title: Aquaporin 9 expression is required for l-lactate to maintain retinal neuronal survival.
abstract: Aquaporin 9 (AQP9), an aquaglyceroporin, is not only permeable to water but also to non-charged solutes, such as lactate. Lactate can be an energy source for retinal neurons. This study aimed to evaluate the effect of the downregulation of AQP9 expression on the survival rates and reactive oxygen species accumulation in RGC-5 cells cultured in a medium containing lactate. The Live/Dead assay revealed that the cell death rate of RGC-5 cells transfected with the control siRNA (siControl) was 3.65%±0.75% in the 5-mM glucose medium. The death rate was significantly increased by five-fold in the no glucose and 10-mM d-lactate media but not in the 10-mM l-lactate medium. In comparison, the death rate of cells transfected with siRNA targeting AQP9 (siAQP9) was 8.07%±1.01% in the 5-mM glucose medium, which was significantly increased by two-fold in the other medium conditions, indicating that the downregulation of AQP9 expression eliminated the prosurvival effect of l-lactate. Few RGC-5 cells transfected with siControl showed dichlorofluorescein (DCF) fluorescence when cultured in 5-mM glucose and 10-mM l-lactate media. However, approximately 70% of those showed DCF fluorescence when cultured in the no glucose and 10-mM d-lactate media. The downregulation of AQP9 significantly increased the DCF fluorescence rate to 50.44%±6.13% in the 10-mM l-lactate medium, whereas, it did not increase the rate in the other medium conditions. These results demonstrate that AQP9 expression is required for l-lactate to maintain retinal neuronal survival.
authors: Division of Ophthalmology, Department of Surgery, Kobe University Graduate School of Medicine, Kobe, Japan.
authors: Azusa
authors: A
authors: Akashi
authors: Division of Ophthalmology, Department of Surgery, Kobe University Graduate School of Medicine, Kobe, Japan.
authors: Akiko
authors: A
authors: Miki
authors: Division of Ophthalmology, Department of Surgery, Kobe University Graduate School of Medicine, Kobe, Japan.
authors: Akiyasu
authors: A
authors: Kanamori
authors: Division of Ophthalmology, Department of Surgery, Kobe University Graduate School of Medicine, Kobe, Japan. Electronic address: manakamu@med.kobe-u.ac.jp.
authors: Makoto
authors: M
authors: Nakamura
mesh_terms: D000818:Animals; D020346:Aquaporins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002470:Cell Survival; D003470:Culture Media; D004734:Energy Metabolism; D055785:Gene Knockdown Techniques; D005947:Glucose / Q000378:metabolism*; D019344:Lactic Acid / Q000378:metabolism*; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D012165:Retinal Ganglion Cells / Q000166:cytology* / Q000378:metabolism
chemical_list: C491637:Aqp9 protein, rat; D020346:Aquaporins; D003470:Culture Media; D017382:Reactive Oxygen Species; D019344:Lactic Acid; D005947:Glucose
keywords: Aquaporin; Lactate; Reactive oxygen species; Retinal ganglion cell; Retinal neuronal survival