Extracellular matrix turnover and inflammation in chemically-induced TMJ arthritis mouse models.

The temporomandibular joint (TMJ) is a fibrocartilaginous tissue critical for chewing and speaking. In patients with temporomandibular disorders (TMDs), permanent tissue loss can occur. Recapitulating the complexity of TMDs in animal models is difficult, yet critical for the advent of new therapies. Synovial fluid from diseased human samples revealed elevated levels of tumor necrosis factor alpha (TNF-alpha). Here, we propose to recapitulate these findings in mice by subjecting murine TMJs with TNF-alpha or CFA (Complete Freund's Adjuvant) in mandibular condyle explant cultures and by local delivery in vivo using TMJ intra-articular injections. Both TNF-alpha and CFA delivery to whole mandibular explants and in vivo increased extracellular matrix deposition and increased cartilage thickness, while TNF-alpha treated explants had increased expression of inflammatory cytokines and degradative enzymes. Moreover, the application of TNF-alpha or CFA in both models reduced cell number. CFA delivery in vivo caused soft tissue inflammation, including pannus formation. Our work provides two methods of chemically induced TMJ inflammatory arthritis through a condyle explant model and intra-articular injection model that replicate findings seen in synovial fluid of human patients, which can be used for further studies delineating the mechanisms underlying TMJ pathology.

Exploiting endogenous fibrocartilage stem cells to regenerate cartilage and repair joint injury.

Tissue regeneration using stem cell-based transplantation faces many hurdles. Alternatively, therapeutically exploiting endogenous stem cells to regenerate injured or diseased tissue may circumvent these challenges. Here we show resident fibrocartilage stem cells (FCSCs) can be used to regenerate and repair cartilage. We identify FCSCs residing within the superficial zone niche in the temporomandibular joint (TMJ) condyle. A single FCSC spontaneously generates a cartilage anlage, remodels into bone and organizes a haematopoietic microenvironment. Wnt signals deplete the reservoir of FCSCs and cause cartilage degeneration. We also show that intra-articular treatment with the Wnt inhibitor sclerostin sustains the FCSC pool and regenerates cartilage in a TMJ injury model. We demonstrate the promise of exploiting resident FCSCs as a regenerative therapeutic strategy to substitute cell transplantation that could be beneficial for patients suffering from fibrocartilage injury and disease. These data prompt the examination of utilizing this strategy for other musculoskeletal tissues.

Periodontal Ligament and Alveolar Bone in Health and Adaptation: Tooth Movement.

The periodontal ligament (PDL) and alveolar bone are two critical tissues for understanding orthodontic tooth movement. The current literature is replete with descriptive studies of multiple cell types and their matrices in the PDL and alveolar bone, but is deficient with how stem/progenitor cells differentiate into PDL and alveolar bone cells. Can one type of orthodontic force with a specific magnitude and frequency activate osteoblasts, whereas another force type activates osteoclasts? This chapter will discuss the biology of not only mature cells and their matrices in the periodontal ligament and alveolar bone, but also stem/progenitor cells that differentiate into fibroblasts, osteoblasts and osteoclasts. Key advances in tooth movement rely on further understanding of osteoblast and fibroblast differentiation from mesenchymal stem/progenitor cells, and osteoclastogenesis from the hematopoietic/monocyte lineage.

Engineered nasal cartilage by cell homing: a model for augmentative and reconstructive rhinoplasty.

BACKGROUND: Current augmentative and reconstructive rhinoplasties use auto logous tissue grafts or synthetic bioinert materials to repair nasal trauma or attain an aesthetic shape. Autologous grafts are associated with donor-site trauma and morbidity. Synthetic materials are widely used but often yield an unnatural appearance and are prone to infection or dislocation. There is an acute clinical need for the generation of native tissues to serve as rhinoplasty grafts without the undesirable features that are associated with autologous grafts or current synthetic materials. METHODS: Bioactive scaffolds were developed that not only recruited cells in the nasal dorsum in vivo, but also induced chondrogenesis of the recruited cells. Bilayered scaffolds were fabricated with alginate-containing gelatin microspheres encapsulating cytokines atop a porous poly(lactic-co-glycolic acid) base. Microspheres were fabricated to contain recombinant human transforming growth factor-ß3 at doses of 200, 500, or 1000 ng, with phosphate-buffered saline-loaded microspheres used as a control. A rat model of augmentation rhinoplasty was created by implanting scaffolds atop the native nasal cartilage surface that was scored to induce cell migration. Tissue formation and chondrogenesis in the scaffolds were evaluated by image analysis and histologic staining with hematoxylin and eosin, toluidine blue, Verhoeff elastic-van Geison, and aggrecan immunohistochemistry. RESULTS: Sustained release of increasing doses of transforming growth factor-ß3 for up to the tested 10 weeks promoted orthotopic cartilage-like tissue formation in a dose-dependent manner. CONCLUSIONS: These findings represent the first attempt to engineer cartilage tissue by cell homing for rhinoplasty, and could potentially serve as an alternative material for augmentative and reconstructive rhinoplasty.

Postnatal epithelium and mesenchyme stem/progenitor cells in bioengineered amelogenesis and dentinogenesis.

Rodent incisors provide a classic model for studying epithelial-mesenchymal interactions in development. However, postnatal stem/progenitor cells in rodent incisors have not been exploited for tooth regeneration. Here, we characterized postnatal rat incisor epithelium and mesenchyme stem/progenitor cells and found that they formed enamel- and dentin-like tissues in vivo. Epithelium and mesenchyme cells were harvested separately from the apical region of postnatal 4-5 day rat incisors. Epithelial and mesenchymal phenotypes were confirmed by immunocytochemistry, CFU assay and/or multi-lineage differentiation. CK14+, Sox2+ and Lgr5+ epithelium stem cells from the cervical loop enhanced amelogenin and ameloblastin expression upon BMP4 or FGF3 stimulation, signifying their differentiation towards ameloblast-like cells, whereas mesenchyme stem/progenitor cells upon BMP4, BMP7 and Wnt3a treatment robustly expressed Dspp, a hallmark of odontoblastic differentiation. We then control-released microencapsulated BMP4, BMP7 and Wnt3a in transplants of epithelium and mesenchyme stem/progenitor cells in the renal capsule of athymic mice in vivo. Enamel and dentin-like tissues were generated in two integrated layers with specific expression of amelogenin and ameloblastin in the newly formed, de novo enamel-like tissue, and DSP in dentin-like tissue. These findings suggest that postnatal epithelium and mesenchyme stem/progenitor cells can be primed towards bioengineered tooth regeneration.

Dentin and dental pulp regeneration by the patient's endogenous cells.

The goal of regenerative endodontics is to restore the functions of the dental pulp-dentin complex. Two approaches are being applied toward dental pulp-dentin regeneration: cell transplantation and cell homing. The majority of previous approaches are based on cell transplantation by delivering ex vivo cultivated cells toward dental pulp or dentin regeneration. Many hurdles limit the clinical translation of cell transplantation such as the difficulty of acquiring and isolating viable cells, uncertainty of what cells or what fractions of cells to use, excessive cost of cell manipulation and transportation, and the risk of immune rejection, pathogen transmission, and tumorigenesis in associated with ex vivo cell manipulation. In contrast, cell homing relies on induced chemotaxis of endogenous cells and therefore circumvents many of the difficulties that are associated with cell transplantation. An array of proteins, peptides, and chemical compounds that are yet to be identified may orchestrate endogenous cells to regenerate dental pulp-dentin complex. Both cell transplantation and cell homing are scientifically valid approaches; however, cell homing offers a number of advantages that are compatible with the development of clinical therapies for dental pulp-dentin regeneration.

Musculoskeletal tissue engineering by endogenous stem/progenitor cells.

From its inception, tissue engineering has had three tenets: cells, biomaterial scaffolds and signaling molecules. Among the triad, cells are the center piece, because cells are the building blocks of tissues. For decades, cell therapies have focused on the procurement, manipulation and delivery of healthy cells for the treatment of diseases or trauma. Given the complexity and potential high cost of cell delivery, there is recent and surging interest to orchestrate endogenous cells for tissue regeneration. Biomaterial scaffolds are vital for many but not all, tissue-engineering applications and serve to accommodate or promote multiple cellular functions. Signaling molecules can be produced by transplanted cells or endogenous cells, or delivered specifically to regulate cell functions. This review highlights recent work in tissue engineering and cell therapies, with a focus on harnessing the capacity of endogenous cells as an alternative or adjunctive approach for tissue regeneration.

Identification of tendon stem/progenitor cells and the role of the extracellular matrix in their niche.

The repair of injured tendons remains a great challenge, largely owing to a lack of in-depth characterization of tendon cells and their precursors. We show that human and mouse tendons harbor a unique cell population, termed tendon stem/progenitor cells (TSPCs), that has universal stem cell characteristics such as clonogenicity, multipotency and self-renewal capacity. The isolated TSPCs could regenerate tendon-like tissues after extended expansion in vitro and transplantation in vivo. Moreover, we show that TSPCs reside within a unique niche predominantly comprised of an extracellular matrix, and we identify biglycan (Bgn) and fibromodulin (Fmod) as two critical components that organize this niche. Depletion of Bgn and Fmod affects the differentiation of TSPCs by modulating bone morphogenetic protein signaling and impairs tendon formation in vivo. Our results, while offering new insights into the biology of tendon cells, may assist in future strategies to treat tendon diseases.

Regulation, regulatory activities, and function of biglycan.

Biglycan is a member of the small leucine repeat proteoglycan family (SLRP). The biglycan gene is located on the X chromosome. Based on the amino acid sequence, the protein core of biglycan can be divided into six distinct domains: (1) a signal sequence, (2) a propeptide region, (3) a N-terminal glycosaminoglycan attachment region, (4) a cysteine loop, followed by (5) a leucine- rich repeat region domain (that makes up over 66% of the core protein), and (6) a final cysteine loop. Biglycan has been found in almost every organ within our body, but it is not uniformly distributed within an organ. Biglycan has been shown to be expressed on the cell surface, pericellularly, and sometimes within the extracellular matrices of a range of specialized cell types within the organ. Its expression pattern has been shown to be altered by growth factors and certain pathologic conditions. The regulation of biglycan expression occurs by both transcriptional and nontranscriptional mechanisms. The currently proposed biglycan functions appear to be dependent on the particular microenvironment and on the organ in question. In this review, we will focus on gene and protein structure, localization, expression, regulation, and function.