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Structure and Function of Cartilage
Published in Kyriacos A. Athanasiou, Eric M. Darling, Grayson D. DuRaine, Jerry C. Hu, A. Hari Reddi, Articular Cartilage, 2017
Kyriacos A. Athanasiou, Eric M. Darling, Grayson D. DuRaine, Jerry C. Hu, A. Hari Reddi
Recently, primary cilium has come into focus as a mechanosensor of fluid flow. The primary cilium is a small membrane protrusion containing microtubules present on almost all vertebrate cells that can act as an “extracellular antenna” for detection of the external environment (Marshall and Nonaka 2006; Singla and Reiter 2006) (Figure 1.12). It also acts as a signaling center for sonic hedgehog (Shh), patched (PTC), and other molecules that can regulate cell survival, growth and differentiation, and tissue homeostasis (Christensen et al. 2008; Veland et al. 2009). For instance, in bone the primary cilium has been demonstrated to deflect under flow and to be independent of Ca2+ flux and stretch-activated ion channels in fluid flow-induced PGE2 release (Malone et al. 2007). Interestingly, in the endothelium of the kidney (Yoder 2007) or vascular system, the primary cilium appears to transduce fluid flow through an increase in intracellular Ca2+ (Van der Heiden et al. 2006). In the kidney, this has been linked to interactions between the primary cilium and polycystins 1 and 2 to form a mechanosensitive ion channel (Forman et al. 2005) (Figure 1.13). In chondrocytes, the length of the primary cilium may be regulated by mechanical loading (McGlashan et al. 2010).
Multi-scale numerical simulation on mechano-transduction of osteocytes in different gravity fields
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Chaohui Zhao, Haiying Liu, Congbiao Tian, Chunqiu Zhang, Wei Wang
The primary cilium is a highly specialized organelle protruding from the cell surface, which is located 0.05 μm under the cell membrane. The primary cilium is composed of nine groups of duplex microtubules, and the cilium membrane is directly connected to the cell membrane and is able to sense a variety of signals around the cells, affect cell growth and differentiation and other related functions(Praetorius and Spring 2005; Singla and Reiter 2006; Satir et al. 2010). Many receptors, ion channels and transporters are present in the primary cilium, which has been established as a mechanical receptor in human tissues(Praetorius and Spring 2005). The primary cilium is critical in coordinating the response signal pathway of mechanical and chemical stimuli. The primary cilium changes direction with mechanical stimulation, which triggers a series of chemical reactions, opening the pathways of some trace elements. For example, the flow of liquid in LCS causes the primary cilium to bend, which affects calcium ion transport in renal cells by lowering the CAMP content of osteocytes or activating calcium ion channels, promoting the expression of specific genes in renal cells(Schwartz et al. 1997; Kwon et al. 2010; Hoey et al. 2011; Masyuk et al. 2013). In vitro experiments have shown that the removal of primary cilium halts the bone formation of cells under shear stress and the production of related proteins. A recent study showed that primary cilium was directly involved in the mechano-transduction of osteocytes in vivo, and that specific knockout of KIF3A from mouse osteoblasts and osteocytes lead to a decrease in bone formation under the same conditions (Temiyasathit et al. 2012). Drugs or changing the external environment of the cell can also regulate the length of the primary cilium(Wilson et al. 2008; Ou et al. 2009). Another experimental study showed that the microtubule structure of the primary cilium depolymerized in microgravity, inhibiting the activity of osteocytes and reducing bone formation. Additionally, increasing the length of primary cilium by drugs or molecular methods can promote bone formation (Shi et al. 2017).