RETROGRADE AXONAL-TRANSPORT OF GLIAL-CELL LINE-DERIVED NEUROTROPHIC FACTOR IN THE ADULT NIGROSTRIATAL SYSTEM SUGGESTS A TROPHIC ROLE IN THE ADULT

The recently cloned, distant member of the transforming growth factor beta (TGF-beta) family, glial cell line-derived neurotrophic factor (GDNF), has potent trophic actions on fetal mesencephalic dopamine neurons. GDNF also has protective and restorative activity on adult mesencephalic dopaminergic neurons and potently protects motoneurons from axotomy-induced cell death. However, evidence for a role for endogenous GDNF as a target-derived trophic factor in adult midbrain dopaminergic circuits requires documentation of specific transport from the sites of synthesis in the target areas to the nerve cell bodies themselves. Here, we demonstrate that GDNF is retrogradely transported by mesencephalic dopamine neurons of the nigrostriatal pathway. The pattern of retrograde transport following intrastriatal injections indicates that there may be subpopulations of neurons that are GDNF responsive. Retrograde axonal transport of biologically active 125I-labeled GDNF was inhibited by an excess of unlabeled GDNF but not by an excess of cytochrome c. Specificity was further documented by demonstrating that another TGF-beta family member, TGF-beta 1, did not appear to affect retrograde transport. Retrograde transport was also demonstrated by immunohistochemistry by using intrastriatal injections of unlabeled GDNF. GDNF immunoreactivity was found specifically in dopamine nerve cell bodies of the substantia nigra pars compacta distributed in granules in the soma and proximal dendrites. Our data implicate a specific receptor-mediated uptake mechanism operating in the adult. Taken together, the present findings suggest that GDNF acts endogenously as a target-derived physiological survival/maintenance factor for dopaminergic neurons

Controlled release of glial cell line-derived neurotrophic factor from poly(ε-caprolactone) microspheres

Glial cell line-derived neurotrophic factor (GDNF), a growth factor expressed in the central nervous system, promotes the survival of both dopaminergic and motor neurons, making it a promising candidate for neurodegenerative disease therapy. Although GDNF is currently being evaluated in clinical trials for the treatment of Parkinson’s disease (PD), the current delivery method using catheter implantation has certain limitations in terms of delivering GDNF safely and effectively. As a proof of concept, we encapsulated GDNF into poly(ε-caprolactone) (PCL) microspheres to enable controlled drug release for 25 days. First, microspheres were loaded with bovine serum albumin (BSA) to determine the optimal fabrication conditions necessary to achieve the desired release rates of protein. BSA was then used as a carrier protein to preserve GDNF activity during the fabrication process in the presence of organic solvents. GDNF-encapsulated microspheres were created and characterized using scanning electron microscopy. Next, the in vitro release of GDNF along with microsphere morphology was tracked over 25 days. Finally, the bioactivity of the released GDNF was confirmed using PC12 cells. This work demonstrates the potential of such microspheres for the delivery of bioactive GDNF with the end goal of developing a suitable, clinically relevant formulation for injection to appropriate regions of the brain in PD patients.The authors would like to acknowledge support from an NSERC Discovery Grant (S.M.W.) and an NSERC Engage Grant with MedGenesis Therapeutix. They would also like to acknowledge the Advanced Microscopy Facility at the University of Victoria and MedGenesis Therapeutix for their on-going support of this project.FacultyReviewe