[Role of lysophosphatidic acid as a mechanosensitizer]

Lysophosphatidic acid induces shear stress-dependent contraction in mouse aortic strip in situ

We previously reported that lysophosphatidic acid (LPA) regulates Ca²⁺ influx of fluid flow in stimulated endothelial cells and that LPA and shear stress showed increment and suppressive effects on phenylephrine-induced vasoconstriction and acetylcholine-induced vasodilatation, respectively. However, a vasoconstrictive effect of LPA alone in the presence of shear stress was not found. The present study examined the effect of LPA alone in the presence of shear stress on Ca²⁺ responses in endothelial and smooth muscle cells and contraction in mouse aortic strip using real-time 2-photon laser scanning microscopy and a custom-made parallel-plate flow chamber. Application of micromolar LPA and high shear stress elicited movement of endothelial cells after Ca²⁺ responses. The endothelial cells moved along the major axis of smooth muscle cells, a direction that was identical to that found during vasoconstriction evoked by the application of phenylephrine. The frequency of Ca²⁺ oscillations in smooth muscle cells was highest according to endothelial movement. Vasoconstriction evoked by LPA and shear stress was significantly reduced by the application of a thromboxane A₂ receptor antagonist, a cyclooxygenase inhibitor, and a thromboxane synthase inhibitor. These results suggest that micromolar LPA and high shear stress elicit vasoconstriction that is caused by Ca²⁺-dependent contraction in medial smooth muscle cells. Thromboxane A₂ may be involved in that response.

Mechanical derivation of functional myotubes from adipose-derived stem cells

Though reduced serum or myoblast co-culture alone can differentiate adipose-derived stem cells (ASCs) into mesenchymal lineages, efficiency is usually not sufficient to restore function in vivo. Often when injected into fibrotic muscle, their differentiation may be misdirected by the now stiffened tissue. Here ASCs are shown to not just simply reflect the qualitative stiffness sensitivity of bone marrow-derived stem cells (BMSCs) but to exceed BMSC myogenic capacity, expressing the appropriate temporal sequence of muscle transcriptional regulators on muscle-mimicking extracellular matrix in a tension and focal adhesion-dependent manner. ASCs formed multi-nucleated myotubes with a continuous cytoskeleton that was not due to misdirected cell division; microtubule depolymerization severed myotubes, but after washout, ASCs refused at a rate similar to pre-treated values. BMSCs never underwent stiffness-mediated fusion. ASC-derived myotubes, when replated onto non-permissive stiff matrix, maintained their fused state. Together these data imply enhanced mechanosensitivity for ASCs, making them a better therapeutic cell source for fibrotic muscle.