The objectives of augmentation of the nucleus pulposus following disc removal are to prevent disc height loss and the associated biomechanical and biochemical changes. Flowable materials may be injected via a small incision, allowing minimally invasive access to the disc space. Fluids can interdigitate with the irregular surgical defects and may even physically bond to the adjacent tissue. Injectable biomaterials allow for incorporation and uniform dispersion of cells and/or therapeutic agents. Injectable biomaterials have been developed that may act as a substitute for the disc nucleus pulposus. Our work has focused on the evaluation of a recombinant protein copolymer consisting of amino acid sequence blocks derived from silk and elastin structural proteins as an injectable biomaterial for augmentation of the nucleus pulposus. This implant, NuCore TM Injectable Nucleus is being developed by Spine Wave (Shelton, CT). The NuCore

Objective. In mice with Col9a1 gene inactivation (Col9a1 ؊/؊ ), osteoarthritis (OA) and intervertebral disc degeneration develop prematurely. The aim of this study was to investigate Col9a1 ؊/؊ mice for functional and symptomatic changes that may be associated with these pathologies.Methods. Col9a1 ؊/؊ and wild-type mice were investigated for reflexes, functional impairment (beam walking, pole climbing, wire hang, grip strength), sensorimotor skills (rotarod), mechanical sensitivity (von Frey hair), and thermal sensitivity (hot plate/tail flick). Gait was also analyzed to determine velocity, stride frequency, symmetry, percentage stance time, stride length, and step width. Postmortem, sera obtained from the mice were analyzed for hyaluronan, and their knees and spines were graded histologically for degeneration.Results. Col9a1 ؊/؊ mice had compensatory gait changes, increased mechanical sensitivity, and impaired physical ability. Col9a1 ؊/؊ mice ambulated with gaits characterized by increased percentage stance times and shorter stride lengths. These mice also had heightened mechanical sensitivity and were deficient in contact righting, wire hang, rotarod, and pole climbing tasks. Male Col9a1 ؊/؊ mice had the highest mean serum hyaluronan levels and strong histologic evidence of cartilage erosion. Intervertebral disc degeneration was also detected, with Col9a1 ؊/؊ mice having an increased incidence of disc tears.Conclusion. These data describe a Col9a1 ؊/؊ behavioral phenotype characterized by altered gait, increased mechanical sensitivity, and impaired function. These gait and functional differences suggest that Col9a1 ؊/؊ mice select locomotive behaviors that limit joint loads. The nature and magnitude of behavioral changes were largest in male mice, which also had the greatest evidence of knee degeneration. These findings suggest that Col9a1 ؊/؊ mice present behavioral changes consistent with anatomic signs of OA and intervertebral disc degeneration.Osteoarthritis (OA) and degenerative disc disease (DDD) are common musculoskeletal disorders, and, as chronic conditions, both have large economic costs (1). Clinically, OA and DDD are associated with joint pain, loss of function, and decreased quality of life. A genetic predisposition to musculoskeletal diseases has been suggested as a determinant of individual risk (2,3), and extracellular matrix mutations have been linked to the premature onset of OA and DDD (4-10). Type IX collagen is a heterotrimeric collagen that associates with type II collagen fibrils and contains domains suited to promote extracellular matrix cohesion (11). Type IX collagen mutations are hypothesized to weaken cartilaginous tissues (8). Mice with inactivation of the Col9a1 gene, henceforth referred to as Col9a1 Ϫ/Ϫ mice, do not form functional type IX collagen molecules (12) and experience spontaneous development of premature cartilage degeneration (as early as 3 months) in the intervertebral disc, knee, and temporomandibular joint that worsens with age (up to 12 months) (12-14). It is not...

Intervertebral disc (IVD) cells experience a broad range of physicochemical stimuli under physiologic conditions, including alterations in their osmotic environment. Cellular responses to altered osmolarity have been documented at the transcriptional and post-translational level, but mainly for extracellular matrix proteins. In this study, the gene expression profile of human IVD cells was quantified with gene array technology following exposure to increased osmolarity in order to capture the biological responses for a broad set of targets. A total of 42 genes were identified in IVD cells as significantly changed following culture under hyper-osmotic conditions. Gene expression patterns were verified using RT-PCR. Genes identified in this study include those related to cytoskeleton remodeling and stabilization (ephrin-B2, muskelin), as well as membrane transport (ion transporter SLC21A12, osmolyte transporter SLC5A3, monocarboxylic acid SLC16A6). An unexpected finding was the differential regulation of the gene for the neurotrophin, brain-derived neurotrophic factor, by hyper-osmotic stimuli that suggests a capability of IVD cells to respond to physicochemical stimuli with factors that may regulate discogenic pain.

Objective. Type IX collagen is an important component of the intervertebral disc extracellular matrix. Mutations in type IX collagen are associated with premature disc degeneration in mice and a predisposition to disc disorders in humans. The aim of this study was to assess the prevalence and timeline of intervertebral disc degeneration in mice homozygous for an inactivated Col9a1 gene.Methods. Intact spine segments were harvested from wild-type (WT) and type IX collagen-knockout (Col9a1 Ϫ/Ϫ ) mice at 3, 6, and 12 months of age. Sagittal spine sections were evaluated for evidence of histologic changes, by 2 blinded graders, using a semiquantitative grading method.Results. There was evidence of more degeneration of the disc and end plate in the spines of Col9a1 ؊/؊ mice compared with those of WT controls, at most time points. These findings were significant for the disc region at 3 and 6 months (P < 0.01) and at 12 months (P < 0.10) and for the end plate region only at 6 months (P < 0.10). Degenerative changes in the disc consisted of cellular changes and mucous degeneration. Degeneration in the end plates was associated with more cell proliferation, cartilage disorganization, and new bone formation. Conclusion.A deletion mutation for type IX collagen is associated with connective tissue changes characteristic of musculoskeletal degeneration in bony and cartilaginous tissue regions. Some of the observed changes were similar to cartilage changes in osteoarthritis, while others were more similar to disc degenerative changes in humans. The finding of premature onset of intervertebral disc degeneration in this mouse model may be useful in studies of the pathology and treatment of human disc degeneration.Arthritic degenerative disorders of the spinal intervertebral disc are the most common of the musculoskeletal conditions and have a major impact on society because of the frequency of occurrence and the economic consequences (1). Environmental factors such as physical activity and mechanical loading may explain only a subset of intervertebral disc disorders when compared with inherited genetic factors (2-5). Intervertebral disc disorders and degeneration have been associated with mutations or polymorphisms in genes encoding matrix proteins, including type IX collagen (6) and aggrecan (7), as well as with genes encoding interleukin-1 (IL-1) (8), IL-6 (9), cartilage intermediatelayer protein (10), and vitamin D receptor (11).Mice with genetic mutations in select extracellular matrix proteins, including type II collagen (12) and type I collagen (13), have been shown to acquire structural and functional matrix alterations in the intervertebral disc. In one study, mice carrying an inactivated allele of the Col2a1 gene showed early vertebral end plate ossification and decreased glycosaminoglycan concentration in the vertebrae, end plate, and annulus fibrosus beginning at 1 month, with differences between mutant mice and wild-type (WT) controls no longer evident by the age of 9 months (12). In another study, mice heterozygou...

Cells of the NP and AF secrete soluble factors in culture at similarly effective doses to stimulate matrix protein gene expression in AF cells of the intervertebral disc. Unlike AF cells, however, NP cell gene expression was not stimulated by any conditioned medium, suggesting that differences exist in the responsiveness of cells of notochordal (NP) and fibrocartilaginous (AF) phenotypes. Understanding these differences between cells of the intervertebral disc may reveal unique stimulatory factors important to repair and regeneration of the degenerated intervertebral disc.

Numerous mitochondria ranging from slightly larger than normal to several micrometers in diameter (giant) were found in about one-half the serous secretory cells in the surface epithelium of the normal gerbil trachea and proximal bronchi. Tracheal serous cells of mice also were found to contain numerous giant mitochondria. Clara cells of gerbil bronchioles contained abundant giant mitochondria in addition to normal tubular mitochondria and the second population of enlarged spherical mitochondria that have been described in Clara cells of several genera. In contrast, mouse Clara cells revealed the normal tubular and the enlarged spherical mitochondria but no giant mitochondria. A survey of a number of cell types in gerbils failed to disclose hypertrophied mitochondria outside tracheobronchial surface epithelium and bronchioles. The mitochondrial enlargement resulted from an increase of matrix but not cristae. The expansion of matrix displaced the relatively sparse cristae into small collections compressed against the outer membrane. The prevalence of giant mitochondria and of granular endoplasmic reticulum is similar among cells, and these two organelles are codistributed within cells. The megamitochondria and granular reticulum occupy a central stratum, whereas normal mitochondria occur in the apical and basal regions. The giant mitochondria are considered related to a normal biologic activity that is characteristic of respiratory tract epithelium of mice and gerbils selectively and is more prominent in secretory cells than in ciliated cells.

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