Quantification of non-neuronal cells containing intracellular α-synuclein in the human Parkinson’s disease olfactory bulb

Abstract

The neuropathological hallmark of Parkinson’s disease (PD) is the presence of aggregated α-synuclein (α-syn) in the form of Lewy bodies and Lewy neurites. It has been well described that α-syn aggregates are found intracellularly within neurons in post-mortem PD brains. However, little is known about the involvement of non-neuronal cells in the pathophysiology of PD. The olfactory bulb has been of particular interest as it is one of the first areas of the brain affected by α-syn pathology, occurring years to decades before the onset of motor symptoms. Within the olfactory bulb, the majority of α-syn accumulates in a region called the anterior olfactory nucleus (AON), a relay point for neurons of the olfactory system. In this study, we aimed to quantify the number of non-neuronal cells – pericytes, astrocytes and microglia, which contain intracellular α-syn aggregates in the AON of post-mortem human PD olfactory bulbs. In a subset of these cases, neurons containing intracellular α-syn were quantified for comparison. Human olfactory bulbs from PD cases (n = 11) and control cases (n = 8) (three sections each, taken 500 um apart) were immunolabeled for phosphorylated α-syn (Ser-129), PDGFRβ for pericytes, GFAP for astrocytes and IBA-1 for microglia. Six of the 11 PD cases were immunolabeled for NeuN for neurons. Sections were imaged using a slidescanning microscope; cells with presumed intracellular α-syn were counted and confirmed with confocal microscope imaging. Within the AON, an average of 4.56 pericytes/mm2, 4.01 astrocytes/mm2, 11.95 microglia/mm2 and 32.49 neurons/mm2 were confirmed to have intracellular α-syn. This study showed for the first time that in addition to neurons, non-neuronal cells also contain intracellular a-syn in post-mortem human PD olfactory bulbs. This suggests that non-neuronal cells may contribute to the progression of PD.