Association of Omi/HtrA2 with γ-secretase in mitochondria.

Omi/HtrA2, a mitochondrial serine protease with chaperone activity, is involved in varied intracellular processes. Dysfunctional Omi/HtrA2 has thus been implicated in various neurodegenerative disorders. Previously, we have shown that γ-secretase complexes are present and active in mitochondria. Here, we demonstrate that peptide corresponding to C-terminus of presenilin-1, as previously reported to activate Omi/HtrA2, interacts with Omi/HtrA2 in isolated mitochondria. Moreover, we show that Omi/HtrA2 interacts with presenilin in active γ-secretase complexes located to mitochondria. Using a biotinylated γ-secretase inhibitor and confocal microscopy, we could further confirm the association of γ-secretase complexes with mitochondrial Omi/HtrA2. Furthermore, determination of γ-secretase complex topology in isolated mitochondria revealed an association of γ-secretase complexes with the outer membrane of mitochondria with the extreme PS1 C-terminus facing the inter-membrane space. We have also studied the impact of Omi/HtrA2 on γ-secretase activity, measuring APP intracellular domain (AICD) production. We found reduced AICD production in mitochondria isolated from Omi/HtrA2 knockout mouse embryonic fibroblasts, indicating a significant role of Omi/HtrA2 on γ-secretase activity. Thus, our results provide information for understanding the interplay between mitochondrial Omi/HtrA2 and γ-secretase complexes in AD.