Age-related reduction in calbindin-D28K expression in the Sprague-Dawley rat lens.

Calcium levels in the lens rise with increasing age and increased intracellular calcium accumulation is known to be a risk factor for cataract formation. Calbindin-D28K (CALB1) is an intracellular calcium buffer. It is not clear whether CALB1 levels change in response to the Ca2+ accumulation in the lens that occurs with age. The present study investigated the distribution of CALB1 in the lenses of Sprague-Dawley (SD) rats and whether this changed with age. Lenses were isolated from SD rats at 1, 6, 12 and 18 months of age. CALB1 distribution was examined using immunohistochemistry. Lens epithelial cells were counted in median sagittal plane slices from the hematoxylin and eosin-stained lens and quantified using western blot analysis. Calb1 gene expression was examined using reverse transcription-quantitative polymerase chain reaction. CALB1 was distributed in the epithelial and fiber cells of the lens. CALB1 levels declined significantly with increasing age, whilst there was no significant accompanying decrease in the number of lens cells. A similar reduction was noted in CALB1 mRNA levels. To the best of our knowledge, this is the first study to demonstrate that CALB1 expression and CALB1 protein levels in SD rat lens decrease with age. This reduction does not reflect a reduction in lens cell numbers but a genuine reduction in gene expression within these cells. Thus, CALB1 may be important in changes occurring in the lens in older age, in particular in the development of cataracts.