Regulation of Superoxide Dismutase in Primary Cultures of Rat Colonic Smooth Muscle Cells

We have observed a rapid induction of manganese superoxide dismutase (MnSOD) in epithelial, neuronal, and smooth muscle cells (SMC) after acetic acid-induced colitis. To examine the regulation of MnSOD in the SMC more specifically, primary cultures of colonic SMC were developed by enzymatic digestion of the circular muscle layer from an adult rat. SMC were treated for 2-72 h with 0.5 microgram/ml Escherichia coli endotoxin [lipopolysaccharide (LPS)], 10 ng/ml tumor necrosis factor (TNF)-alpha, or 2 ng/ml interleukin-1 beta (IL-1 beta). Cotreatments were performed with IL-1 beta and 4 microM actinomycin or 50 microM cycloheximide. Northern analysis demonstrated 23-fold, 8-fold, and 6-fold inductions of MnSOD mRNA by IL-1 beta, LPS, and TNF-alpha, respectively. Induction of MnSOD by IL-1 beta was eliminated by actinomycin but not by cycloheximide, implicating a requirement for de novo transcription. Western analysis resulted in a 23.7-fold induction of MnSOD protein after 48-h treatment with IL-1 beta. Induction of MnSOD by IL-1 beta and other inflammatory mediators may serve as a protective mechanism to reduce oxygen free radical- and nitric oxide-mediated cell damage during inflammation.