Heme-Mediated SPI-C Induction Promotes Monocyte Differentiation into Iron-Recycling Macrophages

“Macrophages in various tissues have distinct tissue-specific homeostatic roles, such as osteoclasts that regulate bone morphogenesis, alveolar macrophages that regulate pulmonary surfactant turnover, and splenic red pulp macrophages (RPM) that regulate erythrocyte degradation and iron recycling (Pollard, 2009; Gordon…”

“Macrophages in various tissues have distinct tissue-specific homeostatic roles, such as osteoclasts that regulate bone morphogenesis, alveolar macrophages that regulate pulmonary surfactant turnover, and splenic red pulp macrophages (RPM) that regulate erythrocyte degradation and iron recycling (Pollard, 2009; Gordon…”

“Recent studies have questioned the monocyte origin of macrophages, instead suggesting that most tissue-resident macrophages are maintained by local proliferation (Schulz et al., 2012a; Hashimoto et al., 2013).”

“Agonist-mediated activation of the nuclear receptors NR1D1, PPARγ, LXRα, and RXRα (Heng and Painter, 2008), which are each highly expressed in RPM, also failed to induce SPIC-EGFP (Figure S3B–S3D).”

“RPM actively accrue heme via erythrophagocytosis, CD163 receptor-mediated uptake of circulating hemoglobin-haptoglobin complexes, and CD91 receptor-mediated uptake of circulating heme-hemopexin complexes (Hvidberg et al., 2005; Kristiansen et al., 2001; Bratosin et al., 1998).”

“These tissue-resident macrophages are thought to be maintained by the differentiation of circulating monocytes and local proliferation (Landsman and Jung, 2007; Jenkins et al., 2011; Hume, 2008).”

“Macrophages in various tissues have distinct tissue-specific homeostatic roles, such as osteoclasts that regulate bone morphogenesis, alveolar macrophages that regulate pulmonary surfactant turnover, and splenic red pulp macrophages (RPM) that regulate erythrocyte degradation and iron recycling (Pollard, 2009; Gordon…”

“Macrophages in various tissues have distinct tissue-specific homeostatic roles, such as osteoclasts that regulate bone morphogenesis, alveolar macrophages that regulate pulmonary surfactant turnover, and splenic red pulp macrophages (RPM) that regulate erythrocyte degradation and iron recycling (Pollard, 2009; Gordon…”

“Ho1−/− mice were obtained (Poss and Tonegawa, 1997a) to generate Ho1−/− Spicigfp/igfp mice.”

“Spic-EGFP BMM were F4/80VCAM1CD11bCD169 CD68 (Figures 1C), which is similar to the reported surface marker profile of the previously described CD169 BMM (Chow et al., 2011; Chow et al., 2013).”

“Macrophages in various tissues have distinct tissue-specific homeostatic roles, such as osteoclasts that regulate bone morphogenesis, alveolar macrophages that regulate pulmonary surfactant turnover, and splenic red pulp macrophages (RPM) that regulate erythrocyte degradation and iron recycling (Pollard, 2009; Gordon…”

“6 3 10(11) erythrocytes are recycled by the macrophage-dependent pathway, supplying the vast majority of the daily iron requirement (Andrews and Schmidt, 2007; Ganz, 2012; Pantopoulos et al., 2012; Bratosin et al., 1998).”

“BMM and RPM were negative for the dendritic cellspecific marker Zbtb46 (Satpathy et al., 2012) and dendritic cells did not express SPICEGFP (Figure S2F).”

“BACH1 and the related factor BACH2 contain a BTB protein-protein interaction motif that mediates transcriptional repression and a basic leucine zipper (bZIP) domain thatmediates heterodimerizationwith other bZIP transcription factors (Oyake et al., 1996).”

“BACH1 has been shown to heterodimerize with MAFK to suppress Ho1 expression (Sun et al., 2002; Sun et al., 2004).”

“…and splenic red pulp macrophages (RPM) that regulate erythrocyte degradation and iron recycling (Pollard, 2009; Gordon and Taylor, 2005; Taylor et al., 2005; Murray and Wynn, 2011; Marks, Jr. and Lane, 1976; Cecchini et al., 1994; Shibata et al., 2001; Dranoff et al., 1994; Kohyama et al., 2009).”

“6 3 10(11) erythrocytes are recycled by the macrophage-dependent pathway, supplying the vast majority of the daily iron requirement (Andrews and Schmidt, 2007; Ganz, 2012; Pantopoulos et al., 2012; Bratosin et al., 1998).”

“Heme is known to inhibit BACH1 repressive activity (Ogawa et al., 2001).”

“Furthermore, Spic-EGFP BMM displayed a striking similarity to RPM (Kohyama et al., 2009; Hemmi et al., 2009), with both cells being CD11b MHCII VCAM1 TREML4 (Figures S2B–S2E).”

“RPM actively accrue heme via erythrophagocytosis, CD163 receptor-mediated uptake of circulating hemoglobin-haptoglobin complexes, and CD91 receptor-mediated uptake of circulating heme-hemopexin complexes (Hvidberg et al., 2005; Kristiansen et al., 2001; Bratosin et al., 1998).”

“Additionally, induction of intravascular hemo- lysis by phenylhydrazine (PDZ) (Itano et al., 1975; Chow et al., 2013) recapitulated this phenomenon (Figures 3C and S5B).”

“…moiety of hemoglobin inside erythrocytes, and each day about 3.6 × 1011 erythrocytes are recycled by the aforementioned macrophagedependent pathway, supplying the vast majority of the daily iron requirement (Andrews and Schmidt, 2007; Ganz, 2012; Pantopoulos et al., 2012; Bratosin et al., 1998).”

“BACH1 has been shown to heterodimerize with MAFK to suppress Ho1 expression (Sun et al., 2002; Sun et al., 2004).”

“The four carboxy-terminal CP motifs are thought to be particularly important for heme-BACH1 interaction and we mutated these four CP to Alanine-Proline (AP) in order to disrupt heme binding (Figure 6F, top) (Zenke-Kawasaki et al., 2007).”

“Notably, high levels of HO1 expression, similar to that in RPM, have been observed in macrophages located in human atherosclerotic plaques (Boyle et al., 2009).”

“RPM, and to some extent bone marrow macrophages (BMM) and liver macrophages, phagocytose senescent or damaged erythrocytes to degrade heme and release the hemeassociated iron (Ganz, 2012; Beaumont and Delaby, 2009).”

“The enzyme HO1 converts heme to biliverdin releasing the heme-associated iron while the enzyme biliverdin reductase (BLVR) converts biliverdin to bilirubin (Beaumont and Delaby, 2009).”

“The microRNA miR-155 has been shown to target Bach1 (Yin et al., 2008).”

“These tissue-resident macrophages are thought to be maintained by the differentiation of circulating monocytes and local proliferation (Landsman and Jung, 2007; Jenkins et al., 2011; Hume, 2008).”

“These tissue-resident macrophages are thought to be maintained by the differentiation of circulating monocytes and local proliferation (Landsman and Jung, 2007; Jenkins et al., 2011; Hume, 2008).”

“Notably, some of the heme-induced genes, such as Ho1, Gclm, Me1, and Slc7a11 were targets of the transcriptional repressor BTB and CNC homology 1 (Bach1) (Figures 5A and 5B) (Warnatz et al., 2011).”

“Heme induced the expression of Ho1 and Blvrb as well as Slc40a1, which encodes the mammalian iron exporter (Figure 5A), in agreement with previous reports (Delaby et al., 2008).”

“Phagocytosis of senescent erythrocytes is the major source of heme in RPM and mouse erythrocytes have a lifespan of about 40 days (Van Putten, 1958).”

“Heme has been suggested to induce polyubiquitination and proteasome-dependent degradation of BACH1 (Zenke-Kawasaki et al., 2007; Tan et al., 2013).”

“Liver macrophages are also known to engulf damaged erythrocytes (Beaumont and Delaby, 2009).”

“Additionally, induction of intravascular hemolysis by phenylhydrazine (PDZ) (Itano et al., 1975; Chow et al., 2013) recapitulated this phenomenon (Figures 3C and S5B).”

“Furthermore, Spic-EGFP BMM displayed a striking similarity to RPM (Kohyama et al., 2009; Hemmi et al., 2009), with both cells being CD11b MHCII VCAM1 TREML4 (Figures S2B–S2E).”

“Results Spic is required for the development of F4/80hi macrophages in the spleen and bone marrow Spic is a member of the Spi subfamily of ETS transcription factors and is required for the development of RPM (Bemark et al., 1999; Carlsson et al., 2002; Kohyama et al., 2009).”

“Given the proficiency of RPM and BMM in erythrophagocytosis, these cells experience significant increases in heme following erythrocyte damage in pathological conditions such as autoimmune hemolytic anemia, drug or toxin induced hemolysis, and sickle cell disease (Guillaud et al., 2012).”

“Indeed, excess intracellular heme is toxic to macrophages even with intact Ho1 (Cambos and Scorza, 2011).”

“Results Spic is required for the development of F4/80hi macrophages in the spleen and bone marrow Spic is a member of the Spi subfamily of ETS transcription factors and is required for the development of RPM (Bemark et al., 1999; Carlsson et al., 2002; Kohyama et al., 2009).”

“Recently, a subset of tissue-resident macrophages have been shown to arise from cells in the primitive ectoderm of the yolk sac without a monocytic intermediate (Schulz et al., 2012a).”

“Heme has been shown to induce Spi-c, a transcription factor (TF) important for red pulp macrophage development (Haldar et al., 2014; Kohyama et al., 2009).”

“Erythrophagocytic macrophages, including red pulp macrophages and Kupffer cells, mainly populated the spleen and liver, as expected, and shared high expression of CD5L, SCL40A1 and the transcription factor SPIC (32).”