Mechanobiology of Inflammation in the Intervertebral Disc

Project Summary: Disability and pain stemming from degenerated intervertebral discs (IVD) affects over 40% of U.S adults and costs >$100 billion annually. The etiology of IVD degeneration (DD) is unknown. There is a significant clinical need for a better mechanistic understanding of DD, and for therapeutic approaches that directly treat the IVD, mitigate DD, and promote recovery of spine function. I nflammation is a key contributor to discogenic pain. High mobility group box 1 ( HMGB1) protein is a ubiquitous nuclear protein that is secreted extracellularly by stressed or dying cells. The biologic function of HMGB1 depends on its cellular location, redox state, and binding partners. Recent studies show that HMGB1 levels increase with DD severity, though the biologic function of HMGB1 in nucleus pulposus (NP) cells and its role in DD are largely unknown. The contributions of HMGB1 to NP cell mechanobiology are similarly unknown, and may be dually related to the pro-inflammatory potential of disulfide HMGB1 and to the chemotactic activity of fully reduced HMGB1. The objective of the proposed studies is to identify the redox dependent function of HMGB1 in DD. Our global hypothesis is that HMGB1 will trigger IVD pro-inflammatory signaling, promote ECM degradation and alter NP cell mechanobiology in a redox dependent manner. Aim 1 studies will quantify the biological and mechanotransduction function of redox isoforms of HMGB1 in human NP cells. We will also identify the specific binding receptors that mediate the pro-inflammatory and mechanobiological activity of HMGB1 isoforms in NP cells. Aim 2 studies will identify the contribution of HMGB1 as a central mediating damage associated molecular pattern (DAMP) in DD inflammation and mechanobiology from acute to chronic stages in vivo. These studies will provide mechanistic evidence about how redox isoforms of HMGB1 contribute to DD and mechanotransduction. Our findings may identify targets for mitigating DD initiation or progression. Since multiple HMGB1 isoforms have the potential to alter the cytoskeleton and thus mechanobiology of NP cells, we predict that our studies will identify strategies for mitigating alterations in IVD mechanotransduction, which are more extensive than regulating inflammatory signaling.