Paracrine and autocrine signals promoting full chondrogenic differentiation of a mesoblastic cell line

Highly porous novel chondro-instructive bioactive glass scaffolds tailored for cartilage tissue engineering

Cartilage injuries remain challenging since the regenerative capacity of cartilage is extremely low. The aim was to design a novel type of bioactive glass (BG) scaffold with suitable topology that allows the formation of cartilage-specific extracellular matrix (ECM) after colonization with chondrogenic cells for cartilage repair. Highly porous scaffolds with interconnecting pores consisting of 100 % BG were manufactured using a melting, milling, sintering and leaching technique. Scaffolds were colonized with porcine articular chondrocytes (pAC) and undifferentiated human mesenchymal stromal cells (hMSC) for up to 35 days. Scaffolds displayed high cytocompatibility with no major pH shift. Scanning electron microscopy revealed the intimate pAC-scaffold interaction with typical cell morphology. After 14 days MSCs formed cell clusters but still expressed cartilage markers. Both cell types showed aggrecan, SOX9 gene and protein expression, cartilage proteoglycan and sulfated glycosaminoglycan synthesis for the whole culture time. Despite type II collagen gene expression could not anymore be detected at day 35, protein synthesis was visualized for both cell types during the whole culturing period, increasing in pAC and declining after day 14 in hMSC cultures. The novel BG scaffold was stable, cytocompatible and cartilage-specific protein synthesis indicated maintenance of pAC's differentiated phenotype and chondro-instructive effects on hMSCs.

Bone health in glucocorticoid-treated childhood acute lymphoblastic leukemia

Glucocorticoids (GCs) are widely used in the treatment of childhood acute lymphoblastic leukemia (ALL), but their long-term use is also associated with bone-related morbidities. Among others, growth deficit, decreased bone mineral density (BMD) and increased fracture rate are well-documented and severely impact quality of life. Unfortunately, no efficient treatment for the management of bone health impairment in patients and survivors is currently available. The overall goal of this review is to discuss the existing data on how GCs impair bone health in pediatric ALL and attempts made to minimize these side effects.

Differences in the Inflammatory Response of White Adipose Tissue and Adipose-Derived Stem Cells

The application of liposuctioned white adipose tissue (L-WAT) and adipose-derived stem cells (ADSCs) as a novel immunomodulatory treatment option is the currently subject of various clinical trials. Because it is crucial to understand the underlying therapeutic mechanisms, the latest studies focused on the immunomodulatory functions of L-WAT or ADSCs. However, studies that examine the specific transcriptional adaptation of these treatment options to an extrinsic inflammatory stimulus in an unbiased manner are scarce. The aim of this study was to compare the gene expression profile of L-WAT and ADSCs, when subjected to tumor necrosis factor alpha (TNFα), and to identify key factors that might be therapeutically relevant when using L-WAT or ADSCs as an immuno-modulator. Fat tissue was harvested by liposuction from five human donors. ADSCs were isolated from the same donors and shortly subjected to expansion culture. L-WAT and ADSCs were treated with human recombinant TNFα, to trigger a strong inflammatory response. Subsequently, an mRNA deep nextgeneration sequencing was performed to evaluate the different inflammatory responses of L-WAT and ADSCs. We found significant gene expression changes in both experimental groups after TNFα incubation. However, ADSCs showed a more homogenous gene expression profile by predominantly expressing genes involved in immunomodulatory processes such as CCL19, CCL5, TNFSF15 and IL1b when compared to L-WAT, which reacted rather heterogeneously. As RNA sequencing between L-WAT and ADSCS treated with TNFα revealed that L-WAT responded very heterogeneously to TNFα treatment, we therefore conclude that ADSCs are more reliable and predictable when used therapeutically. Our study furthermore yields insight into potential biological processes regarding immune system response, inflammatory response, and cell activation. Our results can help to better understand the different immunomodulatory effects of L-WAT and ADSCs.

Activated platelet-rich plasma improves cartilage regeneration using adipose stem cells encapsulated in a 3D alginate scaffold

In the current study, the effect of superimposing platelet-rich plasma (PRP) on different culture mediums in a three-dimensional alginate scaffold encapsulated with adipose-derived mesenchymal stem cells for cartilage tissue repair is reported. The three-dimensional alginate scaffolds with co-administration of PRP and/or chondrogenic supplements had a significant effect on the differentiation of adipose mesenchymal stem cells into mature cartilage, as assessed by an evaluation of the expression of cartilage-related markers of Sox9, collagen II, aggrecan and collagen, and glycosaminoglycan assays. For in vivo studies, following induction of osteochondral lesion in a rabbit model, a high degree of tissue regeneration in the alginate plus cell group (treated with PRP plus chondrogenic medium) compared with other groups of cell-free alginate and untreated groups (control) were observed. After 8 weeks, in the alginate plus cell group, functional chondrocytes were observed, which produced immature matrix, and by 16 weeks, the matrix and hyaline-like cartilage became completely homogeneous and integrated with the natural surrounding cartilage in the defect site. Similar effect was also observed in the subchondral bone. The cell-free scaffolds formed fibrocartilage tissue, and the untreated group did not form a continuous cartilage over the defect by 16 weeks.

The Physiology of Childhood Growth: Hormonal Regulation

The growth patterns of a child changes from uterine life until the end of puberty. Height velocity is highest in utero and declines after birth until puberty when it rises again. Important hormonal regulators of childhood growth are growth hormone, insulin-like growth factor 1, sex steroids, and thyroid hormone. This review gives an overview of these hormonal regulators of growth and their interplay with nutrition and other key players such as inflammatory cytokines.

Recent research on the growth plate: Impact of inflammatory cytokines on longitudinal bone growth

Children with inflammatory diseases usually display abnormal growth patterns as well as delayed puberty. This is a result of several factors related to the disease itself, such as malnutrition, hypercortisolism, and elevated levels of pro-inflammatory cytokines. These factors in combination with glucocorticoid treatment contribute to growth retardation during chronic inflammation by systemically affecting the major regulator of growth, the GH/IGF1 axis. However, recent studies have also shown evidence of a direct effect of these factors at the growth plate level. In conditions of chronic inflammation, pro-inflammatory cytokines are upregulated and released into the circulation. The most abundant of these, tumor necrosis factor α, interleukin 1β (IL1β), and IL6, are all known to directly act on growth plate cartilage to induce apoptosis and thereby suppress bone growth. Both clinical and experimental studies have shown that growth retardation can partly be rescued when these cytokines are blocked. Therefore, therapy modulating the local actions of these cytokines may be effective for preventing growth failure in patients with chronic inflammatory disorders. In this review, we report the current knowledge of inflammatory cytokines and their role in regulating bone growth.

Preparation and evaluation of the electrospun chitosan/PEO fibers for potential applications in cartilage tissue engineering

Fibrous materials have morphological similarities to natural cartilage extracellular matrix and have been considered as candidate for bone tissue engineering scaffolds. In this study, we have evaluated a novel electrospun chitosan mat composed of oriented sub-micron fibers for its tensile property and biocompatibility with chondrocytes (cell attachment, proliferation and viability). Scanning electronic microscope images showed the fibers in the electrospun chitosan mats were indeed aligned and there was a slight cross-linking between the parent fibers. The electrospun mats have significantly higher elastic modulus (2.25 MPa) than the cast films (1.19 MPa). Viability of cells on the electrospun mat was 69% of the cells on tissue-culture polystyrene (TCP control) after three days in culture, which was slightly higher than that on the cast films (63% of the TCP control). Cells on the electrospun mat grew slowly the first week but the growth rate increased after that. By day 10, cell number on the electrospun mat was almost 82% that of TCP control, which was higher than that of cast films (56% of TCP). The electrospun chitosan mats have a higher Young's modulus (P < 0.01) than cast films and provide good chondrocyte biocompatibility. The electrospun chitosan mats, thus, have the potential to be further processed into three-dimensional scaffolds for cartilage tissue repair.

Osteoblast differentiationin vitro andin vivo promoted by Osterix

C3H10T1/2/Osx, a stably transfected cell line with Osterix (Osx), was produced and chondrocytic and osteoblastic differentiation were studied in vitro. Osx promoted osteoblastic lineage that was dexamethasone dependent. Furthermore, in vivo, Osx induced ectopic mineralization in a heterotopic mouse muscle model. Skeletogenesis involves a cascade of molecular activities sequentially performed by osteoblasts and chondroblasts. A transcriptional factor gene Osx appears to influence cell disposition toward the chondrocytic or osteoblastic phenotype and therefore may be an important signaling cue for bone formation. Understanding the molecular conditions involved with Osx promoted osteoblast differentiation will facilitate therapeutic applications of Osx. Consequently, the objective of this study was to investigate chondrocytic and osteoblastic phenotype differentiation using an Osx plasmid DNA exploiting both in vitro and in vivo methodologies. In vitro, a stably transfected C3H10T1/2/Osx cell line was established and promotion of either an osteoblast or chondroblast phenotype was performed by selectively introducing dexamethasone (dex) and assaying mRNA content and phenotype markers. In vivo, a mouse muscle model was used to determine heterotopic ossification using designated Osx plasmid DNA doses incorporated in a (50:50 Poly (D,L-lactide-co-glycolide) (i.e., PLGA) 3D scaffold. Histological assessment was used to determine implant responses. Quantitative real-time polymerase chain reaction (q-RT-PCR) showed a significant increase in mRNA expression of osteocalcin (Ocn), Runx2, osteonectin (On) and osteopontin (Op) (p < 0.05) in the C3H10T1/2/Osx cells compared to the empty vector transfected cell control. At day 21, mineralization was demonstrated in the cultures of C3H10T1/2/Osx exposed to dex, but neither in cultures lacking dex nor controls. In the absence of dex, C3H10T1/2/Osx cells revealed a significantly higher expression of Sox9 and Aggrecan (Agc). In vivo, 80 microg of Osx plasmid DNA induced heterotopic mineralization 4 weeks following implantation in a mouse muscle model and the effect was dependent on the Osx plasmid DNA dose delivered in the PLGA scaffold. Using a non-committed cell line (C3H10T1/2), cell differentiation to an osteoblast phenotype appears to be dependent upon an interaction between intracellular events initiated by the transcriptional factor Osx and the presence of dex. The in vivo findings suggest Osx may promote osteoblast differentiationand mineralization at a heterotopic site.

Articular chondrocyte culturing for cell-based cartilage repair: needs and perspectives

Articular cartilage displays a limited capacity of self-regeneration after injury. Thus, the biology of this tissue and its cellular components - the chondrocytes - has become the focus of several investigations, driven by tissue engineering and the basic and clinical research fields, aiming to ameliorate the present clinical approaches to cartilage repair. In this work, we present a brief recapitulation of the events that lead to cartilage development during the skeletal embryonal growth. The intrinsic phenotypic plasticity of the mesenchymal precursors and the adult chondrocytes is evaluated, dependent on the cell source, its physiopathological state, and as a function of the donor's age. The phenotypic changes induced by the basic culturing techniques are also taken into account, thus highlighting the phenotypic plasticity of the chondrocyte as the main property which could couple the differentiation process to the repair process. Chondrocyte proliferation and the contemporary maintenance of the chondrogenic differentiation potential are regarded as the two primary goals to be achieved in order to fulfill the quantitative needs of the clinical applications and the qualitative requirements of a properly repaired tissue. In this light, the effects of several growth factors and medium supplements are investigated. Finally, the latest improvements in culturing conditions and their possible clinical applications are presented as well.

Dynamic compression regulates the expression and synthesis of chondrocyte-specific matrix molecules in bone marrow stromal cells

The overall objective of the present study was to investigate the mechanotransduction of bovine bone marrow stromal cells (BMSCs) through the interactions between transforming growth factor beta1 (TGF-beta1), dexamethasone, and dynamic compressive loading. Overall, the addition of TGF-beta1 increased cell viability, extracellular matrix (ECM) gene expression, matrix synthesis, and sulfated glycosaminoglycan content over basal construct medium. The addition of dexamethasone further enhanced extracellular matrix gene expression and protein synthesis. There was little stimulation of ECM gene expression or matrix synthesis in any medium group by mechanical loading introduced on day 8. In contrast, there was significant stimulation of ECM gene expression and matrix synthesis in chondrogenic media by dynamic loading introduced on day 16. The level of stimulation was also dependent on the medium supplements, with the samples treated with basal medium being the least responsive and the samples treated with TGF-beta1 and dexamethasone being the most responsive at day 16. Both collagen I and collagen II gene expressions were more responsive to dynamic loading than aggrecan gene expression. Dynamic compression upregulated Smad2/3 phosphorylation in samples treated with basal and TGF-beta1 media. These findings suggest that interactions between mechanical stimuli and TGF-beta signaling may be an important mechanotransduction pathway for BMSCs, and they indicate that mechanosensitivity may vary during the process of chondrogenesis.

Basic science and treatment options for articular cartilage injuries

Articular cartilage injuries can produce significant musculoskeletal morbidity for both young and active aging patient populations. The complex and highly specialized composition of normal hyaline cartilage makes treatment of focal chondral injuries a formidable challenge for the basic scientist, surgeon, and physical therapist. The current array of surgical treatment options offers palliative, reparative, and restorative treatment strategies. Palliative options include simple arthroscopic debridement. Reparative strategies utilize marrow stimulation techniques to induce formation of fibrocartilage within the chondral defect. Restorative tactics attempt to replace damaged cartilage with hyaline or hyaline-like tissue using osteochondral or chondrocyte transplantation. Furthermore, while treatment success is obviously dependent on good surgical selection and technique, the importance of sound, compliant postoperative rehabilitation cannot be understated. The purpose of this article is to review the basic science of articular cartilage, current treatment options available, and outline the clinical decision making involved when using these procedures by presenting the algorithm used at our institution for treating focal cartilage lesions.

Early in vivo and in vitro effects of amelogenin gene splice products on pulp cells

Recombinant amelogenin gene splice products A+4 and A-4, implanted in the pulp, induce the recruitment, proliferation, and differentiation of reparative cells. Our aim was to investigate the precocious events occurring in the pulp 1 d and 3 d after implantation of agarose beads alone or loaded with A+4 or A-4. Proliferation and cell recruitment towards an odonto/osteogenic phenotype were visualized by detection of the proliferation cell nuclear antigen (PCNA) and RP59. After implantation of beads alone or loaded with A+4, at day 3, pulp cells were moderately immunopositive for osteopontin (OP), whereas labeling was strongly positive upon treatment with A-4. Dentin sialoprotein (DSP) labeling was not detectable. Parallel in vitro studies were carried out on odontoblastic and mesenchymal progenitor cells in order to evaluate the effect of the amelogenin peptides on the expression of a series of marker genes involved in the odontoblastic/osteogenic/chondrogenic differentiation pathways. Altogether, our results suggest that the 'signaling' effects of the amelogenin peptides A+4 and A-4 may differ according to the type of target cells, their stage of differentiation, the time of treatment, and the type of amelogenin peptide (A+4 or A-4).

Optimized chondrogenesis of ATCD5 cells through sequential regulation of oxygen conditions

The objective of this study was to determine the optimal oxygen conditions for chondrogenesis of ATDC5 mouse embryonic stem cells. Chondrogenesis was induced by addition of insulin and the cells were then cultured at different oxygen concentrations ranging from 1 to21%. At 2- to 3-day intervals, chondrocyte-specific extracellular matrix (ECM) production was monitored. Furthermore, the transcription of collagen II, an early-phase marker, and collagen X, a marker of hypertrophic conversion, was followed by real-time RT-PCR. Low oxygen concentrations between 1 and 9% inhibited chondrogenic conversion, as evidenced by reduced glycosaminoglycan deposition in the ECM in a manner proportional to the degree of hypoxia. Cells cultured at oxygen concentrations of 12 and 15% underwent a faster and higher degree of early-phase chondrogenesis when compared to control cells cultured at ambient air (21% O2). For the hypertrophic conversion of the ATDC5 cells, all degrees of hypoxia inhibited collagen X expression in a dose-dependent manner. Short-term culturing of the ATDC5 cells for 6 to 8 days at 12% oxygen with subsequent culturing at 21% for the remainder of the experiment resulted in maximal production of major ECM components, including collagen II and glycosaminoglycans. It is thus possible to modify in vitro chondrogenesis through modulation of the gas-phase composition.

Model-based analysis and design of a microchannel reactor for tissue engineering

Recently developed perfusion micro-bioreactors offer the promise of more physiologic in vitro systems for tissue engineering. Successful application of such bioreactors will require a method to characterize the bioreactor environment required to elicit desired cell function. We present a mathematical model to describe nutrient/growth factor transport and cell growth inside a microchannel bioreactor. Using the model, we first show that the nature of spatial gradients in nutrient concentration can be controlled by both design and operating conditions and are a strong function of cell uptake rates. Next, we extend our model to investigate the spatial distributions of cell-secreted soluble autocrine/paracrine growth factors in the bioreactor. We show that the convective transport associated with the continuous cell culture and possible media recirculation can significantly alter the concentration distribution of the soluble signaling molecules as compared to static culture experiments and hence needs special attention when adapting static culture protocols for the bioreactor. Further, using an unsteady state model, we find that spatial gradients in nutrient/growth factor concentrations can bring about spatial variations in the cell density distribution inside the bioreactor, which can result in lowered working volume of the bioreactor. Finally, we show that the nutrient and spatial limitations can dramatically affect the composition of a co-cultured cell population. Our results are significant for the development, design, and optimization of novel micro-channel systems for tissue engineering.

Directing stem cell differentiation into the chondrogenic lineage in vitro

A major area in regenerative medicine is the application of stem cells in cartilage tissue engineering and reconstructive surgery. This requires well-defined and efficient protocols for directing the differentiation of stem cells into the chondrogenic lineage, followed by their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages upon transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying chondrogenesis and cartilaginous tissue biology. The development of pharmacokinetic and cytotoxicity/genotoxicity screening tests for cartilage-related biomaterials and drugs could also utilize protocols developed for the chondrogenic differentiation of stem cells. Hence, this review critically examines the various strategies that could be used to direct the differentiation of stem cells into the chondrogenic lineage in vitro.

Cartilage restoration, part 1: basic science, historical perspective, patient evaluation, and treatment options

Surgical procedures designed to treat focal chondral lesions are evolving and are supported by basic science principles of cartilage physiology and known responses to injury. Selecting the proper treatment algorithm for a particular patient depends on careful patient evaluation, including the recognition of comorbidities such as ligamentous instability, deficient menisci, or malalignment of the mechanical limb axis or extensor mechanism. These comorbidities may need to be treated in conjunction with symptomatic chondral injuries to provide a mutually beneficial effect. A central tenet of cartilage restoration is to leave future treatment options available should they become necessary. In this article (part 1), the authors review the basic science of chondral injuries, the historical perspective of the available surgical options, and present guidelines for patient evaluation and treatment.

New cellular models for tracking the odontoblast phenotype

Odontoblasts and osteoblasts differ functionally and histologically. Because of their close relationship, mesenchymal cells derived from teeth and bone are difficult to distinguish ex vivo. Indeed, the main non-collagenous components of the odontoblastic extracellular matrix, dentin sialoprotein (DSP) or dentin matrix protein 1 (DMP1), have also been detected in osteoblasts. The need to develop cellular models of odontoblast differentiation and to identify markers specific for the odontoblast lineage, has led us to establish clonal cell lines from tooth germs of day 18 mouse embryos transgenic for an adenovirus-SV40 recombinant plasmid. In this study, we analyzed the phenotypes of three independent clones by RT-PCR and Western blot. These clones synthesised DSP, DMP1 and other extracellular matrix proteins typical of the odontoblast and are therefore likely to be derived from the pulp. Transcripts encoding a set of homeobox proteins involved in craniofacial development, such as Pax9, Msx1, Cbfa1, Dlx2 and 5 were also expressed albeit at a different level. These features of the pulpal clones are shared by the C1 mesodermal cells that are capable of differentiating along osteogenic, chondrogenic or adipogenic lineages In contrast, transcripts for two LIM-domain homeobox family genes (Lhx6 and Lhx7) were only detected in the dental clones. Since these genes are preferentially expressed in the mesenchyme of the developing tooth, this suggests that our transgenic-derived cell lines retain intrinsic properties of odontoblastic cells. They may help to characterise genes specifying the odontoblast phenotype and the signalling pathways underlying odontoblast differentiation.