Immunolocalisation of vascular endothelial growth factor (VEGF) in human neonatal growth plate cartilage

Mind Gaps and Bone Snaps: Exploring the Connection Between Alzheimer's Disease and Osteoporosis

PURPOSE OF REVIEW

This comprehensive review discusses the complex relationship between Alzheimer's disease (AD) and osteoporosis, two conditions that are prevalent in the aging population and result in adverse complications on quality of life. The purpose of this review is to succinctly elucidate the many commonalities between the two conditions, including shared pathways, inflammatory and oxidative mechanisms, and hormonal deficiencies.

RECENT FINDINGS

AD and osteoporosis share many aspects of their respective disease-defining pathophysiology. These commonalities include amyloid beta deposition, the Wnt/β-catenin signaling pathway, and estrogen deficiency. The shared mechanisms and risk factors associated with AD and osteoporosis result in a large percentage of patients that develop both diseases. Previous literature has established that the progression of AD increases the risk of sustaining a fracture. Recent findings demonstrate that the reverse may also be true, suggesting that a fracture early in the life course can predispose one to developing AD due to the activation of these shared mechanisms. The discovery of these commonalities further guides the development of novel therapeutics in which both conditions are targeted. This detailed review delves into the commonalities between AD and osteoporosis to uncover the shared players that bring these two seemingly unrelated conditions together. The discussion throughout this review ultimately posits that the occurrence of fractures and the mechanism behind fracture healing can predispose one to developing AD later on in life, similar to how AD patients are at an increased risk of developing fractures. By focusing on the shared mechanisms between AD and osteoporosis, one can better understand the conditions individually and as a unit, thus informing therapeutic approaches and further research. This review article is part of a series of multiple manuscripts designed to determine the utility of using artificial intelligence for writing scientific reviews.

From the Mind to the Spine: The Intersecting World of Alzheimer's and Osteoporosis

PURPOSE OF REVIEW

This comprehensive review delves into the intricate interplay between Alzheimer's disease (AD) and osteoporosis, two prevalent conditions with significant implications for individuals' quality of life. The purpose is to explore their bidirectional association, underpinned by common pathological processes such as aging, genetic factors, inflammation, and estrogen deficiency.

RECENT FINDINGS

Recent advances have shown promise in treating both Alzheimer's disease (AD) and osteoporosis by targeting disease-specific proteins and bone metabolism regulators. Monoclonal antibodies against beta-amyloid and tau for AD, as well as RANKL and sclerostin for osteoporosis, have displayed therapeutic potential. Additionally, ongoing research has identified neuroinflammatory genes shared between AD and osteoporosis, offering insight into the interconnected inflammatory mechanisms. This knowledge opens avenues for innovative dual-purpose therapies that could address both conditions, potentially revolutionizing treatment approaches for AD and osteoporosis simultaneously. This review underscores the potential for groundbreaking advancements in early diagnosis and treatment by unraveling the intricate connection between AD and bone health. It advocates for a holistic, patient-centered approach to medical care that considers both cognitive and bone health, ultimately aiming to enhance the overall well-being of individuals affected by these conditions. This review article is part of a series of multiple manuscripts designed to determine the utility of using artificial intelligence for writing scientific reviews.

Bone angiocrine factors

Angiogenesis in the bone is unique and involves distinctive signals. Whether they are created through intramembranous ossification or endochondral ossification, bones are highly vascularized tissues. Long bones undergo a sequence of processes known as endochondral osteogenesis. Angiogenesis occurs during the creation of endochondral bone and is mediated by a variety of cells and factors. An initially avascular cartilage template is invaded by blood vessels from the nearby subchondral bone thanks to the secreted angiogenic chemicals by hypertrophic chondrocytes. Vascular endothelial growth factor (VEGF), one of several angiogenic molecules, is a significant regulator of blood vessel invasion, cartilage remodeling, and ossification of freshly created bone matrix; chondrocyte proliferation and hypertrophy are facilitated by the production of VEGFA and VEGF receptor-2 (VEGFR-2), which is stimulated by fibroblast growth factors (FGFs). NOTCH signaling controls blood capillaries formation during bone maturation and regeneration, while hypoxia-inducible factor 1 alpha (HIF1-a) promotes chondrocyte development by switching to anaerobic metabolism. To control skeletal remodeling and repair, osteogenic cells release angiogenic factors, whereas endothelial cells secrete angiocrine factors. One of the better instances of functional blood vessels specialization for certain organs is the skeletal system. A subpopulation of capillary endothelial cells in the bone regulate the activity of osteoprogenitor cells, which in turn affects bone formation during development and adult homeostasis. Angiogenesis and osteogenesis are strictly connected, and their crosstalk is essential to guarantee bone formation and to maintain bone homeostasis. Additionally, pathological processes including inflammation, cancer, and aging include both bone endothelial cells and angiocrine factors. Therefore, the study and understanding of these mechanisms is fundamental, because molecules and factors involved may represent key targets for novel and advanced therapies.

Growing Pains: The Need for Engineered Platforms to Study Growth Plate Biology

Growth plates, or physis, are highly specialized cartilage tissues responsible for longitudinal bone growth in children and adolescents. Chondrocytes that reside in growth plates are organized into three distinct zones essential for proper function. Modeling key features of growth plates may provide an avenue to develop advanced tissue engineering strategies and perspectives for cartilage and bone regenerative medicine applications and a platform to study processes linked to disease progression. In this review, a brief introduction of the growth plates and their role in skeletal development is first provided. Injuries and diseases of the growth plates as well as physiological and pathological mechanisms associated with remodeling and disease progression are discussed. Growth plate biology, namely, its architecture and extracellular matrix organization, resident cell types, and growth factor signaling are then focused. Next, opportunities and challenges for developing 3D biomaterial models to study aspects of growth plate biology and disease in vitro are discussed. Finally, opportunities for increasingly sophisticated in vitro biomaterial models of the growth plate to study spatiotemporal aspects of growth plate remodeling, to investigate multicellular signaling underlying growth plate biology, and to develop platforms that address key roadblocks to in vivo musculoskeletal tissue engineering applications are described.

Manufacturing functional hydrogels for inducing angiogenic-osteogenic coupled progressions in hard tissue repairs: prospects and challenges

In large bone defects, inadequate vascularization within the engineered constructs has been a major challenge in developing clinically impactful products. It is fairly determined that bone tissues and blood vessels are established concurrently throughout tissue repairs after an injury. Thus, the coupling of angiogenesis-osteogenesis is an essential course of action in bone tissue restoration. The manufacture of biomaterial-based scaffolds plays a decisive role in stimulating angiogenic and osteogenic progressions (instruction of neovascularization and bone mineralization). Bone hydrogels with optimal conditions are more efficient at healing bone defects. There has been a remarkable advancement in producing bone substitutes in the tissue engineering area, but the sufficient and timely vascularization of engineered constructs for optimal tissue integration and regeneration is lacking due to mismatch in the scaffold characteristics and new bone tissue reconstruction. Therefore, various key challenges remain to be overcome. A deep understanding of angiogenesis and osteogenesis progressions is required to manufacture bone hydrogels with satisfactory results. The current review briefly discusses the fundamentals of bone tissues, the significance of angiogenesis-osteogenesis progressions and their inducers, the efficacy of biomaterials and composite hydrogel-promoted neo-vasculogenesis (i.e. angiogenesis) and bone mineralization (i.e. osteogenesis), and related challenges, including future research directions.

Antagonism Between PEDF and TGF-β Contributes to Type VI Osteogenesis Imperfecta Bone and Vascular Pathogenesis

Osteogenesis imperfecta (OI) is a heterogeneous genetic disorder of bone and connective tissue, also known as brittle bone disease. Null mutations in SERPINF1, which encodes pigment epithelium-derived factor (PEDF), cause severe type VI OI, characterized by accumulation of unmineralized osteoid and a fish-scale pattern of bone lamellae. Although the potent anti-angiogenic activity of PEDF has been extensively studied, the disease mechanism of type VI OI is not well understood. Using Serpinf1(-/-) mice and primary osteoblasts, we demonstrate that loss of PEDF delays osteoblast maturation as well as extracellular matrix (ECM) mineralization. Barium sulfate perfusion reveals significantly increased vessel density in the tibial periosteum of Serpinf1(-/-) mouse compared with wild-type littermates. The increased bone vascularization in Serpinf1(-/-) mice correlated with increased number of CD31(+)/Endomucin(+) endothelial cells, which are involved in the coupling angiogenesis and osteogenesis. Global transcriptome analysis by RNA-Seq of Serpinf1(-/-) mouse osteoblasts reveals osteogenesis and angiogenesis as the biological processes most impacted by loss of PEDF. Intriguingly, TGF-β signaling is activated in type VI OI cells, and Serpinf1(-/-) osteoblasts are more sensitive to TGF-β stimulation than wild-type osteoblasts. TGF-β stimulation and PEDF deficiency showed additive effects on transcription suppression of osteogenic markers and stimulation of pro-angiogenic factors. Furthermore, PEDF attenuated TGF-β-induced expression of pro-angiogenic factors. These data suggest that functional antagonism between PEDF and TGF-β pathways controls osteogenesis and bone vascularization and is implicated in type VI OI pathogenesis. This antagonism may be exploited in developing therapeutics for type VI OI utilizing PEDF and TGF-β antibody. © 2022 American Society for Bone and Mineral Research (ASBMR). This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

The Actions of IGF-1 in the Growth Plate and Its Role in Postnatal Bone Elongation

PURPOSE OF REVIEW

Bone elongation is a complex process driven by multiple intrinsic (hormones, growth factors) and extrinsic (nutrition, environment) variables. Bones grow in length by endochondral ossification in cartilaginous growth plates at ends of developing long bones. This review provides an updated overview of the important factors that influence this process.

RECENT FINDINGS

Insulin-like growth factor-1 (IGF-1) is the major hormone required for growth and a drug for treating pediatric skeletal disorders. Temperature is an underrecognized environmental variable that also impacts linear growth. This paper reviews the current state of knowledge regarding the interaction of IGF-1 and environmental factors on bone elongation. Understanding how internal and external variables regulate bone lengthening is essential for developing and improving treatments for an array of bone elongation disorders. Future studies may benefit from understanding how these unique relationships could offer realistic new approaches for increasing bone length in different growth-limiting conditions.

Effect of CBX7 deficiency on the socket healing after tooth extractions

CBX7 is shown to down-regulate the expression of osteopontin (OPN) that is associated with osteoblast function. Here, we studied the role of CBX7 in the wound healing of tooth extraction socket in which osteoblast activity is critical via comparison between CBX7-knockout (CBX7-/-) mice and their wild-type (WT) counterparts of 6 weeks old with maxillary first molar extracted. Mice were euthanized at 7, 14, and 21 days after extractions, and alveolar sockets were assessed by semi-quantitative histomorphometry for hard tissue healing, including new bone fill (Masson's trichrome staining), osteoblast activity (OPN/osterix, Osx), osteoclast activity (tartrate-resistant acid phosphatase, TRAP), and for soft tissue healing, including blood vessels (alpha smooth muscle actin, α-SMA). Also, the bone microarchitecture was evaluated by micro-CT. In radiological analysis, CBX7-/- mice increased bone mass significantly more than WT mice did. Consistently, both the amount of new bone fill and OPN/Osx-immunopositive cells in the extraction sockets were significantly increased in CBX7-/- mice at each time point with respect to their WT siblings, while osteoclast number exhibited a trend of more increase in CBX7-/- mice at all time points as well. In agreement with enhanced bone formation during socket healing, significantly elevated α-SMA-immunopositive area was noted in CBX7-/- mice in contrast to WT mice. Taken together, these data suggest that CBX7 deficiency has a positive effect on tooth extraction socket healing.

Bone regeneration strategy by different sized multichanneled biphasic calcium phosphate granules: In vivo evaluation in rabbit model

A variety of synthetic materials are currently in use as bone substitutes, among them a new calcium phosphate-based multichannel, cylindrical, granular bone substitute that is showing satisfactory biocompatibility and osteoconductivity in clinical applications. These cylindrical granules differ in their mechanical and morphological characteristics such as size, diameter, surface area, pore size, and porosity. The aim of this study is to investigate whether the sizes of these synthetic granules and the resultant inter-granular spaces formed by their filling critical-sized bone defects affect new bone formation characteristics and to determine the best formulations from these individual types by combining the granules in different proportions to optimize the bone tissue regeneration. We evaluated two types of multichanneled cylindrical granules, 1 mm and 3 mm in diameter, combined the granules in two different proportions (wt%), and compared their different mechanical, morphological, and in vitro and in vivo biocompatibility characteristics. We assessed in vitro biocompatibility and cytotoxicity using MC3T3-E1 osteoblast-like cells using MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and confocal imaging. In vivo investigation in a rabbit model indicated that all four samples formed significantly better bone than the control after four weeks and eight weeks of implantation. Micro-computed tomography analysis showed more bone formation by the 1 mm cylindrical granules with 160 ± 10 µm channeled pore and 50% porosity than the other three samples ( p<.05), which we confirmed by histological analysis.

Sclerostin stimulates angiogenesis in human endothelial cells

Sclerostin, negative regulator of bone formation, has been originally known as an osteocyte product. Recently, it has been also detected in hypertrophic chondrocytes, distinctive cells of avascular cartilage which is invaded by capillaries and then replaced by vascularized bone. Thus, we hypothesized that sclerostin, in addition to its role already known, may exert an angiogenic activity. We first proved that sclerostin increased the proliferation of human umbilical vein endothelial cells (HUVECs), and next, by using the chicken chorioallantoic membrane (CAM) in vivo assay, we demonstrated that it exerts an angiogenic activity similar to that of vascular endothelial growth factor (VEGF). This last finding was reinforced by several in vitro approaches. Indeed, we showed that sclerostin induced the formation of a network of anastomosing tubules, a significant increase in the percentage of tubule number, total tubule length and number of junctions, as well as the ability of sclerostin-stimulated HUVECs to organize capillary-like structures and closed-meshes similar to VEGF. The angiogenic response elicited by the protein may be due to the binding to its receptor, LRP6, which is highly expressed at mRNA and protein levels by sclerostin treated HUVECs and through the production of two well-known pro-angiogenic cytokines, VEGF and placental growth factor (PlGF). Finally, we demonstrated that sclerostin was also responsible for the recruitment of osteoclasts and their circulating monocyte progenitors. Overall, these findings showed for the first time the new angiogenic in vitro role of sclerostin which could be also considered as a novel molecule in angiogenesis-osteogenesis coupling.

CD31hiEmcnhi Vessels Support New Trabecular Bone Formation at the Frontier Growth Area in the Bone Defect Repair Process

CD31hiEmcnhi vessels were a subtype of vessels in the murine skeletal system, with high levels of platelet and endothelial cell adhesion molecule-1 (PECAM-1/CD31) and endomucin (Emcn). They were reported coupling angiogenesis and osteogenesis during bone development. We investigated the distribution of these vessels in rat tibiae and their temporal and spatial distribution during the bone defect repair process to improve our understanding of the importance of these vessels. We confirmed that CD31hiEmcnhi vessels were specially distributed around the trabecular bones near metaphysis and endosteum in rat tibiae. At 3 days post bone injury, CD31hiEmcnhi vessels proliferated and were extensively distributed across the entire repair area. At 7 and 14 days post-injury, these vessels decreased but were specially distributed around the growing trabecular bones near the frontier growth area, suggesting that these vessels support new bone formation. The distribution of CD31hiEmcnhi vessels and the transcriptions of Hif-1α and VEGFA, as well as BMP2 and Osterix decreased at 7 and 14 days post-injury under osteoporotic conditions, in combination with insufficient osteogenesis. Our research is of great significance to help understand the important role of CD31hiEmcnhi vessels in supporting new trabecular bones formation during bone defect repair process.

Vascular Canals in Permanent Hyaline Cartilage: Development, Corrosion of Nonmineralized Cartilage Matrix, and Removal of Matrix Degradation Products

Core areas in voluminous pieces of permanent cartilage are metabolically supplied via vascular canals (VCs). We studied cartilage corrosion and removal of matrix degradation products during the development of VCs in nose and rib cartilage of piglets. Conventional staining methods were used for glycosaminoglycans, immunohistochemistry was performed to demonstrate collagens types I and II, laminin, Ki-67, von Willebrand factor, VEGF, macrophage marker MAC387, S-100 protein, MMPs -2,-9,-13,-14, and their inhibitors TIMP1 and TIMP2. VCs derived from connective tissue buds that bulged into cartilage matrix ("perichondrial papillae", PPs). Matrix was corroded at the tips of PPs or resulting VCs. Connective tissue stromata in PPs and VCs comprised an axial afferent blood vessel, peripherally located wide capillaries, fibroblasts, newly synthesized matrix, and residues of corroded cartilage matrix (collagen type II, acidic proteoglycans). Multinucleated chondroclasts were absent, and monocytes/macrophages were not seen outside the blood vessels. Vanishing acidity characterized areas of extracellular matrix degradation ("preresorptive layers"), from where the dismantled matrix components diffused out. Leached-out material stained in an identical manner to intact cartilage matrix. It was detected in the stroma and inside capillaries and associated downstream veins. We conclude that the delicate VCs are excavated by endothelial sprouts and fibroblasts, whilst chondroclasts are specialized to remove high volumes of mineralized cartilage. VCs leading into permanent cartilage can be formed by corrosion or inclusion, but most VCs comprise segments that have developed in either of these ways. Anat Rec, 300:1067-1082, 2017. © 2016 Wiley Periodicals, Inc.

Review of the Effects of Anti-Angiogenic Compounds on the Epiphyseal Growth Plate

The formation of new blood vessels from a pre-existing vascular bed, termed “angiogenesis,” is of critical importance for the growth and development of the animal since it is required for the growth of the skeleton during endochondral ossification, development and cycling of the corpus luteum and uterus, and for the repair of tissues during wound healing. “Vasculogenesis,” the de novo formation of blood vessels is also important for the proper function and development of the vascular system in the embryo. New blood vessel formation is a prominent feature and permissive factor in the relentless progression of many human diseases, one of the most important examples of which is neoplasia. It is for this reason that angiogenesis is considered to be one of the hallmarks of cancer. The development of new classes of drugs that inhibit the growth and proper functioning of new blood vessels in vivo is likely to provide significant therapeutic benefit in the treatment of cancer, as well as other conditions where angiogenesis is a strong driver to the disease process. During the preclinical safety testing of these drugs, it is becoming increasingly clear that their in vivo efficacy is reflected in the profile of “expected toxicity” (resulting from pharmacology) observed in laboratory animals, so much so, that this profile of “desired” toxicity may act as a signature for their anti-angiogenic effect. In this article we review the major mechanisms controlling angiogenesis and its role during endochondral ossification. We also review the effects of perturbation of endochondral ossification through four mechanisms—inhibition of vascular endothelial growth factor (VEGF), pp60 c-Src kinase and matrix metalloproteinases as well as disruption of the blood supply with vascular targeting agents. Inhibition through each of these mechanisms appears to have broadly similar effects on the epiphyseal growth plate characterised by thickening due to the retention of hypertrophic chondrocytes resulting from the inhibition of angiogenesis. In contrast, in the metaphysis there are differing effects reflecting the specific role of these targets at this site.

Role of angiogenesis in bone repair

Bone vasculature plays a vital role in bone development, remodeling and homeostasis. New blood vessel formation is crucial during both primary bone development as well as fracture repair in adults. Both bone repair and bone remodeling involve the activation and complex interaction between angiogenic and osteogenic pathways. Interestingly studies have demonstrated that angiogenesis precedes the onset of osteogenesis. Indeed reduced or inadequate blood flow has been linked to impaired fracture healing and old age related low bone mass disorders such as osteoporosis. Similarly the slow penetration of host blood vessels in large engineered bone tissue grafts has been cited as one of the major hurdle still impeding current bone construction engineering strategies. This article reviews the current knowledge elaborating the importance of vascularization during bone healing and remodeling, and the current therapeutic strategies being adapted to promote and improve angiogenesis.

Cartilage to bone transitions in health and disease

Aberrant redeployment of the 'transient' events responsible for bone development and postnatal longitudinal growth has been reported in some diseases in what is otherwise inherently 'stable' cartilage. Lessons may be learnt from the molecular mechanisms underpinning transient chondrocyte differentiation and function, and their application may better identify disease aetiology. Here, we review the current evidence supporting this possibility. We firstly outline endochondral ossification and the cellular and physiological mechanisms by which it is controlled in the postnatal growth plate. We then compare the biology of these transient cartilaginous structures to the inherently stable articular cartilage. Finally, we highlight specific scenarios in which the redeployment of these embryonic processes may contribute to disease development, with the foresight that deciphering those mechanisms regulating pathological changes and loss of cartilage stability will aid future research into effective disease-modifying therapies.

Interleukin-1β promotes proliferation and inhibits differentiation of chondrocytes through a mechanism involving down-regulation of FGFR-3 and p21

The proinflammatory cytokine IL-1β is elevated in many childhood chronic inflammatory diseases as well as obesity and can be associated with growth retardation. Here we show that IL-1β affects bone growth by directly disturbing the normal sequence of events in the growth plate, resulting in increased proliferation and widening of the proliferative zone, whereas the hypertrophic zone becomes disorganized, with impaired matrix structure and increased apoptosis and osteoclast activity. This was also evident in vitro: IL-1β increased proliferation and caused a G1-to-S phase shift in the cell cycle in ATDC5 chondrocytes, accompanied by a reduction in fibroblast growth factor receptor-3 (FGFR-3) and its downstream gene, the cell-cycle inhibitor p21 and its family member p57, whereas the cell-cycle promoter E2F-2 was increased. The reduction in FGFR-3, p21, and p57 was followed by delayed cell differentiation, manifested by decreases in proteoglycan synthesis, mineralization, alkaline phosphatase activity, and the expression of Sox9, RunX2, collagen type II, collagen type X, and other matrix proteins. Taken together, we suggest that IL-1β alters normal chondrogenesis and bone growth through a mechanism involving down-regulation of FGFR-3 and p21.

Localization of vascular endothelial growth factor during the early stages of osteochondral regeneration using a bioabsorbable synthetic polymer scaffold

Vascular endothelial growth factor (VEGF) plays a critical role in chondrogenic differentiation in the growth plate of the epiphysis. This function is necessary for chondrocyte survival in cartilage development. We investigated the localization of VEGF in the osteochondral regeneration process using a bioabsorbable polymer scaffold. Osteochondral defects (5 mm in diameter and 5 mm in depth) were made on the femoral condyle of forty-eight skeletally mature female Japanese white rabbits. In total, twenty-four defects were filled with poly(DL-lactide-co-glycolide) scaffolds and the others were left untreated. The regeneration process was investigated macroscopically, histologically, immunohistochemically, and by gene expression analysis. In the early stages of osteochondral regeneration, bone ingrowth was observed in the deep zone of the scaffold with continuous VEGF expression; cartilage regeneration was observed in the superficial zone of the scaffold with decreased VEGF expression. In contrast, when the defect was left untreated, VEGF localization was observed throughout the entire defect area, and cartilage regeneration at the articular surface was delayed. We conclude that decrease in localization of VEGF at the articular surface in the postoperative early stage is closely related to the progression of cartilage regeneration in osteochondral defects.

Don't hedge your bets: hedgehog signaling as a central mediator of endochondral bone development and cartilage diseases

Cell differentiation and patterning are vital processes in the development of the appendicular skeleton. The hedgehog (Hh) signaling pathway plays a central role in regulating the anterior-posterior axis of the distal limb as well as the length of endochondral bones. Ligand-induced Hh signaling inhibits the processing of the Gli transcription factors from activator to repressor isoforms. In the growth plate, Indian hedgehog inhibits Gli processing, resulting in accumulation of Gli activators that induce chondrocyte maturation and hypertrophic differentiation. Parathyroid hormone-like hormone promote and Gli processing to repressor forms, thus regulating the rate of hypertrophic differentiation. In cartilage diseases such as osteoarthritis and cartilage tumors, there is a recapitulation of developmental processes that involve increased Hh signaling. Studies have shown that pharmacological inhibitors of Hh signaling can attenuate the progression osteoarthritis and cartilage tumor growth. Thus, Hh blockade can serve as a potential therapy for the treatment of various cartilage diseases.

Inhibition of prostate cancer osteoblastic progression with VEGF121/rGel, a single agent targeting osteoblasts, osteoclasts, and tumor neovasculature

PURPOSE

A hallmark of prostate cancer (PCa) progression is the development of osteoblastic bone metastases, which respond poorly to available therapies. We previously reported that VEGF(121)/rGel targets osteoclast precursors and tumor neovasculature. Here we tested the hypothesis that targeting nontumor cells expressing these receptors can inhibit tumor progression in a clinically relevant model of osteoblastic PCa.

EXPERIMENTAL DESIGN

Cells from MDA PCa 118b, a PCa xenograft obtained from a bone metastasis in a patient with castrate-resistant PCa, were injected into the femurs of mice. Osteoblastic progression was monitored following systemic administration of VEGF(121)/rGel.

RESULTS

VEGF(121)/rGel was cytotoxic in vitro to osteoblast precursor cells. This cytotoxicity was specific as VEGF(121)/rGel internalization into osteoblasts was VEGF(121) receptor driven. Furthermore, VEGF(121)/rGel significantly inhibited PCa-induced bone formation in a mouse calvaria culture assay. In vivo, VEGF(121)/rGel significantly inhibited the osteoblastic progression of PCa cells in the femurs of nude mice. Microcomputed tomographic analysis revealed that VEGF(121)/rGel restored the bone volume fraction of tumor-bearing femurs to values similar to those of the contralateral (non-tumor-bearing) femurs. VEGF(121)/rGel significantly reduced the number of tumor-associated osteoclasts but did not change the numbers of peritumoral osteoblasts. Importantly, VEGF(121)/rGel-treated mice had significantly less tumor burden than control mice. Our results thus indicate that VEGF(121)/rGel inhibits osteoblastic tumor progression by targeting angiogenesis, osteoclastogenesis, and bone formation.

CONCLUSIONS

Targeting VEGF receptor (VEGFR)-1- or VEGFR-2-expressing cells is effective in controlling the osteoblastic progression of PCa in bone. These findings provide the basis for an effective multitargeted approach for metastatic PCa.

The dose of growth factors influences the synergistic effect of vascular endothelial growth factor on bone morphogenetic protein 4-induced ectopic bone formation

Although vascular endothelial growth factor (VEGF) has been shown to act synergistically with bone morphogenetic protein (BMP)2 and BMP4 to promote ectopic endochondral bone formation via cell-based BMP gene therapy, the optimal ratio of VEGF to either of the BMPs required to obtain this beneficial effect remains unclear. In the current study, two cell types (C2C12, NIH/3T3) were retrovirally transduced to express BMP4 only or both BMP4 and VEGF. The resulting groups of cells were tested for their cellular proliferation, in vitro mineralization capacity, survival potential, and ability to undergo ectopic bone formation when implanted into a gluteofemoral muscle pocket created in severe combined immunodeficient mice. Results showed that VEGF inhibited the in vitro calcification of C2C12 and NIH/3T3 cells transduced to express BMP4. In vivo, C2C12 and NIH/3T3 cells expressing BMP4 and VEGF displayed significantly less bone formation than the same cells expressing only BMP4. In vivo, our results indicated that, when the ratio of VEGF to BMP4 is high, a detrimental effect on ectopic bone formation is observed; however, when the ratio is kept low and constant over time, the detrimental effect that VEGF has on ectopic bone formation is lost. Our studies revealed that VEGF's synergistic role in BMP4 induced ectopic bone formation is dose and cell-type dependent, which is an important consideration for cell-based gene therapy and tissue engineering for bone healing.

A rabbit model of hormone-induced early avascular necrosis of the femoral head

OBJECTIVE

To establish an experimental model of early stage avascular necrosis of the femoral head (ANFH) caused by corticosteroid in adult rabbits and to observe the pathological changes with various imaging techniques.

METHODS

ANFH was induced by a combination of hypersensitivity vasculitis caused by injection of horse serum and subsequent administration of a high dose of corticosteroid. The pathological changes were detected with digital radiography (DR), computed tomography (CT), magnetic resonance imaging (MRI), ink artery infusion angiography, hematoxylin-eosin staining, and immunohistochemistry.

RESULTS

The imageological and pathological changes corresponded to the clinical characteristics of early stage ANFH. DR showed bilaterally increased bone density, an unclear epiphyseal line, and blurred texture of cancellous bone. CT showed spot-like low-density imaging of cancellous bone, thinner cortical bone, osteoporosis, and an unclear epiphyseal line. MRI showed bone marrow edema and spot-like high signals in T2-weighted imaging in cancellous bone. Ink artery infusion angiography showed fewer obstructed blood vessels in the femoral head. HE staining of pathological sections showed fewer trabeculae and thin bone, an increased proportion of empty osteocyte lacunae, decreased hematopoiesis, thrombosis, and fat cell hypertrophy. Immunohistochemistry showed attenuated expression of vascular endothelial growth factor in osteoblasts and chondrocytes, and on the inner membrane of blood vessels.

CONCLUSION

Experimental rabbit model of early stage ANFH caused by corticosteroid can be successfully established and provide the foundation for developing effective methods to treat early stage ANFH.

Prenatal diagnosis of isolated abnormal number of ribs

OBJECTIVE

To determine the incidence of prenatal isolated abnormal number of ribs, using three-dimensional (3D) ultrasound.

METHODS

This was a prospective study of low-risk women with singleton pregnancy and normal fetal anatomy scan. 3D examinations of the fetal ribs were carried out at the time of the routine anomaly scan at 14-16 or 20-24 weeks of gestation. A 3D volume of the spine was acquired with a mechanical sweep that lasted between 2 and 4 s per volume and was performed when the fetus had a minimally flexed head position. Fetal ribs were reviewed on the rendered image (maximal mode), both while the patient was in the clinic and again later.

RESULTS

Three hundred and sixty-seven pregnant women were evaluated. Twenty-three (6.3%) fetuses were found to have an abnormal number of ribs. Fifteen (4.1%) had 11 ribs unilaterally, with the last (12(th)) rib missing. One patient (0.27%) had 13 ribs unilaterally (with a small extra rib after the last rib). Two (0.5%) patients had 13 ribs bilaterally with an extra rib after the 12(th) rib on each side and two (0.5%) patients had 13 ribs bilaterally with an extra cervical rib on each side. Three (0.8%) patients had an extra unilateral cervical rib. In all, 1.4% of patients had extra cervical ribs.

CONCLUSIONS

The incidence of abnormal number of ribs in this normal population was 6.3%. When isolated, this finding is a normal variant.

Functional characterization of hypertrophy in chondrogenesis of human mesenchymal stem cells

OBJECTIVE

Mesenchymal stem cells (MSCs) are promising candidate cells for cartilage tissue engineering. Expression of cartilage hypertrophy markers (e.g., type X collagen) by MSCs undergoing chondrogenesis raises concern for a tissue engineering application for MSCs, because hypertrophy would result in apoptosis and ossification. To analyze the biologic basis of MSC hypertrophy, we examined the response of chondrifying MSCs to culture conditions known to influence chondrocyte hypertrophy, using an array of hypertrophy-associated markers.

METHODS

Human MSC pellet cultures were predifferentiated for 2 weeks in a chondrogenic medium, and hypertrophy was induced by withdrawing transforming growth factor beta (TGFbeta), reducing the concentration of dexamethasone, and adding thyroid hormone (T3). Cultures were characterized by histologic, immunohistochemical, and biochemical methods, and gene expression was assessed using quantitative reverse transcription-polymerase chain reaction.

RESULTS

The combination of TGFbeta withdrawal, a reduction in the level of dexamethasone, and the addition of T3 was essential for hypertrophy induction. Cytomorphologic changes were accompanied by increased alkaline phosphatase activity, matrix mineralization, and changes in various markers of hypertrophy, including type X collagen, fibroblast growth factor receptors 1-3, parathyroid hormone-related protein receptor, retinoic acid receptor gamma, matrix metalloproteinase 13, Indian hedgehog, osteocalcin, and the proapoptotic gene p53. However, hypertrophy was not induced uniformly throughout the pellet culture, and distinct regions of dedifferentiation were observed.

CONCLUSION

Chondrogenically differentiating MSCs behave in a manner functionally similar to that of growth plate chondrocytes, expressing a very similar hypertrophic phenotype. Under the in vitro culture conditions used here, MSC-derived chondrocytes underwent a differentiation program analogous to that observed during endochondral embryonic skeletal development, with the potential for terminal differentiation. This culture system is applicable for the screening of hypertrophy-inhibitory conditions and agents that may be useful to enhance MSC performance in cartilage tissue engineering.

The potential role of vascular endothelial growth factor (VEGF) in cartilage: how the angiogenic factor could be involved in the pathogenesis of osteoarthritis?

Although adult human cartilage is physiologically avascular tissue, angiogenesis can be observed during the process of endochondral bone development. Inflammation in articular joints can also lead to neovascularization in cartilage. In such conditions, the expression of angiogenic factors, such as vascular endothelial growth factor (VEGF), has been shown to play a key role, controlling not only angiogenesis but also chondrocyte metabolism. Here we review recent research findings concerning the potential role of VEGF in cartilage, focusing in particular on its possible involvement in the pathogenesis of osteoarthritis.

Matrix vesicles are carriers of bone morphogenetic proteins (BMPs), vascular endothelial growth factor (VEGF), and noncollagenous matrix proteins

Matrix vesicles (MVs) are well positioned in the growth plate to serve as a carrier of morphogenetic information to nearby chondrocytes and osteoblasts. Bone morphogenetic proteins (BMPs) carried in MVs could promote differentiation of these skeletal cells. Vascular endothelial growth factor (VEGF) in MVs could stimulate angiogenesis. Therefore, a study was undertaken to confirm the presence of bone morphogenetic protein (BMP)-1 through-7, VEGF, and the noncollagenous matrix proteins, bone sialoprotein (BSP), osteopontin (OPN), osteocalcin (OC), and osteonectin (ON) in isolated rat growth plate MVs. MVs were isolated from collagenase-digested rachitic rat tibial and femoral growth plates. The presence of BMP-1 through BMP-7, VEGF, BSP, ON, OPN, and OC was evaluated by Western blot, plus ELISA analyses for BMP-2 and-4 content. The alkaline phosphatase-raising ability of MV extracts on cultured rat growth plate chondrocytes was measured as a reflection of MV ability to promote chondroosseous differentiation. BMP-1 through-7, VEGF, BSP, ON, OPN, and OC were all detected by Western blot analyses. Chondrocytes treated with MV extracts showed a two-to threefold increase in alkaline phosphatase activity over control, indicating increased differentiation. Significant amounts of BMP-2 and BMP-4 were detected in MVs by ELISA. Combined, these data suggest that MVs could play an important morphogenetic role in growth plate and endochondral bone formation.

Contribution of endothelial cells to organogenesis: a modern reappraisal of an old Aristotelian concept

It is well established that many tissue-derived factors are involved in blood vessel formation, but evidence is now emerging that endothelial cells themselves represent a crucial source of instructive signals to non-vascular tissue cells during organ development. Thus, endothelial cell signalling is currently believed to promote fundamental cues for cell fate specification, embryo patterning, organ differentiation and postnatal tissue remodelling. This review article summarizes some of the recent advances in our understanding of the role of endothelial cells as effector cells in organ formation.

VEGF and VEGF receptors are differentially expressed in chondrocytes

During long bone development, cartilage replacement by bone is governed in part by angiogenesis. Although it has been demonstrated that vascular endothelial growth factor (VEGF-A) is crucial during endochondral ossification, little is known about the involvement of the other VEGF family members. Thus, we examined the expression and production of these members on primary chondrocytes and ATDC5 chondrogenic cells. VEGF-A, VEGF-B, VEGF-C and VEGF-D were shown to be expressed and synthesized demonstrating that numerous angiogenic factors can be produced by chondrocytes. In ATDC5 VEGF-A, VEGF-B and VEGF-C were over-expressed in the presence of chondrogenic and bone morphogenetic protein (BMP)-2 treatment suggesting that these factors play an important role during chondrogenesis. In addition, neuropilin-1, VEGF receptor-2 and VEGF receptor-3 gene expression were observed with an increase in VEGF-R2 expression under chondrogenic and BMP-2 treatment, suggesting that VEGF proteins could act in an autocrine/paracrine manner in addition to their angiogenic function. In conclusion, we demonstrated for the first time that chondrocytes secreted the four members of the VEGF family. We also showed that VEGF-B, VEGF-C and VEGF-D were secreted as processed proteins. The up-regulation of VEGF-B and VEGF-C at the mRNA and protein levels under chondrogenic stimulation strongly suggests a major role for these proteins in growth plate physiology.

Immunolocalization of vascular endothelial growth factor on intramuscular ectopic osteoinduction by bone morphogenetic protein-2

When recombinant human bone morphogenetic protein-2 (rhBMP-2) is implanted in soft tissues, bony tissue is induced during the course of endochondral ossification. The relationship between endochondral ossification and vascularization is important in bone formation, and vascular endothelial growth factor (VEGF) is considered to play an important role in this process. In this study, the immunohistological localization of VEGF was investigated in rhBMP-2-induced ectopic endochondral ossification in the calf muscle of rats. In addition, the characteristics of anti-VEGF antibody-reactive cells were histologically investigated using electron microscopy to examine the cause of endochondral ossification induced by recombinant human bone morphogenetic protein-2. The role of VEGF in rhBMP-2-induced osteoinduction and vascular induction was studied by observing the relationship between the localizations of anti-VEGF antibody-reactive cells and vascularization. During the process of rhBMP-2-induced ectopic endochondral ossification, fibroblast-like cells, which were located at the margin of the implant and reactive to BMP-2 at 5 days, were positive for VEGF immunostaining. Hypertrophic chondrocytes appeared 9 days and osteoblasts appeared 14 to 21 days after implantation, and all these cells were reactive with anti-VEGF antibody. Bony trabeculae subsequently appeared in the muscle, and new blood vessels were formed alongside the trabeculae. When VEGF was added to rhBMP, more new blood vessels and bone were formed in the induced bone. These findings suggested that rhBMP-2 induced the differentiation of undifferentiated mesenchymal cells to chondrocytes and osteoblasts, and these differentiated cells expressed VEGF, creating an advantageous environment for vascularization in bony tissue.

Molecular regulation of tumor angiogenesis: mechanisms and therapeutic implications

Angiogenesis, the process of new capillary formation from a pre-existing vessel plays an essential role in both embryonic and postnatal development, in the remodeling of various organ systems, and in several pathologies, particularly cancer. In the last 20 years of angiogenesis research, a variety of angiogenic regulators, both positive and negative, have been identified. The discovery of several anti-angiogenic factors has led to the development of novel cancer therapies based on targeting a tumor's vascular supply. A number of these new therapies are currently being tested in clinical trials in the U.S.A. and elsewhere. A major advance in the field of anti-angiogenic therapy occurred recently when the FDA approved Avastin (bevacizumab), the first solely anti-angiogenesis therapy approved for treatment of human cancer. While it has long been appreciated that tumor growth and progression are dependent on angiogenesis, it is only recently that progress has been made in elucidating the molecular mechanisms that regulate the earliest stage in the angiogenic program, the angiogenic switch. This checkpoint is characterized by the transition of a dormant, avascular tumor into an active, vascular one. Anti-angiogenic therapies to date have essentially been designed to suppress the neovasculature in established tumors. However, identifying the mechanisms that cause a tumor to acquire an angiogenic phenotype may lead to the discovery of new therapeutic modalities and complementary diagnostics that could be used to block the angiogenic switch, thereby preventing subsequent tumor progression. In this chapter on the role of angiogenesis in cancer, we (1) provide an overview of the process of angiogenesis with special regard to the molecules and physiological conditions that regulate this process, (2) review recent studies describing the use of anti-angiogenic approaches in the treatment of a variety of human cancers, and (3) discuss the recent literature focused on the study of the molecules and molecular mechanisms that may be regulating the initiation of the angiogenic phenotype in tumors, and the clinical impact that this knowledge may have in the future.

Osteoclastogenesis in the nonadherent cell population of human bone marrow is inhibited by rhBMP-2 alone or together with rhVEGF

During bone development and repair, angiogenesis, osteogenesis, and bone remodeling are closely associated processes that share some common mediators. In the present study nonadherent human bone marrow mononuclear cells under the induction of sRANKL and M-CSF, differentiated into osteoclasts with TRAP-positive staining, VNR expression, and Ca-P resorptive activity. The effects of various combinations of rhBMP-2 (0, 3, 30, and 300 ng/mL) and rhVEGF (0 and 25 ng/mL) on osteoclastogenesis potentials were examined in this experimental system. The percentages of TRAP-positive multiple nucleated cells represent osteoclast differentiation potential, and the percentages of resorptive areas in the Ca-P coated plates resemble osteoclast resorption capability. The presence of rhBMP-2 at 30 and 300 ng/mL showed inhibitory effects on osteoclast differentiation and their resorptive capability in the human osteoclast culture system. rhVEGF (25 ng/mL) enhanced the resorptive function of osteoclast whenever it was used alone or combined with 3 ng/mL rhBMP-2. However, rhVEGF-induced resorptive function was inhibited by 30 ng/mL and 300 ng/mL rhBMP-2 in a dose-dependent manner. Statistical analysis demonstrated that an interactive effect exists between rhBMP-2 and rhVEGF on human osteoclastogenesis. These findings suggested that an interactive regulation may exist between BMPs and VEGF signaling pathways during osteoclastogenesis; exact mechanisms are yet to be elucidated.

VEGF-A and PlGF-1 stimulate chemotactic migration of human mesenchymal progenitor cells

Vascular endothelial growth factor (VEGF) has been indicated to play a role during endochondral ossification by stimulation of blood vessel invasion into hypertrophic cartilage resulting in its replacement by trabecular bone. We could demonstrate a dose-dependent chemoattractive effect of VEGF-A and PlGF-1, but not VEGF-E or VEGF-C, on human mesenchymal progenitor cells. Quantitative realtime PCR revealed the expression of VEGFR-1 (Flt-1), VEGFR-2 (KDR/Flk-1), and VEGFR-3 (Flt-4), which markedly declined during osteogenic differentiation. In addition, expression of neuropilin-1 and -2 was detected by RT-PCR. In an in vitro kinase assay, we could demonstrate activation of VEGFR-1 and VEGFR-2 upon stimulation with specific ligands. These findings are consistent with the idea that the chemotactic effect of VEGF-A on MPC is mediated via VEGFR-1, and that VEGF-A and PlGF-1, have a functional role for recruitment of osteoprogenitor cells in the course of endochondral bone formation or remodeling.

AZD2171: a highly potent, orally bioavailable, vascular endothelial growth factor receptor-2 tyrosine kinase inhibitor for the treatment of cancer

Inhibition of vascular endothelial growth factor-A (VEGF) signaling is a promising therapeutic approach that aims to stabilize the progression of solid malignancies by abrogating tumor-induced angiogenesis. This may be accomplished by inhibiting the kinase activity of VEGF receptor-2 (KDR), which has a key role in mediating VEGF-induced responses. The novel indole-ether quinazoline AZD2171 is a highly potent (IC50 < 1 nmol/L) ATP-competitive inhibitor of recombinant KDR tyrosine kinase in vitro. Concordant with this activity, in human umbilical vein endothelial cells, AZD2171 inhibited VEGF-stimulated proliferation and KDR phosphorylation with IC50 values of 0.4 and 0.5 nmol/L, respectively. In a fibroblast/endothelial cell coculture model of vessel sprouting, AZD2171 also reduced vessel area, length, and branching at subnanomolar concentrations. Once-daily oral administration of AZD2171 ablated experimental (VEGF-induced) angiogenesis in vivo and inhibited endochondral ossification in bone or corpora luteal development in ovary; physiologic processes that are highly dependent upon neovascularization. The growth of established human tumor xenografts (colon, lung, prostate, breast, and ovary) in athymic mice was inhibited dose-dependently by AZD2171, with chronic administration of 1.5 mg per kg per day producing statistically significant inhibition in all models. A histologic analysis of Calu-6 lung tumors treated with AZD2171 revealed a reduction in microvessel density within 52 hours that became progressively greater with the duration of treatment. These changes are indicative of vascular regression within tumors. Collectively, the data obtained with AZD2171 are consistent with potent inhibition of VEGF signaling, angiogenesis, neovascular survival, and tumor growth. AZD2171 is being developed clinically as a once-daily oral therapy for the treatment of cancer.

Localization of matrix metalloproteinases, (MMPs) their tissue inhibitors, and vascular endothelial growth factor (VEGF) in growth plates of children and adolescents indicates a role for MMPs in human postnatal growth and skeletal maturation

Numerous studies have focused on the expression, regulation, and biological significance of matrix metalloproteinases (MMPs) in the growth plate. Findings in mouse knockout models and in vitro data from various species indicate that MMPs not only degrade extracellular matrix components but may regulate the activity of local growth factors. In this study we investigated the presence, distribution, and activity of various MMPs and inhibitors, tissue transglutaminase (tTG or TG2) and vascular endothelial growth factor (VEGF) in the human child and adolescent growth plates by means of immunohistochemistry and gelatin zymography. Tissue was derived during orthopedic surgery (epiphysiodesis) in two prepubertal and four pubertal patients.MMP-2 and MMP-14 were present in reserve cell chondrocytes. MMP-14 was the most prominent MMP within all zones of the growth plate including proliferating chondrocytes. MMP-1 and MMP-13 (collagenases 1 and 3), MMP-9 (gelatinases B), MMP-10, and MMP-11 (stromelysins) and VEGF were positive in hypertrophic chondrocytes and osteoblasts. MMP-2 showed the same expression pattern but was negative in osteoblasts. Osteoclasts stained positive for MMP-9, MMP-2, and TG2. Tissue inhibitor of MMP (TIMP)-1 was present in all zones of the growth plate, osteoblasts, and osteoclasts; TIMP-2 was found in hypertrophic chondrocytes and osteoblasts. In summary, the presence of MMPs, TIMPs, TG2, and VEGF in our study indicated that the MMPs are relevant in growth plate physiology during the postnatal period in humans. The specific location of MMP expression within the growth plate may be the basis for further studies on the role of MMPs in the local regulation of chondrocyte differentiation, proliferation, and ossification at the chondroosseus junction.

Differential regulation of EP receptor isoforms during chondrogenesis and chondrocyte maturation

Regulation of chondrogenesis and chondrocyte maturation by prostaglandins has been a topic of interest during recent years. Particular focus on this area derives from the realization that inhibition of prostaglandin synthesis with non-steroidal anti-inflammatory drugs could impact these cartilage-related processes which are important in skeletal development and are recapitulated during bone healing either post-trauma or post-surgery. In addition to reviewing the relevant literature focused on prostaglandin synthesis and signaling through the G-protein coupled EP receptors, we present novel findings that establish the expression profile of EP receptors in chondroprogenitors and chondrocytes. Further, we begin to examine the signaling that may be involved with the transduction of PGE2 effects in these cells. Our findings suggest that EP2 and EP4 receptor activation of cAMP metabolism may represent a central axis of events that facilitate the impact of PGE2 on the processes of mesenchymal stem cell commitment to chondrogenesis and ultimate chondrocyte maturation.

Vascular endothelial growth factor plays an important autocrine/paracrine role in the progression of osteoarthritis

Vascular endothelial growth factor (VEGF) plays an essential role in the angiogenesis of growing cartilage. Although VEGF expression in cartilage vanishes in normal adults, VEGF is known to be expressed in chondrocytes of osteoarthritic (OA) cartilage. As little information is available on the VEGF expression in the cartilage of OA-like lesions of the temporomandibular joint (TMJ), VEGF expression in the condylar cartilage of TMJs of rats affected with OA was examined. To evoke OA, mechanical stress was applied by forced jaw opening for 10 or 20 days. After 20 days, marked OA-like lesions were observed in the condyle. VEGF was expressed in the chondrocytes of the mature and hypertrophic cell layers of the intermediate and posterior region of the condyle. The percentage of VEGF immunopositive chondrocytes significantly increased with the period of applied mechanical stress. Furthermore, tartrate-resistant acid phosphatase (TRAP) staining of the condylar cartilage showed significant increment of osteoclasts in the mineralized layer subjacent to the hypertrophic layer where high VEGF expression could be detected. The results suggest that VEGF plays an important role in the progression of OA.

Localization of pigment epithelium-derived factor in growing mouse bone

Pigment epithelium-derived factor (PEDF) is a potent anti-angiogenic factor found in a wide range of fetal and adult tissues, where it is thought to play a role in the regulation of angiogenesis during development. The temporal expression of PEDF during endochondral bone formation has not previously been reported. In this study, we analysed the expression pattern of PEDF in growing mouse hindlimbs from newborn day one through to maturation at week 9, using immunohistochemistry and in situ hybridization. PEDF expression was demonstrated in chondrocytes within the resting, proliferative and upper hypertrophic zones of the epiphyseal growth plate. The pattern of expression was consistent throughout the developmental stages of the mouse. In addition, PEDF was expressed by osteoblasts lining the bone spicules in the ossification zone of metaphyseal bone, as well as by osteoblasts lining cortical periosteum. These novel results demonstrate that PEDF is developmentally expressed in both cartilage and bone cells during endochondral bone formation, and strongly suggest that it may play a regulatory role in the processes of chondrocyte and osteoblast differentiation, endochondral ossification, and bone remodelling during growth and development of long bones.

Osteogenic Potential of Primed Periosteum Graft in the Rat Calvarial Model

Repair of bone defects remains a major concern in plastic and maxillofacial surgery. Based on modern concepts of tissue engineering, periosteum has gained attention as a suitable osteogenic material. We tested the hypothesis that surgically released and immediately repositioned periosteum would exhibit high osteogenic capacity upon grafting in a rat calvarial defect. Seven days after periosteum was released from the tibia and immediately repositioned, the "primed periosteum graft" (PPG; n = 15) was placed into a critical-sized defect of rat calvaria and the process of bone formation was evaluated histologically, immunohistologically, and radiographically at 7, 14, and 21 days after grafting. Findings were compared with a nonprimed periosteal graft (NPG; n = 15). Endochondral ossification was observed in both the PPG and NPG. The PPG showed higher expression of proliferative cell nuclear antigen, bone morphogenetic protein, and vascular endothelial growth factor than the NPG. Three-dimensional radiographic examination revealed significantly increased bone formation in the PPG than in the NPG (P < 0.01). These findings suggested that surgical stimulation of the periosteum enhanced the osteogenic potential of periosteal cells. This method may be suitable for the clinical repair of bone defects.

Development of the microcirculation of the secondary ossification center in rat humeral head

This work investigated the origin and development of microcirculation in the rat humeral head and the expression of vascular endothelial growth factor (VEGF) as a factor supporting the vascular growth and the development of the secondary ossification centers. Sixty rats aging 1, 3-4, 6-8, 11, and 21 days, 5 weeks, and 4 and 8 months were used. Samples of humeral head were collected for histology and immunohistochemistry for VEGF. Some animals were perfused with Mercox resin in order to obtain vascular corrosion casts (vcc) observed by scanning electron microscopy (SEM). No cartilage canals were present at birth. At 6 days postnatal, blood vessels coming from the perichondrium and the region near the capsule attachment invaded the cartilage; at 11 days postnatal, signs of calcification were present and within the third week some bone trabeculae were formed. Just before the vascular invasion of the epiphysis, a positive reaction for VEGF was localized in chondrocytes of the epiphyseal cartilage close to the capsule insertion. During the development and expansion of the secondary ossification center, VEGF expression was higher in chondrocytes but decreased when epiphysis was diffusely ossified. VEGF was expressed also by mesenchymal cells present in and around the fibrous tissue where the secondary ossification center will develop. SEM vcc confirmed that vessels penetrating into the epiphysis arose merely from the periosteal and the capsular networks, and vascular connections with the diaphyseal circulation were not evident. These observations demonstrated that VEGF production by chondrocytes begun some days after birth, supported the rapid vascular growth from the surrounding soft tissues, and was chronologically related to the development of the secondary ossification center in rat proximal humerus. Finally, the possible role of VEGF as mediator of angiogenesis and, at least indirectly, as a trigger factor also in the ossification and the bone remodeling of the secondary ossification centers has been discussed.

Nodular osteochondrogenic activity in soft tissue surrounding osteoma in neurogenic para osteo-arthropathy: morphological and immunohistochemical study

BACKGROUND

Neurogenic Para-Osteo-Arthropathy (NPOA) occurs as a consequence of central nervous system injuries or some systemic conditions. They are characterized by bone formation around the main joints.

METHODS

In order to define some biological features of NPOAs, histological and immunohistological studies of the soft tissue surrounding osteoma and Ultrasound examination (US) of NPOA before the appearance of abnormal ossification on plain radiographs were performed.

RESULTS

We have observed a great number of ossifying areas scattered in soft tissues. US examination have also shown scattered ossifying areas at the early stage of ossification. A high osteogenic activity was detected in these tissues and all the stages of the endochondral process were observed. Mesenchymal cells undergo chondrocytic differentiation to further terminal maturation with hypertrophy, which sustains mineralization followed by endochondral ossification process.

CONCLUSION

We suggest that periosteoma soft tissue reflect early stage of osteoma formation and could be a model to study the mechanism of osteoma formation and we propose a mechanism of the NPOA formation in which sympathetic dystony and altered mechanical loading induce changes which could be responsible for the cascade of cellular events leading to cartilage and bone formation.

Deletion of Vhlh in chondrocytes reduces cell proliferation and increases matrix deposition during growth plate development

The von Hippel Lindau tumor suppressor protein (pVHL) is a component of a ubiquitin ligase that promotes proteolysis of the transcription factor hypoxia-inducible-factor 1alpha (HIF1alpha), the key molecule in the hypoxic response. We have used conditional inactivation of murine VHL (Vhlh) in all cartilaginous elements to investigate its role in endochondral bone development. Mice lacking Vhlh in cartilage are viable, but grow slower than control littermates and develop a severe dwarfism. Morphologically, Vhlh null growth plates display a significantly reduced chondrocyte proliferation rate, increased extracellular matrix, and presence of atypical large cells within the resting zone. Furthermore, stabilization of the transcription factor HIF1alpha leads to increased expression levels of HIF1alpha target genes in Vhlh null growth plates. Lastly, newborns lacking both Vhlh and Hif1a genes in growth plate chondrocytes display essentially the same phenotype as Hif1a null single mutant mice suggesting that the Vhlh null phenotype could result, at least in part, from increased activity of accumulated HIF1alpha. This is the first study reporting the novel and intriguing findings that pVHL has a crucial role in endochondral bone development and is necessary for normal chondrocyte proliferation in vivo.

Immunolocalization of Vascular Endothelial Growth Factor During Heterotopic Bone Formation Induced From Grafted Periosteum

Vessel invasion is an important step in cartilage replacement that leads to bone formation, and vascular endothelial growth factor (VEGF) has been implicated as a key player in this process. Although grafted periosteum undergoes endochondral ossification, little is known about the role of VEGF in this process. In the current study the authors investigated by immunohistochemical, histochemical, and ultrastructural techniques the localization of VEGF during bone formation in periosteal grafts. At day 14 after grafting the tibias of Japanese white rabbits, periosteal cells in the grafted tissue had differentiated into chondrocytes to form cartilage. Some chondrocytes were immunopositive for VEGF expression, and subsequent vessel invasion occurred predominantly in these VEGF-positive areas. At day 45, the cartilage invaded by blood vessels had been replaced by newly formed bone. These findings suggest that VEGF is associated with the process of blood vessel invasion into cartilage before bone replacement in endochondral ossification from grafted periosteum.

VEGF expression in adult permanent thyroid cartilage: implications for lack of cartilage ossification

Vascular endothelial growth factor (VEGF) has been shown to play an important role during endochondral bone formation in hypertrophic cartilage remodeling, ossification, and angiogenesis, but it is not expressed in normal adult articular cartilage. Thyroid cartilage undergoes only partial ossification beginning at the age of about 20. Because it never completely ossifies, we investigated a possible role of VEGF and its receptors (VEGFRs) as well as the angiogenetic inhibitor endostatin in this permanent cartilage. In analysis of cartilage samples from all specimens evaluated, VEGF121 and VEGF165 were identified as the only VEGF splice forms expressed. In addition to VEGF, VEGFR-2 (kinase domain region/fetal liver kinase 1), but not VEGFR-1 (fms-like tyrosine kinase 1), was detectable by RT-PCR in cartilage. However, VEGFR-2 expression was only detectable up to the age of 19 years. Deposition of VEGF and VEGFR was confirmed by immunohistochemistry. VEGF concentrations measured by ELISA in thyroid cartilage increased with age in males but decreased in females. Endostatin concentrations measured by ELISA in thyroid cartilage were three times lower than in articular cartilage and showed no change with age, either in females or males. VEGF was immunostained within the intra- and pericellular matrices of some but not all chondrocytes. Thus, apart from its production in hypertrophic chondrocytes of growth plates, VEGF is also produced in single chondrocytes of thyroid cartilage. The data allow us to speculate that thyroid cartilage persists in an embryological state until it has reached its final size. After reaching its final size at the end of the second decade, VEGFR-2 is downregulated and ossification starts in the posterior part of the thyroid cartilage, proceeding ventrally. Both proteins, VEGF121 and VEGF165, should contribute to this process. VEGF concentration is high and changes in an age-related and sex-specific manner. Therefore, we postulate that VEGF is at least one of the key factors that is important for the lifelong ossification in thyroid cartilage.

Immunolocalization of vascular endothelial growth factor in rat condylar cartilage during postnatal development

It is well known that angiogenesis is essential for the replacement of cartilage by bone during skeletal growth and regeneration. To address angiogenesis of endochondral ossification in the condyle, we examined the appearance of vascular endothelial growth factor (VEGF) and its receptor Flt-1 in condylar cartilage of the growing rat. The early expression of VEGF at various sites during condylar cartilage development indicates that VEGF plays a role in the regulation of angiogenesis at each site of bone formation. From the findings of Flt-1 immunoreactivity, the VEGF produced by the chondrocytes of the hypertrophic zone should contribute to the promotion of endothelial cell proliferation and to stimulate migration and activation of osteoclasts in condylar cartilage, resulting in the invasion of these cells into the mineralized zone.

Expression of VEGF isoforms by epiphyseal chondrocytes during low-oxygen tension is HIF-1 alpha dependent

OBJECTIVE

To establish the role of hypoxia and HIF-1 alpha for VEGF expression of murine epiphyseal chondrocytes. To analyze the effect of hypoxia on VEGF isoform expression.

MATERIALS AND METHODS

VEGF mRNA and VEGF isoform expression was investigated in epiphyses of murine newborns by in situ hybridization and real-time PCR. Further, epiphyseal chondrocytes were isolated from newborn mice with homozygous flanking of the HIF-1 alpha gene with lox-P sites. HIF-1 alpha was deleted by infection with adenovirus containing cre-recombinase. After chondrocytes reached confluency they were exposed to 0.5% or 20% oxygen, respectively. Total VEGF and VEGF isoform mRNA expression levels were measured by real-time PCR. Secreted VEGF protein was determined by ELISA.

RESULTS

VEGF mRNA signals were detected in the hypertrophic zone and in the center of the proliferative zone of the murine epiphysis, which is considered to be hypoxic. Real-time PCR revealed that VEGF(120)is the dominant isoform in vivo. In cultured epiphyseal chondrocytes strongly increased VEGF gene expression levels were detected after exposure to hypoxia. Furthermore, secretion of VEGF protein was significantly enhanced under 0.5% oxygen. Remarkably, functional inactivation of HIF-1 alpha abolished the hypoxic increase of VEGF expression in chondrocytes completely. Furthermore, the soluble isoforms VEGF(120)and VEGF(164)are the most abundantly expressed splice variants in chondrocytes exposed to low oxygen levels.

CONCLUSIONS

The data presented here clearly indicate that hypoxia is able to induce the synthesis of soluble VEGF isoforms by epiphyseal chondrocytes, most likely through stabilization of HIF-1 alpha. Thus it can be speculated that HIF-1 alpha is an essential prerequisite for hypoxic VEGF synthesis in the epiphysis, thereby contributing to the formation and invasion of blood vessels in long bone development.