Differential effects of acute hypoxia and endotoxin on the secretion and expression of bone marrow interleukin-1 and interleukin-6

Dysregulated myelopoiesis and hematopoietic function following acute physiologic insult

PURPOSE OF REVIEW

The purpose of this review is to describe recent findings in the context of previous work regarding dysregulated myelopoiesis and hematopoietic function following an acute physiologic insult, focusing on the expansion and persistence of myeloid-deriver suppressor cells, the deterioration of lymphocyte number and function, and the inadequacy of stress erythropoiesis.

RECENT FINDINGS

Persistent myeloid-derived suppressor cell (MDSC) expansion among critically ill septic patients is associated with T-cell suppression, vulnerability to nosocomial infection, chronic critical illness, and poor long-term functional status. Multiple approaches targeting MDSC expansion and suppressor cell activity may serve as a primary or adjunctive therapeutic intervention. Traumatic injury and the neuroendocrine stress response suppress bone marrow erythropoietin receptor expression in a process that may be reversed by nonselective beta-adrenergic receptor blockade. Hepcidin-mediated iron-restricted anemia of critical illness requires further investigation of novel approaches involving erythropoiesis-stimulating agents, iron administration, and hepcidin modulation.

SUMMARY

Emergency myelopoiesis is a dynamic process with unique phenotypes for different physiologic insults and host factors. Following an acute physiologic insult, critically ill patients are subject to persistent MDSC expansion, deterioration of lymphocyte number and function, and inadequate stress erythropoiesis. Better strategies are required to identify patients who are most likely to benefit from targeted therapies.

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.

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

BACKGROUND

Hematopoietic progenitor cells (HPCs) are mobilized into the peripheral blood (PB) and then sequestered in injured tissue after trauma. Nonselective beta-adrenergic blockade (BB) has been shown to cause a decrease in mobilization of HPCs to the periphery and to injured tissue. Given the vast physiologic effects of nonselective BB, the aim of this study is to delineate the role of selective BB in HPC growth and mobilization.

METHODS

Rats underwent daily intraperitoneal injections of propranolol (Prop), atenolol (B1), butoxamine (B2), or SR59230A (B3) for 3 days to induce BB. All groups then underwent lung contusion (LC). HPC presence was assessed by GEMM, BFU-E, and CFU-E colony growth both in injured lung and bone marrow (BM). Flow cytometry, using c-kit and CD71, was used to determine mobilization into PB.

RESULTS

LC alone decreased BM HPC growth in all erythroid cell types and increased their number in injured lung (all *p < 0.05). beta-Blockade with Prop, B2, and B3 blockades restored BM HPC growth to control levels and decreased HPCs recovered in the injured lung. Similarly, Prop, B2, and B3 blockade prevented HPC mobilization to PB. B1 blockade with atenolol had no impact on HPC growth and mobilization following LC.

CONCLUSIONS

Nonselective BB reduced suppression of HPC growth in BM after injury and prevented the mobilization and subsequent sequestration of HPCs in injured tissue. Our data have shown that this effect is mediated through the B2 and B3 receptors. Therefore, after trauma, treatment with selective B2 or B3 blocker may attenuate the BM suppression associated with tissue injury.

Dose-response relationship between norepinephrine and erythropoiesis: evidence for a critical threshold

BACKGROUND

Severe traumatic injury elicits a neuroendocrine response that activates the sympathetic nervous system. Our previous work suggests that norepinephrine (NE) influences the bone marrow (BM) erythropoietic response. However, the dose-response relationship between NE and erythropoiesis remains unclear.

MATERIALS AND METHODS

Two days following chemical sympathectomy with 6-hydroxydopamine (6-OHDA) or injection with saline vehicle (SHAM), male Sprague-Dawley rats were infused continuously with either saline (NS) or increasing doses of NE for 5 d via osmotic pumps. Erythropoiesis was assessed by growth of erythroid progenitor colonies (BFU-E and CFU-E for early and late progenitors, respectively).

RESULTS

Following chemical sympathectomy with 6-OHDA, both BFU-E and CFU-E growth is inhibited (42%∗ and 43%∗ versus 100% SHAM, ∗P < 0.05). SHAM rats with continuous infusion of exogenous NE show a clear dose-response inhibition of both BFU-E and CFU-E colony growth. In the 6-OHDA rats, continuous infusion of NE restored BFU-E and CFU-E growth at 10(-8) g/h and 10(-9) g/h, respectively.

CONCLUSIONS

Erythroid precursor colony growth is inhibited in sympathectomized rats. In addition, supraphysiologic doses of exogenous NE inhibit normal erythropoiesis in a dose-dependent fashion. Following chemical sympathectomy with 6-OHDA, exogenous NE restores erythropoiesis in a narrow window. Therefore, NE has a complex interaction within the BM and the elevation of NE following traumatic injury impacts BM erythropoietic function.

Resuscitation with hydroxyethyl starch solution prevents bone marrow mononuclear apoptosis in a rat trauma-hemorrhagic shock model

BACKGROUND

: Trauma-hemorrhagic shock (T/HS) has been associated with multiorgan dysfunction, including bone marrow failure. This study examined apoptosis and morphologic alterations in bone marrow mononuclear cells (BMMNCs) with different volume therapies after T/HS.

METHODS

: T/HS was induced in groups of male Sprague-Dawley rats through a fracture of the left femur and continual bleeding for 30 minutes, followed by resuscitation with Ringer's lactate solution (RL), 6% hydroxyethyl starch solution (HES), or 5% albumin (ALB). Mean arterial blood pressure was monitored during the T/HS and resuscitation, and the impacts of various resuscitative fluids on apoptosis and morphology of BMMNCs at 24 hours and 48 hours after resuscitation were examined using flow cytometry, transferase-mediated dUTP nick-end labeling assay, and hematoxylin and eosin staining.

RESULTS

: Fluctuations in mean arterial blood pressure were homogenous among the three treatment groups. The percentage of early BMMNC apoptosis increased significantly at 24 hours and 48 hours (24.65% +/- 5.41% and 29.09% +/- 2.07%, respectively; p < 0.05), and the percentage of late BMMNC apoptosis increased to 13.43% +/- 2.82% (p < 0.05) at 48 hours in the T/HS + RL group. In contrast, resuscitation with HES alone dramatically attenuated the apoptosis. Resuscitation with ALB alleviated BMMNC apoptosis, except for late apoptosis at 48 hours. A greater number of apoptotic BMMNCs as well as morphologic alterations were shown using the transferase-mediated dUTP nick-end labeling assay and hematoxylin and eosin stain in the T/HS + RL group than in the HES or ALB groups.

CONCLUSION

: Intravascular volume replacement with HES showed prevention of BMMNC apoptosis at first 48 hours after T/HS compared with RL and ALB. These findings provide new insights into the intervention mechanism of HES on T/HS-related multiorgan dysfunction.

Mobilization of bone marrow cells to the site of injury is necessary for wound healing

INTRODUCTION

Lung contusion (LC) and hemorrhagic shock (HS) result in early organ failure (lung and bone marrow [BM]), possibly through sequestration of mobilized BM hematopoietic progenitor cells (HPC) into the lung. Postinjury mesenteric lymph has been shown to cause early organ failure. Thus, we hypothesized that diversion of mesenteric lymph would improve early organ dysfunction through decreased mobilization of BM HPC to the lung.

METHODS

Rats were subjected to unilateral LC +/- lymph duct ligation (LDL). Additional groups underwent HS (mean arterial pressure of 35 mm Hg for 90 minutes) with and without LC +/- LDL. Controls were only cannulated. At 3 hours, both lungs and BM were harvested for growth of HPC (BFU-E, CFU-E, and CFU-GEMM). Additional rats were killed on day 14 and the lungs examined by histology.

RESULTS

LC alone decreased BM HPC in all cell types and increased their number in the injured lung (all *p < 0.05 vs. control). Shock exacerbated these results and resulted in a further increase in BM cells in the injured lung and a decrease in BM HPC growth. LDL reversed the response to LC alone. In rats subjected to LC and HS, LDL restored BM HPC growth to levels observed after LC alone and decreased HPC recovered in the contused lung 50% compared with that in shocked rats without LDL. At day 14, all rats subjected to LC demonstrated healing of their injury. In contrast, all LC + LDL rats had evidence of pneumonia, thickened alveoli, and increased numbers of inflammatory cells.

CONCLUSIONS

Diversion of the postinjury mesenteric lymph decreased early BM suppression after LC or LC with HS. However, this improved BM function occurred at the expense of impaired lung healing and an increased susceptibility to pulmonary infection. As mobilized BM cells differentiate into pneumocytes, these data indicate that mobilization of BM cells to the site of injury is an adaptive and necessary response for successful wound healing and tissue repair.

Tac1 regulation by RNA-binding protein and miRNA in bone marrow stroma: Implication for hematopoietic activity

Hematopoiesis is the process by which immune and blood cells are produced from a finite number of relatively few hematopoietic stem cells (HSCs). In adults, hematopoiesis occurs in the adult bone marrow (BM), with the support of stromal cells. This support partly occurs through the production of hematopoietic regulators belonging to the families of cytokines and neuropeptides/neurotransmitters, which mediate their actions through specific receptors. Thus, stromal cells could be central to the neural-hematopoietic-immune axis. This study focuses on Tac1, which encodes hematopoietic regulators belonging to the tachykinin family of neuropeptides. We examined post-transcriptional regulation of Tac1 in BM stroma. Since this gene is inducible in stroma, we selected cytokines with varying hematopoietic effects: stimulator Stem Cell Factor (SCF), broad-acting IL-11 and suppressive TGF-beta1. RNA shift with Tac1 mRNA and cytoplasmic extracts from IL-11 and SCF-stimulated stroma showed RNA shift after 15min at 37 degrees C, whereas a shift was detected with extracts from TGF-beta1-stimulated stroma after 5min at room temperature. Another level of post-transcriptional regulation was observed by the detection of miRNAs that interact with the 3' untranslated region of Tac1 mRNA. In summary, this study showed that cytokine induced miRNA downregulation and RNA-binding protein(s) are involved in post-transcriptional regulation of Tac1 in BM stroma. The broad categories of cytokines as hematopoietic stimulators or inhibitors might depend on the avidity of RNA-binding protein(s) for Tac1 mRNA, as well as the ability to degrade or stabilize the specific miRNAs.

Hematopoietic progenitor cells mobilize to the site of injury after trauma and hemorrhagic shock in rats

BACKGROUND

Trauma and hemorrhagic shock (T/HS) has been demonstrated to result in bone marrow (BM) suppression and the release of hematopoietic progenitor cells (HPC) into the peripheral blood in both human beings and experimental animals. HPC have also been identified in numerous end organs after T/HS and the ongoing loss of progenitor cells from the BM may play a role in posttraumatic BM suppression. We investigated the hypothesis that HPC will specifically migrate to sites of tissue trauma and that this process is exacerbated by hemorrhagic shock (HS).

METHODS

Sprague-Dawley rats (250-400 g) sustaining a unilateral lung contusion (LC) secondary to a blast wave of a percussive nail gun, were subjected to either HS (MAP 40-45 mm Hg for 45 minutes) or sham shock (SS). Animals were killed at 3 hours, 3 days, and 7 days after resuscitation and the right and left lungs from each animal were processed separately and the uninjured left lung served as a control for comparison with the contused right lung. BM mononuclear cells from each individual lung and the femurs were isolated and plated (2 x 10) in duplicate for granulocyte-macrophage colony-forming units (CFU-GM), erythroid colony-forming units (CFU-E), and erythroid burst-forming units (BFU-E) colony growth.

RESULTS

At 3 hours, LC resulted in a significant increase in progenitor colonies able to be grown from the injured lung compared with from the uninjured lung (CFU-GM: 11 +/- 1 vs. 5 +/- 2, CFU-E: 12 +/- 7 vs. 5 +/- 3, BFU-E: 7 +/- 1 vs. 3 +/- 1 colonies per 10 BM mononuclear cells; all p < 0.05). HS resulted in a significant increase of the number of colonies of all three cell types in both the uninjured and the contused lung (all p < 0.05). At day 3 after HS, BM progenitor growth remained suppressed whereas the number of cells recoverable from the lung returned toward baseline. By day 7, hematopoietic progenitor cell growth in the BM and the number of those cells able to be grown from the lung returned to levels observed in unmanipulated rats.

CONCLUSION

Unilateral LC results in the rapid mobilization of a significant number of HPC from the BM to the site of injury. BM function is maintained under this condition. The addition of HS increases HPC mobilization from the BM and sequestration at the site of injury as well as decreasing BM HPC growth. We postulate that the accumulation of progenitor cells in the injured tissue combined with an alteration of normal BM homing, as exemplified by the decrease in progenitor cells from the lung without restoration of BM function, plays a role in posttraumatic BM suppression. The mechanism of shock-mediated mobilization from the BM and the exact role and fate of these cells at the site of injury requires further investigation.

BONE MARROW FAILURE IN MALE RATS FOLLOWING TRAUMA/HEMORRHAGIC SHOCK (T/HS) IS MEDIATED BY MESENTERIC LYMPH AND MODULATED BY CASTRATION

Bone marrow (BM) suppression occurs following trauma/hemorrhagic shock (T/HS) in experimental animals as well as following severe injury in humans. Although the pathophysiology of BM suppression remains poorly understood, mesenteric lymph is thought to play an important role in T/HS-induced BM suppression; however, the direct effect of mesenteric lymph on BM in vitro has never been studied. In addition, recent studies in rats have also shown that female and castrated male rats are protected against T/HS-induced BM failure. We therefore hypothesized that mesenteric lymph is a source of factor(s) causing direct BM suppression and that the effects of mesenteric lymph are gender dependent. To test this hypothesis, we subjected noncastrated (NC) and castrated (C) male and proestrus female rats to T/HS or trauma sham shock (T/SS). Mesenteric lymph collected 3 h postshock was plated (4% v/v) with BM cells collected from unmanipulated male or female rats for granulocyte-macrophage colony-forming units (CFU-GM) and erythroid burst-forming units (BFU-E) colony growth. The T/HS lymph collected from NC-male rats but not from female rats caused a 50% inhibition of CFU-GM and BFU-E colony growth compared with cells cultured without lymph (P < 0.05 versus all other groups (ANOVA + Tukey). T/HS lymph collected from C-male rats also caused no significant inhibition of CFU-GM and BFU-E colony growth compared with cells cultured without lymph. Female and male BM progenitor cells had a similar response to mesenteric lymph from all groups tested. These results show that mesenteric lymph from NC-male rats suppresses CFU-GM and BFU-E progenitor growth in vitro, whereas the lymph from C-male and female rats did not. The effects of mesenteric lymph were the same regardless of whether the target BM was from male or female rats. The results therefore indicate that BM failure in male rats is directly mediated by factors present within the mesenteric lymph that appear to be modulated by castration, and protection against BM failure in female rats occurs at a systemic rather than a local level. Further studies are needed to elucidate potential therapeutic effects of lymph manipulation in hematopoiesis after injury.

Hypoxia-reoxygenation induces premature senescence in FA bone marrow hematopoietic cells

Hematopoietic cells are often exposed to transient hypoxia and reoxygenation as they develop and migrate. Given that bone marrow (BM) failure occurred in patients with Fanconi anemia (FA), we reason that hypoxia-then-reoxygenation represents a physiologically relevant stress for FA hematopoietic progenitor/stem cells. Here we show that expansion of Fancc-/- BM cells enriched for progenitor and stem cells was significantly decreased after 2 continuous cycles of hyperoxic-hypoxic-hyperoxic treatments compared with wild-type (WT) BM cells. This inhibition was attributable to a marked decrease of lineage-depleted (Lin-) ScaI- c-kit+ cells and more primitive Lin- ScaI+ c-kit+ cells in Fancc-/- BM cells following reoxygenation. Evaluation of the cell-cycle profile of long-term BM culture (LTBMC) revealed that a vast majority (70.6%) of reoxygenated Fancc-/- LTBMC cells was residing in the G0 and G1 phases compared with 55.8% in WT LTBMC cells. Fancc-/- LTBMC cells stained intensely for SA-beta-galactosidase activity, a biomarker for senescence; this was associated with increased expression of senescence-associated proteins p53 and p21(WAF1/CIP1). Taken together, these results suggest that reoxygenation induces premature senescence in Fancc-/- BM hematopoietic cells by signaling through p53, up-regulating p21, and causing senescent cell-cycle arrest. Thus, reoxygenation-induced premature senescence may be a novel mechanism underlying hematopoietic cell depletion and BM failure in FA.

Delayed differentiation of HL-60 cells following exposure to hypoxia

OBJECTIVE

Hemorrhagic shock and hypoxia have been shown to alter immune and hematopoietic functions. Cellular hypoxia is thought to be the primary defect and has been shown to induce a variety of biological alterations. In this study, we examined if this defect is at the stage of terminal differentiation with the myelomonocytic cell line HL-60.

METHODS

After hypoxia, HL-60 cells were induced with 1.25% dimethyl sulfoxide (DMSO) to differentiate toward neutrophils (PMN). The ability to differentiate was evaluated by nitroblue tetrazolium staining. The function of the differentiated cells was determined by intracellular calcium levels after exposure to different chemotactic factors, and levels of Id-2 mRNA, a factor associated with terminal differentiation of myeloid cells, were assessed with Northern analysis.

RESULTS

At 48 h following exposure to hypoxia, HL-60 differentiation was significantly blunted (hypoxia 51 +/- 1%, normoxia 69 +/- 1%; P < 0.001). Intracellular calcium levels in DMSO-treated cells stimulated with 1 microM bacterial tripeptide, fMLP, were significantly reduced in the hypoxic cells (381 +/- 11 nM vs 449 +/- 10 nM; P < 0.01). No difference was noted for two other chemotactic factors, C5a and platelet-activating factor. Using Northern analysis to determine the levels of Id-2 mRNA, we demonstrated that hypoxia reduced the levels by 20% over normoxic cells.

CONCLUSION

This study demonstrates that hypoxia blunts the differentiation of HL-60 cells to PMN. This altered function of hypoxia appears to be reversible since hypoxia prolonged the time for HL-60 cells to differentiate and this may be partly explained by the premature downregulation of Id-2 expression.

Hematopoietic failure after hemorrhagic shock is mediated partially through mesenteric lymph

OBJECTIVE

To determine whether hemorrhagic shock-induced bone marrow failure is mediated by the gut through the production of toxic mesenteric lymph and whether shock-induced bone marrow failure could be prevented by division of the mesenteric lymphatics.

DESIGN

Prospective, controlled study.

SETTING

University surgical research laboratory.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Rats were divided into five groups: unmanipulated controls (n = 12), hemorrhagic shock with laparotomy (n = 8), hemorrhagic shock with mesenteric lymph duct ligation (n = 10), sham shock with laparotomy (n = 6), and sham shock with mesenteric lymph duct ligation (n = 7). At either 3 or 6 hrs after resuscitation, bone marrow was obtained for determination of early (cobblestone forming cells) and late (granulocyte-macrophage colony forming unit and erythroid burst forming unit) hematopoietic progenitor cell growth. Parallel cultures were plated with plasma (1% and 2% v/v) from all groups to determine the effect of lymphatic ligation on hematopoiesis.

MEASUREMENTS AND MAIN RESULTS

Bone marrow cellularity, cobblestone forming cells, granulocyte-macrophage colony forming unit, and erythroid burst forming unit growth in rats subjected to hemorrhagic with lymph duct ligation were similar to those observed in sham-treated animals and significantly greater than in rats subjected to shock and laparotomy without lymphatic duct ligation. Plasma from rats subjected to shock without lymph ligation was inhibitory to hematopoietic progenitor cell growth. In contrast, this shock-induced inhibition was not observed with plasma obtained from shocked rats that underwent mesenteric lymph ligation.

CONCLUSIONS

Hemorrhagic shock suppresses bone marrow hematopoiesis as measured by a decrease in early and late progenitor cell growth. This suppression appears mediated through mesenteric lymph as the effect is abrogated by mesenteric lymph duct ligation. These data clearly demonstrate a link between the gut and bone marrow failure after hemorrhagic shock

Trauma inhibits erythroid burst-forming unit and granulocyte-monocyte colony-forming unit growth through the production of TGF-beta1 by bone marrow stroma

OBJECTIVE

To examine the effect of trauma plasma on clonogenic progenitor cultures.

SUMMARY BACKGROUND DATA

Severely injured trauma patients often experience altered hematopoietic functions, manifested by an increased susceptibility to infection and the development of a persistent anemia. Experimental and clinical data suggest that trauma results in the release of cytokines into the plasma that have hematopoietic regulatory function, but few studies have examined human bone marrow.

METHODS

Plasma was obtained from 42 severely injured patients admitted to the surgical intensive care unit from days 1 to 15 after injury. Bone marrow and normal plasma were obtained from volunteers. Bone marrow mononuclear cells were isolated and plated for granulocyte-monocyte colony-forming unit (CFU-GM) and erythroid burst-forming unit (BFU-E) growth. Parallel cultures were incubated with 2% (v/v) trauma or normal plasma. Additional cultures were plated with neutralizing concentrations of antibodies to transforming growth factor (TGF)-beta1 and MIP-1alpha. Circulating plasma TGF-beta1 was determined by bioassay. mRNA from bone marrow stromal cultures was extracted and probed for TGF-beta1 and macrophage inflammatory protein (MIP)-1alpha.

RESULTS

Trauma plasma suppressed CFU-GM and BFU-E colony growth by 40% to 60% at all time periods after injury compared with cultures incubated with normal plasma. Using a noncontact culture system, the authors showed that this inhibition of BFU-E and CFU-GM colony growth was mediated by bone marrow stroma. The inhibition appeared to be due to soluble plasma-induced bone marrow stromal products that did not require direct cell-cell contact. The addition of anti-TGF-beta1 antibodies reversed the suppressive effect of trauma plasma on CFU-GM and BFU-E colony growth during the early but not late time points after injury. Trauma but not normal plasma induced TGF-beta1 mRNA in bone marrow stroma.

CONCLUSIONS

Trauma plasma inhibits bone marrow BFU-E and CFU-GM colony growth for up to 2 weeks after injury. This inhibition is mediated through the interaction of trauma plasma with bone marrow stroma. TGF-beta1 production by bone marrow stroma appears to plays an important role in the early but not late bone marrow suppression after injury.

Effects of hypoxia on granulocytic-monocytic progenitors in rats. Role of bone marrow stroma

Hemorrhagic shock leads to hypoxia and is associated with bone marrow (BM) failure. Hemorrhagic shock is also a predisposing factor in immune dysregulation. Since the BM is the major organ of immune cells in the adult, its failure following hemorrhagic shock may explain the increased susceptibility to infection. The in vitro evidence indicates that hypoxia mediates altered functions in BM stroma. Since similar hematopoietic alterations are reported in hypoxia and hemorrhagic shock, hypoxia alone could be a representative model to study BM responses during hemorrhagic shock. In this study, we use an animal model to dissect the hematopoietic effects of hypoxia. We subjected rats to hypoxia, and at days 1 and 5 post-hypoxia we determined the numbers of granulocytic-monocytic progenitors (CFU-GM) in the BM. We found significant increase (P < 0.05) in CFU-GM at day 1 and a downward trend by day 5. Enhanced BM cellularity could not explain the increase in CFU-GM by day 1. BM stromal cells mediated most of the stimulatory effects by hypoxia. CFU-GM was inversely proportional to bioactive TGF-beta and directly proportional to IL-1. Compared to normoxic rats, IL-6 production was suppressed in BM cells from hypoxic rats. The results show that hypoxia alone initiate a stimulatory response in CFU-GM progenitors. These effects are at least partially mediated through the BM stroma. In the absence of a second insult, CFU-GM reverts to baseline. The data also suggest that hypoxia mediates complex responses that include cytokine production. These results add to the current understanding of hematopoietic responses by hypoxia and adds to the mechanisms of immune dysfunctions following hemorrhagic shock.

Neuroendocrine-induced synthesis of bone marrow-derived cytokines with inflammatory immunomodulating properties

Although cytokines and other soluble regulators of immunity are known to be involved in hematopoiesis, little is known about the signals that induce the synthesis of those mediators locally. Based on recent studies linking the neuroendocrine hormone thyrotropin [thyroid-stimulating hormone (TSH)] to immune cell function in other tissues, we investigated the capacity of TSH to activate cytokine responses from bone marrow cells. These studies reveal that stimulation of the TSH receptor on bone marrow cells-using highly purified or recombinant TSH or by direct stimulation with anti-TSH receptor antibodies-rapidly induces the synthesis of cytokines from bone marrow cells that are classically used in the regulation of inflammatory responses. Of 13 cytokines screened for activity by ELISA or by RNase protection assays for gene expression, IL-6, IFN-beta, TNFalpha, TNFbeta, TGFbeta2, and lymphotoxin-beta responses were reproducibly induced by TSH within 2-3 h of stimulation. Intracellularly, TSH stimulation of bone marrow cells caused rapid increases in cAMP levels and induced the phosphorylation of the Jak2 protein kinase, thereby defining a novel G-protein-coupled receptor/cytokine synthesis pathway. These findings demonstrate that TSH can serve as a primary inductive signal of cytokine production by bone marrow cells.