Tuning stem cell fate with physical energies

Abstract

Defocused extracorporeal low-energy shock waves (DLSW) have long been used successfully in the treatment of bone and joint diseases as well as in the management of pain and inflammatory conditions. Shock waves are generated by an underwater highvoltage condenser spark discharge and focused at the diseased area, using an elliptic reflector. Shock waves are high-amplitude sound waves from a transient pressure disturbance that propagate in three-dimensional space with a sudden increase from ambient pressure to maximum pressure at the wave front. A shock wave is a sonic pulse that has certain physical characteristics. There is an initial increase of a high peak pressure, sometimes >100 MPa (500 bar) within <10 ns, followed by a low tensile amplitude (up to 10 MPa), a short life cycle of approximately 10 ms and a broad-frequency spectrum of 16e20 MHz. There are two basic effects of shock waves: The primary effect is direct generation of mechanical forces that result in the maximally beneficial pulse energy concentrated at the point where treatment is to be provided, and the secondary effect is indirect mechanical forces by cavitation, which may cause a negative effect or damage to the tissues. In the current issue of Cytotherapy, Zhao et al. (1) investigated the effects produced by DLSW on stem cell homeostasis in vitro. The authors used an electromagnetic shock wave machine and exposed rat bone marrow-derived stem cells (BMSCs) to 800 impulses of DLSW at an energy flux density of 0.1 mJ/mm. This treatment was performed before each passage. The shocked BMSCs were found to secrete more vascular endothelial growth factor and CXC ligand 5 than the BMSCs that were not shocked. The expression of CD166, CD44 and CD34 was not affected. The shocked BMSCs also exhibited higher