High cyclophilin D content of synaptic mitochondria results in increased vulnerability to permeability transition.
Mitochondria isolated from synaptosomes are more sensitive to Ca2+ overload and the resultant opening of the mitochondrial permeability transition pore (mPTP) than nonsynaptic mitochondria. To identify the mechanisms underlying these differences in Ca2+ dynamics, we examined relative levels of mPTP components in synaptic versus nonsynaptic mitochondria. Synaptic mitochondria had higher levels of cyclophilin D when compared with nonsynaptic mitochondria, whereas levels of the voltage-dependent anion channel and the adenine nucleotide translocase were similar in the two mitochondrial fractions. These differences in Ca2+ handling between synaptic and nonsynaptic mitochondria were greatly reduced in cyclophilin D null [Ppif-/- (peptidylprolyl isomerase F)] mice. Higher concentrations of cyclosporine A, which interacts with cyclophilin D to delay mPTP opening, were necessary to increase the Ca2+ uptake capacity of synaptic versus nonsynaptic mitochondria. To determine whether the differences in Ca2+ handling might reflect the relative abundance of neuronal and glial mitochondria in the two mitochondrial fractions, we compared cyclophilin D levels in primary cortical neurons and astrocytes. Primary rat cortical neurons possess higher cyclophilin D levels than do primary astrocytes. In the adult rat brain, cyclophilin D immunoreactivity was abundant in neurons but sparse in astrocytes. Together, these results demonstrate that the Ca2+ handling differences observed in synaptic versus nonsynaptic mitochondria are primarily the result of the high levels of cyclophilin D in synaptic mitochondria, reflecting the greater proportion of neuronal mitochondria in this fraction. The high levels of cyclophilin D in neuronal mitochondria result in their greater vulnerability to mPT and in higher levels of cyclosporine A being required to inhibit mPTP opening.
Naga
Kranthi Kumari
KK
Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, Kentucky 40536, USA.
Sullivan
Patrick G
PG
Geddes
James W
JW
D000818:Animals; D001253:Astrocytes / Q000378:metabolism; D002021:Buffers; D002118:Calcium / Q000378:metabolism; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism; D000081406:Peptidyl-Prolyl Isomerase F; D021983:Cyclophilins / Q000378:metabolism*; D016572:Cyclosporine / Q000008:administration & dosage / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008928:Mitochondria / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000083162:Mitochondrial Permeability Transition Pore; D009474:Neurons / Q000378:metabolism*; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D013569:Synapses / Q000378:metabolism*
D002021:Buffers; D000081406:Peptidyl-Prolyl Isomerase F; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; C000631446:PPIF protein, mouse; D016572:Cyclosporine; D021983:Cyclophilins; D002118:Calcium