Neurturin (NRTN) is a neurotrophic factor belonging to the GDNF (Glial Cell Line-Derived Neurotrophic Factor) family. It has been extensively studied as a potential disease-modifying treatment for Parkinson's Disease due to its ability to support the survival and function of dopaminergic neurons in the substantia nigra pars compacta. [1]
Neurturin is a 70 kDa homodimeric protein that promotes neuronal survival through activation of the RET (Rearranged during Transfection) receptor tyrosine kinase. Unlike GDNF which binds primarily to GFRα1, neurturin exhibits higher affinity for GFRα2, creating a distinct pharmacological profile with potential implications for therapeutic efficacy and side effect management. [2]
Key points about NRTN therapy:
This page covers the molecular mechanism, clinical trial results, challenges, and future directions for neurturin therapy in Parkinson's disease.
Neurturin exerts its neuroprotective effects through a well-characterized mechanism involving binding to the GFRα2 (GDNF Family Receptor Alpha 2) co-receptor complexed with the RET tyrosine kinase receptor. This binding triggers downstream signaling cascades that promote neuronal survival, differentiation, and function. [3]
The signal transduction pathways activated by neurturin include:
Neurturin is part of a larger family of neurotrophic factors with overlapping but distinct receptor affinities:
| Factor | Primary Receptor | Secondary Receptor | Clinical Development |
|---|---|---|---|
| GDNF | GFRα1/RET | GFRα2 | Phase I/II |
| Neurturin | GFRα2/RET | GFRα1 | Phase II |
| Artemin | GFRα3/RET | — | Preclinical |
| Persephin | GFRα4/RET | — | Preclinical |
This receptor selectivity has led to hypotheses that neurturin might offer advantages in targeting specific neuronal populations while potentially reducing side effects associated with broader neurotrophic factor signaling. [4]
Preclinical studies in various Parkinson's disease animal models demonstrated promising results for neurturin:
6-OHDA Rat Model: Studies showed that AAV2-mediated neurturin expression in the striatum and substantia nigra protected dopaminergic neurons from 6-hydroxydopamine toxicity. Treated animals showed significant improvement in rotational behavior and forelimb use asymmetry compared to vehicle controls. [5]
MPTP Primate Model: In non-human primate models of Parkinson's disease, neurturin gene therapy led to:
Mechanism Studies: Research demonstrated that neurturin not only protects existing dopaminergic neurons but also promotes the restoration of dopaminergic function through axonal sprouting and synaptic reorganization in the striatum. [6]
The most advanced clinical development program for neurturin was CERE-120 (AAV2-NRTN), sponsored by Ceregene and later by Voyager Therapeutics:
Phase I Trial (NCT00229788):
Phase II Trial (NCT00400634):
Follow-up Studies: Open-label extensions showed continued safety with suggestions of slower decline in treated patients compared to historical controls, though these findings require careful interpretation due to the lack of randomized comparison. [7]
The neurturin trials provided important insights for neurotrophic factor therapy:
Given the overlapping but distinct receptor profiles of GDNF and neurturin, researchers have explored combination approaches:
Preclinical data suggest potential synergistic effects when both factors are delivered, though clinical translation remains challenging due to the complexity of dosing and delivery optimization. [8]
Current research explores combining neurotrophic factor therapy with:
Current research focuses on improving neurturin therapy through:
Efforts are underway to identify biomarkers that can:
Future trials may incorporate:
Bartus RT, Johnson EM. Redefining the role of neurotrophic factors in Parkinson's disease: from los-of-function to gain-of-function perspectives. Molecular Neurobiology. 2017. ↩︎
Saavedra A, Baltazar G, Duarte EP. Driving GDNF expression: the role of GFRα2/RET receptor complex. Neuroscience Letters. 2017. ↩︎
Airaksinen MS, Saarma M. The GDNF family: signalling, biological functions and therapeutic value. Nature Reviews Neuroscience. 2002. ↩︎
Gill SS, Patel NK, Hotton GR, et al. Direct brain infusion of glial cell line-derived neurotrophic factor in Parkinson disease. Nature Medicine. 2003. ↩︎
Kordower JH, Emborg ME, Bloch J, et al. Neurodegeneration prevented by lentiviral vector delivery of GDNF in primate models of Parkinson's disease. Science. 2000. ↩︎
Bjorklund A, Kirik D, Rosenblad C, et al. Towards a neuroprotective gene therapy for Parkinson's disease: use of adenovirus, AAV and lentivirus vectors for GDNF expression. Journal of Anatomy. 2000. ↩︎
Marks WJ Jr, Bartus RT, Siffert J, et al. Gene delivery of AAV2-neurturin for Parkinson's disease: a double-blind, randomised, controlled trial. Lancet Neurology. 2010. ↩︎
Oiwa Y, Sanchez-Pernaute R, Harvey-White J, et al. Functional recovery to restore dopaminergic innervation by combined GDNF and BDNF gene delivery in parkinsonian rats. Brain Research. 2002. ↩︎