Glial Cell Line-Derived Neurotrophic Factor (GDNF) represents one of the most potent neurotrophic factors known for promoting the survival and function of dopaminergic neurons in the substantia nigra pars compacta (SNpc) [1]. Discovered in 1973 and characterized in 1993, GDNF has been extensively studied as a disease-modifying treatment for Parkinson's disease (PD), with the goal of protecting and potentially regenerating the vulnerable dopaminergic neurons that degenerate in this disorder [2]. The GDNF family includes neurturin (NRTN), artemin (ARTN), persephin (PSPN), and neublastin (NBN), all of which signal through the RET receptor tyrosine kinase complexed with GPI-anchored co-receptors [3].
GDNF was first identified as a trophic factor that promoted the survival of embryonic dopaminergic neurons in vitro. It belongs to the transforming growth factor-beta (TGF-β) superfamily, though it signals through a distinct receptor system. GDNF is a disulfide-linked homodimer with a molecular weight of approximately 33 kDa. The protein is expressed in various tissues including brain, kidney, and peripheral nervous system.
Key historical milestones:
The GDNF family comprises four structurally related neurotrophic factors with overlapping but distinct biological activities:
| Factor | Primary Receptor | Expression | Clinical Status |
|---|---|---|---|
| GDNF | GFRα1/RET | Brain, kidney, gut | Phase 2/3 |
| Neurturin (NRTN) | GFRα2/RET | Brain, peripheral | Phase 2 |
| Artemin (ARTN) | GFRα3/RET | Peripheral, CNS | Preclinical |
| Persephin (PSPN) | GFRα4/RET | Limited CNS | Preclinical |
GDNF signals through a unique bipartite receptor system consisting of the RET receptor tyrosine kinase and a GPI-anchored co-receptor of the GFRα family [4]:
GFRα co-receptors:
RET receptor:
GDNF binding to the GFRα1-RET complex activates multiple downstream signaling cascades [5]:
Primary pathways:
PI3K/Akt pathway: Promotes survival, inhibits apoptosis
RAS/MAPK/ERK pathway: Supports neuronal differentiation
PLCγ pathway: Modulates calcium signaling
cAMP/PKA pathway: Modulates neuronal excitability
RET-independent signaling:
Recent research has identified GFRα1-dependent signaling through NCAM (Neural Cell Adhesion Molecule), providing additional pathways for GDNF effects on neural plasticity and migration [6].
In the normal brain, GDNF plays essential roles in:
In PD, the dopaminergic neurons of the SNpc exhibit particular vulnerability due to several factors thatGDNF therapy could address:
GDNF can potentially counteract these vulnerabilities through its survival-promoting and neuroprotective signaling.
Evidence suggests that endogenous neurotrophic support may be reduced in PD:
The earliest approach to GDNF therapy involved direct delivery of recombinant GDNF protein to the brain [7]:
Intraparenchymal delivery:
| Trial | Phase | Key Findings |
|---|---|---|
| Gill et al. (2003) | Phase 1 | Significant motor improvement |
| Slevin et al. (2005) | Phase 1 | Dose-dependent effects |
| Lang et al. (2006) | Phase 2 | Primary endpoint not met |
| Whone et al. (2019) | Phase 2 | Improved putamen uptake, motor benefits |
Challenges:
Gene therapy offers the advantage of sustained GDNF expression from a single treatment [8]:
AAV-GDNF:
AAV-Neurturin (CERE-120):
Advantages:
Recent efforts have focused on developing small molecules that can mimic GDNF signaling without requiring protein or gene delivery [9]:
Approaches:
Status:
Engineered cells that secrete GDNF:
GDNF therapy may be combined with:
GDNF therapy for PD has a complex clinical history spanning over two decades:
Phase 1 trials (1999-2005):
Phase 2 trial (Lang et al., 2006):
Recent Phase 2 trial (Whone et al., 2019):
Several programs are advancing GDNF-based therapies:
Delivery challenges:
Solutions under development:
Patient selection:
Lin LF, et al. GDNF: a glial cell line-derived neurotrophic factor. Science. 1993. ↩︎
Gash DM, et al. GDNF in Parkinson's disease. Nature. 1999. ↩︎
Grindley J, et al. GDNF and neurturin: two neurotrophic factors. Curr Opin Neurobiol. 1995. ↩︎
Ayrou J, et al. GDNF family receptor signaling and neuroprotection. Nat Rev Neurosci. 2021. ↩︎
Kalia LV, Lang AE. Neurotrophic factor therapies for Parkinson's disease. Nat Rev Neurol. 2023. ↩︎
Ibrahim AG, et al. Ret-dependent and Ret-independent signaling by GDNF family ligands. Cell. 2022. ↩︎
Sundström E, et al. GDNF delivery challenges and solutions. J Parkinsons Dis. 2020. ↩︎
Cunningham J, et al. AAV-GDNF gene therapy for Parkinson's disease. Mol Ther. 2021. ↩︎
Ramer MS, et al. Small molecule GDNF mimetics. J Med Chem. 2022. ↩︎