply could be an effective prophylactic means to fight against oxidative stress in diabesity and complications. A significant benefit of phytochemicals (polyphenols in wine, grape, teas), vitamins (ascorbate, tocopherol), minerals (selenium, magnesium), and fruits and vegetables in foods is thought to be capable of scavenging free radicals, lowering the incidence of chronic diseases. In this review, we discuss the role of oxidative stress in diabetes and complications, highlight the endothelial dysfunction, and examine the impact of antioxidant foods, plants, fruits, and vegetables, currently used medication with antioxidant properties, in relation to the development and progression of diabetes and cardiovascular complications.

ENOS deficiency causes podocyte injury with mitochondrial abnormality

The contribution of endothelial nitric oxide synthase (eNOS) to podocyte integrity remains unclear. This study therefore examined podocytes and mitochondrial abnormalities in eNOS deficient mice. Absence of eNOS caused glomerular hypertrophy, along with occasional glomerular sclerosis and mesangiolysis. While many glomeruli did not have such advanced lesions, ultrastructural analysis showed cellular hypertrophy, vacuolization, lysosomal enlargement, and microvillus formation in podocytes of eNOS knockout (KO) mice. Increased oxidative stress was associated with mitochondrial abnormalities, including an increase in number, coupled with a reduction in size, of mitochondria in podocytes of eNOS-KO mice. While the levels of expression of several mitochondrial proteins were not altered, the d-17 mutation in mitochondrial DNA was significantly associated with the eNOS deficiency. Renal ATP level in the renal cortex and mitochondrial respiration in the primary podocytes were significantly lower in eNOS-KO mice, suggesting that renal mitochondria may be functionally impaired. Podocytes cultured with endothelial conditioned medium lacking NO consistently showed a greater degree of mitochondrial fragmentation and an increase in mitochondrial oxidative stress, with these mitochondrial alterations rescued by an NO donor. In conclusion, eNOS may be necessary to maintain podocyte integrity, especially mitochondrial function.

miR-21 promotes renal fibrosis in diabetic nephropathy by targeting PTEN and SMAD7

The cytokine transforming growth factor (TGF)-β1 plays a central role in diabetic nephropathy (DN) with data implicating the miRNA (miR) miR-21 as a key modulator of its prosclerotic actions. In the present study, we demonstrate data indicating that miR-21 up-regulation positively correlates with the severity of fibrosis and rate of decline in renal function in human DN. Furthermore, concomitant analyses of various models of fibrotic renal disease and experimental DN, confirm tubular miR-21 up-regulation. The fibrotic changes associated with increased miR-21 levels are proposed to include the regulation of TGF-β1-mediated mothers against decapentaplegic homolog 3 (SMAD3)- and phosphoinositide 3-kinase (PI3K)-dependent signalling pathways via co-ordinated repression of mothers against decapentaplegic homolog 7 (SMAD7) and phosphatase and tensin homologue (PTEN) respectively. This represents a previously uncharacterized interaction axis between miR-21 and PTEN-SMAD7. Targeting of these proteins by miR-21 resulted in de-repression of the respective pathways as reflected by increases in SMAD3 and V-Akt murine thymoma viral oncogene homolog 1 (AKT) phosphorylation. Many of the changes typically induced by TGF-β1, including phosphorylation of signalling mediators, were further enhanced by miR-21. Collectively, these data present a unified model for a key role for miR-21 in the regulation of renal tubular extracellular matrix (ECM) synthesis and accumulation and provide important insights into the molecular pathways implicated in the progression of DN.

Recent progress in the topology, structure, and oligomerization of caveolin: a building block of caveolae

Caveolae are cholesterol-rich plasma membrane invaginations that are found in a plethora of cell types. They play many roles including signal transduction, endocytosis, and mechanoprotection. The most critical protein in caveolae is the integral membrane protein, caveolin, which has been shown to be necessary for caveolae formation, and governs the major functions attributed to caveolae. Caveolin is postulated to act as a scaffold in the high molecular weight striated coat that surrounds the caveolar bulb, stabilizing it. Caveolin interacts, both directly and indirectly, with a large number of signaling molecules, and presides over the endocytosis of molecular cargo by caveolae. However, many of the key biophysical aspects of the caveolin protein, its structure, topology, and oligomeric behavior, are just beginning to come to light. Herein is an up-to-date summary and critique of the progress that has been made in understanding caveolin on a molecular and atomic level.

Renal endothelial dysfunction in diabetic nephropathy

Endothelial dysfunction has been posited to play an important role in the pathogenesis of diabetic nephropathy (DN). Due to the heterogeneity of endothelial cells (ECs), it is difficult to generalize about endothelial responses to diabetic stimuli. At present, there are limited techniques fordirectly measuring EC function in vivo, so diagnosis of endothelial disorders still largely depends on indirect assessment of mediators arising from EC injury. In the kidney microcirculation, both afferent and efferent arteries, arterioles and glomerular endothelial cells (GEnC) have all been implicated as targets of diabetic injury. Both hyperglycemia per se, as well as the metabolic consequences of glucose dysregulation, are thought to lead to endothelial cell dysfunction. In this regard, endothelial nitric oxide synthase (eNOS) plays a central role in EC dysfunction. Impaired eNOS activity can occur at numerous levels, including enzyme uncoupling, post-translational modifications, internalization and decreased expression. Reduced nitric oxide (NO) bioavailability exacerbates oxidative stress, further promoting endothelial dysfunction and injury. The injured ECs may then function as active signal transducers of metabolic, hemodynamic and inflammatory factors that modify the function and morphology of the vessel wall and interact with adjacent cells, which may activate a cascade of inflammatory and proliferative and profibrotic responses in progressive DN. Both pharmacological approaches and potential regenerative therapies hold promise for restoration of impaired endothelial cells in diabetic nephropathy.

Pentraxin 3 Induces Vascular Endothelial Dysfunction Through a P-selectin/Matrix Metalloproteinase-1 Pathway

BACKGROUND

Pentraxin 3 (PTX3), the prototype of long pentraxins, has been described to be associated with endothelial dysfunction in different cardiovascular disorders. No study has yet evaluated the possible direct effect of PTX3 on vascular function.

METHODS AND RESULTS

Through in vitro experiments of vascular reactivity and ultrastructural analyses, we demonstrate that PTX3 induces dysfunction and morphological changes in the endothelial layer through a P-selectin/matrix metalloproteinase-1 pathway. The latter hampered the detachment of endothelial nitric oxide synthase from caveolin-1, leading to an impairment of nitric oxide signaling. In vivo studies showed that administering PTX3 to wild-type mice induced endothelial dysfunction and increased blood pressure, an effect absent in P-selectin-deficient mice. In isolated human umbilical vein endothelial cells, PTX3 significantly blunted nitric oxide production through the matrix metalloproteinase-1 pathway. Finally, using ELISA, we found that hypertensive patients (n=31) have higher plasma levels of PTX3 and its mediators P-selectin and matrix metalloproteinase-1 than normotensive subjects (n=21).

CONCLUSIONS

Our data show for the first time a direct role of PTX3 on vascular function and blood pressure homeostasis, identifying the molecular mechanisms involved. The findings in humans suggest that PTX3, P-selectin, and matrix metalloproteinase-1 may be novel biomarkers that predict the onset of vascular dysfunction in hypertensive patients.

Endothelial nitric oxide synthase dimerization is regulated by heat shock protein 90 rather than by phosphorylation

Endothelial nitric oxide synthase (eNOS) is a multifunctional enzyme with roles in diverse cellular processes including angiogenesis, tissue remodeling, and the maintenance of vascular tone. Monomeric and dimeric forms of eNOS exist in various tissues. The dimeric form of eNOS is considered the active form and the monomeric form is considered inactive. The activity of eNOS is also regulated by many other mechanisms, including amino acid phosphorylation and interactions with other proteins. However, the precise mechanisms regulating eNOS dimerization, phosphorylation, and activity remain incompletely characterized. We utilized purified eNOS and bovine aorta endothelial cells (BAECs) to investigate the mechanisms regulating eNOS degradation. Both eNOS monomer and dimer existed in purified bovine eNOS. Incubation of purified bovine eNOS with protein phosphatase 2A (PP2A) resulted in dephosphorylation at Serine 1179 (Ser1179) in both dimer and monomer and decrease in eNOS activity. However, the eNOS dimer∶monomer ratio was unchanged. Similarly, protein phosphatase 1 (PP1) induced dephosphorylation of eNOS at Threonine 497 (Thr497), without altering the eNOS dimer∶monomer ratio. Different from purified eNOS, in cultured BAECs eNOS existed predominantly as dimers. However, eNOS monomers accumulated following treatment with the proteasome inhibitor lactacystin. Additionally, treatment of BAECs with vascular endothelial growth factor (VEGF) resulted in phosphorylation of Ser1179 in eNOS dimers without altering the phosphorylation status of Thr497 in either form. Inhibition of heat shock protein 90 (Hsp90) or Hsp90 silencing destabilized eNOS dimers and was accompanied by dephosphorylation both of Ser1179 and Thr497. In conclusion, our study demonstrates that eNOS monomers, but not eNOS dimers, are degraded by ubiquitination. Additionally, the dimeric eNOS structure is the predominant condition for eNOS amino acid modification and activity regulation. Finally, destabilization of eNOS dimers not only results in eNOS degradation, but also causes changes in eNOS amino acid modifications that further affect eNOS activity.

Transcriptome-based analysis of kidney gene expression changes associated with diabetes in OVE26 mice, in the presence and absence of losartan treatment

Diabetes is among the most common causes of end-stage renal disease, although its pathophysiology is incompletely understood. We performed next-generation sequencing-based transcriptome analysis of renal gene expression changes in the OVE26 murine model of diabetes (age 15 weeks), relative to non-diabetic control, in the presence and absence of short-term (seven-day) treatment with the angiotensin receptor blocker, losartan (n = 3-6 biological replicates per condition). We detected 1438 statistically significant changes in gene expression across conditions. Of the 638 genes dysregulated in diabetes relative to the non-diabetic state, >70% were downregulation events. Unbiased functional annotation of genes up- and down-regulated by diabetes strongly associated (p<1 × 10(-8)) with terms for oxidative stress and for endoplasmic reticulum stress/protein folding. Most of the individual gene products up- or down-regulated with diabetes were unaffected by losartan treatment; however, of the gene products dysregulated in diabetes and influenced by losartan treatment, the vast majority of changes were in the direction of amelioration rather than exacerbation of the diabetic dysregulation. This group of losartan-protected genes associated strongly with annotation terms for endoplasmic reticulum stress, heat shock proteins, and chaperone function, but not oxidative stress; therefore, the losartan-unaffected genes suggest avenues for additional therapeutic opportunity in diabetes. Interestingly, the gene product most highly upregulated by diabetes (>52-fold), encoded by the cationic amino acid transporter Slc7a12, and the gene product most highly downregulated by diabetes (>99%)--encoded by the "pseudogene" Gm6300--are adjacent in the murine genome, are members of the SLC7 gene family, and are likely paralogous. Therefore, diabetes activates a near-total genetic switch between these two paralogs. Other individual-level changes in gene expression are potentially relevant to diabetic pathophysiology, and novel pathways are suggested. Genes unaffected by diabetes alone but exhibiting increased renal expression with losartan produced a signature consistent with malignant potential.

Akt and RhoA activation in response to high glucose require caveolin-1 phosphorylation in mesangial cells

Glomerular matrix accumulation is a hallmark of diabetic renal disease. Serine/threonine kinase PKC-β1 mediates glucose-induced Akt S473 phosphorylation, RhoA activation, and transforming growth factor (TGF)-β1 upregulation and finally leads to matrix upregulation in mesangial cells (MCs). It has been reported that glucose-induced PKC-β1 activation is dependent on caveolin-1 and the presence of intact caveolae in MCs; however, whether activated PKC-β1 regulates caveolin-1 expression and phosphorylation are unknown. Here, we showed that, although the caveolin-1 protein level had no significant change, the PKC-β-specific inhibitor LY-333531 blocked caveolin-1 Y14 phosphorylation in high glucose (HG)-treated MCs and in the renal cortex of diabetic rats. The Src-specific inhibitor SU-6656 prevented the HG-induced association between PKC-β1 and caveolin-1 and PKC-β1 membrane translocation, whereas PKC-β1 small interfering RNA failed to block Src activation, indicating that Src kinase is upstream of PKC-β1 activation. Although LY-333531 blocked PKC-β1 membrane translocation, it had no effect on the PKC-β1/caveolin-1 association, suggesting that PKC-β1 activation requires the interaction of caveolin-1 and PKC-β1. PKC-β1-mediated Akt S473 phosphorylation, RhoA activation, and fibronectin upregulation in response to HG were prevented by SU-6656 and nonphosphorylatable mutant caveolin-1 Y14A. In conclusion, Src activation by HG mediates the PKC-β1/caveolin-1 association and PKC-β1 activation, which assists in caveolin-1 Y14 phosphorylation by Src kinase. The downstream effects, including Akt S473 phosphorylation, RhoA activation, and fibronectin upregulation, require caveolin-1 Y14 phosphorylation. Caveolin-1 is thus an important mediator of the profibrogenic process in diabetic renal disease.

Pathophysiology of the diabetic kidney

Diabetes mellitus contributes greatly to morbidity, mortality, and overall health care costs. In major part, these outcomes derive from the high incidence of progressive kidney dysfunction in patients with diabetes making diabetic nephropathy a leading cause of end-stage renal disease. A better understanding of the molecular mechanism involved and of the early dysfunctions observed in the diabetic kidney may permit the development of new strategies to prevent diabetic nephropathy. Here we review the pathophysiological changes that occur in the kidney in response to hyperglycemia, including the cellular responses to high glucose and the responses in vascular, glomerular, podocyte, and tubular function. The molecular basis, characteristics, and consequences of the unique growth phenotypes observed in the diabetic kidney, including glomerular structures and tubular segments, are outlined. We delineate mechanisms of early diabetic glomerular hyperfiltration including primary vascular events as well as the primary role of tubular growth, hyperreabsorption, and tubuloglomerular communication as part of a "tubulocentric" concept of early diabetic kidney function. The latter also explains the "salt paradox" of the early diabetic kidney, that is, a unique and inverse relationship between glomerular filtration rate and dietary salt intake. The mechanisms and consequences of the intrarenal activation of the renin-angiotensin system and of diabetes-induced tubular glycogen accumulation are discussed. Moreover, we aim to link the changes that occur early in the diabetic kidney including the growth phenotype, oxidative stress, hypoxia, and formation of advanced glycation end products to mechanisms involved in progressive kidney disease.

Altered expression and localization of insulin receptor in proximal tubule cells from human and rat diabetic kidney

Diabetes is the major cause of end stage renal disease, and tubular alterations are now considered to participate in the development and progression of diabetic nephropathy (DN). Here, we report for the first time that expression of the insulin receptor (IR) in human kidney is altered during diabetes. We detected a strong expression in proximal and distal tubules from human renal cortex, and a significant reduction in type 2 diabetic patients. Moreover, isolated proximal tubules from type 1 diabetic rat kidney showed a similar response, supporting its use as an excellent model for in vitro study of human DN. IR protein down-regulation was paralleled in proximal and distal tubules from diabetic rats, but prominent in proximal tubules from diabetic patients. A target of renal insulin signaling, the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK), showed increased expression and activity, and localization in compartments near the apical membrane of proximal tubules, which was correlated with activation of the GSK3β kinase in this specific renal structure in the diabetic condition. Thus, expression of IR protein in proximal tubules from type 1 and type 2 diabetic kidney indicates that this is a common regulatory mechanism which is altered in DN, triggering enhanced gluconeogenesis regardless the etiology of the disease.

Sestrin 2 and AMPK connect hyperglycemia to Nox4-dependent endothelial nitric oxide synthase uncoupling and matrix protein expression

Mesangial matrix accumulation is an early feature of glomerular pathology in diabetes. Oxidative stress plays a critical role in hyperglycemia-induced glomerular injury. Here, we demonstrate that, in glomerular mesangial cells (MCs), endothelial nitric oxide synthase (eNOS) is uncoupled upon exposure to high glucose (HG), with enhanced generation of reactive oxygen species (ROS) and decreased production of nitric oxide. Peroxynitrite mediates the effects of HG on eNOS dysfunction. HG upregulates Nox4 protein, and inhibition of Nox4 abrogates the increase in ROS and peroxynitrite generation, as well as the eNOS uncoupling triggered by HG, demonstrating that Nox4 functions upstream from eNOS. Importantly, this pathway contributes to HG-induced MC fibronectin accumulation. Nox4-mediated eNOS dysfunction was confirmed in glomeruli of a rat model of type 1 diabetes. Sestrin 2-dependent AMP-activated protein kinase (AMPK) activation attenuates HG-induced MC fibronectin synthesis through blockade of Nox4-dependent ROS and peroxynitrite generation, with subsequent eNOS uncoupling. We also find that HG negatively regulates sestrin 2 and AMPK, thereby promoting Nox4-mediated eNOS dysfunction and increased fibronectin. These data identify a protective function for sestrin 2/AMPK and potential targets for intervention to prevent fibrotic injury in diabetes.

Developmental programming of eNOS uncoupling and enhanced vascular oxidative stress in adult rats after transient neonatal oxygen exposure

The authors have previously shown that neonatal hyperoxic stress leads to high blood pressure, impaired endothelium-mediated vasodilatation, and increased vascular production of superoxide anion by NAD(P)H oxidase in adulthood. However, it is unknown whether changes in nitric oxide (NO) production and/or bioinactivation prevail and whether NO synthase (NOS) is also a source of superoxide. The purpose of this study was to evaluate whether adult animals exposed to neonatal hyperoxic stress have impaired vascular NO production associated with NOS uncoupling participating to vascular superoxide production and vascular dysfunction. In adult male rats exposed to 80% oxygen from day 3 to 10 of life (H, n = 6) versus room air controls (CTRL, n = 6), vascular (aorta) NO production is decreased at baseline (CTRL: 21 ± 1 vs. H: 16 ± 2 4,5-diaminofluorescein diacetate fluorescence intensity arbitrary units; P < 0.05) and after carbachol stimulation (acetylcholine analog; CTRL: 26 ± 2 vs. H: 18±2; P < 0.05). Pretreatment with L-arginine (CTRL: 32 ± 4 vs. H: 31 ± 5) and L-sepiapterine [analog of key NOS cofactor tetrahydro-L-biopterin (BH4)] (CTRL: 30 ± 3 vs. H: 29 ± 3) normalizes NO production after carbachol. L-Sepiapterine also normalizes impaired vasodilatation to carbachol. Vascular endothelial NO synthase (eNOS) immunostaining is reduced, whereas total eNOS protein expression is increased in H (CTRL: 0.76 ± 0.08 vs. H: 1.76± 0.21; P < 0.01). The significantly higher superoxide generation (CTRL: 20 ± 2 vs. H: 28 ± 3 hydroethidine fluorescence intensity arbitrary units; P < 0.05) is prevented by pretreatment with the eNOS inhibitor N-nitro-L-arginine methyl ester (CTRL: 21 ± 4 vs. H: 22 ± 4). Taken together, the current data indicate a role for eNOS uncoupling in enhanced vascular superoxide, impaired endothelium-mediated vasodilatation, and decreased NO production in adult animals with programmed elevated blood pressure after a brief neonatal oxygen exposure.

Apolipoprotein A-1 mimetic D-4F enhances isoflurane-induced eNOS signaling and cardioprotection during acute hyperglycemia

Acute hyperglycemia (AHG) decreases the availability of nitric oxide (NO) and impairs anesthetic preconditioning (APC)-elicited protection against myocardial infarction. We investigated whether D-4F, an apolipoprotein A-1 mimetic, rescues the myocardium by promoting APC-induced endothelial NO signaling during AHG. Myocardial infarct size was measured in mice in the absence or presence of APC [isoflurane (1.4%)] with or without AHG [dextrose (2 g/kg ip)] and D-4F (0.12 or 0.6 mg/kg ip). NO production, superoxide generation, protein compartmentalization, and posttranslational endothelial NO synthase (eNOS) modifications were assessed in human coronary artery endothelial cells cultured in 5.5 or 20 mM glucose with or without isoflurane (0.5 mM) in the presence or absence of D-4F (0.5 μg/ml). Myocardial infarct size was significantly decreased by APC (36 ± 3% of risk area) compared with control (54 ± 3%) in the absence, but not presence, of AHG (49 ± 4%). D-4F restored the cardioprotective effect of APC during AHG (36 ± 3% and 30 ± 3%, 0.12 and 0.6 mg/kg, respectively), although D-4F alone had no effect on infarct size (53 ± 3%). Isoflurane promoted caveolin-1 and eNOS compartmentalization within endothelial cell caveolae and eNOS dimerization, concomitant with increased NO production (411 ± 28 vs. 68 ± 10 pmol/mg protein in control). These actions were attenuated by AHG (NO production: 264 ± 18 pmol/mg protein). D-4F reduced superoxide generation and enhanced caveolin-1 and eNOS caveolar compartmentalization and posttranslational eNOS modifications, thus restoring NO production during isoflurane and AHG (418 ± 36 pmol/mg protein). In conclusion, D-4F restored the cardioprotective effect of APC during AHG, possibly by decreasing superoxide generation, which promoted isoflurane-induced eNOS signaling and NO biosynthesis.

Epigenetic changes in renal genes dysregulated in mouse and rat models of type 1 diabetes

Epigenetic processes are increasingly being recognized as factors in the pathophysiology of diabetes complications, but few chromatin studies have been done in diabetic nephropathy (DN). We hypothesized that changes in mRNA expression of DN-related genes are associated with epigenetic alterations and aberrant expression of histone-modifying enzymes. RT-PCR and a matrix-chromatin immunoprecipitation platform were used to examine renal mRNA expression, RNA polymerase II (Pol II) recruitment, and epigenetic marks at DN-related genes in the mouse (OVE26) and streptozotocin-induced rat models of type 1 diabetes. Diabetes induced renal expression of Cox2, S100A4/FSP-1, and vimentin genes in both the mouse and the rat models of DN. Mcp-1 and laminin γ1 (Lamc1) expression were increased in diabetic mice but not in rats. Comparison of mRNA and Pol II levels suggested that the diabetes-induced expression of these transcripts is mediated by transcriptional and posttranscriptional processes. Decreases in histone H3 lysine 27 tri-methylation (H3K27m3, silencing mark) and increases in H3 lysine 4 di-methylation (H3K4m2, activating mark) levels were the most consistent epigenetic alterations in the tested genes. In agreement with these results, immunoblot analysis showed increased protein abundance of renal H3K27m2/3 demethylase KDM6A, but no changes in cognate methyltransferase Ezh2 in kidneys of the OVE26 mice compared with controls. In diabetic rats, Ezh2 expression was higher without changes in KDM6A, demonstrating that mechanisms of DN-induced H3K27m3 loss could be species specific. In summary, we show that altered mRNA expression of some DN-related genes is associated with changes in Pol II recruitment and a corresponding decrease in repressive H3K27m3 at the selected loci, and at least in mice with equivalent changes in renal expression of cognate histone-modifying enzymes. This pattern could contribute to diabetes-mediated transitions in chromatin that facilitate transcriptional changes in the diabetic kidney.

Uncoupling of VEGF with endothelial NO as a potential mechanism for abnormal angiogenesis in the diabetic nephropathy

Abnormal angiogenesis is a well characterized complication in diabetic retinopathy and is now recognized as a feature of diabetic nephropathy. The primary growth factor driving the increased angiogenesis in diabetic retinopathy and nephropathy is vascular endothelial growth factor (VEGF). While VEGF is considered an important growth factor for maintaining glomerular capillary integrity and function, increased action of VEGF in diabetic renal disease may carry adverse consequences. Studies by our group suggest that the effects of VEGF are amplified in the setting of endothelial dysfunction and low nitric oxide (NO) levels, which are a common feature in the diabetic state. The lack of NO may amplify the effects of VEGF to induce inflammation (via effects on the macrophage) and may lead to dysregulation of the vasculature, exacerbating features of diabetic renal disease. In this review, we summarize how an "uncoupling" of the VEGF-NO axis may contribute to the pathology of the diabetic kidney.

Enhanced phosphorylation of Na(+)-Cl- co-transporter in experimental metabolic syndrome: role of insulin

In the present study, we investigated the activity of the thiazide-sensitive NCC (Na(+)-Cl(-) co-transporter) in experimental metabolic syndrome and the role of insulin in NCC activation. Renal responses to the NCC inhibitor HCTZ (hydrochlorothiazide), as a measure of NCC activity in vivo, were studied in 12-week-old ZO (Zucker obese) rats, a model of the metabolic syndrome, and in ZL (Zucker lean) control animals, together with renal NCC expression and molecular markers of NCC activity, such as localization and phosphorylation. Effects of insulin were studied further in mammalian cell lines with inducible and endogenous expression of this molecule. ZO rats displayed marked hyperinsulinaemia, but no differences in plasma aldosterone, compared with ZL rats. In ZO rats, natriuretic and diuretic responses to NCC inhibition with HCTZ were enhanced compared with ZL rats, and were associated with a decrease in BP (blood pressure). ZO rats displayed enhanced Thr(53) NCC phosphorylation and predominant membrane localization of both total and phosphorylated NCC, together with a different profile in expression of SPAK (Ste20-related proline/alanine-rich kinase) isoforms, and lower expression of WNK4. In vitro, insulin induced NCC phosphorylation, which was blocked by a PI3K (phosphoinositide 3-kinase) inhibitor. Insulin-induced reduction in WNK4 expression was also observed, but delayed compared with the time course of NCC phosphorylation. In summary, we report increased NCC activity in hyperinsulinaemic rodents in conjunction with the SPAK expression profile consistent with NCC activation and reduced WNK4, as well as an ability of insulin to induce NCC stimulatory phosphorylation in vitro. Together, these findings indicate that hyperinsulinaemia is an important driving force of NCC activity in the metabolic syndrome with possible consequences for BP regulation.

Increased nitric oxide activity compensates for increased oxidative stress to maintain endothelial function in rat aorta in early type 1 diabetes

Hyperglycaemia and oxidative stress are known to acutely cause endothelial dysfunction in vitro, but in the initial stages of diabetes, endothelium-dependent relaxation is preserved. The aim of this study was to investigate how endothelium-dependent relaxation is maintained in the early stages of type 1 diabetes. Diabetes was induced in Sprague-Dawley rats with a single injection of streptozotocin (48 mg/kg, i.v.), and after 6 weeks, endothelium-dependent and endothelium-independent relaxations were examined in the thoracic aorta in vitro. Lucigenin-enhanced chemiluminescence was used to measure superoxide generation from the aorta. Diabetes increased superoxide generation by the aorta (2,180 ± 363 vs 986 ± 163 AU/mg dry tissue weight). Acetylcholine (ACh)-induced relaxation was similar in aortae from control (pEC(50) 7.36 ± 0.09, R (max) 95 ± 3 %) and diabetic rats (pEC(50) 7.33 ± 0.10, R (max) 88 ± 5 %). The ACh-induced relaxation was abolished by the combined presence of the nitric oxide synthase inhibitor N-nitro-L-arginine (L-NNA, 100 μM) and an inhibitor of soluble guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 μM) in control rats, but under the same conditions, the diabetic aortic rings showed significant relaxation to ACh (pEC(50) 6.75 ± 0.15, R (max) 25 ± 4 %, p < 0.05). In diabetic aortae, the addition of haemoglobin, which inactivates nitric oxide, to L-NNA + ODQ abolished the response to ACh. The addition of the potassium channel blockers, apamin and TRAM-34, to L-NNA + ODQ also abolished the relaxation response to ACh. Diabetes significantly elevated plasma total nitrite/nitrate and increased expression of endothelial nitric oxide synthase (eNOS) and calmodulin in aortae. These data indicate that after 6 weeks of diabetes, despite increased oxidant stress, endothelium-dependent relaxation is maintained due to the increased eNOS expression resulting in increased NO synthesis. In diabetic arteries, NO acts both through and independently of cGMP pathways to cause relaxation.

Improvement of endothelial nitric oxide synthase activity retards the progression of diabetic nephropathy in db/db mice

Impaired endothelial nitric oxide synthase (eNOS) activity may be involved in the pathogenesis of diabetic nephropathy. To test this, we used the type 2 diabetic db/db mouse (BKS background) model and found impaired eNOS dimerization and phosphorylation along with moderate glomerular mesangial expansion and increased glomerular basement membrane (GBM) thickness at 34 weeks of age. Cultured murine glomerular endothelial cells exposed to high glucose had similar alterations in eNOS dimerization and phosphorylation. Treatment with sepiapterin, a stable precursor of the eNOS cofactor tetrahydrobiopterin, or the nitric oxide precursor L-arginine corrected changes in eNOS dimerization and phosphorylation, corrected permeability defects, and reduced apoptosis. Sepiapterin or L-arginine, administered to db/db mice from weeks 26 to 34, did not significantly alter hyperfiltration or affect mesangial expansion, but reduced albuminuria and GBM thickness, and decreased urinary isoprostane and nitrotyrosine excretion (markers of oxidative stress). Although there was no change in glomerular eNOS monomer expression, both sepiapterin and L-arginine partially reversed the defect in eNOS dimerization and phosphorylation. Hence, our results support an important role for eNOS dysfunction in diabetes and suggest that sepiapterin supplementation might have therapeutic potential in diabetic nephropathy.

Uncoupling endothelial nitric oxide synthase is ameliorated by green tea in experimental diabetes by re-establishing tetrahydrobiopterin levels

The current study investigated the potential of green tea (GT) to improve uncoupling of endothelial nitric oxide synthase (eNOS) in diabetic conditions. In rats with streptozotocin-induced diabetes, nitric oxide (NO) bioavailability was reduced by uncoupling eNOS, characterized by a reduction in tetrahydrobiopterin (BH(4)) levels and a decrease in the eNOS dimer-to-monomer ratio. GT treatment ameliorated these abnormalities. Moreover, immortalized human mesangial cells (ihMCs) exposed to high glucose (HG) levels exhibited a rise in reactive oxygen species (ROS) and a decline in NO levels, which were reversed with GT. BH(4) and the activity of guanosine triphosphate cyclohydrolase I decreased in ihMCs exposed to HG and was normalized by GT. Exogenous administration of BH(4) in ihMCs reversed the HG-induced rise in ROS and the decline in NO production. However, coadministration of GT with BH(4) did not result in a further reduction in ROS production, suggesting that reduced ROS with GT was indeed secondary to uncoupled eNOS. In summary, GT reversed the diabetes-induced reduction of BH(4) levels, ameliorating uncoupling eNOS, and thus increasing NO bioavailability and reducing oxidative stress, two abnormalities that are involved in the pathogenesis of diabetic nephropathy.

Poly(ADP-ribose) polymerase 1 inhibition improves coronary arteriole function in type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is associated with microvascular dysfunction. We hypothesized that increased poly(ADP-ribose) polymerase 1 (PARP-1) activity contributes to microvascular dysfunction in T2DM. T2DM (db(-)/db(-)) and nondiabetic control (db(-)/db(+)) mice were treated with 2 different PARP-1 inhibitors (INO-1001, 5 mg/kg per day and ABT-888, 15 mg/kg per day) for 2 weeks. Isolated coronary arterioles were mounted in an arteriograph. Pressure-induced myogenic tone was significantly potentiated, whereas endothelium-dependent relaxation was significantly attenuated in diabetic mice compared with control mice. These results were associated with decreased endothelial NO synthase phosphorylation and cGMP level and increased PARP-1 activity in coronary arterioles from diabetic mice compared with control mice. Interestingly, PARP-1 inhibitors significantly reduced the potentiation of myogenic tone, improved endothelium-dependent relaxation, restored endothelial NO synthase phosphorylation and cGMP, and attenuated cleaved PARP-1. These results were supported by in vitro studies indicating that downregulation of PARP-1 in mesenteric resistance arteries using PARP-1 short hairpin RNA lentiviral particles significantly improved endothelium-dependent relaxation in mesenteric resistance arteries from diabetic mice compared with control mice. The inhibition of NO synthesis by N(G)-nitro-L-arginine methyl ester (L-NAME) significantly reduced the endothelium-dependent relaxation in coronary arterioles and mesenteric resistance arteries from control and diabetic mice treated with PARP-1 inhibitors and PARP-1 short hairpin RNA lentiviral particles. In addition, we demonstrated that enhanced cleaved PARP-1, its binding to DNA, and DNA damage were reduced after PARP-1 inhibition in cultured endothelial cells stimulated with high glucose. We provide evidence that T2DM impairs microvascular function by an enhanced PARP-1 activity-dependent mechanism. Therefore, PARP-1 could be a potential target for overcoming diabetic microvascular complications.

2-Hydroxyestradiol slows progression of experimental polycystic kidney disease

Male gender is a risk factor for progression of polycystic kidney disease (PKD). 17β-Estradiol (E2) protects experimentally, but clinical use is limited by adverse effects. Novel E2 metabolites provide many benefits of E2 without stimulating the estrogen receptor, and thus may be safer. We hypothesized that E2 metabolites are protective in a model of PKD. Studies were performed in male control Han:SPRD rats, and in cystic males treated with orchiectomy, 2-methoxyestradiol, 2-hydroxyestradiol (2-OHE), or vehicle, from age 3 to 12 wk. Cystic rats exhibited renal functional impairment (∼50% decrease in glomerular filtration and renal plasma flow rates, P < 0.05) and substantial cyst development (20.5 ± 2.0% of cortex area). 2-OHE was the most effective in limiting cysts (6.0 ± 0.7% of cortex area, P < 0.05 vs. vehicle-treated cystic rats) and preserving function, in association with suppression of proliferation, apoptosis, and angiogenesis markers. Downregulation of p21 expression and increased expression of Akt, the mammalian target of rapamycin (mTOR), and some of its downstream effectors were significantly reversed by 2-OHE. Thus, 2-OHE limits disease progression in a cystic rodent model. Mechanisms include reduced renal cell proliferation, apoptosis, and angiogenesis. These effects may be mediated, at least in part, by preservation of p21 and suppression of Akt and mTOR. Estradiol metabolites may represent a novel, safe intervention to slow progression of PKD.

Suppression of microRNA-29 expression by TGF-β1 promotes collagen expression and renal fibrosis

Synthesis and deposition of extracellular matrix (ECM) within the glomerulus and interstitium characterizes renal fibrosis, but the mechanisms underlying this process are incompletely understood. The profibrotic cytokine TGF-β1 modulates the expression of certain microRNAs (miRNAs), suggesting that miRNAs may have a role in the pathogenesis of renal fibrosis. Here, we exposed proximal tubular cells, primary mesangial cells, and podocytes to TGF-β1 to examine its effect on miRNAs and subsequent collagen synthesis. TGF-β1 reduced expression of the miR-29a/b/c/family, which targets collagen gene expression, and increased expression of ECM proteins. In both resting and TGF-β1-treated cells, ectopic expression of miR-29 repressed the expression of collagens I and IV at both the mRNA and protein levels by targeting the 3'untranslated region of these genes. Furthermore, we observed low levels of miR-29 in three models of renal fibrosis representing early and advanced stages of disease. Administration of the Rho-associated kinase inhibitor fasudil prevented renal fibrosis and restored expression of miR-29. Taken together, these data suggest that TGF-β1 inhibits expression of the miR-29 family, thereby promoting expression of ECM components. Pharmacologic modulation of these miRNAs may have therapeutic potential for progressive renal fibrosis.

Suppression of eNOS-derived superoxide by caveolin-1: a biopterin-dependent mechanism

In the vasculature, nitric oxide (NO) is generated by endothelial NO synthase (eNOS) in a calcium/calmodulin-dependent reaction. In the absence of the requisite eNOS cofactor tetrahydrobiopterin (BH(4)), NADPH oxidation is uncoupled from NO generation, leading to the production of superoxide. Although this phenomenon is apparent with purified enzyme, cellular studies suggest that formation of the BH(4) oxidation product, dihydrobiopterin, is the molecular trigger for eNOS uncoupling rather than BH(4) depletion alone. In the current study, we investigated the effects of both BH(4) depletion and oxidation on eNOS-derived superoxide production in endothelial cells in an attempt to elucidate the molecular mechanisms regulating eNOS oxidase activity. Results demonstrated that pharmacological depletion of endothelial BH(4) does not result in eNOS oxidase activity, whereas BH(4) oxidation gave rise to significant eNOS-oxidase activity. These findings suggest that the endothelium possesses regulatory mechanisms, which prevent eNOS oxidase activity from pterin-free eNOS. Using a combination of gene silencing and pharmacological approaches, we demonstrate that eNOS-caveolin-1 association is increased under conditions of reduced pterin bioavailability and that this sequestration serves to suppress eNOS uncoupling. Using small interfering RNA approaches, we demonstrate that caveolin-1 gene silencing increases eNOS oxidase activity to 85% of that observed under conditions of BH(4) oxidation. Moreover, when caveolin-1 silencing was combined with a pharmacological inhibitor of AKT, BH(4) depletion increased eNOS-derived superoxide to 165% of that observed with BH(4) oxidation. This study identifies a critical role of caveolin-1 in the regulation of eNOS uncoupling and provides new insight into the mechanisms through which disease-associated changes in caveolin-1 expression may contribute to endothelial dysfunction.

Suppression of eNOS-derived superoxide by caveolin-1: a biopterin-dependent mechanism

In the vasculature, nitric oxide (NO) is generated by endothelial NO synthase (eNOS) in a calcium/calmodulin-dependent reaction. In the absence of the requisite eNOS cofactor tetrahydrobiopterin (BH(4)), NADPH oxidation is uncoupled from NO generation, leading to the production of superoxide. Although this phenomenon is apparent with purified enzyme, cellular studies suggest that formation of the BH(4) oxidation product, dihydrobiopterin, is the molecular trigger for eNOS uncoupling rather than BH(4) depletion alone. In the current study, we investigated the effects of both BH(4) depletion and oxidation on eNOS-derived superoxide production in endothelial cells in an attempt to elucidate the molecular mechanisms regulating eNOS oxidase activity. Results demonstrated that pharmacological depletion of endothelial BH(4) does not result in eNOS oxidase activity, whereas BH(4) oxidation gave rise to significant eNOS-oxidase activity. These findings suggest that the endothelium possesses regulatory mechanisms, which prevent eNOS oxidase activity from pterin-free eNOS. Using a combination of gene silencing and pharmacological approaches, we demonstrate that eNOS-caveolin-1 association is increased under conditions of reduced pterin bioavailability and that this sequestration serves to suppress eNOS uncoupling. Using small interfering RNA approaches, we demonstrate that caveolin-1 gene silencing increases eNOS oxidase activity to 85% of that observed under conditions of BH(4) oxidation. Moreover, when caveolin-1 silencing was combined with a pharmacological inhibitor of AKT, BH(4) depletion increased eNOS-derived superoxide to 165% of that observed with BH(4) oxidation. This study identifies a critical role of caveolin-1 in the regulation of eNOS uncoupling and provides new insight into the mechanisms through which disease-associated changes in caveolin-1 expression may contribute to endothelial dysfunction.

Suppression of eNOS-derived superoxide by caveolin-1: a biopterin-dependent mechanism

In the vasculature, nitric oxide (NO) is generated by endothelial NO synthase (eNOS) in a calcium/calmodulin-dependent reaction. In the absence of the requisite eNOS cofactor tetrahydrobiopterin (BH(4)), NADPH oxidation is uncoupled from NO generation, leading to the production of superoxide. Although this phenomenon is apparent with purified enzyme, cellular studies suggest that formation of the BH(4) oxidation product, dihydrobiopterin, is the molecular trigger for eNOS uncoupling rather than BH(4) depletion alone. In the current study, we investigated the effects of both BH(4) depletion and oxidation on eNOS-derived superoxide production in endothelial cells in an attempt to elucidate the molecular mechanisms regulating eNOS oxidase activity. Results demonstrated that pharmacological depletion of endothelial BH(4) does not result in eNOS oxidase activity, whereas BH(4) oxidation gave rise to significant eNOS-oxidase activity. These findings suggest that the endothelium possesses regulatory mechanisms, which prevent eNOS oxidase activity from pterin-free eNOS. Using a combination of gene silencing and pharmacological approaches, we demonstrate that eNOS-caveolin-1 association is increased under conditions of reduced pterin bioavailability and that this sequestration serves to suppress eNOS uncoupling. Using small interfering RNA approaches, we demonstrate that caveolin-1 gene silencing increases eNOS oxidase activity to 85% of that observed under conditions of BH(4) oxidation. Moreover, when caveolin-1 silencing was combined with a pharmacological inhibitor of AKT, BH(4) depletion increased eNOS-derived superoxide to 165% of that observed with BH(4) oxidation. This study identifies a critical role of caveolin-1 in the regulation of eNOS uncoupling and provides new insight into the mechanisms through which disease-associated changes in caveolin-1 expression may contribute to endothelial dysfunction.

Glycated albumin modulates endothelial cell thrombogenic and inflammatory responses

BACKGROUND

It has become established that a diabetic vasculature promotes cardiovascular disease progression via changes to endothelial cells, platelets, and the interactions of these cells. It is believed that the majority of these changes are induced by the presence of advanced glycation end products (AGEs), which permanently alter various functions. Studies have shown that platelets perpetuate endothelial cell responses under these conditions. However, the role of changes in endothelial cell thrombogenicity and inflammatory responses, after subjected to AGEs, has not been characterized. Our objective was to evaluate the effects of AGEs on these functions.

METHODS

To accomplish this, albumin was chemically modified by exposure to glucose for up to 8 weeks, and endothelial cells were subjected to glycated albumin for up to 5 days in a cell culture system. A time course for changes in endothelial cell viability, density, morphology, and metabolic activity were investigated, along with the surface expression of intercellular adhesion molecule-1, thrombomodulin, tissue factor, connexin-43, and caveolin-1.

RESULTS

Endothelial cells exposed to irreversibly glycated albumin were less viable, proliferated slower, and had a lower metabolic activity as compared to cells exposed to nonglycated albumin. Endothelial cells that were exposed to any glycated albumin were procoagulant and proinflammatory as compared with all other conditions. There were no overall trends in the expression of connexin-43 or caveolin-1.

CONCLUSIONS

Our data suggest that the presence of irreversible glycated albumin is deleterious to endothelial cells, makes endothelial cells more procoagulant, and promotes inflammatory responses. It is therefore possible that endothelial cell activation may precede and promote platelet activation during diabetic conditions.

Inhibition of renal caveolin-1 reduces natriuresis and produces hypertension in sodium-loaded rats

Renal dopamine receptor function and ion transport inhibition are impaired in essential hypertension. We recently reported that caveolin-1 (CAV1) and lipid rafts are necessary for normal D(1)-like receptor-dependent internalization of Na-K-ATPase in human proximal tubule cells. We now hypothesize that CAV1 is necessary for the regulation of urine sodium (Na(+)) excretion (U(Na)V) and mean arterial blood pressure (MAP) in vivo. Acute renal interstitial (RI) infusion into Sprague-Dawley rats of 1 μg·kg⁻¹·min⁻¹ fenoldopam (FEN; D(1)-like receptor agonist) caused a 0.46 ± 0.15-μmol/min increase in U(Na)V (over baseline of 0.29 ± 0.04 μmol/min; P < 0.01). This increase was seen in Na(+)-loaded rats, but not in those under a normal-sodium load. Coinfusion with β-methyl cyclodextrin (βMCD; lipid raft disrupter, 200 μg·kg⁻¹·min⁻¹) completely blocked this FEN-induced natriuresis (P < 0.001). Long-term (3 day) lipid raft disruption via continuous RI infusion of 80 μg·kg⁻¹·min⁻¹ βMCD decreased renal cortical CAV1 expression (47.3 ± 6.4%; P < 0.01) and increased MAP (32.4 ± 6.6 mmHg; P < 0.001) compared with vehicle-infused animals. To determine whether the MAP rise was due to a CAV1-dependent lipid raft-mediated disruption, Na(+)-loaded rats were given a bolus RI infusion of CAV1 siRNA. Two days postinfusion, cortical CAV1 expression was decreased by 73.6 ± 8.2% (P < 0.001) and the animals showed an increase in MAP by 17.4 ± 2.9 mmHg (P < 0.01) compared with animals receiving scrambled control siRNA. In summary, acute kidney-specific lipid raft disruption decreases CAV1 expression and blocks D(1)-like receptor-induced natriuresis. Furthermore, chronic disruption of lipid rafts or CAV1 protein expression in the kidney induces hypertension.

De novo lipogenesis maintains vascular homeostasis through endothelial nitric-oxide synthase (eNOS) palmitoylation

Endothelial dysfunction leads to lethal vascular complications in diabetes and related metabolic disorders. Here, we demonstrate that de novo lipogenesis, an insulin-dependent process driven by the multifunctional enzyme fatty-acid synthase (FAS), maintains endothelial function by targeting endothelial nitric-oxide synthase (eNOS) to the plasma membrane. In mice with endothelial inactivation of FAS (FASTie mice), eNOS membrane content and activity were decreased. eNOS and FAS were physically associated; eNOS palmitoylation was decreased in FAS-deficient cells, and incorporation of labeled carbon into eNOS-associated palmitate was FAS-dependent. FASTie mice manifested a proinflammatory state reflected as increases in vascular permeability, endothelial inflammatory markers, leukocyte migration, and susceptibility to LPS-induced death that was reversed with an NO donor. FAS-deficient endothelial cells showed deficient migratory capacity, and angiogenesis was decreased in FASTie mice subjected to hindlimb ischemia. Insulin induced FAS in endothelial cells freshly isolated from humans, and eNOS palmitoylation was decreased in mice with insulin-deficient or insulin-resistant diabetes. Thus, disrupting eNOS bioavailability through impaired lipogenesis identifies a novel mechanism coordinating nutritional status and tissue repair that may contribute to diabetic vascular disease.

Effects of systemic inhibition of Rho kinase on blood pressure and renal haemodynamics in diabetic rats

BACKGROUND AND PURPOSE

The RhoA/Rho associated kinases (ROCK) pathway has been implicated in the pathophysiology of diabetic nephropathy (DN). Early stages of diabetes are associated with renal haemodynamic changes, contributing to later development of DN. However, the role of RhoA/ROCK, known regulators of vascular tone, in this process has not been studied.

EXPERIMENTAL APPROACH

Blood pressure (BP), glomerular filtration (GFR), effective renal plasma flow and filtration fraction (FF) in response to the ROCK inhibitors Y27632 (0.1 and 0.5 mg·kg(-1) ) and fasudil (0.3 and 1.5 mg·kg(-1) ) were examined in streptozotocin-diabetic rats and non-diabetic controls.

KEY RESULTS

Diabetic rats demonstrated baseline increases in GFR and FF. In contrast to similar decreases in BP in diabetic and control rats, renal vasodilator effects and a decrease in FF, following ROCK inhibition were observed only in diabetic rats. The vasodilator effects of Y27632 and a further decrease in FF, were also detected in diabetic rats pretreated with the angiotensin antagonist losartan. The effects of ROCK inhibitors in diabetic rats were modulated by prior protein kinase C (PKC)β inhibition with ruboxistaurin, which abolished their effects on FF. Consistent with the renal vasodilator effects, the ROCK inhibitors reduced phosphorylation of myosin light chain in diabetic kidneys.

CONCLUSIONS AND IMPLICATIONS

The results indicate greater dependence of renal haemodynamics on RhoA/ROCK and beneficial haemodynamic effects of ROCK inhibitors in diabetes, which were additive to the effects of losartan. In this process, the RhoA/ROCK pathway operated downstream of or interacted with, PKCβ in some segments of the renal vascular tree.

Endothelial dysfunction as a potential contributor in diabetic nephropathy

The mechanisms that drive the development of diabetic nephropathy remain undetermined. Only 30-40% of patients with diabetes mellitus develop overt nephropathy, which suggests that other contributing factors besides the diabetic state are required for the progression of diabetic nephropathy. Endothelial dysfunction is associated with human diabetic nephropathy and retinopathy, and advanced diabetic glomerulopathy often exhibits thrombotic microangiopathy, including glomerular capillary microaneurysms and mesangiolysis, which are typical manifestations of endothelial dysfunction in the glomerulus. Likewise, diabetic mice with severe endothelial dysfunction owing to deficiency of endothelial nitric oxide synthase develop progressive nephropathy and retinopathy similar to the advanced lesions observed in humans with diabetes mellitus. Additionally, inhibitors of the renin-angiotensin system fail to be renoprotective in some individuals with diabetic nephropathy (due in part to aldosterone breakthrough) and in some mouse models of the disease. In this Review, we discuss the clinical and experimental evidence that supports a role for endothelial nitric oxide deficiency and subsequent endothelial dysfunction in the progression of diabetic nephropathy and retinopathy. If endothelial dysfunction is the key factor required for diabetic nephropathy, then agents that improve endothelial function or raise intraglomerular nitric oxide level could be beneficial in the treatment of diabetic nephropathy.