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A. Pal, S. Palla, P. A. Ruzycki, B. G. Reddy, J. M. Petrash; Selective Up-Regulation of MAPK Signaling by Aldose Reductase (AKR1B1). Invest. Ophthalmol. Vis. Sci. 2010;51(13):2624.
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© ARVO (1962-2015); The Authors (2016-present)
Patients with diabetes have an increased incidence of blindness that may be linked to hyperglycemia. Activation of the polyol pathway due to increased aldose reductase activity is one of the several mechanisms thought to be associated to lens opacity, but the underlying mechanism remains ambiguous. Here we used human aldose reductase (AKR1B1) and human small intestine reductase (AKR1B10) transgenic mice to investigate how AKR1B1 might influence MAPK activity.We also examined the MAPK signaling pathway stimulated by hyperglycemic conditions in vitro.
Lenses from AKR1B1 and AKR1B10 transgenic mice, together with nontransgenic controls, were screened for expression levels of MAPKs proteins by Western blotting (WB). In lenses, phosphorylation of MAPKs proteins was measured by WB after AKR1B1 inhibitor treatment of above transgenic mice. Effects of hyperglycemia in respect to MAPK proteins were evaluated by WB following high glucose culture of human lens epithelial B3 (HLEB3) cells with or without aldose reductase and MEK/ERK inhibitors.
Strong activation (~10-fold) of ERK1/2 MAPK protein was observed only in AKR1B1 mice but not in AKR1B10 or nontransgenic controls. In transgenic mice, a moderate increase in AKR1B1 is sufficient to induce MAPK activation; however, further elevation (3-fold) of expression levels of AKR1B1 do not further increase activation. This activation effect was attenuated (~60%) by sorbinil, an AKR1B1 inhibitor in both transgenic lenses and HLEB3 cells exposed to 27.5mM glucose. Moreover, high glucose significantly increased (4-fold) the AKR1B1 level in a time-dependent manner and induced ERK1/2 activation. Meanwhile, supplementation of PD98059 and U0126, the specific inhibitors of MAPK/ERK kinase, reversed the activation of ERK1/2 (70-90%) under high glucose in HLEB3 cells.
These results indicate that AKR1B1 plays an important role in the regulation of ERK1/2 MAPK phosphorylation and high glucose can increase AKR1B1 and ERK1/2 MAPK activity in HLEB 3 cells, thereby providing further insight into the molecular mechanism of diabetic eye disease.
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