A major hallmark of Parkinson?s disease (PD) is presence of ?-synuclein (?syn) positive aggregates and cell loss substantia nigra pars compacta (SNpc), yet studies of PD post-mortem brain tissue report that ?syn aggregation and cell loss in the locus coeruleus (LC) is more severe than, and may precede that in the SNpc. The LC is the major noradrenergic center of the brain, and loss of LC neurons is associated with non-motor symptoms of PD, including sleep disturbances, depression, generalized anxiety, and autonomic dysfunction. In experimental models LC lesion potentiates nigrostriatal degeneration, yet little is known of the mechanisms underlying LC cell loss in PD. To date, we have lacked an appropriate animal model to understand how ?syn pathology specifically affects noradrenergic systems in PD, and whether noradrenergic neurons are readily vulnerable to ?syn pathology. This study will test the hypothesis that ?syn accumulation in LC noradrenergic neurons affects ?syn solubility and shifts its conformation towards toxic oligomeric species, which will potentiate the detrimental effects of oxidative stress, reduce noradrenergic cell viability, and induce cell loss in a time-dependent manner.
The Specific aims of the proposed research are 1) to determine how ?syn overexpression in LC neurons affects the biochemical properties and conformation of ?syn and 2) evaluate how ?syn accumulation in LC neurons affects neuronal function, health, and susceptibility to oxidative stress.
These aims will be addressed using a novel BAC transgenic mouse (DBH-hSNCA) overexpressing human wild type ?syn under the dopamine-?-hydroxlase (DBH) promoter. Inducing selective expression of human wild type ?syn in noradrenergic neurons will reveal how ?syn pathology affects the LC. Analysis of post- translational modifications, ?syn solubility, and conformation will be used to evaluate characteristics of ?syn accumulation in LC neurons in young and aged transgenic and non-transgenic DBH-hSNCA mice. Vulnerability of ?syn overexpressing LC neurons to conditions of oxidative stress will be examined in vitro and in vivo by inhibiting the vesicular monoamine transporter 2 (VMAT2). VMAT2 inhibition increases cytosolic catecholamines, where they are rapidly digested into reactive aldehyde intermediates, and result in the formation of reactive oxygen species. Following VMAT2 inhibition, in vitro measurements of neuronal heath will include LC neurite length, number of LC neurons, and detection of reactive oxygen species in primary culture. In vivo, mRNA expression of antioxidant molecules will be assessed, and neuronal loss will be determined using unbiased stereological cell counting of LC neurons in young and aged transgenic and non-transgenic DBH-hSNCA mice. Completion of these studies will reveal the structural and functional consequences of an increased ?syn burden in noradrenergic systems and will advance our understanding of how ?syn accumulation in the LC contributes to disease progression in PD.
The goal of this project is to elucidate the effects of ?-synuclein pathology on noradrenergic neurons, specifically in the locus coeruleus. In Parkinson's disease ?-synuclein-positive inclusions and cell loss in the locus coeruleus are often more severe than in the substantia nigra pars compacta, yet little is known about how ?-synuclein aggregates affect these neurons. Completion of these studies will reveal the structural and functional consequences of an increased ?-synuclein burden in noradrenergic systems and will advance our understanding of how ?-synuclein accumulation in the locus coeruleus contributes to disease progression in Parkinson's disease.
