The emerging role of cell-derived microvesicles in stem cell research and therapy.

Microvesicles (MVs) or microparticles are one type of extracellular vesicles (EVs) which can be produced by all types of cells under physiological or pathological conditions. The diameter of MVs ranges from 100 nm to 1000 nm. MVs are different from exosomes which are smaller (20 nm 100 nm) and originate from multivescular bodies [1]. MV biogenesis is always associated with cell growth, activation or apoptosis. The process involves direct budding of plasma membrane and a wide range of external signals can stimulate cells to produce MVs. The stimulator can be physical stress (such as, shear, hypoxia and oxidative stress), physiological agonists (such as, thrombin and TNFα) or non-physiological activators (such as, phorbol myristate acetate and calcium ionophore). MV generation process is complex and multiples mechanisms have been employed by cells, including caspase activation, lipid rafts, cytoskeletal reorganization and so on [2]. MVs are heterogeneous with respect to their surface marker expression, membrane phospholipid composition, and internal protein and RNA repertoires even when they are produced by the same parent cells but with different stimulations [2].