Spina bifida-predisposing heterozygous mutations in Planar Cell Polarity genes and Zic2 reduce bone mass in young mice

Isabel R Orriss,Stuart Lanham,Philip Stanier,Gabriel L Galea,Nicholas D E Greene,Dawn Savery,Andrew J Copp,Richard Oreffo

doi:10.1038/s41598-018-21718-x

Isabel R Orriss, Stuart Lanham + Show 6 more

Open Access

https://doi.org/10.1038/s41598-018-21718-x

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Abstract

Fractures are a common comorbidity in children with the neural tube defect (NTD) spina bifida. Mutations in the Wnt/planar cell polarity (PCP) pathway contribute to NTDs in humans and mice, but whether this pathway independently determines bone mass is poorly understood. Here, we first confirmed that core Wnt/PCP components are expressed in osteoblasts and osteoclasts in vitro. In vivo, we performed detailed µCT comparisons of bone structure in tibiae from young male mice heterozygous for NTD-associated mutations versus WT littermates. PCP signalling disruption caused by Vangl2 (Vangl2Lp/+) or Celsr1 (Celsr1Crsh/+) mutations significantly reduced trabecular bone mass and distal tibial cortical thickness. NTD-associated mutations in non-PCP transcription factors were also investigated. Pax3 mutation (Pax3Sp2H/+) had minimal effects on bone mass. Zic2 mutation (Zic2Ku/+) significantly altered the position of the tibia/fibula junction and diminished cortical bone in the proximal tibia. Beyond these genes, we bioinformatically documented the known extent of shared genetic networks between NTDs and bone properties. 46 genes involved in neural tube closure are annotated with bone-related ontologies. These findings document shared genetic networks between spina bifida risk and bone structure, including PCP components and Zic2. Genetic variants which predispose to spina bifida may therefore independently diminish bone mass.

Highlights

Genetic analyses of rare human diseases associated with altered fracture risk have identified critical determinants of bone mass and architecture, some of which are established clinical targets[1]
Vangl[2] and Celsr[1] mRNA expression was unaffected by osteoclast activation. This data demonstrates that core planar cell polarity (PCP) components are expressed in osteoblasts and osteoclasts
We tested the hypothesis that mouse genotypes predisposed to spina bifida independently have diminished bone mass

Summary

Introduction

Genetic analyses of rare human diseases associated with altered fracture risk have identified critical determinants of bone mass and architecture, some of which are established clinical targets[1]. Over two hundred genes have been identified which, when mutated, result in NTDs including spina bifida[17,18] Some of these, such as components of the bone morphogenetic protein pathway[19], are very well established to have critical skeletal roles independently of their role in neural tube closure. This raises the hypothesis that genetic variants which predispose to spina bifida may independently diminish bone mass. The outcomes of PCP signalling include regulation of gene expression through the JNK/c-Jun pathway as well as cytoskeletal reorganisation through Rho/ROCK signalling

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