Human alpha 2-macroglobulin is an osteogenic growth peptide-binding protein

Unraveling the Relevance of Tissue-Specific Decellularized Extracellular Matrix Hydrogels for Vocal Fold Regenerative Biomaterials: A Comprehensive Proteomic and In Vitro Study

Decellularized extracellular matrix (dECM) is a promising material for tissue engineering applications. Tissue-specific dECM is often seen as a favorable material that recapitulates a native-like microenvironment for cellular remodeling. However, the minute quantity of dECM derivable from small organs like the vocal fold (VF) hampers manufacturing scalability. Small intestinal submucosa (SIS), a commercial product with proven regenerative capacity, may be a viable option for VF applications. This study aims to compare dECM hydrogels derived from SIS or VF tissue with respect to protein content and functionality using mass spectrometry-based proteomics and in vitro studies. Proteomic analysis reveals that VF and SIS dECM share 75% of core matrisome proteins. Although VF dECM proteins have greater overlap with native VF, SIS dECM shows less cross-sample variability. Following decellularization, significant reductions of soluble collagen (61%), elastin (81%), and hyaluronan (44%) are noted in VF dECM. SIS dECM contains comparable elastin and hyaluronan but 67% greater soluble collagen than VF dECM. Cells deposit more neo-collagen on SIS than VF-dECM hydrogels, whereas neo-elastin (~50 μg/scaffold) and neo-hyaluronan (~ 6 μg/scaffold) are comparable between the two hydrogels. Overall, SIS dECM possesses reasonably similar proteomic profile and regenerative capacity to VF dECM. SIS dECM is considered a promising alternative for dECM-derived biomaterials for VF regeneration.

Pathophysiology of Avascular Necrosis

Avascular necrosis is a complicated, multifactorial disease with potentially devastating consequences. Although the underlying root cause is a lack of appropriate vascular perfusion to affected bone, there are often varying patient-specific, anatomic-specific, and injury-specific predispositions. These factors generally fall into 3 categories: direct vascular disruption, intravascular obliteration, or extravascular compression. The initial stages of disease can be insidiously symptomatic because edematous bone marrow progresses to subchondral collapse and subsequent degenerative arthritis. Although much of the current literature focuses on the femoral head, other common areas of occurrence include the proximal humerus, knee, and the carpus. The low-incidence rate of carpal avascular necrosis poses a challenge in establishing adequately powered, control-based validated treatment options, and therefore, optimal surgical management remains a continued debate among hand surgeons. Appreciation for expectant fracture healing physiology may help guide future investigation into carpal-specific causes of avascular necrosis.

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.

Proteomics Disclose the Potential of Gingival Crevicular Fluid (GCF) as a Source of Biomarkers for Severe Periodontitis

Periodontal disease is a widespread disorder comprising gingivitis, a mild early gum inflammation, and periodontitis, a more severe multifactorial inflammatory disease that, if left untreated, can lead to the gradual destruction of the tooth-supporting apparatus. To date, effective etiopathogenetic models fully explaining the clinical features of periodontal disease are not available. Obviously, a better understanding of periodontal disease could facilitate its diagnosis and improve its treatment. The purpose of this study was to employ a proteomic approach to analyze the gingival crevicular fluid (GCF) of patients with severe periodontitis, in search of potential biomarkers. GCF samples, collected from both periodontally healthy sites (H-GCF) and the periodontal pocket (D-GCF), were subjected to a comparison analysis using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). A total of 26 significantly different proteins, 14 up-regulated and 12 down-regulated in D-GCF vs. H-GCF, were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The main expressed proteins were inflammatory molecules, immune responders, and host enzymes. Most of these proteins were functionally connected using the STRING analysis database. Once validated in a large scale-study, these proteins could represent a cluster of promising biomarkers capable of making a valuable contribution for a better assessment of periodontitis.

Quantitative proteomic study reveals differential expression of matricellular proteins between fibrous dysplasia and cemento-ossifying fibroma pathogenesis

BACKGROUND

Fibrous dysplasia (FD) and cemento-ossifying fibroma (COF) are the most common gnathic fibro-osseous lesions. These diseases exhibit remarkable overlap of several clinicopathological aspects and differential diagnosis depends on the combination of histopathological, radiographic and clinical aspects. Their molecular landscape remain poorly characterized and herein we assessed their proteomic and phosphoproteomic profiles.

METHODS

The quantitative differences in protein profile of FD and COF were assessed by proteomic and phosphoproteomic analyses of formalin-fixed paraffin-embedded tissue samples. Pathway enrichment analyses with differentialy regulated proteins were performed.

RESULTS

FD and COF exhibited differential regulation of pathways related to extracellular matrix organization, cell adhesion, and platelet and erythrocytes activities. Additionally, these lesions demonstrated distinct abundance of proteins involved in osteoblastic differentiation and tumorigenesis and differential abundance of phosphorylation of Ser61 of Yes-associated protein 1 (YAP1).

CONCLUSIONS

In summary, despite the morphological similarity between these diseases, our results demonstrated that COF and DF present numerous quantitative differences in their proteomic profiles.These findings suggest that these fibro-osseous lesions trigger distinct molecular mechanisms during their pathogenesis. Moreover, some proteins identified in our analysis could serve as potential biomarkers for differential diagnosis of these diseases after further validation.

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.

Freeze-Dried Secretome (Lyosecretome) from Mesenchymal Stem/Stromal Cells Promotes the Osteoinductive and Osteoconductive Properties of Titanium Cages

Titanium is one of the most frequently used materials in bone regeneration due to its good biocompatibility, excellent mechanical properties, and great osteogenic performance. However, osseointegration with host tissue is often not definite, which may cause implant failure at times. The present study investigates the capacity of the mesenchymal stem cell (MSC)-secretome, formulated as a ready-to-use and freeze-dried medicinal product (the Lyosecretome), to promote the osteoinductive and osteoconductive properties of titanium cages. In vitro tests were conducted using adipose tissue-derived MSCs seeded on titanium cages with or without Lyosecretome. After 14 days, in the presence of Lyosecretome, significant cell proliferation improvement was observed. Scanning electron microscopy revealed the cytocompatibility of titanium cages: the seeded MSCs showed a spread morphology and an initial formation of filopodia. After 7 days, in the presence of Lyosecretome, more frequent and complex cellular processes forming bridges across the porous surface of the scaffold were revealed. Also, after 14 and 28 days of culturing in osteogenic medium, the amount of mineralized matrix detected by alizarin red was significantly higher when Lyosecretome was used. Finally, improved osteogenesis with Lyosecretome was confirmed by confocal analysis after 28 and 56 days of treatment, and demonstrating the production by osteoblast-differentiated MSCs of osteocalcin, a specific bone matrix protein.

Biohybrid Bovine Bone Matrix for Controlled Release of Mesenchymal Stem/Stromal Cell Lyosecretome: A Device for Bone Regeneration

SmartBone® (SB) is a biohybrid bone substitute advantageously proposed as a class III medical device for bone regeneration in reconstructive surgeries (oral, maxillofacial, orthopedic, and oncology). In the present study, a new strategy to improve SB osteoinductivity was developed. SB scaffolds were loaded with lyosecretome, a freeze-dried formulation of mesenchymal stem cell (MSC)-secretome, containing proteins and extracellular vesicles (EVs). Lyosecretome-loaded SB scaffolds (SBlyo) were prepared using an absorption method. A burst release of proteins and EVs (38% and 50% after 30 min, respectively) was observed, and then proteins were released more slowly with respect to EVs, most likely because they more strongly adsorbed onto the SB surface. In vitro tests were conducted using adipose tissue-derived stromal vascular fraction (SVF) plated on SB or SBlyo. After 14 days, significant cell proliferation improvement was observed on SBlyo with respect to SB, where cells filled the cavities between the native trabeculae. On SB, on the other hand, the process was still present, but tissue formation was less organized at 60 days. On both scaffolds, cells differentiated into osteoblasts and were able to mineralize after 60 days. Nonetheless, SBlyo showed a higher expression of osteoblast markers and a higher quantity of newly formed trabeculae than SB alone. The quantification analysis of the newly formed mineralized tissue and the immunohistochemical studies demonstrated that SBlyo induces bone formation more effectively. This osteoinductive effect is likely due to the osteogenic factors present in the lyosecretome, such as fibronectin, alpha-2-macroglobulin, apolipoprotein A, and TGF-β.

Osteogenic effects of the peptide fraction derived from pepsin-hydrolyzed bovine lactoferrin

Osteoporosis is a common disease that frequently occurs in the older population, particularly in postmenopausal women. It severely compromises the health of the older population, and the drugs commonly used to treat osteoporosis have a variety of adverse effects. Lactoferrin (LF) is a protein present in milk that has recently been found to exhibit osteogenic activity. Lactoferrin is nontoxic and harmless, suggesting that it may have excellent biocompatibility and tolerability after human consumption. Oral consumption of LF in an ovariectomized rat model has been found to ameliorate osteoporosis. However, the mechanism underlying this effect remains to be clarified. In this study, bovine LF (bLF) was first hydrolyzed by pepsin for 1 h, and the hydrolyzed mixture was freeze-dried and collected. The hydrolyzed mixture was then separated into 5 components (E1-E5), of which E3 had the greatest effect in promoting proliferation of osteoblasts (MC3T3-E1). Component E3 was further isolated into 21 components with preparative reversed phase HPLC, and the E3-15 component had maximal bioactivity. With HPLC-mass spectrometry and peptide sequencing, E3-15 was identified to contain amino acids 97 to 208 from the bLF N terminus. Then, E3-15 was divided into 6 different peptide segments (P1-P6), and the corresponding segments were generated by solid-phase synthesis. Only the P1 peptide (amino acids 97-122 from the N terminus of bLF) significantly promoted osteoblast proliferation. The bioactivity of P1 toward osteoblast cells and alkaline phosphatase activity were tested as a function of P1 concentration, and a nonlinear effect was observed.

Drug Delivery Systems Based on Titania Nanotubes and Active Agents for Enhanced Osseointegration of Bone Implants

TiO2 nanotubes (TNTs) are attractive nanostructures for localized drug delivery. Owing to their excellent biocompatibility and physicochemical properties, numerous functionalizations of TNTs have been attempted for their use as therapeutic agent delivery platforms. In this review, we discuss the current advances in the applications of TNT-based delivery systems with an emphasis on the various functionalizations of TNTs for enhancing osteogenesis at the bone-implant interface and for preventing implant-related infection. Innovation of therapies for enhancing osteogenesis still represents a critical challenge in regeneration of bone defects. The overall concept focuses on the use of osteoconductive materials in combination with the use of osteoinductive or osteopromotive factors. In this context, we highlight the strategies for improving the functionality of TNTs, using five classes of bioactive agents: growth factors (GFs), statins, plant derived molecules, inorganic therapeutic ions/nanoparticles (NPs) and antimicrobial compounds.

The effect of adrenocorticotropic hormone on alpha-2-macroglobulin in osteoblasts derived from human mesenchymal stem cells

Nowadays, alpha-2-macroglobulin (A2M) gene has allocated escalating interest among several genes involved in the pathogenesis of avascular necrosis of the femoral head (ANFH). This molecule could interact with several osteogenic-related proteins. It was reported that adrenocorticotropic hormone (ACTH) affects bones through its receptor located on osteoblasts, suggesting it as a potential target in ANFH treatment. In this study, the effect of ACTH on A2M expression was investigated in osteoblasts as well as during the differentiation of human mesenchymal stem cells (MSCs) into osteoblasts. In this study, MSCs derived from bone marrow were isolated and purified using Ficoll gradient and several passaging. MSCs were characterized by induction with osteogenic and adipogenic medium followed by Oil Red O, Alizarin Red and alkaline phosphatase staining. Besides, MSCs were exposed to various concentrations of ACTH to evaluate the cell variability by MTT assay. MSCs and differentiated osteoblasts were treated with 10-8 molar ACTH for 16 and 26 days, respectively. Then, the total RNA was extracted and A2M expression was quantified by real-time qPCR. The protein expression levels of osteoblast markers including alkaline phosphatase (ALPL) and bone gamma-carboxyglutamate protein (BGLAP) were also measured. The results showed that A2M expression in cells treated with ACTH was up-regulated significantly compared to the control group. Similarly, the expression of osteoblast gene markers including ALPL and BGLAP was significantly increased. ACTH, as an osteoblastic differentiation enhancer, up-regulates A2M, which promotes osteoblastic differentiation probably through TGF-β induction.

Relationship of α2-Macroglobulin with Steroid-Induced Femoral Head Necrosis: A Chinese Population-Based Association Study in Southeast China

Objective

The present study aimed to identify the relationship of α‐2‐macroglobulin and microvascular vessel pathology with steroid‐induced femoral head necrosis in the Southeast Chinese population.

Methods

This study enrolled 40 patients diagnosed with steroid‐induced necrosis of the femoral head. Patients had various stages of femoral head necrosis. The differential expression of serum proteins and mRNA from patients with steroid‐induced necrosis of the femoral head (SINFH) and healthy volunteers was analyzed by western blot and quantitative polymerase chain reaction (QT‐PCR). The pathological change in osteocyte necrosis was indicated by hematoxylin and eosin stain and immunohistochemistry.

Results

Hematoxylin and eosin stain showed histopathology changes in the necrotic area of patients with steroid‐induced INFH: bone trabeculae were fewer and thinner, became broken, fragmented and structurally disordered; intraosseous adipose cells became enlarged; the arrangement of the osteoblasts became irregular; and vacant bone lacunae increased. QT‐PCR showed significantly lower levels of α‐2‐macroglobulin in the serum of patients with SINFH than in controls (P < 0.05). Immunohistochemical staining and western blotting demonstrated that the expression of α‐2‐macroglobulin was significantly decreased in the necrotic area of SINFH patients (P < 0.05).

Conclusion

The α‐2‐macroglobulin may be associated with the pathology of SINFH. The multiple pathological reactions occur in SINFH and α‐2‐macroglobulin may serve as a potential biomarker for the diagnosis of SINFH or a promising therapeutic target.

Nonunion fractures, mesenchymal stem cells and bone tissue engineering

Depending on the duration of healing process, 5-10% of bone fractures may result in either nonunion or delayed union. Because nonunions remain a clinically important problem, there is interest in the utilization of tissue engineering strategies to augment bone fracture repair. Three basic biologic elements that are required for bone regeneration include cells, extracellular matrix scaffolds and biological adjuvants for growth, differentiation and angiogenesis. Mesenchymal stem cells (MSCs) are capable to differentiate into various types of the cells including chondrocytes, myoblasts, osteoblasts, and adipocytes. Due to their potential for multilineage differentiation, MSCs are considered important contributors in bone tissue engineering research. In this review we highlight the progress in the application of biomaterials, stem cells and tissue engineering in promoting nonunion bone fracture healing. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2551-2561, 2018.

α2-Macroglobulins: Structure and Function

α₂-macroglobulins are broad-spectrum endopeptidase inhibitors, which have to date been characterised from metazoans (vertebrates and invertebrates) and Gram-negative bacteria. Their structural and biochemical properties reveal two related modes of action: the "Venus flytrap" and the "snap-trap" mechanisms. In both cases, peptidases trigger a massive conformational rearrangement of α₂-macroglobulin after cutting in a highly flexible bait region, which results in their entrapment. In some homologs, a second action takes place that involves a highly reactive β-cysteinyl-γ-glutamyl thioester bond, which covalently binds cleaving peptidases and thus contributes to the further stabilization of the enzyme:inhibitor complex. Trapped peptidases are still active, but have restricted access to their substrates due to steric hindrance. In this way, the human α₂-macroglobulin homolog regulates proteolysis in complex biological processes, such as nutrition, signalling, and tissue remodelling, but also defends the host organism against attacks by external toxins and other virulence factors during infection and envenomation. In parallel, it participates in several other biological functions by modifying the activity of cytokines and regulating hormones, growth factors, lipid factors and other proteins, which has a great impact on physiology. Likewise, bacterial α₂-macroglobulins may participate in defence by protecting cell wall components from attacking peptidases, or in host-pathogen interactions through recognition of host peptidases and/or antimicrobial peptides. α₂-macroglobulins are more widespread than initially thought and exert multifunctional roles in both eukaryotes and prokaryotes, therefore, their on-going study is essential.

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.

New insights into the pathogenesis of glucocorticoid-induced avascular necrosis: microarray analysis of gene expression in a rat model

Introduction

Avascular necrosis of the femoral head (ANFH) occurs variably after exposure to corticosteroids. Microvascular thrombosis is a common pathological finding. Since systemic thrombophilia is only weakly linked with ANFH, we propose that microvascular vessel pathology may be more related to local endothelial dysfunction and femoral head apoptosis. Corticosteroid effects on the endothelium and resultant apoptosis have been reported. We hypothesize that corticosteroids contribute to a differential gene expression in the femoral head in rats with early ANFH.

Methods

Besides bone marrow necrosis, which is a common sign in ANFH and reported in the early stages, we include the presence of apoptosis in this study as a criterion for diagnosing early disease. Forty Wistar Kyoto (WKY) rats were randomized to either a corticosteroid-treated group or an age-matched control group for six months. After sacrifice, the femoral heads were examined for ANFH. Total mRNA was extracted from femoral heads. Affymetrix exon array (Santa Clara, CA, USA) was performed on 15 selected RNA samples. Validation methods included RT-PCR and immunohistochemistry (IHC).

Results

Although rat exon array demonstrated a significant upregulation of 51 genes (corticosteroid(+)/ANFH(+) VS control), alpha-2-macroglobulin (A2M) gene was particularly over-expressed. Results were validated by RT-PCR and IHC. Importantly, A2M is known to share vascular, osteogenic and cartilage functions relevant for ANFH.

Conclusions

The findings suggest that corticosteroid-induced ANFH in rats might be mediated by A2M. Investigation of A2M as a potential marker, and a treatment target, for early ANFH should be carried out.

Hepcidin, the hormone of iron metabolism, is bound specifically to alpha-2-macroglobulin in blood

Hepcidin is a major regulator of iron metabolism. Hepcidin-based therapeutics/diagnostics could play roles in hematology in the future, and thus, hepcidin transport is crucial to understand. In this study, we identify alpha2-macroglobulin (alpha2-M) as the specific hepcidin-binding molecule in blood. Interaction of 125I-hepcidin with alpha2-M was identified using fractionation of plasma proteins followed by native gradient polyacrylamide gel electrophoresis and mass spectrometry. Hepcidin binding to nonactivated alpha2-M displays high affinity (Kd 177 +/- 27 nM), whereas hepcidin binding to albumin was nonspecific and displayed nonsaturable kinetics. Surprisingly, the interaction of hepcidin with activated alpha2-M exhibited a classical sigmoidal binding curve demonstrating cooperative binding of 4 high-affinity (Kd 0.3 microM) hepcidin-binding sites. This property probably enables efficient sequestration of hepcidin and its subsequent release or inactivation that may be important for its effector functions. Because alpha2-M rapidly targets ligands to cells via receptor-mediated endocytosis, the binding of hepcidin to alpha2-M may influence its functions. In fact, the alpha2-M-hepcidin complex decreased ferroportin expression in J774 cells more effectively than hepcidin alone. The demonstration that alpha2-M is the hepcidin transporter could lead to better understanding of hepcidin physiology, methods for its sensitive measurement and the development of novel drugs for the treatment of iron-related diseases.

Osteogenic growth peptide C-terminal pentapeptide [OGP(10-14)] acts on rat bone marrow mesenchymal stem cells to promote differentiation to osteoblasts and to inhibit differentiation to adipocytes

Cumulative evidence indicates that bone marrow mesenchymal stem cells (MSCs) are multipotent cells capable of differentiating to osteogenic and adipogenic lineages when stimulated under appropriate conditions. Whether OGP(10-14) directly regulates the progenitor cells differentiating into osteoblasts or adipocytes remains unknown. In the present study, we investigated the roles of OGP(10-14) in differentiation along these separate lineages using rat bone marrow MSCs. Our results showed that OGP(10-14) promoted osteogenic differentiation of the stem cells and concurrently inhibited adipocyte formation. OGP(10-14) increased alkaline phosphatase (ALP) activity and mineralized nodule formation, and stimulated osteoblast-specific mRNA expression of core-binding factor 1 (cbfa1). In contrast, OGP(10-14) decreased adipocyte numbers and inhibited adipocyte-specific mRNA expression of peroxisome proliferator-activated receptor-gamma 2 (PPARgamma2). These observations suggest that commitment of MSCs into osteogenic or adipogenic lineages is regulated by OGP(10-14).

Osteogenic growth peptide effects on primary human osteoblast cultures: potential relevance for the treatment of glucocorticoid-induced osteoporosis

The osteogenic growth peptide (OGP) is a naturally occurring tetradecapeptide that has attracted considerable clinical interest as a bone anabolic agent and hematopoietic stimulator. In vivo studies on animals have demonstrated that the synthetic peptide OGP (10-14), reproducing the OGP C-terminal active portion [H-Tyr-Gly-Phe-Gly-Gly-OH] increases bone formation, trabecular bone density and fracture healing. In vitro studies performed on cellular systems based on osteoblastic-like cell lines or mouse stromal cells, have demonstrated that OGP (10-14) increases osteoblast proliferation, alkaline phosphatase (ALKP) activity and matrix synthesis and mineralization. In view of a potential application of OGP (10-14) in clinical therapy, we have tested different concentrations of OGP (10-14) on primary human osteoblast (hOB) cultures. We have observed significant increases of hOB proliferation (+35%), ALKP activity (+60%), osteocalcin secretion (+50%), and mineralized nodules formation (+49%). Our experimental model based on mature hOBs was used to investigate if OGP (10-14) could prevent the effects on bone loss induced by sustained glucocorticoid (GC) treatments. A strong decrease in bone formation has been attributed to the effects of GCs on osteoblastogenesis and osteocyte apoptosis, while an increase in bone resorption was due to a transient osteoblastic stimulation, mediated by the OPG/RANKL/RANK system, of osteoclasts recruitment and activation. Moreover, GCs act on hOBs decreasing the release of osteoprotegerin (OPG) a regulator of the RANKL/RANK interaction. Here, we provide evidences that OGP (10-14) inhibits hOB apoptosis induced by an excess of dexamethasone (-48% of apoptotic cells). Furthermore, we show that OGP (10-14) can increase OPG secretion (+20%) and can restore the altered expression of OPG induced by GCs to physiological levels. Our results support the employment of OGP (10-14) in clinical trials addressed to the treatment of different bone remodeling alterations including the GC-induced osteoporosis.

ERK1/2-activated de Novo Mapkapk2 Synthesis Is Essential for Osteogenic Growth Peptide Mitogenic Signaling in Osteoblastic Cells

In osteoblasts, the mitogen-activated protein kinases ERK1/2 and p38 as well as the cAMP-response element-binding protein (CREB) have been implicated in the regulation of proliferation and differentiation. The osteogenic growth peptide (OGP) is a 14-mer bone cell mitogen that increases bone formation and trabecular bone density and stimulates fracture healing. OGP-(10-14) is the physiologically active form of OGP. Using gene array analysis, real-time reverse transcription-PCR, and immunoblot and DNA synthesis assays we show here that in MC3T3 E1 and newborn mouse calvarial osteoblastic cultures the OGP-(10-14) mitogenic signaling is critically dependent on de novo synthesis of mitogen-activated protein kinase-activated protein kinase 2 (Mapkapk2) mRNA and protein. The increase in Mapkapk2 occurs following short term (5-60 min) stimulation of ERK1/2 activity by OGP-(10-14); phosphorylation of p38 remains unaffected. Downstream of Mapkapk2, CREB is phosphorylated on Ser(133) leading to its enhanced transcriptional activity. That these events are critical for the OGP-(10-14) mitogenic signaling is demonstrated by blocking the effects of OGP-(10-14) on the ERK1/2 pathway, Mapkapk2, CREB, and DNA synthesis using the MEK inhibitor PD098059. The OGP-(10-14) stimulation of CREB transcriptional activity and DNA synthesis is also blocked by Mapkapk2 siRNA. These data define a novel mitogenic signaling pathway in osteoblasts whereby ERK1/2 stimulation of CREB phosphorylation and transcriptional activity as well as DNA synthesis are critically dependent on de novo Mapkapk2 synthesis.

Correlation between the expression of the histone H4 mRNA variant H4-v.1 and the levels of histone H4-(86-100) and H4-(89-102) (OGP) in various rat tissues and alveolar macrophages

We studied the expression of the osteogenic and antinociceptive C-terminal histone H4-related peptide fragments, H4-(89-102) (OGP) and H4-(86-100), respectively, within various rat tissues and isolated alveolar macrophages (AM) by radioimmunoassay (RIA). OGP was located mainly within the bone marrow, spleen, thymus, and lungs whereas H4-(86-100) was more concentrated within the bone marrow, lymph nodes, spinal cord, pituitaries and thymus. The expression pattern of the two peptides showed similarities with the tissue expression pattern of the histone H4 mRNA variant H4-v.1. In rat AM, OGP and H4-(86-100) levels were significantly stimulated (2.6- and 1.9-fold, respectively) by LPS (1 microg/ml), along with H4-v.1 mRNA (4.1-fold), but not whole histone H4 (1.1-fold) nor total histone H4 mRNA (1.1-fold). The results suggest that H4-v.1 mRNA may play a role in the synthesis of the naturally occurring peptides H4-(86-100) and OGP via the alternative translation product H4-(84-102), but not whole histone H4.

Osteogenic growth peptide modulates fracture callus structural and mechanical properties

The osteogenic growth peptide (OGP) is a key factor in the mechanism of the systemic osteogenic response to local bone marrow injury. Recent histologic studies have shown that OGP enhances fracture healing in experimental animals. To assess the effect of systemically administered OGP on the biomechanical and quantitative structural properties of the fracture callus, the present study used an integrated approach to evaluate the early stages (up to 4 weeks) of healing of unstable mid-femoral fractures in rats, which included biomechanical, micro-computed tomographic (microCT) and histomorphometric measurements. During the first 3 weeks after fracture, all the quantitative microCT parameters increased in the OGP- and vehicle-treated animals alike. After 4 weeks, the volume of total callus, bony callus, and newly formed bone was approximately 20% higher in animals administered with OGP, consequent to a decrease in the controls. The 4-week total connectivity was 46% higher in the OGP-treated animals. At this time, bridging between the fracture ends by newly formed bone was observed predominantly in the OGP-treated fractures. After 3 and 4 weeks, the OGP-treated animals showed higher biomechanical toughness of the fracture callus as compared to the PBS controls. Significant correlations between structural and biomechanical parameters were restricted to the OGP-treated rats. These data imply that the osteogenic effect of OGP results in enhanced bridging across the fracture gap and consequently improved function of the fracture callus. Therefore, OGP and/or its derivatives are suggested as a potential therapy for the acceleration of bone regeneration in instances of fracture repair and perhaps other bone injuries.

Evidence for autocrine or paracrine roles of alpha2-macroglobulin in regulation of estradiol production by granulosa cells and development of dominant follicles

alpha(2)-Macroglobulin (alpha(2)-M) inhibits proteinases and modulates the actions of growth factors and cytokines. Despite the key roles proteinases, growth factors, and cytokines have in folliculogenesis, the role of alpha(2)-M in follicular development is unknown. Our objectives were to: 1) determine whether granulosa cells produce alpha(2)-M and have alpha(2)-M receptors, 2) examine the effect of alpha(2)-M on estradiol production by granulosa cells, 3) establish whether amounts of alpha(2)-M and alpha(2)-M receptors were altered during dominant nonovulatory follicle development, and 4) examine alpha(2)-M's mechanism of action. The results demonstrated that bovine granulosa cells contain 5.2- and 15-kb mRNAs and 720- and 500-kDa proteins that correspond, respectively, to sizes of mRNAs and proteins for alpha(2)-M and the alpha(2)-M receptor. Treatment of granulosa cells with alpha(2)-M resulted in a specific dose-responsive increase in estradiol production. Cell viability, cell number, and the amount of aromatase in granulosa cells were not altered by alpha(2)-M. Treatment of granulosa cells with factors that bind alpha(2)-M or its receptor did not mimic alpha(2)-M action. Although intrafollicular amounts of alpha(2)-M remained unchanged, amounts of alpha(2)-M receptor in granulosa cells were strongly inversely associated with concentrations of estradiol in dominant and subordinate follicles. Based on these results, we concluded that alpha(2)-M may have autocrine or paracrine roles in granulosa cells potentially important for regulation of estradiol production and development of dominant follicles.

Fluorescence monitoring of the conformational change in alpha 2-macroglobulin induced by trypsin under second-order conditions: the macroglobulin acts both as a substrate and a competitive inhibitor of the protease

The reaction of bovine pancreatic trypsin with human plasma alpha(2)-macroglobulin (alpha(2)M) was studied at 25 degrees C, using equimolar mixtures of E and I in 50 mM potassium phosphate buffer, pH 7. The conformational change in alpha(2)M was monitored through the increase in protein fluorescence at 320 nm (exc lambda, 280 nm). At [alpha(2)M](0) =[E](0) =11.5-200 nM, the fluorescence change data fit the integrated second-order rate equation, (F(infinity) -F(0) )/(F(infinity) -F(t) )=1+k(i,obsd) [alpha(2)M](0) t, indicating that cleavage of the bait region in alpha(2)M was the rate-determining step. The apparent rate constant (k(i,obsd)) was found to be inversely related to reactant concentration. The kinetic behavior of the system was compatible with a model involving reversible, nonbait region binding of E to alpha(2)M, competitively limiting the concentration of E available for bait region cleavage. The intrinsic value of k(i) was (1.7+/-0.24) x 10(7) M(-1) s(-1).K(p), the inhibitory constant associated with peripheral binding, was estimated to be in the submicromolar range. The results of the present study point to a potential problem in interpreting kinetic data relating to protease-induced structural changes in macromolecular substrates. If there is nonproductive binding, as in the case of trypsin and alpha(2)M, and the reactions are monitored under pseudo first-order conditions ([S](0) >>[E](0) ), an intrinsically second-order process (such as the rate-limiting bait region cleavage in alpha(2)M) may become kinetically indistinguishable from an intrinsically first-order process (e.g. rate-limiting conformational change). Hence an excess of one component over the other should be avoided in kinetic studies addressing such systems.

Osteogenic growth peptide: from concept to drug design

Recently, the osteogenic growth peptide (OGP) and its C-terminal pentapeptide H-Tyr-Gly-Phe-Gly-Gly-OH [OGP(10-14)] have attracted considerable clinical interest as bone anabolic agents and hematopoietic stimulators. They are present in mammalian serum in micromolar concentrations, increase bone formation and trabecular bone density, and stimulate fracture healing when administered to mice and rats. In cultures of osteoblastic and other bone marrow stromal cells, derived from human and other mammalian species, OGP regulates proliferation, alkaline phosphatase activity and matrix mineralization via an autocrine/paracrine mechanism. In vivo it also regulates the expression of type I collagen and the receptor for basic fibroblast growth factor. In addition, OGP and OGP(10-14) enhance hematopoiesis, including the stimulation of bone marrow transplant engraftment and hematopoietic regeneration after ablative chemotherapy. Apparently, the hematopoietic effects of these peptides are secondary to their effect on the bone marrow stroma. Detailed structure-activity relationship study identified the side chains of Tyr(10) and Phe(12) as the principal pharmacophores for OGP-like activity. Recently, it has been demonstrated that several cyclostereoisomers of OGP(10-14), including the analogue retro-inverso (Gly-Gly-D-Phe-Gly-D-Tyr), share the full spectrum of OGP-like bioactivities. Taken together, OGP represents an interesting case of a "housekeeping" peptide that plays an important role in osteogenesis and hematopoiesis, and interacts with its putative macromolecular target via distinct pharmacophores presented in a specific spatial organization.

Bioactive pseudopeptidic analogues and cyclostereoisomers of osteogenic growth peptide C-terminal pentapeptide, OGP(10-14)

The osteogenic growth peptide (OGP) is a key factor in the mechanism of the systemic osteogenic response to local bone marrow injury. When administered in vivo, OGP stimulates osteogenesis and hematopoiesis. The C-terminal pentapeptide OGP(10-14) is the minimal amino acid sequence that retains the full OGP-like activity. Apparently, it is also the physiologic active form of OGP. Residues Tyr(10), Phe(12), Gly(13), and Gly(14) of OGP are essential for the OGP(10-14) activity. The present study explored the functional role of the peptide bonds, carboxyl and amino terminal groups, and conformational freedom in OGP(10-14). Transformations replacing the peptide bonds with surrogates such as Psi(CH(2)NH), Psi(CONMe), and Psi(CH(2)CH(2)) demonstrated that amide bonds do not contribute significantly to OGP(10-14) bioactivity. End-to-end cyclization yielded the fully bioactive cyclic pentapeptide c(Tyr-Gly-Phe-Gly-Gly). The retroinverso analogue c(Gly-Gly-phe-Gly-tyr), a cyclostereoisomer of c(Tyr-Gly-Phe-Gly-Gly), is at least as potent as the parent cyclic pentapeptide. The unique structure-activity relations revealed in this study suggest that the spatial presentation of the Tyr and Phe side chains has a major role in the productive interaction of OGP(10-14) and its truncated and conformationally constrained analogues with their cognate cellular target.

The effect of osteogenic growth peptide (OGP) on proliferation and adhesion of HEMC-1 human endothelial cells

Human osteogenic growth peptide (OGP) promotes the growth of osteoblastic, fibroblastic and bone marrow stromal cells. There is no evidence that OGP stimulates the growth or the attachment of endothelial cells to the extracellular matrix. The aim of this study was to test OGP on in vitro cultures of human microvascular endothelial HEMC-1 cells and to characterize its potential angiogenic effect when administered alone or in combination with vascular endothelial growth factor (VEGF) or its binding protein alpha(2)-macroglobulin (alpha(2)M). HEMC-1 cells were cultured in vitro under serum-free conditions to study the effects of OGP (10(-14)- 10(-10)M), VEGF (100 ng ml(-1)), alpha(2)M (20 ng ml(-1)) and their combinations on cell proliferation for 48 h. Furthermore, an adhesion assay was performed incubating the HEMC-1 cells with OGP, VEGF, alpha(2)M and their combinations for 24 h. OGP, alpha(2)M and their combination did not stimulate proliferation of HEMC-1 cells; in contrast, VEGF caused a significant enhancement of cell growth ( +37.3 %;P< 0.05). Pre-incubation with VEGF resulted in a fast and increased adhesion of endothelial cells to the matrix as compared to controls ( +87.5 % at 30 min and +86.6 % at 70 min, P< 0.05); in contrast, incubation with OGP alone determined only a significant increase in the attachment at 100 min ( +52 %;P< 0.05). The combinations of these peptides did not cause significant additive effects. These results suggest that OGP, compared to VEGF, induced neither the proliferation nor an increase in attachment of HEMC-1 cells to a matrix, either alone or in combination with VEGF and alpha(2)M. These in vitro findings may suggest a possible administration of OGP, as a haematopoietic factor, to patients affected by pathological conditions involving angiogenesis.

Mitogenic G(i) protein-MAP kinase signaling cascade in MC3T3-E1 osteogenic cells: activation by C-terminal pentapeptide of osteogenic growth peptide [OGP(10-14)] and attenuation of activation by cAMP

In osteogenic and other cells the mitogen-activated protein (MAP) kinases have a key role in regulating proliferation and differentiated functions. The osteogenic growth peptide (OGP) is a 14 mer mitogen of osteogenic and fibroblastic cells that regulates bone turnover, fracture healing, and hematopoiesis, including the engraftment of bone marrow transplants. It is present in the serum and extracellular fluid either free or complexed to OGP-binding proteins (OGPBPs). The free immunoreactive OGP consists of the full length peptide and its C-terminal pentapeptide OGP(10-14). In the present study, designed to probe the signaling pathways triggered by OGP, we demonstrate in osteogenic MC3T3 E1 cells that mitogenic doses of OGP(10-14), but not OGP, enhance MAP kinase activity in a time-dependent manner. The OGP(10-14)-induced stimulation of both MAP kinase activity and DNA synthesis were abrogated by pertusis toxin, a G(i) protein inhibitor. These data offer direct evidence for the occurrence in osteogenic cells of a peptide-activated, mitogenic Gi protein-MAP kinase-signaling cascade. Forskolin and dBu(2)-cAMP abrogated the OGP(10-14)-stimulated proliferation, but induced only 50% inhibition of the OGP(10-14)-mediated MAP kinase activation, suggesting additional MAP kinase-dependent, OGP(10-14)-regulated, cellular functions. Finally, it is demonstrated that OGP(10-14) is the active form of OGP, apparently generated proteolytically in the extracellular milieu upon dissociation of OGP-OGPBP complexes.

Structure-bioactivity of C-terminal pentapeptide of osteogenic growth peptide [OGP(10-14)]

The amino acid sequence of osteogenic growth peptide (OGP) consists of 14 residues identical to the C-terminal tail of histone H4. Native and synthetic OGP are mitogenic to osteoblastic and fibroblastic cells and enhance osteogenesis and hematopoiesis in vivo. The C-terminal truncated pentapeptide of OGP, H-Tyr-Gly-Phe-Gly-Gly-OH [OGP(10-14)], is a naturally occurring osteoblastic mitogen, equipotent to OGP. The present study assesses the role of individual amino acid residues and side chains in the OGP(10-14) mitogenic activity which showed a very high correlation between osteoblastic and fibroblastic cell cultures. Truncation of either Tyr10 or its replacement by Ala or D-Ala resulted in substantial, but not complete, loss of activity. Nevertheless, only a small loss of activity was observed following removal of the Tyr10 amino group. No further loss occurred consequent to the monoiodination of desaminoTyr10 on meta-position. However, a marked decrease in proliferative activity followed removal of the Tyr10 phenolic or the Phe12 aromatic group. Loss of activity of a similar magnitude also occurred subsequent to replacing Gly11 with L- or D-Ala. Approximately 50% loss of mitogenic activity occurred subsequent to truncation of Gly14 or blocking the C-terminal group as the methyl ester. All other modifications of the C-terminus and L- or D-Ala substitution of Gly13 resulted in 70-97% decrease in activity. Collectively, these data suggest that the integrity of the pharmacophores presented by Tyr and Phe side chains, as well as the Gly residues at the C-terminus, are important for optimal bioactivity of OGP(10-14).

Osteogenic growth peptide normally stimulated by blood loss and marrow ablation has local and systemic effects on fracture healing in rats

Osteogenic growth peptide, a histone H4-related, 14-amino-acid peptide, is an active mediator of local, as well as systemic, osteogenic activity in response to marrow ablation, trauma, and blood loss. In this study, the effect of exogenous osteogenic growth peptide on the healing of femoral fractures in rats was investigated. A fracture at the midshaft of the femur was created in 50 rats. Half of the rats were injected subcutaneously with 25 ng of osteogenic growth peptide per rat per day for the first 7 days after fracture. Radiographs were taken each week, and the diameter of the callus was measured. The femurs of four animals from each group were harvested 1, 2, 3, and 4 weeks after fracture. Two femurs from each group were sectioned for histologic examination, and two were sectioned for measurement of density and mineral content. Marrow was aspirated from the contralateral femurs to establish adhering cell cultures, which were examined for osteogenicity. At 2 weeks, a large increase in mitogenicity and osteogenicity was seen in the marrow-derived cultures from the rats treated with osteogenic growth peptide; this increase was sustained through 4 weeks. Extraction of RNA from the contralateral marrow (systemic expression) and callus (local expression) for amplification with reverse transcription-polymerase chain reaction revealed greater systemic expression of transforming growth factors beta1, beta2, and beta3, fibroblast growth factor-2, insulin-like growth factor-1, and aggrecan throughout the 4 weeks after fracture, whereas types IIA and IIB collagen, link protein, and fibroblast growth factor receptor-3 had a greater local expression. The specimens treated with osteogenic growth peptide had a stronger expression of transforming growth factor-beta1, both locally and systemically. The average diameter of the callus was greater for the treated rats at all time intervals, and peak diameters were 7.58 mm at 3 weeks for the treated rats and 6.64 mm at 2 weeks and 6.63 mm at 3 weeks for the controls. Histological study revealed an earlier organization and faster healing of the treated fractures, as evidenced by the larger, earlier appearance of cartilaginous soft callus and the more rapid organization of bridging trabecular bone. No statistical significance was obtained when these comparisons were made between the groups. These results suggest that osteogenic growth peptide can be used to promote earlier proliferation and differentiation of osteogenic cells in marrow and bone-repair callus, possibly through its effect on the transforming growth factor-beta family.

Isolation of mitogenically active C-terminal truncated pentapeptide of osteogenic growth peptide from human plasma and culture medium of murine osteoblastic cells

The osteogenic growth peptide (OGP) is a 14-amino acid stromal cell mitogen that stimulates in vivo osteogenesis and hematopoiesis. In the blood circulation and cell culture conditioned medium immunoreactive OGP (irOGP), identified using antibodies raised against the OGP C-terminal region, presents free and bound forms. The bound form consists entirely of the full length peptide. The present study was designed to investigate the identity of free irOGP under nondenaturing conditions. Fresh human serum and culture medium conditioned with murine osteoblastic MC3T3 E1 cells were fractionated using ultrafiltration (3000 molecular weight cut-off). Hydrophobic chromatography of the ultrafiltrate, immunoscreening of chromatographic fractions with antibodies directed against the OGP C-terminal region and amino acid sequencing of immunoreactive peaks demonstrated the presence of two mitogens, the full length OGP and a C-terminal truncated form, OGP(10-14). The OGP(10-14) derived from both serum and conditioned medium, as well as the synthetic pentapeptide [sOGP(10-14)], shared the in vitro OGP proliferative activity. However, in a competitive binding assay, devised to assess the OGP-OGP binding protein (OGPBP) complex formation, sOGP(10-14) failed to compete out radiolabeled OGP from the complex. It is concluded that OGP(10-14) is a naturally occurring human and murine mitogen. In addition, the data suggests that the OGP(10-14) is generated from OGP by proteolytic cleavage upon dissociation of the OGP-OGPBP complexes.