Membralin deficiency dysregulates astrocytic glutamate homeostasis, leading to ALS-like impairment
Lu-Lin Jiang, … , Timothy Y. Huang, Huaxi Xu
Lu-Lin Jiang, … , Timothy Y. Huang, Huaxi Xu
Published May 21, 2019
Citation Information: J Clin Invest. 2019;129(8):3103-3120. https://doi.org/10.1172/JCI127695.
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Research Article Cell biology Neuroscience

Membralin deficiency dysregulates astrocytic glutamate homeostasis, leading to ALS-like impairment

Abstract

Mechanisms underlying motor neuron degeneration in amyotrophic lateral sclerosis (ALS) are yet unclear. Specific deletion of the ER-component membralin in astrocytes manifested postnatal motor defects and lethality in mice, causing the accumulation of extracellular glutamate through reducing the glutamate transporter EAAT2. Restoring EAAT2 levels in membralin-KO astrocytes limited astrocyte-dependent excitotoxicity in motor neurons. Transcriptomic profiles from mouse astrocytic membralin-KO motor cortex indicated significant perturbation in KEGG pathway components related to ALS, including downregulation of Eaat2 and upregulation of Tnfrsf1a. Changes in gene expression with membralin deletion also overlapped with mouse ALS models and reactive astrocytes. Our results show that activation of the TNF receptor (TNFR1) NFκB pathway known to suppress Eaat2 transcription was upregulated with membralin deletion. Further, reduced membralin and EAAT2 levels correlated with disease progression in spinal cord from SOD1-mutant mouse models, and reductions in membralin/EAAT2 were observed in human ALS spinal cord. Importantly, overexpression of membralin in SOD1G93A astrocytes decreased TNFR1 levels and increased EAAT2 expression, and improved motor neuron survival. Importantly, upregulation of membralin in SOD1G93A mice significantly prolonged mouse survival. Our study provided a mechanism for ALS pathogenesis where membralin limited glutamatergic neurotoxicity, suggesting that modulating membralin had potential in ALS therapy.

Authors

Lu-Lin Jiang, Bing Zhu, Yingjun Zhao, Xiaoguang Li, Tongfei Liu, Juan Pina-Crespo, Lisa Zhou, Wenxi Xu, Maria J. Rodriguez, Haiyang Yu, Don W. Cleveland, John Ravits, Sandrine Da Cruz, Tao Long, Dongxian Zhang, Timothy Y. Huang, Huaxi Xu

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Figure 5

Changes in global transcription with astrocyte membralin deletion overlap with ALS astrocyte and reactive astrocyte signatures.

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Changes in global transcription with astrocyte membralin deletion overla...
(A) Volcano plot depicting differentially regulated genes (DEGs) identified in Astro–mem-KO and WT mouse motor cortex. (B) Expression of 17 DEGs in the ALS (mmu05014) KEGG pathway category from the 2515 DEGs shown in A using DAVID Functional Analysis. (C–D) Comparison of Astro–mem-KO motor cortex and SOD1G37R spinal cord astrocyte DEGs at disease onset. (C) There were 31 overlapping DEGs identified in Astro–mem-KO motor cortex (red) and SOD1G37R astrocytes (purple). (D) Functional GO-BP analysis of the 31 overlapping genes identified in C. Red bars indicate pathways related to immune function. (E) Comparison of differential regulation profiles of Astro–mem-KO spinal cord/SOD1G37R ALS astrocyte DEGs. The graph on the left shows log2 fold changes in mouse SOD1G37R astrocytes, the graph on the right shows DEGs identified in Astro–mem-KO motor cortex by RNAseq analysis. Red bars represent immune components in the immune-related BP categories shown in D. (F) Comparison of Astro–mem-KO and PFNG118V spinal cord DEGs. There were 306 overlapping DEGs observed in Astro–mem-KO (red) and PFNG118V (dark yellow) spinal cord. (G) There were 23 overlapping DEGs found in Astro–mem-KO (red) and SOD1G37R astrocytes (purple) and PFNG118V spinal cord (dark yellow). (H–I) Overlaps of Astro–mem-KO DEGs with DEGs characterized from A1 neuroinflammatory and A2 ischemia-induced astrocytes. (H) Venn diagrams depicting overlaps of DEGs from Astro–mem-KO spinal cord and pan-reactive (dark yellow), A1 (purple), and A2 (blue) astrocytes. (I) Log2 fold change of overlapping DEGs shown in H as characterized by RNAseq analysis. (J) Fold change in expression of overlapping DEGs from H as characterized previously by microarray in astrocytes treated with LPS or derived from MCAO ischemic models.