Neuronal AMPK coordinates mitochondrial energy sensing and hypoxia resistance

Abstract

Mitochondria coordinate metabolism to adapt to environmental changes such as hypoxia. Using 15 optogenetics to control mitochondrial function with light has allowed precise, reversible control of metabolism 16 to study metabolic adaptation. Using light, we specifically turn off mitochondrial function in different tissues to 17 study behavioral changes in C. elegans that are linked to hypoxia resistance through AMP-activated protein 18 kinase (AMPK) signaling. Our results show that turning off mitochondria in neurons alone is sufficient for 19 whole organism responses, and that neuronal AMPK is sufficient to drive hypoxia resistance triggered by 20 decreased mitochondrial function. These results imply that a perceived energy crisis is sufficient to trigger 21 whole-organism stress resistance. 22 23 24 25 LIST OF ABBREVIATIONS: mtOFF, mitochondria-OFF; IM, inner mitochondrial membrane; PMF, 26 protonmotive force; ETC, electron transport chain; AMPK, AMP-activated protein kinase; mtON, 27 mitochondria-ON; mmCRISPi, Mos1 mediated CRISPR Insertion; NGM, nematode growth medium; ATR, all-28 trans retinal; ChR2, channelrhodopsin 2; IMS, intermembrane space; MTS, mitochondrial targeting sequence; 29 TMRE, tetramethylrhodamine ethyl ester, ΔΨm, mitochondrial membrane potential; ΔpH, pH gradient; 30 2 ABSTRACT 31 32Organisms adapt to their environment through coordinated changes in mitochondrial function and metabolism. 33The mitochondrial protonmotive force (PMF) is an electrochemical gradient that powers ATP synthesis and 34 adjusts metabolism to energetic demands via cellular signaling. It is unknown how or where transient PMF 35 changes are sensed and signaled due to lack of precise spatiotemporal control in vivo. We addressed this by 36 expressing a light-activated proton pump in mitochondria to spatiotemporally "turn off" mitochondrial function 37 through PMF dissipation in tissues with light. We applied our constructmitochondria-OFF (mtOFF)to 38 understand how metabolic status impacts hypoxia resistance, a response that relies on mitochondrial function. 39 mtOFF activation induced starvation-like behavior mediated by AMP-activated protein kinase (AMPK). We 40 found prophylactic mtOFF activation increased survival following hypoxia, and that protection relied on 41 neuronal AMPK. Our study links spatiotemporal control of mitochondrial PMF to cellular metabolic changes 42 that mediate behavior and stress resistance. 43 44 45 46 47 54 Mitochondrial respiration results in a proton gradient across the IM known as the protonmotive force 55 (PMF). Ultimately, respiratory complexes of the electron transport chain (ETC) convert chemical energy into 56 electrical potential energy by pumping protons across the IM, creating this gradient. The PMF can then be 57 consumed at ATP synthase, converting the PMF back to chemical energy in the form of ATP to catalyze 58 reactions (Figure 1A). This process is called oxidative phosphorylation, as ETC activity consumes oxygen to 59 maintain PMF that is then used to phosphorylate ADP ...