Role of HIF-1 in Intervertebral Disc Function

描述（由申请人提供）：椎间盘退行性疾病与背痛和其他脊柱疾病的产生密切相关，对数百万美国人来说，这是衰老过程中一个困难的部分。在椎间盘中，髓核（NP）细胞在一个独特的环境中发挥作用，其特点是非常有限的血管供应，对细胞施加代谢限制和缺氧状态。我们已经证明，在NP中，HIF和PHD形成了一个独特的调控回路：PHD2控制HIF-1的降解？即使在缺氧情况下，PHD3也能促进其转录活性。我们首次证明HIF-2a对PHD介导的降解不敏感。相反,HIF-1吗?同源物以细胞类型特异性的方式差异性控制NP中的PHD表达。与椎间盘疾病直接相关，我们的试点数据表明HIF-PHD回路可以被炎症细胞因子TNF-？和il - 1 ?。基于这些信息，我们建议研究HIF如何控制博士在缺氧NP生态位中的功能，因为博士需要分子O2作为其催化功能的底物。我们将确定HIF-1差异敏感性的潜在机制。PHD介导的降解的同源物，以及阐明HIF-1募集的辅助因子的身份和功能？以博士依赖的方式。为了将这些信息与体内状态联系起来，我们将有条件地删除HIF-1？并分析突变小鼠细胞增殖、存活和分化的变化。接下来，我们将研究其机制

DESCRIPTION (provided by applicant): 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.