NO attenuates insulin signaling and motility in aortic smooth muscle cells via protein tyrosine phosphatase 1B-mediated mechanism

Protein tyrosine phosphatase 1B in metabolic and cardiovascular diseases: from mechanisms to therapeutics

Protein Tyrosine Phosphatase 1B (PTP1B) has emerged as a significant regulator of metabolic and cardiovascular disease. It is a non-transmembrane protein tyrosine phosphatase that negatively regulates multiple signaling pathways integral to the regulation of growth, survival, and differentiation of cells, including leptin and insulin signaling, which are critical for development of obesity, insulin resistance, type 2 diabetes, and cardiovascular disease. Given PTP1B's central role in glucose homeostasis, energy balance, and vascular function, targeted inhibition of PTP1B represents a promising strategy for treating these diseases. However, challenges, such as off-target effects, necessitate a focus on tissue-specific approaches, to maximize therapeutic benefits while minimizing adverse outcomes. In this review, we discuss molecular mechanisms by which PTP1B influences metabolic and cardiovascular functions, summarize the latest research on tissue-specific roles of PTP1B, and discuss the potential for PTP1B inhibitors as future therapeutic agents.

Targeting Mitochondrial ATP-Synthase: Evolving Role of Chromium as a Regulator of Carbohydrate and Fat Metabolism

The micronutrient trivalent chromium, 3 + (Cr(III)), is postulated to play a role in carbohydrate, lipid, and protein metabolism. Although the mechanisms by which chromium mediates its actions are largely unknown, previous studies have suggested that pharmacological doses of chromium improve cardiometabolic symptoms by augmenting carbohydrate and lipid metabolism. Activation of AMP-activated protein kinase (AMPK) was among the many mechanisms proposed to explain the salutary actions of chromium on carbohydrate metabolism. However, the molecular pathways leading to the activation of AMPK by chromium remained elusive. In an elegant series of studies, Sun and coworkers recently demonstrated that chromium augments AMPK activation by binding to the beta-subunit of ATP synthase and inhibiting its enzymatic activity. This mini-review attempts to trace the evolving understanding of the molecular mechanisms of chromium leading to the hitherto novel pathway unraveled by Sun and coworkers and its potential implication to our understanding of the biological actions of chromium.

Flavonoids

Diabetes Mellitus is one of the major healthcare problems faced by the society today and has become alarmingly epidemic in many parts of the world. Despite enormous knowledge and technology advancement, available diabetes therapeutics only provide symptomatic relief by reducing blood glucose level, thereby, just slows down development and progression of diabetes and its associated complications. Thus, the need of the day is to develop alternate strategies that can not only prevent the progression but also reverse already “set-in” diabetic complications. Many flavonoids are reported, traditionally as well as experimentally, to be beneficial in averting diabetes and lowering risk of its accompanying complications. In the present chapter we have convened different flavonoids beneficial in diabetes and comorbid complications and discussed their mechanisms of action. Further, we conclude that coupling current therapeutics with flavonoids might provide exceptional advantage in the management of diabetes and its complications.

Relationships among protein tyrosine phosphatase 1B, angiotensin II, and insulin-mediated aortic responses in type 2 diabetic Goto-Kakizaki rats

OBJECTIVE

We investigated the relationships among protein tyrosine phosphatase 1B (PTP1B), angiotensin II (Ang II), and insulin signaling in the presence of endothelial dysfunction in type 2 diabetic Goto-Kakizaki (GK) rat aortas.

METHODS AND RESULTS

Aortas isolated from GK or control Wistar rats were examined in the presence or absence of Ang II with or without a selective antagonist of the Ang II type 1 (AT1) receptor or a PTP1B inhibitor to evaluate vascular functional and molecular mechanisms, such as insulin-induced relaxation, nitric oxide (NO) production, phosphorylation of insulin receptor substrate (IRS)-1, endothelial NO synthase (eNOS), and phosphorylation, and the subcellular localization of PTP1B. GK aortas exhibited reductions of: 1) insulin-induced relaxation, 2) NO production, 3) Ser(1177)-p-eNOS, and 4) Tyr(612)-p-IRS-1. Pre-incubation with a PTP1B inhibitor normalized these reductions. In Wistar aortas, the four above-mentioned parameters were reduced by Ang II, but were completely inhibited by co-treatment with the PTP1B inhibitor. The membrane expression of PTP1B was greater in GK than in Wistar aortas, and it was increased by Ang II in Wistar rats. The membrane PTP1B expression in the presence of insulin + Ang II was reduced by the PTP1B inhibitor or AT1-receptor antagonist.

CONCLUSIONS

These results suggest that the membrane PTP1B suppressed insulin-mediated aortic relaxation, and this was due to the Ang II-AT1-receptor signaling pathway. The inhibition of PTP1B warrants further investigation as a potential therapeutic target for endothelial dysfunction in type 2 diabetes.

IGF-1R modulation of acute GH-induced STAT5 signaling: role of protein tyrosine phosphatase activity

GH is a potent anabolic and metabolic factor that binds its cell surface receptor (GHR), activating the GHR-associated tyrosine kinase, Janus kinase 2, which phosphorylates and activates the latent transcription factor, signal transducer and activator of transcription 5 (STAT5). Some GH actions are mediated by the elaboration of IGF-1, which exerts effects by binding and activating the heterotetrameric tyrosine kinase growth factor receptor, IGF-1R. In addition to this GH-GHR-IGF-1-IGF-1R scheme, we have demonstrated in primary osteoblasts and in islet β-cells that then deletion or silencing of IGF-1R results in diminished GH-induced STAT5 phosphorylation, suggesting that the presence of IGF-1R may facilitate GH signaling. In this study, we explore potential roles for protein tyrosine phosphatase activity in modulating GH-induced signaling, comparing conditions in which IGF-1R is present or diminished. We confirm that in mouse primary osteoblasts harboring loxP sites flanking the IGF-1R gene, infection with an adenovirus that expresses the Cre recombinase results in IGF-1R deletion and diminished acute GH-induced STAT5 phosphorylation. Furthermore, we present a new model of IGF-1R silencing, in which expression of short hairpin RNA directed at IGF-1R greatly reduces IGF-1R abundance in LNCaP human prostate cancer cells. In both models, treatment with a chemical inhibitor of protein tyrosine phosphatase-1B (PTP-1B), but not one of src homology region 2 domain-containing phosphotase-1 (SHP-1) and SHP-2, reverses the loss of GH-induced STAT5 phosphorylation in cells lacking IGF-1R but has no effect in cells with intact IGF-1R. Furthermore, expression of either a dominant-negative PTP-1B or the PTP-1B-interacting inhibitory protein, constitutive photomorphogenesis 1, also rescues acute GH-induced STAT5 signaling in IGF-1R-deficient cells but has no effect in IGF-1R replete cells. By expressing a substrate-trapping mutant PTP-1B, we demonstrate that tyrosine phosphorylated Janus kinase-2 is a PTP-1B substrate only in cells lacking IGF-1R. Collectively, our data suggest that IGF-1R positively regulates acute GH signaling by preventing access of PTP-1B activity to Janus kinase 2 and thereby preventing PTP-1B-mediated suppression of GH-induced STAT5 activation.

Emerging drugs for the treatment of diabetic ulcers

INTRODUCTION

Diabetic ulcers are chronic nonhealing ulcerations that despite the available medical tools still result in high amputation rates. Growing evidence suggests that alteration of the biochemical milieu of the chronic wound plays a significant role in impaired diabetic wound healing.

AREAS COVERED

The basic pathophysiology and the conventional treatment strategy of diabetic foot ulcers have been reviewed in the first section. In the second part, the most up-to-date bench and translational research in the field are described. The third section focuses on the drugs currently under development and the ongoing clinical trials evaluating their safety and efficacy. Finally, the major drug development issues and the possible scientific approaches to overcome them are analyzed.

EXPERT OPINION

Significant strides in understanding the chronic wound development have led to the development of topical therapies to address aberrant expression of growth factors and overexpression of inflammatory cytokines. Current research in the laboratory suggests that while decreased growth factor expression occurs at the local wound level, increased systemic serum levels of growth factors suggest growth factor resistance.

Bisdemethoxycurcumin inhibits PDGF-induced vascular smooth muscle cell motility and proliferation

SCOPE

A key event in the development of plaque in the arteries is the migration and proliferation of smooth muscle cells (SMCs) from the media to the intima of the blood vessel. This study was conducted to evaluate the effects of bisdemethoxycurcumin (BC), a naturally occurring structural analog of curcumin (CC), on platelet-derived growth factor (PDGF)-stimulated migration and proliferation of SMCs.

METHODS AND RESULTS

CC and BC were synthesized by condensing acetyl acetone with vanillin and 4-hydroxybenzaldehyde, respectively. SMCs isolated from adult rat aorta were stimulated with PDGF in the presence or absence of CC or BC following which, cell migration and proliferation were assessed by monolayer wound healing assay and [(3) H]-thymidine incorporation respectively. PDGF-stimulated phosphorylation of PDGF receptor-β and its downstream effectors Akt and ERK were assessed by Western blotting. Intracellular reactive oxygen species was assessed using the fluorescent dye 5-(6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate. BC elicited a concentration-dependent inhibition of PDGF-stimulated phosphorylation of PDGF receptor-β, Akt and Erk as well as the PDGF-stimulated SMC migration and proliferation. BC was more potent than CC in inhibiting migration and proliferation and suppressing PDGF-signaling in SMCs. Both compounds were equipotent in inhibiting PDGF-stimulated generation of intracellular reactive oxygen species.

CONCLUSION

BC may be of potential use in the prevention or treatment of vascular disease.

Homocysteine activates vascular smooth muscle cells by DNA demethylation of platelet-derived growth factor in endothelial cells

Hyperhomocysteinemia (HHcy), as an independent risk factor of atherosclerosis, facilitates endothelial dysfunction and activation of vascular smooth muscle cells (VSMCs). However, little is known about the crosstalk between endothelial cells (ECs) and VSMCs under HHcy. We investigated whether homocysteine (Hcy) activates VSMCs by aberrant secretion of mitogen platelet-derived growth factors (PDGFs) from ECs in human and in mice. In this study, we found that increased Hcy level did not affect VSMC activity in 24 hrs until the concentration reached 500 μM. In contrast, Hcy at 100 μM significantly promoted proliferation and migration of VSMCs co-cultured with human ECs. This effect was partially reversed by pretreatment with a PDGF receptor inhibitor. Hcy concentration-dependently upregulated the mRNA level of PDGF-A, -C and -D but not PDGF-B in ECs. Hcy reduced the expression and activity of DNA methyltransferase 1, demethylation of PDGF-A, -C and -D promoters and enhanced the binding activity of transcriptional factor SP-1 to the promoter. Hcy upregulation of PDGF was confirmed in the aortic intima of mice with HHcy. Multivariate regression analysis revealed HHcy was a predictor of increased serum PDGF level in patients. Thus, Hcy upregulates PDGF level via DNA demethylation in ECs, affects cross-talk between ECs and VSMCs and leads to VSMC activation.

Molecular mechanisms of chromium in alleviating insulin resistance

Type 2 diabetes is often associated with obesity, dyslipidemia and cardiovascular anomalies and is a major health problem approaching global epidemic proportions. Insulin resistance, a prediabetic condition, precedes the onset of frank type 2 diabetes and offers potential avenues for early intervention to treat the disease. Although lifestyle modifications and exercise can reduce the incidence of diabetes, compliance has proved to be difficult, warranting pharmacological interventions. However, most of the currently available drugs that improve insulin sensitivity have adverse effects. Therefore, attractive strategies to alleviate insulin resistance include dietary supplements. One such supplement is chromium, which has been shown to reduce insulin resistance in some, but not all, studies. Furthermore, the molecular mechanisms of chromium in alleviating insulin resistance remain elusive. This review examines emerging reports on the effect of chromium, as well as molecular and cellular mechanisms by which chromium may provide beneficial effects in alleviating insulin resistance.

Modulatory Role of Nitric Oxide/cGMP System in Endothelin-1-Induced Signaling Responses in Vascular Smooth Muscle Cells

Nitric oxide (NO) is an important vasoprotective molecule that serves not only as a vasodilator but also exerts antihypertrophic and antiproliferative effects in vascular smooth muscle cells (VSMC). The precise mechanism by which the antihypertrophic and antiproliferative responses of NO are mediated remains obscure. However, recent studies have suggested that one of the mechanisms by which this may be achieved includes the attenuation of signal transduction pathways responsible for inducing the hypertrophic and proliferative program in VSMC. Endothelin-1 is a powerful vasoconstrictor peptide with mitogenic and growth stimulatory properties and exerts its effects by activating multiple signaling pathways which include ERK 1/2, PKB and Rho-ROCK. Both cGMP-dependent and independent events have been reported to mediate the effect of NO on these pathways leading to its vasoprotective response. This review briefly summarizes some key studies on the modulatory effect of NO on these signaling pathways and discusses the possible role of cGMP system in this process.

Chronic ethanol consumption up-regulates protein-tyrosine phosphatase-1B (PTP1B) expression in rat skeletal muscle

AIM

to investigate the potential effects of chronic ethanol intake on protein-tyrosine phosphatase-1B (PTP1B) and the insulin receptor signaling pathway in rat skeletal muscle.

METHODS

rats received ethanol treatment at a daily dose of 0 (control), 0.5 (group L), 2.5 (group M) or 5 gxkg(-1) (group H) via gastric gavage for 22 weeks. In vivo insulin sensitivity was measured using a hyperinsulinemic-euglycemic clamp. Expression of PTP1B in skeletal muscles was examined at both the mRNA (real-time PCR) and protein (Western blot) levels. PTP1B activity was assayed with a p-nitrophenol phosphate (PNPP) hydrolysis method. Changes of insulin signaling in skeletal muscle were analyzed with Western blotting.

RESULTS

the activity and expression of PTP1B were dose-dependently elevated 1.6 and 2.0 fold in the skeletal muscle by ethanol, resepctively, at the doses of 2.5 and 5 gxkg(-1)xd(-1). Total IRβ and IRS-1, as well as their phosphorylated forms, were decreased by ethanol at the two higher doses. Moreover, chronic ethanol consumption resulted in a significant inhibition of the association between IRS-1 and the p85 subunit of phosphatidylinositol 3-kinase, inhibition of Akt phosphorylation and reduced levels of mitogen-activated protein kinase phosphorylation.

CONCLUSION

chronic ethanol intake at 2.5 and 5 xkg(-1)xd(-1) sufficient doses can down-regulate the expression of IRβ, P-IRβ, and IRS-1, as well as the phosphorylated forms of IRS-1 and Akt, in rat skeletal muscle, possibly through increased PTP1B activity.

S-alkylating labeling strategy for site-specific identification of the s-nitrosoproteome

S-nitrosylation, a post-translational modification of cysteine residues induced by nitric oxide, mediates many physiological functions. Due to the labile nature of S-nitrosylation, detection by mass spectrometry (MS) is challenging. Here, we developed an S-alkylating labeling strategy using the irreversible biotinylation on S-nitrosocysteines for site-specific identification of the S-nitrosoproteome by LC-MS/MS. Using COS-7 cells without endogenous nitric oxide synthase, we demonstrated that the S-alkylating labeling strategy substantially improved the blocking efficiency of free cysteines, minimized the false-positive identification caused by disulfide interchange, and increased the digestion efficiency for improved peptide identification using MS analyses. Using this strategy, we identified total 586 unique S-nitrosylation sites corresponding to 384 proteins in S-nitroso-N-acetylpenicillamine (SNAP)/l-cysteine-treated mouse MS-1 endothelial cells, including 234 previously unreported S-nitrosylated proteins. When the topologies of 84 identified transmembrane proteins were further analyzed, their S-nitrosylation sites were found to mostly face the cytoplasmic side, implying that S-nitrosylation occurs in the cytoplasm. In addition to the previously known acid/basic motifs, the ten deduced consensus motifs suggested that combination of local hydrophobicity and acid/base motifs in the tertiary structure contribute to the specificity of S-nitrosylation. Moreover, the S-nitrosylated cysteines showed preference on beta-strand, having lower relative surface accessibility at the S-nitrosocysteines.

Suppression of PKG by PDGF or nitric oxide in differentiated aortic smooth muscle cells: obligatory role of protein tyrosine phosphatase 1B

Treatment of aortic smooth muscle cells with PDGF induces the upregulation of protein tyrosine phosphatase 1B (PTP1B). PTP1B, in turn, decreases the function of several growth factor receptors, thus completing a negative feedback loop. Studies have reported that PDGF induces the downregulation of PKG as part of a repertoire of dedifferentiation of vascular smooth muscle cells. Other studies have reported that chronic nitric oxide (NO) treatment also induces the downregulation of PKG. In the present study, we tested the hypothesis that the downregulation of PKG by PDGF or NO in differentiated rat aortic smooth muscle cells can be attributed to the upregulation of PTP1B. We found that treatment with PDGF or NO induced an upregulation of PTP1B levels. Overexpression of PTP1B induced a marked downregulation of PKG mRNA and protein levels, whereas the expression of dominant negative PTP1B or short interfering RNA directed against PTP1B blocked the capacity of PDGF or NO to decrease PKG levels. We conclude that the upregulation of PTP1B by PDGF or NO is both necessary and sufficient to induce the downregulation of PKG via an effect on PKG mRNA levels.

Mechanisms related to NO-induced motility in differentiated rat aortic smooth muscle cells

Nitric oxide (NO) is thought to play an important role as an inhibitor of vascular cell proliferation, motility, and neointima formation. This effect is mediated, in part, via the upregulation of protein tyrosine phosphatase (PTP)1B. Conversely, studies have reported that in presumably hyperinsulinemic mice fed a high-fat diet, NO enhances vascular remodeling, whereas a deficit of NO attenuates vascular remodeling. We have reported that in differentiated cultured smooth muscle cells treated with insulin, NO induces a motogenic effect that is dependent on Src homology-2 domain PTP 2 (SHP2) upregulation. In the present study, we describe novel mechanisms relevant to the motogenic effect of NO. Treatment of cultured cells with the selective angiontensin type 1 receptor antagonist losartan, but not with the selective angiotensin type 2 receptor antagonist PD-123319, blocked the comotogenic capacity of NO and insulin. Insulin and NO increased the secretion of ANG II into the culture media by 2- and 2.5-fold (P < 0.05), respectively, whereas treatment of cells with ANG II uncovered the motogenic effect of NO (1.4-fold above control, P < 0.05) and decreased the levels of PTP1B to 45% of control (P < 0.05). Suppression of PTP1B function was sufficient to uncover the motogenic effect of NO. The capacity of insulin to suppress PTP1B activity was blocked by losartan, implicating ANG II function in mediating this effect. Both insulin and ANG II induced the upregulation of phosphatidyl inositol 3-kinase (PI3K)-δ by two- to threefold (P < 0.05), and this effect was both necessary and sufficient to uncover NO-induced motogenesis. Finally, suppression of PTP1B function potentiated, whereas overexpression of PTP1B inhibited, SHP2-induced motogenesis. These results support the hypothesis that the comotogenic effect of insulin and NO occurs via an ANG II-mediated effect involving the suppression of PTP1B and upregulation of PI3K-δ and SHP2.

Aortic vasoreactivity during a postnatal critical window of the pancreas in rats

Changes in aortic vasoreactivity during the postnatal pancreatic critical window, where insulin and glucose, which modify vasoreactivity, are elevated, were studied and compared to those in control and metabolic syndrome (MS) rats. Twelve 21- and 28-day-old rats were used. To develop MS rats, male Wistar animals were given 30% sucrose in drinking water since weaning and used when 6 months old. Glucose and insulin levels were higher during suckling and decreased after weaning, and insulin and triglycerides levels increased in MS rats. Contraction elicited by norepinephrine (NE) was stronger than KCl contraction at all ages. KCl-induced contraction increased with, age being stronger in control rats; it further increased in MS rats. Norepinephrine-induced contraction increased from day 12 to day 28 but stabilized from day 21 to day 28; it was stronger in controls and increased in MS rats. Vasorelaxation to acetylcholine in NE precontracted rings did not change during the neonatal period, being similar to MS rats and lower than in controls. Insulin-induced increase in contraction elicited by KCl increased from day 12 to day 28 and increased from control to MS rats. There is a postnatal critical window in vasoreactivity that might predispose to cardiovascular diseases in adults.

VASP phosphorylation at serine239 regulates the effects of NO on smooth muscle cell invasion and contraction of collagen

Nitric oxide triggers cGMP-dependent kinase-mediated phosphorylation of the actin regulator vasodilator-stimulated phosphoprotein (VASP) at residue serine239. The function of this phosphorylation for smooth muscle cell (SMC) adhesion, spreading, matrix contraction, and invasion is not well understood. We reconstituted VASP deficient SMC with wild-type VASP (wt-VASP) or VASP mutants that mimic "locked" serine239 phosphorylation (S239D-VASP) or "blocked" serine239 phosphorylation (S239A-VASP). Collagen gel contraction was reduced in S239D-VASP compared to S239A-VASP and wt-VASP expressing cells and nitric oxide (NO) stimulation decreased gel contraction of wt-VASP reconstituted SMC. Invasion of collagen was enhanced in S239D-VASP and NO-stimulated wild-type SMCs compared to S239A-VASP expressing cells. Expression of S239D-VASP impaired SMC attachment to collagen, reduced the number of membrane protrusions, and caused cell rounding compared to expression of S239A-VASP. Treatment of wt-VASP reconstituted SMCs with NO exerted similar effects as expression of S239D-VASP. As unstimulated cells were spreading on collagen S239A-VASP and wt-VASP localized to actin fibers whereas S239D-VASP was enriched in the cytosol. NO interferes with SMC invasion and contraction of collagen matrices. This requires phosphorylation of VASP on serine239, which reduces VASP binding to actin fibers. These findings support the conclusion that VASP phosphorylation at serine239 regulates cytoskeleton remodeling.

Adiponectin improves cardiomyocyte contractile function in db/db diabetic obese mice

Low levels of adiponectin, a fat-derived hormone, are found to be correlated with coronary heart disease, type 2 diabetes, obesity, and insulin resistance. Conversely, high adiponectin levels are predictive of reduced coronary risk in long-term epidemiologic studies. However, the precise role of adiponectin in cardiomyocyte function is still not clear. This study was designed to examine the role of adiponectin in cardiac contractile function in the db/db model of diabetic obesity. Mechanical properties and intracellular Ca(2+) transients were evaluated in cardiomyocytes from lean control and db/db mice with or without adiponectin (10 microg/ml) treatment. Expression and phosphorylation of IRS-1, Akt, c-Jun, and c-Jun N terminal kinase (JNK) as well as markers of endoplasmic reticulum (ER) stress were evaluated using western blotting. Cardiomyocytes from db/db mice exhibited greater cross-sectional area, depressed peak shortening (PS), and maximal velocity of shortening/re-lengthening as well as prolonged duration of re-lengthening. Consistently, myocytes from db/db mice displayed a reduced electrically stimulated rise in intracellular Ca(2+) and prolonged intracellular Ca(2+) decay, which were abrogated by adiponectin treatment. Ratios between phosphorylated c-Jun and c-Jun as well as phosphorylated IRS-1 and IRS-1 were increased in db/db mice, the effect of which was attenuated by adiponectin. Levels of the phosphorylated ER stress makers PERK (Thr980), IRE-1, and eIF2alpha were significantly elevated in db/db mice compared with lean controls, although the effect was unaffected by adiponectin. Collectively, our data suggest that adiponectin improves cardiomyocyte dysfunction in db/db diabetic obese mice through a mechanism possibly related to c-Jun and IRS-1.

Chronic insulin treatment suppresses PTP1B function, induces increased PDGF signaling, and amplifies neointima formation in the balloon-injured rat artery

We tested the hypothesis that hyperinsulinemia induces the suppression of protein tyrosine phosphatase 1B (PTP1B) function, leading to enhanced PDGF receptor (PDGFR) signaling and neointimal hyperplasia. Rats were implanted with insulin-releasing pellets or sham pellets. Blood glucose levels, insulin levels, food and water intake, body weights, and blood pressures were measured. Neointimal hyperplasia was assessed by computerized morphometry 14 days after carotid balloon injury. PTP1B protein expression in injured arteries was determined via Western blot analysis, whereas PTP1B activity was determined via an immunophosphatase assay. Serum insulin levels were two- to threefold greater in hyperinsulinemic rats, whereas systolic blood pressures, food and water intake, serum triglyceride levels, plasma cortisol levels, and urinary catecholamine levels were not affected. Fourteen days after injury, neointima-to-media area ratios were 0.89 +/- 0.23 and 1.35 +/- 0.22 in control and hyperinsulinemic rats, respectively (P < 0.01). PTP1B protein levels and total PTP1B activity in injured carotid arteries from the insulin-treated group were significantly decreased 7 or 14 days after injury, whereas PTP1B specific activity was decreased only 14 days after injury. These findings were associated with decreased PTP1B mRNA levels and increased PDGFR tyrosyl phosphorylation in insulin-treated rats. These observations support the hypothesis that hyperinsulinemia induces the suppression of PTP1B function, leading to enhanced PDGFR signaling and neointimal hyperplasia.

Chromium alleviates glucose intolerance, insulin resistance, and hepatic ER stress in obese mice

OBJECTIVE

Chromium has gained popularity as a nutritional supplement for diabetic patients. This study evaluated the effect of chronic administration of a chromium complex of D-phenylalanine (Cr(D-phe)(3)) on glucose and insulin tolerance in obese mice. The study tested the hypothesis that Cr(D-phe)(3) suppresses endoplasmic reticulum (ER) stress and insulin resistance in these animals.

METHODS AND PROCEDURES

C57BL lean and ob/ob obese mice were randomly divided to orally receive vehicle or Cr(D-phe)(3) (3.8 mug of elemental chromium/kg/day) for 6 months. Insulin sensitivity was evaluated by glucose and insulin tolerance tests. Protein levels of phosphorylated pancreatic ER kinase (PERK), alpha subunit of translation initiation factor 2 (eIF2alpha) and inositol-requiring enzyme-1 (IRE-1), p-c-Jun, and insulin receptor substrate-1 (IRS-1) phosphoserine-307 were assessed by western blotting. In vitro ER stress was induced by treating cultured muscle cells with thapsigargin in the presence or absence of Cr(D-phe)(3).

RESULTS

ob/ob mice showed poor glucose and insulin tolerance compared to the lean controls, which was attenuated by Cr(D-phe)(3). Markers of insulin resistance (phospho-c-Jun and IRS-1 phosphoserine) and ER stress (p-PERK, p-IRE-1, p-eIF2alpha), which were elevated in ob/ob mice, were attenuated following Cr(D-phe)(3) treatment. Chromium treatment was also associated with a reduction in liver triglyceride levels and lipid accumulation. In cultured myotubes, Cr(D-phe)(3) attenuated ER stress induced by thapsigargin.

DISCUSSION

Oral Cr(D-phe)(3) treatment reduces glucose intolerance, insulin resistance, and hepatic ER stress in obese, insulin-resistant mice.

Chronic insulin treatment amplifies PDGF-induced motility in differentiated aortic smooth muscle cells by suppressing the expression and function of PTP1B

Hyperinsulinemia plays a major role in the pathogenesis of vascular disease. Restenosis occurs at an accelerated rate in hyperinsulinemia and is dependent on increased vascular smooth muscle cell movement from media to neointima. PDGF plays a critical role in mediating neointima formation in models of vascular injury. We have reported that PDGF increases the levels of protein tyrosine phosphatase PTP1B and that PTP1B suppresses PDGF-induced motility in cultured cells and that it attenuates neointima formation in injured carotid arteries. Others have reported that insulin enhances the mitogenic and motogenic effects of PDGF in cultured smooth muscle cells and that hyperinsulinemia promotes vascular remodeling. In the present study, we tested the hypothesis that insulin amplifies PDGF-induced cell motility by suppressing the expression and function of PTP1B. We found that chronic but not acute treatment of cells with insulin enhances PDGF-induced motility in differentiated cultured primary rat aortic smooth muscle cells and that it suppresses PDGF-induced upregulation of PTP1B protein. Moreover, insulin suppresses PDGF-induced upregulation of PTP1B mRNA levels, PTP1B enzyme activity, and binding of PTP1B to the PDGF receptor-beta, and it enhances PDGF-induced PDGF receptor phosphotyrosylation. Treatment with insulin induces time-dependent upregulation of phosphatidylinositol 3-kinase (PI3-kinase)-delta and activation of Akt, an enzyme downstream of PI3-kinase. Finally, inhibition of PI3-kinase activity, or its function, by pharmacological or genetic means rescues PTP1B activity in insulin-treated cells. These observations uncover novel mechanisms that explain how insulin amplifies the motogenic capacity of the pivotal growth factor PDGF.

Regulation of Src homology 2-containing protein tyrosine phosphatase by advanced glycation end products: the role on atherosclerosis in diabetes

Advanced glycation end products (AGEs), among the most important causes of atherosclerosis in diabetes mellitus, stimulate the proliferation of smooth muscle cells (SMCs). Smooth muscle cells are central in the formation of atherosclerotic lesions, where they show both increased migration and accelerated proliferation. In investigating how AGEs stimulate SMC proliferation, we focused on protein tyrosine phosphatase, especially Src homology 2-containing protein tyrosine phosphatase (SHP2), which is considered important in regulating cell proliferation. Advanced glycation end products increased activity of SHP2 in the membrane fraction of rat aortic SMCs compared with control bovine serum albumin (P < .05). Upon characterizing the genomic and promoter structure of SHP2, we detected nuclear factor-kappaB (NF-kappaB) binding sites in the promoter area. Advanced glycation end product stimulation increased luciferase activity in cells transfected with SHP2 promoter region including NF-kappaB binding sites (P < .05) and increased SHP2 expression (P < .05). These data indicate that AGE stimulation appears to activate NF-kappaB. Activated NF-kappaB binds to sites on the SHP2 promoter, resulting in increased SHP2 expression, SHP2 activity, and, ultimately, SMC proliferation. It suggests that AGE stimulation induces SMC proliferation via SHP2, underscoring the importance of control of AGE for suppressing macroangiopathy in diabetes mellitus.

cAMP inhibits transforming growth factor-beta-stimulated collagen synthesis via inhibition of extracellular signal-regulated kinase 1/2 and Smad signaling in cardiac fibroblasts

Cardiac fibroblasts produce and degrade extracellular matrix and are critical in regulating cardiac remodeling and hypertrophy. Cytokines such as transforming growth factor-beta (TGF-beta) play a fundamental role in the development of tissue fibrosis by stimulating matrix deposition and other profibrotic responses, but less is known about pathways that might inhibit fibrosis. Increased cAMP formation inhibits myofibroblast differentiation and collagen production by cardiac fibroblasts, but the mechanism of this inhibition is not known. We sought to characterize the signaling pathways by which cAMP-elevating agents alter collagen expression and myofibroblast differentiation. Treatment with 10 microM forskolin or isoproterenol increased cAMP production and cAMP response element binding protein (CREB) phosphorylation in cardiac fibroblasts and inhibited serum- or TGF-beta-stimulated collagen synthesis by 37% or more. These same cAMP-elevating agents blunted TGF-beta-stimulated expression of collagen I, collagen III, and alpha-smooth muscle actin. Forskolin or isoproterenol treatment blocked the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) induced by TGF-beta despite the fact that these cAMP-elevating agents stimulated ERK1/2 activation on their own. cAMP-elevating agents also attenuated the activation of c-Jun NH(2)-terminal kinase and reduced binding of the transcriptional coactivator CREB-binding protein 1 to transcriptional complexes containing Smad2, Smad3, and Smad4. Pharmacological inhibition of ERK completely blocked TGF-beta-stimulated collagen gene expression, but expression of an active mutant of MEK was additive with TGF-beta treatment. Thus, cAMP-elevating agents inhibit the profibrotic effects of TGF-beta in cardiac fibroblasts largely through inhibiting ERK1/2 phosphorylation but also by reducing Smad-mediated recruitment of transcriptional coactivators.

Counter-regulatory function of protein tyrosine phosphatase 1B in platelet-derived growth factor- or fibroblast growth factor-induced motility and proliferation of cultured smooth muscle cells and in neointima formation

OBJECTIVE

We have previously reported that vascular injury or treatment of cultured vascular smooth muscle cells with platelet-derived growth factor-BB (PDGF-BB) or fibroblast growth factor-2 (FGF2) increases the levels of protein tyrosine phosphatase (PTP)1B. The current study was designed to test the hypothesis that PTP1B attenuates PDGF- or FGF-induced motility and proliferation of cultured cells, as well as neointima formation in injured rat carotid arteries.

METHODS AND RESULTS

Treatment of cultured cells with adenovirus expressing PTP1B decreased PDGF-BB- or FGF2-induced cell motility and blocked PDGF-BB- or FGF2-induced proliferation, whereas expression of dominant negative PTP1B (C215S-PTP1B) uncovered the motogenic effect of subthreshold levels of PDGF-BB or FGF2, increased neointimal and medial cell proliferation, and induced neointimal enlargement after balloon injury. The inhibitory effect of PTP1B directed against PDGF in cultured cells was associated with dephosphorylation of the PDGFbeta receptor.

CONCLUSIONS

PTP1B suppresses cell proliferation and motility in cultured smooth muscle cells treated with PDGF-BB or FGF2, and the phosphatase plays a counter-regulatory role in vascular injury-induced cell proliferation and neointima formation. Taken together with previous studies indicating increased PTP1B levels in cells treated with growth factors, the current findings are the first to report the existence of an inhibitory feedback loop involving PDGF or FGF, and PTP1B in blood vessels.

Nitric oxide attenuates IGF-I-induced aortic smooth muscle cell motility by decreasing Rac1 activity: essential role of PTP-PEST and p130cas

Recent data support the hypothesis that reactive oxygen species (ROS) play a central role in the initiation and progression of vascular diseases. An important vasoprotective function related to the regulation of ROS levels appears to be the antioxidant capacity of nitric oxide (NO). We previously reported that treatment with NO decreases phosphotyrosine levels of adapter protein p130(cas) by increasing protein tyrosine phosphatase-proline, glutamate, serine, and threonine sequence protein (PTP-PEST) activity, which leads to the suppression of agonist-induced H(2)O(2) elevation and motility in cultured rat aortic smooth muscle cells (SMCs). The present study was performed to investigate the hypotheses that 1) IGF-I increases the activity of the small GTPase Rac1 as well as H(2)O(2) levels and 2) NO suppresses IGF-I-induced H(2)O(2) elevation by decreasing Rac1 activity via increased PTP-PEST activity and dephosphorylation of p130(cas). We report that IGF-I induces phosphorylation of p130(cas) and activation of Rac1 and that NO attenuates these effects. The effects of NO are mimicked by the overexpression of PTP-PEST or dominant-negative (dn)-p130(cas) and antagonized by the expression of dn-PTP-PEST or p130(cas). We conclude that IGF-I induces rat aortic SMC motility by increasing phosphotyrosine levels of p130(cas) and activating Rac1 and that NO decreases motility by activating PTP-PEST, inducing dephosphorylating p130(cas), and decreasing Rac1 activity. Decreased Rac1 activity lowers intracellular H(2)O(2) levels, thus attenuating cell motility.

Curcumin inhibits platelet-derived growth factor-stimulated vascular smooth muscle cell function and injury-induced neointima formation

OBJECTIVE

Vascular smooth muscle cell (VSMC) migration, proliferation, and collagen synthesis are key events involved in the pathogenesis of cardiovascular disease. Growth factors, such as platelet-derived growth factor (PDGF) and fibroblast growth factor, released during vascular injury plays a pivotal role in regulating these events. Curcumin (diferuloyl methane), a major component of the spice turmeric (Curcuma longa), has been shown recently to have beneficial effects in chronic conditions, such as inflammation, cancer, cystic fibrosis, and Alzheimer's disease. The objective of this study was to investigate the ability of curcumin to inhibit PDGF-stimulated migration, proliferation, and collagen synthesis in cultured VSMCs and neointima formation after carotid artery injury in rats.

METHODS AND RESULTS

Curcumin (1 to 25 microM) produced a concentration-dependent inhibition of PDGF-elicited VSMC migration, proliferation, and collagen synthesis assessed by chemotaxis, [3H]thymidine incorporation, and [3H]-L-proline incorporation, respectively. Curcumin blocked PDGF-induced VSMC actin-cytoskeleton reorganization, attenuated PDGF signal transduction, and inhibited the binding of PDGF to its receptors. Carotid artery neointima formation was significantly attenuated by perivascular curcumin compared with vehicle controls 14 days after injury, characterized by reduced DNA synthesis, collagen synthesis, and PDGF receptor phosphorylation.

CONCLUSIONS

These data suggest that curcumin is a potent inhibitor of key PDGF-stimulated VSMC functions and may play a critical role in regulating these events after vascular injury.

NO mediates mural cell recruitment and vessel morphogenesis in murine melanomas and tissue-engineered blood vessels

NO has been shown to mediate angiogenesis; however, its role in vessel morphogenesis and maturation is not known. Using intravital microscopy, histological analysis, alpha-smooth muscle actin and chondroitin sulfate proteoglycan 4 staining, microsensor NO measurements, and an NO synthase (NOS) inhibitor, we found that NO mediates mural cell coverage as well as vessel branching and longitudinal extension but not the circumferential growth of blood vessels in B16 murine melanomas. NO-sensitive fluorescent probe 4,5-diaminofluorescein imaging, NOS immunostaining, and the use of NOS-deficient mice revealed that eNOS in vascular endothelial cells is the predominant source of NO and induces these effects. To further dissect the role of NO in mural cell recruitment and vascular morphogenesis, we performed a series of independent analyses. Transwell and under-agarose migration assays demonstrated that endothelial cell-derived NO induces directional migration of mural cell precursors toward endothelial cells. An in vivo tissue-engineered blood vessel model revealed that NO mediates endothelial-mural cell interaction prior to vessel perfusion and also induces recruitment of mural cells to angiogenic vessels, vessel branching, and longitudinal extension and subsequent stabilization of the vessels. These data indicate that endothelial cell-derived NO induces mural cell recruitment as well as subsequent morphogenesis and stabilization of angiogenic vessels.

Essential role of protein kinase G and decreased cytoplasmic Ca2+ levels in NO-induced inhibition of rat aortic smooth muscle cell motility

Hyperinsulinemia is a major risk factor for the development of vascular disease. We have reported that insulin increases the motility of vascular smooth muscle cells via a hydrogen peroxide-mediated mechanism and that nitric oxide (NO) attenuates insulin-induced motility via a cGMP-mediated mechanism. Events downstream of cGMP elevation have not yet been investigated. The aim of our study was to test the hypothesis that antimotogenic effects of NO and cGMP in cultured rat aortic smooth muscle cells are mediated via PKG, followed by reduction of cytoplasmic Ca(2+) levels and increased protein tyrosine phosphatase-proline, glutamate, serine, and threonine activity, leading to suppression of agonist-induced elevation of hydrogen peroxide levels and cell motility. Treatment of primary cultures with adenovirus expressing PKG-1alpha mimicked NO-induced inhibition of insulin-elicited hydrogen peroxide elevation and cell motility, whereas treatment with the pharmacological PKG inhibitor Rp-8-bromo-3',5'-cyclic monophosphorothioate (Rp-8-Br-cGMPS) rescued the stimulatory effects of insulin that were suppressed by NO donor. Treatment of cells with insulin failed to increase cytoplasmic Ca(2+) levels, whereas NO donor decreased cytoplasmic Ca(2+) levels in the presence or absence of insulin. Treatment of cells with the Ca(2+) chelator BAPTA mimicked the effects of PKG and the NO donor and increased the activity of PTP-PEST. Finally, treatment with a dominant negative allele of PTP-PEST reversed the inhibitory effect of BAPTA on cell motility and hydrogen peroxide elevation. We conclude that NO-induced inhibition of cell motility occurs via PKG-mediated reduction of basal cytoplasmic Ca(2+) levels, followed by increased PTP-PEST activity, leading to decreased hydrogen peroxide levels and reduced cell motility.

Increase of PTP levels in vascular injury and in cultured aortic smooth muscle cells treated with specific growth factors

Migration and proliferation of vascular smooth muscle cells are key events in injury-induced neointima formation. Several growth factors and ANG II are thought to be involved in neointima formation. A recent report indicated that vascular injury is associated with increased mRNA levels of protein tyrosine phosphatase (PTP)-1B (PTP-1B). In the present study, we tested the following hypotheses: 1) rat carotid artery injury induces the expression of PTP-1B, Src homology-2 domain phosphatase (SHP-2), and PTP-proline, glutamate, serine, and threonine sequence (PEST) protein; and 2) polypeptide growth factors as well as ANG II increase the levels of tyrosine phosphatases in cultured rat aortic smooth muscle cells. We found that vascular injury induced by balloon catheter increases the protein levels of aforementioned phosphatases and that these effects occur in a PTP specific, as well as temporally and regionally specific, manner. Moreover, treatment of cultured primary rat aortic smooth muscle cells with PDGF or bFGF, but not with IGF1, EGF, or ANG II, increases PTP-1B, SHP-2, and PTP-PEST protein levels. These results suggest that increased PDGF and bFGF levels, occurring after vascular injury, may induce expression of several PTPs.

Nitric oxide attenuates insulin- or IGF-I-stimulated aortic smooth muscle cell motility by decreasing H2O2 levels: essential role of cGMP

Insulin and insulin-like growth factor I (IGF-I) both play important roles in vascular remodeling. Moreover, nitric oxide (NO) is well established as a counterregulatory agent that opposes the actions of several vascular agonists, in part by decreasing smooth muscle motility. We tested the hypothesis that NO blocks insulin or IGF-I-induced rat aortic smooth muscle cell motility via a mechanism involving the attenuation of agonist-induced elevation of hydrogen peroxide levels and cGMP as mediator. Insulin or IGF-I induced an increase of hydrogen peroxide levels and cell motility. Both effects were blocked by catalase or diphenyleneiodonium, indicating that hydrogen peroxide elevation is necessary for induction of cell motility. Two NO donors mimicked the effects of catalase, indicating that NO decreases cell motility by suppressing agonist-induced elevation of hydrogen peroxide. A cGMP analogue mimicked the effect of NO, whereas a guanyl cyclase inhibitor blocked the effect of NO on hydrogen peroxide levels, indicating that elevation of cGMP is both necessary and sufficient to account for the reduction of hydrogen peroxide levels. A NO donor as well as a cGMP analogue attenuated insulin-stimulated NADPH activity, indicating that NO decreases hydrogen peroxide levels by inhibiting the generation of superoxide, via a cGMP-mediated mechanism. Finally, exogenous hydrogen peroxide increased cell motility and reversed the inhibitory effect of cGMP. These results support the view that NO plays an antioxidant role via reduction of hydrogen peroxide in cultured rat aortic smooth muscle cells and that this effect is both necessary and sufficient to account for its capacity to decrease cell motility.

Treatment With Insulin Uncovers the Motogenic Capacity of Nitric Oxide in Aortic Smooth Muscle Cells

Contrary to the antimotogenic effect of NO in dedifferentiated vascular smooth muscle cells (VSMCs), we have reported that NO stimulates the motility of differentiated cultured VSMC isolated from adult rats. This process involves upregulation of protein tyrosine phosphatase SHP2, followed by downregulation of RhoA activity. In the present study, we tested the hypothesis that insulin alters the motogenic phenotype of cultured rat aortic smooth muscle cells exposed to NO from inhibition to stimulation of cell motility. We demonstrate for the first time that NO stimulates the motility of VSMCs cultured for several days in the presence but not the absence of insulin. Moreover, we show that NO blocks PDGF-induced cell motility in insulin-naive but not in insulin-treated cells. We also demonstrate that the scaffold adapter protein Gab1, considered a physiological activator of protein tyrosine phosphatase SHP2, increases cell motility in the presence but not the absence of insulin. In cells cultured in the presence of insulin, overexpression of Gab1 mimics, whereas a dominant-negative allele of Gab1 (Gab1YF) blocks, the motility-stimulatory effect of NO. Cotransfection experiments with dominant-negative Gab1 and wild-type SHP2 or wild-type Gab1 and dominant-negative SHP2 indicate that the two proteins work together as a functional unit to induce motility. Because chronic insulin can increase the levels of phosphatidylinositol 3 (PI3) kinase in several models of hyperinsulinemia, we also tested the potential involvement of this enzyme in mechanisms leading to increased cell motility. We found that the motogenic effect of NO, Gab1, and SHP2 was blocked by the selective PI3 kinase inhibitor LY294002, suggesting a requirement of PI3 kinase in mediating motogenesis. These observations may be relevant to molecular mechanisms related to the pathogenesis of vascular disease in hyperinsulinemic diabetes. The full text of this article is available online at http://www.circresaha.org.

Amino acid transport regulates blastocyst implantation

Mouse blastocyst outgrowth in vitro and probably implantation in vivo require amino acid signaling via the target of rapamycin (TOR) pathway. This signaling does not simply support protein synthesis and trophoblast differentiation. Rather, it regulates development of trophoblast protrusive activity and may act as a developmental checkpoint for implantation. Moreover, intracellular amino acids per se are insufficient to elicit TOR signaling. Instead, de novo transport of amino acids, and particularly of leucine, stimulate mTOR activity at the blastocyst stage. The activity of the broad-scope and yet leucine-selective amino acid transport system B0,+ could produce such increases in intracellular amino acid concentrations. For example, system B0,+ uses a Na+ gradient to drive amino acid uptake, and the Na+ concentration in uterine secretions increases by nearly two-fold about 18 h before implantation. The resultant mTOR signaling could trigger polyamine, insulin-like growth factor II, and nitric oxide production in blastocysts and the increased cell motility sometimes associated with synthesis of these bioactive molecules.

Nitric oxide-induced inhibition of aortic smooth muscle cell motility: role of PTP-PEST and adaptor proteins p130cas and Crk

Vascular injury increases nitric oxide (NO) levels, and this effect may play a counterregulatory role in neointima formation, by decreasing vascular smooth muscle cell motility. However, the mechanisms underlying this effect are not well established. We tested the hypothesis that NO decreases cell motility by increasing the activity of a protein tyrosine phosphatase (PTP), PTP-PEST, in cultured rat aortic smooth muscle cells. Two NO donors increased the activity of PTP-PEST. A cGMP analog mimicked the effect of NO, whereas a guanyl cyclase inhibitor blocked it, indicating that elevated cGMP is both necessary and sufficient to induce PTP-PEST activity. Overexpression of wild-type PTP-PEST induced antimotogenesis, whereas expression of dominant negative PTP-PEST blocked the antimotogenic effect of NO, indicating that increased PTP-PEST activity is both sufficient and necessary to explain the effect of NO. Overexpression of PTP-PEST mimicked NO-induced dephosphorylation of adapter protein p130cas, whereas dominant negative PTP-PEST blocked the effect of NO, indicating that upregulation of PTP-PEST is both necessary and sufficient to explain NO-induced p130cas dephosphorylation. Expression of a substrate domain-deleted p130cas decreased motogenesis, whereas overexpression of wild-type p130cas blocked the antimotogenic effect of NO, indicating the functional importance of p130cas dephosphorylation. NO induced dissociation of the Cas-Crk complex, an effect that was mimicked by overexpression of PTP-PEST and opposed by expression of dominant negative PTP-PEST. Our results indicate that NO decreases aortic smooth muscle cell motility via a cGMP-mediated mechanism, involving upregulation of PTP-PEST, in turn inducing dephosphorylation of p130cas, and likely involving Cas-Crk dissociation as a downstream event.

Nitric oxide-induced motility in aortic smooth muscle cells: role of protein tyrosine phosphatase SHP-2 and GTP-binding protein Rho

We have previously reported that SHP-2 upregulation is necessary for NO-stimulated motility in differentiated rat aortic smooth muscle cells. We now test the hypothesis that upregulation of SHP-2 is necessary and sufficient to stimulate cell motility. Overexpression of SHP-2 via recombinant adenoviral vector stimulated motility to the same extent as NO, whereas the expression of C463S-SHP-2, the dominant-negative SHP-2 allele, blocked the motogenic effect of NO. On the basis of previous studies, we next tested the hypothesis that NO decreases RhoA activity and that this event is necessary and sufficient to explain NO-induced motogenesis. We found that NO decreased RhoA activity in a concentration-dependent manner. Moreover, a dominant-negative SHP-2 allele, DSH2, blocked the NO-induced inhibition of RhoA activity, indicating that upregulation of SHP-2 is necessary for this event. Expression of G14V-RhoA, the constitutively active RhoA allele, decreased cell motility and blocked the motogenic effect of NO, whereas the expression of T19N-RhoA, the dominant-negative RhoA allele, increased cell motility to an extent similar to that induced by NO. Dominant-negative RhoA reversed the effect of dominant-negative SHP-2, indicating that RhoA functions downstream from SHP-2. To investigate events downstream from RhoA, we treated cells with fasudil, a selective Rho kinase inhibitor, and found that it increased cell motility. These results indicate that upregulation of SHP-2, leading to downregulation of RhoA, which is followed by decreased Rho kinase activity, is a sequence of events necessary and sufficient to explain NO-induced cell motility in differentiated aortic smooth muscle cells. The results may be of relevance to in vivo events such as neointimal formation, angiogenesis, and vasculogenesis.