Mast cell regranulation involves a metabolic switch promoted by the interaction between mTORC1 and a glucose-6-phosphate transporter

Mast cells (MCs) are highly granulated tissue resident hematopoietic cells and because of their capacity to degranulate and release many proinflammatory mediators, they are major effectors of chronic inflammatory disorders including asthma and urticaria. As MCs have the unique capacity to reform their granules following degranulation in vitro, their potential to undergo multiple cycles of degranulation and regranulation in vivo has been linked to their pathogenesis. However, it is not known what factors regulate MC regranulation let alone if MC regranulation occurs in vivo. Here, we report that IgE-sensitized mice can undergo multiple bouts of regranulation, following repeated anaphylactic reactions. mTORC1, a critical nutrient sensor that activates protein and lipid synthesis, was found necessary for MC regranulation. mTORC1 activity in MCs was regulated by a glucose-6-phosphate transporter, Slc37a2, which was found to be necessary for increased glucose-6-phosphate and ATP levels during regranulation, two upstream signals of mTOR. Slc37a2 is highly expressed at the cell periphery early during regranulation where it appears to colocalize with mTORC1. Additionally, this transporter was found to concentrate extracellular metabolites within endosomes which are trafficked directly into nascent granules. Thus, the metabolic switch associated with MC regranulation is mediated by the interactions of a cellular metabolic sensor and a transporter of extracellular metabolites into MC granules.