Browsing by Author "Berthoud, Viviana M."

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    A crystallin mutant cataract with mineral deposits
    (Elsevier, 2023) Minogue, Peter J.; Gao, Junyuan; Mathias, Richard T.; Williams, James C., Jr.; Bledsoe, Sharon B.; Sommer, Andre J.; Beyer, Eric C.; Berthoud, Viviana M.; Anatomy, Cell Biology and Physiology, School of Medicine
    Connexin mutant mice develop cataracts containing calcium precipitates. To test whether pathologic mineralization is a general mechanism contributing to the disease, we characterized the lenses from a nonconnexin mutant mouse cataract model. By cosegregation of the phenotype with a satellite marker and genomic sequencing, we identified the mutant as a 5-bp duplication in the γC-crystallin gene (Crygcdup). Homozygous mice developed severe cataracts early, and heterozygous animals developed small cataracts later in life. Immunoblotting studies showed that the mutant lenses contained decreased levels of crystallins, connexin46, and connexin50 but increased levels of resident proteins of the nucleus, endoplasmic reticulum, and mitochondria. The reductions in fiber cell connexins were associated with a scarcity of gap junction punctae as detected by immunofluorescence and significant reductions in gap junction-mediated coupling between fiber cells in Crygcdup lenses. Particles that stained with the calcium deposit dye, Alizarin red, were abundant in the insoluble fraction from homozygous lenses but nearly absent in wild-type and heterozygous lens preparations. Whole-mount homozygous lenses were stained with Alizarin red in the cataract region. Mineralized material with a regional distribution similar to the cataract was detected in homozygous lenses (but not wild-type lenses) by micro-computed tomography. Attenuated total internal reflection Fourier-transform infrared microspectroscopy identified the mineral as apatite. These results are consistent with previous findings that loss of lens fiber cell gap junctional coupling leads to the formation of calcium precipitates. They also support the hypothesis that pathologic mineralization contributes to the formation of cataracts of different etiologies.
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    Connexin Mutants Cause Cataracts Through Deposition of Apatite
    (Frontiers Media, 2022-07-22) Minogue, Peter J.; Sommer, Andre J.; Williams, James C., Jr.; Bledsoe, Sharon B.; Beyer, Eric C.; Berthoud, Viviana M.; Anatomy, Cell Biology and Physiology, School of Medicine
    Cataracts are lens opacities that are among the most common causes of blindness. It is commonly believed that cataracts develop through the accumulation of damage to lens proteins. However, recent evidence suggests that cataracts can result from calcium ion accumulation and the precipitation of calcium-containing salts. To test for the presence of precipitates and to identify their components, we studied the lenses of mice that develop cataracts due to mutations of connexin46 and connexin50. Micro-computed tomography showed the presence of radio-dense mineral in the mutant lenses, but not in wild-type lenses. Three-dimensional reconstructions of the scans showed that the distribution of the radio-dense mineral closely paralleled the location and morphology of the cataracts. The mutant lens homogenates also contained insoluble particles that stained with Alizarin red (a dye that stains Ca2+ deposits). Using attenuated total internal reflection micro–Fourier transform infrared spectroscopy, we identified the mineral as calcium phosphate in the form of apatite. Taken together, these data support the novel paradigm that cataracts are formed through pathological mineralization within the lens.