Intervertebral disc human nucleus pulposus cells associated with back pain trigger neurite outgrowth in vitro and pain behaviors in rats

Abstract

Low back pain (LBP) is often associated with the degeneration of human intervertebral discs (IVDs). However, the pain-inducing mechanism in degenerating discs remains to be elucidated. Here, we identified a subtype of locally residing human nucleus pulposus cells (NPCs), generated by certain conditions in degenerating discs, that was associated with the onset of discogenic back pain. Single-cell transcriptomic analysis of human tissues showed a strong correlation between a specific cell subtype and the pain condition associated with the human degenerated disc, suggesting that they are pain-triggering. The application of IVD degeneration-associated exogenous stimuli to healthy NPCs in vitro recreated a pain-associated phenotype. These stimulated NPCs activated functional human iPSC-derived sensory neuron responses in an in vitro organ-chip model. Injection of stimulated NPCs into the healthy rat IVD induced local inflammatory responses and increased cold sensitivity and mechanical hypersensitivity. Our findings reveal a previously uncharacterized pain-inducing mechanism mediated by NPCs in degenerating IVDs. These findings could aid in the development of NPC-targeted therapeutic strategies for the clinically unmet need to attenuate discogenic LBP.

Getting to the Core: Exploring the Embryonic Development from Notochord to Nucleus Pulposus

“…Moreover, further distinctions between the types of NPCs and their differentiation pathways have been found to be linked to certain pathologies and symptoms [ 87 , 88 , 89 ]. For example, Jiang et al [ 90 ] identified a specific MMP3+, SLC7A2+, and TM4SF1+ NPC clusters associated with symptomatic low back pain. In contrast, Han et al [ 91 ] revealed up to seven diverse NPC populations.…”

“…This process is further associated with the progression of IDD and low back pain. Notably, there are clear distinctions among the populations identified between different studies [ 87 , 88 , 89 , 90 , 91 , 92 , 93 ]. This warrants further careful investigations and calls for an evidence-based consensus within the spine community, providing a valuable basis for a future review.…”

TNFR1-mediated senescence and lack of TNFR2-signaling limit human intervertebral disc cell repair in back pain conditions

“…Chronic inflammation from IVDD is a strong contributor to progressive degenerative conditions and pain. This is due to the known roles that pro-inflammatory cytokines play in increased matrix catabolism, neurovascular ingrowth into the IVD, and enhanced nociception ( 7–14 ). Furthermore, infiltration of cytokine-releasing macrophages into the peripheral nervous system and damaged IVD has been observed, suggesting a correlation between immune cell infiltration and discogenic pain ( 15 ).…”

Characterization of pain-related behaviors in a rat model of acute-to-chronic low back pain: single vs. multi-level disc injury

“…The most common and repeatable method for achieving intervertebral disc (IVD) degeneration is a physical injury of the annulus fibrosis using needle puncture (10,14,15). Scraping or surgical blade incision of the annulus fibrosis, injections of inflammatory mediators, DRG or facet joint compression, or applications of various substances (e.g., nucleus pulposus fragments) into discs have also been used to induce IVD injury and/or related pain symptoms (16)(17)(18)(19)(20)(21)(22)(23)(24). Partial penetration of the annulus fibrosis induces a slower degenerative process (reduced IVD height and slowly increasing degeneration) than a full penetration (rapid nuclear avulsion but no degeneration) (10, 13), with the former more closely reproducing the human condition of progressive pathology (14).…”