Pathogenic Role of Serine Protease HtrA2/Omi in Neurodegenerative Diseases

High-temperature-requirement A2 (HtrA2)/Omi/PARK13 is a serine protease with extensive homology to the Escherichia coli HtrAs that are required for bacterial survival at high temperatures. The HtrA2 protein is a key modulator of mitochondrial molecular quality control but under stressful conditions it is released into the cytosol, where it promotes cell death by various pathways, including caspase-dependent pathway and ER stress-mediated apoptosis. Recently, the HtrA2 protein has received great attention for its potential role in neurodegeneration. Here, we review the current knowledge and pathophysiological functions of the HtrA2 protein in neurodegenerative disorders such as Parkinson’s and Alzheimer's disease.