Bacterial Lipopolysaccharides Suppress Erythroblastic Islands and Erythropoiesis in the Bone Marrow in an Extrinsic and G- CSF-, IL-1-, and TNF-Independent Manner

Abstract

Anemia of inflammation (AI) is the second most prevalent anemia after iron deficiency anemia and results in persistent low blood erythrocytes and hemoglobin, fatigue, weakness, and early death. Anemia of inflammation is common in people with chronic inflammation, chronic infections, or sepsis. Although several studies have reported the effect of inflammation on stress erythropoiesis and iron homeostasis, the mechanisms by which inflammation suppresses erythropoiesis in the bone marrow (BM), where differentiation and maturation of erythroid cells from hematopoietic stem cells (HSCs) occurs, have not been extensively studied. Here we show that in a mouse model of acute sepsis, bacterial lipopolysaccharides (LPS) suppress medullary erythroblastic islands (EBIs) and erythropoiesis in a TLR-4- and MyD88-dependent manner with concomitant mobilization of HSCs. LPS suppressive effect on erythropoiesis is indirect as erythroid progenitors and erythroblasts do not express TLR-4 whereas EBI macrophages do. Using cytokine receptor gene knock-out mice LPS-induced mobilization of HSCs is G-CSF-dependent whereas LPS-induced suppression of medullary erythropoiesis does not require G- CSF-, IL- 1-, or TNF-mediated signaling. Therefore suppression of medullary erythropoiesis and mobilization of HSCs in response to LPS are mechanistically distinct. Our findings also suggest that EBI macrophages in the BM may sense innate immune stimuli in response to acute inflammation or infections to rapidly convert to a pro-inflammatory function at the expense of their erythropoietic function.

Fragmentation of macrophages during isolation confounds analysis of single cell preparations from mouse hematopoietic tissues

“…Based upon the preferential binding of CD169 + macrophage remnants to granulocyte populations in BM we tested and confirmed a role for CD169 in control of granulocyte egress into blood during G-CSF-induced granulopoiesis. The preferential binding of F4/80 + CD169macrophage remnants to erythroblasts is more difficult to reconcile with previous evidence (Bisht et al, 2020;Chow et al, 2013;Seu et al, 2017;Tay et al, 2020) but is consistent with in vitro experiments demonstrating that murine CD169 does not bind murine erythroblasts (Kelm et al, 1994).…”

“…Nonetheless, we showed these ex vivo analyses can still provide valuable and robust biological information. Coupling conventional flow cytometry with in situ approaches (Kaur et al, 2018) or bespoke isolation strategies that maintain multicellular aggregates (Bisht et al, 2020;Seu et al, 2017;Tay et al, 2020;Yeo et al, 2019;Yeo et al, 2016) strengthens data interpretation, and confirms some instances of unconventional co-expression of immune markers (Abtin et al, 2014;Yates et al, 2013).…”

Fragmentation of tissue-resident macrophages during isolation confounds analysis of single-cell preparations from mouse hematopoietic tissues

“…Nonetheless, we showed that these ex vivo analyses can still provide valuable and robust biological information. Coupling conventional flow cytometry with in situ approaches (Kaur et al, 2018) or bespoke isolation strategies that maintain multicellular aggregates (Bisht et al, 2020;Seu et al, 2017;Tay et al, 2020;Yeo et al, 2016Yeo et al, , 2019 strengthens data interpretation and confirms some myeloid progenitor and monocyte populations. GEO: GSE83222 (red) and GEO: GSE127980 (green) were comprised of positively selected macrophage populations.…”

Inflammation and Aging of Hematopoietic Stem Cells in Their Niche

“…Similar phenotypes emerge during experimental spondyloarthritis in which mice developed non-resolving inflammation [75]. In addition, consecutive injections of LPS dramatically suppressed erythropoiesis [76]. Most importantly, increasing evidence demonstrates that multiple pro-inflammatory cytokines, including IL-1β [3,4], TNF-α [42], IL-6 [4] and TGFβ1 [2], are present at increased levels in aged BM (Table 2).…”