Molecular Assessment of Cause and Consequence of Cellular Senescence in Diverse Midbrain Cell Types in Parkinson's Disease

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PROJECT SUMMARY/ABSTRACT Parkinson's disease is the second most common age-related neurodegenerative disorder. The underlying cause of idiopathic Parkinson's is unknown. Importantly, prodromal inflammation of the midbrain has been found but remains unexplained. Recently, we have discovered that dopaminergic neurons can enter a state of cellular senescence and found significantly elevated numbers of senescent cells in the midbrain of human Parkinson's disease patients. Cellular senescence is a program that gets activated upon DNA damage signaling and prevents mitotic cells from uncontrolled proliferation. Most senescent cells express the so-called senescence associated secretory phenotype. This phenotype is characterized by the secretion of proinflammatory factors that recruit immune cells and signal “come here and eat me!”. We have also found that senescent human and mouse dopaminergic neurons secrete pro-inflammatory factors and get removed by activated glial cells. The rationale underlying this proposal is that cellular senescence is a generic mechanism in the midbrain leading to dopamine neuron loss which results in Parkinson's disease. The three aims of the proposal focus on 1) unravelling the parkinsonism-related in vitro triggers of cellular senescence in dopaminergic neurons; 2) the characterization of senescence-mediated activation of immune responses and the in vitro spreading of senescence between cell types of the midbrain; and 3) the in vivo induction and spreading of senescence between diverse cell types in the midbrain. In the proposed study, we will identify pathways that induce cellular senescence in dopaminergic neurons and identify factors which are crucial for the spreading of senescence and the activation of an immune response. Finally, we will assess whether ablation of senescent cells in the midbrain at the right time point will interfere with the spreading and can thereby ameliorate the loss of dopaminergic neurons of the midbrain. The molecular understanding of the induction of senescence as well as the identification of released factors that are important to trigger brain inflammation will shed light on the general pathomechanism of Parkinson’s disease and other age-related neurodegenerative disorders. Moreover, our findings will have direct clinical implications to eventually develop methods to interfere with midbrain senescence to ameliorate the progression of Parkinson’s disease.