Aβ-Induced Drp1 phosphorylation through Akt activation promotes excessive mitochondrial fission leading to neuronal apoptosis.
Mitochondrial dysfunction is known as one of causative factors in Alzheimer's disease (AD), inducing neuronal cell death. Mitochondria regulate their functions through changing their morphology. The present work was undertaken to investigate whether Amyloid β (Aβ) affects mitochondrial morphology in neuronal cells to induce apoptosis. Aβ treatment induced not only the fragmentation of mitochondria but also neuronal apoptosis in association with an increase in caspase-9 and -3 activity. Calcium influx induced by Aβ up-regulated the activation of Akt through CaMKII resulting in changes to the phosphorylation level of Drp1 in a time-dependent manner. Translocation of Drp1 from the cytosol to mitochondria was blocked by CB-124005 (an Akt inhibitor). Recruitment of Drp1 to mitochondria led to ROS generation and mitochondrial fission, accompanied by dysfunction of mitochondria such as loss of membrane potential and ATP production. ROS generation and mitochondrial dysfunction by Aβ were attenuated when treated with Mdivi-1, a selective Drp1 inhibitor. Furthermore, the sustained Akt activation induced not only the fragmentation of mitochondria but also the activation of mTOR, eventually suppressing autophagy. Inhibition of autophagic clearance of Aβ led to increased ROS levels and aggravating mitochondrial defects, which were blocked by Rapamycin (an mTOR inhibitor). In conclusion, sustained phosphorylation of Akt by Aβ directly activates Drp1 and inhibits autophagy through the mTOR pathway. Together, these changes elicit abundant mitochondrial fragmentation resulting in ROS-mediated neuronal apoptosis.
BK21 PLUS Creative Veterinary Research Center, Seoul National University, Seoul, South Korea; Department of Veterinary Physiology, College of Veterinary Medicine, Research Institute for Veterinary Science, Seoul National University, Seoul, South Korea. Electronic address: daim530@snu.ac.kr.
Dah Ihm
DI
Kim
BK21 PLUS Creative Veterinary Research Center, Seoul National University, Seoul, South Korea; Department of Veterinary Physiology, College of Veterinary Medicine, Research Institute for Veterinary Science, Seoul National University, Seoul, South Korea. Electronic address: alca2003@snu.ac.kr.
Ki Hoon
KH
Lee
Department of Veterinary Physiology, College of Veterinary Medicine, Research Institute for Veterinary Science, Seoul National University, Seoul, South Korea. Electronic address: amr.ahmed@cu.edu.eg.
Amr Ahmed
AA
Gabr
BK21 PLUS Creative Veterinary Research Center, Seoul National University, Seoul, South Korea; Department of Veterinary Physiology, College of Veterinary Medicine, Research Institute for Veterinary Science, Seoul National University, Seoul, South Korea. Electronic address: oroforof0105@snu.ac.kr.
Gee Euhn
GE
Choi
BK21 PLUS Creative Veterinary Research Center, Seoul National University, Seoul, South Korea; Department of Veterinary Physiology, College of Veterinary Medicine, Research Institute for Veterinary Science, Seoul National University, Seoul, South Korea. Electronic address: jskim7223@snu.ac.kr.
Jun Sung
JS
Kim
BK21 PLUS Creative Veterinary Research Center, Seoul National University, Seoul, South Korea; Department of Veterinary Physiology, College of Veterinary Medicine, Research Institute for Veterinary Science, Seoul National University, Seoul, South Korea. Electronic address: sohi33@snu.ac.kr.
So Hee
SH
Ko
BK21 PLUS Creative Veterinary Research Center, Seoul National University, Seoul, South Korea; Department of Veterinary Physiology, College of Veterinary Medicine, Research Institute for Veterinary Science, Seoul National University, Seoul, South Korea. Electronic address: hjhan@snu.ac.kr.
Ho Jae
HJ
Han
D016229:Amyloid beta-Peptides / Q000633:toxicity*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D001343:Autophagy / Q000187:drug effects; D045744:Cell Line, Tumor; D034281:Dynamins / Q000235:genetics / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism*; D006624:Hippocampus / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology; D006801:Humans; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology; D063154:Mitochondrial Dynamics / Q000187:drug effects*; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology; D018384:Oxidative Stress / Q000187:drug effects; D010446:Peptide Fragments / Q000633:toxicity*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D034622:RNA Interference; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D013997:Time Factors; D014162:Transfection
D016229:Amyloid beta-Peptides; D008869:Microtubule-Associated Proteins; D024101:Mitochondrial Proteins; D010446:Peptide Fragments; D017382:Reactive Oxygen Species; C075222:amyloid beta-protein (1-42); C546842:MTOR protein, human; C546843:mTOR protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D020558:GTP Phosphohydrolases; C110768:DNM1L protein, human; C486391:Dnm1l protein, mouse; D034281:Dynamins
Akt; Amyloid β (Aβ); Autophagy; Drp1; Mitochondrial dynamics; ROS