IF1 ablation prevents ATP synthase oligomerization, enhances mitochondrial ATP turnover and promotes an adenosine-mediated pro-inflammatory phenotype

Abstract

ATPase Inhibitory Factor 1 (IF1) regulates the activity of mitochondrial ATP synthase. The expression of IF1 in differentiated human and mouse cells is highly variable. In intestinal cells, the overexpression of IF1 protects against colon inflammation. Herein, we have developed a conditional IF1-knockout mouse model in intestinal epithelium to investigate the role of IF1 in mitochondrial function and tissue homeostasis. The results show that IF1-ablated mice have increased ATP synthase/hydrolase activities, leading to profound mitochondrial dysfunction and a pro-inflammatory phenotype that impairs the permeability of the intestinal barrier compromising mouse survival upon inflammation. Deletion of IF1 prevents the formation of oligomeric assemblies of ATP synthase and alters cristae structure and the electron transport chain. Moreover, lack of IF1 promotes an intramitochondrial Ca²⁺ overload in vivo, minimizing the threshold to Ca²⁺-induced permeability transition (mPT). Removal of IF1 in cell lines also prevents the formation of oligomeric assemblies of ATP synthase, minimizing the threshold to Ca²⁺-induced mPT. Metabolomic analyses of mice serum and colon tissue highlight that IF1 ablation promotes the activation of de novo purine and salvage pathways. Mechanistically, lack of IF1 in cell lines increases ATP synthase/hydrolase activities and installs futile ATP hydrolysis in mitochondria, resulting in the activation of purine metabolism and in the accumulation of adenosine, both in culture medium and in mice serum. Adenosine, through ADORA2B receptors, promotes an autoimmune phenotype in mice, stressing the role of the IF1/ATP synthase axis in tissue immune responses. Overall, the results highlight that IF1 is required for ATP synthase oligomerization and that it acts as a brake to prevent ATP hydrolysis under in vivo phosphorylating conditions in intestinal cells.