Caenorhabditis elegans ATPase inhibitor factor 1 (IF1) MAI-2 preserves the mitochondrial membrane potential (Δψm) and is important to induce germ cell apoptosis

Abstract

When the electrochemical proton gradient is disrupted in the mitochondria, IF1 (Inhibitor Factor-1) inhibits the reverse hydrolytic activity of the F1Fo-ATP synthase, thereby allowing cells to conserve ATP at the expense of losing the mitochondrial membrane potential (Δψm). The function of IF1 has been studied mainly in different cell lines, but these studies have generated contrasting results, which have not been helpful to understand the real role of this protein in a whole organism. In this work, we studied IF1 function in Caenorhabditis elegans to understand IF1´s role in vivo. C. elegans has two inhibitor proteins of the F1Fo-ATPase, MAI-1 and MAI-2. To determine their protein localization in C. elegans, we generated translational reporters and found that MAI-2 is expressed ubiquitously in the mitochondria; conversely, MAI-1 was found in the cytoplasm and nuclei of certain tissues. By CRISPR/Cas9 genome editing, we generated mai-2 mutant alleles. Here, we showed that mai-2 mutant animals have normal progeny, embryonic development and lifespan. Contrasting with the results previously obtained in cell lines, we found no evident defects in the mitochondrial network, dimer/monomer ATP synthase ratio, ATP concentration or respiration. Our results suggest that some of the roles previously attributed to IF1 in cell lines could not reflect the function of this protein in a whole organism and could be attributed to specific cell lines or methods used to silence, knockout or overexpress this protein. However, we did observe that animals lacking IF1 had an enhanced Δψm and lower physiological germ cell apoptosis. Importantly, we found that mai-2 mutant animals must be under stress to observe the role of IF1. Accordingly, we observed that mai-2 mutant animals were more sensitive to heat shock, oxidative stress and electron transport chain blockade. Furthermore, we observed that IF1 is important to induce germ cell apoptosis under certain types of stress. Here, we propose that MAI-2 might play a role in apoptosis by regulating Δψm. Additionally, we suggest that IF1 function is mainly observed under stress and that, under physiological conditions, this protein does not play an essential role.

Nicotinamide Supplementation Improves Oocyte Quality and Offspring Development by Modulating Mitochondrial Function in an Aged Caenorhabditis elegans Model

“…Abnormal mitochondrial membrane potential (MMP) affects germ cell apoptosis in C. elegans [ 30 ]. Furthermore, mitochondrial dysfunction is one of the prominent phenotypes observed in aged oocytes as previously reported in a mouse model [ 5 ].…”

“…Live images of stained animals were observed under a fluorescence microscope (Zeiss Axioscope, Oberkochen, Germany), and the average pixel intensity of MitoTracker Red fluorescence was measured using ImageJ software. To measure MMP, tetramethylrhodamine methyl ester (TMRM; Thermo Fisher Scientific, Waltham, MA, USA) staining was performed, as previously described [ 30 ]. Briefly, TMRM was added to NGM agar at a final concentration of 30 μM, and the plates were dried overnight and seeded with E. coli OP50 for 24 h in the dark.…”

Apoptosis induced by ursodeoxycholic acid in human melanoma cells through the mitochondrial pathway

“…In addition, ΔΨm arises from respiration. The electron transport chain pumping protons out of the inner membrane is a key step in the production of ATP ( 41 ). Therefore, changes in ΔΨm have been considered as one of the hallmark events of early apoptosis.…”

ATPase Inhibitory Factor-1 Disrupts Mitochondrial Ca2+ Handling and Promotes Pathological Cardiac Hypertrophy through CaMKIIδ

“…It has long been thought that the biological function of IF1 was restricted to conditions of respiratory collapse. Recent studies have, however, uncovered important physiological roles for IF1 under respiring conditions, including, but not restricted to, the regulation of oxidative stress [ 6 ], Ca 2+ handling [ 7 ], cristae formation [ 5 , 7 , 8 , 9 ], glucose metabolism [ 10 , 11 ], and neuronal development [ 12 , 13 ]. While the role of binding to ATP synthase in these processes is disputed, there is general consensus that many of these non-canonical roles of IF1 are governed by mitochondrial-to-nuclear signaling [ 5 , 6 , 7 , 10 , 11 , 14 ].…”