Abstract
Purpose :
Aquaporin-5 (AQP5) is the second most abundant aquaporin in ocular lens fiber cells. Previously we have shown that in bovine outer cortical lens fiber cells, cytoplasmic AQP5 localizes to spheroidal, tubular compartments. Transmission electron microscopy revealed morphologically similar autophagosomes with degrading mitochondria. The connection between, and conservation of, these structures in mammalian lenses is unclear. The purpose of this work is to histologically define AQP5-associated cytoplasmic structures in bovine and mouse lenses to better understand lens AQP5 function and regulation.
Methods :
High resolution immunofluorescence (IF) confocal microscopy was conducted on bovine and mouse lens cryosections. Colocalization analyses of cytoplasmic AQP5 and biological markers of various organelles including TOMM20 (mitochondrial marker), calnexin (endoplasmic reticulum [ER] protein), and DiIC18(3) (DiI; marker dye of lipid membranes) were conducted. Colocalization analysis of LC3B (autophagosomal marker) and TOMM20 was also conducted.
Results :
In the bovine lens outer cortex, AQP5-associated, TOMM-20 positive cytoplasmic compartments are juxtaposed to calnexin-positive compartments. In mouse outer cortical lens fiber cells, AQP5-positive cytoplasmic structures and TOMM20-positive cytoplasmic structures were detected in separate assays. Both of these mouse lens structures are spheroidal, tubular in morphology. In mouse lenses, calnexin-positive compartments are not juxtaposed to AQP5-associated cytoplasmic compartments. In mouse and bovine lenses, TOMM20-positive cytoplasmic structures become LC3B-positive late in fiber cell maturation.
Conclusions :
Bovine lens outer cortical fiber cells contain spheroidal, tubular AQP5-associated, cytoplasmic structures comprised of mitochondrial membranes that associate with the ER. These structures likely undergo autophagic degradation with fiber cell maturation. Similar AQP5-associated cytoplasmic structures are present in the mouse lens but the association of these structures with ER compartments is unclear. Future experiments will focus on further defining the relationship between AQP5, mitochondria, autophagy, and fiber cell differentiation in the mammalian lens.
This is a 2021 ARVO Annual Meeting abstract.