Cytosolic SOD1 proteins can be transported into mitochondria of skeletal muscle.

(A) Western blot to show the expression of human SOD1^G93A in the skeletal muscle of G93A mice. C-SOD1 antibody recognizes both mouse and human SOD1. Lane 1: Control muscle; Lane 2-4: G93A muscle (2,3 and 4-month old). Note the skeletal muscle of G93A mice expresses human SOD1^G93A at all ages. (B) Intact normal muscle fibers expressing SOD1-GFP or SOD1^G93A-GFP. Note, in addition to the cytosolic expression, both SOD1-GFP and SOD1^G93A-GFP show mitochondrial targeting. (C) After cell membrane permeabilization, the cytosolic GFP was lost. The overlay of TMRE and remaining GFP signals indicate the expression of SOD1-GFP or SOD1^G93A-GFP inside mitochondria. Bar: 10 µm.