Lower back and neck pain are leading physical conditions for which patients see their doctors in the United States. The organ commonly implicated in this condition is the intervertebral disc (IVD), which frequently herniates, ruptures, or tears, often causing pain and limiting spinal mobility. To date, approaches for replacement of diseased IVD have been confined to purely mechanical devices designed to either eliminate or enable flexibility of the diseased motion segment. Here we present the evaluation of a living, tissueengineered IVD composed of a gelatinous nucleus pulposus surrounded by an aligned collagenous annulus fibrosus in the caudal spine of athymic rats for up to 6 mo. When implanted into the rat caudal spine, tissue-engineered IVD maintained disc space height, produced de novo extracellular matrix, and integrated into the spine, yielding an intact motion segment with dynamic mechanical properties similar to that of native IVD. These studies demonstrate the feasibility of engineering a functional spinal motion segment and represent a critical step in developing biological therapies for degenerative disc disease.regenerative medicine | total disc replacement | biomaterials | disc arthroplasty | image-based A mong the most common physical conditions for which patients see their doctors are back and neck pain, which carry an estimated annual cost to society up to $100 billion (1). Current conservative and operative treatment options are mostly palliative in nature and fail to restore function to the spine. The most common target for treatment of back and neck pain is the intervertebral disc (IVD) (2-5). IVD degeneration is characterized by loss of proteoglycan, loss of disc height, annulus fibrosus (AF) damage and tears, spondylolisthesis, spinal stenosis, herniated discs, neoinnervation, hypermobility, and inflammation (6-8). Conservative treatments including medication and physiotherapy are the first line of defense in treating these disorders. Despite these treatments, it is estimated that between 1.5 and 4 million patients in the United States await surgical intervention (9).Such surgical interventions may involve the removal of herniated tissue or the entire IVD and replacing it with a mechanical device designed to either fuse the adjacent vertebrae or to preserve some motion. Regardless of approach, motion segment mobility is altered, often precipitating degeneration in adjacent motion segments (10). Nonbiological total disc replacement implants were developed to avoid this loss of motion at the operated level, and as a result, reduce the incidence of adjacent segment disease. The efficacy of such implants is a matter of much debate (11-13); however, it is clear that nonbiological total disc replacement implants suffer from failure modes commonly associated with traditional metal/polyethylene arthroplasty, such as mechanical failure, dislodgement, polyethylene wear, and associated osteolysis and implant loosening. More recently, increasing attention has been turned toward creating tissue engineer...

Many cartilaginous tissues such as intervertebral disc (IVD) display a heterogeneous collagen microstructure that results in mechanical anisotropy. These structures are responsible for mechanical function of the tissue and regulate cellular interactions and metabolic responses of cells embedded within these tissues. Using collagen gels seeded with ovine annulus fibrosus cells, constructs of varying structure and heterogeneity were created to mimic the circumferential alignment of the IVD. Alignment was induced within gels by contracting annular gels around an inner boundary using both a polyethylene center and alginate center to create a composite engineered IVD. Collagen alignment and heterogeneity were measured using second harmonic generation microscopy. Decreasing initial collagen density from 2.5 mg/mL to 1 mg/mL produced greater contraction of constructs, resulting in gels that were 55% and 6.2% of the original area after culture, respectively. As a result, more alignment occurred in annular-shaped 1 mg/mL gels compared with 2.5 mg/mL gels (p < 0.05). This alignment was also produced in a composite-engineered IVD with alginate nucleus pulposus. The resulting collagen alignment could promote further aligned collagen development necessary for the creation of a mechanically functional tissue-engineered IVD.

Cell delivery to the pathological intervertebral disc (IVD) has significant therapeutic potential for enhancing IVD regeneration. The development of injectable biomaterials that retain delivered cells, promote cell survival, and maintain or promote an NP cell phenotype in vivo remains a significant challenge. Previous studies have demonstrated NP cell – laminin interactions in the nucleus pulposus (NP) region of the IVD that promote cell attachment and biosynthesis. These findings suggest that incorporating laminin ligands into carriers for cell delivery may be beneficial for promoting NP cell survival and phenotype. Here, an injectable, laminin-111 functionalized poly(ethylene glycol) (PEG-LM111) hydrogel was developed as a biomaterial carrier for cell delivery to the IVD. We evaluated the mechanical properties of the PEG-LM111 hydrogel, and its ability to retain delivered cells in the IVD space. Gelation occurred in approximately 20 minutes without an initiator, with dynamic shear moduli in the range of 0.9 – 1.4 kPa. Primary NP cell retention in cultured IVD explants was significantly higher over 14 days when cells were delivered within a PEG-LM111 carrier, as compared to cells in liquid suspension. Together, these results suggest this injectable laminin-functionalized biomaterial may be an easy to use carrier for delivering cells to the IVD.

Back pain is a major contributor to disability and has significant socioeconomic impacts worldwide. The degenerative intervertebral disc (IVD) has been hypothesized to contribute to back pain, but a better understanding of the interactions between the degenerative IVD and nociceptive neurons innervating the disc and treatment strategies that directly target these interactions is needed to improve our understanding and treatment of back pain. We investigated degenerative IVD-induced changes to dorsal root ganglion (DRG) neuron activity and utilized CRISPR epigenome editing as a neuromodulation strategy. By exposing DRG neurons to degenerative IVD-conditioned media under both normal and pathological IVD pH levels, we demonstrate that degenerative IVDs trigger interleukin (IL)-6-induced increases in neuron activity to thermal stimuli, which is directly mediated by AKAP and enhanced by acidic pH. Utilizing this novel information on AKAP-mediated increases in nociceptive neuron activity, we developed lentiviral CRISPR epigenome editing vectors that modulate endogenous expression of AKAP150 by targeted promoter histone methylation. When delivered to DRG neurons, these epigenome-modifying vectors abolished degenerative IVD-induced DRG-elevated neuron activity while preserving non-pathologic neuron activity. This work elucidates the potential for CRISPR epigenome editing as a targeted gene-based pain neuromodulation strategy.

Objective To investigate the relationship between NF-κB activity, cytokine levels, and pain sensitivities in a rodent model of osteoarthritis (OA). Method OA was induced in transgenic NF-κB luciferase reporter mice via mono-iodoacetate (MIA) intra-articular injection. Using luminescent imaging we evaluated the temporal kinetics of NF-κB activity and its relationship to the development of pain sensitivities and serum cytokine levels in this model. Results MIA induced a transient increase in joint-related NF-κB activity at early time points (day 3 post-injection) and an associated biphasic pain (mechanical allodynia) response. NF-κB activity, serum IL-6, IL-1β, and IL-10 accounted for ~75% of the variability in pain-related mechanical sensitivities in this model. Specifically, NF-κB activity was strongly correlated to mechanical allodynia and serum IL-6 levels in the inflammatory pain phase of this model (day 3), while serum IL-1β was strongly correlated to pain sensitivities in the chronic pain phase of the model (day 28). Conclusion Our findings suggest that NF-κB activity, IL-6 and IL-1β may be playing distinct roles in pain sensitivity development in this model of arthritis and may act to distinguish the acute from chronic pain phases of this model. This work establishes luminescent imaging of NF-κB activity as a novel imaging biomarker of pain sensitivities in this model of OA.

Nonbiological total disc replacement is currently being used for the treatment of intervertebral disc (IVD) disease and injury, but these implants are prone to mechanical wear, tear and possible dislodgement. Recently, tissue-engineered total disc replacement (TE-TDR) has been investigated as a possible alternative to more fully replicate the native IVD properties. However, the performance of TE-TDRs has not been studied in the native disc space. In this study, MRI and microcomputed tomography imaging of the rat spine were used to design a collagen (annulus fibrosus)/alginate (nucleus pulposus) TE-TDR to a high degree of geometric accuracy, with less than 10% difference between TE-TDR and the native disc dimensions. Image-based TE-TDR implants were then inserted into the L4/L5 disc space of athymic rats (n = 5) and maintained for 16 weeks. The disc space was fully or partially maintained in three of five animals and proteoglycan and collagen histology staining was similar in composition to the native disc. In addition, good integration was observed between TE-TDR and the vertebral bodies, as well as remnant native IVD tissue. Overall, this study provides evidence that TE-TDR strategies may yield a clinically viable treatment for diseased or injured IVD.

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Low back pain is among the leading causes of disability worldwide. The degenerative intervertebral disc (IVD) environment contains pathologically high levels of inflammatory cytokines and acidic pH hypothesized to contribute to back pain by sensitizing nociceptive neurons to stimuli that would not be painful in healthy patients. We hypothesized that the degenerative IVD environment drives discogenic pain by sensitizing nociceptive neurons to mechanical loading. To test this hypothesis, we developed an in vitro model that facilitated the investigation of interactions between the degenerative IVD environment, nociceptive neurons innervating the IVD and mechanical loading of the disc; and, the identification of the underlying mechanism of degenerative IVD induced nociceptive neuron sensitization. In our model, rat dorsal root ganglia (DRG) neurons were seeding onto bovine annulus fibrosus tissue, exposed to degenerative IVD conditioned media and/or acidic pH, and subjected to cyclic tensile strain (1 Hz; 1%‐6% strain) during measurement of DRG sensory neuron activity via calcium imaging. Using this model, we demonstrated that both degenerative IVD conditioned media and degenerative IVD acidic pH levels induced elevated nociceptive neuron activation in response to physiologic levels of mechanical strain. In addition, interleukin 6 (IL‐6) was demonstrated to mediate degenerative IVD conditioned media induced elevated nociceptive neuron activation. These results demonstrate IL‐6 mediates degenerative IVD induced neuron sensitization to mechanical loading and further establishes IL‐6 as a potential therapeutic target for the treatment of discogenic pain. Data further suggests the degenerative IVD environment contains multiple neuron sensitization pathways (IL‐6, pH) that may contribute to discogenic pain.