Regulation of Mitochondrial Fission/Fusion by PP2A and PKA in Neurons

描述（由申请人提供）：线粒体提供能量、缓冲钙和隔离细胞死亡诱导分子，线粒体功能障碍与各种神经病变有关。特别是在神经元中，线粒体是高度动态的细胞器，不断移动、分裂和融合。本研究研究了神经元中线粒体裂变和融合的调控，这是由类似于动力蛋白的大gtpase进行的拮抗过程。其中两种酶Opal和Mfn2的突变是遗传性神经系统疾病的原因。虽然线粒体融合和断裂的适当平衡显然对神经元存活很重要，但线粒体的轴突和树突运输以及突触的发育和功能也需要一些断裂。我们发现线粒体的形状变化是由一种相反的蛋白激酶和磷酸酶控制的，这些蛋白激酶和磷酸酶通过特定的靶向/调节亚基定位于线粒体外膜。在磷酸酶方面，Bp2是神经元特异性的，出生后诱导的蛋白磷酸酶2A （PP2A）调控亚基，在脊髓小脑性共济失调12型中发生突变。Bp2的选择性剪接的N端介导PP2A全酶向线粒体表面的易位，在那里PP2A加速细胞死亡，显然是通过分裂线粒体。反对PP2A/Bp2对线粒体形态和存活影响的激酶是camp依赖性蛋白激酶（PKA），通过A激酶锚定蛋白（AKAP）锚定在OMM上121。目的1研究线粒体外PP2A和PKA控制神经元存活的机制。在目标2中，我们将确定线粒体裂变/融合酶中的相关底物和磷酸化位点。目的3解决PP2A/ pka依赖性线粒体重组在线粒体递送和树突棘发育中的作用。最后，Aim 4在线粒体和突触形态以及对缺血性损伤的抵抗方面表征PP2A/Bp2敲除小鼠。这些研究将促进我们对线粒体的形状转变是如何被调节的，以及这如何影响神经元的脆弱性以及它们之间功能连接的建立。我们的研究可能最终导致更好的治疗中风和神经退行性疾病。

DESCRIPTION (provided by applicant): Mitochondria provide energy, buffer calcium, and sequester cell death-inducing molecules, and mitochondrial dysfunction is implicated in various neuropathologies. Especially in neurons, mitochondria are highly dynamic organelles that constantly move, divide, and fuse. This proposal investigates the regulation of mitochondrial fission and fusion in neurons, which are antagonistic processes carried out by large GTPases similar to dynamin. Mutations in two of these enzymes, Opal and Mfn2, are responsible for hereditary neurological diseases. While a proper balance of mitochondrial fusion and fragmentation is clearly important for neuronal survival, some fragmentation is necessary for axonal and dendritic transport of mitochondria, and consequently for the development and function of synapses. We have found that shape changes of mitochondria are controlled by an opposing protein kinase and phosphatase that are localized to the outer mitochondrial membrane via specific targeting/regulatory subunits. On the phosphatase side, Bp2 is a neuron-specific, postnatally induced protein phosphatase 2A (PP2A) regulatory subunit mutated in spinocerebellar ataxia type 12. The alternatively spliced N terminus of Bp2 mediates translocation of the PP2A holoenzyme to the mitochondrial surface, where PP2A accelerates cell death, apparently by fragmenting mitochondria. The kinase opposing PP2A/Bp2's effect on mitochondrial morphology and survival is cAMP-dependent protein kinase (PKA) anchored to the OMM via A kinase anchoring protein (AKAP)121. Aim 1 investigates the mechanism by which outer-mitochondrial PP2A and PKA control neuronal survival. In Aim 2, we will identify the relevant substrates and phosphorylation sites among mitochondrial fission/fusion enzymes. Aim 3 addresses the role of PP2A/PKA-dependent mitochondrial restructuring in the delivery of mitochondria to and development of dendritic spines. Finally, Aim 4 characterizes PP2A/Bp2 knockout mice in terms of mitochondria and synapse morphology and resistance to ischemic injury. These studies will advance our understanding of how shape transitions of mitochondria are regulated, and how this affects vulnerability of neurons and the establishment of functional connections between them. Our studies may ultimately lead to better therapies for stroke and neurodegenerative disorders.