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E. A. Hoffman, N. W. Baetz, W. D. Stamer; Stretch-Induced Aquaporin-1 Expression in Human Trabecular Meshwork Cells. Invest. Ophthalmol. Vis. Sci. 2008;49(13):680.
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Aquaporin-1 (AQP1) channels expressed by trabecular meshwork (TM) and Schlemm’s canal cells in the juxtacanalicular region of the conventional outflow pathway participate in the bulk transcellular movement of aqueous humor into Schlemm’s canal. However, the magnitude of AQP1’s contribution to bulk flow and role in TM cell function of the uveal region, where preferential pathways for fluid flow are paracellular, are uncertain. In the uveal region, we hypothesize that AQP1 facilitates rapid changes of cell volume that occur due to the frequent mechanical stressors encountered by outflow tissues, and that AQP1 expression is regulated by such mechanical stress.
Primary cultures of human TM cells were plated at confluence onto Bioflex membranes and cultured for two weeks. Cells were then exposed to a single uniform stretch of 10% or 20% (radial and circumferential) for 8 or 24 hours with a Flexcell FX-4000 system. Proteins from cell lysates were fractionated using SDS-PAGE and analyzed by western blot using affinity purified anti-AQP1 IgGs. AQP1 expression levels were analyzed by densitometry and normalized to β-actin expression. The appearance of lactate dehydrogenase in conditioned medium was used to monitor cell viability.
AQP1 expression by TM cells sequentially decreased with increasing passages over time in culture. Following exposure to a 20% stretch, expression of AQP1 was restored by a 4-fold increase compared to controls at both 8 hrs (n=4, p<0.02) and 24 hrs (n=5, p<0.03). Similarly, a 1.5 fold increase in AQP1 expression was observed after 8 and 24 hour 10% stretch (n=2).
Aquaporin-1 expression by cultured human trabecular meshwork cells increases significantly following mechanical stretch of physiologically relevant magnitudes. Such a response is consistent with a protective role for AQP1 in TM cells that populate the mechanically dynamic conventional outflow pathway.
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