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The stress response and stress proteins confer protection against diverse forms of cellular and tissue injury, including acute lung injury. The stress response can inhibit nonstress protein gene expression, therefore transcriptional inhibition of proinflammatory responses could be a mechanism of protection against acute lung injury. To explore this possibility, we determined the effects of the stress response on nuclear translocation of the transcription factor NF-B, an important regulator of proinflammatory gene expression. In

IntroductionHematopoietic stem and progenitor cells (HSPCs) are located in the bone marrow (BM) in close association with a highly organized 3-dimensional structure formed by stroma cells, referred to as the niche. 1,2 It has been demonstrated that these cell-cell interactions are vital for the biology of HSPCs. Systemic administration of cytokines and chemokines or cytotoxic agents mobilize HSPCs from the BM into peripheral blood (PB), where they are collected in clinically useful quantities for stem cell therapies. 3,4 Mobilization of HSPCs in response to these factors requires the de-adhesion of HSPCs from the niche. 5,6 Evidence accumulating over the past decade has proven that there is a measurable and successive functional decline in hematopoietic, intestinal, and muscle stem cell function. 7,8 Given that stem cell activity is necessary to replenish lost differentiated cells, it has been hypothesized that aging of hematopoietic stem cells (HSCs) leads to reduced stem cell renewal and thus reduced tissue homeostasis in aged animals, [7][8][9][10][11] which is emphasized by ageassociated anemia and a decline in function of immune cells in elderly persons. 12-19 HSC aging is intrinsic to the aged cell and cannot be reverted by exposing HSCs from aged animals to a young microenvironment. [18][19][20] The ability of healthy, older patients to undergo stem cell mobilization in response to granulocyte colony-stimulating factor (G-CSF), the standard regimen used for clinical HSPC mobilization, has thus far not been investigated in detail because autologous hematopoietic stem cell transplantation is most often administered to adults younger than 50 years and rarely to patients older than 60 years. 21,22 The limited available information is not conclusive in terms of efficiency of mobilization because it is based primarily on the analysis of mobilization of elderly patients after severe chemotherapy 23,24 and possibly also because 2 different methods of determining mobilization efficiency are used (colony-forming cell [CFC] frequency vs CD34 ϩ cell frequency in PB). Combining general clinical wisdom and these published reports, it is anticipated that the ability to mobilize HSPCs in response to G-CSF may be reduced in elderly patients, [23][24][25][26] hampering the efficient collection of HSPCs for subsequent hematopoietic stem cell therapies. Whether a negative correlation exists between age and mobilization is still under debate. 24,25 The mouse has been used in a wide variety of studies to model human G-CSF-induced mobilization of HSCs, with an overall good correlation between results obtained from murine studies and subsequent results obtained in humans. By investigating mobilization proficiency in aged mice, we report here that aged mice show not only decreased but increased efficiency in mobilizing hematopoietic progenitor cells (HPCs) and HSCs to PB. Materials and methods AnimalsYoung C57BL/6J mice were obtained from The Jackson Laboratory (Bar Harbor, ME) and were subsequently housed in the animal barrier ...

Surfactant protein B (SP-B) is a hydrophobic, 79 amino acid peptide that regulates the structure and function of surfactant phospholipid membranes in the airspaces of the lung. Addition of SP-B to liposomes composed of DPPC/PG (7:3) leads to membrane binding, destabilization, and fusion, ultimately resulting in rearrangement of membrane structure. The goal of this study was to map the fusogenic and lytic domains of SP-B and assess the effects of altered fusion and lysis on surface activity. Synthetic peptides were generated to predicted helices and/or interhelical loops of SP-B and tested for fusion, lytic, and surface activities. The N-terminal half of SP-B (residues 1-37), which includes the nonhelical N-terminal amino acids in addition to helices 1 and 2, promoted rapid liposome fusion whereas shorter peptides were significantly less effective. The requirements for optimal surface tension reduction were similar to those for fusion; in contrast, helix 1 (residues 7-22) alone was sufficient for liposome lysis. The C-terminal half of SP-B (residues 43-79), which includes helices 3, 4, and 5, exhibited significantly lower levels of fusogenic, lytic, and surface tension reducing activities compared to the N-terminal region. These results indicate that SP-B fusion, lytic and surface activities map predominantly to the N-terminal half of SP-B. Amino acid substitutions in synthetic peptides corresponding to the N-terminal half of SP-B indicated that, in general, decreased fusion or lytic activities were associated with altered surface tension reducing properties of the peptide. However, the presence of fusion and lytic activities alone could not account for the surface tension reducing property of SP-B. We propose a model in which association of helix 1 with lipids leads to membrane permeabilization but not aggregation; helix 2 mediates membrane cross-linking (aggregation), which, in turn, facilitates lipid mixing, membrane fusion, and interfacial adsorption/surface tension reduction.

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Surfactant protein B (SP-B) is secreted into the airspaces with surfactant phospholipids where it reduces surface tension and prevents alveolar collapse at end expiration. SP-B is a member of the saposin-like family of proteins, several of which have antimicrobial properties. SP-B lyses negatively charged liposomes and was previously reported to inhibit the growth of Escherichia coli in vitro; however, a separate study indicated that elevated levels of SP-B in the airspaces of transgenic mice did not confer resistance to infection. The goal of this study was to assess the antimicrobial properties of native SP-B and synthetic peptides derived from the native peptide. Native SP-B aggregated and killed clinical isolates of Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, and group B streptococcus by increasing membrane permeability; however, SP-B also lysed RBC, indicating that the membranolytic activity was not selective for bacteria. Both the antimicrobial and hemolytic activities of native SP-B were inhibited by surfactant phospholipids, suggesting that endogenous SP-B may not play a significant role in alveolar host defense. Synthetic peptides derived from native SP-B were effective at killing both Gram-positive and Gram-negative bacteria at low peptide concentrations (0.15–5.0 μM). The SP-B derivatives selectively lysed bacterial membranes and were more resistant to inhibition by phospholipids; furthermore, helix 1 (residues 7–22) retained significant antimicrobial activity in the presence of native surfactant. These results suggest that the role of endogenous SP-B in host defense may be limited; however, synthetic peptides derived from SP-B may be useful in the treatment of bacterial pneumonias.

Mobilization of hematopoietic stem cells (HSCs) from bone marrow (BM) to peripheral blood (PB) by cytokine granulocyte colony-stimulating factor (G-CSF) or the chemical antagonist of CXCR4, AMD3100, is important in the treatment of blood diseases. Due to clinical conditions of each application, there is a need for continued improvement of HSC mobilization regimens. Previous studies have shown that genetic ablation of the Rho GTPase Cdc42 in HSCs results in their mobilization without affecting survival. Here we rationally identified a Cdc42 activity-specific inhibitor (CASIN) that can bind to Cdc42 with submicromolar affinity and competitively interfere with guanine nucleotide exchange activity. CASIN inhibits intracellular Cdc42 activity specifically and transiently to induce murine hematopoietic stem/progenitor cell egress from the BM by suppressing actin polymerization, adhesion, and directional migration of stem/progenitor cells, conferring Cdc42 knockout phenotypes. We further show that, although, CASIN administration to mice mobilizes similar number of phenotypic HSCs as AMD3100, it produces HSCs with better long-term reconstitution potential than that by AMD3100. Our work validates a specific small molecule inhibitor for Cdc42, and demonstrates that signaling molecules downstream of cytokines and chemokines, such as Cdc42, constitute a useful target for long-term stem cell mobilization.

Acute and chronic lung injury secondary to hyperoxia remains an important complication in critically ill patients, and, consequently, there is interest in developing strategies to protect the lung against hyperoxia. Heat shock proteins (HSPs) confer protection against a broad array of cytotoxic agents. In this study, we tested the hypothesis that increased expression of the 70-kDa HSP (HSP70) would protect cultured human respiratory epithelium against hyperoxia. Recombinant A549 cells were generated in which human HSP70 was increased by stable transfection with a plasmid containing human HSP70 cDNA under control of the cytomegalovirus promoter (A549-HSP70 cells). A549-HSP70 cells exposed to hyperoxia had greater acute survival rates and clonogenic capacity compared with wild-type A549 cells and with control cells stably transfected with the empty expression plasmid. Hyperoxia-mediated lipid peroxidation and ATP depletion were also attenuated in A549-HSP70 cells exposed to hyperoxia. Increased expression of HSP70 did not detectably alter mRNA levels of the intracellular antioxidants manganese superoxide dismutase, catalase, and glutathione peroxidase. Collectively, these data demonstrate a specific in vitro protective role for HSP70 against hyperoxia and suggest that potential mechanisms of protection involve attenuation of hyperoxia-mediated lipid peroxidation and ATP depletion.