Adenovirus-mediated gene transfer of hIGF-IB in mouse lungs induced prolonged inflammation but no fibroproliferation

PI3K-Akt-mTOR/PFKFB3 pathway mediated lung fibroblast aerobic glycolysis and collagen synthesis in lipopolysaccharide-induced pulmonary fibrosis

Metabolic reprogramming plays a critical role in many diseases. A recent study revealed that aerobic glycolysis in lung tissue is closely related to pulmonary fibrosis, and also occurs during lipopolysaccharide (LPS)-induced sepsis. However, whether LPS induces aerobic glycolysis in lung fibroblasts remains unknown. The present study demonstrated that LPS promotes collagen synthesis in the lung fibroblasts through aerobic glycolysis via the activation of the PI3K-Akt-mTOR/PFKFB3 pathway. Challenging the human lung fibroblast MRC-5 cell line with LPS activated the PI3K-Akt-mTOR pathway, significantly upregulated the expression of 6-phosphofructo-2-kinase/fructose-2, 6-biphosphatase 3 (PFKFB3), enhanced the aerobic glycolysis, and promoted collagen synthesis. These phenomena could be reversed by the PI3K-Akt inhibitor LY294002, mTOR inhibitor rapamycin, PFKFB3 inhibitor 3PO, or PFKFB3 silencing by specific shRNA, or aerobic glycolysis inhibitor 2-DG. In addition, PFKFB3 expression and aerobic glycolysis were also detected in the mouse model of LPS-induced pulmonary fibrosis, which could be reversed by the intraperitoneal injection of PFKFB3 inhibitor 3PO. Taken together, this study revealed that in LPS-induced pulmonary fibrosis, LPS might mediate lung fibroblast aerobic glycolysis through the activation of the PI3K-Akt-mTOR/PFKFB3 pathway.

IPF pathogenesis is dependent upon TGFβ induction of IGF-1

Pathogenic fibrotic diseases, including idiopathic pulmonary fibrosis (IPF), have some of the worst prognoses and affect millions of people worldwide. With unclear etiology and minimally effective therapies, two-thirds of IPF patients die within 2-5 years from this progressive interstitial lung disease. Transforming Growth Factor Beta (TGFβ) and insulin-like growth factor-1 (IGF-1) are known to promote fibrosis; however, myofibroblast specific upregulation of IGF-1 in the initiation and progression of TGFβ-induced fibrogenesis and IPF have remained unexplored. To address this, the current study (1) documents the upregulation of IGF-1 via TGFβ in myofibroblasts and fibrotic lung tissue, as well as its correlation with decreased pulmonary function in advanced IPF; (2) identifies IGF-1's C1 promoter as mediating the increase in IGF-1 transcription by TGFβ in pulmonary fibroblasts; (3) determines that SMAD2 and mTOR signaling are required for TGFβ-dependent Igf-1 expression in myofibroblasts; (4) demonstrates IGF-1R activation is essential to support TGFβ-driven profibrotic myofibroblast functions and excessive wound healing; and (5) establishes the effectiveness of slowing the progression of murine lung fibrosis with the IGF-1R inhibitor OSI-906. These findings expand our knowledge of IGF-1's role as a novel fibrotic-switch, bringing us one step closer to understanding the complex biological mechanisms responsible for fibrotic diseases and developing effective therapies.

Insulin-Like Growth Factor-1 Signaling in Lung Development and Inflammatory Lung Diseases

Insulin-like growth factor-1 (IGF-1) was firstly identified as a hormone that mediates the biological effects of growth hormone. Accumulating data have indicated the role of IGF-1 signaling pathway in lung development and diseases such as congenital disorders, cancers, inflammation, and fibrosis. IGF-1 signaling modulates the development and differentiation of many types of lung cells, including airway basal cells, club cells, alveolar epithelial cells, and fibroblasts. IGF-1 signaling deficiency results in alveolar hyperplasia in humans and disrupted lung architecture in animal models. The components of IGF-1 signaling pathways are potentiated as biomarkers as they are dysregulated locally or systemically in lung diseases, whereas data may be inconsistent or even paradoxical among different studies. The usage of IGF-1-based therapeutic agents urges for more researches in developmental disorders and inflammatory lung diseases, as the majority of current data are collected from limited number of animal experiments and are generally less exuberant than those in lung cancer. Elucidation of these questions by further bench-to-bedside researches may provide us with rational clinical diagnostic approaches and agents concerning IGF-1 signaling in lung diseases.

Sequential expression of IGF-IB followed by active TGF-β1 induces synergistic pulmonary fibroproliferation in vivo

Pulmonary fibrosis, the end stage of a variety of fibroproliferative lung diseases, is usually induced after repetitive or chronic lung injury or inflammation. The mechanisms of fibroproliferation are poorly understood. Insulin-like growth factor-I (IGF-I) is significantly elevated in patients with pulmonary fibrosis and fibroproliferative acute respiratory distress syndrome. However, we showed that IGF-I overexpression alone in wild-type mouse lungs does not cause fibroproliferation. We therefore questioned whether IGF-I, acting together with active TGF-β1, a known profibrotic cytokine, enhances pulmonary fibroproliferation caused by active TGF-β1. A unique sequential adenoviral transgene mouse model was used expressing AdEmpty/AdTGF-β1 or AdhIGF-IB/AdTGF-β1 transgenes. IGF-IB plus active TGF-β1 transgene expression synergistically increased collagen deposition in the lung parenchyma compared with active TGF-β1 expression alone. The enhanced fibrosis was accompanied by an increased recruitment of macrophages and lymphocytes into the bronchoalveolar lavage fluid (BALF) and inflammatory cells in the lungs. α-Smooth muscle actin expression, a marker of myofibroblast proliferation and differentiation, was also increased. Finally, fibroblasts exposed ex vivo to BALF isolated from AdhIGF-IB/AdTGF-β1-transduced mice showed synergistic collagen induction compared with BALF from AdEmpty/AdTGF-β1-transduced mice. This study provides the first direct evidence that IGF-I is able to synergistically enhance pulmonary fibroproliferation in cooperation with TGF-β1.