Protective effect of supplemental superoxide dismutase on survival of neuronal cells during starvation - Requirement for cytosolic distribution

There is evidence that raising cellular levels of Cu2+/Zn2+ superoxide dism utase (SOD1) can protect neurons from oxidative injury. We compared a novel method of elevating neuronal SOD activity using a recombinant hybrid prote in composed of the atoxic neuronal binding domain of tetanus toxin (C fragm ent or TTC) and human SOD1 (hSOD1) with increasing cellular SOD levels thro ugh overexpression. Fetal murine cortical neurons or N18-RE-105 cells were incubated with the TTC-hSOD1 hybrid protein and compared to cells constitut ively expressing hSOD1 for level of SOD activity, cellular localization of hSOD1, and capacity to survive glucose and pyruvate starvation. Cells incub ated with TTC-hSOD1 showed a threefold increase in cellular SOD activity ov er control cells. This level of increase was comparable to Petal cortical n eurons from transgenic mice constitutively expressing hSOD1 and transfected N18-RE-205 cells expressing a green fluorescent protein-hSOD1 fusion prote in (GFP-hSOD1). Human SOD1 was distributed diffusely throughout the cytopla sm of the transgenic murine neurons and transfected N18-RE-105 cells. In co ntrast, cells incubated with TTC-hSOD1 showed hSOD1 localized to the cell s urface and intra-cytoplasmic vesicles. The cells expressing hSOD1 showed en hanced survival in glucose- and pyruvate-free medium. Neither cortical neur ons nor N18-RE-105 cells incubated in TTC-hSOD1 showed increased survival d uring starvation. Access to the site where toxic superoxides are generated or their targets may be necessary for the protective function of SOD1.