The regulation of the NF-?B inflammatory signaling pathways has primarily focused on immune cell systems that underlie the production of pro-inflammatory cytokines mediating infection as well as sterile immune responses. Recent studies have also clearly established an important role of adipose tissue inflammation and activation of pro-inflammatory cytokines mediating diet induced insulin resistance. However, the transduction pathways and regulatory control of NF-?B signaling within non-immune cells and in particular adipocytes has not been examined and is essential for not only our basic understanding of adipocyte biology but also in the mediation of insulin resistance and diabetes. In this regard, our preliminary data has demonstrated a novel and completely unexpected role for the TIGAR protein as a major regulator of NF-?B signaling adipocytes, insulin sensitivity and adipose tissue inflammation in vivo. Specifically, our preliminary data has demonstrated that TIGAR is highly expressed in adipocytes and is markedly down regulated in ob/ob and db/db mice and following high fat diet (HFD) induced obesity. Moreover, knockdown of TIGAR in 3T3L1 adipocytes resulted in marked inhibition of insulin signaling with increased basal and TNF? stimulated NF-?B signaling. In contrast, over expression of TIGAR enhanced insulin signaling and inhibited basal and TNF?- stimulated NF-?B signaling. Detailed analyses demonstrated that TIGAR suppressed NF-?B signaling upstream of IKK? and surprisingly independent of the TIGAR phosphatase enzymatic activity. Based upon these data and recent preliminary data, we hypothesize that TIGAR suppresses NF-?B signaling through inhibition of the upstream IKK?/IKK? /NEMO ternary complex by directly binding to the HOIL/HOIP- 1L/Sharpin complex responsible for NEMO and RIP1 linear ubiquitination. We further predict the preventing/reversing diet induced obesity down regulation of adipocyte TIGAR protein will protect adipocytes/adipose tissue from metabolic dysfunction. The innovations of this proposal are based upon the identification of a novel regulatory mechanism for a new critical control element in NF-?B signaling and its role in the pathophysiologic dysfunction of diet induced insulin resistance. Thus, three central questions of this proposal are 1) what is the molecular basis for TIGAR inhibition of NF-?B signaling, 2) does TIGAR deficiency cause, contribute to or is a consequence of impaired insulin signaling through promotion of inflammatory signaling; and 3) can physiologic re-expression of TIGAR suppress adipocyte dysfunction in diet-induced obesity and insulin resistance.

Public Health Relevance

TIGAR was originally identified as a 269 amino acid p53-induced gene that is structurally analogous to the sugar phosphatase domains of the dual phosphofructose kinase/fructose 2,6 bisphosphatase (PFKFB) family. The TIGAR catalytic activity converts F2,6-P2 to F6-P and appears to be constitutive dependent upon TIGAR expression levels. As phosphofructose kinase 1 (PFK1) is the rate limiting step in glycolysis and F2,6-P2 is a potent PFK1 allosteric regulator, Tigar and the PFKFB's are thought to control the relative rate of carbon flux through the glycolytic and pentose phosphate pathways, that is high PFK-1 activity drives glycolysis whereas low PFK-1 activity shifts F6-P to the pentose phosphate pathway. More recently, it was reported that TIGAR is also a 2,3-bisphosphoglycerate (2,3BPG) phosphatase although the biological role for 2,3BPG has only been shown in erythrocytes and placenta in promoting the release of oxygen from hemaglobin. In any case, the biological properties and function of TIGAR have primarily been studied in vitro and in cultured tumor cell lines based upon its the F2,6-P phosphatase (FBPase) activity to reduce F2,6-P2 levels and suppress glycolysis. However, we have identified a novel and paradigm shifting function for TIGAR in adipocyte biology. Our preliminary data has demonstrated that TIGAR is highly expressed in adipocytes and is markedly down regulated in ob/ob and db/db mice and following high fat diet (HFD) induced obesity. Moreover, knockdown of TIGAR in 3T3L1 adipocytes resulted in marked inhibition of insulin signaling with increased basal and TNF? stimulated NF-?B signaling. In contrast, over expression of TIGAR enhanced insulin signaling and inhibited basal and TNF?-stimulated NF-?B signaling. Detailed analyses demonstrated that TIGAR suppressed NF-?B signaling upstream of IKK? and surprisingly independent of the TIGAR phosphatase enzymatic activity. Based upon these data and recent preliminary data, we hypothesize that TIGAR suppresses NF-?B signaling through inhibition of the upstream IKK?/IKK?/NEMO ternary complex by directly binding to the HOIL/HOIP-1L/Sharpin complex responsible for NEMO and RIP1 linear ubiquitination. We further predict the preventing/reversing diet induced obesity down regulation of adipocyte TIGAR protein will protect adipocytes/adipose tissue from metabolic dysfunction. Thus, three central questions of this proposal are 1) what is the molecular basis for TIGAR inhibition of NF-?B signaling, 2) does TIGAR deficiency cause, contribute to or is a consequence of impaired insulin signaling through promotion of inflammatory signaling; and 3) can physiologic re-expression of TIGAR suppress adipocyte dysfunction in diet induced obesity and insulin resistance.upstream of IKK and surprisingly independent of the TIGAR phosphatase enzymatic activity. Based upon these data and recent preliminary data, we hypothesize that TIGAR suppresses NF-?B signaling through inhibition of the upstream IKKa/IKK/NEMO ternary complex by directly binding to the HOIL/HOIP-1L/Sharpin complex responsible for NEMO and RIP1 linear ubiquitination. We further predict the preventing/reversing diet induced obesity down regulation of adipocyte TIGAR protein will protect adipocytes/adipose tissue from metabolic dysfunction. Thus, three central questions of this proposal are 1) what is the molecular basis for TIGAR inhibition of NF-?B signaling, 2) does TIGAR deficiency cause, contribute to or is a consequence of impaired insulin signaling through promotion of inflammatory signaling; and 3) can physiologic re-expression of TIGAR suppress adipocyte dysfunction in diet induced obesity and insulin resistance.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK033823-37
Application #
9249020
Study Section
Cellular Aspects of Diabetes and Obesity Study Section (CADO)
Program Officer
Haft, Carol R
Project Start
1984-04-01
Project End
2019-03-31
Budget Start
2017-04-01
Budget End
2018-03-31
Support Year
37
Fiscal Year
2017
Total Cost
$420,839
Indirect Cost
$168,840
Name
Albert Einstein College of Medicine, Inc
Department
Type
Domestic Higher Education
DUNS #
079783367
City
Bronx
State
NY
Country
United States
Zip Code
10461
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