COMMD10 is required for homeostatic maintenance of Kupffer cells

Most tissue-resident macrophages are established prenatally and self-maintain independently of bone marrow (BM) monocytes. Instructed by local cues, these cells adopt unique transcriptional modules that impart tissue-specific functional identity (Varol et al., 2015). In the liver, Kupffer cells (KCs) dominate the homeostatic macrophage pool. They reside in the sinusoidal vessels and in the space of Disse, interacting with hepatic stellate cells (HSC) and hepatocytes (Bonnardel et al., 2019), where they act as sentinels and perform specialized accessory functions involving iron and lipid metabolism (Scott and Guilliams, 2018). Yet, the molecular cues governing KC differentiation and maintanence remain largly elusive. Embryonic lethality of COMMD10 deficiency has hampered the study of its function. Yet, utilizing conditional COMMD10 knockout mice we recently uncovered a role for COMMD10 in supporting phagolysosomal biogenesis and maturation in KCs and BM-derived macrophages infected with Staphylococcus aureus (Ben Shlomo et al., 2019). Here we show that COMMD10-deficient KCs adopt liver-specific identity. Strikingly, COMMD10-deficiency in KCs and in other tissue resident macrophages impedes their homeostatic survival, leading to their continuous replacement by Ly6Chi monocytes. Transcriptional analysis of COMMD10-deficiet KCs reveales a notable reduction in genes encoding for translation initiation- and ribosomal complex proteins, for ubiquitin and the proteasome protein complex, and for key proteins of the mitochondrial respiration chain. These transcriptional alterations allude to protein stress and mitochondrial dysfunction, and hint at the reason of their premature death. Overall design: To target COMMD10 deficiency to KCs we crossed Clec4f+/cre mice (Scott et al., 2018) with Commd10fl/fl mice (Mouhadeb et al., 2018) (Clec4f?Commd10, C57BL/6 background). Isolation of hepatic non-parenchymal cells was performed as previously described (Zigmond et al., 2014). KCs were defined as CD45+CD11bloF4/80+Ly6G-Ly6C- cells, also expressing the KC markers TIM4, VSIG4, CLEC2 and CLEC4F. KCs were sorted to high purity from steady state livers of 8 weeks old male Clec4f?Commd10 and their littermate Commd10fl/fl controls, using the the BD FACSAriaTM FUSION cell sorter (BD Bioscience). A bulk adaptation of the MARS-Seq protocol (Jaitin et al., 2014; Keren-Shaul et al., 2019) was used to generate RNA-Seq libraries for expression profiling.