RNA interference and inhibition of MEK-ERK signaling prevent abnormal skeletal phenotypes in a mouse model of craniosynostosis

Loss-of-function variants in ERF are associated with a Noonan syndrome-like phenotype with or without craniosynostosis

Pathogenic, largely truncating variants in the ETS2 repressor factor (ERF) gene, encoding a transcriptional regulator negatively controlling RAS-MAPK signaling, have been associated with syndromic craniosynostosis involving various cranial sutures and Chitayat syndrome, an ultrarare condition with respiratory distress, skeletal anomalies, and facial dysmorphism. Recently, a single patient with craniosynostosis and a phenotype resembling Noonan syndrome (NS), the most common disorder among the RASopathies, was reported to carry a de novo loss-of-function variant in ERF. Here, we clinically profile 26 individuals from 15 unrelated families carrying different germline heterozygous variants in ERF and showing a phenotype reminiscent of NS. The majority of subjects presented with a variable degree of global developmental and/or language delay. Their shared facial features included absolute/relative macrocephaly, high forehead, hypertelorism, palpebral ptosis, wide nasal bridge, and low-set/posteriorly angulated ears. Stature was below the 3rd centile in two-third of the individuals, while no subject showed typical NS cardiac involvement. Notably, craniosynostosis was documented only in three unrelated individuals, while a dolichocephalic aspect of the skull in absence of any other evidence supporting a premature closing of sutures was observed in other 10 subjects. Unilateral Wilms tumor was diagnosed in one individual. Most cases were familial, indicating an overall low impact on fitness. Variants were nonsense and frameshift changes, supporting ERF haploinsufficiency. These findings provide evidence that heterozygous loss-of-function variants in ERF cause a "RASopathy" resembling NS with or without craniosynostosis, and allow a first dissection of the molecular circuits contributing to MAPK signaling pleiotropy.

Effect of DNA methylation on the osteogenic differentiation of mesenchymal stem cells: concise review

Mesenchymal stem cells (MSCs) have promising potential for bone tissue engineering in bone healing and regeneration. They are regarded as such due to their capacity for self-renewal, multiple differentiation, and their ability to modulate the immune response. However, changes in the molecular pathways and transcription factors of MSCs in osteogenesis can lead to bone defects and metabolic bone diseases. DNA methylation is an epigenetic process that plays an important role in the osteogenic differentiation of MSCs by regulating gene expression. An increasing number of studies have demonstrated the significance of DNA methyltransferases (DNMTs), Ten-eleven translocation family proteins (TETs), and MSCs signaling pathways about osteogenic differentiation in MSCs. This review focuses on the progress of research in these areas.

Ser252Trp mutation in fibroblast growth factor receptor 2 promotes branching morphogenesis in mouse salivary glands

OBJECTIVES

The purpose of this study was to perform morphological and immunohistochemical (IHC) analysis of the submandibular glands (SMGs) in early development in Apert syndrome model mice (Ap mice).

METHODS

ACTB-Cre homozygous mice were mated with fibroblast growth factor receptor 2 (Fgfr2+/Neo-S252W) mice; ACTB-Cre heterozygous mice (ACTB-Cre mice) at embryonic day (E) 13.5 served as the control group, and Fgfr2+/S252W mice (Ap mice) served as the experimental group. Hematoxylin and eosin (H&E) staining was performed on SMGs; Total SMG area and epithelial area were determined, and the epithelial occupancy ratio was calculated. Immunostaining was performed to assess the localization of FGF signaling-related proteins. Next, bromodeoxyuridine (BrdU)-positive cells were evaluated to assess cell proliferation. Finally, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining was performed to assess apoptosis in SMGs.

RESULTS

The epithelial occupancy ratio was significantly higher in SMGs of Ap mice compared with that in SMGs of controls. FGF7 and bone morphogenetic protein 4 (BMP4) exhibited different localizations in SMGs of Ap mice compared with SMGs of controls. Cell proliferation was higher in SMGs of Ap mice compared with that of controls; however, apoptosis did not different significantly between the two groups.

CONCLUSION

Our results suggest that enhanced FGF signaling conferred by missense mutations in FGFR2 promotes branching morphogenesis in SMGs of Ap mice.

Sp1-activated FGFR2 is involved in early-life exposure to nickel-induced craniosynostosis by regulating the ERK1/2 signaling pathway

Nickel, a common environmental hazard, is a risk factor for craniosynostosis. However, the underlying biological mechanism remains unclear. Here, we found that early-life nickel exposure induced craniosynostosis in mice. In vitro, nickel promoted the osteogenic differentiation of human mesenchymal stem cells (hMSCs), and its osteogenic ability in vivo was confirmed by an ectopic osteogenesis model. Further mRNA sequencing showed that ERK1/2 signaling and FGFR2 were aberrantly activated. FGFR2 was identified as a key regulator of ERK1/2 signaling. By promoter methylation prediction and methylation-specific PCR (MSP) assays, we found that nickel induced hypomethylation in the promoter of FGFR2, which increased its binding affinity to the transcription factor Sp1. During pregnancy and postnatal stages, AZD4547 rescued nickel-induced craniosynostosis by inhibiting FGFR2 and ERK1/2. Compared with normal individuals, nickel levels were increased in the serum of individuals with craniosynostosis. Further logistic and RCS analyses showed that nickel was an independent risk factor for craniosynostosis with a nonlinear correlation. Mediated analysis showed that FGFR2 mediated 30.13% of the association between nickel and craniosynostosis risk. Collectively, we demonstrate that early-life nickel exposure triggers the hypomethylation of FGFR2 and its binding to Sp1, thereby promoting the osteogenic differentiation of hMSCs by ERK1/2 signaling, leading to craniosynostosis.

Prenatal and infantile diagnosis of craniosynostosis in individuals with RASopathies

Fetuses with RASopathies can have a wide variety of anomalies including increased nuchal translucency, hydrops fetalis, and structural anomalies (typically cardiac and renal). There are few reports that describe prenatal-onset craniosynostosis in association with a RASopathy diagnosis. We present clinical and molecular characteristics of five individuals with RASopathy and craniosynostosis. Two were diagnosed with craniosynostosis prenatally, 1 was diagnosed as a neonate, and 2 had evidence of craniosynostosis noted as neonates without formal diagnosis until later. Two of these individuals have Noonan syndrome (PTPN11 and KRAS variants) and three individuals have Cardiofaciocutaneous syndrome (KRAS variants). Three individuals had single suture synostosis and two had multiple suture involvement. The most common sutures involved were sagittal (n = 3), followed by coronal (n = 3), and lambdoid (n = 2) sutures. This case series confirms craniosynostosis as one of the prenatal findings in individuals with RASopathies and emphasizes the importance of considering a RASopathy diagnosis in fetuses with multiple anomalies in combination with craniosynostosis.

Unraveling the Complexity of Apert Syndrome: Genetics, Clinical Insights, and Future Frontiers

Apert syndrome (AS), also known as type I acrocephalosyndactyly, is a rare congenital condition characterized by craniosynostosis resulting from missense mutations in the fibroblast growth factor receptor 2 (FGFR2) gene. This comprehensive review delves into AS, covering its clinical manifestations, genetics, diagnosis, medical management, psychosocial considerations, and future research directions. AS presents with distinct features, including a brachycephalic skull, midface hypoplasia, and limb anomalies such as syndactyly. It follows an autosomal dominant inheritance pattern with mutations in the FGFR2 gene. Prenatal diagnosis is possible through advanced imaging techniques and molecular testing. The multidisciplinary approach to AS management involves surgical interventions, orthodontics, and psychological support. Although no curative treatment exists, early interventions can significantly improve function and aesthetics. The quality of life for AS patients is influenced by psychosocial factors, necessitating comprehensive support for both patients and their families. Future research directions include gene therapy, understanding cellular responses to FGFR2 mutations, and addressing genetic heterogeneity. Collaborative efforts are vital to advancing knowledge about AS and its genetic underpinnings. Overall, this review serves as a valuable resource for healthcare professionals, educators, and researchers, contributing to a deeper understanding of AS and facilitating advancements in diagnosis and treatment.

An unusual signal transducer GIV/Girdin engages in the roles of adipocyte-derived hormone leptin in liver fibrosis

Obese patients usually have hyperleptinemia and are prone to develop liver fibrosis. Leptin is intimately linked to liver fibrogenesis, a multi-receptor-driven disease. Gα-Interacting Vesicle-associated protein (GIV) functions as a multimodular signal transducer and a guanine nucleotide exchange factor for Gi controling key signalings downstream of diverse receptors. This study aimed to examine the roles of GIV in leptin-caused liver fibrosis and employed the culture-activated hepatic stellate cells (HSCs) and leptin-deficient mice, respectively. Results indicated that leptin upregulated GIV expression in HSCs. GIV was involved in leptin-induced HSC activation and liver fibrosis. GIV mediated leptin regulation of TIMP1, MMP9, PDGFβ receptor and TGFβ receptor and was required for leptin stimulating the pathways of Erk1/2, Akt1, and Smad3. GIV was also a mediator for leptin-regulation of Cyclin D1 and Caspase-3 activity but GIV reduced Caspase-3 level independently of leptin in vivo. Erk1/2 signaling, Egr1 and c-Jun were associated with the effect of leptin on GIV expression in HSCs. Leptin-induced Erk1/2 signaling increased Egr1 and p-c-Jun levels and promoted their binding to GIV promoter at the sites between -190 bp and -180 bp and between -382 bp and - 376 bp, respectively. Egr1 knockdown lessened leptin-upregulation of GIV in vitro and in vivo. In human cirrhotic livers, the increase in GIV protein level parallelled with the elevated p-Erk1/2 and Egr1 levels in HSCs. In summary, the unusual signal transducer GIV was identified as an important mediator in leptin-induced liver fibrosis. GIV may have significant implications in liver fibrosis progression of obese patients with hyperleptinaemia.

Exosome-mediated small interfering RNA delivery inhibits aberrant osteoblast differentiation in Apert syndrome model mice

OBJECTIVE

Apert syndrome, an autosomal dominant congenital disorder characterized by craniosynostosis, is caused by a missense mutation (S252W or P253R) in fibroblast growth factor receptor 2 (FGFR2). Exosomes are naturally occurring carriers that deliver nucleic acids, including small interfering RNA (siRNA), to induce gene silencing. This study aimed to develop siRNA-loaded exosomes (Ex-siRNA^Fgfr2S252W) to silence the Fgfr2^S252W gain-of-function mutation, thereby inhibiting the increased osteoblastic differentiation caused by the constitutive activation of FGFR2 signaling in calvarial osteoblastic cells isolated from Apert syndrome model mice.

DESIGN

Primary calvarial osteoblast-like cells were isolated from the embryonic calvarial sutures of the Apert syndrome model (Fgfr2^S252W/+) and littermate wild-type mice (Ap-Ob and Wt-Ob, respectively). Exosomes were extracted from the serum of wild-type mice, validated using biomarkers, and used to encapsulate siRNAs. After exosome-mediated siRNA transfection, cells were analyzed under a fluorescence microscope to validate the delivery of Ex-siRNA^Fgfr2S252W, followed by western blot and real-time reverse transcription polymerase chain reaction analyses.

RESULTS

After 24 h of Ex-siRNA^Fgfr2S252W delivery in both Ap-Ob and Wt-Ob, siRNA-loaded exosome delivery was validated. Moreover, p44/42 mitogen-activated protein kinase (MAPK) phosphorylation, runt-related transcription factor 2 (Runx2), and collagen type 1 alpha 1 (Col1a1) mRNA expression, and alkaline phosphatase (ALP) activity were significantly increased in Ap-Ob. The levels of phospho-p44/42 protein, Runx2, Col1a1, and ALP were significantly decreased after Ex-siRNA^Fgfr2S252W transfection but did not affect Wt-Ob.

CONCLUSIONS

These results indicate that exosome-mediated delivery of siRNA targeting Fgfr2^S252W is a potential non-invasive treatment for aberrant FGF/FGFR signaling.

FGF signaling in cranial suture development and related diseases

Suture mesenchymal stem cells (SMSCs) are a heterogeneous stem cell population with the ability to self-renew and differentiate into multiple cell lineages. The cranial suture provides a niche for SMSCs to maintain suture patency, allowing for cranial bone repair and regeneration. In addition, the cranial suture functions as an intramembranous bone growth site during craniofacial bone development. Defects in suture development have been implicated in various congenital diseases, such as sutural agenesis and craniosynostosis. However, it remains largely unknown how intricate signaling pathways orchestrate suture and SMSC function in craniofacial bone development, homeostasis, repair and diseases. Studies in patients with syndromic craniosynostosis identified fibroblast growth factor (FGF) signaling as an important signaling pathway that regulates cranial vault development. A series of in vitro and in vivo studies have since revealed the critical roles of FGF signaling in SMSCs, cranial suture and cranial skeleton development, and the pathogenesis of related diseases. Here, we summarize the characteristics of cranial sutures and SMSCs, and the important functions of the FGF signaling pathway in SMSC and cranial suture development as well as diseases caused by suture dysfunction. We also discuss emerging current and future studies of signaling regulation in SMSCs.

Development of Erf-Mediated Craniosynostosis and Pharmacological Amelioration

ETS2 repressor factor (ERF) insufficiency causes craniosynostosis (CRS4) in humans and mice. ERF is an ETS domain transcriptional repressor regulated by Erk1/2 phosphorylation via nucleo-cytoplasmic shuttling. Here, we analyze the onset and development of the craniosynostosis phenotype in an Erf-insufficient mouse model and evaluate the potential of the residual Erf activity augmented by pharmacological compounds to ameliorate the disease. Erf insufficiency appears to cause an initially compromised frontal bone formation and subsequent multisuture synostosis, reflecting distinct roles of Erf on the cells that give rise to skull and facial bones. We treated animals with Mek1/2 and nuclear export inhibitors, U0126 and KPT-330, respectively, to increase Erf activity by two independent pathways. We implemented both a low dosage locally over the calvaria and a systemic drug administration scheme to evaluate the possible indirect effects from other systems and minimize toxicity. The treatment of mice with either the inhibitors or the administration scheme alleviated the synostosis phenotype with minimal adverse effects. Our data suggest that the ERF level is an important regulator of cranial bone development and that pharmacological modulation of its activity may represent a valid intervention approach both in CRS4 and in other syndromic forms of craniosynostosis mediated by the FGFR-RAS-ERK-ERF pathway.

Inhibition of miR338 rescues cleidocranial dysplasia in Runx2 mutant mice partially via the Hif1a-Vegfa axis

Haploinsufficiency of Runt-related transcription factor-2 (RUNX2) is responsible for cleidocranial dysplasia (CCD), a rare hereditary disease with a range of defects, including delayed closure of the cranial sutures and short stature. Symptom-based treatments, such as a combined surgical-orthodontic approach, are commonly used to treat CCD patients. However, there have been few reports of treatments based on Runx2-specific regulation targeting dwarfism symptoms. Previously, we found that the miR338 cluster, a potential diagnostic and therapeutic target for postmenopausal osteoporosis, could directly target Runx2 during osteoblast differentiation in vitro. Here, we generated miR338^-/-;Runx2^+/- mice to investigate whether inhibition of miR338 could rescue CCD defects caused by Runx2 mutation in vivo. We found that the dwarfism phenotype caused by Runx2 haploinsufficiency was recovered in miR338^-/-;Runx2^+/- mice, with complete bone density restoration and quicker closure of fontanels. Single-cell RNA-seq analysis revealed that knockout of miR338 specifically rescued the osteoblast lineage priming ability of bone marrow stromal cells in Runx2^+/- femurs, which was further confirmed by Osterix-specific conditional knockout of miR338 in Runx2^+/- mice (OsxCre; miR338 ^fl/fl;Runx2^+/-). Mechanistically, ablation of the miR338 cluster in Runx2^+/- femurs directly rescued the Hif1a-Vegfa pathway in Runx2^+/- osteoblasts, as proven by gene expression profiles and ChIP and Re-ChIP assays. Collectively, our data revealed the genetic interaction between Runx2 and the miR338 cluster during osteoblast differentiation and implied that the miR338 cluster could be a potential therapeutic target for CCD.

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.

Cleft Palate in Apert Syndrome

Apert syndrome is a rare genetic disorder characterized by craniosynostosis, midface retrusion, and limb anomalies. Cleft palate occurs in a subset of Apert syndrome patients. Although the genetic causes underlying Apert syndrome have been identified, the downstream signaling pathways and cellular mechanisms responsible for cleft palate are still elusive. To find clues for the pathogenic mechanisms of palatal defects in Apert syndrome, we review the clinical characteristics of the palate in cases of Apert syndrome, the palatal phenotypes in mouse models, and the potential signaling mechanisms involved in palatal defects. In Apert syndrome patients, cleft of the soft palate is more frequent than of the hard palate. The length of the hard palate is decreased. Cleft palate is associated most commonly with the S252W variant of FGFR2. In addition to cleft palate, high-arched palate, lateral palatal swelling, or bifid uvula are common in Apert syndrome patients. Mouse models of Apert syndrome display palatal defects, providing valuable tools to understand the underlying mechanisms. The mutations in FGFR2 causing Apert syndrome may change a signaling network in epithelial–mesenchymal interactions during palatogenesis. Understanding the pathogenic mechanisms of palatal defects in Apert syndrome may shed light on potential novel therapeutic solutions.

The clinical manifestations, molecular mechanisms and treatment of craniosynostosis

Craniosynostosis is a major congenital craniofacial disorder characterized by the premature fusion of cranial suture(s). Patients with severe craniosynostosis often have impairments in hearing, vision, intracranial pressure and/or neurocognitive functions. Craniosynostosis can result from mutations, chromosomal abnormalities or adverse environmental effects, and can occur in isolation or in association with numerous syndromes. To date, surgical correction remains the primary treatment for craniosynostosis, but it is associated with complications and with the potential for re-synostosis. There is, therefore, a strong unmet need for new therapies. Here, we provide a comprehensive review of our current understanding of craniosynostosis, including typical craniosynostosis types, their clinical manifestations, cranial suture development, and genetic and environmental causes. Based on studies from animal models, we present a framework for understanding the pathogenesis of craniosynostosis, with an emphasis on the loss of postnatal suture mesenchymal stem cells as an emerging disease-driving mechanism. We evaluate emerging treatment options and highlight the potential of mesenchymal stem cell-based suture regeneration as a therapeutic approach for craniosynostosis.

Thyroid Cancer-Associated Mitochondrial DNA Mutation G3842A Promotes Tumorigenicity via ROS-Mediated ERK1/2 Activation

Mitochondrial DNA (mtDNA) mutations have been identified in various human cancers, including thyroid cancer. However, the relationship between mtDNA and thyroid cancer remains unclear. Previous studies by others and us strongly suggested that mtDNA mutations in complex I may participate in thyroid cancer processes according to sequencing results of thyroid cancer tissue, although the associated pathogenic processes remain unknown. Here, to investigate whether mtDNA mutations contribute to thyroid cancer, we reanalyzed our sequencing results and characterized thyroid cancer-associated mutations in the mitochondrial complex. The results identified the highest mutation frequencies in nicotinamide adenine dinucleotide hydride (NADH) dehydrogenase subunit 4 gene (ND4) and cytochrome c oxidase subunit 1 gene (COI), which also harbored the highest rates of $\text{G}>\text{A}$ substitutions, with most of the mutations resulting in changes in the polarity of amino acids. We then established cybrids containing the G3842A mutation identified in papillary thyroid carcinoma, which revealed it as a mutation in NADH dehydrogenase subunit 1 gene (ND1) and is previously reported in follicular thyroid carcinoma, thereby suggesting a possibly pathogenic role in thyroid carcinoma. Additionally, we found that the G3842A mutation accelerates tumorigenicity and decreases the abundance and activity of mitochondrial complex I, the oxygen consumption rate, and adenosine triphosphate levels. By contrast, the levels of reactive oxygen species (ROS) were increased to activate extracellular signal-regulated kinase (ERK1/2) signaling, which contributed to tumorigenicity. These findings suggest for the first time that mtDNA mutations help drive tumor development and that G3842A may represent a new risk factor for thyroid cancer. Furthermore, our findings indicate that drugs targeting ROS and ERK1/2 may serve as a viable therapeutic strategy for thyroid cancer.

The Extracellular Signal-Regulated Kinase Mitogen-Activated Protein Kinase Pathway in Osteoblasts

Extracellular signal-regulated kinases (ERKs) are evolutionarily ancient signal transducers of the mitogen-activated protein kinase (MAPK) family that have long been linked to the regulation of osteoblast differentiation and bone formation. Here, we review the physiological functions, biochemistry, upstream activators, and downstream substrates of the ERK pathway. ERK is activated in skeletal progenitors and regulates osteoblast differentiation and skeletal mineralization, with ERK serving as a key regulator of Runt-related transcription factor 2, a critical transcription factor for osteoblast differentiation. However, new evidence highlights context-dependent changes in ERK MAPK pathway wiring and function, indicating a broader set of physiological roles associated with changes in ERK pathway components or substrates. Consistent with this importance, several human skeletal dysplasias are associated with dysregulation of the ERK MAPK pathway, including neurofibromatosis type 1 and Noonan syndrome. The continually broadening array of drugs targeting the ERK pathway for the treatment of cancer and other disorders makes it increasingly important to understand how interference with this pathway impacts bone metabolism, highlighting the importance of mouse studies to model the role of the ERK MAPK pathway in bone formation.

Excessive osteoclast activation by osteoblast paracrine factor RANKL is a major cause of the abnormal long bone phenotype in Apert syndrome model mice

The fibroblast growth factor (FGF)/FGF receptor (FGFR) signaling pathway plays important roles in the development and growth of the skeleton. Apert syndrome caused by gain‐of‐function mutations of FGFR2 results in aberrant phenotypes of the skull, midface, and limbs. Although short limbs are representative features in patients with Apert syndrome, the causative mechanism for this limb defect has not been elucidated. Here we quantitatively confirmed decreases in the bone length, bone mineral density, and bone thickness in the Apert syndrome model of gene knock‐in Fgfr2^S252W/+ (EIIA‐Fgfr2^S252W/+) mice. Interestingly, despite these bone defects, histological analysis showed that the endochondral ossification process in the mutant mice was similar to that in wild‐type mice. Tartrate‐resistant acid phosphatase staining revealed that trabecular bone loss in mutant mice was associated with excessive osteoclast activity despite accelerated osteogenic differentiation. We investigated the osteoblast–osteoclast interaction and found that the increase in osteoclast activity was due to an increase in the Rankl level of osteoblasts in mutant mice and not enhanced osteoclastogenesis driven by the activation of FGFR2 signaling in bone marrow‐derived macrophages. Consistently, Col1a1‐Fgfr2^S252W/+ mice, which had osteoblast‐specific expression of Fgfr2 S252W, showed significant bone loss with a reduction of the bone length and excessive activity of osteoclasts was observed in the mutant mice. Taken together, the present study demonstrates that the imbalance in osteoblast and osteoclast coupling by abnormally increased Rankl expression in Fgfr2^S252W/+ mutant osteoblasts is a major causative mechanism for bone loss and short long bones in Fgfr2^S252W/+ mice.

The genetic overlap between osteoporosis and craniosynostosis

Osteoporosis is the most prevalent bone condition in the ageing population. This systemic disease is characterized by microarchitectural deterioration of bone, leading to increased fracture risk. In the past 15 years, genome-wide association studies (GWAS), have pinpointed hundreds of loci associated with bone mineral density (BMD), helping elucidate the underlying molecular mechanisms and genetic architecture of fracture risk. However, the challenge remains in pinpointing causative genes driving GWAS signals as a pivotal step to drawing the translational therapeutic roadmap. Recently, a skull BMD-GWAS uncovered an intriguing intersection with craniosynostosis, a congenital anomaly due to premature suture fusion in the skull. Here, we recapitulate the genetic contribution to both osteoporosis and craniosynostosis, describing the biological underpinnings of this overlap and using zebrafish models to leverage the functional investigation of genes associated with skull development and systemic skeletal homeostasis.

Craniosynostosis is a feature of Costello syndrome

Costello syndrome (CS) is an autosomal dominant disorder caused by pathogenic variants in HRAS. Craniosynostosis is a known feature of other RASopathies (Noonan and cardiofaciocutaneous syndromes) but not CS. We describe four individuals with CS and craniosynostosis and present a summary of all previously reported individuals with craniosynostosis and RASopathy.

Syndromic Craniosynostosis: Unique Management Considerations

Craniosynostosis involves the premature fusion of 1 or more cranial sutures and commonly presents as an isolated, nonsyndromic diagnosis. A subset of patients have syndromic craniosynostosis. Several unique considerations must be taken into account when managing patients with syndromic craniosynostosis. A multidisciplinary craniofacial team with a central coordinator is particularly useful for coordinating care among various specialists, and close monitoring is mandatory owing to the increased risk of intracranial hypertension. Surgical management varies among centers, but core options include fronto-orbital advancement with cranial vault remodeling, posterior vault expansion, endoscopic-assisted suturectomy with postoperative orthotic therapy, and midface advancement.

Activation of FGFR2 Signaling Suppresses BRCA1 and Drives Triple-Negative Mammary Tumorigenesis That is Sensitive to Immunotherapy

Fibroblast growth factor receptor 2 (FGFR2) is a membrane-spanning tyrosine kinase that mediates FGF signaling. Various FGFR2 alterations are detected in breast cancer, yet it remains unclear if activation of FGFR2 signaling initiates tumor formation. In an attempt to answer this question, a mouse model berrying an activation mutation of FGFR2 (FGFR2-S252W) in the mammary gland is generated. It is found that FGF/FGFR2 signaling drives the development of triple-negative breast cancer accompanied by epithelial-mesenchymal transition that is regulated by FGFR2-STAT3 signaling. It is demonstrated that FGFR2 suppresses BRCA1 via the ERK-YY1 axis and promotes tumor progression. BRCA1 knockout in the mammary gland of the FGFR2-S252W mice significantly accelerated tumorigenesis. It is also shown that FGFR2 positively regulates PD-L1 and that a combination of FGFR2 inhibition and immune checkpoint blockade kills cancer cells. These data suggest that the mouse models mimic human breast cancers and can be used to identify actionable therapeutic targets.

Insights and future directions of potential genetic therapy for Apert syndrome: A systematic review

Apert syndrome is a genetic disorder characterised by craniosynostosis and structural discrepancy of the craniofacial region as well as the hands and feet. This condition is closely linked with fibroblast growth factor receptor-2 (FGFR2) gene mutations. Gene therapies are progressively being tested in advanced clinical trials, leading to a rise of its potential clinical indications. In recent years, research has made great progress in the gene therapy of craniosynostosis syndromes and several studies have investigated its influences in preventing/diminishing the complications of Apert syndrome. This article reviewed and exhibited different techniques of gene therapy and their influences in Apert syndrome progression. A systematic search was executed using electronic bibliographic databases including PubMed, EMBASE, ScienceDirect, SciFinder and Web of Science for all studies of gene therapy for Apert syndrome. The primary outcomes measurements vary from protein to gene expressions. According to the findings of included studies, we conclude that the gene therapy using FGF in Apert syndrome was critical in the regulation of suture fusion and patency, occurred via alterations in cellular proliferation. The superior outcome could be brought by biological therapies targeting the FGF/FGFR signalling. More studies in molecular genetics in Apert syndrome are recommended. This study reviews the current literature and provides insights to future possibilities of genetic therapy as intervention in Apert syndrome.

Erf Affects Commitment and Differentiation of Osteoprogenitor Cells in Cranial Sutures via the Retinoic Acid Pathway

ETS2 repressor factor (ERF) haploinsufficiency causes late-onset craniosynostosis (CRS) (OMIM entry 600775; CRS4) in humans, while in mice Erf insufficiency also leads to a similar multisuture synostosis phenotype preceded by mildly reduced calvarium ossification. However, neither the cell types affected nor the effects per se have been identified so far. Here, we establish an ex vivo system for the expansion of suture-derived mesenchymal stem and progenitor cells (sdMSCs) and analyze the role of Erf levels in their differentiation. Cellular data suggest that Erf insufficiency specifically decreases osteogenic differentiation of sdMSCs, resulting in the initially delayed mineralization of the calvarium. Transcriptome analysis indicates that Erf is required for efficient osteogenic lineage commitment of sdMSCs. Elevated retinoic acid catabolism due to increased levels of the cytochrome P450 superfamily member Cyp26b1 as a result of decreased Erf levels appears to be the underlying mechanism leading to defective differentiation. Exogenous addition of retinoic acid can rescue the osteogenic differentiation defect, suggesting that Erf affects cranial bone mineralization during skull development through retinoic acid gradient regulation.

Septal chondrocyte hypertrophy contributes to midface deformity in a mouse model of Apert syndrome

Midface hypoplasia is a major manifestation of Apert syndrome. However, the tissue component responsible for midface hypoplasia has not been elucidated. We studied mice with a chondrocyte-specific Fgfr2^S252W mutation (Col2a1-cre; Fgfr2^S252W/+) to investigate the effect of cartilaginous components in midface hypoplasia of Apert syndrome. In Col2a1-cre; Fgfr2^S252W/+ mice, skull shape was normal at birth, but hypoplastic phenotypes became evident with age. General dimensional changes of mutant mice were comparable with those of mice with mutations in EIIa-cre; Fgfr2^S252W/+, a classic model of Apert syndrome in mice. Col2a1-cre; Fgfr2^S252W/+ mice showed some unique facial phenotypes, such as elevated nasion, abnormal fusion of the suture between the premaxilla and the vomer, and decreased perpendicular plate of the ethmoid bone volume, which are related to the development of the nasal septal cartilage. Morphological and histological examination revealed that the presence of increased septal chondrocyte hypertrophy and abnormal thickening of nasal septum is causally related to midface deformities in nasal septum-associated structures. Our results suggest that careful examination and surgical correction of the nasal septal cartilage may improve the prognosis in the surgical treatment of midface hypoplasia and respiratory problems in patients with Apert syndrome.

Polycystin-1 modulates RUNX2 activation and osteocalcin gene expression via ERK signalling in a human craniosynostosis cell model

Craniosynostosis refers to the premature fusion of one or more cranial sutures leading to skull shape deformities and brain growth restriction. Among the many factors that contribute to abnormal suture fusion, mechanical forces seem to play a major role. Nevertheless, the underlying mechanobiology-related mechanisms of craniosynostosis still remain unknown. Understanding how aberrant mechanosensation and mechanotransduction drive premature suture fusion will offer important insights into the pathophysiology of craniosynostosis and result in the development of new therapies, which can be used to intervene at an early stage and prevent premature suture fusion. Herein, we provide evidence for the first time on the role of polycystin-1 (PC1), a key protein in cellular mechanosensitivity, in craniosynostosis, using primary cranial suture cells isolated from patients with trigonocephaly and dolichocephaly, two common types of craniosynostosis. Initially, we showed that PC1 is expressed at the mRNA and protein level in both trigonocephaly and dolichocephaly cranial suture cells. Followingly, by utilizing an antibody against the mechanosensing extracellular N-terminal domain of PC1, we demonstrated that PC1 regulates runt-related transcription factor 2 (RUNX2) activation and osteocalcin gene expression via extracellular signal-regulated kinase (ERK) signalling in our human craniosynostosis cell model. Altogether, our study reveals a novel mechanotransduction signalling axis, PC1-ERK-RUNX2, which affects osteoblastic differentiation in cranial suture cells from trigonocephaly and dolichocephaly patients.

Cranial Neural Crest Cells and Their Role in the Pathogenesis of Craniofacial Anomalies and Coronal Craniosynostosis

Craniofacial anomalies are among the most common of birth defects. The pathogenesis of craniofacial anomalies frequently involves defects in the migration, proliferation, and fate of neural crest cells destined for the craniofacial skeleton. Genetic mutations causing deficient cranial neural crest migration and proliferation can result in Treacher Collins syndrome, Pierre Robin sequence, and cleft palate. Defects in post-migratory neural crest cells can result in pre- or post-ossification defects in the developing craniofacial skeleton and craniosynostosis (premature fusion of cranial bones/cranial sutures). The coronal suture is the most frequently fused suture in craniosynostosis syndromes. It exists as a biological boundary between the neural crest-derived frontal bone and paraxial mesoderm-derived parietal bone. The objective of this review is to frame our current understanding of neural crest cells in craniofacial development, craniofacial anomalies, and the pathogenesis of coronal craniosynostosis. We will also discuss novel approaches for advancing our knowledge and developing prevention and/or treatment strategies for craniofacial tissue regeneration and craniosynostosis.

FGF/FGFR signaling in health and disease

Growing evidences suggest that the fibroblast growth factor/FGF receptor (FGF/FGFR) signaling has crucial roles in a multitude of processes during embryonic development and adult homeostasis by regulating cellular lineage commitment, differentiation, proliferation, and apoptosis of various types of cells. In this review, we provide a comprehensive overview of the current understanding of FGF signaling and its roles in organ development, injury repair, and the pathophysiology of spectrum of diseases, which is a consequence of FGF signaling dysregulation, including cancers and chronic kidney disease (CKD). In this context, the agonists and antagonists for FGF-FGFRs might have therapeutic benefits in multiple systems.

RUNX2-modifying enzymes: therapeutic targets for bone diseases

RUNX2 is a master transcription factor of osteoblast differentiation. RUNX2 expression in the bone and osteogenic front of a suture is crucial for cranial suture closure and membranous bone morphogenesis. In this manner, the regulation of RUNX2 is precisely controlled by multiple posttranslational modifications (PTMs) mediated by the stepwise recruitment of multiple enzymes. Genetic defects in RUNX2 itself or in its PTM regulatory pathways result in craniofacial malformations. Haploinsufficiency in RUNX2 causes cleidocranial dysplasia (CCD), which is characterized by open fontanelle and hypoplastic clavicles. In contrast, gain-of-function mutations in FGFRs, which are known upstream stimulating signals of RUNX2 activity, cause craniosynostosis (CS) characterized by premature suture obliteration. The identification of these PTM cascades could suggest suitable drug targets for RUNX2 regulation. In this review, we will focus on the mechanism of RUNX2 regulation mediated by PTMs, such as phosphorylation, prolyl isomerization, acetylation, and ubiquitination, and we will summarize the therapeutics associated with each PTM enzyme for the treatment of congenital cranial suture anomalies.

Iron Oxide Nanoparticles as Autophagy Intervention Agents Suppress Hepatoma Growth by Enhancing Tumoricidal Autophagy

The combined treatment with nanoparticles and autophagy inhibitors, such as chloroquine (CQ) and hydroxychloroquine (HCQ), is extensively explored for cancer therapy. However, the toxicity of autophagy inhibitors and their unselective for tumoricidal autophagy have seriously hindered the application of the combined treatment. In this study, a carboxy-functional iron oxide nanoparticle (Fe2O3@DMSA) is designed and identified to significantly exert an antitumor effect without adding CQ or HCQ. Further investigation indicates that the effective inhibition effect of Fe2O3@DMSA alone on hepatoma growth is triggered by inhibiting the fusion of autophagosomes and lysosomes to enhance tumoricidal autophagy, which is induced by intracellular iron-retention-induced sustained reactive oxygen species (ROS) production. Furthermore, in two hepatoma-bearing mouse models, Fe2O3@DMSA alone effectively suppresses the growth of tumors without obvious toxic side effects. These studies offer a promising strategy for cancer therapy.

ERK signalling: a master regulator of cell behaviour, life and fate

The proteins extracellular signal-regulated kinase 1 (ERK1) and ERK2 are the downstream components of a phosphorelay pathway that conveys growth and mitogenic signals largely channelled by the small RAS GTPases. By phosphorylating widely diverse substrates, ERK proteins govern a variety of evolutionarily conserved cellular processes in metazoans, the dysregulation of which contributes to the cause of distinct human diseases. The mechanisms underlying the regulation of ERK1 and ERK2, their mode of action and their impact on the development and homeostasis of various organisms have been the focus of much attention for nearly three decades. In this Review, we discuss the current understanding of this important class of kinases. We begin with a brief overview of the structure, regulation, substrate recognition and subcellular localization of ERK1 and ERK2. We then systematically discuss how ERK signalling regulates six fundamental cellular processes in response to extracellular cues. These processes are cell proliferation, cell survival, cell growth, cell metabolism, cell migration and cell differentiation.

Fibroblast Growth Factor 10 Attenuates Renal Damage by Regulating Endoplasmic Reticulum Stress After Ischemia-Reperfusion Injury

Renal ischemia–reperfusion (I/R) injury is a predominant cause of acute kidney injury (AKI), the pathologic mechanism of which is highly complex involving reactive oxygen species (ROS) accumulation, inflammatory response, autophagy, apoptosis as well as endoplasmic reticulum (ER) stress. Fibroblast growth factor 10 (FGF10), as a multifunctional growth factor, plays crucial roles in embryonic development, adult homeostasis, and regenerative medicine. Herein, we investigated the molecular pathways underlying the protective effect of FGF10 on renal I/R injury using Sprague–Dawley rats. Results showed that administration of FGF10 not only effectively inhibited I/R-induced activation of Caspase-3 and expression of Bax, but also alleviated I/R evoked expression of ER stress-related proteins in the kidney including CHOP, GRP78, XBP-1, and ATF-4 and ATF-6. The protective effect of FGF10 against apoptosis and ER stress was recapitulated by in vitro experiments using oxidative damaged NRK-52E cells induced by tert-Butyl hydroperoxide (TBHP). Significantly, U0126, a selective noncompetitive inhibitor of MAP kinase kinases (MKK), largely abolished the protective role of FGF10. Taken together, both in vivo and in vitro experiments indicated that FGF10 attenuates I/R-induced renal epithelial apoptosis by suppressing excessive ER stress, which is, at least partially, mediated by the activation of the MEK–ERK1/2 signaling pathway. Therefore, our present study revealed the therapeutic potential of FGF10 on renal I/R injury.

PIN1 Attenuation Improves Midface Hypoplasia in a Mouse Model of Apert Syndrome

Premature fusion of the cranial suture and midface hypoplasia are common features of syndromic craniosynostosis caused by mutations in the FGFR2 gene. The only treatment for this condition involves a series of risky surgical procedures designed to correct defects in the craniofacial bones, which must be performed until brain growth has been completed. Several pharmacologic interventions directed at FGFR2 downstream signaling have been tested as potential treatments for premature coronal suture fusion in a mouse model of Apert syndrome. However, there are no published studies that have targeted for the pharmacologic treatment of midface hypoplasia. We used Fgfr2^S252W/+ knock-in mice as a model of Apert syndrome and morphometric analyses to identify causal hypoplastic sites in the midface region. Three-dimensional geometric and linear analyses of Fgfr2^S252W/+ mice at postnatal day 0 demonstrated distinct morphologic variance. The premature fusion of anterior facial bones, such as the maxilla, nasal, and frontal bones, rather than the cranium or cranial base, is the main contributing factor toward the anterior-posterior skull length shortening. The cranial base of the mouse model had a noticeable downward slant around the intersphenoid synchondrosis, which is related to distortion of the airway. Within a skull, the facial shape variance was highly correlated with the cranial base angle change along Fgfr2 S252W mutation-induced craniofacial anomalies. The inhibition of an FGFR2 downstream signaling enzyme, PIN1, via genetic knockdown or use of a PIN1 inhibitor, juglone, attenuated the aforementioned deformities in a mouse model of Apert syndrome. Overall, these results indicate that FGFR2 signaling is a key contributor toward abnormal anterior-posterior dimensional growth in the midface region. Our study suggests a novel therapeutic option for the prevention of craniofacial malformations induced by mutations in the FGFR2 gene.

RAF1 variant in a patient with Noonan syndrome with multiple lentigines and craniosynostosis

We report the case of a 14 years and 8 months girl, who is the first child of nonconsanguineous parents, with short stature, obstructive hypertrophic cardiomyopathy, multiple facial lentigines, high and wide forehead, downslanting palpebral fissures, low-set ears, short neck, and pectus excavatum; all features suggestive of Noonan syndrome with multiple lentigines (NSML). In addition, the patient exhibited craniosynostosis. Molecular analysis of rats sarcoma (RAS)/mitogen-activated protein kinase (MAPK) pathway genes with high-resolution melting curve analysis followed by sequencing showed a RAF1 amino acid substitution of valine to glycine at position 263 (p.V263G). The present report provides clinical data regarding the first association of a RAF1 variant and craniosynostosis in a patient with clinical diagnosis of NSML.

PIN1 is a new therapeutic target of craniosynostosis

Gain-of-function mutations in fibroblast growth factor receptors (FGFRs) cause congenital skeletal anomalies, including craniosynostosis (CS), which is characterized by the premature closure of craniofacial sutures. Apert syndrome (AS) is one of the severest forms of CS, and the only treatment is surgical expansion of prematurely fused sutures in infants. Previously, we demonstrated that the prolyl isomerase peptidyl-prolyl cis-trans isomerase interacting 1 (PIN1) plays a critical role in mediating FGFR signaling and that Pin1+/- mice exhibit delayed closure of cranial sutures. In this study, using both genetic and pharmacological approaches, we tested whether PIN1 modulation could be used as a therapeutic regimen against AS. In the genetic approach, we crossbred Fgfr2S252W/+, a mouse model of AS, and Pin1+/- mice. Downregulation of Pin1 gene dosage attenuated premature cranial suture closure and other phenotypes of AS in Fgfr2S252W/+ mutant mice. In the pharmacological approach, we intraperitoneally administered juglone, a PIN1 enzyme inhibitor, to pregnant Fgfr2S252W/+ mutant mice and found that this treatment successfully interrupted fetal development of AS phenotypes. Primary cultured osteoblasts from Fgfr2S252W/+ mutant mice expressed high levels of FGFR2 downstream target genes, but this phenotype was attenuated by PIN1 inhibition. Post-translational stabilization and activation of Runt-related transcription factor 2 (RUNX2) in Fgfr2S252W/+ osteoblasts were also attenuated by PIN1 inhibition. Based on these observations, we conclude that PIN1 enzyme activity is important for FGFR2-induced RUNX2 activation and craniofacial suture morphogenesis. Moreover, these findings highlight that juglone or other PIN1 inhibitors represent viable alternatives to surgical intervention for treatment of CS and other hyperostotic diseases.

Current Approaches in the Development of Molecular and Pharmacological Therapies in Craniosynostosis Utilizing Animal Models

The development of the craniofacial skeleton is a spatial and temporal process where cranial sutures play a role in the regulation of morphogenesis and growth. Disruption of these cellular and molecular interactions may lead to craniosynostosis, the premature obliteration of one or more cranial sutures, yielding skull growth restriction and malformation perpendicular to the affected suture. Facial deformity and various functional CNS anomalies are other frequent complications. Cranial vault expansion and reconstructive surgery remain the mainstay of treatment but pose an elevated risk of morbidity for the infant. While the etiology of nonsyndromic craniosynostosis remains to be deciphered, gain-of-function mutations in FGFR1-3 and TWIST1 were found to be responsible for more than 3/4 of the most commonly encountered craniofacial syndromes. Animal models have been invaluable to further dissect the role of genes within the cranial sutures and for the development of alternative nonsurgical treatment strategies. In this review, we will present various molecular and pharmacological approaches for the treatment of craniosynostosis that have been tested using in vitro and in vivo assays as well as discuss their potential application in humans focusing on the case of tyrosine kinase inhibitors.

Craniofacial, orofacial and dental disorders: the role of the RAS/ERK pathway

Deviations from the precisely coordinated programme of human head development can lead to craniofacial and orofacial malformations often including a variety of dental abnormalities too. Although the aetiology is still unknown in many cases, during the last decades different intracellular signalling pathways have been genetically linked to specific disorders. Among these pathways, the RAS/extracellular signal-regulated kinase (ERK) signalling cascade is the focus of this review since it encompasses a large group of genes that when mutated cause some of the most common and severe developmental anomalies in humans. We present the components of the RAS/ERK pathway implicated in craniofacial and orodental disorders through a series of human and animal studies. We attempt to unravel the specific molecular targets downstream of ERK that act on particular cell types and regulate key steps in the associated developmental processes. Finally we point to ambiguities in our current knowledge that need to be clarified before RAS/ERK-targeting therapeutic approaches can be implemented.

Solamargine inhibits gastric cancer progression by regulating the expression of lncNEAT1_2 via the MAPK signaling pathway

Solamargine, a derivative from the steroidal solasodine in Solanum species, has exhibited anticancer activities in numerous types of cancer; however, its role in gastric cancer (GC) remains unknown. In the present study, it was demonstrated that Solamargine suppressed the viability of five gastric cancer cell lines in a dose‑dependent manner and induced notable alterations in morphology. Treatment with Solamargine promoted cell apoptosis (P<0.01). Solamargine increased the expression of long noncoding RNA (lnc) p53 induced transcript and lnc nuclear paraspeckle assembly transcript 1 (NEAT1)_2 (P<0.01) in GC by reducing the phosphorylation of extracellular signal‑regulated kinase (Erk)1/2 mitogen‑activated protein kinase (MAPK). To gain insight into the potential mechanism, an Erk1/2 inhibitor (U0126) was applied. The results revealed that lncNEAT1_2 expression levels increased, which was consistent with the effects of Solamargine. Downregulation of lncNEAT1_2 in GC cells revealed no effect on the expression levels of total Erk1/2 and, and counteracted the effect of Solamargine. Solamargine was observed to increase the expression of lncNEAT1_2 via the Erk1/2 MAPK signaling pathway. Of note, the knockdown of lncNEAT1_2 reduced the inhibitory effect of Solamargine (P<0.05). Additionally, experiments in vivo and in primary GC cells from patients demonstrated that Solamargine significantly suppressed tumor growth (P<0.05). In vivo analysis of a xenograft mouse model further supported that Solamargine could induce the apoptosis of cancer cells in tumor tissue as observed by a terminal deoxynucleotidyl transferase‑mediated dUTP‑biotin nick end labeling and H&E staining (P<0.05). Experiments in primary GC cells from patients verified the anti‑tumor effect of Solamargine. In summary, the findings of the present study indicated that Solamargine inhibited the progression of GC by regulating lncNeat1_2 via the MAPK pathway.

Nonsyndromic craniosynostosis: novel coding variants

BACKGROUND

Craniosynostosis (CS), the premature fusion of one or more neurocranial sutures, is associated with approximately 200 syndromes; however, about 65-85% of patients present with no additional major birth defects.

METHODS

We conducted targeted next-generation sequencing of 60 known syndromic and other candidate genes in patients with sagittal nonsyndromic CS (sNCS, n = 40) and coronal nonsyndromic CS (cNCS, n = 19).

RESULTS

We identified 18 previously published and 5 novel pathogenic variants, including three de novo variants. Novel variants included a paternally inherited c.2209C>G:p.(Leu737Val) variant in BBS9 of a patient with cNCS. Common variants in BBS9, a gene required for ciliogenesis during cranial suture development, have been associated with sNCS risk in a previous genome-wide association study. We also identified c.313G>T:p.(Glu105*) variant in EFNB1 and c.435G>C:p.(Lys145Asn) variant in TWIST1, both in patients with cNCS. Mutations in EFNB1 and TWIST1 have been linked to craniofrontonasal and Saethre-Chotzen syndrome, respectively; both present with coronal CS.

CONCLUSIONS

We provide additional evidence that variants in genes implicated in syndromic CS play a role in isolated CS, supporting their inclusion in genetic panels for screening patients with NCS. We also identified a novel BBS9 variant that further shows the potential involvement of BBS9 in the pathogenesis of CS.

Fibroblast growth factors in skeletal development

Fibroblast growth factors (FGFs) and their receptors (FGFRs) are expressed throughout all stages of skeletal development. In the limb bud and in cranial mesenchyme, FGF signaling is important for formation of mesenchymal condensations that give rise to bone. Once skeletal elements are initiated and patterned, FGFs regulate both endochondral and intramembranous ossification programs. In this chapter, we review functions of the FGF signaling pathway during these critical stages of skeletogenesis, and explore skeletal malformations in humans that are caused by mutations in FGF signaling molecules.

Signaling Mechanisms Underlying Genetic Pathophysiology of Craniosynostosis

Craniosynostosis, is the premature fusion of one or more cranial sutures which is the second most common cranial facial anomalies. The premature cranial sutures leads to deformity of skull shape and restricts the growth of brain, which might elicit severe neurologic damage. Craniosynostosis exhibit close correlations with a varieties of syndromes. During the past two decades, as the appliance of high throughput DNA sequencing techniques, steady progresses has been made in identifying gene mutations in both syndromic and nonsyndromic cases, which allow researchers to better understanding the genetic roles in the development of cranial vault. As the enrichment of known mutations involved in the pathogenic of premature sutures fusion, multiple signaling pathways have been investigated to dissect the underlying mechanisms beneath the disease. In addition to genetic etiology, environment factors, especially mechanics, have also been proposed to have vital roles during the pathophysiological of craniosynostosis. However, the influence of mechanics factors in the cranial development remains largely unknown. In this review, we present a brief overview of the updated genetic mutations and environmental factors identified in both syndromic and nonsyndromic craniosynostosis. Furthermore, potential molecular signaling pathways and its relations have been described.

Overexpression of Fgfr2c causes craniofacial bone hypoplasia and ameliorates craniosynostosis in the Crouzon mouse

FGFR2c regulates many aspects of craniofacial and skeletal development. Mutations in the FGFR2 gene are causative of multiple forms of syndromic craniosynostosis, including Crouzon syndrome. Paradoxically, mouse studies have shown that the activation (Fgfr2cC342Y; a mouse model for human Crouzon syndrome), as well as the removal (Fgfr2cnull), of the FGFR2c isoform can drive suture abolishment. This study aims to address the downstream effects of pathogenic FGFR2c signalling by studying the effects of Fgfr2c overexpression. Conditional overexpression of Fgfr2c (R26RFgfr2c;βact) results in craniofacial hypoplasia as well as microtia and cleft palate. Contrary to Fgfr2cnull and Fgfr2cC342Y, Fgfr2c overexpression is insufficient to drive onset of craniosynostosis. Examination of the MAPK/ERK pathway in the embryonic sutures of Fgfr2cC342Y and R26RFgfr2c;βact mice reveals that both mutants have increased pERK expression. The contrasting phenotypes between Fgfr2cC342Y and R26RFgfr2c;βact mice prompted us to assess the impact of the Fgfr2c overexpression allele on the Crouzon mouse (Fgfr2cC342Y), in particular its effects on the coronal suture. Our results demonstrate that Fgfr2c overexpression is sufficient to partially rescue craniosynostosis through increased proliferation and reduced osteogenic activity in E18.5 Fgfr2cC342Y embryos. This study demonstrates the intricate balance of FGF signalling required for correct calvarial bone and suture morphogenesis, and that increasing the expression of the wild-type FGFR2c isoform could be a way to prevent or delay craniosynostosis progression.

Adeno-Associated Virus-Mediated RNAi against Mutant Alleles Attenuates Abnormal Calvarial Phenotypes in an Apert Syndrome Mouse Model

Apert syndrome (AS), the most severe form of craniosynostosis, is caused by missense mutations including Pro253Arg(P253R) of fibroblast growth factor receptor 2 (FGFR2), which leads to enhanced FGF/FGFR2-signaling activity. Surgical correction of the deformed skull is the typical treatment for AS. Because of constant maldevelopment of sutures, the corrective surgery is often executed several times, resulting in increased patient challenge and complications. Biological therapies targeting the signaling of mutant FGFR2 allele, in combination with surgery, may bring better outcome. Here we screened and found a small interfering RNA (siRNA) specifically targeting the Fgfr2-P253R allele, and we revealed that it inhibited osteoblastic differentiation and matrix mineralization by reducing the signaling of ERK1/2 and P38 in cultured primary calvarial cells and calvarial explants from Apert mice (Fgfr2^+/P253R). Furthermore, AAV9 carrying short hairpin RNA (shRNA) (AAV9-Fgfr2-shRNA) against mutant Fgfr2 was delivered to the skulls of AS mice. Results demonstrate that AAV9-Fgfr2-shRNA attenuated the premature closure of coronal suture and the decreased calvarial bone volume of AS mice. Our study provides a novel practical biological approach, which will, in combination with other therapies, including surgeries, help treat patients with AS while providing experimental clues for the biological therapies of other genetic skeletal diseases.

Mouse Models of Syndromic Craniosynostosis

Craniosynostosis is a common craniofacial birth defect. This review focusses on the advances that have been achieved through studying the pathogenesis of craniosynostosis using mouse models. Classic methods of gene targeting which generate individual gene knockout models have successfully identified numerous genes required for normal development of the skull bones and sutures. However, the study of syndromic craniosynostosis has largely benefited from the production of knockin models that precisely mimic human mutations. These have allowed the detailed investigation of downstream events at the cellular and molecular level following otherwise unpredictable gain-of-function effects. This has greatly enhanced our understanding of the pathogenesis of this disease and has the potential to translate into improvement of the clinical management of this condition in the future.

AKT signaling displays multifaceted functions in neural crest development

AKT signaling is an essential intracellular pathway controlling cell homeostasis, cell proliferation and survival, as well as cell migration and differentiation in adults. Alterations impacting the AKT pathway are involved in many pathological conditions in human disease. Similarly, during development, multiple transmembrane molecules, such as FGF receptors, PDGF receptors or integrins, activate AKT to control embryonic cell proliferation, migration, differentiation, and also cell fate decisions. While many studies in mouse embryos have clearly implicated AKT signaling in the differentiation of several neural crest derivatives, information on AKT functions during the earliest steps of neural crest development had remained relatively scarce until recently. However, recent studies on known and novel regulators of AKT signaling demonstrate that this pathway plays critical roles throughout the development of neural crest progenitors. Non-mammalian models such as fish and frog embryos have been instrumental to our understanding of AKT functions in neural crest development, both in neural crest progenitors and in the neighboring tissues. This review combines current knowledge acquired from all these different vertebrate animal models to describe the various roles of AKT signaling related to neural crest development in vivo. We first describe the importance of AKT signaling in patterning the tissues involved in neural crest induction, namely the dorsal mesoderm and the ectoderm. We then focus on AKT signaling functions in neural crest migration and differentiation.

RAS signalling in energy metabolism and rare human diseases

The RAS pathway is a highly conserved cascade of protein-protein interactions and phosphorylation that is at the heart of signalling networks that govern proliferation, differentiation and cell survival. Recent findings indicate that the RAS pathway plays a role in the regulation of energy metabolism via the control of mitochondrial form and function but little is known on the participation of this effect in RAS-related rare human genetic diseases. Germline mutations that hyperactivate the RAS pathway have been discovered and linked to human developmental disorders that are known as RASopathies. Individuals with RASopathies, which are estimated to affect approximately 1/1000 human birth, share many overlapping characteristics, including cardiac malformations, short stature, neurocognitive impairment, craniofacial dysmorphy, cutaneous, musculoskeletal, and ocular abnormalities, hypotonia and a predisposition to developing cancer. Since the identification of the first RASopathy, type 1 neurofibromatosis (NF1), which is caused by the inactivation of neurofibromin 1, several other syndromes have been associated with mutations in the core components of the RAS-MAPK pathway. These syndromes include Noonan syndrome (NS), Noonan syndrome with multiple lentigines (NSML), which was formerly called LEOPARD syndrome, Costello syndrome (CS), cardio-facio-cutaneous syndrome (CFC), Legius syndrome (LS) and capillary malformation-arteriovenous malformation syndrome (CM-AVM). Here, we review current knowledge about the bioenergetics of the RASopathies and discuss the molecular control of energy homeostasis and mitochondrial physiology by the RAS pathway.

Allele-specific silencing therapy for Dynamin 2-related dominant centronuclear myopathy

Rapid advances in allele-specific silencing by RNA interference established a strategy of choice to cure dominant inherited diseases by targeting mutant alleles. We used this strategy for autosomal-dominant centronuclear myopathy (CNM), a rare neuromuscular disorder without available treatment due to heterozygous mutations in the DNM2 gene encoding Dynamin 2. Allele-specific siRNA sequences were developed in order to specifically knock down the human and murine DNM2-mRNA harbouring the p.R465W mutation without affecting the wild-type allele. Functional restoration was achieved in muscle from a knock-in mouse model and in patient-derived fibroblasts, both expressing the most frequently encountered mutation in patients. Restoring either muscle force in a CNM mouse model or DNM2 function in patient-derived cells is an essential breakthrough towards future gene-based therapy for dominant centronuclear myopathy.

Fibroblast Growth Factor Receptor 2 (FGFR2) Mutation Related Syndromic Craniosynostosis

Craniosynostosis results from the premature fusion of cranial sutures, with an incidence of 1 in 2,100-2,500 live births. The majority of cases are non-syndromic and involve single suture fusion, whereas syndromic cases often involve complex multiple suture fusion. The fibroblast growth factor receptor 2 (FGFR2) gene is perhaps the most extensively studied gene that is mutated in various craniosynostotic syndromes including Crouzon, Apert, Pfeiffer, Antley-Bixler, Beare-Stevenson cutis gyrata, Jackson-Weiss, Bent Bone Dysplasia, and Seathre-Chotzen-like syndromes. The majority of these mutations are missense mutations that result in constitutive activation of the receptor and downstream molecular pathways. Treatment involves a multidisciplinary approach with ultimate surgical fixation of the cranial deformity to prevent further sequelae. Understanding the molecular mechanisms has allowed for the investigation of different therapeutic agents that can potentially be used to prevent the disorders. Further research efforts are need to better understand screening and effective methods of early intervention and prevention. Herein, the authors provide a comprehensive update on FGFR2-related syndromic craniosynostosis.