AJP Endocrinology and Metabolism (AM J PHYSIOL-ENDOC M)

Publications in this journal

• Article: Glucagon-like Peptide1 Receptor Mediated Endosomal cAMP Generation Promotes Glucose Stimulated Insulin Secretion in Pancreatic beta Cells

  Ramya S Kuna, Shravan Babu Girada, Suman Asalla, Joyprashant Vallentyne, Maddika S, James T Patterson, David L Smiley, Richard D DiMarchi, Prasenjit Mitra
  [show abstract] [hide abstract]
  ABSTRACT: Glucagon-like peptide 1 (GLP-1) receptor plays a major role in promoting glucose stimulated insulin secretion in pancreatic beta cells. Here in our present study we synthesized a novel functional analogue of GLP-1 conjugated to tetramethyl rhodamine to monitor the internalization of the receptor. Our data shows that receptor after being internalized is sorted to lysosomes. In endosomes, receptor-ligand complex is found to be co-localized with adenylate cyclase. Pharmacological inhibition of endocytosis attenuates GLP-1 receptor mediated cAMP generation and consequent downstream protein kinase-A substrate phosphorylation and glucose stimulated insulin secretion. Our study underlines a paradigm shift in GLP-1 receptor signaling and trafficking. The receptor ligand complex triggers cAMP generation both in plasma membrane and in endosomes which has implications for receptor mediated regulation of insulin secretion
  AJP Endocrinology and Metabolism 04/2013;
• Article: Cellular cross-talk between epicardial adipose tissue and myocardium in relation to the pathogenesis of cardiovascular disease.

  Cherian S, Lopaschuk GD, Carvalho E
  [show abstract] [hide abstract]
  ABSTRACT: Epicardial and perivascular fat depot size is considered an index of cardiac and visceral obesity. The functional and anatomic proximity of epicardial adipose tissue (EAT) to myocardium has drawn increasing attention among researchers in recent years attempting to elucidate its putative role as an endocrine organ. This includes its role as a lipid storing depot, and as an inflammatory tissue secreting cytokines and chemokines under pathogenic conditions such as cardiovascular diseases. In this review we discuss the current state of knowledge regarding the potential EAT mediators of inflammation and the paracrine cross-talk between EAT and the underlying myocardium. We will also seek to highlight the most recent findings on the causes and correlates of myocardial steatosis/cardiac lipotoxicity and its association with cardiac dysfunction.
  AJP Endocrinology and Metabolism 08/2012;
• Article: Effects of atorvastatin on the regeneration of pancreatic {beta}-cells after streptozotocin treatment in the neonatal rodent. K C Marchand, E J Arany, D J Hill

  K C Marchand, E Arany, D J Hill
  AJP Endocrinology and Metabolism 01/2010; 299(1):E92-E-100.
• Article: A useful list of spontaneously arising animal models of obesity and diabetes.

  Eleazar Shafrir, Ehud Ziv
  AJP Endocrinology and Metabolism 07/2009; 296(6):E1450-2.
• Article: Visfatin activates eNOS via Akt and MAP kinases and improves endothelial cell function and angiogenesis in vitro and in vivo: translational implications for atherosclerosis.

  Fina Lovren, Yi Pan, Praphulla C Shukla, Adrian Quan, Hwee Teoh, Paul E Szmitko, Mark D Peterson, Milan Gupta, Mohammed Al-Omran, Subodh Verma
  [show abstract] [hide abstract]
  ABSTRACT: Improving endothelial nitric oxide synthase (eNOS) bioactivity and endothelial function is important to limit native, vein graft, and transplant atherosclerosis. Visfatin, a NAD biosynthetic enzyme, regulates the activity of the cellular survival factor, Sirt1. We hypothesized that visfatin may improve eNOS expression, endothelial function, and postnatal angiogenesis. In human umbilical vein (HUVEC) and coronary artery endothelial cells, we evaluated the effects of recombinant human visfatin on eNOS protein and transcript expression and mRNA stability, in the presence and absence of visfatin RNA silencing. We also assessed visfatin-induced protein kinase B (Akt) activation and its association with src-tyrosine kinases, phosphorylation of Ser(1177) within eNOS in the presence and absence of phosphatidylinositol 3-kinase (PI 3-kinase) inhibition with LY-294002, and evaluated the contributory role of extracellular signal-regulated kinase 1/2. Finally, we determined the impact of visfatin on HUVEC migration, proliferation, inflammation-induced permeability, and in vivo angiogenesis. Visfatin (100 ng/ml) upregulated and stabilized eNOS mRNA and increased the production of nitric oxide and cGMP. Visfatin-treated HUVEC demonstrated greater proliferation, migration, and capillary-like tube formation but less tumor necrosis factor-alpha-induced permeability; these effects were decreased in visfatin gene-silenced cells. Visfatin increased total Akt and Ser(473)-phospho-Akt expression with concomitant rises in eNOS phosphorylation at Ser(1177); these effects were blocked by LY-2940002. Studies with PP2 showed that the nonreceptor tyrosine kinase, src, is an upstream stimulator of the PI 3-kinase-Akt pathway. Visfatin also activated mitogen-activated protein (MAP) kinase through PI 3-kinase, and mitogen/extracellular signal-regulated kinase inhibition attenuated visfatin-elicited Akt and eNOS phosphorylation. Visfatin-filled Matrigel implants showed an elevated number of infiltrating vessels, and visfatin treatment produced significant recovery of limb perfusion following hindlimb ischemia. These results indicate a novel effect of visfatin to stimulate eNOS expression and function in endothelial cells, via a common upstream, src-mediated signaling cascade, which leads to activation of Akt and MAP kinases. Visfatin represents a translational target to limit endothelial dysfunction, native, vein graft and transplant atherosclerosis, and improve postnatal angiogenesis.
  AJP Endocrinology and Metabolism 05/2009; 296(6):E1440-9.
• Article: Effects of growth differentiation factor 9 on cell cycle regulators and ERK42/44 in human granulosa cell proliferation.

  Qing Huang, Anthony P Cheung, Yu Zhang, He-Feng Huang, Nelly Auersperg, Peter C K Leung
  [show abstract] [hide abstract]
  ABSTRACT: GDF-9 stimulates granulosa cell proliferation and plays important roles during folliclogenesis. However, its molecular mechanisms are still far from clear, particularly its roles in human granulosa cells around the periovulatory stage. Therefore, we investigated the effects of GDF-9 on cell cycle distribution, regulatory molecules, and signaling pathways involved in human luteinized granulosa (hLG) cells in vitro. Primary cultures of hLG cells obtained from women undergoing IVF and treated with and without recombinant GDF-9 were evaluated with and without a specific inhibitor to activin receptor-like kinase 5 (ALK5; SB-431542), ERK42/44 (PD-098059), or Smad3 (SIS3). Cell proliferation, cell cycle distribution, mRNA expression, and protein expression of relevant cell cycle molecules were determined by [(3)H]thymidine incorporation, flow cytometry, quantitative PCR, and immunoblotting, respectively. GDF-9 stimulated [(3)H]thymidine incorporation, enhanced cell transition from G(0)/G(1) to S and G(2)/M phases (whereas both SB-431542 and PD-098059 attenuated these changes), increased mRNA and protein expression of cyclin D(1) and E, and decreased those of the cyclin-dependent kinase (CDK) inhibitors p15(INK4B) and p16(INK4A). GDF-9 also activated Rb protein (a critical G(1) to S-phase regulator), ERK42/44, and Smad3. PD-098059 blocked Rb protein phorsphorylation and the increase in cyclin D(1) and E but not the decrease in p15(INK4B) and p16(INK4A) induced by GDF-9. In contrast, SIS3 reversed the decrease in p15(INK4B) and p16(INK4A) but not the increase in cyclin D(1) and E induced by GDF-9. GDF-9 stimulates hLG cell proliferation by stimulating cyclin D(1) and E and suppressing p15(INK4B) and p16(INK4A) via both Smad-dependent and Smad-independent pathways.
  AJP Endocrinology and Metabolism 05/2009; 296(6):E1344-53.
• Article: Arginine vasopressin regulation in pre- and postpubertal male rats by the androgen metabolite 3beta-diol.

  Toni R Pak, Wilson C J Chung, Laura R Hinds, Robert J Handa
  [show abstract] [hide abstract]
  ABSTRACT: Arginine vasopressin (AVP) is a nonapeptide expressed in several brain regions. In addition to its well-characterized role in osmoregulation, AVP regulates paternal behavior, aggression,circadian rhythms, and the stress response. In the bed nucleus of the stria terminalis (BST), AVP gene expression is tightly regulated by gonadal steroid hormones. However, the degree by which AVP is regulated by gonadal steroid hormones in the suprachiasmatic nucleus (SCN) and medial amygdala (MeA) is unclear. Previous studies have shown that AVP expression in the brain of gonadectomized rats is restored with testosterone, 17beta-estradiol, and 5alpha-dihydrotestosterone(DHT) replacement. In addition, we have demonstrated that 3beta-diol, a metabolite of DHT,increased AVP promoter activity in a neuronal cell line and that the effects of 3beta-diol on AVP promoter activity were mediated by estrogen receptor-beta. To test whether 3beta-diol has a physiological role in the regulation of central AVP expression in vivo, we gonadectomized pre- and postpubertal male rats and followed with once daily injections of estradiol benzoate (EB),DHT-propionate, 3beta-diol-dipropionate, or vehicle. The SCN, BST, and MeA were analyzed for AVP mRNA expression using in situ hybridization. In the BST, intact juveniles had significantly fewer AVP-expressing cells than adults. GDX abolished all AVP mRNA expression in the BST in both age groups, whereas treatment with EB restored >80% and DHTP <10% of the AVP expression. Interestingly, 3beta-diol-proprionate was more effective at inducing AVP expression in juveniles than in adults, suggesting that the regulation of AVP by 3beta-diol might be age dependent [corrected].
  AJP Endocrinology and Metabolism 05/2009; 296(6):E1409-13.
• Article: Dysregulated glutathione metabolism links to impaired insulin action in adipocytes.

  Hironori Kobayashi, Morihiro Matsuda, Atsunori Fukuhara, Ryutaro Komuro, Iichiro Shimomura
  [show abstract] [hide abstract]
  ABSTRACT: Oxidative stress plays an important role in obesity-related metabolic diseases. Glutathione peroxidase (GPX) is an antioxidant enzyme downregulated in adipose tissue of obese mice. However, the role of GPX in adipocytes remains elusive. The objective of this study was to clarify the pathophysiological changes in GPX activity and glutathione metabolism and their roles in the pathogenesis of insulin resistance in adipocytes. To achieve this goal, we measured cellular GPX activity, glutathione (GSH) contents, GSH/GSSG ratio, and mRNA expression of gamma-glutamylcysteine synthetase (gamma-GCS), a rate-limiting enzyme for de novo GSH synthesis, in adipose tissue of control and ob/ob mice and in 3T3-L1 adipocytes treated with insulin, H(2)O(2), free fatty acid (FFA), or TNFalpha. Furthermore, we investigated the effects of GPX inhibition with a specific GPX inhibitor or RNA interference against GPX, H(2)O(2), and reduced GSH on insulin signaling in 3T3-L1 adipocytes. ob/ob Mice showed not only a decrease in cellular activity of GPXs (GPX1, -4, and -7) but also an increase in gamma-GCS expression, resulting in increased GSH contents in adipose tissue. These alterations in glutathione metabolism were also observed during differentiation of 3T3-L1 cells and their exposure to insulin, FFA, or H(2)O(2). Inhibition of GPX activity, addition of GSH, and H(2)O(2) resulted in impaired insulin signaling in 3T3-L1 adipocytes. These results suggest that decreased GPX activity and increased gamma-GCS expression lead to overaccumulation of GSH, which might be involved in the pathogenesis of insulin resistance in obesity.
  AJP Endocrinology and Metabolism 05/2009; 296(6):E1326-34.
• Article: Involvement of SIK2/TORC2 signaling cascade in the regulation of insulin-induced PGC-1alpha and UCP-1 gene expression in brown adipocytes.

  Masaaki Muraoka, Aiko Fukushima, Say Viengchareun, Marc Lombès, Fukuko Kishi, Akira Miyauchi, Mariko Kanematsu, Junko Doi, Junko Kajimura, Ryo Nakai, Tatsuya Uebi, Mitsuhiro Okamoto, Hiroshi Takemori
  [show abstract] [hide abstract]
  ABSTRACT: Salt-inducible kinase 2 (SIK2) is expressed abundantly in adipose tissues and represses cAMP-response element-binding protein (CREB)-mediated gene expression by phosphorylating the coactivator transducer of regulated CREB activity (TORC2). Phosphorylation at Ser(587) of SIK2 diminishes its TORC2 phosphorylation activity. In 3T3-L1 white adipocytes, SIK2 downregulates lipogenic gene in response to nutritional stresses. To investigate the impact of SIK2 on the function of brown adipose tissue (BAT), we used T37i brown adipocytes, mice with diet-induced obesity, and SIK2 mutant (S587A) transgenic mice. When T37i adipocytes were treated with insulin, the levels of peroxisome proliferator-activated receptor-coactivator-1alpha (PGC-1alpha) and uncoupling protein-1 (UCP-1) mRNA were increased, and the induction was inhibited by overexpression of SIK2 (S587A) mutant or dominant-negative CREB. Insulin enhanced SIK2 phosphorylation at Ser(587), which was accompanied by decrease in phospho-TORC2. Similarly, the decrease in the level of SIK2 phosphorylation at Ser(587) was observed in the BAT of mice with diet-induced obesity, which was negatively correlated with TORC2 phosphorylation. To confirm the negative correlation between SIK2 phosphorylation at Ser(587) and TORC2 phosphorylation in BAT, SIK2 mutant (S587A) was overexpressed in adipose tissues by using the adipocyte fatty acid-binding protein 2 promoter. The expression of recombinant SIK2 (S587A) was restricted to BAT, and the levels of phospho-TORC2 were elevated in BAT of transgenic mice. Male transgenic mice developed high-fat diet-induced obesity, and their BAT expressed low levels of PGC-1alpha and UCP-1 mRNA, suggesting that SIK2-TORC2 cascade may be important for the regulation of PGC-1alpha and UCP-1 gene expression in insulin signaling in BAT.
  AJP Endocrinology and Metabolism 05/2009; 296(6):E1430-9.
• Article: Leucine restriction inhibits chondrocyte proliferation and differentiation through mechanisms both dependent and independent of mTOR signaling.

  Mimi S Kim, Ke Ying Wu, Valerie Auyeung, Qian Chen, Philip A Gruppuso, Chanika Phornphutkul
  [show abstract] [hide abstract]
  ABSTRACT: Linear growth in children is sensitive to nutritional status. Amino acids, in particular leucine, have been shown to regulate cell growth, proliferation, and differentiation through the mammalian target of rapamycin (mTOR), a nutrient-sensing protein kinase. Having recently demonstrated a role for mTOR in chondrogenesis, we hypothesized that leucine restriction, acting through mTOR, would inhibit growth plate chondrocyte proliferation and differentiation. The effect of leucine restriction was compared with that of the specific mTOR inhibitor, rapamycin. Leucine restriction produced a dose-dependent inhibition of fetal rat metatarsal explant growth. This was accounted by reduced cell proliferation and hypertrophy but not apoptosis. mTOR activity, as reflected by ribosomal protein S6 phosphorylation, was only partially inhibited by leucine restriction, whereas rapamycin abolished S6 phosphorylation. In chondrogenic ATDC5 cells, leucine restriction inhibited cell number, proteoglycan accumulation, and collagen X expression despite minimal inhibition of mTOR. Microarray analysis demonstrated that the effect of leucine restriction on ATDC5 cell gene expression differed from that of rapamycin. Out of 1,571 genes affected by leucine restriction and 535 genes affected by rapamycin, only 176 genes were affected by both. These findings indicate that the decreased chondrocyte growth and differentiation associated with leucine restriction is only partly attributable to inhibition of mTOR signaling. Thus nutrient restriction appears to directly modulate bone growth through unidentified mTOR-independent mechanisms in addition to the well-characterized mTOR nutrient-sensing pathway.
  AJP Endocrinology and Metabolism 05/2009; 296(6):E1374-82.
• Article: The glucose-dependent insulinotropic polypeptide and glucose-stimulated insulin response to exercise training and diet in obesity.

  Karen R Kelly, Latina M Brooks, Thomas P J Solomon, Sangeeta R Kashyap, Valerie B O'Leary, John P Kirwan
  [show abstract] [hide abstract]
  ABSTRACT: Aging and obesity are characterized by decreased beta-cell sensitivity and defects in the potentiation of nutrient-stimulated insulin secretion by GIP. Exercise and diet are known to improve glucose metabolism and the pancreatic insulin response to glucose, and this effect may be mediated through the incretin effect of GIP. The purpose of this study was to assess the effects of a 12-wk exercise training intervention (5 days/wk, 60 min/day, 75% Vo(2 max)) combined with a eucaloric (EX, n = 10) or hypocaloric (EX-HYPO, pre: 1,945 +/- 190, post: 1,269 +/- 70, kcal/day; n = 9) diet on the GIP response to glucose in older (66.8 +/- 1.5 yr), obese (34.4 +/- 1.7 kg/m(2)) adults with impaired glucose tolerance. In addition to GIP, plasma PYY(3-36), insulin, and glucose responses were measured during a 3-h, 75-g oral glucose tolerance test. Both interventions led to a significant improvement in Vo(2 max) (P < 0.05). Weight loss (kg) was significant in both groups but was greater after EX-HYPO (-8.3 +/- 1.1 vs. -2.8 +/- 0.5, P = 0.002). The glucose-stimulated insulin response was reduced after EX-HYPO (P = 0.02), as was the glucose-stimulated GIP response (P < 0.05). Furthermore, after the intervention, changes in insulin (DeltaI(0-30)/DeltaG(0-30)) and GIP (Delta(0-30)) secretion were correlated (r = 0.69, P = 0.05). The PYY(3-36) (Delta(0-30)) response to glucose was increased after both interventions (P < 0.05). We conclude that 1) a combination of caloric restriction and exercise reduces the GIP response to ingested glucose, 2) GIP may mediate the attenuated glucose-stimulated insulin response after exercise/diet interventions, and 3) the increased PYY(3-36) response represents an improved capacity to regulate satiety and potentially body weight in older, obese, insulin-resistant adults.
  AJP Endocrinology and Metabolism 04/2009; 296(6):E1269-74.
• Article: Ligand-based gene expression profiling reveals novel roles of glucocorticoid receptor in cardiac metabolism.

  Noritada Yoshikawa, Masao Nagasaki, Motoaki Sano, Satori Tokudome, Kazuko Ueno, Noriaki Shimizu, Seiya Imoto, Satoru Miyano, Makoto Suematsu, Keiichi Fukuda, Chikao Morimoto, Hirotoshi Tanaka
  [show abstract] [hide abstract]
  ABSTRACT: Recent studies have documented various roles of adrenal corticosteroid signaling in cardiac physiology and pathophysiology. It is known that glucocorticoids and aldosterone are able to bind glucocorticoid receptor (GR) and mineralocorticoid receptor, and these ligand-receptor interactions are redundant. It, therefore, has been impossible to delineate how these nuclear receptors couple with corticosteroid ligands and differentially regulate gene expression for operation of their distinct functions in the heart. Here, to particularly define the role of GR in cardiac muscle cells, we applied a ligand-based approach involving the GR-specific agonist cortivazol (CVZ) and the GR antagonist RU-486 and performed microarray analysis using rat neonatal cardiomyocytes. We indicated that glucocorticoids appear to be a major determinant of GR-mediated gene expression when compared with aldosterone. Moreover, expression profiles of these genes highlighted numerous roles of glucocorticoids in various aspects of cardiac physiology. At first, we identified that glucocorticoids, via GR, induce mRNA and protein expression of a transcription factor Kruppel-like factor 15 and its downstream target genes, including branched-chain aminotransferase 2, a key enzyme for amino acid catabolism in the muscle. CVZ treatment or overexpression of KLF15 decreased cellular branched-chain amino acid concentrations and introduction of small-interfering RNA against KLF15 cancelled these CVZ actions in cardiomyocytes. Second, glucocorticoid-GR signaling promoted gene expression of the enzymes involved in the prostaglandin biosynthesis, including cyclooxygenase-2 and phospholipase A2 in cardiomyocytes. Together, we may conclude that GR signaling should have distinct roles for maintenance of cardiac function, for example, in amino acid catabolism and prostaglandin biosynthesis in the heart.
  AJP Endocrinology and Metabolism 04/2009; 296(6):E1363-73.
• Article: Muscle-specific differences in the response of mitochondrial proteins to beta-GPA feeding: an evaluation of potential mechanisms.

  Deon B Williams, Lindsey N Sutherland, Marc R Bomhof, Susan A U Basaraba, A Brianne Thrush, David J Dyck, Catherine J Field, David C Wright
  [show abstract] [hide abstract]
  ABSTRACT: Beta-Guanadinopropionic acid (beta-GPA) feeding leads to reductions in skeletal muscle phosphagen concentrations and has been used as a tool with which to study the effects of energy charge on skeletal muscle metabolism. Supplementing standard rodent diets with beta-GPA leads to increases in mitochondrial enzyme content in fast but not slow-twitch muscles from male rats. Given this apparent discrepancy between muscle types we used beta-GPA feeding as a model to study signaling pathways involved in mitochondrial biogenesis. We hypothesized that beta-GPA feeding would result in a preferential activation of p38 MAPK and AMPK signaling and reductions in RIP140 protein content in triceps but not soleus muscle. Despite similar reductions in high-energy phosphate concentrations, 6 wk of beta-GPA feeding led to increases in mitochondrial proteins in triceps but not soleus muscles. Differences in the response of mitochondrial proteins to beta-GPA feeding did not seem to be related to a differential activation of p38 MAPK and AMPK signaling pathways or discrepancies in the induction of PPARgamma coactivator (PGC)-1alpha and -1beta. The protein content and expression of the nuclear corepressor RIP140 was reduced in triceps but not soleus muscle. Collectively our results indicate that chronic reductions in high-energy phosphates lead to the activation of p38 MAPK and AMPK signaling and increases in the expression of PGC-1alpha and -1beta in both soleus and triceps muscles. The lack of an effect of beta-GPA feeding on mitochondrial proteins in the soleus muscles could be related to a fiber type-specific effect of beta-GPA on RIP140 protein content.
  AJP Endocrinology and Metabolism 04/2009; 296(6):E1400-8.
• Article: Diabetes induces and calcium channel blockers prevent cardiac expression of proapoptotic thioredoxin-interacting protein.

  Junqin Chen, Hyunjoo Cha-Molstad, Anna Szabo, Anath Shalev
  [show abstract] [hide abstract]
  ABSTRACT: Cardiomyocyte apoptosis is a critical process in the pathogenesis of ischemic and diabetic cardiomyopathy, but the mechanisms are not fully understood. Thioredoxin-interacting protein (TXNIP) has recently been shown to have deleterious effects in the cardiovascular system and we therefore investigated whether it may also play a role in diabetes-associated cardiomyocyte apoptosis. In fact, TXNIP expression was increased in H9C2 cardiomyocytes incubated at high glucose, and cardiac expression of TXNIP and cleaved caspase-3 were also elevated in vivo in streptozotocin- and obesity-induced diabetic mice. Together, these findings not only suggest that TXNIP is involved in diabetic cardiomyopathy but also that it may represent a novel therapeutic target. Surprisingly, testing putative TXNIP modulators revealed that calcium channel blockers reduce cardiomyocyte TXNIP transcription and protein levels in a dose-dependent manner. Oral administration of verapamil for 3 wk also reduced cardiac TXNIP expression in mice even in the face of severe diabetes, and these reduced TXNIP levels were associated with decreased apoptosis. To determine whether lack of TXNIP can mimic the verapamil-induced decrease in apoptosis, we used TXNIP-deficient HcB-19 mice, harboring a natural nonsense mutation in the TXNIP gene. Interestingly, we found significantly reduced cleaved caspase-3 levels in HcB-19 hearts, suggesting that TXNIP plays a critical role in cardiac apoptosis and that the verapamil effects were mediated by TXNIP reduction. Thus our results suggest that TXNIP reduction is a powerful target to enhance cardiomyocyte survival and that agents such as calcium channel blockers may be useful in trying to achieve this goal and prevent diabetic cardiomyopathy.
  AJP Endocrinology and Metabolism 04/2009; 296(5):E1133-9.
• Article: Endothelium-specific GTP cyclohydrolase I overexpression accelerates refractory wound healing by suppressing oxidative stress in diabetes.

  Lu Tie, Xue-Jun Li, Xian Wang, Keith M Channon, Alex F Chen
  [show abstract] [hide abstract]
  ABSTRACT: Refractory wound is a severe complication that leads to limb amputation in diabetes. Endothelial nitric oxide synthase (eNOS) plays a key role in normal wound repair but is uncoupled in streptozotocin (STZ)-induced type 1 diabetes because of reduced cofactor tetrahydrobiopterin (BH(4)). We tested the hypothesis that overexpression of GTP cyclohydrolase I (GTPCH I), the rate-limiting enzyme for de novo BH(4) synthesis, retards NOS uncoupling and accelerates wound healing in STZ mice. Blood glucose levels were significantly increased in both male endothelium-specific GTPCH I transgenic mice (Tg-GCH; via a tie-2 promoter) and wild-type (WT) littermates 5 days after STZ regimen. A full-thickness excisional wound was created on mouse dorsal skin by a 4-mm punch biopsy. Wound closure was delayed in STZ mice, which was rescued in STZ Tg-GCH mice. Cutaneous BH(4) level was significantly reduced in STZ mice vs. WT mice, which was maintained in STZ Tg-GCH mice. In STZ mice, constitutive NOS (cNOS) activity and nitrite levels were decreased compared with WT mice, paralleled by increased superoxide anion (O(2)(-)) level and inducible NOS (iNOS) activity. In STZ Tg-GCH mice, nitrite level and cNOS activity were potentiated and O(2)(-) level and iNOS activity were suppressed compared with STZ mice. Thus endothelium-specific BH(4) overexpression accelerates wound healing in type 1 diabetic mice by enhancing cNOS activity and suppressing oxidative stress.
  AJP Endocrinology and Metabolism 04/2009; 296(6):E1423-9.
• Article: Muscle inflammatory response and insulin resistance: synergistic interaction between macrophages and fatty acids leads to impaired insulin action.

  Vijayalakshmi Varma, Aiwei Yao-Borengasser, Neda Rasouli, Greg T Nolen, Bounleut Phanavanh, Tasha Starks, Cathy Gurley, Pippa Simpson, Robert E McGehee, Philip A Kern, Charlotte A Peterson
  [show abstract] [hide abstract]
  ABSTRACT: Obesity is characterized by adipose tissue expansion as well as macrophage infiltration of adipose tissue. This results in an increase in circulating inflammatory cytokines and nonesterified fatty acids, factors that cause skeletal muscle insulin resistance. Whether obesity also results in skeletal muscle inflammation is not known. In this study, we quantified macrophages immunohistochemically in vastus lateralis biopsies from eight obese and eight lean subjects. Our study demonstrates that macrophages infiltrate skeletal muscle in obesity, and we developed an in vitro system to study this mechanistically. Myoblasts were isolated from vastus lateralis biopsies and differentiated in culture. Coculture of differentiated human myotubes with macrophages in the presence of palmitic acid, to mimic an obese environment, revealed that macrophages in the presence of palmitic acid synergistically augment cytokine and chemokine expression in myotubes, decrease IkappaB-alpha protein expression, increase phosphorylated JNK, decrease phosphorylated Akt, and increase markers of muscle atrophy. These results suggest that macrophages alter the inflammatory state of muscle cells in an obese milieu, inhibiting insulin signaling. Thus in obesity both adipose tissue and skeletal muscle inflammation may contribute to insulin resistance.
  AJP Endocrinology and Metabolism 04/2009; 296(6):E1300-10.
• Article: Iodide deficiency-induced angiogenic stimulus in the thyroid occurs via HIF- and ROS-dependent VEGF-A secretion from thyrocytes.

  Anne-Catherine Gérard, Sylvie Poncin, Jean-Nicolas Audinot, Jean-François Denef, Ides M Colin
  [show abstract] [hide abstract]
  ABSTRACT: Vascular supply is an obvious requirement for all organs. In addition to oxygen and nutrients, blood flow also transports essential trace elements. Iodine, which is a key element in thyroid hormone synthesis, is one of them. An inverse relationship exists between the expansion of the thyroid microvasculature and the local availability of iodine. This microvascular trace element-dependent regulation is unique and contributes to keep steady the iodide delivery to the thyroid. Signals involved in this regulation, such as VEGF-A, originate from thyrocytes as early TSH-independent responses to iodide scarcity. The question raised in this paper is how thyrocytes, facing an acute drop in intracellular stores of iodine, generate angiogenic signals acting on adjacent capillaries. Using in vitro models of rat and human thyroid cells, we show for the first time that the deficit in iodine is related to the release of VEGF-A via a reactive oxygen species/hypoxia-inducible factor-1-dependent pathway.
  AJP Endocrinology and Metabolism 04/2009; 296(6):E1414-22.