Human lung fibroblasts produce proresolving peroxisome proliferator-activated receptor-γ ligands in a cyclooxygenase-2-dependent manner

Abstract

Human lung fibroblasts (HLFs) act as innate immune sentinel cells that amplify the inflammatory response to injurious stimuli. Here, we use targeted lipidomics to explore the hypothesis that HLFs also play an active role in the resolution of inflammation. We detected cyclooxygenase-2 (COX-2)-dependent production of both proinflammatory and proresolving prostaglandins (PGs) in conditioned culture medium from HLFs treated with a proinflammatory stimulus, IL-1β. Among the proresolving PGs in the HLF lipidome were several known ligands for peroxisome proliferator-activated receptor-γ (PPARγ), a transcription factor whose activation in the lung yields potent anti-inflammatory, antifibrotic, and proresolving effects. Next, we used a cell-based luciferase reporter to confirm the ability of HLF supernatants to activate PPARγ, demonstrating, for the first time, that primary HLFs activated with proinflammatory IL-1β or cigarette smoke extract produce functional PPARγ ligands; this phenomenon is temporally regulated, COX-2- and lipocalin-type PGD synthase-dependent, and enhanced by arachidonic acid supplementation. Finally, we used luciferase reporter assays to show that several of the PGs in the lipidome of activated HLFs independently activate PPARγ and/or inhibit NFκB. These results indicate that HLFs, as immune sentinels, regulate both proinflammatory and proresolving responses to injurious stimuli. This novel endogenous resolution pathway represents a new therapeutic target for globally important inflammatory diseases such as chronic obstructive pulmonary disease.

Exercise promotes a cardioprotective gene program in resident cardiac fibroblasts

“…Subsequent analysis of RNA-Seq data for markers of CMs (Myh6), smooth muscle cells (Myh11), endothelial cells (Cdh5, Pecam), and hematopoietic cells (Ptprc/CD45) revealed variable levels of expression around background, confirming nonfibroblasts were not differentially captured after exercise or disease (Supplemental Figure 1, J-L). However, further evaluation of RNA-Seq data revealed significant alterations in the expression of inflammatory markers Il1β, Tnf, and Nos2 during exercise and TAC, consistent with recent reports that fibroblasts act as sentinels in maintaining tissue homeostasis (Supplemental Figure 1L) (29).…”

“…Additional transcriptional pathways dysregulated in pathological fibroblasts include P53 signaling, PPAR-γ signaling, and KLF2-dependent transcription. Transcription factors that were significantly upregulated after swim compared with disease included a number of proinflammatory transcription factors such as STAT1, NFATC2, NFκB1α, and IRF3/5/7 ( Figure 2D) (29). Consistent with the enrichment of detoxification pathways after exercise, transcription factor analysis also revealed activation of aryl hydrocarbon receptor (AHR) and NFE2L2-dependent (NRF2-dependent) transcriptional programs.…”

Quenching the fires: Pro-resolving mediators, air pollution, and smoking

“…Remarkably, RvD1 attenuated this proinflammatory signaling in all three cell types (Croasdell, et al, 2015;Hsiao, et al, 2013). Interestingly we also found that lung fibroblasts treated with cigarette smoke extract produced both pro-inflammatory and pro-resolving mediators in a temporally regulated manner (Lacy, et al, 2016). At day 1-2 after treatment with cigarette smoke extract, lung fibroblasts expressed increased COX2 and produced pro-inflammatory mediators including IL-6 and PGE 2 ; however, at later time points, COX2 expression and PGE 2 production waned and was replaced by production of anti-inflammatory prostaglandins including ligands for peroxisome proliferator-activated receptor γ (PPARγ).…”

“…Mediator class-switching describes the phenomenon in which the same cell type switches from producing pro-inflammatory mediators early in inflammation, to producing pro-resolving mediators during the resolution phase, by altering the expression of key synthetic enzymes to favor SPMs rather than inflammatory mediators. This was first described in a mouse model of air pouch inflammation, in which neutrophils switched from producing leukotrienes to lipoxins by downregulating 5-LO and upregulating 15-LO (Levy, et al, 2001), and has subsequently been demonstrated in human neutrophils, lung fibroblasts, and other cells (Lacy, et al, 2016). Transcellular biosynthesis is the observation that some cells only produce SPM precursors but lack the enzymes needed to produce the final SPM; while other cell types can produce the final SPM if provided the precursor (Capra, et al, 2015;Serhan, et al, 2000).…”

Resolvin D1 Improves the Resolution of Inflammation via Activating NF-κB p50/p50–Mediated Cyclooxygenase-2 Expression in Acute Respiratory Distress Syndrome

“…While activated, fibroblasts secrete various inflammatory mediators that amplify the immune response (18). Additionally, fibroblasts have emerged as regulators of inflammation resolution that act by producing proresolving peroxisome proliferator-activated receptor-g ligands (19), as well as COX-2 and PGD 2 (20). Recently, accumulating evidence has demonstrated that the growth factors secreted from fibroblasts can promote alveolar barrier function (21)(22)(23), alleviate pulmonary edema (21,24), and protect against lung injury from various stresses, such as LPS (25,26), ventilator (24) and ischemia/reperfusion-induced lung injury (27,28).…”