In vivo imaging of axonal transport of mitochondria in the diseased and aged mammalian CNS

Author(s): Takihara Y (1), Inatani M (2), Eto K (3), Inoue T (4), Kreymerman A (5), Miyake S (6), Ueno S (7), Nagaya M (7), Nakanishi A (7), Iwao K (4), Takamura Y (6), Sakamoto H (8), Satoh K (8), Kondo M (9), Sakamoto T (8), Goldberg JL (5), Nabekura J (3), Tanihara H (4)

1 Department of Ophthalmology, Faculty of Medical Science, University of Fukui, Fukui 910-1193, Japan; Department of Ophthalmology, Faculty of Life Sciences, Kumamoto University, Kumamoto 860-8556, Japan;
2 Department of Ophthalmology, Faculty of Medical Science, University of Fukui, Fukui 910-1193, Japan; Department of Ophthalmology, Faculty of Life Sciences, Kumamoto University, Kumamoto 860-8556, Japan; inatani@u-fukui.ac.jp.
3 Division of Homeostatic Development, Department of Developmental Physiology, National Institute for Physiological Sciences, Aichi 444-8585, Japan; Department of Physiological Sciences, SOKENDAI (The Graduate University for Advanced Studies), Aichi 444-8585, Japan;
4 Department of Ophthalmology, Faculty of Life Sciences, Kumamoto University, Kumamoto 860-8556, Japan;
5 Shiley Eye Institute, University of California, San Diego, La Jolla, CA 92093;
6 Department of Ophthalmology, Faculty of Medical Science, University of Fukui, Fukui 910-1193, Japan;
7 Department of Ophthalmology, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan;
8 Ushimado Marine Institute, Graduate School of Natural Science and Technology, Okayama University, Okayama 701-4303, Japan;
9 Department of Ophthalmology, Mie University Graduate School of Medicine, Mie 514-8507, Japan.

The lack of intravital imaging of axonal transport of mitochondria in the mammalian CNS precludes characterization of the dynamics of axonal transport of mitochondria in the diseased and aged mammalian CNS. Glaucoma, the most common neurodegenerative eye disease, is characterized by axon degeneration and the death of retinal ganglion cells (RGCs) and by an age-related increase in incidence.

RGC death is hypothesized to result from disturbances in axonal transport and in mitochondrial function. Here we report minimally invasive intravital multiphoton imaging of anesthetized mouse RGCs through the sclera that provides sequential time-lapse images of mitochondria transported in a single axon with submicrometer resolution. Unlike findings from explants, we show that the axonal transport of mitochondria is highly dynamic in the mammalian CNS in vivo under physiological conditions.

Furthermore, in the early stage of glaucoma modeled in adult (4-mo-old) mice, the number of transported mitochondria decreases before RGC death, although transport does not shorten. However, with increasing age up to 23-25 mo, mitochondrial transport (duration, distance, and duty cycle) shortens. In axons, mitochondria-free regions increase and lengths of transported mitochondria decrease with aging, although totally organized transport patterns are preserved in old (23- to 25-mo-old) mice. Moreover, axonal transport of mitochondria is more vulnerable to glaucomatous insults in old mice than in adult mice.

These mitochondrial changes with aging may underlie the age-related increase inglaucoma incidence. Our method is useful for characterizing the dynamics of axonal transport of mitochondria and may be applied to other submicrometer structures in the diseased and aged mammalian CNS in vivo.

Proc Natl Acad Sci U S A. 2015 Aug 18;112(33):10515-20. doi: 10.1073/pnas.1509879112. Epub 2015 Aug 3.

PMID: 26240337
http://www.ncbi.nlm.nih.gov/pubmed/26240337

Keywords: aging, in vivo imaging, mammalian CNS, mitochondrial axonal transport, neurodegeneration

Experimental Paper of the Month manager: Andreas Boehm