Stimulatory effects of distinct members of the bone morphogenetic protein family on ligament fibroblasts

Fibroblastic differentiation of mesenchymal stem/stromal cells (MSCs) is enhanced by hypoxia in 3D cultures treated with bone morphogenetic protein 6 (BMP6) and growth and differentiation factor 5 (GDF5)

INTRODUCTION

Culture conditions and differentiation cocktails may facilitate cell maturation and extracellular matrix (ECM) secretion and support the production of engineered fibroblastic tissues with applications in ligament regeneration. The objective of this study is to investigate the potential of two connective tissue-related ligands (i.e., BMP6 and GDF5) to mediate collagenous ECM synthesis and tissue maturation in vitro under normoxic and hypoxic conditions based on the hypothesis that BMP6 and GDF5 are components of normal paracrine signalling events that support connective tissue homeostasis.

METHODS

Human adipose-derived MSCs were seeded on 3D-printed medical-grade polycaprolactone (PCL) scaffolds using a bioreactor and incubated in media containing GDF5 and/or BMP6 for 21 days in either normoxic (5% oxygen) or hypoxic (2% oxygen) conditions. Constructs were harvested on Day 3 and 21 for cell viability analysis by live/dead staining, structural analysis by scanning electron microscopy, mRNA levels by RTqPCR analysis, and in situ deposition of proteins by immunofluorescence microscopy.

RESULTS

Pro-fibroblastic gene expression is enhanced by hypoxic culture conditions compared to normoxic conditions. Hypoxia renders cells more responsive to treatment with BMP6 as reflected by increased expression of ECM mRNA levels on Day 3 with sustained expression until Day 21. GDF5 was not particularly effective either in the absence or presence of BMP6.

CONCLUSIONS

Fibroblastic differentiation of MSCs is selectively enhanced by BMP6 and not GDF5. Environmental factors (i.e., hypoxia) also influenced the responsiveness of cells to this morphogen.

Identification of a Remodeled Neo-tendon After Arthroscopic Latarjet Procedure

PURPOSE

To macroscopically, histologically, and radiologically describe a time-dependent remodeling process of a neo-tendon or -ligament in the shoulder after the arthroscopic Latarjet procedure.

METHODS

During follow-up surgery after the arthroscopic Latarjet procedure, 17 shoulders in 16 patients were evaluated for a remodeled tendon-like structure. The mean overall follow-up period was 27.4 months. The mean time between the arthroscopic Latarjet procedure and revision was 11.6 months. All shoulders were evaluated with magnetic resonance imaging, and seven histologic specimens were obtained during revision surgery.

RESULTS

A distinct, oriented strand of tissue was found in 16 of 17 shoulders on revision surgery. Postoperative magnetic resonance imaging analyses showed a signal-free, longitudinal tendon-like structure originating at the tip of the acromion, traversing the space of the former subcoracoid bursa to attach in the course of the transposed conjoint tendon or the proximal short head of the biceps. Histologic analysis of seven specimens showed a characteristic timeline of remodeling.

CONCLUSIONS

A tendon- or ligament-like structure is remodeled between the anterior bottom tip of the acromion and the transposed coracoid process in a time-dependent manner after the arthroscopic Latarjet procedure.

LEVEL OF EVIDENCE

Level IV, therapeutic case series.

Localization of bone morphogenetic protein 13 in human intervertebral disc and its molecular and functional effects in vitro in 3D culture

Our laboratory has demonstrated that bone morphogenetic protein 13 prevented the effects of annular injury in an ovine model, maintaining intervertebral disc height, cell numbers and increasing extracellular matrix production compared to degenerated controls. The present study sought to examine the molecular effects of bone morphogenetic protein 13 on human degenerated disc cells and localize its expression in both human degenerate and scoliotic disc tissue. Effect of bone morphogenetic protein 13 on human derived nucleus pulposus, annulus fibrosus and endplate cells cultured in alginate beads was evaluated by changes in proteoglycan and collagen content. Migratory potential of disc cells towards bone morphogenetic protein 13 was also examined. Bone morphogenetic protein 13 induced significant proteoglycan accumulation in nucleus (18%), annulus (21%) and endplate (23%) cells cultured in alginate beads (p<0.05) compared to controls. Further bone morphogenetic protein 13 increased collagen I and II protein expression in nucleus and endplate cells. Nucleus cells displayed a significant chemotactic response towards bone morphogenetic protein 13. The endogenous expression of bone morphogenetic protein 13 in degenerate disc tissue was not different to scoliotic disc. Bone morphogenetic protein 13 has the potential to enhance extracellular matrix accumulation and induce cell migration in certain disc cells.

In vitro characterization of self-assembled anterior cruciate ligament cell spheroids for ligament tissue engineering

Tissue engineering of an anterior cruciate ligament (ACL) implant with functional enthesis requires site-directed seeding of different cell types on the same scaffold. Therefore, we studied the suitability of self-assembled three-dimensional spheroids generated by lapine ACL ligament fibroblasts for directed scaffold colonization. The spheroids were characterized in vitro during 14 days in static and 7 days in dynamic culture. Size maintenance of self-assembled spheroids, the vitality, the morphology and the expression pattern of the cells were monitored. Additionally, we analyzed the total sulfated glycosaminoglycan, collagen contents and the expression of the ligament components type I collagen, decorin and tenascin C on protein and for COL1A1, DCN and TNMD on gene level in the spheroids. Subsequently, the cell colonization of polylactide-co-caprolactone [P(LA-CL)] and polydioxanone (PDS) polymer scaffolds was assessed in response to a directed, spheroid-based seeding technique. ACL cells were able to self-assemble spheroids and survive over 14 days. The spheroids decreased in size but not in cellularity depending on the culture time and maintained or even increased their differentiation state. The area of P[LA-CL] scaffolds, colonized after 14 days by the cells of one spheroid, was in average 4.57 ± 2.3 mm(2). Scaffolds consisting of the polymer P[LA-CL] were more suitable for colonization by spheroids than PDS embroideries. We conclude that ACL cell spheroids are suitable as site-directed seeding strategy for scaffolds in ACL tissue engineering approaches and recommend the use of freshly assembled spheroids for scaffold colonization, due to their balanced proliferation and differentiation.

Repairing cartilage defects with bone marrow mesenchymal stem cells induced by CDMP and TGF-β1

The aim of this study was to explore the ability for chondrogenic differentiation of bone marrow mesenchymal stems cells (BMSCs) induced by either cartilage-derived morphogenetic protein 1 (CDMP-1) alone or in the presence of transforming growth factor-β1 (TGF-β1) in vivo and in vitro. BMSCs and poly-lactic acid/glycolic acid copolymer (PLGA) scaffold were analyzed for chondrogenic capacity induced by CDMP-1 and TGF-β1 in vivo and in vitro. Chondrogenic differentiation of BMSCs into chondrocytes using a high density pellet culture system was tested, whether they could be maintained in 3-D PLGA scaffold instead of pellet culture remains to be explored. Under the culture of high-density cell suspension and PLGA frame, BMSCs were observed the ability to repair cartilage defects by either CDMP-1 alone or in the presence of TGF-β1 in vitro. Then the cell-scaffold complex was implanted into animals for 4 and 8 weeks for in vivo test. The content of collagen type II and proteoglycan appeared to increase over time in the constructs of the induced groups (CDMP in the presence of TGF-β1), CDMP group and TGF group. However, the construct of the control group did not express them during the whole culture time. At 4 and 8 weeks, the collagen type II expression of the induced group was higher than the sum of TGF group and CDMP group by SSPS17.0 analysis. BMSCs and PLGA complex induced by CDMP-1 and TGF- β1 can repair cartilage defects more effectively than that induced by CDMP-1 or TGF-β1 only.

The BMP ligand Gdf6 prevents differentiation of coronal suture mesenchyme in early cranial development

Growth Differentiation Factor-6 (Gdf6) is a member of the Bone Morphogenetic Protein (BMP) family of secreted signaling molecules. Previous studies have shown that Gdf6 plays a role in formation of a diverse subset of skeletal joints. In mice, loss of Gdf6 results in fusion of the coronal suture, the intramembranous joint that separates the frontal and parietal bones. Although the role of GDFs in the development of cartilaginous limb joints has been studied, limb joints are developmentally quite distinct from cranial sutures and how Gdf6 controls suture formation has remained unclear. In this study we show that coronal suture fusion in the Gdf6-/- mouse is due to accelerated differentiation of suture mesenchyme, prior to the onset of calvarial ossification. Gdf6 is expressed in the mouse frontal bone primordia from embryonic day (E) 10.5 through 12.5. In the Gdf6-/- embryo, the coronal suture fuses prematurely and concurrently with the initiation of osteogenesis in the cranial bones. Alkaline phosphatase (ALP) activity and Runx2 expression assays both showed that the suture width is reduced in Gdf6+/- embryos and is completely absent in Gdf6-/- embryos by E12.5. ALP activity is also increased in the suture mesenchyme of Gdf6+/- embryos compared to wild-type. This suggests Gdf6 delays differentiation of the mesenchyme occupying the suture, prior to the onset of ossification. Therefore, although BMPs are known to promote bone formation, Gdf6 plays an inhibitory role to prevent the osteogenic differentiation of the coronal suture mesenchyme.

Adenoviral-mediated gene transfer of human bone morphogenetic protein-13 does not improve rotator cuff healing in a rat model

BACKGROUND

Rotator cuff tendon-to-bone healing occurs by formation of a scar tissue interface after repair, which makes it prone to failure. Bone morphogenetic protein-13 (BMP-13) has been implicated in tendon and cartilage repair, and thus may augment rotator cuff repairs. The purpose of this study was to determine if the application of mesenchymal stem cells (MSCs) transduced with BMP-13 could improve regeneration of the tendon-bone insertion site in a rat rotator cuff repair model.

HYPOTHESIS

Mesenchymal stem cells genetically modified to overexpress BMP-13 will improve rotator cuff healing based on histologic and biomechanical outcomes.

STUDY DESIGN

Controlled laboratory study.

METHODS

Sixty Lewis rats underwent unilateral detachment and repair of the supraspinatus tendon and 10 rats were used for MSC harvest. Animals were randomized into 2 groups (30 animals/group). The experimental group received 10⁶ MSCs transduced with adenoviral-mediated gene transfer of human BMP-13 (Ad-BMP-13). The second group received untransduced MSCs. Fifteen animals in each group were sacrificed at 2 and 4 weeks. At each time point, 12 animals were allocated for biomechanical testing, and 3 for histomorphometric analysis.

RESULTS

There were no differences in the amount of new cartilage formation or collagen fiber organization between groups at either time point. There were also no differences in the biomechanical strength of the repairs, the cross-sectional area, peak stress at failure, or stiffness.

CONCLUSION

Application of MSCs genetically modified to overexpress BMP-13 did not improve healing in a rat model of rotator cuff repair.

CLINICAL RELEVANCE

Further studies are needed to evaluate various growth factors and combinations of growth factors to determine the optimal factor for the biologic augmentation of rotator cuff repairs.

Sexual dimorphism in the effect of GDF-6 deficiency on murine tendon

Three members of the growth/differentiation factor (GDF) subfamily of bone morphogenetic proteins (BMPs), GDFs-5, -6, and -7, have demonstrated the potential to augment tendon and ligament repair. To gain further insight into the in vivo role of these molecules, previous studies have characterized intact and healing tendons in mice with functional null mutations in GDF-5 and -7. The primary goal of the present study was to perform a detailed characterization of the intact tendon phenotype in 4- and 16-week-old male and female GDF6-/- mice and their +/+ littermates. The results demonstrate that GDF6 deficiency was associated with an altered tendon phenotype that persisted into adulthood. Among males, GDF6-/- tail tendon fascicles had significantly less collagen and glycosaminoglycan content, and these compositional differences were associated with compromised material properties. The effect of GDF6 deficiency on tendon was sexually dimorphic, however, for among female GDF6-/- mice, neither differences in tendon composition nor in material properties were detected. The tendon phenotype that was observed in males appeared to be stronger in the tail site than in the Achilles tendon site, where some compositional differences were present, but no material property differences were detected. These data support existing in vitro studies, which suggest a potential role for BMP-13 (the human homologue to GDF-6) in tendon matrix modeling and/or remodeling.

BMP13 prevents the effects of annular injury in an ovine model

Chronic back pain is a global health problem affecting millions of people worldwide and carries significant economic and social morbidities. Intervertebral disc damage and degeneration is a major cause of back pain, characterised by histological and biochemical changes that have been well documented in animal models. Recently there has been intense interest in early intervention in disc degeneration using growth factors or stem cell transplantation, to replenish the diseased tissues. Bone Morphogenetic Proteins (BMPs) have been approved for clinical use in augmenting spinal fusions, and may represent candidate molecules for intervertebral disc regeneration.

BMP13 has an important role in embryonic development and recent genetic evidence shows a role in the development of the human spine. This study explores the effect of BMP13 on a damaged intervertebral disc in an ovine model of discal degeneration. We found that, when injected at the time of injury, BMP13 reversed or arrested histological changes that occurred in the control discs such as loss of extracellular matrix proteins. In addition, BMP13 injected discs retained greater hydration after 4months, and possessed more cells in the NP.

Taken together, BMP13 may be a potent clinical therapeutic agent when used early in the degeneration cascade to promote healthy disc tissue.

BMP-13 emerges as a potential inhibitor of bone formation

Bone morphogenetic protein-13 (BMP-13) plays an important role in skeletal development. In the light of a recent report that mutations in the BMP-13 gene are associated with spine vertebral fusion in Klippel-Feil syndrome, we hypothesized that BMP-13 signaling is crucial for regulating embryonic endochondral ossification. In this study, we found that BMP-13 inhibited the osteogenic differentiation of human bone marrow multipotent mesenchymal stromal cells (BM MSCs) in vitro. The endogenous BMP-13 gene expression in MSCs was examined under expansion conditions. The MSCs were then induced to differentiate into osteoblasts in osteo-inductive medium containing exogenous BMP-13. Gene expression was analysed by real-time PCR. Alkaline phosphatase (ALP) expression and activity, proteoglycan (PG) synthesis and matrix mineralization were assessed by cytological staining or ALP assay. Results showed that endogenous BMP-13 mRNA expression was higher than BMP-2 or -7 during MSC growth. BMP-13 supplementation strongly inhibited matrix mineralization and ALP activity of osteogenic differentiated MSCs, yet increased PG synthesis under the same conditions. In conclusion, BMP-13 inhibited osteogenic differentiation of MSCs, implying that functional mutations or deficiency of BMP-13 may allow excess bone formation. Our finding provides an insight into the molecular mechanisms and the therapeutic potential of BMP-13 in restricting pathological bone formation.

Chondrogenesis, bone morphogenetic protein-4 and mesenchymal stem cells

OBJECTIVE

As adult cartilage has very limited potential to regenerate, cartilage repair is challenging. Available treatments have several disadvantages, including formation of fibrocartilage instead of hyaline-like cartilage, as well as eventual ossification of the newly formed tissue. The focus of this review is the application of bone morphogenetic protein-4 (BMP-4) and mesenchymal stem cells (MSCs) in cartilage repair, a combination that could potentially lead to the formation of permanent hyaline-like cartilage in the defect.

METHODS

This review is based on recent literature in the orthopaedic and tissue engineering fields, and is focused on MCSs and bone morphogenetic proteins (BMPs).

RESULTS

BMP-4, a stimulator of chondrogenesis, both in vitro and in vivo, is a potential therapeutic agent for cartilage regeneration. BMP-4 delivery can improve the healing process of an articular cartilage defect by stimulating the synthesis of the cartilage matrix constituents: type II collagen and aggrecan. BMP-4 has also been shown to suppress chondrogenic hypertrophy and maintain regenerated cartilage. Use of an appropriate carrier for BMP-4 is crucial for successful reconstruction of cartilage defects. Due to the relatively short half-life in vivo of BMP-4, there is a need to localize and maintain the delivery of BMP-4 to the injury site. Additionally, the delivery of MSCs to the wound site could improve cartilage regeneration; therefore, the carrier should function both as a cell and a protein delivery vehicle.

CONCLUSION

The role of BMP-4 in chondrogenesis is significant, and successful methods to deliver BMP-4, with or without MSCs, to the cartilage defect site are a promising therapy to treat cartilage defects.

In vivo local administration of osteogenic protein-1 increases structural properties of the overstretched anterior cruciate ligament with partial midsubstance laceration

We report the effects of local administration of osteogenic protein-1 on the biomechanical properties of the overstretched anterior cruciate ligament in an animal model. An injury in the anterior cruciate ligament was created in 45 rabbits. They were divided into three equal groups. In group 1, no treatment was applied, in group II, phosphate-buffered saline was applied around the injured ligament, and in group III, 12.5 μg of osteogenic protein-1 mixed with phosphate-buffered saline was applied around the injured ligament. A control group of 15 rabbits was assembled from randomly-selected injured knees from among the first three groups. Each rabbit was killed at 12 weeks.

The maximum load and stiffness of the anterior cruciate ligament was found to be significantly greater in group III than either group 1 (p = 0.002, p = 0.014) or group II (p = 0.032, p = 0.025). The tensile strength and the tangent modulus of fascicles from the ligament were also significantly greater in group III than either group I (p = 0.002, p = 0.0174) or II (p = 0.005, p = 0.022).

The application of osteogenic protein-1 enhanced the healing in the injured anterior cruciate ligament, but compared with the control group the treated ligament remained lengthened. The administration of osteogenic protein-1 may have a therapeutic role in treating the overstretched anterior cruciate ligament.

Unveiling the bmp13 enigma: redundant morphogen or crucial regulator?

Bone morphogenetic proteins are a diverse group of morphogens with influences not only on bone tissue, as the nomenclature suggests, but on multiple tissues in the body and often at crucial and influential periods in development.

The purpose of this review is to identify and discuss current knowledge of one vertebrate BMP, Bone Morphogenetic Protein 13 (BMP13), from a variety of research fields, in order to clarify BMP13's functional contribution to developing and maintaining healthy tissues, and to identify potential future research directions for this intriguing morphogen. BMP13 is highly evolutionarily conserved (active domain >95%) across diverse species from Zebrafish to humans, suggesting a crucial function. In addition, mutations in BMP13 have recently been associated with Klippel-Feil Syndrome, causative of numerous skeletal and developmental defects including spinal disc fusion. The specific nature of BMP13's crucial function is, however, not yet known.

The literature for BMP13 is focused largely on its activity in the healing of tendon-like tissues, or in comparisons with other BMP family molecules for whom a clear function in embryo development or osteogenic differentiation has been identified. There is a paucity of detailed information regarding BMP13 protein activity, structure or protein processing. Whilst some activity in the stimulation of osteogenic or cartilaginous gene expression has been reported, and BMP13 expression is found in post natal cartilage and tendon tissues, there appears to be a redundancy of function in the BMP family, with several members capable of stimulating similar tissue responses. This review aims to summarise the known or potential role(s) for BMP13 in a variety of biological systems.

Recent advances in annular pathobiology provide insights into rim-lesion mediated intervertebral disc degeneration and potential new approaches to annular repair strategies

The objective of this study was to assess the impact of a landmark annular lesion model on our understanding of the etiopathogenesis of IVD degeneration and to appraise current IVD repairative strategies. A number of studies have utilised the Osti sheep model since its development in 1990. The experimental questions posed at that time are covered in this review, as are significant recent advances in annular repair strategies. The ovine model has provided important spatial and temporal insights into the longitudinal development of annular lesions and how they impact on other discal and paradiscal components such as the NP, cartilaginous end plates, zygapophyseal joints and vertebral bone and blood vessels. Important recent advances have been made in biomatrix design for IVD repair and in the oriented and dynamic culture of annular fibrochondrocytes into planar, spatially relevant, annular type structures. The development of hyaluronan hydrogels capable of rapid in situ gelation offer the possibility of supplementation of matrices with cells and other biomimetics and represent a significant advance in biopolymer design. New generation biological glues and self-curing acrylic formulations which may be augmented with slow delivery biomimetics in microcarriers may also find application in the non-surgical repair of annular defects. Despite major advances, significant technical challenges still have to be overcome before the biological repair of this intractable connective tissue becomes a realistic alternative to conventional surgical intervention for the treatment of chronic degenerate IVDs.

Hormones and growth factors in the pathogenesis of spinal ligament ossification

Ossification of the spinal ligaments (OSL) is a pathologic condition that causes ectopic bone formation and subsequently results in various degrees of neurological deficit, but the etiology of OSL remains almost unknown. Some systemic hormones, such as 1,25-dihydroxyvitamin D, parathyroid hormone (PTH), insulin and leptin, and local growth factors, such as transforming growth factor-beta (TGF-beta), and bone morphogenetic protein (BMP), have been studied and are thought to be involved in the initiation and development of OSL. This review article summarizes these studies, delineates the possible mechanisms, and puts forward doubts and new questions. The related findings from studies of genes and target cells in the ligament of OSL are also discussed. Although these findings may be helpful in understanding the pathogenesis of OSL, much more research needs to be conducted in order to investigate the nature of OSL.