Senescent fibroblasts induce moderate stress in lung epithelial cells in vitro

Epithelial–mesenchymal interactions contribute to functionality and integrity of the lung epithelium, which might change during ageing and associated cellular ageing. Therefore, we studied the effect of senescent versus pre-senescent lung fibroblasts (WI-38) on mitogenic and stress-protective factors in lung epithelial cells (H358). By use of conditioned medium, we found a growth promoting impact of fibroblasts compared with control medium from epithelial cells associated with activation of ERK1/2, Akt, p70S6K, and EGF receptor. Although senescent fibroblasts mediated similar growth stimulation compared with pre-senescent cells, we observed less protection against spontaneous mitochondrial dysfunction in vitro, higher production of reactive oxygen species and activation of copper/zinc superoxide dismutase. Moreover, senescent cells induced activation of caspase-3/7 in epithelial cells, which was associated with down-regulation of the caspase-inhibitory protein XIAP. In summary, senescent lung fibroblasts induce moderate stress in lung epithelial cells in vitro without affecting growth signaling.