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The pro-fibrotic and senescence phenotype of old lung fibroblasts is reversed or ameliorated by genetic and pharmacological manipulation of Slc7a11 expression.

Increased senescence and expression of pro-fibrotic genes in old lung fibroblasts contribute to disrepair responses. We reported that primary lung fibroblasts from old mice have lower expression and activity of the cystine transporter Slc7a11/xCT than cells from young mice, resulting in changes in both the intracellular and extracellular redox environments. This study examines the hypothesis that low Slc7a11 expression in old lung fibroblasts promotes senescence and pro-fibrotic gene expression. The levels of mRNA and protein of Slc7a11, senescence markers, and pro-fibrotic genes were measured in primary fibroblasts from the lungs of old (24 months) and young (3 months) mice. In addition, the effects of genetic and pharmacological manipulation of Slc7a11 were investigated. We found that decreased expression of Slc7a11 in old cells was associated with elevated markers of senescence (p21, p16, p53 and b-galactosidase) and increased expression of pro-fibrotic genes (Tgfb1, Smad3, Acta2, Fn1, Col1a1 and Col5a1). Silencing of Slc7a11 in young cells replicated the aging phenotype, whereas overexpression of Slc7a11 in old cells decreased expression of senescence and pro-fibrotic genes. Young cells were induced to express the senescence and pro-fibrotic phenotype by sulfasalazine, an Slc7a11 inhibitor, whereas treatment of old cells with sulforaphane, an Slc7a11 inducer, decreased senescence without affecting pro-fibrotic genes. Like aging cells, idiopathic pulmonary fibrosis fibroblasts show decreased Slc7a11 expression and increased pro-fibrotic markers. In short, old lung fibroblasts manifest a pro-fibrotic and senescence phenotype that is modulated by genetic or pharmacological manipulation of Slc7a11.