Three-dimensional analysis of somatic mitochondrial dynamics in fission-deficient injured motor neurons using FIB/SEM.
Mitochondria undergo morphological changes through fusion and fission for their quality control, which are vital for neuronal function. In this study, we examined three-dimensional morphologies of mitochondria in motor neurons under normal, nerve injured, and nerve injured plus fission-impaired conditions using the focused ion beam/scanning electron microscopy (FIB/SEM), because the FIB/SEM technology is a powerful tool to demonstrate both 3D images of whole organelle and the intra-organellar structure simultaneously. Crossing of dynamin-related protein 1 (Drp1) gene-floxed mice with neuronal injury-specific Cre driver mice, Atf3:BAC Tg mice, allowed for Drp1 ablation specifically in injured neurons. FIB/SEM analysis demonstrated that somatic mitochondrial morphologies in motor neurons were not altered before or after nerve injury. However, the fission impairment resulted in prominent somatic mitochondrial enlargement, which initially induced complex morphologies with round regions and long tubular processes, subsequently causing a decrease in the number of processes and further enlargement of the round regions, which eventually resulted in big spheroidal mitochondria without processes. The abnormal mitochondria exhibited several degradative morphologies: local or total cristae collapse, vacuolization, and mitophagy. These suggest that mitochondrial fission is crucial for maintaining mitochondrial integrity in injured motor neurons, and multiple forms of mitochondria degradation may accelerate neuronal degradation.
Department of Functional Anatomy & Neuroscience, Nagoya University, Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya, 466-8550, Japan.|Japan Society for the Promotion of Science, Tokyo, 102-8472, Japan.
Hiromi
H
Tamada
Department of Functional Anatomy & Neuroscience, Nagoya University, Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya, 466-8550, Japan.
Sumiko
S
Kiryu-Seo
Department of Functional Anatomy & Neuroscience, Nagoya University, Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya, 466-8550, Japan.
Hiroki
H
Hosokawa
Department of Anatomy, Kurume University School of Medicine, Fukuoka, 830-0011, Japan.
Keisuke
K
Ohta
Department of Protein Biochemistry Institute of Life Science, Kurume University, Kurume, 839-0864, Japan.
Naotada
N
Ishihara
Department of Medicine and Bioregulatory Science, Kyushu University, Fukuoka, 812-8382, Japan.
Masatoshi
M
Nomura
Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Fukuoka, 812-8382, Japan.
Katsuyoshi
K
Mihara
Department of Anatomy, Kurume University School of Medicine, Fukuoka, 830-0011, Japan.
Kei-Ichiro
KI
Nakamura
Department of Functional Anatomy & Neuroscience, Nagoya University, Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya, 466-8550, Japan.
Hiroshi
http://orcid.org/0000-0001-5963-046X
H
Kiyama
D000818:Animals; D034281:Dynamins / Q000172:deficiency* / Q000235:genetics; D005260:Female; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008855:Microscopy, Electron, Scanning / Q000379:methods*; D063154:Mitochondrial Dynamics / Q000502:physiology*; D009046:Motor Neurons / Q000378:metabolism* / Q000648:ultrastructure*
C486391:Dnm1l protein, mouse; D034281:Dynamins
AB_1542690; AB_591819; FIB/SEM; RRID: AB_1500538; SCR_014305; dynamin-related protein 1; mitochondria; mitophagy; motor neuron; nerve injury