HtrA2 interacts with Aβ peptide but does not directly alter its production or degradation

HtrA2/Omi is a mammalian mitochondrial serine protease homologous to the E. coli HtrA/DegP gene products. Recently, HtrA2/Omi was found to have a dual role in mammalian cells, acting as an apoptosis-inducing protein and being involved in maintenance of mitochondrial homeostasis. By screening a human brain cDNA library with Aβ peptide as bait in a yeast two-hybrid system, we identified HtrA2/Omi as a binding partner of Aβ peptide. The interaction between Aβ peptide and HtrA2/Omi was confirmed by an immunoblot binding assay. The possible involvement of HtrA2/Omi in Aβ peptide metabolism was investigated. In vitro peptide cleavage assays showed that HtrA2/Omi did not directly promote the production of Aβ peptide at the β/γ- secretase level, or the degradation of Aβ peptide. However, overexpression of HtrA2/Omi in K269 cells decreased the production of Aβ40 and Aβ42 by up to 30%. These results rule out the involvement of HtrA2/Omi in the etiology of Alzheimer's disease. However, the fact that overexpression of HtrA2/Omi reduces the generation of Aβ40 and Aβ42 suggests that it may play some positive role in mammalian cells.