Aquaporin-0 modulates normal shape of gap junction-associated ball-and-socket domains which display distinct patterns in mouse and monkey lenses

Abstract

Purpose : AQP0 has been shown to play a critical role in controlling the integrity of interlocking protrusions and transparency in mouse lens. Here, we study whether AQP0 modulates the integrity of gap junction-associated ball-and-sockets (GJ-BSs) which are uniquely distributed in metabolically-active superficial fiber cells. The distinct patterns of GJ-BSs between mouse and monkey lenses are systematically compared.

Methods : Whole-mount superficial fiber cells of AQP0-KO and WT mouse lenses (1-4 months old) were prepared for confocal labeling of AQP0, Cx46, Cx50, N-cadherin, WGA and phalloidin. The same samples were further processed for SEM identification. Confocal, SEM, TEM, freeze-fracture and immunogold labeling were used for comparison between mouse and monkey lenses.

Results : AQP0, Cx46 and Cx50 antibodies were labeled consistently in BSs of superficial fiber cells in WT mouse lenses. The GJ-BSs were clearly identified on the matched images of labeled Cx46 (or Cx50) with the WGA-stained round sockets on the preparations. In contrast, many labeled Cx46-BSs specifically showed aberrant elongation in the AQP0-KO lens fiber cells. The presence of elongated, disorganized BSs was confirmed by SEM. Freeze-fracture immunogold TEM showed that GJ particles were greatly dispersed in the elongated BSs. For the identity and distinct patterns of GJ-BSs on the broad-surface of superficial fiber cells, confocal study showed that in mouse lens GJ-BSs (~0.8 μm wide) were found mainly in the middle of cells, averaging 31 GJ-BSs/500 μm² (24,800 μm² measured). In contrast, in monkey lens large GJ-BSs (~1 μm wide) were more often seen along the sides of cells, averaging 40 GJ-BSs/500 μm² (27,875 μm² measured). Importantly, numerous finger-like projections (~0.3 μm wide, 0.8 μm long) were regularly seen across the entire broad-surface superficial fiber cells in monkey, but not in mouse. AQP0 and actin, but not Cx46, Cx50 and N-cadherin, were highly enriched in these finger-like projections.

Conclusions : The integrity of GJ-BSs is also regulated by AQP0. The GJ-BSs are present in both mouse and monkey lenses, and they display distinct patterns between these two species. Importantly, the new type of numerous AQP0-rich finger-like projections, distributed simultaneously with GJ-BSs in superficial fiber cells in the monkey lens, surely warrants further functional investigation.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.