Abstract
Lymphocyte chemotaxis plays important roles in immunological reactions, although the mechanism of its regulation is still unclear. We found that the cytosolic Na+-dependent mitochondrial Ca2+ efflux transporter, NCLX, regulates B lymphocyte chemotaxis. Inhibiting or silencing NCLX in A20 and DT40 B lymphocytes markedly increased random migration and suppressed the chemotactic response to CXCL12. In contrast to control cells, cytosolic Ca2+ was higher and was not increased further by CXCL12 in NCLX-knockdown A20 B lymphocytes. Chelating intracellular Ca2+ with BAPTA-AM disturbed CXCL12-induced chemotaxis, suggesting that modulation of cytosolic Ca2+ via NCLX, and thereby Rac1 activation and F-actin polymerization, is essential for B lymphocyte motility and chemotaxis. Mitochondrial polarization, which is necessary for directional movement, was unaltered in NCLX-knockdown cells, although CXCL12 application failed to induce enhancement of mitochondrial polarization, in contrast to control cells. Mouse spleen B lymphocytes were similar to the cell lines, in that pharmacological inhibition of NCLX by CGP-37157 diminished CXCL12-induced chemotaxis. Unexpectedly, spleen T lymphocyte chemotaxis was unaffected by CGP-37157 treatment, indicating that NCLX-mediated regulation of chemotaxis is B lymphocyte-specific, and mitochondria-endoplasmic reticulum Ca2+ dynamics are more important in B lymphocytes than in T lymphocytes. We conclude that NCLX is pivotal for B lymphocyte motility and chemotaxis.
Highlights
Migration of lymphocytes is one of the fundamental processes of the immune response
When CXCL12 was present in the bottom chamber, there was a significant increase in the movement of A20 B lymphocytes toward the bottom chamber; that is, CXCL12 induced chemotaxis of A20 B lymphocytes (Fig. 1)
NCLX was identified as a mitochondrial Na+-Ca2+ exchanger by Palty et al.[19], and there is a rapidly growing literature on the physiological and pathophysiological roles of NCLX in a variety of cell types, including pancreatic β cells, astrocytes, cardiomyocytes, and B lymphocytes[20,21,22,36,37,38]
Summary
Migration of lymphocytes is one of the fundamental processes of the immune response. In the case of B lymphocytes, circulating naive lymphocytes enter lymph nodes through high endothelial venules, migrate to the B cell area where chemoattractants such as CXCL12 and CXCL13 are highly expressed, and are activated and differentiated into plasma cells[1,2]. Results Facilitation of random migration and inhibition of chemotaxis by NCLX silencing in B lymphocytes. In heterozygous NCLX knockout DT40 B lymphocytes (NCLX+/−), in which NCLX protein expression was negligible[20], CXCL12-induced chemotaxis was significantly suppressed (Supplementary Fig. S1), suggesting that the mitochondrial Na+-Ca2+ exchanger is a key determinant for the chemotaxis of B lymphocytes.
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