Analysis of mouse lens morphological and proteomic abnormalities following depletion of βB3-crystallin.

Crystallin proteins serve as both essential structural and as well as protective components of the ocular lens and are required for the transparency and light refraction properties of the organ. The mouse lens crystallin proteome is represented by αA-, αB-, βA1-, βA2-, βA3-, βA4-, βB1-, βB2-, βB3-, γA-, γB-, γC-, γD-, γE, γF-, γN-, and γS-crystallin proteins encoded by 16 genes. Their mutations are responsible for lens opacification and early onset cataract formation. While many cataract-causing missense and nonsense mutations are known for these proteins, including the human CRYBB3 gene, the mammalian loss-of function model of the gene remains to be established. Herein, we generated the first mouse model via deletion of the Crybb3 promoter that abolished expression of the βB3-crystallin. Histological analysis of lens morphology using newborn βB3-crystallin-deficient lenses revealed disrupted lens morphology with early-onset phenotypic variability. In-depth lens proteomics at four time points (newborn, 3-weeks, 6-weeks, and 3-months) showed both down- and up-regulation of various proteins, with the highest divergence from control mice observed in 3-months lenses. Apart from the βB3-crystallin, another protein Smarcc1/Baf155 was down-regulated in all four samples. In addition, downregulation of Hspe1, Pdlim1, Ast/Got, Lsm7, Ddx23, and Acad11 was found in three time points. Finally, we show that the βB3-crystallin promoter region, which contains multiple binding sites for the transcription factors AP-2α, c-Jun, c-Maf, Etv5, and Pax6 is activated by FGF2 in primary lens cell culture experiments. Together, these studies establish the mouse loss-of-function model and its disrupted crystallin and non-crystallin proteomes.