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

(A) Normal muscle fibers transfected with mt-SOD1-Dendra or mt-SOD1G93A-Dendra. Both proteins preferentially target to mitochondria. 90% of fibers expressing mt-SOD1G93A-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-SOD1G93A-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 (FDendra, green) and TMRE (FTMRE, 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-SOD1G93A-Dendra. 63% of mt-SOD1G93A-Dendra fibers show fragmented mitochondria comparing to only 11% of mt-SOD1-Dendra fibers. Bar: 10 µm.