Proliferation of canine intervertebral disk chondrocytes in three-dimensional alginate microsphere culture

Organotypic Cultures of Intervertebral Disc Cells: Responses to Growth Factors and Signaling Pathways Involved

Intervertebral disc (IVD) degeneration is strongly associated with low back pain, a major cause of disability worldwide. An in-depth understanding of IVD cell physiology is required for the design of novel regenerative therapies. Accordingly, aim of this work was the study of IVD cell responses to mitogenic growth factors in a three-dimensional (3D) organotypic milieu, comprising characteristic molecules of IVD's extracellular matrix. In particular, annulus fibrosus (AF) cells were cultured inside collagen type-I gels, while nucleus pulposus (NP) cells in chondroitin sulfate A (CSA) supplemented collagen gels, and the effects of Platelet-Derived Growth Factor (PDGF), basic Fibroblast Growth Factor (bFGF), and Insulin-Like Growth Factor-I (IGF-I) were assessed. All three growth factors stimulated DNA synthesis in both AF and NP 3D cell cultures, with potencies similar to those observed previously in monolayers. CSA supplementation inhibited basal DNA synthesis rates, without affecting the response to growth factors. ERK and Akt were found to be phosphorylated following growth factor stimulation. Blockade of these two signaling pathways using pharmacologic inhibitors significantly, though not completely, inhibited growth factor-induced DNA synthesis. The proposed culture systems may prove useful for further in vitro studies aiming at future interventions for IVD regeneration.

Matrix Degradative Enzymes and Their Inhibitors during Annular Inflammation: Initial Step of Symptomatic Intervertebral Disc Degeneration

Objective

Symptomatic disc degeneration develops from inflammatory reactions in the annulus fibrosus (AF). Although inflammatory mediators during annular inflammation have been studied, the roles of matrix metalloproteinases (MMPs) and their inhibitors have not been fully elucidated. In this study, we evaluated the production of MMPs and tissue inhibitors of metalloproteinase (TIMPs) during annular inflammation using an in vitro co-culture system. We also examined the effect of notochordal cells on annular inflammation.

Methods

Human AF (hAF) pellet was co-cultured for 48 hours with phorbol myristate acetate-stimulated macrophage-like THP-1 cells. hAF pellet and conditioned media (CM) from co-cultured cells were assayed for MMPs, TIMPs, and insulin-like growth factor (IGF)-1 levels using real-time reverse-transcriptase polymerase chain reaction and enzyem-linked immunosorbent assay. To evaluate whether notochordal cells affected MMPs or TIMPs production on annular inflammation, hAF co-cultured with notochordal cells from adult New Zealand White rabbits, were assayed.

Results

MMP-1, -3, -9; and TIMP-1 levels were significantly increased in CM of hAF co-cultured with macrophage-like cells compared with hAF alone, whereas TIMP-2 and IGF-1 levels were significantly decreased (p<0.05). After macrophage exposure, hAF produced significantly more MMP-1 and -3 and less TIMP-1 and -2. Interleukin-1β stimulation enhanced MMP-1 and -3 levels, and significantly diminished TIMP-2 levels. Co-culturing with rabbit notochordal cells did not significantly influence MMPs and TIMPs production or COL1A2 gene expression.

Conclusion

Our results indicate that macrophage-like cells evoke annular degeneration through the regulation of major degradative enzymes and their inhibitors, produced by hAF, suggesting that the selective regulation of these enzymes provides future targets for symptomatic disc degeneration therapy.

Rabbit notochordal cells modulate the expression of inflammatory mediators by human annulus fibrosus cells cocultured with activated macrophage-like THP-1 cells

STUDY DESIGN

We evaluated the influence of rabbit notochordal cells on the expression of inflammatory mediators by human annulus fibrosus (AF) cells cocultured with macrophage-like cells.

OBJECTIVE

To identify the protective effect of rabbit notochordal cells on AF during in vitro inflammation.

SUMMARY OF BACKGROUND DATA

Discogenic pain, which is an important cause of intractable lower back pain, is associated with macrophage-mediated inflammation in the AF. Although rabbit notochordal cells prevent intervertebral disc degeneration, their effects on human AF inflammation remain unknown.

METHODS

Human AF pellets were cocultured for 48 hours with notochordal cell clusters from adult New Zealand White rabbits and phorbol myristate acetate (PMA)-stimulated human macrophage-like THP-1 cells. Conditioned media (CM) from the cocultures were assayed by enzyme-linked immunosorbent assay. The expression of inflammatory mediators in the AF pellets was evaluated by real-time reverse-transcription polymerase chain reaction.

RESULTS

The levels of mRNA for interleukin (IL)-6, IL-8, and inducible nitric oxide synthase (iNOS) in the AF pellets cocultured with notochordal cells and macrophages (hAF[rNC-M]) were significantly lower than those in the AF pellets cultured with macrophages alone (hAF[M]) (P < 0.05). The levels of IL-6 and IL-8 proteins in the CM of hAF(rNC-M) were significantly lower than those in the CM of hAF(M) (P < 0.05). Coculturing with notochordal cells significantly decreased the levels of mRNA for IL-6, IL-8, and iNOS in the macrophage-exposed AF pellets (P < 0.05). After 1 ng/mL IL-1β stimulation, the levels of IL-6 and IL-8 mRNA and the level of IL-8 protein production were significantly decreased in the AF pellets with notochordal cells compared with naïve AF pellets (P < 0.05).

CONCLUSION

In an in vitro coculture system, rabbit notochordal cells reduced the levels of main inflammatory mediators and gene expression in the human AF during inflammation. Therefore, rabbit notochordal cells may constitute an important protective tool against symptomatic disc development.

Insights into the hallmarks of human nucleus pulposus cells with particular reference to cell viability, phagocytic potential and long process formation

OBJECTIVE

As a main cellular component within the disc, nucleus pulposus (NP) cells play important roles in disc physiology. However, little is known on the biologic hallmarks of human NP cells. Therefore, the present study aimed to address the features of human NP cells.

METHODS

Human NP samples were collected from normal cadavers, patients with scoliosis and disc degeneration as normal, disease control and degenerative NP, respectively. The NP samples were studied using transmission electron microscopy and TUNEL assay. Pre-digested NP samples were studied using flow cytometry with PI/Annexin V staining.

RESULTS

Both control and degenerative human NP consisted of mainly viable cells with a variety of morphology. Both necrosis and apoptosis were noted in human NP as forms of cell death with increased apoptosis in degenerative NP, which was further confirmed by the TUNEL assay. Phagocytic NP cells had the hallmarks of both stationary macrophages with lysosomes and NP cells with the endoplasmic reticulum. Annulus fibrosus cells have similar morphologic characteristics with NP cells in terms of cell nest, phagocytosis and intracellular organs. Moreover, NP cells with long processes existed in degenerative and scoliotic NP rather than normal NP. When cultured in glucose-free medium, NP cells developed long and thin processes.

CONCLUSION

Human degenerative NP consists of primarily viable cells. We present direct and in vivo evidence that both human annulus fibrosus and NP cells have phagocytic potential. Moreover, NP cells with long processes exist in both scoliotic and degenerative NP with lack of glucose as one of the possible underlying mechanisms.

New perspectives in cell delivery systems for tissue regeneration: natural-derived injectable hydrogels

Natural polymers, because of their biocompatibility, availability, and physico-chemical properties have been the materials of choice for the fabrication of injectable hydrogels for regenerative medicine. In particular, they are appealing materials for delivery systems and provide sustained and controlled release of drugs, proteins, gene, cells, and other active biomolecules immobilized.In this work, the use of hydrogels obtained from natural source polymers as cell delivery systems is discussed. These materials were investigated for the repair of cartilage, bone, adipose tissue, intervertebral disc, neural, and cardiac tissue. Papers from the last ten years were considered, with a particular focus on the advances of the last five years. A critical discussion is centered on new perspectives and challenges in the regeneration of specific tissues, with the aim of highlighting the limits of current systems and possible future advancements.

Notochordal cells influence gene expression of inflammatory mediators of annulus fibrosus cells in proinflammatory cytokines stimulation

OBJECTIVE

Notochordal cells in the intervertebral disc interact with nucleus pulposus (NP) cells and support the maintenance of disc homeostasis by regulation of matrix production. However, the influence of notochordal cells has not been evaluated in the annulus fibrosus (AF), which is the primary pain generator in the disc. We hypothesized that the notochordal cell has the capacity to modulate inflammatory mediators secreted by AF cells secondary to stimulation.

METHODS

Notochordal and AF cells were isolated from adult New Zealand white rabbits. AF pellets were cultured with notochordal cell clusters or in notochordal cell-conditioned media (NCCM) for 24 or 48 hours with proinflammatory cytokines at varying concentrations. Gene expression in AF pellets were assayed for nitric oxide synthase (iNOS), cyclo-oxygenase (COX)-2, and interleukin (IL)-6 by real time reverse transcriptase polymerase chain reaction (RT-PCR).

RESULTS

AF pellet in NCCM significantly decreased the iNOS and COX-2 messenger ribonucleic acid (mRNA) levels compared to AF pellets alone and AF pellets with notochordal cells (p < 0.05). AF pellet resulted in dose-dependent iNOS and COX-2 expression in response to IL-1beta, stimulation, demonstrating that 1 ng/ml for 24 hours yielded a maximal response. AF pellet in NCCM significantly decreased the expression of iNOS and COX-2 in response to 1ng/ml IL-1beta, stimulation at 24 hours (p < 0.05). There was no difference in IL-6 expression compared to AF pellets alone or AF pellets with notochordal cell clusters.

CONCLUSION

We conclude that soluble factors from notochordal cells mitigate the gene expression of inflammatory mediators in stimulated AF, as expected after annular injury, suggesting that notochordal cells could serve as a novel therapeutic approach in symptomatic disc development.

Molecular and phenotypic modulations of primary and immortalized canine chondrocytes in different culture systems

This study was conducted to determine physiological and functional features of primary and immortalized canine chondrocytes. Chondrocytes were immortalized by introducing the catalytic component of human telomerase namely human telomerase reverse transcriptase (hTERT). Primary chondrocytes lost their characteristic phenotype and growth properties whereas the immortalized cells remained polygonal with rapid growth rate. The expression of chondrocyte-specific markers decreased many-fold whereas that of chondrocyte-non-specific gene increased in primary chondrocytes. The immortalized cells did not express chondrocyte-specific genes in monolayers. Both primary and immortalized cells were encapsulated in alginate microspheres to construct three-dimensional (3D) culture system. As the primary chondrocytes, also the telomerase-transfected cells adopted a chondrocyte-specific gene expression pattern in alginate culture. Thus, the expression of telomerase represents possibility to expand chondrocytes without limitation while maintaining the chondrocyte-specific phenotype in 3D cultures. Use of such cells provides a standardized tool for testing different tissue engineering applications in canine model.

Association between a variation in LRCH1 and knee osteoarthritis: a genome-wide single-nucleotide polymorphism association study using DNA pooling

OBJECTIVE

To perform a large-scale association analysis of single-nucleotide polymorphisms (SNPs) in patients with radiographically defined osteoarthritis (OA) of the knee.

METHODS

We examined >25,000 SNPs located within approximately 14,000 genes for associations with radiographically defined knee OA, using polymerase chain reaction and MassExtend amplification techniques. Allele frequencies were estimated initially in DNA pools from 335 female patients with knee OA and 335 asymptomatic and radiographically negative female control subjects. All were of northern European ancestry. Significant allele frequency differences were validated by genotyping of individual DNA samples. Confirmed significant findings were verified in 2 additional case-control samples from the UK (443 cases and 303 controls) and Newfoundland (346 cases and 264 controls). Chondrosarcoma cell lines were used to test for potential differences in gene expression.

RESULTS

The marker most strongly associated with the risk of knee OA was rs912428, a C/T polymorphism in intron 1 of LRCH1, a gene on chromosome 13q14 that encodes a novel protein of as-yet-unknown function. The frequency of the T allele compared with controls was consistently increased by 40% across all 3 case-control groups. Additional subanalyses in case-control samples with hip OA and hand OA suggested similar trends, but did not reach statistical significance. Association fine-mapping using 10 additional SNPs in LRCH1 confirmed intron 1 as the region of highest association but failed to reveal variations with significance stronger than the marker SNP, as did the haplotype analysis. LRCH1 was not up-regulated or overexpressed in chondrosarcoma cell lines exposed to inflammatory stimuli, suggesting a possible structural role.

CONCLUSION

A genetic variant in LRCH1 was consistently associated with knee OA in 3 samples from 2 populations. Our results also suggest that the same association with OA may exist at other sites. Additional genetic and experimental work is needed to elucidate the precise mechanism by which the LRCH1 gene influences OA risk.

Three-Dimensional Culture of Feline Articular Chondrocytes in Alginate Microspheres

Chondrocytes isolated from proximal femoral articular cartilage from 3 adult cat cadavers were expanded in monolayer culture and subsequently cultured in alginate microspheres for 24 days. Cell proliferation and production of proteoglycans in alginate microspheres were observed during day 18 and 24. Quantification of chondroitin sulfates (CS) by capillary electrophoresis revealed that cultured chondrocytes synthesized CS6 but not CS4. Three-dimensional culture using alginate microspheres is a useful in vitro technique to study proliferation and metabolism of chondrocytes; however, further modifications are needed to apply the technique to feline articular chondrocytes.

The functional significance of cell clusters in the notochordal nucleus pulposus: survival and signaling in the canine intervertebral disc

STUDY DESIGN

Cell viability was assessed in relation to cell clustering, and mechanisms of cell-cell signaling in the clusters were investigated.

OBJECTIVES

To explore the functional role of cell clustering in the notochordal nucleus pulposus.

SUMMARY OF BACKGROUND DATA

The intervertebral disc of some species contains residual cells from the embryonic notochord. These cells form large three-dimensional clusters in the young, healthy disc but are replaced by chondrocyte-like cells during aging and degeneration.

METHODS

Forty nucleus pulposi of adult dog lumbar intervertebral discs were isolated, and were left untreated, mechanically disrupted through a syringe, or enzymatically digested. The presence of functional gap junctions was determined by the fluorescence recovery after photobleaching method. Cell viability was also assessed over 20 days in vitro.

RESULTS

The cell clusters were interconnected via functional gap junctions. Mechanical disruption of the tissue had little effect on long-term cell viability, but enzymatic disruption of the tissue had a substantial negative impact on cell survival.

CONCLUSIONS

These results demonstrate that the notochordal cells in adult dog nucleus pulposi are able to communicate via cytoplasmic signals and that such communications may influence the functionality of these cells in the young disc.

Temporal Dynamic Changes in Synthesis of Chondroitin Sulfate Isomers in Canine Articular Chondrocyte Culture

To investigate temporal dynamic changes in the synthesis of chondroitin 6-sulfate (CS6) and chondroitin 4-sulfate (CS4) in vitro, normal articular cartilage of femoral heads was harvested from three dogs. Chondrocytes were isolated and cultured in alginate microspheres for 21 days. On days 7, 14 and 21, DNA content was quantified by fluorometric assay using Hoechst 33258. On days 14 and 21, proteoglycans were extracted, and the amounts of CS6 and CS4 were quantified after chondroitinase ABC digestion using capillary electrophoresis. The DNA content and amounts of CS6 and CS4 increased during the culture period. The amounts of CS6 and CS4 divided by DNA content revealed that the synthesis of CS6 was more up-regulated than CS4.