Primary Cilium, a Potential Target of Microgravity Induced Bone Loss-Juniper Publishers

Microgravity in space can cause various problems in different biological systems. One of the most prominent and well recognized physiological challenges accompanying an extended spaceflight is the reduction in bone mass. However, the underlying mechanisms of this phenomenon are still elusive. Primary cilium is a solitary and special organelle that emanates from the surface of most mammalian cells, which is anchored to the cell by mother centriole during the interphase and G₀ of cell cycle. For a long time, primary cilium was considered as a vestigial organelle. Until recently it was found that primary cilium provided a means of sequestering the centriole, so as to inhibit cell division. More significantly, a variety of receptors, ion channels and transporter proteins have been localized to the cilium, which has been proved as a key coordinator of signaling pathways to respond mechanical and chemical stimuli. Primary cilium has been proved as a mechano sensor to regulate bone formation both in osteocytes and osteoblasts. It can act as a sensory organelle to receive extracellular signals and change its orientation to translate mechanical stimuli into biochemical and transcriptional changes, and as a result, bone formation is activated. Inspired by established role as a mechano sensor, the role of primary cilium in microgravity induced bone loss must be studied. In here we present the structure and function of primary cilium in bone metabolism process, and prospect the importance of primary cilia in microgravity stimulated osteoporosis.

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