IPF lung fibroblasts have a senescent phenotype.

The mechanisms of aging that are involved in the development of idiopathic pulmonary fibrosis (IPF) are still unclear. Although it has been hypothesized that the proliferation and activation of human lung fibroblasts (hLFs) are essential in IPF, no studies have assessed how this process works in an aging lung. Our goal was to elucidate if there were age-related changes on primary hLFs isolated from IPF lungs compared with age-matched controls. We investigated several hallmarks of aging in hLFs from IPF patients and age-matched controls. IPF hLFs have increased cellular senescence with higher expression of ß-galactosidase, p21, p16, p53, and cytokines related to the senescence-associated secretory phenotype (SASP) as well as decreased proliferation/apoptosis compared with age-matched controls. Additionally, we observed shorter telomeres, mitochondrial dysfunction, and upon transforming growth factor-ß stimulation, increased markers of endoplasmic reticulum stress. Our data suggest that IPF hLFs develop senescence resulting in a decreased apoptosis and that the development of SASP may be an important contributor to the fibrotic process observed in IPF. These results might change the existing paradigm, which describes fibroblasts as aberrantly activated cells, to a cell with a senescence phenotype.

Senescence of bone marrow-derived mesenchymal stem cells from patients with idiopathic pulmonary fibrosis.

BACKGROUND: Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease for which age is the most important risk factor. Different mechanisms associated with aging, including stem cell dysfunction, have been described to participate in the pathophysiology of IPF. We observed an extrapulmonary effect associated with IPF: increase in cell senescence of bone marrow-derived mesenchymal stem cells (B-MSCs). METHODS: B-MSCs were obtained from vertebral bodies procured from IPF patients and age-matched normal controls. Cell senescence was determined by cell proliferation and expression of markers of cell senescence p16INK4A, p21, and ß-galactosidase activity. Mitochondrial function and DNA damage were measured. Paracrine induction of senescence and profibrotic responses were analyzed in vitro using human lung fibroblasts. The reparative capacity of B-MSCs was examined in vivo using the bleomycin-induced lung fibrosis model. RESULTS: In our study, we demonstrate for the first time that B-MSCs from IPF patients are senescent with significant differences in mitochondrial function, with accumulation of DNA damage resulting in defects in critical cell functions when compared with age-matched controls. Senescent IPF B-MSCs have the capability of paracrine senescence by inducing senescence in normal-aged fibroblasts, suggesting a possible link between senescent B-MSCs and the late onset of the disease. IPF B-MSCs also showed a diminished capacity to migrate and were less effective in preventing fibrotic changes observed in mice after bleomycin-induced injury, increasing illness severity and proinflammatory responses. CONCLUSIONS: We describe extrapulmonary alterations in B-MSCs from IPF patients. The consequences of having senescent B-MSCs are not completely understood, but the decrease in their ability to respond to normal activation and the risk of having a negative impact on the local niche by inducing inflammation and senescence in the neighboring cells suggests a new link between B-MSC and the onset of the disease.