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

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.

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.

B220^lo immature B cells were comparable between WT and KO mice (WT: 2.62±0.30% vs. KO: 3.55±0.67%, Figure1 Aand Table 1); similarly, pre-B cells identified as B220^loCD43+ population were comparable between the two groups (Figure 1B). However, when IgD was applied to separate B220^hi population into IgD⁺ and IgD^- subsets, circulating B cells (B220^hiIgD⁺ 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 B220^hiIgD^- 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 and Table 1). 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

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B cell development in bone marrow.

Figure 1

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B cell development in bone marrow.

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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 and Table 1). 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 and data not shown). Histologically, white pulp areas in KO mice were disorganized compared to WT mice (Figure 2B). These results collectively show that the number and distribution of B cells in spleen is regulated by a-synuclein.

Figure 2

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B cell development in spleen.

Figure 2

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B cell development in spleen.

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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, Figure 3A and data not shown). Normal lymph node cortical/ follicular architecture was missing in KO mice compared to WT controls (Figure 3B). 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

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B cell development in lymph nodes.

Figure 3

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B cell development in lymph nodes.

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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.

No relevant conflicts of interest to declare.