Structural and functional characterization of osteogenic growth peptide from human serum: identity with rat and mouse homologs

Osteogenic growth peptide is a potent anti-inflammatory and bone preserving hormone via cannabinoid receptor type 2

The endocannabinoid system consists mainly of 2-arachidonoylglycerol and anandamide, as well as cannabinoid receptor type 1 (CB1) and type 2 (CB2). Based on previous studies, we hypothesized that a circulating peptide previously identified as Osteogenic Growth Peptide (OGP) maintains a bone-protective CB2 tone. We tested OGP activity in mouse models and cells, and in human osteoblasts. We show that the OGP effects on osteoblast proliferation, osteoclastogenesis, and macrophage inflammation in vitro, as well as rescue of ovariectomy-induced bone loss and prevention of ear edema in vivo are all abrogated by genetic or pharmacological ablation of CB2. We also demonstrate that OGP binds at CB2 and may act as both an agonist and positive allosteric modulator in the presence of other lipophilic agonists. In premenopausal women, OGP circulating levels significantly decline with age. In adult mice, exogenous administration of OGP completely prevented age-related bone loss. Our findings suggest that OGP attenuates age-related bone loss by maintaining a skeletal CB2 tone. Importantly, they also indicate the occurrence of an endogenous peptide that signals via CB2 receptor in health and disease.

Tuning the Biointerface: Low-Temperature Surface Modification Strategies for Orthopedic Implants to Enhance Osteogenic and Antimicrobial Activity

As both the average life expectancy and incidence of bone tissue reconstruction increases, development of load-bearing implantable materials that simultaneously enhance osseointegration while preventing postoperative infection is crucial. To address this need, significant research efforts have been dedicated to developing surface modification strategies for metallic load-bearing implants and scaffolds. Despite the abundance of strategies reported, many address only one factor, for example, surface chemistry or topography. Furthermore, the incorporation of surface features to increase osteocompatibility can increase the probability of infection, by encouraging the formation of bacterial biofilms. To truly advance this field, research efforts must focus on developing multifunctional coatings that concurrently address these complex and competing requirements. In addition, particular emphasis should be placed on utilizing surface modification processes that are versatile, low cost, and scalable, for ease of translation to mass manufacturing and clinical use. The aim of this short Review is to highlight recent advances in scalable and multifunctional surface modification techniques that obtain a programmed response at the bone tissue/implant interface. Low-temperature approaches based on macromolecule immobilization, electrochemical techniques, and solution processes are discussed. Although the strategies discussed in this Review have not yet been approved for clinical use, they show great promise toward developing the next generation of ultra-long-lasting biomaterials for joint and bone tissue repair.

Role of Osteogenic Growth Peptide (OGP) and OGP(10-14) in Bone Regeneration: A Review

Bone regeneration is a process that involves several molecular mediators, such as growth factors, which directly affect the proliferation, migration and differentiation of bone-related cells. The osteogenic growth peptide (OGP) and its C-terminal pentapeptide OGP(10–14) have been shown to stimulate the proliferation, differentiation, alkaline phosphatase activity and matrix mineralization of osteoblastic lineage cells. However, the exact molecular mechanisms that promote osteoblastic proliferation and differentiation are not completely understood. This review presents the main chemical characteristics of OGP and/or OGP(10–14), and also discusses the potential molecular pathways induced by these growth factors to promote proliferation and differentiation of osteoblasts. Furthermore, since these peptides have been extensively investigated for bone tissue engineering, the clinical applications of these peptides for bone regeneration are discussed.

Immobilizing osteogenic growth peptide with and without fibronectin on a titanium surface: effects of loading methods on mesenchymal stem cell differentiation

In this study, to improve the osseointegration of implants, osteogenic growth peptide (OGP) and fibronectin (FN) were loaded within mineral, which was formed on titanium, through adsorption and coprecipitation methods. The release profiles of OGP loaded by either adsorption or coprecipitation and the effects of the loading methods to immobilize OGP with and without FN on rat mesenchymal stem cell (rMSC) osteogenic differentiation were studied. The coprecipitation approach slightly reduced the initial burst release, while the adsorption approach provided a more sustained release. Dual loading of OGP and FN further improved cell attachments compared with either OGP or FN alone. Dually loaded OGP and FN also had a positive impact on rMSC proliferation and osteogenic differentiation. The difference in methods of loading OGP with and without FN also had some effects on osteogenic differentiation. Compared with coprecipitated OGP alone, adsorbed OGP enhanced later differentiation, such as osteocalcin secretion and matrix mineralization. Simultaneously adsorbed OGP and FN led to higher proliferation and higher osteogenic differentiation in both early and late stages compared with sequentially loaded OGP and FN. rMSC culture clearly indicated that simultaneously adsorbed OGP and FN could improve osseointegration, and this treatment represents a potential method for effective surface modification of dental and orthopedic implants.

Stable biofunctionalization of hydroxyapatite (HA) surfaces by HA-binding/osteogenic modular peptides for inducing osteogenic differentiation of mesenchymal stem cells

Hydroxyapatite (HA), the principal component of bone mineral, shows osteoconductive properties when employed for coating metal implants as well as scaffold materials in synthetic bone grafts. With the goal of providing this material with osteoinductive capabilities to promote faster bone regeneration, we show an easy approach to functionalize HA implant surfaces and enrich them with osteoinductive properties by the use of HA-binding modular peptides. The modular peptides are designed as a combination of two domains, an HA-binding peptide motif and an osteogenic peptide motif derived from the osteogenic growth peptide (OGP) or bone morphometric protein 7 (BMP-7). To identify the best HA-binding peptide, several nature-inspired peptides derived from natural bone extracellular matrix proteins (bone sialoprotein, osteonectin, osteocalcin, and salivarin statherin) were compared for HA-binding activity, revealing concentration-dependent and incubation-time-dependent behaviours. We discovered that a Poly-E heptamer (E7) is the best HA-binding peptide, and thus combined it with a second osteogenic peptidic domain to create an osteoinductive modular peptide. After binding/release characterization, we found that the addition of the second osteogenic peptide domain did not change the binding profile of the modular peptides and caused only a slight change in their release kinetics. Mesenchymal stem cells (MSCs) were cultured on the HA substrates functionalized with modular peptides, and cell adhesion, proliferation, and differentiation in a basal medium (i.e., without any osteogenic supplements) were investigated. Gene expression data clearly showed that MSCs were committed to differentiate into osteoblasts in the presence of the modular peptides. HA discs functionalized with the E7 BMP-7 modular peptide showed the best capability in inducing the osteogenic differentiation of MSCs among all modular peptides studied. The modular peptides can easily be used to functionalize the HA implants through its constituent HA-binding motif, leaving the osteogenic peptide motif protruding from the surface for inducing osteogenesis. Our work opens up a new approach to the formulation of new bioactive HA coatings and implants for bone and dental repair.

Facile fabrication of "dual click" one- and two-dimensional orthogonal peptide concentration gradients

Peptides, proteins, and extracellular matrix act synergistically to influence cellular function at the biotic-synthetic interface. However, identifying the individual and cooperative contributions of the various combinations and concentration regimes is extremely difficult. The confined channel deposition method we describe affords highly tunable orthogonal reactive concentration gradients that greatly expand the dynamic range, spatial control, and chemical versatility of the reactive silanes that can be controllably deposited. Using metal-free "dual click" immobilization chemistries, multiple peptides with a variety of functionality can be immobilized efficiently and reproducibly enabling optimal concentration profiling and the assessment of synergistic interactions.

Effects of erythropoietin on the bone microenvironment

It has been well established that blood and bone share a unique, regulatory relationship with one another, though the specifics of this relationship still remain unanswered. Erythropoietin (Epo) is known primarily for its role as a hematopoietic hormone. However, after the discovery of Epo receptor outside the hematopoietic tissues, Epo has been avidly studied for its possible nonhematopoietic effects. It has been proposed that Epo interacts with bone both directly, by activating bone marrow stromal cells, and indirectly, through signaling pathways on hematopoietic stem cells. Yet, the role of Epo in regulating skeletal maintenance and regeneration remains controversial. Here, we review the current state of knowledge pertaining to the effects of Epo on the skeleton.

Erythropoietin couples hematopoiesis with bone formation

Background

It is well established that bleeding activates the hematopoietic system to regenerate the loss of mature blood elements. We have shown that hematopoietic stem cells (HSCs) isolated from animals challenged with an acute bleed regulate osteoblast differentiation from marrow stromal cells. This suggests that HSCs participate in bone formation where the molecular basis for this activity is the production of BMP2 and BMP6 by HSCs. Yet, what stimulates HSCs to produce BMPs is unclear.

Methodology/Principal Findings

In this study, we demonstrate that erythropoietin (Epo) activates Jak-Stat signaling pathways in HSCs which leads to the production of BMPs. Critically, Epo also directly activates mesenchymal cells to form osteoblasts in vitro, which in vivo leads to bone formation. Importantly, Epo first activates osteoclastogenesis which is later followed by osteoblastogenesis that is induced by either Epo directly or the expression of BMPs by HSCs to form bone.

Conclusions/Significance

These data for the first time demonstrate that Epo regulates the formation of bone by both direct and indirect pathways, and further demonstrates the exquisite coupling between hematopoesis and osteopoiesis in the marrow.

Hematopoietic stem cells regulate mesenchymal stromal cell induction into osteoblasts thereby participating in the formation of the stem cell niche

Crosstalk between hematopoietic stem cells (HSCs) and the cells comprising the niche is critical for maintaining stem cell activities. Yet little evidence supports the concept that HSCs regulate development of the niche. Here, the ability of HSCs to directly regulate endosteal development was examined. Marrow was isolated 48 hours after "stressing" mice with a single acute bleed or from control nonstressed animals. "Stressed" and "nonstressed" HSCs were cocultured with bone marrow stromal cells to map mesenchymal fate. The data suggest that HSCs are able to guide mesenchymal differentiation toward the osteoblastic lineage under basal conditions. HSCs isolated from animals subjected to an acute stress were significantly better at inducing osteoblastic differentiation in vitro and in vivo than those from control animals. Importantly, HSC-derived bone morphogenic protein 2 (BMP-2) and BMP-6 were responsible for these activities. Furthermore, significant differences in the ability of HSCs to generate a BMP response following stress were noted in aged and in osteoporotic animals. Together these data suggest a coupling between HSC functions and bone turnover as in aging and in osteoporosis. For the first time, these results demonstrate that HSCs do not rest passively in their niche. Instead, they directly participate in bone formation and niche activities. Disclosure of potential conflicts of interest is found at the end of this article.