The effect of collagen I mimetic peptides on mesenchymal stem cell adhesion and differentiation, and on bone formation at hydroxyapatite surfaces

Effective combination of aligned nanocomposite nanofibers and human unrestricted somatic stem cells for bone tissue engineering

AIM

Bioartificial bone tissue engineering is an increasingly popular technique to solve bone defect challenges. This study aimed to investigate the interactions between matrix composition and appropriate cell type, focusing on hydroxyapatite (HA), to achieve a more effective combination for bone regeneration.

METHODS

Human unrestricted somatic stem cells (USSCs) were isolated from placental cord blood. The cellular and molecular events during the osteo-induction of USSCs were evaluated for 21 d under the following conditions: (1) in basal culture, (2) supplemented with hydroxyapatite nanoparticle (nHA) suspension, and (3) seeded on electrospun aligned nanofibrous poly-ɛ-caprolactone/poly-L-lactic acid/nHA (PCL/PLLA/nHA) scaffolds. The scaffolds were characterized using scanning electron microscope (SEM), fourier transform infrared spectroscopy (FTIR) and tensile test.

RESULTS

Maintenance of USSCs for 21 d in basal or osteogenic culture resulted in significant increase in osteoblast differentiation. With nHA suspension, even soluble osteo-inductive additives were ineffective, probably due to induced apoptosis of the cells. In contrast to the hindrance of proliferation by nHA suspension, the scaffolds improved cell growth. The scaffolds mimic the nanostructure of natural bone matrix with the combination of PLLA/PCL (organic phase) and HA (inorganic phase) offering a favorable surface topography, which was demonstrated to possess suitable properties for supporting USSCs. Quantitative measurement of osteogenic markers, enzymatic activity and mineralization indicated that the scaffolds did not disturb, but enhanced the osteogenic potential of USSCs. Moreover, the alignment of the fibers led to cell orientation during cell growth.

CONCLUSION

The results demonstrated the synergism of PCL/PLLA/nHA nanofibrous scaffolds and USSCs in the augmentation of osteogenic differentiation. Thus, nHA grafted into PCL/PLLA scaffolds can be a suitable choice for bone tissue regeneration.

Mesenchymal stem cells, osteoblasts and extracellular matrix proteins: enhancing cell adhesion and differentiation for bone tissue engineering

Cell adhesion to scaffolds has remained one of the challenges in tissue engineering. Although protein surface modification has been proven to enhance cell adhesion and retention, its specificity depending on cell and biomaterial types means that the best protein and concentration must be established for each specific application. This review focuses on the improvement of cell adhesion for human mesenchymal stem cells with an osteogenesis approach. A brief outline of the cell adhesion process and extracellular matrix proteins precedes an overview of works focused on the adhesion of mesenchymal stem cells and osteoblasts to biomaterials and this effect in their differentiation into osteoblasts.

Suppression of anoikis by collagen coating of interconnected macroporous nanometric carbonated hydroxyapatite/agarose scaffolds

Three dimensional interconnected macroporous (pore diameter: 600-800 μm) hydroxyapatite/agarose disks have been evaluated in this study as potential bone regeneration scaffolds. With this purpose, the adhesion and proliferation of human Saos-2 osteoblasts on this biomaterial were analyzed. As an index of cell function, the following parameters were measured: cell morphology, viability, cell size/complexity, cell cycle, reactive oxygen species (ROS) content, and lactate dehydrogenase (LDH) release. The existence of anoikis induced by inappropriate contacts between the cell and the scaffold has been detected by scanning electron microscopy, confocal microscopy, and flow cytometry. The intracellular nitric oxide content has been also measured as potential inducer of anoikis. The positive effects of previous scaffold coating with type I collagen on osteoblast adhesion as well as the collagen protection against anoikis have been demonstrated in this study.

Engineering the extracellular environment: Strategies for building 2D and 3D cellular structures

Cell fate is regulated by extracellular environmental signals. Receptor specific interaction of the cell with proteins, glycans, soluble factors as well as neighboring cells can steer cells towards proliferation, differentiation, apoptosis or migration. In this review, approaches to build cellular structures by engineering aspects of the extracellular environment are described. These methods include non-specific modifications to control the wettability and stiffness of surfaces using self-assembled monolayers (SAMs) and polyelectrolyte multilayers (PEMs) as well as methods where the temporal activation and spatial distribution of adhesion ligands is controlled. Building on these techniques, construction of two-dimensional cell sheets using temperature sensitive polymers or electrochemical dissolution is described together with current applications of these grafts in the clinical arena. Finally, methods to pattern cells in three-dimensions as well as to functionalize the 3D environment with biologic motifs take us one step closer to being able to engineer multicellular tissues and organs.

Association of collagen with calcium phosphate promoted osteogenic responses of osteoblast-like MG63 cells

In this investigation, the effects of the association of the collagen (COLL) molecules with the calcium phosphate (CaP) film were examined with respect to both the physicochemical properties of the CaP films and the osteoblast responses, such as the adhesion, proliferation, differentiation, and mineralization. The COLL pre-adsorbed CaP film (CaPA) exhibited significant changes in the surface morphology compared to the COLL incorporated CaP film (CaPC). The adhesions of the osteoblast-like MG63 cells were similar on the CaPC or CaPA films. However, the proliferation of the MG63 cells on CaPC was comparable to CaP but considerably different than CaPA. The differentiation of the MG63 cells was greatly improved on CaPC and CaPA compared to CaP and more pronounced on CaPA. The presence of COLL within or on the CaP films significantly modulated the expression of the phenotypic genes, including osteopontin (OPN), alkaline phosphatase (ALP), and the transforming growth factor-β (TGF-β). The expression patterns of these genes elucidated that COLL that was present within or on the CaP film supported the osteoblast proliferation and differentiation. These positive effects were stronger for CaPA than CaPC. The bone-like nodules formed on all of the specimens. However, the mineralization of CaPC and CaPA was significantly higher than CaP, indicating that the association of CaP with COLL promoted the mineral deposition. Therefore, the association of the COLL molecules with the CaP film induced positive effects on the biomineralization. Overall, the incorporation of COLL efficiently enhanced the osteoblast responses of CaP. This system can be utilized in a drug delivery system using calcium phosphate. Although the incorporation effects were slightly higher for the osteoblast responses of CaPA than CaPC, CaPC can be used when the longer drug release times are desirable.

Extracellular matrix-mimetic adhesive biomaterials for bone repair

Limited osseointegration of current orthopedic biomaterials contributes to the failure of implants such as arthroplasties, bone screws, and bone grafts, which present a large socioeconomic cost within the United States. These implant failures underscore the need for biomimetic approaches that modulate host cell-implant material responses to enhance implant osseointegration and bone formation. Bioinspired strategies have included functionalizing implants with extracellular matrix (ECM) proteins or ECM-derived peptides or protein fragments, which engage integrins and direct osteoblast adhesion and differentiation. This review discusses (1) bone ECM composition and key integrins implicated in osteogenic differentiation, (2) the use of implants functionalized with ECM-mimetic peptides/protein fragments, and (3) growth factor-derived peptides to promote the mechanical fixation of implants to bone and to enhance bone healing within large defects.

Enhancement of peptide coupling to hydroxyapatite and implant osseointegration through collagen mimetic peptide modified with a polyglutamate domain

Hydroxyapatite (HA) is a widely-used biomaterial for bone repair due to its high degree of osteoconductivity. However, strategies for improving HA performance by functionalizing surfaces with bioactive factors are limited. In this study, we explored the use of a HA-binding domain (heptaglutamate, "E7") to facilitate coupling of the collagen mimetic peptide, DGEA, to two types of HA-containing materials, solid HA disks and electrospun polycaprolactone matrices incorporating nanoparticulate HA. We found that the E7 domain directed significantly more peptide to the surface of HA and enhanced peptide retention on both materials in vitro. Moreover, E7-modified peptides were retained in vivo for at least two months, highlighting the potential of this mechanism as a sustained delivery system for bioactive peptides. Most importantly, E7-DGEA-coupled HA, as compared with DGEA-HA, enhanced the adhesion and osteoblastic differentiation of mesenchymal stem cells, and also increased new bone formation and direct bone-implant contact on HA disks implanted into rat tibiae. Collectively, these results support the use of E7-DGEA peptides to promote osteogenesis on HA substrates, and further suggest that the E7 domain can serve as a universal tool for anchoring a wide variety of bone regenerative molecules to any type of HA-containing material.

Toward biomimetic materials in bone regeneration: functional behavior of mesenchymal stem cells on a broad spectrum of extracellular matrix components

Bone defect treatments can be augmented by mesenchymal stem cell (MSC) based therapies. MSC interaction with the extracellular matrix (ECM) of the surrounding tissue regulates their functional behavior. Understanding of these specific regulatory mechanisms is essential for the therapeutic stimulation of MSC in vivo. However, these interactions are presently only partially understood. This study examined in parallel, for the first time, the effects on the functional behavior of MSCs of 13 ECM components from bone, cartilage and hematoma compared to a control protein, and hence draws conclusions for rational biomaterial design. ECM components specifically modulated MSC adhesion, migration, proliferation, and osteogenic differentiation, for example, fibronectin facilitated migration, adhesion, and proliferation, but not osteogenic differentiation, whereas fibrinogen enhanced adhesion and proliferation, but not migration. Subsequently, the integrin expression pattern of MSCs was determined and related to the cell behavior on specific ECM components. Finally, on this basis, peptide sequences are reported for the potential stimulation of MSC functions. Based on the results of this study, ECM component coatings could be designed to specifically guide cell functions.

Serotonergic 5-HT(2B) receptor controls tissue-nonspecific alkaline phosphatase activity in osteoblasts via eicosanoids and phosphatidylinositol-specific phospholipase C

In previous studies, we observed that mice knocked out for the serotonin-2B receptor (5-HT(2B)R) show defects in bone homeostasis. The present work focuses on the downstream targets relaying the anabolic function of this receptor in osteoblasts. A functional link between the 5-HT(2B)R and the activity of the tissue-nonspecific alkaline phosphatase (TNAP) is established using the C1 osteoprogenitor cell line. During C1 osteogenic differentiation, both 5-HT(2B)R and TNAP mRNA translations are delayed with respect to extracellular matrix deposition. Once the receptor is expressed, it constitutively controls TNAP activity at a post-translational level along the overall period of mineral deposition. Indeed, pharmacological inhibition of the 5-HT(2B)R intrinsic activity or shRNA-mediated 5-HT(2B)R knockdown prevents TNAP activation, but not its mRNA translation. In contrast, agonist stimulation of the receptor further increases TNAP activity during the initial mineralization phase. Building upon our previous observations that the 5-HT(2B)R couples with the phospholipase A2 pathway and prostaglandin production at the beginning of mineral deposition, we show that the 5-HT(2B)R controls leukotriene synthesis via phospholipase A2 at the terminal stages of C1 differentiation. These two 5-HT(2B)R-dependent eicosanoid productions delineate distinct time windows of TNAP regulation during the osteogenic program. Finally, prostaglandins or leukotrienes are shown to relay the post-translational activation of TNAP via stimulation of the phosphatidylinositol-specific phospholipase C. In agreement with the above findings, primary calvarial osteoblasts from 5-HT(2B)R-null mice exhibit defects in TNAP activity.

Emerging techniques in stratified designs and continuous gradients for tissue engineering of interfaces

Interfacial tissue engineering is an emerging branch of regenerative medicine, where engineers are faced with developing methods for the repair of one or many functional tissue systems simultaneously. Early and recent solutions for complex tissue formation have utilized stratified designs, where scaffold formulations are segregated into two or more layers, with discrete changes in physical or chemical properties, mimicking a corresponding number of interfacing tissue types. This method has brought forth promising results, along with a myriad of regenerative techniques. The latest designs, however, are employing "continuous gradients" in properties, where there is no discrete segregation between scaffold layers. This review compares the methods and applications of recent stratified approaches to emerging continuously graded methods.

Coating of biomaterial scaffolds with the collagen-mimetic peptide GFOGER for bone defect repair

Healing large bone defects and non-unions remains a significant clinical problem. Current treatments, consisting of auto and allografts, are limited by donor supply and morbidity, insufficient bioactivity and risk of infection. Biotherapeutics, including cells, genes and proteins, represent promising alternative therapies, but these strategies are limited by technical roadblocks to biotherapeutic delivery, cell sourcing, high cost, and regulatory hurdles. In the present study, the collagen-mimetic peptide, GFOGER, was used to coat synthetic PCL scaffolds to promote bone formation in critically-sized segmental defects in rats. GFOGER is a synthetic triple helical peptide that binds to the alpha(2)beta(1) integrin receptor involved in osteogenesis. GFOGER coatings passively adsorbed onto polymeric scaffolds, in the absence of exogenous cells or growth factors, significantly accelerated and increased bone formation in non-healing femoral defects compared to uncoated scaffolds and empty defects. Despite differences in bone volume, no differences in torsional strength were detected after 12 weeks, indicating that bone mass but not bone quality was improved in this model. This work demonstrates a simple, cell/growth factor-free strategy to promote bone formation in challenging, non-healing bone defects. This biomaterial coating strategy represents a cost-effective and facile approach, translatable into a robust clinical therapy for musculoskeletal applications.

Specific biofunctional performances of the hydroxyapatite-sodium maleate copolymer hybrid coating nanostructures evaluated by in vitro studies

The nanohybrid structures consisting of hydroxyapatite (HA) and sodium maleate-vinyl acetate copolymer (MP) deposited by Matrix Assisted Pulsed Laser Evaporation (MAPLE) technique on Ti surfaces were investigated for specific biological qualities required in bone implantology. The data from in vitro studies demonstrated that human primary osteoblasts (OBs) firmly adhered to Ti coated with HA-MP as indicated by cytoskeleton and vinculin dynamics. OBs spread onto biomaterial surface and formed groups of cells which during their biosynthetic activity expressed OB phenotype specific markers (collagen and non-collagenous proteins) and underwent controlled proliferation.

Emerging concepts in engineering extracellular matrix variants for directing cell phenotype

Directing specific, complex cell behaviors, such as differentiation, in response to biomaterials for regenerative medicine applications is, at present, a mostly unrealized goal. To date, current technological advances have been inspired by the reductionist point of view, focused on developing simple and merely adequate environments that facilitate simple cellular adhesion. However, even if extracellular matrix (ECM)-derived peptides, such as Arg-Gly-Asp (RGD), have largely demonstrated their utility in supporting cell adhesion, their lack of biological specificity is simply not optimal for controlling more integrated processes, such as cell differentiation. These more complex cellular processes require specific integrin-signaling scaffolds and presumably synergistic integrin and growth factor-receptor signaling. This article will introduce some current efforts to engineer ECM variants that incorporate additional levels of complexity for directing greater integrin specificity and synergistic ECM growth factor signaling toward directing cell phenotype.