Understanding the Role of Endoplasmic Reticulum-Exit Site Upregulation in Neuroprotection Against Parkinson’s Disease

Project Summary Parkinson’s disease (PD) is the second-most common neurodegenerative disorder globally and is increasing in prevalence in the United States. At a cellular level, this devastating disease is characterized by a progressive loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNc), resulting in a wide range of motor and non-motor symptoms. Neuroprotective therapies for PD are currently lacking, and most treatment modalities are designed to reduce motor symptoms rather than inhibit neurodegeneration. With advancements in PD diagnostics offering the promise of earlier detection, there is an urgent need for neuroprotective strategies capable of arresting DA neuron loss at early stages. Endoplasmic reticulum (ER) stress is a convergent mechanism in DA neuron degeneration, making it a key therapeutic target for neuroprotection against PD. Nicotine and the smoking cessation drug cytisine attenuate ER stress at low doses by acting as a pharmacological chaperone for neuronal nicotinic acetylcholine receptors and consequently increasing the formation of Sec24D-containing endoplasmic reticulum-exit sites (Sec24D-ERES). Furthermore, preliminary data show that cytisine upregulates Sec24D-ERES in a female 6- hydroxydopamine (6-OHDA) mouse model of parkinsonism, which is associated with neuroprotection in female mice only. Astrocytes in the SNc, which also contain Sec24D-ERES, ensheathe DA neurons and undergo process retraction as well as reduced GFAP expression after treatment with low-dose cytisine. Therefore, the overarching hypothesis of this proposal is that cytisine-induced increases in Sec24D-ERES formation in both SNc DA neurons and astrocytes is necessary for neuroprotection in a 6-OHDA mouse model of parkinsonism. This hypothesis will be tested by knocking down expression of Sec24D in a cell type-specific manner to address the following aims: Aim 1: To determine the extent to which Sec24D-ERES upregulation in SNc DA neurons is critical for cytisine- mediated neuroprotection in a 6-OHDA mouse model of parkinsonism. Aim 2: To determine the extent to which Sec24D-ERES upregulation in SNc astrocytes is critical for cytisine- mediated neuroprotection in a 6-OHDA mouse model of parkinsonism. These studies are expected to lay the foundation for developing translational treatment strategies for PD focused on Sec24D-ERES upregulation in DA neurons and astrocytes. This aligns with the mission of the National Institute for Neurological Disorders and Stroke, which is to reduce disease burden for all people by conducting basic and translational research. Completion of this training will enable the development of skills to investigate cellular mechanisms of neuroprotective drugs, which is vitally important to a career goal of becoming a physician-scientist investigating translational therapies for neurodegenerative disorders.