Primary cilia respond to fluid shear stress and mediate flow‐induced calcium deposition in osteoblasts

Abstract

Bone turnover in vivo is regulated by mechanical forces such as shear stress originating from interstitial oscillatory fluid flow (OFF), and bone cells in vitro respond to mechanical loading. However, the mechanisms by which bone cells sense mechanical forces, resulting in increased mineral deposition, are not well understood. The aim of this study was to investigate the role of the primary cilium in mechanosensing by osteoblasts. MLO-A5 murine osteoblasts were cultured in monolayer and subjected to two different OFF regimens: 5 short (2 h daily) bouts of OFF followed by morphological analysis of primary cilia; or exposure to chloral hydrate to damage or remove primary cilia and 2 short bouts (2 h on consecutive days) of OFF. Primary cilia were shorter and there were fewer cilia per cell after exposure to periods of OFF compared with static controls. Damage or removal of primary cilia inhibited OFF-induced PGE2 release into the medium and mineral deposition, assayed by Alizarin red staining. We conclude that primary cilia are important mediators of OFF-induced mineral deposition, which has relevance for the design of bone tissue engineering strategies and may inform clinical treatments of bone disorders causes by load-deficiency.—Delaine-Smith, R. M., Sittichokechaiwut, A., Reilly, G. C. Primary cilia respond to fluid shear stress and mediate flow-induced calcium deposition in osteoblasts.

A simple rocker‐induced mechanical stimulus upregulates mineralization by human osteoprogenitor cells in fibrous scaffolds

“…Fluid flow has been shown to enhance osteogenic differentiation of osteoprogenitor cells and calcium deposition by several pathways such as the stretch‐activated ion channels, gap junctions, focal adhesion complexes, paracrine signalling such as prostaglandin E2 (PGE 2 ) and the primary cilia (Delaine‐Smith, Sittichokechaiwut, et al, 2014; Janmey & McCulloch, 2007). Lastly, OFF can stimulate the mineralization of cells by enhanced nutrient distribution and oxygen transportation to cells in scaffolds compared to static culture (McCoy & O'Brien, 2010).…”

“…Several studies have shown that fluid flow‐induced mechanical stress can enhance the osteogenic differentiation of MSCs, as previously reviewed (Delaine‐Smith, MacNeil, & Reilly, 2012; Delaine‐Smith, Sittichokechaiwut, & Reilly, 2014). Oscillatory fluid flow (OFF) is similar to the flow found in the canalicular system in mature bone and in the bone marrow (Gurkan & Akkus, 2008).…”

Pulsed electromagnetic fields promote osteoblast mineralization and maturation needing the existence of primary cilia

“…Primary cilia are solitary rigid structures that extend from the cell body into the extracellular space and are more likely to be the "antennae" to receive or sense the signals from extracellular environment. It has been shown that, during extracellular fluid flow, primary cilia deflect on osteocytes (the major type of bone cells that regulate bone remodeling), and that these primary cilia are required for the osteocytes to trigger an osteogenic or bone resorptive signal to their surroundings in response to dynamic fluid flow (Delaine-Smith et al, 2004;Malone et al, 2007;Nauli et al, 2013). Furthermore, it has been proposed that NO/ cGMP signaling has a strong ciliary basis (Johnson and Leroux, 2010), which may explain the involvement of Ca 2+ /NO/cGMP/PKG pathway in EMF action.…”

In Vitro Bone Cell Models: Impact of Fluid Shear Stress on Bone Formation

“…The cytoskeleton itself, which is composed of actin, microtubules, and intermediate filaments, not only connects all components of the mechanosensing system but actin fibers in cell processes have also been shown to be crucial for osteocyte mechanosensing (Klein-Nulend et al, 2012). The primary cilium, which is a microtubule-based antenna-like extension, has been identified as another mechanosensor in bone cells (Malone et al, 2007; Delaine-Smith et al, 2014). The glycocalyx, which is a cellular coating rich in hyaluronic acid, might also contribute to bone cell mechanotransduction via force transmission to the cytoskeleton and integrins (Reilly et al, 2003; Burra et al, 2011).…”