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Kulandaiappan Varadaraj, Junyuan Gao, Xiurong Sun, Nicholas Browne, Richard T Mathias, Sindhu S Kumari; AQUAPORIN ZERO (AQP0) MODULATES LENS GAP JUNCTION (GJ) CHANNEL FUNCTION IN THE PRESENCE OF BEADED FILAMENTS (BFs). Invest. Ophthalmol. Vis. Sci. 2017;58(8):2473.
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© ARVO (1962-2015); The Authors (2016-present)
Homeostasis of the avascular lens requires a microcirculation facilitated by AQPs, GJ channels and ion channels. We showed previously that AQP0 functions as a water channel and a cell-to-cell adhesion (CTCA) protein, both of which are important in maintaining lens transparency, refractive index gradient and biomechanics. A previous study found no significant alteration in GJs or hydrostatic pressure (HP) between the lenses of AQP0 heterozygous knockout (AQP0-Htz) and wild type (WT) mice in FVB background that lacks BFs. In the current investigation, we examined GJ channel conductance resistance and HP in WT and AQP0-Htz lenses in C57BL/6J background that has BFs, and compared them with similar genotypes in FVB.
Genotyped (C57BL/6J WT and AQP0-Htz or FVB WT and AQP0-Htz) mice from same litters were used. Western blotting was performed to verify the expression of AQP0, BF and connexin proteins. Water permeability (Pf) was measured using fiber cell membrane vesicles. CTCA was assessed qualitatively. Lens transparency was evaluated and quantified. Microelectrode-based intact lens intracellular impedance was measured to determine GJ coupling resistance. A microelectrode/manometer system was used to determine intact lens intracellular HP.
Western blotting of WT and AQP0-Htz membrane proteins from both backgrounds revealed about 50% reduction in AQP0 in the latter genotype with no observable change in connexin expression. AQP0-Htz lenses from both strains showed decreased Pf (~50%) and CTCA compared to WT. Opacity was more distinct in AQP0-Htz lenses in FVB than in C57BL/6J. In C57BL/6J AQP0-Htz lenses, but not in FVB AQP0-Htz, GJ coupling resistance decreased about 2.2-fold and the HP gradient decreased about 1.9-fold compared to their respective WT.
The observed ~2-fold decrease in GJ coupling resistance in C57BL/6J background could be due to the interaction of AQP0 with BFs and potential regulation of GJ coupling conductance. The similar ~2-fold reduction in the pressure gradient suggests no significant change in fluid circulation. Though the circulation was not affected by AQP0-Htz knockout in either the FVB or C57BL/6J genotypes, the opacity in the FVB lenses was significantly more severe. This suggests that AQP0 modulates gap junction channel function in the presence of beaded filaments to maintain lens structural homeostasis and prevent cataract.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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