Abstract
Microenvironments that modulate fate commitments of mesenchymal stromal cells (MSCs) are composed of chemical and physical cues, but the latter ones are much less investigated. Here we demonstrate that intermittent fluid shear stress (IFSS), a potent and physiologically relevant mechanical stimulus, regulates osteogenic differentiation of MSCs through Transient receptor potential melastatin 7 (TRPM7)-Osterix axis. Immunostaining showed the localization of TRPM7 near or at cell membrane upon IFSS, and calcium imaging analysis demonstrated the transient increase of cytosolic free calcium. Expressions of osteogenic marker genes including Osterix, but not Runx2, were upregulated after three-hour IFSS. Phosphorylation of p38 and Smad1/5 was promoted by IFSS as well. TRPM7 gene knockdown abolished the promotion of bone-related gene expressions and phosphorylation. We illustrate that TRPM7 is mechanosensitive to shear force of 1.2 Pa, which is much lower than 98 Pa pressure loading reported recently, and mediates distinct mechanotransduction pathways. Additionally, our results suggest the differential roles of TRPM7 in endochondral and intramembranous ossification. Together, this study elucidates the mechanotransduction in MSCs fate commitments and displays an efficient mechano-modulation for MSCs osteogenic differentiation. Such findings should be taken into consideration when designing relevant scaffolds and microfluidic devices for osteogenic induction in the future.
Highlights
Used in cell therapy and tissue engineering[7,8]
By applying intermittent fluid shear stress (IFSS) ranging from 4 × 10−3 to 1.2 Pa in detachable microfluidic devices, we demonstrated that mechanosensitive TRPM7 modulates osteogenic differentiation of Mesenchymal stromal cells (MSCs) through Osterix pathway via kinase phosphorylation, intracellular calcium increase, and upregulation of the osteogenic marker genes upon the mechanical cue
RT-PCR results on cells harvested during flow showed that gene expression of osteogenic transcription factor Osterix increased in a flow-rate dependent manner and the upregulation was responsive to the intermittent shear stress as low as 4 × 10−3 Pa
Summary
It is important to understand how MSCs sense shear stress and what are the underlying molecular mechanisms regulating MSC fate commitments, in tissue regeneration. Using patch clamp techniques, Xiao et al demonstrated that TRPM7 is mechanosensitive to pressure loading of 1 g/cm[2] (98 Pa), induces cytosolic Ca2+ increase and upregulates Runx[2] gene in human MSCs18. By applying intermittent fluid shear stress (IFSS) ranging from 4 × 10−3 to 1.2 Pa in detachable microfluidic devices, we demonstrated that mechanosensitive TRPM7 modulates osteogenic differentiation of MSCs through Osterix pathway via kinase phosphorylation, intracellular calcium increase, and upregulation of the osteogenic marker genes upon the mechanical cue. The study has shed light on the involvements of mechanosensors in MSC fate commitments and displays an efficient mechano-modulation of MSCs osteogenic differentiation
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