GDNF/RET signaling pathway activation eliminates Lewy Body pathology in midbrain dopamine neurons

Neurodegenerative diseases are associated with proteostasis disturbances and accumulation of fibrillar proteins into insoluble aggregates. Progressive age-related degeneration of dopamine neurons is a primary cause of motor dysfunctions in Parkinson’s disease (PD) and substantial evidence supports critical involvement of α-synuclein (α-syn) in the etiology of PD. α-syn is a cytosolic protein present in high concentrations in pre-synaptic neuronal terminals and a primary constituent of intracellular protein aggregates known as Lewy Neurites or Lewy Bodies. Progression of Lewy pathology is a characteristic feature in the PD brains caused by the prion-like self-templating properties of misfolded α-syn. Modelling Lewy pathology progression with application of exogenously prepared α-syn preformed fibrils, we discovered that glial cell line-derived neurotrophic factor (GDNF) prevented formation of α-syn aggregates in dopamine neurons in culture and in vivo after viral vector expression of GDNF. These effects were abolished by CRISPR/Cas9-mediated deletion of receptor tyrosine kinase Ret , the major GDNF signaling pathway. Similar to GDNF, expression of mutated constitutively active RET (RET_MEN2B) was able to protect dopamine neurons. GDNF protection against α-syn pathology progression was abolished by Src and attenuated by Akt pathway inhibitors. For the first time, we have shown the neurotrophic factor-mediated protection against the misfolded α-syn propagation in dopamine neurons, uncovered underlying receptor and intracellular signaling pathways. These results for the first time demonstrate that activation of GDNF/RET signaling can be an effective therapeutic approach to prevent Lewy pathology spread at early stages of PD.