Autophagy and lipids: tightening the knot.

The degradation of intracellular components in lysosomes, also known as autophagy, participates in a broad range of cellular functions from cellular quality control to cellular remodeling or as mechanism of defense against cellular aggressors. In this review, we focus on the role of autophagy as an alternative source of cellular energy, particularly important when nutrients are scarce. Almost since the discovery of autophagy, it has been known that amino acids obtained through the breakdown of proteins in lysosomes are essential to maintaining the cellular energetic balance during starvation. However, it is only recently that the ability of autophagy to mobilize intracellular lipid stores as an additional source of energy has been described. Autophagy contributes thus to modulating the amount of cellular lipids and allows cells to adapt to lipogenic stimuli. Interestingly, this interplay between autophagy and lipid metabolism is bidirectional, as changes in the intracellular lipid content also contribute to modulating autophagic activity. In this review, we describe the recent findings on the contribution of autophagy to lipid metabolism in different tissues and the consequences that impairments in autophagy have on cellular physiology. In addition, we comment on the regulatory role that lipid molecules and their modifying enzymes play on different steps of the autophagic process.