Di Nardo Alessia, Wertz Mary H, Kwiatkowski Erica, Tsai Peter T, Leech Jarrett D, Greene-Colozzi Emily, Goto June, Dilsiz Pelin, Talos Delia M, Clish Clary B, Kwiatkowski David J, Sahin Mustafa
The F.M. Kirby Neurobiology Center, Department of Neurology, Children's Hospital Boston, Harvard Medical School, Boston, MA 02115, USA.
Division of Translational Medicine, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
Hum Mol Genet. 2014 Jul 15;23(14):3865-74. doi: 10.1093/hmg/ddu101. Epub 2014 Mar 5.
Tuberous sclerosis complex (TSC) is a disorder arising from mutation in the TSC1 or TSC2 gene, characterized by the development of hamartomas in various organs and neurological manifestations including epilepsy, intellectual disability and autism. TSC1/2 protein complex negatively regulates the mammalian target of rapamycin complex 1 (mTORC1) a master regulator of protein synthesis, cell growth and autophagy. Autophagy is a cellular quality-control process that sequesters cytosolic material in double membrane vesicles called autophagosomes and degrades it in autolysosomes. Previous studies in dividing cells have shown that mTORC1 blocks autophagy through inhibition of Unc-51-like-kinase1/2 (ULK1/2). Despite the fact that autophagy plays critical roles in neuronal homeostasis, little is known on the regulation of autophagy in neurons. Here we show that unlike in non-neuronal cells, Tsc2-deficient neurons have increased autolysosome accumulation and autophagic flux despite mTORC1-dependent inhibition of ULK1. Our data demonstrate that loss of Tsc2 results in autophagic activity via AMPK-dependent activation of ULK1. Thus, in Tsc2-knockdown neurons AMPK activation is the dominant regulator of autophagy. Notably, increased AMPK activity and autophagy activation are also found in the brains of Tsc1-conditional mouse models and in cortical tubers resected from TSC patients. Together, our findings indicate that neuronal Tsc1/2 complex activity is required for the coordinated regulation of autophagy by AMPK. By uncovering the autophagy dysfunction associated with Tsc2 loss in neurons, our work sheds light on a previously uncharacterized cellular mechanism that contributes to altered neuronal homeostasis in TSC disease.
结节性硬化症（TSC）是一种由TSC1或TSC2基因突变引起的疾病，其特征是在各个器官中出现错构瘤，并伴有癫痫、智力障碍和自闭症等神经学表现。TSC1/2蛋白复合物对雷帕霉素复合物1（mTORC1）起负向调节作用，mTORC1是蛋白质合成、细胞生长和自噬的主要调节因子。自噬是一种细胞质量控制过程，它将胞质物质隔离在称为自噬体的双膜囊泡中，并在自溶酶体中对其进行降解。先前对分裂细胞的研究表明，mTORC1通过抑制Unc-51样激酶1/2（ULK1/2）来阻断自噬。尽管自噬在神经元稳态中起着关键作用，但关于神经元中自噬的调节机制却知之甚少。在这里，我们发现与非神经元细胞不同，尽管mTORC1依赖于对ULK1的抑制，但Tsc2缺陷型神经元的自溶酶体积累和自噬通量增加。我们的数据表明，Tsc2的缺失通过AMPK依赖的ULK1激活导致自噬活性。因此，在Tsc2敲低的神经元中，AMPK激活是自噬的主要调节因子。值得注意的是，在Tsc1条件性小鼠模型的大脑以及从TSC患者切除的皮质结节中也发现了AMPK活性增加和自噬激活。总之，我们的研究结果表明，神经元TSC1/2复合物活性是AMPK协调调节自噬所必需的。通过揭示与神经元中Tsc2缺失相关的自噬功能障碍，我们的工作揭示了一种以前未被描述的细胞机制，该机制导致TSC疾病中神经元稳态的改变。
