Cell Clusters Are Indicative of Stem Cell Activity in the Degenerate Intervertebral Disc: Can Their Properties Be Manipulated to Improve Intrinsic Repair of the Disc?

The aim of this study was to examine the complexity of the stem cell populations in the intervertebral disc (IVD) and understand their role in disc degeneration, with a view of determining whether the resident stem cells could be developed for therapeutic purposes to combat IVD degeneration. Stem cells have been isolated from disc and paradiscal tissues, including the notochord, annulus fibrosus (AF), nucleus pulposus (NP), cartilaginous endplate (CEP), ligamentum flavum, and vertebral body. Resident AF and NP cells are relatively sparsely distributed occurring as single or occasional doublet cells surrounded by an extensive extracellular matrix (ECM). Small clusters of 4-12 cells also occur close to annular lesions in experimental ovine and canine disc degeneration, these are indicative of an attempted repair response by resident stem cells. The rat IVD also has notochordal and peripheral cell populations in the outer AF, which express CS sulfation motifs (7-D-4, 4-C-3, 3-B-3[-]) characteristic of activated stem cells, the murine IVD also has a cell population in the outer AF adjacent to the vertebral growth plate with characteristics of a progenitor cell population. These have also been observed in rabbit, minipig, ovine, and human IVDs. Chondroid cell nests in the ovine NP may represent a progenitor/stem cell reserve. Such human chondroid cells express CS sulfation motifs (7-D-4, 4-C-3, 3-B-3[-]), cytokeratin-8 and 19, and CD cell surface markers typical of stem cells, including OCT3/4, CD105, CD90, STRO-1, NOTCH1, and JAGGED1. Similar stem cell populations are present in grade IV degenerate human IVDs. A greater understanding of the biology of this chondroid cell population may identify them as a therapeutic resource. A resident therapeutic cell type adapted to the demanding IVD environment may be advantageous in repair strategies.

Intervertebral Disk Degeneration and Repair.

Intervertebral disk (IVD) degeneration is a natural progression of the aging process. Degenerative disk disease (DDD) is a pathologic condition associated with IVD that has been associated with chronic back pain. There are a variety of different mechanisms of DDD (genetic, mechanical, exposure). Each of these pathways leads to a final common result of unbalancing the anabolic and catabolic environment of the extracellular matrix in favor of catabolism. Attempts have been made to gain an understanding of the process of IVD degeneration with in Vitro studies. These models help our understanding of the disease process, but are limited as they do not come close to replicating the complexities that exist with an in Vivo model. Animal models have been developed to help us gain further understanding of the degenerative cascade of IVD degeneration In Vivo and test experimental treatment modalities to either prevent or reverse the process of DDD. Many modalities for treatment of DDD have been developed including therapeutic protein injections, stem cell injections, gene therapy, and tissue engineering. These interventions have had promising outcomes in animal models. Several of these modalities have been attempted in human trials, with early outcomes having promising results. Further, increasing our understanding of the degenerative process is essential to the development of new therapeutic interventions and the optimization of existing treatment protocols. Despite limited data, biological therapies are a promising treatment modality for DDD that could impact our future management of low back pain.

Versican G3 domain enhances cellular adhesion and proliferation of bovine intervertebral disc cells cultured in vitro.

The functional role of versican in influencing intervertebral disc cell adhesion and proliferation was analyzed in bovine intervertebral disc. We have previously demonstrated the C-terminal globular G3 (or selectin-like) domain of versican to influence mesenchymal chondrogenesis and fibroblast proliferation in vitro. For this study, a versican G3 expression construct was generated to examine the role of the G3 domain of versican. Nucleus pulposus and annulus fibrosus cells were isolated from adult bovine caudal discs using sequential enzymatic digestion and versican expression characterized by RT-PCR. In cell proliferation assays, we observed that there was greater cellular proliferation in the presence of versican G3 for both disc cell types. The higher proliferation rate of annulus fibrosus cells when compared to nucleus pulposus cells seeded in monolayer supports heterogeneity of intervertebral disc cell populations. The presence of versican G3 construct enhanced the adhesion of isolated nucleus pulposus and annulus fibrosus cells approximately 4 to 6 fold, respectively. Cellular adhesion was greater in the presence of versican G3 in a dose dependent manner. G3 product was purified using affinity columns, and the purified G3 also enhanced cell adhesion.

An examination of the mechanisms by which neural precursors augment recovery following spinal cord injury: a key role for remyelination.

The mechanisms by which neural precursor cells (NPCs) enhance functional recovery from spinal cord injury (SCI) remain unclear. Spinal cord injured rats were transplanted with wild-type mouse NPCs, shiverer NPCs unable to produce myelin, dead NPCs, or media. Most animals also received minocycline, cyclosporine, and perilesional infusion of trophins. Motor function was graded according to the BBB scale. H&E/LFB staining was used to assess gray and white matter, cyst, and lesional tissue. Mature oligodendrocytes and ED1(+) inflammatory cells were quantitated. Confocal and electron microscopy were used to assess the relationship between the transplanted cells and axons. Pharmacotherapy and trophin infusion preserved gray matter, white matter, and oligodendrocytes. Trophin infusion also significantly increased cyst and lesional tissue volume as well as inflammatory infiltrate, and functional recovery was reduced. Animals transplanted with wild-type NPCs showed greatest functional recovery; animals transplanted with shiverer NPCs performed the worst. Wild-type NPCs remyelinated host axons. Shiverer NPCs ensheathed axons but did not produce MBP. These results suggest that remyelination by NPCs is an important contribution to functional recovery following SCI. Shiverer NPCs may prevent remyelination by endogenous cells capable of myelin formation. These findings suggest that remyelination is an important therapeutic target following SCI.

Canonical Wnt signaling and caveolae play a role in intervertebral disc degeneration; the continuing saga of the mysterious notochordal cell.

Over the past few decades small animal models mainly involving rodents and rabbits have been developed whereby needle puncture, stab incision or enzymatic approaches have been validated to create the degenerative disc. Although important, these models continue to be plagued by biological attributes that limit applicability to the human condition. However, the fascinating story of two naturally occurring subspecies of canine, the non-chondrodystrophic and chondrodystrophic canine, provides us with an animal model that differentially is protected from the development of degenerative disc disease. Here, Smolders and colleagues provide the first steps to understanding some of the secrets held by man's best friend.

Comparative effectiveness of exercise, acupuncture, and spinal manipulation for low back pain.

STUDY DESIGN: Systematic review. OBJECTIVE: We sought to answer the following clinical questions: (1) Is structured exercise more effective in the treatment of chronic low back pain (LBP) than spinal manipulative therapy (SMT)? (2) Is structured exercise more effective in the treatment of chronic LBP than acupuncture? (3) Is SMT more effective in the treatment of chronic LBP than acupuncture? (4) Do certain subgroups respond more favorably to specific treatments? (5) Are any of these treatments more cost-effective than the others? SUMMARY OF BACKGROUND DATA: Exercise, SMT, and acupuncture are widely used interventions in the treatment of chronic LBP. There is evidence that all of these approaches may offer some benefit for patients with chronic LBP when compared with usual care or no treatment. The relative benefits or cost-effectiveness of any one of these treatments when compared with the others are less well-defined, and it is difficult to identify specific subgroups of those with chronic LBP who may preferentially respond to a particular treatment modality. METHODS: A systematic review of the literature was performed to identify randomized controlled trials comparing a structured exercise program, SMT, or acupuncture with one another in patients with chronic LBP. RESULTS: Two studies were identified comparing the use of structured exercise with SMT that met our inclusion criteria. Although these studies utilized different approaches for the exercise and SMT treatment groups, patients in both groups improved in terms of pain and function in both studies. Using random-effects modeling, there was no difference between the exercise and SMT groups when the data from these studies were pooled. We identified no studies meeting our inclusion criteria that compared acupuncture with either structured exercise or SMT or that addressed the relative cost-effectiveness of these approaches in the treatment of patients with chronic LBP. CONCLUSION: The studies identified indicate that structured exercise and SMT appear to offer equivalent benefits in terms of pain and functional improvement for those with chronic LBP with clinical benefits evident within 8 weeks of care. However, the level of evidence is low. There is insufficient evidence to comment on the relative benefit of acupuncture compared with either structured exercise or SMT or to address the differential effects of structured exercise, SMT, or acupuncture for specific subgroups of individuals with chronic LBP. There is also insufficient evidence regarding the relative cost-effectiveness of structured exercise, SMT, or acupuncture in the treatment of chronic LBP. CLINICAL RECOMMENDATIONS: Structured exercise and SMT appear to offer equivalent benefits in the management of pain and function for patients with nonspecific chronic LBP. If no clinical benefit is appreciated after using one of these approaches for 8 weeks, then the treatment plan should be reevaluated and consideration should be given to modifying the treatment approach or using alternate forms of care. Strength of recommendation: Weak.There is insufficient evidence regarding the relative benefits of the acupuncture compared with either structured exercise or SMT in the treatment of chronic LBP.There is insufficient evidence to address differential effects of structured exercise, SMT, or acupuncture for specific subgroups of individuals with chronic LBP. There is insufficient evidence regarding the relative cost-effectiveness of structured exercise, SMT, or acupuncture in the treatment of chronic LBP.