Augmented Ca2+ influx is involved in the mechanism of enhanced proliferation of cultured vascular smooth muscle cells from spontaneously diabetic Goto-Kakizaki rats

Comprehensive Approach for Managing the Older Person with Diabetes Mellitus

Care of the elderly population with diabetes may not be restricted to the management of hyperglycemia, associated risk factors, and specific diabetic complications. An integrated approach should also include the assessment and management of gerontological problems. Both diabetes mellitus and aging interact toward the direction of the increased incidence of geriatric syndromes. Education is a common element of both diabetes control and geriatric syndrome care. However, it has been perceived that conventional education programs for diabetics are not as effective for the elderly. We have designed geriatric reinforced education (GRE) for application in older diabetics with geriatric syndromes. We observed that the application of GRE improved the glucose control and the status of geriatric syndromes in older adults with diabetes. In summary, in terms of integrating the care of coexisting diabetes and geriatric problems, GRE may be a beneficial tool for the management of older adults with diabetes.

Anti-Proliferative Effects of Rutin on OLETF Rat Vascular Smooth Muscle Cells Stimulated by Glucose Variability

PURPOSE

Proliferation of vascular smooth muscle cells (VSMCs) plays a crucial role in atherosclerosis. Rutin is a major representative of the flavonol subclass of flavonoids and has various pharmacological activities. Currently, data are lacking regarding its effects on VSMC proliferation induced by intermittent hyperglycemia. Here, we demonstrate the effects of rutin on VSMC proliferation and migration according to fluctuating glucose levels.

MATERIALS AND METHODS

Primary cultures of male Otsuka Long-Evans Tokushima Fatty (OLETF) rat VSMCs were obtained from enzymatically dissociated rat thoracic aortas. VSMCs were incubated for 72 h with alternating normal (5.5 mmol/L) and high (25.0 mmol/L) glucose media every 12 h. Proliferation and migration of VSMCs, the proliferative molecular pathway [including p44/42 mitogen-activated protein kinases (MAPK), mitogen-activated protein kinase kinase 1/2 (MEK1/2), p38 MAPK, phosphoinositide 3-kinase (PI3K), c-Jun N-terminal protein kinase (JNK), nuclear factor kappa B (NF-κB), and Akt], the migratory pathway (big MAPK 1, BMK1), reactive oxygen species (ROS), and apoptotic pathway were analyzed.

RESULTS

We found enhanced proliferation and migration of VSMCs when cells were incubated in intermittent high glucose conditions, compared to normal glucose. These effects were lowered upon rutin treatment. Intermittent treatment with high glucose for 72 h increased the expression of phospho-p44/42 MAPK (extracellular signal regulated kinase 1/2, ERK1/2), phospho-MEK1/2, phospho-PI3K, phospho-NF-κB, phospho-BMK1, and ROS, compared to treatment with normal glucose. These effects were suppressed by rutin. Phospho-p38 MAPK, phospho-Akt, JNK, and apoptotic pathways [B-cell lymphoma (Bcl)-xL, Bcl-2, phospho-Bad, and caspase-3] were not affected by fluctuations in glucose levels.

CONCLUSION

Fluctuating glucose levels increased proliferation and migration of OLETF rat VSMCs via MAPK (ERK1/2), BMK1, PI3K, and NF-κB pathways. These effects were inhibited by the antioxidant rutin.

Calcium ions and osteoclastogenesis initiate the induction of bone formation by coral-derived macroporous constructs

Coral-derived calcium carbonate/hydroxyapatite macroporous constructs of the genus Goniopora with limited hydrothermal conversion to hydroxyapatite (7% HA/CC) initiate the induction of bone formation. Which are the molecular signals that initiate pattern formation and the induction of bone formation? To evaluate the role of released calcium ions and osteoclastogenesis, 7% HA/CC was pre-loaded with either 500 μg of the calcium channel blocker, verapamil hydrochloride, or 240 μg of the osteoclast inhibitor, biphosphonate zoledronate, and implanted in the rectus abdominis muscle of six adult Chacma baboons Papio ursinus. Generated tissues on days 15, 60 and 90 were analysed by histomorphometry and qRT-PCR. On day 15, up-regulation of type IV collagen characterized all the implanted constructs correlating with vascular invasion. Zoledronate-treated specimens showed an important delay in tissue patterning and morphogenesis with limited bone formation. Osteoclastic inhibition yielded minimal, if any, bone formation by induction. 7% HA/CC pre-loaded with the Ca⁺⁺ channel blocker verapamil hydrochloride strongly inhibited the induction of bone formation. Down-regulation of bone morphogenetic protein-2 (BMP-2) together with up-regulation of Noggin genes correlated with limited bone formation in 7% HA/CC pre-loaded with either verapamil or zoledronate, indicating that the induction of bone formation by coral-derived macroporous constructs is via the BMPs pathway. The spontaneous induction of bone formation is initiated by a local peak of Ca⁺⁺ activating stem cell differentiation and the induction of bone formation.

Using gene-network landscape to dissect genotype effects of TCF7L2 genetic variant on diabetes and cardiovascular risk

The single nucleotide polymorphism (SNP) within the TCF7L2 gene, rs7903146, is, to date, the most significant genetic marker associated with Type 2 diabetes mellitus (T2DM) risk. Nonetheless, its functional role in disease pathology is poorly understood. The aim of the present study was to investigate, in vascular smooth muscle cells from 92 patients undergoing aortocoronary bypass surgery, the contribution of this SNP in T2DM using expression levels and expression correlation comparison approaches, which were visually represented as gene interaction networks. Initially, the expression levels of 41 genes (seven TCF7L2 splice forms and 40 other T2DM relevant genes) were compared between rs7903146 wild-type (CC) and T2DM-risk (CT + TT) genotype groups. Next, we compared the expression correlation patterns of these 41 genes between groups to observe if the relationships between genes were different. Five TCF7L2 splice forms and nine genes showed significant expression differences between groups. RXRα gene was pinpointed as showing the most different expression correlation pattern with other genes. Therefore, T2DM risk alleles appear to be influencing TCF7L2 splice form's expression in vascular smooth muscle cells, and RXRα gene is pointed out as a treatment target candidate for risk reduction in individuals with high risk of developing T2DM, especially individuals harboring TCF7L2 risk genotypes.

Inhibition of NF-κB prevents high glucose-induced proliferation and plasminogen activator inhibitor-1 expression in vascular smooth muscle cells

Recent epidemiologic studies clearly showed that early intensive glucose control has a legacy effect for preventing diabetic macrovascular complications. However, the cellular and molecular processes by which high glucose leads to macrovascular complications are poorly understood. Vascular smooth muscle cell (VSMC) dysfunction due to high glucose is a characteristic of diabetic vascular complications. Activation of nuclear factor-κB (NF-κB) may play a key role in the regulation of inflammation and proliferation of VSMCs. We examined whether VSMC proliferation and plasminogen activator inhibitor-1 (PAI-1) expression induced by high glucose were mediated by NF-κB activation. Also, we determined whether selective inhibition of NF-κB would inhibit proliferation and PAI-1 expression in VSMCs. VSMCs of the aorta of male SD rats were treated with various concentrations of glucose (5.6, 11.1, 16.7, and 22.2 mM) with or without an inhibitor of NF-κB or expression of a recombinant adenovirus vector encoding an IκB-α mutant (Ad-IκBαM). VSMC proliferation was examined using an MTT assay. PAI-1 expression was assayed by real-time PCR and PAI-1 protein in the media was measured by ELISA. NF-κB activation was determined by immunohistochemical staining, NF-κB reporter assay, and immunoblotting. We found that glucose stimulated VSMC proliferation and PAI-1 expression in a dose-dependent manner up to 22.2 mM. High glucose (22.2 mM) alone induced an increase in NF-κB activity. Treatment with inhibitors of NF-κB such as MG132, PDTC or expression of Ad-IκB-αM in VSMCs prevented VSMC proliferation and PAI-1 expression induced by high glucose. In conclusion, inhibition of NF-κB activity prevented high glucose-induced VSMC proliferation and PAI-1 expression.

Calcium homeostasis in vascular smooth muscle cells is altered in type 2 diabetes by Bcl-2 protein modulation of InsP3R calcium release channels

This study examines the extent to which the antiapoptotic Bcl-2 proteins Bcl-2 and Bcl-x(L) contribute to diabetic Ca(2+) dysregulation and vessel contractility in vascular smooth muscle cells (VSMCs) through their interaction with inositol 1,4,5-trisphosphate receptor (InsP(3)R) intracellular Ca(2+) release channels. Measurements of intracellular ([Ca(2+)](i)) and sarcoplasmic reticulum ([Ca(2+)](SR)) calcium concentrations were made in primary cells isolated from diabetic (db/db) and nondiabetic (db/m) mice. In addition, [Ca(2+)](i) and constriction were recorded simultaneously in isolated intact arteries. Protein expression levels of Bcl-x(L) but not Bcl-2 were elevated in VSMCs isolated from db/db compared with db/m age-matched controls. In single cells, InsP(3)-evoked [Ca(2+)](i) signaling was enhanced in VSMCs from db/db mice compared with db/m. This was attributed to alterations in the intrinsic properties of the InsP(3)R itself because there were no differences between db/db and db/m in the steady-state [Ca(2+)](SR) or InsP(3)R expression levels. Moreover, in permeabilized cells the rate of InsP(3)R-dependent SR Ca(2+) release was increased in db/db compared with db/m VSMCs. The enhanced InsP(3)-dependent SR Ca(2+) release was attenuated by the Bcl-2 protein inhibitor ABT-737 only in diabetic cells. Application of ABT-737 similarly attenuated enhanced agonist-induced [Ca(2+)](i) signaling only in intact aortic and mesenteric db/db vessels. In contrast, ABT-737 had no effect on agonist-evoked contractility in either db/db or db/m vessels. Taken together, the data suggest that in type 2 diabetes the mechanism for [Ca(2+)](i) dysregulation in VSMCs involves Bcl-2 protein-dependent increases in InsP(3)R excitability and that dysregulated [Ca(2+)](i) signaling does not appear to contribute to increased vessel reactivity.

Casein phosphopeptides modulate proliferation and apoptosis in HT-29 cell line through their interaction with voltage-operated L-type calcium channels

At the intestinal level, proliferation and apoptosis are modulated by the extracellular calcium concentration; thus, dietary calcium may exert a chemoprotective role on normal differentiated intestinal cells, while it may behave as a carcinogenesis promoter in transformed cells. Calcium in milk is associated with casein and casein phosphopeptides (CPPs), hence is preserved from precipitation. CPPs were demonstrated to induce uptake of extracellular calcium ions by in vitro intestinal tumor HT-29 cells but only upon differentiation. Here, the hypothesis that CPPs could differently affect proliferation and apoptosis in undifferentiated and differentiated HT-29 cells through their binding with calcium ions was investigated. Results showed that CPPs protect differentiated intestinal cells from calcium overload toxicity and prevent their apoptosis favoring proliferation while inducing apoptosis in undifferentiated tumor cells. The CPP effect on undifferentiated HT-29 cells, similar to that exerted by ethyleneglycol-O, O'-bis(2-aminoethyl)-N, N, N', N'-tetraacetic acid (EGTA), is presumably due to the ability in binding the extracellular calcium. The effect on differentiated HT-29 cells is coupled to the interaction of CPPs with the voltage-operated L-type calcium channels, known to activate calcium entry into the cells under depolarization and to exert a mitogenic effect: the use of an agonist potentiates the cell response to CPPs, while the antagonists abolish the response to CPPs (36% of examined cells) or reduce both the percentage of responsive cells and the increase of intracellular calcium concentration. Taken together, these results confirm the potentialities of CPPs as nutraceuticals/functional food and also as modulators of cellular processes connected to the expression of a cancer phenotype.

Sevoflurane does not alter norepinephrine-induced intracellular Ca²(+) changes in the diabetic rat aorta

PURPOSE

The effect of volatile anesthetics on the mechanism(s) of vascular contraction in diabetes mellitus (DM) has not been fully understood. The current study was designed to determine the effects of sevoflurane on the norepinephrine (NE)-induced changes in contractile state and intracellular Ca²(+) concentrations ([Ca²(+)](i)) in the spontaneously developing type 2 DM rat.

METHODS

The effects of sevoflurane on NE (10⁻⁶M)-induced vasoconstriction and increase in [Ca²(+)](i) in the aortas from Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a type 2 DM model, and from age-matched control Long-Evans Tokushima Otsuka (LETO) rats were investigated using an isometric force transducer and fluorometer with fura-2 as an indicator of [Ca²(+)](i).

RESULTS

Norepinephrine-induced increases in tension and [Ca²(+)](i) in OLETF rats were 54.8%, 95% confidence interval (CI) 36.9-72.6% and 58.8%, 95% CI 51.5-66.1%, respectively, and in LETO rats they were 46.4%, 95% CI 39.0-53.7% and 53.8%, 95% CI 46.9-60.7%, respectively, when expressed as the percentage relative to that induced by KCl 30 mM. In LETO rats, sevoflurane at a concentration of 3.4% inhibited the vascular contraction (9.4%, 95% CI 6.3-12.6%; P < 0.001) and the increase in [Ca²(+)](i) (33.3%, 95% CI 27.4-39.2%; P = 0.002). In OLETF rats, however, sevoflurane failed to affect either the NE-induced contraction (43.6%, 95% CI 28.3-58.9%; P = 0.68) or the elevation in [Ca²(+)](i) (60.5%, 95% CI 56.3-64.8%; P = 0.93).

CONCLUSION

Sevoflurane at clinically relevant concentrations inhibited the NE-induced increase in [Ca²(+)](i) in the aortic smooth muscle from normal rats but not in that from type 2 DM rats. Thus, a Ca²(+)- signalling pathway resistant to sevoflurane appears to exist in the type 2 DM rat aorta.

Ang-II-induced Ca(2+) influx is mediated by the 1/4/5 subgroup of the transient receptor potential proteins in cultured aortic smooth muscle cells from diabetic Goto-Kakizaki rats

Angiotensin-II (Ang-II) exerts many of its vascular effects, including the pathophysiological changes associated with type 2 diabetes, through changes in intracellular calcium concentration [Ca(2+)](i). We sought to clarify the mechanism responsible for Ang-II-induced Ca(2+) influx in cultured aortic VSMC using the Goto-Kakizaki (GK) rat model of type 2 diabetes. Ang-II-induced Ca(2+) influx was blocked by neither VDCC nor c-src inhibition but was sensitive to inositol 1,4,5-trisphosphate receptor inhibition, lanthanide and the diacylglycerol analogue, oleoyl-2-acetyl-sn-glycerol. Since transient receptor potential canonical (TRPC)-3 gene expression was undetectable in both WKY and GK VSMCs and TRPC6 gene and protein expression were significantly down-regulated in GK, we believe the 1/4/5 subgroup of TRPC proteins plays a significant role. Furthermore, in GK VSMC the elevated calcium influx observed was not attributable to increased TRPC expression, but rather an alteration of TRPC activity.

Amadori-glycated albumin-induced vascular smooth muscle cell proliferation and expression of inhibitor of apoptosis protein-1 and nerve growth factor-gamma

We investigated the effects of Amadori-glycated serum albumin (GSA) on cell proliferation as well as expressions of antioxidant enzyme genes and marker genes associated with signal transduction pathways in rat aortic vascular smooth muscle cells (VSMCs). Quiescent VSMCs treated with GSA (0-500 microg/mL, 48 h) exhibited a dose-dependent increase in proliferation that was prevented by PD98059 (25 microM), suggesting a MAPK-dependent signaling pathway. Compared with bovine serum albumin (BSA)-treated cells, the GSA (500 microg/mL, 24~h)-treated VSMCs showed a higher superoxide dismutase 2 gene expression in quantitative RT-PCR, suggesting the involvement of oxidative stress. In a focused oligonucleotide array containing 96 signal transduction-related genes, expression of inhibitor of apoptosis protein-1 (IAP-1), nerve growth factor-gamma (NGF-gamma), and c-jun genes was significantly higher in the GSA-treated VSMCs. These results suggest that induction of antiapoptotic proteins like IAP-1 and strong mitogens like NGF-gamma by GSA might further contribute to the VSMC proliferation and accelerated vascular remodeling in diabetes.

Urocortin reduces the viability of adult rat vascular smooth muscle cells via inhibiting L-type calcium channels

The newly isolated peptide, urocortin (UCN), is a member of the corticotropin-releasing factor (CRF)-related peptides that has been found to have potent cardiovascular protective effects. In order to investigate the effect of UCN on the viability of adult rat vascular smooth muscle cells (VSMC) and the relevant mechanisms, we exposed the VSMC to UCN to observe the change in cell viability using MTT assay and intracellular calcium concentration using confocal laser scanning microscope methods. Our results showed that UCN (10(-7)M) inhibited the viability of VSMC by about 26% (P<0.05, compared to control). The effect was concentration-dependent, but it was not dependent on the affecting time. Glybenclamide (Gly, 10(-5)M), the ATP-sensitive potassium channel (K(ATP) channel) blocker, and astressin (10(-6)M), a competitive antagonist of CRF receptors, had no influence on this inhibition. Bay K8644 (10(-6)M), a special L-type calcium channel activator, increased the viability of VSMC. Pre-treatment of the cells with UCN diminished the effect of Bay K8644 (n=6, P<0.05). UCN was also observed to reduce the intracellular Ca2+ increase induced by KCl and Bay K8644. There was no significant difference in nitrite accumulation between UCN groups and the control. In conclusion, UCN reduced the viability of VSMC through L-type calcium channels. These interesting results might suggest that UCN may be a new vasoactive agent involved in hindering vascular remodeling in combination with previous reports about UCN's hypotensive effects.

Emerging functions of 10 types of TRP cationic channel in vascular smooth muscle

1. The influx of Ca2+, Mg2+ and Na+ and the efflux of K+ have central importance for the function and survival of vascular smooth muscle cells, but progress in understanding the influx/efflux pathways has been restricted by a lack of identification of the genes underlying many of the non-voltage-gated cationic channels. 2. The present review highlights evidence suggesting the genes are mammalian homologues of the Transient Receptor Potential (TRP) gene of the fruit-fly Drosophila. The weight of evidence supports roles for TRPC1, TRPP2/1 and TRPC6, but recent studies point also to TRPC3, TRPC4/5, TRPV2, TRPM4 and TRPM7. 3. Activity of these TRP channels is suggested to modulate contraction and sense changes in intracellular Ca2+ storage, G-protein-coupled receptor activation and osmotic stress. Roles in relation to myogenic tone, actions of vasoconstrictors substances, Mg2+ homeostasis and the vascular injury response are suggested. 4. Knowledge that TRP channels are relevant to vascular smooth muscle cells in both their contractile and proliferative phenotypes should pave the way for a better understanding of vascular biology and provide the basis for the discovery of a new set of therapeutic agents targeted to vascular disease.

D-Glucose upregulates adenosine transport in cultured human aortic smooth muscle cells

The etiology of the atherosclerosis that occurs in diabetes mellitus is unclear. Adenosine has been shown to inhibit growth of rat aortic smooth muscle cells. Nucleoside transporters play an integral role in adenosine function by regulating adenosine levels in the vicinity of adenosine receptors. Therefore, we studied the effect of 25 mM d-glucose, which mimics hyperglycemia of diabetes, on adenosine transport in cultured human aortic smooth muscle cells (HASMCs). Although RT-PCR demonstrated the presence of equilibrative nucleoside transporter-1 (ENT-1) and ENT-2 mRNA, functional studies revealed that adenosine transport in HASMCs was predominantly mediated by ENT-1 and inhibited by nitrobenzylmercaptopurine riboside (NBMPR, IC(50) = 0.69 +/- 0.05 nM). Adenosine transport in HASMCs was increased by >30% after treatment for 48 h with 25 mM d-glucose, but not with equimolar d-mannitol and l-glucose. Kinetic studies showed that d-glucose increased V(max) of adenosine transport without affecting K(m). Similarly, d-glucose increased B(max) of high-affinity [(3)H]NBMPR binding, while the dissociation constant (K(d)) was not changed. Consistent with these observations, 25 mM d-glucose increased mRNA and protein expression of ENT-1. Treatment of serum-starved cells with the selective inhibitors of MAPK/ERK, PD-98059 (40 microM) and U-0126 (10 microM), abolished the effect of d-glucose on ENT-1. We conclude that d-glucose upregulates the protein and message expression and functional activity of ENT-1 in HASMCs, possibly via MAPK/ERK-dependent pathways. Pathologically, the increase in ENT-1 activity in diabetes may affect the availability of adenosine in the vicinity of adenosine receptors and, thus, alter vascular functions in diabetes.

Antiproliferative Action of an Angiotensin I-Converting Enzyme Inhibitory Peptide, Val-Tyr, via an L-Type Ca2+ Channel Inhibition in Cultured Vascular Smooth Muscle Cells

Recent antihypertensive studies have demonstrated that small peptides with angiotensin I-converting enzyme (ACE) inhibitory activity had an ability to lower or to modulate a pressor blood pressure response in mild hypertensive subjects. However, the underlying mechanisms still remain unclear. Based on our previous finding that a small peptide, Val-Tyr (VY), was accumulated in the rat aorta and kidney as well as in the circulating blood system, we here investigated whether antihypertensive small peptides exert an antiproliferative effect on serum- or mitogen-induced human vascular smooth muscle cells (VSMCs). Treatment with some ACE inhibitory small peptides (VY, Ile-Trp [IW], and Ile-Val-Tyr [IVY]) had diverse effects on serum-stimulated VSMC proliferation that were independent of their ACE inhibitory activity, though only VY exerted a potent antiproliferative action. VY also showed a greater inhibition of WST-8 incorporation in response to angiotensin (Ang) II-stimulation than the other two small peptides. The attenuation of Ang II-stimulated WST-8 incorporation by VY was not affected by Ang II receptor antagonists (losartan and saralasin ([Sar1, Ile8]-Ang II)), indicating that the antiproliferative action of VY may not be due to the peptide's antagonistic effect against Ang II receptors. Treatment with VY had a significant inhibitory effect on the WST-8 incorporation induced by the stimulation of a voltage-gated L-type Ca2+ channel agonist, Bay K 8644. Even in the presence of a K+ channel blocker (paxillin) the inhibition was apparent, suggesting that VY inhibited the proliferation of VSMCs by serving as a natural L-type Ca2+ channel blocker, but not as a K+ channel agonist.

On the antiatherogenity of calcium channel blockers: studies in proliferating vascular smooth muscle cells on age sensitivity, dose dependent inhibitory effect, and time of action

We study the effect of diltiazem on cultured vascular smooth muscle cells from humans and rats, paying special attention to its activity in relation to the concentrations applied, incubation times after addition and the capacity to act against the mitogenic activity of insulin and insulin-like growth factor 1 (IGF-1). The mitotic activity was measured by means of bromodeoxyuridine DNA incorporation. Smooth muscle cells from old individuals showed a dose-dependent regression of the inhibitory level but not those from the young subjects, which showed a remarkable inhibition of mitosis at all concentrations tested. Around 8 h after addition, diltiazem inhibited cell proliferation at all concentrations tested. The inhibition exerted by 10(-7) M rapidly disappeared, reaching values higher than those initially registered and returning to basal rates after 72 h. The inhibition by 10(-6) and 10(-5) M remained after 30 and 72 h, respectively. Insulin (100 nM) or IGF-1 (1 nM) did not counteract the inhibitory effect of diltiazem (10(-5) M). Despite differences related to doses and age of cells, we conclude that diltiazem--as an L-type calcium channels blocker--is a potent inhibitor of vascular smooth muscle cell proliferation.

Altered functional coupling of coronary K+ channels in diabetic dyslipidemic pigs is prevented by exercise

Chronic hyperglycemia and hypercholesterolemia have been shown to alter ionic currents in vascular smooth muscle. We tested the hypothesis that the combined effect of hyperglycemia and hyperlipidemia (diabetic dyslipidemia) would increase the Ca2+-sensitive K+ (KCa) current as a compensatory response to an increase in intracellular Ca2+ concentration. We also hypothesized that exercise training would prevent this elevation in KCa current. Miniature Yucatan swine were randomly assigned to five groups: control, standard pig chow (C, n = 6); hyperlipidemic, high-fat pig chow (H, n = 5); diabetic, standard pig chow (D, n = 7); diabetic, high-fat pig chow ("diabetic dyslipidemic," DD, n = 12); and exercise-trained DD (DDX, n = 9). High-fat chow consisted of standard minipig chow supplemented with cholesterol (2%) and coconut oil. Increased coronary vasoconstriction assessed in vivo and in vitro in DD was prevented by exercise. Patch-clamp experiments performed on right coronary artery smooth muscle cells resulted in greater K+ current densities in the H, D, and DD groups vs. the DDX group between -10 and 40 mV. In fura 2-loaded cells, current activated by caffeine-induced Ca2+ release was greater in H, D, and DD compared with C and DDX (P < 0.05), whereas intracellular Ca2+ concentration was not different across groups. Finally, there were no differences in the KCa or Kv channel protein content between groups. These data indicate that hyperglycemia, hyperlipidemia, and diabetic dyslipidemia lead to elevated whole cell K+ current and increased functional coupling of KCa and Ca2+ release. Endurance exercise prevented increased coupling of Ca2+ release to KCa channel activation in diabetic dyslipidemia.

Hyperglycemia enhances VSMC proliferation with NF-kappaB activation by angiotensin II and E2F-1 augmentation by growth factors

To clarify the mechanisms of hyperglycemia-induced proliferation of vascular smooth muscle cells (VSMC), we examined the effects of high glucose (HG) on nuclear factor (NF)-kappaB and E2F-1. Angiotensin II (Ang II) significantly enhanced DNA binding activity of NF-kappaB under HG (25.6 mM) conditions with an increase in p65 subunit of NF-kappaB, and did it slightly under normal glucose (NG; 5.6 mM) conditions. Ang II failed to induce E2F-1 expression, or its binding to the cdc2 promoter, even under HG conditions. HG greatly augmented the cdc2 inducibility of fetal calf serum (FCS), through the increase in E2F-1 activity. These data indicate that hyperglycemia contributes to abnormal proliferation of VSMC by two mechanisms; the induction of NF-kappaB activation by Ang II, which facilitates transcription of certain growth factors, and the augmentation of E2F-1 in response to growth factors.

Expression of the AT2 receptor developmentally programs extracellular signal-regulated kinase activity and influences fetal vascular growth

Angiotensin II type 2 (AT2) receptor is abundantly expressed in vascular smooth muscle cells (VSMC) of the fetal vasculature during late gestation (embryonic day 15-20), during which the blood vessels undergo remodeling. To examine directly the influence of AT2 receptor expression in the developmental biology of VSMC, we studied cultures of VSMC from fetal and postnatal wild-type (Agtr2(+)) and AT2 receptor null (Agtr2(-)) mice. Consistent with in vivo data, AT2 receptor binding in cultured Agtr2(+) VSMC increased by age, peaking at embryonic day 20, and decreased dramatically after birth. Angiotensin II-induced growth in Agtr2(+) VSMC (embryonic day 20) was increased by the AT2 receptor blocker PD123319, indicating that the AT2 receptors are functional and exert an antigrowth effect in Agtr2(+) VSMC. Growth of VSMC in response to serum decreased age dependently and was higher in Agtr2(-) than in Agtr2(+), inversely correlating with AT2 receptor expression. However, serum-induced growth in Agtr2(+) and Agtr2(-) VSMC and the exaggerated Agtr2(-) VSMC growth was maintained even in the presence of PD123319 or losartan, an AT1 receptor blocker. Moreover, Agtr2(-) VSMC showed greater growth responses to platelet-derived growth factor and basic fibroblast growth factor, indicating that Agtr2(-) cells exhibit a generalized exaggerated growth phenotype. We studied the mechanism responsible for this phenotype and observed that extracellular signal-regulated kinase (ERK) activity was higher in Agtr2(-) VSMC at baseline and also in response to serum. ERK kinase inhibitor PD98059 inhibited both growth and ERK phosphorylation dose-dependently, while the regression lines between growth and ERK phosphorylation were identical in Agtr2(+) and Agtr2(-) VSMC, suggesting that increased ERK activity in Agtr2(-) VSMC is pivotal in the growth enhancement. Furthermore, the difference in ERK phosphorylation between Agtr2(+) and Agtr2(-) was abolished by vanadate but not by okadaic acid, implicating tyrosine phosphatase in the difference in ERK activity. These results suggest that the AT2 receptor expression during the fetal vasculogenesis influences the growth phenotype of VSMC via the modulation of ERK cascade.

Intracellular Ca2+ mediates lipoxygenase-induced proliferation of U-373 MG human astrocytoma cells

The role of intracellular Ca2+ in the regulation of tumor cell proliferation by products of arachidonic acid (AA) metabolism was investigated using U-373 MG human astrocytoma cells. Treatment with nordihydroguaiaretic acid (NDGA), a lipoxygenase (LOX) inhibitor, or caffeic acid (CA), a specific 5-LOX inhibitor, suppressed proliferation of the tumor cells in a dose-dependent manner. However, indomethacin (Indo), a cyclooxygenase (COX) inhibitor, did not significantly alter proliferation of the tumor cells. At anti-proliferative concentrations, NDGA and CA significantly inhibited intracellular Ca2+ release induced by carbachol, a known intracellular Ca2+ agonist in the tumor cells. Exogenous administration of leukotriene B4 (LTB4), an AA metabolite of LOX pathway, enhanced proliferation of the tumor cells in a concentration-dependent fashion. In addition, LTB4 induced intracellular Ca2+ release. Intracellular Ca2+ inhibitors, such as an intracellular Ca2+ chelator (BAPTA) and intracellular Ca(2+)-release inhibitors (dantrolene and TMB-8), significantly blocked the LTB4-induced enhancement of cell proliferation and intracellular Ca2+ release. These results suggest that LOX activity may be critical for cell proliferation of the human astrocytoma cells and that intracellular Ca2+ may play a major role in the mechanism of action of LOX.