Intramuscular grafts of myoblasts genetically modified to secrete glial cell line-derived neurotrophic factor prevent motoneuron loss and disease progression in a mouse model of familial amyotrophic lateral sclerosis

Effects of ex vivo GDNF gene delivery on the degeneration of motoneurons we re studied in the G1H transgenic mouse model of familial ALS carrying a hum an superoxide dismutase (SOD1) with a Gly(93)Ala mutation (Gurney et al,, 1 994). Retroviral vectors were made to produce human GDNF or E. coEi beta-ga lactosidase (P-Gal) by transient transfection of the Phoenix: cell line and used to infect primary mouse myoblasts. In 6-week-old G1H mice, 50,000 myo blasts per muscle were injected bilaterally into two hindlimb muscles. Untr eated G1H and wild-type mice served as additional controls. At 17 weeks of age, 1 week before sacrifice, these muscles mere injected with fluorogold ( FG) to retrogradely label spinal motoneurons that maintained axonal project ions to the muscles. There were significantly more large FG-labeled alpha m otoneurons at 18 weeks in GDNF-treated G1H mice than in untreated and P-Gal -treated G1H mice. A morphometric study of motoneuron size distribution sho wed that GDNF shifted the size distribution of motoneurons toward larger ce lls compared with control G1H mice, although the average size and number of large motoneurons in GDNF-treated mice were less than that in wild-type mi ce. GDNF also prolonged the onset of disease, delayed the deterioration of performance in tests of motor behavior, and slowed muscle atrophy. Quantita tive, real-time RT-PCR and PCR showed persistence of transgene mRNA and DNA in muscle for up to 12 weeks postgrafting, These observations demonstrate that ex vivo GDNF gene therapy in a mouse model of FALS promotes the surviv al of functional motoneurons, suggesting that a similar approach might dela y the progression of neurodegeneration in ALS.