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Autophagy refers to an essential mechanism that evolved to sustain eukaryotic homeostasis and metabolism during instances of nutrient deprivation. During autophagy, intracellular cargo is encapsulated and delivered to the lysosome for elimination. Loss of basal autophagy in vivo negatively impacts cellular proteostasis, metabolism and tissue integrity. Accordingly, many drug development strategies are focused on modulating autophagic capacity in various pathophysiological states, from cancer to neurodegenerative disease. The role of autophagy in cancer is particularly complicated, as either augmenting or attenuating this process can have variable outcomes on cellular survival, proliferation and transformation. This complexity is compounded by the emergence of several selective autophagy pathways, which act to eliminate damaged or superfluous cellular components in a targeted fashion. The advent of sensitive tools to monitor autophagy pathways in vivo holds promise to clarify their importance in cancer pathophysiology. In this review, we provide an overview of autophagy in cancer biology and outline how the development of tools to study autophagy in vivo could enhance our understanding of its function for translational benefit.

Mitophagy is a quality control mechanism that eliminates damaged mitochondria, yet its significance in mammalian pathophysiology and aging has remained unclear. Here, we report that mitophagy contributes to mitochondrial dysfunction in skeletal muscle of aged mice and human patients. The early disease stage is characterized by muscle fibers with central nuclei, with enhanced mitophagy around these nuclei. However, progressive mitochondrial dysfunction halts mitophagy and disrupts lysosomal homeostasis. Interestingly, activated or halted mitophagy occur in a mosaic manner even in adjacent muscle fibers, indicating cell-autonomous regulation. Rapamycin restores mitochondrial turnover, indicating mTOR-dependence of mitochondrial recycling in advanced disease stage. Our evidence suggests that (1) mitophagy is a hallmark of age-related mitochondrial pathology in mammalian muscle, (2) mosaic halting of mitophagy is a mechanism explaining mosaic respiratory chain deficiency and accumulation of pathogenic mtDNA variants in adult-onset mitochondrial diseases and normal aging, and (3) augmenting mitophagy is a promising therapeutic approach for muscle mitochondrial dysfunction.

One aspect of selective autophagy that has garnered intense interest is mitochondrial autophagy (mitophagy), particularly PINK1-PRKN-mediated mitophagy as this has direct implications for Parkinson...

The autophagic turnover of mitochondria, termed mitophagy, is thought to play an essential role in not only maintaining the health of the mitochondrial network but also that of the cell and organism as a whole. We have come a long way in identifying the molecular components required for mitophagy through extensive in vitro work and cell line characterisation, yet the physiological significance and context of these pathways remain largely unexplored. This is highlighted by the recent development of new mouse models that have revealed a striking level of variation in mitophagy, even under normal conditions. Here, we focus on programmed mitophagy and summarise our current understanding of why, how and where this takes place in mammals.

Photoreception is pivotal to our experience and perception of the natural world; hence the eye is of prime importance for most vertebrate animals to sense light. Central to visual health is mitochondrial homeostasis, and the selective autophagic turnover of mitochondria (mitophagy) is predicted to play a key role here. Despite studies that link aberrant mitophagy to ocular dysfunction, little is known about the prevalence of basal mitophagy, or its relationship to general autophagy, in the visual system. In this study, we utilize the mito-QC mouse and a closely related general macroautophagy reporter model to profile basal mitophagy and macroautophagy in the adult and developing eye. We report that ocular macroautophagy is widespread, but surprisingly mitophagy does not always follow the same pattern of occurrence. We observe low levels of mitophagy in the lens and ciliary body, in stark contrast to the high levels of general MAP1LC3-dependent macroautophagy in these regions. We uncover a striking reversal of this process in the adult retina, where mitophagy accounts for a larger degree of the macroautophagy taking place, specifically in the photoreceptor neurons of the outer nuclear layer. We also show the developmental regulation of autophagy in a variety of ocular tissues. In particular, mitophagy in the adult mouse retina is reversed in localization during the latter stages of development. Our work thus defines the landscape of mitochondrial homeostasis in the mammalian eye, and in doing so highlights the selective nature of autophagy in vivo and the specificity of the reporters used. Abbreviations: ATG: autophagy related; GFP: green fluorescent protein; LC3: microtubule associated protein 1 light chain 3; ONH: optic nerve head; ONL: outer nuclear layer; RPE: retinal pigment epithelium.

Autophagy evolved as a mechanism to sustain cellular homeostasis during instances of nutrient deprivation. Mounting evidence has also clarified that under basal and stress conditions, selective autophagy pathways can target the destruction of specific organelles. Mitochondrial autophagy, or mitophagy, has emerged as a key quality control (QC) mechanism to sustain the integrity of eukaryotic mitochondrial networks. We recently reported the development of mito-QC, a novel reporter mouse model that enables the high-resolution study of mammalian mitophagy with precision, in fixed and live preparations. This model holds significant potential to transform our understanding of mammalian mitophagy pathways in vivo, in a variety of physiological contexts. We outline a detailed protocol for use of our recently described mito-QC mouse model, including tips and troubleshooting advice for those interested in monitoring mitophagy in vitro and in vivo.

Autophagy evolved as a mechanism to sustain cellular homeostasis during instances of nutrient deprivation. Mounting evidence has also clarified that under basal and stress conditions, selective autophagy pathways can target the destruction of specific organelles. Mitochondrial autophagy, or mitophagy, has emerged as a key quality control (QC) mechanism to sustain the integrity of eukaryotic mitochondrial networks. We recently reported the development of mito-QC, a novel reporter mouse model that enables the high-resolution study of mammalian mitophagy with precision, in fixed and live preparations. This model holds significant potential to transform our understanding of mammalian mitophagy pathways in vivo, in a variety of physiological contexts. We outline a detailed protocol for use of our recently described mito-QC mouse model, including tips and troubleshooting advice for those interested in monitoring mitophagy in vitro and in vivo.

The Parkinson's disease (PD)-associated protein kinase, PTEN-induced putative kinase1 (PINK1), and ubiquitin E3 ligase Parkin, function in a common signalling pathway known to regulate mitochondrial network homeostasis and quality control, including mitophagy. The multistep activation of this pathway, as well as an unexpected convergence between the post-translational modifications of ubiquitylation and phosphorylation, has added breadth to our understanding of cellular damage responses during human disease. In concert with these new insights in signal transduction, unique modalities and signatures of vertebrate mitophagy have been unravelled in vivo for the very first time. The cell biology of mammalian mitophagy, and the roles of PINK1-Parkin signalling in vivo have emerged to be more complex than previously thought.

Whether mitophagy occurs within specific cellular subtypes in vivo is unclear. McWilliams et al. present “mito-QC,” a transgenic mouse containing a pH-sensitive fluorescent mitochondrial signal, allowing in vivo detection of mitophagy and mitochondrial morphology at single-cell resolution., Autophagic turnover of mitochondria, termed mitophagy, is proposed to be an essential quality-control (QC) mechanism of pathophysiological relevance in mammals. However, if and how mitophagy proceeds within specific cellular subtypes in vivo remains unclear, largely because of a lack of tractable tools and models. To address this, we have developed “mito-QC,” a transgenic mouse with a pH-sensitive fluorescent mitochondrial signal. This allows the assessment of mitophagy and mitochondrial architecture in vivo. Using confocal microscopy, we demonstrate that mito-QC is compatible with classical and contemporary techniques in histochemistry and allows unambiguous in vivo detection of mitophagy and mitochondrial morphology at single-cell resolution within multiple organ systems. Strikingly, our model uncovers highly enriched and differential zones of mitophagy in the developing heart and within specific cells of the adult kidney. mito-QC is an experimentally advantageous tool of broad relevance to cell biology researchers within both discovery-based and translational research communities.

The past decade has seen an intensive and concerted research effort into the molecular regulation of mitophagy, the selective autophagy of mitochondria. Cell-based studies have implicated mitophagy in the pathology of diverse conditions ranging from cancer to neurodegeneration. However, a definitive link between mitophagy and the etiology of human disease remains to be demonstrated. Moreover, we do not know how pervasive mammalian mitophagy is in vivo and fundamental questions remain unanswered. For example, is mitophagy common to all tissues under basal conditions or does it only occur in highly oxidative tissues under stress? This paucity of knowledge is largely due to a lack of experimentally tractable tools that can measure and monitor mitophagy in tissues. Our recent work describes the development of mito-QC, a mouse model to study mitophagy at single cell resolution in vivo.