Objective: To identify morphological changes in circulating CD14+ monocytes in manifesting and non-manifesting carriers of mutations of the GBA gene and Parkinson’s disease (PD).

Background: Mutations of the GBA gene represent the major genetic risk factor for PD. GBA encodes for a lysosomal enzyme, ß-glucocerebrosidase. Biallelic mutations are responsible for Gaucher’s disease, where the innate immune compartment (i.e., monocytes and macrophages) is primarily involved and presents characteristic morphological changes and inclusions. Ultrastructural changes in monocytes of GBA-related PD can be informative on functional impairments and as early biomarkers of disease.

Method: Transmission electron microscopy was performed on monocytes (n=2 per group) from manifesting (PD-GBA), non-manifesting (CTRL-GBA) GBA carriers, non-carrier controls (CTRL) and idiopathic PD (iPD). CD14+ monocytes were isolated from PBMC, fixed, and resin embedded. Thin sections (75 nm) were collected, counter-stained with uranyl acetate/lead citrate, and imaged using a Hitachi 7500 TEM equipped with an AMT digital camera. Images were sized and adjusted for brightness and contrast.

Results: Preliminary qualitative analysis of our samples showed the following findings: 1) CTRL-GBA and CTRL showed normal cell size (12-20 µm), intact cytoplasm organelles (Golgi, endoplasmic reticulum (ER)/rough ER, ribosomes, pinocytotic vesicles, lysosomal granules, phagosomes, mitochondria, and microtubules), indented nuclei, and pseudopodia extend from cell surfaces; 2) in iPD cell population was relatively intact, although some subpopulations presented highly enhanced cytoplasmic membrane expression and increases vacuole density; 3) in PD-GBA numerous large vacuoles were noted with a diminished vacuole density, and a subpopulation of cells demonstrated highly contrasted cytoplasm and degenerating mitochondria.

Conclusion: Involvement of the innate immune system in the pathogenesis of PD has been supported by many preclinical and clinical evidences as well as its transcriptomic signature. Our data suggest that these changes are reflected also at the ultrastructural level in monocytes. These features can be informative about impaired cellular pathways and can be explored as targets for early detection of phenoconversion in carries of GBA mutations. Further characterization of these changes and quantitative assessments will be necessary to corroborate our observations.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/ultrastructural-characterization-of-monocytes-in-parkinsons-disease-and-gba-mutations/