One third of all diabetic patients exhibit severe periodontal disease which is postulated to stem from an interplay of factors including increased susceptibility to infection, elevated pro-inflammatory cytokines, altered sensitivity to hormones, and hyperglycemia. The delayed regeneration of alveolar bone in the damaged periodontium reflects, in part, inadequate response to the anabolic actions of IGF-1 and insulin which may be down-regulated by cytokines and hyperglycemia. IGF-1 stimulation of osteoblasts, is anti-apoptotic and contributes to cell proliferation, differentiation, migration, matrix deposition and mineralization, and supports osteoclastogenesis. The specificity of the pleiotropic effects elicited by IGF-1R activation are mediated by the insulin receptor substrates, IRS-1 and IRS-2, which are critical to the formation of new bone and maintaining coupling between osteoblasts and osteoclasts. Signaling through the IRS proteins to PI3K/Akt and/or the Grb2/ERK pathways is mediated and modulated by posttranslational regulation. Perturbations in Tyr/Ser/Thr phosphorylation of IRS-1 occur in diabetes and osteoporosis. IRS-1 and IRS-2 are also glycosylated at Ser/Thr residues by N-acetylglucosamine (O-GlcNAc). This unique glycosylation is a reversible posttranslational modification proposed to regulate protein function in a manner analogous to phosphorylation. Using state-of-the-art tandem mass spectrometric approaches, we have identified multiple sites of O-GlcNAc modification on human IRS-1 and IRS-2 and developed methodology to measure the relative stoichiometry of this labile modification in a site-specific manner. The extent of protein O-GlcNAcylation changes rapidly in response to glucose, hormones, and cellular stress and it is implicated in altered insulin signaling and the glucose-induced complications associated with diabetes.
In Aim 1, we propose to characterize the sites of O- GlcNAc modification of IRS-1 and IRS-2 in an osteoblast cell line and define the factors that modulate the extent of modification. We will investigate the interplay of phosphorylation and O-GlcNAc modification as these modifications may mutually exclude one another. The sites of O-GlcNAc modification of IRS-1 identified thus far are in close proximity to multiple SH2 domain binding motifs, thus in Aim 2 we will interrogate the effect of site-specific O-GlcNAc modification on interactions with the receptor and known binding partners and probe for novel protein interactions that may be induced by this modification. The role of the enzymes responsible for catalyzing the incorporation and removal of GlcNAc from proteins, O-GlcNAc transferase (OGT) and O- GlcNAcase (OGA), in modulating IGF-1 action in osteoblasts has not been addressed. Thus, in Aim 3, we will determine the impact of modulation of the expression of these enzymes on the cellular effects elicited by IGF-1 stimulation and whether altered O-GlcNAc modification of IRS-1 influences IGF-1 signaling in osteoblasts.

Public Health Relevance

With the predicted escalation in the number of newly diagnosed cases of diabetes annually in the U.S., understanding the regulation of key molecules critical to the pathogenesis of diabetes and its complications is essential. One-third of diabetic patients exhibit severe periodontal disease, the cause of which is a chronic bacterial infection, but with the underlying changes associated with the diabetic state, the stage is set for an altered response to hormones and cytokines culminating in the degradation of alveolar bone and tooth loss. This research will provide novel information concerning the regulation of two proteins crucial for normal bone formation that are known to be perturbed in diabetes with the ultimate goal of elucidating therapeutic targets to facilitate regeneration of alveolar bone in diabetes-associated periodontal disease.

Agency
National Institute of Health (NIH)
Institute
National Institute of Dental & Craniofacial Research (NIDCR)
Type
Research Project (R01)
Project #
5R01DE020925-03
Application #
8279112
Study Section
Oral, Dental and Craniofacial Sciences Study Section (ODCS)
Program Officer
Wan, Jason
Project Start
2010-07-01
Project End
2015-06-30
Budget Start
2012-07-01
Budget End
2013-06-30
Support Year
3
Fiscal Year
2012
Total Cost
$365,063
Indirect Cost
$117,563
Name
Medical University of South Carolina
Department
Pharmacology
Type
Schools of Medicine
DUNS #
183710748
City
Charleston
State
SC
Country
United States
Zip Code
29425
Song, Jin H; Padi, Sathish K R; Luevano, Libia A et al. (2016) Insulin receptor substrate 1 is a substrate of the Pim protein kinases. Oncotarget 7:20152-65
Wang, Xiaoshi; Yuan, Zuo-Fei; Fan, Jing et al. (2016) A Novel Quantitative Mass Spectrometry Platform for Determining Protein O-GlcNAcylation Dynamics. Mol Cell Proteomics 15:2462-75
Williams, Grace R; Bethard, Jennifer R; Berkaw, Mary N et al. (2016) Exploring G protein-coupled receptor signaling networks using SILAC-based phosphoproteomics. Methods 92:36-50
Nagel, Alexis K; Ball, Lauren E (2015) Intracellular protein O-GlcNAc modification integrates nutrient status with transcriptional and metabolic regulation. Adv Cancer Res 126:137-66
Nagel, Alexis K; Ball, Lauren E (2014) O-GlcNAc modification of the runt-related transcription factor 2 (Runx2) links osteogenesis and nutrient metabolism in bone marrow mesenchymal stem cells. Mol Cell Proteomics 13:3381-95
Nagel, Alexis K; Ball, Lauren E (2014) O-GlcNAc transferase and O-GlcNAcase: achieving target substrate specificity. Amino Acids 46:2305-16
Leymarie, Nancy; Griffin, Paula J; Jonscher, Karen et al. (2013) Interlaboratory study on differential analysis of protein glycosylation by mass spectrometry: the ABRF glycoprotein research multi-institutional study 2012. Mol Cell Proteomics 12:2935-51
Nagel, Alexis K; Schilling, Michael; Comte-Walters, Susana et al. (2013) Identification of O-linked N-acetylglucosamine (O-GlcNAc)-modified osteoblast proteins by electron transfer dissociation tandem mass spectrometry reveals proteins critical for bone formation. Mol Cell Proteomics 12:945-55
Hart, Gerald W; Ball, Lauren E (2013) Post-translational modifications: a major focus for the future of proteomics. Mol Cell Proteomics 12:3443
Darley-Usmar, Victor M; Ball, Lauren E; Chatham, John C (2012) Protein O-linked *-N-acetylglucosamine: a novel effector of cardiomyocyte metabolism and function. J Mol Cell Cardiol 52:538-49