Acquisition of Stress Tolerance in Vascular Smooth Muscle Cells by The Induction of Mn-Sod

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Oxidative stress induces death of smooth muscle cells in vascular tissue, especially in the fibrous cap of atherosclerotic plaque, and leads to disruption of vessel structure via plaque unstabilization. We examined whether manganese superoxide dismutase (Mn-SOD), which is induced in various tissue and acts as one of rescue proteins in response to external stress, is expressed in vascular smooth muscle cells (VSMC) and attenuates cellular injury caused by oxidative stress. Rat aortic smooth muscle cells (RASMC) were cultured from rat aorta and cells were exposed to TNF-a (0-10 ng/ml) or heat shock (42℃, 1 h) to induce Mn-SOD. The concentration of Mn-SOD in RASMC was examined by enzyme linked immunosorbent assay. The concentration of Mn-SOD increased from 55.2±11.8 ng/mg protein to 121.7±10.6 ng/mg protein at 6 h after the exposure of TNF-a (p<0.05 vs. without TNF-a). Mn-SOD also increased from 67.3±5.7 ng/mg protein to 92.0±7.9 ng/mg protein at 12 h after heat shock (p<0.05 vs. without … More heat shock). RASMC were exposed to anoxia (6 h) - reoxygenation (2 h) as oxidative stress at 6 h after exposure to TNF-D or to heat shock, when Mn-SOD was markedly induced in cells, and lactate dehydrogenase (LDH) release was examined as an index of cellular injury. TNF-a attenuated LDH release after anoxia-reoxygenation significantly to 32.1% of control cultures without TNF-a (p<0.01). Heat shock also decreased LDH release to 51.3% of control cultures without heat shock (p<0.05). When Mn-SOD induction was inhibited by antisense oligodeoxyribonucleotide to Mn-SOD (500 nM), attenuation of LDH release after anoxia-reoxygenation by TNF-a was not observed. Rat Mn-SOD expression was transferred into RASMC by lipofection and the cellular injury after anoxia-reoxygenation was examined. The LDH release decreased to 56.4% of control cultures without the lipofection (p<0.01). These results suggest that internal Mn-SOD, which is induced by TNF-a or heat shock, or external Mn-SOD, which is transferred by using a vector containing the gene of rat Mn-SOD, enhances tolerance of vascular smooth muscle cells to oxidative stress. Less