IntroductionEarly degeneration of the intervertebral disc (IVD) involves a change in cellular differentiation from notochordal cells (NCs) in the nucleus pulposus (NP) to chondrocyte-like cells (CLCs). The purpose of this study was to investigate the gene expression profiles involved in this process using NP tissue from non-chondrodystrophic and chondrodystrophic dogs, a species with naturally occurring IVD degeneration.MethodsDual channel DNA microarrays were used to compare 1) healthy NP tissue containing only NCs (NC-rich), 2) NP tissue with a mixed population of NCs and CLCs (Mixed), and 3) NP tissue containing solely CLCs (CLC-rich) in both non-chondrodystrophic and chondrodystrophic dogs. Based on previous reports and the findings of the microarray analyses, canonical Wnt signaling was further evaluated using qPCR of relevant Wnt target genes. We hypothesized that caveolin-1, a regulator of Wnt signaling that showed significant changes in gene expression in the microarray analyses, played a significant role in early IVD degeneration. Caveolin-1 expression was investigated in IVD tissue sections and in cultured NCs. To investigate the significance of Caveolin-1 in IVD health and degeneration, the NP of 3-month-old Caveolin-1 knock-out mice was histopathologically evaluated and compared with the NP of wild-type mice of the same age.ResultsEarly IVD degeneration involved significant changes in numerous pathways, including Wnt/β-catenin signaling. With regard to Wnt/β-catenin signaling, axin2 gene expression was significantly higher in chondrodystrophic dogs compared with non-chondrodystrophic dogs. IVD degeneration involved significant down-regulation of axin2 gene expression. IVD degeneration involved significant down-regulation in Caveolin-1 gene and protein expression. NCs showed abundant caveolin-1 expression in vivo and in vitro, whereas CLCs did not. The NP of wild-type mice was rich in viable NCs, whereas the NP of Caveolin-1 knock-out mice contained chondroid-like matrix with mainly apoptotic, small, rounded cells.ConclusionsEarly IVD degeneration involves down-regulation of canonical Wnt signaling and Caveolin-1 expression, which appears to be essential to the physiology and preservation of NCs. Therefore, Caveolin-1 may be regarded an exciting target for developing strategies for IVD regeneration.

A hydrogel nucleus pulposus prosthesis (NPP) was designed to swell in situ, have intrinsic radiopacity, and restore intervertebral disc height and biomechanical functionality. These features were examined using an ex vivo canine lumbar model. Nine NPPs were implanted in five spines and their visibility was assessed on radiography, computed tomography (CT), and magnetic resonance imaging (MRI). The NPPs were visible on all imaging modalities and 8/9 NPPs stayed intact and in situ. Six other NPPs were tested biomechanically in six canine lumbar spines. Removal of the nucleus pulposus (nuclectomy) caused significant changes in biomechanical parameters. After implantation and swelling of the NPP, values were not significantly different from the native state for range of motion (ROM) of flexion-extension (FE) and lateral bending (LB), the neutral zone (NZ) of all motion directions, and the NZ stiffness (NZS) of FE. Biomechanical restoration by the NPP compared with the nuclectomized state was significant for the ROM of FE and axial rotation, the NZ of FE and LB, and the NZS of FE and LB. Disc height was significantly restored and 6/6 NPPs stayed intact and in situ. In conclusion, the NPPs swell in situ, have intrinsic radiopacity and restored disc height and aforementioned biomechanical properties.

Introduction Early degeneration of the IVD involves a change in the nucleus pulposus (NP) cell population, characterized by the replacement/differentiation of the native notochordal cells (NCs) by/into chondrocyte-like cells (CLCs). In this respect, the NC has received considerable attention as a potential NP progenitor cell and as a target to realize disk regeneration.1,2 The canine species is affected by naturally occurring IVD degeneration, like humans.3 Moreover, with regard to the maintenance of NCs and the occurrence of IVD degeneration, the canine species reveals a unique phenomenon. In chondrodystrophic dogs, NCs are replaced by CLCs before the age of 1 year, with a concurrent onset of IVD degeneration at all spinal levels. By contrast, in nonchondrodystrophic dogs the NC remains the predominant cell type of the NP during the majority of life; replacement of NCs by CLCs and concurrent IVD degeneration only occur at old age. The aim of this study is to investigate gene expression profiles in the process of early NP degeneration, thereby revealing potential biomolecular signaling pathways for IVD regeneration. Materials and Methods Canine IVD samples from chondrodystrophic and nonchondrodystrophic dogs were classified into (1) NP rich in NCs, (2) NP containing both NCs and CLC-cells (Mixed), and (3) early degenerated NP rich in CLCs (Fig. 1). Gene expression profiling of the NP of these three groups was performed using a two-color cDNA-microarray, with subsequent validation (qPCR and immunohistochemistry) in IVD samples and cultures of primary NCs. Results Early IVD degeneration involved significant regulations of various pathways, including extracellular matrix (ECM) remodeling, plasmin, and plasminogen activator urokinase. Bone Morphogenetic Protein (BMP)-, and Wnt/β-catenin-signaling and cytoskeleton remodeling. Wnt/β-catenin signaling plays a crucial role in maintaining the notochordal fate during embryogenesis and stem-cell fate determination, but is also involved in IVD degeneration and regeneration. Whether the differential expression of Wnt/β-catenin-signaling is associated with degeneration or is an attempt to repair the damaged IVD remains uncertain. Both NCs and CLCs showed nuclear and cytoplasmic expression of the Wnt effector protein β-catenin4; axin2 gene expression, a specific read-out for Wnt signaling, revealed a dual response: in the initial stages of NP degeneration tended to increase (Mixed group), but diminished with ongoing degeneration (CLC-rich group). A concurrent increase in Wnt inhibitory factor 1 gene expression was observed, which may be a significant factor involved in the downregulation of canonical Wnt signaling in the chondrodystrophic dogs.5 Caveolin-1, which is known to regulate canonical Wnt signaling,6 emerged as a significantly regulated gene. NCs in culture showed robust caveolin-1 gene and protein expression and IVD degeneration involved significant decrease in Caveolin-1 gene and protein expression. Conclusion Early IVD degeneration involves significant alt...

The aim of this article was to report surgical and medical management, and to evaluate complications and outcome of dogs treated for refractory infection after tibial tuberosity advancement (TTA) with a one-stage revision surgery consisting of implant removal and replacement of a TTA cage. It was a retrospective case series. Seven cases were included in this study. Loss of advancement of the tibial tuberosity or tibial crest fractures did not occur in any case. One-stage revision surgery was successful in 5/7 cases (71%) with good long-term outcomes. Persistent infection resulted in removal of the replaced new cage in 2/7 cases (29%), of which one was associated with septic arthritis caused by multi-resistant bacteria. One-stage revision with immediate replacement of a new TTA cage successfully prevented loss of advancement of the tibial tuberosity and tibial crest fractures in this short case series. Further studies investigating possible improvements in the treatment protocol for refractory infection after TTA are warranted.