Neurodegeneration and early lethality in superoxide dismutase 2-deficient mice: a comprehensive analysis of the central and peripheral nervous systems.

The contribution of oxidative stress to diabetic complications including neuropathy is widely known. Mitochondrial and cellular damage are associated with the overproduction of reactive oxygen species and decreased levels or function of the cellular antioxidant mitochondrial manganese superoxide dismutase (SOD2). We hypothesized that targeted SOD2 deletion in the peripheral nervous system using cre-lox technology under control of the nestin promoter would accelerate neuropathy in a type 2 model of diabetes, the BKS.db/db mouse. SOD2-deficient mice, however, demonstrated severe gait deformities and seizures and died by 20 days of age. Examination of SOD2 expression levels revealed that SOD2 was lost in brain and reduced in the spinal cord, but appeared normal in dorsal root ganglia and peripheral nerves in SOD2-deficient mice. These findings indicate incomplete targeted knockout of SOD2. Morphological examination revealed cortical lesions similar to spongiform encephalopathy in the brain of SOD2-deficient mice. No lesions were evident in the spinal cord, but changes in myelin within the sciatic and sural nerves including a lack of cohesion between layers of compact myelin were observed. Together, these results indicate that targeted neuronal SOD2 knockout using the nestin promoter results in severe central nervous system degeneration and perinatal lethality in mice. A specific peripheral nervous system-targeting construct is required to examine the consequences of SOD2 knockout in diabetic neuropathy.

Neuroprotection using gene therapy to induce vascular endothelial growth factor-A expression.

Engineered zinc-finger protein (ZFP) transcription factors induce the expression of endogenous genes and can be remotely delivered using adenoviral vectors. One such factor, Ad-32Ep65-Flag (Ad-p65), targets and induces expression of vascular endothelial growth factor (VEGF; also called VEGF-A) splice variants in their normal biological stoichiometry. We show that Ad-p65 transfection of primary motor neurons results in VEGF variant expression and a significant increase in axon outgrowth in these cells. Given the neuroprotective effects of VEGF and its ability to increase neurite outgrowth, we examined the efficacy of Ad-p65 to enhance motor neuron regeneration in vivo using rats that have undergone recurrent laryngeal nerve (RLN)-crush injury. Injection of Ad-p65 after RLN crush accelerated the return of vocal fold mobility and the percentage of nerve-endplate contacts in the thyroarytenoid muscle. Overall, adenoviral delivery of an engineered ZFP transcription factor inducing VEGF-A splice variant expression enhances nerve regeneration. ZFP transcription factor gene therapy to increase expression of the full complement of VEGF-A splice variants is a promising avenue for the treatment of nerve injury and neurodegeneration.