Aging promotes pro-fibrotic matrix production and increases fibrocyte recruitment during acute lung injury

Fibrotic lung diseases increase with age. Previously we determined that senescence increases tissue expression of fibronectin EDA (Fn-EDA) and decreases fibroblast expression of Thy-1, and that fibrocytes contribute to fibrosis following bleomycin-induced lung injury in mice. In this study we hypothesized that fibroblasts lacking Thy-1 expression produce an extracellular matrix that promotes fibrocyte retention and myofibroblast transdifferentiation, thereby promoting fibrogenesis. Young and old mice were treated with bleomycin intratracheally;fibrocytes in the bone marrow, blood, and lungs were quantified, and lung fibroblast Thy-1 expression was assessed. Bone marrowderived fibrocytes were cultured on matrices derived from Thy-1(+) or Thy-1(?) fibroblasts ± the pro-fibrotic cytokine TGFβ1. Older mice had more fibrocytes in their bone marrows at baseline and more fibrocytes in their lungs following bleomycin treatment. In parallel, lung fibroblasts in older mice had lower expression of Thy-1 at baseline that increased transiently 7 days after bleomycin treatment but then rapidly waned such that 14 days after bleomycin treatment Thy-1 expression was again markedly lower. Fibrocytes cultured on matrices derived from Thy-1(?) fibroblasts + TGFβ1 had increased gene expression for collagen type 1, fibronectin, Fn-EDA, and α-smooth muscle actin. In parallel, whereas the matrices derived from Thy-1(?) fibroblasts stimulated phosphorylation of Akt in cultured fibrocytes, the matrices derived from Thy-1(+) fibroblasts induced apoptosis. These findings suggest that senescence increases fibrocyte recruitment to the lung following injury and that loss of Thy-1 expression by lung fibroblasts promotes fibrocyte retention and myofibroblast transdifferentiation that renders the “aging lung” susceptible to fibrosis.

Anticancer actions of PPARγ ligands:Current state and future perspectives in human lung cancer

Peroxisome proliferator-activated receptors(PPARs) are ligand-dependent nuclear transcription factors and members of the nuclear receptor superfamily.Of the three PPARs identified to date(PPARγ,PPARβ/δ,and PPARα),PPARγ has been studied the most,in part because of the availability of PPARγagonists(also known as PPARγ ligands)and its significant effects on the management of several human diseases including type 2 diabetes,metabolic syndrome,cardiovascular disease and cancers.PPARγ is expressed in many tumors including lung cancer,and its function has been linked to the process of lung cancer development, progression and metastasis.Studies performed in gynogenic and xenograft models of lung cancer showed decreased tumor growth and metastasis in animals treated with PPARγ ligands.Furthermore,data are emerging from retrospective clinical studies that suggest a protective role for PPARγ ligands on the incidence of lung cancer.This review summarizes the research being conducted in this area and focuses on the mechanisms and potential therapeutic effects of PPARγ ligands as a novel anti-lung cancer treatment strategy.