Glucagon-like peptide receptor agonists attenuate advanced glycation end products-induced inflammation in rat mesangial cells

Abstract

Background: Hyperglycemia-induced advanced glycation end products (AGEs) and receptor for AGEs (RAGE) production play major roles in progression of diabetic nephropathy. Anti-RAGE effect of peroxisome proliferator-activated receptor-delta (PPARδ) agonists was shown in previous studies. PPARδ agonists also stimulate glucagon-like peptide-1 (GLP-1) secretion from human intestinal cells.

Methods: In this study, the individual and synergic anti-inflammatory effects of GLP-1 receptor (exendin-4) and PPARδ (L-165,041) agonists in AGE-treated rat mesangial cells (RMC) were investigated.

Results: The results showed both exendin-4 and L-165,041 significantly attenuated AGE-induced IL-6 and TNF-α production, RAGE expression, and cell death in RMC. Similar anti-inflammatory potency was seen between 0.3 nM exendin-4 and 1 μM L-165,041. Synergic effect of exendin-4 and L-165,041 was shown in inhibiting cytokines production, but not in inhibiting RAGE expression or cell death.

Conclusions: These results suggest that both GLP-1 receptor and PPARδ agonists have anti-inflammatory effect on AGE-treated rat mesangial cells.

Keywords: Diabetic nephropathy; Glucagon-like peptide; Mesangial cell; PPAR delta; Rage.

Fig. 1

L-165,041 attenuates AGE-induced interleukin-6 (IL-6) production in rat mesangial cells. ELISA was used to measure IL-6 concentrations in cell culture supernatants. a AGE stimulated IL-6 production with a dose-dependent manner. A concentration of 200 μM of AGE was chosen for following experiments. b The AGE-induced IL-6 production was inhibited L-165,041 with a dose-dependent manner. A concentration of 1 μM was chosen for following experiments. (N = 6) *P < 0.05 when compared to control. +P < 0.05 when compared to AGE group

Fig. 2

Exendin-4 and L-165,041 inhibit AGE-induced IL-6 (a) and TNF-α (b) production in RMC. The inhibitory action of L-165,041 was reversed by siRNA of PPARδ. L-165,041 and exendin-4 showed synergic effect in inhibiting IL-6 and TNF-α production. L-165,041 or exendin-4 alone had no influence on IL-6 or TNF-α production in the absence of AGE. (N = 6) *P < 0.05 when compared to control. +P < 0.05 when compared to AGE group. #P < 0.05 when compared to L-165,041 or exendin-4 group

Fig. 3

Exendin-4 and L-165,041 inhibit AGE-induced RAGE mRNA (a) and protein (b) expression in RMC. AGE significantly induced RAGE mRNA and protein expression. Both exendin-4 and L-165,041 significantly attenuated AGE-induced RAGE expression. The inhibitory action of L-165,041 was reversed by siRNA of PPARδ. No synergic effect between L-165,041 and exendin-4 in inhibiting RAGE expression was noted. L-165,041 or exendin-4 alone did not change RAGE expression in the absence of AGE. (N = 6) *P < 0.05 when compared to control. +P < 0.05 when compared to AGE group

Fig. 4

The effects of L-165,041 and exendin treatment on the NAPDH oxidase, PKA and HO-1 expressions. a AGE significantly increased the Nox4 expressions. Both L-165,041 and exendin significantly decreased AGE-induced Nox4. b After L-165,041 and exendin treatment, the levels of AGE-inhibited PKA and HO-1 expression significantly increased in mesangial cells. (N = 6) *P < 0.05 when compared to control. +P < 0.05 when compared to AGE group

Fig. 5

Exendin-4 and L-165,041 inhibit AGE-induced cell death of RMC. AGE enhanced death of RMC. Both exendin-4 (a) and L-165,041 (b) significantly attenuated AGE-induced cell death. The effect of L-165,041 was reversed by siRNA of PPARδ. No synergic effect between exendin-4 and L-165,041 in inhibiting AGE-induced cell death was noted. Exendin-4 or L-165,041 alone showed no influence on cell survival in the absence of AGE. (N = 6) *P < 0.05 when compared to control. +P < 0.05 when compared to AGE group