Novel adaptation supports enhanced macrophage efferocytosis in limited-oxygen environments

Abstract

Apoptotic cell clearance (efferocytosis), a process essential for organismal homeostasis, is performed by phagocytes that inhabit a wide range of environments, including physiologic hypoxia. Here, we find macrophages, the predominant tissue-resident phagocyte, display enhanced efferocytosis under prolonged (chronic) physiological hypoxia, characterized by increased internalization and accelerated degradation of apoptotic cells. Analysis of mRNA and protein programs revealed that chronic physiological hypoxia induces two distinct but complimentary states in macrophages. The first, primed state consists of concomitant induction of transcriptional and translational programs broadly associated with metabolism in apoptotic cell-naive macrophages that persist during efferocytosis. The second, poised state consists of transcription, but not translation, of phagocyte function programs in apoptotic cell-naive macrophages that are subsequently translated during efferocytosis. Importantly, we discovered that both states are necessary for enhanced continual efferocytosis. Mechanistically, we find that one such primed state consists of the efficient flux of glucose into a noncanonical pentose phosphate pathway (PPP) loop, whereby PPP-derived intermediates cycle back through the PPP to enhance production of NADPH. Furthermore, we found that PPP-derived NADPH directly supports enhanced continual efferocytosis under chronic physiological hypoxia via its role in phagolysosomal maturation and maintenance of cellular redox homeostasis. Thus, macrophages residing under chronic physiological hypoxia adopt states that both support cell fitness and ensure ability to perform essential homeostatic functions rapidly and safely. Highlights- Macrophages residing in chronic physiological hypoxia have enhanced apoptotic cell uptake and degradation - Chronic physiological hypoxia induces both primed and poised states in macrophages - Both primed and poised state programs directly support enhanced continual efferocytosis - A noncanonical PPP loop, a unique primed state, directly supports enhanced efferocytosis and maintains redox homeostasis