The response of adipose tissues to Mycoplasma pulmonis and Sendai virus infection in C57BL/6 and DBA/2 mice

Adipose tissues in mammals are categorized into white and brown adipose tissues in which cellular morphology, cell functions, and tissue distribution are different. White adipose tissue (WAT) plays a major role in energy reservation, while brown adipose tissue (BAT) mainly relates to the thermoregulation of the body. One interesting function of adipose tissue is the response to the infection, especially the pathogens that cause pneumonia. We have previously reported that DBA/2 (D2) mice are susceptible to pathogens causing pneumonia, Mycoplasma (M.) pulmonis and Sendai virus (SeV), whereas C57BL/6 (B6) mice are resistant to them. Furthermore, morphological alteration of mediastinal fat tissue (MFT) was seen after infection of M. pulmonis in D2 mice but not in B6 mice. In this study, we aimed to exhibit the difference in adipose tissue response in other areas, including interscapular brown adipose tissue (iBAT), inguinal white adipose tissue (ingWAT), and perigonadal WAT (perigoWAT) between resistant strain, B6 and susceptible strain, D2 after challenging them with M. pulmonis and SeV. Compared with B6 mice, D2 mice showed an increase in fat-associated lymphoid cluster in MFT, an increase in BAT in both iBAT and ingWAT after M. pulmonis and SeV infection. The results of this study indicate that pneumonia caused by M. pulmonis and SeV infection induces browning of adipocyte, suggesting that BAT plays a role in pathogen infection and inflammation.

Opposing actions of angiopoietin-2 on Tie2 signaling and FOXO1 activation

Angiopoietin-2 (ANG2) regulates blood vessel remodeling in many pathological conditions through differential effects on Tie2 signaling. While ANG2 competes with ANG1 to inhibit Tie2, it can paradoxically also promote Tie2 phosphorylation (p-Tie2). A related paradox is that both inactivation and overactivation of Tie2 can result in vascular remodeling. Here, we reconciled these opposing actions of ANG2 by manipulating conditions that govern its actions in the vasculature. ANG2 drove vascular remodeling during Mycoplasma pulmonis infection by acting as a Tie2 antagonist, which led to p-Tie2 suppression, forkhead box O1 (FOXO1) activation, increased ANG2 expression, and vessel leakiness. These changes were exaggerated by anti-Tie2 antibody, inhibition of PI3K signaling, or ANG2 overexpression and were reduced by anti-ANG2 antibody or exogenous ANG1. In contrast, under pathogen-free conditions, ANG2 drove vascular remodeling by acting as an agonist, promoting high p-Tie2, low FOXO1 activation, and no leakage. Tie1 activation was strong under pathogen-free conditions, but infection or TNF-α led to Tie1 inactivation by ectodomain cleavage and promoted the Tie2 antagonist action of ANG2. Together, these data indicate that ANG2 activation of Tie2 supports stable enlargement of normal nonleaky vessels, but reduction of Tie1 in inflammation leads to ANG2 antagonism of Tie2 and initiates a positive feedback loop wherein FOXO1-driven ANG2 expression promotes vascular remodeling and leakage.

Cytokine and chemokine transcription profile during Mycoplasma pulmonis infection in susceptible and resistant strains of mice: macrophage inflammatory protein 1beta (CCL4) and monocyte chemoattractant protein 2 (CCL8) and accumulation of CCR5+ Th cells

The progression of murine mycoplasma pneumonia is dependent on T cells and other immune cells. The role of cytokines in immunity are complex, and identifying the network of cytokines produced after infection of mice is essential in dissecting the key cytokine cascades involved mycoplasma disease pathogenesis. In the present study, mRNA expression of 143 different cytokines, chemokines, or receptors were evaluated in lung tissues from both susceptible (BALB/c and C3H/HeN) and resistant (C57BL/6) mice after Mycoplasma pulmonis infection. To accomplish this, membrane-based cDNA microarrays were used to monitor changes mRNA expression in lungs. There was a clear association with disease susceptibility and development of cytokine mRNA expression. In addition to proinflammatory cytokines, mRNA expression of an anti-inflammatory cytokine, interleukin-10, increased with disease severity, suggesting an attempt to moderate the severity of the inflammatory response. Furthermore, it is clear that an array of chemokines produced in susceptible mice could contribute to the recruitment and maintenance of inflammatory cells at the site of disease. In support of this, there was an increase in macrophage inflammatory protein 1beta (MIP-1beta; CCL4) and monocyte chemoattractant protein 2 (MCP-2; CCL8) mRNA levels from mycoplasma-infected mice and a corresponding accumulation of CD4+ Th cells expressing the MIP-1beta/MCP-2 receptor, CCR5, in the lungs of mice. Furthermore, MIP-1beta- and MCP-2-producing cells and CD4+ T cells were found to be in close association in pulmonary lesions. Thus, there was a significant cytokine response associated with disease pathogenesis, and these studies provide important leads and insights into ongoing cytokine- and chemokine-mediated processes in this persistent inflammatory disease.

Reactive species mediate inhibition of alveolar type II sodium transport during mycoplasma infection

RATIONALE

Mycoplasma pneumoniae is a significant cause of pneumonia in humans.

OBJECTIVES

To determine the impact of mycoplasma infection and the host inflammatory response on alveolar type II (ATII) cell ion transport in vivo and in vitro.

METHODS

Mice were infected with M. pulmonis for measurements of alveolar fluid clearance (AFC) in vivo and isolation of ATII cells. ATII cells were infected in vivo for determination of epithelial Na+ channel (ENaC) total and cell surface protein levels by biotinylation and Western blot and in vitro for whole cell patch clamp recording and measurement of nitric oxide (NO) production by chemiluminescence.

RESULTS

Mycoplasma infection significantly inhibited AFC at 24 h and total and amiloride-sensitive AFC by 48 h postinfection (pi). In contrast, infected myeloperoxidase-deficient mice had similar basal and amiloride-sensitive AFC values to uninfected control mice at 48 h pi. Addition of forskolin restored total and amiloride-sensitive AFC to control values at 48 h pi. ATII cells isolated from infected mice demonstrated normal alpha, beta, and gamma ENaC total protein levels; however, infected whole-lung cell-surface levels of gamma ENaC were significantly decreased. Patch-clamp recordings demonstrated a significant decrease in total and amiloride-sensitive Na+ currents at 24 h pi. ATII cells demonstrated a significant increase in the production of NO at 24 h pi and inhibition of NO by ATII cells before infection reversed the decrease in total Na+ currents.

CONCLUSIONS

These data indicate that mycoplasma infection results in decreased AFC and functional ENaC via the production of reactive oxygen nitrogen intermediates.

Identification of a 521-kilodalton protein (Gli521) involved in force generation or force transmission for Mycoplasma mobile gliding

Several mycoplasma species are known to glide on solid surfaces such as glass in the direction of the membrane protrusion, but the mechanism underlying this movement is unknown. To identify a novel protein involved in gliding, we raised monoclonal antibodies against a detergent-insoluble protein fraction of Mycoplasma mobile, the fastest glider, and screened the antibodies for inhibitory effects on gliding. Five monoclonal antibodies stopped the movement of gliding mycoplasmas, keeping them on the glass surface, and all of them recognized a large protein in immunoblotting. This protein, named Gli521, is composed of 4,738 amino acids, has a predicted molecular mass of 520,559 Da, and is coded downstream of a gene for another gliding protein, Gli349, which is known to be responsible for glass binding during gliding. Edman degradation analysis indicated that the N-terminal region is processed at the peptide bond between the amino acid residues at positions 43 and 44. Analysis of gliding mutants isolated previously revealed that the Gli521 protein is missing in a nonbinding mutant, m9, where the gli521 gene is truncated by a nonsense mutation at the codon for the amino acid at position 1170. Immunofluorescence and immunoelectron microscopy indicated that Gli521 localizes all around the base of the membrane protrusion, at the "neck," as previously observed for Gli349. Analysis of the inhibitory effects of the anti-Gli521 antibody on gliding motility revealed that this protein is responsible for force generation or force transmission, a role distinct from that of Gli349, and also suggested conformational changes of Gli349 and Gli521 during gliding.

Pathogenesis of persistent lymphatic vessel hyperplasia in chronic airway inflammation

Edema occurs in asthma and other inflammatory diseases when the rate of plasma leakage from blood vessels exceeds the drainage through lymphatic vessels and other routes. It is unclear to what extent lymphatic vessels grow to compensate for increased leakage during inflammation and what drives the lymphangiogenesis that does occur. We addressed these issues in mouse models of (a) chronic respiratory tract infection with Mycoplasma pulmonis and (b) adenoviral transduction of airway epithelium with VEGF family growth factors. Blood vessel remodeling and lymphangiogenesis were both robust in infected airways. Inhibition of VEGFR-3 signaling completely prevented the growth of lymphatic vessels but not blood vessels. Lack of lymphatic growth exaggerated mucosal edema and reduced the hypertrophy of draining lymph nodes. Airway dendritic cells, macrophages, neutrophils, and epithelial cells expressed the VEGFR-3 ligands VEGF-C or VEGF-D. Adenoviral delivery of either VEGF-C or VEGF-D evoked lymphangiogenesis without angiogenesis, whereas adenoviral VEGF had the opposite effect. After antibiotic treatment of the infection, inflammation and remodeling of blood vessels quickly subsided, but lymphatic vessels persisted. Together, these findings suggest that when lymphangiogenesis is impaired, airway inflammation may lead to bronchial lymphedema and exaggerated airflow obstruction. Correction of defective lymphangiogenesis may benefit the treatment of asthma and other inflammatory airway diseases.

Beta 2 microglobulin and resistance to murine respiratory mycoplasmosis

Mycoplasma pulmonis (MP) infection causes murine respiratory mycoplasmosis (MRM) in mice. This study was designed to determine whether C57BL/6 beta 2 microglobulin knockout (KO) mice (B2m-/-) differed from C57BL/6 B2m(+/+) wild-type (WT) mice in the early events of acute infection and to confirm previous studies that suggested loss of beta 2 microglobulin (B2m) expression was correlated with increased disease susceptibility. Experimentally infected mice were necropsied at various time points after infection. Quantitative cultures were performed on lung, trachea, and nares at each time point. Tissues were collected for histopathology. Both genotypes had marked clearance of MP from all sites within the first 24 h post-infection (p.i.). There were no differences between KO and WT mice in the ability to clear MP from the lung, nares, or trachea during the first 48 h p.i. During chronic infection, there was a significant difference among days p.i. for number of MP isolated from the lungs, nares, and trachea (P<0.05). There were significant differences (P<0.05) between genotypes for number of MP isolated from the lung. Numbers of MP isolated from KO mice were greater than from WT mice at day 10 through day 28 p.i. There was no significant overall difference between genotypes for number of MP isolated from the nares or trachea. However, increased numbers of MP were isolated from the nares of KO mice at days 21 and 28 p.i. and from the trachea of KO mice at days 7 and 21 p.i. During chronic infection, KO mice had increased facial scratching and altered respiration as well as marked weight loss compared with those of WT mice. The KO and WT mice differed (KO more severe) with respect to the presence and extent of neutrophilic exudate in the lung. Differences approached significance for consolidation of lung parenchyma but not for lymphoid infiltration, tending to be more severe in KO mice. Loss of B2m does not appear to affect clearance of MP during the critical first 48 h of infection but does seem to affect chronic infection, which may be because of the loss of CD8(+) Tc1 cells, the CD1-B2m complex, or both.

Placental lesions caused by experimental infection of Sprague-Dawley rats with Mycoplasma pulmonis

PROBLEM

Sprague-Dawley (SD) rats infected during pregnancy with Mycoplasma pulmonis display adverse pregnancy outcomes that are similar to those observed in women with chorioamnionitis and may provide a good model system for this disease. The placental lesions caused by this microorganism, however, have not been thoroughly characterized.

METHOD OF STUDY

Rats were infected with 10(7) colony-forming units (CFU) M. pulmonis or vehicle control on gestation day (gd) 14 and were euthanized on gd 16-18. Tissues were fixed in 10% neutral buffered formalin, embedded in paraffin, sectioned at 4 microm, and stained with hematoxylin and eosin (H & E). The slides were coded and examined by a blinded pathologist using light microscopy.

RESULTS

Infection with M. pulmonis was associated with necrosis of trophoblast giant cells at gd 18. Significantly more neutrophils were observed in the decidual region of the apex of the placenta in M. pulmonis infected animals. The vast majority of neutrophils, however, were observed in the decidua in the lateral regions of the placenta and in the adjacent endometrium.

CONCLUSIONS

Infection of SD rats with M. pulmonis resulted in histological placentitis similar to that described in deciduitis of humans and represents a good model system for investigations into the pathophysiology of intrauterine infection. The influx of neutrophils seems to migrate from the endometrium towards the lateral regions of the placenta near Reichert's membrane and the divergence of the parietal yolk sac.