Autophagy is stimulated by starvation (amino acids and/or glucose deprivation) and growth factor limitation. In addition, mechanical forces are also positive regulators of autophagy. Growth factors and mechanical forces trigger signaling from the cell surface including from the primary cilium (PC) whereas nutrients directly act intracellularly. Many of the stimuli that control autophagy converge on the kinases mTOR and AMPK.

Macroautophagy is a lysosomal degradative pathway for intracellular macromolecules, protein aggregates and organelles. The formation of the autophagosome, a double membrane-bound structure that sequesters cargoes before their delivery to the lysosome, is regulated by several stimuli in multicellular organisms. Pioneering studies in rat liver showed the importance of amino acids, insulin and glucagon in controlling macroautophagy. Thereafter, many studies have deciphered the signaling pathways downstream of these biochemical stimuli to control autophagosome formation. Two signaling hubs have emerged: the kinase mTOR, in a complex at the surface of lysosomes which is sensitive to nutrients and hormones; and AMPK, which is sensitive to the cellular energetic status. Besides nutritional, hormonal and energetic fluctuations, many organs have to respond to mechanical forces (compression, stretching and shear stress). Recent studies have shown the importance of mechanotransduction in controlling macroautophagy. This regulation engages cell surface sensors, such as the primary cilium, in order to translate mechanical stimuli into biological responses.