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Patrick R. Cammarata, Cheng Zhou, Guoli Chen, Inderpal Singh, Rustin E. Reeves, Jerome R. Kuszak, Michael L. Robinson; A Transgenic Animal Model of Osmotic Cataract. Part 1: Over-expression of Bovine Na+/Myo-inositol Cotransporter in Lens Fibers. Invest. Ophthalmol. Vis. Sci. 1999;40(8):1727-1737.
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purpose. Intracellular osmotic stress is believed to be linked to the
advancement of diabetic cataract. Although the accumulation of organic
osmolytes (myo-inositol, sorbitol, taurine) is thought to protect the
lens by maintaining osmotic homeostasis, the physiologic implication of
osmotic imbalance (i.e., hyperosmotic stress caused by intracellular
over-accumulation of organic osmolytes) on diabetic cataract formation
is not clearly understood. Studies from this laboratory have identified
several osmotic compensatory mechanisms thought to afford the lens
epithelium, but not the lens fibers, protection from water stress
during intervals of osmotic crisis. This model is founded on the
supposition that the fibers of the lens are comparatively more
susceptible to damage by osmotic insult than is the lens epithelium. To
test this premise, several transgenic mouse lines were developed that
over-express the bovine sodium/myo-inositol cotransporter (bSMIT) gene
in lens fiber cells.
methods. Of the several transgenic mouse lines generated, two, MLR14 and MLR21,
were analyzed in detail. Transgenic mRNA expression was analyzed in
adult and embryonic transgenic mice by a coupled reverse
transcriptase–polymerase chain reaction (RT–PCR) and in situ
hybridization on embryonic tissue sections, respectively.
Intralenticular myo-inositol content from individual mouse lenses was
quantified by anion exchange chromatography and pulsed electrochemical
detection. Ocular histology of embryonic day 15.5 (E15.5) embryos from
both transgenic (TG) families was analyzed and compared to their
respective nontransgenic (NTG) littermates.
results. Both RT–PCR and in situ hybridization determined that transgene
expression was higher in line MLR21 than in line MLR14. Consistent with
this, intralenticular myo-inositol from MLR21 TG mice was markedly
higher compared with NTG littermates or MLR14 TG mice. Histologic
analysis of E15.5 MLR21 TG embryos disclosed a marked swelling in the
differentiating fibers of the bow region and subcapsular fibers of the
central zone, whereas the lens epithelium appeared morphologically
normal. The lenticular changes, initiated early during lens development
in TG MLR21 embryos, result in severe bilateral nuclear cataracts
readily observable in neonates under normal rearing and dietary
conditions. In contrast, TG MLR14 pups reared under standard conditions
produced no lens opacity.
conclusions. Lens fiber swelling and related cataractous outgrowth positively
correlated to the degree of lens bSMIT gene expression and
intralenticular myo-inositol content. The affected (i.e., swollen) lens
fibers appeared to be unable to cope with the water stress generated by
the transgene-induced over-accumulation of myo-inositol and, as a
result of this inability to osmoregulate, suffered osmotic damage due
to water influx.
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