Hematopoietic progenitor cell mobilization is mediated through beta-2 and beta-3 receptors after injury

Adrenergic Modulation of Erythropoiesis After Trauma

Severe traumatic injury results in a cascade of systemic changes which negatively affect normal erythropoiesis. Immediately after injury, acute blood loss leads to anemia, however, patients can remain anemic for as long as 6 months after injury. Research on the underlying mechanisms of such alterations of erythropoiesis after trauma has focused on the prolonged hypercatecholaminemia seen after trauma. Supraphysiologic elevation of catecholamines leads to an inhibitive effect on erythropoiesis. There is evidence to show that alleviation of the neuroendocrine stress response following trauma reduces these inhibitory effects. Both beta blockade and alpha-2 adrenergic receptor stimulation have demonstrated increased growth of hematopoietic progenitor cells as well as increased pro-erythropoietic cytokines after trauma. This review will describe prior research on the neuroendocrine stress response after trauma and its consequences on erythropoiesis, which offer insight into underlying mechanisms of prolonged anemia postinjury. We will then discuss the beneficial effects of adrenergic modulation to improve erythropoiesis following injury and propose future directions for the field.

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.

The effects of selective beta-adrenergic blockade on bone marrow dysfunction following severe trauma and chronic stress

INTRODUCTION

Propranolol has been shown to improve erythroid progenitor cell growth and anemia following trauma and this study sought to investigate the mechanisms involved by evaluating the effects of selective beta blockade.

METHODS

Male Sprague-Dawley rats were subjected to lung contusion, hemorrhagic shock and chronic stress (LCHS/CS) ± daily selective beta-1, beta-2, or beta-3 blockade (B1B, B2B, B3B). Bone marrow cellularity and growth of erythroid progenitor colonies, hemoglobin, plasma granulocyte colony-stimulating factor (G-CSF), hematopoietic progenitor cell mobilization, and daily weight were assessed.

RESULTS

Selective beta-2 and beta-3 blockade improved bone marrow cellularity, erythroid progenitor colony growth and hemoglobin levels, while decreasing plasma G-CSF, progenitor cell mobilization and weight loss following LCHS/CS.

CONCLUSIONS

Attenuating the neuroendocrine stress response with the use of selective beta-2 and 3 adrenergic blockade may be an alternative to improve bone marrow erythroid function following trauma.

Impact of Injury Severity on the Inflammatory State and Severe Anemia

BACKGROUND

Severe traumatic injury is a major cause of morbidity and mortality. Our goal was to analyze blunt traumatic injury by injury severity score (ISS) and compare with elective hip repair, as a transient injury, and healthy control with the hypothesis that more severe injury would lead to an increase in neuroendocrine activation, systemic inflammation, and worse anemia.

MATERIALS AND METHODS

A prospective observational cohort study was performed at a level 1 trauma center, comparing blunt trauma patients (n = 37), elective hip replacement patients (n = 26), and healthy controls (n = 8). Bone marrow and plasma were assessed for hyperadrenergic state, erythropoiesis, and systemic inflammation. Trauma patient's ISS ranged from 4 to 41 and were broken down into quartiles for analysis. The ISS quartiles were 4-13, 14-20, 21-26, and 27-41.

RESULTS

Plasma norepinephrine, interleukin-6, tumor necrosis factor-alpha, and hepcidin increased progressively as ISS increased. Hemoglobin significantly decreased as ISS increased and packed red blood cell (pRBC) transfusion increased as ISS increased. Elective hip replacement patients had an appropriate increase in the bone marrow expression of erythropoietin and the erythropoietin receptor, which was absent in all trauma patient groups.

CONCLUSIONS

Increased neuroendocrine activation, systemic inflammation, and anemia correlated with worsening injury severity, lower age, and increased pRBC transfusions. Elective hip replacement patients have only minimal systemic inflammation with an appropriate bone marrow response to anemia. This study demonstrates a link between injury severity, neuroendocrine activation, systemic inflammation, and the bone marrow response to anemia.

Effect of Beta-Blockade on the Expression of Regulatory MicroRNA after Severe Trauma and Chronic Stress

BACKGROUND

Beta-blockade administration after lung contusion, hemorrhagic shock, and chronic stress has been shown to improve bone marrow function, decrease hypercatecholaminemia, and reduce inflammation. MicroRNAs (miR) are critical biologic regulators that can downregulate gene expression by causing messenger RNA degradation or inhibition of translation. This study sought to expand our understanding of the molecular mechanisms underlying the reduced inflammatory response after the administration of beta-blockade (BB) in our rodent trauma model.

STUDY DESIGN

Male Sprague-Dawley rats aged 8 to 9 weeks were randomized to lung contusion, hemorrhagic shock with daily restraint stress (LCHS/CS) or LCHS/CS plus propranolol (LCHS/CS+BB). Restraint stress occurred 2 hours daily after LCHS. Propranolol (10 mg/kg) was given daily until day 7. Total RNA and miR were isolated from bone marrow and genome-wide miR expression patterns were assayed. Bone marrow cytokine expression was determined with quantitative polymerase chain reaction.

RESULTS

LCHS/CS led to significantly increased bone marrow expression of interleukin (IL) 1β, tumor necrosis factor-α, IL-6, nitric oxide, and plasma C-reactive protein. There were marked differences in expression of 45 miRs in the LCHS/CS+BB group compared with the LCHS/CS group when using a p value <0.001. Rno-miR-27a and miR-25 were upregulated 7- to 8-fold in the rodents who underwent LCHS/CS+BB compared with LCHS/CS alone, and this correlated with reduced bone marrow expression of IL-1β, tumor necrosis factor-α, IL-6, nitric oxide, and reduced plasma C-reactive protein in the LCHS/CS+BB group.

CONCLUSIONS

The genomic and miR expression patterns in bone marrow after LCHS/CS differed significantly compared with rodents that received propranolol after LCHS/CS. The use of BB after severe trauma can help mitigate persistent inflammation by upregulating Rno-miR-27a and miR-25 and reducing inflammatory cytokines in those who remain critically ill.

Flow Cytometric Analysis of Hematopoietic Populations in Rat Bone Marrow. Impact of Trauma and Hemorrhagic Shock

Severe injury and hemorrhagic shock (HS) result in multiple changes to hematopoietic differentiation, which contribute to the development of immunosuppression and multiple organ failure (MOF). Understanding the changes that take place during the acute injury phase may help predict which patients will develop MOF and provide potential targets for therapy. Obtaining bone marrow from humans during the acute injury phase is difficult so published data are largely derived from peripheral blood samples, which infer bone marrow changes that reflect the sustained inflammatory response. This preliminary and opportunistic study investigated leucopoietic changes in rat bone marrow 6 h following traumatic injury and HS. Terminally anesthetized male Porton Wistar rats were allocated randomly to receive a sham operation (cannulation with no injury) or femoral fracture and HS. Bone marrow cells were flushed from rat femurs and immunophenotypically stained with specific antibody panels for lymphoid (CD45R, CD127, CD90, and IgM) or myeloid (CD11b, CD45, and RP-1) lineages. Subsequently, cell populations were fluorescence-activated cell sorted for morphological assessment. Stage-specific cell populations were identified using a limited number of antibodies, and leucopoietic changes were determined 6 h following trauma and HS. Myeloid subpopulations could be identified by varying levels CD11b expression, CD45, and RP-1. Trauma and HS resulted in a significant reduction in total CD11b + myeloid cells including both immature (RP-1(-)) and mature (RP-1+) granulocytes. Multiple B-cell lymphoid subsets were identified. The total percentage of CD90+ subsets remained unchanged following trauma and HS, but there was a reduction in the numbers of maturing CD90(-) cells suggesting movement into the periphery. © 2019 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of International Society for Advancement of Cytometry.

The Postinjury Inflammatory State and the Bone Marrow Response to Anemia

RATIONALE

The pathophysiology of persistent injury-associated anemia is incompletely understood, and human data are sparse.

OBJECTIVES

To characterize persistent injury-associated anemia among critically ill trauma patients with the hypothesis that severe trauma would be associated with neuroendocrine activation, erythropoietin dysfunction, iron dysregulation, and decreased erythropoiesis.

METHODS

A translational prospective observational cohort study comparing severely injured, blunt trauma patients who had operative fixation of a hip or femur fracture (n = 17) with elective hip repair patients (n = 22). Bone marrow and plasma obtained at the index operation were assessed for circulating catecholamines, systemic inflammation, erythropoietin, iron trafficking pathways, and erythroid progenitor growth. Bone marrow was also obtained from healthy donors from a commercial source (n = 8).

MEASUREMENTS AND MAIN RESULTS

During admission, trauma patients had a median of 625 ml operative blood loss and 5 units of red blood cell transfusions, and Hb decreased from 10.5 to 9.3 g/dl. Compared with hip repair, trauma patients had higher median plasma norepinephrine (21.9 vs. 8.9 ng/ml) and hepcidin (56.3 vs. 12.2 ng/ml) concentrations (both P < 0.05). Bone marrow erythropoietin and erythropoietin receptor expression were significantly increased among patients undergoing hip repair (23% and 14% increases, respectively; both P < 0.05), but not in trauma patients (3% and 5% increases, respectively), compared with healthy control subjects. Trauma patients had lower bone marrow transferrin receptor expression than did hip repair patients (57% decrease; P < 0.05). Erythroid progenitor growth was decreased in trauma patients (39.0 colonies per plate; P < 0.05) compared with those with hip repair (57.0 colonies per plate; P < 0.05 compared with healthy control subjects) and healthy control subjects (66.5 colonies per plate).

CONCLUSIONS

Severe blunt trauma was associated with neuroendocrine activation, erythropoietin dysfunction, iron dysregulation, erythroid progenitor growth suppression, and persistent injury-associated anemia. Clinical trial registered with www.clinicaltrials.gov (NCT 02577731).

Systemic Regulation of Bone Marrow Stromal Cytokines After Severe Trauma

BACKGROUND

Traumatic injury generates a prolonged hypercatecholamine state that is associated with reduced growth of bone marrow erythroid progenitors mediated by the bone marrow stroma. The bone marrow stroma is made up of many cells including fibroblasts, which respond to inflammatory stimuli and alter the cytokine profile. We hypothesized that trauma plasma would increase bone marrow stromal fibroblast expression of interleukin-6 (IL-6), granulocyte colony-stimulating factor (G-CSF), erythropoietin (EPO), stem cell factor (SCF), and activation of nuclear factor kappa-light-chain-enhancer of activated B cells and correlate with injury severity and anemia.

MATERIALS AND METHODS

Plasma from 15 trauma patients was cultured with bone marrow fibroblast cells and compared with that from healthy volunteers. At 6, 24, and 48 h, the expression of IL-6, G-CSF, EPO, SCF, and the activation of nuclear factor kappa-light-chain-enhancer of activated B cells were measured using quantitative polymerase chain reaction. The influence of trauma plasma on cytokine expression was further stratified by injury severity score (ISS).

RESULTS

The average hemoglobin significantly decreased from admission to discharge (10.7 ± 2.5 to 9.2 ± 1.1 g/dL, P < 0.04). The discharge hemoglobin significantly decreased by 14% from the admission hemoglobin. After 48 h, trauma plasma significantly increased IL-6, G-CSF, and EPO bone marrow fibroblast expression when compared with normal plasma. When stratified by ISS, IL-6, G-CSF, and EPO, bone marrow fibroblast expression was highest in the trauma plasma ISS 27-41 group and was significantly elevated compared with normal plasma. When SCF expression was stratified by ISS, there was a significant increase in expression in ISS 27-41. Higher ISS was also associated with a larger decrease in hemoglobin despite no difference in total blood transfusions.

CONCLUSIONS

Severe trauma can systemically increase IL-6, G-CSF, and EPO expression in bone marrow stroma. Increased hematopoietic cytokine expression after traumatic injury correlated with a hypercatecholamine state, anemia, and injury severity.

Alpha2B-Adrenergic Receptor Regulates Neutrophil Recruitment in MSU-Induced Peritoneal Inflammation

Gout is one of the most common metabolic disorders in human. Previous studies have shown that the disease activity is closely associated with sympathetic nervous system (SNS). α_2B-adrenergic receptor (α_2BAR), a subtype of α2 adrenergic receptor, plays a critical role in many diseases. However, the role of α_2BAR in the pathogenesis of gout remains unclear. Here, we assessed the role of α_2BAR in the monosodium urate (MSU) crystals-induced peritonitis that mimics human gout by using the α_2BAR-overexpressing mice (α_2BAR-Tg). We found that the number of recruited neutrophils was significantly increased in the α_2BAR-Tg mice after MSU treatment, when compared with wild type mice. In contrast, the number of macrophages was not changed. Importantly, there is no difference in the IL-1β levels and caspase-1 activity between wild type and α_2BAR-Tg mice in the gout animal model. Notably, the enhanced neutrophil migration in α_2BAR-Tg mice was dependent on the α_2BAR overexpression in neutrophils, but not resulted from other tissues or cells with α_2BAR overexpression. In conclusion, our data provide a direct evidence that α_2BAR plays a critical role in neutrophil migration and MSU-induced inflammation.

Beta blockers in critically ill patients with traumatic brain injury: Results from a multicenter, prospective, observational American Association for the Surgery of Trauma study

BACKGROUND

Beta blockers, a class of medications that inhibit endogenous catecholamines interaction with beta adrenergic receptors, are often administered to patients hospitalized after traumatic brain injury (TBI). We tested the hypothesis that beta blocker use after TBI is associated with lower mortality, and secondarily compared propranolol to other beta blockers.

METHODS

The American Association for the Surgery of Trauma Clinical Trial Group conducted a multi-institutional, prospective, observational trial in which adult TBI patients who required intensive care unit admission were compared based on beta blocker administration.

RESULTS

From January 2015 to January 2017, 2,252 patients were analyzed from 15 trauma centers in the United States and Canada with 49.7% receiving beta blockers. Most patients (56.3%) received the first beta blocker dose by hospital day 1. Those patients who received beta blockers were older (56.7 years vs. 48.6 years, p < 0.001) and had higher head Abbreviated Injury Scale scores (3.6 vs. 3.4, p < 0.001). Similarities were noted when comparing sex, admission hypotension, mean Injury Severity Score, and mean Glasgow Coma Scale. Unadjusted mortality was lower for patients receiving beta blockers (13.8% vs. 17.7%, p = 0.013). Multivariable regression determined that beta blockers were associated with lower mortality (adjusted odds ratio, 0.35; p < 0.001), and propranolol was superior to other beta blockers (adjusted odds ratio, 0.51, p = 0.010). A Cox-regression model using a time-dependent variable demonstrated a survival benefit for patients receiving beta blockers (adjusted hazard ratio, 0.42, p < 0.001) and propranolol was superior to other beta blockers (adjusted hazard ratio, 0.50, p = 0.003).

CONCLUSION

Administration of beta blockers after TBI was associated with improved survival, before and after adjusting for the more severe injuries observed in the treatment cohort. This study provides a robust evaluation of the effects of beta blockers on TBI outcomes that supports the initiation of a multi-institutional randomized control trial.

LEVEL OF EVIDENCE

Therapeutic/care management, level III.

The effects of propranolol and clonidine on bone marrow expression of hematopoietic cytokines following trauma and chronic stress

BACKGROUND

Attenuating post-injury neuroendocrine stress abrogates persistent injury-associated anemia. Our objective was to examine the mechanisms by which propranolol and clonidine modulate this process. We hypothesized that propranolol and clonidine would decrease bone marrow expression of high-mobility group box-1 (HMGB1) and increase expression of stem cell factor (SCF) and B-cell lymphoma-extra large (Bcl-xL).

METHODS

Male Sprague-Dawley rats were allocated to naïve control, lung contusion followed by hemorrhagic shock (LCHS), or LCHS plus daily chronic restraint stress (LCHS/CS) ±propranolol, ±clonidine. Day seven bone marrow expression of HMGB1, SCF, and Bcl-xL was assessed by polymerase chain reaction.

RESULTS

Following LCHS, HMGB1 was decreased by propranolol (49% decrease, p = 0.012) and clonidine (54% decrease, p < 0.010). SCF was decreased following LCHS/CS, and was increased by propranolol (629% increase, p < 0.001) and clonidine (468% increase, p < 0.001). Bcl-xL was decreased following LCHS/CS, and was increased by propranolol (59% increase, p = 0.006) and clonidine (77% increase, p < 0.001).

CONCLUSIONS

Following severe trauma, propranolol and clonidine abrogate persistent injury-associated anemia by modulating bone marrow cytokines, favoring effective erythropoiesis.

Loneliness, Social Isolation, and Cardiovascular Health

SIGNIFICANCE

Social and demographic changes have led to an increased prevalence of loneliness and social isolation in modern society. Recent Advances: Population-based studies have demonstrated that both objective social isolation and the perception of social isolation (loneliness) are correlated with a higher risk of mortality and that both are clearly risk factors for cardiovascular disease (CVD). Lonely individuals have increased peripheral vascular resistance and elevated blood pressure. Socially isolated animals develop more atherosclerosis than those housed in groups.

CRITICAL ISSUES

Molecular mechanisms responsible for the increased cardiovascular risk are poorly understood. In recent reports, loneliness and social stress were associated with activation of the hypothalamic-pituitary-adrenocortical axis and the sympathetic nervous system. Repeated and chronic social stress leads to glucocorticoid resistance, enhanced myelopoiesis, upregulated proinflammatory gene expression, and oxidative stress. However, the causal role of these mechanisms in the development of loneliness-associated CVD remains unclear.

FUTURE DIRECTIONS

Elucidation of the molecular mechanisms of how CVD is induced by loneliness and social isolation requires additional studies. Understanding of the pathomechanisms is essential for the development of therapeutic strategies to prevent the detrimental effects of social stress on health. Antioxid. Redox Signal. 28, 837-851.

Persistent injury-associated anemia and aging: Novel insights

BACKGROUND

Hypercatecholaminemia and bone marrow dysfunction have been implicated in the pathophysiology of persistent injury-associated anemia. The elderly may be more vulnerable to bone marrow dysfunction due to high basal and peak catecholamine levels and impaired hematopoietic progenitor growth. We hypothesized that aging would adversely affect persistent injury-associated anemia.

METHODS

Male Sprague-Dawley rats aged 8 to 9 weeks and F344-BN rats aged 25 months were randomized to naive controls, lung contusion plus hemorrhagic shock (LCHS), and LCHS plus daily chronic restraint stress (LCHS/CS). Urine norepinephrine was measured on Days 1 and 7. Mobilization of hematopoietic progenitor cells (HPCs), bone marrow colony-forming units-erythroid growth, and peripheral blood hemoglobin, mean corpuscular volume (MCV), and red cell distribution width (RDW) were assessed on Day 7 (*p < 0.05 young vs. aged counterpart by one-way analysis of variance).

RESULTS

Aged rats had higher norepinephrine levels at naive baseline (97* vs. 27 ng/mL) and 7 days following LCHS/CS when compared with young (359* vs. 127 ng/mL). Following LCHS/CS, HPC mobilization was greater among young rats when compared with aged (5.4 vs. 2.5%). Colony-forming units-erythroid growth was lower among aged animals for each group (naive: 47* vs. 65; LCHS: 40* vs. 50; LCHS/CS: 38* vs. 44 cells/plate). Aged naive rats had higher initial hemoglobin (15.2* vs. 14.3 g/dL) but lower MCV (48* vs. 59 fL/cell) and larger RDW at baseline and greater differences 7 days after LCHS/CS (MCV: 46* vs. 60 fL/cell; RDW: 17.4* vs. 16.3%).

CONCLUSIONS

Compared with young rats, aged rats had less HPC mobilization despite elevated basal and peak norepinephrine. Aged rats were disproportionately affected by impaired hematopoietic progenitor growth and an iron-restricted red blood cell phenotype at baseline, which persisted 7 days after injury. Further research is needed to assess how the clinical approach to persistent injury-associated anemia should differ for elderly trauma patients.

β-Blockade use for Traumatic Injuries and Immunomodulation: A Review of Proposed Mechanisms and Clinical Evidence

Sympathetic nervous system activation and catecholamine release are important events following injury and infection. The nature and timing of different pathophysiologic insults have significant effects on adrenergic pathways, inflammatory mediators, and the host response. Beta adrenergic receptor blockers (β-blockers) are commonly used for treatment of cardiovascular disease, and recent data suggests that the metabolic and immunomodulatory effects of β-blockers can expand their use. β-blocker therapy can reduce sympathetic activation and hypermetabolism as well as modify glucose homeostasis and cytokine expression. It is the purpose of this review to examine either the biologic basis for proposed mechanisms or to describe current available clinical evidence for the use of β-blockers in traumatic brain injury, spinal cord injury, hemorrhagic shock, acute traumatic coagulopathy, erythropoietic dysfunction, metabolic dysfunction, pulmonary dysfunction, burns, immunomodulation, and sepsis.

Persistent injury-associated anemia in aged rats

BACKGROUND

Hypercatecholaminemia and bone marrow dysfunction have been implicated in the pathophysiology of persistent-injury associated anemia. The elderly may be vulnerable to this phenomenon due to high basal and peak catecholamine levels, impaired erythroid progenitor growth, and baseline anemia. We hypothesized that aged F344-BN rats subjected to severe trauma and chronic stress would have persistent injury-associated anemia.

METHODS

Male F344-BN rats age 25months were randomly allocated to: naïve (n=8), lung contusion (LC, n=9), LC followed by daily chronic restraint stress (LC/CS, n=9), LC followed immediately by hemorrhagic shock (LCHS, n=8), and LCHS followed by daily CS (LCHS/CS, n=8). Urine norepinephrine was measured on days one and seven. Locomotor testing was performed on day five. Bone marrow cellularity, hematopoietic progenitor growth, and peripheral blood hemoglobin levels were assessed at sacrifice on day seven. Data are presented as mean±standard deviation, *p<0.05 vs. naïve.

RESULTS

Norepinephrine levels (ng/mL) were significantly elevated one day after LCHS (420±239* vs. naïve: 97±71) and LCHS/CS (375±185*), and remained significantly elevated on day seven for LCHS/CS (359±99*), but not LCHS (212±130). On locomotor testing, groups subjected to CS traveled shorter distances at lower velocities and spent less time in the center of the cage. Colony forming units-erythroid (colonies/plate), representing late erythroid progenitors, were significantly decreased after LC/CS (40±1* vs. naïve: 47±4), LCHS (40±1*), and LCHS/CS (38±3*). LCHS/CS animals had significantly lower hemoglobin (g/dL) than naïve animals (13.3±1.3* vs. naïve: 15.2±0.9).

CONCLUSIONS

Persistent injury-associated anemia occurs in aged rats. Further research is needed to determine whether the pathophysiology of this phenomenon differs from that of younger rats, and to translate these findings to elderly trauma patients.

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.

Clonidine reduces norepinephrine and improves bone marrow function in a rodent model of lung contusion, hemorrhagic shock, and chronic stress

BACKGROUND

Propranolol has been shown previously to restore bone marrow function and improve anemia after lung contusion/hemorrhagic shock. We hypothesized that daily clonidine administration would inhibit central sympathetic outflow and restore bone marrow function in our rodent model of lung contusion/hemorrhagic shock with chronic stress.

METHODS

Male Sprague-Dawley rats underwent 6 days of restraint stress after lung contusion/hemorrhagic shock during which the animals received clonidine (75 μg/kg) after the restraint stress. On postinjury day 7, we assessed urine norepinephrine, blood hemoglobin, plasma granulocyte colony stimulating factor, and peripheral blood mobilization of hematopoietic progenitor cells, as well as bone marrow cellularity and erythroid progenitor cell growth.

RESULTS

The addition of clonidine to lung contusion/hemorrhagic shock with chronic restraint stress significantly decreased urine norepinephrine levels, improved bone marrow cellularity, restored erythroid progenitor colony growth, and improved hemoglobin (14.1 ± 0.6 vs 10.8 ± 0.6 g/dL). The addition of clonidine to lung contusion/hemorrhagic shock with chronic restraint stress significantly decreased hematopoietic progenitor cells mobilization and restored granulocyte colony stimulating factor levels.

CONCLUSION

After lung contusion/hemorrhagic shock with chronic restraint stress, daily administration of clonidine restored bone marrow function and improved anemia. Alleviating chronic stress and decreasing norepinephrine is a key therapeutic target to improve bone marrow function after severe injury.

Bone Marrow-Derived Progenitor Cells Are Functionally Impaired in Ischemic Heart Disease

To determine whether the presence of ischemic heart disease (IHD) per se, or rather the co-presence of heart failure (HF), is the primum movens for less effective stem cell products in autologous stem cell therapy, we assessed numbers and function of bone marrow (BM)-derived progenitor cells in patients with coronary artery disease (n = 17), HF due to ischemic cardiomyopathy (n = 8), non-ischemic HF (n = 7), and control subjects (n = 11). Myeloid and erythroid differentiation capacity of BM-derived mononuclear cells was impaired in patients with underlying IHD but not with non-ischemic HF. Migration capacity decreased with increasing IHD severity. Hence, IHD, with or without associated cardiomyopathy, is an important determinant of progenitor cell function. No depletion of hematopoietic and endothelial progenitor cells (EPC) within the BM was observed, while circulating EPC numbers were increased in the presence of IHD, suggesting active recruitment. The observed myelosuppression was not driven by inflammation and thus other mechanisms are at play.

Daily propranolol prevents prolonged mobilization of hematopoietic progenitor cells in a rat model of lung contusion, hemorrhagic shock, and chronic stress

INTRODUCTION

Propranolol has been shown previously to decrease the mobilization of hematopoietic progenitor cells (HPCs) after acute injury in rodent models; however, this acute injury model does not reflect the prolonged period of critical illness after severe trauma. Using our novel lung contusion/hemorrhagic shock/chronic restraint stress model, we hypothesize that daily administration of propranolol will decrease prolonged mobilization of HPCs without worsening lung healing.

METHODS

Male Sprague-Dawley rats underwent 6 days of restraint stress after undergoing lung contusion or lung contusion/hemorrhagic shock. Restraint stress consisted of a daily 2-hour period of restraint interrupted every 30 minutes by alarms and repositioning. Each day after the period of restraint stress, the rats received intraperitoneal propranolol (10 mg/kg). On day 7, peripheral blood was analyzed for granulocyte-colony stimulating factor (G-CSF) and stromal cell-derived factor 1 via enzyme-linked immunosorbent assay and for mobilization of HPCs using c-kit and CD71 flow cytometry. The lungs were examined histologically to grade injury.

RESULTS

Seven days after lung contusion and lung contusion/hemorrhagic shock, the addition of chronic restraint stress significantly increased the mobilization of HPC, which was associated with persistently increased levels of G-CSF and increased lung injury scores. The addition of propranolol to lung contusion/chronic restraint stress and lung contusion/hemorrhagic shock/chronic restraint stress models greatly decreased HPC mobilization and restored G-CSF levels to that of naïve animals without worsening lung injury scores.

CONCLUSION

The daily administration of propranolol after both lung contusion and lung contusion/hemorrhagic shock subjected to chronic restraint stress decreased the prolonged mobilization of HPC from the bone marrow and decreased plasma G-CSF levels. Despite the decrease in mobilization of HPC, lung healing did not worsen. Alleviating chronic stress with propranolol may be a future therapeutic target to improve healing after severe injury.

Early propranolol administration to severely injured patients can improve bone marrow dysfunction

BACKGROUND

Bone marrow (BM) dysfunction is common in severely injured trauma patients, resulting from elevated catecholamines and plasma granulocyte colony-stimulating factor (G-CSF) as well as prolonged mobilization of hematopoietic progenitor cells (HPCs). We have previously shown that propranolol (β-blocker [BB]) reduces HPC mobilization in a rodent model of injury and hemorrhagic shock. We hypothesize that BB would prevent BM dysfunction in humans following severe injury.

METHODS

Forty-five severely injured trauma patients were studied in a prospective, randomized pilot trial. Twenty-five patients received BB, and 20 served as untreated controls. The dose of propranolol was adjusted to decrease the heart rate by 10% to 20% from baseline. Blood was analyzed for the presence of HPC (blast-forming unit erythroid cells [BFU-E] and colony-forming unit erythroid cells) and G-CSF. Demographic data, Injury Severity Score (ISS), hemoglobin, reticulocyte number, and outcome data were obtained.

RESULTS

The mean age of the study population was 33 years; 87% were male, with a mean ISS of 29. There is a significant increase in BFU-E in peripheral blood immediately following traumatic injury, and this mobilization persists for 30 days. The use of BB significantly decreases BFU-E and colony-forming unit erythroid cells at all time points. G-CSF is significantly elevated in both groups on admission; the use of BB decreases G-CSF levels by 51% as compared with 37% for controls. The average hemoglobin is nearly 1 g higher on the day of discharge with propranolol treatment (BB, 9.9 ± 0.4 g/dL vs. no BB, 9.1 ± 0.6 g/dL).

CONCLUSION

Following severe trauma, early treatment with propranolol following resuscitation is safe. The use of propranolol blunts early tachycardia, reduces HPC mobilization, and results in a faster return to baseline of the G-CSF peak seen after injury. There is also a trend toward faster recovery and resolution of anemia. Propranolol may be the first therapeutic agent to show improved BM function after severe injury.

LEVEL OF EVIDENCE

Therapeutic study, level III.

Do all β-blockers attenuate the excess hematopoietic progenitor cell mobilization from the bone marrow following trauma/hemorrhagic shock?

BACKGROUND

Severe injury results in increased mobilization of hematopoietic progenitor cells (HPC) from the bone marrow (BM) to sites of injury, which may contribute to persistent BM dysfunction after trauma. Norepinephrine is a known inducer of HPC mobilization, and nonselective β-blockade with propranolol has been shown to decrease mobilization after trauma and hemorrhagic shock (HS). This study will determine the role of selective β-adrenergic receptor blockade in HPC mobilization in a combined model of lung contusion (LC) and HS.

METHODS

Male Sprague-Dawley rats were subjected to LC, followed by 45 minutes of HS. Animals were then randomized to receive atenolol (LCHS + β1B), butoxamine (LCHS + β2B), or SR59230A (LCHS + β3B) immediately after resuscitation and daily for 6 days. Control groups were composed of naive animals. BM cellularity, %HPCs in peripheral blood, and plasma granulocyte-colony stimulating factor levels were assessed at 3 hours and 7 days. Systemic plasma-mediated effects were evaluated in vitro by assessment of BM HPC growth. Injured lung tissue was graded histologically by a blinded reader.

RESULTS

The use of β2B or β3B following LCHS restored BM cellularity and significantly decreased HPC mobilization. In contrast, β1B had no effect on HPC mobilization. Only β3B significantly reduced plasma G-CSF levels. When evaluating the plasma systemic effects, both β2B and β3B significantly improved BM HPC growth as compared with LCHS alone. The use of β2 and β3 blockade did not affect lung injury scores.

CONCLUSION

Both β2 and β3 blockade can prevent excess HPC mobilization and BM dysfunction when given after trauma and HS, and the effects seem to be mediated systemically, without adverse effects on subsequent healing. Only treatment with β3 blockade reduced plasma G-CSF levels, suggesting different mechanisms for adrenergic-induced G-CSF release and mobilization of HPCs. This study adds to the evidence that therapeutic strategies that reduce the exaggerated sympathetic stimulation after severe injury are beneficial and reduce BM dysfunction.

Autonomic regulation of cellular immune function

The nervous system and the immune system (IS) are two integrative systems that work together to detect threats and provide host defense, and to maintain/restore homeostasis. Cross-talk between the nervous system and the IS is vital for health and well-being. One of the major neural pathways responsible for regulating host defense against injury and foreign antigens and pathogens is the sympathetic nervous system (SNS). Stimulation of adrenergic receptors (ARs) on immune cells regulates immune cell development, survival, proliferative capacity, circulation, trafficking for immune surveillance and recruitment, and directs the cell surface expression of molecules and cytokine production important for cell-to-cell interactions necessary for a coordinated immune response. Finally, AR stimulation of effector immune cells regulates the activational state of immune cells and modulates their functional capacity. This review focuses on our current understanding of the role of the SNS in regulating host defense and immune homeostasis. SNS regulation of IS functioning is a critical link to the development and exacerbation of chronic immune-mediated diseases. However, there are many mechanisms that need to be further unraveled in order to develop sound treatment strategies that act on neural-immune interaction to resolve or prevent chronic inflammatory diseases, and to improve health and quality of life.

Social stress up-regulates inflammatory gene expression in the leukocyte transcriptome via β-adrenergic induction of myelopoiesis

Across a variety of adverse life circumstances, such as social isolation and low socioeconomic status, mammalian immune cells have been found to show a conserved transcriptional response to adversity (CTRA) involving increased expression of proinflammatory genes. The present study examines whether such effects might stem in part from the selective up-regulation of a subpopulation of immature proinflammatory monocytes (Ly-6c(high) in mice, CD16(-) in humans) within the circulating leukocyte pool. Transcriptome representation analyses showed relative expansion of the immature proinflammatory monocyte transcriptome in peripheral blood mononuclear cells from people subject to chronic social stress (low socioeconomic status) and mice subject to repeated social defeat. Cellular dissection of the mouse peripheral blood mononuclear cell transcriptome confirmed these results, and promoter-based bioinformatic analyses indicated increased activity of transcription factors involved in early myeloid lineage differentiation and proinflammatory effector function (PU.1, NF-κB, EGR1, MZF1, NRF2). Analysis of bone marrow hematopoiesis confirmed increased myelopoietic output of Ly-6c(high) monocytes and Ly-6c(intermediate) granulocytes in mice subject to repeated social defeat, and these effects were blocked by pharmacologic antagonists of β-adrenoreceptors and the myelopoietic growth factor GM-CSF. These results suggest that sympathetic nervous system-induced up-regulation of myelopoiesis mediates the proinflammatory component of the leukocyte CTRA dynamic and may contribute to the increased risk of inflammation-related disease associated with adverse social conditions.

Beta Blockade Protection of Bone Marrow Following Injury: A Critical Link between Heart Rate and Immunomodulation

Introduction

Severe trauma induces a profound elevation of catecholamines that is associated with bone marrow (BM) hematopoietic progenitor cell (HPC) colony growth suppression, excessive BM HPC mobilization, and a persistent anemia. Previously, propranolol (BB) use after injury and shock has been shown to prevent this BM dysfunction and improve hemoglobin levels. This study seeks to further investigate the optimal therapeutic dose and timing of BB administration following injury and shock.

Methods

Male Sprague-Dawley rats were subjected to a combined lung contusion (LC), hemorrhagic shock (HS) model ± BB. In our dose response experiments, animals received BB at 1, 2.5, 5, or 10 mg/kg immediately following resuscitation. In our therapeutic window experiments, following LCHS rats were given BB immediately, 1 hour, or 3 hours following resuscitation. BM and peripheral blood (PB) were collected in all animals to measure cellularity, BM HPC growth, circulating HPCs, and plasma G-CSF levels.

Results

Propranolol at 5 and 10 mg/kg significantly reduced HPC mobilization, restored BM cellularity and BM HPC growth, and decreased plasma G-CSF levels. Propranolol at 5 and 10 mg/kg also significantly decreased heart rate. When BB was administered beyond 1 hour after LCHS, its protective effects on cellularity, BM HPC growth, HPC mobilization, and plasma G-CSF levels were greatly diminished.

Conclusion

Early Buse following injury and shock at a dose of at least 5mg/kg is required to maintain BM cellularity and HPC growth, prevent HPC mobilization, and reduce plasma G-CSF levels. This suggests that propranolol exerts its BM protective effect in a dose and time dependent fashion in a rodent model. Finally, heart rate may be a valuable clinical marker to assess effective dosing of propranolol.

Is the sympathetic system involved in shock-induced gut and lung injury?

BACKGROUND

β-blockade (BB) has been shown to prevent bone marrow (BM) dysfunction after trauma and hemorrhagic shock (HS). The impact of the sympathetic system and the role of BB on shock-induced distant organ injury is not known. This study will determine if BB has systemic effects and can diminish gut and lung injury after trauma and HS.

METHODS

Male Sprague-Dawley rats were subjected to lung contusion (LC) followed by 45 minute of HS. Animals (n = 6 per group) were then randomized to either receive propranolol (LCHS + BB) immediately after resuscitation or not (LCHS). Gut permeability was evaluated in by diffusion of Mr 4,000 of fluorescein dextran (FD4) from a segment of small bowel into peripheral blood. Villous injury and lung injury were graded histologically by a blinded reader. Plasma-mediated effects of BB were evaluated in vitro by an assessment of BM progenitor growth.

RESULTS

Animals undergoing LCHS had significantly higher plasma levels of FD4 compared with control animals (mean [SEM], 2.8 [0.4] µg/mL vs. 0.8 [0.2] µg/mL). However, animals receiving BB had a significant reduction in plasma FD4 compared with the LCHS group. With the use of BB after LCHS, both ileal and lung injury scores were similar to control. In addition, BM progenitor growth was inhibited by the addition of LCHS plasma, and LCHS + BB plasma showed no inhibition of BM progenitor growth.

CONCLUSION

Propranolol can protect against the detrimental effects of trauma and HS on gut permeability, villous, and lung injury. The effects of BB are likely systemic and appear to be mediated through plasma. BB likely blunts the exaggerated sympathetic response after shock and injury. Propranolol's reduction of both BM dysfunction and distant organ injury further demonstrates the importance of the sympathetic nervous system and its role in potentiating end organ dysfunction after severe trauma.

β-adrenergic receptor inhibition affects cerebral glucose metabolism, motor performance, and inflammatory response after traumatic brain injury

BACKGROUND

The purpose of this study was to evaluate how β-adrenergic receptor inhibition after traumatic brain injury (TBI) alters changes in early cerebral glucose metabolism and motor performance, as well as cerebral cytokine and heat shock protein (HSP) expression.

METHODS

Mouse cerebral glucose metabolism was measured by microPET fluorodeoxyglucose uptake and converted into standardized uptake values (SUV). Four groups of C57/Bl6 mice (wild type [WT]) were initially evaluated: sham or TBI, followed by tail vein injection of either saline or a nonselective β-adrenergic receptor inhibitor (propranolol, 4 mg/kg). Then motor performance, cerebral cytokine, and HSP70 expression were studied at 12 hours and 24 hours after sham injury or TBI in WT mice treated with saline or propranolol and in β1-adrenergic/β2-adrenergic receptor knockout (BARKO) mice treated with saline.

RESULTS

Cerebral glucose metabolism was significantly reduced after TBI (mean SUV TBI, 1.63 vs. sham 1.97, p < 0.01) and propranolol attenuated this reduction (mean SUV propranolol, 1.89 vs. saline 1.63, p < 0.01). Both propranolol and BARKO reduced motor deficits at 24 hours after injury, but only BARKO had an effect at 12 hours after injury. TBI WT mice treated with saline performed worse than propranolol mice at 24 hours after injury on rotarod (23 vs. 44 seconds, p < 0.01) and rearing (130 vs. 338 events, p = 0.01) results. At 24 hours after injury, sham BARKO and TBI BARKO mice were similar on rotarod (21 vs. 19 seconds, p = 0.53), ambulatory testing (2,891 vs. 2,274 events, p = 0.14), and rearing (129 vs. 64 events, p = 0.09) results. Interleukin 1β expression was affected by BARKO and propranolol after TBI; attenuation of interleukin 6 and increased HSP70 expression were noted only with BARKO.

CONCLUSION

β-adrenergic receptor inhibition affects cerebral glucose metabolism, motor performance, as well as cerebral cytokine and HSP expression after TBI.

Does selective beta-1 blockade provide bone marrow protection after trauma/hemorrhagic shock?

BACKGROUND

Previously, nonselective beta-blockade (BB) with propranolol demonstrated protection of the bone marrow (BM) after trauma and hemorrhagic shock (HS). Because selective beta-1 blockers are used commonly for their cardiac protection, the aim of this study was to more clearly define the role of specific beta adrenergic receptors in BM protection after trauma and HS.

METHODS

Male Sprague-Dawley rats underwent unilateral lung contusion (LC) followed by HS for 45 minutes. After resuscitation, animals were injected with a selective beta-blocker, atenolol (B1B), butoxamine (B2B), or SR59230A (B3B). Animals were killed at 3 hours or 7 days. Heart rate and blood pressure were measured throughout the study period. BM cellularity, growth of hematopoietic progenitor cells (HPCs) in BM, and hemoglobin levels (Hb) were assessed.

RESULTS

Treatment with a B2B or B3B after LCHS restored both BM cellularity and BM HPC colony growth at 3 hours and 7 days. In contrast, treatment with a B1B had no effect on BM cellularity or HPC growth but did decrease heart effectively rate throughout the study. Treatment with a B3B after LCHS increased Hb as compared with LCHS alone.

CONCLUSION

After trauma and HS, protection of BM for 7 days was seen with use of either a selective beta-2 or beta-3 blocker. Use of a selective beta-1 blocker was ineffective in protecting the BM despite a physiologic decrease in heart rate. Therefore, the protection of BM is via the beta-2 and beta-3 receptors and it is not via a direct cardiovascular effect.

Beta-blockade prevents hematopoietic progenitor cell suppression after hemorrhagic shock

BACKGROUND

Severe injury is accompanied by sympathetic stimulation that induces bone marrow (BM) dysfunction by both suppression of hematopoietic progenitor cell (HPC) growth and loss of cells via HPC mobilization to the peripheral circulation and sites of injury. Previous work demonstrated that beta-blockade (BB) given prior to tissue injury both reduces HPC mobilization and restores HPC colony growth within the BM. This study examined the effect and timing of BB on BM function in a hemorrhagic shock (HS) model.

METHODS

Male Sprague-Dawley rats underwent HS via blood withdrawal, maintaining the mean arterial blood pressure at 30-40 mm Hg for 45 min, after which the extracted blood was reinfused. Propranolol (10 mg/kg) was given either prior to or immediately after HS. Blood pressure, heart rate, BM cellularity, and death were recorded. Bone marrow HPC growth was assessed by counting colony-forming unit-granulocyte-, erythrocyte-, monocyte-, megakaryocyte (CFU-GEMM), burst-forming unit-erythroid (BFU-E), and colony-forming unit-erythroid (CFU-E) cells.

RESULTS

Administration of BB prior to injury restored HPC growth to that of naïve animals (CFU-GEMM 59 ± 11 vs. 61 ± 4, BFU-E 68 ± 9 vs. 73 ± 3, and CFU-E 81 ± 35 vs. 78 ± 14 colonies/plate). Beta-blockade given after HS increased the growth of CFU-GEMM, BFU-E, and CFU-E significantly and improved BM cellularity compared with HS alone. The mortality rate was not increased in the groups receiving BB.

CONCLUSION

Administration of propranolol either prior to injury or immediately after resuscitation significantly reduced post-shock BM suppression. After HS, BB may improve BM cellularity by decreasing HPC mobilization. Therefore, the early use of BB post-injury may play an important role in attenuating the BM dysfunction accompanying HS.

Does beta blockade postinjury prevent bone marrow suppression?

BACKGROUND

Trauma-induced hypercatecholaminemia negatively impacts bone marrow (BM) function by suppressing BM hematopoietic progenitor cell (HPC) growth and increasing HPC egress to injured tissue. Beta blockade (BB) given before tissue injury alone has been shown to reduce both HPC mobilization and restore HPC colony growth within the BM. In a clinically relevant model, this study examines the effect of BB given after both tissue injury and hemorrhagic shock (HS).

METHODS

Male Sprague-Dawley rats underwent lung contusion (LC) with a blast wave percussion. HS was achieved after LC by maintaining the mean arterial blood pressure 30 mm Hg to 35 mm Hg for 45 minutes. Propranolol (10 mg/kg) was given once the mean arterial blood pressure>80 mm Hg and subsequent doses were given daily (LC/HS/BB). One-day and 7-day postinjury, analysis of BM and lung tissue for the growth of HPCs, hematologic parameters, and histology of lung injury were performed.

RESULTS

LC/HS significantly worsens BM CFU-E growth suppression (15±8 vs. 35±2) and increases CFU-E growth in injured tissue when compared with LC at 1 day and 7 days (33±5 vs. 22±9). The use of BB after LC/HS ameliorated BM suppression, the degree of anemia and HPC growth in the injured lung at 1 day and 7 days postinjury. Lung injury score shows that there was no worsening of lung healing with BB (LC/HS/BB 3.2±2 vs. LC/HS 3.8±0.8).

CONCLUSION

In an injury and shock model, administration of propranolol immediately after resuscitation significantly reduced BM suppression, and the protective effect is maintained at 7 days with daily BB. Although BB appears to improve BM function by decreasing HPC mobilization to injured tissue, there was no worsening of lung healing. Therefore, the use of propranolol after trauma and resuscitation may minimize long-term BM suppression after injury with no adverse impact on healing.

β-blockade protection of bone marrow following trauma: the role of G-CSF

BACKGROUND

Following severe trauma, there is a profound elevation of catecholamine that is associated with a persistent anemic state. We have previously shown that β-blockade (βB) prevents erythroid growth suppression and decreases hematopoietic progenitor cell (HPC) mobilization following injury. Under normal conditions, granulocyte colony stimulating factor (G-CSF) triggers the activation of matrix metalloprotease-9 (MMP-9), leading to the egress of progenitor cells from the bone marrow (BM). When sustained, this depletion of BM cellularity may contribute to BM failure. This study seeks to determine if G-CSF plays a role in the βB protection of BM following trauma.

METHODS

Male Sprague-Dawley rats were subjected to either unilateral lung contusion (LC) ± βB, hemorrhagic shock (HS) ± βB, or both LC/HS ± βB. Propranolol (βB) was given immediately following resuscitation. Animals were sacrificed at 3 and 24 h and HPC mobilization was assessed by evaluating BM cellularity and flow cytometric analysis of peripheral blood for HPCs. The concentration of G-CSF and MMP-9 was measured in plasma by ELISA.

RESULTS

BM cellularity is decreased at 3 h following LC, HS, and LC/HS. HS and LC/HS resulted in significant HPC mobilization in the peripheral blood. The addition of βB restored BM cellularity and reduced HPC mobilization. Three h following HS and LC/HS, plasma G-CSF levels more than double, however LC alone showed no change in G-CSF. βB significantly decreased G-CSF in both HS and LC/HS. Similarly, MMP-9 is elevated following LC/HS, and βB prevents this elevation (390 ± 100 pg/mL versus 275 ± 80 pg/mL).

CONCLUSION

βB protection of the BM following shock and injury may be due to reduced HPC mobilization and maintenance of BM cellularity. Following shock, there is an increase in plasma G-CSF and MMP-9, which is abrogated by βB and suggests a possible mechanism how βB decreases HPC mobilization thus preserving BM cellularity. In contrast, βB protection of BM following LC is not mediated by G-CSF. Therefore, the mechanism of progenitor cell mobilization from the BM is dependent on the type of injury.