Micromolding-based encapsulation of mesenchymal stromal cells in alginate for intraarticular injection in osteoarthritis

Osteoarthritis (OA) is an inflammatory joint disease that affects cartilage, subchondral bone, and joint tissues. Undifferentiated Mesenchymal Stromal Cells are a promising therapeutic option for OA due to their ability to release anti-inflammatory, immuno-modulatory, and pro-regenerative factors. They can be embedded in hydrogels to prevent their tissue engraftment and subsequent differentiation. In this study, human adipose stromal cells are successfully encapsulated in alginate microgels via a micromolding method. Microencapsulated cells retain their in vitro metabolic activity and bioactivity and can sense and respond to inflammatory stimuli, including synovial fluids from OA patients. After intra-articular injection in a rabbit model of post-traumatic OA, a single dose of microencapsulated human cells exhibit properties matching those of non-encapsulated cells. At 6 and 12 weeks post-injection, we evidenced a tendency toward a decreased OA severity, an increased expression of aggrecan, and a reduced expression of aggrecanase-generated catabolic neoepitope. Thus, these findings establish the feasibility, safety, and efficacy of injecting cells encapsulated in microgels, opening the door to a long-term follow-up in canine OA patients.

Posttraumatic Osteoarthritis Damage in Mice: From Histological and Micro-Computed Tomodensitometric Changes to Gait Disturbance

OBJECTIVES

Osteoarthritis is a painful joint disease responsible for walking impairment. Its quantitative assessment by gait analysis in mice may be a relevant and noninvasive strategy to assess the disease severity. In this study, we aimed to determine the severity of osteoarthritis at the tissular and gait levels in unilateral and bilateral posttraumatic murine osteoarthritis.

METHODS

Twenty-four C57BL/6 male mice were randomly assigned to 3 groups (n = 8/group): controls, unilateral surgery, and bilateral surgery. Posttraumatic osteoarthritis was induced unilaterally or bilaterally by destabilization of the medial meniscus. Gait analysis was performed weekly with the CatWalkTM XT system until the 16th week after surgery. After animal sacrifices, histological and micro-computed tomographic assessment was performed.

RESULTS

Operated knees showed a significant increase in the histological score compared with controls (P < 0.001). Calcified anterior medial meniscal bone volume was higher on the ipsilateral side after unilateral destabilization of the medial meniscus (P < 0.001) and on both sides after bilateral intervention (P < 0.01). One week after surgery, the mice mean speed decreased significantly in both operated groups (P < 0.001 and P < 0.05). In the unilateral group, a significant increase in the contralateral hind print area appeared from week 4 to week 16.

CONCLUSIONS

While bilateral destabilization of the medial meniscus induced no detectable gait modification except 1 week after surgery, unilateral model was responsible for a gait disturbance on the contralateral side. Further studies are needed to better define the place of the CatWalkTM in the evaluation of mouse models of osteoarthritis.

Correlation between magnetic resonance, X-ray imaging alterations and histological changes in an ovine model of age-related disc degeneration

Sheep are one of the many animal models used to investigate the pathophysiology of disc degeneration and the regenerative strategies for intervertebral disc (IVD) disease. To date, few studies have thoroughly explored ageing of ovine lumbar IVDs. Hence, the objective of the present study was to concomitantly assess the development of spontaneous age-related lumbar IVD degeneration in sheep using X-ray, magnetic resonance imaging (MRI) as well as histological analyses. 8 young ewes (< 48 months old) and 4 skeletally mature ewes (> 48 months old) were included. Disc height, Pfirrmann and modified Pfirrmann grades as well as T2-wsi and T2 times were assessed by X-ray and MRI. The modified Boos score was also determined using histology sections. Pfirrmann (2 to 3) and modified Pfirrmann (2 to 4) grades as well as Boos scores (7 to 13) gradually increased with ageing, while T2-weighted signal intensity (1.18 to 0.75), T2 relaxation time (114.36 to 70.65 ms) and disc height (4.1 to 3.2 mm) decreased significantly. All the imaging modalities strongly correlated with the histology (p < 0.0001). The present study described the suitability of sheep as a model of age-related IVD degeneration by correlation of histological tissue alterations with the changes observed using X-ray and MRI. Given the structural similarities with humans, the study demonstrated that sheep warrant being considered as a pertinent animal model to investigate IVD regenerative strategies without induction of degeneration.

Injectable silanized hyaluronic acid hydrogel/biphasic calcium phosphate granule composites with improved handling and biodegradability promote bone regeneration in rabbits

Biphasic calcium phosphate (BCP) granules are osteoconductive biomaterials used in clinics to favor bone reconstruction. Yet, poor cohesivity, injectability and mechanical properties restrain their use as bone fillers. In this study, we incorporated BCP granules into in situ forming silanized hyaluronic acid (Si-HA) and hydroxypropylmethylcellulose (Si-HPMC) hydrogels. Hydrogel composites were shown to be easily injectable (F < 30 N), with fast hardening properties (<5 min), and similar mechanical properties (E∼ 60 kPa). In vivo, both hydrogels were well tolerated by the host, but showed different biodegradability with Si-HA gels being partially degraded after 21d, while Si-HPMC gels remained stable. Both composites were easily injected into critical size rabbit defects and remained cohesive. After 4 weeks, Si-HPMC/BCP led to poor bone healing due to a lack of degradation. Conversely, Si-HA/BCP composites were fully degraded and beneficially influenced bone regeneration by increasing the space available for bone ingrowth, and by accelerating BCP granules turnover. Our study demonstrates that the degradation rate is key to control bone regeneration and that Si-HA/BCP composites are promising biomaterials to regenerate bone defects.

Silanization of Chitosan and Hydrogel Preparation for Skeletal Tissue Engineering

Tissue engineering is a multidisciplinary field that relies on the development of customized biomaterial to support cell growth, differentiation and matrix production. Toward that goal, we designed the grafting of silane groups onto the chitosan backbone (Si-chito) for the preparation of in situ setting hydrogels in association with silanized hydroxypropyl methylcellulose (Si-HPMC). Once functionalized, the chitosan was characterized, and the presence of silane groups and its ability to gel were demonstrated by rheology that strongly suggests the presence of silane groups. Throughout physicochemical investigations, the Si-HPMC hydrogels containing Si-chito were found to be stiffer with an injection force unmodified. The presence of chitosan within the hydrogel has demonstrated a higher adhesion of the hydrogel onto the surface of tissues. The results of cell viability assays indicated that there was no cytotoxicity of Si-chito hydrogels in 2D and 3D culture of human SW1353 cells and human adipose stromal cells, respectively. Moreover, Si-chito allows the transplantation of human nasal chondrocytes in the subcutis of nude mice while maintaining their viability and extracellular matrix secretory activity. To conclude, Si-chito mixed with Si-HPMC is an injectable, self-setting and cytocompatible hydrogel able to support the in vitro and in vivo viability and activity of hASC.

In Situ Forming, Silanized Hyaluronic Acid Hydrogels with Fine Control Over Mechanical Properties and In Vivo Degradation for Tissue Engineering Applications

In situ forming hydrogels that can be injected into tissues in a minimally-invasive fashion are appealing as delivery vehicles for tissue engineering applications. Ideally, these hydrogels should have mechanical properties matching those of the host tissue, and a rate of degradation adapted for neo-tissue formation. Here, the development of in situ forming hyaluronic acid hydrogels based on the pH-triggered condensation of silicon alkoxide precursors into siloxanes is reported. Upon solubilization and pH adjustment, the low-viscosity precursor solutions are easily injectable through fine-gauge needles prior to in situ gelation. Tunable mechanical properties (stiffness from 1 to 40 kPa) and associated tunable degradability (from 4 days to more than 3 weeks in vivo) are obtained by varying the degree of silanization (from 4.3% to 57.7%) and molecular weight (120 and 267 kDa) of the hyaluronic acid component. Following cell encapsulation, high cell viability (> 80%) is obtained for at least 7 days. Finally, the in vivo biocompatibility of silanized hyaluronic acid gels is verified in a subcutaneous mouse model and a relationship between the inflammatory response and the crosslink density is observed. Silanized hyaluronic acid hydrogels constitute a tunable hydrogel platform for material-assisted cell therapies and tissue engineering applications.

Controlled release of biological factors for endogenous progenitor cell migration and intervertebral disc extracellular matrix remodelling

The recent description of resident stem/progenitor cells in degenerated intervertebral discs (IVDs) supports the notion that their regenerative capacities could be harnessed to stimulate endogenous repair of the nucleus pulposus (NP). In this study, we developed a delivery system based on pullulan microbeads (PMBs) for sequential release of the chemokine CCL-5 to recruit these disc stem/progenitor cells to the NP tissue, followed by the release of the growth factors TGF-β1 and GDF-5 to induce the synthesis of a collagen type II- and aggrecan-rich extracellular matrix (ECM). Bioactivity of released CCL5 on human adipose-derived stem cells (hASCs), selected to mimic disc stem/progenitors, was demonstrated using a Transwell® chemotaxis assay. The regenerative effects of loaded PMBs were investigated in ex vivo spontaneously degenerated ovine IVDs. Fluorescent hASCs were seeded on the top cartilaginous endplates (CEPs); the degenerated NPs were injected with PMBs loaded with CCL5, TGF-β1, and GDF-5; and the IVDs were then cultured for 3, 7, and 28 days to allow for cell migration and disc regeneration. The PMBs exhibited sustained release of biological factors for 21 days. Ex vivo migration of seeded hASCs from the CEP toward the NP was demonstrated, with the cells migrating a significantly greater distance when loaded PMBs were injected (5.8 ± 1.3 mm vs. 3.5 ± 1.8 mm with no injection of PMBs). In ovine IVDs, the overall NP cellularity, the collagen type II and the aggrecan staining intensities, and the Tie2+ progenitor cell density in the NP were increased at day 28 compared to the control groups. Considered together, PMBs loaded with CCL5/TGF-β1/GDF-5 constitute an innovative and promising strategy for controlled release of growth factors to promote cell recruitment and extracellular matrix remodelling.

A Self-Setting Hydrogel of Silylated Chitosan and Cellulose for the Repair of Osteochondral Defects: From in vitro Characterization to Preclinical Evaluation in Dogs

Articular cartilage (AC) may be affected by many injuries including traumatic lesions that predispose to osteoarthritis. Currently there is no efficient cure for cartilage lesions. In that respect, new strategies for regenerating AC are contemplated with interest. In this context, we aim to develop and characterize an injectable, self-hardening, mechanically reinforced hydrogel (Si-HPCH) composed of silanised hydroxypropymethyl cellulose (Si-HPMC) mixed with silanised chitosan. The in vitro cytocompatibility of Si-HPCH was tested using human adipose stromal cells (hASC). In vivo, we first mixed Si-HPCH with hASC to observe cell viability after implantation in nude mice subcutis. Si-HPCH associated or not with canine ASC (cASC), was then tested for the repair of osteochondral defects in canine femoral condyles. Our data demonstrated that Si-HPCH supports hASC viability in culture. Moreover, Si-HPCH allows the transplantation of hASC in the subcutis of nude mice while maintaining their viability and secretory activity. In the canine osteochondral defect model, while the empty defects were only partially filled with a fibrous tissue, defects filled with Si-HPCH with or without cASC, revealed a significant osteochondral regeneration. To conclude, Si-HPCH is an injectable, self-setting and cytocompatible hydrogel able to support the in vitro and in vivo viability and activity of hASC as well as the regeneration of osteochondral defects in dogs when implanted alone or with ASC.

Tailored Three-Dimensionally Printed Triply Periodic Calcium Phosphate Implants: A Preclinical Study for Craniofacial Bone Repair

Finding alternative strategies for the regeneration of craniofacial bone defects (CSD), such as combining a synthetic ephemeral calcium phosphate (CaP) implant and/or active substances and cells, would contribute to solving this reconstructive roadblock. However, CaP's architectural features (i.e., architecture and composition) still need to be tailored, and the use of processed stem cells and synthetic active substances (e.g., recombinant human bone morphogenetic protein 2) drastically limits the clinical application of such approaches. Focusing on solutions that are directly transposable to the clinical setting, biphasic calcium phosphate (BCP) and carbonated hydroxyapatite (CHA) 3D-printed disks with a triply periodic minimal structure (TPMS) were implanted in calvarial critical-sized defects (rat model) with or without addition of total bone marrow (TBM). Bone regeneration within the defect was evaluated, and the outcomes were compared to a standard-care procedure based on BCP granules soaked with TBM (positive control). After 7 weeks, de novo bone formation was significantly greater in the CHA disks + TBM group than in the positive controls (3.33 mm3 and 2.15 mm3, respectively, P=0.04). These encouraging results indicate that both CHA and TPMS architectures are potentially advantageous in the repair of CSDs and that this one-step procedure warrants further clinical investigation.

Preliminary evaluation of an osteochondral autograft, a prosthetic implant, and a biphasic absorbable implant for osteochondral reconstruction in a sheep model

OBJECTIVE

To determine the ability of three implants to enhance the healing of osteochondral defects: (1) a biphasic construct composed of calcium phosphate (CaP) and chitosan/cellulosic polymer, (2) a titanium-polyurethane implant, and (3) an osteochondral autograft.

STUDY DESIGN

Experimental study.

ANIMALS

Ten adult female sheep.

METHODS

In five sheep, an 8-mm diameter osteochondral defect was created on the medial femoral condyle of a stifle and filled with a synthetic titanium-polyurethane implant. In five sheep, a similar defect was filled with an osteochondral autograft, and the donor site was filled with a biphasic construct combining CaP granules and a chitosan/cellulosic polymer. Sheep were monitored daily for lameness. Stifle radiographs and MRI were evaluated at 20 weeks, prior to animals being humanely killed. Surgical sites were evaluated with histology, microcomputed tomography, and scanning electron microscopy.

RESULTS

Clinical outcomes were satisfactory regardless of the tested biomaterials. All implants appeared in place on imaging studies. Osteointegration of prosthetic implants varied between sites, with limited ingrowth of new bone into the titanium structure. Autografts and biphasic constructs were consistently well integrated in subchondral bone. All autografts except one contained a cartilage surface, and all biphasic constructs except one partially restored hyaline cartilage surface.

CONCLUSION

Biphasic constructs supported hyaline cartilage and subchondral bone regeneration, although restoration of the articular cartilage was incomplete.

CLINICAL IMPACT

Biphasic constructs may provide an alternative treatment for osteochondral defects, offering a less invasive approach compared with autologous grafts and eliminating the requirement for a prosthetic implant.

In vitro and in vivo evaluation of an electrospun-aligned microfibrous implant for Annulus fibrosus repair

Annulus fibrosus (AF) impairment is associated with reherniation, discogenic pain, and disc degeneration after surgical partial discectomy. Due to a limited intrinsic healing capacity, defects in the AF persist over time and it is hence necessary to adopt an appropriate strategy to close and repair the damaged AF. In this study, a cell-free biodegradable scaffold made of polycaprolactone (PCL), electrospun, aligned microfibers exhibited high levels of cell colonization, alignment, and AF-like extracellular matrix deposition when evaluated in an explant culture model. The biomimetic multilayer fibrous scaffold was then assessed in an ovine model of AF impairment. After 4 weeks, no dislocation of the implants was detected, and only one sample out of six showed a partial delamination. Histological and immunohistochemical analyses revealed integration of the implant with the surrounding tissue as well as homogeneously aligned collagen fiber organization within each lamella compared to the disorganized and scarcer fibrous tissue in a randomly organized control fibrous scaffold. In conclusion, this biomimetic electrospun implant exhibited promising properties in terms of AF defect closure, with AF-like neotissue formation that fully integrated with the surrounding ovine tissue.

Laponite nanoparticle-associated silated hydroxypropylmethyl cellulose as an injectable reinforced interpenetrating network hydrogel for cartilage tissue engineering

Articular cartilage is a connective tissue which does not spontaneously heal. To address this issue, biomaterial-assisted cell therapy has been researched with promising advances. The lack of strong mechanical properties is still a concern despite significant progress in three-dimensional scaffolds. This article's objective was to develop a composite hydrogel using a small amount of nano-reinforcement clay known as laponites. These laponites were capable of self-setting within the gel structure of the silated hydroxypropylmethyl cellulose (Si-HPMC) hydrogel. Laponites (XLG) were mixed with Si-HPMC to prepare composite hydrogels leading to the development of a hybrid interpenetrating network. This interpenetrating network increases the mechanical properties of the hydrogel. The in vitro investigations showed no side effects from the XLG regarding cytocompatibility or oxygen diffusion within the composite after cross-linking. The ability of the hybrid scaffold containing the composite hydrogel and chondrogenic cells to form a cartilaginous tissue in vivo was investigated during a 6-week implantation in subcutaneous pockets of nude mice. Histological analysis of the composite constructs revealed the formation of a cartilage-like tissue with an extracellular matrix containing glycosaminoglycans and collagens. Overall, this new hybrid construct demonstrates an interpenetrating network which enhances the hydrogel mechanical properties without interfering with its cytocompatibility, oxygen diffusion, or the ability of chondrogenic cells to self-organize in the cluster and produce extracellular matrix components. This composite hydrogel may be of relevance for the treatment of cartilage defects in a large animal model of articular cartilage defects.

STATEMENT OF SIGNIFICANCE

Articular cartilage is a tissue that fails to heal spontaneously. To address this clinically relevant issue, biomaterial-assisted cell therapy is considered promising but often lacks adequate mechanical properties. Our objective was to develop a composite hydrogel using a small amount of nano reinforcement (laponite) capable of gelling within polysaccharide based self-crosslinking hydrogel. This new hybrid construct demonstrates an interpenetrating network (IPN) which enhances the hydrogel mechanical properties without interfering with its cytocompatibility, O₂ diffusion and the ability of chondrogenic cells to self-organize in cluster and produce extracellular matrix components. This composite hydrogel may be of relevance for the treatment of cartilage defects and will now be considered in a large animal model of articular cartilage defects.

Inverse regulation of early and late chondrogenic differentiation by oxygen tension provides cues for stem cell-based cartilage tissue engineering

BACKGROUND/AIMS

Multipotent stem/stromal cells (MSC) are considered promising for cartilage tissue engineering. However, chondrogenic differentiation of MSC can ultimately lead to the formation of hypertrophic chondrocytes responsible for the calcification of cartilage. To prevent the production of this calcified matrix at the articular site, the late hypertrophic differentiation of MSCs must be carefully controlled. Given that articular cartilage is avascular, we hypothesized that in addition to its stimulatory role in the early differentiation of chondrogenic cells, hypoxia may prevent their late hypertrophic conversion.

METHODS

Early and late chondrogenic differentiation were evaluated using human adipose MSC and murine ATDC5 cells cultured under either normoxic (21%O2) or hypoxic (5%O2) conditions. To investigate the effect of hypoxia on late chondrogenic differentiation, the transcriptional activity of hypoxia-inducible factor-1alpha (HIF-1α) and HIF-2α were evaluated using the NoShift DNA-binding assay and through modulation of their activity (chemical inhibitor, RNA interference). Results : Our data demonstrate that low oxygen tension not only stimulates the early chondrogenic commitment of two complementary models of chondrogenic cells, but also inhibits their hypertrophic differentiation. Conclusion : These results suggest that hypoxia can be used as an instrumental tool to prevent the formation of a calcified matrix in MSC-based cartilage tissue engineering.

Vertebroplasty using bisphosphonate-loaded calcium phosphate cement in a standardized vertebral body bone defect in an osteoporotic sheep model

In the context of bone regeneration in an osteoporotic environment, the present study describes the development of an approach based on the use of calcium phosphate (CaP) bone substitutes that can promote new bone formation and locally deliver in situ bisphosphonate (BP) directly at the implantation site. The formulation of a CaP material has been optimized by designing an injectable apatitic cement that (i) hardens in situ despite the presence of BP and (ii) provides immediate mechanical properties adapted to clinical applications in an osteoporotic environment. We developed a large animal model for simulating lumbar vertebroplasty through a two-level lateral corpectomy on L3 and L4 vertebrae presenting a standardized osteopenic bone defect that was filled with cements. Both 2-D and 3-D analysis of microarchitectural parameters demonstrated that implantation of BP-loaded cement in such vertebral defects positively influenced the microarchitecture of the adjacent trabecular bone. This biological effect was dependent on the distance from the implant, emphasizing the in situ effect of the BP and its release from the cement. As a drug device combination, this BP-containing apatitic cement shows good promise as a local approach for the prevention of osteoporotic vertebral fractures through percutaneous vertebroplasty procedures.

Mice with hypomorphic expression of the sodium-phosphate cotransporter PiT1/Slc20a1 have an unexpected normal bone mineralization

The formation of hydroxyapatite crystals and their insertion into collagen fibrils of the matrix are essential steps for bone mineralization. As phosphate is a main structural component of apatite crystals, its uptake by skeletal cells is critical and must be controlled by specialized membrane proteins. In mammals, in vitro studies have suggested that the high-affinity sodium-phosphate cotransporter PiT1 could play this role. In vivo, PiT1 expression was detected in hypertrophic chondrocytes of murine metatarsals, but its implication in bone physiology is not yet deciphered. As the complete deletion of PiT1 results in embryonic lethality at E12.5, we took advantage of a mouse model bearing two copies of PiT1 hypomorphic alleles to study the effect of a low expression of PiT1 on bone mineralization in vivo. In this report, we show that a 85% down-regulation of PiT1 in long bones resulted in a slight (6%) but significant reduction of femur length in young mice (15- and 30-day-old). However, despite a defect in alcian blue / alizarin red S and Von Kossa staining of hypomorphic 1-day-old mice, using X-rays micro-computed tomography, energy dispersive X-ray spectroscopy and histological staining techniques we could not detect differences between hypomorphic and wild-type mice of 15- to 300-days old. Interestingly, the expression of PiT2, the paralog of PiT1, was increased 2-fold in bone of PiT1 hypomorphic mice accounting for a normal phosphate uptake in mutant cells. Whether this may contribute to the absence of bone mineralization defects remains to be further deciphered.

Laser-treated Nucleus pulposus as an innovative model of intervertebral disc degeneration

This study describes an innovative experimentally induced model of intervertebral disc degeneration. This innovative approach is based on the induction of extracellular matrix disorders in the intervertebral disc (IVD) using a diode laser. For this study, 15 one-year-old and five 30-month-old New Zealand White rabbits were used. Two procedures were tested to trigger IVD degeneration: needle aspiration (reference technique) and a laser approach. The IVD degeneration process was assessed 20, 40, 60, 90 and 120 days after surgery by X-ray radiography (IVD height), magnetic resonance imaging (MRI) (T2 intensity of IVD signal) and histological analysis using modified Boos' scoring. Our data indicate that a marked IVD degeneration was found compared with sham-operated animals regardless of the procedure tested. A significant decrease in disc height on X-ray radiographs was first demonstrated. In addition, MRI disc signals were significantly reduced in both groups. Finally, a statistically significant increase in Boos' scoring was found in both laser and aspiration-induced IVD degeneration. Interestingly, IVD degeneration induced by laser treatment was more progressive compared with aspiration. Moreover, the histological results indicated that laser-induced disc degeneration was quite similar to that obtained during the natural aging process as observed in 30-month-old rabbits. Our study describes the consistency of this innovative experimentally-induced animal model of IVD degeneration. The radiological, MRI and histological data confirm its relevance. The histological examination indicates that IVD degeneration induced by laser treatment is comparable to the degenerative process observed during the onset of spontaneous IVD degeneration. This model could be a useful tool to help us validate biomaterial-assisted, cell-based, regenerative medicine strategies for the prevention and treatment of IVD degeneration.

In vivo experimental imaging of osteochondral defects and their healing using (99m)Tc-NTP 15-5 radiotracer

PURPOSE

A rabbit model of osteochondral defects (OD) and spontaneous healing was longitudinally followed over 12 weeks, by in vivo joint scintigraphy using (99m)Tc-NTP 15-5, and histology.

METHODS

We used two models, one with one OD (OD1 group) in the femoral condyle of one knee and the other with two ODs (OD2 group) in the femoral condyle of one knee, with the contralateral knees serving as the reference. A serial longitudinal imaging study was performed with the scintigraphic ratio (SR, operated knee uptake/contralateral knee uptake) determined at each time-point.

RESULTS

ODs were imaged as radioactive defects. The SR was decreased with respective to controls, with values of 0.73 ± 0.08 and 0.65 ± 0.07 in the OD1 and OD2 groups, respectively, at 4 weeks after surgery. Histology of both OD groups revealed the presence of repair tissue characterized by a small amount of sulphated glycosaminoglycans and collagen.

CONCLUSION

(99m)Tc-NTP 15-5 imaging provided quantitative criteria useful for in vivo evaluation of cartilage trauma and healing.

Pharmacological modulation of human mesenchymal stem cell chondrogenesis by a chemically oversulfated polysaccharide of marine origin: potential application to cartilage regenerative medicine

Mesenchymal stem cells (MSCs) are considered as an attractive source of cells for cartilage engineering due to their availability and capacity for expansion and multipotency. Differentiation of MSC into chondrocytes is crucial to successful cartilage regeneration and can be induced by various biological agents, including polysaccharides that participate in many biological processes through interactions with growth factors. Here, we hypothesize that growth factor-induced differentiation of MSC can be increased by chemically oversulfated marine polysaccharides. To test our hypothesis, human adipose tissue-derived MSCs (hATSCs) were cultured in pellets with transforming growth factor (TGF)-β1-supplemented chondrogenic medium containing either the polysaccharide GY785 DR or its oversulfated isoform GY785 DRS. Chondrogenesis was monitored by the measurement of pellet volume, quantification of DNA, collagens, glycosaminoglycans (GAGs), and immunohistological staining. Our data revealed an increase in pellet volume, total collagens, and GAG production with GY785 DRS and chondrogenic medium. The enhanced chondrogenic differentiation of hATSC was further demonstrated by the increased expression of several chondrogenic markers by real-time reverse transcription-polymerase chain reaction. In addition, surface plasmon resonance analyses revealed that TGF-β1 bound GY785 DRS with higher affinity compared to GY785 DR. In association with TGF-β1, GY785 DRS was found to upregulate the phosphorylation of extracellular signal-regulated kinase 1/2, indicating that oversulfated polysaccharide affects the mitogen activated protein kinase signaling activity. These results demonstrate the upregulation of TGF-β1-dependent stem cell chondrogenesis by a chemically oversulfated marine polysaccharide. This polysaccharide of marine origin is easily producible and therefore could be considered a promising additive to drive efficient and reliable MSC chondrogenesis for cartilage tissue engineering.

The Effect of Two- and Three-Dimensional Cell Culture on the Chondrogenic Potential of Human Adipose-Derived Mesenchymal Stem Cells after Subcutaneous Transplantation with an Injectable Hydrogel

Articular cartilage is an avascular tissue composed of chondrocytes, a unique cell type responsible for abundant matrix synthesis and maintenance. When damaged, it never heals spontaneously under physiological circumstances. Therefore, the delivery of mesenchymal stem cells using hydrogel has been considered for cartilage repair. This study aims at investigating the influence of in vitro chondrogenic differentiation of human adipose tissue-derived stem cells (hATSCs) on in vivo cartilage formation when associated with a cellulose-based self-setting hydrogel (Si-HPMC). hATSCs were characterized for their proliferation, surface marker expression, and multipotency. The in vitro chondrogenic potential of hATSCs cultured within Si-HPMC in control or chondrogenic medium was evaluated by measuring COL2A1, ACAN, SOX9, and COMP expression by real-time PCR. Alcian blue and type II collagen staining were also performed. To determine whether in vitro chondrogenically differentiated hATSCs may give rise to cartilage in vivo, cells differentiated as a monolayer or in pellets were finally associated with Si-HPMC and implanted subcutaneously into nude mice. Cartilage formation was assessed histologically by alcian blue and type II collagen staining. Our data demonstrate that hATSCs exhibited proliferation and self-renewal. hATSCs also expressed typical stem cell surface markers and were able to differentiate towards the adipogenic, osteogenic, and chondrogenic lineages. Real-time PCR and histological analysis indicated that Si-HPMC enabled chondrogenic differentiation of hATSCs in inductive medium, as demonstrated by increased expression of chondrogenic markers. In addition, histological analysis of implants showed that chondrogenically differentiated hATSCs (monolayers or pellets) have the ability to form cartilaginous tissue, as indicated by the presence of sulphated glycosaminoglycans and type II collagen. This study therefore suggests that an in vitro induction of hATSCs in 2D was sufficient to obtain cartilaginous tissue formation in vivo. Si-HPMC associated with autologous hATSCs could thus be a significant tool for regenerative medicine in the context of cartilage damage.

Characterization of the age-dependent intervertebral disc changes in rabbit by correlation between MRI, histology and gene expression

Background

The present study was conducted to address whether the intervertebral disc of rabbit could be considered (i) as a valuable model to provide new insights into the tissue and cellular changes of Nucleus pulposus aging and (ii) as an appropriate tool to investigate the efficacy of Nucleus pulposus cell-based biotherapies.

Methods

Lumbar intervertebral disc from rabbits with increasing ages (1, 6 and 30 month-old) were compared by MRI and histological observation using Pfirrmann's grading and Boos' scoring respectively. The expression of transcripts (COL2A1, AGC1, COL1A1, MMP13, BMP2, MGP and p21) in Nucleus pulposus cells were analysed by quantitative real-time PCR.

Results

MRI analysis indicated an early age-dependent increase in the Pfirrmann's grading. Histological Boos' scoring was also increased. The analysis of transcript expression levels showed that COL2A1 and AGC1 were down-regulated as a function of age. Conversely, COL1A1, MMP-13, BMP-2, MGP and p21 were significantly up-regulated in the Nucleus pulposus cells of aged rabbit intervertebral disc.

Conclusions

Our study describes the consistency of the rabbit as a model of intervertebral disc changes as a function of age by correlating tissue alteration with cellular modification measured.

In vivo bone augmentation in an osteoporotic environment using bisphosphonate-loaded calcium deficient apatite

Resorbable calcium phosphate (CaP) biomaterials have demonstrated considerable efficacy in bone reconstructive surgery. Furthermore, bisphosphonates (BPs) are well known anti-resorptive agents largely used in clinical treatments for osteoporosis. An injectable BP-combined CaP matrix has been developed in order to biologically reinforce osteoporotic bone by increasing the bone fraction and improving bone micro-architecture. Our previous in vitro studies have shown that CaP is effective for loading and releasing BPs at doses that can inhibit excessive bone resorption without affecting osteoblasts. In vivo studies in relevant animal models are necessary to explore the effect of our injectable BP-combined biomaterial on femur bone structure by performing three-dimensional microtomography analysis, histological studies and SEM observations. Firstly, in rat model, our BP-combined CaP matrix significantly improved the bone micro-architecture as compared to CaP alone. The implantation of the BP-loaded biomaterial within proximal femurs of osteoporotic ewes led to a significant increase in relative bone content and an improvement of its micro-architecture. These modifications were confirmed by histological and SEM observations, which revealed CaP granule resorption and new bone trabeculae formation. This approach could be considered in the future for preventing osteoporotic fractures that are preferentially localized in the proximal femur, vertebral bodies or wrist.

Muscle satellite cell heterogeneity: in vitro and in vivo evidences for populations that fuse differently

During development, muscle growth results from the proliferation of satellite cells (SC) and their fusion with fibers. Several studies revealed heterogeneity of SC population notably based on the proliferation rate. Here, we examined the SC characteristics of turkey skeletal muscles in terms of proliferation and more specifically fusion, to define if the ability of these cells to fuse may represent a distinct characteristic between them and could be directly associated with their proliferation properties. Freshly extracted SC were plated in clonal condition and their proliferation rate was assessed 11 days later. To investigate the SC fusion behavior, in vitro and in vivo approaches were developed. Highly and slowly proliferative SC were initially labeled with a nuclear beta-galactosidase (beta-Gal) activity and co-cultured with differentiated primary cultures. After 5 days, distribution of beta-Gal positive (beta-Gal+) nuclei was examined. Also, the two labeled SC types were transplanted into different muscles in autologous model. One week later, number of beta-Gal+ nuclei per fiber and diameter of fibers displaying beta-Gal+ nuclei were determined. In vitro, we showed that SC from turkey skeletal muscle are present as a heterogeneous population in terms of proliferation. Examination of their fusion properties in vitro as well as in vivo revealed that highly proliferative SC exclusively exhibited fusion with differentiated myotubes or myofibers, whereas slowly proliferative SC mainly fused together. Collectively, these data demonstrate for the first time that SC with different proliferation rate also intrinsically differ in their fusion potential, suggesting distinct roles for these sub-populations in muscle growth.