PTEN and pulmonary fibrosis: Low expression of PTEN and activation of the PI3K-Akt pathway have been found in lung fibroblasts from patients with idiopathic pulmonary fibrosis (IPF) [10], [11]; thus, we inferred that LPS may promote lung fibroblast proliferation by down-regulating PTEN expression and activating the PI3K-Akt pathway in the early stages of ALI/ARDS.