ABSTRACT
Glutamate is a major excitatory neurotransmitter in the retina. Glutamate neurotoxicity has been implicated in the pathogenesis of several ocular diseases. Aquaporin 4 (AQP4) is a water-selective membrane transport protein, and its knockout could alter retinal neuron excitability. However, the effect of AQP4 knockout on glutamate metabolism is still unclear in the retina. Here, we reported that the retinas in AQP4 knockout mice showed higher glutamate levels than that in wild-type mice upon light damage. AQP4 knockout could result in accelerated apoptosis of retinal cells, increased reactive gliosis, and attenuated survival of RGCs in response to light damage. Moreover, AQP4 knockout could affect the expression pattern of glutamate metabolism-related proteins such as GLAST and GS. Taken together, this study revealed a novel role of AQP4 in regulating glutamate metabolism. Pharmacological manipulation of AQP4 function may represent as a potent therapeutic target in the treatment of neurological ocular disorders.
Subject(s)
Aquaporin 4/genetics , Glutamic Acid/metabolism , Retina/metabolism , Animals , Female , Light , Mice , Mice, KnockoutABSTRACT
Ultraviolet (UV) radiation and reactive oxygen species (ROS) impair the physiological functions of retinal pigment epithelium (RPE) cells by inducing cell apoptosis, which is the main cause of age-related macular degeneration (AMD). The mechanism by which UV/ROS induces RPE cell death is not fully addressed. Here, we observed the activation of a ceramide-endoplasmic reticulum (ER) stress-AMP activated protein kinase (AMPK) signaling axis in UV and hydrogen peroxide (H2O2)-treated RPE cells. UV and H2O2 induced an early ceramide production, profound ER stress and AMPK activation. Pharmacological inhibitors against ER stress (salubrinal), ceramide production (fumonisin B1) and AMPK activation (compound C) suppressed UV- and H2O2-induced RPE cell apoptosis. Conversely, cell permeable short-chain C6 ceramide and AMPK activator AICAR (5-amino-1-ß-D-ribofuranosyl-imidazole-4-carboxamide) mimicked UV and H2O2's effects and promoted RPE cell apoptosis. Together, these results suggest that UV/H2O2 activates the ceramide-ER stress-AMPK signaling axis to promote RPE cell apoptosis.
Subject(s)
AMP-Activated Protein Kinases/metabolism , Apoptosis/physiology , Ceramides/metabolism , Endoplasmic Reticulum Stress/physiology , Hydrogen Peroxide/pharmacology , Ultraviolet Rays , Apoptosis/drug effects , Apoptosis/radiation effects , Blotting, Western , Cell Line , Cell Survival/drug effects , Cell Survival/physiology , Cell Survival/radiation effects , Ceramides/pharmacology , Cinnamates/pharmacology , Endoplasmic Reticulum Stress/drug effects , Endoplasmic Reticulum Stress/radiation effects , Enzyme Activation/drug effects , Enzyme Activation/radiation effects , Fumonisins/pharmacology , Humans , Oxidants/pharmacology , Retinal Pigment Epithelium/cytology , Signal Transduction/drug effects , Signal Transduction/physiology , Signal Transduction/radiation effects , Thiourea/analogs & derivatives , Thiourea/pharmacologyABSTRACT
Nerve distal axon injury-induced Wallerian degeneration is significantly delayed in Wallerian degeneration slow (Wld(s)) mutant mice, although the associated mechanisms are not completely clear and the role of Wld(s) in retinal ganglion cell (RGC) body damage is not fully understood. In the present study, a Wallerian degeneration model was established in wild-type (WT) and Wld(s) mutant mice by creating mechanical injury in the optic nerves. Wallerian degeneration and RGC body collapse were observed to be significantly delayed in the Wld(s) mice. Electroretinograms (ERG) and visual evoked potentials (VEPs) in Wld(s) mice were also significantly improved at the earlier stages (one week) following injury. The retina immunohistochemistry results showed that Wld(s) mice had more ordered cells and improved inner granular cell layer arrangement compared with the WT mice. Optic nerve Luxol Fast Blue (LFB) staining showed greater axon demyelination in WT mice than in Wld(s) mice. A large number of apoptotic cells were also observed in the WT mice. The present results suggest that the Wld(s) gene may also protect the RGC body following nerve injury.
ABSTRACT
By the methods of polymerase chain reaction-denaturing gradient gel electrophoresis and sequence analysis, a comparative study was conducted on the diversity and community structure of soil ammonia-oxidizing bacteria in the Filifolium sibiricum steppe, Stipa baicalensis steppe, Leymus chinensis steppe, Stipa grandis steppe, and Stipa kryrowi steppe in Hulunbeier Grassland, Inner Mongolia. A significant difference was observed in the community structure of soil ammonia-oxidizing bacteria among the five steppes, with the similarity lower than 50%. The diversity of soil ammonia-oxidizing bacteria was the highest in F. sibiricum steppe, followed by in S. baicalensis steppe, L. chinensis steppe, S. kryrowi steppe, and S. grandis steppe. In the five steppes, Nitrosospira cluster 3 was the dominant group, and the Nitrosospira cluster 1, 2, and 4 as well as Nitrosomonas were also found. The community structure of soil ammonia oxidizing bacteria in F. sibiricum steppe was most complex, while that in L. chinensis steppe and S. grandis steppe was relatively simple. Correlation analysis indicated that there existed significant positive correlations between the diversity of soil ammonia-oxidizing bacteria and the soil moisture, total nitrogen, total organic carbon, and C/N ratio (P<0.05).
