An alternative mitophagy pathway mediated by Rab9 protects the heart against ischemia
Toshiro Saito, … , Mondira Kundu, Junichi Sadoshima
Toshiro Saito, … , Mondira Kundu, Junichi Sadoshima
Published December 4, 2018
Citation Information: J Clin Invest. 2019;129(2):802-819. https://doi.org/10.1172/JCI122035.
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Research Article Cardiology Cell biology

An alternative mitophagy pathway mediated by Rab9 protects the heart against ischemia

Abstract

Energy stress, such as ischemia, induces mitochondrial damage and death in the heart. Degradation of damaged mitochondria by mitophagy is essential for the maintenance of healthy mitochondria and survival. Here, we show that mitophagy during myocardial ischemia was mediated predominantly through autophagy characterized by Rab9-associated autophagosomes, rather than the well-characterized form of autophagy that is dependent on the autophagy-related 7 (Atg) conjugation system and LC3. This form of mitophagy played an essential role in protecting the heart against ischemia and was mediated by a protein complex consisting of unc-51 like kinase 1 (Ulk1), Rab9, receptor-interacting serine/thronine protein kinase 1 (Rip1), and dynamin-related protein 1 (Drp1). This complex allowed the recruitment of trans-Golgi membranes associated with Rab9 to damaged mitochondria through S179 phosphorylation of Rab9 by Ulk1 and S616 phosphorylation of Drp1 by Rip1. Knockin of Rab9 (S179A) abolished mitophagy and exacerbated the injury in response to myocardial ischemia, without affecting conventional autophagy. Mitophagy mediated through the Ulk1/Rab9/Rip1/Drp1 pathway protected the heart against ischemia by maintaining healthy mitochondria.

Authors

Toshiro Saito, Jihoon Nah, Shin-ichi Oka, Risa Mukai, Yoshiya Monden, Yasuhiro Maejima, Yoshiyuki Ikeda, Sebastiano Sciarretta, Tong Liu, Hong Li, Erdene Baljinnyam, Diego Fraidenraich, Luke Fritzky, Peiyong Zhai, Shizuko Ichinose, Mitsuaki Isobe, Chiao-Po Hsu, Mondira Kundu, Junichi Sadoshima

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Figure 1

Ulk1- but not Atg7-dependent autophagy protects the heart against physiological energy stress through activation of mitophagy.

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Ulk1- but not Atg7-dependent autophagy protects the heart against physio...
Mice were subjected to 48 hours of starvation. Error bars indicate the SEM. (A and B) Protein levels of LC3 in the heart were analyzed after chloroquine administration (10 μg/kg i.p.) during the 48-hour starvation period to evaluate autophagic flux. (A) Representative immunoblot and (B) summary of relative expression of LC3-II (n = 7–8 per group). #P < 0.05 versus WT, control, and no chloroquine; †P < 0.05 versus WT, starvation, and no chloroquine; *P < 0.05 versus Ulk1-cKO, control, and no chloroquine; ‡P < 0.05 versus Ulk1-cKO, starvation, and no chloroquine (paired Student’s t test). (C and D) Lysosomal degradation of mitochondria was examined in the hearts of Mito-Keima–Tg mice during starvation. The bright signal corresponding to a high 560/440-nm ratio shows lysosomal localization of Mito-Keima protein, indicating mitophagy. (C) Representative images are shown. Scale bars: 50 μm (top); original magnification, ×3 (enlarged insets, bottom). (D) Summary of signal area/cell area ratio (n = 3 per group). #P < 0.05 versus WT and control; †P < 0.01 versus WT and starvation; *P < 0.01 versus Atg7-cKO and control; §P < 0.05 versus Atg7-cKO and starvation (Tukey-Kramer’s test). CQ, chloroquine; Ctr, control; Stv, starvation.