Figure 8. Effect of NAC, GFX, RBX and proteasome inhibitor on insulin signaling and degradation of IRS1 in RGEC.
A-C. After 48 h of exposure to low glucose (5.5mM) or high glucose (20mM), RGEC were stimulated with insulin (100nmol/l, 30 minutes) with or without an antioxidant, N-Acetyl-L-Cystein (NAC, 10mM), or a PKC-specific inhibitor, GF109203X (GFX, 5μM), or PKCβ-specific inhibitor, LY333531 (RBX, 20nM). One of three independent experiments is shown. **P<0.001 vs. Low/insulin(-)/NAC(-)/GFX(-)/RBX(-). ##P<0.001 vs. Low/insulin(+)/NAC(-)/GFX(-)/RBX(-). †P<0.05 vs. High/insulin(+)/NAC(-)/GFX(-)/RBX(-). ‡P<0.05 vs. High/insulin(+)/NAC(-)/GFX(-)/RBX(-). ¶P<0.05 vs. High/insulin(+)/NAC(-)/GFX(-)/RBX(-). P-Akt(A), p-eNOS(B) and p-GSK3α (C).
D. RGEC were cultured in low glucose (5.5mM) or high glucose (20mM) media for 72 hours with or without NAC(10mM), GFX(5μM), RBX(20nM) or proteasome inhibitor, MG132(25μM). One of three independent experiments is shown. ##P<0.001 vs. 0hr/High/NAC(-)/GFX(-)/RBX(-)/MG132(-). †P<0.001 vs. 72hr/High/NAC(-)/GFX(-)/RBX(-)/MG132(-). ‡P<0.001 vs. 72hr/High/NAC(-)/GFX(-)/RBX(-)/MG132(-). ¶P<0.001 vs. 72hr/High/NAC(-)/GFX(-)/RBX(-)/MG132(-). §P<0.001 vs. 72hr/High/NAC(-)/GFX(-)/RBX(-)/MG132(-).
E. After 48 h of exposure to low glucose (5.5mM) or high glucose (20mM), RGEC were stimulated with insulin (100nmol/l, 30 minutes) with or without NAC (10mM), GFX (5μM), or RBX (20nM). NO levels in the culture media were measured with the Nitric Oxide Colorimeric Assay Kit. **P<0.001 vs. Low/insulin(-)/NAC(-)/GFX(-)/RBX(-). ##P<0.001 vs. Low/insulin(+)/NAC(-)/GFX(-)/RBX(-). †P<0.05 vs. High/insulin(+)/NAC(-)/GFX(-)/RBX(-). ‡P<0.05 vs. High/insulin(+)/NAC(-)/GFX(-)/RBX(-). ¶P<0.05 vs. High/insulin(+)/NAC(-)/GFX(-)/RBX(-). These data are expressed as means ± SD.