Tlr9 and Beclin 1 Cross-Talk Regulates Muscle AMPK Activation in Exercise

The activation of adenosine monophosphate-activated protein kinase (AMPK) in skeletal muscle coordinates systemic metabolic responses to exercise(1). Autophagy, a lysosomal degradation pathway that maintains cellular homeostasis(2), is upregulated during exercise, and a core autophagy protein, beclin 1, is required for skeletal muscle AMPK activation(3). Herein, we describe a role for the innate immune sensing molecule, toll-like-receptor 9 (Tlr9)(4), and its interaction with beclin 1 in exercise-induced muscle AMPK activation. Mice lacking Tlr9 are deficient in exercise-induced skeletal muscle AMPK activation and GLUT4 plasma membrane localization but not autophagy. Tlr9 binds beclin 1, and this interaction is increased by energy stress (glucose starvation and endurance exercise) and decreased by a BCL2 mutation(3, 5) that blocks disruption of BCL2/beclin 1 binding. Tlr9 regulates the assembly of the endolysosomal beclin 1/UVRAG-containing phosphatidylinositol 3-kinase complex (PI3KC3-C2) in skeletal muscle during exercise, and knockout of beclin 1 or UVRAG inhibits glucose starvation-induced cellular AMPK activation. Moreover, Tlr9 functions in a muscle-autonomous fashion in ex vivo contraction-induced AMPK activation, glucose uptake, and beclin 1/UVRAG assembly. These findings reveal a heretofore undescribed role of a toll-like receptor in muscle AMPK activation and glucose metabolism during exercise, as well as unexpected cross-talk between this innate immune sensor and autophagy proteins.