PROLONGED HIGH GLUCOSE TREATMENT INCREASED STIM1/ORAI1 PROTEIN EXPRESSION AND ENHANCED STORE-OPERATED CA2+ ENTRY IN HUMAN GLOMERULAR MESANGIAL CELLS

Purpose: Stromal interaction molecule1 (STIM1) and Orai1 regulate intracellular Ca2+ signaling via store operated Ca2+ entry (SOCE). Our previous study demonstrated that STIM1 is required for SOCE in human mesangial cells (HMC) of kidneys. However, its pathological relevance in HMCs is unknown. The aim of the present study was to determine the effect of high glucose (HG) on STIM1/Orai1 protein expression and SOCE in cultured HMCs. Methods: Western blot was used to detect the expression levels of STIM1/Orai1 proteins. Fura-2 fluorescence ratiometry was utilized to assess SOCE. Whole-cell patch clamp was employed to measure store-operated currents. Results: With 25 mM HG, STIM1/Orai1 protein expressions did not significantly increase until 7 days after treatment. With 7-day incubation, HG significantly elevated STIM1/Orai1 expressions in the range of 10-30 mM concentrations. Ca2+ imaging showed that the cyclopiazoic acid (30 µM)-stimulated Ca2+ entry was significantly enhanced in HMCs with 25 mM HG treatment for 7 days, but not 3 days. The HG-enhanced Ca2+ entry was nearly abolished by GSK-7975 (10 µM). Similarly, the whole cell currents induced by intracellular Ca2+ store depletion were significantly augmented in the HMCs with 7 day HG, but not in HMCs with 1 day HG treatment. Conclusions: Taken together, our results indicate that a prolonged HG treatment enhances SOCE in HMCs by upregulating STIM1/Orai1 protein expression.