Masao Kaneki, M.D., Ph.D.

NO and S-nitrosylation in insulin resistance

Inflammatory and stress signaling pathways have been highlighted as a major culprit of obesity- and stress-induced insulin resistance and diabetes.  Despite intense investigation for a number of years, the molecular mechanisms by which inflammatory responses induce insulin resistance and diabetes are not fully understood.  The overall objectives of the research program are to clarify the roles of inducible nitric oxide synthase (iNOS), a major mediator of inflammation, and protein S-nitrosylation in the pathogenesis of obesity- and stress-induced insulin resistance and pancreatic beta-cell dysfunction.  Protein S-nitrosylation, a covalent attachment of nitric oxide (NO) moiety (NO+) to reactive cysteine thiols, has emerged as the major mediator of diverse actions of NO.  S-nitrosylation does not require enzymatic acitivity.  In contrast, there exists an enzyme involved in decomposition of nitrosothiols (SNOs).  S-nitrosoglutathione reductase (GSNOR) catlyzes de-nitrosyltion of S-nitrosoglutathione (GSNO), which is in equilibrium with S-nitrosylated proteins in the cells, and thereby downregulates protein S-nitrosylation.  The research in this laboratory has identified GSNOR and iNOS as novel potential molecular targets to prevent and/or reverse obesity- and stress-induced insulin resistance, and beta-cell dysfunction.

1)  Inducible nitric oxide synthase (iNOS) and obesity-induced insulin resistance:  iNOS expression is increased by most, if not all, inducers of insulin resistance, including obesity, proinflammatory cytokines (e.g., TNF-a), oxidative stress, and hyperglycemia.  This research program has demonstrated that: (1) iNOS inhibition significantly ameliorates whole-body insulin resistance, and improves depressed expression of insulin receptor substrate (IRS)-1 and IRS-2, and IRSs-mediated insulin signaling in obese, diabetic (ob/ob) mice; (2) S-nitrosylation reversibly inactivates Akt/PKB; and that (3) S-nitrosylated Akt/PKB is increased in insulin sensitive tissues, including skeletal muscle, of diabetic (ob/ob) mice, as compared with wild-type control mice.  Moreover, the recent findings in this laboratory document that: (1) GSNOR deficiency induces insulin resistance on normal chow and exacerbates high-fat diet-induced diabetes in mice; and (2) liver-specific overexpression of iNOS is sufficient to induce insulin resistance and hyperglycemia in mice.  These findings clearly indicate that iNOS and GSNOR plays important roles as downstream effectors of chronic inflammation in obesity-induced insulin resistance in skeletal muscle and liver.  Target molecules of S-nitrosylation in the liver of diabetic (db/db) mice and roles of iNOS and protein S-nitrosylation as an upstream enhancer of the sustained activation of inflammatory/stress signaling pathways in obesity-induced insulin resistance are under investigation.

2)  Role of S-nitrosoglutathione reductase (GSNOR) in pancreatic beta-cell dysfunction: Attenuated insulin secretion and impaired compensatory expansion of pancreatic beta-cell mass are major contributors to hyperglycemia in type 2 diabetes.  Nitric oxide (NO) and iNOS have been implicated in beta-cell dysfunction in diabetes.  Nonetheless, limited knowledge is available about the underlying molecular pathogenesis. The data in this laboratory indicate that: (1) deficiency of S-nitrosoglutathione reductase (GSNOR), results in hyperglycemia with attenuated insulin secretion on normal chow, and aggravation of high-fat diet-induced hyperglycemia and beta-cell compensation failure compared with wild-type mice; (2) iNOS inhibitor ameliorates hyperglycemia with increased plasma insulin levels in diabetic (db/db) mice on BKS background; and (3) gene disruption of GSNOR confers increased susceptibility to streptozotocin-induced diabetes and proinflammatory cytokine- and NO donors-induced beta-cell death.  Investigation on the precise role of GSNOR is underway, using pancreatic beta-cell specific GSNOR overexpressing transgenic mice and GSNOR-/- iNOS-/- double knockout mice.

3)  Stress-induced insulin resistance:  The efficacy and safety of tight glucose control achieved by intensive insulin therapy in critically ill patients has been an issue of intense investigation and controversy for a decade.  Stress-induced hyperglycemia without preexisting diabetes is associated with poor prognosis in critically ill patients.  The research program is aimed to clarify the molecular bases underlying burn injury- and sepsis-induced insulin resistance and to determine the effects of insulin-sensitization on survival in rodent models of critical illness.  The research in this laboratory has shown that iNOS plays an important role in insulin resistance and impairment in the insulin receptor-IRS-1-PI3K-Akt/PKB-GSK-3b in skeletal muscle after burn injury in mice and hepatic insulin resistance and hyperglycemia following endotoxin challenge in rats.  Studies on the molecular mechanisms of insulin resistance (some of them are shared in common by obesity and stress [e.g., burn injury, sepsis], while there are also some distinct mechanisms between the two insulin-resistant states) are currently underway.

References:

  1. Sugita, M., Sugita, H., Kaneki, M.  Increased insulin receptor substrate 1 serine phosphorylation and stress-activated protein kinase/c-Jun N-terminal kinase activation associated with vascular insulin resistance in spontaneously hypertensive rats. Hypertension 2004 Oct;44(4):484-9.  Epub 2004 Aug
  2. Sugita, H., Kaneki, M., Sugita, M., Yasukawa, T., Yasuhara, S., Martyn, J.A.J. (2005) Burn injury impairs insulin-stimulated Akt/PKB activation in skeletal muscle.  Am J Physiol Endo Metab  288; E585-591
  3. Yasukawa,T., Tokunaga, E., Ota, H., Sugita, H., Martyn, J.A.J., Kaneki, M.  S-nitrosylation-dependent inactivation of Akt/PKB in insulin resistance. J Biol Chem 2005; 280: 7511-7518
  4. Sugita, H., Fujimito, M., Yasukawa, T., Shimizu, N., Sugita, M., Yasuhara, S., Martyn, J.A.J., Kaneki, M.  iNOS and NO donor induce IRS-1 degradation in skeletal muscle cells.  J. Biol Chem 2005; 280(14):14203-11
  5. Fujimoto, M., Shimizu, N., Kunii, K., Martyn, J.A.J., Ueki, K., Kaneki, M.  A role for iNOS in fasting hyperglycemia and impaired insulin signaling in the liver of obese, diabetic mice. Diabetes 2005; 54(5):1340-8
  6. Ota, H., Tokunaga, E., Chang, K., Hikasa, M., Iijima. K., Eto, M., Kozaki, K., Akishita, M., Ouchi, Y., Kaneki, M.  Sirt1 inhibitor, Sirtinol , induces senescence-like growth arrest with attenuated Ras-MAPK signaling in human cancer cells. Oncogene 2006; 25(2):176-85
  7. Yasuhara, S., Kaneki, M., Sugita, H., Sugita, M., Tompkins, R.G., Martyn, J.A.J.  Adipocyte apoptosis after burn injury is associated with altered fat metabolism.  J Burn Care Rehabil, 2006, 27 (3) 367-76
  8. Kaneki, M., Shimizu, N., Yamada D., Chang, K.  Nitrosative stress and pathogenesis of insulin resistance. Antioxid Redox Signal, 2007, 9(3):319-29
  9. Ichinose, F., Buys, E., Neilan, T., Furutani, E., Jassal, D., Lim, C., Kaneki, M., Picard, M., Scherrer-Crosbie, M., Janssens, S., Liao, R., Bloch, K.  Myocyte-specific overexpression of NOS3 prevents endotoxin-induced myocardial dysfunction and mortality in mice.    Circ Res, 2007, 100 (1): 130-9
  10. Sugita, M., Sugita, H., Kaneki, M. Farnesyltransferase inhibitor, manumycin A, prevents atherosclerosis development and reduces oxidative stress in ApoE-deficient mice.  Arterioscler Thromb Vasc  Biol, 2007; 27(6): 1390-5
  11. Frick, C., Richtsfeld, M., Sahani, N., Kaneki, M., Blobner. M., Martyn, J.A.J.  Long-term effects of botulium toxin on neuromuscular function.  Anesthesiology, 2007; 106 (6): 1139-46
  12. Asai, A., Sahani, N., Kaneki, M., Ouchi, Y., Martyn, J.A.J., Yasuhara, S.  Primary role of functional ischemia, quantitative evidence for the two-hit mechanism, and phosphodiesterase-5 inhibitor therapy in mouse muscular dystrophy. PLoS One, 2007; 2(8):e806
  13. Ota, H., Akishita, M., Eto, M., Iijima, K., Kaneki, M., Ouchi, Y.  Sirt1 modulates premature senescence-like phenotype in human endothelial cells. J Mol Cell Cardiol, 2007; 43 (5):571-9
  14. Raher, M. J., Thibault, H. B., Buys, E. S., Kuruppu, D., Shimizu, N., Brownell, A. L., Blake, S. L., Rieusset, J., Kaneki, M., Derumeaux, G., Picard, M. H., Bloch, K. D., Scherrer-Crosbie, M.  A short duration of high-fat diet induces insulin resistance and predisposes to adverse left ventricular remodeling after pressure overload.  Am J Physiol Heart Circ Physiol, 2008; 295(6): H2495-502)
  15. Martyn, J.A.J., Kaneki, M., Yasuhara, S. Obesity-induced insulin resistance and hyperglycemia: Etiological Factors and Molecular Mechanisms.  Anesthesiology, 2008, 109(1):137-148
  16. Kaneki, M., Sakai, M., Shimizu, N., Chang. K.  Is normalized mean blood glucose level good enough for the ICU?-Glycemic variability as a new independent predictor of mortality. Crit Care Med, 2008, 36 (11): 3104-6 

 

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