An Introduction to Biomechanics in Primary Cilia

Cilia appear in a wide variety of cell types, including osteoclasts and osteoblasts, where they function as physiologic and biochemical sensors.

Christopher Jacobs, PhD, from Columbia University, discussed the interplay between mechanobiology and biomechanics in primary cilia at the 2014 American Society of Bone and Mineral Research Conference in Houston, Texas.

Individual cells and cell types encounter the outside world differently. Osteoclasts and osteoblasts react to outside forces imposed on them by activities such as strain, exercise, and sitting. Endothelial cells respond to the mechanical stress caused by laminar blood flow, and cellular mechanical transduction is at the center of atherosclerosis.

Primary cilia are single antenna-like structures emerging from each cell. As Dr Jacobs said, “they are not vestigial, not the appendix of the cell.” They specifically function as physiologic and biochemical sensors in cells as diverse as cholangiocytes, osteocytes, and chondrocytes.

In bone, primary cilia function in bone transduction and the lack of cilia interferes with PGE2 release in osteoblasts.

In his talk, Dr Jacobs said that biomechanical changes in the environment alter how the cell can use the cilium as a biochemical sensor. Primary cilia deflect with flow. As a cilium experiences variable timing and force of the flowing air or liquid to which it is exposed, it may change its organization and remodel as it bends.

The microtubular network anchoring the base of cilium becomes enhanced, and this sub-cellular structure seems to be a sensor that adapts to its environment. Primary cilia stiffness can be modulated, as can torsional stiffness. Increased stiffness correlates with the degree of biomechanical sensitivity.

According to Dr Jacobs, future directions for the study of cilia include answering questions about the nature of calcium and other biochemical channels in cilia compared with other cell types. He is also exploring the role of cilia in mesenchymal stem cells.