Final Report Summary - PD-HUMMODEL (Elucidating early pathogenic mechanisms of neurodegeneration in Parkinson's disease through a humanized dynamic in vitro model)
Parkinson’s disease (PD) is an incurable disorder of old age with characteristic impairments of movement, due to the loss of a specific type of dopamine neurons (DAn) in the brain. Despite decades of intense research, the mechanisms underlying PD onset and progression are for the most part still unknown. Understanding how genes and environment come together to increase our propensity for neurodegenerative diseases such as PD is crucial to develop better ways to prevent and treat these disorders. However, studying the human nervous system at the molecular level has always been challenging due to the complexity of the brain, and the difficulty of obtaining live human neurons in the laboratory. The advent of induced pluripotent stem cell (iPSC) technology enables to reprogram human somatic cells to pluripotency, to generate viable human cells affected by the disease. In this project, we developed a human cell-based model for PD using iPSC from patients suffering sporadic or familial (associated to LRRK2 mutations) forms of the disease, and healthy individuals as controls. DAn from PD patients showed PD-relevant phenotypes such as abnormal alpha-synuclein accumulation, alterations in the autophagy machinery, and increased susceptibility to undergo neurodegeneration upon long-term culture. We also generated astrocytes from PD patients and found that they abnormally accumulated toxic alpha-synuclein that was passed on to DAn, revealing an important role for glial cells in PD and offering potential new targets for therapeutic development. By combining functional calcium imaging, biophysical modelling and lineage tracing of DAn, we found that a decrease in DAn neurite length triggered overall functional alterations in the PD networks. Thus, our results identify early alterations in PD neuronal function that predate the onset of DAn neurodegeneration, and could be used for the design of novel tools for early diagnosis of PD patients. Finally, we interrogated our PD iPSC-based model in combination with CRISPR/Cas9 technology to study genetic predisposition to PD, and identified specific genetic variants that provide significant protection in terms of disease onset and progression. In summary, our PD-HUMMODEL project has allowed in-depth exploration of the early molecular and cellular pathogenic mechanisms underlying PD onset and progression, and identified new targets for future development of early diagnostic tests and therapeutic interventions.