Distribution of bovine and rabbit lens alpha-crystallin products by MALDI imaging mass spectrometry.

PURPOSE:To develop a general tissue preparation protocol for MALDI (Matrix-Assisted Laser Desorption Ionization) imaging mass spectrometry of ocular lens tissue, and to compare the spatial distributions of alpha-crystallin and its modified forms in bovine and rabbit lenses. METHODS:Frozen bovine and rabbit lenses were cryosectioned equatorially at -20 degrees C into 12 microm-thick tissue sections. Lens sections were mounted onto conductive glass slides by ethanol soft-landing to maintain tissue integrity. An ethanol/xylene washing procedure was applied to each section before matrix application to facilitate uniform matrix crystal formation across the entire tissue section. Molecular images of both alpha-crystallin subunits and their modified forms were obtained from mass spectral data acquired at 100 microm steps across both whole rabbit and half bovine lens sections. RESULTS:Distinct spatial patterns for the two subunits of alpha-crystallin and their modified forms were observed in the rabbit and bovine lens sections. While alphaA-crystallin was extensively degraded in the lens core of both species, rabbit lenses exhibited a greater degree of larger molecular weight truncation products. In contrast, alphaB-crystallin degradation was limited in both species. Interestingly, phosphorylation of alphaA- and alphaB-crystallin was most abundant in the middle cortex of both species. CONCLUSIONS:An improved method for investigating the spatial distribution of alpha-crystallin in the ocular lens by MALDI imaging mass spectrometry has been developed. The localization of multiple degradation products and specific regions of alpha-crystallin phosphorylation in bovine and rabbit lenses gives new insight into the program of lens fiber cell differentiation and normal lens function.

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