Cell proliferation and apoptosis are both important mechanisms for the regulation of tissue homeostasis. For instance, proliferation is crucial in wound repair, whereas apoptosis is important for removal of damaged cells and resolution of inflammation. Imbalance between cell proliferation and apoptosis can therefore lead to pathological conditions and disease. In inflammatory and fibrotic lung disorders, red blood cells (RBCs) can interact with fibroblasts and connective tissue. In the present study, we therefore hypothesized that the presence of RBCs can affect fibroblast proliferation and apoptosis. Human foetal lung fibroblasts (HFL-1) were cultured in the presence or absence of purified whole RBCs and RBC-conditioned media. RBC significantly decreased fibroblast proliferation as determined both by DNA content analysis (Hoechst 33258 staining, P<0.01; WST-1, P<0.001) and BrdU incorporation. After treatment with staurosporine (STS) for 48 h, apoptosis was determined by TUNEL and propidium iodide staining followed by flow cytometry analysis. RBCs augmented STS-induced apoptosis (median: 46.4%; range 12.0-90.4) compared to control cells (median 26.2%; range 7.1-45.5). Thus, our data indicate that the presence of RBCs affects both fibroblast proliferation and susceptibility to undergo apoptosis. Our findings therefore suggest a role for RBCs in regulating fibroblast homeostasis after tissue injury.
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