BNIP3 Interacting with LC3 Triggers Excessive Mitophagy in Delayed Neuronal Death in Stroke

<jats:title>Summary</jats:title><jats:sec><jats:title>Introduction</jats:title><jats:p>A basal level of mitophagy is essential in mitochondrial quality control in physiological conditions, while excessive mitophagy contributes to cell death in a number of diseases including ischemic stroke. Signals regulating this process remain unknown. <jats:styled-content style="fixed-case">BNIP</jats:styled-content>3, a pro‐apoptotic <jats:styled-content style="fixed-case">BH</jats:styled-content>3‐only protein, has been implicated as a regulator of mitophagy.</jats:p></jats:sec><jats:sec><jats:title>Aims</jats:title><jats:p>Both <jats:italic>in vivo</jats:italic> and <jats:italic>in vitro</jats:italic> models of stroke, as well as <jats:styled-content style="fixed-case">BNIP</jats:styled-content>3 wild‐type and knock out mice were used in this study.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>We show that <jats:styled-content style="fixed-case">BNIP</jats:styled-content>3 and its homologue <jats:styled-content style="fixed-case">BNIP</jats:styled-content>3L (<jats:styled-content style="fixed-case">NIX</jats:styled-content>) are highly expressed in a “delayed” manner and contribute to delayed neuronal loss following stroke. Deficiency in <jats:styled-content style="fixed-case">BNIP</jats:styled-content>3 significantly decreases both neuronal mitophagy and apoptosis but increases nonselective autophagy following ischemic/hypoxic insults. The mitochondria‐localized <jats:styled-content style="fixed-case">BNIP</jats:styled-content>3 interacts with the autophagosome‐localized <jats:styled-content style="fixed-case">LC</jats:styled-content>3, suggesting that <jats:styled-content style="fixed-case">BNIP</jats:styled-content>3, similar to <jats:styled-content style="fixed-case">NIX</jats:styled-content>, functions as a <jats:styled-content style="fixed-case">LC</jats:styled-content>3‐binding receptor on mitochondria. Although <jats:styled-content style="fixed-case">NIX</jats:styled-content> expression is upregulated when <jats:styled-content style="fixed-case">BNIP</jats:styled-content>3 is silenced, up‐regulation of <jats:styled-content style="fixed-case">NIX</jats:styled-content> cannot functionally compensate for the loss of <jats:styled-content style="fixed-case">BNIP</jats:styled-content>3 in activating excessive mitophagy.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p><jats:styled-content style="fixed-case">NIX</jats:styled-content> primarily regulates basal level of mitophagy in physiological conditions, whereas <jats:styled-content style="fixed-case">BNIP</jats:styled-content>3 exclusively activates excessive mitophagy leading to cell death.</jats:p></jats:sec>