The mitochondrial sodium/calcium exchanger NCLX (Slc8b1) in B lymphocytes. (December 2022)

• Record Type: Journal Article
• Authors: Emrich, Scott M.; Yoast, Ryan E.; Fike, Adam J.; Bricker, Kristen N.; Xin, Ping; Zhang, Xuexin; Rahman, Ziaur S.M.; Trebak, Mohamed
• Is Part Of: Cell calcium. Volume 108(2022)
• Publication Date: 2022-12
• Subjects: Ca2+ signaling -- Mitochondrial Ca2+ -- NCLX -- SOCE -- Slc8b1 -- B lymphocytes -- Germinal Center; Calcium -- Metabolism -- Periodicals; Vertebrates -- Physiology -- Periodicals; Calcium -- Physiological effect -- Periodicals; Cell physiology -- Periodicals; Calcium in the body -- Periodicals; 572.516
• DOI: 10.1016/j.ceca.2022.102667
• Languages: English
• ISSNs: 0143-4160

Abstract

Highlights: NCLX has minor, if any, contribution to mitochondrial Ca 2+ extrusion in B cells. NCLX is required for optimal SOCE activity in B cells. NCLX knockout does not alter ER Ca 2+ content and rates of ER depletion and refilling. NCLX loss alters mitochondrial ultrastructure, bioenergetics and oxidant production. B cell-specific NCLX knockout mice have reduced germinal center B cell responses. Abstract: Antigen receptor stimulation triggers cytosolic Ca 2+ signals, which activate transcriptional and metabolic programs critical for immune function. B-cell receptor (BCR) engagement causes rapid cytosolic Ca 2+ rise through the ubiquitous store-operated calcium entry (SOCE) pathway. Slc8b1, which encodes the mitochondrial Na + /Ca 2+ exchanger (NCLX), extrudes Ca 2+ out of the mitochondria and maintains optimal SOCE activity. Inhibition of NCLX in DT40 and A20 B lymphocyte lines was recently shown to impair cytosolic Ca 2+ transients in response to antigen-receptor stimulation, however the downstream functional consequences of this impairment remain unclear. Here, we generated Slc8b1 knockout A20 B-cell lines using CRISPR/Cas9 technology and B-cell specific Slc8b1 knockout mice. Surprisingly, while loss of Slc8b1 in B lymphocytes led to reduction in SOCE, it had a marginal effect on mitochondrial Ca 2+ extrusion, suggesting that NCLX is not the major mitochondrial Ca 2+ extrusion mechanism in B cells. Furthermore, endoplasmic reticulum (ER) Ca 2+ content and rates of ER depletion and refilling remained unaltered in Slc8b1 knockout B cells. Slc8b1 deficiency increased mitochondrial production of oxidants, reduced mitochondrial bioenergetics and altered mitochondrial ultrastructure. B-cell specific Slc8b1 knockout mice showed reduced germinal center B cell responses following foreign antigen and pathogen driven immune responses. Our studies provide novel insights into the function of Slc8b1 in germinal center B cells and its contribution to B-cell signaling and effector function. Graphical Abstract: Image, graphical abstract