Map3k8 controls granulocyte colony-stimulating factor production and neutrophil precursor proliferation in lipopolysaccharide-induced emergency granulopoiesis

Abstract

Map3k8 has been proposed as a useful target for the treatment of inflammatory diseases. We show here that during lipopolysaccharide-induced emergency granulopoiesis, Map3k8 deficiency strongly impairs the increase in circulating mature (Ly6GhighCD11b+) and immature (Ly6GlowCD11b+) neutrophils. After chimaeric bone marrow (BM) transplantation into recipient Map3k8−/− mice, lipopolysaccharide treatment did not increase circulating Ly6GhighCD11b+ cells and strongly decreased circulating Ly6GlowCD11b+ cells. Lipopolysaccharide-treated Map3k8−/− mice showed decreased production of granulocyte colony-stimulating factor (G-CSF), a key factor in neutrophil expansion, and a Map3k8 inhibitor blocked lipopolysaccharide-mediated G-CSF expression in endothelial cell lines. Ly6GlowCD11b+ BM cells from lipopolysaccharide-treated Map3k8−/− mice displayed impaired expression of CCAAT-enhancer-binding protein β, which depends on G-CSF for expression and is crucial for cell cycle acceleration in this life-threatening condition. Accordingly, lipopolysaccharide-treated Map3k8−/− mice showed decreased Ly6GlowCD11b+ BM cell proliferation, as evidenced by a decrease in the percentage of the most immature precursors, which have the highest proliferation capacity among this cell population. Thus, Map3k8 expression by non-haematopoietic tissue is required for lipopolysaccharide-induced emergency granulopoiesis. The novel observation that inhibition of Map3k8 activity decreases neutrophilia during life-threatening systemic infection suggests a possible risk in the proposed use of Map3k8 blockade as an anti-inflammatory therapy.

Chronic activation of endothelial MAPK disrupts hematopoiesis via NFKB dependent inflammatory stress reversible by SCGF

“…2f), indicating that endothelial MAPK activation leads to an inflammatory stress response. It is well established that NF-κB signaling plays pivotal roles in driving inflammatory responses, and recent reports indicate that endothelial MAPK activation can lead to inflammation via downstream activation of canonical NF-κB signaling 28,29,31,32 . To verify this possibility, we performed immunoblot analysis on BM-derived ECs (BMECs) of CDH5-MAPK mice which confirmed an increase in MEK1DD driven ERK1/2 phosphorylation (Fig.…”

“…Prior work from our group has shown that suppression of NF-κB signaling within ECs enhances steady-state hematopoiesis as well as regeneration following myelosuppression, in part by decreasing proinflammatory cytokines 21 . Recent reports suggest that endothelial MAPK likely plays an essential role during inflammatory processes including LPS-induced granulopoiesis and chronic vascular inflammation-associated atherosclerosis 28,29 . Utilizing an ex vivo niche model system, we have previously demonstrated that endothelial MAPK activation drives myeloid-biased differentiation of co-cultured HSCs at the expense of their self-renewal, features that are suggestive of an inflammatory stress 15 .…”

Stress erythropoiesis in atherogenic mice

“…Infections and tissue damage processes that course with inflammation promote a biased BM hematopoiesis towards the myeloid cell lineage, in order to confront the immune distress 18 , 19 . Furthermore, erythroid precursors generated in the BM under these circumstances display a higher apoptosis rate, and their fully differentiated RBC present a lower half-life than normal 20 , 21 , 23 .…”

“…Blood, BM cells and splenocytes were collected as previously described 19 , 40 . The different cell samples (0.5–2 × 10 6 cells) were stained for the indicated surface markers (see Supplemental Table S2 online) for 20 min at room temperature and subsequently washed twice with buffer A.…”

“…Inflammation, by infection or tissue damage, can also generate stress erythropoiesis. In response to infections, the BM cell differentiation is rapidly biased towards the myeloid branch in detriment of erythropoiesis 18 , 19 along with increased levels of erythroblast apoptosis and the subsequent clearance of the apoptotic corpses (erythrophagocytosis) 20 – 23 . This decrease in the input of mature RBC generated in BM is compensated by splenic stress erythropoiesis (reviewed in 23 , 24 ).…”