Influence of Donor Age and Stimulation Intensity on Osteogenic Differentiation of Rat Mesenchymal Stromal Cells in Response to Focused Low-Intensity Pulsed Ultrasound

A focused low-intensity pulsed ultrasound (FLIPUS) was used to investigate the effects of stimulation period, acoustic intensity and donor age on the osteogenic differentiation potential of rat mesenchymal stromal cells (rMSCs). rMSCs from 3- and 12-mo-old female Sprague Drawly rats were isolated from bone marrow and stimulated 20 min/d with either 11.7 or 44.5 mW/cm2 (spatial average temporal average intensity) for 7 or 14 d. Osteogenic differentiation markers, i.e., Runt-related transcription factor 2 (RUNX2), osteocalcin (OCN) and degree of matrix calcification were analyzed. On day 7 of stimulation, OCN gene expression was enhanced 1.9-fold in cells from young rats when stimulated with low intensity. The low intensity also led to a 40% decrease in RUNX2 expression on day 7 in aged cells, whereas high intensity enhanced expression of RUNX2 on day 14. FLIPUS treatment with low intensity resulted in a 15% increase in extracellular matrix mineralization in young but not old rMSCs. These differences suggest the necessity of a donor-age related optimization of stimulation parameters.