Ex vivo Noggin gene therapy inhibits bone formation in a mouse model of postoperative resynostosis

Titania nanotube-based protein delivery system to inhibit cranial bone regeneration in Crouzon model of craniosynostosis

BACKGROUND

Craniosynostosis is a developmental disorder characterized by the premature fusion of skull sutures, necessitating repetitive, high-risk neurosurgical interventions throughout infancy. This study used protein-releasing Titania nanotubular implant (TNT/Ti) loaded with glypican 3 (GPC3) in the cranial critical-sized defects (CSDs) in Crouzon murine model (Fgfr2c342y/+ knock-in mutation) to address a key challenge of delaying post-operative bone regeneration in craniosynostosis.

MATERIALS AND METHODS

A 3 mm wide circular CSD was created in two murine models of Crouzon syndrome: (i) surgical control (CSDs without TNT/Ti or any protein, n=6) and (ii) experimental groups with TNT/Ti loaded with GPC3, further subdivided into the presence or absence of chitosan coating (on nanotubes) (n=12 in each group). The bone volume percentage in CSDs was assessed 90 days post-implantation using micro-computed tomography (micro-CT) and histological analysis.

RESULTS

Nano-implants retrieved after 90 days post-operatively depicted well-adhered, hexagonally arranged, and densely packed nanotubes with average diameter of 120±10 nm. The nanotubular architecture was generally well-preserved. Compared with the control bone volume percentage data (without GPC3), GPC3-loaded TNT/Ti without chitosan coating displayed a significantly lower volume percent in cranial CSDs (P<0.001). Histological assessment showed relatively less bone regeneration (healing) in GPC3-loaded CSDs than control CSDs.

CONCLUSION

The finding of inhibition of cranial bone regeneration by GPC3-loaded TNT/Ti in vivo is an important advance in the novel field of minimally-invasive craniosynostosis therapy and holds the prospect of altering the whole paradigm of treatment for affected children. Future animal studies on a larger sample are indicated to refine the dosage and duration of drug delivery across different ages and both sexes with the view to undertake human clinical trials.

Current Approaches in the Development of Molecular and Pharmacological Therapies in Craniosynostosis Utilizing Animal Models

The development of the craniofacial skeleton is a spatial and temporal process where cranial sutures play a role in the regulation of morphogenesis and growth. Disruption of these cellular and molecular interactions may lead to craniosynostosis, the premature obliteration of one or more cranial sutures, yielding skull growth restriction and malformation perpendicular to the affected suture. Facial deformity and various functional CNS anomalies are other frequent complications. Cranial vault expansion and reconstructive surgery remain the mainstay of treatment but pose an elevated risk of morbidity for the infant. While the etiology of nonsyndromic craniosynostosis remains to be deciphered, gain-of-function mutations in FGFR1-3 and TWIST1 were found to be responsible for more than 3/4 of the most commonly encountered craniofacial syndromes. Animal models have been invaluable to further dissect the role of genes within the cranial sutures and for the development of alternative nonsurgical treatment strategies. In this review, we will present various molecular and pharmacological approaches for the treatment of craniosynostosis that have been tested using in vitro and in vivo assays as well as discuss their potential application in humans focusing on the case of tyrosine kinase inhibitors.

Molecular Analysis of Gli3, Ihh, Rab23, and Jag1 in a Rabbit Model of Craniosynostosis: Likely Exclusion as the Loci of Origin

OBJECTIVE

Craniosynostosis (CS) involves the premature fusion of one or more cranial sutures. The etiology of CS is complex and mutations in more than 50 distinct genes have been causally linked to the disorder. Many of the genes that have been associated with CS in humans play an essential role in tissue patterning and early craniofacial development. Among these genes are members of the Hedgehog (HH) and Notch signal transduction pathways, including the GLI family member Gli3, Indian Hedgehog ( Ihh), the RAS oncogene family member Rab23, and the Notch ligand JAGGED1 ( Jag1). We have previously described a colony of rabbits with a heritable pattern of coronal suture synostosis, although the genetic basis for synostosis within this model remains unknown. The present study was performed to determine if coding errors in Gli3, Ihh, Rab23, or Jag1 could be causally linked to craniosynostosis in this unique animal model.

DESIGN

Sequencing of cDNA templates was performed using samples obtained from wild-type and craniosynostotic rabbits.

RESULTS

Several nucleotide polymorphisms were identified in Gli3, Ihh, and Rab23, although these variants failed to segregate by phenotype. No nucleotide polymorphisms were identified in Jag1.

CONCLUSIONS

These data indicate that the causal locus for heritable craniosynostosis in this rabbit model is not located within the protein coding regions of Gli3, Ihh, Rab23, or Jag1.

Genetic advances in craniosynostosis

Craniosynostosis, the premature ossification of one or more skull sutures, is a clinically and genetically heterogeneous congenital anomaly affecting approximately one in 2,500 live births. In most cases, it occurs as an isolated congenital anomaly, that is, nonsyndromic craniosynostosis (NCS), the genetic, and environmental causes of which remain largely unknown. Recent data suggest that, at least some of the midline NCS cases may be explained by two loci inheritance. In approximately 25-30% of patients, craniosynostosis presents as a feature of a genetic syndrome due to chromosomal defects or mutations in genes within interconnected signaling pathways. The aim of this review is to provide a detailed and comprehensive update on the genetic and environmental factors associated with NCS, integrating the scientific findings achieved during the last decade. Focus on the neurodevelopmental, imaging, and treatment aspects of NCS is also provided.

Molecular Analysis of Ephrin A4 and Ephrin B1 in a Rabbit Model of Craniosynostosis: Likely Exclusion as the Loci of Origin

Craniosynostosis (CS) has a prevalence of approximately 1 in every 2000 live births and is characterized by the premature fusion of one or more cranial sutures. Failure to maintain the cell lineage boundary at the coronal suture is thought to be involved in the pathology of some forms of CS. The Ephrin family of receptor tyrosine kinases consists of membrane-bound receptors and ligands that control cell patterning and the formation of developmental boundaries. Mutations in the ephrin A4 (EFNA4) and ephrin B1 (EFNB1) ligands have been linked to nonsyndromic CS and craniofrontonasal syndrome, respectively, in patient samples. We have previously described a colony of rabbits with a heritable pattern of coronal suture synostosis, although the genetic basis for synostosis within this model remains unknown. The present study was performed to determine if EFNA4 or EFNB1 could be the loci of the causal mutation in this unique animal model. Sequencing of EFNA4 and EFNB1 was performed using templates obtained from wild-type (n = 4) and craniosynostotic (n = 4) rabbits. No structural coding errors were identified in either gene. A single-nucleotide transversion was identified in one wild-type rabbit within the third intron of EFNA4. These data indicate that the causal locus for heritable CS in this rabbit model is not located within the structural coding regions of either EFNA4 or EFNB1.

Differential spatial regulation of BMP molecules is associated with single-suture craniosynostosis

OBJECTIVE The aim of this study was to examine messenger RNA (mRNA) levels of bone morphogenetic protein (BMP) ligands, receptors, and soluble inhibitors in cells isolated from single-suture synostoses from fused coronal, metopic, sagittal, and lambdoid sutures. METHODS Cells were isolated from bone collected from patients undergoing craniotomies at Children's Healthcare of Atlanta. Real-time polymerase chain reaction was used to examine mRNA levels in cells isolated from fused sutures or patent sutures in comparison with levels in normal bone from the same patient. RESULTS Cells isolated from fused sutures in cases of sagittal and coronal synostosis highly expressed BMP2, while cells isolated from fused metopic or lambdoid synostosis expressed high BMP4. Noggin, a BMP inhibitor, was lower in fused sutures and had high expression in patent sutures. CONCLUSIONS These results suggest that BMPs and inhibitors play a significant role in the regulation of suture fusion as well in the maintenance of patency in the normal suture.

Signaling mechanisms implicated in cranial sutures pathophysiology: Craniosynostosis

Normal extension and skull expansion is a synchronized process that prevails along the osteogenic intersections of the cranial sutures. Cranial sutures operate as bone growth sites allowing swift bone generation at the edges of the bone fronts while they remain patent. Premature fusion of one or more cranial sutures can trigger craniosynostosis, a birth defect characterized by dramatic manifestations in appearance and functional impairment. Up until today, surgical correction is the only restorative measure for craniosynostosis associated with considerable mortality. Clinical studies have identified several genes implicated in the pathogenesis of craniosynostosis syndromes with useful insights into the underlying molecular signaling events that determine suture fate. In this review, we exploit the intracellular signal transduction pathways implicated in suture pathobiology, in an attempt to identify key signaling molecules for therapeutic targeting.

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Cranial sutures operate as bone growth sites.

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Premature fusion of one or more cranial sutures can trigger craniosynostosis.

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Several genes are involved in the pathogenesis of craniosynostosis syndromes.

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An array of molecular signaling events determine suture fate.

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Herein, the signal transduction pathways implicated in suture pathobiology are discussed.

Craniosynostosis and Resynostosis: Models, Imaging, and Dental Implications

Craniosynostosis occurs in approximately 1 in 2,000 children and results from the premature fusion of ≥1 cranial sutures. If left untreated, craniosynostosis can cause numerous complications as related to an increase in intracranial pressure or as a direct result from cranial deformities, or both. More than 100 known mutations may cause syndromic craniosynostosis, but the majority of cases are nonsyndromic, occurring as isolated defects. Most cases of craniosynostosis require complex cranial vault reconstruction that is associated with a high risk of morbidity. While the first operation typically has few complications, bone rapidly regrows in up to 40% of children who undergo it. This resynostosis typically requires additional surgical intervention, which can be associated with a high incidence of life-threatening complications. This article reviews work related to the dental and maxillofacial implications of craniosynostosis and discusses clinically relevant animal models related to craniosynostosis and resynostosis. In addition, information is provided on the imaging modalities used to study cranial defects in animals and humans.

Newborn craniofacial malformations: orofacial clefting and craniosynostosis

Craniofacial malformations are among the most common birth defects. Although most cases of orofacial clefting and craniosynostosis are isolated and sporadic, these abnormalities are associated with a wide range of genetic syndromes, and making the appropriate diagnosis can guide management and counseling. Patients with craniofacial malformation are best cared for in a multidisciplinary clinic that can coordinate the care delivered by a diverse team of providers.

Rapidly polymerizing injectable click hydrogel therapy to delay bone growth in a murine re-synostosis model

Craniosynostosis is the premature fusion of cranial sutures, which can result in progressive cranial deformations, increased intracranial pressure, and restricted brain growth. Most cases of craniosynostosis require surgical reconstruction of the cranial vault with the goal of increasing the intracranial volume and correcting the craniofacial deformities. However, patients often experience rapid post-operative bone regrowth, known as re-synostosis, which necessitates additional surgical intervention. Bone morphogenetic protein (BMP) inhibitors have tremendous potential to treat re-synostosis, but the realization of a clinically viable inhibitor-based therapeutic requires the development of a delivery vehicle that can localize the release to the site of administration. Here, we present an in situ rapidly crosslinking injectable hydrogel that has the properties necessary to encapsulate co-administered proteins and demonstrate that the delivery of rmGremlin1 via our hydrogel system delays bone regrowth in a weanling mouse model of re-synostosis. Our hydrogel is composed of two mutually reactive poly(ethylene glycol) macromolecules, which when mixed crosslink via a bio-orthogonal Cu free click reaction. Hydrogels containing Gremlin caused a dose dependent inhibition of bone regrowth. In addition to craniofacial applications, our injectable click hydrogel has the potential to provide customizable protein, small molecule, and cell delivery to any site accessible via needle or catheter.

Effects of Sox9 gene therapy on the healing of bone-tendon junction: An experimental study

BACKGROUND

Sox9 is an operon that positively regulates the transcription of type II collagen. The generation of type II collagen plays a critical role in the healing process of the bone-tendon junction (BTJ).

MATERIALS AND METHODS

Sox9 was injected into an established bone-tendon healing model in order to observe its effect on the healing by determining the biomechanical properties of the BTJ. In addition, the recombinant adenovirus Sox9 was used to transduce the animal model samples and in vivo observations of the effect of the adenovirus-mediated Sox9 transduction as well as its promotion of the healing properties were made.

RESULTS

Sox9 was not only able to promote the healing, but also increased the biomechanical strength. The recombinant Sox9 delivered by adenoviral vector can be expressed at a high level in the damaged tissues of the bone-tendon junction, which can stimulate the production of type II collagen and improve the healing of the BTJ.

CONCLUSIONS

Based on the results of this study, we considered that gene therapy may be applicable in the healing process of the bone-tendon junction.

Rapid re-synostosis following suturectomy in pediatric mice is age and location dependent

Craniosynostosis is the premature fusion of the cranial sutures early in development. If left untreated, craniosynostosis can lead to complications resulting from cranial deformities or increased intracranial pressure. The standard treatment involves calvarial reconstruction, which in many cases undergoes rapid re-synostosis. This requires additional surgical intervention that is associated with a high incidence of life threatening complications. To better understand this rapid healing, a pediatric mouse model of re-synostosis was developed and characterized. Defects (1.5mm by 2.5mm) over the posterior frontal suture were created surgically in weanling (21 days post-natal) and adolescent (50 days post-natal) C57Bl/6J mice. In addition, defects were created in the frontal bone lateral to the posterior frontal suture. The regeneration of bone in the defect was assessed using advanced image processing algorithms on micro-computed tomography scans. The genes associated with defect healing were assessed by real-time PCR of mRNA isolated from the tissue present in the defect. The results showed that the weanling mouse healed in a biphasic process with bone bridging the defect by post-operative (post-op) day 3 followed by an increase in the bone volume on day 14. In adolescent mice, there was a delay in bone bridging across the defect, and no subsequent increase in bone volume. No bridging of the defect by 14 days post-op was seen in identically sized defects placed lateral to the suture in both weanling and adolescent animals. This study demonstrates that bone regeneration in the cranium is both age and location dependent. Rapid and robust bone regeneration only occurred when the defect was created over the posterior frontal suture in immature weanling mice.

Craniosynostosis: molecular pathways and future pharmacologic therapy

Craniosynostosis describes the premature fusion of one or more cranial sutures and can lead to dramatic manifestations in terms of appearance and functional impairment. Contemporary approaches for this condition are primarily surgical and are associated with considerable morbidity and mortality. The additional post-operative problems of suture refusion and bony relapse may also necessitate repeated surgeries with their own attendant risks. Therefore, a need exists to not only optimize current strategies but also to develop novel biological therapies which could obviate the need for surgery and potentially treat or even prevent premature suture fusion. Clinical studies of patients with syndromic craniosynostosis have provided some useful insights into the important signaling pathways and molecular events guiding suture fate. Furthermore, the highly conserved nature of craniofacial development between humans and other species have permitted more focused and step-wise elucidation of the molecular underpinnings of craniosynostosis. This review will describe the clinical manifestations of craniosynostosis, reflect on our understanding of syndromic and non-syndromic craniosynostoses and outline the different approaches that have been adopted in our laboratory and elsewhere to better understand the pathogenesis of premature suture fusion. Finally, we will assess to what extent our improved understanding of the pathogenesis of craniosynostosis, achieved through laboratory-based and clinical studies, have made the possibility of a non-surgical pharmacological approach both realistic and tangible.

The role of vertebrate models in understanding craniosynostosis

BACKGROUND

Craniosynostosis (CS), the premature fusion of cranial sutures, is a relatively common pediatric anomaly, occurring in isolation or as part of a syndrome. A growing number of genes with pathologic mutations have been identified for syndromic and nonsyndromic CS. The study of human sutural material obtained post-operatively is not sufficient to understand the etiology of CS, for which animal models are indispensable.

DISCUSSION

The similarity of the human and murine calvarial structure, our knowledge of mouse genetics and biology, and ability to manipulate the mouse genome make the mouse the most valuable model organism for CS research. A variety of mouse mutants are available that model specific human CS mutations or have CS phenotypes. These allow characterization of the biochemical and morphological events, often embryonic, which precede suture fusion. Other vertebrate organisms have less functional genetic utility than mice, but the rat, rabbit, chick, zebrafish, and frog provide alternative systems in which to validate or contrast molecular functions relevant to CS.

Genetic basis of potential therapeutic strategies for craniosynostosis

Craniosynostosis, the premature fusion of one or more cranial sutures, is a common malformation of the skull that can result in facial deformity and increased intracranial pressure. Syndromic craniosynostosis is present in ∼15% of craniosynostosis patients and often is clinically diagnosed by neurocranial phenotype as well as various other skeletal abnormalities. The most common genetic mutations identified in syndromic craniosynostosis involve the fibroblast growth factor receptor (FGFR) family with other mutations occurring in genes for transcription factors TWIST, MSX2, and GLI3, and other proteins EFNB1, RAB23, RECQL4, and POR, presumed to be involved either upstream or downstream of the FGFR signaling pathway. Both syndromic and nonsyndromic craniosynostosis patients require early diagnosis and intervention. The premature suture fusion can impose pressure on the growing brain and cause continued abnormal postnatal craniofacial development. Currently, treatment options for craniosynostosis are almost exclusively surgical. Serious complications can occur in infants requiring either open or endoscopic repair and therefore the development of nonsurgical techniques is highly desirable although arguably difficult to design and implement. Genetic studies of aberrant signaling caused by mutations underlying craniosynostosis in in vitro calvarial culture and in vivo animal model systems have provided promising targets in designing genetic and pharmacologic strategies for systemic or adjuvant nonsurgical treatment. Here we will review the current literature and provide insights to future possibilities and limitations of therapeutic applications.