Cellular response to force application at craniofacial sutures

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.

An instantly fixable and self-adaptive scaffold for skull regeneration by autologous stem cell recruitment and angiogenesis

Limited stem cells, poor stretchability and mismatched interface fusion have plagued the reconstruction of cranial defects by cell-free scaffolds. Here, we designed an instantly fixable and self-adaptive scaffold by dopamine-modified hyaluronic acid chelating Ca²⁺ of the microhydroxyapatite surface and bonding type I collagen to highly simulate the natural bony matrix. It presents a good mechanical match and interface integration by appropriate calcium chelation, and responds to external stress by flexible deformation. Meanwhile, the appropriate matrix microenvironment regulates macrophage M2 polarization and recruits endogenous stem cells. This scaffold promotes the proliferation and osteogenic differentiation of BMSCs in vitro, as well as significant ectopic mineralization and angiogenesis. Transcriptome analysis confirmed the upregulation of relevant genes and signalling pathways was associated with M2 macrophage activation, endogenous stem cell recruitment, angiogenesis and osteogenesis. Together, the scaffold realized 97 and 72% bone cover areas after 12 weeks in cranial defect models of rabbit (Φ = 9 mm) and beagle dog (Φ = 15 mm), respectively.

Limited stem cells and mismatched interface fusion have plagued biomaterial-mediated cranial reconstruction. Here, the authors engineer an instantly fixable and self-adaptive scaffold to promote calcium chelation and interface integration, regulate macrophage M2 polarization, and recruit endogenous stem cells.

Craniofacial developmental concepts in dynamic osteotomies and the Nautilus technique: A procedure created in Brazil for the treatment of craniosynostosis

Craniofacial development is the major focus of attention in surgical treatments for craniosynostosis. Growth rate, size, shape, and proportion of soft tissue and bone structures of the skull and face are determinant factors in the establishment of the vital functions of swallowing and breathing, as well as in the aesthetic balance of facial features, so important for the patient's psychological identity. This manuscript revisits the concept of craniosynostosis and reviews the major biological and anatomical factors that come into play in the developmental process of craniofacial structures, especially during infancy and early childhood. It also describes the Nautilus surgical technique, a corrective procedure created and implemented in Brazil in 2011-how it was created and how it has evolved: as we look back into the past 10 years, we shed light onto what was learned, on our contributions to improve treatments over time, and on how much we still have to discover in this fascinating area.

Secular change in morphological cranial and mandibular trait frequencies in European Americans born 1824-1987

OBJECTIVES

Secular change in cranial and postcranial morphometrics and morphological traits has been documented in several studies. However, to date, few studies have addressed temporal changes occurring in the expression of cranial morphological traits commonly used in ancestry estimation. This study examines secular change in the expression of 23 cranial and mandibular morphological traits; accounting for age-at-death, sex, and year-of-birth.

MATERIALS & METHODS

Data were collected on 23 morphological cranial and mandibular traits for European American individuals (19-97 years of age) from the Hamann-Todd Skeletal Collection (n = 518) and the William M. Bass Donated Skeletal Collection (n = 602). Individuals were divided into six birth-year cohorts: 1824-1849 (Cohort 1), 1850-1874 (Cohort 2), 1875-1899 (Cohort 3), 1900-1924 (Cohort 4), 1925-1949 (Cohort 5), and 1950-1987 (Cohort 6).

RESULTS

Statistical analyses, including Pearson's chi-square, correspondence analysis, and ordinal regression, demonstrate that secular changes have occurred in 11 traits, including: anterior nasal spine (ANS); malar tubercle (MT); nasal bone contour (NBC); postbregmatic depression (PBD); supranasal suture (SPS); transverse palatine suture (TPS); zygomaticomaxillary suture (ZS); ascending ramus shape (ARS); gonial angle flare (GAF); mandibular tori (MDT); and posterior ramus edge inversion (PREI), with changes occurring in both sexes for ANS, MT, TPS, ZS, GAF, MDT, and PREI. Significant changes in trait expression were found predominately between Cohorts 3 and 4, and Cohorts 4 and 5. While the sex of an individual affected the expression of ANS, MT, NBC, PBD, SPS, ZS, ARS, GAF, and PREI, age-at-death only affected MT and PREI.

DISCUSSION

This study demonstrates that secular change in morphological cranial and mandibular traits has occurred over the last two centuries in European Americans, with the most considerable change appearing at the turn of the twentieth century. Changes in morphological trait expression over a relatively short period of time correspond with changes seen in craniometric analyses and correlate with the industrialization of society and environmental and cultural changes, such as medical advancements, nutrition, and population health/stress.

Effects of continuous and intermittent parathyroid hormone administration on midpalatal suture expansion in rats

OBJECTIVES

The aim of this study was to investigate the effects of continuous parathyroid hormone (cPTH) and intermittent parathyroid hormone (iPTH) on bone formation and bone resorption in midpalatal suture during maxillary expansion.

METHODS

Forty-eight male SD rats were randomly divided into four groups (n = 12 each), including the control, the expansion (E), the E + cPTH, and the E + iPTH. A thermosensitive controlled-release hydrogel was synthesized for cPTH administration. All animals were sacrificed after seven days. Microcomputed tomography, histochemical staining and real-time PCR were used to investigate the bone remodeling of midpalatal suture. Serum chemistry was adopted to evaluate the systemic condition of experimental animals.

RESULTS

The suture width was increased by the expansion, and further elevated by cPTH and iPTH administration. Both regimes improved bone volume fraction and trabecular thickness of suture bone region. Moreover, both cPTH and iPTH decreased SOST expression and enhanced the expression of β-catenin and Col-I. cPTH increased RANKL expression, inhibited OPG expression, and resulted in an increment of osteoclasts, while iPTH had no influence on osteoclastogenesis. The serum calcium concentration was enhanced by PTH administration.

CONCLUSION

Both cPTH and iPTH promote midpalatal suture expansion by enhancing bone formation, probably via SOST downregulation and the resulting β-catenin activation. Our results demonstrated that PTH administration may have potential to be an adjunctive approach for maxillary expansion treatment.

Cichlid fishes as a model to understand normal and clinical craniofacial variation

We have made great strides towards understanding the etiology of craniofacial disorders, especially for 'simple' Mendelian traits. However, the facial skeleton is a complex trait, and the full spectrum of genetic, developmental, and environmental factors that contribute to its final geometry remain unresolved. Forward genetic screens are constrained with respect to complex traits due to the types of genes and alleles commonly identified, developmental pleiotropy, and limited information about the impact of environmental interactions. Here, we discuss how studies in an evolutionary model - African cichlid fishes - can complement traditional approaches to understand the genetic and developmental origins of complex shape. Cichlids exhibit an unparalleled range of natural craniofacial morphologies that model normal human variation, and in certain instances mimic human facial dysmorphologies. Moreover, the evolutionary history and genomic architecture of cichlids make them an ideal system to identify the genetic basis of these phenotypes via quantitative trait loci (QTL) mapping and population genomics. Given the molecular conservation of developmental genes and pathways, insights from cichlids are applicable to human facial variation and disease. We review recent work in this system, which has identified lbh as a novel regulator of neural crest cell migration, determined the Wnt and Hedgehog pathways mediate species-specific bone morphologies, and examined how plastic responses to diet modulate adult facial shapes. These studies have not only revealed new roles for existing pathways in craniofacial development, but have identified new genes and mechanisms involved in shaping the craniofacial skeleton. In all, we suggest that combining work in traditional laboratory and evolutionary models offers significant potential to provide a more complete and comprehensive picture of the myriad factors that are involved in the development of complex traits.

Cell morphologic changes and PCNA expression within craniofacial sutures during monkey Class III treatment

OBJECTIVES

To evaluate and compare the cellular morphologic changes and proliferating cell nuclear antigen (PCNA) expression within craniofacial sutures in growing Rhesus monkeys treated with a Class III functional appliance.

MATERIALS AND METHODS

Six Rhesus monkeys in the mixed dentition stage were divided into three groups: a 45-day experimental group, a 90-day experimental group, and a control group. Monkeys in the experimental groups were fitted with a Class III magnetic twin-block appliance. Cellular changes in six craniofacial sutures-the zygomaticomaxillary, zygomaticotemporal, transverse palatine, pterygopalatine, zygomaticofrontal, and frontomaxillary sutures were qualitatively and quantitatively evaluated by means of histomorphologic analysis, TEM, and immunohistochemical test of PCNA.

RESULTS

Obvious and altered bone remodeling combined with bone deposition and resorption was present in craniofacial sutures in the experimental groups. Increased activity of enlarged fibroblasts with abundant organelles was revealed. PCNA expression increased in the 45-day group compared with the control group, followed by the 90-day group. The highest percentage of PCNA-positive cells was found in the pterygopalatine suture in the 45-day group and the zygomaticomaxillary suture in the 90-day group.

CONCLUSIONS

The pterygopalatine and zygomaticomaxillary sutures are more active among the craniofacial sutures in the craniofacial complex remodeling during Class III treatment. The magnetic twin-block appliance effectively promoted suture remodeling by enhancing the activity and proliferation of osteoblasts, osteoclasts, and fibroblasts, especially in the early phase.

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.

Ectocranial suture fusion in primates: as related to cranial volume and dental eruption

BACKGROUND

Timing of calvarial suture fusion is important in primate ontogeny. Ages at death are difficult to assess especially for museum collections.

METHODS

1550 skulls of Hominoid, Hylobatidae, Macaca and Papio were observed for fusion. Calvarial expansion (early) and dental eruption (late) were utilized as indicators of ontogeny. Homogeneity of slopes and ANOVA were used to determine differences in timing of fusion.

RESULTS

For calvarial growth the great apes all showed small levels of calvarial suture remodeling prior to full calvarial expansion. For dental eruption, Homo and Macaca share a common pattern of fusion in late adulthood. The other species show early remodeling. Papio was observed to have distinct patterns for suture fusion progression.

CONCLUSIONS

Thus, suture fusion progression although influenced by evolutionary changes in the robusticity of the craniofacial skeleton can be modeled by the phylogeny among this group. Overall, Homo appears to have a distinct pattern of delayed suture fusion progression.

Stimulation of bone formation in the expanding premaxillary suture with a GSK-3β inhibitor

OBJECTIVES

Glycogen synthase kinase-3β (GSK-3β)/β-catenin signaling mediates osteogenesis in response to mechanical loading. We tested the hypothesis that local administration of a GSK-3β inhibitor could stimulate new bone formation in the expanding premaxillary suture.

MATERIALS AND METHODS

Thirty-five Sprague-Dawley rats were subjected to premaxillary suture expansion using a helix spring. The experimental rats were given one or two local injections of SB-415286, a small-molecule GSK-3β inhibitor. Animals were administered calcein and sacrificed on day 7 to quantify new bone formation. To evaluate the proliferation and differentiation of osteoblasts, rats were labeled with bromodeoxyuridine on day 1 and sacrificed on day 2 or 4. β-catenin expression was evaluated by immunohistochemical staining.

RESULTS

Two injections of SB-415286 led to an elevation of β-catenin expression and an increase in the number of proliferating osteoblasts in expanding sutures on day 2 and day 4. Consequently, new bone formation in the suture increased significantly on day 7.

CONCLUSIONS

These results suggest that local delivery of a GSK-3β inhibitor could stimulate bone formation in the expanding premaxillary suture by eliciting β-catenin signaling. GSK-3β could be a pharmaceutical target for improving the effect of orthodontic treatments such as rapid palatal expansion.

The mouse palate and its cellular responses to midpalatal suture expansion forces

OBJECTIVES

To investigate the anatomy of the mouse palate, the midpalatal suture, and the cellular characteristics in the sutures before and immediately after midpalatal suture expansion.

MATERIALS AND METHODS

Wild-type C57BL/6 male mice, aged between 6 weeks and 12 months, were chosen for all the experiments. The complete palate of the non-operated group and the midpalatal suture-expanded group at different ages was used for histological, micro-CT, immunohistochemistry, and sutural cell analyses.

RESULTS

This study documents precise morphological and histological characteristics of the mouse palatal sutures. In addition to the opening of the midpalatal suture caused by expansion, both transverse and interpalatine sutures were also seen to be affected. Cellular density was decreased in different types of sutures following the application of mechanical force.

CONCLUSIONS

The detailed morphology and histology of the mouse palate and the cellular changes that occur following midpalatal suture expansion, as described here, will be helpful as a basis for further investigations of palatal suture tissue responses to mechanical force.

Timing of ectocranial suture activity in Gorilla gorilla as related to cranial volume and dental eruption

Research has shown that Pan and Homo have similar ectocranial suture synostosis patterns and a similar suture ontogeny (relative timing of suture fusion during the species ontogeny). This ontogeny includes patency during and after neurocranial expansion with a delayed bony response associated with adaptation to biomechanical forces generated by mastication. Here we investigate these relationships for Gorilla by examining the association among ectocranial suture morphology, cranial volume (as a proxy for neurocranial expansion) and dental development (as a proxy for the length of time that it has been masticating hard foods and exerting such strains on the cranial vault) in a large sample of Gorilla gorilla skulls. Two-hundred and fifty-five Gorilla gorilla skulls were examined for ectocranial suture closure status, cranial volume and dental eruption. Regression models were calculated for cranial volumes by suture activity, and Kendall's tau (a non-parametric measure of association) was calculated for dental eruption status by suture activity. Results suggest that, as reported for Pan and Homo, neurocranial expansion precedes suture synostosis activity. Here, Gorilla was shown to have a strong relationship between dental development and suture activity (synostosis). These data are suggestive of suture fusion extending further into ontogeny than brain expansion, similar to Homo and Pan. This finding allows for the possibility that masticatory forces influence ectocranial suture morphology.

Lithium delivery enhances bone growth during midpalatal expansion

Lithium is an activator of β-catenin signaling, and β-catenin mediates bone acquisition in response to mechanical loading in the bone. We tested the hypothesis that lithium enhances new bone formation during midpalatal suture expansion. Forty-eight Wistar rats with or without suture expansion were gavage-fed daily with lithium chloride or sodium chloride. We labeled the rats with bromodeoxyuridine to evaluate the proliferation and differentiation of the osteoprogenitors. Lithium increased β-catenin expression and cell proliferation in expanding sutures. Initial delay in the differentiation of osteoprogenitors into mature osteoblasts by lithium treatment corresponded with expansion of pre-osteoblasts, which preceded the increase of new bone formation in the suture. These results suggested that β-catenin regulates proliferation of osteoprogenitors and maturation of osteoblasts during midpalatal suture expansion osteogenesis, and that lithium enhances bone regeneration by elevating β-catenin expression. Lithium treatment could be a pharmaceutical aid to improve the stability of orthodontic treatment like rapid palatal expansion.

Test of the relationship between sutural ossicles and cultural cranial deformation: results from Hawikuh, New Mexico

A number of researchers have hypothesized that the biomechanical forces associated with cultural cranial deformation can influence the formation of sutural ossicles. However, it is still difficult to make definitive conclusions about this relationship because the effects appear to be quite weak, and contradictory results have been obtained when specific sutures and deformation types are compared across studies. This research retests the hypothesis using a single archeological sample of lamdoidally deformed, occipitally deformed, and undeformed crania from Hawikuh, New Mexico (AD 1300-1680). Our results show no significant difference in either the prevalence or number of ossicles between deformed and undeformed crania, suggesting that the abnormal strains generated by cranial shape modification during infancy are not a factor in ossicle development for this population. One significant relationship was detected at the right lambdoid suture in crania with asymmetrical occipital deformation. Crania that were more deformed on the left side showed greater numbers of ossicles on the right side, but the effect was small. Furthermore, the relationship may well reflect a sampling error, due to the small number of crania with greater left side deformation and scorable right side lambdoid ossicles (n = 11). Although it is possible that forms of cranial deformation other than the posterior tabular types examined here may affect ossicle expression, our review of the literature suggests that the relationship in humans is complex and incompletely understood at this time.