Slavi Nefeli, Rubinos Clio, Li Leping, Sellitto Caterina, White Thomas W, Mathias Richard, Srinivas Miduturu
From the Department of Biological and Vision Sciences and the Graduate Center for Vision Research, State University of New York College of Optometry, New York, New York 10036 and.
the Department of Physiology and Biophysics, State University of New York, Stony Brook, New York 11794.
J Biol Chem. 2014 Nov 21;289(47):32694-702. doi: 10.1074/jbc.M114.597898. Epub 2014 Oct 7.
Maintenance of adequate levels of glutathione (GSH) in the lens nucleus is critical for protection of lens proteins from the effects of oxidative stress and for lens transparency. How GSH is transported to the nucleus is unknown. We show that GSH diffuses to the nucleus from the outer cortex, where a high concentration of the anti-oxidant is established by synthesis or uptake, via the network of gap junctions. Using electrophysiological measurements, we found that channels formed by Cx46 and Cx50, the two connexin isoforms expressed in the lens, were moderately cation-selective (P(Na)/P(Cl) ∼5 for Cx46 and ∼3 for Cx50). Single channel permeation of the larger GSH anion was low but detectable (P(Na)/P(GSH) ∼12 for Cx46 and ∼8 for Cx50), whereas permeation of divalent anion glutathione disulfide (GSSG) was undetectable. Measurement of GSH levels in the lenses from connexin knock-out (KO) mice indicated Cx46, and not Cx50, is necessary for transport of GSH to the core. Levels of GSH in the nucleus were markedly reduced in Cx46 KO, whereas they were unaffected by Cx50 KO. We also show that GSH delivery to the nucleus is not dependent on the lens microcirculation, which is believed to be responsible for extracellular transport of other nutrients to membrane transporters in the core. These results indicate that glutathione diffuses from cortical fiber cells to the nucleus via gap junction channels formed by Cx46. We present a model of GSH diffusion from outer cells to inner fiber cells through gap junctions.
维持晶状体核中足够水平的谷胱甘肽（GSH）对于保护晶状体蛋白免受氧化应激影响以及保持晶状体透明度至关重要。GSH如何转运至细胞核尚不清楚。我们发现，GSH通过缝隙连接网络从外皮质扩散至细胞核，在外皮质中，通过合成或摄取建立了高浓度的抗氧化剂。通过电生理测量，我们发现晶状体中表达的两种连接蛋白亚型Cx46和Cx50形成的通道具有适度的阳离子选择性（Cx46的P(Na)/P(Cl)约为5，Cx50的约为3）。较大的GSH阴离子的单通道通透性较低但可检测到（Cx46的P(Na)/P(GSH)约为12，Cx50的约为8），而二价阴离子谷胱甘肽二硫化物（GSSG）的通透性则无法检测到。对连接蛋白基因敲除（KO）小鼠晶状体中GSH水平的测量表明，Cx46而非Cx50是GSH转运至晶状体核心所必需的。Cx46基因敲除小鼠细胞核中的GSH水平显著降低，而Cx50基因敲除对其无影响。我们还表明，GSH向细胞核的递送不依赖于晶状体微循环，后者被认为负责将其他营养物质细胞外转运至核心的膜转运体。这些结果表明，谷胱甘肽通过Cx46形成的缝隙连接通道从皮质纤维细胞扩散至细胞核。我们提出了一个GSH通过缝隙连接从外层细胞扩散至内层纤维细胞的模型。
