Genetic modification of prenatal lethality and dilated cardiomyopathy in Mn superoxide dismutase mutant mice

Mn superoxide dismutase (MnSOD), a mitochondrial antioxidant enzyme, has been shown to be essential for animal survival. MnSOD mutant mice (Sod2−/− mice) on the CD1 background develop severe dilated cardiomyopathy and usually die within 10 d after birth. To characterize better the phenotype and understand the mechanism of superoxide-mediated tissue damage in Sod2−/− mice, congenic Sod2−/− mice on inbred backgrounds were generated to ensure genetic homogeneity. When generated on a C57BL/6J background (B6left angle bracketSod2−/−right-pointing angle bracket), more than half of the fetuses develop severe dilated cardiomyopathy by embryonic day 15 and die in the uterus. Those that survive to term usually die within 24 h. In contrast, Sod2−/− mice on DBA/2J (D2left angle bracketSod2−/−right-pointing angle bracket) and B6D2F1 (B6D2F1left angle bracketSod2−/−right-pointing angle bracket) backgrounds develop normally throughout gestation and do not develop dilated cardiomyopathy. However, the D2left angle bracketSod2−/−right-pointing angle bracket mice do develop a severe metabolic acidosis and survive for only up to 12 d after birth. B6D2F1left angle bracketSod2−/−right-pointing angle bracket) mice have a milder form of metabolic acidosis and can survive for up to 3 weeks. The marked difference in lifespans and the development of dilated cardiomyopathy in the B6 but not the D2 or B6D2F1 backgrounds indicate the possible existence of genetic modifiers that provide protection to the developing hearts in the absence of MnSOD.