Cell-type-specific opening of the retinal ganglion cell mitochondrial permeability transition pore.
OBJECTIVE
To study the role of the mitochondrial permeability transition pore (PTP) in apoptosis of axotomized retinal ganglion cells (RGCs) in vitro.


METHODS
Primary rat retinal cultures containing DiI-labeled RGCs were treated with pharmacological agents that modulate the PTP. Ratiometric imaging of the mitochondrial membrane potential (DeltaPsi(m)) were conducted on similarly treated cultures, with the dual-emission probe JC-1, and the correlation with the results of the viability experiments were determined.


RESULTS
The peripheral benzodiazepine receptor agonist PK11195 induced RGC death, but this was not inhibited by cyclosporin A (CsA), which normally maintains the PTP in the closed configuration. Paradoxically, the combination of CsA and PK11195 caused massive RGC death and decreased DeltaPsi(m), suggesting aberrant regulation of the PTP in these cells. Imaging of DeltaPsi(m) revealed morphologic changes in the mitochondria after depolarization, characterized by formation of ringlike bodies, and similar to that with the potassium ionophore valinomycin. There were no such findings with other retinal neurons or neuronally differentiated PC-12 cells. The anomalous RGC death was independent of caspase activation or reactive oxygen species production.


CONCLUSIONS
These results suggest an aberrant opening of the RGC PTP and could be the result of structural differences in its components or its interaction with intracellular ligands. Unique RGC PTP behavior could underlie the pathophysiology of those mitochondrial diseases in which RGCs are specifically affected (e.g., Leber hereditary optic neuropathy).
Vrabec
Joshua P
JP
University of Wisconsin Medical School, Department of Ophthalmology and Visual Sciences, Madison, Wisconsin 53792-4673, USA.
Lieven
Christopher J
CJ
Levin
Leonard A
LA
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D019771:Axotomy; D002232:Carbocyanines / Q000378:metabolism; D002452:Cell Count; D002470:Cell Survival; D002478:Cells, Cultured; D016572:Cyclosporine / Q000633:toxicity; D005456:Fluorescent Dyes / Q000378:metabolism; D058785:GABA-A Receptor Agonists; D007473:Ion Channels / Q000502:physiology*; D007546:Isoquinolines / Q000633:toxicity; D008564:Membrane Potentials / Q000502:physiology; D008928:Mitochondria / Q000502:physiology; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D051381:Rats; D020318:Rats, Long-Evans; D011963:Receptors, GABA-A / Q000378:metabolism; D012165:Retinal Ganglion Cells / Q000166:cytology* / Q000187:drug effects
C035005:3,3'-dihexadecylindocarbocyanine; D002232:Carbocyanines; D005456:Fluorescent Dyes; D058785:GABA-A Receptor Agonists; D007473:Ion Channels; D007546:Isoquinolines; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D011963:Receptors, GABA-A; D016572:Cyclosporine; C037850:PK 11195