Neurotrophic factors for disease-modifying treatments of Parkinson's disease: gaps between basic science and clinical studies

ABSTRACT: BACKGROUND: Neurotrophic factors are endogenous proteins promoting the survival of different neural cells. Therefore, they elicited great interest as a possible treatment for neurodegenerative disorders, including Parkinson’s Disease (PD). PD is the second most common neurodegenerative disorder, scientifically characterized more than 200 years ago and initially linked with motor abnormalities. Currently, the disease is viewed as a highly heterogeneous, progressive disorder with a long presymptomatic phase, and both motor and non-motor symptoms. Presently only symptomatic treatments for PD are available. Neurohistopathological changes of PD affected brains have been described more than 100 years ago and characterized by the presence of proteinaceous inclusions known as Lewy bodies and degeneration of dopamine neurons. Despite more than a century of investigations, it has remained unclear why dopamine neurons die in PD. METHODS: This review summarizes literature data from preclinical studies and clinical trials of neurotrophic factor based therapies for PD and discuss it from the perspective of the current understanding of PD biology. RESULTS: Newest data point towards dysfunctions of mitochondria, autophagy-lysosomal pathway, unfolded protein response and prion protein-like spreading of misfolded alpha-synuclein that is the major component of Lewy bodies. Yet, the exact chain of events leading to the demise of dopamine neurons is unclear and perhaps different in subpopulations of patients. CONCLUSIONS: Gaps in our understanding of underlying disease etiology have hindered our attempts to find treatments able to slow down the progression of PD. GRAPHIC ABSTRACT: [Image: see text]