Oligomeric α-synuclein-specific degradation by HtrA2/Omi to bestow a neuroprotective function

Although the malfunction of HtrA2/Omi leads to Parkinsons disease (PD), the underlying mechanism has remained unknown. Here, we showed that HtrA2/Omi specifically removed oligomeric -Syn but not monomeric -Syn to protect oligomeric -Syn-induced neurodegeneration. Experiments using mnd2 mice indicated that HtrA2/Omi degraded oligomeric -Syn specifically without affecting monomers. Transgenic Drosophila melanogaster experiments of the co-expression -Syn and HtrA2/Omi and expression of genes individually also confirmed that pan-neuronal expression of HtrA2/Omi completely rescued Parkinsonism in the -Syn-induced PD Drosophila model by specifically removing oligomeric -Syn. HtrA2/Omi maintained the health and integrity of the brain and extended the life span of transgenic flies. Because HtrA2/Omi specifically degraded oligomeric -Syn, co-expression of HtrA2/Omi and -Syn in Drosophila eye maintained a healthy retina, while the expression of -Syn induced retinal degeneration. This work showed that the bacterial function of HtrA to degrade toxic misfolded proteins is evolutionarily conserved in mammalian brains as HtrA2/Omi.