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Kulandaiappan Varadaraj, Richard Mathias, Paul G FitzGerald, Alan Shiels, Nikol Palomino, Sindhu S Kumari; AQP0 AND BEADED FILAMENT PROTEINS ARE CRITICAL FOR OCULAR LENS BIOMECHANICS. Invest. Ophthalmol. Vis. Sci. 201657(12):.
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© ARVO (1962-2015); The Authors (2016-present)
We showed previously that AQP0 participates in maintaining lens biomechanics (Kumari et al.,2015,462:339). The present study was undertaken to explore whether AQP0 and BF proteins (CP49 and filensin) together play a role in regulating lens stiffness and resilience which are necessary for ocular lens accommodation.
AQP0 heterozygous knockout mouse expressing CP49 and filensin (AQP0+/-/BF+/+), and AQP0 heterozygous knockout without BF proteins (AQP0+/-/BF-/-) were developed in C57BL/6J strain. Genomic PCR, immunostaining and Western blotting were performed to study the expression or lack of BF proteins, as appropriate. Compression strain test was conducted to study lens stiffness and resilience. Each lens was subjected to gentle compressive strain using weighed glass coverslips. Sagittal images of lens shape changes were digitized. ImageJ software (NIH) was used to measure lens axial (A) and equatorial (E) diameters which were converted to compression-strain (T): T = ((d-d0)/d0); d is 'A' or 'E' diameter at a given load; d0 is 'A' or 'E' diameter at zero load. Resilience was calculated as: R% = ((Ad/Ad0)*100); Ad is 'A' diameter after releasing coverslip load; Ad0 is 'A' diameter before applying load.
Biochemical and molecular experiments confirmed the expression of BF proteins in AQP0+/-/BF+/+ mouse lenses and absence in AQP0+/-/BF-/- lenses. Biomechanical assay revealed that loss of one allele of AQP0 significantly reduced the compressive load-bearing capacity (stiffness; P <0.001) and increased the resilience (P <0.001) compared to WT lenses. Absence of BF proteins (AQP0+/-/BF-/-) caused further reduction in load-bearing capacity and increase in resilience (P <0.01) compared to WT and AQP0+/-/BF+/+ lenses. Lens shape was significantly altered in AQP0+/-/BF+/+ and AQP0+/-/BF-/- mice due to a higher ratio of axial: equatorial diameter.
Data from WT, and AQP0- and/or BF-heterozygous knockout mouse lenses suggest that AQP0 and BF proteins cooperatively maintain lens biomechanics for proper focusing. We postulate that AQP0 and BF proteins could synergistically regulate lens mechanical stiffness and resilience for accommodation. Since shape, mechanical stiffness and resilience need to be maintained for proper focusing of objects on the retina, any alteration in AQP0 functions and its interaction with other proteins such as BF proteins could contribute to presbyopia, opacity and/or cataract.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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