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

When the electrochemical proton gradient is disrupted in the mitochondria, IF(1) (Inhibitor Factor-1) inhibits the reverse hydrolytic activity of the F(1)F(o)-ATP synthase, thereby allowing cells to conserve ATP at the expense of losing the mitochondrial membrane potential (Δψ(m)). The function of IF(1) 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 IF(1) function in Caenorhabditis elegans to understand IF(1)´s role in vivo. C. elegans has two inhibitor proteins of the F(1)F(o)-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 IF(1) 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 IF(1) had an enhanced Δψ(m) and lower physiological germ cell apoptosis. Importantly, we found that mai-2 mutant animals must be under stress to observe the role of IF(1). 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 IF(1) 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 Δψ(m). Additionally, we suggest that IF(1) function is mainly observed under stress and that, under physiological conditions, this protein does not play an essential role.