Burn injury dampens erythroid cell production through reprioritizing bone marrow hematopoietic response

IL-1/MyD88-Dependent G-CSF and IL-6 Secretion Mediates Postburn Anemia

The anemia of critical illness (ACI) is a nearly universal pathophysiological consequence of burn injury and a primary reason burn patients require massive quantities of transfused blood. Inflammatory processes are expected to drive postburn ACI and prevent meaningful erythropoietic stimulation through iron or erythropoietin supplementation, but to this day no specific inflammatory pathways have been identified as a critical mechanism. In this study, we examined whether secretion of G-CSF and IL-6 mediates distinct features of postburn ACI and interrogated inflammatory mechanisms that could be responsible for their secretion. Our analysis of mouse and human skin samples identified the burn wound as a primary source of G-CSF and IL-6 secretion. We show that G-CSF and IL-6 are secreted independently through an IL-1/MyD88-dependent mechanism, and we ruled out TLR2 and TLR4 as critical receptors. Our results indicate that IL-1/MyD88-dependent G-CSF secretion plays a key role in impairing medullary erythropoiesis and IL-6 secretion plays a key role in limiting the access of erythroid cells to iron. Importantly, we found that IL-1α/β neutralizing Abs broadly attenuated features of postburn ACI that could be attributed to G-CSF or IL-6 secretion and rescued deficits of circulating RBC counts, hemoglobin, and hematocrit caused by burn injury. We conclude that wound-based IL-1/MyD88 signaling mediates postburn ACI through induction of G-CSF and IL-6 secretion.

Murine scald models characterize the role of neutrophils and neutrophil extracellular traps in severe burns

Introduction

Severe burns cause unique pathophysiological alterations especially on the immune system. A murine scald model was optimized as a basis for the understanding of immunological reactions in response to heat induced injury. The understanding of the roles of neutrophil extracellular traps (NETs) and DNases will support the development of new surgical or pharmacological strategies for the therapy of severe burns.

Methods

We studied C57BL/6 mice (n=30) and employed four scalding protocols with varying exposure times to hot water. An additional scald group with a shorter observational time was generated to reduce mortality and study the very early phase of pathophysiology. At 24h or 72h, blood was drawn and tissue (wound, liver, lung, spleen) was analyzed for the presence of NETs, oxidative stress, apoptosis, bacterial translocation, and extracellular matrix re-organization. In addition, we analyzed the transcriptome from lung and liver tissues.

Results

Exposure to hot water for 7s led to significant systemic and local effects and caused considerable late mortality. Therefore, we used an observation time of 24h in this groups. To study later phases of burns (72h) an exposure time of 6s is optimal. Both conditions led to significant disorganization of collagen, increased oxidative stress, NET formation (by immunodetection of H3cit, NE, MPO), apoptosis (cC3) and alterations of the levels of DNase1 and DNase1L3. Transcriptome analysis revealed remarkable alterations in genes involved in acute phase signaling, cell cohesion, extracellular matrix organization, and immune response.

Conclusion

We identified two scald models that allow the analysis of early (24h) or late (72h) severe burn effects, thereby generating reproducible and standardized scald injuries. The study elucidated the important involvement of neutrophil activity and the role of NETs in burns. Extensive transcriptome analysis characterized the acute phase and tissue remodeling pathways involved in the process of healing and may serve as crucial basis for future in-depth studies.

M-CSF supports medullary erythropoiesis and erythroid iron demand following burn injury through its activity on homeostatic iron recycling

M-CSF receptor signaling supports the development and survival of mononuclear phagocytes and is thought to play a role in post burn anemia by promoting myeloid lineage bias. We found M-CSF secretion was increased in burn patients and a murine model of post burn ACI, so we neutralized M-CSF in ACI mice to determine if erythropoiesis was improved. Instead, M-CSF blockade further impaired erythropoiesis and erythroid cells access to iron. M-CSF blockade enhanced inflammatory cytokine secretion, further increased systemic neutrophil counts, and led to tissue iron sequestration that was dependent, in part, on augmented IL-6 secretion which induced hepcidin. Deleterious effects of post burn M-CSF blockade were associated with arrest of an iron recycling gene expression signature in the liver and spleen that included Spi-C transcription factor and heme oxygenase-1, which promote heme metabolism and confer a non-inflammatory tone in macrophages. Hepatic induction of these factors in ACI mice was consistent with a recovery of ferroportin gene expression and reflected an M-CSF dependent expansion and differentiation of Spi-C+ monocytes into Kupffer cells. Together, this data indicates M-CSF secretion supports a homeostatic iron recycling program that plays a key role in the maintenance of erythroid cells access to iron following burn injury.

The Hematopoietic Stem/Progenitor Cell Response to Hemorrhage, Injury, and Sepsis: A Review of Pathophysiology

ABSTRACT

Hematopoietic stem/progenitor cells (HSPC) have both unique and common responses following hemorrhage, injury, and sepsis. HSPCs from different lineages have a distinctive response to these "stress" signals. Inflammation, via the production of inflammatory factors, including cytokines, hormones, and interferons, has been demonstrated to impact the differentiation and function of HSPCs. In response to injury, hemorrhagic shock, and sepsis, cellular phenotypic changes and altered function occur, demonstrating the rapid response and potential adaptability of bone marrow hematopoietic cells. In this review, we summarize the pathophysiology of emergency myelopoiesis and the role of myeloid-derived suppressor cells, impaired erythropoiesis, as well as the mobilization of HSPCs from the bone marrow. Finally, we discuss potential therapeutic options to optimize HSPC function after severe trauma or infection.

Pediatric Burn Survivors Have Long-Term Immune Dysfunction With Diminished Vaccine Response

Epidemiological studies have demonstrated that survivors of acute burn trauma are at long-term increased risk of developing a range of morbidities. The mechanisms underlying this increased risk remain unknown. This study aimed to determine whether burn injury leads to sustained immune dysfunction that may underpin long-term morbidity. Plasma and peripheral blood mononuclear cells were collected from 36 pediatric burn survivors >3 years after a non-severe burn injury (<10% total body surface area) and from age/sex-matched non-injured controls. Circulating cytokine and vaccine antibody levels were assessed using multiplex immunoassays and cell profiles compared using a panel of 40 metal-conjugated antibodies and mass cytometry. TNF-α (1.31-fold change from controls), IL-2 (1.18-fold), IL-7 (1.63-fold), and IFN-γ (1.18-fold) were all significantly elevated in the burn cohort. Additionally, burn survivors demonstrated diminished antibody responses to the diphtheria, tetanus, and pertussis vaccine antigens. Comparisons between groups using unsupervised clustering identified differences in proportions of clusters within T-cells, B-cells and myeloid cells. Manual gating confirmed increased memory T-regulatory and central memory CD4+ T-cells, with altered expression of T-cell, B-cell, and dendritic cell markers. Conclusions: This study demonstrates a lasting change to the immune profile of pediatric burn survivors, and highlights the need for further research into post-burn immune suppression and regulation.

Increased risk of blood transfusion in patients with diabetes mellitus sustaining non-major burn injury

BACKGROUND

Due to the increased mortality and morbidity associated with blood transfusion, identifying modifiable predictors of transfusion are vital to prevent or minimise blood use. We hypothesised that burn patients with diabetes mellitus were more likely to be prescribed a transfusion. These patients tend to have increased age, number of comorbidities, infection risk and need for surgery which are all factors reported previously to be associated with blood use.

OBJECTIVE

To determine whether patients with diabetes mellitus who have sustained a burn ≤20% total body surface area (TBSA) are at higher risk of receiving red blood cell transfusion compared to those without diabetes mellitus.

METHOD

This was a retrospective cohort study including patients admitted to the major Burns Unit in Western Australia for management of a burn injury. Only the first hospital admission between May 2008 to February 2017 were included.

RESULTS

Among 2101 patients with burn injuries ≤20% TBSA, 48 (2.3%) received packed red blood cells and 169 (8.0%) had diabetes. There were 13 (7.7%) diabetic patients that were transfused versus 35 (1.8%) non-diabetic patients. Patients with diabetes were 5.2 (p = 0.034) times more likely to receive packed red blood cells after adjusting for percentage TBSA, haemoglobin at admission or prior to transfusion, number of surgeries, total comorbid burden and incidence of infection. As percentage TBSA increases, the probability of packed red blood cell transfusion increases at a higher rate in DM patients.

CONCLUSIONS

This study showed that diabetic patients with burn injuries ≤20% TBSA have a higher probability of receiving packed red blood cell transfusion compared to patients without diabetes. This effect was compounded in burns with higher percentage TBSA.

A Shift in Myeloid Cell Phenotype via Down Regulation of Siglec-1 in Island Macrophages of Bone Marrow Is Associated With Decreased Late Erythroblasts Seen in Anemia of Critical Illness

Burn injury has been shown to significantly dampen erythropoiesis in both burn patients and in murine models. Our previous findings elucidated the erythropoietin independent defects in red cell development stages involving erythroid progenitor production and late stage erythroblast enucleation processes. We hypothesized that macrophages (MØ) in erythroblast islands (EBI) could be yet another roadblock impeding erythropoiesis following burn injury. Here we highlight that the methodology to study EBI can be achieved with single cell suspensions using a simple technique such as flow cytometry, as obtaining the central erythroblast island macrophages (EBIMØs) of interest is a delicate process. We elucidated the requisite of EBIMØ from the erythroblast as well as the MØ perspective. In addition to the primary erythropoiesis organ, the bone marrow (BM), spleens were also examined for extra-medullary erythropoiesis. Femurs and spleens were harvested from adult mice (B₆D₂F₁) subjected to 15% total body surface area (TBSA) scald burn (B) or sham burn (S). Total bone marrow cells (TBM) and splenocytes were probed for total erythrons, early and late erythroblasts and EBIMØ by flow cytometry. There was only a marginal increase in the number of EBIMØ after burn, but, between the signatures of EBIMØ, Siglec-1 expression (MFI) was reduced by 40% in B with and a parallel 44% decrease in TBM erythrons in the BM. There were more (2.5-fold) EEBs and less LEBs (2.4-fold) per million TBM cells in B; with a corresponding decrease in Siglec-1 and Ly6G expressions in EBIMØ associated with EEB. Conversely, extra-medullary erythropoiesis was robust in spleens from B. Not only were the numbers of EBIMØs increased in B (p < 0.002), both EEBs and LEBs associated with EBIMØ were higher by 30 and 75%, respectively. Importantly, an increase in Siglec-1 and Vcam1 expressing F480⁺ splenic macrophages was observed after burn injury. Therefore, stagnant EEBs in the BM after burn injury could be due to low Siglec1 expressing EBIMØ, which perhaps impede their maturation into LEBs and reticulocytes. Repercussion of myeloid cell phenotype specific to BM after burn injury could plausibly account for a defective late stage RBC maturation resulting in anemia of critical illness.

Summary Sentence: Characterization of erythroblast island macrophages (EBIMØ) in the bone marrow and spleen at different stages of erythropoiesis after burn injury.

Uniquely human CHRFAM7A gene increases the hematopoietic stem cell reservoir in mice and amplifies their inflammatory response

The emergence of uniquely human genes during hominid speciation enabled numerous human-specific adaptations that presumably included changes in resilience to disease but potentially increased susceptibility as well. Here we show that the transgenic expression of one such gene, called CHRFAM7A, changes the mouse reservoir of hematopoietic stem cells in bone marrow and amplifies the mouse inflammatory response in a model of human systemic inflammatory response syndrome (SIRS). Because the CHRFAM7A gene is a dominant-negative inhibitor of ligand binding to α7 nicotinic acetylcholine receptor (α7nAChR), a neurotransmitter receptor implicated in immunity, inflammation, neurodegeneration, and cognitive function, the results underscore the importance of understanding the contribution of species-specific genes to human disease and the impact they may have on the fidelity of animal models for translational medicine.

A subset of genes in the human genome are uniquely human and not found in other species. One example is CHRFAM7A, a dominant-negative inhibitor of the antiinflammatory α7 nicotinic acetylcholine receptor (α7nAChR/CHRNA7) that is also a neurotransmitter receptor linked to cognitive function, mental health, and neurodegenerative disease. Here we show that CHRFAM7A blocks ligand binding to both mouse and human α7nAChR, and hypothesized that CHRFAM7A-transgenic mice would allow us to study its biological significance in a tractable animal model of human inflammatory disease, namely SIRS, the systemic inflammatory response syndrome that accompanies severe injury and sepsis. We found that CHRFAM7A increased the hematopoietic stem cell (HSC) reservoir in bone marrow and biased HSC differentiation to the monocyte lineage in vitro. We also observed that while the HSC reservoir was depleted in SIRS, HSCs were spared in CHRFAM7A-transgenic mice and that these mice also had increased immune cell mobilization, myeloid cell differentiation, and a shift to inflammatory monocytes from granulocytes in their inflamed lungs. Together, the findings point to a pathophysiological inflammatory consequence to the emergence of CHRFAM7A in the human genome. To this end, it is interesting to speculate that human genes like CHRFAM7A can account for discrepancies between the effectiveness of drugs like α7nAChR agonists in animal models and human clinical trials for inflammatory and neurodegenerative disease. The findings also support the hypothesis that uniquely human genes may be contributing to underrecognized human-specific differences in resiliency/susceptibility to complications of injury, infection, and inflammation, not to mention the onset of neurodegenerative disease.

A Randomized Controlled Trial: Regenerative Effects, Efficacy and Safety of Erythropoietin in Burn and Scalding Injuries

In adult’s burn injuries belong to the top 15 causes of injury. Annually more than a million patients receive specialized treatment. Improving burned patients’ outcomes is still a challenge. Effects of erythropoietin (EPO) are reported to be pro-angiogenic, pro-regenerative, anti-inflammatory, immunomodulatory and hypoxia/ischemia protective. Study objectives were to demonstrate cytoprotective and regenerative effects of EPO in burned patients in terms of improved wound healing, reduced morbidity and mortality. This was a prospective, placebo-controlled, randomized, double-blind trial. The trial was conducted in 13 specialized burn care centers in Germany. Adult Patients with 2b° or 3° burn injuries were included. Patients received state of the art burn care including obligatory split skin graft transplantation. Study medication was EPO or placebo every other day for 21 days. Between 12/08 and 06/14, 116 patients were randomized, 84 received study medication (EPO 45, Placebo 39). Primary endpoint analysis revealed inconclusive results, as only a minority of patients reached the primary endpoint [100% re-epithelialization: EPO: 23% (9/40); Placebo 30% (11/37)]. Several secondary endpoints such as SOFA score (morbidity), EPO level in blood and wound healing onset revealed clinical, and statistically significant results in favor of the EPO group. Adverse Events (AEs) and Severe Adverse Events (SAEs) were in expected ranges; AEs EPO: 80%, (36/45), Placebo: 77%, (30/39); SAEs EPO: 24%, (11/45), Placebo: 24%, (8/39). Out of 84 patients two died, one per group, thus mortality was lower than expected. Results (SOFA score) indicate a lower morbidity of the EPO group, suggesting pro-regenerative effects of EPO in burned patients. Higher EPO levels might influence the faster onset of re-epithelialization in the first 10 days of the treatment. Both effects could reveal new therapeutic options.

Clinical Trial Registration: ISRCT Number: ISRCTN95777824 and EudraCT Number: 2006-002886-38, Protocol Number: 0506.

Terminal Maturation of Orthochromatic Erythroblasts Is Impaired in Burn Patients

Mechanisms of erythropoietin (Epo)-resistant anemia in burn patients are poorly understood. We have recently found that administering a nonselective beta 1,2-adrenergic blocker propranolol (PR) was effective in reversing myelo-erythroid commitment through MafB regulation and increase megakaryocyte erythrocyte progenitors in burn patients' peripheral blood mononuclear cell (PBMC)-derived ex vivo culture system. Having known that Epo-dependent proliferation of early erythroblasts is intact after burn injury, here we inquired whether or not Epo-independent maturation stage of erythropoiesis is affected by burn injury and the relative role of PR on late-stage erythropoiesis. While majority of erythropoiesis occurs in the bone marrow, maturation into reticulocytes is crucial for their release into sinusoids to occupy the peripheral circulation for which enucleation is vital. peripheral blood mononuclear cells (PBMCs) from burn patients were extended beyond commitment and proliferation stages to late maturation stage in ex vivo culture to understand the role of PR in burn patients. Burn impedes late maturation of orthochromatic erythroblasts into reticulocytes by restricting the enucleation step. Late-stage erythropoiesis is impaired in burn patients irrespective of PR treatment. Further, substituting the microenvironment with control plasma (homologous) in place of autologous plasma rescues the conversion of orthochromatic erythroblasts to reticulocytes. Results show promise in formulating interventions to regulate late-stage erythropoiesis, which can be used in combination with PR to reduce the number of transfusions.

Discrete β-adrenergic mechanisms regulate early and late erythropoiesis in erythropoietin-resistant anemia

BACKGROUND

Anemia of critical illness is resistant to exogenous erythropoietin. Packed red blood cells transfusions is the only treatment option, and despite related cost and morbidity, there is a need for alternate strategies. Erythrocyte development can be divided into erythropoietin-dependent and erythropoietin-independent stages. We have shown previously that erythropoietin-dependent development is intact in burn patients and the erythropoietin-independent early commitment stage, which is regulated by β1/β2-adrenergic mechanisms, is compromised. Utilizing the scald burn injury model, we studied erythropoietin-independent late maturation stages and the effect of β1/β2, β-2, or β-3 blockade in burn mediated erythropoietin-resistant anemia.

METHODS

Burn mice were randomized to receive daily injections of propranolol (nonselective β1/β2 antagonist), nadolol (long-acting β1/β2 antagonist), butoxamine (selective β2 antagonist), or SR59230A (selective β3 antagonist) for 6 days after burn. Total bone marrow cells were characterized as nonerythroid cells, early and late erythroblasts, nucleated orthochromatic erythroblasts and enucleated reticulocyte subsets using CD71, Ter119, and Syto-16 by flow cytometry. Multipotential progenitors were probed for MafB expressing cells.

RESULTS

Although propranolol improved early and late erythroblasts, only butoxamine and selective β3-antagonist administrations were positively reflected in the peripheral blood hemoglobin and red blood cells count. While burn impeded early commitment and late maturation stages, β1/β2 antagonism increased the early erythroblasts through commitment stages via β2 specific MafB regulation. β3 antagonism was more effective in improving overall red blood cells through late maturation stages.

CONCLUSION

The study unfolds novel β2 and β3 adrenergic mechanisms orchestrating erythropoietin resistant anemia after burn, which impedes both the early commitment stage and the late maturation stages, respectively.

Thermal injury of the skin induces G-CSF-dependent attenuation of EPO-mediated STAT signaling and erythroid differentiation arrest in mice

Inflammation-mediated impairment of erythropoiesis plays a central role in the development of the anemia of critical illness (ACI). ACI develops despite elevation of endogenous erythropoietin (EPO), does not respond to exogenous erythropoietin (EPO) supplementation, and contributes significantly to transfusion requirements in burned patients. We have reported previously that the reduction of red blood cell mass in the bone marrow of a burn-injured ACI mouse model is granulocyte colony-stimulating factor (G-CSF) dependent. Given that elevated G-CSF levels also have been associated with lower hemoglobin levels and increased transfusion requirements in trauma victims, we postulated that G-CSF mediates postburn EPO resistance. In ACI mice, we found that bone marrow erythroid differentiation, viability, and proliferation are impaired after thermal injury of the skin. These changes in the marrow were associated with attenuated phosphorylation of known EPO-responsive signaling nodes, signal transducer and activator of transcription 5 (STAT5) Y694 and STAT3 S727, in bone marrow erythroid cells and developed despite highly elevated levels of endogenous EPO. Severely blunted STAT5 Y694 phosphorylation in bone marrow erythroid cells after exogenous EPO supplementation confirmed that EPO signaling was impaired in ACI mice. Importantly, parenteral administration of anti-G-CSF largely rescued postburn bone marrow erythroid differentiation arrest and EPO signaling in erythroid cells. Together, these data provide strong evidence for a role for G-CSF in the development of ACI after burn injury through suppression of EPO signaling in bone marrow erythroid cells.

Myelo-erythroid commitment after burn injury is under β-adrenergic control via MafB regulation

Severely injured burn patients receive multiple blood transfusions for anemia of critical illness despite the adverse consequences. One limiting factor to consider alternate treatment strategies is the lack of a reliable test platform to study molecular mechanisms of impaired erythropoiesis. This study illustrates how conditions resulting in a high catecholamine microenvironment such as burns can instigate myelo-erythroid reprioritization influenced by β-adrenergic stimulation leading to anemia. In a mouse model of scald burn injury, we observed, along with a threefold increase in bone marrow LSK cells (lin^neg Sca1⁺cKit⁺), that the myeloid shift is accompanied with a significant reduction in megakaryocyte erythrocyte progenitors (MEPs). β-Blocker administration (propranolol) for 6 days after burn, not only reduced the number of LSKs and MafB⁺ cells in multipotent progenitors, but also influenced myelo-erythroid bifurcation by increasing the MEPs and reducing the granulocyte monocyte progenitors in the bone marrow of burn mice. Furthermore, similar results were observed in burn patients' peripheral blood mononuclear cell-derived ex vivo culture system, demonstrating that commitment stage of erythropoiesis is impaired in burn patients and intervention with propranolol (nonselective β1,2-adrenergic blocker) increases MEPs. Also, MafB⁺ cells that were significantly increased following standard burn care could be mitigated when propranolol was administered to burn patients, establishing the mechanistic regulation of erythroid commitment by myeloid regulatory transcription factor MafB. Overall, results demonstrate that β-adrenergic blockers following burn injury can redirect the hematopoietic commitment toward erythroid lineage by lowering MafB expression in multipotent progenitors and be of potential therapeutic value to increase erythropoietin responsiveness in burn patients.

The Use of Blood Products in Adult Patients with Burns

Introduction:

Burn anemia represents a common complication following a burn injury. Burn anemia etiology carries distinct features occurring at each stage of the post-injury and treatment periods resulting from different causes. We aimed to analyze the use of blood components in Finnish burn victims and to identify patient- and injury-related factors influencing their use.

Methods:

To study the use of blood products in burn patients, we used data collected from the Optimal Use of Blood registry, developed through co-operation between 10 major hospital districts and the Finnish Red Cross Blood Service. Burn patients ⩾18 years treated at the Helsinki University Hospital between 2005 and 2011 with an in-hospital stay ⩾1 day who received at least one transfusion during their hospital stay were included in this study.

Results:

Among all 558 burn patients, 192 (34%) received blood products during their hospital stay. The transfused cohort comprised 192 burn patients. The study cohort received a total of 6087 units of blood components, 2422 units of leukoreduced red blood cells, 1728 units of leukoreduced platelets, and 420 units of single-donor fresh frozen plasma or, after 2007, 1517 units of Octaplas® frozen plasma. All three types of blood components were administered to 29% of patients, whereas 45% received only red blood cells and 6% received only Octaplas. Transfused patients were significantly older (p < 0.001), experienced fire-/flame-related accidents and burns to multiple locations (p < 0.001), and their in-hospital mortality exceeded that for non-transfused burn patients fivefold (p < 0.05).

Discussion:

We show that Finnish adult burn patients received ample transfusions. The number of blood components transfused varied according to the anatomical location of the injury and patient survival. Whether the additional mortality is related directly to transfusions or is merely a manifestation of the more severe burn injury remains unknown.

Perturbed MafB/GATA1 axis after burn trauma bares the potential mechanism for immune suppression and anemia of critical illness

Patients who survive initial burn injury are susceptible to nosocomial infections. Anemia of critical illness is a compounding factor in burn patients that necessitates repeated transfusions, which further increase their susceptibility to infections and sepsis. Robust host response is dependent on an adequate number and function of monocytes/macrophages and dendritic cells. In addition to impaired RBC production, burn patients are prone to depletion of dendritic cells and an increase in deactivated monocytes. In steady-state hematopoiesis, RBCs, macrophages, and dendritic cells are all generated from a common myeloid progenitor within the bone marrow. We hypothesized in a mouse model of burn injury that an increase in myeloid-specific transcription factor V-maf musculoaponeurotic fibrosarcoma oncogene homolog B at the common myeloid progenitor stage steers their lineage potential away from the megakaryocyte erythrocyte progenitor production and drives the terminal fate of common myeloid progenitors to form macrophages vs. dendritic cells, with the consequences being anemia, monocytosis, and dendritic cell deficits. Results indicate that, even though burn injury stimulated bone marrow hematopoiesis by increasing multipotential stem cell production (Lin^negSca1^poscKit^pos), the bone marrow commitment is shifted away from the megakaryocyte erythrocyte progenitor and toward granulocyte monocyte progenitors with corresponding alterations in peripheral blood components, such as hemoglobin, hematocrit, RBCs, monocytes, and granulocytes. Furthermore, burn-induced V-maf musculoaponeurotic fibrosarcoma oncogene homolog B in common myeloid progenitors acts as a transcriptional activator of M-CSFR and a repressor of transferrin receptors, promoting macrophages and inhibiting erythroid differentiations while dictating a plasmacytoid dendritic cell phenotype. Results from small interfering RNA and gain-of-function (gfp-globin transcription factor 1 retrovirus) studies indicate that targeted interventions to restore V-maf musculoaponeurotic fibrosarcoma oncogene homolog B/globin transcription factor 1 balance can mitigate both immune imbalance and anemia of critical illness.

History of burns: The past, present and the future

Burn injuries are one of the most common and devastating afflictions on the human body. In this article we look back at how the treatment of burns has evolved over the centuries from a primarily topical therapy consisting of weird and wonderful topical concoctions in ancient times to one that spans multiple scientific fields of topical therapy, antibiotics, fluid resuscitation, skin excision and grafting, respiratory and metabolic care and nutrition. Most major advances in burn care occurred in the last 50 years, spurred on by wars and great fires. The use of systemic antibiotics and topical silver therapy greatly reduced sepsis related mortality. This along with the advent of antiseptic surgical techniques, burn depth classification and skin grafting allowed the excision and coverage of full-thickness burns which resulted in greatly improved survival rates. Advancements in the methods of assessing the surface area of burns paved way for more accurate fluid resuscitation, minimising the effects of shock and avoiding fluid over-loading. The introduction of metabolic care, nutritional support and care of inhalational injuries further improved the outcome of burn patients. We also briefly discuss some future directions in burn care such as the use of cell and pharmalogical therapies.

Animal models in burn research

Burn injury is a severe form of trauma affecting more than 2 million people in North America each year. Burn trauma is not a single pathophysiological event but a devastating injury that causes structural and functional deficits in numerous organ systems. Due to its complexity and the involvement of multiple organs, in vitro experiments cannot capture this complexity nor address the pathophysiology. In the past two decades, a number of burn animal models have been developed to replicate the various aspects of burn injury, to elucidate the pathophysiology, and to explore potential treatment interventions. Understanding the advantages and limitations of these animal models is essential for the design and development of treatments that are clinically relevant to humans. This review aims to highlight the common animal models of burn injury in order to provide investigators with a better understanding of the benefits and limitations of these models for translational applications. While many animal models of burn exist, we limit our discussion to the skin healing of mouse, rat, and pig. Additionally, we briefly explain hypermetabolic characteristics of burn injury and the animal model utilized to study this phenomena. Finally, we discuss the economic costs associated with each of these models in order to guide decisions of choosing the appropriate animal model for burn research.

G-CSF drives a posttraumatic immune program that protects the host from infection

Traumatic injury is generally considered to have a suppressive effect on the immune system, resulting in increased susceptibility to infection. Paradoxically, we found that thermal injury to the skin induced a robust time-dependent protection of mice from a lethal Klebsiella pneumoniae pulmonary challenge. The protective response was neutrophil dependent and temporally associated with a systemic increase in neutrophils resulting from a reprioritization of hematopoiesis toward myeloid lineages. A prominent and specific activation of STAT3 in the bone marrow preceded the myeloid shift in that compartment, in association with durable increases in STAT3 activating serum cytokines G-CSF and IL-6. Neutralization of the postburn increase in serum G-CSF largely blocked STAT3 activation in marrow cells, reversing the hematopoietic changes and systemic neutrophilia. Daily administration of rG-CSF was sufficient to recapitulate the changes induced by injury including hematopoietic reprioritization and protection from pulmonary challenge with K. pneumoniae. Analysis of posttraumatic gene expression patterns in humans reveals that they are also consistent with a role for G-CSF as a switch that activates innate immune responses and suppresses adaptive immune responses. Our findings suggest that the G-CSF STAT3 axis constitutes a key protective mechanism induced by injury to reduce the risk for posttraumatic infection.

Peripheral blood mononuclear cell-derived erythroid progenitors and erythroblasts are decreased in burn patients

Patients with large burns suffer from anemia of critical illness. Administration of exogenous erythropoietin is ineffective, and transfusion remains the only effective treatment. We have previously shown that erythroid precursors are decreased 1 week after burn in an animal model. Therefore, we have used a two-phase liquid culture system to quantify peripheral blood mononuclear cell (PBMC) compartment-derived erythroid progenitors (EPs) in burn patients. Institutional review board approval and informed consent were obtained. Blood samples were collected at 1 to 30 days after burn, with a mean TBSA of 37.7 ± 15.8% (n = 10; 90% men; age, 46.0 ± 18 years). Four healthy volunteers served as controls. PBMCs were isolated by Ficoll-Hypaque density-gradient centrifugation and were placed in serum-free expansion medium containing cyclosporine A (1 ng/ml), granulocyte macrophage colony-stimulating factor (20 ng/ml), stem cell factor (30 ng/ml), and interleukin-3 (5 ng/ml; phase I). On day 7, cells were reseeded in serum-free expansion medium containing erythropoietin (1 U/ml), holotransferrin (0.3 mg/ml), and stem cell factor (10 ng/ml; phase II). Aliquots from the phase II culture system on day 6 were incubated with anti-CD71, CD235a, and CD36. EPs (CD71 CD36) and erythroblast subpopulations (colony-forming unit erythroids, Proerythroblasts, and intermediate erythroblasts) were identified based on the expressions of CD71 and CD235a by flow cytometry, calculated per million expanded cells, and expressed as a percentage of controls. Total EPs were significantly decreased by days 28 to 31 after the burn (19%; P < .05). Among the erythroblast subpopulations, colony-forming unit erythroids (11%; P < .004) and proerythroblasts (24%; P < .05), were decreased significantly by days 28 to 31 after the burn. PBMCs of burn patients can be used to study impaired erythropoiesis and anemia of critical illness.

A key role for lipoic acid synthesis during Plasmodium liver stage development

The successful navigation of malaria parasites through their life cycle, which alternates between vertebrate hosts and mosquito vectors, requires a complex interplay of metabolite synthesis and salvage pathways. Using the rodent parasite Plasmodium berghei, we have explored the synthesis and scavenging pathways for lipoic acid, a short-chain fatty acid derivative that regulates the activity of α-ketoacid dehydrogenases including pyruvate dehydrogenase. In Plasmodium, lipoic acid is either synthesized de novo in the apicoplast or is scavenged from the host into the mitochondrion. Our data show that sporozoites lacking the apicoplast lipoic acid protein ligase LipB are markedly attenuated in their infectivity for mice, and in vitro studies document a very late liver stage arrest shortly before the final phase of intra-hepaticparasite maturation. LipB-deficient asexual blood stage parasites show unimpaired rates of growth in normal in vitro or in vivo conditions. However, these parasites showed reduced growth in lipid-restricted conditions induced by treatment with the lipoic acid analogue 8-bromo-octanoate or with the lipid-reducing agent clofibrate. This finding has implications for understanding Plasmodium pathogenesis in malnourished children that bear the brunt of malarial disease. This study also highlights the potential of exploiting lipid metabolism pathways for the design of genetically attenuated sporozoite vaccines.

High MafB expression following burn augments monocyte commitment and inhibits DC differentiation in hemopoietic progenitors

We have previously shown that perturbed bone marrow progenitor development promotes hyporesponsive monocytes following experimental burn sepsis. Clinical and experimental sepsis is associated with monocyte deactivation and depletion of mDCs. Decrease in circulating DCs is reported in burn patients who develop sepsis. In our 15% TBSA scald burn model, we demonstrate a significant reduction in the circulating MHC-II(+) population and mDCs (Gr1(neg)CD11b(+)CD11c(+)) with a corresponding decrease in bone marrow MHC-II(+) cells and mDCs for up to 14 days following burn. We explored the underlying mechanism(s) that regulate bone marrow development of monocytes and DCs following burn injury. We found a robust bone marrow response with a significant increase in multipotential HSCs (LSK) and bipotential GMPs following burn injury. GMPs from burn mice exhibit a significant reduction in GATA-1, which is essential for DC development, but express high levels of MafB and M-CSFRs, both associated with monocyte production. GMPs obtained from burn mice differentiated 1.7 times more into Mϕ and 1.6-fold less into DCs compared with sham. Monocytes and DCs expressed 50% less MHC-II in burn versus sham. Increased monocyte commitment in burn GMPs was a result of high MafB and M-CSFR expressions. Transient silencing of MafB (siRNA) in GMP-derived monocytes from burn mice partially restored DC differentiation deficits and increased GATA-1 expression. We provide evidence that high MafB following burn plays an inhibitory role in monocyte-derived DC differentiation by regulating M-CSFR and GATA-1 expressions.