Sun Jianli, Jacobs Kimberle M
Department of Anatomy and Neurobiology, Virginia Commonwealth University Richmond, VA, USA.
Front Syst Neurosci. 2016 Jul 20;10:63. doi: 10.3389/fnsys.2016.00063. eCollection 2016.
Mitochondria are central to cell survival and Ca(2+) homeostasis due to their intracellular buffering capabilities. Mitochondrial dysfunction resulting in mitochondrial permeability transition pore (mPTP) opening has been reported after mild traumatic brain injury (mTBI). Cyclosporine A provides protection against the mPTP opening through its interaction with cyclophilin-D (CypD). A recent study has found that the extent of axonal injury after mTBI was diminished in neocortex in cyclophilin-D knockout (CypDKO) mice. Here we tested whether this CypDKO could also provide protection from the increased intrinsic and synaptic neuronal excitability previously described after mTBI in a mild central fluid percussion injury mice model. CypDKO mice were crossed with mice expressing yellow fluorescent protein (YFP) in layer V pyramidal neurons in neocortex to create CypDKO/YFP-H mice. Whole cell patch clamp recordings from axotomized (AX) and intact (IN) YFP+ layer V pyramidal neurons were made 1 and 2 days after sham or mTBI in slices from CypDKO/YFP-H mice. Both excitatory post synaptic currents (EPSCs) recorded in voltage clamp and intrinsic cellular properties, including action potential (AP), afterhyperpolarization (AHP), and depolarizing after potential (DAP) characteristics recorded in current clamp were evaluated. There was no significant difference between sham and mTBI for either spontaneous or miniature EPSC frequency, suggesting that CypDKO ameliorates excitatory synaptic abnormalities. There was a partial amelioration of intrinsic properties altered by mTBI. Alleviated were the increased slope of the AP frequency vs. injected current plot, the increased AP, AHP and DAP amplitudes. Other properties that saw a reversal that became significant in the opposite direction include the current rheobase and AP overshoot. The AP threshold remained depolarized and the input resistance remained increased in mTBI compared to sham. Additional altered properties suggest that the CypDKO likely has a direct effect on membrane properties, rather than producing a selective reduction of the effects of mTBI. These results suggest that inhibiting CypD after TBI is an effective strategy to reduce synaptic hyperexcitation, making it a continued target for potential treatment of network abnormalities.
由于线粒体具有细胞内缓冲能力，因此对细胞存活和钙离子稳态至关重要。据报道，轻度创伤性脑损伤（mTBI）后会出现线粒体功能障碍，导致线粒体通透性转换孔（mPTP）开放。环孢素A通过与亲环蛋白-D（CypD）相互作用，为mPTP开放提供保护。最近一项研究发现，在亲环蛋白-D基因敲除（CypDKO）小鼠的新皮层中，mTBI后轴突损伤的程度有所减轻。在此，我们测试了在轻度中枢流体冲击伤小鼠模型中，这种CypDKO是否也能保护小鼠免受mTBI后先前描述的内在和突触神经元兴奋性增加的影响。将CypDKO小鼠与在新皮层第V层锥体神经元中表达黄色荧光蛋白（YFP）的小鼠杂交，以创建CypDKO/YFP-H小鼠。在对CypDKO/YFP-H小鼠进行假手术或mTBI后1天和2天，从横断轴突（AX）和完整（IN）的YFP+第V层锥体神经元进行全细胞膜片钳记录。评估了电压钳记录的兴奋性突触后电流（EPSC）以及电流钳记录的内在细胞特性，包括动作电位（AP）、超极化后电位（AHP）和去极化后电位（DAP）特征。假手术组和mTBI组在自发或微小EPSC频率上均无显著差异，这表明CypDKO改善了兴奋性突触异常。mTBI改变的内在特性有部分改善。AP频率与注入电流图的斜率增加、AP、AHP和DAP幅度增加的情况有所缓解。其他出现反向变化且在相反方向上变得显著的特性包括电流强度阈值和AP超射。与假手术组相比，mTBI组的AP阈值仍处于去极化状态，输入电阻仍增加。其他改变的特性表明，CypDKO可能对膜特性有直接影响，而不是选择性地减轻mTBI的影响。这些结果表明，TBI后抑制CypD是减少突触过度兴奋的有效策略，使其成为潜在治疗网络异常的持续靶点。
