Heterogeneous distribution of axonal cytoskeleton proteins in the human optic nerve.
OBJECTIVE
Cytoskeleton proteins play a critical role in maintaining retinal ganglion cell structure, viability, and function. This study documents the distribution of cytoskeleton protein subunits in the various regions of the normal human optic nerve and identifies important relationships among mitochondria, myelin, and neurofilament proteins.


METHODS
Twenty-three optic nerves from human cadavers were used. Confocal microscopy was used to examine the distribution of neurofilament light, neurofilament medium, neurofilament heavy (phosphorylated and unphosphorylated), neurofilament heavy (phosphorylated only), actin, and microtubule associated protein (MAP)-1 along the sagittal plane of the optic nerve. Comparisons were made among superior, middle, and inferior regions and also among temporal, central, and nasal portions of the optic nerve. Colocalization of neurofilament light, mitochondrial cytochrome c oxidase (COX), and myelin was also performed.


RESULTS
There are significant differences in the pattern and distribution of neurofilament protein subunits, actin, and MAP-1 along the sagittal plane of the optic nerve. Cytoskeleton proteins and COX mitochondria are found in highest concentrations in the prelaminar and lamina cribrosa regions. COX and neurofilament light occurs predominantly in unmyelinated nerve, with a significant decrease in concentration occurring on optic nerve myelination.


CONCLUSIONS
The heterogeneous distribution of cytoskeleton proteins along the sagittal plane may be an important functional adaptation that reflects the nonuniform nature of the physiological and structural environment of the optic nerve. The heterogeneous distribution of cytoskeleton proteins may also partly account for the asymmetric pattern of optic nerve damage after intraocular pressure elevation.
Balaratnasingam
Chandrakumar
C
Centre for Ophthalmology and Visual Science, University of Western Australia, Perth, Australia.
Morgan
William H
WH
Johnstone
Victoria
V
Cringle
Stephen J
SJ
Yu
Dao-Yi
DY
D000199:Actins / Q000378:metabolism*; D000328:Adult; D000368:Aged; D001369:Axons / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000378:metabolism; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D008297:Male; D018613:Microscopy, Confocal; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008875:Middle Aged; D008928:Mitochondria / Q000201:enzymology; D009186:Myelin Sheath / Q000378:metabolism; D016900:Neurofilament Proteins / Q000378:metabolism; D009900:Optic Nerve / Q000378:metabolism*; D014019:Tissue Donors; D055815:Young Adult
D000199:Actins; D003598:Cytoskeletal Proteins; D008869:Microtubule-Associated Proteins; D016900:Neurofilament Proteins; C044882:neurofilament protein L; C061195:neurofilament protein M; D003576:Electron Transport Complex IV