BetaB2-crystallin mutations associated with cataract and glaucoma leads to mitochondrial alterations in lens epithelial cells and retinal neurons

Abstract

Crystallin proteins are the most prominent protein of the lens and have been increasingly shown to play critical roles in other tissues, especially the retina. Members of all 3 sub-families of crystallins, alpha-, beta- and gamma-crystallins have been reported in the retina during diabetes, traumatic injury and other retinal diseases. While their specific role in the retina is still unclear and may vary, beta-crystallin proteins have been shown to play a critical role in ganglion cell survival following trauma. We recently reported the correlation between a gene conversion in the betaB2-crystallin gene and a phenotype of familial congenital cataract. Interestingly, in half of the patients, this phenotype was associated with glaucoma. Taken together, these data suggested that the mutations we recently reported could have an impact on the role of betaB2-crystallin in both lens epithelial cells and retinal neurons. Consistent with this hypothesis, we show in the current study that the gene conversion leading to an amino acid conversion lead to a loss of solubility and a change of subcellular localization of betaB2-crystallin in both cell types. While the overall observations were similar in both cell types, there were some important nuances between them, suggesting different roles and regulation of betaB2-crystallin in lens cells versus retinal neurons. The data reported in this study strongly support a significant role of betaB2-crystallin in both lenticular and retinal ocular tissues and warrant further analysis of its regulation and its impact not only in cataract formation but also in retinal neurodegenerative diseases.

A Triple Mutation of BetaB2-Crystallin is Necessary to Develop Cataract and Glaucoma

“…Consistent with the solubility data presented in Figure 1 , the single and double βB2-crystallin mutants displayed a diffuse pattern indistinguishable from the one observed with the WT protein. The same staining patterns were observed for the βB2-crystallin WT and the triple βB2-crystallin mutant also in lens cells [ 2 ].…”

“…Only the full gene conversion lead to a loss of solubility, shown by the triple mutant being found almost exclusively in the insoluble fraction ( Figure 1 ). Interestingly, this effect is partially cell-type specific as we previously reported that when we expressed the triple mutant βB2-crystallin in lens epithelial cells, we observed a less dramatic shift in solubility of the triple mutant, with 35% of the protein remaining soluble [ 2 ].…”

“…Because over half of these family members also presented with glaucoma, we became interested in the functional consequences of these polymorphisms in lens epithelial cells and retinal neurons, both of which cell types that are responsible for the aforementioned disease conditions. While our initial analysis in both cell types focused only on the functional consequence of the triple mutant βB2-crystallin protein [ 2 ], this subsequent analysis aimed at characterizing the relative contribution of each amino acid conversion to the functional consequence previously reported: protein solubility and aggregate formation.…”

“…We previously demonstrated reduced solubility, increased aggregate formation, translocation to the mitochondria and reduced mitochondrial function of the βB2-crystallin triple mutant protein, that carries the three recently identified polymorphic gene conversions (R145W, Q147R and T150M), in retinal neurons and lens epithelial cells [ 2 ]. The purpose of this study was to analyze the effect of each of the three polymorphic mutations of βB2-crystallin alone or in combination on βB2-crystallin biochemical properties at first in retinal neurons.…”

Two novel mutations identified in ADCC families impair crystallin protein distribution and induce apoptosis in human lens epithelial cells

“…Crystallins are the predominant lens structural proteins of mammals and have a significant function in providing transparency and light transmission to the eye lens 32 . However, mutations in the genes encoding crystallin proteins lead to abnormal expression, which might disrupt lens opacity and even cause blindness 12 , 33 , 34 .…”