Mechanotransduction in Bone via Oscillating Fluid Flow

Principal Investigators: Christopher R. Jacobs, PhD

Co-Investigators: Henry J. Donahue, PhD and R. Lane Smith PhD

Objective: Bone cells occupy fluid filled voids (lacunae) in the mineralized matrix and interconnected by small tubes (canaliculi). As the bone matrix is cyclically loaded, fluid flows in the lacunar-canalicular network from regions of high matrix strain to low matrix strain and back in an oscillatory fashion. Although, it has been demonstrated that bone cells respond to steady and pulsatile fluid flow with a transient elevation in intracellular calcium concentration, increased release of paracrine factors, and increased gene transcription, our preliminary data indicate that these responses are fundamentally different from those observed for oscillating flow. The central hypotheses of the most recently awarded five year funding period is that oscillatory fluid flow regulates bone cell metabolism via a molecular mechanism involving forces transmitted by the cytoskeleton to focal adhesion sites and integrins. The result of this project will be specific knowledge of the molecular mechanism responsible for transduction of mechanical loads in bone.

Research Plan: This project is divided into four specific aims:

1. Undertake a systematic multilevel evaluation of cell structural proteins to include actin, integrins, and linker proteins in terms of how they are regulated by mechanical stimulation.
2. Determine if the proteins examined in (1) are involved in transduction of mechanical signals to the cell’s interior.
3. Determine if focal adhesion kinase phosphorylation signaling is involved in transduction.
4. Utilize a novel microfluidic flow chamber to determine if the osteocyte process is the site of transduction.

Work Accomplished: Our competing continuation application was successful and we were awarded an additional five years of support. Work on the aims involved in this funding period has just begun.

Expected Outcome: The long-term goal of these studies is to better understand the how mechanical loading influences the behavior of bone. Increased understanding of this relationship will lead to the identification of novel targets of therapeutic interventions in bone diseases with a mechanical component such as osteoporosis.

Publications

Rubin, J., Rubin, C., Jacobs, C.R., Mechanical signaling in bone. Gene, 367:1-16, 2006.

Kim, C., You, L., Yellowley, C.E., Jacobs, C.R., Oscillatory Fluid Flow Induced Shear Stress Decreases Osteoclastogenesis through Regulation of RANKL and OPG. Bone, 39:1043-1047, 2006.

Godin, L.M., Suzuki, S., Jacobs, C.R., Donahue, H.J., Donahue, S.W., Mechanically Induced Intracellular Calcium Waves in Osteoblasts Demonstrate Calcium Fingerprints in Bone Cell Mechanotransduction. Biomechanics and Modeling in Mechanobiology, Nov 6, Epub, 2006.

Malone, A.M., Batra, N.N., Shivaram, G, Kwon, R, You, L., Kim, C., Rodriguez, J, Jair, K. Jacobs, C.R., The Role of the Actin Cytoskeleton in Oscillatory Fluid Flow Induced Signaling in MC3T3-E1 Osteoblasts. American Journal of Physiology-Cell, Jan 24, Epub, 2007.

Funding Source: Department of Veterans Affairs - Merit Review