Kuzhali Muthu

Murine hematopoietic stem cells and progenitors express adrenergic receptors

Association between the nervous and immune system is well documented. Immune cells originate within the bone marrow that is innervated. Thermal injury induces adrenergic stimulation, augments monocytopoiesis and alters the beta-adrenergic receptor (AR) profile of bone marrow monocyte committed progenitors. This provides an impetus to study AR expression in hematopoietic progenitors along myeloid lineage. Using FACS analysis and confocal microscopy, we report the expression of alpha1-, alpha2- and beta(2)-AR in enriched populations of ER-MP209(+) and ER-MP12(+) myeloid progenitors, CD117(+) and CD34(+) multi-potential progenitors and more importantly pluripotent stem cells suggesting a plausible role for catecholamine in hematopoietic development.

Perturbed bone marrow monocyte development following burn injury and sepsis promote hyporesponsive monocytes.

The mechanism of monocyte deactivation in critically injured burn patients remains unresolved. Two functionally distinct F4/80+Gr-1+ and F4/80+Gr-1− monocyte subsets have been characterized based on their homing to inflammatory or noninflammatory tissues, respectively. We hypothesized that the posttraumatic milieu in the bone marrow (BM) blunts the production of “inflammatory” monocytes. C57Blk/J male mice were divided into sham (S), burn (B), and burn sepsis (BS) groups. B and BS received a 15% dorsal scald burn and BS was inoculated with 15K colony forming units Pseudomonas aeruginosa at the burn site. Animals were killed and blood and femoral BM were collected 48, 72, and 96 hours after injury. ER-MP20+ monocyte progenitors were isolated from BM and differentiated into macrophage (MØ) or dendritic cells (DCs) and characterized by the cell surface expression of F4/80 and CD11c, respectively. In both cell types, TLR-4 agonist induced cytokine levels were determined. Results showed a 2-fold increase in the F4/80+Gr-1+ subset at 48 hours in BS that started to decline at 72 hours and remained low at 96 hours. ER-MP20+ progenitors isolated at 48 hours exhibited robust MØ differentiation potential but a significant decline in the percentage of the F4/80+Gr-1+ subset (P < .05 vs S) with a concomitant decrease in tumor necrosis factor α production. DC development from ER-MP20+ progenitors and LPS-stimulated tumor necrosis factor α production were impaired. Therefore, BM progenitor derived MØ will replace the transient hyper-responsive circulating monocytes later during the course of the septic insult. Hypo-reactivity of the developing monocytes and DC in the BM and their subsequent egress to the periphery provide a plausible explanation for the immunosuppression that ensues a critical burn injury and sepsis.

Propranolol restores the tumor necrosis factor-alpha response of circulating inflammatory monocytes and granulocytes after burn injury and sepsis.

Beta-adrenergic blockade ameliorates the hypermetabolism and catabolism in severe burn injury. Despite the salutary effects of beta-adrenergic blockade, the immunologic responses that accompany beta-blockade are not known. We have shown that burn sepsis is associated with increased sympathetic activation leading to altered monocytopoiesis and cytokine release in macrophages (MØ). Recent evidence suggests that murine MØ expressing F4/80+Gr1+ are the inflammatory phenotype. Here, we report that propranolol given after burn sepsis modulates the number and function of myeloid cells in circulation. B6D2F1 male mice were divided into sham (S), burn (B), and burn sepsis (BS) groups. Dorsal hair was shaved from S, B, and BS; B and BS received 15% scald burn; BS was inoculated with Pseudomonas Aeruginosa (PA 14, 4000–5000 colony-forming units) at the burn site. Mice from each group were then subjected to two different treatment regimens. One set received subcutaneous injections of propranolol (5 mg/kg body weight) at 24 and 48 hours after the injury while the control groups received saline. Blood was collected by cardiac puncture at 72 hours. The distribution of total F4/80+ monocyte population was determined by flow cytometry. Inflammatory monocyte subset was gated on Gr1+ expression in the F4/80+ fraction. Lipopolysaccharide-stimulated intracellular tumor necrosis factor (TNF)-&agr; (ic-TNF) was also measured as an indicator of inflammatory response. The total F4/80+ monocyte fraction was significantly increased in BS (45 ± 0.8%) vs S and B (10 ± 0.8%; 9.5 ± 0.6%). Propranolol treatment for 2 days reduced the number of circulating monocytes by 60% in BS. The mean fluorescent intensity (MFI) of ic-TNF produced per cell (F4/80+Gr1+ MØ) was significantly decreased in B and BS (S: 3043 ± 213, B: 1638 ± 343, BS: 1463 ± 67). Of importance, propranolol treatment partially restored the MFI of ic-TNF (2177 ± 114) and increased the percentage of inflammatory monocyte subset (F4/80+Gr1+) in BS by 70% compared with saline treatment. In contrast, beta-blockade after BS increased the percentage of granulocytes in circulation (28.4 ± 3.6% in BS propranolol vs 15.4 ± 0.3% in BS saline; P < .05) and augmented their TNF production (MFI = 903 ± 102 in BS propranolol vs 644 ± 5 in BS saline; P < .05). Propranolol reverses burn sepsis-induced monocytosis and simultaneously increases the number of granulocytes and enhances the inflammatory potential of the granulocytes and inflammatory monocyte subsets in circulation suggesting that monitoring MØ subsets and granulocytes in blood is a reliable biomarker to predict the efficacy of beta-blockade.

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

We have previously shown that perturbed bone marrow progenitor development promotes hyporesponsive monocytes following experimental burn sepsis. Clinical and experimental sepsis is associated with monocyte deactivation and depletion of mDCs. Decrease in circulating DCs is reported in burn patients who develop sepsis. In our 15% TBSA scald burn model, we demonstrate a significant reduction in the circulating MHC‐II+ population and mDCs (Gr1negCD11b+CD11c+) with a corresponding decrease in bone marrow MHC‐II+ cells and mDCs for up to 14 days following burn. We explored the underlying mechanism(s) that regulate bone marrow development of monocytes and DCs following burn injury. We found a robust bone marrow response with a significant increase in multipotential HSCs (LSK) and bipotential GMPs following burn injury. GMPs from burn mice exhibit a significant reduction in GATA‐1, which is essential for DC development, but express high levels of MafB and M‐CSFRs, both associated with monocyte production. GMPs obtained from burn mice differentiated 1.7 times more into Mφ and 1.6‐fold less into DCs compared with sham. Monocytes and DCs expressed 50% less MHC‐II in burn versus sham. Increased monocyte commitment in burn GMPs was a result of high MafB and M‐CSFR expressions. Transient silencing of MafB (siRNA) in GMP‐derived monocytes from burn mice partially restored DC differentiation deficits and increased GATA‐1 expression. We provide evidence that high MafB following burn plays an inhibitory role in monocyte‐derived DC differentiation by regulating M‐CSFR and GATA‐1 expressions.

A novel antibacterial gene transfer treatment for multidrug-resistant Acinetobacter baumannii-induced burn sepsis.

Sepsis caused by multidrug-resistant bacterial infections in critically injured patients has become a major clinical problem. Recently, Acinetobacter baumannii (AB) wound infections, especially in our critically injured soldiers fighting in Iraq and Afghanistan, is posing a major clinical problem and an economic burden. ConjuGon, Inc., has developed a novel antibacterial therapeutic technology using bacterial conjugation. The donor cells are attenuated Escherichia coli carrying a conjugative plasmid. The expression of bactericidal genes cloned on the plasmid is tightly repressed in the donor cells but becomes de-repressed once mobilized into a pathogen and disrupts protein synthesis. Here, we tested the efficacy of this novel conjugation technology to control and eradicate a drug-resistant clinical isolate of AB wound infection both in vitro and in a murine burn sepsis model. C57Blk/6J mice were divided into burn (B) and burn sepsis (BS) groups. All animals received a 12% TBSA dorsal scald full-thickness burn. The BS group was inoculated with multidrug-resistant AB (1 × 105 colony-forming units [CFU]) at the burn wound site. BS animals were either untreated or treated with increasing concentrations (103–1010 CFU) of attenuated donor E. coli encoding bactericidal proteins. The survival rate was monitored for 10 days. The ability of donor cells to significantly diminish AB levels in the burn wound 24 hours after injury was determined by quantitative cultures. Donor cells were highly effective in killing AB in vitro. In the burn sepsis model, 90% B group animals survived, and 40% to 50% BS animals survived with no treatment in 5 to 6 days. Treatment with donor cells at 1010 to 106 provided significant survival advantage (P < .05). Quantitative cultures of burn wounds revealed that AB numbers increased from 3 × 104 CFU to 7.8 ± 4.4 × 109 CFU in 24 hours in the untreated group. Single treatment with donor cells (1010 CFU) significantly reduced AB in the burn wound to less than the levels seeded into the wound (1.23 ± 0.5 × 104 CFU; P < .05). Taken together, these results indicate that this novel technology is an efficient method to control drug-resistant AB burn wound infections and prevent their systemic spread.

β-Adrenergic stimulation increases macrophage CD14 expression and E. coli phagocytosis through PKA signaling mechanisms

CD14 is a glycoprotein that binds bacterial LPS in MØ. It is an essential component of the phagocytic system and is increased in septic shock. Critical injury and sepsis result in elevated endogenous CA levels. CAs have a significant impact on MØ inflammatory functions. We tested the hypothesis that β‐adrenergic stimulation regulates CD14 expression and bacterial phagocytosis in BMØ. Murine BMØ stimulated with isoproterenol (>8 h) induced a dose‐dependent increase in cell surface CD14 expression. Specific PKA inhibitor (H‐89) and gene‐silencing (siRNA) studies demonstrated the role of cAMP‐dependent PKA in mediating this response. In addition, we observed a correlation between an isoproterenol‐mediated increase in CD14 expression and live Escherichia coli uptake in BMØ. Further, the essential role of CD14 in an isoproterenol‐mediated increase in E. coli uptake was highlighted from experiments using CD14−/− mice. Moreover, the dose response of isoproterenol stimulation to CD14 expression and E. coli phagocytosis overlapped with similar EC50. Additionally, isoproterenol‐mediated E. coli phagocytosis was prevented by H‐89, suggesting that β‐adrenergic stimulus in BMØ increases CD14 expression and live E. coli phagocytosis through a common signaling pathway. Our studies indicate the potential impact of β‐adrenergic agents on important innate immune functions.