Diabetes-related changes in cAMP response element-binding protein content enhance smooth muscle cell proliferation and migration

Exploring Rosiglitazone's Potential to Treat Alzheimer's Disease through the Modulation of Brain-Derived Neurotrophic Factor

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that debilitates over 55 million individuals worldwide. Currently, treatments manage and alleviate its symptoms; however, there is still a need to find a therapy that prevents or halts disease progression. Since AD has been labeled as "type 3 diabetes" due to its similarity in pathological hallmarks, molecular pathways, and comorbidity with type 2 diabetes mellitus (T2DM), there is growing interest in using anti-diabetic drugs for its treatment. Rosiglitazone (RSG) is a peroxisome proliferator-activated receptor-gamma agonist that reduces hyperglycemia and hyperinsulinemia and improves insulin signaling. In cellular and rodent models of T2DM-associated cognitive decline and AD, RSG has been reported to improve cognitive impairment and reverse AD-like pathology; however, results from human clinical trials remain consistently unsuccessful. RSG has also been reported to modulate the expression of brain-derived neurotrophic factor (BDNF), a protein that regulates neuroplasticity and energy homeostasis and is implicated in both AD and T2DM. The present review investigates RSG's limitations and potential therapeutic benefits in pre-clinical models of AD through its modulation of BDNF expression.

Mulberry-Derived 1-Deoxynojirimycin Prevents Type 2 Diabetes Mellitus Progression via Modulation of Retinol-Binding Protein 4 and Haptoglobin

Pre-diabetic or early-stage type 2 diabetes patients may develop an adverse diabetic progression, leading to several complications and increasing hospitalization rates. Mulberry leaves, which contain 1-deoxynojirimycin (DNJ), have been used as a complementary medicine for diabetes prevention and treatment. Our recent study demonstrated that mulberry leaf powder with 12 mg of DNJ improves postprandial hyperglycemia, fasting plasma glucose, and glycated hemoglobin. However, the detailed mechanisms are still unknown. This study investigates the effect of long-term (12-week) supplementation of mulberry leaves in obese people with prediabetes and patients with early-stage type 2 diabetes. Participants’ blood was collected before and after supplementation. The protein profile of the plasma was examined by proteomics. In addition, the mitochondrial function was evaluated by energetic and homeostatic markers using immunoelectron microscopy. The proteomics results showed that, from a total of 1291 proteins, 32 proteins were related to diabetes pathogenesis. Retinol-binding protein 4 and haptoglobin protein were downregulated, which are associated with insulin resistance and inflammation, respectively. For mitochondrial function, the haloacid dehalogenase-like hydrolase domain-containing protein 3 (HDHD-3) and dynamin-related protein 1 (Drp-1) displayed a significant increment in the after treatment group. In summary, administration of mulberry leaf powder extract in prediabetes and the early stage of diabetes can alleviate insulin resistance and inflammation and promote mitochondrial function in terms of energy production and fission.

Capsaicin and Zinc Promote Glucose Uptake in C2C12 Skeletal Muscle Cells through a Common Calcium Signalling Pathway

Capsaicin and zinc have recently been highlighted as potential treatments for glucose metabolism disorders; however, the effect of these two natural compounds on signalling pathways involved in glucose metabolism is still uncertain. In this study, we assessed the capsaicin- or zinc- induced activation of signalling molecules including calcium/calmodulin-dependent protein kinase 2 (CAMKK2), cAMP-response element-binding protein (CREB), and target of rapamycin kinase complex 1 (TORC1). Moreover, the expression status of genes associated with the control of glucose metabolism was measured in treated cells. The activation of cell signalling proteins was then evaluated in capsaicin- or zinc treated cells in the presence or absence of cell-permeant calcium chelator (BAPTA-AM) and the CAMKK inhibitor (STO-609). Finally, capsaicin- and zinc-induced glucose uptake was measured in the cells pre-treated with or without BAPTA-AM. Our results indicate that calcium flux induced by capsaicin or zinc led to activation of calcium signalling molecules and promoting glucose uptake in skeletal muscle cells. Pharmacological inhibition of CAMKK diminished activation of signalling molecules. Moreover, we observed an increase in intracellular cAMP levels in the cells after treatment with capsaicin and zinc. Our data show that capsaicin and zinc mediate glucose uptake in C2C12 skeletal muscle cells through the activation of calcium signalling.

Insulin-Induced Cardiomyocytes Hypertrophy That Is Prevented by Taurine via β-alanine-Sensitive Na+-Taurine Symporter

Although insulin-induced cardiac hypertrophy is reported, very little information is available on the hypertrophic effect of insulin on ventricular cardiomyocytes and the regulation of sodium and calcium homeostasis. Taurine is a non-essential amino acid synthesized by cardiomyocytes and the brain and is present in low quantities in many foods, particularly seafood. The purpose of this study was to investigate whether chronic exposure to insulin induces hypertrophy of ventricular cardiomyocytes that are associated with changes in Na⁺ and Ca²⁺ homeostasis and whether taurine pre-treatment prevents these effects. Our results showed that chronic treatment with insulin leads to cardiomyocyte hypertrophy that is associated with an increase in basal intracellular Na⁺ and Ca²⁺ levels. Furthermore, long-term taurine treatment prevents morphological and ionic remodeling induced by insulin. In addition, blocking the Na⁺-taurine co-transporter prevented the taurine antihypertrophic effect. Finally, the insulin-induced remodeling of cardiomyocytes was associated with a decrease in the ratio of phospho-CREB (pCREB) to total cAMP response element binding protein (CREB); taurine prevented this effect. In conclusion, our results show that insulin induces ventricular cardiomyocyte hypertrophy via downregulation of the pCREB/tCREB level and that chronic taurine treatment prevents this effect.

Huang-Pu-Tong-Qiao Formula Ameliorates the Hippocampus Apoptosis in Diabetic Cognitive Dysfunction Mice by Activating CREB/BDNF/TrkB Signaling Pathway

Background

Huang-Pu-Tong-Qiao formula (HPTQ), a traditional Chinese medicine (TCM) formula used to improve cognitive impairment. However, the underlying neuroprotective mechanism of HPTQ treated for diabetic cognitive dysfunction (DCD) remains unclear. The purpose of this study was to investigate the neuroprotective mechanism of HPTQ in DCD mice based on molecular docking.

Methods

To investigate the neuroprotective effect of HPTQ in DCD, the Morris water maze (MWM), novel object recognition (NOR) test was used to detect the learning and memory changes of mice; hematoxylin-eosin (HE) staining was used to investigate the damage of hippocampal neurons; the western blot (WB) was used to examine the level of brain-derived neurotrophic factor (BDNF) of hippocampus. To investigate the neuroprotective mechanism of HPTQ in DCD, molecular docking was used to predict the possible target proteins of different active components in HPTQ and then the WB was used to verify the expression of key target proteins in the hippocampus of mice.

Results

HPTQ improved the learning and memory ability, hippocampal neuron damage, and the level of BDNF in the hippocampus of the DCD model treated with HFD/STZ for 12 weeks. Besides, the results of molecular docking showed that the main chemical components of HPTQ could be well combined with the targets of Bcl-2-associated X (Bax) and B-cell lymphoma2 (Bcl-2) and caspase-3. The levels of Bax/Bcl-2 protein ratio and caspase-3 increased in the DCD model while the HPTQ inhibited it. In addition, HPTQ restored DCD-induced decline of p-CREB, BDNF, TrkB, and p-Akt in the hippocampus.

Conclusions

These data indicated that HPTQ ameliorates the hippocampus apoptosis in diabetic cognitive dysfunction mice by activating CREB/BDNF/TrkB signaling pathway.

Ending Restenosis: Inhibition of Vascular Smooth Muscle Cell Proliferation by cAMP

Increased vascular smooth muscle cell (VSMC) proliferation contributes towards restenosis after angioplasty, vein graft intimal thickening and atherogenesis. The second messenger 3′ 5′ cyclic adenosine monophosphate (cAMP) plays an important role in maintaining VSMC quiescence in healthy vessels and repressing VSMC proliferation during resolution of vascular injury. Although the anti-mitogenic properties of cAMP in VSMC have been recognised for many years, it is only recently that we gained a detailed understanding of the underlying signalling mechanisms. Stimuli that elevate cAMP in VSMC inhibit G₁-S phase cell cycle progression by inhibiting expression of cyclins and preventing S-Phase Kinase Associated Protein-2 (Skp2-mediated degradation of cyclin-dependent kinase inhibitors. Early studies implicated inhibition of MAPK signalling, although this does not fully explain the anti-mitogenic effects of cAMP. The cAMP effectors, Protein Kinase A (PKA) and Exchange Protein Activated by cAMP (EPAC) act together to inhibit VSMC proliferation by inducing Cyclic-AMP Response Element Binding protein (CREB) activity and inhibiting members of the RhoGTPases, which results in remodelling of the actin cytoskeleton. Cyclic-AMP induced actin remodelling controls proliferation by modulating the activity of Serum Response Factor (SRF) and TEA Domain Transcription Factors (TEAD), which regulate expression of genes required for proliferation. Here we review recent research characterising these mechanisms, highlighting novel drug targets that may allow the anti-mitogenic properties of cAMP to be harnessed therapeutically to limit restenosis.

Metformin Modulates High Glucose-Incubated Human Umbilical Vein Endothelial Cells Proliferation and Apoptosis Through AMPK/CREB/BDNF Pathway

Cardiovascular disease (CVD) is a leading cause of mortality and morbidity among patients with diabetes. Endothelial dysfunction is an early physiological event in CVD. Metformin, a common oral antihyperglycemic agent, has been demonstrated to directly affect endothelial cell function. Brain-derived neurotrophic factor (BDNF), originally discovered in the brain as a neurotrophin, has also been reported to play a protective role in the cardiovascular system. In our study, we demonstrated that high glucose (HG) reduced cell proliferation and induced cell apoptosis via changes in BDNF expression and that metformin reversed the effects of HG injury by upregulating BDNF expression. Furthermore, we found that cyclic AMP response element binding (CREB) phosphorylation was reduced in HG-treated human umbilical vein endothelial cells (HUVECs), and this effect was reversed by the metformin treatment. However, the metformin effect on BDNF levels in HG-incubated HUVECs was blocked by a CREB inhibitor, which indicated that BDNF expression is regulated by metformin through CREB activation. In addition, we found that adenosine monophosphate-activated protein kinase (AMPK) activation is involved in CREB/BDNF regulation in HG-incubated HUVECs treated with metformin and that an AMPK inhibitor impaired the protective effects of metformin on HG-treated HUVECs. In conclusion, this study demonstrated that metformin affects cell proliferation and apoptosis via the AMPK/CREB/BDNF pathway in HG-incubated HUVECs.

PDGF-BB Carried by Endothelial Cell-Derived Extracellular Vesicles Reduces Vascular Smooth Muscle Cell Apoptosis in Diabetes

Endothelial cell-derived extracellular vesicles (CD31EVs) constitute a new entity for therapeutic/prognostic purposes. The roles of CD31EVs as mediators of vascular smooth muscle cell (VSMC) dysfunction in type 2 diabetes (T2D) are investigated herein. We demonstrated that, unlike serum-derived extracellular vesicles in individuals without diabetes, those in individuals with diabetes (D CD31EVs) boosted apoptosis resistance of VSMCs cultured in hyperglycemic condition. Biochemical analysis revealed that this effect relies on changes in the balance between antiapoptotic and proapoptotic signals: increase of bcl-2 and decrease of bak/bax. D CD31EV cargo analysis demonstrated that D CD31EVs are enriched in membrane-bound platelet-derived growth factor-BB (mbPDGF-BB). Thus, we postulated that mbPDGF-BB transfer by D CD31EVs could account for VSMC resistance to apoptosis. By depleting CD31EVs of platelet-derived growth factor-BB (PDGF-BB) or blocking the PDGF receptor β on VSMCs, we demonstrated that mbPDGF-BB contributes to D CD31EV-mediated bak/bax and bcl-2 levels. Moreover, we found that bak expression is under the control of PDGF-BB-mediated microRNA (miR)-296-5p expression. In fact, while PDGF-BB treatment recapitulated D CD31EV-mediated antiapoptotic program and VSMC resistance to apoptosis, PDGF-BB-depleted CD31EVs failed. D CD31EVs also increased VSMC migration and recruitment to neovessels by means of PDGF-BB. Finally, we found that VSMCs, from human atherosclerotic arteries of individuals with T2D, express low bak/bax and high bcl-2 and miR-296-5p levels. This study identifies the mbPDGF-BB in D CD31EVs as a relevant mediator of diabetes-associated VSMC resistance to apoptosis.

Dual Role of CREB in The Regulation of VSMC Proliferation: Mode of Activation Determines Pro- or Anti-Mitogenic Function

Vascular smooth muscle cell (VSMC) proliferation has been implicated in the development of restenosis after angioplasty, vein graft intimal thickening and atherogenesis. We investigated the mechanisms underlying positive and negative regulation of VSMC proliferation by the transcription factor cyclic AMP response element binding protein (CREB). Incubation with the cAMP elevating stimuli, adenosine, prostacyclin mimetics or low levels of forksolin activated CREB without changing CREB phosphorylation on serine-133 but induced nuclear translocation of the CREB co-factors CRTC-2 and CRTC-3. Overexpression of CRTC-2 or -3 significantly increased CREB activity and inhibited VSMC proliferation, whereas CRTC-2/3 silencing inhibited CREB activity and reversed the anti-mitogenic effects of adenosine A2B receptor agonists. By contrast, stimulation with serum or PDGF_BB significantly increased CREB activity, dependent on increased CREB phosphorylation at serine-133 but not on CRTC-2/3 activation. CREB silencing significantly inhibited basal and PDGF induced proliferation. These data demonstrate that cAMP activation of CREB, which is CRTC2/3 dependent and serine-133 independent, is anti-mitogenic. Growth factor activation of CREB, which is serine-133-dependent and CRTC2/3 independent, is pro-mitogenic. Hence, CREB plays a dual role in the regulation of VSMC proliferation with the mode of activation determining its pro- or anti-mitogenic function.

Prostaglandin E1 Attenuates Pulmonary Artery Remodeling by Activating Phosphorylation of CREB and the PTEN Signaling Pathway

The depletion of cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) and phosphatase and tensin homolog (PTEN) is the critical mediator of pulmonary arterial hypertension (PAH). We hypothesized that the activation of phosphorylated CREB (pCREB) and PTEN could inhibit the AKT signaling pathway to attenuate pulmonary arterial remodeling in rats with monocrotaline-induced PAH. We observed decreased PTEN and pCREB in idiopathic PAH versus control tissue. We reduced PTEN using small interfering RNA in human control pulmonary arterial smooth muscle cells (PASMCs) and observed an increase in pAKT. Consistent with PTEN knockdown in PASMCs, prostaglandin E1 (PGE1) induced pCREB expression to stimulate PTEN protein expression and inhibited pAKT in a time- and dose-dependent manner. The enhanced proliferation and migration of PASMCs following PTEN knockdown were significantly inhibited by PGE1 treatment. The PGE1-induced elevation of PTEN expression in PTEN-depleted PASMCs was decreased by the application of a PKA inhibitor and a CBP-CREB interaction inhibitor. Supplementation with a novel emulsion composition comprising PGE1 in rats with monocrotaline-induced PAH prevented pulmonary arterial remodeling and improved hemodynamics via the induced expression of PTEN. We conclude that PGE1 recruits pCREB/PTEN to decrease the migration and proliferation of PASMCs associated with PAH. This finding elucidates a relevant underlying mechanism of the PGE1/CREB/PTEN signaling pathway to prevent progressive PAH.

Genetic Predictors of Cardiovascular Mortality During Intensive Glycemic Control in Type 2 Diabetes: Findings From the ACCORD Clinical Trial

OBJECTIVE

To identify genetic determinants of increased cardiovascular mortality among subjects with type 2 diabetes who underwent intensive glycemic therapy in the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial.

RESEARCH DESIGN AND METHODS

A total of 6.8 million common variants were analyzed for genome-wide association with cardiovascular mortality among 2,667 self-reported white subjects in the ACCORD intensive treatment arm. Significant loci were examined in the entire ACCORD white genetic dataset (n = 5,360) for their modulation of cardiovascular responses to glycemic treatment assignment and in a Joslin Clinic cohort (n = 422) for their interaction with long-term glycemic control on cardiovascular mortality.

RESULTS

Two loci, at 10q26 and 5q13, attained genome-wide significance as determinants of cardiovascular mortality in the ACCORD intensive arm (P = 9.8 × 10-9 and P = 2 × 10-8, respectively). A genetic risk score (GRS) defined by the two variants was a significant modulator of cardiovascular mortality response to treatment assignment in the entire ACCORD white genetic dataset. Participants with GRS = 0 experienced a fourfold reduction in cardiovascular mortality in response to intensive treatment (hazard ratio [HR] 0.24 [95% CI 0.07-0.86]), those with GRS = 1 experienced no difference (HR 0.92 [95% CI 0.54-1.56]), and those with GRS ≥2 experienced a threefold increase (HR 3.08 [95% CI 1.82-5.21]). The modulatory effect of the GRS on the association between glycemic control and cardiovascular mortality was confirmed in the Joslin cohort (P = 0.029).

CONCLUSIONS

Two genetic variants predict the cardiovascular effects of intensive glycemic control in ACCORD. Further studies are warranted to determine whether these findings can be translated into new strategies to prevent cardiovascular complications of diabetes.

Excitation-Contraction Coupling and Excitation-Transcription Coupling in Blood Vessels: Their Possible Interactions in Hypertensive Vascular Remodeling

Vascular smooth muscle cells (VSMC) display considerable phenotype plasticity which can be studied in vivo on vascular remodeling which occurs during acute or chronic vascular injury. In differentiated cells, which represent contractile phenotype, there are characteristic rapid transient changes of intracellular Ca2+ concentration ([Ca2+]i), while the resting cytosolic [Ca2+]i concentration is low. It is mainly caused by two components of the Ca2+ signaling pathways: Ca2+ entry via L-type voltage-dependent Ca2+ channels and dynamic involvement of intracellular stores. Proliferative VSMC phenotype is characterized by long-lasting [Ca2+]i oscillations accompanied by sustained elevation of basal [Ca2+]i. During the switch from contractile to proliferative phenotype there is a general transition from voltage-dependent Ca2+ entry to voltage-independent Ca2+ entry into the cell. These changes are due to the altered gene expression which is dependent on specific transcription factors activated by various stimuli. It is an open question whether abnormal VSMC phenotype reported in rats with genetic hypertension (such as spontaneously hypertensive rats) might be partially caused by a shift from contractile to proliferative VSMC phenotype.

Targeting mitochondria to restore failed adaptation to exercise in diabetes

Our translational research group focuses on addressing the problem of exercise defects in diabetes with basic research efforts in cell and rodent models and clinical research efforts in subjects with diabetes mellitus. CREB (cAMP-response-element-binding protein) regulates cellular differentiation of neurons, β-cells, adipocytes and smooth muscle cells; it is also a potent survival factor and an upstream regulator of mitochondrial biogenesis. In diabetes and cardiovascular disease, CREB protein content is decreased in the vascular media, and its regulation in aberrant in β-cells, neurons and cardiomyocytes. Loss of CREB content and function leads to decreased vascular target tissue resilience when exposed to stressors such as metabolic, oxidative or sheer stress. This basic research programme set the stage for our central hypothesis that diabetes-mediated CREB dysfunction predisposes the diabetes disease progression and cardiovascular complications. Our clinical research programme revealed that diabetes mellitus leads to defects in functional exercise capacity. Our group has determined that the defects in exercise correlate with insulin resistance, endothelial dysfunction, decreased cardiac perfusion and diastolic dysfunction, slowed muscle perfusion kinetics, decreased muscle perfusion and slowed oxidative phosphorylation. Combined basic and clinical research has defined the relationship between exercise and vascular function with particular emphasis on how the signalling to CREB and eNOS [endothelial NOS (nitric oxide synthase)] regulates tissue perfusion, mitochondrial dynamics, vascular function and exercise capacity. The present review summarizes our current working hypothesis that restoration of eNOS/NOS dysfunction will restore cellular homoeostasis and permit an optimal tissue response to an exercise training intervention.

The role of reactive oxygen species in microvascular remodeling

The microcirculation is a portion of the vascular circulatory system that consists of resistance arteries, arterioles, capillaries and venules. It is the place where gases and nutrients are exchanged between blood and tissues. In addition the microcirculation is the major contributor to blood flow resistance and consequently to regulation of blood pressure. Therefore, structural remodeling of this section of the vascular tree has profound implications on cardiovascular pathophysiology. This review is focused on the role that reactive oxygen species (ROS) play on changing the structural characteristics of vessels within the microcirculation. Particular attention is given to the resistance arteries and the functional pathways that are affected by ROS in these vessels and subsequently induce vascular remodeling. The primary sources of ROS in the microcirculation are identified and the effects of ROS on other microcirculatory remodeling phenomena such as rarefaction and collateralization are briefly reviewed.

Vinpocetine attenuates neointimal hyperplasia in diabetic rat carotid arteries after balloon injury

BACKGROUND

Diabetes exacerbates abnormal vascular smooth muscle cell (VSMC) accumulation in response to arterial wall injury. Vinpocetine has been shown to improve vascular remolding; however, little is known about the direct effects of vinpocetine on vascular complications mediated by diabetes. The objective of this study was to determine the effects of vinpocetine on hyperglycemia-facilitated neointimal hyperplasia and explore its possible mechanism.

MATERIALS AND METHODS

Nondiabetic and diabetic rats were subjected to balloon injury of the carotid artery followed by 3-week treatment with either vinpocetine (10 mg/kg/day) or saline. Morphological analysis and proliferating cell nuclear antigen (PCNA) immunostaining were performed on day 21. Rat VSMCs proliferation was determined with 5-ethynyl-20-deoxyuridine cell proliferation assays. Chemokinesis was monitored with scratch assays, and production of reactive oxygen species (ROS) was assessed using a 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA) flow cytometric assay. Apoptosis was detected by annexin V-FITC/PI flow cytometric assay. Cell signaling was assessed by immunblotting.

RESULTS

Vinpocetine prevented intimal hyperplasia in carotid arteries in both normal (I/M ratio: 93.83 ± 26.45% versus 143.2 ± 38.18%, P<0.05) and diabetic animals (I/M ratio: 120.5 ± 42.55% versus 233.46 ± 33.98%, P<0.05) when compared to saline. The in vitro study demonstrated that vinpocetine significantly inhibited VSMCs proliferation and chemokinesis as well as ROS generation and apoptotic resistance, which was induced by high glucose (HG) treatment. Vinpocetine significantly abolished HG-induced phosphorylation of Akt and JNK1/2 without affecting their total levels. For downstream targets, HG-induced phosphorylation of IκBα was significantly inhibited by vinpocetine. Vinpocetine also attenuated HG-enhanced expression of PCNA, cyclin D1 and Bcl-2.

CONCLUSIONS

Vinpocetine attenuated neointimal formation in diabetic rats and inhibited HG-induced VSMCs proliferation, chemokinesis and apoptotic resistance by preventing ROS activation and affecting MAPK, PI3K/Akt, and NF-κB signaling.

Hyperglycemia enhances function and differentiation of adult rat cardiac fibroblasts

Diabetes is an independent risk factor for cardiovascular disease that can eventually cause cardiomyopathy and heart failure. Cardiac fibroblasts (CF) are the critical mediators of physiological and pathological cardiac remodeling; however, the effects of hyperglycemia on cardiac fibroblast function and differentiation is not well known. Here, we performed a comprehensive investigation on the effects of hyperglycemia on cardiac fibroblasts and show that hyperglycemia enhances cardiac fibroblast function and differentiation. We found that high glucose treatment increased collagen I, III, and VI gene expression in rat adult cardiac fibroblasts. Interestingly, hyperglycemia increased CF migration and proliferation that is augmented by collagen I and III. Surprisingly, we found that short term hyperglycemia transiently inhibited ERK1/2 activation but increased AKT phosphorylation. Finally, high glucose treatment increased spontaneous differentiation of cardiac fibroblasts to myofibroblasts with increasing passage compared with low glucose. Taken together, these findings suggest that hyperglycemia induces cardiac fibrosis by modulating collagen expression, migration, proliferation, and differentiation of cardiac fibroblasts.

The cyclic AMP response element-binding protein (CREB) mediates smooth muscle cell proliferation in response to angiotensin II

The cAMP response element-binding protein (CREB) is a transcription factor that mediates the cellular response to metabolic and mitogenic signals. Whether CREB contributes to vascular function has received little attention, especially in relation to the processes associated with atherosclerotic disease progression and restenosis. This study examined the involvement of CREB in the mitogenic actions of angiotensin II (AngII), a growth factor that promotes neointimal hyperplasia in response to vascular injury. Treatments were performed on quiescent vascular smooth muscle cells (VSMCs) obtained from a porcine explant model. Organ culture was performed on porcine hearts subjected to angioplasty ex vivo. Stimulation of VSMCs with AngII resulted in transient CREB phosphorylation. Proliferation of smooth muscle cells in response to AngII was reduced by 90 % after infection with adenovirus expressing dominant-negative killer CREB (kCREB) mutant. Likewise, expression of kCREB prevented angioplasty-induced neointimal hyperplasia. AngII-induced CREB phosphorylation was independent of cAMP activation. Examination of putative CREB kinases revealed that MSK was responsible for phosphorylating CREB. In addition, inhibition of PKC revealed that this kinase operates upstream and activates MSK. These results indicate that activation of CREB via PKC and MSK is essential for SMC proliferation in response to AngII.

Vascular smooth muscle cell phenotype is defined by Ca2+-dependent transcription factors

Ca(2+) is an important second messenger in vascular smooth muscle cells (VSMCs). Therefore, VSMCs exercise tight control of the intracellular Ca(2+) concentration ([Ca(2+)]i) by expressing a wide repertoire of Ca(2+) channels and transporters. The presence of several pathways for Ca(2+) influx and efflux provides many possibilities for controlling [Ca(2+)]i in a spatial and temporal manner. Intracellular Ca(2+) has a dual role in VSMCs; first, it is necessary for VSMC contraction; and, second, it can activate multiple transcription factors. These factors are cAMP response element-binding protein, nuclear factor of activated T lymphocytes, and serum response factor. Furthermore, it was recently reported that the C-terminus of voltage-dependent L-type Ca(2+) calcium channels can regulate transcription in VSMCs. Transcription regulation in VSMCs modulates the expression patterns of genes, including genes coding for contractile and cytoskeleton proteins, and those promoting proliferation and cell growth. Depending on their gene expression, VSMCs can exist in different functional states or phenotypes. The majority of healthy VSMCs show a contractile phenotype, characterized by high contractile ability and a low proliferative rate. However, VSMCs can undergo phenotypic modulation with different physiological and pathological stimuli, whereby they start to proliferate, migrate, and synthesize excessive extracellular matrix. These events are associated with injury repair and angiogenesis, but also with the development of cardiovascular pathologies, such as atherosclerosis and hypertension. This review discusses the currently known Ca(2+)-dependent transcription factors in VSMCs, their regulation by Ca(2+) signalling, and their role in the VSMC phenotype.

Polymerase delta interacting protein 2 sustains vascular structure and function

OBJECTIVE

On the basis of previous evidence that polymerase delta interacting protein 2 (Poldip2) increases reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4 (Nox4) activity in vascular smooth muscle cells, we hypothesized that in vivo knockdown of Poldip2 would inhibit reactive oxygen species production and alter vascular function.

APPROACH AND RESULTS

Because homozygous Poldip2 deletion is lethal, Poldip2(+/-) mice were used. Poldip2 mRNA and protein levels were reduced by ≈50% in Poldip2(+/-) aorta, with no change in p22phox, Nox1, Nox2, and Nox4 mRNAs. NADPH oxidase activity was also inhibited in Poldip2(+/-) tissue. Isolated aortas from Poldip2(+/-) mice demonstrated impaired phenylephrine and potassium chloride-induced contractions, increased stiffness, and reduced compliance associated with disruption of elastic lamellae and excessive extracellular matrix deposition. Collagen I secretion was elevated in cultured vascular smooth muscle cells from Poldip2(+/-) mice and restored by H2O2 supplementation, suggesting that this novel function of Poldip2 is mediated by reactive oxygen species. Furthermore, Poldip2(+/-) mice were protected against aortic dilatation in a model of experimental aneurysm, an effect consistent with increased collagen secretion.

CONCLUSIONS

Poldip2 knockdown reduces H2O2 production in vivo, leading to increases in extracellular matrix, greater vascular stiffness, and impaired agonist-mediated contraction. Thus, unaltered expression of Poldip2 is necessary for vascular integrity and function.

Impaired response to exercise intervention in the vasculature in metabolic syndrome

Physical activity decreases risk for diabetes and cardiovascular disease morbidity and mortality; however, the specific impact of exercise on the diabetic vasculature is unexamined. We hypothesized that an acute, moderate exercise intervention in diabetic and hypertensive rats would induce mitochondrial biogenesis and mitochondrial antioxidant defence to improve vascular resilience. SHHF/Mcc-fa(cp) lean (hypertensive) and obese (hypertensive, insulin resistant), as well as Sprague Dawley (SD) control rats were run on a treadmill for 8 days. In aortic lysates from SD rats, we observed a significant increase in subunit proteins from oxidative phosphorylation (OxPhos) complexes I-III, with no changes in the lean or obese SHHF rats. Exercise also increased the expression of mitochondrial antioxidant defence uncoupling protein 3 (UCP3) (p < 0.05) in SHHF lean rats, whereas no changes were observed in the SD or SHHF obese rats with exercise. We evaluated upstream signalling pathways for mitochondrial biogenesis, and only peroxisome proliferators-activated receptor gamma coactivator 1α (PGC-1α) significantly decreased in SHHF lean rats (p < 0.05) with exercise. In these experiments, we demonstrate absent mitochondrial induction with exercise exposure in models of chronic vascular disease. These findings suggest that chronic vascular stress results in decreased sensitivity of vasculature to the adaptive mitochondrial responses normally induced by exercise.

Impact of glycemic control on circulating endothelial progenitor cells and arterial stiffness in patients with type 2 diabetes mellitus

BACKGROUND

Patients with type 2 diabetes mellitus (DM) have increased risk of endothelial dysfunction and arterial stiffness. Levels of circulating endothelial progenitor cells (EPCs) are also reduced in hyperglycemic states. However, the relationships between glycemic control, levels of EPCs and arterial stiffness are unknown.

METHODS

We measured circulating EPCs and brachial-ankle pulse wave velocity (baPWV) in 234 patients with type 2 DM and compared them with 121 age- and sex-matched controls.

RESULTS

Patients with DM had significantly lower circulating Log CD34/KDR+ and Log CD133/KDR+ EPC counts, and higher Log baPWV compared with controls (all P < 0.05). Among those 120/234 (51%) of DM patients with satisfactory glycemic control (defined by Hemoglobin A1c, HbA1c < 6.5%), they had significantly higher circulating Log CD34/KDR+ and Log CD133/KDR+ EPC counts, and lower Log baPWV compared with patients with poor glycemic control (all P < 0.05). The circulating levels of Log CD34/KDR+ EPC (r = -0.46, P < 0.001) and Log CD133/KDR+ EPC counts (r = -0.45, P < 0.001) were negatively correlated with Log baPWV. Whilst the level of HbA1c positively correlated with Log baPWV (r = 0.20, P < 0.05) and negatively correlated with circulating levels of Log CD34/KDR+ EPC (r = -0.40, P < 0.001) and Log CD133/KDR+ EPC (r = -0.41, P < 0.001). Multivariate analysis revealed that HbA1c, Log CD34/KDR+ and Log CD133/KDR+ EPC counts were independent predictors of Log baPWV (P < 0.05).

CONCLUSIONS

In patients with type 2 DM, the level of circulating EPCs and arterial stiffness were closely related to their glycemic control. Furthermore, DM patients with satisfactory glycemic control had higher levels of circulating EPCs and were associated with lower arterial stiffness.

Insulin augments tumor necrosis factor-alpha stimulated expression of vascular cell adhesion molecule-1 in vascular endothelial cells

BACKGROUND

Atherosclerosis is an inflammatory disease that is marked by increased presence of Tumor Necrosis Factor-alpha (TNFα), increased expression of Vascular Cell Adhesion Molecule-1 (VCAM-1), increased presence of serum monocytes and activation of the canonical inflammatory molecule, Nuclear Factor Kappa-B (NFκB). Hyperinsulinemia is a hallmark of insulin resistance and may play a key role in this inflammatory process.

METHODS

Using Western blot analysis, immunocytochemistry, flow cytometry and biochemical inhibitors, we measured changes in VCAM-1 protein expression and NFκB translocation in vascular endothelial cells in the presence of TNFα and/or hyperinsulinemia and in the absence or presence of kinase pathway inhibitors.

RESULTS

We report that hyperinsulinemia augmented TNFα stimulated increases in VCAM-1 protein greater than seen with TNFα alone and decreased the time in which VCAM-1 translocated to the cell surface. We also observed that in the presence of Wortmannin, a biochemical inhibitor of phosphatidylinositol 3-kinase (a hallmark of insulin resistance), VCAM-1 expression was greater in the presence of TNFα plus insulin as compared to that seen with insulin or TNFα alone. Additionally, nuclear import of NFκB occurred sooner in the presence of insulin and TNFα together as compared to each alone, and in the presence of Wortmannin, nuclear import of NFκB was greater than that seen with insulin and TNFα alone.

CONCLUSIONS

hyperinsulinemia and insulin resistance appear to augment the inflammatory effects of TNFα on VCAM-1 expression and NFκB translocation, both of which are markers of inflammation in the vasculature.

Do statins have a role in reduction/prevention of post-PCI restenosis?

The pathophysiology of post-PCI restenosis involves neointimal formation that consists of three phases: thrombosis (within 24 h), recruitment (3-8 days), and proliferation, which starts on day 8 of PCI. Various factors suggested to be predictors/risks for restenosis include C-reactive protein (CRP), inflammatory mediators (cytokines and adhesion molecules), oxygen radicals, advanced glycation end products (AGEs) and their receptors (RAGE), and soluble RAGE (sRAGE). The earlier noted factors produce thrombogenesis, vascular smooth muscle cell proliferation, and extracellular matrix formation. Statins have pleiotropic effects. Besides lowering serum cholesterol, they have various other biological effects including antiinflammatory, antithrombotic, CRP-lowering, antioxidant, antimitotic, and inhibition of smooth muscle cell proliferation. They inhibit matrix metalloproteinase and cyclooxygenase-2, lower AGEs, decrease expression of RAGE and increase levels of serum sRAGE. They also increase the synthesis of nitric oxide (NO) by increasing endothelial NO synthase expression and activity. Preprocedural statin therapy is known to reduce peri- and post-PCI myonecrosis and reduce the need for repeat revascularization. There is evidence that statin-eluting stents inhibit in-stent restenosis in animal models. It is concluded that because of the above attributes of statins, they are suitable candidates for reduction of post-PCI restenosis and post-PCI myonecrosis. The future directions for the use of statins in reduction of post-PCI restenosis and myonecrosis have been discussed.

Cilostazol promotes vascular smooth muscles cell differentiation through the cAMP response element-binding protein-dependent pathway

OBJECTIVE

Cilostazol, a potent type 3 phosphodiesterase inhibitor, has recently been found to reduce neointimal formation by inhibiting vascular smooth muscle cell (VSMC) proliferation. The aim of this study is to investigate whether cilostazol exerts an action on phenotypic modulation of VSMCs, another important process in the pathogenesis of neointimal formation.

METHODS AND RESULTS

Cilostazol may convert VSMCs from a serum-induced dedifferentiation state to a differentiated state, as indicated by a spindle-shaped morphology and an increase in the expression of smooth muscle cell differentiation marker contractile proteins. The upregulation of contractile proteins by cilostazol involves the cAMP/protein kinase A (PKA) signaling pathway, because the cAMP analog mimicked and specific cAMP/PKA inhibitors opposed the effect of cilostazol. Furthermore, cilostazol-activated cAMP response element (CRE)-binding protein (CREB), including phosphorylation at Ser133 and its nuclear translocation. Deletion and mutational analysis of the contractile protein promoters along with chromatin immunoprecipitation using anti-CREB antibody showed that CRE is essential for cilostazol-induced contractile protein expression. Transfection of dominant-negative CREB (mutated Ser133) plasmid in VSMCs blocked cilostazol-stimulated contractile protein expression. In vivo, cilostazol upregulated contractile proteins and induced the activation of CREB in the neointima of balloon-injured arteries.

CONCLUSIONS

Cilostazol promotes VSMC differentiation through the cAMP/PKA/CREB signaling cascade.

Thiazolidinediones prevent PDGF-BB-induced CREB depletion in pulmonary artery smooth muscle cells by preventing upregulation of casein kinase 2 alpha' catalytic subunit

BACKGROUND

The transcription factor CREB is diminished in smooth muscle cells (SMCs) in remodeled, hypertensive pulmonary arteries (PAs) in animals exposed to chronic hypoxia. Forced depletion of cyclic adenosine monophosphate response element binding protein (CREB) in PA SMCs stimulates their proliferation and migration in vitro. Platelet-derived growth factor (PDGF) produced in the hypoxic PA wall promotes CREB proteasomal degradation in SMCs via phosphatidylinositol-3-kinase/Akt signaling, which promotes phosphorylation of CREB at 2 casein kinase 2 (CK2) sites. Here we tested whether thiazolidinediones, agents that inhibit hypoxia-induced PA remodeling, attenuate SMC CREB loss.

METHODS

Depletion of CREB and changes in casein kinase 2 catalytic subunit expression and activity were measured in PA SMC treated with PDGF. PA remodeling and changes in medial PA CREB and casein kinase 2 levels were evaluated in lung sections from rats exposed to hypoxia for 21 days.

RESULTS

We found that the thiazolidinedione rosiglitazone prevented PA remodeling and SMC CREB loss in rats exposed to chronic hypoxia. Likewise, the thiazolidinedione troglitazone blocked PA SMC proliferation and CREB depletion induced by PDGF in vitro. Thiazolidinediones did not repress Akt activation by hypoxia in vivo or by PDGF in vitro. However, PDGF-induced CK2 alpha' catalytic subunit expression and activity in PA SMCs, and depletion of CK2 alpha' subunit prevented PDGF-stimulated CREB loss. Troglitazone inhibited PDGF-induced CK2 alpha' subunit expression in vitro and rosiglitazone blocked induction of CK2 catalytic subunit expression by hypoxia in PA SMCs in vivo.

CONCLUSION

We conclude that thiazolidinediones prevent PA remodeling in part by suppressing upregulation of CK2 and loss of CREB in PA SMCs.

Protein tyrosine phosphatase PTPepsilonM negatively regulates PDGF beta-receptor signaling induced by high glucose and PDGF in vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) proliferation and migration and vascular endothelial cell (VEC) dysfunction are closely associated with the development of atherosclerosis. We previously demonstrated that protein tyrosine phosphatase ε M (PTPεM) promotes VEC survival and migration. The present study investigates the biological functions of PTPεM in VSMCs and determines whether PTPεM is implicated in diabetes-accelerated atherosclerosis. We overexpressed wild-type and inactive PTPεM and an small interfering RNA (siRNA) of PTPεM by using an adenovirus vector to investigate the effects of PTPεM upon platelet-derived growth factor (PDGF)- and high glucose (HG)-induced responses of rat VSMCs in vitro. We found that PTPεM decreased PDGF-induced DNA synthesis and migration by reducing the phosphorylation level of the PDGF β-receptor (PDGFRβ) with subsequently suppressed H(2)O(2) generation. The HG content in the medium generated H(2)O(2), upregulated PDGFRβ expression and its tyrosine-phosphorylation, and elevated NADPH oxidase 1 (Nox1) expression even without exogenous PDGF, all of which were downregulated by PTPεM. The PDGFR inhibitor AG1296 also blocked HG-induced Nox1 expression and H(2)O(2) production. Moreover, HG suppressed PTPεM expression itself, which was blocked by the antioxidant N-acetyl-l-cysteine. The effects of PTPεM siRNA were the opposite of those of wild-type PTPεM. Therefore, PTPεM negatively regulates PDGFRβ-mediated signaling pathways that are crucial for the pathogenesis of atherosclerosis, and PTPεM may be involved in diabetes-accelerated atherosclerosis.

Interaction between mineralocorticoid receptor and cAMP/CREB signaling

Besides regulating water and electrolyte homeostasis, the mineralocorticoid receptor (MR) elicits pathophysiological effects in the renocardiovascular system. Although the MR's closest relative, the glucocorticoid receptor (GR), acts as a transcription factor at the same hormone-response-element (HRE), activated glucocorticoid receptor mediates very different effects. One explanation for this discrepancy is that the MR interacts with additional signaling pathways in the cytosol. In the literature, there are several indications for an interaction between aldosterone/MR and the cAMP/CREB signaling. Here we summarize the current knowledge of the cross-talk between the two signaling pathways, including some unpublished observations of our own that indicate that MR/CREB signaling is mediated by calcineurin and has potentially pathophysiological consequences.

CREB downregulation in vascular disease: a common response to cardiovascular risk

OBJECTIVE

To examine the impact of low-density lipoprotein (LDL), an established mediator of atherosclerosis, on the transcription factor cAMP-response element-binding protein (CREB), which is a regulator of vascular smooth muscle cell (VSMC) quiescence.

METHODS AND RESULTS

VSMC CREB content is diminished in rodent models of diabetes and pulmonary hypertension. We examined aortic CREB content in rodent models of aging, hypertension, and insulin resistance, and we determined nuclear CREB protein in the medial VSMC of high-fat-fed LDL receptor-null mice. There was significant loss of CREB protein in all models. In vitro, primary culture rat aortic VSMC exposed to LDL and oxidized LDL exhibited a rapid, transient increase in CREB phosphorylation and transient phosphorylation/activation of Akt, ERK, JNK, ans p38 MAPK. Exposure to oxidized LDL, but not to LDL, for 24 to 48 hours decreased CREB protein in a dose-dependent fashion and led to nuclear exclusion of CREB. Pharmacological reactive oxygen species scavengers and inhibition of ERK activation blocked oxidized LDL-mediated CREB downregulation.

CONCLUSIONS

These data support a model wherein loss of VSMC CREB protein, which renders these cells more susceptible to activation and apoptosis, is a common pathological response to vascular injury and potentially contributes to plaque progression.

Expression of constitutively active cGMP-dependent protein kinase inhibits glucose-induced vascular smooth muscle cell proliferation

Previously, we have demonstrated that cGMP-dependent protein kinase (PKG) activity is downregulated in vessels from diabetic animals or in vascular smooth muscle cells (VSMCs) exposed to high-glucose conditions, contributing to diabetes-associated vessel dysfunction. However, whether decreased PKG activity plays a role in hyperglycemia-induced proliferation of VSMCs is unknown. In this report, high-glucose-mediated decreased PKG activity in VSMCs was restored by transfection of cells with expression vector for the catalytic domain of PKG-I (PKG-CD, constitutive active PKG). The effect of glucose on cell proliferation was determined. Our data demonstrated that high glucose exposure stimulated VSMC proliferation and G1 to S phase progression of the cell cycle, which was inhibited by restoration of PKG activity. Expression of constitutively active PKG inhibited G1 phase exit in VSMCs under high glucose conditions, which was accompanied by an inhibition of retinoblastoma protein (Rb) phosphorylation (a key switch for G1 to S phase cell cycle progression). Glucose-induced cyclin E expression and cyclin E-cyclin-dependent kinase 2 activity was also reduced by expression of PKG-CD in VSMCs. Moreover, expression of PKG-CD suppressed glucose-induced p27 degradation. These data demonstrate that restoring the high-glucose-mediated decrease in PKG activity in VSMCs inhibits glucose-induced abnormal VSMC proliferation occurring upstream of Rb phosphorylation. Our work provides the first direct evidence linking decreased PKG activity to high glucose-induced proliferation and cell cycle progression in VSMCs, suggesting that strategies to increase PKG activity might be useful in preventing abnormal VSMC proliferation in diabetic patients and might provide treatments for diabetes-associated proliferative vascular diseases.

Nonesterified fatty acid exposure activates protective and mitogenic pathways in vascular smooth muscle cells by alternate signaling pathways

Vascular smooth muscle cells (VSMC) are dynamic cells exposed to fluctuating concentrations of nutrients on a daily basis. Nonesterified fatty acids (NEFA) have been indicted as potential mediators of atherosclerosis and exaggerated VSMC remodeling observed in diabetes, and in vitro data support a model of VSMC activation by NEFA. However, recent observations suggest that metabolic stressors such as oxidants and NEFA may also simultaneously induce cytoprotective events as part of a homeostatic "off switch." Our group has established that the transcription factor cyclic adenosine monophosphate response element binding protein (CREB) is important for maintenance of VSMC quiescence, differentiation, and survival. We therefore examined whether acute physiologic NEFA exposure would regulate CREB in primary cultures of bovine aortic VSMC and explored the relationship between signaling to the cytoprotective CREB and the activating mitogen-activated protein kinase pathways. In vitro exposure of VSMC to 3 classes of unsaturated NEFA leads to significant acute, transient, dose-dependent, and repeatedly inducible CREB activation. As expected, extracellular signal-regulated kinase, P38 mitogen-activated protein kinase, Akt, Jun N-terminal kinase, and protein kinase C (PKC) pathways are also activated by NEFA. Using a battery of pharmacologic inhibitors and antioxidants, we demonstrate that CREB activation is mediated by a novel PKC isoform and is reactive oxygen species independent, whereas extracellular signal-regulated kinase activation, in contrast, is mediated by reactive oxygen species and is PKC independent. These data suggest parallel and mechanistically distinct stimulation of separate stabilizing and activating pathways in VSMC response to acute NEFA-mediated stress. Furthermore, the down-regulation of CREB in models of chronic metabolic stress reported in the literature would be expected to disrupt this homeostasis and shift the balance toward VSMC activation, consistent with emerging models of atherosclerosis.

Multidrug resistance-associated protein 4 regulates cAMP-dependent signaling pathways and controls human and rat SMC proliferation

The second messengers cAMP and cGMP can be degraded by specific members of the phosphodiesterase superfamily or by active efflux transporters, namely the multidrug resistance-associated proteins (MRPs) MRP4 and MRP5. To determine the role of MRP4 and MRP5 in cell signaling, we studied arterial SMCs, in which the effects of cyclic nucleotide levels on SMC proliferation have been well established. We found that MRP4, but not MRP5, was upregulated during proliferation of isolated human coronary artery SMCs and following injury of rat carotid arteries in vivo. MRP4 inhibition significantly increased intracellular cAMP and cGMP levels and was sufficient to block proliferation and to prevent neointimal growth in injured rat carotid arteries. The antiproliferative effect of MRP4 inhibition was related to PKA/CREB pathway activation. Here we provide what we believe to be the first evidence that MRP4 acts as an independent endogenous regulator of intracellular cyclic nucleotide levels and as a mediator of cAMP-dependent signal transduction to the nucleus. We also identify MRP4 inhibition as a potentially new way of preventing abnormal VSMC proliferation.

Chronic hyperglicemia and nitric oxide bioavailability play a pivotal role in pro-atherogenic vascular modifications

Diabetes is associated with accelerated atherosclerosis and macrovascular complications are a major cause of morbidity and mortality in this disease. Although our understanding of vascular pathology has lately greatly improved, the mechanism(s) underlying enhanced atherosclerosis in diabetes remain unclear. Endothelial cell dysfunction is emerging as a key component in the pathophysiology of cardiovascular abnormalities associated with diabetes. Although it has been established that endothelium plays a critical role in overall homeostasis of the vessels, vascular smooth muscle cells (vSMC) in the arterial intima have a relevant part in the development of atherosclerosis in diabetes. However, high glucose induced alterations in vSMC behaviour are not fully characterized. Several studies have reported that impaired nitric oxide (NO) synthesis and/or actions are often present in diabetes and endothelial dysfunction. Furthermore, although endothelial cells are by far the main site of vascular NO synthesis, vSMC do express nitric oxyde synthases (NOSs) and NO synthesis in vSMC might be important in vessel's function. Although it is known that vSMC contribute to vascular pathology in diabetes by their change from a quiescent state to an activated proliferative and migratory phenotype (termed phenotypic modulation), whether this altered phenotypic modulation might also involve alterations in the nitrergic systems is still controversial. Our recent data indicate that, in vivo, chronic hyperglycemia might induce an increased number of vSMC proliferative clones which persist in culture and are associated with increased eNOS expression and activity. However, upregulation of eNOS and increased NO synthesis occur in the presence of a marked concomitant increase of O(2-) production. Since NO bioavailabilty might not be increased in high glucose stimulated vSMC, it is tempting to hypothesize that the proliferative phenotype observed in cells from diabetic rats is associated with a redox imbalance responsible quenching and/or trapping of NO, with the consequent loss of its biological activity. This might provide new insight on the mechanisms responsible for accelerated atherosclerosis in diabetes.

Aldose reductase-regulated tumor necrosis factor-alpha production is essential for high glucose-induced vascular smooth muscle cell growth

Diabetes is associated with increased generation of cytokines and tissue inflammation, but it is unclear how increased cytokine synthesis is causally related to the development of diabetic complications. Here, we report that exposure to high (25 mm) glucose, but not iso-osmotic concentrations of mannitol or 3-methyl glucose, increased TNF-alpha secretion by rat and human aortic smooth muscle cells in culture. The increase in TNF-alpha production was prevented by actinomycin D and cycloheximide, indicating transcriptional activation of TNF-alpha gene. High glucose (HG)-induced TNF-alpha release was specifically inhibited by protein kinase C (PKC)-delta inhibitor (Rottlerin; EMD Biosciences, San Diego, CA), but not PKC-beta2 inhibitor (CGP53353; Tocris Cookson Inc., Ellisville, MO), indicating the possible involvement of PKC-delta in HG signaling. TNF-alpha secretion was also prevented by pretreating cells with aldose reductase (AR) inhibitors, sorbinil or tolrestat and in cells treated with antisense AR mRNA. Inhibition of AR also prevented the increase in TNF-alpha mRNA. Addition of anti-TNF-alpha antibodies or soluble TNF-alpha receptors 1 and 2 to the medium or RNA interference ablation of TNF-alpha attenuated nuclear factor-kappaB activation and prevented HG-stimulated cell growth. These data indicate that AR is required for HG-induced TNF-alpha synthesis and release. In vivo, the release of TNF-alpha by HG leading to autocrine stimulation of TNF-alpha synthesis may be a critical step in the development of the cardiovascular complications of diabetes. Interruption of the autocrine effects of TNF-alpha may be a useful strategy for treating diabetic vasculopathies.

Atherosclerosis in diabetes and insulin resistance

Atherosclerosis and cardiovascular disease are the major causes of morbidity and mortality in patients with diabetes and those with insulin resistance and the metabolic syndrome. Both conditions profoundly accelerate the development of atherosclerosis and increase the morbidity and mortality of cardiovascular events. The question, therefore, is what are the molecular/biochemical mechanisms that underlie the potentiating influence of diabetes, the metabolic syndrome and/or insulin resistance on the development and progression of atherosclerosis? The following review will focus on the molecular mechanism whereby hyperglycaemia and/or hyperinsulinemia either directly or indirectly promote atherosclerosis.

Activation of sphingosine kinase-1 mediates inhibition of vascular smooth muscle cell apoptosis by hyperglycemia

Vascular smooth muscle cell (VSMC) apoptosis plays an essential role in vascular development and atherosclerosis. Hyperglycemia inhibits VSMC apoptosis, which may contribute to the development of diabetic vasculopathy. In the present study, we analyzed the mechanism of high-glucose-induced anti-apoptotic effect in cultured human aortic smooth muscle cells (HASMCs). Compared with normoglycemia, exposure of HASMCs to hyperglycemia but not mannitol significantly increased sphingosine kinase 1 (SK1) activity but not SK2 activity. This increase was inhibited by protein kinase C (PKC) inhibitor GF109203X, the antioxidant N-acetylcysteine, and the reduced form of glutathione. The mechanism of SK1 activation by high glucose involves plasma membrane translocation. In addition, hyperglycemia markedly inhibited serum withdrawal-induced apoptosis in HASMCs. Importantly, inhibition of SK1 by either a competitive inhibitor N',N'-dimethylsphingosine or expression of dominant-negative mutant of SK1(G82D) or specific small interference RNA knockdown substantially attenuated hyperglycemia-induced anti-apoptotic effect and anti-apoptotic protein Bcl-2 expression in HASMCs. Moreover, SK1-mediated anti-apoptotic effect requires the intracellular effects of sphingosine-1-phosphate. We conclude that hyperglycemia stimulates SK1 activity via PKC- and oxidative stress-dependent pathways, leading to decreased apoptosis in HASMCs. Taken together, these observations have important implications for understanding the roles of the SK1 signaling pathway in the pathogenesis of diabetic vasculopathy.

Restoration of CREB function is linked to completion and stabilization of adaptive cardiac hypertrophy in response to exercise

Potential regulation of two factors linked to physiological outcomes with left ventricular (LV) hypertrophy, resistance to apoptosis, and matching of metabolic capacity, by the transcription factor cyclic-nucleotide regulatory element binding protein (CREB), was examined in the two models of physiological LV hypertrophy: involuntary treadmill running of female Sprague-Dawley rats and voluntary exercise wheel running in female C57Bl/6 mice. Comparative studies were performed in the models of pathological LV hypertrophy and failure: the spontaneously hypertension heart failure (SHHF) rat and the hypertrophic cardiomyopathy (HCM) transgenic mouse, a model of familial idiopathic cardiomyopathy. Activating CREB serine-133 phosphorylation was decreased early in remodeling in response to both physiological (decreased 50-80%) and pathological (decreased 60-80%) hypertrophic stimuli. Restoration of LV CREB phosphorylation occurred concurrent with completion of physiological hypertrophy (94% of sedentary control), but remained decreased (by 90%) during pathological hypertrophy. In all models of hypertrophy, CREB phosphorylation/activation demonstrated strong positive correlations with 1) expression of the anti-apoptotic protein bcl-2 (a CREB-dependent gene) and subsequent reductions in the activation of caspase 9 and caspase 3; 2) expression of peroxisome proliferator-activated receptor-gamma coactivator-1 (PGC-1; a major regulator of mitochondrial content and respiratory capacity), and 3) LV mitochondrial respiratory rates and mitochondrial protein content. Exercise-induced increases in LV mitochondrial respiratory capacity were commensurate with increases observed in LV mass, as previously reported in the literature. Exercise training of SHHF rats and HCM mice in LV failure improved cardiac phenotype, increased CREB activation (31 and 118%, respectively), increased bcl-2 content, improved apoptotic status, and enhanced PGC-1 content and mitochondrial gene expression. Adenovirus-mediated expression of constitutively active CREB in neonatal rat cardiac recapitulated exercise-induced upregulation of PGC-1 content and mitochondrial oxidative gene expression. These data support a model wherein CREB contributes to physiological hypertrophy by enhancing expression of genes important for efficient oxidative capacity and resistance to apoptosis.

Contribution of aldose reductase to diabetic hyperproliferation of vascular smooth muscle cells

The objective of this study was to determine whether the polyol pathway enzyme aldose reductase mediates diabetes abnormalities in vascular smooth muscle cell (SMC) growth. Aldose reductase inhibitors (tolrestat or sorbinil) or antisense aldose reductase mRNA prevented hyperproliferation of cultured rat aortic SMCs induced by high glucose. Cell cycle progression in the presence of high glucose was blocked by tolrestat, which induced a G0-G1 phase growth arrest. In situ, diabetes increased SMC growth and intimal hyperplasia in balloon-injured carotid arteries of streptozotocin-treated rats, when examined 7 or 14 days after injury. Treatment with tolrestat (15 mg x kg(-1) x day(-1)) diminished intimal hyperplasia and decreased SMC content of the lesion by 25%. Although tolrestat treatment increased immunoreactivity of the lesion with antibodies raised against protein adducts of the lipid peroxidation product 4-hydroxy trans-2-nonenal, no compensatory increase in lesion fibrosis was observed. Collectively, these results suggest that inhibition of aldose reductase prevents glucose-induced stimulation of SMC growth in culture and in situ. Even though inhibition of aldose reductase increases vascular oxidative stress, this approach may be useful in preventing abnormal SMC growth in vessels of diabetic patients.

Ca2+ source-dependent transcription of CRE-containing genes in vascular smooth muscle

Altered Ca2+ handling has immediate physiological and long-term genomic effects on vascular smooth muscle function. Previously we showed that Ca2+ entry through voltage-dependent Ca2+ channels (VDCCs) or store-operated Ca2+ channels (SOCCs) results in phosphorylation of the Ca2+/cAMP response element (CRE)-binding protein in cerebral arteries. Here, oligonucleotide array analysis was used to determine gene transcription profiles resulting from these two Ca2+ entry pathways in human cerebrovascular smooth muscle cell cultures. Results were confirmed and expanded using quantitative RT-PCR, Western blot, and immunofluorescence. A distinct, yet overlapping, set of CRE-regulated genes was induced by VDCC activation using K+ membrane depolarization vs. SOCC activation by thapsigargin (TG). Membrane depolarization selectively induced a sustained increase in early growth response-1 (Egr-1) mRNA and protein, which were inhibited by the VDCC blocker nimodipine and the SOCC inhibitor 2-aminoethoxydiphenylborate (2-APB). TG selectively induced a sustained increase in MAPK phosphatase-1 (MKP-1) mRNA and protein, and these effects were decreased by 2-APB, but not by nimodipine. The physiological agonist ANG II also stimulated expression of Egr-1 and MKP-1. Coadministration of 2-APB prevented expression of Egr-1 and MKP-1, whereas nimodipine blocked only Egr-1 expression. TG and ANG II induced phosphorylation of ERK, which was sensitive to 2-APB and was selectively required for CRE-binding protein phosphorylation. Our findings thus indicate that Ca2+ entry through VDCCs and store-operated Ca2+ entry can differentially regulate CRE-containing genes in vascular smooth muscle and also imply that agonist-induced signals involved in modulation of gene transcription can be controlled by multiple sources of Ca2+.

Involvement of cAMP-response element binding protein-1 in arachidonic acid-induced vascular smooth muscle cell motility

In addition to their role in many vital cellular functions, arachidonic acid (AA) and its eicosanoid metabolites are involved in the pathogenesis of several diseases, including atherosclerosis and cancer. To understand the potential mechanisms by which these lipid molecules could influence the disease processes, particularly cardiovascular diseases, we studied AA's effects on vascular smooth muscle cell (VSMC) motility and the role of cAMP-response element binding protein-1 (CREB-1) in this process. AA exerted differential effects on VSMC motility; at lower doses, it stimulated motility, whereas at higher doses, it was inhibitory. AA-induced VSMC motility requires its conversion via the lipoxygenase (LOX) and cyclooxygenase (COX) pathways. AA stimulated the phosphorylation of extracellular signal-regulated kinases (ERKs), Jun N-terminal kinases (JNKs), and p38 mitogen-activated protein kinase (p38MAPK) in a time-dependent manner, and blockade of these serine/threonine kinases significantly attenuated AA-induced VSMC motility. In addition, AA stimulated CREB-1 phosphorylation and activity in a manner that was also dependent on its metabolic conversion via the LOX and COX pathways and the activation of ERKs and p38MAPK but not JNKs. Furthermore, suppression of CREB-1 activation inhibited AA-induced VSMC motility. 15(S)-Hydroxyeicosatetraenoic acid and prostaglandin F2alpha, the 15-LOX and COX metabolites of AA, respectively, that are produced by VSMC at lower doses, were also found to stimulate motility in these cells. Together, these results suggest that AA induces VSMC motility by complex mechanisms involving its metabolism via the LOX and COX pathways as well as the ERK- and p38MAPK-dependent and JNK-independent activation of CREB-1.

Role of cAMP response element binding protein in cardiovascular remodeling: good, bad, or both?

The cAMP response element binding protein (CREB) is a ubiquitously expressed nuclear transcription factor that is activated by various extracellular stimuli. CREB is known to regulate the expression of genes important to cell proliferation, differentiation, adaptation, and survival in many cell types. Loss of CREB function by transgenic overexpression of dominant negative CREB or targeted deletion of the CREB gene revealed that CREB is involved in the differentiation of T lymphocytes, production of growth hormone, and the long-term potentiation of neuronal memory. The role of CREB in cardiovascular system is incompletely characterized and several controversies remain. A growing body of recent evidence, however, has suggested that CREB plays an important role in the cardiovascular remodeling process, including inflammation, cell migration, and apoptosis. Thus, CREB may be a possible target for the treatment of cardiovascular diseases such as atherosclerosis, restenosis, and reperfusion injury.

CREB mediates ERK-induced survival of mouse renal tubular cells after oxidant stress

BACKGROUND

We showed that extracellular signal-regulated protein kinase (ERK) is prosurvival during oxidant stress both in the kidney and in cultured mouse proximal tubule (TKPTS) cells and demonstrated concomitant activation of ERK as well as the cyclic adenosine monophosphate (cAMP)-responsive element binding protein (CREB), during survival in vitro. We now show that CREB is a necessary prosurvival target of ERK.

METHODS

Ischemia/reperfusion (I/R) injury was induced in 129Sv mice. Oxidant stress was induced by hydrogen peroxide (H(2)O(2)) in TKPTS cells. Activation of CREB was determined by immunohistochemistry and Western blotting. Inhibition and activation of CREB was achieved by mutant or activated CREB-containing adenoviruses in vitro. The effects of oxidant stress on cell survival, CREB binding, and CREB-mediated transcription was determined by cell counting, gelshift analysis, and luciferase assay, respectively.

RESULTS

I/R activates CREB in the surviving distal nephron segments of the kidney. Inhibition of ERK and CREB abrogates survival after 0.5 mmol/L H(2)O(2) treatment, while overexpression of CREB ameliorates necrotic death caused by 1 mmol/L H(2)O(2). Inhibition of ERK also inhibited CREB activation. Binding of phosphorylated CREB to a CREB oligonucleotide was significantly increased after 0.5 mmol/L H(2)O(2) but decreased after 1 mmol/L H(2)O(2). Similarly, CREB-mediated transcription was significantly increased after 0.5 mmol/L H(2)O(2) treatment, while 1 mmol/L H(2)O(2) inhibited it. Interestingly, transcription from the CREB-driven bcl-2 promoter was unchanged after 0.5 mmol/L but decreased after 1 mmol/L H(2)O(2) treatment in agreement with Western blot studies.

CONCLUSION

We show that survival during oxidant stress is mediated through CREB and identification of its downstream targets will reveal important survival pathways.

Ca2+/calmodulin-dependent protein kinase IV activates cysteine-rich protein 1 through adjacent CRE and CArG elements

Smooth muscle-specific transcription is controlled by a multitude of transcriptional regulators that cooperate to drive expression in a temporospatial manner. Previous analysis of the cysteine-rich protein 1 ( CRP1/Csrp) gene revealed an intronic enhancer that is sufficient for expression in arterial smooth muscle cells and requires a serum response factor-binding CArG element for activity. The presence of a CArG box in smooth muscle regulatory regions is practically invariant; however, it stands to reason that additional elements contribute to the modulation of transcription in concert with the CArG. Because of the potential importance of other regulatory elements for expression of the CRP1 gene, we sought to identify additional motifs within the enhancer that are necessary for expression. In this effort, we identified a conserved cAMP response element (CRE) that, when mutated, diminishes the expression of the enhancer in cultured vascular smooth muscle cells. Using transfection and electrophoretic mobility shift assays, we have shown that the CRE binds the cAMP response element-binding protein (CREB) and is activated by Ca2+/calmodulin-dependent protein kinase IV (CaMKIV), but not by CaMKII. Furthermore, our data demonstrate that CaMKIV stimulates CRP1 expression not only through the CRE but also through the CArG box. These findings represent evidence of a functional CRE within a smooth muscle-specific gene and provide support for a mechanism in which CREB functions as a smooth muscle determinant through CaMKIV activation.

Neurotrophin-3-induced production of nerve growth factor is suppressed in Schwann cells exposed to high glucose: involvement of the polyol pathway

Development of hypesthesia, a loss of sensitivity to stimulation, is associated with impaired regeneration of peripheral sensory fibers, in which Schwann cells play a key role by secreting nerve growth factor (NGF). Recent clinical trials indicated that an inhibitor of aldose reductase (AR), the rate-limiting enzyme in the polyol pathway, significantly improved hypesthesia in diabetic patients. The fact that AR is localized in Schwann cells led us to investigate the role of the polyol pathway in NGF production of isolated Schwann cells. Among various endogenous factors examined, increased production of NGF was demonstrated in the cells treated with neurotrophin-3 (NT-3) for 24 h. NT-3-induced NGF production was significantly suppressed when cells were cultured in the medium containing high glucose. In these cells, the levels of glutathione (GSH) and cAMP-response element binding protein (CREB) were reduced, whereas the level of activated nuclear factor-kappaB (NF-kappaB) was elevated. These changes were abolished when an AR inhibitor fidarestat was included in the medium. NT-3-induced NGF production was further attenuated in the cells treated with an inhibitor of GSH synthesis. Together, the enhanced polyol pathway activity under high-glucose conditions seems to elicit reduced NT-3-induced NGF production in Schwann cells. Enhanced oxidative stress linked to the polyol pathway activity may mediate this process.

Antiproliferative mechanisms of raxofelast (IRFI-016) in H2O2-stimulated rat aortic smooth muscle cells

Reactive oxygen species-mediated cellular injury is involved in the pathogenesis of many diseases, including those affecting the cardiovascular system, such as myocardial ischemia-reperfusion injury, inflammation, and atheroscleosis. Raxofelast (IRFI-016; (+/-)-5-acetoxy-2, 3-dihydro-4, 6, 7-trimethyl-2-benzofuran-acetic acid) was designed with the aim of maximizing the antioxidant potency of phenols chemically related to vitamin E. The antioxidant activity of raxofelast has been convincingly demonstrated in several in vitro studies and in various models of ischemia-reperfusion injury. In this study, the antiproliferative effects of raxofelast were investigated to determine whether transduction signals and protooncogenes are affected in H(2)O(2)-stimulated rat aortic smooth muscle cells. In a tetrazolium-based colorimetric assay, the proliferation of rat aortic smooth muscle cells was increased by 3-fold in 0.1% fetal bovine serum/Dulbecco's modified Eagle's medium (DMEM) containing 500 microM H(2)O(2), indicating that exogenous 500 microM H(2)O(2) was a growth stimulator of rat aortic smooth muscle cells. Exogenous H(2)O(2) significantly activated extracellular signal-regulated kinases (ERKs) activity within 30 min and raxofelast inhibited the ERKs activation dose dependently in 500 microM H(2)O(2)-stimulated rat aortic smooth muscle cells (IC(50): 200 microM). Raxofelast reduced the intracellular reactive oxygen species generated by exogenous H(2)O(2) in a dose-dependent manner. In 500 microM H(2)O(2)-stimulated rat aortic smooth muscle cells, raxofelast dramatically attenuated the activation of mitogen-activating protein kinase (MAPK)/ERK kinase 1, 2 (MEK1,2) and protein kinase C (PKC) without affecting Ras expression. Induction of c-myc mRNA was significantly reduced dose dependently up to 100 microM by raxofelast in concentrations. These data indicate that the antiproliferative effects of raxofelast in H(2)O(2)-stimulated rat aortic smooth muscle cells may involve the suppression of intracellular reactive oxygen species formation and the inhibition of ERKs by inactivation through PKC and MEK1,2 and down-regulation of c-myc expression, regardless of Ras activation.