Phagocytosis is crucial for normal tissue development as well as homeostasis within mature tissues. Billions of cells in the human body undergo diverse forms of programmed cell death including apoptosis, necroptosis, pyroptosis, and ferroptosis (Nagata, 2018; Sapar and Han, 2019; Lewandowski et al., 2022). The cell corpses derived from the cell death are promptly cleared through phagocytosis by fibroblasts, epithelial cells, and endothelial cells (Achberger et al., 2019; Kaarniranta et al., 2022). Phagocytes have traditionally been classified into three broad categories: professional, non-professional, and specialized, which although differing in specific tasks share commonalities. For instance, they can all distinguish their substrates for removal, bear the stress of absorbing massive biomass, and finally break down and process the ingested materials (Lakkaraju et al., 2020; Zihni et al., 2022).

Failed professional phagocytosis can lead to inflammatory states caused by the subsequent release of cell contents. The process is implicated in autoimmune diseases such as systemic lupus erythematosus, atherosclerosis, colitis, allergic airway inflammation, and experimental autoimmune encephalitis (Go et al., 2020; Lappalainen et al., 2022; Lewandowski et al., 2022; Tajbakhsh et al., 2022). Furthermore, deficient specialized phagocytosis in certain tissues and organs such as Sertoli cells (SCs) of the testes and the retinal pigment epithelial (RPE) cells of the retina disrupts homoeostasis and leads to degenerative diseases (Penberthy et al., 2018; Notomi et al., 2019; Du and Palczewski, 2022). Impaired SCs phagocytosis can lead to the accumulation of apoptotic germ cells in the seminiferous tubules and might cause infertility. RPEs, another type of specialized phagocyte, prune photoreceptor outer segments (POS) to remove the photo-oxidative waste and sustain normal retinal function (Finnemann et al., 1997; Finnemann et al., 2002; Smith et al., 2003; Yang et al., 2021). The phagocytic ability of RPEs decreases with aging, and is linked to severe retinal degeneration phenotypes such as retinitis pigmentosa and age-related macular degeneration (Green et al., 1985; Kurz et al., 2009; Bertolotti et al., 2014; Molday et al., 2022). There are currently no clinical strategies to effectively treat these degenerative diseases, making the investigation of the underlying mechanisms and pathways related to phagocytosis crucial for the discovery of new therapeutic targets.

Like phosphorylation, O-GlcNAcylation is a reversible post-translational modification that regulates fundamental cellular processes (Wang et al., 2015; Fehl and Hanover, 2022; Ma et al., 2022; Shi et al., 2022; Wu et al., 2022). Unlike other glycosylations occurring outside the cell membrane, O-GlcNAcylation occurs inside the cells and involves the attachment of a single O-linked N-acetylglucosamine (O-GlcNAc) moiety to Ser or Thr residues. As Ser and Thr residues are also phosphorylation sites, O-GlcNAcylation shares many similarities with phosphorylation (Yang and Qian, 2017; Liu et al., 2020; Chatham et al., 2021). However, compared with the many kinases and phosphatases involved in phosphorylation events, only two enzymes regulate the reversible O-GlcNAcylation: O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), which adds or removes the GlcNAc moiety from proteins, respectively. As the nutrient and stress sensor of outside signals, O-GlcNAcylation is highly dynamic and can rapidly respond to almost all types of environmental or physiological stimuli (Hardiville and Hart, 2014; Bond and Hanover, 2015; Wu et al., 2017; Shi et al., 2022). Disruption of O-GlcNAcylation homeostasis has been implicated in the pathogenesis of many diseases including diabetes, neoplasia, and neurodegeneration (Yu et al., 2019; Saha et al., 2021; Yu et al., 2022). However, whether O-GlcNAcylation also participates in the regulation of phagocytosis and related diseases remains elusive. Here we demonstrate that O-GlcNAcylation regulates phagocytosis by modifying Ezrin. O-GlcNAcylation is critical for the localization of Ezrin to the cortex and is thus important in connecting the cytoskeletal structure to the cell membrane for efficient phagocytosis.