PKCγ knockout mouse lenses are more susceptible to oxidative stress damage

Abstract

SUMMARYCataracts, or lens opacities, are the leading cause of blindness worldwide. Cataracts increase with age and environmental insults, e.g. oxidative stress. Lens homeostasis depends on functional gap junctions. Knockout or missense mutations of lens gap junction proteins, Cx46 or Cx50, result in cataractogenesis in mice. We have previously demonstrated that protein kinase Cγ (PKCγ) regulates gap junctions in the lens epithelium and cortex. In the current study, we further determined whether PKCγ control of gap junctions protects the lens from cataractogenesis induced by oxidative stress in vitro, using PKCγ knockout and control mice as our models. The results demonstrate that PKCγ knockout lenses are normal at 2 days post-natal when compared to control. However, cell damage, but not obvious cataract, was observed in the lenses of 6-week-old PKCγ knockout mice,suggesting that the deletion of PKCγ causes lenses to be more susceptible to damage. Furthermore, in vitro incubation or lens oxidative stress treatment by H2O2 significantly induced lens opacification (cataract) in the PKCγ knockout mice when compared to controls. Biochemical and structural results also demonstrated that H2O2 activation of endogenous PKCγ resulted in phosphorylation of Cx50 and subsequent inhibition of gap junctions in the lenses of control mice, but not in the knockout. Deletion of PKCγaltered the arrangement of gap junctions on the cortical fiber cell surface,and completely abolished the inhibitory effect of H2O2on lens gap junctions. Data suggest that activation of PKCγ is an important mechanism regulating the closure of the communicating pathway mediated by gap junction channels in lens fiber cells. The absence of this regulatory mechanism in the PKCγ knockout mice may cause those lenses to have increased susceptibility to oxidative damage.