Basic fibroblast growth factor and transforming growth factor beta-1 expression in the developing dura mater correlates with calvarial bone formation

Novel model of cortical-meningeal organoid co-culture system improves human cortical brain organoid cytoarchitecture

Human cortical organoids (hCOs), derived from human induced pluripotent stem cells (iPSCs), provide a platform to interrogate mechanisms of human brain development and diseases in complex three- dimensional tissues. However, current hCO development methods lack important non-neural tissues, such as the surrounding meningeal layer, that have been shown to be essential for normal corticogenesis and brain development. Here, we first generated hCOs from a single rosette to create more homogenous organoids with consistent size around 250 µm by day 5. We then took advantage of a 3D co-culture system to encapsulate brain organoids with a thin layer of meningeal cells from the very early stages of cortical development. Immunostaining analysis was performed to display different cortical layer markers during different stages of development. Real-time monitoring of organoid development using IncuCyte displayed enhanced morphology and increased growth rate over time. We found that meningeal-encapsulated organoids illustrated better laminar organization by exhibiting higher expression of REELIN by Cajal-Retzius neurons. Presence of meningeal cells resulted in a greater expansion of TBR2 intermediate progenitor cells (IPCs), the deep cortical layer (CTIP2) and upper cortical layer (BRN2). Finally, meningeal-encapsulated organoids enhanced outer radial glial and astrocyte formation illustrated by stronger expression of HOPX and GFAP markers, respectively. This study presents a novel 3D co-culture platform to more closely mimic the in vivo cortical brain structure and enable us to better investigating mechanisms underlying the neurodevelopmental disorders during embryonic development.

Clinical Management of Supratentorial Non-Skull Base Meningiomas

Supratentorial non-skull base meningiomas are the most common primary central nervous system tumor subtype. An understanding of their pathophysiology, imaging characteristics, and clinical management options will prove of substantial value to the multi-disciplinary team which may be involved in their care. Extensive review of the broad literature on the topic is conducted. Narrowing the scope to meningiomas located in the supratentorial non-skull base anatomic location highlights nuances specific to this tumor subtype. Advances in our understanding of the natural history of the disease and how findings from both molecular pathology and neuroimaging have impacted our understanding are discussed. Clinical management and the rationale underlying specific approaches including observation, surgery, radiation, and investigational systemic therapies is covered in detail. Future directions for probable advances in the near and intermediate term are reviewed.

Cranium growth, patterning and homeostasis

Craniofacial development requires precise spatiotemporal regulation of multiple signaling pathways that crosstalk to coordinate the growth and patterning of the skull with surrounding tissues. Recent insights into these signaling pathways and previously uncharacterized progenitor cell populations have refined our understanding of skull patterning, bone mineralization and tissue homeostasis. Here, we touch upon classical studies and recent advances with an emphasis on developmental and signaling mechanisms that regulate the osteoblast lineage for the calvaria, which forms the roof of the skull. We highlight studies that illustrate the roles of osteoprogenitor cells and cranial suture-derived stem cells for proper calvarial growth and homeostasis. We also discuss genes and signaling pathways that control suture patency and highlight how perturbing the molecular regulation of these pathways leads to craniosynostosis. Finally, we discuss the recently discovered tissue and signaling interactions that integrate skull and cerebrovascular development, and the potential implications for both cerebrospinal fluid hydrodynamics and brain waste clearance in craniosynostosis.

Single-Cell Transcriptomic Analyses of the Developing Meninges Reveal Meningeal Fibroblast Diversity and Function

The meninges are a multilayered structure composed of fibroblasts, blood and lymphatic vessels, and immune cells. Meningeal fibroblasts secrete a variety of factors that control CNS development, yet strikingly little is known about their heterogeneity or development. Using single-cell sequencing, we report distinct transcriptional signatures for fibroblasts in the embryonic dura, arachnoid, and pia. We define new markers for meningeal layers and show conservation in human meninges. We find that embryonic meningeal fibroblasts are transcriptionally distinct between brain regions and identify a regionally localized pial subpopulation marked by the expression of μ-crystallin. Developmental analysis reveals a progressive, ventral-to-dorsal maturation of telencephalic meninges. Our studies have generated an unparalleled view of meningeal fibroblasts, providing molecular profiles of embryonic meningeal fibroblasts by layer and yielding insights into the mechanisms of meninges development and function.

Biomaterial and implant induced ossification: in vitro and in vivo findings

Material-induced ossification is suggested as a suitable approach to heal large bone defects. Fiber-reinforced composite-bioactive glasses (FRC-BGs) display properties that could enhance the ossification of calvarial defects. Here, we analyzed the healing processes of a FRC-BG implant in vivo from the perspective of material-induced ossification. Histological analysis of the implant, which was removed 5 months after insertion, showed the formation of viable, noninflammatory mesenchymal tissue with newly-formed mineralized woven bone, as well as nonmineralized connective tissue with capillaries and larger blood vessels. The presence of osteocytes was detected within the newly generated bone matrix. To expand our understanding on the osteogenic properties of FRC-BG, we cultured human adipose tissue-derived mesenchymal stromal cells (AD-MSCs) in the presence of two different BGs (45S5 and S53P4) and Al2 O3 control. AD-MSCs grew and proliferated on all the scaffolds tested, as well as secreted abundant extracellular matrix, when osteogenic differentiation was appropriately stimulated. 45S5 and S53P4 induced enhanced expression of COL2A1, COL10A1, COL5A1 collagen subunits, and pro-osteogenic genes BMP2 and BMP4. The concomitant downregulation of BMP3 was also detected. Our findings show that FRC-BG can support the vascularization of the implant and the formation of abundant connective tissue in vivo. Specifically, BG 45S5 and BG S53P4 are suited to evoke the osteogenic potential of host mesenchymal stromal cells. In conclusion, FRC-BG implant demonstrated material-induced ossification both in vitro and in vivo.

Osteogenic commitment of Wharton's jelly mesenchymal stromal cells: mechanisms and implications for bioprocess development and clinical application

Background

Orthopaedic diseases are one of the major targets for regenerative medicine. In this context, Wharton’s jelly (WJ) is an alternative source to bone marrow (BM) for allogeneic transplantation since its isolation does not require an invasive procedure for cell collection and does not raise major ethical concerns. However, the osteogenic capacity of human WJ-derived multipotent mesenchymal stromal cells (MSC) remains unclear.

Methods

Here, we compared the baseline osteogenic potential of MSC from WJ and BM cell sources by cytological staining, quantitative real-time PCR and proteomic analysis, and assessed chemical and biological strategies for priming undifferentiated WJ-MSC. Concretely, different inhibitors/activators of the TGFβ1-BMP2 signalling pathway as well as the secretome of differentiating BM-MSC were tested.

Results

Cytochemical staining as well as gene expression and proteomic analysis revealed that osteogenic commitment was poor in WJ-MSC. However, stimulation of the BMP2 pathway with BMP2 plus tanshinone IIA and the addition of extracellular vesicles or protein-enriched preparations from differentiating BM-MSC enhanced WJ-MSC osteogenesis. Furthermore, greater outcome was obtained with the use of conditioned media from differentiating BM-MSC.

Conclusions

Altogether, our results point to the use of master banks of WJ-MSC as a valuable alternative to BM-MSC for orthopaedic conditions.

Dilated cardiomyopathy: from epidemiologic to genetic phenotypes: A translational review of current literature

Dilated cardiomyopathy (DCM) is characterized by left ventricular dilatation and, consecutively, contractile dysfunction. The causes of DCM are heterogeneous. DCM often results from myocarditis, exposure to alcohol, drugs or other toxins and metabolic or endocrine disturbances. In about 35% of patients, genetic mutations can be identified that usually involve genes responsible for cytoskeletal, sarcomere and nuclear envelope proteins. Due to its heterogeneity, a detailed diagnostic work-up is necessary to identify the specific underlying cause and exclude other conditions with phenotype overlap. Patients with DCM show typical systolic heart failure symptoms, but, with progress of the disease, diastolic dysfunction is present as well. Depending on the underlying pathology, DCM patients also become apparent through arrhythmias, thromboembolic events or cardiogenic shock. Disease progression and prognosis are mostly driven by disease severity and reverse remodelling within the heart. The worst prognosis is seen in patients with lowest ejection fractions or severe diastolic dysfunction, leading to terminal heart failure with subsequent need for left ventricular assist device implantation or heart transplantation. Guideline-based heart failure medication and device therapy reduces the frequency of heart failure hospitalizations and improves survival.

Transplanted Endothelial Cells Enhance Orthotopic Bone Regeneration

The aim of this study was to determine if endothelial cells could enhance bone marrow stromal-cell-mediated bone regeneration in an osseous defect. Using poly-lactide-co-glycolide scaffolds as cell carriers, we transplanted bone marrow stromal cells alone or with endothelial cells into 8.5-mm calvarial defects created in nude rats. Histological analyses of blood vessel and bone formation were performed, and microcomputed tomography (μCT) was used to assess mineralized bone matrix. Though the magnitude of the angiogenic response between groups was the same, μCT analysis revealed earlier mineralization of bone in the co-transplantation condition. Ultimately, there was a significant increase (40%) in bone formation in the co-transplantation group (33 ± 2%), compared with the transplantation of bone marrow stromal cells alone (23 ± 3%). Analysis of these data demonstrates that, in an orthotopic site, transplanted endothelial cells can influence the bone-regenerative capacity of bone marrow stromal cells.

Models of cranial suture biology

Craniosynostosis is a common congenital defect caused by premature fusion of cranial sutures. The severe morphologic abnormalities and cognitive deficits resulting from craniosynostosis and the potential morbidity of surgical correction espouse the need for a deeper understanding of the complex etiology for this condition. Work in animal models for the past 20 years has been pivotal in advancing our understanding of normal suture biology and elucidating pathologic disease mechanisms. This article provides an overview of milestone studies in suture development, embryonic origins, and signaling mechanisms from an array of animal models including transgenic mice, rats, rabbits, fetal sheep, zebrafish, and frogs. This work contributes to an ongoing effort toward continued development of novel treatment strategies.

A review of hedgehog signaling in cranial bone development

During craniofacial development, the Hedgehog (HH) signaling pathway is essential for mesodermal tissue patterning and differentiation. The HH family consists of three protein ligands: Sonic Hedgehog (SHH), Indian Hedgehog (IHH), and Desert Hedgehog (DHH), of which two are expressed in the craniofacial complex (IHH and SHH). Dysregulations in HH signaling are well documented to result in a wide range of craniofacial abnormalities, including holoprosencephaly (HPE), hypotelorism, and cleft lip/palate. Furthermore, mutations in HH effectors, co-receptors, and ciliary proteins result in skeletal and craniofacial deformities. Cranial suture morphogenesis is a delicate developmental process that requires control of cell commitment, proliferation and differentiation. This review focuses on both what is known and what remains unknown regarding HH signaling in cranial suture morphogenesis and intramembranous ossification. As demonstrated from murine studies, expression of both SHH and IHH is critical to the formation and fusion of the cranial sutures and calvarial ossification. SHH expression has been observed in the cranial suture mesenchyme and its precise function is not fully defined, although some postulate SHH to delay cranial suture fusion. IHH expression is mainly found on the osteogenic fronts of the calvarial bones, and functions to induce cell proliferation and differentiation. Unfortunately, neonatal lethality of IHH deficient mice precludes a detailed examination of their postnatal calvarial phenotype. In summary, a number of basic questions are yet to be answered regarding domains of expression, developmental role, and functional overlap of HH morphogens in the calvaria. Nevertheless, SHH and IHH ligands are integral to cranial suture development and regulation of calvarial ossification. When HH signaling goes awry, the resultant suite of morphologic abnormalities highlights the important roles of HH signaling in cranial development.

Dura mater stimulates human adipose-derived stromal cells to undergo bone formation in mouse calvarial defects

Human adipose-derived stromal cells (hASCs) have a proven capacity to aid in osseous repair of calvarial defects. However, the bone defect microenvironment necessary for osseous healing is not fully understood. In this study, we postulated that the cell-cell interaction between engrafted ASCs and host dura mater (DM) cells is critical for the healing of calvarial defects. hASCs were engrafted into critical sized calvarial mouse defects. The DM-hASC interaction was manipulated surgically by DM removal or by insertion of a semipermeable or nonpermeable membrane between DM and hASCs. Radiographic, histologic, and gene expression analyses were performed. Next, the hASC-DM interaction is assessed by conditioned media (CM) and coculture assays. Finally, bone morphogenetic protein (BMP) signaling from DM was investigated in vivo using novel BMP-2 and anti-BMP-2/4 slow releasing scaffolds. With intact DM, osseous healing occurs both from host DM and engrafted hASCs. Interference with the DM-hASC interaction dramatically reduced calvarial healing with abrogated BMP-2-Smad-1/5 signaling. Using CM and coculture assays, mouse DM cells stimulated hASC osteogenesis via BMP signaling. Through in vivo manipulation of the BMP-2 pathway, we found that BMP-2 plays an important role in DM stimulation of hASC osteogenesis in the context of calvarial bone healing. BMP-2 supplementation to a defect with disrupted DM allowed for bone formation in a nonhealing defect. DM is an osteogenic cell type that both participates in and stimulates osseous healing in a hASC-engrafted calvarial defect. Furthermore, DM-derived BMP-2 paracrine stimulation appears to play a key role for hASC mediated repair.

Primary cellular meningeal defects cause neocortical dysplasia and dyslamination

OBJECTIVE

Cortical malformations are important causes of neurological morbidity, but in many cases their etiology is poorly understood. Mice with Foxc1 mutations have cellular defects in meningeal development. We use hypomorphic and null alleles of Foxc1 to study the effect of meningeal defects on neocortical organization.

METHODS

Embryos with loss of Foxc1 activity were generated using the hypomorphic Foxc1(hith) allele and the null Foxc1(lacZ) allele. Immunohistologic analysis was used to assess cerebral basement membrane integrity, marginal zone heterotopia formation, neuronal overmigration, meningeal defects, and changes in basement membrane composition. Dysplasia severity was quantified using 2 measures.

RESULTS

Cortical dysplasia resembling cobblestone cortex, with basement membrane breakdown and lamination defects, is seen in Foxc1 mutants. As Foxc1 activity was reduced, abnormalities in basement membrane integrity, heterotopia formation, neuronal overmigration, and meningeal development appeared earlier in gestation and were more severe. Surprisingly, the basement membrane appeared intact at early stages of development in the face of severe deficits in meningeal development. Prominent defects in basement membrane integrity appeared as development proceeded. Molecular analysis of basement membrane laminin subunits demonstrated that loss of the meninges led to changes in basement membrane composition.

INTERPRETATION

Cortical dysplasia can be caused by cellular defects in the meninges. The meninges are not required for basement membrane establishment but are needed for remodeling as the brain expands. Specific changes in basement membrane composition may contribute to subsequent breakdown. Our study raises the possibility that primary meningeal defects may cortical dysplasia in some cases.

Paracrine interaction between adipose-derived stromal cells and cranial suture-derived mesenchymal cells

BACKGROUND

Adipose-derived stromal cells are a potential cell source for the successful healing of skeletal defects. In this study, the authors sought to investigate the potential for cranial suture-derived mesenchymal cells to promote the osteogenic differentiation of adipose-derived stromal cells. Various reports have previously examined the unique in vitro attributes of suture-derived mesenchymal cells; this study sought to extend those findings.

METHODS

Suture-derived mesenchymal cells were isolated from wild-type mice (n = 30) from both fusing posterofrontal and patent sagittal sutures. Cells were placed in Transwell inserts with human adipose-derived stromal cells (n = 5 patients) with osteogenic differentiation medium with or without recombinant Noggin (10 to 400 ng/ml). Specific gene expression of osteogenic markers and Hedgehog pathway were assayed; standard osteogenic assays (alkaline phosphatase and alizarin red staining) were performed. All assays were performed in triplicate.

RESULTS

Both posterofrontal and sagittal suture-derived mesenchymal cells induced osteogenic differentiation of adipose-derived stromal cells (p < 0.05). Posterofrontal suture-derived mesenchymal cells induced adipose-derived stromal cell osteogenesis to a greater degree than sagittal suture-derived mesenchymal cells (p < 0.05). This was accompanied by an increase in bone morphogenetic protein expression (p < 0.05). Finally, recombinant Noggin mitigated the pro-osteogenic effects of co-culture accompanied by a reduction in Hedgehog signaling (p < 0.05).

CONCLUSIONS

Suture-derived mesenchymal cells secrete paracrine factors that induce osteogenic differentiation of multipotent stromal cells (human adipose-derived stromal cells). Cells derived from the fusing posterofrontal suture do this to a significantly greater degree than cells from the patent sagittal suture. Enhanced bone morphogenetic protein and Hedgehog signaling may underlie this paracrine effect.

Retinoic acid from the meninges regulates cortical neuron generation

Extrinsic signals controlling generation of neocortical neurons during embryonic life have been difficult to identify. In this study we demonstrate that the dorsal forebrain meninges communicate with the adjacent radial glial endfeet and influence cortical development. We took advantage of Foxc1 mutant mice with defects in forebrain meningeal formation. Foxc1 dosage and loss of meninges correlated with a dramatic reduction in both neuron and intermediate progenitor production and elongation of the neuroepithelium. Several types of experiments demonstrate that retinoic acid (RA) is the key component of this secreted activity. In addition, Rdh10- and Raldh2-expressing cells in the dorsal meninges were either reduced or absent in the Foxc1 mutants, and Rdh10 mutants had a cortical phenotype similar to the Foxc1 null mutants. Lastly, in utero RA treatment rescued the cortical phenotype in Foxc1 mutants. These results establish RA as a potent, meningeal-derived cue required for successful corticogenesis.

Global age-dependent differences in gene expression in response to calvarial injury

Children less than 2 years of age are capable of healing large calvarial defects, whereas adults have been found to lack this endogenous ability. In this study, we used microarray analysis to compare genomewide expression patterns during active regeneration after injury with calvaria in skeletally immature and mature mice. Parietal bone defects were created in 6-day-old (juvenile) and 60-day-old (adult) mice using a 4-mm trephine bit (n = 20 mice per age group). The calvarial disc was removed, leaving the underlying dura mater intact. Two weeks after injury, the region of regeneration with the underlying dura mater was harvested, and RNA was extracted for microarray analysis. The 25 most differentially upregulated genes in juvenile regenerates compared with adults were listed, as well as selected bone-related genes. In addition, QRT-PCR confirmation of specific genes was performed for validation. Juvenile regenerates expressed significantly greater amounts of BMP-2, -4, -7, as well as FGF-2 and its receptor FGFR-1. Various other growth factors were also noted to be upregulated, including IGF-2 and Ptn. This corresponded with the increased expression of markers for osteogenic differentiation of Sparc and Oc. Markers of osteoclast activity, Acp5, Ctsk, and Mmp2, were noted to be greater in juvenile regenerates compared with adults. The observation of Mmp14 upregulation, however, highlights the importance of balanced osteoclast-mediated bone resorption for ultimate healing. The 2 most differentially regulated genes, transthyretin (Ttr) and prostaglandin D2 synthase (Ptgds), highlight the potential role of retinoic acid signaling and the prostaglandin axis on skeletal regeneration. These findings underscore the multitude of biomolecular mechanisms at play, allowing juvenile calvaria to heal after injury. The identification of various growth factors and cytokines involved also suggests novel therapeutic strategies for tissue-engineering purposes.

Proliferation, osteogenic differentiation, and fgf-2 modulation of posterofrontal/sagittal suture-derived mesenchymal cells in vitro

BACKGROUND

Fibroblast growth factor (FGF) signaling is of central importance in premature cranial suture fusion. In the murine skull, the posterofrontal suture normally fuses in early postnatal life, whereas the adjacent sagittal suture remains patent. The authors used a recently developed isolation technique for in vitro culture of suture-derived mesenchymal cells to examine the effects of FGF-2 on proliferation and differentiation of posterofrontal and sagittal suture-derived mesenchymal cells.

METHODS

Skulls were harvested from 40 mice (5-day-old). Posterofrontal and sagittal sutures were dissected, separating sutural mesenchymal tissue from dura mater and pericranium, and cultured. After cell migration from the explant and subculture, differences in proliferation and osteogenic differentiation of these distinct populations were studied. The mitogenic and osteogenic effects of recombinant FGF-2 were then assessed. FGF-2 regulation of gene expression was evaluated.

RESULTS

Suture-derived mesenchymal cells isolated from the posterofrontal suture demonstrated significantly higher proliferation rates and a robust mitogenic response to FGF-2 as compared with suture-derived mesenchymal cells isolated from the sagittal suture. Interestingly, posterofrontal suture-derived mesenchymal cells retained a higher in vitro osteogenic potential, as shown by alkaline phosphatase activity and bone nodule formation. FGF-2 significantly diminished osteogenesis in both suture-derived mesenchymal cell populations. Subsequently, Ob-cadherin and Sox9 were found to be differentially expressed in posterofrontal versus sagittal suture-derived mesenchymal cells and dynamically regulated by FGF-2.

CONCLUSIONS

In vitro osteogenesis of suture-derived mesenchymal cells recapitulates in vivo posterofrontal and sagittal sutural fates. Posterofrontal rather than sagittal suture-derived mesenchymal cells are more responsive to FGF-2 in vitro, in terms of both mitogenesis and osteogenesis.

Definition of topographic organization of skull profile in normal population and its implications on the role of sutures in skull morphology

The geometric configuration of the skull is complex and unique to each individual. This study provides a new technique to define the outline of skull profile and attempt to find the common factors defining the ultimate skull configuration in adult population. Ninety-three lateral skull x-ray from the computed tomographic scan films were selected and digitized. The lateral skull surface was divided into 3 regions based on the presumed location of the coronal and lambdoid sutures. Three main curvatures (frontal, parietal, occipital) were consistently identified to overlap the skull periphery. The radius, cord length, and inclination of each curvature were measured. The average values for 3 defined curvatures of the skull profile were recorded. Factor analysis of the measured values produced 3 factors explaining the skull profile. The first factor explained 32% of total variance and was related to the overall size of the head as represented by total length and the radius of the curvature in the vertex and back of the head. The second factor covered 26% of the variance representing the inverse correlation between the angle of the frontal and parietal curves. The third factor revealed the direct correlation of the occipital and parietal angle. In all of these factors, the frontal zone variation was independent or opposite of the parieto-occipital zone. A strong association between the total length of the skull, occipital curve radius, and length with the sex was shown. In conclusion, the skull profile topography has large variation and can be defined mathematically by 2 distinct territories: frontal and parieto-occipital zones. These territories hinge on the coronal suture. Therefore, the coronal suture may play a dominant role in final skull configuration.

Developmental changes of mast cell populations in the cerebral meninges of the rat

It is known that both the dura and the pia mater attract and support the differentiation of mast cells. The present study shows that unevenly distributed mast cells in the cerebral meninges of the rat can be found in perivascular sites and vessel ramification points, but can also be unrelated to the meningeal vasculature. It also documents changes in the number, localization and staining preferences of the mast cells in the two meninges of the developing and mature rat brain. Quantitative examination of all types of histochemically differentiated meningeal mast cells reveals no major (although some exist) differences between right and left side subpopulations, but strongly suggests a different origin and fate of the dural and the pial mast cells. The number of dural mast cells, already high from postnatal day 0, although declining from postnatal day 21 onwards, remains conspicuous up to postnatal day 180. In contrast, pial mast cells are comparatively very few in the first day of the postnatal life, and despite a transient significant increase in the following two weeks, they reach almost zero levels from postnatal day 21.

Differential effects of TGF-beta isoforms on murine fetal dural cells and calvarial osteoblasts

BACKGROUND

Proteins within the transforming growth factor (TGF)-beta family play a central role in both normal and pathologic calvarial morphogenesis. Previous work has suggested differential functions of the TGF-beta isoforms in these processes. Little is known, however, about effects of TGF-betas on the underlying dura. Furthermore, studies on the effects of TGF-beta isoforms on osteoblasts have been conflicting. The purpose of this study was to determine the effect of TGF-beta isoforms, specifically TGF-beta1 and TGF-beta3, on fetal calvarial osteoblast and dural cell differentiation, proliferation, and apoptosis.

METHODS

Primary cultures of fetal calvarial osteoblasts and dural cells were established from embryonic day-18 CD-1 mice. Cells were treated for 48 hours with TGF-beta1 or TGF-beta3. Northern blot analysis, cell counts, and apoptosis assays were performed.

RESULTS

In dural cells, TGF-beta1 stimulated the expression of early osteodifferentiation genes and resulted in a slight decrease in cell number and no effect on apoptosis. Similar results were observed in osteoblasts. TGF-beta3 had little or no effect on the genes studied in both cell types but resulted in increased apoptosis and concomitant decreases in cell number in both cell types.

CONCLUSIONS

This study demonstrates that dural cells respond to TGF-beta and that this response is isoform-specific. TGF-beta1 stimulates osteodifferentiation of previously uncommitted cells in the dura. It also stimulates early events in bone matrix deposition and has little effect on late markers of bone differentiation in osteoblasts and dural cells. Both isoforms result in decreases in cell number. TGF-beta3 results in greater decreases in cell number and isoform-specific stimulation of apoptosis in both dural cells and calvarial osteoblasts.

Isolation and characterization of posterofrontal/sagittal suture mesenchymal cells in vitro

BACKGROUND

Craniosynostosis, the premature fusion of cranial sutures, affects one in 2500 children. In the mouse, the posterofrontal suture is programed to fuse postnatally, but the adjacent sagittal suture remains patent throughout life. To study the cellular process of suture fusion, the authors isolated and studied suture-derived mesenchymal cells.

METHODS

Skulls were harvested from 80 mice (2 to 5 days old), and posterofrontal and sagittal sutures were dissected meticulously. Suture mesenchymal tissue was separated from the underlying dura mater and overlying pericranium and cultured in growth media. After the cells migrated from the explant tissues, the morphologies of the two cell populations were studied carefully, and quantitative real-time polymerase chain reaction was performed to evaluate gene expression.

RESULTS

Both posterofrontal and sagittal cells exhibited highly heterogeneous morphologies, and the posterofrontal cells migrated faster than the sagittal cells. Accordingly, growth factors such as transforming growth factor-beta1 and fibroblast growth factor (FGF)-2 were expressed significantly more highly in posterofrontal compared with sagittal suture mesenchymal cells. In contrast, FGF receptor 2 and FGF-18 were expressed significantly more in sagittal than in posterofrontal suture cells. Importantly, bone morphogenic protein-3, the only osteogenic inhibitor in the bone morphogenic protein family, and noggin, a bone morphogenic protein antagonist, were expressed significantly more in sagittal than in posterofrontal suture cells, suggesting a possible mechanism of suture patency.

CONCLUSIONS

To the authors' knowledge, this is the first analysis of mouse suture-derived mesenchymal cells. The authors conclude that isolation of suture-derived mesenchymal cells will provide a useful in vitro system with which to study the mechanisms underlying suture biology.

MULTIPLE DIFFERENTIATION POTENTIALS OF NEONATAL DURA MATER-DERIVED CELLS

OBJECTIVE

The involvement of the dura mater in calvarial development and bone healing lead to a hypothesis that progenitor cells with multiple differentiation potentials exist within this tissue. The present study investigated the differentiation potentials of dura mater-derived cells by driving them into several cell-restricted lineages.

METHODS

Dissected dura mater tissue of neonatal rats was washed, finely minced, and enzymatically digested. The harvested cells were exposed to different differentiation (osteogenic, adipogenic, and chondrogenic) and basic media.

RESULTS

At defined time points, dura mater-derived cells were observed to differentiate into osteoblastic, adipoblastic, and chondroblastic cells, evidenced by specific biochemical staining. In addition, gene expressions of osteogenesis (alkaline phosphatase, osteocalcin, and osteopontin), chondrogenesis (collagen Type II and aggrecan core protein) and adipogenesis (peroxisome proliferator activated receptor gamma-2) were up-regulated in the differentiated dura mater-derived cells, confirmed by polymerase chain reaction.

CONCLUSION

Preliminarily, it was concluded that a subpopulation of multiple potential mesenchymal cells exists in neonatal dura mater, which explains the function of the dura mater on neurocranium development and calvarial bone healing.

Prediction of biomechanical stability after callus distraction by high resolution scanning acoustic microscopy

Accurate clinical prediction of the resistance to fracture after callus distraction requires a detailed understanding of structural and elastic properties of the newly formed bone. We investigated 26 sheep that underwent middiaphyseal callus distraction at a rate of 0.5 mm every 12 h for 30 d using a standard unilateral fixator system. The sample population included four groups undergoing different treatments to improve bone healing, including bone grafting and the local application of growth factors. All animals were sacrificed eight weeks after the end of distraction. The fracture forces of the lengthened tibia and the contralateral control tibia from each animal were evaluated by biomechanical (four-point bending) testing. The microstructure and anisotropic acoustic impedance distributions were assessed by quantitative 50-MHz scanning acoustic microscopy. The relationships between resistance to fracture, structural properties and acoustic impedance of the newly formed callus tissue and adjacent cortical tissue were investigated. A significant linear multivariate regression model was developed that predicts the fracture force with a high accuracy (RMSE = 248 N, R(2) = 0.86, p < 0.0001).

Cell mixing at a neural crest-mesoderm boundary and deficient ephrin-Eph signaling in the pathogenesis of craniosynostosis

Boundaries between cellular compartments often serve as signaling interfaces during embryogenesis. The coronal suture is a major growth center of the skull vault and develops at a boundary between cells derived from neural crest and mesodermal origin, forming the frontal and parietal bones, respectively. Premature fusion of these bones, termed coronal synostosis, is a common human developmental anomaly. Known causes of coronal synostosis include haploinsufficiency of TWIST1 and a gain of function mutation in MSX2. In Twist1(+/-) mice with coronal synostosis, we found that the frontal-parietal boundary is defective. Specifically, neural crest cells invade the undifferentiated mesoderm of the Twist1(+/-) mutant coronal suture. This boundary defect is accompanied by an expansion in Msx2 expression and reduction in ephrin-A4 distribution. Reduced dosage of Msx2 in the Twist1 mutant background restores the expression of ephrin-A4, rescues the suture boundary and inhibits craniosynostosis. Underlining the importance of ephrin-A4, we identified heterozygous mutations in the human orthologue, EFNA4, in three of 81 patients with non-syndromic coronal synostosis. This provides genetic evidence that Twist1, Msx2 and Efna4 function together in boundary formation and the pathogenesis of coronal synostosis.

Critical molecular switches involved in BMP-2-induced osteogenic differentiation of mesenchymal cells

Bone morphogenetic protein (BMP)-2 strongly induces bone formation. Introduction of the protein in muscle tissue results in ectopic bone formation. Similarly, BMP-2 treatment also stimulates the in vitro transdifferentiation of myogenic cells to osteogenic cells. The establishment of an in vitro model system has enabled the investigation of intracellular events including BMP receptor activation, BMP-2-induced R-Smad activation, and kinase activation, and the role of osteogenic transcription factors, such as Runx2, Osx, Dlx5, and Msx2. Many reviews have addressed events downstream of BMP-receptor binding but few deal with molecular cascades involved in BMP-2-induced osteogenesis. We focus on critical molecular switches, especially transcription factors, and several kinase pathways involved in osteogenic differentiation.

Expression and Possible Mechanisms of Regulation of BMP3 in Rat Cranial Sutures

BACKGROUND

Clinical genetics data and investigative studies have contributed greatly to our understanding of the role of numerous genes in craniosynostosis. Recent studies have introduced antagonists of osteogenesis as potential key regulators of suture fusion and patency. The authors investigated the expression pattern of the bone morphogenetic protein antagonist BMP3 in rat cranial sutures and the factors regulating its expression in vitro.

METHODS

Microarray analysis was performed on rat posterior frontal and sagittal cranial sutures at 5, 10, 15, 20, and 30 days of life (n = 30 per group). Gene expression was confirmed using quantitative real-time reverse transcriptase polymerase chain reaction. Regulation of BMP3 expression was determined using primary rat calvarial osteoblasts stimulated with recombinant human fibroblast growth factor 2 or recombinant human transforming growth factor beta1, or cultured with primary rat nonsuture dura mater. Gene expression was quantified with quantitative real-time reverse transcriptase polymerase chain reaction.

RESULTS

BMP3 expression in the posterior frontal suture decreased over the time course analyzed, whereas it increased in the sagittal suture. Notably, BMP3 expression was higher in the patent sagittal suture during the window of posterior frontal suture fusion. Stimulation of osteoblasts with recombinant human fibroblast growth factor 2 led to a rapid and sustained suppression of BMP3 expression (85 percent, p < 0.01) when compared with controls. Co-culture with dural cells decreased BMP3 mRNA by 50 percent compared with controls (p < 0.01).

CONCLUSIONS

BMP3 is expressed in rat cranial sutures in a temporal pattern suggesting involvement in cranial suture patency and fusion. Furthermore, BMP3 is regulated in calvarial osteoblasts by recombinant human fibroblast growth factor 2 and by paracrine signaling from dura mater. These data add to our knowledge of the role of osteogenic antagonists in cranial suture biology.

Noggin Improves Bone Healing Elicited by Muscle Stem Cells Expressing Inducible BMP4

The aim of this study was to test the hypothesis that a specific antagonist may enhance the efficacy of its corresponding growth factor in a regulated tissue engineering strategy. Our prior research has led to the development of a retroviral vector that enables optimal regulated bone morphogenetic protein 4 (BMP4) expression in vitro and regulated bone formation in vivo with transduced muscle stem cells. However, when implanted in critical-sized calvarial defects, these cells led to residual bone formation without induction or bone overgrowth with induction, even at reduced cell doses. We thus co-implanted the aforementioned cells with stem cells engineered to express Noggin, a specific BMP antagonist. This approach, while preserving our ability to regulate bone regeneration closely, prevented both the basal level bone regeneration and the bone overgrowth and, more importantly, led to the regeneration of bone that more closely resembled normal bone. We believe that this regulatable tissue engineering strategy, enhanced by utilizing a specific antagonist, constitutes a new paradigm for tissue engineering and regenerative medicine.

Raman imaging demonstrates FGF2-induced craniosynostosis in mouse calvaria

Craniosynostosis is a severe craniofacial disease where one or more sutures, the fibrous tissue that lies between the cranial bones, fuses prematurely. Some craniosynostosis syndromes are known to be caused by mutations in fibroblast growth factor (FGF) receptors. Mutated FGF receptors are thought to cause constitutive signaling. In this study, heparin acrylic beads released fibroblast growth factor 2 (FGF2) to mimic constitutive signaling by mutated receptors, delivering FGF2 in addition to already existing normal tissue amounts. Fetal day 18.5 mouse sutures were treated with FGF2-soaked beads and cultured in serum free media for 48 h. We have shown previously that this treatment leads to fusion and increased Msx2 expression, but here we use near-infrared Raman imaging to simultaneously examine the mineral components and matrix components of cranial tissue while providing light microscopic spatial information. FGF2-treated mouse sutures show increased v1 phosphate and v1 carbonate bandwidths, indicating a slightly chemically modified mineral being rapidly deposited. In addition, FGF2-treated mouse sutures show a marked increase in mineral-to-matrix ratios compared to control mouse sutures, typical of increased mineralization.

Adipose-derived adult stromal cells heal critical-size mouse calvarial defects

In adults and children over two years of age, large cranial defects do not reossify successfully, posing a substantial biomedical burden. The osteogenic potential of bone marrow stromal (BMS) cells has been documented. This study investigates the in vivo osteogenic capability of adipose-derived adult stromal (ADAS) cells, BMS cells, calvarial-derived osteoblasts and dura mater cells to heal critical-size mouse calvarial defects. Implanted, apatite-coated, PLGA scaffolds seeded with ADAS or BMS cells produced significant intramembranous bone formation by 2 weeks and areas of complete bony bridging by 12 weeks as shown by X-ray analysis, histology and live micromolecular imaging. The contribution of implanted cells to new bone formation was 84-99% by chromosomal detection. These data show that ADAS cells heal critical-size skeletal defects without genetic manipulation or the addition of exogenous growth factors.

Age-related changes in the biomolecular mechanisms of calvarial osteoblast biology affect fibroblast growth factor-2 signaling and osteogenesis

The ability of immature animals to orchestrate successful calvarial ossification has been well described. This capacity is markedly attenuated in mature animals and humans greater than 2 years of age. Few studies have investigated biological differences between juvenile and adult osteoblasts that mediate successful osteogenesis. To identify possible mechanisms for this clinical observation, we investigated cellular and molecular differences between primary osteoblasts derived from juvenile (2-day-old) and adult (60-day-old) rat calvaria. Data demonstrated that juvenile osteoblasts contain a subpopulation of less differentiated cells as observed by spindle-like morphology and decreased osteocalcin production. Juvenile, compared with adult, osteoblasts showed increased proliferation and adhesion. Furthermore, following rhFGF-2 stimulation juvenile osteoblasts increased expression of collagen I alpha 1 (5-fold), osteopontin (13-fold), and osteocalcin (16-fold), compared with relatively unchanged adult osteoblasts. Additionally, juvenile osteoblasts organized and produced more matrix proteins and formed 41-fold more bone nodules. Alternatively, adult osteoblasts produced more FGF-2 and preferentially translated the high molecular weight (22 kDa) form. Although adult osteoblasts transcribed more FGF-R1 and juvenile osteoblasts transcribed more FGF-R2 at baseline levels, juvenile osteoblasts translated more FGF-R1 and -R2 and showed increased phosphorylation. Collectively, these findings begin to explain why juvenile, but not adult, osteoblasts successfully heal calvarial defects.

Bone induction capacity of the periosteum and neonatal dura in the setting of the rat zygomatic arch fracture model

OBJECTIVES

Osteogenic properties of the dura and periosteum are thought to contribute to the regenerative capacity of membranous bone tissue. The purpose of this investigation was to elucidate (1) whether dura without underlying neural tissues can induce osteogenesis, (2) to what extent the periosteum participates in membranous bone healing, and (3) the difference between dura-induced and periosteum-induced osteogenesis.

METHODS

A standardized 2-mm defect was created within the middle portion of each zygomatic arch in 30 Wistar albino rats. The rats were divided into 3 groups, 10 animals in each group. In group 1, the periosteum was removed and neonatal dura grafts were transplanted onto the zygomatic arch bone defect circumferentially. In group 2, the overlying periosteum was preserved. In group 3, the periosteum was removed. At 3 and 10 weeks, animals from each group were killed, and specimens were obtained. Data were collected from the 3-dimensional computed tomographic scans and histologic studies to compare the extent of bony repair.

RESULTS

Fracture sites demonstrated osteogenesis associated with chondrogenesis in groups 1 and 2 and only limited osteogenesis with no chondrogenesis in group 3. In some animals in group 3, cortical bone ends underwent resorption. In groups 1 and 2, bone defects were obliterated by the formation of the mature compact bone at 10 weeks postoperatively. The difference between bone regeneration in these groups was not significant (P =.16). In group 3, the defects failed to heal by bony union, and in most of the samples the fibrous union was observed instead. The difference between groups 1 and 3 was significant (P =.03). The difference between groups 2 and 3 was not significant (P =.09).

CONCLUSIONS

The trend toward significance is in agreement with the current clinical practice of preserving periosteum in the manipulations of the membranous bone defects. Newborn dura can exert a potentiating effect on osteogenesis.

Bone growth factors in maxillofacial skeletal reconstruction

A literature review was performed to survey the available information on the potential of bone growth factors in skeletal reconstruction in the maxillofacial area. The aim of this review was to characterize the biological and developmental nature of the growth factors considered, their molecular level of activity and their osteogenic potential in craniofacial bone repair and reconstruction. A total of 231 references were selected for evaluation by the content of the abstracts. All growth factors considered have a fundamental role in growth and development. In postnatal skeletal regeneration, PDGF plays an important role in inducing proliferation of undifferentiated mesenchymal cells. It is an important mediator for bone healing and remodelling during trauma and infection. It can enhance bone regeneration in conjunction with other growth factors but is unlikely to provide entirely osteogenic properties itself. IGFs have an important role in general growth and maintenance of the body skeleton. The effect of local application of IGFs alone in craniofacial skeletal defects has not yet shown a clear potential for enhancement of bone regeneration in the reported dosages. The combination of IGF-I with PDGF has been effective in promoting bone regeneration in dentoalveolar defects around implants or after periodontal bone loss. TGFbeta alone in skeletal reconstruction appears to be associated with uncertain results. The presence of committed cells is required for enhancement of bone formation by TGFbeta. It has a biphasic effect, which suppresses proliferation and osteoblastic differentiation at high concentrations. BMPs, BMP2, BMP4 and BMP7 in particular, appear to be the most effective growth factors in terms of osteogenesis and osseous defect repair. Efficacy of BMPs for defect repair is strongly dependent on the type of carrier and has been subject to unknown factors in clinical feasibility trials resulting in ambiguous results. The current lack of clinical data may prolong the period until this factor is introduced into routine clinical application. PRP is supposed to increase proliferation of undifferentiated mesenchymal cells and to enhance angiogenesis. There is little scientific evidence about the benefit of PRP in skeletal reconstructive and preprosthetic surgery yet and it is unlikely that peri-implant bone healing or regeneration of local bone into alloplastic material by the application of PRP alone will be significantly enhanced.

Blocking endogenous FGF-2 activity prevents cranial osteogenesis

Normal growth and morphogenesis of the cranial vault reflect a balance between cell proliferation in the sutures and osteogenesis at the margins of the cranial bones. In the clinical condition craniosynostosis, the sutures fuse prematurely as a result of precocious osteogenic differentiation and craniofacial malformation results. Mutations in several fibroblast growth factor receptor (FGFR) genes have now been identified as being responsible for the major craniosynostotic syndromes. We have used a grafting technique to manipulate the levels of endogenous FGF-2 ligand in embryonic chick cranial vaults and thereby perturb morphogenesis. Implantation of beads loaded with FGF-2 did not affect normal cranial development at physiological concentrations, although they elicited a morphogenetic response in the limb. Implantation of beads loaded with a neutralising antibody to FGF-2 generated a concentration-dependent response. When a single bead was implanted, the grafts grew to a massive size as a result of increased cell division in the tissue. With greater inactivation of FGF-2 protein (two to three beads implanted), all further bone differentiation and cell proliferation was blocked. These data further support the emerging idea that the intensity of FGF-mediated signalling determines the developmental fate of the skeletogenic cells in the cranial vault. High and low levels correlate with differentiation and proliferation, respectively. A balance between the two ensures normal cranial vault morphogenesis. This is consistent with the observation that several FGFR mutations causing craniosynostosis result in constitutive activation of the receptor.

Gene therapy in plastic surgery

Recent developments in gene therapy have shown promise in the treatment of soft-tissue repair, bone formation, nerve regeneration, and cranial suture development. This special topic article reviews commonly used methods of gene therapy and discusses their various advantages and disadvantages. In addition, an overview of new developments in gene therapy as they relate to plastic surgery is provided.

Dura mater biology: autocrine and paracrine effects of fibroblast growth factor 2

The dura mater, the outermost layer of the meninges, is thought to be essential for calvarial morphogenesis, postnatal suture fusion, and osseous repair of calvarial defects. Despite numerous studies illustrating the fundamental role of the dura mater, there is little information about the autocrine and paracrine mechanisms regulating dural cell biology during calvarial ossification. Previous work conducted in the authors' laboratory demonstrated that non-suture-associated dural cells from 6-day-old rat pups expressed high levels of fibroblast growth factor 2 (FGF-2), whereas dural cells from 60-day-old adult rats expressed very little FGF-2. Because young mammals can successfully heal large calvarial defects, the authors sought to investigate the autocrine and/or paracrine effects of FGF-2 on the proliferation, gene expression, and alkaline phosphatase production of dural cells. Cultures of non-suture-associated dural cells were established from 6-day-old Sprague-Dawley rat pups and then stimulated with recombinant human FGF-2 (rhFGF-2; 10 ng/ml). Dural cells stimulated with rhFGF-2 proliferated significantly faster than untreated dural cells at 24 hours (2.1 x 10(5) +/- 3.2 x 10(4) versus 1.1 x 10(5) +/- 1.8 x 10(4), p < or = 0.001) and 48 hours (2.3 x 10(5) +/- 4.2 x 10(4) versus 1.2 x 10(5) +/- 1.3 x 10(4), p < or = 0.001). Moreover, dural cells stimulated with rhFGF-2 expressed 7-fold more proliferating cell nuclear antigen than did control cultures. Treatment with rhFGF-2 increased dural cell expression of genes important for skeletal repair: FGF-2 (7-fold), transforming growth factor beta 1 (3-fold), transforming growth factor beta 3 (4-fold), and type I collagen (4-fold). Furthermore, rhFGF-2 increased dural cell expression of osteopontin (2-fold), a "late" marker of osteoblastic differentiation. Interestingly, dural cell alkaline phosphatase activity, an "earlier" marker of osteoblast differentiation, was significantly decreased by treatment with rhFGF-2 compared with control cultures at 24 hours (0.005 +/- 0.001 versus 0.01 +/- 0.003, p < or = 0.01) and 48 hours (0.004 +/- 0.0009 versus 0.01 +/- 0.0009). Together these data provide insight into the autocrine and paracrine effects of FGF-2 on the biology of the dura mater.

From genotype to phenotype: the differential expression of FGF, FGFR, and TGFbeta genes characterizes human cranioskeletal development and reflects clinical presentation in FGFR syndromes

Mutations in the fibroblast growth factor receptor (FGFR) genes 1, 2, and 3 are causal in a number of craniofacial dysostosis syndromes featuring craniosynostosis with basicranial and midfacial deformity. Great clinical variability is displayed in the pathologic phenotypes encountered. To investigate the influence of developmental genetics on clinical diversity in these syndromes, the expression of several genes implicated in their pathology was studied at sequential stages of normal human embryo-fetal cranial base and facial ossification (n = 6). At 8 weeks of gestation, FGFR1, FGFR2, and FGFR3 are equally expressed throughout the predifferentiated mesenchyme of the cranium, the endochondral skull base, and midfacial mesenchyme. Both clinically significant isoforms of FGFR2, IgIIIa/c and IgIIIa/b, are coexpressed in maxillary and basicranial ossification. By 10 to 13 weeks, FGFR1 and FGFR2 are broadly expressed in epithelia, osteogenic, and chondrogenic cell lineages. FGFR3, however, is maximally expressed in dental epithelia and proliferating chondrocytes of the skull base, but poorly expressed in the osteogenic tissues of the midface. FGF2 and FGF4, but not FGF7, and TGFbeta1 and TGFbeta3 are expressed throughout both osteogenic and chondrogenic tissues in early human craniofacial skeletogenesis. Maximal FGFR expression in the skull base proposes a pivotal role for syndromic growth dysplasia at this site. Paucity of FGFR3 expression in human midfacial development correlates with the relatively benign human mutant FGFR3 midfacial phenotypes. The regulation of FGFR expression in human craniofacial skeletogenesis against background excess ligand and selected cofactors may therefore play a profound role in the pathologic craniofacial development of children bearing FGFR mutations.

The role of transforming growth factor-beta in the modulation of mouse cranial suture fusion

Transforming growth factor-beta (TGF-beta) is actively expressed during mouse calvarial suture fusion. However, the role TGF-beta plays in this process remains unclear. The present study was performed to investigate whether modulation of suture fusion can be achieved by blocking the bioavailability of TGF-beta. Both in vitro and in vivo models were studied. For the in vitro model, the posterior frontal sutures from 24-day-old mice were harvested and cultured for 2, 3, or 4 weeks in the presence of 20 microg/ml of pan-specific TGF-beta polyclonal antibody or rabbit IgG as a control. Culture media were changed every 48 hours and fresh antibody or rabbit IgG was added during each media change. Suture fusion was evaluated by histometric analysis. For the in vivo model, TGF-beta antisense plasmid DNA complexed with lipofectamine was injected into the subgaleal layer along the frontal suture of 22-day-old mice under anesthesia. For control groups, empty vector plasmid DNA+ complexed with lipofectamine was used. The posterior frontal sutures were harvested at various time points and examined by histometric analysis and reverse transcription and polymerase chain reaction for the detection of messenger RNA. The in vitro studies demonstrated that the presence of TGF-beta antibody in culture media delayed posterior frontal suture fusion. By 3 weeks in culture, new bone area was only 20 percent of that in control groups as determined by histometric analysis. By the end of the fourth week, suture fusion was only 25 percent completed compared with controls. The in vivo studies demonstrated that, compared with the control, posterior frontal suture fusion was significantly delayed in the animals injected with antisense plasmid DNA. Suture fusion was complete in control animals by postnatal day 45. There was a 70 percent inhibition of suture fusion (new bone area) in antisense groups measured with histometric analysis. Four days after antisense plasmid DNA injection (age of 26 days), messenger RNA expression for TGF-beta 1 was 77 percent lower than in the control group. We have demonstrated that modulation of TGF-beta affects calvarial suture formation in vitro and in vivo with TGF-beta antibody and TGF-beta1 antisense plasmid DNA treatment, respectively. These data indicate that TGF-beta may play a causative role in mouse posterior frontal suture fusion. Modulation TGF-beta 1 gene expression in vivo can alter the natural history of cranial suture fusion.

In vivo modulation of FGF biological activity alters cranial suture fate

Gain-of-function mutations in fibroblast growth factor receptors have been identified in numerous syndromes associated with premature cranial suture fusion. Murine models in which the posterior frontal suture undergoes programmed fusion after birth while all other sutures remain patent provide an ideal model to study the biomolecular mechanisms that govern cranial suture fusion. Using adenoviral vectors and targeted in utero injections in rats, we demonstrate that physiological posterior frontal suture fusion is inhibited using a dominant-negative fibroblast growth factor receptor-1 construct, whereas the normally patent coronal suture fuses when infected with a construct that increases basic fibroblast growth factor biological activity. Our data may facilitate the development of novel, less invasive treatment options for children with craniosynostosis.

Biomolecular mechanisms of calvarial bone induction: immature versus mature dura mater

The ability of newborns and immature animals to reossify calvarial defects has been well described. This capacity is generally lost in children greater than 2 years of age and in mature animals. The dura mater has been implicated as a regulator of calvarial reossification. To date, however, few studies have attempted to identify biomolecular differences in the dura mater that enable immature, but not mature, dura to induce osteogenesis. The purpose of these studies was to analyze metabolic characteristics, protein/gene expression, and capacity to form mineralized bone nodules of cells derived from immature and mature dura mater. Transforming growth factor beta-1, basic fibroblast growth factor, collagen type IalphaI, osteocalcin, and alkaline phosphatase are critical growth factors and extracellular matrix proteins essential for successful osteogenesis. In this study, we have characterized the proliferation rates of immature (6-day-old rats, n = 40) and mature (adult rats, n = 10) dura cell cultures. In addition, we analyzed the expression of transforming growth factor beta-1, basic fibroblast growth factor-2, proliferating cell nuclear antigen, and alkaline phosphatase. Our in vitro findings were corroborated with Northern blot analysis of mRNA expression in total cellular RNA isolated from snap-frozen age-matched dural tissues (6-day-old rats, n = 60; adult rats, n = 10). Finally, the capacity of cultured dural cells to form mineralized bone nodules was assessed. We demonstrated that immature dural cells proliferate significantly faster and produce significantly more proliferating cell nuclear antigen than mature dural cells (p < 0.01). Additionally, immature dural cells produce significantly greater amounts of transforming growth factor beta-1, basic fibroblast growth factor-2, and alkaline phosphatase (p < 0.01). Furthermore, Northern blot analysis of RNA isolated from immature and mature dural tissues demonstrated a greater than 9-fold, 8-fold, and 21-fold increase in transforming growth factor beta-1, osteocalcin, and collagen IalphaI gene expression, respectively, in immature as compared with mature dura mater. Finally, in keeping with their in vivo phenotype, immature dural cells formed large calcified bone nodules in vitro, whereas mature dural cells failed to form bone nodules even with extended culture. These studies suggest that differential expression of growth factors and extracellular matrix molecules may be a critical difference between the osteoinductive capacity of immature and mature dura mater. Finally, we believe that the biomolecular bone- and matrix-inducing phenotype of immature dura mater regulates the ability of young children and immature animals to heal calvarial defects.