Primary Cilia‐Mediated Mechanotransduction in Human Mesenchymal Stem Cells

Abstract

Physical loading is a potent stimulus required to maintain bone homeostasis, partly through the renewal and osteogenic differentiation of mesenchymal stem cells (MSCs). However, the mechanism by which MSCs sense a biophysical force and translate that into a biochemical bone forming response (mechanotransduction) remains poorly understood. The primary cilium is a single sensory cellular extension, which has recently been shown to demonstrate a role in cellular mechanotransduction and MSC lineage commitment. In this study, we present evidence that short periods of mechanical stimulation in the form of oscillatory fluid flow (OFF) is sufficient to enhance osteogenic gene expression and proliferation of human MSCs (hMSCs). Furthermore, we demonstrate that the cilium mediates fluid flow mechanotransduction in hMSCs by maintaining OFF-induced increases in osteogenic gene expression and, surprisingly, to limit OFF-induced increases in proliferation. These data therefore demonstrate a pro-osteogenic mechanosensory role for the primary cilium, establishing a novel mechanotransduction mechanism in hMSCs. Based on these findings, the application of OFF may be a beneficial component of bioreactor-based strategies to form bone-like tissues suitable for regenerative medicine and also highlights the cilium as a potential therapeutic target for efforts to mimic loading with the aim of preventing bone loss during diseases such as osteoporosis. Furthermore, this study demonstrates a role for the cilium in controlling mechanically mediated increases in the proliferation of hMSCs, which parallels proposed models of polycystic kidney disease. Unraveling the mechanisms leading to rapid proliferation of mechanically stimulated MSCs with defective cilia could provide significant insights regarding ciliopathies and cystic diseases. Stem Cells2012;30:2561–2570

Brief Reports: TRPM7 Senses Mechanical Stimulation Inducing Osteogenesis in Human Bone Marrow Mesenchymal Stem Cells

“…These results demonstrated the central role of TRPM7 in conducting the mechanical stimulation-induced osteogenesis of MSCs. This proposal is indirectly supported by another study showing that cilia mediated fluid flow mechanostimulaiton in human MSCs, and increased osteogenic gene expressions [27]. Fluid flow was also reported to induce an increase in intracellular calcium in human MSCs [3].…”

The role of mechanical stimuli in the vascular differentiation of mesenchymal stem cells

“…A model for primary-cilia-based mechanosensing has been described in which bending of the cell cilium by shear flow can activate ion channels embedded in the membrane (Janmey and McCulloch, 2007). More recently, a study has provided evidence that primary cilia are involved in the osteogenic differentiation of human bone marrow MSCs (hBMMSCs) (Hoey et al, 2012). Other studies have suggested that transmembrane proteins, including ion channels and integrins, could be activated directly by shear flow as well as cyclic strain because these mechanical forces induce changes to the membranes -including altering membrane tension, which activates ion channel conductance (Liu and Lee, 2014).…”

Mechanically stimulated bone cells secrete paracrine factors that regulate osteoprogenitor recruitment, proliferation, and differentiation

“…This system is used in order to generate large amounts of conditioned media when compared to other experimental apparatus such as the parallel flow plate chamber [27]. MLO-Y4 cells were cultured in T-175 flasks with a total of 10ml media in each flask.…”