The Lineage Specification of Mesenchymal Stem Cells Is Directed by the Rate of Fluid Shear Stress

The effective regulation of fluid shear stress (FSS) on the lineage specification of mesenchymal stem cells (MSCs) remains to be addressed. We hypothesized that when MSCs are recruited to musculoskeletal system following stimulation, their differentiation into osteogenic or chondrogenic cells is directed by the rate of FSS (SS) through modulation of the mechanosensitive, cation-selective channels (MSCCs), intracellular calcium levels, and F-actin. To this end, MSCs were exposed to laminar FSS linearly increased from 0 to 10dyn/cm(2) in 0, 2, or 20min and maintained at 10dyn/cm(2) for a total of 20min (termed as SS 0-0, 0-2, and 0-20, respectively, representing more physiological (0-0) and non-physiological (0-2 and 0-20) SS treatments). Our results showed 0-0 facilitated MSC differentiation towards chondrogenic and not osteogenic phenotype, by promoting moderate intracellular calcium concentration ([Ca2+](i)) increase from the calcium channels with the exception of MSCCs or intracellular calcium stores, and F-actin organization. In contrast, 0-2 promoted MSCs towards osteogenic and not chondrogenic phenotype, by inducing significant [Ca2+](i) increase mainly from the MSCCs, and F-actin assembly. However, 0-20 elicited the modest osteogenic and chondrogenic phenotypes, as it induced the lowest [Ca2+](i) increase mainly from MSCCs, and F-actin assembly. Our results suggest that compared to the more physiological SS, the non-physiological SS favors [Ca2+](i) influx from MSCCs. An appropriate non-physiological SS (0-2) even elicits a large [Ca2+](i) influx from the MSCCs that reverses the lineage specification of MSCs, providing validation for the high mechanosensitivity of MSCs and guidance for training osteoporosis and osteoarthritis patients. J. Cell. Physiol. 231: 1752-1760, 2016. (c) 2015 Wiley Periodicals, Inc.