Effect of ultraviolet A exposure on transport of compatible organic osmolytes in human lens epithelial cells.

Abstract

Compatible organic osmolytes, such as betaine, myoinositol, and taurine, are involved in antioxidant defense, protein stabilization, and stress responses. This osmolyte strategy requires the expression of specific osmolyte transporters such as betaine (BGT-1), myoinositol (SMIT), and taurine (TAUT). In contrast to the kidney, keratinocytes, and neural cells, few studies have examined osmolytes in human lens epithelial cells (HLECs). We examined the expression of mRNA specific for BGT-1, SMIT, and TAUT in HLECs. In comparison to normoosmotic (305 mOsM) controls, there was a 3-5-fold time-dependent reaction of BGT-1, SMIT, and TAUT mRNA levels in HLECs exposed to hyperosmotic stress (405 mOsM). Maximal responses were obtained for BGT-1, SMIT, and TAUT mRNA expression after 3, 24 and 9 h of hyperosmotic exposure, respectively. This expression was correlated with increased osmolyte uptake. In contrast, hypoosmotic (205 mOsM) stimulation led to a significant efflux of osmolytes. Exposure to ultraviolet A (340-400 nm) radiation significantly stimulated osmolyte uptake. Increased osmolyte uptake was associated with upregulation of mRNA steady-state levels for osmolyte transporters in irradiated cells. These results demonstrate that ultraviolet A radiation leads to the accumulation of compatible organic osmolytes in HLECs as hyperosmotic pressure, which can maintain cellular environmental homeostasis.