Autophagy in stress and disease

Abstract

Macroautophagy, here referred to as 'autophagy,' constitutes one of the most spectacular phenomena in cell biology beyond cell fusion, cell division, differentiation and demise. Metaphorically spoken, it constitutes a process in which the cell sequesters portions of itself in its stomach (the autophagosomes) and then assures their complete degradation in its digestive tract (the lysosomes).Autophagy constitutes one of the most elementary reactions that a cell may have to adapt itself to a changing microenvironment. For instance, in conditions of dwindling external resources, be it nutrients, growth factors or oxygen, the cell may mobilize its stock of potentially energy-rich macromolecules by autophagy, thereby converting proteins and lipids into life-preserving fuel for bioenergetic reactions. In addition, the cell can take advantage of the autophagic machinery to remove damaged, dysfunctional and potentially harmful organelles such as uncoupled mitochondria from its cytoplasm or to destroy useless and even dangerous protein aggregates. Hence, autophagy constitutes an essential mechanism for the recycling of cytoplasmic material and in fine cleaning and rejuvenating extranuclear compartments, especially in non-dividing cells such as neurons or cardiomyocytes. Beyond its homeostatic function, autophagy also has a major role in hormetic reactions. Hormesis can be defined as a process in which the exposure of cells, organs or organisms to a mild stress allows them to mount an adaptive response that allow them to tolerate a later, stronger and normally lethal stress. One well-known example of hormesis is ischemic preconditioning in which a short episode of ischemia reduces the death of heart muscle cells to an otherwise fatal infarction. In this context, autophagy induction has a major role in increasing the robustness of the system, protecting it from deadly stress. Nonetheless, there are also specific situations in which an excess of autophagy may ultimately cause the death of cells by excessive self-digestion. This potentially lethal role of autophagy has received the name of 'autosis'.The present Special Issue of Cell Death & Differentiation deals with the physiological and pathological functions of autophagy in cell stress and disease. Liu and Levine 1 provide an overview over the potential roles of autosis and autophagic cell death in health and disease. Filomeni et al.2 demonstrate the importance of autophagy regulation by reactive oxygen species and reactive nitrogen species in the context of cytoplasmic processes and DNA damage signaling. Orhon et al.3 insist on the important role of primary cilia, which are microtubule-based structures located at the cell surface of many cell types, as potential sensors of autophagy-inducing stimuli that are in turn affected in their biogenesis and function by autophagic responses. Nikoletopoulou et al.4 demonstrate the essential role of autophagy for the normal function of neurons in model organisms such as Caenorhabditis elegans, as well as the potential role of autopha...

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