Suture growth modulated by the oscillatory component of micromechanical strain.

Sutures are fibrous connective tissue articulations between intramembranous craniofacial bones. Sutures are composed of fibroblastic cells with their matrices in the center and osteogenic cells in the periphery producing a matrix that is mineralized during skeletal growth. Whether oscillatory forces stimulate sutural growth is unknown. In the present work, we applied static and cyclic forces with the same peak magnitude of 5N to the maxilla in growing rabbits and quantified (1) acute in vivo sutural bone strain responses and (2) chronic growth responses in the premaxillomaxillary suture (PMS) and nasofrontal suture (NFS). Bone strain recordings showed that the waveforms of static force and 1-Hz cyclic force were expressed as corresponding static and cyclic sutural strain patterns in both the PMS and NFS, with the mean peak PMS strain (-1451 +/- 137 microepsilon for the cyclic and -1572 +/- 138 microepsilon for the static) approximately 10-fold higher than the mean peak NFS strain (124 +/- 9 microepsilon for the cyclic and 134 +/- 9 microepsilon for the static). Strain polarity was the opposite: compressive for the PMS but tensile for the NFS. However, on application of repetitive 5N cyclic and static forces in vivo for 10 minutes/day over 12 days, cyclic loading induced significantly greater sutural widths for the compressed PMS (95.1 +/- 8.3 microm) than sham control (69.8 +/- 8.2 microm) and static loading (58.9 +/- 2.8 microm; p < 0.01). Interestingly, the same trend was true for the NFS under tensile strain: significantly greater sutural width for cyclic loading (267.4 +/- 64.2 microm) than sham control (196.0 +/- 10.1 microm) and static loading (169.9 +/- 11.4 microm). Cell counting in 110 x 110 microm grids laid over sutures disclosed significantly more sutural cells on repetitive cyclic loading than sham control and static loading (p < 0.05) for both the PMS and NFS. Fluorescent labeling of newly formed sutural bone demonstrated more osteogenesis on cyclic loading in comparison with sham control and static loading. Thus, the oscillatory component of cyclic force or more precisely the resulting cyclic strain experienced in sutures is a potent stimulus for sutural growth. The increased sutural growth by cyclic mechanical strain in the tensed NFS and compressed PMS suggests that both microscale tension and compression induce anabolic sutural growth response.     

Geometry and cell density of rat craniofacial sutures during early postnatal development and upon in vivo cyclic loading

Cranial sutures are unique to skull bones and consist of multiple connective tissue cell lineages such as mesenchymal cells, fibroblast-like cells, and osteogenic cells, in addition to osteoclasts. Mechanical modulation of intramembranous bone growth in the craniofacial suture is not well understood, especially during postnatal development. This study investigated whether in vivo mechanical forces regulate sutural growth responses in postnatal rats. Cyclic compressive forces with a peak-to-peak magnitude of 300 mN and 4 Hz were applied to the maxilla in each of 17-, 23-and 32-day-old rats for 20 min/day over 5 consecutive days. Computerized histomorphometric analysis revealed that cyclic loading significantly increased the average geometric widths of the premaxillomaxillary suture (PMS) to 86 +/- 7 microm, 99 +/- 12 microm, and 149 +/- 30 microm, representing 32%, 50%, and 39% increases for P17, P23, and P32 in comparison with age-matched sham controls. For the nasofrontal suture (NFS), cyclic loading significantly increased the average sutural widths to 88 +/- 15 microm, 92 +/- 10 microm, and 100 +/- 14 microm, representing 33%, 24%, and 32% increases for P17, P23, and P32 relative to age-matched controls. The average PMS cell density upon cyclic loading was 10182 +/- 132 cells/mm(2), 9752 +/- 661 cells/mm(2), and 9521 +/- 628 cells/mm(2), representing 62%, 35%, and 30% increases for P17, P23, and P32 in comparison with age-matched controls. For the NFS, cyclic loading increased the average cell density to 9884 +/- 893 cells/mm(2), 9818 +/- 1091 cells/mm(2), 9355 +/- 661 cells/mm(2), representing 44%, 46% and 40% increases at P17, P23, and P32 respectively. Osteoblast-occupied sutural bone surface was significantly greater in cyclically loaded sutures for P17, P23, and P32 than corresponding controls for both the PMS and NFS. On the other hand, cyclic loading elicited significantly higher sutural bone surface populated by osteoclast-like cells by P17 and P23 days, but not P32 days, for the PMS. For the NFS, sutural osteoclast surface was significantly higher upon cyclic loading for P23 and P32 days, but not P17. The present data demonstrate that cyclic forces are potent stimuli for modulating postnatal sutural development, potentially by stimulating both osteogenesis and osteoclastogenesis. Cyclic loading may have clinical implications as novel mechanical stimuli for modulating craniofacial growth in patients suffering from craniofacial anomalies and dentofacial deformities.     

A model of the cranial vault as a tensegrity structure,and its significance to normal and abnormal cranial development

BackgroundTraditional views of the human cranial vault are facing challenges as researchers find that the complex details of its development do not always match previous opinions that it is a relatively passive structure. In particular, that stability of the vault is dependant on an underlying brain; and sutural patency merely facilitates cranial expansion. The influence of mechanical forces on the development and maintenance of cranial sutures is well-established, but the details of how they regulate the balance between sutural patency and fusion remain unclear. Previous research shows that mechanical tensional forces can influence intracellular chemical signalling cascades and switch cell function; and that tensional forces within the dura mater affect cell populations within the suture and cause fusion.Understanding the developmental mechanisms is considered important to the prevention and treatment of premature sutural fusion – synostosis – which causes skull deformity in approximately 0.05% of live births. In addition, the physiological processes underlying deformational plagiocephaly and the maintenance of sutural patency beyond early childhood require further elucidation.MethodUsing a disarticulated plastic replica of an adult human skull, a model of the cranial vault as a tensegrity structure which could address some of these issues is presented.ConclusionsThe tensegrity model is a novel approach for understanding how the cranial vault could retain its stability without relying on an expansive force from an underlying brain, a position currently unresolved. Tensional forces in the dura mater have the effect of pushing the bones apart, whilst at the same time integrating them into a single functional unit. Sutural patency depends on the separation of cranial bones throughout normal development, and the model describes how tension in the dura mater achieves this, and influences sutural phenotype. Cells of the dura mater respond to brain expansion and influence bone growth, allowing the cranium to match the spatial requirements of the developing brain, whilst remaining one step ahead and retaining a certain amount of autonomy. The model is compatible with current understandings of normal and abnormal cranial physiology, and has a contribution to make to a hierarchical systems approach to whole body biomechanics.     

Sutural bone deposition rate and strain magnitude during cranial development

It is widely believed that rapid growth of the human brain generates tensile strain in cranial sutures, and that this strain influences the rate of bone deposition at the sutural margins during development. We developed general theoretical techniques for estimating sutural bone deposition rate and strain magnitude during mammalian cranial development. A geometry-based analysis was developed to estimate sutural bone deposition rate. A quasi-static stress analysis was developed to estimate sutural strain magnitude. We applied these techniques to the special case of normal cranial development in humans. The results of the bone deposition rate analysis indicate that average human sutural bone deposition rate is on the order of 100 microm/day at 1 month of age and decreases in an approximately exponential fashion during the first 4 years of life. The results of the strain analysis indicate that sutural strain magnitude is highly dependent on the assumed stiffness of the sutures, with estimated strain at 1 month of age ranging from approximately 20 to 400 microstrain. Regardless of the assumed stiffness of the sutures, the results indicate that sutural strain magnitude is small and decreases in an approximately exponential fashion during the first 4 years of life. The finding that both sutural bone deposition rate and strain magnitude decrease with increasing age is consistent with quasi-static tensile strain in sutures influencing sutural osteoblast activity in a dose-dependent manner. However, the small magnitude of the predicted strains suggests that tissue level strains in sutures may be too small to directly influence osteoblast biology. In light of these results, we suggest other biomechanical mechanisms, such as a tension-induced angiogenic environment in the sutures or mechanotransduction in the underlying dura mater, through which tension across sutures may regulate the rate of bone deposition in sutures.     

颅面多骨缝固定对颅颌形态影响的实验研究

目的通过固定幼兔颅骨缝，模拟颅骨多骨缝早闭，观察固定后颅颌面生长方式的变化及相互影响的关系。方法采用牙科釉质粘合剂固定２周龄幼兔冠状缝、矢状缝和额间缝，模拟颅骨多骨缝早闭。术后不同时期测量颅穹窿长度、高度、面中部高度、上颌骨长度、面角、腭角和颅底角。结果多骨缝早闭后，颅穹窿高度和长度明显减少，使颅骨变短且扁平。面中部高度和上颌骨长度增大，整个面中骨结构有整体向上移动趋势。面、腭和颅底角增大，这与颅穹窿变浅，面中部高度增大相对应。结论兔出生后１０周前是颅骨缝扩张性生长高峰期，在此期间，某些原因影响颅骨正常生长，必然导致颅面畸形。实验结果与临床颅骨骨缝早闭后表现类似，和主张早期手术矫正畸形观点一致     

Cranial deformation in craniosynostosis. A new explanation.

Skull growth after premature fusion of a single suture was described by Virchow in 1851. He observed that growth was restricted in a plane perpendicular to a fused suture. However, he failed to predict the compensatory growth patterns that produce many of the deformities recognized as features of individual craniosynostosis syndromes. The deformities resulting from premature closure of a coronal, sagittal, metopic, or lambdoid suture can be predicted by the following observations: (1) cranial vault bones that are prematurely fused act as a single bone plate with decreased growth potential; (2) asymmetrical bone deposition occurs mainly at perimeter sutures, with increased bone deposition directed away from the bone plate; (3) sutures adjacent to the stenotic suture compensate in growth more than those sutures not contiguous with the closed suture; and (4) enhanced bone deposition occurs along both sides of a nonperimeter suture that is a continuation of the prematurely closed suture. These four rules were derived by critically examining the clinical deformities observed with each form of craniosynostosis. These rules assume that cranial sutures have the capacity to compensate by depositing bone asymmetrically along their edges. Unequal growth patterns have been demonstrated in the frontonasal suture of rabbits by Selman and Sarnat. In addition, unequal bone deposition has also been demonstrated along the parieto-interparietal suture in albino rats by Baer. Human studies to determine if asymmetrical bone deposition actively occurs along cranial vault sutures in response to a stenotic suture have not been performed, however. It is also unclear whether these four guidelines apply to cranial base abnormalities observed with craniosynostosis. As new radiologic techniques develop to define the configuration of the skull in intricate detail, a skull pattern of growth explaining the pathogenesis of all deformities created by premature fusion of a cranial vault suture may become apparent.     

Something of the nature of gross sutural growth

A series of experiments was performed on monkeys, rabbits, and turtles to study gross sutural growth of bones. Radiopaque implants in conjunction with serial gross and radiographic measurements were employed. Differences in growth were observed between 5 facial sutures and also the same suture at different times. Growth was greatest at the zygomaticotemporal suture and least at the premaxillomaxillary suture. The nasal bone side of the frontonasal suture grew about twice as fact as the frontal bone side. In the turtle shell the midsagittal suture grew faster than a transverse suture. In all of the animals the rate of sutural growth decreased with increase in age. No gross regional growth disturbance was noted after resection of the frontonasal, midpalatine, or transpalatine sutures. After extirpation of the median palatine suture, it re-formed, in an eccentric position, in a number of instances. We concluded that bone growth that occurred at sutures was secondary or compensatory to some other factor.     

Regional differentiation of cranial suture-associated dura mater in vivo and in vitro: implications for suture fusion and patency.

Despite its prevalence, the etiopathogenesis of craniosynostosis is poorly understood. To better understand the biomolecular events that occur when normal craniofacial growth development goes awry, we must first investigate the mechanisms of normal suture fusion. Murine models in which the posterior frontal (PF) suture undergoes programmed sutural fusion shortly after birth provide an ideal model to study these mechanisms. In previous studies, our group and others have shown that sutural fate (i.e., fusion vs. patency) is regulated by the dura mater (DM) directly underlying a cranial suture. These studies have led to the hypothesis that calvarial DM is regionally differentiated and that this differentiation guides the development of the overlying suture. To test this hypothesis, we evaluated the messenger RNA (mRNA) expression of osteogenic cytokines (transforming growth factor beta1 [TGF-beta1] and TGF-beta3) and bone-associated extracellular matrix (ECM) molecules (collagen I, collagen III, osteocalcin, and alkaline phosphatase) in freshly isolated, rat dural tissues associated with the PF (programmed to fuse) or sagittal (SAG; remains patent) sutures before histological evidence of sutural fusion (postnatal day 6 [N6]). In addition, osteocalcin protein expression and cellular proliferation were localized using immunohistochemical staining and 5-bromo-2'deoxyuridine (BrdU) incorporation, respectively. We showed that the expression of osteogenic cytokines and bone-associated ECM molecules is potently up-regulated in the DM associated with the PF suture. In addition, we showed that cellular proliferation in the DM associated with the fusing PF suture is significantly less than that found in the patent SAG suture just before the initiation of sutural fusion N6. Interestingly, no differences in cellular proliferation rates were noted in younger animals (embryonic day 18 [E18] and N2). To further analyze regional differentiation of cranial suture-associated dural cells, we established dural cell cultures from fusing and patent rat cranial sutures in N6 rats and evaluated the expression of osteogenic cytokines (TGF-beta1 and fibroblast growth factor 2 [FGF-2]) and collagen I. In addition, we analyzed cellular production of proliferating cell nuclear antigen (PCNA). These studies confirmed our in vivo findings and showed that dural cell cultures derived from the fusing PF suture expressed significantly greater amounts of TGF-beta1, FGF-2, and collagen I. In addition, similar to our in vivo findings, we showed that PF suture-derived dural cells produced significantly less PCNA than SAG suture-derived dural cells. Finally, coculture of dural cells with fetal rat calvarial osteoblastic cells (FRCs) revealed a statistically significant increase in proliferation (*p < 0.001) in FRCs cocultured with SAG suture-derived dural cells as compared with FRCs cocultured alone or with PF suture-derived dural cells. Taken together, these data strongly support the hypothesis that the calvarial DM is regionally differentiated resulting in the up-regulation of osteogenic cytokines and bone ECM molecules in the dural tissues underlying fusing but not patent cranial sutures. Alterations in cytokine expression may govern osteoblastic differentiation and ECM molecule deposition, thus regulating sutural fate. Elucidation of the biomolecular events that occur before normal cranial suture fusion in the rat may increase our understanding of the events that lead to premature cranial suture fusion.     

Roentgen stereophotogrammetric analysis of neurocranial suturectomy in rabbits

This investigation was conducted to further elucidate both the significance of a calvarial suture and the compensatory ability of the cranial vault. Four-week-old male New Zealand White rabbits were subjected to unilateral or bilateral extirpation of the coronal suture after insertion of metallic markers, and were then followed regularly by roentgen stereophotogrammetry until age 21 weeks. Bilateral extirpation of the normal coronal suture resulted in a dramatically increased initial rate of bone separation, which tended to remain supranormal for the rest of the investigation. Unilateral suturectomy showed differences in growth between the sides, the operated side initially separating significantly more than the other. Volumetric calvarial growth in rabbits with unilateral extirpation terminated similar to that in control animals, while volumes in rabbits with bilateral extirpations constantly exceeded control volumes, finally exceeding these by 65%. Responses at intact sutures confirmed the compensatory capacity of cranial vaults. The results indicate that the passive longitudinal and volumetric cranial vault bone growth responds quickly to growth disturbances, thereby demonstrating its plasticity, and that the neurocranial suture is a restraining and modulating component in cranial growth.     

Suture compression induced bone resorption with intensified MMP-1 and 13 expressions

Suture compression is a widely used approach to inhibit maxillary growth; however, biological responses in sutures to compressive force are still unclear. The objective of this pilot study was to investigate the matrix metalloproteinase (MMP) expression and osteoclast activities during the midpalatal suture compression. Methods: 56 six-week old male C57BL/6 mice were randomly assigned to the control and compression groups. The mice in the compression and control groups received helix springs bonded to the maxillary molars delivering initial compressive forces of 0.20 and 0N (no activation), respectively. On Days 1, 4, 7 and 14, animals were sacrificed and scanned using micro-computed tomography to quantify suture width and bone mineral density. Serial histological sections were stained with HE, TRAP, and immunohistochemistry to observe changes in bone resorption, osteoclast activities, and MMP-1, 8, and 13 expressions. Bone volume/total volume (Bv/Tv) ratio, osteoclast count, osteoclast covering area, and MMP expression intensity were measured. The Mann-Whitney and the Kruskal-Wallis tests with Bonferroni post-hoc corrections were performed to compare differences between groups and between time points in the same group at significant level of P<0.05. Results: Compared to the control, suture width in the compression group was significantly reduced on Day 1, but continuously widened with reduced bone mineral density afterwards. With MMP-1 and -13 evidently intensified expressions, osteoclast number and activities significantly increased, leading to reduced Bv/Tv ratio and progressive bone resorption from Days 4 to 14. Conclusions: Suture compression elevated the MMP-1 and 13 expressions, activated osteoclasts, reduced bone density, and induced bone resorption adjacent to the suture. It suggests that suture compression can be used for bone volume reduction.     

Cranial vault growth in craniosynostosis

Skull growth after single suture closure was described in 1851 by Virchow, who noted that growth in the plane perpendicular to a fused suture was restricted. However, this observation failed to predict compensatory growth patterns that produce many of the deformities recognized as features of individual syndromes. The deformities resulting from premature closure of a coronal, sagittal, metopic, or lambdoid suture can be predicted on the basis of the following observations: 1) cranial vault bones that are prematurely fused secondary to single suture closure act as a single bone plate with decreased growth potential; 2) asymmetrical bone deposition occurs mainly at perimeter sutures, with increased bone deposition directed away from the bone plate; 3) sutures adjacent to the prematurely fused suture compensate in growth more than those sutures not contiguous with the closed suture; and 4) enhanced symmetrical bone deposition occurs along both sides of a non-perimeter suture that is a continuation of the prematurely closed suture. These observations regarding growth in craniosynostosis are illustrated with clinical material in this report.     

An analysis of the growth of the cranial vault in rabbits by vital staining with lead acetate

The mode and the rate of formation of individual bones in the cranium were studied by vital staining with lead acetate in 13 New Zealand white rabbits beginning at 35 days of age. These evaluations were compared with⁴⁵Ca uptake at bilaterally comparable sites.The growth patterns differed from one suture to another. Elongation of the cranial vault in the anterior direction in the snout area was rapid. In the sagittal suture complex, active growth was observed on the intrasutural surfaces of the internasal and metopic sutures, while much less growth was taking place in the sagittal suture. Active growth also was taking place at the intrasutural surface of the nasal bone at the naso-premaxillary suture while resorption was found on the surface of the parietal bone in the squamosal suture.Increase in thickness of the cranial vault appeared to be the result of accretion on the ectocranial and to a lesser extent on the endocranial surfaces of the frontal and parietal bones.Good correlations between the linear measurement with the lead lines and⁴⁵Ca uptake were observed in the bones of the cranial vault, especially when⁴⁵Ca was administered 3 or 6 days before sacrifice.Fellowship F05-TW-1029.     

Response of Gli1+ Suture Stem Cells to Mechanical Force Upon Suture Expansion

Normal development of craniofacial sutures is crucial for cranial and facial growth in all three dimensions. These sutures provide a unique niche for suture stem cells (SuSCs), which are indispensable for homeostasis, damage repair, as well as stress balance. Expansion appliances are now routinely used to treat underdevelopment of the skull and maxilla, stimulating the craniofacial sutures through distraction osteogenesis. However, various treatment challenges exist due to a lack of full understanding of the mechanism through which mechanical forces stimulate suture and bone remodeling. To address this issue, we first identified crucial steps in the cycle of suture and bone remodeling based on the established standard suture expansion model. Observed spatiotemporal morphological changes revealed that the remodeling cycle is approximately 3 to 4 weeks, with collagen restoration proceeding more rapidly. Next, we traced the fate of the Gli1⁺ SuSCs lineage upon application of tensile force in three dimensions. SuSCs were rapidly activated and greatly contributed to bone remodeling within 1 month. Furthermore, we confirmed the presence of Wnt activity within Gli1⁺ SuSCs based on the high co-expression ratio of Gli1⁺ cells and Axin2⁺ cells, which also indicated the homogeneity and heterogeneity of two cell groups. Because Wnt signaling in the sutures is highly upregulated upon tensile force loading, conditional knockout of β-catenin largely restricted the activation of Gli1⁺ SuSCs and suppressed bone remodeling under physiological and expansion conditions. Thus, we concluded that Gli1⁺ SuSCs play essential roles in suture and bone remodeling stimulated by mechanical force and that Wnt signaling is crucial to this process. © 2022 American Society for Bone and Mineral Research (ASBMR).     

原子力显微镜检测兔面缝增龄性变化

目的研究兔的前颌缝、鼻额缝、颧颞缝、腭横缝的交错性及纳米弹性性能,及其缝的生物力学特性的增龄性变化,为缝牵引成骨技术的临床应用提供实验依据。方法选取3个月龄及6个月龄同种日本大耳白兔各8只,切取颧颞缝、鼻额缝、前颌缝及腭横缝组织,观察缝大体交错性,并应用原子力显微镜检测缝的微观形貌和生物力学特性,并比较不同年龄组动物之间的差异。结果两组动物的颧颞缝、鼻额缝、前颌缝及腭横缝组织及其相关矿化前缘具有明显不同的交错性、三维微观形貌和弹性材料性能。随年龄的增大、鼻额缝和前颌缝的交错性增加。6个月龄的兔颧颞缝、鼻额缝、前颌缝及腭横缝组织及其矿化前缘表面形貌较3个月龄平滑,而弹性模量则有所增加。结论面缝的微观形貌和弹性模量的增龄性变化提示,大龄上颌发育不全患者可以应用更大的力量进行缝牵引成骨治疗。     

腭骨外侧缝牵张成骨的连续组织学研究

目的　了解腭骨外侧缝牵张的缝组织反应和组织再生机理。方法　采用NiTi SMA缝牵张器牵张幼犬双侧腭骨外侧缝 ,四环素荧光标记和组织学观察缝牵张 3 ,7,14 ,2 8,5 6d连续组织变化过程。结果　缝牵张初期骨缘外侧出现囊状分离带 ,此后成骨和成纤维细胞大量增殖 ,成骨活动沿囊性分隔和周边进行 ,直至新的骨缘形成 ,缝恢复正常形态。结论　缝成骨主要发生在骨缘与缝结缔组织交界处 ,骨组织再生极具空间效率 ,中央带纤维排列方式和修复可能具有屏障作用 ,阻止了跨缝骨性融合。     

Transversal Maxillary Growth in Experimental Submucous Mid-Palatal Clefts: A Roentgen-Cephalometric Study in the Cat

At the average age of 2 1/2 months the mid-palatal suture and adjacent bone was extirpated in 24 domestic cats resulting in a 5 mm wide submucous cleft in the hard palate. In 16 other animals the corresponding mucoperiosteal flap was elevated and replaced without resection of the suture, i.e. testing the effect of the soft tissue trauma implied. Twenty-eight unoperated cats of corresponding age served as controls. The transversal maxillary growth was then studied radiographically by measuring the increase in distance, on cephalograms, between metallic implants inserted into both sides of the hard palate. Up to 50% reduction of transversal growth appeared where the mid-palatal suture had been extirpated. The palatal dimensions of the sham operated- and the unoperated groups did not diverge. The results obtained seem to indicate that growth in the mid-palatal suture is a combination of active growth due to proliferation of the sutural tissue, and passive growth induced by external forces exerting a traction in lateral direction.     

A Pro253Arg mutation in fibroblast growth factor receptor 2 (Fgfr2) causes skeleton malformation mimicking human Apert syndrome by affecting both chondrogenesis and osteogenesis

Apert syndrome is one of the most severe craniosynostosis that is mainly caused by either a Ser252Trp(S252W) or Pro253Arg(P253R) mutation in fibroblast growth factor receptor 2 (FGFR2). As an autosomal dominant disorder, Apert syndrome is mainly characterized by skull malformation resulting from premature fusion of craniofacial sutures, as well as syndactyly, etc. A P253R mutation of FGFR2 results in nearly one-thirds of the cases of Apert syndrome. The pathogenesis of Apert syndrome resulting from P253R mutation of FGFR2 is still not fully understood. Here we reported a knock-in mouse model carrying P253R mutation in Fgfr2. The mutant mice exhibit smaller body size and brachycephaly. Analysis of the mutant skulls and long bones revealed premature fusion of coronal suture, shortened cranial base and growth plates of long bones. In vitro organ culture studies further revealed that, compared with wild-type littermates, the mutant mice have prematurely fused coronal sutures and retarded long bone growth. Treatment of the cultured calvaria and femur with PD98059, an Erk1/2 inhibitor, resulted in partially alleviated coronal suture fusion and growth retardation of femur respectively. Our data indicated that the P253R mutation in Fgfr2 directly affect intramembranous and endochondral ossification, which resulted in the premature closure of coronal sutures and growth retardation of long bones and cranial base. And the Erk1/2 signaling pathway partially mediated the effects of P253R mutation of Fgfr2 on cranial sutures and long bones.     

Expression of high-affinity receptors for TGF-beta during rat cranial suture fusion.

The etiology of craniosynostosis is unknown. The elucidation of the biological pathways responsible for this disorder has been hampered by an inability to evaluate cranial sutures before, during, and after cranial suture fusion. The programmed fusion of the rat posterofrontal (PF) suture postnatally provides an excellent model to study the molecular events that occur during cranial suture fusion. Previous experiments have implicated transforming growth factor beta (TGF-beta) growth factors in the regulation of PF suture fusion. The purpose of these experiments was to localize the expression of high-affinity receptors for these growth factors during cranial suture fusion. Four rats were sacrificed on postnatal days 8, 12, 17, and 40 (N = 16). The PF and sagittal sutures were harvested and prepared for immunohistochemical localization of TGF-beta receptor 1 and receptor 2 (Tbeta-RI, Tbeta-RII) protein. Results indicate that immunostaining for Tbeta-RI and Tbeta-RII is markedly increased in the dura mater and osteoblasts of the sutural margin of the PF suture during active suture fusion (on postnatal days 12, 17, and 40) compared with the osteoblasts and dura mater underlying the patent sagittal suture. These results, in combination with the authors' previous findings as well as studies supporting a role for TGF-beta molecules in the regulation of osteogenesis, implicate TGF-beta signaling in the regulation of suture fusion. The possible mechanisms of ligand-receptor interaction are discussed.     

生长因子在颅缝早闭症中作用的研究进展

颅缝早闭是一种较常见的先天性颅面畸形,表现为一条或多条颅缝过早闭合。多种因素可以在胚胎期及出生后影响头骨的发育,从而导致不同类型的颅缝早闭。目前研究表明,生长因子与颅缝闭合过程有着密切的联系,本文就生长因子在颅缝早闭症中作用的研究进展进行综述。     

骨缝牵引成骨动物模型的建立及应用

目的建立兔颅骨矢状缝牵引成骨的动物实验模型,评价该模型的可行性,并探讨局部应用rhBMP-2对牵引成骨的作用。方法以微型牵引种植钉(Miniscrew implants,MSI)作支抗,镍钛弹簧为牵引力源,建立MSI兔颅骨矢状缝弹力牵引成骨模型。应用该牵引系统对11周龄的新西兰白兔作矢状缝牵引成骨。将动物随机分为实验组(牵引+rh BMP-2,n=7),对照组(单纯牵引,n=7)。牵引29天,于0、5、11、17、23及29 d,应用X线及Micro-CT评价骨缝牵开情况;第7、27天注射四环素,第17天注射钙黄绿素,作为术后荧光组织切片观察标记。观察动物对该牵引成骨系统的耐受性,比较各组骨缝牵开的距离,并观察矢状缝组织形态学变化,验证兔颅骨矢状缝牵引成骨模型的可行性。结果MSI弹力牵引系统成功率为86%,牵引成骨实验可顺利完成。对照组矢状缝牵开的距离大于实验组(D29),两组矢状缝牵开的距离随着牵引持续时间的增加而递增,但骨缝牵开呈现先快后慢的趋势。骨组织形态学显示,两组骨缝间均有新生骨组织形成,说明该牵引成骨模型既能有效牵开骨缝,也能诱导骨缝间成骨。而实验组骨缝间新生骨组织形成速度大于对照组。结论本实验采用自行研制的微型种植钉MSI弹力牵引系统,成功建立了兔矢状缝弹力牵引成骨模型。骨缝牵引过程中,局部应用rhBMP-2可促进骨缝成骨,但导致了骨缝融合。