Intermediate filaments regulate tissue size and stiffness in the murine lens.

PURPOSE: To define the contributions of the beaded filament (BF), a lens-specific intermediate filament (IF), to lens morphology and biomechanics.
METHODS: Wild-type and congenic CP49 knockout (KO) mice were compared by using electrophysiological, biomechanical, and morphometric approaches, to determine changes that occurred because of the absence of this cytoskeletal structure.
RESULTS: Electrophysiological assessment established that the fiber cells lacking the lens-specific IFs were indistinguishable from wild-type fiber cells. The CP49 KO mice exhibited lower stiffness, and an unexpected higher resilience than the wild-type lenses. The absence of these filaments resulted in lenses that were smaller, and exhibited a higher ratio of lens:lens nucleus size. Finally, lens shape differed as well, with the CP49 KO showing a higher ratio of axial:equatorial diameter.
CONCLUSIONS: Previous work has shown that BFs are necessary in maintaining fiber cell and lens structural phenotypes with age, and that absence of these filaments results in a loss of lens clarity. This work demonstrates that several tissue-level properties that are critical to lens function are also dependent, at least in part, on the presence of these lens-specific IFs.