Knockout of cyclophilin D in Ppif−/− mice increases stability of brain mitochondria against Ca2+ stress

• CypD ablation improves complex I-mediated functions of brain mitochondria.
• CypD ablation protects brain mitochondria from Ca2+ stress.
• CypD sensitizes brain mitochondria for PT.

The mitochondrial peptidyl prolyl isomerase cyclophilin D (CypD) activates permeability transition (PT). To study the role of CypD in this process we compared the functions of brain mitochondria isolated from wild type (BMWT) and CypD knockout (Ppif−/−) mice (BMKO) with and without CypD inhibitor Cyclosporin A (CsA) under normal and Ca2+ stress conditions. Our data demonstrate that BMKO are characterized by higher rates of glutamate/malate-dependent oxidative phosphorylation, higher membrane potential and higher resistance to detrimental Ca2+ effects than BMWT. Under the elevated Ca2+ and correspondingly decreased membrane potential the dose response in BMKO shifts to higher Ca2+ concentrations as compared to BMWT. However, significantly high Ca2+ levels result in complete loss of membrane potential in BMKO, too. CsA diminishes the loss of membrane potential in BMWT but has no protecting effect in BMKO. The results are in line with the assumption that PT is regulated by CypD under the control of matrix Ca2+. Due to missing of CypD the BMKO can favor PT only at high Ca2+ concentrations. It is concluded that CypD sensitizes the brain mitochondria to PT, and its inhibition by CsA or CypD absence improves the complex I-related mitochondrial function and increases mitochondria stability against Ca2+ stress.