Extracellular signal-regulated kinase (ERK) in glucose-induced and endothelin-mediated fibronectin synthesis

METTL14 promotes the development of diabetic kidney disease by regulating m6A modification of TUG1

BACKGROUND

Diabetic kidney disease (DKD) is one of the most common diabetic complications. Endoplasmic reticulum stress (ERS) is an important step for renal tubular epithelial cell apoptosis during DKD progression. Herein, the role and regulatory mechanism of METTL14 in ERS during DKD progression were investigated.

METHODS

DKD animal and cell models were established by streptozotocin (STZ) and high glucose (HG), respectively. HE and Masson staining were performed to analyze renal lesions in DKD mouse. Cell viability and proliferation were determined by MTT and EdU staining, respectively. HK2 cell apoptosis was analyzed by flow cytometry. TUG1 m6A level was determined by Me-RIP. The interaction between TUG1, LIN28B and MAPK1 was analyzed by RIP and RNA pull-down assays.

RESULTS

HG stimulation promoted apoptosis and increased ERS marker proteins (GRP78, CHOP and caspase12) expression in HK2 cells, while these changes were reversed by METTL14 knockdown. METTL14 inhibited TUG1 stability and expression level in an m6A-dependent manner. As expected, TUG1 knockdown abrogated METTL14 knockdown's inhibition on HG-induced HK2 cell apoptosis and ERS. In addition, TUG1 inactivated MAPK1/ERK signaling by binding with LIN28B. And TUG1 overexpression's repression on HG-induced HK2 cell apoptosis and ERS was abrogated by MAPK1 signaling activation. Meanwhile, METTL14 knockdown or TUG1 overexpression protected against STZ-induced renal lesions and renal fibrosis in DKD mouse.

CONCLUSION

METTL14 promoted renal tubular epithelial cell apoptosis and ERS by activating MAPK/ERK pathway through m6A modification of TUG1, thereby accelerating DKD progression.

Fibronectin Contributes to a BRAF Inhibitor-driven Invasive Phenotype in Thyroid Cancer through EGR1, Which Can Be Blocked by Inhibition of ERK1/2

Mutations in BRAF are common in advanced papillary and anaplastic thyroid cancer (PTC and ATC). However, patients with BRAF-mutant PTC currently lack therapies targeting this pathway. Despite the approved combination of BRAF and MEK1/2 inhibition for patients with BRAF-mutant ATC, these patients often progress. Thus, we screened a panel of BRAF-mutant thyroid cancer cell lines to identify new therapeutic strategies. We showed that thyroid cancer cells resistant to BRAF inhibition (BRAFi) exhibit an increase in invasion and a proinvasive secretome in response to BRAFi. Using reverse-phase protein array (RPPA), we identified a nearly 2-fold increase in expression of the extracellular matrix protein, fibronectin, in response to BRAFi treatment, and a corresponding 1.8- to 3.0-fold increase in fibronectin secretion. Accordingly, the addition of exogenous fibronectin phenocopied the BRAFi-induced increase in invasion while depletion of fibronectin in resistant cells resulted in loss of increased invasion. We further showed that BRAFi-induced invasion can be blocked by inhibition of ERK1/2. In a BRAFi-resistant patient-derived xenograft model, we found that dual inhibition of BRAF and ERK1/2 slowed tumor growth and decreased circulating fibronectin. Using RNA sequencing, we identified EGR1 as a top downregulated gene in response to combined BRAF/ERK1/2 inhibition, and we further showed that EGR1 is necessary for a BRAFi-induced increase in invasion and for induction of fibronectin in response to BRAFi.

IMPLICATIONS

Together, these data show that increased invasion represents a new mechanism of resistance to BRAF inhibition in thyroid cancer that can be targeted with an ERK1/2 inhibitor.

The role of protein kinase C in diabetic microvascular complications

Protein kinase C (PKC) is a family of serine/threonine protein kinases, the activation of which plays an important role in the development of diabetic microvascular complications. The activation of PKC under high-glucose conditions stimulates redox reactions and leads to an accumulation of redox stress. As a result, various types of cells in the microvasculature are influenced, leading to changes in blood flow, microvascular permeability, extracellular matrix accumulation, basement thickening and angiogenesis. Structural and functional disorders further exacerbate diabetic microvascular complications. Here, we review the roles of PKC in the development of diabetic microvascular complications, presenting evidence from experiments and clinical trials.

Human umbilical cord-derived mesenchymal stem cells not only ameliorate blood glucose but also protect vascular endothelium from diabetic damage through a paracrine mechanism mediated by MAPK/ERK signaling

BACKGROUND

Endothelial damage is an initial step of macro- and micro-vasculature dysfunctions in diabetic patients, accounting for a high incidence of diabetic vascular complications, such as atherosclerosis, nephropathy, retinopathy, and neuropathy. However, clinic lacks effective therapeutics targeting diabetic vascular complications. In field of regenerative medicine, mesenchymal stem cells, such as human umbilical cord-derived MSCs (hucMSCs), have great potential in treating tissue damage.

METHODS

To determine whether hucMSCs infusion could repair diabetic vascular endothelial damage and how it works, this study conducted in vivo experiment on streptozotocin-induced diabetic rat model to test body weight, fasting blood glucose (FBG), serum ICAM-1 and VCAM-1 levels, histopathology and immunohistochemical staining of aorta segments. In vitro experiment was further conducted to determine the effects of hucMSCs on diabetic vascular endothelial damage, applying assays of resazurin staining, MTT cell viability, wound healing, transwell migration, and matrigel tube formation on human umbilical vein endothelial cells (HUVECs). RNA sequencing (RNAseq) and molecular experiment were conducted to clarify the mechanism of hucMSCs.

RESULTS

The in vivo data revealed that hucMSCs partially restore the alterations of body weight, FBG, serum ICAM-1 and VCAM-1 levels, histopathology of aorta and reversed the abnormal phosphorylation of ERK in diabetic rats. By using the conditioned medium of hucMSCs (MSC-CM), the in vitro data revealed that hucMSCs improved cell viability, wound healing, migration and angiogenesis of the high glucose-damaged HUVECs through a paracrine action mode, and the altered gene expressions of IL-6, TNF-α, ICAM-1, VCAM-1, BAX, P16, P53 and ET-1 were significantly restored by MSC-CM. RNAseq incorporated with real-time PCR and Western blot results clarified that high glucose activated MAPK/ERK signaling in HUVECs, while MSC-CM reversed the abnormal phosphorylation of ERK and overexpressions of MKNK2, ERBB3, MYC and DUSP5 in MAPK/ERK signaling pathway.

CONCLUSIONS

HucMSCs not only ameliorated blood glucose but also protected vascular endothelium from diabetic damage, in which MAPK/ERK signaling mediated its molecular mechanism of paracrine action. Our findings provided novel knowledge of hucMSCs in the treatment of diabetes and suggested a prospective strategy for the clinical treatment of diabetic vascular complications.

Inhibition of extracellular regulated kinase (ERK)-1/2 signaling pathway in the prevention of ALS: Target inhibitors and influences on neurological dysfunctions

Cell signal transduction pathways are essential modulators of several physiological and pathological processes in the brain. During overactivation, these signaling processes may lead to disease progression. Abnormal protein kinase activation is associated with several biological dysfunctions that facilitate neurodegeneration under different biological conditions. As a result, these signaling pathways are essential in understanding brain disorders' development or progression. Recent research findings indicate the crucial role of extracellular signal-regulated kinase-1/2 (ERK-1/2) signaling during the neuronal development process. ERK-1/2 is a key component of its mitogen-activated protein kinase (MAPK) group, controlling certain neurological activities by regulating metabolic pathways, cell proliferation, differentiation, and apoptosis. ERK-1/2 also influences neuronal elastic properties, nerve growth, and neurological and cognitive processing during brain injuries. The primary goal of this review is to elucidate the activation of ERK1/2 signaling, which is involved in the development of several ALS-related neuropathological dysfunctions. ALS is a rare neurological disorder category that mainly affects the nerve cells responsible for regulating voluntary muscle activity. ALS is progressive, which means that the symptoms are getting worse over time, and there is no cure for ALS and no effective treatment to avoid or reverse. Genetic abnormalities, oligodendrocyte degradation, glial overactivation, and immune deregulation are associated with ALS progression. Furthermore, the current review also identifies ERK-1/2 signaling inhibitors that can promote neuroprotection and neurotrophic effects against the clinical-pathological presentation of ALS. As a result, in the future, the potential ERK-1/2 signaling inhibitors could be used in the treatment of ALS and related neurocomplications.

Can Wogonin be Used in Controlling Diabetic Cardiomyopathy?

Diabetes Mellitus (DM) is now a well-known factor which initiates many metabolic derangements in various tissues and organs including liver, muscle, pancreas, adipose tissue, cardiovascular and nervous system. Cardiovascular complications are the most crucial , and their effects are so intensive that their derangement leads to cardiac failure even in the absence of ischemic heart diseases. This entity of cardiac pathology in DM is often regarded as diabetic cardiomyopathy (DCM). Recently, many plant-derived drugs have been tested to control and alleviate DCM. Wogonin is one of the drugs the characteristics of which have been deeply studied. Wogonin is a flavonoid having yellow color pigment in their leaves and is obtained from the roots of plant Scutellaria Baicalensis Georgi. Wogonin has long been used as an active anti-cancer drug in Chinese medicine practice. In recent past wogonin has shown to possess notable anti-inflammatory, and anti-allergic properties. Wogonin has demonstrated to possess anti-oxidant, anti-viral, anti-inflammatory and also anti-thrombotic properties. Wogonin has shown to alleviate apoptosis, and ER stress in the cells and this property can also be used in the treatment of cardiovascular diseases. Notably, wogonin has been documented to have an extensive margin of safety as well as displays little or no organ toxicity following extended intravenous administration. In this review, we discuss recently discovered therapeutic potential of wogonin in the treatment of DCM.

Peritoneal Dialysis Fluid-Induced Fragmentation of Golgi Apparatus as a Biocompatibility Marker

In vitro biocompatibility assessments that consider physiologically appropriate conditions of cell exposure to peritoneal dialysis fluids (PDFs) are still awaited. In this study, we found that fragmentation of Golgi apparatus occurred in a pH-dependent manner within 30-min exposure to five distinct commercially available PDFs, which showed no marked difference in their effects on cell viability in the conventional MTT assay. Fluorescence microscopy analysis of labeling antibody against cis-Golgi protein GM130 indicated that the stacked cisternal structure was maintained in the perinuclear area of both M199 culture medium and a neutral-pH PDF groups. However, this specific structure became partially disassembled over time even in a neutral-pH PDF, and fragmentation was markedly enhanced in cells exposed to neutralized-pH PDFs in correspondence with their intracellular pH; moreover, in acidic PDFs, Golgi staining was diffuse and scattered in the entire cytoplasm and showed partial aggregation. The Golgi fragmentation markedly observed with the neutralized PDFs could be reversed by replacing either the media with a neutral-pH medium or a mixture of PDF and PD effluent (PDF) in a gradient manner mimicking clinical conditions. Furthermore, although weaker than pH effect, notable effects of other PDF-related factors were also observed after 30-min exposure to pH-adjusted PDFs. Lastly, the results of studies conducted using MAPK/SAPK inhibitors indicated that the mechanism underlying the Golgi fragmentation described here differs from that associated with the fragmentation that occurs at the G2/M checkpoint in the cell cycle. We conclude that Golgi fragmentation is suitable for rapid biocompatibility assessment of PDF not only because of its strong pH dependence but also because the fragmentation is recognizably affected by PDF constituents.

Probucol prevents atrial ion channel remodeling in an alloxan-induced diabetes rabbit model

Diabetes mellitus (DM) increases the risk of developing atrial fibrillation (AF), but the molecular mechanisms of diabetes-induced atrial remodeling processes have not been fully characterized. The aim of this study was to examine the mechanisms underlying atrial ion channel remodeling in alloxan-induced diabetes model in rabbits. A total of 40 Japanese rabbits were randomly assigned to a control group (C), alloxan-induced diabetic group (DM), probucol-treated control group (Control-P), and probucol-treated diabetic group (DM-P). Using whole-cell voltage-clamp techniques, ICa,L, INa and action potential durations (APDs) were measured in cardiomyocytes isolated from the left atria in the four groups, respectively. In the DM group, increased Ica,L and decreased INa currents were reflected in prolonged APD90 and APD50 values. These changes were reversed in the DM-P group. In conclusion, probucol cured AF by alleviating the ion channel remodeling of atrial myocytes in the setting of diabetes and the promising therapeutic potential of anti-oxidative compounds in the treatment of AF warrants further study.

Kaempferol inhibited VEGF and PGF expression and in vitro angiogenesis of HRECs under diabetic-like environment

Diabetic retinopathy (DR) is one of the common and specific microvascular complications of diabetes. This study aimed to investigate the anti-angiogenic effect of kaempferol and explore its underlying molecular mechanisms. The mRNA expression level of vascular endothelial growth factor (VEGF) and placenta growth factor (PGF) and the concentrations of secreted VEGF and PGF were measured by qTR-PCR and ELISA assay, respectively. Human retinal endothelial cells (HRECs) proliferation, migration, and sprouting were measured by CCK-8 and transwell, scratching wound, and tube formation assays, respectively. Protein levels were determined by western blot. High glucose (25 mM) increased the mRNA expression levels of VEGF and PGF as well as the concentrations of secreted VEGF and PGF in HRECs, which can be antagonized by kaempferol (25 µM). Kaempferol (5-25 µM) significantly suppressed cell proliferation, migration, migration distance and sprouting of HRECs under high glucose condition. The anti-angiogenic effect of kaempferol was mediated via downregulating the expression of PI3K and inhibiting the activation of Erk1/2, Src, and Akt1. This study indicates that kaempferol suppressed angiogenesis of HRECs via targeting VEGF and PGF to inhibit the activation of Src-Akt1-Erk1/2 signaling pathway. The results suggest that kaempferol may be a potential drug for better management of DR.

Asiatic acid mitigates hyperglycemia and reduces islet fibrosis in Goto-Kakizaki rat, a spontaneous type 2 diabetic animal model

The Goto-Kakizaki (GK) rat is a spontaneous type 2 diabetic animal model, which is characterized by a progressive loss of beta islet cells with fibrosis. In the present study, the hypoglycemic effect of asiatic acid (AA) in GK rats was examined. GK rats receiving AA at a daily dose of 25 mg·kg(-1) for four weeks showed a significant reduction in blood glucose levels. Age-matched normal Wistar rats were given 0.5% sodium carboxymethyl cellulose (CMC-Na) solution for the same periods and used as control. Compared to the normal Wistar rats, GK rats treated with AA showed improvement in insulin resistance partially through decreasing glucose level (P < 0.01) and insulin level (P < 0.05). Furthermore, the results of immunohistochemistry indicate that AA treatment reduced islet fibrosis in GK rats. Fibronectin, a key protein related to islet fibrosis, was over-expressed in GK rats, which was reversed significantly by AA treatment (P < 0.05). These findings suggest that AA has a beneficial effect on lowering blood glucose levels in GK rats and improves fibrosis of islets in diabetes, which may play a role in the prevention of islets dysfunction.

SIRT1 reduction causes renal and retinal injury in diabetes through endothelin 1 and transforming growth factor β1

In diabetes, hyperglycaemia causes up-regulation of endothelin 1 (ET-1) and transforming growth factor beta 1 (TGF-β1). Previously we showed glucose reduces sirtuin1 (SIRT1), a class III histone deacetylase. Here, we investigated the regulatory role of SIRT1 on ET-1 and TGF-β1 expression. Human microvascular endothelial cells were examined following incubation with 25 mmol/l glucose (HG) and 5 mmol/l glucose (NG) with or without SIRT1 or histone acetylase p300 overexpression or knockdown. mRNA expressions of ET-1, TGF-β1, SIRT1, p300 and collagen 1α(I) were examined. SIRT1 enzyme activity, ET-1 and TGF-β1 protein levels were measured. Histone acetylation and endothelial permeability were further investigated. Similar analyses were performed in the kidneys and retinas of SIRT1 overexpressing transgenic mice with or without streptozotocin induced diabetes. Renal functions were evaluated. In the endothelial cells (ECs), HG caused increased permeability and escalated production of ET-1, TGF-β1, collagen Iα(I). These cells also showed increased p300 expression, histone acetylation and reduced SIRT1 levels. These changes were rectified in the ECs following p300 silencing or by SIRT1 overexpression, whereas SIRT1 knockdown or p300 overexpression in NG mimicked the effects of HG. High ET-1 and TGF-β1 levels were seen in the kidneys and retinas of diabetic mice along with micro-albuminuria and increased fibronectin protein (marker of glucose-induced cell injury) levels. Interestingly, these detrimental changes were blunted in SIRT1 overexpressing transgenic mice with diabetes. This study showed a novel SIRT1 mediated protection against renal and retinal injury in diabetes, regulated through p300, ET-1 and TGF-β1.

Sweet taste receptor signaling network: possible implication for cognitive functioning

Sweet taste receptors are transmembrane protein network specialized in the transmission of information from special "sweet" molecules into the intracellular domain. These receptors can sense the taste of a range of molecules and transmit the information downstream to several acceptors, modulate cell specific functions and metabolism, and mediate cell-to-cell coupling through paracrine mechanism. Recent reports indicate that sweet taste receptors are widely distributed in the body and serves specific function relative to their localization. Due to their pleiotropic signaling properties and multisubstrate ligand affinity, sweet taste receptors are able to cooperatively bind multiple substances and mediate signaling by other receptors. Based on increasing evidence about the role of these receptors in the initiation and control of absorption and metabolism, and the pivotal role of metabolic (glucose) regulation in the central nervous system functioning, we propose a possible implication of sweet taste receptor signaling in modulating cognitive functioning.

miR-195 regulates SIRT1-mediated changes in diabetic retinopathy

AIMS/HYPOTHESIS

Endothelial cell (EC) damage is a key mechanism causing retinal microvascular injury in diabetes. Several microRNAs (miRNAs) have been found to regulate sirtuin 1 (SIRT1, which is involved in regulation of the cell cycle, survival and metabolism) in various tissues and disease states, but no studies have been conducted on the role of miRNA in regulation of SIRT1 in diabetic retinopathy. Here we investigated the effect of miRNA-195 (miR-195), a SIRT1-targeting miRNA, on the development of diabetes-induced changes in ECs and retina.

METHODS

The level of miR-195 was measured in human retinal and dermal microvascular ECs (HRECs, HMECs) following exposure to 25 mmol/l glucose (high glucose, HG) and 5 mmol/l glucose (normal glucose, NG). SIRT1 and fibronectin levels were examined following transfection with miR-195 mimic or antagomir or forced expression of SIRT1. Retinal tissues from diabetic rats were similarly studied following intravitreal injection of an miR-195 antagomir or mimic. In situ hybridisation was used to localise retinal miR-195.

RESULTS

HG caused increased miR-195 levels and decreased SIRT1 expression (compared with NG) in both HRECs and HMECs. Transfection with miR-195 antagomir and forced expression of SIRT1 prevented such changes, whereas transfection with miR-195 mimic produced HG-like effects. A luciferase assay confirmed the binding of miR-195 to the 3' untranslated region of SIRT1. miR-195 expression was upregulated in retinas of diabetic rats and intravitreal injection of miR-195 antagomir ameliorated levels of SIRT1.

CONCLUSIONS/INTERPRETATION

These studies identified a novel mechanism whereby miR-195 regulates SIRT1-mediated tissue damage in diabetic retinopathy.

Endothelin-1 induces connective tissue growth factor expression in human lung fibroblasts by ETAR-dependent JNK/AP-1 pathway

Endothelin-1 (ET-1) acts as a key mediator of vasoconstriction and tissue repair. Overproduction of connective tissue growth factor (CTGF) underlies the development of lung fibrosis. ET-1 induces expression of matrix-associated genes in lung fibroblasts, however, little is known about the signaling pathway of CTGF expression caused by ET-1. In this study, we found that ET-1 caused concentration- and time-dependently increases in CTGF expression in human embryonic lung fibroblast cell line (WI-38). ET-1-induced CTGF expression was inhibited by BQ123 (ETAR antagonist), but not BQ788 (ETBR antagonist). Moreover, ET-1-induced CTGF expression was significantly reduced by JNK inhibitor (SP600125), the dominant-negative mutants of JNK1/2 (JNK1/2 DN), and AP-1 inhibitor (curcumin). ET-1 induced phosphorylations of JNK and c-Jun in time-dependent manners. AP-1 luciferase activity was concentration-dependently increased by ET-1, and this effect was attenuated by SP600125. We also found that ET-1-induced CTGF expression was most controlled by the AP-1 binding region of CTGF promoter. ET-1-indiced CTGF luciferase activity was predominately controlled by the sequence -747 to -408 bp upstream of the transcription start site on the human CTGF promoter. Furthermore, ET-1 caused the formation of AP-1-specific DNA-protein complex and the recruitment of c-Jun to the CTGF promoter. Moreover, we found that ET-1 induced α-smooth muscle actin (α-SMA) expression, which was inhibited by BQ123, SP600125, curcumin, and anti-CTGF antibody. These results suggest that ET-1 stimulates expressions of CTGF and α-SMA through ETAR/JNK/AP-1 signaling pathway, and CTGF is required for ET-1-induced α-SMA expression in human lung fibroblasts.

Cardiac miR-133a overexpression prevents early cardiac fibrosis in diabetes

Diabetic cardiomyopathy is a cascade of complex events leading to eventual failure of the heart and cardiac fibrosis being considered as one of its major causes. miR-133a is one of the most abundantly expressed microRNAs in the heart. We investigated the role of miR-133a during severe hyperglycaemia. And, our aim was to find out what role miR-133a plays during diabetes-induced cardiac fibrosis. We saw a drastic decrease in miR-133a expression in the hearts of streptozotocin-induced diabetic animals, as measured by RT-qPCR. This decrease was accompanied by an increase in the transcriptional co-activator EP300 mRNA and major markers of fibrosis [transforming growth factor-β1, connective tissue growth factor, fibronectin (FN1) and COL4A1]; in addition, focal cardiac fibrosis assessed by Masson's trichome stain was increased. Interestingly, in diabetic mice with cardiac-specific miR-133aa overexpression, cardiac fibrosis was significantly decreased, as observed by RT-qPCR and immunoblotting of COL4A1, ELISA for FN1 and microscopic examination. Furthermore, Cardiac miR-133a overexpression prevented ERK1/2 and SMAD-2 phosphorylation. These findings show that miR-133a could be a potential therapeutic target for diabetes-induced cardiac fibrosis and related cardiac dysfunction.

O-GlcNAcylation involvement in high glucose-induced cardiac hypertrophy via ERK1/2 and cyclin D2

Continuous hyperglycemia is considered to be the most significant pathogenesis of diabetic cardiomyopathy, which manifests as cardiac hypertrophy and subsequent heart failure. O-GlcNAcylation has attracted attention as a post-translational protein modification in the past decade. The role of O-GlcNAcylation in high glucose-induced cardiomyocyte hypertrophy remains unclear. We studied the effect of O-GlcNAcylation on neonatal rat cardiomyocytes that were exposed to high glucose and myocardium in diabetic rats induced by streptozocin. High glucose (30 mM) incubation induced a greater than twofold increase in cell size and increased hypertrophy marker gene expression accompanied by elevated O-GlcNAcylation protein levels. High glucose increased ERK1/2 but not p38 MAPK or JNK activity, and cyclin D2 expression was also increased. PUGNAc, an inhibitor of β-N-acetylglucosaminidase, enhanced O-GlcNAcylation and imitated the effects of high glucose. OGT siRNA and ERK1/2 inhibition with PD98059 treatment blunted the hypertrophic response and cyclin D2 upregulation. OGT inhibition also prevented ERK1/2 activation. We also observed concentric hypertrophy and similar changes of O-GlcNAcylation level, ERK1/2 activation and cyclin D2 expression in myocardium of diabetic rats induced by streptozocin. In conclusion, O-GlcNAcylation plays a role in high glucose-induced cardiac hypertrophy via ERK1/2 and cyclin D2.

KH902 suppresses high glucose-induced migration and sprouting of human retinal endothelial cells by blocking VEGF and PIGF

AIMS

Vascular endothelial growth factor (VEGF) and placental growth factor (PlGF) are upregulated in many ocular neovascular diseases such as diabetic retinopathy (DR). KH902 is a recombinant fusion protein with its binding ligand taken from the domains of VEGF receptor-1 (VEGFR-1) and VEGF receptor-2 (VEGFR-2) and can bind all VEGF-A isoforms and PlGF. The aim of this study was to investigate the underlying mechanisms of anti-angiogenic effects of KH902.

METHODS

The toxic effect of KH902 on cultured human retinal endothelial cells (HRECs) was measured by Annexin V/PI staining and MTT assay. The concentrations of secreted VEGF and PlGF were measured by ELISA. The migration of HRECs was assessed by scratch wound and transwell assay. The sprouting of HRECs was determined by tube formation assay. The protein levels of Src, p-Src, PI3K, Akt1, p-Akt1, Erk1/2 and p-Erk1/2 were measured by Western blot.

RESULTS

KH902 at the concentrations from 100 ng/ml to 100 µg/ml had no cytotoxicity to cultured HRECs. KH902 bound not only VEGF165, but also PlGF that were secreted by HRECs under high glucose condition. A 500 ng/ml of KH902 significantly suppressed high glucose-induced migration and sprouting of HRECs through downregulating the expression of PI3K and inhibiting the activation of Src, Akt1 and Erk1/2.

CONCLUSION

Our study indicates that KH902 suppresses high glucose-induced migration and sprouting of HRECs through not only binding VEGF, but also PlGF to inhibit the activation of Src-Akt1-Erk1/2 pathway. KH902 is a drug that potentially inhibits angiogenic pathways involving in DR or other ocular neovascular diseases.

miR-320 Regulates Glucose-Induced Gene Expression in Diabetes

miRNAs play an important role in several biological processes. Here, we investigated miR-320 in glucose-induced augmented production of vasoactive factors and extracellular matrix (ECM) proteins. High glucose exposure decreased the expression of microRNA 320 (miR-320) but increased the expression of endothelin 1 (ET-1), vascular endothelial growth factor (VEGF), and fibronectin (FN) in human umbilical vein endothelial cells (HUVECs). Transfection of miR-320 mimics restored ET-1, VEGF and FN mRNA, and protein expression in HUVECs treated with high glucose. Furthermore, miR-320 mimic transfection reduced glucose-induced augmented production of ERK1/2. Data from this study indicates that miR-320 negatively regulates expression of ET-1, VEGF, and FN through ERK 1/2. Identification of such novel glucose-induced mechanism regulating gene expression may offer a new strategy for the treatment of diabetic complications.

Renal, retinal and cardiac changes in type 2 diabetes are attenuated by macitentan, a dual endothelin receptor antagonist

AIMS

Diabetes is known to cause alteration of the endothelin (ET) system. We have previously demonstrated that ETs regulate augmented production of extracellular matrix proteins causing structural alterations in type 1 diabetes. Here we investigated the effects of macitentan, an orally-active, tissue-targeting dual ET receptor antagonist on chronic complications in type 2 diabetes.

MAIN METHODS

db/db mice and their age- and sex-matched controls were examined after 2 and 4 months of diabetes. Groups of diabetic animals were treated with oral macitentan (25mg/kg/day). The animals were monitored with respect to body weight and blood glucose. Urine analyses were performed for albumin. Cardiac hemodynamic studies were carried out. Renal, cardiac and retinal tissues were analyzed for ET-1, transforming growth factor-β1 (TGF-β1), vascular endothelial growth factor (VEGF), fibronectin (FN), extradomain B containing FN (EDB(+)FN) and collagen α-I (IV) mRNA. Cardiac atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were measured. Protein expressions were measured by ELISA and Western blot. Microscopic analyses were performed in the kidneys.

KEY FINDINGS

Diabetic animals showed hyperglycemia, increased urinary albumin and augmented serum creatinine levels. Diabetes caused increased renal, cardiac and retinal ET-1, TGF-β1, VEGF, FN, EDB(+)FN, collagen α-I(IV) mRNA expression along with increased FN and collagen protein and NF-κB activation. Diabetic mice also demonstrated mesangial expansion, cardiac dysfunction and increased expression of ANP and BNP. Treatment with macitentan attenuated such abnormalities.

SIGNIFICANCE

These experiments confirmed that ET system plays a significant role in the pathogenesis of chronic complications in type 2 diabetes. Such diabetes induced changes can be reduced macitentan therapy.

miR-146a-Mediated extracellular matrix protein production in chronic diabetes complications

OBJECTIVE

MicroRNAs (miRNAs), through transcriptional regulation, modulate several cellular processes. In diabetes, increased extracellular matrix protein fibronectin (FN) production is known to occur through histone acetylator p300. Here, we investigated the role of miR-146a, an FN-targeting miRNA, on FN production in diabetes and its relationship with p300.

RESEARCH DESIGN AND METHODS

miR-146a expressions were measured in endothelial cells from large vessels and retinal microvessels in various glucose levels. FN messenger RNA expression and protein levels with or without miR-146a mimic or antagomir transfection were examined. A luciferase assay was performed to detect miR-146a's binding to FN 3'-untranslated region (UTR). Likewise, retinas from type 1 diabetic rats were studied with or without an intravitreal injection of miR-146a mimic. In situ hybridization was used to localize retinal miR-146a. Cardiac and renal tissues were analyzed from type 1 and type 2 diabetic animals.

RESULTS

A total of 25 mmol/L glucose decreased miR-146a expression and increased FN expression compared with 5 mmol/L glucose in both cell types. miR-146a mimic transfection prevented such change, whereas miR-146a antagomir transfection in the cells in 5 mmol/L glucose caused FN upregulation. A luciferase assay confirmed miR-146a's binding to FN 3'-UTR. miR-146a was localized in the retinal endothelial cells and was decreased in diabetes. Intravitreal miR-146a mimic injection restored retinal miR-146a and decreased FN in diabetes. Additional experiments showed that p300 regulates miR-146a. Similar changes were seen in the retinas, kidneys, and hearts in type 1 and type 2 diabetic animals.

CONCLUSIONS

These studies showed a novel, glucose-induced molecular mechanism in which miR-146a participates in the transcriptional circuitry regulating extracellular matrix protein production in diabetes.

Glucose-induced endothelin-1 expression is regulated by ERK5 in the endothelial cells and retina of diabetic rats

Upregulation of endothelin 1 (ET-1) causing blood flow alteration and increased extracellular matrix production are characteristic features of diabetic angiopathy. Several glucose-induced signaling mechanisms cause ET-1 upregulation in diabetic angiopathy. Extracellular signal-regulated kinase 5 (ERK5) is a member of the MAPK family, which plays a key role in cardiovascular development. ERK kinase (MEK) 5 is the specific MEK for ERK5 activation. In this study we examined the role of glucose-induced ERK5 signaling in mediating ET-1 expression in diabetic angiopathy. We investigated retinas from 1-month STZ-induced diabetic rats and human macro- and microvascular endothelial cells to study ERK5-dependent ET-1 alterations. Glucose (25 mmol/L) caused significant upregulation of ET-1 mRNA and downregulation of ERK5 and Kruppel-like factor 2 (KLF2) after 24 h treatment in the endothelial cells. Simultaneously, phospho-ERK5 proteins were reduced. Activation of ERK5 by constitutively active MEK5 (caMEK5) upregulated KLF2 and suppressed ET-1 expression in both cell lines, whereas ERK5 siRNA transfection resulted in decreased ERK5 and KLF2 and increased ET-1 mRNA expression. In addition, caMEK5 prevented glucose-induced upregulation of ET-1. Furthermore, 1 month of diabetes caused a significant increase in retinal ET-1 mRNA and decrease in ERK5 mRNA expression. These data indicate that ERK5 signaling regulates glucose-induced ET-1 expression in diabetes. The ERK5/ET-1 pathway may provide a potential novel target for the treatment of diabetic angiopathy.

Inflammation determines the pro-adhesive properties of high extracellular d-glucose in human endothelial cells in vitro and rat microvessels in vivo

Background

Hyperglycemia is acknowledged as an independent risk factor for developing diabetes-associated atherosclerosis. At present, most therapeutic approaches are targeted at a tight glycemic control in diabetic patients, although this fails to prevent macrovascular complications of the disease. Indeed, it remains highly controversial whether or not the mere elevation of extracellular D-glucose can directly promote vascular inflammation, which favors early pro-atherosclerotic events.

Methods and Findings

In the present work, increasing extracellular D-glucose from 5.5 to 22 mmol/L was neither sufficient to induce intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression, analyzed by flow cytometry, nor to promote leukocyte adhesion to human umbilical vein endothelial cells (HUVEC) in vitro, measured by flow chamber assays. Interestingly, the elevation of D-glucose levels potentiated ICAM-1 and VCAM-1 expression and leukocyte adhesion induced by a pro-inflammatory stimulus, such as interleukin (IL)-1β (5 ng/mL). In HUVEC, high D-glucose augmented the activation of extracellular signal-regulated kinase 1/2 (ERK 1/2) and nuclear transcription factor-κB (NF-κB) elicited by IL-1β, measured by Western blot and electromobility shift assay (EMSA), respectively, but had no effect by itself. Both ERK 1/2 and NF-κB were necessary for VCAM-1 expression, but not for ICAM-1 expression. In vivo, leukocyte trafficking was evaluated in the rat mesenteric microcirculation by intravital microscopy. In accordance with the in vitro data, the acute intraperitoneal injection of D-glucose increased leukocyte rolling flux, adhesion and migration, but only when IL-1β was co-administered.

Conclusions

These results indicate that the elevation of extracellular D-glucose levels is not sufficient to promote vascular inflammation, and they highlight the pivotal role of a pro-inflammatory environment in diabetes, as a critical factor conditioning the early pro-atherosclerotic actions of hyperglycemia.

Transcriptional coactivator p300 regulates glucose-induced gene expression in endothelial cells

Sustained hyperglycemia in diabetes causes alteration of a large number of transcription factors and mRNA transcripts, leading to tissue damage. We investigated whether p300, a transcriptional coactivator with histone acetyl transferase activity, regulates glucose-induced activation of transcription factors and subsequent upregulation of vasoactive factors and extracellular matrix (ECM) proteins in human umbilical vein endothelial cells (HUVECs). HUVECs were incubated in varied glucose concentrations and were studied after p300 small interfering RNA (siRNA) transfection, p300 overexpression, or incubation with the p300 inhibitor curcumin. Histone H2AX phosphorylation and lysine acetylation were examined for oxidative DNA damage and p300 activation. Screening for transcription factors was performed with the Luminex system. Alterations of selected transcription factors were validated. mRNA expression of p300, endothelin-1 (ET-1), vascular endothelial growth factor (VEGF), and fibronectin (FN) and its splice variant EDB(+)FN and FN protein production were analyzed. HUVECs in 25 mmol/l glucose showed increased p300 production accompanied by increased binding of p300 to ET-1 and FN promoters, augmented histone acetylation, H2AX phosphorylation, activation of multiple transcription factors, and increased mRNA expression of vasoactive factors and ECM proteins. p300 overexpression showed a glucose-like effect on the mRNA expression of ET-1, VEGF, and FN. Furthermore, siRNA-mediated p300 blockade or chemical inhibitor of p300 prevented such glucose-induced changes. Similar mRNA upregulation was also seen in the organ culture of vascular tissues, which was prevented by p300 siRNA transfection. Data from these studies suggest that glucose-induced p300 upregulation is an important upstream epigenetic mechanism regulating gene expression of vasoactive factors and ECM proteins in endothelial cells and is a potential therapeutic target for diabetic complications.

Glucose-induced regulation of novel iron transporters in vascular endothelial cell dysfunction

Increased iron indices have been associated with the development of diabetes and its complications. In the present study, we have investigated the glucose-induced alteration of iron transporters, divalent metal transporter-1 (DMT-1), iron regulated transporter protein-1 (IREG-1), and transferrin receptor (TfR), in endothelial cell iron accumulation and oxidative stress. Cells were exposed to high glucose levels and subjected to gene expression, protein expression, iron measurement and assessment of oxidative stress. Our results show, for the first time, expression of DMT-1 and IREG-1 in vascular endothelial cells. Our data further indicates upregulation of DMT-1 and IREG-1 mRNA and protein in response to high levels of glucose. TfR, however, exhibited a modest decrease in response to high levels of glucose. Increased expression of DMT-1 and IREG-1 was associated with iron accumulation and oxidative stress. Furthermore, our results show differential expression of iron transporters with treatment of high glucose-exposed cells with two different iron chelators. In conclusion, our study suggests that glucose-induced alteration of iron transporters may arbitrate iron accumulation and oxidative stress in endothelial cells.

Leptin and endothelin-1 mediated increased extracellular matrix protein production and cardiomyocyte hypertrophy in diabetic heart disease

BACKGROUND

We investigated the role of leptin and its interaction with endothelin 1 (ET-1) in fibronectin (FN) synthesis and cardiomyocyte hypertrophy, two characteristic features of diabetic cardiomyopathy.

METHODS

Endothelial cells [human umbilical vein endothelial cells (HUVECs)] were examined for FN production and neonatal rat cardiomyocytes for hypertrophy, following incubation with glucose, ET-1, leptin and specific blockers. FN, ET-1, leptin and leptin receptors mRNA expression and FN protein were measured. Myocytes were also morphometrically examined. Furthermore, hearts from streptozotocin-diabetic rats were analysed.

RESULTS

Glucose caused increased FN mRNA and protein expression in HUVECs and cardiomyocytes hypertrophy along with upregulation of ET-1 mRNA, leptin mRNA and protein. Glucosemimetic effects were seen with leptin and ET-1. Leptin receptor antagonist (leptin quadruple mutant) and dual endothelin A endothelin B (ETA/ETB) receptor blocker bosentan normalized such abnormalities. Hearts from the diabetic animals showed hypertrophy and similar mRNA changes.

CONCLUSION

These data indicate that in diabetes increased FN production and cardiomyocyte hypertrophy may be mediated through leptin with its interaction with ET-1.

Involvement of NO and MEK/ERK pathway in enhancement of endothelin-1-induced mesenteric artery contraction in later-stage type 2 diabetic Goto-Kakizaki rat

Endothelin (ET)-1 is a likely candidate for a key role in diabetic vascular complications. However, no abnormalities in the vascular responsiveness to ET-1 have been identified in the chronic stage of type 2 diabetes. Our goal was to look for abnormalities in the roles played by ET receptors (ETA and ETB) in the mesenteric artery of the type 2 diabetic Goto-Kakizaki (GK) rat and to identify the molecular mechanisms involved. Using mesenteric arteries from later-stage (32–38 wk old) individuals, we compared the ET-1-induced contraction and the relaxation induced by the selective ETB receptor agonist IRL1620 between GK rats and control Wistar rats. Mesenteric artery ERK activity and the protein expressions for ET receptors and MEK were also measured. In GK rats (vs. age-matched Wistar rats), we found as follows. 1) The ET-1-induced contraction was greater and was attenuated by BQ-123 (ETA antagonist) but not by BQ-788 (ETB antagonist). In the controls, BQ-788 augmented this contraction. 2) Both the relaxation and nitric oxide (NO) production induced by IRL1620 were reduced. 3) ET-1-induced contraction was enhanced by NG-nitro-l-arginine (l-NNA; NO synthase inhibitor) but suppressed by sodium nitroprusside (NO donor). 4) The enhanced ET-1-induced contraction was reduced by MEK/ERK pathway inhibitors (PD-98059 or U0126). 5) ET-1-stimulated ERK activation was increased, as were the ETA and MEK1/2 protein expressions. 6) Mesenteric ET-1 content was increased. These results suggest that upregulation of ETA, a defect in ETB-mediated NO signaling, and activation of the MEK/ERK pathway together represent a likely mechanism mediating the hyperreactivity to ET-1 examined in this study.

Regulation of cardiomyocyte hypertrophy in diabetes at the transcriptional level

Diabetic cardiomyopathy, structurally characterized by cardiomyocyte hypertrophy and increased extracellular matrix (ECM) protein deposition, eventually leads to heart failure. We investigated the role of transcriptional coactivator p300 and its interaction with myocyte enhancer factor 2 (MEF2) in diabetes-induced cardiomyocyte hypertrophy. Neonatal rat cardiomyocytes were exposed to variable levels of glucose. Cardiomyocytes were analyzed with respect to their size. mRNA expression of p300, MEF2A, MEF2C, atrial natriuretic polypeptide (ANP), brain natriuretic polypeptide (BNP), angiotensinogen (ANG), cAMP-responsive element binding protein-binding protein (CBP), and protein analysis of MEF2 were done with or without p300 blockade. We investigated the hearts of STZ-induced diabetic rats and compared them with age- and sex-matched controls after 1 and 4 mo of followup with or without treatment with p300 blocker curcumin. The results were that cardiomyocytes, exposed to 25 mM glucose for 48 h, showed cellular hypertrophy and augmented mRNA expression of ANP, BNP, and ANG, molecular markers of cardiac hypertrophy. Glucose caused a duration-dependent increase of mRNA and protein expression in MEF2A and MEF2C and transcriptional coactivator p300. Curcumin, a p300 blocker, and p300 siRNA prevented these abnormalities. Similarly, ANP, BNP, and ANG mRNA expression was significantly higher in the hearts of diabetic rats compared with the controls, in association with increased p300, MEF2A, and MEF2C expression. Treatment with p300 blocker curcumin prevented diabetes-induced upregulation of these transcripts. We concluded that data from these studies demonstrate a novel glucose-induced epigenetic mechanism regulating gene expression and cardiomyocyte hypertrophy in diabetes.

Cellular signaling and potential new treatment targets in diabetic retinopathy

Dysfunction and death of microvascular cells and imbalance between the production and the degradation of extracellular matrix (ECM) proteins are a characteristic feature of diabetic retinopathy (DR). Glucose-induced biochemical alterations in the vascular endothelial cells may activate a cascade of signaling pathways leading to increased production of ECM proteins and cellular dysfunction/death. Chronic diabetes leads to the activation of a number of signaling proteins including protein kinase C, protein kinase B, and mitogen-activated protein kinases. These signaling cascades are activated in response to hyperglycemia-induced oxidative stress, polyol pathway, and advanced glycation end product formation among others. The aberrant signaling pathways ultimately lead to activation of transcription factors such as nuclear factor-κB and activating protein-1. The activity of these transcription factors is also regulated by epigenetic mechanisms through transcriptional coactivator p300. These complex signaling pathways may be involved in glucose-induced alterations of endothelial cell phenotype leading to the production of increased ECM proteins and vasoactive effector molecules causing functional and structural changes in the microvasculature. Understanding of such mechanistic pathways will help to develop future adjuvant therapies for diabetic retinopathy.

High glucose suppresses expression of equilibrative nucleoside transporter 1 (ENT1) in rat cardiac fibroblasts through a mechanism dependent on PKC-zeta and MAP kinases

Recently it was demonstrated that the elevated concentration of glucose but not lack of insulin is responsible for suppression of equilibrative nucleoside transporter (ENT1) in diabetic rat cardiac fibroblasts (CFs). The present study was undertaken to determine the signaling pathway utilized by glucose to regulate the expression of ENT1 in the primary culture of rat CFs. Pretreatment of CFs with Go 6983, an isozyme non-selective PKC inhibitor, prevented the high glucose (25 mM) effect on ENT1 mRNA level and nitrobenzylthioinosine (NBTI)-sensitive adenosine uptake. Similar effect was observed with a cell-permeable PKC-zeta pseudosubstrate, whereas Go 6976 a selective inhibitor of Ca(2+)-dependent PKC-alpha and PKC-beta isozymes had little effect on high glucose-induced suppression of ENT1 mRNA level. Incubation of CFs with nitric oxide (NO) donors (SNAPE, SNP) or NO synthase inhibitors (L-NAME, L-NMMA) prior to exposition of CFs to high glucose did not change the glucose effect on ENT1 mRNA level. The high glucose-induced suppression of ENT1 expression was blocked by PD9859 (an inhibitor of MEK), whereas neither wortmannin (an inhibitor of PI3K) nor rapamycin (an inhibitor of mTOR) affected the glucose action on ENT1 transcript level. Highly effective in preventing the high glucose effect on ENT1 mRNA level were GW 5074 (an inhibitor of Raf kinase) and SB 203580 (selective p38 MAPK inhibitor). These findings indicate that high glucose suppresses the expression of ENT1 in CFs by NO independent manner involving the signaling through PKC-zeta, Raf-1, MEK, and p38 MAPK pathways.

Akt activation and augmented fibronectin production in hyperhexosemia

Dysmetabolic state in diabetes may lead to augmented synthesis of extracellular matrix (ECM) proteins. In the endothelial cells, we have previously demonstrated that glucose-induced fibronectin (FN) production and that of its splice variant, EDB(+)FN, is regulated by protein kinase B (PKB, also known as Akt). In this study, we investigated the role of Akt1 in ECM protein production in the organs affected by chronic diabetic complications. We studied Akt1/PKBalpha knockout mice and wild-type control littermates. To avoid confounding effects of systemic insulin, we used 30% galactose feeding to induce hyperhexosemia for 8 wk starting at 6 wk of age. We investigated FN mRNA, EDB(+)FN mRNA, and transforming growth factor (TGF)-beta mRNA expression, Akt phosphorylation, Akt kinase activity, and NF-kappaB and AP-1 activation in the retina, heart, and kidney. Renal and cardiac tissues were histologically examined. Galactose feeding caused significant upregulation of FN, EDB(+)FN, and TGF-beta in all tissues. FN protein levels paralleled mRNA. Such upregulation were prevented in Akt1-deficient galactose-fed mice. Galactose feeding caused ECM protein deposition in the glomeruli and in the myocardium, which was prevented in the Akt knockout mice. NF-kappaB and AP-1 activation was pronounced in galactose-fed wild-type mice and prevented in the galactose-fed Akt1/PKBalpha-deficient group. In the retina and kidney, Ser473 was the predominant site for Akt phosphorylation, whereas in the heart it was Thr308. Parallel experiment in streptozotocin-induced diabetic animals showed similar results. The data from this study indicate that hyperhexosemia-induced Akt/PKB activation may be an important mechanism leading to NF-kappaB and AP-1 activation and increased ECM protein synthesis in the organs affected by chronic diabetic complications.

Role of endothelin-1, sodium hydrogen exchanger-1 and mitogen activated protein kinase (MAPK) activation in glucose-induced cardiomyocyte hypertrophy

BACKGROUND

Cardiac hypertrophy is a key structural feature of diabetic cardiomyopathy. Previous studies have shown that diabetes-induced endothelin-1 (ET-1) and sodium hydrogen exchanger-1 (NHE-1) mediate structural and functional deficits in the heart. In order to gain a mechanistic understanding of the role of ET-1 and NHE-1 in cardiomyocyte hypertrophy, we have utilized an in vitro endothelial-myocyte co-culture system to reveal cellular interactions that may arbitrate cardiomyocyte deficits in diabetes.

METHODS AND RESULTS

Rat ventricular cardiomyocytes were cultured in high glucose levels, which caused cellular hypertrophy. Hypertrophic markers, atrial natruritic peptide (ANP) and angiotensinogen (Agt), as well as inducible nitric oxide synthase (iNOS) were upregulated by high glucose. Treatment of cells with ET antagonist bosentan and NHE-1 inhibitor cariporide prevented glucose-induced cardiomyocyte hypertrophy and expression of ANP, Agt, and iNOS. Bosentan and cariporide treatment of cardiomyocytes co-cultured with endothelial cells produced a more pronounced normalization of glucose-induced changes as compared to cardiomyocyte cultured alone. To further explore the signaling mechanisms involved, we investigated the mitogen activated protein kinase (MAPK) pathway and its cross-interaction with signaling proteins known to be altered in diabetes. Our results indicate that MAPK activation is associated with cardiomyocyte hypertrophy and is inhibited by bosentan, cariporide, as well as protein kinase C inhibiton. Furthermore, MAPK activation was found to be upstream of the transcription factors, nuclear factor-kappaB and activating protein-1.

CONCLUSION

These results demonstrate that ET-1 and NHE-1 may mediate cardiomyocyte hypertrophy via MAPK activation and provide an insight into the pathogenesis of diabetic cardiomyopathy.

Hyperglycemia alters the responsiveness of smooth muscle cells to insulin-like growth factor-I

IGF-I stimulation of smooth muscle cell (SMC) migration and proliferation requires alphaVbeta3 ligand occupancy. We hypothesized that changes in the levels of extracellular matrix proteins induced by alterations in glucose concentrations may regulate the ability of SMCs to respond to IGF-I. IGF-I stimulated migration and proliferation of SMCs that had been maintained in 25 mM glucose containing media, but it had no stimulatory effect when tested using SMCs that had been grown in 5 mM glucose. IGF-I stimulated an increase in Shc phosphorylation and enhanced activation of the MAPK pathway in SMCs grown in 25 mM glucose, whereas in cells maintained in 5 mM glucose, IGF-I had no effect on Shc phosphorylation, and the MAPK response to IGF-I was markedly reduced. In cells grown in 25 mM glucose, the levels of alphaVbeta3 ligands, e.g. osteopontin, vitronectin, and thrombospondin, were all significantly increased, compared with cells grown in 5 mM glucose. The addition of these alphaVbeta3 ligands to SMCs grown in 5 mM glucose was sufficient to permit IGF-I-stimulated Shc phosphorylation and downstream signaling. Because we have shown previously that alphaVbeta3 ligand occupancy is required for IGF-I-stimulated Shc phosphorylation and stimulation of SMC growth, our data are consistent with a model in which 25 mM glucose stimulates increases in the concentrations of these extracellular matrix proteins, thus enhancing alphaVbeta3 ligand occupancy, which leads to increased Shc phosphorylation and enhanced cell migration and proliferation in response to IGF-I.

The interdependence of EGF-R and SGK-1 in fibronectin expression in primary kidney cortical fibroblast cells

BACKGROUND

Epidermal growth factor (EGF) has been shown to play a role in the nephromegaly and enhanced sodium reabsorption observed in diabetic nephropathy. This is recognized to be dependent on activation of serine threonine glucocorticoid kinase-1 (SGK-1). However, the roles of EGF and SGK-1 in renal fibrogenesis observed under high glucose conditions have not been established.

METHODS

Primary cultures of human cortical fibroblasts (CFs) were used as the model in which to study the dependent and independent effects of high glucose, EGF and SGK-1 on the expression of the extracellular matrix protein (ECM) fibronectin. Wild type CFs expressing SGK-1, or cells in which SGK-1 was effectively silenced using siRNA methodology, were exposed to normal (5mM) or high (25mM) glucose, or EGF (10ng/ml) for 48hr and fibronectin assessed. The role of the EGF-receptor and its relationship to SGK-1 signaling was studied using concurrent treatment with PKI166, a specific inhibitor of EGF-receptor.

RESULTS

Exposure of CF to high glucose and EGF increased phosphorylated EGF-R, SGK-1, and fibronectin expression in wild-type cells. Inhibition of the EGF-R reduced SGK-1 and fibronectin expression in control, and following exposure to EGF and high glucose conditions. In cells in which SGK-1 was silenced, fibronectin was reduced and there was no significant increase in pEGF-R, suggesting that SGK-1 is downstream of the EGF-R and negatively inhibits EGF-R activation.

CONCLUSION

These results suggest that high glucose induced fibronectin expression is mediated through the EGF-R and downstream expression of SGK-1.

Effect of magnolol on TGF-beta1 and fibronectin expression in human retinal pigment epithelial cells under diabetic conditions

Magnolol, a natural product isolated from Magnolia officinalis, has various pharmacological effects, such inhibition of effect on inflammation and tumor metastasis, protection against cerebral ischaemic injury, and potent antioxidant activity. In this present study, we evaluated the inhibitory effects of magnolol on transforming growth factor-beta1 (TGF-beta1) and fibronectin expression induced by high concentrations of glucose or S100b (a specific receptor of advance glycation end products ligand) in human retinal pigment epithelial cells (human RPE cells). No effect on cell growth was found with magnolol (up to 20 microg/ml) using a colorimetric 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltertrazolium bromide (MTT) assay. High glucose (25 mM) or S100b (5 microg/ml) induced increases in expression of TGF-beta1 and fibronectin. The increases in TGF-beta1 and fibronectin expression with high glucose or S100b were prevented by magnolol in a dose-dependent manner. Also, magnolol inhibited extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK)/Akt activation. The present study demonstrates that high glucose- or S100b-induced TGF-beta1 and fibronectin expression, but this increased expression is inhibited by magnolol via the ERK/MAPK/Akt signaling pathway in human RPE cells.

Intracellular signaling via ERK/MAPK completes the pathway for tubulogenic fibronectin in MDCK cells

A classic in vitro model of branching morphogenesis utilizes the Madin-Darby canine kidney (MDCK) cell line. MDCK Strain II cells form hollow monoclonal cysts in a three-dimensional collagen matrix over the course of 10 days and tubulate in response to hepatocyte growth factor (HGF). We and our colleagues previously showed that activation of the extracellular-signal regulated kinase (ERK, aka MAPK) pathway is necessary and sufficient to induce tubulogenesis in MDCK cells. We also showed in a microarray study that one of the genes upregulated by HGF was the known tubulogene fibronectin. Given that HGF activates a multitude of signaling pathways, including ERK/MAPK, to test the intracellular regulatory pathway, we used two distinct inhibitors of ERK activation (U0126 and PD098059). Following induction of MDCK Type II cells with HGF, tubulogenic fibronectin mRNA was upregulated fourfold by real-time PCR, and minimal or no change in fibronectin expression was seen when HGF was added with either U0126 or PD098059. We confirmed these results using an MDCK cell line inducible for Raf, which is upstream of ERK. Following activation of Raf, fibronectin mRNA and protein expression were increased to a similar degree as was seen following HGF induction. Furthermore, MDCK Strain I cells, which originate from collecting ducts and have constitutively active ERK, spontaneously initiate tubulogenesis. We show here that MDCK Strain I cells have high levels of fibronectin mRNA and protein compared to MDCK Strain II cells. When U0126 and PD098059 were added to MDCK Strain I cells, fibronectin mRNA, and protein levels were decreased to levels seen in MDCK Strain II cells. These data allow us to complete what we believe is the first description of a tubulogenic pathway from receptor/ligand (HGF/CMET), through an intracellular signaling pathway (ERK/MAPK), to transcription and, finally, secretion of a critical tubuloprotein (fibronectin).

Diabetes-induced extracellular matrix protein expression is mediated by transcription coactivator p300

Increased fibronectin expression is a key feature of diabetic angiopathy. We have previously shown that nuclear factor-kappaB (NF-kappaB) mediates fibronectin expression in endothelial cells and in organs affected by diabetes complications. p300, a transcription coactivator, may regulate NF-kappaB activity via poly(ADP-ribose) polymerase (PARP) activation. Hence, we examined the role of p300 in fibronectin expression in diabetes. High glucose induced fibronectin expression in the endothelial cells, which was associated with increased p300, PARP activity, and NF-kappaB activation. This p300 alteration is mediated by mitogen-activated protein kinase and protein kinase C and B. We then used p300 small interfering RNA (siRNA) and showed decreased fibronectin and PARP expression, as well as NF-kappaB activation, in the endothelial cells. Examination of the heart tissues of streptozotocin-induced diabetic mice revealed increased fibronectin and p300 mRNA. Intravenous injection of p300 siRNA resulted in decreased p300 levels and normalized fibronectin expression in the heart. We further investigated retinal tissues from streptozotocin-induced diabetic rats treated with intravitreal p300 siRNA injection. Similar to the heart, p300 siRNA inhibited fibronectin expression in the retina of the diabetic animals. These results indicate that transcriptional coactivator p300 may regulate fibronectin expression via PARP and NF-kappaB activation in diabetes.

Islet inflammation and fibrosis in a spontaneous model of type 2 diabetes, the GK rat

The molecular pathways leading to islet fibrosis in diabetes are unknown. Therefore, we studied gene expression in islets of 4-month-old Goto-Kakizaki (GK) and Wistar control rats. Of 71 genes found to be overexpressed in GK islets, 24% belong to extracellular matrix (ECM)/cell adhesion and 34% to inflammatory/immune response families. Based on gene data, we selected several antibodies to study fibrosis development during progression of hyperglycemia by immunohistochemistry. One-month-old GK and Wistar islets appeared to be similar. Two-month-old GK islets were strongly heterogenous in terms of ECM accumulation compared with Wistar islets. GK islet vascularization, labeled by von Willebrand factor, was altered after 1 month of mild hyperglycemia. Numerous macrophages (major histocompatibility complex class II(+) and CD68(+)) and granulocytes were found in/around GK islets. These data demonstrate that marked inflammatory reaction accompanies GK islet fibrosis and suggest that islet alterations in this nonobese model of type 2 diabetes develop in a way reminiscent of microangiopathy.

Notoginsenoside R1 inhibits TNF-alpha-induced fibronectin production in smooth muscle cells via the ROS/ERK pathway

The matrix fibronectin protein plays an important role in vascular remodeling. Notoginsenoside R1 is the main ingredient with cardiovascular activity in Panax notoginseng; however, its molecular mechanisms are poorly understood. We report that notoginsenoside R1 significantly decreased TNF-alpha-induced activation of fibronectin mRNA, protein levels, and secretion in human arterial smooth muscle cells (HASMCs) in a dose-dependent manner. Notoginsenoside R1 scavenged hydrogen peroxide (H2O2) in a dose-dependent manner in the test tube. TNF-alpha significantly increased intracellular ROS generation and then ERK activation, which was blocked by notoginsenoside R1 or DPI and apocynin, inhibitors of NADPH oxidase, or the antioxidant NAC. Our data demonstrated that TNF-alpha-induced upregulation of fibronectin mRNA and protein levels occurs via activation of ROS/ERK, which was prevented by treatment with notoginsenoside R1, DPI, apocynin, NAC, or MAPK/ERK inhibitors PD098059 and U0126. Notoginsenoside R1 significantly inhibited H2O2-induced upregulation of fibronectin mRNA and protein levels and secretion; it also significantly inhibited TNF-alpha and H2O2-induced migration. These results suggest that notoginsenoside R1 inhibits TNF-alpha-induced ERK activation and subsequent fibronectin overexpression and migration in HASMCs by suppressing NADPH oxidase-mediated ROS generation and directly scavenging ROS.

Endothelial antioxidant actions of dihydropyridines and angiotensin converting enzyme inhibitors

Dihydropyridines and angiotensin converting enzyme inhibitor effects on superoxide and nitric oxide (NO) were compared in high glucose (20 mM, 24 h)-treated human Ea.hy 926 endothelial cells. High glucose stimulated superoxide both extracellularly (lucigenin chemiluminescence, cytochrome c reduction) and intracellularly (dihydrorhodamine 123 fluorescence). The dihydropyridines amlodipine, nisoldipine, BayK 8644 or the angiotensin converting enzyme inhibitors captopril and enalaprilat attenuated extra- and intracellular superoxide formation; nifedipine blocked extracellular increases only, ramiprilat was without antioxidant effect. Dihydropyridines and captopril also prevented NADPH-driven superoxide release. Antioxidant actions were blunted by a bradykinin B(2) receptor antagonist or an inhibitor of p38 mitogen activated protein kinase (MAPK), and were accompanied by improved NO release (amperometric sensor). p38MAPK inhibition prevented the NO-sparing actions of dihydropyridines but not angiotensin converting enzyme inhibitors. Thus, dihydropyridines and angiotensin converting enzyme inhibitors limit high glucose-induced superoxide formation and improve NO bioavailability in human endothelial cells, in part via bradykinin and p38MAPK.

Vascular endothelial dysfunction in diabetic cardiomyopathy: pathogenesis and potential treatment targets

Cardiovascular complications account for significant morbidity and mortality in the diabetic population. Diabetic cardiomyopathy, a prominent cardiovascular complication, has been recognized as a microvascular disease that may lead to heart failure. Pathogenesis of diabetic cardiomyopathy involves vascular endothelial cell dysfunction, as well as myocyte necrosis. Clinical trials have identified hyperglycemia as the key determinant in the development of chronic diabetic complications. Sustained hyperglycemia induces several biochemical changes including increased non-enzymatic glycation, sorbitol-myoinositol-mediated changes, redox potential alterations, and protein kinase C (PKC) activation, all of which have been implicated in diabetic cardiomyopathy. Other contributing metabolic abnormalities may include defective glucose transport, increased myocyte fatty acid uptake, and dysmetabolism. These biochemical changes manifest as hemodynamic alterations and structural changes that include capillary basement membrane (BM) thickening, interstitial fibrosis, and myocyte hypertrophy and necrosis. Diabetes-mediated biochemical anomalies show cross-interaction and complex interplay culminating in the activation of several intracellular signaling molecules. Studies in both animal and human diabetes have shown alteration of several factors including vasoactive molecules that may be instrumental in mediating structural and functional deficits at both the early and the late stages of the disease. In this review, we will highlight some of the important vascular changes leading to diabetic cardiomyopathy and discuss the emerging potential therapeutic interventions.

Glucose-induced Akt1 activation mediates fibronectin synthesis in endothelial cells

AIMS/HYPOTHESIS

Increased expression and decreased degradation of extracellular matrix (ECM) proteins are key features of chronic diabetic complications. Fibronectin, a predominant ECM protein, has been shown to be overexpressed in all target organs of diabetic complications and in endothelial cells cultured in high levels of glucose. The present study was designed to elucidate the role of protein kinase B (Akt/PKB) in glucose-induced fibronectin mRNA expression and protein production in vascular endothelial cells.

METHODS

Human umbilical vein endothelial cells were cultured in the presence of high glucose to study Akt/PKB activation. The upstream and downstream mediators in the Akt/PKB pathway were also investigated using dominant negative transfections and specific inhibitors of signalling pathways. Cells were subjected to real time RT-PCR, western blotting, and confocal microscopy to assess Akt1/PKBalpha activation and fibronectin mRNA expression and protein production. To detect transcription factor activation, electrophoretic mobility shift assay was carried out.

RESULTS

Our data demonstrate that fibronectin mRNA expression and protein production that are induced by high glucose are mediated via activation of Akt/PKB, which is modulated by mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and protein kinase C. Glucose-induced fibronectin mRNA expression and protein production are also mediated by Akt1/PKBalpha-dependent activation of the transcription factors nuclear factor-kappaB and activating protein-1.

CONCLUSIONS/INTERPRETATION

Our study provides insight into the mechanical basis of glucose-induced increases in fibronectin mRNA expression and protein production. High levels of glucose may increase fibronectin mRNA expression and protein production by activating Akt/PKB.

Proinflammatory effects of LIGHT through HVEM and LTbetaR interactions in cultured human umbilical vein endothelial cells

Members of the tumor necrosis factor (TNF) receptor (TNFR) superfamily are known to be potent mediators of immune responses. LIGHT is a member of the TNF superfamily, and its receptors have been identified as lymphotoxin beta receptor (LTbetaR), herpes virus entry mediator (HVEM), and decoy receptor 3 (DcR3). LIGHT can induce either cell death and/or NF-kappaB activation via its interaction with LTbetaR and/or HVEM. In this study, we investigated the effects of LIGHT in human umbilical vein endothelial cells (HUVECs). We demonstrated that both LTbetaR and HVEM, but not DcR3, are present in HUVECs, and LIGHT can induce the secretion of chemokines (IL-8 and GRO-alpha), cell surface expression of adhesion molecules (ICAM-1 and VCAM-1), PGI2 release, and COX-2 expression. However, the LIGHT mutein, LIGHT-R228E, which has been shown to exhibit binding specificity to LTbetaR, could not induce the secretion of GRO-alpha, PGI2, or the expression of COX-2. These results indicate that both LTbetaR and HVEM can discriminatively mediate the expression of different genes in HUVECs, and suggest that LIGHT is a proinflammatory cytokine.

Glucose-induced serum- and glucocorticoid-regulated kinase activation in oncofetal fibronectin expression

Preferential expression of oncofetal extra domain-B fibronectin (EDB(+) FN), a proposed angiogenic marker, has been shown in proliferative diabetic retinopathy. High levels of glucose also increase EDB(+) FN expression in endothelial cells (ECs) via transforming growth factor-beta1 (TGF-beta1) and endothelin-1 (ET-1). The present study was aimed at elucidating the role of serum- and glucocorticoid-regulated kinase (SGK-1) in glucose-induced EDB(+) FN expression. Using human macro- and microvascular ECs, we show that high levels of glucose, TGF-beta1, and ET-1 increase the EDB(+) FN expression via SGK-1 alteration at the mRNA, protein, and activity levels. Inhibition of TGF-beta1 and ET-1 prevented glucose-induced SGK-1 activation and the EDB(+) FN expression. Furthermore, using siRNA-mediated SGK-1 gene silencing, we show that glucose-induced EDB(+) FN expression can be completely prevented. These findings provide first evidence of glucose-induced SGK-1 activation in altered EDB(+) FN expression and provide novel avenues for therapeutic modalities.