Development Of Mature T Lymphocytes Requires Alpha-Synuclein

Synucleins (including α-, β- and γ-synucleins) are a group of proteins that are expressed at high levels in the central nervous system. The physiologic function of these proteins is unknown. Alpha-synuclein has been implicated in the pathogenesis of neurodegenerative disorders such as Parkinson's disease and Lewy body dementia, as it is highly expressed in the Lewy bodies from both disorders. The expression of α-synuclein in hematopoietic system has been shown in erythroid precursors and megakaryocytes in bone marrow, as well as erythrocytes and platelets in peripheral blood. Moreover, some studies demonstrated the expression of α-synuclein on peripheral blood mononuclear cells (PBMC), including B and T lymphocytes, NK cells and monocytes; and its expression is shown to be higher in PBMCs of individuals with Parkinson's disease compared to healthy controls.

In order to study the role of α-synuclein in development of different hematopoietic elements, we compared bone marrow, peripheral blood and lymphoid organs of age and sex-matched α-synuclein knock-out (KO) mice and wild type (WT) animals of the same genetic background (n=10). Flow cytometric analysis of bone marrow elements did not show differences in the percentages and absolute numbers of erythroid, megakryocytic and myeloid lineages (data not shown). However, differential complete blood cell count (CBC) showed statistically significant decrease in red blood cell (RBC) count, hemoglobin (Hb) and hematocrit (Hct) in KO mice compared to WT mice. No difference was noted in other RBC indices (Table 1). However, platelets were smaller in KO mice as measured by the mean platelet volume (MPV). There was no difference in the number of platelets and white blood cell (WBC) counts. There was a significant reduction in the percentage of circulating lymphocytes, and associated increase in the percentage of neutrophils and monocytes in KO mice compared to WT mice, although the difference in the number of lymphocytes did not reach statistical significance (Table 1).

Flow cytometric analysis of T lymphocytes in thymus and peripheral lymphoid organs demonstrated marked defect in development of mature T cells. There was a significant increase in the number of double negative thymocytes in KO mice associated with significant decrease in the number of single positive T cells. Furthermore, splenic CD4+ and CD8+ T cells were markedly decreased in KO mice, indicating that α-synuclein is required for T cell development (Table 2).

In summary, our findings indicate an absolute requirement for α-synuclein in development of mature T lymphocytes. The underlying mechanism for this function is subject of future studies. Moreover, while α-synuclein-deficiency does not affect the development of myeloid lineage and platelets, lack of this protein is associated with lower number of erythrocytes, suggesting its role in development and/or survival red blood cells.

No relevant conflicts of interest to declare.