UCLA

Parkinson’s Disease (PD) is the second most common neurodegenerative disease. Its pathological hallmarks include loss of dopaminergic neurons in the substantia nigra, aggregation of alpha-synuclein (α-syn) leading to the formation of Lewy bodies, and neuroinflammation. Epidemiological studies have reported positive associations between exposure to air pollution (AP) and incidence of PD. This research investigates the mechanisms behind responses of microglia and astroglia to the extract of a major component of AP, diesel exhaust particulates (DEPe), in zebrafish (Danio rerio, ZF). DEPe exposure led to significant injury of dopaminergic neurons in the ZF, and resulted in structural and functional activation of microglia. Elimination of microglia using a morpholino oligonucleotide did not significantly attenuate the DEPe-induced neuron injury, suggesting that microglia may not play a direct role in acute DEPe-induced neuron loss in our ZF model, and that their response is possibly heterogeneous in nature. Microglia were also activated with transgenic overexpression of human α-syn (hα-syn), and were significantly higher in number in the forebrain compared to hα-syn non-expressors. When the ZF overexpressing hα-syn were treated with DEPe, we observed significant neuronal injury, sustained microglial activation, and slightly decreased microglia-neuron interactions compared to control treatment, suggesting that DEPe exposure may affect microglia-neuron interactions, but the microglial response is complex. Single-cell RNA sequencing of larval ZF heads revealed 27 distinct clusters of cells. 55 differentially expressed genes (DEG) were identified in the microglial cluster with DEPe exposure. The DEG suggested that many microglia were activated and inflammatory, but were also mounting an anti-inflammatory and possibly neuroprotective response. 43 DEG were identified in the astroglial cluster. While some upregulated genes were related to astroglial activation and proliferation, other markers of a reactive state in astroglia were lowered, indicating a heterogeneous response. This was supported by IPA Comparison Analysis of pathways most changed with DEPe exposure in microglia and astroglia. Subcluster analysis identified gene expression profiles that suggest the presence of various states of the microglia and astroglia. Ultimately, these studies begin to reveal mechanisms that occur in microglia and astroglia in the context of DEPe exposure that may alter risk of PD development.