Dihydrotestosterone Stimulates Proliferation and Differentiation of Fetal Calvarial Osteoblasts and Dural Cells and Induces Cranial Suture Fusion

Transcriptomic Signatures of Single-Suture Craniosynostosis Phenotypes

Craniosynostosis is a birth defect where calvarial sutures close prematurely, as part of a genetic syndrome or independently, with unknown cause. This study aimed to identify differences in gene expression in primary calvarial cell lines derived from patients with four phenotypes of single-suture craniosynostosis, compared to controls. Calvarial bone samples (N = 388 cases/85 controls) were collected from clinical sites during reconstructive skull surgery. Primary cell lines were then derived from the tissue and used for RNA sequencing. Linear models were fit to estimate covariate adjusted associations between gene expression and four phenotypes of single-suture craniosynostosis (lambdoid, metopic, sagittal, and coronal), compared to controls. Sex-stratified analysis was also performed for each phenotype. Differentially expressed genes (DEGs) included 72 genes associated with coronal, 90 genes associated with sagittal, 103 genes associated with metopic, and 33 genes associated with lambdoid craniosynostosis. The sex-stratified analysis revealed more DEGs in males (98) than females (4). There were 16 DEGs that were homeobox (HOX) genes. Three TFs (SUZ12, EZH2, AR) significantly regulated expression of DEGs in one or more phenotypes. Pathway analysis identified four KEGG pathways associated with at least one phenotype of craniosynostosis. Together, this work suggests unique molecular mechanisms related to craniosynostosis phenotype and fetal sex.

An Investigation of the Relationship Between the Second-to-Fourth Digit Ratio and Sagittal Synostosis

BACKGROUND

The most common presentation of nonsyndromic craniosynostosis is that of the sagittal suture. Amongst this subgroup there is a significant male preponderance. Although the etiology is largely unknown, androgen exposure in utero has been suggested as a contributing factor. The second-to-fourth digit ratio (2D:4D) is a sexually dimorphic trait, reflective of the levels of androgen and estrogen exposure in utero, with a lower 2D:4D ratio associated with higher androgen exposure.This study aimed to examine the difference in 2D:4D ratio between participants with sagittal synostosis (SS) and gender-matched controls, hypothesizing that alterations in androgen exposure would be reflected in participants' 2D:4D ratio.

METHOD

Participants with nonsyndromic SS and gender-matched controls were prospectively recruited from outpatients clinics. Photographs were taken of the right hand, and 3 independent researchers measured the length of the fingers and 2D:4D ratio, with the mean 2D:4D ratio then calculated.

RESULTS

Fifty-six participants were recruited to both groups, with 35 males and 21 females in each. The mean age of the study and control groups were 5.6 and 6.3 years, respectively. There was no difference in the 2D:4D ratio between groups overall (P = 0.126). However, males with SS had a significantly higher 2D:4D ratio in comparison to male controls (0.969 ± 0.379 versus 0.950 ± 0.354, P = 0.038).

CONCLUSIONS

Our results suggest that 1 single hormonal pathway is not responsible for suture fusion. Subsequently we consider that an imbalance between testosterone and estrogen signaling may contribute to the development of sagittal craniosynostosis.

Mechanical and morphological properties of parietal bone in patients with sagittal craniosynostosis

Limited information is available on the effect of sagittal craniosynostosis (CS) on morphological and material properties of the parietal bone. Understanding these properties would not only provide an insight into bone response to surgical procedures but also improve the accuracy of computational models simulating these surgeries. The aim of the present study was to characterise the mechanical and microstructural properties of the cortical table and diploe in parietal bone of patients affected by sagittal CS. Twelve samples were collected from pediatric patients (11 males, and 1 female; age 5.2 ± 1.3 months) surgically treated for sagittal CS. Samples were imaged using micro-computed tomography (micro-CT); and mechanical properties were extracted by means of micro-CT based finite element modelling (micro-FE) of three-point bending test, calibrated using sample-specific experimental data. Reference point indentation (RPI) was used to validate the micro-FE output. Bone samples were classified based on their macrostructure as unilaminar or trilaminar (sandwich) structure. The elastic moduli obtained using RPI and micro-FE approaches for cortical tables (E_RPI 3973.33 ± 268.45 MPa and E_micro-FE 3438.11 ± 387.38 MPa) in the sandwich structure and diploe (E_RPI1958.17 ± 563.79 MPa and E_micro-FE 1960.66 ± 492.44 MPa) in unilaminar samples were in strong agreement (r = 0.86, p < .01). We found that the elastic modulus of cortical tables and diploe were correlated with bone mineral density. Changes in the microstructure and mechanical properties of bone specimens were found to be irrespective of patients' age. Although younger patients are reported to benefit more from surgical intervention as skull is more malleable, understanding the material properties is critical to better predict the surgical outcome in patients <1 year old since age-related changes were minimal.

Stanozolol promotes osteogenic gene expression and apposition of bone mineral in vitro

Stanozolol (ST) is a synthetic androgen with high anabolic potential. Although it is known that androgens play a positive role in bone metabolism, ST action on bone cells has not been sufficiently tested to support its clinical use for bone augmentation procedures. Objective: This study aimed to assess the effects of ST on osteogenic activity and gene expression in SaOS-2 cells. Material and Methods: SaOS-2 deposition of mineralizing matrix in response to increasing doses of ST (0-1000 nM) was evaluated through Alizarin Red S and Calcein Green staining techniques at 6, 12 and 24 days. Gene expression of runt-related transcription factor 2 (RUNX2), vitamin D receptor (VDR), osteopontin (SPP1) and osteonectin (ON) was analyzed by RT-PCR. Results: ST significantly influenced SaOS-2 osteogenic activity: stainings showed the presence of rounded calcified nodules, which increased both in number and in size over time and depending on ST dose. RT-PCR highlighted ST modulation of genes related to osteogenic differentiation. Conclusions: This study provided encouraging results, showing ST promoted the osteogenic commitment of SaOS-2 cells. Further studies are required to validate these data in primary osteoblasts and to investigate ST molecular pathway of action.

Whole-Proteome Analysis of Human Craniosynostotic Tissue Suggests a Link between Inflammatory Signaling and Osteoclast Activation in Human Cranial Suture Patency

BACKGROUND

The pathophysiology of nonsyndromic craniosynostosis remains poorly understood. The authors seek to understand the cause of this condition with a specific focus on how osteoclasts may contribute to craniosynostosis. Here, the authors characterize proteins differentially expressed in patent and fused cranial sutures by comparing their respective proteomes.

METHODS

Fused and patent suture samples were obtained from craniosynostotic patients undergoing surgery at a single academic medical center. Extracted protein from samples was interrogated using mass spectrometry. Differential protein expression was determined using maximum likelihood-based G-test with a q-value cutoffs of 0.5 after correction for multiple hypothesis testing. Immunolocalization of lead protein candidates was performed to validate proteomic findings. In addition, quantitative polymerase chain reaction analysis of corresponding gene expression of proteins of interest was performed.

RESULTS

Proteins differentially expressed in patent versus fused sutures included collagen 6A1 (Col6A1), fibromodulin, periostin, aggrecan, adipocyte enhancer-binding protein 1, and osteomodulin (OMD). Maximum likelihood-based G-test suggested that Col6A1, fibromodulin, and adipocyte enhancer-binding protein 1 are highly expressed in patent sutures compared with fused sutures, whereas OMD is up-regulated in fused sutures compared with patent sutures. These results were corroborated by immunohistochemistry. Quantitative polymerase chain reaction data point to an inverse relationship in proteins of interest to RNA transcript levels, in prematurely fused and patent sutures that potentially describes a feedback loop mechanism.

CONCLUSIONS

Proteome analysis validated by immunohistochemistry may provide insight into the mechanism of cranial suture patency and disease from an osteoclast perspective. The authors results suggest a role of inflammatory mediators in nonsyndromic craniosynostosis. Col6A1 may aid in the regulation of suture patency, and OMD may be involved in premature fusion. Additional validation studies are required.

Dihydrotestosterone, a robust promoter of osteoblastic proliferation and differentiation: understanding of time-mannered and dose-dependent control of bone forming cells

Objective(s):

The present study was aimed to evaluate the time-mannered and dose-dependent effects of 5α-dihydrotestosterone (5α-DHT) on the proliferation and differentiation of bone forming cells using MC3T3-E1 cells.

Materials and Methods:

Cell proliferation was analyzed using MTS and phase contrast microscopic assays. Osteogenic differentiation was assessed through a series of in vitro experiments including crystal violet staining, alkaline phosphatase (ALP) activity, and Van Gieson (VG) staining. Taken together, the efficiency of bone mineralization was examined by using alizarin red s (ARS) staining, Von Kossa staining, scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) analysis.

Results:

The resulting data revealed that 5α-DHT exhibits promising potential particularly at a dose of 0.1 ng/ml, in promoting the growth of MC3T3-E1 cells compared to the control group (CN). Moreover, a significantly higher ALP activity was evident in the experimental group treated with 5α-DHT compared to the CN group at various time intervals. MC3T3-E1 cells treated with 5α-DHT also expressed a remarkably higher collagen deposition and mineralization (calcium and phosphate contents) compared to the CN group at various time intervals.

Conclusion:

Conclusively, we suggest that 5α-DHT exhibits outstanding potential of promoting proliferation and differentiation in osteoblasts which could be the in vitro basis for the efficacy of 5α-DHT in the treatment of androgen-deficient male osteoporosis.

Hormonal alterations in PCOS and its influence on bone metabolism

According to the World Health Organization (WHO) polycystic ovary syndrome (PCOS) occurs in 4-8% of women worldwide. The prevalence of PCOS in Indian adolescents is 12.2% according to the Indian Council of Medical Research (ICMR). The National Institute of Health has documented that it affects approximately 5 million women of reproductive age in the United States. Hormonal imbalance is the characteristic of many women with polycystic ovarian syndrome (PCOS). The influence of various endocrine changes in PCOS women and their relevance to bone remains to be documented. Hormones, which include gonadotrophin-releasing hormone (GnRH), insulin, the leutinizing/follicle-stimulating hormone (LH/FSH) ratio, androgens, estrogens, growth hormones (GH), cortisol, parathyroid hormone (PTH) and calcitonin are disturbed in PCOS women. These hormones influence bone metabolism in human subjects directly as well as indirectly. The imbalance in these hormones results in increased prevalence of osteoporosis in PCOS women. Limited evidence suggests that the drugs taken during the treatment of PCOS increase the risk of bone fracture in PCOS patients through endocrine disruption. This review is aimed at the identification of the relationship between bone mineral density and hormonal changes in PCOS subjects and identifies potential areas to study bone-related disorders in PCOS women.

Activation of the IGF1 pathway mediates changes in cellular contractility and motility in single-suture craniosynostosis

Insulin growth factor 1 (IGF1) is a major anabolic signal that is essential during skeletal development, cellular adhesion and migration. Recent transcriptomic studies have shown that there is an upregulation in IGF1 expression in calvarial osteoblasts derived from patients with single-suture craniosynostosis (SSC). Upregulation of the IGF1 signaling pathway is known to induce increased expression of a set of osteogenic markers that previously have been shown to be correlated with contractility and migration. Although the IGF1 signaling pathway has been implicated in SSC, a correlation between IGF1, contractility and migration has not yet been investigated. Here, we examined the effect of IGF1 activation in inducing cellular contractility and migration in SSC osteoblasts using micropost arrays and time-lapse microscopy. We observed that the contractile forces and migration speeds of SSC osteoblasts correlated with IGF1 expression. Moreover, both contractility and migration of SSC osteoblasts were directly affected by the interaction of IGF1 with IGF1 receptor (IGF1R). Our results suggest that IGF1 activity can provide valuable insight for phenotype-genotype correlation in SSC osteoblasts and might provide a target for therapeutic intervention.

Skull base development and craniosynostosis

Abnormal skull shape resulting in craniofacial deformity is a relatively common clinical finding, with deformity either positional (positional plagiocephaly) or related to premature ossification and fusion of the skull sutures (craniosynostosis). Growth restriction occurring at a stenosed suture is associated with exaggerated growth at the open sutures, resulting in fairly predictable craniofacial phenotypes in single-suture non-syndromic pathologies. Multi-suture syndromic subtypes are not so easy to understand without imaging. Imaging is performed to define the site and extent of craniosynostosis, to determine the presence or absence of underlying brain anomalies, and to evaluate both pre- and postoperative complications of craniosynostosis. Evidence for intracranial hypertension may be seen both pre- and postoperatively, associated with jugular foraminal stenosis, sinovenous occlusion, hydrocephalus and Chiari 1 malformations. Following clinical assessment, imaging evaluation may include radiographs, high-frequency US of the involved sutures, low-dose (20-30 mAs) CT with three-dimensional reformatted images, MRI and nuclear medicine brain imaging. Anomalous or vigorous collateral venous drainage may be mapped preoperatively with CT or MR venography or catheter angiography.

The effect of factors other than age upon skeletal age indicators in the adult

CONTEXT

Estimation of adult age from skeletal remains is problematic due to the weak and variable relationship between age indicators and age.

OBJECTIVES

To assess the proportion of variation in age indicators that is associated with factors other than age and to attempt to identify what those factors might be.

METHODS

The paper focuses on frequently used adult bony age markers. A literature search (principally using Web of Science) is conducted to assess the proportion of variation in age indicators associated with factors other than age. The biology of these age markers is discussed, as are factors other than age that might affect their expression.

RESULTS

Typically, ∼60% of variation in bony age indicators is associated with factors other than age. Factors including inherent metabolic propensity to form bone in soft tissue, vitamin D status, hormonal and reproductive factors, energy balance, biomechanical variables and genetic factors may be responsible for this variation, but empirical studies are few.

CONCLUSION

Most variation in adult skeletal age markers is due to factors other than age; dry bone study of historic documented skeletal collections and high resolution CT scanning in modern cadavers or living individuals is needed to identify these factors.

Osteoblast differentiation profiles define sex specific gene expression patterns in craniosynostosis

Single suture craniosynostosis (SSC) is the premature fusion of one calvarial suture and occurs in 1-1700-2500 live births. Congenital fusion of either the sagittal, metopic, or coronal sutures represents 95% of all cases of SSC. Sagittal and metopic synostosis have a male preponderance (3:1) while premature fusion of the coronal suture has a female preponderance (2:1). Although environmental and genetic factors contribute to SSC, the etiology of the majority of SSC cases remains unclear. In this study, 227 primary calvarial osteoblast cell lines from patients with coronal, metopic, or sagittal synostosis and unaffected controls were established and assayed for ALP activity and BrdU incorporation (n = 226) as respective measures of early stage osteoblast differentiation and proliferation. Primary osteoblast cell lines from individuals with sagittal synostosis demonstrated higher levels of ALP activity and reduced proliferation when compared to control lines. In order to address the sex differences in SSC types, the data was further stratified by sex. Osteoblasts from males and females with sagittal synostosis as well as males with metopic synostosis demonstrated higher levels of ALP activity when compared to sex matched controls, and males with sagittal or metopic synostosis demonstrated reduced levels of proliferation. In order to elucidate genes and pathways involved in these observed phenotypes, correlation analyses comparing ALP activity and proliferation to global gene expression was performed. Transcripts related to osteoblast differentiation were identified both differentially up and downregulated, correlated with ALP activity when compared to controls, and demonstrated a striking sex specific gene expression pattern. These data support that the dysregulation of osteoblast differentiation plays a role in the development of SSC and that genetic factors contribute to the observed sex related differences.

Effect of a single injection of testosterone enanthate on 17β estradiol and bone turnover markers in hypogonadal male patients

PURPOSE

Several clinical studies testify the critical role played by estrogens in male bone metabolism. The aim of our study is to assess the effect of a single injection of testosterone enanthate in a group of hypogonadal men on 17β estradiol serum levels and some bone metabolic parameters.

METHOD

Twenty-one hypogonadal males were given one testosterone enanthate injection (250 mg). Blood samples were drawn before the injection and after 1, 2 and 3 weeks. The following variables were measured: Total testosterone (TT), 17β estradiol (17β E2), Sex hormone binding globulin, total alkaline phosphatase, osteocalcin, and C-telopeptide of type I collagen (CTx).

RESULTS

After testosterone injection, both TT and 17β E2 increased, peaking 1 week after the injection. Individual observation of the response of 17β E2 to testosterone showed that a subgroup (n = 9) failed to respond with any increase in 17β E2 at any of the weekly tests (group E2-), while the remainder (n = 12) showed a significant increase in 17β E2, which reached a mean value three times higher than at baseline (group E2+). The E2- patients reached a TT peak lower than that observed in the E+ group. CTx serum levels declined progressively in the E2+ group, reaching the significance (p = 0.03) at the end of the study, while it did not change in E- group.

CONCLUSION

This study suggests that a single injection of testosterone might have different effects on the production of endogenous estrogens, and a significant reduction of bone resorption parameters takes place only in the patients who show a significant increase of 17ß estradiol in response to testosterone administration.

Craniosynostosis

Craniosynostosis is a complex condition, characterized by the premature fusion of one of more of the cranial sutures. They can be seen individually or as part of multisystem syndromes. This review uses computed tomography (CT) with three-dimensional reconstructions to help describe some of the types and classifications of craniosynostosis, as well as describing some of the associations and the management of craniosynostosis.

Role of RANK-RANKL-OPG axis in cranial suture homeostasis

Craniosynostosis is a significant disorder affecting 1 in 2500 live births worldwide. Although a large body of work has focused on dural regulation and the contributions of molecular mediators such as fibroblast growth factor, bone morphogenetic protein, and transforming growth factor β, minimal attention has been directed toward osteoclast function in cranial suture biology. Receptor activator of nuclear factor κB (RANK) is an essential mediator of osteoclastogenesis and osteoclast activation. In this study, physiologic fusion of posterior frontal sutures in murine development correlated with decreasing protein expression of RANK in comparison to age-matched coronal and sagittal sutures via immunohistochemical survey. However, RANK mRNA did not exhibit a similar pattern suggesting that RANK is regulated at the protein level. Fused cranial sutures in nonsyndromic craniosynostotic children also showed decreased levels of RANK staining in immunohistochemistry in comparison to patent sutures from the same patients. Immunohistochemistry with a RANK ligand antibody did not show differences in fused or patent sutures. Moreover, RANK knockdown in calvarial strip suture cultures displayed increased bone density specifically in the suture line after infection with small interfering RANK viruses. Cranial suture biology, similar to bone biology in general, likely depends on a complex interplay between osteoblasts and osteoclasts. We now report a temporospatial correlation between RANK expression and suture morphology that suggests that osteoclast activity is important in maintenance of cranial suture patency in normal physiology and disease. Furthermore, RANK downregulation promoted suture fusion establishing a causal relationship between the presence of RANK and patency.

Molecular analysis of coronal perisutural tissues in a craniosynostotic rabbit model using polymerase chain reaction suppression subtractive hybridization

BACKGROUND

In the United States, the incidence of craniosynostosis (premature fusion of the sutures of the cranial vault) is one in 2000 to 3000 live births. The condition can cause increased intracranial pressure, severely altered head shape, and mental retardation. The authors have previously described a colony of rabbits with heritable coronal suture synostosis. This model has been instrumental in describing the postsurgical craniofacial growth associated with craniosynostosis. The molecular analysis of this model has been limited by the lack of molecular tools for use in rabbits. To understand the pathogenesis of craniosynostosis, the authors compared gene expression in perisutural tissues between wild-type and craniosynostotic rabbits using polymerase chain reaction suppression subtractive hybridization.

METHODS

Suppression subtractive hybridization polymerase chain reaction was performed on RNA derived from pooled samples of calvariae from 10-day-old wild-type (n = 3) and craniosynostotic (n = 3) rabbits to obtain cDNA clones enriched in either wild-type tissues (underexpressed in craniosynostotic tissue) or craniosynostotic tissues (overexpressed in craniosynostotic compared with wild-type).

RESULTS

Differential expression was identified for approximately 140 recovered cDNA clones up-regulated in craniosynostotic tissues and 130 recovered clones for wild-type tissues. Of these, four genes were confirmed by quantitative reverse-transcriptase polymerase chain reaction as being overexpressed in craniosynostotic sutural tissue: β-globin (HBB), osteopontin (SPP1), osteonectin (SPARC), and cathepsin K (CTSK). Two genes were confirmed to be underexpressed in the craniosynostotic samples: collagen 3, alpha 1 (COL3A1) and ring finger protein 12 (RNF12).

CONCLUSION

The differential expression of these gene products in our naturally occurring craniosynostotic model appears to be the result of differences in the normal bone formation/resorption pathway.

The effects of testosterone on craniosynostotic calvarial cells: a test of the gene/environmental model of craniofacial anomalies

INTRODUCTION

The gene-environmental interaction model for craniofacial development proposes that if a genetic predisposition for an anomaly is coupled with an environmental factor that can exacerbate this predisposition, more severe phenotypes will result. Here, we utilize cells derived from our non-syndromic rabbit model of craniosynostosis to test the hypothesis that an insult, testosterone (TP) administration (exogenous source) will alter the osteogenic activity of these cells.

DESIGN

Calvarial cells from wild-type (WT) (N=13) or craniosynostotic (CS) rabbits (N=11) were stimulated with TP, an androgen receptor blocker, flutamide, and combined treatments. Proliferation and differentiation assays were conducted after 7 days. anova and t-tests were used to determine differences in stimulation and cell type.

RESULTS

The CS cells had significantly greater proliferation after TP administration compared to WT. There were no appreciable changes in differentiation after TP stimulation. Flutamide administration or combined TP and flutamide administration decreased both proliferation and differentiation for both cell types similarly.

CONCLUSIONS

Testosterone exposure caused an increase in cell proliferation for CS osteoblast cells. However, a therapy targeted to mitigate this response (flutamide therapy) similarly affected CS and WT cells, suggesting that the administration of flutamide or TP in the presence of flutamide decreases osteogenesis of these cells. Thus, although our data support a mechanism of gene-environmental interaction, these results would not support a therapeutic intervention based on this interaction.

Signaling pathways implicated in androgen regulation of endocortical bone

Periosteal expansion is a recognized response to androgen exposure during bone development and in profoundly hypogonadal adults. However, androgen also suppresses endocortical bone formation, indicating that its effects on bone are dichotomous and envelope-specific. In fact, enhanced androgen signaling has been shown to have dramatic detrimental effects on whole bone biomechanical properties in two different transgenic models with skeletally targeted androgen receptor (AR) overexpression. As the mechanisms underlying this response are uncharacterized, we compared patterns of gene expression in periosteum-free cortical bone samples derived from AR-overexpressing transgenic male mice and their wild-type counterparts. We then assessed direct androgen effects in both wild-type and AR-overexpressing osteoblasts in primary culture. Among major signaling pathways associated with bone formation, focused quantitative RT-PCR (qPCR) array-based analysis of endocortical bone gene expression from wild-type vs. transgenic males identified the transforming growth factor-beta (TGF-beta) superfamily and bone morphogenetic protein (BMP) signaling as significantly altered by androgen in vivo. Bioinformatic analyses indicated proliferation, osteoblast differentiation and mineralization as major biological processes affected. Consistent with the in vivo array data and bioinformatic analyses, inhibition of differentiation observed with androgen exposure was reduced by exogenous BMP2 treatment of AR-overexpressing cultures to stimulate BMP signaling, confirming array pathway analysis. In addition, nonaromatizable dihydrotestosterone (DHT) inhibited osteoblast proliferation, differentiation and several indices of mineralization, including mineral accumulation and mineralized nodule formation in primary cultures from both wild-type and AR-transgenic mice. These findings identify a molecular mechanism based on altered BMP signaling that contributes to androgen inhibition of osteoblast differentiation and mineralization. Such detrimental effects of androgen on osteoblast function may underlie the generally disappointing results of androgen therapy.

Estrogen/estrogen receptor alpha signaling in mouse posterofrontal cranial suture fusion

Background

While premature suture fusion, or craniosynostosis, is a relatively common condition, the cause is often unknown. Estrogens are associated with growth plate fusion of endochondral bones. In the following study, we explore the previously unknown significance of estrogen/estrogen receptor signaling in cranial suture biology.

Methodology/Principal Findings

Firstly, estrogen receptor (ER) expression was examined in physiologically fusing (posterofrontal) and patent (sagittal) mouse cranial sutures by quantitative RT-PCR. Next, the cranial suture phenotype of ER alpha and ER beta knockout (αERKO, βERKO) mice was studied. Subsequently, mouse suture-derived mesenchymal cells (SMCs) were isolated; the effects of 17-β estradiol or the estrogen antagonist Fulvestrant on gene expression, osteogenic and chondrogenic differentiation were examined in vitro. Finally, in vivo experiments were performed in which Fulvestrant was administered subcutaneously to the mouse calvaria. Results showed that increased ERα but not ERβ transcript abundance temporally coincided with posterofrontal suture fusion. The αERKO but not βERKO mouse exhibited delayed posterofrontal suture fusion. In vitro, addition of 17-β estradiol enhanced both osteogenic and chondrogenic differentiation in suture-derived mesenchymal cells, effects reversible by Fulvestrant. Finally, in vivo application of Fulvestrant significantly diminished calvarial osteogenesis, inhibiting suture fusion.

Conclusions/Significance

Estrogen signaling through ERα but not ERβ is associated with and necessary for normal mouse posterofrontal suture fusion. In vitro studies suggest that estrogens may play a role in osteoblast and/or chondrocyte differentiation within the cranial suture complex.