Copresentation of BMP-6 and RGD Ligands Enhances Cell Adhesion and BMP-Mediated Signaling

Transglutaminase enables highly hydrolytically and proteolytically stable crosslinking of collagen on titanium surfaces and promotes osteogenic differentiation of human mesenchymal stem cells

Collagen with its bioactive ligand motives would be predestined as coating on bone implant surfaces like titanium hip stems to facilitate receptor-mediated cell adhesion and thereby improve early osseointegration. Unfortunately, collagen as coating exhibits very low proteolytic resistance in vivo. To overcome this limitation, different crosslinking methods of collagen (transglutaminase, GTA, EDC/NHS, riboflavin, and lysyl oxidase) with silanized titanium alloy (Ti6Al4V) were investigated in terms of degradation resistance, hydrolysis stability, tensile strength, and metabolic cell activity. The in vitro osteogenic differentiation ability of human mesenchymal stem cells (hMSCs) induced by the surface modification was evaluated by immunofluorescence of early osteogenic markers, Alizarin red staining, and energy dispersive X-ray spectroscopy. The expression of the adhesion-related protein vinculin was analyzed on the different functionalized surfaces. The results revealed that the enzymatic crosslinker transglutaminase offered high degradation resistance, tensile strength, and hydrolysis stability compared to the other crosslinking reagents tested. Remarkably, the adhesion sequences within the collagen were accessible to the hMSCs despite the transglutaminase crosslinking procedure. In conclusion, the organochemical functionalization of Ti6Al4V surfaces with collagen using transglutaminase holds great potential to facilitate an enhanced interaction with attached bone cells and thereby could potentially improve and accelerate osseointegration of a titanium-based bone implant in vivo.

Jiawei Yanghe Decoction Regulates Bone-Lipid Balance through the BMP-SMAD Signaling Pathway to Promote Osteogenic Differentiation of Bone Mesenchymal Stem Cells

Background

The Jiawei Yanghe decoction (JWYHD) is a traditional Chinese medicine formula for the treatment of osteoporosis, but its therapeutic mechanism has not been fully elucidated, and the therapeutic target of the intervention disease needs to be further verified. The dysfunction of bone mesenchymal stem cells (BMSCs) is considered to be an important pathogenesis of postmenopausal osteoporosis (PMOP). The purpose of this study was to explore how JWYHD regulates BMSC differentiation through the BMP-SMAD signal pathway.

Methods

In the in vivo study, we used an ovariectomized PMOP rat (n = 36, 2-month-old, 200 ± 20 g) model and femur micro-CT analysis to study the effect of JWYHD on bone loss in rats. By immunofluorescence, the translocation expression of BMP2, a key protein in the pathway, was detected. Serum bone metabolism was detected by an enzyme-linked immunosorbent assay (ELISA). Alkaline phosphatase (ALP) activity was detected by alkaline phosphatase staining (ALPS), osteogenesis and matrix mineralization were detected by alizarin red staining (ARS), the adipogenic ability of BMSCs was detected by oil red staining (ORS), and CFU is used to detect the ability of cells to form colonies. The expression of related proteins was detected by western blotting.

Results

In vivo and in vitro, the OP phenotypes of SD rats induced by ovariectomy (OVX) included impaired bone mineral density and microstructure, abnormal bone metabolism, and impaired MSC differentiation potential. JWYHD treatment reversed this trend and restored the differentiation potential of MSCs. JWYHD medicated serum and direct intervention of drugs activated the BMP-SMAD signaling pathway, promoted the osteogenic differentiation of BMSCs, and inhibited their adipogenic differentiation.

Conclusions

Our data identified that JWYHD is an effective alternative drug for the treatment of PMOP that functions to stimulate the differentiation of BMSCs into osteoblasts in the BMP-SMAD signaling-dependent mechanism.

The Development of Light-Curable Calcium-Silicate-Containing Composites Used in Odontogenic Regeneration

Pulp regeneration is one of the most successful areas in the field of tissue regeneration, despite its current limitations. The biocompatibility of endodontic biomaterials is essential in securing the oral microenvironment and supporting pulp tissue regeneration. Therefore, the objective of this study was to investigate the new light-curable calcium silicate (CS)-containing polyethylene glycol diacrylate (PEGDA) biocomposites’ regulation of human dental pulp stem cells (hDPSCs) in odontogenic-related regeneration. The CS-containing PEGDA (0 to 30 wt%) biocomposites are applied to endodontics materials to promote their mechanical, bioactive, and biological properties. Firstly, X-ray diffraction and Fourier-transform infrared spectroscopy showed that the incorporation of CS increased the number of covalent bonds in the PEGDA. The diameter tension strength of the CS-containing PEGDA composite was significantly higher than that of normal PEGDA, and a different microstructure was detected on the surface. Samples were analyzed for their surface characteristics and Ca/Si ion-release profiles after soaking in simulated body fluid for different periods of time. The CS30 group presented better hDPSC adhesion and proliferation in comparison with CS0. Higher values of odontogenic-related biomarkers were found in hDPSCs on CS30. Altogether, these results prove the potential of light-curable CS-containing PEGDA composites as part of a ‘point-of-care’ strategy for application in odontogenesis-related regeneration.

2D biointerfaces to study stem cell-ligand interactions

Stem cells have great potential in the field of tissue engineering and regenerative medicine due to their inherent regenerative capabilities. However, an ongoing challenge within their clinical translation is to elicit or predict the desired stem cell behavior once transplanted. Stem cell behavior and function are regulated by their interaction with biophysical and biochemical signals present in their natural environment (i.e., stem cell niches). To increase our understanding about the interplay between stem cells and their resident microenvironments, biointerfaces have been developed as tools to study how these substrates can affect stem cell behaviors. This article aims to review recent developments on fabricating cell-instructive interfaces to control cell adhesion processes towards directing stem cell behavior. After an introduction on stem cells and their natural environment, static surfaces exhibiting predefined biochemical signals to probe the effect of chemical features on stem cell behaviors are discussed. In the third section, we discuss more complex dynamic platforms able to display biochemical cues with spatiotemporal control using on-off ligand display, reversible ligand display, and ligand mobility. In the last part of the review, we provide the reader with an outlook on future designs of biointerfaces. STATEMENT OF SIGNIFICANCE: Stem cells have great potential as treatments for many degenerative disorders prevalent in our aging societies. However, an ongoing challenge within their clinical translation is to promote stem cell mediated regeneration once they are transplanted in the body. Stem cells reside within our bodies where their behavior and function are regulated by interactions with their natural environment called the stem cell niche. To increase our understanding about the interplay between stem cells and their niche, 2D materials have been developed as tools to study how specific signals can affect stem cell behaviors. This article aims to review recent developments on fabricating cell-instructive interfaces to control cell adhesion processes towards directing stem cell behavior.

Controlled delivery of bone morphogenic protein-2-related peptide from mineralised extracellular matrix-based scaffold induces bone regeneration

Ideal bone tissue engineering scaffolds composed of extracellular matrix (ECM) require excellent osteoconductive ability to imitate the bone environment. We developed a mineralised tissue-derived ECM-modified true bone ceramic (TBC) scaffold for the delivery of aspartic acid-modified bone morphogenic protein-2 (BMP-2) peptide (P28) and assessed its osteogenic capacity. Decellularized ECM from porcine small intestinal submucosa (SIS) was coated onto the surface of TBC, followed by mineralisation modification (mSIS/TBC). P28 was subsequently immobilised onto the scaffolds in the absence of a crosslinker. The alkaline phosphatase activity and other osteogenic differentiation marker results showed that osteogenesis of the P28/mSIS/TBC scaffolds was significantly greater than that of the TBC and mSIS/TBC groups. In addition, to examine the osteoconductive capability of this system in vivo, we established a rat calvarial bone defect model and evaluated the new bone area and new blood vessel density. Histological observation showed that P28/mSIS/TBC exhibited favourable bone regeneration efficacy. This study proposes the use of mSIS/TBC loaded with P28 as a promising osteogenic scaffold for bone tissue engineering applications.

An Engineered Biomimetic Peptide Regulates Cell Behavior by Synergistic Integrin and Growth Factor Signaling

Recreating the healing microenvironment is essential to regulate cell-material interactions and ensure the integration of biomaterials. To repair bone, such bioactivity can be achieved by mimicking its extracellular matrix (ECM) and by stimulating integrin and growth factor (GF) signaling. However, current approaches relying on the use of GFs, such as bone morphogenetic protein 2 (BMP-2), entail clinical risks. Here, a biomimetic peptide integrating the RGD cell adhesive sequence and the osteogenic DWIVA motif derived from the wrist epitope of BMP-2 is presented. The approach offers the advantage of having a spatial control over the single binding of integrins and BMP receptors. Such multifunctional platform is designed to incorporate 3,4-dihydroxyphenylalanine to bind metallic oxides with high affinity in a one step process. Functionalization of glass substrates with the engineered peptide is characterized by physicochemical methods, proving a successful surface modification. The biomimetic interfaces significantly improve the adhesion of C2C12 cells, inhibit myotube formation, and activate the BMP-dependent signaling via p38. These effects are not observed on surfaces displaying only one bioactive motif, a mixture of both motifs or soluble DWIVA. These data prove the biological potential of recreating the ECM and engaging in integrin and GF crosstalk via molecular-based mimics.

Biology of bone morphogenetic protein in bone repair and regeneration: A role for autologous blood coagulum as carrier

BMPs were purified from demineralized bone matrix based on their ability to induce new bone in vivo and they represent a large member of the TGF-β superfamily of proteins. BMPs serve as morphogenic signals for mesenchymal stem cell migration, proliferation and subsequently differentiation into cartilage and bone during embryonic development. A BMP when implanted with a collagenous carrier in a rat subcutaneous site is capable of inducing new bone by mimicking the cellular events of embryonic bone formation. Based on this biological principle, BMP2 and BMP7 containing collagenous matrix as carrier have been developed as bone graft substitutes for spine fusion and long bone fractures. Here, we describe a novel autologous bone graft substitute that contains BMP6 delivered within an autologous blood coagulum as carrier and summarize the biology of osteogenic BMPs in the context of bone repair and regeneration specifically the critical role that carrier plays to support osteogenesis.

Learning from BMPs and their biophysical extracellular matrix microenvironment for biomaterial design

It is nowadays well-accepted that the extracellular matrix (ECM) is not a simple reservoir for growth factors but is an organization center of their biological activity. In this review, we focus on the ability of the ECM to regulate the biological activity of BMPs. In particular, we survey the role of the ECM components, notably the glycosaminoglycans and fibrillary ECM proteins, which can be promoters or repressors of the biological activities mediated by the BMPs. We examine how a process called mechano-transduction induced by the ECM can affect BMP signaling, including BMP internalization by the cells. We also focus on the spatio-temporal regulation of the BMPs, including their release from the ECM, which enables to modulate their spatial localization as well as their local concentration. We highlight how biomaterials can recapitulate some aspects of the BMPs/ECM interactions and help to answer fundamental questions to reveal previously unknown molecular mechanisms. Finally, the design of new biomaterials inspired by the ECM to better present BMPs is discussed, and their use for a more efficient bone regeneration in vivo is also highlighted.

Surface Co-presentation of BMP-2 and integrin selective ligands at the nanoscale favors α5β1 integrin-mediated adhesion

Here we present the use of surface nanopatterning of covalently immobilized BMP-2 and integrin selective ligands to determine the specificity of their interactions in regulating cell adhesion and focal adhesion assembly. Gold nanoparticle arrays carrying single BMP-2 dimers are prepared by block-copolymer micellar nanolithography and azide-functionalized integrin ligands (cyclic-RGD peptides or α₅β₁ integrin peptidomimetics) are immobilized on the surrounding polyethylene glycol alkyne by click chemistry. Compared to BMP-2 added to the media, surface immobilized BMP-2 (iBMP-2) favors the spatial segregation of adhesion clusters and enhances focal adhesion (FA) size in cells adhering to α₅β₁ integrin selective ligands. Moreover, iBMP-2 copresented with α₅β₁ integrin ligands induces the recruitment of α_vβ₃ integrins in FAs. When copresented with RGD, iBMP-2 induces the assembly of a higher number of FAs, which are not affected by α₅β₁ integrin blocking. Our dual-functionalized platforms offer the possibility to study the crosstalk between integrins and BMP receptors, and more in general they could be used to address the spatial regulation of growth factors and adhesion receptors crosstalk on biomimetic surfaces.

Cytokine Directed Chondroblast Trans-Differentiation: JAK Inhibition Facilitates Direct Reprogramming of Fibroblasts to Chondroblasts

Osteoarthritis (OA) is a degenerative disease of the hyaline articular cartilage. This disease is progressive and may lead to disability. Researchers proposed many regenerative approaches to treat osteoarthritis, including stem cells. Trans-differentiation of a fully differentiated cell state directly into another different differentiated cell state avoids the disadvantages of fully reprogramming cells to induced pluripotent stem cells (iPSCs) in terms of faster reprogramming of the needed cells. Trans-differentiation also reduces the risk of tumor formation by avoiding the iPSC state. OSKM factors (Oct4, Sox2, Klf4, and cMyc) accompanied by the JAK-STAT pathway inhibition, followed by the introduction of specific differentiation factors, directly reprogrammed mouse embryonic fibroblasts to chondroblasts. Our results showed the absence of intermediate induced pluripotent stem cell formation. The resulting aggregates showed clear hyaline and hypertrophic cartilage. Tumor formation was absent in sub-cutaneous capsules transplanted in SCID mice.