Impact of sex and age on bone marrow immune responses in a murine model of trauma-hemorrhage

Aging Influences Fracture Healing on the Cellular Level and Alters Systemic RANKL and OPG Concentrations in a Murine Model

Clinical complications frequently follow polytrauma and bleeding fractures, increasing the risk of delayed fracture healing and nonunions, especially in aged patients. Therefore, this study examines age's impact on fracture repair with and without severe bleeding in mice. Young (17-26 weeks) and aged (64-72 weeks) male C57BL/6J mice (n = 72 in total, n = 6 per group) are allocated into 3 groups: the fracture group (Fx) undergoes femur osteotomy stabilized via external fixator, the combined trauma group (THFx) additionally receives pressure-controlled trauma hemorrhage (TH) and Sham animals are implanted with catheter and fixator without blood loss or osteotomy. Femoral bones are evaluated histologically 24 h and 3 weeks post-trauma, while RANKL/OPG and β-CTx are measured systemically via ELISA after 3 weeks. Aging results in less mineralized bone and fewer osteoclasts within the fracture of aged mice in contrast to young groups after three weeks. Systemically, aged animals exhibit increased RANKL and OPG levels after fracture compared to their young counterparts. The RANKL/OPG ratio rises in aged Fx animals compared to young mice, with a similar trend in THFx groups. In conclusion, age has an effect during the later course of fracture healing on the cellular and systemic levels.

Exosomal microRNA following severe trauma: Role in bone marrow dysfunction

INTRODUCTION

Severe trauma disrupts bone marrow function and is associated with persistent anemia and altered hematopoiesis. Previously, plasma-derived exosomes isolated after trauma have been shown to suppress in vitro bone marrow function. However, the cargo contained in these vesicles has not been examined. We hypothesized that trauma plasma-derived exosomes exhibit microRNA (miRNA) changes that impact bone marrow function after severe injury.

METHODS

Plasma was collected from a prospective cohort study of trauma patients (n = 15; 7 males, 8 females) with hip and/or femur fractures and an Injury Severity Score of ≥15; elective total hip arthroplasty (THA) patients (n = 8; 4 males, 4 females) served as operative controls. Exosomes were isolated from plasma with the Invitrogen Total Exosome Isolation Kit (Thermo Fisher Scientific, Waltham, MA), and RNA was isolated using a miRNeasy Mini Kit (Qiagen, Hilden, Germany). Direct quantification of miRNA was performed by NanoString Technologies on a human miRNA gene panel and analyzed with nSolver with significance defined as p < 0.05.

RESULTS

There were no differences in age or sex distribution between trauma and THA groups; the average Injury Severity Score was 23. Trauma plasma-derived exosomes had 60 miRNA identities that were significantly downregulated and 3 miRNAs that were upregulated when compared with THA ( p < 0.05). Twelve of the downregulated miRNAs have a direct role in hematopoiesis regulation. Furthermore, male trauma plasma-derived exosomes demonstrated downregulation of 150 miRNAs compared with male THA ( p < 0.05). Female trauma plasma-derived exosomes demonstrated downregulation of only four miRNAs and upregulation of two miRNAs compared with female THA ( p < 0.05).

CONCLUSION

We observed downregulation of 12 miRNAs linked to hematopoiesis along with sexual dimorphism in miRNA expression from plasma-derived exosomes following severe trauma. Understanding sexually dimorphic miRNA expression provides new insight into sex-based changes in postinjury systemic inflammation, immune system dysregulation, and bone marrow dysfunction and will aid us in more precise future potential therapeutic strategies.

LEVEL OF EVIDENCE

Prognostic and Epidemiological; Level III.

Pseudomonas aeruginosa Pneumonia Causes a Loss of Type-3 and an Increase in Type-1 Innate Lymphoid Cells in the Gut

BACKGROUND

Sepsis induces gut barrier dysfunction characterized by increased gut epithelial apoptosis and increased intestinal permeability. The cytokine IL-22 has been demonstrated to regulate gut barrier function. Type-3 innate lymphoid cells (ILC3) are the predominate source of IL-22 in the GI tract. We hypothesized that sepsis may cause changes to the gut ILC3/IL-22 axis.

MATERIALS AND METHODS

Sepsis was induced in WT and IL-22 KO mice by Pseudomonas aeruginosa pneumonia. Changes in gut-associated leukocyte populations were determined by flow-cytometry and ILC-associated transcripts were measured by RT-PCR. The effect of sepsis on gut permeability, pulmonary microbial burden, gut epithelial apoptosis, and survival was compared between WT and IL-22-/- mice.

RESULTS

Sepsis resulted in a significant decrease in the number of ILC3 in the gut, with a reciprocal increase in type-1 ILC (ILC1). Consistent with prior reports, sepsis was associated with increased gut permeability; however there was no difference in gut permeability, gut epithelial apoptosis, pulmonary microbial burden, or survival between WT and IL-22-/- mice.

CONCLUSIONS

Septic pneumonia causes a decrease in gut-associated ILC3 and an associated reciprocal increase in ILC1. This may reflect inflammation-induced conversion of ILC3 to ILC1. Constitutive systemic IL-22 deficiency does not alter sepsis-induced gut barrier dysfunction.

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.

Trauma Induces Emergency Hematopoiesis through IL-1/MyD88-Dependent Production of G-CSF

The inflammatory response to infection or injury dramatically increases the hematopoietic demand on the bone marrow to replace effector leukocytes consumed in the inflammatory response. In the setting of infection, pathogen-associated molecular patterns induce emergency hematopoiesis, activating hematopoietic stem and progenitor cells to proliferate and produce progeny for accelerated myelopoiesis. Sterile tissue injury due to trauma also increases leukocyte demand; however, the effect of sterile tissue injury on hematopoiesis is not well described. We find that tissue injury alone induces emergency hematopoiesis in mice subjected to polytrauma. This process is driven by IL-1/MyD88-dependent production of G-CSF. G-CSF induces the expansion of hematopoietic progenitors, including hematopoietic stem cells and multipotent progenitors, and increases the frequency of myeloid-skewed progenitors. To our knowledge, these data provide the first comprehensive description of injury-induced emergency hematopoiesis and identify an IL-1/MyD88/G-CSF-dependent pathway as the key regulator of emergency hematopoiesis after injury.

Severe Hemorrhagic Shock Leads to a Delayed Fracture Healing and Decreased Bone Callus Strength in a Mouse Model

BACKGROUND

Multiple trauma is frequently associated with hemorrhagic shock and fractures of the extremities. Clinically, the rate of impaired fracture healing (delayed healing and nonunion) seems to be increased in patients with multiple injuries compared with patients with isolated fractures. As the underlying pathogenesis remains poorly understood, we aimed to analyze the biomechanical properties during fracture healing in a murine model.

QUESTIONS

The aim of this study was to determine whether fracture healing after severe hemorrhagic shock results in (1) delayed bridging as determined by macroscopic and radiographic assessment, (2) altered conditions of callus components as determined by µCT, and (3) decreased maximum bending moment measured by a three-point-bending test compared with ordinary fracture healing.

METHODS

Male C57BL/6NCrl mice were randomly assigned to five groups and four different times (five to 10 mice per group and time). Only the right femur from each mouse was used for analysis: the trauma hemorrhage (TH) group received a pressure-controlled hemorrhagic shock via catheter; the osteotomy (Fx) group underwent osteotomy and implantation of an external fixator on the right femur; the combined trauma (THFx) group received hemorrhagic shock and an external fixator with osteotomy; the sham group underwent implantation of a catheter and external fixator but had no blood loss or osteotomy, and the control group underwent no interventions. After 2, 3, 4, or 6 weeks, five to 10 animals of each group were sacrificed. Bones were analyzed macroscopically and via radiographs, µCT, and three-point-bending test. Statistical significance was set at a probability less than 0.05. Comparisons were performed using the Mann-Whitney U or the Kruskal-Wallis test.

RESULTS

In the Fx group, the osteotomy gap was stable and bridged after 2 weeks in contrast to some bones in the THFx group where stable bridging did not occur. No difference was observed between the groups. µCT analysis showed reduced density of bone including callus (THFx: 1.17 g/cm³; interquartile range [IQR], 0.04 g/cm³; Fx: 1.22 g/cm³; IQR, 0.04 g/cm³; p = 0.002; difference of medians [DM], -0.048; 95% CI, -0.073 to -0.029) and increased share of callus per volume of bone mass (%) after 2 weeks in the THFx group compared with the Fx group (THFx: 44.16%; IQR, 8.66%; Fx: 36.73%; IQR, 4.39%; p = 0.015; DM, 7.634; 95% CI, 2.018-10.577). The three-point-bending test established a decreased maximum bending moment in the THFx group compared with the Fx group 2 weeks after surgery (THFx: 7.10 Nmm; IQR, 11.25 Nmm; Fx: 11.25 Nmm; IQR, 5.70 Nmm; p = 0.026; DM, -5.043; 95% CI, -10.867 to -0.74). No differences were observed between the THFx and Fx groups after more than 2 weeks.

CONCLUSION

In this in vivo mouse fracture model, we conclude that hemorrhagic shock retards fracture healing during the early phase of the facture healing process.

CLINICAL RELEVANCE

A severe hemorrhagic shock in patients could result in initial delayed fracture healing and needs special attention. We plan to conduct a prospective, observational clinical research study to analyze if delayed fracture healing occurs in patients after severe blood loss.

A Detailed Characterization of the Dysfunctional Immunity and Abnormal Myelopoiesis Induced by Severe Shock and Trauma in the Aged

The elderly are particularly susceptible to trauma, and their outcomes are frequently dismal. Such patients often have complicated clinical courses and ultimately die of infection and sepsis. Recent research has revealed that although elderly subjects have increased baseline inflammation as compared with their younger counterparts, the elderly do not respond to severe infection or injury with an exaggerated inflammatory response. Initial retrospective analysis of clinical data from the Glue Grant trauma database demonstrated that despite a similar frequency, elderly trauma patients have worse outcomes to pneumonia than younger subjects do. Subsequent analysis with a murine trauma model also demonstrated that elderly mice had increased mortality after posttrauma Pseudomonas pneumonia. Blood, bone marrow, and bronchoalveolar lavage sample analyses from juvenile and 20-24-mo-old mice showed that increased mortality to trauma combined with secondary infection in the aged are not due to an exaggerated inflammatory response. Rather, they are due to a failure of bone marrow progenitors, blood neutrophils, and bronchoalveolar lavage cells to initiate and complete an emergency myelopoietic response, engendering myeloid cells that fail to clear secondary infection. In addition, elderly people appeared unable to resolve their inflammatory response to severe injury effectively.

Abandon the mouse research ship? Not just yet!

Many preclinical studies in critical care medicine and related disciplines rely on hypothesis-driven research in mice. The underlying premise posits that mice sufficiently emulate numerous pathophysiologic alterations produced by trauma/sepsis and can serve as an experimental platform for answering clinically relevant questions. Recently, the lay press severely criticized the translational relevance of mouse models in critical care medicine. A series of provocative editorials were elicited by a highly publicized research report in the Proceedings of the National Academy of Sciences (PNAS; February 2013), which identified an unrecognized gene expression profile mismatch between human and murine leukocytes following burn/trauma/endotoxemia. Based on their data, the authors concluded that mouse models of trauma/inflammation are unsuitable for studying corresponding human conditions. We believe this conclusion was not justified. In conjunction with resulting negative commentary in the popular press, it can seriously jeopardize future basic research in critical care medicine. We will address some limitations of that PNAS report to provide a framework for discussing its conclusions and attempt to present a balanced summary of strengths/weaknesses of use of mouse models. While many investigators agree that animal research is a central component for improved patient outcomes, it is important to acknowledge known limitations in clinical translation from mouse to man. The scientific community is responsible to discuss valid limitations without overinterpretation. Hopefully, a balanced view of the strengths/weaknesses of using animals for trauma/endotoxemia/critical care research will not result in hasty discount of the clear need for using animals to advance treatment of critically ill patients.

Protective immunity and defects in the neonatal and elderly immune response to sepsis

Populations encompassing extremes of age, including neonates and elderly, have greater mortality from sepsis. We propose that the increased mortality observed in the neonatal and elderly populations after sepsis is due to fundamental differences in host-protective immunity and is manifested at the level of the leukocyte transcriptome. Neonatal (5-7 d), young adult (6-12 wk), or elderly (20-24 mo) mice underwent a cecal slurry model of intra-abdominal sepsis. Both neonatal and elderly mice exhibited significantly greater mortality to sepsis (p < 0.05). Neonates in particular exhibited significant attenuation of their inflammatory response (p < 0.05), as well as reductions in cell recruitment and reactive oxygen species production (both p < 0.05), all of which could be confirmed at the level of the leukocyte transcriptome. In contrast, elderly mice were also more susceptible to abdominal peritonitis, but this was associated with no significant differences in the magnitude of the inflammatory response, reduced bacterial killing (p < 0.05), reduced early myeloid cell activation (p < 0.05), and a persistent inflammatory response that failed to resolve. Interestingly, elderly mice expressed a persistent inflammatory and immunosuppressive response at the level of the leukocyte transcriptome, with failure to return to baseline by 3 d. This study reveals that neonatal and elderly mice have profoundly different responses to sepsis that are manifested at the level of their circulating leukocyte transcriptome, although the net result of increased mortality is similar. Considering these differences are fundamental aspects of the genomic response to sepsis, interventional therapies will require individualization based on the age of the population.

Aged mice are unable to mount an effective myeloid response to sepsis

The elderly have increased morbidity and mortality following sepsis; however, the cause(s) remains unclear. We hypothesized that these poor outcomes are due in part to defects in innate immunity, rather than to an exaggerated early inflammatory response. Young (6-12 wk) or aged (20-24 mo) mice underwent polymicrobial sepsis, and subsequently, the aged mice had increased mortality and defective peritoneal bacterial clearance compared with young mice. No differences were found in the magnitude of the plasma cytokine responses. Although septic aged mice displayed equivalent or increased numbers of circulating, splenic, and bone marrow myeloid cells, some of these cells exhibited decreased phagocytosis, reactive oxygen species production, and chemotaxis. Blood leukocyte gene expression was less altered in aged versus young mice 1 d after sepsis. Aged mice had a relative inability to upregulate gene expression of pathways related to neutrophil-mediated protective immunity, chemokine/chemokine receptor binding, and responses to exogenous molecules. Expression of most MHC genes remained more downregulated in aged mice at day 3. Despite their increased myeloid response to sepsis, the increased susceptibility of aged mice to sepsis appears not to be due to an exaggerated inflammatory response, but rather, a failure to mount an effective innate immune response.

Rejuvenation of the inflammatory system stimulates fracture repair in aged mice

Age significantly reduces the regenerative capacity of the skeleton, but the underlying causes are unknown. Here, we tested whether the functional status of inflammatory cells contributes to delayed healing in aged animals. We created chimeric mice by bone marrow transplantation after lethal irradiation. In this model, chondrocytes and osteoblasts in the regenerate are derived exclusively from host cells while inflammatory cells are derived from the donor. Using this model, the inflammatory system of middle-aged mice (12 month old) was replaced by transplanted bone marrow from juvenile mice (4 weeks old), or age-matched controls. We found that the middle-aged mice receiving juvenile bone marrow had larger calluses and more bone formation during early stages and faster callus remodeling at late stages of fracture healing, indicating that inflammatory cells derived from the juvenile bone marrow accelerated bone repair in the middle-aged animals. In contrast, transplanting bone marrow from middle-aged mice to juvenile mice did not alter the process of fracture healing in juvenile mice. Thus, the roles of inflammatory cells in fracture healing may be age-related, suggesting the possibility of enhancing fracture healing in aged animals by manipulating the inflammatory system.

Animal models for trauma research: what are the options?

Even if trauma patients initially avoid death after trauma (due to massive blood volume loss, primary severe brain injury), they are still at risk for multiple organ failure. Thus, it is crucial to elucidate the underlying pathophysiological mechanisms of trauma/hemorrhagic shock and the immune response involved. As of now, many hemorrhagic shock/trauma studies have used various types of animal models. Despite a large number of results from these efforts, some authors have argued that animal model results are difficult to translate directly into the clinical scenario. This review summarizes the advantages and the disadvantages of using animal models in trauma/hemorrhagic shock studies and discusses the relevance of various animal studies to the clinical scenario.

Aging and animal models of systemic insult: trauma, burn, and sepsis

In the acute-care setting, it is widely accepted that elderly patients have increased morbidity and mortality compared with young healthy patients. The reasons for this, however, are largely unknown. Although animal modeling has helped improve treatment strategies for young patients, there are a scarce number of studies attempting to understand the mechanisms of systemic insults such as trauma, burn, and sepsis in aged individuals. This review aims to highlight the relevance of using animals to study the pathogenesis of these insults in the aged and, despite the deficiency of information, to summarize what is currently known in this field.

Embryonic stem cells attenuate myocardial dysfunction and inflammation after surgical global ischemia via paracrine actions

Stem cell treatment may positively influence recovery and inflammation after shock by multiple mechanisms, including the paracrine release of protective growth factors. Embryonic stem cells (ESCs) are understudied and may have greater protective power than adult bone marrow stem cells (BMSCs). We hypothesized that ESC paracrine protective mechanisms in the heart (decreased injury by enhanced growth factor-mediated reduction of proinflammatory cytokines) would be superior to the paracrine protective mechanisms of the adult stem cell population in a model of surgically induced global ischemia. Adult Sprague-Dawley rat hearts were isolated and perfused via Langendorff model. Hearts were subjected to 25 min of warm global ischemia and 40 min of reperfusion and were randomly assigned into one of four groups: 1) vehicle treated; 2) BMSC or ESC preischemic treatment; 3) BMSC or ESC postischemic treatment; and 4) BMSC- or ESC-conditioned media treatment. Myocardial function was recorded, and hearts were analyzed for expression of tissue cytokines and growth factors (ELISA). Additionally, ESCs and BMSCs in culture were assessed for growth factor production (ELISA). ESC-treated hearts demonstrated significantly greater postischemic recovery of function (left ventricular developed pressure, end-diastolic pressure, and maximal positive and negative values of the first derivative of pressure) than BMSC-treated hearts or controls at end reperfusion. ESC-conditioned media (without cells) also conferred cardioprotection at end reperfusion. ESC-infused hearts demonstrated increased VEGF and IL-10 production compared with BMSC hearts. ESC hearts also exhibited decreased proinflammatory cytokine expression compared with MSC hearts. Moreover, ESCs in cell culture demonstrated greater pluripotency than MSCs. ESC paracrine protective mechanisms in surgical ischemia are superior to those of adult stem cells.

Estradiol's salutary effects on keratinocytes following trauma-hemorrhage are mediated by estrogen receptor (ER)-alpha and ER-beta

Although administration of 17beta-estradiol (estrogen) following trauma-hemorrhage attenuates the elevation of cytokine production and mitogen-activated protein kinase (MAPK) activation in epidermal keratinocytes, whether the salutary effects of estrogen are mediated by estrogen receptor (ER)-alpha or ER-beta is not known. To determine which estrogen receptor is the mediator, we subjected C3H/HeN male mice to trauma-hemorrhage (2-cm midline laparotomy and bleeding of the animals to a mean blood pressure of 35 mmHg and maintaining that pressure for 90 min) followed by resuscitation with Ringer's lactate (four times the shed blood volume). At the middle of resuscitation we subcutaneously injected ER-alpha agonist propyl pyrazole triol (PPT; 5 microg/kg), ER-beta agonist diarylpropionitrile (DPN; 5 microg/kg), estrogen (50 microg/kg), or ER antagonist ICI 182,780 (150 microg/kg). Two hours after resuscitation, we isolated keratinocytes, stimulated them with lipopolysaccharide for 24 h (5 microg/mL for maximum cytokine production), and measured the production of interleukin (IL)-6, IL-10, IL-12, and TNF-alpha and the activation of MAPK. Keratinocyte cytokine production markedly increased and MAPK activation occurred following trauma-hemorrhage but were normalized by administration of estrogen, PPT, and DPN. PPT and DPN administration were equally effective in normalizing the inflammatory response of keratinocytes, indicating that both ER-alpha and ER-beta mediate the salutary effects of estrogen on keratinocytes after trauma-hemorrhage.

TGF-alpha increases human mesenchymal stem cell-secreted VEGF by MEK- and PI3-K- but not JNK- or ERK-dependent mechanisms

Transforming growth factor-alpha (TGF-alpha) may be an important mediator of wound healing and the injury response. Human bone marrow mesenchymal stem cells (MSCs) release VEGF as a potentially beneficial paracrine response; however, it remains unknown whether TGF-alpha stimulates the production of VEGF from MSCs and, if so, by which mechanisms. We hypothesized that TGF-alpha would increase human MSC VEGF production by MAP kinase kinase (MAPKK/MEK), phosphatidylinositol 3-kinase (PI3-K)-, ERK, and JNK-dependent mechanisms. To study this, MSCs were cultured and divided into the following groups: 1) with vehicle; 2) with various stimulants alone: TGF-alpha, TNF-alpha, or TGF-alpha+TNF-alpha; 3) with individual kinase inhibitors alone (two different inhibitors for each of the following kinases: MEK, PI3-K, ERK, or JNK); and 4) with the above stimulants and each of the eight inhibitors. After 24-h incubation, a TGF-alpha dose-response curve demonstrated that low-dose TGF-alpha (500 pg/ml) suppressed MSC production of VEGF compared with vehicle (502 +/- 16 pg/10(5) cells/ml to 332 +/- 9 pg/10(5) cells/ml), while high-dose TGF-alpha (250 ng/ml) significantly increased MSC VEGF production (603 +/- 24 pg/10(5) cells/ml). High-dose TGF-alpha also increased TNF-alpha-stimulated release of VEGF from MSCs. MSCs exposed to TGF-alpha and/or TNF-alpha also demonstrated increased activation of PI3-K, JNK, and ERK. The TGF-alpha-stimulated production of VEGF by MSCs and the additive effect of TNF-alpha and TGF-alpha on VEGF production were abolished by MEK and PI3-K inhibition, but not ERK or JNK inhibition. Our data suggest that TGF-alpha increases VEGF production in MSCs via MEK- and PI3-K- but not ERK- or JNK-dependent mechanisms.

Bench-to-bedside review: latest results in hemorrhagic shock

Hemorrhagic shock is a leading cause of death in trauma patients worldwide. Bleeding control, maintenance of tissue oxygenation with fluid resuscitation, coagulation support, and maintenance of normothermia remain mainstays of therapy for patients with hemorrhagic shock. Although now widely practised as standard in the USA and Europe, shock resuscitation strategies involving blood replacement and fluid volume loading to regain tissue perfusion and oxygenation vary between trauma centers; the primary cause of this is the scarcity of published evidence and lack of randomized controlled clinical trials. Despite enormous efforts to improve outcomes after severe hemorrhage, novel strategies based on experimental data have not resulted in profound changes in treatment philosophy. Recent clinical and experimental studies indicated the important influences of sex and genetics on pathophysiological mechanisms after hemorrhage. Those findings might provide one explanation why several promising experimental approaches have failed in the clinical arena. In this respect, more clinically relevant animal models should be used to investigate pathophysiology and novel treatment approaches. This review points out new therapeutic strategies, namely immunomodulation, cardiovascular maintenance, small volume resuscitation, and so on, that have been introduced in clinics or are in the process of being transferred from bench to bedside. Control of hemorrhage in the earliest phases of care, recognition and monitoring of individual risk factors, and therapeutic modulation of the inflammatory immune response will probably constitute the next generation of therapy in hemorrhagic shock. Further randomized controlled multicenter clinical trials are needed that utilize standardized criteria for enrolling patients, but existing ethical requirements must be maintained.

Estradiol-treated mesenchymal stem cells improve myocardial recovery after ischemia

BACKGROUND

Stem cell therapy is a promising treatment modality for injured cardiac tissue. A novel mechanism for this cardioprotection may include paracrine actions. Our lab has recently shown that gender differences exist in mesenchymal stem cell (MSC) paracrine function. Estrogen is implicated in the cardioprotection found in females. It remains unknown whether 17beta-estradiol (E2) affects MSC paracrine function and whether E2-treated MSCs may better protect injured cardiac tissue. We hypothesize that E2-exposed MSCs infused into hearts prior to ischemia may demonstrate increased vascular endothelial growth factor (VEGF) production and greater protection of myocardial function compared to untreated MSCs.

MATERIALS AND METHODS

Untreated and E2-treated MSCs were isolated, cultured, and plated and supernatants were harvested for VEGF assay (enzyme-linked immunosorbent assay). Adult male Sprague-Dawley rat hearts (n = 13) were isolated and perfused via Langendorff model and subjected to 15 min equilibration, 25 min warm global ischemia, and 40 min reperfusion. Hearts were randomly assigned to perfusate vehicle, untreated male MSC, or E2-treated male MSC. Transcoronary delivery of 1 million MSCs was performed immediately prior to ischemia in experimental hearts.

RESULTS

E2-treated MSCs provoked significantly more VEGF production than untreated MSCs (933.2 +/- 64.9 versus 595.8 +/- 10.7 pg/mL). Postischemic recovery of left ventricular developed pressure was significantly greater in hearts infused with E2-treated MSCs (66.9 +/- 3.3%) than untreated MSCs (48.7 +/- 3.7%) and vehicle (28.9 +/- 4.6%) at end reperfusion. There was also greater recovery of the end diastolic pressure with E2-treated MSCs than untreated MSCs and vehicle.

CONCLUSIONS

Preischemic infusion of MSCs protects myocardial function and viability. E2-treated MSCs may enhance this paracrine protection, which suggests that ex vivo modification of MSCs may improve therapeutic outcome.

Sex differences and estrogen modulation of the cellular immune response after injury

Cell-mediated immunity is extremely important for resolution of infection and for proper healing from injury. However, the cellular immune response is dysregulated following injuries such as burn and hemorrhage. Sex hormones are known to regulate immunity, and a well-documented dichotomy exists in the immune response to injury between the sexes. This disparity is caused by differences in immune cell activation, infiltration, and cytokine production during and after injury. Estrogen and testosterone can positively or negatively regulate the cellular immune response either by aiding in resolution or by compounding the morbidity and mortality. It is apparent that the hormonal dysregulation is dependent not only on the type of injury sustained but also the amount of circulating hormones. Therefore, it may be possible to design sex-specific therapies to improve immunological function and patient outcome.

Human mesenchymal stem cells stimulated by TNF-alpha, LPS, or hypoxia produce growth factors by an NF kappa B- but not JNK-dependent mechanism

Understanding the mechanisms by which adult stem cells produce growth factors may represent an important way to optimize their beneficial paracrine and autocrine effects. Components of the wound milieu may stimulate growth factor production to promote stem cell-mediated repair. We hypothesized that tumor necrosis factor-alpha (TNF-alpha), endotoxin (LPS), or hypoxia may activate human mesenchymal stem cells (MSCs) to increase release of vascular endothelial growth factor (VEGF), fibroblast growth factor 2 (FGF2), insulin-like growth factor 1 (IGF-1), or hepatocyte growth factor (HGF) and that nuclear factor-kappa B (NF kappa B), c-Jun NH2-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK) mediates growth factor production from human MSCs. To study this, human MSCs were harvested, passaged, divided into four groups (100,000 cells, triplicates) and treated as follows: 1) with vehicle; 2) with stimulant alone [24 h LPS (200 ng/ml), 24 h TNF-alpha (50 ng/ml), or 24 h hypoxia (1% O2)]; 3) with inhibitor alone [NF kappa B (PDTC, 1 mM), JNK (TI-JIP, 10 microM), or ERK (ERK Inhibitor II, 25 microM)]; and 4) with stimulant and the various inhibitors. After 24 h incubation, MSC activation was determined by measuring supernatants for VEGF, FGF2, IGF-1, or HGF (ELISA). TNF-alpha, LPS, and hypoxia significantly increased human MSC VEGF, FGF2, HGF, and IGF-1 production versus controls. Stem cells exposed to injury demonstrated increased activation of NF kappa B, ERK, and JNK. VEGF, FGF2, and HGF expression was significantly reduced by NF kappa B inhibition (50% decrease) but not ERK or JNK inhibition. Moreover, ERK, JNK, and NF kappa B inhibitor alone did not activate MSC VEGF expression over controls. Various stressors activate human MSCs to increase VEGF, FGF2, HGF, and IGF-1 expression, which depends on an NFkB mechanism.

Immunity, trauma and the elderly

It is believed that an uncontrolled or poorly coordinated immune reaction can be stimulated by major trauma and be responsible for the development of the multiple organ dysfunction syndrome (MODS). The elderly have a reduced ability to mount an effective immune reaction with deficiencies involving both humoral and cellular aspects of immunity that involve poor function of both the stimulatory and immuno-suppressive sides of the immune process. However, there is currently no hard evidence that the excess mortality after major trauma in the elderly is associated with an impaired or excessive immune response. It is possible that their poor resistance to infection is important and immune modulated but the dominant factor in the excess mortality in the elderly population is probably associated with their lack of physiological reserve to respond to a major physiological challenge.

STEM CELL MECHANISMS AND PARACRINE EFFECTS

Heart disease remains the leading cause of death in the industrialized world. Stem cell therapy is a promising treatment modality for injured cardiac tissue. A novel mechanism for this cardioprotection may include paracrine actions. Cardiac surgery represents the unique situation where preischemia and postischemia treatment modalities exist that may use stem cell paracrine protection. This review (1) recalls the history of stem cells in cardiac disease and the unraveling of its mechanistic basis for protection, (2) outlines the pathways for stem cell-mediated paracrine protection, (3) highlights the signaling factors expressed, (4) explores the potential of using stem cells clinically in cardiac surgery, and (5) summarizes all human stem cell studies in cardiac disease to date.

Type I diabetic bone phenotype is location but not gender dependent

Bone is highly dynamic and responsive. Bone location, bone type and gender can influence bone responses (positive, negative or none) and magnitude. Type I diabetes induces bone loss and increased marrow adiposity in the tibia. We tested if this response exhibits gender and location dependency by examining femur, vertebrae and calvaria of male and female, control and diabetic BALB/c mice. Non-diabetic male mice exhibited larger body, muscle, and fat mass, and increased femur BMD compared to female mice, while vertebrae and calvarial bone parameters did not exhibit gender differences. Streptozotocin-induced diabetes caused a reduction in BMD at all sites examined irrespective of gender. Increased marrow adiposity was evident in diabetic femurs and calvaria (endochondrial and intramembranous formed bones, respectively), but not in vertebrae. Leptin-deficient mice also exhibit location dependent bone responses and we found that serum leptin levels were significantly lower in diabetic compared to control mice. However, in contrast to leptin-deficient mice, the vertebrae of T1-diabetic mice exhibit bone loss, not gain. Taken together, our findings indicate that TI-diabetic bone loss in mice is not gender, bone location or bone type dependent, while increased marrow adiposity is location dependent.