Altered numbers and volumes of secondary lysosomes in circulating monocytes in patient with CSF1R-related leukoencephalopathy

Objective: To map morphological changes of circulating monocytes between CSF1R-related leukoencephalopathy and healthy donors using nano x-ray tomography and electron microscope, with a specific focus on the numbers and volumes of secondary lysosomes. Background: CSF1R-related leukoencephalopathy is a neurodegenerative disease mainly caused by CSF1R gene mutations. CSF1R is a receptor tyrosine kinase expressed on microglia within the central nervous system, as well as on myeloid cells in the peripheral circulation. This receptor is implicated in survival, proliferation and differentiation of monocytes along with other cells of myeloid lineage. Design/Methods: Monocytes in peripheral blood mononuclear cells (PBMCs) were purified using CD14+ magnetic-activated cell sorting. For nano X-ray tomography monocytes were plunge-frozen at −170°C and two-dimensional native state images were obtained at X-Ray Microscopy Beamline U41-PGM1-XM at BESSY II, Helmholtz-Zentrum Berlin. Segmentation and volume calculations of secondary lysosome number and volume were performed on three-dimensional reconstructed (3DR) X-ray tomography images. Talos Electron microscopy was used in order to confirm the findings. Results: The 3DR X-ray tomography revealed that the volume, but not the number, of lysosomes was significantly lower in the patient that carries a CSF1R mutation vs healthy donors (Welch Two-sample T test, p=1.994e-06, Student’s Two-sample T test p = 9.341e-07). Conclusions: Morphological differences of secondary lysosomes in circulating monocytes may provide insight of pathology in CSF1R-related leukoencephalopathy. Disclosure: Miss Mickeviciute has nothing to disclose. Lidija Smertinaite has nothing to disclose. Jinming Han has nothing to disclose. Maria Ntzouni has nothing to disclose. Peter Guttmann has nothing to disclose. Robert Harris has nothing to disclose. Anders Sandell has nothing to disclose. Simin Mohseni has nothing to disclose. Dr. Karrenbauer has received personal compensation in the range of $500-$4,999 for serving on a Scientific Advisory or Data Safety Monitoring board for Merck.