Autophagy, an evolutionarily conserved process for the bulk degradation of cytoplasmic components, serves as a cell survival mechanism in starving cells. Although altered autophagy has been observed in various heart diseases, including cardiac hypertrophy and heart failure, it remains unclear whether autophagy plays a beneficial or detrimental role in the heart. Here, we report that the cardiac-specific loss of autophagy causes cardiomyopathy in mice. In adult mice, temporally controlled cardiac-specific deficiency of Atg5 (autophagy-related 5), a protein required for autophagy, led to cardiac hypertrophy, left ventricular dilatation and contractile dysfunction, accompanied by increased levels of ubiquitination. Furthermore, Atg5-deficient hearts showed disorganized sarcomere structure and mitochondrial misalignment and aggregation. On the other hand, cardiac-specific deficiency of Atg5 early in cardiogenesis showed no such cardiac phenotypes under baseline conditions, but developed cardiac dysfunction and left ventricular dilatation one week after treatment with pressure overload. These results indicate that constitutive autophagy in the heart under baseline conditions is a homeostatic mechanism for maintaining cardiomyocyte size and global cardiac structure and function, and that upregulation of autophagy in failing hearts is an adaptive response for protecting cells from hemodynamic stress.

Damaged mitochondria are removed by mitophagy. Although Atg32 is essential for mitophagy in yeast, no Atg32 homologue has been identified in mammalian cells. Here, we show that Bcl-2-like protein 13 (Bcl2-L-13) induces mitochondrial fragmentation and mitophagy in mammalian cells. First, we hypothesized that unidentified mammalian mitophagy receptors would share molecular features of Atg32. By screening the public protein database for Atg32 homologues, we identify Bcl2-L-13. Bcl2-L-13 binds to LC3 through the WXXI motif and induces mitochondrial fragmentation and mitophagy in HEK293 cells. In Bcl2-L-13, the BH domains are important for the fragmentation, while the WXXI motif facilitates mitophagy. Bcl2-L-13 induces mitochondrial fragmentation in the absence of Drp1, while it induces mitophagy in Parkin-deficient cells. Knockdown of Bcl2-L-13 attenuates mitochondrial damage-induced fragmentation and mitophagy. Bcl2-L-13 induces mitophagy in Atg32-deficient yeast cells. Induction and/or phosphorylation of Bcl2-L-13 may regulate its activity. Our findings offer insights into mitochondrial quality control in mammalian cells.

Objectives: We investigated the incidence, clinical characteristics, outcome and factors associated with aphasia and early improvement in acute ischemic stroke. Methods: We consecutively studied 855 patients with acute ischemic stroke who were admitted to our hospital within 48 h after onset and who were not comatose on admission. Assessment of aphasia was performed on admission (day 0) and day 10. We examined the incidence, severity, and subtypes of aphasia, and compared the clinical background of patients with and without aphasia on admission, and also those with and without early improvement by day 10. In addition, we investigated the independent factors associated with the presence of aphasia on admission and with early improvement. Results: Of the 855 patients, 130 (15.2%) had aphasia on admission. The National Institutes of Health Stroke Scale (NIHSS) on admission (OR 1.21; 95% CI 1.17–1.26) was a significant and independent factor associated with the presence of aphasia on admission. Early improvement was seen in 56 of 121 aphasic patients (46.3%) who were still alive on day 10. A history of hypercholesterolemia (OR 3.27; 95% CI 1.14–9.39) was a significant and independent factor associated with early improvement in aphasia during the acute phase and NIHSS on admission (OR 0.95; 95% CI 0.90–0.99) was marginally significant. Conclusion: It is difficult to predict the outcome of aphasia within the first few days after the onset of ischemic stroke.

SummaryDegradation of mitochondria by selective autophagy, termed mitophagy, contributes to the control of mitochondrial quality. Bcl2-L-13 is a mammalian homolog of Atg32, which is an essential mitophagy receptor in yeast. However, the molecular machinery involved in Bcl2-L-13-mediated mitophagy remains to be elucidated. Here, we show that the ULK1 (unc-51-like kinase) complex is required for Bcl2-L-13 to process mitophagy. Screening of a series of yeast Atg mutants revealed that a different set of ATG genes is used for Bcl2-L-13- and Atg32-mediated mitophagy in yeast. The components of the Atg1 complex essential for starvation-induced autophagy were indispensable in Bcl2-L-13-, but not Atg32-mediated, mitophagy. The ULK1 complex, a counterpart of the Atg1 complex, is necessary for Bcl2-L-13-mediated mitophagy in mammalian cells. We propose a model where, upon mitophagy induction, Bcl2-L-13 recruits the ULK1 complex to process mitophagy and the interaction of LC3B with ULK1, as well as Bcl2-L-13, is important for the mitophagy.