Mitochondrial fission facilitates the selective mitophagy of protein aggregates

Within the mitochondrial matrix, protein aggregation activates the mitochondrial unfolded protein response and PINK1–Parkin-mediated mitophagy to mitigate proteotoxicity. We explore how autophagy eliminates protein aggregates from within mitochondria and the role of mitochondrial fission in mitophagy. We show that PINK1 recruits Parkin onto mitochondrial subdomains after actinonin-induced mitochondrial proteotoxicity and that PINK1 recruits Parkin proximal to focal misfolded aggregates of the mitochondrial-localized mutant ornithine transcarbamylase (ΔOTC). Parkin colocalizes on polarized mitochondria harboring misfolded proteins in foci with ubiquitin, optineurin, and LC3. Although inhibiting Drp1-mediated mitochondrial fission suppresses the segregation of mitochondrial subdomains containing ΔOTC, it does not decrease the rate of ΔOTC clearance. Instead, loss of Drp1 enhances the recruitment of Parkin to fused mitochondrial networks and the rate of mitophagy as well as decreases the selectivity for ΔOTC during mitophagy. These results are consistent with a new model that, instead of promoting mitophagy, fission protects healthy mitochondrial domains from elimination by unchecked PINK1–Parkin activity

The mechanisms and roles of selective autophagy in mammals

Autophagy is a process that targets various intracellular elements for degradation. Autophagy can be non-selective — associated with the indiscriminate engulfment of cytosolic components — occurring in response to nutrient starvation and is commonly referred to as bulk autophagy. By contrast, selective autophagy degrades specific targets, such as damaged organelles (mitophagy, lysophagy, ER-phagy, ribophagy), aggregated proteins (aggrephagy) or invading bacteria (xenophagy), thereby being importantly involved in cellular quality control. Hence, not surprisingly, aberrant selective autophagy has been associated with various human pathologies, prominently including neurodegeneration and infection. In recent years, considerable progress has been made in understanding mechanisms governing selective cargo engulfment in mammals, including the identification of ubiquitin-dependent selective autophagy receptors such as p62, NBR1, OPTN and NDP52, which can bind cargo and ubiquitin simultaneously to initiate pathways leading to autophagy initiation and membrane recruitment. This progress opens the prospects for enhancing selective autophagy pathways to boost cellular quality control capabilities and alleviate pathology

Spatiotemporal Control of ULK1 Activation by NDP52 and TBK1 during Selective Autophagy

Selective autophagy recycles damaged organelles and clears intracellular pathogens to prevent their aberrant accumulation. How ULK1 kinase is targeted and activated during selective autophagic events remains to be elucidated. In this study, we used chemically inducible dimerization (CID) assays in tandem with CRISPR KO lines to systematically analyze the molecular basis of selective autophagosome biogenesis. We demonstrate that ectopic placement of NDP52 on mitochondria or peroxisomes is sufficient to initiate selective autophagy by focally localizing and activating the ULK1 complex. The capability of NDP52 to induce mitophagy is dependent on its interaction with the FIP200/ULK1 complex, which is facilitated by TBK1. Ectopically tethering ULK1 to cargo bypasses the requirement for autophagy receptors and TBK1. Focal activation of ULK1 occurs independently of AMPK and mTOR. Our findings provide a parsimonious model of selective autophagy, which highlights the coordination of ULK1 complex localization by autophagy receptors and TBK1 as principal drivers of targeted autophagosome biogenesis

Frequency of migraine and the risk of cardiovascular disease for women : limited evidence of an association

Evaluation of: Kurth T, Schurks M, Logroscino G et al. Migraine frequency and risk of cardiovascular disease in women. Neurology 73, 581&ndash;588 (2009). There is substantial evidence that migraine with aura (MA) is associated with ischemic stroke and myocardial infarction in women. The mechanisms of this association are poorly understood. Analysis of data from the Women&rsquo;s Health Study, from 27,798 women over 45 years of age who were initially free of cardiovascular disease, found that women with baseline MA at a frequency of less than monthly had increased risk of major cardiovascular disease (HR: 2.28; 95% CI: 1.70&ndash;3.07) relative to women without migraine, and those who reported MA with a frequency of more than weekly had more than four-times the risk of ischemic stroke (HR: 4.25; 95% CI: 1.36&ndash;13.29) compared with those without migraine. Low numbers of outcome events in each of the frequency categories and lack of information on migraine frequency during follow-up limit the interpretation of these findings, but they suggest that frequency of migraine may be a moderating factor in the link between MA and cardiovascular disease.<br /