PMID: PMC2628603-2

 

    Legend: Gene, Sites

Title : Erythrocytes are probably among the simplest of human cells

Abstract :
  1. For a long time, erythrocytes had been regarded as a cytoplasm surrounded by a simplified membrane and consisting mainly of hemoglobins
  2. A recent in-depth analysis of the erythrocyte proteome indicated that there are likely far more complex cellular processes inside erythrocytes than previously known (24)
  3. Results presented here suggest that O-GlcNAc actively cycles on erythrocyte proteins
  4. Some of the earliest known GlcNAcylated proteins were detected in human erythrocytes (25)
  5. The challenges of studying O-GlcNAc by mass spectrometry come from its low stoichiometry, suppressed ionization efficiency in presence of unmodified peptides , and intrinsic lability in gas phase (21)
  6. In this study, highly efficient enrichment methods based on chemoenzymatic tagging addressed the first two challenges
  7. Solid-phase chemical derivatization successfully circumvented the lability issue
  8. As the exploratory phase of a project aimed at using O-GlcNAc as a potential biomarker for diagnostic of diabetes, we identified 25 O-GlcNAc modified proteins , mapped 35 O-GlcNAc sites , and compared the O-GlcNAc RORs between erythrocyte lysates obtained from normal and diabetic individuals
  9. By using a rigorous mass spectrometric standard, we also identified 206 erythrocytic proteins and compared their abundance between normal and diabetic samples
  10. A few proteins , such as carbonic anhydrase 1 (diabetic:normal 0.51), glutathione transferase ω 1 (0.79), GLUT1 (0.88), superoxide dismutase (1 .21), and isocitrate dehydrogenase (1.29), were observed as differentially regulated in normal and diabetic samples
  11. Although these protein level dynamics might not be conclusive because of relatively small sample size and inherent variation among individuals, these observations may reflect hyperglycemia and increased oxidative stress in diabetic patients
  12. Clinical diagnosis of diabetes has been evolving since the diagnostic criteria were first initiated in 1979 by the National Diabetes Data Group report (26)
  13. The glycemic criteria have been based on levels of glucose that associate with microvascular, specifically retinopathic, changes characteristic of diabetes
  14. There are major limitations in the current criteria used for the diagnosis of diabetes
  15. Fasting plasma glucose reflects only one aspect of glucose metabolism, which may be stated as the postabsorptive balance of hepatic glucose production and peripheral glucose uptake
  16. It does not reflect the free-living, daily glycemic patterns, the prolonged fasted state, or the even postprandial state
  17. The oral glucose tolerance test, in addition to being clinically cumbersome, is also nonphysiological (assuming most meal ingestion does not include 75 g concentrated sucrose)
  18. Assessing glucose tolerance with the single measure of plasma glucose 2 h after the oral glucose is therefore of limited usefulness
  19. Another commonly used test is to assay for A1C
  20. A1C values reflect an average glycemic status over several months’ time (27)
  21. A1C assay has been recently proposed as a diagnostic criterion (28)
  22. Perhaps the most apparent functional aspect of O-GlcNAc is its role in regulation of insulin signaling and as a mediator of glucose toxicity (2–15,29)
  23. Increasing global GlcNAcylation in adipocytes or muscle blocks insulin signaling at several points (12,29,30)
  24. Moderately increased UDP-GlcNAc levels in muscle induced insulin resistance (31), whereas overexpression of OGT in muscle or adipose causes insulin resistance and hyperleptinemia in transgenic mice (11)
  25. Diabetes is an extremely complicated syndrome
  26. Although some controversies still exist about the roles of O-GlcNAc in diabetes (32), the results presented in this report along with the rapid cycling nature of GlcNAcylation and its sensitivity toward changes in glucose metabolism give site-specific GlcNAcylation on erythrocyte proteins great potential as biomarker(s) for detecting the early stages of diabetes
  27. Given the exploratory nature of the current study, quantitative measurements were based on relatively small sample sizes
  28. Completion of the discovery phase will be followed by a validation phase, for which targeted high-throughput mass spectrometry will be adopted to determine the prevalence of O-GlcNAc dynamics on preselected sites among a large amount of samples
  29. Polyclonal and monoclonal antibodies against O-GlcNAc on specific sites will be developed and used to screen a large number of samples from normal, pre-diabetic, and diabetic patients to further evaluate the feasibility of this approach
  30. In any case, this study not only has identified important GlcNAcylated proteins and sites of modification in human erythrocytes but also suggests that O-GlcNAc cycling plays a role in erythrocyte biology
Output (sent_index, trigger, protein, sugar, site):
  • 29. O-GlcNAc, , -, specific sites, sites
Output(Part-Of) (sent_index, protein, site):
*Output_Site_Fusion* (sent_index, protein, sugar, site):

 

 

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