The development of new therapies to treat amyotrophic lateral sclerosis (ALS) is often hindered by the poor bioavailability of candidate drugs to affected motor neurons within the central nervous system (CNS). Thus, while both glial cell line-derived neurotrophic factor (GDNF) and insulin-like growth factor-1 (IGF-1) have had robust survival promoting effects on injured motor neurons in experimental animals, their success in treating ALS patients appears to have been thwarted by insufficient access to motor neurons in the much larger human CNS. We hypothesize that genetic or chemical fusion of tetanus toxin fragment C (TTC) to either GDNF or IGF-1 will improve growth factor delivery to motor neurons through one or more mechanisms related to the nerve cell binding properties of TTC. The primary goal of this project, then, is to assess whether the neuroprotective activity of IGF-1:TTC and GDNF:TTC in an experimental animal model of ALS is superior to that of the respective growth factor alone. Our study has four specific aims: (1) optimize the design, expression, and purification of IGF-1:TTC and GDNF:TTC; (2) characterize the purity, stability, and basic functional activity of these fusion proteins; (3) examine the bioavailability and functional activity of the fusion proteins in rodent CNS following intracerebroventricular or intramuscular administration; and (4) investigate the neuroprotective activity of the fusion proteins in a transgenic rat model of amyotrophic lateral sclerosis (ALS). The experiments in Aim 1 will use recombinant protein expression and purification techniques to generate the fusion proteins, while the studies in Aims 2 and 3 will employ immunocytochemical, Western blot, enzyme immunoassay, and morphometric techniques to assess the functional properties of GDNF:TTC and IGF-1:TTC in cultured ceils and whole animals. Finally, the experiments in Aim 4 will employ transgenic animals in survival and behavioral experiments to assess the neuroprotective effects of GDNF:TTC and/or IGF-1 :TTC in vivo. While the present work may give rise to a new treatment for ALS, the information obtained from our characterization of IGF-1:TTC and GDNF:TTC may lead to the use of these fusion proteins in other neurological disorders as well.
