Expression of mitochondria-targeted SOD1 in skeletal muscle of normal mice.

(A) Normal muscle fibers transfected with mt-SOD1-Dendra or mt-SOD1^G93A-Dendra. Both proteins preferentially target to mitochondria. 90% of fibers expressing mt-SOD1^G93A-Dendra show aggregated fluorescent proteins inside mitochondria (n=73), while not a single fiber expressing wild type mt-SOD1-Dendra has protein aggregates (n=36). (B) Enlarged boxes (a1 and a2) taken from the mt-SOD1^G93A-Dendra fiber show that fiber regions (1, 2 and 3) with fluorescent protein aggregates have reduced TMRE staining (a1.1 and a2.2). (C) Fluorescence profiles of Dendra (F_Dendra, green) and TMRE (F_TMRE, red) at those three regions indicate that depolarized mitochondria are at the site of protein aggregates. (D). Representative images of normal muscle fibers expressing mt-SOD1-Dendra or mt-SOD1^G93A-Dendra. 63% of mt-SOD1^G93A-Dendra fibers show fragmented mitochondria comparing to only 11% of mt-SOD1-Dendra fibers. Bar: 10 µm.