The microtranscriptome of Parkinson's disease: human and animal studies

Abstract

Parkinson's disease (PD) is a progressive debilitating neurodegenerative disorder affecting 2% of subjects over age 65. The major motor symptoms of PD result from loss of midbrain dopamine-synthesizing neurons and include resting tremor, rigidity, slowed movements (bradykinesia), and postural instability. Although there are known genetic causes, most PD cases have undetermined etiology. Thus, there is considerable interest in identifying biomarkers of early-stage PD to develop effective intervention strategies that might modify the disease course. Studies completed in this dissertation were designed to identify and validate such biomarkers through comprehensive analysis of the oral microtranscriptome in human subjects, as well as in animal and cellular PD models. A total of 300 human subjects were recruited, including 178 with PD and 122 controls. Both groups contained subjects with comorbid or isolated conditions frequently associated with PD, including restless legs syndrome, dystonia, and essential tremor. Subjects completed questionnaires to assess risk factors, medication use, and motor and non-motor symptoms, and underwent formal neurological examination. Approximately half of the subjects also completed olfactory testing and computerized neuromotor, cognitive, and postural testing. Saliva samples were collected using a vial or swab. Levels of microRNA and microbiota were quantified using next generation sequencing. Saliva miRNA levels were also compared in mice expressing wildtype (WT) or A53T mutant copies of human alpha synuclein (SNCA), a known cause of PD. Performance of the mice was also assessed in motor and cognitive tasks during pre- and early-symptomatic stages of the model. Lastly, measurements of both extracellular miRNA and cellular mRNA, as well as oxidative stress and DNA damage, were completed in human iPSC-derived dopaminergic neurons expressing WT or A53T SNCA, combined with exposure to media or Paraquat, an environmental risk factor for PD. All PD subjects fell within the mild-moderate early stage category. Significant differences were observed for olfactory, postural, and more challenging cognitive tests. Profiling of salivary miRNAs revealed subsets highly-changed in early stage PD. The mouse and dopaminergic neuron data strongly supported the findings for two specific miRNAs - miR-103a-3p and miR-107 - and indicate a number of key cellular pathways are altered across the disease and models.