Humanin Protects Neurons Against Hypoxia Induced Cell Death By Preserving Mitochondrial Integrity

Humanin (HN) is a 24-amino acid peptide that was isolated from the brain of a patient with Alzheimer disease. Earlier studies focused on the neuroprotection of HN on neuronal cell death induced by AD-related insults including amyloid peptide (Aβ) and family AD (FAD)-related mutant gene. Recently, studies have revealed that HN appears possessing a broader spectrum of protective activity. For example, HN protects undifferentiated PC12 cells from serum deprivation-induced apoptosis. The incubation of rat cortical neurons with HN prevented cell death and apoptotic events induced by soluble prion protein fragments. Moreover, HNG, a homology of HN, protects mice against cerebral ischemia/reperfusion injury in vivo. However the mechanisms underlying these effects are not well understood. In this study, we investigated the protective role of HN against hypoxia indued neuronal death and its underlying mechanism. Hypoxia for 24 hours indued the death of large numbers of neurons. Pretreatment with HN 16 hours befor hypoxia, both 10μM and 20μM HN protect cells against hypoxia, however 1μM HN had no protective effect. Mitochondrial membrane potential(ΔΨm)were assessed by using the fluorescent voltage-sensitive dye JC-1.ΔΨm were reduced after hypoxia for 24 hours, pretreatment with 20μM HN preserved the loss ofΔΨm. Mitochondrial permeability transition por(emPTP) opening was examined with calcein-AM in the presence of cobalt chloride (CoCl2). Hypoxia induced the opening of mPTP as the calcein fluorescence were decreased in the mitochondria. Pretreatment with 20μM HN repressed the opening of mPTP as most of the calcein fluorescin were still in the mitochondria. In summary, our results demonstrate that HN protects neurons against hypoxia induced cell death by inhibiting the opening of mPTP and preservingΔΨm.