l-Leucine influx through Slc7a5 regulates inflammatory responses of human B cells via mammalian target of rapamycin complex 1 signaling

Abstract

Objectives: Increasing evidence has revealed the close correlation between immune cell functions and their intracellular metabolism. Mammalian target of rapamycin complex 1 (mTORC1) is the important metabolism-modulating signal that regulates cellular activities. In certain types of cell, it is known that mTORC1 activation depends on influx of l-leucine through an amino acid transporter, Slc7a5. In B cells, however, the expression and the role of Slc7a5 have never been investigated.

Methods: CD19⁺ B cells were obtained from peripheral blood of healthy adults and stimulated by a toll-like receptor 9 ligand, CpG oligodeoxynucleotides. The expression of Slc7a5 and l-leucine uptake were evaluated by RT-PCR, flow cytometry and radioisotope assay. Then the effect of Slc7a5 inhibition on mTORC1 activity, plasmablast differentiation and production of IgG and inflammatory cytokines were analyzed.

Results: CpG stimulation significantly induced the expression of Slc7a5 in B cells, resulting in l-leucine influx. Furthermore, inhibition of Slc7a5 abrogated mTORC1 activation, plasmablast differentiation, and production of IgG and inflammatory cytokines in CpG-stimulated B cells.

Conclusion: l-leucine influx through Slc7a5 critically regulates mTORC1 activity and the immunological responses of human B cells. Slc7a5-mTORC1 pathway may provide a novel therapeutic strategy for autoimmune diseases.

Keywords:

• Human B cells
• l-leucine
• mammalian target of rapamycin complex 1
• system L amino acid transporters
• toll-like receptor 9

Acknowledgements

The authors thank the healthy volunteers for their cooperation and for consenting to participate in the study.

Conflict of interest

None.

Additional information

Funding

This work was supported in part by a Grant-in-Aid for Scientific Research from Japan Society for the Promotion of Science [Grant Number 17K16211 to M.T. and 15K01721 to K.G.].