Coronal suture response to distraction osteogenesis in rabbits with delayed-onset craniosynostosis

Whole genome sequencing identifies associations for nonsyndromic sagittal craniosynostosis with the intergenic region of BMP2 and noncoding RNA gene LINC01428

Craniosynostosis (CS) is a major birth defect resulting from premature fusion of cranial sutures. Nonsyndromic CS occurs more frequently than syndromic CS, with sagittal nonsyndromic craniosynostosis (sNCS) presenting as the most common CS phenotype. Previous genome-wide association and targeted sequencing analyses of sNCS have identified multiple associated loci, with the strongest association on chromosome 20. Herein, we report the first whole-genome sequencing study of sNCS using 63 proband-parent trios. Sequencing data for these trios were analyzed using the transmission disequilibrium test (TDT) and rare variant TDT (rvTDT) to identify high-risk rare gene variants. Sequencing data were also examined for copy number variants (CNVs) and de novo variants. TDT analysis identified a highly significant locus at 20p12.3, localized to the intergenic region between BMP2 and the noncoding RNA gene LINC01428. Three variants (rs6054763, rs6054764, rs932517) were identified as potential causal variants due to their probability of being transcription factor binding sites, deleterious combined annotation dependent depletion scores, and high minor allele enrichment in probands. Morphometric analysis of cranial vault shape in an unaffected cohort validated the effect of these three single nucleotide variants (SNVs) on dolichocephaly. No genome-wide significant rare variants, de novo loci, or CNVs were identified. Future efforts to identify risk variants for sNCS should include sequencing of larger and more diverse population samples and increased omics analyses, such as RNA-seq and ATAC-seq.

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.

Application of Laser Capture Microdissection to Craniofacial Biology: Characterization of Anatomically Relevant Gene Expression in Normal and Craniosynostotic Rabbit Sutures

OBJECTIVE

Fusion of the cranial sutures is thought to depend on signaling among perisutural tissues. Mapping regional variations in gene expression would improve current models of craniosynostosis. Laser capture microdissection (LCM) isolates discrete cell populations for gene expression analysis. LCM has rarely been used in the study of mineralized tissue. This study sought to evaluate the potential use of LCM for mapping of regional gene expression within the cranial suture.

DESIGN

Coronal sutures were isolated from 10-day-old wild-type and craniosynostotic (CS) New Zealand White rabbits, and LCM was used to isolate RNA from the sutural ligament (SL), osteogenic fronts (OF), dura mater, and periosteum. Relative expression levels for Fibroblast Growth Factor 2 (FGF2), Fibroblast Growth Factor Receptor 2 (FGFR2), Transforming Growth Factor Beta 2 (TGFβ-2), Transforming Growth Factor Beta 3 (TGFβ-3), Bone Morphogenetic Protein 2 (BMP-2), Bone Morphogenetic Protein 4 (BMP-4), and Noggin were determined using quantitative real-time PCR.

RESULTS

A fivefold increase in TGFβ2 expression was detected in the CS SL relative to wild type, whereas 152-fold less TGFβ-3 was detected within the OF of CS animals. Noggin expression was increased by 10-fold within the CS SL, but reduced by 13-fold within the CS dura. Reduced expression of FGF2 was observed within the CS SL and dura, whereas increased expression of FGFR2 was observed within the CS SL. Reduced expression of BMP-2 was observed in the CS periosteum, and elevated expression of BMP-4 was observed in the CS SL and dura.

CONCLUSIONS

LCM provides an effective tool for measuring regional variations in cranial suture gene expression. More precise measurements of regional gene expression with LCM may facilitate efforts to correlate gene expression with suture morphogenesis and pathophysiology.

Genetic Homozygosity and Phenotypic Variability in Craniosynostotic Rabbits

BACKGROUND

Craniosynostosis ranges in severity from single suture involvement with prenatal onset to multiple suture involvement with postnatal onset. The present study was designed to test the hypothesis that increasing homozygosity may be responsible for more severe phenotypic expression by examining the relationship between inbreeding and phenotypic expression in synostotic rabbits.

METHODS

Data were obtained from 173 litters and 209 rabbits with familial craniosynostosis. Five distinct phenotypes were identified (normal n = 62; unicoronal delayed onset synostosis (DOS) n = 47; bicoronal DOS n = 21; unicoronal early onset synostosis (EOS) n = 26, and bicoronal EOS n= 53). Wright's coefficients of inbreeding (CI) were calculated using CompuPed software. Radiographs were taken at 10, 25, 42, 84, and 126 days of age to assess coronal suture, craniofacial, and skeletal growth. The relationship between CI and growth data was assessed using correlation coefficients.

RESULTS

Mean CIs ranged from 15.68 (±2.22) in normal rabbits to 25.89 (±5.03) in bicoronal DOS, to 36.29 (±2.10) in unicoronal EOS to 42.85 (±2.10) in bicoronal EOS rabbits. Significant differences were noted among groups (F = 11.48; P < .001). Significant negative correlations were noted between CI and sutural and craniofacial growth at 25 (r = -.45, P < .001; and r = -.66, P < .001) through 126 (r = -.40, P < .001 and r = -.46, P < .001) days of age.

CONCLUSIONS

While the synostotic phenotype is inherited in an autosomal dominant fashion in these rabbits, increasing homozygosity is associated with more severely affected phenotypes. These findings suggest that an accumulation of additional, modifier genes may determine the severity of the synostotic phenotype in rabbits.

Blocking bone morphogenetic protein function using in vivo noggin therapy does not rescue premature suture fusion in rabbits with delayed-onset craniosynostosis

BACKGROUND

Craniosynostosis is defined as the premature fusion of one or more cranial sutures. Bone morphogenetic proteins (BMPs), regulators of ossification, have been implicated in premature suture fusion. Noggin, an extracellular BMP inhibitor, has been shown experimentally to inhibit resynostosis following surgery. The present study was designed to test the hypothesis that BMP inhibition using noggin therapy may rescue sutures destined to fuse by inhibiting initial ossification.

METHODS

Twenty-six, 10-day old rabbits with familial, delayed-onset, coronal suture synostosis were randomly divided into three groups: (1) the sham surgical control group, (2) the bovine serum albumin-treated group [10 μg/suture (protein/vehicle controls)], and (3) the noggin therapy group (10 μg/suture; experimental group). Sutural growth was monitored by radiopaque markers implanted at 10 days of age. At 25 days, the bovine serum albumin or noggin was combined with a slow-resorbing collagen vehicle and injected subperiosteally above the coronal suture. Somatic and sutural growth data were collected at 10, 25, 42, and 84 days of age. Coronal sutures were harvested at 84 days to histologically assess fusion.

RESULTS

Results showed no significant (p > 0.05) differences in suture separation at any age. Suture fusion assessed by histomorphology did not differ among the three groups. Although previous data showed noggin to inhibit postoperative resynostosis in this craniosynostotic rabbit model, here there was no effect on initial suture fusion.

CONCLUSION

These results suggest that in this rabbit model of craniosynostosis, BMPs do not play a role in the pathogenesis of craniosynostosis and only play a role in postoperative bony wound healing.

Tensional Forces Influence Gene Expression and Sutural State of Rat Calvariae In Vitro

BACKGROUND

Theories regarding the cause of craniosynostosis that are more than 15 years old cite the role that tensional forces play in the normal and abnormal development of the cranial suture. These theories highlight the effect of stress bands originating from the skull base to the vertex, guiding sutural development.

METHODS

In this study, the normally fusing posterior intrafrontal suture of the rat was subjected to 3 mN of tensional force for 30 minutes per day. The suture was then assessed for patency, proliferation, apoptosis, and transforming growth factor (TGF)-beta signaling components.

RESULTS

Sutures that were subjected to tensional force were histologically patent at the end of 14 days. This was in contrast to sutures that were maintained without force. Proliferative and apoptotic activity was increased also in sutures maintained open artificially. Interestingly, levels of active TGF-beta-signaling components were also increased in force-maintained sutures.

CONCLUSIONS

Sutural maintenance by mechanical force is concurrent with modulation of cellular activity and protein expression reminiscent of the open suture. This study demonstrates the dynamic reciprocity existing between biochemical activity and morphologic state. Although it is known that changes in TGF-betas and fibroblast growth factors can cause sutural fusion, this is the first study to demonstrate that abrogation of sutural closure is responsible for growth factor signaling modulation.

Craniosacral therapy: the effects of cranial manipulation on intracranial pressure and cranial bone movement

STUDY DESIGN

Quasi-experimental design.

OBJECTIVES

To determine if physical manipulation of the cranial vault sutures will result in changes of the intracranial pressure (ICP) along with movement at the coronal suture.

BACKGROUND

Craniosacral therapy is used to treat conditions ranging from headache pain to developmental disabilities. However, the biological premise for this technique has been theorized but not substantiated in the literature.

METHODS

Thirteen adult New Zealand white rabbits (oryctolagus cuniculus) were anesthetized and microplates were attached on either side of the coronal suture. Epidural ICP measurements were made using a NeuroMonitor transducer. Distractive loads of 5, 10, 15, and 20 g (simulating a craniosacral frontal lift technique) were applied sequentially across the coronal suture. Baseline and distraction radiographs and ICP were obtained. One animal underwent additional distractive loads between 100 and 10,000 g. Plate separation was measured using a digital caliper from the radiographs. Two-way analysis of variance was used to assess significant differences in ICP and suture movement.

RESULTS

No significant differences were noted between baseline and distraction suture separation (F = 0.045; P>.05) and between baseline and distraction ICP (F = 0.279; P>.05) at any load. In the single animal that underwent additional distractive forces, movement across the coronal suture was not seen until the 500-g force, which produced 0.30 mm of separation but no corresponding ICP changes.

CONCLUSION

Low loads of force, similar to those used clinically when performing a craniosacral frontal lift technique, resulted in no significant changes in coronal suture movement or ICP in rabbits. These results suggest that a different biological basis for craniosacral therapy should be explored.

Advances in Craniosynostosis Research and Management

The purpose of the present paper is to analyze the most recent advances in the field of craniosynostosis basic and clinical research and management, and to give an overview of the more frequently adopted surgical strategies. After reviewing some basic concepts regarding normal craniofacial embryology and growth, aetiopathogenesis of craniosynostosis and craniofacial dysostosis, classification and diagnosis and historical evolution of surgical treatment, the authors elaborate on a selection of topics that have modified our current understanding of and therapeutical approach to these disease processes. Areas covered include advances in molecular biology and genetics, imaging techniques and surgical planning, resorbable fixation technology, bone substitutes and tissue engineering, distraction osteogenesis and the spring-mediated cranioplasties, resorbable distractor devices, minimally invasive surgery and in utero surgery. A review of the main subtypes of craniosynostosis and craniofacial dysostosis is presented, including their specific clinical features and a commentary on the presently available surgical options.

Rescue of coronal suture fusion using transforming growth factor-beta 3 (Tgf-beta 3) in rabbits with delayed-onset craniosynostosis

Craniosynostosis results in cranial deformities and increased intracranial pressure, which pose extensive and recurrent surgical management problems. Developmental studies in rodents have shown that low levels of transforming growth factor-beta 3 (Tgf-beta 3) are associated with normal fusion of the interfrontal (IF) suture, and that Tgf-beta 3 prevents IF suture fusion in a dose-dependent fashion. The present study was designed to test the hypothesis that Tgf-beta 3 can also prevent or "rescue" fusing sutures in a rabbit model with familial craniosynostosis. One hundred coronal sutures from 50 rabbits with delayed-onset, coronal suture synostosis were examined in the present study. The rabbits were divided into five groups of 10 rabbits each: 1) sham controls, 2) bovine serum albumin (BSA, 500 ng) low-dose protein controls, 3) low-dose Tgf-beta 3 (500 ng), 4) high-dose BSA (1,000 ng) controls, and 5) high-dose Tgf-beta 3 (1,000 ng). At 10 days of age, radiopaque amalgam markers were implanted in all of the rabbits on either side of the coronal suture to monitor sutural growth. At 25 days of age, the BSA or Tgf-beta 3 was combined with a slow-absorbing collagen vehicle and injected subperiosteally above the coronal suture. Radiographic results revealed that high-dose Tgf-beta 3 rabbits had significantly greater (P < 0.05) coronal suture marker separation than the other groups. Histomorphometric analysis revealed that high-dose Tgf-beta 3 rabbits also had patent coronal sutures and significantly (P < 0.01) greater sutural widths and areas than the other groups. The results suggest that there is a dose-dependent effect of TGF-beta 3 on suture morphology and area in these rabbits, and that the manipulation of such growth factors may have clinical applications in the treatment of craniosynostosis.

Changes in the protein expression of hedgehog and patched-1 in perisutural tissues induced by cranial distraction

With the modern emphasis on minimally invasive therapies, the concept of distraction is being applied in the treatment of craniosynostosis. Although specific genetic mutations have been identified in craniosynostotic patients, changes in the gene expression induced by cranial distraction have not yet been explored. The effects of cranial distraction on hedgehog and patched-1 expression were evaluated in a rabbit model for craniosynostosis. Rabbits (n = 8) were divided into four groups: affected rabbits, wild-type rabbits, affected rabbits subject to cranial distraction, and wild-type rabbits subject to distraction. Perisutural tissue was examined using immunohistochemistry in four areas: suture, endosteum, periosteum, and osteocytes, for the expression of Indian hedgehog, sonic hedgehog, and desert hedgehog and their receptor, patched-1. Two experimental groups were compared: (1) wild-type before distraction to wild-type after distraction, and (2) synostotic before distraction to synostotic after distraction. Distraction produced several variable and interesting changes in hedgehog protein presence. In wild-type rabbits, the predominant effect was a mild decrease in Indian hedgehog levels. Sonic and desert hedgehog and patched-1 protein levels were unchanged. In synostotic rabbits, the predominant effect of distraction was to decrease Indian hedgehog, sonic hedgehog, and patched-1 protein levels. This was especially true in the periosteum and endosteum. Cranial distraction of normal and affected rabbits differentially changed both the expression levels and patterns of the hedgehog and patched-1 proteins in the cranial tissues examined. These results suggest that molecular and genetic parameters of distraction and bone response may be different in craniosynostotic individuals, which may influence treatment protocols in these patients.

Calvarial bone distraction with a contractile bioresorbable polymer

The aim of the present study was to evaluate the possibility of mobilizing calvarial bone with a fully implantable and bioresorbable device. The animal model used was the New Zealand white rabbit (n = 12). An island bone flap attached to the dura mater was created in the parietal region and amalgam markers were placed in this bone flap and in the ipsilateral frontal bone. In one group of six rabbits (group 1), a specially processed contractile 70L/30D,L polylactic acid plate, 15 x 6 x 0.6 mm, was attached to the island flap by one extremity, and to the fixed ipsilateral frontal bone by the other. In group 2 (control), no plate was added. Bone marker movement was followed with serial radiography. In group 1, there was a progressive reduction in mean marker distance over the first 48 hours, and stability thereafter. In group 2 (control), mean marker distance remained stable until the second postoperative week, after which time there was a slight increase until the end of the experimental period. At 4 weeks, the mean marker separation differed significantly between group 1 (mean, -3.62 mm; SD, 0.79 mm) and group 2 (mean, 0.34 mm; SD, 0.14 mm; p <0.001). In conclusion, a totally implantable and bioresorbable device was successfully used to mobilize calvarial bone. Polymer contractility will likely constitute the basis of a new generation of bioresorbable distractors for use in craniofacial surgery.

Cranio-facial distraction osteogenesis: a review of the literature. Part II: Experimental studies

In this study the literature dealing with experimental cranio-facial distraction osteogenesis (DO) was reviewed. A PUBMED search (National Library of Medicine [NCBI] revised 1 April 2001) from 1966 through December 2000 was conducted. Key words used in the search were: distraction, lengthening, mandible, mandibular, maxilla, maxillary, midface, midfacial, monobloc, cranial, cranio-facial, maxillofacial. This search revealed a total of 120 experiment-orientated articles that were all analyzed in detail in this study. The purpose of the experimental study, animal model, animal growth status, type of distraction, type of surgery, distraction rate and rhythm, latency and contention period, amount of lengthening, relapse, complications and nature of the distraction device were analyzed. This review revealed that a total of 1207 animals were used in seven different animal models for research on cranio-facial DO: 54 using dogs (45.0%), 25 using rabbits (20.8%), 18 using sheep (15.0%), 11 using minipig (9.2%), seven using monkeys (5.8%), four using rats (3.3%) and one using a cat model (0.8%). Based on the results of this study, an attempt was made to provide biological DO parameters and guidelines for future research on experimental cranio-facial DO related to the appropriate animal model.

Expander elements in craniofacial surgery: an experimental study in rabbits

With the inception of craniofacial surgery elaborate surgical procedures were introduced for the treatment of craniosynostosis. Recently the use of implantable springs to aid simple strip craniectomies for these conditions has been described. Having shown the feasibility of using springs for dynamic skull reshaping, several questions remain to be answered, all of them about how to control the spring action clinically. One of the most important questions concerns force. The purpose of this study was to evaluate experimentally the effect of two springs of different strengths on the growth of rabbit calvaria after strip craniectomy. Thirty-two 6-week-old rabbits were randomised into one of four groups: sham-operation where only amalgam markers were inserted after subperiostal dissection; strip craniectomy of the sagittal suture, no expansion; strip craniectomy of the sagittal suture and insertion of an expander element made of titanium molybdenum alloy (TMA); and strip craniectomy sagittal suture and insertion of an expander element made of stainless steel (SS). SS springs delivered a range of forces from 2.42-2.18 N, whereas the TMA expander elements delivered a range from 1.39-1.09 N. The parietal bone marker separation after 12 weeks was 4.9 mm in the TMA group and 7.4 mm in the SS group. This resulted in a significant increase of the calvarian height compared with control groups. Histological examination showed intramembranous bone formation in the bone gap in all groups.

A new distraction device to compare continuous and discontinuous bone distraction in mini-pigs: a preliminary report

Callus-distraction has become an accepted procedure to lengthen hypoplastic mandibles in humans. Extra- and intraoral devices have been applied successfully. Systematic studies have proven the importance of direction, stability, rate and frequency in callus-distraction. In an experimental animal study a newly developed intraoral microhydraulic osteodistractor was tested. Initially the pressures necessary to distract the mandible in mini-pigs were recorded in discontinuous callus-distraction. These results were used to perform continuous bone distraction. Besides testing the new distractor and evaluating the distraction pressures, the aim of the study was to prove that direct bone growth occurred without preceding cartilage formation. Clinical and microscopic results are presented.