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Method Article
Combined ozone and bacterial endotoxin exposed mice show wide-spread cell death, including that of neutrophils. We observed cellular adaptations such as disruption of cytoskeletal lamellipodia, increased cellular expression of complex V ATP synthase subunit β and angiostatin in broncho-alveolar lavage, suppression of the lung immune response and delayed neutrophil recruitment.
Lungs are continually faced with direct and indirect insults in the form of sterile (particles or reactive toxins) and infectious (bacterial, viral or fungal) inflammatory conditions. An overwhelming host response may result in compromised respiration and acute lung injury, which is characterized by lung neutrophil recruitment as a result of the patho-logical host immune, coagulative and tissue remodeling response. Sensitive microscopic methods to visualize and quantify murine lung cellular adaptations, in response to low-dose (0.05 ppm) ozone, a potent environmental pollutant in combination with bacterial lipopolysaccharide, a TLR4 agonist, are crucial in order to understand the host inflammatory and repair mechanisms. We describe a comprehensive fluorescent microscopic analysis of various lung and systemic body compartments, namely the broncho-alveolar lavage fluid, lung vascular perfusate, left lung cryosections, and sternal bone marrow perfusate. We show damage of alveolar macrophages, neutrophils, lung parenchymal tissue, as well as bone marrow cells in correlation with a delayed (up to 36-72 h) immune response that is marked by discrete chemokine gradients in the analyzed compartments. In addition, we present lung extracellular matrix and cellular cytoskeletal interactions (actin, tubulin), mitochondrial and reactive oxygen species, anti-coagulative plasminogen, its anti-angiogenic peptide fragment angiostatin, the mitochondrial ATP synthase complex V subunits, α and β. These surrogate markers, when supplemented with adequate in vitro cell-based assays and in vivo animal imaging techniques such as intravital microscopy, can provide vital information towards understanding the lung response to novel immunomodulatory agents.
Acute lung injury (ALI) is a crucial pathologic response of lungs to infectious or other harmful stimuli which is marked by simultaneous activation of coagulative, fibrinolytic and innate immune systems1. Neutrophils promptly sense microbial as well as intracellular damage patterns through the Toll-like receptor (TLR) family2,3,4. Neutrophils release preformed cytokines and cytotoxic granule contents, which can then cause collateral tissue damage. The ensuing alveolar damage is marred with secondary cell death leading to release of molecules such as adenosine triphosphate (ATP)5, thus setting in a vicious cycle of immune-dysregulation.
An unsolved problem in the understanding of ALI relates to the question of how the injury is initiated within the alveolar membrane. The electron transport complex V, F1F0 ATP synthase, is a mitochondrial protein known to be expressed ubiquitously, on cell (including endothelial, leukocyte, epithelial) plasma membrane during inflammation. The cell cytoskeleton which is comprised of actin and tubulin, harbors many cell shape and function modulating as well as mitochondrial proteins, respectively. We have recently shown that blockade of the ATP synthase by an endogenous molecule, angiostatin, silences neutrophil recruitment, activation and lipopolysaccharide (LPS) induced lung inflammation6. Thus, both biochemical (ATP synthase) and immune (TLR4) mechanisms might regulate the alveolar barrier during lung inflammation.
Exposure to ozone (O3), an environmental pollutant, impairs lung function, increases susceptibility to pulmonary infections, and short low-levels of O3 exposures increase the risk of mortality in those with underlying cardiorespiratory conditions7,8,9,10,11,12,13,14. Thus, exposure to physiologically relevant concentrations of O3 provides a meaningful model of ALI to study fundamental mechanisms of inflammation7,8. Our lab has recently established a murine model of low-dose O3 induced ALI15. After performing a dose and time-response to low O3 concentrations, we observed that exposure to 0.05 ppm O3 for 2 h, induces acute lung injury that is marked by lung ATP synthase complex V subunit β (ATPβ) and angiostatin expression, similar to the LPS model. Intravital lung imaging revealed disorganization of alveolar actin microfilaments indicating lung damage, and ablation of alveolar septal reactive oxygen species (ROS) levels (indicating abrogation of baseline cell signaling) and mitochondrial membrane potential (indicating acute cell death) after 2 h exposure to 0.05 ppm O315 which correlated with a heterogeneous lung 18FDG retention16, neutrophil recruitment and cytokine release, most notably IL-16 and SDF-1α. The take-home message from our recent studies is that O3 produces exponentially high toxicity when exposed at concentrations below the allowed limits of 0.063 ppm over 8 h (per day) for human exposure. Importantly, no clear understanding exists on whether these sub-clinical O3 exposures can modulate TLR4-mediated mechanisms such as by bacterial endotoxin17. Thus, we studied a dual-hit O3 and LPS exposure model and observed the immune and non-immune cellular adaptations.
We describe a comprehensive fluorescent microscopic analysis of various lung and systemic body compartments, namely the broncho-alveolar lavage fluid (i.e., BAL) which samples the alveolar spaces, the lung vascular perfusate (i.e., LVP) that samples the pulmonary vasculature and the alveolar septal interstitium in the event of a compromised endothelial barrier, left lung cryosections, to look into resident parenchymal and adherent leukocytes left in the lavaged lung tissue, peripheral blood which represents the circulating leukocytes and the sternal and femur bone marrow perfusates that sample the proximal and distal sites of hematopoietic cell mobilization during inflammation, respectively.
The study design was approved by the University of Saskatchewan's Animal Research Ethics Board and adhered to the Canadian Council on Animal Care guidelines for humane animal use. Six-eight week old male C57BL/6J mice were procured. NOTE: Euthanize any animals which develop severe lethargy, respiratory distress or other signs of severe distress before scheduled end point.
NOTE: Prepare the following: 27-18 G needle-blunted (will depend on the mouse tracheal diameter), appropriately sized PE tubing to fit the blunt needle (make a PE cannula for every mouse), cannula, 2 sharp scissors, 2 blunt forceps (small), 1 sharp forceps (small), 3 1 mL syringes, labelled microfuge tubes (for BAL, blood, vascular and bone marrow perfusate collection) and labelled vials (for tissue fixation), sample bags/cryovials for tissue collection, butcher's cotton thread roll (cut into adequate sized ligatures). All chemicals utilized for the experiments are indicated in the Table of Materials.
1. Ozone and LPS exposures for induction of murine lung injury
2. Sample collection
3. Sample processing
4. Cytospin staining and lung histology
Combined O3 and LPS exposure leads to systemic inflammation and bone marrow mobilization at 72 h: Cell counts in different compartments revealed significant changes in peripheral blood and the femur bone marrow total cell counts upon combined O3 and LPS exposures. Although combined O3 and LPS exposures did not induce any changes in the total BAL (Figure 1A) or LVP (Figure 1B
The methods presented in the current study highlight the usefulness of multiple compartment analysis to study multiple cellular events during lung inflammation. We have summarized the findings in Table 2. We and many labs have extensively studied the murine response to intranasal LPS instillation, which is marked by rapid recruitment of lung neutrophils, which peaks between 6-24 h following which, resolution kicks in. And recently, we have shown that sub-clinical O3 (at 0.05 ppm for 2 h) alone...
The authors have no conflicts of interest or disclosures to make.
The research conducted is funded by President's NSERC grant as well as start-up funds from the Sylvia Fedoruk Canadian Center for Nuclear Innovation. The Sylvia Fedoruk Canadian Center for Nuclear Innovation is funded by Innovation Saskatchewan. Fluorescence imaging was performed at the WCVM Imaging Centre, which is funded by NSERC. Jessica Brocos (MSc Student) and Manpreet Kaur (MSc Student) were funded by the start-up funds from the Sylvia Fedoruk Canadian Center for Nuclear Innovation.
Name | Company | Catalog Number | Comments |
33-plex Bioplex chemokine panel | Biorad | 12002231 | |
63X oil (NA 1.4-0.6) Microscope objectives | Leica | HCX PL APO CS (11506188) | |
Alexa 350 conjugated goat anti-mouse IgG (H+L) | Invitrogen | A11045 | |
Alexa 488 conjugated goat anti-mouse IgG (H+L) | Invitrogen | A11002 | |
Alexa 488 conjugated phalloidin | Invitrogen | A12370 | |
Alexa 555 conjugated mouse anti-α tubulin clone DM1A | Millipore | 05-829X-555 | |
Alexa 568 conjugated goat anti-hamster IgG (H+L) | Invitrogen | A21112 | |
Alexa 568 conjugated goat anti-rat IgG (H+L) | Invitrogen | A11077 | |
Alexa 633 conjugated goat anti-rabbit IgG (H+L) | Invitrogen | A21070 | |
Armenian hamster anti-CD61 (clone 2C9.G2) IgG1 kappa | BD Pharmingen | 553343 | |
C57BL/6 J Mice | Jackson Laboratories | 64 | |
Confocal laser scanning microscope | Leica | Leica TCS SP5 | |
DAPI (4′,6-diamidino-2-phenylindole) | Invitrogen | D1306 | aliquot in 2 µl stocks and store at -20°C |
Inverted fluorescent wide field microscope | Olympus | Olympus IX83 | |
Ketamine (Narketan) | Vetoquinol | 100 mg/ml | Dilute 10 times to make a 10 mg/ml stock |
Live (calcein)/Dead (Ethidium homodimer-1) cytotoxicity kit | Invitrogen | L3224 | |
Mouse anti-ATP5A1 IgG2b (clone 7H10BD4F9) | Invitrogen | 459240 | |
Mouse anti-ATP5β IgG2b (clone 3D5AB1) | Invitrogen | A-21351 | |
Mouse anti-NK1.1 IgG2a kappa (clone PK136) | Invitrogen | 16-5941-82 | |
Pierce 660 nm protein assay | Thermoscientific | 22660 | |
Rabbit anti-angiostatin (mouse aa 98-116) IgG | Abcam | ab2904 | |
Rabbit anti-CX3CR1 IgG (RRID 467880) | Invitrogen | 14-6093-81 | |
Rat anti-Ki-67 (clone SolA15) IgG2a kappa | Invitrogen | 14-5698-82 | |
Rat anti-Ly6G IgG2a kappa (clone 1A8) | Invitrogen | 16-9668-82 | |
Rat anti-Ly6G/Ly6C (Gr1) IgG2b kappa (clone RB6-8C5) | Invitrogen | 53-5931-82 | |
Rat anti-mouse CD16/CD32 Fc block (clone 2.4G2) | BD Pharmingen | 553142 | |
Reduced mitotracker orange | Invitrogen | M7511 | |
Xylazine (Rompun) | Bayer | 20 mg/ml | Dilute 2 times to make a 10 mg/ml stock |
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