Cedars-Sinai Board of Governors Regenerative Medicine Institute Los Angeles, California, United States
Abstract: Lower back pain is one of the most common medical complaints in the US with up to 40% of the cases attributed to intervertebral disc (IVD) degeneration. Notochordal cells (NCs) are considered progenitor cells within the IVD and are thought to be lost in humans around age 10. The loss of NCs coinciding with degenerative changes suggests that NCs may play a role in IVD degeneration, however, the mechanism has not been identified. Due to disc size, the mechanism of degeneration in rodents differ substantially from human disease. Here, we developed a comprehensive porcine model for which we can quantitative measure discogenic pain via biobehavioral testing (BBT) and novel MRI. In addition, we applied a multi-omics approach to elucidate the cellular identities and mechanisms driving IVD degeneration and pain development at the molecular and cellular levels. Traditional MRI and histology of the injured discs confirmed development of IVD degeneration. Novel qCEST sequences, BBT, and bulk transcriptomics of DRGs showed the development of pain responses. Proteomic analysis of plasma identified an upregulation of inflammatory and differentiation marker with degeneration. Single cell transcriptomics determined that post injury, IVD makeup shifts from NC progenitors to terminally differentiated Nucleus Pulposus Cell (NPC) dominated. Trajectory analysis predicts cells from injured discs are located later in pseudotime and express markers associated with differentiation. Cell-cell communication analysis predicts terminally differentiated cell types are involved in multiple differentiation pathways and have high intercellular communication, while NCs are mostly silent. Pathway analysis of high communication clusters predicts increased cellular stress, neural outgrowth, inflammation, and differentiation pathways. When NCs were isolated from healthy IVD and exposed to degenerative culture conditions, they were found to differentiate toward fibroblast-like NPCs. Understanding the role of NCs in IVD degeneration will help to, not only to understand their role in degeneration process and pain induction, but also inform the development of cell therapies for low back pain. Additionally, development of a pain assessment assay in large animals can accelerate translation of promising treatments towards the clinic.
Funding Source: This study was supported by NIH (K01AR071512, R01AR066517) and CIRM (DISC2-14049, EDUC4-12751)
