Department of Neuroscience, Tufts University, Boston, Massachusetts 02111, USA.
J Biol Chem. 2013 Mar 8;288(10):7105-16. doi: 10.1074/jbc.M112.410944. Epub 2013 Jan 30.
Perisynaptic astrocytes express important glutamate transporters, especially excitatory amino acid transporter 2 (EAAT2, rodent analog GLT1) to regulate extracellular glutamate levels and modulate synaptic activation. In this study, we investigated an exciting new pathway, the exosome-mediated transfer of microRNA (in particular, miR-124a), in neuron-to-astrocyte signaling. Exosomes isolated from neuron-conditioned medium contain abundant microRNAs and small RNAs. These exosomes can be directly internalized into astrocytes and increase astrocyte miR-124a and GLT1 protein levels. Direct miR-124a transfection also significantly and selectively increases protein (but not mRNA) expression levels of GLT1 in cultured astrocytes. Consistent with our in vitro findings, intrastriatal injection of specific antisense against miR-124a into adult mice dramatically reduces GLT1 protein expression and glutamate uptake levels in striatum without reducing GLT1 mRNA levels. MiR-124a-mediated regulation of GLT1 expression appears to be indirect and is not mediated by its suppression of the putative GLT1 inhibitory ligand ephrinA3. Moreover, miR-124a is selectively reduced in the spinal cord tissue of end-stage SOD1 G93A mice, the mouse model of ALS. Subsequent exogenous delivery of miR-124a in vivo through stereotaxic injection significantly prevents further pathological loss of GLT1 proteins, as determined by GLT1 immunoreactivity in SOD1 G93A mice. Together, our study characterized a new neuron-to-astrocyte communication pathway and identified miRNAs that modulate GLT1 protein expression in astrocytes in vitro and in vivo.
突触旁星形胶质细胞表达重要的谷氨酸转运体，特别是兴奋性氨基酸转运体 2（EAAT2，啮齿动物类似物 GLT1），以调节细胞外谷氨酸水平并调节突触激活。在这项研究中，我们研究了一种令人兴奋的新途径，即外体介导的 microRNA（特别是 miR-124a）转移，这是神经元到星形胶质细胞信号转导中的一种途径。从神经元条件培养基中分离的外体含有丰富的 microRNA 和小 RNA。这些外体可以被星形胶质细胞直接内化，并增加星形胶质细胞的 miR-124a 和 GLT1 蛋白水平。直接转染 miR-124a 也显著且选择性地增加了培养的星形胶质细胞中 GLT1 的蛋白（而不是 mRNA）表达水平。与我们的体外发现一致，向成年小鼠的纹状体中直接注射针对 miR-124a 的特异性反义寡核苷酸，可显著降低纹状体中的 GLT1 蛋白表达和谷氨酸摄取水平，而不会降低 GLT1 mRNA 水平。miR-124a 对 GLT1 表达的调节似乎是间接的，不是通过其抑制假定的 GLT1 抑制性配体 ephrinA3 介导的。此外，miR-124a 在终末期 SOD1 G93A 小鼠的脊髓组织中选择性减少，SOD1 G93A 小鼠是 ALS 的小鼠模型。随后通过立体定向注射体内外源性递送 miR-124a，可显著防止 SOD1 G93A 小鼠中 GLT1 蛋白的进一步病理性丢失，这可通过 GLT1 免疫反应性来确定。总之，我们的研究描述了一种新的神经元到星形胶质细胞的通讯途径，并鉴定了体外和体内调节星形胶质细胞中 GLT1 蛋白表达的 microRNAs。
