129 Stimulating the Cholinergic Anti-inflammatory Pathway Alters Inflammatory Cell Mobilization after Burn Injury

Abstract Introduction Severe burn injury causes a systemic inflammatory response (SIRS) that is characterized by mobilization of inflammatory cells into the circulation and is associated with distant organ injury that can lead to significant morbidity and mortality. The cholinergic anti-inflammatory pathway, mediated by the vagus nerve, regulates the anti-inflammatory response to injury and infection. We have previously shown in models of burn injury that stimulating the vagus nerve may be a potential therapy aimed at limiting SIRS. Here, we hypothesized that stimulating the vagus nerve (VNS) would limit the SIRS response by altering the mobilization and trafficking of inflammatory cells after burn injury. Methods Wild type 10–12-week-old C57BL/6 mice were injured with a 30% total body surface area steam burn. A separate cohort of animals was treated with electrical stimulation of the cervical vagus nerve for 10 minutes immediately post-burn. Bone marrow, blood and lung tissue were collected 24 hours after burn injury. Flow cytometry of bone marrow was performed to measure Lineage- c-kit± Sca-1+ (LSK) hematopoietic stem cells (HSC), then further analyzed to quantify changes in Long-term (LT) HSC, short-term (ST) HSC, and Multipotential Progenitor (MPP) compartments. Bone marrow, blood and perfused lung tissue were analyzed by flow cytometry using a panel of myeloid cell markers. Results Severe burn injury decreased bone marrow LSK expression by 50% compared to sham, with LT-HSC and MPP expression decreasing to a greater degree than ST-HSCs. VNS did not alter burn-induced changes in any bone marrow HSC cell type. Burn injury was associated with increased mobilization of CD45+CD11b+ monocytes and CD11b+Ly6Chi inflammatory monocytes into the peripheral blood and lung, while increased CD11b+Ly6Clo patrolling monocytes and Gr1+Ly6C- neutrophils was seen in the lung only. VNS significantly prevented the burn-induced increase in CD45+ inflammatory cells, CD11b+Ly6Clo patrolling monocytes and Gr1+Ly6C- neutrophils in the lung (see Figure), reducing their expression to sham levels, despite only modest changes to myeloid cell expression in the blood. Conclusions VNS attenuates myeloid cell cell trafficking to the lung after severe burn injury despite having no effect on emergency myelopoiesis in the bone marrow. Further studies are needed to define the mechanism by which the cholinergic anti-inflammatory pathway attenuates the SIRS response to burn.

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844 The alpha-7 Nicotinic Acetylcholine Receptor Mediates a Uniquely Human Response to Burn Injury

Journal of Burn Care & Research ◽

10.1093/jbcr/iraa024.416 ◽

2020 ◽

Vol 41 (Supplement_1) ◽

pp. S261-S261

Author(s):

Todd W Costantini ◽

Elliot C Williams ◽

Olga Cohen ◽

Brian P Eliceiri ◽

Andrew Baird

Keyword(s):

Bone Marrow ◽

Burn Injury ◽

Myeloid Cell ◽

Human Response ◽

Severe Burn ◽

Nicotinic Acetylcholine ◽

Hematopoietic Stem ◽

Alpha 7 ◽

Cell Mobilization ◽

Severe Burn Injury

Abstract Introduction CHRFAM7A is a uniquely human gene that is a dominant negative inhibitor of the alpha-7 nicotinic acetylcholine receptor (a7nAchR). The relative balance of CHRFAM7A and a7nAchR expression may play an important role in mediating the human immune response to injury. We have previously shown that CHRFAM7A expression increased the hematopoietic stem cell reservoir in bone marrow and altered emergency myelopoiesis after injury. Here, we hypothesized that loss of the a7nAchR would produce a phenotype similar to CHRFAM7A overexpression, with an increased bone marrow reservoir of stem cells that would modulate myeloid cell mobilization after burn injury. Methods a7nAchR knockout (KO) mice (CHRNA7-/-) underwent 30% TBSA steam burn and were compared to age- and sex-matched wild-type mice. Bone marrow and blood were harvested 24 hours following burn injury for flow cytometry analysis. To measure bone marrow hematopoietic stem cells (HSC) we used flow cytometry to measure Lin−Sca1+c-Kit+ (LSK) cell expression. Bone marrow short term (ST) and long term (LT) HSCs were identified with CD48 and CD150. Immune cells were identified with myeloid markers including CD45, CD11b, Gr1, Ly6C, and Ly6G. Results a7nAchR KO mice have an increased bone marrow reservoir of LSK HSCs compared to WT. While bone marrow expression of ST-HSC and LT-HSC decreased after severe burn injury in WT mice, a7nAchR KO prevented the burn-induced depletion of ST-HSC and LT-HSC leaving a bone marrow HSC reservoir similar to sham. a7nAchR KO attenuated burn-induced mobilization of CD11b+ monocytes and CD11b+Ly6CHi inflammatory monocytes into the systemic circulation compared to WT. Conclusions Loss of the a7nAchR increases myeloid cell mobilization into the circulation after severe burn injury. There is significant variability in CHRFAM7A expression between individuals, suggesting that the relative balance of CHRFAM7A and a7nAchR expression may alter the host inflammatory response and influence human resilience after injury. Applicability of Research to Practice Understanding the factors that mediate the human response to burn injury could give important insights into variability in the inflammatory response between individuals and lead to therapeutics targeting the uniquely human response to burn injury.

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