Naga Kranthi Kumari, Sullivan Patrick G, Geddes James W
Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, Kentucky 40536, USA.
J Neurosci. 2007 Jul 11;27(28):7469-75. doi: 10.1523/JNEUROSCI.0646-07.2007.
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.
从突触体分离出的线粒体比非突触线粒体对钙离子超载以及由此导致的线粒体通透性转换孔（mPTP）开放更为敏感。为了确定钙离子动态变化中这些差异背后的机制，我们检测了突触线粒体与非突触线粒体中mPTP组分的相对水平。与非突触线粒体相比，突触线粒体中亲环蛋白D的水平更高，而电压依赖性阴离子通道和腺嘌呤核苷酸转位酶在这两种线粒体组分中的水平相似。在亲环蛋白D基因敲除[Ppif-/-（肽基脯氨酰异构酶F）]小鼠中，突触线粒体与非突触线粒体之间在钙离子处理方面的这些差异大幅减少。需要更高浓度的环孢素A（其与亲环蛋白D相互作用以延迟mPTP开放）来提高突触线粒体相对于非突触线粒体的钙离子摄取能力。为了确定钙离子处理方面的差异是否可能反映了这两种线粒体组分中神经元线粒体和胶质线粒体的相对丰度，我们比较了原代皮层神经元和星形胶质细胞中亲环蛋白D的水平。原代大鼠皮层神经元的亲环蛋白D水平高于原代星形胶质细胞。在成年大鼠大脑中，亲环蛋白D免疫反应性在神经元中丰富，但在星形胶质细胞中稀少。总之，这些结果表明，在突触线粒体与非突触线粒体中观察到的钙离子处理差异主要是突触线粒体中亲环蛋白D水平高的结果，这反映了该组分中神经元线粒体的比例更大。神经元线粒体中亲环蛋白D的高水平导致它们对线粒体通透性转换（mPT）更易受损，并且需要更高水平的环孢素A来抑制mPTP开放。
