Primary cilium-mediated MSC mechanotransduction is dependent on Gpr161 regulation of hedgehog signalling.

Gillian P Johnson,David A Hoey,Sean Fair

doi:10.1016/j.bone.2021.115846

Gillian P Johnson, David A Hoey + Show 1 more

Open Access

https://doi.org/10.1016/j.bone.2021.115846

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Journal: Bone	Publication Date: Jan 13, 2021
Citations: 17	License type: cc-by

Affiliation: Trinity College Dublin, University of Limerick

Abstract

The benefits of physical loading to skeletal mass are well known. The primary cilium has emerged as an important organelle in bone mechanobiology/mechanotransduction, particularly in mesenchymal stem/stromal cells, yet the molecular mechanisms of cilium mechanotransduction are poorly understood. In this study, we demonstrate that Gpr161 is a mechanoresponsive GPCR, that localises to the cilium, and is involved in fluid shear-induced cAMP signalling and downstream osteogenesis. This Gpr161-mediated mechanotransduction is dependent on IFT88/cilium and may act through adenylyl cyclase 6 (AC6) to regulate cAMP and MSC osteogenesis. Moreover, we demonstrate that Hh signalling is positively associated with osteogenesis and that Hh gene expression is mechanically regulated and required for loading-induced osteogenic differentiation through a mechanism that involves IFT88, Gpr161, AC6, and cAMP. Therefore, we have delineated a molecular mechanism of MSC mechanotransduction which likely occurs at the cilium, leading to MSC osteogenesis, highlighting novel mechanotherapeutic targets to enhance osteogenesis.

Highlights

The importance of physical loading in regulating skeletal adaptation has long been established (Frost, 1963)
The aim of this study was to delineate the molecular components of Intraflagellar transport protein 88 (Ift88)/ciliamediated-mesenchymal stem/stromal cells (MSC) mechanotransduction leading to osteogenesis; the identification of which could lead to new mechanotherapeutics to enhance bone regeneration
We have previously demonstrated that this cAMP dependent mechanotransduction mechanism, was mediated by the specific adenylyl cyclase, AC, which c -localises to the primary cilium (Johnson et al, in loading-induced Hh signalling, we depleted Ac in MSCs using siRNA, as verified by immunocytochemistry (Fig. C-D) and qPCR (Fig. E)

Summary

Introduction

The importance of physical loading in regulating skeletal adaptation has long been established (Frost, 1963). Due to the finite lifespan and non-proliferative nature of the bone forming osteoblast (Park et al, 2012), this cell type must be replenished from a progenitor stem/stromal cell population (Chen et al, 2016; Chan et al, 2018). It is hypothesised that skeletal mechanoadaptation must require the osteogenic differentiation of lining cells, osteoprogenitors or mesenchymal stem/stromal cells (MSC) Deciphering the mechanisms of bone cell mechanotransduction may provide novel insight into disease aetiology, in addition to new targets for mechanotherapeutic development to promote bone formation, by mimicking the beneficial effects of loading at a molecular level (Rando & Ambrosio, 2018). The primary cilium is a solitary cellular appendage that has recently emerged as a critical mediator of bone cell mechanotransduction and bone mechanoadaptation (Hoey et al, 2012; Chen et al, 2016; Johnson et al, 2018). Extending from the surface of the cell into the extracellular space, the cilium is ideally positioned to sense environmental biophysical cues such as oscillatory fluid shear, which can drive osteogenesis (Stavenschi et al, 2017)

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