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
Gorth, Deborah J; Shapiro, Irving M; Risbud, Makarand V (2018) Transgenic mice overexpressing human TNF-? experience early onset spontaneous intervertebral disc herniation in the absence of overt degeneration. Cell Death Dis 10:7
Choi, Hyowon; Chaiyamongkol, Weera; Doolittle, Alexandra C et al. (2018) COX-2 expression mediated by calcium-TonEBP signaling axis under hyperosmotic conditions serves osmoprotective function in nucleus pulposus cells. J Biol Chem 293:8969-8981
Silagi, Elizabeth S; Schoepflin, Zachary R; Seifert, Erin L et al. (2018) Bicarbonate Recycling by HIF-1-Dependent Carbonic Anhydrase Isoforms 9 and 12 Is Critical in Maintaining Intracellular pH and Viability of Nucleus Pulposus Cells. J Bone Miner Res 33:338-355
Pan, Hehai; Strickland, Adam; Madhu, Vedavathi et al. (2018) RNA binding protein HuR regulates extracellular matrix gene expression and pH homeostasis independent of controlling HIF-1? signaling in nucleus pulposus cells. Matrix Biol :
Silagi, Elizabeth S; Shapiro, Irving M; Risbud, Makarand V (2018) Glycosaminoglycan synthesis in the nucleus pulposus: Dysregulation and the pathogenesis of disc degeneration. Matrix Biol 71-72:368-379
Choi, Hyowon; Tessier, Steven; Silagi, Elizabeth S et al. (2018) A novel mouse model of intervertebral disc degeneration shows altered cell fate and matrix homeostasis. Matrix Biol 70:102-122
Johnson, Zariel I; Doolittle, Alexandra C; Snuggs, Joseph W et al. (2017) TNF-? promotes nuclear enrichment of the transcription factor TonEBP/NFAT5 to selectively control inflammatory but not osmoregulatory responses in nucleus pulposus cells. J Biol Chem 292:17561-17575
Liu, Chao; Choi, Hyowon; Johnson, Zariel I et al. (2017) Lack of evidence for involvement of TonEBP and hyperosmotic stimulus in induction of autophagy in the nucleus pulposus. Sci Rep 7:4543
Schoepflin, Zachary R; Silagi, Elizabeth S; Shapiro, Irving M et al. (2017) PHD3 is a transcriptional coactivator of HIF-1? in nucleus pulposus cells independent of the PKM2-JMJD5 axis. FASEB J 31:3831-3847
Schoepflin, Zachary R; Shapiro, Irving M; Risbud, Makarand V (2016) Class I and IIa HDACs Mediate HIF-1? Stability Through PHD2-Dependent Mechanism, While HDAC6, a Class IIb Member, Promotes HIF-1? Transcriptional Activity in Nucleus Pulposus Cells of the Intervertebral Disc. J Bone Miner Res 31:1287-99

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