The Role of Mast Cells in Elamepritide-Induced Injection Site Reactions and Eosinophilia

Rationale: Mast cell activation by molecules with a net positive charge and bulky hydrophobic groups occurs through activation of the mast-cell-specific receptor MRGPRX2 in humans, and through its ortholog Mrgprb2 in mice (McNeil et al., Nature 519, 237-241 (2015)). Elamipretide fully fits the profile of an MRGPRX2 agonist. Approach: First, we will test whether elamipretide activates MRGPRX2 and Mrgprb2 in heterologous cell lines expressing the receptors. Second, we will test whether elamipretide activates connective tissue mast cells, using human LAD2 cells and primary mouse peritoneal mast cells. Third, if we obtain positive results from both of these phases, and then we will determine whether degranulation is dependent on MRGPRX2 or Mrgprb2 by monitoring responses to elamipretide in LAD2 cells after siRNA-mediated knockdown of MRGPRX2, and in peritoneal cells from Mrgprb2 knockout mice.