BNIP3- and BNIP3L-Mediated Mitophagy Promotes the Generation of Natural Killer Cell Memory

Natural killer (NK) cells are innate lymphocytes that possess traits of adaptive immunity, such as clonal expansion, contraction, and generation of long-lived "memory" cells, processes poorly understood at the molecular level. Here, we found that as proliferating NK cells accumulated dysfunctional mitochondria during viral infection, a protective mitophagy pathway was induced during the contraction phase to promote their survival in a reactive oxygen species (ROS)-dependent manner. Inhibition of mechanistic target of rapamycin (mTOR) or activation of AMP-activated protein kinase (AMPK) during the contraction-to-memory phase transition of the antiviral response increased autophagic activity and enhanced memory NK cell numbers through an Atg3-dependent mechanism. Furthermore, we demonstrated a temporally regulated role for mitophagy-inducing proteins BCL2/adenovirus E1B 19-kDa interacting protein 3 (BNIP3) and BNIP3-like (BNIP3L) in the generation of robust NK cell memory. Thus, our study reveals the functional importance of mitophagy during the dynamic response of these cytolytic innate lymphocytes.