Limper, Andrew H.

Evidence is provided that the fibroproliferative actions of TGF‐β are dependent on a metabolic adaptation that sustains pathologic growth. Specifically, profibrotic TGF‐β signaling is shown to require fatty acid synthase (FASN), an essential anabolic enzyme responsible for the de novo synthesis of fatty acids. With the use of pharmacologic and genetic approaches, we show that TGF‐β‐stimulated FASN expression is independent of Smad2/ 3 and is mediated via mammalian target of rapamycin complex 1. In the absence of FASN activity or protein, TGF‐β ‐driven fibrogenic processes are reduced with no apparent toxicity. Furthermore, as increased FASN expression was also observed to correlate with the degree of lung fibrosis in bleomycin‐treated mice, inhibition of FASN was examined in a murine‐treatment model of pulmonary fibrosis. Remarkably, inhibition of FASN not only decreased expression of profibrotic targets, but lung function was also stabilized/improved, as assessed by peripheral blood oxygenation.—Jung, M.‐Y., Kang, J.‐H., Hernandez, D. M., Yin, X., Andrianifahanana, M., Wang, Y., Gonzalez‐Guerrico, A., Limper, A. H., Lupu, R., Leof, E. B. Fatty acid synthase is required for profibrotic TGF‐β signaling. FASEB J. 32, 3803–3815 (2018). www.fasebj.org

Mechanical ventilation can injure the lung, causing edema and alveolar inflammation. Interleukin-8 (IL-8) plays an important role in this inflammatory response. We postulated that cyclic cell stretch upregulates the production and release of IL-8 by human alveolar epithelium in the absence of structural cell damage or paracrine stimulation. To test this hypothesis, alveolar epithelial cells (A549 cells) were cultured on a deformable silicoelastic membrane. When stretched by 30% for up to 48 h, the cells released 49 ± 34% more IL-8 ( P < 0.001) than static controls. Smaller deformations (20% stretch) produced no consistent increase in IL-8. Stretch of 4 h duration increased IL-8 gene transcription fourfold above baseline. Stretch had no effect on cell proliferation, cell viability as assessed by51Cr release assay, or the release of granulocyte-macrophage colony-stimulating factor and tumor necrosis factor-α. We conclude that deformation per se can trigger inflammatory signaling and that alveolar epithelial cells may be active participants in the alveolitis associated with ventilator-induced lung injury.

The pathogenic fungus Pneumocystis carinii causes severe pneumonia in patients with impaired immunity, particularly patients with acquired immunodeficiency syndrome. The life cycle of P. carinii is poorly understood, and the inability to continuously culture P. carinii is a major limitation in understanding its cell biology. In fungi homologous to P. carinii, pheromone mating factors signal through a mitogen-activated protein kinase (MAPK) signal transduction cascade, resulting in mitotic cell cycle arrest and entry into a pathway of conjugation, cellular differentiation, and proliferation. Using degenerate PCR and library screening, we have identified a MAPK cDNA in P. carinii that is highly homologous to fungal MAPKs involved in the pheromone mating signal transduction cascade, and we demonstrate MAPK activity in P. carinii lysates with a specific antiserum derived from the translated P. carinii MAPK cDNA sequence.

Inflammatory cell recruitment contributes to respiratory impairment during Pneumocystis carinii pneumonia. We evaluated expression of intercellular adhesion molecule-1 (ICAM-1), a key participant in leukocyte accumulation, in rats with P. carinii pneumonia. Immunostaining for ICAM-1 was most marked on bronchiolar epithelium but was also evident on type II pneumocytes, endothelium, and macrophages. Lung from normal and dexamethasone-treated uninfected animals exhibited markedly less ICAM-1. We hypothesized that P. carinii promoted ICAM-1 expression in epithelium through tumor necrosis factor-α (TNF-α) release from macrophages or that P. carinii directly stimulated ICAM-1 expression. Alveolar macrophages were incubated with P. carinii, and the medium was added to A549 epithelial cells. Treatment of macrophages with P. carinii enhanced A549 ICAM-1, which was inhibited with antibody to TNF-α. To determine whether P. carinii alone also stimulated ICAM-1, A549 cells were cultured with P. carinii, also augmenting ICAM-1. Of note, A549 ICAM-1 expression from P. carinii alone was less than with P. carinii-exposed macrophages. Thus ICAM-1 is enhanced in lung epithelium during P. carinii infection, in part, through TNF-α-mediated mechanisms.

AbstractCytomegalovirus (CMV) pneumonia causes major morbidity and mortality. Its diagnosis requires demonstration of viral cytopathic changes in tissue, entailing risks of lung biopsy. This study aimed to determine CMV viral load (VL) thresholds in bronchoalveolar lavage fluid (BALF) for diagnosis of CMV pneumonia in immunocompromised patients. CMV VL in BALF was studied in 17 patients (83% transplant recipients) and 21 control subjects with and without CMV pneumonia, respectively, using an FDA‐approved PCR assay (Cobas® AmpliPrep/Cobas TaqMan® CMV Test, Roche Molecular Systems, Inc.) calibrated to the WHO International Standard for CMV DNA (NIBSC: 09/162). Receiver operating characteristic curve analysis produced a BALF CMV VL threshold of 34 800, IU/mL with 91.7% sensitivity and 100.0% specificity for diagnosis of possible, probable, and proven CMV pneumonia in transplant patients, while a threshold of 656 000 IU/mL yielded 100% sensitivity and specificity among biopsy‐proven cases. For all immunocompromised patients, a VL threshold of 274 IU/mL was selected. VL thresholds also were normalized to BALF cell count yielding a threshold of 0.32 IU/106 cells with 91.7% sensitivity and 90.5% specificity for possible, probable, and proven CMV pneumonia in transplant recipients. Monitoring CMV VL in BALF may be a less invasive method for diagnosing CMV pneumonia in immunocompromised patients.

Abstract Pneumocystis is an important fungal pathogen that causes life-threatening pneumonia in patients with AIDS and malignancy. Lung fungal pathogens are recognized by C-type lectin receptors (CLRs), which bind specific ligands and stimulate innate immune responses. The CLR Dectin-1 was previously shown to mediate immune responses to Pneumocystis spp. For this reason, we investigated a potential role for Dectin-2. Rats with Pneumocystis pneumonia (PCP) exhibited elevated Dectin-2 mRNA levels. Soluble Dectin-2 carbohydrate-recognition domain fusion protein showed binding to intact Pneumocystis carinii (Pc) and to native Pneumocystis major surface glycoprotein/glycoprotein A (Msg/gpA). RAW macrophage cells expressing V5-tagged Dectin-2 displayed enhanced binding to Pc and increased protein tyrosine phosphorylation. Furthermore, the binding of Pc to Dectin-2 resulted in Fc receptor-γ–mediated intracellular signaling. Alveolar macrophages from Dectin-2–deficient mice (Dectin-2−/−) showed significant decreases in phospho-Syk activation after challenge with Pc cell wall components. Stimulation of Dectin-2−/− alveolar macrophages with Pc components showed significant decreases in the proinflammatory cytokines IL-6 and TNF-α. Finally, during infection with Pneumocystis murina, Dectin-2−/− mice displayed downregulated mRNA expression profiles of other CLRs implicated in fungal immunity. Although Dectin-2−/− alveolar macrophages had reduced proinflammatory cytokine release in vitro, Dectin-2−/− deficiency did not reduce the overall resistance of these mice in the PCP model, and organism burdens were statistically similar in the long-term immunocompromised and short-term immunocompetent PCP models. These results suggest that Dectin-2 participates in the initial innate immune signaling response to Pneumocystis, but its deficiency does not impair resistance to the organism.

Abstract Pneumocystis pneumonia (PCP) remains a major cause of morbidity and mortality within immunocompromised patients. In this study, we examined the potential role of macrophage-inducible C-type lectin (Mincle) for host defense against Pneumocystis. Binding assays implementing soluble Mincle carbohydrate recognition domain fusion proteins demonstrated binding to intact Pneumocystis carinii as well as to organism homogenates, and they purified major surface glycoprotein/glycoprotein A derived from the organism. Additional experiments showed that rats with PCP expressed increased Mincle mRNA levels. Mouse macrophages overexpressing Mincle displayed increased binding to P. carinii life forms and enhanced protein tyrosine phosphorylation. The binding of P. carinii to Mincle resulted in activation of FcRγ-mediated cell signaling. RNA silencing of Mincle in mouse macrophages resulted in decreased activation of Syk kinase after P. carinii challenge, critical in downstream inflammatory signaling. Mincle-deficient CD4-depleted (Mincle−/−) mice showed a significant defect in organism clearance from the lungs with higher organism burdens and altered lung cytokine responses during Pneumocystis murina pneumonia. Interestingly, Mincle−/− mice did not demonstrate worsened survival during PCP compared with wild-type mice, despite the markedly increased organism burdens. This may be related to increased expression of anti-inflammatory factors such as IL-1Ra during infection in the Mincle−/− mice. Of note, the P. murina–infected Mincle−/− mice demonstrated increased expression of known C-type lectin receptors Dectin-1, Dectin-2, and MCL compared with infected wild-type mice. Taken together, these data support a significant role for Mincle in Pneumocystis modulating host defense during infection.

ABSTRACTWe explored differential polarization of macrophages during infection using a rat model ofPneumocystispneumonia. We observed enhanced pulmonary M1 macrophage polarization in immunosuppressed (IS) hosts, but an M2 predominant response in immunocompetent (IC) hosts followingPneumocystis cariniichallenge. Increased inflammation and inducible nitric oxide synthase (iNOS) levels characterized the M1 response. However, macrophage ability to produce nitric oxide was defective. In contrast, the lungs of IC animals revealed a prominent M2 gene signature, and these macrophages effectively elicited an oxidative burst associated with clearance ofPneumocystis. In addition, duringP. cariniiinfection the expression of Dectin-1, a critical receptor for recognition and clearance ofP. carinii, was upregulated in macrophages of IC animals but suppressed in IS animals. In the absence of an appropriate cytokine milieu for M2 differentiation,Pneumocystisinduced an M1 response bothin vitroandin vivo. The M1 response induced byP. cariniiwas plastic in nature and reversible with appropriate cytokine stimuli. Finally, we tested whether macrophage polarization can be modulatedin vivoand used to help manage the pathogenesis ofPneumocystispneumonia by adoptive transfer. Treatment with both M1 and M2 cells significantly improved survival ofP. carinii-infected IS hosts. However, M2 treatment provided the best outcomes with efficient clearance ofP. cariniiand reduced inflammation.