The Molecular Mechanisms of Gravisensitivity: From Cells to Extracellular Matrix

Gravity deprivation is one of the major risk factors in spaceflight. Medical and biological studies show that as a result of prolonged exposure to weightlessness, astronauts and cosmonauts experience unfavorable changes in many physiological systems (loss of bone mass, muscle atrophy, cardiovascular insufficiency, sensorimotor disorders, etc.). Physiological and pathophysiological mechanisms of response to microgravity exposure at different levels of organization (molecular, cellular, tissue) and subsequent adaptation are actively studied. Under the Earth gravitational field, multicellular organisms have formed a multicomponent mechanoreceptor apparatus including cellular (nucleo- and cytoskeleton) and extracellular (connective tissue matrix) mechanosensitive elements. The coordination of these compartments is carried out by specialized protein complexes, forming a mechanoreceptor unit. When the Earth’s gravity is deprived, this unit will be the basis for adaptation processes, acting as a kind of complex gravity receptor. Ground-based simulations are particularly important to elucidate the mechanisms that provide the response to microgravity, as flight limitations do not allow large-scale studies in space. In this review, we analyze the current understanding of the molecular mechanisms of gravisensing and the cellular response to microgravity under both real and simulated environments and discuss the directions for further research in this area.