Synthesis of collagen from bone cells in vitro
In response to dynamic loading of the musculoskeletal system, bone undergoes mechanical adaptation by modifying its mass and architecture via two processes: modeling and remodeling. Modeling shapes bone and increases bone mass, particularly during skeletal development, while remodeling renews bone. These processes are carried out on a cellular level by three primary cell types: osteoblasts which synthesize bone matrix, osteoclasts which resorb bone, and osteocytes which act as mechanical sensors and produce signals to activate osteoblasts, osteoclasts, or their progenitors.
Mechanotransduction is the mechanism which converts a physical force into a cellular response and, in bone, consists of four primary stages, as summarized by Turner et al.: 1) mechanocoupling: the process of taking a mechanical force applied to the bone and transducing it into a mechanical signal perceived, on a local scale, by sensing cells such as osteocytes; 2) biochemical coupling: taking that mechanical signal and converting it into a biochemical response that could lead to gene expression or protein activation; 3) signal transmission: occurs via signaling molecules, between the sensing cells and the effector cells including osteoblasts and osteoclasts, and; 4) effector cell response: either bone formation by osteoblasts or bone resorption by osteoclasts on a tissue level.
Our lab studies the response to loading by applying fluid shear stress to the osteocytes (parallel plate flow chamber)and substrate stretching to osteoblasts in vitro. We then characterize the effects of loading by measuring changes in the expression of genes associated with collagen synthesis, post-translational modifications and crosslinking. In addition, the physical and chemcial properties of the matrix that is produced are measured using methods including Fourier Trasnsform Infrared Spectroscopy (FTIR) and AFM.