1. Soluble tumor necrosis factor-alpha-induced hyperexcitability contributes to retinal ganglion cell apoptosis by enhancing Nav1.6 in experimental glaucoma
- Author
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Xinghuai Sun, Lin-Jie Xu, Hong-Ning Wang, Yanying Miao, Fang Li, Bo Lei, Shuo Cheng, and Zhongfeng Wang
- Subjects
Male ,Patch-Clamp Techniques ,genetic structures ,Immunology ,Hyperexcitability ,Apoptosis ,Retinal ganglion cells ,Rats, Sprague-Dawley ,Cellular and Molecular Neuroscience ,chemistry.chemical_compound ,Neuroinflammation ,medicine ,Animals ,RC346-429 ,Nav1.6 ,TUNEL assay ,Tumor Necrosis Factor-alpha ,Chemistry ,Research ,General Neuroscience ,Glaucoma ,Retinal ,Hyperpolarization (biology) ,eye diseases ,Rats ,Cell biology ,Disease Models, Animal ,medicine.anatomical_structure ,Neurology ,Terminal deoxynucleotidyl transferase ,Retinal ganglion cell ,NAV1.6 Voltage-Gated Sodium Channel ,TNF-α ,Tumor necrosis factor alpha ,sense organs ,Neurology. Diseases of the nervous system - Abstract
Background Neuroinflammation plays an important role in the pathogenesis of glaucoma. Tumor necrosis factor-alpha (TNF-α) is a major pro-inflammatory cytokine released from activated retinal glial cells in glaucoma. Here, we investigated how TNF-α induces retinal ganglion cell (RGC) hyperexcitability and injury. Methods Whole-cell patch-clamp techniques were performed to explore changes in spontaneous firing and evoked action potentials, and Na+ currents in RGCs. Both intravitreal injection of TNF-α and chronic ocular hypertension (COH) models were used. Western blotting, immunofluorescence, quantitative real-time polymerase chain reaction (q-PCR), and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) techniques were employed to investigate the molecular mechanisms of TNF-α effects on RGCs. Results Intravitreal injection of soluble TNF-α significantly increased the spontaneous firing frequencies of RGCs in retinal slices. When the synaptic transmissions were blocked, more than 90% of RGCs still showed spontaneous firing; both the percentage of cells and firing frequency were higher than the controls. Furthermore, the frequency of evoked action potentials was also higher than the controls. Co-injection of the TNF-α receptor 1 (TNFR1) inhibitor R7050 eliminated the TNF-α-induced effects, suggesting that TNF-α may directly act on RGCs to induce cell hyperexcitability through activating TNFR1. In RGCs acutely isolated from TNF-α-injected retinas, Na+ current densities were upregulated. Perfusing TNF-α in RGCs of normal rats mimicked this effect, and the activation curve of Na+ currents shifted toward hyperpolarization direction, which was mediated through p38 MAPK and STAT3 signaling pathways. Further analysis revealed that TNF-α selectively upregulated Nav1.6 subtype of Na+ currents in RGCs. Similar to observations in retinas of rats with COH, intravitreal injection of TNF-α upregulated the expression of Nav1.6 proteins in both total cell and membrane components, which was reversed by the NF-κB inhibitor BAY 11-7082. Inhibition of TNFR1 blocked TNF-α-induced RGC apoptosis. Conclusions TNF-α/TNFR1 signaling induces RGC hyperexcitability by selectively upregulating Nav1.6 Na+ channels, thus contributing to RGC apoptosis in glaucoma.
- Published
- 2021