FGFR2c-mediated ERK–MAPK activity regulates coronal suture development

Abstract

Fibroblast growth factor receptor 2 (FGFR2) signaling is critical for proper craniofacial development. A gain-of-function mutation in the 2c splice variant of the receptor’s gene is associated with Crouzon syndrome, which is characterized by craniosynostosis, the premature fusion of one or more of the cranial vault sutures, leading to craniofacial maldevelopment. Insight into the molecular mechanism of craniosynostosis has identified the ERK-MAPK signaling cascade as a critical regulator of suture patency. The aim of this study is to investigate the role of FGFR2c-induced ERK-MAPK activation in the regulation of coronal suture development. Loss-of-function and gain-of-function Fgfr2c mutant mice have overlapping phenotypes, including coronal synostosis and craniofacial dysmorphia. In vivo analysis of coronal sutures in loss-of-function and gain-of-function models demonstrated fundamentally different pathogenesis underlying coronal suture synostosis. Calvarial osteoblasts from gain-of-function mice demonstrated enhanced osteoblastic function and maturation with concomitant increase in ERK-MAPK activation. In vitro inhibition with the ERK protein inhibitor U0126 mitigated ERK protein activation levels with a concomitant reduction in alkaline phosphatase activity. This study identifies FGFR2c-mediated ERK-MAPK signaling as a key mediator of craniofacial growth and coronal suture development. Furthermore, our results solve the apparent paradox between loss-of-function and gain-of-function FGFR2c mutants with respect to coronal suture synostosis.

A Higher Proportion of Craniosynostosis Genes Are Cancer Driver Genes

“…The involvement of FGF (fibroblast growth factor), FGFR (fibroblast growth factor receptor), and MAPK/ERK signaling pathways in CRS has long been discussed in the literature (Marie et al, 2005; Shukla et al, 2007; Kim et al, 2015; Kosty and Vogel, 2015; Pfaff et al, 2016; Timberlake et al, 2017). However, our top hit gene-set is KEGG’s cancer pathway, and this link between CRS and cancer is to our knowledge rarely discussed in the literature.…”

Mouse Models of Syndromic Craniosynostosis

“…Despite some rescue of the suture, longitudinal evaluation of these mice revealed growth restriction in a proportion of treated animals along with spontaneous unexplained death in others [Shukla et al, 2007]. Indeed, the activating nature of FGFR2 has led to the assumption that attenuation of downstream signalling is sufficient to rescue craniofacial malformations [Shukla et al, 2007;Pfaff et al, 2016]. Several studies were able to demonstrate this in vivo: Firstly, craniofacial morphology was rescued when a mutant Frs2α allele was introduced onto the Fgfr2c C342Y/+ mouse, which prevented activation of the downstream RAS-MAPK pathway [Eswarakumar et al, 2006].…”

Signaling networks in joint development

“…Human mutations that increase the activity of FGFR1 or FGFR2 are a major cause of premature suture fusion, known as craniosynostosis (Twigg and Wilkie, ). Similarly, mice carrying orthologous mutations in Fgfr1 and Fgfr2 develop craniosynostosis before birth due to enhanced osteoprogenitor cell proliferation and differentiation (Zhou et al, ; Eswarakumar et al, ; Wang et al, ; Yin et al, ; Wang et al, ; Pfaff et al, ).…”

“…This apparent paradox is later reconciled through growth. The osteogenic fronts of paired frontal and paired parietal bones are slow to approximate, due to decreased osteoprogenitor cell proliferation and differentiation, and eventually fuse during postnatal development (Eswarakumar et al, ; Pfaff et al, ).…”