Degenerative disc disease is closely linked to the generation of back pain and other spinal pathologies, which for millions of Americans represents a difficult part of the aging process. In the intervertebral disc, the cells of the nucleus pulposu (NP) function in a unique environmental niche, characterized by a very limited vascular supply that imposes metabolic constraints and a hypoxic state on cells. We have shown that in the NP, HIF and PHD form a unique regulatory circuit: PHD2 controls degradation of HIF-1? even under hypoxia, while PHD3 promotes its transcriptional activity. For the first time, we have demonstrated that HIF-2a is insensitive to PHD mediated degradation. Conversely, HIF-1? homologues differentially control PHD expression in the NP in a cell type specific manner. Directly relevant to disc disease, our pilot data suggests that the HIF-PHD circuit can be decoupled by inflammatory cytokines TNF-? and IL-1?. Based on this information, we propose to investigate how HIF controls PHD function in the hypoxic NP niche, given that PHDs require molecular O2 as a substrate for their catalytic function. We will determine mechanisms underlying differential sensitivity of HIF-1? homologues to PHD mediated degradation as well as elucidating the identity and function of co-factors that are recruited to HIF-1? in a PHD dependent fashion. To relate this information to the in vivo state, we will conditionally delete HIF-1? in the notochord as well as post natal NP and analyze the mutant mice for changes in cell proliferation, survival and differentiation. Next, we will investigate the mechanisms by which TNF-? and IL-1? decouple the HIF-PHD circuit and test the hypothesis that PHD3 mediates the effects of cytokines on NP cells. Lastly, we will test the hypothesis that PHD3 inactivation slows the progression of degenerative changes in the disc in vivo under inflammatory condition. Conversely, we will ascertain if perturbation of the HIF-PHD circuit in PHD3 null mice influences age dependent changes in the disc. Taken together, the proposed studies will thus test a novel hypothesis in disc research, namely, the HIF-PHD regulatory network is critical in maintenance of NP cell survival and function and decoupling of this circuit by inflammatory cytokines may exacerbate degenerative disc disease. Outcomes from these studies will lead to the development of new pharmacological interventions aimed at maintaining the structural integrity of the disc and mitigating the inflammatory response.

Public Health Relevance

Lower back pain experienced by millions of Americans is closely linked to degenerative disc disease, a condition that afflicts the spine. The goal of the proposal is to understand the mechanism by which cells in the disc survive in a hypoxic environment and respond to inflammatory conditions prevalent during disc disease.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR055655-07
Application #
8632992
Study Section
Skeletal Biology Structure and Regeneration Study Section (SBSR)
Program Officer
Tyree, Bernadette
Project Start
2007-12-01
Project End
2018-05-31
Budget Start
2014-06-01
Budget End
2015-05-31
Support Year
7
Fiscal Year
2014
Total Cost
$360,387
Indirect Cost
$113,183
Name
Thomas Jefferson University
Department
Orthopedics
Type
Schools of Medicine
DUNS #
053284659
City
Philadelphia
State
PA
Country
United States
Zip Code
19107
Schoepflin, Zachary R; Shapiro, Irving M; Risbud, Makarand V (2016) Class I and IIa HDACs Mediate HIF-1α Stability Through PHD2-Dependent Mechanism, While HDAC6, a Class IIb Member, Promotes HIF-1α Transcriptional Activity in Nucleus Pulposus Cells of the Intervertebral Disc. J Bone Miner Res 31:1287-99
Suyama, Kaori; Silagi, Elizabeth S; Choi, Hyowon et al. (2016) Circadian factors BMAL1 and RORα control HIF-1α transcriptional activity in nucleus pulposus cells: implications in maintenance of intervertebral disc health. Oncotarget 7:23056-71
Tian, Ye; Yuan, Wen; Li, Jun et al. (2016) TGFβ regulates Galectin-3 expression through canonical Smad3 signaling pathway in nucleus pulposus cells: implications in intervertebral disc degeneration. Matrix Biol 50:39-52
Binch, Abbie L A; Shapiro, Irving M; Risbud, Makarand V (2016) Syndecan-4 in intervertebral disc and cartilage: Saint or synner? Matrix Biol 52-54:355-62
Choi, Hyowon; Johnson, Zariel I; Risbud, Makarand V (2015) Understanding nucleus pulposus cell phenotype: a prerequisite for stem cell based therapies to treat intervertebral disc degeneration. Curr Stem Cell Res Ther 10:307-16
Ye, Wei; Zhou, Jie; Markova, Dessislava Z et al. (2015) Xylosyltransferase-1 expression is refractory to inhibition by the inflammatory cytokines tumor necrosis factor α and IL-1β in nucleus pulposus cells: novel regulation by AP-1, Sp1, and Sp3. Am J Pathol 185:485-95
Shapiro, Irving M; Landis, William J; Risbud, Makarand V (2015) Matrix vesicles: Are they anchored exosomes? Bone 79:29-36
Johnson, Z I; Schoepflin, Z R; Choi, H et al. (2015) Disc in flames: Roles of TNF-α and IL-1β in intervertebral disc degeneration. Eur Cell Mater 30:104-16; discussion 116-7
Johnson, Zariel I; Gogate, Shilpa S; Day, Rebecca et al. (2015) Aquaporin 1 and 5 expression decreases during human intervertebral disc degeneration: Novel HIF-1-mediated regulation of aquaporins in NP cells. Oncotarget 6:11945-58
Risbud, Makarand V; Schoepflin, Zachary R; Mwale, Fackson et al. (2015) Defining the phenotype of young healthy nucleus pulposus cells: recommendations of the Spine Research Interest Group at the 2014 annual ORS meeting. J Orthop Res 33:283-93

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