Munc13 mediates klotho-inhibitable diacylglycerol-stimulated exocytotic insertion of pre-docked TRPC6 vesicles.

Abstract

α-Klotho is a type 1 transmembrane protein that exhibits aging suppression function. The large amino-terminal extracellular domain of α-klotho is shed as soluble klotho (sKlotho) and functions as a circulating cardioprotective hormone. Diacylglycerol (DAG)-activated calcium-permeable TRPC6 channel plays a critical role in stress-induced cardiac remodeling. DAG activates TRPC6 by acting directly on the channel to increase its activity and by stimulation of channel exocytosis. sKlotho protects the heart by inhibiting DAG stimulation of TRPC6 exocytosis. How DAG stimulates TRPC6 exocytosis and thereby inhibition by sKlotho are unknown. Using a compound that directly activates TRPC6 without affecting channel exocytosis, we validate that sKlotho selectively blocks DAG stimulation of channel exocytosis. We further show that DAG stimulates exocytosis of TRPC6-containing vesicles pre-docked to the plasma membrane. Mnuc13 family proteins play important roles in the proper assembly of SNARE proteins and priming the vesicle competent for fusion. We show that DAG stimulates TRPC6 exocytosis by targeting to the C1 domain of Munc13-2. The results provide fresh insights into the molecular mechanism by which DAG regulates vesicle fusion and how sKlotho protects the heart against injury.