Investigation of Mitochondrial Function in Bipolar Disorder

锂和丙戊酸盐（VPA）是双相情感障碍常用的情绪稳定剂，并被证明通过cAMP反应元件结合蛋白（CREB）、脑源性神经营养因子（BDNF）、Bcl-2和丝裂原活化蛋白激酶（MAPK）等分子间接调节细胞内通路，其活性可能产生一些情绪稳定药物的有益作用。具体来说，锂和丙戊酸盐在体内和体外上调Bcl-2，通过阻断线粒体凋亡程序来防止神经元细胞死亡。越来越多的证据表明，线粒体功能障碍在各种神经退行性疾病和精神疾病的进展中起着关键作用。因此，增强线粒体功能可能有助于改善与各种神经精神疾病相关的神经可塑性和细胞弹性损伤。一系列的研究进行了情绪稳定剂对线粒体功能和线粒体介导的神经毒性的影响。我们发现长期使用锂和VPA治疗可提高细胞呼吸速率。此外，SH-SY5Y细胞的线粒体膜电位和线粒体氧化检测表明，锂或VPA慢性治疗可增强线粒体功能。体内研究表明，长期用锂或VPA治疗可以在线粒体水平上防止甲基苯丙胺引起的毒性。此外，这些药物还能阻止甲基苯丙胺诱导的线粒体细胞色素c、线粒体抗凋亡Bcl-2/Bax比值和线粒体细胞色素氧化酶（COX）活性的降低。DNA微阵列分析表明，甲基苯丙胺改变了与凋亡途径和线粒体功能相关的几种蛋白质的基因表达水平，而锂或VPA处理可减弱这些变化。其中一个基因Bcl-2是锂和VPA的共同靶标。用特定的Bcl-2 siRNA敲低Bcl-2可减少锂离子和vpa诱导的线粒体氧化增加。这些发现表明，锂和VPA可以增强线粒体功能，防止线粒体介导的毒性。这些药物可能在治疗与线粒体功能受损相关的其他疾病（如神经退行性疾病和精神分裂症）方面具有潜在的临床应用价值。

Lithium and valproate (VPA) are common mood stabilizers for bipolar disorder and are shown to indirectly regulate intracellular pathways, using molecules like cAMP response element-binding protein (CREB), brain derived neurotrophic factor (BDNF), Bcl-2, and mitogen-activated protein kinases (MAPK), whose activities may produce some of the beneficial effects of the mood stabilizing drugs. Specifically, lithium and valproate upregulate Bcl-2 in vivo and in vitro, preventing neuronal cell death through blocking the mitochondrial program for apoptosis. Accumulating evidence suggests that mitochondrial dysfunction plays a critical role in the progression of a variety of neurodegenerative and psychiatric disorders. Thus, enhancing mitochondrial function could potentially help ameliorate the impairments of neural plasticity and cellular resilience associated with a variety of neuropsychiatric disorders. A series of studies was undertaken to investigate the effects of mood stabilizers on mitochondrial function and mitochondria-mediated neurotoxicity. We found that long-term treatment with lithium and VPA enhanced cell respiration rate. Furthermore, chronic treatment with lithium or VPA enhanced mitochondrial function as determined by mitochondrial membrane potential and mitochondrial oxidation in SH-SY5Y cells. In vivo studies showed that long-term treatment with lithium or VPA protected against methamphetamine-induced toxicity at the mitochondrial level. Furthermore, these agents prevented the methamphetamine-induced reduction of mitochondrial cytochrome c, the mitochondrial anti-apoptotic Bcl-2/Bax ratio, and mitochondrial cytochrome oxidase (COX) activity. DNA microarray analysis demonstrated that the gene expression levels of several proteins related to the apoptotic pathway and mitochondrial functions were altered by methamphetamine, and these changes were attenuated by treatment with lithium or VPA. One of the genes, Bcl-2, is a common target for lithium and VPA. Knockdown of Bcl-2 with specific Bcl-2 siRNA reduced the lithium- and VPA-induced increases in mitochondrial oxidation. These findings illustrate that lithium and VPA enhance mitochondrial function and protect against mitochondria-mediated toxicity. These agents may have potential clinical utility in the treatment of other diseases associated with impaired mitochondrial function, such as neurodegenerative diseases and schizophrenia. In addition, calcium dysfunction in bipolar disorder is considered the most reproducible biological abnormality described in the illness, and recent data support a role for calcium dysregulation in the mitochondrial and endoplasmic reticulum (ER) of individuals with bipolar disorder. Recent human genetic data show that a single nucleotide polymorphism (SNP) in the Bcl-2 geners956572 (variant AA) is a risk allele for bipolar disorder that is also characterized by low Bcl-2 levels and an increased incidence of apoptosis in carriers of the allele. Since Bcl-2 regulates intracellular Ca++ signaling via its effects on the ER and mitochondria, we have examined the functional role of Bcl-2 in intracellular Ca++ regulation in lymphoblasts from bipolar disorder patients presenting three variants (AA, AG or GG) of this Bcl-2 SNP. We found that the Bcl-2-deficient variant AA presents elevated basal cytosolic Ca++ levels, although there were no quantitative differences between SNP variants in luminal ER and mitochondrial calcium concentrations, nor in Ca++ entry. However, increased cytosolic Ca++ levels after inositol 1, 4, 5-trisphosphate (InsP3)-mediated Ca++ mobilization, in parallel with enhanced reduction of the ER calcium pool, were observed specifically in variant AA and mimicked by Bcl-2 inhibitors in variant GG, showing that decreased Bcl-2 levels are associated with enhanced ER Ca++ release via InsP3 receptors. Functional interaction between Bcl-2 and InsP3 receptors appears relevant to the therapeutics of bipolar disorder, since chronic lithium given to human cells carrying the Bcl-2 risk allele AA induced a decrease in the abnormally high basal cytosolic Ca++ levels and in the extent of InsP3-mediated ER Ca++ release. The results demonstrate that Bcl-2 SNP variations in bipolar disorder facilitate deranged calcium signaling through modulation of InsP3-dependent ER Ca++ release.