Noggin Underexpression and Runx-2 Overexpression in a Craniosynostosis Rabbit Model

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.

The influence of bone type on the gene expression in normal bone and at the bone-implant interface: experiments in animal model

BACKGROUND

Studies on the biological processes in different bone types and the reaction of different bone types to biomaterials are often hindered because of the difficulties in sampling procedures and lack of sensitive techniques.

PURPOSE

The purpose was to assess the suitability of quantitative polymerase chain reaction (qPCR) for investigation of the biological differences between cortical and trabecular bone types and their responses to biomaterials.

MATERIALS AND METHODS

Gene expression of selected markers in rat bone samples from different locations was evaluated. Samples were harvested by trephines from the trabecular femoral epiphysis, cortico-trabecular proximal tibial metaphysic, and the cortical distal tibial metaphysis. Gene expression was also evaluated at the surfaces of anodically oxidized implants retrieved from cortical and trabecular sites after 3 days of implantation. mRNA in the bone samples and in the tissue associated with the implant surfaces was extracted and quantified using qPCR. Tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), alkaline phosphatase (ALP), osteocalcin (OC), tartrate-resistant acid phosphatase (TRAP), cathepsin K (CATK), and 18S ribosomal subunits (18S) were analyzed.

RESULTS

In the bone samples, higher expression of ALP, OC, TRAP, and CATK was found in femoral epiphysis compared to proximal or distal tibial metaphysis, indicating a higher turnover in the trabecular bone. On the other hand, TNF-α and IL-1β showed higher expression in both tibia sites compared with the femur site, which suggests higher inflammatory potential in the cortical bone. In response to the oxidized implants trabecular bone expressed a higher level of IL-1β, whereas the implants in cortical bone were associated with higher expression of ALP and OC.

CONCLUSION

There are biological differences between cortical and trabecular bone types, both in the normal steady-state condition and in response to biomaterials. Such differences can be characterized and discriminated quantitatively using a sensitive technique such as qPCR.

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.

Sagittal craniosynostosis combined with ossified cephalhematoma--a tricky and demanding puzzle

INTRODUCTION

Four cases of sagittal synostosis combined with ossified cephalhematoma prompted the authors to present the data and to discuss the implications. Large cephalhematoma of the vertex at birth with subsequent ossification occurred in all with final sizes of 6.5-10 by 4.0-5.5 by 0.8-1.8 cm. At surgery with 2-6 months, the mean skull index was 64.75, sagittal suture completely closed, and a disfiguring bony mass present in all.

DISCUSSION

In three of the original cohort of 106 sagittal synostoses, ossified cephalhematoma was removed in one piece together with the suture. In contrast to pathogenesis of common parietal cephalhematomas, cephalhematoma in sagittal synostosis is rather induced by periosteal detachment of the midline by strong shearing forces because molding is hindered in the lateral direction. Frequent and fast complete ossification is possibly directed by the same local factors (e.g., Noggin) which lead to premature fusion of cranial sutures. Some treatment principles of ossified cephalhematoma in sagittal synostosis may be applied to surgery of common types.

Autologous stem cell regeneration in craniosynostosis

Craniosynostosis occurs in one of 2500 live human births and may manifest as craniofacial disfiguration, seizure, and blindness. Craniotomy is performed to reshape skull bones and resect synostosed cranial sutures. We demonstrate for the first time that autologous mesenchymal stem cells (MSCs) and controlled-released TGFbeta3 reduced surgical trauma to localized osteotomy and minimized osteogenesis in a rat craniosynostosis model. Approximately 0.5 mL tibial marrow content was aspirated to isolate mononucleated and adherent cells that were characterized as MSCs. Upon resecting the synostosed suture, autologous MSCs in collagen carriers with microencapsulated TGFbeta3 (1 ng/mL) generated cranial suture analogs characterized as bone-soft tissue-bone interface by quantitative histomorphometric and microCT analyses. Thus, surgical trauma in craniosynostosis can be minimized by a biologically viable implant. We speculate that proportionally larger amounts of human marrow aspirates participate in the healing of craniosynostosis defects in patients. The engineered soft tissue-bone interface may have implications in the repair of tendons, ligaments, periosteum and periodontal ligament.

Noggin inhibits postoperative resynostosis in craniosynostotic rabbits

Inhibition of bone formation after surgery to correct craniosynostosis would alleviate the need for secondary surgeries and decrease morbidity and mortality. This study used a single dose of Noggin protein to prevent resynostosis and improve postoperative outcomes in a rabbit model of craniosynostosis.

INTRODUCTION

Craniosynostosis is defined as the premature fusion of one or more of the cranial sutures, which causes secondary deformations of the cranial vault, cranial base, and brain. Current surgical intervention involves extirpation of the fused suture to allow unrestricted brain growth. However, resynostosis of the extirpated regions often occurs. Several bone morphogenetic proteins (BMPs), well-described inducers of ossification, are involved in bone healing. This study tested the hypothesis that a postoperative treatment with Noggin, an extracellular BMP inhibitor, can inhibit resynostosis in a rabbit model of human familial nonsyndromic craniosynostosis.

MATERIALS AND METHODS

Thirty-one New Zealand white rabbits with bilateral coronal suture synostosis were divided into three groups: (1) suturectomy controls (n = 13); (2) suturectomy with BSA in a slow-resorbing collagen vehicle, (n = 8); and (3) suturectomy with Noggin in a slow-resorbing collagen vehicle (n = 10). At 10 days of age, a 3 x 15-mm coronal suturectomy was performed. The sites in groups 2 and 3 were immediately filled with BSA-loaded gel or Noggin-loaded gel, respectively. Serial 3D-CT scan reconstructions of the defects and standard radiographs were obtained at 10, 25, 42, and 84 days of age, and the sutures were harvested for histological analysis.

RESULTS

Radiographic analysis revealed that Noggin-treated animals had significantly greater coronal suture marker separation by 25 days and significantly greater craniofacial length at 84 days of age compared with controls. 3D-CT analysis revealed that Noggin treatment led to significantly greater defect areas through 84 days and to increased intracranial volumes at 84 days of age compared with other groups. Histological analysis supported CT data, showing that the untreated and BSA-treated groups had significant healing of the suturectomy site, whereas the Noggin-treated group had incomplete wound healing.

CONCLUSIONS

These data support our hypothesis that inhibition of BMP activity using Noggin may prevent postoperative resynostosis in this rabbit model. These findings also suggest that Noggin therapy may have potential clinical use to prevent postoperative resynostosis in infants with craniosynostosis.