Conditioned Medium from Dying Smooth Muscle Cell Induced Apoptotic Death

ABSTRACT

In this study, the authors investigated whether death of vascular smooth muscle cell (VSMC) had a pathological pertinence. Conditioned media obtained from rat aorta smooth muscle cell (SMC) that were induced death by expressing FADD in the absence of tetracycline (FADD-SMC) triggered death of normal SMC. DNA fragmentation and caspase-3 activation were observed in dying SMC by conditioned media. FADD-SMC showed transcriptional activation of tumor necrosis factor (TNF)-alpha. Conditioned medium contained TNF-alpha, indicating secretion of the cytokine from dying FADD-SMC. It was investigated if secreted TNF-alpha was functional. Conditioned medium activated ERK and p38 MAPK pathways and induced MMP-9 expression, whereas depletion of the cytokine with its soluble receptor (sTNFR) remarkably inhibited induction of MMP-9 by conditioned medium. These findings suggest that TNF-alpha in conditioned medium seems to be active. Then, contribution of TNF-alpha on death-inducing activity of conditioned medium was examined. Depletion of TNF-alpha with soluble TNF-alpha receptor decreased the death activity of conditioned medium by 35%, suggesting that TNF-alpha play a partial role in the death activity. Boiling of medium almost completely abolished the death-inducing activity, suggesting that other heat labile death inducing proteins existed in conditioned medium. Taken together, these results indicate that SMC undergoing death could contribute to inflammation by expressing inflammatory cytokines and pathological complications by inducing death of neighboring cells.