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Miduturu Srinivas, NEFELI SLAVI; Delivery of NADPH to the Lens Nucleus is Dependent on Gap Junctional Coupling Provided by Cx46.. Invest. Ophthalmol. Vis. Sci. 2018;59(9):3039.
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© ARVO (1962-2015); The Authors (2016-present)
The co-factor NADPH is essential for activities of multiple enzymes including those that participate in the reduction of oxidized glutathione and in cleavage of intra- and inter-molecular disulfides in proteins. In the lens epithelium and cortex, NADPH is produced via the pentose pathway. In contrast, the mechanism by which NADPH levels are established in the lens nucleus, a region of low metabolic activity, remains to be determined. In this study, we examined the role of gap junction channels (GJs) composed of Cx46, which couple central fiber cells to outer lens cells, in the delivery of NADPH to the lens nucleus.
To examine the possible involvement of GJs in NADPH transport, we measured the concentrations of the phosphorylated pyridine nucleotide in lenses obtained from WT and Cx46 knockout (KO) mice. Lenses (~ 4 month of age) were separated into two fractions, with one fraction containing the nucleus and the other consisting of the outer cortex and epithelium. We also assessed whether Cx46 GJs were permeable to NADPH using electrophysiological studies.
In WT lenses, the NADPH concentration was high in the cortical fraction (19.8 ± 2.2 nmol/g wet weight; n= 3), but lower in the nuclear fraction (decrease of ~ 40%), as described previously. The absence of Cx46 did not significantly affect NADPH levels in the cortex (16.2 ± 2.2 nmol/g wet weight; n=3). In contrast, NADPH levels were reduced by ~ 76 % in the nuclear fraction of lenses obtained from Cx46 KO mice (10.2 ± 1.2 in WT vs 2.4 ± 0.4 nmol/g wet weight in Cx46KO; p < 0.05). Single channel conductance measurements suggested that Cx46 GJ’s are poorly permeable to NADPH
These results indicate a significant role for Cx46 GJs in the maintenance of adequate NADPH levels in the nucleus. However, given the low permeability of Cx46 GJs to the pyridine nucleotide, it is likely that diffusion from the cortex is not the sole mechanism for the generation of adequate NADPH levels in the nucleus. Further studies are necessary to identify determine whether modes of NADPH transport operate in the lens.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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