Mitochondrial elongation in the macular RPE of aging monkeys, evidence of metabolic stress.
OBJECTIVE
This study was conducted to determine whether mitochondria of the macular retinal pigment epithelium (RPE) change with age in rhesus monkeys (Macaca mulatta). Mitochondria are the main instigators of oxidative stress, which has often been considered to play a role in the pathogenesis of age-related macular degeneration (AMD). Any pathological changes in the mitochondria of aging macular RPE, the main target of AMD, would be a clue to the pathogenesis of this common retinal degeneration afflicting both monkey and man.


METHODS
Transmission electron microscopy was used to identify mitochondria and to determine their appearance, their density per unit area of RPE cytoplasm and their length. The eyes of seven monkeys, 1, 2, 6.5, 23, 26, 27 and 35 years of age, were studied. Measurements were kept separate for the basal, middle and apical third of each cell. The basal third of the macular RPE had many more mitochondria than the middle third, and the apical third was almost devoid of mitochondria.


RESULTS
Mitochondrial number decreased and length increased with age. The increase in length was associated with an unusual clustering of mitochondria into parallel arrays of elongated mitochondria, with their long axis orthogonal to the basal membrane of the cell, structures not described before in RPE.


CONCLUSIONS
Mitochondrial elongation is associated with metabolic and/or oxidative stress, which implies that age produces stress in macular RPE. The increased clustering of very elongated mitochondria suggests that pathological changes occur in mitochondrial organization with age. These changes support the hypothesis that age-related mitochondrial dysfunction plays a role in the pathogenesis of AMD.
Department of Ophthalmology, Columbia University, New York City, NY, USA. pg10@columbia.edu.|Edward S. Harkness Eye Institute, Research Annex, 635 West 165th Street, Box #76, New York, NY, 10032, USA. pg10@columbia.edu.
Peter
P
Gouras
St. Erik's Eye Hospital, Karolinska Institute, Stockholm, Sweden.
L
L
Ivert
Oregon Health & Science University, Portland, OR, USA.
M
M
Neuringer
Department of Ophthalmology, Columbia University, New York City, NY, USA.
T
T
Nagasaki
D000375:Aging / Q000502:physiology*; D000818:Animals; D008253:Macaca mulatta; D046529:Microscopy, Electron, Transmission; D008928:Mitochondria / Q000378:metabolism* / Q000648:ultrastructure; D053142:Mitochondrial Size / Q000502:physiology*; D018384:Oxidative Stress / Q000502:physiology; D055213:Retinal Pigment Epithelium / Q000378:metabolism* / Q000648:ultrastructure; D013312:Stress, Physiological / Q000502:physiology*
Electron microscopy; Epithelium; Macula; Mitochondria; Monkey; Morphology; Retina