B Cell Development Is Regulated By a-Synuclein, a Key Player In Parkinson’s Disease

Introduction Synucleins comprise a family of small proteins that were first identified in normal and neoplastic brain tissues. As a key component of the Lewy body, a-synuclein plays crucial roles in Parkinson disease and other dementias, and mediates neurotransmitter trafficking. The role of a-synuclein in hematopoiesis is largely unknown; however, in the hematopoietic system, a-synuclein is present in megakaryocytes, platelets, erythroid precursors and erythrocytes. In addition, it has also been detected by RT-PCR in monocytes, T-, B-, and NK-cells. Of interest, there is reduced expression of a-synuclein in the megakaryocytes of myeloproliferative neoplasm (MPN), but not normal reactive marrow or myelodysplastic syndrome, suggesting that a-synuclein could play an important role in the pathogenesis of MPN; while there is increased expression in blasts of megakaryoblastic leukemia. In this study, we utilized a-synuclein-/- mice as a model to investigate the role of a-synuclein in hematopoiesis. We identified an unexpected role of a-synuclein in B cell development and maturation. Methods Age- and sex-matched a-synuclein-/- mice and wild type mice (6-week-old; N=10 each group) were purchased from The Jackson Laboratory (Bar Harbor, ME). Bone marrow cells, splenocytes, and lymph nodes were harvested and flow cytometry analysis performed looking at B cell markers. Histological examination of bone marrow, lymph nodes, and spleen were also performed. Results B220lo immature B cells were comparable between WT and KO mice (WT: 2.62±0.30% vs. KO: 3.55±0.67%, [Figure1 A][1]and [Table 1][2]); similarly, pre-B cells identified as B220loCD43+ population were comparable between the two groups ([Figure 1B][1]). However, when IgD was applied to separate B220hi population into IgD+ and IgD- subsets, circulating B cells (B220hiIgD+ subset), were significantly reduced by 5-fold in KO mice compared to WT (KO: 0.12±0.05% vs. WT: 0.59±0.37%, p=0.02), whereas B220hiIgD- subset representing transitional B cells was similar between WT and KO mice (WT: 1.54±0.22% vs. KO: 2.09±0.70%, [Figure1 A][1] and [Table 1][2]). Therefore, although early B cell development is not affected, the number of mature B cells in bone marrow is reduced in a-synuclein deficient mice. ![Figure 1][3] Figure 1 B cell development in bone marrow. View this table: Table 1 Summary of B cell development in a-synuclein-/- mice In spleen, there was a marked reduction in the number of B cells compared to WT: 5.5+1.6% vs. 14.0+1.9%, respectively ([Figure 2A][1] and [Table 1][2]). The absolute number of B cells was more drastically reduced in KO mice as the total number of splenocytes was only half of that in WT ([Figure 2B][4] and data not shown). Histologically, white pulp areas in KO mice were disorganized compared to WT mice ([Figure 2B][4]). These results collectively show that the number and distribution of B cells in spleen is regulated by a-synuclein. ![Figure 2][3] Figure 2 B cell development in spleen. On the other hand, though the percentage of B cells in lymph nodes was comparable between WT and KO mice, the absolute number of B cells was lower in KO mice and morphologically the lymph nodes from KO mice were smaller than those from WT mice ([Table 1][2], [Figure 3A][5] and data not shown). Normal lymph node cortical/ follicular architecture was missing in KO mice compared to WT controls ([Figure 3B][5]). The number of follicles in KO mice was 5-fold lower than that WT controls (WT: 5±0.2/HPF vs. KO: 1±0.3/HPF, p=0.001). ![Figure 3][3] Figure 3 B cell development in lymph nodes. Conclusion Our data shows that the number and localization of mature B cells in spleen and lymph nodes is in part regulated by a-synuclein. This is the first report to implicate an important role of a-synuclein in B cell development. The mechanism of a-synuclein regulation in B cells is under investigation. Disclosures: No relevant conflicts of interest to declare. [1]: #F1 [2]: #T1 [3]: pending:yes [4]: #F2 [5]: #F3